System for the removal of particulate matter and noxious compounds from engine exhaust gas

1. A system for the removal of volatile organic compounds, particulate matter, and nitrogen oxides from exhaust gas of a compression ignition engine comprising:

an oxidation unit with a catalyst active in oxidation of volatile organic compounds and carbon monoxide to carbon dioxide and water, and oxidation of nitrogen oxide to nitrogen dioxide;

wherein the system is adapted for the introduction of urea solution into the exhaust gas downstream from the oxidation unit;

wherein the system further comprises a catalysed wall flow particulate filter positioned downstream of the oxidation unit and to receive exhaust gas into which urea solution has been introduced, the catalysed wall flow particulate filter comprising a plurality of longitudinal inlet flow channels and outlet flow channels separated by gas permeable porous partition walls, each inlet flow channel having an open inlet end and a closed outlet end, and each outlet flow channel having a closed inlet end and an open outlet end, the catalysed wall flow particulate filter being catalysed with an NH 3 -SCR active catalyst comprising oxides of vanadium and tungsten arranged within the gas permeable porous partition walls and/or on the plurality of the inlet and/or outlet channels;

wherein the system further comprises a three way catalyst unit positioned downstream of the catalysed wall flow particulate filter and having an NH 3 -SCR activity, an ammonia oxidation activity, and an adsorption capacity for volatile vanadium and tungsten compounds volatilized off the NH 3 -SCR active catalyst of the catalysed wall flow particulate filter, the three way catalyst unit comprising compounds selected from the group consisting of metal oxides, zeolites, silica, non-zeolite silica alumina, and mixtures thereof.

2. The system according t claim 1 , further comprising:

an SCR active catalyst comprising oxides of vanadium, tungsten, and titanium, wherein the SCR active catalyst is arranged between the catalysed wall flow particulate filter and the three way catalyst unit.

3. The system according to claim 2 , wherein the three way catalyst unit comprises a bottom layer comprising platinum, alumina, and/or titania, and optionally palladium, coated on a substrate; and a top layer comprising oxides of vanadium, tungsten, and titanium admixed with at least one of ceria, alumina, silica, zirconia, non-zeolite silica alumina, and zeolite.

4. The system according to claim 1 , wherein the three way catalyst unit comprises a bottom layer comprising platinum, alumina, and/or titania, and optionally palladium, coated on a substrate; and a top layer comprising oxides of vanadium, tungsten, and titanium admixed with at least one of ceria, alumina, silica, zirconia, non-zeolite silica alumina, and zeolite.

5. The system according to claim 4 , wherein the top layer has a layer thickness of between 40 μm and 250 μm.

6. The system according to claim 5 , wherein the bottom layer has a layer thickness of between 5 μm and 450 μm.

7. The system according to claim 5 , wherein the top layer has a porosity of between 20% and 80%.

8. The system according to claim 4 , wherein the bottom layer has a layer thickness of between 5 μm and 450 μm.

9. The system according to claim 8 , wherein the top layer has a porosity of between 20% and 80%.

10. The system according to claim 4 , wherein the top layer has a porosity of between 20% and 80%.

11. The system according to claim 4 , wherein the loading of the top layer in the three way catalyst unit is between 50 to 500 g per liter of the substrate.

12. The system according to claim 11 , wherein the loading of the bottom layer in the three way catalyst unit is between 5 and 255 g per liter of the substrate.

13. The system according to claim 4 , wherein the loading of the bottom layer in the three way catalyst unit is between 5 and 255 g per liter of the substrate.

14. The system according to claim 4 , wherein the bottom layer of the three way catalyst unit contains 0.0018 g-0.35 g platinum and/or palladium per liter of the substrate.

15. The system according to claim 14 , wherein the top layer of the three way catalyst unit comprises, per liter of the substrate: 1.0 g-20 g vanadium pentoxide, 3 g-40 g tungsten oxide, 40 g-460 g titania, 0 g-86 g silica, 0 g-86 g ceria, 0 g-86 g alumina, 0 g-86 g non-zeolite silica alumina, and 0 g-86 g of a zeolite.

16. The system according to claim 4 , wherein the top layer of the three way catalyst comprises, per liter of the substrate: 1.0 g-20 g vanadium pentoxide, 3 g-40 g tungsten oxide, 40 g-460 g titania, 0 g-86 g silica, 0 g-86 g ceria, 0 g-86 g alumina, 0 g-86 g non-zeolite silica alumina, and 0 g-86 g of a zeolite.

17. The system according to claim 1 , wherein the three way catalyst unit comprises a substrate with a flow through monolith shape.

18. The system according to claim 1 , wherein the NH 3 -SCR active catalyst of the catalysed wall flow particulate filter further comprises titania.

19. The system according to claim 1 , wherein the catalyst of the oxidation unit comprises platinum and/or palladium supported on silica-alumina and/or alumina and/or titania with a weight ratio of platinum to palladium of 1:0 to 1:1.

20. The system according to claim 19 , wherein the content of platinum and/or palladium is between 0.1 g and 2 g per liter of the catalyst of the oxidation unit.

21. A system for the removal of volatile organic compounds, particulate matter, and nitrogen oxides from exhaust gas of a compression ignition engine comprising:

an oxidation unit with a catalyst active in oxidation of volatile organic compounds and carbon monoxide to carbon dioxide and water, and oxidation of nitrogen oxide to nitrogen dioxide;

wherein the system is adapted for the introduction of NH 3 into the exhaust gas downstream from the oxidation unit;

wherein the system further comprises a catalysed wall flow particulate filter positioned downstream of the oxidation unit and to receive exhaust gas into which NH 3 has been introduced, the catalysed wall flow particulate filter comprising a plurality of longitudinal inlet flow channels and outlet flow channels separated by gas permeable porous partition walls, each inlet flow channel having an open inlet end and a closed outlet end, and each outlet flow channel having a closed inlet end and an open outlet end, the catalysed wall flow particulate filter being catalysed with an NH 3 -SCR active catalyst comprising oxides of vanadium and tungsten arranged within the gas permeable porous partition walls and/or on the plurality of the inlet and/or outlet channels;

wherein the system further comprises a three way catalyst unit positioned downstream of the catalysed wall flow particulate filter and having an NH 3 -SCR activity, an ammonia oxidation activity, and an adsorption capacity for volatile vanadium and tungsten compounds volatilized off the NH 3 -SCR active catalyst of the catalysed wall flow particulate filter, the three way catalyst unit comprising compounds selected from the group consisting of metal oxides, zeolites, silica, non-zeolite silica alumina, and mixtures thereof.