High-efficiency catalyst for electrocatalytic co-reduction of carbon dioxide and nitrate to urea, preparation method and application thereof

Abstract

This invention belongs to the field of environmental engineering and electrocatalyst technology, and discloses a highly efficient catalyst for the electrocatalytic co-reduction of carbon dioxide and nitrate to urea, its preparation method, and its application. The catalyst is a Zn / MoO₂ catalyst. x -CNT composite catalyst, composed of carbon nanotubes supported on molybdenum oxide and zinc nanostructures supported on carbon paper, possesses the properties of Zn and MoO. x Heterogeneous interfaces, in which MoO x The catalyst is composed of molybdenum oxide, zinc nanoparticles, and carbon nanotubes as a support providing conductivity and structural stability. This invention constructs a heterojunction system and employs an electrochemical wet process to create a catalyst with numerous heterojunction interfaces. Through interfacial effects, it enhances electron transfer, regulation, and surface adsorption, effectively improving the efficiency and yield of the co-reduction of carbon dioxide and nitrate to urea. The preparation method is simple, easy to synthesize, uses inexpensive and readily available raw materials, and is easily scaled up, showing promising application prospects.

Description

Technical Field

[0001] This invention relates to the fields of environmental engineering and electrocatalyst technology, specifically to a highly efficient catalyst for the electrocatalytic co-reduction of carbon dioxide and nitrate into urea, its preparation method, and its application. Background Technology

[0002] The excessive consumption of fossil fuels has led to a sharp rise in atmospheric carbon dioxide (CO2) concentrations, exacerbating global climate change. Simultaneously, industrial and agricultural activities are discharging excessive amounts of nitrates (NO3) into water bodies. - Pollutants cause environmental crises such as eutrophication of water bodies and groundwater pollution. Electrochemical reduction technology has become a research focus due to its green and controllable characteristics, especially the co-reduction of CO2 and nitrogen oxides into urea, a high-value-added chemical, which can alleviate environmental pressure and realize the recycling of carbon and nitrogen resources.

[0003] Urea is a major source of nitrogen from plants and an important raw material for the synthetic industry. Traditional urea synthesis, via the Bosch-Meiser process, requires 100-200 atmospheres of pressure and high temperatures, resulting in enormous energy consumption and a significant carbon footprint. Therefore, developing a green and efficient electrocatalytic method for urea synthesis is crucial.

[0004] In recent years, transition metal copper and cobalt-based catalysts have been widely used in the co-reduction synthesis of urea, but they suffer from problems such as low catalytic efficiency, poor activity, and poor stability. The rational construction of heterojunctions is a key strategy for regulating reaction pathways and improving catalytic efficiency. Heterojunctions can regulate the adsorption strength of active sites for key intermediates, promoting the co-activation and directional coupling of multiple reactants. However, existing heterojunction catalysts such as Cu / Cu2O and Ag NWs@CuNi(OH)2 are mostly copper-based systems, which are complex to operate, costly, and difficult to scale up industrially. For example, CN118814203A uses an iron-nickel bimetallic nanoalloy supported on nanoporous carbon (FeNi@C) to utilize the synergistic effect of Fe reducing nitrate and Ni reducing CO2, but it relies on the expensive transition metals Fe and Ni, has low catalytic efficiency, and iron-based catalysts have potential toxicity.

[0005] Therefore, designing a catalyst that is simple to operate, uses inexpensive and readily available raw materials, and exhibits excellent activity and selectivity is of great significance for the co-reduction of CO2 and nitrate to urea. Summary of the Invention

[0006] The purpose of this invention is to provide a highly efficient catalyst for the electrocatalytic co-reduction of carbon dioxide and nitrate into urea, its preparation method, and its application. It abandons copper-based and iron-based raw materials and uses zinc-based and molybdenum-based materials to form a highly efficient catalyst rich in heterogeneous interfaces. Through the interface effect, it increases electron transfer, regulation, and surface adsorption, making it rich in heterogeneous interfaces, thereby solving the technical problems of low activity, poor selectivity, and complex preparation of existing catalysts.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A highly efficient catalyst for the electrocatalytic co-reduction of carbon dioxide and nitrate to urea, wherein the catalyst is Zn / MoO. x -CNT composite catalyst, composed of carbon nanotubes (MoO2) supported on molybdenum oxide. x It is composed of Zn and MoO2 nanoparticles (CNTs) and layered zinc nanostructures supported on carbon paper, and has the properties of Zn and MoO2. x Heterogeneous interfaces, in which MoO x The matrix consists of molybdenum oxide with a x-value of 2-3, zinc nanoparticles (Zn), and carbon nanotubes as a carrier to provide conductivity and structural stability; wherein the loading of Zn is 1.0-5.0 mg, and MoO... x -CNT loading is 1-5 mg, Zn and MoO x The mass ratio of CNTs is (1-5):1; the carbon nanotubes are multi-walled carbon nanotubes with a diameter of 20-30 nm; the Zn nanoparticles have a particle size of 20-100 nm, and MoO... x The nanoparticles have a diameter of 5-10 nm and are uniformly anchored on the surface of carbon nanotubes.

