Berlin 2008 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 55: Poster Session III - MA 141/144 (Methods: Atomic and Electronic Structure; Particles and Clusters; Heterogeneous Catalysis; Semiconductor Substrates: Epitaxy and Growth+Adsorption+Clean Surfaces+Solid-Liquid Interfaces; Oxides and Insulators: Solid-Liquid Interfaces+Epitaxy and Growth; Phase Transitions; Metal Substrates: Adsorption of Inorganic Molecules+Epitaxy and Growth; Surface Chemical Reactions; Bimetallic Nanosystems: Tuning Physical and Chemical Properties; Oxides and insulators: Adsorption; Organic, polymeric, biomolecular films; etc.)

O 55.65: Poster

Mittwoch, 27. Februar 2008, 18:30–19:30, Poster F

Adsorption of CO, O₂ and ethene on Pt_xCe/Pt(111) surface alloys. A HREELS-, TPD-study. — Jan Markus Essen, •Conrad Becker, and Klaus Wandelt — Institut für Physikalische und Theoretische Chemie, Universität Bonn, Wegelerstrasse 12, 53115 Bonn, Germany

It is well known that alloying can change the adsorption and reaction properties of surfaces significantly. In this study we investigated the Pt-Ce system. Evaporating Ce onto Pt(111) followed by annealing to 1000 K forms ordered alloys. Depending on the cerium fraction a (2x2) and a (1,96x1,96)+(1,96x1,96)R30^∘ LEED pattern is observed. Our TPD and HREELS study of CO, O₂ and ethene adsorption shows a very low reactivity of these surface alloys. Concerning CO adsorption we find a significantly decreased desorption temperature of about 280 K compared to 400 K for a CO saturation coverage on pure Pt(111). Likewise oxygen adsorbed at 90 K, followed by annealing, cannot oxidize these surface alloys. In comparison with Pt(111) neither is molecularly bonded oxygen observed at 90 K nor can desorption of oxygen caused by recombination of atomic oxygen at 750 K be detected as on Pt(111). Our results support the model for the Pt_xCe/Pt(111) surface alloy consisting of a Pt Kagomé net as the top layer. Because of the low reactivity we conclude that the top layer of the surface alloy contains no Cerium-atoms.