Carbon-coated transition metal nanocomposite and application thereof

Abstract

The application provides a carbon-coated transition metal nanocomposite and application thereof. The nanocomposite contains a core-shell structure with a shell layer and a core. The shell layer is a nitrogen and oxygen doped graphitized carbon layer, and the core is a transition metal nanoparticle. The acid washing loss rate of the nanocomposite is less than or equal to 10%. The nanocomposite has a tightly coated graphitized carbon layer. The tightly coated nanocomposite can better ensure that the core transition metal has a reduced loss rate during preparation and application, thereby better playing the role of the nanocomposite and ensuring the safety of the nanocomposite. The carbon-coated transition metal nanocomposite has a simple preparation method, wide applicability, and good catalytic effect as a catalyst, and can be used in various hydrogenation reduction reactions.

Description

Technical Field

[0001] This invention relates to the field of carbon / metal composite materials, and more specifically to a carbon-coated transition metal nanocomposite material and its applications. Background Technology

[0002] Transition metal nanoparticles have attracted widespread attention due to their excellent optical, electrical, and magnetic properties. However, their high reactivity makes them prone to aggregation, oxidation, and even combustion in air, significantly impacting their performance and applications. Meanwhile, as non-metallic materials, carbon nanomaterials possess advantages such as resistance to acid and alkali corrosion and chemical stability.

[0003] In recent years, carbon nanotube-coated metal composites have become a hot topic. These materials consist of a single to several layers of curved graphitized carbon forming a shell that tightly encapsulates a core of metal nanoparticles, isolating the metal nanoparticles from the external environment and greatly improving the stability of the composite material. Therefore, this unique core-shell structured nanomaterial has broad application prospects in fields such as catalytic materials, microwave absorbing materials, information storage materials, magneto-optical materials, biomedical materials, and lubricant additives.

[0004] While there are existing reports on the coating of transition metals with carbon materials, these materials still face various problems in practical applications, such as low mass transfer efficiency, low yield, complex processes, poor carbon coating, and instability during use, making them unsuitable for industrial production and application. For example, the pyrolysis method using metal-organic frameworks (MOFs) as precursors requires the preparation of crystalline solid materials (i.e., MOFs) with periodic structures in a solvent under high temperature and pressure. The conditions for preparing MOFs are typically quite stringent, the required ligands are expensive, and mass production is difficult. Furthermore, the coating of metal particles in the composite material prepared by this method is not tight. Another example is CN 105032424A, which discloses a catalyst for the selective hydrogenation of aromatic nitro compounds. This literature uses the pechini method (sol-gel method) to coat metal particles. Similar to the MOF method, this method also requires the preparation of solid coordination polymers in a solvent, and the coating of metal particles in the composite material prepared by this method is also not tight.

[0005] It should be noted that the information disclosed in the foregoing background section is only used to enhance the understanding of the background of the present invention, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a carbon-coated transition metal nanocomposite material with abundant mesoporous structure, which can improve mass transfer efficiency and increase stability.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A carbon-coated transition metal nanocomposite material, the composite material having a core-shell structure with a shell and a core, the shell being a graphitized carbon layer doped with nitrogen and oxygen, and the core being transition metal nanoparticles, wherein the acid pickling loss rate of the nanocomposite material is ≤10%.

[0009] In one embodiment of the nanocomposite material of the present invention, the nanocomposite material is a mesoporous material having at least one mesoporous distribution peak.

[0010] In another embodiment of the nanocomposite material of the present invention, the nanocomposite material is a mesoporous material having more than one mesoporous distribution peak, that is, a mesoporous material having two or more mesoporous distribution peaks.

[0011] In another embodiment of the nanocomposite material of the present invention, the nanocomposite material has a mesoporous distribution peak in the pore size range of 2-5 nm and the pore size range of 6-16 nm, respectively.

[0012] In another embodiment of the nanocomposite material of the present invention, the proportion of the mesopore volume with a pore size in the range of 2 to 5 nm to the total pore volume can be greater than 5%, for example, 10% to 30%.

[0013] In another embodiment of the nanocomposite material of the present invention, the proportion of mesopore volume to total pore volume in the nanocomposite material is greater than 50%, preferably greater than 80%, and more preferably greater than 95%.

[0014] According to one embodiment of the present invention, the mesopore volume in the composite material is 0.05-1.25 cm³. 3 / g, the mesopore volume can also be 0.10-0.40cm³. 3 / g.

[0015] In another embodiment of the nanocomposite material of the present invention, the carbon content in the nanocomposite material is 15-60 wt% and the transition metal content is 30-80 wt% by mass percentage; preferably, the carbon content in the nanocomposite material is 30-60 wt% and the transition metal content is 30-60 wt%.

[0016] In another embodiment of the nanocomposite material of the present invention, the total nitrogen and oxygen content in the nanocomposite material is less than 15% by mass percentage.

[0017] In another embodiment of the nanocomposite material of the present invention, the nitrogen content in the nanocomposite material is 2-8% by mass percentage.

[0018] In another embodiment of the nanocomposite material of the present invention, the oxygen content in the nanocomposite material is 3 to 9% by mass percentage.

[0019] According to the present invention, the sum of the contents of each component in the nanocomposite material is 100%.

[0020] In another embodiment of the nanocomposite material of the present invention, the thickness of the graphitized carbon layer is 0.3 to 6 nm, preferably 0.3 to 3 nm.

[0021] In another embodiment of the nanocomposite material of the present invention, the particle size of the core-shell structure is 1-200 nm, preferably 3-100 nm, and more preferably 4-50 nm.

[0022] In another embodiment of the nanocomposite material of the present invention, the transition metal is selected from one or more of iron, cobalt, nickel, copper and zinc, preferably nickel.

[0023] In another embodiment of the nanocomposite material of the present invention, the lattice structure of the transition metal nanoparticles is a face-centered cubic lattice structure and / or a close-packed hexagonal lattice structure.

