Carbon-loaded nickel-molybdenum alloy catalyst, preparation method thereof and application of carbon-loaded nickel-molybdenum alloy catalyst in synthesis of amine compounds by selective reduction of nitro compounds

Abstract

The invention relates to the technical field of catalysts, and particularly discloses a carbon-loaded nickel-molybdenum alloy catalyst, a preparation method thereof and application of the carbon-loaded nickel-molybdenum alloy catalyst in synthesis of amine compounds by selective reduction of nitro compounds. According to the carbon-loaded nickel-molybdenum alloy catalyst, Ni4Mo is used as an active site, and conductive carbon black is used as a carrier. The catalyst can be used for chemically and selectively hydrogenating nitro compounds into corresponding amine compounds under mild conditions (20-30 DEG C, 10 bar H2). The preparation method of the catalyst is simple, and the catalyst has good catalytic activity in selective reduction of nitro compounds. According to the catalyst, the activity and selectivity of a non-noble metal catalyst are adjusted through intermetallic alloying, and some insights can be provided for subsequent development of cost-effective catalysts.

Description

Technical Field

[0001] The invention relates to the technical field of catalysts, and in particular to a carbon-supported nickel-molybdenum alloy catalyst, a preparation method thereof, and an application thereof in the selective reduction of nitro compounds to synthesize amine compounds. Background Art

[0002] Functionalized aromatic amines, as important components of fine chemicals, have important applications in the production of fine and bulk chemicals such as pharmaceuticals, agrochemicals, pigments, and polymers. The catalytic reduction of readily available functionalized nitroaromatics (R-Ph-NO2) over heterogeneous catalysts has attracted considerable attention as an environmentally friendly and recyclable approach to the synthesis of value-added amines (R-Ph-NH2). Meanwhile, catalytic hydrogenation using H2 in liquid phase is highly desirable because H2 molecules are cheaper and more readily available compared to other hydrogen donor molecules, and it is also environmentally friendly with water as the only byproduct.

[0003] However, the chemically selective reduction of -NO2 groups under mild conditions while retaining other reducible groups (e.g., alkenes, alkynes, halogens, or ketones) is a long-standing challenge. Therefore, it is necessary to rationally utilize heterogeneous catalysts to reduce only -NO2 groups without affecting other reducible groups. Currently, the selective hydrogenation of functionalized nitroaromatic compounds is mainly catalyzed by precious metal catalysts or requires high temperature and high pressure. For example: Yong Zhao used precious metal Pt / Fe2O3 catalysts to reduce nitroaromatic compounds. This method can be carried out at 35°C and 20 barH2, and the conversion rate and selectivity of the reaction for 1-2 hours reached 99% [Small 2023, 19, 2207918.]. Min Wei et al. used RuNi single-atom alloy catalysts to prepare amine compounds using hydrogen as a hydrogen source. At 60°C and a pressure of 10 barH2, the conversion rate and selectivity of the reaction for 3 hours reached 100% [Nature Communications, 13, 3188 (2022)]. Although noble metal catalysts (such as Ru, Pt, or Pd) are active under mild reaction conditions, they usually suffer from high cost, suboptimal selectivity, and low atom utilization.

[0004] Many non-precious metal catalysts have been explored for the catalytic hydrogenation of nitroaromatics. For example, Masayoshi Miyazaki et al. reported a bimetallic alloy Ni 0.75 Fe 0.25 / SiO2 reduces nitro aromatic compounds. This method can be carried out under normal pressure H2. The conversion rate reaches 98% and the selectivity reaches 95% after 4.5 hours of reaction at 140°C [Chemistry Select. 2021, 6 (22), 5538-5544]. Mingbo Wu et al. reported a single-atom Co1-N / PC catalyst to reduce nitro aromatic compounds. This method can be carried out under 20 bar H2. The conversion rate and selectivity reached 99% after 2 hours of reaction at 100°C [Nature Communications, 13, 723 (2022)]. Harsh reaction conditions hinder their full application. Therefore, how to obtain highly active and chemically selective catalysts through reasonable design and fine structure regulation remains a great challenge. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention aims to provide a carbon-supported nickel-molybdenum alloy catalyst and a preparation method thereof and an application thereof in the selective reduction of nitro compounds to generate amine compounds. The carbon-supported nickel-molybdenum alloy catalyst of the present invention uses Ni4Mo sites rather than single Ni or Mo sites as active centers. The carbon-supported nickel-molybdenum alloy catalyst can be used for chemically selectively hydrogenating nitro compounds, especially functionalized nitroaromatic compounds, to corresponding amine compounds under mild conditions (20-30°C, 10 bar H2).

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

[0007] In the first aspect, the present invention provides a carbon-supported nickel-molybdenum alloy catalyst, wherein the carbon-supported nickel-molybdenum alloy catalyst uses a Ni4Mo alloy as an active site and conductive carbon black as a carrier. The mass percentage content of the Ni element in the carbon-supported nickel-molybdenum alloy catalyst is 6.7% to 7.5%, and the mass percentage content of the Mo element is 2.7% to 3.0%.

[0008] In a second aspect, the present invention provides a method for preparing the above-mentioned carbon-supported nickel-molybdenum alloy catalyst, comprising the following steps:

[0009] (1) Nickel nitrate hexahydrate and ammonium molybdate tetrahydrate are dissolved in a mixed solvent of ethylene glycol and deionized water, and magnetic stirring is continued. After complete dissolution, conductive carbon black and concentrated ammonia water are added in sequence, and stirred to obtain a mixed solution. The mixed solution is subjected to hydrothermal treatment, and the precipitate is collected by centrifugation. The precipitate is washed with water and ethanol several times, and finally dried to obtain carbon-supported Ni(OH)2 / MoO4 2- Precursor;

[0010] (2) placing the precursor obtained in step (1) in a tubular furnace, heating it to a target temperature of 350-550° C. in a hydrogen atmosphere, pyrolyzing it for 2-3 h, and cooling it to room temperature to obtain a black powder, which is a carbon-supported nickel-molybdenum alloy catalyst.

