A hollow nitrogen-doped carbon-supported Zn-Co catalyst, preparation method and application

Abstract

The present invention relates to a hollow nitrogen-doped carbon-supported Zn-Co catalyst, a preparation method, and an application, belonging to the technical field of catalysts. The present invention includes surface modification treatment of hollow nitrogen-doped carbon-based micro-nanospheres, preparation of hollow nitrogen-doped carbon-based nanospheres supported by a bimetallic zinc-cobalt organic framework, and preparation of highly dispersed zinc-cobalt-supported hollow nitrogen-doped carbon-based nanosphere catalysts. Specifically, the present invention prepares hollow nitrogen-doped carbon-based micro-nanosphere carbon-based materials by self-assembly and calcination, and constructs a micro-nanoreactor by controlling synthesis by combining MOFs materials and hollow nitrogen-doped carbon-based micro-nanospheres to prepare a hollow nitrogen-doped carbon-based micro-nanosphere-supported zinc-cobalt nanoparticle catalyst having a stable structure, a large specific surface area, excellent electron transport capability, and efficient catalytic activity.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and in particular to a hollow nitrogen-doped carbon-supported Zn-Co catalyst, a preparation method and application thereof. Background Art

[0002] Supported metal catalysts have been shown to be excellent catalysts in a variety of organic synthesis reactions. However, current research has mostly focused on the support of precious metals such as Au, Ag, Pd, Ru, and Ir, with fewer reports on non-precious metals such as Fe, Co, Ni, Cu, and Zn.

[0003] Non-precious metals can be used as co-catalysts to enhance the activity of precious metals. However, the coordination between non-precious metals and the carrier is weak, and they are easily lost during the reaction, leading to environmental pollution and reduced catalyst activity.

[0004] Metal-organic frameworks (MOFs), constructed by combining metal salts with organic ligands, can effectively stabilize and confine metals. However, the metals are typically in a high-valence state, which often results in low catalytic activity during catalytic reactions. Recent reports have shown that M@CN materials, obtained by directly calcining MOFs, can be used as highly efficient catalysts for catalytic reactions.

[0005] However, the original three-dimensional structure of MOFs materials will inevitably collapse during the calcination process. The M@CN materials after calcination often appear as block or lamellar structures, and the role of the carrier in the catalyst cannot be well reflected.

[0006] Therefore, it is necessary to design and construct stable non-precious metal-loaded catalysts and develop their applications in organic synthesis reactions. Summary of the Invention

[0007] In order to solve the above technical problems, the present invention provides a hollow nitrogen-doped carbon-supported Zn-Co catalyst, a preparation method and an application thereof, which specifically include the following contents:

[0008] A method for preparing a hollow nitrogen-doped carbon-supported Zn-Co catalyst comprises the following steps:

[0009] (1) The hollow nitrogen-doped carbon-based micro-nanospheres are mixed with a polydiallyldimethylammonium chloride solution and a sodium polystyrene sulfonate solution respectively to obtain modified hollow nitrogen-doped carbon-based micro-nanospheres;

[0010] (2) The modified hollow nitrogen-doped carbon-based micro-nanospheres, zinc nitrate, cobalt nitrate, 2-methylimidazole solution and methanol were mixed to obtain hollow nitrogen-doped carbon-based nanospheres supported by a bimetallic zinc-cobalt organic framework;

[0011] (3) The hollow nitrogen-doped carbon-based nanospheres supported by the bimetallic zinc-cobalt organic framework are calcined to obtain highly dispersed zinc-cobalt supported hollow nitrogen-doped carbon-based nanosphere catalysts.

[0012] Preferably, the concentrations of the polydiallyldimethylammonium chloride solution and the sodium polystyrene sulfonate solution in step (1) are equal, and the concentration is 0.1-0.5 mol / L.

[0013] Preferably, the weight ratio of the modified hollow nitrogen-doped carbon-based micro-nanospheres, zinc nitrate, cobalt nitrate, and 2-methylimidazole solution in step (2) is 2-3:0.5-1.5:0.5-1.5:30.

[0014] Preferably, the 2-methylimidazole solution in step (2) is a 1 M 2-methylimidazole methanol solution.

[0015] Preferably, the step (3) further includes:

[0016] After calcination, the calcined product was cooled to room temperature and placed in 1 M hydrochloric acid solution and refluxed for 3 to 6 hours.

[0017] Preferably, the calcination conditions in step (3) are: a heating rate of 3-6°C / min, a final temperature of 800-1200°C, and constant temperature for 2-4 hours.

[0018] Preferably, the present invention also provides a hollow nitrogen-doped carbon-supported Zn-Co catalyst prepared by a method for preparing a hollow nitrogen-doped carbon-supported Zn-Co catalyst.

[0019] Preferably, the present invention also provides an application of a hollow nitrogen-doped carbon-supported Zn-Co catalyst in catalyzing N-alkylation reactions and catalyzing reduction reactions of nitroaromatic compounds.

[0020] Preferably, the specific steps of using the hollow nitrogen-doped carbon-supported Zn-Co catalyst in catalyzing N-alkylation reaction are:

[0021] In an inert atmosphere, aniline, benzyl alcohol, KOH and a hollow nitrogen-doped carbon-supported Zn-Co catalyst are mixed in a mass ratio of 20-40:60-80:1:5 and reacted at 100-150°C.

[0022] Preferably, the specific steps of using the hollow nitrogen-doped carbon-supported Zn-Co catalyst in catalyzing the reduction reaction of nitroaromatic compounds are:

[0023] Nitrobenzene, sodium borohydride, water and hollow nitrogen-doped carbon-supported Zn-Co catalyst are mixed in a mass ratio of 200-300:100-120:200-600:1 and reacted at 25-35°C.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The present invention uses hollow nitrogen-doped carbon-based micro-nanospheres, 2-methylimidazole, zinc nitrate, and cobalt nitrate as raw materials. A four-step process of surface modification, self-assembly coating, calcination, and acid treatment is used to obtain a hollow nitrogen-doped carbon-based micro-nanosphere-loaded ultra-dispersed Zn-Co nanoreactor catalyst. The catalyst exhibits excellent stability in both reactions and remains essentially unchanged after eight repeated uses.

[0026] (2) The hollow nitrogen-doped carbon-based micro-nanospheres of the present invention have two main functions: dispersion, which is used to make the active sites more evenly distributed; and electron transport, in which the hollow nitrogen-doped carbon-based micro-nanospheres can serve as carriers of electron transport during the reaction and optimize the electronic structure of the catalyst.

[0027] (3) The present invention uses surfactant polydiallyldimethylammonium chloride solution and sodium polystyrene sulfonate solution to modify the surface of hollow nitrogen-doped carbon-based micro-nanospheres, thereby optimizing the distribution of surface charge of the hollow nitrogen-doped carbon-based micro-nanospheres, increasing the specific surface area and electronegativity, thereby enhancing their adsorption effect on metal ions, and further facilitating the self-assembly coating and uniform surface coverage of ZIF materials.

