SCR Catalyst

Abstract

The present invention relates to a catalyst comprising at least one oxide of vanadium, at least one oxide of tungsten, at least one oxide of cerium, at least one oxide of titanium and at least one oxide of niobium, and an exhaust system containing said oxides.

Claims

1-10. (canceled)

11. A method of making a catalyst comprising at least one oxide of vanadium in an amount of 2 to 6 wt.-%, at least one oxide of cerium in an amount of 2 to 4 wt.-%, at least one oxide of niobium in an amount of 1 to 7 wt.-%, up to 2 wt.-% of at least one oxide of tungsten, and at least one oxide of titanium as a carrier material in an amount measured so as to result in a total of 100 wt.-%, in each case based on the total weight of the catalyst and calculated as V.sub.2O.sub.5, CeO.sub.2, Nb.sub.2O.sub.5, TiO.sub.2, or, if at least one oxide of tungsten is present, WO.sub.3, said method comprising: obtaining oxides of vanadium, cerium, niobium, titanium, and, if present, tungsten, said method comprising: forming a mixture of the oxides, and calcining the mixture.

12. The method of claim 11, wherein the mixture contains at least one oxide of silicon.

13. The method of claim 12, wherein the at least one oxide of silicon is present in amounts of 2 to 7 wt.-%, relative to the weight of the catalyst and calculated as SiO.sub.2.

14. The method of claim 11, wherein the mixture contains at least one oxide of tungsten in an amount of 0.001 to 2 wt.-%, relative to the weight of the catalyst and calculated as WO.sub.3.

15. The method of claim 11, wherein the mixture further comprises at least one oxide of molybdenum, antimony, zirconium, tantalum, and/or hafnium.

16. The method of claim 11, wherein the mixture further comprises at least one oxide of molybdenum, antimony, zirconium, tantalum, and/or hafnium in a total amount of said oxides of 0.5 to 20 wt.-%, relative to the total weight of the catalyst and calculated as MoO.sub.3, Sb.sub.2O.sub.5, ZrO.sub.2, Ta.sub.2O.sub.5, of HfO.sub.2.

17. The method of claim 11, wherein the oxides are provided in powder form.

18. The method of claim 11, wherein the mixture is a slurry of the oxides in water, and the method further comprises drying the slurry before calcining.

19. The method of claim 11, wherein a portion of the oxides are provided in the mixture in the form of an aqueous solution.

20. The method of claim 11, wherein the mixture comprises oxides of tungsten, cerium, niobium, and titanium that have been impregnated with a vanadium oxide.

21. The method of claim 11, wherein the mixture comprises oxides of vanadium, cerium, niobium, and titanium that have been impregnated with a tungsten oxide.

22. The method of claim 11, wherein at least two oxides in the mixtures are provided as one oxide doped with the other oxide.

23. The method of claim 11, wherein the two or more oxides are provided in the mixture as mixed oxide.

24. The method of claim 11, which comprises forming the mixture by dispersing titanium dioxide doped with 5 wt.-% silicon dioxide in water, and adding vanadium dioxide, tungsten trioxide, cerium dioxide, and niobium dioxide thereto.

25. The method of claim 24, wherein the added amounts of vanadium dioxide, tungsten trioxide, cerium dioxide, and niobium pentoxide result in a catalyst composition comprising 85.98 wt.-% TiO.sub.2, 4.53 wt.-% SiO.sub.2, 3.75 wt.-% V.sub.2O.sub.5, 1.00 wt.-% WO.sub.3, 2.00 wt.-% CeO.sub.2, and 2.75 wt.-% Nb.sub.2O.sub.5.

26. The method of claim 24, wherein the added amounts of vanadium dioxide, tungsten trioxide, cerium dioxide, and niobium pentoxide result in a catalyst composition comprising 86.93.-wt % TiO.sub.2, 4.58 wt,-% SiO.sub.2, 3.75 wt.-% V.sub.2O.sub.5, 2.00 wt.-% CeO.sub.2, and 2.75 wt.-% Nb.sub.2O.sub.5.