[0024] On the other hand, the present invention provides the application of the above-mentioned nanocomposite material as a catalyst in hydrogenation reduction reaction.

[0025] In one embodiment of the application of the present invention, the hydrogenation reduction reaction includes: mixing nitrobenzene with the nanocomposite material in a solvent and reacting under a hydrogen atmosphere to synthesize aniline.

[0026] In another embodiment of the application of the present invention, the nitrobenzene is a substituted nitrobenzene, and the substituent is selected from C. 1-20 Alkyl, cycloalkyl, and aryl groups.

[0027] In another embodiment of the invention, the nanocomposite material accounts for 1%-50% of the mass percentage of the nitrobenzene, preferably 5-30%.

[0028] In another embodiment of the invention, the hydrogenation reduction reaction is generally carried out at 60-120°C, and the pressure of the hydrogen gas is generally 0.5-2 MPa.

[0029] In another embodiment of the invention, the solvent is selected from one or more of alcohols, ethers, and water.

[0030] The beneficial effects of this invention are as follows:

[0031] The carbon-coated transition metal nanocomposite material of this invention has a tightly coated graphitized carbon layer structure, without pores or defects that allow reactants to approach the center of the transition metal. This makes the core transition metal material highly stable, non-flammable, acid-resistant, and low-hazardous, suitable for storage and transportation, thus ensuring the safety of the nanocomposite material. This tightly coated nanocomposite material can be used as a catalyst in various hydrogenation reduction reactions, such as the catalytic reduction of nitrobenzene to aniline. As a catalyst, it exhibits advantages such as good reproducibility, high activity, and high selectivity, making it suitable for large-scale industrial production. Attached Figure Description

[0032] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings:

[0033] Figure 1 A photographic schematic diagram showing the magnetic properties of the nitrogen-oxygen-doped carbon-coated nickel nanocomposite material prepared in Example 1 is shown;

[0034] Figure 2 This is a TEM image of the nitrogen-oxygen-doped carbon-coated nickel nanocomposite material prepared in Example 1;

[0035] Figure 3 The image shows the XRD pattern of the nitrogen-oxygen-doped carbon-coated nickel nanocomposite material prepared in Example 1.

[0036] Figure 4a The N2 adsorption-desorption isotherm of the nitrogen-oxygen-doped carbon-coated nickel nanocomposite material prepared in Example 1;

[0037] Figure 4b The image shows the BJH pore size distribution curve of the nitrogen-oxygen doped carbon-coated nickel nanocomposite material prepared in Example 1.

[0038] Figure 5a This is an XPS image of the nitrogen-oxygen-doped carbon-coated nickel nanocomposite material prepared in Example 1;

[0039] Figure 5b This is the Ni 2p spectrum in XPS of the nitrogen-oxygen-doped carbon-coated nickel nanocomposite material prepared in Example 1;

[0040] Figure 5c The XPS results for the O 1s peak in the nitrogen-oxygen-doped carbon-coated nickel nanocomposite material prepared in Example 1 are shown.

[0041] Figure 6 This is a TEM image of the nitrogen-oxygen-doped carbon-coated nickel nanocomposite material prepared in Example 2;

[0042] Figure 7This is the XRD pattern of the nitrogen-oxygen-doped carbon-coated nickel nanocomposite material prepared in Example 2;

[0043] Figure 8 The BJH pore size distribution curve of the nitrogen-oxygen-doped carbon-coated nickel nanocomposite material prepared in Example 2 is shown.

[0044] Figure 9 This is a TEM image of the nitrogen-oxygen-doped carbon-coated cobalt nanocomposite material prepared in Example 3;

[0045] Figure 10 This is the XRD pattern of the nitrogen-oxygen-doped carbon-coated cobalt nanocomposite material prepared in Example 3;

[0046] Figure 11 The BJH pore size distribution curve of the nitrogen-oxygen-doped carbon-coated cobalt nanocomposite material prepared in Example 3 is shown.

[0047] Figure 12 This is the XRD pattern of the solid precursor prepared in Example 4;

[0048] Figure 13 This is a TEM image of the nitrogen-oxygen-doped carbon-coated nickel-cobalt nanocomposite material prepared in Example 4;

[0049] Figure 14 This is the XRD pattern of the nitrogen-oxygen-doped carbon-coated nickel-cobalt nanocomposite material prepared in Example 4;

[0050] Figure 15 The BJH pore size distribution curve of the nitrogen-oxygen-doped carbon-coated nickel-cobalt nanocomposite material prepared in Example 4 is shown.

[0051] Figure 16 This is the XRD pattern of the material prepared in Comparative Example 1. Detailed Implementation

[0052] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are for illustration and explanation only, and are not intended to limit the present invention in any way.

[0053] In this invention, except where expressly stated, any matters or issues not mentioned herein are directly applicable to those known in the art without any modification. Furthermore, any implementation described herein can be freely combined with one or more other implementations described herein, and the resulting technical solutions or concepts are considered part of the original disclosure or original record of this invention, and should not be regarded as new content not disclosed or anticipated herein, unless those skilled in the art consider the combination clearly unreasonable.

[0054] All features disclosed in this invention can be combined arbitrarily, and such combinations should be understood as the content disclosed or described in this invention, unless those skilled in the art consider such combinations to be obviously unreasonable. The numerical points disclosed in this specification include not only the numerical points specifically disclosed in the embodiments, but also the endpoints of each numerical range in the specification. Any range of combinations of these numerical points should be considered as the range disclosed or described in this invention.

[0055] Any terms not directly defined herein shall be construed as having the meanings commonly understood in the art of this invention. Unless otherwise stated, the following terms used throughout this specification shall be construed as having the following meanings.

[0056] the term

[0057] The term "graphitized carbon layer" refers to a carbon structure with a layered structure that can be clearly observed under a high-resolution transmission electron microscope, rather than an amorphous structure, and with an interlayer spacing of 0.34 nm. The nanocomposite material formed by coating transition metal nanoparticles with this graphitized carbon layer is spherical or near-spherical.