[0008] A method for preparing the aforementioned high-efficiency catalyst includes the following steps: S1: Molybdenum oxide carbon nanotubes (MoO) x Synthesis of MoO2 (CNT): Weigh 0.5-1.0 g of multi-walled carbon nanotubes, add 50-80 ml of organic solvent, and sonicate for 30-60 minutes to uniformly disperse the carbon nanotubes. Then add 8-15 g of molybdenum compound, sonicate for 10-30 minutes, add 50-80 ml of ultrapure water, and sonicate for 1-2 hours. Place in the dark for 12-36 hours, centrifuge and wash, then vacuum dry at 50-80℃, and grind into powder to obtain MoO2. x / CNT; S2: Preparation of controllable mass zinc loading (Zn / CP) on carbon paper: A zinc electrolyte was prepared, and a constant potential electrodeposition was performed with carbon paper as the working electrode in a three-electrode system. A layered planar zinc nanostructure (formed by zinc nanoparticle deposition) of 1.0-5.0 mg was deposited on the surface of the carbon paper and dried and cured under an infrared lamp. S3: Physical loading and pre-activation: 1-5 mg MoO2 was applied by drop-coating. x / CNTs were loaded onto Zn / CP, dried under an infrared lamp, and then pre-activated by reduction in a 0.5 mol / L potassium-containing electrolyte at -1.2V for 0.5–2 h to obtain Zn / MoO. x -CNT composite catalyst.

[0009] The organic solvent in step S1 is one of ethanol, methanol or acetone, and the molybdenum compound is one of molybdenum chloride, molybdenum nitrate or molybdenum sulfate; the mass ratio of the multi-walled carbon nanotubes to the molybdenum salt is 1:8 to 1:16; the standing time is 24 h.

[0010] The zinc electrolyte in step S2 is a mixed solution prepared by dissolving 10.0-15.0g of zinc compound and 0.1-0.5g of acid in deionized water. The zinc compound is zinc sulfate or zinc nitrate, and the acid is one of sulfuric acid, nitric acid or hydrochloric acid. The electrodeposition potential is -0.5 V, and the deposition charge is 1.0~8.0 C.

[0011] The potassium-containing electrolyte in step S3 is a potassium sulfate or potassium nitrate solution; the MoO x The loading amount of / CNT is 1~5mg, and the Zn and MoO x The mass ratio is 1:1, 1:3, 3:1, 1:5 or 5:1.

[0012] The application of the aforementioned high-efficiency catalyst in the electrocatalytic co-reduction of carbon dioxide and nitrate to urea includes: using the Zn / MoO2 catalyst... x Using a CNT catalyst as the working electrode, constant potential electrolysis was performed in an electrolyte of 0.1 mol / L KNO3 and CO2 saturation within a potential range of -0.4 V to -0.7 V to co-reduce carbon dioxide and nitrate to urea. At an electrolysis potential of -0.5 V and an electrolysis time of 2 h, the urea yield reached 1.55 mmol / L. -1 gcat -1 Faraday efficiency reached 46.8%.

[0013] Compared with the prior art, the present invention has at least the following beneficial effects: 1. A novel catalyst system: This invention is the first to construct a Zn / MoO catalyst system. x The heterojunction catalyst abandons the traditional copper-based raw materials and utilizes the synergistic effect of zinc-based and molybdenum-based materials to increase electron transfer and regulate surface adsorption through interfacial effects, effectively improving the efficiency and yield of nitrate to urea conversion.

[0014] 2. Excellent catalytic performance: At -0.5 V vs. RHE, the urea yield reaches 1.55 mmol h⁻¹. -1 g -1 The Faraday efficiency reaches 46.8%, far superior to single-component catalysts (Zn or MoO). x / CNT), which is currently the leading catalyst reported.

[0015] 3. Simple and efficient preparation method: It adopts electrochemical wet synthesis, the raw materials are cheap and readily available, the operation is simple, it is easy to scale up production, and it has good prospects for industrial application.

[0016] 4. Outstanding environmental benefits: Using CO2 and nitrates as raw materials, it turns waste into treasure, realizes the recycling of carbon and nitrogen resources, and conforms to the concepts of green chemistry and sustainable development. Attached Figure Description

[0017] Figure 1 Zn / MoO, an embodiment of the present invention x The catalyst preparation process flow chart, in which, Figure 1 (1) is step S1, Figure 1 (2) is step S2. Figure 1 (3) is a schematic diagram of step S3; Figure 2 Zn / MoO with heterogeneous interface is an embodiment of the present invention. x Scanning electron microscope images and elemental distribution diagrams of the catalyst; Figure 3 Zn / MoO, an embodiment of the present invention x Schematic diagram of transmission electron microscopy analysis results for catalysts; Figure 4 Linear scanning voltammetry was used to demonstrate the composite catalyst Zn / MoO in this embodiment of the invention. x The results are shown in the illustration of the comparison of catalytic activity with that of a single catalyst. Figure 5 Zn / MoO, an embodiment of the present invention x -CNT catalysts compared to single catalysts (Zn and MoO) x A schematic diagram showing the comparison of urea Faradaic efficiency and yield ( / CNT); Figure 6 To implement the Zn-MoO of this invention x / CNT XRD pattern, where A is Zn-MoO x / CNT composite catalyst, B is MoO X / CNT catalyst. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0019] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0020] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0021] Basic Implementation A highly efficient catalyst for the electrocatalytic co-reduction of carbon dioxide and nitrate to urea, wherein the catalyst is Zn / MoO. x -CNT composite catalyst, composed of carbon nanotubes (MoO2) supported on molybdenum oxide. x It is composed of Zn and MoO2 nanoparticles (CNTs) and layered zinc nanostructures supported on carbon paper, and has the properties of Zn and MoO2. x Heterogeneous interfaces, in which MoO x The matrix consists of molybdenum oxide with a x-value of 2-3, zinc nanoparticles (Zn), and carbon nanotubes as a carrier to provide conductivity and structural stability; wherein the loading of Zn is 1.0-5.0 mg, and MoO... x -CNT loading is 1-5 mg, Zn and MoO x The mass ratio of CNTs is (1-5):1; the carbon nanotubes are multi-walled carbon nanotubes with a diameter of 20-30 nm; the Zn nanoparticles have a particle size of 20-100 nm, and MoO... x The nanoparticles have a diameter of 5-10 nm and are uniformly anchored on the surface of carbon nanotubes.

