Heteropolyacid catalyst with core-shell structure as well as preparation method and application of heteropolyacid catalyst

Abstract

The invention belongs to the technical field of electro-catalysis, and provides a heteropolyacid catalyst with a core-shell structure as well as a preparation method and application of the heteropolyacid catalyst. The preparation method comprises the following steps: by taking metal nickel as a working electrode, Ag / AgCl as a reference electrode and a platinum sheet as a counter electrode, carrying out electro-deposition in a cobalt nitrate solution to obtain Co (OH) 2 / NF; by taking Co (OH) 2 / NF as a working electrode, Ag / AgCl as a reference electrode and a platinum sheet as a counter electrode, carrying out electro-deposition in a phosphomolybdic acid solution to obtain PMo12atCo (OH) 2 / NF; the PMo12-coated Co (OH) 2 / NF is immersed in a 2-methylimidazole solution for a reaction, and PMo12-coated ZIF-67 / NF is obtained; and immersing the PMo12-coated ZIF-67 / nickel precursor into a nickel nitrate solution for reaction. According to the invention, phosphomolybdic acid is doped in NiCo-LDH with nickel as a substrate, and efficient electrocatalytic oxidation of lignin is realized under mild conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalysis, and in particular to a core-shell structure heteropolyacid catalyst, a preparation method and an application thereof. Background Art

[0002] With the overuse of fossil fuels leading to depletion, increased environmental pollution, and the greenhouse effect, the development of clean energy has become a hot topic. Biomass is the only renewable organic energy source that can replace petroleum resources in the production of energy, materials, and chemicals. Biomass not only provides a carbon source but also stores energy in chemical substances, offering broad application prospects in energy supply and chemical feedstock. Lignin, with its abundant, renewable, readily available, and inexpensive nature, shows great potential for producing fuels and value-added small-molecule aromatic compounds.

[0003] Catalytic processes are crucial in biomass utilization. Electrocatalytic oxidation, with its low energy consumption and simple process, has garnered significant interest in the electrocatalytic oxidation of lignin. Singh et al. used alkali lignin extracted from wheat straw and sucrose as substrates, respectively, to generate vanillin via galvanostatic oxidation reactions on a stainless steel anode, yielding 6% and 6.6%, respectively. Lignin's solubility in the electrolyte is crucial for achieving contact reaction between lignin and the electrode, but its structural complexity results in extremely low solubility in aqueous solutions.

[0004] Therefore, providing efficient catalysts, increasing the contact area between electrodes and lignin, and achieving efficient electrocatalytic lignin under mild conditions have great development prospects. Summary of the Invention

[0005] The purpose of the present invention is to provide a core-shell structure heteropolyacid catalyst and its preparation method and application in view of the deficiencies in the prior art.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a core-shell structured heteropolyacid catalyst, comprising the following steps:

[0008] 1) Using metallic nickel as the working electrode, Ag / AgCl as the reference electrode, and platinum as the counter electrode, electrodeposition was performed in a cobalt nitrate solution to obtain a Co(OH)2 / nickel composite material;

[0009] 2) Using Co(OH)2 / nickel composite material as working electrode, Ag / AgCl as reference electrode and platinum sheet as counter electrode, electroplating was carried out in phosphomolybdic acid solution to obtain PMo 12 @Co(OH)2 / nickel intermediate;

[0010] 3) PMo12 The Co(OH)2 / nickel intermediate was immersed in 2-methylimidazole solution to react and obtain PMo 12 @ZIF-67 / nickel precursor;

[0011] 4) PMo 12 The @ZIF-67 / nickel precursor is immersed in a nickel nitrate solution to react and obtain a core-shell structured heteropolyacid catalyst.

[0012] Preferably, the concentration of the cobalt nitrate solution in step 1) is 0.05 to 0.15 mol / L;

[0013] The electrodeposition in step 1) is carried out by cyclic voltammetry, with a scanning range of -0.4 to -1.6 V, a scanning speed of 0.005 to 0.02 V / s, and a cycle scanning number of 3 to 5 times.

[0014] Preferably, the concentration of the phosphomolybdic acid solution in step 2) is 1.5 to 3 g / L;

[0015] Step 2) The electrodeposition is performed using cyclic voltammetry with a scan range of -0.9 to 0.4 V, a scan rate of 0.03 to 0.05 V / s, and 8 to 12 cycles.

[0016] Preferably, the solvent of the 2-methylimidazole solution in step 3) is methanol, and the concentration of 2-methylimidazole in the 2-methylimidazole solution is 1 to 2 mol / L;

[0017] Step 3) The reaction time is 0.5 to 1.5 hours.

[0018] Preferably, the solvent of the nickel nitrate solution in step 4) is anhydrous ethanol, and the concentration of nickel nitrate in the nickel nitrate solution is 15-20 mmol / L.

[0019] Preferably, the reaction time in step 4) is 10 to 14 hours;

[0020] Step 4) Stirring is performed during the reaction at a speed of 50 to 200 r / min.

[0021] The present invention also provides a core-shell structure heteropolyacid catalyst prepared by the preparation method.

[0022] The present invention also provides the use of the core-shell structure heteropoly acid catalyst in electrocatalytic oxidation of lignin, wherein the core-shell structure heteropoly acid catalyst is used as a working electrode, Ag / AgCl is used as a reference electrode, and a platinum sheet is used as a counter electrode to carry out electrocatalytic oxidation in a lignin solution.

[0023] Preferably, the solvent of the lignin solution is a mixture of methanol and KOH solution, and the volume ratio of methanol to KOH solution is 0.5-1.5:8.5-9.5;

[0024] In the lignin solution, the concentration of lignin is 0.5-2 mmol / L.

