Nitrogen-doped carbon-loaded molybdenum-based monatomic catalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of metal catalyst preparation, in particular to a nitrogen-doped carbon-loaded molybdenum-based monatomic catalyst and a preparation method and application thereof. The preparation method of the nitrogen-doped carbon-loaded molybdenum-based monatomic catalyst comprises the following steps: dissolving a carbon precursor and a template agent in deionized water, stirring to obtain a nitrogen-carbon precursor, then adding soluble molybdate, violently stirring, and then drying to obtain a molybdenum and nitrogen-carbon precursor solid mixture; then, a flash Joule heat technology is adopted, and the nitrogen-doped carbon-loaded molybdenum-based monatomic catalyst with a large number of wrinkled nanosheets and an excellent pore channel structure is synthesized under the coupling action of temperature and an electric field. The molybdenum-based monatomic prepared by the method has good activity in catalysis of hydrogen-free aqueous phase reforming of a lignin model compound and self-reforming hydrogenolysis of lignin.

Description

Technical Field

[0001] This invention relates to the field of metal catalyst preparation technology, and in particular to a nitrogen-doped carbon-supported molybdenum-based single-atom catalyst, its preparation method, and its application. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] In recent years, accelerating the development and utilization of renewable energy has become a global consensus in addressing environmental and energy issues. Under the backdrop of green and sustainable development, finding alternative petrochemical raw materials to solve prominent problems in the energy and chemical industry has significant scientific and social value. Lignocellulosic biomass (dry plant matter) is the most abundant renewable carbon resource on Earth. It is mainly composed of cellulose, hemicellulose, and the aromatic polymer lignin. Lignin is the main component of lignocellulosic biomass (15-30% by weight, 40% energy). Unlike polysaccharides or lipids, lignin is the only biopolymer with a high content of aromatic groups, making it an ideal candidate for renewable resources of aromatic commercial chemicals. Lignin itself has a stable three-dimensional network structure, mainly composed of three types of phenylpropane structural units—p-hydroxyl, guaiacol, and syringyl—linked by CO or C-C bonds. Due to its complex structure, lignin has not yet been developed and utilized on a large scale.

[0004] Currently, lignin depolymerization technologies mainly include acid catalysis, alkali catalysis, pyrolysis, oxidation, and hydrogenolysis. Generally, free radicals generated during lignin degradation undergo self-condensation reactions under high temperature and pressure to form non-degradable molecules and carbon deposits, leading to a decrease in the conversion rate and selectivity of lignin degradation. However, hydrogen atoms in the hydrogenolysis process can combine with free radicals, effectively inhibiting the condensation reaction and thus effectively avoiding the generation of by-products. Lignin catalytic hydrogenolysis has advantages such as high conversion rate and high product selectivity, and can significantly reduce coke content. However, the efficiency of hydrogenopolymerization depends on the hydrogenolysis activity of the catalyst.

[0005] In the lignin hydrogenolysis reaction, the active hydrogen generated by hydrogen dissociation plays a crucial role in determining the selective activation of the CO / CC bond. Kinetically, hydrogen activation relies on a catalyst-supported metal, which transfers electrons to the molecular orbitals of hydrogen to activate the HH bond through the active metal component. Although noble metal catalysts such as Ru, Pt, and Pd exhibit excellent catalytic performance in lignin hydrogenolysis, their scarcity, high cost, and tendency to cause excessive hydrogenation of the benzene ring and numerous byproducts limit their large-scale application. In contrast, transition metals such as Ni, Fe, Mo, and Co are abundant in nature, widely distributed, and inexpensive, possessing potential application value and thus attracting widespread attention in lignin hydrogenolysis.

[0006] Metal particles in active metal catalysts are mostly unevenly distributed, resulting in low utilization. To improve the atomic utilization of active metal catalysts, single-atom catalysts have been developed. In these catalysts, the active metal components are all dispersed on the support surface in the form of single atoms. In single-atom catalysts, every metal atom is exposed, and the fully exposed metal atoms increase the number of active sites, thereby maximizing the atomic efficiency of the metal.

