Defective manganese oxide catalyst as well as preparation method and application thereof

Abstract

The invention discloses a defective manganese oxide catalyst as well as a preparation method and application thereof, and belongs to the technical field of catalyst preparation. According to the invention, potassium permanganate or manganous nitrate is used as a manganese source, and in the process of converting the manganese source into manganese dioxide by means of hydrothermal reaction, a surfactant hexamethylenetetramine is added into a reaction system and is subjected to hydrothermal reaction with the manganese source, so that the defect content of manganese dioxide generated by hydrothermal reaction is increased; defective manganese oxide catalysts with different crystal forms are prepared; the prepared defective manganese oxide catalyst has good electro-catalytic reaction activity, can realize amide synthesis under mild conditions when being applied to a reaction for synthesizing amide by electro-catalytic alcohol oxidative coupling ammonia, overcomes the defects of high temperature and high pressure, high energy consumption and the like in the traditional industrial synthesis of amide, is green and environment-friendly in production process, and is suitable for industrial production. The actual application requirements of actual amide electrosynthesis are met.

Description

Technical Field

[0001] The present invention specifically relates to a defective manganese oxide catalyst and a preparation method and application thereof, belonging to the technical field of catalyst preparation. Background Art

[0002] Amides, an important class of compounds in medicine, chemistry, and biology, have been extensively studied over the past few decades. Formamide, a representative product, is widely used in dyes, pharmaceuticals, pesticides, and organic synthesis. However, the current industrial synthesis of amides is typically achieved through traditional thermal catalysis under harsh conditions such as high temperature and pressure. This results in high energy consumption and complex products, exacerbating energy and environmental issues.

[0003] The electrochemical CN coupling reaction for the synthesis of amides driven by renewable energy is currently attracting increasing attention due to its environmentally friendly, energy-efficient, and environmentally friendly synthetic routes. However, conventional electrochemical CN coupling reactions typically use carbon-containing small molecules such as CO and CO₂, and nitrogen-containing small molecules such as nitrogen oxides, as carbon and nitrogen sources, respectively, for the electrochemical synthesis of methylamine, formamide, and acetamide. Although this approach offers advantages over traditional amide synthesis routes, the electrochemical CN coupling reaction primarily focuses on the electroreduction reaction to form the CN bond. The slow anodic oxygen evolution reaction not only requires a high overpotential but also produces low-value oxygen, significantly reducing its economic viability. Therefore, the electrochemical CN coupling strategy of amides using alcohols and ammonia as substrates instead of nitrogen- and carbon-containing small molecules would provide a new, economically viable approach. In this approach, alcohols undergo oxidation at the anode to form intermediates such as aldehydes or ketones. Simultaneously, ammonia undergoes reduction at the cathode to form amino intermediates. These intermediates undergo coupling reactions on the electrode surface or in solution to form amide bonds, ultimately yielding the amides. This strategy not only enables high-value amide synthesis on the anode side, but also allows the incorporation of hydrogen evolution or other reduction reactions on the cathode side to improve electron utilization. However, the development of anode catalysts with excellent activity remains an urgent problem. Summary of the Invention

[0004] In response to existing problems, the present invention discloses a defective manganese oxide catalyst, a preparation method and an application thereof. The present invention constructs manganese oxides of different crystal phases by means of a hydrothermal reaction, and increases the formation of manganese oxide defects by adding a surfactant. The prepared defective manganese oxide catalysts have good electrocatalytic reaction activity and are applied in the electrocatalytic oxidative coupling of alcohols with ammonia to synthesize amides. The synthesis of amides can be achieved under mild conditions, overcoming the shortcomings of traditional industrial amide synthesis, such as the need for high temperature, high pressure and high energy consumption. The production process is green and environmentally friendly, meeting the actual application needs of actual amide electrosynthesis.

[0005] The technical solutions of the present invention are as follows: The present invention provides a defective manganese oxide catalyst, which is manganese dioxide with oxygen vacancy defects. The crystal form of the manganese dioxide with oxygen vacancy defects includes but is not limited to α-type, β-type, γ-type, and δ-type.

[0006] The present invention also provides a method for preparing a defective manganese oxide catalyst. The preparation method uses potassium permanganate or manganese nitrate as a manganese source for preparing the defective manganese oxide. During the process of converting the manganese source into manganese dioxide by a hydrothermal reaction, a surfactant hexamethylenetetramine is added to the reaction system and hydrothermally reacted with the manganese source, thereby increasing the defect content of the manganese dioxide generated by the hydrothermal reaction, thereby preparing the defective manganese oxide catalyst.

