Research Group Publications
 
  • Priya Lokhande, Kalyani Sonone And and Paresh L. Dhepe , Industry-oriented method for the aqueous phase oxidation of crude 5-hydroxymethyl furfural (HMF) to 2,5-furandicarboxylic acid (FDCA), New Journal of Chemistry., 47, 15325 - 15335 (2023), DOI:10.1039/D3NJ01834B.
  • Jyoti R. Kadam, Tufeil S. Khan And Paresh L. Dhepe, Designing an industrially viable bimetallic catalyst for the polyol synthesis, New Journal of Chemistry., 47, 7548 - 7555 (2023), DOI:10.1039/D3NJ00044C.
  • Singh, S.K., Matsagar, B.M. & Dhepe And P.L., Lignocellulosic biomass analysis: acidic lignin recovery, characterisation, and depolymerization, Biomass Conversion and Biorefinery., , (2022), DOI:10.1007/s13399-022-02705-9.
  • Sandip K. Singh And Paresh L. Dhepe, Alpha-, Beta- and Gamma-Cellulose Quantification and Two-Stage Concentrated-Dilute Acid Lignin Recovery from Three Rice Husks: Lignin Characterization and Depolymerization, Waste and Biomass Valorization., , (2022), DOI:https://doi.org/10.1007/s12649-022-01704-1.
  • Richa Chaudhary and Paresh L. Dhepe, Upgrading lignin-derived monomers over basic supported metal catalysts, Fuel., 306, 121588 - 121588 (2021), DOI:https://doi.org/10.1016/j.fuel.2021.121588.
  • Anup P. Tathod And P.L. Dhepe, Elucidating the effect of a solid base on the hydrogenation of C5 and C6 sugars over Pt-Sn bimetallic catalyst at room temperature, Carbohydrate Research., 505, 108341 (2021), DOI:https://doi.org/10.1016/j.carres.2021.108341.
  • Neha Ghosh and Paresh L. Dhepe, HPLC method development for chitin and chitosan valorization chemistry, Carbohydrate Polymer Technologies and Applications., Volume 2, 25 December 2021, 100139, (2021).
  • Khan, Tufeil; Singh, Dheerendra; Samal, Pragnya; Krishnamurty, Sailaja; Dhepe And Paresh, Mechanistic investigations on catalytic transfer hydrogenation of lignin-derived monomers over Ru catalyst: Theoretical and kinetic studies, ACS Sustainable Chemistry & Engineering., , (2021).
  • Dheerendra Singh And Paresh L. Dhepe, An efficient catalytic transfer hydrogenation-hydrodeoxygenation of lignin-derived monomers: Investigating catalyst properties-activity correlation, Catalysis Communications., 149, (2021).
  • Sandip K. Singh and Paresh L. Dhepe, Formic-Acid-Induced using Recyclable-Ionic Liquids as Catalysts for Lignin Conversion into Aromatic Co-Products, Waste and Biomass Valorization., 11,Issue 11, 6261 - 6272 (2020).
  • Irina Simakova, Paresh Dhepe And ..., Carbon Supported Size-Controlled Ru Catalysts for Selective Levulinic Acid Hydrogenation into gamma-Valerolactone, JOURNAL OF SIBERIAN FEDERAL UNIVERSITY-CHEMISTRY., 13, Issue 1, 5 - 16 (2020).
  • Irina Simakova, Yulia Demidova, Mikhail Simonov, Sergey Prikhodko, Prashant Niphadkar, Vijay Bokade, Paresh Dhepe And Dmitry Murzin, Heterogeneously catalyzed g-valerolactone hydrogenation into 1,4-pentanediol in milder reaction conditions, Reactions., 1 (2), 54 - 71 (2020), DOI:https://doi.org/10.3390/reactions1020006.
  • PARESH LAXMIKANT DHEPE, KALYANI GAJANANRAO SONONE And PRIYA LAXMANRAO LOKHANDE;, CATALYTIC OXIDATION OF 5-HYDROXYMETHYL FURFURAL TO 2, 5-FURAN DICARBOXYLIC ACID, Patent., , (2020).
  • Paresh L Dhepe And Manuraj Kallumkal, DEPOLYMERIZATION OF POLYMERS WITH ESTER, ETHER AND CARBONATE LINKAGES USING ACIDIC IONIC LIQUID (AIL) CATALYST, patent., , (2020), DOI:202011007863.
  • Dheerendra Singh And Paresh L. Dhepe, Understanding the influence of alumina supported ruthenium catalysts synthesis and reaction parameters on the hydrodeoxygenation of lignin derived monomers, Journal Molecular Catalysis., Volume 480,110525, (2020), DOI:https://doi.org/10.1016/j.mcat.2019.110525.
  • Paresh L Dhepe And Neha Ghosh, VALORIZATION OF ANIMAL DERIVED BIOMASS BY USING SOLID ACID CATALYST, Patent., , (2019), DOI:202011031311.
  • Chaudhary, Richa; Dhepe And Paresh L., Depolymerization of Lignin Using a Solid Base Catalyst, ENERGY & FUELS., Volume: 33 Issue: 5, 4369 - 4377 (2019), DOI:10.1021/acs.energyfuels.9b00621.
  • Sandip K. Singh And Paresh L. Dhepe, Lignin Conversion Using Catalytic Ionic Liquids: Understanding the Role of Cations, Anions, and Hammett Acidity Functions, Industrial Engineering Chemistry Research., , (2019), DOI:10.1021/acs.iecr.9b03375.
  • J. H. Khan, Babasaheb Matsagar, Kevin Wu And Paresh L. Dhepe, High surface area nanoporous carbon derived from high quality jute from Bangladesh, MATERIALS CHEMISTRY AND PHYSICS., 216, 491 - 495 (2018), DOI:10.1016/j.matchemphys.2018.05.082.
  • Manisha G. Dohade And Paresh L. Dhepe, One pot conversion of furfural to 2-methylfuran in the presence of PtCo bimetallic catalyst, Clean Technologies and Environmental Policy., Volume 20, Issue 4, 703 - 713 (2018), DOI:10.1007/s10098-017-1408-z.
    Biomass-derived furfural (FAL) is the platform chemical for synthesis of various value-added chemicals and fuels. One of the FAL-derived chemicals, i.e., 2-methylfuran (2-MF), is the potential biofuel due to its attractive chemical and physical properties. Various methods are reported for conversion of FAL to 2-MF which are operated at high temperature and high H2 pressure. In present work, one pot catalytic method was developed in batch mode process for conversion of FAL to 2-MF. Reactions are carried out in the presence of PtCo/C bimetallic catalyst under 0.5–1 MPa H2 pressure. Monometallic and bimetallic catalysts with different Pt and Co loading were prepared by wet impregnation method, and catalysts were characterized by transmission electron microscopy, BET surface area, X-ray photoelectron spectroscopy, X-ray diffraction and inductive coupled plasma atomic emission spectroscopy techniques. 59% 2-MF yield was achieved at 180 °C and lower (0.5 MPa) H2 pressure.
  • Nilesh P. Tangale, P. S. Niphadkar And P. N. Joshi and Paresh L. Dhepe , Hierarchical K/LTL zeolite as a solid base for aqueous phase hydrogenation of xylose to xylitol, Microporous & Mesoporous Materials., Volume 278, 70 - 80 (2018).
