A transition metal nitrogen-doped carbon-based catalyst, a preparation method thereof and application of the catalyst in preparation of 5-formyl-2-furancarboxylic acid

Abstract

This invention belongs to the field of chemical technology, specifically relating to a transition metal nitrogen-doped carbon-based catalyst, its preparation method, and its application in the preparation of 5-formyl-2-furancarboxylic acid. This invention utilizes a process combining solvothermal and high-temperature calcination, selecting Co-TPP as a precursor to provide a Co source and a nitrogen-rich carbon framework, and introducing Fe and Ni for metal doping, successfully preparing a transition metal nitrogen-doped carbon-based catalyst Fe3-Ni@Co4-CN with multiple metal active sites. When this catalyst is applied to the catalytic oxidation of HMF to FFCA, the conversion rate of HMF is 99.6%, and the selectivity for FFCA is 79.2%, providing a theoretical basis for the efficient, green, and large-scale production of FFCA through the directed oxidation of HMF.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, and specifically relates to a transition metal nitrogen-doped carbon-based catalyst, its preparation method, and its application in the preparation of 5-formyl-2-furan carboxylic acid. Background Technology

[0002] With the increasing global demand for renewable energy, utilizing biomass resources to replace traditional fossil fuels has become a research hotspot in the field of green chemistry. 5-Hydroxymethylfurfural (HMF), as a key biomass-based platform compound, can yield 5-formyl-2-furoic acid (FFCA) through the selective oxidation of the hydroxymethyl group in the HMF molecule. FFCA is not only an important precursor for the synthesis of pharmaceutical intermediates, functional polymers, and fine chemicals, but also a highly representative key intermediate in the deep oxidation system of HMF. Therefore, developing an efficient, controllable, and environmentally friendly HMF→FFCA catalytic system has significant scientific and application value.

[0003] However, the selective oxidation of HMF to FFCA is extremely challenging due to the active alcohol hydroxyl and aldehyde groups in the HMF molecule. Although noble metal catalysts (such as Pt, Pd, and Au) exhibit excellent catalytic activity, their high cost and scarcity limit their industrial application. Therefore, developing low-cost, highly active, and highly stable non-noble metal catalysts has become a current research focus.

[0004] In recent years, transition metal-nitrogen-carbon (MNC) materials have shown great potential in the field of catalytic oxidation due to their unique electronic structure, tunable active sites, and excellent acid and alkali resistance. Studies have shown that by constructing a multi-metal center system and utilizing the electronic interactions between different metals, the electron density of the active center can be effectively controlled, thereby optimizing the adsorption energy of reaction intermediates and enabling catalysts with multi-metal active sites to exhibit good catalytic performance during the catalytic process. For example, Professor Wu Wenting's research group used a Co / Zn-containing zeolite imidazole framework (ZIF) material as a precursor and prepared a Co-NC-rich photocatalyst through high-temperature calcination and acid washing. This photocatalyst was used to oxidize HMF to prepare DFF, achieving a yield of 31.7% in two hours.

[0005] However, research on transition metal-nitrogen-carbon catalysts in FFCA is currently scarce. Therefore, developing high-performance transition metal nitrogen-doped carbon-based catalysts, clarifying their active sites, structure-activity relationships, and catalytic mechanisms, and achieving efficient, green, and large-scale production of FFCA through the directed oxidation of HMF have become key technical issues urgently needing to be addressed in the field of high-value biomass conversion. This has significant practical implications for promoting the development of the biomass-based chemicals industry. Summary of the Invention

[0006] To address the above technical problems, this invention proposes a transition metal nitrogen-doped carbon-based catalyst, its preparation method, and its application in the preparation of 5-formyl-2-furanoic acid.

[0007] The technical solution of this invention is:

[0008] The first aspect of the present invention is to provide a transition metal nitrogen-doped carbon-based catalyst, wherein the catalyst is prepared by introducing iron and nickel through a solvothermal reaction combined with a high-temperature calcination process to provide a cobalt source and a nitrogen-rich carbon framework using tetraphenylporphyrin cobalt as a precursor.

[0009] Preferably, the catalyst contains 25% to 30% iron, 20% to 25% cobalt, and 22% to 28% nickel by mass percentage.

[0010] As a further preferred embodiment, the catalyst contains 27% iron, 22% cobalt, and 26% nickel by mass percentage. Preferably, the specific operation of the solvothermal reaction is as follows: tetraphenylporphyrin cobalt, soluble iron salt, and soluble nickel salt are dissolved in an ethanol solution; the system is heated; when the system temperature reaches 80-95°C, a urea solution is added to the system, and the reaction is carried out with continuous stirring.

