Preparation method of ligand recyclable mn-btc derived hollow manganese-based heterojunction catalyst and application thereof in catalytic oxidation of toluene

Abstract

The application belongs to the field of catalytic material synthesis, and relates to a preparation method of a ligand-recyclable Mn-BTC derived hollow manganese-based heterojunction catalyst and application of the catalyst in catalytic oxidation of toluene. The application uses Mn-BTC as a precursor, and realizes ligand recycling and mild shaping of a three-dimensional hollow spherical MnCO3 precursor through a mild alkali treatment-pyrolysis method; and the specific precursor is directionally evolved into a multiple heterojunction with MnO2 and Mn5O8 under a subsequent precisely controlled calcination temperature. Through the whole process of "mild alkali treatment + specific temperature calcination", the application finally realizes the triple effects of "ligand recycling + hollow structure + optimal heterojunction". The heterojunction interface of the catalyst has a lower oxygen vacancy formation energy, which can enhance the adsorption and activation of oxygen, promote the formation of active oxygen species, and accelerate the migration of lattice oxygen, so that efficient catalytic degradation of toluene is realized.

Description

Technical Field

[0001] This invention belongs to the field of catalytic material synthesis, and relates to a method for preparing a ligand-recoverable Mn-BTC-derived hollow manganese-based heterojunction catalyst and its application in the catalytic oxidation of toluene; specifically, it relates to a method for preparing a ligand-recoverable Mn-BTC-derived hollow manganese-based heterojunction catalyst for the catalytic oxidation of toluene and its performance in the application of toluene catalytic oxidation. Background Technology

[0002] With the rapid development of the social economy and the continuous advancement of industrialization, the emissions of volatile organic compounds (VOCs) have been increasing year by year. VOCs, especially aromatic compounds represented by toluene, are not only key precursors to the formation of near-surface ozone, secondary organic aerosols, and photochemical smog, but most also possess high toxicity and carcinogenic, teratogenic, and mutagenic properties, posing a serious threat to the ecological environment and human health. Among numerous VOCs treatment technologies, catalytic oxidation is widely recognized as the most promising VOCs purification technology because it can efficiently and deeply oxidize VOCs into non-toxic and harmless CO2 and H2O at relatively low temperatures without producing secondary pollution. The core of catalytic oxidation technology lies in the degradation performance of the catalyst. Non-precious metal oxide catalysts have become a research hotspot due to their relatively low cost and good thermal stability. Among them, manganese-based catalysts, rich in Mn, are particularly valuable. 2+ / Mn 3+ / Mn 4+ With its multivalent redox couples, excellent oxygen storage capacity, and high lattice oxygen mobility, it shows great potential in the field of VOCs catalytic oxidation.

[0003] In recent years, metal-organic frameworks (MOFs) have been frequently used as self-sacrificing templates or precursors to prepare porous metal oxide catalysts with specific morphologies due to their ultra-high specific surface area, abundant pore structure, and precisely tunable morphology. However, current methods for preparing metal oxides based on MOFs typically employ direct high-temperature calcination. This method not only leads to the complete decomposition and carbonization of expensive organic ligands in MOFs into greenhouse gases, resulting in significant resource waste and extremely poor atom economy, but the violent thermal decomposition process often destroys the original regular structure of MOFs, causing the derivative framework to collapse. Furthermore, the simple calcination process prevents precise control over the crystal phase and oxygen vacancies of the product.

[0004] Regarding existing research on manganese-based catalysts, Liu et al. (Separation and Purification Technology, 2025) improved the catalytic oxidation efficiency of toluene by constructing a Co3O4@MnO2 heterojunction; Zhang et al. (Journal of Hazardous Materials, 2026) reported a Sm-modified MnO2 catalyst. x The catalyst, by constructing a Sm-O-Mn structure, effectively enhanced the low-temperature toluene oxidation activity. Bi et al. (Chemical Engineering Journal, 2024) derived a manganese-based catalyst from Mn-MIL-100 through non-thermal treatment, which improved the toluene oxidation efficiency while enhancing its water resistance. However, these modification methods suffer from problems such as complex preparation processes and expensive doping elements.

