Preparation method and application of two-dimensional flaky MOF (Metal Organic Framework) material containing variable valence transition metal

Abstract

The invention belongs to the field of heterogeneous catalysis, and discloses a preparation method and application of a two-dimensional flaky MOF material containing variable valence transition metal. The preparation method comprises the following steps: mixing a solution of a variable valence transition metal source of a vanadium source, a molybdenum source, an iron source or a cerium source with a solution containing imidazole organic ligands, and then reacting by a temperature-controlled solvothermal method to obtain M-MOF-T. Precise regulation and control of the mixed valence state of metal ions are achieved by regulating and controlling the solvothermal temperature, a vanadium-based MOF product forms a high-crystallinity two-dimensional sheet structure, and other metal-based MOF products all have highly-dispersed mixed valence state active centers. The catalyst shows excellent catalytic activity and selectivity on sulfur-containing compounds such as DBT, 4-MDBT and the like in fuel oil in a system taking ionic liquid [Bmim] BF as an extraction / reaction medium, the desulfurization rate of the vanadium-based catalyst on the DBT within 30 minutes reaches 100%, and the desulfurization rates of the molybdenum-based catalyst, the iron-based catalyst and the cerium-based catalyst exceed 78%; the reaction conditions are mild, the catalyst and the ionic liquid can be synchronously recycled, the process is simple, efficient and environment-friendly, and the industrial application potential is remarkable.

Description

Technical Field

[0001] This invention belongs to the field of heterogeneous catalysis, specifically referring to a method for preparing a two-dimensional sheet-like MOF material containing a variable-valence transition metal and its application in fuel oil oxidative desulfurization. Background Technology

[0002] In the global energy structure, oil, as a traditional core energy source, remains irreplaceable. However, sulfur compounds in fuel oil (such as dibenzothiophene) generate sulfur oxides (SO₄) during combustion. x These sulfur oxides not only cause serious environmental problems such as acid rain and smog, disrupting the ecological balance, but also harm the human respiratory and cardiovascular systems, threatening public health. As countries increasingly prioritize ecological environment and public health, standards for limiting sulfur content in fuel oil are becoming increasingly stringent. Developing efficient technologies capable of deep desulfurization and meeting the production requirements of ultra-low sulfur fuel oil has become a key research topic in the energy and environmental protection fields.

[0003] Oxidative desulfurization (ODS) technology is considered one of the most promising desulfurization technologies for industrial application due to its mild reaction conditions (no high temperature and pressure required), lack of hydrogen consumption, and excellent removal efficiency for recalcitrant sulfur compounds such as DBT. It has become a research hotspot in recent years. Currently, catalysts in oxidative desulfurization mainly include ionic liquids, metal-organic frameworks (MOFs), metal oxides, and polyoxometalates. Among them, MOF materials, with their abundant metal active centers, high porosity, tunable structure, and large specific surface area, have shown significant potential in desulfurization applications. The redox properties of metal elements provide new insights for optimizing the performance of MOF catalysts. Variable valence transition metals (vanadium, molybdenum, iron, cerium) are preferred components for the active centers of MOF materials due to their diverse valence transformation capabilities: vanadium has V... 4+ / V 5+ Price state pair, V 5+ It can effectively activate hydrogen peroxide (H2O2) to generate hydroxyl radicals (·OH); molybdenum is present. 6+ / Mo 5+ Valence state transitions, with higher valence species exhibiting strong catalytic activity for the oxidation of sulfides; iron (Fe) 2+ / Fe 3+ Valence cycle can promote electron transfer; Ce of cerium 3+ / Ce 4+ Valence state changes can enhance the regeneration capacity of active sites. Studies have confirmed that these variable valence metal centers can act as catalytic active sites and promote electron transfer. By precisely controlling the valence state of the node metals in MOFs, the formation of unsaturated active sites can be directionally induced, optimizing the adsorption energy barrier for sulfur species, thereby synergistically improving the efficiency of oxidative desulfurization.

[0004] Based on the above mechanism, this invention employs a temperature-controlled solvothermal method to successfully design and synthesize two-dimensional layered MOF materials containing variable valence transition metals such as vanadium / molybdenum. Metal ions are precisely immobilized in a mixed valence state within the MOF framework as active centers. By optimizing the synthesis temperature, the proportion of high-valence metal ions can be precisely controlled. The resulting MOF product exhibits a highly crystalline two-dimensional sheet-like structure. Other metal-based MOF products also possess mixed valence active centers, demonstrating excellent catalytic performance in oxidative desulfurization. Currently, no related reports have been found. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing two-dimensional sheet-like MOF materials containing variable-valence transition metals.

