nanocatalysis synthesis and applications (polshettiwar/nanocatalysis) || nanocatalysts for biofuels

16

NANOCATALYSTS FOR BIOFUELSVitaliy Budarin, Peter S. Shuttleworth, Brigid Lanigan,

and James H. Clark

INTRODUCTION

Climate Change and Biorefinery Concept

Climate change has been defined by the United Nations Framework Convention onClimate Change as a change of climate, which is attributed directly or indirectly to humanactivity that alters the composition of the global atmosphere and which is in additionto natural climate variability over comparable time periods.1 There are four main typesof gases released by human activity—carbon dioxide, methane, nitrous oxide, and thehalocarbons—all of which accumulate in the Earth’s atmosphere and contribute to theglobal warming and climate change. A significant increase in the concentration of all ofthese gases has been seen since the start of the industrial revolution when manual labourwas largely replaced by industry and machines. Fossil fuel combustion is responsiblefor the majority of CO2 emissions caused by humankind. Electricity generation is thelargest emitter of CO2, accounting for approximately 41% of all CO2 emissions in theUnited States in 2006, followed by the transport sector at 33%.2,3 As a result there is asignificant drive in research and initiatives for the use of renewable and sustainable fuelsto facilitate the development of society, whileminimizing the impact on the environment.The replacement of fossil fuels with biomass can result in a reduction of the net CO2

Nanocatalysis: Synthesis and Applications, First Edition. Edited by Vivek Polshettiwar and Tewodros Asefa.© 2013 John Wiley & Sons, Inc. Published 2013 by John Wiley & Sons, Inc.

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596 NANOCATALYSTS FOR BIOFUELS

released during energy production: the CO2 released during combustion of biomassis equivalent to that captured through photosynthesis during growth. Therefore, it isgenerally accepted that the use of biomass for energy production is carbon neutral. In anattempt to reduce CO2 emissions, the European Commission published a white paper in1997 by which European Union (EU)member states were required to increase the role ofrenewable resources in total energy production to 20% by 2020, with 33% of electricityproduction needs to come from renewable resources.4 The only way to achieve this isto utilize biomass in a manner consistent with green technology principles, includingthe use of efficient process, which do not involve hazardous reagents and produce littlewaste.5

The concept of utilizing biomass for everyday use as fuel has been in existencefor centuries; however, dedicated research into the matter has only taken place in thelast two decades.6 This initiative has been given the general term “biorefinery technol-ogy,” which combines understanding of biomass conversion processes and equipmentto produce fuels, power, and chemicals from biomass. The biorefinery concept is ana-logues to today’s petroleum refineries, which produce multiple fuels and products frompetroleum.7 In the earliest stages of this pioneering work, the “biorefinery” was mainlylimited to readily available energy crops and therefore by the amount of available agri-cultural land, while nonfood materials were not used due to their complex structure,which are extremely difficult to convert into the fuel and chemicals in a continuousprocess.8

Non-food-type materials, such as wood, wood waste, straw, and agricultural waste,consist of three major components: mainly inert crystalline cellulose, relatively activehemicellulose, and hydrophobic lignin (see Figure 16.1). However, current technologieshave overcome these issues and can accept awide spectrumof biomass sources, includingdifferent types of lignocellulosic biomass, and produce biofuels from them using threemain approaches: biochemical conversion, thermochemical conversion, and extraction.Similar to current-day petroleum refineries, the biorefinery concept produces a number ofdifferent fuels, commodity chemicals, and platform molecules from the raw material. Inthe case of a biorefinery, the startingmaterial is in some formof a biomass, which consistsof carbohydrates, lignin, fats, proteins, and various other chemicals that are present atlow levels. The output of a biorefinery can be placed in two categories: high-volumeproducts, such as fuels; and low-volume chemicals, such as succinic acid, sorbitol, andglycerol, which can be used as platform molecules in the polymer and pharmaceuticalindustries.11, 12 The biorefinery using agricultural and forestry waste opens up a newstreamof income for rural economies and enables avoidance of greenhouse gas emissionsassociated with their decay, making them ideal alternatives to current feedstocks (seeFigure 16.2).

The development of novel, energy- and cost-efficient methodologies to high-valuechemicals, materials, and fuels derived from biomass is the major challenge our civi-lization will face in the twenty-first century. It is believed that nanotechnology, whichmanipulates chemical process at an atomic and molecular scale, can provide enoughselectivity and flexibility to answer these challenges to develop greener, sustainable, andinexpensive approaches for biomass valorization.14

INTRODUCTION 597

Figure 16.1. Proposed structure of hemicellulose, cellulose, and lignin.9,10 (See color insert.)

Nanocatalysis

The term “nanoparticle” is used to describe materials that have a structure in which atleast one of its phases has one or more dimensions (length, width, or thickness) in thenanometer size range (1–100 nm). Such materials include nanometer-sized crystallites,nanopore-separated materials, particles with sizes in the nanometer range, or nanometer-sized metallic clusters dispersed within a porous matrix.15 Nanomaterials have attractedmuch attention as prospective catalysts over the last decade due to (i) extraordinaryactivity influenced by a high surface area,16 (ii) enhanced selectivity through a controlof their size and shape, and (iii) the ability to evenly distribute within the structure ofvarious catalysts.17

Nanoparticles are perspective catalysts for many processes, but their industrialapplications could be limited due to high cost and potential instability (see Table 16.1):

The application of nanoparticles in biological systems could have superior benefitsbecause that they are of a similar size range to many common biomolecules.18,19


Figure 16.2. Illustration of biorefinery concept.7,13

Biomass Upgrading for Energy Production

In 2007, only 1.5% of UK energy was produced from biomass and waste residues(Figure 16.3a),20 with direct use of raw biomass only making up a small proportion(Figure 16.3b).

