Carbon-coated transition metal nanocomposite and application thereof

Abstract

The application provides a carbon-coated transition metal nanocomposite and application thereof. The nanocomposite has 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 nanocomposite is a mesoporous material with at least one mesopore distribution peak. The nanocomposite has abundant mesoporous structures and is a catalytic material with excellent performance. The nanocomposite can be used as a catalytic oxidation catalyst to treat volatile organic compounds in industrial waste gas and has a good industrial application prospect.

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] Nanocarbon catalysts, represented by carbon fibers, nanodiamonds, carbon nanotubes, and (oxidized) graphene, exhibit catalytic activity in a range of reactions involving hydrocarbons, including direct dehydrogenation, oxidative dehydrogenation, halogenation, hydroxylation, alkylation, and liquid-phase oxidation and condensation reactions of aldehydes and ketones. The active sites of nanocarbon catalysts are primarily structural defects and heteroatom functional groups within the carbon material itself. Therefore, to improve the catalytic activity of nanocarbon materials, it is necessary to increase the number of structural defects and heteroatom functional groups; however, this can lead to a decrease in the material's inherent stability.

[0003] Transition metal nanomaterials have attracted widespread attention due to their excellent optical, electrical, magnetic and catalytic properties. However, due to the high activity of transition metal nanoparticles, they are prone to agglomeration or oxidation, and may even spontaneously combust in air, which greatly affects the performance and application of these materials.

[0004] Transition metal nanomaterials have high catalytic activity but poor stability, while carbon nanomaterials have good chemical stability but require further improvement in catalytic activity. If the two are combined in an appropriate way, new synergistic effects may be generated, giving them new and unique properties.

[0005] Mesoporous materials generally possess large specific surface areas and relatively regular pore structures, enabling them to play a better role in the separation, adsorption, and catalytic reactions of macromolecules, and potentially serve as microreactors for confined catalysis. Due to their high hydrothermal stability, strong hydrophobicity, and affinity for organic compounds, mesoporous carbon materials exhibit unique advantages in reactions such as hydrogenation, oxidation, and decomposition. Currently, the main methods for preparing mesoporous carbon materials are catalytic activation, organic gel carbonization, and template methods, but these methods are overly complex.

[0006] While there are existing reports on the coating of transition metals with carbon materials, these materials still face various problems in practical applications. These include stringent manufacturing conditions, complex processes, low coating rates, incomplete coating, the need for nitric acid treatment when introducing oxygen-containing groups, easy damage to the carbon coating layer, and adverse effects on the metal core, 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 (MOFs) with periodic structures in a solvent under high temperature and pressure. The conditions for preparing MOFs are typically 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, a catalyst for the selective hydrogenation of aromatic nitro compounds. This literature describes a method for coating metal particles using the Pechini method (sol-gel method). Similar to the MOF method, this method also requires the preparation of a solid coordination polymer in a solvent, and the coating of metal particles in the composite material prepared by this method is also not tight.

[0007] 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

[0008] To address the problems existing in the prior art, this invention provides a carbon-coated transition metal nanocomposite material. This nanocomposite material forms a core-shell structure by coating transition metal nanoparticles with a graphitized carbon layer doped with nitrogen and oxygen, and possesses abundant mesoporous structure, which can improve mass transfer efficiency and increase stability. Furthermore, the nanocomposite material of this invention can also have a multi-level mesoporous structure. This invention also provides the application of the aforementioned material in the treatment of volatile organic compounds (VOCs).

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A carbon-coated transition metal nanocomposite material, wherein the composite material has a core-shell structure having a shell and a core, wherein the shell is a graphitized carbon layer doped with nitrogen and oxygen, and the core is a transition metal nanoparticle, wherein the composite material is a mesoporous material having at least one pore distribution peak.

[0011] According to one embodiment 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.

[0012] 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 2-7 nm and the pore size range of 8-16 nm, respectively.

[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 0.10-0.30cm³. 3 / g.

[0015] According to one embodiment of the present invention, the carbon content in the nanocomposite material is 10.0%-60.0% by mass percentage, and the transition metal content is 30.0%-85.0%; preferably, the carbon content is 30.0%-50.0%, and the transition metal content is 30.0%-60.0%.

[0016] In another embodiment of the nanocomposite material of the present invention, the total content of nitrogen and oxygen in the nanocomposite material is less than 15.0% by mass, preferably 0.2%-12.0%, more preferably 0.5%-10.0%.

