Bimetal nitrogen-doped carbon-based catalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of catalysts and biomass catalytic conversion, in particular to a bimetallic nitrogen-doped carbon-based catalyst and a preparation method and application thereof.The preparation method comprises the steps that ZIF-8 is synthesized with 2-methylimidazole and zinc nitrate hexahydrate as raw materials to serve as a template, and a cobalt source is introduced into a solution system through ion exchange; the iron source is then introduced during calcination by vaporizing deposition of ferrocene. In the carbonization process, iron and carbide are bonded, the zinc element is gasified and volatilized to form defect vacancies, the vacancies are filled with iron and cobalt atoms to form uniform metal active sites, and finally the double-metal nitrogen-doped carbon-based catalyst is prepared. The method has the advantages of simplicity in operation, high controllability, low cost, easiness in industrial production and the like, and the obtained bimetallic nitrogen-doped carbon-based catalyst has a regular dodecahedron-like morphology and shows excellent selectivity, high catalytic efficiency and good stability in selective catalytic conversion of 5-hydroxymethylfurfural (HMF).

Description

Technical Field

[0001] This invention relates to the field of catalysts and biomass catalytic conversion technology, specifically to a bimetallic nitrogen-doped carbon-based catalyst, its preparation method, and its application. Background Technology

[0002] With rapid global economic development and continuous population growth, global energy demand is experiencing explosive growth. Against this backdrop, developing low-cost, clean energy alternatives and advancing green chemistry have become important research directions in the field of chemistry. Biomass, as an abundant and economical renewable resource, offers new hope for alleviating energy pressures and achieving sustainable development. Through the effective conversion and utilization of biomass, various high-value-added chemicals and fuels can be obtained, thereby alleviating dependence on traditional fossil fuels to some extent, reducing carbon emissions, and promoting the achievement of sustainable development goals.

[0003] 5-Hydroxymethylfurfural (HMF) is a highly promising biomass intermediate, obtained through the dehydration of biomass sugars. It can be converted into various chemicals and materials, such as 2,5-dicarboxyfuran (DFF), 5-hydroxymethyl-2-furanic acid (HMFCA), 5-formyl-2-furanic acid (FFCA), and 2,5-furanic acid (FDCA), showing broad application prospects in materials science, pharmaceutical industry, and fine chemicals. FDCA, in particular, as a promising novel polyester monomer to replace terephthalic acid, demonstrates enormous potential in the synthesis of high-performance, biodegradable polyester materials and is considered a key bridge connecting biomass resources and modern materials industry.

[0004] In existing technologies, the conversion of HMF into subsequent products involves complex intermediates, which are prone to over-oxidation during the oxidation process. Most catalysts still suffer from drawbacks such as harsh reaction conditions, long reaction times, and low selectivity. Therefore, it is necessary to develop efficient and selective catalysts to address the challenging chain reaction. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the first objective of this invention is to provide a method for preparing a bimetallic nitrogen-doped carbon-based catalyst. This method is simple to operate, highly controllable, has low production cost, and is easy to industrialize. The prepared bimetallic nitrogen-doped carbon-based catalyst has a regular dodecahedral morphology and has the advantages of high selectivity, good catalytic efficiency, and excellent stability in HMF selective catalysis applications.

[0006] To overcome the shortcomings of the prior art, the second objective of this invention is to provide a bimetallic nitrogen-doped carbon-based catalyst with a regular dodecahedral morphology, which has the advantages of high selectivity, good catalytic efficiency and excellent stability in HMF selective catalysis applications.

[0007] A third objective of this invention is to provide an application of a bimetallic nitrogen-doped carbon-based catalyst.

[0008] To achieve the first objective of the invention, the technical solution adopted by the present invention is as follows:

[0009] This invention provides a method for preparing a bimetallic nitrogen-doped carbon-based catalyst, comprising the following steps:

[0010] Synthesis of S1 and ZIF-8 templates: 2-methylimidazole and zinc nitrate hexahydrate were dissolved in a solvent, stirred and dissolved, and reacted to generate ZIF-8, thus obtaining a ZIF-8 template suspension;

[0011] S2. Preparation of cobalt source solution: Dissolve cobalt nitrate hexahydrate in a solvent, stir to dissolve, and obtain cobalt source solution;

[0012] S3. Cobalt source introduction into ZIF-8 template: The cobalt source solution is added to the ZIF-8 template suspension, and the mixture is stirred to carry out an ion exchange reaction, so that cobalt ions enter the ZIF-8 framework to obtain a precursor solution.

[0013] S4. Separation and treatment of precursor: The precursor solution is allowed to stand at room temperature to obtain a sedimentation layer. Then, it is centrifuged, washed and dried to obtain the precursor.