[0006] Another object of the present invention is to provide the application of the above-mentioned materials and to demonstrate their excellent performance in catalytic oxidative desulfurization.

[0007] A method for preparing a two-dimensional sheet-like MOF material containing a variable-valence transition metal includes the following steps: (1) Dissolve a variable valence transition metal source in a solvent at room temperature and stir until completely dissolved to obtain a metal solution; (2) Dissolve the imidazole organic ligand in a solvent at room temperature and stir until completely dissolved to obtain a ligand solution; (3) Add the metal solution from step (1) dropwise to the ligand solution obtained in step (2) and mix thoroughly; (4) Place the solution obtained in step (3) into an ultrasonic device and sonicate for 30 to 60 minutes until flocculent matter appears to obtain a precursor dispersion. (5) Transfer the precursor solution from step (4) to a high-pressure reactor lined with polytetrafluoroethylene, seal it, and place it in an oven for a solvothermal reaction. (6) Filter the reaction system of step (5), wash it several times with deionized water and ethanol, dry it under vacuum, and grind it to obtain powder M-MOF-T; that is, two-dimensional sheet MOF material containing variable valence transition metal; where M is the transition metal corresponding to the metal source and T is the solvothermal reaction temperature.

[0008] In step (1), the variable valence transition metal source is selected from vanadium, molybdenum, iron, or cerium sources; specifically, it is VOSO4·xH2O, VCl3, or (NH4)6Mo7O. 24 , FeCl3, or Ce(NO3)3.

[0009] In step (2), the imidazole organic ligand is one of imidazole, dimethylimidazolium, and benzimidazole.

[0010] In steps (1) and (2), the solvent is selected from one or a mixture of several of N,N-dimethylformamide (DMF), N,N-diethylformamide (DEF), methanol, and water.

[0011] In step (3), the molar ratio of the imidazole organic ligand to the variable valence transition metal source is 0.5:1 to 16:1, preferably one of 0.5:1, 1:1, or 4:1.

[0012] In step (5), the temperature of the solvothermal reaction is 30~180℃, preferably 120℃, and the reaction time is maintained at 4~72 hours, preferably 24 hours.

[0013] In step (6), the vacuum drying temperature is 80℃ and the time is 6 h.

[0014] The MOF material containing a variable valence transition metal prepared in this invention is mainly used for the catalytic oxidative desulfurization of petroleum products to remove sulfur-containing compounds. Its application is primarily in the catalytic oxidative removal of aromatic sulfides (such as dibenzothiophene) and aliphatic sulfides from fuel oil. This reaction process can be represented by the following formula:

[0015] The two-dimensional sheet-like MOF material containing variable-valence transition metal of the present invention has a high desulfurization rate for different sulfur-containing substrates in oil. Among them, the vanadium-based catalyst has the best performance due to its two-dimensional structure. It can achieve a desulfurization rate of 98.4% for aromatic sulfides: 4-methyldibenzothiophene (4-MDBT) within 1 hour and 100% for DBT within 30 minutes.

[0016] The two-dimensional sheet-like MOF material containing a variable-valence transition metal of the present invention exhibits high catalytic activity for the removal of sulfur-containing compounds from oil products. Its excellent activity is mainly attributed to the following factors: (1) Vanadium-based MOF products have a two-dimensional sheet structure, which effectively alleviates the micropore diffusion limitation, facilitates the rapid diffusion and contact of large sulfur-containing compounds, and improves substrate accessibility; other metal-based MOF materials also ensure mass transfer efficiency due to their high specific surface area and open pore structure.

[0017] (2) In all MOF materials, active metal ions are highly dispersed and uniformly distributed, maximizing the exposure of high-valence active sites (such as V). 5+ Mo 6+ Fe 3+ Ce 4+ This significantly enhances the intrinsic catalytic activity and structural stability.

