Preparation method and application of a core-shell Co-CN@SiO2 catalyst

Abstract

The present invention belongs to the technical field of catalyst preparation, and discloses a preparation method and application of a core-shell Co-CN@SiO2 catalyst. The present invention uses the prepared ZIF-67 as a template, and coats the outer layer with SiO2 to form a ZIF-67@SiO2 precursor; then, a Co-CN@SiO2 catalyst having an intermediate core of hollow nitrogen-doped carbon-loaded Co metal particles and a silicon dioxide outer shell layer is prepared through a solvent thermal reaction and a high-temperature pyrolysis step. The core-shell Co-CN@SiO2 catalyst obtained by the present invention exhibits excellent catalytic activity in the reaction of catalyzing the hydrogenation of benzaldehyde to prepare benzyl alcohol.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst preparation, and particularly relates to a core-shell type Co-CN@SiO 2 The invention relates to a method for preparing a catalyst and application thereof. Background Art

[0002] Benzyl alcohol, as an organic compound with a wide range of uses, plays an important role in drug synthesis, cosmetic flavoring, food seasoning, and the manufacture of spices and dyes. However, existing methods for producing benzyl alcohol, such as benzyl chloride hydrolysis, toluene oxidation, benzaldehyde reduction, and yeast reduction, all have disadvantages to varying degrees, such as harsh reaction conditions, environmental pollution, low conversion rate, many by-products, and long reaction time.

[0003] In order to solve the above problems, researchers have turned their attention to the method of preparing benzyl alcohol by selective hydrogenation of benzaldehyde. Although existing noble metal catalysts such as Au, Ru, Pt and Pd have shown good performance in the heterogeneous catalytic hydrogenation reaction of benzaldehyde, these catalysts are limited in commercial applications due to their high cost and serious toxicity. Therefore, using cheap metals such as Fe, Cu, Co, Mo and Zn to replace noble metal catalysts has become a research hotspot.

[0004] However, when metal particles are used directly as catalysts, the agglomeration of metal particles will lead to poor dispersion and increased particle size, which will reduce the activity and life of the catalyst. In addition, the large amount of metal used also increases the catalytic cost. Therefore, it is particularly important to explore a method that can effectively prepare a non-precious metal-based catalyst with low cost, excellent catalytic effect and strong stability. Summary of the invention

[0005] In order to overcome the above-mentioned shortcomings and deficiencies of the prior art, the primary purpose of the present invention is to provide a core-shell Co-CN@SiO 2 A method for preparing a catalyst.

[0006] The present invention uses the prepared ZIF-67 as a template, and the outer layer is coated with SiO 2 Formation of ZIF-67@SiO 2 Precursor; Subsequently, Co-CN@SiO with hollow nitrogen-doped carbon-supported Co metal particles as the intermediate core and a silica shell layer was prepared through solvothermal reaction and high-temperature pyrolysis steps. 2 Catalyst. The core-shell Co-CN@SiO 2 The catalyst exhibits excellent catalytic activity in the catalytic hydrogenation of benzaldehyde to prepare benzyl alcohol. The preparation method is efficient and environmentally friendly, providing excellent prospects for the industrial production of benzyl alcohol.

[0007] Another object of the present invention is to provide a core-shell Co-CN@SiO prepared by the above method. 2 catalyst.

[0008] Compared with traditional catalysts, the core-shell Co-CN@SiO 2 The catalyst has the characteristics of relatively mild reaction temperature and relatively high yield. Its unique core-shell structure allows the active components in the catalyst to be efficiently dispersed, thereby improving the catalytic activity. At the same time, the presence of the silica shell layer enhances the stability of the catalyst and prolongs its service life.

[0009] Another object of the present invention is to provide the core-shell type Co-CN@SiO 2 Application of catalysts in the hydrogenation reduction of aldehydes.

[0010] The purpose of the present invention is achieved through the following solutions:

[0011] A core-shell Co-CN@SiO 2 The method for preparing a catalyst comprises the following steps:

[0012] (1) mixing a cobalt salt solution and a 2-methylimidazole solution evenly, and allowing the mixture to react, thereby obtaining dimethylimidazole cobalt (ZIF-67) crystals;

[0013] (2) Dispersing the ZIF-67 crystals obtained in step (1), adding 2-methylimidazole solution, and then adding hexadecyltrimethylammonium bromide (CTAB) solution and tetraethyl silicate (TEOS) in sequence, reacting to obtain ZIF-67@SiO 2 ;

[0014] (3) The ZIF-67@SiO obtained in step (2) 2 Disperse, add cobalt salt, heat and react, decompose ZIF-67 into Co-ZIF nanosheets, cool to room temperature, and separate to obtain Co-ZIF@SiO 2 ;

[0015] (4) The Co-ZIF@SiO obtained in step (3) 2 Pyrolysis was performed under an inert atmosphere and cooled to room temperature to obtain Co-CN@SiO 2 .

