Selective Hydrogenation of Cinnamaldehyde to Cinnamyl Alcohol over Au Catalysts: Influence of the Oxide-Supports

Abstract

Uniform Au particles with a mean size of 1.9 nm were initially synthesized with polyvinyl alcohol (PVA) as protecting agent, and then deposited on MgO, Al₂O₃, TiO₂, Fe₂O₃, Co₃O₄, ZnO and In₂O₃. After calcinations at 300 °C in air to remove PVA, Au particles were highly dispersed and immobilized on all the supports, displaying narrow diameter distributions and almost identical mean sizes of 2.5–3.2 nm. The Au-oxides catalysts were further used to catalyze selective hydrogenation of cinnamaldehyde (CAL) to cinnamyl alcohol (COL). It was found that the selectivity of COL was tightly related to the acidity/basicity of the Au/oxides catalysts. The catalyst with only acidic sites such as the Au/Al₂O₃ catalyst gave very low selectivity of COL of 15%. The catalysts with only basic sites such as Au/MgO catalyst displayed medium selectivity of COL of 52%. Interesting, the Au catalysts with both acidic and basic sites such as the Au/In₂O₃ and Au/ZnO catalyts exhibited the highest selectivity of COL of around 86%. The synergistic cooperation of acidic sites and basic sites should be responsible for preferential adsorption and activation of the C=O group than C=C group in CAL, and then preferential hydrogenation of C=O to COL.

Graphical Abstract