z the development of mesoporous ni-based catalysts and...

z Catalysis

The Development of Mesoporous Ni-Based Catalysts andEvaluation of Their Catalytic and PhotocatalyticApplicationsSharanmeet Kour+,[a] Ankit Mishra+,[b] Anil Sinha,*[b] Pawandeep Kaur,[a] and Hari Singh*[a]

Porous Ni-based catalysts have attracted extensive attention fora wide range of applications in energy production and environ-mental remediation due to controllable morphology, highdispersion. These properties are mainly governed by a numberof parameters such as compositions, synthesis methods, theirstructural morphology, and surface area. Various efforts havemade to develop unsupported template-assisted catalysts withspecific nanostructures and surface properties, a new approachin supramolecular chemistry. This review reports a detailed

overview of the development of mesoporous nickel-basedcatalysts for energy and environmental applications. Thisreview also looks at recent advancements, synthesis routes forporous nickel-based catalysts, and comparative study with thereported Ni-based catalysts. This review addresses numerouscharacteristic reactions and processes in the utilization oforganic wastes, highlighting the significance of developingporous, proficient, and stable Ni-based catalysts.

1. Introduction

1.1. Brief history of catalysis

Catalysis is a not often used expression in everyday life, but itplays a major role in our existence. The human body canfunction only with the catalytic activity of enzymes. Also, thesynthesis of ammonia fertilizer is a great achievement in thefield of catalysis for the society. It is estimated that without thechemical production of ammonia from the Haber-Boschprocess, we would not be able to feed more than 1/3rd of theworld population.[1] The Haber- Bosch process is the mostimportant invention of the 19th century. Both Fritz Haber andCarl Bosch were awarded the Nobel prize in chemistry for suchlandmark achievements.[2,3] In 1938, Bergius developed a high-pressure hydrogenation reaction for converting coal to liquidfuel in the presence of iron as a catalyst. The 2018 Nobel Prizein chemistry was awarded for identifying the new enzymesleading to the manufacturing of chemicals, including drugs,and in the production of renewable fuels. Heterogeneouscatalysis is finding new applications in emerging areas such ashydroprocessing, fuel cells, nanotechnology, green chemistry,biorefining, and biotechnology.[4] We surround ourselves with

products whose manufacturing and operation rely on catalyticprocesses every single day. The products range from thegasoline with which we fuel our cars to the batteries of ourmobile phones, and even to the plastic bags, we carry home.Most of the chemical products generated from chemicalindustries are based on the catalytic processes.[4,5] The mostwell-known application of catalysis in everyday life is, withoutdoubt, the automotive three-way catalyst, which is used forscrubbing exhaust gases from gasoline-driven combustionengines in, e.g., automobiles. This is just one example of theutilization of catalysts for environmental protection. Anotherexample is the removal of sulfur impurities from fuels andexhaust gases from, e.g., coal-based power plants. If releasedinto the atmosphere, sulfur leads to the formation of sulfuricacid, which further leads to forest death due to acid rain. Withthe increasing awareness of the environmental problemscaused by the industrialized society, increasing efforts will beput into the development of catalysts, which can prevent ordiminish these potentially devastating issues. Traditionally,catalysts have been developed by simple trial and errormethods, but to continue the development of novel andimproved catalysts for the future, it is essential that weunderstand the fundamental properties of catalysts andcatalytic processes. This report is dedicated to the study ofsome of the fundamental issues concerning different Ni-basedcatalytic systems and the design of new porous support-free Nicatalysts and their application in the hydrogenation andhydrodeoxygenation reactions. This report contains the newsynthesis approach to unsupported mesoporous Ni/NiO cata-lysts and applications of these catalysts in the production ofhydrocarbon fuels and value-added chemicals.

[a] S. Kour,+ P. Kaur, Dr. H. SinghDepartment of Chemistry, School of Basic and Applied Sciences, RIMTUniversity, Mandi Gobindgarh, Punjab, 147301 (INDIA)E-mail: [email protected]

[email protected][b] A. Mishra,+ Prof. Dr. A. Sinha

Hydroprocessed Renewable Fuel Area, Biofuel Division, CSIR- IndianInstitute of Petroleum, Haridwar Road, Dehradun-248005 (INDIA)E-mail: [email protected]

[+] both authors contributed equally.

Supporting information for this article is available on the WWW underhttps://doi.org/10.1002/slct.201904550

ReviewsDOI: 10.1002/slct.201904550

1ChemistrySelect 2020, 5, 1–15 © 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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http://orcid.org/0000-0001-9780-8062

https://doi.org/10.1002/slct.201904550

1.2. Heterogeneous catalysis

Heterogeneous catalysis plays a key role in the manufacture ofmaterials economically and in an environmentally efficientmanner. Most of the industrial catalytic processes (90%) arebased on the heterogeneous catalysts. These catalysts aresometimes called surface catalysts having surface active sites,and all the catalytic reactions go on these active sites. Thediffusion of the reactant through a boundary layer surroundingthe catalyst surface is the first step of any heterogeneouslycatalyzed process. The reactants are then adsorbed on thecatalyst surface. The environment of solid catalyst containsatoms on the surface, which are chemically unsaturated. Theseatoms can bond (chemisorptions) with appropriate molecules.Adsorption is the main step of any heterogeneously catalyzedreaction. The activity of a heterogeneous catalyst is measuredby the turn over number (TON). In addition to the fundamentalproperties that define the efficiency of a heterogeneouscatalyst, i. e., activity and selectivity, industrial applicationrequires that it should be (i) regenerable, (ii) thermally and

mechanically stable, (iii) reproducible, (iv) economical, (i. e.,inexpensive, can be prepared from cheap raw material) (v)suitable morphological characteristics like high surface area,high number of active sites per unit area and crystallinity.Heterogeneous catalysts can either be crystalline or amor-phous.

1.3. Metal oxides as catalysts

Metal oxides can act as an active center or act as support inheterogeneous catalysis. The versatility of the use of oxidesystems can be seen in many organic reactions like oxidation,hydrogenation, dehydrogenation, condensation, cracking, iso-merization, and alkylation, etc.[5] Hence, oxide catalysts areimportant from a commercial point of view and have beenused for manufacturing many valuable products.[6] It is verydifficult to categorize metal oxide catalysts because it has amultiplicity of crystal systems of various compositions with abroad choice of physicochemical properties. Oxides can bringabout electron- and proton- transfer and they can be used in

Prof. Dr. Anil Kumar Sinha was born in Biharand has done his Ph.D. degree (Chemistry) in1999 from CSIR-National Chemical Labora-tory, Pune University. He did Post-doctoralstudies as NCS Taiwan (1999-2000), JISTECJapan (2000-2002), AIST Japan (2002-2003),and also worked as a researcher at ToyotaCRDL, Japan (2003-2007). He is currentlyworking as Senior Principal Scientist at CSIR-Indian Institute of Petroleum, India. He isalso a Professor in Academy of Scientific andInnovative Research (AcSIR), India. His re-search mainly focusses on Heterogeneouscatalysis, including hydroprocessing, photo-catalysis, and biofuels. He has publishedmore than 120 research papers in peer-reviewed journals and 25 patents and twobook chapters. He developed bio-jet fuel forflight at Indian Institute of Petroleum, thefirst time (2018) in India.

Dr. Hari Singh was born in 1988 in Jhansi,India. He pursued his B.Sc. (Hons) IndustrialChemistry in 2010 and M.Sc. IndustrialChemistry in 2012 from Aligarh MuslimUniversity, India. He was awarded the UGCResearch fellowship (RGNF) in 2014. Heobtained his Ph.D. degree in Chemistry(2019) from the Academy of Scientific andInnovative Research (AcSIR)/CSIR-Indian Insti-tute of Petroleum, Dehradun (India) underthe supervision of Dr. Anil Kumar Sinha. He iscurrently an Assistant Professor at RIMTUniversity, Mandi Gobindgarh Punjab (India).He has expertise in Heterogeneous catalysis

for biomass conversion, template synthesis ofmesostructures, Hydrogenation, Biofuels, syn-thesis of surfactants, and various catalystscharacterization techniques. He authoredabout 15 peer-reviewed journal articles withmore than 42 citations.

Shararmeet Kour was born in 1995 inKashmir, India. She completed her M.Sc. inChemistry (2019) from Hemvanti NandanBahuguna Garhwal University, India. She iscurrently doing her doctoral degree underthe guidance of Dr. Hari Singh in the Schoolof Basic and Applied Sciences (ChemistryDepartment), RIMT University, Mandi Go-bindgarh, Punjab, India.

