Preparation and application of cobalt-copper bimetallic nitrogen-doped carbon catalyst for thermocatalytic oxidation of 5-hydroxymethylfurfural

Abstract

The invention discloses a cobalt-copper bimetallic nitrogen-doped carbon catalyst, which is characterized in that CoCu-coated LNC, Co and Cu nanoparticles are anchored on a nitrogen-doped carbon carrier derived from lignin. Accordingly, the inventor also establishes a corresponding preparation method, and the catalyst is prepared by taking lignin as a carrier, cobalt-copper bimetal as an active component and dicyandiamide as a nitrogen source through one-pot pyrolysis. The method has the characteristics of simple and efficient process, high catalyst stability and activity, economy, high efficiency, environmental friendliness and the like. The method is used for preparing 2, 5-furandicarboxylic acid through thermal catalytic oxidation of 5-hydroxymethylfurfural, the yield of the target product FDCA almost reaches 100%, and the application prospect is wide.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of catalysts, and particularly relates to a preparation and application of a cobalt-copper bimetallic nitrogen-doped carbon catalyst for thermocatalytic oxidation of 5-hydroxymethylfurfural. BACKGROUND

[0002] With the aggravation of global energy crisis and environmental pollution, replacing traditional fossil energy with biomass resources has become one of the core paths to realize sustainable development. 5-hydroxymethylfurfural (HMF) is an important biomass platform chemical and a renewable resource that can replace petroleum derivatives. The presence of hydroxymethyl and aldehyde groups makes HMF further converted into many high-value derivatives. Among the many HMF derivatives, 2,5-furan dicarboxylic acid (FDCA) is an aromatic compound with a conjugated ring system, which is an important chemical intermediate, has strong sensitivity and good stability, and can be used to synthesize various fine chemicals and furan-derived polymers. FDCA can be used as a substitute for petroleum-based terephthalic acid (PTA) to synthesize 100% bio-based polyester material PEF (polyethylene 2,5-furan dicarboxylate), which has better gas barrier properties and mechanical strength than traditional PET plastic synthesized by PTA. It is listed as a key breakthrough direction by the European Union's "Plastic Limit Order" and China's bio-economy development plan. In recent years, the technical route for preparing FDCA from HMF has attracted much attention. HMF can be obtained by directional catalytic conversion of biomass such as fructose and glucose, forming a carbon closed-loop system in the whole industry chain of "biomass resources -> platform compounds -> polyester materials", which reduces the carbon emission intensity of petroleum-based materials from the source and precisely meets the technical needs of the chemical industry for low-carbon transformation in the carbon neutral strategy.

[0003] At present, many related researches on the preparation of FDCA from HMF have been reported. Noble metals are widely used in the preparation of FDCA from HMF due to their high activity and FDCA selectivity. Yu et al. (ACS Sustainable Chem. Eng. 2019, 7, 4, 3742-3748) prepared a Pt catalyst supported on activated carbon and used it to catalyze the oxidation of HMF in water at 110 °C and 1 MPa for 5 h. The FDCA yield reached 99%. Activated chitosan was used to prepare a porous carbon material as a Pt-based catalyst carrier, which was used to catalyze the oxidation of HMF in water at 110 °C and 1 MPa for 5 h. The FDCA yield reached 99%. Guan et al. (Journal of Catalysis. 2021, 396, 40-53) prepared a porous nitrogen-doped carbon supported AuPd bimetallic (AuPd / NC) catalyst. HMF was oxidized in series in water, and the FDCA yield was 97.6%. No obvious deactivation was observed after 5 cycles. Pichler et al. (ChemSusChem. 2018, 11, 13, 2083-2090) reported that Ru was supported on a carbon material prepared by activation of chitosan and used it to catalyze the oxidation of HMF in water at 110 °C and 1 MPa for 5 h. The FDCA yield reached 99%. Several different catalysts were synthesized: and -C-Mono, which has the best catalytic performance, with a FDCA yield of 97%. Gao et al. (Journal of Catalysis. 2018, 368, 53-68) studied the catalytic performance of modified catalysts, and at a high HMF / Ru molar ratio (80 / 1), the FDCA yield reached 99%.

[0004] Although noble metal catalytic oxidation of HMF exhibits excellent catalytic performance, its high cost limits its industrial application. Developing new catalytic systems with low cost, high activity, high selectivity, and environmental friendliness is a key path to break through the bottleneck of large-scale production of FDCA and accelerate its commercial application in the field of high-value-added bio-based materials.

