Polyoxometallate nano-catalyst constructed by trinuclear ruthenium clusters and application of polyoxometallate nano-catalyst

Abstract

The invention belongs to the technical field of preparation of polyoxometallate materials, and discloses a polyoxometallate nano-catalyst constructed by a trinuclear ruthenium cluster and application of the polyoxometallate nano-catalyst. The preparation method of the catalyst comprises the following steps: adding Keggin type polyacid, ruthenium trichloride and a 1, 2, 4-triazole ligand into a buffer solution, and inducing coordination of the polyacid, ruthenium and 1, 2, 4-triazole to perform self-assembly under a hydrothermal condition by precisely regulating and controlling the pH value of the solution so as to form a trinuclear ruthenium cluster active center. The catalyst provided by the invention can be applied to a reaction process for preparing urea through electro-catalysis C-N coupling, and has high yield and high selectivity.

Description

Technical Field

[0001] This invention belongs to the field of polyoxometalate material preparation technology, specifically relating to a polyoxometalate nanocatalyst constructed from a trinuclear ruthenium cluster and its application. Background Technology

[0002] Urea, a key nitrogen fertilizer in agricultural production and an important chemical raw material in industrial applications, is traditionally synthesized using a combination of the Haber-Bosch process and subsequent urea synthesis techniques. This traditional process suffers from two major problems: firstly, it relies on non-renewable fossil resources (such as natural gas and coal), requiring harsh high-temperature and high-pressure reaction conditions to produce ammonia, which then reacts with CO2 to generate urea. This process is extremely energy-intensive and generates significant CO2 emissions. Secondly, the process is complex, with low raw material utilization, resulting in substantial resource waste. Therefore, developing a low-energy-consumption and sustainable urea synthesis pathway has become a hot research topic in the industry.

[0003] With the development of electrochemical technology, electrocatalytic reactions driven by renewable energy sources have provided a new approach for urea synthesis. These reactions utilize renewable energy sources (such as electricity converted from solar and wind power) as the power source, and CO2 and nitrates (NO3) as the reactants. - Using N2 and NO2 as raw materials, urea is directly produced via an electrocatalytic CN-coupling reaction. This method offers significant advantages, including mild reaction conditions (room temperature and pressure), a wide availability of raw materials, environmental friendliness, and low energy consumption. It is considered an effective alternative to traditional industrial urea synthesis processes. This method is comparable to other electrocatalytic urea synthesis systems (such as those using N2 and NO2). - Compared to (as a nitrogen source), NO3 - It has higher water solubility and electrochemical activity, CO2 and NO3 - Electrocatalytic coupling reactions can effectively lower the reaction energy barrier, theoretically possessing higher synthesis efficiency and environmental value. However, current methods using NO3... - The electrolytic synthesis of urea from CO2 still faces many serious challenges, making industrial application difficult. The core problems lie in the electrocatalytic reaction process: First, the reactivity is low; CO2 molecules have a stable linear structure, making activation difficult, and NO3... - The reduction process requires a multi-electron transfer step (NO3). - →NO2 - →NO→N2O→NH3 / NH2 - The accumulation of intermediate products can easily occur, leading to the loss of key intermediates required for CN coupling (such as...). NH2, The formation efficiency of CO is low; secondly, the competitive reaction is strong, and side reactions such as hydrogen evolution reaction (HER), reduction of CO2 to CO or CH4, and NO3 are prone to occur in the electrolysis system. -The reduction to N2 or NH3 by side reactions not only consumes electrical energy and raw materials but also inhibits the target CN coupling reaction, ultimately leading to significantly low urea yield and reaction efficiency, failing to meet practical application requirements. Therefore, it is necessary to develop an environmentally friendly, highly efficient, and stable electrocatalyst to address the CO2 and NO3 reduction problem. - The issues of activity and selectivity in electrocatalytic CN coupling reactions have become the core key to this technological breakthrough.

