A tungstate catalyst based on modification by alkali metal hydroxide, its preparation method and use

Abstract

The present application relates to the technical field of electrochemical catalyst, in particular to a tungstate catalyst based on alkali metal hydroxide modification and its preparation method and application. The method comprises the following steps: providing a metal tungstate; contacting the metal tungstate with an alkali metal hydroxide solution, and performing modification treatment to obtain a tungstate catalyst based on alkali metal hydroxide modification. The present application significantly improves the performance of the metal tungstate in the oxygen reduction synthesis of hydrogen peroxide reaction through simple alkali metal hydroxide soaking treatment. The method is simple in operation, low in cost, and suitable for large-scale production. The prepared catalyst is a carbon-free catalyst system, which avoids the problem of carbon corrosion, exhibits excellent hydrogen peroxide selectivity and stability in alkaline medium, and has good application prospect.

Description

Technical Field

[0001] This invention relates to the field of electrochemical catalyst technology, and in particular to a tungstate catalyst based on alkali metal hydroxide modification, its preparation method, and its application. Background Technology

[0002] Hydrogen peroxide (H2O2), as an important green oxidant, has wide applications in papermaking, textiles, printing and dyeing, water treatment, and semiconductors. Currently, the anthraquinone process is mainly used in industry to produce H2O2. Although this process is relatively mature, it suffers from high energy consumption, environmental pollution, and safety hazards, hindering its green and sustainable development. In recent years, the electrochemical oxygen reduction synthesis of hydrogen peroxide has gradually become a research hotspot due to its advantages such as being green, controllable, and allowing for on-site production. The core of this technical route lies in developing catalyst materials that combine high selectivity and high stability.

[0003] Currently, noble metal alloys and carbon-based single-atom catalysts show great potential in improving the selectivity of H2O2. However, the scarcity and high cost of noble metal resources limit their large-scale application; while carbon-based materials are prone to carbon corrosion during long-term operation, leading to structural degradation and performance decline, with significant stability issues. Therefore, there is an urgent need to develop novel catalyst systems that combine low cost, high stability, and no carbon active centers. Transition metal tungstates have gradually attracted attention due to their tunable composition, abundant resources, and stable structure, and are considered potential alternative materials. However, existing studies show that most transition metal tungstates perform poorly in H2O2 selectivity, which is still insufficient to meet practical application requirements. How to effectively improve their selectivity for oxygen reduction synthesis of H2O2 while maintaining their structural advantages has become a key issue in promoting their application.

[0004] Chinese patent CN112264004A discloses a tungstate-based catalytic material, whose main components are one or more of Bi2WO6, CaWO4, SnWO4, ZnWO4, CoWO4, and MnWO4, and its application in the synthesis of hydrogen peroxide from water oxidation, but does not cover its application in the synthesis of H2O2 from oxygen reduction. Another patent (publication number: CN118002140A) discloses a catalytic material containing transition metal tungstates such as FeWO4, CoWO4, NiWO4, and CuWO4, and its application in the synthesis of valerolactam, but similarly does not cover the technical content of oxygen reduction to prepare H2O2. In summary, although methods for preparing transition metal tungstates have been reported, their application in the electrochemical oxygen reduction synthesis of hydrogen peroxide remains a blank area. Summary of the Invention

[0005] The purpose of this invention is to address the problems existing in the prior art by providing a tungstate catalyst modified with alkali metal hydroxide, its preparation method, and its application. The catalyst is modified by contacting a metal tungstate with an alkali metal hydroxide solution to improve the performance of the metal tungstate in the oxygen reduction to hydrogen peroxide synthesis reaction.

[0006] To achieve the above objectives, the present invention provides a method for preparing a tungstate catalyst modified with alkali metal hydroxide, comprising the following steps: S1. Provides metal tungstate; S2. The metal tungstate is contacted with an alkali metal hydroxide solution to perform modification treatment, thereby obtaining a tungstate catalyst modified with alkali metal hydroxide.

[0007] In an optional embodiment, in S1, the method for preparing the metal tungstate includes: mixing a soluble tungsten source and a post-transition metal salt in a solvent and carrying out a hydrothermal reaction to obtain the metal tungstate.

