A monatomic solvent derived from MOF-5 and a preparation method thereof

Abstract

The application discloses MOF-5 derived single-atom solvent and a preparation method thereof, and belongs to the technical field of nano catalytic materials and liquid catalytic preparation. The preparation method uses MOF-5 as a zinc source and a structure template, in-situ dopes a target metal salt, and through one-step high-temperature pyrolysis and a zinc component volatilization strategy, a metal single-atom highly-dispersed nitrogen-doped carbon-based solid material is prepared; the material is further dispersed in a suitable solvent, and is subjected to homogenization treatment to form a highly-stable MOF-5 derived single-atom solvent which can be stored for a long time. The method utilizes the unique high porosity and uniform metal distribution characteristics of MOF-5, and combines the zinc species volatility under high temperature, so that efficient anchoring and stable dispersion of various metal single atoms are realized, the process is simple, and the universality is strong, and the method provides a new way for controllable preparation of a high-performance single-atom liquid catalytic system.

Description

Technical Field

[0001] This invention belongs to the field of nanocatalytic materials and liquid catalytic agents, specifically relating to a MOF-5 derived single-atom solvent and its preparation method. Background Technology

[0002] Single-atom catalysts have attracted widespread attention due to their limiting atom utilization and excellent catalytic performance. Metal-organic frameworks (MOFs), with their tunable structure and uniform metal distribution, have become important precursors for the preparation of single-atom catalysts. Currently, there are numerous reports on the preparation of single-atom catalysts using ZIF-8 and UiO-66 / 67 as templates, but systematic studies using MOF-5 as a template are limited. MOF-5 is formed by the coordination of zinc ions with terephthalic acid, possessing high specific surface area, regular channels, and good thermal stability. Its zinc component readily volatilizes at high temperatures, creating an ideal environment for single-atom anchoring.

[0003] However, there is currently no research on the preparation of single-atom solvents using MOF-5 as a template. Furthermore, traditional single-atom catalysts are mostly solid powders, which exhibit poor dispersibility, limited mass transfer, and inconvenient operation in liquid-phase reactions. Therefore, developing a highly efficient method for preparing single-atom solvents based on MOF-5 templates, possessing high activity, high dispersibility, and ease of operation, would have significant practical value. Summary of the Invention

[0004] In order to overcome the technical problem of lacking efficient preparation of highly dispersed, highly stable and easy-to-operate single-atom catalyst systems based on MOF-5 templates in the prior art, the present invention provides a MOF-5 derived single-atom solvent and its preparation method.

[0005] To achieve the above objectives, the present invention employs the following technical solution: In a first aspect, the present invention provides a method for preparing a MOF-5 derived single-atom solvent, comprising the following steps: Step 1, Synthesis of metal-doped MOF-5 precursor: Zinc salt, terephthalic acid and second metal salt are dissolved in an organic solvent and subjected to a solvothermal reaction to obtain metal-doped MOF-5 precursor; Step 2, high-temperature pyrolysis: The metal-doped MOF-5 precursor obtained in Step 1 is subjected to programmed temperature carbonization under an inert atmosphere, and after cooling, nitrogen-doped carbon solid material supported by metal single atoms is obtained. Step 3, solvation dispersion: The nitrogen-doped carbon solid material obtained in step 2 is subjected to vapor-assisted dispersion treatment with a second solvent to form a stable MOF-5 derived single-atom solvent.

[0006] A further improvement of the present invention is that the zinc salt in step 1 is zinc nitrate, and the organic solvent is N,N-dimethylformamide, N,N-diethylformamide, or dimethyl sulfoxide.

[0007] A further improvement of the present invention is that the molar ratio of zinc salt, terephthalic acid and second metal salt in step 1 is (2-5):1:(0.001-0.1).

[0008] A further improvement of the present invention is that, in step 1, the second metal salt is at least one of platinum salt, cerium salt, palladium salt, cobalt salt, nickel salt, copper salt, iron salt, or manganese salt.