TABLE 16.1. Special properties of nanoparticles: advantages versus disadvantages

No Advantages Disadvantages

1 Stronger, lighter materials Nanotoxicology—not fully understood2 Different properties to bulk materials Very specialized equipment required to

characterize3 Wide range of applications Difficulties in purifying nanomaterials4 Allows miniaturization of various

technologiesExpensive preparation

5 Ability to incorporate hydrophilic andhydrophobic molecules on them

Potential instability (agglomeration)during and after synthesis

INTRODUCTION 599

Figure 16.3. (a) Energy generation from renewable sources (2005–2007), and (b) contribution

of various types of biomass for production of energy (electricity, heat, and transport). (Note:

“Animal biomass” includes farm waste, poultry litter, and meat and bone combustion. “Plant

biomass” includes straw and energy crops.)20 (See color insert.)

With the increasing demand for biomass use in energy production, research is beinginvested in pretreatment methods to produce fuels for engines and power generationfacilities. The current main biomass conversion technologies include21,22

• destructive carbonization of woody biomass to charcoal;• thermal conversion of biomass and waste (e.g., gasification, pyrolysis, and tor-refaction);

• generation of electricity by direct combustion or gasification and pyrolysis(including cofiring with coal);

• biological treatment of biomass and waste (e.g., fermentation and anaerobicdigestion);

• biomass densification (e.g., pelletization, production of briquettes, and torrefac-tion);

• conversion of biomass to a pyrolytic oil for transport fuel;• chemical conversion of biomass to fuels (e.g., biodiesel).

The most extended biomass pretreatment methods are generally divided into twocategories—biochemical and thermochemical processes. Examples of biochemical pro-cessing involve the conversion of biomass to fermentable sugars for the production of


specific alcohols fuels such as ethanol and butanol. The process can be carried out onsmall scales allowing localized processing and energy production. On the other hand,the conversion tends to be slow, requiring a batchwise manufacturing process, and canonly be used to convert polysaccharide components of biomass.

Thermochemical processing produces a range of products through the thermaldecay and chemical reformation of biomass. Transformations are carried out underdiffering concentrations of oxygen, varying from the extremes of direct combustionin air through to gasification in low air levels, to pyrolysis in the absence of oxygen.This route suffers from high capital and operational costs due to the high temperaturesinvolved. In order to be economically competitive with the non-biomass-related process,these must operate on a large regional basis requiring transport of feedstocks overlong distances. Nonetheless, thermochemical processing holds a clear benefit over thebiochemical process as it can essentially convert all the organic components of thebiomass, fully capitalizing on its fuel and chemical potential.23–25A low-temperaturecontinuous process, which can maximize the conversion of the fuel production andchemical potential of biomass into useful products, is probably one of themost interestingand promising avenues for biomass valorization.

NANOCATALYSTS IN THE PRODUCTION OF LIQUID FUELSFROM BIOMASS

Transport systems throughout the developed world rely on the engine-driven internalcombustion of liquid fuels, 98%ofwhich are currently derived from fossil fuels. In indus-trialized countries, transportation accounts for approximately 30% of CO2 emissions.As a result, there is a renewed interest in the field of liquid biofuel production. Biomassfeedstock can be converted into four major types of liquid fuels (see Figure 16.4)23:

1. Biodiesel as monoalkyl esters of long-chain fatty acids derived from renew-able feedstocks, including vegetable oil or animal fats, which are utilized incompression-ignition engines.26

2. Bioethanol, mainly derived from the fermentation of sugar-derived starchcrops.27

3. Bio-oil (tar) as liquid biofuel via thermochemical decomposition of biomasswithout the participation of oxygen (pyrolysis).28

4. Fischer–Tropsch diesel—the Fischer–Tropsch process converts syn-gas (a mix-ture of hydrogen and carbon monoxide) to a range of hydrocarbons.29

Biodiesel and bioethanol are the most extended alternative transport fuels. The useof biofuels in the EU has increased exponentially over the last ten years. Bioethanoluse increased 18-fold, while biodiesel use increased by 13 times to over 3500 ktoe(kilotonnes of oil equivalent) in 2006.8

NANOCATALYSTS IN THE PRODUCTION OF LIQUID FUELS FROM BIOMASS 601

Figure 16.4. Production of liquid fuels from biomass.

First-Generation Biofuel

Biodiesel Derived from Triglycerides (Vegetable Oils/Animal Fats).Although triglycerides can be directly used in diesel engines, their high viscosities andlow volatilities generally result in the formation of engine deposits due to incompletecombustion and incorrect vaporization characteristics. These problems are associatedwith large triglyceride molecules and their higher molecular weight. To overcome thesedifficulties, the oil requires a number of chemical modifications to reduce its viscosity,and transesterification is the most important step to produce a cleaner and environmen-tally safe fuel from vegetable oils.30 The transesterification or alcoholysis of triglyceridescomprises the displacement of glycerol from the triglyceride by an alcohol (see Scheme16.1) to yield fatty acid methyl esters and glycerol as a by-product.

