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The adsorption and reaction of oxygen and carbon monoxide molecules on RuO2 (110) surface have been investigated using density functional theory (DFT) with cluster model and periodic slab model. The stoichiometric surface exposes two types of coordinatively unsaturated atoms: bridging oxygens (Obr) and one-fold (1f) undercoordinated Ru atoms (Rucus-1f), while at the reduced surface the Obr atoms are removed, two-fold (2f) undercoordinated Ru atoms (Rucus-2f) are exposed. The adsorption of gaseous O2 leads to the formation of two additional surface species: a molecularly chemisorbed state with one of the oxygen atom dangled (1η-O2) and Otop atoms in terminal position above the Rucus-1f atoms. The binding energies and geometries of various oxygen species on RuO2 (110) surface, Otop, Obr and 1η-O2, have been calculated by both computational models. Furthermore, the CO oxidation by various oxygen species on RuO2 (110) surface were also investigated by both methods. Our results indicate that the CO oxidation by 1η-O2 has the lowest reaction barrier. Moreover, the CO oxidation reactions on the reduced RuO2 (110) surface were also studied using a periodic slab model. The results demonstrate the low barrier, ~ 0.8 eV, of the diffusion of layer oxygens (3-fold oxygen atoms) to the surface termination, which implies the CO oxidation on reduced RuO2 (110) surface is doable. |