[0014] S5. Iron source vapor deposition: The precursor is mixed with ferrocene and placed in a tube furnace, and calcined under an inert atmosphere to obtain the bimetallic nitrogen-doped carbon-based catalyst.

[0015] This invention discloses a method for preparing a bimetallic nitrogen-doped carbon-based catalyst. First, ZIF-8 is synthesized using 2-methylimidazole and zinc nitrate hexahydrate as a template. ZIF-8, a zeolite imidazolium ester framework material-8, is a porous nanomaterial with excellent chemical and thermal stability. Then, cobalt nitrate hexahydrate is added to the solution to coat ZIF-8. During the settling process, cobalt ions exchange with zinc ions coordinated in the ZIF-8 template, introducing a cobalt source into the ZIF-8 template and obtaining a precursor. The precursor is then calcined and carbonized with ferrocene under an inert atmosphere. During calcination, ferrocene vaporizes and bonds with atoms in the carbides formed after the precursor carbonization, while zinc atoms largely vaporize and volatilize, creating defect vacancies. Iron and cobalt atoms occupy these vacancies to form metal sites, thus obtaining the bimetallic nitrogen-doped carbon-based catalyst. The introduction of the iron source via vapor deposition ensures excellent dispersion of the active metal sites.

[0016] In this invention, a zinc-coordinated ZIF-8 template is first formed, resulting in a material with relatively uniform particle size. A cobalt source is then introduced into the ZIF-8 template. After the cobalt surrounding the ZIF-8 template undergoes ion exchange with the zinc, the material still maintains a relatively uniform particle size. This method of first forming the ZIF-8 template and then introducing the cobalt source effectively ensures the uniformity of the material's particle size and allows for control over the ion exchange between cobalt and zinc, thereby guaranteeing the material's performance.

[0017] The 2-methylimidazole used in this invention has three main functions: first, it acts as a ligand to bond with zinc and cobalt to form coordination compounds, creating metal sites; second, it forms a carbon-nitrogen (NC) framework during carbonization, which has abundant porosity and high specific surface area, providing a large number of active sites to anchor metal atoms and forming metal-nitrogen defects. These defects can adsorb more electrons during the HMF catalytic reaction, promoting the formation of reactive oxygen species and thus promoting the selective catalysis of HMF; third, 2-methylimidazole, as a nitrogen source, can save raw materials, eliminating the need to add other nitrogen sources, and the formed nitrogen-carbon framework is very stable.

[0018] In this invention, the main function of zinc nitrate hexahydrate is to provide metal sites. First, during the static setting process of the precursor preparation, cobalt metal will undergo ion substitution with zinc metal, resulting in more cobalt replacing zinc. Second, during the carbonization process, zinc metal will volatilize and form a large number of vacancies, and iron and cobalt metal will occupy these vacancies in this process, thereby achieving the effect of metal substitution.

[0019] In step S5, during the calcination process, the iron species generated from the gas decomposition of ferrocene are deposited on the surface of the precursor and participate in the carbonization process. This invention uses ferrocene as the iron source in the calcination process, which has two main advantages: first, because ferrocene has a low sublimation temperature, and at this temperature the precursor can form carbides, iron can bond with the carbides, thus anchoring it within the material; second, by introducing the iron source through the gas-phase deposition of ferrocene during calcination, compared to adding other soluble iron salts during precursor synthesis, which easily disrupts the coordination reaction, this invention achieves a higher precursor yield.

[0020] Furthermore, in step S1, the mass-to-volume ratio of 2-methylimidazole, zinc nitrate hexahydrate, and solvent is (7.0~8.0) g : (6.0~7.0) g : (400~600) mL.

[0021] Furthermore, in step S2, the mass-to-volume ratio of cobalt nitrate hexahydrate to solvent is (0.2~1.7) g: 20 mL; and / or.

[0022] In steps S1 and S2, the solvent is at least one of methanol, ethanol, or ultrapure water.

[0023] Furthermore, in step S3, the temperature of the stirring reaction is 20℃~40℃, and / or the stirring speed is 500r / min~1000r / min, and / or the stirring reaction time is 30min~90min.

[0024] Furthermore, in step S4, the settling time is 10h~18h; and / or

[0025] The washing process involves washing 2-3 times with methanol, ethanol, or ultrapure water; and / or

[0026] The drying temperature is 50℃~70℃, and the drying time is 10h~12h.

[0027] Furthermore, in step S5, the mass ratio of the precursor to ferrocene is (0.6~0.8) g : (0.07~0.38) g.

[0028] Furthermore, in step S5, the calcination temperature is 700℃~1000℃, and the calcination time is 1h~3h; and / or

[0029] The heating rate for calcination is 4℃ / min to 6℃ / min.

