A manganese-nickel doped tricobalt tetraoxide catalyst, its preparation method and use

Abstract

The embodiment of the present application relates to a method for preparing manganese-nickel doped cobalt trioxide (Co3O4) by using ternary hydrotalcite precursor, comprising the following steps: dissolving soluble manganese salt, nickel salt and cobalt salt in water according to certain proportions; dissolving strong alkali and soluble carbonate in water; simultaneously dropping the mixed salt solution and mixed alkali solution into buffer solution, controlling the pH value of the solution to be 10+ / -0.3 during the dropping process, increasing the reaction temperature to 50-80 DEG C after the dropping is completed, and continuing the reaction; after the reaction is completed, washing, separating and drying to obtain hydrotalcite material; calcining the dried cobalt-manganese-nickel ternary hydrotalcite precursor for a period of time to convert into manganese-nickel doped Co3O4. The method realizes uniform doping of manganese-nickel at lattice level, the obtained manganese-nickel doped Co3O4 has high specific surface area, is rich in oxygen vacancies, and has excellent low-temperature catalytic performance on volatile organic compounds such as dimethylbenzene.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a manganese-nickel doped cobalt tetroxide catalyst, its preparation method, and its uses. Background Technology

[0002] Transition metal oxides (such as oxides of cobalt, manganese, and nickel) are widely used in catalytic oxidation, energy storage, and electrocatalysis due to their rich valence state variations and excellent redox properties. Among them, spinel-type cobalt tetroxide (Co3O4) has attracted much attention due to its stable crystal structure and abundant surface active sites. Studies have shown that introducing other transition metal ions into the Co3O4 lattice can modulate its electronic structure and increase the oxygen vacancy concentration, thereby significantly improving its catalytic oxidation performance for volatile organic compounds (VOCs). However, achieving uniform distribution of dopant ions at the atomic scale and avoiding the formation of independent phases or surface enrichment has always been a technical challenge in the field of materials preparation. Traditional doping methods (such as impregnation, co-precipitation, and sol-gel methods) are difficult to precisely control the spatial distribution of dopant ions, often leading to problems such as inhomogeneous doping, agglomeration of active components, and phase separation, ultimately affecting the catalytic performance.

[0003] In recent years, the strategy of preparing doped metal oxides through topological transformation using layered bimetallic hydroxides (LDHs, i.e., hydrotalcite) as precursors has attracted widespread attention. This method can maintain a uniform mixing state of metal ions at the atomic scale, and after calcination, derived oxides with uniformly distributed doped ions are obtained. Previous studies have used CuFe-LDH (CN111569923B) or Ce-CuFe-LDH (CN111569922B) for the catalytic oxidation of VOCs, but their catalytic performance still needs further improvement, and the active components involved are mainly based on Cu and Fe, rather than cobalt-based spinel systems.

[0004] Theoretically, if LDH containing Co, Ni, and Mn metal ions can be used as a precursor, Ni- and Mn-doped Co3O4 materials can be directly obtained through topological transformation. This could fundamentally solve the problem of uneven ion distribution in traditional doping methods and fully leverage the synergistic regulatory effect of Ni and Mn on the electronic structure and oxygen vacancies of Co3O4. However, although Mn 2+ The octahedral deformation rule of the [MO6] element allows octahedral elements to theoretically participate in the formation of stable LDH layers by sharing edges. However, due to the Mn... 2+ With Co 2+ Ni 2+ Significant differences exist in the solubility product (Ksp) during the coprecipitation process, making it difficult for the three ions to precipitate into the same hydrotalcite lattice simultaneously and uniformly.

[0005] There are currently no research reports on the preparation of Ni and Mn co-doped Co3O4 based on cobalt-manganese-nickel ternary pure-phase hydrotalcite. The purpose of this invention is to overcome the problem of difficulty in synchronous and uniform precipitation caused by the difference in solubility product of the three metal ions. Summary of the Invention

[0006] This invention proposes a method for preparing manganese-nickel-doped Co3O4 using cobalt-manganese-nickel ternary hydrotalcite as a precursor. This method can achieve uniform doping of Mn and Ni, resulting in spinel-type Co3O4 materials with high specific surface area and rich in oxygen vacancies.

