Electrochemical reaction device and method for producing organic substance

Abstract

An electrochemical reaction device 10 comprises: a first electrode 11; a second electrode 12; a first electrolysis unit 21 having the first electrode 11; a reaction unit 31; and a first connection path 41 connecting the first electrolysis unit 21 and the reaction unit 31. The first electrode 11 includes a first catalyst that promotes a reaction for reducing carbon dioxide to a first reduction product, and the second electrode 12 oxidizes a reduction product A of an oxidation-reduction substance to an oxide B. The first connection path 41 causes the first reduction product generated by the first electrolysis unit 21 to flow out to the reaction unit 31. The reaction unit 31 has a second catalyst for generating an organic substance by the first reduction product and the oxide B.

Description

Electrochemical reaction device and method for producing organic matter

[0001] The present invention relates to an electrochemical reaction device such as a carbon dioxide reduction device for producing an organic substance such as a carbonyl compound using carbon dioxide as a raw material, and to a method for producing an organic substance such as a carbonyl compound.

[0002] Electrochemical synthesis methods have been attracting attention in recent years because they do not require the use of highly toxic substrates or highly explosive oxygen-mixed gases and can directly utilize electricity from renewable energy sources. Furthermore, in recent years, studies have been conducted to generate organic compounds through electrochemical reactions using raw materials such as carbon dioxide or carbon monoxide obtained by reducing carbon dioxide, with the aim of curbing global warming and replacing fossil fuels. Carbon dioxide reduction is known to be performed using an electrochemical cell, in which case carbon dioxide is generally reduced on the cathode side. There are also many known methods for oxidizing organic compounds using the anode of an electrochemical cell to obtain new valuable materials.

[0003] In recent years, in order to more efficiently produce valuable resources from carbon dioxide, methods for producing valuable resources from carbon dioxide using both a cathode and an anode have been studied. For example, Patent Documents 1 and 2 disclose electrochemical cells including a cathode chamber in which a cathode is provided, an anode chamber in which an anode is provided and which contains a reaction substrate such as an alcohol-based compound, an ion transport membrane separating the cathode chamber from the anode chamber, and a connecting path connecting the cathode chamber to the anode chamber. In the electrochemical cells of Patent Documents 1 and 2, carbon dioxide is reduced to carbon monoxide at a first electrode, and the generated carbon monoxide is discharged into the anode chamber via the connecting path, and a valuable resource such as a carbonate compound is produced from the carbon monoxide and the reaction substrate in the anode chamber.

[0004] International Publication No. 2019 / 182164 Special Publication No. 2021-517608

[0005] Although the electrochemical cells described in Patent Documents 1 and 2 produce carbonate compounds with high reaction efficiency, further process improvements are desired. For example, reaction substrates such as alcohol-based compounds are easily oxidized in the anode chamber, and it is desirable to suppress the oxidation of alcohol-based compounds. Furthermore, various improvements have been attempted in the past for devices for producing organic compounds from carbon dioxide, but these often result in complex electrochemical cell structures.

[0006] Furthermore, when producing valuable materials from carbon dioxide, further improvement in production efficiency is desired for industrial practical use, and even in systems that use electrochemical reactions to produce valuable materials such as organic carbonates from carbon monoxide, there is a demand for efficient production of the target valuable materials. There is also a demand for increasing selectivity while improving productivity.

[0007] Therefore, in a first aspect, the present invention aims to provide a carbon dioxide reduction device that can produce an organic substance from carbon dioxide while suppressing oxidation of a reaction substrate such as an alcohol-based compound, without complicating the structure of the electrochemical cell, for example, by utilizing existing electrolysis equipment. In a second aspect, the present invention also aims to provide an electrochemical system that produces a carbonyl compound such as an organic carbonate from carbon monoxide using an electrochemical reaction, and that can produce the target carbonyl compound with high faradaic efficiency. Furthermore, in a third aspect, the present invention aims to provide an electrochemical reaction device that can improve productivity and increase the selectivity when producing the target product.

[0008] In a first aspect, the present invention provides the following [1] and [2]: [1] A carbon dioxide reduction device comprising: a first electrode, a second electrode, a first electrolysis unit having the first electrode, a reaction unit, and a first connecting path connecting the first electrolysis unit and the reaction unit, wherein the first electrode contains a first catalyst that promotes a reaction of reducing carbon dioxide to a first reductant, the second electrode oxidizes a reduction product A of a redox substance to an oxide B, the first connecting path allows the first reductant produced in the first electrolysis unit to flow out to the reaction unit, and the reaction unit has a second catalyst that produces an organic substance from the first reductant and the oxide B. [2] A method for producing an organic substance using the carbon dioxide reduction device described in [1] above, wherein carbon dioxide is reduced to a first reduced product at the first electrode, a reduced product A of a redox substance is oxidized to an oxide B at the second electrode, the first reduced product produced at the first electrode is discharged to the reaction section via the first connecting path, and the reaction section produces an organic substance from the first reduced product and the oxide B. Note that in the above [1] and [2], the carbon dioxide reduction device is an electrochemical reaction device.

[0009] In a second aspect, the present invention provides the following [3] and [4]. [3] An electrochemical system for electrochemically synthesizing at least one carbonyl compound selected from the group consisting of organic carbonates and organic oxalates from carbon monoxide, comprising: an electrode (second electrode), a redox species (oxidation-reduction substance) that causes an oxidation reaction at the electrode, and a catalyst (second catalyst) that produces the carbonyl compound, wherein the catalyst has a catalytically active species and a metal compound that supports the catalytically active species. [4] A method for producing a carbonyl compound, in the electrochemical system described in [3] above, in which at least one carbonyl compound selected from the group consisting of organic carbonates and organic oxalates is electrochemically synthesized from carbon monoxide. Note that in the above [3] and [4], the electrochemical system is also an electrochemical reaction device.

[0010] In a third aspect, the present invention provides the following [5] and [6]. [5] An electrochemical cell comprising a cathode containing a first catalyst that reduces carbon dioxide to carbon monoxide, an anode, an electrolytic solution containing a reactant and an electrolyte, and a second catalyst that synthesizes a carbonyl compound from carbon monoxide and the reactant, wherein the electrolyte concentration of the electrolytic solution in the electrochemical cell is 0.3 M or less, and the current density flowing in the electrochemical cell is 20 mA / cm ２ [6] A method for producing a carbonyl compound in the electrochemical reaction device described in [5] above, comprising reducing carbon dioxide to carbon monoxide by the first catalyst, and synthesizing a carbonyl compound from the resulting carbon monoxide and the reaction substrate.

[0011] According to a first aspect of the present invention, a carbon dioxide reduction device can be provided that synthesizes an organic substance from carbon dioxide without complicating the structure of the device while suppressing oxidation of a reaction substrate such as an alcohol-based compound. According to a second aspect of the present invention, an electrochemical system can be provided that produces a target carbonyl compound from carbon monoxide with high faradaic efficiency. According to a third aspect of the present invention, an electrochemical reaction device can be provided that can improve productivity and increase the selectivity when producing a target product.

[0012] FIG. 1 is a schematic diagram showing a carbon dioxide reduction device according to a first embodiment. FIG. 2 is a schematic diagram showing a carbon dioxide reduction device according to a second embodiment. FIG. 3 is a schematic diagram showing a carbon dioxide reduction device according to a third embodiment. FIG. 4 is a schematic diagram showing a carbon dioxide reduction device according to a fourth embodiment. FIG. 5 is a schematic diagram showing a carbon dioxide reduction device according to a fifth embodiment. FIG. 6 is a schematic diagram showing a carbon dioxide reduction device according to a sixth embodiment. FIG. 7 is a schematic diagram showing a carbon dioxide reduction device according to a seventh embodiment. FIG. 8 is a schematic diagram showing a carbon dioxide reduction device according to an eighth embodiment. FIG. 9 is a schematic diagram showing an electrochemical system according to a ninth embodiment. FIG. 10 is a schematic diagram showing an electrochemical system according to a tenth embodiment. FIG. 12 is a schematic diagram showing an electrochemical system according to a twelfth embodiment. FIG. 13 is a schematic diagram showing an electrochemical reaction device according to a modification of the eleventh embodiment. FIG. 14 is a schematic diagram showing an electrochemical reaction device according to a fourteenth embodiment. FIG. 15 is a schematic diagram showing an electrochemical reaction device according to a sixteenth embodiment. FIG. 16 is a schematic diagram showing an electrochemical reaction device according to a seventeenth embodiment. FIG. 18 is a schematic diagram showing an electrochemical reaction device according to an eighteenth embodiment.

[0013] Hereinafter, a carbon dioxide reduction device according to a first aspect of the present invention and a method for producing organic matter using the carbon dioxide reduction device will be described using embodiments with reference to the drawings. In the following description of the first aspect, elements having the same configuration will be assigned the same reference numerals. In addition, the carbon dioxide reduction device according to the first aspect is also an electrochemical reaction device that produces organic matter, as will be described later.

[0014] <First embodiment> Fig. 1 shows a carbon dioxide reduction device 10 according to a first embodiment of the present invention. The carbon dioxide reduction device 10 according to the first embodiment of the present invention includes a first electrode 11, a second electrode 12, a first ion exchange membrane 15, a first electrolysis unit 21 having the first electrode 11, a first electrolysis unit 22 having the second electrode 12, and a reaction unit 31. Note that Fig. 1 shows representative examples of reactions occurring in each electrolysis unit and reaction unit, and ion behavior in the ion exchange membrane, but is not limited to the configuration shown in Fig. 1. Also, in Fig. 1, X represents a halogen atom, and ROH represents an alcohol-based compound. The same applies to Fig. 2 and subsequent figures.

[0015] (First electrolysis section) The first electrode 11 is a cathode and is disposed in a first electrolysis section 21 that constitutes a cathode chamber. The first electrolysis section 21 is a region in which introduced carbon dioxide is electrochemically reduced. The first electrode 11 includes a first catalyst (carbon dioxide reduction catalyst) that promotes a reduction reaction that reduces carbon dioxide to a first reduced product. Details of the first catalyst and the first electrode 11 will be described later.

[0016] The first electrolysis unit 21 is provided with an inlet 23, through which carbon dioxide is supplied. The carbon dioxide may be supplied as a gas. The inlet 23 is connected to a carbon dioxide supply source (not shown), and carbon dioxide is supplied from the carbon dioxide supply source. The inlet 23 may have any mechanism, such as a flow rate control mechanism, to adjust the flow rate of the supplied carbon dioxide. The carbon dioxide may be supplied to the first electrolysis unit 21 continuously or intermittently. The carbon dioxide supply source is not particularly limited, and may be a gas cylinder or the like. Furthermore, the carbon dioxide may be obtained from exhaust gas emitted from any of a power plant, a steel mill, a cement factory, and a waste incineration plant, and any of these facilities may serve as the carbon dioxide supply source. These facilities generate large amounts of exhaust gas, which generally contains a large amount of carbon dioxide. Therefore, the exhaust gas generated in each of these facilities may be supplied to a carbon dioxide reduction device (electrochemical cell).

[0017] In the first electrolysis unit 21, carbon dioxide is reduced by the first catalyst at the first electrode 11 to generate a reduction product (first reduction product). The reduction products of carbon dioxide generated at the first electrode 11 include CO (carbon monoxide), HCO ３ － , O.H. － , HCO － , H ２ CO, (HCO ２ ) － , H ２ CO ２ , C.H. ３ OH, CH ４ , C ２ H ４ , C.H. ３ CH ２ OH, CH ３ COO － , C.H. ３ COOH, C ２ H ６ , O ２ , (COOH) ２ , (COO － ) ２ Although examples include the above, carbon monoxide is preferred. The reaction at the first electrode when carbon monoxide is produced is represented by the following formula (i) or formula (ii). The following formula (i) is a reaction that generally proceeds under acidic conditions, and the following formula (ii) is a reaction that generally proceeds under basic conditions. CO ２ +2H ＋ +2e － →CO+H ２ O (i) CO ２ +H ２ O + 2e － →CO + 2OH － (ii)

[0018] In this embodiment, the first electrolysis unit 21 is not filled with an electrolyte solution such as water or other organic solvents, and gaseous carbon dioxide is preferably brought into contact with the first electrode 11. That is, a reduction reaction of gaseous carbon dioxide is preferably carried out at the first electrode 11 through a gas-phase reaction. However, the gaseous carbon dioxide may contain moisture. Carbon dioxide may be supplied to the first electrolysis unit 21 either alone or with an inert gas such as helium as a carrier gas. However, carbon dioxide is preferably supplied alone. In the first electrolysis unit 21 that is not filled with a liquid such as an electrolyte solution, the generated first reduction product, such as carbon monoxide, is mixed with unreacted carbon dioxide in the gas phase and flows through the first connecting path 41 to the reaction unit 31, as described below. Water generated as a by-product preferably remains in the first electrolysis unit 21 and is discharged when a certain amount is reached. The first electrolysis unit 21 may be provided with an outlet (not shown) for discharging the by-product water.

[0019] (Second Electrolysis Unit) The second electrode 12 is an anode and is disposed in a second electrolysis unit 22 that constitutes an anode chamber. The second electrode 12 is capable of oxidizing a reduction product A of a redox substance to an oxide B. The second electrolysis unit 22 is filled with an electrolytic solution. The second electrolysis unit 22 also contains a redox substance. The electrolytic solution filled in the second electrolysis unit 22 is an aqueous electrolytic solution or a non-aqueous electrolytic solution. The aqueous electrolytic solution contains a redox substance and water. The redox substance is preferably dissolved in water, but may be dispersed in water without being dissolved. The non-aqueous electrolytic solution contains a redox substance and an alcohol-based solvent or a nitrile-based solvent. In the second electrolysis unit 22, the second electrode 12 is in contact with the electrolytic solution. The electrolytic solution in the second electrolysis unit 22 is preferably an aqueous electrolytic solution.

[0020] The redox substance used is one that can generate halogen ions in the electrolytic solution, and specific examples include a halide salt and a hydrogen halide. A halide salt and a hydrogen halide may be used in combination, but it is preferable to use at least a halide salt or a hydrogen halide. By using a halide salt, halogen, which is an oxide B, is easily generated in the second electrolysis unit 22, and the halogen generated allows the target product to be efficiently generated from carbon monoxide and the reaction substrate in the presence of the second catalyst in the reaction unit 31.

[0021] Examples of halide salts include metal halide salts, and among these, alkali metal halide salts are preferred. Specific examples include lithium halide salts such as lithium chloride and lithium bromide, sodium halide salts such as sodium chloride and sodium bromide, potassium halide salts such as potassium chloride and potassium bromide, and cesium halide salts such as cesium chloride and cesium bromide. Ammonium halides such as ammonium chloride and ammonium bromide are also included. Examples of halide salts include metal halide salts, and alkali metal halide salts are more preferred. Among these, lithium chloride, potassium chloride, sodium chloride, potassium chloride, cesium chloride, lithium bromide, potassium bromide, sodium bromide, potassium bromide, and cesium bromide are even more preferred. Among these, lithium chloride, lithium bromide, sodium chloride, sodium bromide, potassium chloride, and potassium bromide are particularly preferred from the viewpoint of increasing the selectivity of the target product. Examples of hydrogen halides include hydrogen chloride and hydrogen bromide. In the second electrolysis section 22, the concentration of the redox substance in the electrolytic solution is not particularly limited, but is, for example, 0.001 to 5.0M, preferably 0.01 to 1.0M, and more preferably 0.05 to 0.5M.

[0022] The interior of the second electrolysis unit (anode chamber) 22 may be entirely filled with the electrolytic solution, or may have a partial space therein. Furthermore, the components (water, redox material, etc.) constituting the electrolytic solution in the second electrolysis unit 22 may be supplied to the second electrolysis unit 22 in any manner as long as they are introduced into the second electrolysis unit 22. For example, they may be introduced through an inlet (not shown) of the second electrolysis unit 22.

[0023] A power supply 19 is connected to the first electrode 11 and the second electrode 12, and a voltage is applied between the first electrode 11 and the second electrode 12 by the power supply 19. As a result of the application of the voltage, as described above, a reduction reaction occurs on the first electrode 11 side in which carbon dioxide is reduced to a first reductant such as carbon monoxide, and the redox material is oxidized from the reductant A to an oxide B in the second electrolysis unit 22. The oxide B is typically a gas such as a halogen, and the oxide B obtained by oxidation in the second electrolysis unit 22 may be supplied to the reaction unit 31 via the second connecting path 42, as described below.

[0024] (First Ion Exchange Membrane) The first ion exchange membrane 15 is located between the first electrode 11 and the second electrode 12 and separates a first electrolysis section 21 (cathode chamber) from a second electrolysis section 22 (anode chamber). In this embodiment, the first electrode 11 and the second electrode 12 are disposed on either side of the first ion exchange membrane 15 and joined together to form a membrane-electrode assembly. As a result, the first electrolysis section 21 and the second electrolysis section 22 of the carbon dioxide reduction device 10 have a two-chamber diaphragm-type cell structure in which the electrochemical cell is separated into two chambers by the membrane-electrode assembly. However, the formation of a membrane-electrode assembly is not necessarily required, and in this embodiment, any structure in which the first ion exchange membrane 15 separates the first electrolysis section 21 from the second electrolysis section 22 may be used. The first ion exchange membrane 15 and second and third ion exchange membranes 25 and 35, which will be described later, form separators that separate the internal regions of the electrochemical cell.

[0025] The first ion exchange membrane 15 may be a solid membrane, such as a cation exchange membrane permeable to cations such as protons or an anion exchange membrane permeable to anions such as hydroxide ions. From the viewpoints of ion conductivity and cost, a cation exchange membrane is preferred. When the first ion exchange membrane 15 is a cation exchange membrane, the electrolyte within the second electrolysis unit 22 may be adjusted to be acidic. Adjusting the electrolyte to be acidic allows cations such as protons to permeate from the second electrolysis unit 22 to the first electrolysis unit 21, as shown in FIG. 1 , and the reaction represented by the above formula (i) or the like can easily occur on the first electrolysis unit 21 side. When the first ion exchange membrane 15 is an anion exchange membrane, the electrolyte within the second electrolysis unit 22 may be adjusted to be basic. Adjusting the electrolyte to be basic allows anions such as hydroxide ions to permeate from the second electrolysis unit 22 to the first electrolysis unit 21 side, and the reaction represented by the above formula (ii) or the like can easily occur on the first electrolysis unit 21 side.

[0026] Examples of cation exchange membranes include those having at least one of sulfonyl, carboxyl, phosphate, and silicic acid groups as functional groups. Examples of cation exchange membranes having sulfonyl groups as functional groups include hydrocarbon resin-based polysulfonic acids such as polyethylene sulfonic acid and fullerene-crosslinked polysulfonic acid, and fluororesin-based sulfonic acids such as perfluoroethylene sulfonic acid. Examples of perfluoroethylene sulfonic acid include copolymers of tetrafluoroethylene and perfluoro[2-(fluorosulfonylethoxy)propyl vinyl ether], and commercially available products include "Nafion" (a trademark of DuPont). Examples of membranes having carboxyl groups as functional groups include polycarboxylic acids such as polyacrylic acid. Examples of membranes having phosphate or silicic acid groups as functional groups include heteropolyacids such as silicotungstic acid and phosphotungstic acid. Furthermore, cation exchange membranes made of SiO ２ -P ２ O ５ Phosphate glasses such as those listed above, and ceramics such as perovskite oxides can also be used.

[0027] Examples of anion exchange membranes include resins containing quaternary ammonium salts such as poly(styrylmethyltrimethylammonium chloride), polyethers, and polymers containing imidazolium groups. Examples of resins containing ammonium salts include "FAA-3-50" from FuMA-Tech GmbH and "TM1 Durion Grade" from Orion. Examples of polymers containing imidazolium groups include styrene-based polymers containing imidazolium groups, and specific examples include copolymers of styrene and 1-(p-vinylbenzyl)-3-methylimidazolium (PSMIM), copolymers of styrene and 1-(p-vinylbenzyl)-tetramethylimidazolium (PSTMIM), and copolymers of styrene and 1-(p-vinylbenzyl)-2,3-dimethylimidazolium (PSDMIM).

[0028] (Reaction section) The reaction section 31 is constituted by a reactor separate from the first electrolysis section 21 and the second electrolysis section 22. That is, the reaction section 31 is a reaction system separate from the reaction system constituted by the first electrolysis section 21 and the reaction system constituted by the second electrolysis section 22. The reaction section 31 is connected to the first electrolysis section 21 via a first connecting path 41, and is connected to the first electrolysis section 22 via a second connecting path 42. The first connecting path 41 is, for example, a conduit connecting the first electrolysis section 21 and the reaction section 31, and may be provided with a flow rate adjustment mechanism or the like to adjust the flow rate, etc. The second connecting path 42 is, for example, a conduit connecting the second electrolysis section 22 and the reaction section 31, and may be provided with a flow rate adjustment mechanism or the like to adjust the flow rate, etc. The conduits constituting the first connecting passage 41 and the second connecting passage 42 are fitted with check valves or the like, and gas is sent from the first electrolysis section 21 or the second electrolysis section 22 to the reaction section 31 through the first connecting passage 41 or the second connecting passage 42, but gas may not be sent in the opposite direction.

[0029] The first reduced product, such as carbon monoxide, produced in the first electrolysis unit 21 flows out as a gas to the reaction unit 31 through the first connecting path 41. At this time, the first reduced product is supplied to the reaction unit 31 together with, for example, carbon dioxide that was unreacted in the first electrolysis unit 21. Furthermore, oxide B, such as a halogen (e.g., chlorine or bromine), produced in the second electrolysis unit 21 flows out to the reaction unit 31 through the second connecting path 42. Preferably, oxide B, such as a halogen, is separated from the electrolytic solution by a method such as vaporization and flows out as a gas to the reaction unit 31 through the second connecting path 42. The first reduced product and oxide B are preferably supplied to the reaction solution filled in the reaction unit 31 by bubbling, but may be supplied by other methods. Bubbling disperses the second catalyst and the like in the reaction unit 31, facilitating the reaction. The first connecting path 41 is not particularly limited as long as it is capable of transporting the first reduced product, and any means may be used. Similarly, the second connecting path 42 is not particularly limited as long as it can transport the oxide B, and may be any means.

[0030] The reaction section 31 contains a second catalyst. The second catalyst is a catalyst that promotes a reaction that produces an organic substance from the first reduction product and oxide B. The reaction section 31 typically contains a reaction substrate. The second catalyst is preferably a catalyst that promotes a reaction that synthesizes an organic substance (target product) from the first reduction product and reaction substrate in the presence of oxide B. In the reaction section 31, the reaction substrate preferably contains the second catalyst, and the reaction substrate containing the second catalyst is filled in the reaction section 31 as a reaction liquid. The second catalyst may be dispersed or dissolved in the reaction liquid. Furthermore, in the reaction section 31, the second catalyst may be in the form of a fixed bed. Furthermore, the reaction section 31 may be equipped with a stirring device for stirring the reaction liquid.

[0031] In the reaction section 31, as shown in FIG. 1, halogen (X ２ ) to a reduced product A (e.g., halogen ions X －), while the first reduction product such as carbon monoxide reacts with the reaction substrate such as the alcohol compound to produce a target product such as a carbonyl compound. The reaction temperature in the reaction section 31 when the target product is produced is not particularly limited, but is, for example, 0 to 300°C, and preferably 10 to 200°C.