Transesterification can be catalyzed by Brønsted acids, preferably by sulfonic andsulfuric acids as well as by alkaline solutions.31 The basic homogeneous catalyzedprocess, employing potassium hydroxide, sodium hydroxide as well as potassium and

Scheme 16.1. General scheme of triglyceride transesterification.


sodium alkoxides, is commonly used at the industrial level for the transesterification ofvegetable oils with methanol to biodiesel. However, the homogeneous processes havemajor drawbacks due to the difficulties in catalyst recovery and wastewater treatment,thereby increasing biodiesel production costs. To overcome these challenges, heteroge-neous transesterification techniques using solid catalysts have been developed and theyprovide greener methodologies with a simplified downstream process. During recentyears, the immobilized lipase-mediated transesterification reaction for biodiesel produc-tion has been extensively investigated because of the simple recovery of the catalyst fromthe reaction mixture that facilitates its repeated use. A promising route for the produc-tion of biodiesel via transesterification of vegetable oil and animal fat with methanol invery mild conditions has been recently developed using nanoparticles as catalysts.32–34

Meher et al. have successfully grafted the lipase onto magnetic Fe3O4 nanoparticlesvia 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide activation.32 It has been shownthat the modified nanoparticles, with an average diameter of 12.7 nm, retained mostof their activity throughout a wide pH range and temperature compared to that of thefree lipase. The maximal conversion to methyl esters of 94% was attained by using thebound lipase as catalysts. Transesterification of soybean oil (SBO) and poultry fat withmethanol at room temperature has been performed using nanocrystalline calcium oxidesas catalysts, obtaining quantitative biodiesel yields in the system (99% conversion).32

Under the same conditions, laboratory-grade CaO gave only 2% conversion in the caseof SBO, and there was no observable reaction with poultry fat. With the most activecatalyst, deactivation was observed after eight cycles with SBO and after three cycleswith poultry fat (Figure 16.5).

Deactivation has been proposed to be associated with the presence of organicimpurities or enolate formation via the deprotonation of the carbon alpha to the carboxy

Figure 16.5. Conversion obtained after recycling the CaO nanocatalyst in the transesterifi-

cation of SBO compared to laboratory-grade CaO. Reaction conditions: catalyst 0.25 g, SBO

25 ml, and MeOH 100 ml, stirred vigorously at room temperature for 24 h.


group in the triglyceride or FAMES. A high methyl ester yield (up to 97.7%) wasalso obtained in the presence of KF-impregnated nanoparticles of � -Al2O3 (KF loadingof 15 wt%). On the base of the experimental data, it has been concluded that thisrelatively high conversion of vegetable oil to biodiesel is considered to be associated tothe relatively high basicity of the catalyst surface (1.68 mmol/g) and the high surface-to-volume ratio of the � -Al2O3 nanoparticles.31

Bioethanol from Starch-Rich Biomass. Bioethanol is themost commonly usedsubstitute fuel after petrol for road transport vehicles. At the present, the majority ofbioethanol is produced via a two-step process. In the first step, starch from energycrops is hydrolyzed to sugar, which is subsequently fermented to ethanol, lactic acid,or bioethanol in the second step (see Figure 16.4). Among starch hydrolyzing enzymesthat are produced on an industrial scale, �-amylases are of considerable commercialinterest (the annual sale of amylolytic enzymes equates to almost US$25 million world-wide). Using the enzyme-immobilized nanoparticles in a similar way to that shown inbiodiesel production makes their recovery more effective and simple, avoiding any high-speed centrifugation to recover the catalyst. Immobilized �-amylases on the surface ofnanoparticles are preferred to the native enzyme for industrial applications currently. Afew examples of �-amylase immobilization on magnetic (Fe3O4 and Fe2O3) nanopar-ticles and their successful application to starch hydrolysis were recently reported.35–37

Immobilized �-amylase was found to be stable against various types of physical andchemical denaturants and poisons. Stability of these materials has been further provedby reusability experiments, which demonstrated that immobilized �-amylase showed83% residual activity even after the eighth consecutive use. It is interesting to note thatincreasing the temperature of the experiment increases the rate of starch hydrolysis dueto the reduction of viscosity of both starting material and product.

Second-Generation Biofuels

Bioethanol from Lignocellulosic Biomass. Cellulose is a linear condensa-tion polymer consisting of d-anhydro-glucopyranose units joined together by a �-1,4-glycosidic bond. Intermolecular hydrogen bonds and van der Waals forces betweencellulose molecules result in stable supramolecular crystalline fibers of great tensilestrength.38 The potential importance of cellulose hydrolysis in the context of conversionof plant biomass to fuels and chemicals has been widely recognized.39,40 The cellulose-assisted process is usually performed in relatively mild reaction conditions with highspecificity, and can be considered a “greener” approach to bioethanol. However, a criti-cal problem when using cellulases as catalysts is the rapid deactivation of cellulase byenvironmental factors (e.g., temperature), which seriously prohibit its practical use inindustry. Immobilizing cellulase on solid materials may be a feasible way to overcomethis difficulty by enhancing the stability of the cellulase and its catalytic activity.41,42

The optimum reaction conditions for cellulase-immobilized solid nanocatalyst perfor-mance in cellulosic hydrolysis has been reported by Chang and coworkers.40 Duringthese investigations, cellulase was immobilized onto the surface of mesoporous silicananoparticles through both physical adsorption and covalent bonding. It has been shown


Figure 16.6. Yield of glucose for free cellulase, cellulase-adsorbed nanoparticles, and

cellulose-linked nanoparticles.

that catalytic activities of the freshly prepared samples of covalent linked cellulase aswell as free cellulase were similar. However, after 23 days’ storage, catalytic activity offree cellulase diminished significantly compared to that of the covalent bonded cellulase(see Figure 16.6).

