Low-Temperature Oxidation Catalyst With Particularly Marked Hydrophobic Properties ForThe Oxidation Of Organic Pollutants

Abstract

The present invention relates to a catalyst comprising a macroporous noble metal-containing zeolite material and a porous SiO.sub.2-containing binder, wherein the catalyst has a proportion of micropores of more than 70%, based on the total pore volume of the catalyst. The invention is additionally directed to a process for preparing the catalyst and to the use of the catalyst as an oxidation catalyst.

Claims

1-12. (canceled)

13. A method of purifying exhaust, the method comprising: providing an exhaust gas containing an organic pollutant; oxidizing the exhaust gas with a catalyst under conditions sufficient to oxidize the organic pollutant, the catalyst comprising a microporous noble metal-containing zeolite material, the zeolite material having less than 2 mol. % aluminium, the zeolite material being selected from zeolites of the types AFI, AEL, BEA, CHA, EUO, FAU, FER, KFI, LTL, MAZ, MOR, MEL, MTW, OFF, TON and MFI, the noble metal being selected from the group consisting of rhodium, iridium, palladium, platinum, ruthenium, osmium, gold and silver and combinations thereof; and a porous SiO.sub.2-containing binder having less than 0.04 wt % aluminium, wherein the catalyst has a proportion of micropores having a diameter of less than 1 nm of more than 70% relative to the total pore volume of the catalyst.

14. The method according to claim 13, wherein the exhaust gas is an exhaust gas from a combustion process.

15. The method according to claim 13, wherein the exhaust gas is an exhaust gas from a power plant.

16. The method according to claim 13, wherein the exhaust gas is an exhaust gas from an industrial process.

17. The method according to claim 13, wherein the oxidation is performed at a temperature below 300 C.

18. The method according to claim 13, wherein the organic pollutant is a solvent-type organic pollutant.

19. The method according to claim 13, wherein the organic pollutant is a paraffin, an olefin, an aldehyde or an aromatic.

20. The method according to claim 13, wherein the catalyst is provided as a coating on a support.

21. The method according to claim 20, wherein the support is a metal foam.

22. The method according to claim 20, wherein the support is a honeycomb-shaped monolith.

23. The method according to claim 13, wherein the zeolite material of the catalyst contains 0.5-3.0 wt % noble metal relative to the amount of zeolite material.

24. The method according to claim 13, wherein the catalyst has a zeolite material/binder weight ratio in the range of 80:20 to 60:40.

25. The method according to claim 13, wherein the catalyst has an integral pore volume greater than 180 mm.sup.3/g.

26. The method according to claim 13, wherein the noble metal is selected from the group consisting of palladium, platinum, and combinations thereof.

27. The method according to claim 13, wherein the catalyst has a proportion of mesopores having a diameter of 1-50 nanometers and macropores having a diameter in excess of 50 nanometers in the range of 20-30% as compared to the total pore volume of the catalyst.

28. The method according to claim 13, wherein the calcining provides a catalyst having a proportion of micropores having a diameter less than 1 nm of greater than 72% as compared to the total pore volume of the catalyst.

29. The method according to claim 13, wherein the microporous zeolite material has less than 1 mol % aluminium.

30. The method according to claim 13, wherein the binder has less than 0.02 wt % aluminium.

31. The method according to claim 13, wherein the zeolite material of the catalyst contains 0.5-6.0 wt % noble metal relative to the amount of zeolite material, the noble metal being selected from the group consisting of rhodium, iridium, palladium, platinum, ruthenium, osmium, gold and silver and combinations thereof; the zeolite material has less than 1 mol % aluminium; the catalyst has an integral pore volume greater than 100 mm.sup.3/g; and the catalyst has a proportion of mesopores having a diameter of 1-50 nanometers and macropores having a diameter in excess of 50 nanometers in the range of 20-30% as compared to the total pore volume of the catalyst.

32. The method according to claim 13, wherein the zeolite material of the catalyst contains 0.5-3.0 wt % noble metal relative to the amount of zeolite material, the noble metal being selected from the group consisting of palladium, platinum, and combinations thereof; the microporous zeolite material has less than 1 mol % aluminium; the binder has less than 0.02 wt % aluminium; the catalyst has an integral pore volume greater than 180 mm.sup.3/g; and the catalyst has a proportion of micropores having a diameter less than 1 nm of greater than 72% as compared to the total pore volume of the catalyst

Description

[0045] FIG. 1 shows the performance of the catalyst according to the invention in the oxidation of 180 ppmv ethyl acetate in air at a GHSV of 40000 h.sup.1 compared with conventional reference materials.

