Particle filter with SCR-active coating

Abstract

The present invention relates to a particle filter which comprises a wall-flow filter and SCR-catalytically active material, wherein the wall-flow filter comprises ducts which extend in parallel between a first and a second end of the wall-flow filter and which are alternately closed off in gas-type fashion either at the first or at the second end and which are separated by porous walls, and wherein the SCR-active material comprises a zeolite which is exchanged with copper and/or iron and which is situated in the form of a coating in the porous walls of the wall-flow filter, characterized in that the SCR-catalytically active coating comprises palladium.

Claims

1. A particle filter comprising a wall-flow filter and an in-wall coating of an SCR-active material and palladium, wherein the wall-flow filter comprises ducts which extend in parallel between a first and a second end of the wall-flow filter, which are alternatingly closed off in gas-tight fashion either at the first or at the second end, and which are separated by porous walls having pores, wherein the SCR-active material comprises a zeolite exchanged with copper and/or iron, and wherein the SCR-active material and the palladium has penetrated the pores of the porous walls and thereby coats the inner pore surfaces of the porous walls.

2. The particle filter according to claim 1, wherein the palladium is homogeneously distributed in the SCR-active material.

3. The particle filter according to claim 1, wherein the palladium is supported on a carrier material.

4. The particle filter according to claim 3, wherein the carrier material has a BET surface area of 30 to 250 m.sup.2/g (determined in accordance with DIN 66132).

5. The particle filter according to claim 4, wherein the carrier material is aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, or a mixture or a mixed oxide of at least two of these oxides.

6. The particle filter according to claim 1, wherein the in-wall coating contains palladium in amounts of 10 to 1000 ppm in relation to the SCR-active material.

7. The particle filter according to claim 1, wherein the SCR-active material contains a small-pore zeolite that is exchanged with copper and/or iron.

8. The particle filter according to claim 7, wherein the small-pore zeolite belongs to one of the structure types AEI, CHA (chabazite), ERI (erionite), LEV (levyne), and KFI.

9. The particle filter according to claim 1, wherein the SCR-active material (a) contains a copper-exchanged zeolite of the chabazite type and palladium, (b) consists of a copper-exchanged zeolite of the chabazite type and palladium, or (c) consists of a copper-exchanged zeolite of the chabazite type and palladium supported on a carrier material.

10. The particle filter according to claim 1, wherein the SCR-active material (a) contains a copper-exchanged zeolite of the levyne type, (b) consists of a copper-exchanged zeolite of the levyne type and palladium, or (c) consists of a copper-exchanged zeolite of the levyne type and palladium supported on a carrier material.

11. The particle filter according to claim 1, wherein the SCR-active material (a) contains a copper-exchanged zeolite of the AEI type, (b) consists of a copper-exchanged zeolite of the AEI type and palladium, or (c) consists of a copper-exchanged zeolite of the AEI type and palladium supported on a carrier material.

Description

EXAMPLE 1

(1) A commercially available zeolite of the structure type chabazite was exchanged with copper by means of copper acetate so that the copper content was 3.5 wt. % in relation to CuO. Palladium supported on a commercially available carrier material of alumina doped with silicon dioxide was added to the obtained suspension. The amount was calculated in such a way that the content of palladium was 200 ppm in relation to the total solids of the suspension.

(2) A commercially available wall-flow filter of silicon carbide was coated in-wall with the resulting suspension.

(3) The SCR-active coated wall-flow filter obtained in this way is subsequently referred to as C1.

COMPARATIVE EXAMPLE 1

(4) Example 1 was repeated with the difference that palladium was not added to the suspension.

(5) The SCR-active coated wall-flow filter obtained in this way is subsequently referred to as VC1.

COMPARATIVE EXAMPLE 2

(6) Example 1 was repeated with the difference that 200 ppm of supported platinum instead of supported palladium was added to the suspension.

(7) The SCR-active coated wall-flow filter obtained in this way is subsequently referred to as VC2.

COMPARATIVE EXPERIMENTS

(8) Determining the NOx Conversion of C1, VC1 and VC2

(9) a) First, C1, VC1 and VC2 were aged for 16 hours at 800 C. in hydrothermal atmosphere (10% H.sub.2O, 10% O.sub.2, remainder N.sub.2) (for comparison, fresh catalysts C1, VC1 and VC2 were also compared, see FIG. 2)

(10) b) The NOx conversion of the particle filter C1 according to the invention and of the comparative particle filters VC1 and VC1 [sic] as a function of the temperature upstream of the catalyst was determined in a model gas reactor in the so-called NOx conversion test. This NOx conversion test consists of a test procedure that comprises a pretreatment and a test cycle that is run through for various target temperatures. The applied gas mixtures are noted in Table 1.

(11) Test Procedure: 1. Preconditioning at 600 C. in N.sub.2 for 10 min 2. Test cycle repeated for the target temperatures a. Bringing up to the target temperature in gas mixture 1 b. Addition of NO.sub.x (gas mixture 2) c. Addition of NH.sub.3 (gas mixture 3), waiting until NH.sub.3 breakthrough>20 ppm, or a maximum of 30 min duration d. Temperature-programmed desorption up to 500 C. (gas mixture 3)

(12) TABLE-US-00001 TABLE 1 Gas mixtures of the NOx conversion test. Gas mixture 1 2 3 N.sub.2 Balance Balance Balance O.sub.2 10 percent by 10 percent by 10 percent by volume volume volume NOx 0 ppm 500 ppm 500 ppm NO.sub.2 0 ppm 0 ppm 0 ppm NH.sub.3 0 ppm 0 ppm 750 ppm CO 350 ppm 350 ppm 350 ppm C.sub.3H.sub.6 100 ppm 100 ppm 100 ppm H.sub.2O 5 percent by 5 percent by 5 percent by volume volume volume GHSV/h1 60,000 60,000 60,000

(13) The average conversion for the test procedure range 2c is determined for each temperature point. Plotting the average NOx conversion for the various temperature points results in a plot as shown in FIGS. 1 and 2. FIG. 1 shows the average NOx conversions and the N.sub.2O formation of the catalysts aged at 800 C. and FIG. 2 shows the results of the fresh catalyst samples.

(14) It can be seen in FIGS. 1 and 2 that C1 and VC2 have significantly improved average NOx conversions compared to VC1. This is due to the presence of palladium or platinum. Compared to VC2, however, C1 forms substantially less N.sub.2O, i.e. has a consistently better selectivity.