• Volume 126, Issue 2

March 2014,   pages  309-532

• Foreword

• Concept and progress in coupling of dehydrogenation and hydrogenation reactions through catalysts

This review focuses on the importance of coupling of catalytic reactions which involves dehydrogenation and hydrogenation simultaneously and the study of catalytic materials that are designed, adopted and/or modified for these reactions. The special features of these reactions are minimization of H2 utilization and reduction in production cost. Structural and textural properties also play a decisive role in this kind of coupled reactions. This particular review although not comprehensive discusses the significant progress made in the area of coupled reactions and also helps future researchers or engineers to find out the improvements required in areas such as advancements in catalytic material preparation, design of the new reactors and the application of new technologies.

• Pd(OAc)2/DPPF-catalysed microwave-assisted cyanide-free synthesis of aryl nitriles

This study reports microwave-assisted cyanide-free synthesis of aryl nitriles from aryl halides using palladium acetate/1,1-bis(diphenylphosphino)ferrocene as a new catalyst system. Reported protocol is a rapid, cyanide-free, single step reaction, wherein formamide acts as a solvent as well as a source of cyanide. The use of microwave increases the rate of reaction substantially and it was observed that aryl nitriles can be synthesised in 50 min of microwave irradiation compared to conventional thermal heating protocol which requires 48 h.

• DIFLUORPHOS and SYNPHOS in asymmetric catalysis: Synthetic applications

Enantiomerically pure diphosphines play an important role in various homogeneous metalcatalyzed asymmetric reactions. Over the last few years, our group has been involved in the design and synthesis of atropisomeric ligands named SYNPHOS and DIFLUORPHOS with complementary stereoelectronic properties. This paper shows the high catalytic performances of DIFLUORPHOS, SYNPHOS and SYNPHOS analogues for some C-H and C-C bond forming processes as well as for the synthesis of biorelevant targets.

• Engineering reactors for catalytic reactions

Catalytic reactions are ubiquitous in chemical and allied industries. A homogeneous or heterogeneous catalyst which provides an alternative route of reaction with lower activation energy and better control on selectivity can make substantial impact on process viability and economics. Extensive studies have been conducted to establish sound basis for design and engineering of reactors for practising such catalytic reactions and for realizing improvements in reactor performance. In this article, application of recent (and not so recent) developments in engineering reactors for catalytic reactions is discussed. Some examples where performance enhancement was realized by catalyst design, appropriate choice of reactor, better injection and dispersion strategies and recent advances in process intensification/ multifunctional reactors are discussed to illustrate the approach.

• Development of new deactivation method for simulation of fluid catalytic cracking equilibrium catalyst

Selection of a good catalyst is the easiest way to increase profitability of a fluid catalytic cracking (FCC) unit. During operation, these catalysts get deactivated due to operation at high temperatures, steam and deposition of metals on the catalyst. Developing a proper catalyst deactivation method is crucial for optimization of a good catalyst for FCC. Conventional laboratory deactivation procedures include direct metal impregnation method, cyclic deactivation method (CDM) and cyclic propylene steaming (CPS). Direct metal impregnation method gives higher coke and gas yields. CDM and CPS methods implementation is very difficult and time-consuming and there is a deviation in coke and gas yield. New rapid deactivation method has been developed to simulate plant equilibrium catalyst (E-Cat) by modifying metal impregnation, steaming and oxidation/reduction procedures. The E-Cat generated through a new deactivation method was characterized for physico-chemical properties using X ray diffraction (XRD), temperature-programmed reduction (TPR), and SEM-EDX and activity studies. XRD studies show that metals are dispersed well on catalyst samples. SEMEDX studies reveal that the morphology of simulated E-Cat and plant E-Cat catalyst particles appear to be same. E-Cat obtained by new deactivationmethod gives better coke and gas yields. Two E-Cats were also generated through CDM and direct metal impregnation method for comparing with the one generated through new method. New deactivation method also significantly reduces the evaluation time.

