Preparation of hourglass type phosphomolybdic acid two-dimensional complex and application of hourglass type phosphomolybdic acid two-dimensional complex in electrocatalytic synthesis of ammonia

Abstract

The invention relates to preparation of an hourglass type phosphomolybdic acid two-dimensional complex and application of the hourglass type phosphomolybdic acid two-dimensional complex in electrocatalytic synthesis of ammonia. The obtained hourglass type phosphomolybdic acid two-dimensional complex is used for synthesizing ammonia through electro-catalysis nitrate radical reduction at normal temperature and normal pressure. The invention aims to solve the problems of poor stability and low catalytic performance of some multi-acid metal-organic complex crystalline materials used as electrode materials in the application of electrocatalytic nitrate reduction synthesis of ammonia. The chemical formula of the hourglass type phosphomolybdic acid two-dimensional complex disclosed by the invention is [Cu (p-tr2Ph) 2] 2 [Cu (p-tr2Ph)] 2 [Cu (H2O)] 2 [Cu3 (p-tr2Ph) Mo12 (HPO4) 3 (PO4) 5O40] (p-tr2Ph-Cu-P4Mo6 for short). The synthesis method comprises the following steps: adding copper chloride, molybdenum trioxide, phosphoric acid and an organic ligand p-tr2Ph into distilled water, uniformly stirring, adjusting the pH value, carrying out a hydrothermal reaction, and enabling the obtained complex material to have the maximum ammonia production rate of 16.73 mg h <-1 > mg cat <-1 > and the Faraday efficiency of 99.08% in a neutral electrolyte 0.1 M NaNO3 + 0.1 M Na2SO4 under the voltage of-1.0 V vs.RHE. The preparation process is low in energy consumption and low in cost, and a new solution is provided for designing an electrocatalyst for green and efficient synthesis of ammonia.

Description

Technical Field

[0001] The present invention relates to the technical field of catalyst materials for electrocatalytic nitrate reduction ammonia synthesis, and is concerned with the preparation of an hourglass-shaped phosphomolybdic acid-based two-dimensional complex and its application in electrocatalytic ammonia synthesis. Background Art

[0002] Since 1913, ammonia production has primarily relied on large-scale synthesis technologies based on the Haber-Bosch process. However, this process operates under high temperature and pressure, leading to energy loss, disruption of the nitrogen cycle, and significant greenhouse gas emissions. The electrocatalytic nitrate reduction reaction (e-NO3RR) is mild, clean, and pollution-free, making it considered one of the most promising approaches to replace the Haber-Bosch process and achieve green and sustainable ammonia synthesis. However, e-NO3RR currently faces significant challenges, including low catalytic activity, poor selectivity, and unsatisfactory ammonia yields. An efficient catalyst is a crucial component of the e-NO3RR system, facilitating nitrate adsorption, reducing the reaction activation energy, and improving selectivity for ammonia synthesis. Therefore, developing catalysts with high Faradaic efficiency, high ammonia yield, and a cost-effective approach is crucial to addressing these challenges.

[0003] Polyoxometalates (POMs) are an important class of polynuclear metal oxygen cluster compounds, usually composed of transition metals with high oxidation states (mainly W, V, and Mo). Due to their reversible redox properties and rich and regulated structural composition, they have great potential in catalysis, photochemistry, nanotechnology, medicine and other fields. In the POM family, [P4Mo V 6O 31 ] 12- (abbreviated as {P4Mo6}) The anion structure is stable, with small steric hindrance and abundant active oxygen atoms, especially the molybdenum in the structure is in the pentavalent reduced state (Mo V ), an excellent electron donor, also exhibits excellent synergistic effects with metal active sites and organic ligands, making {P4Mo6} highly topologically scalable and offering new insights into electrode materials for the electrocatalytic nitrate reduction to ammonia. Polyoxometalate-based metal-organic complexes are a class of crystalline materials with rich crystal structures and long-range order. Based on their promising application prospects, we have prepared a novel hourglass-shaped two-dimensional complex constructed from phosphomolybdic polyoxometalate. This catalyst efficiently catalyzes the conversion of nitrate to ammonia at room temperature and pressure, while suppressing the formation of byproducts. Summary of the Invention