[0017] In another embodiment of the nanocomposite material of the present invention, the nitrogen content is less than 15% by mass, preferably 0.1-10%, more preferably 1-5%.

[0018] According to the present invention, the sum of the contents of each component in the nanocomposite material is 100%.

[0019] According to one embodiment of the present invention, the pickling loss rate of the composite material is generally ≤40%, and the pickling loss rate can be ≤30%.

[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] According to one embodiment 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] On the other hand, the present invention provides the application of the above-mentioned nanocomposite material as a catalyst in the treatment of volatile organic compounds, including: contacting the volatile organic compounds with the nanocomposite material to carry out a catalytic oxidation reaction.

[0024] In one embodiment of the present invention, the volatile organic compound is a volatile organic compound contained in industrial waste gas.

[0025] In another embodiment of the invention, the volatile organic compound includes butane, and the volume percentage of butane in the industrial waste gas is 0.01 to 2%.

[0026] In another embodiment of the invention, the temperature of the catalytic oxidation reaction is 200–500°C, preferably 350–400°C, and the reaction space velocity is 2000–5000 mL of industrial waste gas / (h·g of the catalyst).

[0027] In another embodiment of the present invention, the industrial waste gas is the industrial waste gas generated from the oxidation of n-butane to produce maleic anhydride.

[0028] The beneficial effects of this invention are as follows:

[0029] This invention constructs a nanocomposite material with abundant mesopores by using an oxygen- and nitrogen-doped graphitized carbon layer as a shell and a transition metal as a core. Since the carbon material itself has catalytic activity in the carbon-coated transition metal nanocomposite material of this invention, it works synergistically with the transition metal, making the mass transfer efficiency of the nanocomposite material higher. In particular, the nanocomposite material of this invention can also have a multi-level mesoporous structure, which is beneficial for better performance in more applications, especially in the field of catalysis.

[0030] The transition metal nanoparticles in this nanocomposite material have high carbon coating rate and tightness, and the content of doped oxygen and nitrogen can be adjusted. It does not require the introduction of oxygen elements by means of nitric acid treatment, and can adjust the electronic properties of the graphitized carbon layer to make it suitable for catalyzing different reactions.

[0031] The carbon-coated transition metal nanocomposite material of this invention contains a strongly magnetic metal core coated with a graphitized carbon layer and a rich porous structure, which better combines magnetic separation and adsorption functions, making it particularly suitable for adsorption separation applications. This carbon-coated transition metal nanocomposite material can be used as a catalyst for various organic reactions, improving the efficiency of catalytic reactions, especially exhibiting excellent catalytic effect and selectivity for catalytic hydrogenation, showing promising industrial application prospects. In one application exemplified by this invention, the composite material, when used as a catalytic oxidation catalyst, exhibits good low-temperature activity, which is of great significance for the complete removal of volatile organic compounds from industrial waste gases through catalytic combustion.

[0032] The carbon-coated transition metal composite material of the present invention does not spontaneously combust in air and can be stored in air for a long time like ordinary commodities without affecting its performance in catalytic oxidation, catalytic hydrogenation and other reactions. Attached Figure Description

[0033] 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:

[0034] 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;

[0035] Figure 2 This is a TEM image of the nitrogen-oxygen-doped carbon-coated nickel nanocomposite material prepared in Example 1;

[0036] Figure 3 The image shows the XRD pattern of the nitrogen-oxygen-doped carbon-coated nickel nanocomposite material prepared in Example 1.

[0037] Figure 4a This is the N2 adsorption-desorption isotherm of the nitrogen-oxygen-doped carbon-coated nickel nanocomposite material prepared in Example 1;

[0038] 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.

[0039] Figure 5a This is an XPS image of the nitrogen-oxygen-doped carbon-coated nickel nanocomposite material prepared in Example 1;

[0040] Figure 5b This is the Ni 2p spectrum in XPS of the nitrogen-oxygen-doped carbon-coated nickel nanocomposite material prepared in Example 1;

[0041] 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.

[0042] Figure 6 This is a TEM image of the nitrogen-oxygen-doped carbon-coated nickel nanocomposite material prepared in Example 2;

[0043] Figure 7 This is the XRD pattern of the nitrogen-oxygen-doped carbon-coated nickel nanocomposite material prepared in Example 2;

[0044] Figure 8 The BJH pore size distribution curve of the nitrogen-oxygen-doped carbon-coated nickel nanocomposite material prepared in Example 2 is shown.