    Post-synthesis modification by alkali treatment was employed for the synthesis of hierarchical K/LTL zeolites with varying degree of mesoporosity. For the alkali treatment, the concentration of aqueous KOH solution was changed from 0.3 to 2.8 M keeping the quantity per gram of zeolite fixed. The influence of the alkali concentration on the chemical composition, powder XRD crystallinity, morphology, basicity, and the textural properties of resultant hierarchical zeolites was investigated. Variation in the concentration of KOH solution was found to control the degree of preferential desilication with the preserved structural fingerprint of K/LTL zeolite. As a result, the generation of mesoporosity was observed along with 1) the decrease in the Si/Al ratio and percentage relative crystallinity, and 2) an increase in BET surface area and mesopore volume. 27Al MAS-NMR results showed that all the aluminum atoms present in the tetrahedral coordination after alkali treatment, which provides an elegant approach for significantly increasing the basic sites in the hierarchical zeolites. As a heterogeneous catalyst, the hierarchical K/LTL zeolites demonstrated the improved performance in the hydrogenation of xylose to xylitol as compared to the parent K/LTL zeolite. The different process parameters were assessed in order to maximize the hydrogenation activity. Among all the hierarchical zeolites, the enhanced catalytic activity was shown by the hierarchical K/LTL prepared by using 1.5 M KOH solution when it is used along with the 3.5 wt% platinum loaded ?-Al2O3 catalyst. This optimum activity may be attributed to the higher surface area, accessible basic sites, nano-sized Pt on ?-Al2O3, and the development of substantial intracrystalline mesoporosity for the enhanced molecular diffusion of reactant to and from the hierarchical zeolite with better-preserved crystallinity.
  • Sandip Kumar Singh And Paresh L. Dhepe, Experimental evidences for the existence of varying moieties and functional groups in assorted crop waste derived organosolv lignins, Industrial Crops and Products (2018)., Volume 119, 1, 144 - 151 (2018).
    Isolation of organosolv lignins (ORGLs, water:ethanol, 180oC, 1h, 93±5% mass balance) from various lignocellulosic materials like rice husk (RH), wheat straw (WS), bagasse (BG) & wood chips (WC) was done and experimental evidences are provided to perceive the differences in the structures of isolated lignins. To achieve this on bulk level, lignins were characterized by XRD, GPC, TGA & elemental analysis and on molecular level using UV-Vis, ATR, 1D/2D HSQC NMR techniques. Besides isolated lignins, crop wastes and pulps were also characterized to divulge details on their properties. It was revealed that lignins have varying concentrations of sinapyl (S), coniferyl (G) and p-coumaryl alcohols (H) and tricin (T) moieties. While, Tricin (T) type lignin moieties are observed only in RH and WS derived lignins, RH derived lignin has higher concentration of side chains than other isolated lignins. Additionally, it is discovered that most lignins have G as main moiety.
  • Manisha Dohade And Paresh L. Dhepe, The efficient method for the cyclopentanone synthesis from furfural: Understanding the role of solvents, solubilities and bimetallic catalytic system, Catalysis Science & Technology., 8, 5259 - 5269 (2018), DOI:10.1039/C8CY01468J.
    The platform chemical, furfural (FAL), is obtained from C5 stream of biomass, and effective conversion into various chemicals including cyclopentanone (CPO) would find many industrial applications. It is desirable to convert FAL to CPO under low H2 pressure with high selectivity. In the current work, bimetallic catalysts with Pt as the base metal supported on carbon are evaluated in the synthesis of CPO using a biphasic solvent system. By tuning the solvent ratio, with toluene/water (3 : 4 v/v), 75% yield of CPO is achieved under 1 MPa H2 at 180 °C. The difference in solubility of the substrate, intermediates and products, along with the optimum ratio of Pt and Co metals plays a crucial role in achieving better yields.
  • Manisha Dohade And Paresh L. Dhepe, Efficient conversion of Sugars to Sugar alcohols in presence of Ru/C catalyst under mild reaction condition, Catalysis in Green Chemistry and Engineering., 1 (3), 247 - 261 (2018), DOI:10.1615/CatalGreenChemEng.2018028533.
    Sugar alcohols (xylitol and sorbitol) produced from biomass derived xylose and glucose finds wide industrial application in food and pharmaceutical Industries. Hence it is worth to produce these sugar alcohols under mild reaction conditions at low temperature and low H2 pressure with concentrated feed (sugar) solution. In this work, Ru metal supported on carbon was used as a catalyst to convert xylose and glucose to yield xylitol and sorbitol respectively. 98% yield of xylitol and sorbitol was achieved under 0.5 MPa H2, at 100 °C. Under low H2 pressure (0.2 MPa) at 100 °C, 94% yield of xylitol and 91% yield of sorbitol was obtained. 98% yield of sugar alcohols (xylitol and sorbitol) was achieved with 40 wt% sugar solution under 1 MPa H2.
  • Nilesh P. Tangale, Prashant S. Niphadkar And Prafulla N Joshi and Paresh Laxmikant Dhepe, KLTL-MCM-41 micro-mesoporous composite as solid base for the hydrogenation of sugars, Catal. Sci. Technol., 2018., 8, 6429 - 6440 (2018), DOI:DOI: 10.1039/C8CY01716F.
    An approach to the synthesis of KLTL-MCM-41 micro-mesoporous composites varying molar SiO2/Al2O3 ratio (20-8) was originated by following the green technology. The synthesis was based on recycling of waste mother liquor containing preformed KLTL zeolite crystals and unutilized reagents. The micro-mesoporous composites consist of preformed KLTL zeolite crystals through hydrothermal treatment in the first step. In the second step, the siliceous mother liquor was transformed into the mesoporous MCM-41. The physico-chemical properties of the KLTL-MCM-41 micro-mesoporous composites were determined by PXRD, ICP-OES, FTIR, CO2-TPD, 27Al MAS-NMR, TEM-EDX, HRTEM, and N2 adsorption-desorption measurements. The mesopores properties of KLTL-MCM-41 composites were depended on the molar SiO2/Al2O3 ratio. The characterization results accounted the following conclusions with decreasing SiO2/Al2O3 molar ratio: 1) lowering the orderliness of mesophase, 2) decreasing the wall thickness of mesopores, and 3) decreasing BET surface area and pore volume. 27Al MAS-NMR showed that only tetrahedrally coordinated aluminium encountered for zeolite KLTL. Moreover, the total amount and the strength of the basic sites of KLTL-MCM-41 micro-mesoporous composites owing to exchangeable potassium content (Al/K ratio-1) decreased in the order: 8 MMC > 10 MMC > 15 MMC > 20 MMC. The catalytic activity of the synthesized micro-mesoporous samples was tested as a solid base for the hydrogenation of xylose to sugar alcohols.
  • Babasaheb M. Matsagar And Paresh L. Dhepe, Glucose isomerization catalyzed by bone char and the selective production of 5-hydroxymethylfurfural in aqueous media, Sustainable Energy Fuels., 2, 2148 - 2153 (2018), DOI:10.1039/c8se00339d.
    The selective production of 5-hydroxymethylfurfural (HMF) is important, and it is difficult with glucose substrates in a water solvent. Here we demonstrate a selective method for glucose-to-HMF conversion using the combined catalysis of bone char and 1-methyl-3-(3-sulfopropyl)-imidazolium hydrogen sulfate acidic ionic liquid catalysts with a high HMF selectivity (54%) in water.
  • Sandip K.Singh And Paresh L. Dhepe, Novel Synthesis of Immobilized Brønsted- Acidic Ionic Liquid: Application in Lignin Depolymerization, Chemistryselect-Sustainable Chemistry., 3, 5461 - 5470 (2018), DOI:DOI: 10.1002/slct.201703050.