Ankit Mishra was born in 1991, Bareilly. Hepursed M.Sc. Rohilkhand University, India. Hequalified CSIR-NET in 2018. Currently, he isworking as Ph.D. student (Chemistry) atCSIR-Indian Institute of Petroleum, under thesupervision of Dr. Anil Kumar Sinha.

Pawandeep Kaur was born in Ludhiana(1994). She has completed M.Sc. Chemistry in2017 from Punjabi University, Patiala. She isworking as M.Phil. Student (Chemistry) underthe supervision of Dr. Hari Singh at RIMTUniversity, Mandi Gobindgarh Punjab, India.

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both redox and acid-base reactions. Therefore, depending ontheir nature, oxide catalysts fall broadly into two generalcategories, either acid/base catalysts or oxidation catalysts. Thecationic material of acid/base catalysts has mainly a distinctoxidation state and are mostly insulating in nature. They havestoichiometric M :O ratios. The s and p group metal oxides andthe zeolites fall into this category. Alkali and alkaline earthmetal oxides act as a base catalyst, and these are active andselective for dehydrogenation and isomerization reactions.[7]

The p-block metal oxides are mainly acid catalysts like alumina,silica, and silica-alumina in their various modified forms andhave been evaluated as a catalyst for alkylation, acylation, andcyclization reactions. Some of the oxides as amphoteric oxidesare normally oxides of weakly electropositive metals like ZnO,SnO2. The other types of oxides which are commonly used inoxidation reactions and photocatalysis are semiconductors orconducting oxides. A semiconductor is a material that haselectrical conductivity between those of a conductor and aninsulator. Transition metal oxides have metal ion with a variableoxidation state.[7]

1.4. Transition metal oxides

Transition metal oxides are extensively used as heterogeneouscatalysts for organic transformations reactions such as oxida-tion, dehydrogenation, reduction, metathesis (production oflong-chain alkenes), and esterification as well as for water-gasshift reaction.[8,9] The transition metal oxides have multiplevalences (different oxidation states) in their orbits resulting inhigh catalytic activity. Among the transition metal oxides, thesuperior behavior could be obtained from the catalysts wheremetal ion species are relatively easy to interchange betweentwo different valence states.[9,10] This can be found in Fe2O3,V2O5, TiO2, CuO or NiO.[10]

1.5. Nickel catalyst

From the aforementioned catalytic systems for hydrogenationand HDO, the systems based on nickel show great potentialbecause of both low cost and high activity of Ni towardshydrogenation. Since the pioneering work by Sabatier,[11] Nicatalysts have been widely studied and utilized as outstandingcatalysts for hydrogenation. In the early days, the Ni catalystwas directly prepared by the reduction of Ni oxides.[12] A blackpowder, known as Ni black, was obtained. The Ni black showslow activity and poor stability due to low surface area.[12,13]

Nowadays, different Ni-based catalysts and the combination ofnickel with other metals and solid acids employed to achievebetter metal dispersion and surface area resulting in higherspecific activity.[13,14] An exception is Raney Ni, or the skeletal Nicatalyst, which is prepared by extraction of aluminium from Ni/Al alloys. Taking advantage of the unique structural, texturaland mechanical properties, Raney Ni is widely applied toindustrial hydrogenation and hydrogenolysis as unsupportedcatalysts.[12–15] Other types of Ni catalysts, such as nickelformate, Ni� Zn composite, and nickel nanoparticles, are alsodescribed in the literature.[13,14] Nowadays it is probably the

most widely used Ni catalyst not only for academic researchbut also for industrial applications.[12–15] Raney Ni is preparedfrom an alloy composed of Ni and a second reactive metal(e.g., Al).[12,15] The alloy is first ground and screened to obtainprecursor particles with diameters between 40 to 80 μm. Theseparticles are then leached with a solution of strong alkali (e.g.,NaOH) under controlled conditions to dissolve the reactivemetal selectively.[14] The leaching and hydrogen evolutionfurther breaks the grounded alloy and also creates porosity,which leads to a sponge structured Ni framework with smallparticle size (several microns), high strength, reasonable surfacearea, and porosity. These properties make Raney Ni suitable forthe application in industrial catalysis.[10–15] The leaching processis highly exothermic.[12] The condition should be thus controlledcarefully. Considerable research was conducted into theoptimization of the alloy composition, reaction temperature,reaction time, and alkali concentration. Ni� Al alloy is the mostsuccessful precursor for Raney Ni preparation, albeit other Nialloys, including the initial Ni� Si alloy patented by Raney, werealso in use. Compared with other Ni alloys, Ni� Al alloy is easierto prepare and pulverize.[12–15] The high reactivity of aluminumin the alkali solution also makes the leaching process moreefficient. Also, the small amount of Al remained in Raney Ni isof great importance for the catalyst properties.[13] In the earlyworks, the leaching usually involved high temperature (80-120 °C) and long reaction time (7-12 h) to leach aluminium asmuch as possible from the alloy.[11–15] This strategy, however,leads to the coating of the catalyst with aluminum trihydroxide(alumina hydrate).[14] The low surface area of the catalyst causedby sintering and enlarged pores is the main disadvantage ofthe leaching, performed at high temperature for a longperiod..[13] As a result, a material with relatively low catalyticactivity is obtained. In the later works, the Ni� Al was subjectedto short reaction time (< 1.5 h) and low temperature (< 50 °C)leaching process. The obtained catalyst contains a largeamount of remaining aluminum (12-13%), and surface ad-sorbed hydrogen and is highly active for hydrogenation.[13] Theremaining aluminum was of great significance for the highactivity of the catalyst.[14,15] First, the Ni2Al3 phase is relativelyresistant to alkaline attack and can be efficiently leached outonly with a concentrated alkaline solution, especially at lowtemperatures.[13–15] Second, the aluminate tends to undergohydrolysis when the pH is increased. This procedure requiresonly catalytic amounts of alkali to produce a highly activecatalyst.[12–15] The crystallite size of the skeleton Ni can varyfrom 1 to 20 nm while a typical crystallite diameter varies from2.5 to 15 nm with a slight anisotropy in different crystalplanes.[14] The crystallite size decreases with temperature andalkaline concentration leaching.[12–15] These crystallites are heldtogether, creating a sponge-like morphology. The voidsbetween the crystallites shape the mesopores. The specificsurface area and the porosity of the catalyst were found to besignificantly influenced by the preparation temperature andthe alkaline concentration. In general, increasing temperatureand alkaline concentration leads in reduction in surface areaand an increase of pore volume and mean pore diameters.Freel et al. extracted Al from the alloy precursor with NaOH at

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107 °C and 50 °C and found that the specific area increasedfrom 80 to 110 m2g� 1 by decreasing the temperature,[14,15] whilethe pore volume decreased from 0.12 to 0.07 cm3g� 1. Further-more, the catalyst obtained at 50 °C has a smaller mean poresize (c.a. 2.5 nm) compared to that prepared at 107 °C (c.a.6 nm).[13–15] The surface of the skeleton catalyst consistspredominantly of NiO and contains a significant amount ofhydrogen, which is produced by the oxidation of aluminiumduring the leaching.[13–15] There are many reports on thedetermination of the amount of hydrogen adsorbed on RaneyNi. Chemical methods, such as selective oxidation of H atomsand the hydrogenation of organic compounds without molec-ular hydrogen,[11,14] usually give hydrogen content above100 cm3g� 1. This value seems to be overestimated since Al inRaney Ni is also very sensitive to oxidation and thus alsoconsumes the oxidant during the measurement. The sameproblem is present when measuring the hydrogen evolved byheating Raney Ni at high temperature.[13–15] During the heatingprocess, alumina hydrate releases water, which then oxidizesaluminum, thus releasing H2. The nature of the hydrogen atomsin Raney Ni has been widely discussed, and it has not fullybeen resolved yet.[14] Early reports by M. Raney and otherssuggested that the hydrogen atoms should be present in theform of nickel hydride (NiH2).