[0011] The mass ratio of tetraphenylporphyrin cobalt: soluble iron salt: soluble nickel salt is 3~5:4~6:1~2; the volume fraction of ethanol in the ethanol solution is 25%~50%; the mass ratio of tetraphenylporphyrin cobalt: urea is 1:3~5.

[0012] Preferably, the mass ratio of tetraphenylporphyrin cobalt: soluble iron salt: soluble nickel salt is 3.5~4.5:4.5~5.5:1; the volume fraction of ethanol in the ethanol solution is 25%~35%; and the mass ratio of tetraphenylporphyrin cobalt: urea is 1:3.5~4.5.

[0013] Preferably, the soluble iron salt is selected from any one of ferric nitrate, ferric chloride, and ferric sulfate; and the soluble nickel salt is selected from any one of nickel chloride and nickel nitrate.

[0014] As a further preferred embodiment, the soluble iron salt is ferric nitrate, and the soluble nickel salt is nickel chloride.

[0015] Preferably, the high-temperature calcination is carried out under nitrogen protection at 500~800℃ for 1.5~3 h.

[0016] As a further preferred embodiment, the high-temperature calcination is carried out under nitrogen protection at 550~650℃ for 1.5~2.5h.

[0017] More preferably, the high-temperature calcination is carried out under nitrogen protection at 600°C for 2 hours.

[0018] A second aspect of the present invention is to provide a method for preparing the transition metal nitrogen-doped carbon-based catalyst, comprising the following steps:

[0019] S1 Weigh out tetraphenylporphyrin cobalt, ferric nitrate, and nickel chloride in proportion, dissolve them in a 25%~35% (v / v) ethanol solution, heat the system, and when the system temperature reaches 85~95℃, add urea solution to the system and stir continuously for 18~28 h. After the reaction is complete, centrifuge, remove the supernatant, and dry the resulting precipitate. The mass ratio of tetraphenylporphyrin cobalt:ferric nitrate:nickel chloride is 3.5~4.5:4.5~5.5:1, and the mass ratio of tetraphenylporphyrin cobalt:urea is 1:3.5~4.5.

[0020] S2: The precipitate obtained in S1 is placed in a tube furnace filled with nitrogen and calcined at 500~700℃ for 1.5~2.5 h. After cooling, it is ground to obtain the final product.

[0021] A third aspect of the invention is the application of the aforementioned transition metal nitrogen-doped carbon-based catalyst in the catalytic oxidation of 5-hydroxymethylfurfural to prepare 5-formyl-2-furanoic acid.

[0022] Preferably, the method of application involves placing the transition metal nitrogen-doped carbon-based catalyst, 5-hydroxymethylfurfural, and water in a stainless steel autoclave under alkaline conditions of pH 10.0–15.0, preferably pH 12.0–14.0, and more preferably pH 13.0, and then introducing oxygen as an oxidant, and reacting at 50–150°C and 0.5–2 MPa. This invention has the following advantages and effects compared to the prior art:

[0023] (1) This invention utilizes a process combining solvothermal heating and high-temperature calcination, selecting Co-TPP as a precursor to provide a Co source and a nitrogen-rich carbon framework, and introducing Fe and Ni for metal doping. This successfully prepared a transition metal nitrogen-doped carbon-based catalyst, Fe3-Ni@Co4-CN, with multiple metal active sites. This catalyst contains multiple transition metal active catalytic sites such as Fe, Co, and Ni, and also possesses a large specific surface area of ​​214.94 m². 2 / g, which lays the structural foundation for its excellent catalytic performance;

[0024] (2) In this invention, the prepared transition metal nitrogen-doped carbon-based catalyst was used to catalyze the oxidation of 5-hydroxymethylfurfural to prepare 5-formyl-2-furan carboxylic acid. The catalyst showed good catalytic performance. The results showed that when the reaction was carried out at 4 eq NaOH, 1 MPa O2, 80℃ and 6 h, the conversion rate of HMF was 99.6% and the selectivity of FFCA was 79.2%. After 5 cycles, the yield of FFCA could still reach 72.1%. Attached Figure Description

[0025] Figure 1 The images shown are XRD patterns (a), SEM images (b) to (d), HR-TEM images (e) of Fe-Ni@Co-CN, and EDS images (f) to (i) of Fe-Ni@Co-CN for different samples of this invention.