[0008] In an optional embodiment, the soluble tungsten source includes at least one of tungstic acid, ammonium tungstate, ammonium metatungstate, ammonium paratungstate, sodium tungstate, sodium metatungstate, sodium paratungstate, potassium tungstate, potassium metatungstate, potassium paratungstate, lithium tungstate, and lithium metatungstate; the post-transition metal salt includes at least one of cadmium nitrate, nickel nitrate, cadmium chloride, nickel chloride, cadmium sulfate, nickel sulfate, cadmium formate, nickel formate, cadmium acetate, and nickel acetate; the solvent includes at least one of water, ethanol, and methanol; and the ratio of the amount of the soluble tungsten source, the post-transition metal salt, and the solvent is (0.5-20) mmol:(0.5-20) mmol:(10-200) mL.

[0009] In an optional embodiment, a surfactant is also added during the mixing process; the surfactant includes at least one of sodium dodecyl sulfonate, polyvinylpyrrolidone, hexadecyltrimethylammonium bromide, and hexadecyltrimethylammonium chloride; the molar ratio of the soluble tungsten source to the surfactant is (0.5-20):(0.5-20).

[0010] In one optional embodiment, the mixing method includes at least one of stirring and ultrasonication; the mixing time is 10-120 min.

[0011] In one optional embodiment, the hydrothermal reaction is carried out at a temperature of 120-190°C for a duration of 5-24 hours.

[0012] In one optional embodiment, after the hydrothermal reaction is completed, the product is naturally cooled to room temperature, and then washed with water and dried sequentially to obtain metal tungstate.

[0013] In an optional embodiment, the alkali metal hydroxide includes at least one of lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide; the concentration of the alkali metal hydroxide solution is 0.01-5 mol / L.

[0014] In one optional implementation, the modification treatment takes 12-72 hours.

[0015] In one optional embodiment, after the modification treatment is completed, the solid product is collected by centrifugation, and then washed with water and dried in sequence to obtain a tungstate catalyst based on alkali metal hydroxide modification.

[0016] The present invention also provides a tungstate catalyst based on alkali metal hydroxide modification, which is prepared according to the preparation method described above.

[0017] In one optional embodiment, the catalyst has a rod-like or granular morphology and a size of 5-500 nm.

[0018] The present invention also provides the application of the alkali metal hydroxide-modified tungstate catalyst in the electrochemical oxygen reduction synthesis of hydrogen peroxide.

[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention provides a simple and low-cost method for modifying alkali metal hydroxides. The method can achieve modification by immersing pre-prepared metal tungstate in an alkali metal hydroxide solution. The entire process is carried out at room temperature and pressure, without the need for complex equipment, and is easy to scale up for production, showing good application prospects.

[0020] (2) The alkali metal hydroxide modified tungstate catalyst prepared in this invention is a carbon-free catalyst system, which avoids the carbon corrosion problem that traditional carbon-based materials are prone to during long-term electrochemical operation, and ensures the electrochemical stability of the catalyst from the material design level.

[0021] (3) This invention significantly improves the selectivity of metal tungstates in the oxygen reduction synthesis of hydrogen peroxide by modifying them with alkali metal hydroxides. This method can effectively regulate the surface properties of metal tungstates, making them more favorable for the two-electron oxygen reduction pathway.

[0022] (4) The method of the present invention has good universality and is applicable to a variety of post-transition metal tungstate systems. It can be modified by different kinds of alkali metal hydroxides, providing a new technical idea for the design of oxygen reduction synthesis hydrogen peroxide catalyst. Attached Figure Description

