Catalyst system for reducing nitrogen oxides
First Claim
1. A catalyst system for reducing nitrogen oxides, comprisinga nitrogen oxide storage catalyst and an SCR catalyst, whereinthe SCR catalyst contains a small-pore zeolite with a maximum ring size of eight tetrahedral atoms and a transition metal,the nitrogen oxide storage catalyst comprises at least two catalytically active washcoat layers A and B on a supporting body,the washcoat layer A is arranged directly on the supporting body and comprises cerium oxide, an alkaline earth compound and/or an alkali compound, as well as platinum and palladium,the washcoat layer B is arranged over the washcoat layer A and comprises cerium oxide, as well as platinum and palladium, and is free of alkali and alkaline earth compounds,a 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, andthe 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 a ratio of platinum to palladium in each of the washcoat layers A and B is 2;
1 to 18;
1.
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Accused Products
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.
19 Citations
14 Claims
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1. A catalyst system for reducing nitrogen oxides, comprising
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, the nitrogen oxide storage catalyst comprises at least two catalytically active washcoat layers A and B on a supporting body, the washcoat layer A is arranged directly on the supporting body and comprises cerium oxide, an alkaline earth compound and/or an alkali compound, as well as platinum and palladium, the washcoat layer B is arranged over the washcoat layer A and comprises cerium oxide, as well as platinum and palladium, and is free of alkali and alkaline earth compounds, a 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, andthe 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), and wherein a ratio of platinum to palladium in each of the washcoat layers A and B is 2;
1 to 18;
1. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 13, 14)
- 2 to 3;
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11. A catalyst system for reducing nitrogen oxides, comprising
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, the nitrogen oxide storage catalyst comprises at least two catalytically active washcoat layers A and B on a supporting body, the washcoat layer A is arranged directly on the supporting body and comprises cerium oxide, an alkaline earth compound and/or an alkali compound, as well as platinum and palladium, the washcoat layer B is arranged over the washcoat layer A and comprises cerium oxide, as well as platinum and palladium, and is free of alkali and alkaline earth compounds, a 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, and 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), and whereinthe washcoat layer A comprises cerium oxide in a quantity of 14 to 95 kg/m3 (from 14 to 95 g/L), platinum and palladium in a mass ratio of 8;
1 to 10;
1, andmagnesium oxide and/or barium oxide; the washcoat layer B comprises platinum and palladium in a mass ratio of 8;
1 to 10;
1, andcerium oxide in a quantity of 46 to 180 kg/m3 (from 46 to 180 g/L); and the SCR catalyst comprises a zeolite or a molecular sieve with a chabazite structure, the zeolite or molecular sieve containing copper in a quantity of 1 to 10 wt %, calculated as CuO and in relation to the SCR catalyst.
- 2 to 3;
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12. A catalyst system for reducing nitrogen oxides, comprising
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, the nitrogen oxide storage catalyst comprises at least two catalytically active washcoat layers A and B on a supporting body, the washcoat layer A is arranged directly on the supporting body and comprises cerium oxide, an alkaline earth compound and/or an alkali compound, as well as platinum and palladium, the washcoat layer B arranged over the washcoat layer A and comprises cerium oxide, as well as platinum and palladium and is free of alkali and alkaline earth compounds, a 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, and 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), and, whereinthe washcoat layer A comprises 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, andmagnesium oxide and/or barium oxide; the washcoat layer B comprises platinum and palladium in a mass ratio of 8;
1 to 10;
1, as well as andcerium oxide in a quantity of 50 to 180 kg/m3 (from 50 to 180 g/L); and the SCR catalyst comprises a zeolite or a molecular sieve with a chabazite structure, the zeolite or molecular sieve containing copper in a quantity of 1 to 10 wt %, calculated as CuO and in relation to the SCR catalyst.
- 2 to 3;
Specification