[0018] (3) This invention employs a temperature-controlled solvothermal method, adaptable to various variable valence transition metal sources such as vanadium, molybdenum, iron, and cerium. The preparation process is simple, efficient, and low-cost, achieving efficient utilization of metal resources. The obtained MOF catalysts all possess mixed valence metal active centers, which synergistically interact with ionic liquids. They can not only efficiently adsorb and enrich sulfur-containing substrates, but also achieve simultaneous recovery and recycling of the catalyst and ionic liquid through simple separation, demonstrating promising prospects for industrial applications. Attached Figure Description

[0019] Figure 1 Scanning electron microscope image of V-MOF-120; Figure 2 X-ray diffraction patterns of V-MOFs prepared at different temperatures; Figure 3 Results of the catalytic activity of V-MOF-120 on different sulfur-containing substrates; Figure 4 Cyclic voltammetry curves of V-MOFs prepared at different temperatures; Figure 5 The image shows the X-ray photoelectron spectra of V 2p under different conditions of the catalyst. Detailed Implementation

[0020] The invention will now be further described in conjunction with the accompanying drawings and specific examples.

[0021] Example 1

[0022] A method for preparing vanadium valence-optimized MOF materials includes the following steps: 1) Weigh 0.195 g (2 mmol) of vanadium oxysulfate into a beaker, add 15 mL of deionized water, and stir at 600 rpm until dissolved to obtain a metal solution.

[0023] 2) Weigh 0.098 g (2 mmol) of 2-methylimidazole into a beaker, add 15 mL of deionized water, and stir at 600 rpm until dissolved.

[0024] 3) Add the metal solution dropwise to the organic ligand solution and stir at 600 rpm for 5 min until well mixed.

[0025] 4) Place the mixed solution into an ultrasonic device and sonicate for 30 minutes to obtain a blue-white flocculent substance, i.e., the precursor dispersion.

[0026] 5) Transfer the precursor dispersion to a high-pressure reactor lined with polytetrafluoroethylene, seal it, and place it in an oven at 120°C for 24 h.

[0027] 6) Filter the reaction system, wash it three times each with deionized water and ethanol, dry it under vacuum at 80°C for 6 h, and grind it to obtain powder V-MOF-120.

[0028] Figure 1 The image shows a scanning electron microscope (SEM) image of V-MOF-120. As can be seen, the obtained material exhibits a typical two-dimensional sheet-like morphology, with individual sheets approximately 5 μm in length, 1 μm in width, and relatively thin, displaying significant anisotropy. Multiple sheet-like structures aggregate in a disordered or staggered manner, forming loosely porous layered aggregates. This sheet-like stacking structure facilitates the exposure of abundant active sites and provides channels for the diffusion and mass transfer of reactant molecules, thereby contributing to improved performance in applications such as catalytic oxidative desulfurization.

[0029] Example 2

[0030] A method for preparing vanadium valence-optimized MOF materials includes the following steps: Steps 1) to 4) are the same as in Example 1.

[0031] 5) Transfer the precursor dispersion to a high-pressure reactor lined with polytetrafluoroethylene, seal it, and place it in an oven at 30°C for 24 h.

[0032] 6) Filter the reaction system, wash it three times each with deionized water and ethanol, dry it under vacuum at 80°C for 6 h, and grind it to obtain powder V-MOF-30.

[0033] Example 3

[0034] A method for preparing vanadium valence-optimized MOF materials includes the following steps: Steps 1) to 4) are the same as in Example 1.

[0035] 5) Transfer the precursor dispersion to a high-pressure reactor lined with polytetrafluoroethylene, seal it, and place it in an oven at 80°C for 24 h.

[0036] 6) Filter the reaction system, wash it three times each with deionized water and ethanol, dry it under vacuum at 80°C for 6 h, and grind it to obtain powder V-MOF-80.

[0037] Example 4

[0038] A method for preparing vanadium valence-optimized MOF materials includes the following steps: Steps 1) to 4) are the same as in Example 1.

[0039] 5) Transfer the precursor dispersion to a high-pressure reactor lined with polytetrafluoroethylene, seal it, and place it in an oven at 150°C for 24 h.

[0040] 6) Filter the reaction system, wash it three times each with deionized water and ethanol, dry it under vacuum at 80°C for 6 h, and grind it to obtain powder V-MOF-150.

[0041] Example 5

[0042] A method for preparing vanadium valence-optimized MOF materials includes the following steps: Steps 1) to 4) are the same as in Example 1.