[0007] Furthermore, the preparation of the defective manganese oxide catalyst can be carried out according to the following steps: dissolving 6~10 mmol potassium permanganate in water, dripping the obtained solution into a mixed solution consisting of 1~2 mol / L nitric acid and 3~6 mmol / L manganese nitrate and stirring it thoroughly at room temperature, then adding 0.01~0.1 mmol hexamethylenetetramine to the solution and continuing to stir, then reacting the obtained mixed solution at 80~90°C for 4~6 hours, cooling to room temperature, and then centrifuging and drying to obtain a black powder to prepare the defective manganese oxide catalyst, which is α-MnO2 with oxygen vacancy defects.

[0008] Furthermore, the preparation of the defective manganese oxide catalyst can be carried out according to the following steps: dissolving 3-5 mmol manganese nitrate in water, adding a potassium permanganate solution with a concentration of 1-3 mmol / L dropwise thereto and stirring thoroughly at room temperature, then adding 0.01-0.1 mmol hexamethylenetetramine and continuing to stir, then reacting the resulting mixed solution at 220-240 ° C for 6-12 hours, cooling to room temperature, and then centrifuging and drying to obtain a black powder to prepare the defective manganese oxide catalyst, which is β-MnO2 with oxygen vacancy defects.

[0009] Furthermore, the preparation of the defective manganese oxide catalyst can be carried out according to the following steps: dissolving 3-5 mmol manganese nitrate in water, adding 1-3 mmol / L potassium permanganate solution dropwise thereto and stirring thoroughly at room temperature, further adding 0.01-0.1 mmol hexamethylenetetramine thereto and continuing stirring, then reacting the resulting mixture at 160-180 ° C for 6-12 hours, then cooling to room temperature and centrifuging and drying to obtain a black powder, thereby preparing the defective manganese oxide catalyst, which is γ-MnO2 with oxygen vacancy defects.

[0010] Furthermore, the preparation of the defective manganese oxide catalyst can be carried out according to the following steps: 2~4 mmol potassium permanganate and 2~4 mmol ammonium chloride are dissolved in water and fully stirred, and then 0.01~0.1 mmol hexamethylenetetramine is added thereto and continued stirring, and then the resulting mixture is reacted at 120~140°C for 18~24 hours, and then cooled to room temperature and centrifuged and dried to obtain a black powder to prepare the defective manganese oxide catalyst, which is δ-MnO2 with oxygen vacancy defects.

[0011] The defective manganese oxide catalyst provided by the present invention can be used in the electrocatalytic oxidative coupling reaction of alcohol and ammonia to synthesize amide.

[0012] Furthermore, the defective manganese oxide catalyst can be made into a defective manganese oxide electrode and used as an anode in the electrocatalytic oxidative coupling reaction of alcohol to ammonia to synthesize amide. The defective manganese oxide electrode is prepared according to the following steps: The defective manganese oxide is dispersed in a mixed solution of isopropyl alcohol and water to obtain a defective manganese oxide slurry, and the defective manganese oxide slurry is evenly sprayed on the surface of carbon paper to obtain a defective manganese oxide electrode.

[0013] Furthermore, the ratio of isopropyl alcohol to water in the isopropyl alcohol and water mixed solution is 3:1 to 1:1.

[0014] Furthermore, the concentration of the defective manganese oxide in the defective manganese oxide slurry is 1-10 mg / mL.

[0015] Furthermore, the loading amount of defective manganese oxide on the surface of the carbon paper in the defective manganese oxide electrode is 0.1-2 mg cm -2 .

[0016] Furthermore, the electrocatalytic oxidative coupling of alcohol with ammonia to synthesize amide uses alcohol and aqueous ammonia as reaction substrates, wherein the alcohol includes methanol, ethanol or glycerol.