[0016] The solvent used in each step of the preparation method is at least one of water and alcohol solvents.

[0017] The cobalt salts in step (1) and step (3) both include (CH 3 COO 2 Co·6H 2 O、Co(NO 3) 2 6H 2 O、CoCl 2 6H 2 At least one of O.

[0018] The concentration of the cobalt salt in the cobalt salt solution of step (1) is 0.125-0.5 mol / L; the concentration of the 2-methylimidazole in the 2-methylimidazole solution is 0.5-4 mol / L.

[0019] The amounts of the cobalt salt solution and the 2-methylimidazole solution used in the mixing in step (1) are such that the molar ratio of cobalt ions to 2-methylimidazole in the mixed solution is 1:(2-8).

[0020] The particle size of the ZIF-67 crystals in step (1) is 100-900 nm.

[0021] The temperature of the standing reaction in step (1) is room temperature and the time is 10-24 hours.

[0022] After the reaction in step (1), the product is washed and then dried at 50-120° C. for 1-24 hours.

[0023] In the dissolution of step (2), the ratio of ZIF-67 crystals to solvent is 0.05-0.4 g: 20-100 mL.

[0024] The dosage ratio of 2-methylimidazole to solvent in the 2-methylimidazole solution of step (2) is 1-10 g: 20-100 mL.

[0025] The mass concentration of the hexadecyltrimethylammonium bromide solution in step (2) is 1-10wt%.

[0026] In step (2), the dosage ratio of the ZIF-67 crystal, 2-methylimidazole, hexadecyltrimethylammonium bromide solution and tetraethyl silicate is 0.05-0.4 g: 1-10 g: 1-4 mL: 0.1-1.2 mL.

[0027] The reaction time of step (2) is 30-60 min.

[0028] After the reaction in step (2), centrifugal washing and drying are performed, wherein the drying includes at least one of freeze drying and vacuum drying.

[0029] In step (3), the ZIF-67@SiO 2 The dosage ratio to the solvent is 10-100 mg: 20-80 mL.

[0030] Step (3) ZIF-67@SiO 2The dosage ratio of cobalt salt is 10-100mg:0.017-0.17mmol.

[0031] The heating reaction time in step (3) is 4-10 hours; the temperature is 100-150°C.

[0032] After the separation in step (3), washing and drying are performed.

[0033] The inert atmosphere in step (4) is at least one of argon and nitrogen.

[0034] The pyrolysis temperature in step (4) is 600°C; the pyrolysis time is 30-600min; and the heating rate is 1-10°C / min.

[0035] The core-shell Co-CN@SiO prepared by the above method 2 catalyst.

[0036] The core-shell Co-CN@SiO 2 The particle size of Co nanoparticles in the catalyst is 10-30nm, and the SiO 2 The shell thickness is 20-80nm.

[0037] The above core-shell Co-CN@SiO 2 Application of catalysts in the hydrogenation reduction of aldehydes.

[0038] The aldehydes include benzaldehyde, o-hydroxybenzaldehyde, p-bromobenzaldehyde, o-nitrobenzaldehyde, and o-iodobenzaldehyde.

[0039] The mechanism of the present invention is:

[0040] In step (1), the cobalt salt solution and the 2-methylimidazole solution are mixed, which is a key synthesis step. The cobalt ions and the 2-methylimidazole form crystal nuclei through coordination and gradually grow, thereby preparing ZIF-67 crystals with uniform dodecahedral structure. The successful implementation of this step is crucial for the subsequent preparation of high-quality and excellent catalysts.

[0041] The core-shell Co-CN@SiO 2 The catalyst has a unique rhombic dodecahedron morphology, consisting of a hollow nitrogen-doped carbon-loaded Co metal particle core and a silicon dioxide shell layer. The particle size of the Co nanoparticles ranges from 10 to 30 nm, with an average particle size of about 20.9 nm. 2 The shell thickness is 20-80nm, which ensures the high efficiency and stability of the catalyst.

