Mesoporous copper nano-tip electrocatalyst for efficiently synthesizing urotropine as well as preparation method and application of mesoporous copper nano-tip electrocatalyst

Abstract

The invention discloses a mesoporous copper nano-tip electrocatalyst for efficiently synthesizing urotropine and a preparation method and application thereof, and belongs to the technical field of catalysts.The method comprises the steps that 1, a copper nitrate solution is dispersed in deionized water, and a solution I is obtained; (2) injecting a freshly prepared sodium borohydride solution into the solution I for reduction reaction; (3) centrifugally washing the reduced product in the step (2) by using a mixed solution of absolute ethyl alcohol and deionized water, and drying to obtain copper oxide powder; and (4) preparing the copper oxide powder obtained in the step (3) into a working electrode, and preparing the mesoporous copper nano-tip electrocatalyst by using an in-situ electrochemical reduction method. The catalyst prepared by the invention not only avoids the use of noble metals, but also realizes the utilization of biomass and environmental wastes and the efficient synthesis of urotropin at normal temperature and normal pressure; the method has the advantages of simple process, energy conservation, emission reduction, good product stability and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrocatalytic materials and organic electrosynthesis, and particularly relates to a mesoporous copper nanotip electrocatalyst for efficient synthesis of hexamethylenetetramine, a preparation method and application thereof. BACKGROUND

[0002] As an important nitrogen-containing heterocyclic compound, hexamethylenetetramine (HMTA) has irreplaceable core application value in the fields of medicine, materials, agriculture and national defense, and is a key precursor for the synthesis of drugs, resins, blowing agents and energetic materials. At present, the industrial production of HMTA is mainly realized by the thermal catalytic reaction of ammonia (NH3) and formaldehyde (HCHO) synthesized by Haber-Bosch process, but this traditional route has inherent energy-intensive defects, such as the use of volatile and irritating ammonia water, which has safety and environmental risks, and the reaction conditions are harsh, and the energy consumption is high.

[0003] In recent years, the electrochemical carbon-nitrogen (C-N) coupling technology driven by renewable energy provides a new paradigm for the green synthesis of HMTA: using industrial nitrogen-containing waste nitrate (NO3 - ) and HCHO to directly couple, realizing the directional construction and cyclization of multiple C-N bonds under mild conditions, and having the advantages of high atom economy and environmental friendliness.

[0004] In principle, the synthesis of HMTA from NO3 - and HCHO is an electrochemical-chemical cascade reaction. The initial electrochemical process involves the electrocatalytic reduction of NO3 - to generate NH3 intermediate (*NH3), and then the *NH3 and active *CHO intermediate are further condensed and cyclized by chemical process. Therefore, when designing an efficient metal catalyst, two fundamental difficulties of the electrochemical-chemical cascade reaction for synthesizing HMTA need to be overcome. Given the significant differences in electronic properties and reactivity between NO3 - and HCHO, the catalyst first needs to achieve efficient chemical adsorption and activation of the reactants, and enhance the mass / electron transfer efficiency to overcome the kinetic bottleneck of the initial electroreduction of NO3 - to NH3 and the subsequent C-N chemical coupling. Secondly, the C-N coupling reaction involves a complex condensation and cyclization process, and the instability of the key intermediate and the generation of thermodynamic / kinetic byproducts also seriously affect the reaction activity and product selectivity. Therefore, it is urgent to design and develop new electrocatalyst materials to realize efficient HMTA electrosynthesis.

[0005] Copper-based materials can effectively regulate the adsorption configuration and charge transfer path of reaction intermediates due to their unique electronic structure and adjustable d-band center, precisely matching the requirements of C-N bond formation for adsorption strength, providing an ideal platform for the directional construction or cyclization of multiple C-N bonds. Recently, based on the surface properties of copper catalysts rich in copper vacancies, a new pathway for the electrocatalytic synthesis of HMTA from nitrate and formaldehyde has been successfully developed. However, the existing copper-based catalytic system still faces the key challenge of insufficient C-N coupling efficiency, which severely restricts the improvement of HMTA selectivity / faradic efficiency, and the reaction mechanism research is not perfect. Therefore, the systematic design and mechanism research of copper-based catalytic materials have become the core method to break through the technical bottleneck of HMTA electro-synthesis.

[0006] Current research focuses on atomic / molecular scale active site engineering (such as single-atom alloy, defect regulation); however, such strategies usually rely on high-precision synthesis processes (such as complex ligand modification or atomic-level dispersion technology), which have high energy consumption, prominent scale-up barriers, and other problems, severely restricting practical application. In contrast, physical engineering of metal catalysts at the mesoscopic level provides a simple and effective catalyst design strategy for optimizing the chemical adsorption and cascade reactivity of organic electro-synthesis.