    Designing of efficient catalyst for the valorization of lignin is a topic of long neglect due to intrinsic properties of lignin. We show designing of an efficient, stable and recyclable Immobilized?Brønsted acidic ionic liquid (I?BAIL), which was further used as a solid acid catalyst for the depolymerization of lignin. The synthesized I?BAIL catalyst with sulfonic acid (–SO3H) groups was found to be stable until 250 °C and has 42.2 wt.% loading of BAIL anchored on silica framework. The detailed characterization (elemental, Thermogravimetric analysis, Fourier transformation?Infrared, Nuclear magnetic resonance) of catalyst disclosed formation of strong covalent bond between Si and carbon of BAIL, which in turn is responsible for achieving a stable catalyst. The catalyst could successfully depolymerize range of lignin substrates with high molecular weight (60000 Dalton) at 200 °C in 1 h to achieve 90% yield of tetrahydrofuran soluble products with good mass balance. The formation of products and correlation of products with lignin was achieved with the help of Nuclear magnetic resonance, gel permeation chromatography, gas chromatography, gas chromatography?mass spectrometry, high performance liquid chromatography etc.
  • Sandip K. Singh And Paresh L. Dhepe, Effect of structural properties of organosolv lignins isolated from different rice husks on their liquefaction using acidic ionic liquids, Clean Technologies and Environmental Policy., Volume 20, Issue 4, 739 - 750 (2017).
    Lignin is the only naturally available sustainable resource of aromatic compound on the Earth. Depending on the properties of lignin and the reaction conditions employed for the liquefaction, it is observed that the product distribution alters. Since, ionic liquids (ILs) are considered as green and have tuneable properties, in the current work, imidazolium based acidic ILs were employed to liquefy organosolv lignins derived from different varieties of rice husks. When liquefaction was carried out at 120 oC for 1 h 36% yield for EtOAc and DEE soluble products with high mass balance (97±3%) was observed. The detailed characterizations of lignins and organic solvent soluble products were done by variety of techniques (GC-MS, FT-IR, UV-Vis, 2D (HSQC) NMR) and based on this, the correlation between activity and properties of catalyst and lignin were established.
  • Sandip K. Singh, Subhrashis Banerjee, Kumar Vanka And Paresh L. Dhepe, Understanding interactions between lignin and ionic Liquids with experimental and theoretical studies during catalytic depolymerization, Catalysis Today., Volume 309, 98 - 108 (2017).
    Compared to H2SO4, Brønsted acidic ionic liquid (BAIL, [C3SO3HMIM][HSO4]) catalyzed depolymerization of lignin yielded higher concentration of low molecular weight products under mild conditions (120 oC) as proven by GC and GC-MS. To comprehend this disparity in catalytic activity among H2SO4 and BAIL (at similar H+ concentration), experimental techniques [1D(1H) NMR, 2D(15N/1H HMBC) NMR and RAMAN] have been employed. Based on these studies, it has been proven that the transfer of electron density from substrate to the electron deficient imidazolium ring via formation of hydrogen bond between –OH/OCH3 (substrate) and -N1C2H2N3- (cation) is possible, while the anion plays an important role. Further, density functional theory (DFT) calculations also corroborated this fact by showing a change in the bond angle and decrease in bond length (C2-H2 in imidazole), due to the presence of weak and strong hydrogen bonding between the substrate and IL.
  • Babasaheb M. Matsagar, ........... , Paresh L. Dhepe And Kevin C-W. Wu, Direct Production of Furfural in One-pot Fashion from Raw Biomass Using Brønsted Acidic Ionic Liquids, Scientific Reports., 7(1), 13508 (2017), DOI:DOI:10.1038/s41598-017-13946-4.
    The conversion of raw biomass into C5-sugars and furfural was demonstrated with the one-pot method using Brønsted acidic ionic liquids (BAILs) without any mineral acids or metal halides. Various BAILs were synthesized and characterized using NMR, FT-IR, TGA, and CHNS microanalysis and were used as the catalyst for raw biomass conversion. The remarkably high yield (i.e. 88%) of C5 sugars from bagasse can be obtained using 1-methyl-3(3-sulfopropyl)-imidazolium hydrogen sulfate ([C3SO3HMIM][HSO4]) BAIL catalyst in a water medium. Similarly, the [C3SO3HMIM][HSO4] BAIL also converts the bagasse into furfural with very high yield (73%) in one-pot method using a water/toluene biphasic solvent system.
  • Babasaheb M. Matsagar And Paresh L. Dhepe, Effects of cations, anions and H+ concentration of acidic ionic liquids in the valorization of polysaccharides into furfural, New Journal of Chemistry., 41, 6137 - 6144 (2017), DOI:10.1039/C7NJ00342K.
    Valorization of hemicellulose to valuable chemicals such as C5 sugars and furfural in the one-pot fashion is crucial. In this work, acidic ionic liquids in presence of water showed high yields of C5 sugars (>80%) with >99% conversion of hemicelluloses at 160 °C. With water+toluene biphasic solvent system, within 4 h, 85% furfural yield was obtained directly from hemicellulose in a one-pot fashion using the catalytic amount of 1-methyl-3-(3-sulfopropyl)-imidazolium hydrogen sulfate. It is seen that BAILs perform better than solid acid [Faujasite and Mordenite zeolites; ion exchange resin, Amberlyst-15] and mineral catalysts [HCl and H2SO4]. The higher activity of BAILs compared to solid acids and mineral acid was correlated to Hammett acidity function (Ho) and ion-dipole type of interaction. The catalysts were characterized using NMR (1H and 13C), elemental analysis and TGA to confirm that those are stable under reaction conditions and thus were recyclable.
  • Manisha Dohade And Paresh L. Dhepe, One pot conversion of furfural to 2-methylfuran in presence of PtCo bimetallic catalyst, Clean Technologies and Environmental Policy., , 1 - 11 (2017), DOI:10.1007/s10098-017-1408-z.
    Biomass-derived furfural (FAL) is the platform chemical for synthesis of various value-added chemicals and fuels. One of the FAL-derived chemicals, i.e., 2-methylfuran (2-MF), is the potential biofuel due to its attractive chemical and physical properties. Various methods are reported for conversion of FAL to 2-MF which are operated at high temperature and high H2 pressure. In present work, one pot catalytic method was developed in batch mode process for conversion of FAL to 2-MF. Reactions are carried out in the presence of PtCo/C bimetallic catalyst under 0.5–1 MPa H2 pressure. Monometallic and bimetallic catalysts with different Pt and Co loading were prepared by wet impregnation method, and catalysts were characterized by transmission electron microscopy, BET surface area, X-ray photoelectron spectroscopy, X-ray diffraction and inductive coupled plasma atomic emission spectroscopy techniques. 59% 2-MF yield was achieved at 180 °C and lower (0.5 MPa) H2 pressure
  • Richa Chaudhary And Paresh L. Dhepe, Solid base catalyzed depolymerization of lignin into low molecular weight products, Green Chemistry., 19, 778 - 788 (2017), DOI:10.1039/C6GC02701F.
    For biorefinery concept to become commercially viable, it is essential to value-add lignin which is the only naturally available aromatic polymer. A one-pot depolymerization of lignin into reactive substituted phenolic compounds (platform chemicals and octane enhancers) with low molecular weightis of paramount interest and for that development of environmentally benign method is necessary. Herein we report, depolymerization of high molecular weight lignin (60,000 Da) over various recyclable solid base catalysts at 250 oC in 1 h. Under this conditions, most of the zeolitic catalysts (NaX, NaY, NaP) showed very high yields of low molecular weight products than other catalysts (MgO, CaO, HT, HAP). But particularly, over NaX maximum yield (51%) of low molecular weight products was achieved. Identification and quantification of products was done by GC, GC-MS, HPLC, LC-MS, CHNS, NMR and FT-IR techniques. The revelation of retention of most of the functional groups on products present in lignin is done by FT-IR studies. It is observed that efficiencies of catalysts were dependent on pH, cation, type and concentration of basic sites etc. A unique study on products adsorption capacities on solids was done and it is recognized that as strength of basic sites increases adsorption enhances.
