Preparation method of binuclear iron complex and application of binuclear iron complex in electro-catalysis of carbon dioxide reduction

Abstract

The invention relates to the field of bio-enzyme chemistry and energy conversion, in particular to a preparation method of a bionic binuclear iron metal complex and application of the bionic binuclear iron metal complex in electro-catalysis of carbon dioxide. The preparation method of the bionic binuclear iron metal complex comprises the following steps: dissolving 4, 4 '-dimethoxybenzoin and phosphorus pentasulfide in 1, 4-dioxane, refluxing, cooling to room temperature, filtering, mixing with a nickel chloride aqueous solution, refluxing, cooling, filtering to obtain a solid, washing, draining, dissolving with Fe3 (CO) 12 in toluene, reacting, spin-drying, and carrying out chromatography to obtain a red solid, namely the complex. According to the complex, the activation energy of the step of catalyzing the reduction reaction of CO2 is reduced through the synergistic catalysis of the double metals, the selectivity of the complex to the catalytic reduction of CO2 is improved by selecting a proper proton source, the carbon dioxide is efficiently catalyzed to be reduced into formic acid, and the complex has a good prospect when being applied to the field of electrocatalytic reduction of the carbon dioxide.

Description

Technical Field

[0001] The invention relates to the field of bioenzyme chemistry and energy conversion technology, and specifically to a method for preparing a binuclear iron complex and its application in electrocatalytic carbon dioxide reduction. Background Art

[0002] Coal, oil and natural gas are the main fossil energy sources, and their usage is increasing day by day. Similarly, the greenhouse effect caused by the large-scale and continuous use of fossil energy has also become a problem that humans need to solve urgently. Directly or indirectly using clean renewable energy to reduce carbon dioxide into low-carbon or other usable chemicals can not only alleviate the over-exploitation of fossil energy, but also improve the greenhouse effect, thereby alleviating the problem of global warming.

[0003] As the final product of most combustion reactions, carbon dioxide has stable chemical properties and needs to overcome a very high energy barrier to achieve activation. For electrocatalytic reduction, a higher overpotential is required to promote the reaction. In addition, the reaction mechanism of electrocatalytic reduction of carbon dioxide is complex and diverse. Different reaction conditions allow electron transfer to have multiple options, and can generate methanol, formic acid or formate, ethylene, methane and other products. However, the hydrogen evolution reaction also occurs in the electrocatalytic reduction of carbon dioxide system, forming a competitive relationship with the carbon dioxide reduction reaction. In addition, the solubility of carbon dioxide in aqueous solution is low, which limits the rate of reduction reaction to a certain extent. It can be seen that it is crucial to find an efficient and inexpensive catalyst.

[0004] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention and should not be regarded as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the above technical defects, provide a method for preparing a binuclear iron complex and apply it to the electrocatalytic carbon dioxide reduction reaction. The bionic binuclear iron metal complex can be used as a catalyst for the reduction of carbon dioxide to formic acid, and has the characteristics of low cost, high chemical selectivity and high catalytic efficiency.

[0006] In order to solve the above problems, the technical solution of the present invention is a method for preparing a binuclear iron complex, comprising the following steps:

[0007] S1: Dissolve 4,4'-dimethoxybenzoin and phosphorus pentasulfide in 1,4-dioxane and reflux for 2h;

[0008] S2: The solution was cooled to room temperature, filtered, mixed with an aqueous solution containing nickel chloride hexahydrate, and refluxed for 2 h;

[0009] S3: The solution was cooled to 0°C, a black solid was precipitated, washed twice with a small amount of CH2Cl2, and dried to obtain a NiS4 complex;

[0010] S4: NiS4 complex and Fe3(CO) 12 Dissolve in toluene and react at 80°C for 24 hours;

[0011] S5: The solvent is dried to obtain a solid, and the solid is chromatographed on a silica gel column using n-hexane and CH2Cl2 as developing agents to obtain a biomimetic binuclear iron metal complex.

[0012] Furthermore, the molar ratio of 4,4'-dimethoxybenzoin to phosphorus pentasulfide in S1 is 1:1-1.4.

[0013] Furthermore, the molar ratio of 4,4'-dimethoxybenzoin to nickel chloride hexahydrate in S2 is 1:0.45-0.50.