[0011] Furthermore, in step (1), the concentration of the concentrated ammonia water is 25-28wt.%, and the usage ratio of the nickel nitrate hexahydrate, ammonium molybdate tetrahydrate, mixed solvent, conductive carbon black, and concentrated ammonia water is 1mmol:0.14mmol:50mL:450mg:2mL; the volume ratio of ethylene glycol and deionized water in the mixed solvent is 9:1.

[0012] Furthermore, in step (1), adding conductive carbon black and concentrated ammonia water and stirring for 1 hour may be: adding conductive carbon black, stirring for 30 minutes, then adding concentrated ammonia water, and continuing to stir for 30 minutes.

[0013] Furthermore, in step (1), the conditions for the hydrothermal treatment of the mixed solution are: the mixed solution is hydrothermally treated at 150° C. for 4 hours.

[0014] Furthermore, in step (1), the drying conditions are: drying at 65-85°C for 6-24h, preferably drying at 70°C for 12h.

[0015] Furthermore, in step (1), the conductive carbon black is Vulcan XC72R conductive carbon black.

[0016] Furthermore, in step (2), the target temperature is 400-500°C; the target temperature is preferably 440-460°C, more preferably 445-455°C, and most preferably 450°C.

[0017] Furthermore, in step (2), the temperature is raised to a target temperature of 450°C at a heating rate of 1-3°C / min, and the pyrolysis time is 2h.

[0018] Preferably, in step (2), the temperature is raised to the target temperature at a heating rate of 2°C / min.

[0019] In a third aspect, the present invention provides the use of the carbon-supported nickel-molybdenum alloy catalyst or the carbon-supported nickel-molybdenum alloy catalyst prepared by the above method in the selective reduction of nitro compounds to synthesize amine compounds, comprising the following steps:

[0020] A carbon-supported nickel-molybdenum alloy catalyst, an organic solvent and a nitro compound are added to a stainless steel high-pressure reactor, which is sealed and replaced with H2 to displace the air in the reactor. The high-pressure reactor is pressurized and sealed with 5-20 bar H2, and then reacted at 20-50° C. with constant stirring to obtain an amine compound in which only the nitro group is reduced and reduced to an amino group, with a yield of more than 94%.

[0021] Furthermore, the organic solvent is one or more of toluene, n-hexane and cyclohexane, preferably cyclohexane.

[0022] Furthermore, the ratio of the carbon-supported nickel-molybdenum alloy catalyst, the organic solvent, and the nitro compound is: (20-40) mg:10 mL:0.5 mmol, preferably 20 mg:10 mL:0.5 mmol.

[0023] Further, the autoclave is pressurized and sealed with 5-10 bar H2, and then the reaction is carried out at 20-50°C with constant stirring, preferably for more than 2 hours, more preferably for more than 4 hours, and more preferably for more than 6 hours.

[0024] Furthermore, the nitro compound is selected from the following functionalized nitro aromatic compounds:

[0025]

[0026] After H2 pressure sealing, the reaction was carried out at 20-30°C with constant stirring to obtain an amine compound in which only the nitro group was reduced and reduced to the amino group, with a yield of more than 94%.

[0027] The nitro compound is selected from the following non-aromatic nitro compounds:

[0028] After H2 pressure sealing, the reaction was carried out at 20-50°C with constant stirring to obtain an amine compound in which only the nitro group was reduced and reduced to the amino group, with a yield of more than 94%.

[0029] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0030] 1. Compared with the metal-based catalysts in the prior art, which use hydrogen (H2), sodium borohydride (NaBH4) and hydrazine hydrate (N2H4·H2O) as reducing agents, the heterogeneous non-precious metal catalyst in the present invention uses H2 to selectively reduce nitro compounds to generate corresponding amine compounds. The method has a simple process, easy operation, mild reaction conditions, and better selectivity for reducing only nitro group compounds in the product.

[0031] 2. The heterogeneous non-precious metal catalyst prepared by the present invention is used for catalytic reduction of nitro compounds to prepare amine compounds. Compared with the existing methods, the reaction temperature and reaction pressure are greatly reduced, making the reaction conditions milder, thereby greatly reducing the preparation cost of amine compounds, and the yield of amine compounds produced by existing heavy metal and precious metal catalysts such as Pt, Pd, and Au is consistent.

[0032] 3. The heterogeneous non-precious metal catalyst prepared by the present invention is easy to separate and can be recycled for more than 5 times while still maintaining a high conversion rate and high selectivity. The catalyst has good stability and has good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Characterization of the catalyst NiMo@C-450 of the present invention: a) XRD pattern; b) TEM image of the NiMo@C-450 catalyst; c) HR-TEM image of the NiMo@C-450 catalyst; d) HADDF-STEM image of the NiMo@C-450 catalyst and the corresponding EDX element mapping image.

[0034] Figure 2 This is the XPS spectrum of the catalyst NiMo@C-450 of the present invention.

[0035] Figure 3 The figure is a brief flow chart of the preparation method of the catalyst NiMo@CT of the present invention.

[0036] Figure 4 Characterization of the catalyst Ni / C-450 of the present invention: a) XRD pattern; b) TEM pattern; c) Ni particle size distribution. DETAILED DESCRIPTION

[0037] The technical solution of the present invention is described in detail below in conjunction with specific embodiments and the accompanying drawings of the specification, but the following embodiments are not intended to limit the scope of protection requested by the claims of the present invention.

