SCR catalyst device containing vanadium oxide and molecular sieve containing iron

Abstract

The invention relates to a catalyst device for purifying exhaust gases containing nitrogen oxide by using selective catalytic reduction (SCR), the catalyst device comprising at least two catalytic layers, the first layer containing vanadium oxide and a mixed oxide comprising titanium oxide and silicon oxide and the second layer containing a molecular sieve containing iron, wherein the first layer is applied onto the second layer. The invention also relates to uses of the catalyst device and a method for purifying exhaust gases.

Claims

1. A catalyst device for purifying exhaust gases containing nitrogen oxide by selective catalytic reduction (SCR), comprising at least two catalytic layers, the first layer comprises the following components: (a) from 0.5 to 10 wt % vanadium oxide, calculated as V.sub.2O.sub.5, (b) from 0 to 17 wt % tungsten oxide, calculated as WO.sub.3, (c) from 0.2 to 10 wt % cerium oxide, calculated as CeO.sub.2, (d) from 25 to 98 wt % titanium oxide, calculated as TiO.sub.2, (e) from 0.5 to 15 wt % silicon oxide, calculated as SiO.sub.2, (f) from 0 to 15 wt % aluminum oxide, calculated as Al.sub.2O.sub.3, in each case based on the weight of the first layer, and the second layer containing a molecular sieve containing iron, wherein the first layer is applied onto the second layer.

2. The catalyst device according to claim 1, wherein, in addition to components (a), (c), (d) and (e), the first layer contains a quantity of at least one of (b) and (f).

3. The catalyst device according to claim 1, wherein the molecular sieve is a zeolite.

4. The catalyst device according to claim 3, wherein the zeolite is an iron-exchanged zeolite.

5. The catalyst device according to claim 3, wherein the zeolite has a structure, whose maximum ring size has more than 8 tetrahedra.

6. The catalyst device according to claim 3, wherein the zeolite has a structure selected from AEL, AFI, AFO, AFR, ATO, BEA, GME, HEU, MEI, MWW, EUO, FAU, FER, LTL, MAZ, MOR, MEL, MTW, OFF and TON.

7. The catalyst device according to claim 1, wherein the first layer is completely applied onto the second layer.

8. The catalyst device according to claim 1, wherein the first layer is applied onto the second layer in certain regions, wherein a region which has a first, upper layer is first in the flow direction, and wherein there are regions in which the lower, second layer comes into direct contact with the exhaust gases.

9. The catalyst device according to claim 1, wherein the second layer is applied onto an inert substrate.

10. The catalyst device according to claim 1, wherein the first layer contains from 1 to 5 wt % vanadium oxide, calculated as V.sub.2O.sub.5.

11. The catalyst device according to claim 1, wherein the first layer contains from 0.5 to 5 wt % cerium oxide, calculated as CeO.sub.2.

12. The catalyst device according to claim 1, wherein the first layer contains from 1 to 5 wt % vanadium oxide, calculated as V.sub.2O.sub.5 and from 0.2 to 5 wt % cerium oxide, calculated as CeO.sub.2.

13. The catalyst device according to claim 1, wherein the first layer contains from 0.5 to 3 wt % cerium oxide, calculated as CeO.sub.2.

14. The catalyst device according to claim 1, wherein the second layer comprises at least two different iron containing zeolites.

15. The catalyst device according to claim 1 wherein (a) is from 1 to 5 wt % vanadium oxide, calculated as V.sub.2O.sub.5, (b) is from 1 to 15 wt % tungsten oxide, calculated as WO.sub.3, (c) is from 0.2 to 5 wt % cerium oxide, calculated as CeO.sub.2, (d) is from 73 to 98 wt % titanium oxide, calculated as TiO.sub.2, (e) is from 1 to 7 wt % silicon oxide, calculated as SiO.sub.2, (f) is from 0.5 to 15 wt % aluminum oxide, calculated as Al.sub.2O.sub.3, in each case based on the weight of the first layer.

16. A method of selective catalytic reduction (SCR), comprising utilizing a catalyst device according to claim 1 for purifying exhaust gases containing nitrogen oxide by selective catalytic reduction (SCR).

17. The method according to claim 16, wherein formation of N.sub.2O downstream of the catalyst device is limited to 50 ppm or less within the temperature range of 180° C. to 450° C.