[0007] Unlike traditional nanospheres or nanoparticles, nanomaterials with a sharp tip effect have inherent advantages: (1) The enhanced surface charge density near the sharp tip can directly or indirectly increase the supply rate of reactants, thereby increasing the collision frequency between active sites and reactants. Therefore, it promotes the effective chemical adsorption of reactants on active sites and improves reaction efficiency; (2) The enhanced surface charge density can efficiently promote electron transfer during the reaction process; (3) The unique geometric and electronic structure helps to adjust the reaction energy barrier; (4) The electric field induced by the nanotip can achieve targeted catalysis and expected selectivity. Thus, the nanotip enhancement effect may solve the first fundamental problem of electrochemical-chemical cascade synthesis of HMTA.

[0008] In addition, mesoporous metals, as a class of porous materials with pore sizes between 2-50 nm, have important application value in catalysis, sensing, and biomedical fields due to their high specific surface area, adjustable pore structure, and excellent mass / electron transport capacity. Unlike conventional nanostructures, the nanometer confined microenvironment of mesoporous metals can act as a kind of "nano-enzyme" catalytic reactor, effectively improving the surface electronic state inside the pore, and may become a functional structural material for stabilizing reaction intermediates and regulating C-N coupling catalytic selectivity.

[0009] However, in the traditional technology, in order to obtain high specific surface area and rich active sites of mesoporous metal materials, the thermodynamic stability and mechanical strength of the materials are essentially sacrificed, and there are technical problems such as poor structural stability, difficult accurate control of pore size, pore channel and component, and non-uniform product.

[0010] The specification of Chinese invention 202310855783.0 describes a method for preparing a nanoporous electrode by using a lyotropic liquid crystal template and its application, which comprises the following steps: S1, mixing a metal salt solution with a surfactant Brij56 and methane sulfonic acid or sodium borohydride, heating to 70-80 DEG C, and obtaining a lyotropic liquid crystal precursor solution; S2, using the lyotropic liquid crystal precursor solution as an electrodeposition solution to perform electrodeposition on a current collector electrode; S3, cleaning to remove the template; S4, keeping the current collector electrode obtained in step S3 at 40-60 DEG C for 6-24 h and naturally cooling, and then drying to obtain a current collector loaded with mesoporous metal nanoparticles. However, during crystallization and high-temperature treatment, the atomic migration rate of the metal precursor is high, which can easily lead to pore collapse, structure shrinkage or crystal aggregation, thereby destroying the mesoporous structure, reducing the specific surface area and reducing the cycle stability. SUMMARY

[0011] The present application aims to provide a mesoporous copper nanotip electrocatalyst for efficient synthesis of urotropine, a preparation method and application, which overcomes the technical problems of low catalytic efficiency and poor stability of existing electrocatalysts, has the advantages of simple operation, low cost, energy saving and emission reduction, and good product stability; the prepared catalyst not only avoids the use of noble metals, has high activity, high selectivity and high stability, but also realizes the utilization of biomass and environmental waste at normal temperature and pressure and the efficient synthesis of urotropine.

[0012] To achieve the above-mentioned purpose, the present application provides a preparation method of a mesoporous copper nanotip electrocatalyst for efficient synthesis of urotropine, comprising the following steps: (1) Preparation of solution I: disperse copper nitrate solution in deionized water to obtain solution I; (2) Inject the freshly prepared sodium borohydride solution into solution I for reduction reaction; (3) After the reaction is completed, centrifugal washing is performed on the product in step (2) using a mixed solution of anhydrous ethanol and deionized water, and the copper oxide powder is obtained after drying; (4) Preparation of mesoporous copper nanotip electrocatalyst: the copper oxide powder obtained in step (3) is made into a working electrode, and a mesoporous copper nanotip electrocatalyst is prepared by using in-situ electrochemical reduction method.

[0013] The present application combines metal copper with a tip and a mesoporous structure to construct a mesoporous copper nanotip electrocatalyst, which innovatively realizes the cross-scale fusion of metal intrinsic properties and structural advantages: at the atomic scale level, through oxidation state regulation and coordination environment construction, the electronic transmission efficiency can be significantly improved, the active intermediate can be stabilized and the reaction energy barrier can be optimized; at the mesoscopic scale level, the nanotip and mesoporous structure can realize the synergistic control of reactant enrichment, reaction kinetics acceleration, intermediate stabilization and guiding of electrochemical-chemical cascade reaction path to selective C-N coupling conversion. The multi-scale synergistic mesoporous copper nanotip material is expected to become a high-efficiency C-N coupling catalyst that breaks through the limitation of HMTA selectivity / faradic efficiency.

[0014] Preferably, the concentration in step (1) is 0.005-0.02 mol•L -1 The concentration of copper nitrate solution is 3-5 parts, and the concentration of deionized water is 49-52 parts.

[0015] Further, step (1) is specifically: at room temperature, 0.01 mol•L -1 of copper nitrate solution 4 parts is dispersed in deionized water 50 parts to obtain solution I.

[0016] Preferably, the concentration in step (2) is 3-7 mg•mL -1 The concentration of sodium borohydride solution is 4.5-5.5 parts, and the reduction reaction time is 10-14 h.

