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O: Fachverband Oberflächenphysik

O 57: Surface Chemical Reactions and Heterogeneous Catalysis II

O 57.4: Vortrag

Donnerstag, 29. März 2007, 16:30–16:45, H38

Is there a “rate determining step” in the catalytic oxidation of CO over RuO₂(110)? — •Hakim Meskine, Karsten Reuter, and Matthias Scheffler — Fritz-Haber-Institut, Faradayweg 4-6, D-14195 Berlin

Out of the several elementary processes in the catalytic cycle, one step is frequently believed to be particularly important, and limiting the overall product formation. We check on this assumption of a rate determining step, using the CO oxidation at RuO₂(110) as a model case. The chemical kinetics is determined with kinetic Monte Carlo simulations, based on rate constants determined by density-functional theory and transition-state theory. The composition and structure of the catalyst surface are computed in reactive environments ranging from ultra-high vacuum (UHV) to technologically relevant conditions (pressures of several atmospheres and elevated temperatures). We employ several forms of sensitivity analyses to identify the rate determining steps under the different environmental conditions. Under UHV conditions we find the catalytic activity indeed predominantly dependent on only one process step, namely the reactant adsorption. However, under catalytically really relevant gas phase conditions, it is not one, but a larger number of elementary processes that contributes equally to the total rate of product formation. The bearings of these findings for the frequently employed approach to extract apparent activation barriers from Arrhenius-type activity plots is critically discussed.