Description

[0072] The invention is explained below in more detail by means of figures and examples. The following are shown:

[0073] FIG. 1: Nitrogen oxide conversions in the standard SCR reaction, measured at catalysts K1 and K2 according to the present invention in comparison to the comparative catalysts VK1, VK2, VK3, and VK4 in the fresh state (K1f, K2f, VK1f, VK2f, VK3f, VK4f).

[0074] FIG. 2: Nitrogen oxide conversions in the standard SCR reaction, measured at catalysts K1 and K2 according to the present invention in comparison to the comparative catalysts VK1, VK2, VK3, and VK4 in the aged state (K1a, K2a, VK1a, VK2a, VK3a, VK4a).

[0075] FIG. 3: Nitrogen oxide conversions in the fast SCR reaction, measured at catalysts K1 and K2 according to the present invention in comparison to the comparative catalysts VK1, VK2, VK3, and VK4 in the fresh state (K1f, K2f, VK1f, VK2f, VK3f, and VK4f).

[0076] FIG. 4: Nitrogen oxide conversions in the fast SCR reaction, measured at catalyst K1 and K2 according to the present invention in comparison to the comparative catalysts VK1, VK2, VK3, and VK4 in the aged state (K1a, K2a, VK1a, VK2a, VK3a, VK4a).

[0077] FIG. 5: Nitrogen oxide conversions in the standard SCR reaction at 200° C. and fast SCR reaction at 300° C. versus the WO.sub.3 content, measured at catalysts K1 and K2 according to the present invention in comparison to the comparative catalysts VK5 and VK6 in the fresh and aged states.

[0078] FIG. 6: Nitrogen oxide conversions in the standard SCR reaction at 200° C. and fast SCR reaction at 300° C. versus the CeO.sub.2 content, measured at catalyst K1 according to the present invention in comparison to the comparative catalysts VK3 and VK7 in the frsh and aged states.

[0079] FIG. 7: Nitrogen oxide conversions in the standard SCR reaction at 200° C. and fast SCR reaction at 300° C. versus the Nb.sub.2O.sub.5 content, measured at catalyst K1 according to the present invention in comparison to the comparative catalysts VK2, VK8, and VK9 in the fresh and aged states.

EXAMPLE 1

[0080] a) A commercially available titanium dioxide in the anatase form doped with 5 wt % silicon dioxide was dispersed in water, and then vanadium dioxide (VO.sub.2), tungsten trioxide (WO.sub.3), cerium dioxide (CeO.sub.2), and ammonium niobium oxalate were added in amounts so as to result in a catalyst of the composition 85.98 wt % TiO.sub.2, 4.53 wt % SiO.sub.2, 3.75 wt % V.sub.2O.sub.5, 1.00 wt % WO.sub.3, 2.00 wt % CeO.sub.2, and 2.75 wt % Nb.sub.2O.sub.5. The mixture was vigorously stirred and then milled in a commercially available agitator bead mill. [0081] b) The dispersion obtained according to a) was coated in a conventional manner onto a commercially available ceramic flow substrate with a volume of 0.5 L and a cell number of 62 cells per square centimeter at a wall thickness of 0.17 mm over its entire length, with a washcoat loading of 360 g/L. The powder thus obtained was dried at 90° C. and then calcined at 600° C. for 2 hours. The catalyst K1 thus obtained is present in the fresh state and is therefore referred to hereinafter as K1f. [0082] c) The catalyst K1 obtained according to b) was subjected to hydrothermal aging for 48 hours in a gas atmosphere (10% O.sub.2, 10% H.sub.2O, remainder N.sub.2) at 700° C. Catalyst K1 is then present in the aged state and is referred to hereinafter as K1a.

