Electroreduction method for synthesizing acetamide by coupling carbon dioxide and nitrate through electrocatalysis

Abstract

The invention relates to an electroreduction method for synthesizing acetamide by coupling carbon dioxide and nitrate through electrocatalysis. The electroreduction method specifically comprises the steps that cobalt salt, copper salt, a nitrogen source and carbon source carbon black are mixed, heated and calcined, and a carbon nitride loaded copper-cobalt diatomic catalyst is prepared; loading the obtained carbon nitride loaded copper-cobalt diatomic catalyst on the surface of carbon paper to prepare a gas diffusion electrode of a three-chamber flow cell electrolytic tank; the obtained gas diffusion electrode is applied to a three-chamber flow cell electrolytic tank to prepare acetamide through electroreduction. The copper-cobalt double-atom catalyst is used for synthesizing acetamide through electrochemical coupling of carbon dioxide and nitrate, the acetamide Faraday efficiency in a flow cell can reach 18% or above, and the yield is 81.2 mg L <-1 >. H <-1 >. Compared with the prior art, the prepared copper-cobalt diatomic catalyst has high selectivity for generation of acetamide through co-reduction coupling of carbon dioxide and nitrate radicals, and synchronous treatment of greenhouse gas carbon dioxide and nitrate wastewater and value-increasing utilization of carbon and nitrogen resources can be achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalysis, and in particular to an electroreduction method for electrocatalytically coupling carbon dioxide and nitrate to synthesize acetamide. Background Art

[0002] Carbon dioxide is a major greenhouse gas. Since the Industrial Revolution, the atmospheric carbon dioxide concentration has been increasing year by year. Its excessive emissions have led to global warming, rising sea levels, extreme weather events, and hindered the sustainable development of society. Traditional carbon dioxide emission reduction technologies (such as carbon capture and storage) are costly, have leakage risks, and low economic benefits. As an abundant carbon source, CO2 can be catalytically converted to synthesize fuels such as methane and methanol or other high-value-added chemicals (such as formic acid, ethylene, ethanol, etc.). Among them, the electrocatalytic CO2 reduction technology has become a widely studied carbon reduction and value-added strategy due to its mild reaction conditions, environmental friendliness, product orientation controllability, and the ability to be driven by renewable energy. However, existing technologies only utilize CO2 as a single reactant, and the reduction products are limited to C1 products such as CO and formic acid or multi-carbon compounds such as ethanol and acetic acid, and the added value of the products needs to be further improved.

[0003] Nitrate pollution caused by agricultural fertilizer runoff, industrial production, soil organic matter nitrification, and domestic sewage discharge has received wide attention. Its excessive emissions can lead to eutrophication of water bodies, algal blooms such as blue-green algae, and seriously damage the aquatic ecosystem; excessive nitrate concentration in drinking water may cause "blue baby syndrome" and a higher cancer risk, threatening human health. Traditional nitrate treatment technologies such as denitrification are widely used, but they require an external organic carbon source, increasing the treatment cost, and are prone to by-product accumulation and secondary pollution, and the denitrification efficiency is inhibited by nitrate concentration and salinity. The electrocatalytic nitrate reduction technology can achieve efficient and selective conversion of both high-concentration and low-concentration nitrate wastewater, and the reaction path is easy to regulate, effectively avoiding the generation of highly toxic by-products and intermediate products. It is a green and efficient denitrification method. However, it only solves the pollution problem or produces a single ammonia product, and fails to utilize the potential value of nitrogen in nitrate in the synthesis of nitrogen-containing chemicals such as urea and amide.

[0004] Acetamide is an excellent solvent and an important organic synthesis raw material, which plays a key role in drug synthesis, pesticide synergism, dye preparation, cosmetic pH adjustment, etc., and has high industrial application value. Currently, the mainstream industrial synthesis method of acetamide is through the reaction of acetic acid and ammonia under high temperature and high pressure conditions. Although the yield is relatively high, the process has high energy consumption and relies on petroleum-based acetic acid raw materials, which is not sustainable. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides an electroreduction method for electrocatalytically coupling carbon dioxide and nitrate to synthesize acetamide. By designing and constructing a copper-cobalt dual-atom catalytic site for the co-reduction of CO2 and nitrate, it selectively reduces them to carbon-based and nitrogen-based reaction intermediates on the dual atoms respectively, and then undergoes C-N bond formation to synthesize acetamide. Applying this electrocatalyst to a flow cell reactor can accelerate the nitrate reduction rate under continuous flow, and at the same time improve the mass transfer rate of CO2 to the catalyst surface through a gas diffusion electrode, realizing the high-yield synthesis of acetamide.

