Method for synthesizing ammonia through electrocatalytic reduction based on zirconium oxyphosphate catalyst

Abstract

The invention provides a method for synthesizing ammonia through electro-catalytic reduction based on a zirconium oxyphosphate catalyst, and belongs to the technical field of electro-catalytic synthesizing.The method comprises the steps that an electro-catalytic system comprising a working electrode and an electrolyte is constructed, and under the electrifying condition, a nitrogen source in the electrolyte is reduced to synthesize ammonia through electro-catalytic ammonia synthesis reaction; wherein the working electrode contains a zirconium oxyphosphate catalyst, and the electrolyte contains a nitrogen source; the nitrogen source is selected from at least one of nitrate, nitrite, nitric oxide, nitrogen dioxide and nitrogen.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic synthesis technology, and particularly relates to a method for the electrocatalytic reduction synthesis of ammonia based on a zirconium oxyphosphate catalyst. Background Technology

[0002] Currently, most ammonia is synthesized via the Harper-Bosch process, which uses nitrogen obtained by cryogenic separation of hydrogen from fossil fuels and air as raw materials. The reaction is carried out under high temperature (300~500℃), high pressure (100-200 bar), and catalytic conditions. This method requires harsh reaction conditions, consumes a lot of energy, and is accompanied by the emission of a large amount of carbon dioxide (CO2).

[0003] Beyond energy and environmental considerations, human activities generate large amounts of nitrogen-containing wastewater and nitrogen compounds. This nitrogen-containing wastewater originates from industrial, agricultural, and aquatic wastewater, landfill leachate, and domestic sewage, and its nitrate and / or nitrite concentrations may exceed 0.6 M. Excessive nitrate and / or nitrite emissions disrupt the nitrogen balance, and pollution of natural water bodies leads to eutrophication, damaging ecosystems and posing potential threats to human health. In particular, nitrite, their incomplete oxidation product, can cause liver damage, methemoglobinemia, and cancer.

[0004] How to utilize potential resources (such as nitrate and / or nitrite, nitrogen compounds, etc.) to produce high-value ammonia is an urgent problem to be solved. Summary of the Invention

[0005] In view of the above, the present invention provides a method for the electrocatalytic reduction synthesis of ammonia based on zirconium oxyphosphate catalyst, in order to at least partially solve the above-mentioned technical problems. The technical solution provided by the present invention is as follows.

[0006] According to an embodiment of the present invention, the method for synthesizing ammonia by electrocatalytic reduction based on zirconium oxyphosphate catalyst includes: constructing an electrocatalytic system comprising a working electrode and an electrolyte; the working electrode contains a zirconium oxyphosphate catalyst, and the electrolyte contains a nitrogen source; under energized conditions, ammonia is synthesized by reducing the nitrogen source in the electrolyte through an electrocatalytic ammonia synthesis reaction; wherein the nitrogen source is selected from at least one of nitrate, nitrite, nitric oxide, nitrogen dioxide, and nitrogen gas.

[0007] In an embodiment of the present invention, a zirconium oxyphosphate catalyst is prepared as a working electrode and an electrocatalytic system is constructed. Under energized conditions, the zirconium oxyphosphate catalyst on the working electrode can reduce the nitrogen source in the electrolyte to synthesize ammonia, thereby realizing the resource utilization of waste resources. At the same time, the method of synthesizing ammonia is relatively simple and eliminates the dependence on harsh conditions of high temperature and high pressure. Attached Figure Description

[0008] Figure 1X-ray diffraction (XRD) pattern of the catalyst in Example 1 of the present invention (Comparative Example 1);

[0009] Figure 2 The following are characterization diagrams of the zirconium oxyphosphate catalyst in Example 1 of the present invention, wherein (a) is a high-resolution transmission electron microscopy (HRTEM) diagram and (b) is an elemental energy dispersive spectroscopy (EDS) diagram.

[0010] Figure 3 The image shows the nitrogen adsorption isotherm (BET) of the zirconium oxyphosphate catalyst measured at 77 K in Example 1 of this invention, with the inset showing the pore size distribution.

[0011] Figure 4 This is a comparison chart of the yield and Faraday efficiency of ammonia synthesis using the zirconium oxyphosphate catalyst at different potentials in Example 1 of the present invention;

[0012] Figure 5 This is a comparison chart of the yield and Faraday efficiency of ammonia synthesis by the catalysts in Example 1 and Comparative Example 1 of the present invention at a potential of -0.7V;

[0013] Figure 6 The image shows the X-ray diffraction (XRD) pattern of the solid product obtained by rotary evaporation after the electrocatalytic reaction in Example 1 of this invention.

[0014] Figure 7 This is a comparison chart of the ammonia synthesis yield and Faraday efficiency of different catalysts in Examples 1-4 of this invention at a potential of -0.7V;

[0015] Figure 8 This is a graph showing the stability test results of the catalyst in Example 1 of the present invention;

[0016] Figure 9 The following are infrared curves of pyridine at different desorption temperatures for different catalysts in Comparative Example 1 and Example 1 of the present invention, where (a) is the zirconium oxyphosphate catalyst in Example 1 and (b) is the catalyst in Comparative Example 1.

