Method, multifunctional filter and system for the removal of particulate matter and noxious compounds from engine exhaust gas
A multifunctional wall flow filter and a system having same performing removal of noxious compounds comprising nitrogen oxides, volatile organic compounds and carbon monoxide and particulate matter from exhaust gas of a compression ignition engine is disclosed.
1. A method for the removal of noxious compounds comprising nitrogen oxides, volatile organic compounds and carbon monoxide and particulate matter from exhaust gas of a compression ignition engine comprising in series the steps of
(a) adding an amount of SCR reductant in form of droplets of an aqueous urea solution to the exhaust gas;
(b) introducing the exhaust gas admixed with the droplets of the aqueous urea solution into inlet channels of a wall flow filter and oxidizing the volatile organic compounds and carbon monoxide to carbon dioxide and water and nitrogen monoxide to nitrogen dioxide in presence of an oxidation catalyst arranged on permeable porous partition walls at inlet side of the wall flow filter, the oxidation catalyst active in;
(c) subsequently evaporating and decomposing the droplets of the aqueous urea solution in the exhaust gas from step (b) to ammonia;
(d) passing the exhaust gas containing the ammonia through the permeable porous partition walls of the wall flow filter to outlet channels of the filter and capturing the particulate matter on surface of the permeable porous partition walls facing the inlet channels of the filter;
(e) removing continuously the captured particulate matter by reaction with the nitrogen dioxide contained in the exhaust gas; and
(f) subsequently removing remaining amounts of nitrogen dioxide from the exhaust gas by reaction with the ammonia in presence of an SCR active catalyst arranged within the gas permeable porous partition walls and/or on wall side facing the outlet channels of the wall flow particle filter.
2. The method of claim 1 , further comprising a step of removing excess of ammonia contained in the exhaust gas by contact with an ammonia slip catalyst arranged at outlet of the outlet channels of the wall flow filter.
3. The method of claim 1 , wherein droplet size of the aqueous urea solution is at least 7 micrometer.
4. The method according to claim 1 , wherein the SCR catalyst comprises oxides of vanadium and/or tungsten and titania.
5. The method according to claim 1 , wherein the SCR active catalyst comprises one or more copper or iron promoted beta-zeolites.
6. The method according to claim 1 , wherein the SCR active catalyst comprises copper promoted SAPO-34 and/or copper promoted SSZ-13.
7. The method according to claim 1 , wherein the oxidation catalyst comprises platinum and/or palladium.
8. The method according to claim 2 , wherein the ammonia slip catalyst comprises platinum and CuSAPO-34 and/or SSZ-13.
9. Multifunctional wall flow filter for cleaning exhaust gas from a compression ignition engine comprising
a plurality of exhaust gas inlet flow channels and a plurality of exhaust gas outlet channels separated by gas permeable porous partition walls;
a diesel oxidation catalyst applied in the exhaust gas inlet flow channels on the partition walls at exhaust gas inlet side; and
an SCR catalyst for selective reduction of nitrogen oxides applied within the partition walls and/or on surface of the partition walls facing the outlet channels in a region between the exhaust gas inlet side and outlet side,
wherein upper layer of the diesel oxidation catalyst is passivated with a coat of an inert material.
10. Multifunctional wall flow filter according to claim 9 , wherein the outlet side of the outlet channels is additionally provided with an ammonia slip catalyst.
11. Multifunctional wall flow filter according to claim 9 , wherein the SCR catalyst comprises, oxides of vanadium and/or tungsten and titania.
12. Multifunctional wall flow filter according to claim 9 , wherein the SCR active catalyst comprises one or more copper or iron promoted beta-zeolites.
13. Multifunctional wall flow filter according to claim 9 , wherein the SCR catalyst comprises copper promoted SAPO-34 and/or copper promoted SSZ-13.
14. Multifunctional wall flow filter according to claim 9 , wherein the oxidation catalyst comprises platinum and/or palladium.
15. Multifunctional wall flow filter according to claim 10 , wherein the ammonia slip catalyst comprises platinum and CuSAPO-34 and/or SSZ-13.
16. Multifunctional wall flow filter according to claim 9 , wherein the coat of an inert layer comprises a material, which does not hydrolyse urea to ammonia.
17. A system for cleaning exhaust gas from a diesel engine comprising
an injector and a downstream multifunctional wall flow filter with a plurality of exhaust gas inlet flow channels and a plurality of exhaust gas outlet channels separated by gas permeable porous partition walls;
a diesel oxidation catalyst applied in the exhaust gas inlet flow channels on the partition walls at exhaust gas inlet side; and
an SCR catalyst for selective reduction of nitrogen oxides applied within the partition walls and/or on surface of the partition walls facing the outlet channels in a region between the exhaust gas inlet side and outlet side,
wherein the injector is adapted to inject droplets of a urea-water-solution into exhaust gas upstream of the multifunctional wall flow filter so that the urea-water-solution comes in contact with the diesel oxidation catalyst in liquid form or the injector is arranged at a distance to the inlet of multifunctional wall flow filter resulting in a droplet size of the urea-water-solution so that the urea-water-solution comes in contact with the diesel oxidation catalyst in liquid form.