[0004] Among numerous candidate catalytic materials, polyoxometalates (POMs) exhibit great potential due to their unique crystal structure and semiconductor properties. POMs are a class of nanoscale compounds composed of metal-oxygen clusters, possessing highly controllable crystal structures and well-defined compositions. Their metal-oxygen cluster units (such as Mo-O and WO clusters) can achieve reversible multi-electron redox reactions, freely absorbing and releasing electrons, earning them the nickname "electron sponges," which effectively promote electron transfer in electrocatalytic reactions. Simultaneously, the surface of POMs is rich in reactive oxygen sites and acidic sites, enabling them to both activate CO2 molecules (by forming coordination bonds with CO2 at oxygen sites to lower the activation energy) and regulate NO3. - The reduction pathway is CO2 and NO3. - The catalytic transformation provides abundant active sites. To further improve the catalytic performance of POMs, existing technologies usually combine them with organic ligands or transition metals (TMs) to form hybrid POMs, thereby optimizing the electronic structure and surface properties of the catalyst through metal-ligand interactions or the synergistic catalytic effect of transition metals.

[0005] In transition metal-polyoxometalate (TMs-POM) catalyst systems, ruthenium (Ru)-based polyoxometalates (Ru-POMs) have attracted much attention due to their unique electronic properties and catalytic activity. Ru has a 4d electron configuration. 6 5s 2 The electron cloud distribution and energy level of the 4d orbital enable it to resist NO3. - The reduction of NO3 exhibits excellent catalytic selectivity and can effectively promote the reduction of NO3. - Directional reduction to generate CN coupling required It acts as an active intermediate for NH2 and inhibits the formation of byproducts such as N2 and NH3; at the same time, the metal-oxygen clusters in the POMs framework can provide abundant surface active oxygen, promoting the reduction of CO2 to NH2. The CO intermediate is used to optimize the coupling reaction kinetics of the two by utilizing the adsorption energy of key intermediates in the catalytic reaction, thereby improving the efficiency of urea synthesis. Furthermore, when a trinuclear ruthenium cluster (Ru3) is introduced into the POMs framework, the trinuclear ruthenium cluster not only forms a stable coordination structure with the POMs framework, enhancing the structural stability of the catalyst (preventing metal ion dissolution during electrolysis), but also further increases the density of active sites. Through the synergistic effect of the Ru3 cluster and the POMs framework, competitive reactions such as hydrogen evolution and byproduct formation are suppressed, further improving the selectivity and stability of the electrocatalytic CN coupling reaction.

[0006] Although Ru-POM catalysts are effective in CO2 and NO3 - Ru-POM catalysts have shown excellent performance potential in the electrocatalytic synthesis of urea, but most existing Ru-POM catalysts are homogeneous, which has two major limitations: First, homogeneous Ru-POM catalysts are easily dissolved and dispersed in the electrolysis system, making them difficult to separate and recover from the reaction system, resulting in significant catalyst loss, increased production costs, and the inability to achieve continuous catalytic reactions. Second, the active sites of homogeneous catalysts are difficult to effectively expose on the electrode surface, and the electron transfer efficiency between the catalyst and the electrode is low, limiting the full realization of their catalytic activity and failing to meet the requirement of "heterogeneous interface reaction" for electrocatalytic reactions. Therefore, how to achieve the transformation of Ru-POM catalysts from homogeneous to heterogeneous through reasonable structural design, and construct heterogeneous Ru-POM electrocatalysts with high activity, high selectivity, high stability, and easy recovery characteristics, has become a key factor in promoting the synthesis of CO2 and NO3. - A key breakthrough for the industrial application of electrocatalytic high-efficiency urea synthesis technology. Summary of the Invention

[0007] The first objective of this invention is to address the current issues of CO2 and NO3. - To address the problems of low reactivity, strong competitive side reactions, and low urea yield and reaction efficiency in the electrocatalytic CN-coupled urea synthesis technology, as well as the issues of easy loss, difficult recovery, and low electron transfer efficiency of existing ruthenium-based polyoxometalate (Ru-POM) catalysts, which are mostly homogeneous systems, this invention provides a method for preparing polyoxometalate nanocatalysts constructed from trinuclear ruthenium clusters. By controlling the crystal structure, active site distribution, and homogeneous-heterogeneous transformation characteristics of the material, this invention ensures that the prepared Ru-POM self-assembled material has both high structural stability, abundant active centers, and efficient electron transfer capability.