[0038] In the following examples, nitro compounds and various organic solvents were purchased from Sinopharm Shanghai Chemical Reagent Co., Ltd. or Shanghai Aladdin Biochemical Technology Co., Ltd. 24 4H2O (mass percentage content>99.5%) was purchased from Sinopharm Shanghai Chemical Reagent Co., Ltd., nickel nitrate hexahydrate (mass percentage content>99.7%) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., and Vulcan XC72R conductive carbon black was purchased from Shanghai Chenqi Chemical Technology Co., Ltd. Molybdenum carbide (mass percentage content>99.95%) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0039] Example 1

[0040] A method for preparing a nickel-molybdenum alloy catalyst NiMo@CT, the steps of which are as follows:

[0041] Step (1), 1.00 mmol of Ni(NO3)2·6H2O and 0.14 mmol of (NH4)6Mo7O 244H2O was dissolved in a mixed solvent of ethylene glycol (45mL) and deionized water (5mL), and magnetic stirring was continued. After complete dissolution, 450mg Vulcan XC72R conductive carbon black was added, and stirred for 30min. Then, 2mL concentrated ammonia (26wt.%) was added and stirred for 30min. Then, the mixture was hydrothermally treated at 150℃ for 4h, the precipitate was collected, washed with deionized water until neutral, and then washed with anhydrous ethanol for 3 times, and finally dried in an oven at 70℃ for 12h to obtain a black powder, which is carbon-supported Ni(OH)2 / MoO4. 2- Precursor.

[0042] Step (2), loading the carbon obtained in the above step (1) with Ni(OH)2 / MoO4 2- The precursor was placed in a tubular furnace and heated from room temperature to a target temperature of 450°C at a heating rate of 2°C / min in a hydrogen (H2) atmosphere, and then maintained at 450°C for 2h (pyrolysis process). The heating was then stopped and the product was naturally cooled to room temperature to obtain a black powder.

[0043] The obtained black powder is the catalyst, which is labeled as NiMo@C-450.

[0044] Comparative Example 1

[0045] A method for preparing a nickel-molybdenum catalyst NiMo@GO, the steps of which are as follows:

[0046] Step (1), preparation of carrier graphene oxide, take 0.5g graphite powder (from Shanghai Aladdin Biochemical Technology Co., Ltd., mass percentage content> 99.9%) and add it to a beaker containing 12mL 98wt% concentrated sulfuric acid, then place the beaker in an ice water bath (0-5°C), slowly add 1.5g potassium permanganate to the beaker while stirring, after addition, stir the beaker containing the mixture at 35°C for 2h, and then dilute with 24mL deionized water. Then heat to 98°C and stir for 30min, cool to room temperature, add 70mL deionized water, and after 2h, add 1.25mL 30% hydrogen peroxide and let stand overnight. Filter out the solid, then use 125mL 5wt% hydrochloric acid to filter and wash to remove metal ions, finally wash with deionized water to neutrality, centrifuge and collect, place in a 70°C vacuum oven and dry for 12h to obtain a black powder, the obtained black powder is graphene oxide (GO).

[0047] Step (2), 1.00 mmol of Ni(NO3)2·6H2O and 0.14 mmol of (NH4)6Mo7O 244H2O was dissolved in a mixed solvent of ethylene glycol (45 mL) and deionized water (5 mL) and magnetic stirring was continued. Then 450 mg of GO prepared in step (1) was added and stirred for 30 min. Then 2 mL of concentrated ammonia (26 wt.%) was added and stirred for 30 min. Then, the mixture was hydrothermally treated at 150 ° C for 4 h, the precipitate was collected, washed with deionized water until neutral, and then washed with anhydrous ethanol for 3 times, and finally dried in an oven at 70 ° C for 12 h to obtain a black powder, which is graphene oxide loaded Ni (OH) 2 / MoO4 2- Precursor.

[0048] Step (3), loading Ni(OH)2 / MoO4 on the graphene oxide obtained in the above step (2) 2- The precursor was placed in a tubular furnace and heated from room temperature to a target temperature of 450°C at a heating rate of 2°C / min in a hydrogen (H2) atmosphere, and then maintained at 450°C for 2h (pyrolysis process). The heating was then stopped and the product was naturally cooled to room temperature to obtain a black powder.

[0049] The obtained black powder is the catalyst, labeled as NiMo@GO-450.

[0050] Example 2

[0051] A method for preparing a nickel-molybdenum alloy catalyst NiMo@CT (NiMo@C-300), comprising the following steps:

[0052] Except that the target temperature in step (2) of Example 1 is adjusted to 300° C., the rest is the same as Example 1, and the prepared catalyst is marked as NiMo@C-300.

[0053] Example 3

[0054] A method for preparing a nickel-molybdenum alloy catalyst NiMo@CT (NiMo@C-350), comprising the following steps:

[0055] Except that the target temperature in step (2) of Example 1 is adjusted to 350° C., the rest is the same as Example 1, and the prepared catalyst is marked as NiMo@C-350.

[0056] Example 4

[0057] A method for preparing a nickel-molybdenum alloy catalyst NiMo@CT (NiMo@C-400), comprising the following steps:

[0058] Except that the target temperature in step (2) of Example 1 is adjusted to 400° C., the rest is the same as Example 1, and the prepared catalyst is marked as NiMo@C-400.

[0059] Example 5

[0060] A method for preparing a nickel-molybdenum alloy catalyst NiMo@CT (NiMo@C-500), comprising the following steps:

[0061] Except that the target temperature in step (2) of Example 1 is adjusted to 500° C., the rest is the same as Example 1, and the prepared catalyst is marked as NiMo@C-500.