[0030] Furthermore, in step S5, the inert atmosphere is argon; and / or

[0031] The flow rate of the inert atmosphere is 20 mL / min.-1 ~30mL / min -1 .

[0032] To achieve the second objective of the invention, the technical solution adopted by the present invention is as follows:

[0033] This invention provides a bimetallic nitrogen-doped carbon-based catalyst, which is prepared by the above-described method for preparing a bimetallic nitrogen-doped carbon-based catalyst.

[0034] The bimetallic nitrogen-doped carbon-based catalyst prepared by this invention exhibits a regular dodecahedral morphology with a particle size of about 260 nm.

[0035] To achieve the third objective of the invention, the technical solution adopted by the present invention is as follows:

[0036] This invention provides an application of a bimetallic nitrogen-doped carbon-based catalyst, specifically the application of the bimetallic nitrogen-doped carbon-based catalyst described above or prepared by the method described above in the selective oxidation of 5-hydroxymethylfurfural to 2,5-furan carboxylic acid.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] (1) A method for preparing a bimetallic nitrogen-doped carbon-based catalyst according to the present invention involves first synthesizing ZIF-8 as a template using 2-methylimidazole and zinc nitrate hexahydrate. Then, in a solution system, cobalt nitrate hexahydrate is used to coat ZIF-8, and during the standing process, cobalt ions and zinc ions undergo ion exchange, thereby introducing a cobalt source into the ZIF-8 template. The precursor and ferrocene are then calcined and carbonized under an inert atmosphere. The ferrocene vaporizes and bonds with atoms in the carbides formed by the calcination of the precursor, while a large number of zinc atoms vaporize and volatilize to form defect vacancies. Iron and cobalt atoms occupy these vacancies to form metal sites, thus obtaining a bimetallic nitrogen-doped carbon-based catalyst. The introduction of the iron source through vapor deposition ensures excellent dispersion of the active metal sites. The preparation method is simple to operate, highly controllable, has low production cost, and is easy to industrialize. The resulting bimetallic nitrogen-doped carbon-based catalyst has a regular dodecahedral morphology and has the advantages of high selectivity, good catalytic efficiency, and excellent stability in HMF selective catalysis applications.

[0039] (2) The bimetallic nitrogen-doped carbon-based catalyst of the present invention has a regular dodecahedral morphology and retains the advantages of large specific surface area and porous structure of metal-organic framework, and increases active metal sites. In HMF selective catalysis applications, it has the advantages of high selectivity, good catalytic efficiency and excellent stability.

[0040] (3) Application of a bimetallic nitrogen-doped carbon-based catalyst of the present invention. This bimetallic nitrogen-doped carbon-based catalyst is used to selectively oxidize HMF to FDCA, and has the advantages of high selectivity, good catalytic efficiency, and excellent stability. Specifically, at 90°C and normal pressure, HMF is completely converted within 3 hours, and the selectivity of 2,5-furandicarboxylic acid (FDCA) reaches 99%. Therefore, this bimetallic nitrogen-doped carbon-based catalyst has a very good application prospect. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 The images show the XRD patterns of the catalysts prepared in Example 1 and Comparative Example 1 of this invention.

[0043] Figure 2 The images show the SEM images of the ZIF-8 template (ZIF-8) and precursor (ZIF-67@ZIF-8) of Embodiment 1 of the present invention.

[0044] Figure 3 This is a SEM image of the bimetallic nitrogen-doped carbon-based catalyst (Fe / Co-NC) of Example 1 of the present invention.

[0045] Figure 4 This is a SEM image of the NC catalyst (NC) of Comparative Example 1.

[0046] Figure 5 The graph shows the catalytic performance test results of the catalysts of Example 1 and Comparative Example 1 for HMF.

[0047] Figure 6 The figure shows the stability test results of the bimetallic nitrogen-doped carbon-based catalyst of the present invention. Detailed Implementation

[0048] To make the technical problem to be solved, the technical solution, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0049] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. In this invention, the singular forms “a,” “described,” and “the” as used in the embodiments and appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0050] In this embodiment of the invention, a method for preparing a bimetallic nitrogen-doped carbon-based catalyst includes the following steps:

[0051] Synthesis of S1 and ZIF-8 templates: 2-methylimidazole and zinc nitrate hexahydrate were dissolved in a solvent, stirred and dissolved, and reacted to generate ZIF-8, thus obtaining a ZIF-8 template suspension;

[0052] S2. Preparation of cobalt source solution: Dissolve cobalt nitrate hexahydrate in a solvent, stir to dissolve, and obtain cobalt source solution;

[0053] S3. Cobalt source introduction into ZIF-8 template: The cobalt source solution is added to the ZIF-8 template suspension, and the mixture is stirred to carry out an ion exchange reaction, so that cobalt ions enter the ZIF-8 framework to obtain a precursor solution.

