A method for synthesizing dimethyl carbonate

Abstract

This invention provides a method for synthesizing dimethyl carbonate, belonging to the field of carbonate compound synthesis technology. The synthesis method of this invention does not require high temperature and high pressure conditions, and can be carried out at room temperature and pressure, significantly reducing energy consumption and equipment requirements. By coupling the reduction and oxidation reactions of photoelectrochemical carbon dioxide conversion, the synthesis energy barrier of dimethyl carbonate is lowered, improving energy utilization efficiency. Using greenhouse gas carbon dioxide as the main raw material, waste resource utilization is achieved, and the energy used is clean energy such as solar or electrical energy, avoiding pollution at the source. This invention couples the carbon dioxide conversion and dimethyl carbonate synthesis steps, realizing the recycling of the reactant methanol within the system, simplifying the process flow. The combined use of light and electrical energy produces a synergistic effect, improving the reaction rate and the selectivity of dimethyl carbonate.

Description

Technical Field

[0001] This invention relates to the field of carbonate compound synthesis technology, and more particularly to a method for synthesizing dimethyl carbonate. Background Technology

[0002] Dimethyl carbonate (DMC) is an important green chemical raw material and organic synthesis intermediate. Due to the presence of methyl, carbonyl, and methoxy functional groups in its molecular structure, it exhibits excellent reactivity and is widely used in polycarbonate synthesis, lithium battery electrolytes, gasoline additives, solvents, and pesticide and pharmaceutical synthesis. With the rapid development of new energy and new materials industries, the market demand for DMC continues to grow. Currently, the traditional methods for industrially synthesizing DMC mainly include the phosgene process, transesterification, and oxidative carbonylation.

[0003] Phosgene process: Due to the extreme toxicity of the raw material phosgene, it has extremely high requirements for equipment and operational safety, and generates a large amount of chlorine-containing waste, causing serious environmental pollution. It has been gradually phased out.

[0004] Transesterification: Using propylene oxide / ethane, carbon dioxide and methanol as raw materials, this method is relatively green, but it usually needs to be carried out under high temperature (150-200℃) and high pressure (2-5 MPa) conditions, which requires high equipment, consumes a lot of energy, and involves intermediate products in the reaction steps, making the process relatively complex.

[0005] Oxidative carbonylation: This method uses methanol, carbon monoxide, and oxygen as raw materials, and is carried out in the presence of a copper-based catalyst. This method also carries the safety risks of high-pressure operation, uses flammable and explosive carbon monoxide gas, and the catalyst is prone to deactivation.

[0006] In recent years, with the advancement of the "dual carbon" goal, utilizing carbon dioxide as a carbon source to synthesize high-value-added chemicals has become a research hotspot. Directly converting the greenhouse gas carbon dioxide into dimethyl carbonate (DMC) not only has economic value but also significant environmental implications. However, carbon dioxide molecules possess extremely high chemical stability, and their activation and conversion typically require overcoming substantial kinetic energy barriers. As mentioned above, existing DMC synthesis technologies involve very low levels of carbon dioxide participation and often rely on harsh reaction conditions of high temperature and pressure, as well as the use of precious metals or complex catalysts, resulting in high energy consumption, high costs, low efficiency, and short catalyst lifetimes throughout the process.

[0007] Photoelectrochemical technology offers new possibilities for activating carbon dioxide under mild conditions and can utilize inexhaustible solar energy, making it a potential pathway for green synthesis. Existing technologies have attempted to reduce carbon dioxide to C1 products such as carbon monoxide, formic acid, and methanol via photoelectrochemistry. However, there are still no studies or reports on the conversion of carbon dioxide to dimethyl carbonate in the field of photoelectrochemistry.

[0008] Therefore, developing a new pathway for the efficient conversion of carbon dioxide into dimethyl carbonate at room temperature and pressure using photoelectrochemical technology not only broadens the application of photoelectrochemical technology but also provides a new form for the resource utilization of carbon dioxide. Summary of the Invention

[0009] In view of this, the purpose of this invention is to provide a method for synthesizing dimethyl carbonate that is mild, energy-efficient, environmentally friendly, and highly effective.