[0025] Preferably, the voltage of the electrocatalytic oxidation is 2.0 to 2.5 V, and the time of the electrocatalytic oxidation is 50 to 80 minutes.

[0026] The beneficial effects of the present invention include the following:

[0027] 1) The present invention adopts an in situ encapsulation and recombination strategy to dope a Keggin-type heteropolyacid (phosphomolybdic acid) into a nickel-based nickel-cobalt layered double hydroxide (NiCo-LDH) to prepare a core-shell structured electrode material. This not only solidifies the soluble heteropolyacid but also increases the specific surface area of the electrode material, increasing the contact area between the electrode material and lignin. This allows for efficient electrocatalytic oxidation of lignin under mild conditions, improving the conversion rate of lignin, and depolymerizing lignin into single benzene ring compounds.

[0028] 2) The present invention optimizes the reaction conditions of electrocatalytic oxidation and selects a mixed solution of methanol and KOH solution as the solvent for lignin, thereby reducing the corrosion risk of the electrode material and providing a stable electrocatalytic oxidation environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The linear sweep voltammetry (LSV) curves of the catalysts prepared in Example 1 and Comparative Examples 2 to 4 are shown in FIG. 12 @NiCo-LDH / NF is the catalyst prepared in Example 1;

[0030] Figure 2 The Tafel curves of the catalysts prepared in Example 1 and Comparative Examples 2 to 4 are shown in FIG. 12 @NiCo-LDH / NF is the catalyst prepared in Example 1;

[0031] Figure 3 is the charge transfer impedance of the catalysts prepared in Example 1 and Comparative Examples 2 to 4, wherein PMo 12 @NiCo-LDH / NF is the catalyst prepared in Example 1;

[0032] Figure 4 The dual capacitors of the catalysts prepared in Example 1 and Comparative Examples 2 to 4, wherein PMo 12 @NiCo-LDH / NF is the catalyst prepared in Example 1;

[0033] Figure 5 The lignin conversion rate and the yield of single benzene ring compounds of Application Example 1 and Comparative Examples 2 to 4 are shown in FIG. 12 @NiCo-LDH / NF electrode is application example 1;

[0034] Figure 6 The lignin conversion rate and the yield of single benzene ring compounds in Application Examples 1-2 and Comparative Example 1 are shown;

[0035] Figure 7 The lignin conversion rate and the yield of single benzene ring compounds of Application Example 1, Application Example 3, and Comparative Application Examples 5 to 7 are shown;

[0036] Figure 8 The lignin conversion rate and the yield of the single benzene ring compound of Comparative Examples 8 to 12 are used;

[0037] Figure 9 The conversion rate and product yield of the core-shell heteropolyacid catalyst electrocatalytically oxidized real lignin in Example 1;

[0038] Figure 10 is the stability curve of the core-shell heteropolyacid catalyst of Example 1;

[0039] Figure 11 The cycle performance of the core-shell heteropolyacid catalyst of Example 1 is shown;

[0040] Figure 12 This is an infrared spectrum of the core-shell heteropolyacid catalyst of Example 1 after five cycles of use and before use;

[0041] Figure 13 This is a scanning electron microscope image of the core-shell structure heteropolyacid catalyst of Example 1 after being recycled 5 times. DETAILED DESCRIPTION

[0042] The present invention provides a method for preparing a core-shell structured heteropolyacid catalyst, comprising the following steps:

[0043] 1) Using metallic nickel as the working electrode, Ag / AgCl as the reference electrode, and platinum as the counter electrode, electrodeposition was performed in a cobalt nitrate solution to obtain a Co(OH)2 / nickel composite material;

[0044] 2) Using Co(OH)2 / nickel composite material as working electrode, Ag / AgCl as reference electrode and platinum sheet as counter electrode, electroplating was carried out in phosphomolybdic acid solution to obtain PMo 12 @Co(OH)2 / nickel intermediate;

[0045] 3) PMo 12 The Co(OH)2 / nickel intermediate was immersed in 2-methylimidazole solution to react and obtain PMo 12@ZIF-67 / nickel precursor;

[0046] 4) PMo 12 The @ZIF-67 / nickel precursor is immersed in a nickel nitrate solution to react and obtain a core-shell structured heteropolyacid catalyst.

[0047] In the present invention, the concentration of the cobalt nitrate solution in step 1) is preferably 0.05 to 0.15 mol / L, more preferably 0.07 to 0.12 mol / L, and more preferably 0.1 mol / L;

[0048] The electrodeposition in step 1) is preferably carried out by cyclic voltammetry, with a scan range of preferably -0.4 to -1.6 V, more preferably -0.6 to -1.2 V; a scan rate of preferably 0.005 to 0.02 V / s, more preferably 0.008 to 0.015 V / s, more preferably 0.01 V / s; and a number of cyclic scans of preferably 3 to 5 times, more preferably 4 times.

[0049] In the present invention, after the electrodeposition in step 1) is completed, the working electrode is preferably cleaned and dried to obtain a Co(OH)2 / nickel composite material;

[0050] In step 1), the cleaning reagent after the electrodeposition is preferably water, the drying is preferably vacuum drying, the vacuum drying temperature is preferably 50 to 100°C, and more preferably 60 to 80°C; the vacuum drying time is preferably 4 to 18 hours, and more preferably 6 to 12 hours; the vacuum degree of vacuum drying is preferably -0.08 to -0.04 MPa, and more preferably -0.06 MPa.

