Polyoxometallic acid modified vanadium-based high-temperature SCR (Selective Catalytic Reduction) catalyst as well as preparation method and application thereof

Abstract

The invention provides a polyoxometallic acid modified vanadium-based high-temperature SCR (Selective Catalytic Reduction) catalyst as well as a preparation method and application thereof. Titanium dioxide is used as a carrier; a mixture of a catalytically active substance and a catalyst promoter loaded on the carrier; the catalytic active substance is vanadium oxide; the catalyst auxiliary agent comprises polyoxometallic acid and other metal oxides; the polyoxometallic acid is phosphotungstic acid and / or phosphomolybdic acid, and the polyoxometallic acid accounts for 0.5-5 wt% of the SCR catalyst. The catalyst is prepared through polyoxometallic acid modification, the NOx conversion efficiency in a high-temperature area can be effectively improved, the generation amount of N2O is obviously reduced, and the catalyst is an SCR catalyst suitable for a generator and other tail gas environments with the high tail gas temperature and the high sulfur content.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and particularly relates to a polyoxometalate-modified vanadium-based high-temperature SCR catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] Vanadium-based catalysts are one of the common selective catalytic reduction (SCR) catalysts, having good catalytic performance, high sulfur tolerance, and low preparation cost. However, the NO x conversion rate of vanadium-based catalysts is relatively low at high temperatures (≥500 °C), and the N 2 O production amount is relatively high, which cannot meet the application requirements of the aftertreatment system of high-power engines. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a polyoxometalate-modified vanadium-based high-temperature SCR catalyst, a preparation method thereof, and an application thereof, and the catalyst has a relatively high NO x conversion rate and a relatively low N 2 O production amount.

[0004] The present invention provides a polyoxometalate-modified vanadium-based high-temperature SCR catalyst, using titanium dioxide as a carrier;

[0005] a mixture of catalytic active substances and catalyst assistants supported on the carrier;

[0006] the catalytic active substance is vanadium oxide;

[0007] the catalyst assistant includes polyoxometalate and other metal oxides;

[0008] the polyoxometalate is phosphotungstic acid and / or phosphomolybdic acid, and the polyoxometalate accounts for 0.5-5 wt% of the SCR catalyst.

[0009] Preferably, the other metal oxides in the catalyst assistant are selected from molybdenum oxide and / or tungsten oxide.

[0010] Preferably, the titanium dioxide carrier accounts for 80-95 wt% of the SCR catalyst;

[0011] the molar ratio of vanadium element in the catalytic active substance to metal elements in the catalyst assistant is 1-10:1.

[0012] The present invention provides a preparation method of the polyoxometalate-modified vanadium-based high-temperature SCR catalyst according to the above technical solution, including the following steps:

[0013] 1) Mix a vanadium oxide precursor, a catalyst assistant precursor, and an oxalic acid solution to obtain a transparent solution;

[0014] 2) Mix the titanium dioxide support and the transparent solution, and stir to obtain a mixed slurry;

[0015] 3) Mix the polyoxometalate solution and the mixed slurry, and dry to obtain a vanadium-based SCR catalyst precursor;

[0016] 4) Calcinate the vanadium-based SCR catalyst precursor to obtain a vanadium-based SCR catalyst;

[0017] 5) Immerse the vanadium-based SCR catalyst in a polyoxometalate solution with a concentration of 1-50 g / L, wash, dry and then calcine to obtain a polyoxometalate-modified vanadium-based high-temperature SCR catalyst.

[0018] Preferably, in step 4), the calcination temperature of the vanadium-based SCR catalyst precursor is 350-550 °C, and the time is 1-5 h;

[0019] In step 5), the calcination temperature is 500-650 °C, and the time is 3-6 h.

[0020] Preferably, in step 1), the vanadium oxide precursor is selected from one or more of ammonium metavanadate, vanadyl sulfate, sodium orthovanadate and sodium metavanadate;

[0021] The catalyst promoter precursor is selected from one or more of ammonium metatungstate, sodium metatungstate, ammonium molybdate and sodium molybdate.

[0022] Preferably, in step 2), the stirring temperature is 40-90 °C, and the time is 1-5 h.

[0023] Preferably, in step 5), the impregnation temperature is 10-30 °C, and the time is 1-12 h.

