Method for synthesizing organic acid ligand hybrid nickel cobalt hydroxide catalyst by one-step hydrothermal method and application thereof

Abstract

The present invention discloses a method for synthesizing an organic acid ligand hybrid nickel cobalt hydroxide catalyst by a one-step hydrothermal method and its application. In this method, nickel foam is used as a substrate and added to a mixed solution of cobalt nitrate, nickel nitrate and sodium organic acid salt in a certain proportion, and an organic acid ligand hybrid nickel cobalt hydroxide catalyst is synthesized by one-step hydrothermal method. The preparation steps of the present invention are simple to operate and can complete the selective electrocatalytic oxidation of HMF to prepare FDCA under mild conditions. The organic acid ligand hybrid nickel cobalt hydroxide catalyst prepared by the invention promotes surface lattice disorder by introducing organic acid ligands, optimizes the surface electronic structure of the catalyst, and improves the intrinsic activity of the catalyst.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts for electrocatalytic oxidation of 5-hydroxymethylfurfural to synthesize 2,5-furandicarboxylic acid, and specifically relates to a method for synthesizing an organic acid ligand hybrid nickel-cobalt hydroxide catalyst by a one-step hydrothermal method and its application. Background Art

[0002] The excessive exploitation of fossil fuels and the over-reliance on petroleum-based chemicals by humans have caused serious environmental pollution and energy crisis and other problems. Developing clean and sustainable energy is the key way to solve these problems. In recent years, biomass has attracted great attention due to its advantages such as low-carbon cleanliness, rich reserves, and wide applications. Various chemicals and fuels produced from biomass have become an indispensable part of the chemical industry and economic system. Converting rich biomass resources into high-value chemicals is a new way to exert the high-value application potential of biomass. 5-Hydroxymethylfurfural (HMF) obtained from cellulose and lignin is one of the important platform compounds, and its oxidation product 2,5-furandicarboxylic acid (FDCA) is the most likely compound to replace petroleum-based terephthalic acid for polyester production. Therefore, the oxidation of HMF to synthesize FDCA has important application development prospects.

[0003] At present, there have been a large number of studies on the catalytic oxidation of HMF to prepare FDCA. Traditional thermal catalysis has advantages in conversion yield and product purity, but the complex reaction conditions and the use of oxidants increase the production cost and limit its large-scale application in industrial production. Although photocatalysis and biocatalysis have simple reaction conditions, their yields are not satisfactory. Electrochemical catalysis technology not only has the advantages of environmental protection and simple operation, but also can realize the selective conversion of HMF to generate FDCA at the anode while producing high-value hydrogen at the cathode, improving the utilization rate of the electrolytic cell. Research shows that oxides, hydroxides of transition metals (such as Ni, Co, Fe, Cu, etc.) or bimetallic materials composed of them have excellent electro-oxidation catalytic activity for HMF. Previous studies have confirmed that Co-based catalysts have strong dual-atom adsorption (O and C atoms) on aldehyde groups, which can promote the conversion of aldehyde groups to carboxyl groups; Ni-based catalysts have appropriate OH adsorption energy in the alcohol dehydrogenation step and show the best hydroxyl oxidation activity. If Ni and Co, which are rich in reserves, are synthesized into efficient electrocatalysts by a simple method to electrocatalytically convert HMF to obtain FDCA, it can get rid of the dependence on noble metal catalysts, save costs, and greatly increase economic benefits, showing great development prospects in actual industrial applications. However, the existing catalyst synthesis methods generally require complicated operation steps, consume a large amount of energy, greatly increase the production cost, and limit their actual industrial application and development. Summary of the Invention

[0004] The technical problem solved by the present invention is to provide a method for synthesizing an organic acid ligand hybrid nickel-cobalt hydroxide catalyst by a one-step hydrothermal method. This method uses nickel foam as a substrate, adds it to a mixed solution of cobalt nitrate, nickel nitrate, and sodium organic acid salt in a certain ratio, and synthesizes the organic acid ligand hybrid nickel-cobalt hydroxide catalyst by one-step hydrothermal synthesis. The preparation steps are simple to operate and can complete the selective electrocatalytic oxidation of HMF to prepare FDCA under mild conditions.

