PLATINUM AND ZINC-CONTAINING ZEOLITE

Abstract

The present invention relates to a zeolite comprising zinc and platinum, and to a catalyst containing said zeolites.

Claims

1. A zeolite comprising zinc and platinum and being selected from the group consisting of zeolites of the structure types AEI, AFX, BEA, CHA, ERI, FER, KFI, LEV and MFI, wherein the zinc (i) is present as zinc cation in ion-exchanged form in the zeolite structure and/or (ii) as zinc oxide in the zeolite structure and/or on the surface of the zeolite structure, and wherein the zeolite has a SAR (silica-to-alumina ratio) value of 2 to 1000.

2. The zeolite according to claim 1, wherein it is selected from the group consisting of zeolites of structure types AEI, AFX, CHA and FER.

3. The zeolite according to claim 1, wherein it belongs to structure type AEI.

4. The zeolite according to claim 1, wherein it belongs to structure type AFX.

5. The zeolite according to claim 1, wherein it belongs to the structure type CHA.

6. The zeolite according to claim 1, wherein it belongs to structure type FER.

7. The zeolite according to claim 1, wherein the zeolite has an SAR (silica-to-alumina molar ratio) value of 2 to 500.

8. The zeolite according to claim 1, wherein the zeolite has an SAR (silica-to-alumina ratio) value of 2 to 100.

9. The zeolite according to claim 1, wherein the zeolite has an SAR (silica-to-alumina ratio) value of 2 to 50.

10. The zeolite according to claim 1, wherein the platinum is present in amounts of 0.01 to 20% by weight, based on the sum of the weights of zeolite, zinc and platinum and calculated as zinc metal and platinum metal.

11. The zeolite according to claim 1, wherein the zinc is present in amounts of 0.01 to 20% by weight, based on the sum of the weights of zeolite, zinc and platinum and calculated as zinc metal and platinum metal.

12. The zeolite according to claim 1, wherein the mass ratio of platinum:zinc is from 6:1 to 1:7, with platinum calculated as platinum metal and zinc as zinc metal.

13. A catalyst comprising a carrier substrate of length L and a zeolite according to claim 1.

14. A method for the oxidation of ammonia contained in an exhaust gas stream, wherein the exhaust gas flow is conducted over a zeolite according to claim 1.

15. A device for purifying the exhaust gases of diesel engines, which comprises a catalyst according to claim 13.

16. A method for the oxidation of ammonia contained in an exhaust gas stream, wherein the exhaust gas flow is conducted over a catalyst according to claim 13.

Description

EXAMPLE 1

[0033] First, a mixed platinum nitrate/zinc acetate solution is produced, the volume of which corresponds to 50 percent water absorption of the zeolite (a commercially available zeolite of the structure type CHA). Based on the final composition of the platinum and zinc-containing zeolite, 0.42% by weight platinum and 0.07% by weight zinc (mass ratio Pt:Zn=6:1) are applied to the zeolite in a mechanical mixer. The subsequent thermal treatment comprises drying at 120° C., calcination at 350° C. and annealing at 550° C. in air.

In the subsequent washcoat preparation, 10% of a commercially available aluminum oxide sol (based on the total loading) is added and a thus a commercially available carrier substrate made of ceramic is coated with a washcoat load of 25 g/l, which is ultimately dried at 120° C., calcined at 350° C. and tempered at 550° C.
The catalyst obtained is referred to below as K1.

EXAMPLE 2

[0034] Example 1 is repeated with the difference that the amount of zinc is 0.2% by weight (mass ratio Pt:Zn=2:1).

The catalyst obtained is referred to below as K2.

EXAMPLE 3

[0035] Example 1 is repeated with the difference that the amount of zinc is 0.6% by weight (mass ratio Pt:Zn=1:1.5).

The catalyst obtained is referred to below as K3.

EXAMPLE 4

[0036] Example 1 is repeated with the difference that the amount of zinc is 2.64% by weight (mass ratio Pt:Zn=1:6.6).

The catalyst obtained is referred to below as K4.

COMPARATIVE EXAMPLE 1

[0037] Example 1 is repeated with the difference that no zinc is used. The catalyst obtained is referred to below as VK1.

EXAMPLE 5

[0038] A commercially available zeolite of structure type CHA is initially provided in water and the pH is adjusted to 10. Pt-TEAH is then added and the suspension is stirred for 24 h. Subsequently, the pH is adjusted to 6, zinc acetate and 10% aluminum oxide sol are added. The mass ratio Pt:Zn was 1:1.7.

Following linear grinding, a commercially available carrier substrate made of ceramic is subsequently coated with a washcoat quantity of 25 g/l. The final temperature treatment in air comprises drying at 120° C. and calcination and tempering at 350 and 550° C. The total noble metal concentration on the final catalyst (hereinafter referred to as K5) is 0.42% by weight.

