FOUR-WAY CONVERSION CATALYST HAVING IMPROVED FILTER PROPERTIES

Abstract

A four-way conversion catalyst for the treatment of an exhaust gas stream of a gasoline engine, the catalyst comprising a porous wall flow filter substrate comprising an inlet end, an outlet end, a substrate axial length extending between the inlet end and the outlet end, and a plurality of passages defined by porous internal walls of the porous wall flow filter substrate, wherein the plurality of passages comprise inlet passages having an open inlet end and a closed outlet end, and outlet passages having a closed inlet end and an open outlet end; wherein in the pores of the porous internal walls and on the surface of the porous internal walls, which surface defines the interface between the porous internal walls and the passages, the catalyst comprises a three-way conversion catalytic coating comprising an oxygen storage compound and a platinum group metal supported on a refractory metal oxide; wherein in the pores of the porous internal walls, the three-way conversion catalytic coating is present as in-wall-coating and on the surface of the porous internal walls, the three-way conversion catalytic coating is present as on-wall-coating; wherein in addition to said three-way conversion catalytic coating, the catalyst comprises no further coating in the pores of the porous internal walls and no further coating on the surface of the porous internal walls.

Claims

1. A four-way conversion catalyst for the treatment of an exhaust gas stream of a gasoline engine, the catalyst comprising: a porous wall flow filter substrate comprising an inlet end, an outlet end, a substrate axial length extending between the inlet end and the outlet end, and a plurality of passages defined by porous internal walls of the porous wall flow filter substrate, wherein the plurality of passages comprise inlet passages having an open inlet end and a closed outlet end, and outlet passages having a closed inlet end and an open outlet end; wherein the surface of the porous internal walls defines the interface between the porous internal walls and the passages, and a three-way conversion catalytic coating comprising an oxygen storage compound and a platinum group metal supported on a refractory metal oxide support; wherein in the pores of the porous internal walls, the three-way conversion catalytic coating is present as an in-wall coating; wherein on the surface of the porous internal walls, the three-way conversion catalytic coating is present as an on-wall coating; and wherein in addition to the three-way conversion catalytic coating, the catalyst comprises no further coating in the pores of the porous internal walls and no further coating on the surface of the porous internal walls.

2. The four-way conversion catalyst of claim 1, comprising the three-way conversion catalytic coating at a total loading, l(total), in the range of from 0.1 to 5 g/in.sup.3, wherein the total loading is the sum of l(in-wall coating) and l(on-wall coating), wherein l(in-wall coating) is the loading of the in-wall coating, and wherein l(on-wall coating) is the loading of the on-wall coating.

3. The four-way conversion catalyst of claim 1, wherein from 95 to 100 weight % of the four-way conversion catalyst consists of the porous wall flow filter substrate and the three-way conversion catalytic coating.

4. The four-way conversion catalyst of claim 1, wherein the porous internal walls comprising the in-wall coating have a relative average porosity in the range of from 20 to 99%, and wherein the relative average porosity is defined as the average porosity of the internal walls comprising the in-wall coating relative to the average porosity of the internal walls not comprising the in-wall coating.

5. The four-way conversion catalyst of claim 1, wherein the porous internal walls comprising the in-wall coating have a relative average pore size in the range of from 10 to 21 micrometer, wherein the relative average pore size is defined as the average pore size of the internal walls comprising the in-wall coating relative to the average pore size of the internal walls not comprising the in-wall coating. internal walls not comprising the in wall coating is in the range of from 9.5 to 21.5 micrometer, preferably in the range of from 11.5 to 20 micrometer, more preferably in the range of from 13.5 to 18.5 micrometer.

6. The four-way conversion catalyst of claim 1, wherein the wall flow filter substrate comprises the three-way conversion catalytic coating at an inlet coating length of x % of the substrate axial length, wherein 0x100; wherein the wall flow filter substrate comprises the three-way conversion catalytic coating at an outlet coating length of y % of the substrate axial length, wherein 0y100; and wherein x+y>0.

7. The four-way conversion catalyst of claim 1, wherein the platinum group metal is at least one selected from the group consisting of ruthenium, palladium, rhodium, platinum, and iridium.

8. The four-way conversion catalyst of claim 1, wherein the oxygen storage compound has a porosity in the range of from 0.05 to 1.5 ml/g.

9. The four-way conversion catalyst of claim 1, wherein the refractory metal oxide support comprises aluminum.

10. The four-way conversion catalyst of claim 1, wherein the three-way conversion catalytic coating further comprises a promotor.

11. The four-way conversion catalyst of claim 1, wherein the three-way conversion catalytic coating further comprises a platinum group metal supported on the oxygen storage compound; and a promotor, and wherein the refractory metal oxide support comprises aluminum.

