Three-way catalyst

Abstract

The present invention relates to a catalyst comprising a carrier substrate of the length L extending between substrate ends a and b and two washcoat zones A and B, wherein washcoat zone A comprises a first platinum group metal and extends starting from substrate end a over a part of the length L, and washcoat zone B comprises the same components as washcoat zone A and in addition a second platinum group metal and extends from substrate end b over a part of the length L, wherein L=L.sub.A+L.sub.B, wherein L.sub.A is the length of washcoat zone A and L.sub.B is the length of substrate length B.

Claims

1. Catalyst comprising a carrier substrate of the length L extending between substrate ends a and b and two washcoat zones A and B, wherein washcoat zone A comprises a first platinum group metal and extends starting from substrate end a over a part of the length L, and washcoat zone B comprises the same components as washcoat zone A and in addition a second platinum group metal and extends from substrate end b over a part of the length L, wherein L=L.sub.A+L.sub.B, wherein L.sub.A is the length of washcoat zone A and L.sub.B is the length of substrate length B, and wherein the predominant or only second platinum group metal content in washcoat zone B is represented by either palladium, rhodium or a combination of palladium and rhodium, and wherein the first platinum group metal is predominantly or only palladium and rhodium and the predominantly or only second platinum group metal is palladium.

2. Catalyst according to claim 1, wherein the first and second platinum group metals are or different.

3. Catalyst comprising a carrier substrate of the length L extending between substrate ends a and b and two washcoat zones A and B, wherein washcoat zone A comprises a first platinum group metal and extends starting from substrate end a over a part of the length L, and washcoat zone B comprises the same components as washcoat zone A and in addition a second platinum group metal and extends from substrate end b over a part of the length L, wherein L=L.sub.A+L.sub.B, wherein L.sub.A is the length of washcoat zone A and L.sub.B is the length of substrate length B, and wherein washcoat zone A comprises two layers A1 and A2, which both extend over the length L.sub.A, wherein layer A1 comprises a first platinum group metal and layer A2 comprises a first platinum group metal different from the first platinum group metal of layer A1 and washcoat zone B comprises two layers B1 and B2, which both extend over the length L.sub.B, wherein layer B1 comprises the same components as layer A1 and layer B2 comprises the same components as layer A2 and wherein layers B1 and B2 comprise in addition a second platinum group metal.

4. Catalyst according to claim 3, wherein the first platinum group metal in layer A1 is palladium and/or rhodium and the first platinum group metal in layer A2 is rhodium.

5. Catalyst according to claim 3, wherein the first platinum group metal in layer A1 is palladium and rhodium and the weight ratio Pd:Rh is 10:1 to 1:10.

6. Catalyst according to claim 1, wherein the first and second platinum group metals are independently from each other supported on a carrier material.

7. Catalyst according to claim 6, wherein the carrier material is selected from the group consisting of alumina, silica, magnesia, titania, zirconia, ceria, mixtures comprising at least two of these materials and mixed oxides comprising at least two of these materials.

8. Catalyst according to claim 1, wherein the carrier substrate of the length L is a flow-through or filter substrate.

9. Catalyst according to claim 1, wherein washcoat zone B is free of platinum.

10. Catalyst system comprising a first three-way catalyst according to claim 1 and a second three-way catalyst.

11. Catalyst system according to claim 10, wherein the first three-way catalyst is followed by the second three-way catalyst, and the second three-way catalyst has a different catalyst composition than the first three-way catalyst.

12. Catalyst system according to claim 10, wherein the first three-way catalyst follows the second three-way catalyst, and the second three-way catalyst has a different catalyst composition than the first three-way catalyst.

13. Method of treating exhaust gases of a combustion engine, wherein the exhaust gas is passed over the catalyst of claim 1, wherein it enters the catalyst at substrate end a and exits it at substrate end b.

14. Method according to claim 13, wherein the catalyst is arranged in close coupled position.

15. Catalyst comprising a carrier substrate of the length L extending between substrate ends a and b and two washcoat zones A and B, wherein washcoat zone A comprises a first platinum group metal and extends starting from substrate end a over a part of the length L, and washcoat zone B comprises the same components as washcoat zone A and in addition a second platinum group metal and extends from substrate end b over a part of the length L, wherein L=L.sub.A+L.sub.B, wherein L.sub.A is the length of washcoat zone A and L.sub.B is the length of substrate length B, and wherein washcoat zone A extends over 70 to 95% of the length L of the carrier substrate and washcoat zone B extends over 5 to 30% of the length L of the carrier substrate.

