Boron-doped titanium-based supported catalyst as well as preparation and application thereof

Abstract

The invention discloses a preparation method of a boron-doped titanium-based supported catalyst, and belongs to the technical field of catalytic materials and organic synthesis.The preparation method of the boron-doped titanium-based supported catalyst comprises the steps that tetrabutyl titanate and terephthalic acid serve as precursors, a titanium-containing MOF precursor is synthesized through a solvothermal method, then a boron source is introduced to achieve in-situ doping of the boron element, and the boron-doped titanium-based supported catalyst is obtained. Then loading metal on the boron-doped MOF precursor in a monatomic form through an impregnation-coordination-high-temperature pyrolysis process; according to the invention, the electron structure and pore characteristics of the carrier are regulated and controlled through boron doping, and the catalyst is endowed with excellent catalytic performance in combination with high exposure active sites of monatomic metal; the catalyst can efficiently catalyze nitro compounds to be reduced to generate corresponding amines under the conditions of no solvent or existence and mild hydrogenation, the yield of target products is larger than 90%, the conversion rate is larger than 95%, the catalyst is simple in preparation process and high in stability, pollution and safety risks caused by organic solvents can be avoided, the requirements of green chemical development are met, and the method is suitable for industrial production. The method is suitable for large-scale production in the fields of fine chemical engineering, pharmacy and the like.

Description

A boron-doped titanium-based supported catalyst, its preparation and application Technical Field

[0001] This invention belongs to the field of organic catalysis and green hydrogenation technology, specifically relating to a method for preparing a boron-doped titanium-based supported catalyst, and the application of this catalyst in the selective hydrogenation reduction of nitro compounds to amine compounds. Background Technology

[0002] The hydrogenation reduction reaction of nitro compounds is a key unit reaction in the field of organic synthesis. Its products, aromatic amines, are widely used in many high-value-added industries such as pharmaceutical intermediates, dyes and pigments, rubber additives, and pesticides and chemicals, playing an irreplaceable role in the upgrading and development of the fine chemical industry (Journal of the American Chemical Society 2024146(43), 29315-29324). For example, aniline, as the core product of nitrobenzene hydrogenation (Adv.Sci. 2025, 12, e11391), is a key raw material for the synthesis of MDI (diphenylmethane diisocyanate), rubber antioxidants, and dye intermediates, with a global annual demand of over 10 million tons; aromatic amines containing substituents (such as o-toluidine, p-chloroaniline, 2-aminophenol, etc.) are core components in the synthesis of specialty dyes and pharmaceutical raw materials, with extremely high market added value. However, existing hydrogenation reduction technologies for nitro compounds still face many bottlenecks: firstly, insufficient catalyst selectivity. Traditional precious metal catalysts (such as Pd / C and Pt / Al2O3) have high activity, but when hydrogenating nitroaromatics containing sensitive substituents (such as chlorine, hydroxyl, and methyl), they are prone to side reactions such as dehalogenation and over-hydrogenation, resulting in a target product yield of less than 90%, which is difficult to meet the stringent purity requirements (≥99.5%) of industries such as pharmaceuticals and electronic chemicals. Secondly, the performance of non-precious metal catalysts is limited. Industrially used Raney nickel and cobalt-based catalysts require high temperature and high pressure conditions to achieve effective activity, which not only increases energy consumption but also poses safety risks such as equipment corrosion and hydrogen leakage; at the same time, these catalysts are prone to agglomeration and deactivation, resulting in short service life (Exploration of the service life of Raney nickel catalysts for hydrogenation reaction [J]. Petrochemical Technology, 2017, 24 (11): 258-259.), leading to high industrial production costs. Third, the catalyst preparation process is complex. Existing single-atom or nanoparticle catalysts are mostly prepared by impregnation or precipitation methods, which have problems such as poor metal dispersion, low utilization of active sites, and insufficient stability, making it difficult to balance catalytic activity and recyclability. Summary of the Invention

