Trinuclear ruthenium cluster constructed polyoxometalate nanocatalyst and application thereof

Abstract

The application belongs to the technical field of polyoxometalate material preparation, and discloses a trinuclear ruthenium cluster constructed polyoxometalate nanocatalyst and application thereof. The preparation method of the catalyst comprises the following steps: adding a Keggin type polyacid, ruthenium trichloride and a 1,2,4-triazole ligand into a buffer solution, precisely controlling the pH of the solution, and inducing the self-assembly of the polyacid, ruthenium and the 1,2,4-triazole ligand under hydrothermal conditions to form a trinuclear ruthenium cluster active center. The catalyst provided by the application can be applied to the reaction process of electrocatalytic C-N coupling for preparing urea, 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 produces 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 object, the application adopts the following technical solutions:

[0010] The application first provides a trinuclear ruthenium cluster constructed polyoxometalate nanocatalyst (denoted as Ru3-POM nanocatalyst), which has a chemical formula of H3[Ru3O(C2H3N3)6Cl3][SiW 12 O 40 ]•7H2O, belongs to a monoclinic system, P 21 / n a space group, belongs to a Keggin type polyoxometalate system, and contains a trinuclear ruthenium cluster active center and a Keggin type polyacid unit in a molecular structure, realizes ordered assembly through coordination, and has a dark green needle-shaped crystal appearance. The Keggin type is the most classic and most widely researched structure configuration in polyoxometalates, and has a structural feature of a cage-shaped skeleton formed by one heteroatom tetrahedron and 12 polyatomic octahedrons.

[0011] The application also provides a preparation method of the trinuclear ruthenium cluster constructed polyoxometalate nanocatalyst.

[0012] Under stirring, the trichloride ruthenium, Na 10 [SiW9O 34 ]•18H2O is dispersed into an acetic acid-sodium acetate buffer solution (1M, initial pH=4.8-5.0), after uniform stirring, 1,2,4-triazole (molecular formula C2H3N3) ligand is added, stirring is performed until complete dissolution, and a uniform reaction solution is obtained; the pH of the reaction solution is regulated to 1.5-2.5 by using hydrochloric acid with a concentration of 4-6M, and stirring is performed at room temperature for 30-40min; finally, the reaction solution is transferred into a high-pressure reaction kettle, and hydrothermal reaction is performed at 120-160℃ for 12-24h; during the hydrothermal reaction process, the trinuclear ruthenium cluster and the polyacid unit are realized through a coordination self-assembly process of the trichloride ruthenium, Na 10 [SiW9O 34 ]•18H2O and the 1,2,4-triazole ligand; after the reaction is completed, cooling is performed to room temperature, and the precipitated dark green needle-shaped crystal is the trinuclear ruthenium cluster constructed polyoxometalate nanocatalyst, denoted as Ru3-POM nanocatalyst. The molar ratio of the trichloride ruthenium, the 1,2,4-triazole ligand and Na 10 [SiW9O 34 ]•18H2O is 1:1-1.5:1.5-2.

[0013] The process of preparing the Ru3-POM nanocatalyst is essentially a two-step synergistic process of room temperature pretreatment regulation of coordination environment and directional self-assembly under hydrothermal conditions, and the specific mechanism of each stage is as follows:

[0014] 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:

[0015] 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.

[0016] 2, the thermal energy provided in the hydrothermal reaction stage breaks the Ru 3+ The Ru-Cl bond and Ru-O (H2O) bond of the intermediate complex initiates the ligand reorganization and clusterization reaction:

[0017] The N atom of the 1,2,4-triazole ligand replaces Ru 3+ The Cl - / H2O, 1 Ru 3+ binds with 2 C2H3N3, 2 Cl - , 1 H2O to form [Ru (C2H3N3) 2Cl2 (H2O)] + (mononuclear, retaining 1 coordination vacancy); 3 mononuclear intermediates in the hydrothermal environment, first through the OH - dissociated by the water molecule 3+ coordinates with Ru 2- , and then dehydrates to form O - , forming a Ru3-O core; the remaining 1,2,4-triazole ligand and Cl 3+ supplement the coordination (each Ru - binds with 1 C2H3N3 ligand and 1 Cl + ), forming [Ru3O (C2H3N3) 6Cl3] 3+ . After the formation of the trinuclear ruthenium cluster, the positively charged Ru 12 on the surface binds with the vacant site of the activated polyacid anion, driving the structural reorganization of the polyacid unit, and finally forming a saturated Keggin-type polyacid anion [SiW 40 O 4- ] + The positively charged [Ru3O (C2H3N3) 6Cl3] 12 binds with the negatively charged [SiW 40 O 4- Through electrostatic interaction, an ion pair is formed, and H + (in the system, from hydrochloric acid and polyacid protonation) binds with the uncoordinated oxygen atom of the polyacid, and finally forms H3[Ru3O (C2H3N3) 6Cl3] [SiW 12 O 40 ]•7H2O.

