Diesel Oxidation Catalyst

Abstract

The present invention relates to a diesel oxidation catalyst comprising a carrier body having a length L extending between a first end face and a second end face, and differently composed material zones A and B arranged on the carrier body, wherein material zone A comprises platinum, palladium, rhodium or a mixture of any two or more thereof applied to a cerium-zirconium mixed oxide, and material zone B comprises platinum, palladium or platinum and palladium applied to a carrier oxide B.

Claims

1. Diesel oxidation catalyst comprising a carrier body, which is a flow-through honeycomb body, having a length L extending between a first end face and a second end face, and differently composed material zones A and B arranged on the carrier body, wherein material zone A comprises platinum, palladium, rhodium or a mixture of any two or more thereof applied to a cerium-zirconium mixed oxide, and material zone B comprises platinum, palladium or platinum and palladium applied to a carrier oxide B.

2. Diesel oxidation catalyst according to claim 1, wherein material zone A comprises platinum and palladium in a weight ratio of 3:1 to 1:50.

3. Diesel oxidation catalyst according to claim 1, wherein the cerium-zirconium mixed oxide comprises 40 to 90% by weight of cerium oxide and 60 to 10% by weight of zirconium oxide.

4. Diesel oxidation catalyst according to claim 1, wherein material zone B comprises platinum and palladium in a weight ratio of 10:1 to 1:3.

5. Diesel oxidation catalyst according to claim 1, wherein carrier oxide B is selected from the group consisting of aluminum oxide, doped aluminum oxide, silicon oxide, titanium dioxide, zirconium oxide and mixed oxides of one or more thereof.

6. Diesel oxidation catalyst according to claim 1, wherein material zone B comprises lanthanum oxide, magnesium oxide, barium oxide and/or strontium oxide.

7. Diesel oxidation catalyst according to claim 1, wherein material zone B comprises a hydrocarbon adsorbent material.

8. Diesel oxidation catalyst according to claim 1, wherein the carrier body comprises a material zone C, which is different from material zones A and B and which comprises platinum, palladium or platinum and palladium applied to a carrier oxide C.

9. Diesel oxidation catalyst according to claim 8, wherein material zone C comprises platinum or platinum and palladium in a weight ratio ≥1.

10. Diesel oxidation catalyst according to claim 8 wherein, carrier oxide C is in particular selected from the group consisting of aluminum oxide, doped aluminum oxide, silicon oxide, zirconium oxide, titanium dioxide and mixed oxides of one or more thereof.

11. Diesel oxidation catalyst according to claim 1, wherein it comprises a carrier body having a length L extending between a first end face and a second end face, and differently composed material zones A, B and C arranged on the carrier body, wherein material zone A comprises platinum and palladium in a weight ratio of 1:1 to 1:10 applied to a cerium-zirconium mixed oxide comprising 40 to 90% by weight of cerium oxide and 60 to 10% by weight of zirconium oxide, material zone B comprises platinum and palladium in a weight ratio of 5:1 to 1:1 applied to aluminum oxide or lanthanum-stabilized aluminum oxide, and material zone C comprising platinum and/or palladium applied to aluminum oxide doped with 1 to 20% by weight of silica based on the doped aluminum oxide.

12. Diesel oxidation catalyst according to claim 1, wherein material zones A and B both extend over the complete length L of the carrier body and material zone A is located below material zone B.

13. 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 the first end face and flows out of the carrier body at the second end face.

14. Method according to claim 13, wherein the diesel oxidation catalyst is operated at an air-fuel ratio of λ≤1 when its temperature is below 200° C. and operated at an air-fuel ratio of λ>1 when its temperature is at or above 200° C.

15. Use of a diesel oxidation catalyst according to claim 1 as cold start catalyst, which heats up to temperatures of 200° C. or more within 180 to 220 seconds when operated at an air-fuel ratio of λ≥1.

16. Device for purification of exhaust gases from diesel engines having a diesel oxidation catalyst according to claim 1.

17. Device according to claim 16, 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

[0047] a) 60 g/l of milled CeZrOx material (CeO.sub.2/ZrO.sub.2=80/20) were added to a solution of soluble Pt salt (0.35315 g/l Pt), followed by 1.05944 g/l of Pd ex nitrate. Finally, 4.5 g/L of Alumina-sol were added. The obtained product was dried and calcined for 2 h at 550° C. [0048] b) A commercially available round flow-through substrate of cordierite having the dimensions 14.4 cm×7.6 cm (5.66″×3.00″) with cell density 62 cpcm (400 cpsi) and wall thickness 102 μm (4.0 mils) was coated over its complete length with a washcoat containing 66 g/l of the product obtained according to a) above. [0049] c) To 66.165 g/l of a milled powder comprising 2.5897 g/l Pt, and 1.2949 g/l Pd fixed on 100 g/l of alumina, 3.18 g/l of La.sub.2O.sub.3 and 25.48 g/l of beta zeolite were added. The powder was calcined for 2 h at 550° C. [0050] d) The coated substrate obtained according to b) above was coated over its complete length with a washcoat containing 94 g/l of the product obtained according to c) above.
The oxidation catalyst obtained corresponds to the second arrangement mentioned above and is called C1 below.

EXAMPLE 2

[0051] Example 1 was repeated with the exception that steps a) and c) were interchanged. The oxidation catalyst obtained corresponds to the first arrangement mentioned above and is called C2 below.

