Application of Mesoporous Metal Oxide Immobilized Gold–Palladium Nanoalloys as Catalysts for Ethanol Oxidation

Abstract

Gold–palladium nanoalloys (AuPd) were synthesized by a dendrimer templating method and the as-prepared nanoalloys were immobilized on several reducible mesoporous metal oxides (MMOs). The MMOs of MnO2, Co3O4 and CeO2 exhibited low catalytic activity in gas-phase oxidation of ethanol. Upon immobilization of the AuPd nanoalloys the activity increased significantly, with high acetaldehyde selectivity at 120 °C. However, this activity increase from pure MMOs to AuPd/MMOs was accompanied by decrease in selectivity to acetaldehyde. One other interesting observation lies on the amount of gold in the nanoalloy. Increasing the ratio of Au:Pd in the nanoalloy from 1:1 to 10:1 lowered the activity by a factor of six but had a positive effect on selectivity. From this, we postulate dissociation absorption of molecular oxygen to the reactive oxides occurs more effectively on the Pd metal surface. With higher Au loading, the acetaldehyde selectivity remained above 90% even at higher reaction temperatures of 160 °C. This led to a postulation of quick desorption of acetaldehyde from the Au surface more than it does on the Pd surface.