[0023] Figure 1This is the XRD analysis diagram of CdWO4-CsOH in Example 1 of the present invention; Figure 2 This is the XRD analysis diagram of NiWO4-KOH in Example 2 of the present invention; Figure 3 This is a TEM characterization image of CdWO4-CsOH in Example 1 of the present invention; Figure 4 This is a TEM characterization image of NiWO4-KOH in Example 2 of the present invention; Figure 5 This is a polarization curve of CdWO4-CsOH in potassium hydroxide solution in Example 1 of the present invention; Figure 6 This is the H2O2 selectivity diagram of CdWO4-CsOH in Example 1 of the present invention; Figure 7 This is the H2O2 selectivity diagram of NiWO4-KOH in Example 2 of the present invention; Figure 8 This is the H2O2 selectivity diagram of CdWO4-CsOH after 40,000 cycles in Example 1 of this invention; Figure 9 This is the H2O2 selectivity diagram of NiWO4-KOH after 20,000 cycles in Example 2 of the present invention; Figure 10 This is a Faraday efficiency diagram of CdWO4-CsOH under different current densities in Embodiment 1 of the present invention; Figure 11 In Example 1 of this invention, CdWO4-CsOH is at 100 mA / cm 2 Stability plot below; Figure 12 This is a Faraday efficiency diagram of NiWO4-KOH under different current densities in Embodiment 2 of the present invention; Figure 13 In Example 2 of this invention, NiWO4-KOH is at 100 mA / cm 2 The stability plot below. Detailed Implementation

[0024] The following embodiments are provided to better understand the present invention and are not limited to the described embodiments. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0025] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0026] Example 1 This embodiment provides a method for preparing a tungstate catalyst modified with alkali metal hydroxide, comprising the following steps: Weigh out 2 mmol sodium tungstate, 3 mmol cadmium nitrate, and 4 mmol hexadecyltrimethylammonium bromide and dissolve them in 60 mL of deionized water. After stirring for 60 min, transfer the solution to a hydrothermal reactor and react at 180 °C for 12 h. After the reaction is complete, allow the solution to cool naturally to room temperature. Wash the product five times with deionized water and dry it at 70 °C for 12 h to obtain metal tungstate (cadmium tungstate).

[0027] Cadmium tungstate was immersed in 15 mL of 0.1 mol / L cesium hydroxide aqueous solution and allowed to stand for 48 h. After the treatment, the solid product was collected by centrifugation, washed 5 times with deionized water, and dried at 70 °C for 12 h to obtain the tungstate catalyst modified by alkali metal hydroxide (cesium hydroxide modified cadmium tungstate catalyst, denoted as CdWO4-CsOH).

[0028] Example 2 This embodiment provides a method for preparing a tungstate catalyst modified with alkali metal hydroxide, comprising the following steps: Weigh 2 mmol sodium tungstate, 3 mmol nickel nitrate, and 4 mmol hexadecyltrimethylammonium bromide and dissolve them in 60 mL of deionized water. After stirring for 60 min, transfer the solution to a hydrothermal reactor and react at 180 °C for 12 h. After the reaction is complete, allow the solution to cool naturally to room temperature. Wash the product five times with deionized water and dry it at 70 °C for 12 h to obtain metallic tungstate (nickel tungstate).

[0029] Nickel tungstate was immersed in 15 mL of 0.1 mol / L potassium hydroxide aqueous solution and allowed to stand for 60 h. After the treatment, the solid product was collected by centrifugation, washed 5 times with deionized water, and dried at 70 °C for 12 h to obtain the tungstate catalyst modified by alkali metal hydroxide (potassium hydroxide modified nickel tungstate catalyst, denoted as NiWO4-KOH).

[0030] Example 3 This embodiment provides a method for preparing a tungstate catalyst modified with alkali metal hydroxides, the difference from Example 1 being that the cesium hydroxide aqueous solution is replaced with a sodium hydroxide aqueous solution. Finally, a tungstate catalyst modified with alkali metal hydroxides (sodium hydroxide-modified cadmium tungstate catalyst, denoted as CdWO4-NaOH) is prepared.

[0031] Experimental Example 1 X-ray diffraction (XRD) analysis was performed on the CdWO4-CsOH prepared in Example 1, and the XRD pattern of CdWO4-CsOH in Example 1 was obtained, as shown in the figure. Figure 1 As shown. Figure 1 In this context, "Intensity" refers to the strength of an object. Figure 1 The diffraction peaks of CdWO4-CsOH correspond well with the standard cadmium tungstate (CdWO4) card, indicating that the modification treatment did not change the crystal structure of cadmium tungstate.

[0032] X-ray diffraction (XRD) analysis was performed on the NiWO4-KOH prepared in Example 2, and the XRD pattern of NiWO4-KOH in Example 2 was obtained, as shown below. Figure 2 As shown. Figure 2 In this context, "Intensity" refers to the strength of an object. Figure 2 It can be seen that the diffraction peaks of NiWO4-KOH correspond well with the standard nickel tungstate (NiWO4) card.