[0028] (4) The present invention will greatly reduce the agglomeration of metals during the calcination process by confining metallic zinc and cobalt in the organic framework structure of ZIF materials and combining them with hollow nitrogen-doped carbon-based micro-nanospheres, and stabilize the metal particles. In addition, the introduction of metallic zinc promotes the uniform coating process of ZIF and the catalytic reaction process, improves the coordination microenvironment around metallic cobalt, and enhances the catalytic reaction activity. The catalyst prepared by the present invention has a yield of 96% in the N-alkylation reaction of aniline and benzaldehyde in a solvent-free-KOH reaction system at 125°C for 18 hours. In the reduction reaction of nitroaromatic compounds, in an ethanol / water system, sodium borohydride is used as the hydrogen source and the reaction is carried out at 30°C for 1 hour, and the yield is 96%. It can be seen that the catalyst prepared by the present invention has good catalytic performance and is worthy of promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the preparation process of the hollow nitrogen-doped carbon-supported Zn-Co catalyst of the present invention;

[0030] Figure 2 This is the substrate expansion diagram for N-alkylation reaction;

[0031] Figure 3 The SEM images of the growth of ZIF-8 with different loading amounts on the modified HCN surface in Example 4 are shown;

[0032] Figure 4 To test the growth of different ZIF-67 loadings on the modified HCN surface in Example 5;

[0033] Figure 5 Figure a is an SEM image of ZIF-8 loaded on hollow nitrogen-doped carbon-based micro-nanosphere material without surface modification, and figure b is an SEM image of ZIF-8 loaded on hollow nitrogen-doped carbon-based micro-nanosphere material with surface modification;

[0034] Figure 6 a is the infrared image of the surface-modified and unmodified hollow nitrogen-doped carbon-based micro-nanosphere materials, b is the Zeta potential of the surface-modified and unmodified hollow nitrogen-doped carbon-based micro-nanosphere materials;

[0035] Figure 7 XRD spectra of the following materials in Example 1 and Comparative Examples 1-2: (a) ZIF-8@HCN, ZIF-67@HCN, ZnCo-ZIF@HCN, HCN; (b) Co@HCN, Zn@HCN, ZnCo@HCN, S-ZnCo@HCN;

[0036] Figure 8 The infrared spectra of the following materials in Example 1 and Comparative Examples 1-2 are as follows: (a) ZIF-8@HCN, ZIF-67@HCN, CoZn-ZIF@HCN, HCN; (b) Co@HCN, Zn@HCN, ZnCo@HCN, S-ZnCo@HCN;

[0037] Figure 9 SEM images of the following materials in Example 1: (a) CoZn-ZIF@HCN, (b) ZnCo@HCN, (c) S-ZnCo@HCN;

[0038] Figure 10 HR-TEM image of the S-ZnCo@HCN material prepared in Example 1;

[0039] Figure 11 This is the XPS spectrum of the S-ZnCo@HCN material prepared in Example 1. DETAILED DESCRIPTION

[0040] The present invention provides a method for preparing a hollow nitrogen-doped carbon-supported Zn-Co catalyst, comprising the following steps:

[0041] (1) The hollow nitrogen-doped carbon-based micro-nanospheres are mixed with a polydiallyldimethylammonium chloride solution and a sodium polystyrene sulfonate solution respectively to obtain modified hollow nitrogen-doped carbon-based micro-nanospheres;

[0042] (2) The modified hollow nitrogen-doped carbon-based micro-nanospheres, zinc nitrate, cobalt nitrate, 2-methylimidazole solution and methanol were mixed to obtain hollow nitrogen-doped carbon-based nanospheres supported by a bimetallic zinc-cobalt organic framework;

[0043] (3) The hollow nitrogen-doped carbon-based nanospheres supported by the bimetallic zinc-cobalt organic framework are calcined to obtain highly dispersed zinc-cobalt supported hollow nitrogen-doped carbon-based nanosphere catalysts.

[0044] In the present invention, the specific process of mixing in step (1) is:

[0045] The hollow nitrogen-doped carbon-based micro-nanospheres are ultrasonically dispersed in a polydiallyldimethylammonium chloride solution, filtered, the filter residue is washed with water, and then ultrasonically dispersed in a sodium polystyrene sulfonate solution again.

[0046] In the present invention, the concentrations of the polydiallyldimethylammonium chloride solution and the sodium polystyrene sulfonate solution in step (1) are equal, preferably 0.1-0.5 mol / L, more preferably 0.1-0.4 mol / L, and even more preferably 0.1-0.3 mol / L.

[0047] In the present invention, the weight ratio of the modified hollow nitrogen-doped carbon-based micro-nanospheres, zinc nitrate, cobalt nitrate, and 2-methylimidazole solution in step (2) is preferably 2-3:0.5-1.5:0.5-1.5:30.

[0048] In the present invention, the 2-methylimidazole solution in step (2) is preferably a 1 M 2-methylimidazole methanol solution.

[0049] In the present invention, the step (3) further comprises:

[0050] After calcination, the calcined product was cooled to room temperature and placed in 1 M hydrochloric acid solution and refluxed for 3 to 6 hours.

[0051] In the present invention, the calcination conditions in step (3) are: the heating rate is preferably 3-6°C / min, the final temperature is preferably 800-1200°C, and the constant temperature is 2-4h.

[0052] The present invention also provides a hollow nitrogen-doped carbon-supported Zn-Co catalyst prepared by a preparation method of a hollow nitrogen-doped carbon-supported Zn-Co catalyst.

[0053] The present invention also provides an application of a hollow nitrogen-doped carbon-supported Zn-Co catalyst in catalyzing N-alkylation reactions and catalyzing reduction reactions of nitroaromatic compounds.

[0054] The specific steps of using the hollow nitrogen-doped carbon-supported Zn-Co catalyst provided in the present invention in catalyzing N-alkylation reaction are:

[0055] In an inert atmosphere, aniline, benzyl alcohol, KOH and a hollow nitrogen-doped carbon-supported Zn-Co catalyst are mixed in a mass ratio of 20-40:60-80:1:5, and reacted at 100-150°C.

[0056] The specific steps of using the hollow nitrogen-doped carbon-supported Zn-Co catalyst provided in the present invention in catalyzing the reduction reaction of nitroaromatic compounds are as follows:

[0057] Nitrobenzene, sodium borohydride, water and hollow nitrogen-doped carbon-supported Zn-Co catalyst are mixed in a mass ratio of 200-300:100-120:200-600:1 and reacted at 25-35°C.

[0058] The present invention also provides a method for preparing hollow nitrogen-doped carbon-based micro-nanospheres, the specific steps of which are as follows:

[0059] Triton Tx-100, distilled water, aniline, pyrrole and 1M ammonium persulfate solution were mixed in a weight ratio of 1:1000:5~8:4~7:100, stirred at 0~5°C until the solution color turned blue-black, allowed to stand for 6~15 hours, filtered with a 0.4~0.5μm microporous filter membrane, and the filter residue was washed with water and ethanol successively, dried at 40~60°C for more than 6 hours, transferred to an inert atmosphere, and heated to 600~1200°C at a heating rate of 4~6°C / min, and calcined at a constant temperature for 2~5 hours, and then naturally cooled to room temperature to obtain hollow nitrogen-doped carbon-based micro-nanospheres.

