Reduction of N2O by CO over Ceria-Modified Three-Way Pt−Rh Catalysts:  Kinetic Aspects

This study reports an extensive kinetic investigation of the CO + N2O reaction which is a major reaction involved with automotive exhaust catalysts during the overall reduction of NO, particularly during the start of a cold engine. Steady-state rate measurements were performed between 217 and 250 °C on Pt−Rh/γ-Al2O3−CeO2 with partial pressures in the range (4.5−12.0) × 10-3 and (2.0−7.4) × 10-3 atm respectively for CO and N2O. Particular attention has been paid toward the influence of ceria on the catalytic performances of noble metals. A bifunctional mechanism is proposed involving the redox properties of ceria which correctly explains the beneficial effect of ceria on the reduction of N2O by CO in the absence of NO. However, subsequent comparisons with previous optimized kinetic and thermodynamic constants for the CO + NO reaction on the same catalyst suggest that the promotional effect of ceria is suppressed. When N2O and NO coexist in the gas phase, only noble metals are active near the light-off temperature, and the subsequent CO + N2O reaction is inhibited by the strong adsorption of NO.