[0054] S4. Separation and treatment of precursor: The precursor solution is allowed to stand at room temperature to obtain a sedimentation layer. Then, it is centrifuged, washed and dried to obtain the precursor.

[0055] S5. Iron source vapor deposition: The precursor is mixed with ferrocene and placed in a tube furnace, and calcined under an inert atmosphere to obtain the bimetallic nitrogen-doped carbon-based catalyst.

[0056] In some embodiments, in step S1, the mass-to-volume ratio of 2-methylimidazole, zinc nitrate hexahydrate, and solvent is (7.0~8.0) g : (6.0~7.0) g : (400~600) mL.

[0057] In some embodiments, in step S2, the mass-to-volume ratio of cobalt nitrate hexahydrate to the solvent is (0.2~1.7) g: 20 mL; and / or

[0058] In steps S1 and S2, the solvent is at least one of methanol, ethanol, or ultrapure water.

[0059] In some embodiments, in step S3, the temperature of the stirring reaction is 20°C to 40°C, and / or the stirring speed is 500 r / min to 1000 r / min, and / or the stirring reaction time is 30 min to 90 min.

[0060] In some embodiments, in step S4, the settling time is 10h~18h; and / or

[0061] The washing process involves washing 2-3 times with methanol, ethanol, or ultrapure water; and / or

[0062] The drying temperature is 50℃~70℃, and the drying time is 10h~12h.

[0063] In some embodiments, in step S5, the mass ratio of the precursor to ferrocene is (0.6~0.8) g: (0.07~0.38) g.

[0064] In some embodiments, in step S5, the calcination temperature is 700℃~1000℃, and the calcination time is 1h~3h; and / or

[0065] The heating rate for calcination is 4℃ / min to 6℃ / min.

[0066] In some embodiments, in step S5, the inert atmosphere is argon; and / or

[0067] The flow rate of the inert atmosphere is 20 mL / min. -1 ~30mL / min -1 .

[0068] In this embodiment of the invention, a bimetallic nitrogen-doped carbon-based catalyst is prepared by the above-described method for preparing a bimetallic nitrogen-doped carbon-based catalyst.

[0069] In this embodiment of the invention, the application of a bimetallic nitrogen-doped carbon-based catalyst, specifically the application of the bimetallic nitrogen-doped carbon-based catalyst described above or prepared by the method described above, in the selective oxidation of 5-hydroxymethylfurfural to 2,5-furan carboxylic acid.

[0070] The following description is based on specific embodiments. Example 1

[0071] A method for preparing a bimetallic nitrogen-doped carbon-based catalyst includes the following steps:

[0072] Synthesis of S1 and ZIF-8 template: 2-methylimidazole and zinc nitrate hexahydrate were dissolved in a solvent and stirred until dissolved. The reaction generated ZIF-8, and a ZIF-8 template suspension was obtained. In this example, the mass-volume ratio of 2-methylimidazole, zinc nitrate hexahydrate and solvent was 7.5 g: 6.5 g: 500 mL.

[0073] S2. Preparation of cobalt source solution: Cobalt nitrate hexahydrate is dissolved in a solvent and stirred until dissolved to obtain a cobalt source solution; in this embodiment, the mass-volume ratio of cobalt nitrate hexahydrate to solvent is 1.0 g: 20 mL;

[0074] In this embodiment, the solvent for steps S1 and S2 is methanol;

[0075] S3. Cobalt source introduction into ZIF-8 template: The cobalt source solution is added to the ZIF-8 template suspension, and the ion exchange reaction is carried out at 30°C with a stirring speed of 700 r / min for 60 min, so that cobalt ions enter the ZIF-8 framework to obtain the precursor solution.

[0076] S4. Separation and treatment of the precursor: The precursor solution was allowed to stand at room temperature for 12 hours to obtain a sedimentation layer. After centrifugation, the solution was washed three times with methanol and dried at 60°C for 11 hours to obtain the precursor (denoted as ZIF-67@ZIF-8).

[0077] S5. Iron source vapor deposition: The precursor is mixed with ferrocene and placed in a ceramic boat in a tube furnace. The furnace is then heated at a flow rate of 20 mL / min. -1 Under argon protection, the temperature was increased to 900℃ at a heating rate of 5℃ / min and calcined for 2h to obtain a bimetallic nitrogen-doped carbon-based catalyst (denoted as Fe / Co-NC).