[0032] (Reaction Substrate) The reaction substrate contained in the reaction section 31 is a compound that serves as a raw material for obtaining a target product by reacting with a first reductant such as carbon monoxide. The reaction substrate is changed depending on the type of target product to be produced. Examples of the target product include carbonyl compounds such as carbonate compounds, oxalate compounds, and urea compounds, and isocyanate compounds. For example, when producing a carbonate compound (organic carbonate), an oxalate compound (organic oxalate), or both, an alcohol compound may be used as the reaction substrate. Furthermore, when producing a urea compound, an amine compound may be used as the reaction substrate. Furthermore, to produce an isocyanate compound, an amine compound may be used as the reaction substrate. Of the above, an alcohol compound is preferably used as the reaction substrate.

[0033] (Alcohol-Based Compound) The alcohol-based compound is a reaction substrate that reacts with carbon monoxide, the first reductant, in the reaction section 31 to produce a carbonate compound, an oxalate compound, or both. The alcohol-based compound may be solid, liquid, or gaseous under the temperature environment of the reaction carried out in the reaction section 31, but is preferably liquid. A liquid alcohol-based compound can be easily filled into the reaction section 31 without using a reaction solvent, which will be described later. The alcohol-based compound is a compound having at least one hydroxyl group, and more specifically, a compound represented by the following general formula (1). In this specification, the term "alcohol-based compound" is a concept that also includes aromatic hydroxy compounds in which a hydroxyl group is directly bonded to an aromatic ring such as a benzene ring, as will be described later, such as phenol.

[0034] ROH (1) (R represents an organic group having 1 to 15 carbon atoms.) The organic group having 1 to 15 carbon atoms represented by R in the above general formula (1) includes a hydrocarbon group having 1 to 15 carbon atoms. Examples of the hydrocarbon group include an alkyl group having 1 to 15 carbon atoms, an alkenyl group having 2 to 15 carbon atoms, and an aryl group having 6 to 15 carbon atoms. Examples of the alkyl group having 1 to 15 carbon atoms include a methyl group, an ethyl group, various propyl groups, various butyl groups, various pentyl groups, various hexyl groups, various heptyl groups, various octyl groups, various nonyl groups, various decyl groups, various dodecyl groups, and various pentadecyl groups. Examples of alkenyl groups having 2 to 15 carbon atoms include vinyl groups, various propynyl groups, various butynyl groups, various pentynyl groups, various hexenyl groups, various heptenyl groups, various octenyl groups, various nonenyl groups, various decenyl groups, various dodecenyl groups, and various pentadecenyl groups. The term "various" refers to various isomers including n-, sec-, tert-, and iso-. The alkyl or alkenyl group may be linear, branched, or cyclic. Examples of aryl groups having 6 to 15 carbon atoms include phenyl and naphthyl groups. The hydrocarbon groups described above may have a substituent, and in such cases, the total carbon number, including the substituent, is 1 to 15.

[0035] Furthermore, the organic group having 1 to 15 carbon atoms in general formula (1) may contain a heteroatom such as a nitrogen atom, an oxygen atom, a sulfur atom, a phosphorus atom, or a halogen atom. Among these, an oxygen atom is preferred. When an oxygen atom is contained, the oxygen atom is preferably either a hydroxyl group or an oxygen atom of an ether bond. Therefore, it is preferable that R is a hydrocarbon group having at least either a hydroxyl group or an ether bond. It is also preferable that R has one hydroxyl group. In other words, the alcohol-based compound may have two hydroxyl groups. More specifically, the alcohol-based compound having two hydroxyl groups is preferably a group represented by the following formula (1-1): HO-R 11 —OH (1-1) In addition, in formula (1-1), R 11 is a divalent saturated hydrocarbon group having 2 to 15 carbon atoms, and R 11The number of carbon atoms is preferably 2 to 4, more preferably 2 to 3.

[0036] As the compound represented by the general formula (1), among the above, R is preferably an alkyl group having 1 to 8 carbon atoms, an alkenyl group having 2 to 8 carbon atoms, or an aryl group having 6 to 8 carbon atoms. 11 Also preferred are those having 2 to 4 carbon atoms. Among these, compounds in which R is an alkyl group or an aryl group are more preferred, and particularly compounds in which R is an alkyl group are even more preferred. The alkyl group more preferably has 1 to 3 carbon atoms, even more preferably has 1 or 2 carbon atoms, and most preferably has 1 carbon atom. Specifically, from the viewpoints of reactivity and production efficiency, methanol, ethanol, phenol, 1-propanol, ethylene glycol, propylene glycol, etc. are preferred, and among these, methanol is more preferred. The alcohol-based compounds may be used alone or in combination of two or more types.

[0037] When an alcohol-based compound is used as the reaction substrate, a reaction (also referred to as the first reaction) in which a carbonate compound is produced from carbon monoxide and the alcohol-based compound generally takes place in the reaction section 31. However, a reaction (also referred to as the second reaction) in which an oxalate compound is produced from carbon monoxide and the alcohol-based compound may also take place, and both the first and second reactions are carried out, but it is preferable that at least the first reaction be carried out.

[0038] The first reaction is a carbonylation reaction in which a carbonate compound is produced. For example, a carbonate compound ((RO)) is produced by the reaction shown in the following formula (iii): ２ CO) is produced. CO + 2ROH + 2X － → (RO) ２CO+2HX (iii) In (iii), X is a halogen atom such as chlorine or bromine. R is the same as above, but preferably R is an alkyl group having 1 to 8 carbon atoms, an alkenyl group having 2 to 8 carbon atoms, or an aryl group having 6 to 8 carbon atoms, more preferably an alkyl group or an aryl group, and even more preferably an alkyl group. The alkyl group more preferably has 1 to 3 carbon atoms, even more preferably has 1 or 2 carbon atoms, and most preferably has 1 carbon atom. However, as mentioned above, two or more alcohol compounds may be used in combination, and in that case, (RO) ２ Two R's in one molecule of CO may be different from each other.

[0039] When ROH is represented by the general formula (1-1), a carbonate compound is produced, for example, by the reaction represented by the following formula (iv). In addition, in formula (iv), X and R 11 is the same as above, but R 11 The number of carbon atoms is preferably 2 to 4, more preferably 2 to 3, and even more preferably 2.

[0040] Specific preferred carbonate compounds include one or more selected from dimethyl carbonate, diethyl carbonate, ethylene carbonate, dipropyl carbonate, propylene carbonate, diphenyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate, and among these, dimethyl carbonate is more preferred.

[0041] The second reaction is a reaction in which carbon monoxide and an alcohol compound produce an oxalate compound represented by the following formula (2). For example, the oxalate compound represented by formula (2) may be synthesized by the reaction represented by the following formula (v). (In formula (2), R is the same as above. However, two R in one molecule may be the same or different.) (Note that in formula (v), X and R are the same as above.)

[0042] When ROH is represented by the general formula (1-1), an oxalate compound represented by the following formula (2-1) is produced by the reaction represented by the following formula (vi). (In addition, in formula (2-1), R １１ is the same as above.) (In formula (vi), X and R １１ is the same as above.)

[0043] Specific preferred oxalate compounds include one or more selected from dimethyl oxalate, diethyl oxalate, ethylene oxalate, dipropyl oxalate, propylene oxalate, diphenyl oxalate, ethyl methyl oxalate, methyl propyl oxalate, and ethyl propyl oxalate. Among these, dimethyl oxalate is more preferred.

[0044] (Amine Compound) The amine compound used as the reaction substrate is an organic compound having at least one amino group, and is preferably a compound represented by the following formula (3): ２ NH ２ (3) (R ２ represents an organic group having 1 to 15 carbon atoms. 2 The organic group having 1 to 15 carbon atoms represented by R includes a hydrocarbon group having 1 to 15 carbon atoms, and specific descriptions thereof are given in the above R 1 The organic group having 1 to 15 carbon atoms in formula (3) may contain a heteroatom such as a nitrogen atom, an oxygen atom, a sulfur atom, or a phosphorus atom. Of these, a nitrogen atom is preferred, and the nitrogen atom is preferably the nitrogen atom of an amino group. Therefore, R ２ is preferably a hydrocarbon group having an amino group. More specifically, an aminoalkyl group having 1 to 15 carbon atoms is preferred. By using an amine compound as a reaction substrate, a urea compound having a urea bond (—NH—CO—NH—) can be synthesized.

[0045] When the above-mentioned reaction substrate is a solid or gas, or when it is necessary to improve the solubility of the redox substance, the reaction substrate (reaction liquid) filled in the reaction section 31 may be diluted with a solvent (hereinafter also referred to as "reaction solvent"). In this case, the reaction substrate may be filled in the reaction section 31 as a mixture with the solvent. Of course, even when the reaction substrate is a liquid, it may be filled as a mixture with the solvent.

[0046] Examples of the reaction solvent include nitrile solvents such as acetonitrile, carbonate solvents such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate, lactone solvents such as γ-butyrolactone, ether solvents such as 1,2-dimethoxyethane, 1-ethoxy-2-methoxyethane, 1,2-diethoxyethane, tetrahydrofuran, and 2-methyltetrahydrofuran, phosphate ester solvents, phosphoric acids, sulfolane solvents, pyrrolidones, etc. These solvents may be used alone or in combination of two or more.

[0047] In the reaction section 31, as described above, a by-product is generated from the reduction product A along with the target product. The by-product is a component derived from the redox material, typically a hydrogen halide, as shown in formulas (iii) to (vi). The by-product may be removed from the reaction section 31. The by-product removed from the reaction section 31 may be supplied to the second electrolysis section 22 by a known supply mechanism. Preferably, the by-product derived from the redox material, such as hydrogen halide, is removed from the reaction section 31 together with the target product obtained in the reaction section 31 and unreacted reaction substrates, and purified in a purification device 32, such as a distillation device. The purified by-product, such as hydrogen halide, is then supplied to the second electrolysis section 22 via a supply path 36 (supply mechanism). As described above, by supplying the by-product to the second electrolysis section 22, the redox material is circulated between the second electrolysis section 22 and the reaction section 31, thereby reducing raw material loss.

[0048] As described above, in this embodiment, a first reduction product is produced at the first electrode 11, an oxide B is produced at the second electrode 12, and an organic substance is produced from the first reduction product and oxide B in the first reaction unit 31 using the second catalyst. This allows the reaction of the redox substances to be prioritized, thereby efficiently producing the target product while suppressing the oxidation of reaction substrates such as alcohol-based compounds. Furthermore, the first electrolysis unit 21 and the second electrolysis unit 22 can be configured using standard electrochemical cells, allowing the target product to be obtained from carbon dioxide without complicating the device structure. Furthermore, when an aqueous electrolyte is used in the second electrolysis unit 22, the electrochemical cells constituting the first electrolysis unit 21 and the second electrolysis unit 22 do not need to use reaction substrates such as alcohol-based compounds. This eliminates the need for alcohol-resistant electrochemical cells, facilitating the conversion of existing electrolysis equipment. Furthermore, water by-produced in the first electrolysis unit 21 is prevented from entering the reaction unit 31 and inhibiting the reaction, thereby further improving the reaction efficiency of the target product. In addition, in this embodiment, the reaction unit 21 can be made electrolyte-free, which facilitates separation and purification of the target product. In addition, in this embodiment, if the first reduction product such as carbon monoxide and the oxide B such as a halogen are both supplied as gases to the reaction unit 31, the first reduction product and the oxide B produced in the electrochemical cell can be supplied efficiently.

[0049] The first catalyst used in the first electrode 11, the configurations of the first and second electrodes 11 and 12, and the configuration of the second catalyst will be described in more detail below. (First Catalyst) The first catalyst is a reduction catalyst capable of reducing carbon dioxide to a first reductant such as carbon monoxide. The first catalyst is not particularly limited as long as it is a catalyst capable of reducing carbon dioxide to a reductant such as carbon monoxide, but may include, for example, a metal element. The metal element may be the metal itself or a metal compound. Examples of the metal element include, but are not limited to, V, Cr, Mn, Fe, Co, Ni, Cu, Sn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Ir, Pt, Au, Hg, Al, Si, In, Sn, Tl, Pb, Bi, Sb, Te, U, Sm, Tb, La, Ce, Zn, Os, and Nd. As the metal compound, inorganic metal compounds and organic metal compounds of these metals can be used, and specific examples thereof include metal halides, metal oxides, metal hydroxides, metal nitrates, metal sulfates, metal acetates, metal phosphates, metal carbonyls, and metal acetylacetonates.

[0050] The metal element used in the first catalyst is preferably a metal element from Groups 7 to 12. Preferred examples include Mn, Fe, Ni, Ru, Co, Rh, Cu, Zn, Ag, Au, Pd, Ir, Pt, and Os, with Co, Fe, Ni, Au, and Ag being more preferred, and Co being particularly preferred. The use of these metal elements makes it easier to increase the efficiency of conversion of carbon dioxide to carbon monoxide, and enhances catalytic activity. The metals used in the metal derivative may be used alone or in combination of two or more.

[0051] The first catalyst may contain a carbon compound in addition to the metal or metal compound. The carbon compound is preferably a conductive carbon compound. More specifically, examples of the carbon compound include mesoporous carbon, activated carbon, carbon black such as ketjen black and acetylene black, graphite, carbon fiber, graphene, and carbon nanotubes. Among these, carbon black is preferred, and conductive carbon black is even more preferred. Furthermore, the carbon compound is preferably porous carbon. When the first catalyst contains a carbon compound, the metal or metal compound may be supported on the carbon compound. Furthermore, the carbon compound may be mixed with a complex containing the metal element and heat-treated to form a catalyst powder. The first catalyst in which the metal or metal compound is supported on the carbon compound may be further supported on an electrode substrate, as described below.

[0052] <Nitrogen-containing metal catalyst> The first catalyst is also preferably a catalyst containing a nitrogen element and a metal element (also referred to as a "nitrogen-containing metal catalyst"). Here, the nitrogen element used in the nitrogen-containing metal catalyst is preferably derived from a nitrogen-containing compound described below. Specific examples of the metal element used in the nitrogen-containing metal catalyst are as described above, and the preferred metal elements are also as described above. Use of a nitrogen-containing metal catalyst increases the efficiency of carbon monoxide production, thereby increasing the selectivity of the target product, such as a carbonyl compound, to be synthesized.

[0053] The nitrogen-containing metal catalyst is preferably a catalyst obtained by heat-treating a mixture containing a metal derivative and a nitrogen-containing compound (hereinafter referred to as a "first catalyst raw material mixture"), and is particularly preferably a catalyst obtained by heat-treating a first catalyst raw material mixture containing a metal derivative, a nitrogen-containing compound, and a carbon compound. The heat treatment is typically calcination. The nitrogen-containing metal catalyst is preferably produced by heat-treating the first catalyst raw material mixture, so that metal-nitrogen element bonds derived from the metal derivative and the nitrogen-containing compound are formed in the catalyst. Furthermore, the carbon compound functions as a support in the catalyst, and components derived from the metal derivative and the nitrogen-containing compound (i.e., metal element and nitrogen element) are supported on the carbon compound. A nitrogen-containing metal catalyst having the above configuration efficiently reduces carbon dioxide to carbon monoxide, thereby increasing the conversion efficiency.

[0054] The metal element in the metal derivative is as described above. The metal derivative preferably contains a metal ion. The metal derivative may be used, for example, in the form of a metal salt. Examples of metal salts include metal nitrates, metal sulfates, metal chlorides, metal bromides, metal iodides, and metal acetates. Among these, metal nitrates are preferred. Specifically, cobalt nitrate (Co(NO3)2), nickel nitrate (Ni(NO3)2), iron nitrate (Fe(NO3)2), manganese nitrate (Mn(NO3)2), copper nitrate (Cu(NO3)2), and zinc nitrate (Zn(NO3)2) are preferred. The metal salts may be used alone or in combination of two or more.

[0055] The metal content derived from the metal derivative in the first catalyst raw material mixture is, for example, 0.1 mass% to 50 mass% but preferably 0.1 mass% to 10 mass% relative to the total amount of the first catalyst raw material mixture. By ensuring that the content is within this range, the metal is contained in the catalyst without agglomerating, and an appropriate number of catalytic active sites are formed. This facilitates increasing the efficiency of conversion to carbon monoxide. From the standpoint of conversion efficiency and the like, the metal content is more preferably 0.5 mass% or more, even more preferably 1.0 mass% or more, even more preferably 1.5 mass% or more, and more preferably 10 mass% or less, and even more preferably 5 mass% or less. The term "total amount of the first catalyst raw material mixture" refers to the total amount of solids in the first catalyst raw material mixture. If volatile components are blended into the first catalyst raw material mixture during its production process, this refers to the amount excluding the volatile components.

[0056] (Nitrogen-Containing Compound) The nitrogen-containing compound is a compound containing nitrogen, and a component derived from the nitrogen-containing compound may form a bond such as a coordinate bond with a metal element derived from the metal derivative in the nitrogen-containing metal catalyst. Specific examples of the nitrogen-containing compound include compounds containing a nitrogen-containing aromatic ring having a nitrogen element as a constituent element of the aromatic ring. Specific examples of the nitrogen-containing compound include pyridine derivatives, imidazole derivatives, pyrazole derivatives, and triazole derivatives. These compounds may be used alone or in combination of two or more. Among these, from the viewpoint of conversion efficiency, a compound selected from pyridine derivatives, imidazole derivatives, and triazole derivatives is preferred, and a pyridine derivative is particularly preferred. That is, the nitrogen-containing metal catalyst is particularly preferably a catalyst obtained by heat-treating a mixture containing a metal derivative, a pyridine derivative, and a carbon compound.

[0057] ((Pyridine Derivative)) A pyridine derivative is a compound having a pyridine ring. The pyridine derivative may be a compound having one, two, three, or four or more pyridine rings per molecule. Examples of the pyridine derivative include 4-aminopyridine, 2,2'-bipyridine, 4,4'-diamino-2,2'-bipyridine, etc., and also include polymers having multiple pyridine rings per molecule and having a weight-average molecular weight of 1,000 or more. Specific examples of the polymer include polypyridines such as poly(2,5-pyridine) and poly(3,5-pyridine), and polyvinylpyridine, which is a polymer of vinylpyridine. Among these, poly(2,5-pyridine) and poly(4-vinylpyridine) are more preferred, and poly(4-vinylpyridine) is even more preferred. From the viewpoint of conversion efficiency and the like, polyvinylpyridines such as poly(4-vinylpyridine) preferably have a molecular weight of a certain level or higher, and the weight-average molecular weight is, for example, 1,000 or higher, 10,000 or higher, preferably 30,000 or higher, and more preferably 50,000 or higher. From the viewpoint of availability and the like, the weight-average molecular weight is, for example, 200,000 or lower, preferably 100,000 or lower. The weight-average molecular weight is a value measured by gel permeation chromatography (GPC), and polystyrene is preferably used as a standard substance.

[0058] The amount of the nitrogen-containing compound in the first catalyst raw material mixture is preferably adjusted so that the molar ratio of the nitrogen-containing aromatic rings of the nitrogen-containing compound to the metal element of the metal derivative (nitrogen-containing aromatic ring / metal element) is 2 or more and 20 or less. Within this range, the occurrence of side reactions can be suppressed, a catalyst containing an appropriate amount of metal-nitrogen element bonds can be produced, and the conversion efficiency described above can be easily increased. From the viewpoint of conversion efficiency, the molar ratio is more preferably 2 or more, even more preferably 4 or more, and more preferably 18 or less, and more preferably 15 or less. The molar ratio represents the ratio between the number of nitrogen-containing aromatic rings contained in the nitrogen-containing compound and the number of moles of the metal element contained in the metal derivative.

[0059] The carbon compound used in the nitrogen-containing metal catalyst is not particularly limited as long as it can support a heat-treated product (e.g., a calcined product) of a metal derivative and a nitrogen-containing compound such as a pyridine derivative, but a conductive carbon compound is preferred. The use of a conductive carbon compound increases the electrical conductivity at the cathode, making it easier to increase the conversion efficiency to carbon monoxide. Specific examples of carbon compounds are as described above, with carbon black being preferred, and conductive carbon black, such as Ketchum black, being even more preferred. The content of the carbon compound in the first catalyst raw material mixture is not particularly limited, but is, for example, 5% by mass or more and 90% by mass or less, preferably 15% by mass or more and 80% by mass or less, and more preferably 20% by mass or more and 70% by mass or less, based on the total amount of the first catalyst raw material mixture. By setting the carbon compound content within the above range, the heat-treated product of the metal derivative and the nitrogen-containing compound can be appropriately supported while maintaining good catalytic activity. The nitrogen-containing metal catalyst is preferably in powder or particulate form. A powder or particulate form makes it easier to support the electrode base material, as described below. In addition, the contact area with carbon dioxide tends to increase, making it easier to improve the conversion efficiency to carbon monoxide.

[0060] As described above, the nitrogen-containing metal catalyst obtained by heat treatment contains a metal element and a nitrogen element. However, from the viewpoints of selectivity, ease of production, and the like, it is preferable that the metal element be contained in the nitrogen-containing metal catalyst as a metal oxide. As described above, the metal element is preferably cobalt, and therefore the nitrogen-containing metal catalyst preferably contains cobalt oxide. Furthermore, it is particularly preferable that the cobalt oxide contains CoO. Furthermore, as described above, the nitrogen-containing metal catalyst preferably contains a component derived from the nitrogen-containing compound by heat treatment, and in particular, it is preferable that it contains a component derived from a pyridine derivative. Therefore, it is particularly preferable that the nitrogen-containing metal catalyst contains CoO and a component derived from a pyridine derivative. Furthermore, it is preferable that the nitrogen atom derived from the nitrogen-containing compound is coordinated to a metal element such as cobalt. The component derived from the nitrogen-containing compound preferably contains a nitrogen-containing aromatic ring structure, and specific examples include a pyridine ring structure, an imidazole ring structure, a pyrazole ring structure, and a triazole ring structure. Among these, a pyridine ring structure, an imidazole ring structure, and a triazole ring structure are preferred, and a pyridine ring structure is particularly preferred. Coordination of cobalt to the nitrogen of the pyridine ring structure is presumed to lower the activation energy of the reaction intermediate, thereby increasing the conversion efficiency. As mentioned above, the nitrogen-containing metal catalyst is produced by heat-treating a mixture containing a nitrogen-containing compound, but the treatment temperature is low. Therefore, the nitrogen-containing aromatic ring contained in the nitrogen-containing compound can be retained in the nitrogen-containing metal catalyst.

[0061] The presence of a nitrogen-containing aromatic ring structure such as a pyridine ring structure in a nitrogen-containing metal catalyst can be confirmed by X-ray photoelectron spectroscopy (XPS) or the like. Furthermore, the coordination of nitrogen elements with metal elements such as cobalt elements can also be confirmed by X-ray photoelectron spectroscopy (XPS). Furthermore, the valence of metal elements, for example, the divalent nature of cobalt oxide, can be confirmed by XPS, X-ray diffraction (XRD), or the like.

[0062] Furthermore, the nitrogen-containing metal catalyst may contain various metal elements as metals in addition to the metal oxides. Thus, when the metal element is cobalt, the catalyst may contain cobalt metal in addition to cobalt oxide. The cobalt metal may, for example, be crystalline. When the nitrogen-containing metal catalyst contains cobalt metal, it preferably has a core-shell structure in which the cobalt metal forms a core and the cobalt oxide is disposed around the core so as to coat the cobalt metal. It is presumed that when the nitrogen-containing metal catalyst has a core-shell structure, the conductivity of the nitrogen-containing metal catalyst is improved, making it easier to improve the carbon dioxide reduction rate, etc. The core-shell structure may be in the form of particles and supported on a carbon compound.

