Preparation method and application of copper-manganese double-site composite catalyst

Abstract

The invention relates to a preparation method and application of a copper-manganese double-site composite catalyst. The method adopts a two-step sequential construction method, and comprises the following steps: firstly, stably anchoring Mn monatomic sites on C3N4 (at) CNT through a high-temperature pyrolysis-pickling process, so as to form Mn1-C3N4 (at) CNT; then, a CuOx cluster is selectively loaded on the precursor through a solvothermal reaction; wherein ethylene glycol is used as a solvent and a reducing agent, copper acetylacetonate is used as a copper source, it is ensured that a small-size CuOx cluster is controllably formed on the surface with the Mn-N4 structure, strong electron interaction between the small-size CuOx cluster and the copper acetylacetonate is established, and the proximity and the synergistic effect of Cu and Mn sites are achieved. The catalyst obtained by the invention has a remarkable effect when being applied to synthesis of urea by coupling carbon dioxide and nitrite C-N.

Description

Technical Field

[0001] This invention relates to a method for preparing a copper-manganese dual-site composite catalyst and its application in the field of electrocatalysis. Specifically, it involves using CuO... x Clusters and individual Mn sites are co-embedded in graphite C3N4-coated carbon nanotubes (CuO). x A Cu-Mn dual-site composite catalyst for efficient urea electrosynthesis was rationally designed and successfully prepared on ( / Mn1-C3N4@CNT). Background Technology

[0002] Emerging electrocatalytic urea synthesis technology uses carbon dioxide (CO2) and nitrate (NO3) to synthesize urea. - ), nitrite (NO2) - The co-reduction reaction of nitrogen oxides such as CO2 and NO3 provides a sustainable alternative route for urea production [Nat. Catal. 2023, 6, 939; Nature Communications. 2023, 14, 4491]. This technology has significant advantages in utilizing renewable energy and efficiently upgrading and transforming polluted resources. - / NO2 - The electrochemical co-reduction process involves complex reaction pathways, including the breaking of C=O and NO bonds, and CN coupling between carbon- and nitrogen-containing intermediates. Therefore, various byproducts are generated during co-reduction, such as separate carbon- and nitrogen-containing products, resulting in a wide product distribution and low overall urea yield. Efficient electrosynthesis of urea can only be achieved when the kinetic activation processes of the two reactants are properly matched.

[0003] The breaking of the C=O bond in CO2 requires a high dissociation energy (526 kJ / mol). -1 )[The Journal of PhysicalChemistry Letters. 2024, 15, 10842], while NO3 - The breaking energy of the NO bond in the middle is relatively low (204 kJ mol). -1 [ACS Energy Letters. 2024, 9, 2484], which indicates that CO2 activation is relative to NO3. - / NO2 - This is even more challenging. This also explains the difference between CO2 and NO3. - / NO2 -This explains why nitrogen-containing products (such as NH3) are often preferentially generated over urea during co-reduction. Therefore, promoting CO2 activation and increasing the supply of carbon-containing intermediates on the catalyst surface can effectively increase the probability of CN coupling, thereby shifting the main product from NH3 to the target product urea. By regulating the electronic state of active sites, the specific adsorption behavior of reaction intermediates can be altered [Angewandte Chemie. 2025, 137, e202500262], thus providing a possibility for achieving kinetic matching between carbon and nitrogen intermediates.

[0004] Currently, single-atom catalysts exhibit good activity in the carbon dioxide reduction reaction due to their extremely high atom utilization efficiency [Advanced Functional Materials. 2025, 20, e15847]. Previous studies have explored single-atom manganese catalysts supported on C3N4@CNT supports [Nat Commun. 2020, 11, 4341] and single-copper nanocluster catalysts (E-Cu...). 14 The catalyst [ACS Catal. 2025, 15, 20853–20863] has been shown to have certain activation capabilities for carbon dioxide and nitrate, respectively. However, such single-site catalysts struggle to simultaneously and efficiently activate both substrates and achieve kinetic matching in carbon dioxide and nitrate / nitrite co-reduction systems. Specifically, the activation barrier for CO2 at the Mn single-atom site remains too high, leading to insufficient supply of carbon-containing intermediates; while the Cu site tends to over-reduce nitrogen-containing species to generate NH3. Both of these situations result in low CN coupling efficiency, with urea Faraday efficiency typically below 35%. In contrast, catalysts with dual active sites can usually efficiently activate carbon dioxide and nitrate / nitrite, respectively, thereby promoting urea electrosynthesis. Therefore, constructing bifunctional active sites on a single support that can synergistically regulate the two reaction pathways, especially precisely controlling the electronic state of the CO2 reduction site to match nitrogen-containing intermediates, has become crucial for overcoming existing technological bottlenecks. Summary of the Invention

