A Mn3O4@(NiO-CeO2) core-shell structure catalyst and a preparation method and application thereof

Abstract

The application discloses a Mn3O4@(NiO-CeO2) core-shell structure catalyst and a preparation method and application thereof, and belongs to the technical field of catalytic materials for volatile organic pollutants (VOCs), wherein a manganese source and a precipitator are dissolved in water to obtain a precursor solution, the precursor solution is subjected to a hydrothermal reaction, and after the reaction is completed, cooling is carried out, and after separation, washing and drying, Mn3O4 nanoparticles are obtained; a nickel source and a cerium source are dissolved in an alcohol solvent to prepare a metal salt mixed solution, the Mn3O4 nanoparticles are added into the metal salt mixed solution, and impregnation treatment is carried out to obtain impregnated materials; the impregnated materials are subjected to solvent evaporation and removal to obtain a solid, and after drying, the solid is subjected to calcination treatment in an air atmosphere, and after cooling, the Mn3O4@(NiO-CeO2) core-shell structure catalyst is obtained. The core-shell structure catalyst prepared by the application exhibits high conversion rate in the catalytic oxidation of formaldehyde, benzene and toluene in a low temperature range.

Description

Technical Field

[0001] This invention belongs to the technical field of catalytic materials for volatile organic pollutants (VOCs), specifically relating to a Mn3O4@(NiO-CeO2) core-shell structure catalyst, its preparation method, and its application. Background Technology

[0002] Volatile organic compounds (VOCs) are organic substances that are easily volatile at room temperature and participate in atmospheric photochemical reactions. Their sources include industrial waste gas, vehicle exhaust, and products from home renovations and daily necessities. VOCs are key precursors to PM2.5 and near-surface O3. Under sunlight, they react with nitrogen oxides to generate photochemical smog and secondary organic aerosols, exacerbating smog. Many VOCs are toxic, and some, such as benzene and formaldehyde, are carcinogens. VOCs treatment technologies are divided into recovery (adsorption, absorption, condensation) and destruction (catalytic oxidation, direct combustion, photocatalysis, biodegradation). Catalytic oxidation, due to its high purification efficiency, lack of secondary pollution, low ignition temperature, and low energy consumption, has become one of the most promising technologies. Its core lies in high-performance catalysts; ideal catalysts need to possess characteristics such as high low-temperature activity, good thermal stability, strong resistance to poisoning, and long lifespan. Industrial catalysts are divided into two categories: precious metals (Pt, Pd, Au) and transition metal oxides. Precious metals exhibit excellent low-temperature activity, but they are costly, scarce, and easily poisoned and deactivated in sulfur- and chlorine-containing waste gases. Therefore, the development of efficient, stable, and low-cost non-precious metal transition metal oxide catalysts has become a current research hotspot.

[0003] Transition metal oxide catalysts have attracted much attention in the field of formaldehyde catalytic oxidation due to their abundant resources, low cost, and environmental friendliness. Manganese oxides (such as Mn3O4) exhibit a wide range of valence states (Mn... 2+ / Mn 3+ / Mn 4+ With its excellent redox properties, Mn3O4 is considered a highly promising non-precious metal formaldehyde oxidation catalyst. Mn3O4 belongs to the tetragonal crystal system and its surface is rich in Mn. 2+ / Mn 3+ Redox pairs can efficiently activate oxygen and decompose formaldehyde. However, single Mn3O4 catalysts have a small specific surface area, their active sites are prone to aggregation, their activity is insufficient at low temperatures, and they are prone to deactivation with long-term use.

[0004] CeO2, due to its strong oxygen storage capacity and abundant oxygen vacancies, is often used as an auxiliary agent in the catalytic oxidation of formaldehyde. Doping with the transition metal Ni can further modulate the electronic structure of CeO2, increasing the oxygen vacancy concentration and the generation rate of surface reactive oxygen species. The resulting (NiO-CeO2) composite oxide possesses both good oxygen storage capacity and redox performance. Constructing a core-shell structure by combining Mn3O4 with (NiO-CeO2) allows the spatial confinement of the shell to prevent the aggregation of Mn3O4 nanoparticles, improving catalyst stability. The synergistic effect at the core-shell interface promotes electron transfer and the migration of reactive oxygen species, thereby enhancing the low-temperature oxidation activity of formaldehyde.