[0022] The preparation method of the high-efficiency catalyst includes the following steps: S1: Molybdenum oxide carbon nanotubes (MoO) xSynthesis of MoO2 (CNT): Weigh 0.5-1.0 g of multi-walled carbon nanotubes, add 50-80 ml of organic solvent, and sonicate for 30-60 minutes to uniformly disperse the carbon nanotubes. Then add 8-15 g of molybdenum compound, sonicate for 10-30 minutes, add 50-80 ml of ultrapure water, and sonicate for 1-2 hours. Place in the dark for 12-36 hours, centrifuge and wash, then vacuum dry at 50-80℃, and grind into powder to obtain MoO2. x / CNT; the organic solvent is one of ethanol, methanol or acetone, and the molybdenum compound is one of molybdenum chloride, molybdenum nitrate or molybdenum sulfate; the mass ratio of the multi-walled carbon nanotubes to the molybdenum salt is 1:8 to 1:15; the standing time is 24 h.

[0023] S2: Preparation of controllable mass zinc loading (Zn / CP) on carbon paper: A zinc electrolyte was prepared, and a constant potential electrodeposition was performed in a three-electrode system with carbon paper as the working electrode, applying an electric charge of 1.0-8.0C to deposit 1.0-5.0 mg of zinc nanostructures on the carbon paper surface. The nanostructures were then dried and cured under an infrared lamp. The zinc electrolyte was a mixed solution prepared by dissolving 10.0-15.0 g of zinc compound and 0.1-0.5 g of acid in deionized water. The zinc compound was zinc sulfate or zinc nitrate, and the acid was one of sulfuric acid, nitric acid, or hydrochloric acid. The electrodeposition potential was -0.5 V, and the deposition charge was 1.0~8.0 C.

[0024] S3: Physical loading and pre-activation: 1-5 mg MoO2 was applied by drop-coating. x / CNTs were loaded onto Zn / CP, dried under an infrared lamp, and then pre-activated by reduction in a 0.5 mol / L potassium-containing electrolyte at -1.2V for 0.5–2 h to obtain Zn / MoO. x -CNT composite catalyst, wherein the potassium-containing electrolyte is a potassium sulfate or potassium nitrate solution; the MoO x The loading amount of / CNT is 1~5 mg, and the Zn and MoO x The mass ratio is 1:1, 1:3, 3:1, 1:5 or 5:1.

[0025] The application of the aforementioned high-efficiency catalyst in the electrocatalytic co-reduction of carbon dioxide and nitrate to urea includes: using the Zn / MoO2 catalyst... x Using a CNT catalyst as the working electrode, constant potential electrolysis was performed in an electrolyte of 0.1 mol / L KNO3 and CO2 saturation within a potential range of -0.4 V to -0.7 V to co-reduce carbon dioxide and nitrate to urea. At an electrolysis potential of -0.5 V and an electrolysis time of 2 h, the urea yield reached 1.55 mmol / L. -1 gcat-1 Faraday efficiency reached 46.8%.

[0026] In the above-mentioned synthesis method of highly efficient catalysts, the three key steps are MoO2 and MoO2. x The raw material ratio in CNT preparation, the ratio of electrodeposition charge to deposition amount of Zn, and the ratio of Zn and MoO x The technical challenges of controlling the proportions include: the specific selection of molybdenum and zinc salts, the reaction sequence, reaction time, required temperature, preparation method, standing time, amount of solution added, reactant ratio, the comprehensive selection of drying methods during catalyst synthesis, and specific electrodeposition operation methods.

[0027] The following describes the process in detail with several examples.

[0028] Example 1 This embodiment employs an electrochemical wet process strategy to prepare a highly efficient catalyst for the electrocatalytic co-reduction of carbon dioxide and nitrate to urea, comprising the following steps: I. Solution Preparation The carbon nanotube alcohol solution used for molybdenum oxide synthesis is freshly prepared and used immediately; the zinc electrolyte and potassium-containing electrolyte are prepared in advance.

[0029] II. Zn / MoO x Preparation of -CNT catalysts S1: Weigh 0.9 g of multi-walled carbon nanotubes, add 60 mL of ethanol and sonicate for 30 min; add 10.2 g of MoCl5 and sonicate for 15 min; add 60 mL of ultrapure water and sonicate for 1 h, then let stand in the dark for 24 h; centrifuge and wash (with deionized water and acetone), vacuum dry at 60℃, and grind to obtain MoO. x / CNT.

[0030] S2: Weigh 14.378 g ZnSO4·7H2O and 0.1 g concentrated H2SO4, dissolve in deionized water and bring to a final volume of 100 mL to prepare a 0.5 mol·L⁻¹ solution. -1 Zinc sulfate electrolyte. Using carbon paper as the working electrode, electrodeposition was performed at -0.5 V vs. RHE. A charge of 1.47 C was applied, and 1.0 mg of metallic zinc was deposited. The zinc was then dried under an infrared lamp to obtain Zn / CP.

[0031] S3: Take 1 mg MoO x / CNTs were drop-coated onto a Zn / CP surface (Zn:MoO) x The sample was dried with an infrared lamp at a mass ratio of 1:1; then reduced in a solution of Ag / AgCl and 0.5 M K2SO4 at -1.2 V for 1 h to obtain Zn / MoO2. x -CNT catalyst.