EXAMPLE 2

[0083] a) A commercially available titanium dioxide in the anatase form stabilized with 5 wt % silicon dioxide was dispersed in water, and then vanadium dioxide (VO.sub.2), cerium dioxide (CeO.sub.2), and ammonium niobium oxalate were added in amounts so as to result in a catalyst of the composition 86.93 wt % TiO.sub.2, 4.58 wt % SiO.sub.2, 3.75 wt % V.sub.2O.sub.5, 2.00 wt % CeO.sub.2, and 2.75 wt % Nb.sub.2O.sub.5. The mixture was vigorously stirred and then milled in a commercially available agitator bead mill. [0084] b) The dispersion obtained according to a) was coated in a customary manner onto a commercially available ceramic flow substrate with a volume of 0.5 L and a cell number of 62 cells per square centimeter at a wall thickness of 0.17 mm over its entire length, with a washcoat loading of 360 g/L. It was then dried at 90° C. and calcined at 600° C. for 2 hours. Catalyst K2 thus obtained is present in the fresh state and is therefore referred to hereinafter as K2f. [0085] c) Catalyst K2 obtained according to b) was subjected to hydrothermal aging in a gas atmosphere (10% O.sub.2, 10% H.sub.2O, remainder N.sub.2) at 700° C. for 48 hours. Catalyst K2 is then present in the aged state and is referred to hereinafter as K2a.

Comparative Example 1

[0086] a) A commercially available titanium dioxide in the anatase form stabilized with 5 wt % silicon dioxide was dispersed in water, and then vanadium dioxide (VO.sub.2) and tungsten trioxide (WO.sub.3) were added in amounts so as to result in a catalyst of the composition 90.49 wt % TiO.sub.2, 4.76 wt % SiO.sub.2, 3.75 wt % V.sub.2O.sub.5, 1.00 wt % WO.sub.3. The mixture was vigorously stirred and then milled in a commercially available agitator bead mill. [0087] b) The dispersion obtained according to a) was coated in a customary manner onto a commercially available ceramic flow substrate with a volume of 0.5 L and a cell number of 62 cells per square centimeter at a wall thickness of 0.17 mm over its entire length, with a washcoat loading of 360 g/L. It was then dried at 90° C. and calcined at 600° C. for 2 hours. Catalyst VK1 thus obtained is present in the fresh state and is therefore referred to hereinafter as VK1f. [0088] c) Catalyst VK1 obtained according to b) was subjected to hydrothermal aging in a gas atmosphere (10% O.sub.2, 10% H.sub.2O, remainder N.sub.2) at 700° C. for 48 hours. Catalyst VK1 is then present in the aged state and is referred to hereinafter as VK1a.

Comparative Example 2

[0089] a) A commercially available titanium dioxide in the anatase form stabilized with 5 wt % silicon dioxide was dispersed in water, and then vanadium dioxide (VO.sub.2), tungsten trioxide (WO.sub.3), and cerium dioxide (CeO.sub.2) were added in amounts so as to result in a catalyst of the composition 88.59 wt % TiO.sub.2, 4.66 wt % SiO.sub.2, 3.75 wt % V.sub.2O.sub.5, 1.00 wt % WO.sub.3, and 2.00 wt % CeO.sub.2. The mixture was vigorously stirred and then milled in a commercially available agitator bead mill. [0090] b) The dispersion obtained according to a) was coated in a customary manner onto a commercially available ceramic flow substrate with a volume of 0.5 L and a cell number of 62 cells per square centimeter at a wall thickness of 0.17 mm over its entire length, with a washcoat loading of 360 g/L. It was then dried at 90° C. and calcined at 600° C. for 2 hours. Catalyst VK2 thus obtained is present in the fresh state and is therefore referred to hereinafter as VK2f. [0091] c) Catalyst VK2 obtained according to b) was subjected to hydrothermal aging in a gas atmosphere (10% O.sub.2, 10% H.sub.2O, remainder N.sub.2) at 700° C. for 48 hours. Catalyst VK2 is then present in the aged state and is referred to hereinafter as VK2a.