[0008] The second objective of this invention is to apply the prepared catalyst material to an electrocatalytic CN-coupling reaction system to achieve efficient activation of CO2 and NO3. - The targeted reduction promotes the generation and coupling of key intermediates, suppresses competitive side reactions, and ultimately achieves the goal of efficient preparation of urea by electrocatalytic CN coupling.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: This invention first provides a trinuclear ruthenium cluster-structured polyoxometalate nanocatalyst (denoted as Ru3-POM nanocatalyst), with the chemical formula H3[Ru3O(C2H3N3)6Cl3][SiW 12 O 40 •7H2O, belongs to the monoclinic crystal system. P twenty one / n The space group belongs to the Keggin-type polyoxometalate system. Its molecular structure contains a trinuclear ruthenium cluster active center and a Keggin-type polyacid unit, which are assembled in an ordered manner through coordination. It appears as dark green needle-like crystals. The Keggin type is the most classic and widely studied structural configuration among polyoxometalates. Its structural feature is a cage-like framework composed of one heteroatom tetrahedron and twelve polyatom octahedra.

[0010] The preparation method of the polyoxometalate nanocatalyst constructed from trinuclear ruthenium clusters of the present invention includes the following steps: Under stirring conditions, ruthenium trichloride and Na 10 [SiW9O 34 • 18H2O was dispersed in an acetate-sodium acetate buffer solution (1M, initial pH = 4.8-5.0), stirred until homogeneous, and then 1,2,4-triazole (molecular formula C2H3N3) ligand was added and stirred until completely dissolved to obtain a homogeneous reaction solution. The pH of the reaction solution was adjusted to 1.5-2.5 with 4-6M hydrochloric acid, and the reaction was stirred at room temperature for 30-40 min. Finally, the reaction solution was transferred to a high-pressure reactor and hydrothermally reacted at 120-160℃ for 12-24 h. During the hydrothermal reaction, ruthenium ions and Na+ ions were released. 10 [SiW9O 34 • 18H₂O and 1,2,4-triazole ligand achieve the ordered construction of trinuclear ruthenium clusters and polyoxometalate units through a coordination self-assembly process; after the reaction, cooling to room temperature, the precipitated dark green needle-like crystals are the trinuclear ruthenium cluster-constructed polyoxometalate nanocatalysts, denoted as Ru₃-POM nanocatalysts. Among them, ruthenium trichloride, 1,2,4-triazole ligand, and Na₂O achieve the ordered construction of trinuclear ruthenium clusters and polyoxometalate units. 10 [SiW9O 34 The molar ratio of 18H2O is 1:1-1.5:1.5-2.

[0011] The process of preparing Ru3-POM nanocatalysts in this invention is essentially a two-step synergistic process of room temperature pretreatment to regulate the coordination environment and directional self-assembly under hydrothermal conditions. The specific mechanisms of each stage are as follows: 1. The room-temperature stirring reaction after pH adjustment with hydrochloric acid lays the coordination foundation for subsequent self-assembly. The specific mechanism is as follows: Before adjusting the pH, Ru 3+ In acetate-sodium acetate buffer, [Ru(H2O)6] 4+ [Ru(H2O)5(CH3COO)] 3+ It exists as a weakly coordinated complex, with low coordination bond energy and unstable structure. After the addition of hydrochloric acid, the system contains a high concentration of Cl... - (Strongly competitive ligands) and H + (Regulating ligand activity) working together to initiate a ligand displacement reaction: Cl - Prioritize replacing Ru 3+ H2O and CH3COO with weak surrounding coordination ability - (CH3COO) - With H + (It combines to form CH3COOH, losing its coordination activity), thus forming [RuCl2(H2O)4. 2+ [RuCl3(H2O)3] + Intermediate complexes with Ru-Cl bonds as the core; simultaneously, H in hydrochloric acid + with Na 10 [SiW9O 34 •18H2O dissociates [SiW9O] 34 ] 10- Ion substitution and protonation reactions occur: [SiW9O] 34 ] 10- Terminal oxygen (=O) and bridging oxygen (-O-) with H + Combining, protonation occurs (-O- + H) + →-OH); during protonation, Na+ bound to the surface of the polyacid anion + H + Displacement, on the one hand, reduces the negative charge density of polyacid anions, weakening their interaction with Ru. 3+ On the one hand, the electrostatic repulsion of (positive charge) increases the lone pair electron cloud density of the O atom due to the electron-donating effect of the -OH group, activating the vacancy sites of polyacids and enabling them to interact with Ru. 3+ Structural conditions for coordination bonding. After stirring at room temperature, two types of key active components are formed in the system: Ru with Ru-Cl bonds as the core and retaining coordination vacancies. 3+ Intermediate complexes; protonated activation, vacancy site exposure H + The polyacid anions are replaced. Meanwhile, the 1,2,4-triazole ligand is uniformly dispersed in the system and binds to the two types of active components through weak interactions (such as hydrogen bonds), preparing for directional self-assembly in the hydrothermal stage.

