An intercalated hydrotalcite catalyst, its preparation method and application

Abstract

This invention provides an intercalated hydrotalcite catalyst, its preparation method, and its application. The preparation method of the intercalated hydrotalcite catalyst of this invention includes the following steps: 1) dissolving a first metal salt, a second metal salt, and an organic base in a solvent to obtain a metal salt solution; the first metal salt is selected from nickel salts, and the second metal salt is selected from cobalt salts and / or iron salts; 2) adding a conductive substrate to the metal salt solution for a hydrothermal reaction to obtain an intercalated hydrotalcite catalyst precursor; 3) adding the intercalated hydrotalcite catalyst precursor to an aqueous solution containing an intercalating agent for ion exchange treatment to obtain the intercalated hydrotalcite catalyst; the intercalating agent includes phosphate or hypophosphite anions. This method utilizes the tunability of interlayer anions in hydrotalcite materials to introduce highly nucleophilic inorganic acid radicals into the interlayer, enhancing the formation of NiOOH active centers from Ni(OH)₂ dehydrogenation and promoting the formation of NiOOH in the bulk phase, thereby giving the catalyst excellent electrocatalytic oxidation activity.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical catalysis, and relates to an intercalated hydrotalcite catalyst, its preparation method, and its application. Background Technology

[0002] Alcohols or aldehydes can be oxidized to produce carboxylic acid products, which are widely used in the production of high-value-added fine chemicals such as polyesters, pharmaceuticals, and daily chemical products, and have significant economic value. Traditional oxidation processes for alcohols or aldehydes mainly involve thermocatalysis, requiring precious metal catalysts. To increase the reaction rate and selectivity of the target product, the reaction needs to be carried out under high temperature and high pressure conditions, leading to high production costs and high carbon emissions, posing a challenge to large-scale green and low-carbon production.

[0003] The electrocatalytic oxidation of alcohols and aldehydes can be carried out at ambient temperature and pressure without the need for additional oxygen or precious metal catalysts. This process offers advantages such as being green, low-carbon, operating under mild conditions, and cost-effective, and has attracted widespread attention in recent years. More importantly, the electrocatalytic oxidation of alcohols and aldehydes can be coupled with the electrolysis of water to produce hydrogen, enabling the co-production of green chemicals and green hydrogen in an electrolyzer, which shows great promise for industrial application.

[0004] Nickel, a non-precious metal, exhibits high oxidative activity and good selectivity for carboxylic acid products in electrocatalytic oxidation, and is considered the most effective active metal. Especially when nickel is doped with other metals to form binary or ternary layered double hydroxides (LDHs), its electronic structure is further modulated, resulting in even better catalytic performance. For example, patent CN111472020A discloses a method for the electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF) using a ternary layered double hydroxide NiCoFe-LDH, achieving an efficiency of 10 mA / cm². 2 At a current density of approximately 100 ppm, the HMF conversion rate can reach 95.4%, and the selectivity for the target product 2,5-furandicarboxylic acid (FDCA) reaches 84.8%.

[0005] Although hydrotalcite catalysts exhibit good catalytic performance in the electrocatalytic oxidation of alcohols and aldehydes, represented by HMF, their limited current density restricts their production efficiency and cannot meet the requirements for industrialization (industrialization requires a current density ≥200 mA / cm²). 2However, there is still considerable room for improvement in catalyst activity. The literature (ACS Catal. 2023, 13, 2916-2927) reports that the high-valence nickel species NiOOH formed by the dehydrogenation of Ni(OH)₂ is the truly active component in the electrocatalytic oxidation of alcohols and aldehydes. This study also points out that the surface NiOOH is the site for adsorption and oxidation of reactants, while the bulk NiOOH is the medium for electron transfer. However, because Ni(OH)₂ in the bulk phase is quite inert, it is difficult to dehydrogenate to form NiOOH, thus limiting the electrocatalytic oxidation activity of alcohols and aldehydes. Therefore, how to promote the dehydrogenation of Ni(OH)₂ to form NiOOH, especially the formation of NiOOH in the bulk phase, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] This invention provides a method for preparing an intercalated hydrotalcite catalyst. This method utilizes the tunability of interlayer anions in hydrotalcite materials to introduce highly nucleophilic inorganic acid radicals such as phosphate and hypophosphite into the interlayer, which is beneficial for the dehydrogenation of Ni(OH)2 to form NiOOH active centers, thereby promoting the formation of NiOOH in the bulk phase and improving the catalyst activity.

[0007] The present invention also provides an intercalated hydrotalcite catalyst, which is prepared by the above preparation method. The catalyst has excellent electrocatalytic oxidation activity and good stability.

[0008] This invention also provides a method for the electrocatalytic oxidation of aldehydes or alcohols, which uses the above-mentioned intercalated hydrotalcite catalyst to electrocatalytically oxidize alcohols or aldehydes, achieving a potential of 200 mA / cm² at low potentials. 2 It achieves industrial-grade current density and exhibits excellent substrate conversion, carboxylic acid product selectivity, and Faraday efficiency.

[0009] The first aspect of this invention provides a method for preparing an intercalated hydrotalcite catalyst, comprising the following steps:

[0010] 1) Dissolve the first metal salt, the second metal salt, and the organic base in a solvent to obtain a metal salt solution;

[0011] The first metal salt is selected from nickel salts, and the second metal salt is selected from cobalt salts and / or iron salts;

[0012] 2) The conductive substrate is added to the metal salt solution for a hydrothermal reaction to obtain the intercalated hydrotalcite catalyst precursor;

[0013] 3) The intercalated hydrotalcite precursor is added to an aqueous solution containing an intercalating agent for ion exchange treatment to obtain the intercalated hydrotalcite catalyst;

[0014] The intercalating agent includes an intercalating anion, which is selected from phosphate ions or hypophosphate ions.

