Method for preparing formic acid by electrocatalytic conversion of methane and oxygen

Abstract

The invention discloses a method for preparing formic acid by electrocatalytic conversion of methane and oxygen. A double-cell high-voltage electrochemical reaction device is utilized, a catalytic material is used as a working electrode, an electrolyte solution is added into a cathode cell and an anode cell, a ferrous compound is added into the cathode cell, methane, oxygen and argon mixed gas is introduced, reduction potential is applied, and methane and oxygen are electrically converted at room temperature to prepare formic acid. The method shows relatively high HCOOH yield and Faraday efficiency, is good in cycling stability and has a relatively good industrial application prospect.

Description

Technical Field

[0001] The present invention relates to a method for electrochemically converting methane and oxygen to formic acid under high reaction pressure, belonging to the fields of chemistry and chemical engineering. Background Art

[0002] Natural gas is a clean and high-quality energy source, and its main component is methane (CH4). Therefore, the direct conversion of CH4 to transportable liquid fuels or chemicals is crucial for the natural gas industry. However, due to the high bond energy of the C-H bond in CH4, which is as high as 104 kcal mol -1 , and its highly symmetric tetrahedral structure, the direct conversion of methane molecules is extremely challenging. The non-oxidative conversion of CH4 molecules generally requires reaction at high temperatures above 600 °C, and there are problems such as catalyst carbon deposition, low selectivity of target products, and high energy consumption. The direct oxidation of CH4 molecules using highly reactive oxygen-containing species to prepare oxygen-containing chemicals can convert CH4 at low temperatures below 200 °C. However, the generation of highly reactive oxygen-containing species usually requires corrosive or expensive oxidants, such as fuming sulfuric acid, ozone, or hydrogen peroxide.

[0003] Electrocatalysis can be a potential method for the conversion of CH4 to liquid fuels. Existing studies have shown that an overpotential of more than 1.5 V needs to be applied at the anode for the CH4 electroconversion reaction to achieve CH4 oxidation, and there are problems such as high energy consumption and serious oxygen evolution side reactions in this process, resulting in very low efficiency. Therefore, it is crucial to develop a new method for efficient CH4 electroconversion. Summary of the Invention

[0004] The present invention aims to provide a method for electrocatalytically converting CH4 and oxygen (O2) to formic acid (HCOOH), which exhibits a high HCOOH yield and Faraday efficiency, and good cycle stability.

[0005] The specific steps of the present invention are as follows:

[0006] A method for electrocatalytically converting CH4 and O2 to formic acid, comprising: using a two-compartment high-voltage electrochemical reaction device, with a catalytic material as the working electrode, adding an electrolyte solution to the cathode compartment and the anode compartment, adding a compound of divalent iron to the cathode compartment, introducing a mixed gas of CH4, O2, and argon (Ar), and applying a reduction potential to achieve the electroconversion of CH4 and O2 to formic acid.

[0007] Further, in the above technical solution, the catalytic material includes at least one of silver, gold, platinum, palladium foil, and their alloy foils.

[0008] Further, in the above technical solution, the iron-containing compound includes at least one of ferrous sulfate, ferrous perchlorate, ferrous nitrate, ferrous oxalate, and ferrous acetylacetonate.

[0009] Furthermore, in the above technical solution, the reaction is carried out under a high reaction pressure, and the total pressure of the CH4, O2, and Ar mixed gas is 1 - 8 MPa, and the preferred pressure is 4 MPa.

[0010] Furthermore, in the above technical solution, the volume percentage of CH4 in the CH4, O2, and Ar mixed gas is 30 - 95%, the volume percentage of oxygen is 0.1 - 10%, and the balance is Ar; the preferred gas volume fraction is 90% CH4, 5% O2, and 5% Ar.

[0011] Furthermore, in the above technical solution, the electrolyte solution includes at least one of HClO4, H2SO4, NaHSO4, LiSO4 (pH = 1 - 4, preferably 3), Na2SO4 (pH = 1 - 4, preferably 3), and K2SO4 (pH = 1 - 4, preferably 3) solutions.

