Method for preparing diacetylmonoxime by electro-catalytic co-reduction of nitrate and butanone

Abstract

The invention discloses a method for preparing diacetylmonoxime through electro-catalytic co-reduction of nitrate and butanone, and the method comprises the following steps: an electrolyte comprises a nitrogen source and butanone, a palladium-based metal alloy aerogel catalyst is used as a cathode catalyst, and the diacetylmonoxime is prepared through electro-catalytic co-reduction of nitrate and butanone under the action of the cathode catalyst. According to the method provided by the invention, the palladium-based metal alloy aerogel catalyst is applied to a reaction for preparing diacetylmonoxime through electro-catalytic co-reduction of nitrate and butanone, so that side reactions such as hydrogen evolution and ammonia production are remarkably inhibited, the production of diacetylmonoxime is efficiently catalyzed, and the method has excellent electrochemical reduction performance and stability.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalysis, and particularly relates to a method for electrocatalytic co-reduction of nitrate and butanone to prepare butanone oxime. Background Art

[0002] Ketoxime is an important class of organic compounds and participates in many chemical industrial reactions. As an important organic synthesis intermediate, butanone oxime (C4H9NO) is also a highly active reagent with wide applications. It is mainly used in the production of products such as oxime-based silanes and hydroxylamines, as well as antioxidants, blocking agents, and corrosion inhibitors for oil-based coatings, and is widely used in fields such as medicine, agriculture, chemical industry, and electronics. Currently, the traditional industrial method for producing butanone oxime is the hydroxylamine method, with raw materials involving toxic gases such as sulfur dioxide, nitrogen oxide, and nitrogen dioxide, resulting in a high environmental pollution index and great harm to the human body in the long term. Moreover, the traditional production process of butanone oxime is long and complicated, with high energy consumption, and a large amount of low-value-added products such as ammonium sulfate and nitrogen oxides will accumulate, not only making the production process uneconomical but also exacerbating environmental pollution, and it is gradually being phased out. Compared with the traditional process, electrocatalytic co-reduction of nitrate and butanone to prepare butanone oxime is considered a feasible method for producing butanone oxime in one step under environmental conditions, with the dual advantages of environmental remediation and energy economy. It not only solves the problem of excessive nitrate emissions in surface water and underground aquifers caused by over-fertilization and industrial sewage, but also simply and efficiently prepares the urgently needed butanone oxime product in the industry.

[0003] For example, for the Zn-Cu alloy reported by Sharp et al., hydroxylamine was in-situ generated using nitrate to react with cyclohexanone, and the Faraday efficiency of synthesizing cyclohexanone oxime reached 27%; the Pd nanoparticles synthesized by Wu et al. achieved a Faraday efficiency of 29.24% for cyclohexanone oxime at a potential of -0.45 V; and for the cyclohexanone oxime synthesized by Sheng et al. using the high-entropy metalene PdCuAgBiIn to co-reduce nitrate and cyclohexanone, the highest Faraday efficiency was 47.6%. Research shows that noble metal-based catalysts with a three-dimensional structure having a high surface area, high conductivity, and a high ratio of unsaturated metal sites can significantly enhance the intrinsic catalytic activity, and at the same time can change the reaction pathway and improve the product selectivity. Noble metal palladium-based materials are considered to be the most promising electrocatalysts, which have good reactivity and high energy efficiency for electrochemical reduction reactions. However, metal palladium-based materials have problems such as low atomic utilization rate, large loading amount, and high cost, which hinder their large-scale industrial application. By hybridizing / combining other non-noble metal species to construct palladium-based metal alloy catalysts, the amount of noble metal palladium component can be effectively diluted, and the metal alloy structure of the catalyst has excellent tunability of elemental species and chemical components, showing unique physical and chemical properties, which has attracted extensive attention in recent years. So far, palladium-based metal alloy catalysts have been reported to be applied in electrocatalytic water splitting for hydrogen and oxygen evolution, carbon dioxide reduction, alcohol oxidation and other reactions. For example, the patent with publication number CN116603538B discloses a palladium-based alloy heteronanoflower catalyst, and the palladium-based alloy material is a PdM alloy, where the metal M is copper, iridium, manganese, chromium, platinum or ruthenium; the patent with publication number CN118299600A discloses a palladium-based ternary alloy nanocage catalyst (d / Ru / Cu octahedron ternary alloy nanocage); the patent with publication number CN119419299A discloses a platinum-palladium-based multi-alloy sub-nanobelt catalyst.