[0005] In existing technologies, urea is often used as a precipitant in the preparation of Mn3O4. However, the drastic pH changes during hydrothermal processes easily lead to uneven particle size and severe agglomeration. Shell coating often employs co-precipitation methods, which frequently result in uneven coating and exposed cores. Furthermore, nitrates are often used as the metal source and water as the solvent, which easily generates nitrogen oxide contamination during calcination, and the poor dispersion of metal ions leads to uneven shell thickness. Currently, there are no known methods for preparing Mn3O4 cores using hexamethylenetetramine as a precipitant, combined with impregnation. Reports have documented the use of core-shell catalysts with an acetate source and anhydrous ethanol as solvent to coat a (NiO-CeO2) shell for VOCs catalytic oxidation via calcination. Therefore, there is an urgent need to provide a VOCs oxidation catalyst with high activity, high stability, and a simple and environmentally friendly preparation process. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of insufficient low-temperature activity, poor stability, and uneven particle coating of existing manganese-based catalysts, and to propose a Mn3O4@(NiO-CeO2) core-shell structure catalyst, its preparation method, and its applications. This catalyst exhibits high VOCs conversion rate, good long-term cycling stability, and moisture resistance, and its preparation process is simple, environmentally friendly, and easily scalable.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a Mn3O4@(NiO-CeO2) core-shell structured catalyst, comprising the following steps: Manganese source and precipitant were dissolved in water to obtain precursor solution. The precursor solution was subjected to hydrothermal reaction. After the reaction was completed, the solution was cooled, separated, washed and dried to obtain Mn3O4 nanoparticles. Nickel and cerium sources were dissolved in an alcohol solvent to prepare a mixed metal salt solution. Mn3O4 nanoparticles were added to the mixed metal salt solution for impregnation to obtain the impregnated material. The impregnated material is evaporated to remove the solvent, resulting in a solid. After drying, the solid is calcined in air and cooled to obtain a Mn3O4@(NiO-CeO2) core-shell structure catalyst.

[0008] Furthermore, the amounts of nickel source and cerium source used satisfy the molar ratio of Ni to Ce as (0.1~0.3):1.

[0009] Furthermore, the total amount of Mn3O4 nanoparticles, nickel source, and cerium source satisfies the following condition: based on the NiO-CeO2 generated after calcination, the mass ratio of Mn3O4 to NiO-CeO2 is 1:1.

[0010] Furthermore, the manganese source is manganese nitrate, and the precipitant is hexamethylenetetramine.

[0011] Furthermore, the nickel source is nickel acetate, the cerium source is cerium acetate, and the alcohol solvent is anhydrous ethanol.

[0012] Furthermore, the hydrothermal reaction temperature is 130℃~150℃, and the reaction time is 8h~10h; after the reaction is completed, it is naturally cooled to room temperature.

[0013] Furthermore, the immersion treatment temperature is 30℃, and the immersion time is 6h to 8h.

[0014] Furthermore, the drying temperature during separation, washing, and drying is 60℃~80℃, and the drying time is 12h; The solid was dried at a temperature of 60℃~80℃ for 6h~8h. The calcination temperature is 350℃~450℃, the calcination time is 3h~5h, and the heating rate is 2℃ / min~5℃ / min.

[0015] Secondly, the present invention provides a Mn3O4@(NiO-CeO2) core-shell structure catalyst, which is prepared using a method for preparing a Mn3O4@(NiO-CeO2) core-shell structure catalyst.

[0016] Thirdly, the present invention provides the application of a Mn3O4@(NiO-CeO2) core-shell structure catalyst in the catalytic oxidation of VOCs.

