A nickel oxide doped manganese dioxide catalyst, its preparation method and use

Abstract

This invention discloses a nickel oxide-doped manganese dioxide catalyst, its preparation method, and its application. The catalyst is prepared by in-situ growth of nickel oxide-doped manganese dioxide on a carbon felt substrate using a solvothermal method. In the application, the catalyst electrode is used as the anode, and an aromatic compound is dissolved in an acidic solution as the anolyte. A counter electrode is used in the cathode chamber, and an acidic solution is used as the cathode reaction solution. After the reaction, an aromatic aldehyde or aromatic ketone can be obtained through a post-treatment process. The catalyst of this invention has a high surface area and porous structure, which increases the specific surface area of ​​the electrode, providing a large number of reaction sites and active sites for the oxidation of the substrate. In addition, the doping of nickel oxide provides more active sites for manganese dioxide, promoting the formation of intermediates and also promoting the desorption of the aromatic aldehyde product, preventing the formation of aromatic acids due to over-oxidation. Furthermore, the nanorod-like three-dimensional structure of the catalyst is beneficial for mass transfer.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic materials, specifically relating to nickel oxide-doped manganese dioxide catalysts, their preparation methods, and their application in the electrocatalytic oxidation to produce aromatic aldehydes. Background Technology

[0002] Aromatic aldehydes play a crucial role in organic synthesis due to their unique structure and reactivity, and are widely used in chemical, pharmaceutical, and materials fields, especially as important intermediates for fragrances, dyes, pharmaceuticals, and polymer materials. However, traditional synthetic methods typically involve multi-step reactions, high energy consumption, and numerous byproducts. Strict control over reaction selectivity and intermediate purity also presents significant challenges, and is not conducive to achieving green production goals.

[0003] Electrochemical oxidation provides a green and efficient new route for the preparation of aromatic aldehydes: first, aromatic compounds are oxidized to methyl alcohol intermediates, and then further oxidized to generate the target product, aromatic aldehyde. However, the core challenge of this method lies in the fact that at high current densities, methyl alcohol intermediates are easily peroxidized to generate byproducts such as aromatic acids, thereby reducing the selectivity and yield of aromatic aldehydes. Therefore, optimizing electrolysis conditions and selecting suitable electrode materials and electrolyte systems are crucial.

[0004] Currently, using nickel oxide-doped manganese dioxide catalysts to improve this problem has potential advantages, as such catalysts are expected to effectively suppress the peroxidation reaction of intermediates by increasing active sites and optimizing electron transfer, thus achieving highly selective and high-yield preparation of aromatic aldehydes. However, no related applications of this catalytic system have been reported, which provides a new direction for future research. Summary of the Invention

[0005] To address the aforementioned problems in existing technologies, the present invention aims to overcome the issues of byproduct generation and low current density in the electrocatalytic oxidation of aromatic compounds. This invention proposes a nickel oxide-doped manganese dioxide catalyst, its preparation method, and its application in the electrocatalytic oxidation of aromatic aldehydes. The nickel oxide-doped manganese dioxide catalyst prepared in this invention does not use precious metals, resulting in low cost. During catalyst preparation, potassium fluoride is introduced to suppress disordered stacking, promote the formation of a porous structure, increase the specific surface area, and expose more active sites. Furthermore, the electrocatalytic oxidation method employs mild reaction conditions, and the reaction rate and progress can be precisely controlled by adjusting the electrolysis conditions. A relatively high current density can be achieved during electrolysis, resulting in a high space-time yield.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a nickel oxide-doped manganese dioxide catalyst includes the following steps:

[0008] 1) The carbon felt is placed in a muffle furnace for high-temperature activation and hydrophilic treatment, and then placed in nitric acid, acetone and ethanol respectively for ultrasonic treatment for 0.5-3 hours to obtain pretreated carbon felt.

[0009] 2) Dissolve nickel salt, manganese salt, and potassium fluoride in deionized water to prepare a reaction solution;

[0010] 3) The carbon felt pretreated in step 1) is fully immersed in the reaction solution in step 2) and transferred to a reaction vessel with a polytetrafluoroethylene liner for solvothermal reaction at high temperature. After the reaction is completed, it is cooled to room temperature, the hydrothermal carbon felt is taken out, and it is repeatedly washed with distilled water and ethanol. After drying, Ni(OH)2 doped manganese dioxide catalyst precursor is obtained.

[0011] 4) After the drying in step 3) is completed, the catalyst precursor is transferred to a tube furnace for heat treatment. It is calcined in an air atmosphere with the temperature controlled within a specific range to promote its transformation into a manganese dioxide phase with good structural stability, thus obtaining the nickel oxide-doped manganese dioxide catalyst.

[0012] Further, in step 1), the high-temperature activation in the muffle furnace is 300-600℃, and the treatment time is 0.5-3h; in step 3), the solvothermal reaction temperature is 120-180℃, and the solvothermal reaction time is 6-24h; in step 2), the molar ratio of manganese salt to nickel salt is 3-8:1, preferably 3-4:1, and the air flow rate is 10-90mL / min; in step 4), the heat treatment temperature is 300-500℃, preferably 400-500℃, and the holding time is 1-5h, preferably 2-3h.

[0013] Furthermore, the manganese salt is manganese nitrate tetrahydrate, potassium permanganate, manganese chloride, manganese acetylacetonate, or manganese sulfate; the nickel salt is nickel chloride, nickel acetylacetonate, or nickel nitrate hexahydrate.

[0014] The present invention also proposes a nickel oxide-doped manganese dioxide catalyst prepared by the above preparation method.

[0015] This invention also specifies the application of the above-mentioned nickel oxide-doped manganese dioxide catalyst in the electrocatalytic oxidation to produce aromatic aldehydes. Using aromatic compound (a) as the reaction substrate, a flow-type diaphragm electrolytic cell is employed during constant current electrolysis. The current is controlled by an electrochemical workstation. The anode and cathode chambers of the flow-type diaphragm electrolytic cell are separated by an ion-exchange membrane. The nickel oxide-doped manganese dioxide catalyst electrode serves as the anode electrode. Aromatic compound (a) is dissolved in an acidic solution as the anolyte. A cathode electrode is set in the cathode chamber, and an acidic solution is used as the cathode liquid. The constant current electrolysis reaction is carried out for 0.5-3 hours. After the reaction, the anolyte is post-treated to obtain product (b). The reaction equation is as follows:

[0016]

[0017] In the formula, R1 on the intermediate represents a benzene ring group and R2 represents a benzene ring group or hydrogen.