[0004] The purpose of the present invention is to provide an hourglass-shaped phosphomolybdic acid-based two-dimensional complex to address the problems of poor stability and low conductivity of polyacid materials. The present invention uses an hourglass-shaped phosphomolybdic acid {P4Mo6} as a basic unit through in-situ growth, introduces the catalytically active element Cu and the organic ligand p-tr2Ph, and obtains an hourglass-shaped phosphomolybdic acid-based two-dimensional complex to improve electrocatalytic selectivity and stability. In order to improve the performance of electrocatalytic nitrate synthesis of ammonia, the present invention provides a preparation method and application of an hourglass-shaped phosphomolybdic acid-based two-dimensional complex. In order to achieve the purpose of the above invention, the present invention provides the following technical solutions:

[0005] 1. Weigh copper chloride, molybdenum trioxide, and p-tr2Ph in a beaker, add deionized water and stir evenly, then add phosphoric acid and stir evenly, and adjust the pH of the suspension to 3.0-4.0.

[0006] The molar ratio of copper chloride to molybdenum trioxide in step 1 is 2:1;

[0007] The molar ratio of copper chloride and p-tr2Ph in step 1 is 1:1;

[0008] The volume ratio of the copper chloride in step 1 to water is 0.6 mmol: 5-10 mL;

[0009] The volume ratio of the copper chloride in step 1 to phosphoric acid is 0.6 mmol:1 mL;

[0010] The pH of the suspension is adjusted to 3.0-4.0 by using a 1 mol / L H3PO4 solution and a 1 mol / L NaOH solution;

[0011] 2. Preparation of an hourglass-shaped phosphomolybdic acid-based two-dimensional complex: Transfer the reaction solution prepared in step 1 with a pH adjusted to 3.0-4.0 to a polytetrafluoroethylene reactor, react at a temperature of 140-160°C for 3-5 days, cool the reaction solution to room temperature and then wash to obtain reddish-brown crystals, i.e., an hourglass-shaped phosphomolybdic acid-based two-dimensional complex.

[0012] The chemical formula of the hourglass-shaped phosphomolybdic acid-based two-dimensional complex described in step 2 is [Cu(p-tr2Ph)2]2[Cu(p-tr2Ph)]2[Cu(H2O)]2[Cu3(p-tr2Ph)Mo 12 (HPO4)3(PO4)5O 40 ] (abbreviated as p-tr2Ph-Cu-P4Mo6), where p-tr2Ph is 1,4-bis(4H-1,2,4-triazole-4-yl)benzene; the crystal system is triclinic

[0013] Crystal system; space group is The unit cell parameters are α=98.130(2)°, β=99.412(2)°, γ=92.574(2)°,

[0014] Preparation of the working electrode: Grind 3 mg of the phosphomolybdic acid-based two-dimensional complex and 3 mg of acetylene black until uniform. Add 3 mg of the mixture to an aqueous solution containing isopropyl alcohol and Nafion and sonicate. Apply an appropriate amount of the mixed solution evenly to the activated carbon cloth and allow to stand.

[0015] 1.25 mL of isopropanol, 10 μL of nafion, and 3.65 mL of water as described in step 3;

[0016] In step 3, the ultrasonication time is 2 h and the standing time is 8 h.

