A catalyst for reducing carbon dioxide, a liquid composition or electrode containing the catalyst for reducing carbon dioxide, an electrolytic cell containing the electrode, and a method for reducing carbon dioxide using the electrode.

Abstract

To provide an excellent carbon dioxide reduction catalyst, a liquid composition or electrode containing the carbon dioxide reduction catalyst, and a carbon dioxide reduction method using the carbon dioxide reduction catalyst. [Solution] The solution comprises a metal complex and a conductive material, wherein the metal complex is of the following formula (I): TIFF2026148219000031.tif37170 A catalyst for carbon dioxide reduction, a liquid composition or electrode containing a metal complex represented by the formula (wherein M is a copper atom, A1 to A4 each independently represent an aromatic ring structure, at least one of A1 to A4 contains one or more nitrogen atoms or sulfur atoms in the atoms constituting the aromatic ring, and substituents may be attached to each of the ring structures of A1 to A4), and a method for carbon dioxide reduction using a carbon dioxide reduction catalyst.

Description

Technical Field

[0001] The present invention relates to a novel catalyst for carbon dioxide reduction, a liquid composition or electrode comprising the catalyst for carbon dioxide reduction, an electrolytic cell comprising the electrode, and a method for reducing carbon dioxide using the electrode. Background Art

[0002] Toward decarbonization as part of global warming countermeasures, production of synthetic fuels manufactured by reduction of carbon dioxide has attracted attention. Conventionally, as a method for synthesizing methane by reducing carbon dioxide (methanation), the so-called Sabatier reaction, in which carbon dioxide is reduced with hydrogen generated by electrolysis of water, has been known. However, this reaction requires high temperature and high pressure, and has a problem that the methane yield remains at about 50%.

[0003] Accordingly, from the viewpoints of improving methane yield, reducing cost, and thermal management, methanation by electrolytic reduction of carbon dioxide has attracted attention. Electrolytic reduction of carbon dioxide is a technology that decomposes carbon dioxide using electrical energy to synthesize more reduced carbon compounds such as methane and carbon monoxide. Synthetic fuels produced by electrolytic reduction of carbon dioxide are called e-fuels and e-methane, and are expected as next-generation fuels because they are not only easy to store but also have high energy density.

[0004] Catalysts are generally used in the electrolytic reduction of carbon dioxide. As carbon dioxide reduction catalysts, those using noble metals or rare metals such as ruthenium and rhenium have been conventionally known.

[0005] However, because rare metals are expensive and their resources are limited, attempts are being made to develop catalysts using cheaper and more abundant materials. Here, metal porphyrins are known to have various catalytic activities, including carbon dioxide reduction. For example, Patent Document 1 describes a cathode electrode for a gas diffusion type electrolytic flow cell that produces carbon dioxide reduction products, and states that by using a predetermined metal as the central metal of the metal complex catalyst, it is possible to reduce the overpotential in the carbon dioxide reduction reaction, and that for this purpose, the central metal of the metal complex is more preferably Co, Mn, or Ru.

[0006] Patent Document 2 describes a method for producing carbon monoxide by an electrochemical reduction reaction of carbon dioxide using an electrode in which a metal porphyrin complex catalyst is supported on a conductive material. However, the method described in Patent Document 2 has the problem that the carbon dioxide reduction activity of the electrode is insufficient due to the low activity of the metal complex catalyst, and that the hydrogen evolution reaction proceeds in competition with the carbon dioxide reduction reaction, resulting in insufficient selectivity for the carbon dioxide reduction reaction. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2023-17501 [Patent Document 2] Japanese Patent Publication No. 2018-34136 [Overview of the project] [Problems that the invention aims to solve]

[0008] Therefore, there was a need to develop a catalyst with excellent carbon dioxide reduction catalytic activity without using precious metals or rare metals. Furthermore, there was a need for a method that could produce methane in a single step with high Faraday efficiency, without passing through carbon monoxide or formic acid during the reduction of carbon dioxide.

[0009] The present invention has been made to solve the problems of the prior art described above, and aims to provide a carbon dioxide reduction catalyst having excellent carbon dioxide reduction catalytic activity, a liquid composition or electrode containing the carbon dioxide reduction catalyst, an electrolytic cell containing the electrode, and a method for reducing carbon dioxide using the electrode. [Means for solving the problem]

[0010] As a result of diligent research into the above-mentioned problems, the inventors unexpectedly discovered that a novel phthalocyanine catalyst having copper as the central metal exhibits excellent carbon dioxide reduction catalytic activity, leading to the present invention. In particular, they found that by keeping the amount of catalyst used low when using a metal complex as a catalyst, very high selectivity is achieved in methane synthesis, thus completing the present invention.

[0011] The object of the present invention is achieved by a carbon dioxide reduction catalyst comprising a metal complex and a conductive material. Preferably, the carbon dioxide reduction catalyst of the present invention has an azaphthalocyanine skeleton.

[0012] [1] A catalyst for carbon dioxide reduction comprising a metal complex and a conductive material, wherein the following formula [ka] (In the formula, M is a copper atom, A1 to A4 each independently represent an aromatic ring structure. At least one of A1 to A4 contains one or more nitrogen atoms or sulfur atoms in the atoms constituting the aromatic ring, (Each of the ring structures A1 to A4 may have substituents attached.) A catalyst for reducing carbon dioxide, represented by the symbol.

[0013] [2] The metal complex is represented by the following formulas (1), (2), or (3): [ka] (In the formula, M is a copper atom, D 1 to D 52 are each independently a nitrogen atom, a sulfur atom or a carbon atom, D 1 to D 16 comprises at least one nitrogen atom, D 29 , D 34 , D 35 , D 40 , D 41 , D 46 , D 47 or D 52 comprises at least one nitrogen atom, (each of said carbon atoms may independently be bonded to a hydrogen atom, a halogen atom, an alkyl group, a cycloalkyl group, an alkenyl group, an alkynyl group, an aryl group, an alkylsulfonyl group, an alkoxy group or an alkylthio group) The catalyst for carbon dioxide reduction according to [1], which is represented by

[0014] [3]D 1 to D 16 The catalyst for carbon dioxide reduction according to [2], wherein are each a nitrogen atom or a carbon atom

[0015] [4]D 1 to D 4 comprises at least one nitrogen atom, D 5 to D 8 comprises at least one nitrogen atom, D 9 to D 12 comprises at least one nitrogen atom, and / or D 13 to D 16 The catalyst for carbon dioxide reduction according to [2] or [3], wherein comprises at least one nitrogen atom

[0016] [5]D 17 to D 28 The catalyst for carbon dioxide reduction according to [2], wherein are each a sulfur atom or a carbon atom

[0017] [6]D29 , D 34 , D 35 , D 40 , D 41 , D 46 , D 47 Or, D 52 The catalyst for reducing carbon dioxide according to [2], wherein the atom is a nitrogen atom or a carbon atom.

