Preparation of nitrogen-doped carbon-coated feconi alloy catalyst and its application in oxidative cleavage of sugarcane bagasse-based lignin into phenols
By preparing a nitrogen-doped carbon-encapsulated FeCoNi alloy catalyst, the problem of low efficiency in breaking C-C bonds in lignin under high temperature and high pressure was solved, and lignin was converted into phenolic compounds with high conversion rate and selectivity under mild conditions. The catalyst separation is simple and has good reproducibility.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- GUANGDONG UNIV OF PETROCHEMICAL TECH
- Filing Date
- 2023-11-27
- Publication Date
- 2026-05-29
AI Technical Summary
Existing technologies have low efficiency in catalyzing the breaking of C-C bonds in lignin under high temperature and high pressure conditions, and the catalysts are expensive, making large-scale application difficult.
A FeCoNi@NC catalyst was prepared by encapsulating a FeCoNi alloy catalyst with nitrogen-doped carbon. The nitrogen-doped carbon material was prepared by hydrothermal method as a support, and a mixture of nickel nitrate, iron nitrate, and cobalt nitrate was loaded onto it. After drying, grinding, and calcination, the FeCoNi@NC catalyst was prepared for the oxidative cleavage of bagasse-based lignin.
Under mild conditions, the catalyst converts lignin into phenolic compounds with a conversion rate of over 99% and a selectivity of 68.6%. The catalyst is easy to separate, has good reproducibility, and the reaction conditions are favorable.
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Figure CN117696087B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of catalytic synthesis technology, specifically relating to the preparation of a nitrogen-doped carbon-encapsulated FeCoNi alloy catalyst and its application in the oxidative cleavage of sugarcane bagasse-based lignin into phenols. Background Technology
[0002] Lignin is an abundant, low-cost, and underutilized renewable biomass. Reusing lignin to produce fuels and small-molecule aromatic compounds is a potential strategy for reducing dependence on fossil fuel resources. However, lignin is a polymer composed of various CO and C-linked methoxyphenylpropane structural units, and the selective breaking of its C-C bonds is a key challenge and difficulty in lignin degradation.
[0003] Selective cleavage strategies for lignin C-C bonds, including hydrolysis, cleavage, reduction, and oxidation, have been studied. Among these, selective catalytic oxidation is the most noteworthy because oxidation can cleave C-C bonds while preserving the aromatic ring structure, transforming lignin into highly functionalized monomeric aromatic compounds such as phenols, aldehydes, ketones, acids, and acid derivatives, which can be directly used as fine chemicals or platform chemicals.
[0004] Studies have shown that homogeneous and heterogeneous catalytic systems exhibit good conversion and C / C bond cleavage selectivity for lignin model compounds under thermal conditions. However, these traditional thermocatalytic processes encounter harsh reaction conditions, such as high temperature and pressure, expensive catalysts, and long reaction times, hindering their large-scale application. Therefore, developing effective alternative strategies for the selective oxidative cleavage of lignin C / C bonds under mild conditions is of great significance. Summary of the Invention
[0005] In view of the above-mentioned shortcomings in the prior art, the purpose of this invention is to provide a method for preparing a nitrogen-doped carbon-encapsulated FeCoNi alloy catalyst. The catalyst prepared by this invention can convert lignin into phenols under mild conditions, with 4-ethylphenol as the main product, the conversion rate being higher than 99% and the selectivity being 68.6%.
[0006] To achieve the above objectives, the present invention provides the following technical solution: a preparation of a nitrogen-doped carbon-encapsulated FeCoNi alloy catalyst, characterized by comprising the following steps:
[0007] (1) Synthesis of nitrogen-doped carbon material support:
[0008] (1.1) Prepare a 20% phenolic resin ethanol solution and refrigerate it for later use;
[0009] (1.2) Add anhydrous ethanol and deionized water to the reactor at a mass ratio of 3:2, add 5-10g of the phenolic resin ethanol solution described in step (1.1) at a reaction temperature of 50℃, and then add 0-2g of dicyandiamine and stir until completely dissolved.
