Regensburg 2000 – scientific programme
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O: Oberflächenphysik
O 11: Postersession (Eröffnung)
O 11.108: Poster
Monday, March 27, 2000, 19:00–22:00, Bereich C
High-Pressure NEXAFS Evidence for an Oxygen-Containing Transient Intermediate during CO Oxidation over Gold — •Sven L.M. Schroeder and Norbert Weiher — FU Berlin, Institut für Chemie, Takustraße 3, 14195 Berlin
The oxidation of carbon monoxide (CO) by dioxygen (O2) over gold has recently received much attention because of the high CO oxidation activities developed by small gold particles supported on base metal oxides. Because of a high activation barrier for O2-dissociation on ordered gold surfaces, information on reaction intermediates by means of Au single crystal studies under UHV conditions is hard to come by. Sufficiently high pressures and elevated temperatures are necessary to overcome the activation barrier and to achieve sufficiently high surface concentrations of reactive species. By means of a high-pressure cell for soft X-ray absorption spectroscopy (XAS) we have now performed an in situ near-edge XAS investigation of a heated polycrystalline Au foil under CO oxidation conditions at O2 pressures in the mbar range. The reaction rate was monitored with a mass spectrometer. We have obtained O K-edge absorption spectra that provide first evidence for the presence of an O-containing reaction intermediate. The surface concentration of this labile intermediate is dependent on the gas phase stoichiometry and changes in the surface temperature. Comparison with O K-edge spectra obtained for gold oxides, oxyhydroxides as well as physisorbed O2 and chemisorbed oxygen on Au(110) has so far not provided unequivocal evidence allowing an assignment of its composition or structure. Other plausible possibilities are currently under investigation and will be discussed.