[0009] A further improvement of the present invention is that the carbonization temperature in step 2 is 700-1000℃, the heating rate is 2-8℃ / min, and the holding time is 1-4 hours.

[0010] A further improvement of the present invention is that, in step 3, the second solvent is at least one of N-methylpyrrolidone, N,N-dimethylformamide, methanol, ethanol, or water.

[0011] A further improvement of the present invention is that the dispersion concentration of the nitrogen-doped carbon solid material in the second solvent in step 3 is 0.5-30 mg / mL.

[0012] A further improvement of the present invention is that the steam-assisted dispersion treatment in step 3 includes: pre-treating the nitrogen-doped carbon solid material by contacting it with volatile solvent vapor, and then mixing it with the second solvent.

[0013] Secondly, the present invention also provides a MOF-5 derived single-atom solvent prepared by the above preparation method, comprising a liquid continuous phase and catalyst particles uniformly dispersed therein; the catalyst particles comprising a nitrogen-doped carbon support and a metal active center anchored on the support in the form of a single atom.

[0014] A further improvement of the present invention is that the metal active center forms an M-Nx coordination structure with the nitrogen atom in the support, wherein M represents the metal active center and x is an integer from 2 to 4.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for preparing MOF-5-derived single-atom solvents. First, by introducing a second metal salt during the in-situ synthesis of MOF-5, the method fully utilizes the ordered structure and uniform metal distribution of MOF-5 to provide highly dispersed initial anchoring sites for the target metal atoms, laying the foundation for the subsequent formation of a uniform single-atom structure. Then, a programmed temperature-controlled pyrolysis within a specific temperature range is employed to selectively volatilize the zinc component under an inert atmosphere, simultaneously achieving nitrogen doping of the carbon support. This not only creates abundant pore and defect structures but also effectively prevents the migration and aggregation of the target metal, thus achieving stable anchoring of the metal in single-atom form on the nitrogen-doped carbon support. Finally, steam-assisted dispersion treatment is used to pre-wet and fill the pores of the hydrophobic microporous carbon support with volatile solvent vapor, significantly improving the penetration efficiency of the target solvent into the support's pore network, thereby achieving highly stable dispersion of catalyst particles in the liquid phase. This results in a final product that combines the excellent mass transfer efficiency of homogeneous catalysts with the practical advantages of easy separation and recovery of heterogeneous catalysts. It also exhibits good storage stability, facilitates precise metering, and is suitable for continuous flow reaction processes. The overall process route is simple, coherent, and easily scaled up.

[0016] The MOF-5-derived single-atom solvent provided by this invention possesses a liquid continuous phase structure that ensures excellent flowability and mass transfer performance, facilitating precise metering and reactor feeding, and is particularly suitable for high-efficiency catalytic processes such as continuous flow. In the uniformly dispersed catalyst particles, the metal active centers are stably anchored as single atoms on the nitrogen-doped carbon support, maximizing metal atom utilization efficiency and exposing abundant catalytic active sites, thereby significantly improving catalytic activity and selectivity. The nitrogen-doped carbon support not only provides a stable coordination environment to inhibit single-atom aggregation, but its own conductivity and chemical stability also help maintain the long-term stability of the catalytic system during the reaction. Attached Figure Description

[0017] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of the invention in any way. Furthermore, the shapes and proportions of the components in the drawings are merely illustrative to aid in understanding the invention and do not specifically limit the shapes and proportions of the components of the invention.

