Berlin 2008 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 13: Heterogeneous Catalysis
O 13.6: Vortrag
Montag, 25. Februar 2008, 15:15–15:30, HE 101
CO oxidation on Palladium(111): Rate hysteresis and periodic breakdowns — •Stefan Karpitschka1, Stefan Wehner1, Helmut Brand2, and Jürgen Küppers1,3 — 1Experimentalphysik III, Universität Bayreuth, 95440 Bayreuth, Germany — 2Theoretische Physik III, Universität Bayreuth, 95440 Bayreuth, Germany — 3Max-Planck-Institut für Plasmaphysik (EURATOM Association), 85748 Garching, Germany
A rate-measurement-study of the catalytic oxidation of carbon monoxide on Pd(111) surfaces in the high vacuum pressure range is presented. The total flux of the feed gas to the surface was held constant while its CO-fraction was varied. The existence of a regime in the feed gas composition in which the system exhibits bistable behavior was shown by long-time measurements. Pulse-like modulations of the feed gas revealed that the experimentally observed high CO-fraction border of the bistable region is determined by the equistability condition of both phases. This behavior could be caused by the presence of predominantly CO-covered defects exceeding the critical size for nucleation. The experimental results and their temperature dependence are well described by a simple mean field model containing no fit parameters.
Applying high CO-fractions in the feed gas just within the bistable range, we furthermore observed periodic breakdowns in the catalytic activity at a very low frequency, which were not yet reported for this surface. Growth and decay of surface oxides as well as noise have been tested as an origin of these periodic breakdowns.