Iron-based amorphous microwire catalyst and method for preparing ammonia gas by electrochemical reduction of nitric acid

Abstract

The application discloses an iron-based amorphous microwire catalyst and a method for preparing ammonia by electrochemically reducing nitric acid. When preparing ammonia, the prepared iron-based amorphous microwire catalyst is subjected to an electrochemical reduction reaction in an electrolyte solution in a three-electrode system electrolytic cell at a low voltage to produce ammonia. The iron-based amorphous microwire catalyst prepared by the application has a diameter of 30 microns, effectively improves the specific surface area of the catalyst, significantly improves the current density of the catalyst, and can be applied to the reduction of nitrate to prepare ammonia. The metastable metal replaces commercial catalysts such as Pt, has low cost, significantly improves the activity of the catalyst, can realize amperometric current at a low voltage, greatly reduces the energy consumption of the reaction, enables higher Faraday efficiency and yield at normal temperature and pressure, and can collect the produced ammonia during the reaction process, realizing the combination of production and collection.

Description

Technical Field

[0001] This invention relates to the field of preparation and application of amorphous alloy electrocatalysts, and particularly to an iron-based amorphous micron-fiber catalyst and a method for preparing ammonia by electrochemical reduction of nitric acid. Background Technology

[0002] Ammonia is an important chemical raw material widely used in chemical, agricultural, and other fields. Currently, industrial ammonia synthesis mainly relies on the Haber-Bosch process. However, the N≡N bond energy (941 kJ mol⁻¹) in the reactant N₂ is very high, requiring a high-temperature, high-pressure environment. This process consumes a large amount of fossil fuels, leading to an energy crisis and excessive CO₂ emissions. Ammonia can be synthesized by electrocatalytic reduction of nitrogen at room temperature and pressure, but this also faces the problem of high N≡N bond energy and low Faraday efficiency. Alternative methods for ammonia synthesis need to be found, and nitrates, with lower bond energies than nitrogen, are one of the ideal nitrogen sources for ammonia synthesis. Furthermore, nitrate ions are a source of water pollution; this technology can utilize nitrate ions from wastewater as a nitrogen source, truly turning waste into a valuable resource.

[0003] Amorphous alloys, also known as metallic glasses, prevent crystal nucleation and growth through rapid cooling technology. Their atoms have a disordered structure and are in a metastable energy state, making them widely used in catalysis. Iron-based amorphous microfilaments, by controlling the material's energy state and giving it more active sites, significantly improve the yield and Faraday efficiency of the catalyst for reducing nitrate to ammonia. Summary of the Invention

[0004] Based on the above, this invention proposes an iron-based amorphous microfilament catalyst and a method for preparing ammonia by electrochemical reduction of nitric acid. The current can reach the ampere level at a relatively low voltage, thus solving the problems of energy shortage and low yield.

[0005] This invention proposes an iron-based amorphous microfilament catalyst and a method for the electrochemical reduction of nitric acid to prepare ammonia. The invention involves the following three changes.

[0006] Firstly, regarding the preparation of the catalyst, Fe, B, Si, Ni, Nb, P, Co, Cr, Cu, and Mn are mixed in atomic ratios to prepare amorphous alloy master alloy rods by arc melting. The master alloy is placed inside a glass tube and softened by heating. The softened part of the master alloy is then drawn through an inverted conical hole and pulled into wire. After cooling and solidification, glass-coated amorphous microfilaments are formed.

[0007] Secondly, the catalyst surface is coated with a layer of high borosilicate glass, which needs to be immersed in HF acid. It is taken out of the acid every 30 seconds and observed under a light microscope until the glass layer is completely removed. Then it is rinsed three times with deionized water.

[0008] Thirdly, the amorphous alloy electrocatalyst is used to catalyze the reduction of ammonia by nitrate. This reaction can be carried out in both H-type electrolytic cells and flowing electrolytic cells, with the anode and cathode connected to a power source.

[0009] Specifically, this invention provides an iron-based amorphous microfilament catalyst, wherein the catalyst has an amorphous microstructure with a diameter of 20-30 μm, and the diameter is on the micrometer scale.

[0010] In this iron-based amorphous microfilament material structure, iron-based amorphous metal wires serve as the core, and the outside is also wrapped with a high borosilicate glass cladding layer.

[0011] This makes it less susceptible to oxidation during cooling; it is particularly noteworthy that the thickness of this coating layer is significantly smaller than the diameter of the metal microfilament.

[0012] The preparation process of iron-based amorphous microfilament catalysts includes the following steps:

[0013] S1. Amorphous alloy master alloy rods are prepared by arc melting.

[0014] S2. Place the master alloy inside a glass tube; soften the master alloy by heating; draw the softened master alloy through an inverted conical hole and then draw it into a filament; after cooling and solidification, form an amorphous microfilament.

