Catalyst for tandem ammonia borane dehydrogenation and nitro-aromatic hydrogenation reaction as well as preparation method and application of catalyst
By enriching the catalyst of palladium nanoparticles in porous nitrogen-doped carbon materials, the problem of the decrease in activity of palladium-based catalysts under harsh conditions is solved, and the efficient and selective ammonia borane dehydrogenation and nitroaromatic hydrocarbon hydrogenation reaction is achieved, which significantly improves the catalytic activity and stability.
Patent Information
- Application Number
- CN202510414575.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-03
- Publication Date
- 2025-06-27
AI Technical Summary
Existing palladium-based catalysts are prone to aggregation, migration and oxidation under harsh reaction conditions, resulting in a decrease in catalytic activity, low hydrogen solubility, low selectivity and slow rate of alcohol reduction reactions.
A catalyst for enriching palladium nanoparticles in porous nitrogen-doped carbon material (NC) was designed, palladium precursors were encapsulated in pores of NC by reverse dual solvent method, and highly dispersed Pd NPs were formed by reducing sodium borohydride.
The catalyst uses water as the solvent and ammonia borane as the hydrogen source at room temperature. It can efficiently reduce nitroaromatic hydrocarbons within 3 minutes, with a conversion rate and selectivity reaching 99.9%. Its turnover frequency (TOF) value is as high as 39415 h-1, which significantly improves catalytic activity and stability.
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention relates to a preparation method and application of a catalyst, specifically to a preparation method and application of an efficient palladium catalyst for tandem dehydrogenation of ammonia borane and hydrogenation of nitroaromatics. Background Art
[0002] Functionalized aromatic amines are important intermediates for synthesizing high-value-added products in the fields of fine chemicals, rubber, agrochemicals, and pharmaceuticals. The traditional method for synthesizing aromatic amines is to hydrogenate nitroaromatics under high-pressure hydrogen conditions in a transition metal-based catalyst system. Among them, palladium-based catalysts are widely used due to their excellent catalytic activity. However, under harsh reaction conditions (strong acids, strong bases, high temperatures), palladium metal sites are prone to aggregation, migration, and oxidation, resulting in a decrease in catalytic activity. Poor stability and high cost limit the widespread application of palladium-based catalysts. Therefore, designing and synthesizing noble metal catalysts with both high stability and high activity is an important challenge at present.
[0003] The reduction of nitroaromatics using hydrogen as a hydrogen source requires high-pressure and high-temperature conditions, and hydrogen has low solubility in most solvents. Alcohols (isopropanol, ethanol) can also be used as hydrogen sources to promote the effective contact between the reducing agent and the substrate. However, the reduction reaction of alcohols has problems of low selectivity and slow rate. Therefore, in-situ generation of hydrogen for the hydrogenation of nitroaromatics in a one-pot reaction is an effective method to solve the above problems. Compared with hydrogen and alcohols, ammonia borane (NH3BH3) has become an ideal hydrogen substitute due to its high hydrogen capacity, non-toxicity, stability, and high solubility in water and alcohol solvents. Noble metals can catalyze the controlled release of hydrogen from ammonia borane. Therefore, cascading the dehydrogenation of ammonia borane and the hydrogenation of nitroaromatics can achieve the efficient reduction of nitroaromatics. Summary of the Invention
[0004] The present invention aims to provide a catalyst, a preparation method, and an application thereof that can be used for the dehydrogenation of ammonia borane and the hydrogenation of nitroaromatics.
[0005] The catalyst for tandem dehydrogenation of ammonia borane and hydrogenation of nitroaromatics in the present invention is a porous nitrogen-doped carbon material with palladium nanoparticles uniformly enriched in its pores, having a specific surface area of 120.18 m 2 / g and an average pore diameter of 4 - 6 nm.
[0006] The preparation method of the catalyst of the present invention is characterized in that the porous nitrogen-doped carbon material is dispersed in water, and then a dichloromethane solution containing Pd(AcO)2 is added thereto. After sufficient stirring, the palladium acetate precursor is encapsulated in the pores of the porous nitrogen-doped carbon material by the reverse double-solvent method. Then, an aqueous sodium borohydride solution is added to the above solution for reduction, and then the catalyst is obtained after filtration, washing, and drying.
