Oxidation catalyst for treating the exhaust gas of a compression ignition engine

1. An oxidation catalyst for treating carbon monoxide (CO) and hydrocarbons (HCs) in exhaust gas from the compression ignition engine, wherein the oxidation catalyst comprises:

a substrate, which is a flow through monolith;

a first layer disposed on the substrate, which first layer is a first zone; and

a second layer disposed on the substrate, which second layer is a second zone; wherein the first zone or the second zone comprises:

a platinum group metal (PGM) component selected from the group consisting of a platinum (Pt) component, a palladium (Pd) component and a combination thereof;

an alkaline earth metal component;

a support material comprising a modified alumina incorporating a heteroatom component; and

wherein the platinum group metal (PGM) component, the alkaline earth metal component and the support material are disposed on the substrate, and the total amount of the alkaline earth metal component is 10 to 500 gft −3 .

2. An oxidation catalyst according to claim 1 , wherein the modified alumina incorporating a heteroatom component is an alumina doped with a heteroatom component, an alkaline earth metal aluminate or a mixture thereof.

3. An oxidation catalyst according to claim 2 , wherein the heteroatom component comprises silicon, magnesium, barium, lanthanum, cerium, titanium, zirconium or a combination of two or more thereof.

4. An oxidation catalyst according to claim 1 , wherein the modified alumina incorporating a heteroatom component is alumina doped with silica.

5. An oxidation catalyst system according to claim 1 , wherein the modified alumina incorporating a heteroatom component is an alkaline earth metal aluminate.

6. An oxidation catalyst according to claim 1 , wherein the alkaline earth metal component comprises magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) or a combination of two or more thereof.

7. An oxidation catalyst according to claim 6 , wherein the alkaline earth metal component comprises strontium (Sr) or barium (Ba).

8. An oxidation catalyst according to claim 1 , wherein the first zone is disposed directly on the substrate.

9. An oxidation catalyst according to claim 1 , wherein the second zone is disposed directly on the substrate.

10. An oxidation catalyst according to claim 1 , wherein the second layer partly overlaps the first layer.

11. An oxidation catalyst according to claim 1 , wherein first zone is upstream of the second zone.

12. An oxidation catalyst according to claim 1 , wherein the second zone is upstream of the first zone.

13. An oxidation catalyst according to claim 1 , wherein the first zone has a length of 10 to 80 % of the length of the substrate.

14. An oxidation catalyst according to claim 1 , wherein the second zone has a length of 10 to 80 % of the length of the substrate.

15. An oxidation catalyst according to claim 1 , wherein the first zone comprises a platinum group metal (PGM) component consisting of a combination of a platinum (Pt) component and a palladium (Pd) component, and the second zone comprises a platinum group metal (PGM) component consisting of a combination of a palladium (Pd) component and a platinum (Pt) component, and wherein the ratio by mass of the platinum (Pt) component to the palladium (Pd) component in the first zone is different to the ratio by mass of the platinum (Pt) component to the palladium (Pd) component in the second zone.

16. An oxidation catalyst according to claim 1 , wherein the first zone comprises a platinum group metal (PGM) component selected from the group consisting of a Pd component and a combination of a palladium (Pd) component and a platinum (Pt) component, and wherein the second zone comprises a platinum group metal (PGM) component consisting of a Pt component.

17. An oxidation catalyst according to claim 1 , wherein the first zone comprises a platinum group metal (PGM) component selected from the group consisting of a platinum (Pt) component and a combination of a palladium (Pd) component and a platinum (Pt) component, and the second zone comprises a platinum group (PGM) component consisting of a palladium (Pd) component.

18. An oxidation catalyst according to claim 1 , wherein the first zone comprises a platinum group (PGM) component selected from the group consisting of a platinum (Pt) component and a palladium (Pd) component, and the second zone comprises a platinum group metal (PGM) component consisting of a combination of a palladium (Pd) component and a platinum (Pt) component.

19. An exhaust system for a compression ignition engine comprising an oxidation catalyst according to claim 1 for treating carbon monoxide (CO) and hydrocarbons (HCs) in exhaust gas from the compression ignition engine.

20. A method of treating carbon monoxide (CO) and hydrocarbons (HCs) in an exhaust gas from a compression ignition engine, which method comprises contacting the exhaust gas with an oxidation catalyst, wherein the oxidation catalyst comprises:

a substrate, which is a flow through monolith;

a first layer disposed on the substrate, which first layer is a first zone; and

a second layer disposed on the substrate, which second layer is a second zone; wherein the first zone or the second zone comprises:

a platinum group metal (PGM) component selected from the group consisting of a platinum (Pt) component, a palladium (Pd) component and a combination thereof;

an alkaline earth metal component;

a support material comprising a modified alumina incorporating a heteroatom component; and

wherein the platinum group metal (PGM) component, the alkaline earth metal component and the support material are disposed on the substrate, and the total amount of the alkaline earth metal component is 10 to 500 gft −3 .