[0018] Furthermore, the main solvent of the acidic solution used for the anode and cathode is hydrochloric acid solution, sulfuric acid solution, nitric acid solution, acetic acid, methanesulfonic acid or perchloric acid, preferably sulfuric acid solution, with a concentration of 0.05-2.0 mol / L.

[0019] Furthermore, this invention specifies that the secondary solvent in the anode chamber is one of tetrahydrofuran, dichloromethane, acetonitrile, or acetone, and the volume ratio of the primary solvent to the secondary solvent is 3:7 to 7:3. The primary solvent serves as the main electrolyte for the electrolytic reaction, while the secondary solvent is used to dissolve the aromatic compound reactants.

[0020] Furthermore, the present invention also specifies that the mixing volume of the cathode chamber and the anode chamber is 50-250 mL.

[0021] Furthermore, the present invention also specifies that the concentration of aromatic compounds in the anolyte is 10-50 mmol / L, preferably 10-30 mmol / L.

[0022] Furthermore, the present invention also specifies that the current density during constant current electrolysis is 20-200 mA / cm². 2 The cathode chamber electrode is a carbon felt.

[0023] Furthermore, the present invention also specifies that during the constant current electrolysis process, the pH of the anolyte reaction solution is stable at 0-4; the temperature of the constant temperature water bath during the reaction is 30-70℃; the voltage between the cathode and the anode is 1-10V; and the reaction time is 0.5-3h.

[0024] Furthermore, the present invention specifies that the organic solvent used for extraction is ethyl acetate, dichloromethane, trichloromethane, or carbon tetrachloride.

[0025] Furthermore, the method for electrocatalytic oxidation of nickel oxide-doped manganese dioxide catalyst to produce aromatic aldehydes is characterized in that the nickel oxide-doped manganese dioxide catalyst electrode is prepared by in-situ solvothermal growth of the nickel oxide-doped manganese dioxide catalyst on a carbon felt as an electrode substrate, and the loading of the nickel oxide-doped manganese dioxide catalyst on the carbon felt is 10-20 mg / cm³. 2 .

[0026] Furthermore, after the reaction is completed, the anolyte is post-treated as follows: after the electro-oxidation reaction, the reaction solution is first neutralized with 0.5M sodium hydroxide solution and the pH is adjusted to neutral; then, the solution is transferred to a separatory funnel, an organic solvent is added for extraction to obtain an organic phase extract, and then the organic phase extract is distilled to obtain the target product; the organic solvent used for extraction is ethyl acetate, toluene, dichloromethane, chloroform or carbon tetrachloride.

[0027] By employing the above-described technology, the beneficial effects achieved by the present invention compared to the prior art are as follows:

[0028] By implementing the above technical solution, compared with the prior art, the present invention exhibits significant advantages in terms of catalytic performance, environmental friendliness, and economy, specifically reflected in the following aspects:

[0029] (1) This invention uses nickel oxide-doped manganese dioxide (NiO-MnO2) nanorods as an electrocatalyst. Its unique doping strategy, combined with a three-dimensional porous structure, significantly improves the specific surface area and active site density of the catalyst, thereby enhancing the mass transfer efficiency and electrocatalytic activity of the reactants. In the electrocatalytic oxidation reaction of 4-methylanisole (Example 1), at 100 mA / cm²... 2 Under conditions of high current density and a reaction time of 8000 s, the substrate conversion rate reached 99.99%, the selectivity of the aromatic aldehyde product was as high as 95.53%, and a conversion rate of 5.85 kg / (m²) was achieved. 3 The space-time yield of the NiO-MnO2 doped catalyst (GF, Example 8) was less than 1%, with an amount of aromatic acid byproducts less than 1%. In contrast, the undoped catalyst (GF, Example 8) showed only 68.21% conversion and 69.30% selectivity, further confirming the key role of the NiO-MnO2 doped structure in improving reaction selectivity.

[0030] (2) This invention provides a highly efficient and environmentally friendly electrocatalyst based on carbon felt and its application method. The carbon felt serves as a catalyst support, exhibiting excellent liquid-holding capacity and significantly extending the residence time of the reaction substrate, thus ensuring a complete reaction. Based on this, by in-situ growing nickel oxide-doped manganese dioxide nanorods on the carbon felt surface, the catalyst prepared in this invention exhibits a large specific surface area, providing abundant reactive sites for substrate oxidation. Simultaneously, nickel oxide doping optimizes the catalyst's performance. On the one hand, it improves reaction selectivity by regulating the adsorption behavior of reaction intermediates; on the other hand, it effectively promotes rapid charge transfer, enabling the catalyst to achieve stable operation for extended periods at high current densities. Compared to traditional heavy metal catalysts, the catalyst system of this invention is environmentally friendly, significantly reducing potential pollution to the ecosystem and aligning with the sustainable development concept of green chemistry.

[0031] (3) The present invention uses a membrane-type flow electrolyzer to carry out the reaction, which can obtain a high space-time yield. Aromatic aldehydes are directly obtained by electrocatalytic oxidation. The reaction steps are simple, the reaction process is at room temperature and pressure, and the reaction conditions are mild and controllable. In addition, the catalyst does not use expensive precious metals and has a low cost, which has great economic value.

[0032] In summary, this invention uses carbon felt as a catalyst support and grows nickel oxide-doped manganese dioxide nanorods in situ on its surface, giving the catalyst a high surface area and porous structure, increasing the electrode specific surface area, and providing a large number of reaction sites and active sites for substrate oxidation. In addition, the doping of nickel oxide provides more active sites for manganese dioxide, promoting the formation of intermediates and also promoting the desorption of aromatic aldehydes, preventing the formation of aromatic acids due to over-oxidation. Furthermore, the three-dimensional nanorod structure of the catalyst is beneficial for mass transfer. Attached Figure Description

[0033] Figure 1 This is a SEM image of the NiO-MnO2 / GF catalyst in Example 1 at 20 μm.