[0006] The purpose of the present invention is to provide an electroreduction method for electrocatalytically coupling carbon dioxide and nitrate to synthesize acetamide, including the following steps:

[0007] Mix and heat-calcine a cobalt salt, a copper salt, a nitrogen source, and a carbon source to prepare a copper-cobalt dual-atom catalyst supported on carbon nitride;

[0008] Load the obtained copper-cobalt dual-atom catalyst supported on carbon nitride onto the surface of carbon paper to prepare a gas diffusion electrode for a three-compartment flow cell electrolyzer;

[0009] Place the obtained gas diffusion electrode and titanium mesh as the cathode and anode respectively above the serpentine flow channels of the cathode gas chamber and the anode liquid chamber, insert a saturated calomel electrode as the reference electrode into the middle cavity, introduce CO2 into the cathode flow channel through the cathode gas chamber inlet, and then diffuse it to the catalyst surface through the gas diffusion electrode to participate in the reaction; wherein, a solution containing nitrate and electrolyte circulates in the middle cathode liquid chamber through a peristaltic pump; the anode electrolyte solution circulates in the anode liquid chamber through a peristaltic pump; apply a constant potential to conduct an electrolysis experiment to synthesize the acetamide.

[0010] In some embodiments of the present invention, the cobalt salt is selected from one or more of cobalt acetate, cobalt nitrate, and cobalt chloride.

[0011] In some embodiments of the present invention, the copper source is selected from one or more of copper acetate, copper nitrate, copper sulfate, and copper chloride.

[0012] In some embodiments of the present invention, the nitrogen source is selected from urea and / or melamine; the carbon source is selected from one or more of carbon black, melamine, and carbon nanotubes.

[0013] In some embodiments of the present invention, the mass ratio of the cobalt salt to the copper salt is (1:2) to (2:1); the mass ratio of the nitrogen source to the carbon source is (1:20) to (1:5).

[0014] In some embodiments of the present invention, the temperature of the heat-calcination is 800 to 1000 °C.

[0015] In some embodiments of the present invention, the electrolyte is selected from one or more of KOH, KHCO3, and NaOH.

[0016] In some embodiments of the present invention, the concentration of nitrate is 0.005 - 0.1 M, and the flow rate of CO2 introduced is 10 - 50 sccm.

[0017] In some embodiments of the present invention, the current density of the electroreduction is 30 - 100 mA·cm -2 。

[0018] In some embodiments of the present invention, the range of the constant potential is -1.4 to -2.4 V vs. SCE.

[0019] Specific usage method of the catalyst of the present invention:

[0020] I. Disperse 4 mg of the catalyst in 200 μL of ethanol, 200 μL of deionized water, and 20 μL of Nafion perfluorinated resin solution, and ultrasonically treat for 1 hour; the obtained catalyst ink is dropped onto a 2×2 cm carbon paper gas diffusion layer to make the catalyst loading reach 1 mg per square centimeter, thereby preparing a gas diffusion electrode.

[0021] II. The electrocatalytic coupling experiment of CO2 and nitrate is carried out under a three - electrode system in a customized three - chamber flow cell. The flow cell is composed of two titanium plates with 2×2 cm serpentine flow channels, which are used as the cathode gas chamber and the anode liquid chamber respectively. A liquid chamber made of PEEK (polyether ether ketone) is sandwiched between them as the cathode liquid chamber. Hoses are connected to both the left and right ends of the three parts for gas / liquid inlet and outlet, and the three modules are separated by fluororubber gaskets. The obtained gas diffusion electrode and titanium mesh are used as the cathode and anode respectively and placed on the serpentine flow channels of the cathode gas chamber and the anode liquid chamber. A saturated calomel electrode is inserted into the middle chamber as the reference electrode. CO2 is introduced into the cathode flow channel through the cathode gas chamber inlet, and then diffuses through the gas diffusion electrode to the catalyst surface to participate in the reaction; the solution containing nitrate and electrolyte circulates in the middle cathode liquid chamber through a peristaltic pump; the anode electrolyte solution circulates in the anode liquid chamber through a peristaltic pump.

[0022] III. The electrochemical experiment of the present invention is realized through an electrochemical workstation. The cathode is the working electrode, the anode is the counter electrode, and the saturated calomel electrode is the reference electrode. A constant potential is applied for the electrolysis experiment. After the reaction, the product is collected in the cathode liquid chamber and quantitatively detected by a nuclear magnetic resonance spectrometer.

