A supported ruthenium nanocluster catalyst Ru / CNT@CN, a preparation method and application thereof

Abstract

The application belongs to the technical field of catalysts, and discloses a supported ruthenium nanocluster catalyst Ru / CNT@CN, a preparation method and application thereof. The catalyst takes carboxylated carbon nanotubes as a carrier, has a carbon nitride shell outside the carrier, and has ruthenium nanoclusters inlaid on the surface of the carbon nitride shell in situ. The preparation steps are as follows: (1) a mixed acid solution composed of concentrated nitric acid and concentrated sulfuric acid is used to perform oxidation treatment on multi-walled carbon nanotubes, and the carbon nanotubes are washed and dried to obtain carboxylated carbon nanotubes, denoted as CNT; (2) first, the CNT, DCD, Ru metal salt and water are stirred at 50-100 DEG C for 2-12 h to obtain a dispersion liquid; then, the dispersion liquid is frozen with liquid nitrogen and subjected to freeze-drying treatment to obtain a catalyst precursor CNT@DCD-Ru; finally, the CNT@DCD-Ru is annealed at 500-700 DEG C for 2-8 h in a hydrogen-inert gas mixed atmosphere to obtain the target catalyst Ru / CNT@CN. The catalyst is applied in the hydrogen production by ammonia borane hydrolysis or the transfer hydrogenation reaction of nitroaromatic compounds. The catalyst prepared by the application has excellent catalytic activity and stability.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a supported ruthenium nanocluster catalyst Ru / CNT@CN, its preparation method, and its application. Background Technology

[0002] Aromatic amines are important intermediates in the synthesis of various dyes, polymers, pharmaceuticals, antioxidants, agrochemicals, and other fine chemicals. Hydrogenation of nitroaromatic compounds using hydrogen is the primary method for producing aromatic amines. However, due to the low solubility of hydrogen in various solvents, the hydrogenation of nitroaromatic compounds typically requires high-temperature and / or high-pressure hydrogen conditions. Furthermore, maximizing the contact between hydrogen and nitroaromatic compounds is a prerequisite for improving catalytic reaction efficiency. To address this challenge, hydrogen transfer reduction using hydrogen storage materials such as sodium borohydride, ammonia borane (AB), formic acid, and hydrazine hydrate is a suitable solution. In this reaction system, the active hydrogen or hydrogen gas generated in situ by the hydrogen storage material under the action of a catalyst readily and immediately reacts with the nitro group, improving reaction efficiency. Among these, AB, with its high hydrogen capacity (up to 19.6 wt%), excellent stability, safety, and non-toxicity, is an excellent hydrogen source for the transfer hydrogenation of nitroaromatic compounds. The use of AB for the transfer hydrogenation of nitroaromatic compounds is expected to significantly increase the reaction rate.

[0003] Supported metal clusters (SMCs), which utilize metal clusters stabilized on solid supports (such as zeolites, mesoporous silica, polymer films, and MOFs) as effective active sites, are a type of heterogeneous catalyst with excellent performance. SMC catalysts possess adjacent metal sites, each cluster has a countable number of atoms, and a well-defined size (typically less than 2 nm). Due to their small size, they provide more exposed catalytic active sites, exhibiting higher catalytic activity. However, because SMCs have high surface energy, they are thermodynamically unstable and prone to aggregation during catalysis, leading to reduced catalytic efficiency. Therefore, developing highly stable SMC catalysts remains a challenge.