[0026] Figure 2 The nitrogen adsorption-desorption isotherms and corresponding pore size distribution curves of Co-TPP (a), Fe-Ni@Co-TPP (b), and Fe-Ni@Co-CN (c) of the present invention are shown.

[0027] Figure 3 The following are FTIR spectra of different samples of the present invention: (a), Fe 2p spectra of Fe-Ni@Co-TPP and Fe-Ni@Co-CN (b), Ni 2p spectra (c), and Co 2p spectra of Co-TPP, Fe-Ni@Co-TPP, and Fe-Ni@Co-CN (d).

[0028] Figure 4 The O 1s spectra of Fe-Ni@Co-TPP and Fe-Ni@Co-CN (a), N 1s spectra of Co-TPP, Fe-Ni@Co-TPP and Fe-Ni@Co-CN (b), EPR spectra of different samples (c), and O2-TPD spectra of different samples (d) are shown.

[0029] Figure 5 The graph shows the effect of the ratio of Co-TPP to (Fe+Ni) (a) and the ratio of Fe to Ni (b) on the catalytic effect of HMF.

[0030] Figure 6 The effects of temperature (a), reaction time (b), NaOH dosage (c), and O2 pressure (d) on the selective oxidation of HMF on Fe3-Ni@Co4-CN catalyst of this invention are shown.

[0031] Figure 7 This invention describes the reaction pathway for the oxidation of HMF to HMFCA in H2O medium.

[0032] Figure 8 This provides a possible mechanism for the oxidation of HMF in H2O solution to FFCA on the Fe3-Ni@Co4-CN catalyst of the present invention.

[0033] Figure 9 The figure shows the results of the recycling test of the Fe3-Ni@Co4-CN catalyst of this invention. Detailed Implementation

[0034] To enable those skilled in the art to better understand the present invention, the present invention will now be further described in conjunction with specific embodiments.

[0035] Example 1

[0036] A transition metal nitrogen-doped carbon-based catalyst is prepared by the following method:

[0037] S1. Weigh out each reactant according to the mass ratio of tetraphenylporphyrin cobalt (Co-TPP): NiCl2·6H2O: Fe(NO3)3·9H2O of 4:5.4:1, and dissolve them in 70 mL of an aqueous ethanol solution (water:ethanol volume ratio of 7:3). Transfer the mixed suspension to a three-necked flask for reaction, heat and stir until the temperature of the suspension stabilizes at 90℃, then add 10 mL of 3 mol·L⁻¹ solution. -1 The urea solution was stirred for 24 hours. After the reaction was completed, the mixture was cooled to room temperature. The resulting suspension was centrifuged to remove the supernatant, and the resulting precipitate was dried at 60°C for 12 hours.

[0038] S2 calcined the precipitate of S1 in a tube furnace under nitrogen atmosphere at 600°C for 2 h. After cooling to room temperature, the resulting catalyst was ground into fine particles to obtain the transition metal nitrogen-doped carbon-based catalyst Fe. y -Ni / Co x -CN, where x=Co-TPP:(Fe+Ni), y=Fe:Ni, and x and y are mass ratios.

[0039] For comparison, the present invention synthesized Fe@Co-CN (without NiCl2·6H2O), Ni@Co-CN (without Fe(NO3)3·9H2O), and Fe-Ni@Co-TPP (without S2 calcination treatment) using the same method.

[0040] Example 2

[0041] The transition metal nitrogen-doped carbon-based catalyst prepared in Example 1 was characterized.

[0042] X-ray diffraction (XRD) patterns: collected at room temperature using a Bruker D8 Advance X-ray diffractometer equipped with a Cu Kα ray source, operating at 40 kV and 30 mA.

[0043] Scanning electron microscopy (SEM) analysis: performed on a Gemini SEM 300 microscope (Zeiss, Germany) with an electron accelerating voltage of 20 kV.

[0044] Elemental distribution: Detected by energy-dispersive X-ray spectroscopy (EDS).

[0045] Transmission electron microscopy (TEM) observations were performed on a Thermo Fisher Talos F200X instrument with an accelerating voltage of 200 kV.

[0046] Fourier transform infrared (FT-IR) spectra: recorded on a Thermo Scientific Nicolet iS50 spectrometer, wavenumber range 4000 to 400 cm⁻¹. -1 Spectral resolution of 4 cm -1 A total of 32 scans were performed.

[0047] Nitrogen adsorption-desorption isotherm: measured at 77 K using a Micromeritics ASAP 2460 analyzer.

