Theoretical investigation of CO oxidation on AuAg (110) alloy surface.

Carbon monoxide (CO) oxidation on the gold-silver (110) binary alloy surface has been investigated by using density functional theory. For clean metal (110) surface, it was found that CO prefers to adsorb on atop and short bridge site of Au(110) surface [1] and O$_{2}$ prefers to adsorb on fourfold hollow (FFH) site of Ag(110) surface [2]. In this work, we present the results of CO, O$_{2}$ adsorption, and CO+O$_{2}$ coadsorption on AuAg(110) surface. The results indicate that the adsorption energies are mainly determined by the type of atoms on the bonding site. For CO, adsorption on Au atop and Au$_{2}$ short bridge site are favored and have an adsorption energy range of 0.43$\sim $0.63 eV. For O$_{2}$, adsorption on FFH site with Au$_{5-n}$Ag$_{n}$ (n$\mathbin{\lower.3ex\hbox{$\buildrel>\over {\smash{\scriptstyle=}\vphantom{_x}}$}} $3) configuration is possible and has an adsorption energy range of 0.12$\sim $0.53 eV. For CO+O$_{2}$ coadsorption, the coadsorption energy on Au$_{5-n}$Ag$_{n}$ (n$\mathbin{\lower.3ex\hbox{$\buildrel>\over {\smash{\scriptstyle=}\vphantom{_x}}$}} $3) FFH site is slightly less than the sum of CO and O$_{2}$ adsorption energy by only 0.05$\sim $0.1 eV. The oxidation of adsorbed CO with O$_{2}$ is found to proceed via formation of an intermediate, OCOO, and has a surprising low energy barrier of 0.2$\sim $0.3 eV. [1] Tatyana E. Shubina, Christoph Hartnig and Marc T. M. Koper, Phys. Chem. Chem. Phys. 6, 4215,(2004) [2] P. A. Gravil and D. M. Bird, Phys. Rev. Lett. 77, 3993(1996)