Catalyst for catalytic degradation of volatile organic compounds, method of preparation and use thereof

Abstract

The application discloses a catalyst for catalytic degradation of volatile organic compounds, a preparation method and application thereof, and the preparation method of the catalyst comprises the following steps: preparing a precursor by a sol-gel method or a precipitation method through spherical α-MnO2 and other raw materials, and finally performing drying and calcination, so that porous nanorod La x A (1‑x) MnO3 / Mn3O4 composite oxide catalyst is obtained. The preparation method of the application omits a hard template agent which is often used in traditional synthesis of a porous catalyst with a large specific surface area, cost is reduced, and the La x A (1‑x) Heterojunction structures are formed between MnO3 and Mn3O4, separation of electron-hole pairs is promoted, the efficiency of the catalyst in the photocatalytic and thermal catalytic degradation of VOCs is improved, and the specific surface area is larger than that of ordinary perovskite materials.

Description

Technical Field

[0001] This invention belongs to the field of environmentally friendly catalytic materials technology, and mainly relates to a La x A (1-x) MnO3 / Mn3O4 perovskite composite oxide catalyst, preparation method and its application in thermal / photothermal catalytic degradation of volatile organic compounds. Background Technology

[0002] Perovskites are excellent catalytic oxidation materials for removing volatile organic compounds, and can replace precious metal catalysts in some fields. However, perovskites have a low specific surface area (generally less than 10 m²). 2 The limited capacity ( / g) restricts its performance in catalytic oxidation to remove volatile organic compounds.

[0003] Researchers often use hard template methods (PS, PMMA, carbon black) to increase the specific surface area of ​​perovskites. For example, some literature adds the hard template agent PMMA to the precursor solution for synthesizing LaCoO3, and then removes the hard template agent PMMA by calcination to obtain three-dimensional ordered macroporous LaCoO3. This method relies on the hard template agent PMMA to create pores in the perovskite material. The process is complex and costly, and it is not suitable for large-scale production (Zhang Chuanhui, etc. Applied Catalysis B: Environmental, 201, 552-560).

[0004] In patent CN 106238066 B, precursor salts such as La, Sr, and Fe react with a spherical porous δ-MnO2 matrix in a low-temperature melting reaction system of sodium nitrate and potassium nitrate, with the reaction proceeding in an atomic molar ratio of 1 at the A(La+Sr) / B(Mn+Fe) sites, to generate single-phase perovskite La. 0.4 Sr 0.6 Mn 0.8 Fe 0.2 O3; furthermore, the low-temperature melting reaction system differs from the usual method for preparing perovskite ABO3, and the low-temperature reaction allows the final product to retain the spherical porous structure of the matrix, resulting in a high specific surface area. However, the precursor spherical porous δ-MnO2 particles are relatively large (4-5 μm), which determines the La 04 Sr 06 Mn 08 Fe 02The large size of the O3 catalyst particles is detrimental to the catalytic reaction. The average pore size of the spherical porous δ-MnO2 is in the nanometer range, making it difficult for precursor salts such as La, Sr, and Fe to fully diffuse into the pores of δ-MnO2 and react uniformly with it in the molten sodium nitrate and potassium nitrate system, thus hindering the formation of a spherical porous structure. This method is highly complex, as the precursor salts easily decompose into amorphous La oxides during diffusion, clogging the pores.

[0005] Patent CN 104549301 B discloses a method for synthesizing Fe2O3@MFe2O4 with a core-shell structure. The method involves preparing a PVP ethanol solution of a soluble metal salt (Mn, Co, Ni, Cu, or Zn), and immersing Fe2O3 in the solution with thorough stirring, causing the soluble metal salt to adsorb onto the Fe2O3 surface. During calcination, Fe2O3 reacts with the adsorbed metal salt in a solid phase, forming an MFe2O4 shell that encapsulates the Fe2O3, thus obtaining a core-shell structured Fe2O3@MFe2O4 catalyst. However, this core-shell structure results in a small specific surface area.