[0015] NiOOH is an important active component of electrocatalytic oxidants. Further mixing with iron and / or cobalt salts on the basis of nickel salts, and the addition of Co and / or Fe, promotes electron transfer from Ni to Co and / or Fe, contributing to the formation of NiOOOH active species. The addition of organic bases provides an alkaline environment for the reaction, facilitating the conversion of the first and second metal salts into metal hydroxides. This invention does not specifically limit the types of nickel, cobalt, and iron salts; they can be selected from soluble nickel, cobalt, and iron salts conventionally used in the art, more preferably nitrates and acetylacetone salts of nickel, cobalt, and iron. The weaker interlayer bonding of nitrate and acetylacetone anions facilitates the insertion of hydroxide ions during hydrothermal synthesis and subsequent ion exchange reactions.

[0016] In step 2), the conductive substrate is added to the metal salt solution for a hydrothermal reaction. The first and second metal salts will transform in situ to form trimetallic or bimetallic layered double hydroxides and couple with the conductive substrate to obtain the intercalated hydrotalcite catalyst precursor. At this time, the interlayer anions in the intercalated hydrotalcite catalyst precursor are mainly hydroxide ions.

[0017] In step 3), the intercalated hydrotalcite catalyst precursor is added to an aqueous solution containing an intercalating agent, which can convert interlayer hydroxide ions into intercalated anions such as phosphate or hypophosphite, thereby obtaining the intercalated hydrotalcite catalyst of the present invention.

[0018] The inventors discovered that phosphate and hypophosphite intercalation anions have strong nucleophilicity and can act as proton transfer mediators to promote the dehydrogenation of Ni(OH)2 in the laminations to form NiOOH active centers, thereby effectively promoting the formation of NiOOH in the bulk phase, enhancing charge transfer, and thus improving the electro-oxidation activity of the catalyst.

[0019] In a preferred embodiment, in step 1), the organic base is selected from triethanolamine and / or diethanolamine. Triethanolamine and diethanolamine have a hydroxymethyl structure, which not only provides basicity to the reaction system but also controls the size of the layers, reduces the lattice energy of the layers, reduces the difficulty of interlayer ion exchange in the hydrotalcite, and facilitates the introduction of intercalated anions.

[0020] In a preferred embodiment, in step 1), the solvent is selected from water and / or ethanol. When the solvent is selected from a mixture of water and ethanol, the volume ratio of water to ethanol is (1-10):1.

[0021] In a preferred embodiment, in step 1), the sum of the concentrations of the first metal salt and the second metal salt in the metal salt solution is 0.01–0.2 mol / L. When the sum of the concentrations of the first metal salt and the second metal salt is within the above range, the catalyst can exhibit excellent electrocatalytic oxidation performance.

[0022] Furthermore, in step 1), the molar ratio of the first metal salt to the second metal salt is (1–4):1. Studies have shown that within this molar ratio range, the catalyst can achieve 200 mA / cm² at low potentials. 2 It has industrial-grade current density and excellent selectivity for carboxylic acid products in the electrocatalytic oxidation of alcohols or aldehydes.

[0023] In a preferred embodiment, in step 1), the concentration of the organic base in the metal salt solution is 0.02–1.0 mol / L. For example, the concentration of the organic base can be within the range of 0.02 mol / L, 0.05 mol / L, 0.1 mol / L, 0.3 mol / L, 0.6 mol / L, 0.8 mol / L, 1.0 mol / L, or any combination thereof.

[0024] The present invention does not impose any particular limitation on the conductive substrate in step 2), as long as it has good dispersibility and conductivity. It can be selected from conductive substrates commonly used in the art, including but not limited to nickel foam, carbon paper, and carbon felt. Preferably, the conductive substrate is selected from nickel foam.

[0025] In a preferred embodiment, in step 2), the hydrothermal reaction temperature is 60–180°C, and the time is 1–12 hours. The temperature and time of the hydrothermal reaction also affect the performance of the catalyst; within the above temperature and time ranges, the catalyst can achieve a potential of 200 mA / cm² at a relatively low voltage. 2 It has industrial-grade current density and excellent electrocatalytic oxidation activity.

[0026] In a preferred embodiment, in step 3), the concentration of the intercalating agent in the aqueous solution is 0.01–3.0 mol / L. For example, the concentration of the intercalating agent can be 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, or any combination thereof.

[0027] The present invention does not specifically limit the type of intercalating agent, which may be selected from metal salts containing the above-mentioned intercalating anions, including but not limited to sodium phosphate, potassium phosphate, sodium hypophosphite, potassium hypophosphite, etc.

[0028] In a preferred embodiment, in step 3), the ion exchange treatment time is 6–48 hours. The ion exchange treatment time has little effect on catalyst performance; within the above time range, ion exchange can be fully completed, allowing the catalyst to operate at 1.5V. RHE The following can reach 200mA / cm 2 It achieves industrial-grade current density, and the selectivity of carboxylic acid products can reach 99%.

[0029] A second aspect of the present invention provides an intercalated hydrotalcite catalyst, prepared according to the preparation method described above.