[0004] Improving the dispersion of metal precursors on the support and reducing the degree of metal agglomeration during thermal reduction are key to the synthesis of SMC catalysts. Do Hyung Kweon et al. (Kweon DH, Okyay MS, Kim SJ, et al. Ruthenium anchored on carbon nanotube electrocatalyst for hydrogen production with enhanced Faradaic efficiency[J]. Nat. Commun., 2020, 11(1): 1278.) first introduced carboxylic acid groups (-COOH) by mild oxidation of multi-walled carbon nanotubes. -COOH can form Ru carboxylic acid complexes with metal precursors, thereby improving the dispersion of metal precursors. Uniform and small Ru nanoparticles (NPs) with a size of about 3.4 nm were formed by sodium borohydride reduction and subsequent heat treatment under inert conditions, which exhibited excellent catalytic performance in the HER reaction. Although the dispersion of the metal precursor was improved by the oxidation strategy of the support, Ru NPs still had a large size due to agglomeration during the thermal reduction process, failing to reach the level of nanoclusters (NCs). Wang et al. (Wang D, Liu J, Xi J, et al. Pd-Fe dual-metal nanoparticles confinedin the interface of carbon nanotubes / N-doped carbon for excellent catalytic performance[J]. Appl. Surf. Sci., 2019, 489: 477-484.) obtained a bimetallic CNT / PdFe / NC catalyst by adding polydopamine to a CNT / PdFe composite material loaded with Pd and Fe bimetallic NPs, forming a polydopamine (PDA) coating layer on its surface, and finally pyrolyzing it at high temperature. This catalyst can effectively prevent the aggregation and leaching of the supported metal NPs. However, this non-porous nitrogen-doped carbon shell may mask some active sites, thus leading to a decrease in catalyst activity. Summary of the Invention

[0005] In order to overcome the shortcomings of the existing technology, the purpose of this invention is to provide a supported ruthenium nanocluster catalyst Ru / CNT@CN, its preparation method and application.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A supported ruthenium nanocluster catalyst, wherein the catalyst is Ru / CNT@CN, where CNT represents carbon nanotubes and CN represents carbon nitride; the catalyst uses carboxylated carbon nanotubes as a support, and a carbon nitride shell is formed outside the support, with ruthenium nanoclusters (Ru NCs) in situ embedded on the surface of the carbon nitride shell.

[0008] The preparation method of the supported ruthenium nanocluster catalyst includes the following steps:

[0009] (1) Multi-walled carbon nanotubes were oxidized by a mixed acid solution composed of concentrated nitric acid and concentrated sulfuric acid, washed and dried to obtain carboxylated carbon nanotubes, denoted as CNTs;

[0010] (2) First, the CNTs, melamine (DCD), Ru metal salt and water prepared in step (1) are stirred at 50~100 ℃ for 2~12 h to obtain a dispersion; then, the dispersion is frozen with liquid nitrogen and freeze-dried to obtain the catalyst precursor CNT@DCD-Ru; finally, CNT@DCD-Ru is annealed at 500~700 ℃ for 2~8 h in a hydrogen-inert gas mixed atmosphere to obtain the target catalyst Ru / CNT@CN; wherein, the Ru metal salt is calculated based on the Ru element, and the raw material ratio is CNT∶DCD∶Ru metal salt∶water = 200 mg∶(0.1~0.5) mmol∶(5~50) mg∶(20~200) mL.

[0011] Preferably, the Ru metal salt is ruthenium acetylacetonate Ru (acac)3.

[0012] Preferably, in a hydrogen-inert gas mixed atmosphere, the volume percentage of hydrogen is 5-20%.

[0013] Preferably, in the hydrogen-inert gas mixed atmosphere, the inert gas is argon or nitrogen.

[0014] Preferably, the temperature is increased to the annealing temperature at a heating rate of 2~20 °C / min.

[0015] Ideally, the freeze-drying process should be carried out at a temperature of -50 to -30 ℃ for 8 to 24 hours.

[0016] Application of the supported ruthenium nanocluster catalyst in hydrogen production by hydrolysis of ammonia borane.

[0017] Application of the supported ruthenium nanocluster catalyst in the transfer hydrogenation reaction of nitroaromatic compounds.

[0018] Mechanism of this invention: Further oxidation of commercially available CNTs with a mixture of concentrated nitric acid and concentrated sulfuric acid increases the number of oxygen-containing functional groups (especially -COOH) on the CNT surface, which is beneficial to improving their dispersibility in water. Simultaneously, by forming Ru carboxylic acid complexes, Ru ions (Ru...) are released... 3+ The Ru precursor is adsorbed onto the CNT surface to improve its dispersion. Furthermore, the oxidized multi-walled carbon nanotubes have a good affinity for dicyandiamide, forming a thin layer of dicyandiamide on their surface. Then, the solvent in the mixture is removed by freeze-drying to obtain the CNT@DCD-Ru precursor product, in which Ru is dispersed in the CNT@DCD matrix in an ionic or coordinated state. Subsequently, it is reduced at high temperature in a reducing atmosphere to form a Ru / CNT@CN supported catalyst. During the thermal reduction process, DCD polymerizes into ultrathin CN sheets, inhibiting the growth of Ru NCs.