[0010] To achieve the above objectives, the present invention provides the following technical solution: A method for synthesizing dimethyl carbonate includes the following steps: (1) Carbon dioxide is introduced into the cathode chamber of an electrolytic cell containing potassium bicarbonate electrolyte, and a photoelectrochemical reaction is carried out at room temperature and pressure. Methanol is generated at the photocathode, forming a methanol mixed solution. (2) The methanol mixture is transported to the anode chamber of the electrolytic cell to form an electrolyte containing methanol. Carbon dioxide is continuously introduced and photoelectrochemical catalytic reaction is carried out at the photoelectro-anode to obtain dimethyl carbonate product.

[0011] Preferably, the flow rate of carbon dioxide introduced in step (1) is 5~50 mL / min.

[0012] Preferably, the concentration of potassium bicarbonate in the electrolyte in step (1) is 50~1000 mmol / L.

[0013] Preferably, the photocathode in step (1) comprises a co-catalyst and a silicon substrate covered with titanium oxide; the co-catalyst is a copper-based alloy catalyst; the copper-based alloy catalyst contains copper and other metals; the other metals include at least one of bismuth, zinc, tin, palladium, molybdenum, and cerium.

[0014] Preferably, the light intensity of the light source for the photoelectrochemical reaction in step (1) is 45~550 mW / cm². 2 The wavelength of the light source is 350~1200nm; the applied voltage for the photoelectrochemical reaction is 0~1.8V.

[0015] Preferably, in step (2), the concentration of methanol in the methanol-containing electrolyte is 0.1~0.5 mol / L; and the flow rate of carbon dioxide is 5~50 mL / min.

[0016] Preferably, the electrolyte in step (2) is at least one of phosphate buffer, potassium bicarbonate solution, potassium carbonate solution, sodium bicarbonate solution, potassium carbonate solution, hydrochloric acid solution, sulfuric acid solution, sodium hydroxide, and potassium hydroxide.

[0017] Preferably, the pH value of the methanol-containing electrolyte in step (2) is 8-8.5.

[0018] Preferably, the photoanode in step (2) comprises an n-type semiconductor absorber, a metal conductive layer, and a co-catalyst; the n-type semiconductor absorber is at least one of titanium oxide (TiO2), hematite (α-Fe2O3), and bismuth vanadate (BiVO3); the co-catalyst is a metal and its oxide, wherein the metal is at least one of palladium, copper, cerium oxide, and chromium oxide; the metal conductive layer is a transition metal and a noble metal, wherein the transition metal is at least one of iron and copper, and the noble metal is at least one of palladium and gold.

[0019] Preferably, the light intensity of the light source for the photoelectrochemical reaction in step (2) is 45~550 mW / cm². 2 The wavelength of the light source is 350~1200nm; the applied voltage for the photoelectrochemical reaction is 0~1.8V.

[0020] Compared with the prior art, the present invention has the following beneficial effects: (1) Mild conditions and low energy consumption: The synthesis method of the present invention does not require high temperature and high pressure conditions, and can be carried out at room temperature and pressure, which significantly reduces energy consumption and equipment requirements. By coupling the reduction and oxidation reactions of photoelectrochemical carbon dioxide conversion, the synthesis energy barrier of dimethyl carbonate is lowered and the energy utilization efficiency is improved.

[0021] (2) Green and environmentally friendly, sustainable: This invention uses greenhouse gas carbon dioxide as the main raw material, realizing the resource utilization of waste. The energy used is clean energy such as solar energy or electricity, avoiding pollution at the source. No toxic or harmful substances are involved or generated in the whole process, and the atom economy is high.

[0022] (3) Simplified process and high efficiency: This invention couples the two steps of carbon dioxide conversion and dimethyl carbonate synthesis, realizing the recycling of methanol, a reactant, within the system and simplifying the process flow. The combined use of light and electricity produces a synergistic effect, improving the reaction rate and the selectivity of dimethyl carbonate.

