阅读说明：本技术 一种氮掺杂碳负载杂多酸纳米复合材料的制备方法及应用 (Preparation method and application of nitrogen-doped carbon-loaded heteropoly acid nanocomposite ) 是由 高文秀 吕杰琼 邢树宇 娄大伟 张志会 王集思 谢晖 高永平 于 2021-09-17 设计创作，主要内容包括：本发明公开了一种氮掺杂碳负载杂多酸纳米复合材料的制备方法及应用。利用简易的浸渍法将杂多酸固载到由富氮共价有机骨架材料高温碳化得到的氮掺杂碳纳米材料上,将制备的氮掺杂碳负载杂多酸纳米复合材料作为催化剂应用在硝基苯加氢反应中。制备纳米复合材料所用原料价廉易得,制备方法简单；催化体系选用廉价、安全的水合肼作为还原剂,催化反应条件温和,反应时间短,硝基苯的转化率高,苯胺的选择性好。催化剂的催化效率高,稳定性好,可用于工业化大规模生产。(The invention discloses a preparation method and application of a nitrogen-doped carbon-loaded heteropoly acid nano composite material. The heteropoly acid is immobilized on the nitrogen-doped carbon nano material obtained by high-temperature carbonization of the nitrogen-rich covalent organic framework material by using a simple impregnation method, and the prepared nitrogen-doped carbon-loaded heteropoly acid nano composite material is used as a catalyst to be applied to nitrobenzene hydrogenation reaction. The raw materials for preparing the nano composite material are cheap and easy to obtain, and the preparation method is simple; the catalytic system adopts cheap and safe hydrazine hydrate as a reducing agent, the catalytic reaction condition is mild, the reaction time is short, the conversion rate of nitrobenzene is high, and the selectivity of aniline is good. The catalyst has high catalytic efficiency and good stability, and can be used for industrial large-scale production.)

1. A preparation method of a nitrogen-doped carbon-loaded heteropoly acid nano composite material is characterized by comprising the following steps:

(1) preparing a nitrogen-doped carbon nano material: mixing a mixture of 1: 1.5, dispersing melamine and 1, 4-diformylpiperazine in dimethyl sulfoxide, carrying out reaction at 165 ℃ for 72 hours, carrying out suction filtration, washing a filter cake with ethanol, tetrahydrofuran, acetone and dichloromethane in sequence, drying to obtain white powder, and carbonizing the white powder to obtain black powder, namely the nitrogen-doped carbon nano material;

(2) preparing a nitrogen-doped carbon-loaded heteropoly acid nano composite material: and (2) ultrasonically dispersing the nitrogen-doped carbon nano material prepared in the step (1) and heteropoly acid in an ethanol water solution, heating and stirring for 24h at 80 ℃, filtering, washing with deionized water, and vacuum drying for 12h at 80 ℃ to obtain the nitrogen-doped carbon supported heteropoly acid nano composite material.

2. The method for preparing the nitrogen-doped carbon-supported heteropoly acid nanocomposite as claimed in claim 1, wherein the carbonization in the step (1) is performed in a tubular furnace at 500-800 ℃ for 2 h.

3. The preparation method of the nitrogen-doped carbon-supported heteropoly acid nanocomposite material as claimed in claim 1, wherein the heteropoly acid in the step (2) is PCuMo₁₁The mass ratio of the nitrogen-doped carbon nanomaterial to the heteropoly acid is 1: (0.5-1.5).

4. The application of the nitrogen-doped carbon-supported heteropoly acid nanocomposite material as claimed in any one of claims 1 to 3 in the catalysis of nitrobenzene hydrogenation reaction is characterized by comprising the following processes:

the nitrogen-doped carbon-supported heteropoly acid nano composite material is uniformly dispersed in an organic solvent, then reactant nitrobenzene and a reducing agent are added, and the mixture is heated and magnetically stirred for reaction.

5. The use of the nitrogen-doped carbon-supported heteropoly acid nanocomposite as claimed in claim 4, wherein the organic solvent is one of ethanol, toluene and cyclohexane.

