Catalyst for hydrogenation to prepare aromatic amines, preparation method thereof, and hydrogenation preparation method

Abstract

The present invention relates to a catalyst for hydrogenation to prepare aromatic amines, a preparation method thereof, and a hydrogenation preparation method, specifically relating to the technical field of catalysts. The catalyst includes: nitrogen-doped carbon, and metallic cobalt and titanium dioxide grown on the nitrogen-doped carbon; the metallic cobalt in the catalyst is 5-20% by mass percentage; the titanium dioxide in the catalyst is 5-10% by mass percentage. The catalyst involved in the present invention realizes the high-activity and high-selectivity hydrogenation conversion of nitroaromatic compounds into aromatic amines under the condition of room temperature by virtue of the synergistic cooperation effect of nitrogen-doped carbon, metallic cobalt and TiO2, and at the same time, rapid separation operation can be carried out by means of the magnetism of the catalyst, significantly reducing the production cost.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and particularly relates to a catalyst for hydrogenation to prepare aromatic amines, a preparation method thereof, and a hydrogenation preparation method, and more particularly relates to a catalyst for hydrogenating nitroaromatic compounds to prepare aromatic amines, a preparation method thereof, and a hydrogenation preparation method. Background Art

[0002] Currently, aromatic amine compounds are important raw materials for many fine chemical products and are widely used in many fields such as pharmaceuticals, dyes, pesticides, and polymer materials. The hydrogenation reduction of nitroarenes is a very promising method for producing aromatic amines. Noble metal catalysts have been used in the reaction of preparing aromatic amines from nitroarenes and all have high activity and stability (such as gold, platinum, palladium, ruthenium, etc.), but noble metals also have defects such as high cost and unsatisfactory selectivity, which limit their application in industrial production. Therefore, it is a very meaningful work to develop non-noble metal-based catalysts with low cost, strong selectivity, high activity, and strong stability.

[0003] CN117899873A discloses a transition metal catalyst with a core-shell structure, a preparation method thereof, and a catalytic application. The catalyst uses transition metal nanoparticles (such as iron, cobalt, nickel, copper, preferably nickel) as the core, and the outer layer is coated with a composite shell layer composed of a carbon shell and a transition metal oxide layer. The metal particles are separated by a carbon layer or an oxide layer to form a core-shell-multilevel interface structure. The XPS spectrum of the nickel-based catalyst shows the coexistence of zero-valent nickel (Ni 2p 3 / 2 binding energy 851.4 eV) and positive-valent nickel (853.8 eV), indicating the synergistic effect between the metal and the oxide. The preparation method realizes carbon coating and surface oxide layer regulation by dissolving transition metal precursors and organic carbon sources (such as citric acid, glucose), evaporating the solvent, calcining in an inert atmosphere (400 - 1200 °C), and oxidation treatment (20 - 300 °C). The process is simple and scalable. The catalyst shows excellent performance in the hydrogenation reaction of sulfur- or halogen-containing nitroarenes (such as 4-nitroanisole sulfide, o-chloronitrobenzene): under the conditions of hydrogen pressure of 0.4 - 6 MPa and temperature of 50 - 300 °C, the nitro conversion rate > 99%, the amino selectivity > 99%, and there is no inactivation after recycling 4 times. Its anti-poisoning mechanism is due to the carbon shell blocking the direct contact between sulfur / halogen species and the metal active sites, and at the same time the surface oxide layer maintains the catalytic activity through hydrogen spillover, solving the problems of easy poisoning of traditional catalysts in sulfur-containing systems and halogen competitive desorption. However, the reaction conditions are about 100 °C and the hydrogen pressure is 3 MPa, the reaction conditions are harsh, and the reaction time is long.

[0004] In summary, the existing catalyst systems for hydrogenating nitroaromatic compounds to prepare aromatic amines have disadvantages such as relatively harsh reaction conditions, insufficient catalyst activity, and cumbersome preparation processes. Summary of the Invention

[0005] In view of the problems existing in the prior art, the purpose of the present invention is to provide a catalyst for hydrogenation to prepare aromatic amines, a preparation method thereof, and a hydrogenation preparation method, so as to solve the defects of poor hydrogenation conversion effect and low selectivity caused by poor temperature activity of the hydrogenation catalyst for hydrogenating nitroaromatic compounds to prepare aromatic amines.

[0006] To achieve this purpose, the present invention adopts the following technical solutions:

[0007] In the first aspect, the present invention provides a catalyst for hydrogenation to prepare aromatic amines, and the catalyst includes:

[0008] Nitrogen-doped carbon, and metallic cobalt and titanium dioxide grown on the nitrogen-doped carbon;

[0009] The metallic cobalt in the catalyst is 5-20% by mass percentage;

[0010] The titanium dioxide in the catalyst is 5-10% by mass percentage.

[0011] The catalyst involved in the present invention realizes the high-activity and high-selectivity hydrogenation conversion of nitroaromatic compounds into aromatic amines under the condition of room temperature by means of the synergistic cooperation effect of nitrogen-doped carbon, metallic cobalt and TiO2. At the same time, the catalyst can be rapidly separated by virtue of its magnetism, significantly reducing the production cost.

[0012] In the second aspect, the present invention provides a preparation method of the catalyst as described in the first aspect, and the preparation method includes:

[0013] Mix and impregnate a titanium dioxide-modified carbon nitride suspension and a metallic cobalt precursor, and then obtain an impregnated material through solid-liquid separation;

[0014] Pyrolyze the impregnated material to obtain a catalyst for hydrogenating nitroaromatics to prepare aromatic amines.

