CN107442154A - A kind of cryptomelane based composite metal element catalyst and its production and use - Google Patents

Abstract

The invention provides a cryptopotassium manganese-based composite metal element catalyst, a preparation method and application thereof. The cryptopotassium-based composite metal element catalyst includes cryptopotassium-type manganese oxide molecular sieves and doped metal elements, the doped metal elements enter the cryptopotassium-type manganese oxide molecular sieve framework, and the manganese element in the cryptopotassium-type manganese oxide molecular sieves is mixed with doping metal elements. The molar ratio of heterometallic elements is (100:1)～(10:1), wherein the cryptopotassium manganese oxide-type manganese oxide molecular sieve is obtained through the reaction of heptavalent manganese and divalent manganese, and the molar ratio of heptavalent manganese to divalent manganese is ( 2:1) ~ (0.5:1). The cryptopotassium manganese ore-based composite metal element catalyst of the present invention has high catalytic activity, does not require or reduce the use of precious metals, greatly reduces the cost of the catalyst, and the catalyst does not need to be reduced and activated by hydrogen, and the use conditions are simple, and can be widely used in smelters and oil refineries Purification treatment of benzene contained in exhaust gas emitted from stationary sources such as chemical plants and chemical plants.

Description

A kind of cryptopotassium manganese base compound metal element catalyst and its preparation method and application

technical field

The invention belongs to the technical field of catalysts, and relates to a cryptopotassium-based composite metal element catalyst, a preparation method and application thereof.

Background technique

As the intensity of human industrial activities increases, a large amount of volatile organic compounds (Volatile Organic Compounds, VOCs for short) are discharged into the atmosphere, causing environmental pollution through a series of chemical reactions. For example, some highly active VOCs can react photochemically with another atmospheric pollutant, nitrogen oxides (NO _x ), causing an increase in the concentration of surface ozone and forming photochemical smog pollution; some VOCs with low vapor pressure can also nucleate through complex processes It grows up to form secondary organic aerosol, and secondary organic aerosol is an important part of fine particulate matter PM2.5. It can be seen that VOCs are important precursors for the formation of photochemical pollution and atmospheric haze. In addition, VOCs themselves can pose a huge threat to human health. For example, common VOCs such as formaldehyde, benzene, toluene, etc. have carcinogenic and teratogenic hazards. Therefore, to remove photochemical smog, reduce particulate pollution, improve urban air quality, and protect people's health, it is imperative to control and remove VOCs emissions.

VOCs come from a wide range of sources, mainly including petroleum, chemical industry, medicine, packaging, printing, coating, etc. Taking the coating industry as an example, its VOCs emissions are nearly 7 million tons per year, accounting for about 1/3 of the total VOCs emissions . In the field of VOCs elimination and purification in the coating industry, major western developed countries and Japan started earlier. In 1955, the United States promulgated the "Air Pollution Control Act", which made detailed regulations on the types and total amount of air pollutant emissions. In 1966, special regulations were formulated specifically for VOCs emissions in the coating industry, namely "Regulation 66". Driven by legal constraints and corporate interests, different technologies for eliminating VOCs have been developed and used.

At present, my country attaches great importance to the pollution of VOCs, and requires that by 2020, the whole process of VOCs emission reduction from raw materials to products, from production to consumption will be basically realized. Therefore, VOCs emission reduction technologies have been extensively researched and explored.

Benzene is one of the most toxic volatile organic compounds. The "Code for Indoor Environmental Pollution Control of Civil Construction Engineering" GB50325-2001 strictly limits its concentration, requiring its concentration to be less than 0.09mg/m ³ . Therefore, it is very necessary to treat the tail gas containing benzene from the emission source. Catalytic combustion of benzene is currently a relatively efficient control technology. However, at present, traditional powder catalysts have the disadvantages of using a large amount of precious metals such as palladium and platinum, which makes the preparation cost of the catalyst high and the catalytic activity needs to be improved.

Contents of the invention

Aiming at the deficiencies of the prior art, one of the purposes of the present invention is to provide a cryptopotassium manganese-based composite metal element catalyst, which has high catalytic activity, does not use or reduces the use of precious metals, and greatly reduces the cost of the catalyst.

