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 NiOx was
elucidated, which has been regarded as essential for the reaction.
The results showed that the active oxygen species in the oxidized
NiOx, such as O2, 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.