[0058] The term "mesopore" is defined as a pore with a diameter in the range of 2–50 nm. Pores with a diameter less than 2 nm are defined as micropores, and pores with a diameter greater than 50 nm are defined as macropores.

[0059] The term "mesoporous material" is defined as a porous material containing mesoporous channels.

[0060] The term "carbon coating ratio" reflects the proportion of transition metals effectively coated by graphitized carbon layers, and can be characterized by high-resolution transmission electron microscopy (HRTEM) analysis and experimental results of catalytic oxidation reactions.

[0061] The term "carbon coating tightness" reflects the proportion of transition metals that are isolated from the external environment by the graphitized carbon layer, and can be characterized by high-resolution transmission electron microscopy (HRTEM) analysis results, transition metal content analysis results, and acid washing experiment results.

[0062] In the term "nitrogen- and oxygen-doped graphitized carbon layer", "nitrogen" refers to nitrogen element and "oxygen" refers to oxygen element. "Oxygen content" refers to the content of oxygen element. Specifically, it means that in the preparation process of carbon-coated nanocomposite materials, the graphitized carbon layer formed contains oxygen element in various forms. The "oxygen content" is the total content of all forms of oxygen element. Similarly, "nitrogen content" refers to the content of nitrogen element, that is, the total content of all forms of nitrogen element.

[0063] The term "mesopore distribution peak" refers to the mesopore distribution peak on the pore distribution curve obtained by calculating the desorption curve according to the Barrett-Joyner-Halenda (BJH) method.

[0064] The term "acid treatment" refers to the treatment of the products generated after the high-temperature pyrolysis step in the preparation of carbon-coated transition metal nanocomposites, and is a step in the preparation of composite materials.

[0065] The term "acid pickling loss rate" refers to the proportion of transition metal lost after acid pickling of a prepared carbon-coated transition metal nanocomposite product. It reflects the tightness of the graphitized carbon layer's coating of the transition metal. If the graphitized carbon layer's coating of the transition metal is not tight, the transition metal in the core will be dissolved and lost by the acid after acid treatment. A higher acid pickling loss rate indicates a lower degree of tightness in the graphitized carbon layer's coating of the transition metal, and vice versa. In this invention, an acid pickling loss rate ≤10% is defined as a "tightly coated" core-shell structured nanocomposite material.

[0066] The "pickling loss rate" is measured and calculated as follows:

[0067] Add 1 g of sample to 20 mL of sulfuric acid aqueous solution (1 mol / L), treat the sample at 90 °C for 8 h, then wash with deionized water until neutral, dry, weigh, and analyze. Calculate the pickling loss rate using the following formula: Pickling loss rate = [1 - (mass fraction of transition metal in the composite material after pickling × mass of the composite material after pickling) ÷ (mass fraction of transition metal in the composite material to be pickled × mass of the composite material to be pickled)] × 100%.

[0068] Reagents, Instruments and Tests

[0069] Unless otherwise specified, all reagents used in this invention are of analytical grade and are commercially available, such as those purchased from Sigma-Aldrich.

[0070] The XRD diffractometer used in this invention is an XRD-6000 X-ray powder diffractometer (Shimadzu, Japan). The XRD test conditions are: Cu target, Kα rays (wavelength λ = 0.154 nm), tube voltage of 40 kV, tube current of 200 mA, and scanning speed of 10° (2θ) / min.

[0071] The high-resolution transmission electron microscope (HRTEM) used in this invention is model JEM-2100 (HRTEM) (Nippon Electron Ltd.), and the high-resolution transmission electron microscope test conditions are: accelerating voltage of 200kV.

[0072] The X-ray photoelectron spectroscopy (XPS) used in this invention is an ESCALab220i-XL model manufactured by VG Scientific and equipped with Avantage V5.926 software. The X-ray photoelectron spectroscopy analysis and testing conditions are as follows: the excitation source is monochromatic AlKα X-rays, the power is 330W, and the basic vacuum during analysis and testing is 3×10⁻⁶. -9 mbar. Additionally, the electron binding energy was corrected using the C1s peak (284.6 eV), and the subsequent peak splitting software was XPSPEAK.

[0073] Analysis of the four elements—carbon (C), hydrogen (H), oxygen (O), and nitrogen (N)—was performed on an Elementar Micro Cube elemental analyzer. The specific operating methods and conditions were as follows: 1-2 mg of sample was weighed in a tin cup, placed in the autosampler tray, and introduced into the combustion tube through a ball valve for combustion at 1000°C (helium purging was used to remove atmospheric interference during sample introduction). The combusted gas was then reduced with copper to form nitrogen, carbon dioxide, and water. The mixed gas was separated by three desorption columns and sequentially detected by a TCD detector. Oxygen analysis utilized high-temperature decomposition; under the action of a carbon catalyst, oxygen in the sample was converted to CO, which was then detected by a TCD. Since the composite material of this invention contains only carbon, hydrogen, oxygen, nitrogen, and a metal element, the total content of the metal element can be determined from the total content of the four elements.

[0074] The proportions of different metallic elements were determined using an X-ray fluorescence spectrometer (XRF). The content of each metallic element in the composite material was calculated from the known total content of carbon, hydrogen, oxygen, and nitrogen. The X-ray fluorescence spectrometer (XRF) used in this invention was a Rigaku 3013, and the X-ray fluorescence spectroscopy analysis conditions were: a scan time of 100 s and an air atmosphere.

[0075] BET testing method: In this invention, the pore structure properties of the sample were determined by a Quantachrome AS-6B analyzer, the specific surface area and pore volume of the catalyst were obtained by the Brunauer-Emmett-Taller (BET) method, and the pore distribution curve was calculated from the desorption curve using the Barrett-Joyner-Halenda (BJH) method.