[0060] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the embodiments described are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0061] Example 1

[0062] This embodiment provides a method for preparing a hollow nitrogen-doped carbon-supported Zn-Co catalyst:

[0063] (1) Preparation of hollow nitrogen-doped carbon-based micro-nanospheres

[0064] 0.30 g of Triton Tx-100, 300 mL of distilled water, 1.91 mL of aniline, and 1.45 mL of pyrrole were added to a 500 mL beaker. Ultrasonication was performed at 50 Hz for 1 hour to completely disperse the compounds in the solution. The solution was then transferred to a jacketed reaction flask and maintained at a temperature between 0 and 5°C through a circulating coolant. Stirring was continued for 1 hour. 30 mL of pre-chilled 1 M ammonium persulfate solution was slowly added to the reaction flask and vigorously stirred for 5 minutes to mix thoroughly. Stirring was stopped when the solution turned from colorless and transparent to bluish-black. The solution was then placed in a refrigerator at 0°C overnight. The catalyst was filtered through a 0.45 μm microporous filter and the solution was clarified by washing with water and ethanol. The solid was dried in a vacuum oven at 60°C for 8 hours before use. The sample was labeled: PACP.

[0065] A 4.00 g PACP sample was placed in a covered bar crucible and calcined in a tube furnace under an Ar atmosphere. The heating program was as follows: heating to 800 °C at 5 °C / min from room temperature, holding for 3 h, and then naturally cooling to room temperature. The sample was labeled: HCN.

[0066] (2) Surface modification of hollow nitrogen-doped carbon-based micro-nanospheres

[0067] Take 200 mg of HCN material, add 30 mL of 0.2 mol / L PDDA (polydiallyldimethylammonium chloride) solution, ultrasonically disperse and react for 1 hour, filter and separate, wash with water, and record it as PDDA-HCN. Disperse PDDA-HCN in 30 mL of 0.2 mol / L PSS (sodium polystyrene sulfonate) solution again, continue ultrasonic reaction for 1 hour, filter and separate, wash with water, and vacuum dry, and record it as PSS-PDDA-HCN.

[0068] (3) Preparation of hollow nitrogen-doped carbon-based nanospheres supported by bimetallic ZnCo organic framework

[0069] 200 mg of modified HCN material was dispersed in 30 mL of methanol solution and ultrasonically dispersed for 30 minutes. 0.08 g of zinc nitrate and 0.08 g of cobalt nitrate were added, and ultrasonication was continued for another 30 minutes. Then, the material was transferred to a jacketed reaction flask and pre-cooled to 0°C. 1 M 2-methylimidazole dissolved in 30 mL of methanol was added to the reaction flask, and the reaction was stirred at zero temperature for 1.5 hours. The temperature was raised to 40°C for 30 minutes, centrifuged, washed with methanol, and dried in vacuo. The material was recorded as ZnCo-ZIF@HCN.

[0070] (4) Preparation of highly dispersed ZnCo-loaded hollow nitrogen-doped carbon-based nanosphere catalysts

[0071] ZnCo-ZIF@HCN was placed in a tube furnace under argon atmosphere and heated to 800°C at 5°C / min, then calcined at 800°C for 2 hours and naturally cooled to room temperature. The obtained sample was recorded as ZnCo@HCN.

[0072] The obtained ZnCo@HCN material was placed in a 1 M hydrochloric acid solution and refluxed for 4 hours. The sample obtained after filtration, washing and drying was recorded as S-ZnCo@HCN.

[0073] Example 2

[0074] This embodiment provides a method for preparing a hollow nitrogen-doped carbon-supported zinc and cobalt catalyst:

[0075] (1) Preparation of hollow nitrogen-doped carbon-based micro-nanospheres

[0076] 0.30 g of Triton Tx-100, 300 mL of distilled water, 1.63 mL of aniline, and 1.27 mL of pyrrole were added to a 500 mL beaker and sonicated at 50 Hz for 1 h to completely disperse the compounds. The solution was then transferred to a jacketed reaction flask, maintained at 0–5°C through a circulating coolant, and stirred for 1 h. 30 mL of pre-chilled 1 M ammonium persulfate solution was slowly added to the flask and vigorously stirred for 5 min to mix thoroughly. When the solution transitioned from colorless to blue-black, stirring was stopped and the mixture was allowed to stand overnight in a refrigerator at 0°C. The catalyst was filtered through a 0.40 μm microporous filter. The solution was clarified by washing with water and ethanol. The solid was dried in a vacuum oven at 60°C for 8 h. 4.00 g of the solid was placed in a covered strip crucible and calcined in a tube furnace under an Ar atmosphere. The heating program was as follows: heating to 600°C at 4°C / min at room temperature, holding for 5 h, and then naturally cooling to room temperature to obtain hollow nitrogen-doped carbon-based micro-nanospheres.

[0077] (2) Surface modification of hollow nitrogen-doped carbon-based micro-nanospheres

[0078] Take 200 mg of hollow nitrogen-doped carbon-based micro-nanospheres, add 30 mL of 0.1 mol / L polydiallyldimethylammonium chloride solution, ultrasonically disperse and react for 1 hour, filter and separate, and wash with water; the above-obtained material is dispersed in 30 mL of 0.1 mol / L sodium polystyrene sulfonate solution, continue ultrasonic reaction for 1 hour, filter and separate, wash with water, and vacuum dry to obtain hollow nitrogen-doped carbon-based micro-nanospheres.

[0079] (3) Preparation of hollow nitrogen-doped carbon-based nanospheres supported by bimetallic ZnCo organic framework

[0080] 200 mg of modified hollow nitrogen-doped carbon-based micro-nanosphere material was dispersed in 30 mL of methanol solution and ultrasonically dispersed for 30 minutes. 0.05 g of zinc nitrate and 0.05 g of cobalt nitrate were added, and ultrasonication was continued for another 30 minutes. Then, the material was transferred to a jacketed reaction bottle and pre-cooled to 0°C. 1M 2-methylimidazole dissolved in 30 mL of methanol was added to the reaction bottle, and the reaction was stirred at zero degree for 1 hour. The temperature was raised to 30°C for 30 min, centrifuged, washed with methanol, and vacuum dried to obtain hollow nitrogen-doped carbon-based nanospheres supported by a bimetallic ZnCo organic framework.

[0081] (4) Preparation of highly dispersed ZnCo-loaded hollow nitrogen-doped carbon-based nanosphere catalysts

[0082] The above-mentioned metal-loaded material was placed in a tubular furnace under an argon atmosphere and heated to 600°C at 4°C / min, and then calcined at 600°C for 4 hours. The sample obtained after calcination was placed in a 1M hydrochloric acid solution and refluxed for 3 hours. After filtering, the filter residue was washed with water and dried to obtain a highly dispersed zinc-cobalt loaded hollow nitrogen-doped carbon-based nanosphere catalyst.

[0083] Example 3

[0084] This embodiment provides a method for preparing a hollow nitrogen-doped carbon-supported zinc and cobalt catalyst:

[0085] (1) Preparation of hollow nitrogen-doped carbon-based micro-nanospheres

[0086] 0.30 g of Triton Tx-100, 300 mL of distilled water, 2.27 mL of aniline, and 1.89 mL of pyrrole were added to a 500 mL beaker and sonicated at 50 Hz for 1 h to completely disperse the compounds. The solution was then transferred to a jacketed reaction flask, maintained at 0–5°C with circulating coolant, and stirred for 1 h. 30 mL of pre-chilled 1 M ammonium persulfate solution was slowly added to the flask and stirred vigorously for 5 min to mix thoroughly. When the solution transitioned from colorless to blue-black, stirring was stopped and the mixture was allowed to stand overnight in a refrigerator at 0°C. The catalyst was filtered through a 0.50 μm microporous filter. The solution was clarified by washing with water and ethanol. The solid was dried in a vacuum oven at 60°C for 8 h. 4.00 g of the solid was placed in a covered strip crucible and calcined in a tube furnace under an Ar atmosphere. The heating program was as follows: heating to 1000°C at 6°C / min at room temperature, holding for 2 h, and then naturally cooling to room temperature to obtain hollow nitrogen-doped carbon-based micro-nanospheres.