[0007] This invention utilizes pure-phase cobalt-manganese-nickel ternary layered double hydroxide (TLD) as a precursor. Taking advantage of the atomically uniform distribution of metal ions within the LTD layers, a manganese- and nickel-doped Co3O4 spinel material was successfully prepared by inducing a crystal phase topological transformation in the layer structure through controlled calcination. During the thermal conversion process, due to the highest thermodynamic stability of the Co3O4 spinel phase, Mn and Ni respectively substituted the six-coordinate and four-coordinate Co sites in situ, achieving precise metal ion doping. Simultaneously, interlayer anions were removed in the form of gases such as CO2 and H2O, constructing a rich mesoporous structure in situ. Benefiting from its large specific surface area, stable crystal structure, and the synergistic catalytic effect of oxygen vacancies and multiple metal sites, this material exhibits excellent performance in the catalytic oxidation of volatile organic compounds (VOCs) such as xylene, toluene, and chlorobenzene, especially demonstrating low-temperature catalytic performance.

[0008] The inventors have discovered that pure-phase ternary layered double hydroxides (LDHs) can be formed by using cobalt, nickel, and manganese ions in a specific molar ratio under a particular coprecipitation environment. Maintaining a relatively stable pH in the reaction solution during coprecipitation is crucial to preventing the formation of single-phase impurities from cobalt, nickel, and manganese, thus yielding pure-phase LDHs. This invention uses a buffer solution (preferably an NH3 (0.56 M) - NH4Cl (0.1 M) buffer solution) to maintain a relatively stable pH during the reaction process. A mixed salt solution and a mixed alkali solution are added simultaneously, maintaining the pH of the reaction solution at 10 ± 0.3. After a certain period of nucleus growth, a stable pure-phase cobalt-manganese-nickel ternary LDH material can be formed. Using this LDH material as a precursor, during calcination at 300–500 °C, the lamellar structure undergoes a topological transformation, and Co, Ni, and Mn ions rearrange at the atomic scale, ultimately forming a Co3O4 spinel structure with controllable Mn and Ni doping.

[0009] According to a first aspect of the present invention, a method for preparing manganese-nickel-doped Co3O4 using a ternary hydrotalcite precursor is provided, comprising the following steps: Step (1) Prepare a mixed salt solution: Dissolve soluble manganese salt, nickel salt, and cobalt salt in water at a molar ratio of Co:Ni:Mn = 2:(0.5~1.5):(0.5~1.5), with a total metal ion concentration of 0.3~2.0 mol / L; Step (2) Prepare a mixed alkaline solution: Dissolve the strong base and soluble carbonate in water, and control the concentration of hydroxide ions to be 0.6~4.0 mol / L and the concentration of carbonate ions to be 0.06~0.5 mol / L; Step (3) Coprecipitation reaction: The mixed salt solution and the mixed alkali solution are simultaneously added dropwise to the buffer solution. During the addition process, the pH value of the solution is controlled to be 10±0.3. After the addition is completed, the reaction temperature is raised to 50~80℃ and the reaction continues. Step (4) Separation, washing and drying: The product obtained in step (3) is washed, separated and dried to obtain a pure phase cobalt manganese nickel ternary hydrotalcite precursor; Step (5) High-temperature calcination: The dried cobalt-manganese-nickel ternary hydrotalcite precursor is calcined at 300-500℃ for a period of time to transform it into manganese-nickel doped Co3O4.

[0010] In one embodiment, the manganese salt, nickel salt, and cobalt salt in step (1) are nitrates, chlorides, sulfates, and / or their hydrates.

[0011] In one embodiment, in step (1), the manganese salt is Mn(NO3)2, the nickel salt is Ni(NO3)2·6H2O, and the cobalt salt is Co(NO3)2·6H2O.

[0012] In one embodiment, the strong base in step (2) is NaOH and / or KOH, and the soluble carbonate is Na2CO3.

[0013] In one embodiment, the concentration of hydroxide ions in step (2) is twice the total metal ion concentration in step (1), and the concentration of carbonate ions in step (2) is 0.5 times the manganese ion concentration in step (1).

[0014] In one embodiment, in step (3), the buffer solution is an ammonia-ammonium chloride buffer solution, wherein the concentration of ammonia in the buffer solution is 0.5 mol / L and the concentration of ammonium chloride solution is 0.1 mol / L.

