RuSn bimetallic catalysts for selective hydrogenation of levulinic acid to γ-valerolactone

Abstract

Carbon-supported ruthenium catalysts containing different amounts of tin were studied for the hydrogenation of levulinic acid (LA) to gamma-valerolactone (GVL) in a 2-sec-butyl-phenol (SBP) solvent. Results from reaction kinetics measurements (453K and 35bar H2) showed that the Ru/C catalyst was initially more active for hydrogenation of both LA and SBP (i.e., 0.051s−1 for conversion of LA to GVL), followed by continuous deactivation versus time on stream. In contrast, the catalyst containing equal amounts of Ru and Sn had a lower activity for LA to GVL conversion (0.005s−1), but displayed stable activity versus time on stream and showed 100% selectivity for hydrogenation of LA versus the SBP solvent. Increasing the amount of Sn to a 1 to 4 Ru:Sn atomic ratio creates an additional phase, β-Sn, that is not active for hydrogenation, leaches into the SBP solvent, and sinters under reaction conditions. Results from CO and O2 chemisorption and electron microscopy measurements indicated that the Ru-based metal particles did not leach or sinter at reaction conditions, and that the surfaces of these particles became progressively enriched with Sn as the Sn-loading increases. In addition, Sn did not significantly leach from the catalysts when present as an intermetallic alloy with Ru, such as Ru2Sn3 and Ru3Sn7. Using LA produced from corn stover, the RuSn4/C catalyst was stable and demonstrated that it is a promising catalyst to produce valuable chemicals and fuels from real biomass.