[0004] Although certain research progress has been made in the development of palladium-based metal alloy catalysts, their application as electrocatalysts for the electrocatalytic co-reduction of nitrate and butanone to prepare butanone oxime has not been developed and lacks in-depth research. In addition, the electrocatalytic co-reduction to prepare butanone oxime still faces problems such as low selectivity caused by over-reduction of hydroxylamine and poor stability of the catalyst itself. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for electrocatalytic co-reduction of nitrate and butanone to prepare butanone oxime, which significantly inhibits side reactions and realizes the efficient production of butanone oxime.

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

[0007] A method for electrocatalytic co - reduction of nitrate and butanone to prepare butanone oxime, the method comprising: in a three - electrode system, the electrolyte comprises a nitrogen source and butanone, and a palladium - based metal alloy aerogel catalyst is used as the working electrode to electrocatalytically co - reduce nitrate and butanone to prepare butanone oxime.

[0008] The preparation principle of the present invention is as follows: as a cathode catalyst, the palladium - based metal alloy aerogel electrocatalytically reduces nitrate to preferentially produce NH2OH rather than NH3, and the in - situ produced NH2OH further undergoes a nucleophilic addition reaction with butanone in the solution to form butanone oxime. The present invention realizes the electrochemical synthesis of butanone oxime through a palladium - based metal alloy aerogel catalyst. At the same time, the introduction of other heterogeneous metals can further regulate the electronic structure of the noble metal palladium, improve the electro - reduction activity and stability, and achieve the electro - synthesis of butanone oxime with high activity, high selectivity and high stability, which is of great significance for realizing large - scale electrochemical preparation of high - concentration butanone oxime.

[0009] In the present invention, the palladium - based metal catalyst is a metal alloy aerogel with a loose and porous network cross - linked structure.

[0010] The palladium - based metal alloy aerogel catalyst comprises palladium atoms and heterogeneous metal atoms that exist in the aerogel structure in a single - phase form. The heterogeneous metal is selected from one or more of tin, lead or indium. The molar proportion of palladium atoms in the palladium - based metal alloy aerogel catalyst is 22 - 90%.

[0011] Preferably, the molar proportion of palladium atoms in the palladium - based metal alloy aerogel catalyst is 56 - 83%. When the molar proportion of palladium atoms is 56 - 83%, it is beneficial to improve the selectivity and catalytic effect of the palladium - based metal alloy aerogel catalyst for electrocatalytic preparation of butanone oxime.

[0012] The preparation method of the palladium - based metal alloy aerogel catalyst comprises: mixing an inorganic mixed metal salt, sodium borohydride and ammonium fluoride in a solvent to obtain a precursor solution, and after standing, the product is washed and freeze - dried to obtain the palladium - based metal alloy aerogel catalyst; the inorganic mixed metal salt is a mixture of a metal palladium salt and other heterogeneous metal salts, and the heterogeneous metal is one or more of tin, lead, indium.

[0013] In the present invention, a specific palladium - based metal is selected to prepare a metal alloy aerogel. Sodium borohydride is used as a reducing agent and ammonium fluoride is used as an ion regulator to control the growth of the palladium - based metal alloy aerogel, resulting in the formation of an alloy aerogel with a spatial network structure. The palladium - based metal alloy aerogel catalyst exhibits excellent electrocatalytic activity and stability for the preparation of butanone oxime.

