The impact of CO and C3H6 pulses on PtOx reduction and NO oxidation in a diesel oxidation catalyst

Abstract

A reversible deactivation of a diesel oxidation catalyst (DOC) due to the platinum oxide (PtOx) formation is observed under lean conditions. Among others, the gradual build-up of PtOx leads to a decreasing activity for NO oxidation. It is known that PtOx formation is caused by O2 and NO2 present in the gas mixture and that platinum oxide can be reduced by NO at lower temperatures or thermally decomposed at high temperatures. In this paper we present experimental and modeling results showing that PtOx can be reduced also by CO and C3H6 pulses.First, temperature ramps from 120 to 420°C and back to 120°C were performed with a constant inlet gas composition starting with a reduced catalyst. A higher NO oxidation activity was observed during the heat-up phase than during the subsequent cool-down phase, indicating formation of PtOx. The catalytic activity during the cool-down ramp was partially restored by pulses with an increased CO and C3H6 concentration (while still keeping lean conditions). The maximum effect of pulses was observed around the light-off temperature for CO and C3H6 oxidation.A global kinetic model was developed, considering PtOx existence and its reduction by CO and C3H6 pulses. The model was further validated by isothermal experiments, showing gradual decrease of NO oxidation activity and its recovery by CO and C3H6 at several different temperatures.