devaki nandan 2015

SYNTHESIS OF POROUS CARBON COMPOSITES AND

METAL OXIDES FOR CATALYTIC APPLICATIONS

Thesis Submitted to AcSIR for the Award of

the Degree of

DOCTOR OF PHILOSOPHY

in

Chemistry

By

Devaki Nandan

(Enrollment No. 10CC11J19012)

Under the guidance of Dr. Nagabhatla Viswanadham, Principal Scientist

Refining Technology Division

CSIR-Indian Institute of Petroleum Dehradun -248 005,

Uttarakhand, India

February 2015

Dedicated

To My parents,

wife, brother and our daughter

Disha

Acknowledgements

Ph. D. Thesis of Mr. Devaki Nandan CSIR-IIP

First and foremost, I thank my supervisor, Dr. Nagabhatla Viswanadham. During my

tenure, he rewarded me by giving intellectual freedom in my work, engaging me in

new ideas, and demanding a high quality of work in all my endeavors.

I would like to thanks Director, Indian Institute of Petroleum, Dr. M. O. Garg for

allowing me to utilize the facilities of IIP and permitting me to submit my research

work in the form of thesis.

Besides my advisor, I would like to thank my Doctoral Advisory Committee

(DAC) members, Dr. A. K. Chatterjee, Dr. S. M. Nanoti, Dr. O. P. Khatri, and

Dr. V. V. D. N Prasad for their encouragement, inspiring discussions and

suggestions throughout the research work.

In addition, I also express my sincere thanks to Mr. S. K. Ganguly, AcSIR-IIP

coordinator, for his valuable support and also thankful to Dr. A. K. Jain,

DAC coordinator and Shaloo Vanodhia Madam, for helping me at any time

throughout my stay in IIP.

The faculty members of course work Dr. B. Sain, Dr. Y. K. Sharma, Dr. S. L. Jain, are

thankful to giving me knowledge to complete course work.

I also express my sincere gratitude to all the members of analytical division of IIP

specially Mr. S. Saran for XRD, Dr. Manoj Kumar for porosimetry, Mr. S. K.

Konathala for SEM, Dr. Pankaj K. Kanaujia and Mr. D. Tripathi for GC-MS, Mr. G.

M. Bahuguna and Mr. R. Singh for FT-IR, Dr. R. K. Chauhan and A. Naidu for AES-

ICP analysis.

I would like to thank my lab members in Light stock processing and reforming group

Mr. Amit Sharma, Dr. Sandeep K. Saxena, Mr. Rajeev Panwar, Dr. Peta

Acknowledgements


Sreenivasulu, Mr. Deepak Rohilla, Mr. Tryambakesh Sharma for their kind

cooperation and cheerful atmosphere in the laboratory.

My IIP friends and colleagues Nilesh, Harshal, Subhash, Aamir, Arvind, Rajeev and

Vipin and Sibi are thank full to give me friendly and cooperative atmosphere.

From the beginning of my research work in IIP, I am in contact with various senior

researchers Dr. Bharat Singh Rana, Dr. Bhawan Singh, Dr. Deepak Verma, Dr.

Sanny Verma and Mr. Subodh Kumar they all are helpful to me whenever I need their

help.

During this period I also had the chance to work with various trainees specially

Pankaj Singh, Rakesh thakur are the person whom I have enjoyed my time.

I am deeply indebted to my teachers in school and college Dr. Uma Pathak,

Dr. Sanjay Kumar, Dr. Aashutosh Pandey, Dr. Vipin Joshi; seniors Dr. Kamal

Kumar Bisht, Dr. Girdhar Joshi, Veer Singh Palyal, Girish Pant and Dr. Sanjay

Kumar inspired me and laid foundation for me to pursue higher studies.

Heartfelt thanks to Bhuwan Tiwari, Rajendra Joshi, Veeru, Subhash, Gaurav,

Mannu, Priyanka Tiwari, Manoj Kaloni, Devendra Dhami, Charu, for their

affectionate company and moral support from college study to till date.

During my research work I had an opportunity to work at CSIRO-Earth Science and

Resource Engineering, Clayton Melbourne Australia with Dr. Ken Chiang's group

and interacted with N. Burke, Zim Patel, Jarrod Newnham, Vankat, S. Ali and for

that Department of Science and Technology, India and CSIRO, Australia are

acknowledged to giving me this opportunity

Acknowledgements


The words are not sufficient to express my love and gratitude to my parents

for their blessings and moral support. I would like to thank my wife Lalita. Her

support, encouragement, quiet patience and unwavering love were undeniably the

bedrock upon which the past five years of my life have been built. Her tolerance of my

occasional vulgar moods is a testament in itself of her unyielding devotion and love.

I am in dearth of words in expressing my warm feelings of love to my sisters, brother,

sister in law and our daughter Disha.

I also owe a deep sense of thanks to my father-in-law and mother-in-law, brother in

law for their boundless and unconditional support throughout my doctoral study.

I would like to thank the Council of Scientific and Industrial Research (CSIR) New

Delhi, for financial assistance in the form of Research Fellowship during the

course of my research work and CSIR-Indian Institute of Petroleum for

providing me this platform to work on.

Last, but not least, thanks to be my almighty Fatak Shila Baba, whose spirit, gave me

strength and peace during all my life. This thesis would not have been possible unless

Baba’s mercy and love upon me. May my Lord be praised, honored, and loved for all

eternity.

Devaki Nandan

Preface


The thesis entitled “Synthesis of porous carbon composites and metal oxides for

catalytic applications” deals with the synthesis and characterization of various novel

porous materials based on carbon, carbon silica composite, carbon embedded metal

nanoparticle and metal oxides and their application have been explored in the field

of catalysis, particularly in the various industrially important organic

transformation reactions such as alkylation of phenol by the direct one-pot liquid

phase reaction, selective hydrogenation in protic environment and glycerol value

addition towards solketal. In this investigation, various acid functionalized carbon

composite, acid functionalized carbon silica composite, hierarchical mesoporous

silica, carbon embedded metal nanoparticle and hierarchical metal oxides have been

synthesized.

The present research work has been carried out in Refining Technology

Division (RTD) CSIR-Indian Institute of Petroleum (IIP), Dehradun-248005,

India, under the supervision of Dr. Nagabhatla Viswanadham. The contents of this

thesis have been presented in seven chapters.

Chapter 1 describes the overview and comprehensive literature survey about porous

carbon composites and metal oxides including their synthesis strategies and catalytic

applications. The chapter concludes the objectives and outlook of the present work.

Chapter 2 comprises the detailed description of different instrumentation and

characterization techniques used to characterize lab synthesized materials. These

Techniques are, Powder X-Ray diffraction (XRD), N2 adsorption-desorption, Fourier

Transform Infrared Spectroscopy (FT-IR), Thermogravimetric Analysis (TGA),

Temperature Programmed Desorption (TPD), Transmission Electron Microscopy

(TEM), Field Emission Scanning Electron Microscopy (FE-SEM), Energy-Dispersive

X-ray Spectroscopy (EDX) and Titration.

Chapter 3 encloses the synthesis, characterization and catalytic activity of sulfonated

nonporous carbon, sulfonated carbon silica composite which has been developed in

laboratory by simultaneous carbonization and sulfonation. The properties of

mesoporous silica material obtained by simple calcination of composite material also

described.

Preface


Chapter 4 consists of synthesis, characterization and catalytic activity of various

sulfonated carbon silica composite materials by varying the glucose concentration and

method of synthesis. The properties of mesoporous silica material obtained by simple

calcination of composite material also described.

Chapter 5 describes synthesis, characterization and catalytic activity of magnetically

separable carbon embedded metal-nanoparticles.

Chapter 6 describes the synthesis, characterization of hierarchical ZSM-5 and their

catalytic activity for the tertiary butylation reaction.

Chapter 7 comprises concluding remarks and future prospects of carried out works.

Content


Chapter 1 Introduction 1-45

1.1 General Overview to Porous Materials 1

1.2 Foundation and Development of the Field 3

1.2.1 Functionalized porous carbon and carbon composites 3

1.2.2 Zeolites or Porous Metal Oxides 6

1.3 Synthesis Methodologies of Porous Carbon Composites and Metal 10

Oxide Materials Based on Literature Review

1.3.1 Synthesis Methods for Sulfonated Carbon Based Materials 10

1.3.1.1 Sulfonated Non-porous Carbon 10

1.3.1.2 Sulfonated Mesoporous Carbon or Ordered Mesoporous Carbon (OMCs) 12

1.3.1.3 Sulfonic Acid-modified Carbon Nanotubes 13

1.3.1.4 Sulfonic Acid-modified Resins 13

1.3.2 Synthesis Methods for Acid Functionalized Carbon-silica Composite Materials 14

1.3.2.1 Post Oxidation Method 14

1.3.2.2 In-situ Oxidation Method 17

1.3.2.3 Carbonization and Sulfonation Method 18

1.3.3 Synthesis Methods for Porous Carbon Embedded Metal Nano-particles 19

1.3.4 Synthesis Methods for Porous zeolites 20

1.3.4.1 Non-Tempalating Method 20

1.3.4.2 Tempalating Method 21

1.3.4.2.1 Solid Templating 21

1.3.4.2.2 Supramolecular Templating 23

1.3.3.2.3. Indirect Templating 24

1.3.5 Application of Porous Materials in Catalysis 24

1.3.5.1 Acid-Catalysed Reactions 26

1.3.5.2 Base-Catalysed Reactions 27

1.3.5.3 Hydrogenation Reactions 28

Content


1.4 Objectives and Outlook of Present work 29

1.5 References 32

Chapter 2 Techniques Used for Characterization of Lab Synthesized

Materials 47-72

2.1 Introduction 47

2.2 Characterization techniques 48

2.2.1 Powder X-Ray Diffraction Analysis 48

2.2.2 Porosimetry 50

2.2.2.1 BET Surface Area 53

2.2.2.2 Pore Volume and Pore Size Distribution Analysis 54

2.2.3 Scanning Electron Microscopy (SEM) 56

2.2.4 Transmission Electron Microscope (TEM) 59

2.2.5 Energy Dispersive X-Ray Spectroscopy 61

2.2.6 Thermo Gravimetric analysis (TGA) 62

2.2.7 Temperature Programmed Desorption (TPD) 63

2.2.8 Fourier Transform Infrared Spectroscopy (FT-IR) 64

2.2.9 Inductively Coupled Plasma -Atomic Emission Spectrometry (ICP-AES) 66

2.2.10. Titration Method 67

2.3 References 67

Chapter 3 Facile synthesis of Sulfonated Nano-porous Carbon,

Sulfonated Carbon-silica-meso Composite and Mesoporous Silica 71-96

3.1 Introduction 71

3.2 Experimental Details 74

3.2.1 Reagents and Chemicals 74

3.2.2 Synthesis of Sulfonated Carbon 74

Content


3.2.3 Synthesis of sulfonated Carbon-silica Composite and Mesoporous Silica 74

3.2.4 Catalytic Application of the Synthesized Materials towards Tertiary Butylation

of Phenol 75

3.2.4.1 Liquid Phase Reaction in Round Bottom Flask 76

3.2.4.2 Liquid Phase Reaction in High Pressure Parr Reactor 76

3.3 Results and Discussion 76

3.3.1 Properties of Acid Functionalized Nano Porous Carbon Composite 76

3.3.2 Properties of Acid Functionalized Carbon-silica-meso Composite and

Mesoporous Silica 82

3.3.2.1 Proposed Mechanism for the Formation of SCS and MS 88

3.3.3 Performance of the Catalysts towards Tertiary Butylation of Phenol 89

3.3.3.1 Liquid phase reaction in round bottom flask 89

3.3.3.2 Liquid Phase Reaction in Parr Reactor 90

3.4 Conclusions 93

3.5 References 93

Chapter 4 Optimization of Acid Functionalized Carbon-Silica Composite

Structure for its Catalytic Applications & Mesoporous

Silica Preparation 97-126

4.1 Introduction 97



4.2.2 Synthesis of Sulfonated Carbon-silica Meso Composite and Mesoporous

Silica Materials 101

4.2.3 Application of Synthesized Composite Materials for Solketal Synthesis 103

4.3 Results and discussion 104

Content


4.3.1 Effect of Synthesis Conditions on Material Properties 104

4.3.2 Porosity and Acidic Properties of the Synthesized Materials 108

4.3.3 Plausible Mechanism for the Formation of SCS, HSCS and HMS Materials 116

4.3.4 Performance of SCS and HSCS Materials towards Solketal Production 119

4.4 Conclusion 122

4.5 References 123

Chapter 5 Synthesis of Carbon Embedded MFe2O4 (M = Ni, Zn and Co)

Nano-particles as Efficient Hydrogenation Catalysts 127-152

5.1 Introduction 127



5.2.2. Synthesis of MFe2O4@C Materials 130

5.2.3 Application of Materials for Selective Hydrogenation Reaction 130


5.3.1. Scanning Electron Microscopy and Transmission Electron Microscopy

and High Resolution Microscopy 132

5.3.2. X-Ray Diffraction and Porosimetry 134

5.3.3. FT-IR, EDX, CHNS, and ICP-AES Investigation 136

5.3.4 Proposed Mechanism for the Formation of MFe2O4@C Materials 141

5.3.5 Catalytic Performance of Materials for Hydrogenation Reaction 142

5.3.6 Reusability of the Catalyst 146

5.4 Conclusions 148

5.5 References 149

Chapter 6 Synthesis of Hierarchical ZSM-5 Using Glucose as

Templating Precursor and its Catalytic Application 153-170

6.1 Introduction 153

Content




6.2.2. Synthesis of Hierarchical ZSM-5 Materials 156

6.2.3. Application of Materials for Tertiary Butylation of Phenol 158


6.3.1 Crystallinity, Porosity and Acidic Properties of the Synthesized Materials 158

6.3.2. Catalytic Application Materials 165

6.4 Conclusions 167

6.5 References 167

Chapter 7 Concluding Remarks and Future Prospects 171-178

7.1 Facile synthesis of Sulfonated Nano-porous Carbon, Sulfonated

Carbon-silica-meso Composite and Mesoporous Silica 172

7.2 Optimization of Acid Functionalized Carbon-Silica Composite Structure for its

Catalytic Applications & Mesoporous Silica Preparation 172

7.3 Synthesis of Carbon Embedded MFe2O4 (M = Ni, Zn and Co) Nano-particles as

Efficient Hydrogenation Catalysts 173

7.4 Synthesis of Hierarchical ZSM-5 Using Glucose as Templating Precursor and its

Catalytic Application 173

7.5 List of Publications 175

7.6 List of Patents Applied/Filled 177

7.7 Papers Presented/Accepted in Conference, Symposium and Seminar 177

Chapter: 1 Introduction

Chapter 1: Introduction

Porous materials lead accessibility to molecular diffusion


Chapter 1. Introduction

Ph. D. Thesis of Mr. Devaki Nandan Page 1 CSIR-IIP

Chapter 1: Introduction

1.1 General Overview to Porous Materials

Porous nano-structured carbon composites based materials and zeolite materials have

attracted considerable interest in the field of catalysis in recent years. Owing to

unique structural, surface and physicochemical properties, porous materials are

widely used in laboratory scale, pilot and industrial scale in diverse research areas,

such as in petrochemicals,1 medicine

2 fine and speciality chemistry,

3 purification,

separation, catalysis, biology, catalyst supports, chemical industry, environment,

energy and advance composites materials.4-16

This subject is a hot topic in recent

years and would be continue to remain so in the coming years. Efficient porous

materials should have high thermal, chemical and mechanical stabilities as well as

appropriate particle size with high surface area and large pore volume.17,18

In

addition, it should have a narrow pore size distribution, which is critical for

size-specific application and a readily tuneable pore size allowing flexibility for

host-guest interaction. One such class of materials, which have been found

great research interest on both academic and industrial levels19

, is the

microporous, mesoporous, and hierarchical materials. According to the

International Union of Pure and applied chemistry (IUPAC)17

classification,

porous materials have been categorized into three categories depending on their pore

size. The porous materials are classified in categories i.e. microporous (pore diameter

<2 nm), mesoporous (pore diameter 2–50 nm) and macroporous (pore diameter >50

nm) materials. Some illustrative examples are depicted in the Figure 1.1 reproduced

from litrature.20

Out of these porous materials, acid functionalized porous carbon-

based composite materials including sulfonated carbon, sulfonated carbon silica



composites, carbon supported metal nano-particles (showing magnetic properties) and

hierarchical zeolites are playing an increasingly significant role in the development of

alternative clean and sustainable energy technologies.21

Figure 1.1 Examples of micro, meso and macroporous materials, showing pore size

domains and typical pore size distributions



1.2 Foundation and Development of the Field

1.2.1 Functionalized Porous Carbon and Carbon Composites

From the last 1 decades researchers interest on the development of porous materials

exponentially increasing the first are focusing on the development of porous

materials. Many chemical reactions such as Friedel Crafts alkylation, acetalation,

hydration, esterification, and hydrolysis reactions can be catalyzed by catalysts which

play a vital role in these reactions. Many of these reactions are still carried out by

using conventional liquid acid catalysts like H2SO4. These liquid acid catalysts create

many avoidable problems, such as high toxicity, corrosion, generation of solid

wastes, and difficulty in separation and recovery. The generation of acidity in solid

acid can solve these problems have a number of advantages over the liquid ones, such

as less corrosion, no or less waste, and easy separation and recovery from the reaction

medium. As a result, there has been a great deal of research interest in searching for

environmentally friendly solid acid catalysts to replace environmentally unfriendly

liquid acid catalysts. Over the past decade, various solids with sulfonic acid groups (-

SO3H) have been reported.22-24

The reported structure of the materials are shown in

Figure 1.2. The -SO3H groups can be introduced on porous silica through two main

approaches. One is the post-oxidation method and other is in-situ oxidation method.22-

26 In post-oxidation method the supported thiol groups, which were introduced

through grafting or co-condensation method, were oxidized by post synthetical

technique. However, the porous structure cannot be maintained well after the

postoxidation.23

To solve this drawback, another method named in-situ oxidation

method was subsequently developed.23

In an in-situ oxidation method the silica

precursor, organosulfonic precursor, and oxidant were added together into the



synthesis process and the oxidation of thiol groups can occur with the preparation.

Sulfonic acid functionalized porous silicas with uniform pores, high surface area and

good stability have been found to exhibit excellent catalytic activities in many

reactions, such as esterification26

condensation and addition reactions27

and alcohol

coupling to ethers.28

To tune the acidic strength of sulfonic acid solids, arene-sulfonic

acid groups were introduced on mesoporous silica materials.29

Figure 1.2 Reported structure of various types of acid functionalized materials in

literature

Organosulfonic-modified periodic mesoporous organosilicas (PMO) have

been shown to display a great catalytic performance. Organosulfonic-modified PMO

catalyst was first used in the alkylation of phenol with 2-propanol.30

Subsequently,

PMO catalysts were tested in many kinds of chemical reactions, such as

esterification31

and condensation.32

Carbon-based materials have always attracted



much attention in heterogeneous catalysis due to its virtues such as easy modification,

high surface area, high pore volume and their low cost. By introducing -SO3H groups

on carbon, Hara and coworkers21a

discovered a carbon-based solid sulfonic acid

catalyst, which displayed a very high catalytic activity. However, these carbon

materials possess a low surface area, which is not favourable for some catalytic

reactions. The second field of interest for the development of efficient carbon

supported catalyst is to create magnetic properties on the catalyst material as shown

in Figure 1.3. The carbon supported metal nano-particle in its oxide form can be used

as a catalyst to solve the separation problem of small nano-particle. The porous

carbon supported metal nano-particle not only gives the stability to the metal nano

particle but also give higher surface area to the material.

Figure 1.3 Photograph showing magnetic separation of NiFe2O4 nano-particle @C.



1.2.2 Zeolites or Porous Metal Oxides

Zeolites are a unique class of crystalline aluminosilicates exhibits systematic ring of

pores. The particular properties of zeolites have fascinated scientists from different

backgrounds for over 250 years. They were discovered by mineralogist Axel

Cronstedt in 1756, who noticed an unusually pronounced steam formation upon

heating the mineral stilbite in a blow pipe.33

Accordingly, he coined the material

‘zeolite’, originating from classic Greek, where ‘zeo’ means ‘to boil’ and ‘lithos’

means ‘stone’. It was about 200 years later that, in the 1940s and 1950s, the

pioneering contributions by Barrer, Breck, and Milton on zeolite synthesis enabled to

establish the tremendous potential of zeolites. As a result, in 1954 Union Carbide

commercialized synthetic zeolites as new class of industrial materials for separation

and purification. Few years later, synthetic zeolites were marketed as isomerisation

and cracking catalysts (Mobil Oil). Now a day, zeolites are used in roughly 70

industrial catalyzed reactions in oil refining, petrochemical, and fine chemical

industries.34,35

Out of millions of theoretically possible frameworks36

due to the

connectivity of the zeolite SiO4 or AlO4 tetrahedra over 200 have been synthesized

experimentally.37

A particular framework topology can be ascribed to various zeolites

based on differences in composition (mostly Si/Al ratio) or crystal morphology.

These differences usually originate from zeolite synthesis by variation of gel

composition, crystallization time and temperature, or template used. To date, ~1000

different zeolitic materials have been included in the Atlas of Zeolite Structure

Types.37

This relatively low number related to the meta-stability of zeolites, due to

the majority of the hypothetical structures which are unstable.36

Moreover, of the

synthesized structures, many are not truly zeolites or molecular sieve materials, since

they are not stable upon template removal. Zeolites are typically classified by



Figure 1.4 Structures and dimensions of different types of zeolite.38

their pore size and composition. Table 1.1 summarizes the most common commercial

zeolites. The size of the pores is typically expressed as the number of Si or Al atoms

on the smallest possible cross-section, e.g. 8, 10, or 12 member rings (Figure 1.4).

Alternatively, they can be categorized by their Si/Al ratio, forming four classes: high,

intermediate, and low Si/Al ratio zeolites and only silica zeolites. The exceptional

performance of zeolites catalyzed reactions due to their strong acidity and uniformly-

sized micropores. These assets enable to catalyze a wide variety of chemical

conversions, while yielding very narrow product distributions. The other concept for

the zeolites is ‘shape selectivity’ (zeolite micropores directing the conversion of a

reagent into a specific product).39

Various types of shape selectivity are distinguished,

depending on whether the pore size limits the entrance of the reacting molecule, the

departure of the product molecule, or the formation of certain transition states as

shown in figure 1.5. These exceptional catalytic features, combined with the ability

to tune both acidity and micropore size, has made the tremendous role of zeolites in



catalysis. Therefore, based on size exclusion, zeolites can be used to separate

relatively large molecules from smaller ones. In addition to this advantage,

substitution of tetravalent Silicon by trivalent Aluminium in the framework gives rise

to a net negative charge, which is compensated by cations, e.g. H+, Cs

+. These

cations, located in the micropores, are readily exchangeable, making zeolites

prolificion exchangers, for example in detergents. Moreover, if these cationic sites are

exchanged to H+, strong Brønsted acid sites are formed, enabling the application of

zeolites in catalysis. Despite the obvious success of zeolites as solid catalysts, their

potential is only partially exploited due to diffusion and access limitations. The

Table. 1. Pore size and ring size of some known zeolites

Zeolite Framework type Ring member (pore size) Pore size Å

High Si/Al ratio (10-100)

ZSM-5 MFI 10 5.5X5.1

10 5.6X5.3

ZSM-22 TON 10 4.6X5.7

ZSM-12 MTW 12 6.0X5.6

MCM-22 MWW 10 5.5X4.0

10 5.1X4.1

Beta BEA 12 6.7X6.6

12 5.6 X 5.6

Ferrierite FEA 10 5.4 X 4.2

8 4.8 X 3.5

Intermediate Si/Al ratio (2-5)

Clinoptilolite HEU 10 7.5 X 3.1

8 4.6 X 3.6

8 4.7 X 2.8

Mordeniteb MOR 12 7.0 X 6.5

8 5.7 X 2.6

Erionite ERI 8 5.1 X 3.6

Chabazite CHA 8 3.8 X 3.8

Y FAU 12 7.4 X 7.4

L LTA 12 7.1 X 7.1

Low Si/Al (1-1.5)

A LTA 8 4.1 X 4.1

X FAU 12 7.4 X 7.4

Only silica

Silicalite-1 MFI 10 5.5 X 5.1

10 5.6 X 5.3



Figure 1.5 Types of shape selectivity operate in zeolite

limited size of the micropores with respect to the size of the molecules enforces an

intra-crystalline ‘single file’, or ‘configurational’, diffusion.40

As a result, only the

part of the micropores close the external surface is used in most catalyzed reactions.