[0012] Furthermore, in the above technical solution, the concentration of the electrolyte solution is 0.01 - 2 mol / L, preferably 0.2 mol / L.

[0013] Furthermore, in the above technical solution, the concentration of the divalent iron compound in the electrolyte is 0.05 - 50 mmol / L, preferably 2 mmol / L.

[0014] Furthermore, in the above technical solution, a platinum wire electrode is used as the counter electrode, the counter electrode is in the anodic cell, and the working electrode is in the cathodic cell.

[0015] Furthermore, in the above technical solution, a saturated Ag / AgCl electrode is used as the reference electrode, and the reference electrode is in the cathodic cell.

[0016] Furthermore, in the above technical solution, the reduction potential is -0.5 V - 0.5 V vs. RHE, the time is 0.1 - 24 hours, preferably 8 hours, the rotor speed is 50 - 600 r / min, preferably 600 r / min, and the working electrode area is 0.5 - 30 cm -2 , preferably 10 cm -2 , and the reaction temperature is 1 - 80 °C, preferably 25 °C.

[0017] The present invention electrochemically converts CH4 and O2 to prepare HCOOH by using the above method.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] (1) The present invention exhibits excellent performance in the electroconversion of CH4 to produce HCOOH. Under the reaction conditions of a total gas pressure of 4 MPa, 25 °C, and an applied voltage of 0.2 V vs. RHE, the HCOOH yield is as high as 9.1 mmol g Fe -1 h -1 , and the Faraday efficiency of HCOOH is as high as 78.8%, and the current density is 1.67 mA cm -2 .

[0020] (2) By increasing the pressure of O2, the solubility of O2 in the electrolyte solution is increased, promoting the H2O2 yield. By increasing the pressure of CH4, the solubility of CH4 in the electrolyte solution is increased, thereby promoting the collision probability between CH4 and ·OH.

[0021] In summary, using this method, CH4 and O2 can be efficiently converted into HCOOH, and the catalyst has good cycle stability, showing broad application prospects. Detailed implementation mode

[0022] The method for electroconverting CH4 and O2 to produce HCOOH under high reaction pressure provided by the present invention is further described in detail below. However, the scope of the claims of the present invention is not limited by these examples. At the same time, the examples only give some of the conditions for achieving this purpose, but it does not mean that these conditions must be met to achieve this purpose.

[0023] Example 1

[0024] Using a two-compartment high-pressure electrochemical reaction device, which includes a reaction kettle body, a reaction kettle cover, and an inner and outer pool of the reaction kettle. The inner and outer pools are separated by a proton exchange membrane. A high-pressure reference electrode, a counter electrode, a working electrode, a gas conduit, and a thermocouple sleeve are embedded in the kettle cover (the application publication number of the device: CN 113529115 A), and a 10 cm 2 silver foil is fixed on the working electrode, a platinum wire electrode is used as the counter electrode, and a saturated Ag / AgCl electrode is used as the reference electrode. The working electrode and the reference electrode are in the outer pool, and the counter electrode is in the inner pool. 80 ml of 0.1 M HClO4 and 2 mM FeSO4 are added as the outer pool electrolyte solution, and 10 ml of 0.1 M HClO4 is added as the inner pool electrolyte solution. A mixture of O2 and Ar (O2 / Ar = 1 / 1) is introduced into the high-pressure reaction kettle, and the air in the system is discharged by replacement three times. Subsequently, 0.4 MPa of O2 and Ar (O2 / Ar = 1 / 1) are respectively charged, and then 3.6 MPa of CH4 gas is charged, and the mixture is stirred at a speed of 600 r / min at 25 °C. Connect a three-electrode electrochemical workstation, and electrolyze for 8 hours at a constant voltage of 0.2 V vs. RHE potential. The electrolysis products are analyzed by NMR and gas chromatography, and the specific reaction performance is listed in Table 1.