[0017] Further, step (2) is specifically: 5 mg•mL -1 of freshly prepared sodium borohydride solution is quickly injected into solution I for reduction reaction, and the reduction reaction time is 12 h.

[0018] Preferably, in step (3), the ratio of anhydrous ethanol to deionized water is 2-4:1; vacuum drying for 10-14 h at a temperature of 50-70℃.

[0019] Step (3) is specifically: after the reaction is completed, the precipitated product in step (2) is washed by centrifugation using a mixed solution of anhydrous ethanol and deionized water in a ratio of 3:1, and dried in a vacuum drying oven at 60℃ for 12 h to obtain copper oxide powder.

[0020] Preferably, in step (4), the reduction reaction is electrolytic reduction in an alkaline electrolyte with a concentration of 0.5-1.5 M at a voltage of-1.4 V to-1.8 V (vs. Ag / AgCl) for 0.3-0.7 h.

[0021] Further preferably, the reduction reaction in step (4) is electrolytic reduction in an alkaline electrolyte with a concentration of 0.8-1.2 M at a voltage of-1.5 V to-1.7 V (vs. Ag / AgCl) for 0.4-0.6 h.

[0022] Specifically, step (4) is: preparing the copper oxide powder obtained in step (3) into a working electrode, electrolytic reduction of the copper oxide electrode in 1.0 M KOH solution at a voltage of-1.6 V for 0.5 h to prepare the mesoporous copper nanotip electrocatalyst.

[0023] The present application also provides a mesoporous copper nanotip electrocatalyst (CuMNTs) prepared by the above preparation method. The catalyst has a high specific surface area, abundant active sites and a unique geometry with dual characteristics of mesopores and nanotips. The high specific surface area is beneficial to the mass transfer and diffusion of the reactants (NO3 - , HCHO) and the product (HMTA).

[0024] The mesoporous copper nanotip electrocatalyst has abundant interconnected mesoporous channels in the tip, and the channel diameter is 2-5 nm.

[0025] The mesoporous copper nanotip electrocatalyst is used for electrochemical carbon-nitrogen coupling synthesis of hexamethylenetetramine (HMTA).

[0026] The method for electrocatalytic synthesis of hexamethylenetetramine comprises the following steps: A. The mesoporous copper nanotip electrocatalyst (CuMNTs) is used as a working electrode, a saturated Ag / AgCl electrode is used as a reference electrode, and a platinum sheet electrode is used as a counter electrode to form a three-electrode system; B. A mixed aqueous solution containing nitrate, formaldehyde and supporting electrolyte is used as an electrolyte; C. Constant potential electrolysis is carried out at a reaction temperature of 20-30℃ and a potential of-0.1 V to-0.8 V relative to the reversible hydrogen electrode (RHE), so that hexamethylenetetramine is generated at the cathode.

[0027] Preferably, the electrolyte composition is: 0.1 mol·L -1 KOH, 0.5 mol·L -1 K2SO4, 0.1 mol·L -1 KNO3 and 0.3 mol· -1 HCHO, and the reaction temperature is 25℃.

[0028] The present application realizes the use of CuMNTs electrocatalyst to electrolyze nitrate NO3 -, and formaldehyde HCHO through an electrocatalytic carbon-nitrogen coupling route to directly synthesize hexamethylenetetramine (HMTA).

[0029] The beneficial effects of the present application are: (1) The catalyst prepared by the present application has unique functional characteristics, which is applied to the electrochemical carbon-nitrogen coupling synthesis of hexamethylenetetramine. The mesoporous copper nanotip catalyst has the structure of nanotip and interconnected mesoporous network, which can realize the structural synergistic effect of promoting electrochemical-chemical cascade reaction. The use of the catalyst can realize the optimal activity, selectivity and stability of the electrochemical synthesis of HMTA at the same time.

[0030] (2) The catalyst prepared by the present application avoids the use of noble metals, greatly reduces the raw material cost; and the process is simple, easy to operate, the reaction conditions are mild, the product stability is good, and it can be prepared in large quantities, which is suitable for large-scale industrial production.

[0031] (3) The catalyst prepared by the present application enriches the methods and types of physical mesoscopic level catalyst design, and realizes the efficient electrochemical-chemical cascade synthesis of HMTA at normal temperature and pressure through hierarchical structure engineering. The catalyst provides some opportunities for promoting electrochemical-chemical cascade catalysis to synthesize various high-value-added chemicals and products from biomass and environmental waste. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 The X-ray diffraction pattern (XRD) of the mesoporous copper nanotip electrocatalyst (Cu MNTs) prepared for Example 1 of the present application and the comparative catalyst (copper nanotip (Cu NTs), mesoporous Cu nanoparticles (Cu MNs), Cu nanoparticles (Cu NPs)).

[0033] Figure 2 The transmission electron microscopy (TEM) image of the Cu MNTs catalyst prepared for Example 1 of the present application.