[0017] Figure 10 Comparative Example 1: A comparison of ammonia temperature-programmed desorption curves for different catalysts in Example 1 of this invention;

[0018] Figure 11 The figures show the LSV (linear sweep voltammetry) test curves of the electrocatalytic system containing the catalyst in Example 1 of this invention in aqueous system and deuterated system, respectively, with the inset showing the solvent kinetic isotope effect (SKIE value) under different applied potentials.

[0019] Figure 12 The following are LSV test curves of the electrocatalytic system of the present invention containing the catalyst in Example 1, with and without the addition of tert-butanol;

[0020] Figure 13 The electrocatalytic system containing the catalyst in Example 1 was tested without the addition of nitrite ions (NO2). - ), Adding nitrite ions (NO2) - LSV test curves in the system;

[0021] Figure 14 The LSV test curves of the electrocatalytic system containing the catalyst in Example 1 in argon (Ar) and nitrogen (N2) systems are shown. Detailed Implementation

[0022] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the invention. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the invention for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0023] To address the problems of demanding high-temperature, high-pressure conditions and high energy consumption in existing ammonia synthesis methods, this invention proposes a novel method for ammonia synthesis, which, compared to traditional energy-intensive methods (11.7-12.5 kWh kg-N), achieves a higher efficiency. -1 The denitrification biological treatment method (converting nitrate into nitrogen) treats high-concentration wastewater. The electrocatalytic NO3RR driven by electricity generated from renewable energy can not only solve the problem of nitrate pollution in the environment, but also produce green ammonia and help reduce greenhouse gases, showing potential application prospects.

[0024] Electrocatalytic reduction method for ammonia synthesis

[0025] Specifically, the method for electrocatalytic reduction synthesis of ammonia based on zirconium oxyphosphate catalyst provided by the present invention includes: constructing an electrocatalytic system comprising a working electrode and an electrolyte, wherein the working electrode contains a zirconium oxyphosphate catalyst and the electrolyte contains a nitrogen source; and synthesizing ammonia by reducing the nitrogen source in the electrolyte through an electrocatalytic ammonia synthesis reaction under energized conditions; wherein the nitrogen source is selected from nitrate (NO3). - ), nitrite (NO2) - It contains at least one of nitric oxide (NO), nitrogen dioxide (NO2), and nitrogen (N2).

[0026] In this invention, a zirconium oxyphosphate catalyst is prepared as a working electrode and an electrocatalytic system is constructed. Under energized conditions, the zirconium oxyphosphate catalyst on the working electrode can catalyze the reduction of nitrogen source in the electrolyte to synthesize ammonia, thereby realizing the resource utilization of waste resources. At the same time, the method of synthesizing ammonia is relatively simple and eliminates the dependence on harsh conditions of high temperature and high pressure.

[0027] According to embodiments of the present invention, the electrolyte further includes 0.1-6M KOH; wherein the concentration of nitrate and / or nitrite is 0.01-3M. Further, nitrate may be provided by potassium nitrate (KNO3) or by other water-soluble nitrates; nitrite may be provided by potassium nitrite (KNO2) or by other water-soluble nitrites.

[0028] According to an embodiment of the present invention, the electrocatalytic reaction system can be carried out in an H-type electrolyzer.

[0029] According to an embodiment of the present invention, the operating voltage for the electrocatalytic ammonia synthesis reaction is 0V vs. RHE ~ -1.5V vs. RHE.

[0030] According to an embodiment of the present invention, the working time of the electrocatalytic ammonia synthesis reaction is 1h-4h, and the working time can be extended as needed.

[0031] According to an embodiment of the present invention, the method for electrocatalytic reduction synthesis of ammonia based on zirconium oxyphosphate catalyst further includes: extracting the electrocatalytic product after the electrocatalytic synthesis reaction is completed.

[0032] Specifically, the extraction of electrocatalytic products includes: pumping electrolyte into a receiving container, carrying out ammonia from the receiving container under the condition of passing in inert gas or air, and collecting it with an acidic solution to obtain an ammonium solution; recovering ammonium chloride from the ammonia solution by rotary evaporation; wherein the acidic solution is selected from any one of hydrochloric acid, sulfuric acid, and phosphoric acid.

[0033] For example: 40 mL to 100 mL of the electrolyzed electrolyte is pumped into a three-hole gas washing bottle placed in a 70°C water bath using a peristaltic pump (1 mL / min to 5 mL / min). Argon (Ar) or air is continuously introduced into the washing bottle throughout the process, and the mixture is continuously and vigorously stirred (700 rpm / min). Then, the gaseous ammonia (NH3) extracted by argon or air is collected using 0.1 M to 4 M HCl. Finally, the solvent (such as water) is evaporated using a rotary evaporator at a temperature of 40°C to 60°C, yielding a white, lumpy solid, NH4Cl.

[0034] Electrocatalytic system

[0035] According to an embodiment of the present invention, the electrocatalytic system includes a working electrode of an oxygen-containing zirconium phosphate catalyst, a reference electrode, a counter electrode, and an electrolyte containing a nitrogen source.

[0036] According to an embodiment of the present invention, the working electrode comprises a conductive support and the aforementioned zirconium oxyphosphate catalyst, wherein the conductive support is selected from carbon cloth, carbon black, and conductive polymer; and the loading amount of the zirconium oxyphosphate catalyst on the conductive support is 0.1 mg·cm³. -2 ~1.0 mg·cm -2 .