[0046] FIG. 2 shows a comparison of the conversion at a temperature of 225 C., plotted against the noble metal doping.

EMBODIMENT EXAMPLE 1

[0047] A H-BEA-150 zeolite was dried overnight for approx. 16 h at 120 C. in order to obtain an informative result later during the water absorption. The water absorption of the zeolite was then determined by means of the incipient wetness method. For this, approx. 50 g of the zeolite to be impregnated was added to a bag, a container tared with water and water added and kneaded in until the zeolite was still just about absorbing the water (absorption: 38.68 g=77.36%).

[0048] An acid Pt(NO.sub.3).sub.2 solution was used for the Pt impregnation (15.14 wt.-%). As, in this case, the Pt loading is predetermined by the solids loading in the honeycomb, the reference loading must be back-calculated with the Pt quantity to be doped.

[0049] The target loading of the honeycomb is 30 g/l. At 3.375 l per honeycomb, this corresponds to a reference loading of 101.25 g washcoat with a noble metal loading of 0.5 g/l (m reference .sub.(at 3.375 l)=1.68 g). The ratio of zeolite to Bindzil was 70/30. Solids content (Bindzil, wt.-% SiO.sub.2=34%); m (reference loading without Bindzil)=90.92 g Pt-BEA-150.

[0050] At a Pt content of 1.68 g, a BEA-150 is thus to be impregnated with 1.85% Pt. For 1500 g Pt-BEA-150, this corresponds to a Pt loading of 27 g and thus a quantity of Pt(NO.sub.3).sub.2 solution (wt.-% Pt=15.14) of 183.88 g. At an absorption of 77.36%, the Pt(NO.sub.3).sub.2 solution must be diluted with 1008.65 g water once more.

[0051] The impregnation was carried out in a mixer from Netzsch with a butterfly agitator. For this, the quantity of zeolite was pre-weighed in a container (can) (1 can=102.77 g corresponding to 15 cans at 1500 g). The total quantity of the solution was extrapolated to the number of cans (at 102.77 g zeolite->79.50 g Pt(NO.sub.3).sub.2 solution which consists of 12.26 g Pt(NO.sub.3).sub.2 and 67.24 g demineralized water). The mixture was started at 250 rpm and the solution was added slowly. The rotational speed was increased during the addition. After the solution had been added, the rotational speed was increased to 500 rpm and stirring was carried out for approx. 0.5 min. The powder was then transferred into a ceramic bowl and dried at 120 C. for approx. 6 h. Then the Pt zeolite was calcined at 550 C./5 h (heating rate 60 C./h) under argon (throughflow 50 l/h). During this, the noble metal remains almost exclusively in the micropores of the catalyst, which results in a very high oxidative activity and stability at a high concentration of water vapour.

[0052] Ceramic Honeycomb Coating:

[0053] Washcoat type: Pt-BEA-150

[0054] Reference loading [g/l]: 30.00

[0055] Reference loading [g]: 101.25

[0056] Support material Ceramic substrate, 100 cpsi

[0057] Size

[0058] Length: [dm]: 1.500

[0059] Width: [dm]: 1.500

[0060] Height: [dm]: 1.500

[0061] Volume: [l]: 3.3750

[0062] Washcoat Production:

[0063] Amounts used:

[0064] Demineralized water 2052.0 g Conductivity: 1.0 S

[0065] Pt-BEA-150 1359.30 g LOI [%] 1.50 1380.0 g

[0066] Bindzil 2034 DI 377.40 g FS [%] 34.00 691.90 g

[0067] Before preparation, the particle size distribution of the zeolite powder was measured in physical analysis.

[0068] Result: D10=3.977 m; D50=10.401 m; D90=24.449 m

[0069] The test was carried out according to a standard method. The preparation container was a 5 l beaker. The zeolite powder was suspended in demineralized water and the pH was measured (pH: 2.62). The Bindzil was added to the suspension and the pH was measured (pH: 2.41). The suspension was then dispersed with an Ultra Turrax stirrer for approx. 10 min. A sample was taken from the suspension and the particle distribution was determined.

[0070] Results after Ultra Turrax: D10=2.669 m; D50=6.971 m; D90=18.575 m

[0071] The washcoat was further stirred on a magnetic stirrer and used for coating. [0072] Solids content [%] 40.10 [0073] pH: 2.41

[0074] Coating

[0075] The washcoat was diluted with 15% demineralized water. The solids content after dilution was 13.62%. For the coating, the washcoat was stirred until no more sediment remained and the washcoat was measured. For this, the support was completely immersed in the washcoat container and moved until no more bubbles formed (time: approx. 30 s) The support was then retrieved and blown with a compressed air nozzle from both sides evenly to approximately half of the reference loading. The support was dried at 150 C. overnight. A circulating air drying oven was used for drying. After drying, the support was cooled and weighed. If the reference loading was not achieved, the support was coated further until the reference value was achieved. The coated honeycombs were dried between the coatings. Calcining was then carried out under standard conditions in a circulating air oven.