[0005] Hayashi et al. (J. Am. Chem. Soc. 2019, 141, 2, 890-900) reported and NaHCO3 together under 10 bar O2, 100 °C, 24 h, with a FDCA yield of 74% and a FFCA yield of 15%. Jin et al. (Catalysis Today. 2021, 367, 2-8) prepared Co-based and Ce-based bimetallic catalysts to catalyze HMF oxidation at 130 °C for 4 h. The conversion rate of HMF was 100%, the FDCA yield was 86.3%, and the DFF yield was 13.7%. Yan et al. (Catal. Sci. Technol. 2018, 8, 164-175) prepared a series of non-noble metal catalysts, among which has the highest activity, with a HMF conversion rate of 99.9% and a FDCA yield of 60.6%. Compared with noble metal-based catalysts, non-noble metal catalysts have lower cost, but their catalytic activity and selectivity are generally lower than those of noble metal-based catalysts. The reaction conditions used are harsh, and the selectivity of the FDCA product is not high. Yang et al. (ACS Catalysis. 2022, 12, 971-981) prepared a cobalt-nitrogen-doped carbon catalyst Co / N-CNTs, which was used to catalyze HMF oxidation at , 100 °C for 8 h, with a HMF conversion rate of 100% and a FDCA yield of 96%. Jing (Research on Co-Cu-ZIF-8 Precursor Prepared by Pyrolysis for Selective Oxidation of 5-Hydroxymethylfurfural [D]. Jiangsu University, 2023.) prepared Co-Cu-CN xCatalyst, 10 bar O2, 100 °C, 12 h, 96% yield of FDCA. The study shows that nitrogen-doped carbon support can effectively promote the conversion of HMF and improve the selectivity of target product FDCA. However, the preparation of traditional nitrogen-doped carbon support is highly dependent on the precursor such as ZIF, and such materials are derived from petroleum chemical products (such as imidazole organic matter), which has problems of high raw material cost and large carbon emission in the preparation process. SUMMARY

[0006] The application discloses a kind of cheap and efficient, easy to prepare and good cyclic stability for thermal catalytic oxidation 5-hydroxymethyl furfural of cobalt copper bimetallic nitrogen-doped carbon catalyst and application.

[0007] To solve the above technical problems, the application adopts the following technical solutions:

[0008] The cobalt copper bimetallic nitrogen-doped carbon catalyst is CoCu@LNC, and Co and Cu nanoparticles are anchored on a nitrogen-doped carbon support derived from lignin.

[0009] Under a transmission electron microscope, the catalyst has a layered structure, and its metal lattice includes lattice spacings of 0.205 nm and 0.181 nm.

[0010] The preparation method of the above-mentioned cobalt copper bimetallic nitrogen-doped carbon catalyst uses lignin as a carrier, cobalt copper bimetal as an active component, and dicyandiamide as a nitrogen source, and is prepared by one-pot pyrolysis.

[0011] The preparation method includes the following steps:

[0012] <1> lignin is added to deionized water, stirred uniformly at room temperature to obtain a lignin solution, and reserved; and are added to deionized water, stirred uniformly at room temperature to obtain a mixed solution, and reserved;

[0013] <2> the mixed solution in step <1> is added dropwise to the lignin solution, the pH is adjusted, and stirring is performed at room temperature;

[0014] <3> after the mixed solution in step <2> is left to stand at room temperature, the solid product is centrifuged and separated, washed with deionized water, dried in a vacuum oven, and ground and grinded after being crushed to reserve;

[0015] <4> the solid product in step <3> is grinded with dicyandiamide in a mortar, pyrolyzed in a tube furnace under an Ar atmosphere, and a cobalt copper bimetallic nitrogen-doped carbon catalyst is obtained.

[0016] In step <1>, the mass concentration of the lignin solution is 10 g / L, and the mass concentration of the mixed solution is and ​The molar ratio of Co(NO3)2.6H2O and Cu(NO3)2.3H2O in the mixed solution is 10:40-50:10;

[0017] In step <2>, the pH is adjusted to 1.4-10.4 by dilute nitric acid or commercially available ammonia water, and stirring is carried out at room temperature for 12 h.

[0018] In step <3>, the solution is left to stand at room temperature for 12 h, washed with deionized water for 3 times, and dried in a vacuum oven at 80 °C.

[0019] In step <4>, the solid product is pyrolyzed with dicyandiamide at a mass ratio of 0-1:15 at a temperature of 600-1000 °C for 1-6 h.

[0020] In step <1>, the molar ratio of Co(NO3)2.6H2O and Cu(NO3)2.3H2O in the mixed solution is 10:40;

[0021] In step <2>, the pH is adjusted to 6.4 by dilute nitric acid or commercially available ammonia water.