[0019] Beneficial effects:

[0020] (1) In this invention, CNTs carboxylated with concentrated nitric acid and concentrated sulfuric acid are used as a carrier, and the carboxyl groups react with the metal precursor Ru. 3+ The coordination effect of the catalyst improves the dispersion of the metal precursor, and the in-situ polymerization of dicyandiamide into a CN layer inhibits the growth of Ru nanoclusters, thus preparing a Ru / CNT@CN catalyst with ultrafine Ru nanoclusters (approximately 1.12 nm in diameter).

[0021] (2) The catalyst Ru / CNT@CN prepared in this invention exhibits excellent catalytic performance for AB hydrolysis to produce hydrogen and for AB to be used in the hydrogen transfer reaction of nitroaromatics. It is superior to Ru / CNT without nitrogen source and Ru / CNT-Pure catalyst with unoxidized support. Among them, the TOF value of Ru / CNT@CN for AB hydrolysis to produce hydrogen is as high as 643.6 min. ﹣1 It outperforms most ruthenium-based catalysts, and the transfer hydrogenation reaction of nitroaromatic compounds exhibits high conversion and selectivity under mild conditions;

[0022] (3) The catalyst Ru / CNT@CN prepared by the present invention has excellent stability. Attached Figure Description

[0023] Figure 1 The structural characterization diagrams of the catalyst Ru / CNT@CN prepared in Example 1 are as follows: (a) TEM image and corresponding particle size distribution histogram; (b) HRTEM image; (c) high-resolution lattice image and IFFT image of a single Ru NCs; (d) HAADF-STEM image and corresponding elemental mapping image; (e) X-ray energy spectrum; (f) content percentage of each element.

[0024] Figure 2TEM images of the catalysts Ru / CNT (a) and Ru / CNT-Pure (b) prepared in Comparative Examples 1-2.

[0025] Figure 3 The images show the XRD patterns of the catalyst Ru / CNT@CN prepared in Example 1, the catalysts Ru / CNT, Ru / CNT-Pure, CNT@CN, and CNT prepared in Comparative Examples 1-3.

[0026] Figure 4 The catalytic activity (a) and corresponding TOF values ​​(b) of Ru / CNT@CN, Ru / CNT, Ru / CNT-Pure, 5wt%Ru / C, and CNT@CN for hydrogen production from AB hydrolysis at 298 K are shown.

[0027] Figure 5 The catalytic performance of Ru / CNT@CN on different nitroaromatic substrates.

[0028] Figure 6 Figure (a) shows the performance test results of Ru / CNT@CN catalyst AB for nitroaromatic transfer hydrogenation cycle and the overflow experiment (b). Detailed Implementation

[0029] To make the present invention clearer and more explicit, the present invention will be further described in detail below. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0030] Example 1

[0031] A method for preparing a supported ruthenium nanocluster catalyst Ru / CNT@CN, comprising the following steps:

[0032] (1) 2 g of commercial multi-walled carbon nanotubes (CNT-Pure) were added to a 250 mL beaker, followed by 30 mL of concentrated HNO3 (65~68 wt%). Then, 120 mL of concentrated sulfuric acid (98 wt%) was added to 30 mL of concentrated nitric acid while stirring in an ice-water bath. The mixture was then magnetically stirred for 12 h in an oil bath at 80 ℃. The resulting slurry was diluted with a large amount of distilled water (about 1.5 L), collected by centrifugation, and washed repeatedly with water and anhydrous ethanol to completely remove residual acid and other impurities. The sample was finally vacuum dried at 60 ℃ for 24 h and stored for later use, and was designated as CNT.