[0007] In existing technologies, Ni1 / β-Mo2C was synthesized via impregnation. A single-atom catalyst composed of Ni1SAC was used for the hydrodeoxygenation of lignin derivatives. Studies have shown that Ni1 / β-Mo2C has significant potential in the catalytic hydrodeoxygenation of lignin derivatives to produce biofuels. A single-atom nickel catalyst was synthesized using a simple hydrothermal synthesis method. The single-atom xNi / CeO2-S catalyst promoted the hydrogenolysis of lignin by cellulose hydrolase, and the single-atom Ni site effectively promoted the hydrodeoxygenation of methoxy aromatic compounds to alkylphenols. However, single-atom catalysts also have drawbacks. Due to the high free energy and mobility of isolated metal atoms, metal particles are prone to aggregation during catalyst preparation, leading to catalyst deactivation. Improving the bonding strength between the catalyst support and the single atom is crucial to ensure higher stability of the single-atom catalyst. Among catalyst supports, activated carbon is widely used in the field of lignin hydrogenolysis due to its large specific surface area, large pore volume, abundant pore structure, good heat resistance, and excellent adsorption performance. However, the interaction between activated carbon and active metals is poor. Summary of the Invention

[0008] In view of this, the present invention provides a nitrogen-doped carbon-supported molybdenum-based single-atom catalyst, its preparation method and application.

[0009] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a method for preparing a nitrogen-doped carbon-supported molybdenum-based single-atom catalyst, comprising the following steps: (1) Dissolve the carbon precursor and template agent in water, stir to dissolve, then add molybdate and stir to obtain a homogeneous mixture; (2) Under stirring conditions, the mixture obtained in step (1) is reacted at 80-100 °C for 200-240 min to obtain a solid mixture; (3) The solid mixture obtained in step (2) is dried and ground, and then rapidly pyrolyzed using flash Joule heating under an argon atmosphere; (4) Grind the product after pyrolysis in step (3) to obtain the final product.

[0010] Furthermore, in step (1), the carbon precursor is glucose, glucosamine hydrochloride, chitosan, or fructose; the carbon precursor is widely available and very inexpensive.

[0011] Further, in step (1), the template agent is melamine, dicyandiamine, or cyanamide. The template agent can provide nitrogen atoms and be doped into the carbon framework, and can coordinate with Mo.

[0012] Further, in step (1), the molybdate is ammonium molybdate or ammonium tetramolybdate.

[0013] Further, in step (1), the mass ratio of carbon precursor, template agent and molybdate is 1-2:10-20:0.03-0.12.

[0014] Furthermore, in step (1), the stirring and dissolution time is 1-3 h; after adding molybdate, stirring is carried out for 1-3 h.

[0015] Furthermore, in step (1), the mass ratio of carbon precursor to water is 1-2:40-45.

[0016] Furthermore, in step (2), the stirring is magnetic stirring.

[0017] Furthermore, in step (3), the drying parameters are: 80-100 ℃, 10-15 h.

[0018] Furthermore, in step (3), the parameters used in the flash Joule heating technology are: voltage of 55-60 volts, current of 50-60 amperes, resistance of 100-150 ohms, power-on time of 1-2 seconds, and temperature of 800-1200 ℃.

[0019] A nitrogen-doped carbon-supported molybdenum single-atom catalyst was prepared using a flash Joule heating method. Under high temperature, the pretreated soluble molybdate and nitrogen-carbon precursor solid mixture decomposed, generating a large amount of volatile gases and nitrogen free radicals. The nitrogen free radicals and volatile gases generated by the pyrolysis of melamine etched and doped into the carbon framework, optimizing the catalyst's pore structure and increasing its specific surface area. Simultaneously, the addition of melamine not only increased the nitrogen content of the catalyst but also altered the form of nitrogen species; molybdenum and nitrogen formed coordination bonds (Mo-N), promoting the dispersion of the active metal and preventing metal agglomeration. This enhanced the interaction between the active metal and the support, improving the catalyst's stability.

[0020] In a second aspect, the present invention provides a nitrogen-doped carbon-supported molybdenum-based single-atom catalyst prepared by the preparation method described in the first aspect.

