CuPd/Al2O3 single atom alloy catalyst facilitates the catalytic transfer hydrodeoxygenation of furfural to 2-methylfuran

Abstract

Alloying Cu-based catalysts by doping other metals at single atom level is an effective way to improve their hydrogenation performance of biomass-derived molecules. However, the application of Cu-based single atom alloy catalyst in the catalytic hydrogen transfer reaction system remains to be unrevealed. Here, we develop Al₂O₃ supported CuPd alloy catalysts, among which the single atom alloy catalyst with Pd dispersed in single atomic level on the surface was successfully obtained by controlling the metal amount, such as Cu₈Pd₁/Al₂O₃ with the Cu/Pd Molar ratio of 8: 1. The catalytic performance for furfural hydrodeoxygenation to 2-methylfuran of the CuPd/Al₂O₃ catalysts, using isopropanol as a hydrogen donor, shows a volcano-type relationship to the Cu/Pd ratio. The highest 2-methylfuran yield (81% at 220 °C) was achieved on the single atom alloy catalyst Cu₈Pd₁/Al₂O₃. The underlying reaction mechanism of furfural hydrodeoxidation on Cu₈Pd₁/Al₂O₃ was revealed by a series of isotopic labeling experiments, that the furfural was firstly hydrogenated to be furfuralcohol by a metal site-mediated catalytic transfer hydrogenation pathway, and then the furfuralcohol was converted to be 2-methylfuran by a Lewis acid-mediated furan ring activation route. The weak Lewis acid site that formed by single atom Pd alloyed with CuO matrix on Cu₈Pd₁/Al₂O₃ was proposed as the active site for the highly selective generation of 2-methylfuran.