Poisoning and regeneration of NOx adsorbing catalysts for automotive applications

Abstract

The effeciency and product formation as a function of temperature, time and gas stoichiometry, in the regeneration of an SO2 poisoned NOx storage and reduction (NSR) catalyst has been studied. Using these results a simple model for sulphur poisoning and regeneration of this type of catalyst is proposed. SO2 poisons the catalyst, which results in a decrease of the NOx conversion with increasing SO2 exposure time. The NOx storage capacity can be regained after regeneration of the catalyst. The regeneration is most effective using long regeneration time, high temperature and low lambda value. A measure of the regeneration efficiency, activity based sulphur removal (ASR), is defined. ASR is used to model the regeneration efficiency with the independent variables; regeneration time, temperature and lambda value. The model describes the experimental results well. The amounts of released SO2, H2S and COS, during the regeneration differ depending on regeneration conditions. Low lambda values give high amounts of H2S and low amounts of SO2, whereas the reverse is true for high lambda values. The production of COS is low in all cases. The results can schematically be described with a model where sulphur can migrate between deactivating and non-deactivating positions on the catalyst surface.