[0043] 5) Transfer the precursor dispersion to a high-pressure reactor lined with polytetrafluoroethylene, seal it, and place it in an oven at 180°C for 24 h.

[0044] 6) Filter the reaction system, wash it three times each with deionized water and ethanol, dry it under vacuum at 80°C for 6 h, and grind it to obtain powder V-MOF-180.

[0045] Figure 2 The X-ray diffraction patterns of V-MOF-120, V-MOF-80, and V-MOF-150 prepared in Examples 1, 3, and 4 of this invention are shown. As can be seen from the figures, all three samples exhibit consistent characteristic diffraction peaks at the same diffraction angle (2θ), indicating that they have the same crystal structure, confirming the successful synthesis of the target vanadium-based two-dimensional sheet-like MOF material. Furthermore, the diffraction peak intensity gradually increases with increasing solvothermal reaction temperature, indicating that the crystallinity of the product increases with temperature. Notably, although V-MOF-150 has the highest crystallinity, catalytic oxidation desulfurization performance tests show that V-MOF-120 (120℃) exhibits the best catalytic activity. This indicates that moderate crystallinity combined with a good sheet-like morphology and the synergistic effect of mixed-valence vanadium centers is more conducive to exposing active sites and promoting reactant mass transfer, thereby achieving the highest desulfurization efficiency.

[0046] Example 6

[0047] A method for preparing vanadium valence-optimized MOF materials includes the following steps: 1) Weigh 0.195 g (2 mmol) of vanadium oxysulfate into a beaker, add 15 mL of deionized water, and stir at 600 rpm until dissolved to obtain a metal solution.

[0048] 2) Weigh 0.049 g (1 mmol) of 2-methylimidazole into a beaker, add 15 mL of deionized water, and stir at 600 rpm until dissolved to obtain a ligand solution (ligand to metal source molar ratio 0.5:1).

[0049] Steps 3) to 6) are the same as in Example 1, and powder V-MOF-120-R0.5 is obtained (R is the molar ratio of ligand to metal).

[0050] Example 7

[0051] A method for preparing vanadium valence-optimized MOF materials includes the following steps: 1) Weigh 0.195 g (2 mmol) of vanadium oxysulfate into a beaker, add 15 mL of deionized water, and stir at 600 rpm until dissolved to obtain a metal solution.

[0052] 2) Weigh 0.392 g (8 mmol) of 2-methylimidazole into a beaker, add 15 mL of deionized water, and stir at 600 rpm until dissolved to obtain a ligand solution (ligand to metal source molar ratio 4:1).

[0053] Steps 3) to 6) are the same as in Example 1, and powder V-MOF-120-R4 is obtained.

[0054] Example 8

[0055] A method for preparing vanadium valence-optimized MOF materials includes the following steps: 1) Weigh 0.195 g (2 mmol) of vanadium oxysulfate into a beaker, add 15 mL of deionized water, and stir at 600 rpm until dissolved to obtain a metal solution.

[0056] 2) Weigh 0.784 g (16 mmol) of 2-methylimidazole into a beaker, add 15 mL of deionized water, and stir at 600 rpm until dissolved to obtain a ligand solution (ligand to metal source molar ratio 8:1).

[0057] Steps 3) to 6) are the same as in Example 1, and powder V-MOF-120-R8 is obtained.

[0058] Example 9

[0059] A method for preparing a molybdenum valence-optimized MOF material includes the following steps: 1) Weigh 0.228 g (0.286 mmol) of ammonium molybdate ((NH4)6Mo7O 24 Add 15 mL of DMF to a beaker and stir at 600 rpm until dissolved to obtain a metal solution.

[0060] 2) Weigh 0.098 g (2 mmol) imidazole into a beaker, add 15 mL DMF, and stir at 600 rpm until dissolved to obtain the ligand solution.

[0061] 3) Add the metal solution dropwise to the ligand solution and stir at 600 rpm for 5 min until well mixed.

[0062] 4) Place the mixed solution in an ultrasonic device and sonicate for 30 minutes to obtain a light yellow flocculent substance, which is the precursor dispersion.

[0063] 5) Transfer the precursor dispersion to a high-pressure reactor lined with polytetrafluoroethylene, seal it, and place it in an oven at 120 °C for 24 h.

[0064] 6) The post-processing steps are the same as in Example 1 to obtain powdered Mo-MOF-120.