[0030] The intercalated hydrotalcite catalyst of the present invention has strongly nucleophilic inorganic acid radicals between its layers, which can promote the dehydrogenation of Ni(OH)2 in the layers to form NiOOH active centers, thereby effectively promoting the formation of NiOOH in the bulk phase and enhancing charge transfer. Therefore, this catalyst has excellent electrocatalytic oxidation activity.

[0031] In a preferred embodiment, in step 3), the hydrothermal reaction is carried out at a temperature of 60–180°C for 2–12 hours. Catalysts synthesized hydrothermally within the above temperature and time ranges all exhibit good electrocatalytic oxidation activity and selectivity for carboxylic acid products.

[0032] A third aspect of the present invention provides a method for the electrocatalytic oxidation of alcohols or aldehydes, comprising the following steps:

[0033] A three-electrode system is used, with the intercalated hydrotalcite catalyst provided in the second aspect of the present invention as the working electrode and an electrolyte solution containing dissolved alcohols or aldehydes as the electrolyte, to carry out an electrochemical catalytic oxidation reaction under constant reaction potential or constant reaction current density.

[0034] As is known to those skilled in the art, a three-electrode system consists of a working electrode, a reference electrode, and a counter electrode. The working electrode is the research electrode, where the oxidation reaction of the alcohols or aldehydes studied in this invention occurs. The potential of the reference electrode is unaffected by changes in the electrolyte composition and has a constant value; it can be selected from conventionally used reference electrodes in the art, such as Hg / HgO electrodes or RHE electrodes. The counter electrode, also known as the auxiliary electrode, forms a circuit with the working electrode, ensuring the current flows smoothly through the working electrode. The counter electrode is typically made of a relatively stable material, such as platinum or graphite.

[0035] The above method uses the intercalated hydrotalcite of the present invention as the working electrode to catalyze the electrocatalytic oxidation of alcohols or aldehydes. Because the intercalated anions in the catalyst have strong nucleophilicity, they can act as proton transfer mediators, promoting the dehydrogenation of Ni(OH)₂ in the layers to form NiOOH active centers, thereby effectively promoting the formation of NiOOH in the bulk phase and enhancing charge transfer. Therefore, it exhibits good catalytic activity in the electrocatalytic oxidation reaction, reaching 200 mA / cm² at a relatively low potential. 2 The industrial-grade current density, and taking 5-hydroxymethylfurfural as an example, the selectivity of its carboxylic acid product 2,5-furandicarboxylic acid can basically reach over 98%.

[0036] This invention does not specifically limit the alcohol or aldehyde compounds, which can be selected from common alcohol or aldehyde compounds in the field of organic chemistry, including but not limited to one or more of 5-hydroxymethylfurfural, furfural, ethanol, and benzyl alcohol.

[0037] When an electrochemical oxidation reaction is carried out under a constant reaction potential, the preferred reaction potential value is 1.2–1.8 V. RHE When an electrochemical oxidation reaction is carried out at a constant reaction current density, the preferred reaction current density is 10–500 mA / cm². 2 More preferably, the constant reaction potential is 1.5V. RHE The constant reaction current density is 10–150 mA / cm². 2 Electrochemical oxidation reactions of alcohols or aldehydes under constant reaction potential or constant reaction current density can achieve excellent substrate conversion, carboxylic acid product selectivity, and Faraday efficiency.

[0038] In a preferred embodiment, the electrolyte solution is selected from one or more of sodium hydroxide solution, potassium hydroxide solution, sodium phosphate solution, potassium phosphate solution, sodium hypophosphite solution, and potassium hypophosphite solution. Studies have shown that the intercalated hydrotalcite catalyst of the present invention exhibits excellent catalytic activity and selectivity for carboxylic acid products in all of the above-mentioned electrolyte solutions.

[0039] When two electrolytes are dissolved in an electrolyte solution, the preferred molar ratio of the two electrolytes is 1:(1 to 10).

[0040] In a preferred embodiment, the molar concentration of the electrolyte solution is 0.1–5.0 mol / L. Within this concentration range, superior substrate conversion, carboxylic acid product selectivity, and Faraday efficiency can be obtained.

[0041] In addition to the electrolyte, the electrolyte also contains dissolved reaction substrates such as alcohols or aldehydes. In a preferred embodiment, the molar concentration of alcohols or aldehydes in the electrolyte solution is 5–500 mmol / L. Within this concentration range, it is advantageous to achieve a combination of high substrate conversion, carboxylic acid product selectivity, and Faraday efficiency.

[0042] The implementation of this invention has at least the following beneficial effects:

[0043] 1. The preparation method of the intercalated hydrotalcite catalyst provided by this invention utilizes the tunability of interlayer anions in the hydrotalcite structure to introduce inorganic acid anions such as phosphate and hypophosphite with strong nucleophilicity into the interlayer. This facilitates the dehydrogenation of Ni(OH)₂ to form NiOOH active centers, thereby promoting the formation of NiOOH in the bulk phase, enhancing charge transfer, and thus improving the electro-oxidation activity of the catalyst.

[0044] 2. The intercalated hydrotalcite catalyst provided by this invention has excellent electrocatalytic oxidation activity and cycle stability.