[0022] In step <4>, the solid product is pyrolyzed with dicyandiamide at a mass ratio of 1:10 at a temperature of 900 °C for 2 h.

[0023] The cobalt-copper bimetallic nitrogen-doped carbon catalyst or the cobalt-copper bimetallic nitrogen-doped carbon catalyst prepared by the above method is used in the thermal catalytic oxidation of 5-hydroxymethylfurfural to prepare 2,5-furan dicarboxylic acid.

[0024] The method for preparing 2,5-furan dicarboxylic acid by thermal catalytic oxidation of 5-hydroxymethylfurfural uses the cobalt-copper bimetallic nitrogen-doped carbon catalyst or the cobalt-copper bimetallic nitrogen-doped carbon catalyst prepared by the above method.

[0025] The above method comprises the following steps:

[0026] <1> HMF is dissolved in deionized water, and cobalt-copper bimetallic nitrogen-doped carbon catalyst and Na2CO3 are placed in a high-temperature and high-pressure reaction kettle.

[0027] <2> The reaction system is stirred and reacted under O2 atmosphere.

[0028] In step <1>, the mass ratio of HMF and cobalt-copper bimetallic nitrogen-doped carbon catalyst is 1:1-1:5, and the mass ratio of HMF and Na2CO3 is 1:1-1:5.

[0029] In step <2>, the pressure of the gas in the reaction kettle is 0.5-3 Mpa, and the reaction is carried out at 100-200 °C under the condition of a stirring rate of 500-800 rpm for 0-5 h.

[0030] In view of the problems of high production cost and poor cycle stability of the catalyst for the thermal catalytic oxidation of 5-hydroxymethylfurfural, the inventors develop a cobalt-copper bimetallic nitrogen-doped carbon catalyst, CoCu@LNC, in which Co and Cu nanoparticles are anchored on a nitrogen-doped carbon support derived from lignin. Accordingly, the inventors also establish a corresponding preparation method. The catalyst uses lignin as a carrier, cobalt-copper bimetallic as an active component, and dicyandiamide as a nitrogen source, and is prepared by one-pot pyrolysis.

[0031] Compared with the prior art, the present application has the following outstanding advantages:

[0032] (1) Simple and efficient process: a simple one-pot pyrolysis strategy is adopted, and the oxygen-containing functional groups such as phenolic hydroxyl and carboxyl groups in lignin are used to form coordination bonds with metal ions to form a uniformly dispersed lignin-metal complex. After introducing a nitrogen source, the lignin-metal complex is converted into a nitrogen-doped carbon skeleton by one-pot pyrolysis, avoiding the dependence on ZIF precursors and simplifying the preparation process. Moreover, thanks to the renewable and low-cost characteristics of lignin, the economic and efficient production of FDCA is realized.

[0033] (2) The catalyst of the present application uses cobalt-copper bimetallic as an active component and dicyandiamide as a nitrogen source, which promotes the high dispersion of cobalt-copper nanoparticles and exposes more metal catalyst active centers, thereby improving the activity and stability of the cobalt-copper nanoparticle nitrogen-doped carbon catalyst. The synergistic effect of cobalt and copper bimetallic effectively regulates the selectivity of the reaction and accelerates the process of preparing FDCA from HMF oxidation. The complex formed by lignin not only enables the uniform dispersion of metal particles, but also stabilizes them by virtue of the natural structure of lignin, thereby improving the stability and activity of the catalyst and facilitating the recovery and reuse of the catalyst.

[0034] (3) The present application has the characteristics of economic efficiency and environmental friendliness. The cobalt-copper bimetallic nitrogen-doped carbon catalyst has excellent catalytic activity, with a high conversion rate of raw material HMF of up to 100% and a yield of target product FDCA of almost 100%, which has good industrialization prospects. Lignin, as a natural biomass carbon source, is the second largest natural biopolymer in the world, with an annual output of about 500 million tons, which is abundant in source and low in price, providing a new idea for the green preparation of nitrogen-doped carbon carriers. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 is a result graph of the optimization of the carbon source of the present application.

[0036] Figure 2 is a result graph of the optimization of the mass ratio of the precursor to dicyandiamide of the present application.

[0037] Figure 3 is a result graph of the optimization of the Co and Cu molar ratio of the present application.

[0038] Figure 4 is the result graph of optimizing pyrolysis temperature of the present application.

[0039] Figure 5 is the result graph of optimizing pyrolysis time of the present application.

[0040] Figure 6 is the result graph of optimizing preparation pH of the present application.

[0041] Figure 7 is the microscopic result graph of the product of the present application, in which: (a) the transmission electron microscope graph of CoCu@LNC; (b), (c) the high-resolution lattice graph of CoCu@LNC.

