Active SCR catalyst

Abstract

The invention relates to a catalyst comprising a small-pore zeolite that contains iron and copper and has a maximum ring size of eight tetrahedral atoms, characterized in that the channel width of the small-pore zeolite amounts to >3.8 Å (0.38 nm) in at least one dimension.

Claims

1. A catalyst comprising a small-pore zeolite that contains iron and copper and has a maximum ring size of eight tetrahedral atoms, wherein the small-pore zeolite has a structure of type EAB, ERI, ESV, JBW or LEV, and wherein a channel width of the small-pore zeolite amounts to ≥0.47 nm (4.7 Å) in at least one dimension, and wherein the small-pore zeolite comprises copper in an amount of 1.0 to 1.9 wt. %, calculated as Cu, and iron in an amount of 1.0 to 2.0 wt. %, calculated as Fe, based in each case on the total weight of the small-pore zeolite with the copper and iron, and wherein the small pore zeolite contains no further metal besides copper and iron.

2. A catalyst comprising a small-pore zeolite that contains iron and copper and has a maximum ring size of eight tetrahedral atoms, wherein the small-pore zeolite has a structure type of EAB, ERI, ESV, JBW or LEV, and wherein a channel width of the small-pore zeolite amounts to >0.38 nm (3.8 Å) in at least one dimension, and wherein the small-pore zeolite comprises copper in an amount of 1.5 wt. %, calculated as Cu, and iron in an amount of 1.3 wt. %, calculated as Fe, based in each case on the total weight of the small-pore zeolite with the copper and iron, and wherein the small pore zeolite contains no further metal besides copper and iron.

3. The catalyst according to claim 1, wherein the small-pore zeolite is of the structure type ERI or LEV.

4. The catalyst according to claim 1, wherein the small-pore zeolite has a SAR value of 1 to 50.

5. The catalyst according to claim 1, wherein the small-pore zeolite is of the structure type ERI and has an SAR value of 5 to 15.

6. The catalyst according to claim 2, wherein the molar ratio of Cu:Al is 0.03 to 0.10.

7. The catalyst according to claim 2, wherein the molar ratio of (Cu+Fe):Al is 0.12 to 0.2.

8. The catalyst according to claim 1, wherein the small-pore zeolite is of the structure type LEV and has a SAR value of 20 to 40.

9. The catalyst according to claim 8, wherein a molar ratio of Cu:Al is 0.15 to 0.30.

10. The catalyst according to claim 8, wherein a molar ratio of (Cu+Fe):A1 is 0.32 to 0.50.

11. The catalyst according to claim 1, wherein the catalyst is present in a form of a coating on a carrier substrate.

12. The catalyst according to claim 11, wherein the carrier substrate is a flow-through substrate or a wall-flow filter.

13. The catalyst according to claim 11, wherein the carrier substrate is inert and consists of silicon carbide, aluminum titanate or cordierite.

14. The catalyst according to claim 11, wherein the carrier substrate comprises a catalytically active material.

15. The catalyst according to claim 14, wherein the carrier substrate comprises an SCR catalytically active material.

16. The catalyst according to claim 14, wherein the catalytically active material comprises a mixed oxide containing vanadium, titanium and tungsten compounds.

17. The catalyst according to claim 1, wherein the catalyst is present as part of a carrier substrate.

18. The catalyst according to claim 17, wherein the carrier substrate is a flow-through substrate or a wall-flow filter.

19. The catalyst according to claim 17, wherein the carrier substrate is coated with a catalytically active material.

20. The catalyst according to claim 2, wherein the channel width of the small-pore zeolite is ≥0.47 nm (4.7 A) in at least one dimension.

21. A method for purifying exhaust gas of lean-operated combustion engines, wherein the exhaust gas is passed over a catalyst according to claim 1.

22. A system for purifying exhaust gas from lean-operated combustion engines, wherein the system comprises the catalyst according to claim 1 as well as an injector for aqueous urea solution, wherein the injector is located upstream of the catalyst.

23. The system according to claim 22, wherein the system further comprises an oxidation catalyst.

24. The system according to claim 23, wherein the oxidation catalyst includes platinum.

25. A catalyst comprising a small-pore zeolite that contains iron and copper and has a maximum ring size of eight tetrahedral atoms, and wherein the small-pore zeolite comprises copper in an amount of 1.0 to 1.9 wt. %, calculated as Cu and iron in an amount of 1.0 to 2.0 wt. %, calculated as Fe, based in each case on the total weight of the small-pore zeolite with the copper and iron, and wherein the small pore zeolite contains no further metal besides copper and iron, wherein the small-pore zeolite has either a structure type of ERI with an SAR value of 5 to 15, or a structure type of LEV with an SAR value of 20 to 40, and wherein a channel width of the small-pore zeolite is 0.48 to 0.51 nm in at least one dimension.

Description

(1) The invention is explained in more detail in the following examples and figures.