[0024] Preferably, in step 1), the molar ratio of oxalic acid to vanadium element in the vanadium oxide precursor is 1-10:1;

[0025] The molar ratio of vanadium element in the vanadium oxide precursor to metal element in the catalyst promoter precursor is 1-10:1;

[0026] In step 5), the mass ratio of the vanadium-based SCR catalyst to the 1-50 g / L polyoxometalate solution is 0.95-1.05:10.

[0027] The present invention provides an application of the polyoxometalate-modified vanadium-based high-temperature SCR catalyst described in the above technical solution in the treatment of diesel engine exhaust gas.

[0028] The present invention provides a polyoxometalate-modified vanadium-based high-temperature SCR catalyst, which uses titanium dioxide as a carrier; a mixture of catalytically active substances and catalyst promoters supported on the carrier; the catalytically active substance is vanadium oxide; the catalyst promoter includes polyoxometalate and other metal oxides; the polyoxometalate is phosphotungstic acid and / or phosphomolybdic acid, and the polyoxometalate accounts for 0.5-5 wt% of the SCR catalyst. The above catalyst is prepared by modification with polyoxometalate, which can effectively improve the NO x conversion efficiency in the high-temperature region, and the generation amount of N 2 O is significantly reduced. It is an SCR catalyst suitable for tail gas environments with high tail gas temperature and high sulfur content such as generators. Description of the Drawings

[0029] Figure 1 It is a process schematic diagram for preparing vanadium-based high-temperature SCR catalyst powder in a specific embodiment of the present invention;

[0030] Figure 2 It is an XRD comparison chart before and after calcination of phosphotungstic acid used in Example 1. Detailed Embodiments

[0031] The present invention provides a polyoxometalate-modified vanadium-based high-temperature SCR catalyst, which uses titanium dioxide as a carrier;

[0032] a mixture of catalytically active substances and catalyst promoters supported on the carrier;

[0033] the catalytically active substance is vanadium oxide;

[0034] the catalyst promoter includes polyoxometalate and other metal oxides;

[0035] the polyoxometalate is phosphotungstic acid and / or phosphomolybdic acid, and the polyoxometalate accounts for 0.5-5 wt% of the SCR catalyst.

[0036] The polyoxometalate-modified vanadium-based high-temperature SCR catalyst provided by the present invention uses titanium dioxide as a carrier. The titanium dioxide carrier accounts for 80-95 wt% of the polyoxometalate-modified vanadium-based high-temperature SCR catalyst; the specific proportion is 80 wt%, 81 wt%, 82 wt%, 83 wt%, 84 wt%, 85 wt%, 86 wt%, 87 wt%, 8 wt%, 89 wt%, 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt% or 95 wt%.

[0037] The multi-metal-oxo-acid modified vanadium-based high-temperature SCR catalyst provided by the present invention comprises a catalytically active substance and a catalyst promoter supported on the carrier; the catalytically active substance is vanadium oxide. The vanadium oxide is vanadium oxide; it is formed by calcining a precursor of vanadium oxide, and the precursor of vanadium oxide is selected from one or more of ammonium metavanadate, vanadyl sulfate, sodium orthovanadate, and sodium metavanadate. The molar ratio of vanadium element in the vanadium oxide precursor to the metal element in the catalyst promoter is 1 to 10:1; it can be 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1.

[0038] In the present invention, the catalyst promoter comprises a multi-metal-oxo-acid and other metal oxides; the multi-metal-oxo-acid is phosphotungstic acid and / or phosphomolybdic acid, and the multi-metal-oxo-acid accounts for 0.5 to 5 wt% of the SCR catalyst; specifically, it can be 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, or 5.0%.

[0039] The other metal oxides are selected from molybdenum oxide and / or tungsten oxide. The other metal oxides are formed by calcining one or more of ammonium metatungstate, sodium metatungstate, ammonium paramolybdate, and sodium paramolybdate.