[0032] Example 2 This embodiment describes the preparation of catalysts with different mass ratios.

[0033] Referring to the method in Example 1, MoO was controlled respectively. x / CNT loading, to prepare Zn:MoO x A series of composite catalysts with mass ratios of 1:3, 3:1, 1:5, and 5:1 are as follows: (1) Zn:MoO x Preparation of composite catalysts with a mass ratio of 1:3 Step 1: Synthesis of molybdenum oxide-loaded carbon nanotubes. The specific preparation process is as follows: Weigh 0.9 g of multi-walled carbon nanotubes, place them in a beaker, add 60 ml of ethanol, and sonicate for 45 minutes to uniformly disperse the multi-walled carbon nanotubes in the organic solution, increasing the surface area for adhesion. Then, quickly weigh 10.2 g of molybdenum chloride and add it to the uniform ethanol solution of multi-walled carbon nanotubes. Sonicate for 20 minutes, then add 60 ml of ultrapure water and sonicate for 1.5 h. Place in the dark for 24 h. After the reaction is complete, pour the solution from the beaker into a centrifuge tube, centrifuge and wash, washing successively with deionized water and acetone. Dry under vacuum at 60 °C to obtain a dry catalyst solid. Grind it into powder using a mortar and pestle to obtain molybdenum oxide-loaded carbon nanotubes.

[0034] Step 2: Preparation of controllable zinc loading on carbon paper. Nano-zinc materials were prepared using a constant potential electrodeposition method. The specific experimental procedure is as follows: First, 14.378 g of zinc sulfate heptahydrate and 0.1 g of concentrated sulfuric acid were dissolved in an appropriate amount of deionized water. After ultrasonic-assisted dissolution, the solution was transferred to a 100 mL volumetric flask and diluted to volume to obtain 0.5 mol·L⁻¹ zinc nanoparticles. -1 Zinc electrolyte. Electrochemical deposition was performed in a three-electrode system using carbon paper as the working electrode (fixed area) at a constant potential of -0.5 V vs. RHE. The zinc loading on the carbon paper substrate was precisely controlled. Based on the previously established quantitative relationship between charge and deposition amount (Q = 1.47 C / mgZn), a charge of 1.47 C was applied to deposit 1.0 mg of metallic zinc nanostructures on the carbon paper surface, which were then dried and cured under an infrared lamp.

[0035] The third step, physical loading and pre-activation: Zn / MoO was prepared using a combination of electrochemical deposition and physical loading. x A composite catalyst with a CNT mass ratio of 1:3. The specific preparation process is as follows: 3 mg of MoO2 was applied using a drop-coating method. x -CNT catalyst was uniformly loaded onto the zinc-modified carbon paper described above, and dried under an infrared lamp to obtain Zn / MoO. xA composite catalyst with a CNT mass ratio of 1:3 was pre-activated by reduction in a 0.5 M potassium sulfate solution at -1.2 V (vs. Ag / AgCl) for 1 h.

[0036] (2) Zn:MoO x Preparation of composite catalysts with a mass ratio of 3:1 Step 1: Synthesis of molybdenum oxide-loaded carbon nanotubes. The specific preparation process is as follows: Weigh 0.8 g of multi-walled carbon nanotubes and place them in a beaker. Add 70 ml of methanol and sonicate for 50 minutes to uniformly disperse the multi-walled carbon nanotubes in the organic solution, increasing the surface area for adhesion. Then, quickly weigh 12 g of molybdenum nitrate and add it to the uniform methanol solution of multi-walled carbon nanotubes. Sonicate for 25 minutes, then add 70 ml of ultrapure water and sonicate for 2 hours. Place in the dark for 30 hours. After the reaction is complete, pour the solution from the beaker into a centrifuge tube, centrifuge and wash, successively with deionized water and acetone, and vacuum dry at 70 °C to obtain a dry catalyst solid. Grind it into powder using a mortar and pestle to obtain molybdenum oxide-loaded carbon nanotubes.

[0037] Step 2: Preparation of controllable zinc loading on carbon paper. Nano-zinc materials were prepared using a constant potential electrodeposition method. The specific experimental procedure is as follows: First, 12.0 g of zinc nitrate hexahydrate and 0.3 g of nitric acid were dissolved in an appropriate amount of deionized water. After ultrasonic-assisted dissolution, the solution was transferred to a volumetric flask and diluted to volume to prepare a zinc electrolyte. In a three-electrode system, using carbon paper as the working electrode (fixed area), electrochemical deposition was performed at a constant potential. The zinc loading on the carbon paper substrate was precisely controlled. Based on the previously established quantitative relationship between charge and deposition amount (Q = 1.47 C / mg Zn), a charge of 4.41 C was applied, resulting in the deposition of 3.0 mg of metallic zinc nanostructures on the carbon paper surface. These nanostructures were then dried and cured under an infrared lamp.

[0038] The third step, physical loading and pre-activation: Zn / MoO was prepared using a combination of electrochemical deposition and physical loading. x A composite catalyst with a CNT mass ratio of 3:1. The specific preparation process is as follows: 1 mg of MoO2 was applied using a drop-coating method. x -CNT catalyst was uniformly loaded onto the zinc-modified carbon paper described above, and dried under an infrared lamp to obtain Zn / MoO. x A composite catalyst with a CNT mass ratio of 3:1 was pre-activated by reduction in a 0.5 M potassium nitrate solution at -1.2 V (vs. Ag / AgCl) for 1.5 h.