[0045] 3. The intercalated hydrotalcite catalyst provided by this invention can be used for the electrocatalytic oxidation of alcohols or aldehydes at a minimum voltage of 1.41V. RHE The electrode potential reaches 200 mA / cm 2 It achieves industrial-grade current density, and its substrate conversion, carboxylic acid product selectivity, and Faraday efficiency can reach 99%. Attached Figure Description

[0046] Figure 1 NiCo-PO4 3- XRD pattern of -LDHs-1;

[0047] Figure 2 NiCo-H2PO2 - XRD pattern of -LDHs-15;

[0048] Figure 3 NiCo-PO4 3- LSV curve of -LDHs-1 / NF in 1.0 mol / L KOH + 50 mmol / L 5-hydroxymethylfurfural electrolyte;

[0049] Figure 4 NiCo-CO3 2- XRD patterns of -LDHs;

[0050] Figure 5 NiCo-CO3 2- LSV curve of -LDHs / NF in 1.0 mol / L KOH + 50 mmol / L 5-hydroxymethylfurfural electrolyte. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0052] It should be noted that, unless otherwise specified, the raw materials used in the following embodiments can be obtained by commercial purchase or conventional methods, and the experimental methods without specific conditions are all conventional methods and conditions well known in the art.

[0053] Example 1

[0054] This embodiment provides a phosphate-intercalated hydrotalcite catalyst, NiCo-PO4. 3- The preparation method of -LDHs-1 / NF includes the following steps:

[0055] 1) Dissolve 225 μmol nickel acetylacetonate, 75 μmol cobalt acetylacetonate, and 1.275 mmol triethanolamine in a mixed solvent containing deionized water and ethanol (the volume ratio of deionized water to ethanol is 1:1) and bring the volume to 15 mL to obtain a metal salt solution with a total metal salt concentration of 0.02 mol / L and an alkali concentration of 0.085 mol / L.

[0056] 2) Place a piece of nickel foam (15mm×10mm) into a hydrothermal reactor containing a metal salt solution and keep it at 120℃ for 6 hours to carry out the hydrothermal reaction. The product is repeatedly washed with deionized water and anhydrous ethanol, and then dried in a vacuum drying oven overnight to obtain the intercalated hydrotalcite catalyst precursor NiCo-LDHs-1 / NF.

[0057] 3) NiCo-LDHs / NF was immersed in an intercalating agent solution containing 1.0 mol / L potassium hydroxide and 0.1 mol / L sodium phosphate for ion exchange for 24 h. The resulting product was repeatedly washed with deionized water and ethanol, and then dried overnight in a vacuum drying oven to obtain the phosphate intercalated hydrotalcite catalyst NiCo-PO4. 3- -LDHs-1 / NF.

[0058] If the catalyst prepared above is directly characterized, the diffraction peak of NF is too strong to clearly see NiCo-PO4. 3- The diffraction peak elution of -LDHs-1, therefore, in the catalyst NiCo-PO4 3-NiCo-PO4 was obtained by scraping the surface of -LDHs-1 / NF. 3- -LDHs-1 powder was characterized by XRD. Figure 1 NiCo-PO4 3- XRD pattern of -LDHs-1, from Figure 1 It can be seen that the sample exhibits NiCo-PO4 3— The characteristic diffraction peaks of the (003), (006), (012) and (110) crystal planes of LDHs-1 material indicate that a well-structured layered hydrotalcite material was synthesized, while the (003) diffraction peak is located at 8.9 degrees, indicating the intercalation of phosphate ions.

[0059] Example 2

[0060] This embodiment provides a phosphate-intercalated hydrotalcite catalyst, NiCo-PO4. 3- The preparation method of -LDHs-2 / NF is basically the same as that in Example 1, except that in step 1), nickel acetylacetone is replaced with nickel nitrate and cobalt acetylacetone is replaced with cobalt nitrate. All other steps are the same as in Example 1.

[0061] Example 3

[0062] This embodiment provides a phosphate-intercalated hydrotalcite catalyst, NiCo-PO4. 3- The preparation method of -LDHs-3 / NF is basically the same as that in Example 1, except that in step 1), triethanolamine is replaced with diethanolamine, and the other steps are the same as in Example 1.

[0063] Example 4

[0064] This embodiment provides a phosphate-intercalated hydrotalcite catalyst, NiCo-PO4. 3- The preparation method of -LDHs-4 / NF is basically the same as that in Example 1, except that in step 1), the solvent is replaced by deionized water instead of the mixed solvent of deionized water and ethanol. All other steps are the same as in Example 1.

[0065] Example 5

[0066] This embodiment provides a phosphate-intercalated hydrotalcite catalyst, NiCo-PO4. 3- The preparation method of -LDHs-5 / NF is basically the same as that in Example 1, except that in step 1), the volume ratio of deionized water to ethanol is changed from 1:1 to 10:1, and the other steps are the same as those in Example 1.

[0067] Example 6

[0068] This embodiment provides a phosphate-intercalated hydrotalcite catalyst, NiCo-PO4. 3- The preparation method of -LDHs-6 / NF includes the following steps:

[0069] 1) Dissolve 2.25 mmol nickel acetylacetonate, 750 μmol cobalt acetylacetonate and 12.75 mmol triethanolamine in a mixed solvent containing deionized water and ethanol (the volume ratio of deionized water to ethanol is 1:1) and bring the volume up to 15 mL to obtain a mixed solution with a total metal salt concentration of 0.2 mol / L and an alkali concentration of 0.1 mol / L.

[0070] Steps 2) and 3) are the same as in Example 1, and will not be repeated here.

[0071] Example 7

[0072] This embodiment provides a phosphate-intercalated hydrotalcite catalyst, NiCo-PO4. 3- The preparation method of -LDHs-7 / NF is basically the same as that in Example 1, except that in step 1), the amount of nickel acetylacetone is replaced from 225 μmol to 150 μmol, and the amount of cobalt acetylacetone is replaced from 75 μmol to 150 μmol. All other steps are the same as in Example 1.