[0007] Preferably, the method for preparing the catalyst of the present invention is as follows: Dissolve 15 g of ammonium citrate and 4.786 g of NaCl in 50 mL of water. After stirring for 2 hours, add 100 mL of an ethanol solution (the volume ratio of ethanol to water is 8:1), and continue stirring for 1 hour to form a white precipitate. After filtering and drying the precipitate, pyrolyze it at 450 °C for 2 hours under a nitrogen atmosphere, then pyrolyze it at 600 °C for 2 hours, and finally wash it with water to remove NaCl. After drying, a porous nitrogen-doped carbon material is obtained; Then disperse 30 mg of the porous nitrogen-doped carbon material in 30 mL of water, add 0.24 mL of a dichloromethane solution in which 0.0898 g of Pd(AcO)2 is dissolved. The two solutions are mixed and stirred overnight. The palladium precursor is encapsulated into the pores of NC by the reverse double-solvent method. Then, add 2 mL of an aqueous solution of NaBH4 (3 M) to the solution and stir for 4 hours for reduction. After filtering, washing, and drying, the catalyst of the present invention is obtained, hereinafter briefly referred to as the Pd@NC catalyst.
[0008] The catalyst of the present invention is used for the tandem dehydrogenation of ammonia borane and hydrogenation of nitroarene.
[0009] The nitrogen atoms (especially pyridine nitrogen) in the catalyst of the present invention can effectively anchor palladium nanoparticles, prevent their aggregation and migration, and improve the stability of the catalyst. The catalyst has excellent hydrophobicity, which is beneficial to the adsorption of reactants and the desorption of products, thereby improving the reaction efficiency.
[0010] The catalyst of the present invention has the following advantages: Green synthesis: Throughout the synthesis process, water is used as the solvent, avoiding the use of organic solvents, which conforms to the concept of green chemistry.
[0011] High activity: The Pd@NC catalyst exhibits excellent activity towards the tandem reaction of ammonia borane dehydrogenation and nitroarene hydrogenation. At room temperature, using water as the solvent and ammonia borane as the hydrogen source, the catalyst can efficiently reduce nitroarene within 3 minutes, and both the conversion rate and selectivity reach 99.9%. Its turnover frequency (TOF) value is as high as 39415 h -1 , for this reaction, its activity is 9 - 1713 times that of other reported Pd-based catalysts. For example, the currently reported catalyst with the best activity, Pd1 / In2O 3-x (Appl.Catal. B-Environ. 2022, 313.), has a TOF value of 4286 h-1, and the activity of the Pd@NC catalyst is 9 times that of it.
[0012] High selectivity: The catalyst has a wide applicability to various nitroarene substrates, and no dehalogenation occurs during the reduction reaction of halogenated nitroarenes (X = F, Cl, and Br), showing excellent functional group tolerance.
[0013] High stability: The catalyst has good cyclic stability. After 6 cycles of use, the catalytic activity remains above 96%. Description of the Drawings
[0014] Figure 1 Flow chart of the Pd@NC catalyst prepared in Example 1 of the present invention.
[0015] Figure 2 TEM and SEM images of the Pd@NC catalyst prepared in Example 1 of the present invention.
[0016] Figure 3 XRD pattern of the Pd@NC catalyst prepared in Example 1 of the present invention.
[0017] Figure 4 N2 adsorption - desorption isotherm and pore size distribution diagram of the Pd@NC catalyst prepared in Example 1 of the present invention.
[0018] Figure 5 XPS spectrum of the Pd@NC catalyst prepared in Example 1 of the present invention.
[0019] Figure 6 Cyclic stability test results of the Pd@NC catalyst prepared in Example 1 of the present invention. Detailed Description of the Invention
[0020] Dissolve 15 g of ammonium citrate and 4.786 g of NaCl in 50 mL of water. After stirring for 2 hours, add 100 mL of ethanol solution (volume ratio of ethanol to water is 8:1), and continue stirring for 1 hour to form a white precipitate. After filtering and drying the precipitate, pyrolyze it at 450 °C for 2 hours in a nitrogen atmosphere, then pyrolyze it at 600 °C for 2 hours, and finally wash it with water to remove NaCl, and obtain a porous nitrogen - doped carbon material after drying.
