Reduction of NO by propene under lean-bum exhaust conditions and oxidation of NO were studied on two Pt/gamma-Al2O3 catalysts of 4.4% and 82% dispersion of Pt. At 265 degrees C, the turnover frequency for the oxidation of NO was over 100 times higher on the low dispersion than the high dispersion catalyst. The difference was much less pronounced for the reduction of NO. In the reduction of NO, the N2O/N-2 ratio in the product was found to increase with the conversion of hydrocarbon, while depend much less on Pt dispersion, temperature, or NO conversion.