Small pore molecular sieve supported copper catalysts durable against lean/rich aging for the reduction of nitrogen oxides

1. A system for treating a flowing exhaust gas comprising:

(a) a lean NOx trap;

(b) a catalyzed soot filter;

(c) an ammonia or an ammonia precursor metering system for metering ammonia or an ammonia precursor into the flowing exhaust gas; and

(d) an SCR catalyst, wherein the SCR catalyst is disposed downstream of the lean NOx trap and comprises copper and/or iron supported on a small pore molecular sieve, wherein the small pore molecular sieve has a framework selected from the group consisting of AEI, AFT, AFX, DDR, ERI, LEV, KFI, and SAV.

2. The system of claim 1 , wherein said metering is controlled in response to the quantity of nitrogen oxides in the exhaust gas.

3. The system of claim 1 , wherein the small pore molecular sieve is a SAPO.

4. The system of claim 1 , wherein the small pore molecular sieve has a silica-to-alumina ratio of 8 to 150.

5. The system of claim 1 , wherein the small pore molecular sieve has an AEI framework.

6. The system of claim 1 , wherein the catalyzed soot filter comprises a copper-loaded small pore molecular sieve.

7. The system of claim 1 , wherein the SCR catalyst is coated on flow-through monolith.

8. The system of claim 1 , wherein the catalyzed soot filter is coated with an SCR catalyst.

9. The system of claim 1 , wherein the small pore molecular sieve has an AFT Framework.

10. The system of claim 1 , wherein the small pore molecular sieve has an AFX Framework.

11. The system of claim 1 , wherein the small pore molecular sieve has an DDR framework.

12. The system of claim 1 , wherein the small pore molecular sieve has an ERI framework.

13. The system of claim 1 , wherein the small pore molecular sieve has an LEV framework.

14. The system of claim 1 , wherein the small pore molecular sieve has an KFI framework.

15. The system of claim 1 , wherein the small pore molecular sieve has an SAV framework.