[0017] Different from the prior art, the present invention has the following beneficial effects: 1. The present invention provides a method for preparing a defective manganese oxide catalyst, wherein potassium permanganate or manganese nitrate is used as a manganese source. During the process of converting the manganese source into manganese dioxide by a hydrothermal reaction, hexamethylenetetramine is added to the reaction system and reacted with the manganese source under hydrothermal conditions to prepare the defective manganese oxide catalyst. In this preparation method, the addition of hexamethylenetetramine not only serves as a means of regulating the surface defects of manganese dioxide, changing the electron density of oxygen atoms around the surface of the generated manganese dioxide, reducing the oxygen vacancy formation energy, and in situ promoting the formation of oxygen vacancy defects in manganese dioxide, but also serves as a dispersant to improve the water dispersibility of the manganese dioxide formed by the reaction during the hydrothermal process, effectively reducing the size of the formed manganese dioxide crystals, promoting the exposure of defects and improving the catalytic activity. Therefore, the catalyst prepared by the present invention has good electrochemical activity and stability. At the same time, by regulating the type and amount of raw materials, hydrothermal temperature, and hydrothermal time in the hydrothermal conditions, the preparation method of the present invention is also applicable to the preparation of defective manganese oxides with different crystal structures, which also makes the catalyst prepared by the preparation method of the present invention have an excellent adjustable structure.

[0018] 2. The defective manganese oxide catalyst provided by the present invention is well applied in the electrocatalytic oxidative coupling of alcohol to ammonia synthesis of amide reaction, showing the advantages of controllable electrocatalysis, low energy consumption, mild reaction conditions, etc., and can realize the synthesis of amide under mild conditions, overcoming the shortcomings of traditional industrial synthesis of amide requiring high temperature and high pressure and high energy consumption. The production process is green and environmentally friendly. In the electrocatalytic oxidative coupling of alcohol to ammonia synthesis of amide reaction, when the selected alcohol substrate is methanol or glycerol, the present invention can realize the synthesis of formamide, and when the alcohol substrate is ethanol, the present invention can synthesize acetamide. The catalyst of the present invention has broad substrate applicability. By changing the alcohol substrate, the present invention can realize the synthesis of various amide compounds, which meets the practical application needs of amide electrosynthesis. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 These are the XRD patterns of defective manganese oxides of different crystal forms in Examples 1, 4, 7, and 10.

[0020] Figure 2 The XPS spectra of defective manganese oxides of different crystal forms in Examples 1, 4, 7, and 10 are shown.

[0021] Figure 3 The reaction activity and Faradaic efficiency of the defective manganese oxide catalysts in Application Examples 1 to 4 for the electrocatalytic oxidative coupling of alcohols with ammonia to formamide are shown.

[0022] Figure 4 The reaction activity and Faradaic efficiency of the defective manganese oxide catalysts in Application Examples 5-9 for the electrocatalytic oxidative coupling of alcohols with ammonia to synthesize amides are shown. DETAILED DESCRIPTION

[0023] The present invention will be further described below in conjunction with the accompanying drawings and preferred embodiments. The given embodiments are only for illustrating the present invention, rather than for limiting the scope of the present invention.

[0024] Unless otherwise specified, the materials, reagents, etc. used in the following examples can be obtained from commercial sources; the methods in the following examples are conventional methods unless otherwise specified.

[0025] Example 1 This embodiment provides a method for preparing a defective manganese oxide catalyst, comprising the following steps: (1) Dissolve 9 mmol KMnO4 in 25 mL of water and add it dropwise to a 25 mL mixed solution of 2 M HNO3 and 6 mM Mn(NO3)2. The mixture is then stirred at room temperature for 0.5 h. (2) After that, 0.03 mmol of hexamethylenetetramine was further added and stirring was continued for 0.5 h; (3) The solution obtained in step (2) was further transferred to a vial and stirred at 85 °C for 6 hours; (4) After the reaction solution obtained in step (3) is cooled to room temperature, the solution is centrifuged to obtain a black powder, which is then fully washed with deionized water and dried at 80° C. overnight to obtain a defective manganese oxide catalyst.

[0026] The defective manganese oxide catalyst prepared is manganese oxide α-MnO2-O with oxygen vacancy defects. v .

[0027] Example 2 This embodiment provides a method for preparing a defective manganese oxide catalyst, comprising the following specific steps: (1) Dissolve 6 mmol KMnO4 in 25 mL water and add it dropwise to a 25 mL mixed solution of 1.5 M HNO3 and 5 mM Mn(NO3)2. The mixture is then stirred at room temperature for 0.5 h. (2) further adding 0.01 mmol of hexamethylenetetramine and continuing stirring for 0.5 hours; (3) The solution obtained in step (2) was further transferred to a vial and stirred at 80°C for 4 hours; (4) After the reaction solution obtained in step (3) is cooled to room temperature, the solution is centrifuged to obtain a black powder, which is then fully washed with deionized water and dried at 80° C. overnight to obtain a defective manganese oxide catalyst.