[0015] According to a second aspect of the present invention, the present invention provides a manganese-nickel-doped Co3O4 prepared according to one of the above methods.

[0016] According to a third aspect of the present invention, the present invention provides the use of manganese-nickel doped Co3O4 prepared according to one of the above methods in the catalytic oxidation of volatile organic compounds.

[0017] In one embodiment, the volatile organic compound is xylene, toluene, or chlorobenzene.

[0018] In one embodiment, the volatile organic compound is o-xylene.

[0019] The present invention has the following technical effects: This invention utilizes pure-phase cobalt-manganese-nickel ternary layered double hydroxide (TLD) as a precursor. Taking advantage of the atomically uniform distribution of metal ions within the LTD layers, a manganese- and nickel-doped Co3O4 spinel material was successfully prepared by inducing a crystal phase topological transformation in the layer structure through controlled calcination. During the thermal conversion process, due to the highest thermodynamic stability of the Co3O4 spinel phase, Mn and Ni respectively substituted the six-coordinate and four-coordinate Co sites in situ, achieving precise metal ion doping. Simultaneously, interlayer anions were removed in the form of gases such as CO2 and H2O, constructing a rich mesoporous structure in situ. Benefiting from its large specific surface area, stable crystal structure, and the synergistic catalytic effect of oxygen defects and multiple metal sites, this material exhibits excellent performance in the catalytic oxidation of VOCs such as xylene, toluene, and chlorobenzene, especially at low temperatures.

[0020] (1) Atomic-level uniform doping: XRD results show that the obtained Mn / Ni-Co3O4 material is a single spinel phase, without impurities such as MnO2 or NiO. The cell parameters show a regular change compared to pure Co3O4, achieving atomic-level uniform doping. Specific surface area and electron paramagnetic resonance analysis show that the Mn / Ni-Co3O4 material has a high specific surface area and oxygen defect concentration.

[0021] (2) Excellent catalytic oxidation performance of VOCs: The Mn / Ni-Co3O4 composite material of the present invention exhibits excellent low-temperature catalytic oxidation activity when used for the catalytic oxidation of o-xylene (a representative VOCs pollutant). Ignition temperature (T 10 The temperature at which o-xylene degradation reaches 10% is as low as 110–130°C, and the complete conversion temperature (T) is... 90 At temperatures as low as ~150℃, and after continuous operation at 160℃ for 72 hours, the conversion rate of o-xylene remains greater than 95%. It also exhibits good catalytic oxidation activity for other VOCs such as p-toluene and chlorobenzene.

[0022] (3) The preparation process is simple and easy to scale up: The preparation method of the present invention has a low reaction temperature and short time, adopts co-precipitation and calcination process, does not require precious metals and complex equipment, has low raw material cost, and is suitable for large-scale production. Attached Figure Description

[0023] Figure 1 This is the XRD pattern of Co2NiMn-LDH prepared in Example 1.

[0024] Figure 2 This is a SEM image of Co2NiMn-LDH prepared in Example 1.

[0025] Figure 3 The image shows the XRD pattern of Mn / Ni-Co3O4 prepared in Example 1. Compared with the Co3O4 standard card, its diffraction peaks are shifted to higher angles, proving that Mn / Ni doping causes lattice shrinkage.

[0026] Figure 4 This is a SEM image of the Mn / Ni-Co3O4 prepared in Example 1. After calcination, it still retains to some extent the original sheet-like nanosheet morphology of Co2NiMn-LDH.

[0027] Figure 5 This is the BET diagram of Mn / Ni-Co3O4 prepared in Example 1, which has a certain mesoporous structure and a higher specific surface area compared with ordinary oxides.

[0028] Figure 6 The image shows the EPR spectrum of Mn / Ni-Co3O4 prepared in Example 1, which has a certain oxygen vacancy signal.

[0029] Figure 7 It is the Co2Ni prepared in Example 2 0.5 Mn 0.5 XRD pattern of -LDH.

[0030] Figure 8 This is the XRD pattern of Mn / Ni-Co3O4 prepared in Example 2.

[0031] Figure 9 This is a SEM image of the Mn / Ni-Co3O4 prepared in Example 2.

[0032] Figure 10 It is the Co2Ni prepared in Example 3 1.5 Mn 1.5 XRD pattern of -LDH.