[0017] The advantages and effects of the present invention are as follows:

[0018] First, the present invention successfully prepared an hourglass-shaped two-dimensional phosphomolybdic acid-based complex for the first time using p-tr2Ph, molybdenum trioxide, and copper chloride through a simple hydrothermal reaction. Single crystal X-ray diffraction results show that the crystalline material prepared by the present invention is a two-dimensional complex constructed of an hourglass-shaped phosphomolybdic acid polyacid {P4Mo6}, a metal Cu ion, and p-tr2Ph. In the polyacid-based complex structure constructed with the phosphomolybdic acid polyacid {P4Mo6}, one metal Cu ion connects the phosphomolybdic acid polyacid {P4Mo6} to form an hourglass-shaped structure, four metal Cu ions connect the organic ligand p-tr2Ph, two metal Cu ions connect the organic ligand p-tr2Ph and the hourglass-shaped phosphomolybdic acid polyacid {P4Mo6}, and two metal Cu ions connect {P4Mo6} and water molecules. The resulting complex forms a stable two-dimensional structure through hydrogen bonds formed between the amino group in p-tr2Ph, water molecules, and copper-oxygen bonds, as well as electrostatic interactions.

[0019] Second, the hourglass-shaped phosphomolybdic acid-based two-dimensional complex prepared in this embodiment was used as a catalyst for electrocatalytic nitrate synthesis of ammonia. In a 0.1M NaNO3+0.1M Na2SO4 solution, a Faradaic efficiency of 99.08% was measured at a voltage of -1.0V vs. RHE, and an ammonia yield of 16.73mg h –1 mg cat . –1The excellent catalytic effect is mainly based on the following reasons: 1. This two-dimensional layered structure constructed with hourglass-shaped phosphomolybdic acid {P4Mo6} can provide abundant surface active sites, and the Mo-O-Cu coordination units in the phosphomolybdic acid framework can form uniformly distributed copper active centers; 2. The hourglass-shaped geometric structure can promote the adsorption and mass transfer of nitrates through the confinement effect; 3. The phosphomolybdic acid group can regulate the electronic state of copper through coordination bonds, reduce the d-band center of Cu, and enhance the adsorption of NO3 – 4. The rigid structure of the benzene ring in the organic ligand p-tr2Ph and the strong coordination ability of the triazole group synergistically form a stable two-dimensional framework, inhibiting the aggregation or dissolution of metal active centers during catalysis and improving the material's cyclic stability. This approach overcomes the limitations of traditional catalysts in terms of active site density, conductivity, and stability, providing new insights into the development of high-performance electrocatalytic materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 a and b are basic unit structure diagrams of an hourglass-shaped phosphomolybdic acid-based two-dimensional complex prepared in Example 1 of the present invention.

[0021] Figure 2 Schematic diagram of the stacking arrangement of an hourglass-shaped phosphomolybdic acid-based two-dimensional complex prepared in Example 1 of the present invention observed along the a, b and c axes.

[0022] Figure 3 This is the powder X-ray diffraction (XRD) pattern of an hourglass-shaped phosphomolybdic acid-based two-dimensional complex prepared in Example 1 of the present invention.

[0023] Figure 4 This is an infrared spectrum of an hourglass-shaped phosphomolybdic acid-based two-dimensional complex prepared in Example 1 of the present invention.

[0024] Figure 5 An hourglass-shaped phosphomolybdic acid-based two-dimensional complex prepared in Example 1 of the present invention was subjected to nitrate reduction to synthesize ammonia in a 0.1 mol / L NaNO3 + 0.1 mol / L Na2SO4 solution, and the UV-visible absorption spectra at different voltages were plotted.

[0025] Figure 6 An hourglass-shaped phosphomolybdic acid-based two-dimensional complex prepared in Example 1 of the present invention was subjected to nitrate reduction to synthesize ammonia in a 0.1 mol / L NaNO3 + 0.1 mol / L Na2SO4 solution, and ammonia yield and Faradaic efficiency at different voltages were plotted. DETAILED DESCRIPTION

[0026] The present invention is further described in detail below with reference to implementation and comparative examples and accompanying drawings, but the embodiments of the present invention are not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention that does not depart from the spirit of the technical solution of the present invention shall be included in the scope of protection of the present invention.