6. The use of the nitrogen-doped carbon-supported heteropoly acid nanocomposite as claimed in claim 4, wherein the addition ratio of nitrobenzene to nitrogen-doped carbon-supported heteropoly acid nanocomposite is 0.5 mmol: (2.5-5) mg.

7. The use of the nitrogen-doped carbon-supported heteropoly acid nanocomposite material according to claim 4, wherein the reducing agent is any one of hydrazine hydrate, alkali sulfide and hydrogen.

8. Use of the nitrogen-doped carbon-supported heteropoly acid nanocomposite as claimed in claim 4, wherein the molar ratio of the nitrobenzene to the reducing agent is 1: (4-6).

9. The application of the nitrogen-doped carbon-supported heteropoly acid nanocomposite material as claimed in claim 4, wherein the reaction temperature is 60-80 ℃ and the reaction time is 1-15 min.

Technical Field

The invention belongs to the technical field of fine chemical engineering, and particularly relates to a preparation method of a nitrogen-doped carbon-loaded heteropoly acid nano composite material and a method for preparing aniline by catalyzing nitrobenzene hydrogenation.

Background

Hydrogenation of nitroaromatic to produce amine is a common reaction widely used in the production of chemical products such as pigments, drugs and polymers. The metal-containing catalyst is the most commonly used catalyst in the hydrogenation reaction of nitro compounds at present, and comprises noble metals such as palladium, gold, ruthenium and the like. Literature (high hly efficiency Hydrogenation of Nitrobenzene to Aniline over Pt/CeO)₂ Catalysts:Shape Effect of Support and Key Role ofAdditional Ce³⁺Sites) with H₂PtCl₆Pt is a Pt precursor, and Pt is loaded on CeO by an immersion method₂Pt/CeO prepared by reducing on nano-rod at 600 DEG C₂600 catalyst, H at room temperature 1MPa₂The reaction was carried out under pressure for 3h, allowing complete conversion of nitrobenzene, but selectivity to aniline was only 40.9%. The literature (Two-dimensional ultraprotein surfactants-encapsulating polyoxometalate platelets as carriers for monomeric nanoparticles with high catalytic activity and stability) makes use of dodecyl dimethyl ammonium bromide (DODA) and molybdenum Phosphate (PMO)₁₂) Ag/DODA-PMO prepared by self-assembling two-dimensional ultrathin surfactant encapsulated polyoxometallate nanosheets for loading Ag nanoparticles₁₂Can be used as a catalyst in NaBH₄The catalyst system for catalyzing p-nitrophenol to be reduced into p-aminophenol at room temperature in the reducing agent and the isopropanol solvent has higher catalytic efficiency. However, these catalytic systems require high temperature, high H₂Gas pressure and noble metal catalyst. In particular, noble metals such as palladium and platinum have a limitation of low selectivity.

In view of the existing limitations of noble metals, it is of great interest to develop new inexpensive catalysts, in particular non-noble metal based catalysts, with high activity and high selectivity towards aniline. Literature (high dry Selective Transfer Hydrogenation of Fu)NCTIONIONALYDROARENES Using Cobalt-bas edNANOCATALYSTS) catalyst Co (OAc)₂the-Phen/C is composed of active cobalt oxide particles wrapping a nitrogen-doped carbon layer, and the unique structure is realized by depositing a metal-o-phenanthroline complex on a carbon carrier through pyrolysis at 800 ℃. In the catalytic system, formic acid is used as a reducing agent, tetrahydrofuran is used as a solvent, and the nitrobenzene conversion rate is increased after the reaction is carried out for 15 hours at the temperature of 100 DEG C>99 percent, 96 percent of aniline yield and high selectivity to aniline, but the reaction time is too long, so the method is not suitable for industrial production.