[0015] As a preferred technical solution of the present invention, the preparation process of the titanium dioxide-modified carbon nitride suspension is as follows:

[0016] Functionalize and then modify with titanium a carbon nitride dispersion liquid in sequence to obtain a titanium dioxide-modified carbon nitride suspension;

[0017] The carbon nitride dispersion liquid is obtained by dispersing carbon nitride with an alcohol; the functionalization includes: performing a first mixing of the carbon nitride dispersion liquid and a functionalizing agent; the titanium modification includes: adding a titanate and water to the material obtained by the functionalization for a second mixing;

[0018] The metallic cobalt precursor is obtained by complexing a cobalt salt, polyacrylonitrile and a solvent.

[0019] As a preferred technical solution of the present invention, the dispersion method includes: ultrasonic; the dispersion time ≥ 10 min;

[0020] The functionalizing agent includes: one or a combination of at least two of polyethylene glycol, benzyl alcohol, ethylenediamine, or ethylene glycol;

[0021] The stirring speed of the first mixing is 400 - 600 r / min, and the time is 0.5 - 5 h;

[0022] The stirring speed of the second mixing is 400 - 600 r / min, and the time is 0.5 - 5 h;

[0023] In the preparation process of the titanium dioxide modified carbon nitride suspension, the molar ratio of the titanate, functionalizing agent, alcohol, and water used is 1:(1 - 10):(50 - 200):(1 - 10); the solid-liquid ratio g / mL of the titanium dioxide modified carbon nitride suspension is 1:(10 - 40);

[0024] The mass ratio of the cobalt salt to the polyacrylonitrile is 1:(1 - 5); the solid-liquid ratio g / mL of the cobalt salt to the solvent is 1:(150 - 180); the temperature of the complexation is 100 - 120 °C, and the time ≥ 1 h.

[0025] As a preferred technical solution of the present invention, the mixing and impregnation includes: stirring at a stirring rate of 400 - 600 r / min for 1 - 5 h;

[0026] In the mixing and impregnation, the mass ratio of the metal cobalt precursor to the carbon nitride in the titanium dioxide modified carbon nitride suspension is 1:(1 - 5).

[0027] As a preferred technical solution of the present invention, the pyrolysis includes: pyrolyzing at a temperature of 600 - 900 °C for 0.5 - 5 h in an inert atmosphere.

[0028] In the third aspect, the present invention provides a method for preparing aromatic amines by hydrogenation, and the hydrogenation preparation method includes:

[0029] Using the catalyst described in the first aspect to carry out catalytic hydrogenation to prepare aromatic amines.

[0030] As a preferred technical solution of the present invention, the hydrogenation preparation method includes:

[0031] Catalytically hydrogenating the nitroaromatic compound in a hydrogen atmosphere using the catalyst described in the first aspect to obtain aromatic amines.

[0032] As a preferred technical solution of the present invention, the catalytic hydrogenation is carried out in a solvent medium; the solvent medium includes any one or a combination of at least two of water, tetrahydrofuran, methanol, isopropanol, ethanol, cyclohexane, cyclohexylamine, n-butanol, toluene, N-methylpyrrolidone or tert-butanol.

[0033] The mass of the solvent medium is 50-200% of the mass of the nitroaromatic compound; the mass of the catalyst is 1-30% of the mass of the nitroaromatic compound.

[0034] As a preferred technical solution of the present invention, the initial hydrogen pressure in the catalytic hydrogenation is ≥0.5 MPa;

[0035] The temperature of the catalytic hydrogenation is ≥20 °C;

[0036] The time of the catalytic hydrogenation is ≥0.5 h.

[0037] Compared with the prior art solutions, the present invention has the following beneficial effects:

[0038] (1) The nitrogen-doped carbon in the catalyst provided by the present invention has a high specific surface area, which is beneficial to the loading and dispersion of metallic cobalt; and the nitrogen-doped carbon contains abundant nitrogen basic sites, which is beneficial to the progress of the nitro hydrogenation reaction.

[0039] (2) The catalyst provided by the present invention uses TiO2 and uses non-noble metal cobalt salts and polyacrylonitrile as precursors, which greatly reduces the cost compared with noble metals. At the same time, high conversion of nitroaromatic compounds hydrogenation and high selectivity for aromatic amines are achieved. The conversion of nitroaromatic compounds can reach 100% at a lower temperature, pressure or shorter time, and the selectivity of aromatic amines > 99%.

[0040] (3) The catalyst provided by the present invention can be rapidly recovered by the magnetism carried by the catalyst itself in the reaction for preparing aromatic amines by hydrogenating nitroaromatic compounds, greatly simplifying the subsequent separation operation, reducing the production cost, and reducing the discharge of waste liquid and waste residue; under mild conditions, high-activity and high-selectivity hydrogenation conversion of nitroaromatic compounds into aromatic amines is achieved. Description of the Drawings

[0041] Figure 1 is the scanning electron microscope image of the catalyst obtained in Example 1 of the present invention at 20 k;

[0042] Figure 2 is the scanning electron microscope image of the catalyst obtained in Example 1 of the present invention at 40 k;

[0043] Figure 3 is the transmission electron microscope particle size distribution diagram of the catalyst obtained in Example 1 of the present invention;

[0044] Figure 4It is the transmission electron microscope lattice fringe image of the catalyst obtained in Example 1 of the present invention;

[0045] Figure 5 It is the gas chromatogram of the aromatic amine product obtained in Application Example 1 of the present invention.

[0046] The present invention will be further described in detail below. However, the following examples are merely simple examples of the present invention and do not represent or limit the scope of the claimed protection of the present invention. The scope of protection of the present invention shall be subject to the claims. Detailed implementation manners

[0047] To better illustrate the present invention and facilitate understanding of the technical solution of the present invention, typical but non-limiting embodiments of the present invention are as follows:

[0048] This embodiment provides a catalyst for the hydrogenation of nitroaromatics to prepare aromatic amines, and the catalyst includes:

[0049] Nitrogen-doped carbon, and metallic cobalt and titanium dioxide grown on the nitrogen-doped carbon;

[0050] Among them, the metallic cobalt in the catalyst is 5-20% by mass percentage, for example, it can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20% etc., but not limited to the listed values, and other unlisted values within this range also meet the requirements.