[0087] (2) Surface modification of hollow nitrogen-doped carbon-based micro-nanospheres

[0088] Take 300 mg of hollow nitrogen-doped carbon-based micro-nanospheres, add 30 mL of 0.5 mol / L polydiallyldimethylammonium chloride solution, ultrasonically disperse and react for 1 hour, filter and separate, and wash with water; the above-obtained material is dispersed in 30 mL of 0.5 mol / L sodium polystyrene sulfonate solution, continue ultrasonic reaction for 1 hour, filter and separate, wash with water, and vacuum dry to obtain hollow nitrogen-doped carbon-based micro-nanospheres.

[0089] (3) Preparation of hollow nitrogen-doped carbon-based nanospheres supported by bimetallic ZnCo organic framework

[0090] 300 mg of modified hollow nitrogen-doped carbon-based micro-nanosphere material was dispersed in 30 mL of methanol solution and ultrasonically dispersed for 30 minutes. 0.15 g of zinc nitrate and 0.15 g of cobalt nitrate were added, and ultrasonication was continued for another 30 minutes. Then, the material was transferred to a jacketed reaction flask and pre-cooled to 0°C. 1M 2-methylimidazole dissolved in 30 mL of methanol was added to the reaction flask, and the reaction was stirred at zero temperature for 2 hours. The temperature was raised to 50°C for 30 min, centrifuged, washed with methanol, and vacuum dried to obtain hollow nitrogen-doped carbon-based nanospheres supported by a bimetallic ZnCo organic framework.

[0091] (4) Preparation of highly dispersed ZnCo-loaded hollow nitrogen-doped carbon-based nanosphere catalysts

[0092] The above-mentioned metal-loaded material was placed in a tubular furnace under an argon atmosphere and heated to 1000°C at 6°C / min, and then calcined at 1000°C for 2 hours. The sample obtained after calcination was placed in a 1M hydrochloric acid solution and refluxed for 6 hours, filtered, and the filter residue was washed with water and dried to obtain a highly dispersed zinc-cobalt loaded hollow nitrogen-doped carbon-based nanosphere catalyst.

[0093] Comparative Example 1

[0094] This embodiment provides a method for preparing a hollow nitrogen-doped carbon-supported Zn catalyst:

[0095] (1) Same as Example 1.

[0096] (2) Take 200 mg of HCN material, add 30 mL of 0.2 mol / L PDDA (polydiallyldimethylammonium chloride) solution, ultrasonically disperse and react for 1 hour, filter and separate, wash with water, and disperse the above-obtained material in 30 mL of 0.2 mol / L PSS (sodium polystyrene sulfonate) solution. Continue ultrasonic reaction for 1 hour, filter and separate, wash with water, and vacuum dry for use.

[0097] (3) 200 mg of modified HCN material was dispersed in 30 mL of methanol solution and ultrasonically dispersed for 30 minutes. 0.08 g of zinc nitrate was added and ultrasonicated for another 30 minutes. Then the material was transferred to a jacketed reaction flask and pre-cooled to 0°C. 1 M 2-methylimidazole dissolved in 30 mL of methanol was added to the reaction flask and stirred at zero temperature for 1.5 hours. The material was heated to 40°C for 30 minutes, centrifuged, washed with methanol, and dried under vacuum. The product was recorded as ZIF8@HCN.

[0098] (4) ZIF8@HCN was placed in a tube furnace under an argon atmosphere and heated to 800°C at a rate of 5°C / min. It was then calcined at 800°C for 2 hours and naturally cooled to room temperature. The obtained sample was recorded as Zn@HCN.

[0099] Comparative Example 2

[0100] This embodiment provides a method for preparing a hollow nitrogen-doped carbon-supported Co catalyst:

[0101] (1) Same as Example 1.

[0102] (2) Take 200 mg of HCN material, add 30 mL of 0.2 mol / L PDDA (polydiallyldimethylammonium chloride) solution, ultrasonically disperse and react for 1 hour, filter and separate, wash with water, and disperse the above-obtained material in 30 mL of 0.2 mol / L PSS (sodium polystyrene sulfonate) solution. Continue ultrasonic reaction for 1 hour, filter and separate, wash with water, and vacuum dry for use.

[0103] (3) 200 mg of modified HCN material was dispersed in 30 mL of methanol solution and ultrasonically dispersed for 30 minutes. 0.08 g of cobalt nitrate was added and ultrasonicated for another 30 minutes. Then the material was transferred to a jacketed reaction flask and pre-cooled to 0°C. 1 M 2-methylimidazole dissolved in 30 mL of methanol was added to the reaction flask and stirred at zero temperature for 1.5 hours. The material was heated to 40°C for 30 minutes, centrifuged, washed with methanol, and dried under vacuum. The product was recorded as ZIF67@HCN.

[0104] (4) ZIF67@HCN was placed in a tube furnace under an argon atmosphere and heated to 800°C at a rate of 5°C / min. It was then calcined at 800°C for 2 hours and naturally cooled to room temperature. The obtained sample was recorded as Co@HCN.

[0105] Comparative Example 3

[0106] This embodiment provides a method for preparing a hollow nitrogen-doped carbon-supported Zn-Co catalyst:

[0107] (1) Same as Example 1.

[0108] (2) Disperse 200 mg of HCN material in 30 mL of methanol solution and ultrasonically disperse for 30 minutes. Add 0.08 g of zinc nitrate and 0.08 g of cobalt nitrate and ultrasonically disperse for another 30 minutes. Then transfer it to a jacketed reaction bottle and precool it to 0°C. Add 1 M 2-methylimidazole dissolved in 30 mL of methanol to the reaction bottle. Keep stirring at zero temperature for 1.5 hours, heat to 40°C for 30 minutes, centrifuge, wash with methanol, and vacuum dry. It is recorded as ZnCo-ZIF / HCN-1.

[0109] (3) ZnCo-ZIF / HCN-1 was placed in a tube furnace under an argon atmosphere and heated to 800°C at a rate of 5°C / min. It was then calcined at 800°C for 2 hours and naturally cooled to room temperature. The resulting sample was recorded as ZnCo / HCN-1.

[0110] Comparative Example 4

[0111] This comparative example provides a preparation method of a supported Zn catalyst obtained by calcining ZIF-8 material alone:

[0112] 0.08 g of zinc nitrate was added to a jacketed reaction flask and pre-cooled to 0°C. 1 M 2-methylimidazole dissolved in 30 mL of methanol was added to the reaction flask and stirred at zero temperature for 1.5 hours. The temperature was raised to 40°C and reacted for 30 min. The reaction was centrifuged, washed with methanol, and dried in vacuo. The reaction was recorded as Zn-ZIF@CN.

[0113] Zn-ZIF@CN was placed in a tube furnace under argon atmosphere and heated to 800°C at 5°C / min, then calcined at 800°C for 2 hours and naturally cooled to room temperature. The obtained sample was recorded as Zn@CN.