For reaching this purpose, the present invention adopts following technical scheme:

A kind of cryptopotassium-based composite metal element catalyst, the active component of the catalyst comprises cryptopotassium-type manganese oxide molecular sieve and doping metal element, the manganese element in the cryptopotassium-type manganese oxide molecular sieve and the doped The molar ratio of metal elements is (100:1)～(10:1), wherein the cryptopotassium manganese ore-type manganese oxide molecular sieve is obtained by reacting heptavalent manganese and divalent manganese, and the heptavalent manganese and the divalent manganese The molar ratio is (2:1)～(0.5:1).

Cryptopotassium manganese oxide molecular sieve is a new type of material similar to zeolite molecular sieve structure. It has the advantages of large specific surface area, low isoelectric point, strong oxidation ability and high cation exchange capacity. It has rich pore structure, making it It exhibits excellent electrical conductivity, magnetism, ion exchange, selective adsorption, and catalytic properties. The present invention prepares a catalyst with excellent catalytic activity by doping rare earth metals, transition metals or a small amount of precious metal elements on the cryptopotassium manganese oxide molecular sieve without changing the crystal form of the cryptopotassium manganese oxide molecular sieve. The activity is comparable to that of noble metal catalysts, and _H2 reduction activation is not required.

The molar ratio of the manganese element in the cryptopotassium manganese oxide molecular sieve to the doped metal element is (100:1) to (10:1), for example, the molar ratio of the manganese element to the doped metal element is 100:1, 90:1, 80:1, 70:1, 60:1, 50:1, 40:1, 30:1, 20:1, 10:1, preferably 80:1, more preferably 40 :1.

Preferably, the molar ratio of the heptavalent manganese to the divalent manganese is (2:1) to (0.5:1), for example, the molar ratio of the heptavalent manganese to the divalent manganese is 2:1, 1.5:1, 1:1, 0.8:1, 0.5:1, preferably (1:1) to (0.5:1), more preferably 0.87:1.

The doping metal element is one or a mixture of at least two of iron, copper, molybdenum, tungsten, cobalt, nickel, silver, palladium, platinum, iridium, niobium and cerium.

The _second object of the present invention is to provide a preparation method of the above-mentioned cryptopotassium manganese-based composite metal element catalyst, the method is simple and easy, without H Reduction and activation step, the cost of raw materials used is low, convenient and easy to implement, the preparation method Including the following steps:

1) Potassium permanganate solution is prepared: Potassium permanganate is dissolved in deionized water, and potassium permanganate solution is obtained after stirring;

2) Prepare a divalent manganese salt mixed solution containing doped metal elements: dissolve the divalent manganese salt in deionized water, and stir to obtain a divalent manganese salt solution; dissolve the salt containing doped metal elements in the divalent manganese salt In the manganese salt solution, add acid after stirring, and continue to stir to obtain a divalent manganese salt mixed solution containing doped metal elements;

3) Quantitatively inject the potassium permanganate solution prepared in step 1) into the mixed solution prepared in step 2), stir and then transfer to the reaction kettle for hydrothermal reaction;

4) Filtrating and washing the product after the hydrothermal reaction in step 3) to obtain a filter cake, drying the filter cake, roasting, and tableting to obtain the cryptopotassium manganese-based composite metal element catalyst.

In step 1), the solid-liquid ratio of the potassium permanganate and the deionized water is (1:10)～(1:100) g/mL, for example, the solid-liquid ratio is 1:10g/mL, 1: 20g/mL, 1:30g/mL, 1:40g/mL, 1:50g/mL, 1:60g/mL, 1:70g/mL, 1:80g/mL, 1:90g/mL, 1:100g/mL mL, preferably 1:20g/mL.

In step 2), the solid-to-liquid ratio of the divalent manganese salt to the deionized water is (1:4) to (1:20) g/mL, for example, the solid-to-liquid ratio is 1:4 g/mL, 1: 5g/mL, 1:6g/mL, 1:7g/mL, 1:8g/mL, 1:9g/mL, 1:10g/mL, 1:11g/mL, 1:12g/mL, 1:13g/mL mL, 1:14g/mL, 1:15g/mL, 1:16g/mL, 1:17g/mL, 1:18g/mL, 1:19g/mL, 1:20g/mL, preferably 1:5g/mL mL.