[0034] Figure 2 This is a SEM image of the NiO-MnO2 / GF catalyst in Example 1 at 10 μm.

[0035] Figure 3 This is a TEM image of the NiO-MnO2 / GF catalyst in Example 1 at 5 nm.

[0036] Figure 4 This is a graph showing the relative concentration changes of the raw materials and products during the reaction in Example 1;

[0037] Figure 5Linear sweep voltammetry curves were used to determine the presence of the substrate 4-methylanisole in 0.5 M H2SO4 solution of the NiO-MnO2 / GF-V1 catalyst in Example 1.

[0038] Figure 6 BET analysis of NiO-MnO2 and MnO2 in Example 1. Inset: Pore volume of NiO-MnO2;

[0039] Figure 7 The conversion and yield changes were observed after eight cycles of the reaction in Example 7. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0041] Example 1: Synthesis of nickel oxide-doped manganese dioxide catalyst and its application in the electrocatalytic oxidation of 4-methyl anisole

[0042] 1) Cut the carbon felt into rectangles of 3cm×3.5cm and place them in a muffle furnace for high-temperature hydrophilic treatment at 500℃ for 1h. Then, sonicate the carbon felt with concentrated nitric acid, acetone and ethanol for 0.5h respectively.

[0043] 2) Then weigh out 3.5 mmol potassium permanganate, 1 mmol nickel nitrate hexahydrate and 2 mmol potassium fluoride respectively, mix them and dissolve them in 60 mL deionized water, place them in an ultrasonic bath and sonicate and stir to make them fully dissolved.

[0044] 3) The hydrophilic carbon felt obtained in step 1) is fully immersed in the solution obtained in step 2) and transferred to a reaction vessel with a polytetrafluoroethylene liner. A solvothermal reaction is carried out at a high temperature of 140°C for 12 hours. After the reaction, a manganese dioxide precursor doped with Ni(OH)2 is obtained. This precursor is then transferred to an oven for further drying to obtain a catalyst precursor.

[0045] 4) After drying, the catalyst precursor was transferred to a tube furnace for heat treatment. Calcination was performed under an air atmosphere of 60 mL / min, with the temperature increased to 450℃ at a rate of 5℃ / min and held at that temperature for 2 hours. The catalyst was then cooled to room temperature. The resulting nickel oxide-doped manganese dioxide catalyst had a loading of 10 mg / cm³ on the carbon felt. 2 Labeled as NiO-MnO2 / GF-V1, its scanning electron microscope image is as follows: Figure 1 and Figure 2 As shown. From Figure 1 , Figure 2 It can be observed that the NiO-MnO2 / GF-V1 catalyst grows uniformly on the carbon felt surface in the form of nanorods, with a size of approximately 1 micrometer. Meanwhile, high-resolution transmission electron microscopy (HRTEM) images are shown below. Figure 3 As shown, the catalyst exhibits lattice fringes of NiO and MnO2, with a hybrid interface between them, which helps to regulate the electronic structure of MnO2 and optimize its oxidation activity.

[0046] The catalytic performance of the NiO-MnO2 / GF-V1 catalyst electrode prepared in Example 1 was tested using the following methods:

[0047] Figure 5 Linear sweep voltammetry (LSV) curves of the NiO-MnO2 / GF-V1 catalyst in Example 1 were used to determine the presence of the substrate 4-methylanisole in 0.5 M H2SO4 solution. The LSV curves showed that after the addition of 4-methylanisole (1a) to NiO-MnO2 / GF-V1, the anolyte current density increased to 15.8 mA cm⁻² at 1.2 V vs. RHE, and the oxidation onset potential shifted negatively from 1.15 V to 1.05 V vs. RHE (ΔE = 100 mV). This performance improvement stems from the synergistic effect of the NiO-MnO2 heterostructure, which jointly optimizes charge transport and substrate adsorption, significantly reducing the reaction energy barrier.

[0048] Through nitrogen adsorption-desorption isotherms ( Figure 6 The pore structures of NiO-MnO2 and pure MnO2 prepared in Example 1 were systematically characterized. The results showed that NiO-MnO2 exhibited a typical Type IV isotherm with an H3-type hysteresis loop, indicating a hierarchical porous structure dominated by mesopores; while pure MnO2 exhibited approximately Type II isotherm characteristics, reflecting its microporous-non-porous properties. BET surface area analysis showed that the specific surface area of ​​NiO-MnO2 was as high as 94.79 m². 2 ·g-1, relatively pure MnO2 (15.67m 2 The pore size distribution (·g⁻¹) increased by approximately 6 times, a significant difference attributed to the regulatory effect of nickel doping on the growth of MnO₂ crystals. The pore size distribution was calculated using the BJH model. Figure 6 (Illustration) The pore size of NiO-MnO2 is concentrated in the 2-30 nm (mesoporous range), and the cumulative pore volume reaches 0.43 cm³. 3 g-1 further confirms the formation of its three-dimensional interconnected porous network. This hierarchical porous structure optimizes mass transfer, promoting rapid diffusion of reactant products.

[0049] The NiO-MnO2 / GF-V1 catalyst obtained above was directly used as the anode. The current was controlled using an electrochemical workstation, and the reaction was carried out in a flow-through diaphragm electrolyzer. The anode and cathode chambers of the flow-through diaphragm electrolyzer were separated by an ion-exchange membrane. 20 mmol of 4-methylanisole (denoted as 1a) was weighed as the reaction substrate and dissolved in 100 mL of an acidic mixed solvent as the anode solution. The main solvent was a 0.5 mol / L sulfuric acid solution, and the secondary solvent was acetonitrile, with a volume ratio of 4:6. In the cathode chamber, carbon felt was used as the counter electrode, and a 0.5 mol / L sulfuric acid solution was used as the cathode solution. The pH of the anode reaction solution was monitored and maintained at 0.5-1.5 using a pH meter. The reaction system temperature was 30℃, and the current density was 100 mA / cm². 2 The reaction was electrolyzed at a constant current for 8000 s. After the anolyte was cooled to room temperature, it was repeatedly extracted three times with dichloromethane. The dichloromethane phase was then evaporated and separated to obtain 4-methoxybenzaldehyde (denoted as 1b). With increasing reaction time, the amount of feedstock 1a gradually decreased, while the amount of main product 1b gradually increased. When the reaction reached 8000 s, the conversion rate of 1a reached 99.99%, the selectivity of 1b was 95.53%, and the calculated space-time yield reached 5.85 kg / (m²). 3 ·h).