[15] Some of the more recent worksproposed that the hydrogen should be chemisorbed on Nisurface,[12,14] while other early reports also considered H as apart of the lattice in the metal.[14,15] A report by Freidlin et al.showed that Raney Ni loses activity when all the hydrogen isremoved from the material.[14] Smith et al. studied the hydro-genation of benzene catalyzed with Raney Ni and found thatthe activity of the catalyst decreases linearly with the decreaseof the H-content.[13–16] Continuous loss of surface area wasnoted along with the decreases in H-species on the surface.Based on this result, they proposed that the adsorbed hydro-gen works as a promoter of the catalyst.[16] The H-atomsadsorbed on Ni can protect the Al from being oxidized by theresidual water.[15] They suggested that removal of H-content ofRaney Ni might be the cause in the deactivation of the catalyst.Alkenes are readily hydrogenated into alkanes over Raney Niunder low-severity conditions, even at room temperature andless than 5 bar hydrogen.[14–16] However, high temperature andH2 pressure are often applied on a large scale reactioncatalyzed by nickel catalysts for economic reasons.[14–16]

1.6. Supported nickel catalysts

The performance of Ni catalyst can be significantly improvedby dispersing Ni on another solid material.[17] The supportprovides Ni a high surface area, high mechanical strength, andbetter stability against sintering.[18] Also, the support is in somecases catalytically active, providing new functionalities ortuning the selectivity of the Ni catalyst by metal-support-interactions.[17,19] Impregnation and precipitation are the mostcommon methods for the dispersion of the precursor, but othermethods, such as thermal decomposition and ion-exchange arealso reported for some particular catalyst systems.[16,19] SeveralNi salts can be used as a precursor, e.g., nickel sulfate, nickel

chloride, nickel acetate, and nickel nitrate.[17] Nickel nitrate isused in most of the academic publications because of the highsolubility in water of this salt. Industrially, Ni sulfate is, however,the precursor of choice because of its low price.[16] After theimpregnation or precipitation, calcination is carried out toremove the volatiles completely from the support or todecompose the precursor. This step causes, however, thesintering of the particle and may lead to large particle sizes.[17]

Before use, the material is activated by reduction, whichconverts the Ni oxide into Ni nanoparticles. The reduction of Niis carried out at elevated temperatures with H2 or diluted H2 inan inert gas (N2 or Ar). The reduction rate depends upon theprecursor loading, dispersion, the catalyst-support interaction,and the activation temperature.[15–17] The degree of reductionincreases with temperature, albeit high temperatures lead to aloss in the dispersion. A complete reduction is difficult toachieve. Nonetheless, partially reduced nickel oxides are oftenmore active than the fully reduced ones.[20] The selection ofsupport is important to control the desired properties of thecatalyst. The most used supports for Ni catalysts includealumina,[17] silica,[16] active carbon[17] silica/alumina,[17] andzeolite. Some novel supports, such as ordered mesoporoussilica and carbon nanofibers[15–17] were also recently exploited.The support provides a high specific area to Ni catalysts. Forexample, γ-Al2O3 has a specific area of up to 400 m2g� 1; andmesoporous silica, activated carbon, and zeolites can provide aspecific area of up to 1000 m2g� 1.[18,19] The high specific arealeads to good dispersion of the active metal and high activity(in some cases even as high as that for Raney Ni) forhydrogenation reactions.[15–17] The literature report showed thehydrocracking of asphaltene to maltene using Ni catalystsupported on SBA-15. The mesoporous structure of the supportwas found to be the key to convert large molecules.[17–19] Somesupports have active catalytic sites and can thus cooperatewith Ni forming a so-called bifunctional catalyst. Several reportshave shown that acidic supports (e.g., zeolite and silica) cancatalyze the deoxygenation of phenolic compounds,[18,20] andbenzaldehyde when combined with a Ni catalyst. Otherreactions, including hydrogenolysis, hydrolysis, andreforming,[18–20] were also reported to be catalyzed by Nicatalyst supported on acidic or basic carriers.[18,19] In supportedNi-based catalysts, support allows Ni catalysts to achieve highmetal dispersion, good stability, high selectivity, and catalyticactivity. Besides skeletal Ni and supported Ni catalysts, thereare many other forms of Ni catalysts reported in the literature.Finely divided, catalytically active Ni particles can be obtainedby the thermal decomposition of Ni formate or oxalate.[15–18]

This catalyst type was originally applied to the hydrodeoxyge-nation of oleic acid.[17–19] In this process, the Ni formate wasadded into the system as a catalyst precursor. The Ni catalystwas in-situ generated by thermal decomposition. Ni formatedehydrates at 140 °C and starts to decompose at temperaturesabove 210 °C, generating metallic Ni together with theevolution of CO, CO2, H2, and water. Finely divided Ni particleswith high catalytic activity for hydrogenation of unsaturatedcompounds, such as olefin fatty acid and aromatic nitrocompounds,[18,19,21] are obtained by this method. Surprisingly,

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this method leads to Ni particles stable in air.[18] Recently, Ninanoparticles are attracting increasing attention as catalysts forselective hydrogenations. Alonso et al. reported the productionof Ni nanoparticles by a similar principle as the production ofUrushibara Ni.[19] Wojcieszak et al. prepared supported Ni nano-particles by reducing the Ni acetate precursor on activatedcarbon with hydrazine. The particle sizes were reportedlyproposed to be smaller than 5 nm, but TEM showed that the Niparticles were not visible.[18] High activity for benzene hydro-genation (comparable to that of Pt/C) was achieved by thiscatalyst. Tang et al. used hydrazine to reduce nickel chloridesupported on poly (acrylic acid) grafted multi-walled carbonwith NaOH as a catalyst.[19] The obtained Ni nanoparticlesshowed high catalytic activity and selectivity for the selectivehydrogenation reaction.

1.7. Sulphided catalyst in hydroprocessing

In a petroleum refinery, hydroprocessing unit is related tocracking and elimination of heteroatoms (N, S, O) frompetroleum-derived feedstocks such as gas oil and heavy oil viaHDN, HDS, and HDO routes. Hydroprocessing of non-ediblevegetable oils or bio-oils is performed at temperatures (300-600 °C) with high-pressure H2 using sulphided catalysts such asNiMo, NiW, and CoMo-based catalysts. The production ofaromatics from vegetable oils (Jatropha oil) with low aromaticyield (30wt%) was also reported over the zeolite catalyst (ZSM-5).[18] The hydrocracking of jatropha oil using sulphided NiMo-hierarchical ZSM-5 catalyst with the maximum aromatic yield(50wt%) was reported.[18,19] The available active-site of hierarch-ical zeolite in which the diffusion of hydrocarbons is lessinhibited (is preserved due to mesopores the zeolitic proper-ties). The porous structure can elongate catalyst life byincreasing the endurance to coking (deactivation) during thereaction. The renewable fuel produced through this routeshowed much higher cetane value compared to conventionaldiesel, which is commercially attractive. The use of sulphidedcatalysts in the processing of non-edible oil to renewable fuelresults in the harmful environmental outcomes of sulfur dioxideemissions, corrosion of reactor, and sulfur residues inproducts.[19] Keeping in mind problems related to catalysis, wetried to develop the porous, cost-effective, sulfur-free (environ-ment-friendly) and support-free magnetically recoverable cata-lyst.

1.8. Types of porous Ni-catalysts

The various types of porous Ni-based catalysts are reportedand discussed in detail.

1.8.1. Ni foam

The Ni metal was prepared in the form of Ni foam using nickelnitrate and glycine by microwave-assisted combustion method.In the typical synthesis process, the known amount of glycinewas dissolved in a water-based solution of Ni(NO3)2. Theobtained solution was kept in an open glass voil followed by

irradiated in a microwave oven at 1000 W of power for 1 h. Nifoam is porous in nature with 16 m2/g surface area andapplicable to make electrodes for solid oxide fuel cells.[19b]

1.8.2. Porous NiO

The porous NiO was prepared by a hydrothermal andsolvothermal process followed by calcination.[20b] The aqueoussolution of nickel is prepared using NiCl2.6H2O as a nickelprecursor under ambient conditions. The pH of the solutionwas then maintained to 12–14 with the NaOH solution.[20b] Thesolution was stirred continuously at 60 s and transferred to anautoclave (steel). The autoclave was sealed and maintained at160 °C for 2 days, and then allowed to cool to room temper-ature. The product was washed with ethanol followed by waterand centrifuging. The obtained green precipitate of Ni(HCO3)2and Ni(OH)2 was calcined at 400 °C for 2 h to accomplish porousnickel oxide with the surface area of 100 m2/g. The porous NiOmaterial shows a potential application for the supercapacitorelectrodes.[20b]

1.8.3. Mesoporous NiO

The mesoporous NiO was synthesized with the facile methodusing octylamine template and post calcination.[21a] In a typicalsynthesis, NiCl26H2O was dissolved in ethanol with the additionof HCl added and then octylamine is added dropwise.[21a] Thegreen solid precipitate was formed instantly with the additionof the NaOH solution to the resulting mixture. The precipitateswere filtered and washed with distilled water. The greenprecipitates were then heated with ethanol at 78 °C for 1 h toremove the template. The obtained product is dried at 80 °C toremove the ethanol. The final sample is then calcined in the airunder different temperatures to achieve mesoporous NiO butcalcination also induces cracking. Mesoporous NiO attains ahigh surface area of 350 m2/g.[21a]