[0062] Example 6

[0063] A method for preparing a nickel-molybdenum alloy catalyst NiMo@CT (NiMo@C-550), comprising the following steps:

[0064] Except that the target temperature in step (2) of Example 1 is adjusted to 550° C., the rest is the same as Example 1, and the prepared catalyst is marked as NiMo@C-550.

[0065] Example 7

[0066] A method for preparing a nickel-molybdenum alloy catalyst NiMo@CT (NiMo@C-600), comprising the following steps:

[0067] Except that the target temperature in step (2) of Example 1 is adjusted to 600° C., the rest is the same as Example 1, and the prepared catalyst is marked as NiMo@C-600.

[0068] Example 8

[0069] The steps and operations are the same as step (1) of Example 1, and step (2) is not required. The prepared catalyst is marked as Precursor.

[0070] Example 9

[0071] Except for the addition of (NH4)6Mo7O 24 Except for the addition of 4H2O, the other steps and operations were the same as those in Example 1, and the prepared catalyst was marked as Ni / C-450.

[0072] Example 10

[0073] Except for not adding Ni(NO3)2·6H2O, the remaining steps and operations were the same as those in Example 1. The prepared catalyst was labeled as MoO x @C.

[0074] Embodiment 11

[0075] The contents of Ni and Mo in the precursor and NiMo@CT catalyst were determined by inductively coupled plasma optical emission spectroscopy (ICP-OES). The results are as follows:

[0076] In Precursor, the Ni content is 6.4 ± 0.1 wt.%;

[0077] In NiMo@C-300, the content of Ni is 6.7±0.1wt.%, and the content of Mo is 2.7±0.1wt.%;

[0078] In NiMo@C-350, the content of Ni is 6.8±0.1wt.%, and the content of Mo is 2.8±0.1wt.%;

[0079] In NiMo@C-450, the content of Ni is 6.9±0.1wt.%, and the content of Mo is 2.8±0.1wt.%;

[0080] In NiMo@C-550, the content of Ni is 7.4±0.1wt.%, and the content of Mo is 2.9±0.1wt.%;

[0081] In NiMo@C-600, the content of Ni is 7.4±0.1wt.%, and the content of Mo is 2.9±0.1wt.%;

[0082] The calcination temperature is 350-550°C, the mass percentage content of Ni element in the above NiMo@CT catalyst is about 6.7%-7.5%, the mass percentage content of Mo element is about 2.7%-3.0%, and the molar ratio of Ni / Mo element is approximately 4: 1. The Ni content in NiMo@C-550 and NiMo@C-600 is slightly higher than 7.0wt.%, which may be due to the more obvious decomposition of carbon at high temperature, forming Mo2C at 600°C.

[0083] Characterization results

[0084] The catalyst NiMo@C-450 prepared in Example 1 was characterized. Figure 1 . Figure 1 In the figure, a) is the XRD pattern of NiMo@CT catalyst; b) is the TEM pattern of NiMo@C-450 catalyst, c) is the HR-TEM pattern of NiMo@C-450 catalyst, d) is the HADDF-STEM pattern of NiMo@C-450 catalyst, and the remaining figures are the corresponding EDX element mapping images.

[0085] XRD pattern: A weak and broad peak with 2θ centered at 24.8° was found in the XRD spectrum of the NiMo@CT catalyst, which was attributed to the (002) crystal plane of graphite in the Vulcan carbon support. The diffraction peaks of the metal phase were observed in all NiMo@CT samples, but the composition of the metal phase changed with the pyrolysis temperature T. The diffraction peak of α-Ni(OH)2 was observed in NiMo@C-300, indicating that the precursor was not completely transformed into Ni-Mo alloy at a pyrolysis temperature of 300°C. A weak diffraction peak at 2θ=43.5° was also seen, and its intensity was weak, which was attributed to the carbon phase or the (121) crystal plane of Ni4Mo. At higher pyrolysis temperatures, the narrower the diffraction peak, the stronger the intensity. An additional peak at 51.2° can be found in the XRD spectra of NiMo@C-450, NiMo@C-550 and NiMo@C-600, which is attributed to the (002) plane of the Ni4Mo phase, indicating that the nickel and molybdenum elements exist in the form of Ni4Mo alloy. This can also be attributed to the better graining and increasing size of the Ni4Mo alloy at higher pyrolysis temperatures. As the pyrolysis temperature is further increased to 600°C, new diffraction peaks appear at 34.6°, 39.5°, 52.5°, 61.9° and 69.8°, belonging to the Mo2C phase. The formation of the Mo2C phase at 600°C may be due to the combination of part of the Mo in the Ni4Mo phase with the in-situ CH4* generated by the high-temperature pyrolysis of the Vulcan carbon support.

[0086] TEM image: Analysis of the TEM image of NiMo@C-450 shows that the Ni4Mo particle size is 7.9±2.2nm and is evenly distributed on the carbon support.

[0087] HR-TEM image: In the high-resolution TEM (HR-TEM) image of NiMo@C-450, lattice fringes with a lattice spacing of d = 0.178 nm and a lattice spacing of d = 0.207 nm were measured, corresponding to the (002) and (121) planes of Ni4Mo, respectively, which is consistent with the XRD results.

[0088] High-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) images show that Ni4Mo nanoparticles (bright areas) are uniformly distributed on the carbon support.

[0089] Energy dispersive elemental (EDX) mapping further revealed the uniform distribution of Ni and Mo elements on the carbon support in the NiMo@C-450 catalyst.