• Novel nanostructured CeO2 as efficient catalyst for energy and environmental applications

We report here versatile methods to engineer the microstructure and understand the fundamental physicochemical properties of CeO2 to improve its catalytic viability for practical applications. In this context, different morphologies of CeO2 are synthesized using tailored homogeneous precipitation methods and characterized by XRD, BET, SEM and TPR methods. The shuttle-shaped CeO2 prepared under hydrothermal condition shows higher surface area and low-temperature reducibility. The 0.5 wt% Pt-impregnated shuttle-shaped CeO2 shows lower-temperature CO oxidation behaviour as compared to its bulk-like CeO2 (with 0.5 wt% Pt) counterpart, synthesized by conventional-reflux method. Further, nanorod morphology of CeO2 prepared with Cl−as counter ion shows lower-temperature oxidation of soot as compared to the mesoflower morphology of CeO2, prepared with NO$^−_3$ as counter ion in the reaction medium. Further, linear sweep voltammetry, chronopotentiometry and CO-stripping voltammetry studies are performed to evaluate the promoting activity of CeO2 to Pt/C for ethanol electro-oxidation reaction in acidic media. Results show that CeO2 provides active triple-phase-interfacial sites for suitable adsorption of OH species which effectively oxidize the COads on Pt/C. The results presented here are significant in the context of understanding the physicochemical fine prints of CeO2 and CeO2 based hetero-nanocomposites for their suitability to important catalytic and energy-related applications.

• Value addition to lignocellulosics and biomass-derived sugars: An insight into solid acid-based catalytic methods

For the synthesis of important platform chemicals such as sugars (xylose and arabinose) and furans (furfural and 5-hydroxymethylfurfural (HMF)) from carbohydrates (hemicellulose and fructose) solid acid catalysts are employed. Similarly, over solid acid catalysts, conversion of lignin into aromatic monomers is performed. It is observed that in the dehydration of fructose, because of higher hydrothermal stability, silicoaluminophosphate (SAPO) catalysts give better activity (78% HMF yield) compared with other solid acid catalysts (&lt;63% HMF yield) at 175°C. Particularly, SAPO-44 catalyst can be reused at least 5 times with marginal decrease in the activity. Zeolite, HUSY (Si/Al = 15) is active in the conversion of isolated (pure) hemicellulose to produce 41% C5 sugars in water. The catalyst is also active in the selective conversion of hemicellulose from bagasse to yield 59% C5 sugars. It is possible to obtain high yields of furfural (54%) directly from bagasse if instead of water, water+toluene solvent system is used. Depolymerization of lignin using HUSY catalyst produced aromatic monomers with 60% yield at 250°C. A detailed catalyst characterization study is performed to understand the correlation between catalyst activity and morphology. To understand the effect of impurities present in the substrate over solid acid catalysts, metal-exchange study is carried out.

• Effective utilization of glycerol for the synthesis of 2-methylpyrazine over ZnO-ZnCr2O4 catalyst

Bioglycerol an inevitable by-product in the production of biodiesel was effectively utilized for the synthesis of 2-methylpyrazine (2-MP) by vapour phase dehydrocyclization with ethylenediamine over ZnOZnCr2O4(Zn-Cr-O) mixed oxides. These Zn-Cr-O samples were obtained from hydrotalcite precursors synthesized by precipitation method at different pH (∼7 and 9) and calcination in air at 450°C. X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) analysis confirmed the presence of ZnCr2O4 species. Transmission electron microscopy (TEM) images indicated spherical particles with mean diameter of 35.8 and 24 nm for the Zn-Cr-O prepared at pH ∼ 7 and ∼9, respectively. Surface Zn enrichment was observed in the near-surface region of Zn-Cr-Oprepared at pH∼9. Differences in dehydrocyclization activity of Zn-Cr-Omixed oxideswere established based on spectroscopic data that emphasized changes in structural properties of Zn-Cr-O obtained at different pH.