1.8.4. Ni-phosphate/phosphonate

Porous Ni-phosphonate material was synthesized by the hydro-thermal method without any structure-directing agent ortemplate using Hexamethylenediamine-tetrakis-(meth-ylphosphonic acid as the organophosphorus precursor.[22a] Thebrief synthesis procedure was reported in the literature usingNiCl26H2O, water and aqueous solution of hexameth-ylenediamine-N, N, N0, N0-tetrakis-(methyl phosphonic acid).[22a]

The resulting solution followed the hydrothermal treatment ina Teflon-lined stainless-steel autoclave at 170 °C for 2 days. Theobtained product filtered and dried at room temperature. TheBET surface area of Ni-phosphate/phosphonate catalyst isreported 241 m2g 1. The Ni-phosphate/phosphonate, which isan organic-inorganic hybrid material shows a strong affinity formetal cations like Hg2+, Cd2+, Cr3+, Pb2+ , due to the presence ofnitrogen donor sites in the framework and surface phospho-nate groups. These materials can be efficiently applied for theelimination of heavy metal ions from polluted water. The Ni-

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phosphate/phosphonate also reported good catalytic activity inthe reduction of nitro benzenes.[22a]

1.8.5. Mesoporous Nickel–Aluminum Mixed Oxide

The synthesis of mesoporous Ni–Al mixed oxide material hasbeen reported in one-step hydrothermally using long-chainfatty acid molecules (lauric acid as a capping agent).[22b] Thedetailed synthesis of mesoporous Nickel–Aluminum MixedOxide reported in the literature.[22b] Nickel chloride andaluminum chloride, water, and lauric acid mixed to form asolution at 40 °C to achieve a clear solution. The thick blueprecipitate was formed with the drop wise addition ofammonia solution. The pH of the mixture was adjusted to 10.The resulting solution was then treated hydrothermally in anautoclave at 100 °C for 48 h, followed by filtration and washedwith water. The synthesized material was then treated with themixture of ethylenediamine and ethanol several times at roomtemperature followed by calcination at 500 °C in the air toremove the capping agent. The mesoporous Ni–Al basedmaterial showed a high specific surface area (337 m2g–1). Thismaterial showed efficient catalytic activity in the reduction ofnitroarenes.[22b]

1.8.6. Ni-MOFs Catalysts

Ni-MOFs was synthesised by hydrothermal method, using Ni(NO3)2⋅6H20, trimesic acid, and Polyvinylpyrrolidone (PVP).[23] Inthe synthesis process, the above mixture is dissolved in anothermixture solution containing water, ethanol, and DMF. Theresultant green colour solution obtained is tightly kept into aTeflon autoclave and heated at a temperature of 150 °C for1 day. The resulting Ni-MOFs obtained was filtered, washedwith ethanol for several times and dried at 80 °C.[23a]

Ni/C composite from Ni-MOFS

The Ni/C composite material was prepared by facile pyrolysistreatment of synthesised Ni-MOFs.[24a] In typical synthesis, driedNi-MOFs powders were heated to 500 °C under a N2 atmos-phere for 2 h and then eventually cooled to obtain black Ni@Csample. The synthesised catalyst exhibit the characteristicproperties like high activity and stability for CO2 methanationreaction at low temperature.[23a]

1.8.7. Ni/C composite

The synthesis of Ni NPS denoted as Ni/C, dispersed on graphitecarbon was reported by the impregnation-reduction methodunder controlled conditions.[23a]

1.8.8. Ni-based photo catalysts

The numerous Ni-based catalysts has been developed andemployed such as alloys/metals, oxides, hydroxides, sulfides,borides, carbides, nitrides to carry out the photocatalyticevolution of hydrogen.[23b] Various noble-metal-based materials

such as Pt, Pd, Ag, and Au), abundant-metal-based (i. e., Ni, Cu,Mo, Fe, Co, and W), metal free carbon-based, and their hybridmaterials have been reported in photocatalytic H2 production.Among the large variety of hydrid materials, the Ni-basedmaterials have indulge in photocatalytic H2 generation due totheir higher physico-chemical properties including easy fabrica-tion, high efficiency and low cost. These co-catalyst displaymulti-use for increasing the charge separation and enhancingthe H2-evolution activity and stability of photocatalyst.[23]

Though a large amount of progress is made in the field ofdevelopment of efficient Ni-based H2-evolution cocatalysts, it isstill very necessary to accurately disclose active sites andmechanism relating to the catalyst at atomic and molecularlevels. The highest H2-production rate could be achieved bynanoconfined Ni@C-modified CdS nanomaterial. Carbon andNiO-coated core-shell materials have been considerably usedto produce hydrogen via photocatalytic method. The focushave been paid to gradually increase Ni-based nanomaterialwith remarkable nanoconfinement effects for the futurestudies.[23b]

1.8.9. Unsupported mesoporous Ni/NiO catalyst

The novel nickel-based catalysts (Figure 1) is developed withthe aim to prevent metal leaching, catalyst deactivation, orcoke deposition and metal sintering.[21,24] To resolve thisproblem, support-free magnetically recoverable porous nickelnanostructured catalysts have been proposed.[23–25] Variousbreakthrough research has been dedicated to the improvementof nickel-based nanomaterials.[19–21b] The synthesis of porousmetal oxides such as NiO and their composites is a relativelysuccessful move in the field of catalysis.[17–25] The nanoporousnickel material could be synthesized by heat-treating thecorresponding precursors without using a template or surfac-tant, but they have inadequate benefit due to low porosity andlesser number of active sites.[23–25] Support-free catalysts areinexpensive as well as save catalyst preparation time. Porousmetals eliminate support influence and have the advantage of

Figure 1. Parameters and properties for the design of catalysts.[22,54] Copyright1999–2019 John Wiley & Sons, Inc.

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having a large surface area. Support-free metal catalysts mayhave an advantage against the sintering effect.[25] Also, themorphology and structure of porous metal catalysts can becontrolled. Support-free magnetically recoverable mesoporousNi/NiO catalyst was synthesized using an organosilane tem-plate by chemical reduction followed by precipitation.

The mesoporous Ni/NiO has a high surface area (250 m2/g),high porosity (80%), and high metal dispersion (15%) anduniformly homogenous distributed Ni nanoparticles.[22,25] Theporous catalysts are recently reported in the hydrogenationand hydrodeoxygenation of the fatty acid as the fatty acidsdiffuse and then adsorb on active sites of catalysts to reactwith hydrogen converting to the desired product.[5,8,22]

1.9. Synthesis of Ni/NiO via Hydrothermal method

The synthesis of Ni/NiO catalyst was done using an organo-silane template by a hydrothermal process (Figure 2). In thesynthesis process, 2 g of Nickel nitrate hexahydrate was takenat room temperature and dissolved in approximately 500 ml ofwater by continuous stirring. The temperature was raised to40 °C after an interval of 1 hour, and PH was maintained at11.6. Dropwise ODAC (Octadecyl dimethyl 3- trimethoxy silylpropyl ammonium chloride) was added, and the solution waskept for 4 h at a temperature of 80 °C. After cooling andautoclaving the solution at a temperature of 150 °C for a periodof 2 days, the resultant material was filtered, and the precip-itate was collected, which was green in color. The collectedprecipitate was calcined at 550 °C for 6 h. The final productobtained is magnetically separable mesoporous NiO containingsilica. To obtain the optimized mol ratio of (3 : 1), Ni: templateratio was varied. The synthesized mesoporous Ni/NiO catalyst

was activated by reducing the catalyst at 400 °C and then usedfor the characterization of the reaction.

1.9.1. Synthesis of Ni/NiO via chemical reduction followed byprecipitation method

The catalyst was synthesized by chemical reduction methodreported in the literature.[22,24] Nickel nitrate hexahydrate (Ni(NO)2.H2O) was taken as nickel precursor in water as thesolvent. ODAC (octadecyl dimethyl 3-trimethyl silyl propylammonium chloride) as a mesoporous template was addeddropwise. The pH was maintained at 11.5 by adding NaOHsolution. The temperature was maintained at 60 °C, whilecontinuously stirring. Further, 30 ml hydrazine hydrate (1 M)and 50 ml sodium borohydride (1 M) were added as reducingagents, and the temperature was increased to 80 °C, along withstirring at 500 rpm for 2 h. The resulting reducing solutionchanged its color from green to black. The resulting precipitatewas filtered and then dried at 80 °C. This dried material wasextracted for 2 h, in ethanol, at 80 °C, to remove organicmoieties and template. The synthesized Ni/NiO catalyst wasmagnetic in nature. Finally, the synthesized catalyst wascalcined at 500 °C for 4 h. The sample was calcined at 500 °C tocreate crystallinity and then was further reduced with hydrogento maximize the Ni0 state.