[0014] The molar ratio of the inorganic mixed metal salt, ammonium fluoride, and sodium borohydride is 1:5-15:20-50. Sodium borohydride is used to reduce the mixed metal salt, and at this dosage, it can ensure the complete reduction of the metal salt without causing the metal alloy particle size to be too large; ammonium fluoride is used as an ion regulator to adjust the reaction process and trigger the salting-out effect. The inorganic mixed metal salt refers to soluble salts of various metals, including one of nitrates, chlorides, and their hydrates, etc.

[0015] The molar ratio of the metal palladium salt to other heterogeneous metal salts in the inorganic mixed metal salt is 1-5:1-1.5. In the present invention, the ratio of palladium atoms to tin atoms in the palladium-based metal alloy aerogel catalyst is adjusted by the addition amount of the reactants.

[0016] The molar ratio of the metal palladium salt to other heterogeneous metal salts in the inorganic mixed metal salt is 1-3:1. This is beneficial to improving the selectivity and catalytic effect of the palladium-based metal alloy aerogel catalyst for the electrocatalytic preparation of butanone oxime.

[0017] The mixing temperature is room temperature, the stirring and mixing time is 10-30 min, and it is left standing at room temperature for 12-24 h. The sediment is aggregated through long-term standing treatment to form a stable gel state.

[0018] The washing is carried out by replacing with deionized water 4-6 times, and the total time is 2-3 days; the solvent is selected from any one or more of water, ethanol, and tert-butanol. The replacement with water effectively ensures that the structure of the gel material is not damaged, and after multiple exchanges, the soluble NaBH4 reducing agent and NH4F ion regulator are fully removed.

[0019] In the reaction for the electrocatalytic preparation of butanone oxime, the operating potential is 0.1- -0.5 V vs. RHE. The catalyst shows the highest selectivity for butanone oxime at -0.1 V vs. RHE, and the catalyst shows the highest yield of butanone oxime at -0.3 V vs. RHE. The electrolyte is an aqueous solution of one or more of neutral phosphate buffer solution, sodium hydroxide, potassium hydroxide, potassium sulfate, sodium bicarbonate, or potassium bicarbonate, with a concentration of 0.1-0.5 M, preferably 0.5 M phosphate buffer solution. The nitrogen source is nitrate, nitrite, nitrogen, nitric oxide, etc., preferably potassium nitrate. The reaction temperature is room temperature.

[0020] The cathode catalyst described in the present invention is metal palladium or a metal alloy aerogel formed by it and other metals. Preferably, the other metal is selected from p-block metals tin, lead, and indium. The catalyst is coated on a conductive substrate as a working electrode, and the conductive substrate is carbon paper, carbon cloth, nickel foam, copper foam, etc., preferably carbon paper.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) In the method provided by the present invention, the palladium-based metal alloy aerogel catalyst significantly inhibits side reactions such as hydrogen evolution and ammonia production in the electrocatalytic co-reduction of nitrate and butanone to prepare butanone oxime, realizes the efficient catalysis for the production of butanone oxime, and has excellent electrochemistry reduction performance and stability. It solves the problems of complex process, long production process, lack of economy and environmental protection in the traditional synthesis method of butanone oxime.

[0023] (2) The present invention obtains a palladium-tin metal alloy aerogel catalyst by freeze-drying method. Due to its unique morphology size and geometric / electronic structure characteristics (loose and porous network structure, large specific surface area, fast mass transfer rate), it is conducive to the full utilization of catalyst active sites, and thus exhibits excellent electrocatalytic co-reduction activity of nitrate and butanone to prepare butanone oxime. The palladium-tin metal alloy aerogel material has good electrochemical performance and stability.

[0024] (3) The preparation method of the palladium-tin metal alloy aerogel catalyst of the present invention is simple, efficient, low-cost, highly controllable and has good reproducibility, and is suitable for industrial production. Description of the Drawings

[0025] Figure 1 Scanning electron microscope image of the palladium-tin metal alloy aerogel catalyst prepared in Example 1.

[0026] Figure 2 Transmission electron microscope image of the palladium-tin metal alloy aerogel catalyst prepared in Example 1.

[0027] Figure 3 Yield and Faraday efficiency diagram of the electrocatalytic co-reduction of nitrate and butanone to prepare butanone oxime by the palladium-tin metal alloy aerogel catalyst prepared in Example 1.

