Preparation method of nickel phosphide catalyst applicable to preparation of adipic acid through electro-oxidation of cyclohexanone and electrolysis device

Abstract

The invention provides a preparation method of a nickel phosphide catalyst applicable to preparation of adipic acid by electro-oxidation of cyclohexanone and an electrolysis device, and belongs to the technical field of new energy chemical engineering, and the preparation method specifically comprises the following steps: putting foamed nickel into a high-pressure reaction kettle containing a mixed solution of nickel nitrate, ammonium fluoride and urea, reacting at 100-120 DEG C for 8-12 hours, filtering, washing, and drying to obtain the nickel phosphide catalyst applicable to preparation of adipic acid by electro-oxidation of cyclohexanone. The obtained nickel hydroxide is placed at the downstream of a tubular furnace, the obtained sodium hypophosphite is placed at the upstream of the tubular furnace, heating is conducted for 2-4 hours at the temperature of 300-400 DEG C under the inert atmosphere, the nickel phosphide catalyst with high adipic acid selectivity in the cyclohexanone electrooxidation reaction is obtained, the nickel phosphide catalyst is especially suitable for large-current and long-time catalytic reaction, and the productivity and efficiency in unit time are greatly improved. Meanwhile, the problem that a high-performance catalyst is complex to prepare is solved, the synthesis condition is mild, the process is simple, the reproducibility is good, expensive raw materials or complex equipment is not needed, the production cost is remarkably reduced, and a solid foundation is laid for large-scale industrial application.

Description

Technical Field

[0001] This invention belongs to the field of new energy chemical technology, specifically relating to a method for preparing a nickel phosphide catalyst and an electrolysis device suitable for the electro-oxidation of cyclohexanone to adipic acid. Background Technology

[0002] Currently, almost all commercially operating adipic acid production plants worldwide employ the "benzene-cyclohexane-KA oil-adipic acid" process route. This route first catalytically hydrogenates benzene to produce cyclohexane, then oxidizes it under high temperature and pressure in air to convert the cyclohexane into a mixture of cyclohexanol and cyclohexanone (i.e., KA oil), and finally uses nitric acid to oxidize the KA oil to produce adipic acid. While this traditional method is technologically mature, it suffers from serious environmental problems and technological shortcomings. The nitric acid oxidation step generates large amounts of nitrogen oxides (NOx). x This includes harmful gases such as nitric oxide, nitrogen dioxide, and nitrous oxide. These gases are not only highly irritating to the human respiratory tract, but are also major precursors to acid rain and photochemical smog. Among them, nitrous oxide is also a gas with a strong greenhouse effect, and its potential impact on global warming is about 300 times that of carbon dioxide.

[0003] From a chemical reaction perspective, the process of oxidizing KA oil with nitric acid to prepare adipic acid involves a complex multiphase redox reaction, with the reaction mechanism including multiple stages such as free radical initiation, chain propagation, and termination. In this process, nitric acid acts not only as an oxidant but also as a reaction medium, requiring a high concentration (typically 50%–60%) of nitric acid solution to ensure reaction efficiency. This highly corrosive medium places extremely high demands on the materials used in the reaction equipment, necessitating the use of special stainless steel or titanium, significantly increasing equipment investment and maintenance costs. Furthermore, due to the strong oxidizing properties of nitric acid, selective control during the reaction faces severe challenges, often resulting in the formation of various byproducts, such as dicarboxylic acids like glutaric acid and succinic acid, which reduce the yield and purity of the target product, adipic acid, and increase the difficulty and energy consumption of subsequent separation and purification.

[0004] Besides environmental issues, traditional processes also face challenges related to resource sustainability. Benzene feedstock is entirely derived from petroleum, a non-renewable resource. With the increasing depletion of global petroleum resources and price fluctuations, the production cost pressure of adipic acid is constantly rising. Meanwhile, the hydrogenation process requires high-purity hydrogen and is carried out under high temperature and pressure conditions, posing safety hazards and high energy consumption. To address these technological bottlenecks, the global scientific and industrial communities have been actively exploring green synthesis technologies to replace the traditional nitric acid route. Among these, the electrocatalytic oxidation of cyclohexanone to adipic acid, as an environmentally friendly technological route, has received widespread attention in recent years.

