Debdut Roy

Development of simple and reliable protocols for the immobilization of catalytically active metal nanoparticles is an important aspect of the nanomaterials field. Amine groups bind very strongly to platinum and palladium nanoparticles; therefore, we have attempted to entrap aqueous platinum and palladium nanoparticles on the surface of micron-sized zeolite particles functionalized with amine groups. In this paper, we demonstrate that platinum and palladium nanoparticles bound at high surface coverage on 3-aminopropyltrimethoxysilane (APTS)-functionalized Na−Y zeolites are excellent heterogeneous catalysts for hydrogenation and Heck reactions. The assembly of platinum or palladium nanoparticles on the zeolite surface occurs via an interaction with the amine groups present in APTS leading to a new class of catalyst. The synthesized catalysts were well-characterized by UV−vis, FTIR, TGA, XRD, XPS, and TEM. TEM images of the fresh and used catalysts indeed show that the platinum and palladium nanoparticles supported on amine-functionalized zeolites remain unchanged at the end of the reactions. The rate of hydrogenation and Heck reactions over these catalysts was much higher than those obtained using conventionally prepared catalysts.

Cu based catalysts with a base promoter are reported for the first time for the synthesis of lactic acid from glycerol without using either a reductant or an oxidant. The catalytic route presented here gives high yields at lower temperatures (473 K) and lower molar NaOH/glycerol ratios (1.5) compared to the known hydrothermal (553−573 K) route. Further, the Cu2O catalyst shows excellent recyclability.

The kinetics of the aqueous-phase hydrogenolysis of glycerol to 1,2-propanediol (1,2-PDO) was studied using a bimetallic Ru−Re/C catalyst in a slurry reactor in a temperature range of 493−513 K and a hydrogen pressure of 2.4−9.6 MPa. Glycerol hydrogenolysis to produce 1,2-PDO via C−O cleavage (i) proceeds with parallel C−C cleavage, reforming, water-gas shift, and Fischer−Tropsch reactions, (ii) results in a very complex reaction network with several gaseous- and liquid-phase products, and (iii) poses a challenge to design selective catalysts. It is observed that Ru−Re bimetallic catalyst shows higher hydrogenolysis activity (glycerol conversion of X = 57.7%) and 1,2-PDO selectivity (S = 36.6%), compared to the monometallic Ru catalyst (X = 52.1%; S = 18.9%) but the monometallic Re catalyst showed no catalytic activity for the reaction. Stirred-batch reactor data on the transient concentrations of reactants and products in both the gas and liquid phases were obtained using a bimetallic Ru−Re/C catalyst under different conditions to understand the reaction pathways, selectivity behavior, and intrinsic kinetics of the different reaction steps. For kinetic modeling, several experiments were performed at different initial pressures of hydrogen, catalyst concentration, and temperatures. The proposed rate equations, along with the regressed kinetic and activation energy parameters, were found to represent the experimental data for the multistep hydrogenolysis reaction very satisfactorily.

Conversion of renewable biopolyols to value-added chemicals such as lactic acid and glycols usually demands excess hydrogen/oxygen or harsh reaction conditions in strong alkaline medium (220–350 °C). This unfortunately promotes significant side reactions resulting in low carbon selectivity to liquid products, posing significant challenges for the development of sustainable technologies. We report here a new atom economical catalytic conversion of various biopolyols (glycerol, xylitol, mannitol, and sorbitol) to lactic acid with glycols and linear alcohols as co-products at much lower temperatures (115–160 °C) without external addition of either hydrogen or oxygen. Among various metal-based catalysts (Pt, Pd, Rh, Ru, Raney Ni, Raney Co, and Cu) evaluated, Pt/C catalyst gives the highest chemoselectivity (S > 95%) for lactic acid, glycols, and linear alcohols at 115–160 °C. An important finding is that approximately two-thirds of the hydrogen generated in situ via dehydrogenation of polyols over Pt/C catalyst is efficiently utilized for the conversion of the remaining polyols and intermediates to useful products (e.g., glycols and linear alcohols instead of gaseous products) with the remaining available hydrogen for use elsewhere in a biorefinery. The Pt/C catalyst is thus multifunctional facilitating tandem dehydrogenation/hydrogenolysis of polyols. Furthermore, it is observed that Ba2+ alkali ion promotes the activity of the Pt/C catalyst by almost 12-fold compared to other alkali promoters such as NaOH, KOH, and Ca(OH)2. In addition to being the first reported study on the conversion of C5∼C6 polyols (e.g., xylitol and sorbitol) to lactic acid at relatively low temperatures, the results also provide new insights into the mechanism of tandem catalysis of biopolyols conversion to value-added commodity chemicals.