[0050] Example 2: Synthesis of nickel oxide-doped manganese dioxide catalyst and its application in the electrocatalytic oxidation of 4-nitrotoluene

[0051] 1) Cut the carbon felt into rectangles of 3cm×3.5cm and place them in a muffle furnace for high-temperature hydrophilic treatment at 500℃ for 1h. Then, sonicate the carbon felt with concentrated nitric acid, acetone and ethanol for 0.5h respectively.

[0052] 2) Then weigh out 8 mmol of manganese nitrate tetrahydrate, 2 mmol of nickel acetylacetonate hexahydrate and 2 mmol of potassium fluoride respectively, mix them and dissolve them in 60 mL of deionized water, place them in an ultrasonic bath and sonicate and stir to make them fully dissolved.

[0053] 3) The hydrophilic carbon felt obtained in step 1) is fully immersed in the solution obtained in step 2) and transferred to a reaction vessel with a polytetrafluoroethylene liner. A solvothermal reaction is carried out at a high temperature of 180°C for 16 hours. After the reaction, a manganese dioxide precursor doped with Ni(OH)2 is obtained. This precursor is then transferred to an oven for further drying to obtain a catalyst precursor.

[0054] 4) After drying, the catalyst precursor was transferred to a tube furnace for heat treatment. Calcination was performed under an air atmosphere of 60 mL / min, with the temperature increased to 450℃ at a rate of 5℃ / min and held at that temperature for 3 hours. The catalyst was then cooled to room temperature. The resulting nickel oxide-doped manganese dioxide catalyst had a loading of 10 mg / cm³ on the carbon felt. 2 It is labeled as NiO-MnO2 / GF-V2.

[0055] The catalytic performance of the NiO-MnO2 / GF-V2 catalyst prepared in Example 2 was tested using the following methods:

[0056] The NiO-MnO2 / GF-V2 catalyst obtained above was directly used as the anode. The current was controlled using an electrochemical workstation, and the reaction was carried out in a flow-through diaphragm electrolyzer. The anode and cathode chambers of the flow-through diaphragm electrolyzer were separated by an ion-exchange membrane. 15 mmol of 4-nitrotoluene (denoted as 2a) was weighed as the reaction substrate and dissolved in 100 mL of an acidic mixed solvent as the anode solution. The main solvent was a 1.0 mol / L nitric acid solution, and the secondary solvent was acetonitrile, with a volume ratio of 3:7. A carbon felt was used as the counter electrode in the cathode chamber, and a 1.0 mol / L nitric acid solution was used as the catholyte. The pH of the anode reaction solution was monitored and maintained at 0-1.5 using a pH meter. The reaction system temperature was 40℃, and the current density was 100 mA / cm². 2 The reaction was electrolyzed at a constant current for 5800 s. After the anolyte was cooled to room temperature, it was repeatedly extracted three times with dichloromethane. The dichloromethane phase was then evaporated and separated to obtain 4-nitrobenzaldehyde (denoted as 2b). With increasing reaction time, the reactant 2a gradually decreased, while the main product 2b gradually increased. When the reaction reached 5800 s, the conversion rate of 2a reached 93.32%, the selectivity of 2b was 95.33%, and the calculated space-time yield reached 6.26 kg / (m²). 3 ·h).

[0057] Example 3: Synthesis of nickel oxide-doped manganese dioxide catalyst and its application in the electrocatalytic oxidation of 4-fluorotoluene

[0058] 1) Cut the carbon felt into rectangles of 3cm×3.5cm and place them in a muffle furnace for 2 hours of high-temperature hydrophilic treatment at 500℃. Then, sonicate the carbon felt with concentrated nitric acid, acetone and ethanol for 0.5 hours respectively.

[0059] 2) Then weigh out 3 mmol manganese chloride, 1 mmol nickel sulfate and 1 mmol potassium fluoride respectively, mix them and dissolve them in 60 mL of deionized water, place them in an ultrasonic bath and sonicate and stir to make them fully dissolved.

[0060] 3) The hydrophilic carbon felt obtained in step 1) is fully immersed in the solution obtained in step 2) and transferred to a reaction vessel with a polytetrafluoroethylene liner. A solvothermal reaction is carried out at a high temperature of 120°C for 12 hours. After the reaction, a manganese dioxide precursor doped with Ni(OH)2 is obtained. This precursor is then transferred to an oven for further drying to obtain a catalyst precursor.

[0061] 4) After drying, the catalyst precursor was transferred to a tube furnace for heat treatment. Calcination was performed under an air atmosphere of 80 mL / min, with the temperature increased to 450℃ at a rate of 5℃ / min and held at that temperature for 4 hours. The catalyst was then cooled to room temperature. The resulting nickel oxide-doped manganese dioxide catalyst had a loading of 8 mg / cm³ on the carbon felt. 2 It is labeled as NiO-MnO2 / GF-V3.

[0062] The catalytic performance of the NiO-MnO2 / GF-V3 catalyst prepared in Example 3 was tested using the following methods:

[0063] The NiO-MnO2 / GF-V3 catalyst obtained above was directly used as the anode. The current was controlled using an electrochemical workstation, and the reaction was carried out in a flow-through diaphragm electrolyzer. The anode and cathode chambers of the flow-through diaphragm electrolyzer were separated by an ion-exchange membrane. 50 mmol of 4-fluorotoluene (denoted as 3a) was weighed as the reaction substrate and dissolved in 100 mL of an acidic mixed solvent as the anode solution. The main solvent was a 0.5 mol / L methanesulfonic acid solution, and the secondary solvent was acetone, with a volume ratio of 1:1. In the cathode chamber, carbon felt was used as the counter electrode, and a 0.5 mol / L methanesulfonic acid solution was used as the cathode liquid. The pH of the anode reaction solution was monitored and maintained at 0.5–2 using a pH meter. The reaction system temperature was 30 °C, and the current density was 200 mA / cm². 2 The reaction was electrolyzed at a constant current for 10,000 s. After the anolyte was cooled to room temperature, it was repeatedly extracted three times with ethyl acetate. The ethyl acetate phase was then evaporated and separated to obtain 4-fluorobenzaldehyde (denoted as 3b). With increasing reaction time, the amount of reactant 3a gradually decreased, while the amount of main product 3b gradually increased. When the reaction reached 10,000 s, the conversion rate of 3a reached 99.99%, the selectivity of 3b was 91.30%, and the calculated space-time yield reached 20.40 kg / (m²). 3 ·h).