[0028] The defective manganese oxide catalyst prepared is manganese oxide α-MnO2-O with oxygen vacancy defects. v .

[0029] Example 3 This embodiment provides a method for preparing a defective manganese oxide catalyst, comprising the following specific steps: (1) Dissolve 10 mmol of KMnO4 in 25 mL of water and dropwise add it into a 25 mL mixed solution of 1 M HNO3 and 3 mM Mn(NO3)2. The mixture is then stirred at room temperature for 0.5 h. (2) further adding 0.1 mmol of hexamethylenetetramine and continuing stirring for 0.5 hours; (3) The solution obtained in step (2) was further transferred to a vial and stirred at 90 °C for 6 hours; (4) After the reaction solution obtained in step (3) is cooled to room temperature, the solution is centrifuged to obtain a black powder, which is then fully washed with deionized water and dried at 80° C. overnight to obtain a defective manganese oxide catalyst.

[0030] The defective manganese oxide catalyst prepared is manganese oxide α-MnO2-O with oxygen vacancy defects. v .

[0031] Example 4 This embodiment provides a method for preparing a defective manganese oxide catalyst, comprising the following specific steps: (1) Dissolve 3 mmol Mn(NO3)2 in water (25 mL) and add dropwise to 25 mL 3 mM KMnO4 solution. Then, stir the mixed solution at room temperature for 0.5 h.

[0032] (2) Thereafter, 0.03 mmol of hexamethylenetetramine was further added and stirring was continued for 0.5 hour.

[0033] (3) The solution obtained in step (2) was transferred to a polytetrafluoroethylene reactor and subjected to a hydrothermal reaction at 240 °C for 6 hours.

[0034] (4) After the reaction solution obtained in step (3) is cooled to room temperature, the solution is centrifuged to obtain a black powder, which is then washed with deionized water and dried at 80°C overnight to obtain a defective manganese oxide catalyst.

[0035] The defective manganese oxide catalyst prepared is manganese oxide β-MnO2-O with oxygen vacancy defects. v .

[0036] Example 5 This embodiment provides a method for preparing a defective manganese oxide catalyst, comprising the following specific steps: (1) Dissolve 5 mmol Mn(NO3)2 in water (25 mL) and add dropwise to 25 mL 1 mM KMnO4 solution. Then, stir the mixed solution at room temperature for 0.5 h.

[0037] (2) Thereafter, 0.01 mmol of hexamethylenetetramine was further added and stirring was continued for 0.5 hour.

[0038] (3) The solution obtained in step (2) was transferred to a polytetrafluoroethylene reactor and subjected to a hydrothermal reaction at 220 °C for 6 hours.

[0039] (4) After the reaction solution obtained in step (3) is cooled to room temperature, the solution is centrifuged to obtain a black powder, which is then washed with deionized water and dried at 80°C overnight to obtain a defective manganese oxide catalyst.

[0040] The defective manganese oxide catalyst prepared is manganese oxide β-MnO2-O with oxygen vacancy defects. v .

[0041] Example 6 This embodiment provides a method for preparing a defective manganese oxide catalyst, comprising the following specific steps: (1) Dissolve 4 mmol Mn(NO3)2 in water (25 mL) and add dropwise to 25 mL 2 mM KMnO4 solution. Then, stir the mixed solution at room temperature for 0.5 h.

[0042] (2) Thereafter, 0.1 mmol of hexamethylenetetramine was further added and stirring was continued for 0.5 hours.

[0043] (3) The solution obtained in step (2) was transferred to a polytetrafluoroethylene reactor and subjected to a hydrothermal reaction at 230 °C for 6 to 12 hours.

[0044] (4) After the reaction solution obtained in step (3) is cooled to room temperature, the solution is centrifuged to obtain a black powder, which is then washed with deionized water and dried at 80°C overnight to obtain a defective manganese oxide catalyst.

[0045] The defective manganese oxide catalyst prepared is manganese oxide β-MnO2-O with oxygen vacancy defects. v .

[0046] Example 7 This embodiment provides a method for preparing a defective manganese oxide catalyst, comprising the following specific steps: (1) Dissolve 3 mmol Mn(NO3)2 in water (25 mL) and add dropwise to 25 mL 2 mM KMnO4 solution. Then, stir the mixed solution at room temperature for 0.5 h.

