Role of Pt in Pt/Ba/Al2O3 NOx storage and reduction traps

Abstract

The stability of stored NO_x under air, lean propene–air mixtures and stoichiometric air–propene mixtures has been studied for Pt/Ba/Al₂O₃ catalysts under temperature programmed and constant λ conditions to simulate, with a simplified gas composition, the conditions experienced by a NO_x storage and reduction catalyst during the warm-up period. The stability of stored NO_x was mainly influenced by gas-phase oxygen concentration. Although the presence of propene lowered the onset temperature of NO_x desorption, increasing the partial pressure of propene in the system had little influence on the stored NO_x stability. Under the conditions of the experiments, the majority of NO_x was desorbed before the onset of propene combustion. Results suggest that NO_x desorption from the alumina and baria components undergo reverse spillover onto the platinum surface which inhibits the activation of propene thereby increasing the light-off temperature to produce CO₂.