  • Manisha Dohade And Paresh L. Dhepe, Efficient hydrogenation of concentrated aqueous furfural solutions in to furfuryl alcohol under ambient conditions in presence of PtCo bimetallic catalysts, Green Chemistry., 19, 1144 - 1154 (2017), DOI:10.1039/C6GC03143A.
    One of the biomass derived significant chemical furfural (FAL) can be hydrogenated to yield industrially important platform chemical, furfuryl alcohol (FOL). Although heterogeneous catalysts based methods are known to yield FOL from dilute solutions of FAL, those mainly operate at higher temperatures and/or high pressures of hydrogen and in presence of organic solvents. In this work, we employ bimetallic PtCo/C catalysts with varying metal concentrations to achieve maximum possible FOL yield (100%) at 35 oC under 0.1 MPa H2 in water. With concentrated FAL (40 wt%) at 50 oC and under 1 MPa H2 pressure, 86% yield for FOL was observed. Moreover, efficient recycling of catalyst in at least 4 runs with marginal loss in activity due to handling error and isolation of FOL in pure form confirmed by NMR and HPLC is attractive. The characterization of catalysts with several physico-chemical techniques (XRD, TEM, XPS, ICP,TPR) reveal the presence of electron rich Pt and ionic Co species in proximity with each other and those work synergistically to facilitate accomplishment of maximum possible yield of FOL under ambient conditions and in water medium.
  • Sandip K. Singh And Paresh L. Dhepe, Isolation of lignin by Organosolv process from different varieties of rice husk: Understanding their physical and chemical properties, Bioresource Technology., 221, 310 - 317 (2016), DOI:https://doi.org/10.1016/j.biortech.2016.09.042.
    The aim of this work was to study the difference in properties of lignins, those (organosolv lignins (ORGLs, 12±3% yield and 93±5% mass balance) were isolated from diverse rice husk (RH) substrates using organosolv procedure (water:ethanol, H2SO4) carried out at 180?C for 1 h. To identify the possible alterations in lignin structures several bulk and molecular level advanced characterization tools were employed. Even though lignins were extracted using common isolation procedure from three varieties of similar species of RH; from XRD, GPC, and elemental analysis it was found that those have comparable properties on bulk level. But molecular level analysis conducted using UV-Vis, ATR, 1D/2D HSQC NMR techniques could help disclose that isolated lignins have varying concentrations of G, H, S and T substructures. Additionally, the double bond equivalence of 4.4-4.7 reveals that few of the aromatic rings are devoid of substituent.
  • Prasenjit Bhaumik And Paresh L. Dhepe, From Lignocellulosic Biomass to Furfural: Insight into the Active Species of a Silica-Supported Tungsten Oxide Catalyst, ChemCatChem., , (2016), DOI:10.1002/cctc.201600784R1.
    A sol-gel synthesized silica supported tungsten oxide catalyst that has Lewis acidity was characterized and employed as a solid acid catalyst in the synthesis of furfural directly from lignocellulosic biomass (isolated xylans and crop wastes). In a one-pot method, 71% furfural formation from isolated xylan was possible using a water/toluene (1:2 v/v) biphasic solvent system at 170°C after 10 h over 10 wt^% WO3/SiO2. The WO3/SiO2 catalyst in the selective conversion of pentosan from crop wastes (bagasse, wheat straw, and rice husk) yielded 72-87% furfural under the optimum reaction conditions. Additionally, the catalyst presented excellent recyclability in at least eight runs after simple water washing. From the catalyst characterization studies, it was suggested that silicotungstic-type acid species are anchored on the WO3/SiO2 catalyst that help to achieve a good catalytic activity.
  • Sandip K. Singh And Paresh L. Dhepe, Ionic liquids catalyzed lignin liquefaction: mechanistic studies using TPO-MS, FT-IR, RAMAN and 1D, 2D-HSQC/NOSEY NMR, Green Chemistry., 18, 4098 - 4108 (2016), DOI:10.1039/C6GC00771F.
    Valorization of a profusely available alternate resource, biomass and in particular its 3-D intricate component lignin into low molecular weight aromatic products are used as platform chemicals and fuel additives, and developing a low temperature catalytic process is imperative in preserving atom efficiency. Ionic liquids, due to their unique properties, offer an advantage to develop such methods under milder conditions. Herein, we show use of –SO3H functionalized imidazolium based various recyclable Brønsted acidic ionic liquids (BAILs) in catalytic quantity under ambient pressure at 120 °C for depolymerization of lignin (60000 g mol?1) into THF soluble products with high efficiency (78% yield, 95% ± 5% mass balance). The decoding of this efficiency by 1D and 2D (HSQC/NOSEY) NMR, FT-IR and RAMAN studies exemplify that the –OH group(s) interact with the electron deficient BAIL cation. The mechanistic insights unraveled in this study open a plethora of opportunities to design catalysts for developing efficient processes.
  • Prasenjit Bhaumik And Paresh L. Dhepe, Conversion of Biomass into Sugars, Biomass Sugars for Non-Fuel Applications., 43, 1 - 53 (2015), DOI:10.1039/9781782622079.
  • Prasenjit Bhaumik and Paresh L. Dhepe, Solid Acid Catalyzed Synthesis of Furans from Carbohydrates, Cat. Rev.-Sci. Eng., , (2015), DOI:10.1080/01614940.2015.1099894.
    The alternative feedstock, biomass (particularly lignocelluloses) having profuse availability is promising for the synthesis of several value-added chemicals which are currently obtained from fossil feedstock. In this review, the synthesis of two extremely significant furan chemicals viz. furfural and 5-hydroxymethylfurfural (HMF) are discussed. In the synthesis of furans from biomass, numerous challenges for instance, use of edible sugars as substrates, selectivity to furans, their isolation in pure form, reuse of catalyst, environmental issues etc. are perceived and in recent past researchers tried to resolve those by developing advance methodologies. This review summarizes latest progresses made in the above mentioned areas comprehensively and also commentary is given on the analyses of results, rationale for observed activity and mechanisms etc. Review also discusses future aspects of this work.
  • Babasaheb. M. Matsagar, Mudassir. K. Munshi, Ashutosh A. Kelkar And Paresh L. Dhepe, Conversion of concentrated sugar solutions into 5-hydroxymethyl furfural and furfural using Brönsted acidic ionic liquids, Catal. Sci. Tenchnol., , (2015), DOI:10.1039/C5CY00858A.
    Catalytic amounts of recyclable Brönsted acidic ionic liquids (BAILs) yielded HMF (73%) and furfural (81%) with high selectivity from highly concentrated solutions of D-fructose (40 wt%) and D-xylose (3 wt%), respectively. With a 6 wt% D-xylose solution, 73% yield was observed. An activity–property correlation of BAIL is established.
  • Prasenjit Bhaumik And Paresh L. Dhepe, Effects of careful designing of SAPO-44 catalysts on the efficient synthesis of furfural, Catal. Today., 251, 66 - 72 (2015), DOI:10.1016/j.cattod.2014.10.042.
