Small pore molecular sieve supported copper catalysts durable against lean/rich aging for the reduction of nitrogen oxides
AssigneeJohnson Matthey Public Limited Company
InventorsPaul Joseph Andersen, Hai-Ying Chen, Joseph Michael Fedeyko, Erich Weigert
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Abstract
A method of using a catalyst comprises exposing a catalyst to at least one reactant in a chemical process. The catalyst comprises copper and a small pore molecular sieve having a maximum ring size of eight tetrahedral atoms. The chemical process undergoes at least one period of exposure to a reducing atmosphere. The catalyst has an initial activity and the catalyst has a final activity after the at least one period of exposure to the reducing atmosphere. The final activity is within 30% of the initial activity at a temperature between 200 and 500° C.
Claims20
A method for using a catalyst comprising:
- exposing an SCR catalyst comprising copper and a small-pore molecular sieve having eight-member rings or smaller to a reducing atmosphere comprising NH3 generated over a NOx adsorber catalyst and using the SCR catalyst to store NH3 during the exposing step,
- contacting the SCR catalyst with NOx in a non-reducing atmosphere to effect selective reduction of said NOx by the stored NH3.
A method for treating an exhaust gas comprising:
- a. exposing a NOx adsorber catalyst and an SCR catalyst to a lean exhaust gas, wherein said SCR catalyst is disposed downstream of said NOx adsorber catalyst relative to exhaust gas flow and wherein said SCR catalyst comprises copper and a small-pore molecular sieve having eight-member rings or smaller;
- b. exposing said NOx adsorber catalyst and said SCR catalyst to a reducing atmosphere;
- and
- c. repeating steps (a) and (b) in a cyclical manner;
- wherein said NOx adsorber catalyst stores NOx during step (a) and releases NOx to generate NH3 during step (b);
- and said SCR catalyst stores NH3 generated by said NOx adsorber catalyst during step (b) and uses the stored NH3 to selectively reduce NOx during step (a).
A system for treating exhaust gas comprising a NOx adsorber catalyst disposed upstream of an SCR catalyst, wherein said SCR catalyst comprises copper and a small-pore molecular sieve having eight-member rings or smaller.
Dependencies are inferred from the claim text.