Diesel oxidizing catalytic converter

Abstract

The present invention relates to a diesel oxidizing catalytic converter which comprises a supporting body with a length L which extends between a first end surface a and a second end surface b, and catalytically active material zones A and B of different composition which are arranged on the supporting body, wherein material zone A comprises palladium or platinum and palladium in a weight ratio Pt:Pd of <1 and, starting from the end surface a, extends to from 20% to 80% of the length L, and material zone B comprises platinum and palladium in a weight ratio Pt:Pd of <10 and extends to from 80% to 100% of the length L, and wherein material zone B is arranged above material zone A and the weight ratio Pt:Pd in relation to the material zones A and B is from 1.5 to 3.0.

Claims

1. Diesel oxidation catalyst comprising a carrier body having a length L extending between a first end face a and a second end face b, and differently composed catalytically active material zones A and B arranged on the carrier body, wherein material zone A contains palladium or platinum and palladium in a weight ratio Pt:Pd of 1 and extends starting from end face a to 20 to 80% of length L, and material zone B contains platinum and palladium in a weight ratio Pt:Pd of <10 and extends to 80 to 100% of length L, and wherein material zone B is arranged above material zone A and the weight ratio Pt:Pd relative to the material zones A and B is 1.5 to 3.0.

2. The diesel oxidation catalyst according to claim 1, further comprising carrier oxides, and wherein in the material zones A and B, palladium or platinum and palladium are present on the carrier oxides.

3. The diesel oxidation catalyst according to claim 2, wherein the carrier oxides that are present in material zones A and B are identical to or different from one another and are selected from the group consisting of aluminum oxide, doped aluminum oxide, silicon oxide, titanium dioxide and mixed oxides of one or more thereof.

4. The diesel oxidation catalyst according to claim 1, wherein the material zone A contains an alkaline-earth metal.

5. The diesel oxidation catalyst according to claim 4, wherein the alkaline-earth metal in material zone A is strontium, barium, or strontium and barium.

6. The diesel oxidation catalyst according to claim 1, wherein the length of the material zone B is 95% or 100% of the total length L of the carrier body.

7. The diesel oxidation catalyst according to claim 1, wherein the material zone B contains platinum and palladium in a weight ratio Pt:Pd of 3.0 to <10.

8. The diesel oxidation catalyst according to claim 1, wherein the material zone B contains platinum and palladium in a weight ratio Pt:Pd of 3.0 to 6.0.

9. The diesel oxidation catalyst according to claim 1, wherein the length of the material zone A is 50% to 80%.

10. The diesel oxidation catalyst according to claim 1, wherein the material zone A comprises an alkaline-earth metal selected from the group consisting of strontium, barium, or strontium and barium in an amount of 0.5 to 5% by weight of the material zone A.

11. The diesel oxidation catalyst according to claim 1, wherein the material zone A includes strontium in an amount of 1 to 3% by weight of the material zone A.

12. The diesel oxidation catalyst according to claim 1, wherein the material zone A includes barium in an amount of 2.5 to 4.5% by weight of the material zone A.

13. The diesel oxidation catalyst according to claim 1, wherein the material zone A includes platinum and palladium in a weight ratio Pt:Pd of 1 to 0.15.

14. The diesel oxidation catalyst according to claim 13, wherein the material zone B contains platinum and palladium in a weight ratio Pt:Pd of 3.0 to 6.0.

15. The diesel oxidation catalyst according to claim 1, wherein the Pt:Pd ratio in zone A results in more Pd than Pt.

16. The diesel oxidation catalyst according to claim 1, wherein the weight ratio Pt:Pd relative to the material zones A and B is 1.5 to 2.4.

17. The diesel oxidation catalyst according to claim 1, wherein both Pt and Pd are present in each of zones A and B.

18. A method for treating diesel exhaust gases wherein the diesel exhaust gas is conducted through a diesel oxidation catalyst according to claim 1, wherein the diesel exhaust gas flows into the carrier body at end face a and flows out of the carrier body at end face b.

19. A device for purification of exhaust gases from diesel engines comprising a diesel oxidation catalyst according to claim 1.

20. A device for purification of exhaust gases from diesel engines comprising a diesel oxidation catalyst according to claim 1, wherein the diesel oxidation catalyst is arranged upstream of a diesel particulate filter and/or a catalyst for the selective catalytic reduction of nitrogen oxides.

Description

EXAMPLE 1

(1) a) A commercially available round flow-through substrate of cordierite having the dimensions 14.4 cm10.2 cm (5.664.00) with cell density 62 cpcm (400 cpsi) and wall thickness 165 m (6.5 mils) was coated starting from one end (corresponding to end face a) over 50% of its length with a washcoat containing 48.23 WI of a commercially available lanthanum doped aluminum oxide, 1.00 g/l strontium oxide (ex Sr(OH).sub.2), 0.47086 g/l of a standard water-soluble Pd compound, and 0.23543 g/l of a standard water-soluble Pt compound. The Pt:Pd weight ratio was 1:2.

(2) b) The coated substrate obtained according to a) was coated over its entire length with a washcoat containing 49.23 g/l of a lanthanum-doped mesoporous aluminum oxide, 0.60540 g/l of a standard water-soluble Pt compound, and 0.10090 g/l of a standard water-soluble Pd compound. The Pt:Pd weight ratio was 6:1.