The nitrogen-rich covalent organic framework material contains light elements such as carbon, hydrogen and the like, and also contains rich nitrogen elements. After the materials are roasted, nitrogen-doped carbon nano materials are formed. The nitrogen-doped carbon nano material is considered as an important carrier material for preparing the heterogeneous catalyst due to the strong chemical and electrical properties of the nitrogen-doped carbon nano material. Doping with nitrogen atoms can result in slight distortions of the carbon material lattice, thereby causing defects. In recent decades, the incorporation of non-noble metals into nitrogen-doped carbon nanomaterials not only becomes a substitute of noble metal-based catalysts, but also finds and reports excellent performance in catalytic hydrogenation, and therefore, how to provide a nitrogen-doped carbon-supported non-noble metal catalyst with higher catalytic efficiency and lower cost is an urgent problem to be solved by the technical personnel in the field.

Disclosure of Invention

In view of the above, the invention provides a preparation method and application of a nitrogen-doped carbon-supported heteropoly acid nanocomposite, wherein a nitrogen-doped carbon nanomaterial derived from a covalent organic framework material is used as a carrier, and the nanocomposite loaded with heteropoly acid by a simple impregnation method is used as a catalyst for catalyzing nitrobenzene hydrogenation reaction, so that the catalytic efficiency can be improved, and hydrazine hydrate is used as a reducing agent to avoid corrosion to a reaction device, and the nitrogen-doped carbon-supported heteropoly acid nanocomposite has mild reaction conditions, is low in cost and environment-friendly and has certain practical value.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention provides a preparation method of a nitrogen-doped carbon-loaded heteropoly acid nano composite material, which comprises the following steps:

(1) preparing a nitrogen-doped carbon nano material: mixing a mixture of 1: 1.5, dispersing melamine and 1, 4-diformylpiperazine in dimethyl sulfoxide, carrying out reaction at 165 ℃ for 72 hours, carrying out suction filtration, washing a filter cake with ethanol, tetrahydrofuran, acetone and dichloromethane in sequence, drying to obtain white powder, and carbonizing the white powder to obtain black powder, namely the nitrogen-doped carbon nano material;

(2) preparing a nitrogen-doped carbon-loaded heteropoly acid nano composite material: and (2) ultrasonically dispersing the nitrogen-doped carbon nano material prepared in the step (1) and heteropoly acid in an ethanol water solution, heating and stirring for 24h at 80 ℃, filtering, washing with deionized water, and vacuum drying for 12h at 80 ℃ to obtain the nitrogen-doped carbon supported heteropoly acid nano composite material.

Preferably, the carbonization in the step (1) is performed in a tubular furnace at 500-800 ℃, and the carbonization time is 2 h.

The beneficial effects of the above technical scheme are: the nitrogen-doped carbon nanomaterial is obtained by carbonizing a nitrogen-rich covalent organic framework material at high temperature, has high nitrogen content and more nitrogen defect sites, and has certain catalytic activity in the nitrobenzene hydrogenation reaction; meanwhile, the porous structure in the material is also beneficial to the heteropolyacid to be stably and uniformly dispersed in the cavity and pores of the carrier, so that the agglomeration is reduced and the catalytic efficiency can be increased.

Preferably, the heteropoly acid in the step (2) is PCuMo₁₁The mass ratio of the nitrogen-doped carbon nanomaterial to the heteropoly acid is 1: (0.5-1.5), more preferably 1: 1;

the heteropoly acid PCuMo₁₁The preparation method comprises the following steps:

saturated NaHCO is dripped into 0.1mol/L phosphomolybdic acid aqueous solution under the constant temperature condition of 50 DEG C₃Adjusting pH of the solution to 4-5, and adding 0.3mol/L CuSO₄·5H₂Stirring O water solution thoroughly for 30min, standing, evaporating to semi-thick, standing until colorless needle-like Na₂SO₄Separating out, collecting filtrate, separating out block crystal, recrystallizing to obtain heteropoly acid PCuMo₁₁. Wherein the phosphomolybdic acid aqueous solution and CuSO₄·5H₂The volume ratio of the O aqueous solution is 1: 1.

