AVS 45th International Symposium
    Surface Science Division Monday Sessions
       Session SS2-MoA

Paper SS2-MoA3
Visualization of Heterogeneously Catalytic Processes

Monday, November 2, 1998, 2:40 pm, Room 309

Session: Surface Chemistry on Model Catalysts
Presenter: M. Getzlaff, University of Hamburg, Germany
Authors: M. Bode, University of Hamburg, Germany
M. Getzlaff, University of Hamburg, Germany
R. Wiesendanger, University of Hamburg, Germany
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The goal of this study is to a get deeper insight into the understanding of heterogeneous catalysis by combining the special merits of scanning tunneling microscopy/spectroscopy (STM/STS) and ultra-violett photoemission spectroscopy (UPS). We report on the electronic structure and the development of the adsorption process of hydrogen covered Gadolinium films being exposed to carbon monoxide. Clean Gd(0001) films were epitaxially grown on W(110). These films were exposed to hydrogen which leads to a local quenching of the d@sub z@@super 2@-like surface state being characteristic for the clean Gd(0001) surface. Due to the high spatial resolution of STM and its sensitivity to the local density of states at close to the Fermi-level, the adsorption process can be visualized and directly be correlated to the electronic properties measured by from UPS. The adsorption process at room temperature consists of five steps. At the very beginning the total amount of CO causes a removal of hydrogen from the surface. In the next two steps the rest of the adsorbed hydrogen atoms is removed and carbon and oxygen remains at the surface. In the intermediate regime CO dissociates and carbon and oxygen is adsorbed at or near the surface. This information is corroborated by investigations of clean Gd(0001) being exposed to CO and oxygen, respectively. The last step demonstrates the oxidation to Gd@sub 2@O@sub 3@ acting as catalyst for the transformation of CO to CO@sub 2@ which creates stable carbonate species at the surface.