[0012] 2. The thermal energy provided during the hydrothermal reaction stage breaks the Ru at room temperature 3+The Ru-Cl and Ru-O (H2O) bonds in the intermediate complex initiate ligand recombination and clustering reactions: The N atom of the 1,2,4-triazole ligand substitutes for Ru 3+ Cl in coordination - / H2O, 1 Ru 3+ With 2 C2H3N3 and 2 Cl - One H2O molecule combines to form [Ru(C2H3N3)2Cl2(H2O)] + (Monuclear, retaining 1 coordination vacancy); the three mononuclear intermediates, under hydrothermal conditions, first pass through the OH group dissociated from water molecules. - With Ru 3+ Coordination, followed by dehydration to generate O 2- It forms a Ru3-O core; the remaining 1,2,4-triazole ligands react with Cl... - Supplemental coordination (per Ru) 3+ Then combine one C2H3N3 ligand and one Cl - ), forming [Ru3O(C2H3N3)6Cl3] + After the formation of a trinuclear ruthenium cluster, the positively charged Ru on its surface... 3+ Binding to the vacancy sites of activated polyacid anions drives structural reconstruction of polyacid units, ultimately forming saturated Keggin-type polyacid anions [SiW]. 12 O 40 ] 4- [Ru3O(C2H3N3)6Cl3] is positively charged. + With negatively charged [SiW 12 O 40 ] 4- Ion pairs are formed through electrostatic interactions, while H+ in the system... + (From the protonation of hydrochloric acid and polyacids) it combines with the uncoordinated oxygen atoms of polyacids to ultimately form H3[Ru3O(C2H3N3)6Cl3][SiW 12 O 40 •7H2O.

[0013] Therefore, this invention controls the coordination environment through a room-temperature displacement reaction and the crystal structure through a hydrothermal self-assembly reaction, ensuring that the final product possesses both a trinuclear ruthenium cluster active center and a Keggin-type polyacid unit, thus providing structural and performance guarantees for subsequent electrocatalytic CN-coupling urea production.

[0014] Furthermore, the trinuclear ruthenium cluster-constructed polyoxometalate nanomaterials prepared in this invention can serve as electrocatalysts for the electrocatalytic coupling of nitrate and CO2 to produce urea, achieving highly efficient nitrate-CO2 coupling. The specific application method is as follows: the Ru3-POM nanocatalyst is dispersed in a mixed solvent of organic solvent and water to form a uniform dispersion; the dispersion is sprayed onto carbon paper using a spray gun, and after drying, a working electrode for the electrocatalytic nitrate-CO2 coupling reaction is obtained. Under ambient temperature and pressure conditions, an electrolytic system is constructed using this working electrode as the core to directly carry out the electrocatalytic coupling reaction of nitrate and CO2 to produce urea. The trinuclear ruthenium cluster active centers in the material can directionally promote the production of NO3-. - Reduction generation The NH2 intermediate, the Keggin-type polyacid unit, can activate CO2 generation. The synergistic effect of CO intermediates and CN significantly improves the coupling efficiency, enabling efficient urea synthesis without the need for any co-catalysts during the electrocatalytic process. The material obtained in this invention exhibits excellent cycle stability; after being recycled and reused seven times, the urea yield shows no significant decrease, solving the problems of easy loss and poor stability of traditional catalysts. Furthermore, the reaction is carried out at ambient temperature and pressure, eliminating the need for high-temperature and high-pressure conditions. The raw materials are CO2 and nitrates, resulting in lower energy consumption and less pollution compared to traditional urea synthesis processes, aligning with the direction of green economic development.

[0015] Compared with existing technologies, the beneficial effects of this invention are reflected in: 1. The Keggin-type polyoxometalate nanocatalyst constructed from trinuclear ruthenium clusters provided by this invention can achieve precise control of the catalyst structure by controlling the pH value of the reaction solution, and finally form a heterogeneous Ru-POM catalyst. It has the characteristics of easy recovery, sufficient exposure of active sites and high electron transfer efficiency. Moreover, the preparation method is simple to operate, mild and highly controllable, which is convenient for large-scale production.