12. A process for preparing the four-way conversion catalyst of claim 1, comprising: (i) providing a porous wall flow filter substrate comprising an inlet end, an outlet end, a substrate axial length extending between the inlet end and the outlet end, and a plurality of passages defined by porous internal walls of the porous wall flow filter substrate, wherein the plurality of passages comprise inlet passages having an open inlet end and a closed outlet end, and outlet passages having a closed inlet end and an open outlet end, wherein the internal walls have an average pore size in the range of from 9 to 22 micrometer, and wherein the average porosity of the internal walls of the internal walls is in the range of from 20 to 75%; (ii) providing a washcoat slurry comprising particles of a source of the three-way conversion catalytic coating, said particles having a volume based particle size distribution Dv90 in the range of from 11 to 21 micrometer, wherein (ii) comprises: (ii.1) impregnating a source of a platinum group metal onto a refractory metal oxide support; admixing the platinum group metal supported on the refractory metal oxide with one or more of an adjuvant and a source of a promotor, obtaining a slurry comprising particles of a source of the three-way conversion catalytic coating, said particles having a volume based particle size distribution Dv90 of more than 21 micrometer; and milling said slurry obtaining a slurry wherein the particles comprised in said slurry have a volume based particle size distribution Dv90 in the range of from 11 to 21 micrometer; (ii.2) impregnating a source of a platinum group metal onto an oxygen storage compound; admixing the platinum group metal supported on the oxygen storage compound with one or more of an adjuvant and a source of a promotor, obtaining a slurry comprising particles of a source of the three-way conversion catalytic coating, said particles having a volume based particle size distribution Dv90 in the range of from 11 to 21 micrometer; and milling said slurry obtaining a slurry wherein the particles comprised in said slurry have a volume based particle size distribution Dv90 in the range of from 11 to 21 micrometer; (ii.3) admixing the slurry obtained from (ii.1) and the slurry obtained from (ii.2), obtaining the washcoat slurry comprising a source of the three-way conversion catalytic coating; and (iii) coating the porous internal walls of the porous wall flow filter substrate provided in (i) with the particles of the washcoat slurry provided in (ii).

13. The process of claim 12, wherein milling said slurry according to (ii.1) comprises: obtaining a first slurry wherein the particles comprised in the first slurry have a volume based particle size distribution Dv90 in the range of from 16 to 21 micrometer milling the remaining portion of said slurry obtaining a second slurry wherein the particles comprised in the second slurry have a volume based particle size distribution Dv90 in the range of from 4 to 8 micrometer; and combining said first slurry and said second slurry, and/or wherein milling said slurry according to (ii.2) comprises: obtaining a first slurry wherein the particles comprised in the first slurry have a volume based particle size distribution Dv90 in the range of from 16 to 21 micrometer; milling the remaining portion of said slurry obtaining a second slurry wherein the particles comprised in the second slurry have a volume based particle size distribution Dv90 in the range of from 4 to 8 micrometer; and combining said first slurry and said second slurry.

14. The process of claim 12, wherein according to (iii), coating the porous internal walls of the porous wall flow filter substrate provided in (i) with the particles of the washcoat slurry provided in (ii) comprises immersing the porous wall flow filter substrate into the washcoat slurry, exposing the porous wall flow filter substrate to the washcoat slurry for a period of time, and removing the porous wall flow filter substrate from the washcoat slurry, wherein the inlet passages of the porous wall flow filter substrate are exposed to the washcoat slurry and the outlet passages of the porous wall flow filter substrate are not exposed to the washcoat slurry, wherein the inlet passages are exposed to the washcoat slurry over x % of the substrate axial length, wherein 0<x100, or wherein the outlet passages of the porous wall flow filter substrate are exposed to the washcoat slurry and the inlet passages of the porous wall flow filter substrate are not exposed to the washcoat slurry, wherein the outlet passages are exposed to the washcoat slurry over y % of the substrate axial length, wherein 0<y100, or wherein the inlet passages and the outlet passages of the porous wall flow filter substrate are exposed to the washcoat slurry, wherein the inlet passages are exposed to the washcoat slurry over x % of the substrate axial length, wherein 0<x100, wherein the outlet passages are exposed to the washcoat slurry over y % of the substrate axial length, wherein 0<y100.

15. An exhaust gas treatment system downstream of and in fluid communication with a gasoline engine, the system comprising the four-way conversion catalyst of claim 1.

16. A method of treating an exhaust gas stream from a gasoline engine, comprising contacting the exhaust gas stream with the four-way conversion catalyst of claim 1.

17. The four-way conversion catalyst of claim 2, having a loading ratio of l(on-wall coating): l(in-wall coating) in the range of from 1:99 to 50:50.

18. The four-way conversion catalyst of claim 3, which consists of the porous wall flow filter substrate and the three-way conversion catalytic coating.