[0090] The catalyst NiMo@C-450 prepared in Example 1 was characterized by XPS. Figure 2 .

[0091] The chemical states of Ni and Mo on the surface of a representative NiMo@C-450 catalyst were investigated using X-ray photoelectron spectroscopy (XPS). Figure 2 As shown in the figure, the high-resolution XPS spectrum of Ni 2p orbitals shows two obvious peaks at binding energies of 870.0 eV and 852.7 eV, respectively, which are attributed to the metallic Ni 2p 1 / 2 and Ni 2p 3 / 2 At the same time, the two peaks at around 873.6eV and 855.9eV may be Ni 2+ The two broad peaks with binding energies of 879.6 eV and 861.4 eV belong to the satellite peaks of Ni2p orbital. In the high-resolution XPS spectrum of Mo 3d orbital, metallic Mo 3d 3 / 2 and metal Mo 3d 5 / 2 The peaks of Mo are located at 230.7eV and 227.6eV respectively. 4+ 3d 3 / 2 and Mo 4+ 3d 5 / 2 Another group of peaks are located at 232.4eV and 229.3eV. In addition, the two peaks centered at 235.0eV and 231.9eV can be attributed to Mo 6+ .

[0092] The catalyst Ni / C-450 prepared in Example 9 was characterized. Figure 4 . Figure 4 In the figure, a) is the XRD pattern of Ni / C-450 catalyst; b) is the TEM pattern of Ni / C-450 catalyst; and c) is the particle distribution pattern of Ni / C-450 catalyst.

[0093] Depend on Figure 4 As shown in the XRD spectrum, Ni / C-450 has three characteristic peaks at 2θ=44.4°, 51.7°, and 76.3°, corresponding to the (111), (200), and (220) crystal planes of metal Ni nanoparticles (cubic Ni metal phase, JCPDS PDF#No.15-0806). Through transmission electron microscopy (TEM), metal Ni nanoparticles can be clearly seen, with an average particle size of 53.1±7.1nm.

[0094] Examples 12-23

[0095] The catalysts prepared in Examples 1-10, the catalyst prepared in Comparative Example 1, and commercially available molybdenum carbide are respectively used in the selective reduction of nitroaromatics to generate corresponding amine compounds, and the steps are as follows:

[0096] 20 mg of catalyst, 10 mL of toluene, and 0.5 mmol of 4-nitrostyrene were added to a 25 mL stainless steel reactor, which was sealed. After the air in the reactor was replaced with hydrogen for 5 times, 10 bar of reducing gas (H2) was filled in and sealed, stirring was started, and the magnetic stirring rate was adjusted to 700 rpm. The reaction was carried out at 30 ° C for 2 h to obtain a reduced product. After the reaction was completed, the spent catalyst was collected by centrifugation, and the product was identified by gas chromatography-mass spectrometry (GC-ms) with ethylbenzene as the internal standard, and the product was quantitatively analyzed by GC (Shimadzu, GC-2010 Plus), the same below.

[0097] In the above system, 4-nitrostyrene is reduced, product 1a is the target product, product 2a is the by-product produced by the over-reduction of 4-nitrostyrene, and product 3a is the intermediate of hydrogenating 4-nitrostyrene to 4-vinylaniline.

[0098] The effects of different catalysts on the selective hydrogenation of 4-nitrostyrene are shown in Table 1. It can be seen from Table 1 that:

[0099] Example 8 Catalyst Carbon Supported Ni(OH)2 / MoO4 Prepared 2- The precursor has no catalytic activity for the conversion of 4-nitrostyrene.

[0100] The catalyst Ni / C-450 prepared in Example 9 has no catalytic activity for the conversion of 4-nitrostyrene.

[0101] Catalyst MoO prepared in Example 10 x @C has no catalytic activity for the conversion of 4-nitrostyrene.

[0102] The commercially available catalyst Mo2C has little catalytic activity for the conversion of 4-nitrostyrene.

[0103] The catalyst NiMo@GO-450 prepared in Comparative Example 1 showed strong catalytic activity in catalyzing the conversion of 4-nitrostyrene, but the selectivity for the target product 1a (4-aminostyrene) was only 55.8%, that is, the catalyst could not selectively catalyze the nitro group in the presence of other reducible groups.

[0104] The catalyst NiMo@CT prepared in Examples 1-7 shows catalytic activity for the conversion of 4-nitrostyrene, can inhibit the hydrogenation of vinyl (C=C) in 4-nitrostyrene, and has a low selectivity for the byproduct 2a (4-ethylaniline) (<1.5%). Among them: when NiMo@C-300 prepared in Example 2 is used as a catalyst, the conversion rate of 4-nitrostyrene is 13.3%, and the selectivity of the target product is 68.4%, which is due to the fact that only part of the Ni4Mo alloy is formed at 300°C. When NiMo@C-350 prepared in Example 3 is used as a catalyst, the conversion rate of 4-nitrostyrene is increased to 50.0%, and the selectivity of the target product 1a is about 90%; when NiMo@C-400 prepared in Example 4 is used as a catalyst, the conversion rate of 4-nitrostyrene is 51.8%, and the selectivity of the target product 1a is about 90%; when NiMo@C-450 prepared in Example 1 is used as a catalyst, the conversion rate of 4-nitrostyrene is further increased to 65.7%, and the selectivity of the target product 1a is more than 90%. At 300-450°C, as the pyrolysis temperature increases, the proportion of the reduced Ni4Mo phase increases, and the performance of the catalyst improves; at 450-550°C, as the pyrolysis temperature increases, the performance of the catalyst tends to decrease due to the gradual transformation of part of the Ni4Mo phase into Mo2C, but the conversion rate is above 50%, and the selectivity of the target product 1a is above 90%. When the NiMo@C-600 prepared in Example 7 is used as a catalyst, the catalytic efficiency deteriorates, which may be due to the transformation of the Ni4Mo phase into Mo2C, which does not work in the hydrogenation of 4-nitrostyrene.