[0028] Figure 4 Yield and Faraday efficiency diagram of the electrocatalytic co-reduction of nitrate and butanone to prepare butanone oxime by the palladium-tin metal alloy aerogel catalysts with different ratios prepared in Examples 1-4.

[0029] Figure 5 Faraday efficiency diagram of the electrocatalytic co-reduction to prepare butanone oxime corresponding to the aerogel catalysts of Examples 1, 5-6 and Comparative Examples 1-3.

[0030] Figure 6 Electrocatalytic stability test diagram of the palladium-tin metal alloy aerogel catalyst prepared in Example 1. Detailed Embodiments

[0031] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Those skilled in the art who make modifications or equivalent replacements based on the understanding of the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention shall all be covered within the protection scope of the present invention.

[0032] The raw materials used in the following specific embodiments are all purchased from the market, and the atomic ratios of various metals in the obtained catalyst are estimated by testing with an energy dispersive X-ray spectrometer (EDX).

[0033] Example 1

[0034] (1) Add 2.25 mL of 0.1 M H2PdCl4 and 0.75 mL of 0.1 M SnCl4·5H2O solution to 200 mL of deionized water and stir well.

[0035] (2) Add 424 mg of sodium borohydride and 111 mg of ammonium fluoride to the solution obtained in step (1) to react and form a precursor solution.

[0036] (3) After mixing the precursor solution for 15 min, then let it stand for 12 - 24 h, replace it with deionized water 4 - 6 times, and the time is 2 - 3 days. Finally, place the above-treated sample in a freeze dryer at -80 °C for 12 - 24 h to obtain a black gel product (palladium-tin aerogel Pd3Sn1).

[0037] The surface morphology of the obtained catalyst was observed by scanning electron microscopy and transmission electron microscopy, and the results are as Figure 1 and Figure 2 shown. It can be seen from the figure that the palladium-tin metal alloy aerogel catalyst presents a loose and porous network structure, with uniform particle size and no agglomeration.

[0038] Example 2

[0039] According to the preparation process of Example 1, change 2.25 mL of 0.1 M H2PdCl4 in step (1) to 2.5 mL, and change 0.75 mL of 0.1 M SnCl4·5H2O solution to 0.5 mL to obtain a palladium-tin metal alloy aerogel catalyst Pd5Sn1 with different Sn metal contents.

[0040] Example 3

[0041] According to the preparation process of Example 1, change 2.25 mL of 0.1 M H2PdCl4 in step (1) to 1.5 mL, and change 0.75 mL of 0.1 M SnCl4·5H2O solution to 1.5 mL to obtain the palladium-tin metal alloy aerogel catalyst Pd1Sn1 with different Sn metal contents.

[0042] Example 4

[0043] According to the preparation process of Example 1, change 2.25 mL of 0.1 M H2PdCl4 in step (1) to 1.2 mL, and change 0.75 mL of 0.1 M SnCl4·5H2O solution to 1.8 mL to obtain the palladium-indium metal alloy aerogel catalyst Pd2Sn3.

[0044] Example 5

[0045] According to the preparation process of Example 1, keep 2.25 mL of 0.1 M H2PdCl4 in step (1) unchanged, and change 0.75 mL of 0.1 M SnCl4·5H2O solution to 0.1 M Pb(NO3)2 to obtain the palladium-lead metal alloy aerogel catalyst Pd3Pb.

[0046] Example 6

[0047] According to the preparation process of Example 1, keep 2.25 mL of 0.1 M H2PdCl4 in step (1) unchanged, and change 0.75 mL of 0.1 M SnCl4·5H2O solution to 0.1 M In(NO3)3·4H2O to obtain the palladium-indium metal alloy aerogel catalyst Pd3In.

[0048] Comparative Example 1

[0049] According to the preparation process of Example 1, change 2.25 mL of 0.1 M H2PdCl4 in step (1) to 0.75 mL, and change 0.75 mL of 0.1 M SnCl4·5H2O solution to 2.25 mL to obtain the palladium-tin metal alloy aerogel catalyst Pd1Sn3 with different Sn metal contents.

