(144c) NOx Reduction and Ammonia Generation Over Three-Way Catalysts and LNTs for Use in Lean Gasoline Vehicles Equipped with SCR

The introduction of lean gasoline vehicles and their associated improved fuel efficiency are limited due to the difficulty in meeting emissions requirements; specifically the reduction of NOx.  This effort addresses NOx, CO, and hydrocarbon emission control challenges and studies a variety of catalytic approaches to meet them under typical lean gasoline conditions.  Currently only bench reactor results will be discussed.  A three-way catalyst (TWC), which will be required on the system due to periodic stoichiometric operation, will not be able to reduce NOx under the lean conditions.  However, under mildly rich conditions it has been shown that TWCs can aggressively convert NOx to NH₃.  This ammonia when combined with a zeolite-based SCR system can be stored during these rich conditions and used to convert NOx during lean operation.  Results evaluating NH₃ formation over a variety of TWCs will be presented.  Additionally, Lean NOx Traps (LNT) have illustrated the ability to make high levels of NH₃ during cyclic operation.  We will show results on a commercially relevant LNT and how lean-rich timing impacts NH₃ generation, including the potential benefits and problems associated with including NOx storage capacity in TWC formulation.