[0063] <<Method for Producing Nitrogen-Containing Metal Catalyst>> The nitrogen-containing metal catalyst can be produced by heat-treating a first catalyst raw material mixture containing a metal derivative and a nitrogen-containing compound such as a pyridine derivative, or a metal derivative, a nitrogen-containing compound, and a carbon compound. In this case, the first catalyst raw material mixture is preferably heated to a heat treatment temperature of 150°C or higher and 550°C or lower. The heat treatment temperature is more preferably 180°C or higher and 500°C or lower, and even more preferably 200°C or higher and 470°C or lower. The heat treatment is preferably carried out in an inert gas atmosphere such as argon or nitrogen gas.

[0064] By heat-treating the first catalyst raw material mixture at the heat treatment temperature described above, a metal-nitrogen bond can be formed and components derived from the metal derivative and the nitrogen-containing compound can be supported on the carbon compound. The heat treatment time (heat treatment time) is not particularly limited, but is, for example, 0.5 hours to 10 hours, preferably 1 hour to 8 hours, and more preferably 2 hours to 5 hours. The first catalyst raw material mixture to be heat-treated is preferably in a powder or particulate form. By being in a powder or particulate form, a powder or particulate catalyst can be obtained by heat treatment. Furthermore, the first catalyst raw material mixture to be heat-treated more preferably consists of a metal derivative, a nitrogen-containing compound, and a carbon compound.

[0065] The first catalyst raw material mixture may be obtained, for example, by preparing a diluted solution of the first catalyst raw material mixture by diluting a metal derivative and a nitrogen-containing compound, or a metal derivative, a nitrogen-containing compound, and a carbon compound, with a dilution solvent, and then drying the diluted solution. The first catalyst raw material mixture may be obtained, for example, in the form of a powder or particles. In the diluted solution of the first catalyst raw material mixture, each component (metal derivative, nitrogen-containing compound, and carbon compound) is preferably dispersed or dissolved in the dilution solvent. By dispersing or dissolving each component in the dilution solvent, a first catalyst raw material mixture in which each component is homogeneously mixed can be obtained. The method for obtaining the diluted solution of the first catalyst raw material mixture is not particularly limited. For example, the nitrogen-containing compound may be first added and dispersed in a dispersion medium, and then the metal derivative and, if necessary, the carbon compound may be added to the dispersion. The dilution solvent used to dilute the first catalyst raw material mixture may be water or an organic solvent, with organic solvents being preferred. Examples of organic solvents include, but are not limited to, ester solvents, ketone solvents, ether solvents, alcohol solvents, glycol ethers, amide solvents, nitrile solvents, carbonate solvents, halogenated hydrocarbons, hydrocarbons, sulfone solvents, sulfoxides, and formamide. Furthermore, a mixed solvent of an organic solvent and water may be used as the diluent. The concentration of the diluent for the first catalyst raw material mixture is not particularly limited, but is, for example, 0.01 to 50 g / L, and preferably 1 to 10 g / L.

[0066] In addition to the above, the first catalyst may be a carbon compound containing at least one of a heteroatom such as nitrogen, a metal, or a metal compound. Examples of such carbon compounds include nitrogen-containing graphite, nitrogen-containing carbon nanotubes, nitrogen-containing graphene, Ni- and nitrogen-containing graphite, Ni- and nitrogen-containing carbon nanotubes, Ni- and nitrogen-containing graphene, Cu- and nitrogen-containing graphite, Cu- and nitrogen-containing carbon nanotubes, Cu- and nitrogen-containing graphene, Co- and nitrogen-containing graphite, Co- and nitrogen-containing carbon nanotubes, and Co- and nitrogen-containing graphene. In the electrochemical cell 10, the first catalyst may be used alone or in combination of two or more types.

[0067] (First electrode) The first electrode 11 may have an electrode substrate (current collector). The electrode substrate is not particularly limited as long as it is a current collector conventionally used in carbon dioxide reduction electrodes, and examples thereof include a carbon substrate, a metal substrate, and a metal oxide substrate, and it is preferable that the electrode substrate has conductivity. The electrode substrate may also be a porous body. The substrate is a base material that constitutes the electrode, and may be, for example, in the form of a sheet or plate, or may be in the form of a layer laminated on the wall surface of the electrolysis section (electrochemical cell).

[0068] Examples of carbon substrates include porous carbon such as carbon nonwoven fabric. The carbon nonwoven fabric is not particularly limited, and known carbon nonwoven fabrics can be used. For example, commercially available carbon nonwoven fabrics for fuel cells can be used, such as "TORAYCA" (registered trademark) carbon paper and Toray 060 manufactured by Toray Industries, Inc., "AvCarb 1071HCB" manufactured by New Metals and Chemicals, and the BC series manufactured by SGL. Examples of metal substrates include metal mesh, and metals used include gold, silver, platinum, nickel, titanium, and chromium. Examples of metal oxides used in metal oxide substrates include indium oxide, tin oxide, tin-doped indium oxide, and fluorine-doped tin oxide (FTO).

[0069] The first catalyst may be supported on an electrode substrate. The method for supporting the first catalyst on the electrode substrate is not particularly limited. The first catalyst may be attached to the electrode substrate, and it is particularly preferable to attach the nitrogen-containing metal catalyst described above to the electrode substrate. Here, "attached" refers to a state in which the catalyst is physically fixed to the electrode substrate, and the atoms constituting the electrode substrate are not chemically bonded to the atoms constituting the catalyst. Therefore, even if the electrode substrate contains a carbon compound such as porous carbon, the carbon compound itself does not have the metal-nitrogen element bond described above. Furthermore, it does not have a metal-carbon element bond. Here, the carbon element refers to the carbon element constituting the carbon compound such as porous carbon, and the metal refers to a metal element derived from a metal derivative. By attaching the nitrogen-containing metal catalyst to the electrode substrate without chemically bonding it, the conversion efficiency to carbon monoxide is more easily improved and the production thereof is also easier. However, the atoms constituting the first catalyst may be chemically bonded to the atoms constituting the electrode substrate. For example, when the electrode substrate contains a carbon compound such as porous carbon, the carbon compound itself may have the above-mentioned metal-nitrogen element bond or metal-carbon element bond.

[0070] The first catalyst may be supported on the electrode substrate together with a catalyst additive or the like. The catalyst additive also functions as a binder when supporting the catalyst on the electrode substrate. Furthermore, it also functions as an ion conductor, improving the efficiency of the electrochemical reaction. Examples of the catalyst additive include cation-conductive compounds, anion-conductive compounds, and fluorine compounds other than cation-conductive compounds and anion-conductive compounds. Examples of the cation-conductive compound include compounds having a functional group with a Brønsted acid or a salt thereof, which becomes anionized when a hydrogen ion or the like is liberated. Examples of the cation-conductive compound include compounds having at least one functional group such as a sulfonyl group, a phosphate group, a hydroxyl group, or a silicic acid group. Specifically, a commercially available product such as "Nafion" (a trademark of DuPont) can be mentioned.

[0071] Anion-conducting compounds can also be used as catalyst additives. Examples of anion-conducting compounds include compounds having a functional group containing a Bronsted base or a salt thereof, such as a compound having a functional group that becomes cationized when a proton is added. Anion-conducting compounds have excellent conductivity of anions such as hydroxide ions. Specific examples of anion-conducting compounds include compounds having functional groups such as pyridinium groups, imidazolium groups, amino groups, and ammonium groups. Commercially available anion-conducting compounds include "Fumion FAA-3-SOLUT-10" from FuMA-Tech GmbH and "PowerMax NXS125 OH" from Resin Tech Co., Ltd. Furthermore, examples of fluorine compounds other than cation-conducting compounds and anion-conducting compounds include polytetrafluoroethylene (PTFE), tetrafluoroethylene oligomer (TFEO), fluorinated graphite ((CF)n), and fluorinated pitch (FP).

[0072] The catalyst additive may be, for example, in the form of a powder or particles. When a catalyst additive is used, the first catalyst may be mixed with the catalyst additive and the mixture (catalyst composition) may be supported on the electrode substrate. When the catalyst is supported on the electrode substrate together with the catalyst additive, the content of the catalyst additive relative to the total amount of the catalyst additive and the catalyst is preferably 10% by mass or more and 50% by mass or less, more preferably 15% by mass or more and 45% by mass or less, and even more preferably 20% by mass or more and 40% by mass or less, from the viewpoint of increasing the conversion efficiency of the catalyst.

[0073] The method for supporting the first catalyst on the electrode substrate is not particularly limited, and examples include a method in which the first catalyst and components other than the catalyst, such as optional catalyst additives, are diluted with a dilution solvent and then coated on the electrode substrate using various coating devices or by spray coating, and then dried; and a method in which the electrode substrate is immersed in the diluted solution and then dried. In the first electrode (cathode), the first catalyst (or catalyst composition) may be formed as a layer on the surface of the electrode substrate by, for example, applying a coating liquid containing the catalyst. The catalyst layer may be formed in a layer such that a portion or the entire layer impregnates the interior of the electrode substrate over a portion or the entire thickness direction of the electrode substrate. For example, the catalyst layer may be formed from the surface to the interior of the electrode substrate. The catalyst layer may have appropriate voids. The cathode may have a catalyst supported on one surface to form a catalyst layer, but the other surface may not have a catalyst supported on the other surface, or the catalyst may be supported on both surfaces, or a catalyst layer may be formed on both surfaces. The dilution liquid is preferably a dispersion liquid in which the catalyst or the catalyst and components other than the catalyst are dispersed in a dilution solvent, and the dilution solvent may be water or an organic solvent. The organic solvent is as described above, but preferably an alcohol solvent, a ketone solvent, a nitrile solvent, or the like may be used. The dilution liquid may also be a mixed solution of an organic solvent and water.

[0074] (Second Electrode) The second electrode 12 may have an electrode substrate (current collector). The electrode substrate is not particularly limited as long as it is a current collector conventionally used in the anode of an electrochemical cell, and examples thereof include a carbon substrate, a metal substrate, and a metal oxide substrate, and it is preferable that the electrode substrate has conductivity. The electrode substrate may also be a porous body. The substrate is a substrate that constitutes the electrode, and may be, for example, in the form of a sheet or plate, or may be in the form of a layer laminated on the wall surface of the electrolysis section, etc. The carbon substrate, metal substrate, and metal oxide substrate as the electrode substrate used for the second electrode are as described above.

[0075] As described above, the second electrode may not contain a catalyst, but may contain a catalyst (also referred to as a "third catalyst") as long as it can oxidize the reduction product A of the redox substance to the oxide B. As the third catalyst, a known catalyst used in an anode in hydrochloric acid electrolysis, chloroalkali electrolysis, etc. can be used, and specifically, iridium oxide, ruthenium oxide, iridium-ruthenium oxide, platinum, etc. can be used.

[0076] (Second Catalyst) The second catalyst used in the present invention preferably promotes a chemical reaction in the presence of an oxidation-reduction substance to synthesize a target product such as a carbonyl compound from a first reduction product such as carbon monoxide and a reaction substrate, and preferably contains a metal element, and particularly preferably contains a metal element selected from elements of Groups 8 to 11. Use of an element of Groups 8 to 11 as the catalyst facilitates electrochemical synthesis of a carbonyl compound, particularly a carbonate compound, from carbon monoxide with high selectivity.

[0077] The Group 8 to Group 11 elements used in the second catalyst are as described in the ninth embodiment described below. The metal elements used in the second catalyst may be used alone or in combination of two or more. Details of the use of two or more types are also as described in the ninth embodiment described below.

[0078] The second catalyst may be an active particle-containing catalyst, a metal salt, or a combination of these. By using an active particle-containing catalyst or a metal salt, carbonyl compounds, particularly carbonate compounds, can be produced from carbon monoxide with high conversion efficiency. Among these, the use of an active particle-containing catalyst is particularly preferred.

[0079] <<Active Particle-Containing Catalyst>> The active particles in the active particle-containing catalyst have catalytic ability to promote the reaction when synthesizing carbonyl compounds from carbon monoxide. The active particles are also called catalytically active species. The active particles containing a metal element are not particularly limited as long as they contain a metal element, and may be composed of a metal oxide, a metal itself, or both a metal oxide and a metal. The metal elements used in the active particles are as described above.

[0080] In the second catalyst, the active particles are, for example, in the form of fine particles. Although not particularly limited, they are preferably nano-sized particles, preferably having an average particle diameter of 100 nm or less, more preferably 1 nm to 40 nm. By nanostructuring the active particles, the active area increases, and various performances of the catalyst are likely to be improved. The particle diameter means the diameter of a circle equivalent to the area, as will be explained in the ninth embodiment described later.

[0081] Furthermore, it is preferable that the active particle-containing catalyst further contains a support, and the active particles are supported on the support. Supports used in the active particle-containing catalyst are not particularly limited, but include carbon, silica, aluminum oxide, zirconium oxide, etc., and from the viewpoint of synthesizing carbonyl compounds from carbon monoxide with high selectivity, porous carbon, silica, and aluminum oxide are preferred. Therefore, it is preferable that the active particle-containing catalyst is a catalyst having active particles containing a metal element and at least one of porous carbon, silica, and aluminum oxide supporting the active particles. When the support is porous carbon, silica, or aluminum oxide, the reaction substrate can be appropriately diffused in the catalyst, which makes it easier to improve the selectivity and reaction efficiency when synthesizing carbonyl compounds. The support may be used alone or in combination of two or more types. It is preferable that the support is porous, such as porous carbon, and it is also preferable that silica and aluminum oxide are porous.

[0082] As described below, an active particle-containing catalyst having a support such as porous carbon can be produced by mixing a metal precursor with a support (e.g., porous carbon, silica, or aluminum oxide) and heat treating the mixture. The metal precursor is converted into active particles by heat treatment, and the active particles are supported on the support. The porous carbon used in the active particle-containing catalyst is not particularly limited, but is preferably made of a powder or particulate carbon compound, and therefore the active particle-containing catalyst is also preferably powder or particulate. When the active particle-containing catalyst is powder or particulate, it is easier to disperse it in the electrolyte and the contact area with the first reductant such as carbon monoxide is likely to be larger, which makes it easier to improve the selectivity and reaction efficiency when synthesizing organic substances such as carbonyl compounds.

[0083] The BET specific surface area of ​​the porous carbon used in the active particle-containing catalyst is, for example, 10 m 2 / g or more 3000m 2 / g or less, preferably 100m 2 / g or more 1500m 2 / g or less. The BET specific surface area can be measured by gas adsorption analysis. The average primary particle diameter of the porous carbon used in the active particle-containing catalyst is, for example, 1 nm or more and 1000 nm or less, preferably 10 nm or more and 300 nm or less. The average primary particle diameter of the porous carbon can be measured, for example, by observation using an electron microscope. Specifically, there is mentioned a method of determining the area of ​​each particle and calculating the diameter from the area assuming each particle to be a circle to determine the area-equivalent circle diameter. The average pore diameter of the porous carbon is, for example, 0.5 nm or more and 100 nm or less, preferably 1 nm or more and 50 nm or less. The average pore diameter of the porous carbon can be measured by gas adsorption analysis.

[0084] The porous carbon used in the active particle-containing catalyst is not particularly limited as long as it can support the active particles, but a conductive carbon compound is preferred. The use of a conductive carbon compound increases the electrical conductivity of the electrode, making it easier to improve reaction efficiency, etc. More specific examples of porous carbon include mesoporous carbon, activated carbon, carbon black such as ketjen black and acetylene black, carbon nanotubes, graphite, graphene, etc., of which carbon black is preferred, and conductive carbon black is even more preferred.

[0085] The active particle-containing catalyst may further contain a component derived from a nitrogen-containing compound. The active particle-containing catalyst containing a component derived from a nitrogen-containing compound is likely to improve the conversion efficiency, selectivity, and other properties of the carbonyl compound during synthesis. The component derived from the nitrogen-containing compound preferably contains a nitrogen element, and the nitrogen element may be coordinated to a metal element (e.g., a metal element constituting a metal oxide) constituting the active particle, forming a metal-nitrogen bond through a coordinate bond. The component derived from the nitrogen-containing compound may be supported on a support such as porous carbon, silica, or aluminum oxide. That is, the component derived from the nitrogen-containing compound may be coordinated to a metal element constituting the active particle and supported on a support such as porous carbon. The nitrogen-containing compound preferably has a nitrogen-containing aromatic ring structure in which nitrogen is contained in the aromatic ring. When the active particle-containing catalyst contains a component derived from a nitrogen-containing compound, it can be obtained by heat-treating a mixture of a metal precursor, a support such as porous carbon, silica, or aluminum oxide, and the nitrogen-containing compound, as described below. Therefore, the component derived from the nitrogen-containing compound is a component obtained by heat-treating the nitrogen-containing compound. In the present invention, by lowering the heat treatment temperature as described below, the nitrogen-containing aromatic ring structure formed by the nitrogen-containing compound remains in the catalyst. The components derived from the nitrogen-containing compound in the active particle-containing catalyst preferably have a nitrogen-containing aromatic ring structure. Details of the nitrogen-containing compound and the nitrogen-containing aromatic ring structure are as described in the first catalyst.

[0086] <<Method for Producing an Active Particle-Containing Catalyst>> Next, a method for producing an active particle-containing catalyst will be described. The above-mentioned active particle-containing catalyst may be obtained by heat-treating at least a metal precursor, but preferably by mixing a metal precursor with a support such as porous carbon, silica, or aluminum oxide, and heat-treating the mixture containing the metal precursor and the support such as porous carbon. The metal precursor, or a mixture containing a metal precursor and a support such as porous carbon, which serves as the raw material for the active particle-containing catalyst, is hereinafter also referred to as the second catalyst raw material. The heat treatment is typically calcination. Furthermore, when the active particle-containing catalyst contains a component derived from a nitrogen-containing compound, the nitrogen-containing compound may be further mixed with a support such as a metal precursor and porous carbon, and the second catalyst raw material may contain a metal precursor, a support such as porous carbon, and a nitrogen-containing compound.

[0087] The metal precursor is a compound that becomes the above-mentioned active particles by heat treatment. Therefore, the metal precursor may be a precursor containing a metal element selected from the above-mentioned Group 8 to Group 11 elements, and suitable metal elements are also as described above. The metal element used in the metal precursor may be used alone or in combination of two or more. When two or more types are used in combination, the combination of metal elements is as described above. When two or more types of metal precursors are used in combination, the active particle-containing catalyst may be obtained by mixing two or more types of metal precursors, or by mixing two or more types of metal precursors with a support such as porous carbon, silica, or aluminum oxide, and then heat treating the mixture; therefore, two or more types of metal precursors may be contained in the second catalyst raw material.

[0088] The metal precursor preferably contains a metal ion. The metal precursor may be used, for example, in the form of a metal salt. Examples of metal salts include metal nitrates, metal sulfates, metal chlorides, metal bromides, metal iodides, and metal acetates. Among these, metal chlorides and metal nitrates are preferred, and metal nitrates are more preferred from the viewpoint of forming suitable active particles. Specific examples of the metal nitrates and metal chlorides used in the metal precursor are the same as the metal salts used as the second catalyst described below, and therefore, further explanation is omitted. The metal salt may also be a hydrate. The porous carbon and nitrogen-containing compound used as raw materials in this production method are as described for the first catalyst above.

[0089] The content of the metal derived from the metal precursor in the second catalyst raw material is preferably 0.01% by mass or more and 70% by mass or less, and more preferably 0.12% by mass or more and 50% by mass or less, based on the total amount of the second catalyst raw material. By keeping the content within this range, the metal is contained in the catalyst without agglomerating, and an appropriate amount of catalytic active sites is formed. This makes it easier to increase the selectivity when synthesizing carbonyl compounds, and also increases the reaction efficiency.

[0090] The content of the support in the second catalyst raw material is not particularly limited, but is, for example, 10% by mass to 99.99% by mass, preferably 20% by mass to 99.9% by mass, and more preferably 30% by mass to 80% by mass. By setting the content of the support within the above range, it is possible to appropriately support the active particles and components derived from the nitrogen-containing compound while maintaining good catalytic activity. When a nitrogen-containing compound is used, the amount of the nitrogen-containing compound in the second catalyst raw material is preferably adjusted so that the molar ratio of the nitrogen-containing aromatic ring of the nitrogen-containing compound to the metal element derived from the metal precursor (nitrogen-containing aromatic ring / metal element) is 0.1 to 30, more preferably 1 to 20.

[0091] The temperature at which the second catalyst raw material is heat-treated is preferably 150°C or higher and 800°C or lower, more preferably 180°C or higher and 550°C or lower, and even more preferably 200°C or higher and 380°C or lower. The heat-treatment time is not particularly limited, but is, for example, 0.25 hours or higher and 10 hours or lower, preferably 0.5 hours or higher and 8 hours or lower, and more preferably 1 hour or higher and 5 hours or lower. The heat treatment may be carried out in an inert gas atmosphere such as argon or nitrogen gas, or in a reducing atmosphere such as hydrogen.

[0092] The second catalyst raw material to be heat-treated is preferably in powder, particulate, or pellet form. If the second catalyst raw material is powder or particulate, the catalyst obtained by heat treatment can also be powder or particulate. Furthermore, the second catalyst raw material to be heat-treated more preferably consists of a metal precursor and a support such as porous carbon, or a metal precursor, a support such as porous carbon, and a nitrogen-containing compound. The second catalyst raw material can be obtained, for example, by preparing a diluted solution of the second catalyst raw material and drying the diluted solution. In the diluted solution of the second catalyst raw material, each component (the metal precursor and a support such as porous carbon, or the metal precursor, the nitrogen-containing compound, and a support such as porous carbon) is preferably dispersed or dissolved in a dilution solvent. By dispersing or dissolving each component in the dilution solvent, a second catalyst raw material in which each component is homogeneously mixed can be obtained. The dilution solvent used to dilute the second catalyst raw material can be water or an organic solvent, preferably water.

[0093] Metal salts used as the second catalyst include metal nitrates, metal sulfates, metal chlorides, metal bromides, metal iodides, and metal acetates. Among these, metal chlorides and metal nitrates are preferred, and metal chlorides are more preferred. Specifically, metal nitrates include cobalt nitrate (Co(NO)), nickel nitrate (Ni(NO)), copper nitrate (Cu(NO)), rhodium nitrate (Rh(NO)), and the like. ３ ), palladium nitrate (Pd(NO3) ２ ), silver nitrate (AgNO ３ ), iridium nitrate (Ir(NO3) ４), platinum nitrate (Pt(NO3) ４ ), gold nitrate (AuNO3), ruthenium nitrate (Ru(NO3) ３ ), iron nitrate (Fe(NO ３ ) ３ ), manganese nitrate (Mn(NO ３ ) ２ ), zinc nitrate (Zn(NO ３ ) ２ ), chromium nitrate (Cr(NO ３ ) 　３ ), tin nitrate (Sn(NO ３ ) ４ ) and the like. Specific examples of metal chlorides include PdCl ２ , RuCl ３ , IrCl ３ , PtCl ４ , AuCl ３ Also, HAuCl ４ Among these, PdCl ２ , HAuCl ４ , Ir(III)Cl ３ is preferred.

[0094] The metal salt used as the second catalyst may be supported on a support. The support is as described above, and is preferably porous carbon, silica, or aluminum oxide. The metal salt may be supported on the support by, for example, dispersing the support and the metal salt in a solvent and drying the resulting dispersion. The second catalyst may be used alone or in combination of two or more types.

