Steering photocatalytic selectivity of Au/γ-Al2O3 for benzyl alcohol oxidation via direct photoexcitation

Nanometal photocatalysts are widely used for accelerating reactions and adjusting the selectivity of multipath reactions by energetic electrons activating specific adsorbates. However, the effect of excited charge carriers on the adsorption strength of reactant molecules has been overlooked. Herein, we demonstrate that light irradiation alters the selectivity of aerobic oxidation of benzyl alcohol over Au/& gamma;-Al2O3 by changing the main product from benzaldehyde in dark to benzoic acid under light. It was found that the competitive adsorption of benzyl alcohol and benzaldehyde plays a crucial role in selectivity. Energetic electrons arising from ultraviolet excitation are directly injected into the metal-adsorbate antibonding orbital to weaken the adsorption strength of benzyl alcohol. The resulted d band holes facilitate more benzaldehyde adsorbed on the surface of Au nanoparticles (NPs), which are further oxidized to benzoic acid. This work proposes a new understanding of nanometal photocatalysis and a feasible approach to adjust the catalytic performance by optically excited charge carriers modulating the adsorption strength of adsorbates.