Catalyst, preparation method thereof and application of catalyst in synthesis of primary amine

Abstract

The invention belongs to the technical field of catalysts, and particularly relates to a catalyst, a preparation method thereof and application of the catalyst in synthesis of primary amine compounds. The preparation method of the catalyst comprises the following steps: dissolving Ni (NO3) 2 and terephthalic acid in a solvent, uniformly mixing, carrying out a hydrothermal reaction at a certain temperature to obtain Ni-MOF, washing, drying, and reducing in an H2 / Ar atmosphere to obtain the catalyst Ov-NiO / Ni-C-T (X) (wherein T represents the reduction temperature, the unit is DEG C, and X represents the reduction time, the unit is h). The preparation method of the catalyst is simple, the catalyst can be recycled for 7 times without obvious loss of catalytic activity and selectivity, and the catalyst has high catalytic activity for synthesis of primary amine through reductive amination of aldehyde compounds and ketone compounds.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and particularly relates to a catalyst, a preparation method thereof, and an application in the synthesis of primary amines. Background Art

[0002] As an important nitrogen-containing compound in organic chemistry, primary amines play an irreplaceable core role in the fields of medicine, pesticides, polymer materials, and functional chemicals. In drug research and development, primary amines are key structural units of antibiotics (such as cephalosporins), anti-tumor drugs (such as imatinib), and neurotransmitters (such as dopamine). The strong nucleophilicity and coordination ability of their amino groups provide active sites for molecular functionalization modification. In the pesticide industry, primary amine derivatives are widely used in the synthesis of herbicides (such as phenoxycarboxylic acids) and fungicides, and their biological activities are closely related to the precise regulation of molecular structures. In addition, as precursors of polymer materials such as polyurethanes and epoxy resins, primary amines directly affect the mechanical properties and stability of the materials. With the rapid development of the biomedical and green materials industries, the development of efficient and green primary amine synthesis strategies has become the focus of common concern in the academic and industrial communities.

[0003] From a chemical structure perspective, the primary amine molecule contains only one amino group directly connected to a carbon atom, and this structure endows it with high reactivity and diversity. Primary amines can participate in various chemical reactions, such as amidation, alkylation, oxidation, etc., thereby constructing more complex organic molecular structures, providing rich reaction paths and possibilities for organic synthetic chemistry. The structural diversity of primary amines also enables them to meet specific requirements in different application scenarios. By adjusting the carbon chain length, substituent type, etc. of primary amines, primary amine derivatives with specific properties and functions can be prepared, providing a wide range of selection spaces for various fields.

[0004] Traditionally, the synthesis of primary amines mainly relies on reductive amination reactions, that is, carbonyl compounds react with ammonia or amines under the action of reducing agents. However, this method usually requires high temperature, high pressure, and excessive reducing agents, resulting in energy waste, increased costs, and more side reactions. In recent years, with the pursuit of efficient and green synthesis methods, significant progress has been made in the field of primary amine synthesis. The development of new catalysts has become a research hotspot. Noble metal catalysts such as palladium, platinum, ruthenium, etc. exhibit good catalytic performance, but they are costly; while non-noble metal catalysts such as nickel-based catalysts have significantly improved performance through special preparation processes and structural designs, which can provide new ways for the green synthesis of primary amines. Summary of the Invention

[0005] Aiming at the deficiencies existing in the prior art, the purpose of the present invention is to provide a catalyst (O v -NiO / Ni@C-T(X)) and its preparation method and application in the synthesis of primary amines.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] The present invention provides a catalyst O v -NiO / Ni@C-T(X), the catalyst is a two-component Ni-based catalyst coexisting with carbon-coated Ni and O v -NiO, where O v represents oxygen vacancy, and its active substance is Ni-NiO nanoparticles wrapped by a carbon layer.

[0008] The present invention also provides a preparation method of the above catalyst, and the preparation method sequentially includes the following steps:

[0009] (1) Dissolve Ni(NO3)2 and terephthalic acid in solvent A; dropwise add an aqueous NaOH solution until pH = 8, stir evenly to obtain a mixed solution; perform hydrothermal reaction on the mixed solution, and sequentially wash the obtained solid product with distilled water and methanol, and then dry it in air to obtain Ni-MOF;

[0010] (2) Heat Ni-MOF from room temperature to a target temperature of 300-400 °C (preferably 350 °C) at a heating rate of 1-4 °C / min (preferably 2 °C / min) in an atmosphere of a hydrogen / argon mixed gas, and then maintain it at the target temperature for 1-6 h (preferably 2 h) for reduction; after cooling to room temperature, obtain O v -NiO / Ni@C-T(X) catalyst;

[0011] T represents the reduction temperature, with the unit of °C, and X represents the reduction time, with the unit of h.