[0105] The above results show that the Ni site and MoO x The Mo site of @C catalyst has no catalytic activity towards 4-nitrostyrene. The Ni4Mo site is the active center for the selective reduction of 4-nitrostyrene to 4-aminostyrene.

[0106] Table 1. Effect of different catalysts on the selective hydrogenation of 4-nitrostyrene a

[0107]

[0108]

[0109] a Reaction conditions: 4-nitrostyrene (0.5 mmol), catalyst (20 mg), toluene (10 mL), H2 (10 bar), 30°C, 2 h.

[0110] Examples 24-34

[0111] In order to optimize the reaction conditions of the NiMo@C-450 catalyst for the selective catalytic hydrogenation of 4-nitrostyrene to 4-aminostyrene, different solvents were first screened. The catalyst NiMo@C-450 catalyzed the selective catalytic hydrogenation of 4-nitrostyrene to 4-aminostyrene, and the steps were as follows:

[0112] 20 mg of the NiMo@C-450 catalyst prepared in Example 1, 10 mL of solvent and 0.5 mmol of 4-nitrostyrene were added to a stainless steel reactor. The stainless steel reactor was sealed and the air in the reactor was replaced with H2. After replacing the air 5 times, 10 bar of reducing gas (H2) was filled and sealed. Stirring was started, and the magnetic stirring rate was adjusted to 700 rpm. Then, the reaction was carried out at 30°C for 2 h to obtain a hydrogenation product.

[0113] The effects of different solvents on the selective hydrogenation of 4-nitrostyrene are shown in Table 2. It can be seen from Table 2 that the reaction solvent has a significant effect on the hydrogenation reaction of 4-nitrostyrene. Non-polar hydrocarbon solvents, such as n-hexane, cyclohexane and toluene, are good solvents for the hydrogenation of 4-nitrostyrene. The conversion rate after 2 hours of hydrogenation is moderate (65.7%-75.6%), and the selectivity of 1a is excellent (>90%). Cyclohexane is the best reaction solvent, and the conversion rate of 4-nitrostyrene is the highest, reaching 75.6%. In the solvents containing heteroatoms, including methanol, anhydrous ethanol, 1,4-dioxane, acetonitrile and tetrahydrofuran, there is no conversion of 4-nitrostyrene, which may be due to the adsorption competition between the solvents containing heteroatoms and 4-nitrostyrene, and these solvents can be more firmly combined with Ni4Mo alloy.

[0114] In order to determine the adsorption competition between heteroatom-containing solvents and 4-nitrostyrene on the surface of NiMo@C-450 catalyst, the total amount of solvent was kept at 10 mL, and the catalytic hydrogenation experiment of 4-nitrostyrene was carried out in cyclohexane containing different amounts of anhydrous ethanol. The effect of different amounts of anhydrous ethanol on the selective hydrogenation of 4-nitrostyrene in cyclohexane is shown in Table 3. After adding 6.5 equivalents of anhydrous ethanol, the conversion rate of n-hexane dropped sharply from 75.6% to 45.7%, and with the increase of the amount of anhydrous ethanol added, the conversion rate continued to decrease, and finally the conversion rate dropped to <1% when 52 equivalents (about 1.5 mL) of anhydrous ethanol was added. These results confirm that the presence of these heteroatom-containing solvents can competitively adsorb on the surface of Ni4Mo alloy, blocking the active sites for the adsorption and activation of 4-nitrostyrene.

[0115] Table 2. Effect of different solvents on the selective hydrogenation of 4-nitrostyrene a

[0116]

[0117] aReaction conditions: 4-nitrostyrene (0.5 mmol), catalyst (20 mg), solvent (10 mL), H2 (10 bar), 30°C, 2 h.

[0118] Table 3. Effect of the amount of anhydrous ethanol on the hydrogenation of 4-nitrostyrene in cyclohexane a

[0119]

[0120] a Reaction conditions: 4-nitrostyrene (0.5 mmol), NiMo@C-450 (20 mg), cyclohexane / ethanol mixed solvent (10 mL), 10 bar H2, 30 °C, 2 h.

[0121] b molar ratio of 4-nitrostyrene.

[0122] Examples 35-38

[0123] The H2 pressure of catalytic hydrogenation of 4-nitrostyrene was further optimized on NiMo@C-450 catalyst, and the optimal reaction hydrogen pressure was screened. The catalyst NiMo@C-450 catalyzed the selective catalytic hydrogenation of 4-nitrostyrene to produce 4-aminostyrene, and the steps were as follows:

[0124] 20 mg of the NiMo@C-450 catalyst prepared in Example 1, 10 mL of cyclohexane and 0.5 mmol of 4-nitrostyrene were added to a stainless steel reactor. The stainless steel reactor was sealed and the air in the reactor was replaced with H2 (1-20 bar). After the air was replaced with hydrogen 5 times, 1-20 bar of reducing gas (H2) was filled and sealed. Stirring was started, the magnetic stirring rate was adjusted to 700 rpm, and then the reaction was carried out at 30°C for 2 h to obtain a hydrogenation product.

[0125] The effect of H2 pressure on the hydrogenation of 4-nitrostyrene is shown in Table 4. It can be seen from Table 4 that H2 pressure is positively correlated with catalytic efficiency because more H2 is available on the catalyst surface at higher H2 pressure. In addition, even at 20 bar H2 pressure, the selectivity of 2a is still low, indicating good chemical selectivity in the nitro hydrogenation process. Due to the high selectivity for 1a, increasing H2 pressure can also accelerate the conversion of 3a to 1a. 10 bar was selected as the optimized H2 pressure because the conversion rate did not differ significantly when the pressure was doubled to 20 bar.