[0018] [7] Metal complexes are given by the following formula: [ka] [ka] A catalyst for reducing carbon dioxide, represented as [1] or [2].

[0019] [8] A catalyst for reducing carbon dioxide according to any one of [1] to [7], wherein the conductive material is a carbon material.

[0020] [9] The catalyst for carbon dioxide reduction according to [8], wherein the carbon material is graphite, amorphous carbon, activated carbon, graphene, carbon black, carbon fiber, fullerene, or carbon nanotube.

[0021]

[10] The catalyst for carbon dioxide reduction according to [9], wherein the carbon material is carbon nanotubes, carbon black, or graphene.

[0022] A liquid composition comprising a carbon dioxide reduction catalyst and solvent described in any one of

[11] to

[10] .

[0023] An electrode comprising a carbon dioxide reduction catalyst described in any one of

[12] [1] to

[10] .

[0024]

[13] An electrode comprising a carbon dioxide reduction catalyst according to any one of [1] to

[10] supported on a carbon sheet.

[0025]

[14] An electrode comprising a metal complex supported on a carbon sheet or nickel foam, wherein the metal complex is defined by the following formula: [ka] (In the formula, M is a copper atom, A1 to A4 each independently represent an aromatic ring structure. At least one of A1 to A4 contains one or more nitrogen atoms or sulfur atoms in the atoms constituting the aromatic ring, (Each of the ring structures A1 to A4 may have substituents attached.) An electrode, represented by the symbol.

[0026] An electrolytic cell having the electrodes described in

[15]

[12] .

[0027] An electrolytic cell having the electrodes described in

[16]

[13] .

[0028] An electrolytic cell having the electrodes described in

[17] and

[14] .

[0029] A method for reducing carbon dioxide, using an electrode containing a carbon dioxide reduction catalyst described in any one of [1] to

[10] .

[0030]

[19] The method according to

[18] , which produces one or more selected from the group consisting of formic acid, methane, ethylene, and carbon monoxide. [Effects of the Invention]

[0031] According to the present invention, by using the carbon dioxide reduction catalyst of the present invention, a catalyst having excellent carbon dioxide reduction catalytic activity can be provided. Furthermore, the carbon dioxide reduction catalyst of the present invention can produce methane in a single step with high Faraday efficiency without passing through carbon monoxide or formic acid during the reduction of carbon dioxide.

[0032] Furthermore, since the present invention can obtain excellent carbon dioxide reduction catalytic activity without using rare metals such as platinum, it is possible to provide a carbon dioxide reduction catalyst at a relatively low cost. [Brief explanation of the drawing]

[0033] [Figure 1] This figure shows that formic acid, methane, ethane, and carbon monoxide are produced by the reduction reaction of carbon dioxide using the carbon dioxide reduction catalyst of the present invention. [Modes for carrying out the invention]

[0034] [Catalyst for carbon dioxide reduction] The carbon dioxide reduction catalyst of the present invention is characterized by comprising a metal complex and a conductive material. While only one metal complex may be used, two or more metal complexes may be used in combination. The metal complex preferably has an azaphthalocyanine skeleton, and is represented by the following formula (I): [ka] (In the formula, M is a copper atom, A1 to A4 each independently represent an aromatic ring structure. At least one of A1 to A4 contains one or more nitrogen atoms or sulfur atoms in the atoms constituting the aromatic ring, (Each of the ring structures A1 to A4 may have substituents attached.) It is represented

[0035] Metal complexes are given by the following formulas (1), (2), or (3): [ka] (In the formula, M is a copper atom, D 1 From D 52 These are, independently, a nitrogen atom, a sulfur atom, or a carbon atom. D 1 From D16 contains at least one nitrogen atom, D 29 , D 34 , D 35 , D 40 , D 41 , D 46 , D 47 or D 52 contains at least one nitrogen atom, Each of the carbon atoms may independently be bonded to a hydrogen atom, a halogen atom, an alkyl group, a cycloalkyl group, an alkenyl group, an alkynyl group, an aryl group, an alkylsulfonyl group, an alkoxy group, or an alkylthio group. It is more preferable to express it as follows:

[0036] In the present invention, examples of substituents include hydrogen atoms, halogen atoms, alkyl groups, cycloalkyl groups, alkenyl groups, alkynyl groups, aryl groups, alkylsulfonyl groups, alkoxy groups, and alkylthio groups.

[0037] The bond between the nitrogen atom and M signifies the coordination of the nitrogen atom to M. M may also have a halogen atom, a hydroxyl group, or a hydrocarbon group having 1 to 8 carbon atoms bonded to it as a ligand. Furthermore, an anionic counterion may be present to ensure electrical neutrality.

[0038] The valency of M is not particularly limited. To ensure the metal complex is electrically neutral, a halogen atom, a hydroxyl group, or a C1-C8 alkyloxy group may be bonded as a ligand (e.g., an axial ligand), and an anionic counterion may be present. Examples of anionic counterions include halide ions, hydroxide ions, nitrate ions, and sulfate ions. Furthermore, the alkyl group structure of the C1-C8 alkyloxy group may be linear, branched, or cyclic.

[0039] Examples of halogen atoms in this invention include fluorine, chlorine, bromine, and iodine.

[0040] In the present invention, an alkyl group refers to a linear or branched monovalent hydrocarbon group. The number of carbon atoms in an alkyl group is preferably 1 to 20, more preferably 1 to 12, and even more preferably 1 to 6. Examples of alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, sec-pentyl, tert-pentyl, and n-hexyl groups.

[0041] In the present invention, a cycloalkyl group represents a cyclic monovalent hydrocarbon group. The number of carbon atoms in the cycloalkyl group is preferably 3 to 20, more preferably 3 to 12, and even more preferably 3 to 6. Examples of cycloalkyl groups include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, 1-methylcyclopropyl, 2-methylcyclopropyl, and 2,2-dimethylcyclopropyl.

[0042] In the present invention, an alkenyl group refers to a linear or branched monovalent hydrocarbon group containing a double bond. The number of carbon atoms in an alkenyl group is preferably 2 to 20, more preferably 2 to 12, and even more preferably 2 to 6. Examples of alkenyl groups include vinyl group, 1-propenyl group, 2-propenyl group, 1-butenyl group, 2-butenyl group, 3-butenyl group, 1-methyl-2-propenyl group, 2-methyl-2-propenyl group, 1-pentenyl group, 2-pentenyl group, 3-pentenyl group, 4-pentenyl group, 1-methyl-2-butenyl group, 2-methyl-2-butenyl group, 1-hexenyl group, 2-hexenyl group, 3-hexenyl group, 4-hexenyl group, and 5-hexenyl group.

