Method for preparing methylal by electrocatalytic reduction of carbon dioxide

Abstract

The invention relates to the technical field of electrocatalytic reduction of carbon dioxide, and discloses a method for preparing methylal by electrocatalytic reduction of carbon dioxide. According to the method, an H-type electrolytic tank is adopted as a reactor, and the H-type electrolytic tank comprises a cathode chamber and an anode chamber; a working electrode in the cathode chamber is a tin-based catalyst, the cathode chamber and the anode chamber are separated by a proton exchange membrane, and an electrolyte of the cathode chamber and the anode chamber is a sodium perchlorate-methanol solution; the method comprises the following steps: under an electrocatalytic reduction condition, introducing carbon dioxide into the cathode chamber, and carrying out electrocatalytic reduction to obtain methylal; and carrying out electrocatalytic oxidation on methanol in the electrolyte in the anode chamber to obtain methylal. The method for preparing methylal by electrocatalytic reduction of carbon dioxide provided by the invention has the advantages of high methylal selectivity, mild reaction conditions, environmental friendliness and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalytic carbon dioxide reduction, and particularly to a method for electrocatalytic reduction of carbon dioxide to prepare dimethoxymethane. Background Art

[0002] Climate change is a global issue faced by humanity. With the carbon dioxide emissions of various countries, the greenhouse effect is intensifying, posing a threat to the life system. Exploring new artificial carbon cycles and efficiently converting and utilizing CO 2 through new and green methods is of great practical significance. At the same time, reducing greenhouse gas emissions and lowering the level of CO 2 in the atmosphere have reached a broad consensus in the international community.

[0003] With continuous breakthroughs in renewable energy technologies such as solar energy, wind energy, geothermal energy, and nuclear energy, the status of green renewable energy in the global energy structure has become increasingly prominent. At the same time, with the electric energy generated by these renewable energies, the energy utilization efficiency and economy have also been continuously improved.

[0004] Reducing carbon dioxide to high-energy-density organic small molecules (such as carbon monoxide, methane, methanol, and formaldehyde, etc.) using renewable electric energy provides a new way to solve the problems of energy storage and carbon emissions. This method can not only revolutionize the traditional chemical production process, converting heat-driven into electric energy-driven, but also achieve the closed-loop cycle of carbon dioxide. Such a method highly conforms to the sustainable development goals and has obvious multiple advantages, gradually becoming a key technology to promote the transformation of the low-carbon economy. Among them, the electrochemical carbon dioxide reduction reaction (CO 2 RR) exhibits great application potential and commercial value due to its high reaction rate, adjustable selectivity, simple operation at normal temperature and pressure, and potential integration with renewable electric energy, etc., attracting extensive attention from the scientific research and industrial circles.

[0005] Dimethoxymethane, also known as methylal, is one of the most important downstream products of methanol. It has low toxicity, good solubility, low boiling point, and good water miscibility. It is an ideal new type of green environmental protection solvent and is widely used in products such as cosmetics, pharmaceuticals, household products, automotive industrial products, pesticides, leather polishers, cleaners, rubber industry, paints, and inks. At the same time, dimethoxymethane has good oil removal ability and volatility. As a cleaner, it can also replace F11 and F113 and chlorine-containing solvents, and is an ideal environmental protection product to replace Freon. Using dimethoxymethane as a raw material, high-value-added ethyl methoxyacetate, ethylene glycol, and the clean diesel additive polymethoxydimethylether can be synthesized.

[0006] Industrially, the synthesis of methylal mainly uses the aldol condensation technology with methanol and formaldehyde as raw materials. This process needs to be prepared and produced through two consecutive steps in industrial production: First, use the iron method or silver method to catalytically oxidize methanol in the gas phase to obtain formaldehyde; then, in the second reactor, use liquid acid as a catalyst to carry out liquid-phase acetalization of methanol and formaldehyde to generate methylal. A large amount of liquid acid is used in this process, resulting in the formation of a homogeneous mixture of the product and the catalyst system, and it is necessary to add a liquid-liquid separation process, increasing the complexity of the process; and a large amount of acidic organic sewage containing formaldehyde is generated, which is not environmentally friendly; at the same time, the acidic medium causes serious corrosion to the reaction equipment, increasing the equipment maintenance cost and posing safety hazards.