[0017] Compared with the prior art, the present invention has the following beneficial technical effects: This invention proposes a method for preparing a Mn3O4@(NiO-CeO2) core-shell structured catalyst: (1) Optimized core preparation process, significant differentiation, and better particle performance: Hexamethylenetetramine (HMT) is used to replace traditional urea as a slow-release precipitant. The pH value changes slowly and evenly during the hydrothermal process. The prepared Mn3O4 nanoparticles have uniform particle size, good sphericity, strong monodispersity, and large specific surface area, which can expose more active sites and improve the intrinsic activity of the catalyst from the source. At the same time, it forms a significant difference from the general solution. (2) The shell coating process is environmentally friendly and efficient, and the coating uniformity is greatly improved: The impregnation-calcination method is used to replace the traditional co-precipitation method, forming a clear core-shell structure and effectively preventing Mn3O4 agglomeration; Nickel acetate and cerium acetate are used instead of nitrates as metal sources, and anhydrous ethanol is used instead of deionized water as solvent, resulting in better metal ion dispersion, more uniform and dense shell coating, and no problems such as exposed core or excessively thick coating. (3) Significant core-shell synergistic effect, comprehensive improvement of catalytic performance: The (NiO-CeO2) shell formed by Ni doping CeO2 has abundant oxygen vacancies and excellent oxygen storage and release capacity. It forms a strong interfacial electronic synergistic effect with the Mn3O4 core, which can promote electron transfer and reduce the energy barrier of formaldehyde oxidation reaction. At the same time, the spatial confinement effect of the shell can effectively inhibit the aggregation of core particles, significantly improving the low-temperature activity, cycle stability and moisture resistance of the catalyst. Detailed Implementation

[0018] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0019] The present invention will now be described in further detail: A method for preparing a Mn3O4@(NiO-CeO2) core-shell structure catalyst is disclosed. The core-shell structure consists of an active core and a modified shell uniformly coated on the outer surface of the core. The active core is manganese tetroxide (Mn3O4) nanoparticles, and the modified shell is a nickel-doped cerium dioxide composite oxide (NiO-CeO2). The molar ratio of Ni to Ce is 0.1:1 to 0.30:1, and the mass ratio of the Mn3O4 nanoparticle core to the (NiO-CeO2) shell is 1:1. The core employs a two-step process. First, a hydrothermal method is used to prepare the Mn3O4 nanoparticle core using manganese nitrate as the manganese source and hexamethylenetetramine as the precipitant. Then, an impregnation-calcination method is used, using nickel acetate and cerium acetate as metal sources and anhydrous ethanol as the solvent, to in-situ coat the (NiO-CeO2) composite oxide shell onto the surface of the Mn3O4 core. The catalyst is then activated by calcination to obtain the target catalyst.

[0020] Includes the following steps: (1) Mn3O4 nanoparticle cores were prepared by hydrothermal method. The manganese source and precipitant were dissolved in deionized water, stirred evenly, and then transferred to a hydrothermal reactor for hydrothermal reaction. After the reaction was completed, the mixture was naturally cooled, centrifuged, washed, and dried to obtain Mn3O4 nanoparticles. Specifically, the preparation of the Mn3O4 nanoparticle core: The manganese source is manganese nitrate, and the precipitant is hexamethylenetetramine (HMT). Dissolve 2-4 g of manganese nitrate and 2 g of hexamethylenetetramine in 50-70 mL of deionized water and stir magnetically at room temperature for 30 min until completely dissolved to obtain a uniform and transparent precursor solution. Transfer the precursor solution to a hydrothermal reactor, seal it, and place it in an oven. Perform a hydrothermal reaction at a temperature of 130-150 °C for 8-10 h. After the reaction is completed, allow it to cool naturally to room temperature. Centrifuge the resulting suspension and wash the precipitate 3-5 times with deionized water until the supernatant is neutral. Then, place the precipitate in an oven and dry it at a temperature of 60-80 °C for 12 h. After grinding, obtain Mn3O4 nanoparticle powder.

[0021] (2) The (NiO-CeO2) shell was coated by impregnation-calcination method. The nickel source and cerium source were dissolved in an alcohol solvent to prepare a uniform metal salt mixed solution. The Mn3O4 nanoparticles prepared in step (1) were added to the mixed solution and ultrasonically dispersed evenly. After that, the mixture was heated to 30°C. o Impregnation treatment is carried out under C conditions; Specifically, the (NiO-CeO2) shell coating: Nickel salt and cerium salt were dissolved in anhydrous ethanol at a Ni to Ce molar ratio of 0.1:1 to 0.3:1 and stirred at room temperature until completely dissolved to prepare a homogeneous metal salt mixed solution. The Mn3O4 nanoparticle powder prepared above was added to the mixed solution and impregnated at 30°C for 6 to 8 hours, with uniform stirring maintained during the impregnation process. The nickel salt was nickel acetate and the cerium salt was cerium acetate.