[0064] Example 4: Synthesis of nickel oxide-doped manganese dioxide catalyst and its application in the electrocatalytic oxidation of diphenylmethane

[0065] 1) Cut the carbon felt into rectangles of 3cm×3.5cm and place them in a muffle furnace for 2 hours of high-temperature hydrophilic treatment at 500℃. Then, sonicate the carbon felt with concentrated nitric acid, acetone and ethanol for 0.5 hours respectively.

[0066] 2) Then weigh out 6 mmol of manganese acetylacetone, 2 mmol of nickel chloride and 1 mmol of potassium fluoride, mix them and dissolve them in 60 mL of deionized water. Place them in an ultrasonic bath and sonicate and stir to make them fully dissolved.

[0067] 3) The hydrophilic carbon felt obtained in step 1) is fully immersed in the solution obtained in step 2) and transferred to a reaction vessel with a polytetrafluoroethylene liner. A solvothermal reaction is carried out at a high temperature of 160°C for 24 hours. After the reaction, a manganese dioxide precursor doped with Ni(OH)2 is obtained. This precursor is then transferred to an oven for further drying to obtain a catalyst precursor.

[0068] 4) After drying, the catalyst precursor was transferred to a tube furnace for heat treatment. Calcination was performed under an air atmosphere of 80 mL / min, with the temperature increased to 500℃ at a rate of 5℃ / min and held at that temperature for 4 hours. The catalyst was then cooled to room temperature. The resulting nickel oxide-doped manganese dioxide catalyst had a loading of 15 mg / cm³ on the carbon felt. 2 It is labeled as NiO-MnO2 / GF-V4.

[0069] The catalytic performance of the NiO-MnO2 / GF-V4 catalyst prepared in Example 4 was tested using the following methods:

[0070] The NiO-MnO2 / GF-V4 catalyst obtained above was directly used as the anode. The current was controlled using an electrochemical workstation, and the reaction was carried out in a flow-through membrane electrolyzer. The anode and cathode chambers of the flow-through membrane electrolyzer were separated by an ion-exchange membrane. 50 mmol of diphenylmethane (denoted as 4a) was weighed as the reaction substrate and dissolved in 100 mL of an acidic mixed solvent as the anode solution. The main solvent was a 2.0 mol / L acetic acid solution, and the secondary solvent was tetrahydrofuran, with a volume ratio of 7:3. In the cathode chamber, carbon felt was used as the counter electrode, and a 2.0 mol / L acetic acid solution was used as the cathode solution. The pH of the anode reaction solution was monitored and maintained at 2-4 using a pH meter. The reaction system temperature was 60℃, and the current density was 200 mA / cm². 2 The reaction was electrolyzed at a constant current for 9700 s. After the anolyte was cooled to room temperature, it was repeatedly extracted three times with ethyl acetate. The ethyl acetate phase was then evaporated and separated to obtain benzophenone (denoted as 4b). With increasing reaction time, the amount of reactant 4a gradually decreased, while the amount of main product 4b gradually increased. When the reaction reached 10000 s, the conversion rate of 4a reached 99.99%, the selectivity of 4b was 96.50%, and the calculated space-time yield reached 16.38 kg / (m²). 3 ·h).

[0071] Example 5: Synthesis of nickel oxide-doped manganese dioxide catalyst and its application in the electrocatalytic oxidation of 4-trifluorotoluene

[0072] 1) Cut the carbon felt into rectangles of 3cm×3.5cm and place them in a muffle furnace for 2 hours of high-temperature hydrophilic treatment at 500℃. Then, sonicate the carbon felt with concentrated nitric acid, acetone and ethanol for 0.5 hours respectively.

[0073] 2) Then weigh out 6 mmol of manganese sulfate, 1 mmol of nickel chloride and 1 mmol of potassium fluoride, mix them and dissolve them in 60 mL of deionized water. Place them in an ultrasonic bath and sonicate and stir to ensure they are fully dissolved.

[0074] 3) The hydrophilic carbon felt obtained in step 1) is fully immersed in the solution obtained in step 2) and transferred to a reaction vessel with a polytetrafluoroethylene liner. A solvothermal reaction is carried out at a high temperature of 180°C for 8 hours. After the reaction, a manganese dioxide precursor doped with Ni(OH)2 is obtained. This precursor is then transferred to an oven for further drying to obtain a catalyst precursor.

[0075] 4) After drying, the catalyst precursor was transferred to a tube furnace for heat treatment. Calcination was performed under an air atmosphere of 90 mL / min, with the temperature increased to 450℃ at a rate of 5℃ / min and held at that temperature for 4 hours. The catalyst was then cooled to room temperature. The resulting nickel oxide-doped manganese dioxide catalyst had a loading of 5 mg / cm³ on the carbon felt. 2 It is labeled as NiO-MnO2 / GF-V5.

[0076] The catalytic performance of the NiO-MnO2 / GF-V5 catalyst prepared in Example 5 was tested using the following methods:

[0077] The NiO-MnO2 / GF-V5 catalyst obtained above was directly used as the anode. The current was controlled using an electrochemical workstation, and the reaction was carried out in a flow-through diaphragm electrolyzer. The anode and cathode chambers of the flow-through diaphragm electrolyzer were separated by an ion-exchange membrane. 20 mmol of 4-trifluoromethyltoluene (denoted as 5a) was weighed as the reaction substrate and dissolved in 100 mL of an acidic mixed solvent as the anode solution. The main solvent was a 1.0 mol / L hydrochloric acid solution, and the secondary solvent was acetonitrile, with a volume ratio of 3:7. In the cathode chamber, carbon felt was used as the counter electrode, and a 1.0 mol / L hydrochloric acid solution was used as the cathode solution. The pH of the anode reaction solution was monitored and maintained at 1-3 using a pH meter. The reaction system temperature was 50 °C, and the current density was 50 mA / cm². 2The reaction was electrolyzed at a constant current for 8000 s. After the anolyte was cooled to room temperature, it was repeatedly extracted three times with dichloromethane, and then the dichlorotoluene phase was separated to obtain 4-trifluoromethylbenzaldehyde (denoted as 5b). With increasing reaction time, the reactant 5a gradually decreased, while the main product 5b gradually increased. When the reaction reached 8000 s, the conversion rate of 5a reached 98.5%, the selectivity of 5b was 96.5%, and the calculated space-time yield reached 7.53 kg / (m³). 3 ·h).