18. A method for purifying exhaust gases, comprising the steps of: (i) providing a catalyst device according to claim 1, (ii) introducing exhaust gases containing nitrogen oxides into the catalyst device, (iii) introducing a reductant containing nitrogen into the catalyst device, and (iv) reducing nitrogen oxides in the catalyst device by selective catalytic reduction (SCR).

19. A catalyst device for purifying exhaust gases containing nitrogen oxide by selective catalytic reduction (SCR), comprising at least two catalytic layers, the first layer containing a catalytic oxide mixture and non-catalytic metal oxide support material, and the second layer containing a molecular sieve containing iron, wherein the first layer is applied onto the second layer, wherein the catalytic oxide mixture in the first layer comprises the following components: (a) from 0.5 to 10 wt % vanadium oxide, calculated as V.sub.2O.sub.5, (b) from 0 to 17 wt % tungsten oxide, calculated as WO.sub.3, (c) from 0.2 to 10 wt % cerium oxide, calculated as CeO.sub.2, in each case based on the weight of the first layer, and wherein the non-catalytic metal oxide support material in the first layer comprises the following components: (d) from 25 to 98 wt % titanium oxide, calculated as TiO.sub.2, (e) from 0.5 to 15 wt % silicon oxide, calculated as SiO.sub.2, (f) from 0 to 15 wt % aluminum oxide, calculated as Al.sub.2O.sub.3, in each case based on the weight of the first layer.

20. The catalyst device according to claim 19, wherein the amount of titanium oxide is greater than 50% wt % up to 86.4 wt %, the amount of vanadium oxide is 1 to 5 wt %; the amount of cerium oxide is 0.2 to 5 wt %, the amount of silicon oxide is 1 to 7 wt %, and the amount of tungsten oxide is 1 to 15 wt %.

21. The catalyst device according to claim 20, wherein the catalyst device is operative in use to purify exhaust gases having a NO.sub.2/NO.sub.x ratio range of >0.5 to 0.75 while the exhaust gases temperature ranges fully within a temperature range of 180 to 450° C.

Description

(1) FIGS. 1 to 5 show in graph form the results of the SCR reaction according to Exemplary Embodiment 3 with model exhaust gases with catalyst devices according to the invention and comparative devices, which were produced according to Example 2. In all of the figures, measured values are given for different temperatures of the model exhaust gases. Figures a and b each show the proportion of NOx removed from the model exhaust gas by the catalyst device. Figures c in each case indicate the concentration of N.sub.2O that was measured after the catalyst device.

(2) FIGS. 6 and 7 show the dependence of the conversion on the respective NO and NO.sub.2 content of the exhaust gas.

EXEMPLARY EMBODIMENTS

(3) Preliminary Tests

(4) FIGS. 1 and 2 show the dependence of the conversion of nitrogen monoxide (see FIG. 1) or of nitrogen dioxide (NO.sub.2/NOX=75%) (see FIG. 2) on the cerium content of the SCR catalyst.

(5) In FIGS. 1 and 2:

(6) Reference=SCR catalyst consisting of 3% V.sub.2O.sub.5, 4.3% WO.sub.3 and the remainder TiO.sub.2 with 5% SiO.sub.2

(7) 1% cerium oxide=as reference, but TiO.sub.2/SiO.sub.2 replaced by cerium oxide up to a cerium oxide content of the catalyst of 1%

(8) 5% cerium oxide=as reference, but TiO.sub.2/SiO.sub.2 replaced by cerium oxide up to a cerium oxide content of the catalyst of 5%

(9) 10% cerium oxide=as reference, but TiO.sub.2/SiO.sub.2 replaced by cerium oxide up to a cerium oxide content of the catalyst of 10%

(10) The catalysts were coated in the usual way on commercially available flow-through substrates with a wash coat loading of 160 g/l and the NOx conversion was measured at GHSV=60000 1/h with the following test gas composition: NOx: 1000 ppm

(11) TABLE-US-00001 NO.sub.2/NOx: 0% (FIG. 1) or 75% (FIG. 2) NH.sub.3: 1100 ppm (FIG. 1) or 1350 ppm (FIG. 2) O.sub.2: 10% H.sub.2O:  5% N.sub.2: Remainder

(12) As shown in FIG. 1, the conversion of NO deteriorates as the content of cerium oxide increases, while in FIG. 2, the conversion at NO.sub.2/NOx=75% improves as the content of cerium oxide increases.