[0114] Comparative Example 5

[0115] This comparative example provides a preparation method of a supported Co catalyst obtained by calcining ZIF-67 material alone:

[0116] 0.08 g of cobalt nitrate was added to a jacketed reaction flask and pre-cooled to 0°C. 1 M 2-methylimidazole dissolved in 30 mL of methanol was added to the reaction flask and stirred at zero temperature for 1.5 hours. The temperature was raised to 40°C and reacted for 30 min. The reaction was centrifuged, washed with methanol, and dried in vacuo. The reaction was recorded as Co-ZIF@CN.

[0117] Co-ZIF@CN was placed in a tube furnace under argon atmosphere and heated to 800°C at 5°C / min, then calcined at 800°C for 2 hours and naturally cooled to room temperature. The obtained sample was recorded as Co@CN.

[0118] Application Example 1

[0119] Application in catalytic N-alkylation reactions

[0120] In the examples of the present invention, the catalyst activity was evaluated by the N-alkylation reaction of aniline with benzyl alcohol. The optimized reaction conditions are shown in Table 1. First, the solvent was screened. The solvation effect of the solvent significantly influenced the reaction. o-xylene and toluene performed well as solvents, with yields reaching 87% and 79% (entries 1 and 2). Water, ethanol, acetonitrile, and DMF performed poorly, with yields ranging from 14% to 45% (entries 3-6). However, the reaction was particularly effective in the absence of solvent, with a conversion of aniline reaching 98% and a yield of the target compound of 97% (entry 7). The effects of several bases were then compared in the absence of solvent. Strong bases yielded higher yields (KOH: 97%, KOMe: 87%), while potassium phosphate, cesium carbonate, and potassium carbonate yielded yields of 68%, 67%, and 44%, respectively (entries 9-11). Blank experiments demonstrated that the reaction could proceed without the addition of an external base, albeit with a lower yield of only 25% (entry 12). This suggests that the presence of a base is not essential for this reaction; it may serve to accelerate the reaction. Subsequently, temperature and time optimization (entries 13-16) were performed. After comprehensive consideration, the optimal reaction conditions were: potassium hydroxide, 125°C, 3 mmol of aniline, 6 mmol of benzyl alcohol, and 5 mg of catalyst. The reaction time was 18 hours, resulting in an aniline conversion of 98% and a yield of 96% for the target compound.

[0121] The catalyst-catalyzed N-alkylation reaction formula is as follows:

[0122]

[0123] Table 1 Catalytic reaction conditions screening table

[0124]

[0125] The present invention also uses aniline and benzyl alcohol with different substituent groups to test the universality of the catalyst in this reaction system. The results are as follows: Figure 2 As shown, the presence of an electron-donating group at the para position of benzyl alcohol enhances the reaction activity (3b and 3c). When the para position of benzyl alcohol is substituted with a sterically hindered benzene ring, the yield decreases slightly due to steric hindrance (3d). This steric hindrance is particularly evident in the reaction with 3,5-dimethoxybenzyl alcohol as a substrate, reducing the yield to 83% (3e). Electron-withdrawing substituents on benzyl alcohol are less active than electron-donating substituents (3f). In addition to substituents on benzyl alcohol, the activity of 3-methyl, 4-methoxy, and 4-chloro groups on aniline was also tested, and all of these yielded the target compounds (3g-3i) in moderate to high yields.

[0126] This embodiment provides an application of a hollow nitrogen-doped carbon-supported zinc and cobalt catalyst in catalyzing N-alkylation reactions:

[0127] 3 mmol of aniline, 6 mmol of benzyl alcohol, 10 mg of hollow nitrogen-doped carbon-supported zinc, cobalt catalyst, and 0.9 mmol of KOH were added to a 10 mL reaction tube, and the mixture was reacted at 125 °C under argon protection for 18 hours.

[0128] Application Example 2

[0129] Application in catalytic reduction of nitroaromatic compounds

[0130] In addition to N-alkylation reactions, the present invention also tested the catalytic activity of the S-ZnCo@HCN catalyst in the liquid-phase reduction of nitroaromatic compounds. The reaction conditions were optimized, as shown in Table 2. Sodium borohydride was first selected as the reducing agent, and the reaction solvents were screened. Considering the green nature of the reaction, the reactivity was tested in alcoholic solvents and water. The catalyst produced the target compound with a 94% yield in ethanol, with a slightly higher yield in methanol (95%). Although the yield in pure water was lower than that in alcoholic solvents, it still achieved a yield of 87%. Using a mixed solvent of ethanol and water, the yield was increased to 98%. This is likely due to the shared advantages of both solvents, which facilitate the dissolution of the reactants and the dispersion of the catalyst. Furthermore, the activity was tested using hydrazine hydrate as the reducing agent. Unfortunately, the catalyst failed to catalyze the reaction in this solvent. Finally, the reaction time and catalyst dosage were optimized, and the optimal reaction conditions were obtained: a mixture of water and ethanol = 1:1 as solvent, sodium borohydride as reducing agent, 3 mg of S-ZnCo@HCN catalyst, and reaction time of 1 hour at 30°C, the yield can reach 97%.

[0131] The reduction reaction of nitroaromatic compounds catalyzed by S-ZnCo@HCN catalyst is as follows:

[0132]

[0133] Table 2 Optimization of nitro reduction reaction conditions

[0134]

[0135] This embodiment provides an application of a hollow nitrogen-doped carbon-supported zinc and cobalt catalyst in catalyzing the reduction reaction of nitroaromatic compounds:

[0136] In a 15 mL reaction bottle, 1 mmol of nitrobenzene, 1.5 mmol of sodium borohydride, 5 mg of hollow nitrogen-doped carbon-supported zinc, cobalt catalyst, and 2 mL of water were added, stirred and mixed evenly, and reacted at 30°C. The reaction progress was monitored by thin-layer chromatography.

[0137] Test Example 1

[0138] This test example provides an application of a hollow nitrogen-doped carbon-supported zinc and cobalt catalyst in catalyzing the reduction reaction of nitroaromatic compounds:

[0139] In a 15 mL reaction bottle, 1 mmol of nitrobenzene, 1.5 mmol of sodium borohydride, 5 mg of hollow nitrogen-doped carbon-supported zinc, cobalt catalyst, and 2 mL of water were added, stirred and mixed evenly, and reacted at 30°C. The reaction progress was monitored by thin-layer chromatography.

[0140] Test Example 1

[0141] This test example provides a method for testing the catalytic N-alkylation activity of hollow nitrogen-doped carbon-supported zinc and cobalt catalysts:

[0142] To a 10 mL reaction tube, 3 mmol of aniline, 6 mmol of benzyl alcohol, 5 mg of catalyst, and 1.5 mmol of KOH were added. Seven parallel experiments were conducted, using the ZnCo@HCN, ZnCo-ZIF@HCN, and S-ZnCo@HCN catalysts from Example 1, the Zn@HCN from Comparative Example 1, the Co@HCN from Comparative Example 2, the Zn@CN from Comparative Example 4, and the Co@CN from Comparative Example 5, respectively. All other conditions remained unchanged. The reaction was carried out at 125°C under argon for 18 hours. After completion, the reaction was quenched, and the organic phase was collected. The conversion and yield were determined by gas chromatography (n-hexadecane as an internal standard). Three runs were performed for each sample, and the average was calculated. Chromatographic conditions: Initial column temperature: 80°C, temperature program: 10°C / min to 180°C, hold for 10 minutes. Chromatographic column: Agilent HP-5 capillary column.