[0014] Further, the reaction environment in the S4 is one of nitrogen or argon, the temperature is 80-100°C, the NiS4 complex and Fe3(CO) 12 The molar ratio is 1:1.6-2.0.

[0015] Furthermore, the volume ratio of n-hexane to CH2Cl2 as the developing agent in S5 is 9-5:1, and the column chromatography should be performed quickly to avoid adsorption of the complex.

[0016] Furthermore, the complex has a rigid, conjugated S^S bridge structure, and the complex with this structure has higher carbon dioxide reduction activity.

[0017] Furthermore, the preparation method of the binuclear iron complex is applied in catalytic carbon dioxide reduction, characterized in that the bionic binuclear iron metal complex is used for electrocatalytic reduction of carbon dioxide to formic acid.

[0018] The advantages of the present invention compared with the prior art are:

[0019] 1. The bionic binuclear iron metal complex containing S^S bridging structure prepared by the present invention is a new compound and has the ability to catalyze the reduction of carbon dioxide to formic acid. The two carbon-sulfur bridges in its structure are believed to have the effect of promoting the catalytic reduction of carbon dioxide, and functionally simulate the carbon dioxide reduction ability of [NiFe]CODHs.

[0020] 2. The structural characteristics of the bionic binuclear iron metal complex prepared by the present invention are completely different from the different types of binuclear iron metal complexes that have been disclosed, that is, the molecular structure of the target complex described in the present invention contains both a diiron-disulfide metal organic skeleton and a 4,4'-dimethoxystilbene macroconjugated structure, which well simulates the bimetallic structure of the [NiFe]CODHs active center in terms of structure. However, the molecular structures of different types of bionic binuclear iron metal complexes in the existing patents have not been found to have electrocatalytic carbon dioxide reduction performance.

[0021] 3. The preparation method of the present invention is simple and convenient to operate, the raw materials are cheap and easily available, and the reaction conditions are easy to control, and a variety of bionic binuclear iron-metal complexes can be prepared. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The cyclic voltammetry curve of the complex 1 in the present invention is shown in FIG. 1, with a scan rate of 0.1 Vs -1 .

[0023] Figure 2 is a cyclic voltammetry curve of the complex 1 in the embodiment of the present invention when the concentration of methanol in a CO2-saturated acetonitrile solution increases from 0 M to 1.75 M, Figure 2 The inset is a graph showing the relationship between the catalytic peak current and the methanol concentration of the complex 1 according to the embodiment of the present invention.

[0024] Figure 3 The cyclic voltammetry curves of the complex 1 in the CO2-saturated acetonitrile solution containing methanol and the cyclic voltammetry curves of the control experiment without methanol, CO2 or catalyst are shown in the figure.

[0025] Figure 4 a is a cyclic voltammetry curve of the complex 1 at different scanning speeds in the present invention under an argon atmosphere; Figure 4 b is a relationship diagram between the catalytic peak current of the complex 1 obtained from the cyclic voltammetry curve and the half of the scan rate.

[0026] Figure 5 a is the cyclic voltammetry curve of the complex 1 of different concentrations in an acetonitrile solution containing 2.0 M methanol under a CO2 atmosphere according to the embodiment of the present invention; Figure 5 b is the relationship between the catalytic current of complex 1 and its concentration obtained from the cyclic voltammetry curve.

[0027] Figure 6 a is the cyclic voltammetry curves of 1.0 mM complex 1 in a saturated CO2 solution containing 2.0 M methanol and acetonitrile at different scan rates according to the embodiment of the present invention; Figure 6 b is the linear relationship between the ratio of the catalytic current to the non-catalytic current of complex 1 obtained from the cyclic voltammetry curve and the negative half power of the scan rate.

[0028] Figure 7 This is the electrolysis curve of the embodiment of the present invention in which 0.5 mM complex 1 was electrolyzed in a CO2-saturated acetonitrile solution of 0.5 M MeOH and 0.1 M nBu4NPF6 at a potential of -2.25 V for 10 hours.

[0029] Figure 8 It is the chemical molecular formula diagram of the bionic binuclear iron metal complex 1 of the present invention.