[0018] Figure 1 The image shows the XRD pattern of Ce-SAS / MOF-5 in Embodiment 1 of this invention; Figure 2 This is a SEM image of Ce-SAS / MOF-5 in Embodiment 1 of the present invention; Figure 3The X-ray absorption fine structure (XAFS) spectrum of Embodiment 1 of the present invention is shown below; (a) is the Ce K-edge XANES spectrum of CeO2 and Ce-SAS / MOF-5; (b) is the Ce K-edge FT-EXAFS spectrum of Ce-SAS / MOF-5; (c) is the fitting analysis of Ce K-edge EXAFS in R space; and (de) is the Ce K-edge WT-EXAFS contour plot of Ce-SAS / MOF-5 and CeO2. Detailed Implementation

[0019] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0020] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0021] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0022] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0023] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0024] This invention provides a method for preparing a MOF-5-derived single-atom solvent, comprising the following steps: Step 1, Synthesis of metal-doped MOF-5 precursor: Zinc salt (zinc nitrate), terephthalic acid, and a second metal salt are dissolved in an organic solvent at a molar ratio of (2-5):1:(0.001-0.1). The second metal salt is at least one selected from platinum (Pt), cerium (Ce), palladium (Pd), cobalt (Co), nickel (Ni), copper (Cu), iron (Fe), or manganese (Mn). The organic solvent is N,N-dimethylformamide, N,N-diethylformamide, or dimethyl sulfoxide. The metal-doped MOF-5 precursor is obtained through a solvothermal reaction. Step 2, high-temperature pyrolysis: The metal-doped MOF-5 precursor obtained in Step 1 is subjected to programmed temperature carbonization under an inert atmosphere. The carbonization temperature is 700-1000℃, preferably 800-950℃, the heating rate is 2-8℃ / min, and the holding time is 1-4 hours. After cooling, a nitrogen-doped carbon solid material supported by a single metal atom is obtained. Step 3, solvation dispersion: The nitrogen-doped carbon solid material obtained in Step 2 is first pretreated by contacting it with volatile solvent (methanol) vapor, and then mixed with the second solvent to form a stable MOF-5 derived single-atom solvent; wherein the dispersion concentration of the nitrogen-doped carbon solid material in the second solvent is 0.5-30 mg / mL, and the second solvent is at least one of N-methylpyrrolidone, N,N-dimethylformamide, methanol, ethanol or water; Specifically, the alloy metal-doped MOF-5 precursor described in step 1 also includes the step of adding an auxiliary nitrogen source. The introduction of the auxiliary nitrogen source provides nitrogen species in advance for the subsequent pyrolysis process, making up for the lack of nitrogen in MOF-5 itself, and is the key to constructing a nitrogen-rich carbon support environment.

[0025] The synthesis of the metal-doped MOF-5 precursor is carried out using a one-pot solvothermal method, in which zinc salt, terephthalic acid, target metal salt and auxiliary nitrogen source are dissolved together in a polar organic solvent and reacted at a certain temperature to obtain a metal and nitrogen co-doped MOF-5 precursor.

[0026] The high-temperature pyrolysis described in step 2 involves subjecting the MOF-5 precursor to programmed temperature rise heat treatment under an inert gas atmosphere. During the pyrolysis process in step 2, the organic framework of MOF-5 is carbonized, which assists in the decomposition of the nitrogen source and its incorporation into the carbon network to form a nitrogen-doped carbon matrix. Simultaneously, zinc species volatilize to create pores and defects, while the target metal ions are captured by the nitrogen-rich active species generated during the pyrolysis process, reduced, and stably anchored to a single-atom state, thereby obtaining a nitrogen-doped carbon solid powder loaded with metal single atoms.