[0048] Specific surface area and pore volume: calculated using the BET method and the BJH method, respectively.

[0049] The surface electronic structure and elemental composition of the catalyst were analyzed using a Thermo Scientific K-Alpha photoelectron spectroscopy (XPS) instrument.

[0050] Low-temperature electron paramagnetic resonance (EPR) spectra were recorded at 77 K using a Bruker EMXplus-10 / 12 spectrometer, which operates in the X-band at a frequency of 9.4 GHz.

[0051] Oxygen temperature-programmed desorption (O2-TPD) was performed as follows: approximately 50–100 mg of sample was loaded into a quartz reactor and heated from room temperature to 300°C with a He gas flow (30 mL / min) at a heating rate of 10°C / min for 1 h. The sample was then cooled to 50°C and subsequently saturated with a 10% O2 / He mixture (30–50 mL / min) for 1 h. The sample was then purged with He gas (30 mL / min) for 1 h to remove weakly adsorbed oxygen. Finally, the sample was heated to 700°C with a He gas flow (30 mL / min) at a heating rate of 10°C / min. The desorption gas was monitored using a thermal conductivity detector.

[0052] Figure 1 In the figure, (a) is the XRD spectrum of different samples, (b)~(d) are the SEM images of Co-TPP, Fe-Ni@Co-TPP and Fe-Ni@Co-CN respectively, (e) is the HR-TEM image of Fe-Ni@Co-CN, and (f)~(i) are the EDS images of Fe-Ni@Co-CN.

[0053] like Figure 1 As shown in Figure (a), no crystallization peaks of iron and nickel were found in Fe-Ni@Co-TPP, and the intensity of the characteristic peaks of Co-TPP decreased. Characteristic peaks at 44.5°–51.8° were found in Fe-Ni@Co-CN and Ni@Co-CN, belonging to elemental Ni (PDF#04-0850). A characteristic peak at 44.6° was found in Fe-Ni@Co-CN and Fe@Co-CN, belonging to elemental Fe (PDF#50-1275). These results indicate that Ni and Fe were successfully deposited on Co-CN. Figure (b) shows the SEM image of Co-TPP, clearly showing its regular sheet-like structure. Figure (c) shows the SEM image of Fe-Ni@Co-TPP, demonstrating the successful deposition of nickel and iron metal particles on Co-TPP. Figure (d) shows the SEM image of Fe-Ni@Co-CN, where the regular sheet-like structure of Co-TPP collapsed, forming a blocky structure. Figure (e) shows the HR-TEM image of Fe-Ni@Co-CN, in which long lattice fringes are observed with clear interplanar spacings of 0.217 nm and 0.178 nm, corresponding to the (1 0 0) crystal plane of Fe and the (2 0 0) crystal plane of Ni, respectively, indicating that elemental Ni and Fe are formed after calcination. Figures (f) to (i) show the EDS images of Fe-Ni@Co-CN, and as can be seen, Fe, Co, and Ni are uniformly distributed in the sample.

[0054] The specific surface area and pore size distribution of different catalysts at 77 K were tested using nitrogen adsorption-desorption experiments. The results are shown in Table 1. Figure 2 .

[0055] Table 1. Physicoadsorption data of N2 for different catalysts Catalyst types <![CDATA[Specific surface area (m 2 / g)]]> BJH aperture (nm) <![CDATA[BJH pore volume (m 3 / g)]]> Fe-Ni@Co-CN 214.94 2.82 0.257 Fe-Ni@Co-TPP 32.9 3.40 0.072 Co-TPP 7.91 3.83 0.058

[0056] Depend on Figure 2 It can be seen that all different catalysts exhibit type IV isotherms, with a relatively obvious adsorption-desorption hysteresis loop, indicating that the catalysts have a mesoporous structure.

[0057] Furthermore, based on the data on the physical adsorption of N2 by different catalysts in Table 1, the specific surface area of ​​Co-TPP is 7.91 m². 2 The specific surface area of ​​Fe-Ni@Co-TPP is 32.9 m² / g. 2 The specific surface area of ​​Fe-Ni@Co-CN is 214.94 m² / g. 2 / g. The calcined Fe-Ni@Co-CN has the largest specific surface area, indicating that the collapse of the Co-TPP structure produced more porous structures, which is consistent with the SEM results.

