Regensburg 2010 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 59: Poster Session II (Nanostructures at surfaces: Dots, particles, clusters; Nanostructures at surfaces: arrays; Nanostructures at surfaces: Wires, tubes; Nanostructures at surfaces: Other; Plasmonics and nanooptics; Metal substrates: Epitaxy and growth; Metal substrates: Solid-liquid interfaces; Metal substrates: Adsoprtion of organic / bio molecules; Metal substrates: Adsoprtion of inorganic molecules; Metal substrates: Adsoprtion of O and/or H; Metal substrates: Clean surfaces; Density functional theory and beyond for real materials)

O 59.62: Poster

Mittwoch, 24. März 2010, 17:45–20:30, Poster B1

Temperature-induced modifications of PdZn surface alloys on Pd(111) and first results for Ga on Pd(111) — •Werner Stadlmayr, Christoph Rameshan, Simon Penner, Berhard Klötzer, and Norbert Memmel — Institut für Physikalische Chemie, Universität Innsbruck, Innrain 52a, 6020 Innbruck, Austria

Pd-Zn and Pd-Ga alloy films on Pd(111) are model systems aiming for a microscopic understanding of the mechanisms in Pd-Zn and Pd-Ga based catalysis for methanol steam reforming. The temperature-induced compositional and structural changes of these films are investigated in the catalytically relevant temperature range. We find that upon heating from 550 K to 630 K the alloy films change from a multilayer PdZn system to a "monolayer" situation due to diffusion of subsurface Zn into the Pd bulk. The change in subsurface stoichiometry triggers an inversion of the surface corrugation from Zn-out/Pd-in to Pd-out/Zn-in. This modification in surface geometric (and electronic) structure provides an explanation for the recently observed drastic changes in catalytic selectivity.

Furthermore, first results for Ga on Pd(111) are presented. Similar to Zn/Pd(111) we observe, that in the temperature window around 500 K an alloy with a 1:1 surface composition is formed. However in contrast to the Zn/Pd system no long-range order is observed in the alloyed state, while the short range order is preserved.