[0078] In this embodiment, the mass ratio of the precursor to ferrocene is 0.7g:0.093g. Example 2

[0079] A method for preparing a bimetallic nitrogen-doped carbon-based catalyst includes the following steps:

[0080] Synthesis of S1 and ZIF-8 template: 2-methylimidazole and zinc nitrate hexahydrate were dissolved in a solvent and stirred until dissolved. The reaction generated ZIF-8, and a ZIF-8 template suspension was obtained. In this example, the mass-volume ratio of 2-methylimidazole, zinc nitrate hexahydrate and solvent was 7.0 g: 6.0 g: 400 mL.

[0081] S2. Preparation of cobalt source solution: Cobalt nitrate hexahydrate is dissolved in a solvent and stirred until dissolved to obtain a cobalt source solution; in this embodiment, the mass-volume ratio of cobalt nitrate hexahydrate to solvent is 0.2g:20mL;

[0082] In this embodiment, the solvent for steps S1 and S2 is ethanol;

[0083] S3. Cobalt source introduction into ZIF-8 template: The cobalt source solution is added to the ZIF-8 template suspension, and the ion exchange reaction is carried out at 20°C with a stirring speed of 500 r / min for 90 min, so that cobalt ions enter the ZIF-8 framework and the precursor solution is obtained.

[0084] S4. Separation and treatment of the precursor: The precursor solution was allowed to stand at room temperature for 10 hours to obtain a sedimentation layer. After centrifugation, the solution was washed twice with ethanol and dried at 50°C for 12 hours to obtain the precursor (denoted as ZIF-67@ZIF-8).

[0085] S5. Iron source vapor deposition: The precursor is mixed with ferrocene and placed in a ceramic boat in a tube furnace. The furnace is then heated at a flow rate of 30 mL / min. -1 Under argon protection, the temperature was increased to 800℃ at a heating rate of 4℃ / min and calcined for 1 hour to obtain a bimetallic nitrogen-doped carbon-based catalyst (denoted as Fe / Co-NC).

[0086] In this embodiment, the mass ratio of the precursor to ferrocene is 0.7g:0.07g. Example 3

[0087] A method for preparing a bimetallic nitrogen-doped carbon-based catalyst includes the following steps:

[0088] Synthesis of S1 and ZIF-8 template: 2-methylimidazole and zinc nitrate hexahydrate were dissolved in a solvent and stirred until dissolved. The reaction generated ZIF-8, and a ZIF-8 template suspension was obtained. In this example, the mass-volume ratio of 2-methylimidazole, zinc nitrate hexahydrate and solvent was 8.0 g: 7.0 g: 600 mL.

[0089] S2. Preparation of cobalt source solution: Cobalt nitrate hexahydrate is dissolved in a solvent and stirred until dissolved to obtain a cobalt source solution; in this embodiment, the mass-volume ratio of cobalt nitrate hexahydrate to solvent is 1.7g:20mL;

[0090] In this embodiment, the solvent for steps S1 and S2 is ultrapure water;

[0091] S3. Cobalt source introduction into ZIF-8 template: The cobalt source solution is added to the ZIF-8 template suspension, and the ion exchange reaction is carried out at 40°C with a stirring speed of 1000 r / min for 30 min, so that cobalt ions enter the ZIF-8 framework to obtain the precursor solution.

[0092] S4. Separation and treatment of the precursor: The precursor solution was allowed to stand at room temperature for 18 hours to obtain a sedimentation layer. After centrifugation, the solution was washed three times with ultrapure water and dried at 70°C for 10 hours to obtain the precursor (denoted as ZIF-67@ZIF-8).

[0093] S5. Iron source vapor deposition: The precursor is mixed with ferrocene and placed in a ceramic boat in a tube furnace. The furnace is then heated at a flow rate of 25 mL / min. -1Under argon protection, the temperature was increased to 950℃ at a heating rate of 6℃ / min and calcined for 3h to obtain a bimetallic nitrogen-doped carbon-based catalyst (denoted as Fe / Co-NC).

[0094] In this embodiment, the mass ratio of the precursor to ferrocene is 0.6g:0.15g. Example 4

[0095] A method for preparing a bimetallic nitrogen-doped carbon-based catalyst includes the following steps:

[0096] Synthesis of S1 and ZIF-8 template: 2-methylimidazole and zinc nitrate hexahydrate were dissolved in a solvent and stirred until dissolved. The reaction generated ZIF-8, and a ZIF-8 template suspension was obtained. In this example, the mass-volume ratio of 2-methylimidazole, zinc nitrate hexahydrate and solvent was 7.2 g: 6.3 g: 450 mL.