[0076] In this invention, the average particle size of carbon-coated transition metal nanoparticles is calculated using the Scherrer formula: D = kγ / (B cosθ) after peak separation of the XRD pattern. Where k is the Scherrer constant, k = 0.89; B is the full width at half maximum (FWHM); θ is the diffraction angle in radians; and γ is the X-ray wavelength, 0.154054 nm.

[0077] The carbon-coated transition metal nanocomposite material provided by the present invention has a core-shell structure with a shell and a core. The shell is a graphitized carbon layer doped with nitrogen and oxygen, and the core is transition metal nanoparticles. The acid washing loss rate of the nanocomposite material is ≤10%.

[0078] The nanocomposite material of this invention is a composite material composed of "transition metal nanoparticles tightly coated (without contact with the outside world) by a graphitized carbon layer" and a carbon material with a mesoporous structure. Compared with loosely coated composite materials, this tightly coated composite material can better ensure a lower loss rate of the core transition metal during preparation and application, thus better leveraging the composite material's function. Furthermore, it is generally accepted in the art that the active center of catalytic hydrogenation reactions is the transition metal; regardless of the specific structure of the catalyst, it must be possible for the reactants to contact the metal center. The transition metal nanocomposite material of this invention, tightly coated by a graphitized carbon layer, still exhibits excellent catalytic hydrogenation reduction ability of organic compounds, further demonstrating that the tightness of the graphitized carbon layer encapsulating the transition metal core is crucial to its catalytic performance, and the transition metal plays an indispensable modifying role.

[0079] In some embodiments, the nanocomposite material is a mesoporous material with at least one mesoporous distribution peak, and the mesoporous structure is beneficial for improving the mass transfer efficiency of the material. Specifically, the nanocomposite material has at least one mesoporous distribution peak on the pore distribution curve calculated according to the Barrett-Joyner-Halenda (BJH) method for desorption curves. In some embodiments, a single batch of the composite material has two distribution peaks in the mesoporous range; if multiple batches of the composite material are mixed, there can be more distribution peaks in the mesoporous range. When the nanocomposite material has a hierarchical mesoporous structure with different pore size ranges, it can exhibit more unique properties, and the hierarchical mesoporous structure is applicable to a wider range of applications.

[0080] In some embodiments, the mesoporous structure exhibits a mesoporous distribution peak in the mesoporous ranges of 2–7 nm and 8–20 nm, respectively. Abundant mesoporous structures facilitate the diffusion of reactants and products, improving the mass transfer efficiency of nanocomposite materials as catalysts and significantly enhancing their catalytic performance. Furthermore, more distribution peaks can be obtained by mixing composite materials manufactured in multiple batches within the mesoporous pore size range.

[0081] In some embodiments, the proportion of mesopore volume with a pore size in the range of 2 to 7 nm to the total pore volume is greater than 5%. By controlling the proportion of mesopore volume to the total pore volume, the composite material can have a rich mesopore structure, which can ensure higher mass transfer efficiency.

[0082] In some embodiments, the mesopore volume can be 0.05-1.25 cm³. 3 / g, or 0.10-0.40cm 3 / g.

[0083] In some embodiments, the carbon content in the nanocomposite material is 15-60 wt%, and the transition metal content is 30-80 wt%, by mass percentage.

[0084] The nanocomposite material of the present invention is doped with oxygen and nitrogen in a graphitized carbon layer. The oxygen content can be adjusted by introducing additional oxygen-containing compounds, such as polyols, during the manufacturing process. The nitrogen content can be adjusted by introducing additional nitrogen-containing compounds during the manufacturing process. By adjusting the oxygen and nitrogen content in the nanocomposite material, the catalytic performance of the graphitized carbon layer can be tuned to suit different catalytic reactions. In some embodiments, the nanocomposite material contains 0.1–10 wt% oxygen and 0.1–12 wt% hydrogen by weight, and also contains a small amount of hydrogen, with a hydrogen content of 0.2–2%.

[0085] In the nanocomposite material of the present invention, the sum of the contents of each component is 100%.

[0086] In some embodiments, the thickness of the graphitized carbon layer is 0.3–6.0 nm, preferably 0.3–3 nm. In some embodiments, the particle size of the core-shell structure is 1–200 nm, preferably 3–100 nm, and more preferably 4–50 nm.

[0087] In some embodiments, the transition metal is selected from one or more of iron (Fe), cobalt (Co), nickel (Ni), copper (Cu) and zinc (Zn), preferably nickel (Ni).

[0088] In another embodiment of the nanocomposite material of the present invention, the crystal structure of the transition metal nanoparticles is a face-centered cubic (fcc) crystal structure and / or a hexagonal close-packed (hcp) crystal structure, that is, only a face-centered cubic crystal structure exists, or both a face-centered cubic crystal structure and a hexagonal close-packed crystal structure exist simultaneously.

[0089] In some embodiments, the above-mentioned carbon-coated transition metal nanocomposite material is prepared by the following method:

[0090] A homogeneous solution is formed by mixing a transition metal salt, "a polycarboxylic acid and a nitrogen-containing compound, or a nitrogen-containing organic polycarboxylic acid", and other organic compounds in a solvent, and then removing the solvent to form a water-soluble mixture containing the transition metal.

[0091] The water-soluble mixture is pyrolyzed at high temperature under an inert atmosphere.

[0092] The product after high-temperature pyrolysis was treated with acid to obtain a carbon-coated transition metal nanocomposite material.

[0093] Specifically, the water-soluble mixture mentioned in the preparation method refers to a solution in which a transition metal salt, "polycarboxylic acids and nitrogen-containing compounds, or nitrogen-containing organic polycarboxylic acids," and other organic compounds besides the former are dissolved in water, ethanol, etc., to form a homogeneous solution, and then the water is directly evaporated to obtain a water-soluble mixture containing the transition metal. The temperature and process for evaporating the water can employ any feasible existing technology, such as spray drying at 80-120°C or drying in an oven.