[0022] (3) Evaporate the solvent from the impregnated suspension, dry the resulting solid powder, calcine it in air atmosphere, and then cool it naturally to obtain the Mn3O4@(NiO-CeO2) core-shell structure catalyst.

[0023] Specifically, the drying and calcination activation process involves placing the impregnated suspension in a water bath and stirring at 80°C until all anhydrous ethanol is removed. The resulting solid powder is then placed in an oven and dried at 80°C for 6–8 hours. Subsequently, the dried powder is placed in a muffle furnace and heated to 350–450°C at a rate of 2–5°C / min in air atmosphere for 3–5 hours to obtain the Mn3O4@(NiO-CeO2) core-shell structure catalyst.

[0024] A Mn3O4@(NiO-CeO2) core-shell structure catalyst was prepared by the above method, wherein the molar ratio of Ni to Ce in the catalyst is 0.1:1 to 0.3:1.

[0025] Application of this catalyst in the catalytic oxidation of formaldehyde, benzene and toluene.

[0026] The catalyst proposed in this invention uses Mn3O4 as the active core and Ni-doped CeO2 to form a (NiO-CeO2) composite oxide as the shell. The preparation method employs a two-step process: hydrothermal synthesis of the core and in-situ coating of the shell using an impregnation-calcination method. The core is prepared using manganese nitrate as the manganese source and hexamethylenetetramine as the slow-release precipitant. The shell coating is completed using nickel acetate and cerium acetate as metal sources and anhydrous ethanol as the solvent. This invention's preparation method is simple and operates under mild conditions. The resulting core-shell catalyst exhibits high conversion rates for the catalytic oxidation of formaldehyde, benzene, and toluene in the low-temperature range, efficiently degrading them into carbon dioxide and water, making it suitable for VOCs purification applications.

[0027] Example 1 A method for preparing a Mn3O4 catalyst includes the following steps: Weigh 3g of manganese nitrate and 2g of hexamethylenetetramine, dissolve them in 60mL of deionized water, and stir at room temperature for 30min until completely dissolved to obtain a homogeneous precursor solution. Transfer the solution to a 100mL hydrothermal reactor, seal it, and place it in an oven for hydrothermal reaction at 140℃ for 9h. After the reaction is completed, allow it to cool naturally to room temperature, centrifuge to separate the precipitate, wash it three times with deionized water until the supernatant is neutral, dry it at 70℃ for 12h, and grind it to obtain Mn3O4 nanoparticle powder, denoted as M1.

[0028] Example 2 A method for preparing a Mn3O4@(NiO-CeO2) core-shell structure catalyst includes the following steps: the preparation of Mn3O4 is consistent with the method used in Example 1.

[0029] According to a Ni:Ce molar ratio of 0.1:1, weigh 0.028 g of nickel acetate and 0.414 g of cerium acetate, dissolve them in 70 mL of anhydrous ethanol, and stir at room temperature until completely dissolved to obtain a mixed solution of metal salts; weigh 0.2 g of Mn3O4 powder and add it to the mixed solution (ultrasonically treat for 25 min to ensure uniform dispersion), then 30 o C. Stir and soak for 7 hours.

[0030] The impregnated suspension was placed in an 80°C water bath and stirred until the anhydrous ethanol was completely removed. The resulting solid powder was dried at 80°C for 7 hours. Subsequently, it was placed in a muffle furnace and heated to 400°C at a rate of 4°C / min under air atmosphere, held at that temperature for 4 hours, and then ground after natural cooling to obtain a Mn3O4@(NiO-CeO2) core-shell structure catalyst, denoted as C1. The molar ratio of Ni to Ce was 0.1:1, and the mass ratio of Mn3O4 to (NiO-CeO2) was 1:1.