The proposed cellulase-assisted biocatalyst exhibits a high cellulose-to-glucoseconversion efficiency (>80%) with outstanding stability. The catalytic activity of thenanoparticle-immobilized cellulase in tandem saccharification and glucose fermentationprocesses of cellulose was investigated by Lupoi and Smith.42 It was found that ethanolyields obtained in this two-stage process were nearly double when using cellulasephysisorbed on silica nanoparticles with respect to those of the free enzyme in solution.

Pyrolysis of Biomass. Pyrolysis dates back to at least ancient Egyptian times,when tar for caulking boats and certain embalming agents were obtained by pyrol-ysis. Currently there are three main thermal processes—gasification, pyrolysis, andtorrefaction—which preferentially convert the biomass to three major forms of biofuels:biogas, bio-oil, and biochar. Figure 16.7 gives an overview of the applications of theproducts of thermal treatment and decomposition of biomass.

The liquid fraction, known as bio-oil, is a dark brown liquid (Figure 16.8), thecomposition of which greatly varies depending on the starting biomass feedstock.

Bio-oil contains a complex mixture of oxygenated organic components, formedas a result of degradation of holocellulose and lignin within the biomass, along with asignificant amount of water (15–50%wt).25 The liquid contains several hundred types of


Figure 16.7. Energy production through thermochemical treatment of biomass. MTO,

methanol to olefin, CH3OH → C2H4 + 2H2O; MTG, methanol to gasoline, C1–C4 + H2O.43

chemicals in varying proportions, including formaldehyde, acetic acid, high-molecular-weight phenols, oligosaccharides, and anhydrosugars. The pyrolysis of biomass is aversatile process; the relative yields of the products (i.e., bio-oil and biogas composition)can be controlled through variation of system parameters, such as heating rate, maximumtemperature, and residence time (see Table 16.2).44

Figure 16.8. Digital image of a typical bio-oil. (See color insert.)


TABLE 16.2. Influence of pyrolysis parameters on product distribution

Type of pyrolysisTemperature

(◦C)Heating rate(◦C min−1) Main product

Slow pyrolysis/torrefactionFast pyrolysisGasification

200–350400–550550–1000

�100100–10,000100–10,000

BiocharBio-oilBiogas

As can be seen from the table, increasing the rate of pyrolysis leads to increasingyield of products with a small molecular weight (as result of high heating rate andfinal temperature). Nanoparticles that exhibit a catalytic activity in a broad range oftransformations could significantly reduce the temperature of pyrolysis and substantiallymodify the pyrolysis product distribution. However, only a limited number of studies areavailable in the open literature related to the application of nanoparticles or nanocatalystsin direct biomass pyrolysis/gasification.45,46 Gokdai et al. investigated the catalyticactivities of nano-SnO2 in the pyrolysis of hazelnut shell.45 Due to its high surface areas,nano-SnO2 showed strong effects on gas generation through the acceleration of therate of both primary and secondary decomposition reactions. Furthermore, the bio-oilcomposition was found to be completely changed, as illustrated in Table 16.3.

Fabbri et al. studied the effects of nanopowder metal oxides (e.g., SiO2, Al2O3,MgO, TiSO4, and Al2O3–TiO2) on the pyrolytic production of chiral anhydrosugarsfrom cellulose.46,47 As a result, nanopowder metal oxides, with exception of SiO2,influenced bio-oil composition by increasing levoglucosan yield (see Table 16.4).

Bio-oil Upgrading. Bio-oils are not suitable for direct blending with standardhydrocarbon fuels and require special systems for utilization. The simplest applicationfor bio-oil is in stationary fuel burners such as boilers, furnaces, and turbines for elec-tricity production, but high viscosity, poor storage stability, and corrosiveness hinder itslarge-scale implementation in those industries.25 As a result a great deal of research has

TABLE 16.3. Gas chromatography-mass spectrography analysis of pyrolysis oil obtainedfrom hazelnut shell with and without nano-SnO2

Conventional pyrolysis Pyrolysis in the presence of nano-SnO2

No Bio-oil component Peak area (%) Bio-oil component Peak area (%)

1 Tetracosane 15.6 Tetrapentacosane 92 Bicyclo[3.3.1]nonane 6.5 Methoxyphenol 5.83 1-Dodecanol 5.6 2-Methoxy-4-methylphenol 5.54 Ethyl-benzenediol 5.2 Methoxy-propenylphenol 5.35 1,2-Benzenediol 4.8 2-Methoxy-4-ethenylphenol 4.16 Dimethyl-cyclopentenone 1.8 1,2-Benzenediol 3.77 Furanmethanol 1.8 2-Methoxy-4-ethylphenol 3.5


TABLE 16.4. Yields of chiral anhydrosugars from off-line pyrolysis of cellulose in the presenceof nanopowder metal oxides and aluminium titanate powder