[0012] Further, the solvent A in step (1) is N,N-dimethylformamide.

[0013] Further, the molar ratio of Ni(NO3)2 to terephthalic acid in step (1) is (3-9):(6-10), preferably 1:1; the molar concentration of the aqueous NaOH solution is 0.1 M.

[0014] Further, the conditions of the hydrothermal reaction in step (1) are to rise from room temperature to 130-170 °C at a heating rate of 1-5 °C / min (preferably 2.5 °C / min) and maintain for 62-82 hours (preferably rise to 150 °C and maintain for 72 hours); the conditions of the washing are to wash with distilled water and methanol respectively more than 3 times (preferably wash with distilled water and methanol respectively 3 times) to remove impurities and NaOH until the filtrate is neutral; the conditions of the drying are to dry in an oven at 40-90 °C for 9-14 h, preferably dry at 70 °C for 12 h.

[0015] Further, in the step (2), the volume percentage of hydrogen in the hydrogen / argon mixed gas is 10%.

[0016] The present invention also provides an application of the above catalyst in the reductive amination of aldehyde compounds or ketone compounds to synthesize primary amines.

[0017] Further, the steps of the application are as follows: adding the above catalyst and aldehyde or ketone compound in a ratio of (10 - 40) mg : (0.5 - 2) mmol to a reaction vessel, adding solvent B, sealing and filling with a reducing gas, and reacting under heating conditions to obtain the product primary amine.

[0018] Further, in the application, the structural formula of the aldehyde compound is one of the following:

[0019]

[0020]

[0021] and / or the structural formula of the ketone compound is one of the following:

[0022]

[0023]

[0024] Further, in the application, the reducing gas filled is 1.0 bar hydrogen; the reaction conditions are reacting at 20 - 60 °C for 5 - 36 h.

[0025] Further, the solvent B is a mixed solution formed by mixing one or more of methanol, ethanol, isopropanol, acetonitrile, tetrahydrofuran, toluene, hexane, water (preferably methanol) and ammonia water in a volume ratio of (7 - 10) : (0.2 - 3), and the preferred volume ratio is 9 : (1 - 2); the concentration of the ammonia water is 10 - 18 mmol / mL, preferably 14.0 mmol / mL.

[0026] Compared with the prior art, the advantages and beneficial effects of the catalyst and its application of the present invention are as follows:

[0027] The catalyst adopts a carbon - coated structure, effectively preventing the agglomeration and loss of active components, and significantly improving the stability of the catalyst. For example, the O v -NiO / Ni@C-350 catalyst can still maintain high catalytic activity after 7 cycles of use. For industrial applications, the use cost of the catalyst is greatly reduced. In the synthesized catalyst, O v-The NiO and metallic Ni two-component mixed interface structure provides abundant active sites, enabling the catalyst to exhibit excellent catalytic activity in various reactions. The catalyst shows high selectivity in the reactions of various substrates. For example, in the process of the reductive synthesis of primary amines from aldehydes or ketones, it can selectively carry out reductive amination without affecting other functional groups. In particular, it shows good tolerance to substrates containing functional groups such as halogens, hydroxyl groups, carboxyl groups, and nitrile groups, broadening its scope of application. Low hydrogen pressure: In some reactions, such as the reductive coupling of nitro compounds and carbonyl compounds, it can be carried out under a lower hydrogen pressure, further reducing the severity of the reaction conditions.

[0028] The catalyst prepared by the present invention is a non-precious metal catalyst with the characteristics of low cost, simple preparation process, and wide substrate range.

[0029] This catalyst is applicable to systems using methanol, ethanol, isopropanol, acetonitrile, tetrahydrofuran, toluene, hexane, or water as solvents, and can achieve high conversion rates in all cases.