16. Catalyst according to claim 15, wherein the first platinum group metal is predominantly or only platinum, palladium and/or rhodium and the predominant or only second platinum group metal is palladium or rhodium.

17. Catalyst according to claim 15, wherein the first platinum group metal is predominantly or only palladium and rhodium and the predominantly or only second platinum group metal is palladium.

18. Catalyst according to claim 15, wherein only rhodium represents the second platinum group metal in washcoat zone B.

19. Catalyst according to claim 15, wherein only rhodium and palladium represent the second platinum group metal in washcoat zone B.

20. Catalyst according to claim 15, wherein only palladium represents the second platinum group metal in washcoat zone B.

21. Method for the manufacturing of a catalyst according to claim 15 by a two-step process which comprises coating of the carrier substrate with a coating suspension (washcoat) which contains the components of washcoat zone A over its entire length L and dipping the coated carrier substrate in a aqueous solution containing a water soluble compound of the second platinum group metal until a length which corresponds with the length of washcoat zone B, so as to form washcoat zone B.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 illustrates catalysts according to the present invention.

(2) FIG. 2 illustrates catalyst systems according to the present invention.

(3) FIG. 3 shows the THC emissions (weighted mg/mile) obtained in the tests C1 a, C1 b and CC1, respectively.

(4) FIG. 4 shows the THC emissions (weighted mg/mile) thus obtained.

DETAILED DESCRIPTION

(5) FIG. 1 illustrates catalysts according to the present invention. The upper part of the figure shows a detail of an inventive catalyst (1) which comprises a carrier substrate (3) which extends between substrate ends a and b and which carries washcoat zone A (4) and washcoat zone B (5).

(6) The lower part of the figure shows a detail of another embodiment of the invention. Catalyst (2) comprises a carrier substrate (3) which extends between substrate ends a and b. Washcoat zone A comprises layer A1 (6) and A2 (7) whereas washcoat zone B comprises layer B1 (9) and layer B2 (8). Layers A1 (6) and B1 (9) differ only in that B1 (9) comprises a second platinum group metal compared to A1 (6). Likewise, layers A2 (7) and B2 (8) differ only in that B2 (8) comprises a second platinum group metal compared to A2 (7).

(7) FIG. 2 illustrates catalyst systems according to the present invention.

(8) The upper part shows an inventive catalyst system (11) which comprises an inventive catalyst (1) and an conventional three-way catalyst (10). Both catalysts are arranged so that washcoat zone B (5) is followed by the conventional three-way catalyst (10).

(9) The lower part shows an inventive catalyst system (12) which comprises an inventive catalyst (1) and an conventional three-way catalyst (10). Both catalysts are arranged so that washcoat zone B (5) follows the conventional three-way catalyst (10).

Comparison Example 1

(10) Comparison Example 1 is a 2-Layer Pd/Rh technology that was prepared as follows:

(11) a) For the 1st layer (Pd layer) a slurry was prepared by first adding nitric acid to water at 1 wt %. BaSO.sub.4 was then added with stirring followed by the OSC material. The OSC material consisted of CeO2=44 wt %, ZrO.sub.2+HfO.sub.2=42 wt %, La.sub.2O.sub.3=9.5 wt % and Pr.sub.6O.sub.11=4.5 wt %. The slurry was stirred for 15 minutes and then alumina was added slowly. After stirring for 30 minutes, sucrose was added at 10 wt % based on solids and finally a dispersible boehmite binder was added. The slurry was then milled using a Sweco type mill to a mean particle size of greater than 2 micrometers, 90% of the diameter distribution was 6.0 to 7.0 micrometers and a 100% pass of less than 25 micrometers (i.e., 100% of the particles had a particle size less than 25 micrometers). The slurry was then weighed and the LOI (loss on ignition) measured at 540° C. to determine the total calcined solids content. Based on this value the Pd loading were calculated. Pd nitrate solution was then added to the slurry dropwise while stirring. After the Pd addition the slurry specific gravity was in the range of 1.49 to 1.52.