[0040] The present invention provides a preparation method of the multi-metal-oxo-acid modified vanadium-based high-temperature SCR catalyst described in the above technical solution, comprising the following steps:

[0041] 1) Mix an ammonium metavanadate precursor, a catalyst promoter precursor, and an oxalic acid solution to obtain a transparent solution;

[0042] 2) Mix a titanium dioxide carrier and the transparent solution, and stir to obtain a mixed slurry;

[0043] 3) Mix a multi-metal-oxo-acid solution and the mixed slurry, and dry to obtain a vanadium-based SCR catalyst precursor;

[0044] 4) Calcine the vanadium-based SCR catalyst precursor to obtain a vanadium-based SCR catalyst;

[0045] 5) Immerse the vanadium-based SCR catalyst in a multi-metal-oxo-acid solution with a concentration of 1 to 50 g / L, wash, dry, and then calcine to obtain a multi-metal-oxo-acid modified vanadium-based high-temperature SCR catalyst.

[0046] The method provided by the present invention modifies the vanadium-based catalyst, uses the multi-metal-oxo-acid to increase the surface acidity of the vanadium-based catalyst and thus increase the ammonia storage capacity, ensuring the rapid progress of the catalytic NO x reduction reaction at high temperatures, and solving the problem of low NO x conversion efficiency in the high-temperature region of the vanadium-based catalyst and low N 2The problem of high O generation amount. The multi-metal-oxo acid modified vanadium-based high-temperature SCR catalyst prepared by this method can realize the application of vanadium-based catalysts in the continuous high-temperature tail gas environment such as generators.

[0047] In the present invention, a vanadium oxide precursor, a catalyst promoter precursor and an oxalic acid solution are mixed to obtain a transparent solution. In the present invention, an appropriate amount of oxalic acid is added to deionized water and stirred to form an oxalic acid solution; the mass ratio of the oxalic acid solution to the vanadium oxide precursor is 1-10:1. In the present invention, the oxalic acid solution provides an acidic environment and can promote the dissolution of the vanadium precursor. The oxalic acid is oxalic acid dihydrate. In a specific embodiment, the mass ratio of oxalic acid dihydrate to the vanadium oxide precursor is 24:11;

[0048] In step 1) of the present invention, the vanadium oxide precursor is selected from one or more of ammonium metavanadate, vanadyl sulfate, sodium orthovanadate and sodium metavanadate; the catalyst promoter precursor is selected from one or more of ammonium metatungstate, sodium metatungstate, ammonium molybdate and sodium molybdate.

[0049] After obtaining the transparent solution, in the present invention, a titanium dioxide support and the transparent solution are mixed and stirred to obtain a mixed slurry. In the present invention, the titanium dioxide support is slowly added to the transparent solution, and the stirring temperature is 40-90 °C and the time is 1-5 h; preferably, it is placed in a water bath to reach the required temperature.

[0050] In the present invention, a multi-metal-oxo acid solution and the mixed slurry are mixed and dried to obtain a vanadium-based SCR catalyst precursor. In the present invention, preferably, a multi-metal-oxo acid solid is dissolved in water to obtain a multi-metal-oxo acid solution; the multi-metal-oxo acid solid is selected from phosphotungstic acid and / or phosphomolybdic acid. The multi-metal-oxo acid accounts for 0.5-5 wt% of the SCR catalyst.

[0051] In the present invention, preferably, the multi-metal-oxo acid solution is added dropwise to the mixed slurry, and during the heating and stirring process, as the water evaporates, when it presents a semi-solid state, it is transferred to an oven and dried overnight.

[0052] In the present invention, the vanadium-based SCR catalyst precursor is calcined to obtain a vanadium-based SCR catalyst. In the present invention, preferably, the vanadium-based SCR catalyst precursor is fully ground, sieved and placed in a muffle furnace for calcination; the calcination temperature of the vanadium-based SCR catalyst precursor is 350-550 °C and the time is 1-5 h; in a specific embodiment, the calcination temperature of the vanadium-based SCR catalyst precursor is 500 °C and the time is 2 h.

[0053] After obtaining the vanadium-based SCR catalyst, the present invention impregnates the vanadium-based SCR catalyst in a polyoxometallic acid solution with a concentration of 1-50 g / L, washes it, dries it, and then calcines it to obtain a polyoxometallic acid-modified vanadium-based high-temperature SCR catalyst. In the present invention, the polyoxometallic acid solution is prepared by mixing polyoxometallic acid solid and deionized water; the mass concentration of the polyoxometallic acid solution is 1-50 g / L, preferably 10-35 g / L; in specific embodiments, the mass concentration of the polyoxometallic acid solution is 25 g / L. The mass ratio of the vanadium-based catalyst to the polyoxometallic acid solution is 0.95-1.05:10. The impregnation is carried out under stirring conditions; the impregnation is carried out at room temperature, preferably 10-35 °C, and the impregnation time is 1-12 h. After impregnation, it is washed, preferably by centrifugal washing 3-5 times. After washing, it is dried; the drying is preferably carried out in an oven; the drying temperature is 60-80 °C, and the time is 10-14 h.