[0042] Figure 8 is the XRD graph of the product CoCu@LNC of the present application.

[0043] Figure 9 is the curve graph of HMF conversion rate and FDCA yield of the product of the present application with time. DETAILED DESCRIPTION

[0044] Process screening of preparation method of cobalt-copper bimetallic nitrogen-doped carbon catalyst

[0045] Example 1 Screening of optimal carbon source

[0046] (1) 5 g of carbon source, lignin, eucalyptus powder, sugarcane residue, peanut shell powder, rice straw, cellulose powder, and activated carbon, were added to 500 mL of deionized water and stirred uniformly at room temperature. Co(NO3)2·6H2O and Cu(NO3)2·3H2O were added to 100 mL of deionized water at a molar ratio of 40:10 (corresponding to 40 mmol:10 mmol) and stirred uniformly at room temperature. The mixed solution of Co(NO3)2·6H2O and Cu(NO3)2·3H2O was added dropwise to the carbon source solution, and after stirring uniformly, the pH was adjusted to 6.4 with commercially available ammonia water, and stirred at room temperature for 12 h. After stirring, the solid product was separated by centrifugation, washed with deionized water for 3 times, dried in a vacuum oven at 80 °C, and ground after crushing for standby use. The solid product was ground with dicyandiamide at a mass ratio of 1:10 in a mortar, pyrolyzed at 900 °C for 2 h in a tube furnace under Ar atmosphere, with a heating rate of 5.0 °C / min and a cooling rate of 3.0 °C / min, to obtain catalyst samples with different carbon sources.

[0047] ​​(2) A series of Co-Cu bimetallic nitrogen-doped carbon catalysts prepared were used as catalysts to screen the best-performing catalyst. 0.1 g of catalyst, 0.1261 g of HMF and 0.212 g of Na2CO3 were weighed and 10 mL of deionized water was added to a high-temperature and high-pressure reaction kettle. The system was purged with oxygen for 3 times to replace the air in the reaction kettle, and then oxygen was introduced to 1 MPa. The reaction was carried out at 100 °C and 550 rpm for 3.5 h. After the reaction, the reaction kettle was placed in an ice-water mixture for quenching, and the obtained solution was filtered through a 0.22 μm filter membrane to obtain the product.

[0048] (3) The conversion of HMF, the yield and selectivity of FDCA were determined by high performance liquid chromatography (Perkinelmer, LC300, USA). The mobile phase was 5 mmol / L ammonium formate-methanol (8:2, v / v) and the flow rate was 0.5 mL / min. The Epic C18 column (250x4.6 mm, 5 μm, column oven 30 °C) was used as the chromatographic column, and the diode array detector (PDA) was used to monitor the peak of the above-mentioned substances. The results are shown in Figure 1

[0049]

[0050] It can be seen from Figure 1 that the FDCA yield of the catalyst prepared by using lignin as carbon source is 100%, which is better than that of the catalyst prepared by using eucalyptus powder, sugarcane residue, peanut shell powder, rice straw, cellulose powder and activated carbon as carbon source, which shows that lignin as carbon source has greater advantages. This may be due to the three-dimensional amorphous structure of lignin, which is rich in various functional groups, and forms stable complexes with transition metal ions. Such complexes can firmly anchor cobalt and copper metal atoms, improving the catalytic efficiency of the catalyst.

[0051] Example 2 Screening of precursor and dicyandiamide mass ratio

[0052] ​(1) 5 g of lignin was added to 500 mL of deionized water and stirred uniformly at room temperature. Co(N03)2-6H20 and Cu(N03)2-3H20 were added to 100 mL of deionized water at a molar ratio of 40:10 (corresponding to 40 mmol:10 mmol) and stirred uniformly at room temperature. The above mixture solution of Co(N03)2-6H20 and Cu(N03)2-3H20 was added dropwise to the lignin solution, and after stirring uniformly, the pH was adjusted to 6.4 with commercially available ammonia water, and stirred at room temperature for 12 h. After stirring, it was left to stand at room temperature for 12 h, and the solid product was separated by centrifugation and washed with deionized water 3 times. It was dried in a vacuum oven at 80 °C until dry, ground and pulverized, and used as is. The solid product was ground with dicyandiamide at a mass ratio of 1:0, 1:3, 1:5, 1:7, 1:9, 1:10, 1:15, respectively, and pyrolyzed at 900 °C for 2 h in a tube furnace under Ar atmosphere, with a heating rate of and a cooling rate of to obtain the sample.

[0053] (2) The reaction was carried out under the same application conditions as in Example 1(2).