[0094] In some embodiments, the organic polycarboxylic acids used in the preparation include, but are not limited to, citric acid. Transition metal salts are soluble salts, including but not limited to acetates. Nitrogen-containing compounds include, but are not limited to, hexamethylenetetramine. Other organic compounds include, but are not limited to, organic polyols.

[0095] In some embodiments, the inert atmosphere in the high-temperature pyrolysis step is protected by nitrogen or argon. The pyrolysis process includes a heating section and an isothermal section. The heating rate in the heating section is 0.5–10 °C / min, preferably 2.5–10 °C / min. The temperature in the isothermal section is 400–1300 °C, preferably 500–800 °C. The isothermal time is 20–600 min, preferably 30–300 min.

[0096] In some embodiments, the mass ratio of transition metal salt, polycarboxylic acid, nitrogen-containing compound and other organic compound is 1:0.5 to 10:0.5 to 10:0 to 10, preferably 1:1 to 3:1 to 3:0 to 3, that is, no other organic compound may be added.

[0097] In some embodiments, the acid treatment is preferably performed with a non-oxidizing strong acid, which includes, but is not limited to, one or any combination of hydrofluoric acid, hydrochloric acid, nitric acid and sulfuric acid, preferably hydrochloric acid and / or sulfuric acid.

[0098] In some embodiments, the acid treatment conditions are: treatment at 30°C to 100°C for more than 1 hour, preferably treatment at 60°C to 100°C for 1 hour to 20 hours, and more preferably treatment at 70°C to 90°C for 1 hour to 10 hours.

[0099] Compared with existing technologies, the preparation of nanocomposite materials of the present invention is simple and efficient. The high-temperature pyrolysis precursor is directly prepared by the reaction of transition metal salts with poly-organic carboxylic acids and nitrogen-containing compounds in aqueous solution. The atomic utilization rate of the transition metal in the precursor can reach 100%. This overcomes the disadvantages of existing technologies in preparing metal-organic framework precursors, such as the need for self-assembly in a high-temperature and high-pressure reactor, large waste of carbon source precursors and organic solvents, and cumbersome purification steps.

[0100] This invention also provides the application of the above-mentioned nanocomposite material as a catalyst in hydrogenation reduction reactions. For example, the composite material of this invention can be used to catalytically hydrogenate nitrobenzene to aniline. In the prior art, catalysts used for catalytic hydrogenation of nitrobenzene are mainly noble metal catalysts such as platinum (Pt), palladium (Pd), and rhodium (Rh), and non-noble metal catalysts such as copper (Cu), nickel (Ni), lead (Zn), and molybdenum (Mo). Raney Ni catalysts are the most commonly used catalysts in industrial catalytic reduction of nitrobenzene compounds to aniline compounds due to their low cost and relatively high catalytic activity; however, they still have many drawbacks, such as the high flammability of skeletal nickel in air, making them unstorable; the presence of hydrogen in the hydrogenation workshop, posing a high risk of explosion; large amounts of reaction byproducts; low product yield; and low catalytic activity. The carbon-coated transition metal nanocomposite material of this invention, with its graphitized carbon layer tightly encapsulating the transition metal core, ensures safety during use and transportation. Furthermore, as mentioned above, the graphitized carbon layer has excellent catalytic ability to hydrogenate and reduce organic compounds, which is beneficial for further improving the catalytic performance of this composite material.

[0101] In some embodiments, the hydrogenation reduction reaction includes: mixing nitrobenzene with the nanocomposite material in a solvent and reacting under a hydrogen atmosphere to synthesize aniline.

[0102] In some embodiments, nitrobenzene is substituted nitrobenzene, and the substituents are selected from C. 1-20 Alkyl, cycloalkyl, and aryl groups.

[0103] In some embodiments, the nanocomposite material accounts for 1%-50% of the mass of nitrobenzene, preferably 5-30%.

[0104] In some embodiments, the hydrogenation reduction reaction is generally carried out at 60-120°C, and the pressure of hydrogen is generally 0.5-2 MPa.

[0105] In some embodiments, the solvent is selected from one or more of alcohols, ethers, and water.

[0106] When the carbon-coated transition metal nanocomposite material of the present invention is used as a catalytic material, it has the advantages of good reproducibility, high activity and high selectivity, and is suitable for large-scale industrial production.

[0107] Example

[0108] Preparation Example 1

[0109] (1) Weigh 10g of nickel acetate, 10g of citric acid and 20g of hexamethylenetetramine, add them to a beaker containing 30mL of deionized water, stir at 70℃ to obtain a homogeneous solution, and continue to heat to dryness to obtain a solid.

[0110] (2) The precursor obtained in step (1) was placed in a ceramic boat, and then the ceramic boat was placed in the constant temperature zone of a tube furnace. Nitrogen gas was introduced at a flow rate of 100 mL / min, and the temperature was increased to 650 °C at a rate of 5 °C / min. After holding at this temperature for 2 hours, the heating was stopped, and the material was cooled to room temperature under a nitrogen atmosphere to obtain carbon-coated nickel nanomaterials.

[0111] (3) Add the material obtained in step (2) to 100 mL of 10% hydrochloric acid, treat at reflux temperature for 12 h, then wash the sample with deionized water until neutral, and dry. Figure 1 As shown, the nanocomposite material was placed in water to form a suspension. A magnet was placed outside the container. After a period of time, the nanocomposite material was attracted to one side of the magnet, indicating that the nanocomposite material has magnetic properties. The mass percentage of the elements contained in the material is listed in Table 1.