[0021] Furthermore, the surface area of ​​the catalyst is 400-500 m². 2 / g.

[0022] The nitrogen-doped carbon-supported molybdenum-based single-atom catalyst prepared in this invention uses a nitrogen-doped carbon support (NC) as the support. The use of a nitrogen-doped carbon support improves the poor interaction between the activated carbon support and the active metal. The introduction of nitrogen improves the electronic structure of the carbon support, increases the electrical conductivity between the active metal and the carbon support, and simultaneously, nitrogen coordinates with the active metal to form metal-N bonds, anchoring the active metal, promoting its dispersion, and preventing metal agglomeration, thereby improving the stability of the catalyst.

[0023] In this invention, transition metal molybdenum is used as the active component of the catalyst. The addition of the template agent not only improves the overall morphology and pore structure of the catalyst and increases its specific surface area, but also achieves the purpose of nitrogen doping on the carbon support. The introduction of nitrogen is beneficial for anchoring and dispersing the active metal and strengthening the interaction between the active metal molybdenum and the nitrogen-carbon support. The catalyst possesses an atomically dispersed active metal, excellent pore structure, and a large specific surface area (400-500 m²). 2 This catalyst exhibits characteristics such as high catalytic activity and excellent stability for the hydrogenolysis of lignin to prepare monophenolic compounds. Not only does it possess good lignin hydrogenolysis activity, but its catalytic activity did not significantly decrease after five consecutive uses, demonstrating excellent reusability and cyclic stability.

[0024] Thirdly, the present invention provides the application of the nitrogen-doped carbon-supported molybdenum-based single-atom catalyst described in the second aspect in hydrogen-free aqueous reforming of lignin model compounds and hydrogen depolymerization of lignin self-reforming.

[0025] Fourthly, the present invention provides a method for depolymerizing lignin using the nitrogen-doped carbon-supported molybdenum-based single-atom catalyst described in the second aspect.

[0026] Further, the steps of the lignin depolymerization method are as follows: lignin, nitrogen-doped carbon-supported molybdenum-based single-atom catalyst and water are mixed, a protective gas is introduced, and the mixture is reacted at 220-280 °C for 150-200 min. After the reaction is completed, the mixture is cooled, extracted, and centrifuged to obtain the depolymerization product.

[0027] Furthermore, the extractant is ethyl acetate.

[0028] Furthermore, the reaction was carried out under stirring at a speed of 500-700 rpm / min.

[0029] Compared with the prior art, the present invention has achieved the following beneficial effects: (1) The nitrogen-doped carbon-supported molybdenum-based single-atom catalyst synthesized in this invention can have its specific morphology and pore structure altered by changing the amount of carbon precursor and template agent added, and the size of the molybdenum metal particles (single atom or nanocluster) can be controlled by changing the amount of soluble molybdate added. The active metal of the nitrogen-doped carbon-supported molybdenum-based single-atom catalyst synthesized in this invention exhibits atomic dispersion and has a large specific surface area (400-500 m²). 2 The metal was dispersed evenly (g) and no metal agglomeration was observed.

[0030] (2) The nitrogen-doped carbon-supported molybdenum-based monometallic catalyst synthesized in this invention can be used for hydrogen-free aqueous reforming of lignin model compounds and hydrogen depolymerization of lignin self-reforming, and the catalyst has high cycle stability. Attached Figure Description