[0006] Therefore, to address the shortcomings of existing technological inventions, such as the complexity and high cost of the hard template method; for example, patents<CN106238066 B> The synthesis process requires high precision in terms of precursor structure and technique, especially for single-phase perovskite La 0.4 Sr 0.6 Mn 0.8 Fe 0.2 The photothermal catalytic oxidation performance of O3 still has room for improvement; and the patent <cn104549301b>The Fe2O3@MFe2O4 catalyst has a small specific surface area; therefore, it is necessary to develop a new method for preparing perovskite-structured catalysts. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies, the purpose of this invention is to provide a La x A (1-x) Preparation method and application of MnO3 / Mn3O4 perovskite composite oxide catalyst. The preparation method is simple and conducive to increasing the specific surface area of ​​the prepared perovskite catalyst material.

[0008] To achieve the first aspect of the aforementioned objective, the present invention employs the following technical solution:

[0009] A method for preparing a catalyst for the catalytic degradation of volatile organic compounds, wherein the catalyst is La. x A (1-x) The MnO3 / Mn3O4 perovskite composite oxide catalyst includes the following steps:

[0010] (1) The raw materials containing soluble salts of metal elements A and La and α-MnO2 powder are obtained by sol-gel method or precipitation method to obtain precursor dry powder containing metal elements A and La and α-MnO2.

[0011] (2) The dry powder of the precursor is calcined to obtain La. x A (1-x) MnO3 / Mn3O4 perovskite composite oxide catalyst;

[0012] Wherein, x is 0.5-1, for example 0.6, 0.7, 0.8 or 0.9, and metal element A is selected from alkaline earth metals; in the precursor mixture obtained in step c, the total amount of metal element A and La: the molar ratio of a-MnO2 is (0.1-0.8):1, preferably (0.5-0.8):1, for example 0.6:1 or 0.7:1.

[0013] According to the preparation method of the present invention, the precursor dry powder is prepared in step (1) by sol-gel method or precipitation method. In one embodiment, the process of preparing the precursor dry powder in step (1) is as follows:

[0014] a. Mix α-MnO2 powder and ethylene glycol aqueous solution, and disperse by thorough stirring to obtain α-MnO2 suspension;

[0015] b. Add soluble salts of metal elements A and La to an aqueous solution of citric acid to dissolve and obtain a sol;

[0016] c. Mix the α-MnO2 suspension obtained in step a with the sol obtained in step b until homogeneous to obtain the precursor mixture; and

[0017] d. Evaporate the precursor mixture to dryness to obtain a gel, and further dry and pulverize the obtained gel to obtain precursor powder;

[0018] Preferably, in the precursor mixture obtained in step c, the molar ratio of citric acid to α-MnO2 is (0.05–2.4):1, for example, 0.1:1, 0.5:1, 1:1, or 2:1, and the molar ratio of ethylene glycol to α-MnO2 is (0.1–4.8):1, for example, 0.5:1, 1:1, 2:1, 3:1, 4:1, or 4.5:1.

[0019] In one embodiment, the process of preparing the precursor dry powder in step (1) is as follows:

[0020] a' Add α-MnO2 powder to an ethylene glycol aqueous solution containing soluble salts of metal elements A and La, and disperse thoroughly by stirring to obtain a mixed suspension;

[0021] c'. Add sodium carbonate and / or sodium hydroxide solution to the mixed suspension to adjust the pH of the mixed suspension to 10-11, thereby obtaining the precursor mixture; and

[0022] d' Filter the precursor mixture to obtain a filter cake, and further dry and pulverize the filter cake to obtain precursor dry powder;

[0023] Preferably, in the precursor mixture obtained in step c', the molar ratio of ethylene glycol to α-MnO2 is (0.1–4.8):1.

[0024] Steps a and b or step a' of the present invention are material mixing steps. Those skilled in the art will understand that the material mixing order can be appropriately adjusted without affecting the mixing effect.

[0025] In this invention, the α-MnO2 powder used can be spherical α-MnO2 known in the art, such as the spherical α-MnO2 prepared in "Preparation and Electrochemical Performance of Spherical α-MnO2" (Tong Mengliang et al., Power Supply Technology, No. 10, 2009) or the sea urchin-shaped microspheres α-MnO2 prepared in "Controllable Synthesis and Catalytic Performance of Manganese Dioxide with Different Crystal Forms and Morphologies" (Zhang Bentian et al., Fine Chemicals, No. 11, 2016).