[0030] The catalyst prepared by the present invention has a simple preparation process, good stability, and can be recycled more than 7 times. Description of the Drawings

[0031] Figure 1 In (a) and (b) are the transmission electron microscopy and high-resolution transmission electron microscopy images of the O v -NiO / Ni@C-300 catalyst prepared in Example 1; (c) and (d) are the O v -transmission electron microscopy and high-resolution transmission electron microscopy images of the NiO / Ni@C-350 catalyst prepared in Example 2; (e) and (f) are the O v -transmission electron microscopy and high-resolution transmission electron microscopy images of the NiO / Ni@C-400 catalyst prepared in Example 3;

[0032] Figure 2 For the O prepared in Examples 1, 2, and 3 v -NiO / Ni@C-300, O v -NiO / Ni@C-350, O v -XRD patterns of the NiO / Ni@C-400 catalyst;

[0033] Figure 3 For the O prepared in Example 7 v -EPR spectra of the NiO / Ni@C-T and Ni / Graphene samples;

[0034] Figure 4 For the O prepared in Example 2 v -energy dispersive X-ray diffraction spectrum of the NiO / Ni@C-350 sample, and O during depth profile analysis vXPS spectra of Ni 2p, O 1s and C 1s of -NiO / Ni@C-350;

[0035] Figure 5 O prepared for Example 2 v Cyclic stability test results of the -NiO / Ni@C-350 catalyst. Detailed implementation manners

[0036] The following are some specific examples for further illustrating the present invention, but not for limiting the scope of the present invention claimed.

[0037] The catalyst of the present invention is denoted as O v -NiO / Ni@C-T(X), where T represents the reduction temperature in °C and X represents the reduction time in h; if the reduction time is 2 h, then X is not written, denoted as O v -NiO / Ni@C-T.

[0038] Example 1:

[0039] A preparation method of a two-component Ni-based catalyst (O v -NiO / Ni@C-300) in which carbon-coated Ni and O v -NiO coexist, includes the following steps:

[0040] Dissolve Ni(NO3)2·6H2O (3.5 g, 12.0 mmol) and terephthalic acid (2.0 g, 12.0 mmol) in a DMF (120 mL, analytical pure, the same below) solution, and dropwise add an NaOH aqueous solution (0.1 M, the same below) to pH = 8 at a dropping rate of 0.05 mL / s, stir evenly, and then raise the temperature from room temperature to 150 °C at a heating rate of 2.5 °C / min and keep for 72 hours; wash the filtered solid product with distilled water and methanol 3 times respectively to remove impurities and NaOH until the filtrate is neutral (pH = 7, the same below); dry in an oven at 70 °C for 12 h to obtain Ni-MOF. Then, reduce Ni-MOF in a H2 / Ar atmosphere (the volume percentage of H2 is 10%, the same below) (heat up to 300 °C at a heating rate of 2 °C / min and reduce for 2 h) and then cool to room temperature to obtain the catalyst, denoted as: O v -NiO / Ni@C-300.

[0041] Figure 1 In (a) and (b) are the transmission electron microscope image and high-resolution transmission electron microscope image of the O v -NiO / Ni@C-300 catalyst prepared in Example 1.

[0042] Example 2:

[0043] A two-component Ni-based catalyst with carbon-coated Ni and O v -NiO coexistence (O v -NiO / Ni@C-350) preparation method, comprising the following steps:

[0044] Dissolve Ni(NO3)2·6H2O (3.5 g, 12.0 mmol) and terephthalic acid (2.0 g, 12.0 mmol) in DMF (120 mL) solution, dropwise add NaOH aqueous solution until pH = 8, after stirring evenly, heat from room temperature to 150 °C at a heating rate of 2.5 °C / min and keep for 72 hours; Wash the filtered solid product with distilled water and methanol 3 times respectively to remove impurities and NaOH until the filtrate is neutral; Dry in an oven at 70 °C for 12 h to obtain Ni-MOF. Then, reduce Ni-MOF in H2 / Ar atmosphere (heat to 350 °C at a heating rate of 2 °C / min and reduce for 2 h) and then cool to room temperature to obtain the catalyst, denoted as: O v -NiO / Ni@C-350.

[0045] Figure 1 In (c) and (d) are the O v -TEM image and high-resolution TEM image of the NiO / Ni@C-350 catalyst prepared in Example 2.