[0078] Example 6: Synthesis of nickel oxide-doped manganese dioxide catalyst and its application in the electrocatalytic oxidation of 4-methoxyethylbenzene

[0079] 1) Cut the carbon felt into rectangles of 3cm×3.5cm and place them in a muffle furnace for 2 hours of high-temperature hydrophilic treatment at 500℃. Then, sonicate the carbon felt with concentrated nitric acid, acetone and ethanol for 0.5 hours respectively.

[0080] 2) Then weigh out 8 mmol of manganese acetylacetone, 1 mmol of nickel chloride and 1 mmol of potassium fluoride, mix them and dissolve them in 60 mL of deionized water. Place them in an ultrasonic bath and sonicate and stir to make them fully dissolved.

[0081] 3) The hydrophilic carbon felt obtained in step 1) is fully immersed in the solution obtained in step 2) and transferred to a reaction vessel with a polytetrafluoroethylene liner. A solvothermal reaction is carried out at a high temperature of 180°C for 12 hours. After the reaction, a manganese dioxide precursor doped with Ni(OH)2 is obtained. This precursor is then transferred to an oven for further drying to obtain a catalyst precursor.

[0082] 4) After drying, the catalyst precursor was transferred to a tube furnace for heat treatment. Calcination was performed under an air atmosphere of 90 mL / min, with the temperature increased to 450℃ at a rate of 5℃ / min and held at that temperature for 4 hours. The catalyst was then cooled to room temperature. The resulting nickel oxide-doped manganese dioxide catalyst had a loading of 12 mg / cm³ on the carbon felt. 2 It is labeled as NiO-MnO2 / GF-V6.

[0083] The catalytic performance of the NiO-MnO2 / GF-V6 catalyst prepared in Example 6 was tested using the following methods:

[0084] The NiO-MnO2 / GF-V6 catalyst obtained above was directly used as the anode. The current was controlled using an electrochemical workstation, and the reaction was carried out in a flow-through diaphragm electrolyzer. The anode and cathode chambers of the flow-through diaphragm electrolyzer were separated by an ion-exchange membrane. 30 mmol of 4-methoxyethylbenzene (denoted as 6a) was weighed as the reaction substrate and dissolved in 100 mL of an acidic mixed solvent as the anode solution. The main solvent was a 1.0 mol / L perchloric acid solution, and the secondary solvent was acetonitrile, with a volume ratio of 3:7. In the cathode chamber, carbon felt was used as the counter electrode, and a 1.0 mol / L hydrochloric acid solution was used as the cathode liquid. The pH of the anode reaction solution was monitored and maintained at 1-3 using a pH meter. The reaction system temperature was 50℃, and the current density was 200 mA / cm². 2 The reaction was electrolyzed at a constant current for 5800 s. After the anolyte was cooled to room temperature, it was repeatedly extracted three times with dichloromethane, and then the dichlorotoluene phase was separated to obtain 4-methoxyacetophenone (denoted as 6b). With increasing reaction time, the reactant 6a gradually decreased, while the main product 6b gradually increased. When the reaction reached 5800 s, the conversion rate of 6a reached 96.32%, the selectivity of 6b was 98.64%, and the calculated space-time yield reached 26.57 kg / (m²). 3 ·h).

[0085] Example 7: Preparation of nickel oxide-doped manganese dioxide catalyst and its electrocatalytic oxidation of 4-methyl anisole

[0086] Example 7: The preparation steps of the nickel oxide-doped manganese dioxide catalyst electrode were repeated in Example 1.

[0087] The catalytic performance of NiO-MnO2 / GF-V1 prepared in Example 1 was tested after 7 reactions, and the specific method is as follows:

[0088] The NiO-MnO2 / GF-V1 catalyst, after seven reactions, was directly used as the anode. The current was controlled using an electrochemical workstation, and the reaction was carried out in a flow-through diaphragm electrolyzer. The anode and cathode chambers of the flow-through diaphragm electrolyzer were separated by an ion-exchange membrane. 20 mmol of 4-methylanisole was weighed as the reaction substrate and dissolved in 100 mL of an acidic mixed solvent as the anolyte solution. The primary solvent was a 0.5 mol / L sulfuric acid solution, and the secondary solvent was acetonitrile, with a volume ratio of 4:6. In the cathode chamber, carbon felt was used as the counter electrode, and a 0.5 mol / L sulfuric acid solution was used as the catholyte. The pH of the anolyte solution was monitored and maintained at 0.5–1.5 using a pH meter. The reaction system temperature was 30 °C, and the current density was 100 mA / cm². 2The solution was electrolyzed under constant current for 8000 s. After the anolyte was cooled to room temperature, it was repeatedly extracted with dichloromethane three times. Then, the dichloromethane phase was evaporated and separated to obtain the 4-methoxybenzaldehyde product. The conversion rate was 99.9% and the selectivity was 93.5%.

[0089] Example 7 is a cyclic reuse test of a nickel oxide-doped manganese dioxide catalyst. The yields and conversions of these eight reactions are as follows: Figure 7 As shown in the figure. Meanwhile, the yield of the oxidation product 4-methoxybenzaldehyde (1b) did not decrease significantly in the eighth reaction, demonstrating the excellent stability of the catalyst.