[0023] The copper-cobalt dual-atom catalyst prepared by the present invention has excellent adsorption and activation functions for both carbon dioxide and nitrate as reactants. Its selectivity for acetamide products mainly involves the reduction of CO2 to ketene intermediates by copper sites, and the copper-cobalt atoms synergistically promote the reduction transformation of nitrate to ammonia. The locally high concentration of ammonia on the catalyst surface nucleophilically attacks the ketene intermediate to form a C-N bond, and then acetamide is generated. When this dual-atom catalyst is applied to the electrocatalytic C-N coupling to synthesize acetamide, it exhibits high electrocatalytic performance. In a flow cell electrolytic cell, with 0.5 mol / L potassium hydroxide as the electrolyte, the Faraday efficiency of acetamide can reach up to 18.1%, and the maximum acetamide yield is 81.2 mg L -1 ·h -1 . This invention provides a technical and theoretical basis for promoting the industrial application of electrocatalytic acetamide synthesis.

[0024] The above technical solution of the present invention has the following advantages compared with the prior art:

[0025] 1) By using the method of the present invention, the greenhouse gas CO2 and the water environment pollutant nitrate can be treated simultaneously, achieving the purpose of turning waste into treasure and killing two birds with one stone.

[0026] 2) The present invention can achieve the green synthesis of high-value-added acetamide products, with no secondary pollution during the process and being environmentally friendly.

[0027] 3) The method of the present invention is easy to operate, easy to scale up and apply to industrial production. Description of the Drawings

[0028] In order to make the content of the present invention easier to be clearly understood, the following further details the present invention according to the specific embodiments of the present invention and in combination with the drawings, where

[0029] Figure 1 is the scanning electron microscope image of the copper-cobalt dual-atom catalyst in Example 1 of the present invention;

[0030] Figure 2 is the Faraday efficiency and current density of the copper-cobalt dual-atom catalyst in Example 1 of the present invention for electrocatalytic coupling of CO2 and nitrate to synthesize acetamide in a flow cell electrolytic cell;

[0031] Figure 3 is the yield of the copper-cobalt dual-atom catalyst in Example 1 of the present invention for electrocatalytic coupling of CO2 and nitrate to synthesize acetamide in a flow cell electrolytic cell;

[0032] Figure 4 is the device diagram of the three-compartment flow cell electrolytic cell used in the present invention, and this device is a conventional three-compartment flow cell electrolytic cell in the art. Detailed Embodiments

[0033] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the specific embodiments cited do not limit the present invention.

[0034] Example 1

[0035] This example provides a catalytic material and an electroreduction method for the electrocatalytic coupling of carbon dioxide and nitrate to synthesize acetamide, which are specifically as follows:

[0036] I. Preparation of the catalytic material:

[0037] Weigh 12.5 mg of cobalt acetate, 10.0 mg of copper acetate, 30 mg of urea and 400 mg of carbon black, dissolve them in 50 mL of absolute ethanol, ultrasonically stir for 4 hours, heat the mixture in an oil bath at 60 °C and continuously stir until the solvent is completely evaporated. The obtained black solid is ground and placed in a tubular furnace. Under a constant-temperature argon bath, it is continuously heated and reacted at 800 °C for 3 hours. After the reaction, it is cooled to room temperature to obtain a copper-cobalt dual-atom catalyst supported on carbon nitride.

[0038] II. Structure characterization: The obtained copper-cobalt dual-atom catalyst is subjected to structure characterization, and the results are shown in Figure 1 the scanning electron microscope. As can be seen from the figure, the nanoparticle structure of carbon black after pyrolysis is retained, and no obvious metal clusters are observed.

[0039] III. Electroreduction method:

[0040] In a three-compartment flow cell electrolytic cell at room temperature, using 0.5 M KOH as the electrolyte, the nitrate concentration is 0.02 M, and the current density is 70 mA cm -2 , specifically as follows:

[0041] I. Disperse 4 mg of the copper-cobalt dual-atom catalyst supported on carbon nitride in 200 μL of ethanol, 200 μL of deionized water and 20 μL of Nafion perfluorinated resin solution, and ultrasonically treat for 1 hour; the obtained catalyst suspension is dropped onto a 2×2 cm carbon paper gas diffusion layer to make the catalyst loading reach 1 mg per square centimeter, thereby preparing a gas diffusion electrode.