[0037] According to an embodiment of the present invention, the method for preparing the working electrode includes: dispersing a zirconium oxyphosphate catalyst and a Nafion solution in a mixed solution containing water and an organic solvent, mixing them uniformly to obtain a dispersion; coating the dispersion onto carbon cloth, and curing it to obtain a working electrode containing the zirconium oxyphosphate catalyst. The organic solvent is selected from at least one of isopropanol and anhydrous ethanol. In the dispersion, the volume fraction of the Nafion solution is 0.1 vol% to 1.0 vol%.

[0038] For example: Accurately weigh 3 mg of the prepared zirconium oxyphosphate catalyst and mix thoroughly with 3 μL of Nafion solution, 27 μL of isopropanol, 500 μL of deionized water, and 470 μL of anhydrous ethanol to obtain a dispersion. Take a certain amount of the dispersion and drop it onto a 1*1 cm... 2 On carbon cloth, a zirconium oxyphosphate catalyst with a loading of 0.3 mg / cm³ was obtained. 2 The working electrode.

[0039] According to embodiments of the present invention, the counter electrode comprises a platinum electrode, which undergoes the oxygen evolution reaction. The reference electrode may be an Hg / HgO (mercury / mercury oxide) electrode.

[0040] Zirconium oxyphosphate catalyst

[0041] According to embodiments of the present invention, the zirconium oxyphosphate catalyst possesses an amorphous crystalline phase structure and an ordered mesoporous structure, with an average mesopore diameter of 4.0 nm-5.0 nm. The amorphous structure of the zirconium oxyphosphate catalyst indicates that its atomic arrangement exhibits long-range disorder and short-range order, demonstrating the presence of numerous defects (such as vacancies) on its surface. These defects can serve as active sites, providing a richer interfacial environment, which is beneficial for the selective adsorption of multiple intermediates during the electrocatalytic ammonia synthesis reaction, resulting in superior electrochemical performance and improved ammonia production and efficiency. The ordered mesoporous structure of the zirconium oxyphosphate catalyst provides abundant pores, ensuring rapid diffusion of reactants (nitrogen source) and products (ammonia), thus giving the catalyst excellent electrocatalytic and ammonia production performance.

[0042] According to an embodiment of the present invention, the pyridine adsorption infrared spectrum of the zirconium oxyphosphate catalyst of the present invention has a value at 1640 cm⁻¹. -1 and 1540 cm -1The characteristic peak representing Brønsted acids (hereinafter referred to as "B acids") is located at 1610 cm⁻¹. -1 and 1450cm -1 The characteristic peaks representing Lewis acids (hereinafter referred to as "L acids") at 1490 cm⁻¹, and at 1490 cm⁻¹ -1 The presence of mixed signals from Brønsted and Lewis acids at the site indicates that the presence of Brønsted acid active sites facilitates proton hydrogen transfer, while the presence of Lewis acid active sites facilitates the adsorption and activation of the nitrogen source. Through the synergistic effect of the Brønsted and Lewis acid active sites, the reduction of the nitrogen source in the electrocatalytic ammonia synthesis reaction can be jointly promoted to synthesize ammonia.

[0043] Preparation method of zirconium oxyphosphate catalyst

[0044] According to an embodiment of the present invention, the zirconium oxyphosphate catalyst is synthesized by an evaporation-induced self-assembly process using a nonionic surfactant as a structure directing agent; wherein, the nonionic surfactant is selected from F127 (poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol)) or P123 ((ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide)).

[0045] Specifically, the preparation of zirconium oxyphosphate catalyst includes the following steps 1-3.

[0046] Step 1: After the structure-directing agent is dissolved in an alcohol solvent, add a phosphorus source and a zirconium source and mix thoroughly to obtain a reaction solution.

[0047] Step 2: During the heat treatment process, the reaction solution induces the structure-directing agent to self-assemble and form micelles, while the phosphorus source and zirconium source are confined on the micelles and polycondense and solidify to obtain a gel.

[0048] Step 3: The gel is annealed to remove the micelles formed by the structure directing agent, yielding the zirconium oxyphosphate catalyst.

[0049] In embodiments of the present invention, after adding a structure-directing agent (which acts as a template agent), it induces self-assembly during the evaporation of volatile solvents. At this time, hydrophobic segments in the copolymer aggregate to form micelle cores, while hydrophilic blocks are bonded to the inorganic precursors (zirconium source, phosphorus source) through hydrogen bonds and encapsulated around the micelles. As the alcohol solvent continues to evaporate, these micelles spontaneously arrange themselves into a highly ordered two-dimensional hexagonal liquid crystal phase, and the inorganic precursors are confined in continuous regions between the micelles and undergo condensation and solidification. Finally, the structure-directing agent is removed by annealing, leaving uniformly arranged mesoporous channels in the positions previously occupied by the micelles, thereby forming a tubular zirconium oxyphosphate catalyst with an ordered mesoporous structure.

