CATALYST SYSTEM FOR REDUCING NITROGEN OXIDES

• US 20170218809A1
• Filed: 08/12/2015
• Published: 08/03/2017
• Est. Priority Date: 08/13/2014
• Status: Active Grant

• Current Assignee: Umicore AG & Company KG (Umicore S.A.)
• Original Assignee: Umicore AG & Company KG (Umicore S.A.)
• Inventors: SEYLER, Michael, SCHIFFER, Michael, SCHUETZE, Frank-Walter, UTSCHIG, Thomas, HOYER, Ruediger
• Granted Patent: US 10,443,463 B2
• Time in Patent Office: Days
• CPC Class Codes: B01D 2255/1021 Platinum
• CPC Class Codes: B01D 2255/1023 Palladium
• CPC Class Codes: B01D 2255/202 Alkali metals
• CPC Class Codes: B01D 2255/204 Alkaline earth metals
• CPC Class Codes: B01D 2255/2042 Barium
• CPC Class Codes: B01D 2255/2047 Magnesium
• CPC Class Codes: B01D 2255/2065 Cerium
• CPC Class Codes: B01D 2255/20738 Iron
• CPC Class Codes: B01D 2255/20746 Cobalt
• CPC Class Codes: B01D 2255/20761 Copper
• CPC Class Codes: B01D 2255/50 Zeolites
• CPC Class Codes: B01D 2255/9022 Two layers
• CPC Class Codes: B01D 2255/91 NOx-storage component incorporated in the catalyst
• CPC Class Codes: B01D 2258/012 Diesel engines and lean burn gasoline engines
• CPC Class Codes: B01D 53/9418 for removing nitrogen oxides by selective catalytic reduction [SCR] using a reducing agent in a lean exhaust gas
• CPC Class Codes: B01D 53/9422 for removing nitrogen oxides by NOx storage or reduction by cyclic switching between lean and rich exhaust gases (LNT, NSC, NSR)
• CPC Class Codes: B01D 53/9477 with catalysts positioned on separate bricks, e.g. exhaust systems
• CPC Class Codes: B01J 23/02 of the alkali- or alkaline earth metals or beryllium
• CPC Class Codes: B01J 23/10 of rare earths
• CPC Class Codes: B01J 23/44 Palladium
• CPC Class Codes: B01J 23/464 : Rhodium
• CPC Class Codes: B01J 23/63 : with rare earths or actinides
• CPC Class Codes: B01J 29/763 : CHA-type, e.g. Chabazite, LZ-218
• CPC Class Codes: B01J 35/19 : Catalysts containing parts with different compositions
• CPC Class Codes: B01J 35/56 : Foraminous structures having flow-through passages or channels, e.g. grids or three-dimensional monoliths
• CPC Class Codes: B01J 37/0244 : Coatings comprising several layers
• CPC Class Codes: B01J 37/0246 : Coatings comprising a zeolite
• CPC Class Codes: F01N 13/009 : having two or more separate purifying devices arranged in series
• CPC Class Codes: F01N 2330/06 : Ceramic, e.g. monoliths
• CPC Class Codes: F01N 2370/02 : used in catalytic reactors
• CPC Class Codes: F01N 2510/063 : zeolites
• CPC Class Codes: F01N 3/0814 : combined with catalytic converters, e.g. NOx absorption/storage reduction catalysts
• CPC Class Codes: F01N 3/0842 : Nitrogen oxides
• CPC Class Codes: F01N 3/2066 : Selective catalytic reduction [SCR]
• CPC Class Codes: F01N 3/281 : Metallic honeycomb monoliths made of stacked or rolled sheets, foils or plates
• CPC Class Codes: F01N 3/2828 : Ceramic multi-channel monoliths, e.g. honeycombs
• CPC Class Codes: Y02A 50/20 : Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
• CPC Class Codes: Y02T 10/12 : Improving ICE efficiencies

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.

Claims

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).

2. Catalyst system according to claim 1, characterized in that the washcoat layer B contains cerium oxide in a quantity of 46 to 180 kg/m³ (from 46 to 180 g/L).

3. Catalyst system according to claim 1, characterized in that the washcoat layer A contains cerium oxide in a quantity of 14 to 95 kg/m³ (from 14 to 95 g/L).

4. Catalyst according to claim 1, characterized in that the total washcoat loading of the supporting body is 300 to 600 kg/m³ (300 to 600 g/L), in relation to the volume of the supporting body.

5. Catalyst system according to claim 4, characterized in that the loading with washcoat layer A amounts to 150 to 500 kg/m³ (150 to 500 g/L), and the loading with washcoat layer B amounts to 50 to 300 kg/m³ (50 to 300 g/L), in relation to the volume of the supporting body in each case.

6. Catalyst system according to claim 4, characterized in that the loading with washcoat layer A amounts to 250 to 300 kg/m³ (250 to 300 g/L), and, with washcoat layer B, amounts to 100 to 200 kg/m³ (100 to 200 g/L), in relation to the volume of the supporting body in each case.

7. Catalyst system according to claim 1, characterized in that the ratio of platinum to palladium in the washcoat layers A and B is 2:

1 to 18;

1.

8. The catalyst according to claim 1, characterized in that the alkaline earth compound in washcoat layer A is magnesium oxide, barium oxide, and/or strontium oxide.

9. Catalyst system according to claim 1, characterized in that the SCR catalyst contains a zeolite which belongs to the AEI, CHA, KFI, ERI, LEV, MER, or DDR structure type and is exchanged with cobalt, iron, copper, or mixtures of two or three of these metals.

10. Catalyst according to claim 1, characterized in that the SCR catalyst contains a zeolite of a chabazite type, which is exchanged with copper, iron, or copper and iron.

11. Catalyst according to claim 1, characterized in that the nitrogen oxide storage catalyst contains

a bottom washcoat layer A

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, as well as

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 as

cerium 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.

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 as

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 as

cerium 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.

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.

14. Method for converting NO_x 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); and

wherein 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.