[0027] In the solvation dispersion process described in step 3, for the MOF-5-derived nitrogen-doped carbon support with high hydrophobicity and abundant micropores, the dispersion mechanism can be further explained as a pore activation principle based on the synergistic effect of capillary force and phase change. The core of this principle lies in utilizing the gas-phase diffusion capability of volatile solvent vapors to overcome the enormous capillary resistance encountered when liquid solvents directly fill ultramicropores (<2 nm). Specifically, when the solid powder obtained from pyrolysis comes into contact with the solvent, the vapors of volatile components (such as methanol) can preferentially and spontaneously adsorb and condense on the inner surface of all micropores through gas-phase diffusion, achieving "pre-wetting" of the pore network. This vapor phase change-driven capillary permeation process lays the foundation for the subsequent full filling of pores by the target solvent through liquid-phase capillary displacement and molecular diffusion, thereby promoting the final stable dispersion of catalyst particles in the liquid phase. This invention breaks through the traditional dilemma of direct liquid wetting of micropores and pioneers a two-step permeation strategy of "vapor first, liquid follow-up". It utilizes the advantage of gas phase diffusion without resistance to bypass capillary walls, and then uses liquid phase capillary displacement to complete the replacement of the main solvent. It is an extremely ingenious physical solution.

[0028] The preparation method provided by this invention innovatively adopts a "MOF-5 template + auxiliary nitrogen source co-doping" strategy. By introducing nitrogen sources such as dicyandiamide during the in-situ synthesis of MOF-5, the nitrogen deficiency problem of the direct pyrolysis product of MOF-5 is cleverly solved, creating a nitrogen-defect-rich carbon support environment for the efficient and stable anchoring of metal single atoms. This method has the advantages of simple and efficient process, with the entire process from co-doped precursor synthesis to pyrolysis and then to dispersion formulation being sequential, requiring no complex post-processing modifications, and is easy to scale up. At the same time, the obtained product has significant morphological advantages, combining the mass transfer characteristics of homogeneous catalysts with the easy separation advantages of heterogeneous catalysts. In addition, this preparation method has strong universality and is applicable to the preparation of single-atom solvents of various transition metals such as iron, cerium, cobalt, nickel, copper, manganese, and silver, and has broad application potential.

[0029] This invention also provides a MOF-5-derived single-atom solvent prepared by the above-described method, comprising a liquid continuous phase and catalyst particles uniformly dispersed therein; the catalyst particles comprise a nitrogen-doped carbon support and metal active centers anchored to the support in single-atom form. In this solvent, the metal active centers form an M-Nx coordination structure with nitrogen atoms in the support (where M represents the metal active center and x is an integer from 2 to 4), and the single-atom solvent shows no visible sedimentation or stratification after standing at 25°C for 14 days. The obtained single-atom solvent combines the excellent mass transfer characteristics of homogeneous catalysts with the advantages of easy separation of heterogeneous catalysts. Its catalyst particles are uniformly dispersed and highly stable, facilitating precise metering via pipetting and use in continuous flow reaction systems.

[0030] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0031] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" represents weight percentage, "parts" represents parts by weight, and "ratio" represents weight proportion.

[0032] Example 1 This embodiment provides a method for preparing a cerium-based MOF-5 single-atom solvent (Ce-SAS / MOF-5 / NMP), including the following steps: (1) Synthesis of Ce / N co-doped MOF-5 precursor: Accurately weigh 2.97 g (10 mmol) of zinc nitrate hexahydrate (Zn(NO3)2·6H2O), 0.434 g (1 mmol) of cerium nitrate hexahydrate (Ce(NO3)3·6H2O), and 1.66 g (10 mmol) of terephthalic acid (H2BDC), and add them together to a 100 mL polytetrafluoroethylene-lined reactor. Then add 1.12 g (13.3 mmol) of dicyandiamide (DCD) as an auxiliary nitrogen source. Add 80 mL of N,N-dimethylformamide (DMF) as a solvent to the reactor. Stir the mixture magnetically at room temperature for 2 hours until a homogeneous milky white suspension is formed. Seal the reactor and place it in a constant temperature oven at 120 °C for 36 hours. After the reaction, allow it to cool naturally to room temperature, and centrifuge to obtain a white precipitate. Wash the precipitate three times with fresh DMF and three times with anhydrous ethanol to thoroughly remove unreacted raw materials and solvent. Finally, the washed product was dried in a vacuum drying oven at 80°C for 12 hours to obtain a white powdery Ce / N co-doped MOF-5 precursor.