[0090] Comparative Example 1: The catalytic performance of GF was tested using the following methods:

[0091] GF was used directly as the anode, and the current was controlled using an electrochemical workstation. The reaction was carried out in a flow-through diaphragm electrolyzer, where the anode and cathode chambers were separated by an ion-exchange membrane. 20 mmol of 4-methylanisole (denoted as 1a) was weighed as the reaction substrate and dissolved in 100 mL of an acidic mixed solvent as the anolyte solution. The primary solvent was a 0.5 mol / L sulfuric acid solution, and the secondary solvent was acetonitrile, with a volume ratio of 4:6. In the cathode chamber, carbon felt was used as the counter electrode, and a 0.5 mol / L sulfuric acid solution was used as the catholyte. The pH of the anolyte solution was monitored and maintained at 0.5–1.5 using a pH meter. The reaction system temperature was 30 °C, and the current density was 100 mA / cm². 2 The reaction was electrolyzed at a constant current for 8000 s. After the anolyte was cooled to room temperature, it was repeatedly extracted three times with dichloromethane. The dichloromethane phase was then evaporated and separated to obtain 4-methoxybenzaldehyde (denoted as 1b). As the reaction time increased, the amount of feedstock 1a gradually decreased, while the amount of main product 1b gradually increased. When the reaction reached 8000 s, the conversion rate of 1a reached 68.21%, the selectivity of 1b was 69.30%, and the calculated space-time yield reached 2.90 kg / (m²). 3 ·h).

[0092] For the electrocatalytic methyl oxidation reaction of aromatic compounds, a comparison was made between the six catalysts prepared above.

[0093] The conversion efficiency, selectivity, and time-space production of (NiO-MnO2 / GF, GF) under different instances are shown in Table 1.

[0094] Comparative Example 2: The catalytic performance of MnO2 / GF was tested using the following methods:

[0095] 1) Cut the carbon felt into rectangles of 3cm×3.5cm and place them in a muffle furnace for high-temperature hydrophilic treatment at 500℃ for 1h. Then, sonicate the carbon felt with concentrated nitric acid, acetone and ethanol for 0.5h respectively.

[0096] 2) Then weigh out 3.5 mmol of potassium permanganate and 2 mmol of potassium fluoride, mix them and dissolve them in 60 mL of deionized water, place them in an ultrasonic bath, sonicate and stir to make them fully dissolved.

[0097] 3) The hydrophilic carbon felt obtained in step 1) is fully immersed in the solution obtained in step 2) and transferred to a reaction vessel with a polytetrafluoroethylene liner. A solvothermal reaction is carried out at a high temperature of 140°C for 12 hours. After the reaction is completed, a manganese dioxide precursor is obtained, which is then transferred to an oven for further drying to obtain a catalyst precursor.

[0098] 4) After drying, the catalyst precursor was transferred to a tube furnace for heat treatment. Calcination was performed under an air atmosphere of 60 mL / min, with the temperature increased to 450℃ at a rate of 5℃ / min and held at that temperature for 2 hours. The catalyst was then cooled to room temperature. The resulting nickel oxide-doped manganese dioxide catalyst had a loading of 9 mg / cm³ on the carbon felt. 2 It is labeled as MnO2 / GF.

[0099] The MnO2 / GF catalyst obtained above was used directly as the anode. The current was controlled using an electrochemical workstation, and the reaction was carried out in a flow-through diaphragm electrolyzer. The anode and cathode chambers of the flow-through diaphragm electrolyzer were separated by an ion-exchange membrane. 20 mmol of 4-methylanisole (denoted as 1a) was weighed as the reaction substrate and dissolved in 100 mL of an acidic mixed solvent as the anode solution. The main solvent was a 0.5 mol / L sulfuric acid solution, and the secondary solvent was acetonitrile, with a volume ratio of 4:6. In the cathode chamber, carbon felt was used as the counter electrode, and a 0.5 mol / L sulfuric acid solution was used as the cathode solution. The pH of the anode reaction solution was monitored and maintained at 0.5-1.5 using a pH meter. The reaction system temperature was 30℃, and the current density was 100 mA / cm². 2 The reaction was electrolyzed at a constant current for 8000 s. After the anolyte was cooled to room temperature, it was repeatedly extracted three times with dichloromethane. The dichloromethane phase was then evaporated and separated to obtain 4-methoxybenzaldehyde (denoted as 1b). With increasing reaction time, the amount of feedstock 1a gradually decreased, while the amount of main product 1b gradually increased. When the reaction reached 8000 s, the conversion rate of 1a reached 96.4%, the selectivity of 1b was 80.6%, and the calculated space-time yield reached 4.75 kg / (m³). 3 ·h).

[0100] Table 1. Conversion rate, selectivity, and space-time production of catalysts in different examples.

[0101] Serial Number catalyst Conversion rate Selective <![CDATA[Spatial-temporal yield Kg / (m 3 ·h)]]> Example 1 <![CDATA[NiO-MnO2 / GF-V1]]> 99.99％ 95.53％ 5.85 Example 2 <![CDATA[NiO-MnO2 / GF-V2]]> 93.32％ 95.33％ 6.26 Example 3 <![CDATA[NiO-MnO2 / GF-V3]]> 99.99％ 91.30％ 20.40 Example 4 <![CDATA[NiO-MnO2 / GF-V4]]> 99.99％ 96.50％ 16.38 Example 5 <![CDATA[NiO-MnO2 / GF-V5]]> 98.50％ 94.23％ 7.35 Example 6 <![CDATA[NiO-MnO2 / GF-V6]]> 96.32％ 98.64％ 26.57 Example 7 <![CDATA[NiO-MnO2 / GF-V1]]> 99.99％ 93.50％ 5.73 Comparative Example 1 GF 68.21％ 69.30％ 2.90 Comparative Example 2 <![CDATA[MnO2 / GF]]> 96.4％ 80.6％ 4.75

[0102] As shown in Table 1, under different reaction conditions, NiO-MnO2 / GF exhibited excellent conversion, selectivity, and space-time yield in the electrocatalytic methyl oxidation of aromatic compounds. In contrast, Comparative Example 1, using unsupported GF, and Comparative Example 2, using MnO2 / GF, showed significantly lower conversion, selectivity, and space-time yield than Example 1, despite maintaining consistent substrate and other reaction conditions. This indicates that NiO-MnO2 / GF possesses significantly superior electrocatalytic activity compared to pure GF and MnO2 / GF. Its performance advantage stems from the synergistic effect of nickel oxide and manganese dioxide doped on the catalyst surface, effectively increasing the number of active sites during catalysis and thus promoting the formation of key intermediates. Furthermore, the rod-like three-dimensional structure of this catalyst not only enhances the contact between the substrate and the catalyst but also facilitates the timely desorption of the aromatic aldehyde product, thereby inhibiting the formation of acidic byproducts due to over-oxidation. This structural feature strongly supports the high efficiency and selectivity of the reaction.

