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

The stability of stored NOx under air, lean propene - air mixtures and stoichiometric air - propene mixtures has been studied for Pt/ Ba/ Al2O3 catalysts under temperature programmed and constant lambda conditions to simulate, with a simplified gas composition, the conditions experienced by a NOx storage and reduction catalyst during the warm-up period. The stability of stored NOx was mainly influenced by gas-phase oxygen concentration. Although the presence of propene lowered the onset temperature of NOx desorption, increasing the partial pressure of propene in the system had little influence on the stored NOx stability. Under the conditions of the experiments, the majority of NOx was desorbed before the onset of propene combustion. Results suggest that NOx 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.