Preparation method of phosphorus and oxygen co-doped nitrogen-doped carbon core-shell structure catalyst and method for preparing aromatic amine by transfer hydrogenation reduction of nitro-aromatic hydrocarbon

Abstract

The invention discloses a preparation method of a phosphorus and oxygen co-doped nitrogen-doped carbon core-shell structure catalyst and a method for preparing aromatic amine through transfer hydrogenation reduction of nitro-aromatic hydrocarbon, and the preparation method of the catalyst comprises the following steps: step (1), respectively dissolving heteroatom salt, zinc salt and dimethylimidazole in deionized water to obtain respective solutions, the preparation method comprises the following steps: adding organic amine into a dimethylimidazole solution, stirring, then adding a heteroatom salt solution, finally adding a zinc salt solution to obtain a mixed solution, reacting the mixed solution for a set time, centrifugally filtering and washing a reaction product, and carrying out vacuum drying to obtain a ZIF-8 precursor compound; and (2) calcining the ZIF-8 precursor compound at a high temperature in an inert atmosphere to obtain the phosphorus and oxygen co-doped nitrogen-doped carbon core-shell structure catalyst. According to the preparation method of the phosphorus and oxygen co-doped nitrogen-doped carbon core-shell structure catalyst disclosed by the embodiment of the invention, the prepared catalyst is low in cost, not easy to inactivate and high in catalytic reaction activity.

Description

Technical Field

[0001] The present invention relates to the field of catalysts, in particular to a method for preparing a phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalyst and a method for preparing aromatic amines by transfer hydrogenation reduction of nitroaromatic hydrocarbons. Background Art

[0002] Aromatic amines are important intermediates in the fine chemical industry, including anti-AIDS and anti-cancer drugs, synthetic dyes, and rubber additives. Efficient reduction of nitroaromatics using heterogeneous catalysts can provide high-quality aromatic amine raw materials for the chemical industry, reduce production costs, expand applicability, and provide technical support for the green upgrade of the chemical industry. However, traditional nitroaromatic reduction often uses iron / hydrochloric acid or high-pressure hydrogen, which poses safety risks and environmental pollution. Catalytic transfer hydrogenation, on the other hand, can replace high-pressure hydrogen with green hydrogen sources such as ethanol and formic acid, reducing energy consumption and waste emissions. It offers advantages such as simple synthetic steps, high atom economy, and environmental friendliness, and has become a research hotspot in the field of green synthesis. However, traditional hydrogen sources serve only as proton donors. Nitroheterocyclic compounds, with their high hydrogen storage density, chemical stability, and facility compatibility, can act as catalysts, providing active hydrogen species for the reduction of nitroaromatics through dehydrogenation. These compounds themselves are then converted into aromatic ring compounds, which can be recycled and reused as high-value-added fine chemicals, thus adhering to the principle of "atom economy."

[0003] In recent years, most heterogeneous catalytic transfer hydrogenation systems for nitrogen heterocyclic compounds and nitroaromatics are still based on metals, which generally have the following bottlenecks: (1) high cost and easy deactivation due to metal leaching; (2) strict inert high-pressure system increases process complexity; (3) the active hydrogen species produced by the dehydrogenation of nitrogen heterocyclic compounds are unstable, resulting in difficulty in selective control. On the other hand, there is currently only one report on the research work on metal-free carbon-based catalysts in this type of transfer hydrogenation reaction. In 2023, Zhang Zehui's team at South-Central University for Nationalities proposed the preparation of oxygen-induced zigzag graphene catalysts, in which pyridine nitrogen and carbonyl groups synergistically catalyze the capture of H atoms at the NH / CH sites in nitrogen heterocyclic compounds. However, the reaction conditions in this study are relatively harsh (1MPa N2, 180℃), and the high-pressure and high-temperature inert atmosphere limits large-scale application.

[0004] It can be seen that in the relevant technologies, most heterogeneous catalytic transfer hydrogenation systems of nitrogen heterocyclic compounds and nitroaromatics are still based on metal construction, and the reaction process needs to be combined with an inert high-pressure system, which is costly and easily deactivated by metal leaching, and the reaction process is highly complex. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, one object of the present invention is to provide a method for preparing a phosphorus-oxygen co-doped nitrogen-carbon core-shell structure catalyst. The phosphorus-oxygen co-doped nitrogen-carbon core-shell structure catalyst prepared by this preparation method is low-cost, not easily deactivated, and has high catalytic reaction activity. Furthermore, when performing the catalytic transfer hydrogenation reduction reaction of nitroaromatic hydrocarbons to prepare aromatic amines, the reaction process is less complex.

[0006] The present invention also provides a method for preparing aromatic amines by transfer hydrogenation reduction of nitroaromatics.

[0007] According to the first embodiment of the present invention, the preparation method of the phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalyst comprises: step (1), dissolving a heteroatom salt, a zinc salt and dimethylimidazole in deionized water, stirring them separately and then ultrasonically treating them to obtain a heteroatom salt solution, a zinc salt solution and a dimethylimidazole solution respectively, first adding an organic amine to the dimethylimidazole solution and stirring it, then adding the heteroatom salt solution, and finally adding the zinc salt solution to obtain a mixed solution, after the mixed solution reacts for a set time, centrifuging and washing the reaction product and vacuum drying it to obtain a ZIF-8 precursor complex; step (2), calcining the ZIF-8 precursor complex at a high temperature under an inert atmosphere to obtain a phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalyst.

