Composition and structure of the ${\mathrm{RuO}}_2\mathrm{}\left(110\right)\mathrm{}$ surface in an ${\mathrm{O}}_2$ and CO environment: Implications for the catalytic formation of ${\mathrm{CO}}_2$

The phase diagram of surface structures for the model catalyst ${\mathrm{RuO}}_2\mathrm{}\left(110\right)\mathrm{}$ in contact with a gas environment of ${\mathrm{O}}_2$ and CO is calculated by density-functional theory and atomistic thermodynamics. Adsorption of the reactants is found to depend crucially on temperature and partial pressures in the gas phase. Assuming that a catalyst surface under steady-state operation conditions is close to a constrained thermodynamic equilibrium, we are able to rationalize a number of experimental findings on the CO oxidation over ${\mathrm{RuO}}_2\mathrm{}\left(110\right).$ We also calculated reaction pathways and energy barriers. Based on the various results the importance of phase coexistence conditions is emphasized as these will lead to an enhanced dynamics at the catalyst surface. Such conditions may actuate an additional, kinetically controlled reaction mechanism on ${\mathrm{RuO}}_2\mathrm{}\left(110\right).$