[0050] According to an embodiment of the present invention, in step 1, the molar ratio of phosphorus source to zirconium source is 0.5-1.5:1, for example, it can be 0.5:1, 0.75:1, 1.0:1, 1.2:1, 1.5:1, or any numerical ratio within this range. Maintaining the phosphorus-zirconium (P / Zr) molar ratio between 0.5:1 and 1.0:1 creates a "phosphate ligand shortage" chemical environment, preventing zirconium ions from obtaining sufficient phosphate to form a regular eight-coordinate structure. This also induces numerous competitive zirconium-oxygen-zirconium condensation reactions, resulting in highly random local chemical bond connections. Within the confined space of the block copolymer soft template, this mixed bonding network rapidly solidifies, kinetically suppressing the long-range ordered arrangement of atoms, thereby forcing the material to exist in a thermodynamically metastable amorphous state, thus obtaining an amorphous zirconium oxyphosphate catalyst. Furthermore, as the P / Zr molar ratio increases, the pore size and disorder of the zirconium oxyphosphate catalyst increase, which is beneficial for the electrocatalytic nitrogen reduction to ammonia synthesis reaction. If the P / Zr molar ratio is too low (e.g., <0.5:1), a large number of Zr-O-Zr-O- segments will appear in the zirconium oxyphosphate catalyst. At this time, the zirconium center is unsaturated and exhibits strong electrophilicity, which will lead to excessive adsorption of nitrogen sources (such as nitrate) and poisoning. At the same time, the lack of hydrophilic phosphate groups on the surface of the zirconium oxyphosphate catalyst is not conducive to the enrichment and transport of protons (H⁺) at the reaction interface, forcing H⁺ to directly gain electrons at Zr sites to undergo the hydrogen evolution reaction (HER), resulting in a sharp decrease in Faraday efficiency. If the P / Zr molar ratio is too high (e.g., greater than 1.5), the surface of the zirconium oxyphosphate catalyst is covered with a large number of terminal -PO3H2 and -PO- groups, forming a negatively charged and highly hydrophilic surface. This results in strong electrostatic repulsion of nitrate by the negative charge enriched on the surface, preventing its adsorption and activation, leading to low ammonia yield. At the same time, the protons are fixed by a large number of phosphate groups, promoting the direct reduction of water molecules rather than nitrogen reduction to synthesize ammonia.

[0051] According to an embodiment of the present invention, the zirconium source is selected from at least one of zirconium oxychloride (ZrOCl2·8H2O), zirconium chloride, and zirconium oxynitrate; the phosphorus source is selected from at least one of trimethyl phosphate, triethyl phosphate, and tributyl phosphate.

[0052] According to an embodiment of the present invention, the phosphorus source and zirconium source are mixed and stirred with the alcohol solvent of the structure directing agent for a time of 6 hours or more in order to obtain a uniformly mixed reaction solution.

[0053] In some embodiments, the phosphorus source and zirconium source are mixed and stirred with the alcohol solvent of the structure-directing agent for 6-12 hours.

[0054] According to an embodiment of the present invention, the heat treatment in step 2 is a two-stage heat treatment, wherein the temperature of the first heat treatment is lower than the temperature of the second heat treatment. Specifically, the temperature of the first heat treatment is 40-80℃, and the treatment time is 24h-72h, preferably 60-80℃ and 24h-48h; the temperature of the second heat treatment is 60-200℃, and the treatment time is 12h-36h, preferably 100℃ and 24h. The two-stage heat treatment method makes the reaction more controllable. The lower temperature of the first heat treatment facilitates the slow reaction of the reactants, forming the basic structural framework; the second heat treatment, performed after raising the temperature, results in a more vigorous reaction, allowing for a rapid reaction beyond the initial stage. Compared to a single heat treatment, the two-stage heat treatment ensures the formation of an ordered structure, avoiding the inability to form a mesoporous structure due to an excessively high initial reaction temperature, or resulting in a disordered and irregular structure. If the first heat treatment temperature (<40℃) and the second heat treatment temperature are too low (<60℃), the structure may collapse during subsequent annealing due to insufficient strength of the framework formed by the polymerization reaction. The polymerization reaction refers to: 1) the condensation reaction between Zr-OH groups generated from the reaction of zirconium oxychloride and ethanol; 2) the hydrolysis of phosphorus source to generate phosphate and hydrogen phosphate; and 3) the polymerization reaction between Zr-OH and phosphate and hydrogen phosphate. If the first heat treatment temperature (>80℃) and the second heat treatment temperature (>200℃) are too high, the template formed by the structure-directing agent will decompose prematurely, affecting the formation of the tubular structure of the zirconium oxyphosphate catalyst, and even causing collapse. Excessively high heat treatment temperatures may cause the inorganic framework to condense too quickly, resulting in strong stress that forms mesoporous materials with microcracks. It may also damage its amorphous structure, leading to the final product of crystalline, non-porous nanoparticles, making it difficult to form an amorphous zirconium oxyphosphate catalyst.

[0055] In some embodiments, the reaction solution is first subjected to a first heat treatment at 60°C for 48 hours, followed by a second heat treatment at 100°C for 24 hours.

[0056] According to an embodiment of the present invention, the gel annealing temperature in step 3 is 200℃-900℃, for example, 200℃, 300℃, 500℃, 700℃, 900℃, but not limited to the values ​​listed; the gel annealing time is 2h-6h, for example, 2h, 4h, 6h, but not limited to the values ​​listed. If the annealing temperature is too high (e.g., >900℃), the specific surface area of ​​the material will gradually decrease, destroying its amorphous ordered mesoporous structure, causing the zirconium oxyphosphate catalyst to tend to crystallize, making it difficult to prepare an amorphous zirconium oxyphosphate catalyst; an excessively high annealing temperature may even cause the structure to collapse completely. If the annealing temperature is too low (e.g., <200℃), the structure-directing agent will not be completely removed, resulting in a smaller mesopore size in the prepared zirconium oxyphosphate catalyst, hindering the mass transfer of reactants and products in the electrocatalytic ammonia synthesis reaction, which is not conducive to improving catalytic performance.

