Dresden 2006 – wissenschaftliches Programm
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O: Oberflächenphysik
O 28: Surface reactions II
O 28.9: Vortrag
Dienstag, 28. März 2006, 17:45–18:00, WIL C207
On the oxidation and reduction of Co nanoparticles on thin aluminum oxide films — •Tobias Nowitzki1, Thomas Risse2, Volkmar Zielasek1, and Marcus Bäumer1 — 1Institut für Angewandte und Physikalische Chemie, Universität Bremen, Leobener Str. NW II, 28359 Bremen — 2Abteilung Chemische Physik, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin
Cobalt is used as a catalyst for the hydration of carbon monoxide, the so called Fischer-Tropsch process. As a model catalyst for this reaction, Co nanoparticles on thin aluminum oxide films have been studied in ultrahigh vacuum (UHV) with respect to their oxidation and reduction behaviour. The Co particles were prepared in UHV by physical vapor deposition on a thin aluminum oxide film grown on a NiAl(110) single crystal. X-ray photoelectron (XP) and thermal desorption (TD) spectroscopy data show that Co particles are entirely oxidized at room temperature. After heating to temperatures > 500 K, XPS shows mostly metallic Co, indicating reduction, while TDS shows a mixture of metallic and oxidic components, revealing the existence of a thin surface oxide. Our results indicate that the surface oxide formation depends on particle size. We also find that carbon monoxide can dissociate on metallic particles, which is interesting for the Fischer-Tropsch reaction. In the XP spectra, the oxidic component of the Al 2p substrate signal is increased after heating in presence of the Co particles. Obviously, the aluminum oxide film gets thicker during this procedure, enhancing its thermal stability.