[0015] Iron-based amorphous microwires exist in alloy form, with the following composition based on the metal atomic ratio:

[0016] Fe: ≥50at%, Si: 3at%~12at%, B: 5at%~15at%, P: 5at%~10at%, Nb: 0at%~3at%, Ni: 5at%~20at%, and optional elements of 0at%~10at%, with optional elements being one or more combinations of Co, Cr, Cu, and Mn.

[0017] Iron-based amorphous microfilament catalysts are Fe alloys. 63 Ni6Cr 6.5 Nb1B 13 P 6.5 Si4.

[0018] Iron-based amorphous microfilament catalysts can produce ammonia through electrochemical reduction reactions in an electrolyte solution within a three-electrode electrolytic cell at relatively low voltages. The low voltage range is -0.28 to -1.08 V. The electrolyte solution can be neutral or alkaline; specifically, it can be a nitrate concentration ranging from 0.1 M to 2 M or a 1 M sodium hydroxide solution.

[0019] When iron-based amorphous microfilament catalysts are used in H-type electrolytic cells, the cathode region and the anode region are composed of two interconnected electrolytic cells, and the interconnected parts are separated by a proton exchange membrane.

[0020] When iron-based amorphous microfilament catalysts are used in a flow electrolyzer, the cathode and anode regions are two interconnected electrolyzers. Both electrolyzers have outlets and inlets at the top and bottom, respectively. The electrolyte solution flows between the electrodes, and the interconnected parts are separated by a proton exchange membrane.

[0021] The iron-based amorphous microfilament catalyst used in this invention has significant advantages in the reduction of nitrate to ammonia. Compared with other catalysts, it has a wider range of applications.

[0022] More importantly, it can achieve ampere-level current at lower voltages, which greatly reduces reaction energy consumption. These characteristics demonstrate the advantages of this catalyst in terms of electron transfer and energy utilization efficiency.

[0023] The present invention has significant advantages over the prior art as follows:

[0024] 1. This invention prepares an iron-based amorphous microfilament catalyst with a diameter of 30 micrometers, effectively increasing the specific surface area of ​​the catalyst and significantly improving the current density, making it suitable for the reduction of nitrate to ammonia. This invention replaces commercial catalysts such as Pt with metastable metals, resulting in low cost and significantly improved catalyst activity. Ampere-level currents can be achieved at lower voltages, greatly reducing reaction energy consumption and enabling higher Faradaic efficiency and yield at room temperature and pressure. Furthermore, the generated ammonia gas can be collected during the reaction, achieving a combined production and collection process. 2. This method is simple to operate and can significantly improve yield and Faradaic efficiency while reducing costs, and allows for simultaneous production and collection. Attached Figure Description

[0025] Figure 1 The image shows a scanning electron microscope (SEM) image of the iron-based amorphous microfilament catalyst provided in the embodiment of the present invention. As can be seen from the image, there is only one glass layer on the outside of the iron-based amorphous microfilament, and the core diameter is about 30 μm.

[0026] Figure 2 The image shown is a transmission electron microscope (TEM) image of the iron-based amorphous microfilament catalyst provided in the embodiment of the present invention. The high-resolution image shows that the iron-based material in the core is amorphous.

[0027] Figure 3 The image shows the energy dispersive spectroscopy (EDS) pattern of the iron-based amorphous microfilament catalyst provided in this embodiment of the invention. As can be seen from the image, the seven elements are evenly distributed in the iron-based amorphous microfilament.

[0028] Figure 4 Linear voltammetric scans of the iron-based amorphous microfilament catalyst provided in the embodiments of the present invention at different nitrate concentrations.

[0029] Figure 5 The electrochemical stability diagram of the iron-based amorphous microfilament catalyst provided in the embodiments of the present invention at a current of 3A for 25 hours is shown.

[0030] Figure 6 This is the XRD pattern of the NH4Cl crystal obtained by acid absorption in this invention. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0032] This invention provides a method for preparing an electrocatalyst. The method involves preparing a master alloy rod using an electric arc melting method, with elements in an atomic ratio of Fe:Ni:Cr:Nb:B:P:Si = 63:6:6.5:1:13:6.5:4. The master alloy is placed inside a glass tube; it is softened by heating; the softened portion of the master alloy is then drawn through an inverted conical hole and pulled into a wire. After cooling and solidification, a glass-coated amorphous microfilament is formed. Electron microscopy scanning of the filament yields the following results: Figure 1 As shown.

[0033] The catalyst generated by this invention has a layer of high borosilicate glass on its surface, which needs to be soaked in HF acid. It is taken out of the acid every 30 seconds and observed under a light microscope until the glass layer is completely removed. Then it is rinsed three times with deionized water.

