THREE-WAY DIESEL CATALYST FOR COLD START TECHNOLOGY

Abstract

The present invention relates to a catalyst, in particular to a three-way diesel catalyst, for the treatment of a diesel exhaust gas, the catalyst comprising a substrate and two specific coatings disposed thereon, wherein the first coating particularly comprises a first platinum group metal component supported on a first oxidic support material, a second platinum group metal component supported on a second oxidic support material, and a first oxygen storage component, wherein at least 30 weight-% of the first oxygen storage component consist of cerium oxide, calculated as CeOa, and wherein the second coating particularly comprises a third platinum group metal component and a fourth platinum group metal component, wherein the third platinum group metal component and the fourth platinum group metal component are supported on a third oxidic support material. Further, a process for the preparation of such a catalyst is disclosed as well as a use thereof.

Claims

1. A catalyst for the treatment of a diesel exhaust gas, the catalyst comprising (i) a substrate comprising an inlet end, an outlet end, a substrate axial length extending from the inlet end to the outlet end of the substrate and a plurality of passages defined by internal walls of the substrate extending therethrough; (ii) a first coating disposed on the surface of the internal walls of the substrate and extending over at least 50% of the axial length of the substrate from the inlet end toward the outlet end, wherein the first coating comprises a first platinum group metal component supported on a first oxidic support material, a second platinum group metal component supported on a second oxidic support material, wherein the first platinum group metal component is different to the second platinum group metal component, and a first oxygen storage compound, wherein at least 30 weight-% of the first oxygen storage compound consist of cerium oxide, calculated as CeO.sub.2; and (iii) a second coating extending over at least 50% of the axial length of the substrate from the outlet end toward the inlet end and disposed either on the surface of the internal walls of the substrate, or on the surface of the internal walls of the substrate and the first coating, or on the first coating, wherein the second coating comprises a third platinum group metal component and a fourth platinum group metal component, wherein the third platinum group metal component and the fourth platinum group metal component are supported on a third oxidic support material, and wherein the third platinum group metal component is different to the fourth platinum group metal component.

2. The catalyst of claim 1, wherein the first oxygen storage component further comprises one or more of aluminum oxide and zirconium oxide.

3. The catalyst of claim 1, wherein at least 80 weight-% of the first oxygen storage component consist of cerium oxide, calculated as CeO.sub.2, and one or more of aluminum oxide, calculated as Al.sub.2O.sub.3, and zirconium oxide, calculated as ZrO.sub.2, based on the weight of the first oxygen storage component.

4. The catalyst of claim 2, wherein the first oxygen storage component further comprises aluminum oxide.

5. The catalyst of claim 1, wherein the first oxygen storage component further comprises zirconium oxide and one or more of lanthanum oxide and praseodymium oxide.

6. The catalyst of claim 1, further comprising in the first coating a second oxygen storage component different from the first oxygen storage component, said second oxygen storage component comprising cerium oxide.

7. The catalyst of claim 1, wherein the first platinum group metal component, the second platinum group metal component, the third platinum group metal component, and the fourth platinum group metal component independently from each other comprises one more of Ru, Os, Rh, Ir, Pd, and Pt.

8. The catalyst of claim 1, wherein the first oxidic support material and the third oxidic support material independently from each other comprises one or more of alumina, silica, zirconia, titania, lanthana, alumina-zirconia, alumina-silica, alumina-titania, alumina-lanthana, silica-zirconia, silica-titania, silica-lanthana, zirconia-titania, zirconia-lanthana, and titania-lanthana.

9. The catalyst of claim 1, wherein the second oxidic support material comprises, preferably consists of, one or more of alumina, zirconia, lanthana, alumina-zirconia, alumina-lanthana, zirconia-lanthana, and alumina-zirconia-lanthana.

10. The catalyst of claim 1, wherein the weight ratio of the third platinum group metal component to the fourth platinum group metal component is in the range of from 1:1 to 20:1.

11. The catalyst of claim 1, further comprising in the first coating a fifth platinum group metal component supported on a zeolitic material.

12. The catalyst of claim 11, wherein the zeolitic material has a framework type selected from the group consisting of AEL, AFO, BEA, CHA, FAU, FER, HEU, GIS, GME, LEV, LTA, MOR, MTT, MEL, MFS, MFI, MWW, OFF, RRO, SZR, TON, USY, a mixture of two or more thereof and a mixed type of two or more thereof.

13. A process for preparing a catalyst, preferably a catalyst according to claim 1, the process comprising (a) providing a substrate comprising an inlet end, an outlet end, a substrate axial length extending from the inlet end to the outlet end of the substrate and a plurality of passages defined by internal walls of the substrate extending therethrough, and a first slurry comprising water, a first platinum group metal component supported on a first oxidic support material, a second platinum group metal component supported on a second oxidic support material, wherein the first platinum group metal component is different to the second platinum group metal component, a first oxygen storage compound; (b) disposing the first slurry on the internal walls of the substrate from the inlet end toward the outlet end over at least 50% of the substrate axial length; obtaining a substrate having a first coating disposed thereon; (c) optionally drying of the substrate having a first coating disposed thereon obtained in (b) in a gas atmosphere; (d) calcining of the substrate having a first coating disposed thereon obtained in (b), or (c), in a gas atmosphere, obtaining a calcined substrate having a first coating disposed thereon; (e) providing a second slurry comprising water, a third platinum group metal component and a fourth platinum group metal component, wherein the third platinum group metal component and the fourth platinum group metal component are supported on a third oxidic support material, wherein the third platinum group metal component is different to the fourth platinum group metal component; (f) disposing the second slurry on the substrate having a first coating disposed thereon from the outlet end toward the inlet end the substrate over at least 50% of the substrate axial length; obtaining a substrate having a first and a second coating disposed thereon; (g) optionally drying of the substrate having a first and a second coating disposed thereon obtained in (f) in a gas atmosphere; (h) calcining of the substrate having a first and a second coating disposed thereon obtained in (f), or (g), in a gas atmosphere; obtaining the catalyst.

14. A catalyst for the treatment of a diesel exhaust gas obtainable or obtained by a process according to claim 13.

15. A method for the treatment of an exhaust gas of a diesel combustion engine, comprising providing an exhaust gas from a diesel combustion engine and passing said exhaust gas through a catalyst according to claim 1.

16. Use of a catalyst according to claim 1 for the treatment of an exhaust gas of a diesel combustion engine, said use comprising passing said exhaust gas through said catalyst.

Description

BRIEF DESCRIPTION OF FIGURES

[0436] FIG. 1: shows the NOx emissions at the inlet and outlet of the catalyst. The time in s is shown on the abscissa, the NOx emissions in ppm are shown on the left ordinate and the Lambda is shown on the right ordinate.

[0437] FIG. 2: shows the NOx emissions at the inlet and outlet of the tested catalysts. The time in s is shown on the abscissa and the NOx emissions in ppm are shown on the ordinate.

[0438] FIG. 3: shows the NOx emissions at the inlet and outlet of Examples 5 and 6. The time in s is shown on the abscissa, the NOx emissions in ppm are shown on the left ordinate and the Lambda is shown on the right ordinate.

[0439] FIG. 4: shows the NOx emissions from at the inlet and outlet of the examples 5 and 7. The time in s is shown on the abscissa, the NOx emissions in ppm are shown on the left ordinate and the Lambda is shown on the right ordinate.

CITED LITERATURE

[0440] EP 0904482 B2