[0005] Electrochemical synthesis technology utilizes electrons as clean reaction reagents, precisely controlling the reaction direction and rate by adjusting electrode potentials. This avoids the use of chemical oxidants or reductants in traditional redox processes, earning it the reputation as a representative technology of "green synthesis." In the field of adipic acid synthesis, research on the electrocatalytic oxidation of cyclohexanone has evolved from exploring basic electrochemical behavior to catalyst design and process intensification, gradually forming various technical routes. Although significant progress has been made in the technical research of the electrooxidation of cyclohexanone to adipic acid, several key technological bottlenecks still need to be overcome before large-scale industrial application can be achieved.

[0006] Mass transfer limitation is the primary factor affecting electro-oxidation efficiency. Cyclohexanone, as a hydrophobic organic compound, has extremely low solubility in aqueous electrolytes (less than 2.5 g / 100 mL water at room temperature), resulting in slow mass transfer rates at the electrode surface and difficulty in achieving sufficient contact with catalytically active sites. In conventional electrochemical reactors, the organic phase and aqueous phase form a liquid-liquid two-phase system, and the mass transfer resistance at the phase interface significantly reduces the overall reaction rate. Especially under high current density conditions, the concentration of cyclohexanone at the electrode surface decreases sharply, making the competitive oxygen evolution reaction dominant and significantly reducing the Faradaic efficiency of the target reaction. Therefore, improving the mass transfer behavior of hydrophobic organic substrates in hydrophilic electrolytes has become a key scientific issue for improving electro-oxidation efficiency.

[0007] Balancing catalyst activity and stability is another significant challenge. Most reported electrocatalysts, while exhibiting good initial activity under certain conditions, often face problems such as active component dissolution and surface structure reconstruction during long-term operation, leading to a gradual decline in catalytic performance. This is particularly true for non-noble metal catalysts, where the chemical stability of the metal component is often poor at the anodic oxidation potential and in strongly acidic or alkaline media. For example, nickel-based electrodes undergo anodic dissolution in acidic media, while while stability improves in alkaline media, catalytic activity remains low. Developing catalyst systems with excellent stability and activity across a wide potential window and in alkaline media is crucial for advancing the practical application of cyclohexanone electrooxidation technology. Summary of the Invention

[0008] To address the technical problems existing in the prior art, this invention provides a method for preparing a nickel phosphide catalyst and an electrolytic device suitable for the electro-oxidation of cyclohexanone to adipic acid. By synthesizing a nickel phosphide catalyst under mild conditions with a simple and highly reproducible strategy, the efficient, stable, and easily industrialized electro-oxidation of cyclohexanone to adipic acid is achieved, laying a solid foundation for large-scale industrial applications.

[0009] The technical solution adopted in this invention is as follows:

[0010] A method for preparing a nickel phosphide catalyst suitable for the electro-oxidation of cyclohexanone to adipic acid includes the following steps:

[0011] Step 1: Pretreatment of nickel foam;

[0012] Step 2: Place the foamed nickel into a high-pressure reactor containing a mixed solution of nickel nitrate, ammonium fluoride and urea, and react at 100-120 degrees Celsius for 8-12 hours. After the reaction is completed, dry to obtain nickel hydroxide.

[0013] Step 3: Place nickel hydroxide downstream of the tube furnace and sodium hypophosphite upstream of the tube furnace. Heat at 300-400 degrees Celsius for 2-4 hours under an inert atmosphere. After cooling, obtain a nickel phosphide catalyst suitable for the electro-oxidation of cyclohexanone to adipic acid.

[0014] Furthermore, the nickel phosphide catalyst obtained in step 3, suitable for the electro-oxidation of cyclohexanone to adipic acid, has a layered porous structure.

