Three-zone diesel oxidation catlayst

Abstract

The invention relates to a diesel oxidation catalyst which has a support body with a length L extending between a first end face a and a second end face b and catalytically active material zones A, B, and C arranged on the support body, whereinmaterial zone A contains palladium or platinum and palladium in a weight ratio of Pt:Pd of 1 and an alkaline earth metal and extends over 20 to 80% of the length L starting from the end face a, material zone B contains ceroxide, is free of platinum, and extends over 20 to 80% of the length L starting from the end face b, material zone C contains platinum or platinum and palladium in a weight ratio of Pt:Pd of 5, and neither material zone A nor material zone C is arranged over material zone B.

Claims

1. A 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 catalytically active material zones A, B and C arranged on the carrier body, wherein material zone A contains palladium or platinum and palladium in a weight ratio Pt:Pd of 1 and an alkaline earth metal and extends from end face a to 20 to 80% of length L, material zone B contains cerium oxide and is free of platinum and extends from end face b to 20 to 80% of length L, and material zone C contains platinum or platinum and palladium in a weight ratio Pt:Pd of 5, and neither material zone A nor material zone C are arranged above material zone B.

2. The Diesel oxidation catalyst according to claim 1, wherein in the material zones A and C palladium, platinum or platinum and palladium are present on a carrier oxide.

3. The diesel oxidation catalyst according to claim 1 wherein the carrier oxides in material zones A and C are identical 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 alkaline earth metal in material zone A is present in an amount of 0.5 to 5% by weight relative to the weight of the material zone A.

5. The diesel oxidation catalyst according to claim 1, wherein the alkaline earth metal in material zone A is strontium or barium or strontium and barium.

6. The diesel oxidation catalyst according to claim 1, wherein material zone B contains palladium.

7. The diesel oxidation catalyst according to claim 6, wherein material zone B contains palladium in an amount of 0.01 to 5% by weight relative to the weight of material zone B.

8. The diesel oxidation catalyst according to claim 1, wherein material zone C extends over the entire length L of the carrier body.

9. The diesel oxidation catalyst according to claim 1, wherein material zones A and B are arranged on material zone C.

10. The diesel oxidation catalyst according to claim 1, wherein material zone C is arranged on material zone A and material zone B is arranged on material zone C.

11. The diesel oxidation catalyst according to claim 1, wherein material zones A and B each extend to 50% and material zone C to 100% of the length L of the carrier body.

12. 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 the end face a and flows out of the carrier body at the end face b.

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

14. The device according to claim 13, wherein the diesel oxidation catalyst is arranged upstream of a diesel particle filter and/or a catalyst for selective catalytic reduction of nitrogen oxides.

Description

(1) FIG. 1 shows a comparison of the heat-up behavior of Examples 1 to 3 and Comparative Examples 1 to 3.

EXAMPLE 1

(2) a) A commercially available round flow-through substrate of cordierite of dimensions 14.38 cm10.16 cm (5.664.00) with a cell density of 62 cells per square centimeter (400 cpsi) and wall thickness 0.16 mm (6.5 mil) 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.

(3) b) The coated substrate obtained according to a) was coated from one end (inlet side in the tests described below) to 50% of its length with a washcoat containing 48.23 g/L of a commercially available lanthanum-doped aluminum oxide, 1.00 g/L strontium oxide (ex Sr(OH)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.

(4) c) In a further step, the substrate obtained according to b) was coated, starting from the other end (in the tests described below on the outlet side), to 50% of its length with a washcoat containing 45 g/L of a commercially available aluminum oxide and 5 g/L of a commercially available cerium oxide.

COMPARATIVE EXAMPLE 1

(5) Example 1 was repeated with the difference that step c) was omitted.

COMPARATIVE EXAMPLE 2

(6) Example 1 was repeated with the difference that step b) was omitted.