Example 1: Preparation of the Coating Suspensions (Wash Coats)

(13) Preparation of Coating Suspension A (Vanadium SCR)

(14) A commercially available titanium dioxide in the anatase form doped with 5 wt % silicon dioxide was dispersed in water. Next, an aqueous solution of ammonium metatungstate and ammonium metavanadate dissolved in oxalic acid were added as a tungsten or vanadium precursor in an amount such that a catalyst of composition 87.4 wt % TiO.sub.2, 4.6 wt % SiO.sub.2, 5.0 wt % WO.sub.3 and 3.0 wt % V.sub.2O.sub.5 was the result. The mixture was stirred thoroughly and finally homogenized in a commercially available agitator ball mill and ground to d90<2 μm.

(15) Preparation of Coating Suspension B (Vanadium SCR with 1% Cerium Oxide)

(16) A commercially available titanium dioxide in the anatase form doped with 5 wt % silicon dioxide was dispersed in water. Next, an aqueous solution of ammonium metatungstate as a tungsten precursor, ammonium metavanadate dissolved in oxalic acid as a vanadium precursor, and an aqueous solution of cerium acetate as a cerium precursor were added in an amount such that a catalyst of a composition that is calculated as 86.4 wt % TiO.sub.2, 4.6 wt % SiO.sub.2, 5.0 wt % WO3, and 3.0 wt % V.sub.2O.sub.5 and 1% CeO.sub.2 was the result. The mixture was stirred thoroughly and finally homogenized in a commercially available agitator ball mill and ground to d90<2 μm.

(17) Preparation of Coating Suspension C (Fe SCR, SAR=25)

(18) A coating suspension was prepared for a commercially available SCR catalyst based on an iron-exchanged beta zeolite. For this purpose, a commercial SiO.sub.2 binder, a commercial boehmite binder (as coating aids), iron(III) nitrate nonahydrate, and commercially available beta zeolite having a molar SiO.sub.2/Al.sub.2O.sub.3 ratio (SAR) of 25 were suspended in water so that a catalyst of composition 90 wt % β-zeolite and an iron content, calculated as Fe.sub.2O.sub.3, of 4.5 wt % was the result.

(19) Preparation of Coating Suspension D (Fe-SCR, SAR=10)

(20) A coating suspension was prepared for a commercially available SCR catalyst based on an iron-exchanged beta zeolite. For this purpose, a commercial SiO.sub.2 binder, a commercial boehmite binder (as coating aids), iron(III) nitrate nonahydrate, and commercially available beta zeolite having a molar SiO.sub.2/Al.sub.2O.sub.3 ratio (SAR) of 10 were suspended in water so that a catalyst of composition 90 wt % β-zeolite and an iron content, calculated as Fe.sub.2O.sub.3, of 4.5 wt % was the result.

Example 2: Preparation of the Catalyst Devices

(21) Various catalyst devices were prepared by coating ceramic substrates with coating suspensions A to D. Conventional ceramic monoliths with parallel flow channels (flow-through substrates) open at both ends were used as substrates. In this case, a first and a second layer (S1, S2) were applied to each substrate, wherein each layer was subdivided into two adjacent zones (Z1, Z2). The exhaust gases to be purified flow in the flow direction into the catalyst device, i.e. via the upper layer 2 and from zone 1 to zone 2. In Scheme 1, the structure of the catalyst devices is shown with four catalytic regions located in two layers and two zones.

(22) Scheme 1: Schematic Structure of the Catalyst Devices Produced According to the Exemplary Embodiments

(23) Flow Direction.fwdarw.

(24) TABLE-US-00002 Substrate Layer 2 Zone 1 Layer 2 Zone 2 (S2Z1) (S2Z2) Layer 1 Zone 1 Layer 1 Zone 2 (S1Z1) (S1Z2)

(25) The compositions and the amounts of coating suspensions A to D used are summarized in Table 1 below. The table also shows which catalytic layers S1 and S2 and zones Z1 and Z2 were applied. The catalysts VK1 and VK3 are comparative catalysts.

