| 简介 |
PROBLEM TO BE SOLVED : To provide an emissions treatment system with ammonia-generating and SCR catalysts.
SOLUTION : Provided are emissions treatment systems for an exhaust stream having an ammonia-generating component, such as an NOx storage reduction (NSR) catalyst or a lean NOx trap (LNT) catalyst 12, and an SCR catalyst 16 disposed downstream of the ammonia-generating catalyst. The LNT can have a layered structure, which has : 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 a particulate form, the top washcoat layer being substantially free of alkaline earth components. The SCR catalyst 16 can be a molecular sieve having the CHA crystal structure, for example SSZ-13 or SAPO-34, which can be ion-exchanged with copper.
SELECTED DRAWING : Figure 1A
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