[0003] To address the problems existing in the prior art, this invention provides a boron-doped titanium-based supported catalyst and its preparation method. The catalyst uses a MOF precursor containing titanium vacancies as a substrate, introduces boron through ligand exchange, loads a metal through ion exchange, and is prepared by calcination in a hydrogen / nitrogen mixed atmosphere. It simultaneously contains a single metal atom (M). SA ) and nanoparticles (M NP The active site, with boron doped in the form of lattice substitution, can efficiently activate hydrogen and nitro compounds, achieving selective reduction of nitro groups to amino groups. The preparation process is simple, stable, and exhibits excellent recyclability. The preparation method of the boron-doped titanium-based supported catalyst of this invention is as follows: 1. Add anhydrous methanol to a terephthalic acid-N,N-dimethylformamide dispersion, mix well, and then add tetrabutyl titanate dropwise under stirring. Transfer the mixture to a reaction vessel, seal it, heat at 90-140℃ for 12-36 h, and then naturally cool to room temperature. Centrifuge to collect the solid product, wash and dry it, and vacuum dry to obtain the titanium-containing MOF precursor; the mass-to-volume ratio of terephthalic acid to tetrabutyl titanate is 2-3:1 (g:mL). The mass-to-volume ratio of acid to anhydrous methanol (g:mL) is 1:1-3; 2. Anhydrous methanol and titanium-containing MOF precursor are added to 4-carboxyphenylboronic acid-DMF solution or 4-hydroxyphenylboronic acid-DMF solution. After ultrasonic dispersion, the dispersion is transferred to a reaction vessel, sealed, and heated at 90-140℃ for 12-36 hours. After cooling to room temperature, the solid is collected by centrifugation, washed with DMF and anhydrous methanol, and vacuum dried to obtain the boron-doped MOF precursor; wherein: 4-carboxyphenylboronic acid or 4-hydroxyphenylboronic acid: The mass-to-volume ratio of anhydrous methanol (g:mL) is 1:8-11, and the mass ratio of 4-carboxyphenylboronic acid or 4-hydroxyphenylboronic acid to titanium-containing MOF precursor is 1:1-3. 3. Disperse the boron-doped MOF precursor in deionized water, add a metal salt solution, stir at room temperature for 10-16 h, collect the solid by centrifugation, wash the solid with deionized water until the filtrate is neutral, vacuum dry at 60-80 ℃, and calcine the dried product at 350-700 ℃ for 2-6 h (heating rate 2-5 ℃ / min) in a N2 atmosphere containing 10% H2 to obtain the boron-doped titanium-based supported catalyst M-TiO2-B. The metal salt is one or more of nickel, cobalt, iron, and copper salts, and the amount of metal salt added is 1-20% of the mass of the boron-doped MOF precursor.

[0004] The boron-doped titanium-based supported catalyst prepared by the above method is used in the catalytic reduction of nitro compounds to prepare amines. Specifically, under a hydrogen atmosphere, at 100-120°C, and with or without a solvent, the catalyst is mixed with a nitro compound and subjected to a hydrogenation reduction reaction to obtain the target amine product. The nitro compound is selected from nitrobenzene, o-nitrotoluene, p-nitrochlorobenzene, m-nitrobenzyl alcohol, m-nitrotoluene, m-iodo-nitrobenzene, 2,5-dimethylnitrobenzene, m-fluoro-nitrobenzene, 3-nitro-o-xylene, m-chloronitrobenzene, and p-nitrotoluene. The catalyst of this invention has high catalytic activity and can accurately achieve selective reduction of nitro groups, avoiding side reactions of substituents. The advantages and technical effects of this invention are as follows: 1. High atom utilization: By maximizing the utilization of metal atoms, reducing the cost of precious metals, and minimizing side reactions and pollutant emissions in the hydrogenation reaction of nitro compounds with low metal loading, atom economy and catalytic efficiency are synergistically optimized. 2. Excellent catalytic performance: The catalyst possesses both metal single-atom and nanoparticle active sites. The synergistic effect of boron doping and titanium vacancies can efficiently activate hydrogen and nitro compounds, resulting in high yield (>90%) and high conversion rate (>95%) of the target product. It exhibits outstanding resistance to side reactions, especially for nitro aromatics containing sensitive substituents. 3. Good stability: The synergistic effect of boron doping and carbon material matrix inhibits the agglomeration and deactivation of metal active sites. After five cycles of catalyst recycling, the activity and selectivity remain stable (decline <3%). 4. Wide applicability: It can catalyze the hydrogenation reduction of various nitro compounds such as nitrobenzene, o-nitrotoluene, p-nitrochlorobenzene, and 2-nitrophenol. It is particularly suitable for the synthesis of high-value-added substituted aromatic amines and has broad application prospects.