[0007] Currently, more research also includes the one-step oxidation of methanol to methylal technology. This technology is to complete the oxidative dehydrogenation of methanol at the noble metal active site to generate formaldehyde intermediates, and then formaldehyde undergoes acetalization reaction with excessive methanol at the acidic sites of heteropolyacids to directly synthesize methylal. The reaction needs to be carried out under the conditions of 400 °C and 5-10 bar. Compared with the aldol condensation process, it omits the process of oxidizing methanol to formaldehyde, shortens the process flow, and reduces the investment and production costs. However, this process requires high-temperature and high-pressure reaction conditions. At the same time, the heteropolyacid catalyst is easy to decompose, the metal catalyst is costly, and the conversion rate of methanol can only reach about 50%, which seriously restricts the economy and sustainability of industrial applications.

[0008] In view of the above existing problems, it is of great significance to develop a new process for preparing methylal with mild reaction conditions and environmental friendliness. Summary of the Invention

[0009] The object of the present invention is to provide a method for electrocatalytic reduction of carbon dioxide to prepare methylal with high methylal selectivity, mild reaction conditions and environmental friendliness.

[0010] To achieve the above object, the present invention provides a method for electrocatalytic reduction of carbon dioxide to prepare methylal. This method uses an H-type electrolytic cell as a reactor. The H-type electrolytic cell includes a cathode chamber and an anode chamber; the working electrode in the cathode chamber is a tin-based catalyst. The cathode chamber and the anode chamber are separated by a proton exchange membrane, and the electrolytes in the cathode chamber and the anode chamber are sodium perchlorate-methanol solutions. This method includes:

[0011] Under electrocatalytic reduction conditions, carbon dioxide is introduced into the cathode chamber and undergoes electrocatalytic reduction to obtain methylal; and, in the anode chamber, methanol in the electrolyte is electrocatalytically oxidized to obtain methylal.

[0012] Through the above technical solutions, the present invention has at least the following beneficial technical effects:

[0013] (1) The method for electrocatalytic reduction of carbon dioxide to prepare dimethoxymethane provided by the present invention uses CO 2 as a reaction raw material to convert greenhouse gas into high-value-added dimethoxymethane, realizing the recycling of carbon resources and meeting the goal of carbon neutrality.

[0014] (2) The method provided by the present invention breaks through the complex process of traditional preparation of dimethoxymethane, couples the reduction of CO 2 and the oxidation of methanol in a single electrochemical reaction system, produces dimethoxymethane through the cooperation of the cathode and anode, significantly shortens the reaction path, couples the electron transfer of the cathode and anode, improves the current efficiency, and reduces the overall energy consumption.

[0015] (3) The method provided by the present invention uses a non-precious metal tin-based catalyst, which is suitable for large-scale application. Compared with precious metal catalysts (such as Ag, Au) or complex alloy catalysts, the tin-based catalyst is more economical, greatly reduces the process cost, and still maintains good catalytic performance. Description of the Drawings

[0016] Figure 1 is a scanning electron microscope schematic diagram of the tin-based catalyst SnS 2 powder prepared in Example 1;

[0017] Figure 2 is a scanning electron microscope schematic diagram of the tin-based catalyst SnSe 2 powder prepared in Example 2;

[0018] Figure 3 is a scanning electron microscope schematic diagram of the tin-based catalyst SnO 2 powder prepared in Example 3;

[0019] Figure 4 is a schematic diagram of the Faraday efficiency results of dimethoxymethane electrolyzed in Examples 1 - 6, Comparative Example 1, and Comparative Example 2;

[0020] Figure 5 is a schematic diagram of the test results of electrochemical linear sweep voltammetry (LSV) in Examples 1 - 3 and Example 6;

[0021] Figure 6 is a schematic diagram of the test results of electrochemical linear sweep voltammetry (LSV) in Example 1 and Comparative Example 2.

