Density functional theory calculations for the interaction of oxygen with reduced M/SnO2(1 1 0) (M=Pd, Pt) surfaces

Density functional theory calculations within the generalized gradient approximation have been performed for the interaction of oxygen with reduced M/SnO2(1 1 0) (M=Pd, Pt) surfaces. There are larger dissociation barriers of side-on type chemisorbed O2 molecules assigned as a superoxo (O2−) species for Pd/SnO2, an intermediate oxygen species between O2− and preoxo (O22−) for Pt/SnO2 than the barrier less dissociation of O22− for the reduced SnO2(1 1 0) surface. An adsorbed O− species produced by the dissociation of these species shows higher migration barriers of ≈30–40 kcal/mol over the noble metal, indicating its limited migration on the surfaces. It is also found that the catalytic activity of O− is much weakened at vacant bridging oxygen sites connected to the noble metal. These characters of O− on the surfaces may favor the selective oxidation of methane to C1-oxygenates (methanol and formaldehyde) compared to the SnO2 surface remaining a highly catalytically active O− under the lower migration barriers.