[0031] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0032] Figure 1 These are SEM images, TEM images, and aberration-corrected HAADF-STEM images of the catalyst Mo1@NC of this invention; wherein, (a) is a SEM image; (b) is a TEM image; and (c) is a HAADF-STEM image. Figure 2 These are the XRD pattern and N2 adsorption-desorption isotherm diagram of the catalyst Mo1@NC of the present invention; wherein, (a) is the XRD pattern; and (b) is the N2 adsorption-desorption isotherm diagram. Figure 3 These are SEM and TEM images of the Mo2@NC catalyst of the present invention; wherein, (a) is the SEM image; and (b) is the TEM image. Figure 4These are SEM and TEM images of the catalyst Mo3@NC of the present invention; wherein, (a) is a SEM image; and (b) is a TEM image. Figure 5 These are SEM and TEM images of the catalyst Mo4@NC of the present invention; wherein, (a) is a SEM image; and (b) is a TEM image. Figure 6 These are SEM and TEM images of the catalyst Mo5@NC of the present invention; wherein, (a) is a SEM image; and (b) is a TEM image. Figure 7 These are SEM and TEM images of the catalyst Mo6@NC of the present invention; wherein, (a) is a SEM image; and (b) is a TEM image. Figure 8 These are the N2 adsorption-desorption isotherms and TEM images of the catalyst Mo7@NC of the present invention; wherein, (a) is the N2 adsorption-desorption isotherm; and (b) is the TEM image. Figure 9 These are the N2 adsorption-desorption isotherms and TEM images of the catalyst Mo8@C of the present invention; wherein, (a) is the N2 adsorption-desorption isotherm; and (b) is the TEM image. Detailed Implementation

[0033] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0034] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0035] Example 1 (1) In a 250 mL beaker, weigh 1 g of glucose and 10 g of melamine and add them to 40 mL of deionized water. Stir for 2 h. Then add 0.035 g of ammonium molybdate and continue stirring for 2 h to form a uniform milky white mixture.

[0036] (2) Transfer the mixture into an oil bath magnetic stirrer and heat it to 80 °C at a rate of 10 °C / min for 180 min to obtain a solid mixture.

[0037] (3) Transfer the white mixture into an 80 ℃ oven and dry for 12 h.

[0038] (4) After grinding the dried solid mixture, place it in a quartz tube and perform rapid pyrolysis using flash Joule heating technology. The parameters used for flash Joule heating are: voltage of 55 volts, current of 50 amperes, resistance of 100 ohms, energizing time of 1 second, and temperature of 1000 ℃. Rapid pyrolysis is carried out under an argon atmosphere. The resulting black solid is ground to obtain a nitrogen-doped carbon-supported molybdenum-based single-atom catalyst, labeled as Mo1@NC.

[0039] Figure 1 These are SEM images, TEM images, and aberration-corrected HAADF-STEM images of the catalyst Mo1@NC of this invention; where (a) is the SEM image; (b) is the TEM image; and (c) is the HAADF-STEM image. As shown in the figure, the catalyst surface has a wrinkled carbon nanosheet structure. Figure 2 The figures show the XRD pattern and N2 adsorption-desorption isotherm of the catalyst Mo1@NC of this invention; (a) is the XRD pattern; and (b) is the N2 adsorption-desorption isotherm. The figures show that molybdenum single atoms are uniformly dispersed on the nitrogen-carbon support, and the adsorption-desorption isotherm of the catalyst is a distinct Type IV curve with a specific surface area of ​​435 m². 2 / g. The presence of H4 hysteresis rings indicates that the material is mesoporous, further demonstrating that the catalyst has an excellent pore structure.

[0040] Performance testing 0.3 g lignin, 0.06 g catalyst Mo1@NC, and 20 mL deionized water were added to a 100 mL high-pressure reactor. The reactor was purged three times with argon gas, then 1 MPa argon gas was introduced. The reaction was carried out at 260 °C, 600 rpm / min, and for 180 min. After the reaction, the mixture was cooled to room temperature, and the degradation solution was extracted with 20 mL ethyl acetate. The extract was then centrifuged. Using dodecane as an internal standard, the lignin depolymerization effect was tested using gas chromatography-mass spectrometry (Agilent 5975-7890A), and the yield of aromatic monomers was quantitatively calculated.

[0041] Example 2 (1) In a 250 mL beaker, weigh 1 g of anhydrous glucose and 10 g of melamine and add them to 40 mL of deionized water. Stir for 2 h. Then add 0.075 g of ammonium molybdate and continue stirring for 2 h to form a uniform milky white mixture.

[0042] (2) Transfer the mixture into an oil bath magnetic stirrer and heat it to 80 °C at a rate of 10 °C / min for 180 min to obtain a solid mixture.

[0043] (3) Place the solid mixture in an 80 ℃ oven and dry for 12 h.