[0026] In one embodiment, the α-MnO2 powder can be prepared by the following method:

[0027] Ammonium persulfate ((NH4)2S2O8), potassium persulfate (K2S2O8), and manganese sulfate monohydrate (MnSO4·H2O) are added to deionized water in a molar ratio of (0-1):1:1, for example, (0.2-0.8):1:1 or 0.5:1:1. The mixture is stirred thoroughly until dissolved, resulting in a manganese ion concentration of 0.16-0.32 mol / L, such as 0.2 mol / L, 0.25 mol / L, or 0.3 mol / L. Then concentrated sulfuric acid is added... For example, 98% concentrated sulfuric acid, the volume of which is 0.3%-4.5% of the volume of the deionized water, such as 0.5%, 1%, 2%, 3% or 4%. After stirring, it is transferred to a hydrothermal reactor and subjected to a hydrothermal reaction at 110-180℃ for 0.25-12 hours, such as 1, 3, 5 or 8 hours. After the hydrothermal reaction is completed, the reaction product is washed with deionized water until the filtrate is neutral, and then dried, for example in an oven at 60℃ for 12 hours, to obtain spherical α-MnO2 powder.

[0028] In one embodiment, the α-MnO2 powder can be prepared by the following method: ammonium persulfate, potassium persulfate, and manganese sulfate monohydrate in a molar ratio of 0.5:1:1 (1.8406g (NH4)2S2O8, 4.368g K2S2O8, 2.7264g MnSO4·H2O) are added to 75mL of deionized water and stirred thoroughly until all solids are dissolved. Then, 0.6mL of 98% concentrated sulfuric acid is added, and the mixture is stirred for 30min before being transferred to a hydrothermal reactor and reacted at 130℃ for 2h. The product after the reaction is washed with deionized water until the filtrate is neutral, and then dried in an oven at 60℃ for 12h to obtain the spherical α-MnO2.

[0029] According to the preparation method of the present invention, in one embodiment, the metal element A is strontium and / or barium, both of which are commonly used substitution / partial substitution elements at the A-site in the perovskite phase ABO3. Similarly, those skilled in the art can readily conceive of similar substitution or partial substitution at the B-site. Given that there are many types of perovskite catalytic materials, such as LaMnO3, LaFeO3, and LaCoO3, those skilled in the art can reasonably expect that the perovskite phase in the above-mentioned catalyst can also be replaced with perovskites such as LaMnO3, LaFeO3, and LaCoO3, and can also be prepared using the same or similar methods described above, and used for thermal or photothermal catalytic degradation of volatile organic compounds, such as styrene, toluene, and ethyl acetate.

[0030] According to the preparation method of the present invention, in one embodiment, x is 0.5-1, such as 0.6, 0.7, 0.8 or 0.9; in another embodiment, x = 1, that is, the catalyst does not contain the metal element A.

[0031] In this invention, the purpose of steps d and d' is to separate and dry the water in the obtained precursor mixture to obtain a uniformly mixed precursor powder. The separation and drying methods used are well known in the art and will not be described in detail here.

[0032] In step (2) of this invention, the obtained dry powder is calcined. By controlling the amounts of metal elements A and La relative to Mn, Mn is relatively excessive, thus preventing the complete production of the perovskite phase. Therefore, perovskite La is obtained through calcination. x A (1-x) A complex of MnO3 and oxide Mn3O4 is used as a catalyst. In one embodiment, in step (2), the calcination temperature is 600-900°C, for example 700, 750, 800 or 850°C, and the calcination time is 3-6 hours, for example 4 or 5 hours.

[0033] In one embodiment, in step (2), the dry powder is first treated at 280-450℃, for example, 300-400℃, for example, 350℃ for 2-8 hours, for example, 4-6 hours, for example, 5 hours, and then heated to the calcination temperature for calcination, wherein the heating rate is no more than 5℃ / min, preferably 3-5℃ / min, for example, 4℃ / min.

[0034] According to the preparation method of the present invention, in one embodiment, ultrasonic dispersion is used during mixing in step a'; or, ultrasonic dispersion is used during mixing in step a'. Ultrasonic dispersion is well known in the art. In one embodiment, the ultrasonic conditions used may be: ultrasonic frequency of 30-50kHz, for example 40kHz, ultrasonic power of 200-500W, for example 300 or 400W, and time of 10-150min, for example 30-120min, for example 60 or 80min.

[0035] To achieve another aspect of the above-described objective, the present invention also provides a catalyst prepared according to the above-described preparation method, wherein the prepared La x A (1-x) The specific surface area of ​​MnO3 / Mn3O4 perovskite composite oxide catalysts can reach 40-50 m². 2 / g; Crystal phase is perovskite La x A (1-x) A composite phase of MnO3 and oxide Mn3O4.

