@article {46411, title = {Altering the O/C ratio of lignin derived monomers without sacrificing atom efficiency}, journal = {ChemistrySelect}, volume = {4}, year = {2019}, month = {DEC}, pages = {14050-14055}, type = {Article}, abstract = {

Synthesis of platform and fuel grade chemicals from lignin without losing atom efficiency and lowering O/C ratio is a challenge in a bio-refinery concept. In this work, we report solid acid catalysed alkylation of lignin derived variety of monomers such as guaiacol, veretrole, phenol, anisole, and catechol using numerous alcohols as alkylating agents. Results elaborate that the type of acidity and structure of catalyst play important role in achieving higher dialkylated products (DAP). With 85\% conversion of guaiacol, 30.9\% DAP formation was achieved at 250 degrees C within 2 h. A unique substrate adsorption study on the catalyst surface and effect of solubility of substrates on the activity of catalyst is evaluated. Catalyst was observed to be recyclable with marginal loss in the activity due to handling error.

}, keywords = {Alcohols, Alkylation, lignin, Monomers, solid acid catalyst, Up-gradation}, issn = {2365-6549}, doi = {10.1002/slct.201903320}, author = {Singh, Dheerendra and Dhepe, Paresh L.} } @article {46424, title = {Formic-acid-induced using recyclable-ionic liquids as catalysts for lignin conversion into aromatic co-products}, journal = {Waste and Biomass Valorization}, year = {2019}, month = {NOV}, type = {Article; Early Access}, abstract = {

Lignin has been widely named as a sustainable and renewable bioresource of energy, fuels, chemicals and materials, particularly phenolic chemicals production on Earth. These bio-derived compounds are in great potential need of biorefinery to valorize complete plant biomass. Lignin depolymerization showed a great promise approach to convert into low molecular aromatic products. In this report, high molecular weight (54,000 Da) lignin depolymerization into maximum yields (87\%), (\>= 95 +/- 6\% mass balance) using a formic acid along with dual (-SO3H) functionalized imidazole-based recyclable (4 times) Bronsted acidic ionic liquids (BAILs) as catalysts have been investigated in H2O-CH3OH (1:5, v/v) at 120 degrees C for 1 h. The structural correlations between the lignin and aromatic products were studied by bulk (CHNS, GPC, etc.) and molecular (UV-Vis, FT-IR, NMR (1D/2D) levels experimental techniques. Additionally, the identification of aromatic products was carried out by applying HPLC, GC and GC-MS techniques. Graphic Addition of a formic acid into Bronsted acidic ionic liquids improved the catalytic efficiency significantly for lignin depolymerization into 87\% low molecular weight aromatic products. [GRAPHICS] .

}, keywords = {Bulk and molecular levels analysis, depolymerization, Dual functionalized ionic liquids, Formic acid, lignin}, issn = {1877-2641}, doi = {10.1007/s12649-019-00896-3}, author = {Singh, Sandip K. and Dhepe, Paresh L.} } @article {46306, title = {Understanding the influence of alumina supported ruthenium catalysts synthesis and reaction parameters on the hydrodeoxygenation of lignin derived monomers}, journal = {Molecular Catalysis}, volume = {480}, year = {2020}, month = {JAN}, pages = {UNSP 110525}, type = {Article}, abstract = {

Up-gradation of lignin derived monomers to value-added and fuel grade products is important to make overall bio-refinery process economical. Although, few studies are devoted on this work yet, systematic study on commercially viable (low loading of metal, recyclable catalyst, mild conditions, high selectivities etc.) is scarce and typically done under harsh conditions. Herein, we report, the methodical effect of support (SiO2, Al2O3 (acidic, basic and neutral), SiO2-Al2O3) on the hydrodeoxygenation (HDO) of lignin derived various monomers, guaiacol, veretrol, eugenol, phenol using very low loading (0.5 wt\%) Ru catalyst. Very high yield (82\%) of cyclohexanol from guaiacol could be achieved in presence of cyclohexane as a solvent and Ru/Al2O3-Acidic catalyst at 225 degrees C and under 1 MPa H-2 pressure. The detailed study on the effect of solvent, stability and adsorption of reactant \& products etc. is done and it was observed that products are more prone to adsorb and undergo further reactions. The complete characterization of fresh and spent catalysts revealed that lower catalyst reduction temperature and presence of Ru in partially higher oxidation state proved by XPS, helps in enhancing the cyclohexanol formation. Subsequently, role of Ru particle size and support on the activity was also investigated.

}, keywords = {Cyclohexanol, Hydrodeoxygenation, lignin, reaction pathway, supported metal catalyst}, issn = {2468-8231}, doi = {10.1016/j.mcat.2019.110525}, author = {Singh, Dheerendra and Dhepe, Paresh L.} } @article {47109, title = {Efficient catalytic transfer hydrogenation-hydrodeoxygenation of lignin derived monomers: investigating catalyst properties-activity correlation}, journal = {Catalysis Communications}, volume = {149}, year = {2021}, month = {JAN }, pages = {106220}, type = {Article}, abstract = {

Reduction of O/C ratio of lignin derived monomers via hydrodeoxygenation (HDO) pathway is conventionally furnished using molecular hydrogen under severe conditions. Nonetheless, due to a prerequisite to accomplish HDO through commercially attractive methodology we report, HDO reactions of various phenolic compounds via catalytic transfer hydrogenation (CTH) pathway using very low loading of Ru (0.5 wt\%) on neutral and acidic Al2O3 under nitrogen atmosphere. With guaiacol as a substrate, 74\% cyclohexanol yield at 225 degrees C in the presence of IPA is realized. Bi-functionality of metal state, acidity of support and nature of alcohol are perceived to be responsible for the variation in activity.