[0005] The present invention adopts the following technical solutions to solve the above technical problems. A method for synthesizing an organic acid ligand hybrid nickel-cobalt hydroxide catalyst by a one-step hydrothermal method is characterized in that the specific steps are as follows:

[0006] Step S1: Cut the nickel foam into sheets, and ultrasonically clean them in absolute ethanol and hydrochloric acid in sequence to obtain nickel foam A;

[0007] Step S2: Add sodium organic acid salt, nickel nitrate, and cobalt nitrate to deionized water, stir until the solution is evenly mixed, then pass nitrogen to reach a saturated state to remove dissolved carbon dioxide in the solution to obtain a mixed solution B. The sodium organic acid salt is one or more of sodium benzoate, sodium benzenesulfonate, sodium phenolate, or sodium phenylphosphonate. The molar ratio of nickel nitrate, cobalt nitrate to sodium organic acid salt is 1:0.5~2:1~3;

[0008] Step S3: Add the nickel foam A obtained in Step S1 and the mixed solution B obtained in Step S2 to a reaction kettle and react at 90~100°C to obtain material C;

[0009] Step S4: Wash the material C obtained in Step S3 repeatedly with deionized water and absolute ethanol, and then dry the material C to obtain the target product, the organic acid ligand hybrid nickel-cobalt hydroxide catalyst. In this catalyst, the binary transition metals Ni-Co participate in the electrocatalytic oxidation of 5-hydroxymethylfurfural synergistically. The organic acid ligand promotes the disordering of the crystal lattice on the catalyst surface, thereby optimizing the surface electronic structure of the catalyst. The synergistic effect of the bimetallic sites and the coordination effect of the organic acid ligand realize the highly selective electrocatalytic oxidation of 5-hydroxymethylfurfural to synthesize 2,5-furandicarboxylic acid. Moreover, the catalyst presents a nanowire structure, which can expose a large number of accessible active sites. The nanowire structure provides an open space for the diffusion of the electrolyte, which is conducive to electron transfer. This catalyst has a 2,5-furandicarboxylic acid yield as high as 97.33% and a Faraday efficiency of 96.59% during the electrocatalytic oxidation of 5-hydroxymethylfurfural.

[0010] Further limited, in Step S1, the thickness of the nickel foam is 1~3 mm, and the cut size is 2×3 cm 2 , and the ultrasonic times in absolute ethanol and hydrochloric acid are 10 min and 40 min respectively.

[0011] Further limitation: in step S2, the nitrogen saturation time is 10 - 20 min, the stirring speed is 100 rpm, and the stirring time is 10 min.

[0012] Further limitation: in step S2, the molar ratio of nickel nitrate, cobalt nitrate to sodium organic acid salt is 1:1:2.

[0013] Further limitation: in step S3, the reaction time is 12 h and the reaction temperature is 95 °C.

[0014] The application of the organic acid ligand hybrid nickel cobalt hydroxide catalyst of the present invention as a working electrode to form a three - electrode system for electrocatalytic oxidation of 5 - hydroxymethylfurfural to synthesize 2,5 - furandicarboxylic acid in an alkaline electrolyte.

[0015] Further limitation: in the three - electrode system, a platinum sheet and a Hg / HgO electrode are used as the counter electrode and the reference electrode respectively. The alkaline electrolyte is 1 M KOH or NaOH solution, the concentration of 5 - hydroxymethylfurfural dissolved is 10 - 50 mmol / L, the applied external potential is 1.2 - 1.6 V (vs. RHE), and the organic acid ligand hybrid nickel cobalt hydroxide catalyst electrocatalytically oxidizes 5 - hydroxymethylfurfural to prepare 2,5 - furandicarboxylic acid with high selectivity in the alkaline electrolyte.

[0016] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0017] 1. The present invention provides a preparation method of an organic acid ligand hybrid nickel cobalt hydroxide catalyst. The advantage is that binary transition metals Ni - Co are introduced to participate in the electrocatalytic oxidation of HMF synergistically. On the one hand, the Co site can provide a lower starting potential and has strong dual - atom adsorption (O and C atoms) on the aldehyde group, which can promote the conversion of the aldehyde group to the carboxyl group. On the other hand, the Ni site can provide faster reaction kinetics and has an appropriate OH adsorption energy in the alcohol dehydrogenation step, showing excellent hydroxyl oxidation activity.

