Bimetallic catalysts for selective ammonia oxidation

1. A catalyst for oxidizing ammonia to nitrogen and NO x , the catalyst comprising:

an aluminosilicate molecular sieve having a silica-to-alumina ratio (SAR) less than about 10, the molecular sieve comprising ion-exchanged copper and ion-exchanged platinum, wherein the catalyst is effective to oxidize ammonia to nitrogen and NO x at 250° C. and above, and wherein the catalyst catalyzes substantially complete conversion of ammonia at about 250° C.

2. The catalyst of claim 1 , further comprising an amount of zero valent or metallic platinum.

3. The catalyst of claim 2 , wherein the ion-exchanged platinum is added via a cation-exchanged process using a platinum precursor.

4. The catalyst of claim 2 , wherein the aluminosilicate molecular sieve comprises a zeolite having a crystal framework type selected from FAU, MFI, MOR, BEA, HEU, and OFF.

5. The catalyst of claim 4 , wherein the zeolite has a SAR less than about 6.

6. The catalyst of claim 1 , having up to about 1 weight % Pt and up to 5 weight % copper on a weight per washcoat basis.

7. The catalyst of claim 3 , wherein the catalyst is capable of providing greater than about 60% selectivity for oxidizing the ammonia to dinitrogen at about 250° C.

8. The catalyst of claim 3 , wherein the catalyst is capable of providing greater than about 60% selectivity for oxidizing the ammonia to dinitrogen at about 400° C.

9. The catalyst of claim 1 , wherein the catalyst is coated on a refractory ceramic support.

10. The catalyst of claim 9 , wherein the total loading of the molecular sieve on the refractory ceramic support is in the range of about 0.3 g/in 3 and about 3.0 g/in 3 , based on total catalyst volume.

11. The catalyst of claim 1 , wherein the Pt loading comprises at least about 2000 ppm.

12. The catalyst of claim 11 , wherein the aluminosilicate molecular sieve comprises a zeolite having a FAU crystal framework type.

13. The catalyst of claim 1 , wherein the platinum is present as well-faceted particles with dimensions between 10 and 50 nm.

14. The catalyst of claim 1 , wherein the copper is dispersed on the zeolite as discrete Cu 2+ sites.

15. The catalyst of claim 1 , wherein the catalyst is obtained by a process comprising

(a) ion-exchange of copper on the aluminosilicate molecular sieve,

(b) calcination of the aluminosilicate molecular sieve obtained in (a), and

(c) ion-exchange of platinum on the aluminosilicate molecular sieve obtained in (b).

16. A method for treating emissions produced in the exhaust gas stream of a diesel or lean-burn vehicle, the method comprising:

passing a vehicle's engine exhaust stream through at least a NO x abatement catalyst; and passing the exhaust stream exiting the NO x abatement catalyst and containing ammonia through the oxidation catalyst of claim 1 .

17. The method of claim 16 , wherein the NOx abatement catalyst is selected from one or more of an SCR catalyst, a lean NO x trap catalyst, or other catalyst for the destruction of NO x that results in slippage of ammonia from the NO x abatement catalyst.

18. The method of claim 16 , wherein the NO x , abatement catalyst and oxidation catalyst composition are disposed on separate substrates.

19. The method of claim 16 , wherein the NO x abatement catalyst and the oxidation catalyst are disposed on the same substrate.

20. The method of claim 17 , wherein the molecular sieve comprises a zeolite.

21. The method of claim 16 , wherein the SAR is less than about 6.

22. A system for treating an exhaust gas stream comprising:

an SCR catalyst in communication with the exhaust gas stream;

an ammonia or ammonia precursor injection port in communication with the exhaust gas stream and located upstream from the SCR catalyst; and

the catalyst of claim 1 in communication with the exhaust gas stream and located downstream from the SCR catalyst.