• Enhancement of reaction rates for catalytic benzaldehyde hydrogenation and sorbitol dehydration in water solvent by addition of carbon dioxide

The effect of pressured carbon dioxide on heterogeneous hydrogenation of benzaldehyde and homogeneous dehydration of sorbitol in water solvent was studied. Initial hydrogenation rates of benzaldehyde over a charcoal-supported palladium catalyst in water at 313 K were enhanced by the addition of carbon dioxide. The initial rate increased with an increase in carbon dioxide pressure and became a maximum at 5 MPa. Dehydration of sorbitol proceeded in water phase at 500 K and initial dehydration rates were enhanced by addition of 30 MPa of carbon dioxide.

• Novel catalysts for valorization of biomass to value-added chemicals and fuels

Key furan compounds such as 5-hydroxymethylfurfural (HMF), 2,5-furandicarboxylic acid (FDCA) and 2,5-dimethylfuran (DMF) were synthesized from renewable feedstocks. Dehydration of fructose was carried out in biphasic conditions employing several solid acid catalysts by targeting selective formation of HMF. Its selectivity is linearly dependent on total acidity clearly revealing that lower acidity favours selective formation of HMF. Oxidation and hydrogenolysis of HMF has been explored using 2 wt% Ru-K-OMS-2. The catalysts used for each transformation were subjected to detailed characterization using XRD, BET surface area, temperature-programmed desorption and transmission electron microscopy. The effect of various reaction parameters was also investigated for obtaining high yields of desired chemical intermediates. High FDCA yields of 93.4 mol% and 66 mol% were achieved in alkaline and base-free conditions, respectively. The 2 wt% Ru-K-OMS-2 is a versatile catalyst as it also catalyses HMF hydrogenolysis giving 33 mol% of DMF. Thus, utility of various novel materials as catalysts has been demonstrated in the multistep transformations of hexoses to furan-based fuels and chemicals.

• Role of catalysis in sustainable production of synthetic elastomers

Elastomer business plays a significant role in the transportation industry. In fact, elastomers make the world move. Due to limited availability of natural rubber, synthetic elastomers bridge the gap between demand and supply in today’s growing tyre and automobile industry.With more than ∼10000 KTA total world productions, the impact of synthetic elastomer business cannot be overlooked. The need of synthetic elastomers for tyre and automobile industries is stringently specific. Catalysis plays an inevitable role in achieving the growing demand of specific synthetic elastomers. The present study will describe how catalysis plays a significant role in the sustainable development of elastomers with special reference to polybutadiene rubber.

• Facile synthesis of catalytically active CeO2-Gd2O3 solid solutions for soot oxidation

CeO2-Gd2O3 oxides were synthesized by a modified coprecipitation method and subjected to thermal treatments at different temperatures to understand their thermal behaviour. The obtained samples were characterized by XRD, BET, TEM, Raman and TPR techniques. Catalytic efficiencies for oxygen storage/release capacity (OSC) and soot oxidation were evaluated by a thermogravimetric (TG) method. XRD and Raman results indicated the formation of Ce0.8Gd0.2O$_{2−\delta}$ (CG) solid solutions at lower calcination temperatures, and TEM studies confirmed nanosized nature of the particles. Raman studies further confirmed the presence of oxygen vacancies and lattice defects in the CG sample. TPR measurements indicated a facile reduction of ceria after Gd3+ addition. Activity studies revealed that incorporation of Gd3+ into the ceria matrix favoured the creation of more structural defects, which accelerates the oxidation rate of soot compared to pure ceria.

• Effect of method of preparation on hydrodesulphurization activity of Co- or Ni-promoted MoS2/SBA-15 catalysts

Ordered mesoporous material SBA-15 was synthesized and used as a support for the preparation of molybdenum sulphide catalysts through precipitation from homogeneous solution (PFHS) technique with the Mo content varying from 2-12 wt%. The prepared catalysts were evaluated for thiophene hydrodesulphurization catalytic activities at 400\$^\circRC. Catalysts prepared through PFHS method resulted in highly dispersed MoS2 catalysts, which were inferred from powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), low temperature oxygen chemisorptions (LTOC) and BET surface area analysis. The relationship between XPS intensity ratio, oxygen chemisorption and catalytic activities is discussed in terms of highly dispersed nano particles of MoS2 and its consequence in accommodating more promoted atoms at the edge sites.