[0023] (4) Low cost and high flexibility: The raw material carbon dioxide is widely available (such as industrial waste gas, atmospheric capture, etc.) and is inexpensive. This method can be combined with renewable energy (such as solar and wind power) power generation systems to achieve stable storage and conversion of "renewable energy → chemical energy", which has high flexibility and sustainability. Attached Figure Description

[0024] Figure 1 Here is a surface SEM image of the photocathode prepared in Example 1 of this invention; Figure 2This is a graph showing the change in current density over time during the synthesis of dimethyl carbonate in Example 1 of the present invention. Figure 3 The LSV (linear sweep voltammetry) curve is obtained by testing the change of current density over time under the light-chopping conditions during the synthesis of dimethyl carbonate in Example 1 of this invention (for comparison of LSV of photocurrent and dark current).

[0025] Figure 4 The above is the 1H NMR spectrum of the dimethyl carbonate product synthesized in Example 1 of this invention; Figure 5 The graph shows the yield and Faraday efficiency of dimethyl carbonate at different potentials during the synthesis of dimethyl carbonate in Examples 1, 2, 3, and 4 of this invention. Figure 6 This is a diagram of the apparatus used in this invention to synthesize dimethyl carbonate by combining photoelectrochemical reduction-oxidation reactions. Detailed Implementation

[0026] This invention provides a method for synthesizing dimethyl carbonate, comprising the following steps: (1) Carbon dioxide is introduced into the cathode chamber of an electrolytic cell containing potassium bicarbonate electrolyte, and a photoelectrochemical reaction is carried out at room temperature and pressure. Methanol is generated at the photocathode, forming a methanol mixed solution. (2) The methanol mixture is transported to the anode chamber of the electrolytic cell to form an electrolyte containing methanol. Carbon dioxide is continuously introduced and photoelectrochemical catalytic reaction is carried out at the photoelectro-anode to obtain dimethyl carbonate product.

[0027] Preferably, the flow rate of carbon dioxide introduced in step (1) is 5~50 mL / min, and more preferably 20~40 mL / min.

[0028] Preferably, the concentration of potassium bicarbonate in the electrolyte in step (1) is 50~1000 mmol / L.

[0029] Preferably, the photocathode in step (1) comprises a co-catalyst and a silicon substrate covered with titanium oxide; the co-catalyst is a copper-based alloy catalyst; the copper-based alloy catalyst contains copper and other metals; the other metals include at least one of bismuth, zinc, tin, palladium, molybdenum, and cerium.

[0030] Preferably, the light intensity of the light source for the photoelectrochemical reaction in step (1) is 45~550 mW / cm². 2 The wavelength of the light source is 350~1200nm; the applied voltage for the photoelectrochemical reaction is 0~1.8V.

[0031] Preferably, the concentration of methanol in the methanol-containing electrolyte in step (2) is 0.1~0.5 mol / L.

[0032] Preferably, the electrolyte in step (2) is at least one of phosphate buffer, potassium bicarbonate solution, potassium carbonate solution, sodium bicarbonate solution, potassium carbonate solution, hydrochloric acid solution, sulfuric acid solution, sodium hydroxide, and potassium hydroxide.

[0033] Preferably, the pH value of the methanol-containing electrolyte in step (2) is 8-8.5; the flow rate of the carbon dioxide is 5-50 mL / min, preferably 20-40 mL / min.

[0034] Preferably, the photoanode in step (2) comprises an n-type semiconductor absorber, a metal conductive layer, and a co-catalyst; the n-type semiconductor absorber is at least one of titanium oxide (TiO2), hematite (α-Fe2O3), and bismuth vanadate (BiVO3); the co-catalyst is a metal and its oxide, wherein the metal is at least one of palladium, copper, cerium oxide, and chromium oxide; the metal conductive layer is a transition metal and a noble metal, wherein the transition metal is at least one of iron and copper, and the noble metal is at least one of palladium and gold.

[0035] Preferably, the light intensity of the light source for the photoelectrochemical reaction in step (2) is 45~550 mW / cm². 2 The wavelength of the light source is 350~1200nm; the applied voltage for the photoelectrochemical reaction is 0~1.8V.