[0025] Example 2

[0026] Using a dual - cell high - pressure electrochemical reaction device, which includes a reaction kettle body, a reaction kettle cover, and the inner and outer cells of the reaction kettle. The inner and outer cells are separated by a proton exchange membrane. The kettle cover is embedded with a high - pressure reference electrode, a counter electrode, a working electrode, a gas conduit, and a thermocouple sleeve (device application publication number: CN 113529115 A), 10 cm 2 A gold foil is fixed on the working electrode, a platinum wire electrode is used as the counter electrode, and a saturated Ag / AgCl electrode is used as the reference electrode. The working electrode and the reference electrode are in the outer cell, and the counter electrode is in the inner cell. Add 80 ml of 0.1 M HClO4 and 2 mM FeSO4 as the outer - cell electrolyte solution, and add 10 ml of 0.1 M HClO4 as the inner - cell electrolyte solution. Pass O2 and Ar (O2 / Ar = 1 / 1) into the high - pressure reaction kettle, and displace the air in the system three times. Subsequently, charge 0.4 MPa of O2 and Ar (O2 / Ar = 1 / 1) respectively, and then charge 3.6 MPa of CH4 gas. Stir at 25 °C at a speed of 600 r / min. Connect a three - electrode electrochemical workstation, electrolyze for 8 hours at a constant voltage of 0.2 V vs. RHE potential, and analyze the electrolysis products by NMR and gas chromatography. The specific reaction performance is listed in Table 1.

[0027] Example 3

[0028] Using a dual - cell high - pressure electrochemical reaction device, which includes a reaction kettle body, a reaction kettle cover, and the inner and outer cells of the reaction kettle. The inner and outer cells are separated by a proton exchange membrane. The kettle cover is embedded with a high - pressure reference electrode, a counter electrode, a working electrode, a gas conduit, and a thermocouple sleeve (device application publication number: CN 113529115 A), 10 cm 2 A platinum foil is fixed on the working electrode, a platinum wire electrode is used as the counter electrode, and a saturated Ag / AgCl electrode is used as the reference electrode. The working electrode and the reference electrode are in the outer cell, and the counter electrode is in the inner cell. Add 80 ml of 0.1 M HClO4 and 2 mM FeSO4 as the outer - cell electrolyte solution, and add 10 ml of 0.1 M HClO4 as the inner - cell electrolyte solution. Pass O2 and Ar (O2 / Ar = 1 / 1) into the high - pressure reaction kettle, and displace the air in the system three times. Subsequently, charge 0.4 MPa of O2 and Ar (O2 / Ar = 1 / 1) respectively, and then charge 3.6 MPa of CH4 gas. Stir at 25 °C at a speed of 600 r / min. Connect a three - electrode electrochemical workstation, electrolyze for 8 hours at a constant voltage of 0.2 V vs. RHE potential, and analyze the electrolysis products by NMR and gas chromatography. The specific reaction performance is listed in Table 1.

[0029] Example 4

[0030] Using a dual - cell high - pressure electrochemical reaction device, the device includes a reaction kettle body, a reaction kettle cover, and the inner and outer pools of the reaction kettle. The inner and outer pools are separated by a proton exchange membrane. A high - pressure reference electrode, a counter electrode, a working electrode, a gas pipe, and a thermocouple sleeve are embedded in the kettle cover (device application publication number: CN 113529115 A), 10 cm 2 The palladium foil is fixed on the working electrode, the platinum wire electrode is used as the counter electrode, and the saturated Ag / AgCl electrode is used as the reference electrode. The working electrode and the reference electrode are in the outer pool, and the counter electrode is in the inner pool. 80 ml of 0.1 M HClO4 and 2 mM FeSO4 are added as the outer - pool electrolyte solution, and 10 ml of 0.1 M HClO4 is added as the inner - pool electrolyte solution. O2 and Ar (O2 / Ar = 1 / 1) are introduced into the high - pressure reaction kettle, and the air in the system is discharged by replacement three times. Subsequently, 0.4 MPa of O2 and Ar (O2 / Ar = 1 / 1) are respectively charged, and then 3.6 MPa of CH4 gas is charged. Stir at 25 °C at a speed of 600 r / min. Connect a three - electrode electrochemical workstation, electrolyze for 8 hours at a constant voltage of 0.2 V vs. RHE potential, and analyze the electrolysis products by NMR and gas chromatography. The specific reaction performance is listed in Table 1.