[0034] Figure 3 The linear sweep voltammetry (LSV) curve (different electrolytes) of the Cu MNTs catalyst prepared for Example 1 of the present application.

[0035] Figure 4 The HMTA electrochemical synthesis performance chart (electrolysis for 2 h under different voltages, electrolyte is 0.1 mol•L -1 KOH + 0.5 mol•L -1 K2SO4 + 0.1 mol•L -1 KNO3+ 0.3 mol•L -1 HCHO) of the Cu MNTs catalyst prepared for Example 1 of the present application and the comparative catalyst (Cu NTs, Cu MNs, Cu NPs).

[0036] Figure 5 Cyclic stability performance chart of Cu MNTs catalyst prepared for Example 1 of the present application (electrolyte is 0.1 mol•L -1 KOH + 0.5 mol•L -1 K2SO4 + 0.1 mol•L -1 KNO3+ 0.3 mol•L -1 HCHO). DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the protection scope of the present application. In the following embodiments, the experimental methods are all routine methods unless otherwise specified; and the reagents and materials are all commercially available unless otherwise specified.

[0038] Example 1 (1) Preparation of mesoporous copper nanotip electrocatalyst (Cu MNTs): At room temperature, 4.0 mL of 0.01 mol•L -1 of copper nitrate solution was dispersed in 50 mL of deionized water; then 5 mL of freshly prepared 5 mg•mL -1 of sodium borohydride solution was quickly injected into the above reaction solution for reduction reaction, and the reaction time was 12 h; after the reaction was completed, the precipitated product was washed by centrifugation using a mixed solution of anhydrous ethanol and deionized water at a ratio of 3:1, and dried in a vacuum drying oven at 60°C for 12 h to obtain copper oxide powder; the obtained copper oxide powder was made into a working electrode; the copper oxide electrode was electrolytically reduced in 1.0 M KOH solution at a voltage of-1.6 V (vs. Ag / AgCl) for 0.5 h to obtain mesoporous copper nanotip electrocatalyst (Cu MNTs).

[0039] (2) Preparation of working electrode: 10 mg of prepared copper oxide powder was weighed and mixed with 0.4 mL of deionized water, 0.52 mL of anhydrous ethanol and 0.08 mL of naphthol solution, and 0.1 mL of copper oxide solution at a concentration of 10 mg mL -1 was obtained after ultrasonic treatment of the above mixed solution for 0.5 h. 0.1 mL of catalyst solution was uniformly dropped on a 1 cm×2 cm clean carbon paper using a pipette, so that the catalyst loading was 2 mg•cm -2After drying, it is used as a working electrode with a sandwich electrode. The carbon paper is washed several times with an ethanol / water solution before use to remove possible contaminants. The electrode preparation is a conventional technique.

[0040] (3) HMTA synthesis by electrocatalytic carbon-nitrogen coupling reaction: The HMTA synthesis by electrocatalytic carbon-nitrogen coupling reaction was carried out on a CHI 660e electrochemical workstation. The test used a typical three-electrode system, and the Cu MNTs after electrochemical reduction treatment were used as the working electrode, a saturated Ag / AgCl electrode was used as the reference electrode, and a 1 cm x 2 cm platinum sheet electrode was used as the counter electrode. The electrolytic cell used was an H-type electrolytic cell, and the electrolyte was a mixture of 0.1 mol•L -1 -1 KOH, 0.5 mol•L -1 -1 K2SO4, 0.1 mol•L -1 -1 KNO3 and 0.3 mol•L -1 HCHO solution. In the electrochemical test, the reaction temperature was 25℃, and the applied potential was-0.1 V to-0.8 V vs. RHE.

[0041] Example 2 A mesoporous copper nanotip electrocatalyst (Cu MNTs) was prepared as follows: (1) Preparation of solution I: At room temperature, 3 parts of a copper nitrate solution with a concentration of 0.005 mol•L -1 -1 was dispersed in 49 parts of deionized water to obtain solution I; (2) 4.5 parts of a freshly prepared sodium borohydride solution with a concentration of 3 mg•mL -1 -1 was injected into solution I for reduction reaction, and the reduction reaction time was 10 h; (3) After the reaction was completed, the product in step (2) was centrifugally washed with a mixed solution of anhydrous ethanol and deionized water, and the copper oxide powder was obtained after drying; the ratio of anhydrous ethanol to deionized water was 2:1; vacuum drying was performed for 10 h at a temperature of 50℃; (4) Preparation of mesoporous copper nanotip electrocatalyst: The copper oxide powder obtained in step (3) was made into a working electrode, and a mesoporous copper nanotip electrocatalyst was prepared by in-situ electrochemical reduction method; the reduction reaction was electrolytic reduction at a voltage of-1.4 V (vs. Ag / AgCl) in a 0.5 M KOH electrolyte for 0.7 h.