[0030] Fig. 9 It is a synthetic route map of the bionic binuclear iron metal complex 1 of the present invention. DETAILED DESCRIPTION

[0031] In order to make the contents of the present invention more clearly understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0032] The present invention provides a method for preparing a bionic binuclear iron metal complex and electrocatalytic carbon dioxide, comprising the following steps:

[0033] Dissolve 4,4'-dimethoxybenzoin (32g, 0.12mol) and phosphorus pentasulfide (38g, 0.086mol) in 1,4-dioxane (200mL) and reflux for 2 hours. The solution slowly changes from a yellow turbid liquid to a red transparent liquid, during which hydrogen sulfide gas is released;

[0034] The solution was cooled to room temperature, the insoluble matter was filtered off, and the solution was mixed with 200 mL of aqueous solution containing nickel chloride hexahydrate (12.5 g, 0.053 mol) to turn into a black emulsion, which was refluxed for 2 hours. The solution was cooled to about 0°C to precipitate a black solid, and the filtered solid was washed twice with a small amount of CH2Cl2 and dried to obtain a NiS4 complex (14 g);

[0035] Under nitrogen atmosphere, NiS4 complex (1.0 g, 1.5 mmol) and Fe3(CO) 12 (1.5 g, 3 mmol) was dissolved in 50 mL of toluene and reacted at 80 °C for 24 hours. The solvent was dried and the obtained solid was chromatographed on a silica gel column using n-hexane / CH2C l2 (v / v, 9:1) was used as the developing solvent to obtain 1.7 g of red solid with a yield of 82%.

[0036] The experimental method of electrochemical cyclic voltammetry of biomimetic binuclear iron metal complexes is as follows:

[0037] The experiment was conducted on a CHI 630E electrochemical workstation using a classic three-electrode system with a 3mm diameter glassy carbon electrode as the working electrode, a platinum wire as the counter electrode, and an Ag / AgCl electrode as the reference electrode in a cylindrical tank under an argon atmosphere. Before each test, the glassy carbon electrode was polished with aluminum oxide powder, then ultrasonically cleaned in water, rinsed with acetone, and dried with cold air. The solvent of the test system was 10ml of chromatographically pure acetonitrile, the supporting electrolyte was 0.1mol / L nBu4NPF6, and the protonic acid was methanol of different concentrations. The potentials obtained from the test were all reduction potentials corrected by ferrocene.

[0038] In the electrolysis experiment, the working electrode is 2.0 cm 2 The working electrode and the auxiliary electrode were a 10×10 mm platinum mesh, and the reference electrode was an Ag / AgCl electrode, forming a three-electrode system. In order to reduce the voltage drop caused by the solution resistance, the working electrode and the auxiliary electrode were placed as close as possible. In addition, the platinum mesh, as an auxiliary electrode, had an area similar to that of the working electrode to avoid excessive accumulation of electrons or protons on one side of the electrode. In the experiment, 0.1 M nBu4NPF6 was used as a supporting electrolyte, and chromatographically pure acetonitrile was used as the solvent. The electrolytic cell used a well-sealed "H" type electrolytic cell, and the cathode and anode were separated by a pre-treated proton exchange membrane (DuPont N117) to ensure the isolation of the cathode and anode electrolytes. The amount of electrolyte in the cathode and anode cells was approximately 8 ml and 7 ml, respectively, ensuring that the proton exchange membrane was completely covered by the electrolyte. Before the experiment began, the electrolyte was saturated with CO2 gas for about 30 minutes. During the entire test process, the system remained sealed and the electrolyte was continuously stirred to ensure uniformity.

[0039] Depend on Figure 1 It can be seen that the redox properties of the biomimetic binuclear iron metal complex are: at -1.26V (unless otherwise specified, all potentials in the present invention are relative to Fc + / 0 ) a redox peak appears, corresponding to Fe I Fe I / Fe 0 Fe 0 The process is a two-electron reduction process.

[0040] Depend on Figure 2 It can be seen that in the CO2-saturated MeCN solution, as the concentration of MeOH gradually increases, the catalytic peak current of the complex gradually increases. When the concentration of MeOH reaches 1.5M, the catalytic peak current of the complex reaches the maximum value (622μA). When the concentration of MeOH is less than 1.5M, the catalytic peak current of the complex gradually increases with the concentration of methanol; when the concentration of MeOH is greater than 1.5M, the catalytic peak current of the complex hardly changes.