COMPARATIVE EXAMPLE 3

(7) a) A commercially available flow-through substrate of cordierite having dimensions 14.38 cm10.16 cm (5.664.00) with a cell density of 62 cells per square centimeter (400 cpsi) and wall thickness 0.16 mm (6.5 mil) was coated over its entire length with a washcoat containing 73.85 g/L of a lanthanum-doped mesoporous aluminum oxide, 0.90810 g/L of a standard water-soluble Pt compound, and 0.15135 g/L of a standard water-soluble Pd compound. The Pt:Pd weight ratio was 6:1.

(8) b) In a further step, the substrate obtained according to a) was coated from one end (outlet side in the tests described below) to 50% of its length with a washcoat containing 45 g/L of a commercially available aluminum oxide and 5 g/L of a commercially available cerium oxide.

EXAMPLE 2

(9) a) A commercially available flow-through substrate of cordierite with dimensions of 14.38 cm10.16 cm (5.664.00) with cell density of 62 cells per square centimeter (400 cpsi) and wall thickness 0.16 mm (6.5 mils) was coated from one end (in the tests described below on the inlet side) over 50% of its length with a washcoat containing 48.23 g/L 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.

(10) b) The coated substrate obtained according to a) was coated over its entire length (i.e., on the inlet side on the zone according to a), on the outlet side directly on the carrier substrate) with a washcoat containing 49.23 g/L of a commercially available lanthanum-doped aluminum oxide, 1.00 g/L strontium oxide (ex Sr(OH)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.

(11) c) In a further step, the substrate obtained according to b) was coated, starting from the other end (in the tests described below on the outlet side) to 50% of its length, i.e. on the zone according to a) with a washcoat containing 45 g/L of a commercially available aluminum oxide and 5 g/L of a commercially available cerium oxide.

EXAMPLE 3

(12) A commercially available flow-through substrate of cordierite of dimensions 14.38 cm10.16 cm (5.664.00) with a cell density of 62 cells per square centimeter (400 cpsi) and wall thickness 0.16 mm (6.5 mil) was sawn into three parts of equal length.

(13) The three parts were each coated over their entire length with the washcoat materials mentioned in Examples 1 a), b) and c).

(14) For the tests described below, the three substrate parts were joined together in the direction of the flowing exhaust gas in the order:

(15) 1st part coated with washcoat according to Example 1 b)

(16) 2nd part coated with washcoat according to Example 1 a)

(17) 3rd part coated with washcoat according to Example 1 c)

(18) Carrying Out Comparative Tests

(19) a) Hydrothermal Furnace Aging

(20) The catalysts according to Examples 1 to 3 and Comparative Examples 1 to 3 were aged at 750 C. for 16 hours. The comparative tests described below were carried out with the catalysts aged in this way, unless stated otherwise.

(21) b) Determination of the NO.sub.2 Formation and the CO Conversion in the Model Gas; for all Measurements, the Following Items Apply:

(22) Space velocity=37,500 1/h

(23) Bore core dimension 2.54 cm10.16 cm (14) (bored from substrates according to Examples 1 to 3 and Comparative Examples 1 to 3)

(24) Investigated temperature range: 75 C. to 500 C., wherein the values at the temperatures 200, 250 and 300 C. are documented in the tables below.

(25) Ramp/heating rate=15 K/min

(26) Tests were carried out with three different gas compositions:

(27) TABLE-US-00001 Test conditions: 1 2 3 Unit [ppm] [ppm] [ppm] CO 350 250 500 H2 116 0 167 Propene as C3 60 0 200 Propane as C3 30 0 67 Toluene as C7 0 0 8.6 N-decane as C 0 0 14 10 NO 270 750 150 Unit [%] [%] [%] O2 6 10 13 H2O 5 7.5 10 CO2 10.7 7 5 N2 Rest Rest Rest

(28) The following results were obtained:

(29) TABLE-US-00002 TABLE 1 T.sub.50CO and NO.sub.2 formation under test conditions 1 Test conditions 1 T.sub.50CO NO.sub.2@200 C. NO.sub.2@250 C. NO.sub.2@300 C. [ C.] [%] [%] [%] Example 1 150 15 28 44 Comparative 149 17 34 49 example 1 Comparative 155 18 33 50 example 2 Comparative 152 19 35 55 example 3 Example 2 151 16 29 45 Example 3 153 14 28 41