[0042] Example 3 A mesoporous copper nanotip electrocatalyst (Cu MNTs) was prepared as follows:

[0043] (1) Preparation of solution I: At room temperature, 3 parts of a copper nitrate solution with a concentration of 0.02 mol•L-1 Copper nitrate solution 5 parts was dispersed in deionized water 52 parts to obtain solution I; (2) 5.5 parts of freshly prepared sodium borohydride solution with a concentration of 7 mg•mL-1 was injected into solution I to carry out the reduction reaction, and the reduction reaction time was 14 h; (3) After the reaction was completed, the product in step (2) was centrifuged and washed with a mixed solution of anhydrous ethanol and deionized water, and then dried to obtain copper oxide powder; the ratio of anhydrous ethanol to deionized water was 4:1; vacuum drying for 14 h at a temperature of 70°C; (4) Mesoporous copper nanotip electrocatalyst preparation: the copper oxide powder obtained in step (3) was made into a working electrode, and a mesoporous copper nanotip electrocatalyst was prepared by in-situ electrochemical reduction method; wherein the reduction reaction was electrolytic reduction at a voltage of -1.8 V (vs. Ag / AgCl) in a 1.5 M KOH electrolyte for 0.3 h.

[0044] Example 4 A mesoporous copper nanotip electrocatalyst (Cu MNTs) was prepared by the following steps:

[0045] (1) Solution I preparation: 4 parts of copper nitrate solution with a concentration of 0.015 mol•L-1 was dispersed in 50 parts of deionized water at room temperature to obtain solution I; (2) 4.5-5.5 parts of freshly prepared sodium borohydride solution with a concentration of 6 mg•mL-1 was injected into solution I to carry out the reduction reaction, and the reduction reaction time was 13 h; (3) After the reaction was completed, the product in step (2) was centrifuged and washed with a mixed solution of anhydrous ethanol and deionized water, and then dried to obtain copper oxide powder; the ratio of anhydrous ethanol to deionized water was 3:1; vacuum drying for 13 h at a temperature of 55°C; (4) Mesoporous copper nanotip electrocatalyst preparation: the copper oxide powder obtained in step (3) was made into a working electrode, and a mesoporous copper nanotip electrocatalyst was prepared by in-situ electrochemical reduction method; wherein the reduction reaction was electrolytic reduction at a voltage of -1.7 V (vs. Ag / AgCl) in a 0.8 M electrolyte for 0.4 h, to obtain the mesoporous copper nanotip electrocatalyst.

[0046] Example 5 The other contents are the same as those in Example 1, wherein the reduction reaction in step (4) is electrolytic reduction at a voltage of -1.5 V (vs. Ag / AgCl) in a 0.8 M alkaline electrolyte for 0.6 h.

[0047] Example 6 Other contents are as in Example 1, wherein the reduction reaction in step (4) is electrolytic reduction in an alkaline electrolyte with a concentration of 1.2 M at a voltage of -1.7 V (vs. Ag / AgCl) for 0.4 h.

[0048] Example 7 A method for electrocatalytic synthesis of urotropine, comprising the following steps: A. Taking the mesoporous copper nanotip electrode (Cu MNTs) as the working electrode, a saturated Ag / AgCl electrode as the reference electrode, and a platinum sheet electrode as the counter electrode to form a three-electrode system; B. Taking a mixed aqueous solution containing nitrate, formaldehyde and supporting electrolyte as the electrolyte; C. Carrying out constant potential electrolysis at a reaction temperature of 25℃ and a potential of -0.1 V to -0.8 V relative to the reversible hydrogen electrode (RHE), so that urotropine is generated at the cathode.

[0049] wherein the electrolyte composition is: 0.1 mol·L -1 KOH, 0.5 mol·L -1 K2SO4, 0.1 mol·L -1 KNO3 and 0.3 mol·L -1 HCHO, and the reaction temperature is 25℃.

[0050] Example 8 Other contents are as in Example 5, and the reaction temperature in step C is 20℃.

[0051] Example 9 Other contents are as in Example 5, and the reaction temperature in step C is 30℃.

[0052] Comparative Example 1 Preparation of copper nanotips (Cu NTs): The Cu NTs were synthesized by a two-step method of hydrothermal synthesis and electrochemical reduction. First, equal volumes of 0.2 mol•L -1 Cu(NO3)2·3H2O and 0.2 mol•L -1 NaOH solution were mixed and continuously stirred. Subsequently, it was transferred to a stainless steel autoclave (capacity of 60 mL). It was kept at a temperature of 120-180℃ for more than 20 h, and then cooled to room temperature. The obtained black precipitate was thoroughly washed with a mixed solution of anhydrous ethanol and deionized water with a volume ratio of 3:1, and finally vacuum dried at 75℃ for 6 h. The obtained cuprous oxide powder was made into a working electrode; the cuprous oxide electrode was electrolytically reduced in a 1.0 M KOH solution at a voltage of -1.6 V (vs. Ag / AgCl) for 0.5 h to prepare the copper nanotip (Cu NTs) electrocatalyst.