Comparative Example 3

[0092] a) A commercially available titanium dioxide in the anatase form stabilized with 5 wt % silicon dioxide was dispersed in water, and then vanadium dioxide (VO.sub.2), tungsten trioxide (WO.sub.3), and ammonium niobium oxalate were added in amounts such as to result in a catalyst of the composition 87.88 wt % TiO.sub.2, 4.63 wt % SiO.sub.2, 3.75 wt % V.sub.2O.sub.5, 1.00 wt % WO.sub.3, and 2.75 wt % Nb.sub.2O.sub.5. The mixture was vigorously stirred and then milled in a commercially available agitator bead mill. [0093] b) The dispersion obtained according to a) was coated in a customary manner onto a commercially available ceramic flow substrate with a volume of 0.5 L and a cell number of 62 cells per square centimeter at a wall thickness of 0.17 mm over its entire length, with a washcoat loading of 360 g/L. It was then dried at 90° C. and calcined at 600° C. for 2 hours. Catalyst VK3 thus obtained is present in the fresh state and is therefore referred to hereinafter as VK3f. [0094] c) Catalyst VK3 obtained according to b) was subjected to hydrothermal aging in a gas atmosphere (10% O.sub.2, 10% H.sub.2O, remainder N.sub.2) at 700° C. for 48 hours. Catalyst VK3 is then present in the aged state and is referred to hereinafter as VK3a.

Comparative Example 4

[0095] a) A commercially available titanium dioxide in the anatase form was dispersed in water, and then vanadium dioxide (VO.sub.2), tungsten trioxide (WO.sub.3), cerium dioxide (CeO.sub.2), and ammonium niobium oxalate were added in amounts so as to result in a catalyst of the composition 90.50 wt % TiO.sub.2, 3.75 wt % V.sub.2O.sub.5, 1.00 wt % WO.sub.3, 2.00 wt % CeO.sub.2, and 2.75 wt % Nb.sub.2O.sub.5. The mixture was vigorously stirred and then milled in a commercially available agitator bead mill. [0096] b) The dispersion obtained according to a) was coated in a customary manner onto a commercially available ceramic flow substrate with a volume of 0.5 L and a cell number of 62 cells per square centimeter at a wall thickness of 0.17 mm over its entire length, with a washcoat loading of 360 g/L. It was then dried at 90° C. and calcined at 600° C. for 2 hours. Catalyst VK4 thus obtained is present in the fresh state and is therefore referred to hereinafter as VK4f. [0097] c) Catalyst VK4 obtained according to b) was subjected to hydrothermal aging in a gas atmosphere (10% O.sub.2, 10% H.sub.2O, remainder N.sub.2) at 700° C. for 48 hours. Catalyst VK4 is then present in the aged state and is referred to hereinafter as VK4a.

Comparative Example 5

[0098] a) A commercially available titanium dioxide in the anatase form stabilized with 5 wt % silicon dioxide was dispersed in water, and then vanadium dioxide (VO.sub.2), tungsten trioxide (WO.sub.3), cerium dioxide (CeO.sub.2), and ammonium niobium oxalate were added in amounts so as to result in a catalyst of the composition 86.45 wt % TiO.sub.2, 4.55 wt % SiO.sub.2, 3.75 wt % V.sub.2O.sub.5, 0.50 wt % WO.sub.3, 2.00 wt % CeO.sub.2, and 2.75 wt % Nb.sub.2O.sub.5. The mixture was vigorously stirred and then milled in a commercially available agitator bead mill. [0099] b) The dispersion obtained according to a) was coated in a customary manner onto a commercially available ceramic flow substrate with a volume of 0.5 L and a cell number of 62 cells per square centimeter at a wall thickness of 0.17 mm over its entire length, with a washcoat loading of 360 g/L. It was then dried at 90° C. and calcined at 600° C. for 2 hours. Catalyst VK5 thus obtained is present in the fresh state and is therefore referred to hereinafter as VK5f. [0100] c) Catalyst VK5 obtained according to b) was subjected to hydrothermal aging in a gas atmosphere (10% O.sub.2, 10% H.sub.2O, remainder N.sub.2) at 700° C. for 48 hours. Catalyst VK5 is then present in the aged state and is referred to hereinafter as VK5a.