[0033] Experiment Example 2 The morphology of CdWO4-CsOH in Example 1 was observed using transmission electron microscopy (TEM), and the TEM characterization image of CdWO4-CsOH in Example 1 was obtained, as shown below. Figure 3 As shown, CdWO4-CsOH exhibits a nanorod-like structure with a width of 50-180 nm.

[0034] The morphology of NiWO4-KOH in Example 2 was observed using transmission electron microscopy (TEM), and the TEM characterization image of NiWO4-KOH in Example 2 was obtained, as shown below. Figure 4 As shown, NiWO4-KOH exhibits a nanoparticle structure with a particle size of 5-20 nm.

[0035] Experimental Example 3 The oxygen reduction synthesis of hydrogen peroxide by CdWO4-CsOH in Example 1 was tested using a rotating ring-disk electrode in an oxygen-saturated 0.1 mol / L potassium hydroxide solution. The test conditions were: scan rate 10 mV / s, electrode rotation speed 1600 r / min. The polarization curves of CdWO4-CsOH in potassium hydroxide solution in Example 1 were obtained, as shown below. Figure 5 As shown; the H2O2 selectivity diagram of CdWO4-CsOH in Example 1, as shown. Figure 6 As shown. Figure 5 and Figure 6In this context, "Potential" refers to voltage, "Current density" refers to current density, and "0.1 M KOH solution" refers to a 0.1 mol / L potassium hydroxide solution. The results show that the hydrogen peroxide selectivity of CdWO4-CsOH at 0.1 V vs. RHE is 84.3%.

[0036] The NiWO4-KOH in Example 2 was tested using the same testing method as described above, and the H2O2 selectivity diagram of NiWO4-KOH in Example 2 was obtained, as shown below. Figure 7 As shown. Figure 7 In this context, "Potential" refers to voltage, and "0.1M KOH solution" refers to a 0.1 mol / L potassium hydroxide solution. The results show that the hydrogen peroxide selectivity of NiWO4-KOH at 0.1 V vs. RHE is 93%.

[0037] Experiment Example 4 Cyclic voltammetry was performed on CdWO4-CsOH in Example 1 for 40,000 cycles within the range of 0.1-0.7 V. After the scan, the hydrogen peroxide selectivity was tested again to obtain the H2O2 selectivity curve of CdWO4-CsOH in Example 1 after 40,000 cycles, as shown below. Figure 8 As shown. Figure 8 In this context, "Potential" refers to voltage, "After 40,000 cycles" means after 40,000 cycles, "Initial" means the initial state, and "0.1M KOH solution" refers to a 0.1 mol / L potassium hydroxide solution. Figure 8 It can be seen that after 40,000 cycles, the catalyst exhibits a hydrogen peroxide selectivity of up to 93.7% at 0.1 V vs. RHE.

[0038] The same method was used to perform 20,000 cyclic voltammetric scans on NiWO4-KOH in Example 2. After the scan, the hydrogen peroxide selectivity was tested again to obtain the H2O2 selectivity diagram of NiWO4-KOH after 20,000 cycles in Example 2, as shown below. Figure 9 As shown. Figure 9 In this context, "Potential" refers to voltage, "After 20000 cycles" means after 20000 cycles, "Initial" means the initial state, and "0.1MKOH solution" refers to a 0.1 mol / L potassium hydroxide solution. From... Figure 9 It can be seen that after 20,000 cycles, the selectivity of the catalyst for hydrogen peroxide at 0.1 V vs. RHE is still as high as 87%.

[0039] Experimental Example 5 The Faradaic efficiency of CdWO4-CsOH obtained in Example 1 was tested in a flow cell at different current densities, resulting in the Faradaic efficiency graph of CdWO4-CsOH in Example 1 at different current densities, as shown below. Figure 10 As shown. Figure 10 In this context, Currentdensity refers to current density, and FE refers to Faraday efficiency. Figure 10 It can be obtained that the catalyst is at 100 mA / cm 2 The Faraday efficiency at current density is 85.1%.