[0050] Comparative Example 2

[0051] According to the preparation process of Example 1, change 0.75 mL of 0.1 M SnCl4·5H2O solution in step (1) to 0.1 M Co(NO3)3·6H2O, and keep 2.25 mL of 0.1 M H2PdCl4 unchanged to obtain the palladium-cobalt metal alloy aerogel catalyst Pd3Co.

[0052] Comparative Example 3

[0053] According to the preparation process of Example 1, change 2.25 mL of 0.1 M H2PdCl4 in step (1) to 3 mL, and change 0.75 mL of 0.1 M SnCl4·5H2O solution to 0.5 mL to obtain the palladium metal aerogel catalyst.

[0054] The contents of various metal elements in the catalysts prepared in Examples 1-6 and Comparative Examples 1-3 are shown in Table 1.

[0055] Table 1 Contents of various metal elements in the catalysts prepared in Examples 1-6 and Comparative Examples 1-3

[0056] Element content % Pd Sn / In / Pb / Co Example 1 83 17(Sn) Example 2 90 10(Sn) Example 3 56 44(Sn) Example 4 22 78(Sn) Example 5 75 15(Pb) Example 6 82 18(In) Comparative Example 1 13 87(Sn) Comparative Example 2 83 17(Co) Comparative Example 3 100 /

[0057] Application Example The catalyst is used for the electrocatalytic co-reduction of nitrate and butanone to prepare butanone oxime

[0058] The specific steps are as follows: Prepare a dispersion with an ethanol / Nafion volume ratio of 9:1, and then drop 100 μL of the catalyst dispersion prepared in the above examples onto the carbon paper respectively. After natural drying, it is used as the working electrode. The counter electrode is a platinum sheet, the reference electrode is a silver / silver chloride electrode, and the electrolyte is 0.5 M phosphate buffer solution, 0.1 M potassium nitrate and 0.02 M butanone solution;

[0059] Cyclic voltammetry (CV) activation: Use a Shanghai Chenhua CHI 660E electrochemical workstation, adopt the CV program, the test range is 0.2~-1.0 V vs. RHE, and the scan rate is 50 mV s -1 , and cycle scan 20 circles until the electrode reaches a stable state.

[0060] Linear sweep voltammetry (LSV) test: After CV activation, switch the program to the LSV program, the test range is 0.2~-1.0 V vs. RHE, and the scan rate is 10 mV s -1 .

[0061] The results are as Figure 3 shown. The palladium-tin metal alloy aerogel catalyst prepared in the examples has excellent reaction performance for the electrocatalytic co-reduction of nitrate and butanone to prepare butanone oxime. At a potential of -0.1 V vs. RHE, the Faraday efficiency of butanone oxime is as high as 72%, and at a potential of -0.3 V vs. RHE, the yield of butanone oxime is about 114 mg h -1 mg cat -1 .

[0062] In addition, Figure 4Yield (a) and Faraday efficiency (b) diagrams of electrocatalytic co-reduction for the preparation of butanone oxime in Examples 1-4. It can be seen that the proportion of metal components in the metal alloy has a great influence on the overall performance of the aerogel catalyst. When the palladium atomic ratio is about 83%, the selectivity of the catalyst for electrocatalytic preparation of butanone oxime is the highest and the catalytic effect is the best. Especially at -0.1 V, the Faraday efficiencies of Examples 1-4 almost all remain above 50%, further proving the excellent performance of the palladium-based metal alloy aerogel catalyst within this palladium-tin ratio range in the electrochemical reduction preparation of butanone oxime.