[0053] Comparative Example 2 Preparation of mesoporous copper nanoparticles (Cu MNs): CuMNs were synthesized using a two-step method involving liquid-phase synthesis and electrochemical reduction. 250 mg of CuSO4·5H2O was added to 20 mL of 0.1 mol•L⁻¹ water. -1 In NaOH aqueous solution, the blue Cu(OH)₂ precipitate formed by ultrasonic treatment was dispersed into a uniform dispersion. Then, 176 mg of ascorbic acid was added under vigorous stirring. After the reaction solution turned pale yellow within 1 min, stirring was continued for 20 min at room temperature. The resulting precipitate was collected, thoroughly washed with a mixture of anhydrous ethanol and deionized water in a volume ratio of 3:1, and vacuum dried at 50 °C. The obtained cuprous oxide powder was used to prepare a working electrode; the cuprous oxide electrode was electrolytically reduced in 1.0 M KOH solution at -1.6 V (vs. Ag / AgCl) for 0.5 h to prepare a mesoporous copper nanoparticle (Cu MNs) electrocatalyst.

[0054] Comparative Example 3 Preparation of copper nanoparticles (Cu NPs): Cu NPs were synthesized using a two-step method involving liquid-phase synthesis and electrochemical reduction. At room temperature, 1.0 mL of 1.2 mol•L⁻¹ solution was used. -1 CuSO4 was dispersed in 400 mL of deionized water. After stirring for 5 min, 1.0 mL of 4.8 mol•L⁻¹ solution was added to the above solution. -1 NaOH. The clear blue solution immediately turned cloudy blue, indicating the formation of Cu(OH)₂. After 5 min, 1.0 mL of 1.2 mol•L⁻¹ was injected. -1 Freshly prepared ascorbic acid was reacted for 0.5 h. The solution color rapidly changed from turbid blue to yellowish-brown. Washing and centrifugation with a 3:1 volume ratio of anhydrous ethanol to deionized water yielded Cu₂O precipitate. The obtained cuprous oxide powder was used to prepare the working electrode; the cuprous oxide electrode was electrolytically reduced in 1.0 M KOH solution at -1.6 V (vs. Ag / AgCl) for 0.5 h to prepare copper nanoparticle (Cu NPs) electrocatalysts.

[0055] Experiment 1 The Cu MNTs catalyst prepared in Example 1 of this invention and the comparative catalysts (Cu MNTs, CuMNs, Cu NPs) of Comparative Examples 1-3 were subjected to X-ray diffraction (XRD) patterns, as shown below. Figure 1 As shown. The instrument used is a D / max 2500 VL / PC diffractometer (Japan).

[0056] from Figure 1 As can be seen, the characteristic peaks of all four catalysts belong to Cu (PDF # 04-0836), indicating that the electrochemical reduction method successfully converted the copper oxide precursor into elemental copper. This also helps to reveal the influence of the material's structural advantages on its catalytic performance.

[0057] Experiment 2 The Cu MNTs catalyst prepared in Example 1 of this invention was subjected to transmission electron microscopy, as shown in Figure 1. Figure 2 As shown. The instrument used was a JEM-F200, JEOL Ltd., Japan.

[0058] from Figure 2 As can be seen from AC, Figure 2 Figure a shows the structural features of a catalyst composed of densely packed nanotipples. In this invention, a mesoporous structure with abundant nanotipples was successfully formed.

[0059] Figure 2 The high-magnification HAADF-STEM image further reveals abundant interconnected mesoporous channels within the tip, with diameters ranging from 2 to 5 nm.

[0060] Furthermore, the medium-to-high resolution HAADF-STEM images reveal a clear lattice spacing of 0.21 nm, corresponding to the (111) crystal plane of face-centered cubic Cu, further indicating that... Figure 2 The metallic phase of the product shown in c. These characterization results clearly verify the successful preparation of Cu MNTs in this invention, thus providing a material basis for the subsequent electrochemical-chemical grade synthesis of HMTA.

[0061] Experiment 3 Comparative Examples 4-6 are as follows: Comparative Example 4: Nitrate Reduction Reaction (NO3-RR) Activity Test Repeat the process of Example 7, but replace the electrolyte with 0.1 mol•L. -1 KOH, 0.5 mol•L -1 K2SO4 and 0.1 mol•L -1 KNO3 (excluding HCHO).

[0062] Comparative Example 5: Formaldehyde Reduction Reaction (HCHO-RR) Activity Test Repeat the process of Example 7, but replace the electrolyte with 0.1 mol•L. -1 KOH, 0.5 mol•L -1 K2SO4 and 0.3 mol•L -1 HCHO (KNO3-free).

[0063] Comparative Example 6: Hydrogen evolution reaction (HER) activity test The procedure of Example 7 was repeated, but the electrolyte was replaced with 0.1 mol•L -1 KOH and 0.5 mol•L -1 K2SO4 (neither containing KNO3 nor HCHO).

[0064] The LSV curves of Cu MNTs catalyst prepared in Example 1 of the present application in Example 7, and the products obtained in Comparative Examples 4-6 in electrochemical tests are shown in Figure 3 The instrument used was CHI 660E electrochemical workstation (Chenhua, Shanghai).