TABLE-US-00001 Heating Time [h] 4 Temperature [ C.] from 40 to 550 Holding Time [h] 3 Temperature [ C.] at 550 Cooling Time [h] 4 Temperature [ C.] from 550 to 80

[0076] Washcoat type: Pt-BEA-150

TABLE-US-00002 TABLE 1 Coating results Support number 1 2 3 4 5 6 1st coating empty weight [g] 1806 1781 1811 1770 1802 1806 1st coating moist - reference [g] 2549 2524 2554 2513 2545 2549 1st coating moist - actual [g] 2120 2118 2123 2108 2133 2145 1st coating dry [g] 1830 1812 1835 1802 1836 1840 1st coating loading [g] 25 31 24 32 34 34 2nd coating empty weight [g] 1830 1812 1835 1802 1836 1840 2nd coating moist - reference [g] 0 2524 2554 2513 2545 2549 2nd coating moist - actual [g] 2152 2159 2177 2160 2167 2194 2nd coating dry [g] 1856 1845 1868 1841 1868 1881 2nd coating loading [g] 26 33 33 39 32 41 3rd coating empty weight [g] 1856 1845 1868 1841 1868 1881 3rd coating moist - reference [g] 2599 2588 2611 2584 2611 2624 3rd coating moist - actual [g] 2196 2206 2192 2185 2193 2224 3rd coating dry [g] 1879 1882 1897 1878 1901 1916 3rd coating loading [g] 23.00 37.00 29.00 37.00 33.00 35.00 4th coating empty weight [g] 1879 1897 4th coating moist - reference [g] 1885 1903 4th coating moist - actual [g] 2189 2225 4th coating dry [g] 1911 1947 4th coating loading [g] 32.00 0.00 50.00 0.00 0.00 0.00 Total loading [g] 105.5 100.90 136.10 108.20 98.90 110.40 Total loading [g/l] 31.26 29.90 40.33 32.06 29.30 32.71 Weight, calcined [g] 1911.00 1881.00 1947.00 1880.00 1898.00 1915.00 Total loading, calcined [g] 105.50 99.90 136.10 110.20 95.90 109.40 Total loading [g/l] 31.26 29.60 40.33 32.65 28.41 32.41

[0077] The proportions of micro- and meso/macropores of the catalysts according to the invention were investigated by means of the t-plot method and the values evaluated in m.sup.2/g (see Table 2).

TABLE-US-00003 TABLE 2 Pore proportion Sio.sub.2 binder [wt.-%] 10% 20% 40% Micropores [m.sup.2/g] 461 415 358 Meso/macropores [m.sup.2/g] 121 125 134 Total pores [m.sup.2/g] 582 549 492

COMPARISON EXAMPLE 1

[0078] A ceramic honeycomb was coated with 50 g/l of a washcoat consisting of wt.-% TiO.sub.2 and 20 wt.-% Al.sub.2O.sub.3. For this, the aqueous TiO.sub.2/Al.sub.2O.sub.3 suspension was first agitated intensively. The ceramic honeycomb was then immersed into the washcoat suspension. After immersion, non-adhering washcoat was removed by blowing the honeycomb channels. The honeycomb body was then dried at 120 C. and calcined at 550 C. for 3 h. The noble metal was applied by immersing the catalyst honeycomb coated with washcoat into a solution of Pt nitrate and Pd nitrate. After impregnation, the honeycomb was blown again, dried at 120 C. for 2 h and calcined at 550 C. for 3 h.

COMPARISON EXAMPLE 2

[0079] A ceramic honeycomb was coated with 100 g/l of a washcoat consisting of Al.sub.2O.sub.3. For this, the aqueous Al.sub.2O.sub.3 suspension was first agitated intensively. The ceramic honeycomb was then immersed into the washcoat suspension. After immersion, non-adhering washcoat was removed by blowing the honeycomb channels. The honeycomb body was then dried at 120 C. and calcined at 550 C. for 3 h. The noble metal was applied by two impregnation steps with intermediate drying and calcining. In the first part-step, the honeycomb coated with washcoat was impregnated by immersion into a solution of Pt sulphite. After impregnation, the honeycomb was blown, dried at 120 C. for 2 h and calcined at 550 C. for 3 h. In a second part-step, the honeycomb was impregnated with a solution of tetraammine Pd nitrate by immersion. The honeycomb was then blown again, dried at 120 C. for 2 h and calcined at 550 C. for 3 h.