[0010] (1.3) Add 100-200 μL of concentrated nitric acid to the solution from step (1.2) to adjust the pH of the solution to acidic, and then heat the solution at 50°C and a rotation speed of 400 r / min. -1 Stir for 0.5 hours under the specified conditions;
[0011] (1.4) Place the solution after stirring in step (1.3) in an oven at 50°C for 6 hours and then react at 100°C for 24 hours.
[0012] (1.5) After the sample cools down, it is placed in a tube furnace for carbonization treatment to obtain a nitrogen-doped carbon material carrier for later use.
[0013] (2) Synthesis of nitrogen-doped carbon-encapsulated FeCoNi alloy catalyst:
[0014] (2.1) Dry and dehydrate 0.5-1.0g of the nitrogen-doped carbon material carrier for 12h, then cool it for later use;
[0015] (2.2) Dissolve nickel nitrate, cobalt nitrate and ferric nitrate in water at a mass ratio of 1:1:1 to prepare an impregnation solution. Load the above impregnation solution onto the surface of the nitrogen-doped carbon material carrier by ultrasonic vibration, and then place it in a vacuum drying oven at a temperature of 80-100℃ for 3-5 hours.
[0016] (2.3) After drying, cool to room temperature, grind into powder, and under nitrogen conditions, heat the temperature to 600-800℃ in a tube furnace at a rate of 3℃ / min, maintain calcination for 5-6 hours, cool, and finally obtain FeCoNi@NC catalyst.
[0017] Further, in step (1.1), a 20% phenolic resin ethanol solution is prepared: 4.88g of phenol and 1.04g of 20wt% NaOH solution are placed in a reactor, stirred evenly, and then 8.4g of 37wt% formaldehyde solution is added. The reaction is carried out at 70℃ for 1h. After the reaction mixture is cooled to room temperature, the pH is adjusted to about 7.0-7.5 with 0.6mol / L HCl solution. The mixture is then rotary evaporated for 2h, and 15g of anhydrous ethanol solution is added. The mixture is then refrigerated for later use.
[0018] Furthermore, in step (1.5), the tubular furnace carbonization treatment is as follows: the temperature is increased to 800°C at a rate of 3°C / min, and calcined at 800°C for 5 hours.
[0019] Furthermore, before carbonization, nitrogen gas is introduced into the tubular furnace at room temperature for 30 minutes.
[0020] Furthermore, in step (2.1), the carrier is subjected to vacuum drying and dehydration treatment at a temperature of 110°C.
[0021] Further, in step (2.2), the impregnation solution is prepared by completely dissolving 0.33g of cobalt nitrate, 0.33g of nickel nitrate, and 0.33g of ferric nitrate in 2mL of water by ultrasonication.
[0022] Furthermore, the prepared nitrogen-doped carbon-encapsulated iron-cobalt-nickel alloy catalyst was ground and added to a 0.1 M / L HNO3 solution. After stirring at 60 °C for 6 h, the mixture was filtered, washed with deionized water until neutral, and then dried in a vacuum oven at 70 °C before storage.
[0023] Application of nitrogen-doped carbon-encapsulated FeCoNi alloy catalyst prepared by the above method in the oxidative cleavage of sugarcane bagasse-based lignin into phenols.
[0024] Further, 20 mg of nitrogen-doped carbon-encapsulated FeCoNi alloy catalyst, 15 mL of formic acid water and 68 mg of lignin were weighed and placed in a reaction vessel for catalytic reaction. The reaction temperature was 200-240℃ and the reaction time was 3-12 h. Nitrogen gas at 30 bar was introduced into the reaction vessel.
[0025] Furthermore, before the reaction, nitrogen gas needs to be introduced into the reactor to purge the air inside before the catalytic reaction can proceed.