[0065] As shown in Figure 3 , the onset reduction potential of NO3 - Reduction was significantly better than that of HCHO reduction and hydrogen evolution reaction (HER), and the highest current density indicated that it was more thermodynamically favorable. At the same time, when NO3 - and HCHO coexist, the current density of C-N coupling reaction is slightly lower than that of NO3 - Reduction, which is mainly due to the competitive adsorption of HCHO, which occupies part of the active sites of NO3 - Reduction. These results clearly highlight the potential high activity of Cu MNTs for HMTA synthesis.

[0066] Test four is the carbon-nitrogen coupling reaction of Cu MNTs catalyst prepared in Example 1 of the present application and comparative catalysts (Cu MNTs, Cu MNs, Cu NPs) of Comparative Examples 1-3, and the HMTA yield and Faraday efficiency performance are shown in Figure 4 The instrument used was nuclear magnetic resonance spectrometer AVIII400 HD (400M).

[0067] As shown in Figure 4 , the Cu MNTs catalyst achieved the best Faraday efficiency of 94.2% at -0.4 V vs. RHE, corresponding to an HMTA yield of 0.227 mmol h -1 cm -2 , which is significantly better than the comparative catalysts Cu MNTs, Cu MNs and Cu NPs.

[0068] Test five The Cu MNTs catalyst prepared in Example 1 in the present application was used to carry out the electro-synthesis of HMTA. The specific steps were as follows: after electro-reduction, the electrolyte was taken out, and 1H NMR (400 MHz) was used to further quantify with maleic acid as an external standard. First, a calibration curve was established: (1) a series of HMTA solutions with known concentrations were prepared as standard solutions; (2) 0.50 mL of the standard solutions with different concentrations were mixed with 10 mg of maleic acid; (3) 50 μL of D2O was added to the above 0.50 mL mixed solution for 1H NMR detection; (4) since the peak area ratio of the sample to maleic acid was positively correlated, the peak area ratio of the sample to maleic acid was used for calibration.

[0069] The HMTA detection method of the electrolyte after electro-reduction was as above, 0.50 mL of the cathode electrolyte solution was mixed with 10 mg of maleic acid; 0.50 mL of the above mixed solution was taken, 50 μL of D2O was added for 1H NMR detection; and the standard curve prepared was used for quantitative analysis. The cyclic stability diagram is shown in Figure 5

[0070] As shown in Figure 5 , after 50 cycles, the performance of the Cu MNTs catalyst almost did not attenuate, indicating high stability.

[0071] In the above test of electro-catalytic carbon-nitrogen coupling to synthesize HMAT, linear sweep voltammetry (LSV) was used to record the current density (j) j in the applied voltage range, which can be used to characterize the electrochemical behavior in the voltage range, wherein the LSV scan rate is 10 mV s -1 , and the scan voltage range is -0.6 V~+0.4 V vs. RHE relative to the reversible hydrogen electrode; the constant voltage method can be used to record the current-time (i-t) i-t curve at the applied potential, and the charge quantity (Q) Q is recorded to calculate the Faraday efficiency (FE); the applied voltage range in the present application is -0.8 V~-0.1 V vs. RHE relative to the reversible hydrogen electrode; and the classic nuclear magnetic resonance hydrogen spectrum is used to quantify the HMTA after reaction.

[0072] The Faraday efficiency calculation method of HMTA is as follows: FE HMTA = (32 × F × C HMTA × V × 10 -3 ) / Q × 100% The ammonia yield calculation method is as follows: ​Yield rate (HMTA) = ( C HMTA × V ) / ( t × m ) wherein C HMTA is the measured HMTA concentration (mol•L -1 ); V is the volume of electrolyte (30 mL); m is the mass of catalyst (1 mg); t is the electrolysis time (2 h); F is the Faraday constant (96485 C mol -1 ); Q (C) is the total charge passed through the electrode, which is the result of the curve integration. i-t

[0073] The present application first synthesizes mesoporous copper nanotip catalyst with unique functional characteristics, and applies it to electrochemical carbon-nitrogen coupling to form HMTA. Cu MNTs with tip enhancement effect and mesoporous induced nanometer confinement mechanism can perfectly realize the structural synergistic effect of promoting electrochemical-chemical cascade production of HMTA. On the one hand, the dense nanotip structure on the surface of the catalyst can form a local enhanced electric field at the electrode-electrolyte interface, and the synergistic tip enhancement enrichment effect not only greatly promotes the adsorption and activation of the reactants, but also significantly accelerates the interface electron transfer rate, effectively reduces the energy barrier of the protonation step, thereby breaking the reaction kinetic bottleneck of the initial NO3 - reduction to NH3 and the subsequent C-N bond formation. On the other hand, the three-dimensional mesoporous network in the catalyst can act as a nanoscale reactor, and the unique confined microenvironment formed can effectively enrich and stabilize the reaction active intermediates, greatly increasing their local concentration and residence time near the active site. This not only promotes the effective collision and directional assembly between *NH3 and *CHO, but also provides a thermodynamic driving force for the subsequent non-electrochemical condensation reaction. Therefore, the use of this electrocatalyst can simultaneously achieve better activity, selectivity and stability for the electrochemical synthesis of HMTA.