[0051] The titanium dioxide in the catalyst is 5-10% by mass percentage, for example, it can be 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5% or 10% etc., but not limited to the listed values, and other unlisted values within this range also meet the requirements.

[0052] Furthermore, this embodiment provides a preparation method of the aforementioned catalyst for the hydrogenation of nitroaromatics to prepare aromatic amines, and the preparation method includes:

[0053] Mix and impregnate the titanium dioxide-modified carbon nitride suspension and the metallic cobalt precursor, and then perform solid-liquid separation to obtain the impregnated material;

[0054] Pyrolyze the impregnated material to obtain a catalyst for the hydrogenation of nitroaromatics to prepare aromatic amines.

[0055] In this solution, the preparation process of the titanium dioxide-modified carbon nitride suspension is as follows:

[0056] Functionalize and modify the carbon nitride dispersion with titanium in sequence to obtain the titanium dioxide-modified carbon nitride suspension.

[0057] In this solution, the carbon nitride dispersion liquid is obtained by dispersing carbon nitride in alcohol.

[0058] In this solution, the carbon nitride used can be selected as a commercially available carbon nitride product, or prepared by calcining any one or at least two combinations of cyanamide, dicyandiamide, melamine, thiourea, urea or guanidine hydrochloride in an inert atmosphere at a temperature of 600-900 °C for 0.5-5 h.

[0059] In the preparation process of carbon nitride in this solution, exemplary combinations of reagents are as follows: the combination of cyanamide and dicyandiamide, the combination of dicyandiamide and melamine, the combination of thiourea and urea, etc., but are not limited to the listed combinations, and other unlisted combinations within this range also meet the requirements.

[0060] In this solution, the alcohols used include common alcohol solvents in the art such as methanol, ethanol or glycerol.

[0061] In this solution, the dispersion method includes: ultrasonic treatment.

[0062] In this solution, the dispersion time is ≥10 min, for example, it can be 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min or 120 min, etc., but is not limited to the listed values, and other unlisted values within this range also meet the requirements.

[0063] In this solution, the functionalization includes: first mixing the carbon nitride dispersion liquid and the functionalizing agent.

[0064] In this solution, the functionalizing agent includes: one or at least two combinations of polyethylene glycol (with a molecular weight of 200-8000), benzyl alcohol, ethylenediamine or ethylene glycol.

[0065] Exemplarily, the combinations of the functionalizing agent include: the combination of polyethylene glycol and benzyl alcohol, the combination of benzyl alcohol and ethylenediamine, the combination of ethylenediamine and ethylene glycol, etc.

[0066] In this solution, the stirring speed of the first mixing is 400-600 r / min, for example, it can be 400 r / min, 420 r / min, 440 r / min, 460 r / min, 480 r / min, 500 r / min, 520 r / min, 540 r / min, 560 r / min, 580 r / min or 600 r / min, etc., but is not limited to the listed values, and other unlisted values within this range also meet the requirements.

[0067] In this solution, the time of the first mixing is 0.5 - 5 h. For example, it can be 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, or 5 h, etc., but not limited to the listed values. Other unlisted values within this range also meet the requirements.

[0068] In this solution, the titanium modification includes: adding a titanate and water to the material obtained by functionalization and performing a second mixing.

[0069] In this solution, the titanate includes: one or a combination of at least two of tetrabutyl titanate, isopropyl titanate, or ethyl titanate.

[0070] Exemplarily, the combinations of titanates include: the combination of tetrabutyl titanate and isopropyl titanate, the combination of isopropyl titanate and ethyl titanate, the combination of tetrabutyl titanate and ethyl titanate, etc., but not limited to the listed combinations. Other unlisted combinations within this range also meet the requirements.

[0071] In this solution, the stirring speed of the second mixing is 400 - 600 r / min. For example, it can be 400 r / min, 420 r / min, 440 r / min, 460 r / min, 480 r / min, 500 r / min, 520 r / min, 540 r / min, 560 r / min, 580 r / min, or 600 r / min, etc., but not limited to the listed values. Other unlisted values within this range also meet the requirements.

[0072] In this solution, the time of the second mixing is 0.5 - 5 h. For example, it can be 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, or 5 h, etc., but not limited to the listed values. Other unlisted values within this range also meet the requirements.

[0073] In this solution, the molar ratio of the titanate, functionalizing agent, alcohol, and water used in the preparation process of the titanium dioxide modified carbon nitride suspension is 1:(1 - 10):(50 - 200):(1 - 10). For example, it can be 1:1:50:1, 1:2:100:2, 1:4:150:5, 1:10:200:10, 1:5:100:5, 1:2:100:10, 1:8:150:5, 1:10:50:1, 1:1:200:1, 1:1:50:10, or 1:10:200:1, etc., but not limited to the listed values. Other unlisted values within this range also meet the requirements.

[0074] In this solution, the solid-liquid ratio of the titanium dioxide modified carbon nitride suspension is 1:(10 - 40) g / mL. For example, it can be 1:10, 1:15, 1:20, 1:25, 1:30, 1:35 or 1:40, etc., but it is not limited to the listed values, and other unlisted values within this range also meet the requirements.

[0075] In this solution, after the titanium modification is completed, a solvent system identical to that of the metal cobalt precursor can be optionally added to form the titanium dioxide modified carbon nitride suspension.