[0033] (2) Programmable temperature pyrolysis: Take 0.5 g of the dried Ce / N co-doped MOF-5 precursor, place it in a quartz boat and spread it evenly. Place the quartz boat in the isothermal zone of a tube furnace. Before the reaction begins, purge with high-purity nitrogen (purity ≥99.999%) at a flow rate of 200 mL / min for 30 minutes to fully purge air from the furnace tube. Then, under the protection of continuous nitrogen purging (flow rate reduced to 100 mL / min), the temperature is programmed to rise to 900℃ at a heating rate of 5℃ / min. After reaching the set temperature, carbonize at this temperature for 3 hours. After carbonization, allow it to cool naturally to room temperature in a nitrogen atmosphere to obtain a fluffy gray-black solid block. Gently grind this solid block in an agate mortar to obtain a fine powder of cerium-based single-atom catalyst solid, denoted as Ce-SAS / MOF-5.

[0034] (3) Preparation of single-atom solvents: Accurately weigh 50.0 mg of the Ce-SAS / MOF-5 solid powder prepared in step (2) and place it in a 20 mL clean glass sample vial. Place the sample vial in a sealed container containing an appropriate amount of methanol and keep it at 60°C for 2 hours to allow methanol vapor to fully penetrate and condense into the pores of the solid powder, thus completing the pre-wetting. Then remove the sample vial and add 10.0 mL of N-methylpyrrolidone (NMP) as a dispersion solvent to combine the solid powder with the dispersion solvent, resulting in a uniform, dark gray-black cerium-based MOF-5 single-atom solvent dispersion with a solid catalyst concentration of approximately 5 mg / mL.

[0035] The Ce-SAS / MOF-5 prepared in Example 1 was characterized by X-ray diffraction (XRD), and the obtained spectra are shown below. Figure 1 As shown in the figure, Ce-SAS / MOF-5 exhibits broadened diffraction peaks at approximately 13°, 26°, and 43°, corresponding to the (100), (002), and (101) crystal planes of amorphous carbon, respectively, while no characteristic diffraction peaks of elemental Ce or its oxides were observed. This result indicates that Ce species did not crystallize or agglomerate during pyrolysis, but rather existed in an atomically dispersed form within the carbon matrix.

[0036] The morphology of Ce-SAS / MOF-5 was observed using scanning electron microscopy (SEM), and the results are as follows: Figure 2 As shown, the pyrolyzed material exhibits a porous network composed of stacked structural units, with abundant pores and cracks on its surface. These structural features stem from the volatilization of zinc components and the decomposition of organic ligands during pyrolysis, contributing to the formation of a high specific surface area and abundant defect sites, thereby providing excellent mass transfer channels and active site supports for catalytic reactions.

[0037] To elucidate the electronic structure and coordination environment of the cerium active center in the Ce-SAS / MOF-5 catalyst at the atomic scale, this study employed X-ray absorption fine structure (XAFS) spectroscopy for systematic analysis. Figure 3 (a) shows the Ce L3 edge XANES spectra of Ce-SAS / MOF-5 and CeO2. The absorption edge position of Ce-SAS / MOF-5 is close to that of CeO2, indicating that the average oxidation state of cerium in Ce-SAS / MOF-5 is close to +4 and there is a certain degree of reduction (shifting towards +3). This confirms that the cerium species exists in a higher oxidation state in the support and has significant electronic interactions with nitrogen ligands.

[0038] Its local structure was further analyzed using EXAFS. Figure 3 In (b), k is the value of Ce-SAS / MOF-5. 3 The Fourier transform spectrum of the weighted EXAFS signal shows a dominant peak at approximately 2.21 Å, which can be attributed to the Ce–N coordination shell. No significant scattering peaks were observed at the characteristic distances corresponding to Ce–O (~1.87 Å) and Ce–Ce (~3.59 Å), indicating that cerium exists in atomically dispersed single-atom form, without forming oxide clusters or metal aggregates. Wavelet transform analysis ( Figure 3 The results further support this conclusion: the signal distribution of Ce-SAS / MOF-5 in R space is significantly different from that of CeO2, reflecting characteristics related to the nitrogen-coordinated single-atom structure.