Comparative Example 6

[0101] a) A commercially available titanium dioxide in the anatase form stabilized with 5 wt % silicon dioxide was dispersed in water, and then vanadium dioxide (VO.sub.2), tungsten trioxide (WO.sub.3), cerium dioxide (CeO.sub.2), and ammonium niobium oxalate were added in amounts so as to result in a catalyst of the composition 85.03 wt % TiO.sub.2, 4.48 wt % SiO.sub.2, 3.75 wt % V.sub.2O.sub.5, 2.00 wt % WO.sub.3, 2.00 wt % CeO.sub.2, and 2.75 wt % Nb.sub.2O.sub.5. The mixture was vigorously stirred and then milled in a commercially available agitator bead mill. [0102] b) The dispersion obtained according to a) was coated in a customary manner onto a commercially available ceramic flow substrate with a volume of 0.5 L and a cell number of 62 cells per square centimeter at a wall thickness of 0.17 mm over its entire length, with a washcoat loading of 360 g/L. It was then dried at 90° C. and calcined at 600° C. for 2 hours. Catalyst VK6 thus obtained is present in the fresh state and is therefore referred to hereinafter as VK6f. [0103] c) Catalyst VK6 obtained according to b) was subjected to hydrothermal aging in a gas atmosphere (10% O.sub.2, 10% H.sub.2O, remainder N.sub.2) at 700° C. for 48 hours. Catalyst VK6 is then present in the aged state and is referred to hereinafter as VK6a.

Comparative Example 7

[0104] a) A commercially available titanium dioxide in the anatase form stabilized with 5 wt % silicon dioxide was dispersed in water, and then vanadium dioxide (VO.sub.2), tungsten trioxide (WO.sub.3), cerium dioxide (CeO.sub.2), and ammonium niobium oxalate were added in amounts so as to result in a catalyst of the composition 84.08 wt % TiO.sub.2, 4.43 wt % SiO.sub.2, 3.75 wt % V.sub.2O.sub.5, 1.00 wt % WO.sub.3, 4.00 wt % CeO.sub.2, and 2.75 wt % Nb.sub.2O.sub.5. The mixture was vigorously stirred and then milled in a commercially available agitator bead mill. [0105] b) The dispersion obtained according to a) was coated in a customary manner onto a commercially available ceramic flow substrate with a volume of 0.5 L and a cell number of 62 cells per square centimeter at a wall thickness of 0.17 mm over its entire length, with a washcoat loading of 360 g/L. It was then dried at 90° C. and calcined at 600° C. for 2 hours. Catalyst VK7 thus obtained is present in the fresh state and is therefore referred to hereinafter as VK7f. [0106] c) Catalyst VK7 obtained according to b) was subjected to hydrothermal aging in a gas atmosphere (10% O.sub.2, 10% H.sub.2O, remainder N.sub.2) at 700° C. for 48 hours. Catalyst VK7 is then present in the aged state and is referred to hereinafter as VK7a.

Comparative Example 8

[0107] a) A commercially available titanium dioxide in the anatase form stabilized with 5 wt % silicon dioxide was dispersed in water, and then vanadium dioxide (VO.sub.2), tungsten trioxide (WO.sub.3), cerium dioxide (CeO.sub.2), and ammonium niobium oxalate were added in amounts so as to result in a catalyst of the composition 84.79 wt % TiO.sub.2, 4.46 wt % SiO.sub.2, 3.75 wt % V.sub.2O.sub.5, 1.00 wt % WO.sub.3, 2.00 wt % CeO.sub.2, and 4.00 wt % Nb.sub.2O.sub.5. The mixture was vigorously stirred and then milled in a commercially available agitator bead mill. [0108] b) The dispersion obtained according to a) was coated in a customary manner onto a commercially available ceramic flow substrate with a volume of 0.5 L and a cell number of 62 cells per square centimeter at a wall thickness of 0.17 mm over its entire length, with a washcoat loading of 360 g/L. It was then dried at 90° C. and calcined at 600° C. for 2 hours. Catalyst VK8 thus obtained is present in the fresh state and is therefore referred to hereinafter as VK8f. [0109] c) Catalyst VK8 obtained according to b) was subjected to hydrothermal aging in a gas atmosphere (10% O.sub.2, 10% H.sub.2O, remainder N.sub.2) at 700° C. for 48 hours. Catalyst VK8 is then present in the aged state and is referred to hereinafter as VK8a.