[0031] Example 5

[0032] Using a dual - cell high - pressure electrochemical reaction device, the device includes a reaction kettle body, a reaction kettle cover, and the inner and outer pools of the reaction kettle. The inner and outer pools are separated by a proton exchange membrane. A high - pressure reference electrode, a counter electrode, a working electrode, a gas pipe, and a thermocouple sleeve are embedded in the kettle cover (device application publication number: CN 113529115 A), 10 cm 2 The silver foil is fixed on the working electrode, the platinum wire electrode is used as the counter electrode, and the saturated Ag / AgCl electrode is used as the reference electrode. The working electrode and the reference electrode are in the outer pool, and the counter electrode is in the inner pool. 80 ml of 0.1 M HClO4 and 0.2 mM FeSO4 are added as the outer - pool electrolyte solution, and 10 ml of 0.1 M HClO4 is added as the inner - pool electrolyte solution. O2 and Ar (O2 / Ar = 1 / 1) are introduced into the high - pressure reaction kettle, and the air in the system is discharged by replacement three times. Subsequently, 0.4 MPa of O2 and Ar (O2 / Ar = 1 / 1) are respectively charged, and then 3.6 MPa of CH4 gas is charged. Stir at 25 °C at a speed of 600 r / min. Connect a three - electrode electrochemical workstation, electrolyze for 8 hours at a constant voltage of 0.2 V vs. RHE potential, and analyze the electrolysis products by NMR and gas chromatography. The specific reaction performance is listed in Table 1.

[0033] Example 6

[0034] Using a dual-chamber high-pressure electrochemical reaction device, which includes a reaction kettle body, a reaction kettle cover, and the inner and outer chambers of the reaction kettle. The inner and outer chambers are separated by a proton exchange membrane. A high-pressure reference electrode, a counter electrode, a working electrode, a gas conduit, and a thermocouple sleeve are embedded in the kettle cover (device application publication number: CN 113529115 A), 10 cm 2 A silver foil is fixed on the working electrode. A platinum wire electrode is used as the counter electrode, and a saturated Ag / AgCl electrode is used as the reference electrode. The working electrode and the reference electrode are in the outer chamber, and the counter electrode is in the inner chamber. 80 ml of 0.1 M HClO4 and 5 mM FeSO4 are added as the electrolyte solution in the outer chamber, and 10 ml of 0.1 M HClO4 is added as the electrolyte solution in the inner chamber. O2 and Ar (O2 / Ar = 1 / 1) are introduced into the high-pressure reaction kettle, and the air in the system is discharged by replacement three times. Subsequently, 0.4 MPa of O2 and Ar (O2 / Ar = 1 / 1) are respectively charged, and then 3.6 MPa of CH4 gas is charged. Stirring is carried out at 25 °C at a rotation speed of 600 r / min. Connect a three-electrode electrochemical workstation, and electrolyze for 8 hours at a constant voltage of 0.2 V vs. RHE potential. The electrolysis products are analyzed by nuclear magnetic resonance and gas chromatography, and the specific reaction performance is listed in Table 1.