    Considering the growing importance of furfural, it is necessary to develop a robust solid acid catalyst for the conversion of xylan (hemicelluloses) into furfural in a one-pot method. In this study, the effects of various components (Si, Al and P) and crystallization time on the preparation of acidic materials and their properties are extensively described. It is seen that with the increase in crystallization time (0, 48, 96, 176 h) during the synthesis of silicoaluminophosphate (SAPO-44), materials morphology changes from amorphous to AFI to CHA and the best activity for furfural synthesis (82%) from xylan was observed with SAPO-44 catalyst aged for 176 h. Since, acidity in the SAPO-44 is guided by the incorporation of Si in the ALPO framework, study on Si molar concentration (0.8, 1.0, 1.2, 1.4 and 1.6) in SAPO-44 was carried out and it was observed that SAPO-44 having 1.0 mole of Si content is the best catalyst for the xylan/xylose conversion to furfural. Catalyst structure-activity correlation is thoroughly defined with the help of several physico-chemical properties.
  • Anup P. Tathod And Paresh L. Dhepe, Efficient method for the conversion of agricultural waste into sugar alcohols over supported bimetallic catalysts, Bioresour. Technol., 178, 36 - 44 (2015), DOI:10.1016/j.biortech.2014.10.036.
    Promoter effect of Sn in the PtSn/g-Al2O3 (AL) and PtSn/C bimetallic catalysts is studied for the conversion of variety of substrates such as, C5 sugars (xylose, arabinose), C6 sugars (glucose, fructose, galactose), hemicelluloses (xylan, arabinogalactan), inulin and agricultural wastes (bagasse, rice husk, wheat straw) into sugar alcohols (sorbitol, mannitol, xylitol, arabitol, galactitol). In all the reactions, PtSn/AL showed enhanced yields of sugar alcohols by 1.5 to 3 times than Pt/AL. Compared to C, AL supported bimetallic catalysts showed prominent enhancement in the yields of sugar alcohols. Bimetallic catalysts characterized by X-ray diffraction study revealed the stability of catalyst and absence of alloy formation thereby indicating that Pt and Sn are present as individual particles in PtSn/AL. The TEM analysis also confirmed stability of the catalysts and XPS study disclosed formation of electron deficient Sn species which helps in polarizing carbonyl bond to achieve enhanced hydrogenation activity.
  • A. K. Deepa And Paresh L. Dhepe, Lignin depolymerization into aromatic monomers over solid acid catalysts, ACS Catal., 5, 365 - 379 (2015), DOI:10.1021/cs501371q.
    It is imperative to develop an efficient and environmentally benign pathway to valorize profusely available lignin, a component of non-edible lignocellulosic materials into value-added aromatic monomers, which can be used as fuel additives and platform chemicals. To convert lignin, earlier studies used mineral bases (NaOH, CsOH) or supported metal catalysts (Pt, Ru, Pd, Ni on C, SiO2, Al2O3 etc.) under hydrogen atmosphere but these methods face several drawbacks such as corrosion, difficulty in catalyst recovery, sintering of metals, loss of activity etc. Here we show that under inert atmosphere various solid acid catalysts can efficiently convert six different types of lignins in to value-added aromatic monomers. Particularly, SiO2, Al2O3 catalyst gave exceptionally high yields of ca. 60 % for organic solvent soluble extracted products with 95±10 % mass balance in the depolymerization of Dealkaline lignin, Bagasse lignin, ORG and EORG lignins at 250 oC within 30 min. The GC, GC-MS, HPLC, LC-MS, and GPC analysis of organic soluble extracted products confirmed the formation of aromatic monomers with ca. 90 % selectivity. In the products, confirmation of retention of aromatic nature as present in lignin and appearance of several functional groups is done by FT-IR, 1H and 13C NMR studies. Further, isolation of major products by column chromatography was carried out to obtain aromatic monomers in pure form and their further characterization by NMR is presented. Detailed characterization of six different types of lignins obtained from various sources helped in substantiating the catalytic results obtained in these reactions. Meticulous study on fresh and spent catalysts revealed that the amorphous catalysts are preferred to obtain reproducible catalytic results.
  • Babasaheb M. Matsagar And Paresh L. Dhepe, Brönsted acidic ionic liquids catalyzed conversion of hemicellulose into sugars, Catal. Sci. Technol., 5, 531 - 539 (2015), DOI:10.1039/C4CY01047G.
    Development of competent method for the conversion of hemicelluloses, a lignocellulosic component into sugars is essential. In a one-pot method, at 160 °C and in water media, Brönsted acidic ionic liquid (BAIL) catalyzed hydrolysis of hardwood hemicellulose gives 87% yield for C5 sugars (xylose+arabinose). The efficiency of the ILs and acid strength both followed the similar trend, [C3SO3HMIM][HSO4] > [C3SO3HMIM][PTS] > [C3SO3HMIM][Cl] > [BMIM][Cl]. The ion-dipole type interaction present between BAIL and substrate which is proposed by 1H NMR study is suggested to help in achieving better activity with BAIL compared to mineral acid, H2SO4.
  • Anup P. Tathod And Paresh L. Dhepe, Towards efficient synthesis of sugar alcohols from mono- and poly-saccharides: Role of metals, supports & promoters, Green Chem., 16, 4944 - 4954 (2014), DOI:10.1039/C4GC01264J.
    Biomass derived sugar alcohols (xylitol, arabitol) find numerous uses in the food, oral and pharmaceutical industries. Their direct synthesis from poly-saccharides however still remains an immense challenge. In this study, we demonstrate in detail, the effects of metals, supports and promoters in enhancing the yields of sugar alcohols from mono- and poly-saccharides. We undertook, synthesis of bimetallic catalysts, M-M’/S (M, Metal=Pt, Ru; M’, Promoter=Sn, Ga, Fe; S, support=g-Al2O3 (AL), SiO2-Al2O3 (SA), Carbon (C)) with varying metal loadings (Pt/Ru=2, 3.5wt%; Sn=0.22, 0.43, 0.87, 1.5, 3.5wt%; Ga/Fe=0.25wt%) by co-impregnation method. The catalytic activities of these catalysts were evaluated in the synthesis of sugar alcohols from xylose (mono-saccharide) and hemicellulose (xylan, poly-saccharide) at 130-190oC. Among all bimetallic catalysts, Pt(3.5)Sn(0.43)/AL catalyst (50%) showed 2.8 times improvement in the sugar alcohols yield compared to monometallic Pt(3.5)/AL catalyst (18%). Similarly, in xylose reaction also 2.4 times enhancement in sugar alcohols yield over Pt(3.5)Sn(0.43)/AL (79%) was observed as against 33% yield obtained with Pt(3.5)/AL. By conducting several experiments it is confirmed that the residual Cl- remained on the catalyst even after calcinations and reductions carried out at 400oC, does not play any role in catalysis. The stability of the Pt(3.5)Sn(0.43)/AL catalyst confirmed by XRD and ICP analysis was responsible in achieving reproducible activity in at least 5 consecutive runs. Formation of electron deficient Sn confirmed by XPS analysis helped polarizing carbonyl group which in turn enhanced the sugar alcohols yields. Formation of PtSn and Pt3Sn species was observed when Sn loading is more than 0.87%.
  • A. K. Deepa And Paresh L. Dhepe, Function of metals and supports on the hydrodeoxygenation of phenolic compounds, ChemPlusChem., 79, 1573 - 1583 (2014), DOI:10.1002/cplu.201402145R1.