[0054] (3) The determination conditions were the same as in Example 1(3). The results are shown in Figure 2 .

[0055] As can be seen from Figure 2 , when the mass ratio of the precursor to dicyandiamide is 1:0, the FDCA yield is the lowest, about 20%, and as the proportion of dicyandiamide increases, the product yield shows an overall upward trend, and when the mass ratio is increased to 1:10 and 1:15, the yield is close to 100%. This is because dicyandiamide is the core nitrogen source, and as the proportion increases, the concentration of active nitrogen species (such as -CN, -MN) in the reaction system is higher. At the same time, dicyandiamide will release gas during pyrolysis, which can create pores in the material, increase the reaction contact area, and promote the carbon-nitrogen bond crosslinking to combine with the carbon precursor more efficiently, and at a high proportion, it can more effectively regulate the product structure and optimize the catalytic performance.

[0056] Example 3 Screening of Optimal Co / Cu Molar Ratio

[0057] (1) Add 5 g of lignin to 500 mL of deionized water and stir evenly at room temperature. Add Co(NO3)2·6H2O and Cu(NO3)2·3H2O in molar ratios of 10:40 (10 mmol:40 mmol), 20:30 (20 mmol:30 mmol), 30:20 (30 mmol:20 mmol), 40:10 (40 mmol:10 mmol), and 50:10 (50 mmol:10 mmol) to 100 mL of deionized water and stir evenly at room temperature. Add the above mixed solution of Co(NO3)2·6H2O and Cu(NO3)2·3H2O dropwise to the lignin solution, adjust the pH to 6.4 with commercially available ammonia, and stir at room temperature for 12 h. After stirring, let stand at room temperature for 12 h, centrifuge to separate the solid product, and wash three times with deionized water. Dry to dryness in a vacuum oven at 80 °C, pulverize and grind for later use. The solid product and dicyandiamide were ground thoroughly in a mortar at a mass ratio of 1:10, and then pyrolyzed in a tube furnace at 900 °C for 2 h under an Ar atmosphere, with a heating rate of [missing information]. The cooling rate is 3.0 °C·min. The sample was obtained.

[0058] (2) The reaction was carried out under the same application conditions as in Example 1 (2).

[0059] (3) The same measurement conditions as in Example 1 (3) were used. The results are as follows: Figure 3 As shown.

[0060] Depend on Figure 3 It can be seen that when the ratio of Co(NO3)2·6H2O to Cu(NO3)2·3H2O increased from 10:40 to 40:10, the yield of FDCA significantly increased from 38.12% to 100%. When the ratio of Co(NO3)2·6H2O to Cu(NO3)2·3H2O was further increased to 50:10, the yield of FDCA remained at 100%. The data indicate that there is a synergistic catalytic effect between cobalt and copper bimetals, and that an appropriate ratio can optimize the distribution of active sites and electronic structure, promoting the conversion of HMF to FDCA.

[0061] Example 4: Optimal pyrolysis temperature screening

[0062] (1) Add 5 g of lignin to 500 mL of deionized water and stir evenly at room temperature. Add Co(NO3)2·6H2O and Cu(NO3)2·3H2O to 100 mL of deionized water at a molar ratio of 40:10 (40 mmol:10 mmol) and stir evenly at room temperature. Add the above mixed solution of Co(NO3)2·6H2O and Cu(NO3)2·3H2O dropwise to the lignin solution, adjust the pH to 6.4 with commercially available ammonia water, and stir at room temperature for 12 h. After stirring, let stand at room temperature for 12 h, centrifuge to separate the solid product, and wash it 3 times with deionized water. Dry it to dryness in a vacuum oven at 80 °C, pulverize and grind it for later use. The solid product and dicyandiamide were ground thoroughly in a mortar at a mass ratio of 1:10. The mixture was then pyrolyzed in a tube furnace under an Ar atmosphere at specific temperatures (600 °C, 700 °C, 800 °C, 900 °C, 1000 °C) for 4 h at a heating rate of [missing information]. The cooling rate is The sample was obtained.

[0063] (2) The reaction was carried out under the same application conditions as in Example 1 (2).

[0064] (3) The same measurement conditions as in Example 1 (3) were used. The results are as follows: Figure 4 As shown.