[0015] Furthermore, the nickel foam mentioned in step 1 is in sheet form, with a planar size of 1×1 square centimeter to 5×5 square centimeters and a thickness of 0.1 to 0.3 centimeters.

[0016] Furthermore, the specific pretreatment process in step 1 is as follows: the surface oxide layer and grease are removed by ultrasonic treatment with dilute hydrochloric acid, anhydrous ethanol and deionized water in sequence.

[0017] Furthermore, each ultrasound treatment lasts for 5 to 30 minutes.

[0018] Furthermore, the concentration of the dilute hydrochloric acid is 0.5 to 2 mol per liter.

[0019] Further, in the mixed solution described in step 2, the concentration of nickel nitrate is 0.01~0.2 mol / L, the concentration of ammonium fluoride is 0.1~0.5 mol / L, and the concentration of urea is 0.5~2 mol / L.

[0020] Furthermore, in step 2, the nickel foam needs to be immersed in the mixed solution.

[0021] Furthermore, the drying temperature in step 2 is 40-80 degrees Celsius.

[0022] Furthermore, in step 3, the ratio of the amount of sodium hypophosphite (grams) to the area (square centimeters) of nickel hydroxide is 1 to 3 grams per square centimeter.

[0023] The present invention also proposes an electrolytic device for the electro-oxidation of cyclohexanone to adipic acid, specifically using the nickel phosphide catalyst suitable for the electro-oxidation of cyclohexanone to adipic acid as the working electrode and cyclohexanone under alkaline conditions as the anolyte.

[0024] Furthermore, the electrolytic device for the electro-oxidation of cyclohexanone to adipic acid is designed based on an H-type electrolytic cell, a flow electrolytic cell, a membrane electrode electrolytic cell, or a membrane-free electrolytic cell.

[0025] Furthermore, the electrolytic device for the electro-oxidation of cyclohexanone to adipic acid operates using either a constant current method or a constant voltage method. The anode current applied in the constant current method ranges from 0.05 to 8.75 amperes, while the potential applied in the constant voltage method ranges from 0.5 to 4 volts.

[0026] Furthermore, the concentration of cyclohexanone in the anolyte ranges from 0.05 to 1 mol per liter.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] 1. This invention proposes a method for preparing a nickel phosphide catalyst and an electrolysis device suitable for the electro-oxidation of cyclohexanone to adipic acid. It has made breakthrough progress in three aspects: stability, catalytic activity and preparation process. Its comprehensive performance is significantly better than that of the catalysts reported in the past. It breaks through the bottleneck of traditional adipic acid production technology and produces hydrogen at the same time. It establishes an innovative process route with high atom economy, environmental friendliness and low energy consumption, providing a reliable green raw material supply route for the nylon and polyurethane industries and promoting the sustainable development of the entire chemical industry.

[0029] 2. In terms of stability, compared with the problem of existing catalysts being prone to deactivation during long-term electro-oxidation, the present invention, after running continuously for more than 650 hours under normal temperature and pressure conditions, shows a performance degradation of less than 5%, and its service life is greatly extended, meeting the stringent requirements of industrial applications for catalyst durability.

[0030] 3. In terms of catalytic activity, the nickel phosphide catalyst obtained by this invention has high selectivity for adipic acid and achieves high efficiency reaction at high current density. Specifically, it can operate stably at a high current density of ≥200 mA / cm², increasing the reaction rate by several times. It can maintain a high Faradaic efficiency of over 90% at its best. It is especially suitable for high current and long-term catalytic reactions, which greatly improves the production capacity per unit time and the efficiency of the electrolysis device.

[0031] 4. In terms of preparation process, this invention overcomes the problem of complex preparation of high-performance catalysts. It adopts a simple synthesis strategy under mild conditions, which is simple, reproducible, and does not require expensive raw materials or complex equipment, thus significantly reducing production costs. It also has excellent scalability, laying a solid foundation for large-scale industrial applications. Attached Figure Description

[0032] Figure 1 This is an aberration-corrected scanning transmission electron microscope image of the nickel phosphide catalyst obtained in Example 1 of this invention;

[0033] Figure 2 The images show the aberration-corrected scanning transmission electron microscope (STEM) compositional distribution surface and line scan images of the nickel phosphide catalyst obtained in Example 1 of this invention.

