Dynamic Restructuring Induced Oxygen Activation on AgCu Near Surface Alloys.

Recent studies have shown that the addition of Cu to Ag catalysts improves their epoxidation performance by increasing the overall selectivity of the bimetallic catalyst. We have prepared AgCu near-surface alloys and used scanning tunneling microscopy to gain an atomistic picture of O-2 dissociation on the bimetallic system. These data reveal a higher dissociative sticking probability for O-2 on AgCu than on Ag(111), and density functional theory (DFT) confirms that the O-2 dissociation barrier is 0.17 eV lower on the alloy. Surprisingly, we find that, after a slow initial uptake of O-2, the sticking probability increases exponentially. Further DFT calculations indicate that surface oxygen reverses the segregation energy for AgCu, stabilizing Cu atoms in the Ag layer. These single Cu atoms in the Ag surface are found to significantly lower the O-2 dissociation barrier. Together, these results explain nonlinear effects in the activation of O-2 on this catalytically relevant surface alloy.