[0051] In the present invention, the concentration of the phosphomolybdic acid solution in step 2) is preferably 1.5 to 3 g / L, more preferably 1.8 to 2.8 g / L, and more preferably 2 to 2.5 g / L;

[0052] In step 2), the electrodeposition is preferably carried out by cyclic voltammetry, with a scan range of preferably -0.9 to 0.4 V, more preferably -0.7 to 0.2 V; a scan rate of preferably 0.03 to 0.05 V / s, more preferably 0.035 to 0.045 V / s, more preferably 0.04 V / s; and a cycle scan number of preferably 8 to 12 times, more preferably 9 to 11 times, more preferably 10 times.

[0053] In the present invention, after the electrodeposition in step 2) is completed, PMo is preferably obtained on the working electrode. 12 @Co(OH)2 / nickel intermediate.

[0054] In the present invention, the solvent of the 2-methylimidazole solution in step 3) is preferably methanol, and the concentration of 2-methylimidazole in the 2-methylimidazole solution is preferably 1 to 2 mol / L, more preferably 1.3 to 1.8 mol / L, and more preferably 1.5 mol / L;

[0055] The reaction time in step 3) is preferably 0.5 to 1.5 h, more preferably 0.8 to 1.2 h, and even more preferably 1 h.

[0056] In the present invention, after the reaction in step 3) is completed, it is preferably washed and dried to obtain PMo 12 @ZIF-67 / nickel precursor;

[0057] In step 3), the cleaning reagent after the reaction is preferably methanol, the drying temperature is preferably 50-80° C., more preferably 60-70° C.; the drying time is preferably 20-28 h, more preferably 24 h.

[0058] In the present invention, the solvent of the nickel nitrate solution in step 4) is preferably anhydrous ethanol, and the concentration of nickel nitrate in the nickel nitrate solution is preferably 15-20 mmol / L, more preferably 16-18 mmol / L, and more preferably 16.8 mmol / L.

[0059] In the present invention, the reaction time of step 4) is preferably 10 to 14 hours, more preferably 11 to 13 hours, and more preferably 12 hours;

[0060] In step 4), the reaction is preferably stirred, and the stirring speed is preferably 50 to 200 r / min, more preferably 100 to 150 r / min.

[0061] In the present invention, after the reaction in step 4) is completed, it is preferably washed and dried to obtain a core-shell structure heteropolyacid catalyst;

[0062] In step 4), the cleaning reagent after the reaction is preferably anhydrous ethanol, the drying is preferably vacuum drying, the vacuum drying temperature is preferably 50 to 80° C., more preferably 60 to 70° C.; the vacuum drying time is preferably 20 to 28 h, more preferably 24 h; the vacuum degree of vacuum drying is preferably -0.08 to -0.04 MPa, more preferably -0.06 MPa.

[0063] The present invention also provides a core-shell structure heteropolyacid catalyst prepared by the preparation method.

[0064] In the present invention, the core-shell structure heteropoly acid catalyst is preferably PMo 12 @NiCo-LDH / NF composite material.

[0065] The present invention also provides the use of the core-shell structure heteropoly acid catalyst in electrocatalytic oxidation of lignin, wherein the core-shell structure heteropoly acid catalyst is used as a working electrode, Ag / AgCl is used as a reference electrode, and a platinum sheet is used as a counter electrode to carry out electrocatalytic oxidation in a lignin solution.

[0066] In the present invention, the solvent of the lignin solution is preferably a mixture of methanol and KOH solution, and the volume ratio of methanol to KOH solution is preferably 0.5-1.5:8.5-9.5, more preferably 0.7-1.2:8.8-9.3, and more preferably 1:9;

[0067] In the lignin solution, the concentration of lignin is preferably 0.5 to 2 mmol / L, more preferably 1 to 1.5 mmol / L.

[0068] In the present invention, the voltage of the electrocatalytic oxidation is preferably 2.0 to 2.5 V, more preferably 2.1 to 2.4 V, and more preferably 2.2 to 2.3 V; the time of the electrocatalytic oxidation is preferably 50 to 80 min, and more preferably 60 to 70 min.

[0069] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0070] Example 1

[0071] A 2 cm × 2 cm nickel mesh (NF) was ultrasonically cleaned sequentially with acetone, 22.5% hydrochloric acid, anhydrous ethanol, and deionized water at a frequency of 50 kHz, with each ultrasonic cleaning lasting 15 minutes. After ultrasonic cleaning, the nickel mesh was dried at 60°C for 8 h. Cyclic voltammetry was used in a 0.1 mol / L cobalt nitrate solution using a three-electrode system on a CHI760E electrochemical workstation, using NF as the working electrode, Ag / AgCl as the reference electrode, and a platinum sheet as the counter electrode. The scan range was -0.4 to -1.6 V, the scan rate was 0.01 V / s, and the number of cycles was four. After electrodeposition, the working electrode was removed, rinsed with deionized water, and dried at 60°C under a vacuum of -0.08 MPa for 12 h to obtain a Co(OH)2 / nickel composite material, labeled Co(OH)2 / NF.

[0072] 25 mg Keggin type heteropoly acid (phosphomolybdic acid H3PMo 12 O 40) was dissolved in 10 mL of deionized water to obtain a 2.5 g / L phosphomolybdic acid solution. Using Co(OH)2 / NF as the working electrode, Ag / AgCl as the reference electrode, and platinum as the counter electrode, a three-electrode system was used on the electrochemical workstation CHI760E. Cyclic voltammetry was used for electrodeposition in the phosphomolybdic acid solution. The scan range was -0.9 to 0.4 V, the scan rate was 0.04 V / s, and the number of cyclic scans was 10. After the electrodeposition was completed, the working electrode was removed, which was PMo 12 @Co(OH)2 / nickel intermediate.