[0034] Figure 3 These are scanning electron microscope images and component distribution surface scans of the nickel phosphide catalyst obtained in Example 1 of the present invention; wherein, (a) and (b) are scanning electron microscope images; (c) to (f) are component distribution surface scans of (b);

[0035] Figure 4 The X-ray diffraction patterns are those of the nickel phosphide catalyst obtained in Example 1 of this invention and the initial catalyst (nickel hydroxide) without phosphorus content.

[0036] Figure 5 The Faraday efficiency of the phosphorus-free initial catalyst obtained in Example 1 of this invention in catalyzing the oxidation of cyclohexanone in an H-type electrolytic cell;

[0037] Figure 6 The Faraday efficiency of the nickel phosphide catalyst obtained in Example 1 of this invention for catalyzing the oxidation of cyclohexanone in an H-type electrolytic cell;

[0038] Figure 7 The potential-time curve and Faraday efficiency-time curve are obtained from the constant current stability test of the nickel phosphide catalyst obtained in Example 1 of this invention in the cyclohexanone oxidation reaction in an H-type electrolytic cell.

[0039] Figure 8 The potential-time curve and Faraday efficiency-time curve are obtained from the constant current stability test of the nickel phosphide catalyst obtained in Example 2 of this invention in the cyclohexanone oxidation reaction in an H-type electrolytic cell.

[0040] Figure 9 The potential-time curve and Faraday efficiency-time curve are obtained from the constant current stability test of the nickel phosphide catalyst obtained in Example 3 of this invention in the cyclohexanone oxidation reaction in an H-type electrolytic cell.

[0041] Figure 10 Example 4 of the present invention uses a mixed solution of cyclohexanone with a concentration of 0.4 mol / L and potassium hydroxide with a concentration of 1 mol / L as the anolyte, or a potassium hydroxide solution with a concentration of 1 mol / L as the anolyte, and obtains the current-voltage curves in the membrane electrode electrolysis cell.

[0042] Figure 11 The Faraday efficiency and production rate of the nickel phosphide catalyst obtained in Example 4 of this invention for the electro-oxidation of cyclohexanone in a membrane electrode electrolyzer.

[0043] Figure 12The potential-time curves and Faraday efficiency-time curves are obtained from the constant current stability test of the nickel phosphide catalyst obtained in Example 4 of this invention in the electro-oxidation reaction of cyclohexanone in a membrane electrode electrolytic cell. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0045] Example 1

[0046] This embodiment prepares a nickel phosphide catalyst suitable for the electro-oxidation of cyclohexanone to adipic acid, specifically including the following steps:

[0047] Step 1: Cut the purchased 0.15 cm thick commercial nickel foam into 2.5 × 3.5 cm square sheets, and then ultrasonically treat them with 1 mol / L dilute hydrochloric acid, anhydrous ethanol, and deionized water to remove the surface oxide layer and grease, thus obtaining pretreated nickel foam.

[0048] Step 2: Immerse the pretreated nickel foam in a stainless steel autoclave lined with polytetrafluoroethylene containing a mixed solution of 0.1 mol / L nickel nitrate, 0.28 mol / L ammonium fluoride and 1 mol / L urea, and heat at 100 degrees Celsius for 10 hours to obtain nickel hydroxide precursor.

[0049] Step 3: After the stainless steel autoclave has completely cooled, remove the nickel hydroxide precursor and dry it in a 40-degree Celsius oven overnight to obtain the phosphorus-free initial catalyst, i.e., nickel hydroxide.

[0050] Step 4: Place all the obtained nickel hydroxide into the downstream of the tube furnace, and place 2 grams of sodium hypophosphite into the upstream of the tube furnace. Heat at 300 degrees Celsius for 3 hours in an argon atmosphere.

