Carbon monoxide (CO) oxidation has attracted much interest in recent years due to its important applications in many technologies such as car-exhaust emission control and relative simplicity. CO oxidation on Ag(111) surface has been reported experimentally via chemisorbed oxygen molecules [1,2]. At high pressures and elevated temperatures, where subsurface oxygen were present, it has been suggest that CO react with subsurface oxygen.[3,4] To understand the mechanisms behind, we perform density functional theory calculations of CO oxidation on Ag(111). For clean surface, it is found that both of CO and atomic oxygen bind weakly to the surface and CO oxidation barrier is calculated to be 0.19 eV. O2 dissociation barrier is 0.94 eV, and is therefore rate limiting step. With presence of the subsurface oxygen, silver surfaces is activated, and adsorption of CO, oxygen atom and oxygen molecule are stabilized pronouncedly. Nevertheless, CO oxidation with atomic oxygen is unlikely because dissociation barrier of oxygen molecules, 0.83 eV, is still considerably high. CO oxidation with the subsurface oxygen is prevented too due to significant barrier of emerging of oxygen from the subsurface region. However, our calculations show that, in the activated surfaces, adsorbed carbon monoxides and oxygen molecules can form a meta-stable four center O-O-CO intermediate with a small barrier, 0.23 eV, which will eventually decomposes further into carbon dioxide and atomic oxygen.
References: [1] Burghaus, U.; Conrad, H. Surf. Sci. 1996, 364, 109. [2] Barth, J. V.; Zambelli, T. Surf. Sci. 2002, 513, 359. [3] Qu, Z. -P.; Cheng, M. -J.; Huang, W. -X.; Bao, X. -H. J. Catal. 2005, 229, 446. [4] Andre C. van Veen, O. Hinrichsen.; M. Muhler. J. Catal. 2002, 210, 53.
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