[0046] Example 3:

[0047] A two-component Ni-based catalyst with carbon-coated Ni and O v -NiO coexistence (O v -NiO / Ni@C-400) preparation method, comprising the following steps:

[0048] Dissolve Ni(NO3)2·6H2O (3.5 g, 12.0 mmol) and terephthalic acid (2.0 g, 12.0 mmol) in DMF (120 mL) solution, dropwise add NaOH aqueous solution until pH = 8, after stirring evenly, heat from room temperature to 150 °C at a heating rate of 2.5 °C / min and keep for 72 hours; Wash the filtered solid product with distilled water and methanol 3 times respectively to remove impurities and NaOH until the filtrate is neutral; Dry in an oven at 70 °C for 12 h to obtain Ni-MOF. Then, reduce Ni-MOF in H2 / Ar atmosphere (heat to 400 °C at a heating rate of 2 °C / min and reduce for 2 h) to obtain the catalyst and then cool to room temperature, denoted as: O v -NiO / Ni@C-400.

[0049] Figure 1 In (e) and (f) are the O vTEM and HRTEM images of the -NiO / Ni@C-400 catalyst.

[0050] Figure 2 For the O prepared in Examples 1, 2, and 3 v -NiO / Ni@C-300, O v -NiO / Ni@C-350, O v XRD patterns of the -NiO / Ni@C-300, -NiO / Ni@C-350, and -NiO / Ni@C-400 catalysts.

[0051] From Figure 1 it can be seen that nanoparticles of Ni (green) and NiO (yellow-brown) species were observed in all samples, which is consistent with the XRD results ( Figure 2 ); the results of Ar ion etching XPS characterization showed ( Figure 4 ) that the signal of carbon decreased after etching, and the signal related to Ni increased, indicating that the carbon layer wrapped the Ni-NiO nanoparticles, making the catalyst have excellent stability during storage in air or during the reaction. Metal Ni (111) crystal planes with a lattice spacing of 0.204 nm and NiO (200) crystal planes with a lattice spacing of 0.210 nm were observed in the HR-TEM of all O v -NiO / Ni@C-T samples. In addition, NiO (111) crystal planes with a lattice spacing of 0.241 nm were observed in the O v -NiO / Ni@C-400 sample. TEM showed the hierarchical structure of the O v -NiO / Ni@C-350 sample, that is, carbon-coated NiO and Ni nanoparticles were formed on the carbon layer, and NiO and Ni were randomly distributed inside the carbon-coated structure, forming more NiO / Ni interfaces. At the same time, HAADF-STEM ( Figure 1 in (b), (d), (f)) and EDS images ( Figure 4 ) showed that the Ni nanoparticles were wrapped by the carbon layer. The inside was mainly metallic Ni, and the cross of Ni and O elements near the carbon layer was due to the presence of the NiO phase.

[0052] Example 4: Effect of different solvents on the activity of the O v -NiO / Ni@C-350 catalyst prepared in Example 2

[0053] 20 mg of the O v -NiO / Ni@C-350 catalyst prepared in Example 2, 1.0 mmol of benzaldehyde or acetophenone were added to the reaction vessel, and a mixed solution composed of 10 mL of organic solvent (analytical pure) and ammonia water (200.0 μL, 2.8 mmol) was added as the solvent. After sealing, 1.0 bar of hydrogen was charged, and the reaction was carried out at 25 °C for 8 h to obtain the product primary amine, which was quantitatively detected by gas chromatography.

[0054] The results are shown in Table 1. Benzaldehyde can be directly reductive aminated to three organic nitrogen-containing compounds, namely benzylamine (Table 1, product a), N-benzylidene benzylamine (Table 1, product b), and dibenzylamine (Table 1, product c), and directly reduced to the by-product benzyl alcohol (Table 1, product d) at normal temperature and pressure in different solvents.

[0055] The product distributions in different reaction solvents are inconsistent. The similar feature is that the by-product benzyl alcohol is formed in both polar and non-polar solvents. However, the main reductive amination products in polar solvents are benzylamine and N-benzylidene benzylamine (Table 1, serial number 1), while the main reductive amination product in non-polar solvents is N-benzylidene benzylamine (Table 1, serial numbers 8 and 9). A medium-polarity solvent is more favorable for the formation of N-benzylidene benzylamine, and there is no or only a small amount of the by-product benzyl alcohol formed (Table 1, serial numbers 5 - 7). On the one hand, NH₃·H₂O has poor solubility in non-polar solvents, which is more conducive to the direct hydrogenation reduction of benzaldehyde; on the other hand, some polar solvents can be adsorbed on the catalyst surface, resulting in poor adsorption of the aldehyde imine intermediate formed by the condensation of aldehyde and NH₃, and competitive reactions occur. In addition, the acetonitrile solvent is partially reduced, and there are more other by-products in the H₂O solvent. In order to obtain benzylamine in high yield, the reaction conditions in methanol solvent were optimized. After reacting for 8 h with NH₃·H₂O (1.0 mL, 14.0 mmol), the yield of benzylamine > 99% (Table 1, serial number 2). Ketone compounds require more stringent reaction conditions to inhibit the formation of alcohol. Under the reaction temperature (60 °C) and NH₃·H₂O (2.0 mL, 28.0 mmol), the yield of α-methylbenzylamine is 97.8% after reacting for 20 h (Table 1, serial number 12).