[0005] Chinese patent CN113083288B discloses a method for preparing and using a manganese dioxide catalyst for the catalytic oxidation of toluene, but the oxygen vacancy concentration and lattice oxygen activation rate are still insufficient at lower temperatures; Chinese patent CN111479630B discloses a manganese catalyst for the catalytic oxidation of formaldehyde and its preparation and application, but the ignition temperature for the deep oxidation of recalcitrant aromatic VOCs such as toluene is too high; Chinese patent CN113976115B discloses a layered core-shell structure catalyst (CeO2@MnO2-Pt), which has excellent catalytic performance but depends on the precious metal platinum, resulting in high production costs and hindering large-scale industrial applications.

[0006] Among the aforementioned existing technologies, the disclosed manganese-based catalysts all suffer from problems such as unstable catalytic performance, high raw material costs, and complex synthesis methods, resulting in poor prospects for industrial application. Therefore, how to retain the excellent pore structure of MOF-derived catalysts and improve their catalytic performance while achieving efficient recovery and recycling of high-value organic ligands is a pressing technical challenge in this field, and it has significant practical implications for reducing the industrial production cost of catalysts. Summary of the Invention

[0007] In view of the above-mentioned technical problems, this invention provides a method for preparing a ligand-recoverable Mn-BTC-derived hollow manganese-based heterojunction catalyst and its application in the catalytic oxidation of toluene. This invention uses Mn-BTC as a precursor and, through an alkali treatment-pyrolysis method, converts solid blocky Mn-BTC into three-dimensional hollow spherical MnCO3, achieving complete extraction and recovery of the organic ligand H3BTC; further, by controlling the calcination temperature, a highly efficient hollow manganese-based catalyst with multiple heterostructures is obtained.

[0008] To achieve the above objectives, the present invention adopts the following technical solution.

[0009] A method for preparing a ligand-recoverable Mn-BTC derived hollow manganese-based heterojunction catalyst includes the following steps: Step 1: Dissolve pyromellitic acid (H3BTC) and manganese nitrate (Mn(NO3)2) in a solvent and stir until completely dissolved to obtain mixed solution A; Step 2: Transfer the mixed solution A to a polytetrafluoroethylene-lined high-pressure reactor for hydrothermal reaction to obtain white crystals; Step 3: Collect the white crystals and wash them several times with the solvent from Step 1 and anhydrous ethanol, respectively; dry the crystals to obtain a white powder, named Mn-BTC; Step 4: Add Mn-BTC to sodium bicarbonate (NaHCO3) solution and stir at room temperature until completely dissolved to obtain mixed solution B; Step 5: Centrifuge and filter the mixed solution B to obtain filtrate C and filter residue D; adjust the pH of filtrate C with dilute hydrochloric acid, then collect the white solid precipitated in filtrate C, wash it several times with deionized water, and dry it to obtain the recovered organic ligand H3BTC. Step 6: Wash the filter residue D multiple times with deionized water and anhydrous ethanol, respectively; dry the crystals to obtain a brown powder, named xMn; Step 7: Calcine the brown powder xMn in a muffle furnace to obtain the catalyst xMn-T.

[0010] Further, in step 1, the amount of trimesic acid (H3BTC) is 1.0~5.0 parts by mass and the amount of manganese nitrate (Mn(NO3)2) is 1.0~5.0 parts by mass.

[0011] Further, in step 1, the solvent is one of N,N-dimethylformamide (DMF), water, or ethanol, and the amount added is 50-80 parts by volume.

[0012] Furthermore, in step 2, the hydrothermal reaction temperature is 100~200 ℃; the hydrothermal time is 6~24 h.

[0013] Furthermore, in step 3, the sample is washed 1 to 5 times each with the solvent used in step 1 and anhydrous ethanol.

[0014] Furthermore, in step 4, the amount of Mn-BTC added is 0.1~10 parts by mass, the concentration of NaHCO3 solution is 0.1~2.0 mol / L, and the amount added is 50-100 parts by volume.

[0015] Furthermore, in step 5, the concentration of dilute hydrochloric acid is 0.1~5.0 mol / L, the pH value is adjusted to 3~4 with dilute hydrochloric acid, and the product is washed 1~5 times with deionized water.

[0016] Furthermore, in step 6, the sample is washed 1 to 5 times with deionized water and anhydrous ethanol, respectively.

[0017] Furthermore, in step 7, the calcination temperature is 450-550 ℃; the calcination time is 1~12 h.

