Sulfur Poisoning of a NO
Storage Catalyst - A Comprehensive Modelling Approach
This paper describes the development of a 0-D-sulfur poisoning model for a NOx storage catalyst (NSC). The model was developed and calibrated using findings and data obtained from a passenger car diesel engine used on testbed. Based on an empirical approach, the developed model is able to predict not only the lower sulfur adsorption with increasing temperature and therefore the higher SOx (SO2 and SO3) slip after NSC, but also the sulfur saturation with increasing sulfur loading, resulting in a decrease of the sulfur adsorption rate with ongoing sulfation. Furthermore, the 0-D sulfur poisoning model was integrated into an existing 1-D NOx storage catalyst kinetic model. The combination of the two models results in an “EAS Model” (exhaust aftertreatment system) able to predict the deterioration of NOx-storage in a NSC with increasing sulfation level, exhibiting higher NOx-emissions after the NSC once it is poisoned. Additionally, the so called “deterioration factors”, used to reflect the lower NOx-conversion and higher NO2/NOx-ratio with increasing sulfation, were determined for different sulfur levels. Finally, the impact of sulfur poisoning on the NSC performance was assessed in steady state operating conditions, as well as under dynamic conditions, such as the US06 and the Federal Test Procedure (FTP75). The latter was used to evaluate the quality of the model under transient operating conditions. Thereby, simulated deterioration of NOx-emissions for a sulfured catalyst, compared to a desulfated one, differ only about 2% from the measurement results, representing the high accuracy of the developed model.