[0054] The present invention preferably fully grinds and sieves the dried polyoxometallic acid-modified vanadium-based SCR catalyst precursor and then places it in a muffle furnace for calcination; the calcination temperature is 500-650 °C, and the time is 2-6 h; in specific embodiments, the calcination temperature is 500 °C, and the time is 2 h.

[0055] The polyoxometallic acid-modified vanadium-based high-temperature SCR catalyst prepared by the present invention has a NO x conversion rate of more than 80% at 300-550 °C, and the N 2 O production amount is reduced by about 50%.

[0056] Figure 1 is a process schematic diagram for preparing vanadium-based high-temperature SCR catalyst powder in specific embodiments of the present invention; oxalic acid, vanadium precursor, and promoter solution are mixed, and TiO 2 support is added under water bath stirring conditions to obtain a vanadium catalyst slurry; the vanadium catalyst slurry and polyoxometallic acid solution are mixed, dried and calcined to obtain a once-modified vanadium catalyst powder; it is mixed with the polyoxometallic acid solution again and impregnated under stirring conditions to obtain a twice-modified vanadium catalyst slurry, and then dried and calcined again to obtain vanadium-based high-temperature SCR catalyst powder.

[0057] The present invention provides an application of the polyoxometallic acid-modified vanadium-based high-temperature SCR catalyst described in the above technical solution in the treatment of diesel engine exhaust gas.

[0058] The polyoxometallic acid-modified vanadium-based high-temperature SCR catalyst described in the above technical solution is applicable to exhaust gas environments with relatively high exhaust gas temperature and relatively high sulfur content, such as generators.

[0059] To further illustrate the present invention, a polyoxometalate-modified vanadium-based high-temperature SCR catalyst provided by the present invention, its preparation method and application will be described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0060] Example 1

[0061] This example provides a polyoxometalate-modified vanadium-based high-temperature SCR catalyst. The vanadium-based SCR catalyst uses titanium dioxide as an active substance carrier, vanadium oxide as a catalytically active substance, and phosphotungstic acid and tungsten oxide as catalyst assistants.

[0062] The preparation method of the polyoxometalate-modified vanadium-based high-temperature SCR catalyst includes the following steps:

[0063] (1) Take 2 ml of deionized water, and successively add 0.168 g of oxalic acid dihydrate, 0.077 g of ammonium metavanadate, and 0.213 g of ammonium metatungstate. After stirring evenly, add 1.74 g of titanium dioxide carrier, and place it in a water bath at 65 °C and stir for 3 hours to obtain a vanadium-based SCR catalyst precursor;

[0064] (2) Weigh 0.15 g of phosphotungstic acid and dissolve it in 1 ml of deionized water, and gradually add it to the vanadium-based SCR catalyst precursor, continue to stir for 1 h, and then dry overnight at 80 °C;

[0065] (3) The obtained solid catalyst is ground, sieved, and then placed in a muffle furnace and calcined at 500 °C for 2 hours to obtain a once-modified vanadium-based high-temperature SCR catalyst;

[0066] (4) Weigh 0.75 g of phosphotungstic acid and dissolve it in 30 ml of deionized water, add 3.0 g of the once-modified vanadium-based high-temperature SCR catalyst, stir for 6 hours, and then centrifuge. Place the obtained slurry in an oven and dry overnight at 80 °C;

[0067] (5) The obtained solid catalyst is ground, sieved, and then placed in a muffle furnace and calcined at 500 °C for 2 hours to obtain the target catalyst: polyoxometalate-modified vanadium-based high-temperature SCR catalyst.

[0068] The polyoxometalate-modified vanadium-based high-temperature SCR catalyst provided in this example has good catalytic reduction activity for NOx and is suitable for the exhaust gas treatment environment of diesel engines with high temperature and high sulfur characteristics. Its specific performance parameters are shown in Table 1.

