Effect of periodic operation on the low-temperature activity for propane oxidation over Pt/Al2O3 catalysts

We report experimental results for the oxidation of propane over alumina supported platinum catalysts with varying Pt dispersions. Flow-reactor experiments introducing 0.15 vol% C3H8 while changing the oxygen concentration step-wise (step-response experiments) from rich to lean composition or periodically (pulse-response experiments) switching between rich and lean O2 concentrations, at a constant inlet gas temperature of 250 °C have been performed. Complementary in situ FTIR spectroscopy experiments for surface analysis have also been carried out. The results reveal a strong correlation between the reactant composition and the catalytic activity, showing an optimum reaction rate for compositions close to the stoichiometric value for complete oxidation of propane. For lean gas compositions the activity is low probably due to a high O-coverage (O self-poisoning) which in turn is likely to also cause platinum oxide formation. However, by periodically introducing rich periods (periodic operation) the activity can temporarily be restored and the surface composition can be kept close to the optimum, leading to an overall improvement of the oxidation rate. Generally, the introduction of short rich periods to a slightly lean mixture (lean-rich cycling) seems to be more efficient than the corresponding rich-lean cycling since the latter suffers from oxygen deficiency limiting the reaction during the long periods