[0033] (2) First, 200 mg of CNT, 0.24 mmol of DCD and 27 mg of Ru (acac)3 prepared in step (1) were dispersed in 50 mL of deionized water and stirred at 50 °C for 8 h to obtain a dispersion. Then, the dispersion was rapidly frozen with liquid nitrogen and freeze-dried at -40 °C for 6 h to obtain the catalyst precursor CNT@DCD-Ru. Finally, CNT@DCD-Ru was heated to 600 °C at a heating rate of 2 °C / min in a hydrogen-argon gas mixed atmosphere (hydrogen accounts for 10 v%) and annealed for 2 h to obtain the target catalyst Ru / CNT@CN.

[0034] Compare with Example 1

[0035] The preparation method of the Ru / CNT catalyst differs from that in Example 1 in that DCD is not added. The specific steps are as follows:

[0036] (1) Same as step (1) in Example 1;

[0037] (2) First, 200 mg of CNT prepared in step (1) and 27 mg of Ru (acac)3 were dispersed in 50 mL of deionized water and stirred at 50 °C for 8 h to obtain a dispersion. Then, the dispersion was rapidly frozen with liquid nitrogen and freeze-dried at -40 °C for 6 h to obtain the catalyst precursor CNT-Ru. Finally, CNT-Ru was heated to 600 °C at a heating rate of 2 °C / min in a hydrogen-argon gas mixed atmosphere (hydrogen accounts for 10 v%) and annealed for 2 h to obtain the catalyst Ru / CNT.

[0038] Compare with Example 2

[0039] The preparation method of the catalyst Ru / CNT-Pure differs from that in Example 1 in that DCD was not added, and untreated commercial multi-walled carbon nanotubes (CNT-Pure) were used. The specific steps are as follows:

[0040] First, 200 mg of commercial CNT-Pure (without further oxidation treatment with concentrated nitric acid-concentrated sulfuric acid mixture) and 27 mg of Ru (acac)3 were dispersed in 50 mL of deionized water and stirred at 50 °C for 8 h to obtain a dispersion. Then, the dispersion was rapidly frozen with liquid nitrogen and freeze-dried at -40 °C for 6 h to obtain the catalyst precursor CNT-Pure-Ru. Finally, CNT-Pure-Ru was heated to 600 °C in a hydrogen-argon gas mixed atmosphere (hydrogen accounting for 10 v%) at a heating rate of 2 °C / min and annealed for 2 h to obtain the catalyst Ru / CNT-Pure.

[0041] Compare with Example 3

[0042] The preparation method of the catalyst CNT@CN differs from that in Example 1 in that no ruthenium source is added. The specific steps are as follows:

[0043] (1) Same as step (1) in Example 1;

[0044] (2) First, 200 mg of CNT prepared in step (1) and 0.24 mmol of DCD were dispersed in 50 mL of deionized water and stirred at 50 °C for 8 h to obtain a dispersion. Then, the dispersion was rapidly frozen with liquid nitrogen and freeze-dried at -40 °C for 6 h to obtain the catalyst precursor CNT@DCD. Finally, CNT@DCD was heated to 600 °C at a heating rate of 2 °C / min in a hydrogen-argon gas mixed atmosphere (hydrogen accounts for 10 v%) and annealed for 2 h to obtain the target catalyst CNT@CN.

[0045] Product structure characterization

[0046] Figure 1 The structural characterization images of the Ru / CNT@CN catalyst prepared in Example 1 are as follows: (a) TEM image and corresponding particle size distribution histogram; (b) HRTEM image; (c) high-resolution lattice image and IFFT image of individual Ru NCs; (d) HAADF-STEM image and corresponding elemental mapping image; (e) X-ray energy distribution spectrum; (f) content percentage of each element. The Ru NCs are uniformly distributed on the surface of the CNTs without significant aggregation. The average size of the Ru NCs is approximately 1.12 nm. Figure 1 a). For example Figure 1 As shown in (b), a clear graphite structure can be seen inside the material, corresponding to the CNT carrier. Outside the CNTs, a thin, fur-like shell without graphite texture (marked by a yellow ellipse) corresponding to a small number of CN shells can be observed, proving the formation of the CN shell. In addition, in the high-resolution lattice map and fast inverse Fourier transform (IFFT) image of a single Ru NCs, spatial lattice fringes of the Ru (101) crystal plane (lattice spacing of approximately 0.207 nm) were also observed, which proves that the black spots in the Ru / CNT@CN image are Ru NCs ( Figure 1 c). White bright spots were observed in high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images, further confirming the presence of Ru NCs. Furthermore, the corresponding elemental mapping images showed that Ru, C, and N were uniformly distributed in the Ru / CNT@CN sample region. Simultaneously, the uniform distribution of N indicated the formation of a uniform CN layer on the carbon surface. Figure 1 d). Localized X-ray energy distribution of the catalyst ( Figure 1e) C, N, Ru, and Cu elements were detected. The Cu element was derived from the micro-grid Cu mesh used in the test. According to the elemental mapping image scanning results, the content percentages of each element were: C 98.63%, N 0.37%, and Ru 1.00% (…). Figure 1 f).

