A method for electrocatalytic co-reduction of nitrate and butanone to prepare butanone oxime

Abstract

This invention discloses a method for the electrocatalytic co-reduction of nitrate and butanone to prepare butanone oxime. The method includes: an electrolyte comprising a nitrogen source and butanone; using a palladium-based metal alloy aerogel catalyst as a cathode catalyst; and electrocatalyzing the co-reduction of nitrate and butanone to prepare butanone oxime under the action of the cathode catalyst. In the method provided by this invention, the palladium-based metal alloy aerogel catalyst, when applied to the electrocatalytic co-reduction of nitrate and butanone to prepare butanone oxime, significantly suppresses side reactions such as hydrogen evolution and ammonia production, achieving highly efficient catalytic production of butanone oxime, and exhibiting excellent electrochemical reduction performance and stability.

Description

Technical Field

[0001] This invention relates to the field of electrocatalysis technology, specifically to a method for the electrocatalytic co-reduction of nitrate and butanone to prepare butanone oxime. Background Technology

[0002] Ketone oximes are an important class of organic compounds that participate in many chemical industrial reactions. Butanone oxime (C4H9NO), as an important organic synthesis intermediate and a widely used highly reactive reagent, is mainly used in the production of oxime-based silanes and hydroxylamines, and as an antioxidant, sealant, and corrosion inhibitor in oil-based coatings. It is widely used in pharmaceuticals, agriculture, chemicals, and electronics. Currently, the traditional industrial method for producing butanone oxime is the hydroxylamine process, which involves toxic gases such as sulfur dioxide, nitrogen oxides, and nitrogen oxides as raw materials, resulting in high environmental pollution levels and significant long-term health risks. Furthermore, the traditional butanone oxime production process is lengthy, complex, and energy-intensive, leading to the accumulation of low-value-added products such as ammonium sulfate and nitrogen oxides. This not only makes the production process uneconomical but also exacerbates environmental pollution, and it is gradually being phased out. Compared with traditional processes, the electrocatalytic co-reduction of nitrate and methyl ethyl ketone (MEK) to prepare MEK oxime is considered a feasible method for producing MEK oxime under environmental conditions. It has the dual advantages of environmental remediation and energy economy. It solves the problem of excessive nitrate discharge from surface water and groundwater aquifers caused by excessive fertilization and industrial wastewater. At the same time, it can produce MEK oxime products that are urgently needed in industry in a simple and efficient manner.

[0003] For example, Sharp et al. reported that a Zn-Cu alloy, utilizing the in-situ generation of hydroxylamine from nitrate and its reaction with cyclohexanone, synthesized cyclohexanone oxime with a Faradaic efficiency of 27%; Wu et al. synthesized Pd nanoparticles achieving a Faradaic efficiency of 29.24% for cyclohexanone oxime at a potential of -0.45 V; and Sheng et al. synthesized cyclohexanone oxime using the high-entropy metal alkene PdCuAgBiIn co-reduction of nitrate and cyclohexanone, achieving a Faradaic efficiency of up to 47.6%. Studies have shown that noble metal-based catalysts with three-dimensional structures possessing high surface area, high conductivity, and a high ratio of unsaturated metal sites can significantly enhance intrinsic catalytic activity, while also altering reaction pathways and improving product selectivity. Noble metal palladium-based materials are considered the most promising electrocatalysts, exhibiting good reactivity and high energy efficiency in electrochemical reduction reactions. However, palladium-based materials suffer from low atom utilization, high loading, and high cost, hindering their large-scale industrial application. Constructing palladium-based metal alloy catalysts by hybridizing / composite with other non-noble metal species can effectively dilute the amount of noble palladium. Furthermore, the metal alloy structure of the catalyst exhibits excellent tunability in elemental species and chemical composition, displaying unique physical and chemical properties, which has attracted widespread attention in recent years. To date, palladium-based metal alloy catalysts have been reported to be used in electrocatalytic reactions such as hydrogen and oxygen evolution from water, carbon dioxide reduction, and alcohol oxidation. For example, CN116603538B discloses a palladium-based alloy heterogeneous nanoflower catalyst, where the palladium-based alloy material is a PdM alloy, and the metal M is copper, iridium, manganese, chromium, platinum, or ruthenium; CN118299600A discloses a palladium-based ternary alloy nanocage catalyst (d / Ru / Cu octahedral ternary alloy nanocage); and CN119419299A discloses a platinum-palladium-based multi-element alloy sub-nanobelt catalyst.