[0073] Dissolve 40 mmol of 2-methylimidazole in 25 mL of methanol to obtain a 2-methylimidazole solution with a concentration of 1.6 mol / L. 12 The Co(OH)2 / nickel intermediate was immersed in 2-methylimidazole solution and reacted for 1 hour. After the reaction was completed, it was taken out and washed with methanol three times, and then dried at 60℃ for 24 hours to obtain PMo 12 @ZIF-67 / nickel precursor, labeled PMo 12 @ZIF-67 / NF.

[0074] Dissolve 0.42mmolNi(NO3)2·6H2O in 25mL of anhydrous ethanol to obtain a nickel nitrate solution with a concentration of 16.8mmol / L. 12 The ZIF-67 / NF was immersed in a nickel nitrate solution and stirred at 100 r / min at room temperature for 12 hours. After the reaction, the product was removed and washed three times with anhydrous ethanol. The product was then dried at 60°C and -0.08 MPa vacuum for 24 hours to obtain a core-shell heteropolyacid catalyst.

[0075] The core-shell heteropoly acid catalyst prepared in this example is marked as PMo 12 @NiCo-LDH / NF-25.

[0076] Example 2

[0077] The phosphomolybdic acid solution in Example 1 was modified as follows: 15 mg Keggin type heteropoly acid (phosphomolybdic acid H3PMo 12 O 40 ) was dissolved in 10 mL of deionized water to obtain a phosphomolybdic acid solution with a concentration of 1.5 g / L, and the rest was the same as in Example 1.

[0078] The core-shell heteropoly acid catalyst prepared in this example is marked as PMo 12 @NiCo-LDH / NF-15.

[0079] Example 3

[0080] A 2 cm × 2 cm nickel mesh (NF) was ultrasonically cleaned sequentially with acetone, 22.5% hydrochloric acid, anhydrous ethanol, and deionized water at a frequency of 50 kHz, with each ultrasonic cleaning lasting 15 minutes. After ultrasonic cleaning, the nickel mesh was dried at 60°C for 8 hours. Cyclic voltammetry was used in a 0.05 mol / L cobalt nitrate solution using a CHI760E electrochemical workstation with a three-electrode system using NF as the working electrode, Ag / AgCl as the reference electrode, and a platinum sheet as the counter electrode. The scan range was -0.4 to -1.6 V, the scan rate was 0.02 V / s, and the number of cycles was three. After electrodeposition, the working electrode was removed, rinsed with deionized water, and dried at 60°C under a vacuum of -0.08 MPa for 12 hours to obtain a Co(OH)2 / nickel composite.

[0081] 30 mg Keggin type heteropoly acid (phosphomolybdic acid H3PMo 12 O 40 ) was dissolved in 10 mL of deionized water to obtain a 3 g / L phosphomolybdic acid solution. Using Co(OH)2 / nickel composite material as the working electrode, Ag / AgCl as the reference electrode, and platinum sheet as the counter electrode, the electrochemical workstation CHI760E three-electrode system was used to perform cyclic voltammetry in the phosphomolybdic acid solution. The scanning range was -0.9 to 0.4 V, the scanning speed was 0.03 V / s, and the number of cyclic scans was 8 times. After the electrodeposition was completed, the working electrode was taken out, which was PMo 12 @Co(OH)2 / nickel intermediate.

[0082] Dissolve 50mmol of 2-methylimidazole in 25mL of methanol to obtain a 2mol / L 2-methylimidazole solution. 12 The Co(OH)2 / nickel intermediate was immersed in 2-methylimidazole solution and reacted for 1.5 hours. After the reaction was completed, it was taken out and washed with methanol three times, and then dried at 50°C for 28 hours to obtain PMo 12 @ZIF-67 / nickel precursor.

[0083] Dissolve 0.375mmol Ni(NO3)2·6H2O in 25mL of anhydrous ethanol to obtain a nickel nitrate solution with a concentration of 15mmol / L. 12 The ZIF-67 / nickel precursor was immersed in a nickel nitrate solution and stirred at 50 r / min at room temperature for 10 hours. After the reaction, the precursor was removed, washed three times with anhydrous ethanol, and then dried at 70°C and -0.08 MPa vacuum for 20 hours to obtain a core-shell heteropolyacid catalyst.

[0084] Example 4

[0085] A 2 cm × 2 cm nickel mesh (NF) was ultrasonically cleaned sequentially with acetone, 22.5% hydrochloric acid, anhydrous ethanol, and deionized water at a frequency of 50 kHz, with each ultrasonic cleaning lasting 15 minutes. After ultrasonic cleaning, the nickel mesh was dried at 60°C for 8 hours. Cyclic voltammetry was used in a 0.15 mol / L cobalt nitrate solution using a three-electrode system on a CHI760E electrochemical workstation, using NF as the working electrode, Ag / AgCl as the reference electrode, and a platinum sheet as the counter electrode. The scan range was -0.4 to -1.6 V, the scan rate was 0.005 V / s, and the number of cycles was five. After electrodeposition, the working electrode was removed, rinsed with deionized water, and dried at 60°C under a vacuum of -0.08 MPa for 12 hours to obtain a Co(OH)2 / nickel composite.