[0036] In another aspect of achieving the above-mentioned objective, the present invention also provides the application of the catalyst prepared according to the above preparation method in the catalytic degradation of volatile organic compounds; preferably, the volatile organic compounds are styrene, toluene, or ethyl acetate.

[0037] In one embodiment, the reaction conditions for the catalytic degradation are a volatile organic compound volume concentration of 80-200 ppm, such as 100-160 ppm, 120 ppm, or 150 ppm, and a space velocity of 10,000-50,000 h⁻¹. -1 For example, 20000-40000h -1 or 30000h -1 The temperature is 150–300°C, for example, 180–270°C, 200°C, or 250°C. In one embodiment, the catalytic degradation reaction is carried out under illumination, with the illumination conditions being a xenon lamp power of 200–400W, for example, 300W, a wavelength of 300–800nm, for example, 400–600nm or 500nm, and a light power density of 10–30 mW / cm². -2 For example, 15, 20, or 25 mW / cm -2 .

[0038] Compared with the prior art, the present invention has the following advantages:

[0039] This invention utilizes α-MnO2 powder as a precursor to deposit La precursors (lanthanum salts and alkaline earth metal salts) on the surface of α-MnO2, thereby generating LaMnO3 / Mn3O4 through a solid-state reaction. Surprisingly, it was found that the material has a porous structure. The pores may be due to the low melting point of α-MnO2 oxide, the internal pores left after the outward diffusion and reaction with La, or the formation of the crystal structure when it transforms into Mn3O4.

[0040] Meanwhile, the preparation method of the present invention (1) is simple to synthesize, using the common sol-gel method (or precipitation method) to synthesize LaMnO3 / Mn3O4, combining LaMnO3 with Mn3O4 in one step, and using the high-temperature sintering-resistant LaMnO3 perovskite outer layer to protect the highly active but easily deactivated Mn3O4 by high-temperature sintering; (2) In α-MnO2, due to the reaction of some α-MnO2 with the precursor salt, there is a disintegration process, which spontaneously generates a porous structure, increasing the specific surface area, and does not require the matrix to be a porous structure; at the same time, compared with single-phase LaMnO3, the conversion rate of photothermal catalytic degradation of volatile organic compounds of LaMnO3 / Mn3O4 with heterojunction structure is significantly improved.

[0041] To address the issue of small specific surface area in perovskite materials and to construct heterojunction structures, this invention specifically utilizes α-MnO2 as a hard template and precursor for the synthesis of perovskite LaMnO3. α-MnO2, acting as a hard template, leaves internal pores after participating in the solid-state reaction, forming porous nanorods. Furthermore, the precursor LaMnO2 is controlled... 3+ When the / ɑ-MnO2 ratio is less than 0.8, the product is a composite phase LaMnO3 / Mn3O4, and the formed LaMnO3 coats Mn3O4. The outer perovskite LaMnO3 protects the highly active but easily deactivated Mn3O4 by high-temperature sintering, thus improving its thermal catalytic efficiency for volatile organic compounds. At the same time, LaMnO3 and Mn3O4 also form a heterojunction structure, which promotes electron-hole pair separation efficiency and improves its photothermal catalytic efficiency. This is different from the pure hard template method.

[0042] The specific surface area, mineralization rate of volatile organic compounds under thermal and photothermal catalytic conditions were tested on the catalyst material obtained by the present invention, and compared with ordinary perovskite catalysts. The results showed that the present invention has significant advantages. Attached Figure Description

[0043] Figure 1 This is a SEM image of the spherical α-MnO2 powder synthesized in Example 1;

[0044] Figure 2 The image shows the XRD pattern of the LaMnO3 / Mn3O4 material synthesized in Example 1.

[0045] Figure 3 This is a SEM image of the porous nanorod-shaped LaMnO3 / Mn3O4 catalyst synthesized in Example 1. Detailed Implementation

[0046] The present invention will be further described below with reference to the embodiments and accompanying drawings. However, the present invention is not limited to the listed embodiments, but should also include equivalent improvements and modifications of the technical solutions defined in the claims appended to the present invention patent application.

[0047] Unless otherwise specified, all reagents used in the following examples / comparative examples are of analytical grade.