[0042] II. The electrocatalytic CO2 and nitrate coupling experiment was carried out under a three-electrode system in a customized three-compartment flow cell. The flow cell consists of two titanium plates with 2×2 cm serpentine flow channels, which are used as the cathode gas chamber and the anode liquid chamber respectively. A liquid chamber made of PEEK (polyether ether ketone) is sandwiched between them as the cathode liquid chamber. Hoses are connected to both the left and right ends of the three components for gas / liquid inlet and outlet, and the three modules are separated by fluororubber gaskets. The obtained gas diffusion electrode and titanium mesh are used as the cathode and anode respectively and placed on the serpentine flow channels of the cathode gas chamber and the anode liquid chamber. The saturated calomel electrode is used as the reference electrode and inserted into the middle chamber. CO2 is introduced into the cathode flow channel through the inlet of the cathode gas chamber, and then diffuses through the gas diffusion electrode to the catalyst surface to participate in the reaction. The solution containing nitrate and electrolyte (0.5M KOH) circulates in the middle cathode liquid chamber through a peristaltic pump. The anode electrolyte solution (0.5M KOH) circulates in the anode liquid chamber through a peristaltic pump.

[0043] III. The electrochemical experiment of the present invention is realized through an electrochemical workstation. The cathode is the working electrode, the anode is the counter electrode, and the saturated calomel electrode is the reference electrode. A constant potential of -1.8V vs. SCE is applied for the electrolysis experiment. After the reaction, the products are collected in the cathode liquid chamber and quantitatively detected by a nuclear magnetic resonance spectrometer. The experimental results are shown in Figure 2 、 3 and it can be known from Figure 2 that the Faraday efficiency of acetamide can reach up to 18.1%, indicating that the catalyst of the present invention has good selectivity for acetamide. Figure 3 It can be known from -1 that the yield of acetamide can reach 81.2 mg L -1 h

[0044] Example 2

[0045] Weigh 21.8 mg of cobalt nitrate, 18.2 mg of copper nitrate, 45 mg of urea and 600 mg of carbon black and dissolve them in 75 mL of absolute ethanol. Ultrasonic and stir for 4 hours. Heat the mixture in an oil bath at 60 °C and continue stirring until the solvent is completely evaporated. The obtained black solid is ground and placed in a tubular furnace. Under a constant temperature argon bath, heat and react at 900 °C for 3 hours. After the reaction, cool to room temperature to obtain a copper-cobalt dual-atom catalyst supported on carbon nitride.

[0046] Example 3

[0047] Weigh 17.4 mg of cobalt nitrate, 15.0 mg of copper sulfate, 36 mg of urea, and 480 mg of carbon black, dissolve them in 60 mL of absolute ethanol, sonicate and stir for several hours. Heat the mixture in an oil bath at 60 °C and continuously stir until the solvent is completely evaporated. Grind the obtained black solid and place it in a tube furnace. Under a constant-temperature argon bath, continuously heat and react at 1000 °C for 2 hours. After the reaction, cool it to room temperature to obtain a copper-cobalt dual-atom catalyst supported on carbon nitride.

[0048] Example 4

[0049] Weigh 9.2 mg of cobalt chloride, 11.9 mg of copper chloride, 42 mg of urea, and 560 mg of carbon black, dissolve them in 70 mL of absolute ethanol, sonicate and stir for several hours. Heat the mixture in an oil bath at 60 °C and continuously stir until the solvent is completely evaporated. Grind the obtained black solid and place it in a tube furnace. Under a constant-temperature argon bath, continuously heat and react at 800 °C for 2 hours. After the reaction, cool it to room temperature to obtain a copper-cobalt dual-atom catalyst supported on carbon nitride.

[0050] Example 5

[0051] Weigh 24.9 mg of cobalt acetate, 24.2 mg of copper nitrate, 60 mg of urea, and 800 mg of carbon black, dissolve them in 100 mL of absolute ethanol, sonicate and stir for several hours. Heat the mixture in an oil bath at 60 °C and continuously stir until the solvent is completely evaporated. Grind the obtained black solid and place it in a tube furnace. Under a constant-temperature argon bath, continuously heat and react at 850 °C for 2 hours. After the reaction, cool it to room temperature to obtain a copper-cobalt dual-atom catalyst supported on carbon nitride.

[0052] It can be seen from the above examples that the copper-cobalt dual-atom catalyst prepared by the present invention can achieve the electrochemical co-reduction of carbon dioxide and nitrate ions. The adjacent active sites promote the coupling and bonding of carbon-based intermediates and nitrogen-based intermediates, realizing the selective generation of acetamide products.