[0033] Figure 11 This is the XRD pattern of Mn / Ni-Co3O4 prepared in Example 3.

[0034] Figure 12 This is a SEM image of the Mn / Ni-Co3O4 prepared in Example 3.

[0035] Figure 13 This is the XRD pattern of Mn / Ni-Co3O4 prepared in Comparative Example 1.

[0036] Figure 14 This is a SEM image of Mn-Co3O4 prepared in Comparative Example 1.

[0037] Figure 15 This is the XRD pattern of Mn-Co3O4 prepared in Comparative Example 2.

[0038] Figure 16 This is a SEM image of Mn-Co3O4 prepared in Comparative Example 2.

[0039] Figure 17 The graphs show the changes in the conversion rate of o-xylene catalytic oxidation as a function of temperature in Examples 1, 2, and 3.

[0040] Figure 18 The graph shows the change in conversion rate of o-xylene oxidation as a function of temperature for comparative examples 1 and 2.

[0041] Figure 19 This is a schematic diagram of the method for preparing manganese-nickel-doped Co3O4 according to an embodiment of the present invention. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. However, those skilled in the art will understand that this invention is not limited to the accompanying drawings and the following embodiments.

[0043] Example 1: Refer to Figure 19 This embodiment provides a method for preparing Mn / Ni-Co3O4 using Co2NiMn-LDH precursor, comprising the following steps: Step (1) Prepare a mixed salt solution (Co: Ni: Mn = 2:1:1): Weigh 15 mmol of Co(NO3)2·6H2O, 7.5 mmol of Ni(NO3)2·6H2O, and 7.5 mmol of Mn(NO3)2 and dissolve them in 30 mL of deionized water, stirring until completely dissolved.

[0044] Step (2) Prepare the mixed alkaline solution: Weigh 60 mmol of NaOH and 3.75 mmol of Na2CO3 and dissolve them in 30 mL of deionized water, stirring until completely dissolved.

[0045] Step (3) Coprecipitation reaction: Place a flask containing 40 mL of a buffer solution of NH3 (0.56 M) - NH4Cl (0.1 M) in a water bath. While stirring at room temperature, add the mixed salt solution from step (1) and the mixed alkali solution from step (2) dropwise to the above dilute ammonia solution. Adjust the water bath temperature to 60℃ and react at a constant temperature for 6 h.

[0046] Step (4) Separation, washing and drying: The product obtained after the reaction in step (3) was separated by centrifugation with deionized water, washed 3 times, and dried in an oven at 60℃ for 8 h to obtain the Co2NiMn-LDH precursor.

[0047] Step (5) High-temperature calcination: The dried Co2NiMn-LDH powder is placed in a muffle furnace and heated to 400℃ at a heating rate of 5℃ / min. It is then calcined in a nitrogen atmosphere for 2 hours and naturally cooled to obtain Mn / Ni-Co3O4 material.

[0048] Figure 1 and Figure 2 The images shown are the XRD and SEM images of the Co2NiMn-LDH prepared in this embodiment. Figure 1 The XRD pattern showed typical diffraction peaks (003), (006) and (009) of the LDH material with carbonate intercalation, proving that the Co2NiMn-LDH material was successfully prepared. Figure 2 This indicates that Co2NiMn-LDH has a relatively uniform nanosheet morphology with a diameter of approximately 200–300 nm. Figure 3 and Figure 4 The images shown are the XRD and SEM images of the Mn / Ni-Co3O4 prepared in this embodiment. Figure 3 The XRD pattern shows a spinel-type Co3O4 diffraction peak, but the diffraction peak is slightly shifted to a higher angle, proving that Mn / Ni doping causes lattice shrinkage. Figure 4 This indicates that Mn / Ni-Co3O4, similar to Co2NiMn-LDH, also exhibits a nanosheet morphology. Figure 5 and Figure 6 The images show the BET and EPR spectra of the Mn / Ni-Co3O4 prepared in this embodiment. Specific surface area and electron paramagnetic resonance analyses indicate that the Mn / Ni-Co3O4 material possesses a high specific surface area and oxygen defect concentration.