[0005] This invention addresses the shortcomings of current technologies, particularly the substrate activation mismatch and low CN coupling efficiency issues encountered by single-site catalysts in the electrocatalytic co-reduction of carbon dioxide and nitrite to urea. It provides a method for preparing and applying a copper-manganese dual-site composite catalyst. This method employs a two-step sequential construction approach: first, a high-temperature pyrolysis-acid washing process is used to stably anchor Mn single-atom sites on C3N4@CNT (forming Mn1-C3N4@CNT); then, a solvothermal reaction is carried out to convert CuO... xClusters are selectively loaded onto the precursor; ethylene glycol is used as both solvent and reducing agent, and copper acetylacetone is used as the copper source to ensure the controllable formation of small-sized CuO on the surface where the Mn-N4 structure already exists. x Clustering and establishing strong electronic interactions between the two sites achieves proximity and synergistic effects between Cu and Mn sites, rather than simple physical mixing. This invention constructs atomically dispersed manganese (Mn) single-atom sites and nanoscale copper oxide (CuO) on a graphitic carbon nitride (C3N4)-coated carbon nanotube (CNT) support. x The complex active center (CuO) formed by tightly bound clusters x / Mn1-C3N4@CNT), the application of carbon dioxide and nitrite CN in the synthesis of urea has shown significant effects.

[0006] The technical solution of this invention is as follows: A method for preparing a copper-manganese dual-site composite catalyst, comprising the following steps: (1) Multi-walled carbon nanotubes were stirred with a strong oxidizing mixed acid solution at room temperature for 12 to 48 hours. The product was washed with deionized water until the pH was neutral, and then vacuum dried at 50 to 70 °C to obtain carbon oxide nanotubes (O-MWCNTs). For every 100-300 mg of multi-walled carbon nanotubes, 25-75 mL of a strongly oxidizing mixed acid solution is added. The mixed acid solution is a mixture of concentrated sulfuric acid and concentrated nitric acid, with a volume ratio of 2:1 to 4:1. (2) The carbon oxide nanotubes, dicyandiamide (DCD) and manganese acetate tetrahydrate obtained in the previous step were dissolved in deionized water; the mixture was ultrasonically treated for 1-3 hours, heated in an oil bath at 40-60 ℃ for 8-12 hours, rapidly frozen with liquid nitrogen, and freeze-dried in vacuum at -30 to -50 ℃ for 12-36 hours; the resulting solid was ground and calcined in a tube furnace at 500-700 ℃ for 0.5-2 hours under an argon atmosphere; the product was then acid-washed with hydrochloric acid at 70-90 ℃ for 2-6 hours, washed with deionized water until pH neutral, and then vacuum-dried at 50-70 ℃ to obtain a manganese single-atom catalyst (Mn1-C3N4@CNT) supported on carbon nanotubes coated with carbon nitride. Each of the following components is prepared: 6.2–25 mg of carbon nanotubes, 18.8–75 mg of dicyandiamide, and 9–36 mg of manganese acetate tetrahydrate, dissolved in 25–75 mL of deionized water. The concentration of the hydrochloric acid is 0.5~2 M.

[0007] (3) Disperse the manganese single-atom catalyst obtained in the previous step in ethylene glycol and sonicate it for 0.5 to 2 hours; then add copper acetylacetone, stir at room temperature for 0.5 to 2 hours, and reflux at 100 to 140 °C for 2 to 6 hours; wash the product with ethanol and then vacuum dry it at 50 to 70 °C for 10 to 14 hours to finally obtain the copper-manganese dual-site composite catalyst. The mass of manganese single-atom catalyst added to each 12.5~50 mL of ethylene glycol is 7.5~30 mg; In step (1), the stirring speed is 300~800 rpm; In step (2), the ultrasonic power is 100 W to 500 W; In step (3), the ultrasonic power is 100 W to 500 W and the stirring speed is 300 to 800 rpm.