[0022] Figure 7 is a schematic diagram of the specific reaction principle of electrocatalytic reduction of carbon dioxide to prepare dimethoxymethane. Detailed Embodiments

[0023] The endpoints and any values in the ranges disclosed herein are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0024] As described above, the present invention provides a method for electrocatalytic reduction of carbon dioxide to prepare methylal. This method uses an H-type electrolytic cell as the reactor, and the H-type electrolytic cell includes a cathode chamber and an anode chamber; the working electrode in the cathode chamber is a tin-based catalyst, the cathode chamber and the anode chamber are separated by a proton exchange membrane, and the electrolytes in the cathode chamber and the anode chamber are sodium perchlorate-methanol solutions; this method includes:

[0025] Under electrocatalytic reduction conditions, carbon dioxide is introduced into the cathode chamber and undergoes electrocatalytic reduction to obtain methylal; and, in the anode chamber, methanol in the electrolyte is electrocatalytically oxidized to obtain methylal.

[0026] According to a specific embodiment, the method for electrocatalytic reduction of carbon dioxide to prepare methylal of the present invention includes: under electrocatalytic reduction conditions, carbon dioxide is introduced into the cathode chamber. Carbon dioxide is first electrocatalytically reduced to formic acid, and formic acid reacts with hydrogen ions transported from the anode and methanol in the electrolyte to obtain methyl formate. Methyl formate is electrocatalytically reduced to formaldehyde, and formaldehyde condenses with methanol in the electrolyte to obtain methylal; and, in the anode chamber, methanol in the electrolyte is electrocatalytically oxidized to obtain formaldehyde, and formaldehyde condenses with methanol in the electrolyte to obtain methylal.

[0027] According to a preferred embodiment, in the cathode chamber, the conditions for electrocatalytic reduction include: using the constant voltage method, the working voltage is -1.2V to -2.2V, and the charge quantity is 20 - 80C.

[0028] According to a more preferred embodiment, in the cathode chamber, the conditions for electrocatalytic reduction include: the working voltage is -1.8V to -2.2V, and the charge quantity is 40 - 60C. The inventors of the present invention have found that in this preferred case, the method for electrocatalytic reduction of carbon dioxide to prepare methylal of the present invention has higher methylal selectivity and Faraday efficiency.

[0029] According to a preferred embodiment, the initial concentration of the electrolyte based on sodium perchlorate is 0.1 - 0.6mol / L.

[0030] It should be noted that the initial concentration of the electrolyte in the present invention refers to the concentration of the electrolyte in the cathode chamber and the anode chamber before the electrocatalytic reaction, calculated as sodium perchlorate.

[0031] According to a particularly preferred embodiment, the initial concentration of the electrolyte calculated as sodium perchlorate is 0.5 - 0.6 mol / L. The inventors of the present invention have found that in this preferred case, the method for electrocatalytic reduction of carbon dioxide to prepare dimethoxymethane of the present invention has a higher Faraday efficiency and current density for the production of dimethoxymethane.

[0032] Preferably, the method further includes preparing the tin-based catalyst by an operation comprising the following steps:

[0033] (1) Performing a first reaction on a tin precursor and a ligand in a solvent I to obtain an intermediate I;

[0034] (2) Post-treating the intermediate I to obtain the tin-based catalyst;

[0035] The tin precursor is tin tetrachloride pentahydrate and / or stannous chloride dihydrate; the ligand is selected from at least one of sodium citrate, sodium borohydride, selenium, and thioacetamide.

[0036] More preferably, in step (1), the weight ratio of the amount of the tin precursor to the ligand is 1:0.8 - 2.

[0037] Further preferably, in step (1), the solvent I is at least one of deionized water, ethanol, and isopropanol.

[0038] Even more preferably, in step (1), the conditions of the first reaction include: temperature is 120 - 200 °C, and time is 8 - 24 h.

[0039] Particularly preferably, in step (2), the post-treatment includes washing treatment and drying treatment of the intermediate I; the conditions of the drying treatment include: temperature is -80 °C to -60 °C, vacuum degree is below 10 Pa, and time is 12 - 24 h.

[0040] According to a preferred specific embodiment, the washing treatment includes performing operations of washing with deionized water, dispersing with ethanol, and centrifugal separation on the intermediate I, repeating this operation three times, wherein the conditions of centrifugal separation are rotation speed 8000 rpm and time 10 min, to obtain a washed catalyst powder.

[0041] According to a preferred embodiment, the method further includes pre-treating the tin-based catalyst before using it as the working electrode, and the steps of the pre-treatment include:

[0042] a. Coat a slurry containing Solvent II and the raw material tin-based catalyst onto carbon paper to obtain Intermediate Material I;

[0043] b. Activate the Intermediate Material I in the electrolyte.