[0049] Example 2: This example provides a method using Co2Ni 0.5 Mn 0.5 A method for preparing the same type of Mn / Ni-Co3O4 from -LDH precursor includes the following steps: Step (1) Prepare a mixed salt solution (Co: Ni: Mn = 2: 0.5: 0.5): Weigh 40 mmol of CoCl2·6H2O, 10 mmol of NiCl2·6H2O, and 10 mmol of Mn(NO3)2 and dissolve them in 30 mL of deionized water. Stir until completely dissolved.

[0050] Step (2) Prepare the mixed alkaline solution: Weigh 120 mmol of NaOH and 5 mmol of Na2CO3 and dissolve them in 30 mL of deionized water, stirring until completely dissolved.

[0051] Step (3) Coprecipitation reaction: Place a flask containing 40 mL of NH3 (0.56 M) - NH4Cl (0.1 M) buffer solution in a water bath. While stirring at room temperature, add the mixed salt solution from step (1) and the mixed alkali solution from step (2) dropwise to the above dilute ammonia solution. Adjust the water bath temperature to 80℃ and react at a constant temperature for 6 h.

[0052] Step (4) Separation, washing and drying: The product obtained after the reaction in step (3) was separated by centrifugation with deionized water, washed 3 times, and dried in an oven at 60℃ for 8 h to obtain Co2Ni. 0.5 Mn 0.5 -LDH precursor.

[0053] Step (5) High-temperature calcination: The dried Co2Ni 0.5 Mn 0.5 -LDH powder was placed in a tube furnace and heated to 300°C at a heating rate of 5°C / min. It was then calcined in a nitrogen atmosphere for 2 hours and allowed to cool naturally to obtain Mn / Ni-Co3O4 material.

[0054] Figure 7 It is the Co2Ni prepared in Example 2 0.5 Mn 0.5 XRD pattern of -LDH. Figure 8 This is the XRD pattern of Mn / Ni-Co3O4 prepared in Example 2. Figure 9 This is a SEM image of the Mn / Ni-Co3O4 prepared in Example 2.

[0055] Example 3: This example provides a method using Co2Ni 1.5 Mn 1.5 A method for preparing the same type of Mn / Ni-Co3O4 from -LDH precursor includes the following steps: Step (1) Prepare a mixed salt solution (Co: Ni: Mn = 2: 1.5: 1.5): Weigh 4 mmol of Co(NO3)2·6H2O, 3 mmol of Ni(NO3)2·6H2O, and 3 mmol of Mn(NO3)2 and dissolve them in 30 mL of deionized water, stirring until completely dissolved.

[0056] Step (2) Prepare the mixed alkaline solution: Weigh 20 mmol of NaOH and 1.5 mmol of Na2CO3 and dissolve them in 30 mL of deionized water, stirring until completely dissolved.

[0057] Step (3) Coprecipitation reaction: Place a flask containing 40 mL of NH3 (0.56 M) - NH4Cl (0.1 M) buffer solution in a water bath. While stirring at room temperature, add the mixed salt solution from step (1) and the mixed alkali solution from step (2) dropwise to the above dilute ammonia solution. Adjust the water bath temperature to 50℃ and react at a constant temperature for 6 h.

[0058] Step (4) Separation, washing and drying: The product obtained after the reaction in step (3) was separated by centrifugation with deionized water, washed 3 times, and dried in an oven at 60℃ for 8 h to obtain Co2Ni. 1.5 Mn 1.5 -LDH precursor.

[0059] Step (5) High-temperature calcination: The dried Co2Ni 1.5 Mn 1.5 -LDH powder was placed in a muffle furnace and heated to 500°C at a heating rate of 5°C / min. It was then calcined in a nitrogen atmosphere for 2 hours and allowed to cool naturally to obtain Mn / Ni-Co3O4 material.

[0060] Figure 10 It is the Co2Ni prepared in Example 3 1.5 Mn 1.5 XRD pattern of -LDH. Figure 11 This is the XRD pattern of Mn / Ni-Co3O4 prepared in Example 3. Figure 12 This is a SEM image of the Mn / Ni-Co3O4 prepared in Example 3.

[0061] Comparative Example 1: This comparative example provides a method for coprecipitating Co₂NiMn(OH) using a traditional coprecipitation method. x A method for preparing another type of Mn / Ni-Co3O4 as a precursor includes the following steps: Step (1) Prepare the mixed salt solution: Weigh 15 mmol of Co(NO3)2·6H2O, 7.5 mmol of Ni(NO3)2·6H2O, and 7.5 mmol of Mn(NO3)2 and dissolve them in 50 mL of deionized water, stirring until completely dissolved.