[0097] S2. Preparation of cobalt source solution: Cobalt nitrate hexahydrate is dissolved in a solvent and stirred until dissolved to obtain a cobalt source solution; in this embodiment, the mass-volume ratio of cobalt nitrate hexahydrate to solvent is 0.5g:20mL;

[0098] In this embodiment, the solvent for steps S1 and S2 is methanol;

[0099] S3. Cobalt source introduction into ZIF-8 template: The cobalt source solution is added to the ZIF-8 template suspension, and the ion exchange reaction is carried out at 25°C with a stirring speed of 600 r / min for 80 min, so that cobalt ions enter the ZIF-8 framework to obtain the precursor solution.

[0100] S4. Separation and treatment of the precursor: The precursor solution was allowed to stand at room temperature for 15 hours to obtain a sedimentation layer. After centrifugation, the solution was washed twice with methanol and dried at 55°C for 11.5 hours to obtain the precursor (denoted as ZIF-67@ZIF-8).

[0101] S5. Iron source vapor deposition: The precursor is mixed with ferrocene and placed in a ceramic boat in a tube furnace. The furnace is then heated at a flow rate of 22 mL / min. -1 Under argon protection, the temperature was increased to 1000℃ at a heating rate of 5℃ / min and calcined for 1.5h to obtain a bimetallic nitrogen-doped carbon-based catalyst (denoted as Fe / Co-NC).

[0102] In this embodiment, the mass ratio of the precursor to ferrocene is 0.8g:0.38g. Example 5

[0103] A method for preparing a bimetallic nitrogen-doped carbon-based catalyst includes the following steps:

[0104] Synthesis of S1 and ZIF-8 template: 2-methylimidazole and zinc nitrate hexahydrate were dissolved in a solvent and stirred until dissolved. The reaction generated ZIF-8, and a ZIF-8 template suspension was obtained. In this example, the mass-volume ratio of 2-methylimidazole, zinc nitrate hexahydrate and solvent was 7.8 g: 6.7 g: 550 mL.

[0105] S2. Preparation of cobalt source solution: Cobalt nitrate hexahydrate is dissolved in a solvent and stirred until dissolved to obtain a cobalt source solution; in this embodiment, the mass-volume ratio of cobalt nitrate hexahydrate to solvent is 1.5g:20mL;

[0106] In this embodiment, the solvent for steps S1 and S2 is methanol;

[0107] S3. Cobalt source introduction into ZIF-8 template: The cobalt source solution is added to the ZIF-8 template suspension, and the ion exchange reaction is carried out at 35°C with a stirring speed of 800 r / min for 40 min, so that cobalt ions enter the ZIF-8 framework to obtain the precursor solution.

[0108] S4. Separation and treatment of the precursor: The precursor solution was allowed to stand at room temperature for 13 hours to obtain a sedimentation layer. After centrifugation, the solution was washed three times with methanol and dried at 65°C for 10.5 hours to obtain the precursor (denoted as ZIF-67@ZIF-8).

[0109] S5. Iron source vapor deposition: The precursor is mixed with ferrocene and placed in a ceramic boat in a tube furnace. The furnace is then heated at a flow rate of 28 mL / min. -1 Under argon protection, the temperature was increased to 700℃ at a heating rate of 5℃ / min and calcined for 2.5h to obtain a bimetallic nitrogen-doped carbon-based catalyst (denoted as Fe / Co-NC).

[0110] In this embodiment, the mass ratio of the precursor to ferrocene is 0.7g:0.25g. Example 6

[0111] A bimetallic nitrogen-doped carbon-based catalyst is prepared by any one of the preparation methods of bimetallic nitrogen-doped carbon-based catalysts in Examples 1 to 5. The prepared bimetallic nitrogen-doped carbon-based catalyst has a regular dodecahedral morphology. Example 7

[0112] Application of a bimetallic nitrogen-doped carbon-based catalyst: The application of the bimetallic nitrogen-doped carbon-based catalyst prepared by any one of the preparation methods of bimetallic nitrogen-doped carbon-based catalysts in the selective oxidation of HMF to FDCA in Examples 1 to 5.

[0113] Comparative Example 1

[0114] A method for preparing an NC catalyst, the difference between this comparative example and Example 1 is that this comparative example does not introduce a cobalt source and an iron source, and includes the following steps:

[0115] Synthesis of S1 and ZIF-8 templates: 2-methylimidazole and zinc nitrate hexahydrate were dissolved in a solvent and stirred to dissolve, thus preparing a ZIF-8 template solution; wherein the mass-volume ratio of 2-methylimidazole, zinc nitrate hexahydrate and solvent was 7.5 g: 6.5 g: 500 mL.

[0116] S2. Preparation of precursor: The precursor solution was allowed to stand at room temperature for 12 hours to obtain a sedimentation layer, then centrifuged, washed three times with methanol, and dried at 60°C for 11 hours to obtain the precursor.