[0018] Therefore, the present application controls the coordination environment through the replacement reaction at room temperature and controls the crystal structure through the self-assembly reaction in the hydrothermal stage, ensuring that the final product has both a trinuclear ruthenium cluster active center and a Keggin-type polyacid unit, providing structural and performance guarantees for subsequent electrocatalytic C-N coupling to produce urea.

[0019] Further, the trinuclear ruthenium cluster constructed polyoxometalate nanomaterial prepared by the present application can be used as an electrocatalyst for electrocatalytic C-N coupling to produce urea, and high-efficiency C-N coupling is realized. The specific application method is as follows: the Ru3-POM nanocatalyst is dispersed in a mixed solvent of an organic solvent and water to form a uniform dispersion liquid; the dispersion liquid is sprayed onto carbon paper by a spray gun, and a working electrode for electrocatalytic C-N coupling reaction is prepared after drying. In a normal temperature and pressure condition, the working electrode is used as a core to construct an electrolysis system, and electrocatalytic coupling of nitrate and CO2 to produce urea is directly carried out. The trinuclear ruthenium cluster active center in the material can directionally promote the reduction of NO3 - to generate NH2 intermediate, and the Keggin-type polyacid unit can activate CO2 to generate CO intermediate, and the synergistic effect of the two significantly improves the C-N coupling efficiency, realizes high-efficiency synthesis of urea, and no additional catalyst is needed in the electrocatalytic process. The material obtained by the present application has excellent cycle stability, and after being recycled and reused for 7 times, the urea yield does not decrease obviously, solving the problems of easy loss and poor stability of traditional catalysts; at the same time, the reaction is carried out in a normal temperature and pressure condition, and no high-temperature and high-pressure conditions are needed, and compared with the traditional urea synthesis process, the energy consumption is lower and the pollution is smaller, which meets the green economic development direction.

[0020] Compared with the prior art, the present application has the following beneficial effects:

[0021] 1. The trinuclear ruthenium cluster constructed Keggin-type polyoxometalate nanocatalyst provided by the present application can realize precise regulation of the structure of the catalyst by controllable regulation of the pH value of the reaction solution, finally form a heterogeneous Ru-POM catalyst, and has the characteristics of easy recovery, sufficient exposure of active sites and high efficiency of electron transfer, and the preparation method is simple in operation, mild in conditions, strong in controllability and convenient for large-scale production.

[0022] 2. The material obtained by the present application has trinuclear ruthenium cluster as an active center and Keggin-type polyacid as a carrier, can reversibly carry out oxidation-reduction reaction, and has N-type semiconductor characteristics, realizes high-efficiency C-N coupling in a normal temperature and pressure condition, and has the advantages of high activity, high stability and no need of auxiliary catalyst, and the yield and Faraday efficiency of urea synthesis can reach 27.2 mmol h -1 g -1 cat. -1 and 56.3%, respectively, reaching the international advanced level. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 , (a) is Ru3SiW 12polyhedron / club representation; (b) is a club representation of Ru3trz6Cl3 + three-dimensional structure; (d) is the coordination environment of Ru1ion in Ru3SiW 12 three-dimensional structure; (d) is the coordination environment of Ru1ion in Ru3SiW 12 three-dimensional structure; (d) is the coordination environment of Ru1ion in Ru3SiW 12 three-dimensional structure; (d) is the coordination environment of Ru1ion in Ru3SiW 12 three-dimensional structure; (d) is the coordination environment of Ru1ion in Ru3SiW

[0024] Figure 2 XPS spectra of Ru3SiW 12 (a) Si 2p, (b) Ru 3p, (c) W 4f.

[0025] Figure 3 IR spectra of Ru3SiW 12 and before and after electrocatalysis of C-N coupling.

[0026] Figure 4 TG analysis of Ru3SiW 12

[0027] Figure 5 XRD spectra of Ru3SiW 12

[0028] Figure 6 UV spectra of Ru3SiW 12 material electrocatalysis of C-N coupling.

[0029] Figure 7 Faraday efficiency spectra of Ru3SiW 12 material electrocatalysis of C-N coupling.

[0030] Figure 8 Yield spectra of Ru3SiW 12 material electrocatalysis of C-N coupling.

[0031] Figure 9 (a) is the time-temperature curve of Ru3SiW 12 (b) is the UV-Vis spectra of Ru3SiW 12 electrocatalysis of C-N coupling to produce urea every 1 hour cycle test at -0.3 V. DETAILED DESCRIPTION

[0032] In order to make the above objectives, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application will be described in detail below with reference to the examples. However, the scope of protection of the present application is not limited thereto. ​​

[0033] 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).

[0034] Example 1

[0035] 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:

[0036] 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.

[0037] 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:

[0038] 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.

[0039] Table 1

[0040]

[0041] 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 O 40 • 7H2O is highly consistent and contains no obvious impurity elements.

[0042] 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.

[0043] Table 2

[0044]

[0045] 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.

[0046] 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.

