Berlin 2008 – scientific programme
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O: Fachverband Oberflächenphysik
O 18: Poster Session I - MA 141/144 (Atomic Wires; Size-Selected Clusters; Nanostructures; Metal Substrates: Clean Surfaces+Adsorption of Organic / Bio Molecules+Solid-Liquid Interfaces+Adsorption of O and/or H; Surface or Interface Magnetism; Oxides and Insulators: Clean Surfaces)
O 18.60: Poster
Monday, February 25, 2008, 18:30–19:30, Poster F
Ab initio study of oxygen adsorption and initial incorporation in Pd-Pt alloy — •Arezoo Dianat, Manfred Bobeth, and Wolfgang Pompe — Institut fuer Werkstoffwissenschaft, Technische Universitaet Dresden, Germany
In order to get insight into the catalytic behavior of the bimetallic alloy Pd-Pt, the adsorption of oxygen on the alloy surface as well as the initial oxygen incorporation have been studied by means of density-functional theory. Due to segregation processes the composition of the near-surface layers of the alloy is in general different from the bulk composition. In this work, ordered bulk phases (L10,L12) of PdxPt1−x with compositions x = 0.25, 0.5, 0.75 as well as different compositions and atom configurations of the two outermost layers have been investigated. Adsorption energies for oxygen adsorbed on the (111) alloy surface and for oxygen in sub-surface position have been calculated for different oxygen coverages (0.25 to 1 ML). In the case of oxygen adsorption on the surfaces, the highest adsorption energy at low oxygen coverage (≤ 0.25 ML) has been found for the Pd0.5Pt0.5 composition o f the two outermost layers, whereas at higher coverage the oxygen binding energy is highest for a Pd-rich first monolayer and Pt-rich second monolayer. Interestingly, on the latter layer system the oxygen adsorption energy is higher than on pure Pd(111). Oxygen occupation of sub-surface sites starts at a coverage of 0.5 ML for all alloy models considered. The calculated oxygen adsorption energy depends only weakly on the bulk composition. It increases slightly with Pt bulk concentration, but it differs less than 50 meV.