[0008] According to the preparation method of the phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalyst of the embodiment of the present invention, phosphorus atoms are directly doped and embedded into the nitrogen-carbon skeleton structure by phosphorus and oxygen doping nitrogen-carbon, thereby increasing the local electron density, synergistically catalyzing with the active site to reduce the dehydrogenation barrier, and improving the ability to adsorb, activate and stabilize active hydrogen intermediates. Phosphine oxygen groups and carbon material defects can preferentially occupy oxygen adsorption sites and inhibit the oxidative side effects of oxygen. It is not easy to deactivate during the catalytic reaction of nitroaromatic hydrocarbon transfer hydrogenation reduction to prepare aromatic amines using the catalyst. The raw materials used in the preparation method are cheap and the preparation process is simple, which can reduce the cost of catalyst preparation. Through hydrogen bonding, the catalyst can be used to generate a large amount of nitroaromatic hydrocarbons. and hydrophilic properties, and has excellent chemical stability, antioxidant properties, catalytic reaction activity and selectivity, and recyclability in the aqueous phase. The catalytic reaction activity is further improved by utilizing the strong charge transfer effect formed at the core-shell interface. When the catalyst is used to carry out the catalytic reaction of nitroaromatic hydrocarbon transfer hydrogenation reduction to prepare aromatic amines, the catalyst is mixed with the substrate and the solvent, and the reaction can occur in an air atmosphere, and the reaction process is less complex. The phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalyst has the characteristics of low cost, not easy to deactivate, and high catalytic reaction activity. When the catalytic reaction of nitroaromatic hydrocarbon transfer hydrogenation reduction to prepare aromatic amines is carried out, the reaction process is less complex.

[0009] According to some embodiments of the present invention, the heteroatom salt is selected from at least one of ammonium phosphate, sodium hypophosphite, sodium hydrogen phosphate and sodium dihydrogen phosphate; the zinc salt is selected from at least one of zinc nitrate hexahydrate and zinc acetate dihydrate; and the organic amine is selected from at least one of aniline and benzylamine.

[0010] According to some embodiments of the present invention, in step (1), the molar ratio of the heteroatom salt, the zinc salt, the organic amine and the dimethylimidazole is (1-5):8:32:32.

[0011] According to some embodiments of the present invention, in step (1), the reaction conditions of the mixed solution include: a reaction temperature of 25°C, a reaction time of 4-12 hours; and a vacuum drying temperature of 60-80°C.

[0012] According to some embodiments of the present invention, in step (2), the high-temperature calcination conditions include: a calcination temperature of 800-1200°C, a calcination time of 2-5h, a heating rate of 1-10°C / min, and an inert atmosphere of nitrogen or argon.

[0013] According to a second embodiment of the present invention, a method for preparing aromatic amines by carrying out transfer hydrogenation reduction of nitroaromatics using the catalyst of the first embodiment of the present invention, and a method for preparing aromatic amines by carrying out transfer hydrogenation reduction of nitroaromatics using a nitrogen heterocyclic compound as a hydrogen donor, comprises: placing nitroaromatics, nitrogen heterocyclic compounds, solvents, and catalysts in a pressure-resistant tube for sealing treatment; placing the pressure-resistant tube in an oil bath for heating and stirring, and converting the nitrogen heterocyclic compounds and nitroaromatics into aromatic ring compounds and aromatic amines through the action of the catalyst; after the reaction is completed, cooling the pressure tube to room temperature, diluting the reaction solution with ethyl acetate and filtering, and separating and purifying the product by column chromatography.

[0014] According to the method for preparing aromatic amines by transfer hydrogenation reduction of nitroaromatics using a catalyst according to an embodiment of the present invention, the catalyst is mixed with a substrate and a solvent through a mild reaction system. The reaction can occur in an air atmosphere without the need for an inert high-pressure system. The conversion rates of nitroaromatics and nitrogen heterocyclic compounds are respectively increased to 92% or above. The reaction conditions are simple and the conversion rate is high.

[0015] According to some embodiments of the present invention, the solvent includes one of water, toluene, o-dichlorobenzene and mesitylene.

[0016] According to some embodiments of the present invention, the nitrogen heterocyclic compound includes at least one of indoles, 1,2,3,4-tetrahydroquinolines, and 1,2,3,4-tetrahydroquinoxalines; and the nitroaromatic hydrocarbon is a nitrobenzene compound.

[0017] According to some embodiments of the present invention, the molar ratio of the nitroaromatic hydrocarbon to the nitrogen heterocyclic compound is 1:(1.5-3), and the mass of the catalyst is 0.5-2 times the mass of the nitroaromatic hydrocarbon.

[0018] According to some embodiments of the present invention, the reaction conditions for converting the nitrogen heterocyclic compound and the nitroaromatic hydrocarbon into aromatic ring compounds and aromatic amines by the action of the catalyst include: reaction temperature of 130-180° C. and reaction time of 12-36 hours.