[0056] Table 1 Effects of different solvents on the reductive amination of aldehyde or ketone compounds

[0057]

[0058]

[0059] Note: Reaction conditions: benzaldehyde (1.0 mmol), O v -NiO / Ni@C-350 catalyst (20.0 mg), reaction temperature (25 °C), solvent (10 mL), NH₃·H₂O (200.0 μL, 2.8 mmol), H₂ (1.0 bar, external H₂ balloon), and reaction time (8 h); a NH₃·H₂O (1.0 mL, 14.0 mmol); b Reaction temperature (60 °C) and NH₃·H₂O (2.0 mL, 28.0 mmol); c The reaction conditions are the same as those in "b", but the reaction time is (20 h).

[0060] Example 5: O prepared in Example 2 v Catalytic activity of -NiO / Ni@C-350 catalyst towards different aldehyde compounds

[0061] Add 20 mg of the O v -NiO / Ni@C-350 catalyst prepared in Example 2 and 1.0 mmol of the aldehyde compound substrate into a reaction vessel, add a mixed solution composed of 9 mL of methanol (analytical pure, the same below) and 1 mL of ammonia water (14.0 mmol) as the solvent, seal it and fill it with 1.0 bar of hydrogen, and react at 25 °C for 8 - 26 h to obtain the product primary amine, and quantitatively detect it by gas chromatography.

[0062] O v -NiO / Ni@C-350 catalyst obtains 45 kinds of primary amines including aromatic, furan, thiophene, aliphatic, alicyclic and heterocyclic ones with high yields (92 - 99%) (Table 2). The results in Table 2 can be summarized as follows:

[0063] (1) The electronic properties of the substituents have little effect (Table 2, No. 1 - 5 vs 14 - 22), while the ortho-substituted groups react slower (Table 2, No. 2 vs 4 and 16 vs 18).

[0064] (2) In the reductive amination reaction, O v -NiO / Ni@C-350 catalyst has good functional group tolerance, and it is observed that groups such as halogen, hydroxyl, carboxyl and nitrile groups show good tolerance throughout the substrate range (Table 2, No. 6 - 8, 10 - 22, 33 and 34).

[0065] (3) Substrates containing N heteroatoms require a larger amount of NH3·H2O (2.0 mL) to be completely converted into the corresponding benzylamine (Table 2, No. 24 - 30), which may be due to the interaction between N and the catalyst, partially inhibiting the catalytic activity.

[0066] (4) Biomass-derived furan aldehydes, such as: furfural, 5-methylfurfural, 5-hydroxymethylfurfural and 5-formyl-2-furoic acid can all obtain the corresponding furanamines in quantitative yields (Table 2, No. 31 - 34). 5-Formyl-2-furoic acid containing a carboxyl group also obtains the corresponding furanamine in quantitative yield, indicating that the catalyst has good tolerance to organic acids, which provides a reference for the direct amination of carboxylic acid compounds (Table 2, No. 34).

[0067] (5) O v-NiO / Ni@C-350 catalyst also has excellent catalytic activity for alicyclic and aliphatic aldehyde compounds (Table 2, serial numbers 36-45). These results together indicate that this study provides a simple method for catalytically synthesizing amine compounds from aldehyde compounds under normal temperature and pressure conditions, greatly optimizing the reaction conditions of this process.

[0068] Table 2O v Catalytic activity of -NiO / Ni@C-350 catalyst for different types of aldehyde compounds

[0069]

[0070]

[0071]

[0072]

[0073]

[0074] Note: a Indicates NH3·H2O (2.0 mL, 28.0 mmol)

[0075] Example 6: Prepared in Example 2O v Catalytic activity of -NiO / Ni@C-350 catalyst for different ketone compounds

[0076] Add 20 mg of the O prepared in Example 2 v -NiO / Ni@C-350 catalyst and 1.0 mmol of ketone compound substrate into a reaction vessel, add a mixed solution composed of 9 mL of methanol and 2 mL of ammonia water (28.0 mmol) as a solvent, seal and fill with 1.0 bar of hydrogen, and react at 60 °C for 7-36 h to obtain the product primary amine, and quantitatively detect it by gas chromatography.

