Liquid phase hydrogenation of furfural under mild conditions over Pd/C catalysts of various acidity

Abstract

The hydrogenation of furfural (FU) under mild conditions (isopropyl alcohol, 35 °C, 6 bar) was studied over 2 wt% Pd supported on non-treated (Pd/C) and SO3H-modified carbon supports. The catalysts of similar metal particles size (5–6 nm) were prepared by the colloid-based microemulsion method. The products of the Pd-catalyzed FU hydrogenation as well as the acid-sites catalyzed reactions of FU acetalization and etherification were formed. The SO3H groups in the carbon supports influence reactivity of the Pd-sites due to the Pd-electron deficient species formation manifested by the enhanced promotion of furan ring hydrogenation producing tetrahydrofurfuryl alcohol and 2-methyltetrahydrofuran. Furfural diisopropyl acetal was formed even over the Pd/C catalyst of very low acid capacity and acetalization reaction was enhanced over the catalysts with SO3H groups. The furfural diisopropyl acetal content slowly decreased with furfural conversion, assisted by the growth of furfuryl isopropyl ether content. The capacity of acid sites did not strongly affect the process of ether formation evidenced by similar selectivity (10–15%) over all studied catalysts.