Preferably, in step 2), the divalent manganese salt is one or a mixture of at least two of manganese nitrate, manganese sulfate, manganese acetate, manganous carbonate, manganous sulfate, manganese chloride, manganese dihydrogen phosphate .

Preferably, in step 2), the molar ratio of the doping metal element to the divalent manganese element is (1:10) to (1:100), for example, the doping metal element and the divalent manganese The molar ratio of elements is 1:10, 1:20, 1:30, 1:40, 1:50, 1:60, 1:70, 1:80, 1:90, 1:100, preferably (1: 20) ~ (1:30).

Preferably, in step 2), the salt containing doped metal elements is iron nitrate, copper nitrate, molybdenum nitrate, tungsten nitrate, cobalt nitrate, nickel nitrate, silver nitrate, palladium nitrate, platinum nitrate, ammonium iridium chloride, One or a mixture of at least two of niobium chloride and cerium nitrate;

Preferably, in step 2), the particle size of the catalyst is reduced after pickling, which is conducive to improving the activity of the catalyst, wherein the mass ratio of the acid to the manganese in the divalent manganese salt solution is (4:1)～ (0.5:1), for example, the mass ratio of manganese in the acid and the divalent manganese salt solution is 4:1, 3.5:1, 3:1, 2.5:1, 2:1, 1.5:1, 1: 10.5:1.

Preferably, in step 2), the acid is one of oxalic acid, glacial acetic acid, and carbonic acid.

In step 3), the potassium permanganate solution is quantitatively injected into the mixed solution by a syringe pump, because the solubility of the potassium permanganate solution is not high, and the hydrothermal reaction itself is relatively slow, so the potassium permanganate The injection rate of the solution should be properly controlled. Preferably, the flow rate of the syringe pump is 1-100mL/min, such as 1mL/min, 10mL/min, 20mL/min, 30mL/min, 40mL/min, 50mL/min, 60mL /min, 70mL/min, 80mL/min, 90mL/min, 100mL/min.

Preferably, in step 3), the temperature conditions of the hydrothermal reaction are: the room temperature is raised to 80-200° C., the temperature is kept constant for 12-72 hours, and the temperature is naturally lowered.

Preferably, in step 3), the molar ratio of the potassium permanganate to the mixed solution is 0.87:1.

In step 4), the washing is deionized water until the filtrate is neutral.

Preferably, in step 4), the drying temperature is 100° C., and the drying time is 12 hours.

In step 4), the calcination is carried out in a muffle furnace, the conditions of the calcination are: the temperature is slowly raised to the calcination temperature and then the temperature is kept constant, the rate of the temperature rise is 2-10°C/min, and the calcination temperature is 450-600°C, the time for constant temperature is 2-5 hours.

The third object of the present invention is to provide a kind of purposes of the above-mentioned cryptopotassium manganese-based composite metal element catalyst, the catalyst is used for the catalytic combustion of volatile organic compound benzene, and the highly toxic pollutant benzene can be completely decomposed through catalytic combustion It is non-toxic and harmless carbon dioxide and water, and can be widely used in the purification treatment of benzene contained in waste gas discharged from stationary sources such as smelters, oil refineries, and chemical plants.

Compared with prior art, the beneficial effect of the present invention is:

(1) The cryptopotassium manganese ore-based composite metal element catalyst of the present invention does not need or reduce the use of precious metals, greatly reduces the cost of the catalyst, and has high catalytic activity. When used for the catalytic combustion of benzene, the space velocity is 90L/(g h ), the conversion rate of benzene can reach more than 90% when the reaction temperature is 250°C, and its catalytic activity can be compared with noble metal catalysts.

(2) The preparation method of the cryptopotassium manganese ore-based composite metal element catalyst of the present invention is simple and easy, without _H2 reduction and activation step, the cost of raw materials used is low, and it is convenient and easy to implement. The cryptopotassium-based composite metal element catalyst of the present invention is obtained through one-step hydrothermal synthesis, without adding other active components to the load, and the catalyst keeps the basic structure of the cryptopotassium-based molecular sieve unchanged, and doped metal elements can enter the molecular sieve framework .

(3) The cryptopotassium manganese ore-based composite metal element catalyst of the present invention is used for the catalytic combustion of benzene, a volatile organic compound. After catalytic combustion, the highly toxic pollutant benzene can be completely decomposed into non-toxic and harmless carbon dioxide and water, and can be widely used in smelting Purification treatment of benzene contained in waste gas emitted from stationary sources such as factories, refineries, and chemical plants.