[0112] Material characterization: TEM images of the material are shown below. Figure 2 As shown, this material is a nanocomposite material containing a carbon-coated metal core-shell structure. A carbon layer with a certain degree of graphitization is wrapped around the nickel nanoparticles, forming a complete core-shell structure. The X-ray diffraction pattern of the carbon-coated nickel nanomaterial is shown below. Figure 3 As shown, the diffraction pattern of this material contains diffraction peaks corresponding to graphitic carbon (2θ angle of 25.97°) and fcc Ni (2θ angles of 44.47°, 51.34° and 76.26°). The average particle size of the carbon-coated nickel nanoparticles is calculated to be 8.1 nm using the Scherrer formula.

[0113] BET testing shows that the specific surface area of ​​this material is 200 m². 2 / g, pore volume is 0.204cm³ 3 / g, of which the mesopore volume is 0.201cm³ 3 / g, accounting for 98.6% of the total pore volume; of which the pore volume of 2-5nm is 0.0245cm³. 3 / g, accounting for 12.0% of the total pore volume. Figure 4a and Figure 4b The N2 adsorption-desorption isotherm and BJH pore size distribution curve of the material show that the composite material has two mesoporous distribution peaks at 3.79 nm and 10.01 nm.

[0114] The X-ray photoelectron spectroscopy (XPS) of this nanocomposite material is as follows: Figures 5a-5c As shown, from Figure 5a The presence of XPS peaks for C, O, N, and Ni clearly demonstrates the effective doping of N and O elements. From... Figure 5b It can be seen that the Ni valence state is 0. From Figure 5cIt can be seen that the O in this composite nanomaterial does not contain metal-oxygen (MO) bonds, but only carboxyl oxygen, carbonyl oxygen and hydroxyl oxygen, which fully proves that this core-shell structure effectively isolates the highly active Ni nanoparticles from the air and the core-shell structure is intact.

[0115] The pickling loss rate of the composite material prepared in this example was measured and calculated according to the methods described in the terminology section. Further increasing the pickling time based on the methods described in the terminology section did not significantly change the pickling loss rate.

[0116] Preparation Example 2

[0117] (1) Weigh 10g of nickel acetate, 20g of citric acid and 20g of hexamethylenetetramine, add them to a beaker containing 100mL of deionized water, stir at 80℃ to obtain a homogeneous solution, and continue to heat to dryness to obtain a solid.

[0118] (2) Place the precursor obtained in step (1) into a ceramic boat, then place the ceramic boat in the constant temperature zone of a tube furnace, introduce nitrogen gas at a flow rate of 150 mL / min, and heat it to 600°C at a rate of 5°C / min. After holding the temperature for 2 hours, stop heating and cool it to room temperature under a nitrogen atmosphere to obtain carbon-coated nanomaterials.

[0119] (3) The material obtained in step (2) was added to 80 mL of 10% hydrochloric acid and treated at reflux temperature for 10 h. The sample was then washed with deionized water until neutral and dried. The mass percentage of elements contained in the material was determined by elemental analysis and X-ray fluorescence spectrometry (XRF) and is listed in Table 1.

[0120] Material characteristics: TEM image of this nanocomposite material is shown below. Figure 6 As shown, this nanocomposite material contains nanoparticles with a core of nano-metallic nickel and a shell of carbon with a certain degree of graphitization; the X-ray diffraction pattern of this material is shown below. Figure 7 As shown, the XRD diffraction pattern of this material exhibits diffraction peaks corresponding to carbon (2θ angle 26.1°), fcc Ni (44.6°, 51.8°, and 76.4°), and hcp Ni (2θ angles 41.7°, 44.6°, 47.6°, and 62.4°). The average particle size of the carbon-coated nickel nanoparticles was calculated to be 34.5 nm using the Scherrer equation. BET analysis showed that the specific surface area of ​​this material was 183 m². 2 / g, pore volume is 0.278cm³ 3 / g, of which the mesopore volume is 0.276cm³ 3 / g, accounting for 99.3% of the total pore volume; of which the pore volume of 2-5nm is 0.0646cm³. 3 / g, accounting for 23.2% of the total pore volume. Figure 8The BJH pore size distribution curve of the material shows that the composite material has two mesoporous distribution peaks at 3.83 nm and 9.97 nm.

[0121] The pickling loss rate of the composite material prepared in this example was measured and calculated according to the methods described in the terminology section. Further increasing the pickling time based on the methods described in the terminology section did not significantly change the pickling loss rate.

[0122] Preparation Example 3

[0123] (1) Weigh 10g cobalt acetate, 10g citric acid and 20g hexamethylenetetramine, add them to a beaker containing 150mL deionized water, stir at 60℃ to obtain a homogeneous solution, and continue to heat to dryness to obtain a solid.

[0124] (2) Place the precursor powder obtained in step (1) into a ceramic boat, then place the ceramic boat in the constant temperature zone of a tube furnace, introduce nitrogen gas at a flow rate of 100 mL / min, and heat it to 700°C at a rate of 5°C / min. After holding the temperature for 1 hour, stop heating and cool it to room temperature under a nitrogen atmosphere to obtain carbon-coated nanomaterials.

[0125] (3) The material obtained in step (2) was added to 80 mL of 10% hydrochloric acid and treated at reflux temperature for 6 h. The sample was then washed with deionized water until neutral and dried. The mass percentage of elements contained in the nanocomposite material was determined by elemental analysis and X-ray fluorescence spectrometry (XRF) and is listed in Table 1.

[0126] Material characteristics: TEM image of this nanocomposite material is shown below. Figure 9 As shown, this nanocomposite material contains nanoparticles with a cobalt core and a carbon shell with a certain degree of graphitization; the X-ray diffraction pattern of this material is shown below. Figure 10 As shown, the XRD diffraction pattern of this material exhibits diffraction peaks corresponding to carbon (2θ angle 25.96°) and fcc Co (44.4°). The average particle size of the carbon-coated cobalt nanoparticles was calculated to be 14.2 nm using the Scherrer equation. BET analysis indicates that the specific surface area of ​​this material is 256 m². 2 / g, pore volume is 0.244cm³ 3 / g, of which the mesopore volume is 0.244cm³ 3 / g, accounting for 100% of the total pore volume; of which the pore volume of 2-5nm is 0.073cm³. 3 / g, accounting for 29.9% of the total pore volume. Figure 11 The BJH pore size distribution curve of the material shows that the composite material has two mesoporous distribution peaks at 3.66 nm and 13.52 nm.