[0016] 2. The material obtained in this invention uses a trinuclear ruthenium cluster as the active center and a Keggin-type polyacid as the support, enabling reversible redox reactions. Furthermore, Ru3-POM exhibits N-type semiconductor characteristics, achieving efficient CN-C coupling at room temperature and pressure. This demonstrates advantages such as high activity, high stability, and no need for auxiliary catalysts. The yield and Faradaic efficiency of urea synthesis can reach 27.2 mmol / h. -1 g -1 cat. -1 The percentage was 56.3%, reaching the international advanced level. Attached Figure Description

[0017] Figure 1 In the middle, (a) is Ru3SiW 12 (a) Polyhedral / bat representation; (b) Ru3trz6Cl3 +The bat is represented by (c) Ru3SiW 12 The three-dimensional structure; (d) is Ru3SiW 12 The coordination environment of Ru1 ions; (e) is Ru3SiW 12 The coordination environment of Ru2 ions; (f) is Ru3SiW 12 The coordination environment of Ru3 ions.

[0018] Figure 2 The present invention is Ru3SiW 12 XPS spectra, in which: (a) Si 2p, (b) Ru 3p, (c) W 4f.

[0019] Figure 3 Ru3SiW 12 The infrared spectra of the electrons and the infrared spectra before and after electrocatalytic CN coupling.

[0020] Figure 4 Ru3SiW 12 Thermogravimetric analysis.

[0021] Figure 5 Ru3SiW 12 XRD pattern.

[0022] Figure 6 Ru3SiW 12 UV diagram of CN coupling in material electrocatalysis.

[0023] Figure 7 Ru3SiW 12 Faraday efficiency diagram of CN-C coupled electrocatalysis in materials.

[0024] Figure 8 Ru3SiW 12 Yield diagram of CN-coupling electrocatalysis in materials.

[0025] Figure 9 In the middle, (a) is Ru3SiW 12 (a) Time-temperature curves of Ru3SiW after 7 cycles (1 hour each) at -0.3 V; (b) Ru3SiW 12 The UV-Vis spectrum of urea production by electrocatalytic CN coupling at -0.3 V, cyclically tested every 1 hour. Detailed Implementation

[0026] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to examples. However, the scope of protection of the present invention is not limited thereto.

[0027] The Keggin-type polyacid Na used in the following examples 10[SiW9O 34 • 18H2O was synthesized according to the method described in the literature (Inorg Chem, 1977, 16: 2115-2117).

[0028] Example 1 This embodiment provides a Keggin-type polyoxometalate (Ru3-POM) nanocatalyst constructed from a trinuclear ruthenium cluster, the synthesis method of which includes the following steps: Under stirring conditions, ruthenium trichloride (RuCl3•nH2O, 0.060 g, 0.28 mmol) and Na... 10 [SiW9O 34 •18H₂O (0.950 g, 0.45 mmol) was dispersed in 10 mL of acetate-sodium acetate buffer (pH = 4.8, 1 M) and stirred for 30 min. Then, 1,2,4-triazole (0.020 g, 0.29 mmol) was added and stirred until completely dissolved to obtain a homogeneous reaction solution. Subsequently, the pH of the solution was adjusted to 2.00 with 4 M HCl and stirred at room temperature for 30 min. Finally, the reaction solution was transferred to an autoclave and slowly heated to 160 °C in an oven at a heating rate of 1.5 °C / min, and the reaction was maintained at this temperature for 24 h. After the reaction was completed, the solution was allowed to cool naturally to room temperature, and dark green needle-like crystals precipitated. The crystals were filtered, washed, and dried to obtain the Ru₃-POM nanocatalyst.

[0029] The Ru3-POM nanocatalyst prepared in this invention has the chemical formula H3[Ru3O(C2H3N3)6Cl3][SiW 12 O 40 •7H2O, corresponding to the molecular formula C 12 H 35 N 18 Ru3Cl3Si1W 12 O 48 (abbreviated as Ru3SiW) 12 The structure was verified through elemental analysis and infrared spectroscopy (IR), and the specific results are as follows: Elemental analysis was performed using an elemental analyzer. By comparing the theoretically calculated values ​​with the experimentally determined values, the consistency between the material composition and the target chemical formula was verified. The results are shown in Table 1. Table 1

[0030] The experimentally determined content of each element deviates from the theoretically calculated value within the allowable error range (usually ≤ ±0.3%), proving that the actual composition of the prepared material is consistent with the target chemical formula H3[Ru3O(C2H3N3)6Cl3][SiW 12 O40 • 7H2O is highly consistent and contains no obvious impurity elements.