[0086] 15 mg Keggin type heteropoly acid (phosphomolybdic acid H3PMo 12 O 40 ) was dissolved in 10 mL of deionized water to obtain a 1.5 g / L phosphomolybdic acid solution. Using Co(OH)2 / nickel composite material as the working electrode, Ag / AgCl as the reference electrode, and platinum sheet as the counter electrode, the electrochemical workstation CHI760E three-electrode system was used to perform cyclic voltammetry in the phosphomolybdic acid solution. The scanning range was -0.9 to 0.4 V, the scanning speed was 0.05 V / s, and the number of cyclic scans was 12 times. After the electrodeposition was completed, the working electrode was taken out, which was PMo 12 @Co(OH)2 / nickel intermediate.

[0087] Dissolve 25mmol of 2-methylimidazole in 25mL of methanol to obtain a 2-methylimidazole solution with a concentration of 1mol / L. 12 The Co(OH)2 / nickel intermediate was immersed in 2-methylimidazole solution and reacted for 0.5 h. After the reaction was completed, it was taken out and washed with methanol three times, and then dried at 70 ° C for 20 h to obtain PMo 12 @ZIF-67 / nickel precursor.

[0088] Dissolve 0.5mmolNi(NO3)2·6H2O in 25mL of anhydrous ethanol to obtain a nickel nitrate solution with a concentration of 20mmol / L. 12 The ZIF-67 / nickel precursor was immersed in a nickel nitrate solution and stirred at 50 rpm for 14 hours at room temperature. After the reaction, the precursor was removed, washed three times with anhydrous ethanol, and then dried at 50°C and -0.08 MPa vacuum for 28 hours to obtain a core-shell heteropolyacid catalyst.

[0089] Comparative Example 1

[0090] The phosphomolybdic acid solution in Example 1 was modified as follows: 35 mg Keggin type heteropoly acid (phosphomolybdic acid H3PMo 12 O 40 ) was dissolved in 10 mL of deionized water to obtain a 3.5 g / L phosphomolybdic acid solution, and the rest was the same as in Example 1.

[0091] The core-shell heteropoly acid catalyst prepared in this comparative example is marked as PMo 12 @NiCo-LDH / NF-35.

[0092] Comparative Example 2

[0093] A 2 cm x 2 cm nickel mesh (NF) was ultrasonically cleaned in acetone, 22.5% hydrochloric acid, anhydrous ethanol, and deionized water, sequentially, at a frequency of 50 kHz for 15 minutes per cleaning cycle. After ultrasonic cleaning, the mesh was dried at 60°C for 8 hours to obtain a nickel electrode, labeled NF.

[0094] Comparative Example 3

[0095] A 2 cm x 2 cm nickel mesh (NF) was ultrasonically cleaned in acetone, 22.5% hydrochloric acid, anhydrous ethanol, and deionized water, sequentially, at a frequency of 50 kHz for 15 minutes per cleaning cycle. After ultrasonic cleaning, the mesh was dried at 60°C for 8 hours.

[0096] 25 mg Keggin type heteropoly acid (phosphomolybdic acid H3PMo 12 O 40 ) was dissolved in 10 mL of deionized water to obtain a 2.5 g / L phosphomolybdic acid solution. Using NF as the working electrode, Ag / AgCl as the reference electrode, and platinum as the counter electrode, a three-electrode system was used on an electrochemical workstation CHI760E. Cyclic voltammetry was used for electrodeposition in the phosphomolybdic acid solution with a scan range of -0.9 to 0.4 V, a scan rate of 0.04 V / s, and 10 cycles. After the electrodeposition was completed, the working electrode was removed to obtain PMo 12 / nickel composite material, labeled as PMo 12 / NF.

[0097] Comparative Example 4

[0098] A 2 cm × 2 cm nickel mesh (NF) was ultrasonically cleaned sequentially with acetone, 22.5% hydrochloric acid, anhydrous ethanol, and deionized water at a frequency of 50 kHz, with each ultrasonic cleaning lasting 15 minutes. After ultrasonic cleaning, the nickel mesh was dried at 60°C for 8 hours. Cyclic voltammetry was used in a 0.1 mol / L cobalt nitrate solution using a three-electrode system on a CHI760E electrochemical workstation, using NF as the working electrode, Ag / AgCl as the reference electrode, and a platinum sheet as the counter electrode. The scan range was -0.4 to -1.6 V, the scan rate was 0.01 V / s, and the number of cycles was four. After electrodeposition, the working electrode was removed, rinsed with deionized water, and dried at 60°C under a vacuum of -0.08 MPa for 12 hours to obtain a Co(OH)2 / nickel composite material, labeled Co(OH)2 / NF.

[0099] Dissolve 40 mmol of 2-methylimidazole in 25 mL of methanol to obtain a 1.6 mol / L 2-methylimidazole solution. Immerse the Co(OH)2 / NF in the 2-methylimidazole solution and allow it to react for 1 hour. After the reaction, remove the NF, wash it three times with methanol, and then dry it at 60°C for 24 hours to obtain the ZIF-67 / nickel precursor, labeled ZIF-67 / NF.

[0100] 0.42 mmol of Ni(NO₃)₂·6H₂O was fully dissolved in 25 mL of anhydrous ethanol to obtain a nickel nitrate solution with a concentration of 16.8 mmol / L. The ZIF-67 / NF was immersed in the nickel nitrate solution and stirred at 100 rpm at room temperature for 12 hours. After the reaction, the ZIF-67 / NF was removed and washed three times with anhydrous ethanol. The resulting composite material, NiCo-LDH / NF, was then dried at 60°C under a vacuum of -0.08 MPa for 24 hours.