• Characterization and reactivity of 11-molybdo-1-vanadophosphoric acid catalyst supported on zirconia for dehydration of glycerol to acrolein

• Cs salt of tungstophosphoric acid-promoted zirconium titanium phosphate solid acid catalyst: An active catalyst for the synthesis of bisphenols

A series of novel 𝑥CsTPA-ZTP (𝑥 = 30, 40, 50, 60 and 80 wt%) solid acid composite catalysts were synthesized by ion-exchange process using cesium nitrate, tungstophosphoric acid (TPA), zirconium titanium phosphate (ZTP) with varied surface areas, acidities and microstructures. Detailed characterizations of the composite catalysts were done by Powder X-ray Diffraction (PXRD), Fourier Transform Infrared (FTIR) Spectroscopy, N2 adsorption desorption, Scanning Electron Microscopy (SEM-EDS) analysis, X-ray Photoelectron Spectroscopy (XPS) and Temperature Programmed Desorption (TPD).We have studied the catalytic activities, kinetics and reusability of the catalysts. 60CsTPA-ZTP is found to be an effective and re-usable catalyst for the synthesis of bisphenol A (BPA) and bisphenol F (BPF) using acetonitrile as solvent.

• Role of vanadium in Keggin heteropoly molybdate supported on titania catalysts for oxidation reactions

Vanadium-incorporated molybdophosporic acid catalysts supported on titania were prepared and characterized by FT-IR, X-ray diffraction and laser Raman spectroscopy. Characterization data reveals the incorporation of vanadium into the primary structure of Keggin ion of MPA. Catalysts activities were evaluated for oxidation of 1,2-benzenedimethanol using H2O2 and O2 as oxidants. Vanadium-containing catalysts showed high activity compared to their parent heteropoly acids. Oxidation ability depended on the number of V atoms present in Keggin heteropoly molybdate. Effect of reaction parameters on the oxidation ability was also evaluated.

• Anomalous hydrocracking of triglycerides over CoMo-catalyst-influence of reaction intermediates

Reaction intermediates have been identified and followed to understand anomalous cracking of jathropha oil triglycerides in the presence of sulphided Co-Mo/Al2O3 catalyst. Undesirable C-C coupling reactions are favoured at temperatures between 320° and 340°C, giving waxy oligomerization products, whereas at temperatures above 340°C, direct hydrocracking of triglycerides to lighter and middle distillates were favoured. To minimize undesirable waxy oligomerization products, higher pressures (&gt;80 bar) and higher H2/feed ratios (&gt;1500) were necessary. Aldol condensation and ketonization reactions between the reaction intermediates are counter-productive as they result in waxy long chain oxygenated products which tend to accumulate on the catalyst surface, choke the reactor and cause rapid catalyst deactivation. Reaction conditions have to be optimized to minimize condensation reaction during this process.

• CO2 hydrogenation to hydrocarbons over iron nanoparticles supported on oxygen-functionalized carbon nanotubes

Hydrogenation of CO2 to hydrocarbons over iron nanoparticles supported on oxygenfunctionalized multi-walled carbon nanotubes was studied in a fixed-bed U-tube reactor at 25 bar with a H2:CO2 ratio of 3. Conversion of CO2 was approximately 35% yielding C1-C5 products at 360°C with methane and CO as major products. The CO2 equilibrium conversion for temperatures in the range of 320° to 420°C was analysed by using CHEMCAD simulation software. Comparison between experimental and simulated degrees of CO2 conversion shows that reverse water gas shift equilibrium had been achieved in the investigated temperature range and that less than 47% of CO2 can be converted to CO at 420°C.