[0026] Compared with the prior art, the present invention has the following beneficial effects:
[0027] 1. This invention uses a hydrothermal one-pot method to prepare nitrogen-doped carbon materials as a carrier. A mixture of nickel nitrate, iron nitrate, and cobalt nitrate is loaded by an equal-volume impregnation method. After drying and grinding, the mixture is calcined or reduced with sodium borohydride solution to prepare FeCoNi@NC catalyst. This catalyst has good selectivity.
[0028] 2. The catalyst provided by this invention converts lignin into phenols with a high conversion rate (≥99%) under mild conditions, with 4-ethylphenol as the main product. The selectivity is 68.6%.
[0029] 3. The catalyst provided by this invention can be used to catalyze the oxidative cleavage of lignin. The catalyst separation is simple and reproducible, and its catalytic performance is very stable.
[0030] 4. The catalytic lignin oxidative cleavage method provided by this invention does not require any organic solvents, and the reaction conditions are mild and environmentally friendly. Attached Figure Description
[0031] Figure 1 TEM images and mapping diagrams of the nitrogen-doped carbon-encapsulated FeCoNi alloy catalyst prepared in this invention;
[0032] Figure 2 X-ray powder diffraction patterns of the nitrogen-doped carbon-encapsulated FeCoNi alloy catalyst and NC prepared in this invention;
[0033] Figure 3 The N2 adsorption-desorption curves of the nitrogen-doped carbon-encapsulated FeCoNi alloy catalyst and NC prepared in this invention are shown. Detailed Implementation
[0034] The method of the present invention will be described in detail below with reference to specific embodiments. In the present invention, dicyandiamine can be abbreviated as DCDA.
[0035] I. Preparation of a nitrogen-doped carbon-encapsulated FeCoNi catalyst
[0036] Example 1
[0037] (1) Synthesis of nitrogen-doped carbon material support:
[0038] (1.1) Place 4.88g of phenol and 1.04g of 20wt% NaOH solution in a reactor, stir well, and then add 8.4g of 37wt% formaldehyde solution. React at 70℃ for 1h. After the reaction mixture cools to room temperature, adjust its pH to about 7.0-7.5 with 0.6mol / L HCl solution. Rotary evaporate for 2h, and add 15g of anhydrous ethanol solution to obtain a 20% phenolic resin ethanol solution, which is then refrigerated for later use.
[0039] (1.2) Add anhydrous ethanol and deionized water to the reactor at a mass ratio of 3:2. Add 5g of the phenolic resin ethanol solution described in step (1.1) at a reaction temperature of 50°C, and then add 2g of dicyandiamine. Stir until completely dissolved.
[0040] (1.3) Add 200 μL of concentrated nitric acid to the solution in step (1.2), adjust the pH of the solution to acidic, and stir for 0.5 h at a temperature of 50 °C and a speed of 400 rpm.
[0041] (1.4) Place the solution after stirring in step (1.3) in an oven at 50°C for 6 hours and then react at 100°C for 24 hours.
[0042] (1.5) After the sample cools down, nitrogen gas is first introduced into the tube furnace at room temperature for 30 min. Then the sample is placed in the tube furnace and heated to 800℃ at a rate of 3℃ / min. The sample is then kept at 800℃ for calcination for 5 h to obtain nitrogen-doped carbon material carrier for later use.
[0043] (2) Synthesis of nitrogen-doped carbon-encapsulated FeCoNi alloy catalyst:
[0044] (2.1) Place 1g of nitrogen-doped carbon material carrier under vacuum drying and dehydration treatment at 110℃ for 12h, and then cool it for later use;
[0045] (2.2) 0.33g cobalt nitrate, 0.33g nickel nitrate and 0.33g iron nitrate were completely dissolved in 2mL of water by ultrasonication to obtain an impregnation solution. The above impregnation solution was gradually loaded onto the surface of the nitrogen-doped carbon material support and then placed in a vacuum drying oven at 80℃ for 5h.