[0095] <Second embodiment> Next, a second embodiment of the present invention will be described. Fig. 2 shows a carbon dioxide reduction device 10B according to a second embodiment of the present invention. The carbon dioxide reduction device 10B according to this embodiment differs from the first embodiment in that the first reaction section 31 and the second electrolysis section 22 are further connected via a second ion exchange membrane 25. The differences between the first embodiment and the second embodiment will be described below.

[0096] In this embodiment, the reaction section 31 and the second electrolysis section 22 are separated by a second ion exchange membrane 25, and therefore, in this embodiment, the electrochemical cell is separated into three regions, the first electrolysis section 21, the second electrolysis section 22, and the first reaction section 31, by two ion exchange membranes.

[0097] Details of the ion exchange membranes that can be used for the second ion exchange membrane 25 are the same as those described for the first ion exchange membrane 15. However, it is preferable to use the same type of ion exchange membrane as the first ion exchange membrane 15 for the second ion exchange membrane 25. Therefore, if the first ion exchange membrane 15 is a cation exchange membrane, it is preferable that the second ion exchange membrane 25 is also a cation exchange membrane. Furthermore, if the second ion exchange membrane 15 is an anion exchange membrane, it is preferable that the second ion exchange membrane 25 is also an anion exchange membrane.

[0098] In this embodiment, as in the first embodiment, a reduction reaction occurs at the first electrode 11 in which carbon dioxide is reduced to a first reductant such as carbon monoxide, and at the second electrode 12, the redox material is oxidized from the reductant A to an oxide B, and the first reductant and the oxide B are supplied to the reaction section 31 via the first connecting path 41 and the second connecting path 42, respectively. Then, in the reaction section 31, the halogen (X ２ ) to a reduced product A (e.g., halogen ion X － ), while the first reduction product such as carbon monoxide reacts with a reaction substrate such as an alcohol compound to produce a target product such as a carbonyl compound.

[0099] 2, a purification device, a supply mechanism, and the like may be provided, and similarly to the first embodiment, the by-products produced in the reaction section 31 may be purified as necessary and then supplied to the second electrolysis section 22. The purification device may be a distillation device as described above, but may also be a solid-liquid separation device in cases where a solid substance such as a metal halide salt is produced as a by-product, as will be described later.

[0100] Furthermore, in the second embodiment, anions or cations move between the second electrolysis section 22 and the reaction section 31 via the second ion exchange membrane 25, and for example, the reaction in the reaction section 31 can proceed more efficiently. More specifically, when the first and second ion exchange membranes 15 and 25 are cation exchange membranes, protons (H ＋ ) moves through the second ion exchange membrane 25 and the first ion exchange membrane 15 to the second electrolysis section 22 and further to the first electrolysis section 21. Therefore, the protons (H ＋ ) concentration decreases, and the reaction in the reaction section 31 easily proceeds. Furthermore, the first electrolysis section 21 is supplied with protons (H ＋ ) is easily supplied, and reduction in the first electrolysis section 21 is easily promoted.

[0101] In addition, for example, when the first and second ion exchange membranes 15 and 25 are anion exchange membranes, hydroxide ions (OH － ) moves through the first ion exchange membrane 15 and the second ion exchange membrane 25 to the second electrolysis section 22 and further to the reaction section 31. Therefore, protons (H ＋ ) is neutralized, and protons (H ＋ ) concentration decreases, and the reaction in the reaction section 31 easily proceeds. － ), moves to another reaction system (the second electrolysis section 22 or the reaction section 31), which facilitates the progress of the reduction reaction in the first electrolysis section 21.

[0102] Furthermore, when the second ion exchange membrane 25 is a cation exchange membrane and the redox material contained in the second electrolysis unit 22 is a metal halide salt, metal ions (preferably alkali metal ions such as sodium and lithium) may move from the second electrolysis unit 22 to the reaction unit 31 and react with hydroxy ions in the reaction unit 31 to produce a metal hydroxide. That is, in this embodiment, a metal hydroxide may be produced as a by-product in the reaction unit 31. Furthermore, a metal halide salt may be produced in reaction with halogen ions. Therefore, in this embodiment, a metal halide salt may be produced as a by-product in the reaction unit 31.

[0103] Furthermore, when the second ion exchange membrane 25 is an anion exchange membrane, the halogen ions generated in the first reactant 31 may migrate to the second electrolysis section 22 via the second ion exchange membrane 25 (anion exchange membrane). Therefore, it is not necessary to return the halogen ions that have once migrated to the reaction section 31 to the second electrolysis section 22 via the supply mechanism, which further simplifies the device.

[0104] <Third Embodiment> Next, a third embodiment of the present invention will be described. Fig. 3 shows a carbon dioxide reduction device 10C according to a third embodiment of the present invention. In the third embodiment, Z represents an alkali metal salt. The following describes the third embodiment, focusing on the differences from the first embodiment.

[0105] In the carbon dioxide reduction device 10C according to the third embodiment, the first electrolysis unit 21A having the first electrode 11 is filled with an electrolytic solution. Therefore, carbon dioxide introduced through the inlet 23 contacts the first electrode 11 while contained in the electrolytic solution and is reduced to a first reductant such as carbon monoxide at the first electrode 11. The electrolytic solution in the first electrolysis unit 21A is an aqueous electrolytic solution. The aqueous electrolytic solution may consist of water alone, or may contain water to which a known electrolyte salt has been added. Examples of the electrolyte salt include metal hydroxides, metal halides, metal perchlorates, metal sulfates, and metal carbonates. In this embodiment, the first ion exchange membrane 15 is preferably a cation exchange membrane.

[0106] As in the first embodiment, the second electrolysis unit 22 is preferably filled with an aqueous electrolyte containing a redox material and water, and the redox material may contain a metal halide salt, preferably an alkali metal halide salt. In the second electrolysis unit 22, halogen is generated as the oxide B, and metal ions, such as alkali metal ions, derived from the redox material migrate to the first electrolysis unit 21A through the first ion exchange membrane 15.

[0107] Therefore, in the first electrolysis unit 21A, a first reduction product such as carbon monoxide is generated, and metal ions transferred from the second electrolysis unit 22 react with carbon dioxide to generate a metal carbonate. The electrolytic solution filled in the first electrolysis unit 21A is preferably basic, which allows hydroxide ions generated by the reduction reaction of carbon dioxide to carbon monoxide to react with metal ions to produce a metal hydroxide, and the metal hydroxide and carbon dioxide to produce a metal carbonate. The type of metal carbonate generated in the first electrolysis unit 21A is determined depending on the type of oxidation-reduction material introduced into the second electrolysis unit 22, and is preferably lithium carbonate, potassium carbonate, or sodium carbonate. Of these, lithium carbonate and sodium carbonate are more preferred, and sodium carbonate is even more preferred.

[0108] The metal carbonate produced in the first electrolysis unit 21A may be appropriately removed from the first electrolysis unit 21A. The metal carbonate removed from the first electrolysis unit 21A may be supplied to the reaction unit 31 by a known supply mechanism. Preferably, the metal carbonate is removed from the first electrolysis unit 21A together with the electrolytic solution in the first electrolysis unit 21 and purified in a purification device 33 such as a solid-liquid separator. The purified metal carbonate is then supplied to the reaction unit 31 via a supply path 37 (supply mechanism). By supplying the metal carbonate produced in the first electrolysis unit 21A to the reaction unit 31 as described above, the metal carbonate can be contained in the reaction unit 31 without the need to prepare a separate raw material, as will be described later.

[0109] In this embodiment, the first reduction product such as carbon monoxide produced in the first electrolysis section 21A flows as a gas into the reaction section 31 through the first connecting passage 41, and the halogen (oxide B) produced in the second electrolysis section 22 flows as a gas into the reaction section 31 through the second connecting passage 42.

[0110] As in the first embodiment, the reaction section 31 contains a second catalyst and typically also contains a reaction substrate. The reaction section 31 may be filled with a reaction substrate (reaction solution) containing the second catalyst. The reaction solution may also be diluted with a reaction solvent. In this embodiment, the reaction solution in the reaction section 31 may further contain a metal carbonate. The concentration of the metal carbonate in the reaction solution is not particularly limited, but is, for example, 0.001 to 1 M or 0.005 to 0.5 M. Examples of metal carbonates include lithium carbonate, potassium carbonate, sodium carbonate, and cesium carbonate. Of these, lithium carbonate, potassium carbonate, and sodium carbonate are preferred, and sodium carbonate is more preferred. The metal carbonate produced in the first electrolysis section 21A as described above may be supplied to the reaction section 31 via the supply mechanism 37. Alternatively, a metal carbonate other than that produced in the first electrolysis section 21A may be introduced into the reaction section 31 through an inlet (not shown) in the reaction section 31.

[0111] In this embodiment, as shown in FIG. 3, in the reaction section 31, halogen (X ２ ) to a reduced product A (e.g., halogen ions X － ), the first reduction product such as carbon monoxide reacts with the reaction substrate such as an alcohol-based compound to produce a target product such as a carbonyl compound. In this embodiment, the reaction section 31 contains a metal carbonate, so that protons (H ＋ ) is neutralized, and protons (H ＋ ) decreases, and the reaction in the reaction section 31 proceeds more easily.

[0112] In addition, in the reaction section 31 of this embodiment, salts (e.g., metal halide salts, metal bicarbonate salts, etc.) are generated as by-products by neutralization. The salts generated as by-products may be removed from the reaction section 31. The by-products removed from the reaction section 31 may be supplied to the second electrolysis section 22 by a known supply mechanism. Preferably, the salts generated as by-products are removed from the reaction section 31 together with the target product obtained in the reaction section 31 and unreacted reaction substrates, and purified in a purification device 32A such as a solid-liquid separator. Of the purified by-products, those usable as redox materials (metal halide salts) are preferably supplied to the second electrolysis section 22 via the supply path 36 (supply mechanism). As described above, by supplying the by-products to the second electrolysis section 22, the redox materials are circulated between the second electrolysis section 22 and the reaction section 31, thereby reducing raw material loss. Furthermore, in the first reaction section 31, by-products derived from halogens (oxidation-reduction substances) can be removed in the form of salts, which improves the workability when separating and removing them.

[0113] <Fourth embodiment> Next, a fourth embodiment of the present invention will be described. Fig. 4 shows a carbon dioxide reduction device 10D according to a fourth embodiment of the present invention. Below, the fourth embodiment will be described, focusing on the differences from the first embodiment. In the first embodiment, the reaction section and the second electrolysis section were configured using different reaction systems, but in this embodiment, the reaction section is omitted, and the second electrolysis section also functions as a reaction section. In addition, the second connecting path connecting the reaction section 31 and the second electrolysis section 22 is also omitted. In the description of this embodiment, the second electrolysis section will be described as an "electrolysis reaction section."

[0114] That is, the carbon dioxide reduction device 10D according to the fourth embodiment includes a first electrode 11, a second electrode 12, a first ion exchange membrane 15, and a first electrolysis unit 21 having the first electrode 11, which are the same as those in the first embodiment. Furthermore, an electrolysis reaction unit (second electrolysis unit) 22A has a second electrode 12, which is an anode, and constitutes an anode chamber. The electrolysis reaction unit 22A is filled with an electrolytic solution. Furthermore, the first electrolysis unit 21 and the electrolysis reaction unit 22A are connected via a first connecting path 41A. The configuration of the first connecting path 41A is as described in the first embodiment.

[0115] The electrolytic reaction section 22A contains a second catalyst and typically also contains a reaction substrate. In the electrolytic reaction section 22A, the reaction substrate may contain the second catalyst, and the reaction substrate containing the second catalyst may be filled into the electrolytic reaction section 22A. The reaction substrate filled into the electrolytic reaction section 22A may also be diluted with the reaction solvent described above. Therefore, the second catalyst may be contained in the reaction substrate or a mixture of the reaction substrate and the reaction solvent. The second catalyst may be dispersed or dissolved in the reaction substrate or the mixture. The reaction substrate containing the second catalyst or a mixture of the reaction substrate and the reaction solvent may constitute the electrolyte filled into the electrolytic reaction section 22A. The electrolyte may be in contact with the second electrode 12 and may fill the entire interior of the electrolytic reaction section 22A, or may not fill the entire interior and may leave some space.

[0116] The electrolytic solution filled in the electrolytic reaction section 22A may further contain a redox substance. The redox substance may be dissolved or dispersed in the electrolytic solution. The concentration of the redox substance in the electrolytic solution filled in the second electrolytic section 22A is not particularly limited, but is, for example, 0.001 to 5.0 M, preferably 0.01 to 1.0 M, and more preferably 0.05 to 0.5 M. The content of the second catalyst in the electrolytic solution filled in the second electrolytic section 22A is also not particularly limited, but is, for example, 0.001 to 50 g, preferably 0.005 to 25 g, and more preferably 0.01 to 10 g per 1 L of the electrolytic solution.

[0117] In this embodiment, as in the first embodiment, a reduction reaction occurs at the first electrode 11 in which carbon dioxide is reduced to a first reductant such as carbon monoxide, and the first reductant flows out to the electrolysis reaction section 22A via the first connecting path 41. Furthermore, at the second electrode 12, the redox material is oxidized from the reductant A to an oxide B, and the oxidized oxide B is supplied as is to the electrolysis reaction section 22A. Then, in the electrolysis reaction section 22A, a halogen (X ２ ) to a reduced product A (e.g., halogen ions X － ), while the first reduction product such as carbon monoxide reacts with a reaction substrate such as an alcohol compound to produce a target product such as a carbonyl compound.

[0118] As described above, in this embodiment, the first reduction product is generated at the first electrode 11, the oxide B is generated at the second electrode 12, and the first reduction product and the oxide B are used to generate an organic substance in the electrolysis reaction unit 22A using the second catalyst. This allows the reaction of the redox substances to be prioritized in the electrolysis unit, thereby efficiently producing the target product while suppressing the oxidation of reaction substrates such as alcohol-based compounds. Furthermore, the first electrolysis unit 21 and the electrolysis reaction unit 22A can be configured using a general electrochemical cell, making it possible to obtain the target product from carbon dioxide without complicating the device structure. Furthermore, water by-produced in the first electrolysis unit 21 is prevented from entering the electrolysis reaction unit 22A and inhibiting the reaction, thereby further improving the reaction efficiency of the target product.

[0119] Fifth Embodiment Next, a fifth embodiment of the present invention will be described. Fig. 5 shows a carbon dioxide reduction device 10E according to a fifth embodiment of the present invention. The fifth embodiment differs from the first embodiment in that the first reduced product contains carbon monoxide and a separation mechanism 45 that separates carbon monoxide and carbon dioxide is provided on the first connection path 41A. The fifth embodiment will be described below, focusing on the differences from the first embodiment.

[0120] In this embodiment, it is preferable to use a carbon dioxide separator as the separation mechanism 45. A carbon dioxide separator is a device that separates carbon dioxide and carbon monoxide by absorbing, adsorbing, or selectively permeating carbon dioxide. Examples of carbon dioxide separators include separators that use an amine absorption method, separators that use a physical adsorption method, and separators that use a membrane separation method. Examples of separators that use an amine absorption method include separators that use an absorption liquid containing an amine compound or an absorbent in which an amine compound is coated on the surface of a porous material. Examples of separators that use a physical adsorption method include adsorbents that physically adsorb carbon dioxide using a porous material such as zeolite. Examples of separators that use a membrane separation method include permeable membranes that are also known as molecular gate membranes and that selectively allow carbon dioxide to pass through.

[0121] In this embodiment, by separating and removing carbon dioxide using the separation mechanism 45, the carbon dioxide concentration of the gas effluent from the first electrolysis unit 21 can be reduced while the carbon monoxide concentration can be increased by passing through the separation mechanism 45. Therefore, the carbon monoxide concentration in the reaction solution in the reaction unit 31 can be increased, and the production efficiency of the target product in the reaction unit 31 can be further increased.

[0122] Note that, although Figure 5 shows an aspect in which the separation mechanism 45 is applied to the carbon dioxide reduction device 10 according to the first embodiment, the separation mechanism 45 can be applied to any of the carbon dioxide reduction devices according to the second to fourth embodiments.

[0123] <Sixth embodiment> Next, a sixth embodiment of the present invention will be described. Fig. 6 shows a carbon dioxide reduction device 10F according to the sixth embodiment of the present invention. In the first embodiment, a first ion exchange membrane is provided between the first electrode and the second electrode, but in this embodiment, the first ion exchange membrane is omitted. In this case, the electrolysis unit formed by the electrochemical cell is not partitioned by the first ion exchange membrane, but consists of a single electrolysis unit (first electrolysis unit 21B). That is, while the first embodiment was a two-chamber type, this embodiment is a single-chamber type. Furthermore, the second connecting path is omitted, and the connecting path consists of a first connecting path 41B that connects the first electrolysis unit 21B and the reaction unit 31.

[0124] In this embodiment, the first electrolysis unit 21B is filled with an electrolytic solution. The electrolytic solution may be an aqueous electrolytic solution containing a redox substance in water. The redox substance is as described above, and the concentration of the redox substance in the electrolytic solution is also as described for the second electrolysis unit 22 of the first embodiment. The first electrode 11B and the second electrode 12B are preferably disposed inside the first electrolysis unit 21B so as to be in contact with the electrolytic solution.

[0125] In this embodiment, carbon dioxide is introduced into the first electrolysis unit 21B via the inlet 23B, and the carbon dioxide is reduced at the first electrode 11B to produce a first reduction product such as carbon monoxide. Meanwhile, at the second electrode 12B, the reduction product A of the redox substance is oxidized to an oxide B, thereby producing an oxide B such as a halogen.

[0126] The first reduction product and oxide B obtained in the first electrolysis unit 21B are both discharged as gases through the first connecting passage 41B to the reaction unit 31. In this embodiment, as in the first embodiment, in the reaction unit 31, halogen (X ２ ) to a reduced product A (e.g., halogen ion X － ), while the first reduction product such as carbon monoxide reacts with a reaction substrate such as an alcohol compound to produce a target product such as a carbonyl compound.

[0127] As described above, in this embodiment, too, a first reduction product is generated at the first electrode 11B, an oxide B is generated at the second electrode 12B, and an organic substance is generated in the reaction unit 31 using the first reduction product and the oxide B in the presence of a second catalyst. This allows the reaction of the redox substances to be prioritized in the electrolysis unit, thereby efficiently producing the target product while suppressing the oxidation of reaction substrates such as alcohol-based compounds. Furthermore, since the first electrolysis unit 21B can be configured using a general electrochemical cell, the target product can be obtained from carbon dioxide without complicating the device structure. Furthermore, since an aqueous electrolyte can be used in the electrolysis unit 21B, it is not necessary to use reaction substrates such as alcohol-based compounds in the electrochemical cell that constitutes the electrolysis unit 21B. Therefore, there is no need for the electrochemical cell to be alcohol-resistant, and it is easy to repurpose existing electrolysis equipment.

[0128] In this embodiment, halogens such as chlorine (X ２ Both chlorine and carbon monoxide are supplied to the reaction section 31 through the first connecting passage 41B. However, in order to prevent harmful substances such as phosgene from being generated as a result of a reaction between chlorine and carbon monoxide, it is preferable that the first connecting passage 41B does not use a carbon material or the like. In this embodiment, the first ion exchange membrane is omitted from the carbon dioxide reduction device 10 according to the first embodiment. However, the second, third, and fifth embodiments may also similarly omit the first ion exchange membrane.

[0129] <Seventh Embodiment> Next, a seventh embodiment of the present invention will be described. Differences between the seventh embodiment and the second embodiment will be described with reference to FIG. 7 . In the carbon dioxide reduction device 10B according to the second embodiment described above, the first reaction unit 31 and the second electrolysis unit 22 are connected via the second ion exchange membrane 25. However, in the carbon dioxide reduction device 10G according to this embodiment, the first reaction unit 31 is connected to the first electrolysis unit 21 via the second ion exchange membrane 25, which is different from the second embodiment. Furthermore, in the seventh embodiment, the first electrolysis unit 21 having the first electrode 11 is filled with an electrolyte. The electrolyte is preferably an aqueous electrolyte. Details of the aqueous electrolyte used in the first electrolysis unit 21 are as described in the third embodiment above. As described in the second embodiment, the second electrolysis unit 22 is filled with an electrolyte, and the electrolyte is preferably an aqueous electrolyte.

[0130] Furthermore, in this embodiment, the first electrolysis unit 21 and the second electrolysis unit 22 are each provided with a first supply port 51A and a second supply port 52A for supplying the electrolytic solution, and a first outlet 51B and a second outlet 52B for discharging the electrolytic solution from the first electrolysis unit 21 and the second electrolysis unit 22, respectively. The electrolytic solution is supplied to the first electrolysis unit 21 through the first supply port 51A and discharged through the first outlet 51B. Similarly, the electrolytic solution is supplied to the second electrolysis unit 22 through the second supply port 52A and discharged through the second outlet 52B. The supply and discharge of the electrolytic solution may be appropriately repeated or may be performed continuously. As described above, the supply and discharge of the electrolytic solution in each of the electrolysis units 21 and 22 prevents the concentrations of carbon dioxide and redox substances from decreasing due to reactions and can be maintained constant, making it possible to produce the first reduced product and oxide B with high reaction efficiency. Typically, a portion of the electrolyte solution filled in each electrolysis unit may be discharged, and new electrolyte solution may be supplied to each electrolysis unit according to the amount of the discharged electrolyte solution. Furthermore, the electrolyte solution may be repeatedly discharged and supplied so that the discharged solution is circulated by being resupplied. In this case, the electrolyte solutions discharged from the first and second electrolysis units may be returned to the first and second electrolysis units after impurities have been removed and electrolytes or redox substances have been added.

[0131] In this embodiment, as in the second embodiment, a reduction reaction occurs at the first electrode 11 in which carbon dioxide is reduced to a first reductant such as carbon monoxide, and at the second electrode 12, the redox material is oxidized from the reductant A to an oxide B, and the first reductant and the oxide B are supplied to the reaction section 31 via the first connecting path 41 and the second connecting path 42, respectively. Then, in the reaction section 31, the halogen (X ２ ) to a reduced product A (e.g., halogen ions X － ), while the first reduction product such as carbon monoxide reacts with a reaction substrate such as an alcohol compound to produce a target product such as a carbonyl compound.

[0132] Anions or cations move between the first electrolysis section 21 and the reaction section 31 through the second ion exchange membrane 25. Furthermore, cations (Y ＋ ) moves, and for example, the reaction in the reaction section 31 can proceed more efficiently.

[0133] More specifically, when the first and second ion exchange membranes 15 and 25 are cation exchange membranes, as shown in FIG. 7, the protons (H ＋ ) is supplied to the first electrolysis unit 21 through the second ion exchange membrane 25. The cation Y remaining in the second electrolysis unit 22 when halogen is produced from the metal halide salt is supplied to the first electrolysis unit 21 through the second ion exchange membrane 25. ＋ is supplied to the first electrolysis unit 21 via the first ion exchange membrane 15. Alternatively, the second ion exchange membrane 25 may be an anion exchange membrane, and the first ion exchange membrane may be a cation exchange membrane. In this case, hydroxide ions (OH － ) moves to the reaction section 31 through the second ion exchange membrane 25. Therefore, for example, protons (H ＋ ) is neutralized, and protons (H ＋ ) is reduced, facilitating the reaction in the reaction section 31. By adopting this embodiment, hydrogen halide, which is a by-product generated in the first reaction section 31, can be efficiently removed.

