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O: Oberflächenphysik

O 3: Adsorption I

O 3.1: Vortrag

Montag, 27. März 2006, 11:15–11:30, TRE Phys

Ligand Effects Observed For The CO Adsorption At CoPt-Alloys — •Daniela Fenske, Dirk Hoogestraat, Denis Greshnyk, Stefanie Neuendorf, Holger Borchert, Wai-Leung Yim, Thorsten Klüner, and Katharina Al-Shamery — Carl v.Ossietzky University Oldenburg, Faculty V, Institute of Pure and Applied Chemistry, Germany

The use of bimetallic compounds instead of monometallic catalysts can strongly enhance the efficiency of heterogeneous catalysts which may be attributed either to structural and/or to ligand effects. Results on the influence of the adsorption of CO at CoPt-alloys will be reported as a function of surface composition. The alloys were obtained by evaporating a thin film of Co-atoms onto a Pt(111) crystal under UHV-conditions and subsequent annealing to various temperatures. The final composition of the surface itself could be tuned because Pt tends to segregate at the surface as a function of temperature. The exact surface composition of the different alloys was investigated by XPS. FT-IRAS as well as TPD measurements exhibited that CO-adsorption strongly depends on the actual surface composition which is mainly attributed to strong ligand effects (either preferential adsorption at Pt- (Pt rich surfaces) or Co-sites (Co rich surfaces)). Within TPD desorption peaks are lower than for pure platinum but larger than for pure cobalt sites. Supplementary data on a Co3Pt(111) single crystal will be presented. Theoretical calculations (DFT) reveal the dependence between surface composition, the composition of the second and third layer and changing IR-frequencies and desorption temperatures.