EMISSIONS TREATMENT SYSTEM WITH AMMONIA-GENERATING AND SCR CATALYSTS

摘要

Provided are emissions treatment systems for an exhaust stream having an ammonia- generating component, such as a NOx storage reduction (NSR) catalyst or a lean NOx trap (LNT) catalyst, and an SCR catalyst disposed downstream of the ammonia-generating catalyst. The SCR catalyst can be a molecular sieve having the CHA crystal structure, for example SSZ- 13 or SAPO-34, which can be ion-exchanged with copper. The LNT can be layered, having an undercoat washcoat layer comprising a support material, at least one precious metal, and at least one NOx sorbent selected from the group consisting of alkaline earth elements, rare earth elements, and combinations thereof and a top washcoat layer comprising a support material at least one precious metal, and ceria in particulate form, the top washcoat layer being substantially free of alkaline earth components, The emissions treatment system is advantageously used for the treatment of exhaust streams from diesel engines and lean burn gasoline engines.