Since the external surface area of zeolite crystals is only a fraction (5%) of the total

surface area, an under utilization of the zeolite volume is consequently unimplied.41

As a response to the limited utilization of the active volume in conventional zeolites,



for over a decade, now an intense and persistent scientific attention focused on

increasing the accessibility of the zeolites active sites by widening of the micropore

channels,41

reducing the transport issues by coupling the intrinsic microporosity with

an auxiliary mesopore network of inter- or intracrystalline nature,42,43

In the latter

case, each porosity level fulfils a distinct complementary task 1) the micropores hold

catalytically active sites, 2) whose access is facilitated by the newly introduced

mesoporosity.41

A large array of lab-scale approaches to synthesize hierarchical

zeolites has been realized.44-53

Bottom-up routes include the modification of the

synthesis protocol resulting in nanosized zeolite crystals46

or zeolites including a

secondary mesopore template.47,50

Top-down routes comprise post-synthetic

treatments of previously grown zeolites by demetallation. Examples here of comprise

steam51

, acid54

or base48

treatments. The more refined approaches that include

swelling agents,52,53

irradiation,55,56

and/or strong oxidizing reagents.56

Although most

of the above-mentioned routes are successful in acquiring mesoporosity and improved

performance in catalyzed reactions. However the majority of bottom-up methods are

not easily amended to industrialization since they involve substantial amounts of

costly and unavailable templates or lead to crystals that are not easily separated from

the mother liquor. Futrher research is going on to achieve hierarchical mesoporous

zeolite for better material having vivid applications.

1.3 Synthesis Methodologies of Porous Carbon Composites and Metal

Oxide Materials Based on Literature Review

1.3.1 Synthesis Methods for Sulfonated Carbon Based Materials

1.3.1.1 Sulfonated Non-porous Carbon



Hara et al.57

first time reported a new kind of carbon moiety having -SO3H protonic

acid group by incomplete carbonization of hydrocarbons (naphthalene) by

sulfonation. The sulfonation reaction was carried out under high reaction temperature

(200-300 ºC). However, this new kind of carbon-based sulfonic acid catalyst having

the leached out problem during liquid phase reactions above 100 ºC and its catalytic

activity is heavy limited for bulky molecular transformations (long chain fatty acids).

Later on Toda et al.21a

follow the two step method for the preparation of material

(scheme 1.1). They have employed sucrose, starch or cellulose as the carbon

precursor for low temperature carbonization process (400 ºC) to producs small

polycyclic aromatic carbon sheets in first step followed by sulfonation by sulfuric

acid (concentrated or fuming) in second step. Amorphous carbon prepared by this

method enhanced the stability of resultant carbon sulfonic acid catalysts greatly. The

effect of the carbonization temperature was also investigated by Okamura et al.58,59

The authors found that the active centres for the carbon carbonized at 550 ºC are not

fully available for reactants. Because with increasing carbonization temperature,

carbon materials become dense and the fewer sites for sulfonation remain for

sulfonation (sulfonation at surface is only possible). Sulfonated amorphous carbon

Scheme 1.1 Synthesis procedure for preparation of sugar based catalyst21a



prepared under lower temperature shows better catalytic performance because of high

phenolic -OH and -COOH in addition to -SO3H groups on the catalyst.

1.3.1.2 Sulfonated Mesoporous Carbon or Ordered Mesoporous Carbon

(OMCs)

These catalyst supports possessing high surface, narrow pore size distribution, large

pore volume, high densities of functional groups and good accessibility to active sites

facilitate the bulky molecular reactions. Lee et al., 60

Ryoo et al., 61

combindely

discovered the OMCs consisting of three-dimensional regular arrays of uniform

mesopores where they have employed ordered mesoporous silica MCM-48 as the

template. This process includes three steps of sythesis 1) polymerization of carbon

source in the pores of the templates, 2) carbonization at high temperature under

nitrogen atmospheres and 3) subsequent removal of the templates. There after various

researchers employed different mesoporous silica as a template to prepare various

OMCs62

. Wang et al.63

functionalized OMCs by covalent attachment of sulfonic acid-

containing aryl radicals. Wang et al.64

Compared CMK-5 with CMK-5-SO3H which

can be viewed as a material with a hydrophobic substrate and hydrophilic functional

groups. Such amphiphilic properties would allow CMK-5-SO3H to be an efficient

solid catalyst in both hydrophobic and hydrophilic environments. The CMK-5-SO3H

exhibits high activity for esterification reaction of acetic acid with methanol and good

recyclability, due to strong attachment of aryl sulfonic acid group on the substrate

through the stable C-C bond. CMK-5-SO3H also shows high catalytic activity for the

production of biodiesel involving long chain molecular structure because of larger

pores and higher surface area. Introducing the -SO3H groups onto OMCs can also be



allowed through sulfonation reaction using concentrated sulphuric acid (98%) under

high temperature (150 ºC to obtain the carbon based sulfonic acid catalysts.64

1.3.1.3 Sulfonic Acid-modified Carbon Nano-tubes

The CNT was first sulfonated by Peng and co-worker 65

using concentrated sulphuric

acid under high temperature (250 ºC). The resultant sulfonated CNT exhibiting high

acid density and thermal stability was observed to be suitable for high catalytic

activity through the esterification reaction of methanol with acetic acid. Later on Yu

et al.,66

have chosen Single-walled carbon nano-tubes (SWCNTs) as the support for

the high temperature sulfonation reaction. The high catalytic activity for sulfonated

SWCNTs can be explained by the strong acidity of sulfonic group and the ability of

SWCNTs to support functional groups.

1.3.1.4 Sulfonic Acid-modified Resins

Amberlyst is a polymer based catalysts having the sulfonic acid type groups. These

types of catalysts are adding advantage to catalysis as have both economic and

environmental drivers to improve organic transformations. Hart and co-workers67

prepared series of macroporous sulfonated poly(styrene-co-divinylbenzene) ion-

exchange resins with varying levels of sulfonation. They have used the catalyst for

the dehydration of 1-hexanol under flow conditions and for the hydration of propene.

These persulfonated resins, which were sulfonated at levels above one sulfonic acid

group per aromatic ring, also showed higher thermal stabilities than conventional

resins, which were sulfonated at just below one acid group per aromatic ring. Both the

increase in acid concentration in the internal solution and in the level of di-

sulfonation contributes to an increase in acid strength.



1.3.2 Synthesis Methods for Acid Functionalized Carbon-silica Composite

Materials

There are several methods reported for the synthesis of carbon silica composite

materials among these the following three methods are widely used given in scheme

1.2.

Scheme 1.2 Common synthetic methodologies employed for acid functionalized

carbon-silica composite materials in literature.

1.3.2.1 Post Oxidation Method

The introduced thiol groups could be oxidized into sulfonic acid groups by using

large excess of oxidant such as hydrogen peroxide as shown in scheme 1.3. Post

oxidative synthesis method for the preparation of silica based sulfonic acid catalysts

based on the covalent attachment of Periodic mesoporous organosilicas (PMO)

composed of hybrid inorganic-organic frameworks with ordered mesopores were first



synthesized in the late 1990s (Inagaki et al.,68

Melde et al.,69

). The synthesis strategy

of PMO is based on the condensation of organosilanes such as in the presence of the

corresponding surfactant, in which the organic moiety is covalently attached to two

trialkoxysilyl groups. PMO exhibited a homogeneous distribution of organic

fragments and inorganic oxide within the framework accompanied by highly ordered

structures and uniform pore size distributions, which is highly desired in the

applications of catalysis. The combination of acidic groups and hydrophobic

framework may result in interesting surface properties enhancing diffusion of

reactants and products in acid-catalyzed reactions. Inagaki et al.68

reported the

synthesis of PMO with crystal-like pore walls having a surface structure with

alternating hydrophilic and hydrophobic layers, composed of silica and benzene with

a periodicity of 7.6 Å. Through the direct sulfonation reaction using fumed sulfuric

Scheme 1.3 Synthesis scheme for -SO3H functionalized carbon-silica composite

materials by post oxidative method.

acid, -SO3H groups were attached onto the pheneylene group located within

hydrophobic benzene layers. Yang et al.,70

symthesized a material by co-condensation

of 1,4-bis(triethoxysilyl)benzene and 3- mercaptopropyltrimethoxysilane using a

surfactant template in basic conditions the thiol-functionalized benzene-silicas

possessing mercaptopropyl (-C3H6SH) groups which upon postoxidation gave novel -



SO3H functionalized mesoporous benzene-silica materials. Kapoor et al.71

also

reported the synthesis of bi-phenylene bridged bi-functional hybrid mesoporous

materials functionalized with sulfonic-acid functionalities by co-condensation of 4,4-

bis- (triethoxysilyl)biphenyl precursor and 3-mercaptopropyltrimethoxysilane in a

basic medium and cationic surfactant followed by an oxidation treatment. The authors

claimed that due to the equimolar ratio of phenylene to silica, which provides the

possibility to exert an enhanced hydrophobic character in the resulted PMO material.

The attachment of alkyl sulfonic acid groups to the surface of MCM and HMS type

materials were also done. Van Rhijn et al., first functionalized calcined MCM and

HMS samples with propane-thiol groups by reaction of the surface silanols with 3-

mercaptopropyltrimethoxysilane (MPTMS)72

. Both grafting and direct reaction

methods were adopted in this work. In grafting processes the surface concentration of

organic groups is constrained by the number of reactive surface silanol groups present

and by diffusion limitations. These restrictions may be overcome by direct synthesis

reported by Van Rhijn et al.,73

in which they employed MPTMS and TEOS

(Si(OEt)4), which were hydrolyzed together in the presence of an ionic or a non-ionic

surfactant (viz. C16NMe3Br and nC12-amine), leading to MCM or HMS type

materials, respectively. Following these pioneering works, the post oxidative

synthesis strategy has been expanded to the use of other different surfactants and

synthesis conditions. Thiol containing mesoporous silica material was also

synthesized by Margolese et al.,23

adopting co-condensation of TEOS, MPTMS and

employing a triblock copolymer (poly(ethyleneoxide)-poly-(propyleneoxide)-

poly(ethyleneoxide), Pluronic 123, EO20-PO70EO20) as template under acidic

conditions. Organosulfonic-modified porous silica materials prepared in

postoxidation method have yielded the material with lower scattering intensities in



XRD that indicated relatively poor long-range ordering in comparison to the starting

material containing the thiol groups22

, following a decrease in the surface area and

pore volume after oxidation of thiol groups incorporated and reduces the potential

application of these catalysts.24

The post oxidation method not only needs a large

excess of oxidant used in the process but also does not allow quantitative reaction of

thiol groups, and in some cases, leaching of sulphur species is clearly evidenced. The

presence of un-oxidized sulphur species might have a negative effect on the catalytic

performance of these materials.

1.3.2.2 In-situ Oxidation Method

Margolese et al.,23

used the in-situ oxidation method to create periodic ordered

propylsulfonic-modified mesoporous silica with pore sizes up to 70 Å through

cocondensation of TEOS and MPTMS, which employed Pluronic 123

(EO20/PO70/EO20) as the templating surfactant in acid medium.23

The in-situ

oxidation method as shown in scheme 1.4 profoundly influences the physical and

chemical properties of the propylsulfonic-modified mesoporous material relative


materials by in-situ oxidation method.



to that made by post oxidation technique. The in-situ oxidation method produces

SBA-15 modified materials with greater oxidation efficiency (100% vs 25-77%), with

larger more uniform pores, higher surface areas and good long-range order in contrast

to post oxidative method. The resultant sulfonic mesoporous silica with acid

capacities several times greater than those achieved with post oxidative method and

with thermal stabilities to 450 ºC in air. Van Grieken et al.74

employed non ionic

surfactants other than Pluronic 123 (EO20/PO70/EO20), through the in-situ oxidation

procedure to prepare propyl sulfonic modified hexagonally meso-structured materials.

They tailored the pore size of these sulfonic mesoporous materials from 30Å to 110Å

conveniently modifying the synthesis conditions using Pluronic 123 as template and

acid conditions. Popylsulfonic-modified SBA-15 synthesized through the in-situ

oxidation demonstrated significant activity toward biodiesel production under

relatively mild conditions with refined and crude vegetable oils as feedstock.74

The

large surface area and pore diameter of the mesoporous support as well as the

moderate acid strength of acid sites are helpful for the remarkable catalytic

performance, which are necessary to improve internal diffusion of bulky oil species

and to minimize possible deactivation of catalytic sites by strong adsorption of polar

by products such as water and glycerol.

1.3.2.3 Carbonisation and Sulfonation Method

The third method involves two step process of carbonization of the silica-carbon

composite material followed by its sulfonation as shown in Scheme 1.5.75-78

S. V.

Vyver, et al.75

synthesized the silica carbon composite by applying a method in which

they used sucrose as carbon precursor, Pluronic F127 triblock copolymer

(EO106PO70EO106, Mw = 12600) F127 as structure-directing amphiphilic



surfactant and tetra-ethyl orthosilicate (TEOS) as a silica source. In first step they

take F127 ethanol then added HCl to form a clear solution followed by addition of

TEOS and sucrose. The mixture was then left for 20 h at 40 ºC to evaporate ethanol

and for 24 h at 150 ºC to thermo polymerise. The obtained material then carbonised at

different temperature under nitrogen for 15 h. In second step the obtained material

was treated with concentrated sulphuric acid at 140 ºC for 15 h in Teflon-lined

autoclave and got sulfonated silica/carbon nano-composites. Later on Gupta et al.76

prepared a similar type of material by using natural organic compounds (glucose,

maltose, cellulose, chitosan and starch) and silica. In their synthetic procedure they

partially carbonise the precursors followed by its sulfonation to synthesize the final

material.


materials by carbonization and sulfonation method.

1.3.3 Synthesis Methods for Porous Carbon Embedded Metal Nano-

particles

According to the research findings on the synthesis steps of carbon based materials,

the carbon source first polymerizes to form small spheres or agglomerated particles

which begin to carbonize to form multi-aromatic carbon sheets that eventually lead to

the formation of a well condensed inner dense carbon matrix with an outer layer of a



multi aromatic ring during the process of hydrothermal synthesis and heat

treatments.79-83

The high temperature carbonization treatments applied during the

process give the material thermal and chemical stabilities to efficiently protect the

metal spheres from being dissolved in a protic environment. Moreover, the outer

multi-carbon layer of the material can have many functional groups, such as

carboxylic, aldehyde and hydroxyl groups on their surface, suitable for establishing a

chemical interaction with the desired compounds such as noble metal nanoparticles

(NPs) to obtain metal functionalized catalysts.84,85

Based on the above advantages,

many researchers have tried to attach metal spheres or metal nanoparticles onto the

carbon support.86–88

Wang et al.,89

used oleic-acid-decorated Fe3O4 NPs as the core of

Fe3O4/ carbon spheres. Zhang et al.90

reported the fabrication of functional 1D

magnetic NP chains with thin carbon coatings using urea as the surfactant.

1.3.4 Synthesis Methods for Zeolites (Porous Crystalline Aluminosilicate)

1.3.4.1 Non-Tempalating Method

This method is widely used in industry to introduce hierarchical porosity to the

material. It involves post synthesis demetalation of the material. In dematalation of

the material is carried out through various approaches such as steam treatment34

, acid

leaching37

, and desilication31

. The most well studied demetalation methods for

introducing intracrystalline pores in zeolites are dealumination and desilication.

Dealumination involves preferential extraction of framework aluminium by acid

leaching using nitric or hydrochloric acid solutions at temperatures ranging from

323 to 373ºC, or by steam treatment at relatively high temperatures between 500–

600°C. However, the resultant meso-structured zeolites obtained from

dealumination contain less crystallinity compared to its parent zeolite materials.



On the other hand, desilication, the preferential extraction of Si from the zeolite

framework by treatment in aqueous alkaline solution has proven to be more effective

way for creating meso-porosity in the zeolites crystals compared to the dealumination

method.

1.3.4.2 Templating Method

Templating method is one of the most widely used methods for the synthesis

of hierarchical structured zeolite materials with different morphologies and

characteristics. Generally, it is categorized into three categories: solid templating,

supramolecular templating, and indirect templating. In solid and supramolecular

templating, the zeolites crystal is in intimate contact with either a solid material or a

supramolecular assembly of used surfactant molecules that are subsequently removed

to generate the meso-porosity. Depending on method of synthesis various type of

porous structure can be prepared (Table 1.2)

1.3.4.2.1 Solid Templating

A large variety of solid templates (such as polymers, resins, carbon, organic aerogels,

materials with different structures, inorganic compounds, and biological templates

etc.) have been used for the synthesis of hierarchical mesoporous zeolites

materials with different morphology and characteristics. 91-95

In spite of these

different variety of solid templates, the use of different types of porous carbon

as a solid templates seems to be the most effective and versatile approach.

Porous carbon can be used to produce nano-meter sized supported zeolite crystals and

hierarchically arranged zeolites crystals. Jacobsen et al.91

reported the first example of

the creation of meso-structured zeolites by a solid templating method. They



have used nano carbon particles, pre-treated with acidic/alkaline solution as

mesoporous templates. These nano carbon particles were encapsulated by growing

Table 1.2 Hierarchy in zeolitic crystals-some examples classified with respect to their

synthesis methods

Method

Type of template Type of zeolite Type of porosity Reference

1. Templating

A. Solid

templating

Carbon blacks,

carbon

nanofibers,

carbon

nanotubes

MFI,Si-1,

ZMM-12

Micro/Meso/Macr 91

colloidal silica,

carbon

mesoporous,

molecular sieves

MFI,

Mesoporous

aluminosilicate

molecular

sieves

Micro/Meso 92

Aerogels,

polymer, resin,

BEA, MFI, Y Micro/Meso 93

Inorganic

compound

Silicate-1 Micro/Meso 94

Organosilane MFI,LTA,TS-1 Micro/Meso 95

B. Supramolecular

templating

Microemulsion,

reverse micelles

Silicalite-1 96

Surfactant

mediated oating

of zeolite

MCM-

41/FAU,

MOR/MCM-

41, MCM-

41/BEA

Micro/Meso 97

Delamination ITQ-2, ITQ-6,

MFI

Micro/Meso 98

C. Indirect

Templating

Crystallization

of zeolites seed

on mesoporous

materials

MFI, Y Micro/Meso 99

2 Non-Templating (Demetalation)

Dealumination MOR, MFI,

FER

Micro/Meso 100

Desilication MFI, BEA,

ZSM-12,

MOR, FER,

MCM-22,

ITQ-4,

Silicalite-1

Micro/Meso 101



zeolites crystals during synthesis, resulting in zeolites crystals embedded with carbon

after zeolites crystallization. Removal of the embedded carbon matrix after synthesis,

results in ZSM-5 zeolite crystals with case like meso-porosity. However, for the

processing of bulky molecules, the cave-like meso-porosity in the ZSM-5 zeolite

creates accessibility and mass transfer problems. To overcome this problem, meso-

structured long carbon nano-tube or nano-fiber templates have been used for the

synthesis of zeolites crystals with uniform and straight mesoporous channels of

diameter from 12-30 nm. Recently, a novel and facile method has been employed to

synthesize zeolites with mesopores using meso-structured carbon nano-tubes as

templates.91

1.3.4.2.2 Supramolecular Templating

In this method, an organized assembly of surfactant molecules is used as the

template for creating intercrystalline or intracrystalline meso-porosity within

zeolites. In all successful synthesis of mesoporous zeolites by using the

supramolecular templating method, the silica based species in the synthesis of

zeolites were in direct contact with the supramolecular template during the

crystallization process.96-98

Due to the presence of various factors (e.g. interaction

with silica-based species, stability, and morphology) during the zeolite

crystallization process, the selection of appropriate supramolecular template is of

vital importance in creating the mesoporous structure. Using soft-templates that

have strong interactions with silica-based species has the more chance of fabricating

mesoporous zeolites. Over the past few years, numerous successful examples of the

use of soft-templates to create mesoporous zeolites have been reported.,96-98

Ryoo

et al.95a

first time developed a direct synthesis route to mesoporous MFI



zeolites with easily tunable, uniform mesopores using amphiphilic organosilanes

([(CH3O)3SiC3H6N(CH3)2CnH2n+1]Cl), as supramolecular template.

1.3.4.2.3. Indirect Templating

Indirect templating method deals with the formation of hierarchical material in the

absence of a distinct mesopores or micropores template. In this method materials are

formed either from material or by controlled deposition of zeolites crystals onto

a mesoporous supporting material.99

In both strategies, the overall morphology of

the hierarchical mesoporous zeolites material is more or less retained during the

zeolites crystallization or deposition step. There are only a few different preparative

approaches belonging to this category, the majority of which related to partial zeolite

crystallization in ordered mesoporous materials. Using this methodology, zeolites

materials with hierarchical porosity can be produced by crystallization of mesoporous

materials such as SBA-15 in the presence of appropriate molecular zeolite structure

directing agents. This method include the following two steps: (i) assembly of an

mesoporous phase by templating; (ii) partial crystallization of the mesophase to

a zeolites phase.

1.3.5 Application of Porous Materials in catalysis

The fascinating characteristics of porous materials have made these materials

highly desirable candidate for many applications, particularly in catalytic

application as catalysts and catalyst supports. The development of different

class of porous materials like porous carbon, porous composites, porous

magnetically separable carbon composites, porous mesoporous zeolites and

hierarchical mesoporous zeolites has led to a revolution in the field of



heterogeneous catalysis. These materials have been extensively used in various

catalytic applications depending upon their unique properties. Zeolites and related

microporous molecular sieves have been implemented successfully in various

industrial applications such as petroleum refining, petro chemistry, and fine

chemical synthesis, due to their remarkable stability (mechanical, hydrothermal,

thermal and chemical), acidic nature, and high catalytic activity. However, despite

these distinguished properties, the different pore window sizes of zeolites ranging

from 5 Å to 12 Å cause a mass transfer problem in processing of large molecules

and viscous fluids. Other drawback of these zeolites is that they are not stable in

aqueous environment. Therefore, to meet these demands, numerous synthetic

strategies to create zeo-type materials with pore diameter larger than those of

the traditional zeolites and porous carbon composite having acidity were developed.

These porous materials with pore diameter in the range of mesopores provide

improved diffusion and accessibility for larger molecules and viscous fluids. Owing

to the extremely high surface area and large pore size, ordered porous materials

can be employed as effective heterogeneous catalysts for performing several

catalytic reactions. Ordered porous materials have frequently been used as supports

for catalysts rather than as catalysts as such. Acidic and redox functionalities were

generated in the materials by the incorporation of active sites in the silica walls or by

the encapsulation of well-defined homogeneous complexes inside the pores. Hence,

the catalytic activities of all the porous materials are basically dependent on the acid,

base and redox properties of the materials, which have been summarized in the

subsequent section.



1.3.5.1 Acid Catalysed Reactions

Propylsulfonic-modified FSM-16 mesoporous silica was investigated in the

acetalization of carbonyl compounds with ethylene glycol, which showed a higher

rate and 1,3-dioxolane yield than conventional heterogeneous solid acids such as

zeolites, montmorillonite K10 clay, silica-alumina, and the sulfonic resin (Amberlyst-

15)27b

. Propylsulfonic-modified FSM exhibits stable recycle catalytic activity with no

leaching of sulfonic acid groups. Inorganic solid acid materials have been found

to be a strong candidates in various acid catalyzed chemical reactions such as

etherification,102

esterification,103

alkylation,104

Acetalation,105

cracking,106

,

dehydration,107

oligomerization,108

isomerization109

etc. These inorganic solid acid

materials provide an environmentally friendly alternative replacement of

corrosive liquid acid catalysts such as H2SO4, HF, and H3PO4 for acid–

catalyzed processes. In the last two decades, mesoporous zeolites and porous

carbon composite materials have attracted a great attention as solid acid catalysts and

used in various industrial processes and fine chemical synthesis. One of the most

important examples is the catalytic alkylation of aromatic hydrocarbons carried

out in the presence of various mesoporous materials. J. Shinae et al.104j

reported

the alkylation of benzene using benzyl alcohol as alkylating agent over Al-

MCM-41 solid acid catalyst. The selective formation of cumene as the main product

in the isopropylation of benzene by isopropanol was reported by Valtierraet al.104k

Further, the large pore of MCM-41 combined with acidity on the walls was

specially conceived to carry out catalytic cracking of large molecules. The acidity

of mesoporous materials like Al-MCM-41 is much weaker than that of

microporous zeolites. In order to overcome this drawback, hybrid inorganic organic

mesoporous materials with alkyl sulfonic acid groups have been synthesized and



studied for their applicability in various reactions.110

Das et al.,111

reported that

mesoporous MCM-41 and MCM-48 silicas anchored with sulfonic acid (–

SO3H) groups via post synthesis modification are very effective for the synthesis

of Bisphenol-A by liquid-phase condensation of phenol with acetone. Exceptionally

high yield of the acetylated products in the acetylation of anisole was observed by

Kwon et al.,112

in the presence of sulfonic acid-modified MCM-41 mesoporous

materials that was prepared using a silane containing tetrasulfide linkages.