[0044] It should be noted that the raw material tin-based catalyst is the tin-based catalyst powder obtained after post-treating Intermediate I. This tin-based catalyst powder is a nanosheet with regular shape and uniform size, which has a large specific surface area and stable catalytic performance.

[0045] The present invention has no special requirements for the type of the carbon paper, and the carbon paper known in the art can be used in the solution of the present invention. In particular, the inventors of the present invention have found that when the hydrophilic carbon paper is selected as the carbon paper, the method of the present invention has a higher Faraday efficiency for the formation of dimethoxymethane.

[0046] According to a more preferred embodiment, in step b, the activation is a cyclic voltammetry treatment, and the treatment conditions include: the scanning rate is 100 - 500 mV / s, the scanning range is -3.0 V to +3.0 V, and the number of cycles is 5 - 20 times.

[0047] Preferably, Solvent II is selected from at least one of deionized water, ethanol, isopropanol, and perfluorinated resin solution.

[0048] More preferably, the content of the raw material tin-based catalyst in the slurry is 20 - 50 mg / mL.

[0049] Further preferably, carbon dioxide is introduced into the cathode chamber to saturate the electrolyte solution, and then carbon dioxide is continuously introduced at a rate of 20 - 55 mL / min.

[0050] According to a preferred specific embodiment, in the cathode chamber, before starting the electrocatalytic reduction reaction, carbon dioxide is introduced at a rate of 50 - 55 mL / min for 30 - 40 min, and during the electrocatalytic reduction reaction, the flow rate of the introduced carbon dioxide is maintained at 25 - 30 mL / min.

[0051] Even more preferably, the reference electrode in the cathode chamber is an Ag / AgCl electrode.

[0052] Particularly preferably, the anode chamber contains a Pt electrode.

[0053] The present invention will be described in detail below through examples. In the following examples, without special instructions, various instruments and raw materials used are ordinary commercially available products.

[0054] Example 1

[0055] (1) Weigh 128 mg of tin(IV) chloride pentahydrate and 256 mg of thioacetamide, add them to 35 mL of isopropanol, and ultrasonically mix for 5 min to obtain a mixed solution. Transfer the above mixed solution to a 50 mL hydrothermal reactor, react at 180 °C for 24 h to obtain Intermediate I. Wash the Intermediate I three times with distilled water, ethanol, and distilled water in sequence. After centrifugation, place the obtained precipitate in a vacuum freeze dryer at -60 °C for drying treatment for 24 h to obtain SnS 2 Catalyst powder.

[0056] (2) Weigh 10 mg of the above SnS 2 catalyst powder, ultrasonically mix it with 40 μL of deionized water, 120 μL of ethanol, and 40 μL of perfluorinated resin solution (Nafion solution) for 10 min to obtain SnS 2 catalyst slurry. Coat the SnS 2 catalyst slurry on hydrophilic carbon paper to obtain SnS 2 catalyst-loaded carbon paper.

[0057] (3) Using an H-type electrolytic cell as the reactor, use the above SnS 2 catalyst-loaded carbon paper as the working electrode, an Ag / AgCl electrode as the reference electrode, place the working electrode and the reference electrode in the cathode chamber, place a Pt electrode in the anode chamber, set an injection hole and a sampling hole in the cathode chamber, set a sampling hole in the anode chamber, use a Nafion 117 proton exchange membrane to separate the anode chamber and the cathode chamber, and add 75 mL of a sodium perchlorate-methanol solution with a concentration of 0.6 mol / L (calculated based on sodium perchlorate) as the electrolyte in both the anode chamber and the cathode chamber.

[0058] (4) In the cathode chamber, first introduce carbon dioxide at a rate of 50 mL / min for 35 min to saturate the electrolyte, and then continuously introduce carbon dioxide at a rate of 25 mL / min. Under the constant voltage mode, apply a working voltage of -2V to carry out the electrocatalytic reduction reaction. After passing 40 C of electrons, the product dimethoxymethane is obtained. In the anode chamber, methanol undergoes an electrocatalytic oxidation reaction to obtain dimethoxymethane.