[0018] 2. The organic acid ligand hybrid nickel cobalt hydroxide catalyst prepared by the present invention promotes surface lattice disorder by introducing an organic acid ligand, optimizes the surface electronic structure of the catalyst, and improves the intrinsic activity of the catalyst.

[0019] 3. The optimal catalyst synthesized by the present invention presents a nanowire structure, exposing a large number of accessible active sites. In addition, the nanowire structure also provides an open space for the diffusion of the electrolyte, which is beneficial to electron transfer. The optimal catalyst has a low starting potential of 1.19 V, and can achieve a FDCA yield of up to 97.33% and a Faraday efficiency of 96.59%.

[0020] 4. The organic acid ligand hybrid nickel-cobalt hydroxide active layer synthesized by the present invention is in-situ grown on a nickel foam substrate, with a firm structure and excellent stability, and still maintains a high FDCA yield and Faraday efficiency after 5 cycles of electrolysis. Description of the Drawings

[0021] Figure 1 Scanning electron microscope image of the target product D1 prepared in Example 1.

[0022] Figure 2 X-ray diffraction pattern of the target product D1 prepared in Example 1.

[0023] Figure 3 Comparison diagram of linear sweep voltammetry curves of OER and HMFOR for the target product D1 prepared in Example 1.

[0024] Figure 4 Linear sweep voltammogram of HMFOR for the target products D1-D5 prepared in Examples 1-4 and Comparative Example 1.

[0025] Figure 5 Reaction product change diagram of electro-oxidizing HMF to prepare FDCA with the target product D1 prepared in Example 1.

[0026] Figure 6 Diagram of HMF conversion rate, FDCA yield, FDCA selectivity and Faraday efficiency of electro-oxidizing HMF for five cycles with the target product D1 prepared in Example 1. Detailed Description of the Invention

[0027] The above content of the present invention will be further described in detail through the following examples, but it should not be understood that the scope of the above theme of the present invention is limited to the following examples. All technologies implemented based on the above content of the present invention belong to the scope of the present invention. Examples

[0028] Step S1: Cut a 2×3 cm 2 nickel foam, ultrasonically clean it in absolute ethanol for 5 min, and then ultrasonically clean it with 1 mol / L hydrochloric acid for 40 min to obtain nickel foam A1;

[0029] Step S2: Add cobalt nitrate, nickel nitrate and sodium benzoate to 30 mL of deionized water, stir until the solution is mixed evenly, and then saturate it with nitrogen for 10 min to obtain a mixed solution B1, where the concentrations of cobalt nitrate, nickel nitrate and sodium benzoate are 50 mmol / L, 50 mmol / L and 100 mmol / L respectively;

[0030] Step S3: Add nickel foam A1 and the mixed solution B1 to a reaction kettle, place the reaction kettle in a forced-air drying oven, react at 95 °C for 12 h, and then take it out to obtain product C1;

[0031] Step S4: Wash the product C1 repeatedly with deionized water and absolute ethanol, and then place the product C1 in a blast drying oven and dry it at 60 °C for 6 h to obtain the target product D1.

[0032] Step S5: Add 30 mL of KOH electrolyte solution to the cathode / anode chambers of the H-type electrolytic cell respectively. Then add 50 mmol / L of 5-hydroxymethylfurfural to the anode chamber. Use the target product D1 as the working electrode, Hg / HgO as the reference electrode, and a platinum sheet as the counter electrode. Conduct the HMF conversion reaction at a potential of 1.4 V (vs. RHE). Take samples every 10 C of charge, and finally analyze the HMF conversion rate and FDCA yield of the reaction solution by high performance liquid chromatography. Example

[0033] Step S1: Cut a 2×3 cm 2 nickel foam, ultrasonically clean it in absolute ethanol for 5 min, and then ultrasonically clean it with 1 mol / L hydrochloric acid for 40 min to obtain nickel foam A2;