The beneficial effects of the above technical scheme are: the proper increase of the amount of the heteropoly acid is beneficial to the improvement of the catalytic activity, and the excessive heteropoly acid can cause the blockage of partial cavities or pores in the carrier, thereby influencing the catalytic effect.

The invention further provides an application of the nitrogen-doped carbon-supported heteropoly acid nano composite material in the technical scheme in the catalytic nitrobenzene hydrogenation reaction, and the application is characterized by comprising the following processes:

the nitrogen-doped carbon-supported heteropoly acid nano composite material is uniformly dispersed in an organic solvent, then reactant nitrobenzene and a reducing agent are added, and the mixture is heated and magnetically stirred for reaction.

Preferably, the organic solvent is one of ethanol, toluene and cyclohexane.

Preferably, the addition ratio of the nitrobenzene to the nitrogen-doped carbon-supported heteropoly acid nanocomposite is 0.5 mmol: (2.5-5) mg, and increasing the amount of catalyst appropriately promoted the conversion of nitrobenzene.

Preferably, the reducing agent is any one of hydrazine hydrate, sodium sulfide and hydrogen, preferably hydrazine hydrate, the reduction efficiency of the sodium sulfide is low, harmful gas is released during reaction, the hydrogen is flammable and explosive, the hydrazine hydrate is dangerous at high temperature and high pressure, the hydrazine hydrate is cheap and easy to obtain, the reaction conditions are easy to control, and the method is suitable for industrial production.

Preferably, the molar ratio of the nitrobenzene to the reducing agent is 1: (4-6).

Preferably, the reaction temperature is 60-80 ℃, preferably 70 ℃ and the reaction time is 1-15 min.

Compared with the prior art, the invention discloses a preparation method for loading heteropoly acid to a nitrogen-doped carbon nano material by an impregnation method to obtain the nitrogen-doped carbon-loaded heteropoly acid nano composite material and application of the nitrogen-doped carbon-loaded heteropoly acid nano composite material in nitrobenzene hydrogenation reaction, and the preparation method has the following beneficial effects:

in the aspect of catalyst preparation, the nitrogen-doped carbon-supported heteropoly acid nano composite material can be obtained by a simple and convenient impregnation method. Meanwhile, the preparation method of the carbon nano material doped with the carrier nitrogen and the heteropoly acid is simple, the raw materials are low in price, and the method is suitable for large-scale production.

In the aspect of catalyzing nitrobenzene hydrogenation reaction, the selected reducing agent hydrazine hydrate has high activity and wide industrial application. The catalytic reaction condition is mild, the conversion rate of nitrobenzene is high (99 percent), and the p-aniline has high selectivity>99.9%), high catalyst utilization (TOF 396 × 10)^-3mol·g^-1·h^-1) And has application value in industrial production process.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.

FIG. 1 attached drawing is PCuMo₁₁CC-700 and PCuMo₁₁FT-IR spectrum of @ CC-700;

FIG. 2 attached drawing is PCuMo₁₁SEM image of @ CC-700;

FIG. 3 is a drawing of PCuMo₁₁The line graph (a) and the line graph (b) of interruption experiment data of the @ CC-700 catalytic nitrobenzene hydrogenation reaction.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the following embodiments, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Preparing a nitrogen-doped carbon-loaded heteropoly acid nano composite material:

(1) preparing a nitrogen-doped carbon nano material: dispersing 300mg of melamine and 507mg of 1, 4-diformylpiperazine in 36mL of dimethyl sulfoxide solution, transferring the solution mixture to a reaction kettle at 165 ℃ for reaction for 72h, naturally cooling, performing suction filtration on the product, sequentially washing the product with ethanol, acetone, tetrahydrofuran and dichloromethane for multiple times, drying the product to obtain white powder, and carbonizing the white powder at the high temperature of 800 ℃ for 2h in a tubular furnace to obtain a carbon nano material CC-X (X represents the carbonization temperature, and X is 500, 600, 700 and 800);