[0077] As shown in Table 3, the reductive amination of ketone compounds is more difficult than that of aldehyde compounds because ketone compounds are more easily reduced to alcohol compounds. However, using the O of the present invention v -NiO / Ni@C-350 catalyst can obtain 44 types of primary amines including aromatic, furan, alicyclic and aliphatic ones in high yields (76-99%). The results in Table 3 can be summarized as:

[0078] (1) Consistent with aldehydes, the electronic properties of substituents have little effect on the reductive amination of ketone compounds (Table 3, serial numbers 1-8 vs 2-16), but the ortho-substituents have poorer selectivity and obtain lower yields of primary amines (Table 3, serial numbers 2 vs 4 and 13 vs 15).

[0079] (2) Substrates with alkyl-end substitution of ketone compounds show that the longer the carbon chain, the slower the reaction rate (Table 3, Nos. 19 - 21), requiring a longer reaction time, but having no effect on the product selectivity.

[0080] (3) O v The O-NiO / Ni@C-350 catalyst is catalytically active for aromatic ketone compounds such as benzoin, benzil, and acetophenone (Table 3, Nos. 24, 25, and 30).

[0081] (4) The catalytic activity of alicyclic and aliphatic ketone compounds is equally excellent (Table 3, Nos. 31 - 40 and 42 - 44); it should be particularly emphasized that for the reductive amination of α-ionone, enamine with neither double bond reduced can be obtained by appropriately adjusting the concentration of NH3·H2O (42.0 mmol / mL) (Table 3, No. 34 vs 35), but for isophorone, only the amination product with double bond reduced can be obtained (Table 3, No. 36). Additionally, when the substrate is 2,5 - hexanedione, O v The O-NiO / Ni@C-350 catalyst directly reductively amines to 2,5 - dimethylpyrrole with a yield of 97% (Table 3, No. 43).

[0082] (5) O v The O-NiO / Ni@C-350 catalyst can be used to catalytically reduce aminate benzoylformic acid to phenylglycine with a yield of 87% (Table 3, No. 41), indicating that the catalyst has a wide range of applications.

[0083] Table 3 O v Catalytic activity of the O-NiO / Ni@C-350 catalyst for different types of ketone compounds

[0084]

[0085]

[0086]

[0087]

[0088]

[0089] Example 7: Characterize the O-NiO / Ni@C-T(X) catalyst of the present invention by low-temperature electron paramagnetic resonance (EPR) v -NiO / Ni@C-T(X) catalyst

[0090] Dissolve Ni(NO3)2·6H2O (3.5 g, 12.0 mmol) and terephthalic acid (2.0 g, 12.0 mmol) in DMF (120 mL) solution, dropwise add aqueous NaOH solution until pH = 8, after stirring evenly, raise the temperature from room temperature to 150 °C at a heating rate of 2.5 °C / min and keep it for 72 hours; wash the obtained solid product successively with distilled water and methanol 3 times to remove impurities and NaOH, wash until the filtrate is neutral, and dry in an oven at 70 °C in air for 12 h to obtain Ni-MOF. Then, reduce Ni-MOF under H2 / Ar atmosphere (heat up to 300 - 400 °C at a heating rate of 2 °C / min and reduce for 1 - 6 h), and then cool to room temperature to obtain the catalyst, denoted as: O v -NiO / Ni@C-T(X). Where T = 300, 350, 400, the unit is °C; X = 1, 2, 6, the unit is h. To study the roles of O v -NiO and metallic Ni sites in the bimetallic catalyst, O v -NiO / Ni@C-300 catalyst is pre-oxidized in air at 250 °C to obtain O v -NiO / Ni@C-300(air) catalyst.

[0091] Dissolve Ni(NO3)2·6H2O (3.1 mmol, 900.0 mg) in a mixed solution of 4 mL of water and ethanol (V 水 :V 乙醇 = 1:1), and then add graphene (0.5 g). Then stir the mixture at room temperature for 0.5 h, and then dry in an oven at 70 °C for 12 h to obtain the catalyst precursor. Reduce the catalyst precursor under H2 / Ar atmosphere at a heating rate of 2 °C / min to 350 °C and reduce for 2 h. After the sample is cooled to room temperature, passivate it with O2 / N2 atmosphere (volume percentage of O2 is 1%) for 2 h to obtain the graphene-supported Ni nanoparticle catalyst, denoted as Ni / Graphene; this catalyst is stored in a vacuum desiccator for standby.