Comparative Example 9

[0110] a) A commercially available titanium dioxide in the anatase form stabilized with 5 wt % silicon dioxide was dispersed in water, and then vanadium dioxide (VO.sub.2), tungsten trioxide (WO.sub.3), cerium dioxide (CeO.sub.2), and ammonium niobium oxalate were added in amounts so as to result in a catalyst of the composition 81.94 wt % TiO.sub.2, 4.31 wt % SiO.sub.2, 3.75 wt % V.sub.2O.sub.5, 1.00 wt % WO.sub.3, 2.00 wt % CeO.sub.2, and 7.00 wt % Nb.sub.2O.sub.5. The mixture was vigorously stirred and then milled in a commercially available agitator bead mill. [0111] b) The dispersion obtained according to a) was coated in a customary manner onto a commercially available ceramic flow substrate with a volume of 0.5 L and a cell number of 62 cells per square centimeter at a wall thickness of 0.17 mm over its entire length, with a washcoat loading of 360 g/L. It was then dried at 90° C. and calcined at 600° C. for 2 hours. Catalyst VK9 thus obtained is present in the fresh state and is therefore referred to hereinafter as VK9f. [0112] c) Catalyst VK9 obtained according to b) was subjected to hydrothermal aging in a gas atmosphere (10% O.sub.2, 10% H.sub.2O, remainder N.sub.2) at 700° C. for 48 hours. Catalyst VK9 is then present in the aged state and is referred to hereinafter as VK9a. [0113] Table 1 summarizes the compositions of the catalysts of the examples mentioned. The composition of the catalyst according to the invention is not limited to explicitly shown examples.

TABLE-US-00001 TABLE 1 Compositions of the Catalysts of the Examples Composition V.sub.2O.sub.5 WO.sub.3 CeO.sub.2 Nb.sub.2O.sub.5 SiO.sub.2 TiO.sub.2 Example (wt %) (wt %) (wt %) (wt %) (wt %) (wt %)  K1 3.75 1.00 2.00 2.75 4.53 85.98  K2 3.75 2.00 2.75 4.58 86.93 VK1 3.75 1.00 4.76 90.49 VK2 3.75 1.00 2.00 4.66 88.59 VK3 3.75 1.00 2.75 4.63 87.88 VK4 3.75 1.00 2.00 2.75 90.50 VK5 3.75 0.50 2.00 2.75 4.55 86.45 VK6 3.75 2.00 2.00 2.75 4.48 85.03 VK7 3.75 1.00 4.00 2.75 4.43 84.07 VK8 3.75 1.00 2.00 4.00 4.46 84.79 VK9 3.75 1.00 2.00 7.00 4.31 81.94

Nitrogen Oxide Conversion Assay as a Measure of Scr Activity

[0114] The NO conversions of the catalysts and comparative catalysts prepared according to the examples and comparative examples described above were determined in a quartz glass reactor. Drill cores with L=3″ and D=1″ were tested between 200 and 400° C. under steady-state conditions. Testing was carried out in a laboratory model gas system under the following conditions.

TABLE-US-00002 Composition of the model gas Standard SCR Fast SCR reaction reaction NO.sub.x [vol. ppm]: 1,000 1,000 NO.sub.2/NO.sub.x [%] 0 75 NH.sub.3 [vol. ppm]: 1,100 1,350 O.sub.2 [vol %]: 10 10 H.sub.2O [vol %] 5 5 N.sub.2: Remainder Remainder General test conditions Space velocity [h.sup.−1]: 60.000 Temperature [° C.]: 200; 250; 300; 350; 400 Conditioning before start of Model gas atmosphere; 550° C.; measurement: several minutes