EXAMPLE 2

(3) a) In a manner analogous to the method described in example 1, a commercially available round flow-through substrate made of cordierite having the dimensions 14.4 cm10.2 cm (5.664.00) with cell density 62 cpcm (400 cpsi) and wall thickness 165 m (6.5 mils) was coated starting from one end (corresponding to end face a) over 80% of its length with a washcoat comprising 0.293 g/l (8.3 g/ft.sup.3) platinum and palladium in a 1:1 weight ratio.

(4) b) The coated substrate obtained according to a) was coated over its entire length with a washcoat comprising 0.473 g/l (13.4 g/ft.sup.3) platinum and palladium in a 3:1 weight ratio. The total Pt:Pd ratio over the entire catalyst was 2:1.

COMPARATIVE EXAMPLE 1

(5) a) In a manner analogous to the method described in example 1, a commercially available round flow-through substrate made of cordierite having the dimensions 14.4 cm10.2 cm (5.664.00) with cell density 62 cpcm (400 cpsi) and wall thickness 165 m (6.5 mils) was coated over its entire length with a washcoat comprising 0.357 g/l (10.1 g/ft.sup.3) platinum and palladium in a 1.4:1 weight ratio.

(6) b) The coated substrate obtained according to a) was coated over its entire length with a washcoat comprising 0.350 g/l (9.9 g/ft.sup.3) platinum and palladium in a 3:1 weight ratio.

(7) The total Pt:Pd ratio over the entire catalyst was 2:1.

(8) Comparative example 1 is analogous to example 6 of US2008/045405.

EXAMPLE 3

(9) a) In a manner analogous to the method described in example 1, a commercially available round flow-through substrate made of cordierite having the dimensions 14.4 cm10.2 cm (5.664.00) with cell density 62 cpcm (400 cpsi) and wall thickness 165 m (6.5 mils) was coated starting from one end (corresponding to end face a) over 80% of its length with a washcoat comprising 0.636 g/l (18 g/ft.sup.3) platinum and palladium in a 1:1 weight ratio.

(10) b) The coated substrate obtained according to a) was coated over its entire length with a washcoat comprising 0.198 g/l (5.6 g/ft.sup.3) platinum and palladium in a 6:1 weight ratio.

(11) The overall Pt:Pd ratio over the entire catalyst was 1.5:1.

COMPARATIVE EXAMPLE 2

(12) a) In a manner analogous to the method described in example 1, a commercially available round flow-through substrate made of cordierite having the dimensions 14.4 cm10.2 cm (5.664.00) with cell density 62 cpcm (400 cpsi) and wall thickness 165 m (6.5 mils) was coated over its entire length with a washcoat comprising 0.618 g/l (17.5 g/ft.sup.3) platinum and palladium in a weight ratio of 1:2.

(13) b) The coated substrate obtained according to a) was coated starting from one end (corresponding to end face a) over 50% of its length with a washcoat comprising 0.177 g/l (5 g/ft.sup.3) platinum and palladium in a 1:2 weight ratio.

(14) The overall Pt:Pd ratio over the entire catalyst was 1.2.

(15) Comparative example 2 is analogous to catalyst Y of WO2010/133309 A1.

(16) Comparative Experiments

(17) With examples 2 and 3, as well as comparative examples 1 and 2, so-called heat-up experiments were carried out. To this end, on a conventional passenger car engine test bench (2.0 L displacement, 4 cylinder, diesel, TDI, common rail), energy in the form of heat was released (exothermically) via secondary fuel injection by catalytic combustion of that very fuel above the diesel oxidation catalyst to be tested in each case.

(18) A constant pre-catalyst temperature of 320 C. was set in a first engine operating point (MBP1). A theoretically expected post-catalyst temperature was then reached (or not reached) in precisely defined steps by injection of exactly calculated quantities of diesel fuel. The aim is to successively realize a post-catalyst temperature of approx. 550 C. in four defined equidistant steps from the given pre-catalyst temperature. This four-stage procedure at a pre-catalyst temperature of 320 C. is subsequently repeated again at pre-catalyst temperatures of 310 C. at an engine operating point 2 (MBP2), at a pre-catalyst temperature of 300 C. at an engine operating point 3 (MBP3) and at a pre-catalyst temperature of 290 C. at an engine operating point 4 (MBP4).

(19) It tends to be more important to evaluate MBP4 than MBP3, more important to evaluate MBP3 than MBP2 and more important to evaluate the latter than MBP1, since it becomes increasingly difficult to generate the required heat at lower pre-catalyst temperature by means of excellent ignition behavior.

(20) In this test, the suitability of an oxidation catalyst to initiate the thermal regeneration of a downstream diesel particulate filter is tested. The higher the temperature reached is, the better suited is the oxidation catalyst.

(21) FIG. 1 shows the comparison of example 2 (solid line) with comparative example 1 (dashed line). Accordingly, example 2 produces a significantly higher exothermic reaction than comparative example 1 and is thus better suited to initiate the thermal regeneration of a downstream diesel particulate filter.

(22) FIG. 2 shows the comparison of example 3 (solid line) with comparative example 2 (dashed line). Accordingly, example 3 produces a significantly higher exothermic reaction than comparative example 2 and is thus better suited to initiate the thermal regeneration of a downstream diesel particulate filter.