[0058] Figure 3 In Figure (a), the FT-IR spectra of different samples are shown. As shown in the figure, the deposition of Fe and Ni reduces the intensity of the absorption peak in Co-TPP. No absorption peak of Co-TPP was found in Fe-Ni@Co-CN, which proves that the structure of Co-TPP is destroyed in Fe-Ni@Co-CN. Figure 3 Figure (b) shows the Fe 2p spectra of Fe-Ni@Co-TPP and Fe-Ni@Co-CN. As shown in the figure, the peak at 711.03 eV corresponds to Fe 2p. 3 / 2 The peak at 724.62 eV corresponds to Fe 2p 1 / 2 Fe is present in both Fe-Ni@Co-TPP and Fe-Ni@Co-CN. 3+ / Fe 2+ Mixed valence states, while Fe appears in Fe-Ni@Co-CN. 0 Furthermore, Fe-Ni@Co-CN in Fe2p 3 / 2 Fe 2 + The binding energy of Fe shifted to higher energies by 0.97 eV. 3+ The binding energy shifted to higher energies by 0.45 eV in Fe2p. 1 / 2 Fe 2+ The binding energy of Fe shifted to higher energies by 0.95 eV. 3+The binding energy shifted to a higher energy level by 0.87 eV. This shift in binding energy indicates a change in the electron density around Fe. Figure 3 Figure (c) shows the Ni 2p spectra of Fe-Ni@Co-TPP and Fe-Ni@Co-CN. As shown in the figure, the peak at 855.35 eV corresponds to Ni 2p. 3 / 2 The peak at 873.03 eV corresponds to Ni 2p 1 / 2 Ni exists in Fe-Ni@Co-TPP 3+ / Ni 2+ The mixed valence state of Ni in Fe-Ni@Co-CN 3+ Ni disappears and appears 0 Furthermore, Fe-Ni@Co-CN in Ni2p 3 / 2 Ni 2+ The binding energy shifted to higher energies by 0.89 eV in Ni2p. 1 / 2 Ni 2+ The binding energy shifted to higher energies by 0.96 eV. Figure 3 Figure (d) shows the Co 2p spectra of Co-TPP, Fe-Ni@Co-TPP, and Fe-Ni@Co-CN. As shown in the figure, the peak at 780.03 eV corresponds to Co 2p. 3 / 2 The peak at 794.04 eV corresponds to Co 2p 1 / 2 In Co-TPP, Fe-Ni@Co-TPP, and Fe-Ni@Co-CN, Co is expressed as Co. 3+ / Co 2+ Mixed valence states exist. Fe-Ni@Co-CN exists in Co2p 3 / 2 Co 3+ The binding energy shifted to higher energies by 1.25 eV in Co2p 1 / 2 Co 3+ The binding energy shifted to higher energies by 1.03 eV. Fe-Ni@Co-TPP in Co2p 3 / 2 Co 2+ The binding energy of Fe-Ni@Co-CN shifts to a higher energy level by 0.79 eV compared to Co-TPP. 3 / 2 Co 2+ The binding energy of Fe-Ni@Co-TPP shifts to a higher energy level by 1.43 eV compared to Fe-Ni@Co-TPP. Fe-Ni@Co-TPP has a higher binding energy at Co2p. 1 / 2 Co 2+ The binding energy of Fe-Ni@Co-CN shifts to a higher energy level by 0.64 eV compared to Co-TPP. 1 / 2 Co 2+The binding energy of this compound shifts to a higher energy level by 1.53 eV compared to Fe-Ni@Co-TPP.

[0059] Figure 4 (a) shows the O 1s spectra of Fe-Ni@Co-TPP and Fe-Ni@Co-CN. After peak fitting, lattice oxygen (O) was identified in the O 1s spectra. L , 529.6) and defect-related oxygen (O def Two principal components. O def / O L The ratio is significantly higher in Fe-Ni@Co-CN than in Fe-Ni@Co-TPP, indicating that the pyrolysis process not only introduces more oxygen vacancies but also leads to a decrease in the oxygen electron density of adjacent lattices and weakening of bonding. This is due to the O V Enriched indirect but reliable XPS evidence.

[0060] also, Figure 4 (b) shows the N 1s spectra of Co-TPP, Fe-Ni@Co-TPP, and Fe-Ni@Co-CN. The figure shows that MN and pyrrole nitrogen species are present in all samples, while graphitic nitrogen species appear in Fe-Ni@Co-CN. The relative content of pyrrole nitrogen species increases in Fe-Ni@Co-CN, which indicates that the defect sites and local electronic state density are increased, enhancing the surface chemical reactivity and adsorption capacity.