2. Why renewable sources

It is necessary to focus on a renewable and clean alternativefuel source to meet the increasing energy demand, protect theenvironment, and save the petroleum assets for the future.[29]

The overwhelming sources of fuel and energy for transport and

Figure 2. Synthesis of Ni/NiO catalyst via hydrothermal route.

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manufacturing sectors are non-renewable fossil fuels such asnatural gas, petroleum, and coal.[29,30] Development of fuel-efficient vehicles, improving catalytic converters to reducecarbon dioxide emission, electric vehicles, fuel cell, and energysaving are few options in this direction.[30] Moreover, these,alternative renewable energy sources are long term option.Among renewable energy resources, plant oils are an excellentsource for liquid transportation fuel due to their high energydensity.[31] Vegetable oil occupies an essential position in theprogress of alternative fuels, which involves the production ofbiofuels from plant-derived oils[30,31] particularly, non-edible andused oils such as used cooking oil, jatropha oil, algae oil, etc.The plant and animals derived oil cannot be used directly dueto high oxygen, have a higher viscosity, and poor atomizationand lubricity[31,32] and hence are further processed via manyroutes such as hydrodeoxygenation, hydrogenation, pyrolysisto convert into suitable renewable fuels or biofuels. Thetransesterification of fatty acids is the primary route for theproduction of biofuels with its drawbacks, such as theproduction of glycerol as a by-product in a large amount andbig capital investment in plant operation.[32–34] The structure ofvegetable oil contained glycerol as the spine and fatty acidchains to form a triglyceride molecule.[34] Hydroprocessing oflipids produces liquid biofuels of similar properties to hydro-carbon-based fuels.[33,35] Researchers have used different sour-ces of lipids for hydroprocessing reactions such asjatropha,[32,36–45] soyabean oil,[35] sunflower oil,[45] palm oil, rape-seed oil,[47–50] pomace oil, algal oil,[11] castor oil,[36,40–50] and manymore. They have hydro-processed these sources of lipids eitherdirectly or co-processed these oils with crude based gasoils.[35,37–47] Model compounds such as tristearin, triolein,tricaprylin, palmitic acid, stearic acid, oleic acid, etc. have alsobeen hydro-processed over different catalysts in the presenceof hydrogen and inert atmospheres to identify the reactionpathways and intermediate species formed.[35–45] Lipids gener-ally contain oxygen and nitrogen as impurities, and these needto be removed by hydrotreatment over non-acidic supportssuch as γ-Al2O3 or activated carbon[45,47] with strong hydro-genation functionality provided by mono-metallic Pd, Pt, Ni,etc. or bi-metallic catalysts such as PtRe, NiW, NiMo, CoMo.Acidic supports such as zeolites, silica-alumina, gamma-alumi-na, and silico-aluminophosphates, etc.,[35,40–45] along with hydro-genation functionality, are used as a bi-functional catalyst toperform hydrocracking, hydrogenation, hydroisomerizationreactions.[36–43,46] The properties of the catalyst materials such ashydrogenation functionality, acidity, porosity, surface area,hydrothermal stability, etc. can be tuned and surface morphol-ogy controlled to favor a particular set of reactions andincreased catalyst life and performance.

The vegetable oils, animal fats, and biomass-derived oil,renewable farnesane hydrocarbon fuel, Fischer-Tropsch (FT)process based on biomass are some of the options available toproduce renewable fuel (Figure 3).[42] The feedstock can beclassified into many categories based on the downstreamprocess, such as oil-containing biomass, lignocellulose biomass,sugars, and starch biomass (Figure 4).

2.1. Biomass alternative source

Biomass is a renewable source for the production ofchemicals.[8,22] The lignocellulosic feedstocks can convert intovalue-added chemicals and fuels through catalyticprocesses.[35,42]

Various catalytic conversion pathways, such as pyrolysis,hydrolysis, and hydrodeoxygenation, have been explored toconvert the various lignocellulosic biomass to renewablechemicals (Figure 4).[48] Lignocellulosic biomass is constituted ofalmost 1/2 part cellulose. The transformation of cellulose andcellulose-derived molecules (glucose) into high-value sustain-able chemicals and liquid fuels is well reported.[46–48] Biomassconversion and catalytic processes for the biomass trans-formation into fuels and chemicals have received increasingattention for the sustainable growth of society.[47] The completecatalyst recovery after the biomass-derived feedstock process-ing is challenging because a complex mixture is generallyobtained after the reaction. The design of catalyst (magneticallyseparable) and methods for the ease of product separation isvery significant for industrial processes.

Many pathways are technically feasible for the productionof biofuels from the lignocellulosic biomass-derived feedstocksbut economically unaffordable. Improvement of the highlyactive, selective, cost-effective catalysts, and economicallyviable technologies is a goal to be overcome with theinterdisciplinary research involving process engineering,chemistry, chemical science, and material chemistry.

Biomass consist of (cellulose polymer) carbon, hydrogen,and oxygen as the main constituent.[47–49] The biomass-derivedfuels can be blended with petroleum fuel to meet the energyrequirement move sustainably. The main use of biomass is toproduce biofuels. Another use of biomass is to produce ethanolas a power fuel through the process of fermentation.[48] Theethanol production started in the mid-1970s with the soaredprices of gasoline for the first time. Brazil is the leadingproducer of ethanol used as fuel. Ethanol can also blend withgasoline to serve as power petrol.

The catalytic conversion of biomass to biofuels throughdifferent technologies is currently being investigated globally.The thermochemical route is a significant pathway thatconverts biomass into liquid fuels.[50–55] Bio-oils are producedthrough the pyrolysis route of biomass at a temperature of550 °C. The yield of bio-oils is almost 45% through the pyrolysisalong with gases and char. The composition of the bio-oilsvaried depending upon the source biomass. Bio-oil containsvarious compounds such as acids, esters, cyclic ketones,phenols, other oxygenated cyclic compounds, ethers, nitrogencompounds, and water.[50,51] The bio-oil obtained can be furtherprocessed to get chemicals and fuels. Upgraded bio-oil byremoving oxygen via hydrodeoxygenation, can be used as fuelsuch as gasoline, renewable diesel, or jet fuel.[51] The catalyticprocess for oxygen removal is found to be most efficient.[54,55]

The catalytic processes for deoxygenation can be categorizedinto two different methods, fast catalytic pyrolysis, and hydro-deoxygenation (HDO). The microporous catalysts such aszeolites (HZSM-5) and mesoporous catalysts such as Al-MCM-

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Figure 3. Various processes for the transformations of biomass-derived molecules into biofuels (renewable energy) and fuel additives.[48] Copyright 2006 WILEY-VCH.

Figure 4. Catalytic conversion of biomass to renewable fuel and high-value chemicals.

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48, Al-MCM-41, Al-SBA-15, etc.)[53,55] have been used in thecatalytic fast pyrolysis reaction.

2.2. Benefits of biomass energy

Biomass and biomass-derived feedstocks can be either useddirectly or processed to build high value-added products. It is arenewable source of power and energy with manyadvantages.[28]

No harmful emissions: Non-renewable and petroleum-derived fuels produce harmful gases that cause damage to theozone layer and enhance the effects of greenhouse gases,resulting in global warming. Biofuel generated from biomass isa clean fuel with emitted carbon dioxide taken back by theplants and trees during photosynthesis.[30]

Abundant and Renewable: Biomass-derived fuel and energyare renewable as biomass is abundant. While they areoriginated from the living sources and biodegradable waste,and life is cyclical, even processed byproducts need not runout. So long as there is something living on earth, it is possibleto process living things components and waste products intorenewable energy.[50–53]

Different Products: Biomass is a versatile source of energyand chemicals. Different high-value products and chemicalscan be synthesized using different lignocellulosic biomass viavarious catalytic and thermal processes. For example, ethanoland other comparable fuels can be produced from corn andother crops.

Catalytic conversion of biomass to biofuels or for theproduction of hydrogen from biomass has gained remarkableattention in the past decade, and several catalysts used forthese processes have thus been widely studied. In particular,formic acid, containing 4.4 wt% hydrogen, is a byproduct ofmany chemical processes and is thus a promising hydrogenstorage source. As an example, formic acid is producedalongside levulinic acid in an intermediate step for theconversion of cellulose to gamma-Valerolactone (GVL), a greenbiofuel. In the past few years, several researchers have focusedon heterogeneous catalytic reactions based on metallic or non-metallic nanoparticles, and utilization of catalytic processes forthe production of renewable energy and chemicals.

