SCR catalyst having improved adhesion of the zeolite-containing catalytic layer

Abstract

The invention relates to: a catalytic composition that is active in the selective catalytic reduction of nitric oxides, containing an iron-containing MFI-type zeolite and an iron-containing BEA-type zeolite, wherein the weight average particle size d50 of the MFI-type zeolite and the BEA-type zeolite is different; a method for producing an SCR catalyst; and the SCR catalyst produced in this way. The adhesion of the coating is improved in that the weight average particle sizes of the MFI-type and BEA-type zeolites are different.

Claims

1. A catalytic composition comprising an iron-containing MFI-type zeolite and an iron-containing BEA-type zeolite, wherein the weight-average particle sizes d50 of the zeolites are different, wherein the weight-average particle sizes d50 of the zeolites differ by at least 0.5 m and wherein the BEA-type zeolite has a weight-average particle size d50 in the range from 0.1 to 3 m and the MFI-type zeolite has a weight-average particle size d50 in the range from 2 to 10 m.

2. A catalytic composition as claimed in claim 1, wherein the weight-average particle sizes d50 of the zeolites differ by at least 2 m.

3. A catalytic composition as claimed in claim 1, wherein the BEA-type zeolite has a weight-average particle size d50 in the range from 0.2 to 2 m.

4. A catalytic composition as claimed in claim 1, wherein the MFI-type zeolite has a weight-average particle size d50 in the range from 4 to 8 m.

5. A catalytic composition as claimed in claim 1, wherein the weight ratio of the MFI-type zeolite to the BEA-type zeolite is in the range of 1:10 to 10:1.

6. A catalytic composition as claimed in claim 1, wherein the MFI-type zeolite comprises iron in amounts by weight of 0.7 to 4.9 wt %, based on the weight of the iron-containing MFI-type zeolite, and the BEA-type zeolite comprises iron in amounts by weight of 0.3 to 3.9 wt %, based on the weight of the iron-containing BEA-type zeolite.

7. A composition active in the selective catalytic reduction of nitrogen oxides comprising a catalytic composition as claimed in claim 1.

8. A washcoating composition comprising the catalytic composition as claimed in claim 1.

9. A method for producing an SCR catalyst, comprising the steps of: a) providing a washcoat as claimed in claim 8, b) contacting the washcoat with, a support material, and c) drying the support material obtained according to step b).

10. A method as claimed in claim 9, wherein the support material is a metallic or a ceramic support material.

11. An SCR catalyst comprising the catalytic composition as claimed in claim 1.

12. An SCR catalyst produced by the method as claimed in claim 9.

Description

EXAMPLES

(1) Determination of Particle Size

(2) The weight-average particle size d50 of the zeolites which are used in this invention is determined using a Malvern Mastersizer 2000 and a Malvern Hydro 2000S dispersing unit. This apparatus, produced by Malvern Instruments, Malvern, England, utilizes the principle of Mie scattering, using a low-energy He/Ne laser. Ahead of the measurement, the sample is initially dispersed with ultrasound in water for 5 minutes to form an aqueous suspension. This suspension is stirred before being measured with the measuring technique described in the operating instructions for the apparatus. The Malvern Mastersizer measures the weight-average particle size distribution of the zeolite. The weight-average particle size d50 is readily obtainable from the data generated by the apparatus.

(3) Materials 1. Iron-containing zeolite of type MFI (Fe-MFI) from Sd-Chemie Zeolites GmbH (tradename: Fe-TZP-302), iron content: 2.8 wt %, distribution of weight-average particle size: d10=1.98 m, d50=6.42 m, d90=12.21 m. 2. Iron-containing zeolite of type BEA (Fe-BEA) from Sd-Chemie Zeolites GmbH (tradename: Fe-TZB-2231), iron content: 2.1 wt %, distribution of weight-average particle size: d10=0.19 m, d50=0.47 m, d90=2.45 m. 3. Iron-containing zeolite of type MFI (FeCZP 30.2) from Sd-Chemie Zeolites GmbH, iron content: 2.2 wt %, distribution of weight-average particle size: d10=2.73 m, d50=7.41 m, d90=13.81 m. 4. Iron-containing zeolite of type BEA (FeCZB 30) from Sd-Chemie Zeolites GmbH, iron content: 2.2 wt %, distribution of weight-average particle size: d10=0.6 m, d50=6.73 m, d90=13.93 m.

(4) Production of Washcoat Suspension and of Coated Substrate

Example 1

(5) 75 g of Fe-BEA and 75 g of Fe-MFI were dispersed in 275 ml of water. Then 130 g of AL 20 DW (colloidal aluminum sol) from Nyacol were added. The suspension was dispersed for several minutes. This was followed by coating of a metallic substrate (1 inch diameter, 2 inch length, 400 cpsi) by immersion of the substrate into the washcoat suspension and subsequent suction removal or blowing out in order to remove excess washcoat suspension. Depending on the desired catalyst loading, one to two coating steps were required.

Example 2

(6) The suspension and the coated substrate were produced as in example 1, but using the samples FeCZP 30.2 and FeCZB 30.

(7) Determination of Adhesion

(8) The adhesion of the washcoat can be determined by means of what is called the thermal shock test. For this purpose, a metal honeycomb coated as described above was weighed, then heated to a temperature in the range from 650 C. to 850 C., and subsequently cast into a vessel containing cold water. The water underwent sudden evaporation. The evaporation of water, in conjunction with the sudden cooling, represents a very great physical load on the washcoat. The amount of washcoat delaminated was then ascertained. This was done by drying the substrate at 120 C. and subsequently weighing it. The weight difference found corresponds to the amount of delaminated washcoat.

(9) The thermal shock test described above was carried out a number of times, with table 1 summarizing the results.

(10) TABLE-US-00001 TABLE 1 d50 MFI d50 BEA Loss Catalyst [m] [m] [%] Example 1 6.42 0.47 13.6 Example 2 7.41 6.73 33.3 FeBEA 0.47 41.6

(11) The examples show that as the difference in the weight-average particle sizes d50 goes up between the two types of zeolite (d50 value MFI and d50 value BEA), there is an increase in the adhesion of the washcoat on the honeycomb. The loss of washcoat in the case of examples 1 and 2 is 13.6% and 33.3% respectively, based on the amount of washcoat originally present, whereas the loss in the case of a catalyst coated only with Fe-BEA is 41.6%, based on the amount of washcoat originally present. Since low washcoat loss points to improved adhesion, the catalysts coated in accordance with the invention exhibit improved adhesion of the washcoat on the support material.