[0073] Example 8

[0074] This embodiment provides a phosphate-intercalated hydrotalcite catalyst, NiCo-PO4. 3- The preparation method of -LDHs-8 / NF is basically the same as that in Example 1, except that in step 1), the amount of nickel acetylacetone is replaced from 225 μmol to 75 μmol, and the amount of cobalt acetylacetone is replaced from 75 μmol to 225 μmol. All other steps are the same as in Example 1.

[0075] Example 9

[0076] This embodiment provides a phosphate-intercalated hydrotalcite catalyst, NiCo-PO4. 3- The preparation method of -LDHs-9 / NF is basically the same as that in Example 1, except that in step 2), the temperature of the hydrothermal reaction is changed from 120°C to 60°C, and the other steps are the same as those in Example 1.

[0077] Example 10

[0078] This embodiment provides a phosphate-intercalated hydrotalcite catalyst, NiCo-PO4. 3-The preparation method of -LDHs-10 / NF is basically the same as that of Example 1, except that in step 2), the hydrothermal reaction time is changed from 120℃ to 180℃, and the other steps are the same as those of Example 1.

[0079] Example 11

[0080] This embodiment provides a phosphate-intercalated hydrotalcite catalyst, NiCo-PO4. 3- The preparation method of -LDHs-11 / NF is basically the same as that of Example 1, except that in step 2), the hydrothermal reaction temperature is changed from 6 hours to 1 hour, and the other steps are the same as those of Example 1.

[0081] Example 12

[0082] This embodiment provides a phosphate-intercalated hydrotalcite catalyst, NiCo-PO4. 3- The preparation method of -LDHs-12 / NF is basically the same as that of Example 1, except that in step 2), the hydrothermal reaction temperature is changed from 6 hours to 12 hours, and the other steps are the same as those of Example 1.

[0083] Example 13

[0084] This embodiment provides a phosphate-intercalated hydrotalcite catalyst, NiCo-PO4. 3- The preparation method of -LDHs-13 / NF is basically the same as that in Example 1, except that in step 3), sodium phosphate is replaced with potassium phosphate, and the other steps are the same as those in Example 1.

[0085] Example 14

[0086] This embodiment provides a phosphate-intercalated hydrotalcite catalyst, NiCo-PO4. 3- The preparation method of -LDHs-14 / NF is basically the same as that in Example 1, except that in step 3), the intercalating agent solution containing 1.0 mol / L potassium hydroxide and 0.1 mol / L sodium phosphate is replaced with an intercalating agent solution containing 1.0 mol / L potassium phosphate. All other steps are the same as in Example 1.

[0087] Example 15

[0088] This embodiment provides a hypophosphite-intercalated hydrotalcite catalyst, NiCo-H2PO2. - The preparation method of -LDHs-15 / NF is basically the same as that in Example 1, except that in step 3), sodium phosphate is replaced with sodium hypophosphite, and the other steps are the same as in Example 1.

[0089] From the catalyst NiCo-H2PO2 - NiCo-H2PO2 was obtained by surface scraping of -LDHs-15 / NF. - -LDHs-15 powder was characterized by XRD. Figure 2 NiCo-H2PO2 - XRD pattern of -LDHs-15, from Figure 2 It can be seen that the sample exhibits NiCo-H2PO2. - The characteristic diffraction peaks of the (003), (006), (012) and (110) crystal planes of the -LDHs-15 material indicate that a well-structured layered hydrotalcite material has been synthesized, while the (003) diffraction peak is located at 11.0 degrees, indicating the intercalation of hypophosphite ions.

[0090] Example 16

[0091] This embodiment provides a hypophosphite-intercalated hydrotalcite catalyst, NiCo-H2PO2. - The preparation method of -LDHs-16 / NF is basically the same as that in Example 1, except that in step 3), sodium phosphate is replaced with potassium hypophosphite, and the other steps are the same as in Example 1.

[0092] Example 17

[0093] This embodiment provides a phosphate-intercalated hydrotalcite catalyst, NiCo-PO4. 3- The preparation method of -LDHs-17 / NF is basically the same as that in Example 1, except that in step 3), the concentration of potassium hydroxide is replaced from 1.0 mol / L to 0.01 mol / L and the concentration of sodium phosphate is replaced from 0.1 mol / L to 0.01 mol / L. All other steps are the same as in Example 1.

[0094] Example 18

[0095] This embodiment provides a phosphate-intercalated hydrotalcite catalyst, NiCo-PO4. 3- The preparation method of -LDHs-18 / NF is basically the same as that in Example 1, except that in step 3), the concentration of potassium hydroxide is replaced from 1.0 mol / L to 3.0 mol / L. All other steps are the same as in Example 1.

[0096] Example 19

[0097] This embodiment provides a phosphate-intercalated hydrotalcite catalyst, NiCo-PO4. 3-The preparation method of -LDHs-19 / NF is basically the same as that in Example 1, except that in step 3), the ion exchange time is changed from 24h to 6h, and the other steps are the same as those in Example 1.

[0098] Example 20

[0099] This embodiment provides a phosphate-intercalated hydrotalcite catalyst, NiCo-PO4. 3- The preparation method of -LDHs-20 / NF is basically the same as that in Example 1, except that in step 3), the ion exchange time is changed from 24h to 48h, and the other steps are the same as those in Example 1.