[0065] Example 10

[0066] A method for preparing an iron valence state optimized MOF material includes the following steps: 1) Weigh 0.325 g (2 mmol) of ferric chloride (FeCl3) into a beaker, add a mixed solvent of 10 mL methanol and 5 mL deionized water, and stir at 600 rpm until dissolved to obtain a metal solution.

[0067] 2) Weigh 0.118 g (2 mmol) of benzimidazole into a beaker, add a mixed solvent of 10 mL methanol and 5 mL deionized water, and stir at 600 rpm until dissolved to obtain the ligand solution.

[0068] Steps 3) to 6) are the same as in Example 1, and Fe-MOF-120 powder is obtained.

[0069] Example 11

[0070] A method for preparing a cerium valence-optimized MOF material includes the following steps: 1) Weigh 0.868 g (2 mmol) of cerium nitrate (Ce(NO3)3) into a beaker, add 15 mL of DEF, and stir at 600 rpm until dissolved to obtain a metal solution.

[0071] 2) Weigh 0.098 g (2 mmol) of 2-methylimidazole into a beaker, add 15 mL of DEF, and stir at 600 rpm until dissolved to obtain the ligand solution.

[0072] Steps 3) to 6) are the same as in Example 1, and Ce-MOF-120 powder is obtained.

[0073] Example 12

[0074] In a homemade double-necked flask equipped with a reflux condenser, 10 mg of the target MOF catalyst (V-MOF-120, Mo-MOF-120, Fe-MOF-120, and Ce-MOF-120 prepared in Examples 1, 9, 10, and 11, respectively), 24 μL of H2O2 (30%), 1 mL of [BMIM]BF4, and 5 mL of DBT model oil with a sulfur content of 500 ppm were added. The reaction was carried out in a water bath with stirring at 30 °C. After the reaction was completed, the solution was allowed to stand until the catalyst completely precipitated to the bottom layer of the oil. The upper oil phase was then collected, and the sulfur content in the oil was quantitatively analyzed by GC.

[0075] Taking dibenzothiophene (DBT) as an example, the reaction formula is: ;

[0076] Figure 3 The figures show the catalytic activity of V-MOF-120 prepared in Example 1 on different sulfur-containing substrates. As can be seen from the figures, under mild reaction conditions, V-MOF-120 exhibits extremely high catalytic activity for dibenzothiophene (DBT), achieving a 100% desulfurization rate within 30 minutes. For 4-MDBT, which has some steric hindrance, the desulfurization rate still reaches 98.4% within 1 hour, demonstrating good substrate adaptability. However, for 4,6-dimethyldibenzothiophene (4,6-DMDBT), which has stronger steric hindrance, the desulfurization rate is less than 50%, indicating that molecular size and substituent steric hindrance have a certain influence on reaction efficiency. These results demonstrate that V-MOF-120, with its two-dimensional plate-like open structure, can effectively promote the adsorption and oxidation of moderately sterically hindered sulfides, and is particularly suitable for fuel systems mainly composed of DBT and 4-MDBT, showing significant potential in deep desulfurization applications.

[0077] Figure 4 The figure shows the cyclic voltammetry curves of V-MOFs prepared at different temperatures. It can be seen from the figure that, at the same scan rate, all three samples exhibit a pair of reversible redox peaks in the potential range of approximately -1 to -1.4 V (vs. Ag / AgCl), corresponding to V... 4+ / V 5+The reversible redox process of the vanadium redox couple was observed. V-MOF-120 exhibited the most significant oxidation and reduction peak currents, with the smallest peak potential difference, indicating the fastest electron transfer kinetics and the highest electrochemical activity. In contrast, V-MOF-80 showed weaker redox peaks, suggesting a lower mixed valence state ratio or insufficient crystallinity leading to limited exposure of active sites. While V-MOF-150 had high crystallinity, its redox current was lower than that of V-MOF-120, possibly related to its overly dense lamellar stacking or excessive aggregation of high-valence vanadium species, which is detrimental to interfacial electron transfer. These results confirm that 120℃ is the optimal synthesis temperature for achieving synergistic improvement in vanadium valence state optimization and electron conductivity, consistent with the activity of V-MOF-120 in ODS.