[0045] Figure 9 This is a TEM image of the nitrogen-oxygen-doped carbon-coated cobalt nanocomposite material prepared in Example 3;

[0046] Figure 10 This is the XRD pattern of the nitrogen-oxygen-doped carbon-coated cobalt nanocomposite material prepared in Example 3;

[0047] Figure 11 The BJH pore size distribution curve of the nitrogen-oxygen-doped carbon-coated cobalt nanocomposite material prepared in Example 3 is shown.

[0048] Figure 12 This is the XRD pattern of the solid precursor prepared in Example 4;

[0049] Figure 13 This is a TEM image of the nitrogen-oxygen-doped carbon-coated nickel-cobalt nanocomposite material prepared in Example 4;

[0050] Figure 14 This is the XRD pattern of the nitrogen-oxygen-doped carbon-coated nickel-cobalt nanocomposite material prepared in Example 4;

[0051] Figure 15 The image shows the BJH pore size distribution curve of the nitrogen-oxygen-doped carbon-coated nickel-cobalt nanocomposite material prepared in Example 4.

[0052] Figure 16 This is the XRD pattern of the material prepared in Comparative Example 2. Detailed Implementation

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] the term

[0058] 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, with an interlayer spacing of approximately 0.34 nm. The nanocomposite material formed by coating transition metal nanoparticles with this graphitized carbon layer is spherical or near-spherical.

[0059] 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.

[0060] The term "mesoporous material" is defined as a porous material containing mesoporous channels.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] The term "acid pickling loss rate" refers to the proportion of transition metal lost after acid pickling of the prepared carbon-coated transition metal nanocomposite product. It reflects the tightness of the coating of the transition metal by the graphitized carbon layer. If the graphitized carbon layer does not tightly coat the transition metal, 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 coating tightness of the graphitized carbon layer on the transition metal, and vice versa.

[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, and calculate the acid washing loss rate according to the following formula.

[0068] 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%.

[0069] Reagents, Instruments and Tests

[0070] Unless otherwise specified, all reagents used in this invention are of analytical grade and are commercially available, such as those purchased from Sigma-Aldrich.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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 a transition metal nanoparticle. The nanocomposite material is a mesoporous material with at least one mesoporous distribution peak.

[0079] The nanocomposite material of this invention is a composite material composed of "transition metal nanoparticles tightly coated (not in contact with the outside world) by a graphitized carbon layer", "confined transition metal nanoparticles that can contact the outside world", and carbon materials with mesoporous structures. This nanocomposite material has abundant defect sites on the surface of its nitrogen- and oxygen-doped graphitized carbon layer. The carbon material itself possesses catalytic activity, which, in synergy with the transition metal nanoparticles, enables the nanocomposite material of this invention to exhibit superior catalytic performance. Furthermore, as is known to those skilled in the art, mesoporous materials generally have a large specific surface area and a relatively regular pore structure, enabling them to play a better role in the separation, adsorption, and catalytic reactions of macromolecules, and potentially serve as microreactors for confined catalysis. The nanocomposite material of this invention has abundant mesoporous structures, resulting in higher mass transfer efficiency and thus superior catalytic performance.

[0080] In some embodiments of the nanocomposite materials according to the present invention, 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 can be applied to a wider range of applications.

[0081] In some embodiments of the nanocomposite material according to the present invention, the mesoporous structure has a mesoporous distribution peak in the mesoporous ranges of 2-5 nm and 6-15 nm, respectively.

[0082] In some embodiments of the nanocomposite material according to the present invention, the mesoporous structure has a mesoporous distribution peak in the mesoporous ranges of 2–7 nm and 8–20 nm, respectively.

[0083] According to the nanocomposite material of the present invention, the proportion of mesopore volume to total pore volume is greater than 50%, preferably greater than 80%. In some embodiments, the proportion of mesopore volume to total pore volume is 100%.

[0084] The nanocomposite material according to the present invention has a mesopore volume of 0.05-1.25 cm³. 3 / g, or 0.10-0.30cm 3 / g.

[0085] The nanocomposite material of the present invention generally has a specific surface area greater than 140 m². 2 / g, can be greater than 200m 2 / g.

[0086] The nanocomposite material according to the present invention does not spontaneously combust in air and can be stored in air.