[0034] Step S2: Add cobalt nitrate, nickel nitrate, and sodium phenoxide to 30 mL of deionized water. Stir until the solution is mixed evenly and then saturate it with nitrogen for 10 min to obtain a mixed solution B2, where the concentrations of cobalt nitrate, nickel nitrate, and sodium phenoxide are 50 mmol / L, 50 mmol / L, and 100 mmol / L respectively;

[0035] Step S3: Add the nickel foam A2 and the mixed solution B2 to a reaction kettle, place the reaction kettle in a blast drying oven, react at 95 °C for 12 h, and then take it out to obtain the product C2;

[0036] Step S4: Wash the product C2 repeatedly with deionized water and absolute ethanol, and then place the product C2 in a blast drying oven and dry it at 60 °C for 6 h to obtain the target product D2.

[0037] Step S5: Add 30 mL of KOH electrolyte solution to the cathode / anode chambers of the H-type electrolytic cell respectively. Then add 50 mmol / L of 5-hydroxymethylfurfural to the anode chamber. Use the target product D2 as the working electrode, Hg / HgO as the reference electrode, and a platinum sheet as the counter electrode. Conduct the HMF conversion reaction at a potential of 1.4 V (vs. RHE). Example

[0038] Step S1: Cut a 2×3 cm 2 nickel foam, ultrasonically clean it in absolute ethanol for 5 min, and then ultrasonically clean it with 1 mol / L hydrochloric acid for 40 min to obtain nickel foam A3;

[0039] Step S2: Cobalt nitrate, nickel nitrate, and sodium benzenesulfonate were added to 30 mL of deionized water. After stirring until the solution was evenly mixed, nitrogen was introduced to saturate for 10 min to obtain a mixed solution B3, where the concentrations of cobalt nitrate, nickel nitrate, and sodium benzenesulfonate were 50 mmol / L, 50 mmol / L, and 100 mmol / L, respectively;

[0040] Step S3: The nickel foam A3 and the mixed solution B3 were added to a reaction kettle, and the reaction kettle was placed in a forced-air drying oven and reacted at 95 °C for 12 h, and then taken out to obtain a product C3;

[0041] Step S4: The product C3 was repeatedly washed with deionized water and absolute ethanol, and then the product C3 was placed in a forced-air drying oven and dried at 60 °C for 6 h to obtain the target product D3.

[0042] Step S5: 30 mL of KOH electrolyte was added to the cathode / anode chambers of the H-type electrolytic cell. 5-Hydroxymethylfurfural at a concentration of 50 mmol / L was further added to the anode chamber. The target product D3 was used as the working electrode, Hg / HgO was used as the reference electrode, and a platinum sheet was used as the counter electrode. The HMF conversion reaction was carried out at a potential of 1.4 V (vs. RHE). Example

[0043] Step S1: Cut 2×3 cm 2 nickel foam, ultrasonically cleaned in absolute ethanol for 5 min, and then ultrasonically cleaned with 1 mol / L hydrochloric acid for 40 min to obtain nickel foam A4;

[0044] Step S2: Cobalt nitrate, nickel nitrate, and sodium phenylphosphonate were added to 30 mL of deionized water. After stirring until the solution was evenly mixed, nitrogen was introduced to saturate for 10 min to obtain a mixed solution B4, where the concentrations of cobalt nitrate, nickel nitrate, and sodium phenylphosphonate were 50 mmol / L, 50 mmol / L, and 100 mmol / L, respectively;

[0045] Step S3: The nickel foam A4 and the mixed solution B4 were added to a reaction kettle, and the reaction kettle was placed in a forced-air drying oven and reacted at 95 °C for 12 h, and then taken out to obtain a reaction product C4;

[0046] Step S4: The product C4 was repeatedly washed with deionized water and absolute ethanol, and then the product C4 was placed in a forced-air drying oven and dried at 60 °C for 6 h to obtain the target product D4.

