Characterizing the copper-based catalyst for the oxygen-assisted water-gas shift reaction at a sub-nano scale.

To obtain insight into the structure and surface stoichiometry of copper-based catalysts in commercially important chemical reactions such as the oxygen-assisted water-gas shift reaction, we perform density-functional theory calculations to investigate the stability of oxide surfaces. Taking into account the pressure and temperature through the framework of \textit{ab initio} thermodynamics [1,2] our earlier investigation found that for the conditions relevant to technical catalysis, the bulk oxide is energetically most favourable. Using the same technique, we examine the relative stability of low-index copper oxide surfaces [3], and identify two low energy surface structures that are most stable under such conditions which could be catalytically relevant. These oxide surface structures are found to be non-stoichiometric (with surface defects) and exhibit a metallic character. \\ $[1]$ A. Soon, M. Todorova, B. Delley and C. Stampfl, \textit{Phys. Rev. B} \textbf{73}, 165424 (2006) \\ $[2]$ C. Stampfl, \textit{Catal. Today} \textbf{105}, 17 (2005). \\ $[3]$ A. Soon, M. Todorova, B. Delley and C. Stampfl, submitted to \textit{Phys. Rev. B}.