[0087] According to the nanocomposite material of the present invention, the pickling loss rate of the composite material is generally ≤40%, and can be ≤10%, 10%~20%, 20%~30%, or 30%~40%. As mentioned above, the pickling loss rate reflects the tightness of the graphitized carbon layer's coating on the transition metal.

[0088] In some embodiments, the carbon content in the nanocomposite material is 10.0%-60.0% by mass, and the transition metal content is 30.0%-85.0%; preferably, the carbon content is 30.0%-50.0%, and the transition metal content is 30.0%-60.0%.

[0089] The nanocomposite material according to the present invention has nitrogen and oxygen doped in the carbon layer. The nitrogen and oxygen content can be adjusted by introducing additional oxygen-containing compounds and nitrogen-containing compounds, such as hexamethylenetetramine and polyols, during the manufacturing process. By adjusting the nitrogen and oxygen content in the nanocomposite material, the catalytic performance of the carbon layer can be adjusted to suit reactions different from those catalyzed. In some embodiments, the total nitrogen and oxygen content in the nanocomposite material is less than 15.0% by mass, preferably 0.2%-12.0%, more preferably 0.5%-10.0%, wherein the nitrogen content is less than 15.0%, preferably 0.1-10%, more preferably 1-5%.

[0090] According to the present invention, the sum of the contents of each component in the nanocomposite material is 100%.

[0091] In some embodiments, the thickness of the graphitized carbon layer is 0.3 nm to 6.0 nm, preferably 0.3 nm to 3 nm.

[0092] 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.

[0093] 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 one or more of iron, cobalt, nickel, and copper, more preferably nickel (Ni).

[0094] In some embodiments, the crystal structure of the transition metal nanoparticles is a face-centered cubic (fcc) crystal structure.

[0095] In some embodiments, the lattice structure of the transition metal nanoparticles is a face-centered cubic (fcc) lattice structure and a hexagonal close-packed (hcp) lattice structure.

[0096] In some embodiments, the above-mentioned carbon-coated transition metal nanocomposite material is prepared by the following method:

[0097] A water-soluble mixture containing a transition metal is formed by mixing a transition metal salt, "a polycarboxylic acid and a nitrogen-containing compound, or a nitrogen-containing organic polycarboxylic acid" and optional other organic compounds in a solvent.

[0098] The water-soluble mixture is pyrolyzed at high temperature under an inert or reducing atmosphere.

[0099] Specifically, the water-soluble mixture mentioned in the preparation method refers to a homogeneous solution obtained by dissolving "polycarboxylic acids and nitrogen-containing compounds, or nitrogen-containing organic polycarboxylic acids" and optional other organic compounds other than the former in solvents such as water and ethanol, and then directly evaporating to remove the solvent to obtain a water-soluble mixture containing transition metals. The temperature and process for evaporating the solvent can employ any feasible existing technology, such as spray drying at 80-120°C or drying in an oven.

[0100] In some embodiments, the organic polycarboxylic acids used in the preparation include, but are not limited to, citric acid; nitrogen-containing organic polycarboxylic acids include, but are not limited to, ethylenediaminetetraacetic acid (EDTA); transition metal salts include, but are not limited to, acetates; nitrogen-containing compounds include, but are not limited to, hexamethylenetetramine; and other organic compounds include, but are not limited to, organic polyols.

[0101] In some embodiments, the inert atmosphere in the high-temperature pyrolysis step is protected by nitrogen or argon, and the reducing atmosphere can be an atmosphere doped with a small amount of hydrogen. The pyrolysis process includes a heating section and a 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 400–800 °C, preferably 500–700 °C; and the isothermal time is 20–600 min, preferably 30–300 min.

[0102] 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.

[0103] This invention prepares the carbon-coated transition metal composite material using the above method, instead of the MOF method. This allows for easier adjustment of the oxygen and nitrogen content in the graphitized carbon layer during the preparation process, thereby facilitating the adjustment of the catalytic performance of the nanocomposite material to suit different catalytic reactions.