Description of drawings

Fig. 1 is that the catalyst that the embodiment 1-7 of the present invention makes is used for the catalytic combustion of benzene, the comparative figure of the transformation rate of benzene;

Fig. 2 is the catalyst that embodiment 1, 4, 5, 6 of the present invention makes and Pd/Al ₂ O ₃ is used for the catalytic combustion of benzene, the comparative figure of the transformation rate of benzene;

Fig. 3 is the catalyst that the embodiment 5 of the present invention makes and Pd/Al ₂ O ₃ are used for the catalytic combustion of benzene, the comparative figure of carbon dioxide production rate;

Fig. 4 is the comparative schematic diagram of the XRD spectrum of the catalyzer that embodiment 1-7 of the present invention makes and cryptomelane standard substance;

Fig. 5 is the catalyst that the embodiment of the present invention 5,8,9,10 system is used for the catalytic combustion of benzene, the comparative figure of the transformation rate of benzene;

Fig. 6 is that the catalyst that the embodiment 5 of the present invention, 11-14 makes is used for the catalytic combustion of benzene, the comparative figure of the transformation rate of benzene;

Fig. 7 is a comparison chart of the conversion rate of benzene when the catalysts prepared in Examples 5, 15 and 16 of the present invention are used for the catalytic combustion of benzene.

detailed description

The technical solution of the present invention will be further described below in conjunction with the accompanying drawings 1-3 and through specific embodiments.

Example 1

Prepare solution 1: weigh 10.27g of potassium permanganate, put the solution in 400mL of water, stir vigorously for later use.

Solution 2: Weigh 18.38g of manganese acetate and dissolve it in 200mL of water. Add 12.5mL of glacial acetic acid to seal and stir magnetically.

Solution 1 was added dropwise to solution 2 with a syringe pump at an injection rate of 2.4 ml per minute. Solution 2 was sealed while stirring magnetically. After the injection, the mixture of solution 1 and solution 2 was transferred into a 1L hydrothermal reaction kettle. The reaction kettle is placed in an oven for hydrothermal reaction. The hydrothermal conditions are: constant temperature of 150°C for 24 hours, and natural cooling. After cooling down to room temperature, the crystalline product was washed and filtered until the filtrate was neutral. The filter cake is dried and then roasted in a muffle furnace. The roasting conditions are as follows: the heating rate is 5°C per minute, the temperature is raised to 500°C, and the temperature is kept constant for 3 hours. The obtained catalyst was compressed into tablets and sieved into 40-60 meshes for evaluation and use.

Catalyst evaluation conditions: the composition of the reaction mixture is: benzene [C ₆ H ₆ ]=1500ppm, [O ₂ ]=20%, N ₂ is used as the balance gas, the total gas flow rate is 300mL/min, and the space velocity is 90L/(g h), the reaction temperature is 150-400°C. The concentrations of benzene, carbon dioxide, oxygen and other gases were determined by gas chromatography (Agilent-7980B, FID and TCD).

Example 2

In solution 2, the third element is doped. The operation method is: after adding 12.7g of manganese acetate, add 0.9326g of palladium nitrate dihydrate, and mix and stir the solution. Other parameters are unchanged as in Example 1.

Example 3

In solution 2, the third element is doped. Mix 1.52g of cerium nitrate hexahydrate, mix well and vigorously stir. Other parameters are unchanged as in Example 1.

Example 4

In solution 2, the third element is doped. Mix 1.54 g iridium ammonium chlorate, mix well and stir vigorously. Other parameters are unchanged as in Example 1.

Example 5

In solution 2, the third element is doped. Mix in 0.59g of silver nitrate and mix vigorously. Other parameters are unchanged as in Example 1.

Example 6

In solution 2, the third element is doped. Mix 0.84g of copper nitrate trihydrate, mix well and vigorously stir. Other parameters are unchanged as in Example 1.

Example 7

In solution 2, the third element is doped. Mix 1.41g ferric nitrate nonahydrate, mix well and vigorously stir. Other parameters are unchanged as in Example 1.

Example 8

In solution 2, the third element is doped. Mix in 0.59g of silver nitrate and mix vigorously. No acid is added, and other parameters are unchanged as in Example 1.

