Modeling of the Competitive Storage of NOx and Sulfur in Automotive Exhaust Catalysts

Automotive exhaust catalysts with NOx and/or oxygen storage functionalities remain one of the key contributors to the high environmental performance of internal combustion engines. However, the exposure of catalysts to sulfur during real-world operation reduces progressively their NOx abatement performance. The aim of this paper is to demonstrate the capability of advanced physico-chemical models to simulate the competitive storage of sulfur and NOx on the catalyst surface and predict the various interactions, in particular the negative effect of sulfur on NOx storage and reduction efficiency. It is clarified that predicting the sulfur storage on sites where NOx can be adsorbed and on sites which are not related to NOx storage allows the accurate simulation of the NOx storage efficiency over sulfur loading. Moreover, the spatial interplay of the formed nitrites, nitrates and sulfates during the sulfation of the catalyst is highlighted. The model is validated in steady state conditions using synthetic gas bench tests and ultimately in transient conditions using actual driving cycles data derived from engine test bench measurements.