[0069] The present invention compared the XRD characteristic peaks of phosphotungstic acid before and after calcination at 500 °C for 2 h, and the results are as Figure 2 shown; Figure 2 is the XRD comparison chart of phosphotungstic acid before and after calcination; from Figure 2 it can be seen that: after calcination, the miscellaneous peaks of phosphotungstic acid disappear, replaced by phosphotungstic acid and a small amount of existing PO2 and P 2 O 5 Moreover, no obvious WO 3 characteristic peak was found in XRD, which proved that only a very small amount of phosphotungstic acid decomposed and surface impurities were removed by roasting after the calcination of phosphotungstic acid, and most of the samples existed in the form of phosphotungstic acid crystals.

[0070] Example 2

[0071] This example provides a polyoxometalate-modified vanadium-based high-temperature SCR catalyst. The vanadium-based SCR catalyst uses titanium dioxide as the active substance carrier, vanadium oxide as the catalytically active substance, and phosphomolybdic acid and tungsten oxide as catalyst assistants.

[0072] The preparation method of the polyoxometalate-modified vanadium-based high-temperature SCR catalyst includes the following steps:

[0073] (1) Take 2 ml of deionized water, and successively add 0.168 g of oxalic acid dihydrate, 0.077 g of ammonium metavanadate, and 0.213 g of ammonium metatungstate. After stirring evenly, add 1.74 g of titanium dioxide carrier, and place it in a water bath at 65 °C and stir for 3 hours to prepare a vanadium-based SCR catalyst precursor;

[0074] (2) Weigh 0.15 g of phosphomolybdic acid and dissolve it in 1 ml of deionized water, and gradually add it to the vanadium-based SCR catalyst precursor, continue to stir for 1 h, and then dry it overnight at 80 °C;

[0075] (3) The obtained solid catalyst is ground, sieved, and then placed in a muffle furnace and calcined at 500 °C for 2 hours to obtain a once-modified vanadium-based high-temperature SCR catalyst;

[0076] (4) Weigh 0.75 g of phosphomolybdic acid and dissolve it in 30 ml of deionized water, add 3.0 g of the once-modified vanadium-based high-temperature SCR catalyst, stir for 6 hours, and then centrifuge. Place the obtained slurry in an oven and dry it overnight at 80 °C;

[0077] (5) The obtained solid catalyst is ground, sieved, and then placed in a muffle furnace and calcined at 500 °C for 2 hours to obtain the target catalyst: polyoxometalate-modified vanadium-based high-temperature SCR catalyst.

[0078] The polyoxometalate-modified vanadium-based high-temperature SCR catalyst provided in this example has good catalytic reduction of NO x activity and is suitable for the exhaust gas treatment environment of diesel engines with high temperature and high sulfur characteristics. Its specific performance parameters are shown in Table 1.

[0079] Example 3

[0080] This embodiment provides a polyoxometalate-modified vanadium-based high-temperature SCR catalyst. The vanadium-based SCR catalyst uses titanium dioxide as the active substance carrier, vanadium oxide as the catalytically active substance, and phosphomolybdic acid and tungsten oxide as catalyst additives.

[0081] The preparation method of the polyoxometalate-modified vanadium-based high-temperature SCR catalyst includes the following steps:

[0082] (1) Take 2 ml of deionized water, and successively add 0.168 g of oxalic acid dihydrate, 0.077 g of ammonium metavanadate, and 0.213 g of ammonium metatungstate. After stirring evenly, add 1.74 g of titanium dioxide carrier, and place it in a water bath at 65 °C and stir for 3 hours to prepare a vanadium-based SCR catalyst precursor.

[0083] (2) Weigh 0.15 g of phosphomolybdic acid and dissolve it in 1 ml of deionized water, and gradually add it to the vanadium-based SCR catalyst precursor. Continue stirring for 1 h and then dry overnight at 80 °C.

[0084] (3) The obtained solid catalyst is ground, sieved, and then placed in a muffle furnace and calcined at 500 °C for 2 hours to obtain a once-modified vanadium-based high-temperature SCR catalyst.

[0085] (4) Weigh 0.75 g of phosphotungstic acid and dissolve it in 30 ml of deionized water. Add 3.0 g of the once-modified vanadium-based high-temperature SCR catalyst, stir for 6 hours, and then centrifuge. Place the obtained slurry in an oven and dry overnight at 80 °C.