[0143] Test Example 2

[0144] This test example provides a method for testing the activity of hollow nitrogen-doped carbon-supported zinc and cobalt catalysts in catalytic nitro reduction reactions:

[0145] To a 15 mL reaction flask, add 1 mmol of nitrobenzene, 1.5 mmol of sodium borohydride, 5 mg of S-ZnCo@HCN, and 2 mL of water. Stir and mix thoroughly. Incubate at 30°C and monitor the reaction progress using thin-layer chromatography. While other conditions remain unchanged, perform the nitro reduction reaction on different substrates for 1 hour.

[0146] Test Example 3

[0147] Catalyst recycling performance test

[0148] (1) Catalytic N-alkylation reaction cycle activity test

[0149] A 10 mL reaction tube was charged with 3 mmol of aniline, 6 mmol of benzyl alcohol, 5 mg of S-ZnCo@HCN, and 1.5 mmol of KOH. The reaction was incubated at 125°C under argon for 18 hours. After completion, the reaction was quenched and the organic phase collected. The yield was determined by gas chromatography (n-hexadecane as the internal standard). Each sample was tested three times and the average was calculated. After each reaction, the catalyst was filtered, washed with ethyl acetate, and dried under vacuum at 60°C before being reused in the next reaction. This process was repeated after each reaction. Chromatographic conditions: Initial column temperature: 80°C, temperature program: 10°C / min to 180°C, hold for 10 minutes. Chromatographic column: Agilent HP-5 capillary column.

[0150] (2) Catalytic nitrobenzene reduction reaction cycle activity test

[0151] To a 15 mL reaction flask, add 1 mmol of nitrobenzene, 1.5 mmol of sodium borohydride, 5 mg of S-ZnCo@HCN, and 2 mL of water. Stir and mix thoroughly. React at 30°C, monitoring the reaction progress using thin-layer chromatography. After each reaction, filter and separate the catalyst, wash with ethyl acetate, and dry under vacuum at 60°C. The catalyst is then reused for the next reaction, and this process is repeated after each reaction.

[0152] Test Example 4

[0153] Detection of the effect of different loading amounts on the growth of ZIF-8 on the modified HCN surface

[0154] While keeping other conditions unchanged, during the experimental preparation process, 200 mg of modified HCN and a sufficient amount of 2-methylimidazole (0.84 g) were added, and the feeding amounts of zinc nitrate were controlled to be: 0.32 g, 0.24 g, 0.16 g, and 0.08 g, respectively.

[0155] Test Example 5

[0156] Detection of the effect of different loading amounts on the growth of ZIF-67 on the modified HCN surface

[0157] Keeping other factors unchanged, during the experimental preparation process, 200 mg of modified HCN and a sufficient amount of 2-methylimidazole (0.84 g) were added, and the feeding amounts of cobalt nitrate were controlled to be: 0.32 g, 0.24 g, 0.16 g, and 0.08 g, respectively.

[0158] Test results

[0159] Table 3 is a comparative table of the catalytic activities of the catalysts prepared in Example 1 and Comparative Examples 1 to 5 in the catalytic N-alkylation reaction activity test.

[0160]

[0161] Table 3 shows that the catalytic activity of the Zn@CN material obtained by calcining ZIF-8 alone was very low, with a yield of only 27%. However, the Co@CN material obtained by calcining ZIF-67 achieved a 79% aniline conversion and a 76% yield of the target compound, indicating that Co is more active than Zn in this reaction system. ZIF-8 and ZIF-67 were supported on HCN to obtain ZIF-8@HCN and ZIF-67@HCN, respectively, and then calcined to obtain Zn@HCN and Co@HCN materials. These materials exhibited higher activity than those without HCN support, indicating that the HCN support enhances catalytic activity. When ZnCo@HCN, prepared by calcining ZnCo-ZIF@HCN with cobalt and zinc metals, was used as the catalyst, the reaction activity was significantly improved, with an aniline conversion of 93%, demonstrating a bimetallic synergistic effect when Co and Zn are present. XRD data revealed the presence of a ZnS impurity phase within the ZnCo@HCN catalyst, accompanied by some metal agglomeration. Experimental results demonstrated that the S-ZnCo@HCN material was significantly more active than the ZnCo@HCN material in the N-alkylation of aniline and benzyl alcohol, achieving 98% aniline conversion and 96% yield of the target product. This suggests that the agglomerated metal particles and ZnS material are not the true catalytic active sites, but rather the metal dispersed on the HCN. Finally, the bimetallic catalyst ZnCo / HCN-1, prepared from unmodified HCN, was used as a catalyst. The yield of the target compound was only 80%, far lower than that of the ZnCo@HCN and S-ZnCo@HCN materials. This further demonstrates the role of the HCN support. Although HCN itself cannot catalyze the reaction, its role as a metal support can enhance catalytic activity.

[0162] Table 4 shows the substrate expansion and yield of nitroaromatic compounds in the catalytic nitro reduction reaction activity test

[0163]

[0164] Table 4 shows the substrate expansion and yield of nitroaromatic compounds in the catalytic nitro reduction reaction activity test. As can be seen from the table, the catalyst has good universality across different substrates, and the target compounds can all be obtained with moderate or higher yields. In comparison, electron-donating groups are more active than electron-withdrawing groups. Among the different substitution positions, the para position has the highest activity, followed by the meta position, and the ortho position has the lowest activity. This may be related to the spatial structure of the substituent group, with the ortho position having greater steric hindrance. Among the halogen elements, F has the highest yield, while Cl and Br have the lowest yield, which is related to electronegativity. However, iodine is more active than chlorine and bromine substitutions, which may be due to the special properties of the iodine group atom. In addition, compounds substituted with naphthalene and benzyl bromide also obtained the target compounds with excellent yields.

[0165] Table 5 is a table showing the recycling activity test of the S-ZnCo@HCN catalyst prepared in Example 1 in N-alkylation reaction and nitrobenzene reduction reaction.

[0166]

[0167] Table 5 shows the cyclic performance of the S-ZnCo@HCN catalyst in N-alkylation and nitrobenzene reduction reactions. Because the N-alkylation reaction requires a strong base and a temperature of 125°C, the reaction conditions are more stringent, so the yield of the S-ZnCo@HCN catalyst decreases slightly during recycling. However, the yield of the target compound still reaches 90% by the eighth cycle. In the nitro reduction reaction, the catalyst's activity remains essentially unchanged after multiple uses, and the experiment can be completed with a yield of over 92%. In summary, the S-ZnCo@HCN catalyst has good recyclability and can still produce the target compound in moderate to high yields after multiple uses.

[0168] Depend on Figure 3 It can be seen that when the zinc nitrate dosage is 0.32 g, ZIF-8 particles aggregate significantly on the surface of the modified HCN. After coating the modified HCN, the remaining material grows in the gaps of the composite material, resulting in severe adhesion. The size of the ZIF-8 particles growing in the gaps is significantly larger than the particles coating the surface of the modified HCN material. As the zinc nitrate dosage decreases, the ZIF-8 coating of the modified HCN becomes more regular. When the zinc nitrate dosage is 0.16 g and 0.08 g, the surface coating is uniform, and the spherical structure is clearly visible.