[0039] (3) Zn:MoO x Preparation of composite catalysts with a mass ratio of 1:5 Step 1: Synthesis of molybdenum oxide-loaded carbon nanotubes. The specific preparation process is as follows: Weigh 1.0 g of multi-walled carbon nanotubes, place them in a beaker, add 80 ml of acetone, and sonicate for 60 minutes to uniformly disperse the multi-walled carbon nanotubes in the organic solution, increasing the surface area for adhesion. Then, quickly weigh 15 g of molybdenum sulfate and add it to the uniform acetone solution of multi-walled carbon nanotubes. Sonicate for 30 minutes, then add 80 ml of ultrapure water and sonicate for 2 hours. Place in the dark for 36 hours. After the reaction is complete, pour the solution from the beaker into a centrifuge tube, centrifuge and wash, washing successively with deionized water and acetone. Dry under vacuum at 80 °C to obtain a dry catalyst solid. Grind it into powder using a mortar and pestle to obtain molybdenum oxide-loaded carbon nanotubes.

[0040] Step 2: Preparation of controllable zinc loading on carbon paper. Nano-zinc materials were prepared using a constant potential electrodeposition method. The specific experimental procedure is as follows: First, 10.0 g of zinc sulfate and 0.5 g of hydrochloric acid were dissolved in an appropriate amount of deionized water. After ultrasonic-assisted dissolution, the solution was transferred to a volumetric flask and diluted to volume to prepare a zinc electrolyte. In a three-electrode system, using carbon paper as the working electrode (fixed area), electrochemical deposition was performed at a constant potential. The zinc loading on the carbon paper substrate was precisely controlled. Based on the previously established quantitative relationship between charge and deposition amount (Q = 1.47 C / mg Zn), an electric charge of 1.47 C was applied, resulting in the deposition of 1.0 mg of metallic zinc nanostructures on the carbon paper surface. These nanostructures were then dried and cured under an infrared lamp.

[0041] The third step, physical loading and pre-activation: Zn / MoO was prepared using a combination of electrochemical deposition and physical loading. x A composite catalyst with a CNT mass ratio of 1:5. The specific preparation process is as follows: 5 mg of MoO2 was applied using a drop-coating method. x -CNT catalyst was uniformly loaded onto the zinc-modified carbon paper described above, and dried under an infrared lamp to obtain Zn / MoO. x A composite catalyst with a CNT mass ratio of 1:5 was pre-activated by reduction in a 0.5 M potassium sulfate solution at -1.2 V (vs. Ag / AgCl) for 2 h.

[0042] (4) Zn:MoO x Preparation of composite catalysts with a mass ratio of 5:1 Step 1: Synthesis of molybdenum oxide-loaded carbon nanotubes. The specific preparation process is as follows: Weigh 0.5 g of multi-walled carbon nanotubes, place them in a beaker, add 50 ml of ethanol, and sonicate for 30 minutes to uniformly disperse the multi-walled carbon nanotubes in the organic solution, increasing the surface area for adhesion. Then, quickly weigh 8 g of molybdenum chloride and add it to the uniform ethanol solution of multi-walled carbon nanotubes. Sonicate for 10 minutes, then add 50 ml of ultrapure water and sonicate for 1 hour. Place in the dark for 12 hours. After the reaction is complete, pour the solution from the beaker into a centrifuge tube, centrifuge and wash, washing successively with deionized water and acetone. Dry under vacuum at 50 °C to obtain a dry catalyst solid. Grind it into powder using a mortar and pestle to obtain molybdenum oxide-loaded carbon nanotubes.

[0043] Step 2: Preparation of controllable zinc loading on carbon paper. Nano-zinc materials were prepared using a constant potential electrodeposition method. The specific experimental procedure is as follows: First, 15.0 g of zinc nitrate and 0.2 g of sulfuric acid were dissolved in an appropriate amount of deionized water. After ultrasonic-assisted dissolution, the solution was transferred to a volumetric flask and diluted to volume to prepare a zinc electrolyte. In a three-electrode system, using carbon paper as the working electrode (fixed area), electrochemical deposition was performed at a constant potential. The zinc loading on the carbon paper substrate was precisely controlled. Based on the previously established quantitative relationship between charge and deposition amount (Q = 1.47 C / mg Zn), a charge of 7.35 C was applied, resulting in the deposition of 5.0 mg of metallic zinc nanostructures on the carbon paper surface. These nanostructures were then dried and cured under an infrared lamp.

[0044] The third step, physical loading and pre-activation: Zn / MoO was prepared using a combination of electrochemical deposition and physical loading. x A composite catalyst with a CNT mass ratio of 5:1. The specific preparation process is as follows: 1 mg of MoO2 was applied using a drop-coating method. x -CNT catalyst was uniformly loaded onto the zinc-modified carbon paper described above, and dried under an infrared lamp to obtain Zn / MoO. x A composite catalyst with a CNT mass ratio of 5:1 was pre-activated by reduction in a 0.5 M potassium nitrate solution at -1.2 V (vs. Ag / AgCl) for 0.5 h.

[0045] See Figure 6 The graph, through comparative analysis with standard cards (MoO2 PDF#04-005-4546 and CNT PDF#97-008-8812), reveals that Zn-MoO x The diffraction pattern of the CNT composite catalyst (spectral line A) simultaneously exhibits characteristic diffraction peaks of hexagonal Zn (2θ=43.2° corresponding to the (101) crystal plane, 54.3° corresponding to the (102) crystal plane) and characteristic peaks of monoclinic MoO2 (such as the (-202) crystal plane); while the control sample MoO2... x / CNT (spectral line B) mainly shows the characteristic diffraction peaks of MoO2 ((011) and (210) crystal planes), confirming the successful composite of Zn and MoO2 in the composite catalyst.