[0047] Step S5: 30 mL of KOH electrolyte was added to the cathode / anode chambers of the H-type electrolytic cell. 5-Hydroxymethylfurfural at a concentration of 50 mmol / L was further added to the anode chamber. The target product D4 was used as the working electrode, Hg / HgO was used as the reference electrode, and a platinum sheet was used as the counter electrode. The HMF conversion reaction was carried out at a potential of 1.4 V (vs. RHE).

[0048] Comparative Example 1

[0049] Step S1: Cut a 2×3 cm 2 nickel foam, ultrasonically clean it in absolute ethanol for 5 min, and then ultrasonically clean it in 1 mol / L hydrochloric acid for 40 min to obtain nickel foam A5;

[0050] Step S2: Add cobalt nitrate and nickel nitrate to 30 mL of deionized water, stir until the solution is evenly mixed, and then saturate it with nitrogen for 10 min to obtain a mixed solution B5, where the concentrations of cobalt nitrate and nickel nitrate are 50 mmol / L and 50 mmol / L, respectively;

[0051] Step S3: Add nickel foam A5 and the mixed solution B5 to a reaction kettle, place the reaction kettle in a forced-air drying oven, react at 95 °C for 12 h, and then take it out to obtain product C5;

[0052] Step S4: Wash product C5 repeatedly with deionized water and absolute ethanol, and then place product C5 in a forced-air drying oven and dry it at 60 °C for 6 h to obtain the target product D5.

[0053] Step S5: Add 30 mL of KOH electrolyte to the cathode / anode chambers of an H-type electrolytic cell respectively. Add 50 mmol / L of 5-hydroxymethylfurfural to the anode chamber. Use the target product D5 as the working electrode, Hg / HgO as the reference electrode, and a platinum sheet as the counter electrode. Carry out the HMF conversion reaction at a potential of 1.4 V (vs. RHE).

[0054] Electrocatalytic oxidation performance test of HMF:

[0055] To study the electrocatalytic oxidation performance of the catalyst material for HMF, a traditional three-electrode system was used for testing. Cut the target product D1 as the working electrode (effective area is 1×1 cm 2 ), Hg / HgO as the reference electrode, and a platinum sheet as the counter electrode. The electrolytic cell is an H-type electrolytic cell with a DuPont proton exchange membrane (Nafion-117) in the middle, and the electrolyte used is 1 M KOH solution. During the test, add 30 mL of KOH solution to the cathode / anode chambers respectively, and add 50 mmol / L of 5-hydroxymethylfurfural to the anode chamber. The scanning rate for measuring the linear sweep voltammogram is 10 mV s –1 , and the scanning range is 0.9~1.8 V (vs. RHE). Samples D2, D3, and D4 were tested in the same way, and sample D5 was used as the control sample.

[0056] The performance characterization of the samples in all examples is as follows:

[0057] As Figure 1 shown, it is the scanning electron microscope image of the target product D1 obtained in Example 1, which has an obvious nanoline structure. Figure 2XRD pattern of the target product D1 shows that the surface phase of D1 is Ni(OH)(C6H5COO)H2O. Figure 3 Comparison chart of linear sweep voltammetry curves of OER and HMFOR of the target product D1. The chart shows that the initial potential of the target product D1 is close during the OER and HMFOR processes, but the HMFOR process has a larger current density, reaching 100 mA cm –1 The overpotential at this time is 310 mV lower than that of OER. Figure 4 Linear sweep voltammetry curves of the target products D1 - D5. It can be seen from the figure that the target product D1 has a lower initial potential and a higher current density compared to other target products, indicating that the target product D1 promotes the oxidation of HMF and inhibits the oxygen evolution reaction. Figure 5 Variation chart of reaction products for the electro - oxidation of HMF to FDCA by the target product D1. It can be seen that the main forms during the oxidation process are HMF and FDCA. As the reaction progresses, a 99.56% HMF conversion rate and a 97.33% FDCA yield can be finally achieved, demonstrating excellent performance. Figure 6 Graphs of HMF conversion rate, FDCA yield, FDCA selectivity, and Faraday efficiency for five - cycle electro - oxidation of HMF by the target product D1. It can be seen that high FDCA yield and Faraday efficiency are still maintained after 5 - cycle electrolysis, showing excellent stability.