[0100] Example 21

[0101] This embodiment provides a phosphate-intercalated hydrotalcite catalyst NiFe-PO4. 3- The preparation method of -LDHs-21 / NF is basically the same as that of Example 1, except that in step 1), cobalt acetylacetone is replaced with iron acetylacetone, and the other steps are the same as those of Example 1.

[0102] Example 22

[0103] This embodiment provides a phosphate-intercalated hydrotalcite catalyst, NiCoFe-PO4. 3- The preparation method of -LDHs-22 / NF is basically the same as that in Example 1, except that step 1) is: 225 μmol nickel acetylacetone, 37.5 μmol cobalt acetylacetone, 37.5 μmol iron acetylacetone and 1.275 mmol triethanolamine are dissolved in a mixed solvent containing deionized water and ethanol (the volume ratio of deionized water to ethanol is 1:1) and the volume is adjusted to 15 mL to obtain a metal salt solution with a total metal salt concentration of 0.02 mol / L and an alkali concentration of 0.085 mol / L.

[0104] Test case

[0105] The electrocatalytic oxidation performance of the catalysts prepared in Examples 1-22 was tested using the following methods:

[0106] Using an electrochemical workstation and a three-electrode system, the catalyst electrode prepared in the above examples was used as the working electrode, a platinum sheet as the counter electrode, and Hg / HgO as the reference electrode. 50 mmol / L of 5-hydroxymethylfurfural was added to a 1.0 mol / L KOH electrolyte solution as the electrolyte for the electrocatalytic oxidation of 5-hydroxymethylfurfural. Linear voltammetry (LSV) was performed on the catalyst, and the onset potential was recorded. The current density reached 200 mA / cm². 2The required potential and the selectivity for oxidation to 2,5-furandicarboxylic acid (FDCA) were determined. Specific results are shown in Table 1.

[0107] Table 1

[0108]

[0109]

[0110] As shown in Table 2, the catalysts used in Examples 1-22 can all electrocatalyze the oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid with high selectivity, all above 94%, with a maximum selectivity of 99.2%. Furthermore, the onset potential of the catalysts is consistently around 1.4V. RHE The following values ​​can all reach 200 mA / cm at relatively low potentials. 2 Industrial-grade current density, requiring as little as 1.41V. RHE .

[0111] Example 23

[0112] This embodiment provides a method for preparing 2,5-furandicarboxylic acid by electrocatalytic oxidation of 5-hydroxymethylfurfural, comprising the following steps:

[0113] Using an electrochemical workstation and a three-electrode system, the NiCo-PO4 prepared in Example 1 was subjected to... 3- Using -LDHs-1 / NF as the working electrode, a platinum sheet as the counter electrode, and Hg / HgO as the reference electrode, 50 mmol / L 5-hydroxymethylfurfural was added to a 1.0 mol / L KOH electrolyte solution as the electrolyte to conduct an electrocatalytic oxidation experiment of 5-hydroxymethylfurfural.

[0114] The above system was subjected to linear voltammetric scanning (LSV) testing. Figure 3 NiCo-PO4 3- The LSV curve of -LDHs-1 / NF in 1.0 mol / L KOH + 50 mmol / L 5-hydroxymethylfurfural electrolyte, from... Figure 3 As can be seen from this, at 1.41V RHE It can reach 200mA / cm 2 The current density.

[0115] At 1.50V RHE Under constant potential, NiCo-PO4 was used 3-The -LDHs-1 / NF electrode was used for the electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF), achieving a HMF conversion of 99.9%, a 2,5-furandicarboxylic acid (FDCA) selectivity of 99.5%, and a Faradaic efficiency of 99.3%. This electrode was then cycled 10 times continuously at this constant potential for the electrocatalytic oxidation of HMF. The HMF conversion, FDCA selectivity, and Faradaic efficiency from the 1st to the 10th cycle are shown in Table 2.

[0116] Table 2

[0117] Loop count HMF conversion rate / % FDCA selectivity / % Faraday efficiency / % 1 99.9 99.5 99.3 2 99.9 99.8 99.6 3 99.9 99.8 99.7 4 99.9 99.4 99.2 5 99.8 99.6 99.1 6 99.9 99.3 99.1 7 99.9 99.5 99.2 8 99.8 99.4 99.2 9 99.9 99.6 99.4 10 99.9 99.3 99.1

[0118] As can be seen from the data in Table 2, after 10 consecutive cycles, the catalyst electrode prepared in Example 1 did not show significant deactivation, and the HMF conversion rate and FDCA selectivity remained above 99%, indicating that the intercalated hydrotalcite catalyst prepared in this invention has good activity and stability in HMF electrocatalytic oxidation.

[0119] Examples 24 to 39

[0120] Examples 24-39 provide a method for preparing the corresponding carboxylic acid by electrocatalytic oxidation of alcohols or aldehydes. The specific steps are basically the same as those in Example 23. The differences are listed in Table 3. For easy comparison, the relevant parameters of Example 23 are also listed in Table 3.

[0121] Table 3

[0122]

[0123]

[0124]

[0125] Example 40

[0126] This embodiment provides a method for preparing 2,5-furandicarboxylic acid by electrocatalytic oxidation of 5-hydroxymethylfurfural, comprising the following steps:

[0127] Using an electrochemical workstation and a three-electrode system, the NiCo-PO4 prepared in Example 1 was... 3- -LDHs-1 / NF was used as the working electrode, a platinum sheet as the counter electrode, and Hg / HgO as the reference electrode. 50 mmol / L 5-hydroxymethylfurfural was added to a 1.0 mol / L KOH electrolyte solution as the electrolyte. The electrolyte was set at 10 mA / cm². 2 At a current density, NiCo-PO4 3--LDHs-1 / NF electrodes were used for the constant current oxidation of 5-hydroxymethylfurfural, achieving a 5-hydroxymethylfurfural conversion rate of 99.2%, a 2,5-furandicarboxylic acid selectivity of 93.9%, and a Faraday efficiency of 91.3%.