[0043] In the present invention, an alkynyl group refers to a linear or branched monovalent hydrocarbon group containing a triple bond. The number of carbon atoms in the alkynyl group is preferably 2 to 20, more preferably 2 to 12, and even more preferably 2 to 6. Examples of alkynyl groups include ethynyl, 1-propynyl, 2-propynyl, 1-butynyl, 2-butynyl, 3-butynyl, 1-methyl-2-propynyl, 2-methyl-3-butynyl, 1-pentynyl, 2-pentynyl, 3-pentynyl, 4-pentynyl, 1-methyl-2-butynyl, 2-methyl-3-pentynyl, 1-hexynyl, and 1,1-dimethyl-2-butynyl.

[0044] In the present invention, an aryl group refers to a monovalent aromatic hydrocarbon group. The number of carbon atoms in an aryl group is preferably 6 to 40, and more preferably 6 to 30. Examples of aryl groups include phenyl, biphenyl, terphenyl, naphthyl, fluorenyl, benzofluorenyl, dibenzofluorenyl, phenanthryl, anthracenyl, benzophenanthryl, benzoanthracenyl, crisenyl, pyrenyl, fluoranthenyl, triphenylenyl, benzofluoranthenyl, dibenzoanthracenyl, perilenyl, and hericenyl groups.

[0045] In the present invention, an alkylsulfonyl group refers to a monovalent group in which an alkyl group is bonded to a sulfonyl group. The alkyl group in the alkylsulfonyl group can be any of the groups described above as "alkyl group". The number of carbon atoms in the alkylsulfonyl group is preferably 1 to 20, more preferably 1 to 12, and even more preferably 1 to 8. Examples include methylsulfonyl group, ethylsulfonyl group, n-propylsulfonyl group, isopropylsulfonyl group, n-butylsulfonyl group, sec-butylsulfonyl group, tert-butylsulfonyl group, n-pentylsulfonyl group, isopentylsulfonyl group, tert-pentylsulfonyl group, neopentylsulfonyl group, 2,3-dimethylpropylsulfonyl group, 1-ethylpropylsulfonyl group, 1-methylbutylsulfonyl group, n-hexylsulfonyl group, isohexylsulfonyl group, 1,1,2-trimethylpropylsulfonyl group, and 2-ethylhexylsulfonyl group.

[0046] In the present invention, an alkoxy group refers to a monovalent group to which a hydrocarbon group is bonded via an ether bond. The number of carbon atoms in an alkoxy group is preferably 1 to 20, more preferably 1 to 12, and even more preferably 1 to 6. Examples of alkoxy groups include methoxy, ethoxy, n-propoxy, n-butoxy, n-pentyloxy, n-hexyloxy, isopropoxy, isobutoxy, sec-butoxy, tert-butoxy, and isohexyloxy.

[0047] In the present invention, an alkylthio group refers to a group in which the oxygen atom in the ether bond of an alkoxy group is replaced by a sulfur atom. The alkylthio group preferably has 1 to 20 carbon atoms, more preferably 1 to 16, and even more preferably 1 to 12. Examples of alkylthio groups include methylthio group, ethylthio group, n-propylthio group, n-butylthio group, n-pentylthio group, n-hexylthio group, isopropylthio group, and 2-ethylhexylthio group.

[0048] Alkyl groups, cycloalkyl groups, alkenyl groups, alkynyl groups, aryl groups, alkylsulfonyl groups, alkoxy groups, and alkylthio groups may be unsubstituted substituents, but each may be substituted with one or more substituents such as halogens, alkyl groups, alkenyl groups, alkynyl groups, aryl groups, alkoxy groups, alkylthio groups, cyano groups, carbonyl groups, carboxyl groups, amino groups, nitro groups, silyl groups, and sulfo groups.

[0049] D 1 From D 16 It is preferably a nitrogen atom or a carbon atom, D 1 From D 16 It contains at least one nitrogen atom. 17 From D 28 It is preferably a sulfur atom or a carbon atom. 1 From D 16 The number of nitrogen atoms in this compound is preferably 2 to 12, and more preferably 4 to 8. 17 From D 28 The number of sulfur atoms in this compound is preferably 2 to 10, and more preferably 4 to 8.

[0050] Preferably, the metal complex is a compound represented by the following formula.

[0051] [ka] [ka]

[0052] The method for producing metal complexes is not particularly limited, but an example is a method in which a dicyano compound such as pyridine-2,3-dicarbonitride and a metal atom are heated in an alcohol solvent in the presence of a basic substance. Examples of basic substances include inorganic bases such as potassium carbonate, sodium carbonate, calcium carbonate, sodium bicarbonate, and sodium acetate; and organic bases such as triethylamine, tributylamine, and diazabicycloundecene.

[0053] The conductive material is not particularly limited as long as it possesses conductivity, but examples include carbon materials, metal materials, and metal oxide materials. Carbon materials are preferred as the conductive material. One type of conductive material may be used alone, or two or more types may be used in combination.

[0054] The carbon material is preferably derived from conductive carbon. Specific examples of carbon materials include graphite, amorphous carbon, activated carbon, graphene, carbon black, carbon fibers, mesocarbon microbeads, microcapsule carbon, fullerene, carbon nanoforms, carbon nanotubes, and carbon nanohorns. Among these, the carbon material is preferably graphite, amorphous carbon, activated carbon, graphene, carbon black, carbon fibers, fullerene, or carbon nanotubes, and more preferably carbon nanotubes, carbon black, or graphene.

[0055] Examples of carbon nanotubes include single-walled carbon nanotubes (hereinafter referred to as "SWCNTs"), double-walled carbon nanotubes (hereinafter referred to as "DWCNTs"), and multi-walled carbon nanotubes (hereinafter referred to as "MWCNTs").

[0056] The carbon material may contain heteroatoms. Examples of heteroatoms include oxygen atoms, nitrogen atoms, phosphorus atoms, sulfur atoms, and silicon atoms. When the carbon material contains heteroatoms, it may contain one type of heteroatom alone or two or more types of heteroatoms. The carbon material may be oxidized, hydroxylated, nitrided, phosphated, sulfurized, or silicified.

[0057] Examples of metallic materials include titanium and tin. Examples of metal oxide materials include titanium oxide and tin oxide (SnO2, ITO, ATO), etc.

[0058] The specific surface area of ​​conductive materials is 0.8 m². 2 Preferably 10m / g or more, 2 More preferably 50m 2 More preferably 100m / g or more. 2 / g or more is particularly preferred, 500m 2 A value of 0.8 m² or more is most preferable. 2 When the amount is greater than / g, it becomes easier to increase the amount of catalyst supported, and the catalytic activity of the catalyst in reducing carbon dioxide can be further enhanced. The upper limit of the specific surface area is not particularly limited, but for example, 3500m 2 It can be expressed as / g. The specific surface area can be measured using a specific surface area measuring device by the nitrogen adsorption BET method.