[0127] The pickling loss rate of the composite material prepared in this example was measured and calculated according to the method described in the terminology section. Further increasing the pickling time based on the method described in the terminology section did not significantly change the pickling loss rate.

[0128] Preparation Example 4

[0129] (1) Weigh 10g of nickel acetate, 10g of cobalt acetate, 20g of citric acid, and 10g of hexamethylenetetramine, and add them to a beaker containing 150mL of deionized water. Stir and react at 60℃ for 24h, then continue heating to evaporate to dryness to obtain a solid. The X-ray diffraction pattern of this solid precursor is shown below. Figure 12 As shown.

[0130] (2) Place the precursor powder obtained in step (1) into a ceramic boat, then place the ceramic boat in the constant temperature zone of a tube furnace, introduce nitrogen gas at a flow rate of 100 mL / min, and heat it to 600 °C at a rate of 4 °C / min. After holding the temperature for 2 hours, stop heating and cool it to room temperature under a nitrogen atmosphere to obtain carbon-coated nanomaterials.

[0131] (3) The material obtained in step (2) was added to 80 mL of 10% hydrochloric acid and treated at reflux temperature for 4 h. The sample was then washed with deionized water until neutral and dried. The mass percentage of elements contained in the nanocomposite material was determined by elemental analysis and X-ray fluorescence spectrometry (XRF) and is listed in Table 1.

[0132] Material characteristics: TEM image of this nanocomposite material is shown below. Figure 13 As shown, this nanocomposite material contains nanoparticles with nano-metallic nickel and cobalt as the core and graphitized carbon as the shell; the X-ray diffraction pattern of this material is shown below. Figure 14 As shown, the XRD diffraction pattern of this material exhibits diffraction peaks corresponding to carbon (2θ angle 26.2°) and fcc Ni or Co diffraction peaks (44.5°, 51.7°, and 76.1°). The average particle size of the carbon-coated nickel-cobalt nanoparticles was calculated to be 13.4 nm using the Scherrer equation. BET analysis indicates that the specific surface area of ​​this material is 324 m². 2 / g, pore volume is 0.389cm³ 3 / g, of which the mesopore volume is 0.389cm³ 3 / g, accounting for 100% of the total pore volume; of which the pore volume of 2-5nm is 0.048cm³. 3 / g, accounting for 12.3% of the total pore volume. Figure 15 The BJH pore size distribution curve of this material shows that the composite material has two mesoporous distribution peaks at 3.74 nm and 6.59 nm.

[0133] The pickling loss rate of the composite material prepared in this example was measured and calculated according to the method described in the terminology section. Further increasing the pickling time based on the method described in the terminology section did not significantly change the pickling loss rate.

[0134] Table 1

[0135] Preparation Example Carbon, wt% Hydrogen, wt% Nitrogen, wt% Oxygen, wt% Nickel, wt% Cobalt, wt% Preparation Example 1 47.55 1.33 4.27 4.84 42.01 _ Preparation Example 2 48.57 1.35 4.61 5.79 39.68 _ Preparation Example 3 52.02 1.44 6.48 7.56 _ 32.5_ Preparation Example 4 42.68 1.82 3.27 7.51 24.27 20.45

[0136] Comparative Example 1

[0137] 10g of nickel acetate solid was placed in a porcelain boat, which was then placed in the isothermal zone of a tube furnace. Nitrogen gas was introduced at a flow rate of 150mL / min, and the temperature was increased to 600℃ at a rate of 5℃ / min. After holding at this temperature for 2 hours, heating was stopped, and the mixture was cooled to room temperature under a nitrogen atmosphere to obtain the sample material. Elemental analysis and X-ray fluorescence spectrometry (XRF) determined the mass percentage of elements in the composite material to be: carbon 1.34%, hydrogen 0.32%, oxygen 0.18%, and nickel 98.16%. The X-ray diffraction pattern of this nanocomposite material is shown below. Figure 16 As shown, it can be seen that there are diffraction peaks (44.2°, 51.6° and 76.2°) corresponding to fcc Ni in the diffraction pattern of this material.

[0138] According to the methods described in the terminology section, the pickling loss rate of the composite material prepared in this comparative example is 100%.

[0139] Example 1

[0140] The nanocomposite material obtained in Preparation Example 1 was used as a catalyst for the hydrogenation of nitrobenzene to prepare aniline. The specific experimental steps were as follows:

[0141] 0.1 g of nanocomposite material, 1.97 g of nitrobenzene, and 100 mL of ethanol were added to a reaction vessel. After purging the reaction vessel three times with H2, the pressure inside the vessel was increased to 3 MPa. The mixture was stirred and heated to the predetermined reaction temperature of 60 °C. After a predetermined reaction time of 3 hours, heating was stopped, and the mixture was cooled to room temperature. The pressure was released, and the product aniline was collected from the reaction vessel for chromatographic analysis. The conversion rate of the reactants and the selectivity of the target product were calculated using the following formulas:

[0142] Conversion rate = (Mass of reactants reacted / Amount of reactants added) × 100%

[0143] Selectivity = (Mass of target product / Mass of reaction product) × 100%

[0144] Analysis revealed that the nitrobenzene conversion rate was 100% and the aniline selectivity was 99.3%.