Recently, Melero et al.,113

have shown that SBA-15-PrSO3H is a promising and

recyclable catalyst for transesterification of various vegetable oils. More

recently, periodic mesoporous silica (PMO) functionalized materials have been used

in biodiesel production. Karimi et al., 114

reported biodiesel production via direct

transesterification of a variety of vegetable oils in the presence of sulfonic acid based

PMO materials.

1.3.5.2 Base Catalysed Reactions

Porous materials with basic properties have shown considerable potential for a

number of industrially important reaction.115

Ion-exchanged or ion impregnated

microporous zeolite materials were used as base catalyst from the beginning of the

1990s. However, the low basic strength of the ion-exchanged zeolites, limits

their use in organic synthesis. In order to increase the basicity or base sites, various

alkali salts have been impregnated in to the cavities of zeolites.115

Kloetstra et

al.115b

reported that Cs+ ion exchanged MCM-41 showed high activity in

Knoevenagel condensation reaction as compared to the Na+ ion exchanged MCM-

41 due to the high basicity of the Cs-MCM-41. The catalytic activity of the

alkali metal ion exchanged zeolite materials is strongly dependent on the type of



alkali cation present, the order being K > Rb > CS > Na > Li. A new synthesis

strategy has been adopted for the development of porous basic catalysts. This

strategy involves high temperature (700-1000 °C) treatment of amorphous

aluminium orthophosphate, zircononium phosphate and vanadophosphates materials

with ammonia. In this strategy oxygen atom is replaced by nitrogen that provides

basic sites. The amorphous oxynitrides are considered to be more strongly basic

catalysts than alkali ion-exchanged zeolites and comparable to hydrotalcites or MgO

base catalyst. Similarly, various organic bases could be bound to the surface of

porous silica materials by using the reaction of silanol groups of silica based

materials with 3-chloropropyltriethoxysilane and different organic base such as

piperidine, pyrrolidine, pyrimidine in subsequent steps. These materials were

reported to be effective base catalysts for various reactions such as Claisen–Schmidt

condensation,116

Knoevenagel condensations117

etc.

1.3.5.3 Hydrogenation Reactions

The selective hydrogenation of organic molecules is one of the most important

chemical reactions for the synthesis of new compounds and the synthesis of effective

catalysts that can catalyze hydrogenation of arenes under milder conditions remains a

significant challenge.118

The reaction can be catalyzed homogeneously or

heterogeneously, but it is well recognized that the heterogeneous version is by far

more interesting from an industrial point of view,119

offering well-known benefits in

terms of waste reduction, easy separation of the catalysts and its recyclability.120

With

the aim of improving efficiencies, new catalysts and supports are being developed

continuously. Transition metals, such as Pd, Pt, Ru, Rh or Ni, both homogenous and

heterogeneous, are catalysts of choice for this reaction. However, in an effort to



develop a more sustainable approach, their cost, toxicity and potential depletion has

fuelled the development of alternative hydrogenation catalysts. Iron, Cobalt and

Nickel complexes were shown to be active catalysts121

for the hydrogenation of

olefins,122

and the selective hydrogenation of alkynes to alkenes. Recent

developments in nano materials provided efficient methods for catalyst development

and the use of iron in the form of suspendable nano particles for its applications in

catalysis is interesting as it also provides magnetic properties suitable for easy

separation of the catalyst from the reaction mixture. One of the challenging tasks in

this regard is the achieving stability of metal nano particles on the catalyst support.

Stein et.al,123

have overcame this limitation by stabilizing Fe NPs made by

decomposition of Fe(CO)5 onto graphene sheets. Although the resulting particles

were active hydrogenation catalysts, they were prone to oxidation in the presence of

either oxygen or water atmosphere prevail during the reaction.

1.4 Objectives and Outlook of the Present Work

Based on the above discussion, the materials to possess good catalytic activity should

have properties such as porosity with inter connectivity of pores, crystallinity, high

surface area, thermal stability, acid bearing capacity or acid site density and strength

of acid sites. Zeolites, by virtue of most of above mentioned properties, have been

emerged as industrial catalyst in petrochemical refineries, may also extend to specific

application in fine chemicals. However the presence of smaller micropores that

cannot accommodate larger molecules make the application limited and demands

novel synthesized materials for having large dimension porosity such as meso, or

combination of micro-meso and micro-meso-macro (hierarchical pores). To solve

these problems porous carbon composites and metal oxides with infinite network



materials can be functionalized by acid or metal ions or ion–clusters are emerging as

tremendous scope in chemical and material research field. Thus Precise designing

strategies for acid functionalized porous carbon composite, metal supported nano-

particles and hierarchical zeolitic metal oxides by using low cost carbon source (such

as petroleum waste, glucose, levulinic acid and phloroglucinol) or structure directing

agent are the key factors for development of cost effective synthetic protocols are the

contemporary challenges of this field which need to be addressed.

The present work is focused on the development of new 1) porous carbon

composites, with acidity and magnetic properties 2) hierarchical porous zeolites

having diverse structural features enriching the priori information useful towards the

‘designing’ of novel materials. In view of the importance of porous materials the

present work aimed to develop new porous material which is stable in liquid phase

reactions or gas phase reactions where polar compounds are the side products. These

reactions are alkylation of phenol, glycerol value addition, hydrogenation in protic

environment and bio-oil up gradation. Notable emphasis on the preparation of acid

functionalized porous carbon, magnetically separable carbon composite and

hierarchical metal oxide has been given by applying the following novel concepts.

The simultaneous carbonization and sulfonation of low cost carbon precursors

(coal tar or glucose) has been adopted to synthesize thermally stable acid

functionalized nanoporous carbon, acid functionalized carbon silica composite

material having high acidity, high surface area useful for bulky molecular

transformations. The acid functionalized carbon silica composite also can be

used for the synthesis of mesoporous silica by simple calcination and the



resultant mesoporous silica has wide application depends on metal

functionalization.

Various acid functionalized carbon silica composite samples has been

synthesized by varying the glucose concentration adopting thermal and

hydrothermal method.

A novel concept of using levulinic acid for the synthesis of carbon

supported metal nano-particle has been adopted having the carboxylic for

interaction with M2+

and Fe 3+ and carbonyl groups for interaction with

phloroglucinol. The levulinic acid also establishes effective metal-support

interaction in which interaction of levulinic acid restricts the agglomeration of

metal nano-particle so that their size remains smaller. The Simultaneous

polymerization then carbonization at higher temperature gives stable carbon

supported nano-particle (no leaching and oxidation in protic solvent viz.

ethanol). The advantage of the present study is that both the chemicals

levulinic acid and phloroglucinol used are cheaper, renewable, non-hazardous

which can avoid use of high cost surfactant for stabilizing

nanoparticles. The synthesized materials have been applied for the selective

side chain hydrogenation reaction.

A novel concept of using low cost glucose as a templating precursor

has been adopted to get hierarchical ZSM-5. In the present study cheaper,

renewable, non-hazardous compound glucose was used as carbon source that

avoids use of high cost surfactant and organosilane. Further , aqueous

ammonia instead of NaOH was used as alkali source during crystallization

for the direct production of protonic zeolite that avoids the otherwise

required additional steps of ion-exchange with ammonia and calcination of



the final material. The other important advantage of the present method lies in

obtains desired porosity by simple method of varying glucose concentration

for fine tuning the pore size. The materials are applied for bulky molecular

transformation of t-butylation of phenol also an industrially important

reaction.

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Chapter 2. Techniques Used for Characterization of Lab Synthesized Materials

Chapter 2: Techniques Used for Characterization of Lab

Synthesized Materials

Characterization defines the catalyst




Chapter 2: Techniques Used for Characterization of Lab

Synthesized Materials

2.1 Introduction

Porous materials with nanometer scale exponentially gaining interest in different

scientific disciplines such as physics, chemistry and biology having their fascinating

characteristics like the nature of their framework such as crystallinity, well

defined physical and chemical properties and the tailorable porosity (high

surface area and hierarchical pore size distribution). These characteristics

fascinated their use in several application such as heterogeneous catalysis, sensor

devices, adsorption, ion-exchange, medical therapy, modification of polymers and

hosts in numerous of technical processes.1 The increasing demand of porous

materials in various fields has become possible due to the knowledge of their new

characteristics with the help of the sophisticated tools and characterization

techniques. To explore the reason behind the reactivity of catalytic sites one should

know the structure and chemical nature of the active component and its change due

to nature and structure of support or due to additives or due to preparation

variables and post preparation modification. The rapid development of the

advanced sophisticated tools and characterization techniques over the last decades

has come up to the understanding of porous material structures. These

characterization methods are Porosimetry, Temperature Programmed Desorption, X-

ray Diffraction, Scanning Electron Microscopy, Transmission Electron

microscopy, Energy Dispersive X-Ray Spectroscopy, Inductively coupled plasma

atomic emission spectroscopy, and Fourier transform infrared spectroscopy.



In this context, a comprehensive discussion regarding the detailed

characterization techniques used for the characterization of all the porous supports

and catalysts, synthesized throughout the research period, have been presented.

2.2 Characterization Techniques

2.2.1 Powder X-Ray Diffraction Analysis

Powder X-ray diffraction is a non destructive technique that is one of most

preliminary and powerful instrumental technique required for the characterization

of nano-porous and nano-structured materials to know about their crystalline and

porous nature. The diffraction of X-Ray arises when it interacted with a periodic

structure of crystalline material.2 In X-ray diffraction technique, a fixed wave length

(λ), is chosen for the incident radiation and Bragg Peaks are measured by observing

the intensity of the scattered radiation as a function of scattering angle 2θ. By

scanning the sample through a range of 2θ angles, all possible diffraction patterns of

the lattice should be attained due to the random orientation of the powdered material.

Conversion of the diffraction peaks to d-spacing allows identification of the

material because each material has a set of unique d-spacing. Typically, this is

achieved by comparison of d-spacing with standard reference patterns. The d spacing

is calculated from the values of the peaks observed from the Bragg's equation

(equation i). The position of the diffraction peaks gives information about the

structure of the material.

nλ = 2d sin θ ---------- i

Where, n is the order of reflection and the values are 1, 2, 3,..., λ is the

wave length of the X-ray radiation, d is the interplanar spacing between two



successive planes and θ is the angle between the incident ray and the scattering

planes. Knowing θ, n and λ, the lattice spacing d can be easily calculated.

X-ray diffractometer consists of a circular table with a stationary X

-ray source and a moving detector, usually a proportional counter, which

records the intensity of the reflected beam as a function of the reflected angle. This

technique provides a wealth of useful information about the geometry of the crystal

lattice, specific atoms and their arrangement in the unit cell of the crystal structure,

degree of crystallinity of the sample, and allows qualitative identification of the

crystalline phase. The position and relative intensity of the lines in the X-ray

diffraction pattern serve as a finger print for a given type of crystalline

material. By comparing an X-ray diffraction pattern against the patterns

collected for known crystalline compounds, the crystallinity and porous nature

material can be determined.

X-ray line broadening of the peak shape of one or more diffraction lines

can be used to estimate the crystal size in powder materials.3 As the particle

size decreases, the reflections in the XRD pattern will be broadened. This correlation

is used in Scherrer's equation (ii) to calculate the particle size.

K cos

= iiDB

Where DB = mean crystallite diameter

K = Scherrer's constant

λ = X-ray wave length (1.5418 Å for Cu Kα radiation)

β = full width at half maximum



θ = Bragg's angle

In addition to crystallite size of the materials, X-ray line broadening

gives information about dispersion and the degree of metal oxide present at the

surface of the support. The minimum detection limit for crystallite size is 4 nm and

the two-dimensional metal oxide over layers cannot be detected by XRD. In the

present course of work, XRD pattern of the support and catalysts were obtained on a

Bruker D8 diffractometer, with nickel filtered Cu Kα radiation (λ=1.5418 Å) with an

applied voltage and current of 40 kV and 20 mA respectively. Bruker D8

diffractometer has two detectors viz. Scintillation counter detector and lynx eye

super speed detector. Scintillation counter detector has been used for the

analysis of samples in which 2 value start below 1° known as low angle XRD

pattern. On the other hand, lynx eye super speed detector has been used to acquiring

the wide angle XRD pattern.

2.2.2 Porosimetry

N2-adsorption desorption measurement is one of the commonly used characterization

tools to determine the specific surface area, nature of pores, pore size distribution, and

to probe surface properties of porous materials.4

The amount of adsorbed/desorbed

nitrogen is measured as a function of the applied pressure, giving rise to the

adsorption/desorption isotherm. The shape of the physisorption isotherm depends

on the porous texture of the measured solid and the operational temperature.

Linearity of the isotherms is generally observed at very low surface coverage and

therefore cannot be easily detected at the higher temperatures so this techniques

normally used for studying the complete range of relative pressure P/P0 at

temperature -196 οC for nitrogen adsorption. The deviation from linearity may be



either towards or away from the pressure axis, depending on the scale of

surface heterogeneity and the magnitude of the adsorbate-adsorbate interactions.

Figure 2.1 IUPAC classifications of different types of sorption isotherms

According to the IUPAC classification, six types of isotherms can be

distinguished as shown in Figure 2.1. Reversible Type I isotherms are given by

the microporous materials such as zeolites molecular sieves and many activated

carbons having relatively small external surface area. Type II & III isotherm is

the normal form obtained with a non-porous or macroporous adsorbents. The type II

isotherm represents unrestricted monolayer-multilayer adsorption. The type IV

isotherms are given by mesoporous adsorbents. In this case, the initial monolayer-

multilayer adsorption on the mesopores walls is followed by capillary condensation.

A characteristic feature of most Type IV and V isotherms is the appearance of

hysteresis loops (Figure 2.2). Hysteresis gives information regarding pore shapes5can



be seen in figure 2.3. A characteristic feature of most Type IV isotherms is the

appearance of H1 or H2 hysteresis loops. The H1 loop is indicative of a

narrow range of uniform mesopores, whereas the more common H2 loop can

usually be attributed to percolation effects in a complex pore network with ink-bottle

type pores.

Figure 2.2 Hysteresis loop seen from type IV isotherm

Figure 2.3 Shape of the pore according to hysteresis loop



2.2.2.1 BET Surface Area

BET theory was first introduced by Brunner, Emmett, and Teller in 1938.6 It is the

most widely used technique in determining surface areas by physical adsorption

of gases at their boiling temperatures. The significance of the BET theory lies in its

ability to determine the number of molecules required to form a monolayer of

adsorbed gas on a solid surface. The basic equation for finding out the surface area

by BET method is given below in eqn. (iii)

P

Va(Po - P)1

Vm C

C -1

Vm C

P

Po+= x iii

Where P is Adsorption equilibrium pressure

PO is Saturated vapour pressure of adsorbate

Va is Volume of adsorbate corresponding to pressure P

Vm is Volume of adsorbate required for monolayer coverage

And C is A constant relating to the heat of adsorption.

According to the BET method, a plot of P/Va(PO-P) against P/PO

yields a straight line when P/PO < 0.3. From the slope and intercept of the straight

line, volume of monolayer (Vm)7

can be calculated which in turn is used in

calculating the specific surface area of the catalyst:

SBET(m2/g)Vm x N

22,414 x W= x ivAm



Where

Vm is Monolayer volume in ml @ STP

N is The Avogadro number (6.0231023)

W is Weight of the sample (g)

Am is Cross sectional area of the adsorbate molecule (0.162 nm2

for N2)

2.2.2.2 Pore Volume and Pore Size Distribution Analysis

Micropore volume and micropore size distribution of microporous zeolites materials

were usually determined by using the t-plots8 and Harvath-Kawazoe method.

9 The t-

plot method consists of a comparison of the amount adsorbed with the statistical

thickness of the adsorbed layer of a known reference isotherm at the same

relative pressure. According to Lippins, Linsen and de Boer8

the thickness t, of

nitrogen monolayer at any point of isotherm is calculated by using the equation (v).

Va

Vm= vt 3.54 Å

Where Va is the volume adsorption at pressure P, and Vm is the volume

of monolayer. A plot of Va verses t is known as the t-plot. Extrapolation of the linear

portion to the ordinate axis gives a positive intercept equivalent to the micropore

volume.

The total pore volume is calculated by measuring the volume of nitrogen

adsorbed at P/P0 near unity. At this relative pressure, adsorbate is assumed to be

condensed inside the pores of the zeolite. The measured total pore volume of zeolite

is larger than the micropore volume due to condensation of adsorbate in the



intercrystalline voids between zeolite crystals, or, in the case of hierarchical zeolite,

in the mesopores. Thus the total pore volume is often assumed to be the sum of

micropore and mesopore volumes in the case of hierarchical zeolite materials.

The pore size distribution of mesoporous materials is based on the

capillary condensation phenomenon and its quantitative expression is given by

Kelvin's equation (eqn. vi)10

relating the adsorbate condensation pressure (Pc) to

the radius of the pore rp. The calculation method is described by Barrett, Joyner

and Halenda, hence called the BJH method.11

Pc

Po

cos

RTrm= viln

Where; γ is the surface tension of the adsorbate at the temperature T, rm

is the mean radius of curvature of the liquid meniscus (Kelvin radius), R is the perfect

gas constant, θ is the angle of contact, V is the molar volume of the liquid

(condensate), rp is the radius of the pore, t is the adsorbed layer thickness. As the

angle θ is generally assumed to be equal to zero because the nitrogen condensate

completely wets the pores, the radius of the pore (rp) and Kelvin‟s radius (rm) only

differ from each other by the thickness (t) of the adsorbed film. The equation

is enlightening with regard to hysteresis. In a straight capillary open at both ends, the

mean radius is related to the two primary radii r1 and r2.

vii1/rm = 1/2 [1/r1 + 1/r2]

only the radius r1 is operative when pores are filling (since r2 = ∞) hence rm in the

equation (eqn. vii) equals 2r1 during filling. However, when pores are emptying

rm = r1= r2. No pore, whether filling or emptying of condensate, is without

adsorptive because of the film of thickness t on the pore walls. The value of t is



derived from an equation or from a reference isotherm. Thus when all pores are

indeed open-ended and cylindrical, eq.vi can be rewritten as follows

Ln [P/Po] = - [ V/RT(r-t )] (for the adsorption branch)

Ln [P/Po] = - [2 V/RT(r-t )] (for the desorption branch)

N2 adsorption/desorption measurements of the all samples during the

course of this research program were carried out by using BELSORB MAX, Japan

instrument and ASAP-2010 unit from Micromeritics (USA) in the relative pressure

range P/P0 from 1 x 10-6

to 1 at liquid nitrogen temperature (-196 οC).

2.2.3 Scanning Electron Microscopy (SEM)

Scanning electron microscopy technique is another powerful tool for studying the

morphological and structural features of the porous materials.12

It produces

images of the sample by scanning it in a raster pattern on the specimen

surface with a focused beam of electrons. The interaction between the electron

beam and the specimen surface produces various types of energetic emissions,

including back scattered electrons, secondary electrons, Auger electrons,

continuous X-rays, and characteristics X-rays. The electrons interact with atoms in

the sample, producing various signals that can be detected and that contain

information about the samples surface topography and composition. The image

displayed on the cathode ray tube comes from the secondary and backscattered

electrons. The secondary electrons are the excited electrons emitted from the

specimen due to bombardment of the electron beam. Scanning electron



microscopy has a large depth of field, which allows a large amount of the sample to

be in focus at one time. The SEM also produces images of high resolution, which

means that closely spaced features can be examined at a high magnification.

Preparation of the samples is relatively easy since most SEM only require the

sample to be conductive. The combination of higher magnification, larger depth

of focus, greater resolution, and ease of sample observation makes the SEM one of

the most important tool used in research areas today. A representative SEM

image of CoFe2O4@C material has been shown in figure 2.4. A simple schematic

diagram of the SEM can be seen in Figure 2.5.

Figure 2.4 SEM image of carbon embedded CoFe2O4 nano-particles.



Figure 2.5 A schematic diagram of the scanning electron microscope (reproduced

from http://www.purdue.edu/ehps/rem/rs/sem.htm).

In order to reveal the surface morphologies of the samples under

investigation in this study, scanning electron micrographs were obtained using a

Quanta-200F field-emission scanning electron microscope (FE-SEM) operated at

1-20 kV with an energy dispersive spectrometer (EDS) attachment. Because the

SEM utilizes vacuum conditions and uses electrons to form an image, special

preparations must be done to the sample. All water must be removed from the

samples because the water would vaporize in the vacuum. All metals are conductive



and require no preparation before being used. All non-metals need to be made

conductive by covering the sample with a thin layer of conductive material. Samples

for SEM were prepared by adding a very minute amount of the finely powered

samples onto a carbon tape. Then the samples was coated with a film of gold and then

mounted over the probe for scanning.

2.2.4 Transmission Electron Microscope (TEM)

Transmission electron microscopy (TEM) is a vital characterization tool frequently

used for the detailed examination of nano-structured materials. It measures the

quantitative particle or grain size, size distribution, and morphology (such as shape,

geometry, and dimensions) of the nano-structured materials.13

Further, in the

analysis of mesoporous materials, TEM techniques give a clear indication of

ordered structure with long narrow channels and ordered pore openings. The

basic principle of the TEM is same as of the light microscope, but it uses electron

instead of light. Transmission electron microscopes use electrons as light source and

their much reduced wavelength make it possible to achieve resolutions of one

thousand times better than with a light microscope. Thus, objects of the order of 10-

1nm can be resolved. The typical TEM image of CoFe2O4@C is given in figure 2.6.

The schematic diagram of a transmission electron microscope is shown in Figure 2.7.

In this technique, a beam of electrons is transmitted through a sample containing

specimen and images are formed from the interaction of the electrons. Then, the

image is magnified and focused onto a fluorescent screen with the help of

electromagnetic lenses or detected by sensor such as a charge couple device

(CCD) camera. In terms of magnification and resolution, TEM has an

advantage compared to SEM. TEM has up to a 50 million magnification level

while SEM only offers 2 million as a maximum level of magnification. The



Figure 2.6 TEM image of carbon embedded CoFe2O4 nano-particles.

Figure 2.7 A schematic diagram of the scanning electron microscope (reproduced

from http://www.britannica.com/EBchecked/topic/602949/transmission-electron-

microscope-TEM).



resolution of TEM is 0.5 angstroms while SEM has 0.4 nanometers. However,

SEM images have a better depth of field compared to TEM produced images.

Another point of difference is the sample thickness, “staining,” and preparations.

The sample in TEM is cut thinner in contrast to a SEM sample. In addition,

SEM sample is “stained” by an element that captures the scattered electrons.

2.2.5 Energy Dispersive X-Ray Spectroscopy

Energy-dispersive X-ray spectroscopy is a qualitative and quantitative X-ray

micro analytical technique that can be used for the identification of elements and

their relative proportion in terms of atomic percentage present within the materials.

It can be combined with other imaging tools such as scanning electron microscopy

(SEM), transmission electron microscopy (TEM), and scanning transmission

electron microscopy (STEM) for the identification of the elements present on areas

as small as nanometers in diameter. As a type of spectroscopy, it relies on the

investigation of a sample through interactions between electromagnetic radiation

and matter, analyzing x-rays emitted by the matter in response to being hit

with the electromagnetic radiation. Its characterization capabilities are due in large

part to the fundamental principle that each element has a unique atomic structure

allowing x-rays that are characteristic of an element's atomic structure to be identified

uniquely from each other.