[0115] During measurement, the nitrogen oxide concentrations of the model gas after flowing through the catalyst were recorded using a suitable analysis method. From the known, dosed nitrogen oxide contents that were verified during conditioning at the beginning of the respective test flow with a pre-catalyst exhaust gas analysis, and the nitrogen oxide conversion contents measured after flowing through the catalyst, the nitrogen oxide conversion, relative to the ratio of NH.sub.3 to NO, over the catalyst was calculated for each temperature measuring point as follows:

[00001]$U_{{\mathrm{NO}}_x}\left[\%\right]=\left(1-\frac{C_{\mathrm{output}}\left({\mathrm{NO}}_x\right)}{C_{\mathrm{input}}\left({\mathrm{NO}}_x\right)}\right)\times 100$

with

C.sub.input/output(NO.sub.x)=C.sub.input/output(NO)+C.sub.input/output(N.sub.2O)+C.sub.input/output(N.sub.2O)

[0116] The resulting nitrogen oxide conversion values U.sub.NOx [%] were plotted as a function of the temperature measured before to the catalyst, in order to evaluate the SCR activity of the investigated materials.

[0117] Table 2 shows the NOx conversion in the standard SCR reaction for the examples described above.

TABLE-US-00003 TABLE 2 NOx Conversion in the Standard SCR Reaction Nitrogen oxide conversion (%) in standard SCR reaction after hydrothermal fresh aging at 700° C. for 48 h 400° C. 350° C. 300° C. 250° C. 200° C. 400° C. 350° C. 300° C. 250° C. 200° C.  K1 98.54 98.78 97.82 91.93 63.64 22.57 29.70 25.94 14.31  5.09  K2 98.78 99.07 98.59 94.36 64.88 78.75 83.91 76.95 51.79 20.65 VK1 97.88 97.98 96.05 84.57 43.45 −3.39  3.43  3.20  2.00  0.91 VK2 98.34 98.28 96.47 85.23 42.56  6.33  7.43  7.15  4.89  2.03 VK3 98.90 99.25 98.55 93.35 62.44  9.62 18.23 15.89  9.17  3.14 VK4 98.95 99.39 98.97 95.29 70.15  5.07  6.35  6.30  4.19  1.60 VK5 99.06 99.37 98.87 94.82 66.63 26.39 34.77 30.01 16.70  6.03 VK6 99.46 99.69 99.40 96.20 68.88 12.37 18.49 16.43  9.47  3.22 VK7 98.81 99.21 98.54 93.89 67.28 93.78 95.09 97.77 72.47 31.61 VK8 98.99 99.35 98.76 93.80 65.65 24.57 30.70 27.26 15.09  5.39 VK9 98.94 99.40 98.95 94.38 67.22 36.05 41.96 37.18 20.49  7.30

[0118] The results of the standard SCR reaction of the fresh catalysts are shown in FIG. 1.

[0119] The results of the standard SCR reaction of the aged catalysts are shown in FIG. 2.

[0120] Table 3 shows the NOx conversion in the fast SCR reaction for the examples described above.

TABLE-US-00004 TABLE 3 NOx Conversion in the Fast SCR Reaction Nitrogen oxide conversion (%) in fast SCR reaction after hydrothermal fresh aging at 700° C. for 48 h 400° C. 350° C. 300° C. 250° C. 200° C. 400° C. 350° C. 300° C. 250° C. 200° C.  K1 98.61 90.75 70.50 61.59 60.92 62.69 54.34 49.10 43.04 31.35  K2 98.32 89.15 68.88 61.01 59.82 93.29 74.46 57.47 52.83 50.97 VK1 97.55 79.12 60.80 57.07 50.40 15.90 21.91 21.69 18.71 11.21 VK2 98.38 91.22 69.91 59.35 52.61 34.02 37.31 38.09 32.95 18.65 VK3 99.07 85.50 64.57 61.54 62.93 51.59 48.35 45.83 38.11 24.33 VK4 99.60 96.66 76.89 62.23 62.86 30.62 35.51 37.83 33.77 22.23 VK5 99.30 92.60 71.73 62.86 63.11 69.13 57.50 51.84 47.09 35.50 VK6 99.76 95.59 72.97 62.51 64.86 51.03 49.07 46.70 39.70 25.94 VK7 98.26 92.87 74.15 62.79 62.71 97.25 88.89 69.05 57.82 56.82 VK8 98.72 93.08 72.22 61.93 63.67 63.89 55.38 51.21 45.98 33.41 VK9 98.95 96.32 79.12 63.80 64.53 70.04 57.62 52.22 48.88 38.15

[0121] The results of the fast SCR reaction of the fresh catalysts are shown in FIG. 3.