[0035] Example 7

[0036] Using a dual-chamber high-pressure electrochemical reaction device, which includes a reaction kettle body, a reaction kettle cover, and the inner and outer chambers of the reaction kettle. The inner and outer chambers are separated by a proton exchange membrane. A high-pressure reference electrode, a counter electrode, a working electrode, a gas conduit, and a thermocouple sleeve are embedded in the kettle cover (device application publication number: CN 113529115 A), 10 cm 2 A silver foil is fixed on the working electrode. A platinum wire electrode is used as the counter electrode, and a saturated Ag / AgCl electrode is used as the reference electrode. The working electrode and the reference electrode are in the outer chamber, and the counter electrode is in the inner chamber. 80 ml of 0.1 M HClO4 and 15 mM FeSO4 are added as the electrolyte solution in the outer chamber, and 10 ml of 0.1 M HClO4 is added as the electrolyte solution in the inner chamber. O2 and Ar (O2 / Ar = 1 / 1) are introduced into the high-pressure reaction kettle, and the air in the system is discharged by replacement three times. Subsequently, 0.4 MPa of O2 and Ar (O2 / Ar = 1 / 1) are respectively charged, and then 3.6 MPa of CH4 gas is charged. Stirring is carried out at 25 °C at a rotation speed of 600 r / min. Connect a three-electrode electrochemical workstation, and electrolyze for 8 hours at a constant voltage of 0.2 V vs. RHE potential. The electrolysis products are analyzed by nuclear magnetic resonance and gas chromatography, and the specific reaction performance is listed in Table 1.

[0037] Example 8

[0038] Using a dual-chamber high-pressure electrochemical reaction device, which includes a reaction kettle body, a reaction kettle cover, and the inner and outer chambers of the reaction kettle. The inner and outer chambers are separated by a proton exchange membrane. A high-pressure reference electrode, a counter electrode, a working electrode, a gas conduit, and a thermocouple sleeve are embedded in the kettle cover (the application publication number of the device: CN 113529115 A), 10 cm 2 A silver foil is fixed on the working electrode, a platinum wire electrode is used as the counter electrode, and a saturated Ag / AgCl electrode is used as the reference electrode. The working electrode and the reference electrode are in the outer chamber, and the counter electrode is in the inner chamber. 80 ml of 0.1 M HClO4 and 2 mM FeSO4 are added as the electrolyte solution in the outer chamber, and 10 ml of 0.1 M HClO4 is added as the electrolyte solution in the inner chamber. O2 and Ar (O2 / Ar = 1 / 1) are introduced into the high-pressure reaction kettle, and the air in the system is discharged by replacement three times. Subsequently, 0.4 MPa of O2 and Ar (O2 / Ar = 1 / 1) are respectively charged, and then 1.2 MPa of CH4 gas is charged. Stirring is carried out at 25 °C at a rotation speed of 600 r / min. Connect a three-electrode electrochemical workstation, electrolyze for 8 hours at a constant voltage of 0.2 V vs. RHE potential, and analyze the electrolysis products by nuclear magnetic resonance and gas chromatography. The specific reaction performance is listed in Table 1.

[0039] Example 9

[0040] Using a dual-chamber high-pressure electrochemical reaction device, which includes a reaction kettle body, a reaction kettle cover, and the inner and outer chambers of the reaction kettle. The inner and outer chambers are separated by a proton exchange membrane. A high-pressure reference electrode, a counter electrode, a working electrode, a gas conduit, and a thermocouple sleeve are embedded in the kettle cover (the application publication number of the device: CN 113529115 A), 10 cm 2 A silver foil is fixed on the working electrode, a platinum wire electrode is used as the counter electrode, and a saturated Ag / AgCl electrode is used as the reference electrode. The working electrode and the reference electrode are in the outer chamber, and the counter electrode is in the inner chamber. 80 ml of 0.1 M HClO4 and 2 mM FeSO4 are added as the electrolyte solution in the outer chamber, and 10 ml of 0.1 M HClO4 is added as the electrolyte solution in the inner chamber. O2 and Ar (O2 / Ar = 1 / 1) are introduced into the high-pressure reaction kettle, and the air in the system is discharged by replacement three times. Subsequently, 0.2 MPa of O2 and Ar (O2 / Ar = 1 / 1) are respectively charged, and then 3.6 MPa of CH4 gas is charged. Stirring is carried out at 25 °C at a rotation speed of 600 r / min. Connect a three-electrode electrochemical workstation, electrolyze for 8 hours at a constant voltage of 0.2 V vs. RHE potential, and analyze the electrolysis products by nuclear magnetic resonance and gas chromatography. The specific reaction performance is listed in Table 1.