[0018] The terms "parts by mass" and "parts by volume" are relative units of proportion, with 1 part by mass corresponding to 1 g and 1 part by volume corresponding to 1 mL; in actual preparation, the scale can be scaled up or down proportionally.

[0019] The aforementioned ligand-recoverable Mn-BTC-derived hollow manganese-based heterojunction catalyst is a multi-heterojunction hollow manganese-based catalyst that simultaneously includes multiple manganese oxides such as Mn5O8 and MnO2.

[0020] The catalyst described above has a rich heterogeneous interface composed of Mn5O8 and MnO2, which has a lower oxygen vacancy formation energy.

[0021] The aforementioned ligand-recoverable Mn-BTC-derived hollow manganese-based heterojunction catalysts can be used in toluene catalytic oxidation applications.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention uses Mn-BTC as a precursor and employs a mild alkali treatment-pyrolysis method to achieve both ligand recovery (economic efficiency) and the gentle shaping of a three-dimensional hollow spherical MnCO3 precursor (structural properties). This specific precursor then undergoes a precise calcination process at a controlled temperature, ultimately evolving into a multi-heterojunction possessing both MnO2 and Mn5O8 characteristics (performance-critical). This invention, through a complete process of "mild alkali treatment + specific temperature calcination," ultimately achieves the triple benefits of "ligand recovery + hollow structure + optimal heterojunction."

[0023] The catalyst has a lower oxygen vacancy formation energy at the heterogeneous interface, which can enhance the adsorption and activation of oxygen, promote the formation of active oxygen species, and accelerate the migration of lattice oxygen, thereby achieving efficient catalytic degradation of toluene.

[0024] 2. Regarding the preparation method, this invention has advantages such as controllable conditions, simple synthesis process, and recyclable organic ligand H3BTC. Compared with other manganese-based catalyst synthesis routes, this invention is simple to operate, the raw materials are recyclable, and the preparation cost is low, making it more conducive to industrial scale-up. In addition, the entire synthesis process produces no by-products or pollutants, demonstrating outstanding environmental performance.

[0025] In summary, this invention has significant advantages in raw material recovery, reaction system design, and catalytic efficiency, which can significantly reduce production costs and provide a highly efficient and reliable catalytic material for industrial waste gas purification. Attached Figure Description

[0026] Figure 1 The images show the X-ray diffraction patterns of the catalysts prepared in the embodiments and comparative examples of this invention.

[0027] Figure 2 These are scanning electron microscope (SEM) images of the catalysts prepared in the embodiments and comparative examples of this invention.

[0028] Figure 3 The figures show the toluene catalytic oxidation performance curves of the catalysts prepared in the embodiments and comparative examples of this invention. Detailed Implementation

[0029] The embodiments of the technical solution of this application are described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0030] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0031] To address the challenges of simultaneously achieving low cost, high activity, and simple synthesis in manganese-based catalytic materials, while avoiding the problems of high raw material costs, low reaction efficiency, and complex synthesis processes in existing technologies, this application provides a novel method for synthesizing manganese-based and direct catalytic materials. Using Mn-BTC as a precursor, solid blocky Mn-BTC is converted into three-dimensional hollow spherical MnCO3 through a mild alkali treatment-pyrolysis method; further, by controlling the calcination temperature, a highly efficient hollow manganese-based catalyst with multiple heterostructures is obtained.

[0032] I. Mild Alkali Treatment - Pyrolysis Process NaHCO3 aqueous solution hydrolyzes to produce HCO3- - OH - A mild, weakly alkaline environment was constructed. Under these conditions, the thermodynamic stability of the metal-ligand coordination bonds in Mn-BTC was disrupted, leading to bond breakage and the loss of Mn. 2+ The H3BTC ligand is dissolved and released into the liquid phase, remaining free in the filtrate, and can be efficiently recovered by subsequent acidification. Mn is dissolved. 2+ With CO3 in the system 2- In-situ nucleation generates rhombohedral MnCO3 primary grains; the grains continuously self-assemble and reconstruct, transforming from the original irregular blocky Mn-BTC into hollow spherical MnCO3 intermediates. Controllable etching using a weakly alkaline system enables precise morphology control, while the spherical hollow structure simultaneously widens the channels and increases the specific surface area.