[0008] The copper-manganese dual-site composite catalyst prepared by the method is used as an electrode material for the electrocatalytic coupling of carbon dioxide and nitrite (CN) to urea.

[0009] Specifically, the steps include the following: In a three-electrode system, Ag / AgCl was used as the reference electrode, platinum wire as the counter electrode, and carbon paper coated with catalyst ink as the working electrode. The electrolyte consisted of 0.1 M KHCO3 and 200 ppm N-NO2. - Mixed solution; electrolyze at a constant voltage of -0.2 to -0.6 V (vs. RHE) for 15 to 120 min to obtain urea; The method for preparing the working electrode is as follows: CuO x / Mn1-C3N4@CNT is added to a mixed solvent and ultrasonically dispersed for 15-30 min to obtain a dispersion; then the dispersion is dropped onto a substrate and allowed to dry naturally at room temperature to obtain a working electrode. Each milliliter of the mixed solvent consists of 475 μL of anhydrous ethanol, 475 μL of deionized water, and 50 μL of 0.5 wt.% Nafion solution. Add 1-10 mg of CuO per milliliter of mixed solvent. x / Mn1-C3N4@CNT; per 1 cm 2 Add 50~150 μL of dispersion to the substrate.

[0010] The substrate is carbon paper.

[0011] The essential features of this invention are: Currently, the electrochemical co-reduction process of carbon dioxide with nitrates / nitrites involves complex reaction pathways, including the breaking of C=O and NO bonds, and CN coupling between carbon- and nitrogen-containing intermediates. Therefore, various byproducts are generated during the co-reduction process, such as separate carbon- and nitrogen-containing products, resulting in a wide product distribution and low overall urea yield. Efficient electrosynthesis of urea can only be achieved when the kinetic activation processes of the two reactants are properly matched.

[0012] This invention synthesizes a copper-manganese dual-site composite catalyst by introducing manganese single atoms and copper clusters together on carbon nanotubes coated with carbon nitride. Electrons in the catalyst originate from CuO. x The transfer of clusters to single-atom Mn sites induces the delocalization of Mn 3d electrons and further promotes the transformation of its spin configuration from a low-spin state to a high-spin state. This electronic state modulation enhances the electron-donating ability of Mn sites to reactants, thereby significantly increasing the activation energy of CO2 and the surface coverage of carbon-containing intermediates, effectively promoting its coupling reaction with nitrogen-containing intermediates.

[0013] The beneficial effects of this invention are: (1) This invention provides a method to precisely control the electronic state of carbon dioxide reduction sites through the interaction of dual active sites and improve the surface coverage of carbon-containing intermediates to dynamically match nitrogen-containing intermediates. The synergistic effect of dual active sites promotes the CN coupling process of carbon dioxide and nitrite, inhibits the generation of byproducts such as NH3, and realizes the efficient electrosynthesis of urea. (2) The copper-manganese dual-site composite catalyst prepared in this invention exhibits excellent electrochemical performance in the electrocatalytic coupling reaction of carbon dioxide and nitrite (CN) to urea. Under 0.1 M KHCO3 electrolyte and 200 ppm N-NO2 conditions... - Under the same conditions, the Faradaic efficiency of urea synthesis by catalysts containing only a single manganese site is only 32.37%, and that of catalysts containing only a single copper site is only 30.58%. In contrast, the copper-manganese dual-site composite catalyst constructed in this invention achieves a urea Faradaic efficiency of 60.18% under the same conditions, nearly doubling the performance and significantly outperforming catalysts with single metal sites, demonstrating a clear synergistic enhancement effect. Furthermore, the catalyst of this invention exhibits near 100% carbon selectivity for urea production within a wide potential window of -0.2 V to -0.5 V (vs. RHE) of 400 mV, demonstrating extremely high reaction directionality. During a stability test lasting 336 hours, the catalyst activity and selectivity did not show significant decline, with a cumulative urea yield of 202.4 mg, demonstrating excellent potential for practical application. Attached Figure Description

[0014] Figure 1CuO obtained in Example 1 x High-angle annular dark-field scanning transmission electron microscope image of / Mn1-C3N4@CNT.

