Enhanced reducibility of well-defined Cr oxide nanostructures on Au(111) through Zn doping

Abstract

Mixed oxides play important roles in many heterogeneous catalytic processes, and understanding of interaction between different oxide components is crucial for synthesizing the catalysts with high performances. Here, we introduce trace of metallic Zn species into well-defined chromium oxide (Cr oxide) nanostructures grown on Au(111) including CrO2-bilayer nanoislands and Cr2O7dinuclear clusters and study the impact of the dopant on reducibility of the Cr oxides. Combining low-temperature scanning tunneling microscopy (LT-STM) and X-ray photoelectron spectroscopy (XPS), we demonstrate that incorporation of 2.5 at.% Zn can lower the initial reduction temperature of Cr oxides by 70–160 K upon heating in ultrahigh vacuum. The reduction degree of Zn-doped Cr oxide is much larger than the pure oxide at the same heating temperature. Density functional theory (DFT) calculations reveal that the enhanced reducibility of the pristine oxide via introduction of Zn dopant mainly comes from the promoted activity of oxygen atoms due to Zn substitution of surface Cr.