    Hydrodeoxygenation (HDO) is an important process to remove oxygen from lignin derived phenolic monomers to obtain chemicals which can be used as fuel or fuel additives. A systematic study is performed to check the effects of supports (acidic, neutral, basic) and noble metals (Pd, Pt, Ru) on HDO of phenol, guaicol and eugenol. When the combinations of metals and supports were evaluated under the similar reaction conditions, it was found that the metals supported on highly acidic support (SiO2-Al2O3) show complete hydrogenation products with a possibility of C-O bond cleavage to achieve a real HDO activity. While on a mildly acidic support (g-Al2O3), complicated product distribution is achieved, neutral (C) and basic (HT) supports gave restricted hydrogenation activity but yielded the products with very high selectivity. Based on the results, reaction pathways are suggested and deliberated. Catalysts showed reproducible activity in recycle runs. Catalysts were characterized by various (XRD, TEM, TPD, ICP-OES) techniques to establish catalyst activity-property relationship.
  • Prasenjit Bhaumik, Tanushree Kane And Paresh L. Dhepe, Silica and zirconia supported tungsten, molybdenum and gallium oxide catalysts for the synthesis of furfural, Catal. Sci. Technol., 4, 2904 - 2907 (2014), DOI:10.1039/C4CY00530A.
    SiO2 and ZrO2 supported W, Mo and Ga oxide catalysts were prepared by sol-gel and wet-impregnation method. The 10wt% WO3/SiO2 (sol-gel) catalyst showed 61±2% furfural yield from hemicellulose in one-pot fashion at least in 8 cycles. Based on XRD, TPD, Hammett acidity characterizations catalyst structure-activity correlation was drawn.
  • Prasenjit Bhaumik And Paresh L. Dhepe, Exceptionally high yields of furfural from assorted raw biomass over solid acids, RSC Adv., 4, 26215 - 26221 (2014), DOI:10.1039/C4RA04119D.
    Development of stable and recyclable solid acid catalysts in the efficient valorisation of hemicellulose to yield C5 sugars and furfural is vital to boost the prospects of using lignocelluloses for the chemicals synthesis. Using SAPO-44 catalyst an environmentally benign process of furfural synthesis from diversified real substrates (without any treatment & the need for separation of its components) is shown. In an efficient one-pot methodology, at 443 K and in the presence of biphasic solvent system, selective conversions of hemicelluloses from raw biomass (bagasse, rice husk & wheat straw) to extraordinarily high yields of furfural of about 93% were attainable. Under similar reaction conditions, 82% yield of furfural is also achievable directly from isolated hemicellulose within 10 h. Hydrophilic SAPO-44 having higher hydrothermal stability showed similar activity for all the substrates minimum up to 8 times in recycle runs. Various physico-chemical characterizations (XRD, TGA-DTG, TPD-NH3, solid state NMR) of fresh and spent catalysts edify on the SAPO-44 stability.
  • Paresh L. Dhepe , Ashutosh Kelkar, Babasaheb Matsagar And Sandip Singh, Acidic ionic liquids catalyzed depolymerization of lignin, Patent., IN, (2014).
  • Paresh L. Dhepe And Anup Tathod, Production of sugar alcohols, xylitol and arabbitol using bimetallic supported metal catalysts, Patent., IN, (2014).
  • Paresh L. Dhepe And Babasaheb Matsagar, Conversion of hemicellulose using acidic ionic liquids, Patent., IN, (2014).
    Patent applied on a process for acidic ionic liquid catalyzed hemicellulose conversion
  • Prasenjit Bhaumik, A. K. Deepa, Tanushree Kane And Paresh L. Dhepe, Value addition to lignocellulosics and biomass-derived sugars: An insight into solid acid-based catalytic methods, J. Chem. Sci., 126, 373 - 385 (2014), DOI:10.1007/s12039-014-0574-3.
    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 (<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.
  • A. K. Deepa And Paresh L. Dhepe, Solid acid catalyzed depolymerization of lignin into value added aromatic monomers, RSC Adv., 4, 12625 - 12629 (2014), DOI:10.1039/C3RA47818A.
    Depolymerization of lignin to produce value-added aromatic monomers has attracted a lot of attention since these monomers can potentially be used as fuel additives (octane enhancers) and in turn can improve the prospects of cellulosic ethanol technology to become economically feasible. Here we show that solid acid catalysts could efficiently convert lignin into value added aromatic monomers with 60% yields and ca. 95% mass balance when depolymerization reactions were carried out at 250°C for 30–120 minutes. We found that the reaction parameters have a remarkable effect on improving the yields.
  • Ramakanta Sahu And Paresh L. Dhepe, Synthesis of 2,5-furandicarboxylic acid by the aerobic oxidation of 5-hydroxymethyl furfural over supported metal catalysts, Reac. Kinet. Mech. Cat., 112, 173 - 187 (2014), DOI:10.1007/s11144-014-0689-z.
    Supported Pt catalysts are synthesized, characterized and are used in the liquid phase air oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA). Under the optimum reaction conditions of a stepwise increase in the reaction temperature (75 and 140°C for 12 h each), we achieved as high as 96% FDCA yield in presence of 1 bar oxygen pressure over Pt/g-Al2O3. It is shown that as the oxygen pressure increases (1–10 bar), the FDCA yields decrease, since at higher partial pressure of oxygen, overoxidation reactions of substrate and product(s) are possible. It is interesting to note that even with air as an oxidant, we obtained similar yields of FDCA as that with oxygen. Moreover, the effects of base (weak or strong), its concentration (equimolar or excess) were studied in detail. It is important to increase the reaction temperature in a stepwise manner to achieve higher yields of FDCA since at higher temperatures HMF undergoes self-degradation and thus the yields of FDCA decrease. The self-degradation of HMF is also proved by undertaking the reaction under nitrogen environment. The study on the effect of substrate/catalyst ratio is done to improve up on the economics of overall process. The effect of supports (reducible and non-reducible) and their oxygen storage capacity is discussed and is proposed to be one of the factors to change the course of reaction. Furthermore, we have shown that FDCA formed in the reaction can be successfully isolated (91%, isolated yield) in the pure form and its purity is confirmed by NMR, melting point, and elemental analysis. The catalysts were characterized with X-ray powder diffraction, transmission electron microscopy and inductively coupled plasma-optical emission spectroscopy techniques.
  • Prasenjit Bhaumik And Paresh L. Dhepe, Influence of properties of SAPO's on the one-pot conversion of mono-, di- and poly-saccharides into 5-hydroxymethylfurfural, RSC Adv., 3, 17156 - 17165 (2013), DOI:10.1039/C3RA43197E.
    Synthesis of 5-hydroxymethylfurfural (5-HMF) from biomass derived mono- and poly-saccharides is gaining importance because of its usefulness in the preparation of important chemicals. In our work, we have synthesized several silicoaluminophosphate (SAPO) catalysts, and have shown that in the absence of any other pH modifying reagents, those are active in converting mono- and poly-saccharides into 5-HMF under biphasic reaction condition at 175°C. Particularly, SAPO-44 catalyst showed the best activity in the conversion of fructose to yield 78% 5-HMF with 88% selectivity. On the contrary, all other catalysts showed lower yields (H-MOR: 63%, SAPO-5: 32%, 2DCT: 60%). Over SAPO-44, good yields for 5-HMF were observed when glucose (67%), maltose (57%), cellobiose (56%) and starch (68%) were used as substrates. Recycle study carried out with SAPO-44 catalyst in the fructose conversion reaction showed marginal decrease in the activity up to 3rd run and then afterwards constant activity was observed up to 5th run (1st: 78%, 2nd: 71%, 3rd: 66%, 4th: 65%, 5th: 65%). Catalyst characterizations revealed that SAPO catalysts have higher hydrophilic nature than H-MOR (Si/Al = 10) and hence it is postulated that this property may help in achieving better results. Further studies on the catalyst characterizations revealed that SAPO-44 undergoes modifications in its structure. However, ICP-OES data suggests that Al and/or P are not leached out in the solution indicating that change in local environment around elements is possible. The influence of acid amount, type of acid site etc. on the catalytic activity is discussed and found out that strong acid sites are required to boost the 5-HMF yields.