(12) b) Coating was performed by dipping one end of a honeycomb ceramic monolith (commercially available flow through substrate made of cordierite (3.54″×5.16″×2.5″long; 900 cpsi/2 mill) into the washcoat slurry, followed by drawing the slurry up into the channels using a vacuum. The monolith was then removed from the slurry and the channels cleared by applying a vacuum to its other end. Washcoat loading was controlled by varying specific gravity, and other coating parameters such as vacuum time and the amount of slurry drawn into the honeycomb channels. After applying the washcoat, the monolith was calcined at 540° C. for 2 hours. The final WC loading on a dry calcined basis was alumina sol=3 g/L, stabilized alumina=52 g/L, BaSO.sub.4=15 g/L and OSC=34 g/L giving a total loading for Layer 1=104 g/L. The layer was coated over the total length of the monolith.

(13) c) This process was then repeated for the second layer (Rh layer) except that Rh was added instead of Pd. The final WC loading on a dry calcined based was alumina sol=3 g/L, stabilized alumna=34 g/L, BaSO.sub.4=6 g/L and OSC=49 g/L giving a total loading for Layer 2=92 g/L. The second layer was as well coated over the total length of the monolith.

(14) The resulting product was dried and calcined. The catalyst obtained is subsequently called CC1.

Example 1

(15) CC1 obtained according to Comparison Example 1 was dipped into an aqueous solution of palladium nitrate in order to form a zone of 1.25″ length comprising a total of 246 g/ft.sup.3 (8.69 g/l) of palladium. The resulting product was dried and calcined. The catalyst obtained is subsequently called C1.

Comparison of CC1 and C1

(16) a) CC1 and C1 were engine-aged to a FUL (full useful life) 150K mile condition using a 4-mode aging cycle for 90 hours. Each 4-mode cycle lasts for 60 seconds and the aging cycle is repeated 4500 times. The first 50 hours of aging were done with a phosphorous doped fuel using the additive DMA4 as the dopant. The remaining 40 hours was thermal aging only. The individual modes are: stoichiometric, rich, rich+air-injection, and stoichiometric+air-injection. Peak temperatures measured in CC1 and C1 catalysts were ˜990° C. A detailed description of the aging is given in the 2016 SAE World Congress Paper 2016-01-0925.

(17) b) The aged catalyst C1 was tested in a vehicle testing using a Ford Escape 2.0 L (4×FTP/US06). The catalyst was arranged in close coupled position directly following the exhaust manifold. The exhaust gas entered the catalyst on substrate end a and left it on the side with the increased amount of palladium of 246 g/ft.sup.3 (8.69 g/l) (substrate end b). The results of this test are given in FIG. 3 as “Test C1 a”.

(18) c) The test described in b) was repeated with the exception that the exhaust gas entered the catalyst on the side with the increased amount of palladium of 246 g/ft.sup.3 (8.69 g/l) (substrate end b) and left it on (substrate end a). The results of this test are given in FIG. 3 as “Test C1 b”.

(19) d) The test described in b) was repeated with the exception that catalyst CC1 was used. The results of this test are given in FIG. 3 as “Test CC1”.

(20) e) FIG. 3 shows the THC emissions (weighted mg/mile) obtained in the tests C1 a, C1 b and CC1, respectively,

Comparison Example 2

(21) Comparison Example: 1 was repeated with the exception that 96 g/ft.sup.3 (3.4 g/l) of palladium and 4 g/ft.sup.3 (0.14 g/l) of rhodium were coated over the total length of the substrate.

(22) Two of the obtained substrates were combined to form a catalyst system which is subsequently called CCS1.

Example 2

(23) Catalyst CC1 was combined with catalyst C1 to form a catalyst system. The catalysts were arranged so that the exhaust gas first entered substrate end a of catalyst C1 and after having left catalyst C1 at substrate end b entered catalyst CC1. The catalyst system thus obtained is subsequently called CS1.

Example 3

(24) Catalyst CC1 was combined with catalyst C1 to form a catalyst system. The catalysts were arranged so that the exhaust gas first entered catalyst CC1 and after having left it entered catalyst C1 at substrate end b. The catalyst system thus obtained is subsequently called CS2.

Comparison of CCS1, CS1 and CS2

(25) CCS1, CS1 and CS2 were aged and tested in line with the steps a) and b) above. FIG. 4 shows the THC emissions (weighted mg/mile) thus obtained.