Comparison Example 1

[0052] a) To 103.88 g/l of a milled powder comprising 2.5897 g/l Pt, and 1.2949 g/l of Pd fixed on 100 g/l of alumina, 5 g/l of La.sub.2O.sub.3 and 40 g/l of beta zeolite were added. The powder was calcined for 2 h at 550° C. [0053] b) A commercially available round flow-through substrate of cordierite having the dimensions 14.4 cm×7.6 cm (5.66″×3.00″) with cell density 62 cpcm (400 cpsi) and wall thickness 102 μm (4.0 mils) was coated over its complete length with a washcoat containing 148 g/l of the product obtained according to a) above.
The oxidation catalyst obtained is called CC1 below.

Comparison Example 2

[0054] a) To 103.88 g/l of a milled powder comprising 0.97 g/l Pt, and 2.91 g//l of Pd fixed on a CeZrOx material (CeO.sub.2/ZrO.sub.2=80/20) and 5 g/l of La.sub.2O.sub.3 were added. The powder was calcined for 2 h at 550° C. [0055] b) A commercially available round flow-through substrate of cordierite having the dimensions 14.4 cm×7.6 cm (5.66″×3.00″) with cell density 62 cpcm (400 cpsi) and wall thickness 102 μm (4.0 mils) was coated over its complete length with a washcoat containing 109 g/l of the product obtained according to a) above.
The oxidation catalyst obtained is called CC2 below.

EXAMPLE 3

[0056] Comparative experiments to determine T.sub.50CO— and T.sub.50C.sub.3H.sub.6-light off values [0057] a) Cores were taken out of catalysts C1, C2 and CC1 and CC2. All cores were aged 16 h at 800° C. under hydrothermal atmosphere. [0058] b) T.sub.50CO— and T.sub.50C.sub.3H.sub.6-light off values of all catalyst cores were determined on a synthetic gas bench with the gas mixture given in Table 1. Before testing catalysts were preconditioned under lean conditions with the gas mixture given in Table 1 at 600° C. for 30 minutes.
The complete experimentation is shown in FIG. 2.

TABLE-US-00001 TABLE 1 Lean Determination conditioning of light-off GHSV [1/h] 60000 60000 NO [ppm] 500 250 NO.sub.2 [ppm] 0 0 O.sub.2 [vol %] 12.5 12.5 CO [ppm] 0 1000 HC [ppm C3] 0 300 (300) (C.sub.3H.sub.6) CO.sub.2 [vol %] 6 6 H.sub.2O [vol %] 6.5 6.5 N.sub.2 rest rest [0059] c) The results obtained are given in FIG. 3.

EXAMPLE 4

[0060] Comparative Experiments to Determine Heat-Up [0061] a) Cores were taken out of catalysts C1, C2 and CC1. All cores were aged 16 h at 800° C. under hydrothermal atmosphere. [0062] b) All cores were heated up on a synthetic gas bench with the gas mixture given in Table 2 with 30K/min. Before testing catalysts were preconditioned with the same gas mixture at 650° C. for 30 minutes. The temperatures at the catalyst inlet and outlet were determined.

TABLE-US-00002 TABLE 2 GHSV [1/h] 60000 NO [ppm] 500 O.sub.2 [vol %] 10.5 CO [ppm] 800 HC [ppm C3] 130 (C.sub.3H.sub.6) CO.sub.2 [vol %] 6.3 H.sub.2O [vol %] 7 N.sub.2 rest

[0063] All catalysts behaved identically. While the temperature at the catalyst inlet increased with the temperature ramp of 30K/min, the temperature at the catalyst outlet was less than that at the inlet and reached 200° C. after 600 seconds. No exotherm could be determined. [0064] c) Additional cores were taken out of catalysts C1, C2 and CC1 and aged 16 h at 800° C. under hydrothermal atmosphere according to step a) above. Before testing the cores were preconditioned with the gas mixture given in table 3 at 450° C. for 30 minutes.
Finally, the cores were heated up on a synthetic gas bench with the gas mixture given in Table 4 with 30K/min with average λ=0.998 at a frequency of 1 Hz and an amplitude +0.038/−0.034. The temperatures at the catalyst inlet and outlet were determined.

TABLE-US-00003 TABLE 3 GHSV [1/h] 60000 NO [ppm] 1000 O.sub.2 [vol %] 1.15 CO [ppm] 1.5 HC [ppm C3] 333/167 (C.sub.3H.sub.6/C.sub.3H.sub.8) CO.sub.2 [vol %] 14 H.sub.2O [vol %] 10 N.sub.2 rest

TABLE-US-00004 TABLE 4 GHSV [1/h] 60000 NO [ppm] 1000 O.sub.2 stat [vol %] 0.825 O.sub.2 dyn [vol %] 0.325 H.sub.2 stat [vol %] 0.28 H.sub.2 dyn [vol %] 0.22 CO [ppm] 1.5 HC [ppm C3] 333/167 (C.sub.3H.sub.6/C.sub.3H.sub.8) CO.sub.2 [vol %] 14 H.sub.2O [vol %] 10 N.sub.2 rest

[0065] While CC1 behaved identically to the test described under b) above, the temperature at the outlet of C1 and C2 increased rapidly and reached 200° C. after 205 and 210 seconds, respectively. After 250 seconds the outlet temperature of C1 and C2 was more than 100° C. higher compared to CC1.

EXAMPLE 5

[0066] The coated substrate obtained according to Example 1 above was coated over 50% of its length with 77 g/l of a washcoat containing platinum and palladium in a weight ratio of 12:1 fixed on an alumina-silica-mixed oxide. The oxidation catalyst obtained corresponds to the eleventh arrangement mentioned above.

EXAMPLE 6

[0067] The coated substrate obtained according to Example 2 above was coated over 50% of its length with 77 g/l of a washcoat containing platinum and palladium in a weight ratio of 12:1 fixed on an alumina-silica-mixed oxide. The oxidation catalyst obtained corresponds to the tenth arrangement mentioned above.