Novel synthesis of Ru/OMS catalyst by solvent-free method: Selective hydrogenation of levulinic acid to γ-valerolactone in aqueous medium and kinetic modelling

Abstract

γ-Valerolactone (GVL) is an important bio-derived molecule that could be used for the sustainable production of value-added chemicals and fuels. It is mainly synthesized by hydrogenation of levulinic acid by using supported ruthenium catalyst. Here we are reporting the synthesis of ruthenium supported on manganese oxide octahedral molecular sieve (OMS-2) catalyst prepared by different methods. Three different methods, i.e. reflux, hydrothermal and solventless protocols were used for the preparation of OMS-2. The prepared catalysts were used for the selective hydrogenation of biomass-derived levulinic acid (LA) to GVL using molecular hydrogen in water. Solventless synthesized OMS (OMS-2S) is energy efficient, rapid and economical way of synthesis. Among three different catalysts, Ru supported on solventless OMS-2 i.e. 1 wt% Ru/OMS-2S catalyst showed LA conversion of 99.9% and yield of 99.8% towards GVL in 1 h with the overall turnover frequency of 0.95 s−1 at mild conditions (100 °C, 30 atm H2). Different OMS-2 supported Ru catalysts showed a very high turnover frequency in comparison with those reported in literature for the synthesis of GVL. The specific textural and chemical properties of catalysts were characterized by various techniques. Moreover, 1 wt% Ru/OMS-2S catalyst was reusable up to four times without significant loss of activity and was very stable. By studying the effects of different process parameters, a kinetic model was developed based on LHHW type of mechanism. The apparent activation energy for LA hydrogenation to GVL is 11.75 kcal/mol.