[0005] Therefore, this invention provides a hydrogenation reduction catalyst for nitro compounds that has a simple preparation process, high catalytic activity, strong selectivity, and good stability. It has important practical significance and industrial application value for promoting the development of the green chemical industry and reducing the production cost of high value-added amine compounds. Attached Figure Description

[0006] Figure 1 shows the Ni catalyst prepared in Example 1. （3） X-ray diffraction pattern of TiO2-B. Detailed Implementation

[0007] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. However, the scope of protection of the present invention is not limited to the contents described. Unless otherwise specified, the reagents and methods used in the embodiments are all conventional reagents and conventional methods. Example 1: Preparation and application of boron-doped titanium-based supported catalyst Ni-TiO2-B. At room temperature, 3g of terephthalic acid and 54mL of DMF were mixed and stirred for 15min. Then, 6mL of anhydrous methanol was added, and 1.25mL of tetrabutyl titanate was added dropwise while stirring. After the addition was completed, the mixture was stirred for 10min. The mixture was transferred to a 100mL hydrothermal reactor and sealed. After reacting at 130℃ for 20h, it was naturally cooled to room temperature. The solid product was collected by centrifugation. The solid was washed three times each with DMF and methanol to obtain a white titanium-containing MOF precursor. 0.5g of 4-hydroxyphenylboronic acid and 45mL of DMF were mixed and stirred at room temperature for 10min. Then, 5mL of anhydrous methanol and 1g of titanium-containing MOF precursor were added. After ultrasonic dispersion for 10min, the mixture was transferred to a 100mL hydrothermal reactor. The mixture was sealed in a mL hydrothermal reactor and reacted at 130℃ for 20 h. After natural cooling to room temperature, the solid was collected by centrifugation and washed three times each with DMF and methanol to obtain a grayish-white boron-doped MOF precursor. At room temperature, 0.3 g of the grayish-white boron-doped MOF precursor and 30 mg of nickel chloride hexahydrate were dispersed in 30 mL of deionized water and stirred for 12 h. The solid was collected by centrifugation and washed with deionized water until neutral. It was then vacuum dried at 60℃ for 12 h. The dried material was placed in a quartz boat in a tubular furnace, and the air inside the furnace was replaced four times with a 10% H2 / N2 mixed gas. The temperature was then increased to 400℃ at a rate of 3℃ / min and calcined at this temperature for 3 h to obtain a boron-doped titanium-based supported catalyst Ni. （3） -TiO2-B; its X-ray diffraction pattern is shown in Figure 1. From the figure, it can be seen that Ni （3） The TiO2-B catalyst is mainly composed of the anatase phase of titanium dioxide. No diffraction peaks related to nickel species were detected, indicating that nickel species are well and uniformly dispersed in the catalyst. Furthermore, nickel is distributed on the support surface in the form of atomic-level dispersion or ultra-small nanoparticles (<2nm). This means that nickel can expose more isolated active sites, and the density of sites that can participate in the reaction per unit mass of nickel is much higher than that of large-particle nickel, thus improving catalytic efficiency.