[0036] Preferably, the method for preparing the photocathode in step (1) includes the following steps: S1-1 involves metal-catalyzed chemical etching of the p-type Si substrate. The specific steps are as follows: S1-1-1 was ultrasonically cleaned with acetone, ethanol and deionized water at 100W power for 20 minutes to remove surface impurities, and then rinsed with 5% hydrofluoric acid (HF) for 30 seconds to remove the oxide layer. S1-1-2 is immersed in a solution of HF (5M) and 0.02M silver nitrate (AgNO3) in a volume ratio of 1:1 for 60 seconds at room temperature to uniformly deposit a layer of silver nanoparticles on the silicon surface. S1-1-3 The deposited substrate is immersed in the core etching solution (HF, H2O2:H2O volume ratio of 1:1:10) and reacted at room temperature for 10 min to 1 h. The silver nanoparticles catalyze the vertical dissolution of the silicon below them to form nanowires. S1-1-4 is soaked in concentrated nitric acid (68%) for 15-30 minutes to completely remove the silver nanoparticles on the surface, and then washed and dried with deionized water to finally obtain a pure silicon nanowire array, resulting in a pretreated substrate with a porous structure with an average pore size of 20nm~50nm and an average pore depth of 50nm~200nm. S1-1-5 On the pretreated substrate, plasma-enhanced chemical vapor deposition is used to deposit a phosphorus-doped amorphous silicon thin film with a thickness of 50-150 nm to form an n-type layer under the conditions of temperature 250-350℃ and power 30-60W, by introducing a mixed gas of silane and phosphine (flow rate ratio SiH4:PH3=100:1). S1-1-6 is thermally annealed at 600-800℃ for 1-5 minutes in a nitrogen atmosphere to partially crystallize it and activate the dopant, forming the n+p structure surface. S1-1-7 Perform metal-catalyzed chemical etching on the surface of the n+p structure: Immerse it in a solution of HF (40%) and AgNO3 (0.02M) in a volume ratio of 4:1 for 1 minute to deposit silver particles, then transfer it to an etching solution of HF, H2O2 and H2O in a volume ratio of 1:1:10 and react for 10-30 minutes (room temperature). The silver particles simultaneously catalyze the penetration of the n-type layer into the p-type substrate, forming a vertical porous structure; finally, soak it in concentrated nitric acid (68%) for 20 minutes to remove the silver particles, and obtain an n+p type porous Si substrate.

[0037] In step S1-2, an amorphous transparent TiO2 semiconductor thin film with a thickness of 6-10 nm is formed on the surface of the n+p type porous Si substrate obtained in step S1-1 by magnetron sputtering, which serves as an electron transport layer. The parameters for the magnetron sputtering are as follows: the target material is Ti; the sputtering gas is a mixture of Ar and O2, the total pressure of the sputtering gas is 3.0 Pa, and the partial pressure of O2 is 50%; the distance between the target and the substrate is 10 cm; the deposition time is 80 min; the RF power applied to the target is 150 W; and the chamber temperature at the end of deposition is 40 °C. In step S1-3, a co-catalyst CuIn or CuBi, isopropanol, and Nafion solution (perfluorosulfonic acid-based polymer, 5 wt%) are mixed (2 mg co-catalyst + 960 μL isopropanol + 40 μL Nafion solution). The mixture is then ultrasonically dispersed at 100 W for 20 minutes to obtain a slurry containing CuIn or CuBi co-doped carbon composite material. 50 μL of the uniformly mixed catalyst slurry is then evenly drop-coated onto the surface of the TiO2 film obtained in step S1-2. After natural drying, a co-catalyst layer is formed, resulting in a photocathode.