[0076] In this solution, the metal cobalt precursor is obtained by complexing cobalt salt, polyacrylonitrile and a solvent.

[0077] In this solution, the cobalt salt includes: cobalt nitrate and / or cobalt acetate.

[0078] In this solution, the solvent includes: N,N-dimethylformamide.

[0079] In this solution, the mass ratio of the cobalt salt to polyacrylonitrile is 1:(1 - 5). For example, it can be 1:1, 1:2, 1:3, 1:4 or 1:5, etc., but it is not limited to the listed values, and other unlisted values within this range also meet the requirements.

[0080] In this solution, the number average molecular weight of polyacrylonitrile is 120000 - 170000.

[0081] In this solution, the solid-liquid ratio of the cobalt salt to the solvent is 1:(150 - 180) g / mL. For example, it can be 1:150, 1:155, 1:160, 1:165, 1:170, 1:175 or 1:180, etc., but it is not limited to the listed values, and other unlisted values within this range also meet the requirements.

[0082] In this solution, the temperature of the complexation is 100 - 120 °C. For example, it can be 100 °C, 105 °C, 110 °C, 115 °C or 120 °C, etc., but it is not limited to the listed values, and other unlisted values within this range also meet the requirements.

[0083] In this solution, the time of the complexation is ≥1 h. For example, it can be 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h or 5 h, etc., but it is not limited to the listed values, and other unlisted values within this range also meet the requirements.

[0084] In this solution, stirring is supplemented during the mixed impregnation at a stirring rate of 400 - 600 r / min. For example, it can be 400 r / min, 420 r / min, 440 r / min, 460 r / min, 480 r / min, 500 r / min, 520 r / min, 540 r / min, 560 r / min, 580 r / min, or 600 r / min, etc. However, it is not limited to the listed values, and other unlisted values within this range also meet the requirements.

[0085] In this solution, the time of the mixed impregnation is 1 - 5 h. For example, it can be 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, or 5 h, etc. However, it is not limited to the listed values, and other unlisted values within this range also meet the requirements.

[0086] In this solution, the mass ratio of the metal cobalt precursor to carbon nitride in the titanium dioxide - modified carbon nitride suspension during the mixed impregnation is 1:(1 - 5). For example, it can be 1:1, 1:2, 1:3, 1:4, or 1:5, etc. However, it is not limited to the listed values, and other unlisted values within this range also meet the requirements.

[0087] In this solution, the pyrolysis is carried out under an inert atmosphere.

[0088] In this solution, the inert atmosphere refers to a gas that does not react with the reactants, such as nitrogen, helium, neon, or argon, etc.

[0089] In this solution, the temperature of the pyrolysis is 600 - 900 °C. For example, it can be 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, 850 °C, or 900 °C, etc. However, it is not limited to the listed values, and other unlisted values within this range also meet the requirements.

[0090] In this solution, the time of the pyrolysis is 0.5 - 5 h. For example, it can be 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, or 5 h, etc. However, it is not limited to the listed values, and other unlisted values within this range also meet the requirements.

[0091] Furthermore, this embodiment provides a method for preparing aromatic amines by hydrogenation, and the hydrogenation preparation method includes:

[0092] Catalytic hydrogenation of the nitro - aromatic compound is carried out using the aforementioned catalyst under a hydrogen atmosphere to obtain the aromatic amine.

[0093] In this solution, the nitro - aromatic compound includes at least one of the compounds shown in formula (Ⅰ):

[0094] Formula (Ⅰ)

[0095] Among them, R is selected from one of H, F, Cl, Br, saturated hydrocarbon groups or unsaturated hydrocarbon groups having 1 to 4 carbon atoms.

[0096] Exemplarily, the saturated hydrocarbon groups having 1 to 4 carbon atoms include: methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, etc.

[0097] Exemplarily, the unsaturated hydrocarbon groups having 1 to 4 carbon atoms include: vinyl, propenyl, allyl, isopropenyl, etc.

[0098] In this solution, the catalytic hydrogenation is carried out in a solvent medium.

[0099] In this solution, the solvent medium includes: any one or a combination of at least two of water, tetrahydrofuran, methanol, isopropanol, ethanol, cyclohexane, cyclohexylamine, n-butanol, toluene, N-methylpyrrolidone or tert-butanol. Preferably, it is an alcohol and water with a volume ratio of (3 - 5):1, and the alcohol includes one or a combination of at least two of methanol, isopropanol, ethanol or n-butanol.

[0100] Exemplarily, the combinations of the solvent medium include: the combination of tetrahydrofuran and methanol, the combination of isopropanol and ethanol, the combination of cyclohexane and cyclohexylamine, etc., but are not limited to the listed combinations, and other unlisted combinations within this range also meet the requirements.

[0101] In this solution, the mass of the solvent medium is 50 - 200% of the mass of the nitroaromatic compound. For example, it can be 50%, 60%, 70%, 80%, 90%, 100%, 110%, 120%, 130%, 140%, 150%, 160%, 170%, 180%, 190% or 200%, etc., but is not limited to the listed values, and other unlisted values within this range also meet the requirements.

[0102] In this solution, the mass of the catalyst is 1 - 30% of the mass of the nitroaromatic compound. For example, it can be 1%, 1%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28% or 30%, etc., but is not limited to the listed values, and other unlisted values within this range also meet the requirements.

[0103] In this solution, the initial hydrogen pressure in the catalytic hydrogenation is ≥0.5 MPa. For example, it can be 0.5 MPa, 1 MPa, 2 MPa, 3 MPa, 4 MPa, 5 MPa, 6 MPa, 7 MPa, 8 MPa, 9 MPa or 10 MPa, etc., but is not limited to the listed values, and other unlisted values within this range also meet the requirements.