[0015] Figure 2 CuO obtained in Example 1 x X-ray diffraction pattern of / Mn1-C3N4@CNT.

[0016] Figure 3 CuO obtained in Examples 1, 2, and 3 x / Mn1-C3N4@CNT、CuO x X-ray photoelectron spectra of -C3N4@CNT and Mn1-C3N4@CNT. Figure 3 a is CuO x / Mn1-C3N4@CNT and CuO x Cu 2p energy spectrum of -C3N4@CNT, Figure 3 b is CuO x Mn 2p spectra of / Mn1-C3N4@CNT and Mn1-C3N4@CNT.

[0017] Figure 4 CuO obtained in Examples 1 and 3 x Figure of the Physical Property Measurement System (PPMS) for Mn1-C3N4@CNT and Mn1-C3N4@CNT.

[0018] Figure 5 CuO obtained in Example 1 x Electrosynthesis performance diagram of urea from / Mn1-C3N4@CNT.

[0019] Figure 6 CuO obtained in Example 1 x Long-term stability test graph of / Mn1-C3N4@CNT.

[0020] Figure 7 CuO obtained in Example 2 x Electrosynthesis performance of urea from -C3N4@CNT.

[0021] Figure 8 The graph shows the electrosynthesis performance of urea obtained from Mn1-C3N4@CNT in Example 3. Detailed Implementation

[0022] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0023] The multi-walled carbon nanotubes involved in this invention are well-known materials. The multi-walled carbon nanotubes used in the following examples are from Chengdu Zhongke Times Nanomaterials Co., Ltd., and the model is TNAIM. However, this is not the only possibility.

[0024] Example 1: Copper-manganese dual-site composite catalyst (CuO) x Preparation of / Mn1-C3N4@CNT): 200 mg of multi-walled carbon nanotubes were dispersed in 50 mL of a mixed acid solution (sulfuric acid:nitric acid = 3:1 v / v; sulfuric acid concentration was 18.4 mol / L, and nitric acid concentration was 15.9 mol / L), and stirred at 500 rpm for 24 hours at room temperature. The product was washed with deionized water until pH neutral, and then vacuum dried at 50–70 °C to obtain carbon oxide nanotubes (O-MWCNTs).

[0025] 12.5 mg of carbon oxide nanotubes, 37.5 mg of dicyandiamide (DCD), and 18 mg of manganese acetate tetrahydrate were dissolved in 50 mL of deionized water. The mixture was sonicated at 400 W for 2 hours, heated in an oil bath at 50 °C for 10 hours, rapidly frozen with liquid nitrogen, and then freeze-dried under vacuum at -40 °C for 24 hours. The resulting solid was thoroughly ground and calcined in a tube furnace at 600 °C for 1 hour under an argon atmosphere at a heating rate of 5 °C / min. The product was then acid-washed with 1 M hydrochloric acid at 80 °C for 4 hours, washed with deionized water until pH neutral, and then vacuum-dried at 50–70 °C to obtain a manganese single-atom catalyst (Mn1-C3N4@CNT) supported on carbon nanotubes coated with carbon nitride.

[0026] 15 mg of Mn1-C3N4@CNT was dispersed in 25 mL of ethylene glycol, and the mixture was sonicated at 400 W for 1 hour. Then, 10 mg of copper acetylacetonate was added, and the mixture was stirred at 500 rpm for 1 hour at room temperature, followed by reflux at 120 °C for 4 hours. The product was thoroughly washed with ethanol to remove residual ethylene glycol, and then vacuum dried at 50–70 °C for 12 hours to finally obtain CuO. x / Mn1-C3N4@CNT.

[0027] Electrochemical performance testing: Weigh out 4 mg of CuO x / Mn1-C3N4@CNT was added, along with 475 μL of anhydrous ethanol, 475 μL of deionized water, and 50 μL of 0.5 wt.% Nafion solution. The mixture was ultrasonically dispersed for 30 min to form a uniform dispersion.

[0028] 100 μL of the resulting dispersion was dropped onto carbon paper (1 × 1 cm).2 Let it air dry at room temperature.