[0061] To further investigate the relationship between oxygen vacancy content in different catalysts, electron paramagnetic resonance (EPR) technology was used to measure the oxygen vacancy content in different catalyst samples, such as... Figure 4 As shown in (c), the G value of all different samples was 2.003, which is due to oxygen vacancies. The Fe3-Ni@Co4-CN sample had the strongest G value, indicating the presence of more oxygen vacancies.

[0062] The types and migration of active O2 species were characterized by O2-TPD. Generally, desorption peaks below 250°C indicate the presence of weakly adsorbed O2 species on the catalyst surface, such as O2 species involved in physisorption (P-O2). Desorption peaks in the range of 250–600°C indicate the presence of strongly adsorbed O2 species, showing chemisorption (C-O2). Figure 4 As shown in Figure (d), no adsorption peaks belonging to surface active oxygen were found in different samples within the range of 100–350°C, two adsorption peaks were found in different samples within the range of 350–670°C, while Fe3-Ni@Co4-CN had three adsorption peaks, indicating the presence of more surface lattice oxygen and bulk lattice oxygen.

[0063] Example 3

[0064] Experimental verification of the preparation of FFCA by the catalytic oxidation of HMF using a transition metal nitrogen-doped carbon-based catalyst in Example 1.

[0065] HMF oxidation procedure: HMF (0.40 mmol, 0.05 g), a specific amount of catalyst, and 20 mL of H2O were placed in a 100 mL batch Teflon-lined stainless steel autoclave. Oxygen was introduced as the oxidant, and the reactor was heated to a specific reaction temperature and maintained for a specific time under magnetic stirring at 500 rpm. After the reaction, the used catalyst was separated by high-speed centrifugation, washed with water, and then vacuum dried at 80°C for 12 h, and could be reused directly in subsequent catalytic runs.

[0066] The reaction mixture was analyzed using an Agilent 2695 high-performance liquid chromatography (HPLC) system equipped with a C-18-A column (Diamosil, 5 μm, 4.6 mm × 250 mm) and a UV-Vis detector. HMF, 5-hydroxymethyl-2-furanoic acid (HMFCA), and FFCA were analyzed at 254 nm using a water-acetonitrile mixture (95:5, v / v + 0.1% glacial acetic acid) as the mobile phase (flow rate 0.8 mL / min, 30°C). Quantification was performed using external standard methods based on the corresponding real standards.

[0067] The conversion rate of HMF, the yield of HMFCA, and the yield of FFCA are calculated using the following formula.

[0068] ;

[0069] ;

[0070] In the above formula, X represents HMFCA, FFCA, and FDCA.

[0071] Table 2 shows the comparison of the catalytic performance of various catalysts in the aerobic oxidation of HMF.

[0072] Table 2 Comparison of the performance of various catalysts in the HMF catalytic oxidation process.

[0073] As shown in Table 2, the catalytic conversion rate of HMF and the selectivity of FFCA of different transition metal nitrogen-doped carbon-based catalysts vary greatly. Co-TPP itself exhibits good catalytic activity, but its selectivity for FFCA is only 21.5%. Fe-Ni@Co-CN has the highest catalytic conversion rate of HMF and the highest selectivity for FFCA.

[0074] Example 4

[0075] Using Fe-Ni@Co-CN as a catalyst, the ratio of different elements in the catalyst and the reaction conditions were optimized. Among these, the alkali concentration, temperature, reaction time, and O2 pressure had a significant impact on the reaction results, as shown in the figure. Figure 5 As shown.

[0076] Figure 5 In Figure (a), the ratio of Co-TPP to (Fe+Ni) is optimized. As shown in the figure, the selectivity of FFCA is the highest when the ratio of Co-TPP to (Fe+Ni) is 4:1. Figure 5 Figure (b) shows the optimization of the Fe to Ni ratio. As can be seen from the figure, FFCA reaches its maximum value when the Fe to Ni ratio is 3:1. Therefore, the reaction conditions were subsequently optimized by selecting Co-TPP with (Fe+Ni)=4:1 and Fe:Ni=3:1, i.e., Fe3-Ni@Co4-CN catalyst.

[0077] Figure 6 The effects of temperature (a), reaction time (b), NaOH dosage (c), and O2 pressure (d) on the selective oxidation of HMF on Fe3-Ni@Co4-CN catalyst were shown. The reaction conditions were as follows: (a) 0.05 g catalyst, 1 MPa O2, 0.05 g HMF, 6 h, 4 eq NaOH; (b) 0.05 g catalyst, 1 MPa O2, 0.05 g HMF, 80°C, 4 eq NaOH; (c) 0.05 g catalyst, 1 MPa O2, 0.05 g HMF, 80°C, 6 h; (d) 0.05 g catalyst, 0.05 g HMF, 80°C, 4 eq NaOH, 6 h.