[0038] Preferably, the method for preparing the photoanode in step (2) includes the following steps: S2-1 deposits anatase TiO2 semiconductor thin films with a thickness of over 1000 nm on the surface of an FTO substrate using magnetron sputtering, serving as an n-type semiconductor light absorber; The parameters for the magnetron sputtering are as follows: the target material is Ti; the sputtering gas is a mixture of Ar and O2, the total pressure of the sputtering gas is 2.0 Pa, and the partial pressure of O2 is 50%; the distance between the target and the substrate is 4 cm; the deposition time is 300 min; the DC power applied to the target is 460 W; and the chamber temperature at the end of deposition is 150 °C. In step S2-2, a PdCu alloy layer with a thickness of 6-10 nm is deposited on the surface of the n-type semiconductor light absorber obtained in step S2-1 by magnetron sputtering, serving as an electron transport layer. The parameters for the magnetron sputtering are as follows: the target material is Pd and Cu (mass ratio of 1:1 to 1:10); the sputtering gas is Ar gas, and the sputtering pressure is 2.0 Pa; the distance between the target and the substrate is 10 cm; the deposition time is 2 min; the RF power applied to the target is 6 W; and the chamber temperature at the end of deposition is 20 °C. S2-3 By magnetron sputtering, an amorphous transparent CeO2 semiconductor thin film with a thickness of 2~5nm is formed on the surface of the n-type semiconductor absorber / metal conductive layer obtained in step S2-2, as a co-catalyst; The parameters for magnetron sputtering are as follows: the target material is Ce; the sputtering gas is a mixture of Ar and O2, the total pressure of the sputtering gas is 3.0 Pa, and the partial pressure of O2 is 50%; the distance between the target and the substrate is 10 cm; the deposition time is 10 min; the RF power applied to the target is 150 W; and the chamber temperature at the end of deposition is 20 °C.

[0039] The present invention will be further described below with reference to the embodiments.

[0040] Example 1 A method for synthesizing dimethyl carbonate, comprising the following steps: Step 1: Fabrication of the photocathode: (1) A p-type Si substrate is subjected to metal-catalyzed chemical etching to obtain a pretreated substrate with a porous structure having an average pore size of (5-7) nm and an average pore depth of (200) nm; n-type Si is deposited on the surface of the pretreated substrate to obtain an n+p-type porous Si substrate; the specific steps are as follows: S1-1-1 was ultrasonically cleaned with acetone, ethanol and deionized water at 100W power for 20 minutes to remove impurities on the p-type Si substrate surface, and then rinsed with 5% hydrofluoric acid (HF) for 30 seconds to remove the oxide layer. S1-1-2 is immersed in a 1:1 mixture of HF (5M) and 0.02M silver nitrate (AgNO3) at room temperature for 60 seconds to uniformly deposit a layer of silver nanoparticles on the silicon surface. S1-1-3 The deposited substrate is immersed in the core etching solution (HF, H2O2:H2O volume ratio of 1:1:10) and reacted at room temperature for 10 min to 1 h. The silver nanoparticles catalyze the vertical dissolution of the silicon below them to form nanowires. S1-1-4 is soaked in concentrated nitric acid (68%) for 15-30 minutes to completely remove the silver nanoparticles on the surface, and then washed and dried with deionized water to finally obtain a pure silicon nanowire array, resulting in a pretreated substrate with a porous structure with an average pore size of 20nm~50nm and an average pore depth of 50nm~200nm. S1-1-5 On the pretreated substrate, plasma-enhanced chemical vapor deposition is used to deposit a phosphorus-doped amorphous silicon thin film with a thickness of 50-150 nm to form an n-type layer under the conditions of temperature 250-350℃ and power 30-60W, by introducing a mixed gas of silane and phosphine (flow rate ratio SiH4:PH3=100:1). S1-1-6 is thermally annealed at 600-800℃ for 1-5 minutes in a nitrogen atmosphere to partially crystallize it and activate the dopant, forming the n+p structure surface. S1-1-7 Perform metal-catalyzed chemical etching on the surface of the n+p structure: Immerse it in a solution of HF (40%) and AgNO3 (0.02M) in a volume ratio of 4:1 for 1 minute to deposit silver particles, then transfer it to an etching solution of HF, H2O2 and H2O in a volume ratio of 1:1:10 and react for 10-30 minutes (room temperature). The silver particles simultaneously catalyze the penetration of the n-type layer and enter the p-type substrate to form a vertical porous structure. Finally, soak it in concentrated nitric acid (68%) for 20 minutes to remove the silver particles and obtain an n+p type porous Si substrate.

[0041] (2) By magnetron sputtering, an amorphous transparent TiO2 semiconductor thin film with a thickness of (5-10) nm is formed on the surface of the n+p type porous Si substrate obtained in step (1) as an electron transport layer; The parameters for magnetron sputtering are as follows: the target material is Ti; the sputtering gas is a mixture of Ar and O2, the total pressure of the sputtering gas is 3.0 Pa, and the partial pressure of O2 is 50%; the distance between the target and the substrate is 10 cm; the deposition time is 80 min; the RF power applied to the target is 150 W; and the chamber temperature at the end of deposition is 40 °C.

