EMISSIONS TREATMENT SYSTEM WITH AMMONIA-GENERATING AND SCR CATALYSTS

摘要

PROBLEM TO BE SOLVED: To provide 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.SOLUTION: In the emissions treatment systems, 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; and the LNT can have a layered structure with an undercoat washcoat layer comprising a support material, at least one precious metal, and at least one NOx sorbent selected from among alkaline earth elements, rare earth elements and combinations thereof, and with a top washcoat layer comprising a support material, at least one precious metal, and ceria in a particulate form, the top washcoat layer being substantially free of alkaline earth components.