Theoretical Investigation of the Heterojunction Effect on the Catalytic Activity and Selectivity of an Au@NiO Core-Shell Catalyst in Aerobic Oxidation

Numerous experimental reports have addressed the advantages of the Au@NiO core-shell catalyst in the synthesis of methyl methacrylate. However, its high activity toward the oxidation of 1-methoxy-2 methylprop-2-en-1-ol and its inability to be oxidized to MeOH has not been elucidated. Herein, the direct oxidative esterification by an Au@NiO core-shell catalyst was studied using density functional theory calculations. Accordingly, particular attention was given to the stabilities of the adsorbed species, activation barrier, and intermediates; furthermore, the role of the highly oxidized NiO was elucidated, which has been regarded as essential for the reaction. The results showed that the active oxygen species in the oxidized NiO, such as O-2, OOH, and OH, were stabilized on the NiO bonded to the Au. These stabilized species improved the activity and selectivity of the reaction. Furthermore, the Ni vacancy in the subsurface generates a strong basic site on the surface of the catalyst, which traps the substrate and diminishes the activation barrier.