[0019] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0021] Figure 1 1 is a schematic flow chart of a method for preparing a phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalyst according to some embodiments of the present invention;

[0022] Figure 2 is a schematic flow chart of a method for preparing aromatic amines by transfer hydrogenation reduction of nitroaromatics using catalysts according to some embodiments of the present invention;

[0023] Figure 3 is an X-ray Diffraction (XRD) spectrum of the catalyst of Comparative Example 1;

[0024] Figure 4 This is a scanning electron microscope (SEM) image of the catalyst of Comparative Example 1;

[0025] Figure 5 is the XRD spectrum of the catalyst of Comparative Example 1;

[0026] Figure 6 is a SEM image of the ZIF-8 precursor complex according to Example 1 of the present invention;

[0027] Figure 7 is a transmission electron microscope (TEM) spectrum of the catalyst according to Example 1 of the present invention;

[0028] Figure 8 is the XRD spectrum of the catalyst according to Example 1 of the present invention;

[0029] Figure 9 TEM spectrum of the ZIF-8 precursor complex according to Example 2 of the present invention;

[0030] Figure 10 is a TEM spectrum of the catalyst according to Example 2 of the present invention;

[0031] Figure 11 is an XRD spectrum of the catalyst according to Example 2 of the present invention;

[0032] Figure 12 is an element distribution diagram (hereinafter referred to as "Mapping") of the catalyst according to Example 2 of the present invention;

[0033] Figure 13 is a mass spectrum of 2-methylaniline, the reaction product of Example 3 of the present invention;

[0034] Figure 14 is a mass spectrum of quinoline, the reaction product of Example 3 of the present invention;

[0035] Figure 15 is a mass spectrum of quinoxaline, the reaction product of Example 4 of the present invention;

[0036] Figure 16 5 is a mass spectrum of indole, the reaction product of Example 5 of the present invention. DETAILED DESCRIPTION

[0037] The following describes embodiments of the present invention in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended only to explain the present invention and are not to be construed as limiting the present invention.

[0038] For numerical ranges, the endpoints of each range, the endpoints of each range and individual endpoints, and the individual endpoints can be combined to form one or more new numerical ranges, which are to be considered as specifically disclosed herein. Reagents or instruments used without manufacturer designation are commercially available conventional products.

[0039] Reference below Figures 1-16 The preparation method of the phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalyst according to an embodiment of the present invention is described.

[0040] refer to Figure 1 The method for preparing a phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalyst according to the first embodiment of the present invention comprises:

[0041] Step (1), dissolving a heteroatom salt, a zinc salt and dimethylimidazole in deionized water, stirring them separately and then ultrasonically treating them to obtain a heteroatom salt solution, a zinc salt solution and a dimethylimidazole solution, respectively; first adding an organic amine to the dimethylimidazole solution and stirring it, then adding the heteroatom salt solution, and finally adding the zinc salt solution to obtain a mixed solution; after the mixed solution reacts for a set time, the reaction product is centrifuged, washed and vacuum-dried to obtain a ZIF-8 precursor complex;

[0042] Step (2): calcining the ZIF-8 precursor complex at a high temperature under an inert atmosphere to obtain a phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalyst.

[0043] The heteroatom salt, zinc salt and dimethylimidazole are dissolved in deionized water respectively to increase the contact area between the reactants and facilitate the reaction.

[0044] Adding the organic amine to the dimethylimidazole solution and stirring the solution first can wrap the dimethylimidazole with the organic amine, and polymerize on the surface of the dimethylimidazole to form an organic amine polymer, which is beneficial to the formation of a shell structure in the subsequent step.

[0045] Adding a heteroatom salt solution facilitates the doping of phosphorus and oxygen into dimethylimidazole. Heteroatom salts provide phosphorus and oxygen for doping by providing phosphorus salts. Phosphorus and oxygen co-doping nitrogen-carbon allows phosphorus atoms to be directly doped and embedded into the nitrogen-carbon skeleton structure, increasing local electron density and synergistically catalyzing active sites to reduce the dehydrogenation barrier, such as carbonyl and carbon-nitrogen sites. This improves the ability to adsorb, activate, and stabilize active hydrogen intermediates. Phosphine oxygen groups and carbon material defects can preferentially occupy oxygen adsorption sites and suppress the oxidative side effects of oxygen.

[0046] Finally, a zinc salt solution is added. The zinc ions in the zinc salt enter the structure of the dimethylimidazole doped with phosphorus and oxygen, coated with an organic amine polymer, and form ZIF-8 with the dimethylimidazole. The ZIF-8, doped with phosphorus and oxygen, forms a ZIF-8 precursor complex coated with the organic amine polymer. ZIF-8 exhibits porosity, a large specific surface area, and excellent chemical stability. The flexible pore size adjustment of ZIF-8 allows for the effective adsorption and separation of molecules of specific sizes, which facilitates the stability of the phosphorus and oxygen doping.