[0046] See Figure 2 The figure shows a scanning electron microscope image and elemental distribution of a Zn / MoOx-CNT catalyst with a heterogeneous interface. As can be seen from the image, it uses carbon nanotubes as a support, and zinc nanoparticles and molybdenum oxide nanoparticles are loaded onto the carbon nanotubes. A Zn / MoOx interface is formed between the zinc nanoparticles and the molybdenum oxide nanoparticles. x Heterogeneous interface; Zn nanoparticles, with a particle size of approximately 20-100 nm, are distributed from the substrate onto the sample surface after pre-reduction. Carbon nanotubes, serving as the support framework, maintain an intact one-dimensional tubular structure, with a diameter of approximately 20-30 nm, providing conductivity and structural stability for the catalyst. MoO x Nanoparticles with a size of 5-10 nm are uniformly anchored on the surface of carbon nanotubes, forming a tight heterogeneous interface with Zn particles. This structure is beneficial for promoting electron transfer and intermediate adsorption during the reaction process.

[0047] See Figure 3 The figure shows Zn / MoO x The results of transmission electron microscopy (TEM) analysis of the catalyst are shown in the following figures: (a) is a high-resolution TEM image, (b) is a selected area electron diffraction (SED) image, and (c) is a high-angle annular dark-field scanning TEM image and the corresponding energy-dispersive X-ray (EDS) elemental mapping image. The high-resolution TEM image shows that the adjacent lattice spacings of 0.209 nm and 0.2915 nm correspond to the (101) crystal plane of Zn and MoO, respectively. x The (111) crystal plane indicates that Zn and MoO x It has a rich interface. The synthesized Zn / MoO x Electrocatalysts exhibit large-area contact between Zn and MoO x The heterojunction surfaces can serve as key active sites for the reduction reaction of carbon dioxide and nitrate, promoting the reaction. For Zn / MoO... x Selected area electron diffraction of the sample indicates that Zn / MoO x The catalyst exhibits polycrystalline characteristics, corresponding to the (101) crystal plane of Zn and the MoO crystal plane. x The reflection from the (111) crystal plane is the result. High-angle annular dark-field images and corresponding elemental analyses demonstrate the uniform distribution of Zn, Mo, and O elements in the sample.

[0048] Example 3 This embodiment tests the electrocatalytic performance of the high-efficiency catalyst prepared in the above embodiments.

[0049] First, the electrochemical reduction of nitrate to urea was tested: a three-electrode system (graphite rod counter electrode, Ag / AgCl reference electrode, and catalyst working electrode prepared in Example 1) was used, and electrolysis was carried out at a constant potential for 2 h in 0.1 M KNO3 (CO2 saturated) electrolyte at -0.5 V vs. RHE.

[0050] Specifically, CO2 gas was introduced into a 0.1M KNO3 electrolyte solution until saturation was achieved. Then, a linear sweep voltammetry test and a 2-h current-time electrolysis test were performed. Finally, the urease decomposition method was used to detect the urea products in order to quantitatively obtain the urea's Faradaic efficiency and urea yield.

[0051] Urea detection uses a combination of urease decomposition and indophenol blue method: prepare 18 U·mL -1 Urease solution: Mix 400 μL of electrolyte with 1.4 mL of phosphate buffer (10 mM, pH 6.4) and 200 μL of urease solution, and incubate at 37 ℃ for 1 h to completely decompose urea into ammonia; add colorimetric reagents (Solution A: salicylic acid-trisodium citrate-NaOH; Solution B: sodium hypochlorite; Solution C: sodium nitrosoferricyanide), and react at room temperature in the dark for 1 h. Measure the absorbance at 655 nm using a UV-Vis spectrophotometer.

[0052] The results showed that, at -0.5 V vs. RHE, the urea yield reached 1.55 mmol h. -1 g -1 The Faraday efficiency of the catalyst reached 46.8%. In comparison, the Faraday efficiency of a single Zn catalyst was 31.6%, and that of a single MoO catalyst was... x The CNT ratio is only 2.3%, indicating that the composite catalyst performs significantly better than the single-component catalyst.

[0053] In this embodiment, the urease method is used to determine the Faradaic efficiency and yield of urea. The specific operation steps are as follows: (1) Preparation of ammonia standard solution Prepare 10 μg·mL -1 To prepare the ammonium ion standard solution, 0.3146 g of ammonium chloride was dissolved in a 100 mL volumetric flask and then diluted 100 times to obtain the target standard solution. Samples were taken from the standard solution in increments of 20 μL, from 20 μL to 200 μL, and added to 15 mL sample tubes. The corresponding electrolyte was then added to dilute to 2 mL, resulting in a standard solution of 0.1, 0.2, and 1 µg·mL⁻¹ ammonium ions.

[0054] (2) Preparation of colorimetric reagent: The colorimetric reagent for the indophenol blue method requires the use of solutions A, B, and C together. Solution A: Dissolve 5g of salicylic acid, 5g of trisodium citrate trihydrate and 4g of sodium hydroxide in deionized water, and dilute to 100mL in a volumetric flask. Solution B: Take 8.9 mL from a sodium hypochlorite solution with 4% available chlorine and dilute to 100 mL with deionized water in a volumetric flask. Solution C: Weigh 0.25 g of sodium nitrosoferricyanide dihydrate and dilute to 25 mL in a volumetric flask with deionized water.

