Density functional study of Pd adsorbates at SnO2(1 1 0) surfaces

Palladium adatoms adsorbed on various SnO2(1 1 0) surfaces with sub-monolayer coverages is studied theoretically by using the density functional method. At low coverages, the binding is found to occur essentially between Pd, surface Sn atoms. Twofold coordinated bridging oxygens of stoichiometric (1 1 0), (1 0 0), (1 0 1)SnO2 surfaces also bind to Pd, but the threefold coordinated in-plane oxygens are inert. At low Pd coverages, the stability of Pd adsorbates is slightly increased due to interaction between Pd atoms which occupy neighboring SnO2(1 1 0) surface unit cells. This can lead to alignment of Pd adatoms on the (1 1 0) surface along [0 0 1] direction. Among the different sites that Pd may occupy and be adsorbed at, the in-plane oxygen vacancies at reduced SnO2(1 1 0) are predicted to be preferred. Substitution of tin atoms by palladium is energetically most favorable in the cases of least coordinated surface tin atoms of oxygen deficient surface. Main features of the evaluated electronic structures and charge distributions of the Pd/SnO2(1 1 0) surfaces are considered.