[0046] (2.3) After drying, cool to room temperature, grind into powder, and under nitrogen conditions, heat the temperature to 600℃ in a tube furnace at a rate of 3℃ / min, maintain calcination for 5 hours, and then cool.
[0047] (2.4) The ground nitrogen-doped carbon-encapsulated iron-cobalt-nickel alloy catalyst was added to a 0.1 M / L HNO3 solution, stirred at 60 °C for 6 h, filtered, washed with deionized water until neutral, dried in a vacuum oven at 70 °C and stored, named FeCoNi@NC-600.
[0048] Example 2
[0049] (1) Synthesis of nitrogen-free carbon material carriers:
[0050] (1.1) Place 4.88g of phenol and 1.04g of 20wt% NaOH solution in a reactor, stir well, and then add 8.4g of 37wt% formaldehyde solution. React at 70℃ for 1h. After the reaction mixture cools to room temperature, adjust its pH to about 7.0-7.5 with 0.6mol / L HCl solution. Rotary evaporate for 2h, and add 15g of anhydrous ethanol solution to obtain a 20% phenolic resin ethanol solution, which is then refrigerated for later use.
[0051] (1.2) Add anhydrous ethanol and deionized water to the reactor at a mass ratio of 3:2, and add 5g of the phenolic resin ethanol solution described in step (1.1) at a reaction temperature of 50℃ and stir until it is completely dissolved.
[0052] (1.3) Add 100 μL of concentrated nitric acid to the solution in step (1.2), adjust the pH of the solution to acidic, and stir for 0.5 h at a temperature of 50 °C and a speed of 400 rpm.
[0053] (1.4) Place the solution after stirring in step (1.3) in an oven at 50°C for 6 hours and then react at 100°C for 24 hours.
[0054] (1.5) After the sample cools down, nitrogen gas is first introduced into the tube furnace at room temperature for 30 min. Then the sample is placed in the tube furnace and heated to 800℃ at a rate of 3℃ / min. The sample is then kept at 800℃ for calcination for 5 h to obtain nitrogen-doped carbon material carrier for later use.
[0055] (2) Synthesis of carbon-coated FeCoNi alloy catalyst:
[0056] (2.1) Place 1g of nitrogen-doped carbon material carrier under vacuum drying and dehydration treatment at 110℃ for 12h, and then cool it for later use;
[0057] (2.2) 0.33g cobalt nitrate, 0.33g nickel nitrate and 0.33g iron nitrate were completely dissolved in 2mL of water by ultrasonication to obtain an impregnation solution. The above impregnation solution was gradually loaded onto the surface of the nitrogen-doped carbon material support and then placed in a vacuum drying oven at 100℃ for 3h.
[0058] (2.3) After drying, cool to room temperature, grind into powder, and under nitrogen conditions, heat the temperature to 700°C in a tube furnace at a rate of 3°C / min, maintain calcination for 5.5 hours, and then cool.
[0059] (2.4) The ground nitrogen-doped carbon-encapsulated iron-cobalt-nickel alloy catalyst was added to a 0.1 M / L HNO3 solution, stirred at 60 °C for 6 h, filtered, washed with deionized water until neutral, dried in a vacuum oven at 70 °C and stored, named FeCoNi@C.
[0060] Example 3
[0061] (1) Synthesis of nitrogen-doped carbon material support:
[0062] (1.1) Place 4.88g of phenol and 1.04g of 20wt% NaOH solution in a reactor, stir well, and then add 8.4g of 37wt% formaldehyde solution. React at 70℃ for 1h. After the reaction mixture cools to room temperature, adjust its pH to about 7.0-7.5 with 0.6mol / L HCl solution. Rotary evaporate for 2h, and add 15g of anhydrous ethanol solution to obtain a 20% phenolic resin ethanol solution, which is then refrigerated for later use.