[0104] This invention also provides the application of the aforementioned nanocomposite material as a catalyst in the treatment of volatile organic compounds (VOCs). Industrial waste gas often contains VOCs, which are generally organic compounds with a saturated vapor pressure greater than 70 Pa at room temperature and a boiling point below 250°C at normal pressure. Common examples include alkanes, aromatics, ether alcohols, and halogenated hydrocarbons. VOCs are the primary source of generation and emission in the chemical and petrochemical industries, and are also commonly encountered in daily life (e.g., formaldehyde from home renovations). For instance, in the production of maleic anhydride using industrial n-butane as a raw material, the raw material and oxygen in the air cannot be 100% converted into the product under the action of a catalyst, resulting in the generation of VOCs. VOCs have become one of the main causes of photochemical smog, and along with nitrogen oxides and inhalable particulate matter, they are important pollutants for controlling air quality. Furthermore, they are highly toxic and carcinogenic, thus necessitating the use of high-performance catalytic oxidation materials for their treatment.

[0105] The present invention uses the above-mentioned nanocomposite material as a catalyst to treat the volatile organic compounds in the above-mentioned industrial waste gas. The specific method is to contact the nanocomposite material with the gaseous volatile organic compounds to carry out a catalytic oxidation reaction, wherein the volatile organic compounds include butane, and the volume percentage of butane in the industrial waste gas is 0.01-2%.

[0106] In some embodiments, the temperature of the catalytic oxidation reaction is 200–500°C, preferably 350–400°C. The reaction space velocity is 2000–5000 mL of industrial waste gas / (h·g of the catalyst). Using the composite material of the present invention as a catalyst can reduce the severity of the reaction. For example, at 350°C, butane components with a content of 0.01–2 vol% in the waste gas generated from the maleic anhydride production process can be catalytically oxidized to CO2 with an elimination rate of over 90 vol%. At 400°C, the butane components can be completely catalytically oxidized to CO2. Compared with the prior art, the reaction temperature can be reduced and the reaction space velocity can be increased, achieving complete oxidation of low-concentration butane in the waste gas generated from chemical production processes at a lower temperature, which has good prospects for industrial application.

[0107] Example

[0108] 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 heating to evaporate to dryness to obtain a solid precursor. Experiments show that the solid precursor obtained in this step is soluble in water.

[0110] (2) The precursor obtained in step (1) is placed in a ceramic boat, and then the ceramic boat is placed in the constant temperature zone of a tube furnace. Nitrogen gas with a flow rate of 100 mL / min is introduced, and the temperature is increased to 650°C at a rate of 5°C / min. After holding at this temperature for 2 hours, heating is stopped, and the mixture is cooled to room temperature under a nitrogen atmosphere to obtain a carbon-coated nickel nanocomposite material. 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 elements contained in the nanocomposite material was determined by elemental analysis and X-ray fluorescence spectrometry (XRF), and is listed in Table 1.

[0111] Material characterization: TEM images of the material are shown below. Figure 2 As can be seen, this material is a carbon-coated metal nanocomposite material, with a carbon layer of a certain degree of graphitization surrounding the nickel nanoparticles, forming a complete core-shell structure. The X-ray diffraction pattern of the carbon-coated nickel nanocomposite material is shown below. Figure 3 As shown, the diffraction pattern of this nanocomposite material contains diffraction peaks corresponding to graphite carbon (2θ angle of 25.96°) and fcc Ni (2θ angles of 44.38°, 51.83° and 76.42°). The average particle size of the carbon-coated nickel nanoparticles is calculated to be 6.3 nm using the Scherrer formula.

[0112] BET testing showed that the specific surface area of ​​this nanocomposite material was 114 m². 2 / g, pore volume is 0.181cm³ 3 / g, of which the mesopore volume is 0.173cm³ 3 / g, accounting for 95.6% of the total pore volume. Figure 4a and Figure 4b The N2 adsorption-desorption isotherm and BJH pore size distribution curve of the nanocomposite material show that there are two mesoporous distribution peaks at 3.75 nm and 10.03 nm.

[0113] 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 5c It 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.

[0114] According to the methods described in the terminology section, the pickling loss rate of the composite material prepared in this embodiment is 14%. Based on the methods described in the terminology section, further increasing the pickling time does not significantly change the pickling loss rate.

[0115] Example 2

[0116] (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 precursor.

[0117] (2) The precursor obtained in step (1) was placed in a ceramic boat, and then the ceramic boat was placed in the isothermal zone of a tube furnace. Nitrogen gas was introduced at a flow rate of 150 mL / min, and the temperature was increased to 600 °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 nanomaterials. 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.