[0074] ​The prepared catalyst enriches the method and kind of physical mesoscopic level catalyst design, realizes efficient electrochemical-chemical cascade to HMTA at normal temperature and pressure through hierarchical structure engineering. Through reasonable design of tip enhancement effect and mesoporous induced nano reactor, the physical design structure is successfully customized for selective C-N coupling reaction. This work provides some opportunities for promoting electrochemical-chemical cascade catalysis to synthesize various high value-added chemicals and products from biomass and environmental waste. More importantly, the structure / component advantage of the prepared catalyst can avoid the use of noble metal: on raw material cost, the noble metal Pd Pt Rh precursor is expensive, and the market price may be about 1000 yuan / 1g, while the price of copper nitrate is dozens of yuan / bottle (250g / 500g), thereby greatly reducing the raw material cost; and the process is simple, easy to operate, the reaction condition is mild, the product stability is good and can be prepared in large quantities, suitable for large-scale industrial production.

[0075] Finally, it should be noted that: the above only for the preferred embodiments of the present application, and not for limiting the present application, although the foregoing embodiments of the present application are described in detail, for those skilled in the art, it still can be modified, or part of the technical features of the equivalent replacement of the technical solutions recorded in the foregoing embodiments. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for the preparation of mesoporous copper nanotip electrocatalyst for efficient synthesis of urotropine, characterized by: The method comprises the following steps: (1) Preparation of solution I: disperse copper nitrate solution in deionized water to obtain solution I; (2) inject freshly prepared sodium borohydride solution into solution I to perform a reduction reaction; (3) after the reaction is completed, centrifugal wash the product in step (2) using a mixed solution of anhydrous ethanol and deionized water, and dry to obtain copper oxide powder; (4) Preparation of mesoporous copper nanotip electrocatalyst: use the copper oxide powder obtained in step (3) as a working electrode, and prepare by using an in-situ electrochemical reduction method.

2. A method for preparing mesoporous copper nanotip electrocatalyst for efficient synthesis of urotropine according to claim 1, characterized by: The amount is by volume weight parts, the concentration in step (1) is 0.005-0.02 mol•L -1 Copper nitrate solution 3-5 parts, deionized water 49-52 parts.

3. A method for the preparation of mesoporous copper nanotip electrocatalyst for the efficient synthesis of urotropine according to claim 1, characterized by: The concentration in step (2) is 3-7 mg•mL -1 Sodium borohydride solution 4.5-5.5 parts, reduction reaction time 10-14 h.

4. The method according to claim 1, wherein the method for the preparation of mesoporous copper nanotip electrocatalyst for the efficient synthesis of urotropine is characterized by: In step (3), the ratio of anhydrous ethanol to deionized water is 2-4:1; vacuum drying is performed for 10-14h at a temperature of 50-70℃.

5. The method for preparing mesoporous copper nanotip electrocatalyst for efficient synthesis of urotropine according to any one of claims 1-4, characterized in that: In step (4), the reduction reaction is electrolytic reduction in an alkaline electrolyte with a concentration of 0.5-1.5 M at a voltage of-1.4 V to-1.8 V for 0.3-0.7h.

6. The method according to claim 5, wherein the method is characterized by: In step (4), the reduction reaction is electrolytic reduction in an alkaline electrolyte with a concentration of 0.8-1.2 M at a voltage of-1.5 V to-1.7 V for 0.4-0.6h.

7. A mesoporous copper nanotip electrocatalyst prepared by the above preparation method.

8. Application of the mesoporous copper nanotip electrocatalyst of claim 7 in electrochemical carbon-nitrogen coupling synthesis of urotropine.

9. A method of electrocatalytic synthesis of methenamine, characterized by: The method comprises the following steps: A. The mesoporous copper nanotip electrocatalyst prepared by the above preparation method is used as a working electrode, a saturated Ag / AgCl electrode is used as a reference electrode, and a platinum sheet electrode is used as a counter electrode to form a three-electrode system; B. A mixed aqueous solution containing a nitrate salt, formaldehyde and a supporting electrolyte is used as an electrolyte; C. Perform constant potential electrolysis at a reaction temperature of 20-30℃ and a potential of-0.1 V to-0.8 V relative to a reversible hydrogen electrode (RHE), so that urotropine is generated at the cathode.

10. A method of electrocatalytic synthesis of methenamine according to claim 9, characterized by that: The electrolyte composition is: 0.1 mol·L -1 KOH, 0.5 mol·L -1 K2SO 4、 0.1 mol·L -1 KNO3 and 0.3 mol·L -1 HCHO, the reaction temperature is 25℃.

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