[0042] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0043] (1) The catalyst preparation method provided by the present invention cleverly uses cheap metal Co as the core raw material, significantly reducing the preparation cost of the catalyst and making large-scale production of the catalyst possible. At the same time, the preparation process strictly follows the green environmental protection principle and meets the requirements of modern industry for sustainable development.

[0044] (2) The catalyst of the present invention uses SiO 2 The core-shell structure of Co-CN is coated with hollow nitrogen-doped carbon-loaded Co metal particles as the middle core and silicon dioxide as the outer shell to form a porous core-shell structure. This innovative design brings multiple advantages: SiO 2 The layer effectively prevents the agglomeration of Co nanoparticles during the reaction, ensuring the stability and activity of the catalyst; at the same time, the formed "sieve"-like external structure promotes the transmission of reactant molecules and improves the catalytic efficiency.

[0045] (3) The catalyst prepared by the present invention not only exhibits excellent reaction conversion rate and selectivity, but also has excellent stability. The catalyst prepared by the present invention also has the advantages of being easy to separate and reuse. Under the action of an external magnetic field, the catalyst can be quickly separated and reused after simple cleaning, which greatly improves the utilization efficiency of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a scanning electron microscope (SEM) image of ZIF-67 obtained in step (1) of Example 1.

[0047] Figure 2 The Co-ZIF@SiO obtained in step (3) of Example 1 2 -1 scanning electron microscope (SEM) image.

[0048] Figure 3 Co-CN@SiO obtained in Example 1 2 -1 scanning electron microscope (SEM) and transmission electron microscope (TEM) images; where a is Co-CN@SiO 2 -1 is the scanning electron microscope image of the catalyst; b is the scanning electron microscope image of Co-CN@SiO 2 -1 TEM image of the overall morphology of the catalyst, c is Co-CN@SiO 2 -1 transmission electron microscopy image of the local morphology of the catalyst, the inset in c is the statistical analysis of the particle size of Co nanoparticles, and d is the catalyst particle SiO 2 High-magnification TEM image inside the shell.

[0049] Figure 4 Co-CN@SiO obtained in Example 1 2 -1's X-ray diffraction (XRD) pattern.

[0050] Figure 5 Co-CN@SiO obtained in Example 1 2 -1 Catalyst performance test results.

[0051] Figure 6 Co-CN@SiO obtained in Example 1 2 -1 Catalyst recycling performance test results. DETAILED DESCRIPTION

[0052] The present invention is further described in detail below in conjunction with the examples and drawings, but the embodiments of the present invention are not limited thereto. If specific conditions are not specified in the examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0053] Unless otherwise specified, the reagents used in the examples can be purchased from the market.

[0054] Example 1

[0055] (1) Preparation of ZIF-67

[0056] Weigh 1.092 g of Co(NO 3 ) 2 6H 2 O and 1.232g of 2-methylimidazole, and then they were uniformly dispersed in 30mL of methanol solution, this step was carried out under ultrasonic conditions to obtain solution A and solution B. Then, solution A was poured into solution B while stirring, stirring was continued for 10s, and then the reaction was allowed to stand at room temperature for 20h. After the reaction was completed, the reaction mixture was transferred to a centrifuge tube, centrifuged and washed three times at 6000r / min using a high-speed centrifuge, and the centrifuged product was placed in an oven and dried at 70°C for 5h to collect the purple powder of ZIF-67 with an average particle size of about 700nm.

[0057] (2) ZIF-67@SiO 2 Preparation of -1

[0058] Weigh 180 mg of ZIF-67 and 4 g of 2-methylimidazole, and disperse them uniformly in 60 mL of methanol solution and 60 mL of deionized water by ultrasonic technology, respectively. Mix the methanol solution of ZIF-67 and the aqueous solution of 2-methylimidazole evenly, add 4 mL of 5 wt% hexadecyltrimethylammonium bromide (CTAB) solution, and stir with a magnetic stirrer for 30 min. Add 0.1 mL of tetraethyl silicate (TEOS) evenly under stirring, and then stir at room temperature for 1 h. After the reaction is completed, centrifuge and wash 3 times, and vacuum dry for 5 h to obtain ZIF-67@SiO 2-1 solid. The obtained ZIF-67@SiO 2 -1SiO 2 The thickness of the shell is 20nm, which provides a more stable structural basis for subsequent catalytic reactions.