[0029] All electrochemical tests in this invention were performed using a conventional three-electrode cell on a CHI760E electrochemical workstation, with an electrolyte of 0.1 M KHCO3 and 200 ppm N-NO2. - Mixed solution. Using Ag / AgCl as the reference electrode, platinum wire as the counter electrode, and carbon paper coated with catalyst ink as the working electrode, the conversion formula between electrode potential and RHE is: E (vs. RHE) = E (vs. Ag / AgCl) + 0.224 V + 0.0596 × pH.

[0030] The test was conducted in a CO2-saturated environment with 0.1 M KHCO3 and 200 ppm N-NO2. - Urea electrosynthesis test was performed in the electrolyte, CuO x The / Mn1-C3N4@CNT urea production process achieves a maximum Faraday efficiency of 60.18% and a yield of 1597.79 mg / h·g. cat. -1 The copper-manganese dual-site composite catalyst prepared by this invention exhibits high selectivity and high activity in urea electrosynthesis.

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of Embodiment 1 will be briefly introduced below: Figure 1 CuO obtained in the examples x High-angle annular dark-field scanning transmission electron microscopy (STEM) image of / Mn1-C3N4@CNT. The image clearly shows the uniformly distributed copper oxide metal clusters within the 1-1.5 nm range, as well as single manganese metal sites.

[0032] Figure 2 CuO obtained in the examples x The X-ray diffraction pattern of / Mn1-C3N4@CNT shows the corresponding peak of the g-C3N4 amorphous coating layer at 26°, with no metallic peaks observed, indicating that copper and manganese have not agglomerated into nanoparticles, which is consistent with the high-angle annular dark-field scanning transmission electron microscopy image.

[0033] Figure 3 CuO obtained in the examples x X-ray photoelectron spectroscopy of / Mn1-C3N4@CNT. After introducing Mn sites, the 2p... 1 / 2 The peak shifts significantly by 0.32 eV towards higher binding energies, indicating a significant electron transfer from Cu to Mn. This phenomenon is evident when comparing Mn1-C3N4@CNT with Mn...2+ The increase in the proportion has been further confirmed.

[0034] Figure 4 The diagram shows the Physical Property Measurement System (PPMS) obtained in the example. The spin states of Mn were analyzed; the effective magnetic moment (μeff) of Mn1-C3N4@CNT is 3.04 μB, while that of CuO... x / Mn1-C3N4@CNT has a value of 4.78 μB. According to the formula for the number of unpaired electrons (n) = -1 + (μeff) 2 + 1) 1 / 2 CuO x / Mn1-C3N4@CNT has 4 unpaired electrons, indicating that it is in a high-spin (HS) state; while Mn1-C3N4@CNT exhibits a low-spin (LS) state with an n value of 2.

[0035] Figure 5 The CuO obtained in Example 1 of this invention x Electrosynthesis performance of urea from / Mn1-C3N4@CNT. CuO x / Mn1-C3N4@CNT exhibits excellent electrosynthetic urea performance, with a maximum urea Faradaic efficiency of 60.18%, and also features high current density and yield.

[0036] Figure 6 The CuO obtained in Example 1 of this invention x The long-term stability test results for / Mn1-C3N4@CNT are shown in the figure. During the 336-hour stability test, the catalyst activity and current density did not show significant decay. After purification, the electrolyte yielded 202.4 mg of urea, demonstrating excellent potential for practical application.

[0037] Example 2 Single copper site catalyst (CuO) x Preparation of -C3N4@CNT): 200 mg of multi-walled carbon nanotubes were dispersed in 50 mL of a mixed acid solution (sulfuric acid:nitric acid = 3:1 v / v; sulfuric acid concentration was 18.4 mol / L, and nitric acid concentration was 15.9 mol / L), and stirred at 500 rpm for 24 hours at room temperature. The product was washed with deionized water until pH neutral, and then vacuum dried at 50–70 °C to obtain carbon oxide nanotubes (O-MWCNTs).