[0062] Step (2) Prepare alkaline solution: Weigh 60 mmol of NaOH and dissolve it in 50 mL of deionized water, stirring until completely dissolved.

[0063] Step (3) Coprecipitation reaction: The metal salt solution prepared in step (1) is placed in a flask in a water bath. Under stirring at room temperature, the alkaline solution in step (2) is added dropwise to the above solution. The water bath temperature is adjusted to 60°C and the reaction is carried out at a constant temperature for 6 hours.

[0064] Step (4) Separation, washing and drying: The product obtained after the reaction in step (3) was separated by centrifugation with deionized water, washed 3 times, and dried in an oven at 60℃ for 8 h to obtain Co2NiMn(OH). x Precursor.

[0065] Step (5) High-temperature calcination: The dried Co2NiMn(OH) x The powder was placed in a muffle furnace and heated to 400°C at a heating rate of 5°C / min. It was then calcined in a nitrogen atmosphere for 2 hours and allowed to cool naturally to obtain another type of Mn / Ni-Co3O4 material.

[0066] Figure 13 This is the XRD pattern of Mn / Ni-Co3O4 prepared in Comparative Example 1. Figure 14 This is a SEM image of Mn-Co3O4 prepared in Comparative Example 1.

[0067] Comparative Example 2: This comparative example provides a method for preparing Mn-Co3O4 using CoMn-LDH precursor, comprising the following steps: Step (1) Prepare a mixed salt solution (Co: Mn = 2: 1): Weigh 15 mmol of Co(NO3)2⋅6H2O and 7.5 mmol of Mn(NO3)2 and dissolve them in 30 mL of deionized water, stirring until completely dissolved.

[0068] Step (2) Prepare the mixed alkaline solution: Weigh 45 mmol of NaOH and 3.75 mmol of Na2CO3 and dissolve them in 30 mL of deionized water, stirring until completely dissolved.

[0069] Step (3) Coprecipitation reaction: Place a flask containing 40 mL of NH3 (0.56 M) - NH4Cl (0.1 M) buffer solution in a water bath. While stirring at room temperature, add the mixed salt solution from step (1) and the mixed alkali solution from step (2) dropwise to the above dilute ammonia solution. Adjust the water bath temperature to 60℃ and react at a constant temperature for 6 h.

[0070] Step (4) Separation, washing and drying: The product obtained after the reaction in step (3) was separated by centrifugation with deionized water, washed 3 times, and dried in an oven at 60℃ for 8 h to obtain the CoMn-LDH precursor.

[0071] Step (5) High-temperature calcination: The dried CoMn-LDH powder is placed in a tube furnace and heated to 400°C at a heating rate of 5°C / min. It is then calcined in a nitrogen atmosphere for 2 hours and naturally cooled to obtain Mn-Co3O4 material.

[0072] Figure 15This is the XRD pattern of Mn-Co3O4 prepared in Comparative Example 2. Figure 16 This is a SEM image of Mn-Co3O4 prepared in Comparative Example 2.

[0073] Catalytic oxidation of o-xylene The catalytic oxidation performance of o-xylene prepared in the test examples and comparative examples includes three steps: preparation of simulated VOCs gas, catalytic oxidation reaction, and detection of reaction products. Specifically, these steps include: Preparation of simulated VOCs gas: Nitrogen gas at a flow rate of 40 mL / min was used as the carrier gas and introduced into a narrow-mouthed bottle containing o-xylene. The nitrogen gas carrying o-xylene vapor was mixed with oxygen at a flow rate of 10 mL / min and then introduced into a high-temperature reactor as the simulated VOCs gas. The concentration of o-xylene carried in the simulated gas could be adjusted by controlling the temperature of the narrow-mouthed bottle containing o-xylene.

[0074] (2) Catalytic oxidation reaction: 0.5 g of catalyst with a particle size of 40-60 mesh is mixed evenly with 1.5 g of quartz sand with a particle size of 40-60 mesh, and loaded into a quartz tube with a diameter of 1 cm. The quartz tube is placed in a horizontal high-temperature reactor with adjustable temperature to simulate the catalytic oxidation reaction of o-xylene by passing VOCs gas through the quartz tube containing the catalyst.