[0041] Example 10

[0042] Using a dual-chamber high-pressure electrochemical reaction device, which includes a reaction kettle body, a reaction kettle cover, and the inner and outer chambers of the reaction kettle. The inner and outer chambers are separated by a proton exchange membrane. A high-pressure reference electrode, a counter electrode, a working electrode, a gas pipe, and a thermocouple sleeve are embedded in the kettle cover (the application publication number of the device: CN 113529115 A), 10 cm 2 A silver foil is fixed on the working electrode, a platinum wire electrode is used as the counter electrode, and a saturated Ag / AgCl electrode is used as the reference electrode. The working electrode and the reference electrode are in the outer chamber, and the counter electrode is in the inner chamber. 80 ml of 0.1 M HClO4 and 2 mM FeSO4 are added as the electrolyte solution for the outer chamber, and 10 ml of 0.1 M HClO4 is added as the electrolyte solution for the inner chamber. O2 and Ar (O2 / Ar = 1 / 1) are introduced into the high-pressure reaction kettle, and the air in the system is discharged by replacement three times. Subsequently, 0.4 MPa of O2 and Ar (O2 / Ar = 1 / 1) are respectively charged, and then 2.4 MPa of CH4 gas is charged. Stirring is carried out at 25 °C at a rotation speed of 600 r / min. Connect a three-electrode electrochemical workstation, and electrolyze for 8 hours at a constant voltage of 0.2 V vs. RHE potential. The electrolysis products are analyzed by NMR and gas chromatography, and the specific reaction performance is listed in Table 1.

[0043] Example 11

[0044] Using a dual-chamber high-pressure electrochemical reaction device, which includes a reaction kettle body, a reaction kettle cover, and the inner and outer chambers of the reaction kettle. The inner and outer chambers are separated by a proton exchange membrane. A high-pressure reference electrode, a counter electrode, a working electrode, a gas pipe, and a thermocouple sleeve are embedded in the kettle cover (the application publication number of the device: CN 113529115 A), 10 cm 2 A silver foil is fixed on the working electrode, a platinum wire electrode is used as the counter electrode, and a saturated Ag / AgCl electrode is used as the reference electrode. The working electrode and the reference electrode are in the outer chamber, and the counter electrode is in the inner chamber. 80 ml of 0.1 M HClO4 and 2 mM FeSO4 are added as the electrolyte solution for the outer chamber, and 10 ml of 0.1 M HClO4 is added as the electrolyte solution for the inner chamber. O2 and Ar (O2 / CH4 = 1 / 1) are introduced into the high-pressure reaction kettle, and the air in the system is discharged by replacement three times. Subsequently, 0.2 MPa of O2 and Ar (O2 / CH4 = 1 / 1) are respectively charged, and then 1.8 MPa of CH4 gas is charged. Stirring is carried out at 25 °C at a rotation speed of 600 r / min. Connect a three-electrode electrochemical workstation, and electrolyze for 8 hours at a constant voltage of 0.2 V vs. RHE potential. The electrolysis products are analyzed by NMR and gas chromatography, and the specific reaction performance is listed in Table 1.

