PASSIVE NITROGEN OXIDE ADSORBER HAVING OXIDATION-CATALYTICALLY ACTIVE FUNCTION

Abstract

The present invention relates to the use of a material B containing palladium and platinum in a weight ratio of 2:3 to 10:1 for increasing the low-temperature storage of nitrogen oxides by means of a material A containing palladium and zeolite, wherein material A and material B are present on a carrier substrate of the length L, and wherein material A and material B are different from one another.

Claims

1. Use of a material B containing palladium and platinum in a weight ratio of 2:3 to 10:1 for increasing the low-temperature storage of nitrogen oxides by means of a material A containing palladium and zeolite, wherein material A and material B are present on a carrier substrate of the length L, and wherein material A and material B are different from one another.

2. Use according to claim 1, characterized in that the zeolite is of structure type ABW, AEI, AFX, BEA, CHA, ERI, ESV, FAU, FER, KFI, LEV, LTA, MWW, SOD or STT.

3. Use according to claim 1, characterized in that the zeolite is of structure type AEI, AFX, BEA, CHA, FER or LEV.

4. Use according to claim 1, characterized in that the palladium is present in material A in amounts of from 0.01 to 20% by weight, based on the sum of the weights of zeolite and palladium and calculated as palladium metal.

5. Use according to claim 1, characterized in that material A contains platinum in addition to palladium.

6. Use according to claim 5, characterized in that palladium and platinum are present in a weight ratio of 20:1 to 1:1.

7. Use according to claim 1, characterized in that the support body is a flow-through substrate or a wall flow filter.

8. Use according to claim 1, characterized in that material A and material B are present in the form of coatings (coating A and coating B) on the carrier substrate.

9. Use according to claim 8, characterized in that coating A is present directly on the carrier substrate and coating B is present on coating A.

10. Use according to claim 8, characterized in that a zeolite of structure type ABW, AEI, AFX, BEA, CHA, ERI, ESV, FAU, FER, KFI, LEV, LTA, MWW, SOD or STT having from 0.5 to 5% by weight of palladium is present as a coating directly on the carrier substrate over its entire length L, and a coating containing palladium and platinum in a weight ratio of 2:1 to 4:1 is present likewise over the entire length L on this coating.

11. Use according to claim 1, characterized in that an SCR catalyst is present in addition to the carrier substrate of length L on which materials A and B are present.

12. Use according to claim 11, characterized in that the SCR catalyst is a zeolite of structure type BEA, AEI, AFX, CHA, KFI, ERI, LEV, MER or DDR and is exchanged with cobalt, iron, copper, or mixtures of two or three of these metals.

13. Use according to claim 11, characterized in that an injection device for reducing agent is located between the catalyst comprising a carrier substrate of length L, material A and material B, and the SCR catalyst.

Description

EXAMPLE 1

[0074] The catalyst according to comparative example is provided with a second coating. To this end, a washcoat consisting of Pt/Pd with a ratio of ¼ supported on a silicon-doped aluminum and a beta zeolite is applied to the first layer with a loading of 71 g/L, so that the EM loading is 43 g/ft3. The catalyst obtained is referred to below as K1.

EXAMPLE 2

[0075] Example 1 was repeated with the difference that the Pt/Pd ratio in the upper layer was 1:1. The catalyst obtained is referred to below as K2.

EXAMPLE 3

[0076] Example 1 was repeated with the difference that the Pt/Pd ratio in the upper layer was 3:2. The catalyst obtained is referred to below as K2.

[0077] For comparison of catalysts K1 to K3, the stored quantity of NOx [g/L] was determined at different efficiencies (25%, 50% and 75%). The result is shown in Table 1. Accordingly, the quantity of NOx stored (in the lower layer) increases with increasing Pd content in the (upper) layer.

[0078] For comparison of catalysts VK1 and K1, the stored quantity of NOx [g/L] at the engine was determined for the WLTC driving cycle. The result is shown in Table 2. The results show that K1 stores a larger quantity of NOx than VK1.