Berlin 2005 – wissenschaftliches Programm
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O: Oberflächenphysik
O 3: Oberfl
ächenreaktionen I
O 3.3: Vortrag
Freitag, 4. März 2005, 11:15–11:30, TU EB420
Reduction of the Surface Oxide Layer on Rh(111) by CO and H2 — •Jan Klikovits1, Michael Schmid1, Edvin Lundgren2, Jasper N. Andersen2, Lukas Köhler3, Georg Kresse3, and Peter Varga1 — 1Institut für Allgemeine Physik, TU Wien, A-1040 Wien, Austria — 2Department of Synchrotron Radiation Research, Lund University, Box 118, S-221 00, Sweden — 3Inst. f. Materialphysik, Universität Wien, A-1090 Wien, Austria
We have studied the surface oxide on Rh(111) and its reduction by CO and H2. The structure of the surface oxide has already been solved [1]. Reducing the oxide by CO requires temperatures of about 100 ∘C. Essentially all CO adsorbs at reduced areas, thus the reduction rate increases while the amount of oxide decreases at the surface. STM images show that the reduction starts at step edges and islands. A (2 x 2) superstructure is observed in the reduced areas. We argue that the CO molecules are immobilized by a oxygen superstructure which is in thermodynamic equilibrium with the oxide. The reduction of the surface oxide by H2 was observed in-situ by STM. It starts already at room temperature, almost exclusively in stepped areas. We can also initiate the reduction process by deliberately creating defects with the STM tip allowing us to examine the reduction kinetics in detail. At low H2 pressures or small reduced areas the reduction rate is limited by the hydrogen adsorption on the reduced area. For large reduced areas the reduction rate is limited by the processes at the border of the reduced area.
[1]: J. Gustafson et al., Phys. Rev. Lett 92, 126102, (2004).