[0101] Electrochemical performance was tested using linear sweep voltammetry (LSV) using the catalysts prepared in Example 1 and Comparative Examples 2-4 as working electrodes, Ag / AgCl as reference electrodes, and platinum sheets as counter electrodes. A 1 mmol / L 2-phenoxy-1-phenylethanol solution was used as the electrolyte (the solvent in the electrolyte was a mixture of methanol and KOH solution in a volume ratio of 1:9, with a KOH concentration of 1 mol / L). All potentials during the tests were calibrated to the reversible hydrogen electrode (RHE) potential, and the ohmic voltage drop due to solution resistance was deducted.

[0102] Figure 1 The linear sweep voltammetry (LSV) curves of the catalysts prepared in Example 1 and Comparative Examples 2 to 4 are shown in FIG. 12@NiCo-LDH / NF is the catalyst prepared in Example 1. Figure 1 It can be seen that the catalyst prepared in Example 1 has the best electrochemical performance. -2 It has the lowest overpotential.

[0103] Figure 2 The Tafel curves of the catalysts prepared in Example 1 and Comparative Examples 2 to 4 are shown in FIG. 12 @NiCo-LDH / NF is the catalyst prepared in Example 1. Figure 2 It can be seen that the Tafel slope of the catalyst prepared in Example 1 during the electrocatalytic oxidation of 2-phenoxy-1-phenylethanol is 48.3 mV·dec -1 , which is better than Comparative Examples 2 to 4.

[0104] Figure 3 is the charge transfer impedance of the catalysts prepared in Example 1 and Comparative Examples 2 to 4, wherein PMo 12 @NiCo-LDH / NF is the catalyst prepared in Example 1. Figure 3 As can be seen, the catalyst prepared in Example 1 has the lowest charge transfer resistance (5.04Ω), which is superior to that of Comparative Examples 2-4. This lower charge transfer resistance promotes the kinetics of the electrocatalytic oxidation of lignin. This demonstrates that the core-shell heteropolyacid catalyst of the present invention successfully modulates the electrocatalytic oxidation activity of lignin and improves the oxidation kinetics of both the catalyst and lignin.

[0105] Figure 4 The dual capacitors of the catalysts prepared in Example 1 and Comparative Examples 2 to 4, wherein PMo 12 @NiCo-LDH / NF is the catalyst prepared in Example 1. Figure 4 It can be seen that the dual capacitance of the catalyst prepared in Example 1 is higher than that in Comparative Examples 2 to 4, and the electrochemical performance is more excellent.

[0106] Application Example 1

[0107] 2-Phenoxy-1-phenylethanol (PPE) was selected as the lignin model compound, and a mixture of methanol and KOH solution (the concentration of KOH solution was 1 mol / L) with a volume ratio of 1:9 was used as the electrolyte, wherein the concentration of lignin was 1 mmol / L. 12@NiCo-LDH / NF-25 was used as the working electrode, Ag / AgCl as the reference electrode, and platinum sheet as the counter electrode. A three-electrode system was used on an electrochemical workstation CHI760E, and electrocatalytic oxidation was carried out at a voltage of 2.0 V for 60 minutes. After the electrocatalytic oxidation was completed, the electrolyte was extracted with ethyl acetate to obtain the upper layer solution. The upper layer solution was analyzed by high-performance liquid chromatography to calculate the yield of the monophenyl ring compound (benzoic acid) and the conversion rate of lignin. The conditions for the high-performance liquid chromatography analysis were: UV-vis detector 210 nm, C18 column (4.6 mm × 150 mm, 5 μm), injection volume of 20 μL, sample flow rate of 1 mL / min, mobile phase of H2O / acetonitrile (40 / 60, v / v), mobile phase flow rate of 1.0 mL·min -1 .

[0108] Application Example 2

[0109] The working electrode in Application Example 1 was replaced with the core-shell heteropolyacid catalyst PMo prepared in Example 2. 12 @NiCo-LDH / NF-15, other parameters are the same as those in Application Example 1.

[0110] Application Example 3

[0111] The electrocatalytic oxidation time in Application Example 1 was modified to 80 min, and the rest was the same as in Example 1.

[0112] Comparative Application Example 1

[0113] The working electrode in Application Example 1 was replaced with the core-shell heteropolyacid catalyst PMo prepared in Comparative Example 1. 12 @NiCo-LDH / NF-35, other parameters are the same as those in Application Example 1.

[0114] Application Comparative Example 2

[0115] The working electrode in Application Example 1 was replaced with the nickel electrode NF prepared in Comparative Example 2, and the rest was the same as in Application Example 1.

[0116] Application Comparative Example 3

[0117] The working electrode in Application Example 1 was replaced with the PMo prepared in Comparative Example 3. 12 / NF, other parameters are the same as those in Application Example 1.

[0118] Comparative Application Example 4

[0119] The working electrode in Application Example 1 was replaced with the NiCo-LDH / NF prepared in Comparative Example 4, and the rest was the same as in Application Example 1.

[0120] Application Comparative Example 5

[0121] The electrocatalytic oxidation time in Application Example 1 was modified to 20 min, and the rest was the same as in Application Example 1.

[0122] Application Comparative Example 6

[0123] The electrocatalytic oxidation time in Application Example 1 was modified to 40 min, and the rest was the same as in Application Example 1.

[0124] Application Comparative Example 7

[0125] The electrocatalytic oxidation time in Application Example 1 was modified to 100 min, and the rest was the same as Application Example 1.

[0126] Comparative Application Example 8

[0127] The voltage of the electrocatalytic oxidation in Application Example 1 was modified to 1.8 V, and the rest was the same as in Application Example 1.

[0128] Comparative Application Example 9

[0129] The voltage of the electrocatalytic oxidation in Application Example 3 was modified to 1.8 V, and the rest was the same as in Application Example 3.