[0059] Example 2

[0060] (1) Weigh 1.056 g of tin(IV) chloride pentahydrate, 0.48 g of sodium borohydride, and 0.48 g of selenium, add them to 60 mL of deionized water, and ultrasonically mix for 5 min to obtain a mixed solution. Transfer the above mixed solution to a 100 mL hydrothermal reactor, react at 200 °C for 12 h to obtain Intermediate I. Wash the Intermediate I three times with distilled water, ethanol, and distilled water in sequence. After centrifugation, place the obtained precipitate in a vacuum freeze dryer at -60 °C for drying treatment for 24 h to obtain SnSe 2 Catalyst powder.

[0061] (2) Weigh the above-mentioned SnSe 2 10 mg of catalyst powder, and ultrasonically mix it with 40 μL of deionized water, 120 μL of ethanol, and 40 μL of perfluorinated resin solution (Nafion solution) for 10 min to obtain SnSe 2 catalyst slurry; the SnSe 2 catalyst slurry is coated on hydrophilic carbon paper to obtain SnSe 2 carbon paper loaded with catalyst.

[0062] (3) Using an H-type electrolytic cell as the reactor, the above-mentioned SnSe 2 carbon paper loaded with catalyst is used as the working electrode, the Ag / AgCl electrode is used as the reference electrode, and the working electrode and the reference electrode are placed in the cathode chamber. The Pt electrode is placed in the anode chamber, and a sampling hole is set in the cathode chamber and a sampling hole is set in the anode chamber. A Nafion 117 proton exchange membrane is used to separate the anode chamber and the cathode chamber. 75 mL of sodium perchlorate-methanol solution with a concentration of 0.5 mol / L (calculated based on sodium perchlorate) is added to each of the anode chamber and the cathode chamber as the electrolyte.

[0063] (4) In the cathode chamber, first introduce carbon dioxide at a rate of 50 mL / min for 35 min to saturate the electrolyte, and then continuously introduce carbon dioxide at a rate of 25 mL / min. Under the constant voltage mode, apply a working voltage of -2.2 V to carry out the electrocatalytic reduction reaction; after passing 50 C of electrons, the product dimethoxymethane is obtained; in the anode chamber, methanol undergoes an electrocatalytic oxidation reaction to obtain dimethoxymethane.

[0064] Example 3

[0065] (1) Weigh 564 mg of stannous chloride dihydrate and 1.29 g of sodium citrate, add them to a mixed solution of 2 mL of deionized water and 20 mL of ethanol, and ultrasonically mix for 5 min to obtain a mixed solution; transfer the above mixed solution to a 100 mL hydrothermal reaction kettle, and react at 180 °C for 8 h to obtain Intermediate I; wash the Intermediate I with distilled water, ethanol, and distilled water three times in sequence, and after centrifugation, place the obtained precipitate in a vacuum freeze dryer at -60 °C for 24 h of drying treatment to obtain SnO 2 catalyst powder.

[0066] (2) Weigh 10 mg of the above-mentioned SnO 2 catalyst powder, and ultrasonically mix it with 40 μL of deionized water, 120 μL of ethanol, and 40 μL of perfluorinated resin solution (Nafion solution) for 10 min to obtain SnO 2 catalyst slurry; the SnO 2 catalyst slurry is coated on hydrophilic carbon paper to obtain SnO2 Catalyst-loaded carbon paper.

[0067] (3) Using an H-type electrolytic cell as the reactor, the above-mentioned SnO 2 The catalyst-loaded carbon paper is used as the working electrode, the Ag / AgCl electrode is used as the reference electrode, and the working electrode and the reference electrode are placed in the cathode chamber. The Pt electrode is placed in the anode chamber. An injection hole and a sampling hole are provided in the cathode chamber, and a sampling hole is provided in the anode chamber. A Nafion 117 proton exchange membrane is used to separate the anode chamber and the cathode chamber. 75 mL of a sodium perchlorate-methanol solution with a concentration of 0.6 mol / L (calculated based on sodium perchlorate) is added to each of the anode chamber and the cathode chamber as the electrolyte.

[0068] (4) In the cathode chamber, carbon dioxide is first introduced at a rate of 50 mL / min for 35 min to saturate the electrolyte, and then carbon dioxide is continuously introduced at a rate of 25 mL / min. Under the constant voltage mode, a working voltage of -1.8 V is applied to carry out the electrocatalytic reduction reaction; after 60 C of electrons, the product dimethoxymethane is obtained; in the anode chamber, methanol undergoes an electrocatalytic oxidation reaction to obtain dimethoxymethane.