[0059] The average particle size of the conductive material is not particularly limited, but is preferably 5 nm to 1000 μm, more preferably 10 nm to 100 μm, and even more preferably 50 nm to 10 μm. The following (A1) to (A3) are examples of methods for adjusting the average particle size of the conductive material to the above numerical range. (A1): A method of crushing particles using a ball mill or the like, dispersing the resulting coarse particles in a dispersant to obtain the desired particle size, and then drying them. (A2): A method of crushing particles using a ball mill or the like, and then separating the particle size of the resulting coarse particles by sieving or the like. (A3): A method for optimizing manufacturing conditions and adjusting particle size when manufacturing conductive materials. The average particle size can be measured using a particle size distribution analyzer or an electron microscope.

[0060] In the carbon dioxide reduction catalyst of the present invention, the content of the metal complex is preferably 75% by mass or less, more preferably 50% by mass or less, and even more preferably 30% by mass or less, based on 100% by mass of the total amount of the metal complex and the conductive material. When the content of the metal complex is below the upper limit, the conductivity of the catalyst is excellent. Furthermore, the content of the metal complex is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, based on 100% by mass of the total amount of the metal complex and the conductive material. When the proportion of the metal complex is above the lower limit, the carbon dioxide reduction catalytic activity of the catalyst can be further enhanced.

[0061] In the carbon dioxide reduction reaction catalyst of the present invention, it is desirable that the metal complex, as the catalyst molecule, is supported at the molecular level on the surface of a conductive material, which serves as the support. For example, a metal complex-supported material can be obtained by mixing the metal complex and the conductive material in a solvent in which the metal complex can dissolve, irradiating with ultrasound, and then filtering, washing, and drying. Here, the weight ratio of the metal complex to the conductive material in the solvent is preferably 5:5 to 0.5:9.5, more preferably 4:6 to 1:9, and particularly preferably 3.5:6.5 to 2:8. Suitable solvents include dimethyl sulfoxide, dimethylformamide, dimethylacetamide, hexafluoro-2-propanol, sulfolane, and dimethylimidazolidinone. The carbon dioxide reduction reaction catalyst of the present invention may be manufactured by other manufacturing processes as long as the metal complex is adsorbed in a single-molecule state. By supporting the metal complex, as the catalyst molecule, at the molecular level on the surface of the conductive material, which serves as the support, the metal complex can be utilized more effectively and catalytic performance can be improved compared to the case where the metal complex is compounded in a crystalline state.

[0062] Since the catalyst for carbon dioxide reduction reactions of the present invention can be obtained by a manufacturing method that does not include a high-temperature calcination process, energy costs can be reduced.

[0063] The applications of the carbon dioxide reduction catalyst of the present invention are not particularly limited, but because it has excellent carbon dioxide reduction catalytic activity, it can be used as a carbon dioxide reduction electrode in methanation technology by electrolysis of carbon dioxide.

[0064] [Liquid composition] In one embodiment, the present invention relates to a liquid composition comprising a carbon dioxide reduction catalyst and a solvent. The solvent may be a solvent that readily dissolves the carbon dioxide reduction catalyst (i.e., has high solubility), or a solvent that does not readily dissolve the carbon dioxide reduction catalyst (i.e., has low solubility). When the solvent readily dissolves the carbon dioxide reduction catalyst, the liquid composition is in the form of a solution. When the solvent does not readily dissolve the carbon dioxide reduction catalyst, the liquid composition is in the form of a dispersion.

[0065] The solvent is not particularly limited and may be an inorganic solvent such as water, or an organic solvent. Specific examples of organic solvents include alcohols such as methanol, ethanol, propanol, isopropanol (2-propanol), and 1-hexanol; dimethyl sulfoxide; tetrahydrofuran; aprotic polar solvents such as N-methylpyrrolidone, dimethylformamide, and acetone; and nonpolar solvents such as chloroform, dichloromethane, 1,4-dioxane, benzene, and toluene. One solvent may be used alone, or two or more may be used in combination.

[0066] The liquid composition may optionally contain any conductive agent, binder, and other additives. It may also contain a perfluorocarbon material comprising a polytetrafluoroethylene-based structural unit and a perfluoro side chain having a sulfonic acid group. A specific example of a perfluorocarbon material is Nafion (product name: manufactured by DuPont).

[0067] Liquid compositions can be prepared by mixing or kneading a carbon dioxide reduction catalyst, a solvent, and, if necessary, a perfluorocarbon material. Mixing or kneading may be performed using ultrasonic treatment, mixers, blenders, kneaders, homogenizers, bead mills, ball mills, etc. The average particle size may be adjusted using sieves or the like before and after the kneading operation. When preparing a liquid composition containing a perfluorocarbon material, the carbon dioxide reduction catalyst, the perfluorocarbon material, and, if necessary, water and alcohol may be mixed and stirred until homogeneous.

[0068] The liquid composition can be applied to the surface of various substrates. For example, by applying the liquid composition to the surface of a substrate and removing the solvent, a layer containing a carbon dioxide reduction catalyst (hereinafter referred to as the "catalyst layer") can be provided on the surface of various substrates. That is, the liquid composition can be used, for example, as a coating liquid applied to a substrate when manufacturing electrodes. The liquid composition may be used as a coating liquid as is, or the content of the carbon dioxide reduction catalyst or the solid content concentration may be adjusted before use as a coating liquid.

[0069] The substrate is not particularly limited, but examples include aluminum foil, electrolytic aluminum foil, aluminum mesh (expanded metal), foamed aluminum, perforated aluminum, aluminum alloys such as duralumin, copper foil, electrolytic copper foil, copper mesh (expanded metal), foamed copper, perforated copper, copper alloys such as brass, brass foil, brass mesh (expanded metal), foamed brass, perforated brass, nickel foil, nickel mesh, corrosion-resistant nickel, nickel mesh (expanded metal), perforated nickel, nickel foam, sponge nickel, metallic zinc, corrosion-resistant metallic zinc, zinc foil, zinc mesh (expanded metal), steel plates, perforated steel plates, silver, etc. In addition, substrate-like substrates such as silicon substrates; metal substrates such as gold, iron, stainless steel, copper, aluminum, and lithium; alloy substrates containing any combination of these metals; oxide substrates such as indium tin oxide (ITO), indium zinc oxide (IZO), and antimony tin oxide (ATO); and carbon substrates such as carbon sheets, glassy carbon, pyrolytic graphite, and carbon felt can also be used. Preferably, it can be applied to a substrate selected from nickel foam, sponge nickel, carbon sheet, glassy carbon, or carbon felt. When used in a flow-type electrolytic cell, a gas diffusion electrode (GDE) made of a carbon sheet having gas permeability, water repellency, and conductivity is preferred.