In this technique, a beam of electrons was focused on the sample

in either a scanning microscope or a transmission electron microscope. The

electrons from the primary beam penetrate the sample and interact with the

atoms as a result of which two types of X-rays "Bremsstrahlung X-rays" and

"Characteristic X-rays" were generated. The X-rays are detected by an Energy



Dispersive Detector, which displays the signal as a spectrum, or histogram, of

intensity versus Energy. The energies of the characteristic X-rays allow the

elements making up the sample to be identified, while the intensities of the

characteristic X-ray allow the concentrations of the elements to be quantified.

2.2.6 Thermo Gravimetric Analysis (TGA)

It provides a quantitative measurement of any weight change associated with a

transition. This also provides temperature at which dehydration or

decomposition takes place. Changes in weight are a result of the rupture and/or

formation of various physical and chemical bonds at elevated temperatures that lead

to the evolution of volatile products or the formation of heavier reaction products.

From such curves, data are obtained concerning the thermodynamics and kinetics

of the various chemical reactions, reaction mechanisms and the intermediate and final

reaction products.14

. TGA is a technique by which the mass of the sample is

monitored as a function of temperature or time, while the sample is subjected to a

controlled temperature program. Thermo gravimetric analysis is mainly directed in

establishing optimum temperature ranges for drying or igniting precipitates.

However, it has a much wider potential in estimating the composition of

moisture content, solvent content, additives, polymer content and filler content. 14

DTA (Differential Thermal Analysis) analysis gives information about the

changes in phase during heating. In differential thermal analysis, the temperature

of a sample and thermally inert reference material is measured as a function of

temperature.15

Any transition that the sample undergoes will result in the liberation or

absorption of energy by the sample with a corresponding deviation of its

temperature from that of the reference. This differential temperature versus the

programmed temperature at which the whole system is being changed shows the



transition temperature whether the transition is exothermic or endothermic. TGA

technique is employed in the present study in order to determine the thermal

stability of the zeolite framework, weight loss occur due to water removal from

zeolite lattice and the weight loss occur during the decomposition of the

organic templating agents that are used at the time of synthesis. The Diamond

Thermogravimetric/Differential Thermal Analyzer (TG/DTA) of Perkin Elmer

combines the high flexibility of the differential temperature analysis (DTA)

feature with proven capabilities of the Thermogravimetry (TG) measurement

technology. The combination not only ensures that the sample is exposed to identical

thermal treatment and environment but allows one to determine whether an

endothermic or exothermic transition is associated with weight loss in contrast to a

melting or crystallization process. Thermo-gravimetric analyzer. The thermograms

of the samples are recorded between 25-800 οC with a heating rate of 10

οC/min at atmospheric pressure. In present study the thermogravimetric analysis

was carried out by using Perkin Elmer-Pyris Diamond TG/DTA instrument.

2.2.7 Temperature Programmed Desorption (TPD)

Temperature programmed desorption (TPD) is based on the basis that stronger acid

sites require more energy to desorbs the ammonia than that of weaker acidic sites.

The acidity of the catalyst is measured by temperature programmed desorption of

NH3 (NH3-TPD) using a Micromeritics chemisorbs 2750 pulse chemisorption system

where 0.1 g sample is used for each TPD experiment. It is carried out after of the

catalyst sample is dehydrated at 300 οC in helium gas (30 cm

3min

−1) for 1 h. The

temperature is decreased to room temperature (30 οC) and NH3 is adsorbed by

exposing sample treated in this manner to a stream containing 10% NH3 in helium for

1 h at 30 οC. It is then flushed with helium for another 1 h to remove physicosorbed



NH3. The desorption of NH3 is carried out in helium gas flow (30 cm3min

−1) by

increasing the temperature up to desired temperature 10 οC /min heating rate, to

measure NH3 desorption using TCD detector.

2.2.8 Fourier Transform Infrared Spectroscopy (FT-IR)

Fourier transform infrared spectroscopy techniques have been extensively used in

heterogeneous catalysis for the identification of various properties of the catalysts

and catalyst support, which are categorized into the following groups.16

Functional groups at the catalyst surface

Active transient species and reaction intermediates

Framework structure of the materials

Species responsible for surface modification such as catalytic poisoning

Surface acidity of the catalysts

The basic principle of this technique implies that a molecule can

exist in a variety of vibrational energy levels and can move from one level to

another by absorption/release of energy, which is equivalent to the difference in

energy of the two involved levels. The absorption/emission of an electromagnetic

radiation accomplishes these transitions and this forms a basis of vibrational

spectroscopy. A particular given transition between the two energy states usually

ground state (E0) and the first excited state (E1) can be correlated by the following

equations. From the fundamentals of IR spectroscopy the equation relating the force

constant, the reduced mass and the frequency of absorption is:

ῡ = (1/2+V) 1/2πc)√(k/µ) ----------(i)

So E = hν E = E1– E0 = hc/λ = hῡ



As chemical bond is assumed to be harmonic oscillator so from that

concept V is the vibrational quantum number may be 0, 1, 2, 3……etc. So for

fundamental IR bands E=hῡ where E is the energy difference between two

energy levels, h is Planck's c is the velocity of light and ῡ in the wave number.

The most commonly used range of infrared spectrum is between 4000 cm-

1at high frequency end and 400 cm

-1at lower frequency end. The range from

4000 to 1500 cm-1

is generally considered as the functional group region and all

frequencies below 1500 cm-1

are considered characteristic of the fingerprint region.

In the case of porous materials, this technique has been extensively used for

identifying the framework structure of the materials, as well as for identifying the

various functional groups of the support. In addition, it is also used for identifying the

various functional groups of the active component, and to measure the surface acidity

of the catalysts.16

In present study the infrared induced vibrations of the samples under

investigation were recorded using Perkin Elmer FT-IR X 1760 instrument by means

of KBr pellet procedure. In this procedure, a small amount of the sample was

mixed with KBr and finely ground to get a homogeneous mixture. This mixture

was then taken in a die and pressed under high pressure into a transparent pellet

before recording the spectra. Spectra were taken in the transmission mode and the

samples were evacuated before making the pellet and the spectra were taken under

atmospheric pressure and at temperature of 20 οC. Changes in the absorption bands

were investigated in the 400-4000 cm-1

region.



2.2.9 Inductively Coupled Plasma -Atomic Emission Spectrometry (ICP-AES)

ICP- AES is an emission spectrophotometric technique, the principle of ICP-AES is

that excited electrons emit energy at a given wavelength as they return to ground state

after excitation by high temperature Argon Plasma. The fundamental characteristic of

this process is that each element emits energy at specific wavelengths peculiar to its

atomic character. The energy transfer for electrons when they fall back to ground

state is unique to each element as it depends upon the electronic configuration of the

orbital. The energy transfer is inversely proportional to the wavelength of

electromagnetic radiation, Although each element emits energy at multiple

wavelengths, in the ICP-AES technique it is most common to select a single

wavelength (or a very few) for a given element. The intensity of the energy emitted at

the chosen wavelength is proportional to the concentration of that element in the

sample being analyzed. Thus, by determining which wavelengths are emitted by a

sample and by determining their intensities, the analyst can qualitatively and

quantitatively find the elements from the given sample relative to a reference

standard. The wavelengths used in AES ranges from the upper part of the vacuum

ultraviolet (160 nm) to the limit of visible light (800 nm). As borosilicate glass

absorbs light below 310 nm and oxygen in air absorbs light below 200 nm, optical

lenses and prisms are generally fabricated from quartz glass and optical paths are

evacuated or filled by a non absorbing gas such as Argon.

In present study Inductively Aoupled Plasma Atomic Emission

Spectroscopic (ICP-AES) analysis (model: PS 3000 uv, (DRE), Leeman Labs, Inc.,

USA) was carried out for analyzing the presence of metals in catalyst.



2.2.10 Titration Method

Standard acid base titration method was used for existence of total acidity on acid

functionalised carbon silica composite and acid functionalized nonporous carbon. In a typical

method certain amount of catalyst sample was taken and treated with concentrated NaCl

solution by which all the acidic H ions on the acidic groups was replaced by Na ions. The

filtrate (having H ions ) was titrated by NaOH solution to get the total acidity.

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Catal., 2006, 239, 299. (d) A. Katz, M. E. Davis, Nature, 2000, 403, 286.

Chapter 3. Facile Synthesis of Sulfonated Nano-porous …………….Composite and Mesoporous Silica

Chapter 3: Facile Synthesis of Sulfonated Nano-porous

Carbon, Sulfonated Carbon-silica-meso Composite and

Mesoporous Silica

Renewable sources and waste materials produce cheaper materials




Chapter 3: Facile Synthesis of Sulfonated Nano-porous

Carbon, Sulfonated Carbon-silica-meso Composite and

Mesoporous Silica

3.1 Introduction

The concentration and pKa values of catalyst play vital role in organic

transformations, where a high density of accessible strong BrØnsted acid sites

possessing stability in aqueous environment is desired for catalyst development.1 The

use of liquid acids such as sulfuric acid for example suffers from energy inefficiency

and requires separation and recycling steps of acid waste residue. The usability of

recyclable solid materials as replacement to homogeneous acid catalysts is usually

limited due to the low density and strength of the acid sites on the solid surface.2 The

method of immobilization of homogeneous catalyst on to solid supports such as

sulfonation of activated carbon resin and metallic oxide has come up to solve the

problem of acid density, but the procedure is time consuming and involves several

preparation steps.3,4

Moreover, the immobilization of acidic functional group is

difficult and also yields low acid density.

To produce cheaper material the utilisation of low cost chemicals and waste

materials are the great choice of selection as catalyst support or template. These

sources are renewable or waste materials. The one cheaper material available is

petroleum waste coal tar which is easily available for further functionalization by acid

while other sources are the various saccharides. Using of these low cost fossil source

and saccharides leads to environment friendly concept. Further the usability of

recyclable solid materials as replacement to homogeneous acid catalysts is usually



limited due to the low density and strength of the acid sites on the solid surface. In the

preparation of an efficient alternative solid acid catalyst for acid attributed reactions,

in present study a simple one-step method is developed for the synthesis of a new

class of sulfonated nanoporous carbon (SNC) material containing hydrophobic carbon

moiety with hydrophilic -SO3H, -OH and -COOH groups with its high acidic

properties in one hand and sulfonated carbon silica composite (SCS) material

containing hydrophobic carbon moiety with hydrophilic -SO3H, -OH and -COOH

groups surrounded by outer silica shell in other hand. These materials are not only

suitable for further functionalization with acid or metal ions but also provide good

mechanical and thermal stability for catalytic applications.

In present study, petroleum waste coal tar was used as a cheaper and green

carbon precursor for the preparation of nano-porous carbon while glucose was used as

carbon source and structure directing precursor for the preparation of acid

functionalized carbon-silica composite material. The use of these low cost sources are

the alternative to the commonly used high cost resins, ionic surfactants and P123

block co-polymers.5

In order to prepare an efficient alternative solid acid catalyst for acid

attributed reactions, facile and simple one step synthesis of a new class of nano-

porous acid functionalized carbon, sulfonated-carbon-silica composite catalyst have

been carried out and detailed characterization and properties of materials also

investigated.

Tert-Butylation of phenol is an industrially important reaction, and its

products like 4-tert-butyl phenol (4-TBP) and 2,4-ditert-butyl phenol (2,4-DTBP) are

widely used as intermediates. Habitually 4-TBP is used to manufacture various



antioxidants, varnish and lacquer resins, fragrances and protecting agents for plastics.

2,4-DTBP is largely used to produce substituted triaryl phosphates6,7

. The tertiary

butylation of phenol reaction is a typical Friedel–Crafts alkylation reaction, and can

be catalyzed by a variety of acid catalysts like homogeneous Lewis acids. The

product 2,4-DTBP is highly commercially interesting because of the important

application in the production of stabilizers for PVC or UV absorbers in polyolefins.8

In general, the tertiary butylation of phenol is conventionally carried out in vapour

phase reaction at higher reaction temperatures (above 140 ºC) (Table 3.1). However,

the recent developments in novel materials giving opportunity for low temperature

liquid phase catalytic reactions.9,10

The tert-butylation reaction of phenol requires a

large space (for the interaction of bulky reactant molecules , bulky intermediates and

Table 3.1 Tertiary butylation of phenol by different catalyst in literature.

Catalyst Reaction temperature ºC Phenol conversion%

HZOP-31 70 25.1211

H-AlMCM-48 175 59.112

Sulfated titania 200 32.2013

Mesoporous Galosilicate 175 37.014

H-Y(5.2) 130 10015

HPW/MCM-41 130 9915

H-beta 130 7215

FeSBA-1 200 78.516

Ga-FSM-16 160 80.317

MCM-22 145 9418



the products) along with strong acid sites. It is therefore the material synthesized in

this study has been explored whether the composite catalyst possesses both of these

properties for the tert-butylation reaction of phenol.

3.2 Experimental Details

3.2.1 Reagents and Chemicals

Tetraethyl-orthosilicate (TEOS) was purchased from Merck, Germany. Sulphuric acid

was purchased from RFCL India private limited. Phenol and tertiary butanol were

purched from Merck India Ltd. while glucose was purchased from Rankem India Ltd.

Coal tar was used from petroleum waste at IIP. All chemicals were used as received.

3.2.2 Synthesis of Sulfonated Carbon

The synthesis procedure is very simple that involves drop by drop addition of

sulphuric acid (55 gm) to 10 gm of coal tar obtained from petroleum waste followed

by treatment at 100 ºC for 24 h and then carbonization of the resultant mixture in

nitrogen atmosphere at 300 ºC to facilitate the decomposition and transformation of

the petroleum waste to hydrophobic carbon residue bearing sulfonyl groups. The

catalyst material was left for 4 hours in boiling water followed by washing with cold

water to remove the weakly bound acid sites and carbon before using as a catalyst.

3.2.3 Synthesis of Sulfonated Carbon-silica Composite and Mesoporous Silica

Sulfonated carbon silica composite and mesoporous silica were synthesized by the

evaporation–induced di-constituent co-assembly method. Wherein glucose was used

as carbon source as well as templating precursor and tetra-ethyl ortho-silicate (TEOS)

as silica precursor. In a typical preparation 20 gm of glucose was dissolve in 20 ml of

deionized water then 60 gm of TEOS solution was added drop wise under stirring for



three hours to form a miscible gel, after complete mixing 25 gm of H2SO4 drop wise

added to this solution, after two hours the mixture was solidified and turns black due

to hydrolysis of glucose and TEOS. The final precursors have molar composition of

TEOS : 0.385 glucose : 4.8 H2O : 0.88 H2SO4, was left overnight at 100 ºC for

incomplete carbonization and sulfonation , next day the sample was carbonize at 300

ºC for four hours to get sulfonated carbon-silica-meso composite. The resulting

material was washed with hot distilled water until no sulfate ions were detected in the

washed water by using barium carbonate solution. Finally the as synthesized

composite on calcination at 600 ºC for five hours yields mesoporous silica.

3.2.4 Catalytic Application of the Synthesized Materials towards Tertiary

Butylation of Phenol

The reaction of tertiary butanol (TBA) with phenol in presence of solid acid catalyst

mainly produces three products namely 2,4- di-tertiary butyl phenol (2,4-DTBP), 4-

tertiry butyl phenol (4-TBP) and 2-tertiary butyl phenol (2-TBP) having the

decreasing size of 2,4-DTBP>4-TBP>2-TBP, as shown in Scheme 3.1. In present

study, we have applied the liquid phase phenol butylation in two manners one is in

round bottom flask and other is inside Parr reactor.

Scheme 3.1 Structure of reactants and expected products.



3.2.4.1 Liquid Phase Reaction in Round Bottom Flask

Phenol butylation reaction was carried out in round bottom flask equipped with reflux

condenser joint with freezing pump for the continuous water supply reaction

condition. In a round bottom flask 0.5 g of SNC or SCS catalyst (5 wt. % of Phenol+

TBA) was taken then phenol and tertiary butyl alcohol were added to it with the

molar ratio of 1:2.5, then temperature was increases up to 120 ºC and product was

collected after nine hours and used catalyst was separated by filtration, washed with

ethanol dried at 100 ºC and reused for three times.

3.2.4.2 Liquid Phase Reaction in High Pressure Parr Reactor

We have applied the synthesized material for solvent free liquid phase reaction in

Parr reactor at 130 ºC for 5 h. In a typical reaction study, 0.5 g catalyst (5 wt. % of

Phenol+TBA) was taken and transferred into Parr reactor and reactor was pressurized

upto 1 bar then temperature increased by slow heating with PID controlled program

up to 130 οC. The Phenol to TBA molar ratio was 1 : 2.5. The product was collected

after 5 hours and used catalyst was separated by filtration washed with ethanol dried

at 100 ºC and reused for four times.

3.3 Results and Discussion

3.3.1 Properties of Acid Functionalized Nano Porous Carbon Composite

The wide angle XRD pattern (Figure 3.1) of the sample shows the ordered amorphous

nature of the material. The morphology and internal structure of the material analyzed

by SEM, TEM and HRTEM images (Figure 3.2) indicate the formation of porous

carbon matrix consists of interconnected nano particles of about 10 nm. The HRTEM

image of the material shows the nano porous structure of the carbon with uniform



Figure 3.1 XRD pattern of material.

Figure 3.2 A) SEM, B &C) TEM and D) HRTEM images of material.



Figure 3.3 A) N2 adsorption-desorption isotherms and B) The BJH pore size

distribution of the material.

pore size. The porous nature of the material is further supported by N2 adsorption

desorption isotherm (Figure 3.3A). The BJH pore size distribution of the sample

clearly shows that the major contributions of pores are between 1.7 to 2.6 nm (Figure

3.3B).



The FT-IR spectra of the sample (Figure 3.4A) shows broad band centered

around 3,400 cm-1

representing the OH stretching along with peaks around 2929 cm-1

and 2860 cm-1

related to C–H stretching vibrations. The other band appeared around

1715 cm-1

is due to -C=O stretching and that of 1606 cm-1

is related to -OH bending.

The peaks related to -SO3H stretching and O=S=O stretching are appeared at 1207

Figure 3.4 A) FTIR and B) EDX spectra of the material.



cm-1

and 1040 cm-1

respectively. Overall, the FT-IR spectra indicate the presence of -

COOH, -OH, -SO3H and -CH groups in the material. The elemental analysis and

EDX analysis of the material further confirms the presence of carbon, oxygen and

sulphur (Figure 3.4 B). The origin of phenolic -OH and -COOH groups can be

attributed to the open-air synthesis procedure adopted during the simultaneous

carbonization and sulfonation of the material.

The acidity of the functionalized material is determined by acid-base titration

method (Table 3.2,) indicates significantly high acid loading occurred on the material

(as high as 4.03 m mol/g) by the sulfonation method adopted in the present study. The

composition analysis of the material described above indicates the contribution of

three functional groups responsible for this acidity, namely, -SO3H, -COOH and -OH.

Among these, the -SO3H is observed to contribute 1.43 mmol/g of acidity

(determined by CHNS and EDX analysis). Rest of the acidity (2.6 mmol/g) can be

ascribed to the combined contribution of -COOH and -OH groups. Overall, the

presence of -SO3H, -COOH and phenolic –OH groups in the material are observed to

be responsible for the creation of significantly high acidity in the carbon material.

Further, the hydrophilic nature of these functional groups on the material is also

expected to contribute to the chemical interaction with the hydrophilic reactant

Table 3.2 Textural properties and acidity of SNC material

Sample SABET a

(m2g

-1)

Vtotb

(cm3g

-1)

C%c S%

c Acid density due to

–SO3H (mmol/g)

Total

Acidityd

SNC 7.6 0.0252 59 4.57 1.43 4.03

aBET surface area.

btotal pore volume taken from the volume of N2 adsorbed at P/P0 =

0.995. CDetermined by CHNS elemental analysis.

dDetermined by acid base titration.



molecules to facilitate the reaction in an effective manner.19,20

The thermal stability of the material was determined by TGA analysis (Figure

3.5) which shows the initial weight loss at three places; 1) About 7 % weight loss at

190 ºC 2) about 3 % weight loss between 190-282 ºC and the major weight loss of 30

% above 282 ºC that can be ascribed to the removal of water/moisture, weekly stable

carbon moiety and carbon material respectively. The high moisture and water content

possessed by the material can be ascribed to the presence of various hydrophilic

groups. This envisions that the material is stable up to 282 ºC and is suitable for

catalytic applications.

Figure 3.5 DT/TGA spectra of the material.



3.3.2 Properties of Acid Functionalized Carbon-silica-meso Composite and

Mesoporous Silica

The wide angle XRD pattern of both SCS and MS shows that both the materials are

amorphous in nature (Figure 3.6). The small-angle x-ray scattering (SAXS) patterns

of the as-synthesized (SCS) and calcined (MS) samples are shown in Figure 3.7. One

broad peak signifying the average pore-center-to-pore-center correlation length is

observed in both the samples.21

However; the peak is highly intensified in MS and

indicates the significant increase in the order of the meso-structure due to the removal

Figure 3.6 Wide angle XRD patterns of SCS and MS.

Figure 3.7 Small angle XRD patterns of SCS and MS.



of the sulfonated carbon moiety during calcination. This is further reflected in

nitrogen adsorption-desorption isotherms of SCS and MS (Figure 3.8A).

Figure 3.8 A: N2 adsorption-desorption isotherms of MS and SCS, B: The respective

pore size distribution using BJH method are Shown.



The isotherms of both the samples are of type IV, characteristic of mesoporous

materials according to IUPAC Classification, but hysteresis loop of MS sample

appears to be H2 type indicating that the MS has good pore connectivity that usually

observed for large mesopores resulting from removal of sulfonated-carbon moiety.21

The pore volumes of SCS and MS are 0.52cm3/g and 0.87cm

3/g respectively, that

confirms the removal of sulfonated-carbon moiety in SCS and is responsible for

significant increase in pore volume in MS Table 3.3. This phenomenon is further

reflected in the increase in average pore diameter of the SCS from 2.6 nm to 5.3 nm

after calcination (MS) (Figure 3.8 B).

The EDX elemental analysis of samples also supported the removal of the

carbon moiety after calcination (Figure 3.9). The SEM images of samples also

support the phenomenon of removal of carbon moiety during calcination of SCS,

where the black spots representing carbon moiety observed in SCS are disappeared in

MS (Figure 3.10).

Table 3.3: Textural properties of SCS and MS, by N2 adsorption at -196 οC.

Sample SABET

m2g

-1a

SAmi

m2g

-1b

SAmc

m2g

-1c

Vtot

cm3g

-1d

Vmi

cm3g

-1e

D

nmf

SCS 779.67 240.44 539.23 0.52 0.10 2.6

MS 656.47 0 656.47 0.87 0 5.3

aBET surface area.

bmicropore surface area calculated from t-plot.

cmesopore surface area

were calculated as SABET-SAmi. dtotal pore volume taken from the volume of N2 adsorbed

at P/P0 = 0.995. emicropore volume calculated from t-plot.

fBJH adsorption average pore

diameter.



Figure 3.9 EDX spectra of SCS and MS.

The porous nature of SCS can be seen in TEM images Figure 3.11. In TEM images,

we can see the uniform pores are visible supports the porosity pattern of the samples

as seen in figure 3.7a.

TPD analysis of samples reveal that SCS has high acidity than that of MS

(Figure 3.12A) as SCS contains the acid group bearing carbon moiety which

disappears during calcination and absent in the resulting MS. Moreover, the SCS

exhibited acidity similar to sulfonated zirconia.22

The IR spectra of the samples show

the interaction between sulfonated-carbon moiety and mesoporous silica in SCS

(Figure 3.12B). It is known that sulfonated carbon exhibits two characteristic bands

representing -OSO3H group at 1712 cm-1

and 1207 cm-1

.23

In our study, the SCS also

exhibited a band at 1712 cm-1

, but the second one at 1207cm-1

is not distinct as it is

merged with the band at 1090 cm-1

related to silica. The additional bands obtained at

3447 cm-1

and 803 cm-1

are due to presence of –OH and SiO2 stretching vibrations.

