SCR-active material

Abstract

The present invention relates to an SCR-active material, comprising a small-pore zeolite, aluminum oxide and copper, characterized in that it contains 5 to 25 wt-% of aluminum oxide in relation to the entire material and that the copper is present on the aluminum oxide in a first concentration and on the small-pore zeolite in a second concentration.

Claims

1. An SCR-active material comprising (i) small-pore zeolites, (ii) aluminum oxide, and (iii) copper, wherein it contains 5 to 25 wt-% aluminum oxide based on the entire material and the copper is present on the aluminum oxide in a first concentration and on the small-pore zeolite in a second concentration, wherein the total amount of copper calculated as CuO and based on the total SCR-active material is 1 to 15 wt-%, wherein the first concentration is higher than the second concentration, and Wherein the small-pore zeolite forms a core and the aluminum oxide forms a shell encasing said core.

2. The SCR-active material according to claim 1, wherein the first concentration is at least 1.5 times higher than the second concentration.

3. The SCR-active material according to claim 1, wherein the zeolite has an atomic ratio of copper to framework aluminum of 0.25-0.6.

4. The SCR-active material according to claim 1, wherein the small-pore zeolite is an aluminosilicate and belongs to the structure type AEI, CHA (chabazite), ERI (erionite), LEV (levyne), AFX, DDR, or KFI.

5. The SCR-active material according to claim 4, wherein the small-pore zeolite has an SAR value of 5 to 50.

6. The SCR-active material according to claim 1, wherein the small-pore zeolite is a silicoaluminosilicate or aluminophosphate and belongs to the structure type AEI, CHA (chabazite), ERI (erionite), LEV (levyne), AFX, DDR, or KFI.

7. The SCR-active material according to claim 1, wherein the average crystallite size (d50) of the small-pore zeolite is 0.1 to 20 m.

8. The SCR-active material according to claim 1, wherein it is present in powder form.

9. The SCR-active material according to claim 1, wherein it is present (A) in the form of a coating on a carrier substrate or (B) in the form of a substrate that was extruded in combination with a matrix component.

10. The SCR-active material according to claim 1, wherein it is present in the form of a coating suspension, said coating suspension further comprises water.

11. A method for purifying exhaust gas of lean-operated combustion engines, wherein the exhaust gas is passed over an SCR-active material according to claim 1.

12. A device for purifying exhaust gas of lean-operated combustion engines, wherein it comprises an SCR-active material according to claim 1, and an injector for providing a reducing agent.

13. The device according to claim 12, wherein the reducing agent is an aqueous urea solution.

14. The device according to claim 12, and further comprising an oxidation catalyst.

15. The device according to claim 12, and further comprising a nitrogen oxide storage catalyst.

16. A method for the production of the SCR-active material according to claim 1, which comprises drying an aqueous suspension of the small-pore zeolites, copper salt, and aluminum oxide or precursor thereof to obtain a dried product, and subsequently calcining the dried product.

17. The method according to claim 16, wherein the drying is by spray drying.

18. The method according to claim 16, wherein the calcining is performed in an air or in an air/water atmosphere at temperatures between 500 C. and 900 C.

19. The method according to claim 16, which comprises placing the small-pore zeolite in water, then adding a soluble copper salt while stirring, and then adding the aluminum oxide or precursor thereof.

20. The SCR-active material according to claim 9, wherein the carrier substrate of (A) comprises a combination of an inert matrix component and the SCR-active material.

Description

EXAMPLE 1

(1) a) Preparation of a Material EM-1 According to the Invention

(2) 100.4 grams of copper(II)-acetate-1-hydrate and 960 grams of ammonium chabazite with an SiO.sub.2/Al.sub.2O.sub.3-ratio of 30 are slurried in 2500 grams of water. The resulting suspension is stirred for 2 hours. To this are added 400 grams of boehmite sol with a content of 20 wt-% Al.sub.2O.sub.3. Stirring is then continued for 2 hours.