[0051] Step 5: After heating is complete, wait for the tube furnace to cool to room temperature to obtain a nickel phosphide catalyst suitable for the electro-oxidation of cyclohexanone to adipic acid.

[0052] The structure of the nickel phosphide catalyst obtained in this embodiment is characterized, and the catalytic performance of the cyclohexanone electro-oxidation reaction is tested.

[0053] Figure 1 The image shown is a spherical aberration corrected scanning transmission electron microscope image of the nickel phosphide catalyst obtained in this embodiment. Its lattice spacing is consistent with that of nickel phosphide (111), indicating that the nickel phosphide catalyst was indeed synthesized.

[0054] Figure 3 The images shown are scanning electron microscope (SEM) images and component distribution surface scans of the nickel phosphide catalyst obtained in this embodiment. Figure 3 (a) and Figure 3 (b) is a scanning electron microscope image, which shows that the obtained nickel phosphide catalyst has a layered porous structure. Figure 3 (c)~ Figure 3 (f) is a surface scan of the composition, which shows that the three elements are evenly distributed, and also confirms the synthesis of the nickel phosphide catalyst.

[0055] Figure 4 The X-ray diffraction patterns of the nickel phosphide catalyst obtained in this embodiment and the initial catalyst without phosphorus are compared with the corresponding PDF card, which further confirms the synthesis of the nickel phosphide catalyst and that the initial catalyst without phosphorus obtained in step 3 is nickel hydroxide.

[0056] In this embodiment, the catalytic performance of the electro-oxidation reaction of cyclohexanone was tested in an H-type electrolytic cell. Specifically, the obtained nickel phosphide catalyst or the initial catalyst without phosphorus was used as the working electrode, nickel foam as the counter electrode, and mercury / mercury oxide (containing a 1 mol / L potassium hydroxide solution) as the reference electrode. A mixed solution of 0.4 mol / L cyclohexanone and 0.5 mol / L potassium hydroxide was used as the anolyte, and a 0.5 mol / L potassium hydroxide solution was used as the catholyte. The constant current method was used for testing, with the applied anolyte current density ranging from 50 to 350 mA / cm². The liquid products of the reaction were detected by high-performance liquid chromatography (HPLC), and the coulombic amount corresponding to the product concentration was calculated. The selectivity, activity, and other data of the catalytic reaction were obtained based on the total coulombic amount recorded by the electrochemical workstation.

[0057] After catalytic performance testing, the working electrode, made of nickel phosphide catalyst, was removed, and its aberration-corrected scanning transmission electron microscope image is shown below. Figure 1 As shown, its component distribution was scanned, and the results are as follows. Figure 2 As shown, after the catalytic reaction, a layer of amorphous phosphate appears on the surface of the nickel phosphide catalyst.

[0058] Figure 5 The figure shows the Faradaic efficiency of the phosphorus-free initial catalyst obtained in this embodiment for the electro-oxidation of cyclohexanone in an H-type electrolytic cell. It can be seen that under different current densities, the main product of the electro-oxidation of cyclohexanone using the phosphorus-free initial catalyst is adipic acid, and the byproduct is a small amount of glutaric acid. Furthermore, the Faradaic efficiency decreases sharply with the increase of current density.

[0059] Figure 6The figure shows the Faradaic efficiency of the nickel phosphide catalyst obtained in this embodiment for the electro-oxidation of cyclohexanone in an H-type electrolytic cell. It can be seen that under different current densities, the main product of the electro-oxidation of cyclohexanone using the nickel phosphide catalyst is adipic acid, and the byproduct is a very small amount of glutaric acid. Moreover, as the current density increases, the Faradaic efficiency can still be maintained above 90%, and the production rate is much greater than that of the initial catalyst without phosphorus, showing excellent adipic acid selectivity and catalytic activity.

[0060] Figure 7 The potential-time curve and Faraday efficiency-time curve are shown for the constant current stability test of the nickel phosphide catalyst obtained in this embodiment in the electro-oxidation reaction of cyclohexanone in an H-type electrolytic cell. After 650 hours of constant current testing, the catalytic performance of the nickel phosphide catalyst has very little decay, indicating that its stability is very good and it is suitable for use in long-term catalytic reactions.

