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O: Fachverband Oberflächenphysik

O 64: Metal substrates: Adsorption of inorganic molecules

O 64.3: Vortrag

Freitag, 27. März 2009, 11:45–12:00, SCH A215

Interaction of CO with PdAg/Pd(111) surface alloys — Yunsheng Ma, •Joachim Bansmann, Thomas Diemant, Albert Engstfeld, Harry Hoster, and Behm Behm — Institute of Surface Chemistry and Catalysis, Ulm University, D-89069 Ulm

The surface composition, distribution of different Pd ensembles and adsorption properties of PdAg/Pd(111) surface alloys have been investigated by Scanning Tunneling Microscopy (STM), Temperature Programmed Desorption (TPD) and High Resolution Electron Energy Loss Spectroscopy (HREELS) using CO as a probe molecule. The statistical analysis of atomic resolution STM images with chemical contrast reveals a nearly random distribution of the surface atoms on PdAg/Pd(111) surface alloys. The presence of Ag on the surface first suppresses the adsorption of CO on the preferred Pd threefold-hollow sites. For these sites, the adsorption energy does not change for small Ag coverages, indicative for a geometric (ensemble) effect. With increasing Ag surface concentration, CO mostly adsorbs on bridge sites of Pd dimers and top sites of Pd monomers surrounded by Ag atoms. At higher CO coverage, a transition of CO adsorption from bridge to top sites occurs on Pd dimers to accommodate more CO molecules, similar to the case on PdAu/Pd(111) surface alloys [1].

[1] M. Ruff et al., ChemPhysChem 8 (2007) 2068.