[0041] Depend on Figure 3 It can be seen that the catalytic performance of the complex is as follows: in the electrochemical test system containing the biomimetic binuclear iron metal complex, after adding methanol (proton source), the peak current (catalytic current) of the reduction peak of the complex is significantly increased. Control experiments show that when there is no MeOH, no CO2, or no catalyst in the system, no catalytic current is observed before -2.35V. This shows that the biomimetic binuclear iron metal complex prepared above has catalytic carbon dioxide reduction activity.

[0042] In order to calculate the kinetic data of the catalytic carbon dioxide reduction of the complex TOF max , certain conditions need to be met: Figure 4 and Figure 5 The non-catalytic current i p With v 1 / 2 The catalytic current i c It is linearly related to the catalyst concentration. Figure 6 It is known that the scanning speed is between 50 and 200 mV s -1 When c / i p With v 1 / 2 The TOF is calculated based on the linear relationship max 183s -1 .

[0043] In order to avoid the HCOOH generated during the CO2 reduction process from inducing proton reduction and hydrogen production, which would interfere with the electrochemical test, a mercury cell was selected as the working electrode in the controlled potential electrolysis experiment of the complex. Figure 7 It is known that the electrolysis experiment of the complex was carried out at a potential of -2.25V and in a CO2-saturated methanol (0.5M) / acetonitrile solution. The catalytic current of the complex can be stabilized at about 0.4mA. Limited by the stability of the catalytic system, the electrolysis current decayed after 10h. Analysis of the electrolysis products of the first hour revealed that the electrolyte contained HCOOH, and the gas phase contained CO and H2, with Faraday efficiencies of 61%, 8% and 16% respectively.

[0044] The present invention and its embodiments are described above, which is not restrictive. The drawings are only one of the embodiments of the present invention. In short, if ordinary technicians in the field are inspired by it and design structural methods and embodiments similar to the technical solution without creativity without departing from the purpose of the invention, they should all fall within the protection scope of the present invention.

Claims

1. A method for preparing a binuclear iron complex, characterized in that , including the following steps: S1: Dissolve 4,4'-dimethoxybenzoin and phosphorus pentasulfide in 1,4-dioxane and reflux for 2h; S2: The solution was cooled to room temperature, filtered, mixed with an aqueous solution containing nickel chloride hexahydrate, and refluxed for 2 h; S3: The solution was cooled to 0°C, a black solid was precipitated, washed twice with a small amount of CH2Cl2, and dried to obtain a NiS4 complex; S4: NiS4 complex and Fe3(CO) 12 Dissolve in toluene and react at 80°C for 24 hours; S5: The solvent is dried to obtain a solid, and the solid is chromatographed on a silica gel column using n-hexane and CH2Cl2 as developing agents to obtain a biomimetic binuclear iron metal complex.

2. The method for preparing a binuclear iron complex according to claim 1, characterized in that: The molar ratio of 4,4'-dimethoxybenzoin to phosphorus pentasulfide in S1 is 1:1-1.

4.

3. The method for preparing a binuclear iron complex according to claim 1, characterized in that: The molar ratio of 4,4'-dimethoxybenzoin to nickel chloride hexahydrate in S2 is 1:0.45-0.

50.

4. The method for preparing a binuclear iron complex according to claim 1, characterized in that: The reaction environment in the S4 is one of nitrogen or argon, the temperature is 80-100°C, the NiS4 complex and Fe3(CO) 12 The molar ratio is 1:1.6-2.

0.

5. The method for preparing a binuclear iron complex according to claim 1, characterized in that: The n-hexane and CH2C l2 The volume ratio of the developing solvent is 9-5:1, and the column chromatography should be performed quickly to avoid adsorption of the complex.

6. The method for preparing a binuclear iron complex according to claim 1, characterized in that: The complex has a rigid, conjugated S^S bridge structure, and the complex with this structure has higher carbon dioxide reduction activity.

7. The method for preparing a binuclear iron complex according to claims 1-6 is used in catalytic carbon dioxide reduction, characterized in that: The bionic binuclear iron metal complex is used for electrocatalytic reduction of carbon dioxide to formic acid.

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