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 and palladium applied to a cerium-titanium mixed oxide, and material zone B comprises platinum and palladium applied to a carrier oxide B.

Claims

1. 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 and palladium applied to a cerium-titanium mixed oxide, and material zone B comprises platinum and palladium applied to a carrier oxide B.

2. Diesel oxidation catalyst according to claim 1, characterized in that 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, characterized in that the cerium-titanium mixed oxide comprises 20 to 98% by weight of cerium oxide and 80 to 2% by weight of titanium oxide.

4. Diesel oxidation catalyst according to claim 1, characterized in that 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, characterized in that 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, characterized in that material zone B comprises lanthanum oxide, magnesium oxide, barium oxide and/or strontium oxide.

7. Diesel oxidation catalyst according to claim 1, characterized in that material zone B comprises a hydrogen adsorbent material.

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

10. Diesel oxidation catalyst according to claim 8, characterized in that 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, characterized in that 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-titanium mixed oxide comprising 25 to 95% by weight of cerium oxide and 75 to 5% by weight of titanium 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, characterized in that 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, characterized in that 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. Device for purification of exhaust gases from diesel engines having a diesel oxidation catalyst according to claim 1.

15. Device according to claim 14, characterized in that 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

[0064] a) 60 g/l of milled CeTiOx material (CeO.sub.2/TiO.sub.2=95/5) 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.

[0065] 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.

[0066] 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.

[0067] 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 arrangement 2 mentioned above and is called C1 below.

COMPARISON EXAMPLE 1

[0068] Steps a) and b) of Example 1 were repeated with the exception that in step a) 100 g/l of milled CeTiOx material (CeO.sub.2/TiO.sub.2=95/5) were added to a solution of soluble Pt salt (0.9712 g/l Pt), followed by 2.9135 g/l of Pd ex nitrate.

[0069] The oxidation catalyst obtained is called CC1 below.

COMPARISON EXAMPLE 2

[0070] a) To 103.88 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), 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.

[0071] 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.

[0072] The oxidation catalyst obtained is called CC2 below.

EXAMPLE 2

[0073] a) 42 g/l of milled CeTiOx material (CeO.sub.2/TiO.sub.2=95/5) were added to a solution of soluble Pt salt (1.059 g/l Pt), followed by 1.059 g/l of Pd ex nitrate. Finally, 18 g/l of milled alumina and then 4.5 g/L of Alumina-sol were added. The obtained product was dried and calcined for 2 h at 550° C.

[0074] 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 starting from its first end face over 50% of its length with a washcoat containing 67 g/l of the product obtained according to a) above.

[0075] c) 50 g/l of milled alumina were added to a solution of a Pt salt (0.942 g/l Pt). Subsequently, 0.471 g/l Pd ex nitrate, 3 g/l of La.sub.2O.sub.3, 30 g/l beta zeolite and 4.5 g/l of alumna-sol were added. The product obtained was dried and calcined for 2 h at 550° C.

[0076] d) The coated substrate obtained according to b) above was coated starting from its first end face over 50% of its length with a washcoat containing 89 g/l of the product obtained according to c) above.

[0077] e) 150 g/l of alumina doped with 10% by weight of silica were added to a solution containing 2.608 g/l of Pt and 0.217 g/l of Pd (both in form of their nitrates). The product obtained was dried and calcined for 2 h at 550° C.

[0078] f) The coated substrate obtained according to d) above was coated starting from its second end face over 50% of its length with a washcoat containing 150 g/l of the product obtained according to e) above.

[0079] The oxidation catalyst obtained corresponds to arrangement 4 mentioned above and is called C2 below.

EXAMPLE 3

[0080] Example 2 above was repeated with the exception that the substrate was first coated with a washcoat containing the product obtained according to step c) of Example 2 and subsequently with a washcoat containing the product obtained according to step a) of Example 2.

[0081] The oxidation catalyst obtained corresponds to arrangement 5 mentioned above and is called C3 below.

EXAMPLE 4

[0082] a) 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 with a washcoat containing 89 g/l of the product obtained according to step c) of Example 2.

[0083] b) The coated substrate obtained according to a) above was coated starting from its first end face over 50% of its length with a washcoat containing 67 g/l of the product obtained according to step a) of Example 2.

[0084] c) 100 g/l of alumina doped with 10% by weight of silica were added to a solution containing 1.304 g/l of Pt and 0.109 g/l of Pd (both in form of their nitrates). The product obtained was dried and calcined for 2 h at 550° C.

[0085] d) The coated substrate obtained according to b) above was coated starting from its second end face over 50% of its length with a washcoat containing 102 g/l of the product obtained according to c) above.

[0086] The oxidation catalyst obtained corresponds to arrangement 6 mentioned above and is called C4 below.

EXAMPLE 5

[0087] a) 84 g/l of milled CeTiOx material (CeO.sub.2/TiO.sub.2=95/5) were added to a solution of soluble Pt salt (1.413 g/l Pt), followed by 1.413 g/l of Pd ex nitrate. Finally, 36 g/l of milled alumina and then 9 g/L of Alumina-sol were added. The obtained product was dried and calcined for 2 h at 550° C.