[0038] 12.5 mg of carbon oxide nanotubes, 37.5 mg of dicyandiamide (DCD), and 10 mg of copper acetylacetonate were dissolved in 50 mL of deionized water. The mixture was sonicated at 400 W for 2 hours, heated in a 50 °C oil bath for 10 hours, rapidly frozen with liquid nitrogen, and then freeze-dried under vacuum at -40 °C for 24 hours. The resulting solid was thoroughly ground and calcined in a tube furnace at 600 °C for 1 hour under an argon atmosphere at a heating rate of 5 °C / min. The product was then acid-washed with 1 M hydrochloric acid at 80 °C for 4 hours, washed with deionized water until pH neutral, and then vacuum-dried at 50–70 °C to obtain a copper oxide cluster catalyst (CuO) supported on carbon nanotubes coated with carbon nitride. x -C3N4@CNT).

[0039] The same electrochemical testing method as in Example 1 was used.

[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of Embodiment 2 will be briefly introduced below: Figure 7 The CuO obtained in Example 2 of this invention x Electrosynthesis performance of urea from -C3N4@CNT catalyst. Single copper site catalyst CuO x On -C3N4@CNT, the highest urea Faraday efficiency reached only 30.58%, which is not as good as the copper-manganese dual-site composite catalyst.

[0041] Example 3 Preparation of single-manganese-site catalyst (Mn1-C3N4@CNT): 200 mg of multi-walled carbon nanotubes were dispersed in 50 mL of a mixed acid solution (sulfuric acid:nitric acid = 3:1 v / v; sulfuric acid concentration was 18.4 mol / L, and nitric acid concentration was 15.9 mol / L), and stirred at 500 rpm for 24 hours at room temperature. The product was washed with deionized water until pH neutral, and then vacuum dried at 50–70 °C to obtain carbon oxide nanotubes (O-MWCNTs).

[0042] 12.5 mg of carbon oxide nanotubes, 37.5 mg of dicyandiamide (DCD), and 18 mg of manganese acetate tetrahydrate were dissolved in 50 mL of deionized water. The mixture was sonicated at 400 W for 2 hours, heated in a 50 °C oil bath for 10 hours, rapidly frozen with liquid nitrogen, and then freeze-dried under vacuum at -40 °C for 24 hours. The resulting solid was thoroughly ground and calcined in a tube furnace at 600 °C for 1 hour under an argon atmosphere at a heating rate of 5 °C / min. The product was then acid-washed with 1 M hydrochloric acid at 80 °C for 4 hours, washed with deionized water until pH neutral, and then vacuum-dried at 50–70 °C to obtain a manganese single-atom catalyst (Mn1-C3N4@CNT) supported on carbon nanotubes coated with carbon nitride.

[0043] The same electrochemical testing method as in Example 1 was used.

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of Embodiment 2 will be briefly introduced below: Figure 8 The image shows the electrosynthetic urea performance of Mn1-C3N4@CNT obtained in Example 3 of this invention. The highest urea Faradaic efficiency on the single-manganese-site catalyst Mn1-C3N4@CNT was only 32.37%, which is also inferior to the copper-manganese dual-site composite catalyst.

[0045] Example 4 The other steps are the same as in Example 1, except that the volume ratio of concentrated sulfuric acid to concentrated nitric acid in the mixed acid solution used in step (1) is changed from 3:1 to 2:1; and the high-temperature calcination temperature in step (2) is changed from 600 ℃ to 500 ℃.

[0046] The obtained material has a maximum Faraday efficiency of 58.6% for synthesizing urea, and its performance is similar to that of Example 1; Example 5 The other steps are the same as in Example 1, except that the vacuum drying temperature in step (1) is replaced by 70°C instead of 60°C; and the stirring speed in step (3) is replaced by 700 rpm instead of 500 rpm.

[0047] The obtained material has a maximum Faraday efficiency of 60.07% for synthesizing urea, and its performance is similar to that of Example 1; In summary, the copper-manganese dual-site catalyst CuO prepared by this invention... x / Mn1-C3N4@CNT achieves a leap in urea synthesis performance through a unique synergistic mechanism. The key lies in CuO. xElectron transfer between the cluster and the single-atom site of Mn modulates the electronic structure of the Mn center, causing its spin state to shift towards higher spin. This shift effectively enhances the electron-donating capacity of the Mn site, not only promoting the activation of CO2 and the enrichment of carbon-containing intermediates, but also matching its coupling kinetics with nitrogen-containing intermediates, thereby driving the efficient CN-CN coupling synthesis of urea.

[0048] Matters not covered in this invention are common knowledge.