[0042] (3) 2 mg of CuIn co-catalyst powder particles were mixed with 50-200 nm, 960 μL of isopropanol and 40 μL of nafion (perfluorosulfonic acid polymer, 5 wt%), and ultrasonically dispersed for 20 min to obtain a slurry containing CuIn co-doped carbon composite material; the slurry containing CuIn co-doped carbon composite material was uniformly drop-coated onto the surface of the TiO2 semiconductor film obtained in step (2), and after natural drying, a catalytic layer was formed to obtain a photocathode.

[0043] Step 2: Preparation of the photoanode: (1) A 2000 nm thick anatase TiO2 semiconductor thin film was deposited on the surface of an FTO substrate by magnetron sputtering to serve as an n-type semiconductor light absorber; The parameters for the magnetron sputtering are as follows: the target material is Ti; the sputtering gas is a mixture of Ar and O2, the total pressure of the sputtering gas is 2.0 Pa, and the partial pressure of O2 is 50%; the distance between the target and the substrate is 4 cm; the deposition time is 300 min; the DC power applied to the target is 460 W; and the chamber temperature at the end of deposition is 150 °C. (2) By magnetron sputtering, a PdCu alloy layer with a thickness of 6~10nm is deposited on the surface of the n-type TiO2 absorber obtained in step (1) as an electron transport layer; The parameters for the magnetron sputtering are as follows: the target material is Pd and Cu (molar ratio of 1:1), the sputtering gas is Ar gas, the sputtering pressure is 2.0 Pa, the distance between the target and the substrate is 10 cm, the deposition time is 2 min, the RF power applied to the target is 6 W, and the chamber temperature at the end of deposition is 20 °C. (3) By magnetron sputtering, an amorphous transparent CeO2 semiconductor thin film with a thickness of 2~5nm is formed on the surface of the n-type semiconductor light absorber / metal conduction layer obtained in step (2) as a co-catalyst to form a photoanode (TiO2 / PdCu / CeO2). The parameters for magnetron sputtering are as follows: the target material is Ce; the sputtering gas is a mixture of Ar and O2, the total pressure of the sputtering gas is 3.0 Pa, and the partial pressure of O2 is 50%; the distance between the target and the substrate is 10 cm; the deposition time is 10 min; the RF power applied to the target is 150 W; and the chamber temperature at the end of deposition is 20 °C.

[0044] Step 3: Preparation of dimethyl carbonate (1) The photocathode and photoanode are used as the working electrodes of the cathode chamber and anode chamber, respectively, and the cathode chamber and anode chamber are separated by a Nafion membrane; 15 mL of potassium bicarbonate electrolyte (potassium bicarbonate concentration of 0.1 mol / L) is added to the cathode chamber and anode chamber, respectively, and carbon dioxide is continuously introduced. The power supply is turned on, and the applied voltage is (-0.4) V, and the light intensity is (100) mW / cm. 2 A light source with a wavelength of (460) nm illuminates the photocathode and the photoanode; (2) Carbon dioxide is introduced into the cathode chamber of the electrolytic cell containing electrolyte at a flow rate of 30 mL / min. The photoelectrochemical reaction is carried out at room temperature and pressure, and methanol is generated at the photocathode to form a methanol mixed solution. (3) The methanol mixture is transported to the anode chamber of the electrolytic cell to form a potassium bicarbonate electrolyte containing methanol (the concentration of potassium bicarbonate is 0.1 mol / L, the concentration of methanol is 10 mmol / L, and the pH of the electrolyte is 8.3). Carbon dioxide is continuously introduced at a flow rate of 30 mL / min, and a photoelectrochemical catalytic reaction is carried out at the photoanode to obtain dimethyl carbonate product.

[0045] The surfaces of the photoanode and photocathode prepared in Example 1 were characterized using field emission scanning electron microscopy. The surface SEM image of the photoanode prepared in Example 1 is shown in Figure 1.