[0128] Example 41

[0129] This embodiment provides a method for preparing 2,5-furandicarboxylic acid by electrocatalytic oxidation of 5-hydroxymethylfurfural, comprising the following steps:

[0130] Using an electrochemical workstation and a three-electrode system, the NiCo-PO4 prepared in Example 1 was... 3- -LDHs-1 / NF was used as the working electrode, a platinum sheet as the counter electrode, and Hg / HgO as the reference electrode. 50 mmol / L 5-hydroxymethylfurfural was added to a 1.0 mol / L KOH electrolyte solution as the electrolyte. The electrolyte was measured at 500 mA / cm². 2 At a current density, NiCo-PO4 3- -LDHs-1 / NF electrodes were used for the constant current oxidation of 5-hydroxymethylfurfural, achieving a 5-hydroxymethylfurfural conversion rate of 99.1%, a 2,5-furandicarboxylic acid selectivity of 99.2%, and a Faraday efficiency of 67.0%.

[0131] Example 42

[0132] This embodiment provides a method for preparing 2,5-furandicarboxylic acid by electrocatalytic oxidation of 5-hydroxymethylfurfural, comprising the following steps:

[0133] Using an electrochemical workstation and a three-electrode system, the NiCo-PO4 prepared in Example 1 was... 3- -LDHs-1 / NF was used as the working electrode, a platinum sheet as the counter electrode, and Hg / HgO as the reference electrode. 50 mmol / L 5-hydroxymethylfurfural was added to a 1.0 mol / L KOH electrolyte solution as the electrolyte. The electrolyte was set at 150 mA / cm². 2 At a current density, NiCo-PO4 3- -LDHs-1 / NF electrodes were used for the constant current oxidation of 5-hydroxymethylfurfural, achieving a 5-hydroxymethylfurfural conversion rate of 99.1%, a 2,5-furandicarboxylic acid selectivity of 99.1%, and a Faraday efficiency of 98.9%.

[0134] The following conclusions can be drawn from the comparison of Examples 23 to 42:

[0135] 1) A comparison of Examples 23 and 38-42 shows that both controlling the reaction potential and controlling the reaction current density for electrocatalytic oxidation result in high substrate conversion, carboxylic acid product selectivity, and Faradaic efficiency. A comparison of Examples 21 and 36-37 shows that a reaction potential of 1.50V is optimal. RHE At a given reaction potential, the substrate conversion, carboxylic acid product selectivity, and faradaic efficiency are highest. As the reaction potential decreases, the substrate conversion, carboxylic acid product selectivity, and faradaic efficiency decrease, but the decrease is not significant. As the reaction potential increases, the substrate conversion and carboxylic acid product selectivity remain essentially unchanged, but the faradaic efficiency decreases significantly.

[0136] 2) As can be seen from the comparison of Examples 23 to 26, the catalyst electrode of the present invention exhibits excellent catalytic activity in the electro-oxidation of aldehydes and alcohols such as 5-hydroxymethylfurfural, furfural, ethanol, and benzyl alcohol, with substrate conversion, carboxylic acid product selectivity and Faraday efficiency of not less than 96%.

[0137] 2) As can be seen from the comparison of Examples 23, 27-33, the catalyst of the present invention exhibits excellent catalytic activity in different types of electrolyte solutions.

[0138] 3) As can be seen from the comparison of Examples 23 and 34-35, when the concentration of electrolyte is too low, the conversion rate of HMF, the selectivity of carboxylic acid products and the Faradaic efficiency all decrease. When the concentration of electrolyte is too high, the conversion rate of HMF remains basically unchanged, but the selectivity of carboxylic acid products and the Faradaic efficiency both decrease.

[0139] 4) As can be seen from the comparison of Examples 23 and 36-37, the concentration of the substrate in the electrolyte solution also affects the catalytic oxidation effect. When the concentration of HMF is 50 mmol / L, the substrate conversion rate, carboxylic acid product selectivity and Faraday efficiency are optimal.

[0140] Comparative Example 1

[0141] This comparative example provides a carbonate-intercalated hydrotalcite catalyst, NiCo-CO3. 2- The preparation method of -LDHs / NF includes the following steps:

[0142] 1) Dissolve 225 μmol nickel nitrate, 75 μmol cobalt nitrate and 1.275 mmol urea in deionized water and bring the volume to 15 mL to obtain a mixed solution with a total metal salt concentration of 0.02 mol / L and an alkali concentration of 0.085 mol / L;

[0143] 2) A piece of nickel foam (15mm × 10mm) was placed in a hydrothermal reactor containing a mixed solution and kept at 120℃ for 6 hours to carry out the hydrothermal reaction. The resulting product was repeatedly washed with deionized water and anhydrous ethanol, and then dried overnight in a vacuum drying oven to obtain the carbonate intercalated hydrotalcite catalyst NiCo-CO3. 2- -LDHs / NF.