[0044] (4) After grinding the dried solid mixture, place it in a quartz tube and perform rapid pyrolysis using flash Joule heating technology. The parameters used for flash Joule heating are: voltage of 55 volts, current of 50 amperes, resistance of 100 ohms, energizing time of 1 second, and temperature of 1200 ℃. Rapid pyrolysis is carried out under an argon atmosphere. The resulting black solid is ground to obtain a nitrogen-doped carbon-supported Mo-based single-atom catalyst, labeled as Mo2@NC.

[0045] Figure 3 These are SEM and TEM images of the Mo2@NC catalyst of this invention; where (a) is the SEM image and (b) is the TEM image. The images show that the catalyst surface has a wrinkled graphene-like carbon nanosheet structure.

[0046] Performance testing 0.3 g lignin, 0.06 g catalyst Mo2@NC, and 20 mL deionized water were added to a 100 mL high-pressure reactor. The reactor was purged three times with argon gas, then 1 MPa argon gas was introduced. The reaction was carried out at 260 °C and 600 rpm / min for 180 min. After the reaction, the mixture was cooled to room temperature, and the degradation solution was extracted with 20 mL ethyl acetate. The extract was then centrifuged. Using dodecane as an internal standard, the lignin depolymerization effect was tested using gas chromatography-mass spectrometry (Agilent 5975-7890A), and the yield of aromatic monomers was quantitatively calculated.

[0047] Example 3 (1) In a 250 mL beaker, weigh 1 g of anhydrous glucose and 10 g of melamine and add them to 40 mL of deionized water. Stir for 2 h. Then add 0.119 g of ammonium molybdate and continue stirring for 2 h to form a uniform milky white mixture.

[0048] (2) Transfer the mixture into an oil bath magnetic stirrer and heat it to 80 °C at a rate of 10 °C / min for 180 min to obtain a solid mixture.

[0049] (3) Place the solid mixture in an 80 ℃ oven and dry for 12 h.

[0050] (4) After grinding the dried solid mixture, place it in a quartz tube and perform rapid pyrolysis using flash Joule heating technology. The parameters used for flash Joule heating are: voltage of 55 volts, current of 50 amperes, resistance of 100 ohms, energizing time of 1 second, and temperature of 800℃. Rapid pyrolysis is carried out under an argon atmosphere. The resulting black solid is ground to obtain a nitrogen-doped carbon-supported molybdenum-based single-atom catalyst, labeled as Mo3@NC.

[0051] Figure 4These are SEM and TEM images of the Mo3@NC catalyst of this invention; where (a) is the SEM image and (b) is the TEM image. The images show that the catalyst surface has a wrinkled graphene-like carbon nanosheet structure.

[0052] Performance testing 0.3 g lignin, 0.06 g catalyst Mo3@NC, and 20 mL deionized water were added to a 100 mL high-pressure reactor. The reactor was purged three times with argon gas, then 1 MPa argon gas was introduced. The reaction was carried out at 260 °C, 600 rpm / min, and for 180 min. After the reaction, the mixture was cooled to room temperature, and the degradation solution was extracted with 20 mL ethyl acetate. The extract was then centrifuged. Using dodecane as an internal standard, the lignin depolymerization effect was tested using gas chromatography-mass spectrometry (Agilent 5975-7890A), and the yield of aromatic monomers was quantitatively calculated.

[0053] Example 4 (1) In a 250 mL beaker, weigh 1 g of anhydrous glucose and 10 g of melamine and add them to 40 mL of deionized water. Stir for 2 h. Then add 0.114 g of ammonium tetramolybdate and continue stirring for 2 h to form a uniform milky white mixture.

[0054] (2) Transfer the mixture into an oil bath magnetic stirrer and heat it to 80 °C at a rate of 10 °C / min for 180 min to obtain a solid mixture.

[0055] (3) Place the white mixture in an 80 ℃ oven and dry for 12 h.

