Oxidation catalyst for a diesel engine exhaust

1. An oxidation catalyst for treating an exhaust gas produced by a diesel engine comprising a catalytic region and a substrate, wherein the catalytic region comprises a catalytic material comprising:

bismuth (Bi) or an oxide thereof with a bismuth loading of 7.5 to 60 g ft −3 ;

an alkali metal or an oxide thereof with an alkali metal loading of 7.5 to 60 g ft −3 , the alkali metal being selected from the group consisting of potassium (K), caesium (Cs) and a combination of thereof;

a platinum group metal (PGM) selected from the group consisting of (i) platinum (Pt), and (ii) platinum (Pt) and palladium (Pd); and

a support material comprising an alumina doped with silica in a total amount of 0.5 to 15% by weight of the alumina;

wherein the bismuth or an oxide thereof is supported on the support material;

wherein the alkali metal or an oxide thereof is supported on the support material;

wherein the catalytic material comprises a ratio by weight of the PGM to bismuth of 10:1 to 1:2.

2. An oxidation catalyst according to claim 1 , wherein the alkali metal is caesium (Cs).

3. An oxidation catalyst according to claim 1 , wherein the catalytic material comprises a total loading of bismuth of 15 to 40 g ft −3 .

4. An oxidation catalyst according to claim 1 , wherein the catalytic material comprises bismuth in an amount of 0.1 to 5.0% by weight of the support material.

5. An oxidation catalyst according claim 1 , wherein the catalytic material comprises a total loading of an alkali metal of 15 to 40 g ft −3 .

6. An oxidation catalyst according to claim 1 , wherein the catalytic material comprises an alkali metal in a total amount of 0.1 to 5.0% by weight of the support material.

7. An oxidation catalyst according to claim 1 , wherein the platinum group metal (PGM) is platinum (Pt).

8. An oxidation catalyst according to claim 1 , wherein the catalytic region further comprises a zeolite hydrocarbon adsorbent material.

9. An oxidation catalyst according to claim 1 , wherein the catalytic region is disposed on the substrate.

10. An oxidation catalyst according to claim 1 , wherein the catalytic region is a first catalytic region and the oxidation catalyst further comprises a second catalytic region.

11. An oxidation catalyst according to claim 10 , wherein the first catalytic region is a first catalytic layer and the second catalytic region is a second catalytic layer, and the first catalytic layer is disposed on the second catalytic layer.

12. An oxidation catalyst according to claim 10 , wherein the first catalytic region is a first catalytic layer and the second catalytic region is a second catalytic layer, and the second catalytic layer is disposed on the first catalytic layer.

13. An oxidation catalyst according to claim 10 , wherein the first catalytic region is a first catalytic zone and the second catalytic region is a second catalytic zone, and wherein the first catalytic zone is disposed upstream of the second catalytic zone.

14. An oxidation catalyst according to claim 10 , wherein the first catalytic region is a first catalytic zone and the second catalytic region is a second catalytic zone, and the second catalytic zone is disposed upstream of the first catalytic zone.

15. An oxidation catalyst according to claim 10 , wherein the first catalytic region is disposed on the second catalytic region.

16. An oxidation catalyst according to claim 15 , wherein the second catalytic region is a second catalytic layer and the first catalytic region is a first catalytic zone, and wherein an entire length of the first catalytic zone is disposed on the second catalytic layer.

17. An oxidation catalyst according to claim 15 , wherein the second catalytic region is a second catalytic zone and the first catalytic region is a first catalytic zone or a first catalytic layer, and wherein the first catalytic zone or the first catalytic layer is disposed on the second catalytic zone.

18. An oxidation catalyst according to claim 10 , wherein the second catalytic region is disposed on the first catalytic region.

19. An oxidation catalyst according to claim 18 , wherein the first catalytic region is a first catalytic layer and the second catalytic region is a second catalytic zone, and wherein an entire length of the second catalytic zone is disposed on the first catalytic layer.

20. An oxidation catalyst according to claim 18 , wherein the first catalytic region is a first catalytic zone and the second catalytic region is a second catalytic zone or a second catalytic layer, and wherein the second catalytic zone or the second catalytic layer is disposed on the first catalytic zone.

21. An oxidation catalyst according to claim 10 , wherein the second catalytic region, layer or zone has PNA activity and comprises a molecular sieve catalyst comprising a noble metal and a molecular sieve, wherein the molecular sieve contains the noble metal.

22. An oxidation catalyst according to claim 10 , wherein the second catalytic region, layer or zone has LNT activity and comprises a nitrogen oxides (NO x ) storage material.

23. An oxidation catalyst according to claim 10 , wherein the second catalytic region, layer or zone has DOC activity and comprises platinum (Pt), manganese (Mn) and a support material.

24. An oxidation catalyst according to claim 10 , further comprising a third catalytic region, wherein the third catalytic region is a third catalytic layer.

25. An oxidation catalyst according to claim 24 , wherein the first catalytic region, layer or zone is disposed on the third catalytic layer.

26. An oxidation catalyst according to claim 24 , wherein the second catalytic region, layer or zone is disposed on the third catalytic layer.

27. An oxidation catalyst according to claim 24 , wherein the third catalytic region, layer or zone has PNA activity and comprises a molecular sieve catalyst comprising a noble metal and a molecular sieve, wherein the molecular sieve contains the noble metal.

28. An oxidation catalyst according to claim 24 , wherein the third catalytic region, layer or zone has LNT activity and comprises a nitrogen oxides (NO x ) storage material.

29. An oxidation catalyst according to claim 24 , wherein the third catalytic region, layer or zone has DOC activity and comprises platinum (Pt), manganese (Mn) and a support material.

30. An oxidation catalyst according to claim 1 , wherein the substrate is a flow-through monolith or a filtering monolith.

31. An exhaust system for treating an exhaust gas produced by a diesel engine, wherein the exhaust system comprises the oxidation catalyst of claim 1 and optionally an emissions control device.

32. A vehicle comprising a diesel engine and an oxidation catalyst according to claim 1 .

33. A method of treating an exhaust gas produced by a diesel engine, wherein the method comprises the step of passing an exhaust gas produced by a diesel engine through an exhaust system comprising the oxidation catalyst of claim 13 or through an exhaust system according to claim 31 .

34. An oxidation catalyst according to claim 1 , wherein the catalytic material comprises a ratio by weight of bismuth to total alkali metal of 5:1 to 1:5.

35. An oxidation catalyst according to claim 1 , wherein the catalytic region has a total loading of the PGM of 10 to 250 g ft −3 .