[0065] Depend on Figure 4 It can be seen that when the pyrolysis temperature is 600 °C, the FDCA yield is 7.31%. When the pyrolysis temperature increases from 600 °C to 900 °C, the FDCA yield significantly increases from 7.31% to 100%. When the temperature is further increased to 1000 °C, the FDCA yield drops sharply to 15.12%. When the pyrolysis temperature is between 600 and 700 °C, lignin is partially carbonized, dicyandiamide is decomposed to generate a small amount of nitrogen-containing functional groups, and the metal precursors of cobalt and copper are partially reduced. When the pyrolysis temperature is increased to 800-900 °C, the lignin precursor is deeply carbonized, and dicyandiamide is completely decomposed to generate stable pyridine nitrogen and graphitic nitrogen. Both are deeply graphitized to form a stable nitrogen-doped carbon framework, and cobalt-copper nanoparticles appear and are well dispersed on the lignin-derived nitrogen-doped carbon support (LNC). As the pyrolysis temperature gradually increases to 1000 °C, the pyrrole nitrogen in the generated LNC support may decrease, and the cobalt and copper metal sites may increase in size and agglomerate, leading to a reduction in the number of metal active sites and a decrease in the yield of FDCA.

[0066] Example 5: Optimal Pyrolysis Time Screening

[0067] (1) Add 5 g of lignin to 500 mL of deionized water and stir evenly at room temperature. Add Co(NO3)2·6H2O and Cu(NO3)2·3H2O to 100 mL of deionized water at a molar ratio of 40:10 (40 mmol:10 mmol) and stir evenly at room temperature. Add the above mixed solution of Co(NO3)2·6H2O and Cu(NO3)2·3H2O dropwise to the lignin solution, adjust the pH to 6.4 with commercially available ammonia, and stir at room temperature for 12 h. After stirring, let stand at room temperature for 12 h, centrifuge to separate the solid product, and wash it 3 times with deionized water. Dry it to dryness in a vacuum oven at 80 °C, pulverize and grind it for later use. Grind the solid product and dicyandiamide at a mass ratio of 1:10 in a mortar until fully ground, and pyrolyze it in a tube furnace at 900 °C for a certain time (1 h, 2 h, 3 h, 4 h, 5 h, 6 h) under Ar atmosphere, with a heating rate of The cooling rate is 3.0 °C·min. The sample was obtained.

[0068] (2) The reaction was carried out under the same application conditions as in Example 1 (2).

[0069] (3) The same measurement conditions as in Example 1 (3) were used. The results are as follows: Figure 5 As shown.

[0070] Depend on Figure 5 It was found that the FDCA yield was 95% when the pyrolysis time was 1 h. The yield reached a peak of 100% when the pyrolysis time was 2 h. When the pyrolysis time increased from 3 h to 6 h, the FDCA yield decreased from 97% to 90%. The experiment shows that the carbonization process was fully completed when the pyrolysis time increased from 1 h to 2 h. At a pyrolysis time of 2 h, the number and stability of active sites reached a balance, resulting in optimal oxidation performance. When the pyrolysis time exceeded 2 h, nitrogen was lost, especially pyrrole nitrogen volatilized, and a small amount of cobalt and copper metal sites may agglomerate, leading to a reduction in the number of metal active sites and a decrease in catalytic activity.

[0071] Example 6 Optimal pH Screening for Preparation

[0072] (1) Add 5 g of lignin to 500 mL of deionized water and stir evenly at room temperature. Add Co(NO3)2·6H2O and Cu(NO3)2·3H2O to 100 mL of deionized water at a molar ratio of 40:10 (40 mmol:10 mmol) and stir evenly at room temperature. Add the above mixed solution of Co(NO3)2·6H2O and Cu(NO3)2·3H2O dropwise to the lignin solution, stir evenly, and adjust the pH to 1.4, 2.4, 3.4, 5.4, 6.4, 8.4, 9.4 and 10.4 respectively with commercially available dilute nitric acid or ammonia water, and stir at room temperature for 12 h. After stirring, let stand at room temperature for 12 h, centrifuge to separate the solid product, and wash it 3 times with deionized water. Dry it to dryness in a vacuum oven at 80 °C, pulverize and grind it for later use. The solid product and dicyandiamide were ground thoroughly in a mortar at a mass ratio of 1:10, and then pyrolyzed in a tube furnace at 900 °C for 2 h under an Ar atmosphere, with a heating rate of 5.0 °C·min. The cooling rate is The sample was obtained.

[0073] (2) The reaction was carried out under the same application conditions as in Example 1 (2).

[0074] (3) The same measurement conditions as in Example 1 (3) were used. The results are as follows: Figure 6 As shown.

