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. 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 zone A and an amount of 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 washcoat zone B.

2. Catalyst according to claim 1, wherein the zeolite of 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 the zeolite comprises a metal.

6. Catalyst according to claim 5, wherein the metal is iron, copper, manganese, nickel, cobalt, tin, palladium, platinum, rhodium, silver or a mixture of two or more thereof.

7. Catalyst according to claim 5, wherein the metal is palladium and is present in washcoat zone B at a higher concentration compared to washcoat zone A.

8. 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 a 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 and wherein layers B1 and B2 comprise palladium and an higher amount of palladium compared to layers A1 and A2, respectively.

9. Catalyst according to claim 1, wherein washcoat zones A and B are, apart from the amount of palladium in washcoat zone B, and an higher amount of palladium compared to layers A1 and A2, respectively, identical.

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

11. Catalyst according to claim 1, wherein it comprises palladium in washcoat zone B in an amount of 2 to 20 g/l, based on the volume of the carrier substrate and calculated as palladium metal.

12. 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.

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

14. 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.

Description

COMPARISON EXAMPLE 1

[0050] 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.

[0051] 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

[0052] 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).