[0031] Example 3 A method for preparing a Mn3O4@(NiO-CeO2) core-shell structure catalyst includes the following steps: the preparation of Mn3O4 is consistent with the method used in Example 1.

[0032] According to a Ni:Ce molar ratio of 0.2:1, weigh 0.053 g of nickel acetate and 0.397 g of cerium acetate, dissolve them in 70 mL of anhydrous ethanol, and stir at room temperature until completely dissolved to obtain a mixed metal salt solution; weigh 0.2 g of Mn3O4 powder and add it to the mixed solution (ultrasonically treat for 25 min to ensure uniform dispersion), then 30 o C. Stir and soak for 7 hours.

[0033] The impregnated suspension was placed in an 80°C water bath and stirred until the anhydrous ethanol was completely removed. The resulting solid powder was dried at 80°C for 7 hours. Subsequently, it was placed in a muffle furnace and heated to 400°C at a rate of 4°C / min under air atmosphere, held at that temperature for 4 hours, and then ground after natural cooling to obtain a Mn3O4@(NiO-CeO2) core-shell structure catalyst, denoted as C2. The molar ratio of Ni to Ce was 0.2:1, and the mass ratio of Mn3O4 to (NiO-CeO2) was 1:1.

[0034] Example 4 A method for preparing a Mn3O4@(NiO-CeO2) core-shell structure catalyst includes the following steps: the preparation of Mn3O4 is consistent with the method used in Example 1.

[0035] According to a Ni:Ce molar ratio of 0.3:1, weigh 0.077 g of nickel acetate and 0.382 g of cerium acetate, dissolve them in 70 mL of anhydrous ethanol, and stir at room temperature until completely dissolved to obtain a mixed solution of metal salts; weigh 0.2 g of Mn3O4 powder and add it to the mixed solution (ultrasonically treat for 25 min to ensure uniform dispersion), then 30 o C. Stir and soak for 7 hours.

[0036] The impregnated suspension was placed in an 80°C water bath and stirred until the anhydrous ethanol was completely removed. The resulting solid powder was dried at 80°C for 7 hours. Subsequently, it was placed in a muffle furnace and heated to 400°C at a rate of 4°C / min under air atmosphere, held at that temperature for 4 hours, and then ground after natural cooling to obtain a Mn3O4@(NiO-CeO2) core-shell structure catalyst, denoted as C3. The molar ratio of Ni to Ce was 0.3:1, and the mass ratio of Mn3O4 to (NiO-CeO2) was 1:1.

[0037] Comparative Example 1 The preparation of Mn3O4 is the same as that used in Example 1.

[0038] Weigh 0.397 g of cerium acetate and dissolve it in 70 mL of anhydrous ethanol. Stir at room temperature until completely dissolved to obtain a mixed solution of metal salts. Weigh 0.2 g of Mn3O4 powder and add it to the mixed solution (ultrasonically treat for 25 min to ensure uniform dispersion), then... o C. Stir and soak for 7 hours.

[0039] The impregnated suspension was placed in an 80°C water bath and stirred until the anhydrous ethanol was completely removed. The resulting solid powder was dried at 80°C for 7 hours. Subsequently, it was placed in a muffle furnace and heated to 400°C at a rate of 4°C / min under air atmosphere, held at that temperature for 4 hours, and then ground after natural cooling to obtain the Mn3O4@CeO2 catalyst, denoted as D1. The mass ratio of Mn3O4 to CeO2 was 1:1.

[0040] Catalyst performance testing The catalyst was evaluated in a micro fixed-bed reactor. 50 mg of catalyst (40–60 mesh) was weighed and packed into a U-shaped reaction tube (id = 6 mm). Formaldehyde was generated by passing air (21 vol.% O2 / N2) at a flow rate of 50 mL / min through the U-shaped tube containing paraformaldehyde, or by using a bubbling method to generate benzene and toluene from a benzene and toluene solution. The reaction conditions were: 600 ppm HCHO, 600 ppm benzene or 600 ppm toluene, 50% RH (relative humidity), and a mass hourly space velocity (HHSV) of 60,000 mL g. cat -1 h -1 Analysis was performed using gas chromatography equipped with a flame ionization detector (FID), a thermal conductivity detector (TCD), and a Ni conversion furnace.