The TGA analysis of SCS (Figure 3.13) shows weight loss at two places; 1. about 8

% weight loss below 119 ºC and 2. About 14 % weight loss between 300 ºC and 750

ºC which can be ascribed to the removal of water/moisture and carbon moiety



respectively. This envisions that the catalyst is stable at the chosen reaction

temperature i.e 120 ºC under solvent free conditions.

Figure 3.10 SEM images of SCS and MS.



Figure 3.11 TEM images of SCS.

Figure 3.12 A) TPD spectra of SCS and MS, B) FT-IR spectra of SCS and MS.



Figure 3.13: TGA spectra of SCS.

3.3.2.1 Proposed Mechanism for the Formation of SCS and MS

Based on the textural properties of the materials obtained (Table 3.3), we have

proposed a schematic model for the synthesis of SCS and MS (Scheme 3.2).

Tetraethyl orthosilicate and glucose vigorously hydrolyse under the synthetic

conditions to give -SiOH groups and sulfonyl groups bearing aromatic organic

moiety. This supramolecular assembly of glucose molecule helps to form the cage-

like structure inside the SiO2 where, –SO3H group acts as hydrophilic agent that can

facilitate the interaction between hydrophobic carbon moiety and the hydrophilic

silica moiety for the successful formation of SCS composite, which upon calcinations

expels the sulfonated-carbon moiety to give MS with increased average pore diameter

and pore volume (Figure 3.8B). Aggregation or even close-packing of the SiO2 can

also result in the formation of a mesoporous structure.24

Thus, SiO2 units are self assembled, and their structure effectively sustains the

local strain caused during the carbon removal and mesopore formation. Upon

calcinations, the supramolecular assembly of sulfonated sulfonated glucose molecule



breaks from the SiO2 structure. Contrary to the previously reported templating

pathways using surfactants or block-co-polymers where the interaction between the

template molecules and the silica framework is through hydrogen or ionic bonding,

25,26 in present study covalent bonding is observed to exist between the carbon moiety

and SiO2 of the SCS composite as it is confirmed by the presence of two IR bands at

1712 cm-1

and 1633 cm-1

representing -OSO3H ester bond and aromatic ring

respectively. As a result, the SCS of the present study exhibits pore expansion (Figure

3.8B) rather than the pore contraction (as conventionally observed for surfactants or

block-co-polymer templated materials), up on calcination.

Scheme 3.2 The proposed templating and sulfonation pathway for the synthesis of

SCS and MS.

3.3.3 Performance of the Catalysts towards Tertiary Butylation of Phenol

3.3.3.1 Liquid Phase Reaction in Round Bottom Flask

The SNC and SCS material synthesized in the present studies indicated the promising

catalytic functionality of the SNC and SCS, where, the SNC catalyst exhibited as high

as 65% conversion based on phenol (>97% conversion based on alcohol) than that of

50% for SCS catalyst (Table 3.4). If we compare the product selectivity in case of



SNC catalyst it was found 40.5%, 34.5% and 25% to 2,4-ditertiary butyl phenol (2,4-

DTBP), 4-tertiry butyl phenol (4-TBP) and 2-tertiary butyl phenol (2-TBP)

respectively (Table 3.3) but in case of SCS catalyst it was 18%, 30% and 52% to 2,4-

ditertiary butyl phenol (2,4-DTBP), 4-tertiry butyl phenol (4-TBP) and 2-tertiary

butyl phenol (2-TBP) respectively. The reusability of the catalyst (SCS) synthesized

in this work was investigated by filtering the reaction solution, washing with ethanol

and drying at 120 ºC between consecutive cycles. From above discussion, it can be

seen that SNC has better conversion of phenol and better selectivity towards 2,4-

DTBP. This may be ascribed due to the nonporous nature of SNC gave higher

conversion and with higher bulky molecular selectivity. The results indicate

comparable or better performance of the SNC and SCS catalyst with the reported

results (Table 3.1).

3.3.3.2 Liquid Phase Reaction in Parr Reactor

Table 3.4 Performance of the synthesized catalyst for tertiary butylation of phenol

Catalyst Reaction

time(h)

Conversion of

phenol ( mol% )

Selectivity of product ( mol% )

2-TBP 4-TBP 2,4-DTBP

SNCa 9 65 25 34.5 40.5

SNCb 9 66 24 35.0 41

SCSa 9 50 52 30 18

SCSb 9 49 53 29 18

aFresh catalyst.

bUsed catalyst after three reaction cycle



To see the effect of pressure the reaction was performed in high pressure Parr reactor.

The SNC catalyst exhibited as high as 85% conversion based on phenol (>98%

conversion based on alcohol) with product selectivity of 64.5%, 14.5% and 14% to

2,4-ditertiary butyl phenol (2,4-DTBP), 4-tertiry butyl phenol (4-TBP) and 2-tertiary

butyl phenol (2-TBP) respectively (Table 3.5) while SCS catalyst gave 60%

conversion with 22%, 38% and 36% to 2,4-ditertiary butyl phenol (2,4-DTBP), 4-

tertiry butyl phenol (4-TBP) and 2-tertiary butyl phenol (2-TBP) respectively.

From above discussion, It can be seen that in Parr reactor we have more

phenol conversion as well as more 2,4-DTBP selectivity then that of round bottom

flask and SNC catalyst give better performance than that of respective SCS catalyst.

This may be ascribed to due to better contact between reactant and catalyst inside

autoclave which is not possible in round bottom flask. The higher performance of the

catalyst observed in the present study in compression of reported results having

nearly similar conditions (Table 3.6) can be ascribed to the high acid density of the

Table 3.5 Catalytic performance of the materials

Sample RT

(h)

Conversion of

phenol ( wt% )

Selectivity of product

( wt% )

2-TBP 4-TBP 2,4-DTBP Unidentified

SNCa

5 85.0 14.5 14.0 64.4 7.1

SNCb

5 83.0 15.0 14.0 65.0 6.0

SCSa

5 60.0 36 38 22 4.0

SCSb

5 59.0 35 39 23 3.0

aFresh catalyst.

bUsed catalyst after four reaction cycle



SNC and SCS materials obtained in the single step carbonization and

functionalization adopted during the synthesis. The present materials also exhibited

much higher catalytic activity when compared to the similar –SO3H containing

supports reported in the literature. This may be due to the co-presence of the

hydrophilic –COOH and phenolic –OH groups in the carbon moiety of both the

material that is expected to play an important role in promoting the effective

interaction between hydrophilic reactants and the active sites of the catalyst. Thus the

presence of acidic -SO3H groups along with hydrophilic groups (-COOH & -OH)

present in hydrophobic carbon of present study provides a beneficial factor for the

development of the catalytic process for alkylation reactions, and the catalyst also

exhibits constant phenol conversion up to the 4 reaction cycles (Table 3.5). The

reusability of the catalyst synthesized in this work was investigated by filtering the

reaction solution, washing the spent catalyst with ethanol and drying at 120 ºC

between consecutive reaction cycles.

Table 3.6 Tertiary butylation of phenol compression with literature

This work Sulfated Fe2O3–TiO27 Solid sulfanilic acid

8

Temperature

130 ºC 120 ºCa 120 ºC

Conversion in respect of

phenol

85% - -

Conversion in respect of

TBA

˃97% ~40%b 95%

Time hours 5 9 9

Feed ratio Phenol to TBA 2 2 2



3.4 Conclusions

The findings of the work demonstrated a facile and single step synthesis method for

the preparation of high quality acid functionalised nano-porous carbon (SNC) and

acid functionalized carbon-silica composite materials (SCS). The novel approach of

simultaneous carbonization and sulfonation of coal tar (petroleum waste) produced

acid functionalized nano porous carbon. While simultaneous carbonization and

sulfonation of glucose in an organic silica medium, where glucose acts as a carbon

source as well as a template precursor produced SCS. The SCS is a potential source

for the mesoporous silica preparation by simple calcination. The method is cheaper

and produces thermally stable material suitable for catalytic applications involving

bulky organic transformations. Here we have achieved as high as 4.03 mm/g acidity

in SNC material responsible for as high as 85% phenol conversion in the alkylation

reaction. The porous nature of the material also reflected in the production of high

amount of bulky 2,4-DTBP (65%) product. The phenol conversion and the selectivity

towards 2,4-DTBP on the present catalysts system are observed to be highest ever

reported on the functionalized carbon materials to the best of our knowledge.

Moreover, the active material does not suffer from leaching problems and can be

efficiently reused in consecutive catalytic cycles.

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Chapter 4. Optimization of Acid Functionalized Carbon-Silica………..…… ……Silica preparation

Chapter 4: Optimization of Acid Functionalized Carbon-

Silica Composite Structure for its Catalytic Applications &

Mesoporous Silica Preparation

Glucose concentration and interaction with silica tailors the porosity




Chapter 4: Optimization of Acid Functionalized Carbon-

Silica Composite Structure for its Catalytic Applications &

Mesoporous Silica Preparation

4.1 Introduction

Acidity is an important parameter in catalyst development, where the liquid acids

such as H2SO4, HF and H3PO4 have been proven as efficient catalysts for various

industrial processes by virtue of their higher pKa values and their efficient interaction

with the reactant molecules. However, the toxicity and corrosive nature of the liquid

acids are demanding alternative sources especially those of solid acids that are having

advantage of easy separation from the product, reusability for recycle operation and

their environment friendly nature.1 But, the main limitation in using solid acids lies in

their lower density and strength of acid sites. Moreover, the accessibility of the

reactant to the active sites and their stability in the aqueous environment need to be

established. In order to take advantage of the positive aspects of liquid acids and solid

acids, the method of immobilization of liquid acids on to the solid support, viz.

sulfonation of activate carbon or metal oxides, came into practice in recent years that

provides high acid functionality bearing solid materials for catalytic applications.2

In present study, we have adopted a novel approach of simultaneous

carbonization and sulfonation of glucose in the presence of organic silica (TEOS),

where glucose act as cheaper carbon source as well as structure directing precursor

through sulfonation for the formation of the acidic sulfonated carbon-silica-meso

composite material as described in previous chapter. The previous work inspired us to

study the role of various synthesis parameters such as the concentration of glucose,



sulphuric acid and the method of treatment (thermal or hydrothermal) used for

facilitating interaction between carbon and silica moiety in the SCS material. In

present study various SCS materials has been prepared exhibiting wide range of

properties such as morphology, surface area, porosity and acidity that are expected to

exhibit different catalytic properties. The composite material possessing high surface

area and acidic properties is not only suitable for further functionalization with acid

or metal ions but also provides good mechanical and thermal stability for catalytic

applications.

The production of biodiesel is continuously gaining importance due to its

biodegradable, non-toxic and renewable nature, which is relevant to the present

scenario of call out for the alternative fuels to the traditional fossil fuels. The process

of biodiesel formation involves transesterification reaction between vegetable oils or

animal fats and methanol in the presence of an acid or a basic catalyst, where huge

amount (~10wt%) of glycerol is produced as unavoidable bi-product.3 The properties

of glycerol such as diesel- immiscibility make it not suitable even for fuel blending

and research is on for value addition of glycerol through its chemical conversion to

useful products and to find new applications for this cheap and off grade glycerol

obtained from biodiesel plants. Wide variety of chemicals and fuel blending stocks

were reported to produce from glycerol through the chemical reactions;4 selective

oxidation for dihydroxyacetone, glyceraldehyde, glyceric acid, glycolic acid,

hydroxypyruvic acid, mesoxalic acid, oxalic acid and tartronic acid; reduction for 1,3-

propanediol; and 1,2-propanediol; hydrogenolysis for propylene glycol; dehydration

for acrolein or 3-hydroxypropionaldehyde; halogenation for 1,3-dichloropropanol;

fermentation for 1,3-propanediol; polymerization for polyglycerols and polyglycerol

esters (Table 4.1).



The production of oxygenates from glycerol gains much importance due to

the excellent diesel-blending property of the oxygenates that not only improve the

quality of the fuel but also increases the overall yield of the biodiesel in helping to

meet the target for energy production from renewable sources for transport in the

energy utilization directive. Olefins such as butene or alcohols such as tertiary butyl

alcohol are commonly used as etherifying agents of glycerol, but the main drawback

involved in the use of olefin is the formation of undesired di-olefins and the

formation of huge amount of water in case of using alcohols.12

Esterification with low

molecular weight acids, transesterification with low molecular weight esters and

acetalization with aldehydes or ketones are the other promising and economically

viable alternative routes for the conversion of glycerol.13

Acetalization with ketones,

especially acetone is gaining importance due to the fact that acetone is widely

produced from biomass conversion as well as from the chemical process of cumene

Table 4.1 Value added products from glycerol conversion

Catalyst Reactant Con.% product Selectivity Ref

AC1 @ Bi/Pt (.9) Glycerol 87-97 dihydroxyacetone 50-88 5

[email protected]%Au NaOH &

Glycerol

100 glyceric acid 92 6

0.8%Ce-1.5%Bi-

0.75%Pt-3%Pd/C

Glycerol 100 tartronic acid 58 7

2.7Pt/NaY Aq Glycerol

& H2

98.7 1,2-propanediol 95.9 8

CuCr2O4 Glycerol - propylene glycol 73 9

CsPW Glycerol 100 acrolein 98 10

CeBiPt/C Glycerol polyglycerols 11



cracking. Hence, facilitating reaction between two biomass derived products glycerol

and acetone is advantageous as they constitute an excellent component for the

formulation of gasoline, diesel and biodiesel fuels. These oxygenated compounds,

when incorporated into standard diesel fuel, have led to a decrease in particles,

hydrocarbons, carbon monoxide and unregulated aldehyde emissions. Likewise, these

products also can act as improvers of cold flow and flash point properties of biodiesel

along with simultaneous reduction its viscosity desirable for fuel applications.13b

The main challenge involved in glycerol acetalization is the production of

water, which has to be removed in order to hinder the reversibility of the reaction.

Continuous processes for the formation of solketal employing heterogeneous

catalysts, such as the commercial macro porous acid resins of the Amberlyst family,

have been described by in the literature.13a

More recently, G. Vicente et al.13d

reported

the suitability of sulfonic meso-structured silica as a catalyst for the acetalization of

glycerol. Wider pores, large specific surface area, a relatively hydrophobic surface

and the amount of accessible acid sites were identified as the factors that positively

influence the catalytic performance in this reaction. In the present study, we would

like to explore the applicability of the SCS materials synthesized by using glucose

alone as carbon source as well as templating precursor and to understand the effect of

various synthesis parameters on the properties of catalyst materials and their role in

solketal synthesis. The concentration of glucose and method of synthesis were varied

to see the effect on the final material. In addition to the SCS materials, the study also

focus on the synthesis of hierarchical mesoporous silica (HMS) exhibiting a range of

porosity properties tuneable for the desired applications such as organic mass

transformations, adsorption of gases and immobilization of different organic moieties



and inorganic metals,14

by varying the glucose concentration in the initial synthetic

mixture followed by the simple calcination of the SCS composite materials.

4.2 Experimental Details


Tetraethyl-orthosilicate (TEOS) was purchased from Merck, Germany. Glucose,

Sulphuric acid, Glycerol and Acetone was purchased from RFCL India private

limited. All chemicals were used as received.

4.2.2 Synthesis of sulfonated Carbon-silica Meso Composite and Mesoporous

Silica Materials

Two different methods have been adopted for the synthesis of various sulfonated

carbon silica composite materials (Scheme 4.1). While both the methods follow the

similar procedure and composition of the gel precursors, the main difference lies in

adopting thermal or hydrothermal treatment for controlling extent of interaction

between carbon and silicon species. In a typical synthesis procedure, a solution

obtained by dissolving 20 g of glucose in 20 g de-ionized water was added drop-wise

to the 60 g TEOS solution, followed by drop-wise addition of 23 g of concentrated

sulphuric acid (98%). The solutions were continuously under vigorous stirring

throughout the procedure and the resultant mixture was further allowed for mixing

under stirring for 3 h. The synthesis procedure is common in both the methods up to

this stage while the procedure differs in the following steps. In the thermal treatment

method, the dry gel thus obtained was heated at 120 οC for 12 h in air. On the other

hand, in the second method the gel obtained in the first step was treated inside the

Teflon-lined autoclave at 150 οC for 15 h for hydrothermal synthesis. The ramping



Scheme 4.1 Schematic for the synthesis of materials.

method is used to achieve the temperature (150 οC) maintained by P. I. D. Controller,

where the gradual raise in temperature was carried out with the rate 2.5 οC per minute

and the targeted temperature of 150 οC was achieved in 1h. The third step is common

in both the methods, wherein the resultant solid black mass was treated at 300 οC for

4 h under nitrogen atmosphere to obtain the solid form of sulfonated carbon-silica-

meso composite material. The materials were washed with ample amount of cold-

followed by hot deionized water until no sulphate ions appeared in filtrate solution

(by checking with barium hydroxide solution) and dried at 120 οC temperature for 12

h. The materials synthesised by first method are denoted as sulfonated carbon-silica-

meso composite (SCS) and the materials synthesised by second method are denoted

as hydrothermally treated sulfonated carbon-silica-meso composite (HSCS). Since,

glucose is the carbon source as well as structure directing agent, the concentration of

glucose is varied in both the methods to understand its role in the carbonization and

final properties of the materials. The materials thus obtained are denoted as SCS1/0.3,

SCS1/1, SCS1/2, HSCS1/0.3, HSCS1/1 and HSCS1/2, where the numeric value



indicates the weight ratio of TEOS/glucose taken in the synthesis mixture. Since, the

use of sulphuric acid is for the sulfonation of the carbon moiety, the molar ratio of

glucose to sulphuric acid was kept constant for the synthesis of all the materials. The

SCS and HSCS samples synthesized by the above mentioned methods are acted as

potential source for the production of hierarchical mesoporous silica (MS) materials

that are formed by simple calcination of the SCS/HSCS at 600 οC for 10 h.

4.2.3 Application of Synthesized Composite Materials for Solketal Synthesis

All the synthesized composite materials were used for acetalization of

glycerol with acetone to yield solketal (scheme 4.2). In a typical experiment, 0.25 g of

catalyst (5% of glycerol weight) was taken in a round bottom flask and 18.91 g of

acetone and 5 g of glycerol with glycerol to acetone molar ratio 1:6 was added to it

and the mixture was refluxed at 70 οC for different time duration viz. from 30 min to

4 h. After reaction was completed products were analysed by GC.

Scheme 4.2 Structure of reactants and products.




Carbonization and sulfonation are the two important steps that influence the nature

and properties of the sulfonated carbon-silica composite materials. The rate and

extent of carbonization also influence the amount of sulfonyl bearing groups on the

carbon moiety which are related with the acidity of the final material. Due to these

reasons, the strategy adopted in the present study is related to the change in

concentration of the carbon precursor, glucose and the conditions to facilitate

effective interaction between carbon and silicon species during the simultaneous

carbonization and sulfonation synthesis. The variation in glucose concentration is also

expected to alter the material quality due to the fact of the structure directing property

of its intermediate species. To know the effect of glucose on the properties of

materials such as acidity, porosity and surface area we have varied the glucose

concentration while keeping the TEOS concentration constant. Further, to facilitate

the effective interaction between carbon and silicon species, we have adopted

additional step of hydrothermal treatment of the reaction mixture so as to improve the

simultaneous sulfonation and carbonization.

4.3.1 Effect of Synthesis Conditions on Material Properties

The influence of synthesis conditions, such as the amount of glucose and

concentration of sulphuric acid, on the morphology of SCS, HSCS are investigated.

The SEM images of the samples prepared by varying glucose concentration and

synthesis method have been given in Figure 4.1. The SCS samples synthesized by

thermal method exhibited non-uniform (hierarchical) morphology of agglomerated

spheres in the composite, while those of hydrothermally synthesised samples (HSCS)

appeared in uniform spherical morphology. Among the hydrothermally treated



samples, the sample HSCS 1/0.3 exhibits smoothly surfaced spherical agglomerates

that may be due to the excess amount of silica species that superfluous to generate

sufficient primary silica particles on the surface besides its interaction with carbon in

the carbon silica composite material. At higher glucose concentrations the material

(HSCS1/2) exhibited cracked sphere morphology that is attributed to the formation of

thinner outer shell prone to breakage. The above results demonstrated that the shell

morphology of composite material could be easily controlled by adjusting the ratio of

glucose to silica concentration. However, a commonality observed in both the

methods (SCS as well as HSCS) is the increase in agglomerate size with glucose

concentration. The IR spectra of the samples shows the interaction between silica and

carbon moiety in both SCS and HSCS materials (Figure 4.2 A and B). It is known

that sulfonated carbon exhibits two characteristic bands representing the –OSO3H

group at 1712 cm-1

and 1207 cm-1

.15

In our study, all the SCS and HSCS samples also

exhibited a band at 1712 cm-1

, but the second one at 1207 cm-1

is not distinct as it is

merged with the band at 1090 cm-1

related to silica. Further as the synthesis of

material was carried out in air, there is a fair chance for the oxidation of glucose in

presence of concentrated sulphuric acid to form the –COOH groups. Thus, the band at

1712 cm-1

obtained for the materials may also due to stretching vibration of (C=O) of

-COOH group. The additional bands obtained at 3447 cm-1

and 803 cm-1

are due to

presence of –OH and SiO2 stretching, vibrations. The presence of aromatic carbon is

confirmed by the presence of band at 1620 cm-1

.



Figure 4.1 SEM images of the materials synthesized by thermal method (A, B and C)

and hydrothermal methods (D, E and F).



Figure 4.2 FT-IR spectra of synthesised materials (A) SCS and (B) HSCS.



4.3.2 Porosity and Acidic Properties of the Synthesized Materials

Small angle X-ray diffraction patterns of the samples (Figure 4.3) reveal the presence

of larger meso-porosity in the synthesized materials.16

Textural properties of the

materials given in table 4.2 reveal that the materials synthesised by thermal method

(SCS) exhibit higher surface area and micropore surface areas compared to those

Figure 4.3 low angle XRD of various synthesized materials.



synthesised by hydrothermal method (HSCS). However, a common feature observed

in both SCS and HSCS materials is the increase in the micropore surface area with

the glucose concentration that is indeed expected from the formation of more

microporous carbon material with increasing carbon source, glucose in the synthesis

mixture. Accordingly, except SCS 1/1, the percentage of mesoporous surface area is

lower in SCS materials (Table 4.2). The nitrogen adsorption–desorption isotherms of

Figure 4.4 (A) and (C) N2 adsorption–desorption isotherms of the samples of SCS

and HSCS respectively (B) and (D) is the respective pore size distribution using BJH

method.



SCS samples (Figure 4.4A) indicate that the hysteresis loop representing mesopores

is not H1 type (observed for larger mesopores) in SCS1/0.3, but it is shifted to H1

type with increasing glucose concentration (as in case of SCS1/1 and SCS1/2). In

SCS 1/0.3 the hysteresis loop was broad with range of nitrogen adsorption volume

from 0.2–0.7 P/P0 (relative pressures) signifying the presence of small mesopores.

But in case of SCS1/1, the hysteresis loop representing the range of nitrogen

adsorption volume shifted to higher level (0.6–1.0 P/P0) signifying the presence of

meso-porosity with larger mesopores.16

However, further increase of glucose concentration as in case of SCS1/2 could

not continue this increase rather decrease in area of hysteresis loop was observed.

There seems an optimum amount of glucose required in SCS material, for its effective

interaction with silica species to form larger pores where, the concentration of

glucose used in SCS1/1 (with equal wt. ratios of glucose and TEOS) produced the

material with best porosity properties. This phenomenon is also supported by the pore

size distribution of corresponding samples (Figure 4.4B) where the average pore

diameter of SCS1/0.3 was 2.6 nm which is initially increased with glucose

concentration to 5.6 nm in SCS1/1, while further increase in glucose concentration

resulted in reversible effect of decrease in the size to 3 nm in SCS1/2 sample. Overall,

sample SCS1/1 exhibited superior properties in terms of porosity and average pore

size. Unlike this, all the three materials synthesized by hydrothermal method (HSCS)

exhibited uniform pores of type IV with H1 type hysteresis loop configuration

representing the larger mesopores (Figure 4.4C). The presence of larger mesoporosity

was evident from the sharp uptakes of nitrogen volume adsorbed at relative pressures

of 0.7–0.1.0 P/P0 as a result of capillary condensation inside the mesopores

HSCS1/0.3. Increase in the glucose concentration resulted in significant change in



loop configuration where the area inside the loop is decreased in both HSCS1/1 and

HSCS1/2 samples. This phenomenon is also supported by pore size distribution of the

corresponding materials (Figure 4.4D) where ordered and larger mesopores are

formed (average pore diameter (13.8 nm) at low glucose (SCSS1/0.3) concentrations.