[0144] From the catalyst NiCo-CO3 2- NiCo-CO3 was obtained by surface scraping of -LDHs / NF. 2- -LDHs powder was characterized by XRD. Figure 4 NiCo-CO3 2- XRD patterns of -LDHs, from Figure 4 As can be seen, the sample exhibits a distinct diffraction peak at 2θ = 11.4° (003), which is attributed to NiCo-CO3. 2- The characteristic peaks of -LDHs, while the (003) diffraction peak is located at 2θ=11.4°, indicating the intercalation of carbonate ions.

[0145] Comparative Example 2

[0146] This comparative example provides a method for preparing 2,5-furandicarboxylic acid by electrocatalytic oxidation of 5-hydroxymethylfurfural, including the following steps:

[0147] Using an electrochemical workstation and a three-electrode system, the NiCo-CO3 prepared in Comparative Example 1 was analyzed. 2- Using an LDHs / NF electrode as the working electrode, a platinum sheet as the counter electrode, and Hg / HgO as the reference electrode, 50 mmol / L 5-hydroxymethylfurfural was added to a 1.0 mol / L KOH electrolyte solution as the electrolyte to conduct an electrocatalytic oxidation experiment of 5-hydroxymethylfurfural.

[0148] The above system was subjected to linear voltammetric scanning (LSV) testing. Figure 5 NiCo-CO3 2- The LSV curve of -LDHs / NF in 1.0 mol / L KOH + 50 mmol / L 5-hydroxymethylfurfural electrolyte, from... Figure 5 As can be seen from this, at 1.41V RHE It can only reach 74mA / cm 2 The current density.

[0149] At 1.50V RHE Under constant potential, NiCo-CO3 was used 2--LDHs / NF were used for the electrocatalytic oxidation of 5-hydroxymethylfurfural, achieving a 5-hydroxymethylfurfural conversion rate of 93.8%, a 2,5-furandicarboxylic acid selectivity of 93.9%, and a Faraday efficiency of 88.1%.

[0150] As can be seen from the comparison between Example 23 and Comparative Example 2, the use of NiCo-CO3... 2- When 5-hydroxymethylfurfural is electrocatalyzed using LDHs / NF as a catalyst, the current density is low, the electro-oxidation rate is slow, 5-hydroxymethylfurfural undergoes significant degradation, and the selectivity and Faradaic efficiency of 2,5-furandicarboxylic acid are significantly lower than those of NiCo-PO4. 3- -LDHs-1 / NF catalyst. The reason may lie in NiCo-CO3. 2- -LDHs / NF catalysts have weak nucleophilicity of carbonate ions in the interlayer, and cannot act as a proton transfer medium to accelerate the dehydrogenation process of metal hydroxides, resulting in an insufficient number of NiOOH active sites formed.

[0151] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing an intercalated hydrotalcite catalyst, characterized in that, Includes the following steps: 1) Dissolve the first metal salt, the second metal salt, and the organic base in a solvent to obtain a metal salt solution; The first metal salt is selected from nickel nitrate or acetylacetonate, the second metal salt is selected from cobalt and / or iron nitrate or acetylacetonate, and the organic base is selected from triethanolamine and / or diethanolamine; 2) The conductive substrate is added to the metal salt solution for hydrothermal reaction, and the first metal salt and the second metal salt are transformed in situ to form a trimetallic or bimetallic layered double hydroxide and coupled with the conductive substrate to obtain an intercalated hydrotalcite catalyst precursor with hydroxide ions in the interlayer. 3) The intercalated hydrotalcite catalyst precursor is added to an aqueous solution containing an intercalating agent for ion exchange treatment to obtain the intercalated hydrotalcite catalyst. The ion exchange treatment is to replace the hydroxide ions between the layers with intercalated anions so that the intercalated anions act as a proton transfer medium to promote the dehydrogenation of Ni(OH)2 in the layers to form an active center for electrocatalytic oxidation of NiOOH. The intercalating agent includes an intercalating anion, which is selected from phosphate ions or hypophosphite ions; The intercalating agent is selected from sodium phosphate, potassium phosphate, sodium hypophosphite, or potassium hypophosphite. The concentration of the intercalating agent in the aqueous solution is 0.01~3.0 mol / L.

2. The preparation method according to claim 1, characterized in that, In step 1), the solvent is selected from water and / or ethanol.

3. The preparation method according to claim 1 or 2, characterized in that, In step 1), the sum of the concentrations of the first metal salt and the second metal salt in the metal salt solution is 0.01~0.2 mol / L; and / or, the concentration of the organic base in the metal salt solution is 0.02~1.0 mol / L.

4. The preparation method according to claim 3, characterized in that, In step 1), the molar ratio of the first metal salt to the second metal salt is (1~4):

1.

5. The preparation method according to claim 1, characterized in that, In step 2), the conductive substrate is selected from one of nickel foam, carbon paper, and carbon felt.

6. The preparation method according to claim 1, characterized in that, In step 2), the temperature of the hydrothermal reaction is 60~180℃ and the time is 1~12h.

7. The preparation method according to claim 1, characterized in that, In step 3), the ion exchange treatment time is 6~48h.

8. An intercalated hydrotalcite catalyst, characterized in that, Prepared by the preparation method according to any one of claims 1-7.

9. A method for the electrocatalytic oxidation of aldehydes or alcohols, characterized in that, The process includes the following steps: using a three-electrode system, with the intercalated hydrotalcite catalyst as described in claim 8 as the working electrode, and an electrolyte solution containing the alcohol or aldehyde compound as the electrolyte, to carry out an electrochemical catalytic oxidation reaction under constant reaction potential or constant reaction current density.

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