[0008] Simultaneously prepare catalyst Ni （0.5） -TiO2-B、Ni （1） -TiO2-B、Ni （2） -TiO2-B、Ni （4） -TiO2-B、Ni （5） -TiO2-B, the method is the same as above, the difference is that the amount of nickel chloride hexahydrate added is 5mg, 10mg, 20mg, 40mg, 50mg.

[0009] 2. Add 1.2g of nitrobenzene and 0.05g of the above catalyst to a closed high-pressure reactor, mix thoroughly, without adding any solvent, purge with hydrogen four times to remove air and maintain a hydrogen pressure of 3.5MPa, heat and stir at 120℃ for 1.5h-5h for reduction reaction, filter the reaction solution with an organic filter head, and detect by gas chromatography (Agilent 7860A). The results are shown in the table below. .

[0010] Example 2: Preparation and Application of Co-TiO2-B Catalyst 1. Catalyst preparation was the same as step 1 in Example 1, except that 30 mg of nickel chloride hexahydrate was replaced with 38 mg of cobalt nitrate hexahydrate to obtain catalyst Co-TiO2-B; 2. 1.2 g of nitrobenzene and 0.05 g of catalyst Co-TiO2-B were added to a closed high-pressure reactor and mixed evenly. No solvent was added. The reactor was purged with hydrogen four times to remove air and maintained at a hydrogen pressure of 3.5 MPa. The reactor was heated and stirred at 120°C for 8 hours for reduction. The reaction solution was filtered through an organic filter and analyzed by gas chromatography (Agilent 7860A). The yield of aniline was 90.5%.

[0011] Example 3: Preparation and Application of NiM-TiO2-B Catalyst 1. Preparation of Titanium-containing MOF Precursor and Boron-doped MOF Precursor: Same as in Example 1; 0.3g of boron-doped MOF precursor, 15mg of nickel chloride hexahydrate, and 19mg of cobalt nitrate hexahydrate were dispersed in 30mL of deionized water and stirred for 12h. The solid was collected by centrifugation, washed with deionized water until neutral, and vacuum dried at 60℃ for 12h. The dried material was placed in a quartz boat in a tubular furnace, and the air inside the furnace was replaced four times with a 10% H2 / N2 mixed gas. The temperature was then increased to 400℃ at a rate of 3℃ / min and calcined at this temperature for 3h to obtain the boron-doped titanium-based supported catalyst NiCo-TiO2-B. Simultaneously, catalysts NiFe-TiO2-B and NiCu-TiO2-B were prepared using the same method, except that 19mg of cobalt nitrate hexahydrate was replaced with 20.3mg of cobalt nitrate hexahydrate. 1. Ferric chloride hexahydrate and 17.1 mg copper nitrate trihydrate; 2. Aniline was prepared by catalytic reduction of nitrobenzene using the above catalysts, in the same manner as in Example 1. The aniline yield of catalyst NiCo-TiO2-B was 90.5%, that of catalyst NiFe-TiO2-B was 97.3%, and that of catalyst NiCu-TiO2-B was 96.4%.

[0012] Example 4: Ni catalyst in Example 1 （3）Catalytic reduction reaction of TiO2-B on different nitro compounds: 1 mmol substrate, 5 mL anhydrous ethanol, 1 MPa hydrogen, 120 °C, 50 mg catalyst; the reaction solution was filtered through an organic filter and detected by gas chromatography (Agilent 7860A). The results are shown in the table below.

[0013] The results in the table above fully demonstrate the effectiveness of the Ni catalyst of this invention. （3） -TiO2-B exhibits broad applicability and high catalytic activity to nitro compounds with different substituents (electron-withdrawing / electron-donating, aromatic ring / side chain).