[0059] (3) Co-ZIF@SiO 2 Preparation of -1

[0060] Take 20 mg of ZIF-67@SiO 2 -1 was evenly dispersed in 50 mL of methanol solution by ultrasonication, and 10 mg of Co(NO 3 ) 2 6H 2 O, and then the mixed solution was transferred to a reactor and reacted at 120°C for 4 hours. After the reactor was cooled to room temperature, the solid product was separated from the solution by suction filtration and washed with methanol three times. Finally, the washed solid product was dried to obtain the desired Co-ZIF@SiO 2 -1.

[0061] (4) Core-shell Co-CN@SiO 2 -1 Preparation of catalyst

[0062] The Co-ZIF@SiO obtained in step (3) 2 -1 powder was placed in a tube furnace. Under the protection of nitrogen, the temperature was first rapidly raised to 200°C at a rate of 10°C / min to stabilize the material. Then, the temperature was raised to 600°C at a rate of 5°C / min to ensure that the material can be heated evenly during the carbonization process to avoid thermal stress. The pyrolysis temperature was maintained at 600°C for 120 minutes to stabilize the Co-ZIF@SiO 2 -1 can be fully carbonized. During the carbonization process, the organic framework is gradually transformed into carbonitride, while retaining SiO 2 After the tube furnace process was completed, the material was allowed to cool naturally to room temperature to obtain Co-CN@SiO 2 -1, of which SiO 2 The thickness of the shell is 20 nm.

[0063] The operation process of using the core-shell catalyst obtained in this example for the hydrogenation of benzaldehyde to prepare benzyl alcohol is as follows:

[0064] 20 mg of Co-CN@SiO 2-1 catalyst was placed in a 25mL autoclave, 1mmol benzaldehyde was taken as the reactant, and 5mL water was added as the solvent. After the two were mixed evenly, they were added into the autoclave together. The autoclave was sealed, and the reaction temperature was set to 120°C and the hydrogen pressure was set to 2.0MPa. During the reaction, the stirring speed was maintained at 300rpm. The reaction was continued for 24h.

[0065] The reaction product was analyzed by gas chromatography, and it was found that the conversion rate of benzaldehyde was 100%, and the selectivity of benzyl alcohol was 99.3%.

[0066] Example 2

[0067] The difference from Example 1 is that the amount of tetraethyl silicate (TEOS) added in step (2) is adjusted to 0.4 mL, thereby obtaining a quartz crystal with a SiO 2 Shell thickness of Co-CN@SiO 2 -2 catalyst.

[0068] The reaction product was analyzed by gas chromatography, and it was found that the conversion rate of benzaldehyde was 97.7% and the selectivity of benzyl alcohol was 96.8%.

[0069] Example 3

[0070] The difference from Example 1 is that the amount of tetraethyl silicate (TEOS) added in step (2) is adjusted to 1 mL, thereby obtaining a 3D printed circuit board having a SiO layer of about 80 nm. 2 Shell thickness of Co-CN@SiO 2 -3 catalyst.

[0071] The reaction product was analyzed by gas chromatography, and it was found that the conversion rate of benzaldehyde was 85.2% and the selectivity of benzyl alcohol was 97.1%.

[0072] Comparative Example 1

[0073] The difference from Example 1 is that the pyrolysis temperature in step (4) is 700°C, thereby obtaining Co-CN@SiO with a larger Co nanoparticle size. 2 -4 catalyst.

[0074] Compared with Co-CN@SiO 2 -1, this adjustment has an impact on the particle structure of the catalyst. In the reaction of benzaldehyde hydrogenation to prepare benzyl alcohol, Co-CN@SiO 2 -4 catalysts exhibited different catalytic properties.

[0075] The reaction product was analyzed by gas chromatography, and it was found that the conversion rate of benzaldehyde was 78.8% and the selectivity of benzyl alcohol was 99.4%.

[0076] Comparative Example 2

[0077] The difference from Example 1 is that the pyrolysis temperature in step (4) is 800°C, thereby obtaining Co-CN@SiO 2 -5 catalyst.

[0078] Compared with Co-CN@SiO 2 -4, the Co nanoparticles of this catalyst are larger and show excessive aggregation.

[0079] The reaction product was analyzed by gas chromatography, and it was found that the conversion rate of benzaldehyde was 36.4% and the selectivity of benzyl alcohol was 99.0%.

