Small pore molecular sieve supported copper catalysts durable against lean/rich aging for the reduction of nitrogen oxides
View Patent ↗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.
1. A method for using a catalyst comprising:
a. exposing an SCR catalyst comprising copper and a small-pore molecular sieve having an AFX structure to a reducing atmosphere comprising NH 3 generated over a NO x adsorber catalyst and using the SCR catalyst to store NH 3 during the exposing step, and
b. contacting the SCR catalyst with NO x in a non-reducing atmosphere to effect selective reduction of said NO x by the stored NH 3 .
2. The method of claim 1 , wherein the small pore molecular sieve comprises SAPO-56 or SSZ-16.
3. The method of claim 1 , wherein said small pore molecular sieve is SSZ-16 and has a silica-to-alumina ratio of 8 to 150.
4. A system for treating exhaust gas comprising a NO x adsorber catalyst disposed upstream of an SCR catalyst, wherein said SCR catalyst comprises copper and small-pore molecular sieve having an AFX structure.
5. The system of claim 4 , wherein the small pore molecular sieve comprises SAPO-56 or SSZ-16.
6. The system of claim 4 , wherein the small pore molecular sieve is SSZ-16 and has a silica-to-alumina ratio of about 4 to about 200.
7. The system of claim 4 , wherein said copper is present in said small pore molecular sieve in an amount from 0.5 to 5 weight percent.
8. The system of claim 4 , wherein said NO x adsorber catalyst comprises a precious metal and a basic material selected from the group consisting of an alkali metal, an alkaline earth metal, and a rare earth metal.
9. The system of claim 4 , further comprising an ammonia component, wherein said ammonia component is generated by said NO x adsorber catalyst.
10. The system of claim 4 , further comprising an alternating reducing atmosphere and an oxidizing atmosphere, wherein said SCR catalyst is exposed to said alternating atmospheres.
11. The system of claim 10 , wherein said reducing atmosphere is a lean exhaust gas and said oxidizing atmosphere is a rich exhaust gas.
12. The system of claim 4 , wherein said NO x adsorber catalyst is loaded on a first substrate and said SCR catalyst is loaded on a second substrate and the first substrate is disposed in front of the second substrate with respect to the normal flow of exhaust gas through the system.