Example 9

Prepare solution 1: weigh 10.27g of potassium permanganate, put the solution in 400mL of water, stir vigorously for later use.

Prepare solution 2: Weigh 7.96g of manganese acetate, mix with 0.59g of silver nitrate, and dissolve in 200mL of water. Add 20 mL of glacial acetic acid to seal, and stir magnetically; (Mn ⁷⁺ :Mn ²⁺ =2:1).

Example 10

Prepare solution 1: weigh 10.27g of potassium permanganate, put the solution in 400mL of water, stir vigorously for later use.

Prepare solution 2: Weigh 31.86g of manganese acetate, mix with 0.59g of silver nitrate, and dissolve in 200mL of water. Add 20 mL of glacial acetic acid to seal, and stir magnetically (Mn ⁷⁺ :Mn ²⁺ =0.5:1).

Example 11

In solution 2, the third element is doped. Mix 2.38g of silver nitrate and mix vigorously. Other parameters are unchanged as in Example 1.

Example 12

In solution 2, the third element is doped. Mix in 1.19g of silver nitrate, mix well and stir vigorously. Other parameters are unchanged as in Example 1.

Example 13

In solution 2, the third element is doped. Mix in 0.39g of silver nitrate and mix vigorously. Other parameters are unchanged as in Example 1.

Example 14

In solution 2, the third element is doped. Mix in 0.29g of silver nitrate and mix vigorously. Other parameters are unchanged as in Example 1.

Example 15

Weigh 5 g of the catalyst in Example 1, dissolve 0.229 g of silver nitrate (Mn:Ag=40:1) in 100 mL of water, mix the catalyst and the solution, and stir. The slurry was rotovaped at 60 degrees. The obtained product was dried in an oven at 120°C overnight, and the catalyst was heated to 500°C at a heating rate of 5°C per minute, and kept at a constant temperature for 3 hours. The obtained catalyst was sieved into 40-60 meshes by tableting and evaluated for future use to prepare an impregnated MnAg catalyst. Catalyst evaluation conditions: the composition of the reaction mixture is: benzene [C ₆ H ₆ ]=1500ppm, [O ₂ ]=20%, N ₂ is used as the balance gas, the total gas flow rate is 300mL/min, and the space velocity is 90L/(g h), the reaction temperature is 150-400°C. The concentrations of benzene, carbon dioxide, oxygen and other gases were determined by gas chromatography (Agilent-7980B, FID and TCD).

Example 16

Mix and dissolve 24.01g of manganese acetate and 0.407g of silver nitrate in 372mL of deionized water (Mn:Ag=40:1), add 64.3g of urea, and stir vigorously. Afterwards, the temperature of the water bath was raised to 90° C., and the co-precipitation slurry was obtained overnight for 12 hours. The co-precipitated MnAg catalyst was prepared by washing, filtering, drying and roasting. Catalyst evaluation conditions: the composition of the reaction mixture is: benzene [C ₆ H ₆ ]=1500ppm, [O ₂ ]=20%, N ₂ is used as the balance gas, the total gas flow rate is 300mL/min, and the space velocity is 90L/(g h), the reaction temperature is 150-400°C. The concentrations of benzene, carbon dioxide, oxygen and other gases were determined by gas chromatography (Agilent-7980B, FID and TCD).

The catalysts prepared in Examples 1-7 were used for the catalytic combustion of benzene, and the comparative activity results are shown in FIG. 1 . Compared with Pd/Al ₂ O ₃ with a mass content of 1 wt% of the conventional noble metal catalyst Pd, the catalysts prepared in Examples 1, 4, 5, and 6 and Pd/Al ₂ O ₃ were used for the catalytic combustion of benzene, The comparative activity results are shown in Figure 2. Example 5 is compared with the carbon dioxide production rate of commonly used noble metal catalysts, and the results are shown in Figure 3. The crystal structures of the catalysts prepared in Examples 1-7 were detected, and the experimental results are shown in FIG. 4 .

In summary, it can be seen from Fig. 4 that the cryptoplandranite-based composite metal element catalysts prepared by the preparation method of the present invention all present the basic crystal structure of cryptoplandoxite, that is, the catalyst prepared after doping metal elements has no By changing the basic crystal form of the Caymanite, the doped metal elements enter the lattice framework of the Caymanite molecular sieve.