[0014] Example 5: Catalyst Cycling Experiment In practical applications, the cyclic stability of a catalyst is also one of the criteria for evaluating its quality. The Ni catalyst from Example 1 was used. （3） The performance of the TiO2-B catalyst in terms of cycle stability was evaluated as follows: 50 mg of catalyst, 1 mmol of nitrobenzene, and 5 mL of anhydrous ethanol were added to a high-pressure reactor. After replacing the air with hydrogen 5-6 times, 1 MPa of H2 was introduced, the autoclave was heated to 120 °C, and the reaction was stirred at 600 r / min for 2 h. After the reaction was completed, the reaction solution was centrifuged, the solid was washed three times with ethanol, and then dried overnight in a vacuum oven at 50 °C. The obtained catalyst was used for the next reaction. After filtering the reaction solution with an organic filter, the results were analyzed by gas chromatography (Agilent 7860A). The results are shown in the table below.

[0015] The catalyst can be recycled 5 times, and the yield of aniline decreases by ≤3%, indicating that the catalyst has excellent stability.

[0016] The above description of the embodiments is only for the purpose of helping to understand the method and core idea of ​​the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principle of the present invention, and these improvements and modifications should all fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a boron-doped titanium-based supported catalyst, characterized in that, The steps are as follows: (1) Add anhydrous methanol to the terephthalic acid-N,N-dimethylformamide dispersion, mix well, add tetrabutyl titanate dropwise under stirring, transfer the mixture to a reaction vessel and seal it, heat at 90-140℃ for 12-36h, cool naturally to room temperature, collect the solid product by centrifugation, wash and dry, and vacuum dry to obtain the titanium-containing MOF precursor; (2) Add anhydrous methanol and the titanium-containing MOF precursor to 4-carboxyphenylboronic acid-DMF solution or 4-hydroxyphenylboronic acid-DMF solution, disperse by ultrasonication, transfer the dispersion to a reaction vessel, seal it and heat at 90-140℃ for 12-36h, cool to room temperature, collect the solid by centrifugation, wash, and vacuum dry to obtain the boron-doped MOF precursor; (3) Disperse the boron-doped MOF precursor in deionized water, add metal salt solution, stir at room temperature for 10-16h, collect the solid by centrifugation, wash the solid, vacuum dry, and dry the dried product containing 10% Boron-doped titanium-based supported catalyst was prepared by calcination at 350-700℃ for 2-6 hours under a N2 atmosphere of H2; the metal salt is one or more of nickel salt, cobalt salt, iron salt, and copper salt.

2. The method for preparing the boron-doped titanium-based supported catalyst according to claim 1, characterized in that: The mass-to-volume ratio of terephthalic acid to tetrabutyl titanate (g:mL) is 2-3:1, and the mass-to-volume ratio of terephthalic acid to anhydrous methanol (g:mL) is 1:1-3.

3. The method for preparing the boron-doped titanium-based supported catalyst according to claim 1, characterized in that: The mass-to-volume ratio of 4-carboxyphenylboronic acid or 4-hydroxyphenylboronic acid to anhydrous methanol (g:mL) is 1:8-11, and the mass ratio of 4-carboxyphenylboronic acid or 4-hydroxyphenylboronic acid to titanium-containing MOF precursor is 1:1-3.

4. The method for preparing the boron-doped titanium-based supported catalyst according to claim 1, characterized in that: The amount of metal salt added is 1-20% of the mass of the boron-doped MOF precursor.

5. The boron-doped titanium-based supported catalyst prepared by the method of any one of claims 1-4.

6. The application of the boron-doped titanium-based supported catalyst according to claim 5 in the catalytic reduction of nitro compounds to prepare amines.

7. The application according to claim 6, characterized in that: Nitro compounds are selected from nitrobenzene, o-nitrotoluene, p-nitrochlorobenzene, m-nitrobenzyl alcohol, m-nitrotoluene, m-iodo-nitrobenzene, 2,5-dimethylnitrobenzene, m-fluoro-nitrobenzene, 3-nitro-o-xylene, m-chloronitrobenzene, and p-nitrotoluene.

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