[0004] Although some progress has been made in the development of palladium-based metal alloy catalysts, their application as electrocatalysts in the electrocatalytic co-reduction of nitrate and butanone to prepare butanone oxime has not yet been developed and lacks in-depth research. Furthermore, the electrochemical co-reduction preparation of butanone oxime still faces challenges such as low selectivity due to excessive reduction of hydroxylamine and poor catalyst stability. Summary of the Invention

[0005] The purpose of this invention is to provide a method for the electrocatalytic co-reduction of nitrate and butanone to prepare butanone oxime, which significantly suppresses side reactions and achieves highly efficient catalytic production of butanone oxime.

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

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

[0008] The preparation principle of this invention is as follows: as a cathode catalyst, palladium-based metal alloy aerogel electrocatalyzes the reduction of nitrate to preferentially generate NH2OH rather than NH3. The in-situ generated NH2OH further undergoes a nucleophilic addition reaction with butanone in solution to form butanone oxime. This invention achieves the electrochemical synthesis of butanone oxime through a palladium-based metal alloy aerogel catalyst. Furthermore, the introduction of other heterometals can further modulate the electronic structure of the noble metal palladium, enhancing its electroreduction activity and stability. This enables the highly active, selective, and stable electrosynthesis of butanone oxime, which is of great significance for the large-scale electrochemical preparation of high-concentration butanone oxime.

[0009] In this 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, both existing in a single-phase form in the aerogel structure. The heterogeneous metal is selected from one or more of tin, lead, or indium, and the molar percentage of palladium atoms in the palladium-based metal alloy aerogel catalyst is 22% to 90%.

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

[0012] 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, allowing it to stand, and then washing and freeze-drying the product to obtain the palladium-based metal alloy aerogel catalyst; the inorganic mixed metal salt is a mixture of metallic palladium salt and other heterogeneous metal salts, and the heterogeneous metal is one or more of tin, lead and indium.

[0013] In this 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 a three-dimensional network structure alloy aerogel. This palladium-based metal alloy aerogel catalyst exhibits excellent electrocatalytic activity and stability in 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; this dosage ensures complete reduction of the metal salt without causing excessively large metal alloy particle size. Ammonium fluoride acts as an ion regulator, modulating the reaction process and inducing a salting-out effect. The inorganic mixed metal salt refers to a soluble salt of each metal, including nitrates, chlorides, and their hydrates.

[0015] The molar ratio of palladium salt to other heterogeneous metal salts in the inorganic mixed metal salt is 1–5:1–1.5. This invention adjusts the ratio of palladium atoms to tin atoms in the palladium-based metal alloy aerogel catalyst by adjusting the amount of reactants added.

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

[0017] The mixing temperature is room temperature, the stirring time is 10–30 min, and the mixture is left to stand at room temperature for 12–24 h. This prolonged standing process allows the deposits to aggregate and form a stable gel state.

[0018] The washing process involves 4-6 cycles of deionized water replacement, with a total time of 2-3 days. The solvent is selected from one or more of water, ethanol, and tert-butanol. Water replacement effectively prevents damage to the gel material structure, and subsequent multiple exchanges thoroughly remove soluble NaBH4 reducing agent and NH4F ion modifier.

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

[0020] The cathode catalyst described in this invention is palladium or a metal alloy aerogel formed with other metals. Preferably, the other metals are p-region metals such as tin, lead, and indium. The catalyst is coated on a conductive substrate as a working electrode. The conductive substrate is carbon paper, carbon cloth, nickel foam, copper foam, etc., with carbon paper being preferred.

[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, thereby achieving highly efficient catalytic production of butanone oxime and exhibiting excellent electrochemical reduction performance and stability; it solves the problems of complex process, lengthy production process, lack of economy and environmental protection in the traditional synthesis method of butanone oxime.