[0056] (4) After grinding the dried solid mixture, place it in a quartz tube and perform rapid pyrolysis using flash Joule heating technology. The parameters used for flash Joule heating are: voltage of 55 volts, current of 50 amperes, resistance of 100 ohms, energizing time of 1 second, and temperature of 900 ℃. Rapid pyrolysis is carried out under an argon atmosphere. The resulting black solid is ground to obtain a nitrogen-doped carbon-supported Mo-based single-atom catalyst, labeled as Mo4@NC.

[0057] Figure 5 These are SEM and TEM images of the Mo4@NC catalyst of this invention; where (a) is the SEM image and (b) is the TEM image. The images show that the catalyst surface has a wrinkled graphene-like carbon nanosheet structure.

[0058] Performance testing 0.3 g lignin, 0.06 g catalyst Mo4@NC, and 20 mL deionized water were added to a 100 mL high-pressure reactor. The reactor was purged three times with argon gas, then 1 MPa argon gas was introduced. The reaction was carried out at 260 °C, 600 rpm / min, and for 180 min. After the reaction, the mixture was cooled to room temperature, and the degradation solution was extracted with 20 mL ethyl acetate. The extract was then centrifuged. Using dodecane as an internal standard, the lignin depolymerization effect was tested using gas chromatography-mass spectrometry (Agilent 5975-7890A), and the yield of aromatic monomers was quantitatively calculated.

[0059] Example 5 (1) In a 250 mL beaker, weigh 1.5 g of glucosamine hydrochloride and 10 g of melamine and add them to 40 mL of deionized water. Stir for 2 h. Then add 0.0355 g of ammonium molybdate and continue stirring for 2 h to form a uniform milky white mixture.

[0060] (2) Transfer the mixture into an oil bath magnetic stirrer and heat it to 80 °C at a rate of 10 °C / min for 180 min to obtain a solid mixture.

[0061] (3) Place the solid mixture in an 80 ℃ oven and dry for 12 h.

[0062] (4) After grinding the dried solid mixture, place it in a quartz tube and perform rapid pyrolysis using flash Joule heating technology. The parameters used for flash Joule heating are: voltage of 55 volts, current of 50 amperes, resistance of 100 ohms, energizing time of 1 second, and temperature of 1100 ℃. Rapid pyrolysis is carried out under an argon atmosphere. The resulting black solid is ground to obtain a nitrogen-doped carbon-supported molybdenum-based single-atom catalyst, labeled as Mo5@NC.

[0063] Figure 6 These are SEM and TEM images of the Mo5@NC catalyst of this invention; where (a) is the SEM image and (b) is the TEM image. The images show that the catalyst surface has a wrinkled graphene-like carbon nanosheet structure.

[0064] Performance testing 0.3 g lignin, 0.06 g catalyst Mo5@NC, and 20 mL deionized water were added to a 100 mL high-pressure reactor. The reactor was purged three times with argon gas, then 1 MPa argon gas was introduced. The reaction was carried out at 260 °C, 600 rpm / min, and for 180 min. After the reaction, the mixture was cooled to room temperature, and the degradation solution was extracted with 20 mL ethyl acetate. The extract was then centrifuged. Using dodecane as an internal standard, the lignin depolymerization effect was tested using gas chromatography-mass spectrometry (Agilent 5975-7890A), and the yield of aromatic monomers was quantitatively calculated.

[0065] Example 6 (1) In a 250 mL beaker, weigh 1.5 g of glucosamine hydrochloride and 20 g of dicyandiamine and add them to 40 mL of deionized water. Stir for 2 h. Then add 0.0355 g of ammonium molybdate and continue stirring for 2 h to form a uniform milky white mixture.

[0066] (2) Transfer the mixture into an oil bath magnetic stirrer and heat it to 80 °C at a rate of 10 °C / min for 180 min to obtain a solid mixture.

[0067] (3) Place the solid mixture in an 80 ℃ oven and dry for 12 h.

[0068] (4) The obtained composite was ground and placed in a quartz tube, and rapid pyrolysis was performed using flash Joule heating technology. The parameters used for flash Joule heating were: voltage of 55 volts, current of 50 amperes, resistance of 100 ohms, energizing time of 1 second, and temperature of 1000 ℃. Rapid pyrolysis was performed under an argon atmosphere. The black solid obtained was ground to obtain a nitrogen-doped carbon-supported Mo-based single-atom catalyst, labeled as Mo6@NC.