[0045] Example 12

[0046] Using a dual-chamber high-voltage electrochemical reaction device, which includes a reaction kettle body, a reaction kettle cover, and the inner and outer chambers of the reaction kettle. The inner and outer chambers are separated by a proton exchange membrane. A high-voltage reference electrode, a counter electrode, a working electrode, a gas pipe, and a thermocouple sleeve are embedded in the kettle cover (device application publication number: CN 113529115 A), 10 cm 2 A silver foil is fixed on the working electrode, a platinum wire electrode is used as the counter electrode, and a saturated Ag / AgCl electrode is used as the reference electrode. The working electrode and the reference electrode are in the outer chamber, and the counter electrode is in the inner chamber. 80 ml of 0.1 M HClO4 and 2 mM FeSO4 are added as the electrolyte solution in the outer chamber, and 10 ml of 0.1 M HClO4 is added as the electrolyte solution in the inner chamber. O2 and Ar (O2 / CH4 = 1 / 1) are introduced into the high-voltage reaction kettle, and the air in the system is discharged by replacement three times. Subsequently, 0.1 MPa of O2 and Ar (O2 / Ar = 1 / 1) are respectively charged, and then 0.9 MPa of CH4 gas is charged. Stirring is carried out at 25 °C at a speed of 600 r / min. Connect a three-electrode electrochemical workstation, and electrolyze for 8 hours at a constant voltage of 0.2 V vs. RHE potential. The electrolysis products are analyzed by nuclear magnetic resonance and gas chromatography. The specific reaction performance is listed in Table 1.

[0047] Example 12

[0048] Using a dual-chamber high-voltage electrochemical reaction device, which includes a reaction kettle body, a reaction kettle cover, and the inner and outer chambers of the reaction kettle. The inner and outer chambers are separated by a proton exchange membrane. A high-voltage reference electrode, a counter electrode, a working electrode, a gas pipe, and a thermocouple sleeve are embedded in the kettle cover (device application publication number: CN 113529115 A), 10 cm 2 A silver foil is fixed on the working electrode, a platinum wire electrode is used as the counter electrode, and a saturated Ag / AgCl electrode is used as the reference electrode. The working electrode and the reference electrode are in the outer chamber, and the counter electrode is in the inner chamber. 80 ml of 0.1 M HClO4 and 2 mM FeSO4 are added as the electrolyte solution in the outer chamber, and 10 ml of 0.1 M HClO4 is added as the electrolyte solution in the inner chamber. A mixture of O2 and Ar (O2 / Ar = 1 / 1) is introduced into the high-voltage reaction kettle, and the air in the system is discharged by replacement three times. Subsequently, 0.4 MPa of O2 and Ar (O2 / Ar = 1 / 1) are respectively charged, and then 3.6 MPa of CH4 gas is charged. Stirring is carried out at 25 °C at a speed of 600 r / min. Connect a three-electrode electrochemical workstation, and electrolyze for 8 hours at a constant voltage of 0.2 V vs. RHE potential. The electrolysis products are analyzed by nuclear magnetic resonance and gas chromatography. After the reaction, the electrolyte solution and the reaction gas are replaced with new ones, and the silver foil and the remaining materials are not replaced. This reaction is cycled 10 times. The specific cycle stability performance is listed in Table 2.

[0049] Comparative Example 1

[0050] Using a dual-chamber high-pressure electrochemical reaction device, which includes a reaction kettle body, a reaction kettle cover, and the inner and outer chambers of the reaction kettle. The inner and outer chambers are separated by a proton exchange membrane. A high-pressure reference electrode, a counter electrode, a working electrode, a gas pipe, and a thermocouple sleeve are embedded in the kettle cover (device application publication number: CN 113529115 A), 10 cm 2 A silver foil is fixed on the working electrode. A platinum wire electrode is used as the counter electrode, and a saturated Ag / AgCl electrode is used as the reference electrode. The working electrode and the reference electrode are in the outer chamber, and the counter electrode is in the inner chamber. 80 ml of 0.1 M HClO4 and 0 mM FeSO4 are added as the electrolyte solution in the outer chamber, and 10 ml of 0.1 M HClO4 is added as the electrolyte solution in the inner chamber. O2 and Ar (O2 / CH4 = 1 / 1) are introduced into the high-pressure reaction kettle, and the air in the system is discharged by replacement three times. Subsequently, 0.4 MPa of O2 and Ar (O2 / CH4 = 1 / 1) are respectively charged, and then 3.6 MPa of CH4 gas is charged. Stir at a speed of 600 r / min at 25 °C. Connect a three-electrode electrochemical workstation and electrolyze for 8 hours at a constant voltage of 0.2 V vs. RHE potential. The electrolysis products are analyzed by NMR and gas chromatography, and the specific reaction performance is listed in Table 1.