[0069] Example 4

[0070] This example uses a method similar to that of Example 1. The difference is that in step (4), the working voltage of the electrocatalytic reduction reaction is set to -1.3 V.

[0071] Example 5

[0072] This example uses a method similar to that of Example 1. The difference is that in step (4), the charge amount of the electrocatalytic reduction reaction is set to 20 C.

[0073] Example 6

[0074] This example uses a method similar to that of Example 1. The difference is that in step (3), the concentration of the electrolyte in the cathode chamber and the anode chamber, calculated based on sodium perchlorate, is adjusted to 0.1 mol / L.

[0075] Comparative Example 1

[0076] This example uses a method similar to that of Example 1. The difference is that a tin sheet is used instead of the tin-based catalyst as the working electrode.

[0077] The pretreatment of the tin sheet includes: cutting the purchased metallic tin into tin sheets with a size of 1.5 cm × 1.5 cm, immersing them in a sulfuric acid solution with a concentration of 0.1 mol / L for 30 minutes to remove the surface oxide layer, taking them out and washing them with ethanol 3 - 5 times, and using the tin sheets as the working electrode after the surface solvent has evaporated.

[0078] Comparative Example 2

[0079] This example uses a method similar to that of Example 1. The difference is that in step (4), carbon dioxide is not introduced into the cathode chamber.

[0080] Test Example

[0081] This test example provides the Faraday efficiency of the methylal obtained in each of the above examples, as well as the electrochemical linear sweep voltammetry (LSV) test for some examples.

[0082] Specifically, the calculation formula for the Faraday efficiency of methylal is:

[0083] Cathode:

[0084] Anode:

[0085] Overall: F 总 = F 阴极 + F 阳极

[0086] In the formula:

[0087] F 阴极 : The Faraday efficiency of the cathode for producing methylal, %;

[0088] F 阳极 : The Faraday efficiency of the anode for producing methylal, %;

[0089] F 总 : The Faraday efficiency of the entire electrochemical device for producing methylal, %;

[0090] nDMM: The yield of methylal, mol;

[0091] 96485: The Faraday constant, C / mol;

[0092] Q: The charge passing through the electrode during the reaction, C.

[0093] And, the test conditions for the electrochemical linear sweep voltammetry (LSV) test are:

[0094] The scan rate is 10 - 100 mV / s, and the scan range is from 0 V to -2.5 V.

[0095] Figure 1 、 Figure 2 and Figure 3 are the SEM images of the tin-based catalysts prepared in Example 1, Example 2, and Example 3, respectively. It can be seen from the figures that the tin-based catalyst is a nanosheet structure with regular shape and uniform size, and has a very high specific surface area, so as to provide a large number of active sites and improve the catalytic performance.

[0096] Figure 4 Schematic diagram of the Faraday efficiency results of dimethoxymethane electrolyzed in Examples 1 - 6, Comparative Example 1, and Comparative Example 2. As can be seen from Figure 4 it, the method for electrocatalytic reduction of carbon dioxide to prepare dimethoxymethane according to the present invention has a relatively high Faraday efficiency for dimethoxymethane, and the sum of the anodic and cathodic Faraday efficiencies of dimethoxymethane is as high as 182.5%.

[0097] Figure 5 Schematic diagram of the test results of electrochemical linear sweep voltammetry (LSV) corresponding to Examples 1, 2, 3, and 6. Figure 6 Schematic diagram of the test results of electrochemical linear sweep voltammetry (LSV) of Example 1 and Comparative Example 2. As can be seen from Figure 5 , Figure 6 it, for the preparation method of the present invention, the catalyst shows high - selective catalytic activity for CO 2 molecules, can effectively inhibit the hydrogen evolution reaction, and this electrocatalytic reduction of carbon dioxide process has a relatively large current within a wide potential window, can achieve industrial - level current density, and effectively produce dimethoxymethane.

