Oxygen Species Enhanced Catalytic Efficiency of Au₁Ag_<i>x</i>/SiO₂ Catalysts for CO Oxidation

A series of Au₁Ag_<i>x</i> alloys (<i>x</i> = 0, 0.2, 0.3, 1.0, and 3.0) supported over SiO₂ has been prepared and pretreated via different atmospheric processes. The physical-chemical properties of these materials have been systematically characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible (UV-vis) spectroscopy, and transmission electron microscopy (TEM). The results reveal that oxygen species are doped into the alloy structure by the oxygen-involved pretreatment, leading to lattice expansion as well as a significant increase in catalytic activity. Improvement in the catalytic activity of Au₁Ag_0.3/SiO₂ through sequential reduction and oxidation pretreatment was evidenced by a decrease in the temperature of 100% CO conversion by approximately 500 K. A volcano trend in catalytic activity is found as the Ag composition is increased in the alloy structure. Density-functional theory (DFT) calculations suggest that the introduced oxygen species are likely present at the subsurface of the AuAg alloy and involved in the reaction or in modifying the electronic structure of surface Ag, thereby enhancing the catalytic activity for CO oxidation.