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

[0024] (3) The method for preparing palladium-tin metal alloy aerogel catalyst of the present invention is simple, efficient, low-cost, highly controllable, and reproducible, and is suitable for industrial production. Attached Figure Description

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

[0026] Figure 2 This is a transmission electron microscope (TEM) image of the palladium-tin metal alloy aerogel catalyst prepared in Example 1.

[0027] Figure 3 The graph shows the yield and Faraday efficiency of the palladium-tin alloy aerogel catalyst prepared in Example 1 for the electrocatalytic co-reduction of nitrate and butanone to prepare butanone oxime.

[0028] Figure 4 The graph shows the yield and Faraday efficiency of the electrocatalytic co-reduction of nitrate and butanone to prepare butanone oxime using palladium-tin alloy aerogel catalysts with different proportions prepared in Examples 1-4.

[0029] Figure 5 The diagram shows the Faraday efficiency of the electrocatalytic co-reduction preparation of butanone oxime using the aerogel catalysts in Examples 1, 5-6 and Comparative Examples 1-3.

[0030] Figure 6 The image shows the electrocatalytic stability test results of the palladium-tin metal alloy aerogel catalyst prepared in Example 1. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention, without departing from the spirit and scope of the invention, should be covered within the protection scope of this invention.

[0032] The raw materials used in the following specific embodiments were all purchased from the market, and the atomic ratios of each metal in the obtained catalyst were estimated by energy dispersive X-ray spectroscopy (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 thoroughly.

[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, it was then allowed to stand for 12–24 h, and the solution was replaced with deionized water 4–6 times for 2–3 days. Finally, the sample after the above treatment was placed at -80℃ for freeze drying for 12–24 h to obtain a black gel product (palladium tin aerogel Pd3Sn1).

[0037] The surface morphology of the obtained catalyst was observed using scanning electron microscopy and transmission electron microscopy, and the results are as follows: Figure 1 and Figure 2 As shown in the figure, the palladium-tin metal alloy aerogel catalyst exhibits a loose, porous network structure with uniform particle size and no agglomeration.

[0038] Example 2

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

[0040] Example 3

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

[0042] Example 4

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

[0044] Example 5

[0045] Following the preparation process of Example 1, the 2.25 mL 0.1 M H2PdCl4 in step (1) was kept unchanged, and the 0.75 mL 0.1 M SiCl4·5 H2O solution was changed to 0.1 M Pb(NO3)2 to obtain the palladium-lead metal alloy aerogel catalyst Pd3Pb.

[0046] Example 6

[0047] Following the preparation process of Example 1, the 2.25 mL 0.1 M H2PdCl4 in step (1) was kept unchanged, and the 0.75 mL 0.1 M SiNCl4·5H2O solution was changed to 0.1 M In(NO3)3·4H2O to obtain the palladium-indium metal alloy aerogel catalyst Pd3In.

[0048] Comparative Example 1

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

[0050] Comparative Example 2

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

[0052] Comparative Example 3

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

[0054] The content of each metal element in the catalysts prepared in Examples 1-6 and Comparative Examples 1-3 is shown in Table 1.

[0055] Table 1. Content of each metal element 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. Then, drop 100 μL of the catalyst dispersion prepared in the above example onto carbon paper. After natural drying, use it 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, 0.1 M potassium nitrate, and 0.02 M butanone solution.

[0059] Cyclic voltammetry (CV) activation: A Shanghai Chenhua CHI 660E electrochemical workstation was used with a CV program. The test range was 0.2 to -1.0 V vs. RHE, and the scan rate was 50 mV / s. -1 After 20 cyclic scans, the electrode reaches a stable state.