[0031] Infrared spectra were measured, and the presence of key functional groups and Keggin-type structures in the material was verified by assigning characteristic absorption peaks. Specific data and peak assignments are shown in Table 2. Table 2

[0032] The characteristic peaks of the infrared spectrum are highly matched with the material structure: 3557 cm⁻¹ -1 The strong absorption peaks at 2817-1640 cm⁻¹ prove the presence of water of crystallization in the crystal; -1 The series of peaks correspond to the characteristic vibrations of the C2H3N3 ligand, proving that the ligand has successfully ligated with Ru. 3+ Coordination; 1134–640 cm -1 The characteristic peak is a Keggin-type polyacid unit ([SiW) 12 O 40 ] 4- The typical absorption peak of 1569 cm⁻¹ proves that the polyacid unit has been reconstructed into a complete Keggin-type structure. -1 The strong absorption peaks confirm the existence of the trinuclear ruthenium cluster (Ru3-O core), further verifying the successful preparation of the target material.

[0033] The Ru3-POM nanocatalyst prepared in this embodiment was subjected to X-ray single-crystal diffraction test. Its crystal system, space group, molecular configuration and structural characteristics were determined by crystal structure analysis. The specific test and analysis results are shown in Table 3.

[0034] Table 3 Compound Ru3SiW 12 Crystallographic data

[0035] In the table: R 1 represents the traditional deviation factor. wR 2 is the weighted bias factor. I For diffraction intensity, 2 σ ( I ) represents the standard deviation of the diffraction intensity, and [all data] refers to all independent diffraction points collected in the crystal test; As can be seen from Table 3: Compound Ru3SiW 12 It belongs to the monoclinic crystal system. P twenty one / n Space group. Figure 1 Analysis in (a) shows that Ru3SiW 12 From Keggin-type anions [SiW] 12 O 40 ]4- and the trinuclear ruthenium cluster [Ru3O(C2H3N3)6Cl3] + cation, 7 water molecules and 3 hydrogen ions. The results of valence bond calculations and XPS ( Figure 2 ) show that the valence states of W, Ru, and Si are +6, +4, and +4, respectively. As shown in Figure 1 (b), each structurally symmetric [Ru3O(C2H3N3)6Cl3] + cation consists of 3 ruthenium atoms, 6 1,2,4-triazole ligands, 3 chlorine atoms, and a central μ3-oxygen atom. The six 1,2,4-triazole ligands and three ruthenium atoms are alternately connected in sequence to form a stable equilateral triangle structure. Protected by the ligands, Ru3SiW 12 forms a planar network structure as shown in Figure 1 (c), while SiW 12 is staggered on the ligand-connected surface to form a proton transfer channel, promoting proton exchange during the electrochemical process. Interestingly, Ru3SiW P with n symmetry has three crystallographically independent Ru atoms, and each Ru atom is located in a six-coordinate configuration, forming a distorted octahedral geometry (as shown in 12 (d), Figure 1 (e), Figure 1 (f)). Figure 1

[0036] Figure 3 is the infrared spectrum of Ru3SiW 12 . The FT-IR spectrum clearly shows that the characteristic peaks of SiW 12 and Ru3 in Ru3SiW 12 appear in the range of 600 - 1050 cm -1 , corresponding to the classical vibration bands of W-O and Si-O bonds in the Ru3SiW 12 cluster, while in the range of 1100 - 1250 cm -1 , they are the vibration bands belonging to the Ru3 cluster.

[0037] Figure 4 is the thermogravimetric analysis graph. Ru3SiW 12 shows two weight loss stages from 25 to 800 °C in N2 atmosphere. The first weight loss from 30 °C to 300 °C is due to the loss of lattice water molecules. Thermogravimetric analysis shows that Ru3SiW 12 has high thermal stability, meeting the requirements of heterogeneous catalysts.

[0038] Figure 5 ​The X-ray powder diffraction pattern is shown. The simulated X-ray single crystal diffraction pattern matches the experimental pattern well, proving that the collected crystal sample is relatively pure.