[0021] Disperse 30 mg of the porous nitrogen - doped carbon material in 30 mL of water, and add 0.24 mL of dichloromethane solution dissolved with 0.0898 g of Pd(AcO)2. Mix and stir the two solutions overnight. Since NC has a large number of hydrophobic pores and nitrogen coordination sites, the Pd(AcO)2 droplets dissolved in dichloromethane can be enriched in the pores by capillary force, and a large amount of water solvent is beneficial to the suspension and impregnation process of NC, enriching the palladium precursor into the pores of NC, that is, the reverse double - solvent method. After reduction with sodium borohydride, highly dispersed Pd NPs are confined in the pore structure of NC instead of being deposited on the surface of NC. Subsequently, add 2 mL of NaBH4 (3 M) aqueous solution, stir for 4 hours for reduction, and obtain the Pd@NC catalyst after filtration, washing and drying.
[0022] Disperse 1 mg of Pd@NC catalyst in 2 mL of water, add 0.2 mmol of nitroarene substrate, and then inject 1 mL of aqueous ammonia borane solution (25 mg / mL). Stir for 3 minutes at room temperature. After the reaction is completed, analyze the products by gas chromatography-mass spectrometry (GC-MS).
[0023] The catalyst exhibits excellent catalytic activity towards a variety of nitroarene substrates, with both the conversion rate and selectivity reaching 99.9%. The reduction reaction of halogenated nitroarenes (X = F, Cl, and Br) does not show dehalogenation, indicating excellent functional group tolerance.
[0024]
[0025] When the Pd@NC catalyst is used for the reduction reaction of nitrobenzene, the catalytic activity remains above 96% after 6 cycles of use, indicating that the catalyst has good cycle stability.
Claims
1. A catalyst for the series reaction of ammonia borane dehydrogenation and nitro aromatic hydrogenation, characterized in that The catalyst is a porous nitrogen-doped carbon material with palladium nanoparticles uniformly enriched in its pores, and its specific surface area is 120.18 m 2 / g, the average pore size is 4-6 nm.
2. The method for preparing the catalyst according to claim 1, characterized in that The porous nitrogen-doped carbon material is dispersed in water, and then a dichloromethane solution containing palladium acetate (Pd(AcO)2) is added thereto. After sufficient stirring, the palladium acetate precursor is encapsulated in the pores of the porous nitrogen-doped carbon material by a reverse double solvent method. Then, a sodium borohydride aqueous solution is added to the aforementioned solution for reduction, and finally, the catalyst is obtained after filtering, washing and drying.
3. The method for preparing a catalyst according to claim 2, characterized in that Dissolve 15 g of ammonium citrate and 4.786 g of NaCl in 50 mL of water, stir for 2 hours, add 100 mL of ethanol solution (the volume ratio of ethanol to water is 8:1), continue stirring for 1 hour, and a white precipitate is formed. After filtering and drying the precipitate, pyrolyze it at 450 °C for 2 hours in a nitrogen atmosphere, and then pyrolyze it at 600 °C for 2 hours. Finally, wash with water to remove NaCl, and dry it to obtain a porous nitrogen-doped carbon material; Then, 30 mg of porous nitrogen-doped carbon material was dispersed in 30 mL of water, and 0.0898 g of Pd(AcO)2 solution dissolved in 0.24 mL of dichloromethane was added. The two solutions were mixed and stirred overnight. The palladium acetate precursor was encapsulated into the pores of NC by the reverse double solvent method. Then, 2 mL of NaBH4 (3 M) aqueous solution was added to the solution and stirred for 4 hours for reduction. The Pd@NC catalyst was obtained after filtration, washing and drying.
4. The catalyst according to claim 1 is used for the series reaction of ammonia borane dehydrogenation and nitroaromatic hydrogenation.