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

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

[0062] in addition, Figure 4The figures (a) and (b) show the yield (or faradaic efficiency) of the electrocatalytic co-reduction preparation of butanone oxime in Examples 1-4. It can be seen that the proportion of metal components in the metal alloy has a significant impact on the overall performance of the aerogel catalyst. When the palladium atomic ratio is around 83%, the catalyst exhibits the highest selectivity and optimal catalytic effect in the electrocatalytic preparation of butanone oxime. Especially at -0.1V, the faradaic efficiency of Examples 1-4 remains almost always above 50%, further demonstrating 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 The Faradaic efficiencies for the electrocatalytic co-reduction preparation of butanone oxime using aerogel catalysts in Examples 1, 5-6 and Comparative Examples 1-3 are shown. At -0.1V vs. RHE, all examples, regardless of whether they used Pd3Sn, Pd3Pb, or Pd3In, exhibited Faradaic efficiencies exceeding 40%. In the comparative examples, when the Pd content was low (13%), the Faradaic efficiency of the produced butanone oxime was less than 10%; when Sn was replaced with other transition metals, such as Co, the Faradaic efficiency of the produced butanone oxime was less than 2%; and when the Pd metal aerogel was used alone as a catalyst, the Faradaic efficiency of the produced butanone oxime was negligible. This demonstrates that the metal alloy aerogel formed by Pd and p-block metals provided by this invention exhibits high selectivity for the electrochemical reduction preparation of butanone oxime.

[0064] Figure 6 The results show the electrocatalytic stability of the palladium-tin metal alloy aerogel catalyst prepared in Example 1. Figure 6 As shown, under a potential of -0.2V vs. RHE, after 6 cycles of stability testing, the yield and Faraday efficiency remained basically consistent, indicating that the catalyst has stable electrochemical performance.

[0065] The metal element content in the palladium-based metal alloy aerogel catalysts prepared in the examples was determined by EDX, and the results are shown in Table 1. The catalysts prepared in Examples 1-6 exhibited good selectivity for butanone oxime, while the comparative examples 1-3 showed lower selectivity. This is because the in-situ generated NH2OH in the comparative examples was too small, and most of it could not be directly utilized and was easily over-reduced to NH3. In addition, the hydrogen evolution side reaction was severe, resulting in a decrease in electrocatalytic activity.

Claims

1. A method for the electrocatalytic co-reduction of nitrate and butanone to produce butanone oxime, characterized in that, The method includes: an electrolyte comprising a nitrogen source and butanone, using a palladium-based metal alloy aerogel catalyst as a cathode catalyst, and electrocatalyzing the co-reduction of nitrate and butanone under the action of the cathode catalyst to prepare butanone oxime; The palladium-based metal alloy aerogel catalyst comprises palladium atoms and heterogeneous metal atoms, both existing in a single-phase form in the aerogel structure, wherein the heterogeneous metal is selected from one or more of tin, lead, or indium. The palladium-based metal alloy aerogel catalyst has a molar ratio of 22% to 90% palladium atoms.

2. The method of claim 1, wherein, 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, allowing it to stand, and then washing and freeze-drying the product to obtain the palladium-based metal alloy aerogel catalyst; the inorganic mixed metal salt is a mixture of metallic palladium salt and other heterogeneous metal salts, and the heterogeneous metal is one or more of tin, lead and indium.

3. The method of claim 2, wherein, The molar ratio of the inorganic mixed metal salt, ammonium fluoride, and sodium borohydride is 1:5~15:20~50.

4. The method of claim 2, wherein, The molar ratio of palladium salt to other heterogeneous metal salts in the inorganic mixed metal salt is 1~5: 1~1.

5.

5. The method of claim 2, wherein, The molar ratio of palladium salt to other heterogeneous metal salts in the inorganic mixed metal salt is 1~3:

1.

6. The method of claim 2, wherein, The mixing temperature is room temperature, the stirring time is 10-30 min, and the mixture is left to stand at room temperature for 12-24 h; the washing involves replacing the water with deionized water 4-6 times, with a total time of 2-3 days; the solvent includes one or more of water, ethanol, and tert-butanol.

7. The method according to any one of claims 1 to 6, characterized in that, Electrocatalytic co-reduction of nitrate and butanone to prepare butanone oxime at 0.1 ~ -0.5 V vs. RHE.

8. The method according to any one of claims 1 to 6, characterized in that, The nitrogen source is selected from nitrates; the electrolyte includes one or more aqueous solutions of neutral phosphate buffer solution, sodium hydroxide, potassium hydroxide, potassium sulfate, sodium bicarbonate or potassium bicarbonate.

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