Zoned diesel oxidation catalyst

1. An oxidation catalyst for treating an exhaust gas from a diesel engine, which oxidation catalyst comprises:

a substrate;

a first washcoat region disposed on the substrate, wherein the first washcoat region comprises a first platinum group metal (PGM) and a first support material;

a second washcoat region adjacent to the first washcoat region, wherein the second washcoat region comprises a second platinum group metal (PGM) and a second support material;

a third washcoat region disposed on the substrate, wherein the third washcoat region comprises a third platinum group metal (PGM) and a third support material; and

wherein the second washcoat region is disposed on the third washcoat region, and further wherein:

(a) the total loading of the second PGM in the second washcoat region is greater than the total loading of the first PGM in the first washcoat region; and/or

(b) the total loading of the second PGM in the second washcoat region is greater than the total loading of the third PGM in the third washcoat region; and/or

(c) the total loading of the first PGM in the first washcoat region is greater than the total loading of the third PGM in the third washcoat region.

2. The oxidation catalyst according to claim 1 , wherein the first washcoat region comprises a first washcoat layer or a first washcoat zone, the second washcoat region comprises a second washcoat layer, and the third washcoat region comprises a third washcoat layer.

3. The oxidation catalyst according to claim 1 , wherein the first washcoat region consists of a first washcoat layer.

4. The oxidation catalyst according to claim 2 , wherein the first washcoat zone comprises a first washcoat layer and a fourth washcoat layer, wherein the fourth washcoat layer is disposed on the first washcoat layer.

5. The oxidation catalyst according to claim 1 , wherein the total loading of the second PGM in the second washcoat region is greater than the total loading of the third PGM in the third washcoat region.

6. The oxidation catalyst according to claim 1 , wherein the total loading of the first PGM in the first washcoat region is greater than the total loading of the third PGM in the third washcoat region.

7. The oxidation catalyst according to claim 1 , wherein the total loading of the second PGM in the second washcoat region is greater than the total loading of the first PGM in the first washcoat region.

8. The oxidation catalyst according to claim 1 , wherein the first PGM is selected from the group consisting of platinum and a combination of platinum and palladium.

9. The oxidation catalyst according to claim 1 , wherein the second PGM is selected from the group consisting of platinum and a combination of platinum and palladium.

10. The oxidation catalyst according to claim 1 , wherein the third PGM is selected from the group consisting of platinum and a combination of platinum and palladium.

11. The oxidation catalyst according to claim 1 , wherein the first support material comprises a refractory metal oxide selected from the group consisting of alumina, silica, titania, zirconia, ceria and mixed or composite oxides of two or more thereof.

12. The oxidation catalyst according to claim 1 , wherein the second support material comprises a refractory metal oxide selected from the group consisting of alumina, silica, titania, zirconia, ceria and mixed or composite oxides of two or more thereof.

13. The oxidation catalyst according to claim 1 , wherein the third support material comprises a refractory metal oxide selected from the group consisting of alumina, silica, titania, zirconia, ceria and mixed or composite oxides of two or more thereof.

14. An exhaust system comprising an oxidation catalyst according to claim 1 , and an emissions control device.

15. A vehicle comprising a diesel engine and the exhaust system according to claim 14 .

16. The oxidation catalyst according to claim 1 , wherein the second washcoat region has a ratio by total weight of manganese (Mn) to platinum in a range of from of 5:1 to 0.2:1.

17. The oxidation catalyst according to claim 1 , wherein the second washcoat region comprises palladium.

18. The oxidation catalyst according to claim 1 , wherein the second washcoat region has a ratio of platinum to palladium by total weight of from 1:0 to 2:1.

19. The oxidation catalyst according to claim 1 , wherein at least one of the first support material, the second support material, or the third support material comprises alumina doped with silica or silica-alumina.

20. The oxidation catalyst according to claim 1 , wherein the first washcoat region further comprises at least one of an alkali metal, alkaline earth metal and a rare earth metal selected from the group consisting of lanthanum, yttrium and a combination thereof.

21. The oxidation catalyst according to claim 1 , wherein the first PGM is disposed or supported on the first support material.

22. The oxidation catalyst according to claim 1 , wherein the first support material comprises a refractory metal oxide comprising an alkaline earth metal aluminate.

23. The oxidation catalyst according to claim 1 , wherein the first support material comprises a refractory metal oxide selected from the group consisting of alumina, silica, titania, zirconia, ceria and a mixed or composite oxide thereof, optionally doped with a dopant.

24. The oxidation catalyst according to claim 1 , wherein the first PGM is a combination of platinum and palladium, and wherein at least one of the platinum and the palladium is disposed or supported on the first support material.

25. The oxidation catalyst according to claim 1 , wherein the first PGM is a combination of platinum and palladium, a combination of palladium and rhodium or a combination of platinum, palladium and rhodium, and wherein the first washcoat region further comprises a palladium support material.

26. The oxidation catalyst according to claim 25 , wherein at least one of the platinum and the rhodium is disposed or supported on the first support material and the palladium is disposed or supported on the palladium support material.

27. The oxidation catalyst according to claim 26 , wherein the palladium support material comprises a refractory metal oxide comprising ceria or a mixed or composite oxide of ceria.

28. The oxidation catalyst according to claim 1 , wherein the substrate is a through-flow substrate.

29. The oxidation catalyst according to claim 4 , wherein the total loading of the first PGM is greater than the total loading of each of the second PGM and the third PGM.