[0080] Comparative Example 3

[0081] The difference from Example 1 is that step (1) is not performed, and commercially available ZIF-67 (purchased from Shanghai Kaishu Chemical Technology Co., Ltd., with a particle size of 500 nm-1 um) is used as a raw material in step (2).

[0082] Since the nano-size of commercially available ZIF-67 is not uniform and difficult to disperse, only a portion of the material can successfully form the target Co-CN@SiO during the synthesis process. 2 structure, and a large number of heteronuclear-grown silica microspheres were generated, which affected the uniformity and performance of the catalyst.

[0083] The reaction product was analyzed by gas chromatography, and it was found that the conversion rate of benzaldehyde was 21.5%, and the selectivity of benzyl alcohol was 99.1%.

[0084] Comparative Example 4

[0085] The difference from Example 1 is that in this example, the Co-CN@SiO prepared in step (4) 2 The material was further treated with aqua regia to remove the cobalt metal, thus obtaining CN@SiO 2 catalyst.

[0086] The reaction product was analyzed by gas chromatography, and it was found that the conversion rate of benzaldehyde was 12.1% and the selectivity of benzyl alcohol was 99.5%.

[0087] This result shows that cobalt metal is 2 The importance of nanostructured carbon as a key catalytic active center in materials.

[0088] The benzaldehyde used as the reaction raw material in the catalyst application of Example 1 was replaced with other similar aromatic aldehyde substrates, and the substrate dosage was kept at 1 mmol. As shown in Table 1, the catalyst of the present invention was applied to the hydrogenation reaction of other similar aromatic aldehyde substrates, and maintained a relatively high activity.

[0089] Table 1 Hydrogenation of different aromatic aldehyde substrates into corresponding alcohols

[0090]

[0091] Catalyst recovery and treatment:

[0092] After the hydrogenation reaction of Example 1 is completed, the core-shell structure catalyst is quickly separated from the reaction solution using a magnet. Subsequently, the catalyst is washed with water and ethanol to remove the reactants and impurities remaining on the surface to ensure the purity of the catalyst. The washed catalyst is transferred to a vacuum drying oven and dried overnight at 60° C. to remove moisture and residual solvent in the catalyst to obtain a recovered catalyst.

[0093] The recovered catalyst is directly used for the next batch of reactions without the need for additional activation or treatment steps, which greatly simplifies the operation process and improves the utilization efficiency of the catalyst. 2 The catalyst has excellent stability and recyclability. Figure 6 As shown, the activity of the catalyst did not decrease significantly after being recycled five times using an external magnetic field, which proves the stability and high efficiency of the catalyst.

[0094] Analysis of attached pictures:

[0095] from Figure 1 In the scanning electron microscope (SEM) image, it can be clearly observed that the ZIF-67 material prepared by step (1) presents a dodecahedral structure.

[0096] from Figure 2 In the scanning electron microscope (SEM) image, it can be clearly observed that the Co-ZIF@SiO prepared in step (3) 2 The material has a unique structure. The central part is composed of two-dimensional Co-ZIF nanosheets formed by the decomposition of ZIF-67, and the periphery is uniformly covered with SiO 2 This structure verifies that the present invention successfully synthesized Co-ZIF@SiO with a core-shell structure in step (3). 2 Material.

[0097] Figure 3 Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images reveal that Co-CN@SiO 2 The detailed morphology of the particles. Figure 3 As shown in Figure a, the particles show a typical dodecahedral morphology; TEM images b and c confirm the hollow core-shell structure of the catalyst particles. The high-magnification TEM image of Figure d further shows that SiO 2 The interplanar spacing of the nanoparticles in the shell is 0.21 nm, which is consistent with the (111) interplanar spacing of Co nanoparticles. This finding indicates that during the high-temperature pyrolysis process, Co-ZIF@SiO 2 Co 2+ It was successfully reduced to metallic Co nanoparticles. In addition, the particle size statistical analysis of the inset of Figure c indicates that the average particle size of the Co nanoparticles is about 20.9nm, and it can be seen in Figure c that Co-CN is distributed in SiO 2 The shell layer together constitutes Co-CN@SiO with a hollow core-shell structure. 2 Nanocomposite materials.

[0098] pass Figure 4 The X-ray diffraction (XRD) pattern of Co-CN@SiO 2 The material has three significant diffraction peaks at 44.2°, 51.5° and 75.8°, which correspond to the (111), (200) and (220) crystal planes of Co metal nanocrystal particles, respectively, further confirming that the cobalt metal ions in the material were successfully reduced to Co metal nanoparticles under high temperature conditions.