[0033] II. Pyrolysis Process Air calcination experiments were conducted on spherical MnCO3 intermediates at different temperatures: at 200-300℃, only adsorbed water and trace impurities were removed, and the MnCO3 phase was intact. Upon heating to 400℃, MnCO3 underwent stepwise thermal decomposition, releasing CO2. The crystal framework was reconstructed, generating numerous intrinsic lattice defects and initial oxygen vacancies, entering a two-phase transformation transition period. At 500℃, pyrolysis simultaneously generated MnO2 and Mn5O8 crystal phases. The two phases intertwined to form rich heterogeneous interfaces, maintaining the intact hollow spherical framework. CO2 escaped, creating pores and further increasing the specific surface area. The heterogeneous interface regulated electron redistribution, lowered the oxygen vacancy formation energy, promoted the activation of surface-adsorbed oxygen and the migration of lattice oxygen, and enhanced the MnO3 content. 3+ / Mn 4+ The redox cycle ratio is adjusted to significantly enhance the low-temperature oxidation activity of the catalyst. At temperatures exceeding 600℃, Mn5O8 is completely oxidized to Mn2O3, resulting in the collapse of the hollow structure, sintering of the pores, and the disappearance of numerous activity defects. This pyrolysis phase transition mechanism enables the directional construction of a two-phase heterogeneous oxygen-rich vacancy catalytic system, representing a core thermodynamic control method for achieving high activity in low-temperature toluene oxidation. In contrast, if the untreated raw Mn-BTC precursor is directly calcined at 500℃, its organic ligands undergo direct oxidative decomposition, failing to form the MnO2 / Mn5O8 two-phase structure described in this invention, and the resulting product is only a single Mn2O3 phase.

[0034] In the above synthesis process, the H3BTC ligand remains in the filtrate, which can be efficiently recovered through acidification, with no loss or byproduct generation. This results in extremely high atom utilization and effectively reduces catalyst production costs. Simultaneously, the spherical hollow structure increases the catalyst's specific surface area, thereby improving reaction efficiency.

[0035] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0036] The specific preparation method of the Mn-BTC precursor material is as follows: 3.0 g of H3BTC and 4.0 g of Mn(NO3)2·4H2O were weighed and added to 65 mL of DMF, and stirred at room temperature until completely dissolved; the entire mixture was transferred to a high-pressure reactor with a Teflon liner and hydrothermally crystallized at 120 °C for 12 h; the collected white crystals were washed three times each with DMF and anhydrous ethanol; the washed and purified crystals were then dried at 60 °C for 12 h to obtain Mn-BTC.

[0037] Example 1.

[0038] The specific preparation method of 1.0Mn-500 is as follows: 3.0 g of Mn-BTC was weighed and added to 80 mL of 1.0 mol / L NaHCO3 solution. The mixture was stirred at room temperature for 4 h to obtain mixed solution B. Mixed solution B was centrifuged and filtered to obtain filtrate C and filter residue D. Filtrate C was adjusted to pH=3 with 5.0 mol / L dilute hydrochloric acid. The white solid precipitated in filtrate C was then collected and washed three times with deionized water. After drying at 60 °C for 12 h, the recovered organic ligand H3BTC was obtained. Filter residue D was washed three times with anhydrous ethanol and deionized water, respectively, and then dried at 80 °C for 16 h. The resulting brown powder was named 1.0Mn. 1.0Mn was calcined in a muffle furnace at 500 °C for 3 h to obtain catalyst 1.0Mn-500.

[0039] Comparative Example 1.

[0040] The specific preparation method of 1.0Mn-200 is as follows: 3.0 g of Mn-BTC was weighed and added to 80 mL of 1.0 mol / L NaHCO3 solution. The mixture was stirred at room temperature for 4 h to obtain mixed solution B. Mixed solution B was centrifuged and filtered to obtain filtrate C and filter residue D. Filtrate C was adjusted to pH=3 with 5.0 mol / L dilute hydrochloric acid. The white solid precipitated in filtrate C was then collected and washed three times with deionized water. After drying at 60 ℃ for 12 h, the recovered organic ligand H3BTC was obtained. Filter residue D was washed three times with anhydrous ethanol and deionized water, respectively, and then dried at 80 ℃ for 16 h. The resulting brown powder was named 1.0Mn. 1.0Mn was calcined in a muffle furnace at 200 ℃ for 3 h to obtain catalyst 1.0Mn-200.