[0069] Figure 7 These are SEM and TEM images of the Mo6@NC catalyst of this invention; (a) is the SEM image; and (b) is the TEM image. The images show that the catalyst surface has a wrinkled graphene-like carbon nanosheet structure.

[0070] Performance testing 0.3 g lignin, 0.06 g catalyst Mo6@NC, and 20 mL deionized water were added to a 100 mL high-pressure reactor. The reactor was purged three times with argon gas, then 1 MPa argon gas was introduced. The reaction was carried out at 260 °C, 600 rpm / min, and for 180 min. After the reaction, the mixture was cooled to room temperature, and the degradation solution was extracted with 20 mL ethyl acetate. The extract was then centrifuged. Using dodecane as an internal standard, the lignin depolymerization effect was tested using gas chromatography-mass spectrometry (Agilent 5975-7890A), and the yield of aromatic monomers was quantitatively calculated.

[0071] Comparative Example 1 (1) In a 250 mL beaker, weigh 10 g of melamine and 0.035 g of ammonium molybdate and add them to 40 mL of deionized water. Stir for 2 h to form a homogeneous mixture.

[0072] (2) Transfer the mixture into an oil bath magnetic stirrer and heat it to 80 °C at a rate of 10 °C / min for 180 min to obtain a solid mixture.

[0073] (3) Place the solid mixture in an 80 ℃ oven and dry for 12 h.

[0074] (4) After grinding the dried solid mixture, place it in a quartz tube and perform rapid pyrolysis using flash Joule heating technology. The parameters used for flash Joule heating are: voltage of 55 volts, current of 50 amperes, resistance of 100 ohms, energizing time of 1 second, and temperature of 1200 ℃. Rapid pyrolysis is carried out under an argon atmosphere. The resulting black solid is ground to obtain a nitrogen-doped carbon-supported Mo-based single-atom catalyst, labeled as Mo7@N.

[0075] Figure 8 These are the N2 adsorption-desorption isotherms and TEM images of the Mo7@NC catalyst of this invention; where (a) is the N2 adsorption-desorption isotherm and (b) is the TEM image. The figures show that the active metal in the catalyst exhibits aggregation, and the specific surface area of ​​Mo7@NC is 412 m². 2 / g.

[0076] Performance testing 0.3 g lignin, 0.06 g catalyst Mo7@N, and 20 mL deionized water were added to a 100 mL high-pressure reactor. The reactor was purged three times with argon gas, then 1 MPa argon gas was introduced. The reaction was carried out at 260 °C, 600 rpm / min, and for 180 min. After the reaction, the mixture was cooled to room temperature, and the degradation solution was extracted with 20 mL ethyl acetate. The extract was then centrifuged. Using dodecane as an internal standard, the lignin depolymerization effect was tested using gas chromatography-mass spectrometry (Agilent 5975-7890A), and the yield of aromatic monomers was quantitatively calculated.

[0077] Comparative Example 2 (1) In a 250 mL beaker, weigh 1 g of anhydrous glucose and 0.035 g of ammonium molybdate and add them to 40 mL of deionized water. Stir for 2 h to form a homogeneous mixture.

[0078] (2) Transfer the mixture into an oil bath magnetic stirrer and heat it to 80 °C at a rate of 10 °C / min for 180 min to obtain a solid mixture.

[0079] (3) Place the solid mixture in an 80 ℃ oven and dry for 12 h.

[0080] (4) After grinding the dried solid mixture, place it in a quartz tube and perform rapid pyrolysis using flash Joule heating technology. The parameters used for flash Joule heating are: voltage of 55 volts, current of 50 amperes, resistance of 100 ohms, energizing time of 1 second, and temperature of 900 ℃. Rapid pyrolysis is carried out under an argon atmosphere. The resulting black solid is ground to obtain a nitrogen-doped carbon-supported Mo-based single-atom catalyst, labeled as Mo8@C.