[0047] (2) Thereafter, 0.03 mmol of hexamethylenetetramine was further added and stirring was continued for 0.5 hour.

[0048] (3) The solution obtained in step (2) was transferred to a polytetrafluoroethylene reactor and subjected to a hydrothermal reaction at 160 °C for 6 hours.

[0049] (4) After the reaction solution obtained in step (3) is cooled to room temperature, the solution is centrifuged to obtain a black powder, which is then washed with deionized water and dried at 80°C overnight to obtain a defective manganese oxide catalyst.

[0050] The defective manganese oxide catalyst prepared is manganese oxide γ-MnO2-O with oxygen vacancy defects. v .

[0051] Example 8 This embodiment provides a method for preparing a defective manganese oxide catalyst, comprising the following specific steps: (1) Dissolve 4 mmol Mn(NO3)2 in water (25 mL) and add dropwise to 25 mL 3 mM KMnO4 solution. Then, stir the mixed solution at room temperature for 0.5 h.

[0052] (2) Thereafter, 0.01 mmol of hexamethylenetetramine was further added and stirring was continued for 0.5 hour.

[0053] (3) The solution obtained in step (2) was transferred to a polytetrafluoroethylene reactor and subjected to a hydrothermal reaction at 170 °C for 10 hours.

[0054] (4) After the reaction solution obtained in step (3) is cooled to room temperature, the solution is centrifuged to obtain a black powder, which is then washed with deionized water and dried at 80°C overnight to obtain a defective manganese oxide catalyst.

[0055] The defective manganese oxide catalyst prepared is manganese oxide γ-MnO2-O with oxygen vacancy defects. v .

[0056] Example 9 This embodiment provides a method for preparing a defective manganese oxide catalyst, comprising the following specific steps: (1) Dissolve 3 mmol Mn(NO3)2 in water (25 mL) and add dropwise to 25 mL 1 mM KMnO4 solution. Then, stir the mixed solution at room temperature for 0.5 h.

[0057] (2) Thereafter, 0.1 mmol of hexamethylenetetramine was further added and stirring was continued for 0.5 hours.

[0058] (3) The solution obtained in step (2) was transferred to a polytetrafluoroethylene reactor and subjected to a hydrothermal reaction at 180 °C for 12 hours.

[0059] (4) After the reaction solution obtained in step (3) is cooled to room temperature, the solution is centrifuged to obtain a black powder, which is then washed with deionized water and dried at 80°C overnight to obtain a defective manganese oxide catalyst.

[0060] The defective manganese oxide catalyst prepared is manganese oxide γ-MnO2-O with oxygen vacancy defects. v .

[0061] Example 10 This embodiment provides a method for preparing a defective manganese oxide catalyst, comprising the following specific steps: (1) Dissolve 2 mmol KMnO4 and 2 mmol NH4Cl in 35 mL water and stir for 0.5 h.

[0062] (2) Thereafter, 0.03 mmol of hexamethylenetetramine was further added and stirring was continued for 0.5 hour.

[0063] (3) The solution obtained in step (2) was transferred to a polytetrafluoroethylene reactor and reacted at 120 °C for 24 hours.

[0064] (4) After the reaction solution obtained in step (3) is cooled to room temperature, the solution is centrifuged to obtain a black powder, which is then washed with deionized water and dried at 80°C overnight to obtain a defective manganese oxide catalyst.

[0065] The defective manganese oxide catalyst prepared is manganese oxide δ-MnO2-O with oxygen vacancy defects. v .

[0066] Example 11 This embodiment provides a method for preparing a defective manganese oxide catalyst, comprising the following specific steps: (1) Dissolve 3 mmol KMnO4 and 3 mmol NH4Cl in 35 mL water and stir for 0.5 h; (2) After that, 0.01 mmol of hexamethylenetetramine was further added and stirring was continued for 0.5 hours; (3) Transfer the solution obtained in step (2) to a polytetrafluoroethylene reactor and react at 140 °C for 18 hours; (4) After the reaction solution obtained in step (3) is cooled to room temperature, the solution is centrifuged to obtain a black powder, which is then washed with deionized water and dried at 80°C overnight to obtain a defective manganese oxide catalyst.

[0067] The defective manganese oxide catalyst prepared is manganese oxide δ-MnO2-O with oxygen vacancy defects. v .