[0047] Figure 2 TEM images of the catalysts Ru / CNT (a) and Ru / CNT-Pure (b) prepared in Comparative Examples 1-2. In Ru / CNT ( Figure 2 a) Similar to Ru / CNT@CN, a clear graphite structure corresponding to carbon nanotubes can also be observed inside the material. The Ru / CNT surface has relatively uniformly distributed Ru NPs without obvious aggregation, with an average particle size of approximately 1.95 nm, but a small number of larger NPs (approximately 3.5 nm). In Ru / CNT-Pure ( Figure 2 (b) Although smaller NPs or NCs were also formed, large clusters of black particles (some larger than 20 nm) were observed, indicating severe metal agglomeration. These results suggest that the strategy of using mixed acid oxidation of CNTs and in-situ polymerization of DCD thin layers into CN layers effectively limits ruthenium cluster agglomeration, resulting in the preparation of Ru NCs with relatively uniform distribution and smaller size.

[0048] Figure 3 XRD patterns of the catalyst Ru / CNT@CN prepared in Example 1, the catalysts Ru / CNT, Ru / CNT-Pure, CNT@CN prepared in Comparative Examples 1-3, and CNT (prepared in step (1) of Example 1). Figure 3 As shown, all samples were in 2 θ The two peaks at 26.2° and 43.6° are attributed to the typical graphitic carbon (002) and (100) diffraction peaks of CNT (JCPDs Card No. 65-6212). In 2 θ The diffraction peak at 44.0° is attributed to elemental Ru (101), consistent with electron microscopy results. This indicates that during high-temperature annealing at 600 °C in an H2 / Ar mixed atmosphere, Ru... 3+ It is reduced to elemental Ru. The weaker diffraction peak (44.0°) in Ru / CNT@CN and Ru / CNT is due to the small size or high dispersion of the generated Ru NCs or NPs. However, in Ru / CNT-Pure, the larger Ru NPs result in a weaker peak at 2... θ The diffraction peak at 44.0° is stronger than that of the two samples mentioned above, which is consistent with the electron microscopy results. These results further illustrate that the metal particles generated by Ru / CNT@CN are smaller.

[0049] Performance testing

[0050] (I) Hydrogen production performance of ammonia borane (AB) by hydrolysis

[0051] The contents of metallic Ru in the catalysts Ru / CNT@CN, Ru / CNT, and Ru / CNT-Pure prepared in Example 1 and Comparative Examples 1-2, as determined by ICP-AES, were 3.2 wt%, 3.0 wt%, and 3.9 wt%, respectively.

[0052] Set the water bath temperature to a constant 298 K. Secure a 20 mL three-necked flask in the water bath, sealing the middle and one side of the flask with ground glass stoppers and the other side with a glass stopper connected to a flexible rubber tube. Insert the flask into an inverted 100 mL graduated cylinder filled with water. Collect the generated hydrogen gas using the downward displacement method. After assembling the apparatus, check its airtightness. Then, weigh an appropriate amount of catalyst (Ru-containing catalyst: 0.325 mmol Ru; CNT@CN catalyst: 10 mg) and place it in the three-necked flask. Add 8 mL of water, sonicate for 15 min, add a magnetic stir bar, and start stirring at 300 rpm. Then add 2 mL of an aqueous solution containing 1.49 mmol AB. Start timing when the first bubble forms and continue until no more bubbles are generated.