[0078] Depend on Figure 6 As shown in (a), the Fe3-Ni@Co4-CN catalyst can achieve a high HMF conversion rate even at a relatively low temperature (60°C), exhibiting an FFCA selectivity of 76.9%. When the reaction temperature reaches 80°C, the HMF conversion rate can reach 99.6%, and the FFCA selectivity reaches 79.2%. With the increase of temperature, although the conversion rate increases, the FFCA selectivity decreases. Therefore, 80°C was chosen as the reaction temperature in subsequent experiments.

[0079] Figure 6Figure (b) shows the effect of reaction time on HMF oxidation. Figure (b) shows that on the Fe3-Ni@Co4-CN catalyst, the conversion of HMF exceeds 99% after 6 hours of reaction, and thereafter it does not change significantly with reaction time. The selectivity of FFCA also reaches its maximum at 6 h; therefore, 6 h was chosen as the reaction time in subsequent experiments.

[0080] Figure 6 Figure (c) shows the effect of NaOH dosage on HMF oxidation. The results in the figure show that as the NaOH dosage increased from 1 eq to 4 eq, the HMF conversion gradually increased, while the FFCA selectivity decreased. At 4 eq, both the HMF conversion and FFCA yield were the highest. Therefore, in subsequent experiments, a NaOH dosage of 4 eq was selected.

[0081] Figure 6 Figure (d) shows the effect of oxygen pressure on HMF oxidation. At an oxygen pressure of 0 MPa, the HMF conversion rate is 81.8%. When the oxygen pressure increases to 0.5 MPa, the HMF conversion rate reaches 94.2%. At 1.0 MPa, the selectivity of FFCA reaches a maximum of 79.2%. Thereafter, with further increases in oxygen pressure, the selectivity of FFCA decreases to 70.5%. Therefore, the optimal O2 pressure is 1 MPa.

[0082] The above studies show that, under optimal experimental conditions (0.05 g catalyst, 4 eq NaOH, 0.05 g HMF, 1 MPa O2, 80°C, reaction time 6 h), the HMF conversion rate of the Fe3-Ni@Co4-CN catalyst is 99.6%, the FFCA selectivity is 79.2%, and the FFCA yield is 78.9%.

[0083] In this invention, the reaction pathway for the oxidation of HMF to HMFCA in an aqueous medium is as follows: Figure 7 As shown, the oxidation of HMF to FDCA occurs via two pathways: one is the DFF intermediate, and the other is the HMFCA intermediate. These two pathways may also occur simultaneously. Analysis of products at different time points indicates that the oxidation of HMF in this study involves the HMF-HMFCA-FFCA-FDCA pathway.

[0084] The possible mechanism of Fe3-Ni@Co4-CN catalyst catalyzing the oxidation of HMF to FFCA in H2O solution is as follows: Figure 8As shown. First, in the first stage, HMF is adsorbed onto the catalyst surface and rapidly oxidized to HMFCA. In this step, the aldehyde group in HMF undergoes reversible hydration to form a geminal diol via nucleophilic addition of OH- to the carbonyl group and subsequent proton transfer from H2O to the alkoxy group. Then, Fe3-Ni@Co4-CN and OH- promote the activation and dissociation of CH to remove H, thereby converting the geminal diol to a carboxyl group to form HMFCA. Second, in the second stage, HMFCA needs to be further oxidized to FFCA. The Fe3-Ni@Co4-CN catalyst provides electrons and O2 to the reaction system. V The adsorbed O2 will act as an electron scavenger and be converted into reactive oxygen species O2. - After that, O2 - H is captured from H2O and reduced to peroxide species, which are then decomposed into OH-, maintaining the OH- concentration required for the reaction to proceed. At this point, Fe3-Ni@Co4-CN and OH- continue to promote the cleavage of CH to remove H, thereby producing FFCA.

[0085] Example 5

[0086] Catalyst stability verification: After the HMF oxidation test, the reaction mixture containing the catalyst was centrifuged to recover the catalyst. The catalyst was then washed with water and ethanol, dried in an oven, and reused. Figure 9 Therefore, the yield of FFCA was 72.1% after 5 cycles, indicating that the catalyst has good stability.

