Hydrocarbon trap 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 zeolite having a smallest lower channel width of at least 0.4 nm and extends starting from substrate end a over a part of the length L, and washcoat zone B comprises the same components as washcoat A and palladium 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. A hydrocarbon trap catalyst for treating exhaust gas generated by a predominately stoichiometric running engine, 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 is arranged as an upstream positioned zone on the carrier substrate that comes in contact with the exhaust gas generated by the predominately stoichiometric running engine, the washcoat zone A comprises a zeolite having a smallest lower channel width of at least 0.4 nm and extends starting from substrate end a over a part of the length L, and washcoat zone B is arranged as a downstream positioned zone on the carrier substrate that comes in contact with the exhaust gas generated by the predominately stoichiometric running engine after the first washcoat zone A, the washcoat zone B comprises the same components as washcoat zone A, but for washcoat zone B having a higher palladium amount than washcoat zone A, and washcoat zone B extends from substrate end b over a part of the length L, wherein the palladium loading in washcoat zone B is 3.5 to 20 g/I based on the volume of the carrier and calculated as palladium metal, and 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 washcoat zone B.

2. Catalyst according to claim 1, wherein the zeolite has a smallest lower channel width of 0.4 nm to 0.8 nm.

3. Catalyst according to claim 1, wherein the zeolite belongs to the structure type code BEA, FAU, FER, MFI or MOR.

4. Catalyst according to claim 1, wherein the zeolite is ZSM-5 or beta zeolite.

5. Catalyst according to claim 1, wherein washcoat zone A comprises two layers A1 and A2, which both extend over the length L.sub.A, wherein layer A1 comprises the zeolite having a smallest lower channel width of at least 0.4 nm and layer A2 comprises rhodium, 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, but for layers B1 and B2 comprising a higher palladium amount as compared to layers A1 and A2, respectively.

6. Catalyst according to claim 1, wherein washcoat zones A and B are, apart from the amount of palladium in washcoat zone B, identical in composition.

7. Catalyst according to claim 1, wherein zeolite is present in washcoat zones A and B in an amount of 120 to 340 g/l based on the volume of the carrier substrate.

8. Catalyst according to claim 1, wherein washcoat zone A extends over 70 to 90% of the length L of the carrier substrate and washcoat zone B extends over 10 to 30% of the length L of the carrier substrate.

9. Catalyst according to claim 1, wherein the carrier substrate of the length L is a flow through substrate.

10. Catalyst according to claim 1 wherein the zeolite in washcoat zone A comprises iron, and the zeolite in washcoat zone B comprises palladium and iron, and the metal content in each of washcoat zones A and B is in an amount of 0.1 to 10% by weight based on the weight of the zeolite and calculated as oxide.

11. Catalyst according to claim 1, wherein the zeolite in each of washcoat zones A and B comprises iron.

12. Catalyst according to claim 1, wherein the same components present in each of washcoat zones A and B are received in a common washcoat layer that extends for length L.

13. Catalyst according to claim 1, wherein washcoat zone A is free of palladium.

14. A hydrocarbon trap catalyst for treating exhaust gas generated by a predominately stoichiometric running engine, 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 is arranged as an upstream positioned zone on the carrier substrate that comes in contact with the exhaust gas generated by the predominately stoichiometric running engine, the washcoat zone A comprises a zeolite having a smallest lower channel width of at least 0.4 nm and extends starting from substrate end a over a part of the length L, and washcoat zone B is arranged as a downstream positioned zone on the carrier substrate that comes in contact with the exhaust gas generated by the predominately stoichiometric running engine after the first washcoat zone A, the washcoat zone B comprises the same components as washcoat zone A, but for washcoat zone B having a higher palladium amount than washcoat zone A, and washcoat zone B extends from substrate end b over a part of the length L, wherein the palladium loading in washcoat zone B is 3.5 to 20 g/l based on the volume of the carrier and calculated as palladium metal, and 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 washcoat zone B, wherein the zeolite comprises at least one metal, wherein the at least one metal includes palladium that is present in each of washcoat zones A and B.