[0122] The results of the fast SCR reaction of the aged catalysts are shown in FIG. 4.

[0123] The influence of the WO.sub.3 content of the catalyst on the NOx conversion in the standard SCR reaction at 200° C. and in the fast SCR reaction at 300° C. in the fresh and aged states is shown in Table 4. The amounts of V.sub.2O.sub.5, CeO.sub.2, and Nb.sub.2O.sub.5 were kept constant at 3.75 wt %, 2.00 wt %, and 2.75 wt %, respectively, while the WO.sub.3 content was varied from 0.00 wt % (K2) to 0.50 wt % (VK5), 1.00 wt % (K1), and 2.00 wt % (VK6).

TABLE-US-00005 TABLE 4 Influence of WO.sub.3 Content on the NOx Conversion Influence of WO.sub.3 content on NOx conversion In the standard SCR In the fast SCR WO.sub.3 content reaction at 200° C. reaction at 300° C. [wt %] fresh aged fresh aged 0 64.9 20.7 68.9 57.5 0.5 63.6 5.1 70.5 49.1 1 66.6 6.0 71.73 51.8 2 68.9 3.2 73.0 46.7

[0124] The results of the influence of the WO.sub.3 content are shown in FIG. 5.

[0125] The influence of the CeO.sub.2 content of the catalyst on the NOx conversion in the standard SCR reaction at 200° C. and in the fast SCR reaction at 300° C. in the fresh and aged states is shown in Table 5. The amounts of V.sub.2O.sub.5, WO.sub.3, and Nb.sub.2O.sub.5 were held constant at 3.75 wt %, 1.00 wt %, and 2.75 wt %, respectively, while the CeO.sub.2 content was varied from 0.00 wt % (VK3) to 2.00 wt % (K1) and 2.00 wt % (VK7).

TABLE-US-00006 TABLE 5 Influence of CeO.sub.2 Content on NOx Conversion Influence of CeO.sub.2 content on NOx conversion In the standard SCR In the fast SCR CeO.sub.2 content reaction at 200° C. reaction at 300° C. [wt %] fresh aged fresh aged 0 43.4 0.9 60.8 21.7 2 63.6 5.1 70.5 49.1 4 67.3 31.6 74.2 69.1

[0126] The results of the influence of the CeO.sub.2 content are shown in FIG. 6.

[0127] The influence of the Nb.sub.2O.sub.5 content of the catalyst on the NOx conversion in the standard SCR reaction at 200° C. and in the fast SCR reaction at 300° C. in the fresh and aged states is shown in Table 6. The amounts of V.sub.2O.sub.5, WO.sub.3, and CeO.sub.2 were held constant at 3.75 wt %, 1.00 wt %, and 2.00 wt %, respectively, while the Nb.sub.2O.sub.5 content was varied from 0.00 wt % (VK2) to 2.75 wt % (K1), 4.00 wt % (VK8), and 7.00 wt % (VK9).

TABLE-US-00007 TABLE 6 Influence of Nb.sub.2O.sub.5 Content on NOx Conversion Influence of Nb.sub.2O.sub.5 content on NOx conversion In the standard SCR In the fast SCR Nb.sub.2O.sub.5 content reaction at 200° C. reaction at 300° C. [wt %] fresh aged fresh aged 0 42.6 2.0 69.9 38.1 2.75 63.6 5.1 70.5 49.1 4 65.6 5.4 72.2 51.2 7 67.2 7.3 79.1 52.2

[0128] The results of the influence of the Nb.sub.2O.sub.5 content are shown in FIG. 7.