[0075] Depend on Figure 6 It can be seen that as the precursor pH value increases from 1.4 to 6.4, the FDCA yield gradually increases, reaching its highest value of 100% at pH 6.4. When the pH value continues to increase to 8.4, the FDCA yield decreases slightly but still remains at a relatively high level of 84.38%; while at pH 10.4, the FDCA yield further decreases to 46.48%. When the pH is below 6.4, the negative charges of the phenolic hydroxyl and carboxyl groups in lignin are weaker, and they react more readily with Co. 2+ and Cu 2+ The chelating ability is relatively weak; when the pH is 6.4, most of the carboxyl and phenolic hydroxyl groups in lignin lose protons, and lignin binds with Co. 2+ and Cu 2+ The chelating ability was significantly enhanced, with increased electrostatic attraction and chelation, resulting in more metal sites in the prepared CoCu@LNC and the highest FDCA yield. When the pH was above 6.4, the carboxyl and phenolic hydroxyl groups in lignin were almost completely deprotonated, leading to better lignin-Co chelation. 2+ and Cu 2+ The chelating ability is significantly enhanced, but metal ions may undergo hydrolysis and precipitation of Co and Cu, which may make it difficult for metals to be loaded onto the lignin framework, resulting in a low number of metal sites in the prepared catalyst and a decrease in FDCA yield.

[0076] From Examples 1-6, the optimal process conditions for preparing the cobalt-copper bimetallic nitrogen-doped carbon catalyst are: using lignin as the carbon source, mixing Co(NO3)2·6H2O and Cu(NO3)2·3H2O at a molar ratio of 40:10, preparing the precursor at a pH of 6.4, and then mixing the precursor with dicyandiamide at a mass ratio of 1:10, and pyrolyzing at 900 °C for 2 h.

[0077] Example 7 Preparation and characterization of cobalt-copper bimetallic nitrogen-doped carbon catalyst under optimal process conditions

[0078] (1) 5 g of lignin was added to 500 mL of deionized water and stirred uniformly at room temperature. Co(NO3)2·6H2O and Cu(NO3)2·3H2O were added to 100 mL of deionized water at a molar ratio of 40:10 (40 mmol:10 mmol) and stirred uniformly at room temperature. The mixed solution of Co(NO3)2·6H2O and Cu(NO3)2·3H2O was added dropwise to the lignin solution, and the pH was adjusted to 6.4 with commercially available ammonia water, and stirred at room temperature for 12 h. After stirring, it was left to stand at room temperature for 12 h, and the solid product was separated by centrifugation and washed with deionized water 3 times. It was dried in a vacuum oven at 80 °C until dry, ground and pulverized, and then used. The solid product and dicyandiamide were ground in a mortar at a mass ratio of 1:10, pyrolyzed at 900 °C for 2 h under Ar atmosphere, with a heating rate of 5.0 °C / min and a cooling rate of 3.0 °C / min, to obtain the catalyst CoCu@LNC. (2) From

[0079] (a) The transmission electron microscopy image shows that CoCu@LNC has a layered structure, and Co and Cu nanoparticles can be clearly observed to have been successfully anchored on the surface of the carrier, achieving effective loading. Further analysis of the high-resolution transmission electron microscopy images in Figure 7 (b) and (c) shows that the metal lattice fringes can be identified, with a lattice spacing of 0.205 nm matching the (111) crystal plane of Co and a lattice spacing of 0.181 nm corresponding to the (200) crystal plane of Cu, proving the successful anchoring of Co and Cu nanoparticles to the nitrogen-doped carbon carrier derived from lignin. Figure 7

[0080] (3) XRD test. From Figure 8 ​​The XRD patterns show that the characteristic peaks of the prepared CoCu@LNC correspond to the standard cards of Co and Cu. At 43.3°, 50.44°, and 74.1°, they correspond to the (111), (200), and (220) crystal planes of Cu, respectively. At 44.2°, 51.5°, and 75.8°, they correspond to the (111), (200), and (220) crystal planes of Co, respectively. This demonstrates that Co and Cu were successfully anchored to a nitrogen-doped carbon support in nanoparticle form.

[0081] (4) The reaction was carried out under the same application conditions as in Example 1 (2). The reaction times were: 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, and 3.5 h. The trends of HMF conversion and FDCA yield over time were obtained.

[0082] (5) The same measurement conditions as in Example 1 (3) were used. The results are as follows: Figure 9 As shown.

[0083] Figure 9 The graphs show the changes in the conversion rate of HMF and the yield of FDCA catalytic oxidation by the catalyst prepared in this embodiment over time. After reacting at 100 °C for 3 h, the conversion rate of HMF was 99.99%, and the yield of the target product FDCA reached 95.88%. After reacting at 100 °C for 3.5 h, the conversion rate of HMF was 100%, and the yield of the target product FDCA was as high as 100%.