(2) heteropolyacid PCuMo₁₁The preparation of (1): saturated NaHCO is added dropwise into 20mL of 0.1mol/L phosphomolybdic acid aqueous solution at constant temperature of 50 DEG C₃Adjusting pH of the mixture to 4-5, and adding 20mL of 0.3mol/L CuSO₄·5H₂Stirring O water solution at constant temperature of 50 deg.C for 30min, standing, evaporating at 50 deg.C until the solution is semi-thick, removing Na₂SO₄Collecting the crystal, collecting the filtrate, recrystallizing to obtain PCuMo₁₁A crystal;

(3) nitrogen-doped carbon-loaded heteropoly acid nanocomposite PCuMo₁₁Preparation of @ CC-X: 100mg of CC-X material is evenly dispersed in 90mL of ethanol water solution, 10mL of 10g/L PCuMo is added₁₁Stirring the aqueous solution for 24 hours at the temperature of 80 ℃, filtering, washing the aqueous solution for multiple times by deionized water, and drying the aqueous solution for 12 hours in vacuum at the temperature of 80 ℃ to obtain the catalyst PCuMo₁₁@CC-X。

The [email protected] CC-X catalyst prepared by the method is used for catalyzing nitrobenzene hydrogenation reaction, and the catalytic reaction comprises the following steps:

adding catalyst PCuMo into round-bottom flask equipped with reflux condenser and magnetic stirring₁₁@ CC-X, 4mL of organic solvent, 0.5mmol of nitrobenzene and 2-3mmol of hydrazine hydrate, heating, magnetically stirring, reacting for a certain time, sampling, filtering by a filter membrane, and detecting the conversion rate of nitrobenzene and the yield of aniline by gas chromatography.

Wherein, the gas phase detection conditions are as follows: the temperature of the gasification chamber is 240 ℃, the temperature of the detector is 280 ℃, the initial column temperature is 80 ℃, the temperature is increased to 160 ℃ at the speed of 10 ℃/min, the temperature is maintained for 1min, the temperature is increased to 240 ℃ at the speed of 20 ℃/min, and the temperature is maintained for 5 min.

Specific example differences and test results are shown in Table 1 below, with examples 1-14 of Table 1 representing different PCuMo' s₁₁The catalytic effect of @ CC-X in catalyzing nitrobenzene hydrogenation reaction.

In the table, when nitrobenzene is 0.5mmol and hydrazine hydrate is 2mmol, it is referred to as n (nitrobenzene): n (hydrazine hydrate) ═ 1: 4.

TABLE 1 PCuMo₁₁Evaluation data of @ CC-X catalytic nitrobenzene hydrogenation reaction

In table 1, example 1 is a blank experiment with no catalyst; experiment 2 is PCuMo₁₁Homogeneous catalysis nitrobenzene hydrogenation reaction; examples 3, 4, 5 and 6 are obtained by mixing PCuMo₁₁Catalyst PCuMo supported on nitrogen-doped carbon nanomaterial CC-X (X500, 600, 700, 800)₁₁The catalyst is prepared by the following steps of (1) catalyzing nitrobenzene hydrogenation reaction by @ CC-X (X ═ 500, 600, 700 and 800); the mass ratio of nitrobenzene to hydrazine hydrate in examples 5 and 7 is 1: 4. 1: 6; the solvents added in the reactions of examples 7, 8 and 9 are ethanol, toluene and cyclohexane respectively; the temperatures for catalyzing the nitrobenzene hydrogenation reaction in examples 7, 10 and 11 are 80, 70 and 60 ℃ respectively; the time for catalyzing hydrogenation reaction of nitrobenzene in examples 12, 13, 14 and 10 is 3min, 4min, 5min and 15min respectively.