The main objective of this review is to the detaileddiscussion of synthesizing, and catalytically application ofenvironment-friendly support-free magnetically separable Ni/NiO nanoparticles with homogeneously distributed Ni nano-particles for the production of value-added chemicals and fuels.Furthermore, we aimed to investigate the activity, stability, andlife of the support-free Ni/NiO catalysts on the differentindustrial catalytic processes performed in batch and fixed-bedreactors, mainly hydrogenation and dehydrogenation.

Recently, several reviews based on homogeneous Ni-basedcomplexes were published, focusing mainly on biomass up-gradation.[22,51] Two excellent reviews based on heterogeneousNi-based catalysts were published, focusing exclusively onsteam reforming[12–15,22] Nevertheless, to the best of our knowl-edge, there is currently no review focused on mesoporous Ni/NiO catalysts that provides a detailed discussion on their

energy and environmental applications. We hope that thiscontribution will be a good addition to the existing literature,and will provide useful information for future research.

2.3. Upgradation of biomass-derived Levulinic acid toγ-valerolactone over Ni/NiO Catalyst

Biomass has particular potential as a replacement for fossil-based products.[22] In this context, fermentation-derived mole-cules, lignin-derived aromatics, and carbohydrate-derived poly-ols, furfural, HMF, and levulinic acid are attractive candidatesfor catalytic reforming to produce targeted fuels and chemicals.Extensive efforts have been made to convert cellulose intoethanol and other biofuels. A recent report compasses thepotential use of Ni-based catalysts as biomass-derived biofuelblended with gasoline in the synthesis of γ-Valerolactone (GVL)from levulinic acid.[8,37] In the study conducted, an excellentconversion of levulinic acid into γ-valerolactone is reportedunder mild conditions. Here the catalyst used is a porous nickelcatalyst, which is synthesized by a green method. The nickelcatalyst was synthesized by using double reduction byincorporating metallic nickel into nickel oxide sites by using anorganosilane template. The catalyst also has inherent lewis andBronsted acidity, which promotes hydrogenation. The resultingmesoporous Ni/NiO catalyst is magnetically separable andreusable with 5% loss in the activity and 2% loss in GVLselectivity.[37] All the hydrogenation reactions reported in thisstudy were done by taking Ni/NiO as a catalyst. The reactionswere carried out under different temperatures and pressuresand with varying amounts of catalysts. Powered X-ray diffrac-tion (XRD) pattern shows the presence of both Ni and NiO inthe sample.[22,37] The high surface area of Ni/NiO catalystcontributes to the higher probability of active sites to interactwith the reactant and eventually can increase the rate ofreaction.[37] During the hydrogenation reaction of levulinic acidcarried over, the Ni/NiO catalyst showed higher mass activityfor γ-valerolactone formation. The reaction takes place be-tween adsorbed levulinic acid over the Ni/NiO surface withadsorbed hydrogen, which seems to be the most feasiblepathway for the conversion.[8,37]

2.4. Support-free Ni/NiO catalyst for conversion ofoxygenates to fuels and chemicals

The recent report[8] encircles the overall efficiency of Ni-basedcatalysts as an effective, low-cost system for hydrogenationand dehydrogenation reactions. Nickel-based catalyst is usedfor the conversion of renewable feedstocks, which comprises oflipid and noncellulosic into biofuels by hydrogenation, hydro-cracking, and hydrodeoxygenation reactions. Porous nickelmaterials were synthesized to prevent nickel deactivation dueto coke deposition. The catalyst was synthesized by organo-silane-template assisted by chemical reduction method withthe varied molar ratio of the template. The resulting catalystsare used for phenol hydrogenation and hydrodeoxygenation ofmethyl oleate and jatropha oil. The catalyst formed is magneti-cally separable using an external magnet. The morphology of

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the catalyst was studied using a scanning electron microscope(SEM) and TEM analysis.[22] The plausible mechanism for thephenol hydrogenation as a model compound using Ni/NiOcatalysts also reported understanding lignin hydrogenation.Lignin is the main component of lignocellulosic biomass.Therefore phenol mechanism using Ni/NiO would help tounderstand the hydrogenation and hydrolysis of biomass.[52]

The mechanism for hydrogenation of methyl oleate (ester offatty acid) also reported as esters of fatty acid derived fromlignocellulose. Methyl oleate hydrogenation shows indirectdegradation of biomass using Ni/NiO catalyst. TEM analysisindicates the presence of Ni nanoparticles on NiO nanosheets(Figure 5). The Ni/NiO catalyst is a selective hydrogenationcatalyst under mild reaction conditions and works as acomplete hydrodeoxygenation catalyst under severeconditions.[22,52] This study reveals in-depth catalysis chemistryand hydrogenation of biomass-derived materials to usefulproducts.

2.5. Hydrogenation of Cashew Nut Shell Oil to Value-AddedProducts over Ni/NiO

Various reports on nickel-based catalysts revolve around thebiomass-derived materials that can be a viable source for themanufacture of different hydrocarbon fuels and chemicals viacatalytic hydrogenation route.[19,20,24,29] For value-added prod-ucts, the waste cashew nut shell liquid (CNSL) has a wide rangeof applications.[24] CNSL is an agricultural side product ofprocessed cashew nut and has a long-chain carbon-containingphenolic group in its structure.[24] CNSL has the capacity toproduce a large number of synthetic compounds and chemicalcompounds by exploiting various reactive sites such asphenolic hydroxyl group and unsaturation in the side andaromatic ring. For hydrogenation, the nickel-based catalyst isgenerally used due to its high thermal stability. Hydrogenationof guaiacol (phenolic compound) was performed over Ni/NiOsystem for the ease of identification of the product in order tounderstand the mechanistic pathway. The lignocellulosic bio-mass was converted to bioenergy and high-value chemicals bythe route of hydrogenation, hydrodeoxygenation (HDO), and

Figure 5. TEM analysis of mesoporous Ni/NiO catalyst and distribution of Ni nanoparticles.

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catalytic cracking. A combination of the metal catalyst, RaneyNi, and solid acid Nafion/SiO2 was used for the reduction ofaromatic ring and hydrolysis.[22,24] Whereas Ni/NiO catalyst hasintrinsic acidity with the high surface area, which avoid the useof external solid acid during hydrodeoxygenation and hydrol-ysis. Ni/NiO catalyst is a composite of metallic nickel and nickeloxide, which was further reduced with molecular hydrogen fora maximum reduction of NiO to metallic nickel. The TEManalysis of Ni/NiO catalyst reveals the high porosity, structuralcomposition, and distribution of Ni nanoparticles (Figure 5).The high porosity improves the rate of diffusion of hydro-genation reaction. Hydrogenation of CNSL to value-addedchemicals is the example of catalytic up-gradation of biomassto a useful product.[24]

2.6. Hydrogen production from organic waste viapyrolysis-reforming

The conversion of solid biomass and organic waste allowseffective and environmentally friendly production of synthesisgas, hydrogen, and other valuable products. Catalyst plays avital role in improving the hydrogen production in biomasspyrolysis and gasification.[22] For this purpose, the catalyst Ni/NiO should have high activity, which is economical, easilyseparable, and reusable. Ni-based catalyst has been frequentlywith smaller particle size and high dispersion show highercatalytic activity and lower deactivation. Porous nickel oxidenanoparticle was synthesized using nickel precursor andorganosilane octadecyl dimethyl ammonium chloride (ODAC).The organosilane acted as a mesopore template, and its Siportion was incorporated into porous Ni structure givingstructural stability to the material. SEM images reported thatthe sample had a porous flake type morphologies.[22,37,52] X-rayspectroscopy determines the elemental composition andatomic distribution of Si and Ni within the sample. Thehydrogen production increased more than three times in theabsence of a reduced Ni/NiO catalyst. When carbonization ofsunflower husk was carried out in the absence of catalyst, ahigh value of CO2 and a low content of hydrogen wereobtained. The better activity of reduced Ni/NiO catalyst ascompared to uncalcined Ni/NiO and other supported Nicatalysts may be due to its higher surface area, high aciddensity, and higher Ni content. During pyrolysis, hydrocarbonsvapors interact with nickel catalyst by dissociation-adsorptionon the surface of the catalyst to perform hydrogenationreaction. The SAED patterns show that the catalyst is highlycrystalline. The cost of magnetically separable Ni/NiO catalystswas lower as compared to the cost of commercial Ni-basedcatalyst and hence makes it potentially economic for thecarbonization of organic waste.[22]