[0057] In some embodiments, the gel is heated to 500°C at a heating rate of 1°C / min and annealed at 500°C for 5 hours to obtain a zirconium oxyphosphate catalyst.

[0058] The method for ammonia synthesis based on the electrocatalytic reduction of zirconium oxyphosphate catalyst of the present invention will be described in detail below with reference to specific embodiments and accompanying drawings. It should be noted that these examples are merely specific embodiments of the present invention and do not limit the scope of protection of the present invention.

[0059] Example 1

[0060] Preparation of zirconium oxyphosphate catalyst

[0061] 1.2 g of F127 was dissolved in 15 mL of anhydrous ethanol. After the F127 was completely dissolved, 5 mmol of zirconium oxychloride (ZrOCl2·8H2O) and 3.75 mmol of trimethyl phosphate (PO(OCH3)3) (P / Zr molar ratio of 0.75) were added to the above solution under vigorous stirring (700 rpm / min) and stirred for 6 hours to obtain a reaction solution. Then, the transparent reaction solution was transferred to a petri dish and heat-treated at 60 °C for 48 h and then at 100 °C for 24 h to obtain a gel. Finally, the obtained transparent dry gel was heated to 500 °C at a heating rate of 1 °C / min and annealed at 500 °C for 5 h to prepare the zirconium oxyphosphate catalyst (denoted as ZrPO).

[0062] Comparative Example 1

[0063] The zirconia catalyst was prepared using the same method as in Example 1, except that no phosphorus source was used.

[0064] Specifically: 1.2 g of F127 was dissolved in 15 mL of anhydrous ethanol. After the F127 was completely dissolved, 5 mmol of ZrOCl2·8H2O was added to the solution under vigorous stirring (700 rpm / min) and stirred for 6 hours to obtain a reaction solution. Then, the transparent reaction solution was transferred to a petri dish and heat-treated at 60 °C for 48 h and then at 100 °C for 24 h to obtain a gel. Finally, the obtained transparent dry gel was heated to 500 °C at a heating rate of 1 °C / min and annealed at 500 °C for 5 h to prepare the zirconium oxide catalyst (denoted as ZrO2).

[0065] The catalysts obtained in Example 1 and Comparative Example 1 were subjected to X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), elemental distribution analysis, and nitrogen adsorption isotherm (BET) analysis, respectively. Specific test results are as follows: Figures 1-3 As shown.

[0066] Figure 1 The image shows the X-ray diffraction (XRD) pattern of the catalyst in Example 1 of the present invention, which is a comparative example.

[0067] like Figure 1 As shown, the zirconium oxyphosphate catalyst prepared in Example 1 has an amorphous structure.

[0068] Figure 2 The image shows the characterization of the zirconium oxyphosphate catalyst in Example 1 of this invention, where (a) is a high-resolution transmission electron microscopy (HRTEM) image and (b) is an elemental energy dispersive spectroscopy (EDS) image.

[0069] like Figure 2 As shown, the zirconium oxyphosphate catalyst in Example 1 has a well-organized mesoporous structure, and the Zr, P and O elements are evenly distributed.

[0070] Figure 3 The image shows the nitrogen adsorption isotherm (BET) of the zirconium oxyphosphate catalyst measured at 77 K in Example 1 of this invention, with the inset showing the pore size distribution.

[0071] like Figure 3 As shown, the zirconium oxyphosphate catalyst prepared in Example 1 is a mesoporous material with an average pore size of about 4.5 nm.

[0072] Example 2

[0073] The zirconium oxyphosphate catalyst was prepared using the same method as in Example 1, except that 3.75 mmol of trimethyl phosphate (PO(OCH3)3) was replaced with 2.5 mmol of trimethyl phosphate (PO(OCH3)3), and the P / Zr molar ratio was 0.5.

[0074] Example 3

[0075] The zirconium oxyphosphate catalyst was prepared using the same method as in Example 1, except that 3.75 mmol of trimethyl phosphate (PO(OCH3)3) was replaced with 5 mmol of trimethyl phosphate (PO(OCH3)3), and the P / Zr molar ratio was 1.0.

[0076] Example 4

[0077] The zirconium oxyphosphate catalyst was prepared using the same method as in Example 1, except that 3.75 mmol of trimethyl phosphate (PO(OCH3)3) was replaced with 7.5 mmol of trimethyl phosphate (PO(OCH3)3), and the P / Zr molar ratio was 1.5.

[0078] Application Example 1

[0079] (1) Preparation of working electrode

[0080] 4 mg of the zirconium oxyphosphate catalyst from Example 1 was thoroughly mixed with 3 μL of commercial Nafion solution, 27 μL of isopropanol, 500 μL of deionized water, and 470 μL of anhydrous ethanol to obtain a dispersion. 75 μL of the dispersion was uniformly drop-coated onto a 1*1 cm substrate using catalyst ink. 2 On carbon cloth, a zirconium oxyphosphate catalyst with a loading of 0.3 mg / cm³ was obtained. 2 The working electrode.