[0063] (1.2) Add anhydrous ethanol and deionized water to the reactor at a mass ratio of 3:2. Add 10g of the phenolic resin ethanol solution described in step (1.1) at a reaction temperature of 50°C, and then add 1g of dicyandiamide. Stir until completely dissolved.
[0064] (1.3) Add 150 μL of concentrated nitric acid to the solution in step (1.2) and stir for 0.5 h at a temperature of 50 °C and a speed of 400 rpm.
[0065] (1.4) Place the solution after stirring in step (1.3) in an oven at 50°C for 6 hours and then react at 100°C for 24 hours.
[0066] (1.5) After the sample cools down, nitrogen gas is first introduced into the tube furnace at room temperature for 30 min. Then the sample is placed in the tube furnace and heated to 800℃ at a rate of 3℃ / min. The sample is then kept at 800℃ for calcination for 5 h to obtain nitrogen-doped carbon material carrier for later use.
[0067] (2) Synthesis of nitrogen-doped carbon-encapsulated FeCoNi alloy catalyst:
[0068] (2.1) Place 1g of nitrogen-doped carbon material carrier under vacuum drying and dehydration treatment at 110℃ for 12h, and then cool it for later use;
[0069] (2.2) 0.33g cobalt nitrate, 0.33g nickel nitrate and 0.33g iron nitrate were completely dissolved in 2mL of water by ultrasonication to obtain an impregnation solution. The above impregnation solution was gradually loaded onto the surface of the nitrogen-doped carbon material support and then placed in a vacuum drying oven at 90℃ for 4h.
[0070] (2.3) After drying, cool to room temperature, grind into powder, and under nitrogen conditions, heat the temperature to 800℃ in a tube furnace at a rate of 3℃ / min, maintain calcination for 6 hours, and then cool.
[0071] (2.4) The ground nitrogen-doped carbon-encapsulated iron-cobalt-nickel alloy catalyst was added to a 0.1 M / L HNO3 solution, stirred at 60 °C for 6 h, filtered, washed with deionized water until neutral, dried in a vacuum oven at 70 °C and stored, named FeCoNi@NC-800.
[0072] Example 4
[0073] (1) Synthesis of nitrogen-doped carbon materials:
[0074] (1.1) Place 4.88g of phenol and 1.04g of 20wt% NaOH solution in a reactor, stir well, and then add 8.4g of 37wt% formaldehyde solution. React at 70℃ for 1h. After the reaction mixture cools to room temperature, adjust its pH to about 7.0-7.5 with 0.6mol / L HCl solution. Rotary evaporate for 2h, and add 15g of anhydrous ethanol solution to obtain a 20% phenolic resin ethanol solution, which is then refrigerated for later use.
[0075] (1.2) Add anhydrous ethanol and deionized water to the reactor at a mass ratio of 3:2. Add 5g of the phenolic resin ethanol solution described in step (1.1) at a reaction temperature of 50°C, and then add 2g of dicyandiamine. Stir until completely dissolved.
[0076] (1.3) Add 200 μL of concentrated nitric acid to the solution in step (1.2) and stir for 0.5 h at a temperature of 50 °C and a speed of 400 rpm.
[0077] (1.4) Place the solution after stirring in step (1.3) in an oven at 50°C for 6 hours and then react at 100°C for 24 hours.
[0078] (1.5) After the sample cools down, nitrogen gas is first introduced into the tube furnace at room temperature for 30 min. Then the sample is placed in the tube furnace and heated to 800℃ at a rate of 3℃ / min. The sample is then calcined at 800℃ for 5 h to obtain nitrogen-doped carbon material, which is named NC.
