CATALYST SYSTEM FOR REDUCING NITROGEN OXIDES
First Claim
1. Catalyst system for reducing nitrogen oxides, which comprises a nitrogen oxide storage catalyst and an SCR catalyst, wherein the SCR catalyst contains a small-pore zeolite with a maximum ring size of eight tetrahedral atoms and a transition metal, and wherein the nitrogen oxide storage catalyst consists of at least two catalytically active washcoat layers A and B on a supporting body, andthe washcoat layer A is arranged directly on the supporting body and contains cerium oxide, an alkaline earth compound and/or an alkali compound, as well as platinum and palladium;
- andthe washcoat layer B is arranged over the washcoat layer A and contains cerium oxide, as well as platinum and palladium, and is free of alkali and alkaline earth compounds;
characterized in thatthe ratio of cerium oxide in washcoat layer B to cerium oxide in washcoat layer A, calculated in kg/m3 (g/L) and in relation to the volume of the supporting body, is 1;
2 to 3;
1, wherein the sum of cerium oxide in washcoat layer A and washcoat layer B, calculated in kg/m3 (g/L) and in relation to the volume of the supporting body, is 100 to 240 kg/m3 (100 to 240 g/L).
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Abstract
The invention relates to a catalyst system for reducing nitrogen oxides, which comprises a nitrogen oxide storage catalyst and an SCR catalyst, wherein the nitrogen oxide storage catalyst consists of at least two catalytically active washcoat layers on a supporting body, wherein a lower washcoat layer A contains cerium oxide, an alkaline earth compound and/or alkali compound, as well as platinum and palladium, and an upper washcoat layer B, which is arranged over the washcoat layer A, contains cerium oxide, platinum and palladium, and no alkali compound and no alkaline earth compound. The invention also relates to a method for converting NOx in exhaust gases of motor vehicles that are operated by means of engines that are operated in a lean manner.
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Citations
14 Claims
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1. Catalyst system for reducing nitrogen oxides, which comprises a nitrogen oxide storage catalyst and an SCR catalyst, wherein the SCR catalyst contains a small-pore zeolite with a maximum ring size of eight tetrahedral atoms and a transition metal, and wherein the nitrogen oxide storage catalyst consists of at least two catalytically active washcoat layers A and B on a supporting body, and
the washcoat layer A is arranged directly on the supporting body and contains cerium oxide, an alkaline earth compound and/or an alkali compound, as well as platinum and palladium; - and
the washcoat layer B is arranged over the washcoat layer A and contains cerium oxide, as well as platinum and palladium, and is free of alkali and alkaline earth compounds; characterized in that the ratio of cerium oxide in washcoat layer B to cerium oxide in washcoat layer A, calculated in kg/m3 (g/L) and in relation to the volume of the supporting body, is 1;
2 to 3;
1, wherein the sum of cerium oxide in washcoat layer A and washcoat layer B, calculated in kg/m3 (g/L) and in relation to the volume of the supporting body, is 100 to 240 kg/m3 (100 to 240 g/L).- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
magnesium oxide and/or barium oxide; and a top washcoat layer B is arranged over the bottom washcoat layer A and contains no alkaline earth compound and no alkali compound, platinum and palladium in a mass ratio of 8;
1 to 10;
1, as well ascerium oxide in a quantity of 46 to 180 kg/m3 (from 46 to 180 g/L), and wherein the SCR catalyst comprises a zeolite or a molecular sieve with a chabazite structure, which contains copper in a quantity of 1 to 10 wt %, calculated as CuO and in relation to the SCR catalyst.
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12. Catalyst according to claim 1, characterized in that the nitrogen oxide storage catalyst contains at least two catalytically active washcoat layers on a supporting body,
wherein a bottom washcoat layer A contains cerium oxide in a quantity of 25 to 120 kg/m3 (from 25 to 120 g/L), platinum and palladium in a mass ratio of 8: - 1 to 10;
1, as well asmagnesium oxide and/or barium oxide; and a top washcoat layer B is arranged over the bottom washcoat layer A and contains no alkaline earth compound and no alkali compound, platinum and palladium in a mass ratio of 8;
1 to 10;
1, as well ascerium oxide in a quantity of 50 to 180 kg/m3 (from 50 to 180 g/L), and wherein the SCR catalyst comprises a zeolite or a molecular sieve with a chabazite structure, which contains copper in a quantity of 1 to 10 wt %, calculated as CuO and in relation to the SCR catalyst.
- 1 to 10;
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13. Catalyst system according to claim 1, characterized in that nitrogen oxide storage catalysts and SCR catalysts are arranged on different supporting bodies or that nitrogen oxide storage catalysts and SCR catalysts are arranged on the same supporting body.
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14. Method for converting NOx in exhaust gases of motor vehicles that are operated by means of engines that are operated in a lean manner, characterized in that the exhaust gas is fed over a catalyst system for reducing nitrogen oxides, which comprises a nitrogen oxide storage catalyst and an SCR catalyst, wherein the SCR catalyst contains a small-pore zeolite with a maximum ring size of eight tetrahedral atoms and a transition metal, and wherein the nitrogen oxide storage catalyst consists of at least two catalytically active washcoat layers A and B on a supporting body, and
the washcoat layer A is arranged directly on the supporting body and contains cerium oxide, an alkaline earth compound and/or an alkali compound, as well as platinum and palladium; - and
the washcoat layer B is arranged over the washcoat layer A and contains cerium oxide, as well as platinum and palladium, and is free of alkali compounds and alkaline earth compounds; and characterized in that the ratio of cerium oxide in washcoat layer B to cerium oxide in washcoat layer A, calculated in kg/m3 (g/L) and in relation to the volume of the supporting body, is 1;
2 to 3;
1, wherein the sum of cerium oxide in washcoat layer A and washcoat layer B, calculated in kg/m3 (g/L) and in relation to the volume of the supporting body, is 100 to 240 kg/m3 (100 to 240 g/L); andwherein the exhaust gas is fed through the catalyst system such that it flows through first the nitrogen oxide storage catalyst and then the SCR catalyst.
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Specification