[0169] Depend on Figure 4It can be seen that when cobalt nitrate is used as a raw material to in situ grow ZIF-67 on the surface of modified HCN, the coating situation is not ideal. ZIF-67 will aggregate on the surface of the material, resulting in a portion of the modified HCN not being coated. In addition, the particle size of ZIF-67 obtained under this experimental scheme is significantly larger than that of ZIF-8. Adjusting the feeding amount of different cobalt nitrates does not improve the problem of uneven loading. This uneven coating will cause a portion of the metal organic framework material to exist independently in the material, which cannot well reflect the synergistic effect after combining it with the HCN material.

[0170] like Figure 5 As shown in a, ZIF-8 cannot be directionally coated on HCN materials without surface modification.

[0171] like Figure 5 As shown in Figure b, it can be clearly observed that the surface of the surface-modified HCN material is relatively evenly coated with ZIF-8 particles, which shows that surface modification is the key to achieving uniform coating of ZIF-8.

[0172] like Figure 6 As shown in a, the infrared spectrum of the HCN material modified with PDDA solution is at 1047 cm -1 、883 cm -1 Two new peaks appeared at 1617 cm, which may be related to the attachment of PDDA molecules on the surface of HCN material. After the modification with PSS solution, the two peaks weakened, but the peak at 1617 cm -1 The peak at 1586 cm-1 shifted slightly to 1586 cm-1. -1 This may be related to the change of the overall structural charge of the material.

[0173] like Figure 6 As shown in Figure 2b, the Zeta of the HCN surface is 18.3 mV, while that of the DDA-HCN material is 33.5 mV. This is because PDDA, a cationic surfactant, optimizes the surface charge of the HCN material. The Zeta of the PSS-PDDA-HCN material, further modified with an anionic surfactant, is -22.0 mV. This modifies the HCN surface charge from positive to negative, which facilitates metal adsorption and adhesion. Consequently, ZIF-8 can grow uniformly along the surface of the modified material.

[0174] like Figure 7 As shown in Figure a, ZIF-8@HCN, ZIF-67@HCN and Co / Zn-ZIF@HCN materials all show the characteristic peaks of metal-organic frameworks. Since the three materials are MOFs materials synthesized using 2-methylimidazole as raw material, the characteristic peaks of the three materials are basically the same, which also proves that the composite of MOFs and HCN materials is successful.

[0175] Figure 7 b shows the spectra of the calcined material and the final acid-treated S-ZnCo@HCN material. ZIF-8@HCN calcined under an argon atmosphere to obtain the Zn@HCN material exhibits a distinct set of diffraction peaks, which were confirmed to be those of ZnS. After tracing the source of the sulfur in the material, analysis suggests that (NH₄)₂S₂O₂ was used as an oxidation initiator during the HCN synthesis. Although most of the sulfur was removed during the calcination of the PACP material to prepare the HCN material, a very small amount of sulfur remained in the material. During the calcination of the ZIF-8@HCN material to prepare the Zn@HCN material, despite pyrolysis under an argon atmosphere, the S element readily combines with the Zn element, resulting in the preferential formation of ZnS species during the pyrolysis of the ZIF-8 material in the composite. Because HCN is an amorphous carbon material and the ZnS is highly crystalline, the distinct diffraction peaks appear in the spectra. However, the above phenomenon did not occur when ZIF-67@HCN was calcined to prepare Co@HCN material, and the peaks in the resulting material were confirmed to be peaks of Co metal. This is related to the properties of metal compounds. Sulfur does not combine with Co. The ZnCo@HCN material obtained by calcining Co / Zn-ZIF@HCN showed peaks of two phases, ZnS and Co metal. Usually, sharp diffraction peaks will appear in the XRD spectrum only when metal compounds agglomerate together to form particles. Therefore, it was considered to place the ZnCo@HCN material in a 1M hydrochloric acid solution and reflux for 4 hours to remove the agglomerated metal and impurities such as ZnS on the surface of the material. It can be found that the diffraction peaks of the final S-ZnCo@HCN material are basically consistent with those of HCN, showing only the amorphous broad peak of the carrier skeleton, and the diffraction peak of the metal disappears, indicating that the remaining metal in the material is already ultra-dispersed on the carrier.

[0176] Figure 8 The infrared spectra of the materials are shown. The uncalcined precursors ZIF-8@HCN, ZIF-67@HCN and Co / Zn-ZIF@HCN materials show the same absorption peaks, which are the same as the absorption peaks of ZIF-8 and ZIF-67, indicating that the surface of the material is coated with ZIF. The spectrum of the calcined material Figure 5 These absorption peaks disappear in b, and the overall peak shapes of several materials are basically consistent with those of HCN materials. However, after careful comparison, it is found that the peak center of Zn@HCN is at 1591 cm -1 The peak at 1618 cm-1 shifts to 1618 cm-1 in materials containing Co. -1 , which may be related to the interaction between metallic cobalt and carbon and nitrogen elements in the support.

[0177] Figure 9SEM images of Co / Zn-ZIF@HCN, ZnCo@HCN, and S-ZnCo@HCN materials are shown. The ZIF particles in the Co / Zn-ZIF@HCN material, prepared by mixing zinc and cobalt, are uniformly coated on the HCN surface, overcoming the uneven coating problem of ZIF-67 alone. However, compared to the ZIF-8 coated material, the particle size of the surface of the Co / Zn-ZIF composite material is slightly larger. Figure 9 b is an SEM image of the ZnCo@HCN material obtained after calcination. It can be clearly observed that there is a clear spherical structure in the ZnCo@HCN material, but there is a sticky phenomenon between the spheres. It can also be found that there are many fine particles on the spherical surface. This is because the carbon and nitrogen elements of the metal organic framework coated on the surface are partially reconnected after high-temperature calcination, and the originally coated ZIF shrinks at high temperature. In addition, some obvious block structures were observed in the ZnCo@HCN material, which are believed to be agglomerated metals or metal compounds. Figure 9 In the S-ZnCo@HCN material (c), this bulk structure disappears after hydrochloric acid treatment. However, the small particles on the spheres' surfaces remain, confirming that they are not bare metal particles but rather spheres coated with carbon and nitrogen. These structures can be considered to be numerous tiny reactors assembled on the hollow HCN surface, providing active sites and locations for reactions.

[0178] Figure 10 HR-TEM images and elemental mapping images of S-ZnCo@HCN materials are shown in the figure. Figure 10 It can be found in (a, b) that the S-ZnCo@HCN material maintains the hollow cavity structure of the HCN material, and many small black spots evenly distributed around the HCN material are considered to be metal particles dispersed on the surface. After local magnification, it can be clearly observed that these metal particles are not directly exposed to the outside, but are wrapped by a layer of nitrogen-doped carbon. This is because the metal in the precursor material of the S-ZnCo@HCN material is confined in the metal-organic framework ZIF. During the calcination process, the metal is thermally reduced to a zero-valent state to form particles, and the organic framework is carbonized to form a coating. Due to the restriction of the organic framework, the metal particles do not show obvious aggregation and growth. After measuring the lattice fringes, the fringes with a lattice spacing of 0.204nm were attributed to the 111 crystal plane of metal Co ( Figure 10 c). Figure 10 (d) is a polycrystalline diffraction pattern of the S-ZnCo@HCN material, which is believed to expose the 001, 111, and 022 crystal planes of cobalt. No obvious lattice fringes or diffraction spots of metallic Zn were found in the HRTEM, which may be related to the presence and dispersion of metallic Zn. Figure 10(ej) shows the elemental scanning results of the S-ZnCo@HCN material. The C, N, and O elements are very evenly distributed, while the Co element appears as small aggregates, further confirming that the metal particles in the HR-TEM image are primarily metallic Co. The mapping of metallic zinc does not reveal a clear hollow spherical structure. The green spots in the image occupy the entire field of view. This is due to the forced appearance of points in the image by the selected zinc element in the mapping test. However, it also indicates that the metallic zinc content is very low and there is no agglomeration. Figure 10 k shows the dark field projection image of the S-ZnCo@HCN material. The bright spots in the image are considered to be metal particles, which is consistent with the Figure 10 The position of the metal cobalt is basically consistent, indicating that the aggregated metal particles in the figure are metal cobalt, not metal zinc or cobalt-zinc alloy. The particle size distribution diagram of the metal cobalt was obtained by measuring the particle size of the metal cobalt ( Figure 10 L)), the average particle size of metallic cobalt is 5.4 nm.