[0079] II. Performance Testing of Nitrogen-Doped Carbon-Encapsulated FeCoNi Catalysts
[0080] (1) TEM test
[0081] Carefully remove the microgrid copper mesh with tweezers, place it flat on white filter paper with the membrane side facing up; add appropriate amounts of powder and ethanol to small beakers and sonicate for 10-30 minutes. After 3-5 minutes, use a glass capillary to draw up the homogeneous mixture of powder and ethanol, and then drop 2-3 drops of this mixture onto the microgrid copper mesh. Wait for at least 15 minutes until the ethanol has evaporated as much as possible, then place the sample on the sample stage and insert it into the electron microscope for testing.
[0082] Figure 1 This is a TEM image of the nitrogen-doped carbon-encapsulated FeCoNi alloy catalyst prepared in this invention. Figure 1 (a) The TEM image shows that spherical nanoparticles (NPs) are uniformly distributed on the NC scaffold, with an average size of 12.7 nm. Figure 1(b) Under magnification, it can be observed that the NPs are encapsulated by a graphite carbon layer, which effectively protects them from acid corrosion in the reaction environment. During the preparation process, the metal salt aggregates under the protection of PEG to form FeCoNi alloy NPs, which then serve as catalytic active centers to form the graphite carbon layer. Furthermore, some cavities can be observed as the acid leaching process removes poorly encapsulated NPs. Figure 1 (c) High-resolution TEM (HRTEM) images show polycrystalline Fe / Co / Ni lattices and graphite carbon stripes with lattice spacings of 0.20 nm and 0.35 nm, corresponding to the (111) plane of the FeCoNi alloy and the (002) plane of graphite, respectively.
[0083] (2) XRD test
[0084] Add the powder sample to the center of the groove in the sample holder, making the loose sample powder slightly higher than the plane of the sample holder; take a glass slide and gently press it on the sample surface to make the powder sample surface level with the plane of the frame, and scrape off any excess powder that is not in the groove, keeping the entire surface uniform and flat and consistent with the plane of the groove. Place the sample holder into the slot of the testing instrument for testing.
[0085] Figure 2 The XRD patterns of the nitrogen-doped carbon-encapsulated FeCoNi alloy catalyst and NC prepared for this invention show two distinct peaks at 24.5° and 43.3°, corresponding to the (002) and (100) planes of graphite, respectively. With the introduction of a metal salt during preparation, the FeCoNi@NC diffraction peaks are located at 43.8°, 51.0°, and 75.1°, between the peaks of pure Fe and pure Ni, indicating the formation of FeCoNi alloy NPs. The size of the FeCoNi NPs calculated based on the Scherrer equation is approximately 13.2 nm, consistent with the previously mentioned TEM results. Furthermore, for FeCoNi@NC, the (002) diffraction peak of graphene is stronger and sharper than that of NC, further confirming that the metal NPs promote the formation of the graphitic carbon shell, thereby enhancing the graphitization of FeCoNi@NC.
[0086] (3) BET test
[0087] After grinding and drying the powder sample, it is placed into a sample tube. Under low temperature (liquid nitrogen bath) conditions, a certain amount of adsorbate gas (N2) is introduced into the sample tube. The adsorption partial pressure is directly measured by controlling the equilibrium pressure in the sample tube. The adsorption amount at that partial pressure point is obtained by the gas law. By gradually introducing adsorbate gas to increase the adsorption equilibrium pressure, the adsorption-desorption isotherm is obtained.
[0088] The specific surface area and pore size distribution of NC and nitrogen-doped carbon-encapsulated FeCoNi alloy catalysts were studied using the N2 adsorption method. Figure 3The figure shows the N2 adsorption-desorption curves of the nitrogen-doped carbon-encapsulated FeCoNi alloy catalyst and NC prepared in this invention. As can be seen from the figure, the adsorption and desorption isotherms of both the nitrogen-doped carbon-encapsulated FeCoNi alloy catalyst and NC are type IV curves, and the hysteresis loop is type h1, indicating that they are mesoporous materials. The specific surface area of NC is 557.0 m². 2 / g, after introducing a metal precursor into the nitrogen-doped carbon-encapsulated FeCoNi alloy catalyst, the specific surface area was significantly reduced to 248.9m². 2 / g. However, the pore volume decreased from 0.42 cm⁻¹ in NC. 3 / g increased to 0.69cm³ of nitrogen-doped carbon-encapsulated FeCoNi alloy catalyst. 3 / g, which may be due to the formation of some cavities after the removal of alloy NPs.