[0117] S3. Calcination: 0.7g of the precursor was placed in a ceramic boat and calcined at 900℃ for 2h under argon protection at a flow rate of 20ml / min-1 and a heating rate of 5℃ / min to obtain the NC catalyst (i.e., NC).

[0118] Structural morphology characterization

[0119] (a) X-ray diffraction analysis

[0120] The bimetallic nitrogen-doped carbon-based catalyst (Fe / Co-NC) prepared in Example 1 and the NC catalyst (NC) prepared in Comparative Example 1 were subjected to X-ray diffraction (XRD) analysis, respectively. Figure 1 As shown.

[0121] Depend on Figure 1 As can be seen, the bimetallic nitrogen-doped carbon-based catalyst (Fe / Co-NC) in Example 1 only exhibits two broad carbon-related peaks, indicating that cobalt and iron may be uniformly distributed throughout the system. The NC catalyst (NC) in Comparative Example 1 also only exhibits two broad carbon-related peaks.

[0122] (II) Morphological characterization by scanning electron microscopy

[0123] The ZIF-8 template (ZIF-8), precursor (ZIF-67@ZIF-8), and bimetallic nitrogen-doped carbon-based catalyst (Fe / Co-NC) prepared in Example 1, as well as the NC catalyst (NC) prepared in Comparative Example 1, were characterized by scanning electron microscopy (SEM). The SEM images of the ZIF-8 template (ZIF-8) and precursor (ZIF-67@ZIF-8) from Example 1 are shown below. Figure 2 As shown, the SEM image of the bimetallic nitrogen-doped carbon-based catalyst (Fe / Co-NC) in Example 1 is as follows. Figure 3 As shown, the SEM image of the NC catalyst (NC) in Comparative Example 1 is as follows. Figure 4 As shown.

[0124] Depend on Figure 2 and Figure 3 As can be seen, the bimetallic nitrogen-doped carbon-based catalyst (Fe / Co-NC) prepared in Example 1 of this invention, after introducing cobalt source and iron source sequentially on the basis of ZIF-8 template, still retains the dodecahedral framework of ZIF-8 template (ZIF-8) and precursor (ZIF-67@ZIF-8), and has good particle size uniformity with an average particle size of 260 nm.

[0125] Depend on Figure 4 As can be seen, the NC catalyst of Comparative Example 1 retains the ZIF-8 template dodecahedral framework, with an average particle size of 280 nm.

[0126] Depend on Figure 3 and Figure 4 As can be seen, the NC catalyst prepared in Comparative Example 1 has a smooth surface, while the bimetallic nitrogen-doped carbon-based catalyst (Fe / Co-NC) prepared in Example 1 of this invention has obvious metal particles on its surface, proving the successful introduction of Fe and Co metals.

[0127] Performance testing

[0128] (a) Catalytic performance test

[0129] The bimetallic nitrogen-doped carbon-based catalyst (Fe / Co-NC) prepared in Example 1 and the NC catalyst (NC) prepared in Comparative Example 1 were used to determine the catalytic performance of the catalysts for HMF in a heterogeneous catalytic system.

[0130] The test method is as follows: 0.315 mmol HMF, 0.945 mmol K2CO3, 100 mg catalyst, and 20 mL water were added to a 50 mL three-necked flask. Then, the solution was added to the reactor at a rate of 20 mL / min at room temperature. -1 O2 was introduced at a flow rate of 0.1 MPa, and the mixture was stirred (750 rpm) and heated to 90°C for 3 hours. The reactants in the solution after 3 hours were then subjected to chromatographic analysis. The test results are as follows: Figure 5 As shown.

[0131] Depend on Figure 5As can be seen, the bimetallic nitrogen-doped carbon-based catalyst (Fe / Co-NC) of Example 1 of this invention achieves complete HMF conversion within 3 hours at 90°C and atmospheric pressure, with a selectivity of 99% for 2,5-furandicarboxylic acid (FDCA). In contrast, the NC catalyst (NC) of Comparative Example 1, although containing some zinc metal, only achieves a HMF conversion rate of 67% and an FDCA selectivity of only 4%, indicating that zinc is not an active site for the selective conversion of HMF to FDCA. Furthermore, it demonstrates that the bimetallic nitrogen-doped carbon-based catalyst prepared in this invention exhibits significantly better HMF conversion and FDCA selectivity than the NC catalyst of Comparative Example 1. Therefore, it is evident that Fe and Co bimetallic loading plays a crucial role in the selective catalysis of HMF in nitrogen-doped carbon-based materials, and the Fe and Co bimetallic compounds, acting as active sites, synergistically promote HMF oxidation.