15. Catalyst according to claim 14, wherein the metal further includes iron, copper, manganese, nickel, cobalt, tin, platinum, rhodium, silver or a mixture of two or more thereof.

16. Method of treating exhaust gases of a predominately stoichiometric running combustion engine, comprising; passing the exhaust gas produced by the predominately stoichiometric running combustion engine over the catalyst of claim 1, wherein the exhaust gas enters the catalyst at substrate end a and exits at substrate end b.

17. Catalyst according to claim 1, wherein the zeolite in each of washcoat zones A and B includes iron, and the washcoat zone A is free of palladium.

18. The method of claim 16 wherein the catalyzed carrier substrate is an under-body located hydrocarbon trap catalyzed carrier substrate that is positioned downstream from a close coupled three way catalyst also receiving exhaust gas from the predominately stoichiometric running engine.

19. A hydrocarbon trap catalyst for treating exhaust gas generated by a predominately stoichiometric running engine, comprising a flow through carrier substrate of the length L extending between substrate ends a and b and two washcoat zones A and B, wherein washcoat zone A represents an upstream positioned zone on the carrier substrate that is arranged to come in contact with the exhaust gas generated by the predominately stoichiometric running engine, the washcoat zone A comprises a zeolite having a smallest lower channel width of at least 0.4 nm and extends starting from the flow through carrier substrate end a over a part of the length L, and washcoat zone B represents a downstream positioned zone on the carrier substrate that is arranged to come in contact with the exhaust gas generated by the predominately stoichiometric running engine after the first washcoat zone A, the washcoat zone B comprises the same components as washcoat zone A, but for washcoat zone B having a higher palladium loading than washcoat zone A, and washcoat zone B 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 washcoat zone B, and wherein washcoat zone A includes Pd, Rh, or Pd and Rh, and washcoat zone B includes Pd at a washcoat loading of 3.5 g/l to 20 g/l.

20. Catalyst according to claim 19 wherein the zeolite in washcoat zone A comprises iron, and the zeolite in washcoat zone B comprises palladium and iron, and the metal content in each of washcoat zones A and B is in an amount of 0.1 to 10% by weight based on the weight of the zeolite and calculated as oxide.

21. Catalyst according to claim 19, wherein the zeolite in each of washcoat zones A and B comprises iron.

22. Catalyst according to claim 19, wherein washcoat zone A is free of palladium.

Description

COMPARISON EXAMPLE 1

(1) a) Slurry preparation begins with addition of an alumina stabilized silica sol (Aeroperl 3375/20 purchased from Evonik) to water and mixing. This material represents 4.5 wt % of the final calcined washcoat loading. This step is followed by the addition of a boehmite (SASOL SCF-55 purchased from Sasol) and iron nitrate at contents of 1.0 and 4.5 wt % respectively of the final calcined washcoat. Finally beta zeolite in the ammonium form and having a SAR value of 25 was added and the slurry was then aged for two days.

(2) b) This slurry was then coated onto a ceramic substrate having 400 cpsi/4.3 mill cell structure and 4.66″ round by 4.5″ long giving a total volume of 1.26 Liters and a WC load of 4.0 g/in.sup.3 or 258 g/l. Calcination of the coated trap was done at 540° C. in air.

EXAMPLE 1

(3) An inventive catalyst was prepared as described in Example 1 but in this case a Pd solution band was applied by dipping one end of the catalyst in a Pd nitrate solution containing citric acid and 2 wt % ethanol. The substrate used was a 400 cpsi/4.3 mill cell structure, 4.66″ round by 4.5″ long giving a total volume of 1.26 Liters. The concentration of the dipped solution was adjusted such that with a solution band length of 3 cm (1.2″) long the Pd concentration was 250 g/ft.sup.3 in the dipped zone. The PGM loading averaged over the full part was 60 g/ft.sup.3 © 0:11:1 (includes the Pd in the band and in the TWC layer).