[0075] (3) Detection of reaction products: The gas exiting the high-temperature reactor was passed into a gas chromatograph to detect the concentrations of products such as o-xylene and CO2. Specifically, o-xylene gas was continuously passed into the high-temperature reactor at 80℃ for 2 h to allow the catalyst system to reach o-xylene adsorption equilibrium. The o-xylene equilibrium concentration collected by the gas chromatograph was recorded as the concentration of unreacted o-xylene. Subsequently, the temperature was programmed to rise at a rate of 1℃ / min, and the concentration of o-xylene was measured every 10 min. The activity of the catalyst was evaluated by the degradation rate of o-xylene, where (T 90 Defined as the reaction temperature at which the degradation rate of o-xylene reaches 90%.

[0076] Figure 17 The graphs show the changes in the conversion rate of o-xylene catalytic oxidation as a function of temperature in Examples 1, 2, and 3. Figure 18 The graph shows the change in conversion rate of o-xylene oxidation as a function of temperature for comparative examples 1 and 2.

[0077] Based on the test results, the T values ​​of Mn / Ni-Co3O4 prepared in Examples 1, 2, and 3, and the Mn / Ni-Co3O4 prepared in Comparative Example 1 and Comparative Example 2 for catalytic oxidation of o-xylene were compared. 90 The temperatures were 153℃, 164℃, 164℃, 179℃, and 175℃, respectively. It can be seen that the Mn / Ni-Co3O4 prepared in this invention has excellent low-temperature catalytic performance for volatile organic compounds.

[0078] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing manganese-nickel-doped Co3O4 using a ternary hydrotalcite precursor, characterized in that, Includes the following steps: Step (1) Prepare a mixed salt solution: Dissolve soluble manganese salt, nickel salt, and cobalt salt in water at a molar ratio of Co:Ni:Mn = 2:(0.5~1.5):(0.5~1.5), with a total metal ion concentration of 0.3~2.0 mol / L; Step (2) Prepare a mixed alkaline solution: Dissolve the strong base and soluble carbonate in water, and control the concentration of hydroxide ions to be 0.6~4.0 mol / L and the concentration of carbonate ions to be 0.06~0.5 mol / L; Step (3) Coprecipitation reaction: The mixed salt solution and the mixed alkali solution are simultaneously added dropwise to the buffer solution. During the addition process, the pH value of the solution is controlled to be 10±0.

3. After the addition is completed, the reaction temperature is raised to 50~80℃ and the reaction continues. Step (4) Separation, washing and drying: The product obtained in step (3) is washed, separated and dried to obtain the cobalt-manganese-nickel ternary hydrotalcite precursor; Step (5) High-temperature calcination: The dried cobalt-manganese-nickel ternary hydrotalcite precursor is calcined at 300-500℃ for a period of time to transform it into manganese-nickel doped Co3O4.

2. The method as described in claim 1, characterized in that, The manganese salt, nickel salt, and cobalt salt mentioned in step (1) are nitrates, chlorides, sulfates, and / or their hydrates.

3. The method as described in claim 1, characterized in that, In step (1), the manganese salt is Mn(NO3)2, the nickel salt is Ni(NO3)2·6H2O, and the cobalt salt is Co(NO3)2·6H2O.

4. The method as described in claim 1, characterized in that, The strong base in step (2) is NaOH and / or KOH, and the soluble carbonate is Na2CO3.

5. The method as described in claim 1, characterized in that, The concentration of hydroxide ions in step (2) is twice the total metal ion concentration in step (1), and the concentration of carbonate ions in step (2) is 0.5 times the manganese ion concentration in step (1).

6. The method as described in claim 1, characterized in that, In step (3), the buffer solution is an ammonia-ammonium chloride buffer solution, wherein the concentration of ammonia in the buffer solution is 0.5 mol / L and the concentration of ammonium chloride solution is 0.1 mol / L.

7. A manganese-nickel-doped Co3O4 prepared according to any one of claims 1-6.

8. Use of a manganese-nickel doped Co3O4 prepared according to any one of claims 1-6 in the catalytic oxidation of volatile organic compounds.

9. The use as described in claim 8, characterized in that, The volatile organic compound is xylene, toluene, or chlorobenzene.

10. The use as described in claim 9, characterized in that, The volatile organic compound is o-xylene.

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