[0041] Comparative Example 2.

[0042] The specific preparation method of 1.0Mn-700 is as follows: 3.0 g of Mn-BTC was weighed and added to 80 mL of 1.0 mol / L NaHCO3 solution. The mixture was stirred at room temperature for 4 h to obtain mixed solution B. Mixed solution B was centrifuged and filtered to obtain filtrate C and filter residue D. Filtrate C was adjusted to pH=3 with 5.0 mol / L dilute hydrochloric acid. The white solid precipitated in filtrate C was then collected and washed three times with deionized water. After drying at 60 ℃ for 12 h, the recovered organic ligand H3BTC was obtained. Filter residue D was washed three times with anhydrous ethanol and deionized water, respectively, and then dried at 80 ℃ for 16 h. The resulting brown powder was named 1.0Mn. 1.0Mn was calcined in a muffle furnace at 700 ℃ for 3 h to obtain catalyst 1.0Mn-700.

[0043] Comparative Example 3.

[0044] The specific preparation method of 1.0Mn is as follows: 3.0 g of Mn-BTC was weighed and added to 80 mL of 1.0 mol / L NaHCO3 solution. The mixture was stirred at room temperature for 4 h to obtain mixed solution B. Mixed solution B was centrifuged and filtered to obtain filtrate C and filter residue D. Filtrate C was adjusted to pH=3 with 5.0 mol / L dilute hydrochloric acid. The white solid precipitated in filtrate C was then collected and washed three times with deionized water. After drying at 60 ℃ for 12 h, the recovered organic ligand H3BTC was obtained. Filter residue D was washed three times with anhydrous ethanol and deionized water, respectively, and then dried at 80 ℃ for 16 h. The resulting brown powder was named 1.0Mn.

[0045] Comparative Example 4.

[0046] The specific preparation method of Mn-500 is as follows: Weigh 3.0 g of Mn-BTC and calcine it in a muffle furnace at 500 °C for 3 h to obtain catalyst Mn-500.

[0047] The crystal phase structure of the catalytic materials in the examples and comparative examples was characterized using XRD. The XRD patterns are shown below. Figure 1 As shown. The test results show that: Example 1 (1.0Mn-500) contains both MnO2 and Mn5O8 biphases; Comparative Example 1 (1.0Mn-200) has MnCO3 (standard PDF card: 86-0172) as the main phase; the main phase of Comparative Example 2 (1.0Mn-700) is transformed into Mn2O3 (standard PDF card: 24-0508); Comparative Example 3 (1.0Mn) is a rhombohedral MnCO3 (standard PDF card: 86-0172); and Comparative Example 4 (Mn-500) corresponds to the rhombohedral Mn2O3 (standard PDF card: 24-0508). The above results confirm that the calcination temperature of the present invention can effectively control the crystal phase composition of the catalyst and generate multiple heterostructures.

[0048] The microstructure of the catalytic materials in the examples and comparative examples was observed using SEM characterization. SEM images are shown below. Figure 2 As shown in the figures, the observation results indicate that the surface roughness of Example 1 (1.0Mn-500) is significantly increased, exhibiting a lychee-like wrinkled texture; Comparative Example 1 (1.0Mn-200) maintains the original spherical morphology of MnCO3; Comparative Example 2 (1.0Mn-700) shows complete disintegration of the internal rhombohedral substructure, with the original spherical framework collapsing, ultimately forming irregularly aggregated nanoparticles with small particle sizes; Comparative Example 3 (1.0Mn) has a uniform morphology and is a regular spherical shape; Comparative Example 4 (Mn-500) has a layered structure with a size of approximately 4 μm. Based on the above XRD and SEM characterization results, the multiple heterogeneous structures of the catalytic material are confirmed.

[0049] The examples and comparative examples were applied to the catalytic oxidation degradation of toluene, and the catalytic performance of the synthesized catalysts was tested.

[0050] The experiment was conducted on the Zhongjiao Jinyuan CEL-GPPCM micro-thermal catalytic microreactor system: 100 mg of the prepared catalyst was placed into a quartz tube with a diameter of 6 mm. A feed gas consisting of 1000 ppm toluene and 20 vol% O2 balanced with N2 was introduced into the reactor, with a total gas flow rate of 100 mL / min. -1 The corresponding GHSV value is 60,000 mL·g -1 ·h -1 The reaction temperature was programmed to increase from 100℃ to 300℃. Toluene consumption and carbon dioxide production were detected using an online gas chromatograph (GC7900, Ar carrier gas, FID and TCD detectors), and recorded every 20℃.