[0068] Example 12 This embodiment provides a method for preparing a defective manganese oxide catalyst, comprising the following specific steps: (1) Dissolve 4 mmol KMnO4 and 4 mmol NH4Cl in 35 mL water and stir for 0.5 h; (2) After that, 0.1 mmol of hexamethylenetetramine was further added and stirring was continued for 0.5 h; (3) Transfer the solution obtained in step (2) to a polytetrafluoroethylene reactor and react at 130 °C for 24 hours; (4) After the reaction solution obtained in step (3) is cooled to room temperature, the solution is centrifuged to obtain a black powder, which is then washed with deionized water and dried at 80°C overnight to obtain a defective manganese oxide catalyst.

[0069] The defective manganese oxide catalyst prepared is manganese oxide δ-MnO2-O with oxygen vacancy defects. v .

[0070] Application Example 1 In this application example, the α-MnO2-O v Defective manganese oxides are used in the electrocatalytic oxidative coupling of alcohols with ammonia to synthesize amides. The reaction process includes the following steps: S1, take 10 mg α-MnO2-O v The catalyst powder was dispersed into a mixed solution of 5 mL of isopropanol and water, where the ratio of isopropanol to water was 3:1. 40 μL of Nafion was further added and ultrasonicated for 0.5 h to obtain α-MnO2-O with a concentration of 2 mg / mL. v The prepared α-MnO2-Ov slurry was then evenly sprayed on the treated carbon paper surface with a coating area of ​​1 cm 2 , the catalyst loading was 0.5 mg, and α-MnO2-O v electrode; S2, and then the prepared α-MnO2-O v The electrode was used as the anode, and the electrocatalytic oxidative coupling of alcohol to ammonia to synthesize amide was carried out using a single-chamber electrolytic cell and a three-electrode system. The electrolyte composition was 60 mL of 1 M sodium bicarbonate solution and 15 mL of a mixed solution of methanol and ammonia water, wherein the volume ratio of methanol to ammonia water was 4:1. At 120 mA cm -2 The electrochemical tests were carried out in a constant current density range.

[0071] Application Example 2 This application example follows the same steps and conditions as application example 1 to prepare the β-MnO2-O v Defective manganese oxides are used in the electrocatalytic oxidative coupling of alcohols with ammonia to synthesize amides.

[0072] Application Example 3 This application example follows the same steps and conditions as application example 1 to prepare the γ-MnO2-O v Defective manganese oxides are used in the electrocatalytic oxidative coupling of alcohols with ammonia to synthesize amides.

[0073] Application Example 4 This application example follows the same steps and conditions as application example 1 to prepare the δ-MnO2-O v Defective manganese oxides are used in the electrocatalytic oxidative coupling of alcohols with ammonia to synthesize amides.

[0074] Application Example 5 In this application example, the β-MnO2-O v The application of defective manganese oxide in the electrocatalytic oxidative coupling of alcohols with ammonia to synthesize amides is different from Application Example 2 in that: In the electrocatalytic oxidative coupling reaction of alcohol to ammonia to synthesize amide, the ratio of methanol to ammonia water is different, and the volume ratio of methanol to ammonia water is 3:2. The remaining conditions and steps are the same as those in Application Example 2 and are not repeated here.

[0075] Application Example 6 In this application example, the β-MnO2-O v The application of defective manganese oxide in the electrocatalytic oxidative coupling of alcohols with ammonia to synthesize amides is different from Application Example 2 in that: In the electrocatalytic oxidative coupling reaction of alcohol to ammonia to synthesize amide, the ratio of methanol to ammonia water is different, that is, the volume ratio of methanol to ammonia water is 3:2. The remaining conditions and steps are the same as those in Application Example 2 and are not repeated here.

[0076] Application Example 7 In this application example, the β-MnO2-O v The application of defective manganese oxide in the electrocatalytic oxidative coupling of alcohols with ammonia to synthesize amides is different from Application Example 2 in that: In the electrocatalytic oxidative coupling reaction of alcohol to ammonia to synthesize amide, the ratio of methanol to ammonia water is different, and the volume ratio of methanol to ammonia water is 1:1. The remaining conditions and steps are the same as those in Application Example 2 and are not repeated here.

[0077] Application Example 8 In this application example, the β-MnO2-O v The application of defective manganese oxide in the electrocatalytic oxidative coupling of alcohols with ammonia to synthesize amides is different from Application Example 2 in that: In the electrocatalytic oxidative coupling reaction of alcohol to ammonia to synthesize amide, the ratio of methanol to ammonia water is different, that is, the volume ratio of methanol to ammonia water is 2:3. The remaining conditions and steps are the same as those in Application Example 2 and are not repeated here.