Claims

1. A method for producing a copper-manganese dual site composite catalyst, characterized by, The method comprises the following steps: (1) stirring multi-walled carbon nanotubes with a strong oxidizing mixed acid solution at room temperature for 12-48 hours, washing the product with deionized water until neutral pH, and then vacuum drying at 50-70 ℃ to obtain oxidized carbon nanotubes O-MWCNTs; wherein 25-75 mL of the strong oxidizing mixed acid solution is added per 100-300 mg of the multi-walled carbon nanotubes; the mixed acid solution is a mixture of concentrated sulfuric acid and concentrated nitric acid, with a volume ratio of 2:1-4:1; (2) dissolving the oxidized carbon nanotubes obtained in the previous step, dicyandiamide DCD, and manganese acetate tetrahydrate in deionized water; ultrasonic treatment of the mixture for 1-3 hours, heating in an oil bath at 40-60 ℃ for 8-12 hours, freezing with liquid nitrogen, vacuum freeze-drying, grinding the solid, calcining at 500-700 ℃ in a tube furnace under argon atmosphere for 0.5-2 hours; the product is then acid-washed with hydrochloric acid at 70-90 ℃ for 2-6 hours, washed with deionized water until neutral pH, and then vacuum dried at 50-70 ℃ to obtain a manganese monatomic catalyst Mn1-C3N4@CNT supported on carbon nanotubes coated with nitrogenized carbon; wherein 18.8-75 mg of dicyandiamide and 9-36 mg of manganese acetate tetrahydrate are dissolved in 25-75 mL of deionized water per 6.2-25 mg of the oxidized carbon nanotubes; (3) dispersing the manganese monatomic catalyst obtained in the previous step in ethylene glycol, ultrasonic treatment for 0.5-2 hours; then adding copper acetylacetonate, stirring at room temperature for 0.5-2 hours, and then refluxing at 100-140 ℃ for 2-6 hours; the product is washed with ethanol and vacuum dried at 50-70 ℃ for 10-14 hours to finally obtain a copper-manganese dual-site composite catalyst; wherein the mass of the manganese monatomic catalyst added per 12.5-50 mL of ethylene glycol is 7.5-30 mg.

2. The method for preparing a copper-manganese dual site composite catalyst according to claim 1, wherein In step (1), the stirring speed is 300-800 rpm; In step (2), the ultrasonic power is 100 W-500 W; In step (3), the ultrasonic power is 100 W-500 W, and the stirring speed is 300-800 rpm.

3. The preparation method of the copper-manganese dual-site composite catalyst as described in claim 1, characterized in that, In step (2), the concentration of the hydrochloric acid is 0.5-2 M.

4. The preparation method of the copper-manganese dual-site composite catalyst as described in claim 1, characterized in that, In step (2), the freeze-drying is vacuum freeze-drying at -30 to -50 ℃ for 12-36 hours.

5. Use of the copper-manganese bi-site complex catalyst prepared according to the method of claim 1, characterized in that, As an electrode material for electrocatalytic coupling of carbon dioxide and nitrite C-N to form urea.

6. Use according to claim 5, wherein the compound is ###0002### Comprises the following steps: In a three-electrode system, Ag / AgCl was used as the reference electrode, platinum wire as the counter electrode, carbon paper coated with catalyst ink as the working electrode, and the electrolyte was 0.1 M KHCO3 and 200 ppm N-NO2 - Mixed solution; electrolysis at a constant voltage of -0.2 to -0.6 V (vs. RHE) for 15-120 min to obtain urea; The preparation method of the working electrode: CuO x / Mn1-C3N4@CNT was added into the mixed solvent and ultrasonically dispersed for 15-30 min to obtain a dispersion liquid; then the dispersion liquid was dropped on the substrate and naturally dried at room temperature to obtain a working electrode; wherein the composition of each milliliter of the mixed solvent comprises 475 μL of anhydrous ethanol, 475 μL of deionized water, and 50 μL of a 0.5wt.% Nafion solution; 1-10 mg of CuO was added per ml of mixed solvent x / Mn1-C3N4@CNT; per 1 cm 2 50 to 150 μL of the dispersion solution was dropped on the substrate.

7. Use according to claim 5, wherein the compound is ###0002### the substrate is carbon paper.

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