[0134] Eighth Embodiment Next, an eighth embodiment of the present invention will be described. In the second and seventh embodiments, the reaction unit 31 was connected to only one of the first electrolysis unit 21 and the second electrolysis unit 22 via the ion exchange membrane 25. However, in the eighth embodiment, the reaction unit 31 is connected to both the first electrolysis unit 21 and the second electrolysis unit 22 via the ion exchange membrane. Hereinafter, with reference to FIG. 8 , differences between the eighth embodiment and the seventh embodiment will be described, and portions that will not be described are the same as those in the seventh embodiment.

[0135] In the eighth embodiment, a third ion exchange membrane 35 is further provided in addition to the first and second ion exchange membranes 15, 25. The first reaction section 31 is connected to the first electrolysis section 21 via the second ion exchange membrane 25, and is connected to the second electrolysis section 22 via the third ion exchange membrane 35. The ion exchange membranes constituting the second ion exchange membrane 25 and the third ion exchange membrane 35 are as described above, but it is preferable that the second ion exchange membrane 25 is a cation exchange membrane and the third ion exchange membrane 35 is an anion exchange membrane. However, the first to third ion exchange membranes 15, 25, 35 are arranged so as not to be in contact with each other.

[0136] In this embodiment, as in the seventh embodiment, a reduction reaction occurs at the first electrode 11 in which carbon dioxide is reduced to a first reductant such as carbon monoxide, and at the second electrode 12, the redox material is oxidized from the reductant A to an oxide B. The first reductant and the oxide B are supplied to the reaction section 31 via the first connecting path 41 and the second connecting path 42, respectively. Then, in the reaction section 31, the halogen (X ２ ) to a reduced product A (e.g., halogen ion X － ), while the first reduction product such as carbon monoxide reacts with a reaction substrate such as an alcohol compound to produce a target product such as a carbonyl compound.

[0137] In addition, cations move between the first electrolysis section 21 and the reaction section 31 through the second ion exchange membrane 25. Therefore, protons (H ＋ ) is supplied to the first electrolysis unit 21 through the second ion exchange membrane 25. In addition, since the first ion exchange membrane 15 is a cation exchange membrane, the cation Y ＋is supplied to the first electrolysis unit 21 through the first ion exchange membrane 15. Furthermore, anions also move between the second electrolysis unit 22 and the reaction unit 31 through the third ion exchange membrane 35. Therefore, halogen ions, which are the reduction product A of the redox substance, are supplied to the second electrolysis unit 22 through the third ion exchange membrane 35. With the above configuration, the reduction reaction in the first electrolysis unit 21 and the chemical reaction in the reaction unit 31 can be carried out efficiently. Furthermore, the redox substance supplied as oxide A to the reaction unit 31 through the second connecting path 42 can be returned as reduction product B to the second electrolysis unit 22 through the third ion exchange membrane 35, so that the process of producing carbonyl compounds can be carried out over a long period of time without the need to add new redox substance to the second electrolysis unit 22.

[0138] <Other Embodiments> In the first, second, and fourth embodiments described above, the first electrolysis unit 21 is not filled with an electrolyte, and a reduction reaction is performed on gaseous carbon dioxide by a gas-phase reaction. However, as in the third embodiment, in the first, second, and fourth embodiments, the first electrolysis unit 21 may be filled with an aqueous electrolyte, and carbon dioxide contained in the electrolyte may contact the first electrode 11 and be reduced to the first reduced product. For example, when the ion exchange membrane 15 is a cation exchange membrane, not only protons but also alkali metal cations move from the second electrolysis unit 22 to the first electrolysis unit 21, which may cause alkali metal carbonate salts to precipitate on the surface of the first electrode 11. However, when the first electrolysis unit 21 is filled with an electrolyte, the alkali metal carbonate salts precipitated on the surface of the first electrode 11 are easily removed, facilitating long-term operation. In this case, it is preferable that the electrolytes in the first and second electrolysis units 21 and 22 are both aqueous electrolytes in terms of the solubility of alkali metal carbonate salts. Furthermore, in each of the above embodiments, the carbon monoxide produced in the first electrolysis section 11 and the oxide B produced in the second electrolysis section 21 are supplied to the reaction section 31 in a gaseous state, but they may also be supplied in liquid form together with the electrolytic solution, etc.

[0139] An electrochemical system according to a second aspect of the present invention and a method for producing a carbonyl compound using the electrochemical system will be described below with reference to the accompanying drawings. In the following description of the second aspect, elements having the same configurations are designated by the same reference numerals. The electrochemical system according to the second aspect is also an electrochemical reaction device, and typically also a carbon dioxide reduction device.

[0140] Ninth Embodiment An electrochemical system 70 according to a ninth embodiment of the present invention is a system (also referred to as an electrochemical reaction device) for electrochemically synthesizing a carbonyl compound. In the electrochemical system 70, the carbonyl compound produced is an organic carbonate, an organic oxalate, or both. The electrochemical system 70 includes a redox species (oxidation-reduction substance) as described below, and a carbonyl compound is synthesized using the redox species (oxidation-reduction substance). As shown in FIG. 9 , the electrochemical system 70 includes an electrochemical cell 60 and a reaction chamber 71 (first reaction section). The electrochemical cell 60 includes an anode (second electrode) 61 and a cathode (first electrode) 62. The anode 61 and the cathode 62 are disposed inside the electrochemical cell 60. The electrochemical cell 60 includes a separator 75 disposed between the anode 61 and the cathode 62. The separator 75 divides the interior of the electrochemical cell 60 into a region on the cathode 62 side (cathode chamber 60Y or first electrolysis section) and a region on the anode 61 side (anode chamber 60X or second electrolysis section). The cathode chamber 60Y is the region where a reduction reaction occurs, and the anode chamber 60X is the region where an oxidation reaction occurs. In this embodiment, the reaction chamber 71 (first reaction section) contains a second catalyst 64 that synthesizes a carbonyl compound. The second catalyst 64 is filled inside the reaction chamber 71. The cathode chamber 60Y also contains a first catalyst 65 that reduces carbon dioxide to carbon monoxide. The first catalyst 65 may be contained in the cathode 62.

[0141] The electrochemical cell 60 is provided with first and second supply ports 66X, 66Y as supply ports of the electrochemical cell 60 and first and second outlet ports 67X, 67Y as outlet ports. The first supply port 66X and the first outlet port 67X are provided in the anode chamber 60X. The first outlet port 67X is connected to a supply port 71A of the reaction chamber 71 via a connection path 68A, and the first supply port 66X is connected to an outlet 71B of the reaction chamber 71 via a connection path 68B. The connection path and a supply path 74 described below may be formed of, but are not limited to, piping or the like. As a result, an oxidant (oxide B) of the redox species is generated in the anode chamber 60X as described below, and the anode chamber 60X and the reaction chamber 71 are connected so that the oxidant (redox species) is supplied from the anode chamber 60X to the reaction chamber 71. In addition, in the reaction chamber 71, the redox species are reduced to form reduced species (reduced product A), and the anode chamber 60X and the reaction chamber 71 are connected so that the reduced species (redox species) are supplied from the reaction chamber 71 to the anode chamber 60X.

[0142] The second supply port 66Y and the second exhaust port 67Y are provided in the cathode chamber 60Y. The second supply port 66Y is connected to a carbon dioxide supply source (not shown) via a supply path 74, and supplies carbon dioxide to the cathode chamber 60Y. Carbon dioxide may be supplied to the cathode chamber 60Y alone, or may be supplied together with other gases such as an inert gas such as argon or nitrogen, or oxygen gas. Details of the carbon dioxide supply source are as described above.

[0143] The second outlet 67Y allows carbon monoxide, which has been reduced from carbon dioxide in the cathode chamber 60Y, to be discharged from the cathode chamber 60Y and supplied to the reaction chamber 71 through the supply port 71A via the connection path 68A along the flow of convection F. This connects the cathode chamber 60Y and the reaction chamber 71 so that carbon monoxide is supplied from the cathode chamber 60Y to the reaction chamber 71. In this embodiment, carbon dioxide is reduced to carbon monoxide by a gas-phase reaction in the cathode chamber 60Y. That is, gaseous carbon dioxide comes into contact with the first catalyst 65 on the cathode 62, generating carbon monoxide. Therefore, carbon monoxide is supplied as a gas from the cathode chamber 60Y to the reaction chamber 71. Note that the gas supplied from the cathode chamber 60Y to the reaction chamber 71 usually also contains unreacted carbon dioxide.

[0144] Although the first and second exhaust ports 67X and 67Y are connected to the supply port 71A of the reaction chamber 71 via the same connection path 68A, they may be connected via separate connection paths (not shown). Also, the reaction chamber 71 may be provided with two supply ports, and the two supply ports may be connected to the exhaust ports 67X and 67Y via separate connection paths.

[0145] The electrochemical system 70 includes an electrolyte 63. The electrolyte 63 contains a reaction substrate and redox species, and is filled inside the anode chamber 60X and the reaction chamber 71. The redox species usually serves as an electrolyte. The redox species undergo an oxidation reaction in which they are oxidized at the anode 61. Details of the redox species will be described later. In the reaction chamber 71, the electrolyte 63 serves as a reaction liquid for producing a carbonyl compound.

[0146] In the electrochemical system 70, the electrolytic solution 63 flows from the first supply port 66X to the first discharge port 67X in the anode chamber 60X, and the electrolytic solution 63 discharged from the first discharge port 67X is supplied to the reaction chamber 71 from the supply port 71A via the connection path 68A. The electrolytic solution 63 then flows from the supply port 71A to the discharge port 71B in the reaction chamber 71 and is discharged from the discharge port 71B. The electrolytic solution 63 discharged from the discharge port 71B is preferably supplied to the anode chamber 60X from the first supply port 66X via the connection path 68B. In this manner, the electrolytic solution 63 is circulated between the anode chamber 60X and the reaction chamber 71 by convection F. The circulation of the electrolytic solution 63 is preferably performed repeatedly and continuously. The electrolytic solution 63 may be caused to flow along the convection F by a pump such as a diaphragm pump, a syringe pump, or a peristaltic pump, but may also be caused to flow by known means other than a pump, such as by utilizing gravity to form the convection F. This also applies to the tenth and subsequent embodiments described later.

[0147] A voltage is applied between the anode 61 and the cathode 62 by a power supply 69. When the voltage is applied, carbon dioxide supplied to the inside of the electrochemical cell 60 is reduced by the first catalyst 65 at the cathode 62 to produce carbon monoxide. The electrochemical reaction that takes place at the cathode 62 is typically as shown in formula (i) above, but may also take place as shown in formula (ii).

[0148] On the other hand, when a voltage is applied to the anode 61, the redox species (oxidation-reduction substance) formed by the electrolyte is converted from a reduced species (reduced product A) to an oxidized product (e.g., a redox mediator, oxide B). When the electrolyte is a brominated salt, the reaction that occurs at the anode 61 is as shown in the following formula (B), and bromine is produced as an oxidized product: 2Br － →Br ２ +2e － (B)

[0149] Carbon monoxide produced at the cathode 62 is supplied to the reaction chamber 71, and the oxidant (redox species) produced at the anode 61 is supplied to the reaction chamber 71 together with the electrolytic solution 63 by convection F. In the reaction chamber 71, a carbonyl compound is produced from the carbon monoxide, the oxidant (redox species), and the reaction substrate by the action of the second catalyst 64. The carbonyl compound is at least one of an organic carbonate and an organic oxalate, with organic carbonate being preferred.

[0150] Although not particularly limited, an example of a reaction in which the reaction substrate is methanol and the electrolyte (redox species) is a bromide salt is shown in the following formula (C). When the reaction substrate is methanol and the redox species is a bromide salt, carbon monoxide and methanol react in the reaction chamber 71 to produce dimethyl carbonate (DMC). Bromine is also reduced to bromide ions, which produce, for example, hydrogen bromide. CO + Br ２ +CH ３ OH → DMC+2HBr (C)

[0151] When a carbonyl compound is synthesized, the oxidant is converted to a reduced species in the reaction chamber 71. The synthesized carbonyl compound and reduced species are returned to the anode chamber 60X along the convection current F together with the electrolytic solution. This circulation is continuously repeated; however, for example, when the concentration of the carbonyl compound in the electrolytic solution 63 reaches a certain level, the electrolytic solution may be withdrawn to the outside through an outlet 71B or the like. The redox species returned to the anode chamber 60X may be re-oxidized in the anode chamber 60X. In the electrochemical system 70, the reaction may be carried out batchwise or continuously. When carried out continuously, the circulating electrolytic solution may be continuously carried out by withdrawing a portion to the outside, for example, through an outlet 71B, while new electrolytic solution is supplied from the outside through, for example, a supply port 66X. The temperatures inside the anode chamber 60X, the cathode chamber 60Y, and the reaction chamber 71 in the electrochemical system 70 are not particularly limited, but are preferably around room temperature, for example, about 0 to 60°C, and preferably about 10 to 40°C.

[0152] Each component used in the electrochemical system will be described in detail below. [Cathode] The cathode chamber 60Y contains a first catalyst 65 that reduces carbon dioxide to carbon monoxide as described above. The cathode 62 is disposed inside the cathode chamber 60Y, and the cathode 62 preferably contains the first catalyst 65. The cathode 62 preferably contains an electrode substrate (current collector). Details of the electrode substrate (current collector) are as described above, and will not be described here. The current collector of the cathode 62 may be made of the same material as the current collector of the anode, or may be made of a different material.

[0153] (First Catalyst) The cathode 62 may contain a first catalyst 65. The first catalyst 65 may be supported on an electrode substrate that constitutes the cathode 62. The first catalyst is a reduction catalyst that can reduce carbon dioxide to a reduced product such as carbon monoxide. Details of the first catalyst and the electrode substrate are as described in the first embodiment. The first catalyst may also be supported on the electrode substrate as described above, together with a catalyst additive or the like.

[0154] (Second catalyst) The second catalyst is a catalyst for producing a carbonyl compound from carbon monoxide and a reaction substrate in the presence of an oxidant of a redox species. The second catalyst has a catalytically active species and a metal compound that supports the catalytically active species. In the present invention, by using a metal compound as a support that supports the catalytically active species, it is possible to synthesize a carbonyl compound with high faradaic efficiency. Although the mechanism behind this is unclear, it is presumed that the use of a metal compound as a support prevents oxidants such as halogens from being adsorbed onto the support, thereby allowing the reaction by the second catalyst to proceed appropriately.

[0155] The second catalyst contains, as a catalytically active species, at least one metal element selected from elements of Groups 8 to 11. By using an element of Groups 8 to 11 in the second catalyst, it becomes easier to synthesize a carbonyl compound from carbon monoxide with high faradaic efficiency.

[0156] Specific examples of Group 8 to Group 11 elements used in the catalyst include Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au. Among these, Co, Ni, Cu, Rh, Pd, Ag, Ir, Au, and Pt are preferred, with Pd, Au, Cu, and Ir being more preferred, Au and Pd being even more preferred, and Pd being particularly preferred. The use of any of the above elements facilitates the synthesis of organic carbonates, organic oxalates, or both from carbon monoxide with high faradaic efficiency. Au and Pd are more preferred as metal elements contained in the catalyst, with Pd being particularly preferred. The use of Au facilitates the production of organic oxalates with high faradaic efficiency, while the use of Pd facilitates the production of organic carbonates with high faradaic efficiency.

[0157] The metal element used in the catalyst may be used alone or in combination of two or more. When two or more elements are used in combination, two or more metal elements selected from Groups 8 to 11 may be used in combination, or a metal element from Groups 8 to 11 may be used in combination with a metal element other than Groups 8 to 11. The metal element other than Groups 8 to 11 is preferably a metal element from Period 4, but may also be a metal element other than Period 4. Specifically, it is preferable to combine Au with at least one selected from Ti, Mn, Fe, Co, Ni, Cu, and Zn. It is also preferable to combine Pd with at least one selected from Ti, Co, Ni, Cr, Mn, Fe, Cu, Zn, Ru, Rh, Ag, Ir, Pt, Au, and Sn. It is also preferable to combine Ir with at least one selected from Au, Rh, and Ru. Such a combination makes it possible to maintain a high faradaic efficiency when synthesizing a carbonyl compound while reducing the amount of precious metal used.

[0158] When two or more metal elements are used in combination, the metal element used in the catalyst preferably contains at least two metal elements selected from Groups 8 to 11, from the viewpoint of improving the Faraday efficiency. Among these, it is more preferable to use either Pd or Ir in combination with at least one element selected from Groups 8 to 11 other than Pd or Ir. Specifically, a combination of Pd with at least one element selected from Ag, Au, Pt, Ir, and Cu, or a combination of Ir with one element selected from Au, Rh, and Ru is more preferable.

[0159] The catalytically active species may be active particles containing a metal element. As described below, the second catalyst can be produced by mixing a metal precursor with a metal compound that serves as a support and then heat treating the mixture. The metal precursor is converted into catalytically active species (active particles) by heat treatment, and the catalytically active species is supported on the metal compound that serves as a support. The catalytically active species has catalytic activity that promotes the reaction when synthesizing an organic carbonate, an organic oxalate, or both from carbon monoxide. The catalytically active species may be composed of, for example, a metal itself, or a metal oxide. Alternatively, the catalytically active species may be a metal ion whose counter anion is an anion derived from a metal salt of the metal precursor, as described below. The catalytically active species may be an appropriate combination of these. The counter anion is not particularly limited, but examples include chloride ions, nitrate ions, sulfate ions, iodide ions, bromide ions, etc., and preferably chloride ions.

[0160] In the second catalyst, the catalytically active species are preferably fine particle-shaped active particles, and the fine particle-shaped catalytically active species are preferably supported on a metal compound support. The active particles are not particularly limited, but may be, for example, nano-order or angstrom-order particles, preferably having an average particle diameter of 0.1 nm to 100 nm, more preferably 0.5 nm to 40 nm. The active particles have the above particle diameter, and by nanostructuring them, the active area increases, making it easier to improve various performances of the catalyst. Note that the particle diameter refers to the area-equivalent circle diameter, which is calculated by determining the area of ​​each particle in image observation using TEM-EDX or the like, and calculating the diameter from the area assuming each particle to be a circle.

[0161] The metal element in the metal compound constituting the support also includes metal elements known as semimetals, such as silicon. Examples of the metal element in the metal compound constituting the support include metal elements of Groups 1 to 6 and metal elements of Groups 13 to 14, and specific examples include silicon, zirconium, magnesium, titanium, cerium, niobium, tungsten, and aluminum. Examples of the metal compound include metal oxides, metal nitrides, metal borides, and metals, with metal oxides being preferred.

[0162] Specific examples of metal compounds include silica, magnesia, titanium oxide, zirconia, alumina, cerium oxide, niobium oxide, silica-alumina, silica-magnesia, tungstate zirconia, zeolite, sulfated zirconia, and titanosilicate. Among these, alumina, silica, magnesia, titanium oxide, zirconia, cerium oxide, niobium oxide, silica-alumina, silica-magnesia, tungstate zirconia, and zeolite are preferred, with alumina, silica-alumina, and silica-magnesia being particularly preferred. The alumina is not particularly limited, and examples include α-alumina, β-alumina, and γ-alumina, with γ-alumina being preferred. Zeolites that can be used include, but are not limited to, mordenite (MOR), FAU (Y), BEA (beta), and MFI (ZSM-5). The metal compounds may be used alone or in combination of two or more.

[0163] The metal compound is preferably porous so that it can adequately support catalytically active species. The BET specific surface area of ​​the metal compound is, for example, 10 m 2 / g or more 1000m 2 / g or less, but preferably 20m 2 / g or more 500m 2 / g or less, more preferably 40m 2 / g or more 200m 2 / g or less. When the surface area of ​​the metal compound is equal to or greater than the above lower limit, an appropriate amount of catalytically active species can be supported on the metal compound. Therefore, the second catalyst has appropriate catalytic activity, and it is easy to improve the faradaic efficiency and reaction efficiency when synthesizing a carbonyl compound. Furthermore, when it is equal to or less than the above upper limit, it is easy to prevent oxidized forms of redox species such as halogens from being adsorbed on the metal compound, and it is easy to improve the reaction efficiency. The BET specific surface area of ​​the catalyst can be measured by gas adsorption analysis. Furthermore, the metal compound is not particularly limited, and may be, for example, in powder or particulate form. Furthermore, the particle size of the metal compound is not particularly limited as long as it can be used as a support for catalytically active species.

[0164] The amount of metal of the active catalyst species in the second catalyst is, for example, 0.05 parts by mass or more and 20 parts by mass or less, preferably 0.1 parts by mass or more and 10 parts by mass or less, and more preferably 0.2 parts by mass or more and 4 parts by mass or less, relative to 100 parts by mass of the metal compound. When the content of the metal element constituting the active catalyst species is equal to or greater than the above-mentioned lower limit, the carbonyl compound can be appropriately synthesized by the second catalyst. On the other hand, when the content is equal to or less than the above-mentioned upper limit, an effect commensurate with the content can be easily obtained.

[0165] In this embodiment, the catalytic performance can be improved by adding a second metal, which is different from the metal component of the metal compound, to the second catalyst in addition to the metal compound. The second metal may be any one selected from alkali metal elements and alkaline earth metal elements. The second metal may be contained in the metal compound. Specifically, the metal compound may be pretreated with a metal salt of the second metal, as described below. The inclusion of the second metal in the metal compound can improve the catalytic performance.

[0166] Specifically, the second metal may be pretreated with an alkali metal element or an alkaline earth metal element and then added to the metal compound. The pretreatment method can be carried out by adding a metal salt to the metal compound and then performing a heat treatment, as described below. Specific examples of the second metal include lithium, beryllium, sodium, potassium, magnesium, calcium, and barium, and preferably lithium, magnesium, and sodium. The second metal may be used alone or in combination of two or more.

[0167] (Method for producing second catalyst) Next, a method for producing the second catalyst will be described. The second catalyst described above can be obtained by mixing a metal precursor and a metal compound, and heat-treating the mixture containing the metal precursor and the metal compound (hereinafter referred to as the "catalyst raw material mixture").

[0168] The metal precursor is a compound that becomes the above-described catalytically active species upon heat treatment. Therefore, the metal precursor is preferably a precursor containing a metal element selected from the above-described Group 8 to Group 11 elements, and suitable metal elements are also as described above. The metal element used in the metal precursor may be used alone or in combination of two or more. When two or more types are used in combination, it is preferable to use two or more precursors containing a metal element selected from the above-described Group 8 to Group 11 elements in combination, or to use a precursor containing a metal element selected from the Group 8 to Group 11 elements in combination with a precursor containing a metal element other than Group 8 to Group 11 (e.g., a metal element of the fourth periodic element). When two or more types of metal precursors are used in combination, the second catalyst is preferably obtained by mixing two or more types of metal precursors and a metal compound and then heat-treating the mixture. Therefore, it is preferable that the catalyst raw material mixture contains two or more types of metal precursors.

[0169] The metal precursor preferably contains a metal ion. The metal precursor may be used in the form of, for example, a metal salt. Examples of metal salts include metal nitrates, metal sulfates, metal chlorides, metal bromides, metal iodides, and metal acetates. Among these, metal chlorides and metal nitrates are preferred, and metal chlorides are more preferred from the viewpoint of forming suitable active particles. Specifically, examples of metal nitrates include cobalt nitrate (Co(NO3)2), nickel nitrate (Ni(NO3)2), copper nitrate (Cu(NO3)2), and rhodium nitrate (Rh(NO3) ３ ), palladium nitrate (Pd(NO3) ２ ), silver nitrate (AgNO ３ ), iridium nitrate (Ir(NO3) ４ ), platinum nitrate (Pt(NO3) ４ ), gold nitrate (AuNO3), ruthenium nitrate (Ru(NO3) ３ ), iron nitrate (Fe(NO ３ ) ３ ), manganese nitrate (Mn(NO ３ ) ２ ), zinc nitrate (Zn(NO ３ ) ２ ), chromium nitrate (Cr(NO ３ ) ３ ), tin nitrate (Sn(NO ３ ) ４ ) and the like. Specific examples of metal chlorides include PdCl ２ , RuCl ３ , IrCl ３ , PtCl ４ , AuCl ３ Also, HAuCl ４ Among these, PdCl ２ , HAuCl ４ The metal salts may be used alone or in combination of two or more.