[0048] Example 1

[0049] ① Synthesis of α-MnO2: Ammonium persulfate, potassium persulfate, and manganese sulfate monohydrate in a molar ratio of 0.5:1:1 (1.8406 g (NH4)2S2O8, 4.368 g K2S2O8, 2.7264 g MnSO4·H2O) were added to 75 mL of deionized water and stirred thoroughly until all solids dissolved. Then, 0.6 mL of 98% concentrated sulfuric acid was added, and the mixture was stirred for 30 min before being transferred to a hydrothermal reactor and reacted at 130 °C for 2 h. The product was washed with deionized water until the filtrate was neutral, and then dried in an oven at 60 °C for 12 h to obtain spherical α-MnO2 powder.

[0050] ② Preparation of precursor solution: The molar ratio of citric acid: ethylene glycol: lanthanum nitrate: α-MnO2 is 1.8:3.6:0.6:1. Weigh 4.2g of citric acid, 2.7g of ethylene glycol, 3.2g of lanthanum nitrate, and 1.0596g of α-MnO2 as raw materials for later use.

[0051] During preparation, 2.7g of ethylene glycol was first added to 20g of deionized water to form an ethylene glycol aqueous solution, followed by the addition of 1.0596g of α-MnO2. The solution was then ultrasonically dispersed for 120min to form α-MnO2 suspension A.

[0052] Add 4.2g of citric acid and 3.2g of lanthanum nitrate to 30g of deionized water and stir thoroughly until all solids dissolve to form sol B;

[0053] Mix suspension A with sol B and continue stirring at room temperature for 6 hours.

[0054] ③ Transfer the mixed suspension from step ② to an 80°C water bath and continue stirring until the excess liquid evaporates to obtain a gel.

[0055] ④ Place the gel from step ③ in a 110℃ oven and dry for 12 hours, then grind it to obtain gel powder.

[0056] ⑤ Calcination: The gel powder from step ④ is placed in a muffle furnace and calcined at 400℃ for 3 hours, then heated to 750℃ for 4 hours at a heating rate of 5℃ / min to obtain porous nanorod-shaped LaMnO3 / Mn3O4 material.

[0057] ⑥ The specific surface area of ​​the obtained LaMnO3 / Mn3O4 material was tested, and its mineralization rate of styrene was tested under dark and light conditions.

[0058] Example 2

[0059] LaMnO3 / Mn3O4 materials were synthesized according to the method of Example 1, and their specific surface area and mineralization rate of styrene under dark and light conditions were tested. The difference from Example 1 is that the ratio of precursor and complexing agent in step ② was changed. The molar ratio of citric acid: ethylene glycol: lanthanum nitrate: α-MnO2 was 1.3:2.5:0.8:1. 2.8g of citric acid, 1.82g of ethylene glycol, 4.22g of lanthanum nitrate, and 1.0g of α-MnO2 were weighed.

[0060] Example 3

[0061] La was synthesized according to the method of Example 1. 0.67 Ba 0.33 MnO3 / Mn3O4 materials were used, and their specific surface area and mineralization rate of styrene under dark and light conditions were tested. The difference from Example 1 was that some lanthanum nitrate was replaced with barium nitrate. The following ingredients were weighed according to the molar ratio of citric acid: ethylene glycol: lanthanum nitrate: barium nitrate: α-MnO2 = 1.8:3.6:0.4:0.2:1: 4.2 g citric acid, 2.7 g ethylene glycol, 2.0 g lanthanum nitrate, 0.6 g barium nitrate, and 1.0 g α-MnO2.

[0062] Example 4

[0063] ①The synthesis of MnO2 is the same as step ① in Example 1.

[0064] ②Preparation of precursor solution:

[0065] According to Example 1, weigh the relevant raw materials, first add ethylene glycol and lanthanum nitrate to deionized water to form an ethylene glycol lanthanum nitrate aqueous solution, then add the spherical α-MnO2 synthesized in step ①, and use ultrasonic dispersion for 2 hours to form a mixed suspension of lanthanum nitrate and α-MnO2.

[0066] Add sodium carbonate or sodium hydroxide solution to the mixture and stir continuously to maintain the pH of the mixture at 10-11.

[0067] ③ Filtration and drying: Filter the mixed suspension from step ② and dry it in a 110℃ oven for 12 hours, then grind it.

[0068] ④ Calcination: The dry powder from step ③ is placed in a muffle furnace and calcined at 300℃ for 3 hours, then heated to 800℃ for 4 hours at a heating rate of 3℃ / min, thereby obtaining nanorod LaMnO3 / MnO2 materials with porous structures.