[0103] The above description is only a partial embodiment of the present invention and is not intended to limit the present invention. However, all equivalent variations and modifications made to the present invention are within the scope of protection of the present invention.

Claims

1. A method for preparing a nickel oxide-doped manganese dioxide catalyst, characterized in that, Includes the following steps: 1) The carbon felt is placed in a muffle furnace for high-temperature activation and hydrophilic treatment, and then placed in nitric acid, acetone and ethanol respectively for ultrasonic treatment for 0.5-3 h to obtain pretreated carbon felt. 2) Dissolve nickel salt, manganese salt, and potassium fluoride in deionized water to prepare a reaction solution; 3) The carbon felt pretreated in step 1) is fully immersed in the reaction solution in step 2) and transferred to a reaction vessel with a polytetrafluoroethylene liner for solvothermal reaction at high temperature. After the reaction is completed, it is cooled to room temperature, the hydrothermal carbon felt is taken out, and it is repeatedly washed with distilled water and ethanol. After drying, Ni(OH)2 doped manganese dioxide catalyst precursor is obtained. 4) After the drying in step 3) is completed, the catalyst precursor is transferred to a tube furnace for heat treatment. It is calcined in an air atmosphere with the temperature controlled within a specific range to promote its transformation into a manganese dioxide phase with good structural stability, thus obtaining the nickel oxide-doped manganese dioxide catalyst.

2. The method for preparing a nickel oxide-doped manganese dioxide catalyst according to claim 1, characterized in that, In step 1), the high-temperature activation in the muffle furnace is carried out at a temperature of 300-600℃ for 0.5-3 h; in step 3), the solvothermal reaction temperature is 120-180℃ for 6-24 h; in step 2), the molar ratio of manganese salt to nickel salt is 3-8:1, and the air flow rate is 10-90 mL / min; in step 4), the heat treatment temperature is 300-500℃, and the holding time is 1-5 h.

3. The method for preparing a nickel oxide-doped manganese dioxide catalyst according to claim 1, characterized in that, The manganese salt is manganese nitrate tetrahydrate, potassium permanganate, manganese chloride, manganese acetylacetonate, or manganese sulfate; the nickel salt is nickel chloride, nickel acetylacetonate, or nickel nitrate hexahydrate.

4. A nickel oxide-doped manganese dioxide catalyst, characterized in that, It is prepared by the preparation method described in any one of claims 1-3.

5. The application of the nickel oxide-doped manganese dioxide catalyst as described in claim 4 in the electrocatalytic oxidation to produce aromatic aldehydes, characterized in that, Using aromatic compound (a) as the reaction substrate, a flow-type diaphragm electrolyzer was employed during constant current electrolysis. The current was controlled by an electrochemical workstation. The anode and cathode chambers of the flow-type diaphragm electrolyzer were separated by an ion-exchange membrane. A nickel oxide-doped manganese dioxide catalyst electrode was used as the anode electrode. Aromatic compound (a) was dissolved in an acidic solution as the anolyte. A cathode electrode was set in the cathode chamber, and an acidic solution was used as the cathode solution. The constant current electrolysis reaction was carried out for 0.5-3 h. After the reaction, the anolyte was post-treated to obtain product (b). The reaction equation is as follows: ； In the formula, R1 on the intermediate is a group with a benzene ring and R2 is hydrogen.

6. The application of the nickel oxide-doped manganese dioxide catalyst according to claim 5 in the electrocatalytic oxidation to produce aromatic aldehydes, characterized in that, The primary solvent of the acidic solutions used for the anode and cathode is hydrochloric acid solution, sulfuric acid solution, nitric acid solution, acetic acid, phosphoric acid, methanesulfonic acid solution or perchloric acid solution, with a concentration of 0.05-2.0 mol / L; the secondary solvent in the anode chamber is one of tetrahydrofuran, dichloromethane, acetonitrile or acetone, and the volume ratio of the primary solvent to the secondary solvent is 3:7-7:

3.

7. The application of the nickel oxide-doped manganese dioxide catalyst according to claim 5 in the electrocatalytic oxidation to produce aromatic aldehydes, characterized in that, The concentration of aromatic compounds in the anolyte is 10-50 mmol / L.

8. The application of the nickel oxide-doped manganese dioxide catalyst according to claim 5 in the electrocatalytic oxidation to produce aromatic aldehydes, characterized in that, During constant current electrolysis, the current density is 20-200 mA / cm2; the cathode electrode is carbon felt; during constant current electrolysis, the pH of the anolyte is 0-4; the temperature of the constant temperature water bath is 30-70 °C, the cell voltage is 1-10 V, and the reaction time is 0.5-3 h.

9. The application of the nickel oxide-doped manganese dioxide catalyst according to claim 5 in the electrocatalytic oxidation to produce aromatic aldehydes, characterized in that, After the reaction, the post-treatment of the anolyte is as follows: After the electro-oxidation reaction, the reaction solution is first neutralized with 0.5 M sodium hydroxide solution and the pH is adjusted to neutral; then, the solution is transferred to a separatory funnel, an organic solvent is added for extraction to obtain an organic phase extract, and then the organic phase extract is distilled to obtain the target product; the organic solvent used for extraction is ethyl acetate, toluene, dichloromethane, trichloromethane or carbon tetrachloride.

10. The application of the nickel oxide-doped manganese dioxide catalyst according to claim 5 in the electrocatalytic oxidation to produce aromatic aldehydes, characterized in that, The nickel oxide-doped manganese dioxide catalyst electrode is prepared by in-situ growth of the nickel oxide-doped manganese dioxide catalyst on a carbon felt substrate using a solvothermal method. The loading of the nickel oxide-doped manganese dioxide catalyst on the carbon felt is 10-20 mg / cm³. 2 .

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