[0092] As Figure 3 shown, the ex-situ EPR spectra of the prepared samples were tested at -173 °C, and all O v -NiO / Ni@C-T samples showed strong EPR signals. In EPR, unpaired electrons generated due to bond breakage caused by vacancy formation absorb microwave radiation and generate EPR signals when exposed to a strong magnetic field, which are widely used to identify oxygen vacancies and oxygen vacancy-related defect states. All samples showed a broad signal at g ≈ 2.27, which is a characteristic of paramagnetic Ni δ+ feature. O v -NiO / Ni@C-300 and O v-NiO / Ni@C-300(air), it can be seen that the metal Ni in the pre-oxidized sample 0 and Ni δ+ is oxidized to Ni 2+ , Ni δ+ decreases, and O v -NiO / Ni@C-300(air) only shows a weak EPR signal. In addition, O v -NiO / Ni@C-T samples show similar anisotropic ferromagnetic signals, but with different line shapes and intensities, indicating that these materials contain different amounts of Ni δ+ . The Ni / Graphene sample (as a blank control without O v and Ni δ+ ) has a very weak signal, indicating that it contains a very small amount of Ni δ+ , and these results are consistent with other characterization results.

[0093] Example 8: Using Ar ion etching XPS to characterize the structure of the O v -NiO / Ni@C-350 sample prepared in Example 2

[0094] Using Ar ion etching XPS characterization technology further confirms the structure of the O v -NiO / Ni@C-350 sample prepared in Example 2. As Figure 4 shown in (a) of, the intensity of the XPS Ni 2p peak becomes stronger after the outer layer C is corroded. Notice that before the outer layer C is corroded, the intensity ratio of the Ni 2+ -O peak in the XPS Ni 2p spectrum is stronger than that of metallic Ni 0 , and metallic Ni 0 gradually becomes stronger during the outer layer carbon corrosion process as the Ar ion etching time increases. And, this process is accompanied by a shift of the binding energy of metallic Ni 0 towards higher binding energy, which may be caused by partial C doping of the Ni crystal, but mainly metallic Ni. Due to the low Ni-C content and the binding energy being between NiO and metallic Ni, it is difficult to explain the change in the intensity of the Ni-C peak in the XPS Ni 2p spectrum during the etching process. The intensity of the Ni 2+ -O peak in the XPS O 1s spectrum changes little, but C=O gradually decreases as the Ar ion etching time increases, and O-C=O gradually increases and levels off as the Ar plasma etching time increases ([[]] Figure 4 in (b)). This shows that after the outer layer C containing a large amount of C=O is gradually etched, the Ni-O-C=O interface is gradually exposed, which is the reason for the formation of the C-encapsulated structure of this catalyst. Notice that XPS C 1s([[]] Figure 4The peak intensities of (c) and (d) in [reference] decreased from the start to 10 min because the outer C encapsulation structure was gradually etched, which led to a gradual decrease in C-C / C═C and C-O with increasing Ar ion etching time. More importantly, the XPS peak intensity at low binding energy in the XPS C 1s spectrum increased, and the Ni-C peak increased, that is, more C-Ni interfaces at the junction of the exposed metal Ni nanoparticles and the carbon encapsulation structure edge were exposed with increasing etching time.

[0095] In summary, these results indicate that metallic Ni should be located in the more inward part of the carbon-encapsulated O v -NiO / Ni nanoparticles, and the C-Ni and Ni-O-C═O edges of O v -NiO and metallic Ni should be more located near the carbon layer. Figure 1 The TEM image in [reference] can also directly observe this structure, and the TEM is consistent with the etching XPS results. Based on XRD, TEM, and etching XPS, it is speculated that the possible structure of the O v -NiO / Ni@C-350 sample is as follows: the outermost layer is encapsulated by a carbon layer, and mainly the C-Ni, Ni-O-C═O edges of metallic Ni and O v -NiO mixture layer are inside, and then there is a mixture layer of metallic Ni and O v -NiO mixture layer, metallic Ni and O v -NiO mixture is not fixed in a certain layer, but is randomly distributed in a disorderly manner in the carbon encapsulation structure, thus forming more O v -NiO / Ni (inverted type: Ni / O v -NiO) interfaces, exposing more active sites and improving the catalytic activity of the catalyst.