[0053] Figure 4 The catalyst Ru / CNT@CN prepared in Example 1, the catalysts Ru / CNT, Ru / CNT-Pure, CNT@CN prepared in Comparative Examples 1-3, and a commercial 5 wt% Ru / C catalyst were compared at 298 K for catalytic hydrogen production from AB hydrolysis (a) and their corresponding TOF values ​​(b). Figure 4 The results show that pure CNT@N has no catalytic activity, thus eliminating the influence of the inherent catalytic activity of the catalyst support itself; the TOF values ​​of Ru / CNT@CN, Ru / CNT, Ru / CNT-Pure, and Ru / C are 643.6, 385.8, 181.6, and 106.3 min, respectively. ﹣1Ru / CNT@CN exhibited better catalytic activity than other Ru-based catalysts, with Ru / CNT@CN demonstrating the most superior catalytic activity. Combining the above experimental results and electron microscopy characterization analysis, it can be seen that acid treatment of the catalyst support and the addition of dicyandiamide during synthesis effectively prevent further Ru aggregation, thereby obtaining smaller NCs (non-carbon nanoparticles), providing more active sites for the reaction, and resulting in relatively high catalytic activity. The catalytic activity of Ru / CNT@CN (NCs particle size approximately 1.12 nm) is 1.67 times that of the Ru / CNT catalyst without dicyandiamide (nanoparticle size approximately 1.95 nm). Furthermore, due to severe nanoparticle aggregation, commercial carbon nanotubes alone exhibit lower catalytic activity than carboxylated carbon nanotubes when used as a support, highlighting the necessity of carbon nanotube oxidation.

[0054] (II) Transfer hydrogenation performance of nitroaromatics

[0055] A certain amount of catalyst (Ru-containing catalyst with 0.325 mmol Ru and CNT@CN catalyst with 10 mg) and 0.1 mmol of nitroaromatic substrate were dispersed in a vial containing an aqueous solution of methanol (4 mL MeOH, 6 mL H2O). The dispersion system was ultrasonicated to ensure uniform mixing of the catalyst and substrate. Then, at 298 K and with stirring at 300 rpm, 2.0 mL of AB aqueous solution (AB concentration of 0.5 mmol / mL) was injected into the vial, and timing was started. Samples were taken at a fixed reaction time (t = 10 min). Finally, after filtering to remove the catalyst, the content of each component was analyzed by gas chromatography using the area normalization method.

[0056] Taking the conversion of nitrobenzene as an example, the content of nitrobenzene and aromatic amines in the sample was analyzed using an Agilent gas chromatograph (GC7820A). The chromatographic column was SH-RXI-5SIL-MS (30 m × 0.25 mm × 0.25 μm), and the detector was an FID detector. Chromatographic conditions: injector temperature 270 ℃, detector temperature 270 ℃, injection volume 1.0 μL, split ratio 100:1. Separation was performed using a programmed temperature ramp method: initial temperature 70 ℃, holding time 1 min, then ramped up at 20 ℃ for 1 min. −1 The temperature was increased to 270 °C at a rate of [missing information] and held for 5 min. All products were analyzed using the area-corrected normalization method.

[0057] Taking the conversion of nitrobenzene as an example, the formulas for calculating the conversion rate of nitrobenzene, the selectivity of aniline, and the yield of aniline are as follows:

[0058] ;

[0059] Where C0 is the concentration (mol / L) of nitrobenzene in the reaction system at the beginning of the reaction, C t Let C be the concentration (mol / L) of nitrobenzene in the reaction system at time t. An The concentration (mol / L) of aniline in the reaction system at reaction time t.

[0060] Taking nitrobenzene as an example, the hydrogenation performance of various catalysts for nitroaromatics transfer is shown in Table 1. Table 1 shows that Ru / CNT@CN can completely convert nitrobenzene to aniline within 1 min, with no byproducts generated, and no hydrogen generation observed at the initial stage of the reaction; bubbles only appear after the nitrobenzene conversion is complete. In contrast, Ru / CNT requires 5 min to completely convert nitrobenzene. Using a 5 wt% Ru / C catalyst with the same Ru content, only 12% of nitrobenzene is converted to aniline within a 10 min conversion time. Based on the above performance study of AB catalysts for hydrogen production, the rate of hydrogen production from AB is positively correlated with the catalytic rate of AB catalysts for nitroaromatics transfer hydrogenation.