But, increase in glucose concentration resulted in change from ordered mesopores to

hierarchical mesopores of lower pore diameter (average pore diameter of 5.7-5.9 nm),

and the hierarchy of the pores is further increased with glucose concentration

(SCSS1/2). It is interesting to see, at same glucose concentrations, the materials

synthesized by hydrothermal method exhibited larger pore diameter. For example, the

average pore diameter of the HSCS1/0.3 is 13.8 nm against 2.6 nm of the SCS1/0.3.

Table 4.2 Textural properties of the synthesized composite materials.

Sample SABET a

(m2g

-1)

SAmi b

(m2g

-1)

SAmes c

(m2g

-1)

SAmes

(%)

Vtot d

(cm3g

-1)

Vmi e

(cm3g

-1)

Df

(nm)

SCS1/0.3 779 240 539 69.19 0.52 0.10 2.6

SCS1/1 426 166 260 61.03 0.61 0.07 5.6

SCS1/2 425 274 151 35.52 0.32 0.11 3.0

HSCS1/0.3 238 21 217 91.17 0.82 0.00 13.8

HSCS1/1 176 82 94 53.40 0.25 0.03 5.9

HSCS1/2 242 119 123 50.82 0.35 0.04 5.7

aBET surface area.


17

cmesopore surface

area were calculated from (a-b). dtotal pore volume taken from the volume of N2 adsorbed

at P/P0 = 0.995. emicropore volume calculated from t-plot.

fBJH adsorption average pore

diameter.



Figure 4.5 TEM images of the materials synthesized by thermal method and

hydrothermal method.

The porous nature of SCS and HSCS samples is supported by TEM images

Figure 4.5. TEM images shows that SCS1/0.3 and SCS1/1 has uniform porosity while

SCS1/2 has hierarchical porosity in thermally prepared samples. Same trend can be

seen for hydrothermally prepared samples but size of the pores are higher in this case.

The properties of hierarchical mesoporous silica (HMS) samples obtained by

simple calcination of corresponding composite material (for removal of carbon

moiety Table 4.3) indicates that average pore diameter as well as the percentage of

meso pore surface area of the materials increased after the removal of carbon moiety.

This observation suggests that the carbon moiety is surrounded by silica moiety in the

omposite material. Further, increase of glucose concentration in the initial gel resulted

in increase in average meso pore diameter of the resultant HMS.



The acidity of the synthesized composite samples is measured by four

methods; elemental sulphur analysis by CHNS (Table 4.4), EDX analysis (Figure

4.6), Temperature programmed desorption of ammonia (Figure 4.7) and acid-base

titration (Table 4.4). The common trend of increase in acidity of the composite

materials with the glucose concentration was observed for all the samples, further, the

acidity related to –SO3H groups of the samples is lower than the total acidity

measured by titration method. This may be due to the contribution of other functional

groups (-COOH, phenolic – OH), which is supported by IR analysis. But, the only

difference observed between the properties of the materials synthesized by two

methods is increase in acidity is significant in the materials synthesised by

Table 4.3 Textural properties of mesoporous silica with tunable properties.

Sample SA a

(m2/g)

SAb

(m2/g)

SA c

(m2/g)

% SA

( m2/g)

Vtotd

(cm3/g)

Vmie

(cm3/g)

Vmcf

(cm3/g)

D g

(nm)

HMS1/0.3h 656 0 656 100 0.87 0.0 0.87 5.3

HMS1/1h 419 41 378 90 0.66 .01 0.65 6.6

HMS1/2h 345 11 334 96 0.67 .001 0.669 7.7

HMS1/0.3i 388 36 362 93 1.58 0.01 1.57 17.3

aBET surface area,

bmicropore surface area calculated from t-plot,


were calculated from (a-b), dtotal pore volume taken from the volume of N2 adsorbed at

P/P0 = 0.995, emicropore volume calculated from t-plot,

fmesopore volume were calculated

as Vtot -Vmi, gBJH adsorption average pore diameter,

h and

iare the hierarchical

mesoporous silica are synthesized by thermal method and hydrothermal method

respectively.



Figure 4.6 The EDX spectra shows the presence of sulphur in all the synthesized materials.

hydrothermal method (HSCS) when compared to those synthesized by thermal

method (SCS).

TGA analysis of the composite materials synthesized by thermal and

hydrothermal methods (Figure 4.8) shows weight loss at two places: (1) below 100 οC

due to the removal of moisture and (2) between 300 οC and 750

οC due to the removal

of carbon material from the composite material. The above discussion envisions that

the catalysts are stable at the chosen reaction temperature i.e. 70 οC under solvent free

conditions.



Figure 4.7 TPD spectra of synthesised (A) SCS and (B) HSCS materials.



Figure 4.8 TGA spectra of synthesised (A) SCS and (B) HSCS materials.

4.3.3 Plausible Mechanism for the Formation of SCS, HSCS and HMS Materials

Based on the surface area and porosity, morphology of the materials obtained by

SEM images and acidity trends observed in TPD analysis of the composite materials

we have proposed a schematic model for the formation of SCS and HSCS materials

Table 4.4 Elemental composition and acid density of the synthesised materials

Sample Carbon % Hydrogen

%

Sulfur % Acid density due to

-SO3Ha (mmol/g)

TODb

(mmol/g)

SCS1/0.3 22.96 1.93 0.36 0.11 0.90

SCS1/1 30.59 1.79 0.45 0.14 1.20

SCS1/2 48.28 2.18 0.58 0.18 1.35

HSCS1/0.3 25.70 1.45 0.20 0.06 1.05

HSCS1/1 33.38 1.86 0.21 0.06 1.50

HSCS1/2 42.53 1.58 0.23 0.07 2.25

aCalculated from sulfur content assuming all S atoms are in the SO3H form.

bTotal acid

density determined by acid base titration.



obtained by thermal and hydrothermal routes (Scheme 4.3). The TEOS and Glucose

undergo hydrolysis in presence of sulphuric acid to produce the silica and carbon

species in the first step, which is common in both thermal and hydrothermal methods.

However, the direct interaction between hydrophobic carbon species and hydrophilic

silica species is not possible. Here, sulphuric acid can act as sulfonation agent and the

interaction of sulphuric acid with unsaturated cyclic carbon moiety creates the

polarity in the molecule. This supramolecular assembly of glucose molecules helps to

form the cage-like structure inside the SiO2, where otherwise difficult interaction

between hydrophobic carbon moiety and hydrophilic silica moiety is facilitated by the

presence of hydrophilic -SO3H functional groups on the hydrophobic carbon moiety

for the successful formation of the composite.18

In the present synthesis, there is no

structure directing agent is used in the initial gel mixture, but the sulfonyl carbon

Scheme 4.3 plausible mechanisms for the formation of SCS, HSCS and HMS

materials.

species formed by the sulphuric acid treatment of glucose in the initial gel itself acts

as structure directing agent and its further interaction with silica species facilitates the

formation of mesopores (carbon-silica-composite material). Hence, the high amount

of mesopores formed in the hydrothermal method gives indirect evidence to the better



interaction between carbon and silica moiety. The extent of carbonization of the

carbon moiety and its interaction with silica moiety is strongly influenced by the

concentration of sulfonyl group functionalized on the carbon moiety. Hence, the key

factor in the synthesis of composite material seems to be governed by the

carbonization and sulfonation reactions, where thermal and hydrothermal methods

adopted (in the second step of the synthesis) in the present study were observed to

influence the properties of the material. As shown in scheme 4.3, compared to

thermal method, the hydrothermal method adopted in step 2 of the synthesis

facilitates effective sulfonation of the carbon moiety due to the presence of the

autogenous pressure created in the autoclave that results in enhanced interaction

between carbon and silicon moieties. Third step is common in both the methods,

where the solid materials obtained in the second step are treated at high temperatures

under nitrogen atmosphere for the complete carbonization of the materials to obtain

sulfonyl functionalized thermally stable carbon-silica composite materials. As shown

in scheme 4.3, the carbonization step yields different type of materials in two

different methods, where, the effective interaction of sulfonyl groups with carbon

moiety facilitated in hydrothermal method yields homogenously distributed sulfonyl

interacted carbon-silica composite (HSCS) with larger mesopores, while the thermal

method results in the formation of heterogeneously distributed carbon having

localized carbon moieties along with silicon interacted carbon responsible for

formation of considerable micropores and smaller mesopores in SCS materials. The

fourth and final step is the production of mesoporous silica from the composite

materials by thermal treatment to remove the carbon moiety in the composite

material, where both HSCS and SCS materials produced hierarchical mesoporous



silica (HMS), with only difference of producing larger mesopores in hydrothermal

method and smaller mesopores in thermal method.

From above discussions, the hydrothermal method seems to be better to

synthesize the composite material (HSCS) with larger mesopores and higher acidity

required for the catalytic transformation of bulky molecules. However, the presence

of micropores and the low diameter mesopores in SCS 1/0.3 resulted in high surface

area of this material. Hence, this material also exhibits lower average pore diameter

values that further confirm the presence of carbon/carbon-silica inside the silica shell

which finds applications in catalysis due to its high surface area and hierarchical

porosity.

4.3.4 Performance of SCS and HSCS Materials towards Solketal Production

All the composite materials synthesized in this study have been tested for glycerol to

solketal reaction under similar conditions by taking reactant mixture in the round

bottomed flask attached with reflux condenser at 70 0C reaction temperature and

glycerol/acetone molar ratio of 1/6. In a typical reaction conducted on HSCS1/2

indicated the gradual increase of conversion from 30% to 82 up to the reaction time

of 30 minutes and the conversion levels are stabilized and no further change in these

values observed with reaction time (Fig. 4.9). Hence, the reaction time of 30 minutes

is considered for equilibrium attainment of the reaction and the product is collected

after this time period on all the catalysts. A blank reaction conducted in the absence

of catalyst ascertained that there is no production of solketal. Among the various

catalysts, the highest glycerol conversion of 82% along with 99 % selectivity to

solketal was obtained over the HSCS1/2 (Table 4.5). The highest conversion of

glycerol observed on HSCS1/2, despite of its lower porosity and low surface area



Figure 4.9 Performance of a typical composite catalyst with reaction time.

Table 4.5 Catalytic activity and product distribution with time.a

Catalyst Conversion (%) Solketal Sel. (%) TOF/hb

SCS1/0.3 76 95 39

SCS1/1 79 76 37

SCS1/2 75 90 30

HSCS1/0.3 79 98 35

HSCS1/1 80 98 32

HSCS1/2 82 99 30

Amberlyst-1531 85.1 -

a0.25 g of catalyst (5% of glycerol weight) was taken in a round bottom flask and 18.91g of

acetone and 5 g of glycerol with glycerol to acetone molar ratio 1:6 was added to it and

reflux at 70 0C for 30 min. bTOF value is based on the moles of the glycerol converted per

mole of total acid site per h.



indicate that the mesopores size alone is not responsible for the catalytic activity of

these composite materials. Since, the reaction under study is of acid catalyzed nature,

the catalytic activity of the materials may be related with the acidity of the samples.

The acidity patterns given in TPD spectra and total acidity measured by NaOH

titration indeed indicate the highest activity exhibiting sample HSCS1/2 also exhibits

highest acidity that supports the direct role of acidity in catalytic activity. All other

composite materials also exhibited the higher conversion values of > 75 % (lower

when compared to HSCS1/2) of glycerol. A general trend observed in catalytic

activity is that the hydrothermally treated composite materials (HSCS) outperformed

the corresponding samples prepared by thermal method (SCS) at all the glucose

concentrations. This may be due to the higher total acid density and larger mesopore

formation facilitated in the hydrothermal treatment method. However, TOF values

calculated for HSCS samples are comparable with those of the SCS samples (Table

3). Further, the performances of HSCS materials are also comparable with those

reported for sulfonic acid modified silica catalysts (82.5% for Ar-SBA-15 and 79.0%

Pr-SBA-15) (Table 4.5). However, the performances of the catalysts are not directly

correlated with the amount of sulphur estimated by elemental analysis. This may be

due to the combined contribution of -COOH and phenolic - OH groups (in addition to

-SO3H) to the total acidity. This is in accordance with the results reported for the

sulfonated carbon catalysts.19

Further, the co-presence of the hydrophilic –COOH and

phenolic –OH groups in the HSCS materials of the present study may also play an

important role in promoting the activity of the catalyst by creating strong affinity

between the hydrophilic parts of the reactants with the catalyst. Thus the presence of

acidic SO3H groups along with hydrophilic groups (-COOH & -OH) present in



composite material of present study provides a beneficial factor for the development

of the catalytic process for solketal production, and the catalyst also exhibits constant

glycerol conversion up to the 4 reaction cycles (Table 4.6).

4.4 Conclusions

The synthesis of sulfonated carbon-silica-meso composite materials with

tuneable acidity and porosity are adopted for first time by applying simple one step

method of simultaneous carbonization and sulfonation. The simplicity involved in the

material synthesis using low cost glucose as a carbon source as well as structure

directing precursor makes the present method novel to those relevant works reported

in the prior art. The materials exhibited excellent catalytic activity in the acetalization

of acetone with a renewable feedstock, glycerol to produce 2,2-dimethyl-1,3-

dioxolane-4-methanol (solketal) thus provides an efficient heterogenous catalyst for

the value addition of the undesired bi-product glycerol obtained in the biodiesel

synthesis. The glycerol conversion and product selectivities achieved on these

Table 4.6 Recycling experiments on the HSCS1/2 catalyst for the synthesis of solketala

Run Glycerol conversion Total acid densityb (mmol/g)

1 82 2.25

2 80 2.20

3 81 2.19

4 79 2.15

a0.25 g of catalyst (5% of glycerol weight) was taken in a round bottom flask and 18.91g

of acetone and 5 g of glycerol with glycerol to acetone molar ratio 1:6 was added to it and

reflux at 70 0C for 30 min bacidity was determined by acid base titration.



materials are comparable to those reported for other sulfonated materials. Moreover,

the active mesoporous materials do not suffer from leaching problems and can be

efficiently reused in consecutive catalytic cycles. The synthesized SCS materials and

the mesoporous silica (MS) obtained by carbon removal through simple calcination of

SCS exhibit different porosity and can be used as catalysts and supports for vivid

catalytic applications.

4.5 References

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Chapter 5. Synthesis of Carbon Embedded MFe2O4…. ………………………Efficient Hydrogenation Catalysts

Chapter 5: Synthesis of Carbon Embedded MFe2O4 (M =

Ni, Zn and Co) Nano-particles as Efficient Hydrogenation

Catalysts

Effective interaction between precursors produces quality materials

Ph.D. Thesis of Mr. Devaki Nandan CSIR-IIP


Ph.D. Thesis of Mr. Devaki Nandan Page 127 CSIR-IIP

Chapter 5: Synthesis of Carbon Embedded MFe2O4 (M =

Ni, Zn and Co) Nano-particles as Efficient Hydrogenation

Catalysts

5.1 Introduction

Recently carbon materials are gaining importance as catalyst supports because of

their energy efficient and environment friendly synthesis process facilitated by simple

hydrothermal treatment of low-cost chemicals such as glucose. 1-5

This type of

synthesis process belongs to “green chemistry” because the reactant is safe and the

preparative process causes no contamination to the environment. Moreover, the

material also possesses the properties suitable for functionalization with acidic and

metal groups required for catalytic applications. According to the research findings on

the synthesis steps of carbon based materials, the carbon source first polymerize to

form small spheres or agglomerated particles which begin to carbonize to form multi

aromatic carbon sheets that eventually lead to the formation of well condensed inner

dense carbon matrix with outer layer of multi aromatic ring during the process of

hydrothermal synthesis and heat treatments.1, 6-9

The high temperature carbonization

treatments given during the process give the material thermal and chemical stabilities

to efficiently protect the metal spheres from being dissolved in protic environment as

the dense structure of the materials inhibit the hydrogen or hydroxyl ion to get in

contact with metal. Moreover, the outer multi carbon layer of the material can have

many functional groups, such as carboxylic, aldehyde, and hydroxyl groups, on their

surface suitable for establishing chemical interaction with the desired compounds

such as noble metal nano-particles (NPs) to obtain metal functionalized catalysts.10,11

From above advantages, many researchers have tried to attach metal spheres or metal



nano-particle on to the carbon support.12-14

Wang et al. used oleic-acid-decorated

Fe3O4 NPs as the core of Fe3O4/carbon spheres.15

Zhang et al. reported the fabrication

of functional 1D magnetic NPs chains with thin carbon coatings by using urea as the

surfactant.16

However, the size uniformity and the thickness of carbon layer still need

to be better controlled and its application as catalyst support needs to be investigated.

In the present work, magnetically separable carbon supported MFe2O4 nano-

particles (MFe2O4 @C) where M = Ni2+

, Zn2+

and Co2+

have been successfully

synthesized by adopting a novel route of using environment-friendly phloroglucinol

as carbon source and levulinic acid possessing both carbonyl and carboxyl functional

groups as connecting agent between metal ions and the carbon source through

hydrothermal treatment followed by carbonization, where, the interaction of carboxyl

groups with the metal ions is believed to be responsible for the formation of MFe2O4

nano particles. The synthesized materials are explored for their catalytic application

in selective hydrogenation reactions.

The selective hydrogenation of organic molecules is one of the most important

chemical reactions for the synthesis of new compounds and the synthesis of effective

catalysts that can catalyze hydrogenation of arenes under milder conditions remains a

significant challenge.17

The reaction can be catalyzed homogeneously or

heterogeneously, but it is well recognized that the heterogeneous version is by far

more interesting from an industrial point of view,18

offering well-known benefits in

terms of waste reduction, easy separation of the catalysts and its recyclability.19

With

the aim of improving efficiencies, new catalysts and supports are being developed

continuously. Transition metals, such as Pd, Pt, Ru and Rh or Ni, both homogenous

and heterogeneous, are catalysts of choice for this reaction. However, in an effort to

develop a more sustainable approach, their cost, toxicity and potential depletion has



fuelled the development of alternative hydrogenation catalysts. Iron, Cobalt and

Nickel complexes were shown to be active catalysts 20

for the hydrogenation of

olefins,21

and the selective hydrogenation of alkynes to alkenes. Recent developments

in nano materials provided efficient methods for catalyst development and the use of

iron in the form of suspendable nano particles for its applications in catalysis is

interesting as it also provides magnetic properties suitable for easy separation of the

catalyst from the reaction mixture. One of the challenging tasks in this regard is the

achieving stability of metal nano particles on the catalyst support. Stein et al.,22

have

overcame this limitation by stabilizing Fe NPs made by decomposition of Fe(CO)5 on

to graphene sheets. Although the resulting particles were active hydrogenation

catalysts, they were prone to oxidation in the presence of either oxygen or water

atmosphere prevail during the reaction.

The present method deals with the concept of simultaneous carbonization and

metal dispersion to synthesize MFe2O4 oxide nano-particles embedded carbon

support (MFe2O4@C) useful for the selective hydrogenation of double bond present

in cyclic hydrocarbons (non-aromatic) and side chains. The catalyst NiFe2O4@C

exhibits excellent activity in selective hydrogenation of styrene to achieve as high as

100% selectivity towards side chain hydrogenation to form ethyl benzene as well as

hydrogenation of cyclohexene to cyclohexane (75%). The materials also possess

stability in the protic environment of the solvent such as ethanol that makes the

method advantageous for catalytic applications. Compared to the reported prior art

catalysts, the as-synthesized catalyst of the present study exhibits higher or

comparable catalytic activity and better recyclability towards the reduction of styrene

and cyclohexene in the presence of protic solvent viz. ethanol.



5.2 Experimental


All the reagents were of analytical grade (Merck India Ltd.) and used without further

purification including phloroglucinol, glucose, Fe(NO3)3, Zn(NO3)2, Co(NO3)2 and

levulinic acid, while deionized water was used for preparing the solutions.

5.2.2 Synthesis of MFe2O4@C Materials

The MFe2O4 nanoparticles were prepared by the hydrothermal method. In a typical

synthesis procedure a certain amount of phloroglucinol was dissolved in water to

form a clear solution, followed by sequential addition of Fe(NO3)3 solution, bivalent

metal solution (NiCl2 or Zn(NO3)2 or Co(NO3)2) and levulinic acid. The mixture with

the molar ratio of 1 Fe(NO3)3: 1.05 phloroglucinol : 4.5 levulinic acid : 1.68 M salt

(NiCl2 or Zn(NO3)2 or Co(NO3)2) : 73 H2O was stirred vigorously for 60 minutes and

then sealed in a Teflon-lined stainless-steel autoclave (250 ml capacity). The

autoclave was heated and maintained at 170 °C for 48 h, and then allowed to cool to

room temperature. The black solid product obtained at the end of the synthesis was

then carbonised at 500 °C for 4 h under a nitrogen atmosphere, cooled down to room

temperature and washed several times with ample amount of water followed by

ethanol, which was finally dried at 60 °C for 6 h.

5.2.3 Application of Synthesized Materials for Selective Hydrogenation Reaction

The catalytic performance of all the synthesized materials has been studied towards

the hydrogenation of three types of reactants (scheme 5.1) namely (1) styrene, (2)

cyclohexene and (3) cyclohexanone. In a typical reaction procedure, 10 ml ethanol

was added to a mixture of 1 mol styrene/cyclohexene/cyclohexanone and 5 mol% of



Scheme 5.1 Chemical structures of reactants and products.

catalyst and the whole mixture was transferred to a Parr reactor autoclave of 25 ml

volume capacity, sealed tightly and pressurised by hydrogen up to 40 bar. The

reaction was conducted at 80 °C for 24 h and the product obtained at the end of the

run was filtered and analysed by GC/GC-MS. The qualitative measurement of the

product was performed by GC-MS, while the quantitative analysis was performed

with GC results. The reaction product is analyzed using a GC equipped with the

DBwax column and the FID detector. After the completion of the reaction, the

catalyst was recovered from the reaction mixture via magnetic separation followed by

washing with hot water, ethanol, dried at 100 °C and reused for multiple cycles. The

recyclability of the as-synthesized catalyst was determined using the spent catalyst up

to 4 cycles. Further to see the effect on reaction kinetics the 4th time recycled catalyst

was used and the reaction product was analyzed at different time intervals. The



reaction was also conducted homogeneously under the same reaction conditions so as

to check the activity of free metal ions where NiCl2 and Fe(NO3)3 salt solutions were

directly used as the source of Ni2+

and Fe3+

ions with the concentration of ions

equivalent to those in the heterogeneous NiFe2O4@C catalyst.


5.3.1 Scanning Electron Microscopy and Transmission Electron Microscopy and

High Resolution Microscopy

The morphology and structure of the materials were examined by field emission

scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM)

and high resolution TEM (HRTEM). The FE-SEM images of as synthesized materials

shown in Figure 5.1 reveal the difference in morphology of the particles, where, well-

defined and uniform size spherical particles of ~30 nm is observed for CoFe2O4@C

sample. The ZnFe2O4@C also exhibited similar size and morphology but the particles

are appeared as close agglomerates in this sample. On the other hand, the

NiFe2O4@C material exhibited compact agglomerated morphology without showing

any clear defined particles. The TEM images of NiFe2O4@C, ZnFe2O4@C and

CoFe2O4@C materials (Figure 5.2) clearly show the presence of metal oxide nano-

particles at carbon with a grain size range of 10–20 nm. The size of metal oxide nano-

particles (indicated with arrows in images) in case of NiFe2O4@C is smaller than that

of ZnFe2O4@C and CoFe2O4@C materials. Further, the HRTEM images of

NiFe2O4@C (Figure 5.3) reveal, well-resolved lattice fringes with an inter plane

distance of 0.252 nm (representing the spinel type of the lattice structure of MFe2O4)

arising from the (311) plane of MFe2O4.



Figure 5.1 SEM images of MFe2O4 nano-particles@C.



Figure 5.2 TEM images of MFe2O4 nano-particles@C.



Figure 5.3 HRTEM images of MFe2O4 nano-particles@C.