(26) First of all, starting from the inlet side, one of dispersions A to D was applied by a conventional dipping method over the length of region Z1S1 of a commercially available flow-through substrate having 62 cells per square centimeter, a cell wall thickness of 0.17 millimeters and a length of 76.2 mm. The partially coated component was first dried at 120° C., Next, starting from the outlet side, one of dispersions A to D was applied over the length of region Z2S1 by the same method. The coated component was then dried at 120° C., for 15 minutes at 350° C., then calcined at 600° C. for a period of 3 hours. When dispersion and wash coat loading were identical in regions Z1S1 and Z2S1, one of dispersions A-D was applied by a conventional dipping method to a commercially available flow-through substrate having 62 cells per square centimeter and a cell wall thickness of 0.17 millimeters over its entire length of 76.2 mm. It was then dried at 120° C., for 15 minutes at 350° C., then calcined at 600° C. for a period of 3 hours.

(27) Starting from the inlet side, the component thus calcined was then coated according to the aforementioned method over the length of region Z1S2 with one of suspensions A-D and dried at 120° C. The above-described step was skipped when no coating was provided for region Z1S2. Starting from the outlet side, the coating was then applied over the length of region Z2S2 using one of suspensions A-D. It was then dried at 120° C. The above-described step was skipped when no coating was provided for region Z2S2. It was then dried for 15 minutes at 350° C., then calcined at 600° C. for a period of 3 hours. When dispersion and wash coat loading were identical in regions Z1S2 and Z2S2, one of dispersions A-D was applied over the entire length of the component of 76.2 mm by the method described above. It was then dried at 120° C., for 15 minutes at 350° C., then calcined at 600° C. for a period of 3 hours.

(28) TABLE-US-00003 TABLE 1 Preparation of the catalyst devices having coating suspensions A to D in the first and second (S1, S2) and in the first and second zone (Z1, Z2). This shows in each case the total quantity in g/l in each of the four regions (S1Z1 to S2Z2) after drying, calcination and heat treatment, and also the length of the zones in % based on the total length of the catalyst device. The catalysts VK1 to VK4 are comparative catalyts. Metal Coating suspension Z1S2 Z2S2 Z1S2 Z2S2 No. Z1S1 Z2S1 Z1S1 Z2S1 VK1 Fe Fe 100 g/l C, L = 50% 100 g/l C, L = 50% V V 280 g/l A, L = 50% 280 g/l A, L = 50% VK3 Fe V 65 g/l D, L = 33% 140 g/l A, L = 67% Fe V 65 g/l D, L = 33% 140 g/l A, L = 67% K1 V V 280 g/l A, L = 50% 280 g/l A, L = 50% Fe Fe 100 g/l C, L = 50% 100 g/l C, L = 50% K2 V—Ce V—Ce 280 g/l B, L = 50% 280 g/l B, L = 50% Fe Fe 50 g/l C, L = 50% 50 g/l C, L = 50% K3 V V 160 g/l A, L = 50% 160 g/l A, L = 50% Fe Fe 100 g/l C, L = 50% 100 g/l C, L = 50% K4 V V 160 g/l A, L = 50% 160 g/l A, L = 50% Fe Fe 50 g/l C, L = 50% 50 g/l C, L = 50% K5 V V 280 g/l A, L = 50% 280 g/l A, L = 50% Fe Fe 50 g/l C, L = 50% 50 g/l C, L = 50% K6 V V 160 g/l A, L = 50% 160 g/l A, L = 50% Fe Fe 100 g/l D, L = 50% 100 g/l D, L = 50%

(29) As an alternative to the described method, it would also be possible to prepare two catalysts (Z1, Z2) corresponding to zones Z1 and Z2 described above and to test the two catalysts one after the other (Z1 before Z2).

(30) Catalyst Z1: First of all, apply one of dispersions A to D over the entire length of the substrate with the length Z1 (Z1S1 region), dry at 120° C., then for 15 minutes at 350° C., then calcine at 600° C. for a period of 3 hours. If so intended, apply one of dispersions A to D over the entire length of the component thus obtained (Z1S2 region), then [dry] for 15 minutes at 350° C., then calcine at 600° C. for a period of 3 hours.

(31) Catalyst Z2; First of all, apply one of dispersions A to D over the entire length of the substrate with the length Z2 (Z2S1 region), dry at 120° 0, then for 15 minutes at 350° C., then calcine at 600° C. for a period of 3 hours. If so intended, next apply one of dispersions A to D over the entire length of the component thus obtained (Z2S2 region), then [dry] for 15 minutes at 350° C., then calcine at 600° C. for a period of 3 hours.