Anhydrosugar

Catalyst aLGO % mass bLAC % mass cDGP % mass dLGA % mass

Without catalyst 3.7 ± 0.9 1.5 ± 0.6 2.6 ± 0.9 10.5 ± 3Al2O3 nanopowder 7.7 ± 0.9 4.5 ± 0.5 2.2 ± 0.7 9.1 ± 2MgO nanopowder 2.2 ± 2 6.1 ± 3 3.9 ± 4 11 ± 8SiO2 nanopowder 0.2 ± 0.1 0.2 ± 0.1 1.0 ± 0.1 2.8 ± 0.3TiSiO4 nanopowder 11 ± 3 4.9 ± 2 2.1 ± 0.4 7.0 ± 3Al2O3TiO2 nanopowder 19 ± 5 5.9 ± 0.2 1.6 ± 0.2 2.3 ± 0.4Al2O3TiO2 powder 2.9 ± 1.8 1.3 ± 0.2 2.1 ± 1 7.0 ± 3aLevoglucosenone.b1-Hydroxy, (1R)-3,6-dioxabicyclo[3.2.1]octan-2-one.c1,4:3,6-Dianhydro-�-d-glucopyranose.dLevoglucosan.

been carried out to seek processes that can upgrade bio-oil to make them more suitablefor the various desired applications. The main upgrading routes include hydrogenation,esterification, hydrodeoxygenation, and catalytic cracking of the pyrolysis vapors, aswell as steam reforming and physical emulsification of bio-oil with diesel. However,the majority of these require complicated and expensive procedures, and rely on theuse of catalysts that are subject to fouling during processing (see Figure 16.7).48–50Apromising methodology for bio-oil upgrading was proposed by Crossley and cowork-ers,51 who reported a family of solid nanohybrid materials that could stabilize water–oilemulsions and catalyze biphasic hydrodeoxygenation of vanillin (phenolic compoundthat is a common component of pyrolysis oil derived from the lignin fraction) at theliquid–liquid interface. The catalysts were prepared by depositing palladium onto carbonnanotube–inorganic oxide hybrid nanoparticles. The turnover number measured for thiscatalyst was in a similar magnitude to that observed by others in the reaction catalyzedby Pd/C in amonophasic system, but at a temperature less than 50 ◦C. The higher activityobserved in the biphasic system could be ascribed to a better state of particle dispersionat the interface as compared with that in the monophasic system and enhanced hydrogenconcentration at the interface (hydrogen has higher solubility in organic phase than inwater).

A high activity of nanoparticles in the hydrogenation of phenols (one of the majorcomponents of pyrolysis bio-oil) was also proved by Yan et al.52 A complex systemcomposed of metal nanoparticles (Ru, Pd, and Pt) and a functionalized Brønsted acidicionic liquid was designed, which could simultaneously catalyze the hydrogenation reac-tions and demonstrate high efficiency in upgrading lignin-derived phenolic compoundsinto alkanes (see Figure 16.9).

Conversion of bio-oil into syn-gas under carefully controlled heating in the presenceof oxygen is one of the most common ways to obtain high-quality biofuel.10 Theobtained syn-gas (a gas mixture that mainly contains carbon monoxide and hydrogen)


Complex catalyst

I. Metal nanoparticles (Ru)

II. BrØnsted acidic ionic liquids

N N R SO3H

H2

H2DehydrationH2

–H2O

+

OHOH O

A−+

Figure 16.9. Key steps involved in the formation of cyclohexane from phenol in the presence

complex catalytic system.

can be converted to a variety of hydrocarbons (CnH(2n+2)) through the Fischer–Tropschprocess (see Figure 16.7). Selectivity and efficiency of syn-gas conversion still remainsa problem. It has recently been reported that it is possible to convert synthesis gas toC2 through C4 olefins with selectivity up to 60 wt%, using catalysts that constitute ironnanoparticles (promoted by sulfur plus sodium) homogeneously dispersed on weaklyinteractive �-alumina or carbon nanofiber supports.53

The methanol-to-propylene reaction together with the methanol-to-olefin (MTO)process are also promising ways to large-scale production of olefins from biomethanol,which has drawn much attention from the chemical industry over the last two decades.54

For MTO catalyzation, the utilization of nanocrystal �-Mn2O3 demonstrates that thecatalytic selectivity toward ethylene is greater than that of bulk manganese oxide dueto higher levels of oxygen adsorption on its surface (verified by O2-TPD spectra).55

The reaction follows a reaction route of methanol → formaldehyde → ethylene, withthe nanocatalyst showing enhanced activity during the second step of the process. Amethanol conversion of 35% and a maximum selectivity of 80% toward ethylene wereobtained at 250◦C. Sun et al. have also demonstrated that gold-supported nanoparticleson zeolite ZSM lead to greater propylene formation from methanol.56 It was foundthat this was due to the effect nanogold has in its unique ability to participate in thedehydrogenation stage of the process.

Gasification of Biomass. Biomass gasification is another promising technologyfor converting biomass to energy. Gasification is the conversion of solid biomass intogas mixtures, the so-called syn-gas, which are rich in CO, CO2, CH4, and H2 and needto be subsequently transformed into chemicals and fuels (see Table 16.5) or used to heatindustrial processes.

Under conventional heating conditions, gasification is carried out between 750 ◦Cand 1800 ◦C. The process is carried out by partial oxidation in air or by steamgasification.


TABLE 16.5. Syn-gas upgrading processes

No Process name Process equation

1 Fischer–Tropsch transformation (2n+1)H2 + nCO→ CnH(2n+2) + nH2O2 Water gas shift reaction H2O + CO→ H2 + CO23 Steam reforming H2O + CH4 → CO + 3H2

Using oxygen as the oxidationmedium results in gases of a medium heating value (∼10–12 MJ m−3), which are significantly better than the results associated with oxidationin air (∼5 MJ m−3). Steam gasification is a two-step process with similar productsbut an improved medium heating value of approximately 15–20 MJ m−3 due to thehigher levels of CH4 and hydrocarbons within the gas stream. After production of theprimary gas, biochar residues are burnt in a second reactor to provide heat for the nextgasification, maximizing the overall energy efficiency of the system. The use of thegas and the potential production of value-added products depend on the levels of thevarious components within the stream, which in turn determines the heating value ofthe gas.25 Figure 16.10 shows the various potential applications of products of biomassgasification.