[0078] Application Example 9 In this application example, the β-MnO2-O v The application of defective manganese oxide in the electrocatalytic oxidative coupling of alcohols with ammonia to synthesize amides is different from Application Example 2 in that: In the electrocatalytic oxidative coupling reaction of alcohol to ammonia to synthesize amide, the ratio of methanol to ammonia water is different, and the volume ratio of methanol to ammonia water is 1:4. The remaining conditions and steps are the same as those in Application Example 2 and are not repeated here.

[0079] Performance Testing Figure 1 From the X-ray powder diffraction patterns (XRD) of defective manganese oxide catalyst samples of different crystal forms prepared by the preparation methods provided in Examples 1, 4, 7, and 10 of the present invention, it can be found that the preparation method provided by the present invention successfully prepared manganese oxide catalysts of different crystal phases.

[0080] Figure 2 X-ray photoelectron spectroscopy (XPS) of defective manganese oxide catalysts of different crystalline forms prepared by the preparation methods provided in Examples 1, 4, 7, and 10 of the present invention. The XPS results show that the Mn 2p 3 / 2 In the spectrum ( Figure 2 a), there are three peaks at 642.7 eV, 641.7 eV and 640.4 eV, which are respectively attributed to Mn 4+ 、Mn 3+ and Mn 2+ After further Gaussian fitting calculation, the surface of MnO2 is unsaturated with low-valent Mn (Mn 2+ and Mn 3+ The average proportions of β-MnO2-O v (0.85)>γ-MnO2-Ov. In addition, in the O 1s spectrum ( Figure 2 b), the peaks at 532.8 eV, 531.0 eV, and 529.4 eV can be attributed to the surface hydroxyl oxygen (O OH ), surface adsorbed oxygen (O ads ) and lattice oxygen (O latt ). Calculate various MnO2-O v O ads / O latt It is worth noting that β-MnO2-O v O ads The highest content (O ads / O latt is 0.44), followed by γ-MnO2-O v (0.39), δ-MnO2-O v , according to the unsaturated Mn and O ads It can be concluded that the content of α-MnO2-O v ,γ-MnO2-O v and δ-MnO2-O v Compared with β-MnO2-O v With higher oxygen vacancies (O v )content.

[0081] Figure 3 The electrocatalytic synthesis reaction was carried out using a single-chamber electrolytic cell and a three-electrode system. The electrolyte was a mixed solution of 60 mL of 1 M sodium bicarbonate solution and 15 mL of methanol and ammonia water, wherein the volume ratio of methanol to ammonia water was 1:4. The reaction was carried out at 120 mA cm -2 The activity test found that all defective manganese oxide catalysts can effectively promote the improvement of electrocatalytic performance, and the optimal β-MnO2-O v The catalyst showed a 265 μmol h -1 mg cat. -1 The yield of formamide was 0.01% and the Faradaic efficiency was 26%.

[0082] Figure 4 For β-MnO2-O in Application Examples 5~9 v The reaction activity and Faraday efficiency of the electrocatalytic oxidative coupling of alcohol to ammonia to synthesize amide were statistically analyzed under different substrate ratios. The test results showed that the β-MnO2-Ov catalyst had the best formamide synthesis performance when the volume ratio of methanol to ammonia was 1:4.

[0083] In summary, thanks to the defect construction of manganese dioxide by hexamethylenetetramine, the present invention successfully prepared defective manganese oxide catalysts of different crystal forms. This defect structure gives the catalyst good catalytic performance and can achieve the synthesis of amides under mild conditions, effectively overcoming the shortcomings of traditional industrial synthesis of amides requiring high temperature, high pressure and high energy consumption. In addition to the methanol used in the above application examples, this defect structure also enables the catalyst of the present invention to perform well in the electrocatalytic oxidation of other alcohols such as ethanol and glycerol. By replacing the methanol used in steps S2 of the above application examples 1 to 4 with glycerol or ethanol, the present invention can also achieve the electrochemical synthesis of formamide or acetamide. The catalyst of the present invention has broad substrate applicability. By changing the alcohol substrate used in the reaction, the present invention can achieve the electrochemical synthesis of various amide compounds, which meets the practical application needs of amide electrosynthesis.