[0047] The ZIF-8 precursor complex is calcined at high temperature under an inert atmosphere. Under high temperature conditions, the polymer formed by the polymerization of organic amines is thermally decomposed into a carbon-based material, wherein the carbon-based material serves as the shell structure of the catalyst and ZIF-8 serves as the core structure of the catalyst, forming a phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalyst.

[0048] The phosphorus- and oxygen-co-doped nitrogen-carbon core-shell catalyst has a core-shell structure. Through carbon shell encapsulation and heteroatom doping, it significantly improves the catalyst's oxidation resistance and stability in air. It also suppresses oxidative side reactions during transfer hydrogenation and enhances reaction selectivity. Compared to traditional nitrogen-carbon non-metallic catalysts, this catalytic material exhibits superior transfer hydrogenation performance. Using nitrogen heterocyclic compounds as hydrogen donors, it can reduce nitroaromatics to aniline compounds with conversion rates exceeding 92%.

[0049] According to the preparation method of the phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalyst of the embodiment of the present invention, phosphorus atoms are directly doped and embedded into the nitrogen-carbon skeleton structure by phosphorus and oxygen doping nitrogen-carbon, thereby increasing the local electron density, synergistically catalyzing with the active site to reduce the dehydrogenation barrier, and improving the ability to adsorb, activate and stabilize active hydrogen intermediates. Phosphine oxygen groups and carbon material defects can preferentially occupy oxygen adsorption sites and inhibit the oxidative side effects of oxygen. It is not easy to deactivate during the catalytic reaction of nitroaromatic hydrocarbon transfer hydrogenation reduction to prepare aromatic amines using the catalyst. The raw materials used in the preparation method are cheap and the preparation process is simple, which can reduce the cost of catalyst preparation. Through hydrogen bonding, the catalyst can be used to generate a large amount of nitroaromatic hydrocarbons. and hydrophilic properties, and has excellent chemical stability, antioxidant properties, catalytic reaction activity and selectivity, and recyclability in the aqueous phase. The catalytic reaction activity is further improved by utilizing the strong charge transfer effect formed at the core-shell interface. When the catalyst is used to carry out the catalytic reaction of nitroaromatic hydrocarbon transfer hydrogenation reduction to prepare aromatic amines, the catalyst is mixed with the substrate and the solvent, and the reaction can occur in an air atmosphere, and the reaction process is less complex. The phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalyst has the characteristics of low cost, not easy to deactivate, and high catalytic reaction activity. When the catalytic reaction of nitroaromatic hydrocarbon transfer hydrogenation reduction to prepare aromatic amines is carried out, the reaction process is less complex.

[0050] According to some embodiments of the present invention, the heteroatom salt is selected from at least one of ammonium phosphate, sodium hypophosphite, sodium hydrogen phosphate and sodium dihydrogen phosphate; the zinc salt is selected from at least one of zinc nitrate hexahydrate and zinc acetate dihydrate; and the organic amine is selected from at least one of aniline and benzylamine.

[0051] Among them, the heteroatom salt is selected from at least one of ammonium phosphate, sodium hypophosphite, sodium hydrogen phosphate and sodium dihydrogen phosphate. It can be one of the heteroatom salts selected from ammonium phosphate, sodium hypophosphite, sodium hydrogen phosphate and sodium dihydrogen phosphate, or it can be a plurality of heteroatom salts selected from ammonium phosphate, sodium hypophosphite, sodium hydrogen phosphate and sodium dihydrogen phosphate. By adding heteroatom salts containing phosphate and hypophosphite, the doped phosphorus and oxygen elements are provided.

[0052] The zinc salt is selected from at least one of zinc nitrate hexahydrate and zinc acetate dihydrate. The zinc salt can be selected from one of zinc nitrate hexahydrate and zinc acetate dihydrate respectively, or zinc nitrate hexahydrate and zinc acetate dihydrate can be selected at the same time. By adding the hydrated zinc salt, the zinc element for synthesizing ZIF-8 is provided.

[0053] The organic amine is selected from at least one of aniline and benzylamine, and may be one of aniline and benzylamine, or may be both aniline and benzylamine. The addition of the organic amine serves to provide a raw material for the shell of the core-shell structure in the phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalyst.

[0054] According to some embodiments of the present invention, in step (1), the molar ratio of the heteroatom salt, the zinc salt, the organic amine and the dimethylimidazole is (1-5):8:32:32.

[0055] For example, the molar ratio of the heteroatom salt, zinc salt, organic amine, and dimethylimidazole can be 1:8:32:32, 2:8:32:32, 3:8:32:32, 4:8:32:32, 5:8:32:32, etc. By adjusting the proportion of the heteroatom salt in the reactants, the ratio of phosphorus and oxygen doping can be adjusted.

[0056] According to some embodiments of the present invention, in step (1), the reaction conditions of the mixed solution include: reaction temperature of 25°C, reaction time of 4-12h; vacuum drying temperature of 60-80°C.

[0057] For example, the reaction time of the mixed solution can be 4 hours, 6 hours, 8 hours, 10 hours, or 12 hours. If the reaction time of the mixed solution is too short, the mixed solution cannot fully react. If the reaction time of the mixed solution is too long, the reaction efficiency is reduced. By adjusting the appropriate reaction time, the reaction of the mixed solution can be ensured to be complete while saving the reaction time.