One of the major issues in biomass gasification/pyrolysis is dealing with the tarformed during the process. Catalytic cracking, which could operate at relatively lowertemperatures and generate high tar removal efficiency, has been recognized as the mostefficient method to diminish the tar content in the gasification gas mixture. There hasbeen a significant amount of information published on bio-oil upgrading in the presence

Figure 16.10. Application of products of biomass gasification.25


of nanoparticles.6, 57, 58 The objective of these studies has mostly been in the develop-ment of a novel supported nanocatalyst for tar removal in biomass gasification/pyrolysisto significantly enhance the quality of the produced gases. For this purpose, the sup-ported nano-NiO/� -Al2O3 catalyst was prepared by deposition–precipitation.47 Theresults showed that the active components of catalyst were spherical NiO nanoparticlescoated on the surface of the supports with a size range of 12−18 nm. Furthermore, theexperiments demonstrated that the tar yield, after addition of the catalyst, was reducedsignificantly; the tar removal efficiency reached 99% for catalytic pyrolysis at 800 ◦C,and the gas yield after addition of the catalyst remarkably increased. The compositions ofgas products before and after addition of the catalyst in the process also changed signifi-cantly. The percentages of CO2 and CH4 in the product gas after addition of the catalystswere obviously reduced, while those of the valuable H2 and CO strongly increased.Therefore, using the prepared NiO/� -Al2O3 catalyst in biomass gasification/pyrolysiscan significantly improve the quality of the produced gas and meanwhile efficientlyeliminate the tar generation in the gasification step.

Recently nanoparticles were successfully applied to anaerobic digestion of biomass(see Figure 16.9).59 The effects of hematite nanoparticles concentration (0–1600 mg/l)and initial pH (4.0–10.0) on hydrogen production were investigated in batch assaysusing sucrose-fed anaerobic mixed bacteria at 35◦C. The optimum hematite nanoparticleconcentration with an initial pH 8.48 was 200 mg/l, with the maximum hydrogen yieldof 3.21 mol H2/mol sucrose, which was 32.64% higher than the blank test.

NANOPARTICLES AND THE BIOREFINERY: PROSPECTSAND OUTLOOK

In summary, nanocatalysts are showing a great promise in biofuel production, leading togreener processing steps, higher yields of desired products, and ultimatelymore econom-ically favorable conditions to be cost-competitive with crude oil alternatives. However,there are a number of strategically significant issues that are of ultimate importance totake into account for a further implementation of this area of nanotechnology:

• Design of recyclable, highly active, and selective heterogeneous nanocatalystsfor biofuel production.

• Scaling-up nanotechnology for process intensification for diesel and gasolineproduction from synthesis gas by Fischer–Tropsch synthesis (FTS), which woulddramatically decrease the economic cost of the process compared to traditionalFTS processes.

• Development of nanoparticle-based catalytic systems for specific thermochemi-cal processing of biomass to high-quality bio-oil (at the moment only nanocata-lysts for biomass gasification have been reported).

• Development of new nanocatalyst hybrid materials, which will be robust in thepresence of typical products of biomass decomposition, as well as impuritiessuch as acids, alkali metals, nitrogen, and sulfur-containing compounds.

REFERENCES 611

• Development of novel catalysts to convert biomass-derived sugars to hydrox-ymethylfurfural, furfural, and furans followed by their conversion to “green”diesel and biofuels.

REFERENCES

1. IPIECA. Climate Change: A Glossary of Terms. International Petroleum Industry Environ-mental Conservation Association; 2001.

2. Denman K. L., Brasseur G., Chidthaisong A., Ciais P., Cox P. M., Dickinson R. E., Hauglus-taine D., Heinze C., Holland E., Jacob D., Lohmann U., Ramachandran S., da Silva Dias P.L., Wofsy S. C., Zhang X. In: Solomon S., Qin D., Manning M., Chen Z., Marquis M., AverytK. B., Tignor M., Miller H. L. editors, Climate Change 2007: The Physical Science Basis.Contribution of Working Group I to the Fourth Assessment Report of the IntergovernmentalPanel on Climate Change. New York: Cambridge University Press; 2007, p. 500–587.

3. U.S. Environmental Protection Agency. Inventory of the U.S. greenhouse gas emissions andsinks: 1990–2006: U.S. Environmental Protection Agency. 2008.

4. European Commission. Energy for the Future: Renewable Sources of Energy. White Paperfor a Community Strategy and Action Plan. COM(97)599. 1997.

5. Anastas P., Warner J. Green Chemistry: Theory and Practice. Oxford University Press; 1998.

6. Tran N. H., Bartlett J. R., Kannangara G. S. K., Milev A. S., Volk H., Wilson M. A. Catalyticupgrading of biorefinery oil from micro-algae. Fuel 2010;89:265–274.

7. National Renewable Energy Laboratory (US). Conceptual biorefinery. Available athttp://www.nrel.gov/biomass/biorefinery.html. Accessed Aug 2007.

