CATALYTIC COATING

Abstract

The present invention is directed towards a catalytic coating comprising a composite oxide which accelerates soot combustion. The oxide is used in a catalytic coating in soot filters for the abatement of noxious pollutants in exhaust gases from combustion processes. A process for the production of catalytic coatings comprising these composite oxides is also given.

Claims

1. Catalytic coating on the inlet channels of a wall-flow filter for the combustion of soot comprising a composite oxide according to the formula:
Pr.sub.2-xA.sub.xCe.sub.2-yB.sub.yO.sub.z in which A is an alkaline earth metal, an alkaline metal or a transition metal; B is a transition metal different from A; and x and y are values from 0-1, wherein x and/or y>0; and z has a value that serves for electroneutrality of the composite oxide.

2. Catalytic coating according to claim 1, wherein A is be selected from the group consisting of Mg, Ca, Sr, Ba, K, Cs, La, Bi, Y, Zn; and B is be selected from the group consisting of Sn, Zr, Ti, Fe, Mn, Al, Ga, Bi, Ni, Co, Cu.

3. Catalytic coating according to claim 1, wherein x has a value from 0.05-0.5.

4. Catalytic coating according to claim 1, wherein y has a value from 0.05-0.5.

5. Catalytic coating according to claim 1, wherein it does not comprise a PGM.

6. Catalytic coating according to claim 1, wherein the composite oxide has a defective fluorite or pyrochlore structure.

7. Catalytic coating according to claim 1, wherein the composite oxide has a needle-type morphology having an aspect ratio of 5:1-30:1.

8. Catalytic coating according to claim 1, wherein the composite oxide has a d50 of 0.5-10.

9. Process for the production of catalytic coating, wherein the composite oxide according to the formula:
Pr.sub.2-xA.sub.xCe.sub.2-yB.sub.yO.sub.z in which A is an alkaline earth metal, an alkaline metal or a transition metal; B is a transition metal different from A; and x and y are values from 0-1, wherein x and/or y>0; and z has a value that serves for electroneutrality of the composite oxide; is prepared by a process comprising the following steps in that order: co-precipitate a precursor of the composite oxide by adding a base to a solution of ions that can form the precursor by base addition; optionally age the precursor at temperatures between 60 C.-160 C.; optionally separate the precursor from the liquid and wash the precursor at least one time with water; spray-dry the resulting precursor to become the composite oxide; and incorporate the composite oxide into a suspension for coating a wall-flow filter.

10. Use of a catalytic coating according to claim 1, in the inlet channels of soot filters of the wall-flow type for the exhaust treatment of combustion processes.

11. Use according to claim 10, wherein the soot filter is present in an exhaust system comprising at least 2 further three-way-catalysts each of them positioned on a separate flow-through substrate.

Description

EXAMPLES

Exemplary Procedure for Composite Oxide Preparation

[0059] Pr.sub.2Ce.sub.1.9Sn.sub.0.1O.sub.xThe appropriate amount of Ce(NO.sub.3).sub.3.Math.6H.sub.2O, Pr(NO).sub.3.Math.6H.sub.2O and SnCl.sub.4.Math.5H.sub.2O are dissolved in 500 ml of distilled water at room temperature. Synthesis is carried out via precipitation, where NH.sub.4OH is added dropwise into the solution under stirring conditions until pH=9 is reached. Then, the solution gel is aged at 60 C. for 16 h. Afterwards, the material is filtered and thoroughly washed with distilled water. Wet cake is redissolved in water and spray-dried. Finally, the catalyst is calcined at 800 C. for 2 h at 10 C./min temperature increase. The final catalyst is subsequently hydrothermally aged at 800 C. for 16 h in the presence of 10% H.sub.2O.

[0060] Pr.sub.2Ce.sub.1.9Bi.sub.0.1O.sub.7-zThe appropriate amount of Ce(NO.sub.3).sub.3.Math.6H.sub.2O, Pr(NO.sub.3).sub.3.Math.6H.sub.2O and Bi(NO.sub.3).sub.3.Math.xH.sub.2O are dissolved in 500 mL of distilled water at room temperature. Synthesis is carried out via precipitation, where NH.sub.4OH is added dropwise into the solution under stirring conditions until pH=9 is reached. Afterwards, the material is filtered and thoroughly washed with distilled water. Wet cake is redissolved in water and spray-dried. Finally, the catalyst is calcined at 800 C. for 2 h at 10 C./min. The final catalyst is subsequently hydrothermally aged at 800 C. for 16 h in the presence of 10% H.sub.2O.

[0061] Pr.sub.2Ce.sub.1.9Cu.sub.0.1O.sub.7-zThe appropriate amount of Ce(NO.sub.3).sub.3.Math.6H.sub.2O, Pr(NO.sub.3).sub.3.Math.6H.sub.2O and Cu(NO.sub.3).sub.2.Math.2.5H.sub.2O are dissolved in 500 mL of distilled water at room temperature. Synthesis is carried out via precipitation, where NH.sub.4OH is added dropwise into the solution under stirring conditions until pH=9 is reached. Afterwards, the material is filtered and thoroughly washed with distilled water. Wet cake is redissolved in water and spray-dried. Finally, the catalyst is calcined at 800 C. for 2 h at 10 C./min. The final catalyst is subsequently hydrothermally aged at 800 C. for 16 h in the presence of 10% H.sub.2O.