[0099] Figure 5 The performance test results of the catalyst in Example 1 in the reaction of benzaldehyde hydrogenation to benzyl alcohol are shown. 2 Under the action of the catalyst, the yield of benzyl alcohol steadily increases with the extension of the reaction time. In particular, after 24 hours of reaction, benzaldehyde is almost completely converted into benzyl alcohol. This outstanding performance fully proves the excellent performance of the catalyst obtained by the present invention in terms of catalytic activity.

[0100] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing a core-shell Co-CN@SiO2 catalyst, characterized in that The following steps are involved: (1) mixing the cobalt salt solution and the 2-methylimidazole solution evenly, allowing them to react to obtain ZIF-67 crystals; (2) dispersing the ZIF-67 crystals obtained in step (1), adding 2-methylimidazole solution, and then sequentially adding hexadecyltrimethylammonium bromide solution and tetraethyl silicate, reacting to obtain ZIF-67@SiO2; (3) dispersing the ZIF-67@SiO2 obtained in step (2), adding cobalt salt, heating to react, decomposing ZIF-67 into Co-ZIF nanosheets, cooling to room temperature, and separating to obtain Co-ZIF@SiO2; (4) pyrolyzing the Co-ZIF@SiO2 obtained in step (3) under an inert atmosphere and cooling to room temperature to obtain Co-CN@SiO2; The heating reaction time in step (3) is 4-10 h and the temperature is 100-150°C; The pyrolysis temperature in step (4) is 600°C; the pyrolysis time is 30-600 min; the heating rate is 1-10°C / min; The Co-CN@SiO2 is used in the reaction of hydrogenating benzaldehyde to benzyl alcohol.

2. The method for preparing the core-shell Co-CN@SiO2 catalyst according to claim 1, characterized in that: The cobalt salt in step (1) and step (3) includes at least one of (CH3COO)2Co·6H2O, Co(NO3)2·6H2O, and CoCl2·6H2O; The concentration of cobalt salt in the cobalt salt solution in step (1) is 0.125-0.5 mol / L; the concentration of 2-methylimidazole in the 2-methylimidazole solution is 0.5-4 mol / L; The amounts of the cobalt salt solution and the 2-methylimidazole solution used in the mixing in step (1) are such that the molar ratio of cobalt ions to 2-methylimidazole in the mixed solution is 1:(2-8); The particle size of the ZIF-67 crystals in step (1) is 100-900 nm; The temperature of the static reaction in step (1) is room temperature and the time is 10-24 hours.

3. The method for preparing the core-shell Co-CN@SiO2 catalyst according to claim 1, characterized in that: The ratio of ZIF-67 crystals to solvent in the dispersion of step (2) is 0.05-0.4 g: 20-100 mL; The ratio of 2-methylimidazole to solvent in the 2-methylimidazole solution of step (2) is 1-10 g: 20-100 mL; The mass concentration of the hexadecyltrimethylammonium bromide solution in step (2) is 1-10wt%.

4. The method for preparing the core-shell Co-CN@SiO2 catalyst according to claim 1, characterized in that: In step (2), the amount ratio of the ZIF-67 crystal, 2-methylimidazole, hexadecyltrimethylammonium bromide solution and tetraethyl silicate is 0.05-0.4 g: 1-10 g: 1-4 mL: 0.1-1.2 mL; The reaction time of step (2) is 30-60 min.

5. The method for preparing the core-shell Co-CN@SiO2 catalyst according to claim 1, characterized in that: In step (3), the ratio of ZIF-67@SiO2 to solvent in the dispersion is 10-100 mg: 20-80 mL; In step (3), the dosage ratio of ZIF-67@SiO2 to cobalt salt is 10-100 mg: 0.017-0.17 mmol.

6. The method for preparing the core-shell Co-CN@SiO2 catalyst according to claim 1, characterized in that: The inert atmosphere in step (4) is at least one of argon and nitrogen.

7. A core-shell Co-CN@SiO2 catalyst prepared by the method of claims 1-6.

8. The core-shell Co-CN@SiO2 catalyst according to claim 7, characterized in that: The particle size of the Co nanoparticles in the core-shell Co-CN@SiO2 catalyst is 10-30 nm, and the thickness of the SiO2 shell is 20-80 nm.

Images