(2) FIG. 1 shows the SCR activity of K1, VK1 and VK2 in the fresh state

(3) FIG. 2 shows the SCR activity of K1, VK1 and VK2 in the aged state

(4) FIG. 3 shows the SCR activity of K2, VK3 and VK4 in the fresh state

(5) FIG. 4 shows the SCR activity of K2, VK3 and VK4 in the aged state

(6) FIG. 5 shows the SCR activity of VK5, VK6 and VK7 in the fresh state

(7) FIG. 6 shows the SCR activity of VK5, VK6 and VK7 in the aged state

EXAMPLE 1

(8) 1.24 g copper acetylacetonate (24.4 wt. % Cu) and 1.65 iron acetylacetonate (15.8 wt. % Fe) were roughly mixed with 19.8 g of an erionite having an SAR value of 8, homogenized and then calcined at 550° C. for 2 hours. This resulted in about 20 g of an erionite exchanged with 1.5 wt. % copper and 1.3 wt. % iron, called K1 below.

COMPARATIVE EXAMPLE 1

(9) The procedure described in example 1 was repeated with the difference that the iron acetylacetonate was omitted. This resulted in about 20 g of an erionite exchanged with 1.5 wt. % copper, called VK1 below.

COMPARATIVE EXAMPLE 2

(10) The procedure described in example 1 was repeated with the difference that the copper acetylacetonate was omitted and iron acetylacetonate was used in an amount of 2.53 g. This resulted in about 20 g of an erionite exchanged with 2.0 wt % iron, called VK2 below.

EXAMPLE 2

(11) The procedure described in example 1 was repeated with the difference that 19.8 g of a levyne with an SAR value of 30 were used instead of erionite. This resulted in about 20 g of a levyne exchanged with 1.5 wt. % copper and 1.3 wt. % iron, called K2 below.

COMPARATIVE EXAMPLE 3

(12) The procedure described in example 2 was repeated with the difference that the iron acetylacetonate was omitted. This resulted in about 20 g of a levyne exchanged with 1.5 wt. % copper, called VK3 below.

COMPARATIVE EXAMPLE 4

(13) The procedure described in example 2 was repeated with the difference that the copper acetylacetonate was omitted and iron acetylacetonate was used in an amount of 2.53 g. This resulted in about 20 g of a levyne exchanged with 2.0 wt. %, iron, called VK4 below.

COMPARATIVE EXAMPLE 5

(14) The procedure described in example 1 was repeated with the difference that 19.8 g of a chabazite with an SAR value of 28 was used instead of erionite. This resulted in about 20 g of a chabazite exchanged with 1.5 wt. % copper and 1.3 wt. % iron, called VK5 below.

COMPARATIVE EXAMPLE 6

(15) The procedure described in comparative example 5 was repeated with the difference that the iron acetylacetonate was omitted. This resulted in about 20 g of a chabazite exchanged with 1.5 wt. % copper, called VK6 below.

COMPARATIVE EXAMPLE 7

(16) The procedure described in comparative example 5 was repeated with the difference that the copper acetylacetonate was omitted and iron acetylacetonate was used in an amount of 2.53 g. This resulted in about 20 g of a chabazite exchanged with 2.0 wt. % iron, called VK7 below.

COMPARATIVE EXPERIMENTS

(17) a) The catalysts K1 and K2 as well as VK1 to VK7 were fresh and compared. The aging was carried out at 580° C. in 10% H.sub.2O and 10% 02 in N.sub.2 for 100 hours.

(18) b) The SCR activity of aged catalysts K1 and K2 as well as VK1 to VK7 was tested in a fixed bed quartz reactor under the conditions given in the table below.

(19) For this purpose, the catalyst powders were first screened and the fraction of 500 to 700 μm was used for the test.

(20) They were then heated in N.sub.2 to 600° C., then to the test gas (see table below) and cooled to 100° C. at 2 K/min. Meanwhile, the conversion of NO with NH.sub.3 was monitored by means of online FT-IR.

(21) TABLE-US-00001 Gas/Parameter Concentration/Conditions NH.sub.3 450 ppm NO 500 ppm H.sub.2O 5% O.sub.2 5% N.sub.2 Rest Temperature Cooling 600 to 100° C. @ −2° C./min Space velocity 130.000 h.sup.−1

(22) The results are shown in FIGS. 1 to 6.

(23) In the fresh state, K1 (copper- and iron-containing erionite) thus already exhibits distinct advantages compared to VK1 (copper-containing erionite) and VK2 (iron-containing erionite), which still increase in the aged state. A similar picture results when comparing K2 (copper- and iron-containing levyne) with VK3 (copper-containing levyne) and VK4 (iron-containing levyne). While K2 and VK3 deliver approximately the same results in the fresh state, K2 has considerable advantages in the aged state. A different picture results when comparing the chabazite-containing VK5, VK6 and VK7. Here, VK6 containing only copper provides the best results in the fresh and aged state.