[0058] For example, the vacuum drying temperature can be 60°C, 65°C, 70°C, 75°C, 80°C, etc. If the vacuum drying temperature is too low, the drying effect will not be good. If the vacuum drying temperature is too high, the surface of the phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalyst will harden too quickly, hindering the diffusion of internal moisture and thus reducing the drying efficiency. By adjusting the appropriate vacuum drying temperature, a good drying effect can be achieved.

[0059] Among them, the reaction temperature of the mixed solution is 25°C, which is close to room temperature and is easier to achieve reaction conditions. The smaller temperature difference with room temperature also reduces the influence of external temperature interference.

[0060] According to some embodiments of the present invention, in step (2), the high-temperature calcination conditions include: a calcination temperature of 800-1200°C, a calcination time of 2-5h, a heating rate of 1-10°C / min, and an inert atmosphere of nitrogen or argon.

[0061] For example, the calcination temperature can be 800°C, 900°C, 1000°C, 1100°C, 1200°C, etc.; the calcination time can be 2 hours, 3 hours, 4 hours, 5 hours, etc.; the heating rate can be 1°C / min, 3°C / min, 5°C / min, 8°C / min, 10°C / min, etc.; the inert atmosphere can be nitrogen or argon. High-temperature calcination in an inert atmosphere can prevent air from oxidizing the reactants.

[0062] refer to Figure 2 According to the second embodiment of the present invention, a method for preparing aromatic amines by transfer hydrogenation reduction of nitroaromatics using the catalyst of the first embodiment of the present invention is carried out, wherein a nitrogen heterocyclic compound is used as a hydrogen donor and the method comprises:

[0063] The nitroaromatic hydrocarbon, nitrogen heterocyclic compound, solvent and catalyst are placed in a pressure-resistant tube for sealed treatment;

[0064] The pressure-resistant tube is placed in an oil bath for heating and stirring, and the nitrogen heterocyclic compounds and nitroaromatic hydrocarbons are converted into aromatic ring compounds and aromatic amines through the action of the catalyst;

[0065] After the reaction was completed, the pressure tube was cooled to room temperature, the reaction solution was diluted with ethyl acetate and filtered, and the product was separated and purified by column chromatography.

[0066] The catalyst is a phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalyst.

[0067] Among them, nitroaromatic hydrocarbons, nitrogen heterocyclic compounds, solvents and catalysts are placed in a pressure-resistant tube for sealed treatment. The pressure-resistant tube can withstand high internal pressure to ensure that it will not rupture due to excessive internal pressure during the reaction; an oil bath is used to heat to a constant temperature to maintain the reaction temperature at a stable state; the reaction liquid is diluted with ethyl acetate and filtered, and the good solubility of ethyl acetate is used to dilute the reaction liquid, which is conducive to further separation and purification.

[0068] Nitroaromatic hydrocarbons, nitrogen heterocyclic compounds, solvents and catalysts can react in an air atmosphere at room temperature without the need for heating or inert high-pressure treatment, and the reaction process is low in complexity. During the use of the phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalyst, phosphine oxygen groups and carbon material defects can preferentially occupy oxygen adsorption sites and inhibit the oxidative side effects of oxygen. The catalyst is not easily deactivated during the catalytic reaction of nitroaromatic hydrocarbon transfer hydrogenation reduction to prepare aromatic amines.

[0069] Column chromatography is a separation method based on distribution equilibrium. Its core principle is to exploit the differences in the distribution coefficients of components in a mixture between the stationary and mobile phases, achieving separation through repeated adsorption and desorption processes. Substances with higher polarity are more easily adsorbed by the stationary phase, while substances with lower polarity migrate more easily with the mobile phase, thus achieving separation.

[0070] According to the method for preparing aromatic amines by transfer hydrogenation reduction of nitroaromatics using a catalyst according to an embodiment of the present invention, the catalyst is mixed with a substrate and a solvent through a mild reaction system. The reaction can occur in an air atmosphere without the need for an inert high-pressure system. The conversion rates of nitroaromatics and nitrogen heterocyclic compounds can be increased to 92% or above, respectively. The reaction conditions are simple and the conversion rate is high.

[0071] According to some embodiments of the present invention, the solvent includes one of water, toluene, o-dichlorobenzene, and mesitylene. By dissolving the nitroaromatic hydrocarbon and the nitrogen heterocyclic compound in the solvent, the contact area between the nitroaromatic hydrocarbon and the nitrogen heterocyclic compound is increased, and the dissolved nitroaromatic hydrocarbon and the nitrogen heterocyclic compound are more easily contacted with the catalyst, thereby accelerating the reaction rate.

[0072] According to some embodiments of the present invention, the nitrogen heterocyclic compound includes at least one of indoles, 1,2,3,4-tetrahydroquinolines, and 1,2,3,4-tetrahydroquinoxalines; and the nitroaromatic hydrocarbon is a nitrobenzene compound.