[0118] Material characterization: This nanocomposite material contains a core-shell structure with nano-sized nickel as the core and graphitized carbon as the shell. TEM images are shown below. Figure 6 As shown; the X-ray diffraction pattern of the carbon-coated nickel nanocomposite is as follows. Figure 7 As shown, the XRD diffraction pattern of this nanocomposite material exhibits diffraction peaks corresponding to fcc Ni (2θ angles of 44.4°, 51.9°, and 76.5°) and hcp Ni (2θ angles of 41.9°, 44.4°, and 47.5°). The average particle size of the carbon-coated nickel nanoparticles is calculated to be 31.4 nm using the Scherrer equation. BET test results are as follows... Figure 8 As shown, the specific surface area of ​​this nanocomposite material is 126 m². 2 / g, pore volume is 0.213cm³ 3 / g, of which the mesopore volume is 0.207cm³ 3 / g, accounting for 97.1% of the total pore volume. By measuring the N2 adsorption-desorption isotherm and BJH pore size distribution curve of the nanocomposite, two mesoporous distribution peaks were found at 3.83 nm and 11.16 nm.

[0119] According to the methods described in the terminology section, the pickling loss rate of the composite material prepared in this embodiment is 9.3%. Based on the methods described in the terminology section, further increasing the pickling time does not significantly change the pickling loss rate.

[0120] Example 3

[0121] (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 precursor.

[0122] (2) The precursor obtained in step (1) was placed in a ceramic boat, and then the ceramic boat was placed in the isothermal zone of a tube furnace. Nitrogen gas was introduced at a flow rate of 100 mL / min, and the temperature was increased to 700 °C at a rate of 5 °C / min. After holding at this temperature for 1 h, the heating was stopped, and the mixture was cooled to room temperature under a nitrogen atmosphere to obtain a carbon-coated cobalt nanocomposite material. 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.

[0123] Material characterization: This nanocomposite material contains a core-shell structure with nano-cobalt as the core and graphitized carbon as the shell. TEM images are shown below. Figure 9 As shown; the X-ray diffraction pattern of the carbon-coated cobalt nanocomposite is as follows. Figure 10 As shown, the XRD diffraction pattern of this nanocomposite material shows a cobalt diffraction peak (2θ angle of 44.42°). The average particle size of the carbon-coated cobalt nanoparticles was calculated to be 17.5 nm using the Scherrer equation. BET test results are as follows: Figure 11 As shown, the specific surface area of ​​this nanocomposite material is 140 m². 2 / g, pore volume is 0.158cm³ 3 / g, of which the mesopore volume is 0.158cm³ 3 / g, accounting for 100% of the total pore volume. By measuring the N2 adsorption-desorption isotherm and BJH pore size distribution curve of the nanocomposite material, two mesoporous distribution peaks were found at 3.77 nm and 13.32 nm.

[0124] According to the method described in the terminology section, the pickling loss rate of the composite material prepared in this embodiment is 31.2%. Based on the method described in the terminology section, further increasing the pickling time does not significantly change the pickling loss rate.

[0125] Example 4

[0126] (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 precursor. The X-ray diffraction pattern of this solid precursor is shown below. Figure 12 As shown.

[0127] (2) The precursor obtained in step (1) was placed in a ceramic boat, and then the ceramic boat was placed in the isothermal zone of a tube furnace. Nitrogen gas was introduced at a flow rate of 100 mL / min, and the temperature was increased to 600 °C at a rate of 4 °C / min. After holding at this temperature for 2 hours, the heating was stopped, and the mixture was cooled to room temperature under a nitrogen atmosphere to obtain a carbon-coated nickel and cobalt nanocomposite material. The mass percentage of the elements contained in the nanocomposite material was determined by elemental analysis and X-ray fluorescence spectrometry (XRF) and is listed in Table 1.

[0128] Material characteristics: This nanocomposite material contains a core-shell structure with nano-metallic nickel and cobalt as the core and graphitized carbon as the shell. TEM images are shown below. Figure 13 As shown; the X-ray diffraction pattern of the carbon-coated nickel-cobalt nanocomposite material is shown below. Figure 14 As shown, the XRD diffraction pattern of this nanocomposite material exhibits diffraction peaks corresponding to fcc Ni or Co (44.5°, 51.7°, and 76.2°). The average particle size of the carbon-coated nanoparticles was calculated to be 24.4 nm using the Scherrer equation. BET test results are as follows... Figure 15 As shown, the specific surface area of ​​this nanocomposite material is 182 m². 2 / g, pore volume is 0.256cm³ 3 / g, of which the mesopore volume is 0.256cm³ 3 / g, accounting for 100% of the total pore volume. By measuring the N2 adsorption-desorption isotherm and BJH pore size distribution curve of the nanocomposite material, two mesoporous distribution peaks were found at 3.7 nm and 6.34 nm.