[0084] The above-mentioned embodiments and application examples are all preferred implementation methods of the present invention, but the implementation methods of the present invention are not limited to the above-mentioned embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of this patent should be considered as equivalent replacement methods and are included in the scope of protection of this patent.

Claims

1. A method for preparing a defective manganese oxide catalyst, using potassium permanganate or manganese nitrate as a manganese source and converting the manganese source into manganese dioxide by a hydrothermal reaction, characterized in that: The defective manganese oxide catalyst is prepared by adding hexamethylenetetramine and performing a hydrothermal reaction with a manganese source, thereby increasing the defect content of the manganese dioxide generated by the hydrothermal reaction.

2. The method for preparing a defective manganese oxide catalyst according to claim 1, wherein: The specific steps include: 6-10 mmol potassium permanganate is dissolved in water, and the resulting solution is added dropwise to a mixed solution consisting of 1-2 mol / L nitric acid and 3-6 mmol / L manganese nitrate and fully stirred at room temperature. 0.01-0.1 mmol hexamethylenetetramine is then added to the solution and stirred continuously. The resulting mixed solution is then reacted at 80-90°C for 4-6 hours, cooled to room temperature, centrifuged, and dried to obtain a black powder, thereby preparing the defective manganese oxide catalyst.

3. The method for preparing a defective manganese oxide catalyst according to claim 1, wherein: The specific steps include: 3-5 mmol manganese nitrate is dissolved in water, and a potassium permanganate solution with a concentration of 1-3 mmol / L is added dropwise thereto and stirred thoroughly at room temperature. Then, 0.01-0.1 mmol hexamethylenetetramine is added and stirred continuously. The resulting mixed solution is then reacted at 220-240°C for 6-12 hours, cooled to room temperature, centrifuged, and dried to obtain a black powder, thereby preparing the defective manganese oxide catalyst.

4. The method for preparing a defective manganese oxide catalyst according to claim 1, wherein: The specific steps include: 3-5 mmol manganese nitrate is dissolved in water, 1-3 mmol / L potassium permanganate solution is added dropwise thereto and stirred thoroughly at room temperature, 0.01-0.1 mmol hexamethylenetetramine is further added thereto and stirred continuously, and the resulting mixture is reacted at 160-180°C for 6-12 hours, cooled to room temperature, centrifuged, and dried to obtain a black powder, thereby preparing the defective manganese oxide catalyst.

5. The method for preparing a defective manganese oxide catalyst according to claim 1, wherein: The specific steps include: 2-4 mmol potassium permanganate and 2-4 mmol ammonium chloride were dissolved in water and stirred thoroughly. 0.01-0.1 mmol hexamethylenetetramine was then added and stirred continuously. The resulting mixture was then reacted at 120-140 °C for 18-24 h, cooled to room temperature, centrifuged, and dried to obtain a black powder, thereby preparing the defective manganese oxide catalyst.

6. A defective manganese oxide catalyst, characterized in that The defective manganese oxide catalyst is prepared by the preparation method of the defective manganese oxide catalyst according to any one of claims 1 to 5.

7. The defective manganese oxide catalyst according to claim 6, characterized in that The defective manganese oxide catalyst is manganese dioxide with oxygen vacancy defects, and the crystal form of the manganese dioxide with oxygen vacancy defects includes but is not limited to α-type, β-type, γ-type, and δ-type.

8. Using the defective manganese oxide catalyst as claimed in claim 6 in the electrocatalytic oxidative coupling reaction of alcohols and ammonia to synthesize amides.

9. The use of the defective manganese oxide catalyst according to claim 8, characterized in that: The defective manganese oxide catalyst is prepared into a defective manganese oxide electrode and used as an anode in the electrocatalytic oxidative coupling reaction of alcohol to ammonia to synthesize amide. The defective manganese oxide electrode is prepared according to the following steps: The defective manganese oxide catalyst is dispersed in a mixed solution of isopropyl alcohol and water to prepare a defective manganese oxide slurry, and the defective manganese oxide slurry is evenly sprayed on the surface of carbon paper to prepare a defective manganese oxide electrode.

10. The use of the defective manganese oxide catalyst according to claim 8, characterized in that: The electrocatalytic oxidative coupling reaction of alcohol to ammonia to synthesize amide uses alcohol and ammonia water as reaction substrates, wherein the alcohol includes methanol, ethanol or glycerol.

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