[0086] (5) The obtained solid catalyst is ground, sieved, and then placed in a muffle furnace and calcined at 500 °C for 2 hours to obtain the target catalyst: the polyoxometalate-modified vanadium-based high-temperature SCR catalyst.

[0087] The polyoxometalate-modified vanadium-based high-temperature SCR catalyst provided by this embodiment has good catalytic reduction activity of NO x and is suitable for the diesel engine exhaust gas treatment environment with high temperature and high sulfur characteristics. Its specific performance parameters are shown in Table 1.

[0088] Comparative Example 1

[0089] This comparative example provides a vanadium-based high-temperature SCR catalyst. The modified vanadium-based SCR catalyst uses titanium dioxide as the active substance carrier, vanadium oxide as the catalytically active substance, and tungsten oxide as the catalyst additive.

[0090] The preparation method of the vanadium-based high-temperature SCR catalyst includes the following steps:

[0091] (1) Take 2 ml of deionized water, and successively add 0.168 g of oxalic acid dihydrate, 0.077 g of ammonium metavanadate, and 0.213 g of ammonium metatungstate. After stirring evenly, add 1.74 g of titanium dioxide support, and place it in a water bath at 65 °C and stir for 3 hours to prepare a vanadium-based SCR catalyst precursor, which is then placed in an oven and dried overnight at 80 °C;

[0092] (2) The obtained solid catalyst is ground, sieved, and then placed in a muffle furnace and calcined at 500 °C for 2 hours to obtain a vanadium-based high-temperature SCR catalyst.

[0093] Comparative Example 2

[0094] This comparative example provides a vanadium-based SCR catalyst. The vanadium-based SCR catalyst uses titanium dioxide as the active substance support, vanadium oxide as the catalytically active substance, and tungsten oxide as the catalyst promoter.

[0095] The preparation method of the vanadium-based SCR catalyst includes the following steps:

[0096] (1) Take 2 ml of deionized water, and successively add 0.168 g of oxalic acid dihydrate, 0.077 g of ammonium metavanadate, and 0.426 g of ammonium metatungstate. After stirring evenly, add 1.54 g of titanium dioxide support, and place it in a water bath at 65 °C and stir for 3 hours to obtain a vanadium-based SCR catalyst precursor, which is then placed in an oven and dried overnight at 80 °C;

[0097] (2) The obtained solid catalyst is ground, sieved, and then placed in a muffle furnace and calcined at 500 °C for 2 hours to obtain a vanadium-based SCR catalyst.

[0098] The present invention conducts performance tests on the catalysts prepared in the examples and comparative examples, and the specific test results are shown in Tables 1 and 2.

[0099] Table 1 NO x conversion efficiency (%)

[0100] catalyst 175℃ 200℃ 250℃ 300℃ 350℃ 400℃ 450℃ 500℃ 550℃ Example 1 10.0 20.3 59.8 89.4 96.7 97.6 97.7 94.7 82.0 Example 2 9.8 21.0 58.8 90.0 95.5 96.8 97.7 93.4 80.0 Example 3 10.2 20.3 59.6 88.8 96.4 96.8 98.0 94.4 81.1 Comparative Example 1 7.2 18.3 55.7 84.1 93.5 95.5 94.1 82.7 49.9 Comparative Example 2 8.9 18.6 58.2 87.8 96.1 97.6 97.1 90.9 65.8

[0101] Table 2 N 2 O production

[0102]

[0103]

[0104] By analyzing the data in Tables 1 and 2, compared with Comparative Examples 1-2, it can be seen that by changing the proportion of WO 3 in the catalyst, although the NO x conversion efficiency has increased, the N 2 O production increases at high temperatures, proving that simply WO3 An increase in will reduce the N of the catalyst 2 selectivity.