[0061]

[0062] Halogenated anilines are important pharmaceutical intermediates and raw materials for pesticides such as amide azole and herbicides (PUMA). However, in traditional industrial production, noble metal-based catalysts often generate dehalogenation byproducts when catalyzing the production of corresponding chloroaromatic amines from chloronitrobenzene, making it difficult to separate the target product and severely reducing product quality. This invention uses Ru / CNT@CN prepared in Example 1 as a catalyst and AB as a reducing agent to selectively reduce methyl-substituted, chloro, and fluoronitro compounds, with a reaction time of 10 min. Figure 5 The catalytic performance of Ru / CNT@CN on various nitroaromatic substrates is shown. Figure 5 As shown, all methyl-substituted and halonitrobenzenes can be successfully converted into the corresponding aromatic amines, with the aromatic amine conversion, selectivity and yield all being 100%.

[0063] Figure 6 Figure (a) shows the performance test results of Ru / CNT@CN catalyst AB for nitroaromatic transfer hydrogenation cycle, along with an overflow experiment (b). Figure 6 As shown in Figure a, after three cycles (the catalyst was collected by centrifugation after each reaction and then used in the next reaction), the catalytic activity of the catalyst did not show significant loss and remained at 100%. Figure 6As shown in b, when the reaction time was 30 s, we used an organic filter to remove the catalyst (leaving only the reaction liquid), and the conversion rate of nitrobenzene was detected to be 58%, with a selectivity of 100%. When the reaction proceeded to 300 s, the product was analyzed and it was found that the conversion rate of nitrobenzene remained at 58%, without significant change, and the selectivity of aniline remained at 100%, indicating that Ru NCs did not detach and that Ru NCs could stably exist on the catalyst surface.

Claims

1. The application of a supported ruthenium nanocluster catalyst in the hydrolysis of ammonia borane to produce hydrogen or in the transfer hydrogenation reaction of nitroaromatic compounds; the catalyst uses carboxylated carbon nanotubes as a support, with a carbon nitride shell formed outside the support, and ruthenium nanoclusters in situ embedded on the surface of the carbon nitride shell; the preparation steps of the catalyst are as follows: (1) Multi-walled carbon nanotubes were oxidized by a mixed acid solution composed of concentrated nitric acid and concentrated sulfuric acid, washed and dried to obtain carboxylated carbon nanotubes, denoted as CNTs; (2) First, the CNTs, melamine DCD, Ru metal salt, and water prepared in step (1) are stirred at 50-100 °C for 2-12 h to obtain a dispersion; then, the dispersion is frozen with liquid nitrogen and freeze-dried to obtain the catalyst precursor CNT@DCD-Ru; finally, CNT@DCD-Ru is annealed at 500-700 °C for 2-8 h in a hydrogen-inert gas mixed atmosphere to obtain the target catalyst Ru / CNT@CN; wherein, The raw material ratio for Ru metal salt, calculated based on the Ru element, is CNT∶DCD∶Ru metal salt∶water = 200mg∶(0.1~0.5)mmol∶(5~50)mg∶(20~200)mL.

2. The application as described in claim 1, characterized in that: Ru metal salt is ruthenium acetylacetonate.

3. The application as described in claim 1, characterized in that: In a hydrogen-inert gas mixture atmosphere, the volume percentage of hydrogen is 5-20%.

4. The application as described in claim 1 or 3, characterized in that: In a hydrogen-inert gas mixed atmosphere, the inert gas is argon or nitrogen.

5. The application as described in claim 1, characterized in that: Heat to the annealing temperature at a heating rate of 2~20 ℃ / min.

6. The application as described in claim 1, characterized in that: The freeze-drying process is carried out at a temperature of -50 to -30 ℃ for 8 to 24 hours.

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