Defective Mesocrystal ZnO-Supported Gold Catalysts: Facilitating CO Oxidation via Vacancy Defects in ZnO

Abstract

We present a strategy to prepare a highly active Au/ZnO catalyst for CO oxidation by introducing abundant Zn- and O-vacancy defects into a ZnO support of mesocrystal form. Two different ZnO supports were chosen for comparison; almost defect-free ZnO nanorods (NR-ZnO) and twin-brush-like ZnO mesocrystals (TB-ZnO) with rich Zn/O-vacancy defects gave Au/NR-ZnO and Au/TB-ZnO upon deposition of gold nanoparticles. The catalytic test of CO oxidation over Au/TB-ZnO catalyst showed an enhanced catalytic activity that was 153 times greater than the activity of Au/NR-ZnO. The dramatic enhancement in CO oxidation is attributed to a room-temperature Mars–van Krevelen (MvK) mechanism on the surface of the Au/TB-ZnO catalyst, which was promoted by extensive vacancy defects in TB-ZnO. To elucidate the increase in activity, the vacancy ratio (i.e., [VO•]/[VZn•]) of TB-ZnO was systematically modulated by adjusting calcination conditions. The defective ZnO support altered the tendency in the variation of size, valence stat...