Selective catalytic reduction: Adding an ammonia slip catalyst mitigates dosing errors

Abstract

AbstractThis paper uses computational simulation to compare the performance of two catalytic systems designed for the removal of oxides of nitrogen from automotive engine exhaust using selective catalytic reduction (SCR). The first system is comprised of an SCR catalyst alone, whilst the second system adds an ammonia slip catalyst (ASC) to the end of an SCR catalyst. Both systems had the same total length. Comparisons of the NOx removal efficiency and the degree of ammonia slip are made using driving cycles and an optimized ammonia dosing strategy. Comparisons are also made for the case where a constant error in the ammonia dosing occurs. The addition of the ASC reduces ammonia slip during over‐dosing scenarios and gives a greater NOx conversion during under‐dosing cases. This work concludes that the ASC is a positive addition to the SCR in meeting the exhaust emission regulations. Although it does not necessarily allow for a higher NOx conversion, its ability to cope with under‐ and over‐dosing situations can be beneficial in catalyst aging and unpredictable driving conditions.