[0051] Comparative Example 2

[0052] Using a dual-chamber high-pressure electrochemical reaction device, which includes a reaction kettle body, a reaction kettle cover, and the inner and outer chambers of the reaction kettle. The inner and outer chambers are separated by a proton exchange membrane. A high-pressure reference electrode, a counter electrode, a working electrode, a gas pipe, and a thermocouple sleeve are embedded in the kettle cover (device application publication number: CN 113529115 A), 10 cm 2 A silver foil is fixed on the working electrode. A platinum wire electrode is used as the counter electrode, and a saturated Ag / AgCl electrode is used as the reference electrode. The working electrode and the reference electrode are in the outer chamber, and the counter electrode is in the inner chamber. 80 ml of 0.1 M HClO4 and 2 mM FeSO4 are added as the electrolyte solution in the outer chamber, and 10 ml of 0.1 M HClO4 is added as the electrolyte solution in the inner chamber. CH4 gas is introduced into the high-pressure reaction kettle, and the air in the system is discharged by replacement three times. Subsequently, 3.6 MPa of CH4 gas is charged. Stir at a speed of 600 r / min at 25 °C. Connect a three-electrode electrochemical workstation and electrolyze for 8 hours at a constant voltage of 0.2 V vs. RHE potential. The electrolysis products are analyzed by NMR and gas chromatography, and the specific reaction performance is listed in Table 1.

[0053] Table 1

[0054]

[0055]

[0056] Table 2

[0057]

Claims

1. A method for electrocatalytically converting methane and oxygen to prepare formic acid, characterized in that: Using a dual-cell high-voltage electrochemical reaction device, with a catalytic material as the working electrode, electrolyte solutions are added to the cathode cell and the anode cell. A compound of divalent iron is added to the cathode cell, and a mixed gas of methane, oxygen, and argon is introduced. A reduction potential is applied to achieve the electrotransformation of methane and oxygen to prepare formic acid.

2. The method according to claim 1, wherein: The catalytic material includes at least one of silver, gold, platinum, palladium foil, or their alloy foils.

3. The method according to claim 1, wherein: The compound of divalent iron includes at least one of ferrous sulfate, ferrous perchlorate, ferrous nitrate, ferrous oxalate, and ferrous acetylacetonate.

4. The method according to claim 1, wherein: The pressure of the mixed gas of methane, oxygen, and argon is 1 - 8 MPa.

5. The method according to claim 1, wherein: In the mixed gas of methane, oxygen, and argon, the volume percentage of methane is 30 - 95%, the volume percentage of oxygen is 0.1 - 10%, and the balance is argon.

6. The method according to claim 1, characterized in that: The electrolyte solution includes at least one of HClO4, H2SO4, NaHSO4, LiSO4, and Na2SO 4、 K2SO4 solution; wherein, the pH of the LiSO4, Na2SO4, or K2SO4 solution is 1-4.

7. The method according to claim 1, characterized in that: The concentration of the electrolyte solution is 0.01 - 2 mol / L -1 .

8. The method according to claim 1, wherein: The concentration of the divalent iron compound in the electrolyte solution is 0.05 - 50 mmol / L -1 .

9. The method according to claim 1, characterized in that: The reduction potential is -0.5V - 0.5V vs. RHE, the time is 0.1 - 24 hours, the rotor speed is 50 - 600 r / min, and the working electrode area is 0.5 - 30 cm -2 , and the reaction temperature is 1 - 80 °C.

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