19. The four-way conversion catalyst of claim 5, wherein the average pore size of the internal walls not comprising the in-wall coating is in the range of from 9.5 to 21.5 micrometer.

20. The four-way conversion catalyst of claim 6, wherein 0x5 or 0y5.

Description

SHORT DESCRIPTION OF THE FIGURES

[0247] FIG. 1 shows a schematic section through a portion of a porous wall-flow substrate used according to the present invention prior to application of the coating. The reference numbers used in FIG. 1 stand for: [0248] 1a porous wall of the wall flow filter substrate [0249] 1b porous wall of the wall flow filter substrate [0250] 1c porous wall of the wall flow filter substrate [0251] 2 inlet passage defined by the porous internal walls 1a and 1b of the porous wall flow filter substrate [0252] 3 closed outlet end of the inlet passage 2 [0253] 4 pore of the porous internal wall 1b of the wall flow filter substrate [0254] 5 outlet passage defined by the porous internal walls 1b and 1c of the porous wall flow filter substrate [0255] 6 pore of the porous internal wall 1c of the wall flow filter substrate [0256] 7 closed inlet end of the outlet passage 5

[0257] FIG. 2 shows a schematic section through the catalyst according to the present invention, in particular the inlet in-wall and on-wall coating. The reference numbers used in FIG. 2 stand for: [0258] 1 porous wall of the wall flow filter substrate [0259] 2 closed outlet end of the inlet passage 7 [0260] 3 closed inlet end of the outlet passage 8 [0261] 4 particle of the in-wall coating [0262] 5 particle of the on-wall coating [0263] 6 pore of the porous internal wall 1 of the wall flow filter substrate [0264] 7 inlet passage defined by the wall 1 of the porous wall flow filter substrate and another wall (not shown) [0265] 8 outlet passage defined by the wall 1 of the porous wall flow filter substrate and another wall (not shown) [0266] The arrow at the left hand side of the figure indicates the inlet side of the catalyst.

[0267] FIG. 3 shows a schematic section through the catalyst according to the present invention, in particular the outlet in-wall and on-wall coating. The reference numbers used in FIG. 3 stand for: [0268] 1 porous wall of the wall flow filter substrate [0269] 2 closed outlet end of the inlet passage 7 [0270] 3 closed inlet end of the outlet passage 8 [0271] 4 particle of the in-wall coating [0272] 5 pore of the porous internal wall 1 of the wall flow filter substrate [0273] 6 particle of the on-wall coating [0274] 7 inlet passage defined by the wall 1 of the porous wall flow filter substrate and another wall thereof (not shown) [0275] 8 outlet passage defined by the wall 1 of the porous wall flow filter substrate and another wall (not shown) [0276] The arrow at the left hand side of the figure indicates the inlet side of the catalyst.

[0277] FIG. 4 shows a SEM picture of a portion of a coated substrate of standard four-way catalyst according to Comparative Example 1. According to this picture, the washcoat (bright portions) is completely in the pores of the internal walls the filter substrate.

[0278] FIG. 5 shows a SEM picture of a portion of a coated substrate of standard four-way catalyst according to Comparative Example 1, compared to FIG. 4 an enlarged section. Also according to this picture, the washcoat (bright portions) is completely in the pores of the internal walls the filter substrate.

[0279] FIG. 6 shows a SEM picture of a portion of a coated substrate of four-way catalyst according to Example 1. According to this picture, a portion of the washcoat (bright portions) is present as on-wall coating, and a portion of the washcoat is in the pores as in-wall coating of the internal walls of the filter substrate.

[0280] FIG. 7 shows a SEM picture of a portion of a coated substrate of four-way catalyst according to Example 1, compared to FIG. 6 an enlarged section According to this picture, a portion of the washcoat (bright portions) is present as on-wall coating, and a portion of the washcoat is in the pores as in-wall coating of the internal walls of the filter substrate.

[0281] FIG. 8 shows the volume based particle size distribution curve of the washcoat slurry (combined slurry) obtained from (3) of Comparative Example 1.

[0282] FIG. 9 shows the volume based particle size distribution curve of the slurry (alumina slurry) obtained from (1) of Comparative Example 1.

[0283] FIG. 10 shows the volume based particle size distribution curve of the slurry (OSC slurry) obtained from (2) of Comparative Example 1.

[0284] FIG. 11 shows the volume based particle size distribution curve of the washcoat slurry (combined slurry) obtained from (3) of Example 1.

[0285] FIG. 12 shows the volume based particle size distribution curve of the slurry (OSC slurry) obtained from (2) of Example 1.

[0286] FIG. 13 shows the volume based particle size distribution curve of the slurry (alumina slurry) obtained from (1) of Example 1.

CITED PRIOR ART

[0287] U.S. 2012/124974 A1