[0089] III. Testing of lignin oxidative cleavage to prepare phenolic products catalyzed by FeCoNi@NC catalyst
[0090] 20 mg of nitrogen-doped carbon-coated FeCoNi alloy catalyst, 15 mL of (2 M / L) formic acid, and 68 mg of lignin were weighed and placed in a sealed stainless steel mechanical reactor. The reactor was purged with nitrogen and then 3 MPa of nitrogen gas was added. The reaction was carried out at 220 °C for 6 hours. The catalytic reaction results are shown in Table 1.
[0091] Table 1 shows the catalytic reaction results.
[0092]
[0093] Extraction with ethyl acetate and detection of the reactants using gas chromatography with a FID hydrogen fire detector were performed. The table shows that the active sites of the iron-cobalt-nickel alloy catalyst are located in the alloy metal, and its nitrogen-doped, metal-free NC support showed no catalytic reaction under the same conditions. Controlling temperature and reaction time revealed that as the reaction temperature increased, the lignin conversion was complete at 220℃, with optimal selectivity; therefore, 220℃ is the most suitable temperature for this catalyst. Changing the reaction time showed that longer reaction times altered both the lignin conversion rate and the selectivity for 4-ethylphenol. Analysis determined that the optimal time for the FeCoNi@NC-600 catalyst to catalyze lignin conversion is 6 hours.
[0094] The reaction was carried out in 15 mL of 2 M / L formic acid water, with a catalyst dosage of 20 mg, a nitrogen pressure of 3 MPa, a lignin dosage of 68 mg, a reaction time of 6 h, and a rotation speed of 800 r·min. -1Under the given conditions, the catalyst after the reaction was magnetically separated, washed with double-distilled water, and dried before being used in the next catalytic reaction. The reusability of catalyst FeCoNi@NC-600 under a nitrogen atmosphere was investigated, and the results are shown in Table 2. The results show that after three repeated uses, the catalyst activity gradually decreased, but its conversion rate remained above 80%, and the catalytic performance did not decline significantly, indicating that the catalyst has good stability and high reusability.
[0095] Table 2 Repeatability Tests of FeCoNi@NC-600
[0096] Number of times used Lignin conversion rate (%) 4-Ethylphenol selectivity (%) 1 100 83.80 2 93.59 81.38 3 83.37 72.24
[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.
Claims
1. A method for preparing a nitrogen-doped carbon-encapsulated FeCoNi alloy catalyst for catalytic oxidation and cleavage of sugarcane bagasse-based lignin into phenols, characterized in that, Includes the following steps: (1) Synthesis of nitrogen-doped carbon material carriers: (1.1) Preparation of 20% phenolic resin ethanol solution: Place 4.88 g phenol and 1.04 g 20wt% NaOH solution in a reactor, stir well, and then add 8.4 g 37wt% formaldehyde solution. React at 70℃ for 1 h. After the reaction mixture cools to room temperature, adjust its pH to 7.0~7.5 with 0.6 mol / L HCl solution. Rotary evaporate for 2 h, add 15 g anhydrous ethanol solution, and store for later use. (1.2) Add anhydrous ethanol and deionized water to the reactor at a mass ratio of 3:2, add 5~10 g of the phenolic resin ethanol solution described in step (1.1) at a reaction temperature of 50℃, and then add 1~2 g of dicyandiamine and stir until completely dissolved. (1.3) Add 100~200 uL of concentrated nitric acid to the solution in step (1.2), adjust the pH of the solution to acidic, and then stir for 0.5 h at a temperature of 50℃ and a speed of 400 r·min-1. (1.4) Place the solution after stirring in step (1.3) in an oven at 50°C for 6 h and then