[0070] [electrode] In one embodiment, the present invention relates to an electrode containing the carbon dioxide reduction catalyst of the present invention. The electrode may comprise a layer containing the carbon dioxide reduction catalyst of the present invention (i.e., a catalyst layer) on the above-mentioned substrate and can be used as a catalyst for a carbon dioxide reduction reaction. The catalyst layer may be in direct contact with the substrate, or other layers may be present between the substrate and the catalyst layer. In one embodiment, the electrode more preferably includes the carbon dioxide reduction catalyst of the present invention supported on a substrate, and even more preferably includes the carbon dioxide reduction catalyst of the present invention supported on a carbon sheet.

[0071] The method for manufacturing electrodes is not particularly limited, but for example, they may be manufactured by coating a liquid composition onto the surface of a conductive substrate and removing components other than the carbon dioxide reduction catalyst. When removing components other than the carbon dioxide reduction catalyst, heating and drying may be performed, or pressing may be performed after drying. Alternatively, the catalyst layer may be formed on the surface of the substrate by vacuum deposition or the like. The electrode may have the catalyst layer on only one side of the substrate, or on both sides of the substrate.

[0072] The thickness of the catalyst layer is not particularly limited, but can be, for example, 0.01 to 100 μm. When the thickness is above the lower limit, the electrode durability is excellent. When the thickness is below the upper limit, the electrode performance is less likely to deteriorate. The basis weight is 0.1 μg / cm³. 2 More than 1000μg / cm 2 Preferably, the following: More preferably 1 μg / cm³ 2 More than 100μg / cm 2 The following is more preferably 2 μg / cm³ 2 More than 10μg / cm 2 The results are as follows: Surprisingly, the smaller the amount of catalyst coated on the electrode, the higher the selectivity in the carbon dioxide reduction reaction.

[0073] In this case, it is preferable that the liquid composition does not contain binders such as PTFE or conductive carriers such as carbon black, other than the carbon dioxide reduction catalyst, and that the carbon dioxide reduction catalyst is directly coated onto a gas diffusion electrode such as a carbon sheet to form a catalyst layer. Methods for coating the liquid composition to appropriately control the basis weight of the catalyst layer include spray coating, inkjet coating, and mist coating.

[0074] The electrode functions as a catalyst for the carbon dioxide reduction reaction and acts as a catalyst for at least one of the reduction reactions shown below. CO2 + 2H + +2e - →CO+H2O CO2 + H2O + 2e - →CO+2OH- CO2 + 2H + +2e - →HCOOH CO2 + 8H + +8e - →CH4+2H2O CO2 + 12H + +12e - →C2H4+4H2O

[0075] [A method for reducing carbon dioxide using an electrode containing a catalyst for carbon dioxide reduction] In one embodiment, the present invention relates to a method for reducing carbon dioxide using an electrode containing a carbon dioxide reduction catalyst comprising a metal complex and a conductive material. The carbon dioxide reduction catalyst of the present invention is particularly useful as a carbon dioxide reduction catalyst for electrodes, and by using an electrode containing the carbon dioxide reduction catalyst of the present invention, carbon dioxide can be reduced with high Faraday efficiency.

[0076] A method for reducing carbon dioxide using an electrode containing the carbon dioxide reduction catalyst of the present invention produces one or more substances selected from the group consisting of formic acid, methane, ethylene, and carbon monoxide. [Examples]

[0077] The present invention will be described more specifically below using examples and comparative examples, but the scope of the present invention is not limited to the examples.

[0078] <Example 1> (Synthesis of catalysts for carbon dioxide reduction) Synthesis of compound (1) 1.0 g of 3,4-dicyanopyridine, 192 mg of copper(I) chloride, 118 mg of 1,8-diazabicyclo[5.4.0]undeca-7-ene, and 20 ml of 2-ethoxyethanol were mixed and refluxed for 12 hours. After cooling to room temperature, water was added and the precipitate was collected by filtration. This solid was washed with methanol, acetone, and water, and the target product was obtained by vacuum drying at room temperature. The yield was 81.2%. [ka]

[0079] Synthesis of compound (2) Synthesis of pyridine-2,3-dicarboxylate diethyl N-oxide 25.0 g of diethyl pyridine-2,3-dicarboxylate was mixed with 150 mL of methylene chloride and stirred. 100 mg of methyltrioxorenium was added to this solution, and 3 mL of 30% hydrogen peroxide solution was added at a time while monitoring the reaction by TLC. Stirring was continued for 2 days. Since residual starting material was confirmed, 100 mg of methyltrioxorenium and hydrogen peroxide solution were added until the starting material was completely eliminated.

[0080] After the raw materials had disappeared, 200 mL of water was added and the mixture was stirred. After separating the organic phase, the aqueous phase was extracted three times with methylene chloride. The organic phases were combined and dehydrated with anhydrous sodium sulfate, then concentrated and purified by silica gel column chromatography. The target product was obtained as colorless crystals. Yield: 20.2 g.

[0081] Synthesis of 6-chloropyridine-2,3-diethyl carboxylate 4.28 g of diethyl pyridine-2,3-dicarboxylate N-oxide was mixed with 15 mL of acetonitrile and stirred. 5.5 g of phosphorus oxychloride was added to this solution at room temperature, and the mixture was heated under reflux for 5 hours. After cooling, the reaction mixture was poured into ice water and extracted with ethyl acetate. The organic phase was dried over anhydrous sodium sulfate, concentrated, and purified by silica gel column chromatography. Yield: 2.7 g.

[0082] Synthesis of 6-methoxypyridine-2,3-dicarboxylic acid 2.5 g of diethyl 6-chloropyridine-2,3-dicarboxylate was added to 20 mL of methanol, followed by 2.0 g of potassium carbonate, and the mixture was stirred at room temperature. After 4 hours, the inorganic components were filtered off, and the solvent was removed by distillation under reduced pressure. Another 20 mL of methanol was added to the residue, and the mixture was stirred. Then, 1.63 g of lithium hydroxide monohydrate was added. After 5 hours, the reaction mixture was poured into dilute hydrochloric acid water and extracted with ethyl acetate. The organic phase was dehydrated with anhydrous sodium sulfate and concentrated to obtain the target product. Yield: 0.62 g.