[0073] For example, the nitrogen heterocyclic compound includes at least one of indoles, 1,2,3,4-tetrahydroquinolines, and 1,2,3,4-tetrahydroquinoxalines. The nitrogen heterocyclic compound may include one of indoles, 1,2,3,4-tetrahydroquinolines, and 1,2,3,4-tetrahydroquinoxalines, or may be a plurality of compounds selected from indoles, 1,2,3,4-tetrahydroquinolines, and 1,2,3,4-tetrahydroquinoxalines. The nitroaromatic hydrocarbon may be nitrobenzene, or a nitrobenzene compound such as 2-methylnitrobenzene.

[0074] According to some embodiments of the present invention, the molar ratio of the nitroaromatic hydrocarbon to the nitrogen heterocyclic compound is 1:(1.5-3), and the mass of the catalyst is 0.5-2 times the mass of the nitroaromatic hydrocarbon.

[0075] For example, the molar ratio of nitroaromatic hydrocarbon to nitrogen heterocyclic compound can be 1:1.5, 1:2, 1:2.5, 1:3, etc.; the mass of the catalyst can be 0.5 times, 1 times, 1.5 times, 2 times, etc. of the mass of the nitroaromatic hydrocarbon. An appropriate ratio of nitroaromatic hydrocarbon to nitrogen heterocyclic compound can be selected based on the type and ratio of the nitroaromatic hydrocarbon. When the mass ratio of the catalyst is too large, the concentration of the nitroaromatic hydrocarbon is affected, thereby slowing the reaction rate. When the mass ratio of the catalyst is too small, the contact area between the catalyst and the nitroaromatic hydrocarbon is reduced, thereby slowing the reaction rate. By adjusting the mass ratio of the catalyst to the nitroaromatic hydrocarbon, the catalyst can achieve the best catalytic effect.

[0076] According to some embodiments of the present invention, the reaction conditions for converting nitrogen heterocyclic compounds and nitroaromatic hydrocarbons into aromatic ring compounds and aromatic amines by the action of a catalyst include: a reaction temperature of 130-180° C. and a reaction time of 12-36 hours.

[0077] For example, the reaction temperature can be 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, etc.; the reaction time can be 12 hours, 18 hours, 24 hours, 30 hours, 36 hours, etc. If the reaction temperature is too high, the catalyst may be deactivated; if the reaction temperature is too low, the catalyst may not be sufficiently active. By adjusting the appropriate reaction temperature and reaction time, the catalyst can achieve the best catalytic effect.

[0078] Refer to the following Figure 3-Figure 12 The preparation methods of phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalysts according to comparative examples and some embodiments of the present invention are described.

[0079] Comparative Example 1,

[0080] The catalyst in Comparative Example 1 is a phosphorus and oxygen co-doped nitrogen-carbon catalyst, and the preparation of the phosphorus and oxygen co-doped nitrogen-carbon catalyst.

[0081] The phosphorus and oxygen co-doped nitrogen-carbon catalyst in Comparative Example 1 is a ZIF-8 derived NC catalyst.

[0082] Accurately weigh 8.0 mmol of Zn(NO₃)₂·6H₂O and 32.0 mmol of dimethylimidazole. Dissolve these compounds in deionized water and stir ultrasonically to dissolve them completely. Slowly add the Zn(NO₃)₂·6H₂O solution to the dimethylimidazole solution, and continue stirring the mixture at room temperature for 12 hours. The treated mixture is centrifuged and rinsed several times with deionized water to remove impurities. The resulting ZIF-8 product is then placed in a vacuum oven and dried at 80°C for 12 hours. The dried sample is calcined in a tube furnace at 900°C for 2 hours under a nitrogen atmosphere at a heating rate of 5°C / min to obtain the NC catalyst.

[0083] Refer to the attached Figure 3 and Figure 4 The XRD pattern and SEM pattern of the ZIF-8 precursor prepared in this comparative example show that the precursor is a regular dodecahedral ZIF-8 structure; Figure 5 In the XRD spectrum of the catalyst prepared in this comparative example, the diffraction peak position is consistent with that of graphitized carbon (PDF#01-0646), which shows that the component of the phosphorus and oxygen co-doped nitrogen-carbon catalyst prepared in this comparative example is nitrogen-carbon.

[0084] Example 1,

[0085] The catalyst in Example 1 is a phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalyst, and the preparation of the phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalyst.

[0086] The phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalyst in Example 1 is a ZIF-8 derived core-shell structure NC-900 catalyst.

[0087] Accurately weigh 8.0 mmol of Zn(NO₃)₂·6H₂O and 32.0 mmol of dimethylimidazole. Dissolve these compounds in deionized water and stir ultrasonically until completely dissolved. Add 32.0 mmol of aniline to the dimethylimidazole solution and continue stirring. Finally, add the Zn(NO₃)₂·6H₂O solution to the mixture and continue stirring at room temperature for 12 hours. The treated mixture is centrifuged and rinsed multiple times with deionized water to remove impurities. The resulting spherical ZIF-8 precursor complex is then placed in a vacuum oven and dried at 80°C for 12 hours. The dried sample is calcined in a tube furnace at 900°C for 2 hours under a nitrogen atmosphere at a heating rate of 5°C / min to obtain a phosphorus- and oxygen-codoped nitrogen-carbon core-shell catalyst.