Specifically, examples 1, 2, and 3 are blank, homogeneous, and heterogeneous experiments. From experimental data it can be seen that: in a blank experiment, nitrobenzene hydrogenation reaction can hardly be carried out; PCuMo₁₁When the catalyst is used as a homogeneous catalyst to catalyze the nitrobenzene hydrogenation reaction, the conversion rate of nitrobenzene is also low; when using PCuMo₁₁The catalytic activity of the @ CC-500 catalyst in the hydrogenation reaction of nitrobenzene is obviously improved. Thus, it can be known that PCuMo₁₁@ CC-X is a catalyst more suitable for catalyzing hydrogenation of nitrobenzene to prepare aniline.

The carbonization temperatures in the synthesis processes of the carbon-doped nano materials CC-X in the examples 3, 4, 5 and 6 are different, and PCuMo₁₁The loading and catalytic reaction conditions are the same. With the increase of the carbonization temperature, the graphitization degree of the catalyst is increased, and as can be seen from experimental data,PCuMo₁₁the @ CC-700 has better catalytic effect in catalyzing nitrobenzene hydrogenation reaction, so the carbonization temperature is preferably 700 ℃.

In examples 5 and 7, PCuMo was used₁₁The @ CC-700 is used as a catalyst, but the dosage of hydrazine hydrate added as a reducing agent is different, and other catalytic reaction conditions are the same. According to experimental data, increasing the dosage of the reducing agent hydrazine hydrate can promote the conversion of nitrobenzene and improve the yield of aniline. It is therefore preferred that the mass ratio of nitrobenzene to hydrazine hydrate is 1: 6.

the catalytic reaction conditions of examples 7, 8 and 9 are the same, except that the organic solvent used in the catalytic system is ethanol, toluene or cyclohexane. From the experimental data, the polarity of the solvent has a great influence on the conversion of nitrobenzene. In contrast, the nitrobenzene conversion is highest in the most polar ethanol solvent after the reaction is complete.

The catalytic reaction conditions in examples 7, 10 and 11 were the same, except that the reaction temperature of the catalytic system was 80 deg.C, 70 deg.C and 60 deg.C, respectively. According to experimental data, the increase of the reaction temperature is beneficial to the conversion of nitrobenzene, the conversion rate of the nitrobenzene can reach 99% at the temperature of 70 ℃, and the TOF value of the catalyst is only 4 multiplied by 10 different from that of the catalyst at the temperature of 80 DEG C^-3mol/(g.h). In order to reduce the energy consumption, the optimal reaction temperature is 70 ℃.

The catalytic reaction conditions of examples 12, 13, 14 and 10 are the same, and the differences are only that the catalytic reaction time is 3min, 4min, 5min and 15min respectively. As can be seen from the experimental data, the yield of aniline increases significantly with increasing reaction time.

In addition, the invention also relates to PCuMo₁₁CC-700 and PCuMo₁₁@ CC-700 Infrared Spectroscopy test was performed, see FT-IR characterization Spectrum of FIG. 1, 806cm^-1The peak at (A) belongs to PCuMo₁₁Characteristic peak of (C), PCuMo₁₁@ CC-700 keeps the characteristic peak (1616 cm) of CC-700 nitrogen-doped carbon nano-material^-1). No PCuMo was observed due to the strong characteristic absorption peak of CC-700₁₁Other characteristic absorption peaks.

Referring to FIG. 2, is catalyst PCuMo₁₁SEM image of @ CC-700. As can be seen, the morphology of the composite material is nano spherical particles.

See FIG. 3 for PCuMo₁₁Line graph of interruption data of @ CC-700 catalytic nitrobenzene hydrogenation reaction. Wherein the a-curve is 5mg PCuMo₁₁The catalyst is prepared by the following steps of putting a @ CC-700 catalyst in 4mL of ethanol solvent, wherein the catalytic molar ratio is 1: 6 nitrobenzene and hydrazine hydrate, the aniline production varies with the reaction time. The b-curve is a line graph of the aniline production as a function of reaction time after the reaction was interrupted for 5 min. Comparison of the curves a and b in FIG. 3 illustrates PCuMo₁₁The @ CC-700 has good stability in the reaction system, and is a high-efficiency catalyst for preparing aniline by nitrobenzene hydrogenation.

The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.