2.7. Glucose hydrogenation to sorbitol over unsupportedmesoporous Ni/NiO

Biomass-derived feedstocks have great potential as a substitutefor fossil fuels to meet our growing energy needs and also forthe production of value-added chemicals. Sorbitol is the polyol

with its wide use in nutrition, cosmetics, medicinal, andindustrial applications.[52] Sorbitol is the hydrogenation productof glucose and maybe catalytically converted into a mixture ofglycerol, ethylene glycol, and 1,2-propanediol. In the initialstages, the conversion of D-Glucose to sorbitol was achieved.Among the transition metals, Ni would be the most capablecatalyst for the reaction as the hydrogenation of glucose tosorbitol has been performed over Raney Ni catalyst.[52] Cellulosecan be hydrolyzed into glucose and subsequently hydro-genated into sorbitol and mannitol.[52] A mesoporous carbonsupported Ni catalyst was reported to be active for theconversion of cellulose into sorbitol, but this catalyst deacti-vates within three reuses.[52] The sharp peaks in the XRD patternindicate the crystalline nature of the synthesized catalyst.[52]

The chemical composition of spent Ni/NiO was determined byelemental mapping and energy dispersive X-ray (EDX) analysis.X-ray photoelectron spectroscopy (XPS) analysis indicated thatthe material is a mixture of nickel oxide and metallic Ni.[52] Thecatalyst showed high conversion and high selectivity forhydrogenation for glucose to sorbitol. Figure 6 shows the threedifferent routes, such as hydrolysis, hydrogenation, andpyrolysis can be utilized for the conversion of biomass andorganic waste to renewable chemicals. This review reports onlycatalytic hydrogenation and pyrolysis of biomass and biomass-derived materials to fuels and useful products.

2.8. Recent application of Ni/NiO catalysts and itscomparative study

Table 1 summarised the recent catalytic application of meso-porous Ni/NiO catalysts via different pathways to produce fuelsand value-added chemicals. The Catalytic yield of Sorbitol wasobserved to be 88% when hydrogenation of glucose wasperformed over a template at 130 °C using Ni/NiO as thecatalyst. When hydrogenation of celluboise was done at 240 °Cusing the impregnation method over Ni/SiO2 as a catalyst, theoverall yield of hexitol was 44%. Using Ni/Al2O3 as the catalyst,hydrogenation was conducted on celluboise at a temperatureof 240 °C using the impregnation method, the yield of hexitolwas 28% only. The yield of GVL was found to be 94% when thehydrogenation of levulinic acid was carried out using thetemplate-assisted method over Ni/NiO catalyst. The likelyoutcome of GVL was about 94%, when hydrogenation oflevulinic acid was performed over Ni/NiO using the precipita-tion method. Methyl oleate on hydrogenation at 200 °C usingthe template-assisted technique over Ni/NiO yielded Methylstearate (100%). On carrying out hydrogenation of CNSL, overNi/NiO catalyst at 300 °C, phenol is obtained as a product witha yield of 35%. Dehydrogenation of sugarcane was performedusing a template over Ni/NiO at a temperature of 600 °C; theyield of H2 obtained was 32 g/kg. Using Ni/NiO catalyst fordehydrogenation of brown coal (T=500 °C) yielded 22 g/kg H2.When the photochemical reaction was conducted on CO2 overthe modified Ni/NiO catalyst, the H2 yield obtained was0.5 mmol� 1. Carbon monoxide reduction using hydrogenationreaction over Ni/NiO or Ni-25, was yielded 21% C5-C7 hydro-carbon and CH4 with 38% yield, respectively. Mesoporous Ni/

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NiO, a part of supramolecular chemistry, would be an effectivecatalyst for hydrogenation, dehydrogenation as well photo-catalysts for CO2 mitigation.

3. Conclusions and perspectives

This report shows the contribution to the design of supportfree nickel-based catalysts and their catalytic applicationrelated to energy production and environmental applications.Catalyst design is based on supramolecular chemistry using anorganosilane template. The detailed synthesis of mesoporousNi/NiO catalysts and comparative study to traditionally re-

ported Ni-based in catalytic reactions, especially hydrogenationand pyrolysis shown in the review article. Key factors thatdefine the catalytic activity of the nickel-based catalyst are themetal particle size and surface area, and metal dispersion. Smallcrystallite size and a high degree of metal dispersion lead tohigh catalytic activity. This is the first review of the support-freeNi-based catalyst for hydrogenation and dehydrogenationreactions. The development of a mesoporous Ni/NiO catalystwith a template effect is the new approach in catalysis.Templating species in the mesoporous Ni/NiO catalyst inducescyclization of metallic Ni homogenously, which enhances therate of diffusion in the reactions. Synthesis of mesoporous Ni/

Figure 6. Catalytic conversion of organic waste to renewable fuel and high-value chemicals.

Table 1. Catalytic performance of various Ni-based catalysts for fuels and energy applications through different routes.

Catalyst Synthesis method Reactant Reaction Temp/ °C Reaction performance

Ni/NiO Template assisted Glucose Hydrogenation 130 Sorbitol yield 88%[52]

Ni/SiO2 Impreganation Celluboise Hydrogenation 240 Hexitol yield 44%[52]

Ni/Al2O3 Impreganation Celluboise Hydrogenation 240 Hexitol yield 28%[52]

Ni/NiO Template assisted Levulenic acid Hydrogenation 120 GVL yield 94%[37]

Ni/NiO Precipitaion Levulenic acid Hydrogenation 120 GVL yield 94%[37]

Ni/NiO Template assisted Methyl oleate Hydrogenation 200 Methyl stearate yield 100%[39]

Ni/NiO Template assisted CNSL Hydrogenation 300 Phenol yield 35%[24]

Ni/NiO Template assisted Sugarcane Dehydrogenation 600 H2 yield 32 g/Kg[22]

Ni/NiO Template assisted Brown coal Dehydrogenation 500 H2 yield 22 g/Kg[22]

Modified Ni/NiO Template assisted CO2 Photoelectrochemical 25 H2 yield 0.5 mmol� 1 g � 1[55]

NiO/Ni or(Ni-525) NiO reduction CO Hydrogenation none C5-C7 yield1% & CH4 38%[54]

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NiO catalyst and its application is one of the best examples ofsupramolecular chemistry.

Acknowledgments

SK thanks RIMT University for Ph.D. PK acknowledges RIMTUniversity for M.Phil. AM thanks CSIR for research fellowship.

Conflict of Interest

The authors declare no conflict of interest.

Keywords: Biomass · Hydrogenation · Mesoporous materials ·Nickel · Pyrolysis

[1] Q. Xia, Z. Chen, Y. Shao, X. Gong, H. Wang, X. Liu, S. F. Parker, X. Han, S.Yang, Y. Wang, Nat. Commun. 2016, 7, 11162.

[2] O. Muth, M. Froba, Stud. Surf. Sci. Catal. 2000, 129, 357–366.[3] M. J. Clement, A. Corma, S. Iborra, M. J. Sabater, ACS Catal. 2014, 4, 870–

891.[4] Q. Xia, Z. Chen, Y. Shao, X. Gong, H. Wang, X. Liu, S. F. Parker, X. Han, S.

Yang, Y. Wang, Nat. Commun. 2016, 7, 11162.[5] a) S. De, J. Zhang, R. Luque, N. Yan, Energy Environ. Sci. 2016, 9, 3314–

3347; b) J. Li, Y. He, L. Tan, P. Zhang, X. Peng, A. Oruganti, G. Yang, H.Abe, Y. Wang, N. Tsubaki, Nat.Catal. 2018, 1, 787–793.

[6] X. Lyu, L. Xu, J. Wang, X. Lu, Catal. Commun. 2019, 119, 46–50.[7] S. Song, S. Yao, J. Cao, L. Di G Wu, N. Guan, L. Li, Applied Catal. B. 2017,

217, 115–124.[8] W. Li, H. Wang, X. Jiang, J. Zhu, Z. Liu, X. Guo, C. Song, RSC Adv. 2018, 8,

7651–7669.[9] F. Stud, I. Sharafutdinov, F. Abild-Pedersen, C. F. Elkjear, J. S. Hum-

melshqj, S. Dahl, J. K. Nørskov, Nat. Chem. 2014, 6, 320–324.[10] N. W. Kwak, S. J. Jeong, H. G. Seo, S. Lee, Y. J. Kim, J. K. Kim, P. Byeon, S-

Y. Chun, W. C. Jung, Nat. Commun. 2018, 9, 4829.[11] M. Roiaz, E. Monachino, C. Dri, M. Greiner, A. Knop-Gericke, R. Schlogl, G.

Comelli, E. Vesselli, J. Am, Chem. Soc. 2016, 138, 4146–4154.[12] P. Fouilloux, Appl. Catal. 1983, 8, 1–42.[13] X. Wang, R. Rinaldi, Energy Environ. Sci. 2012, 5, 8244–8260.[14] W. M. Czaplik, J-M. Neudorfl, A. J. Wangelin, Green Chem. 2007, 9, 1163–

1165.[15] R. J. Kokes, P. H. Emmett, J. Am. Chem. Soc. 1959, 81, 5032–5037.[16] P. Mars, T. v d Mond, J. J. F. Scholten, Ind. Eng. Chem. Prod. Res. Dev.