[0083] 500 mg of 6-methoxypyridine-2,3-dicarboxylic acid, 6 g of urea, 63 mg of copper(I) chloride, and 22 mg of hexaammonium heptamolybdate tetrahydrate were mixed and stirred, and heated in an oil bath set to 190°C. After reacting for 3 hours, the mixture was cooled to 100°C, water was added, and the mixture was stirred for a further 10 minutes. After reaching room temperature, the solid was collected by vacuum filtration, washed with water, washed with methanol, and finally washed with acetone and dried. The yield was 52.4%. [ka]

[0084] Synthesis of compound (3) 5.0 g of 5-ethylpyridine-2,3-dicarboxylic acid, 634 mg of copper(I) chloride, 12.31 g of urea, 390 mg of diazabicycloundecene, 31.7 mg of hexaammonium heptamolybdate tetrahydrate, and 25 ml of 1,3-dimethyl-2-imidazolidinone were mixed and refluxed under nitrogen flow for 12 hours. After cooling to 140°C, the mixture was subjected to reduced-pressure thermal filtration and washed with hot water and methanol. The solid was vacuum-dried at 80°C to obtain the target product. The yield was 23.4%. [ka]

[0085] Synthesis of compound (4) The synthesis procedure was the same as for compound (1), except that 1.0 g of 2,3-dicyanopyridine, 192 mg of copper(I) chloride, 118 mg of 1,8-diazabicyclo[5.4.0]undeca-7-ene, and 20 ml of 2-ethoxyethanol were used. The yield was 42.1%. [ka]

[0086] Synthesis of compound (5) 500 mg of 6-methoxypyridine-3,4-dicarboxylic acid, 6 g of urea, 63 mg of copper(I) chloride, and 22 mg of hexaammonium heptamolybdate tetrahydrate were mixed and stirred, and heated in an oil bath set to 190°C. After reacting for 3 hours, the mixture was cooled to 100°C, water was added, and the mixture was stirred for a further 10 minutes. After reaching room temperature, the solid was collected by vacuum filtration, washed with water, washed with methanol, and finally washed with acetone and dried. The yield was 61.2%. [ka]

[0087] Synthesis of compound (6) Synthesis of thiophene-2,3-dicarbaldehyde dioxime 5.2 g of thiophene-2,3-dicarbaldehyde, 50 mL of methanol, and 6.3 g of hydroxylamine hydrochloride were mixed and stirred. 7.4 g of sodium acetate was added, and the mixture was heated under reflux for 6 hours. After adding 0.9 g of hydroxylamine hydrochloride, the reaction was carried out overnight. After concentration, ethyl acetate and water were added for extraction. The organic phase was dehydrated with anhydrous sodium sulfate, concentrated, and crystallized with hexane and ethyl acetate. This was filtered to obtain thiophene-2,3-dicarbonitrile dioxime. The yield was approximately 6 g.

[0088] Synthesis of thiophene-2,3-dicarbonitride Approximately 6 g of the above dioxime was dissolved in 60 mL of acetonitrile, and the reaction was carried out at room temperature for 5 days with 16 mL of triethylamine and 11.5 g of acetic anhydride. After concentration, water and ethyl acetate were added for extraction, and the organic phase was dried over anhydrous sodium sulfate. The mixture was then purified by silica gel column chromatography to obtain thiophene-2,3-dicarbonitrile. The yield was 3.8 g.

[0089] A methanol solution of 10% lithium methoxide in 1 g was added to 3 mL of 1-octanol, and the mixture was heated in an oil bath set to 230°C to evaporate the methanol. 360 mg of thiophene-2,3-dicarbonitride was added to this solution. After reacting for 15 minutes, the mixture was cooled to 100°C, and 66 mg of copper(I) chloride was added. The reaction was continued for 1 hour, and 15 mL of methanol was added to precipitate the solid, which was then collected by filtration. N,N-dimethylformamide and silica gel were added to the obtained solid, and after heating and dissolution, the solvent was removed by vacuum distillation. The solid was placed on a silica gel column and eluted with N,N-dimethylformamide. The blue component was collected and concentrated to obtain compound (6). The yield was 35.2%. [ka]

[0090] Synthesis of compound (7) Synthesis of 5,6-dimethoxy-2,3-pyrazinedicarbonitrine 2.0 g of 5,6-dichloro-2,3-pyrazine dicarbonitride was mixed with 15 mL of methanol and stirred at room temperature. 3.0 g of potassium carbonate was added, and the reaction was carried out overnight. 80 mL of water was added to the reaction mixture, and the precipitated crystals were collected by filtration. The mixture was washed with water and methanol, and dried to obtain the target product. Yield: 1.90 g.

[0091] 1.0 g of 5,6-dimethoxy-2,3-pyrazine dicarbonitride was mixed with 130 mg of copper(I) chloride, followed by 5 mL of 1-pentanol and 1 mL of pyridine. The mixture was heated in an oil bath at 155°C. After the reaction overnight, the mixture was cooled, methanol was added, and the precipitated solid was purified by silica gel column chromatography. A chloroform-methanol mixture was used as the elution solvent. The yield was 7.8%. [ka]

[0092] Synthesis of compound (8) Synthesis of 5,6-dimethyl-2,3-pyrazinedicarbonitrine 3.24 g of diaminomaleonitrile was mixed with 10 mL of acetic acid, then 2.64 mL of diacetyl was added, and the mixture was heated under high heat for 1 hour. Crystals precipitated upon cooling. 10 mL of water was added, and the crystals were collected by filtration. After washing with water, the mixture was dried to obtain the target product. Yield: 4.45 g. 6.32 g of 5,6-dimethyl-2,3-pyrazine dicarbonitrate was mixed with 30 mL of 1-pentanol, followed by 989 mg of copper(I) chloride and 1.9 mL of 4-methylpyridine. The mixture was heated in an oil bath set to 145°C to carry out the reaction. After 5 hours of reaction, heating was stopped. When the reaction mixture reached 100°C, 30 mL of methanol was added dropwise. After cooling to room temperature, the mixture was filtered under reduced pressure, carefully washed with water and methanol, then washed with acetone and dried. The yield was 85.8%. [ka]

[0093] Synthesis of compound (9) Synthesis of 5-bromopyridine-2,3-dicarboxylate dimethyl 30.0 g of pyridine-2,3-dicarboxylic acid was mixed with 250 mL of methanol and stirred. 10 mL of concentrated sulfuric acid was added dropwise to this reaction mixture, followed by 20 mL of trimethyl orthoformate. The mixture was heated under reflux for 2 days, 20 mL of trimethyl orthoformate was added, and reflux continued for another day. After cooling to 40°C, the temperature was kept below 55°C, and 16 mL of bromine was added gradually while monitoring the reaction by TLC. After 1 day, 8 mL of bromine was added, and the reaction was continued at 58°C for 3 days. This reaction mixture was gradually poured into a mixture of ethyl acetate, water, and sodium bicarbonate (an amount sufficient to neutralize the acidic component) while stirring. After liquid-liquid extraction, the organic phase was washed with an aqueous sodium sulfite solution. The organic phase was dehydrated with anhydrous sodium sulfate, concentrated, and crystallized with cooled isopropanol, then filtered. After washing with isopropanol, the mixture was washed with hexane and dried to obtain the target product. Yield: 34.4 g.