5.3.2. X-Ray Diffraction and Porosimetry

HRTEM images of MFe2O4 (Figure 5.3) revealed the well-resolved lattice fringes

with an inter plane distance of 0.252 nm (representing the spinel type of the lattice

structure of MFe2O4) arising from the (311) plane of MFe2O4@C materials, which are

consistent with the X-ray diffraction results (Figure 5.4A). The wide angle XRD

analysis (Figure 5.4A) revealed that the positions and relative intensities of the

diffraction peaks matched well with those of the standard MFe2O4. The peaks at 2θ

values at 18.50, 30.28, 35.76, 37.20, 43.72, 54.08 and 57.40 indexed to the (111),

(220), (311), (222), (400), (422) and (511) planes of a face-centered cubic M2+

iron

spinel phase respectively, which are consistent with the standard XRD data of the

MFe2O4 phase (JCPDS No. 10-325). If we compare the intensity of the NiFe2O4@C

it is sharp and intense than that of ZnFe2O4@C and CoFe2O4@C this may be due to

less carbon encapsulated (more carbon embedded) structure of this sample.23

The

XRD spectra of ZnFe2O4@C exhibited other peaks at 2θ 31.6, 34.4, 36.2 are indexed

to the (100), (002) and (101) planes of hexagonal ZnO wurtzite structure (as

Figure 5.4 (A) Wide angle XRD patterns of MFe2O4 nano-particles@C materials (B)

enlarged XRD of ZnFe2O4@C.



impurity), (JCPDS data no. 36-1451) (Figure 5.4B)24-26

while such crystalline

impurities are not observed in other two samples i.e NiFe2O4@C and CoFe2O4@C.

The particle size of the materials is further supported by the average crystallite size of

the materials estimated from the full width at half maxima of the respective peaks at

2θ values of 29–60ο (in XRD), using Scherrer’s equation (Table 5.1). The particle

size measured by XRD further match with the size measured by TEM images of

NiFe2O4@C, ZnFe2O4@ and CoFe2O4@C materials as shown in figure 5.2.

The porous nature of the materials was confirmed by measurement of the

nitrogen adsorption–desorption isotherm (Figure 5.5) that represents the type-IV

isotherm with a hysteresis loop in the range of 0.7–1.0 P/P0, suggesting the capillary

condensation of the adsorbed gas in the narrow pores of the material (Figure 5.5).

Figure 5.5 N2 adsorption desorption isotherm and respective pore size distribution (inset) of

MFe2O4 nano-particles @ carbon. (A) NiFe2O4@C (B) ZnFe2O4@Cand (C) CoFe2O4@C.



The pore size distribution of the corresponding sample measured by the Barrett–

Joyner–Halenda (BJH) method (Figure 5.5 inset) further reveals the hierarchical

nature of the porous MFe2O4@C sample where the presence of mesopores of

different diameter was observed to coexist. The BET surface area and total pore

volume measurements of the hierarchical porous NiFe2O4@C of the present study are

13 m2g

−1 , 0.12 cm

3g

−1which are almost similar to that of the single crystal magnetite

hollow spheres of Fe3O4 reported in the literature (13.5 m2g

−1 total pore volume is

0.21 cm3g

−1), while the surface area and the total pore volume of ZnFe2O4@C and

CoFe2O4@C are 27 m2g

−1, 0.17 cm

3g

−1and 39 m

2g

−1, 0.18 cm

3g

−1respectively show

that these materials are more porous than that of NiFe2O4@C.

5.3.3. FT-IR, EDX, CHNS and ICP-AES Investigation

The Fourier Transmission Infrared (FT-IR) spectra (Figure 5.6) of the NiFe2O4@C,

ZnFe2O4@C and CoFe2O4@C demonstrate the evidence for the formation of carbon

supported MFe2O4, where we can see the two bands -OH stretching and C=C in-plane

Table 5.1 Textural properties of synthesized materials.

Sample SABET a

m2g

-1

Vtot b

cm3g

-1

Vmi c

cm3g

-1

Vmes d

cm3 g

-1

D e

nm

Crystallite f

Size (nm)

NiFe2O4@C 13.2 0.12 0.05 0.07 27.6 36.24

ZnFe2O4@C 27.2 0.17 0.02 0.15 21.0 15.5

CoFe2O4@C

39.3 0.18 0.01 0.17 18.9 18.2

aBET surface area.

btotal pore volume taken from the volume of N2 adsorbed at P/P0 =

0.995. cmicropore volume calculated from t-plot.

dmesopore volume calculated by

Vtot-

Vmi. eBJH adsorption average pore diameter.

fcrystal size measured by Scherrer's equation

for the peak 2θ value 30-60ο.



vibrations27

respectively. The band at 591-600 cm-1

could be ascribed to the typical

lattice absorption property of MFe2O4@C that confirms the existence of MFe2O4

structure.28

The elemental composition of the sample analyzed by EDX spectra (Figure

5.7) further confirms the presence of carbon, M2+

metal and iron metal in the

materials. The percentage of metal and carbon is given in Table 5.2, where the metal

percentage was determined by ICP and percentage of carbon was determined by EDX

and CHNS analysis. All the three samples exhibited the comparable carbon content of

23-25 wt.% and is in accordance with the weight of the carbon source and levulinic

acid taken in initial gel (taken similar in the synthesis mixture). The wt% of divalent

metal ions (Ni2+

, Zn2+

and Co2+

) is observed to be higher than that of the trivalent one

(Fe3+

) which is again in accordance with the weight of metal salts taken during the

synthesis.

Table 5.2 Elemental composition of synthesized materials.

Sample C (wt%) Fea

(wt%)

Nia

(wt%)

Zna

(wt%)

Co a

(wt%) EDX CHNS

NiFe2O4@Cb 37.02 24.25 21.08 38.70 0 0

NiFe2O4@Cc 35.05 23.15 20.70 36.00 0 0

ZnFe2O4@Cb 31.72 23.04 28.03 0 37.77 0

CoFe2O4@Cb 30.02 25.09 26.38 0 0 37.85

NiFe2O4@Cd - - 0 0 0 0

aMetal % determined by ICP-AES.

bFresh catalyst.

cCatalyst after 4

th cycle.

dICP-

AES analysis using hot filtration after reaction



Figure 5.6 (A) FT-IR spectra of NiFe2O4@C nano-particles, (B) FT-IR spectra of

ZnFe2O4@C nano-particles and (C) FT-IR spectra of CoFe2O4@C nano-particles.

Figure 5.7 (A) EDX spectra of NiFe2O4@C nano-particles, (B) EDX spectra of ZnFe2O4@C

nano-particle and (C) EDX spectra of CoFe2O4@C nano-particles.



5.3.4 Proposed Mechanism for the Formation of MFe2O4@C Materials

The formation of such a high quality nano-particles MFe2O4@C material obtained in

the present study can be explained by the schematic reaction path of reactants

facilitated during the synthesis (Scheme 5.2) which is proposed based on the XRD,

TEM and porosimetry properties of the material. It is known from the prior art that

the carboxylic group containing compounds are used for the stabilization of metal

nano-particles29,30

and carbonyl group containing compounds are used for the

formation of polymer by reacting with phloroglucinol.31,32

Using this information, the

novel concept of establishing the metal-carbon support interaction in the monomer

level itself is achieved in the present study, where, the levulinic acid possessing both

carboxyl and carbonyl groups is used to facilitate interaction with M2+

and Fe3+

metal

ions on one side and with the carbon source phloroglucinol on the other side

respectively. Scheme 5.2 shows the possible formation of metal ion interacted

polymer species through the reaction among various chemical ingredients when

treated under autogenous pressure conditions inside the autoclave at 170 οC. The

material obtained from the autoclave is allowed for heat treatment at 500 οC for 4 h to

facilitate the carbonization that eventually lead to the formation of well dispersed

metal nano particles on the carbon support. The advantage and novelty of the present

method is involved in the first step of achieving metal- carbon source interaction

before starting any carbonization of carbon source, which up on subsequent

carbonization forms the well dispersed metal particles on the carbon support. Here,

the carboxyl group interaction of the metal ions helps to control any agglomeration of

the metal ions during the hydrothermal and carbonization steps.



Scheme 5.2 Schematic illustration of the formation of MFe2O4@C nano-particles.

5.3.5 Catalytic Performance of Materials for Hydrogenation Reaction

The catalytic performance of the all the materials synthesized in the present study

has been tested for the hydrogenation of styrene having double bond at side chain

while keeping the similar reaction conditions of 80 οC, 40 bar H2 pressure. In a

typical procedure the reaction is conducted by taking 5 mol% of the catalyst and 1

mol of styrene/cyclohexene in a high pressure autoclave reactor (Parr 4848) where

reaction mixture was left under stirring condition at 500 rpm for 24h. To see the

effect heterogeneous conditions a reaction was also conducted homogeneously at

same reaction condition by taking same metal ions (Ni and Fe) in the same ratio as

that of heterogeneous NiFe2O4@C catalyst (Table 5.3). Out of three catalysts

NiFe2O4@C gave highest styrene conversion (100%) while ZnFe2O4@C and

CoFe2O4@C gave 85% and 75% styrene conversion respectively. No conversion was

observed in homogeneous condition. A common thing observed with all three



catalysts is the highest product selectivity (100%) towards ethyl benzene (table 5.3).

The NiFe2O4@C catalyst stands as the best among the three catalysts and is further

explored for the conversion of other reactants; 1. Cyclohexene, having double bond in

the cyclic ring and 2. Cyclohexanone, where the double bond position is between

carbon of the cyclic ring and oxygen. The material also exhibited promising catalytic

activity in cyclohexene hydrogenation, but the conversion is less (70%) compared to

that of styrene. Contrary to this, no noticeable conversion is observed in the

cyclohexanone hydrogenation reaction on this material at similar reaction conditions

(Table 5.4). Hence, it is interesting to see that the material exhibited different

activities towards the hydrogenation of three different reactants; excellent catalytic

activity in the selective hydrogenation of styrene to ethyl benzene (as high as 100%

conversion and 100% selectivity), moderate activity towards cyclohexene to

cyclohexane (~60%) while no activity for cyclohexanone hydrogenation. These

results reveal that the material is highly selective for the hydrogenation of side chain

Table 5.3 Hydrogenation of styrene over synthesized materials.a

Catalyst Conversion (%) Product Ethyl benzene selectivity (%)

NiFe2O4@C 100 Ethyl benzene 100

ZnFe2O4@C 85 Ethyl benzene 100

CoFe2O4@C 75 Ethyl benzene 100

Ni2+

Fe3+

ionsb 0 - -

aReaction Conditions: reaction temperature= 80

oC, H2 pressure = 40 bar, reactant = 1

mmol, catalyst = 5 mol%, reaction time = 24 h, bNi

2+ & Fe

3+ ions with same ratio as in

NiFe2O4@C.



double bond, moderately active for isolated double bond in the cyclic rings but

ineffective for the hydrogenation of carbonyl groups. This observation clearly

emphasizes the selective hydrogenation functionality of the present catalyst system to

apply for the hydrogenation of side chain double bonds with high conversion and

selectivity. The reaction parameters such as time and pressure were varied to see the

effect on conversion and selectivity. Figure 5.8A shows the effect of pressure on the

conversion, where increase of reaction pressure enhanced the conversion of styrene;

at initial 10 bar pressure the styrene conversion was only 35 % which was increased

to almost 100% at 40 bar pressure. Similar trend in increased styrene conversion was

also observed with the increase of the reaction time (Figure 5.8B). The curve shows

three regions, an exponential increase in conversion up to 3 h, followed by linear

increase up to 24 h reaction time; while the conversion is levelled off up to the

studied period of 26 h. We have seen that the optimum conversion (100%) on the

catalyst was achieved after 24 h reaction time. At any level of conversion the catalyst

exhibited as high as 100 % selectivity to the ethyl benzene product. The linear

increase of conversion with reaction time may be due to initial inhibition in

interaction of the reactant with the active sites of the catalyst in presence of the

Table 5.4 NiFe2O4@C catalysed hydrogenation reactions

S. No Reactant Product Conversion(%) Selectivity(%)

1a Styrene Ethyl benzene 100 100

2a Cyclohexene Cyclohexane 70 100

3a Cyclohexanone Cyclohexanol 0 -

aReaction Conditions: reaction temperature= 80

oC, H2 pressure = 40 bar, reactant = 1

mmol, catalyst = 5 mol%, reaction time = 24 h



Figure 5.8 (A) Effect of pressure on conversion and (B) effect of time on conversion at 80 0C

reaction temperature by fresh NiFe2O4@C (■) and 4th time recycled NiFe2O4@C (▼) as a

catalyst.



moiety towards hydrogenation. As the reaction time progress, the interaction of

molecules with the catalyst will be facilitated due to the porous nature of carbon that

results in increase in conversion values.

5.3.6 Reusability of the Catalyst

The catalyst NiFe2O4@C displayed a high leaching resistance capability. Reuse of the

recovered catalyst in four consecutive runs did not lead to any significant decrease in

its catalytic activity in terms of its conversion, yield and selectivity. Recycling and

reusability of the catalyst were examined by introducing the used catalyst up to four

times. The catalyst exhibited the magnetic nature that allowed separating the catalyst

from the reaction mixture using the magnet (Figure 5.9). After each run the catalyst

was separated by magnet and washed by hot water followed by ethanol and dried at

100 oC. The catalyst was effective enough to give comparable conversions after each

cycle (Figure 5.10), that demonstrates no significant loss in the catalytic activity was

observed during recycle operation. Further, the used catalyst obtained after the fourth

cycle was studied for its performance with reaction time of up to 26 h and the

performance with time is compared with that of the fresh catalyst in Figure 5.8B. It is

interesting to see almost identical conversion patterns of both fresh and recycled

catalyst at all the reaction time values studied that confirms the intact of active sites in

the catalyst during recycle operation and proves the recyclability performance of the

catalyst. The ICP-AES results along with the carbon percent given in Table 5.2 shows

that no leaching of the metals as well as carbon occurred during the reaction that

further supports the intact of active sites in the catalyst The leaching test was

performed for Ni2+

and Fe3+

by ICP-AES analysis using hot infiltration after reaction,



Figure 5.9 Photograph of magnetic separation of NiFe2O4 nano-particle @C.

where no Ni2+

or Fe3+

ions were present in the filtrate. We also observed that the

amount of Ni2+

and Fe3+

present in the spent catalyst after four cycles of reuse is the

same as that of the fresh catalyst as estimated by ICP-AES (Table 5.2). A reference

experiment was also conducted in the absence of the catalyst to see catalytic role of

NiFe2O4@C where no conversion was obtained. To see the effect heterogeneous

conditions a reaction was also conducted homogeneously at same reaction condition

by taking same metal ions (Ni and Fe) in the same ratio as that of heterogeneous

NiFe2O4@C catalyst (Table 5.3). No reaction was progressed on the catalyst at

homogenous conditions thus supports the catalytic role of NiFe2O4 active sites in the

heterogeneous catalyst.

By virtue of its higher conversion of the double bond containing hydrocarbons

to produce a side chain hydrogenated product with high selectivity, the catalyst has

potential applications in the dye industry, fine chemical synthesis and petrochemicals.



Figure 5.10 Reusability of NiFe2O4@C catalyst.

5.4 Conclusions

In summary, highly crystalline, uniform size spinel of MFe2O4

nanoparticles@C was obtained in the present study through the sol–gel hydrothermal

synthesis method followed by carbonization, adopting a novel approach of

establishing an interaction between the carbon source and metal ions in the monomer

level itself. The levulinic acid possessing both carboxyl and carbonyl functional

groups used in the presentstudy might be responsible for facilitating interaction with

the carbon source on the one hand and the metal ions on the other hand so as to form

the carbon embedded metal nanoparticles. Further, the–COOH group in levulinic acid

might be responsible for the stabilization of the NiFe2O4 unit against agglomeration

during polymerization/carbonization reactions of phloroglucinol. The NiFe2O4@C

catalyst exhibiting well dispersed small size nanoparticles of∼10 to 20 nm obtained in

the present study provides a scope for the synthesis of other metal nanoparticle

supported catalytic systems by adopting this novel approach of using bi-functional



levulinic acid as a binding molecule for establishing strong metal–support interaction.

Excellent activity in selective hydrogenation of styrene to ethyl benzene exhibited by

the present catalyst system envisions its scope for industrial applications through the

hydrogenation of various non-aromatic double bonds involved in chemicalsystems

related to fine chemicals and drug delivery.

5.5 References

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Chem. Commun., 2008, 3759.

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6. Y. Meng, D. Gu, F. Zhang, Y. Shi, H. Yang, Z. Li, C. Yu, B. Tu and D. Zhao,

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8. N. Liu, H. Song and X. Chen, J. Mater. Chem., 2011, 21, 5345.

9. W. Chaikittisilp, M. Hu, H. Wang, H. Huang, T. Fujita, K. C. W. Wu, L.

Chen, Y. Yamauchi and K. Ariga, Chem.Commun., 2012, 48, 7259.

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12. Y. Si, T. Ren, B. Ding, J. Yub and G. Sun, J. Mater. Chem., 2012, 22, 4619.

13. T. Ren, Y. Si, J. Yang, B. Ding, X. Yang, F. Hong and J. Yu, J. Mater. Chem.,

2012, 22, 15919.

14. Z. Zarnegar and J. Safari, RSC Adv., 2014, 4, 20932.

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16. Z. Zhang, H. Duan, S. Li and Y. Lin, Langmuir, 2010, 26, 6676.

17. M. J. Climent, A. Corma and S. Iborra, Chem. Rev., 2011, 111, 1072.

18. P. A. Chase, T. Jurca and D. W. Stephan, Chem. Commun., 2008, 1701.

19. P. A. Chase and D. W. Stephan, Angew. Chem., Int. Ed., 2008, 47, 7433.

20. S. C. Bart, E. Lobkovsky and P. J. Chirik, J. Am. Chem. Soc., 2004, 126,

13794.

21. E. Karaoğlu, U. Özel, C. Caner, A. Baykal, M. M. Summak and H.

Sözeri, Mater. Res. Bull., 2012, 47, 4316.

22. M. Stein, J. Wieland, P. Steurer, F. Toelle, R. Muelhaupt and B. Breit, Adv.

Synth. Catal., 2011, 353, 523.

23. J. Huo, H. Song and X. Chen, Carbon, 2004, 42, 3177.

24. S. C. Pillai, J. M. Kelly, R. Rameshc and D. E. McCormackad, J. Mater.

Chem. C, 2013, 1, 3268.

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Sci.: Mater. Int., 2012, 22, 639.



26. A. M. Díez-Pascual, C. Xu and R. Luque, J. Mater. Chem. B, 2014, 2, 3065.

27. M. Acik, G. Lee, C. Mattevi, M. Chhowalla, K. Cho and Y. J. Chabal, Nat.

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Chapter 6. Synthesis of Hierarchical ZSM-5 Using Glucose as ….. …..its Catalytic Application

Chapter 6: Synthesis of Hierarchical ZSM-5 Using Glucose

as Templating Precursor and its Catalytic Application

Cheaper template glucose produce hierarchical material upon steam assisted

crystallization

Ph.D. Thesis of Mr. Devaki Nandan CSIR-IIP



Chapter 6: Synthesis of Hierarchical ZSM-5 Using Glucose

as Templating Precursor and its Catalytic Application

6.1 Introduction

Zeolites with their inherent porous crystalline acidic nature possessing uniform

pore size and large internal surface area find wide range of applications in catalysis,

separation and ion-exchange.1-3

Especially, the medium pore ZSM-5 zeolite attracted

much attention due to its shape-selective features responsible for its excellent

performance in the selective organic transformations. The narrow pores of this zeolite

exhibiting linear selectivity provide a special feature for the synthesis of para-xylene

from ortho- and meta-xylenes which is considered as a milestone in zeolite and

heterogeneous catalysis research fields. However, an obvious shortcoming of zeolite

materials originates from their intrinsic micro pores that strongly inhibit the diffusion

of bulky reactants and products, which prevents their wide use in fine chemical and

petrochemical processing. Al-containing mesoporous molecular sieves with large and

high specific surface could be the catalysts for the conversion of bulky reactants.4-6

But, these materials suffer from poor thermal and hydrothermal stability due to the

thin and amorphous nature of their walls. Therefore, the preparation of hierarchical

pore zeolite molecular sieves possessing the positive aspects of both micro-pores

(high activity and stability) and meso pores (larger pore size for accommodating

bulky molecules) has become the hot point of research recently. The most widely

used method to prepare hierarchical pore zeolite is by adopting special chemicals as

templates including hard and supramolecular structured compounds. Jacobsen et al.7

did pioneering work in the hard templating method and successfully synthesized



mesopore zeolites using carbon materials such carbon nano-tubes. The three-

dimensionally ordered mesoporous (3DOM) carbon materials are also used by other

researchers for the synthesis of mesoporous zeolite materials.8 Nevertheless, the

templates used in these methods are very costly. Later carbon aero gels9 and ordered

mesoporous carbons10,11

are also used as templates to prepare hierarchical zeolite, but

the preparation process of this carbon template itself is complicated and requires high

temperature and inert gas atmosphere during carbonization. In supra-molecular

templating method, the templates used are mainly Cetyltrimethylammoniumbromide

(CTABr),12

poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock

copolymer (P123)13

, and organosilane14

agents but they are also expensive. Recently,

through the combination of conventional soft templates such as TEA, copolymer

Pluronic F127, organosilane and steam-assisted crystallization (SAC) process,

hierarchically structured c-TUD-1, TS-1 and ZSM-5 zeolites15

have been facilely

produced, but use of these templates makes the process costly. Very recently,

monosaccharide's such as, glucose and disaccharides such as sucrose etc. are

identified as cheaper yet potential precursor for meso pore structure-directing agent.

Kustova et al.,16

synthesized zeolite single crystals with controlled mesoporosity by in

situ sugar decomposition for templating of hierarchical zeolites which is a three step

process where they synthesized first silica carbon composite in inert atmosphere and

used this composite material as a template which upon crystallization and calcination

yields Na-ZSM-5. The material was further treated with ammonium nitrate to obtain

NH4-ZSM-5 and the high temperature decompositions of which finally yields H-

ZSM-5. Ma et al.,17

synthesized mesoporous ZSM-5 where a precursor of ZSM-5 is

first prepared by sequential reaction between aluminium sulphate, solution,

Tetrapropylammonium hydroxide and Tetraethyl orthosilicate in a specific manner.



The resultant ZSM-5 precursor was added to the aqueous solution of glucose

followed by its heating to the crystallization temperature. The final solid product

obtained is calcined to remove the organic template, followed by ion exchange with

NH4NO3 and calcinations treatments so as to yield H-ZSM-5. Similar method was

also reported with difference of using starch derived bread instead of glucose for the

synthesis of the hierarchical ZSM-518,

Wang et al., 19,20

synthesized hierarchical TS-1

by using sucrose as meso macro template in presence of isopropyl alcohol where they

have used high cost ethylendiamine as crystallising agent. In present study, the

mesoporous silica have been successfully synthesized by using glucose as template

precursor in acidic medium. However, the same method is not applicable for the

synthesis of mesoporous ZSM-5 due to the fact that the metal to metal (silicon and

aluminium) bond formation is difficult to occur in acidic medium to yield any

crystalline material.

A novel method has been adopted in present study for the successful synthesis

of the hierarchical ZSM-5 zeolite material using environmentally benign glucose in

basic medium created by the addition of low cost aqueous ammonium hydroxide,

where the pore size pattern of the synthesized material is significantly influenced by

the concentration of glucose in the synthetic mixture. The present work gains

advantage over the existing methods as it uses a simple, low cost, non-surfactant

common chemical ‘‘glucose’’ as a template precursor that spontaneously get

converted to hard template during partial carbonization by drying of synthesis gel at

170 oC in air. Further, the use of ammonium hydroxide as alkaline agent instead of

sodium hydroxide makes the process simple to give proton form of ZSM-5 directly

and avoids the additional step of ion-exchange of sodium with ammonium ion. The

ammonium ZSM-5 to acidic ZSM-5 was formed during calcination, where at higher



temperature ammonium gas was escape out to leave H-ZSM-5. This is the first of its

kind to synthesize crystalline hierarchical aluminosilicate, MFI type material from

glucose and ammonium hydroxide medium to the best of our knowledge. The

catalytic performance of hierarchical ZSM-5 towards the bulky molecular reaction

was studied by choosing the alkylation of phenol with tertiary butanol.