[0179] Figure 11 The valence bond structure of S-ZnCo@HCN material was studied by X-ray photoelectron spectroscopy. Figure 11 shown. Figure 11 (a) is the survey spectral data of the material. It can be found that the material contains oxygen C, N, O, Co, and Zn elements, and the mass contents of the five elements are 67.4%, 15.2%, 5.4%, 7.1%, and 4.9% respectively through semi-quantitative analysis. The nitrogen content in the material is significantly higher than that in HCN (tested in the previous section: 9.78%). This is because the 2-methylimidazole in the precursor material contains a large amount of nitrogen. During the calcination process, the nitrogen element was reintegrated and not all converted into gas molecules and removed. The C 1s spectral data of the material was fitted into four peaks, and the peaks centered at 284.80 eV, 285.98 eV, 288.38 eV, and 291.60 eV were attributed to the satellite peaks of CC / C=C, CO / C=N, NC=N, and π-π stacking, respectively ( Figure 8 b). All data were peak-corrected based on the peak position of 284.80 eV. The N 1s spectrum in the material was fitted to three characteristic peaks, representing graphitic nitrogen, pyrrolic nitrogen, and pyridinic nitrogen (11c). Figure 11 d is the fine energy spectrum of the 1s orbital of the O element in the material. Because the calcination was carried out in an argon atmosphere, the oxygen content in the material was low, only 5.4%. At this time, the oxygen in the material was mainly produced by organic matter and water adsorbed in the air when the material was exposed to air and stored. By fitting the 2p orbital of the Zn element, the Zn element in the material was confirmed to be zero-valent metal Zn ( Figure 11e). Cobalt also exists in only one valence state, but unlike the standard peak spectrum data, the binding energy of the Co 2p orbital is slightly increased, with the peak centers appearing at 780.1 eV and 795.41 eV, indicating that the cobalt in the material may form N-Co.

[0180] Table 6 is the analysis table of Zn and Co content in S-ZnCo@HCN material

[0181]

[0182] Table 6 shows the Zn and Co contents in the S-ZnCo@HCN material. The data obtained by TEM and XPS provide semi-quantitative data on the material surface. The metallic Co content is significantly higher than that obtained by ICP. This indicates that the metal is still more distributed on the material surface. While TEM elemental scanning is not very accurate, ICP testing provides quantitative information on the metallic Zn and Co content, confirming that both metals are present and not completely lost due to acid treatment. Furthermore, the ratio of the two metals is close to the input during catalyst preparation, approximately 1:1 by mass.

[0183] In summary, as shown in Test Examples 1, 2, and 3, the catalyst can produce the N-alkylation product of aniline and benzaldehyde with a 96% yield in a solvent-free KOH reaction system at 125°C for 18 hours. The reduction product of the nitroaromatic compound can also be obtained with a 97% yield in an ethanol / water system using sodium borohydride as the hydrogen source. Furthermore, the catalyst exhibits excellent stability in both reactions, with virtually no change in reactivity after eight reuses.

[0184] Although the embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principles and spirit of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A method for preparing a hollow nitrogen-doped carbon-supported Zn-Co catalyst, characterized in that: The following steps are involved: (1) The hollow nitrogen-doped carbon-based micro-nanospheres are mixed with a polydiallyldimethylammonium chloride solution and a sodium polystyrene sulfonate solution respectively to obtain modified hollow nitrogen-doped carbon-based micro-nanospheres; (2) The modified hollow nitrogen-doped carbon-based micro-nanospheres, zinc nitrate, cobalt nitrate, 2-methylimidazole solution and methanol were mixed to obtain hollow nitrogen-doped carbon-based nanospheres supported by a bimetallic zinc-cobalt organic framework; (3) The hollow nitrogen-doped carbon-based nanospheres supported by the bimetallic zinc-cobalt organic framework are calcined to obtain highly dispersed zinc-cobalt supported hollow nitrogen-doped carbon-based nanosphere catalysts.

2. The method for preparing a hollow nitrogen-doped carbon-supported Zn-Co catalyst according to claim 1, characterized in that: The concentrations of the polydiallyldimethylammonium chloride solution and the sodium polystyrene sulfonate solution in step (1) are equal, and the concentration is 0.1-0.5 mol / L.

3. The method for preparing a hollow nitrogen-doped carbon-supported Zn-Co catalyst according to claim 1, characterized in that: The weight ratio of the modified hollow nitrogen-doped carbon-based micro-nanospheres, zinc nitrate, cobalt nitrate, and 2-methylimidazole solution in step (2) is 2-3:0.5-1.5:0.5-1.5:

30.

4. The method for preparing a hollow nitrogen-doped carbon-supported Zn-Co catalyst according to claim 1, characterized in that: The 2-methylimidazole solution in step (2) is a 1M 2-methylimidazole methanol solution.

5. The method for preparing a hollow nitrogen-doped carbon-supported Zn-Co catalyst according to claim 1, characterized in that: The step (3) further includes: After calcination, the calcined product was cooled to room temperature and placed in 1 M hydrochloric acid solution and refluxed for 3 to 6 hours.

6. The method for preparing a hollow nitrogen-doped carbon-supported Zn-Co catalyst according to claim 1, characterized in that: The calcination conditions in step (3) are: a heating rate of 3-6°C / min, a final temperature of 800-1200°C, and constant temperature for 2-4 hours.

7. A hollow nitrogen-doped carbon-supported Zn-Co catalyst prepared according to the method for preparing a hollow nitrogen-doped carbon-supported Zn-Co catalyst according to any one of claims 1 to 6.

8. Use of the hollow nitrogen-doped carbon-supported Zn-Co catalyst according to claim 7 in catalyzing N-alkylation reactions and catalyzing reduction reactions of nitroaromatic compounds.

9. The use according to claim 8, characterized in that The specific steps of applying the hollow nitrogen-doped carbon-supported Zn-Co catalyst in catalyzing N-alkylation reaction are: In an inert atmosphere, aniline, benzyl alcohol, KOH and a hollow nitrogen-doped carbon-supported Zn-Co catalyst are mixed in a mass ratio of 20-40:60-80:1:5 and reacted at 100-150°C.

10. The use according to claim 8, characterized in that The specific steps of applying the hollow nitrogen-doped carbon-supported Zn-Co catalyst in catalyzing the reduction reaction of nitroaromatic compounds are as follows: Nitrobenzene, sodium borohydride, water and hollow nitrogen-doped carbon-supported Zn-Co catalyst are mixed in a mass ratio of 200-300:100-120:200-600:1 and reacted at 25-35°C.

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