[0063] Figure 5 Faraday efficiencies of electrocatalytic co-reduction for the preparation of butanone oxime corresponding to the aerogel catalysts of Examples 1, 5-6 and Comparative Examples 1-3. At -0.1 V vs. RHE, whether it is Example Pd3Sn, Pd3Pb or Pd3In, they all show a Faraday efficiency exceeding 40%. In the comparative examples, when the Pd content is low (13%), the Faraday efficiency of the produced butanone oxime is less than 10%; when Sn is replaced by other transition metals, such as Co, the Faraday efficiency of the produced butanone oxime is less than 2%; when the Pd metal aerogel is used alone as the catalyst, the Faraday efficiency of the produced butanone oxime is hardly detectable. It shows that the metal alloy aerogel formed by Pd and p-block metals provided by the present invention has high selectivity for the electrochemical reduction preparation of butanone oxime.

[0064] Figure 6 Results of the electrocatalytic stability test of the palladium-tin metal alloy aerogel catalyst prepared in Example 1. As Figure 6 shown, at a potential of -0.2 V vs. RHE, after 6 cycles of stability tests, its yield and Faraday efficiency basically remain the same, indicating that the catalyst has stable electrochemical performance.

[0065] The metal element contents in the palladium-based metal alloy aerogel catalysts prepared in the examples were determined by EDX, and the results are shown in Table 1. The catalysts prepared in Examples 1-6 have good selectivity for butanone oxime, while the selectivity for butanone oxime in Comparative Examples 1-3 is low. This is because too little NH2OH is in-situ generated in the comparative examples, and most of it cannot be directly utilized and is easily over-reduced to NH3. Coupled with the serious hydrogen evolution side reaction, the electrocatalytic activity decreases.

Claims

1. A method for electrocatalytic co - reduction of nitrate and butanone to prepare butanone oxime, characterized in that, The method includes: the electrolyte includes a nitrogen source and methyl ethyl ketone, using a palladium-based metal alloy aerogel catalyst as the cathode catalyst, and electrocatalytically co-reducing nitrate and methyl ethyl ketone under the action of the cathode catalyst to prepare methyl ethyl ketoxime.

2. The method according to claim 1, characterized in that, The palladium-based metal alloy aerogel catalyst includes palladium atoms and heterogeneous metal atoms that exist in the aerogel structure in a single-phase form, and the heterogeneous metal is selected from one or more of tin, lead, or indium.

3. The method according to claim 2, characterized in that, The molar proportion of palladium atoms in the palladium-based metal alloy aerogel catalyst is 22-90%.

4. The method according to claim 1, characterized in that The preparation method of the palladium-based metal alloy aerogel catalyst includes: mixing an inorganic mixed metal salt, sodium borohydride, and ammonium fluoride in a solvent to obtain a precursor solution, and after standing, the product is washed and freeze-dried to obtain the palladium-based metal alloy aerogel catalyst; the inorganic mixed metal salt is a mixture of a metal palladium salt and other heterogeneous metal salts, and the heterogeneous metal is one or more of tin, lead, and indium.

5. The method according to claim 4, characterized in that, The molar ratio of the inorganic mixed metal salt, ammonium fluoride, and sodium borohydride is 1:5-15:20-50.

6. The method according to claim 4, characterized in that, The molar ratio of the metal palladium salt and other heterogeneous metal salts in the inorganic mixed metal salt is 1-5:1-1.

5.

7. The method according to claim 4, characterized in that The molar ratio of the metal palladium salt and other heterogeneous metal salts in the inorganic mixed metal salt is 1-3:

1.

8. The method according to claim 4, characterized in that, The mixing temperature is room temperature, the stirring and mixing time is 10-30 min, and it is left standing at room temperature for 12-24 h; the washing is carried out by replacing with deionized water 4-6 times, with a total time of 2-3 days; the solvent includes any one or more of water, ethanol, and tert-butanol.

9. The method according to any one of claims 1-8, characterized in that Electrocatalytically co-reduce nitrate and methyl ethyl ketone to prepare methyl ethyl ketoxime at 0.1- -0.5 V vs. RHE.

10. The method according to any one of claims 1-7, characterized in that, The nitrogen source is selected from nitrates, nitrites, nitrogen, or nitric oxide; the electrolyte includes an aqueous solution of one or more of neutral phosphate buffer solution, sodium hydroxide, potassium hydroxide, potassium sulfate, sodium bicarbonate, or potassium bicarbonate.

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