[0088] Refer to the attached Figure 6 The ZIF-8 precursor complex prepared in this embodiment is a Ph-NH2-ZIF-8 precursor. According to its SEM image, the ZIF-8 precursor complex is a spherical structure uniformly wrapped by an organic amine polymer; Figure 7 The TEM spectrum of the catalyst prepared in this embodiment shows that the catalyst has a core-shell structure. Figure 8 In the XRD spectrum of the catalyst prepared in this example, the diffraction peak position is consistent with that of graphitized carbon (PDF#01-0646), which shows that the component of the ZIF-8-derived core-shell structure NC-900 catalyst prepared in this example is nitrogen-carbon.

[0089] Example 2,

[0090] The catalyst in Example 2 is a phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalyst, and the preparation of the phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalyst.

[0091] The phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalyst in Example 2 is a ZIF-8 derived core-shell structure NCPO-900-1 catalyst.

[0092] Accurately weigh 8.0 mmol of Zn(NO₃)₂·6H₂O, 400 mg of ammonium phosphate, and 32.0 mmol of dimethylimidazole. Dissolve these compounds in deionized water and stir ultrasonically until completely dissolved. Add 32.0 mmol of aniline to the dimethylimidazole solution and continue stirring. Then, add the ammonium phosphate solution to the mixture and stir. Finally, add the Zn(NO₃)₂·6H₂O solution and continue stirring at room temperature for 12 hours. The treated mixture is centrifuged and rinsed several times with deionized water to remove impurities. The resulting spherical ZIF-8 precursor complex is then placed in a vacuum oven and dried at 80°C for 12 hours. The dried sample is calcined in a tube furnace at 900°C for 2 hours under a nitrogen atmosphere at a heating rate of 5°C / min to obtain a phosphorus- and oxygen-codoped nitrogen-carbon core-shell catalyst.

[0093] Refer to the attached Figure 9 The ZIF-8 precursor complex prepared in this embodiment is a PO-Ph-NH2-ZIF-8 precursor. According to its TEM image, the ZIF-8 precursor complex is a spherical structure uniformly wrapped by an organic amine polymer; Figure 10 The TEM image of the catalyst prepared in this embodiment shows that the material has a core-shell structure; Figure 11 The XRD spectrum of the catalyst prepared in this example shows that the diffraction peak position is consistent with that of graphitized carbon (PDF#01-0646), which shows that the component of the core-shell heteroatom-doped carbon-based catalyst prepared in this example is nitrogen-carbon. Figure 12 From the element distribution mapping of the catalyst prepared in this example, it can be seen that phosphorus and oxygen atoms have been successfully and evenly doped into the nitrogen-carbon.

[0094] Refer to the following Figure 13-16 The method for preparing aromatic amines by transfer hydrogenation reduction of nitroaromatic hydrocarbons according to some embodiments of the present invention is described.

[0095] Example 3,

[0096] Example 3 is the use of the catalyst of Example 2 in the catalytic transfer hydrogenation reaction of 2-methylnitrobenzene and 1,2,3,4-tetrahydroquinoline.

[0097] 0.4 mmol of 2-methylnitrobenzene, 0.8 mmol of 1,2,3,4-tetrahydroquinoline, 4 mL of deionized water, and 40 mg of the phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalyst prepared in Example 2 were sequentially added to a glass pressure tube, and the mixture was stirred in an air atmosphere, a pressure of 0.1 MPa, and a reaction speed of 500 rpm for 24 hours at 150°C. After the reaction, the mixture was taken out and the aqueous phase was extracted with ethyl acetate to separate the catalyst. The yields of the target products aniline and quinoline were determined by gas chromatography-mass spectrometry to be 98% and 99%, respectively.

[0098] in, Figure 13 The mass spectrum can reflect the molecular structure and relative molecular mass of the reaction product 2-methylaniline; Figure 14 The mass spectrum can reflect the molecular structure and relative molecular mass of the reaction product quinoline.

[0099]

[0100] Example 4,

[0101] Example 4 is the use of the catalyst of Example 2 in the catalytic transfer hydrogenation reaction of nitrobenzene and 1,2,3,4-tetrahydroquinoxaline.

[0102] 0.4 mmol of nitrobenzene, 0.8 mmol of 1,2,3,4-tetrahydroquinoxaline, 4 mL of deionized water, and 40 mg of the phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalyst prepared in Example 2 were sequentially added to a glass pressure tube, and the mixture was stirred in an air atmosphere at a pressure of 0.1 MPa and 150° C. (speed of 500 rpm) for 24 h. After the reaction, the mixture was taken out and the aqueous phase was extracted with ethyl acetate to separate the catalyst. The yields of the target products aniline and quinoxaline were determined by gas chromatography-mass spectrometry to be 99% and 99%, respectively.

[0103] in, Figure 15 The mass spectrum can reflect the molecular structure and relative molecular mass of the reaction product quinoxaline.