[0061] Example 2

[0062] This embodiment prepares a nickel phosphide catalyst suitable for the electro-oxidation of cyclohexanone to adipic acid. The preparation process is the same as in Example 1, except that in step 2, "heating the reaction at 100 degrees Celsius for 10 hours" is changed to "heating the reaction at 120 degrees Celsius for 10 hours". All other steps remain the same.

[0063] The catalytic performance of the nickel phosphide catalyst obtained in this embodiment for the electro-oxidation of cyclohexanone was tested using the same method as in Example 1.

[0064] Figure 8 The figure shows the Faradaic efficiency of the nickel phosphide catalyst obtained in this embodiment for the electro-oxidation of cyclohexanone in an H-type electrolytic cell. It can be seen that under different current densities, the main product of the electro-oxidation of cyclohexanone using the nickel phosphide catalyst is adipic acid, and the byproduct is a very small amount of glutaric acid. Moreover, the Faradaic efficiency can still be maintained above 75% as the current density increases.

[0065] Example 3

[0066] This embodiment prepares a nickel phosphide catalyst suitable for the electro-oxidation of cyclohexanone to adipic acid. The preparation process is the same as in Example 1, except that in step 4, "heating at 300 degrees Celsius for 3 hours in an argon atmosphere" is changed to "heating at 350 degrees Celsius for 3 hours in an argon atmosphere". All other steps remain the same.

[0067] The catalytic performance of the nickel phosphide catalyst obtained in this embodiment for the electro-oxidation of cyclohexanone was tested using the same method as in Example 1.

[0068] Figure 9The figure shows the Faradaic efficiency of the nickel phosphide catalyst obtained in this embodiment for the electro-oxidation of cyclohexanone in an H-type electrolytic cell. It can be seen that under different current densities, the main product of the electro-oxidation of cyclohexanone using the nickel phosphide catalyst is adipic acid, and the byproduct is a very small amount of glutaric acid. Moreover, the Faradaic efficiency can still be maintained above 80% as the current density increases.

[0069] Example 4

[0070] This embodiment prepares a nickel phosphide catalyst suitable for the electro-oxidation of cyclohexanone to adipic acid. The preparation process is the same as in Example 1, except that in step 1, "cutting into 2.5×3.5 square centimeter sheets" is changed to "cutting into 5×5 square centimeter sheets". All other steps remain the same.

[0071] The high-current catalytic performance of the nickel phosphide catalyst obtained in this embodiment for the electro-oxidation of cyclohexanone is tested below.

[0072] Specifically, the reaction was carried out in a membrane electrode electrolysis cell with an area of ​​5×5 square centimeters. The obtained nickel phosphide catalyst was used as the anode catalyst, and commercially available platinum-titanium plating felt was used as the cathode catalyst. A mixed solution of 0.4 mol / L cyclohexanone and 1 mol / L potassium hydroxide was used as the anolyte, or a 1 mol / L potassium hydroxide solution was used as the anolyte, and a 0.5 mol / L sulfuric acid solution was used as the cathode electrolyte. The anode and cathode were separated by a proton exchange membrane. In this embodiment, a constant current method was used for testing, with the applied anolyte current ranging from 0.5 to 8.75 amperes. The liquid-phase products of the reaction were detected by high-performance liquid chromatography (HPLC), and the coulombic amount corresponding to the product concentration was calculated. The selectivity and activity of the catalyst were obtained based on the total coulombic amount recorded by the DC power supply.

[0073] Figure 10 In this embodiment, the current-voltage curves obtained using a mixed solution of 0.4 mol / L cyclohexanone and 1 mol / L potassium hydroxide, or a 1 mol / L potassium hydroxide solution as the anolyte, show that under the same current, the voltage using the mixed solution of 0.4 mol / L cyclohexanone and 1 mol / L potassium hydroxide as the anolyte is less than the voltage using the 1 mol / L potassium hydroxide solution as the anolyte. This proves that the cyclohexanone oxidation reaction is an ideal alternative to the oxygen evolution reaction for coupling hydrogen production.