  • Prasenjit Bhaumik And Paresh L. Dhepe, Efficient, stable, and reusable silicoaluminophosphate for the one-pot production of furfural from hemicellulose, ACS Catal., 3, 2299 - 2303 (2013), DOI:10.1021/cs400495j.
    Development of stable, reusable, and water-tolerant solid acid catalysts in the conversion of polysaccharides to give value-added chemicals is vital because catalysts are prone to undergo morphological changes during the reactions. With the anticipation that silicoaluminophosphate (SAPO) catalysts will have higher hydrothermal stability, those were synthesized, characterized, and employed in a one-pot conversion of hemicellulose. SAPO-44 catalyst at 170°C within 8 h could give 63% furfural yield with 88% mass balance and showed similar activity up to at least 8 catalytic cycles. The morphological studies revealed that SAPO catalysts having hydrophilic characteristics are stable under reaction conditions.
  • Anup Tathod, Tanushree Kane, E. S. Sanil And Paresh L. Dhepe, Solid base supported metal catalysts for the oxidation and hydrogenation of sugars, J. Mol. Catal. A: Chem., 388-389, 90 - 99 (2013), DOI:10.1016/j.molcata.2013.09.014.
    Pt impregnated on g-Al2O3 (acidic support) and hydrotalcite (basic support) catalysts were synthesized, characterized and used in the oxidation and hydrogenation reactions of C5 and C6 sugars. In the absence of homogeneous base, 83% yield for gluconic acid; an oxidation product of glucose can be achieved over Pt/hydrotalcite (HT) catalyst at 50°C under atmospheric oxygen pressure. Similarly, 57% yield for xylonic acid, an oxidation product of xylose is also possible over Pt/HT catalyst. Hydrogenation of glucose conducted using Pt/g-Al2O3 + HT catalytic system showed 68% sugar alcohols (sorbitol + mannitol) formation. The 82% yield for C5 sugar alcohols (xylitol + arabitol) was obtained by subjecting xylose to hydrogenation over Pt/g-Al2O3 + HT at 60°C. UV analysis helped to establish the fact that under alkaline conditions sugars prefer to remain in open chain form in the solution and thus exposes single -CHO group which further undergoes oxidation and hydrogenation reactions to yield acids and alcohols.
  • Paresh L. Dhepe And Deepa A. K., Depolymerization of lignin over solid acid catalysts, Patent., US20120302796 A1, BR, ES, IN, (2012).
    Patent applied on lignin depolymerization over solid acid catalysts
  • Wenhao Fang, Cyril Pirez, MickaelCapron, Sebastien Paul, Thirumalaiswamy Raja, Wenhao Fang, Paresh L. Dhepe, Franck Dumeignilabe And Louise Jalowiecki-Duhamel, Ce-Ni mixed oxide as efficient catalyst for H2 production and nanofibrous carbon material from ethanol in the presence of water, RSC Adv., 2, 9626 - 9634 (2012), DOI:10.1039/C2RA21701E.
    Hydrogen production from ethanol steam reforming(H2O/C2H5OH = 3) was studied over Ce–Ni based catalysts issued from different preparation methods (co-precipitation (CP), impregnation (IMP) and incipient wetness impregnation (IWI)). Catalysts prepared by the CP method exhibit higher activity and much better stability compared to the other two types of catalysts. The Ni1CeOY–CP catalyst is able to completely convert ethanol at 450°C to H2, CO2 and CH4 (almost no CO is observed), with a H2 yield of 3 moles of hydrogen produced per mole of ethanol converted. A very high H2 yield of 4.6 mol molEtOH?1 is achieved over the Ni1CeOY–CP mixed oxide at 650 °C. Correlations between the preparation method, catalytic activity and stability, and type of carbon deposition are discussed. The CP method forms very active small sized NiO (15 nm) and CeO2 (4 nm) nanoparticles, leading to the formation of a lower amount of carbon deposition in the form of nanofibrous carbon materials, the size of which depends on the Ni related nanoparticles. For CP catalysts, the graphitic filaments obtained correspond to carbon nanofibers (CNFs) and carbon nanotubes (CNTs) with a much smaller and homogenous size compared to the filamentous carbon formed over the catalysts issued from the other preparation methods, in relation to the active particles size. The catalytic stability is attributed to the type of carbon formed.
  • Paresh L. Dhepe And Ramakanta Sahu, A one-pot method for the selective conversion of hemicellulose from crop waste into C5 sugars and furfural by using solid acid catalysts, ChemSusChem., 5, 751 - 761 (2012), DOI:10.1002/cssc.201100448.
    We present a solid-acid catalyzed one-pot method for the selective conversion of solid hemicellulose without its separation from other lignocellulosic components, such as cellulose and lignin. The reactions were carried out in aqueous and biphasic media to yield xylose, arabinose, and furfural. To overcome the drawbacks posed by mineral acid methods in converting hemicelllulose, we used heterogeneous catalysts that work at neutral pH. In a batch reactor, these heterogeneous catalysts, such as solid acids (zeolites, clays, metal oxides etc.), resulted in >90% conversion of hemicellulose. It has been shown that the selectivity for the products can be tuned by changing the reaction conditions, for example, a reaction carried out in water at 170°C for 1h with HBeta (Si/Al=19) and HUSY (Si/Al=15) catalysts gave yields of 62 and 56% for xylose and arabinose, respectively. With increased reaction time (6h) and in presence of only water, HUSY resulted in yields of 30% xylose+arabinose and 18% furfural. However, in a biphasic reaction system (water+p-xylene, 170°C, 6h) yields of 56% furfural with 17% xylose+arabinose could be achieved. It was shown that with the addition of organic solvent the furfural yield could be increased from 18 to 56%. Under optimized reaction conditions, >90% carbon balance was observed. The study revealed that catalysts were recyclable with a 20% drop in activity for each subsequent run. It was observed that temperature, pressure, reaction time, substrate to catalyst ratio, solvent, and so forth had an effect on product formation. The catalysts were characterized by means of X-ray diffraction, temperature-programmed desorption of NH3, inductively coupled plasma spectroscopy, elemental analysis, and solid-state NMR (29Si, 27Al) spectroscopy techniques.
  • Paresh L. Dhepe And Ramakanta Sahu, A one pot and single step hydrolytic process for the conversion of lignocellulose into value added chemicals, Patent., EP2529036 A1, WO/2011/092711, (2011).
  • Hirokazu Kobayashi, Yukiko Ito, Tasuku Komanoya, Yuto Hosaka, Paresh L. Dhepe, Koji Kasai, Kenji Haraa And Atsushi Fukuoka, Synthesis of sugar alcohols by hydrolytic hydrogenation of cellulose over supported metal catalysts, Green Chem., 13, 326 - 333 (2011), DOI:10.1039/C0GC00666A.