[0069] ⑤ The specific surface area of ​​the obtained LaMnO3 / Mn3O4 material was tested, and its mineralization rate of styrene was tested under dark and light conditions.

[0070] Comparative Example 1

[0071] LaMnO3 powder was synthesized according to the reference "Ji Qingling, Zou Zhengguang, Long Fei, Wu Yi. Synthesis of perovskite-type rare earth manganese oxide LaMnO3 by sol-gel method [J]. Journal of Materials Science and Engineering, 2016, 34(06):947-950+1019". The specific synthesis method is as follows:

[0072] Lanthanum nitrate hexahydrate and manganese acetate tetrahydrate were weighed out at a molar ratio of 1:1, and dissolved in 50 ml of deionized water. 4.20 g of citric acid was added, and the mixture was stirred continuously at 80°C for 5 hours to form a gel. The gel was then dried in a constant-temperature drying oven at 120°C for 24 hours. The resulting dry gel was ground into powder and calcined in a muffle furnace at 600°C for 2 hours and then at 700°C for 4 hours to obtain LaMnO3 powder.

[0073] Test characterization

[0074] 1. Sample specific surface area test: The specific surface area and porosity were measured using a Micromeritics (3-Flex) specific surface area and porosity analyzer, and the specific surface area of ​​the sample was calculated using the BET (Brunauer-Emmett-Teller) model.

[0075] 2. Styrene mineralization rate test of samples: The powdered sample was loaded into a fixed-bed reactor, and the reaction gas was introduced. After the flow rates of each gas stabilized, the reactor was sequentially heated to 200℃, 250℃, and 300℃, and the xenon lamp (300W power, 300-800nm ​​wavelength, 15mW / cm² light power density) was turned on at each temperature. -2 Turn off the xenon lamp and stabilize for at least 30 minutes under each test condition. Record the styrene concentration at the reactor inlet and the CO2 concentration at the reactor outlet, and calculate the mineralization rate of the sample to styrene. Test conditions: 100 ppm styrene, 5% O2, nitrogen as the balance gas, 50 mg catalyst, space velocity 30000 h⁻¹. -1 .

[0076] Formula for calculating styrene mineralization rate η (%):

[0077]

[0078] Among them, C 苯乙烯 The concentration of styrene at the reactor inlet is expressed in ppm. This represents the CO2 concentration at the reactor outlet, in ppm.

[0079] Examples 1 to 4 were subjected to specific surface area and styrene mineralization rate determination, and were recorded as Test Examples 1 to 4.

[0080] Comparative Example 1 was selected, and its specific surface area and styrene mineralization rate were measured. This was recorded as Test Example 5.

[0081] Table 1. Specific surface area and pore volume of test examples 1-5

[0082]

[0083] Table 2. Styrene mineralization rate (%) in Test Examples 1-5

[0084]

[0085] Examples 1-4 are La prepared using the method of this patent. x A (1-x) MnO3 / Mn3O4 composite oxide catalysts all have a specific surface area exceeding 39 m². 2 / g, styrene can be completely mineralized at 300℃.

[0086] Compared with the perovskite material synthesized by conventional method in Comparative Example 1, Examples 1-4 not only show a significant increase in specific surface area, but also a much higher mineralization rate of styrene. This indicates that the method disclosed in this patent invention can effectively increase the specific surface area of ​​perovskite materials and improve the thermal or photothermal mineralization rate of volatile organic compounds.

Claims

1. A La x A (1-x) Application of MnO3 / Mn3O4 perovskite composite oxide catalyst in the catalytic degradation of volatile organic compounds; the crystal phase of the catalyst is perovskite La. x A (1-x) The catalyst is a composite phase of MnO3 and Mn3O4 oxide, and the preparation method includes the following steps: (1) The raw materials containing soluble salts of metal elements A and La and α-MnO2 powder are obtained by sol-gel method or precipitation method to obtain precursor dry powder containing metal elements A and La and α-MnO2. (2) The precursor powder is calcined to obtain La. x A (1-x) MnO3 / Mn3O4 perovskite composite oxide catalyst; Where x is 0.5-1, and metal element A is selected from alkaline earth metals; in the precursor dry powder obtained in step (1), the total amount of metal element A and La in molar quantity: the molar ratio of α-MnO2 is (0.1~0.8):

1.