It can be seen from Fig. 1 that, compared with Example 1, after adding doping metal elements in Examples 2, 3, 4, 5, 6, and 7, the conversion rate of benzene in the prepared catalyst has been greatly improved. With reference to Fig. 2, according to the activity comparison of Examples 3-7, it can be known that doping a small amount of the third element silver or iridium has the highest activity and is the preferred catalyst. Among them, the activity of the catalyst prepared with silver-doped components was compared with that of conventional noble metal catalysts (1wt% Pd/Al ₂ O ₃ ). As shown in Figure 3, compared with the commercial precious metal catalyst (1wt% Pd/Al ₂ O ₃ ), the catalyst of cryptoplandoxite-based composite silver (Example 5) has a stronger ability to convert toxic benzene vapor into non-toxic and harmless carbon dioxide , with superior performance. It can be seen from Example 6 and Example 7 that the activity of the prepared catalyst is still relatively high without adding noble metal elements, but conventional copper and iron metal elements. As shown in Figure 5, when no acid is added and the compounding amount of silver is kept constant, the catalyst activity obtained by adjusting the ratio of the two precursors of manganese is poor. Therefore, the addition of acetic acid is necessary, and the optimum Mn The molar ratio of ⁷⁺ :Mn ²⁺ is 0.87.

The loading of silver was optimized, and the catalysts prepared in Examples 5 and 11-14 were used for the catalytic combustion of benzene, and the comparative activity results are shown in FIG. 6 . Wherein in embodiment 11, the performance of Mn:Ag=10:1 is optimal, but the consumption of metallic silver is too large, and corresponding to it is embodiment 5 Mn:Ag=40:1, and metallic silver consumption is less, and catalytic performance is higher Excellent, is the optimal ratio. If the amount of silver is further reduced to Mn:Ag=60:1 and 80:1, the activity of the catalyst will be reduced more, which has no application value.

Contrast the activity of the MnAg catalyst prepared by one-step hydrothermal method, impregnation method and co-precipitation method (both Mn:Ag=40:1), that is, the catalyst prepared in Examples 5, 15, and 16 is used for the catalytic combustion of benzene, The comparative activity results are shown in FIG. 7 . As shown in the figure, the catalyst prepared by the one-step hydrothermal method has the crystallization characteristics of cryptopotassium manganese, and the silver species are dispersed in the molecular sieve framework, reflecting the best catalytic activity. Although the sample by impregnation method also maintains the crystal form of cryptopotassium manganese, but the silver species is impregnated outside the molecular sieve framework, and its activity is poor. It shows that the active silver species can play a good catalytic performance only in the molecular sieve framework. The co-precipitation samples had the worst activity because they could not form the favorable cryptopotassium manganese structure, and the active silver was also embedded in the co-precipitated manganese oxide.

The cryptomelane-based composite transition metal catalyst of the present invention has high catalytic activity, does not require or reduce the use of precious metals, greatly reduces the cost of the catalyst, and the catalyst does not need to be activated by hydrogen reduction, and the use conditions are simple. It is used for the volatile organic compound benzene. Catalytic combustion, through catalytic combustion, the highly toxic pollutant benzene can be completely decomposed into non-toxic and harmless carbon dioxide and water, which can be widely used in the purification treatment of benzene contained in the waste gas emitted by stationary sources such as smelters, oil refineries, and chemical plants.

The above examples are only used to illustrate the detailed methods of the present invention, and the present invention is not limited to the above detailed methods, that is, it does not mean that the present invention can only be implemented depending on the above detailed methods. Those skilled in the art should understand that any improvement of the present invention, the equivalent replacement of each raw material of the product of the present invention, the addition of auxiliary components, the selection of specific methods, etc., all fall within the scope of protection and disclosure of the present invention.

