Aerobic Oxidation of Alcohols over Isolated Single Au Atoms Supported on CeO₂ Nanorods: Catalysis of Interfacial [O–Ov–Ce–O–Au] Sites

Abstract

The oxidation of alcohols is a kind of very important reaction in industry and has caused great concern in recent years, especially with molecular oxygen as the oxidant. Among various catalysts reported in the literature, Au/CeO2 exhibits excellent catalytic performance in the oxidation of alcohols, with aldehydes as the target product. However, there is still not a clear consensus regarding the nature of the active sites of Au/CeO2 related catalysts. In this contribution, three distinctly different Au species supported on CeO2 nanorods (CeO2-NR) were prepared (viz., isolated single Au atoms (Au-SA), Au nanoclusters (Au-NC), and Au nanoparticles (Au-NP)); their catalytic performances in the aerobic oxidation of alcohols was comparatively investigated in order to discriminate the active sites in Au/CeO2. A series of characterization results combining with DFT calculation illustrates that the performance of Au/CeO2 catalysts in alcohol oxidation is closely related to the size of Au species and the concentration of oxygen vacancies (Ov), where the interfacial [O–Ov–Ce–O–Au] sites between Au species and CeO2 support play an important role in catalyzing the alcohol oxidation. The oxygen vacancies in CeO2 facilitate the adsorption of alcohol and the dissociation of the O–H bond, whereas the adjacent Au3+/Au+ species can promote the elimination of β-hydride in the alkoxide intermediate. As the Au-SA/CeO2-NR catalyst is provided with abundant active [O–Ov–Ce–O–Au] sites, it exhibits much higher activity in the oxidation of alcohols, in comparison with Au-NC/CeO2-NR and Au-NP/CeO2-NR. The insight shown in this work should be helpful in understanding the catalysis of interfacial sites between metal and an oxide support and developing better catalysts for the oxidation of alcohols.