Biobased green process: selective hydrogenation of 5-hydroxymethylfurfural to 2,5-dimethyl furan under mild conditions using Pd-Cs_2.5H_0.5PW₁₂O₄₀/K-10 clay

Abstract

Conversion of biomass into valuable chemicals is a highly sought process across the globe. 5-Hydroxymethyl furfural (HMF) is a biobased platform chemical that can be valorized into a spectrum of fuels and chemicals. In the current work, HMF was transformed into 2,5-dimethyl furan (2,5-DMF) using a number of catalysts among which a novel bifunctional metal-acid catalyst, Pd-Cs_2.5H_0.5PW₁₂O₄₀/K-10 clay, palladium–cesium dodeca-tungstophosphoric acid supported on K-10 acidic clay, was found to be the best. Because of its high energy density, 2,5-DMF is a potential biofuel additive. The acidic nature of Cs-DTP/K-10 facilitates rapid hydrogenolysis of HMF at mild reaction conditions. 2% Pd-20% w/w CsDTP/K-10 clay designated as 2Pd-20CsDTP/K-10 gives 98% conversion of HMF with 81% selectivity to 2,5-DMF at 90 °C and 10 atm hydrogen pressure in 2 h. The catalyst was prepared by a simple and cheap wet impregnation method and characterized, both before and after reuse, by XRD, FTIR, BET surface area, NH₃-TPD, TGA, TEM, and SEM. The catalyst was robust and could be used with very minimal loss of activity. The reaction mechanism and kinetics are also presented. The overall process is clean, green, and sustainable.