Effect of potassium and water vapor on the catalytic reaction of nitric oxide and dioxygen over platinum

The turnover rate (TOR) per unit surface Pt atom for NO oxidation by O2 on a Pt/K/Al2O3 NOx storage-reduction catalyst was 2.5 times higher at 300 °C than the rate on a Pt/Al2O3 catalyst with the same Pt loading. The power rate law orders with respect to NO, O2 and NO2 on the Pt/K/Al2O3 catalyst were identical to those on Pt/Al2O3, viz. r = k[NO]1[O2]1[NO2]−1, but the apparent activation energy obtained for the K-promoted catalyst was 60 kJ mol−1, about 22 kJ mol−1 lower than on the Pt/Al2O3 catalyst. The presence of water vapor in the feed resulted in an initial and irreversible decrease in the Pt surface area and NO conversion for both Pt/K/Al2O3 and Pt/Al2O3 catalysts, but no changes in the reaction orders or apparent activation energy were observed. Water did not affect the NO oxidation turnover rates.