Introducing a new catalyst family in gasoline aftertreatment

This paper is to introduce a new catalyst family in gasoline aftertreatment. Indeed, it has been shown that under certain driving conditions, three-way catalysts produce significant amounts of toxic NH3 and the strong greenhouse gas N2O, which are both very unwanted emissions. In a self-committed approach, OEMs could want to minimize these noxious pollutants, especially if this can be done with no architecture change, namely without additional underfloor catalyst. In this paper we will compare different approaches: regular underfloor TWC, SCR derived from diesel aftertreatment, gasoline dedicated Ammonia Slip Catalyst (ASC) and especially developed novel gasoline Secondary Emission Treatment (SET) catalyst, providing both ammonia abatement and underfloor three-way functionality. The data will show that SCR only reduces NH3 from a passive SCR reaction in a limited amount in the cold start including the need of oxygen presence, namely secondary air introduction. ASC is efficient in cold start phase, but does not contribute in hot conditions and it converts NH3 with a significant selectivity towards N2O under lean conditions. Underfloor TWC helps to delay NH3 breakthroughs in rich and hot conditions by providing additional OSC, but does not have any contribution in cold start phase. SET is the most promising combination addressing both cold start phase and hot driving conditions. Indeed, SET will provide passive SCR-like function in NH3 trapping and conversion in cold start phase and underfloor three-way-like NH3 conversion. In addition, it fulfills the role of a underfloor three-way catalyst, namely CO and NOx hot phase treatment.