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O: Fachverband Oberflächenphysik

O 12: Metal substrates: Adsorption of O / H and inorganic molecules I

O 12.1: Vortrag

Montag, 14. März 2011, 15:00–15:15, WIL A317

Adsorption of atomic oxygen on PdAg/Pd(111) surface alloys and coadsorption of CO — •Arnold P. Farkas^1,2, Joachim Bansmann¹, Thomas Diemant¹, and R. Jürgen Behm¹ — ¹Institute of Surface Chemistry and Catalysis, Ulm University, D-89069 Ulm, Germany — ²Reaction Kinetics Research Group at the University of Szeged, Chemical Research Center of the Hungarian Academy of Sciences, H-6720 Szeged , Hungary

The interaction of dissociated oxygen with structurally well-defined PdAg/Pd(111) surface alloys and the coadsorption of CO was studied by high resolution electron energy loss spectroscopy (HREELS) and temperature-programmed desorption (TPD). After oxygen saturation of the non-modified Pd(111) surface at RT, we observed the formation of a prominent peak in the HREEL spectra at 60 meV corresponding to the perpendicular vibration of oxygen atoms adsorbed in threefold hollow sites. Deposition of small Ag amounts does not change the signal intensity of this peak; it decreases only above 20% Ag. Beyond this Ag content, the peak intensity steeply declines and disappears at around 55-60% Ag. CO coadsorption on the oxygen pre-covered surfaces at 120 K leads to the formation of additional features in HREELS. For a surface alloy with 29% Ag, three loss features due to CO adsorption in on-top, bridge, and threefold-hollow sites can be discriminated already after the lowest CO exposure. Annealing of the co-adsorbed layer to 200 K triggers a decrease of the oxygen concentration due to CO₂ formation. These findings are corroborated by TPD spectra of the CO desorption and CO₂ production.