[0040] In a flow cell at 100 mA / cm 2 A constant current test was performed on the CdWO4-CsOH obtained in Example 1. After 34 hours of testing, the CdWO4-CsOH in Example 1 was found to have a discharge current of 100 mA / cm². 2 The stability plot below, such as Figure 11 As shown. Figure 11 In this context, "Time" refers to time, "Potential" refers to voltage, and "FE" refers to Faraday efficiency. Figure 11 The average Faraday efficiency over 34 hours is 84.3%.

[0041] The Faraday efficiency of NiWO4-KOH in Example 2 was tested using the same method, and the Faraday efficiency diagrams of NiWO4-KOH at different current densities in Example 2 were obtained, as shown below. Figure 12 As shown. Figure 12 In this context, "Current density" refers to the current density, and "FE" refers to the Faraday efficiency. In a flow cell, at a current density of 100 mA / cm²... 2 A constant current test was performed on the NiWO4-KOH obtained in Example 2. After 20 hours of testing, the NiWO4-KOH in Example 2 was found to be able to withstand continuous discharge at 100 mA / cm². 2 The stability plot below, such as Figure 13 As shown. Figure 13 In this context, "Time" refers to time, "Potential" refers to voltage, and "FE" refers to Faraday efficiency. Figure 12 and 13 It can be obtained that the catalyst operates at 100 mA / cm². 2 The Faraday efficiency reached 90.77%, and the average Faraday efficiency over 20 hours of discharge reached 90%.

[0042] In summary, this invention employs the above-mentioned tungstate catalyst modified with alkali metal hydroxide, its preparation method, and its application. By modifying the tungstate by contacting it with an alkali metal hydroxide solution, the performance of the tungstate in the oxygen reduction to hydrogen peroxide synthesis reaction is improved.

[0043] Finally, it should be noted that the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a tungstate catalyst modified with alkali metal hydroxide, characterized in that, Includes the following steps: S1. Provides metal tungstate; S2. The metal tungstate is contacted with an alkali metal hydroxide solution to perform modification treatment, thereby obtaining a tungstate catalyst modified with alkali metal hydroxide.

2. The preparation method according to claim 1, characterized in that, In S1, the preparation method of the metal tungstate includes: mixing a soluble tungsten source and a post-transition metal salt in a solvent and carrying out a hydrothermal reaction to obtain the metal tungstate.

3. The preparation method according to claim 2, characterized in that, The soluble tungsten source includes at least one of tungstic acid, ammonium tungstate, ammonium metatungstate, ammonium paratungstate, sodium tungstate, sodium metatungstate, sodium paratungstate, potassium tungstate, potassium metatungstate, potassium paratungstate, lithium tungstate, and lithium metatungstate; the post-transition metal salt includes at least one of cadmium nitrate, nickel nitrate, cadmium chloride, nickel chloride, cadmium sulfate, nickel sulfate, cadmium formate, nickel formate, cadmium acetate, and nickel acetate; the solvent includes at least one of water, ethanol, and methanol. The ratio of the amount of the soluble tungsten source, the post-transition metal salt, and the solvent is (0.5-20) mmol: (0.5-20) mmol: (10-200) mL.

4. The preparation method according to claim 2, characterized in that, A surfactant is also added during the mixing process; the surfactant includes at least one of sodium dodecyl sulfonate, polyvinylpyrrolidone, hexadecyltrimethylammonium bromide, and hexadecyltrimethylammonium chloride. The molar ratio of the soluble tungsten source to the surfactant is (0.5-20):(0.5-20).

5. The preparation method according to claim 2, characterized in that, The hydrothermal reaction is carried out at a temperature of 120-190℃ for 5-24 hours.

6. The preparation method according to claim 1, characterized in that, The alkali metal hydroxide includes at least one of lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide; the concentration of the alkali metal hydroxide solution is 0.01-5 mol / L.

7. The preparation method according to claim 1, characterized in that, The modification treatment takes 12-72 hours.

8. A tungstate catalyst based on alkali metal hydroxide modification, characterized in that, Prepared by the method according to any one of claims 1-7.

9. The tungstate catalyst based on alkali metal hydroxide modification according to claim 8, characterized in that, The catalyst has a rod-shaped or granular morphology and a size of 5-500 nm.

10. The application of the tungstate catalyst modified with alkali metal hydroxide as described in claim 8 or 9 in the electrochemical oxygen reduction synthesis of hydrogen peroxide.

Images