[0039] Quantitative fitting based on EXAFS data ( Figure 3 (c) The precise coordination parameters of the cerium center in Ce-SAS / MOF-5 were obtained. The fitting results show that each cerium atom is coordinated with an average of about 4 nitrogen atoms (CN≈4), and the average Ce–N bond length is 1.95 Å. This configuration is consistent with the typical planar tetragonal M–N4 structure. This clear coordination model confirms at the atomic scale that cerium is stably anchored in the nitrogen-doped carbon support in a single-atom form. This is corroborated by the characterization results of metal-free crystalline phase by XRD and porous support morphology by SEM, forming a complete chain of evidence from microstructure, crystal structure to coordination environment. This provides key structural basis for understanding the high activity and high selectivity of this catalyst.

[0040] Storage stability tests showed that the Ce-SAS / MOF-5 / NMP single-atom solvent remained macroscopically homogeneous after standing for 72 hours, with no aggregation or stratification observed.

[0041] Example 2 This embodiment provides a method for preparing a copper-based MOF-5 single-atom solvent (Cu-SAS / MOF-5 / EtOH), comprising the following steps: (1) Precursor preparation: Referring to step (1) of Example 1, the second metal source was replaced with 0.242 g (1 mmol) of copper nitrate trihydrate (Cu(NO3)2·3H2O), and the auxiliary nitrogen source remained 1.12 g of dicyandiamide. The types, amounts, and reaction conditions of other materials remained unchanged. After the reaction was completed, the precursor was obtained by centrifugation, washing, and drying, resulting in a light blue powdery Cu / N co-doped MOF-5 precursor.

[0042] (2) High-temperature pyrolysis: Same as step (2) in Example 1, carbonize at 900°C for 3 hours under nitrogen protection to obtain a black solid powder, denoted as Cu-SAS / MOF-5.

[0043] (3) Solvation: Weigh 50.0 mg of Cu-SAS / MOF-5 solid powder and place it in a 20 mL clean glass sample vial. Place the sample vial in a sealed container containing an appropriate amount of methanol and keep it at 60°C for 2 hours to allow methanol vapor to fully penetrate and condense in the pores of the solid powder, thus completing the pre-wetting. Then remove the sample vial and add 10.0 mL of anhydrous ethanol as a dispersion solvent to combine the solid powder with the dispersion solvent, resulting in a uniform dark brown copper-based single-atom solvent dispersion.

[0044] Example 3 This embodiment provides a method for preparing an iron-based MOF-5 single-atom solvent (Fe-SAS / MOF-5 / H2O), including the following steps: (1) Preparation of precursor: Referring to step (1) of Example 1, the second metal source was replaced with 0.404 g (1 mmol) of ferric nitrate nonahydrate (Fe(NO3)3·9H2O), and a pale yellow precursor was obtained after the reaction.

[0045] (2) High-temperature pyrolysis: The precursor was heated to 850°C at 5°C / min under a nitrogen atmosphere, held for 4 hours, and then cooled to obtain black Fe-SAS / MOF-5 solid.

[0046] (3) Solvation: Weigh 100.0 mg of Fe-SAS / MOF-5 solid powder and place it in a 20 mL clean glass sample vial. Place the sample vial in a sealed container containing an appropriate amount of methanol and keep it at 60°C for 2 hours to allow methanol vapor to fully penetrate and condense in the pores of the solid powder, thus completing the pre-wetting. Then remove the sample vial and add 20.0 mL of deionized water as a dispersion solvent to combine the solid powder with the dispersion solvent, resulting in a uniform gray-black water-based monoatom solvent.