[0098] Figure 7 Schematic diagram of the specific reaction process for electrocatalytic reduction of carbon dioxide to prepare dimethoxymethane. As can be seen from Figure 7 it, the method of the present invention innovatively couples the cathodic CO 2 reduction reaction with the anodic methanol oxidation reaction to form a synergistic reaction network of proton - coupled electron transfer. The specific reaction path is as follows: in the cathode chamber, CO 2 first generates a formic acid intermediate through a two - electron reduction path. The formic acid reacts with the protons (H + ) transported from the anode and methanol in the electrolyte to undergo an esterification reaction to form methyl formate; methyl formate is further electrocatalytically reduced to generate the key intermediate formaldehyde, and formaldehyde reacts with methanol in the electrolyte to undergo an acetalization reaction to form the target product dimethoxymethane. At the same time, in the anode chamber, methanol is directly electrocatalytically oxidized to generate formaldehyde, and the generated formaldehyde also condenses with methanol in the electrolyte to form dimethoxymethane. This dual - channel reaction mechanism realizes the full utilization of reaction materials and the efficient conversion of energy through the synergistic effect of the anodic and cathodic reactions, enabling the overall Faraday efficiency of the system to break through the theoretical limit of 100%.

[0099] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for preparing methylal by electrocatalytic reduction of carbon dioxide, characterized in that: The method uses an H-type electrolytic cell as a reactor, wherein the H-type electrolytic cell comprises a cathode chamber and an anode chamber; the working electrode in the cathode chamber is a tin-based catalyst, the cathode chamber and the anode chamber are separated by a proton exchange membrane, and the electrolytes in the cathode chamber and the anode chamber are sodium perchlorate-methanol solution; The method includes: Under electrocatalytic reduction conditions, introducing carbon dioxide into the cathode chamber to obtain methylal through electrocatalytic reduction; And, in the anode chamber, methanol in the electrolyte is electrocatalytically oxidized to obtain methylal.

2. The method according to claim 1, wherein: In the cathode chamber, the conditions of the electrocatalytic reduction include: using a constant voltage method, an operating voltage of -1.2V to -2.2V, and a charge of 20-80C; Preferably, in the cathode chamber, the conditions for the electrocatalytic reduction include: an operating voltage of -1.8V to -2.2V, and a charge of 40-60C.

3. The method according to claim 1, wherein: The initial concentration of the electrolyte calculated as sodium perchlorate is 0.1-0.6 mol / L.

4. The method according to any one of claims 1 to 3, wherein: The method also includes preparing the tin-based catalyst by an operation comprising the following steps: (1) a tin precursor and a ligand are subjected to a first reaction in a solvent I to obtain an intermediate I; (2) post-treating the intermediate I to obtain the tin-based catalyst; The tin precursor is tin tetrachloride pentahydrate and / or stannous chloride dihydrate; the ligand is selected from at least one of sodium citrate, sodium borohydride, selenium and thioacetamide.

5. The method according to claim 4, wherein: In step (1), the weight ratio of the tin precursor to the ligand is 1:0.8-2; And / or, the solvent I is at least one of deionized water, ethanol and isopropanol; And / or, the conditions of the first reaction include: temperature of 120-200° C. and time of 8-24 h.

6. The method according to claim 4, wherein: In step (2), the post-treatment includes washing and drying the intermediate I; the drying conditions include: temperature of -80°C to -60°C, vacuum degree of less than 10Pa, and time of 12-24h.

7. The method according to any one of claims 1 to 3, wherein: The method further comprises pre-treating the tin-based catalyst before using it as the working electrode, wherein the pre-treating step comprises: a. coating a slurry containing solvent II and a raw material tin-based catalyst on carbon paper to obtain an intermediate material I; b. activating the intermediate material I in the electrolyte; And / or, in step b, the activation is a cyclic voltammetry treatment, and the treatment conditions include: a scan rate of 100-500 mV / s, a scan range of -3.0 V to +3.0 V, and a cycle number of 5-20 times.

8. The method according to claim 7, wherein: The solvent II is selected from at least one of deionized water, ethanol, isopropanol and a perfluorinated resin solution; And / or, the content of the raw material tin-based catalyst in the slurry is 20-50 mg / mL.

9. The method according to any one of claims 1 to 3, wherein: Carbon dioxide was introduced into the cathode chamber to saturate the electrolyte solution, and then carbon dioxide was continuously introduced at a rate of 20-55 mL / min.

10. The method according to claims 1-3, wherein: The reference electrode in the cathode chamber is an Ag / AgCl electrode; And / or, the anode chamber contains a Pt electrode.

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