[0041] Table 1 shows the performance of different catalysts in catalytic oxidation of formaldehyde, and the performance of different catalysts in catalytic oxidation of benzene. See Table 2. The performance of different catalysts in catalytic oxidation of toluene is shown in Table 3.

[0042] Table 1 Performance of different catalysts in catalytic oxidation of formaldehyde

[0043] Table 2 Performance of different catalysts for catalytic oxidation of benzene

[0044] Table 3 Performance of different catalysts for the catalytic oxidation of toluene

[0045] The data in the table show that the formaldehyde conversion rate of all samples increased with increasing temperature. Mn3O4 (M1) had the lowest activity, with the conversion rate increasing from 24.7% to 71.6% from 20℃ to 60℃. Mn3O4@CeO2 (D1) was slightly higher, increasing from 34.2% to 82.0%. The activity of Mn3O4@(NiO-CeO2) samples was significantly improved, with the Ni / Ce=0.2:1 sample performing the best. The conversion rate reached 72.5% at 20℃, increased to 93.3% at 30℃, and was close to complete conversion (99.9%) at 40℃. It reached 100% at both 50℃ and 60℃. The Ni / Ce=0.3:1 sample was the second best, with a conversion rate of 95.4% at 40℃ and complete conversion at 50℃. The Ni / Ce=0.1:1 sample was relatively low, but still reached 98.7% at 60℃. The overall activity order is “Ni / Ce=0.2:1>Ni / Ce=0.3:1>Ni / Ce=0.1:1>Mn3O4@CeO2>Mn3O4”, indicating that an appropriate amount of NiO has the best synergistic catalytic effect with CeO2 and Mn3O4.

[0046] According to the data in Table 2, the conversion rate of benzene for all catalysts increased with increasing temperature. The sample with a Ni / Ce molar ratio of 0.2:1 showed the best activity: 34.5% conversion at 120℃, rising to 78.9% at 210℃, reaching 92.3% at 240℃, and achieving complete conversion (100%) at 270℃. The sample with a Ni / Ce molar ratio of 0.3:1 was the second best (90.3% at 270℃), followed by the sample with a Ni / Ce molar ratio of 0.1:1 (78.7% at 270℃). Mn3O4 (M1) and Mn3O4@CeO2 (D1) showed the lowest activity, with Mn3O4 showing only 56.8% at 270℃. The overall activity order was Ni / Ce=0.2:1 > Ni / Ce=0.3:1 > Ni / Ce=0.1:1 > Mn3O4@CeO2 > Mn3O4. The reason for this phenomenon can be explained by the characteristics of the (NiO-CeO2) shell formed by Ni-doped CeO2: the shell has abundant oxygen vacancies and excellent oxygen storage and release capabilities. When it is combined with the Mn3O4 core, a strong electronic synergy effect is generated at the interface, which promotes electron transfer and reduces the reaction energy barrier. At the same time, the spatial confinement effect of the shell can inhibit the aggregation of core particles.

[0047] According to the data in Table 3, the conversion rate of toluene for all catalysts increased with increasing temperature, and the activity order was Ni / Ce=0.2:1 > Ni / Ce=0.3:1 > Ni / Ce=0.1:1 > Mn3O4@CeO2 > Mn3O4. The Ni / Ce=0.2:1 sample showed the best conversion rate: 31.0% at 120℃, 71.2% at 210℃, 90.3% at 240℃, and nearly complete (98.9%) at 270℃; Mn3O4@CeO2 (D1) only achieved 58.6% at 270℃. This is because the (NiO-CeO2) shell formed by Ni-doped CeO2 is rich in oxygen vacancies and has a strong oxygen storage and release capacity. When Ni / Ce = 0.2:1, Ni is nearly monolayered on the CeO2 surface, exhibiting the strongest interfacial electronic synergy, promoting electron transfer and reactive oxygen species transport, and significantly reducing the oxidation energy barrier of toluene. Insufficient Ni results in insufficient interfacial activity, while excessive Ni leads to the covering of oxygen vacancies or aggregation. Due to the electron-donating effect of the methyl group, the oxidation activity of toluene falls between that of formaldehyde (high efficiency at room temperature) and benzene (complete conversion at 270℃). Introducing a Mn3O4 core can generate strong interfacial synergy and spatial confinement effects with the shell, further enhancing low-temperature activity and stability.