[0081] Figure 9 These are the N2 adsorption-desorption isotherms and TEM images of the catalyst Mo8@C of this invention; where (a) is the N2 adsorption-desorption isotherm and (b) is the TEM image. It can be seen from the figures that the catalyst has a small specific surface area, only 168 m². 2 / g, active metals showed obvious aggregation.

[0082] Performance testing 0.3 g lignin, 0.06 g catalyst Mo8@C, and 20 mL deionized water were added to a 100 mL high-pressure reactor. The reactor was purged three times with argon gas, then 1 MPa argon gas was introduced. The temperature was 260 °C, the rotation speed was 600 rpm / min, and the reaction time was 180 min. After the reaction, the mixture was cooled to room temperature, and the degradation solution was extracted with 20 mL ethyl acetate. The extract was then centrifuged. Using dodecane as an internal standard, the lignin depolymerization effect was tested using gas chromatography-mass spectrometry (Agilent 5975-7890A), and the yield of aromatic monomers was quantitatively calculated.

[0083] The evaluation data of lignin depolymerization activity in Examples 1-6 and Comparative Examples 1-2 of the present invention are shown in Table 1.

[0084] Table 1

[0085] As can be seen from Table 1, the catalyst prepared in the embodiments of the present invention has a much higher lignin depolymerization activity than the two comparative examples (no carbon precursor, no template agent), and the highest yield of aromatic monomers can reach 23.61%.

[0086] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a nitrogen-doped carbon-supported molybdenum-based single-atom catalyst, characterized in that, Includes the following steps: (1) Dissolve the carbon precursor and template agent in water, stir to dissolve, then add molybdate and stir to obtain a homogeneous mixture; (2) Under stirring conditions, the mixture obtained in step (1) is reacted at 80-100 °C for 200-240 min to obtain a solid mixture; (3) The solid mixture obtained in step (2) is dried and ground, and then rapidly pyrolyzed using flash Joule heating under an argon atmosphere; (4) Grind the product after pyrolysis in step (3) to obtain the final product; The carbon precursor is glucose, glucosamine hydrochloride, chitosan, or fructose; The template agent is melamine, dicyandiamide, or cyanamide.

2. The preparation method according to claim 1, characterized in that, In step (1), the molybdate is ammonium molybdate or ammonium tetramolybdate.

3. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of carbon precursor, template agent and molybdate is 1-2:10-20:0.03-0.

12.

4. The preparation method according to claim 1, characterized in that, In step (1), the stirring and dissolution time is 1-3 h; after adding molybdate, the stirring is carried out for 1-3 h. Alternatively, in step (1), the mass ratio of carbon precursor to water is 1-2:40-45.

5. The preparation method according to claim 1, characterized in that, In step (2), the stirring is magnetic stirring; or, in step (3), the drying parameters are: 80-100 ℃, 10-15 h.

6. The preparation method according to claim 1, characterized in that, In step (3), the parameters used in the flash Joule heating technology are: voltage of 55-60 volts, current of 50-60 amperes, resistance of 100-150 ohms, power-on time of 1-2 seconds, and temperature of 800-1200 ℃.

7. The nitrogen-doped carbon-supported molybdenum-based single-atom catalyst prepared by the preparation method according to any one of claims 1-6.

8. The application of the nitrogen-doped carbon-supported molybdenum-based single-atom catalyst as described in claim 7 in hydrogen-free aqueous reforming of lignin model compounds and hydrogen depolymerization of lignin self-reforming.

9. A method for depolymerizing lignin, characterized in that, The nitrogen-doped carbon-supported molybdenum-based single-atom catalyst of claim 7 is used.

10. The lignin depolymerization method as described in claim 9, characterized in that, The steps of the lignin depolymerization method are as follows: lignin, nitrogen-doped carbon-supported molybdenum-based single-atom catalyst and water are mixed, a protective gas is introduced, and the reaction is carried out at 220-280 °C for 150-200 min. After the reaction is completed, the mixture is cooled, extracted, and centrifuged to obtain the depolymerization product. Preferably, the extractant is ethyl acetate. Preferably, the reaction is carried out under stirring at a speed of 500-700 rpm / min.

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