2. The application according to claim 1, characterized in that, In the precursor dry powder obtained in step (1), the total amount of metal elements A and La: the molar ratio of α-MnO2 is (0.5~0.8):

1.

3. The application according to claim 1, characterized in that, The process of preparing the precursor dry powder in step (1) is as follows: a. Mix α-MnO2 powder and ethylene glycol aqueous solution, and disperse by thorough stirring to obtain α-MnO2 suspension; b. Add soluble salts of metal elements A and La to an aqueous solution of citric acid to dissolve and obtain a sol; c. Mix the α-MnO2 suspension obtained in step a with the sol obtained in step b to obtain a precursor mixture; and d. Evaporate the precursor mixture to obtain a gel, and further dry and pulverize the obtained gel to obtain precursor powder.

4. The application according to claim 3, characterized in that, In the precursor mixture obtained in step c, the molar ratio of citric acid to α-MnO2 is (0.05~2.4):1, and the molar ratio of ethylene glycol to α-MnO2 is (0.1~4.8):

1.

5. The application according to claim 1, characterized in that, The process of preparing the precursor dry powder in step (1) is as follows: a' Add α-MnO2 powder to an ethylene glycol aqueous solution containing soluble salts of metal elements A and La, and disperse by thorough stirring to obtain a mixed suspension; c' Add sodium carbonate and / or sodium hydroxide solution to the mixed suspension to adjust the pH of the mixed suspension to 10-11 to obtain the precursor mixture; and d' Filter the precursor mixture to obtain a filter cake, and further dry and pulverize the filter cake to obtain precursor dry powder.

6. The application according to claim 5, characterized in that, In the precursor mixture obtained in step c', the molar ratio of ethylene glycol to α-MnO2 is (0.1~4.8):

1.

7. The application according to any one of claims 1-6, characterized in that, The α-MnO2 powder is spherical α-MnO2.

8. The application according to claim 7, characterized in that, The α-MnO2 powder was prepared by the following process: Ammonium persulfate, potassium persulfate, and manganese sulfate monohydrate were added to deionized water in a molar ratio of (0-1):1:1 and stirred until dissolved, with a manganese ion concentration of 0.16-0.32 mol / L. Then, concentrated sulfuric acid was added, with the volume of concentrated sulfuric acid being 0.3%-4.5% of the volume of the deionized water. After stirring, the mixture was transferred to a hydrothermal reactor and subjected to a hydrothermal reaction at 110-180℃. After the hydrothermal reaction was completed, the reaction product was washed with deionized water until the filtrate was neutral, and then dried to obtain the α-MnO2 powder.

9. The application according to claim 8, characterized in that, Add ammonium persulfate, potassium persulfate and manganese sulfate monohydrate to deionized water in a molar ratio of (0.2-1):1:

1.

10. The application according to claim 1, characterized in that, Metal element A is strontium and / or barium.

11. The application according to claim 1, characterized in that, x=1。 12. The application according to any one of claims 1-6 and 8-11, characterized in that, In step (2), the calcination temperature is 600-900℃ and the calcination time is 3-6 hours.

13. The application according to claim 12, characterized in that, In step (2), the dry powder is first treated at 280-450℃ for 2-8 hours, and then heated to the calcination temperature for calcination, wherein the heating rate is no more than 5℃ / min.

14. The application according to claim 13, characterized in that, The heating rate is 3-5℃ / min.

15. The application according to any one of claims 3-6, characterized in that, In step a, ultrasonic dispersion is used during mixing; or, in step a', ultrasonic dispersion is used during mixing.

16. The application according to claim 15, characterized in that, The ultrasonic conditions are: ultrasonic frequency of 30-50kHz, ultrasonic power of 200-500W, and duration of 10-150min.

17. The application according to any one of claims 1-6, 8-11, 13-14 and 16, wherein the volatile organic compound is styrene, toluene or ethyl acetate.

18. The application according to claim 17, characterized in that, The reaction conditions for the catalytic degradation of volatile organic compounds are: volatile organic compound volume concentration of 80-200 ppm and space velocity of 10,000-50,000 h⁻¹. -1 Temperature 150~300℃; The catalytic degradation reaction of volatile organic compounds is carried out under light irradiation, with the following conditions: xenon lamp power 200-400W, wavelength 300-800nm, and light power density 10-30Mw / cm². 2 .

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