[0074] Figure 11 The present invention describes the Faradaic efficiency and production rate of the nickel phosphide catalyst obtained in this embodiment for the electro-oxidation of cyclohexanone in a flow electrolytic cell. It can be seen that under high current, the main product of the electro-oxidation of cyclohexanone using the nickel phosphide catalyst is adipic acid, and the byproduct is a very small amount of glutaric acid. Furthermore, the Faradaic efficiency can still be maintained above 90% as the current density increases, and the production rate is also excellent. This demonstrates that the nickel phosphide catalyst has excellent scalability and is expected to achieve large-scale industrial application.

[0075] Figure 12 The potential-time curve and Faraday efficiency-time curve are shown for the constant current stability test of the nickel phosphide catalyst obtained in this embodiment in the electro-oxidation reaction of cyclohexanone in a flow electrolyzer. After 153 hours of constant current testing, the performance degradation of the nickel phosphide catalyst is very small, indicating that it has good stability under high current and is suitable for application in long-term catalytic reactions under high current.

[0076] It should be noted that this is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a nickel phosphide catalyst suitable for the electro-oxidation of cyclohexanone to adipic acid, characterized in that, Includes the following steps: Step 1: Pretreatment of nickel foam; Step 2: Place the foamed nickel into a high-pressure reactor containing a mixed solution of nickel nitrate, ammonium fluoride and urea, and react at 100~120 degrees Celsius for 8~12 hours. After drying, nickel hydroxide is obtained. Step 3: Place nickel hydroxide downstream of the tube furnace and sodium hypophosphite upstream of the tube furnace. Heat at 300-400 degrees Celsius for 2-4 hours under an inert atmosphere. After cooling, obtain a nickel phosphide catalyst suitable for the electro-oxidation of cyclohexanone to adipic acid.

2. The method for preparing a nickel phosphide catalyst suitable for the electro-oxidation of cyclohexanone to adipic acid according to claim 1, characterized in that, The nickel foam mentioned in step 1 is in sheet form, with a planar size of 1×1 square centimeter to 5×5 square centimeters and a thickness of 0.1 to 0.3 centimeters.

3. The method for preparing a nickel phosphide catalyst suitable for the electro-oxidation of cyclohexanone to adipic acid according to claim 2, characterized in that, In step 2, the concentration of nickel nitrate in the mixed solution is 0.01-0.2 mol / L, the concentration of ammonium fluoride is 0.1-0.5 mol / L, and the concentration of urea is 0.5-2 mol / L.

4. The method for preparing a nickel phosphide catalyst suitable for the electro-oxidation of cyclohexanone to adipic acid according to claim 1, characterized in that, In step 3, the ratio of sodium hypophosphite added to the area of ​​nickel hydroxide is 1-3 grams per square centimeter.

5. An electrolytic apparatus for the electro-oxidation of cyclohexanone to adipic acid, characterized in that, The nickel phosphide catalyst obtained by the method described in any one of claims 1 to 4 is used as the working electrode, and cyclohexanone under alkaline conditions is used as the anolyte.

6. The electrolytic apparatus for the electro-oxidation of cyclohexanone to adipic acid according to claim 5, characterized in that, Designed based on H-type electrolytic cells, flow electrolytic cells, membrane electrode electrolytic cells, or membrane-free electrolytic cells.

7. The electrolytic apparatus for the electro-oxidation of cyclohexanone to adipic acid according to claim 5, characterized in that, It operates using either a constant current method or a constant voltage method. The anode current applied in the constant current method ranges from 0.05 to 8.75 amperes, while the potential applied in the constant voltage method ranges from 0.5 to 4 volts.

8. The electrolytic apparatus for the electro-oxidation of cyclohexanone to adipic acid according to claim 5, characterized in that, The concentration of cyclohexanone in the anolyte ranges from 0.05 to 1 mol per liter.

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