• Ammoxidation of 2-methyl pyrazine on supported ammonium salt of 12-molybdophosphoric acid catalysts: The influence of nature of support

• Solid, double-metal cyanide catalysts for synthesis of hyperbranched polyesters and aliphatic polycarbonates

Fe-Zn and Co-Zn double-metal cyanide (DMC) complexes exhibit highly efficient and selective catalytic activity for synthesis of hyperbranched polyesters (glycerol-succinic acid (G-SA) and glycerol-adipic acid (G-AA)) and aliphatic polycarbonates (via., alternative co-polymerization of cyclohexene oxide and CO2), respectively. The influence of method of preparation of DMC, in particular the mode of addition of reagents, on its physicochemical and catalytic properties was investigated. Co-Zn DMC was found highly selective for polycarbonate (than polyethers) formation. Catalysts prepared using tert-butanol and PEG-4000 as complexing and co-complexing agents, respectively, were found superior to those prepared without these agents. Apart from its role as a coordinating ligand, tert-butanol activated the Lewis acidic Zn2+ sites for reactions in polyester and polycarbonate formation. Hydrophobicity, micro-mesoporosity, acid strength and the amount of coordinated complexing agent are some of the crucial factors influenced the catalytic activity of DMC complexes.

• Determination of conduction and valence band electronic structure of anatase and rutile TiO2

Electronic structures of rutile and anatase polymorph of TiO2 were determined by resonant inelastic X-ray scattering measurements and FEFF9.0 calculations. Difference between crystalline structures led to shifts in the rutile Ti 𝑑-band to lower energy with respect to anatase, i.e., decrease in band gap. Anatase possesses localized states located in the band gap where electrons can be trapped, which are almost absent in the rutile structure. This could well explain the reported longer lifetimes in anatase. It was revealed that HR-XAS is insufficient to study in-depth unoccupied states of investigated materials because it overlooks the shallow traps.

• Synthesis and visible light photocatalytic activity of nanocrystalline PrFeO3 perovskite for hydrogen generation in ethanol-water system

Nanocrystalline PrFeO3 perovskite type orthoferrite was synthesized at 700°C by using three different synthesis methods, namely sol-gel, template and combustion method. The synthesized materials were characterized by XRD, BET-SA, SEM, HRTEM, XPS, FTIR and UV-DRS techniques to understand their physico-chemical properties. Characterization data reveal the formation of nanocrystalline PrFeO3 perovskite composition with improved physical properties, possibly due to lower synthesis temperature used. PrFeO3 synthesized by sol-gel method consists of crystallite size of about 20 nm with absorption maxima at 595 nm wavelength in visible light range. This photocatalyst shows hydrogen generation of about 2847 𝜇mol.g-1.h-1, under visible light irradiation in ethanol-water system. The photocatalyst was further investigated for various operational parameters such as photocatalyst dose variation, illumination intensity, time, etc. in a view to optimize the hydrogen generation as well as to understand mechanistic aspects. This material appears to follow a semiconductor type mechanism for ethanol-assisted visible light photocatalyic water-splitting and can also be an interesting candidate to develop hetero-junction type photocatalysts.

• Metal organic framework MIL-101(Cr) for dehydration reactions

Porous chromium terephthalate MIL-101 (Cr-MIL-101) has been prepared by direct method under hydrothermal conditions and characterized using X-ray diffraction, N2 sorption, TGA and FT-IR. The nitrogen adsorption-desorption isotherm shows that the Cr-MIL-101 possesses BET specific surface area of 2563 m2/g. Catalytic performance of Cr-MIL-101 in the dehydration of 1,4-butanediol and 1-phenylethanol is assessed under vapour phase conditions in the temperature range of 513-533 K and time on stream (TOS) at 513 K. Cr-MIL-101 demonstrates superior catalytic activity with conversion of 95% of 1-phenylethanol. Moreover, high surface area and nanocages with coordinated unsaturated sites of Cr-MIL-101 have allowed us to attain higher dehydrated products selectivity than Cr-supported activated carbon (Cr/AC), amberlyst-15 and HZSM-5 catalysts.

• # Journal of Chemical Sciences

Volume 132, 2020
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Continuous Article Publishing mode

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019