react at 100°C for 24 h. (1.5) After the sample cools down, it is placed in a tube furnace and heated to 800°C at a rate of 3°C / min. It is then kept at 800°C for calcination for 5 hours to obtain a nitrogen-doped carbon material carrier for later use. (2) Synthesis of nitrogen-doped carbon-encapsulated FeCoNi alloy catalyst: (2.1) Dry and dehydrate 0.5-1.0 g of the nitrogen-doped carbon material carrier for 12 h, then cool it for later use; (2.2) Dissolve nickel nitrate, cobalt nitrate and ferric nitrate in water at a mass ratio of 1:1:1 to prepare an impregnation solution. Load the above impregnation solution onto the surface of the nitrogen-doped carbon material carrier by ultrasonic vibration, and then place it in a vacuum drying oven at a temperature of 80~100℃ for 3-5 h. (2.3) After drying, cool to room temperature, grind into powder, and under nitrogen conditions, heat the temperature to 600-800℃ in a tube furnace at a rate of 3℃ / min, maintain calcination for 5-6 h, cool, and finally obtain FeCoNi@NC catalyst.
2. The method for preparing a nitrogen-doped carbon-encapsulated FeCoNi alloy catalyst for catalytic oxidation and cleavage of sugarcane bagasse-based lignin into phenols according to claim 1, characterized in that, Before carbonization, nitrogen gas is introduced into the tubular furnace at room temperature for 30 minutes.
3. The method for preparing the nitrogen-doped carbon-encapsulated FeCoNi alloy catalyst for catalytic oxidation and cleavage of sugarcane bagasse-based lignin into phenols according to claim 1, characterized in that, In step (2.1), the carrier is subjected to vacuum drying and dehydration treatment at a temperature of 110°C.
4. The method for preparing the nitrogen-doped carbon-encapsulated FeCoNi alloy catalyst for catalytic oxidation and cleavage of sugarcane bagasse-based lignin into phenols according to claim 1, characterized in that, In step (2.2), the impregnation solution is prepared by completely dissolving 0.33g cobalt nitrate, 0.33g nickel nitrate, and 0.33g ferric nitrate in 2 mL of water by ultrasonication.
5. The method for preparing a nitrogen-doped carbon-encapsulated FeCoNi alloy catalyst for catalytic oxidation and cleavage of sugarcane bagasse-based lignin into phenols according to claim 1, characterized in that, The prepared nitrogen-doped carbon-encapsulated iron-cobalt-nickel alloy catalyst was ground and added to a 0.1 M HNO3 solution. After stirring at 60 °C for 6 h, the mixture was filtered, washed with deionized water until neutral, and then dried in a vacuum oven at 70 °C before storage.
6. An application of a nitrogen-doped carbon-encapsulated FeCoNi alloy catalyst, characterized in that, Application of nitrogen-doped carbon-encapsulated FeCoNi alloy catalysts prepared by any one of the methods described in claims 1 to 5 in the oxidative cleavage of sugarcane bagasse-based lignin into phenols.
7. The application of the nitrogen-doped carbon-encapsulated FeCoNi alloy catalyst according to claim 6, characterized in that, Weigh 20 mg of nitrogen-doped carbon-encapsulated FeCoNi alloy catalyst prepared by any one of claims 1 to 5, 15 mL of formic acid water and 68 mg of lignin and place them in a reaction vessel for catalytic reaction. The reaction temperature is 200-240℃ and the reaction time is 3-12 h. Nitrogen gas at 30 bar is introduced into the reaction vessel.
8. The application of the nitrogen-doped carbon-encapsulated FeCoNi alloy catalyst according to claim 7, characterized in that, Before the reaction, nitrogen gas needs to be introduced into the reactor until the air inside the reactor is purged before the catalytic reaction can proceed.