[0055] (3) Colorimetric reaction: Add 4 mL of colorimetric solution A and 2 mL of colorimetric solution C to 4 mL of blank electrolyte, then add 400 μL of colorimetric solution C to prepare a blank control sample. Then add 2 mL of colorimetric solution A, 1 mL of colorimetric solution B, and 200 μL of colorimetric solution C to 2 mL of standard ammonium ion solution to be tested. Let the reaction stand at room temperature in the dark for 1 h, and perform wavelength scanning using a UV-Vis spectrophotometer with a scan width of 800 nm to 500 nm, where the maximum absorption wavelength of ammonia is 655 nm. Prepare a standard concentration curve based on the obtained data.

[0056] (4) Decompose urea, the steps are as follows: First, prepare 18U mL -1 The urease solution (using deionized water as solvent) was prepared and stored in the refrigerator after preparation. Next, a 10 mM phosphate buffer solution with pH 6.4 was prepared: first, 1 mol / L of the buffer solution was prepared... -1 100 mL each of Na2HPO4 and NaH2PO4 were prepared (and diluted to volume in a 100 mL volumetric flask). Then, 255 μL of Na2HPO4 and 745 μL of NaH2PO4 were mixed thoroughly and diluted to volume in a 100 mL volumetric flask to obtain a 10 mM phosphate buffer solution with pH=6.4.

[0057] The decomposition ratio of urea is: 400 μL electrolyte + 1.4 mL phosphate buffer solution + 200 μL urease solution (pay close attention to the order of addition). After adding, incubate in a water bath at 37°C for 1 hour to achieve complete decomposition. The ammonia concentration in the solution after decomposition is equal to the sum of the original ammonia concentration in the solution and the ammonia concentration produced by the decomposition of urea.

[0058] (5) Measure the concentration of ammonia after decomposition. Blank sample: 800 μL electrolyte + 3.2 mL phosphate buffer solution + 4 mL reagent a + 2 mL reagent b + 0.4 mL reagent c, react at room temperature for 1 h.

[0059] Samples with different potentials: 2 mL of decomposed electrolyte + 2 mL of reagent a + 1 mL of reagent b + 0.2 mL of reagent c, react at room temperature for 1 h.

[0060] First, calibrate the UV-Vis spectrophotometer using a blank sample to establish a baseline. After samples at different potentials have reacted, measure the absorbance using the UV-Vis spectrophotometer in the 500-800 nm range. The absorbance at 655 nm is the absorbance of NH3. Subtract the absorbance of the undecomposed NH3 from the absorbance of the decomposed NH3, and substitute the resulting absorbance into the ammonia standard curve. Divide the resulting ammonia concentration by 2 to obtain the actual concentration of urea.

[0061] The urea Faradaic efficiency and yield are based on the formula:

[0062]

[0063] Where N is the number of electrons transferred to produce 1 mol of urea, F is the Faraday constant, t is the reaction time, n is the amount of urea produced, j is the current magnitude, V is the electrolyte volume, and A is the electrode area. The concentration at which urea is produced.

[0064] See Figure 4 The linear sweep voltammetry method was used to verify the composite catalyst Zn / MoO x -CNTs exhibit superior catalytic activity compared to single catalysts. The composite catalyst shown in the figure is Zn / MoO. x -CNT, at the same potential, the current density under CO2 atmosphere was significantly higher than that under Ar atmosphere. This result indicates that both catalysts exhibit a tendency for the co-reduction reaction of CO2 and NO3⁻, suggesting their potential activity in this reaction. Further comparison of the current densities of the two catalysts under saturated CO2 atmosphere reveals that the current density of the composite catalyst is significantly higher than that of the single catalyst. This phenomenon further confirms the higher activity of the composite catalyst in the co-reduction reaction of carbon dioxide and nitrate.

[0065] See Figure 5 Zn / MoO x - The urea Faradaic efficiency and yield of CNT catalysts are significantly higher than those of single catalysts (Zn and MoO). x The composite catalyst ( / CNT) significantly improved selectivity and urea yield. In the figure, urea yield represents urea yield, and FE is the abbreviation for Faradaic efficiency. The composite catalyst exhibited significant performance advantages at both -0.4 V and -0.5 V potentials, especially at -0.5 V, where its Faradaic efficiency reached 1.5 times that of pure Zn (FEurea = 31.6%) and MoO, respectively. x 20 times that of / CNT (FEurea=2.3%).

[0066] The synthesis of the high-efficiency catalyst in the above embodiments of the present invention adopts an electroreduction synthesis method ( Figure 1 First, carbon nanotubes loaded with molybdenum oxide were synthesized via a static method. Then, metallic zinc was deposited on carbon paper via electrodeposition. Finally, a highly efficient heterojunction interfacial catalyst was synthesized via an electroreduction method. The catalyst prepared by this method is rich in Zn and MoO. x Heterogeneous interfaces ( Figure 2 , Figure 3 , Figure 6 This catalyst exhibits excellent electrocatalytic performance, and the synthesized Zn / MoO₂... x The catalyst exhibits excellent activity in the co-reduction of carbon dioxide and nitrate to urea: in a 0.1 M KNO3 (CO2-saturated) solution, linear sweep voltammetry confirmed that the catalyst has good catalytic activity (compared to a single catalyst). Figure 4 Within the range of -0.4 V to -0.7 V (vs. RHE), the catalyst exhibited optimal catalytic selectivity for urea during co-catalytic reduction in 0.1 M KNO3 (CO2-saturated) solution. At -0.5 V (vs. RHE), the urea yield and Faradaic efficiency reached 1.55 mmol h⁻¹ gcat⁻¹ and 46.8%, respectively, significantly outperforming the performance of single-component catalysts and ranking among the best reported catalysts to date. Figure 5 ).