Example 3: Reduction of Nitrogen Oxides by SCR

(32) Measurement Method

(33) The catalyst devices prepared according to Example 2 were tested for their activity and selectivity in the selective catalytic reduction of nitrogen oxides. In doing so, the nitrogen oxide conversion was measured at various defined temperatures (measured on the inlet side of the catalyst) as a measure of the SCR activity and the formation of nitrous oxide. On the inlet side, model exhaust gases containing preset proportions of NO, NH.sub.3, NO.sub.2 and O.sub.2, among other things, were introduced. The nitrogen oxide conversions were measured in a reactor made of quartz glass. Drill cores with L=3″ and D=1″ were tested between 190 and 550° C. under steady-state conditions. The measurements were taken under the test conditions summarized below. GHSV is the gas hourly space velocity (gas flow rate:catalyst volume). The conditions of measurement series TP1 and TP2 are summarized below:

(34) Test Parameter Set TP1:

(35) Gas hourly space velocity GHSV=60000 1/h with the synthesis gas composition: 1000 vppm NO, 1100 vppm NH.sub.3, 0 vppm N.sub.2O

(36) a=xNH.sub.3/xNO.sub.x=1.1

(37) xNO.sub.x=xNO+xNO.sub.2+XN.sub.2O, wherein x in each case means a concentration (vppm) of 10 vol % O.sub.2, 5 vol % H.sub.2O, remainder N.sub.2.

(38) Test Parameter Set TP2

(39) GHSV=60000 1/h with the synthesis gas composition:

(40) 250 vppm NO, 750 vppm NO.sub.2, 1350 vppm NH.sub.3, 0 vppm N.sub.2O

(41) a=xNH.sub.3/xNO.sub.x=1.35

(42) xNO.sub.x=xNO+xNO.sub.2+xN.sub.2O, wherein x in each case means a concentration (vppm) of 10 vol % O.sub.2, 5 vol % H.sub.2O, remainder N.sub.2.

(43) The nitrogen oxide concentrations (nitrogen monoxide, nitrogen dioxide, nitrous oxide) were measured downstream of the catalyst device. The nitrogen oxide conversion over the catalyst device for each temperature measurement point was calculated as follows from the nitrogen oxide contents set in the model exhaust gas, which were verified during conditioning at the beginning of particular test run with a pre-catalyst exhaust gas analysis, and from the measured nitrogen oxide contents after the catalyst device (x is in each case the concentration in vppm):
U.sub.NOx[%]=(1−X.sub.output(NO.sub.x)/X.sub.input(NO.sub.x))*100[%]
with
X.sub.input(NO.sub.x)═X.sub.input(NO)+X.sub.input(NO.sub.2)
X.sub.output(NO.sub.x)═X.sub.output(NO)+X.sub.output(NO.sub.2)+2*X.sub.output(N.sub.2O).
X.sub.output(N.sub.2O) was weighted with the factor 2 in order to take the stoichiometry into account.

(44) In order to determine the manner in which aging of the catalysts affects the result, the catalyst devices were subjected to hydrothermal aging for 100 hours at 580° C. in a gas atmosphere (10% O.sub.2, 10% H.sub.2O, remainder N.sub.2). Next, the conversions of nitrogen oxides were determined according to the method described above.

(45) Results

(46) The results of measurement series TP1, in which the model exhaust gas contained only NO as the nitrogen oxide, are summarized in Table 2. The results of measurement series TP2, wherein the model exhaust gas contained NO and NO.sub.2 in the ratio 1:3 as the nitrogen oxides, are summarized in Table 3. In each case, the tables indicate which catalyst according to Example 2 (Table 1) was used. For each defined temperature value, it is indicated what percentage of the initial concentration of NOx was removed. Table 3 also specifies for each temperature value 2 to 7 what absolute quantity of N.sub.2O was measured at each temperature value after the catalyst. In FIGS. 1 to 5, the results are also shown graphically for the purposes of comparison. Tables 4 and 5 summarize the conditions and results of the tests with catalyst devices after aging.