[0027] Specific embodiment 1: This embodiment describes an hourglass-shaped phosphomolybdic acid-based two-dimensional complex, the molecular formula of which is [Cu(p-tr2Ph)2]2[Cu(p-tr2Ph)]2[Cu(H2O)]2[Cu3(p-tr2Ph)Mo 12 (HPO4)3(PO4)5O 40 ] (abbreviated as p-tr2Ph-Cu-P4Mo6), whose basic structural unit contains nine metal copper ions, seven 1,4-bis(4H-1,2,4-triazole-4-yl)benzene organic ligands, two {P4Mo6} type polyacid anions and six water molecules. There are four chemical environments of Cu in the crystal, marked as Cu(1), Cu(2), Cu(3) and Cu(4), among which Cu(1) is a hexacoordinate octahedral structure, and two {P4Mo6} type anions covalently form an hourglass-shaped structural unit with Cu(1); Cu(2) is connected to a N atom in the organic ligand p-tr2Ph, a N atom in another identical ligand p-tr2Ph, and the hourglass-shaped phosphomolybdic acid {P4Mo6}; Cu(3) connects {P4Mo6} and water molecules; Cu(4) is connected to a N atom in the organic ligand p-tr2Ph and a N atom in another identical ligand p-tr2Ph, forming a metal organic complex constructed with the hourglass-shaped phosphomolybdic acid as the matrix.

[0028] Specific embodiment 2: The preparation method of an hourglass-shaped phosphomolybdic acid-based two-dimensional complex electrode material for electrocatalytic nitrate reduction to synthesize ammonia in this embodiment is completed according to the following steps.

[0029] 1. Weigh 0.10 g of copper chloride, 0.04 g of molybdenum trioxide, and 0.13 g of p-tr2Ph into a beaker, add 5 mL of deionized water and concentrated phosphoric acid, and stir for 1 hour. Then, adjust the pH of the suspension to 3.0-4.0 using 1 mol / L phosphoric acid solution and 1 mol / L NaOH solution.

[0030] The molar ratio of copper chloride to molybdenum trioxide in step 1 is 2:1;

[0031] The molar ratio of copper chloride and p-tr2Ph in step 1 is 1:1;

[0032] The volume ratio of the copper chloride in step 1 to water is 0.6 mmol: 5-10 mL;

[0033] The volume ratio of the copper chloride in step 1 to phosphoric acid is 0.6 mmol:1 mL;

[0034] The pH of the suspension is adjusted to 3.0-4.0 by using a 1 mol / L H3PO4 solution and a 1 mol / L NaOH solution;

[0035] 2. Prepare an hourglass-shaped phosphomolybdic acid-based two-dimensional complex; transfer the reaction solution prepared in step 1 with a pH adjusted to 3.0-4.0 into a 25mL polytetrafluoroethylene reactor, react at a temperature of 140-160°C for 3-5 days, cool the reaction solution to room temperature and then wash to obtain reddish-brown crystals, i.e., an hourglass-shaped phosphomolybdic acid-based two-dimensional complex.

[0036] The chemical formula of the hourglass-shaped phosphomolybdic acid-based two-dimensional complex described in step 2 is [Cu(p-tr2Ph)2]2[Cu(p-tr2Ph)]2[Cu(H2O)]2[Cu3(p-tr2Ph)Mo 12 (HPO4)3(PO4)5O 40 ] (abbreviated as p-tr2Ph-Cu-P4Mo6), where p-tr2Ph is 1,4-bis(4H-1,2,4-triazole-4-yl)benzene; the crystal system is triclinic

[0037] Crystal system; space group is The unit cell parameters are α=98.130(2)°, β=99.412(2)°, γ=92.574(2)°,

[0038] Preparation of the working electrode: Grind 3 mg of the phosphomolybdic acid-based two-dimensional complex and 3 mg of acetylene black until uniform. Add 3 mg of the mixture to an aqueous solution containing isopropyl alcohol and Nafion and sonicate. Apply an appropriate amount of the mixed solution evenly to the activated carbon cloth and allow to stand.

[0039] 1.25 mL of isopropanol, 10 μL of nafion, and 3.65 mL of water as described in step 3;

[0040] In step 3, the ultrasonication time is 2 h and the standing time is 8 h.