(3) The final suspension is converted in a spray dryer to a dry powder, which is then calcined for 2 hours at 500 C. in air.

(4) b) Characterization of the Cu Distribution of EM-1 Between Zeolite and Aluminum Oxide

(5) The material EM-1 obtained according to step a) is embedded in a finely dispersed manner in a polymer resin. Thin-section samples are then prepared and examined in the transmission electron microscope. An exemplary TEM image of the material is shown in FIG. 1. The regions of the aluminum oxide and zeolite can be clearly distinguished based on the aluminum content determined by EDX and by the morphology. It shows a section of a zeolite crystallite with an aluminum oxide casing. 2 regions were marked in the receptacle to illustrate the differences between the aluminum oxide (region A) and the zeolite region (region B). At these two locations, the copper concentration was determined in weight percent by EDX and the concentration determined in region A was divided by the concentration determined in region B.

(6) Analogously, this procedure was carried out on further TEM images of zeolite crystallites with aluminum oxide casing in order to allow statistical evaluation. In all cases, it was found that the concentration of copper in the region of the aluminum oxide shell was markedly higher than on the zeolite, as can be inferred from the following table.

(7) TABLE-US-00001 Concentration Cu on Al.sub.2O.sub.3 [wt-%] divided by concentration of Cu on the zeolite [wt-%] according to TEM/EDX Sample 1 8.7 Sample 2 3.2 Sample 3 4.8

COMPARATIVE EXAMPLE 1

(8) Preparation of Comparative Material VM-1

(9) 100.4 grams of copper(II)acetate-1-hydrate and 960 grams of ammonium chabazite with a SiO.sub.2/Al.sub.2O.sub.3-ratio of 30 are slurried in 2500 grams of water. The resulting suspension is stirred for 2 hours. Unlike example 1, no boehmite sol is added. The final suspension is converted in a spray dryer to a dry powder, which is calcined for 2 hours at 500 C. in air.

(10) The amount of copper used in this preparation, based on the zeolite, is thus the same as in Example 1. However, no additional Al.sub.2O.sub.3 is present in the material on which copper can spread.

(11) Comparison of the Catalytic Activity of EM-1 and VM-1

(12) The SCR activity of the EM-1 material and the VM-1 material is tested on a powder reactor. For this purpose, 200 mg of the corresponding material are each introduced into a U-tube reactor of quartz glass and fixed with quartz wool.

(13) The nitrogen oxide conversion at a reaction temperature of 450 C. is determined in each case under the following measuring conditions: 500 ppm nitric oxide, 750 ppm ammonia, 5% water, 5% oxygen, balance nitrogen, flow cm.sup.3/min (mL/min).

(14) The EM 1-material provides 96% NO.sub.x conversion, whereas the VM-1 material provides 89% NO.sub.x conversion, only.

EXAMPLE 2

(15) Preparation of a Coated Honeycomb Body WEM-1 with EM-1 Material

(16) 950 grams of EM-1 material and 250 grams of boehmite sol containing 20 weight percent Al.sub.2O.sub.3 are made into a suspension with water. The added boehmite sol serves as a binder system in order to achieve good adhesion of the EM-1 material to a commercially available cordierite honeycomb body.

(17) The resulting suspension thus contains the following compounds or components according to sample weight and calculation of copper as CuO:

(18) TABLE-US-00002 Compounds/component Origin Proportion CuO ex EM-1 powder 3.5 wt-% Zeolite ex EM-1 powder 84.5 wt-% Aluminum oxide ex EM-1 powder 7.0 wt-% Total Aluminum oxide ex binder system 5.0 wt-% 12.0 wt-%

(19) Via a common dip method, a cordierite honeycomb body (14.4 cm (5.66 inches) diameter, 7.6 cm (3 inches) length, 62 cpscm (400 cpsi) cellular character and 0.15 mm (6 mil) wall thickness) is coated with a washcoat loading of 150 g/L catalyst volume, dried at 90 C. and annealed at 500 C.