[0104] In this solution, the temperature of the catalytic hydrogenation is ≥20°C. For example, it can be 20°C, 25°C, 30°C, 50°C, 100°C, or 100°C, etc., but it is not limited to the listed values. Other unlisted values within this range also meet the requirements.

[0105] In this solution, the time of the catalytic hydrogenation is ≥0.5 h. For example, 0.5 h, 1 h, 5 h, 10 h, 24 h, 30 h, 36 h, or 48 h, etc., but it is not limited to the listed values. Other unlisted values within this range also meet the requirements.

[0106] Furthermore, in order to illustrate the catalytic effect that can be achieved by the catalyst provided by the present invention for hydrogenation to prepare aromatic amines, the following practical examples are used for specific illustration as follows:

[0107] The conditions for gas chromatography analysis involved in the following application examples are as follows: chromatographic column model GsBP-1; initial column temperature 80°C, hold for 1 min, increase to 125°C at 10°C / min, hold for 2 min, then increase to 230°C at 20°C / min, hold at 230°C for 5 min; control mode is pressure control, pressure 50 kPa, purge flow rate 3 mL / min, split ratio 30; vaporization temperature 250°C.

[0108] Example 1

[0109] This example provides a catalyst for hydrogenating nitroaromatic compounds to prepare aromatic amines, and its preparation method is as follows:

[0110] (1) Place urea in a crucible, cover it with a lid, and calcine it in a muffle furnace at 550°C for 4 h. The obtained solid is rinsed three times with deionized water and ethanol respectively, and then dried in a blast drying oven at 100°C for 12 h to obtain carbon nitride;

[0111] (2) Ultrasonically disperse 1 g of carbon nitride in a solvent for 0.5 h, mix it with 0.27 g of benzyl alcohol for functionalization for 3 h, then add 0.17 g of tetrabutyl titanate and 0.045 g of water to introduce TiO2 for titanium modification for 3 h to obtain TiO2-modified carbon nitride. Stir, centrifuge, and then add DMF to obtain a modified carbon nitride suspension;

[0112] (3) Mix 250 mg of cobalt acetate tetrahydrate and 500 mg of polyacrylonitrile (number average molecular weight of 150,000) in a mass ratio of 1:2 in 40 mL of N,N-dimethylformamide, and then complex it in an oil bath at 100°C for 1 h to obtain a metal cobalt precursor;

[0113] (4) Mix the carbon nitride suspension obtained in step (2) with the metal cobalt precursor obtained in step (3), and stir and impregnate for 1 h;

[0114] (5) Filter the impregnated suspension, and dry the obtained solid at 80 °C for 8 h;

[0115] (6) Place the dried solid in a tubular furnace and pyrolyze it at 800 °C for 2 h under a nitrogen atmosphere to obtain the catalyst.

[0116] The scanning electron microscope photos of the obtained catalyst are as Figure 1 and Figure 2 shown, and the transmission electron microscope images are as Figure 3 and Figure 4 shown. It can be seen from the scanning electron microscope images that the nitrogen-doped carbon support of the catalyst is in the form of three-dimensional nanosheets (3D nanosheets), and has a variety of disordered interconnected pores of different sizes formed by the bending or stacking of abundant nanosheets, so that the structure of the catalyst is porous, which is conducive to the progress of the catalytic reaction. The transmission electron microscope image shows that the average particle size of the metal particles on the surface of the catalyst is 28.8 ± 0.5 nm. The lattice fringes with a spacing of 0.2 nm correspond to the Co(002) crystal plane. The fringes with a lattice spacing of 0.35 nm are attributed to the TiO2(101) crystal plane.

[0117] Example 2

[0118] This example provides a catalyst for the hydrogenation of nitroaromatic compounds to prepare aromatic amines, and its preparation method is as follows:

[0119] (1) Place urea and melamine in a crucible according to a mass ratio of 4:1, cover the lid, and calcine at 550 °C in a muffle furnace for 4 h. The obtained solid is rinsed three times with deionized water and ethanol respectively, and then dried at 100 °C in a forced-air drying oven for 12 h to obtain carbon nitride;

[0120] (2) Ultrasonically disperse 1 g of carbon nitride in a solvent for 0.5 h, mix it with 0.27 g of ethylenediamine for functionalization for 0.5 h, and then add 0.17 g of tetrabutyl titanate and 0.045 g of water to introduce TiO2 for titanium modification for 5 h to obtain TiO2-modified carbon nitride. Stir, centrifuge and then add DMF to obtain a modified carbon nitride suspension;

[0121] (3) Mix 125 mg of cobalt acetate tetrahydrate and 250 mg of polyacrylonitrile (number-average molecular weight of 150,000) in a mass ratio of 1:2 in 40 mL of N,N-dimethylformamide and complex at 100 °C in an oil bath for 1 h to obtain a metal cobalt precursor;

[0122] (4) Mix the carbon nitride suspension obtained in step (2) with the metal cobalt precursor obtained in step (3) and impregnate with stirring for 1 h;

[0123] (5) Filter the impregnated suspension, and dry the obtained solid at 80 °C for 8 h;

[0124] (6) Place the dried solid in a tubular furnace and carry out high-temperature pyrolysis at 600 °C under a nitrogen atmosphere for 5 h to obtain the catalyst.

[0125] Example 3

[0126] This example provides a catalyst for the hydrogenation of nitroaromatic compounds to prepare aromatic amines, and its preparation method is as follows:

[0127] (1) Place melamine in a crucible, cover the lid, and calcine it in a muffle furnace at 550 °C for 4 h. The obtained solid is rinsed three times with deionized water and ethanol respectively, and then placed in a forced-air drying oven at 100 °C for drying for 12 h to obtain carbon nitride.