[0078] Figure 5 The figures show the X-ray photoelectron spectra of the catalyst at different V 2p states. As can be seen from the figures, all samples at V 2p... 3 / 2 The regions all exhibit two distinct characteristic peaks, which are attributed to V. 4+ and V 5+ This confirms that vanadium exists in the material in a mixed valence state. Combined with the XPS fitting data in Table 1, it can be seen that as the synthesis temperature increases from 80℃ to 120℃, V... 5+ The proportion of vanadium in the total vanadium content increases significantly; and when the temperature further rises to 150℃, V 5+ The proportion decreased slightly. This trend indicates that 120 °C is the optimal temperature for regulating the vanadium valence state towards higher reactivity (V). 5+ The optimal synthesis temperature for enrichment. Due to V 5+ The site has a stronger activation ability for H2O2, so V-MOF-120 exhibits the best oxidative desulfurization performance, which is highly consistent with the catalytic activity test results.

[0079] Table 1 shows the peak area ratio V of the fitted XPS spectra of the catalyst under different states. 5+ / (V 5+ +V 4+ ) Determined V 5+ Relative species content

[0080]

[0081] Table 2. Catalytic activity of catalysts synthesized under different conditions for DBT oxidation

Claims

1. A method for preparing a two-dimensional sheet-like MOF material containing a variable-valence transition metal, characterized in that, Includes the following steps: (1) Dissolve a variable valence transition metal source in a solvent at room temperature and stir until completely dissolved to obtain a metal solution; (2) Dissolve the imidazole organic ligand in a solvent at room temperature and stir until completely dissolved to obtain a ligand solution; (3) Add the metal solution from step (1) dropwise to the ligand solution obtained in step (2) and mix thoroughly; (4) Place the solution obtained in step (3) into an ultrasonic device and sonicate for 30-60 min until flocculent matter appears to obtain a precursor dispersion. (5) Transfer the precursor solution from step (4) to a high-pressure reactor lined with polytetrafluoroethylene, seal it, and place it in an oven for a solvothermal reaction. (6) The reaction system of step (5) was filtered, washed several times with deionized water and ethanol, dried under vacuum, and ground to obtain a two-dimensional sheet MOF material containing a variable valence transition metal.

2. The method for preparing a two-dimensional sheet-like MOF material containing a variable-valence transition metal as described in claim 1, characterized in that, In step (1), the variable valence transition metal source is selected from vanadium, molybdenum, iron, or cerium sources; specifically, it is VOSO4·xH2O, VCl3, or (NH4)6Mo7O. 24 , FeCl3, or Ce(NO3)3.

3. The method for preparing a two-dimensional sheet-like MOF material containing a variable-valence transition metal as described in claim 1, characterized in that, In step (2), the imidazole organic ligand is one of imidazole, dimethylimidazolium, and benzimidazole.

4. The method for preparing a two-dimensional sheet-like MOF material containing a variable-valence transition metal as described in claim 1, characterized in that, In steps (1) and (2), the solvent is selected from one or a mixture of several of N,N-dimethylformamide DMF, N,N-diethylformamide DEF, methanol, and water.

5. The method for preparing a two-dimensional sheet-like MOF material containing a variable-valence transition metal as described in claim 1, characterized in that, In step (3), the molar ratio of imidazole organic ligands to variable valence transition metal sources is 0.5:1 to 16:

1.

6. The method for preparing a two-dimensional sheet-like MOF material containing a variable-valence transition metal as described in claim 5, characterized in that, In step (3), the molar ratio of the imidazole organic ligand to the variable valence transition metal source is 0.5:1, 1:1, or 4:

1.

7. The method for preparing a two-dimensional sheet-like MOF material containing a variable-valence transition metal as described in claim 1, characterized in that, In step (5), the temperature of the solvothermal reaction is 30~180℃ and the reaction time is maintained at 4~72 hours.

8. The method for preparing a two-dimensional sheet-like MOF material containing a variable-valence transition metal as described in claim 7, characterized in that, In step (5), the temperature of the solvothermal reaction is 120°C and the reaction time is 24 h.

9. The method for preparing a two-dimensional sheet-like MOF material containing a variable-valence transition metal as described in claim 1, characterized in that, In step (6), the vacuum drying temperature is 80℃ and the time is 6 h.

10. The application of the two-dimensional sheet-like MOF material containing a variable-valence transition metal prepared by the preparation method according to any one of claims 1 to 9 in the oxidative desulfurization of fuel oil.

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