[0081] (2) Construction of electrocatalytic system

[0082] Electrochemical experiments were conducted using an electrochemical workstation (CHI 760E, Shanghai Chenhua Instrument Co., Ltd.) in a three-electrode system. The working electrode, reference electrode, and counter electrode consisted of a carbon cloth electrode, an Hg / HgO electrode, and a platinum electrode, respectively, all loaded with the zirconium oxyphosphate catalyst from Example 1. The experiments were carried out in an H-type electrolytic cell, with the anode and cathode electrolytes separated by Nafion 117. The cathode and anode electrolytes were 1M KOH and 0.2M KNO3, respectively. Argon gas was introduced for 30 minutes before the start of the test. The electrocatalytic nitrogen reduction performance after 2 hours of electrolysis at different potentials was tested using the chronoamperometry (it test), and the liquid-phase products were detected by ultraviolet spectrophotometry.

[0083] (3) Electroreduction of nitrate to synthesize ammonia

[0084] Under energized conditions, ammonia is synthesized by reducing nitrate ions in the electrolyte via an electrocatalytic ammonia synthesis reaction. The performance test results of the zirconium oxyphosphate catalyst in Example 1 at different potentials for ammonia yield and Faradaic efficiency (FE) are shown in Table 1 and [Table data would be inserted here]. Figure 3 As shown.

[0085] (4) Extraction of electrocatalytic products

[0086] The electrolyte after the electrolysis reaction was pumped into a receiving bottle at 70°C using a peristaltic pump. Ammonia was carried out by passing Ar into the receiving bottle and collected with 0.5M HCl. After 2 hours, the collected ammonium chloride was separated and extracted by rotary evaporation.

[0087] Table 1

[0088]

[0089] As shown in Table 1, when the zirconium oxyphosphate catalyst from Example 1 was applied to the electrocatalytic reduction of nitrate to ammonia, the highest ammonia yield reached 2.57 mol / cm³. -2 h -1 The Faraday efficiency reached 94.97%.

[0090] Figure 4 This is a comparison chart of the yield and Faraday efficiency of ammonia synthesis using the zirconium oxyphosphate catalyst at different potentials in Example 1 of this invention.

[0091] like Figure 4 As shown, compared to other potentials, the zirconium oxyphosphate catalyst in Example 1 exhibits superior NH3 yield and Faraday efficiency at -0.7V vs. RHE.

[0092] Figure 5 This is a comparison chart of the yield and Faraday efficiency of ammonia synthesis by the catalyst in Example 1 and Comparative Example 1 of the present invention at a potential of -0.7V.

[0093] like Figure 5 As shown, compared to the catalyst in Comparative Example 1, the zirconium oxyphosphate catalyst in Example 1 exhibits higher yield and Faradaic efficiency when applied to the electrocatalytic reduction of nitrate to ammonia, with an NH3 yield reaching 2.57 mol g. -1 cat h -1 The Faraday efficiency reached 94.97%. This is because the zirconium oxyphosphate catalyst in Example 1 has an amorphous structure, exhibiting long-range disorder and short-range order, resulting in a richer interfacial environment that is more conducive to the adsorption and activation of multiple intermediate reactants in the nitrate reduction reaction, thus leading to superior electrochemical performance. Furthermore, the zirconium oxyphosphate catalyst prepared in Example 1 possesses an ordered mesoporous structure, providing abundant pores and ensuring rapid diffusion of reactants and products, which is also a key reason for its superior performance.

[0094] Figure 6 The image shows the XRD pattern of the solid product obtained by rotary evaporation after the electrocatalytic reaction in Example 1 of this invention.

[0095] like Figure 6As shown, the electrocatalytic product extraction method in Application Example 1 was used to treat the electrolyte after electrolysis, and the solid product NH4Cl was successfully extracted.

[0096] Application Example 2

[0097] The catalysts from Examples 2-4 were prepared into working electrodes, electrocatalytic systems were constructed, nitrate was electroreduced to synthesize ammonia, and the electrocatalytic products were extracted using the same method as in Application Example 1. The yields and Faraday efficiencies of the catalysts in Examples 2-4 for electroreduction of nitrate to ammonia were as follows: Figure 7 As shown.

[0098] Figure 7 This is a comparison chart of the ammonia synthesis yield and Faraday efficiency of different catalysts at a potential of -0.7V in Examples 1-4 of this invention.

[0099] like Figure 7 As shown, compared with the catalysts in Examples 2-4, the catalyst in Example 1 has the best NH3 yield and Faraday efficiency, which indicates that the P / Zr molar ratio of 0.75 has better electrocatalytic performance.

[0100] Furthermore, the stability of the catalyst in Example 1 of this invention was tested, and the specific test results are as follows: Figure 8 As shown.

[0101] Figure 8 The figure shows the stability test results of the catalyst in Example 1 of this invention.

[0102] like Figure 8 As shown, after 120 hours of operation, the NH3 yield, current density and Faraday efficiency of the catalyst in Example 1 did not decrease significantly, indicating that the catalyst prepared in Example 1 of this invention has long-term working stability.

[0103] Furthermore, the active sites of the zirconium oxyphosphate catalyst in Example 1 and the catalyst in Comparative Example 1 were analyzed. To this end, the pyridine adsorption infrared spectra of the zirconium oxyphosphate catalyst in Example 1 and the catalyst in Comparative Example 1 were tested at desorption temperatures of 150℃, 200℃, 300℃ and 350℃, respectively. The specific test results are shown in Figure 9.

[0104] Figure 9 The following are infrared curves of pyridine at different desorption temperatures for different catalysts in Comparative Example 1 and Example 1 of the present invention, where (a) is the zirconium oxyphosphate catalyst in Example 1 and (b) is the catalyst in Comparative Example 1.

