Dynamic transformation between bilayer islands and dinuclear clusters of Cr oxide on Au(111) through environment and interface effects

Abstract

Dynamic control of oxide nanostructures is crucial for the design of advanced oxide catalysts, which is also significant for understanding the active site and reaction mechanism in oxide catalysis. Here, we demonstrate reversible dynamic conversion between Cr oxide (CrOx) nanoislands with the same thickness and CrOx clusters with identical size supported on an Au(111) surface under different redox treatments. The CrOx nanoislands feature a CrO2 bilayer (BL) structure consisting of two Cr2O3 monolayers bridged by one layer of O, and the CrOx clusters have a Cr2O7 stoichiometry. Oxidation treatment in O3 can disperse the CrO2 BL nanoislands into the Cr2O7 dinuclear clusters, which can be dynamically converted back to the CrO2 BL by annealing in ultrahigh vacuum. Surface science experiments and theoretical simulations reveal that both surface oxygen atoms dissociated from O3 and the confinement effect of the Au substrate play important roles in formation of the Cr2O7 dinuclear clusters. This study suggests that oxide nanocatalysts with controlled size and structure can be stabilized by the specific environment and the oxide–metal interface.