COMPARATIVE EXAMPLE 2

(20) Preparation of a Coated Honeycomb Body WVM-1 with VM-1 Material

(21) 880 grams of VM-1 material and 600 grams of boehmite sol containing 20 weight percent Al.sub.2O.sub.3 are made into a suspension with water. Via a common dip method, a cordierite honeycomb body (14.4 cm (5.66 inches) diameter, 7.6 cm (3 inches) length, 62 cpscm (400 cpsi) cellular character and 0.15 mm (6 mil) wall thickness) is coated with a washcoat loading of 150 g/L catalyst volume, dried at 90 C. and annealed at 500 C.

(22) The resulting suspension thus contains proportionately the same amounts of the following components as Example 2, wherein unlike Example 2, this time the aluminum oxide component is derived exclusively from the binder.

(23) TABLE-US-00003 Component Origin Proportion CuO ex EM-1 powder 3.5 wt-% Zeolite ex EM-1 powder 84.5 wt-% Aluminum oxide ex binders 12.0 wt-%
Comparison of the Catalytic Activity of WEM-1 and WVM-1
a) In a Fresh State

(24) A bore core with a 2.54 cm (1 inch) diameter and 7.6 cm (3 inches) length was drilled out of the two honeycomb bodies WEM-1 and WVM-1 and tested for their catalytic activity in a model gas system.

(25) The following measurement condition was selected: 500 ppm NO, 750 ppm NH.sub.3, 5 vol-% H.sub.2O, 10 vol-% O.sub.2, residual N.sub.2 at a space velocity of 60000 h.sup.1 at reaction temperatures of 500 C. and 650 C.

(26) At both measurement temperatures, WEM-1 has higher NO.sub.x conversions compared to WVM-1.

(27) TABLE-US-00004 Reaction temperature 500 C. 650 C. WEM-1 97% NO.sub.x conversion 58% NO.sub.x conversion WVM-1 95% NO.sub.x conversion 54% NO.sub.x conversion
b) After Aging

(28) The two drill cores of WEM-1 and WVM-1 were treated at 750 C. for 16 hours in a gas mixture of 10 vol-% water, 10 vol-% oxygen and 80 vol-% nitrogen in order to simulate aging of the catalysts during driving operation.

(29) After this simulated aging, the catalytic activity under the above conditions indicated under a) is tested again. The catalyst WEM-1 based on the material EM-1 according to the invention has significantly higher NO.sub.x conversion rates than the comparative catalyst WVM-1.

(30) TABLE-US-00005 Reaction temperature 500 C. 650 C. WEM-1 85% NO.sub.x conversion 43% NO.sub.x conversion WVM-1 82% NO.sub.x conversion 28% NO.sub.x conversion

EXAMPLE 3

(31) The material EM-1 according to the invention is coated with a washcoat load of 100 g/L as an in-wall coating onto a silicon carbide filter substrate. The coated filter FEM-1 is obtained.

COMPARATIVE EXAMPLE 3

(32) Analogously to Example 3, a silicon carbide filter substrate is coated with the comparative material VEM-1. The coated filter FVM-1 is obtained.

(33) Comparison of the Catalytic Activity of FEM-1 and FVM-1

(34) In each case one drill core is removed from both coated filters according to Example 3 and Comparative Example 3. These are treated at 800 C. for 16 hours in a gas mixture of 10 vol-% water, 10 vol-% oxygen and 80 vol-% nitrogen in order to simulate the hard aging of a particulate filter coated with an SCR-active material during driving operation.

(35) Subsequently, both drill cores are measured using the model gas under the following measurement condition: 500 ppm NO, 750 ppm NH.sub.3, 5 vol-% H.sub.2O, 10 vol-% O.sub.2, residual N.sub.2 at a space velocity of 100,000 h.sup.1 at a reaction temperature of 650 C.

(36) While FVM-1 only achieves an NO.sub.x conversion of 8%, the FEM-1 sample converts 18% of the dosed nitrogen oxides.