1962, 1, 161–164.[17] G. C. A. Schuit, N. H. D. Boer, Nature 1951, 168, 1040–1041.[18] M. H. Peyrovi, T. Rostamikia, N. Parsafard, Energy Fuels 2018, 32, 11432–

11439.[19] a) I. Hachemi, K. Jenistova, P. M. Arvela, N. Kumar, K. Eranen, J. Hemming,

D. Y. Murzin, Catal. Sci. Technol. 2016, 6, 1476–1487; b) E. Ruiz-Trejo,A. K. Azad, J. T. S. Irvine, J. Electrochem. Soc. 2015, 162, F273-F279.

[20] a) S. K. Wu, P. C. Lai, Y. C. Lin, H. P. Wan, H. T. Lee, Y.H Chang, ACSSustainable Chem. Eng. 2013, 1, 349–358; b) X. Zhang, W. Shi, J. Zhu, W.Zhao, J. Ma, S. Mhaisalkar, T. L. Maria, Y. Yang, H. Zhang, H. H. Hng, Q.Yan, Nano Res. 2010, 3, 643–652.

[21] a) J. Shi, E. Wu, Microporous Mesoporous Mater. 2013, 168, 188–194;b) W. Wang, K. Zhang, H. Liu, Z. Qiao, Y. Y. K. Ren, Catal. Commun. 2013,41, 41–46.

[22] a) A. Dutta, A. K. Patra, A. Bhaumik, Microporous Mesoporous Mater.2012, 155, 208–214; b) M. Paul, N. Pal, A. Bhaumik, Eur. J. Inorg. Chem.2010, 5129–5134.

[23] a) X. Lin, S. Wang, W. Tu, Z. Hu, Z. Ding, Y. Hou, R. Xu, W. Dai, Catal. Sci.Technol. 2019, 9, 731–738; b) R. Shen, J. Xie, Q. Xiang, X. Chen, J. Jiang,X. Li, Chin. J. Catal. 2019, 40, 240–288.

[24] a) H. Singh, R. Yadav, S. A. Farooqui, O. Dudnyk, A. K. Sinha, Int. J.Hydrogen Energy. 2019, 44, 19573–19584; b) L. Zhou, Y. Guo, K. Hideo,AIChE J. 2014, 60, 2907–2917.

[25] H. Singh, R. Yadav, P. Rajput, D. Bhattacharyya, S. N. Jha, A. K. Sinha,Energy Fuels 2019, 33, 5332–5342.

[26] L. Rye, S. Blakey, C. W. Wilson, Energy Environ. Sci. 2013, 3, 17–27.[27] I. Kubickova, D. Kubicka, Valor. 2010, 1, 293–308.[28] W-T. Chen, Y. Zhang, T. H. Lee, Z. Wu, B. Si, C. F. Lee, A. Lin, B. K. Sharma,

Nature Sustainability 2018, 1, 702–710.[29] D. M. Alonso, J. Q. Bond, J. A. Dumesic, Green Chem. 2010, 12, 1493–

1513.[30] C. Wu, K. M. K. Yu, F. L&&SURNAME&&, N. Young, P. Nellist, A. Dent,

A. Kroner, S. C. E. Tsang, Nat. Commun. 2012, 3, 1050.[31] R. L. Wingad, E. J. E. Bergstrom, M. Everett, K. J. Pellow, D. F. Wass, Chem.

Commun. 2016, 52, 5202–5204.[32] R. Kumar, B. S. Rana, R. Tiwari, D. Verma, R. Kumar, R. K. Joshi, M. O. Garg,

A. K. Sinha, Green Chem. 2010, 12, 2232–2239.[33] A. F. Lee, J. A. Bennett, J. C. Manayil, K. Wilson, Chem. Soc. Rev. 2014, 43,

7887–7916.[34] P-C. Lau, T-L. Kwong, K-F. Yung, Sci. Rep. 2016, 6, 23822.[35] A. L. Mascarelli, Nature 2009, 461, 460–461.[36] A. A. Lappas, S. Bezergianni, I. A. Vasalos, Catal. Today 2009, 159, 55–62.[37] H. Singh, N. Iyengar, R. Yadav, A. Rai, A. K. Sinha, Sustainable Energy Fuels

2018, 2, 1699–1706.[38] G. W. Huber, P. O. Connor, A. Corma, Appl. Catal. A: Gen. 2007, 329, 120–

129.[39] H. Singh, I. Nishant, A. K. Sinha, Mater. Res. Bull. 2019, 112, 363–375.[40] J. Q. Bond, A. A. Upadhye, H. Olcay, G. A. Tompsett, J. Jae, R. Xing, D. M.

Alonso, D. Wang, T. Zhang, R. Kumar, A. Foster, S. M. Sen, C. T.Maravelias, R. Malina, S. R. H. Barrett, R. Lobo, C. E. Wyman, J. A. Dumesic,G. W. Huber, Energy Environ. Sci. 2014, 7, 1500–1523.

[41] H. Olcay, A. V. Subrahmanyam, R. Xing, J. Lajoie, J. A. Dumesic, G. W.Huber, Energy Environ. Sci. 2013, 6, 205–216.

[42] R. Tiwari, B. S. Rana, R. Kumar, D. Verma, R. Kumar, R. K. Joshi, M. O. Garg,A. K. Sinha, Catal. Commun. 2011, 12, 559–562.

[43] B. Veriansyah, J. Y. Han, S. K. Kim, S. A. Hong, Y. J. Kim, J. S. Lim, Y. W.Shu, S. G. Oh, and J. Kim, Fuel. 2012, 94, 578–585.

[44] J. Cheng, T. Li, R. Huang, J. Zhou, K. Cen, Bioresour. Technol. 2014, 158,378–382.

[45] P. Simacek, D. Kubicka, I. Kubickova, F. Homola, M. Pospisil, Fuel 2011,90, 2473–2479.

[46] S. Bezergianni, A. Kalogianni, I. A. Vasalos, Bioresour. Technol. 2009, 100,3036–3042.

[47] M. Stocker, Angew. Chem. Int. Ed. 2008, 47, 9200–9211.[48] J. O. Metzger, Angew. Chem. Int. Ed. 2006, 45, 696–698.[49] M. Krar, S. Kovacs, D. Kallo, J. Hancsok, Bioresour. Technol. 2010, 101,

9287–9293.[50] D. Mohan, C. U. Pittman Jr., P. H. Steele, Energy Fuels 2017, 31, 3525–

3536.[51] K. Wang, D. C. Dayton, J. E. Peters, O. D. Mante, Green Chem. 2017,19,

3243–3251.[52] H. Singh, A. Rai, R. Yadav, A. K. Sinha, Mol. Catal. 2018, 451, 186–191.[53] G. Zhou, P. A. Jensen, D. M. Le, N. O. Knudsen, A. D. Jensen, ACS

Sustainable Chem. Eng. 2016, 4, 5432–5440.[54] Y. Zhao, B. Zhao, J. Liu, G. Chen, R. Gao, S. Yao, M. Li, Q. Zhang, L. Gu, J.

Xie, X. Wen, L. Wu, C. Tung, D. Ma, T. Zhang, Angew. Chem. Int. Ed. 2016,55, 4215–4219.

[55] P. K. Prajapati, H. Singh, R. Yadav, A. K. Sinha, S. Szunerits, R.Boukherroub, S. L. Jain, Appl. Surf. Sci. 2019, 467-468, 370–381.

Submitted: November 29, 2019Accepted: March 17, 2020

Reviews



Artikel_Svenja / 162447 [S. 14/15] 1

REVIEWS

Obtaining chemicals from biomassand carbon dioxide via catalytic andphotocatalytic are attractive routesrespectively to achieve sustainableobjectives. The review gives aninsight into the different methods forthe synthesis of porous Ni-basedcatalysts. It includes the comparativestudy of different types of porous Ni-based catalysts. This review alsoreports on the developments ofdifferent porous Ni-based catalystsand the evaluation of their catalyticand photocatalytic applications.

S. Kour, A. Mishra, Prof. Dr. A. Sinha*,P. Kaur, Dr. H. Singh*

1 – 15

The Development of MesoporousNi-Based Catalysts and Evaluationof Their Catalytic and PhotocatalyticApplications

Author Contributions

A.S. Conceptualization:Lead; Supervision:Equal

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Artikel_Svenja / 162447 [S. 15/15] 1

z the development of mesoporous ni-based catalysts and...

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