[0067] In summary, the above embodiments of the present invention, by selecting specific Zn / MoO x The heterojunction system, prepared using a unique electrochemical wet process, gives the catalyst numerous heterojunction interfaces. Through interfacial effects, it enhances electron transfer, regulation, and surface adsorption, effectively improving the efficiency and yield of the co-reduction of carbon dioxide and nitrate to urea. This invention represents a significant difference and improvement over existing technologies in terms of catalyst composition, structure, preparation method, and catalytic performance. Its preparation method is simple to operate, easy to synthesize, uses inexpensive and readily available raw materials, and is easy to scale up, showing promising application prospects.

[0068] It should be particularly noted that other technical solutions obtained by specific selection within the range of components, proportions, and process parameters described in this invention can all achieve the technical effects of this invention, and therefore will not be listed one by one. Furthermore, other catalyst technical solutions obtained by using equivalent components, proportions, preparation methods, and applications as described in this invention are all included within the protection scope of this invention.

[0069] In the description of this invention, the terms "one embodiment," "some embodiments," "specific embodiment," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this invention, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A highly efficient catalyst for the electrocatalytic co-reduction of carbon dioxide and nitrate to urea, characterized in that, The catalyst is Zn / MoO. x -CNT composite catalyst, composed of carbon nanotubes (MoO2) supported on molybdenum oxide. x It is composed of Zn and MoO2 nanostructures loaded on carbon paper and is composed of CNTs. x Heterogeneous interfaces, in which MoO x The molybdenum oxide has a value of 2-3, the zinc nanoparticles are zinc metal, and the carbon nanotubes serve as a carrier to provide conductivity and structural stability.

2. The high-efficiency catalyst according to claim 1, characterized in that, The loading amount of Zn is 1.0-5.0 mg, the loading amount of MoOx-CNT is 1-5 mg, and the Zn and MoO... x The mass ratio of -CNT is (1-5):

1.

3. The high-efficiency catalyst according to claim 1, characterized in that, The carbon nanotubes are multi-walled carbon nanotubes with a diameter of 20-30 nm; the Zn nanoparticles have a particle size of 20-100 nm, and the MoO... x The nanoparticles have a diameter of 5-10 nm and are uniformly anchored on the surface of carbon nanotubes.

4. A method for preparing the high-efficiency catalyst according to claim 1, characterized in that, Includes the following steps: S1: Molybdenum oxide carbon nanotubes (MoO) x Synthesis of MoO2 (CNT): Weigh 0.5-1.0 g of multi-walled carbon nanotubes, add 50-80 ml of organic solvent, and sonicate for 30-60 minutes to uniformly disperse the carbon nanotubes. Then add 8-15 g of molybdenum compound, sonicate for 10-30 minutes, add 50-80 ml of ultrapure water, and sonicate for 1-2 hours. Place in the dark for 12-36 hours, centrifuge and wash, then vacuum dry at 50-80℃, and grind into powder to obtain MoO2. x / CNT; S2: Preparation of controllable mass zinc-loaded Zn / CP on carbon paper: Zinc electrolyte was prepared, and constant potential electrodeposition was performed with carbon paper as the working electrode in a three-electrode system. 1.0-8.0C of charge was applied to deposit 1.0-5.0mg of zinc nanostructures on the surface of carbon paper, which were then dried and cured under an infrared lamp. S3: Physical loading and pre-activation: 1-5 mg MoO2 was applied by drop-coating. x / CNTs were loaded onto Zn / CP, dried under an infrared lamp, and then pre-activated by reduction in a 0.5 mol / L potassium-containing electrolyte at -1.2V for 0.5–2 h to obtain Zn / MoO. x -CNT composite catalyst.

5. The preparation method according to claim 4, characterized in that, The organic solvent in step S1 is one of ethanol, methanol or acetone, and the molybdenum compound is one of molybdenum chloride, molybdenum nitrate or molybdenum sulfate; the mass ratio of the multi-walled carbon nanotubes to the molybdenum salt is 1:(8~16); the standing time is 24 h.

6. The preparation method according to claim 4, characterized in that, The zinc electrolyte in step S2 is a mixed solution prepared by dissolving 10.0-15.0g of zinc compound and 0.1-0.5g of acid in deionized water. The zinc compound is zinc sulfate or zinc nitrate, and the acid is one of sulfuric acid, nitric acid or hydrochloric acid. The electrodeposition potential is -0.5 V, and the deposition charge is 1.0~8.0 C.

7. The preparation method according to claim 4, characterized in that, The potassium-containing electrolyte in step S3 is a potassium sulfate or potassium nitrate solution; the MoO x The loading amount of / CNT is 1~5 mg, and the Zn and MoO x The mass ratio is 1:1, 1:3, 3:1, 1:5 or 5:

1.

8. The use of the high-efficiency catalyst according to any one of claims 1 to 3 in the electrocatalytic co-reduction of carbon dioxide and nitrate to urea.

9. The application according to claim 8, characterized in that, The application includes: using the Zn / MoO x Using a CNT catalyst as the working electrode, constant potential electrolysis is performed in an electrolyte saturated with 0.1 mol / L KNO3 and CO2, within a potential range of -0.4 V to -0.7 V, to co-reduce carbon dioxide and nitrate to urea.

10. The application according to claim 9, characterized in that, At an electrolysis potential of -0.5V and an electrolysis time of 2 hours, the urea yield reached 1.55 mmol / h. -1 gcat -1 Faraday efficiency reached 46.8%.

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