[0130] Comparative Application Example 10

[0131] The voltage of the electrocatalytic oxidation in Comparative Application Example 5 was modified to 1.8 V, and the rest was the same as Comparative Application Example 5.

[0132] Comparative Application Example 11

[0133] The voltage of the electrocatalytic oxidation in Comparative Example 6 was modified to 1.8 V, and the rest was the same as Comparative Example 6.

[0134] Application Comparative Example 12

[0135] The voltage of the electrocatalytic oxidation in Comparative Application Example 7 was modified to 1.8 V, and the rest was the same as Comparative Application Example 7.

[0136] Figure 5 The lignin conversion rate and the yield of single benzene ring compounds of Application Example 1 and Comparative Examples 2 to 4 are shown in FIG. 12 @NiCo-LDH / NF electrode is application example 1. Figure 5 It can be seen that the core-shell structure heteropoly acid catalyst of the present invention has better current response than other catalyst electrodes; PMo electroplated on NF 12 Obtained PMo 12The lignin conversion rate and the yield of single benzene ring compounds of PMo / NF were significantly improved compared with NF, indicating that the introduction of Mo can effectively promote the adsorption of lignin on the catalyst surface; when NiCo-LDH was introduced, there was no significant effect on the lignin conversion rate, but the current density and the selectivity of single benzene ring compounds were significantly improved, which was attributed to the good oxidizing property of Ni but low selectivity, while Co improved the selectivity; the introduction of PMo 12 After in situ encapsulation and reorganization with NiCo-LDH, PMo 12 @NiCo-LDH / NF, in PMo 12 The synergistic effect of NiCo-LDH and PMo-LDH resulted in a higher lignin conversion rate (84.6%) and a higher yield of single benzene ring compounds (benzoic acid yield 64.1%). 12 There is also a strong electronic interaction between NiCo-LDH and PMo, and electrons tend to transfer from NiCo-LDH to PMo 12 , which accelerates the kinetic process of electrocatalytic oxidation.

[0137] Figure 6 The lignin conversion rate and the yield of single benzene ring compounds in Application Examples 1-2 and Comparative Example 1 are shown in Table 1. Figure 6 It can be seen that with the PMo 12 With the increase of PMo content, the conversion rate of lignin and the yield of monophenyl ring compound benzoic acid show a trend of first increasing and then decreasing. 12 It has good oxidizability, which enhances the oxidizability of electrode materials and can promote the oxidation and cleavage of CC bonds in lignin. However, too high PMo 12 The content may reduce the surface area of the catalyst, hinder the contact between the active sites in the electrode material and lignin, and instead reduce the electrocatalytic oxidation activity.

[0138] Figure 7 The lignin conversion rates and the yields of single benzene ring compounds of Application Example 1, Application Example 3, and Comparative Application Examples 5 to 7 are shown. Figure 8 The conversion rate of lignin and the yield of single benzene ring compounds of Comparative Examples 8 to 12 are shown in Table 1. Figure 7 、 Figure 8 It can be seen that at 1.8 V and 2.0 V, respectively, as the electrocatalytic oxidation time increases, the conversion rate of lignin continues to increase, while the yield of the single benzene ring compound benzoic acid first increases and then decreases, reaching a maximum value at 60 min. This is because the extension of the electrocatalytic oxidation time may lead to the occurrence of side reactions, thereby reducing the yield of the product; compared with 1.8 V, 2.0 V has a higher lignin conversion rate and single benzene ring compound yield, which is due to the increase in voltage, increase in current density, and enhanced oxidation potential.

[0139] The activity of the core-shell heteropolyacid catalyst of the present invention in electrocatalytic oxidation of real lignin to prepare vanillin and guaiacol was tested: the lignin model compound of Application Example 1 was replaced by pine, birch and alkali lignin (alkali lignin purchased from Shanghai MacLean Biochemical Co., Ltd.), respectively, and the rest was the same as Example 1. Figure 9 The conversion rate and product yield of the core-shell heteropoly acid catalyst electrocatalytic oxidation of real lignin in Example 1 are as follows. Figure 9 As can be seen, the conversion rate of pine wood was 57.1%, the yield of vanillin was 25.8%, and the yield of guaiacol was 17.9%. The yields of vanillin and guaiacol were both higher than those of birch wood and alkaline lignin. The conversion rate of birch wood was 71.4%, and the conversion rate of alkaline lignin was 95.2%. Alkaline lignin had the highest conversion rate, but the lowest yield of guaiacol. Pine wood had the lowest conversion rate, but the highest yields of vanillin and guaiacol. This difference stems from the inherent structural characteristics and functional groups of authentic lignin, as well as the interaction between the catalyst and lignin.

[0140] The core-shell heteropoly acid catalyst PMo prepared in Example 1 12 @NiCo-LDH / NF-25 was tested for stability. The test conditions were as follows: 2-phenoxy-1-phenylethanol was used as the lignin model compound, a mixture of methanol and KOH solution (the concentration of KOH solution was 1 mol / L) with a volume ratio of 1:9 was used as the electrolyte, the concentration of the lignin model compound was 1 mmol / L, and PMo 12 @NiCo-LDH / NF-25 was used as the working electrode, Ag / AgCl as the reference electrode, and platinum sheet as the counter electrode. A three-electrode system of electrochemical workstation CHI760E was used, and electrocatalytic oxidation was carried out using a constant current method (0.15 A) for 24 h.

[0141] Figure 10 PMo is a core-shell heteropolyacid catalyst 12 @NiCo-LDH / NF-25 stability curve. Figure 10 It can be seen that PMo 12 The performance of @NiCo-LDH / NF-25 did not show a significant decline after 24 hours of electrocatalytic oxidation, indicating that the core-shell heteropolyacid catalyst of the present invention has good stability.