[0094] Synthesis of 5-(2-ethylhexylthio)pyridine-2,3-dicarboxylate dimethyl 3.2 g of 2-ethylhexanethiol was mixed with 5.9 g of dimethyl 5-bromopyridine-2,3-dicarboxylate, and then 25 mL of N,N-dimethylformamide was added and the mixture was stirred. 6.1 g of potassium carbonate was then added, and the mixture was heated in an oil bath at 85°C. The reaction was carried out overnight, and 120 mL of ethyl acetate was added. After washing the organic phase with an aqueous potassium carbonate solution, the mixture was concentrated and purified by silica gel column chromatography to obtain the target product. The yield was 6.2 g.

[0095] Synthesis of 5-(2-ethylhexylthio)pyridine-2,3-dicarboxylic acid 5.0 g of dimethyl 5-(2-ethylhexylthio)pyridine-2,3-dicarboxylate was mixed with 50 mL of methanol, and 2.5 g of lithium hydroxide monohydrate was added. After the reaction was complete, the solution was acidified with dilute hydrochloric acid and extracted with ethyl acetate. The organic phase was washed three times with water and concentrated. Toluene was added to this concentrate, and the process of removing the concentrate under reduced pressure was repeated three times to obtain the target product.

[0096] 1.07 g of 5-(2-ethylhexylthio)pyridine-2,3-dicarboxylic acid was mixed with 3.2 g of urea and 30 mg of ammonium heptamolybdate tetrahydrate, and heated in an oil bath set to 160°C for 30 minutes. 89 mg of copper(I) chloride and 3.2 g of urea were added to this reaction mixture, and the reaction was carried out for 1 hour at 200°C in the oil bath. 6 mL of N-methylpyrrolidone was added and heated for another hour. After cooling to room temperature, water was added, the precipitated solid was filtered, washed with methanol, and then purified by silica gel column chromatography to obtain compound (9). Yield: 45.8%. [ka]

[0097] Synthesis of compound (10) 6.0 g of dimethyl 5-(2-ethylhexylthio)pyridine-2,3-dicarboxylate was mixed with 80 mL of acetic acid and 300 mg of sodium tungstate dihydrate, and the mixture was stirred. This was heated to 40°C, and 4.4 mL of 30% hydrogen peroxide solution was added dropwise while monitoring the reaction by TLC. After adding the entire amount of hydrogen peroxide solution, the reaction was allowed to proceed for 1 hour, and then 150 mL of water was added. After extraction with ethyl acetate, the organic phase was washed twice with aqueous sodium bicarbonate solution and twice with aqueous sodium sulfite solution, and then water was removed with anhydrous sodium sulfite before concentration. The residue was purified by silica gel column chromatography to obtain the target product as a colorless oil. Yield: 6.0 g.

[0098] Synthesis of 5-(2-ethylhexylsulfonyl)pyridine-2,3-dicarboxylic acid 13.6 g of dimethyl 5-(2-ethylhexylsulfonyl)pyridine-2,3-dicarboxylate was mixed with 150 mL of methanol and stirred. 6.8 g of lithium hydroxide was added, and the reaction was carried out at room temperature for 2 hours. After the reaction was complete, the solution was acidified with dilute hydrochloric acid and extracted with ethyl acetate. The organic phase was washed three times with water and concentrated. Toluene was added to this concentrate, and the solution was removed by vacuum distillation, a process repeated three times to obtain the target product.

[0099] 1.0 g of 5-(2-ethylhexylsulfonyl)pyridine-2,3-dicarboxylic acid was mixed with 3.0 g of urea and 25.3 mg of ammonium heptamolybdate tetrahydrate, and heated in an oil bath set to 160°C for 30 minutes. Then, 75 mg of copper(I) chloride and 3.0 g of urea were added, and the reaction was carried out at 200°C for 3 hours. After cooling to room temperature, water was added, and the precipitated solid was collected by filtration. This solid was purified by silica gel column chromatography to obtain compound (10). The yield was 26.3%. [ka]

[0100] Synthesis of compound (11) 5.0 g of quinoline-2,3-dicarboxylic acid, 570 mg of copper(I) chloride, 360 mg of diazabicycloundecene, 11.1 g of urea, 27 mg of hexaammonium heptamolybdate tetrahydrate, and 25.7 ml of 1,3-dimethyl-2-imidazolidinone were mixed and refluxed under nitrogen flow for 12 hours. After cooling to 140°C, the mixture was subjected to reduced-pressure thermal filtration and washed with hot water and methanol. The solid was vacuum-dried at 80°C to obtain the target product. The yield was 32.7%. [ka]

[0101] Synthesis of compound (12) The synthesis procedure was the same as for compound (1), except that 1.0 g of 2,3-dicyanopyrazine, 190 mg of copper(I) chloride, 117 mg of 1,8-diazabicyclo[5.4.0]undeca-7-ene, and 20 ml of 2-ethoxyethanol were used. The yield was 75.2%. [ka]

[0102] Synthesis of compound (13) Phenylenediamine and dicyanomaleonitrile were added in small amounts to acetic acid and refluxed. The reaction mixture was added dropwise to water to precipitate. The precipitate was filtered and vacuum-dried. The synthesis procedure was the same as for compound (1), except that 1.0 g of 2,3-quinoxaline dicarbonitride, 190 mg of copper(I) chloride, 117 mg of 1,8-diazabicyclo[5.4.0]undeca-7-ene, and 20 ml of 2-ethoxyethanol were used. The yield was 45.2%. [ka]

[0103] Synthesis of compound (14) Small amounts of pyrazinodiamine and dicyanomaleonitrile were added to acetic acid and refluxed. The reaction mixture was added dropwise to water to precipitate. The precipitate was filtered and vacuum-dried. The synthesis procedure was the same as for compound (1), except that 1.0 g of pyrazino[2,3-b]pyrazine-2,3-dicarbonitride, 190 mg of copper(I) chloride, 117 mg of 1,8-diazabicyclo[5.4.0]undeca-7-ene, and 20 ml of 2-ethoxyethanol were used. The yield was 12.7%. [ka]

[0104] <Example 2> (Electrode fabrication) As Example 2-1, an ink containing a catalyst with compound (4) dissolved in DMSO / IPA (1:3) at a concentration of 1.0 mg / mL was spray-coated onto a gas diffusion electrode (GDL, Mitsubishi Pyrochemical, Pyrofil GDL·MFK-A), and then vacuum-dried in a vacuum oven at 60°C to prepare a working electrode. As comparative examples, electrodes were prepared under the same conditions as in Example 2-1, with Comparative Example 1 using Fe instead of Cu as the central metal and Comparative Example 2 using Ni instead. The basis weight in Example 2-1 was 41.7 μg / cm³. 2 In Comparative Example 1, the concentration was 117 μg / cm³. 2 In Comparative Example 2, the concentration was 52.8 μg / cm³.2 That was the case.