[0105] like Figure 9 As shown, the catalyst of Example 1 was at 1640 cm⁻¹ -1 and 1540cm -1The characteristic peak of Brønsted acid (B acid) appears at 1610 cm⁻¹. -1 and 1450cm -1 The characteristic peak of Lewis acid (L acid) appears at 1490 cm⁻¹. -1 The absorption peak at that point represents a mixed signal of Brønsted acid and Lewis acid. The catalyst in Comparative Example 1 only showed characteristic peaks for Lewis acid, indicating that its surface contains almost no Brønsted acid sites.

[0106] Furthermore, the number (acidity) of pyridine infrared acidic sites in the catalyst of Example 1 and the catalyst of Comparative Example 1 at different desorption temperatures was quantitatively evaluated, and the specific test results are shown in Table 2.

[0107] Table 2

[0108]

[0109] As shown in Table 2, the test results of the catalyst in Example 1 show that as the desorption temperature increases from 150°C to 350°C, the number of Brønsted acid sites increases from 21.18 μmol·g⁻¹. -1 Decreased to 3.35 μmol·g -1 The number of L acid sites increased from 118.39 μmol·g -1 Reduced to 21.18 μmol·g -1 This indicates that the acidity of both Brønsted (B) and Lewis (L) acids gradually decreases with increasing temperature. Nevertheless, at a high temperature of 350°C, significant Brønsted (B) and Lewis (L) acid signals were still detected in Example 1, demonstrating the good thermal stability of its acidic sites. In contrast, Comparative Example 1 only detected Lewis (L) acid sites, and its highest acidity was only 14.87 μmol·g. -1 The content of L-acid is much lower than that of Example 1 under the same conditions.

[0110] Figure 10 Comparative Example 1: A comparison of ammonia temperature-programmed desorption curves for different catalysts in Example 1 of this invention.

[0111] like Figure 10 The signal peaks at 193℃, 400℃, and 600℃ shown in Figure a correspond to the weak acid (such as Zr-OH), medium acid, and strong acid sites of the ZrPO catalyst, respectively. These signals can be attributed to Zr-OH (weak acid), P-OH, or some L acid sites (such as coordinate-unsaturated Zr). 4+ (medium-strong acids), and highly coordinated unsaturated Zr 4+ (Strong acid), which indicates the presence of Zr in the amorphous ZrPO catalyst. 4+ Species such as P-OH. Figure 10 The presence of a weak acid signal peak at 179℃ shown in Figure b indicates that the acidity of ZrO2 originates from the L acid site.

[0112] Furthermore, the catalyst and its electrocatalytic system from Example 1 were subjected to linear sweep voltammetry (LSV) tests (85% IR compensation) in aqueous, deuterated, tert-butanol-added, and unadded tert-butanol systems to determine the pathway of electrocatalytic nitrogen reduction to ammonia synthesis. Specific test results are as follows: Figures 11-12 As shown.

[0113] Figure 11 The figures show the LSV (linear sweep voltammetry) test curves of the electrocatalytic system containing the catalyst in Example 1 of this invention in aqueous and deuterated systems, respectively. The inset shows the solvent kinetic isotope effect (SKIE value) under different applied potentials.

[0114] like Figure 11 As shown, at a potential of -0.6V, the current density in the deuterated system (NaOD+D2O+KNO3) is almost half that of the aqueous system (NaOH+H2O+KNO3), and the observed SKIE values ​​are between 2 and 3 under different applied potentials, indicating that the transfer of active *H species is the rate-determining step of the nitrate reduction reaction.

[0115] Figure 12 The LSV test curves of the electrocatalytic system containing the catalyst in Example 1 of this invention were obtained by performing 85% IR compensation on the addition of tert-butanol and the absence of tert-butanol.

[0116] like Figure 12 As shown, the current density of the electrochemical catalytic system constructed with the catalyst in Example 1 rapidly decreased after the addition of tert-butanol. This result indicates that the active hydrogen species (*H) generated by the Brønsted acid sites on the catalyst surface in Example 1 plays a crucial role in promoting the nitrate reduction reaction.

[0117] In summary, the Brønsted acid (B) and Lewis acid (L) sites in the ordered mesoporous, amorphous zirconium oxyphosphate material of this invention jointly promote the electrocatalytic reduction of nitrate to ammonia. KIE experiments and tert-butanol quenching experiments show that the B acid sites promote H₂O dissociation, generating active hydrogen species and accelerating their migration on the catalyst surface; the L acid sites effectively activate NO₃⁻ by adsorbing lone pairs of electrons (such as N / O) from nitrate ions through their empty orbitals. - This also promotes its dissociation. Therefore, the synergistic effect of Brønsted acid and Lewis acid achieves efficient conversion of nitrate, continuous supply of active hydrogen, and rapid surface proton transfer, thereby significantly improving catalytic performance.

[0118] Application Example 3

[0119] The catalyst from Example 1 was prepared into a working electrode and an electrocatalytic system was constructed using the same method as in Application Example 1. The difference was that ammonia was synthesized by electrocatalytic reduction of nitrite ions, and the electrocatalytic system containing the catalyst from Example 1 was subjected to electrocatalysis without the addition of nitrite ions (NO2).- ), Adding nitrite ions (NO2) - The LSV (linear sweep voltammetry) test was performed on the system (without Ir compensation), and the specific test results are as follows: Figure 13 As shown.