[0170] The metal compounds to be blended into the catalyst raw material mixture are as described above. The blending ratio of the metal compound to the metal precursor in the catalyst raw material mixture may be adjusted so that the metal amount of the metal element constituting the active catalyst species relative to the metal compound is as described above.

[0171] Furthermore, the metal compound to be blended in the catalyst raw material mixture may be pretreated with a metal salt containing a second metal as described above. Examples of the metal salt containing a second metal include metal nitrates, metal sulfates, metal chlorides, metal bromides, metal iodides, and metal acetates, and among these, metal nitrates and metal chlorides are preferred. Specific examples of metal nitrates include lithium nitrate (LiNO ３ ), beryllium nitrate (Be(NO ３ ) ２ ), sodium nitrate (NaNO ３ ), magnesium nitrate (Mg(NO ３ ) ２ ), potassium nitrate (KNO ３ ), calcium nitrate (Ca(NO ３ ) ２ ), barium nitrate (Ba(NO ３ ) ２ ), and metal chlorides include lithium chloride (LiCl), sodium chloride (NaCl), magnesium chloride (MgCl ２ ) and the like. The metal salt containing the second metal may be used alone or in combination of two or more. The pretreatment may be carried out by adding the metal salt containing the second metal to a metal compound, mixing them, and heat-treating the mixture. The heat treatment temperature in the pretreatment is preferably 100°C or higher and 1000°C or lower from the viewpoint of properly adhering the metal salt to the metal compound. The heat treatment temperature is more preferably 400°C or higher and 1000°C or lower, and even more preferably 500°C or higher and 900°C or lower. The time for heat treatment at the above temperature is not particularly limited, but is, for example, 0.25 hours or higher and 10 hours or lower, preferably 0.5 hours or higher and 8 hours or lower, and more preferably 1 hour or higher and 5 hours or lower.

[0172] The temperature for heat-treating the catalyst raw material mixture described above is preferably 150°C or higher and 1000°C or lower. By setting the heat treatment temperature within this range, catalytically active species can be appropriately formed from the metal precursor while suppressing the generation of unnecessary by-products. Furthermore, it becomes possible to appropriately support the catalytically active species on the metal compound. Furthermore, migration of the catalytically active species can be prevented, thereby reducing the particle size of the catalytically active species and making it easier to increase the surface area of ​​the second catalyst. From the above perspectives, the heat treatment temperature is preferably 180°C or higher and 1000°C or lower, and more preferably 190°C or higher and 500°C or lower. The heat treatment time is not particularly limited, but is, for example, 0.25 hours or higher and 10 hours or lower, preferably 0.5 hours or higher and 8 hours or lower, and more preferably 1 hour or higher and 5 hours or lower. The heat treatment may be performed in air, in an inert gas atmosphere such as argon or nitrogen gas, or in a reducing gas atmosphere such as hydrogen or carbon monoxide. After the heat treatment, a reduction treatment may be carried out as appropriate. Examples of the reduction treatment include a method of reducing the material with a reducing gas such as hydrogen or carbon monoxide, or a method of reducing the material with NaBH ４ Examples of such methods include wet reduction treatment using reducing compounds such as hydrogen, carbon monoxide, etc. When reduction treatment is performed using a reducing gas such as hydrogen or carbon monoxide, it is more preferable to perform the treatment at a high temperature. Specifically, the temperature is preferably 100°C or higher and 300°C or lower, and more preferably 130°C or higher and lower than 200°C. By performing this reduction treatment, it becomes easier to increase the proportion of zero-valent metal elements (i.e., metal itself) in the catalytically active species, and it becomes easier to enhance the catalytic activity.

[0173] The catalyst raw material mixture to be heat-treated is preferably in powder or particulate form. If the second catalyst mixture is in powder or particulate form, the catalyst obtained by heat treatment can also be in powder or particulate form. The catalyst raw material mixture can be obtained, for example, by preparing a diluted solution of the catalyst raw material mixture and drying the diluted solution. In the diluted solution of the catalyst raw material mixture, each component (metal precursor and metal compound) is preferably dispersed or dissolved in a dilution solvent. By dispersing or dissolving each component in a dilution solvent, a catalyst raw material mixture in which each component is homogeneously mixed can be obtained.

[0174] The dilution solvent used to dilute the catalyst raw material mixture may be water or an organic solvent, with water being preferred. Alternatively, a mixed solvent of an organic solvent and water may be used as the dilution solvent. The dilution solvent may also contain an acid component such as hydrochloric acid, nitric acid, sulfuric acid, acetic acid, citric acid, or lauric acid, or a base component such as ammonia. The concentration of the diluted solution of the catalyst raw material mixture is not particularly limited, but the amount of metal precursor is, for example, 0.01 to 25 g / L, preferably 0.1 to 5 g / L.

[0175] The second catalyst 64 may be contained within the reaction chamber 71. The second catalyst 64 may be dispersed in the electrolytic solution 63 in the reaction chamber 71, or may be packed in a layer. When packed in a layer, the second catalyst 64 may be packed on a support such as a tray or mesh, or a support may not be provided. Furthermore, when dispersed within the reaction chamber 71, the second catalyst 64 may be dispersed by flowing it using convection F or other means of dispersion. For example, the second catalyst 64 may be dispersed by bubbling with a gas supplied from the cathode chamber 60Y, bubbling with a gas other than the gas supplied from the cathode chamber 60Y, or by stirring using a stirring device such as a stirring blade installed within the anode chamber 60X. The content of the second catalyst in the reaction chamber 71 is not particularly limited, but may be, for example, approximately 0.1 to 200 g / L, preferably approximately 1 to 100 g / L. Note that the content here refers to the amount of the second catalyst per 1 L of the electrolytic solution (i.e., reaction solution) contained in the reaction chamber 71.

[0176] [Electrolyte Solution] In this embodiment, as described above, the anode chamber 60X and the reaction chamber 71 are filled with the electrolyte solution 63. The electrolyte solution 63 contains redox species. The redox species may be an electrolyte in the electrolyte solution 63. The redox species may be dissolved in a reaction substrate or a mixture of a reaction substrate and a solvent, which will be described later.

[0177] (Redox species (oxidation-reduction substance)) As the redox species, for example, those having a molecular or ionic size smaller than that of the reaction substrate, such as an alcohol-based compound described below, and having redox activity can be used. Specific examples of electrolytes that can serve as redox species include halide salts, organic redox, and complex redox. Among these, halide salts are preferred from the viewpoint of increasing the faradaic efficiency and productivity.

[0178] In this embodiment, the electrolytic solution contains redox species as an electrolyte, which generates a redox mediator (an oxidant such as a halogen) at the anode 61, and this redox mediator enables efficient production of carbonyl compounds from carbon monoxide and a reaction substrate in the presence of the second catalyst 64. Furthermore, when the redox mediator comes into contact with the first catalyst 65, it inhibits the reduction reaction of carbon dioxide. However, in this embodiment, the electrolytic solution 63 flows due to convection F, which makes it difficult for the redox mediator to come into contact with the first catalyst 65 and therefore less likely to inhibit the reduction reaction of carbon dioxide.

[0179] Examples of halide salts include metal halide salts. Specific examples of metal halide salts include lithium halide salts such as lithium chloride, lithium bromide, and lithium iodide, sodium halide salts such as sodium chloride, sodium bromide, and sodium iodide, potassium halide salts such as potassium chloride, potassium bromide, and potassium iodide, and cesium halide salts such as cesium chloride, cesium bromide, and cesium iodide. Examples of halide salts also include ammonium halide salts such as ammonium chloride, ammonium bromide, and ammonium iodide.

[0180] Examples of organic redox compounds include TEMPO-based radical compounds such as 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl (MeO-TEMPO), and azaadamantane-N-oxyl (AZADO). Examples of complex redox compounds include palladium acetylacetonate (Pd(OAc) ２ ), tetrakis(triphenylphosphine)palladium (Pd(PPh３ ) ４ complex), tris(2,2'-bipyridine)cobalt (Co(bpy) ３ complex), tris[1,3-bis(4-pyridyl)propane]cobalt (Co(bpp) ３ complexes) and other cobalt-based complexes.

[0181] Among the above, metal halide salts are preferred as redox species from the viewpoint of increasing the selectivity of carbonyl compounds, and metal chloride salts and metal bromide salts are more preferred, with metal bromide salts being even more preferred. Therefore, the electrolyte contains halogen ions such as chloride ions and bromide ions as redox ions, with bromide ions being particularly preferred. Preferred examples of metal chloride salts include lithium chloride, potassium chloride, and sodium chloride, with sodium chloride being preferred from the viewpoint of easy availability. Preferred examples of metal bromide salts include lithium bromide, potassium bromide, and sodium bromide, with lithium chloride and lithium bromide being preferred from the viewpoint of increasing the selectivity of carbonyl compounds, with lithium bromide being particularly preferred. The redox species may be used alone or in combination of two or more.

[0182] The concentration of the redox species in the electrolyte is not particularly limited and may be adjusted to a level at which the synthesis of an oxygen-containing organic substance such as a carbonyl compound proceeds appropriately. A specific concentration of the redox species is, for example, 0.001 M or more and 5.0 M or less, preferably 0.01 M or more and 1.0 M or less, and more preferably 0.05 M or more and 0.5 M or less.

[0183] (Reaction Substrate) The reaction substrate is a compound that serves as a raw material for the carbonyl compound. In this embodiment, an alcohol-based compound is preferably used as the reaction substrate. By using an alcohol-based compound as the reaction substrate, an organic carbonate, an organic oxalate, or both of them can be easily produced from carbon monoxide in the presence of an oxidant of the redox species and the second catalyst.

[0184] (Alcohol-Based Compound) The alcohol-based compound is a reaction substrate that reacts with carbon monoxide in the electrochemical system (in the reaction chamber 71 in this embodiment) to produce an organic carbonate, an organic oxalate, or both. The alcohol-based compound may be solid, liquid, or gaseous in the environment in which the electrochemical reaction occurs in the electrochemical system, but is preferably liquid. A liquid alcohol-based compound can be easily filled into the reaction chamber 71, the anode chamber 60X, and the like without using a solvent, which will be described later. The details of the alcohol-based compound and the product are the same as those in the first embodiment, and therefore a description thereof will be omitted.

[0185] (Solvent) When the above-mentioned reaction substrate is a solid or gas, or when it is necessary to improve the solubility of the redox species, the electrolyte solution 63 may further contain a solvent. In this case, the reaction substrate may be filled into the reaction chamber 71 or the anode chamber 60X as a mixed solution with the solvent. Of course, even when the reaction substrate is a liquid, it may be filled as a mixed solution with the solvent. The solvent can be appropriately selected from solvents commonly used in electrochemical reactions, and for example, the solvents listed above as reaction solvents can be appropriately selected and used. One solvent may be used alone, or two or more solvents may be used in combination.

[0186] As described above, it is preferable that the electrolytic solution 63 contains a redox species as an electrolyte, but the electrolyte may also contain an electrolyte other than the redox species in addition to the redox species. Examples of electrolytes other than the redox species include perchlorates such as sodium perchlorate (NaClO), zinc perchlorate, barium perchlorate, lithium perchlorate, and ammonium perchlorate, as well as sodium sulfate, potassium sulfate, and ammonium sulfate. These electrolytes other than the redox species may be used alone or in combination of two or more.

[0187] [Anode] In the anode chamber 60X, the anode 61 oxidizes the redox species to generate an oxidant (e.g., a redox mediator such as a halogen) as an active intermediate species, as described above. In the anode chamber 60X, the anode 61 is preferably positioned so as to contact the electrolyte 63 filled in the anode chamber 60X. A reference electrode or the like may be provided in the electrochemical cell 60 (e.g., the anode chamber 61). Preferably, the anode 61 does not contain a catalyst. Adding a catalyst to the anode 61 requires a process of applying a catalyst-containing coating solution to an electrode substrate or immersing the electrode substrate in a catalyst-containing immersion solution to support the catalyst on the electrode. However, if the anode does not contain a catalyst, these processes are unnecessary. Therefore, carbonyl compounds can be synthesized with a simple configuration. Furthermore, the anode 61 can generate an oxidant even without a catalyst.

[0188] The catalyst not contained in the anode 61 is a carbonyl compound synthesis catalyst such as a second catalyst that promotes an electrochemical reaction that synthesizes an organic carbonate, an organic oxalate, or both from carbon monoxide. Therefore, it is preferable that the anode 61 does not support a carbonyl compound synthesis catalyst such as a second catalyst. However, for example, as in the eleventh embodiment described below, when the anode 61 comes into contact with an electrolyte (catalyst-containing electrolyte) that contains a catalyst (second catalyst), the catalyst contained in the catalyst-containing electrolyte may adhere to the anode 61. However, in this specification, an embodiment in which the catalyst contained in the catalyst-containing electrolyte adheres to the anode 61 is not included in the embodiment in which "the anode (electrode) contains a catalyst."

[0189] The anode 61 is made of, for example, an electrode substrate. Details of the electrode substrate are as described in the first embodiment above, but in this embodiment, a carbon substrate is preferred, and porous carbon is more preferred. A specific example of porous carbon is carbon nonwoven fabric.

[0190] 9 shows a configuration in which the anode 61 and the cathode 62 are disposed at positions spaced apart from the separator 75, but the anode 61 and the cathode 62 may be disposed at positions in contact with the separator 75. Specifically, the anode 61 may form a stack together with a separator 75 formed of an ion exchange membrane or the like, which will be described later, and a first electrode (cathode). The stack may be a stack having the anode 61, the separator 75 such as an ion exchange membrane, and the cathode 62, in this order. The stack may be a membrane-electrode assembly in which the anode 61 and the cathode 62 are joined together, for example, via an ion exchange membrane.

[0191] [Separator Membrane] The separator membrane 75 preferably separates the carbon monoxide generated in the first catalyst 65 (cathode 62) from the oxidant generated in the anode 61. The separator membrane 75 may be any membrane that is permeable to ions but not permeable to the electrolyte 63, carbon monoxide, or oxidant, and specifically, an ion exchange membrane is preferred. Examples of the ion exchange membrane include a solid membrane, such as a cation exchange membrane that is permeable to cations such as protons, and an anion exchange membrane that is permeable to anions such as hydroxide ions. However, a cation exchange membrane is preferred from the viewpoints of ion conductivity and cost. Details of the cation exchange membrane and the anion exchange membrane are as described above.

[0192] As described above, the electrochemical system 70 according to the ninth embodiment produces carbonyl compounds from carbon monoxide using redox species. However, by using a second catalyst 64 for producing carbonyl compounds that contains catalytically active species and a metal compound supporting the catalytically active species, carbonyl compounds can be synthesized with high faradaic efficiency. Furthermore, because the electrolytic solution 63 circulates between the reaction chamber 71 for producing carbonyl compounds and the anode chamber 60X for oxidizing the redox species, the production rate of carbonyl compounds can be further improved.

[0193] Tenth Embodiment Next, an electrochemical system according to a tenth embodiment of the present invention will be described. FIG. 10 shows an electrochemical system 70A according to the tenth embodiment. In the ninth embodiment, redox species are oxidized to oxidants by a liquid-phase reaction in the anode chamber 60X, and a solution containing the oxidized redox species is supplied to the reaction chamber 71 via the connection path 68A. However, in the tenth embodiment, a gas containing the redox species oxidized in the anode chamber 60X is supplied to the reaction chamber 71 via the connection path 68A. Furthermore, in the ninth embodiment, a connection path 68B is provided in addition to the connection path 68A, and the electrolyte is circulated between the anode chamber 60X and the reaction chamber 71. However, the connection path 68B is omitted, and the electrolyte is not circulated between the anode chamber 60X and the reaction chamber 71. Differences between the tenth embodiment and the ninth embodiment will be described below.

[0194] In the tenth embodiment, the anode chamber 60X is filled with an electrolyte solution 63A. The electrolyte solution 63A is an electrolyte solution containing redox species and a solvent, and the redox species may be dissolved in the solvent as an electrolyte. Details of the redox species are as described above. However, among the redox species, halide salts are preferred, and metal chloride salts are particularly preferred, from the viewpoint of easily supplying the oxidant to the reaction chamber 71 as a gas. Details and preferred examples of metal chloride salts are as described in the ninth embodiment. In this embodiment, by using metal chloride salts as the redox species, the generated oxidant can be chlorine, as shown in FIG. 10 . Because chlorine is a gas at room temperature (23°C), it can be easily supplied as a gas from the anode chamber 60X to the reaction chamber 71. However, as long as it can be supplied as a gas, metal chloride salts are not required, and other redox species can also be used. For example, by raising the temperature of the electrolyte solution 63A in the electrochemical cell 60, bromine and other species can be converted into a gas, so metal bromide salts, for example, can also be used. The concentration of the redox species in the electrolytic solution 63A is as described in the ninth embodiment.

[0195] The electrolyte solution 63A in the anode chamber 60X may be any solvent containing redox species, as described above. Specific examples of the solvent are as described in the ninth embodiment, but the alcohol-based compounds listed as reaction substrates can also be used as solvents. The reaction chamber 71 may be filled with a reaction solution 63B. The reaction solution 63B is not particularly limited as long as it contains a reaction substrate. However, it may consist of a reaction substrate or contain a solvent in addition to the reaction substrate. Details of the reaction substrate and solvent are as described in the ninth embodiment. However, since no electrochemical reaction occurs in the reaction chamber 71, the reaction solution 63B may not contain an electrolyte. Therefore, although the reaction solution 63B in the reaction chamber 71 may contain an oxidized form of the redox species supplied from the anode chamber 60X, the reaction chamber 71 does not need to contain any electrolytes, such as redox species, other than those supplied from the anode chamber 60X. The reaction chamber 71 may be provided with a supply port 71C in addition to the supply port 71A, and for example, a reaction substrate or the like may be supplied to the reaction chamber 71 from the supply port 71C.

[0196] In the tenth embodiment described above, a gas containing carbon monoxide is supplied from the cathode chamber 60Y and a gas containing an oxidized form of the redox species is supplied from the anode chamber 60X to the reaction chamber 71 via the connecting path 68A along the flow of the convection current F. In the reaction chamber 71, a carbonyl compound is produced from the reaction substrate, carbon monoxide, and the oxidized form of the redox species contained in the electrolytic solution 63B in the reaction chamber 71 by the action of the second catalyst 64. In this embodiment, the second catalyst 64 contains catalytically active species and a metal compound supporting the catalytically active species, so that the carbonyl compound can be synthesized with high faradaic efficiency in the reaction chamber 71. Furthermore, in this embodiment, the electrolytic solution (reaction solution) is not circulated, but the raw materials for producing the carbonyl compound (carbon monoxide and the oxidized form of the redox species) are supplied to the reaction chamber 71 as gases. Therefore, the carbonyl compound can be continuously synthesized over a long period of time without extracting the reaction solution 63B filled in the reaction chamber 71 or with little increase in the volume of the reaction solution 63B. Therefore, in this embodiment as well, the production rate of carbonyl compounds in the reaction chamber 71 can be further improved.

[0197] Of the gases (carbon monoxide and oxidized redox species) supplied from the electrochemical cell 60 to the reaction chamber 71, any excess gas not used in the synthesis of carbonyl compounds may be appropriately discharged from an outlet 71B or the like. In this embodiment, carbon dioxide is continuously supplied to the cathode chamber 60Y, and thus carbon monoxide and oxidized redox species are also continuously supplied to the reaction chamber 71. This causes the generated carbonyl compounds to accumulate in the reaction chamber 71, increasing the carbonyl compound content. Furthermore, the oxidized redox species are consumed in the carbonyl compound production reaction and converted to reduced species, so the reduced species content similarly increases. Therefore, it is advisable to withdraw the reaction solution 63B from the reaction chamber 71 when the carbonyl compound content or the reduced species content reaches a certain level or higher.

[0198] However, in the tenth embodiment, the reaction does not necessarily have to be carried out in a batchwise manner as described above, and may be carried out in a continuous manner. In the case of a continuous reaction, for example, the reactant or a mixture of the reactant and the solvent may be continuously supplied from the supply port 71C. The reactant supplied from the supply port 71C may be reacted with carbon monoxide while flowing along the convection F to the outlet 71B, where it is converted into a carbonyl compound and discharged from the outlet 71B. In this case, the carbonyl compound may be discharged together with the unreacted reactant and the redox species (unreacted oxidant or reduced species after the reaction).

[0199] Eleventh Embodiment Next, an electrochemical system according to an eleventh embodiment of the present invention will be described. In the above ninth and tenth embodiments, a reaction chamber 71 separate from the electrochemical cell 60 is provided, and a reaction for producing a carbonyl compound is carried out in the reaction chamber 71. However, in an electrochemical system 20B according to the eleventh embodiment, a reaction chamber 21 is not provided, and a reaction for producing a carbonyl compound is carried out in the electrochemical cell, similar to the electrochemical cell of the fourth embodiment ( FIG. 4 ).

[0200] Differences between the eleventh embodiment and the ninth embodiment will be described below. The reference numerals in FIG. 9 will be referenced in the description. In the eleventh embodiment, the anode chamber 60X is filled with the electrolytic solution 63, as in the ninth embodiment. The configuration of the electrolytic solution 63 is the same as in the ninth embodiment, and therefore a description thereof will be omitted. However, in the eleventh embodiment, the electrolytic solution 63 further contains a second catalyst 64, forming a catalyst-containing electrolytic solution.

[0201] The second catalyst 64 in the anode chamber 60X may be dispersed in the electrolytic solution 63. When the second catalyst 64 is dispersed inside the anode chamber 60X, it may be dispersed by fluidizing it using convection F or other means of dispersion. For example, the second catalyst 64 may be dispersed by bubbling with a gas supplied from the cathode chamber 60Y, bubbling with a gas other than the gas supplied from the cathode chamber 60Y, or stirring using a stirring device such as a stirring blade inside the anode chamber 60X. The content of the second catalyst 64 in the anode chamber 60X is not particularly limited, but may be, for example, about 0.1 to 200 g / L, preferably about 1 to 100 g / L. Note that the content here refers to the amount of the second catalyst 64 per 1 L of the electrolytic solution (i.e., the reaction solution) contained in the anode chamber 60X. In addition to the supply ports 66X and 66Y, the electric cell 60 may be provided with a third supply port (not shown) in the anode chamber 60X, and, for example, a reaction substrate or the like may be supplied to the anode chamber 60X via the third supply port.

[0202] In the eleventh embodiment, the supply port 66X of the anode chamber 60X and the discharge port 67Y of the cathode chamber 60Y are connected via a connecting path (not shown). Therefore, the carbon monoxide-containing gas generated in the cathode chamber 60Y is supplied to the anode chamber 60X via the connecting path (not shown). Furthermore, in the anode chamber 60X, the redox species is oxidized in the anode 61 to form an oxidant. Therefore, in the anode chamber 60X, a carbonyl compound is generated from the carbon monoxide supplied from the cathode chamber 60Y, the oxidant, and the reaction substrate contained in the electrolytic solution 63, as in the ninth embodiment.