[0132] (ii) Stability test

[0133] The bimetallic nitrogen-doped carbon-based catalyst (Fe / Co-NC) prepared in Example 1 was subjected to catalytic stability testing.

[0134] The test method is as follows: The reaction solution after the above catalytic performance test was centrifuged, freeze-dried for 12 hours, and then placed in a tube furnace and calcined at 400℃ for 1 hour at a rate of 5℃ / min. Its catalytic performance was then measured. This process was repeated five times for the stability test. The test results are as follows: Figure 6 As shown.

[0135] Depend on Figure 6 As can be seen, in five cycles of testing, the bimetallic nitrogen-doped carbon-based catalyst (Fe / Co-NC) of this invention maintained a 100% HMF conversion and an FDCA selectivity of over 94%. This indicates that the bimetallic nitrogen-doped carbon-based catalyst of this invention possesses excellent stability.

[0136] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing a bimetallic nitrogen-doped carbon-based catalyst, characterized in that, Includes the following steps: Synthesis of S1 and ZIF-8 templates: 2-methylimidazole and zinc nitrate hexahydrate were dissolved in a solvent, stirred and dissolved, and reacted to generate ZIF-8, thus obtaining a ZIF-8 template suspension; S2. Preparation of cobalt source solution: Dissolve cobalt nitrate hexahydrate in a solvent, stir to dissolve, and obtain cobalt source solution; S3. Cobalt source introduction into ZIF-8 template: The cobalt source solution is added to the ZIF-8 template suspension, and the mixture is stirred to carry out an ion exchange reaction, so that cobalt ions enter the ZIF-8 framework to obtain a precursor solution. S4. Separation and treatment of precursor: The precursor solution is allowed to stand at room temperature to obtain a sedimentation layer. Then, it is centrifuged, washed and dried to obtain the precursor. S5. Iron source vapor deposition: The precursor is mixed with ferrocene and placed in a tube furnace, and calcined under an inert atmosphere to obtain the bimetallic nitrogen-doped carbon-based catalyst.

2. The method for preparing a bimetallic nitrogen-doped carbon-based catalyst as described in claim 1, characterized in that, In step S1, the mass-to-volume ratio of 2-methylimidazole, zinc nitrate hexahydrate, and solvent is (7.0~8.0) g : (6.0~7.0) g : (400~600) mL.

3. The method for preparing a bimetallic nitrogen-doped carbon-based catalyst as described in claim 1, characterized in that, In step S2, the mass-to-volume ratio of cobalt nitrate hexahydrate to the solvent is (0.2~1.7) g: 20 mL; and / or In steps S1 and S2, the solvent is at least one of methanol, ethanol, or ultrapure water.

4. The method for preparing a bimetallic nitrogen-doped carbon-based catalyst as described in claim 1, characterized in that, In step S3, the temperature of the stirring reaction is 20℃~40℃, and / or the stirring speed is 500r / min~1000r / min, and / or the stirring reaction time is 30min~90min.

5. The method for preparing a bimetallic nitrogen-doped carbon-based catalyst as described in claim 1, characterized in that, In step S4, the settling time is 10h~18h; and / or The washing process involves washing 2-3 times with methanol, ethanol, or ultrapure water; and / or The drying temperature is 50℃~70℃, and the drying time is 10h~12h.

6. The method for preparing a bimetallic nitrogen-doped carbon-based catalyst as described in claim 1, characterized in that, In step S5, the mass ratio of the precursor to ferrocene is (0.6~0.8) g : (0.07~0.38) g.

7. The method for preparing a bimetallic nitrogen-doped carbon-based catalyst as described in claim 1, characterized in that, In step S5, the calcination temperature is 700℃~1000℃, and the calcination time is 1h~3h; and / or The heating rate for calcination is 4℃ / min to 6℃ / min.

8. The method for preparing a bimetallic nitrogen-doped carbon-based catalyst as described in claim 1, characterized in that, In step S5, the inert atmosphere is argon; and / or The flow rate of the inert atmosphere is 20 mL / min. -1 ~30mL / min -1 .

9. A bimetallic nitrogen-doped carbon-based catalyst, characterized in that, It is prepared by the method described in claims 1 to 8 for preparing a bimetallic nitrogen-doped carbon-based catalyst.

10. The application of a bimetallic nitrogen-doped carbon-based catalyst, characterized in that, The application of the bimetallic nitrogen-doped carbon-based catalyst according to claim 9 or the bimetallic nitrogen-doped carbon-based catalyst prepared by any one of claims 1 to 8 in the selective oxidation of 5-hydroxymethylfurfural to 2,5-furan carboxylic acid.

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