[0128] (2) Ultrasonically disperse 1 g of carbon nitride in a solvent for 0.5 h, mix it with 0.27 g of ethylene glycol for functionalization for 1 h, then add 0.17 g of tetrabutyl titanate and 0.045 g of water to introduce TiO2 for titanium modification for 4 h to obtain TiO2-modified carbon nitride. Stir, centrifuge, and then add DMF to obtain a modified carbon nitride suspension.

[0129] (3) Mix 75 mg of cobalt acetate tetrahydrate and 125 mg of polyacrylonitrile (number-average molecular weight of 150,000) in a mass ratio of 1:2 in 40 mL of N,N-dimethylformamide, and then carry out complexation in an oil bath at 100 °C for 1 h to obtain a metal cobalt precursor.

[0130] (4) Mix the carbon nitride suspension obtained in step (2) with the metal cobalt precursor obtained in step (3), and impregnate it with stirring for 1 h.

[0131] (5) Filter the impregnated suspension, and dry the obtained solid at 80 °C for 8 h.

[0132] (6) Place the dried solid in a tubular furnace and carry out high-temperature pyrolysis at 900 °C under a nitrogen atmosphere for 0.5 h to obtain the catalyst.

[0133] Example 4

[0134] This example provides a catalyst for the hydrogenation of nitroaromatic compounds to prepare aromatic amines, and its preparation method is as follows:

[0135] (1) Place urea in a crucible, cover the lid, and calcine it in a muffle furnace at 550 °C for 4 h. The obtained solid is rinsed three times with deionized water and ethanol respectively, and then placed in a forced-air drying oven at 100 °C for drying for 12 h to obtain carbon nitride.

[0136] (2) Ultrasonically disperse 1 g of carbon nitride in a solvent for 0.5 h, mix it with 1.35 g of polyvinyl alcohol (molecular weight 4000) for functionalization for 4 h, then add 0.85 g of tetrabutyl titanate and 0.225 g of water to introduce TiO₂ for titanium modification for 2 h to obtain TiO₂-modified carbon nitride. Stir, centrifuge, and then add DMF to obtain a suspension of modified carbon nitride;

[0137] (3) Mix 250 mg of cobalt acetate tetrahydrate and 500 mg of polyacrylonitrile (number average molecular weight 150000) in a mass ratio of 1:2 in 40 mL of N,N-dimethylformamide, and then carry out complexation in an oil bath at 100 °C for 1 h to obtain a metal cobalt precursor;

[0138] (4) Mix the carbon nitride suspension obtained in step (2) with the metal cobalt precursor obtained in step (3), and impregnate for 1 h under stirring;

[0139] (5) Filter the impregnated suspension, and dry the obtained solid at 80 °C for 8 h;

[0140] (6) Place the dried solid in a tubular furnace, and carry out high-temperature pyrolysis at 800 °C in a nitrogen atmosphere for 2 h to obtain a catalyst.

[0141] Example 5

[0142] This example provides a catalyst for the hydrogenation of nitroaromatic compounds to prepare aromatic amines, and its preparation method is as follows:

[0143] (1) Place urea in a crucible, cover the lid, and calcine in a muffle furnace at 550 °C for 4 h. The obtained solid is rinsed three times with deionized water and ethanol respectively, and then dried in a forced-air drying oven at 100 °C for 12 h to obtain carbon nitride;

[0144] (2) Ultrasonically disperse 1 g of carbon nitride in a solvent for 0.5 h, mix it with 2.7 g of benzyl alcohol for functionalization for 5 h, then add 1.7 g of tetrabutyl titanate and 0.45 g of water to introduce TiO₂ for titanium modification for 0.5 h to obtain TiO₂-modified carbon nitride. Stir, centrifuge, and then add DMF to obtain a suspension of modified carbon nitride;

[0145] (3) Mix 250 mg of cobalt acetate tetrahydrate and 500 mg of polyacrylonitrile (number average molecular weight 150000) in a mass ratio of 1:2 in 40 ml of N,N-dimethylformamide, and then carry out complexation in an oil bath at 100 °C for 1 h to obtain a metal cobalt precursor;

[0146] (4) Mix the carbon nitride suspension obtained in step (2) with the metal cobalt precursor obtained in step (3), and impregnate for 1 h under stirring;

[0147] (5) Filter the impregnated suspension, and dry the obtained solid at 80 °C for 8 h;

[0148] (6) Place the dried solid in a tubular furnace and pyrolyze it at 800 °C for 2 h under a nitrogen atmosphere to obtain the catalyst.

[0149] Comparative Example 1

[0150] The difference from Example 1 is only that carbon nitride is not modified with titanium dioxide, that is, the obtained catalyst does not contain titanium dioxide, and cobalt with the same mass as titanium dioxide is loaded to ensure that the total amount of metal substances on the catalyst remains unchanged.

[0151] Comparative Example 2

[0152] The difference from Example 1 is only that carbon nitride is replaced with an equal amount of activated carbon.

[0153] Comparative Example 3

[0154] The difference from Example 1 is only that the carbon nitride suspension obtained in step (2) is directly subjected to steps (5) and (6), that is, the obtained catalyst does not contain cobalt, and titanium dioxide with the same mass as cobalt is loaded to ensure that the total amount of metal substances on the catalyst remains unchanged.

[0155] Application Example 1

[0156] This application example provides a method for preparing aromatic amines using nitroaromatic compounds as raw materials, as follows:

[0157] Add 0.123 g of nitrobenzene, 0.03 g of the catalyst prepared in Example 1, and 8 mL of ethanol plus 2 mL of water solvent into a stainless steel autoclave. Replace the autoclave with nitrogen and hydrogen three times, and finally fill it with 1 MPa of H2. After confirming good sealing, heat the reaction kettle to 30 °C and keep it warm for 2 h;

[0158] After the reaction is completed, cool the autoclave to 20 °C with cold water. After releasing the gas in the kettle, open the reaction kettle, centrifuge to separate the catalyst, and take the supernatant for gas chromatography analysis of the composition. The results are listed in Table 1. The gas chromatography analysis spectrum is as Figure 5 shown (from left to right in the figure are the ethanol peak and the aniline peak).