COMPARISON EXAMPLE 3

[0080] A dried H-BEA-35 was loaded with an acid Pt(NO.sub.3).sub.2 solution by means of the incipient wetness method. For this, 48.5 g H-BEA-35 was impregnated with 47.1 g of a Pt(NO.sub.3).sub.2 solution containing 3.2 wt.-% Pt. After impregnation, the material was dried overnight at 120 C. and then calcined under argon. The calcining was carried out for 5 h at 550 C., the heating rate beforehand was 2 K/min. The finished Pt-BEA-35 powder contained 3 wt.-% Pt.

[0081] A catalyst honeycomb of cordierite was then coated with the pulverulent Pt-BEA material. For this, 33.3 g Pt-BEA material, 57 g H-BEA 35 and 29.4 g Bindzil (binder material, containing 34 wt.-% SiO.sub.2) were dispersed in 300 g water and then ground to a washcoat in a planetary ball mill at 350 rpm in 5-minute intervals for 30 min. The suspension was then transferred into a plastic bottle in each case, in order to coat the cordierite honeycomb (200 cpsi) with it. The achieved coating quantity was 100 g/l w/c. After coating, the honeycomb was calcined for 5 h at 550 C.

[0082] The noble metal dopings of all of the catalyst honeycombs are summarized in Table 3 below.

TABLE-US-00004 TABLE 3 Noble metal contents Washcoat Noble metal content [g/L] Catalyst according to Pt-BEA 150 Pt 0.54 the invention Comparison example 1 TiO.sub.2/Al.sub.2O.sub.3 Pt 0.66 Pd 0.13 Comparison example 2 Al.sub.2O.sub.3 Pt 1.32 Pd 0.26 Comparison example 3 Pt-BEA35 Pt 0.97

[0083] Catalytic Tests

[0084] The performance of the catalyst according to the invention was determined in the oxidation of 180 ppmv ethyl acetate in air at a GHSV of 40000 h.sup.1 and compared with that of conventional reference materials. The results are contained in FIG. 1 (data in Tables 4 to 7). In comparison example 3, the performance data were scaled to a comparable active honeycomb surface area, wherein points >90% conversion were omitted. FIG. 2 (data in Table 8) shows a comparison of the conversion at a temperature of 225 C., plotted against the noble metal doping, with the result that the improvement in performance of the catalyst according to the invention is made clearer.

TABLE-US-00005 TABLE 4 BEA150/550 C. Catalyst according to the invention Ethyl acetate T ave. T cat in C. [ C.] X(EA) 350 358 0.85829088 300 308 0.8241848 250 257 0.74022719 225 230 0.49238606 200 203 0.14086464 175 177 0.01479201 150 151.5 0.0213844 125 126.5 0.01206789 100 101 0

TABLE-US-00006 TABLE 5 Comparison example 1 Ethyl acetate T ave. T cat in C. [ C.] X(EA) 350 359 0.83930539 300 307.5 0.73694979 250 254.5 0.28581921 225 228 0.143067 200 202.5 0.04795131 175 177 0.03100572 150 152 0.01731284 125 126.5 0.01647343 100 101 0.05004984

TABLE-US-00007 TABLE 6 Comparison example 2 Ethyl acetate T ave. T cat in C. [ C.] X(EA) 350 357.5 0.79291201 300 306.5 0.59849077 250 253.5 0.15655572 225 227.5 0.03657189 200 202.5 0.04578898 175 177 0 150 151.5 0.03026546 125 126.5 0 100 101 0

TABLE-US-00008 TABLE 7 Comparison example 3 80000 h.sup.1 Ethyl acetate T ave. Pt-BEA35 Scaled over active T catalyst in C. [ C.] X(EA) surface area to 100 cpsi 350 360.5 0.97468104 300 309.5 0.96286223 250 259.5 0.89021857 0.6148467 225 232.5 0.69879339 0.48263519 200 205 0.3460093 0.23897802 175 178.5 0.17144694 0.11841315 150 152.5 0.09633073 0.06653268 125 127 0.0270003 0.01864828 100 102 0 0

TABLE-US-00009 TABLE 8 Cell WC loading Pt Pd X(EA) density WC g/l g/l g/l Total NM 225 C. Catalyst according 100 Pt- 30 0.54 0.54 0.492 to the invention BEA150 Comparison example 1 100 D530 50 0.66 0.13 0.79 0.143 Comparison example 2 100 SCFa 140 100 1.32 0.26 1.58 0.037 (PT1358) Comparison example 3 200 Pt-BEA35 97.10 0.97 0.97 0.482