[0041] The structure of an hourglass-shaped phosphomolybdic acid-based two-dimensional complex prepared in Example 2 was determined:

[0042] Conclusion ① X-ray crystallography parameters: see Table 1

[0043] Table 1 Crystallographic parameters of materials

[0044]

[0045] Table 1 Crystallographic parameters of materials

[0046]

[0047] a R1=∑║F o │─│F c ║ / ∑│F o │. b wR2={∑[w(F o 2 ─F c 2 ) 2 ] / ∑[w(F o 2 ) 2 ]} 1 / 2

[0048] An hourglass-shaped phosphomolybdic acid-based two-dimensional complex has the chemical formula [Cu(p-tr2Ph)2]2[Cu(p-tr2Ph)]2[Cu(H2O)]2[Cu3(p-tr2Ph)Mo 12 (HPO4)3(PO4)5O 40 ](abbreviation

[0049] is p-tr2Ph-Cu-P4Mo6), the crystal system is triclinic; the space group is The unit cell parameters are α=98.130(2)°, β=99.412(2)°, γ=92.574(2)°,

[0050] The present invention will be further described below with reference to the accompanying drawings:

[0051] Figure 1 This is a schematic diagram of the structure of an hourglass-shaped phosphomolybdic acid-based two-dimensional complex prepared in Example 2 of the present invention. Figure 1 a and b are schematic diagrams of basic structural units.

[0052] Figure 2 The stacking arrangement diagram of an hourglass-shaped phosphomolybdic acid-based two-dimensional complex prepared in Example 2 of the present invention observed along the a, b and c axes reflects the spatial arrangement and combination of the complex.

[0053] Figure 3 The following is an X-ray diffraction (XRD) pattern of an hourglass-shaped phosphomolybdic acid-based two-dimensional complex prepared in Example 2 of the present invention. Figure 3It can be seen that the peak positions of the experimentally measured spectrum are consistent with those of the spectrum obtained by crystal simulation. It can be determined that the crystal structure obtained by the experiment is the same as the structure analyzed by the software and has a high purity.

[0054] Figure 4 This is an infrared spectrum of an hourglass-shaped phosphomolybdic acid-based two-dimensional complex prepared in Example 2 of the present invention. Figure 4 As shown, the infrared spectrum at 1057 cm -1 、957cm -1 、698-840cm -1 The spectral bands are respectively attributed to the characteristic peaks of stretching vibration of ν(PO), ν(Mo-O) and ν(Mo-O-Mo) of the complex; the vibration peak is at 1000 cm -1 ~1650cm -1 The organic ligands are classified within the range.

[0055] Figure 5 The UV-visible absorption spectra (UV-vis) of an hourglass-shaped phosphomolybdic acid-based two-dimensional complex prepared in Example 2 of the present invention at different voltages in a neutral electrolyte of 0.1 mol / L Na2SO4 + 0.1 mol / L NaNO3 are shown. Electrochemical IT curves were tested at different voltages in a neutral electrolyte using a three-electrode system. After one hour of measurement, 10 mL of the electrolyte in the cathode electrolytic cell was taken, and then color development was performed. The UV-visible absorption spectra were obtained using a UV spectrophotometer. Figure 5 It can be seen that as the applied voltage increases, the absorbance of the electrolyte that develops color after the electrocatalytic test also gradually increases in the absorbance test.

[0056] Figure 6 An hourglass-shaped phosphomolybdic acid-based two-dimensional complex prepared in Example 2 of the present invention was subjected to nitrate reduction to synthesize ammonia in a 0.1 mol / L Na2SO4 + 0.1 mol / L NaNO3 solution, and the ammonia yield and Faraday efficiency at different voltages were plotted. Figure 6 It can be seen that at a potential of -1.0 V vs. RHE, the best Faradaic efficiency is 99.08%, and the corresponding ammonia production is 16.73 mg h –1 mg cat . –1 Therefore, the hourglass-shaped phosphomolybdic acid-based two-dimensional complex can be used as a highly efficient electrocatalytic nitrate reduction catalyst for ammonia synthesis.