[0084] Example 8

[0085] The CoCu@LNC catalyst was prepared using the same method as in Example 7, and the reaction was carried out under the same application conditions as in Example 1 (2). The determination conditions were the same as in Example 1 (3).

[0086] After the CoCu@LNC catalyst was added to the reaction to catalyze the preparation of FDCA, it was centrifuged, washed, and dried for later use. The collected catalyst was added to the same test reaction as in Example 1 (2) for a second round of cycle stability testing. The cycle stability of the catalyst was measured after 6 cycles, and the results are shown in Table 1.

[0087]

[0088] As shown in Table 1, the CoCu@LNC catalyst can still maintain an FDCA yield and selectivity of over 99% after being reused 6 times, exhibiting good cycle stability and promising industrial application prospects.

Claims

1. A cobalt-copper bimetallic nitrogen-doped carbon catalyst characterized in that For CoCu@LNC, Co and Cu nanoparticles are anchored on the nitrogen-doped carbon support derived from lignin.

2. The cobalt-copper bimetallic nitrogen-doped carbon catalyst of claim 1, wherein: Under transmission electron microscopy, the catalyst has a layered structure, and its metal lattice includes lattice spacings of 0.205 nm and 0.181 nm.

3. The method for preparing the cobalt-copper bimetallic nitrogen-doped carbon catalyst of claim 1, characterized in that: The catalyst is prepared by one-pot pyrolysis using lignin as the carrier, cobalt-copper bimetal as the active component, and dicyandiamide as the nitrogen source.

4. The method of claim 3, wherein The method comprises the following steps: <1> lignin was added into deionized water, stirred uniformly at room temperature, and a lignin solution was obtained and reserved; and a mixed solution of was obtained and reserved; <2> The mixed solution of step <1> is added dropwise to a lignin solution, the pH is adjusted, and stirring is performed at room temperature; <3> After the mixed solution of step <2> is left to stand at room temperature, the solid product is separated by centrifugation, washed with deionized water, dried in a vacuum oven, and ground and grinded to be used; <4> The solid product of step <3> is grinded with dicyandiamide in a mortar, pyrolyzed in a tube furnace under an Ar atmosphere, and a cobalt-copper bimetal nitrogen-doped carbon catalyst is obtained.

5. The method of claim 4, wherein In step <1>, the mass concentration of the lignin solution is 10 g / L, and the molar ratio of the mixed solution of and is 10:40-50:

10. In step <2>, dilute nitric acid or commercially available ammonia water is used to adjust the pH to 1.4-10.4, and stirring is performed at room temperature for 12 h; In step <3>, the solution is left to stand at room temperature for 12 h, washed with deionized water for 3 times, and dried in a vacuum oven at 80 °C; In step <4>, the solid product and dicyandiamide are in a mass ratio of 0-1:15, the pyrolysis temperature is 600-1000 °C, and the pyrolysis time is 1-6 h.

6. The method of claim 5, wherein In step <1>, the molar ratio of the mixed solution and is 10:40; In step <2>: adjust with dilute nitric acid or commercially available ammonia water to 6.4; In step <4>, the solid product and dicyandiamide are in a mass ratio of 1:10, the pyrolysis temperature is 900 °C, and the pyrolysis time is 2 h.

7. Use of the cobalt-copper bimetal nitrogen-doped carbon catalyst of claim 1 or 2, or the cobalt-copper bimetal nitrogen-doped carbon catalyst obtained by the preparation method of any one of claims 3-6, in the thermal catalytic oxidation of 5-hydroxymethylfurfural to prepare 2,5-furan dicarboxylic acid.

8. A method for the thermal catalytic oxidation of 5-hydroxymethylfurfural to 2,5-furan dicarboxylic acid, characterized in that The cobalt-copper bimetal nitrogen-doped carbon catalyst of claim 1 or 2, or the cobalt-copper bimetal nitrogen-doped carbon catalyst obtained by the preparation method of any one of claims 3-6, is used.

9. The method of claim 8, wherein The method comprises the following steps: <1> Take HMF dissolved in deionized water, and take cobalt copper bimetallic nitrogen-doped carbon catalyst and , into a high-temperature high-pressure reaction kettle; <2> The reaction system is stirred under an atmosphere of atmosphere.

10. The method of claim 9, wherein: In step <1>, the mass ratio of HMF and cobalt-copper bimetallic nitrogen-doped carbon catalyst was 1:1-1:5, and the mass ratio of HMF and 1:1-1:

5. In step <2>, the pressure of the gas in the reaction kettle is 0.5-3 Mpa, the reaction is performed at 100-200 °C, the stirring rate is 500-800 rpm, and the reaction time is 0-5 h.

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