[0145] Example 2

[0146] The nanocomposite material obtained in Preparation Example 1 was used as a catalyst for the hydrogenation of nitrobenzene to prepare aniline. The specific experimental steps were as follows:

[0147] 0.1 g of nanocomposite material, 0.49 g of nitrobenzene, and 30 mL of ethanol were added to a reaction vessel. After purging the reaction vessel three times with H2, the pressure inside the vessel was increased to 0.5 MPa with H2. The mixture was stirred and heated to the predetermined reaction temperature of 120°C. After a predetermined reaction time of 0.5 hours, heating was stopped, and the mixture was allowed to cool to room temperature. The pressure was released, and the product aniline was collected and subjected to chromatographic analysis. The conversion rate of the reactants and the selectivity of the target product were calculated using the formulas listed in Example 1.

[0148] Analysis revealed that the nitrobenzene conversion rate was 100% and the aniline selectivity was 99.6%.

[0149] Example 3

[0150] The nanocomposite material obtained in Preparation Example 1 was used as a catalyst for the hydrogenation of nitrobenzene to prepare aniline. The specific experimental steps were as follows:

[0151] 0.1 g of nanocomposite material, 0.33 g of nitrobenzene, and 30 mL of ethanol were added to a reaction vessel. After purging the reaction vessel three times with H2, the pressure inside the vessel was increased to 1 MPa. The mixture was stirred and heated to the predetermined reaction temperature of 60°C. After a predetermined reaction time of 2 hours, heating was stopped, and the mixture was cooled to room temperature. The pressure was released, and the product aniline was collected from the reaction vessel for chromatographic analysis. The conversion rate of the reactants and the selectivity of the target product were calculated using the formulas listed in Example 1.

[0152] Analysis revealed that the nitrobenzene conversion rate was 100% and the aniline selectivity was 99.9%.

[0153] Example 4

[0154] The nanocomposite material obtained in Preparation Example 2 was used as a catalyst for the hydrogenation of nitrobenzene to prepare aniline. The specific experimental steps were as follows:

[0155] 0.1 g of nanocomposite material, 0.66 g of nitrobenzene, and 50 mL of ethanol were added to a reaction vessel. After purging the reaction vessel three times with H2, the pressure inside the vessel was increased to 1 MPa. The mixture was stirred and heated to the predetermined reaction temperature of 100°C. After a predetermined reaction time of 1 hour, heating was stopped, and the mixture was allowed to cool to room temperature. The pressure was released, and the product aniline was collected from the reaction vessel for chromatographic analysis. The conversion rate of the reactants and the selectivity of the target product were calculated using the formulas listed in Example 1.

[0156] Analysis revealed that the nitrobenzene conversion rate was 100% and the aniline selectivity was 99.7%.

[0157] The experimental data above show that the carbon-coated metal composite material provided by this invention can be applied to the hydrogenation reaction of nitrobenzene to prepare aniline, and has good conversion rate and selectivity.

[0158] Those skilled in the art should note that the embodiments described in this invention are merely exemplary, and various other substitutions, changes, and improvements can be made within the scope of this invention. Therefore, this invention is not limited to the above embodiments, but is defined only by the claims.

Claims

1. A carbon-coated transition metal nanocomposite material, wherein the nanocomposite material contains a core-shell structure having a shell and a core, the shell being a graphitized carbon layer doped with nitrogen and oxygen, the core being transition metal nanoparticles, the transition metal being nickel, the carbon content in the nanocomposite material being 15-60 wt%, the transition metal content being 30-80 wt%, and the nitrogen content being 2-8 wt%; the nanocomposite material is a mesoporous material having at least one mesoporous distribution peak; the acid washing loss rate of the nanocomposite material is ≤10%, and the carbon-coated transition metal nanocomposite material is prepared by the following method: Transition metal salts, polycarboxylic acids, nitrogen-containing compounds, and other organic compounds are mixed in a solvent to form a homogeneous solution, and then the solvent is removed to form a water-soluble mixture containing transition metals. The water-soluble mixture is pyrolyzed at high temperature under an inert atmosphere. The product from high-temperature pyrolysis was treated with acid to obtain a carbon-coated transition metal nanocomposite material. The organic polycarboxylic acid is citric acid, the transition metal salt is acetate, the nitrogen-containing compound is hexamethylenetetramine, and the other organic compounds are organic polyols.

2. The nanocomposite material according to claim 1, wherein the nanocomposite material is a mesoporous material having two or more mesoporous distribution peaks.

3. The nanocomposite material according to claim 1 or 2, wherein the mesoporous material has a mesopore volume accounting for more than 50% of the total pore volume.

4. The nanocomposite material according to claim 1, wherein the mesoporous material has a mesoporous volume accounting for more than 80% of the total pore volume.

5. The nanocomposite material according to claim 1, wherein the total nitrogen and oxygen content in the nanocomposite material is less than 15% by mass percentage.

6. The nanocomposite material according to claim 1, wherein the thickness of the graphitized carbon layer is 0.3~6 nm.

7. The nanocomposite material according to claim 1, wherein the particle size of the core-shell structure is 1~200 nm.

8. The nanocomposite material according to claim 1, wherein the crystal structure of the transition metal nanoparticles is a face-centered cubic lattice structure and / or a close-packed hexagonal lattice structure.

9. The application of the nanocomposite material according to any one of claims 1-8 as a catalyst in hydrogenation reduction reaction.

10. The application according to claim 9, wherein the hydrogenation reduction reaction comprises: Nitrobenzene and the nanocomposite material were mixed in a solvent and reacted under a hydrogen atmosphere to synthesize aniline.

11. The application according to claim 10, wherein the nitrobenzene is a substituted nitrobenzene, and the substituent is selected from C 1-20 Alkyl, cycloalkyl, and aryl groups.

12. The application according to claim 10, wherein the nanocomposite material accounts for 1%-50% of the mass percentage of the nitrobenzene.

13. The application according to claim 10, wherein the hydrogenation reduction reaction is carried out at 60-120°C and the pressure of the hydrogen gas is 0.5-2 MPa.

14. The application according to any one of claims 10 to 13, wherein the solvent is selected from one or more alcohols, ethers and water.

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