[0034] When used in an H-type electrolytic cell, the cathode and anode regions are two interconnected 50ml electrolytic cells, separated by a proton exchange membrane. When used in a flowing electrolytic cell, the cathode and anode regions are two specially designed interconnected electrolytic cells (both have inlets and outlets at the top and bottom, and the electrolyte solution flows between the electrodes), also separated by a proton exchange membrane. After the electrolyte flows out from the outlet, it passes through a capillary tube where NH3 overflows and is absorbed by the acid.

[0035] The three electrodes used in this invention are: a working electrode is a catalyst, a counter electrode is a platinum electrode, and a reference electrode is a Hg / HgO electrode. The electrolyte solutions used are 1M sodium hydroxide solution and 0.1-2M sodium nitrate solution, and the applied voltage (vs. RHE) ranges from -0.28 to -1.08V.

[0036] Example 1

[0037] In an H-type electrolytic cell, a three-electrode system was used for the electrochemical reduction of nitrate. The working electrode was a catalyst, the counter electrode was a platinum electrode, and the reference electrode was a Hg / HgO electrode. The cathode electrolyte was 50 mL of sodium nitrate (1 mol / L) and sodium hydroxide (1 mol / L) solution, and the anolyte was 50 mL of sodium hydroxide (1 mol / L) solution. Electrolysis was performed at a constant potential at -0.88 V for five hours. The nitrate to ammonia reduction efficiency was 85.9%, with a yield of 26.4 mmol / h / cm³. 2 .

[0038] Example 2

[0039] In an H-type electrolytic cell, a three-electrode system was used for the electrochemical reduction of nitrate. The working electrode was a catalyst, the counter electrode was a platinum electrode, and the reference electrode was a Hg / HgO electrode. The cathode electrolyte was 50 mL of sodium nitrate (1 mol / L) and sodium hydroxide (1 mol / L) solution, and the anolyte was 50 mL of sodium hydroxide (1 mol / L) solution. Electrolysis was performed at a constant potential at -1.08 V for five hours. The reduction of nitrate to ammonia achieved a Faraday efficiency of 80%, with a yield of 22.4 mmol / h / cm³. 2 .

[0040] Example 3

[0041] Electrochemical reduction of nitrate was performed in an H-type electrolytic cell using a three-electrode system. The working electrode was a catalyst, the counter electrode was a platinum electrode, and the reference electrode was a Hg / HgO electrode. The cathode electrolyte consisted of 50 mL of sodium nitrate (0.5 mol / L) and sodium hydroxide (1 mol / L) solution, while the anolyte consisted of 50 mL of sodium hydroxide (1 mol / L) solution. Electrolysis was performed at a constant potential at -0.68 V for five hours. The reduction of nitrate to ammonia achieved a Faraday efficiency of 85.24% and a yield of 10.4 mmol / h / cm³. 2 .

[0042] Example 4

[0043] In an H-type electrolytic cell, a three-electrode system was used for the electrochemical reduction of nitrate. The working electrode was a catalyst, the counter electrode was a platinum electrode, and the reference electrode was a Hg / HgO electrode. The cathode electrolyte was 50 mL of sodium nitrate (0.1 mol / L) and sodium hydroxide (1 mol / L) solution, and the anolyte was 50 mL of sodium hydroxide (1 mol / L) solution. Electrolysis was performed at a constant potential at -1.08 V for five hours. The nitrate to ammonia reduction efficiency was 52.15%, with a yield of 4.5 mmol / h / cm³. 2 .

[0044] Example 5

[0045] In an H-type electrolytic cell, a three-electrode system was used for the electrochemical reduction of nitrate. The working electrode was a catalyst, the counter electrode was a platinum electrode, and the reference electrode was a Hg / HgO electrode. The cathode electrolyte was 50 mL of sodium nitrate (1 mol / L) and sodium hydroxide (1 mol / L) solution, and the anolyte was 50 mL of sodium hydroxide (1 mol / L) solution. Electrolysis was performed at a constant potential at -0.88 V for five hours. The nitrate to ammonia reduction efficiency was 82.7%, and the yield was 17.9 mmol / h / cm³. 2 .

[0046] Example 6

[0047] Electrochemical reduction of nitrate was performed in an H-type electrolytic cell using a three-electrode system. The working electrode was a catalyst, the counter electrode was a platinum electrode, and the reference electrode was a Hg / HgO electrode. The cathode electrolyte consisted of 50 mL of a 1 mol / L sodium nitrate and a 1 mol / L sodium hydroxide solution, while the anolyte consisted of 50 mL of a 1 mol / L sodium hydroxide solution. Electrolysis was carried out at a high current of 3 A / cm² for 25 hours, yielding a yield of 10.2 mmol / h / cm². 2 .