[0120] Figure 13 The electrocatalytic system containing the catalyst in Example 1 was tested without the addition of nitrite ions (NO2). - ), Adding nitrite ions (NO2) - LSV test curves in the system.

[0121] like Figure 13 As shown, using the catalyst from Example 1 as the working electrode, the current density increased significantly after the addition of nitrite under energized conditions, indicating that NO2 - Reduction is the main reason for the increase in current density, indicating that ZrPO has a positive effect on NO2. - The reduction exhibits high catalytic activity and can achieve ammonia production through electrocatalytic reduction of nitrate.

[0122] Application Example 4

[0123] The catalyst from Example 1 was prepared as a working electrode and an electrocatalytic system was constructed using the same method as in Application Example 1. The difference was that ammonia was synthesized by electrocatalytic nitrogen reduction. The electrocatalytic system containing the catalyst from Example 1 was subjected to LSV (linear sweep voltammetry) tests in argon (Ar) and nitrogen (N2) gas purging systems (without Ir compensation). The specific test results are as follows: Figure 14 As shown.

[0124] Figure 14 The LSV test curves of the electrocatalytic system containing the catalyst in Example 1 in argon (Ar) and nitrogen (N2) systems are shown.

[0125] like Figure 14 As shown, using the catalyst in Example 1 as the working electrode, under energized conditions, the LSV curve of N2 showed a significant increase in current density compared to the LSV curve of Ar, indicating that the ZrPO catalyst in Example 1 can promote the reduction of N2 to synthesize ammonia.

[0126] Similarly, the catalyst in the embodiments of the present invention can also be used to electrocatalyze the reduction of nitric oxide (NO) and nitrogen dioxide (NO2) to synthesize ammonia.

[0127] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for the electrocatalytic reduction synthesis of ammonia based on zirconium oxyphosphate catalyst, characterized in that, include: An electrocatalytic system comprising a working electrode and an electrolyte is constructed, wherein the working electrode contains a zirconium oxyphosphate catalyst and the electrolyte contains a nitrogen source; Under energized conditions, ammonia is synthesized by reducing the nitrogen source in the electrolyte through an electrocatalytic ammonia synthesis reaction. The nitrogen source is selected from at least one of nitrate, nitrite, nitric oxide, nitrogen dioxide, and nitrogen.

2. The method according to claim 1, characterized in that, The pyridine adsorption infrared spectrum of the zirconium oxyphosphate catalyst shows a value at 1640 cm⁻¹. -1 and 1540 cm -1 The characteristic peak representing Brønsted acid is at 1610 cm⁻¹. -1 and 1450 cm -1 The characteristic peaks representing Lewis acids at [location], and at 1490 cm⁻¹ -1 The mixed signal of Brønsted acid and Lewis acid at the location.

3. The method according to claim 1, characterized in that, The zirconium oxyphosphate catalyst has an amorphous crystalline phase structure and an ordered mesoporous structure, with the average pore size of the mesopores being 4.0 nm to 5.0 nm.

4. The method according to claim 1, characterized in that, The zirconium oxyphosphate catalyst was synthesized by evaporation-induced self-assembly using a nonionic surfactant as a structure directing agent. The nonionic surfactant is selected from F127 or P123.

5. The method according to claim 4, characterized in that, The zirconium oxyphosphate catalyst is obtained through the following steps: After the structure-directing agent is dissolved in an alcohol solvent, a phosphorus source and a zirconium source are added and mixed evenly to obtain a reaction solution; During heat treatment, the reaction solution induces the structure directing agent to self-assemble and form micelles. The phosphorus source and the zirconium source are confined on the micelles and polycondense and solidify to obtain a gel. The gel is annealed to remove the micelles formed by the structure directing agent, yielding the zirconium oxyphosphate catalyst.

6. The method according to claim 5, characterized in that, The molar ratio of the phosphorus source to the zirconium source is 0.5-1.5:1; The zirconium source is selected from at least one of zirconium oxychloride, zirconium chloride, and zirconium oxynitrate. The phosphorus source is selected from at least one of trimethyl phosphate, triethyl phosphate, and tributyl phosphate.

7. The method according to claim 1, characterized in that, The working electrode includes a conductive support and the zirconium oxyphosphate catalyst; The zirconium oxyphosphate catalyst is loaded at a rate of 0.1 mg·cm⁻¹ on the conductive support. -2 ~1.0 mg·cm -2 .

8. The method according to claim 1, characterized in that, The electrolyte also includes 0.1-6M KOH; The concentration of nitrate and / or nitrite is 0.01-3M.

9. The method according to claim 1, characterized in that, The operating voltage for the electrocatalytic ammonia synthesis reaction is 0V vs. RHE ~ -1.5V vs. RHE.

10. The method according to any one of claims 1-9, characterized in that, The method further includes: extracting the electrocatalytic product after the electrocatalytic ammonia synthesis reaction is completed; The extraction of the electrocatalytic product includes: The electrolyte is pumped into a receiving container, and the ammonia in the receiving container is carried out under the condition of passing in an inert gas or air, and collected with an acidic solution to obtain an ammonium solution. The ammonia solution is used to recover ammonium chloride by rotary evaporation; The acidic solution is selected from any one of hydrochloric acid, sulfuric acid, and phosphoric acid.

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