[0203] In this embodiment, too, continuous supply of carbon monoxide to the anode chamber 60X (i.e., supply of carbon dioxide to the cathode chamber 60Y) causes the generated carbonyl compounds to accumulate in the anode chamber 60X, increasing the carbonyl compound content. Therefore, the electrolytic solution (reaction solution) 63 may be withdrawn, for example, through the outlet 67X, when the carbonyl compound content reaches a certain level. However, the eleventh embodiment does not necessarily require a batchwise process, and may also be conducted continuously. In the case of a continuous process, the reaction substrate or a mixture of the reaction substrate and the solvent may be continuously supplied through a supply port (e.g., a supply port provided separately from the supply port 66X). In the anode chamber 60X, the reaction substrate supplied through the supply port is reacted with carbon monoxide while flowing along the convection current F to the outlet 67X, where it is converted into the carbonyl compound and discharged through the outlet 67X. In this case, the carbonyl compound may be discharged together with the unreacted reaction substrate and the redox species (unreacted oxidized product or reduced species after reaction).

[0204] In the eleventh embodiment, carbonyl compounds are also produced from carbon monoxide using redox species. However, by using a second catalyst 64 for producing carbonyl compounds that contains catalytically active species and a metal compound supporting the catalytically active species, carbonyl compounds can be synthesized with high faradaic efficiency. Furthermore, in this embodiment, there is no need to provide a separate reaction chamber other than the electrochemical cell 60, which simplifies the device configuration of the electrochemical system. Furthermore, because the second catalyst 64 does not significantly inhibit the oxidation of redox species, a decrease in the reaction efficiency of carbonyl compounds can be prevented even if the oxidation of redox species and the production of carbonyl compounds occur in the same reaction chamber (anode chamber 60X).

[0205] 11 is a schematic diagram showing an electrochemical system 70B according to a twelfth embodiment. In the twelfth embodiment, similar to the eleventh embodiment, the reaction chamber 71 is not provided, and the reaction for producing the carbonyl compound takes place in the electrochemical cell 60, but the reaction for producing the carbonyl compound takes place in the cathode chamber 60Y. Differences between the twelfth embodiment and the ninth embodiment will be described below.

[0206] In the twelfth embodiment, the anode chamber 60X is filled with an electrolytic solution 63. The cathode chamber 60Y is also filled with the electrolytic solution 63. The electrolytic solution 63 may include a redox species and a reaction substrate. The electrolytic solution 63 may further contain a solvent. Details of the electrolytic solution 63 are similar to those of the electrolytic solution 63 in the ninth embodiment, and therefore a detailed description thereof will be omitted. However, the electrolytic solution 63 in the cathode chamber 60Y further contains a second catalyst 64, thereby constituting a catalyst-containing electrolytic solution 63Y. The second catalyst 64 in the catalyst-containing electrolytic solution 63Y may be dispersed by a dispersion means such as bubbling, flow, or stirring, similar to the catalyst-containing electrolytic solution.

[0207] In this embodiment, the anode chamber 60X is provided with a supply port 66X and a discharge port 67X, as in the ninth embodiment. Meanwhile, the cathode chamber 60Y is provided with a supply port 66P in addition to the supply port 66Y and the discharge port 67Y. The supply port 66P of the cathode chamber 60Y and the discharge port 67X of the anode chamber 60X are connected via a connection channel 68E. Similarly to the ninth embodiment, the supply port 66Y is connected to a carbon dioxide source via a supply channel 74, and carbon dioxide is supplied from the supply port 66Y. Furthermore, the cathode 62 contains a first catalyst 65, while the anode 61 does not need to contain a catalyst.

[0208] In the electrochemical system 70B having the above configuration, in the anode chamber 60X, redox species are oxidized on the anode 61 to generate an oxidant, as in the ninth embodiment. The electrolyte solution 63 containing the oxidant is supplied from the anode chamber 60X to the cathode chamber 60Y via the connection path 68E along the convection F. Carbon dioxide supplied from the supply port 66Y via the supply path 74 is reduced to carbon monoxide in the cathode chamber 60Y. Then, in the cathode chamber 60Y, a carbonyl compound is synthesized from the carbon monoxide generated in the cathode 62, the reaction substrates contained in the electrolyte solution 63, and the oxidant of the redox species supplied from the anode chamber 60X by the action of the second catalyst 64.

[0209] In this embodiment, for example, a reactant (or a mixture of a reactant and a solvent) is continuously supplied from the supply port 66X of the anode chamber 60X, thereby forming a convection current F, and an oxidized form of the redox species is continuously supplied to the cathode chamber 60Y. Carbon dioxide is also continuously supplied from the supply port 66Y of the cathode chamber 60Y, thereby continuously generating carbon monoxide, which results in continuous production of carbonyl compounds in the cathode chamber 60Y. The electrolytic solution 13 flows along the convection current F from the supply port 66P to the discharge port 67Y while the reactant is converted to carbonyl compounds by the action of the second catalyst 64. After a certain proportion of the reactant is converted to carbonyl compounds, the electrolytic solution 13 is preferably discharged to the outside from the discharge port 17Y. As described above, in this embodiment, the reaction is preferably carried out continuously, but of course the reaction may also be carried out batchwise.

[0210] <Modifications> The electrochemical systems in the above-described embodiments of the second aspect (the ninth to twelfth embodiments) are merely examples, and are not limited to the above-described systems. The present invention may be modified as appropriate without departing from the spirit of the present invention. For example, in the eleventh embodiment, the second catalyst 64 is dispersed in the electrolytic solution 63 in the anode chamber 60X. However, as shown in FIG. 9 , the second catalyst 64 may be stacked or may be otherwise configured. Furthermore, as shown in FIG. 12 , an isolation membrane 76 (second isolation membrane) may be further provided in the anode chamber 60X, and the anode chamber 60X may be separated by the isolation membrane 76. The configuration of the electrochemical system 70C according to this modification can also be said to be a configuration in which the second electrolysis section and the first reaction section 63X are connected via the isolation membrane 76. Specifically, as shown in FIG. 12 , the cathode chamber 60Y may be separated into a first region (second electrolysis region) where the anode 61 is provided and a second region (first reaction region 63X) where no anode is provided, and the second region where no anode is provided may be filled with a second catalyst 64. The separator 76 may be a membrane that allows the electrolyte solution 63 to pass through but not the second catalyst 14, and may be, for example, a mesh filter. This configuration separates the region where the redox species is oxidized from the region where the carbonyl compound is produced, thereby reducing side reactions. Similarly to the twelfth embodiment, the second catalyst 64 may be stacked in the cathode chamber 60Y as shown in FIG. 9 or may be in another configuration. Furthermore, similar to the configuration shown in FIG. 12 , the cathode chamber 60Y may be separated by a separator into a first region where the cathode 62 is provided and a second region where no cathode is provided, and the second region where no cathode is provided may be filled with the second catalyst 64. That is, the first electrolysis unit and the first reaction unit may be connected via a separation membrane. Also, for example, the reaction substrate may be supplied to the reaction unit 63X from a supply port 66Z, and then reacted with carbon monoxide while flowing along the convection F to an outlet 67X, where it is converted into a carbonyl compound and then discharged from the outlet 67X.

[0211] Furthermore, in the ninth to eleventh embodiments, carbon dioxide is converted to carbon monoxide in the cathode chamber 60Y by a gas-phase reaction. However, carbon dioxide may be converted to carbon monoxide by a liquid-phase reaction. In this case, the cathode chamber 60Y may also be filled with an electrolytic solution. That is, carbon dioxide may be at least partially dissolved in the electrolytic solution and may be converted to carbon monoxide upon contact with the cathode together with the electrolytic solution. In this case, the generated carbon monoxide may be supplied as a gas to the anode chamber 60X or the reaction chamber 71, or, for example, at least partially dissolved in the electrolytic solution and supplied to the anode chamber 60X or the reaction chamber 71 together with the electrolytic solution.

[0212] Furthermore, in each of the above-described embodiments (the ninth to twelfth embodiments), the electrochemical cell 60 is separated into the anode chamber 60X and the cathode chamber 60Y by the separator 75. However, in the present invention, the separator 75 separating the anode chamber 60X and the cathode chamber 60Y may be omitted. In that case, for example, in the ninth and tenth embodiments, the electrochemical cell is filled with an electrolyte, and both the generation of carbon monoxide and the oxidation of the redox species may be carried out by liquid-phase reactions.

[0213] In the above embodiments (the ninth to twelfth embodiments), an example has been described in which carbon dioxide is reduced to carbon monoxide in the cathode chamber 60Y and a carbonyl compound is synthesized using the carbon monoxide produced in the cathode chamber 60Y. However, in the above embodiments, it is not necessary to produce carbon monoxide in the cathode chamber 60Y. In that case, for example, a substance to be reduced other than carbon dioxide may be supplied to the cathode chamber 60Y, and the substance to be reduced may be appropriately reduced at the cathode. The substance to be reduced is not particularly limited, but may be, for example, water, CO, N ２Alternatively, protons, etc. may be used. In this case, the cathode chamber 60Y may or may not be filled with an electrolytic solution. The cathode 62 is not particularly limited, but may have a reduction catalyst that promotes reduction. For example, the cathode 62 may be an electrode base material containing a reduction catalyst. When carbon monoxide is not generated in the cathode chamber 60Y, for example, in the ninth and tenth embodiments, carbon monoxide may be supplied to the reaction chamber 61 from a carbon monoxide supply source (not shown) via the supply port 71A. In the eleventh embodiment, carbon monoxide may be supplied to the anode chamber 60X via the supply port 66X. In this case, the ninth to eleventh embodiments are similar in other respects except that carbon monoxide is supplied from a carbon monoxide supply source instead of the cathode chamber 60Y, and therefore further description will be omitted.

[0214] Furthermore, the second catalyst described in the second aspect can also be used as the second catalyst in other aspects, and may be used as the second catalyst in each embodiment of the first aspect described above. It may also be used as the second catalyst in each embodiment of the third aspect described below. Furthermore, in the ninth to twelfth embodiments described above, the second catalyst does not have to be the second catalyst described in the second aspect, and the second catalyst used in the first aspect may be used.

[0215] Hereinafter, an electrochemical reaction device and a method for producing a carbonyl compound using the electrochemical reaction device according to a third aspect of the present invention will be described using embodiments with reference to the drawings. In the following description, elements having the same configuration will be denoted by the same reference numerals. The electrochemical reaction device according to the third aspect may also be referred to as an electrochemical system or a carbon dioxide reduction device.

[0216] <Thirteenth Embodiment> An electrochemical reaction device 90 according to a thirteenth embodiment of the present invention is constituted by an electrochemical cell 80. The electrochemical cell 80 includes a cathode 81, an anode 82, and an electrolytic solution 83. The electrolytic solution 83 contains a reactant and an electrolyte, and is filled inside the electrochemical cell 80. The electrolyte may be any material that can serve as a redox species, but is preferably a halide salt. Details of the electrolyte will be described later. The electrochemical cell 80 according to the thirteenth embodiment contains a first catalyst 84 that reduces carbon dioxide to carbon monoxide and a second catalyst 85 that synthesizes a carbonyl compound from carbon monoxide and the reactant. In the electrochemical cell 80, the first catalyst 84 is contained in the cathode 81.

[0217] The electrochemical cell 80 in this embodiment may be a single-compartment electrochemical cell (first electrolysis section). That is, the electrochemical cell 80 is not partitioned into an anode compartment and a cathode compartment by a separator such as an ion exchange membrane, but is composed of a single electrolysis compartment, in which both a cathode 81 and an anode 82 are provided and which is filled with an electrolytic solution 83. As shown in FIG. 13 , the cathode 81 and the anode 82 may be arranged in any manner as long as they are in contact with the electrolytic solution 83. In this embodiment, the second catalyst 85 is contained in the anode 82.

[0218] A voltage is applied between the cathode 81 and the anode 82 by a power source 89. When the voltage is applied, carbon dioxide supplied to the inside of the electrochemical cell 80 is reduced by the first catalyst at the cathode 81 to generate carbon monoxide. The generated carbon monoxide may diffuse into the electrolyte 83. Meanwhile, when the voltage is applied at the anode 82, a redox species (oxidation-reduction substance) formed by the electrolyte is converted from a reduced species (reduced product A) to an oxidized product (e.g., a redox mediator, oxide B). Then, a carbonyl compound is synthesized from carbon monoxide and a reaction substrate in the electrolyte 83 by the generated oxidized product and the second catalyst 85. When the carbonyl compound is synthesized, the oxidized product is converted to a reduced species. The converted reduced species may be converted back to an oxidized product at the anode 82. When the redox species is a halide salt, the reduced species is a halogen ion, and the oxidized product is a halogen.

[0219] 13 shows an example of a reaction in which the reaction substrate is methanol and the electrolyte is a bromide salt, although this is not a limitation. When the reaction substrate is methanol and the electrolyte is a bromide salt, bromide ions, which are the reducing species, are converted to bromine, which is the oxidant, at the anode 82. Then, in the presence of bromine and the second catalyst, carbon monoxide and methanol (methoxide ions) react to produce dimethyl carbonate (DMC).

[0220] The electrochemical cell 80 may be provided with a supply port 86 for supplying carbon dioxide, an electrolyte, and the like into the electrochemical cell 80. A supply channel (not shown) may be connected to the supply port 86. The supply channel is a line for supplying carbon dioxide, an electrolyte, and the like to the supply port 86, and may be formed of piping or the like. Other supply channels, connection channels, and discharge channels, which will be described later, may also be formed of piping or the like. The supply port 86 may supply an electrolyte containing carbon dioxide to the electrochemical cell 80, but the electrolyte and carbon dioxide may be supplied to the electrochemical cell 80 separately. The electrochemical cell 80 may also be provided with an outlet 87. The outlet 87 may be used to discharge carbonyl compounds and the like generated from carbon dioxide and reaction substrates.

[0221] In the third aspect of the present invention, the electrolyte concentration in the electrolytic solution contained in the electrochemical cell 80 is 0.3 M or less, and the current density flowing in the electrochemical cell 80 is 20 mA / cm ２ That's all. As described above, by setting both the electrolyte concentration and the current density within a predetermined range, it is possible to increase the selectivity when producing the target product with high productivity. In the electrical reaction of an electrochemical cell, increasing the current density improves the production rate, but does not increase the selectivity. As a result, subsequent steps such as separation and purification require additional man-hours, increasing production costs. In contrast, in the present invention, surprisingly, by setting the electrolyte concentration below a certain level, it is possible to increase the selectivity even when the current density is increased, thereby reducing production costs.

[0222] The current density is preferably 30 mA / cm ２ More preferably, 40 mA / cm ２ Furthermore, by setting the current density to a certain level or less, it becomes possible to control the oxidation-reduction potential of the catalyst within an appropriate range, and the selectivity of the target product can be improved, for example, at a current density of 100 mA / cm ２ Preferably 80 mA / cm or less ２ or less, more preferably 60 mA / cm ２ The electrolyte concentration is preferably 0.24 M or less, more preferably 0.14 M or less, from the viewpoint of increasing the selectivity. Furthermore, the electrolyte concentration is, for example, 0.02 M or more, preferably 0.05 M or more, more preferably 0.08 M or more, from the viewpoint of increasing the amount of target product produced. By making the electrolyte concentration equal to or greater than the above lower limit, it is possible to prevent the voltage applied to the electrochemical cell from increasing, and to suppress the power required to produce the target product.

[0223] The distance between the cathode 81 and the anode 82 in the electrochemical cell 80, i.e., the inter-electrode distance, is preferably a certain distance or less from the viewpoint of increasing electrode density at a low voltage and improving productivity. Specifically, it is preferably 50 mm or less, more preferably 45 mm or less, and even more preferably 40 mm or less. The inter-electrode distance is not particularly limited, but is preferably 5 mm or more, more preferably 10 mm or more, and even more preferably 15 mm or more. By setting the inter-electrode distance to a certain distance or more, electrical conduction between the cathode and the anode can be prevented, and the generation of carbon monoxide and the conversion of redox species to oxidants can be performed in different regions. Regarding the inter-electrode distance, it is preferable that the shortest distance between the cathode 81 and the anode 82 be within the above range.

[0224] The halogen concentration in the electrochemical cell 80 is preferably 4.5 mM or less, more preferably 4.0 mM or less, and more preferably 3.2 mM or less. By keeping the halogen concentration in the electrochemical cell 80 at a certain level or less, the generation of by-products caused by the halogen can be suppressed, preventing a decrease in the selectivity of the target product. Furthermore, suppressing the halogen concentration can prevent an increase in electrical resistance and therefore an increase in power consumption. The halogen concentration is the concentration of the halogen contained in the electrolytic solution 83. The halogen contained in the electrolytic solution 83 may be a halogen supplied in advance as a raw material to the electrolytic solution 83, or may be a halogen generated during the electrochemical reaction in the electrochemical cell 80.

[0225] As described above, it is preferable to use a halide salt for the electrolyte. However, when a halide salt is used, a halogen is generated as an oxidant at the anode 82. As the halogen concentration increases over time, the selectivity for the target product may decrease and power consumption may increase, as described above. However, by controlling the halogen concentration in the electrochemical cell 80 to a certain level or lower as described above, the decrease in selectivity for the target product can be prevented and power consumption can also be reduced. The presence of halogen in the electrochemical cell 80 allows the oxidation reaction of carbon monoxide and the reaction substrate to proceed appropriately. Therefore, from the viewpoint of ensuring the oxidation reaction to proceed appropriately, the halogen concentration should be set to a certain level or higher, preferably 0.1 mM or higher, more preferably 0.5 mM or higher, and even more preferably 1.0 mM or higher.

[0226] As will be described later, it is preferable to use a bromide salt as the halide salt, and the halogen contained in electrochemical cell 80 is also preferably bromine. Therefore, the bromine concentration in electrolyte solution 83 of electrochemical cell 80 is preferably 4.5 mM or less, more preferably 4.0 mM or less, and even more preferably 3.2 mM or less, and may be 0 mM or more, but is preferably 0.1 mM or more, more preferably 0.5 mM or more, and even more preferably 1.0 mM or more. The carbon dioxide concentration in electrolyte solution 83 in electrochemical cell 80 is not particularly limited, but is preferably 5 to 20 g / L, and more preferably 7 to 10 g / L.

[0227] Each component used in this embodiment will be described in more detail below. [Electrolyte] In this embodiment, the electrolyte includes a reaction substrate and an electrolyte. (Electrolyte) The electrolyte 83 preferably includes a redox species as the electrolyte. The electrolyte may be dissolved in the electrolyte. The electrolyte serving as the redox species may have a molecular or ionic size smaller than that of the reaction substrate, such as an alcohol-based compound described below, and may have redox activity. Specific examples of the electrolyte include halide salts, organic redox, and complex redox. Among these, halide salts are preferred from the viewpoint of improving selectivity and productivity. In this embodiment, the electrolyte 83 includes a redox species as the electrolyte, thereby generating an oxidant at the anode 82. The oxidant can then efficiently generate a carbonyl compound from carbon monoxide and the reaction substrate in the presence of the second catalyst 85. Details of the halide salts, organic redox, and complex redox are as described in the ninth embodiment.

[0228] Among the above, from the viewpoint of increasing the selectivity of carbonyl compounds, halide salts are preferred as the electrolyte, with chloride salts and bromides being more preferred, and bromides being even more preferred. Therefore, the electrolyte contains, as redox ions, halogen ions such as chloride ions and bromide ions, with bromide ions being particularly preferred. It is preferable that halogen ions such as chloride and bromide are generated as oxidants at the anode. The cation type of the halide salt is preferably any one of lithium, sodium, and potassium.

[0229] Specific examples of chloride salts (metal chloride salts) are as described in the ninth embodiment, and among these, sodium chloride is preferred from the viewpoint of easy availability. Specific examples of bromide salts (metal bromide salts) are as described in the ninth embodiment, and preferred examples include lithium bromide, potassium bromide, and sodium bromide. Among these, lithium bromide and sodium bromide are more preferred, and sodium bromide is even more preferred, from the viewpoint of increasing the selectivity for carbonyl compounds. The electrolyte may be used alone or in combination of two or more.

[0230] As described above, it is preferable to use a halide salt as the electrolyte, but when a halide salt is used, the electrolyte may be composed of the halide salt alone, or may contain an electrolyte other than the halide salt as long as the effects of the present invention are not impaired. The content of the halide salt in the electrolytic solution contained in electrochemical cell 80 is preferably 50% by mass or more and 100% by mass or less, more preferably 70% by mass or more and 100% by mass or less, and even more preferably 90% by mass or more and 100% by mass or less, based on the total electrolyte.

[0231] (Reaction Substrate) The reaction substrate is a compound that serves as a raw material for the carbonyl compound. The reaction substrate is changed depending on the type of target product to be produced. For example, when producing an organic carbonate, an organic oxalate, or both, an alcohol-based compound may be used as the reaction substrate. Furthermore, when producing a urea-based compound, an amine-based compound may be used as the reaction substrate. Of the above, it is preferable to use an alcohol-based compound as the reaction substrate. Details of the alcohol-based compound, the amine-based compound, and the carbonyl compound obtained therefrom are as described in the first embodiment above.

[0232] As in the first embodiment, the electrolytic solution may further contain a solvent for the electrolytic solution. The solvent for the electrolytic solution and the electrolytic solution when the solvent for the electrolytic solution is contained are as described above.

[0233] [Cathode] As described above, the cathode (first electrode) 81 is disposed inside the electrochemical cell 80 and includes a first catalyst 84. The cathode 81 is an electrode used when electrochemically synthesizing a reduced product such as carbon monoxide from carbon dioxide. The first catalyst is a reduction catalyst capable of reducing carbon dioxide to a reduced product such as carbon monoxide. The cathode 81 may have an electrode substrate (current collector). Details of the first catalyst and the cathode (first electrode) are as described in the first embodiment above, and therefore will not be described again.

[0234] [Anode] As described above, the anode 82 is an electrode disposed inside the electrochemical cell 80. The anode 82 may have an electrode substrate (current collector). Details of the electrode substrate (current collector) are the same as those of the cathode, and a description thereof will be omitted. The current collector of the anode 82 may be made of the same material as the current collector of the cathode, or may be made of a different material. In this embodiment, the anode 82 contains a second catalyst 85.

[0235] (Second Catalyst) The second catalyst used in the present invention is not particularly limited as long as it promotes the chemical reaction that synthesizes a carbonyl compound from carbon monoxide and a reaction substrate, but it may contain a metal element, details of which are as described in the first embodiment. In this embodiment, the second catalyst 85 may be contained in the anode by being supported on an electrode substrate. The second catalyst 85 may also be supported on the electrode substrate together with a catalyst additive or the like. The method for supporting the second catalyst, or the second catalyst and catalyst additive (catalyst composition) on the electrode substrate is not particularly limited, but is the same as the method for supporting the first catalyst on the electrode substrate, and therefore a description thereof will be omitted.

[0236] The cathode 81 and the anode 82 may be disposed so as to face each other as shown in Fig. 13. The first catalyst 84 may be disposed between the cathode 81 and the anode 82, and therefore the first catalyst 84 contained in the cathode 81 may be supported on at least the surface facing the anode 82. Similarly, the second catalyst 85 may be disposed between the cathode 81 and the anode 82, and therefore the second catalyst 85 contained in the anode 82 may be supported on the surface facing the cathode 81. By disposing the first and second catalysts 84, 85 as described above, a carbonate compound can be efficiently produced from carbon monoxide produced at the cathode 81 and an oxidant produced at the anode 82.