[0129] According to the method described in the terminology section, the pickling loss rate of the composite material prepared in this embodiment is 38.4%. Based on the method described in the terminology section, further increasing the pickling time does not significantly change the pickling loss rate.

[0130] Table 1

[0131] Example Carbon, wt% Hydrogen, wt% Nitrogen, wt% Oxygen, wt% Nickel, wt% Cobalt, wt% Example 1 43.30 1.08 3.88 3.99 47.75 - Example 2 46.86 1.20 4.26 5.22 42.46 - Example 3 44.75 0.98 3.25 3.68 - 47.34 Example 4 32.35 0.52 1.68 1.21 30.72 33.52

[0132] Comparative Example 1

[0133] (1) Preparation of Ni-MOF material: Weigh 3.09g nickel nitrate, 2.8g terephthalic acid and 0.95g triethylenediamine and add them to 120mL dimethylformamide. Heat at 120℃ for 8h, then seal and let stand at 120℃ for 40h. After filtration, wash with dimethylformamide and methanol, and vacuum dry to obtain Ni-MOF material.

[0134] (2) Synthesis of Ni@CN material: The Ni-MOF obtained in (1) 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 200℃ at a rate of 4℃ / min and held at 2h. Then the temperature was increased to 500℃ and held at 8h. The heating was stopped and the material was cooled to room temperature under a nitrogen atmosphere to obtain carbon-coated Ni@CN nanomaterial.

[0135] Characterization of the material: The material forms a core-shell structure with nano-metallic nickel as the core and graphitized carbon as the shell; fcc Ni diffraction peaks (44.45°, 51.32° and 76.16°) are present in the XRD diffraction pattern of the material.

[0136] According to the method described in the terminology section, the pickling loss rate of the composite material prepared in this embodiment is 64.2%. Based on the method described in the terminology section, further increasing the pickling time does not significantly change the pickling loss rate.

[0137] Comparative Example 2

[0138] 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.

[0139] According to the methods described in the terminology section, the pickling loss rate of the composite material prepared in this comparative example is 100%.

[0140] Comparative Example 3

[0141] 2.0 g of the nano-carbon composite material obtained in Example 1 was weighed and washed with 80 mL of 1M sulfuric acid at 90 °C for 8 h. It was then washed with deionized water until neutral and dried at 120 °C to obtain the acid-washed carbon nanocomposite material. The mass percentage of elements in the composite material was determined by elemental analysis and X-ray fluorescence spectrometry (XRF): carbon 46.70%, hydrogen 1.28%, oxygen 4.56%, nitrogen 4.17%, and nickel 43.29%.

[0142] Test case

[0143] The nanocomposites prepared in Examples 1-4, the materials in Comparative Examples 2-3, and commercially available nickel oxide (NiO) (analytical grade, batch number: 20160803, manufacturer: Sinopharm Chemical Reagent Company) were used as catalysts in experiments to completely catalyze the elimination of butane from the waste gas generated during the industrial process of oxidizing n-butane to maleic anhydride. The butane elimination rate of the catalytic materials was evaluated. Under the same conditions, a higher butane elimination rate indicates higher catalyst activity. The specific evaluation method is as follows:

[0144] The collected maleic anhydride production process waste gas containing butane is sent into a fixed-bed reactor loaded with composite materials to contact the composite materials as a catalyst and carry out a catalytic oxidation reaction. The reaction products are analyzed by gas chromatography, and the butane elimination rate is calculated as follows: Butane elimination rate = 100% - volume of butane in the reaction products / volume of butane in the maleic anhydride production process waste gas × 100%.

[0145] The exhaust gas from the maleic anhydride production process contains approximately 1% by volume butane, with the remainder being air and trace amounts of carbon monoxide and carbon dioxide. The reaction space velocity is 5000 mL of industrial exhaust gas / (h·g catalyst), and the evaluation time is 5 hours. Specific reaction temperature and butane elimination rate data are shown in Table 2.