8. Luque R., Herrero-Davila L., Campelo J. M., Clark J. H., Hidalgo J. M., Luna D., MarinasJ. M., Romero A. A. Biofuels: a technological perspective. Energ. Environ. Sci. 2008;1:542–564.

9. Lin S. Y., Dence C. W. Methods in Lignin Chemistry (Springer Series in Wood Science).Springer; 1992.

10. Mohan D., Pittman C. U., Steele P. H. Pyrolysis of wood/biomass for bio-oil: a critical review.Energ. Fuel. 2006;20:848–889.

11. Fernando S., Adhikari S., Chandrapal C., Murali N. Biorefineries: current status, challenges,and future direction. Energ. Fuel. 2006;20:1727–1737.

12. Werpy T., Petersen G. Top value added chemicals from biomass. U.S. Department of Energy;2004.

13. Zverlov V. V., Berezina O., Velikodvorskaya G. A., Schwarz W. H. Bacterial acetone andbutanol production by industrial fermentation in the Soviet Union: use of hydrolyzed agri-cultural waste for biorefinery. Appl. Microbiol. Biotechnol. 2006;71:587–597.

14. Roco M. C. Nanotechnology: convergence with modern biology and medicine. Curr. Opin.Biotechnol. 2003;14:337–346.

15. White R. J., Luque R., Budarin V. L., Clark J. H., Macquarrie D. J. Supported metal nanopar-ticles on porous materials. Methods and applications. Chem. Soc. Rev. 2009;38:481–494.

16. Luque R., Clark J. H. Water-tolerant Ru-Starbon (R) materials for the hydrogenation oforganic acids in aqueous ethanol. Catal. Commun. 2010;11:928–931.

17. Balu A. M., Campelo J. M., Luque R., Rajabi F., Romero A. A. Biomaterials supported CdSnanocrystals.Mater. Chem. Phys. 2010;124:52–54.


18. West J. L., Halas N. J. Applications of nanotechnology to biotechnology-commentary. Curr.Opin. Biotechnol. 2000;11:215–217.

19. Balu A. M., Baruwati B., Serrano E., Cot J., Garcia-Martinez J., Varma R. S., Luque R.Magnetically separable nanocomposites with photocatalytic activity under visible light for theselective transformation of biomass-derived platformmolecules.Green Chem. 2011;13:2750–2758.

20. BERR. Digest of United Kingdom Energy Statistics 2008. TSO; 2008.

21. Demirbas A. Combustion characteristics of different biomass fuels. Prog. Energy Combust.Sci. 2004;30:219–230.

22. Demirbas A. Sustainable cofiring of biomass with coal. Energ. Convers. Manage.2003;44:1465–1479.

23. Gomez L. D., Steele-King C. G., McQueen-Mason S. J. Sustainable liquid biofuels frombiomass: the writing’s on the walls. New Phytologist. 2008;178:473–485.

24. Sun Y., Cheng J. Y. Hydrolysis of lignocellulosic materials for ethanol production: a review.Bioresour. Technol. 2002;83:1–11.

25. Bridgwater T. Review: biomass for energy. J. Sci. Food Agric. 2006;86:1755–1768.

26. Ma F. R., Hanna M. A. Biodiesel production: a review. Bioresour. Technol. 1999;70:1–15.

27. Hahn-Hagerdal B., Galbe M., Gorwa-Grauslund M. F., Liden G., Zacchi G. Bio-ethanol-thefuel of tomorrow from the residues of today. Trends Biotechnol. 2006;24:549–556.

28. Mohan D. Pittman C. U., Steele P. H. Pyrolysis of wood/biomass for bio-oil: a critical review.Energ. Fuel. 2006;20:848–889.

29. Dry M. E. High quality diesel via the Fischer-Tropsch process-a review. J. Chem. Technol.Biotechnol. 2002;77:43–50.

30. Meher L. C., Sagar D. V., Naik S. N. Technical aspects of biodiesel production bytransesterification-a review. Renew. Sustain. Energ. Rev. 2006;10:248–268.

31. Freedman B., Butterfield R. O., Pryde E. H. Transesterification kinetics of soybean oil. J. Am.Oil Chem. Soc. 1986;63:1375–1380.

32. Xie W. L., Ma N. Enzymatic transesterification of soybean oil by using immobilized lipaseon magnetic nano-particles. Biomass Bioenerg. 2010;34:890–896.

33. Boz N., Degirmenbasi N., Kalyon D. M. Conversion of biomass to fuel: Transesterification ofvegetable oil to biodiesel using KF loaded nano-gamma-Al(2)O(3) as catalyst. Appl. Catal.B-Environ. 2009;89:590–596.

34. Reddy C., Reddy V., Oshel R., Verkade J. G. Room-temperature conversion of soybeanoil and poultry fat to biodiesel catalyzed by nanocrystalline calcium oxides. Energ. Fuel.2006;20:1310–1314.

35. UygunD. A., Ozturk N., Akgol S., Denizli A. Novel magnetic nanoparticles for the hydrolysisof starch with Bacillus licheniformis �-amylase. J. Appl. Polym. Sci. 2012;123:2574–2581.

36. Vamvuka D., Troulinos S., Kastanaki E. The effect of mineral matter on the physical andchemical activation of low rank coal and biomass materials. Fuel 2006;85:1763–1771.

37. KhanM. J., HusainQ.,AzamA. Immobilization of Porcine Pancreatic�-amylase onMagneticFe2O3 Nanoparticles: Applications to the Hydrolysis of Starch. Biotechnol. Bioprocess Eng.2012;17:377–384.