[0046] Electrochemical it (current-time) measurements were performed using an Autolab electrochemical workstation to obtain the current density versus time curve during the synthesis of dimethyl carbonate in Example 1, as shown in the figure below. Figure 2 As shown, by Figure 2 It can be seen that the photoelectric-driven synthesis process of dimethyl carbonate in Example 1 has good stability.

[0047] Electrochemical detection was performed using an Autolab electrochemical workstation, and the LSV (linear sweep voltammetry) curves during the synthesis of dimethyl carbonate in Example 1 are shown in the figure below. Figure 3 As shown, Figure 3 To show the change in current density with potential under chopping conditions, from Figure 3 It can be seen that the photoanode and photocathode prepared in Example 1 have good response under illumination conditions.

[0048] The 1H NMR spectrum of the dimethyl carbonate product synthesized in Example 1, as detected by nuclear magnetic resonance spectroscopy, is shown below. Figure 4 As shown, by Figure 4 It can be seen that in the photoelectrochemical reaction process in Example 1, under the catalysis of the photoanode and photocathode, the reaction of carbon dioxide and methanol to produce dimethyl carbonate was successfully promoted.

[0049] Example 1: Statistical graphs of dimethyl carbonate yield and Faraday efficiency at different potentials during the synthesis of dimethyl carbonate under different electrical potentials are shown below. Figure 5 As shown, the column represents the yield of dimethyl carbonate, and the broken line represents the Faraday efficiency. Figure 5 As can be seen, Example 1 utilizes the oxidative coupling of carbon dioxide and methanol to form dimethyl carbonate, achieving a dimethyl carbonate yield of 88.12 mg·h⁻¹. -1 ·cm -2 It has a Faraday efficiency of up to 60%, exhibiting high dimethyl carbonate yield and Faraday efficiency.

[0050] Example 2 Dimethyl carbonate was synthesized using the same method as in Example 1, except that TiO2 / Cu / CeO2 was used as the photoelectric anode (the preparation method was the same as in Example 1, but the target material for magnetron sputtering in step (2) was Cu).

[0051] The current density versus time curve during the synthesis of dimethyl carbonate in Example 2 was obtained using an Autolab electrochemical workstation. Figure 6 As shown, by Figure 6 It can be seen that the process of using TiO2 / Cu / CeO2 photoanode to promote the coupling of CO2 and methanol to form dimethyl carbonate in Example 2 has good stability.

[0052] The yield and Faraday efficiency of dimethyl carbonate synthesis in Example 2 were obtained by NMR detection, as shown in the following graph. Figure 5 As shown, the column represents the yield of dimethyl carbonate, and the broken line represents the Faraday efficiency. Figure 5 As can be seen, Example 2 utilizes a TiO2 / Cu / CeO2 photoelectroanode to catalyze the coupling of carbon dioxide and methanol to form dimethyl carbonate, with a dimethyl carbonate yield reaching 66.7 mg·h⁻¹. -1 ·cm -2 The Faraday efficiency can reach (53.6)%, which has a high dimethyl carbonate yield and Faraday efficiency.

[0053] Example 3 Dimethyl carbonate was synthesized using the same method as in Example 1, except that TiO2 / CeO2 was used as the photoanode.

[0054] The yield and Faraday efficiency of dimethyl carbonate at different potentials during the synthesis of dimethyl carbonate in Example 3 were obtained by NMR detection, as shown in the following figure. Figure 5 As shown, the column represents the yield of dimethyl carbonate, and the broken line represents the Faraday efficiency. Figure 5As can be seen, Example 3 utilizes a TiO2 / PdCu / CeO2 photoelectroanode to catalyze the coupling of carbon dioxide and methanol to form dimethyl carbonate, with a dimethyl carbonate yield reaching 63.46 mg·h⁻¹. -1 ·cm -2 The Faraday efficiency can reach (47.15%), which has a high amino acid yield and Faraday efficiency.

[0055] Example 4 Dimethyl carbonate was synthesized using the same method as in Example 1, except that TiO2 / PdCu was used as the photoanode.