}, keywords = {Catalytic transfer hydrogenation (CTH), Cyclohexanol, Hydrodeoxygenation, lignin, Supported metal catalysts}, issn = {1566-7367}, doi = {10.1016/j.catcom.2020.106220}, author = {Singh, Dheerendra and Dhepe, Paresh L.} } @article {47679, title = {Upgrading lignin derived monomers over basic supported metal catalysts}, journal = {Fuel}, volume = {306}, year = {2021}, month = {DEC}, pages = {121588}, type = {Article}, abstract = {Catalytic upgradation of aromatic monomers derived from lignin depolymerization is of high interest for the production of sustainable fuels and chemicals. Basic support has potential to provide advantages of better substrate-support interaction and reduced coke formation. Hence, we report the effect of various basic supports for metal catalysts (Pt, Pd, Ru) on the upgradation of phenol, guaiacol and eugenol. The complete hydrogenation product is achieved due to the strong interaction of the substrate with catalyst. Phenol is converted (55\%) into cyclohexanol (49\% yield) with low loading of Pt catalyst (1 wt\%), supported by the higher TON of 1 wt\% Pt/NaX (TON = 14844) than 3 wt\% Pt/NaX (TON = 5128). Effect of basic support with moderate (NaX) and strong (CHT) basic strengths are corelated for the higher cyclohexanone formation. Presence of strong basic sites and higher TON of 3 wt\% C-HT (TON = 6806) directs the significant substrate-support interaction. Catalytic activity and recyclability are supported by the comparable performance of recycle runs and characterizations of the fresh and spent catalysts.}, keywords = {aromatic monomers, Hydrogenation, lignin, Solid bases, supported metal catalyst, Upgradation}, issn = {0016-2361}, doi = {10.1016/j.fuel.2021.121588}, author = {Chaudhary, Richa and Dhepe, Paresh L.} } @article {48005, title = {Alpha-, beta- and gamma-cellulose quantification and two-stage concentrated-dilute acid lignin recovery from three rice husks: lignin characterization and depolymerization}, journal = {Waste and Biomass Valorization}, volume = {13}, year = {2022}, month = {JUN}, pages = {2963-2977}, type = {Article}, abstract = {

Investigations on the compositional analysis of lignocellulosic materials and their properties upon recovery are essential to be studied in order to examine the effects of recovery method, their dependency on the substrate, etc. In this work, three rice husks (RHs) samples were subjected for alpha-, beta- and gamma-cellulose, pentosan, and silica quantifications. Correlations between the source of biomass, lignin recovery by two-stage concentrated and dilute sulphuric acid treatment, their properties and their depolymerization into low molecular mass aromatic fractions using homogeneous and heterogeneous Bronsted acidic ionic liquids as catalysts, is carried out. Correlation between the properties of RHs and recovered lignin were performed using destructive (CHNS, TGA, ICP-OES, etc.) and non-destructive (XRD, UV-Visible, FT-IR, and C-13 CP-MAS NMR) analytical techniques. It was observed that the recovered lignin was polysaccharides free and associated with dibenzodioxocin, spirodienone, and tricin type moieties with variable intensities. The effects of lignin structures showed a change of depolymerisation product pattern. [GRAPHICS] .

}, keywords = {Holocellulose, Homogeneous and heterogeneous catalysts, lignin, Rice husks}, issn = {1877-2641}, doi = {10.1007/s12649-022-01704-1}, author = {Singh, Sandip K. and Dhepe, Paresh L.} } @article {49797, title = {Continuous flow hydrodeoxygenation of lignin-derived guaiacol to cyclohexanol over durable Al2O3 hollow fiber supported co catalyst}, journal = {ChemCatChem}, volume = {17}, year = {2025}, month = {SEP}, type = {Article}, abstract = {

The drive to decarbonize the chemical, oil, and gas industries through use of bio-derived resources is intensifying. This study focuses on converting lignin-derived phenolic compounds into cyclohexanol, a precursor for adipic acid production. The alumina hollow fiber supported cobalt catalyst (5Co/AHF@capillary) prepared by capillary action method was found to consist cobalt in both metallic and +delta oxidation states. Initial tests in a batch-mode reactor showed promising results, with 5Co/AHF@capillary catalyst demonstrating catalytic activity comparable to Ru/Al2O3 systems (225 degrees C, 1 MPa H-2, 4 h), achieving similar to 86\% cyclohexanol yield in guaiacol hydrodeoxygenation reactions. The catalytic system was then adapted for continuous flow reactors under milder conditions (300 degrees C, 2.5 MPa H-2, 18 mL min(-1)), resulting in 83\% guaiacol conversion and 74\% cyclohexanol yield. The durability of the catalyst was checked for \>80 h and results claim that catalyst was active in yielding consistent results. The roles of catalyst preparation method, hydrogen pressure, solvent, WHSV were thoroughly checked and discussed.

}, keywords = {biomass valorization, Carbon, Co/Al2O3, Cyclohexanol, lignin}, issn = {1867-3880}, doi = {10.1002/cctc.202500656}, author = {Singh, Dheerendra and Jogdand, Shunottara M. and Devi, R. Nandini and Dhepe, Paresh L.} }