Reference Materials

[0062] 1% Pt/Al.sub.2O.sub.3 Appropriate amount of Pt nitrate solution PNA-type (20% wt) is dissolved in water in order to deposit 1% wt Pt via incipient wetness impregnation on a commercially available Al.sub.2O.sub.3 support (ScFa140). The material is dried overnight and calcined at 550 C. for 2 h at 10 C./min. The catalyst is subsequently hydrothermally aged at 800 C. for 16 h in the presence of 10% H.sub.2O.

[0063] Pr.sub.2Ce.sub.2O.sub.xThe appropriate amount of Ce(NO.sub.3).sub.3.Math.6H.sub.2O and Pr(NO.sub.3).sub.3.Math.6H.sub.2O are dissolved in 500 mL of distilled water at room temperature. Synthesis is carried out via precipitation, where NH.sub.4OH is added dropwise into the solution under stirring conditions until pH=9 is reached. Afterwards, the material is filtered and thoroughly washed with distilled water. Half of the wet cake is redissolved in water and spray-dried. The other half is dried in a static oven at 90 C. overnight. Finally, both composite oxides are calcined at 800 C. for 2 h at 10 C./min. The final composite oxides are subsequently hydrothermally aged at 800 C. for 16 h in the presence of 10% H.sub.2O.

[0064] Pr.sub.2Ce.sub.2O.sub.xThe appropriate amount of Ce(NO.sub.3).sub.3.Math.6H.sub.2O and Pr(NO.sub.3).sub.3.Math.6H.sub.2O are dissolved in 500 mL of distilled water at room temperature. Synthesis is carried out via precipitation, where NH.sub.4OH is added dropwise into the solution under stirring conditions until pH=9 is reached. Then, the solution gel is aged at 60 C. for 16 h. Afterwards, the material is filtered and thoroughly washed with distilled water. Wet cake is redissolved in water and spray-dried. The composite oxide is calcined at 800 C. for 2 h at 10 C./min. The final composite oxides are subsequently hydrothermally aged at 800 C. for 16 h in the presence of 10% H.sub.2O.

[0065] 10% Cu/Pr.sub.2Ce.sub.2O.sub.xThe appropriate amount of Cu(NO.sub.3).sub.2.Math.2.5H.sub.2O is dissolved in water in order to deposit 10% wt Cu via incipient wetness impregnation on Pr.sub.2Ce.sub.2O.sub.x. The material is dried overnight and calcined at 800 C. for 2 h at 10 C./min. The catalyst is subsequently hydrothermally aged at 800 C. for 16 h in the presence of 10% H.sub.2O.

Soot Oxidation Tests in TGA:

[0066] Samples are prepared by soft mechanical mixing (loose conditions) of a commercial carbon soot (Printex U) and each catalyst in a 1:4 mass ratio. TGA tests are performed up to 800 C. under air flow (10 C./min) to follow the weight loss of the burnt soot versus the controlled temperature conditions. This mass loss can be directly converted into soot conversion values considering the indicated soot:catalyst ratio (FIG. 1). T.sub.50 parameter (temperature when 50% soot has been converted/burnt) can be calculated considering initial and final values. Moreover, a blank measurement (without soot) and at least 2 TGA measurements are always carried out to validate these T.sub.50 values, by confirming sample homogeneity and excluding weight loss effects derived from water or other organic compounds adsorbed on the catalyst surface. Therefore, all T.sub.50 values expressed in this invention are an average of 2-3 measurements for each sample. Results are shown in the table below.

Results

[0067] Soot oxidation activity of composite oxides compared to other PGM-free catalysts after 16H800 ageing conditions

TABLE-US-00001 Composition Synthesis method T.sub.50( C.) 1% Pt/Al.sub.2O.sub.3 Incipient wetness impregnation 602 Pr.sub.2Ce.sub.2O.sub.x Co-precipitation + oven drying 563 Pr.sub.2Ce.sub.2O.sub.x Co-precipitation + spray drying 502 Pr.sub.2Ce.sub.2O.sub.x Co-precipitation + ageing 60 C. + 479 spray-drying Pr.sub.2Ce.sub.1.9Sn.sub.0.1O.sub.x Co-precipitation + ageing 60 C. + 464 spray-drying Pr.sub.2Ce.sub.1.9Bi.sub.0.1O.sub.x Co-precipitation + spray-drying 474 Pr.sub.2Ce.sub.1.9Cu.sub.0.1O.sub.x Co-precipitation + spray-drying 450 10% Cu/Pr.sub.2Ce.sub.2O.sub.x Co-precipitation + wet impregnation 578