[0047] Table 3 Compound Ru3SiW 12 Crystallographic data

[0048]

[0049] 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;

[0050] As can be seen from Table 3: The compound Ru3SiW 12 belongs to the monoclinic system, P 21 / n space group. Figure 1 From (a), it can be analyzed that Ru3SiW 12 is composed of the Keggin-type anion [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 calculation 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 is composed 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 surface connected by the ligands to form a proton transfer channel, promoting proton exchange during the electrochemical process. Interestingly, Ru3SiW P with 21 / 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 (f)).

[0051] 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 belong to the vibration bands of the Ru3 cluster.

[0052] Figure 4 is the thermogravimetric analysis diagram, Ru3SiW 12Two weight loss stages were observed from 25 to 800℃ under N2 atmosphere. The first weight loss from 30 to 300℃ was due to the loss of lattice water molecules. The thermogravimetric analysis showed that Ru3SiW 12 has high thermal stability, which meets the requirements of heterogeneous catalysts.

[0053] Figure 5 X-ray powder diffraction pattern, in which the simulated pattern of X-ray single crystal diffraction is in good agreement with the experimental pattern, proves that the collected crystal sample is relatively pure.

[0054] Ru3SiW 12 materials prepared in this example were tested for electrocatalytic C-N coupling in H-cell electrolysis cell: Ru3SiW 12 was uniformly dispersed in a mixed solution of ethanol, water and 5wt% Nafion solution (volume ratio of the three is 4:1:0.01). A uniform dark green slurry was formed, which was then sprayed on carbon paper by airbrush to obtain Ru3SiW 12 loaded working electrode with a loading of 0.2 mg / cm 2 . In the H-cell electrolysis cell, platinum sheet was used as the counter electrode, Ag / AgCl as the reference electrode, and 0.1 M potassium nitrate electrolyte as the anode and cathode electrolyte. CO2 was introduced into the electrolysis cell at a flow rate of 20 sccm, and different voltages were applied externally for electrocatalytic reaction (-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 electrolysis cell was collected and treated with diacetyl monoxime color development method, followed by quantitative analysis by ultraviolet spectrophotometer. The infrared spectra of Ru3SiW 12 materials before and after electrocatalytic C-N coupling are shown in Figure 3 , the UV-Vis absorption spectra of urea produced by electrocatalytic C-N coupling are shown in Figure 6 , and the Faraday efficiency and yield diagrams are shown in Figure 7 and Figure 8 , respectively. It can be seen that at -0.3 V (vs. RHE), the yield and Faraday efficiency of urea are the highest, which are 27.2 mmol h -1 g -1 cat. -1 and 56.3%, respectively. The stability of Ru3SiW 12 electrocatalytic synthesis of urea was evaluated by 7 independent cycle tests (the same working electrode, 7 times of cycle catalysis, 1 h each time) (as shown in Figure 9 ), which proves that the obtained catalyst material has high Faraday efficiency and yield of C-N coupling to produce urea and good stability.

[0055] The above merely provides the illustration and description of the concept of the present application. Those skilled in the art can make various modifications or supplements to the described specific embodiments or adopt similar ways instead, as long as they do not deviate from the concept of the present application or exceed the scope defined by the present claims.

Claims

1. A method for the preparation of a nanocatalyst of a polylmetalloxometalate built on a trinuclear ruthenium cluster, characterized by that, The method comprises the following steps: Under stirring, ruthenium trichloride, Na 10 [SiW9O 34 ]•18H2O was dispersed into acetic acid-sodium acetate buffer solution, after stirring uniformly, 1,2,4-triazole ligand was added, and stirred until completely dissolved to obtain a uniform reaction solution; the pH of the reaction solution was adjusted to 1.5-2.5 with hydrochloric acid, and the reaction was stirred at room temperature; finally, the reaction solution was transferred to a high-pressure reaction kettle for hydrothermal reaction, and in the reaction process, ruthenium ions, Na 10 [SiW9O 34 ]•18H2O and 1,2,4-triazole ligand were self-assembled through coordination to realize the ordered construction of trinuclear ruthenium clusters and polyacid units; after the reaction was completed, it was cooled to room temperature, and the needle-shaped crystals precipitated were the polyoxometalate nanocatalyst constructed by trinuclear ruthenium clusters, recorded as Ru3-POM nanocatalyst.

2. The production method according to claim 1, characterized by, The chemical formula of the obtained Ru3-POM nanocatalyst is H3[Ru3O(C2H3N3)6Cl3][SiW 12 O 40 ]•7H2O, belonging to monoclinic crystal system, P 21 / 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 ]•18H2O in a molar ratio of 1:1-1.5:1.5-2.

4. The method of claim 1, wherein, The concentration of hydrochloric acid used is 4-6 M.

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

6. The method of claim 1, wherein, The hydrothermal reaction is carried out at 120-160 ℃ for 12-24 h.

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

8. Use of the Ru3-POM nanocatalyst of claim 7 in electrocatalytic C-N coupling reactions, characterized in that, The Ru3-POM nanocatalyst is used for electrocatalytic co-reduction of carbon dioxide and nitrate at room temperature to produce urea.

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