COMPARATIVE EXAMPLE 2

[0039] Example 5 is repeated with the difference that, after addition of Pt-TEAH, the mixture is stirred for 20 h and no zinc is used. The catalyst obtained is referred to below as VK2.

Determination of the NH.sub.3 light off and the N.sub.2O formation

a) Aging

[0040] From catalysts K1 to K5 and VK1 and VK2, 4 drill cores each were cut, of which two were measured in a fresh state and two following hydrothermic aging (10% H.sub.2O, 10% O.sub.2, residue N.sub.2) in an oven for 16 hours at 800° C. (given below as: 16H800).

b) Test Conditions in the Laboratory Reactor

[0041] In a laboratory reactor, a synthetic test exhaust gas consisting of 300 ppm NH.sub.3, 5% O.sub.2, 5% H.sub.2O, residue N.sub.2 (test A or B) or a test exhaust gas consisting of 300 ppm NH.sub.3, 200 ppm NO, 5% O.sub.2, 5% H.sub.2O, residue N.sub.2 (test C or D) was passed through the drill cores obtained according to A) at 1950 L/hour. In this case, the temperature of the test exhaust gas after a conditioning phase (˜30 K/min of 150 to 600° C. in 5% O.sub.2, residue N.sub.2) was increased at 10 K/min from 150° C. to 600° C., and the NH.sub.3 reaction was determined by means of a conventional method.

c) Results

[0042] The following tables show the results obtained:

TABLE-US-00001 TABLE 1 Test A: fresh, only NH.sub.3 K1 K2 K3 K4 VK1 K5 VK2 NH.sub.3 T50/° C. 222 221 220 218 228 208 220 NH.sub.3 conversion (350° C.)/% 99 99 99 99 99 99 98 NH.sub.3 conversion (550° C.)/% 99 99 99 100 100 100 99 NO formation (210-400° C.)/ppm 79 70 77 89 65 113 70 NO formation (550° C.)/ppm 206 200 206 235 196 225 202 N.sub.2O formation (210-400° C.)/ppm 44 48 48 48 47 35 44 N.sub.2O formation max./ppm 81 86 85 86 87 66 79

TABLE-US-00002 TABLE 2 Test B: 16H800, only NH.sub.3 K1 K2 K3 K4 VK1 K5 VK2 NH.sub.3 T50/° C. 209 207 205 203 210 194 202 NH.sub.3 conversion (350° C.)/% 97 97 97 97 97 95 97 NH.sub.3 conversion (550° C.)/% 98 98 98 98 98 95 98 NO formation (210-400° C.)/ppm 124 125 128 133 125 155 135 NO formation (550° C.)/ppm 252 252 251 257 254 265 254 N.sub.2O formation (210-400° C.)/ppm 34 34 33 32 35 25 31 N.sub.2O formation max./ppm 54 55 53 47 54 44 51

TABLE-US-00003 TABLE 3 Test C: fresh, NH.sub.3 + NO K1 K2 K3 K4 VK1 K5 VK2 NH.sub.3 T50/° C. 206 202 203 198 206 209 210 NH.sub.3 conversion (350° C.)/% 99 99 99 99 99 99 99 NH.sub.3 conversion (550° C.)/% 99 100 99 100 100 100 100 NO formation (210-400° C.)/ppm 192 175 186 200 168 238 195 NO formation (550° C.)/ppm 364 354 363 403 346 389 384 N.sub.2O formation (210-400° C.)/ppm 77 82 83 82 84 59 75 N.sub.2O formation max./ppm 149 160 157 162 159 119 138

TABLE-US-00004 TABLE 4 Test D: 16H800, NH.sub.3 + NO K1 K2 K3 K4 VK1 K5 VK2 NH.sub.3 T50/° C. 214 213 214 215 217 212 214 NH.sub.3 conversion (350° C.)/% 96 97 97 97 96 95 97 NH.sub.3 conversion (550° C.)/% 98 98 98 98 97 96 98 NO formation (210-400° C.)/ppm 269 270 273 279 268 304 296 NO formation (550° C.)/ppm 434 433 433 440 432 453 461 N.sub.2O formation (210-400° C.)/ppm 60 60 57 55 60 42 49 N.sub.2O formation max./ppm 105 105 102 94 102 83 91

[0043] The test results show that, as a function of the zinc content of the inventive catalysts K1 to K4 or K5, the light off temperatures for ammonia fall compared to the comparative catalysts VK1 and VK2 containing platinum only. Although this higher activity leads to a higher NO formation, it leads to a lower rather than a higher N.sub.2O formation. The addition of zinc thus leads to a higher NO selectivity and a lower N.sub.2O selectivity. However, the higher NO selectivity is not disadvantageous since NO can be converted by an SCR layer to nitrogen and oxygen.