[0058] The above embodiments describe the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principle of the present invention. Without departing from the scope of the principle of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for synthesizing an organic acid ligand hybrid nickel-cobalt hydroxide catalyst by a one-step hydrothermal method, characterized in that The specific steps are as follows: Step S1: Cut the nickel foam into sheets, and sequentially place them in absolute ethanol and hydrochloric acid for ultrasonic cleaning to obtain nickel foam A; Step S2: Add sodium salt, nickel nitrate, and cobalt nitrate to deionized water, stir until the solution is uniformly mixed, then introduce nitrogen until it reaches a saturated state to remove the dissolved carbon dioxide in the solution, obtaining a mixed solution B. The sodium salt is one or more of sodium benzoate, sodium benzenesulfonate, sodium phenolate, or sodium phenylphosphonate. The molar ratio of nickel nitrate, cobalt nitrate to the sodium salt is 1:0.5 - 2:1 - 3; Step S3: Add the nickel foam A obtained in Step S1 and the mixed solution B obtained in Step S2 to a reaction kettle and react at 90 - 100 °C to obtain material C; Step S4: Wash the material C obtained in Step S3 repeatedly with deionized water and absolute ethanol, and then dry the material C to obtain the target product organic acid ligand hybrid nickel cobalt hydroxide catalyst. In this catalyst, the binary transition metals Ni - Co participate in the electrocatalytic oxidation of 5 - hydroxymethylfurfural synergistically. The organic acid ligand promotes the disordering of the surface lattice of the catalyst, thereby optimizing the surface electronic structure of the catalyst. The synergistic effect of the bimetallic sites and the coordination effect of the organic acid ligand achieve the highly selective electrocatalytic oxidation of 5 - hydroxymethylfurfural to synthesize 2,5 - furandicarboxylic acid. Moreover, the catalyst presents a nanowire structure, which can expose a large number of accessible active sites. The nanowire structure provides an open space for the diffusion of the electrolyte, facilitating electron transfer.

2. The method for synthesizing an organic acid ligand hybrid nickel cobalt hydroxide catalyst by a one-step hydrothermal method according to claim 1, characterized in that: The thickness of the nickel foam described in step S1 is 1-3 mm, and the cut size is 2×3 cm 2 , and the ultrasonic times in absolute ethanol and hydrochloric acid are 10 min and 40 min respectively.

3. The method for synthesizing an organic acid ligand hybrid nickel cobalt hydroxide catalyst by a one-step hydrothermal method according to claim 1, characterized in that: In Step S2, the nitrogen saturation time is 10 - 20 min, the stirring speed is 100 rpm, and the stirring time is 10 min.

4. The method for synthesizing an organic acid ligand hybrid nickel cobalt hydroxide catalyst by a one-step hydrothermal method according to claim 1, wherein: In Step S2, the molar ratio of nickel nitrate, cobalt nitrate to the sodium salt is 1:1:

2.

5. The method for synthesizing an organic acid ligand hybrid nickel-cobalt hydroxide catalyst by a one-step hydrothermal method according to claim 1, characterized in that: In Step S3, the reaction time is 12 h and the reaction temperature is 95 °C.

6. Use of the organic acid ligand hybrid nickel cobalt hydroxide catalyst prepared by the method according to any one of claims 1 to 5, characterized in that: This catalyst is used as a working electrode to form a three - electrode system to achieve the electrocatalytic oxidation of 5 - hydroxymethylfurfural to synthesize 2,5 - furandicarboxylic acid in an alkaline electrolyte.

7. The application according to claim 6, wherein The specific process is as follows: In the three - electrode system, the platinum sheet and the Hg / HgO electrode are the counter electrode and the reference electrode respectively. The alkaline electrolyte is 1 M KOH or NaOH solution, the concentration of 5 - hydroxymethylfurfural dissolved is 10 - 50 mmol / L, and the applied external potential is 1.2 - 1.6 V. The organic acid ligand hybrid nickel cobalt hydroxide catalyst highly selectively electrocatalytically oxidizes 5 - hydroxymethylfurfural in the alkaline electrolyte to prepare 2,5 - furandicarboxylic acid.

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