Gold Nanoparticles for Oxidation Reactions: Critical Role of Supports and Au Particle Size

Supported gold nanoparticles (Au NPs) exhibit unique catalytic properties for the oxidation of organic compounds. The catalytic activities and the selectivities of the supported Au catalysts largely depend on the kind of support and the particle size of Au. For oxidation of alcohols to aldehydes and ketones, the reducibility of metal oxide (MO_x) supports plays a prominent role, while the basicity of the supports or the size of Au particles are more important factors for non-reducible MO_x, non-oxides, and other supports. The size effect is more pronounced for dehydrogenation than aerobic oxidation because dehydrogenation takes place mainly on the low-coordinated edge and corner Au atoms. Oxidation of alkenes to epoxides using O₂ as a sole oxidant has been achieved by supported Au clusters having a diameter of 2 nm or less. For oxidation of cyclohexane using O₂ as a sole oxidant, the presence of Brønsted acid sites contributes to the production of K/A oil. The size of Au particles also largely affects the reaction rate and product selectivity; sub-nanometer Au clusters exhibited significantly higher catalytic activity and K/A oil selectivity than Au NPs.