[0146] Table 2

[0147]

[0148] As shown in Table 2, the nanocomposite materials prepared in Examples 1-4 of this invention can achieve a 100% butane removal rate in maleic anhydride production process waste gas containing 1% by volume butane at 350℃, and the required temperature is significantly lower than that of Comparative Examples 2-3 and commercially available nickel oxide. This demonstrates that the nanocomposite materials of this invention exhibit excellent low-temperature activity when used as a catalytic oxidation catalyst, which is of great significance for the complete removal of volatile organic compounds from industrial waste gas through catalytic combustion. The graphitized carbon layer acts as a separator to stabilize the active metal centers under reaction conditions, effectively preventing the aggregation and deactivation of the active centers. When the catalytic material provided by this invention is applied to the treatment of maleic anhydride production process waste gas, it can significantly reduce the reaction temperature, maintain catalyst stability, and reduce energy consumption.

[0149] 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. The application of a carbon-coated transition metal nanocomposite material as a catalyst in the complete removal of volatile organic compounds from industrial waste gas by catalytic combustion, comprising: The volatile organic compound is brought into contact with the nanocomposite material to carry out a catalytic oxidation reaction. The nanocomposite material 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 a transition metal nanoparticle. The transition metal is one or more selected from cobalt and nickel. The nanocomposite material is a mesoporous material with at least one mesoporous distribution peak. The pickling loss rate of the nanocomposite material is 9.3-40%, and the "pickling loss rate" is measured and calculated as follows: Add 1 g of sample to 20 mL of 1 mol / L sulfuric acid aqueous solution, treat the sample at 90 °C for 8 h, then wash with deionized water until neutral, dry, weigh, and analyze. Calculate the acid washing 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%; The total nitrogen and oxygen content in this nanocomposite material is less than 15.0% by mass percentage. The industrial waste gas is generated from the oxidation of n-butane to produce maleic anhydride. The volatile organic compounds include butane, and the volume percentage of butane in the industrial waste gas is 0.01-2%. The temperature of the catalytic oxidation reaction is 200-500°C, and the reaction space velocity is 2000-5000 mL of industrial waste gas / (h•g of the catalyst).

2. The application according to claim 1, wherein, The nanocomposite material has a distribution peak with more than one mesopore.

3. The application according to claim 1, wherein, The mesoporous material has a mesopore volume that accounts for more than 50% of the total pore volume.

4. The application according to claim 2, wherein, The mesoporous material has a mesopore volume that accounts for more than 50% of the total pore volume.

5. The application according to claim 1, wherein, The mesoporous material has a mesoporous volume that accounts for more than 80% of the total pore volume.

6. The application according to claim 2, wherein, The mesoporous material has a mesoporous volume that accounts for more than 80% of the total pore volume.

7. The application according to claim 1, wherein, By mass percentage, the carbon content in this nanocomposite material is 10.0%-60.0%, and the transition metal content is 30.0%-85.0%.

8. The application according to claim 1, wherein, By mass percentage, the carbon content in this nanocomposite material is 30.0%-50.0%, and the transition metal content is 30.0%-60.0%.

9. The application according to claim 1, wherein, The total nitrogen and oxygen content in this nanocomposite material is 0.2%-12.0% by mass percentage.

10. The application according to claim 1, wherein, The total nitrogen and oxygen content in this nanocomposite material is 0.5%-10.0% by mass percentage.

11. The application according to claim 1, wherein, The nitrogen content is less than 15% by mass percentage.

12. The application according to claim 1, wherein, The nitrogen content is 0.1-10% by mass percentage.

13. The application according to claim 1, wherein, The nitrogen content is 1-5% by mass percentage.

14. The application according to claim 1, wherein, The thickness of the graphitized carbon layer is 0.3~6.0 nm.

15. The application according to claim 1, wherein, The thickness of the graphitized carbon layer is 0.3~3 nm.

16. The application according to claim 1, wherein, The core-shell structure has a particle size of 1~200nm.

17. The application according to claim 1, wherein, The core-shell structure has a particle size of 3~100nm.

18. The application according to claim 1, wherein, The core-shell structure has a particle size of 4~50nm.

19. The application according to any one of claims 1 to 18, wherein, The transition metal is nickel.

20. The application according to claim 19, wherein, The transition metal nanoparticles have a face-centered cubic lattice structure and / or a close-packed hexagonal lattice structure.

21. The application according to claim 1, wherein, The catalytic oxidation reaction is carried out at a temperature of 350-400°C and a reaction space velocity of 2000-5000 ml of industrial waste gas / (h•g of catalyst).

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