[0048] Many embodiments and applications beyond the examples provided will be apparent to those skilled in the art upon reading the foregoing description. Therefore, the scope of this teaching should not be determined by reference to the foregoing description, but rather by reference to the foregoing and the full scope of its equivalents. For purposes of completeness, all articles and references, including disclosures in patent applications and publications, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein is not intended as a waiver of that subject matter, nor should it be construed as an indication that the applicant has not considered that subject matter as part of the disclosed inventive subject matter.

[0049] The above content provides a further detailed description of the present invention. It should not be construed that the specific embodiments of the present invention are limited to this. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all such deductions or substitutions should be considered to fall within the defined protection scope of the present invention.

Claims

1. A method for preparing a Mn3O4@(NiO-CeO2) core-shell structured catalyst, characterized in that, Includes the following steps: Manganese source and precipitant were dissolved in water to obtain a precursor solution. The precursor solution was subjected to a hydrothermal reaction. After the reaction was completed, the solution was cooled, separated, washed, and dried to obtain Mn3O4 nanoparticles. Nickel and cerium sources are dissolved in an alcohol solvent to prepare a metal salt mixed solution. The Mn3O4 nanoparticles are then added to the metal salt mixed solution for impregnation to obtain the impregnated material. The impregnated material is evaporated to remove the solvent, resulting in a solid. The solid is then dried and calcined in air. After cooling, a Mn3O4@(NiO-CeO2) core-shell structure catalyst is obtained.

2. The method for preparing a Mn3O4@(NiO-CeO2) core-shell structure catalyst according to claim 1, characterized in that, The amounts of the nickel source and the cerium source are such that the molar ratio of Ni to Ce is (0.1 to 0.3):

1.

3. The method for preparing a Mn3O4@(NiO-CeO2) core-shell structure catalyst according to claim 2, characterized in that, The total amount of the Mn3O4 nanoparticles and the nickel and cerium sources satisfies the following condition: the mass ratio of Mn3O4 to NiO-CeO2 generated after calcination is 1:

1.

4. The method for preparing a Mn3O4@(NiO-CeO2) core-shell structure catalyst according to claim 1, characterized in that, The manganese source is manganese nitrate, and the precipitant is hexamethylenetetramine.

5. The method for preparing a Mn3O4@(NiO-CeO2) core-shell structured catalyst according to claim 1, characterized in that, The nickel source is nickel acetate, the cerium source is cerium acetate, and the alcohol solvent is anhydrous ethanol.

6. The method for preparing a Mn3O4@(NiO-CeO2) core-shell structured catalyst according to claim 1, characterized in that, The hydrothermal reaction was carried out at a temperature of 130℃ to 150℃ for 8 to 10 hours, and then allowed to cool naturally to room temperature after the reaction was completed.

7. The method for preparing a Mn3O4@(NiO-CeO2) core-shell structured catalyst according to claim 1, characterized in that, The immersion treatment is performed at a temperature of 30°C for 6 to 8 hours.

8. The method for preparing a Mn3O4@(NiO-CeO2) core-shell structured catalyst according to claim 1, characterized in that, The drying temperature during the separation, washing, and drying processes is 60℃~80℃, and the drying time is 12h. The solid is dried at a temperature of 60℃ to 80℃ for a time of 6h to 8h. The calcination treatment temperature is 350℃~450℃, the calcination time is 3h~5h, and the heating rate is 2℃ / min~5℃ / min.

9. A Mn3O4@(NiO-CeO2) core-shell structured catalyst, characterized in that, The catalyst was prepared using the method described in any one of claims 1-8 for a Mn3O4@(NiO-CeO2) core-shell structure catalyst.

10. The application of the Mn3O4@(NiO-CeO2) core-shell structure catalyst according to claim 9 in the catalytic oxidation of VOCs.

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