[0053] Comparative Example 1 (single-atom cobalt catalyst)

[0054] Weigh 25.0 mg of cobalt acetate, 30 mg of urea, and 400 mg of carbon black, dissolve them in 50 mL of absolute ethanol, sonicate and stir for several hours. Heat the mixture in an oil bath at 60 °C and continuously stir until the solvent is completely evaporated. Grind the obtained black solid and place it in a tube furnace. Under a constant-temperature argon bath, continuously heat and react at 800 °C for 3 hours. After the reaction, cool it to room temperature to obtain a cobalt single-atom catalyst supported on carbon nitride. Applied to the electrocatalytic coupling reaction of CO2 and nitrate ions, the Faraday efficiency of synthesizing acetamide is 3.3%, and the acetamide yield is 10.1 mg L -1 h -1 。

[0055] Comparative Example 2 (Single-atom copper catalyst)

[0056] Weigh 20.0 mg of copper acetate, 30 mg of urea and 400 mg of carbon black, dissolve them in 50 mL of absolute ethanol, sonicate and stir for several hours. Heat the mixture in an oil bath at 60 °C and continue stirring until the solvent completely evaporates. Grind the obtained black solid and place it in a tubular furnace. Under a constant-temperature argon bath, heat and react continuously at 800 °C for 3 hours. After the reaction, cool to room temperature to obtain a carbon nitride-supported single-atom copper catalyst. Applied to the electrocatalytic coupling reaction of CO2 and nitrate, the Faradaic efficiency for the synthesis of acetamide is 6.2%, and the acetamide yield is 21.7 mg L -1 h -1 。

[0057] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation modes. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to enumerate all the implementation modes here. And the obvious changes or variations derived therefrom are still within the protection scope of the present invention.

Claims

1. An electroreduction method for the electrocatalytic coupling of carbon dioxide and nitrate to synthesize acetamide, characterized in that, It includes the following steps: Mix cobalt salt, copper salt, nitrogen source and carbon source and heat them by calcination to prepare a copper-cobalt dual-atom catalyst supported on carbon nitride; Load the obtained copper-cobalt dual-atom catalyst supported on carbon nitride on the surface of carbon paper to prepare a gas diffusion electrode of a three-chamber flow cell electrolyzer; Respectively place the obtained gas diffusion electrode and titanium mesh as the cathode and anode above the serpentine flow channels of the cathode gas chamber and the anode liquid chamber. The saturated calomel electrode is inserted into the middle cavity as a reference electrode. CO2 is introduced into the cathode flow channel through the cathode gas chamber inlet, and then diffuses to the catalyst surface through the gas diffusion electrode to participate in the reaction; wherein, the solution containing nitrate and electrolyte circulates in the middle cathode liquid chamber through a peristaltic pump; the anode electrolyte solution circulates in the anode liquid chamber through a peristaltic pump; Apply a constant potential to conduct an electrolysis experiment to synthesize the acetamide.

2. The electroreduction method according to claim 1, characterized in that, The cobalt salt is selected from one or more of cobalt acetate, cobalt nitrate, and cobalt chloride.

3. The electroreduction method according to claim 1, wherein, The copper source is selected from one or more of copper acetate, copper nitrate, copper sulfate, and copper chloride.

4. The electroreduction method according to claim 1, characterized in that The nitrogen source is selected from urea and / or melamine; the carbon source is selected from one or more of carbon black, melamine, and carbon nanotubes.

5. The electroreduction method according to claim 1, wherein The mass ratio of the cobalt salt to the copper salt is (1:2) to (2:1); the mass ratio of the nitrogen source to the carbon source is (1:20) to (1:5); The loading amount of the copper-cobalt dual-atom catalyst supported on carbon nitride in the gas diffusion electrode is 0.5 mg / cm 2 ~5 mg / cm 2 .

6. The electroreduction method according to claim 1, characterized in that, The temperature of the heating calcination is 800 to 1000 °C.

7. The electroreduction method according to claim 1, wherein The electrolyte solution is selected from one or more of KOH, KHCO3, and NaOH.

8. The electroreduction method according to claim 1, wherein The concentration of nitrate is 0.005 to 0.1 M; the flow rate of the introduced CO2 is 10 to 50 sccm.

9. The electroreduction method according to claim 1, wherein The current density of electroreduction is 30 to 100 mA·cm -2 .

10. The electroreduction method according to claim 1, wherein The range of the constant potential is -1.4 to -2.4 V vs. SCE.

Images