(47) FIGS. 1a, b show that catalysts K1 and K2 according to the invention, in which a first, upper layer with a vanadium catalyst overlies a second, lower layer with an iron exchanged zeolite, remove nitrogen oxides significantly more efficiently than a comparative catalyst VK1, in which a layer with iron-exchanged zeolite overlies a vanadium oxide layer. The effect is particularly pronounced at temperatures below about 400° C. The effect is obtained even in the case of a model exhaust gas having a high NO.sub.2 content of 66.7% (FIG. 1b). FIG. 1c shows that significantly less N.sub.2O is formed with catalysts K1 and K2 according to the invention than with catalyst VK1. This effect is also particularly pronounced at temperatures below 400° C.

(48) Catalysts K1 and K2 differ in that catalyst K2 contains a cerium oxide in the first, upper layer in addition to the vanadium oxide. The results show that in particular in the temperature range below 350° C., a further improvement is achieved by adding a cerium oxide, wherein both the removal of NOx is further improved and the formation of N.sub.2O is further reduced.

(49) In FIG. 2, further comparisons of the conventional catalyst VK1 and catalysts K1, K3, K4 and K5 according to the invention are shown in graph form, wherein the catalysts according to the invention differ with regard to the amount of the catalysts used in the upper and lower layers. The results show that even with considerable variation in the amounts of catalyst, a significant effect is achieved. Catalyst K1 shows the most pronounced effect in preventing the formation of N.sub.2O (FIG. 2c).

(50) FIG. 3 shows a comparison of the conventional catalyst VK1 and catalysts K3 and K6 according to the invention. FIG. 3 also demonstrates that the catalysts according to the invention remove NOx considerably more efficiently while significantly reducing the formation of N.sub.2O.

(51) FIG. 4 shows results for catalyst devices subjected to an artificial aging process as described above. FIG. 4 shows a comparison of the conventional catalyst VK1 with catalysts K1 and K2 according to the invention. The results show that, even after aging, the catalyst according to the invention depletes NOx significantly more efficiently and reduces the formation of N.sub.2O more than the comparative catalyst. The tests also show that the advantages of having cerium oxide in the vanadium catalyst are particularly pronounced especially after aging. When adding cerium oxide, a more significant improvement of catalyst K2 compared to the comparative catalyst but also compared to catalyst K1 is found both in the depletion of NOx and in the prevention of nitrous oxide.

(52) FIG. 5 shows further results obtained with catalysts after the aging process for catalysts K1, K4 and K5 according to the invention and for comparative catalyst VK1. FIG. 5 also shows a marked improvement of the catalysts according to the invention after aging with regard to the NOx depletion and the prevention of the formation of nitrous oxide.

(53) In the case of comparative catalyst VK3, the two catalysts are not in layers one on top of the other, but the exhaust gases first enter a zone with the iron-containing zeolite on the inlet side and then pass into an outlet-side zone with the vanadium catalyst. The results summarized in Tables 2 and 3 show that such a comparative catalyst not only exhibits comparatively low conversions of NOx with both with exhaust gases rich in NO and with exhaust gases rich in NO.sub.2 but also causes a greater formation of nitrous oxide.

(54) Overall, the experiments show that the SCR catalysts according to the invention, in which a vanadium oxide layer is disposed on a zeolite layer containing iron, deliver significant improvements in the removal of NOx and the prevention of the formation of nitrous oxide. The catalyst devices according to the invention are suitable not only for the reaction with exhaust gases rich in NO but also for the treatment of exhaust gases rich in NO.sub.2. The advantages with exhaust gases rich in NO.sub.2 are particularly pronounced in the temperature range below 450° C. or below 350° C. The catalyst devices according to the invention thus combine several advantageous properties, namely a high efficiency with exhaust gases rich in NO.sub.2 in the temperature range from about 180° C. to 500° C., and in particular at low temperatures; a high efficiency with exhaust gases rich in NO; and the prevention of the formation of nitrous oxide. The effects are evident both with freshly prepared catalysts and after an aging process. The effect can even be improved, if a cerium oxide is added to the vanadium catalyst, which is in particular advantageous in the case of aged catalysts.