[0104]

[0105] Example 5,

[0106] Example 5 is the use of the catalyst of Example 2 in the catalytic transfer hydrogenation reaction of nitrobenzene and dihydroindoline.

[0107] 0.4 mmol of nitrobenzene, 1.6 mmol of indoline, 4 mL of deionized water, and 40 mg of the phosphorus-oxygen co-doped nitrogen-carbon core-shell structure catalyst prepared in Example 2 were sequentially added to a glass pressure tube, and the mixture was stirred in an air atmosphere at a pressure of 0.1 MPa and 150° C. (rotation speed of 500 rpm) for 24 h. After the reaction, the mixture was taken out and the aqueous phase was extracted with ethyl acetate to separate the catalyst. The yields of the target products aniline and indole were determined by gas chromatography-mass spectrometry to be 92% and 99%, respectively.

[0108] in, Figure 16 The mass spectrum can reflect the molecular structure and relative molecular mass of the reaction product indole.

[0109]

[0110] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" means that a specific feature, structure, material, or characteristic described in conjunction with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, illustrative uses of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0111] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to the embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the claims and their equivalents.

Claims

1. A method for preparing a phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalyst, characterized in that: include: Step (1), dissolving a heteroatom salt, a zinc salt and dimethylimidazole in deionized water, stirring them separately and then ultrasonically treating them to obtain a heteroatom salt solution, a zinc salt solution and a dimethylimidazole solution, respectively; first adding an organic amine to the dimethylimidazole solution and stirring it, then adding the heteroatom salt solution, and finally adding the zinc salt solution to obtain a mixed solution; after the mixed solution reacts for a set time, the reaction product is centrifuged, washed and vacuum-dried to obtain a ZIF-8 precursor complex; Step (2): calcining the ZIF-8 precursor complex at a high temperature under an inert atmosphere to obtain a phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalyst.

2. The method for preparing the phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalyst according to claim 1, characterized in that: The heteroatom salt is selected from at least one of ammonium phosphate, sodium hypophosphite, sodium hydrogen phosphate and sodium dihydrogen phosphate; the zinc salt is selected from at least one of zinc nitrate hexahydrate and zinc acetate dihydrate; and the organic amine is selected from at least one of aniline and benzylamine.

3. The method for preparing the phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalyst according to claim 1, characterized in that: In the step (1), the molar ratio of the heteroatom salt, the zinc salt, the organic amine and the dimethylimidazole is (1-5):8:32:

32.

4. The method for preparing the phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalyst according to claim 1, characterized in that: In the step (1), the reaction conditions of the mixed solution include: reaction temperature of 25° C., reaction time of 4-12 h; and vacuum drying temperature of 60-80° C.

5. The method for preparing the phosphorus and oxygen co-doped nitrogen-carbon core-shell structure catalyst according to claim 1, characterized in that: In the step (2), the high-temperature calcination conditions include: calcination temperature of 800-1200°C, calcination time of 2-5h, heating rate of 1-10°C / min, and inert atmosphere of nitrogen or argon.

6. A method for preparing aromatic amines by transfer hydrogenation reduction of nitroaromatics using the catalyst according to any one of claims 1 to 5, characterized in that: A method for preparing aromatic amines by transfer hydrogenation reduction of nitroaromatics using a nitrogen heterocyclic compound as a hydrogen donor comprises: The nitroaromatic hydrocarbon, nitrogen heterocyclic compound, solvent and catalyst are placed in a pressure-resistant tube for sealed treatment; placing the pressure-resistant tube in an oil bath for heating and stirring, and converting the nitrogen heterocyclic compound and the nitroaromatic hydrocarbon into aromatic ring compounds and aromatic amines through the action of the catalyst; After the reaction was completed, the pressure tube was cooled to room temperature, the reaction solution was diluted with ethyl acetate and filtered, and the product was separated and purified by column chromatography.

7. The method for preparing aromatic amines by transfer hydrogenation reduction of nitroaromatics using the catalyst according to claim 6, characterized in that: The solvent includes one of water, toluene, o-dichlorobenzene and mesitylene.

8. The method for preparing aromatic amines by transfer hydrogenation reduction of nitroaromatics using the catalyst according to claim 6, characterized in that: The nitrogen heterocyclic compound includes at least one of indoles, 1,2,3,4-tetrahydroquinolines, and 1,2,3,4-tetrahydroquinoxalines; and the nitroaromatic hydrocarbon is a nitrobenzene compound.

9. The method for preparing aromatic amines by transfer hydrogenation reduction of nitroaromatics using the catalyst according to claim 6, characterized in that: The molar ratio of the nitroaromatic hydrocarbon to the nitrogen heterocyclic compound is 1:(1.5-3), and the mass of the catalyst is 0.5-2 times the mass of the nitroaromatic hydrocarbon.

10. The method for preparing aromatic amines by transfer hydrogenation reduction of nitroaromatics using the catalyst according to claim 6, characterized in that: The reaction conditions for converting the nitrogen heterocyclic compound and the nitroaromatic hydrocarbon into aromatic ring compounds and aromatic amines by the action of the catalyst include: a reaction temperature of 130-180° C. and a reaction time of 12-36 hours.

Images