[0057] In summary: In the second embodiment, an hourglass-shaped phosphomolybdic acid-based two-dimensional complex [Cu(p-tr2Ph)2]2[Cu(p-tr2Ph)]2[Cu(H2O)]2[Cu3(p-tr2Ph)Mo 12 (HPO4)3(PO4)5O 40] (abbreviated as p-tr2Ph-Cu-P4Mo6) was successfully prepared using a simple hydrothermal synthesis method and successfully applied to the electrocatalytic nitrate reduction to ammonia synthesis. The present invention uses hourglass-shaped phosphomolybdic acid {P4Mo6} as a basic unit through in situ growth, introduces the catalytically active element Cu and the organic ligand p-tr2Ph, and obtains an hourglass-shaped phosphomolybdic acid-based two-dimensional complex to improve electrocatalytic selectivity and stability. This material exhibits excellent redox activity, excellent conductivity, and stability, and has great potential for the electrocatalytic nitrate reduction to ammonia synthesis.

Claims

1. Preparation of an hourglass-shaped phosphomolybdic acid-based two-dimensional complex and its application in electrocatalytic ammonia synthesis, characterized in that The chemical formula of the two-dimensional polyacid complex constructed with hourglass-shaped phosphomolybdic acid is [Cu(p-tr2Ph)2]2[Cu(p-tr2Ph)]2[Cu(H2O)]2[Cu3(p-tr2Ph)Mo 12 (HPO4)3(PO4)5O 40 ] (abbreviated as p-tr2Ph-Cu-P4Mo6), where p-tr2Ph is 1,4-bis(4H-1,2,4-triazole-4-yl)benzene; the crystal system is triclinic; the space group is The unit cell parameters are α=98.130(2)°, β=99.412(2)°, γ=92.574(2)°, 2. The method for preparing an hourglass-shaped phosphomolybdic acid-based two-dimensional complex according to claim 1 is completed by the following steps: (1) Weigh copper chloride, molybdenum trioxide, and p-tr2Ph in a beaker, add deionized water and stir evenly, then add phosphoric acid and stir evenly, and adjust the pH of the suspension to 3.0-4.0; (2) The reaction solution prepared in (1) was adjusted to a pH of 3.0 to 4.0 and transferred to a polytetrafluoroethylene reactor, and reacted at a temperature of 140 to 160° C. for 3 to 5 days. The reaction solution was cooled to room temperature and then washed to obtain reddish-brown crystals. That is, an hourglass-shaped phosphomolybdic acid-based two-dimensional complex.

3. The method for preparing an hourglass-shaped phosphomolybdic acid-based two-dimensional complex according to claim 2, wherein: The molar ratio of copper chloride to molybdenum trioxide in step (1) is 2:

1.

4. The method for preparing an hourglass-shaped phosphomolybdic acid-based two-dimensional complex according to claim 2, wherein: The molar ratio of copper chloride and p-tr2Ph in step (1) is 1:

1.

5. The method for preparing an hourglass-shaped phosphomolybdic acid-based two-dimensional complex according to claim 2, wherein: The volume ratio of the amount of copper chloride described in step (1) to water is 0.6mmol:5-10mL.

6. The method for preparing an hourglass-shaped phosphomolybdic acid-based two-dimensional complex according to claim 2, characterized in that: The volume ratio of the amount of copper chloride and phosphoric acid described in step (1) is 0.6 mmol:1 mL.

7. The method for preparing an hourglass-shaped phosphomolybdic acid-based two-dimensional complex according to claim 2, characterized in that: The pH of the suspension is adjusted to 3.0-4.0 in step (1) by using a H3PO4 solution with a substance concentration of 1 mol / L and a NaOH solution with a substance concentration of 1 mol / L.

8. An hourglass-shaped phosphomolybdic acid-based two-dimensional complex prepared according to claims 1 to 7, which is used to electrocatalyze the nitrate synthesis of ammonia at room temperature and pressure.

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