[0051] The activity test results show that, among all tested samples (Examples and Comparative Examples), the catalyst of Example 2 (1.0Mn-500) exhibits the best low-temperature catalytic oxidation activity for toluene, with a toluene conversion rate reaching 90% at the characteristic temperature T. 90 As low as 196 °C. Compared to Comparative Example 3 (1.0 Mn) and Comparative Example 4 (Mn-500), the T of this catalyst is... 90 Lowering the temperature by 45 °C and 84 °C respectively resulted in a significant improvement in catalytic activity at low temperatures, fully demonstrating that the biphase heterostructure constructed in this process has a significant catalytic enhancement effect on the toluene oxidation reaction.

[0052] Table 1. Results of the toluene catalytic oxidation performance of the catalysts prepared in the examples and comparative examples.

Claims

1. A method for preparing a ligand-recoverable Mn-BTC derived hollow manganese-based heterojunction catalyst, characterized in that, Includes the following steps: Step 1: Dissolve pyromellitic acid and manganese nitrate in a solvent and stir until completely dissolved to obtain mixed solution A; Step 2: Transfer the mixed solution A to a polytetrafluoroethylene-lined high-pressure reactor for hydrothermal reaction to obtain white crystals; Step 3: Collect the white crystals and wash them several times with the solvent from Step 1 and anhydrous ethanol, respectively; dry the crystals to obtain a white powder, named Mn-BTC; Step 4: Add Mn-BTC to the sodium bicarbonate solution and stir at room temperature until completely dissolved to obtain mixed solution B; Step 5: Centrifuge and filter the mixed solution B to obtain filtrate C and filter residue D; adjust the pH of filtrate C with dilute hydrochloric acid, then collect the white solid precipitated in filtrate C, wash it several times with deionized water, and dry it to obtain the recovered organic ligand H3BTC. Step 6: Wash the filter residue D multiple times with deionized water and anhydrous ethanol, respectively; dry the crystals to obtain a brown powder, named xMn; Step 7: Calcine the brown powder xMn in a muffle furnace to obtain the catalyst xMn-T.

2. The method for preparing the heterojunction catalyst according to claim 1, characterized in that, In step 1, the amount of trimesic acid is 1.0 to 5.0 parts by weight, and the amount of manganese nitrate is 1.0 to 5.0 parts by weight.

3. The method for preparing the heterojunction catalyst according to claim 1, characterized in that, In step 1, the solvent is one of N,N-dimethylformamide, water, or ethanol, and the amount added is 50-80 parts by volume.

4. The method for preparing the heterojunction catalyst according to claim 1, characterized in that, In step 2, the hydrothermal reaction temperature is 100~200 ℃; the hydrothermal time is 6~24 h.

5. The method for preparing the heterojunction catalyst according to claim 1, characterized in that, In step 3, the sample is washed 1 to 5 times each with the solvent used in step 1 and anhydrous ethanol.

6. The method for preparing the heterojunction catalyst according to claim 1, characterized in that, In step 4, the amount of Mn-BTC added is 0.1 to 10 parts by mass, the concentration of sodium bicarbonate solution is 0.1 to 2.0 mol / L, and the amount added is 50 to 100 parts by volume.

7. The method for preparing the heterojunction catalyst according to claim 1, characterized in that, In step 5, the concentration of dilute hydrochloric acid is 0.1~5.0 mol / L, the pH value is adjusted to 3~4 with dilute hydrochloric acid, and the water is washed 1~5 times with deionized water.

8. The method for preparing the heterojunction catalyst according to claim 1, characterized in that, In step 6, the sample is washed 1 to 5 times with deionized water and anhydrous ethanol, respectively.

9. The method for preparing the heterojunction catalyst according to claim 1, characterized in that, In step 7, the calcination temperature is 450~550 ℃; the calcination time is 1~12 h.

10. The application of a ligand-recoverable Mn-BTC-derived hollow manganese-based heterojunction catalyst as described in any of the preceding claims in the catalytic oxidation of toluene.

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