Defect-Mediated Gold Substitution Doping in ZnO Mesocrystals and Catalysis in CO Oxidation

Highly dispersed supported gold with strong metal-support interaction is a desirable material for heterogeneous catalysis. Unlike current dispersion strategies of depositing gold from solution to support, we report herein a new method of producing highly dispersed gold clusters on ZnO mesocrystal. The gold clusters appeared on defect-rich twin-brush ZnO mesocrystals (TB-ZnO) via an in-and-out process: (i) a mixed Au/Zn oxide was formed first after deposition-precipitation of Au with AuCl₄^-, (ii) fine Au clusters grow from the underneath to the surface of the oxide after heating. The TB-ZnO behaved like a sponge allowing gold atoms to heavily disperse into the wurtzite structure of ZnO with Zn-substitution by gold. After mild thermal treatment, the embedded gold emerged from underneath of the ZnO support to form highly dispersed Au nanoparticles of ∼2 nm on the ZnO surface. DFT calculation shows energetically favored Au-doping in TB-ZnO and facile defect-mediated migration of Au in it. The material (Au/TB-ZnO) gave outstanding activities for the catalysis of CO oxidation. The use of mesocrystals of metal oxide as supports, with rich vacancy defects, provides a new route for preparing highly dispersed and active supported metal catalysts.