[0056] The yield and Faraday efficiency of dimethyl carbonate at different potentials during the synthesis of dimethyl carbonate in Example 4 were obtained by NMR detection, as shown in the following figure. Figure 5 As shown, the column represents the yield of dimethyl carbonate, and the broken line represents the Faraday efficiency. Figure 5 As can be seen, Example 4 utilizes a TiO2 / PdCu photoelectroanode to catalyze the coupling of carbon dioxide and methanol to form dimethyl carbonate, with a dimethyl carbonate yield reaching 8.06 mg·h⁻¹. -1 ·cm -2 The Faraday efficiency can reach (2.65%), which has a high dimethyl carbonate yield and Faraday efficiency.

[0057] In summary, the photoanodes prepared in Examples 1-3 using the method provided by this invention exhibit good response under illumination, demonstrate good stability in promoting the coupling of CO2 and methanol to form dimethyl carbonate, and exhibit high dimethyl carbonate yield and Faraday efficiency.

[0058] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for synthesizing dimethyl carbonate, characterized in that, Includes the following steps: (1) Carbon dioxide is introduced into the cathode chamber of an electrolytic cell containing potassium bicarbonate electrolyte, and a photoelectrochemical reaction is carried out at room temperature and pressure. Methanol is generated at the photocathode, forming a methanol mixed solution. (2) The methanol mixture is transported to the anode chamber of the electrolytic cell to form an electrolyte containing methanol. Carbon dioxide is continuously introduced and photoelectrochemical catalytic reaction is carried out at the photoelectro-anode to obtain dimethyl carbonate product.

2. The method for synthesizing dimethyl carbonate according to claim 1, characterized in that, The carbon dioxide flow rate in step (1) is 5~50 mL / min.

3. The method for synthesizing dimethyl carbonate according to claim 1, characterized in that, The concentration of potassium bicarbonate in the electrolyte in step (1) is 50~1000 mmol / L.

4. The method for synthesizing dimethyl carbonate according to claim 1, characterized in that, The photocathode in step (1) includes a co-catalyst and a silicon substrate covered with titanium oxide; the co-catalyst is a copper-based alloy catalyst; the copper-based alloy catalyst contains copper and other metals; the other metals include at least one of bismuth, zinc, tin, palladium, molybdenum, and cerium.

5. The method for synthesizing dimethyl carbonate according to claim 1, characterized in that, The light intensity of the light source for the photoelectrochemical reaction in step (1) is 45~550 mW / cm². 2 The wavelength of the light source is 350~1200nm; the applied voltage for the photoelectrochemical reaction is 0~1.8V.

6. The method for synthesizing dimethyl carbonate according to claim 1, characterized in that, In step (2), the concentration of methanol in the methanol-containing electrolyte is 0.1~0.5 mol / L; the flow rate of carbon dioxide is 5~50 mL / min.

7. The method for synthesizing dimethyl carbonate according to claim 1, characterized in that, The electrolyte in step (2) is at least one of phosphate buffer, potassium bicarbonate solution, potassium carbonate solution, sodium bicarbonate solution, potassium carbonate solution, hydrochloric acid solution, sulfuric acid solution, sodium hydroxide, and potassium hydroxide.

8. The method for synthesizing dimethyl carbonate according to claim 1, characterized in that, The pH value of the methanol-containing electrolyte in step (2) is 8-8.

5.

9. The method for synthesizing dimethyl carbonate according to claim 1, characterized in that, The photoanode in step (2) comprises an n-type semiconductor absorber, a metal conductive layer, and a co-catalyst; the n-type semiconductor absorber is at least one of titanium oxide, hematite, and bismuth vanadate; the co-catalyst is a metal and its oxide, wherein the metal is at least one of palladium, copper, cerium oxide, and chromium oxide; the metal conductive layer is a transition metal and a noble metal, wherein the transition metal is at least one of iron and copper, and the noble metal is at least one of palladium and gold.

10. The method for synthesizing dimethyl carbonate according to claim 1, characterized in that, The light intensity of the light source for the photoelectrochemical reaction in step (2) is 45~550 mW / cm². 2 The wavelength of the light source is 350~1200nm; the applied voltage for the photoelectrochemical reaction is 0~1.8V.

Images