[0096] Example 9: Cyclic experiment to explore the stability of the O v -NiO / Ni@C-350 catalyst prepared in Example 2

[0097] 20 mg of the O v -NiO / Ni@C-350 catalyst prepared in Example 2 and 1.0 mmol of acetophenone were added to a reaction vessel, and a mixed solution composed of 9 mL of methanol and 1 mL of ammonia water (14.0 mmol) was added as a solvent. After sealing, 1.0 bar of hydrogen was charged, and the reaction was carried out at 60 °C for 8 h. After the reaction, the O v -NiO / Ni@C-350 was collected by centrifugation to avoid mass loss, then washed 5 times with absolute ethanol, and then the used O v -NiO / Ni@C-350 was vacuum dried at 40 °C for 12 h for the next round of reaction. The results are as Figure 5 shown, O vThe -NiO / Ni@C-350 catalyst can be recycled 7 times without significant loss of catalytic activity and selectivity.

Claims

1. A catalyst, characterized in that: The catalyst is a two-component Ni-based catalyst with carbon-coated Ni and O v -NiO coexisting, where the O v represents oxygen vacancies, and its active substance is Ni-NiO nanoparticles encapsulated by a carbon layer.

2. The preparation method of the catalyst according to claim 1, characterized in that, The preparation method successively comprises the following steps: (1) Dissolve Ni(NO3)2 and terephthalic acid in solvent A; dropwise add an aqueous NaOH solution until pH = 8, stir evenly to obtain a mixed solution; perform a hydrothermal reaction on the mixed solution, and successively wash the obtained solid product with distilled water and methanol, and then dry it in air to obtain Ni-MOF; (2) The Ni-MOF is heated from room temperature to the target temperature of 300 - 400 °C at a heating rate of 1 - 4 °C / min in an atmosphere of a hydrogen / argon mixed gas, and then maintained at the target temperature for 1 - 6 h for reduction; after cooling to room temperature, an O v -NiO / Ni@C-T(X) catalyst is obtained; T represents the reduction temperature, with the unit of °C, and X represents the reduction time, with the unit of h.

3. The preparation method according to claim 2, characterized in that: In step (1), solvent A is N,N-dimethylformamide DMF; the molar ratio of Ni(NO3)2 to terephthalic acid is (3 - 9):(6 - 10); the molar concentration of the aqueous NaOH solution is 0.1 M.

4. The preparation method according to claim 2, characterized in that: The conditions of the hydrothermal reaction in step (1) are to raise the temperature from room temperature to 130 - 170 °C at a heating rate of 1 - 5 °C / min and maintain for 62 - 82 hours; the conditions of the washing are to wash with distilled water and methanol successively for more than 3 times to remove impurities and NaOH until the filtrate is neutral; the conditions of the drying are to dry at 40 - 90 °C for 9 - 14 h.

5. The preparation method according to claim 2, characterized in that: In step (2), the volume percentage of hydrogen in the hydrogen / argon mixed gas is 10%.

6. Use of the catalyst according to claim 1 or the catalyst obtained by the preparation method according to any one of claims 2 - 5 in the synthesis of primary amines.

7. The application according to claim 6, wherein The steps of the use are as follows: Add the catalyst according to claim 1 or the catalyst obtained by the preparation method according to any one of claims 2 - 5 and an aldehyde or ketone compound in a ratio of (10 - 40) mg:(0.5 - 2) mmol into a reaction vessel, add solvent B, seal it and fill it with a reducing gas, and react under heating conditions to obtain the product primary amine.

8. The application according to claim 7, wherein: In the use, the structural formula of the aldehyde compound is one of the following: and / or the structural formula of the ketone compound is one of the following:

9. The application according to claim 7, wherein: In the use, the reducing gas filled is 1.0 bar hydrogen; the reaction conditions are to react at 20 - 60 °C for 5 - 36 h.

10. The application according to claim 7, wherein: Solvent B is a mixed solution formed by mixing one or more of methanol, ethanol, isopropanol, acetonitrile, tetrahydrofuran, toluene, hexane, water with ammonia water in a volume ratio of (7 - 10):(0.2 - 3); The concentration of the ammonia water is 10 - 18 mmol / mL.

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