[0048] Example 7

[0049] In an H-type electrolytic cell, a three-electrode system was used for the electrochemical reduction of nitrate. The working electrode was a catalyst, the counter electrode was a platinum electrode, and the reference electrode was a Hg / HgO electrode. Under sulfate interference, the cathode electrolyte consisted of 50 ml of sodium nitrate (1 mol / L) and sodium hydroxide (1 mol / L) solution, and the anolyte consisted of 50 ml of sodium hydroxide (1 mol / L) solution. Electrolysis was performed at a constant potential of -0.68 V for five hours. The nitrate to ammonia reduction efficiency was 60.32%, with a yield of 10.37 mmol / h / cm³. 2 .

[0050] Example 8

[0051] In a flowing electrolytic cell, a three-electrode system was used for the electrochemical reduction of nitrate. The working electrode was a catalyst, the counter electrode was a platinum electrode, and the reference electrode was a Hg / HgO electrode. The cathode electrolyte consisted of 50 ml of sodium nitrate (1 mol / L) and sodium hydroxide (1 mol / L) solution, and the anolyte consisted of 50 ml of sodium hydroxide (1 mol / L) solution. Electrolysis was performed at a constant potential of -0.88 V for five hours. After the electrolyte flowed out of the outlet, it passed through a capillary tube where NH3 overflowed and was absorbed by the acid, achieving a combined collection and generation process. Figure 6 As shown, after absorbing the hydrochloric acid solution, it is placed in an oven and dried at 80°C for 12 hours to obtain ammonium salt solid powder. XRD verification shows that the crystalline powder is ammonium chloride.

[0052] Table 1 shows the Faraday efficiency and yield of ammonia production by the iron-based amorphous microfilament catalyst provided in the embodiments of the present invention.

[0053] Table 1

[0054]

[0055]

[0056] The above description is merely the preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An iron-based amorphous microfilament catalyst, characterized in that, In the iron-based amorphous microfilament catalyst, the microstructure has an amorphous state with a diameter of 20-30 μm, and the diameter is on the micrometer scale. In this iron-based amorphous microfilament material structure, iron-based amorphous metal wires serve as the core, and are further encapsulated by a high borosilicate glass coating layer. The iron-based amorphous microfilament catalyst exists in Fe alloy form. 63 Ni6Cr 6.5 Nb1B 13 P 6.5 Si4.

2. The iron-based amorphous microfilament catalyst according to claim 1, characterized in that, The preparation process of iron-based amorphous microfilament catalysts includes the following steps: S1. Preparation of amorphous alloy master alloy rods by electric arc melting; S2. Place the master alloy inside a glass tube; soften the master alloy by heating; draw the softened master alloy through an inverted conical hole and then draw it into a wire; after cooling and solidification, form an amorphous micron filament.

3. A method for preparing ammonia by electrochemical reduction of nitric acid based on any one of the iron-based amorphous microfilament catalysts according to claims 1-2, characterized in that, Ammonia is produced by electrochemical reduction of an iron-based amorphous micron-fiber catalyst in an electrolyte solution within a three-electrode electrolytic cell at a relatively low voltage.

4. The method for preparing ammonia by electrochemical reduction of nitric acid using the iron-based amorphous micron-fiber catalyst according to claim 3, characterized in that, In a three-electrode system, the electrolytic cell includes either an H-type electrolytic cell or a flow electrolytic cell, both of which include an anode region, a cathode region, a proton exchange membrane, and an electrolyte solution.

5. The method for preparing ammonia by electrochemical reduction of nitric acid using the iron-based amorphous micron-fiber catalyst according to claim 4, characterized in that, When iron-based amorphous microfilament catalysts are used in H-type electrolytic cells, the cathode region and the anode region are composed of two interconnected electrolytic cells, and the interconnected parts are separated by a proton exchange membrane. When iron-based amorphous microfilament catalysts are used in a flow electrolyzer, the cathode and anode regions are two interconnected electrolyzers. Both electrolyzers have outlets and inlets at the top and bottom, respectively. The electrolyte solution flows between the electrodes, and the interconnected parts are separated by a proton exchange membrane.

6. The method for preparing ammonia by electrochemical reduction of nitric acid using the iron-based amorphous micron-fiber catalyst according to claim 3, characterized in that, The electrolyte solution can be neutral or alkaline; specifically, the nitrate concentration ranges from 0.1M (low concentration) to 2M (high concentration) and 1M sodium hydroxide solution.

7. The method for preparing ammonia by electrochemical reduction of nitric acid using the iron-based amorphous micron-fiber catalyst according to claim 3, characterized in that, The low voltage range is -0.28 ~ -1.08V.

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