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Free keywords:
Catalysis; Heterogeneous Catalysis; In-Situ FTIR Spectroscopy; Oscillation Mechanisms; Periodic Reaction Rates
Abstract:
The CO/NO reaction on Platinum supported catalysts exhibits oscillatory behaviour at temperatures between 650 and 750 K and NO/CO ratios between 0.8 and 4. The oscillations are accompanied with large temperature variations which seem to be necessary to synchronize the instabilities at different crystallites. IR spectroscopic investigations reveal appreciable shifts of the position of the L-CO band on Pt. This leads to a model involving the hex ⇄ 1 × 1 surface transformation of the Pt(100) plane as the crucial step during an oscillation cycle. A comparison with results of other groups confirms this proposition. Concerning the CO/O2 reaction, however, no indication for the applicability of the hex ⇄ 1 × 1 model for oscillations at atmospheric pressures could be found by means of IR spectroscopy. Also oxidation-reduction models could be excluded. The only mechanism discussed in the literature which is in agreement with our findings explains the oscillations by reversible microfacetting of the Pt(110) plane.