[0159] Application Example 2

[0160] The difference from Application Example 1 is only that the reaction temperature is controlled at 25 °C and the reaction holding time is 2.5 h. Take the supernatant for gas chromatography analysis of the composition. The results are listed in Table 1.

[0161] Application Example 3

[0162] The difference from Application Example 1 is only that the initial pressure of hydrogen is controlled at 3 MPa, the reaction temperature is 25 °C, and the reaction heat preservation time is 2 h. The supernatant is taken and analyzed for its composition by gas chromatography, and the results are listed in Table 1.

[0163] Application Example 4

[0164] The difference from Application Example 1 is only that the reaction temperature is controlled from 30 °C to 20 °C, the heat preservation time is 3 h, and other conditions are the same as those in Application Example 1. The supernatant is taken and analyzed for its composition by gas chromatography, and the results are listed in Table 1.

[0165] Application Example 5

[0166] The difference from Application Example 1 is only that nitrobenzene is replaced by p-nitrotoluene, and the heat preservation time for catalytic hydrogenation is 2.5 h. The supernatant is taken and analyzed for its composition by gas chromatography, and the results are listed in Table 1.

[0167] Application Example 6

[0168] The difference from Application Example 1 is only that nitrobenzene is replaced by p-chloronitrobenzene, and the solvent medium in catalytic hydrogenation is methanol. The supernatant is taken and analyzed for its composition by gas chromatography, and the results are listed in Table 1.

[0169] Application Example 7

[0170] The difference from Application Example 1 is only that nitrobenzene is replaced by m-chloronitrobenzene, and the solvent medium in catalytic hydrogenation is methanol. The supernatant is taken and analyzed for its composition by gas chromatography, and the results are listed in Table 1.

[0171] Application Example 8

[0172] The difference from Application Example 1 is only that nitrobenzene is replaced by o-chloronitrobenzene, and the solvent medium in catalytic hydrogenation is methanol. The supernatant is taken and analyzed for its composition by gas chromatography, and the results are listed in Table 1.

[0173] Application Example 9

[0174] The difference from Application Example 1 is only that 8 mL of ethanol and 2 mL of water are replaced by 10 mL of pure water, and the heat preservation time for catalytic hydrogenation is controlled at 2.5 h. The supernatant is taken and analyzed for its composition by gas chromatography, and the results are listed in Table 1.

[0175] Application Example 10

[0176] The difference from Application Example 1 is only that 8 mL of ethanol and 2 mL of water are replaced by 10 mL of ethanol, and the heat preservation time for catalytic hydrogenation is controlled at 2.5 h. The supernatant is taken and analyzed for its composition by gas chromatography, and the results are listed in Table 1.

[0177] Application Example 11

[0178] The difference from Application Example 1 is only that the catalyst is replaced with the catalyst prepared in Example 2, and the catalytic hydrogenation temperature is 40°C. The supernatant was taken and analyzed for its composition by gas chromatography, and the results are listed in Table 1.

[0179] Application Example 12

[0180] The difference from Application Example 1 is only that the catalyst is replaced with the catalyst prepared in Example 3, and the catalytic hydrogenation temperature is 50°C. The supernatant was taken and analyzed for its composition by gas chromatography, and the results are listed in Table 1.

[0181] Application Example 13

[0182] The difference from Application Example 1 is only that the catalyst is replaced with the catalyst prepared in Example 4, and the catalytic hydrogenation temperature is 50°C. The supernatant was taken and analyzed for its composition by gas chromatography, and the results are listed in Table 1.

[0183] Application Example 14

[0184] The difference from Application Example 1 is only that the catalyst is replaced with the catalyst prepared in Example 5, and the catalytic hydrogenation temperature is 60°C. The supernatant was taken and analyzed for its composition by gas chromatography, and the results are listed in Table 1.

[0185] Comparative Application Example 1

[0186] The difference from Application Example 1 is only that the catalyst is replaced with the catalyst prepared in Comparative Example 1. The supernatant was taken and analyzed for its composition by gas chromatography, and the results are listed in Table 1.

[0187] Comparative Application Example 2

[0188] The difference from Application Example 1 is only that the catalyst is replaced with the catalyst prepared in Comparative Example 2. The supernatant was taken and analyzed for its composition by gas chromatography, and the results are listed in Table 1.

[0189] Comparative Application Example 3

[0190] The difference from Application Example 1 is only that the catalyst is replaced with the catalyst prepared in Comparative Example 3. The supernatant was taken and analyzed for its composition by gas chromatography, and the results are listed in Table 1.

[0191] Table 1

[0192]

[0193] It can be seen from the data in Table 1 that for the catalyst prepared by the method of the present invention, cobalt salt and polyacrylonitrile are used as raw materials, and after adding TiO2, it is used to catalyze the hydrogenation of nitroaromatic compounds to synthesize aromatic amines. The conversion rate of nitroaromatic compounds is 100%, and the selectivity of aniline is greater than 99%. Moreover, when the reaction temperature is increased and decreased, and the reaction time is correspondingly shortened and increased, the catalyst can still achieve the best catalytic effect. This catalyst realizes the preparation of aniline by catalytic hydrogenation of nitrobenzene with a non-noble metal catalyst at room temperature.