(55) TABLE-US-00004 TABLE 2 Conditions and results of the reduction of NO with different catalyst devices (test TP1) at different actually measured temperatures 1 to 8. The depletion of NOx at the catalyst device outlet is shown in % based on the initial amount used. Test Temperature [° C.] NOx [%] TP 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 VK1 1 541 492 444 395 345 296 247 197 93% 97% 96%  95%  91% 81% 56% 20% VK3 1 535 489 442 394 344 295 246 197 88% 95% 98%  98%  97% 93% 73% 31% K1 1 543 496 449 400 350 300 251 201 67% 93% 99% 100% 100% 98% 86% 44% K2 1 537 490 443 395 346 296 247 198 78% 94% 98%  99%  98% 94% 76% 34% K3 1 542 496 448 400 350 300 251 201 76% 96% 99% 100% 100% 97% 76% 31% K4 1 543 496 448 400 350 300 250 201 72% 95% 99% 100% 100% 96% 72% 27% K5 1 543 496 448 400 350 300 251 201 65% 92% 99% 100% 100% 98% 86% 42% K6 1 543 496 448 400 350 300 250 201 78% 97% 100%  100% 100% 97% 80% 40%

(56) TABLE-US-00005 TABLE 3 Test conditions and results of the reduction of NO.sub.2:NO in the ratio 3:1 (test TP2) at different actually measured temperatures. For measurements 2 to 7, the depletion of NOx at the catalyst device outlet is shown in % based on the initial amount used and the measured values for N.sub.2O at the catalyst device outlet are shown in ppm. Test Temperature [° C.] NOx [%] Amount of N.sub.2O [ppm] No. TP 2 3 4 5 6 7 2 3 4 5 6 7 2 3 4 5 6 7 VK1 2 492 445 397 347 298 249 98% 92% 81% 73% 66% 58% 10 40 92 127 148 133 VK3 2 489 441 392 343 293 244 97% 95% 89% 80% 65% 62% 12 27 56 83 98 56 K1 2 496 447 399 349 300 250 97% 99% 98% 86% 69% 60% 10 5 9 39 83 92 K2 2 490 442 394 344 295 246 96% 97% 95% 90% 78% 82% 14 17 26 38 69 76 K3 2 496 447 399 349 300 250 99% 99% 96% 84% 71% 62% 6 5 19 66 110 113 K4 2 496 448 399 349 300 250 98% 98% 95% 82% 67% 60% 9 8 24 73 110 83 K5 2 496 447 399 349 300 250 97% 99% 97% 83% 65% 58% 14 7 13 50 96 78 K6 2 496 447 399 349 300 250 99% 99% 97% 86% 70% 59% 5 5 15 58 110 123

(57) TABLE-US-00006 TABLE 4 Conditions and results of the reduction of NO with different catalyst devices after aging (test TP1) at different actually measured temperatures 1 to 8. The depletion of NOx at the catalyst device outlet is shown in % based on the initial amount used. Test Temperature [° C.] NOx [%] No. TP 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 VK1 1 539 493 445 397 348 298 249 200 79% 88% 91%  91% 87% 77% 53% 20% K1 1 542 496 448 400 350 300 251 201 74% 95% 99% 100% 100%  97% 77% 31% K2 1 543 495 447 398 348 299 249 199 70% 93% 97%  98% 97% 93% 71% 28% K4 1 542 496 448 400 350 300 250 201 77% 95% 99% 100% 99% 90% 54% 17% K5 1 542 496 448 400 350 300 250 201 68% 93% 99% 100% 100%  97% 77% 31%

(58) TABLE-US-00007 TABLE 5 Test conditions and results of the reduction of NO.sub.2:NO in the ratio 3:1 (test TP2) with different catalyst devices after aging at different actually measured temperatures. For measurements 2 to 7, the depletion of NOx at the catalyst device outlet is shown in % based on the initial amount used and the measured values for N2O at the catalyst device outlet are shown in ppm. Test Temperature [° C.] NOx [%] Amount of N.sub.2O [ppm] No. TP 2 3 4 5 6 7 2 3 4 5 6 7 2 3 4 5 6 7 VK1 2 494 446 398 348 298 249 90% 87% 82% 74% 60% 57% 45 62 81 106 141 122 K1 2 495 447 398 349 299 250 97% 99% 97% 80% 62% 56% 12 7 14 56 102 108 K2 2 495 447 398 348 298 249 92% 95% 95% 92% 77% 60% 28 20 19 28 60 74 K4 2 495 447 399 349 300 250 93% 94% 94% 76% 59% 56% 35 30 30 68 100 89 K5 2 495 447 398 349 300 250 92% 96% 97% 81% 61% 56% 34 20 16 42 83 76