[0105] Comparing Comparative Examples 1-2 and Example 1 in Table 2, it can be seen that the improvement in catalyst performance caused by phosphotungstic acid doping in Example 1 is significantly different from the simple WO 3 content increase, and the amount of NO generated at high temperature is significantly reduced, that is, the N of the catalyst is improved 2 selectivity. It can be determined that the reason for the improvement in the performance of the modified vanadium-based catalyst is the phosphotungstic acid doped on the catalyst surface. 2

[0106] As can be seen from the above examples, the present invention provides a polyoxometalate-modified vanadium-based high-temperature SCR catalyst, with titanium dioxide as the carrier; a mixture of catalytically active substances and catalyst promoters supported on the carrier; the catalytically active substance is vanadium oxide; the catalyst promoter includes polyoxometalate and other metal oxides; the polyoxometalate is phosphotungstic acid and / or phosphomolybdic acid, and the polyoxometalate accounts for 0.5-5 wt% of the SCR catalyst. The above catalyst is prepared by polyoxometalate modification, which can effectively improve the NO x conversion efficiency in the high-temperature region, and the amount of NO generated is significantly reduced. It is an SCR catalyst suitable for tail gas environments with high tail gas temperatures and high sulfur contents such as generators. 2

[0107] The above is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.​​

Claims

1. A polyoxometallic acid modified vanadium-based high-temperature SCR catalyst, characterized in that: Titanium dioxide is used as a carrier; a mixture of a catalytically active substance and a catalyst promoter supported on the carrier; The catalytically active substance is vanadium oxide; The catalyst promoter includes polyoxometallic acid and other metal oxides; The polyoxometallic acid is phosphotungstic acid and / or phosphomolybdic acid, and the polyoxometallic acid accounts for 0.5-5wt% of the SCR catalyst.

2. The polyoxometallic acid-modified vanadium-based high-temperature SCR catalyst according to claim 1, characterized in that: The other metal oxides in the catalyst promoter are selected from molybdenum oxide and / or tungsten oxide.

3. The polyoxometallic acid-modified vanadium-based high-temperature SCR catalyst according to claim 1, characterized in that: The titanium dioxide carrier accounts for 80-95 wt% of the SCR catalyst; The molar ratio of the vanadium element in the catalytically active substance to the metal element in the catalyst promoter is 1 to 10:

1.

4. A method for preparing the polyoxometallic acid-modified vanadium-based high-temperature SCR catalyst according to claim 1, comprising the following steps: 1) mixing a vanadium oxide precursor, a catalyst promoter precursor and an oxalic acid solution to obtain a transparent solution; 2) mixing the titanium dioxide carrier and the transparent solution, stirring to obtain a mixed slurry; 3) mixing the polyoxometallic acid solution and the mixed slurry, and drying to obtain a vanadium-based SCR catalyst precursor; 4) calcining the vanadium-based SCR catalyst precursor to obtain a vanadium-based SCR catalyst; 5) The vanadium-based SCR catalyst is immersed in a 1-50 g / L polyoxometallic acid solution, washed, dried and then calcined to obtain a polyoxometallic acid-modified vanadium-based high-temperature SCR catalyst.

5. The preparation method according to claim 4, characterized in that: The vanadium-based SCR catalyst precursor in step 4) is calcined at a temperature of 350 to 550° C. for a time of 1 to 5 hours; In step 5), the calcination temperature is 500-650° C. and the calcination time is 2-6 hours.

6. The preparation method according to claim 4, characterized in that: In step 1), the vanadium oxide precursor is selected from one or more of ammonium metavanadate, vanadyl sulfate, sodium orthovanadate and sodium metavanadate; The catalyst promoter precursor is selected from one or more of ammonium metatungstate, sodium metatungstate, ammonium metamolybdate and sodium metamolybdate.

7. The preparation method according to claim 4, characterized in that: The stirring temperature in step 2) is 40-90° C. and the stirring time is 1-5 h.

8. The preparation method according to claim 4, characterized in that: The immersion temperature in step 5) is 10-30° C. and the time is 1-12 hours.

9. The preparation method according to claim 4, characterized in that: In step 1), the molar ratio of oxalic acid to vanadium element in the vanadium oxide precursor is 1 to 10:1; The molar ratio of the vanadium element in the vanadium oxide precursor to the metal element in the catalyst promoter precursor is 1 to 10:1; In step 5), the mass ratio of the vanadium-based SCR catalyst to 1-50 g / L of the polyoxometallic acid solution is 0.95-1.05:

10.

10. Use of the polyoxometallic acid modified vanadium-based high-temperature SCR catalyst according to claim 1 in treating exhaust gas from a diesel engine.

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