[0087] Based on the above analysis, this invention utilizes a strategy combining solvothermal treatment and high-temperature calcination, selecting Co-TPP as a precursor to provide a Co source and a nitrogen-rich carbon framework, and introducing Fe and Ni for metal doping. This successfully prepared a transition metal nitrogen-doped carbon-based catalyst, Fe3-Ni@Co4-CN, with multiple metal active sites. Furthermore, the catalyst's crystal structure, morphology, elemental composition, and valence states were characterized. The reaction conditions for the catalytic oxidation of HMF to FFCA were optimized, yielding the optimal conditions of 4 eq NaOH, 1 MPa O2, 80℃, and 6 h, achieving a HMF conversion rate of 99.6% and an FFCA selectivity of 79.2%. Simultaneously, the possible reaction mechanism of the catalyst oxidizing HMF to FFCA in H2O with oxygen as the oxidant was hypothesized, providing a theoretical basis for the efficient, green, and large-scale production of FFCA through the directional oxidation of HMF.

[0088] The above are merely preferred embodiments of the present invention and do not limit the scope of the patent. All equivalent changes and modifications made within the scope of the present invention should still fall within the scope of the present invention.

Claims

1. A transition metal nitrogen-doped carbon-based catalyst, characterized in that, The catalyst is prepared by introducing iron and nickel through a solvothermal reaction combined with a high-temperature calcination process, using tetraphenylporphyrin cobalt as a precursor to provide a cobalt source and a nitrogen-rich carbon framework.

2. The transition metal nitrogen-doped carbon-based catalyst according to claim 1, characterized in that, The catalyst contains, by mass percentage, 25% to 30% iron, 20% to 25% cobalt, and 22% to 28% nickel.

3. The transition metal nitrogen-doped carbon-based catalyst as described in claim 2, characterized in that, The catalyst contains 27% iron, 22% cobalt, and 26% nickel by mass percentage.

4. The transition metal nitrogen-doped carbon-based catalyst as described in claim 1, characterized in that, The solvothermal reaction involves dissolving tetraphenylporphyrin cobalt, soluble iron salt, and soluble nickel salt in an ethanol solution, heating the system, and adding urea solution to the system when the system temperature reaches 80-95°C, while continuously stirring to carry out the reaction. The mass ratio of tetraphenylporphyrin cobalt: soluble iron salt: soluble nickel salt is 3~5:4~6:1~2; the volume fraction of ethanol in the ethanol solution is 25%~50%; the mass ratio of tetraphenylporphyrin cobalt: urea is 1:3~5.

5. The transition metal nitrogen-doped carbon-based catalyst as described in claim 4, characterized in that, The soluble iron salt is selected from any one of ferric nitrate, ferric chloride, and ferric sulfate; the soluble nickel salt is selected from any one of nickel chloride and nickel nitrate.

6. The transition metal nitrogen-doped carbon-based catalyst according to claim 1, characterized in that, The high-temperature calcination is carried out under nitrogen protection at 500~800℃ for 1.5~3 hours.

7. A method for preparing the transition metal nitrogen-doped carbon-based catalyst according to any one of claims 1 to 6, characterized in that, The steps include the following: S1 Weigh out tetraphenylporphyrin cobalt, ferric nitrate, and nickel chloride in proportion, dissolve them in a 25%~35% (v / v) ethanol solution, heat the system, and when the system temperature reaches 85~95℃, add urea solution to the system and stir continuously for 18~26 h. After the reaction is complete, centrifuge, remove the supernatant, and dry the resulting precipitate. The mass ratio of tetraphenylporphyrin cobalt:ferric nitrate:nickel chloride is 3.5~4.5:4.5~5.5:1, and the mass ratio of tetraphenylporphyrin cobalt:urea is 1:3.5~4.

5. S2: The precipitate obtained in S1 is placed in a tube furnace filled with nitrogen and calcined at 500~700℃ for 1.5~2.5 h. After cooling, it is ground to obtain the final product.

8. The use of the transition metal nitrogen-doped carbon-based catalyst according to any one of claims 1 to 6 in the catalytic oxidation of 5-hydroxymethylfurfural to prepare 5-formyl-2-furanoic acid.

9. The method of application according to claim 8, characterized in that, Under alkaline conditions of pH 10.0~15.0, the transition metal nitrogen-doped carbon-based catalyst, 5-hydroxymethylfurfural, and water are placed in a stainless steel autoclave, oxygen is introduced as an oxidant, and the reaction is carried out at 50~150℃ and 0.5~2 MPa.

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