6.2 Experimental


Tetraethyl ortho silicate (TEOS), ammonia solution 25%,

tetrapropylammonium bromide (TPABr), phenol, tertiary butanol and aluminium

nitrate were purched from Merck while glucose was purchased from Rankem, The

reference ZSM-5 sample is obtained from Sud-Chemie India Ltd.

6.2.2 Synthesis of Hierarchical ZSM-5 Materials

As depicted in scheme 6.1, the typical synthesis procedure involves the drop by drop

admixing of Tetrapropylammonium bromide (TPABr) solution, Tetraethyl

orthosilicate (TEOS) , Aluminium nitrate solution and Glucose solution with the

molar ratio of TPABr : 5.2 TEOS : 0.215 aluminium nitrate : 2.4 to 4.9 glucose : 60

water. The resultant gel is treated at 170 oC in air and the dry gel obtained from the

mixture is allowed for steam assisted crystallization in a specially designed autoclave

equipped with porous metallic boat for holding the dry gel which is allowed to be in

contact with the steam produced from the bottom of the autoclave during heat

treatment (scheme 6.1). In a typical synthesis procedure 12.5 g tetrapropylammonium

bromide with required amount of glucose and water is added to TEOS followed by

the addition of 3.75 g of aluminium nitrate solution (in 5 g water). For studying the



effect of template precursor (glucose) the synthesis is conducted by varying the

glucose to TEOS weight ratio in the initial gel mixture from 0.40 to 0.64. The

resultant solution was dried in a water bath by treating at 80 oC for 2 h, and the

resulting viscous gel was further heated at 170 oC for 28 h to obtain the dry gel

(brown in colour). Finally, the dry gel (solid phase), along with a mixture of aqueous

ammonia (25%) and deionized water containing aqueous phase were transferred into

a specially designed autoclave, in which the solid phase was separated from the

aqueous phase. The crystallization was carried out at 170 oC for 6 days, where the

steam obtained from the aqueous phase comes in contact with the upper solid phase to

facilitate the crystallization process of the zeolite. At the end of the treatment, the

black colour solid product obtained was collected by filtration, washed with deionized

water, dried at 100 oC and calcined at 650℃ for 10 h to remove the template. The

final materials obtained in the synthesis are denoted by MZ0.40, MZ0.48 and MZ0.64

respectively, where the suffix indicates the wt. ratio of glucose to TEOS.

Scheme 6.1 Synthesis route of hierarchical ZSM-5 zeolite.



6.2.3. Application of Materials for Tertiary Butylation of Phenol

The catalyst performance studies of the materials have been conducted in the present

work towards the alkylation of Phenol. In a typical reaction procedure, 1 mol of

phenol was added to a 2.5 mol of tertiary butyl alcohol and 5 mol% of catalyst. The

whole mixture was transferred in to a 25 ml volume capacity Parr reactor autoclave,

sealed tightly and pressurised by N2 up to 2 bar. The reaction was conducted at 150

oC for 7h and the product obtained at the end of the run was filtered and analysed by

GC equipped with the DB wax column and FID detector.


6.3.1 Crystallinity, Porosity and Acidic Properties of the Synthesised Materials

The SEM images of the samples shown in Figure 6.1 indicate the formation of

uniform crystals in case of MZ0.40, when compared to those of MZO.48 and

MZ0.64. This can be ascribed to the variation in the concentration of templating

precursor, glucose taken in the synthesis gel. The non-uniform distribution of

templating precursor resulted at excess glucose concentration may be the reason for

the formation of non uniform semi-crystalline ZSM-5 materials. The powder X-ray

diffraction (XRD) patterns of the samples are given in Figure 6.2, where a standard

ZSM-5 sample of SAR is also taken for comparison purpose. All the three

synthesized materials depict the characteristic diffraction peaks occurred at 2θ of 8.0,

8.9, 23.2, 24 and 24.5 representing the ZSM-5 framework structure without any

crystalline impurity phases. The crystallite size of the materials was estimated from

full width at half maximum of the respective peaks between 2θ values, 7-10 using

Scherrer's equation and the average of the crystallite size is given in Table 6.1. The

data indicate the comparable crystal size of the materials synthesized in this study



Figure 6.1 SEM images of synthesized materials.



Figure 6.2 Wide angle XRD patterns of synthesized materials

Table 6.1 Textural properties of the synthesized materials.

Sample SABET a

(m2g

-1)

SAmi b

(m2g

-1)

SAme c

(m2g

-1)

Vtot d

(cm3g

-1)

Vmi e

(cm3g

-1)

Vme/ma f

(cm3 g

-1)

D g

(nm)

Sizeh

(nm)

ZSM-5 294 207 87 0.18 0.08 0.10 2.2 50.3

MZ0.40

305 113 192 0.18 0.05 0.13 2.3 51.7

MZ0.48

107 25 82 0.18 0.01 0.17 6.7 57.0

MZ0.64

128 42 86 0.23 0.01 0.22 7.2 47.4

aBET surface area.



were calculated as (a-b). d

total pore volume taken from the volume of N2 adsorbed at P/P0 =

0.995. emicropore volume calculated from t-plot.

fmesopore /macropore volume calculated

by Vtot-Vmi.

gBJH adsorption average pore diameter.

haverage crystal size measured by

Scherrer's equation for the peaks between 2θ value 7ο-10

ο



with that of the conventional ZSM-5 zeolite. The small angle X-ray scattering

(SAXS) patterns of the as-synthesized samples (Figure 6.3) suggest the presence of

larger mesopores in the materials,21

which is indeed confirmed by N2 adsorption-

desorption isotherm curves of the corresponding samples (Figure 6.4A). All the

samples exhibited the type IV isotherm with H1 type hysteresis loop which usually

observed for the larger mesopores. The sharp uptake in nitrogen adsorption at relative

pressures of 0.6–0.9 P/P0 reveals the capillary condensation of the gas inside the

mesopores. A steep increase at relative pressure P/P0 <0.02 and a significant

adsorption at high relative pressure P/P0 0.9-1.0, indicates the co-existence of intrinsic

micro, meso and macropores in all three samples. However, the concentration of

glucose in the initial synthetic gel was observed to influence the porosity of the

samples significantly. At lower glucose concentration, the isotherm exhibited the

formation of more micropores (pressure range of P/P0 < 0.02), while at higher glucose

concentration dramatically shifted the porosity in to meso/macropores (relative

Figure 6.3 Low angle XRD patterns of synthesized samples



Figure 6.4 A: N2 adsorption-desorption isotherms of synthesized materials, B: Pore

size distribution of the respective samples measured by BJH method.



pressure range of 0.6–0.9 P/P0). This phenomenon of enhanced mesopores/macropore

formation at higher glucose concentrations is further reflected in the pore size

distribution patterns of the materials (Figure 6.4B). All the materials exhibited the

hierarchical pore size distribution patterns with significant contribution of mesopores

as well as macropores (Figure 6.4B). However, the population of such hierarchical

pores is dramatically increased in the higher glucose used samples and the increase is

following the glucose concentration. Thus the increasing order of hierarchical

porosity is observed as follows; ZSM-5< MZ0.40 < MZ0.48 < MZ0.64. The finding

of increased hierarchical pore size distribution with glucose concentration can be

understood from the XRD results, where the increase in glucose concentration is

observed to increase the amorphous nature of the material (lower crystallinity). This

is to say that the semi crystalline ZSM-5 material containing more amount of

amorphous material is forming at higher glucose concentration and the presence of

such amorphous material is contributing to the formation of meso and macropores.

Such material with lower micropores and high amounts of meso/macropores is

expected to give lower surface area, which is indeed observed in the samples (Table

6.1). But, it is important to note that the total pore volume as well as

mesopores/macropore volume is increased in the higher glucose based synthesized

samples. This has resulted in the overall increase in the average pore diameter of the

samples with glucose concentration. The BJH adsorption average pore diameter of the

corresponding samples are 2.2, 2.3, 6.7 and 7.2 nm further suggests that increase of

glucose concentration leads to shift the mean pore diameter to higher value. Here

glucose undergoes dehydration and partial carbonization to form templating

carbonaceous species during the heat treatment of the gel at 170 oC which is

responsible for the creation of meso/macro pores in the final material up on steam



assisted crystallization. The formation of such meso/macropores is increased with

increased concentration of glucose. Overall, the increased formation of

meso/macropores with glucose concentration clearly envisions the meso/macro pore

directing role of glucose precursor.

The acidity patterns of the samples measured by TPD (Figure 6.5) also

followed the crystallinity trends of the samples. All the samples exhibited a two peak

pattern with desorption peaks at ~ 100 oC and ~350

oC representing the weak and

strong

Figure 6.5 TPD spectra of synthesised and reference materials.

acidity respectively. The acidity patterns of a reference ZSM-5 sample (Si/Al=15)

also given for comparison that envisions the acidity of all the three samples (Si/Al



=60) of the present study is less (less number of acid sites) compared to the reference

sample, following the aluminium content. Among the three ZSM-5 samples

synthesized the present study, the acidity is decreased with increasing glucose

concentration. This is in accordance with the XRD and porosity patterns, as the

increased amorphous nature of the material is expected to give low acidity (less

number of strong acid sites) to the ZSM-5 samples. The results together summarize

the role of glucose as meso-macro pore directing agent and the partially crystalline

hierarchical ZSM-5 obtained at higher glucose loadings exhibit moderate acidity

along with high amount of meso/macropores. With the higher pore volume and larger

space in mesopores, the samples are expected to exhibit potential catalytic

applications in bulky molecular reactions such as tertiary butylation of phenol.

6.3.2 Catalytic Performance of Materials for Tertiary Butylation of Phenol

The tertiary butylation of phenol is catalyzed by conventional homogeneous acid

catalysts in liquid phase at lower reaction temperatures, but the acid contamination

and difficulty involved in separation of the product (also adds to cost ) limits their

use. Recently solid acid catalysts are applying for solvent-free liquid phase reactions

for low cost and environment-friendly process, where the easy separation of catalysts

from the reaction system makes it suitable for industrial applications.22

In this regard,

hierarchical ZSM-5 samples are observed to exhibit excellent catalytic properties

especially in terms of di-alkylated product. The hierarchical mesoporous ZSM-5

samples of the present study possessing meso/macroporosity along with its zeolitic

microporosity are also expected to exhibit promising catalytic activity towards this

bulky reaction. In the present study we would like to explore the effect of glucose-

dependent meso/macroporosity created in the ZSM-5 samples on the conversion and

product selectivity towards the tertiary butylation of phenol. All the three hierarchical



ZSM-5 samples exhibited higher conversions (34-46%) when compared to the mere

microporous ZSM-5 zeolite (Table 2). The lower conversion of microporous ZSM-5

obtained in the reaction in spite of its higher acidity (Figure 6.5) clearly suggests the

importance of meso/macropores for this reaction and the lack of such porosity in the

standard ZSM-5 sample may be responsible for its lower activity. The catalytic

performance of the three hierarchical mesoporous ZSM-5 samples also followed the

porosity trend, where, the higher meso/macrporous material (MZ0.64) exhibited

higher conversion (44%) and relatively higher 4-TBP selectivity (81%). This sample

also produced highest di-alkylated product (2,4-DTBP).

Table 6.2 Tert-Butylation of phenol over hierarchical ZSM-5 samplesa

Catalysts Conversion of phenol

(mol% )

Selectivity of product (% )

2-TBP 4-TBP 2,4-DTBP

MZ0.40 34 38.2 57.3 4.5

MZ0.48 46.6 11.1 81.5 5.4

MZ0.64 44 10.6 80.9 8.5

ZSM-5 13.7 63.5 32.84 Nil

aCatalyst: 0.5 g, reaction temperature 150

oC, pressure 2 bar N2 ; reaction time 7h; Phenol:

TBA 1 : 2.5 (molar ratio).



6.4 Conclusions

In summary, the hierarchical ZSM-5 zeolite samples have been successfully

synthesized by using the low-cost template precursor glucose in basic medium that

can directly get converted to hard template during heat treatment of the gel to give

glucose-dependent porosity patterns in the samples. This method also provides scope

in using other kinds of sugars as template precursors for the synthesis hierarchical

materials. The synthesis method provides an economical path for the production of

hierarchical aluminosilicates with tailored meso/macroporosity (controlled by

glucose) for various industrial applications and could be extended for the synthesis of

other types of zeolites. The materials possessing well-connected network of

micro/meso/macropores can be source for the variety of bulky molecular reactions

and better replacement for conventional ZSM-5. The materials indeed exhibited

improved catalytic performance in tertiary butylation of phenol as a result of

overcoming the diffusion limitation of the reactants.

6.5 References

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Chapter 7 Concluding Remarks and Future Prospects

Chapter 7: Concluding Remarks and Future Prospects


Chapter 7. Concluding Remarks and Future Prospects


Chapter 7: Concluding Remarks and Future Prospects

Porous carbon composites and metal oxides of infinite network can be functionalized

by acid or metal ions for catalytic application. The ion–clusters connected with

hydrophobic carbon moiety or zeolite framework is observed to be subject in an

exponentially emerging chemical and material research field owing to its aesthetic

structural versatility as well as modularity for a wide spectrum of applications ranging

from adsorption, separation and catalysis to refinery, bio-oil, magnetism and

biomedical purposes. Precise designing strategies for acid functionalized porous

carbon composite, metal supported nano-particles and hierarchical zeolitic metal

oxides by using low cost carbon source such as petroleum waste, glucose, levulinic

acid and phloroglucinol or structure directing agent are the key factors for

development of cost effective synthetic protocols.

This Ph.D. thesis comprises of the research focused on the development of new 1)

porous carbon composites possessing acidity and magnetic properties and 2)

hierarchical porous zeolites having diverse structural features enriching the priori

information useful towards the ‘designing’ of novel materials. Some of the acid

functionalized, and metal functionalized porous carbon composites and hierarchical

metal oxides are synthesized, characterized and examined for their acidic, magnetic

and catalytic activity. Notable emphasize on the preparation of acid functionalized

porous carbon, magnetically separable carbon composite and hierarchical metal oxide

has been given by using low cost precursors. Efforts have also been made towards

the development of energy efficient catalytic applications such as alkylation of

phenol, value addition of glycerol and hydrogenation. The prime results described in



each chapter and their relevance to the practical applications is briefly summarized as

follows.

7.1 Facile synthesis of sulfonated carbon, carbon-silica-meso composite and

mesoporous silica

The simultaneous carbonization and sulfonation of low cost carbon

precursors (coal tar) has been adopted to synthesize thermally stable acid

functionalized nanoporous carbon without using any costly structure

directing agent.

Use of renewable glucose as carbon source as well as templating precursor

was successfully demonstrated for the preparation of sulfonated carbon-

silica meso composite (SCS).

The acid functionalized carbon silica composite also can be used for the

synthesis of mesoporous silica by simple calcination and the resultant

mesoporous silica has wide application depends on metal functionalization.

7.2 Optimization of carbon silica composite structure and their catalytic

applications

Glucose as a carbon source and structure directing precursor has been used

for the synthesis of various carbon silica composite materials.

Tailorble porosity of composite materials has been achieved by varying the

glucose concentration in initial synthesis mixture

The synthesized materials have been successfully used for the value

addition of glycerol for the solketal production



7.3 Synthesis of carbon embedded MFe2O4 (M = Ni, Zn and Co) nano-particles

as efficient hydrogenation catalysts

A novel concept of using levulinic acid having both carboxylic

(for interaction with M2+

and Fe 3+) and carbonyl groups (for

interaction with phloroglucinol) has been successfully adopted for the

synthesis of carbon embedded metal nano-particles.

Interaction of levulinic acid restricts the agglomeration of metal nano-

particle so that their size remains smaller.

Simultaneous polymerization then carbonization of the precursors at higher

temperature gives stable carbon supported nano-particle (no leaching and

oxidation in protic solvent viz. ethanol).

Both the chemicals levulinic acid and phloroglucinol are cheaper,

renewable, non-hazardous which can avoid use of high cost

surfactant for stabilizing nanoparticles.

The synthesized NiFe2O4@C materials have been identified to be excellent

side chain hydrogenation catalysts (selective hydrogenation) towards

model reaction of styrene hydrogenations where as high as 100%

conversion of styrene to produce 100% ethyl benzene was obtained. This

shows potential side chain selective hydrogenation ability of the new

compound NiFe2O4@C.

7.4 Synthesis of hierarchical ZSM-5 using glucose as templating precursor and

its application



A novel concept of using low cost glucose as a templating precursor

has been realized to get hierarchical ZSM-5.

In the present study glucose was used as a cheaper, renewable, non-

hazardous which can avoid use of high cost surfactant and organosilane.

Aqueous ammonia instead of NaOH as alkali source has been used

during crystallization for the direct production of protonic zeolite that

avoids the otherwise required additional steps of ion-exchange with

ammonia and calcination of the final material.

The other important advantage of the present method lies in obtains desired

porosity by simple method of varying glucose concentration for fine tuning

the pore size.

Overall the present research work addresses the facile synthesis of various types of

materials adopting novel concepts for successful production of the materials such as

acid functionalized nanoporous carbon, acid functionalized carbon silica composite,

hierarchical mesoporous silica, magnetically separable carbon embedded metal nano-

particle (NiFe2O4@C, ZnFe2O4@C and CoFe2O4@C) and hierarchical ZSM-5 to

have potential catalytic applications. Each category of material has been readily

applied for an industrially important reaction in addition to their in depth contribution

to the basic understanding of the chemistry. Some of the reactions studied in this

regard are bulky molecular aryl alkylation reaction, value addition of glycerol

towards solketal synthesis and selective hydrogenation of alkyl aryls. The studies

indicated the potential applicability of the synthesized materials with their ready

suitability for additional functionalization with other metals for catalytic

transformations but the complete study of the spectrum of reactions that can actually



catalyzed by the synthesized materials is beyond the scope of this study. However,

the each type of reaction studied in the present work represents a class of molecular

conversions that can be explored by using the materials of the present study and has a

wide scope for process development in the important areas of catalysis, adsorption,

drug delivery, magnetic separation etc.

7.5 Papers Published in International Journals

1. Facile single step synthesis of an acid functionalized nano porous carbon

composite as an efficient catalyst for tertiary butylation of phenol, Devaki

Nandan and Nagabhatla Viswanadham, RSC Adv., 2014, 4, 57223. (Impact

Factor 3.708).

2. Synthesis of carbon embedded MFe2O4 (M = Ni, Zn and Co) nano-particles

as efficient hydrogenation catalysts, Devaki Nandan, Peta Sreenivasulu,

Nagabhatla Viswanadham , Ken Chiang and Jarrod Newnham, Dalton

Transactions, 2014, 43, 12077. (Impact Factor 4.02)

3. Synthesis of hierarchical ZSM-5 using glucose as templating precursor

and its application, Devaki Nandan, Sandeep K. Saxena and Nagabhatla

Viswanadham, J. Mater. Chem. A, 2014, 2 , 1054. (Impact Factor NA)

4. Acid functionalized carbon–silica composite and its application for solketal

production, Devaki Nandan, Peta Sreenivasulu, L.N. Sivakumar Konathala,

Manoj Kumar, Nagabhatla V iswanadham, Microporous and Mesoporous

Materials, 2013, 179, 182 (Impact Factor 3.365)

5. Facile synthesis of a sulfonated carbon silica-meso composite and

mesoporous silica, Devaki Nandan, Peta Sreenivasulu, Sandeep K. Saxena

http://pubs.rsc.org/en/results?searchtext=Author%3ADevaki%20Nandan

http://pubs.rsc.org/en/results?searchtext=Author%3ASreenivasulu%20Peta





and Nagabhatla Viswanadham, Chem. Commun., 2011, 47, 11537 (Impact

Factor 6.7)

6. Synthesis and catalytic applications of hierarchical mesoporous

AlPO4/ZnAlPO4 for direct hydroxylation of benzene to phenol using hydrogen

peroxide, Peta Sreenivasulu, Devaki Nandan, Manoj Kumar and Nagabhatla

Viswanadham, J. Mater. Chem. A, 2013, 1, 3268 (Impact Factor 6.101)

7. Room temperature synthesis of ZnAlPO4 nanoparticles and their catalytic

applications, Peta Sreenivasulu, Devaki Nandan, B. Sreedhar and Nagabhatla

Viswanadham, RSC Advances, 2013, 3, 13651 (Impact Factor 3.7)

8. Synthesis and catalytic applications of amine interacted Cu2(OH)PO4

nanoplates (copper NPs) and tubes (copper NTs), Peta Sreenivasulu,

Nagabhatla Viswanadham, Devaki Nandan, L. N. Sivakumar Konathala and

B. Sreedhar, RSC Advances, 2013, 3, 729. (Impact Factor 3.7)

9. Catalytic performance of nano crystalline H-ZSM-5 in ethanol to gasoline

(ETG) reaction, Nagabhatla Viswanadham, Sandeep K. Saxena, Jitendra

Kumar, Peta Sreenivasulu, Devaki Nandan, Fuel, 2012, 95, 298. (Impact

Factor 3.357)

10. Sulfated Galactans of Champia indica and Champia parvula (Rhodymeniales,

Rhodophyta) of Indian Waters, Sanjay Kumar, Devaki Nandan, Ramavatar

Meena, Kamalesh Prasad and Arup K. Siddhanta, Journal of

Carbohydrate Chemistry, 2011, 30, 47. (Impact Factor 1.18)



7.6 List of Patents Applied/Filled

1. Nagabhatla Viswanadham and Devaki Nandan, Sulfonated carbon silica

composite material and process for the preparation US8722573

2. N Viswanadham, Peta Sreenivasulu, Sandeep K Saxena, Rajiv Panwar,

Devaki Nandan and Jagdish Kumar, A single-step catalytic process for

conversion of naphtha to diesel-range hydrocarbons, WO 2014073006 A4

7.7 Papers presented/accepted in conference, symposium and Seminar

1. Development of functionalized hierarchical carbon-silica composite material

for catalytic applications. Devaki Nandan, Amit Sharma, Sandeep Saran,

Deependra Tripathi and Nagabhatla Viswanadham, "22nd

National

Symposium on Catalysis, CSIR-CSMCRI, Bhavnagar" held on 7-9 January

2015.

2. A novel method for the synthesis of hierarchical ZSM-5 for catalytic

applications. Devaki Nandan, Peta Sreenivasulu, K. L. N. Sivakumar,

Raghuvir Singh and Nagabhatla Viswanadham, Poster presentation in the

"The National Symposia CATALYSIS FOR SUSTAINABLE

DEVELOPMENT CATSYMP-21" held on Feb 11 to Feb 13, 2013 at

CSIR-IICT Hyderabad.

3. Synthesis and catalytic applications of copper hydroxyl phosphate nanoplates

(copper NPs) and tubes (copper NTs). Peta Sreenivasulu, Devaki

Nandan, Sandeep Saran, G M Bahuguna and Nagabhatla Viswanadham,

Poster presentation in the "The National Symposia CATALYSIS FOR



SUSTAINABLE DEVELOPMENT CATSYMP-21" held on Feb 11 to

Feb 13, 2013 at CSIR-IICT Hyderabad.

4. Chemo-selective catalytic conversion of glycerol as a biorenewable source for

oxygenated additive for the diesel fuel, N Viswanadham, Sandeep K Saxena,

Devaki Nandan, P Sreenivasulu, Basant Kumar and M O Garg, International

Mexican Congress on Chemical Reaction Engineering (IMCCRE 2012),

Ixtapa-Zihuatanejo, Guerrero, Mexico, June 10-15, 2012.

5. Catalytic conversion of ethanol to transportation fuel. Sandeep K.

Saxena, Peta Sreenivasulu, Devaki Nandan, Sarabjeet Singh, N.

Viswanadham, Oral presentationin 8th International Symposium on Fuels

& Lubricants (ISFL) 5-7th March 2012, New Delhi.

6. Synthesis of a sulfonated carbon-silica-meso composite and mesoporous

silica. Devaki Nandan, Peta Sreenivasulu, Sandeep K. Saxena, Nagabhatla

Viswanadham, Poster presentation in Emerging Trends in Chemistry and

Biology Interphase 3-4th

November 2011, Kumaun University, Nainital.

devaki nandan 2015

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