[0126] Table 4. Effect of H2 pressure on hydrogenation of 4-nitrostyrene a

[0127]

[0128] a Reaction conditions: 4-nitrostyrene (0.5 mmol), NiMo@C-450 (20 mg), cyclohexane (10 mL), H2 (1-20 bar), 30°C, 2 h.

[0129] Examples 39-70: Catalyst activity on different substrates at different reaction times

[0130] Inspired by the excellent catalytic performance of 4-nitrostyrene in the process of chemical selective hydrogenation, we further studied the substrate scope of this method to obtain different types of primary amines. Different nitro compounds (0.5mmol), cyclohexane (10mL) and NiMo@C-450 catalyst (20mg) prepared in Example 1 were added to a stainless steel reactor, the stainless steel reactor was sealed and the air in the reactor was replaced with H2. After the air was replaced with hydrogen 5 times, 10bar reducing gas (H2) was filled and sealed, stirring was started, the magnetic stirring rate was adjusted to 700rpm, and then the reaction was carried out at a certain temperature to obtain hydrogenation products. The yield of the target product is shown in Table 5.

[0131] As can be seen from Table 5, various substituted nitroaromatics, condensed ring nitro compounds, and even inert aliphatic nitro compounds can be smoothly converted into the corresponding amines with high yields (>94.1%). The electronic properties of the substituents affect the reactivity of these substrates. Substrates with electron-donating groups are more active than substrates with electron-withdrawing groups. Obvious stereo effects have also been found in nitrobenzene derivatives with substituents (such as chlorine atoms and methyl groups) at the ortho position. Compared with meta-substituted or para-substituted substrates, they require longer times to obtain higher yields (such as Examples 42, 44, 47, and Examples 52, 53, and 54). Other bulky substituents at the ortho position, such as amines and aromatic rings, also have lower reaction rates and require longer reaction times to obtain high yields of the corresponding amines. Steric hindrance can also be observed in nitro compounds containing more than two substituents or condensed rings. Due to the strong affinity of ethanol for Ni4Mo alloy nanoparticles, the hydrogenation reaction of 4-nitrostyrene in ethanol was inhibited, while the successful hydrogenation of nitro groups containing heterocyclic rings or side-carrying heteroatoms indicated that -NO2 groups were preferentially adsorbed on the surface of Ni4Mo alloy nanoparticles and had good tolerance to easily reducible groups such as halogens, olefins, esters, nitriles, ethers, secondary amines, and sulfides. NiMo@C-450 catalyst has broad application prospects in the synthesis of functional drugs and agricultural chemicals.

[0132] Table 5. Activity of NiMo@C-450 catalyst for different substrates at different reaction times

[0133]

[0134]

[0135] a Example 39-68 Reaction conditions: substrate (0.5 mmol), NiMo@C-450 (20 mg), cyclohexane (10 mL), H2 (10 bar), 30°C.

[0136] b The reactions of Examples 69-70 were carried out at 50°C.

[0137] Embodiment 71:

[0138] The effect of reaction time on the catalytic hydrogenation of 4-nitrostyrene was further investigated on the NiMo@C-450 catalyst. The catalyst NiMo@C-450 catalyzed the selective catalytic hydrogenation of 4-nitrostyrene to produce 4-aminostyrene, and the steps were as follows:

[0139] 20 mg of the NiMo@C-450 catalyst prepared in Example 1, 10 mL of cyclohexane and 0.5 mmol of 4-nitrostyrene were added to a stainless steel reactor. The stainless steel reactor was sealed and the air in the reactor was replaced with H2. After the air was replaced with hydrogen 5 times, 10 bar of reducing gas (H2) was filled and sealed. Stirring was started, the magnetic stirring rate was adjusted to 700 rpm, and then the reaction was carried out at 30°C for 1-6 h to obtain a hydrogenation product.

[0140] The effect of reaction time on the selective catalytic hydrogenation of 4-nitrostyrene is shown in Table 6. As can be seen from Table 6, the conversion rate increases sharply to 93.2% in the first 4 hours of the reaction, and the conversion rate increases slowly after 4 hours. After 6 hours, the conversion rate can reach >99%, and the selectivity of 4-aminostyrene is 97.4%.

[0141] Table 6. Effect of reaction time on selective catalytic hydrogenation of 4-nitrostyrene

[0142]

[0143]

[0144] Reaction conditions: 4-nitrostyrene (0.5 mmol), NiMo@C-450 (20 mg), cyclohexane (10 mL), H2 (10 bar), 30 °C.

[0145] Example 72: Catalyst Selective Catalytic Hydrogenation Cycle Experiment

[0146] The most important advantage of heterogeneous catalysts is the recyclability of the catalyst. In order to better study the catalytic stability of the NiMo@C-450 catalyst, based on the catalyst NiMo@C-450 in Example 1, the chemically selective catalytic hydrogenation of nitro compounds to generate corresponding amine compounds was studied, and the steps were as follows:

[0147] 20 mg of the NiMo@C-450 catalyst prepared in Example 1, 10 mL of cyclohexane and 0.5 mmol of 4-nitrostyrene were added to a stainless steel reactor, the stainless steel reactor was sealed, the air in the reactor was replaced with H2, the air was replaced with hydrogen 5 times, 10 bar of reducing gas (H2) was filled and sealed, stirring was started, the magnetic stirring rate was adjusted to 700 rpm, and then the reaction was carried out at 30° C. for 6 h to obtain a selective hydrogenation product. When the NiMo@C-450 catalyst was used for the first time, the conversion rate of 4-nitrostyrene was>99.0%, which was significantly higher than the conversion rate (75.6%) of the catalyst after 2 h of reaction, and the selectivity for 4-aminostyrene was 97.4%.