[0194] The catalyst prepared by the present invention comprises a porous nitrogen-doped carbon material and cobalt supported thereon. The nitrogen basic sites contained in the porous nitrogen-doped carbon material itself make the catalyst more conducive to nitro hydrogenation. The large number of nitrogen sites is also very conducive to the active dispersion of cobalt sites, greatly enhancing the catalytic performance of the catalyst. The introduced TiO2 further increases the reactive sites in the catalyst, enabling nitroaromatic compounds to react under relatively mild temperature and pressure, achieving high conversion of nitroaromatic compounds hydrogenation and high selectivity for aromatic amines.

[0195] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0196] In addition, it should be noted that, in the case of no conflict, the various specific technical features described in the above specific embodiments can be combined in any appropriate manner. To avoid unnecessary repetition, the present invention will not separately describe various possible combination manners.

[0197] Furthermore, any combination can be made between various different embodiments of the present invention, as long as it does not violate the idea of the present invention, and it should also be regarded as the content disclosed by the present invention.

Claims

1. A catalyst for preparing aromatic amines by hydrogenation, characterized in that: The catalyst comprises: Nitrogen-doped carbon, and metallic cobalt and titanium dioxide grown on the nitrogen-doped carbon; The metal cobalt content in the catalyst is 5-20% by mass; The mass percentage of titanium dioxide in the catalyst is 5-10%; The preparation process is as follows: The titanium dioxide modified carbon nitride suspension and the metal cobalt precursor are mixed and impregnated, and then the impregnated material is obtained by solid-liquid separation; The impregnated material is pyrolyzed to obtain a catalyst for hydrogenating nitroaromatic hydrocarbons to prepare aromatic amines; Wherein, the preparation process of the titanium dioxide modified carbon nitride suspension is as follows: The carbon nitride dispersion is sequentially functionalized and titanium modified to obtain a titanium dioxide modified carbon nitride suspension; The carbon nitride dispersion is obtained by dispersing carbon nitride with alcohol; the functionalization comprises: first mixing the carbon nitride dispersion and the functionalizing agent; the titanium modification comprises: adding titanate and water to the functionalized material for second mixing; the functionalizing agent comprises: one or a combination of at least two of polyethylene glycol, benzyl alcohol, ethylenediamine or ethylene glycol; The metal cobalt precursor is obtained by complexing cobalt salt, polyacrylonitrile and a solvent.

2. A method for preparing the catalyst according to claim 1, characterized in that: The preparation method comprises: The titanium dioxide modified carbon nitride suspension and the metal cobalt precursor are mixed and impregnated, and then the impregnated material is obtained by solid-liquid separation; The impregnated material is pyrolyzed to obtain a catalyst for hydrogenating nitroaromatic hydrocarbons to prepare aromatic amines; Wherein, the preparation process of the titanium dioxide modified carbon nitride suspension is as follows: The carbon nitride dispersion is sequentially functionalized and titanium modified to obtain a titanium dioxide modified carbon nitride suspension; The carbon nitride dispersion is obtained by dispersing carbon nitride with alcohol; the functionalization comprises: first mixing the carbon nitride dispersion and the functionalizing agent; the titanium modification comprises: adding titanate and water to the functionalized material for second mixing; The metal cobalt precursor is obtained by complexing cobalt salt, polyacrylonitrile and a solvent.

3. The preparation method according to claim 2, characterized in that: The dispersion method includes: ultrasound; the dispersion time is ≥ 10 min; The stirring speed of the first mixing is 400-600 r / min, and the time is 0.5-5 h; The stirring speed of the second mixing is 400-600r / min, and the time is 0.5-5h; The molar ratio of titanate, functionalizing agent, alcohol and water used in the preparation process of the titanium dioxide modified carbon nitride suspension is 1:(1-10):(50-200):(1-10); the solid-liquid ratio g / mL of the titanium dioxide modified carbon nitride suspension is 1:(10-40); The mass ratio of the cobalt salt to polyacrylonitrile is 1:(1-5); the solid-liquid ratio of the cobalt salt to the solvent is 1:(150-180) g / mL; the complexing temperature is 100-120° C., and the time is ≥1h.

4. The preparation method according to claim 2, characterized in that: The mixed impregnation comprises: stirring at a stirring rate of 400-600 r / min for 1-5 hours; The mass ratio of the metal cobalt precursor to the carbon nitride in the titanium dioxide modified carbon nitride suspension in the mixed impregnation is 1:(1-5).

5. The preparation method according to claim 2, characterized in that: The pyrolysis comprises: pyrolysis at a temperature of 600-900° C. for 0.5-5 h under an inert atmosphere.

6. A method for preparing aromatic amines by hydrogenation, characterized in that: The hydrogenation preparation method comprises: Aromatic amines are prepared by catalytic hydrogenation using the catalyst as claimed in claim 1.

7. The hydrogenation preparation method according to claim 6, characterized in that: The hydrogenation preparation method comprises: The nitro aromatic compound is subjected to catalytic hydrogenation under a hydrogen atmosphere using the catalyst as claimed in claim 1 to obtain aromatic amine.

8. The hydrogenation preparation method according to claim 7, characterized in that: The catalytic hydrogenation is carried out in a solvent medium; the solvent medium comprises: any one or a combination of at least two of water, tetrahydrofuran, methanol, isopropanol, ethanol, cyclohexane, cyclohexylamine, n-butanol, toluene, N-methylpyrrolidone or tert-butanol; The mass of the solvent medium is 50-200% of the mass of the nitro aromatic compound; the mass of the catalyst is 1-30% of the mass of the nitro aromatic compound.

9. The hydrogenation preparation method according to claim 7, characterized in that: The initial hydrogen pressure in the catalytic hydrogenation is ≥0.5MPa; The temperature of the catalytic hydrogenation is ≥20°C; The time of the catalytic hydrogenation is ≥0.5h.

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