[0105] (Electrolysis experiment) An electrolytic cell was assembled using a prepared catalyst-supported GDL (1.5 cm square) as the working electrode, a Pt mesh as the counter electrode, and a reversible hydrogen electrode as the reference electrode. A 1 M KHCO3 aqueous solution was circulated through the cell as the electrolyte, and CO2 gas was flowed towards the working electrode. -50 mA / cm 2 After conditioning for 5 minutes, -100 mA / cm 2 and -150 mA / cm 2 Each electrolysis was performed for 10 minutes, and the gas obtained from each electrolysis was measured by gas chromatography (GC). The Faraday efficiency (FE) was calculated from the obtained gas composition and electrolysis current value. In addition, the impedance was measured at -0.8 V to determine the solution resistance.

[0106] The results of the carbon dioxide reduction are shown in Figure 1. The Faraday efficiency of the electrolytic products was calculated as the ratio of the amount of charge used to produce the observed products to the total amount of charge used in the reaction. When the catalyst of the present invention was used, the carbon dioxide reduction reaction proceeded with a Faraday efficiency of approximately 60%, producing formic acid, ethane, methane, and carbon monoxide. On the other hand, when a catalyst with iron as the central metal was used, the Faraday efficiency of the carbon dioxide reduction reaction was remarkably low at less than 10%, and when a catalyst with nickel as the central metal was used, no carbon dioxide reduction reaction was observed. These results are shown in the table below and in Figure 1. [Table 1]

[0107] <Example 3> Optimization of catalyst quantity Compound (4) was dissolved in a DMSO / IPA mixed solution at a concentration of 0.5 mg / mL, and a sample (approximate basis weight) of 2.5 μg / cm² was coated once onto GDL. 2Using a ) as the working electrode, a 1M KOH aqueous solution as the electrolyte, a Pt mesh as the counter electrode, and Hg / HgO as the reference electrode, a potential of -3.5V vs Hg / HgO (current density approximately) of -300 mA / cm 2 Electrolysis was performed using ). The obtained gas was measured by GC and the FE was calculated, showing that CH4 had a high selectivity of 76.2% FE. As the amount of compound (4) supported increased, FE CH4 The percentage decreased to 30 μg / cm³. 2 In that case, the figure was 19%. [Industrial applicability]

[0108] The carbon dioxide reduction catalyst of the present invention makes it possible to obtain synthetic fuels with high energy density and high Faraday efficiency without using rare metals or precious metals. When using the carbon dioxide reduction catalyst of the present invention in a carbon dioxide reduction reaction, methane can be produced with very high selectivity and high Faraday efficiency by keeping the amount of catalyst used low.

Claims

1. A catalyst for carbon dioxide reduction comprising a metal complex and a conductive material, The following equation (I): 【Chemistry 1】 (In the formula, M is a copper atom, A1 to A4 each independently represent an aromatic ring structure. At least one of A1 to A4 contains one or more nitrogen atoms or sulfur atoms in the atoms constituting the aromatic ring, (Each of the ring structures A1 to A4 may have substituents attached.) A catalyst for reducing carbon dioxide, represented by the symbol.

2. The metal complex is one of the following formulas (1), (2), or (3): 【Chemistry 2】 (In the formula, M is a copper atom, D １ From D ５２ These are, independently, a nitrogen atom, a sulfur atom, or a carbon atom. D １ From D １６ contains at least one nitrogen atom, D ２９ , D ３４ , D ３５ , D ４０ , D ４１ , D ４６ , D ４７ or D ５２ contains at least one nitrogen atom, Each of the carbon atoms may independently be bonded to a hydrogen atom, a halogen atom, an alkyl group, a cycloalkyl group, an alkenyl group, an alkynyl group, an aryl group, an alkylsulfonyl group, an alkoxy group, or an alkylthio group. A catalyst for reducing carbon dioxide according to claim 1, comprising a metal complex represented by [the specified metal complex].

3. D １ From D １６ The catalyst for reducing carbon dioxide according to claim 2, wherein the atom is a nitrogen atom or a carbon atom.

4. D １ From D ４ However, it contains at least one nitrogen atom, D ５ From D ８ However, it contains at least one nitrogen atom, D ９ From D １２ but containing at least one nitrogen atom and / or D １３ From D １６ However, it contains at least one nitrogen atom, The catalyst for reducing carbon dioxide according to claim 2.

5. D １７ From D ２８ The catalyst for reducing carbon dioxide according to claim 2, wherein the atom is a sulfur atom or a carbon atom.

6. D ２９ , D ３４ , D ３５ , D ４０ , D ４１ , D ４６ , D ４７ Or, D ５２ The catalyst for reducing carbon dioxide according to claim 2, wherein the atom is a nitrogen atom or a carbon atom.

7. The following formula: 【Transformation 3】 【Chemistry 4】 A catalyst for reducing carbon dioxide according to claim 1, as represented by [the specified figure].

8. The catalyst for reducing carbon dioxide according to claim 1, wherein the conductive material is a carbon material.

9. The catalyst for reducing carbon dioxide according to claim 8, wherein the carbon material is graphite, amorphous carbon, activated carbon, graphene, carbon black, carbon fiber, fullerene, or carbon nanotube.

10. The catalyst for reducing carbon dioxide according to claim 9, wherein the carbon material is carbon nanotubes, carbon black, or graphene.

11. A liquid composition comprising a carbon dioxide reduction catalyst and a solvent according to any one of claims 1 to 10.

12. An electrode comprising a carbon dioxide reduction catalyst according to any one of claims 1 to 10.

13. An electrode comprising a catalyst according to any one of claims 1 to 10, supported on a carbon sheet.

14. An electrode comprising a metal complex supported on a carbon sheet or nickel foam, wherein the metal complex is of the following formula (I): 【Transformation 5】 (In the formula, M is a copper atom, A1 to A4 each independently represent an aromatic ring structure. At least one of A1 to A4 contains one or more nitrogen atoms or sulfur atoms in the atoms constituting the aromatic ring, (Each of the ring structures A1 to A4 may have substituents attached.) An electrode, represented by the symbol.

15. An electrolytic cell comprising the electrode described in claim 12.

16. An electrolytic cell comprising the electrode described in claim 13.

17. An electrolytic cell comprising the electrode described in claim 14.

18. A method for reducing carbon dioxide, using an electrode containing a carbon dioxide reduction catalyst according to any one of claims 1 to 10.

19. The method according to claim 18, wherein one or more substances selected from the group consisting of formic acid, methane, ethylene, and carbon monoxide are produced.

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