    Cellulose is converted into sorbitol and related sugar compounds over water-tolerant and durable carbon-supported Pt catalysts under aqueous hydrogenation conditions. Pre-treatment of cellulose with ball-milling effectively reduces the crystallinity and particle size of cellulose, which results in high conversion of cellulose to sorbitol and mannitol. The selectivity of sorbitol increases by using Cl-free metal precursors in the catalyst preparation as residual Cl on the catalysts promotes the side-reactions. The transformation of cellulose to sorbitol consists of the hydrolysis of cellulose to glucose via water-soluble oligosaccharides and the successive hydrogenation of glucose to sorbitol. The hydrolysis of cellulose is the rate-determining step, and the Pt catalysts promote both the hydrolysis and the hydrogenation steps.
  • Paresh L. Dhepe And Ramakanta Sahu, A single step hydrolytic process for the conversion of hemicellulose into value added chemicals, Patent., US20120192860 A1, AU2010344335 (A1), JP2013-517792, IN34/2010, CN, BR, ES, (2010).
  • Paresh L. Dhepe And Ramakanta Sahu, A solid acid based process for the conversion of hemicellulose, Green Chem., 12, 2153 - 2156 (2010), DOI:10.1039/C004128A.
    We describe a solid acid catalyzed conversion of hemicellulose (a component of lignocellulosic material) into xylose, arabinose and furfural in aqueous media.
  • Atsushi Fukuoka And Paresh L. Dhepe, Sustainable green catalysis by supported metal nanoparticles, Chem. Rec., 9, 224 - 235 (2009), DOI:10.1002/tcr.200900004.
    The recent progress of sustainable green catalysis by supported metal nanoparticles is described. The template synthesis of metal nanoparticles in ordered porous materials is studied for the rational design of heterogeneous catalysts capable of high activity and selectivity. The application of these materials in green catalytic processes results in a unique activity and selectivity arising from the concerted effect of metal nanoparticles and supports. The high catalytic performances of Pt nanoparticles in mesoporous silica is reported. Supported metal catalysts have also been applied to biomass conversion by heterogeneous catalysis. Additionally, the degradation of cellulose by supported metal catalysts, in which bifunctional catalysis of acid and metal plays the key role for the hydrolysis and reduction of cellulose, is also reported.
  • Paresh L. Dhepe And Atsushi Fukuoka, Modification of mesoporous silicas, their characterization and catalysis, American Scientific Publishers., in Bottom-up nanofabrication: Supramolecules, Self-Assemblies, and Organized Films, (2008).
  • Paresh L. Dhepe And Atsushi Fukuoka, Chapter 26 – Template synthesis and catalysis of metal nanoclusters in ordered mesoporous silicas, Metal Nanoclusters in Catalysis and Materials Science: The Issue of Size Control., , 383 - 390 (2008), DOI:10.1016/B978-044453057-8.50028-3.
    Zeolites have ordered micropores smaller than 2 nm in diameter and are widely used as catalysts and supports in many practical reactions. Some zeolites have solid acidity and show shape-selectivity, which gives crucial effects in the processes of oil refining and petrochemistry. Metal nanoclusters and complexes can be synthesized in zeolites by the ship-in-a-bottle technique, and the composite materials have also been applied to catalytic reactions. However, the decline of catalytic activity was often observed due to the diffusion-limitation of substrates or products in the micropores of zeolites. To overcome this drawback, newly developed mesoporous silicas such as FSM-16, MCM-41, and SBA-15 have been used as catalyst supports, because they have large pores (2–10 nm) and high surface area (500–1000 m2g-1). The internal surface of the channels accounts for more than 90% of the surface area of mesoporous silicas. With the help of the new incredible materials, template synthesis of metal nanoclusters inside mesoporous channels is achieved and the nanoclusters give stupendous performances in various applications. In this chapter, nanoclusters include nanoparticles and nanowires, and we focus on the synthesis and catalytic application of noblemetal nanoclusters in mesoporous silicas.
  • Paresh L. Dhepe And Atsushi Fukuoka, Cellulose conversion under heterogeneous catalysis, ChemSusChem., 1, 969 - 975 (2008), DOI:10.1002/cssc.200800129.
    In view of current problems such as global warming, high oil prices, food crisis, stricter environmental laws, and other geopolitical scenarios surrounding the use of fossil feedstocks and edible resources, the efficient conversion of cellulose, a non-food biomass, into energy, fuels, and chemicals has received much attention. The application of heterogeneous catalysis could allow researchers to develop environmentally benign processes that lead to selective formation of value-added products from cellulose under relatively mild conditions. This minireview gives insight into the importance of biomass utilization, the current status of cellulose conversion, and further transformation of the primary products obtained.
  • Paresh L. Dhepe And Atsushi Fukuoka, Cracking of cellulose over supported metal catalysts, Catal. Surv. Asia., 11, 186 - 191 (2007), DOI:10.1007/s10563-007-9033-1.
    Cellulose is cracked over supported Pt or Ru catalysts under hydrogenolysis conditions in water to give sorbitol as a main product. Among the catalysts tested, Pt/g-Al2O3 gave the highest yield and selectivity, and this catalyst was recyclable in repeated runs. It is proposed that cellulose is hydrolyzed by in situ generated acid sites to form glucose, and glucose is immediately reduced to sorbitol over the metal catalyst.
  • Atsushi Fukuoka And Paresh L. Dhepe, Catalytic conversion of cellulose into sugar alcohols, Angew. Chem. Int. Ed., 45, 5161 - 5163 (2006), DOI:10.1002/ange.200601921.
    Pt or Ru catalysts supported on inorganic oxides show high activity for the conversion of cellulose into sugar alcohols (mainly sorbitol) in water under hydrogen pressure; furthermore, the catalysts can be recycled over repeated runs. Glucose is produced in low yields, thus suggesting that the Pt (or Ru)/oxide works as a bifunctional catalyst for the hydrolysis of cellulose and subsequent reduction to sugar alcohols.
  • Atsushi Fukuoka And Paresh L. Dhepe, Biorefinery with heterogeneous catalysts: hydrolysis of sugars, Stud. Surf. Sci. Tech., 172, 197 - 200 (2006).
    In the hydrolysis of starch to glucose, sulfonated mesoporous silicas showed higher activity than conventional ion-exchanged resins and sulfonated amorphous silica. We also found that supported Pt or Ru catalysts are able to convert cellulose into sugar alcohols(mainly sorbitol) under H2 pressure. Metal-free supports gave only glucose in low yields, thus showing that the Pt (or Ru)/oxide works as a bifunctional catalyst for the hydrolysis of cellulose by acids and the subsequent reduction of glucose by metals.
  • Paresh L. Dhepe, Masataka Ohashi, Shinji Inagaki, Masaru Ichikawa And Atsushi Fukuoka, Hydrolysis of sugars catalyzed by water-tolerant sulfonated mesoporous silicas, Catal. Lett., 102, 163 - 169 (2005), DOI:10.1007/s10562-005-5850-x.
    Mesoporous silicas are modified with sulfonic acid groups either by one-pot or by grafting method. In the hydrolysis of sucrose and starch, the sulfonated mesoporous silicas work as water-tolerant recyclable solid acid catalysts, showing higher conversion and turnover frequency than conventional Amberlyst-15, Nafion-silica and HZSM-5 catalysts.
  • Paresh L. Dhepe, Atsushi Fukuoka And Masaru Ichikawa, Preparation of highly dispersed RhPt alloy catalysts in mesoporous silica using supercritical carbon dioxide and selective synthesis of ethane in butane hydrogenolysis, Chem. Commun., , 590 - 591 (2003), DOI:10.1039/B211680D.
    RhPt alloy catalysts were prepared in mesoporous silica using supercritical carbon dioxide in impregnation to achieve high dispersion with controlled morphology; catalytic activity and ethane selectivity are enhanced in butane hydrogenolysis.