Claims (10)

1. a cryptoplandoxite-based composite metal element catalyst, characterized in that, the active component of the catalyst comprises cryptopotassium manganese oxide molecular sieve and a doping metal element, and the doping metal element enters the cryptopotash ore type manganese oxide molecular sieve framework, the molar ratio of the manganese element in the cryptopotassium manganese oxide molecular sieve to the doping metal element is (100:1)～(10:1), wherein the cryptopotassium manganese ore type oxide The manganese molecular sieve is obtained by reacting heptavalent manganese and divalent manganese, and the molar ratio of the heptavalent manganese to the divalent manganese is (2:1)˜(0.5:1). 2. cryptoplandoxite-based composite metal element catalyst according to claim 1, is characterized in that, the mol ratio of manganese element and described doping metal element in the described cryptopotassium manganese ore type manganese oxide molecular sieve is (80:1 )～(10:1); Preferably, the molar ratio of the heptavalent manganese to the divalent manganese is (2:1)˜(0.5:1). 3. according to claim 1 and 2 described cryptomelane base composite metal element catalysts, it is characterized in that, described doping metal element is iron, copper, molybdenum, tungsten, cobalt, nickel, silver, palladium, platinum, iridium , niobium, cerium or a mixture of at least two. 4. according to the preparation method of the cryptomelane-based composite metal element catalyst described in one of claims 1-3, it is characterized in that, comprising the steps: 1) Potassium permanganate solution is prepared: Potassium permanganate is dissolved in deionized water, and potassium permanganate solution is obtained after stirring; 2) Prepare a divalent manganese salt mixed solution containing doped metal elements: dissolve the divalent manganese salt in deionized water, and stir to obtain a divalent manganese salt solution; dissolve the salt containing doped metal elements in the divalent manganese salt In the manganese salt solution, add acid after stirring, and continue to stir to obtain a divalent manganese salt mixed solution containing doped metal elements; 3) Quantitatively inject the potassium permanganate solution prepared in step 1) into the mixed solution prepared in step 2), stir and then transfer to the reaction kettle for hydrothermal reaction; 4) Filtrating and washing the product after the hydrothermal reaction in step 3) to obtain a filter cake, drying the filter cake, roasting, and tableting to obtain the cryptopotassium manganese-based composite metal element catalyst. 5. the preparation method according to claim 4, is characterized in that, in step 1), the solid-liquid ratio of described potassium permanganate and described deionized water is (1:10)～(1:100) g /mL. 6. according to the described preparation method of claim 4 or 5, it is characterized in that, in step 2), the solid-liquid ratio of described divalent manganese salt and described deionized water is (1:4)～(1:20 ) g/mL; Preferably, the divalent manganese salt is one or a mixture of at least two of manganese nitrate, manganese sulfate, manganese acetate, manganous carbonate, manganous sulfate, manganese chloride, and manganese dihydrogen phosphate; Preferably, in step 2), the molar ratio of the doping metal element to the divalent manganese element is (1:10)-(1:100), preferably (1:20)-(1:30) ; Preferably, the salt containing doped metal elements is iron nitrate, copper nitrate, molybdenum nitrate, tungsten nitrate, cobalt nitrate, nickel nitrate, silver nitrate, palladium nitrate, platinum nitrate, ammonium iridium chloride, niobium chloride, nitric acid One or a mixture of at least two of cerium; Preferably, in step 2), the mass ratio of the acid to the manganese in the divalent manganese salt solution is (4:1) to (0.5:1); Preferably, the acid is one of oxalic acid, glacial acetic acid, and carbonic acid. 7. according to the preparation method described in one of claim 4-6, it is characterized in that, step 3) in, described potassium permanganate solution is quantitatively injected in the described mixed solution by syringe pump, and the The flow rate is 1-100mL/min; Preferably, in step 3), the temperature conditions of the hydrothermal reaction are: the room temperature is raised to 80-200°C, the temperature is kept constant for 12-72 hours, and the temperature is naturally lowered; Preferably, the molar ratio of the potassium permanganate to the mixed solution is 0.87:1. 8. The preparation method according to any one of claims 4-7, characterized in that, in step 4), the washing is deionized water washing until the filtrate is neutral; Preferably, in step 4), the drying temperature is 100° C., and the drying time is 12 hours. 9. according to the described preparation method of one of claim 4-8, it is characterized in that, in step 4), described roasting is carried out in muffle furnace, and the condition of described roasting is: after slowly heating up to roasting temperature Constant temperature, the temperature increase rate is 2-10°C/min, the calcination temperature is 450-600°C, and the constant temperature time is 2-5h. 10. The use of the cryptoplandoxene-based composite metal element catalyst according to any one of claims 1-3, characterized in that the catalyst is used for the catalytic combustion of benzene, a volatile organic compound.