38. Zhang Y. H. P., Lynd L. R. Toward an aggregated understanding of enzymatic hydrolysis ofcellulose: Noncomplexed cellulase systems. Biotechnol. Bioeng. 2004;88:797–824.

39. Lynd L. R., Cushman J. H., Nichols R. J., Wyman C. E. Fuel ethanol from cellulosic biomass.Science 1991;251:1318–1323.

REFERENCES 613

40. Falkowski P., Scholes R. J., Boyle E., Canadell J., Canfield D., Elser J., Gruber N., HibbardK., Hogberg P., Linder S., Mackenzie F. T., Moore B., Pedersen T., Rosenthal Y., SeitzingerS., Smetacek V., Steffen W. The global carbon cycle: a test of our knowledge of earth as asystem. Science 2000;290:291–296.

41. Chang R. H.-Y., Jang J., Wu K. C. W. Cellulase immobilized mesoporous silica nanocatalystsfor efficient cellulose-to-glucose conversion. Green Chem. 2011;13:2844–2850.

42. Lupoi J. S., Smith E. A. Evaluation of nanoparticle-immobilized cellulase for improvedethanol yield in simultaneous saccharification and fermentation reactions.Biotechnol. Bioeng.2011;108:2835–2843.

43. Raveendran K., Ganesh A. Heating value of biomass and pyrolysis products. Fuel1996;75:1715–1720.

44. Domınguez A., Menendez J. A., Fernandez Y., Pis J. J., Nabais J. M. V., Carrott P. J. M.,Carrott M. M. L. R. Conventional and microwave induced pyrolysis of coffee hulls for theproduction of a hydrogen rich fuel gas. J. Anal. Appl. Pyrolysis. 2007;79:128–135.

45. Gokdai Z., Sinag A., Yumak T. Comparison of the catalytic efficiency of synthesized nano tinoxide particles and various catalysts for the pyrolysis of hazelnut shell. Biomass Bioenergy.2010;34:402–410.

46. Fabbri D., Torri C., Baravelli V. Effect of zeolites and nanopowder metal oxides on thedistribution of chiral anhydrosugars evolved from pyrolysis of cellulose: an analytical study.J. Anal. Appl. Pyrolysis. 2007;80:24–29.

47. Torri C., Lesci I. G., Fabbri D. Analytical study on the pyrolytic behaviour of cellulose in thepresence of MCM-41 mesoporous materials. J. Anal. Appl Pyrolysis. 2009;85:192–196.

48. Tang Y., YuW., Mo L., Lou H., Zheng X. One-step hydrogenation−esterification of aldehydeand acid to ester over bifunctional pt catalysts: a model reaction as novel route for catalyticupgrading of fast pyrolysis bio-oil. Energy Fuels. 2008;22:3484–3488.

49. Junming X., Jianchun J., Yunjuan S., Yanju L. Bio-oil upgrading by means of esterificationof ethyl ester production in reactive distillation to remove water and to improve storage andfule charachteristics. Biomass Bioenergy. 2008;32:1056–1061.

50. Qi Z., Jie C., Tiejun W., Ying X. Review of biomass pyrolysis oil properties and upgradingresearch. Energ. Convers Manage. 2007;48:87–92.

51. Crossley S., Faria J., ShenM., Resasco D. E. Solid nanoparticles that catalyze biofuel upgradereactions at the water/oil interface. Science 2010;327:68–72.

52. Yan N., Yuan Y., Dykeman R., Kou Y., Dyson P. J. Hydrodeoxygenation of lignin-derivedphenols into alkanes by using nanoparticle catalysts combined with bronsted acidic ionicliquids. Angew. Chem. Int. Ed. 2010;49:5549–5553.

53. Galvis H. M. T., Bitter J. H., Khare C. B., Ruitenbeek M., Dugulan A. I., de Jong K. P.Supported iron nanoparticles as catalysts for sustainable production of lower olefins. Science2012;335:835–838.

54. Haw J. F., Song W. G., Marcus D. M., Nicholas J. B. The mechanism of methanol tohydrocarbon catalysis. Acc. Chem. Res. 2003;36:317–326.

55. Xu J., Ouyang L., Luo Y., Xu X. M., Yang Z., Zhang C., Gong J. Mechanistic insightsinto methanol-to-olefin reaction on an �-Mn2O3 nanocrystal catalyst. AIChE J. 2012,doi:10.1002/aic.13725.

56. Sun C., Yang Y., Du J., Qin F., Liu Z., Shen W., Xu H., Tang T. Dehydrogenation inhibitionon nano-Au/ZSM-5 catalyst: a novel route for anti-coking in methanol to propylene reaction.Chem. Commun. 2012, doi:10.1039/C2CC30607G.


57. Li J., Yan R., Xiao B., Liang D. T., Du L. Development of nano-NiO/Al(2)O(3) catalyst tobe used for tar removal in biomass gasification. Environ. Sci. Technol. 2008;42:6224–6229.

58. Li J., Yan R., Xiao B., Liang D. T., Lee D. H. Preparation of nano-NiO particles and evaluationof their catalytic activity in pyrolyzing biomass components. Energ. Fuel. 2008;22:16–23.

59. Han H., Cui M., Wei L., Yang H., Shen J. Enhancement effect of hematite nanoparticles onfermentative hydrogen production. Bioresour. Technol. 2011;102:7903–7909.

nanocatalysis synthesis and applications (polshettiwar/nanocatalysis) || nanocatalysts for biofuels

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