[0148] After the reaction is completed, the catalyst NiMo@C-450 after the reaction is collected by centrifugation, washed with cyclohexane 3-5 times and then directly used for the next catalysis; this method is used to recover the catalyst after each repetition, and after the recovery is completed, it is weighed, and the recovery rate each time is >95%. Repeat the above steps (since the catalyst recovered after each use has a loss of less than 5%, the newly prepared catalyst NiMo@C-450 is added to make up to 20 mg for the next use), and the conversion rate and yield of each use are shown in Table 7. The yield of 4-aminostyrene is determined by offline analysis by gas chromatography. The test results show that the catalyst NiMo@C-450 has been recycled for 6 times, and the catalytic activity has not decreased significantly, indicating that the catalyst is stable.

[0149] Table 7.4-Nitrostyrene Selective Catalytic Hydrogenation Cycle Experimental Results

[0150]

[0151] Reaction conditions: 4-nitrostyrene (0.5 mmol), NiMo@C-450 (20 mg), cyclohexane (10 mL), H2 (10 bar), 30°C, reaction time 6 h.

Claims

1. A carbon-supported nickel-molybdenum alloy catalyst, characterized in that: The carbon-supported nickel-molybdenum alloy catalyst uses Ni4Mo alloy as active sites and conductive carbon black as a carrier. The mass percentage content of Ni element in the carbon-supported nickel-molybdenum alloy catalyst is 6.7% to 7.5%, and the mass percentage content of Mo element is 2.7% to 3.0%.

2. The method for preparing the carbon-supported nickel-molybdenum alloy catalyst according to claim 1, characterized in that: The following steps are involved: (1) Nickel nitrate hexahydrate and ammonium molybdate tetrahydrate are dissolved in a mixed solvent of ethylene glycol and deionized water, and magnetic stirring is continued. After complete dissolution, conductive carbon black and concentrated ammonia water are added in sequence, and stirred to obtain a mixed solution. The mixed solution is subjected to hydrothermal treatment, and the precipitate is collected by centrifugation. The precipitate is washed with water and ethanol several times, and finally dried to obtain carbon-supported Ni(OH)2 / MoO4 2- Precursor; (2) placing the precursor obtained in step (1) in a tubular furnace, heating it to a target temperature of 350-550° C. in a hydrogen atmosphere, pyrolyzing it for 2-3 h, and cooling it to room temperature to obtain a black powder, which is a carbon-supported nickel-molybdenum alloy catalyst.

3. The preparation method according to claim 2, characterized in that: In step (1), the concentration of the concentrated ammonia water is 25-28wt.%, the usage ratio of the nickel nitrate hexahydrate, ammonium molybdate tetrahydrate, mixed solvent, conductive carbon black and concentrated ammonia water is 1mmol:0.14mmol:50mL:450mg:2mL; the volume ratio of ethylene glycol and deionized water in the mixed solvent is 9:1; preferably, the conductive carbon black is Vulcan XC72R conductive carbon black.

4. The preparation method according to claim 2, characterized in that: In step (1), the conditions for the hydrothermal treatment of the mixed solution are: the mixed solution is hydrothermally treated at 150° C. for 4 h; and / or In step (1), the drying conditions are: drying at 65-85°C for 6-24h, preferably drying at 70°C for 12h.

5. The preparation method according to claim 2, characterized in that: In step (2), the target temperature is 400-500°C; the target temperature is preferably 440-460°C, more preferably 445-455°C, and most preferably 450°C; and / or In step (2), the temperature is raised to the target temperature at a heating rate of 1-3°C / min.

6. Use of the carbon-supported nickel-molybdenum alloy catalyst according to claim 1 or the carbon-supported nickel-molybdenum alloy catalyst prepared by any of the methods of claims 2 to 5 in the selective reduction of nitro compounds to synthesize amine compounds, characterized in that: The steps include: The carbon-supported nickel-molybdenum alloy catalyst according to claim 1 or the carbon-supported nickel-molybdenum alloy catalyst prepared by any of the methods of claims 2 to 5, an organic solvent and a nitro compound are added to a stainless steel high-pressure reactor, the air in the reactor is replaced with H2 after sealing, the high-pressure reactor is pressurized and sealed with 5-20 bar H2, and then reacted at 20-50° C. with constant stirring to obtain an amine compound in which only the nitro group is reduced and reduced to an amino group, with a yield of more than 94%; The organic solvent is one or more of toluene, n-hexane and cyclohexane.

7. The use according to claim 6, characterized in that: The ratio of the carbon-supported nickel-molybdenum alloy catalyst, the organic solvent, and the nitro compound is: (20-40) mg: 10 mL: 0.5 mmol.

8. The use according to claim 6, characterized in that: The autoclave is pressurized and sealed with 5-10 bar H2, and then the reaction is carried out at 20-50°C with constant stirring, preferably for more than 2 hours, more preferably for more than 4 hours, and more preferably for more than 6 hours.

9. The use according to any one of claims 6 to 8, characterized in that: The nitro compound is selected from the following functionalized nitro aromatic compounds: After H2 pressure sealing, the reaction was carried out at 20-30°C with constant stirring to obtain an amine compound in which only the nitro group was reduced to an amino group.

10. The use according to any one of claims 6 to 8, characterized in that: The nitro compound is selected from the following non-aromatic nitro compounds:

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