Exhaust gas treatment system with upstream SCR catalyst

1. A system for treatment of an exhaust gas stream from an engine, the system comprising:

a first selective catalytic reduction (SCR) catalyst that is in fluid communication with the exhaust gas stream, wherein the first SCR catalyst receives the exhaust gas stream without any intervening catalyst;

a diesel oxidation catalyst (DOC) in fluid communication with the first SCR catalyst, wherein the diesel oxidation catalyst is positioned downstream of the first SCR catalyst;

a catalyzed soot filter (CSF) in fluid communication with the diesel oxidation catalyst, wherein the catalyzed soot filter is positioned downstream of the diesel oxidation catalyst;

a second SCR catalyst in fluid communication with the catalyzed soot filter, wherein the second SCR catalyst is positioned downstream of the catalyzed soot filter; and

a first AMOx catalyst that is either integrated with the second SCR catalyst or in fluid communication with and downstream of the second SCR catalyst.

2. The system of claim 1 , wherein the first SCR catalyst is in a close-coupled position.

3. The system of claim 1 , where the first SCR catalyst is in an underfloor position.

4. The system of claim 1 , further comprising a second AMOx catalyst integrated with the first SCR catalyst, in the form of an SCR/AMOx catalyst.

5. The system of claim 4 , wherein the second AMOx catalyst comprises platinum.

6. The system of claim 4 , wherein the SCR/AMOx catalyst is in the form of two or more washcoats on a flow-through substrate, wherein the flow-through substrate has an upstream inlet end and a downstream outlet end, and wherein the second AMOx catalyst comprises platinum and is at the outlet end and extends less than a full length of the SCR/AMOx catalyst.

7. The system of claim 6 , wherein the SCR/AMOx catalyst comprises: a bottom washcoat comprising the second AMOx catalyst in direct contact with the flow through substrate, wherein the second AMOx catalyst extends less than the full length of the SCR/AMOx catalyst; and a top washcoat comprising the SCR catalyst extending the full length of the SCR/AMOx catalyst.

8. The system of claim 1 , wherein the first SCR catalyst comprises a vanadium component.

9. The system of claim 1 , wherein the first SCR catalyst comprises copper-promoted molecular sieves.

10. The system of claim 1 , wherein the first SCR catalyst comprises Cu-CHA.

11. The system of claim 1 , further comprising a dual injector system, comprising a first injector adapted for the addition of a first reductant to the exhaust gas stream upstream of the first SCR catalyst and a second injector adapted for the addition of a second reductant to the exhaust gas stream upstream of the second SCR catalyst.

12. The system of claim 11 , wherein the first and second reductants comprise ammonia or an ammonia precursor.

13. The system of any of claim 1 , wherein the CSF comprises one or more washcoats on a wall flow filter, and wherein the one or more washcoats comprise platinum and palladium.

14. The system of claim 13 , wherein the platinum and palladium in the one or more washcoats of the CSF are supported on alumina and are present in a ratio of about 4:1 Pt:Pd.

15. The system of claim 1 , wherein the DOC comprises one or more washcoats on a flow-through substrate having an upstream inlet end and a downstream outlet end, and wherein the one or more washcoats comprise platinum and palladium on alumina.

16. The system of claim 15 , wherein the DOC comprises:

a first washcoat coated from the upstream inlet end comprising platinum and palladium on alumina, extending less than a full length of the flow-through substrate, with a platinum:palladium ratio of about 1:1; and

a second washcoat coated from the downstream outlet end comprising platinum and palladium on alumina, extending less than the full length of the flow-through substrate, with a platinum:palladium ratio of greater than 2:1.

17. The system of claim 1 , wherein the DOC is associated with the CSF, in the form of a zoned DOC/CSF having an upstream inlet end and a downstream outlet end, wherein the DOC is at the upstream inlet end and extends less than a full length of the CSF.

18. The system of claim 17 , wherein the zoned DOC/CSF is in the form of two or more washcoats on a wall flow filter, comprising:

a first washcoat extending a full length of the wall flow filter comprising platinum and palladium on alumina, with a platinum:palladium ratio of greater than 5:1, and

a second washcoat extending from the upstream inlet end less than the full length of the wall flow filter, comprising platinum and palladium on alumina, with a platinum:palladium ratio of greater than 5:1 and a loading of about 50 g/ft 3 or greater.

19. The system of claim 1 , wherein the first AMOx catalyst is in fluid communication with and downstream of the second SCR catalyst, and wherein the first AMOx catalyst is integrated with a third SCR catalyst.

20. The system of claim 1 , wherein the second SCR catalyst has an upstream inlet end and a downstream outlet end, and comprises an iron-promoted molecular sieve extending from the inlet end to less than a full length of the SCR catalyst and comprises a copper-promoted molecular sieve extending from the outlet end to less than the full length of the SCR catalyst.

21. The system of claim 20 , wherein the iron-promoted molecular sieve is Fe-CHA and the copper-promoted molecular sieve is Cu-CHA.

22. The system of claim 1 , wherein the engine is a lean burn engine.

23. The system of claim 1 , wherein the engine is a diesel engine.

24. A method of treating an exhaust gas stream, comprising contacting the exhaust gas stream with the system of claim 1 such that nitrogen oxides (NOx) in the exhaust gas stream are reduced.