[0039] The Ru3SiW prepared in this embodiment 12 Electrocatalytic CN coupling experiments were conducted on the materials in an H-cell electrolyzer: Ru3SiW 12 The solution was uniformly dispersed in a mixed solution of ethanol, water, and 5 wt% Nafion solution (volume ratio of 4:1:0.01). This formed a uniform dark green slurry, which was then sprayed onto carbon paper using a spray gun to obtain Ru3SiW. 12 The loading capacity was 0.2 mg / cm³. 2 The working electrode was used. In an H-cell electrolytic cell, a platinum sheet was used as the counter electrode, Ag / AgCl as the reference electrode, and 0.1 M potassium nitrate electrolyte was used as both the anode and cathode electrolyte. CO2 was introduced into the cell at a flow rate of 20 sccm. Different voltages were applied to induce electrocatalytic reactions (-0.2, -0.3, -0.4, -0.5, -0.6 V (vs. RHE)), and the reaction time was 1 h. After the reaction, the electrolyte in the cathode electrolytic cell was collected, and the electrolyte was subjected to colorimetric treatment using a diacetyl monooxime method, followed by quantitative analysis using a UV spectrophotometer. Ru3SiW 12 Infrared spectra of the material before and after CN electrocatalysis are shown below. Figure 3 As shown, the UV-Vis absorption spectrum of urea production via electrocatalytic CN coupling is as follows: Figure 6 As shown, the Faraday efficiency and yield diagrams are respectively as follows: Figure 7 and Figure 8 As shown in the figure, it can be seen that at -0.3 V (vs. RHE), the yield and Faraday efficiency of urea are both the highest, at 27.2 mmol / h. -1 g -1 cat. -1 And 56.3%. The Ru3SiW was evaluated through seven independent cycle tests (same working electrode, seven cycles of catalysis, 1 h each time). 12 Stability of electrocatalytic synthesis of urea (e.g.) Figure 9 As shown in the figure, the obtained catalyst material has high Faraday efficiency and yield for CN-coupled urea production and good stability.

[0040] The above description is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the concept of the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A method for preparing polyoxometalate nanocatalysts constructed from trinuclear ruthenium clusters, characterized in that, Includes the following steps: Under stirring conditions, ruthenium trichloride and Na 10 [SiW9O 34 • 18H₂O was dispersed in an acetate-sodium acetate buffer solution and stirred until homogeneous. Then, 1,2,4-triazole ligand was added and stirred until completely dissolved to obtain a homogeneous reaction solution. The pH of the reaction solution was adjusted to 1.5-2.5 with hydrochloric acid, and the reaction was carried out under stirring at room temperature. Finally, the reaction solution was transferred to a high-pressure reactor for hydrothermal reaction. During the reaction, ruthenium ions and Na₂O were released. 10 [SiW9O 34 • 18H2O and 1,2,4-triazole ligands coordinate self-assembly to achieve the ordered construction of trinuclear ruthenium clusters and polyoxometalate units; after the reaction is completed, the reaction is cooled to room temperature, and the precipitated needle-like crystals are the polyoxometalate nanocatalysts constructed from trinuclear ruthenium clusters, denoted as Ru3-POM nanocatalysts.

2. The preparation method according to claim 1, characterized in that, The chemical formula of the obtained Ru3-POM nanocatalyst is H3[Ru3O(C2H3N3)6Cl3][SiW 12 O 40 •7H2O, belongs to the monoclinic crystal system. P twenty one / n Space group.

3. The preparation method according to claim 1, characterized in that, Ruthenium trichloride, 1,2,4-triazole ligand and Na 10 [SiW9O 34 The molar ratio of 18H2O is 1:1-1.5:1.5-2.

4. The preparation method according to claim 1, characterized in that, The concentration of hydrochloric acid used is 4-6M.

5. The preparation method according to claim 1, characterized in that, The stirring reaction time at room temperature is 30-40 minutes.

6. The preparation method according to claim 1, characterized in that, The hydrothermal reaction is carried out at 120-160℃ for 12-24 hours.

7. A Ru3-POM nanocatalyst prepared by the preparation method according to any one of claims 1 to 6.

8. The application of the Ru3-POM nanocatalyst according to claim 7 in the electrocatalytic CN coupling reaction, characterized in that, The Ru3-POM nanocatalyst was used for the electrocatalytic co-reduction reaction of carbon dioxide and nitrate at room temperature to produce urea.

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