[0142] The core-shell heteropoly acid catalyst PMo prepared in Example 1 12 @NiCo-LDH / NF-25 was tested for cycling performance. The test steps were as follows: After the electrocatalytic oxidation of Application Example 1, the core-shell heteropoly acid catalyst PMo 12 @NiCo-LDH / NF-25 repeats the electrocatalytic oxidation process of Application Example 1, and so on.

[0143] Figure 11 PMo is a core-shell heteropolyacid catalyst 12 Cycling performance of @NiCo-LDH / NF-25. Figure 11 It can be seen that the core-shell structure heteropoly acid catalyst PMo 12 After five cycles of use, the lignin conversion rate and product yield of @NiCo-LDH / NF-25 did not show a significant decrease, indicating that the core-shell heteropolyacid catalyst of the present invention has excellent recyclability.

[0144] Figure 12 PMo is a core-shell heteropolyacid catalyst 12 @NiCo-LDH / NF-25 infrared spectrum after 5 cycles and before use. Figure 12 It can be seen that the PMo after 5 cycles and before use 12 The infrared spectrum of @NiCo-LDH / NF-25 did not show any significant changes. This indicates that the PMo synthesized by the in situ encapsulation recombination strategy 12 @NiCo-LDH / NF has excellent chemical stability, which is attributed to the NiCo-LDH nanocages to PMo 12 The stabilizing confinement effect, specifically PMo 12 Electrostatic recombination between the staggered NiCo-LDH nanosheets and PMo 12 @NiCo-LDH / NF has a unique hollow nanocage structure. NiCo-LDH nanocage acts as a barrier to effectively prevent PMo 12 Leaching and loss.

[0145] Figure 13 PMo is a core-shell heteropolyacid catalyst 12 @NiCo-LDH / NF-25 scanning electron microscope image after 5 cycles. Figure 13 It can be seen that the recycled core-shell heteropoly acid catalyst PMo 12 @NiCo-LDH / NF-25 can still maintain the hollow nanocage morphology before use and remains tightly bonded to the nickel foam substrate without any obvious dissolution or shedding.

[0146] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a core-shell structured heteropolyacid catalyst, characterized in that: The following steps are included: 1) Using metallic nickel as the working electrode, Ag / AgCl as the reference electrode, and platinum as the counter electrode, electrodeposition was performed in a cobalt nitrate solution to obtain a Co(OH)2 / nickel composite material; 2) Using Co(OH)2 / nickel composite material as working electrode, Ag / AgCl as reference electrode and platinum sheet as counter electrode, electroplating was carried out in phosphomolybdic acid solution to obtain PMo 12 @Co(OH)2 / nickel intermediate; 3) PMo 12 The Co(OH)2 / nickel intermediate was immersed in 2-methylimidazole solution to react and obtain PMo 12 @ZIF-67 / nickel precursor; 4) PMo 12 The @ZIF-67 / nickel precursor is immersed in a nickel nitrate solution to react and obtain a core-shell structured heteropolyacid catalyst.

2. The preparation method according to claim 1, characterized in that Step 1) The concentration of the cobalt nitrate solution is 0.05 to 0.15 mol / L; The electrodeposition in step 1) is carried out by cyclic voltammetry, with a scanning range of -0.4 to -1.6 V, a scanning speed of 0.005 to 0.02 V / s, and a cycle scanning number of 3 to 5 times.

3. The preparation method according to claim 1 or 2, characterized in that Step 2) the concentration of the phosphomolybdic acid solution is 1.5-3 g / L; Step 2) The electrodeposition is performed using cyclic voltammetry with a scan range of -0.9 to 0.4 V, a scan rate of 0.03 to 0.05 V / s, and 8 to 12 cycles.

4. The preparation method according to claim 3, characterized in that Step 3) The solvent of the 2-methylimidazole solution is methanol, and the concentration of 2-methylimidazole in the 2-methylimidazole solution is 1 to 2 mol / L; Step 3) The reaction time is 0.5 to 1.5 hours.

5. The preparation method according to claim 4, characterized in that Step 4) The solvent of the nickel nitrate solution is anhydrous ethanol, and the concentration of nickel nitrate in the nickel nitrate solution is 15-20 mmol / L.

6. The preparation method according to claim 4 or 5, characterized in that Step 4) The reaction time is 10 to 14 hours; Step 4) Stirring is performed during the reaction at a speed of 50 to 200 r / min.

7. A core-shell heteropolyacid catalyst prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the core-shell heteropolyacid catalyst according to claim 7 in electrocatalytic oxidation of lignin, characterized in that: Electrocatalytic oxidation is carried out in a lignin solution using the core-shell structure heteropoly acid catalyst as a working electrode, Ag / AgCl as a reference electrode, and a platinum sheet as a counter electrode.

9. Use of the core-shell structure heteropolyacid catalyst according to claim 8 in electrocatalytic oxidation of lignin, characterized in that: The solvent of the lignin solution is a mixture of methanol and KOH solution, and the volume ratio of methanol to KOH solution is 0.5-1.5:8.5-9.5; In the lignin solution, the concentration of lignin is 0.5-2 mmol / L.

10. Use of the core-shell heteropolyacid catalyst according to claim 8 or 9 in electrocatalytic oxidation of lignin, characterized in that: The voltage of the electrocatalytic oxidation is 2.0 to 2.5 V, and the time of the electrocatalytic oxidation is 50 to 80 minutes.

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