Catalysed soot filter for treating the exhaust gas of a compression ignition engine

1. A catalysed soot filter comprising an oxidation catalyst for treating carbon monoxide (CO) and hydrocarbons (HCs) in exhaust gas from a compression ignition engine disposed on a filtering substrate, wherein the oxidation catalyst comprises a plurality of layers on the filtering substrate, wherein a layer 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; and

a support material comprising a modified alumina incorporating a heteroatom component.

2. A catalysed soot filter according to claim 1 , wherein the total amount of the alkaline earth metal component is 10 to 500 gft −3 .

3. A catalysed soot filter according to claim 1 , wherein the filtering substrate comprises a plurality of inlet channels and a plurality of outlet channels; the oxidation catalyst comprises a single layer on the inlet channels and a single layer on the outlet channels; and wherein the single layer on the inlet channels comprises the platinum group metal (PGM) component, the alkaline earth metal component and the support material.

4. A catalysed soot filter according to claim 1 , wherein the filtering substrate comprises inlet channels and outlet channels; the oxidation catalyst comprises a single layer on the inlet channels and a single layer on the outlet channels; and wherein the single layer on the outlet channels comprises the platinum group metal (PGM) component, the alkaline earth metal component and the support material.

5. A catalysed soot filter according to claim 1 , wherein the oxidation catalyst comprises two layers, wherein a first layer is disposed on the filtering substrate and a second layer is disposed on the first layer, and wherein the first layer comprises the platinum group metal (PGM) component, the alkaline earth metal component and the support material.

6. A catalysed soot filter according to claim 1 , wherein the oxidation catalyst comprises two layers, wherein a first layer is disposed on the filtering substrate and a second layer is disposed on the first layer, and wherein the second layer comprises the platinum group metal (PGM) component, the alkaline earth metal component and the support material.

7. A catalysed soot filter 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.

8. A catalysed soot filter according to claim 1 , wherein the heteroatom component comprises silicon, magnesium, barium, lanthanum, cerium, titanium, zirconium or a combination of two or more thereof.

9. A catalysed soot filter according to claim 1 , wherein the modified alumina incorporating a heteroatom component is alumina doped with silica.

10. A catalysed soot filter according to claim 9 , wherein the alumina is doped with silica in an amount of 0.5 to 45% by weight.

11. A catalysed soot filter according to claim 1 , wherein the modified alumina incorporating a heteroatom component is an alkaline earth metal aluminate.

12. A catalysed soot filter according to claim 11 , wherein the alkaline earth metal aluminate is magnesium aluminate.

13. A catalysed soot filter 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.

14. A catalysed soot filter according to claim 13 , wherein the alkaline earth metal component comprises strontium (Sr) or barium (Ba).

15. A catalysed soot filter according to claim 1 , wherein the filtering substrate is a ceramic wallflow filter.

16. An exhaust system for a compression ignition engine comprising a catalysed soot filter according to claim 1 .

17. An exhaust system according to claim 16 , comprising a diesel oxidation catalyst disposed on a separate flow-through substrate monolith, which is disposed upstream of the catalysed soot filter.

18. A compression ignition engine comprising an exhaust system according to claim 16 .

19. A method of treating carbon monoxide (CO) and hydrocarbons (HCs) and NO 2 in an exhaust gas from a compression ignition engine, which method comprises contacting the exhaust gas with a catalysed soot filter according to claim 1 .