[0088] 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 starting from its first end face over 50% of its length with a washcoat containing 134 g/l of the product obtained according to a) above.

[0089] c) The coated substrate obtained according to b) above was coated starting from its second end face over 50% of its length with a washcoat containing 66.8 g/l of the product obtained according to step c) of Example 2.

[0090] d) 100 g/l of alumina doped with 10% by weight of silica were added to a solution containing 2.282 g/l of Pt and 0.109 g/l of Pd (both in form of their nitrates). The product obtained was dried and calcined for 2 h at 550° C.

[0091] e) The coated substrate obtained according to c) above was coated starting from its second end face over 50% of its length with a washcoat containing 102 g/l of the product obtained according to d) above.

[0092] The oxidation catalyst obtained corresponds to arrangement 8 mentioned above and is called C5 below.

EXAMPLE 6

[0093] a) 84 g/l of milled CeTiOx material (CeO.sub.2/TiO.sub.2=95/5) were added to a solution of soluble Pt salt (1.413 g/l Pt), followed by 1.413 g/l of Pd ex nitrate. Finally, 36 g/l of alumina and 9 g/L of Alumina-sol were added. The obtained product was dried and calcined for 2 h at 550° C.

[0094] 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.

[0095] c) The coated substrate obtained according to b) above was coated starting from its first end face over 50% of its length with a washcoat containing 66.8 g/l of the product obtained according to step c) of Example 2.

[0096] d) The coated substrate obtained according to c) above was coated starting from its second end face over 50% of its length with a washcoat containing 102 g/l of the product obtained according to step d) of Example 5.

[0097] The oxidation catalyst obtained corresponds to arrangement 7 mentioned above and is called C6 below.

[0098] Comparative Experiments

[0099] a) Cores were taken out of catalysts C1 to C6, CC1 and CC2. All cores were aged 16 h at 800° C. under hydrothermal atmosphere.

[0100] b) T.sub.50CO— and T.sub.50C3H.sub.6-light off values of all catalysts were determined on a synthetic gas bench with a gas mixture given in Tab 1. Before testing catalysts were preconditioned under the same gas atmosphere at 650° C.

TABLE-US-00001 TABLE 1 GHSV [1/h] 60000 NO [ppm] 500 O.sub.2 [vol %] 10.5 CO [ppm] 800 HC [ppm C3] (C.sub.3H.sub.6) 130 CO.sub.2 [vol %] 6.3 H.sub.2O [vol %] 7 N.sub.2 rest

[0101] c) The results obtained are given in FIG. 2.

[0102] Additional Experiments

[0103] A. Catalysts C7 to C10 were produced by coating washcoats on usual commercially available flow-through substrates via a usual coating technique. All catalysts contained 110 g/ft.sup.3 of platinum and/or palladium on alumina and the washcoat loading was 110 g/l in each case. The catalysts differed as follows: [0104] C7 contained platinum only [0105] C8 contained platinum and palladium in a weight ratio Pt:Pd of 2:1 [0106] C9 contained platinum and palladium in a weight ratio Pt:Pd of 1:3 [0107] C10 contained palladium only

[0108] Platinum was applied as solution of a soluble Pt salt and palladium ex nitrate.

[0109] B. Catalysts C11 to C14 were produced by coating washcoats on usual commercially available flow-through substrates via a usual coating technique. All catalysts contained 110 g/ft.sup.3 of platinum and/or palladium on ceria and the washcoat loading was 110 g/l in each case. In addition, each washcoat contained 7 g/l of Alusol. The catalysts differed as follows: [0110] C11 contained platinum only [0111] C12 contained platinum and palladium in a weight ratio Pt:Pd of 2:1 [0112] C13 contained platinum and palladium in a weight ratio Pt:Pd of 1:3 [0113] C14 contained palladium only

[0114] Platinum was applied as solution of a soluble Pt salt and palladium ex nitrate.

[0115] C. T.sub.50CO-light off values of catalysts C7 to C14 in fresh and aged (16 h at 800° C. under hydrothermal atmosphere) condition were determined on a synthetic gas bench with a gas mixture given in Tab 2. Before testing catalysts were preconditioned under the same gas atmosphere at 500° C.

TABLE-US-00002 TABLE 2 GHSV [1/h] 50000 NO [ppm] 50 NO.sub.2 [ppm] 50 O.sub.2 [vol %] 5 CO [ppm] 1000 HC [ppm C3] (C.sub.3H.sub.6/C.sub.3H.sub.8)) 150 (75/75) CO.sub.2 [vol %] 10 H.sub.2O [vol %] 6.6 N.sub.2 rest

[0116] The results are given in Table 3

TABLE-US-00003 T.sub.50CO-light off T.sub.50CO-light off [° C.], fresh [° C.], aged C7 173.9 195.9 C8 139.6 165.9 C9 171.1 182.1 C10 179.9 183.1 C11 233.7 263.3 C12 156.8 163.9 C13 145.3 145.9 C14 144.3 144.0