[0047] Comparative Example 1 This comparative example provides a method for preparing pure MOF-5 pyrolysis products (without metal doping), including the following steps: (1) Preparation of precursor: Only 2.97 g of zinc nitrate hexahydrate and 1.66 g of terephthalic acid were weighed and dissolved in 80 mL of DMF without adding any second metal salt or auxiliary nitrogen source. The reaction was carried out at 120 °C for 24 hours, and the pure MOF-5 white powder was obtained after washing and drying.

[0048] (2) High-temperature pyrolysis: Pyrolysis under the same conditions (nitrogen, 900℃, 3h).

[0049] (3) Product analysis: Black carbon material powder was obtained. This material does not contain any metal active centers and did not show any catalytic activity in subsequent catalytic reaction tests (such as the synthesis of 1,6-dicarbamate (HDC)), which confirms the necessity of metal single-atom active centers for catalysis.

[0050] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing a MOF-5 derived single-atom solvent, characterized in that, Includes the following steps: Step 1, Synthesis of metal-doped MOF-5 precursor: Zinc salt, terephthalic acid and second metal salt are dissolved in an organic solvent and subjected to a solvothermal reaction to obtain metal-doped MOF-5 precursor; Step 2, high-temperature pyrolysis: The metal-doped MOF-5 precursor obtained in Step 1 is subjected to programmed temperature carbonization under an inert atmosphere, and after cooling, nitrogen-doped carbon solid material supported by metal single atoms is obtained. Step 3, solvation dispersion: The nitrogen-doped carbon solid material obtained in step 2 is subjected to vapor-assisted dispersion treatment with a second solvent to form a stable MOF-5 derived single-atom solvent.

2. The method for preparing a MOF-5 derived single-atom solvent according to claim 1, characterized in that, The zinc salt mentioned in step 1 is zinc nitrate, and the organic solvent is N,N-dimethylformamide, N,N-diethylformamide, or dimethyl sulfoxide.

3. The method for preparing a MOF-5 derived single-atom solvent according to claim 1, characterized in that, The molar ratio of zinc salt, terephthalic acid and second metal salt in step 1 is (2-5):1:(0.001-0.1).

4. A method for preparing a MOF-5 derived single-atom solvent according to claim 1 or 3, characterized in that, In step 1, the second metal salt is at least one of platinum salt, cerium salt, palladium salt, cobalt salt, nickel salt, copper salt, iron salt, or manganese salt.

5. The method for preparing a MOF-5 derived single-atom solvent according to claim 1, characterized in that, The carbonization temperature in step 2 is 700-1000℃, the heating rate is 2-8℃ / min, and the holding time is 1-4 hours.

6. The method for preparing a MOF-5 derived single-atom solvent according to claim 1, characterized in that, In step 3, the second solvent is at least one of N-methylpyrrolidone, N,N-dimethylformamide, methanol, ethanol, or water.

7. The method for preparing a MOF-5 derived single-atom solvent according to claim 1, characterized in that, In step 3, the dispersion concentration of the nitrogen-doped carbon solid material in the second solvent is 0.5-30 mg / mL.

8. The method for preparing a MOF-5 derived single-atom solvent according to claim 1, characterized in that, The steam-assisted dispersion treatment in step 3 includes: pre-treating the nitrogen-doped carbon solid material by contacting it with volatile solvent vapor, and then mixing it with the second solvent.

9. A MOF-5 derived single-atom solvent prepared by the preparation method according to any one of claims 1-8, characterized in that, It comprises a liquid continuous phase and catalyst particles uniformly dispersed therein; the catalyst particles comprise a nitrogen-doped carbon support and metal active centers anchored on the support in the form of single atoms.

10. A MOF-5 derived single-atom solvent according to claim 9, characterized in that, The metal active center forms an M-Nx coordination structure with the nitrogen atom in the support, where M represents the metal active center and x is an integer from 2 to 4.

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