(30) TABLE-US-00003 TABLE 2 T.sub.50CO and NO.sub.2 formation under test conditions 2 Test conditions 2 T.sub.50CO NO.sub.2@200 C. NO.sub.2@250 C. NO.sub.2@300 C. [ C.] [%] [%] [%] Example 1 168 15 26 39 Comparative 166 18 30 45 example 1 Comparative 173 16 27 42 example 2 Comparative 170 19 29 48 example 3 Example 2 168 14 25 38 Example 3 171 4 25 36

(31) TABLE-US-00004 TABLE 3 T.sub.50CO and NO.sub.2 formation under test conditions 3 Test conditions 3 T.sub.50CO NO.sub.2@200 C. NO.sub.2@250 C. NO.sub.2@300 C. [ C.] [%] [%] [%] Example 1 171 5 16 30 Comparative 168 8 22 38 example 1 Comparative 172 7 19 35 example 2 Comparative 168 8 20 38 example 3 Example 2 170 4 14 26 Example 3 170 0 15 28
c) Determination of the NO.sub.2 Formation and the CO Conversion in the Engine Light-Off Test:

(32) By raising the torque at a constant rotational speed of the engine, an increase in the precatalyst temperature is achieved; the test runs from low to high temperatures, analogous to the model gas procedure.

(33) The conversion of the pollutants is measured by AMA lines and calculated; the NO.sub.2 formation is determined by means of a CLD.

(34) The following results were obtained:

(35) TABLE-US-00005 TABLE 4 T.sub.50CO and NO.sub.2 formation on engine T.sub.50CO NO.sub.2max NO.sub.2@300 C. [ C.] [%] [%] Example 1 157 19 25 Comparative example 1 160 23 20 Comparative example 2 169 22 17 Comparative example 3 160 25 22 Example 2 159 33 32 Example 3 157 18 15
d) Determination of the Heat-Up Behavior in the Engine Test (3-Point-Heat-Up Test):

(36) A stationary engine operating point is approached by a suitable combination of torque and rotational speed. This is kept constant for a certain time; diesel fuel is then injected in a finely nebulized state upstream of the catalyst via a secondary/external injector, which then converts the fuel and thus generates a certain exotherm/heat, which is measured by means of thermocouples installed in the catalyst.

(37) The test is run from high to low temperatures; the temperatures are:

(38) 1) 280 C. precatalyst temperature

(39) 2) 270 C. precatalyst temperature

(40) 3) 260 C. precatalyst temperature.

(41) The results are shown in FIG. 1.

(42) e) Determination of Platinum Migration

(43) The catalysts used in Examples 1 to 3 and Comparative Examples 1 to 3 were subjected in a fresh state to a model gas of the following composition in a standard synthesis gas plant with isothermal reactor at a constant temperature of 650C for 18 hours: CO 71 ppm NO 820 ppm O.sub.2 6.3 volume percent CO.sub.2 8.9 volume percent H.sub.2O 11 volume percent in the measurements lasting 18 hours, and 5 volume percent in the measurements lasting 60 hours N.sub.2 Balance

(44) The gas leaving downstream of the respective catalyst was guided through a flow-through substrate having a length of 5.08 cm (2) and coated with an SCR catalyst of the iron--zeolite type.

(45) The amount of platinum bound in the SCR catalyst was then determined for each catalyst. To this end, a drilling core of the catalyst was melted in a crucible by means of an NiS fire assay, and the platinum was then determined by means of ICP-OES.

(46) The following results were obtained:

(47) TABLE-US-00006 Amount of platinum [ppm] Example 1 1.2 Comparative example 1 3.0 Comparative example 2 0.3 Comparative example 3 0.9 Example 2 0.4 Example 3 0.4