[0237] However, in this embodiment, the second catalyst 85 does not need to be contained in the anode 82, and may be contained in the electrolytic solution 83, or may be contained in both the anode 82 and the electrolytic solution 83. When the second catalyst 85 is contained in the electrolytic solution 83, it may be dissolved in the electrolytic solution 83, but generally it is sufficient that the second catalyst 85 is dispersed in the electrolytic solution 83 without being dissolved. When the second catalyst 85 is contained in the electrolytic solution 83, a stirring means or the like may be provided so that the second catalyst 85 can be dispersed in the electrolytic solution 83. When the second catalyst 85 is contained in the electrolytic solution 83, it is preferable to attach a filter to the outlet 87 or the supply port 86 to prevent the second catalyst 85 from being discharged to the outside of the electrochemical cell 80 together with the electrolytic solution 83.

[0238] The electrochemical reaction device 90 according to the thirteenth embodiment may produce carbonyl compounds by a so-called batch process. In the thirteenth embodiment, an electrochemical cell 80 is first prepared, for example, with a cathode 81 having a first catalyst 84 and an anode 82 having a second catalyst 85 disposed therein. Next, the electrochemical cell 80 is filled with an electrolyte solution 83 containing, for example, carbon dioxide. The electrolyte solution containing carbon dioxide may be supplied to the electrochemical cell 80. However, the electrolyte solution and carbon dioxide may be supplied separately to the electrochemical cell 80. For example, the electrolyte solution may be supplied first, and then carbon dioxide may be blown into the supplied electrolyte solution. Then, a voltage may be applied to the electrode 89 to carry out an electrochemical reaction. The voltage application is continued until a certain amount of carbonyl compounds is produced. The electrolyte solution 83 containing the carbonyl compounds may be removed from the outlet 87. After removing the electrolyte solution 83, the electrochemical cell 80 may be refilled with the electrolyte solution 83 containing carbon dioxide, and the electrochemical reaction may be carried out in the same manner. On the other hand, the extracted electrolytic solution containing the carbonyl compound may then be separated and purified as necessary using a separator, a distiller, or the like.

[0239] However, the production of a carbonyl compound does not have to be carried out in a batch system, and may be carried out in a flow system. Hereinafter, an example of producing a carbonyl compound in a flow system using an electrochemical reaction device 90A according to a fourteenth embodiment shown in FIG. 14 will be specifically described. In the following description, configurations that are not specifically described are the same as those in the thirteenth embodiment.

[0240] <Fourteenth Embodiment> An electrochemical reaction device 90A according to the fourteenth embodiment further includes a storage unit 95 in addition to the electrochemical cell 80 similar to that of the thirteenth embodiment. The electrochemical reaction device 90A also includes a supply channel 97 connecting the storage unit 95 and a supply port 86. The storage unit 95 is configured as a tank that stores an electrolytic solution 83 therein. The electrolytic solution 83 stored in the storage unit 95 is as described in the thirteenth embodiment and includes at least a reaction substrate and an electrolyte. The electrolytic solution 83 stored in the storage unit 95 further contains carbon dioxide. A carbon dioxide supply source (not shown), for example, is connected to the storage unit 95 via an inlet channel 92. The carbon dioxide supplied to the storage unit 95 via the inlet channel 92 may be blown into the electrolytic solution 83 stored in the storage unit 95 by bubbling or the like, thereby introducing carbon dioxide into the electrolytic solution 83. The carbon dioxide supply source is as described above.

[0241] The carbon dioxide-containing electrolytic solution 83 stored in the reservoir 95 is supplied from a supply port 86 to the interior of the electrochemical cell 80 via a supply channel 97. As in the thirteenth embodiment, the carbon dioxide contained in the electrolytic solution 83 supplied from the supply port 86 to the interior of the electrochemical cell 80 is converted into carbon monoxide and then into carbonyl compounds in the electrochemical cell 80. The carbonyl compound-containing electrolytic solution 83 is then preferably discharged from an outlet 87. By continuously supplying and discharging the electrolytic solution 83 in this manner, a convection flow F is formed so that the electrolytic solution 83 flows in one direction (from top to bottom in FIG. 14 ) through the electrochemical cell 80, thereby enabling continuous production of carbonyl compounds. The supply and discharge of the electrolytic solution 83 may be performed intermittently or continuously.

[0242] <Fifteenth embodiment> Next, a fifteenth embodiment of the present invention will be described. Fig. 15 shows an electrochemical reaction device 90B according to the fifteenth embodiment. The electrochemical reaction device 90B further includes a reaction section (first reaction section) 100 in addition to an electrochemical cell 80B and a storage section 95. The reaction section 100 constitutes a reaction chamber separate from the electrolysis chamber constituted by the electrochemical cell 80B.

[0243] In the thirteenth and fourteenth embodiments, the second catalyst 85 was contained within the electrochemical cell. However, in this embodiment, the second catalyst 85 is not contained within the electrochemical cell, but is contained within the reaction unit 100 (reaction chamber). That is, the electrochemical cell 80B may be the same as those of the thirteenth and fourteenth embodiments except that the second catalyst 85 is not contained. The reservoir 95 may also be the same as that of the fourteenth embodiment. Meanwhile, the reaction unit 100 may be filled with the second catalyst 85. The reaction unit 100 is also filled with the electrolytic solution 83. In the reaction unit 100, the second catalyst 85 may be, but is not limited to, a catalyst layer, which may be filled in the reaction unit 100 in a layered form. The catalyst layer may be filled on a support such as a tray or mesh within the reaction unit 100, but a support need not be provided. However, the second catalyst 85 does not need to form a catalyst layer in the reaction unit 100, and may be dispersed in the electrolytic solution 83 inside the reaction unit 100. When the second catalyst 85 is dispersed in the electrolytic solution 83 inside the reaction unit 100, it is preferable to attach filters to the reaction unit supply port 96 and the reaction unit outlet 98 described below to prevent the second catalyst 85 from being discharged from the reaction unit 100 to the outside together with the electrolytic solution 83. The reaction unit 100 has the reaction unit supply port 96 and the reaction unit outlet 98. Furthermore, the electrochemical reaction device 90B has a connection path 99 that connects the reaction unit supply port 96 and the outlet 87 of the electrochemical cell 80B.

[0244] With the above configuration, the electrochemical reaction device 90B is provided with an electrochemical cell 80B having a cathode 81 with a first catalyst 84 and an anode 82, and a reaction unit 100 having a second catalyst 85. An electrolytic solution 83 containing carbon dioxide flows from a supply port 86 of the electrochemical cell 80B through the electrochemical cell 80B toward a discharge port 87, and the electrolytic solution 83 discharged from the discharge port 87 passes through a connection path 99 and is supplied to the reaction unit 100 from a reaction unit supply port 96. The electrolytic solution 83 then passes through the reaction unit 100 and is discharged from a reaction unit discharge port 98.

[0245] In this embodiment, by flowing the electrolytic solution 83 as described above, the direction of convection F is such that the electrolytic solution 83 flows through the first electrochemical cell 80B and then through the reaction unit 100. At the cathode 81, the first catalyst 84 promotes the reduction of carbon dioxide, producing carbon monoxide. Meanwhile, at the anode 82, the electrolyte produces an oxidant (e.g., a halogen such as bromine, or an oxide B), which is an active intermediate species. The carbon monoxide and oxidant produced in the electrochemical cell 80B are supplied to the reaction unit 100 by convection F, along with the electrolytic solution 83. In the reaction unit 100, a carbonyl compound is produced from the carbon monoxide, oxidant, and reaction substrate by the action of the second catalyst 85. Furthermore, in the reaction unit 100, by-products such as hydrogen halide are also produced from the oxidant.

[0246] 15 shows an example of a reaction in which the reaction substrate is methanol and the electrolyte is a bromide salt, although this is not a limitation. When the reaction substrate is methanol and the electrolyte is a bromide salt, the anode 82 converts bromide ions, which are the reducing species, into bromine, which is the oxidant. Then, in the reaction section 100, dimethyl carbonate (DMC) is produced from carbon monoxide and methanol by the action of the second catalyst 85 and bromine.

[0247] In this embodiment, as in the thirteenth embodiment, by keeping the electrolyte concentration and current density contained in the electrochemical cell 80B within the above-mentioned predetermined ranges, carbon monoxide and an oxidant (oxide B) can be efficiently produced, thereby increasing the selectivity for producing the target product with high productivity. Note that the oxidants such as halogens produced in the electrochemical cell 80B are sent to the reaction section 100 without being consumed in the electrochemical cell 80B. Note that, in this embodiment, too, carbonyl compounds are produced in the electrochemical cell, and at that time, the halogens are converted to halogen ions inside the electrochemical cell, which reduces production efficiency. Therefore, it is preferable to keep the halogen concentration below a certain level as described above.

[0248] Next, an example using an electrochemical reaction device according to a sixteenth embodiment will be described. The sixteenth embodiment differs from the fifteenth embodiment in that an electrochemical cell 80C includes an isolation layer 101, and that first and second supply ports 86X and 86Y are provided as supply ports of the electrochemical cell 80C, and first and second discharge ports 87X and 87Y are provided as discharge ports.

[0249] The isolation layer 101 is disposed between the cathode 81 and the anode 82 and is provided to separate the region on the cathode 81 side (cathode chamber) from the region on the anode 82 side (anode chamber). The isolation layer 101 is also referred to as an isolation membrane. The isolation layer 101 preferably separates carbon monoxide generated on the cathode 81 side from the oxidant (oxide B) generated on the anode 82 side. The isolation layer 101 may be permeable to ions but not to reaction substrates, electrolyte solvents, carbon monoxide, or oxidants; specifically, an ion exchange membrane is preferred. The isolation layer 101 is permeable to ions but not to the electrolyte 83, etc.; therefore, in this embodiment, when a voltage is applied between the cathode 81 and the anode 82, an electrochemical reaction occurs between the cathode 81 and the anode 82.

[0250] Examples of the ion exchange membrane include a cation exchange membrane and an anion exchange membrane, but the cation exchange membrane is preferred from the viewpoint of ion conductivity and cost. The details of the cation exchange membrane and the anion exchange membrane are as described above.

[0251] The first supply port 86X and the first discharge port 87X are provided in the cathode chamber, and allow the supply and discharge of the electrolytic solution containing carbon dioxide to and from the cathode chamber, respectively. The second supply port 86Y and the second discharge port 87Y are provided in the anode chamber, and allow the supply and discharge of the electrolytic solution to and from the anode chamber, respectively. The electrolytic solution containing carbon dioxide is preferably supplied from a reservoir 95 via a supply path 97.

[0252] In this embodiment, with the above configuration, the electrolytic solution 83 containing carbon dioxide is supplied from the first supply port 86X. In the region on the cathode 81 side, the carbon dioxide is reduced to carbon monoxide, and the electrolytic solution 83 containing the reduced carbon monoxide is supplied to the reaction unit 100 via the connection path 99. The electrolytic solution 83 is also supplied to the region on the anode 82 side from the second supply port 86Y. The electrolyte contained in the electrolytic solution 83 is converted to an oxidant (e.g., a halogen such as bromine), which is an active intermediate species, and the electrolytic solution containing the oxidant is supplied to the reaction unit 100 via the connection path 99. In the reaction unit 100, a carbonyl compound is produced from the carbon monoxide and the reaction substrate by the action of the second catalyst 85 and the oxidant. In addition, by-products such as hydrogen halide are also produced from the oxidant.

[0253] In this embodiment, as in the thirteenth embodiment, by keeping the electrolyte concentration and current density in the electrochemical cell 80C within the above-described predetermined ranges, carbon monoxide and oxidants can be efficiently produced, thereby achieving high productivity and high selectivity for producing the target product. In this embodiment, it is preferable that the electrolyte concentration in at least the anode chamber of the electrochemical cell 80C be within the above-described ranges. However, it is preferable that the electrolyte concentrations in both the anode chamber and the cathode chamber be within the above-described ranges. Meanwhile, in this embodiment, oxidants such as halogens produced in the electrochemical cell 80C (anode chamber) are sent to the reaction section 100 without being consumed in the electrochemical cell 80C. Therefore, since the halogen concentration (or bromine concentration) in the anode chamber increases when a halide salt is used, it is not necessary to keep the halogen concentration (or bromine concentration) in the anode chamber below a certain level in this embodiment. However, as described below, in this embodiment, when a second catalyst is contained in the electrochemical cell (preferably the anode chamber, more preferably the anode), halogen is converted to halogen ions inside the electrochemical cell as carbonyl compounds are generated, so the halogen concentration may be set to a certain level or lower as described above. On the other hand, the halogen generated in the anode chamber is not substantially supplied to the cathode chamber due to the presence of the isolation layer 101. Therefore, the halogen concentration in the cathode chamber is substantially 0 mM. Note that "substantially 0 mM" means a concentration of 0 mM or close to 0 mM; for example, a concentration of approximately 0.1 mM or less can be considered to be substantially 0 mM.

[0254] Furthermore, the separator 101 does not allow carbon monoxide generated in the region on the cathode 81 side (cathode chamber) to pass through to the region on the anode 82 side (anode chamber), and does not allow oxidants (halogens such as bromine) generated on the anode 82 side to pass through to the region on the cathode 81 side. Therefore, on the cathode 81 side, the reaction is prevented from being inhibited by the oxidant, and by-products are prevented from being generated due to the oxidant. Similarly, on the anode 82 side, the reaction for generating the oxidant is prevented from being inhibited by carbon monoxide, and by-products are prevented from being generated. Therefore, the electrochemical reaction device 90C of this embodiment can generate carbonate compounds more efficiently. While this embodiment has shown an embodiment in which an electrolytic solution containing carbon dioxide is supplied to both the cathode chamber and the anode chamber, an electrolytic solution not containing carbon dioxide may be supplied to the anode chamber.

[0255] Although the electrochemical reaction devices according to the fourteenth to sixteenth embodiments have been described above as examples in which carbonyl compounds are produced by a flow system, these electrochemical reaction devices do not necessarily have to produce carbonyl compounds by a flow system, and may produce carbonyl compounds by a batch system. In this case, in the fourteenth embodiment, as described in the thirteenth embodiment, an electrolytic solution 83 containing carbon dioxide may be supplied from the reservoir 95 to the electrochemical cell 80, the supply of the electrolytic solution 83 may then be stopped, and an electrochemical reaction may be carried out. Then, after the electrochemical reaction is completed, the electrolytic solution 83 may be extracted from the electrochemical cell 80. Similarly, in the fifteenth and sixteenth embodiments, carbonyl compounds may be produced by a batch system.

[0256] Seventeenth Embodiment In the present invention, carbonyl compounds may be produced by a circulation system. When producing carbonyl compounds by a circulation system, the electrochemical reaction device may have a circulation mechanism that circulates the electrolytic solution discharged from the electrochemical cell and supplies it back to the electrochemical cell. Note that the electrolytic solution discharged from the electrochemical cell has a low carbon dioxide concentration because carbon dioxide is converted to carbonyl compounds in the electrochemical cell. Therefore, the electrochemical reaction device may have a carbon dioxide supply mechanism that blows carbon dioxide into the electrolytic solution discharged from the electrochemical cell to increase the carbon dioxide concentration in the electrolytic solution. An example of producing carbonyl compounds by a circulation system will be described below with reference to FIG. 17 using an electrochemical reaction device 90D according to the seventeenth embodiment. The following mainly focuses on differences from the electrochemical reaction device 90A according to the fourteenth embodiment. Note that in the electrochemical reaction device 90D described below, the supply channel 97, the discharge channel 91, and the reservoir 95 may constitute a circulation mechanism, and the reservoir 95 may constitute a carbon dioxide supply mechanism, as described below.

[0257] The electrochemical reaction device 90D according to the seventeenth embodiment includes a storage unit 95 storing an electrolytic solution 83 containing carbon dioxide, similar to the fourteenth to sixteenth embodiments. The storage unit 95 is provided with an inlet 92 for introducing carbon dioxide into the electrolytic solution 83, similar to the fourteenth embodiment. In addition to the inlet 92, an exhaust path 106 may be provided. The exhaust path 106 may have an inlet disposed inside the electrolytic solution 83 stored in the storage unit 95. When carbon dioxide is introduced into the electrolytic solution 83 through the inlet 92, excessive amounts of gas components containing carbon dioxide contained in the electrolytic solution 83 may escape from the electrolytic solution 83. The exhaust path 106 serves as a path for exhausting such gas components from the storage unit 95. By introducing carbon dioxide into the storage unit 95 and exhausting the gas components in the electrolytic solution 83, the carbon dioxide concentration in the electrolytic solution 83 can be increased.

[0258] In this embodiment, as in the fourteenth embodiment, the electrolytic solution 83 containing carbon dioxide is supplied from the reservoir 95 to the electrochemical cell 80D via the supply path 97, and a carbonyl compound is synthesized in the electrochemical cell 80D. The carbonyl compound-containing electrolytic solution 83 is then sent to the reservoir 95 via the discharge path 91. The carbon dioxide concentration of the electrolytic solution 83 sent to the reservoir 95 is increased as described above, and the electrolytic solution 83 is then supplied to the electrochemical cell 80D again via the supply path 97. In this manner, in this embodiment, by circulating the electrolytic solution 83 via the supply path 97, the discharge path 91, and the reservoir 95, the carbon dioxide contained in the electrolytic solution 83 can be efficiently converted to a carbonyl compound in the electrochemical cell 80D, thereby making the device suitable for mass production. The circulation of the electrolytic solution 83 may be performed repeatedly and continuously. Furthermore, in this embodiment, the carbon dioxide concentration of the circulating electrolytic solution 83 is increased in the reservoir 95, thereby further improving productivity.

[0259] Eighteenth Embodiment An electrochemical reactor according to another aspect applicable to the circulation system will be described below as an electrochemical reactor 90E according to an eighteenth embodiment. In the fifth embodiment, the second catalyst 85 was contained in the electrochemical cell 80E, and a carbonyl compound was synthesized in the electrochemical cell 80E. However, in the eighteenth embodiment, a reaction unit 100 separate from the electrochemical cell 80E is provided, as in the sixteenth embodiment. Similarly to the sixteenth embodiment, carbon monoxide produced at the cathode 81 and an oxidant (e.g., a halogen such as bromine) produced at the anode 82 may be supplied to the reaction unit 100 via a connection path 99, and a carbonyl compound may be produced in the reaction unit 100. Similarly to the seventeenth embodiment, the carbonyl compound-containing electrolyte 83 in the reaction unit 100 may be delivered to a reservoir 95 and then supplied to the electrochemical cell 80E via a supply path 97, thereby circulating the electrolyte 83, as in the seventeenth embodiment. Furthermore, carbon dioxide may be introduced into the storage section 95 to increase the carbon dioxide concentration in the electrolytic solution 83. The electrochemical cell 80E according to this embodiment is shown to have the isolation layer 101, similar to the electrochemical cell 80C according to the sixteenth embodiment, but may also have an aspect in which the isolation layer 101 is not provided in the electrochemical cell 80E, similar to the fifteenth embodiment.

[0260] Other Embodiments In the above description, as in the fifteenth, sixteenth, and eighteenth embodiments, when a reaction section containing a second catalyst is provided, the electrochemical cell does not contain the second catalyst. However, even when a reaction section containing a second catalyst is provided, the electrochemical cell may contain the second catalyst. In this case, the second catalyst is preferably contained in the anode as described in the thirteenth embodiment, but it may also be contained in the electrolytic solution (e.g., the anode chamber). Note that in the fifteenth, sixteenth, and eighteenth embodiments, when the electrochemical cell contains the second catalyst, a carbonyl compound is produced at the anode from carbon monoxide and a reaction substrate in the presence of the second catalyst and an oxidant. That is, a carbonyl compound is produced on the anode in addition to the reaction section.

[0261] In each embodiment of the third aspect described above, the electrochemical reaction device may include a measuring device for measuring the halogen concentration in the electrolyte. This is particularly effective in a circulating electrochemical reaction device, as in the seventeenth and eighteenth embodiments, because halogen reacted on the anode tends to remain without being used in the reaction with the carbonyl compound. A specific example of the measuring device is an absorbance measuring device that measures absorbance based on an absorption peak specific to halogen. Measuring the halogen concentration makes it easy to maintain the halogen concentration of the electrolyte in the electrochemical cell of the electrochemical reaction device at a certain level or lower, as described below. Since a bromide salt is preferably used as the electrolyte, as described above, the measuring device is preferably configured to measure the bromine concentration.

[0262] In particular, when measuring the halogen concentration (preferably, the bromine concentration) in a circulation-type electrochemical reactor such as the seventeenth and eighteenth embodiments, it is advisable to appropriately adjust the halogen concentration (preferably, the bromine concentration) in the electrochemical cell 80 so that it falls within the above-specified range in accordance with the measured halogen concentration. It is effective to measure the halogen concentration (preferably, the bromine concentration) in the electrochemical cell and adjust the halogen concentration (preferably, the bromine concentration) in accordance with the measurement results. By measuring the halogen concentration of the electrolyte in the electrochemical cell in the circulation chamber and adjusting the halogen concentration to fall within the above-specified range, the generation of by-products at the cathode due to halogens can be suppressed, and a decrease in the selectivity for the target product can be prevented. As shown in the eighteenth embodiment, in a two-compartment electrochemical cell provided with a separator, the halogen generated at the anode is also circulated to the cathode chamber as a result of the circulation of the electrolyte. Therefore, it is preferable to measure the halogen concentration in one or both of the anode chamber and the cathode chamber and adjust the halogen concentration in one or both of the anode chamber and the cathode chamber as described above. However, from the viewpoint of improving selectivity, it is more preferable to measure the halogen concentration in the cathode chamber and adjust the halogen concentration in the cathode chamber as described above.

[0263] The means for adjusting the halogen concentration is not particularly limited, but it is preferable to adjust it by promoting or suppressing the reaction of converting halogen to halogen ions or the reaction of converting halogen ions to halogen. Specifically, it is preferable to adjust the halogen concentration by providing a dehalogenation mechanism to reduce halogen to halogen ions. The dehalogenation mechanism may be achieved by adding an additive that reduces halogen to the electrolyte, or by electrically reducing the halogen. Examples of the reducing additive include sodium thiosulfate. In a two-compartment electrochemical cell provided with a separator as shown in the eighteenth embodiment, the additive that reduces halogen may be added to either the cathode chamber or the anode chamber, but is preferably added to the cathode chamber.

[0264] Furthermore, as in the sixteenth and eighteenth embodiments, when a separator layer is provided, carbon monoxide is generated in the cathode chamber, and oxidants such as halogens are generated in the anode chamber, and these are sent to a separate reaction section where a carbonyl compound is generated. However, even when a separator layer is provided, a reaction section may not be provided and the carbonyl compound may be generated in the electrochemical cell. In this case, the anode chamber may contain a second catalyst, preferably the anode. Also, a connecting path may be provided connecting the anode chamber and the cathode chamber. An electrolyte containing carbon dioxide is supplied to the cathode chamber, carbon monoxide is generated in the cathode chamber, and the electrolyte containing carbon monoxide is sent to the anode chamber via the connecting path. In the anode chamber, the electrolyte (e.g., halide salt) contained in the electrolytic solution is converted from a reduced species to an oxidant (e.g., a halogen) at the anode, and carbonyl compounds are generated in the presence of the second catalyst by carbon monoxide sent from the cathode chamber, reaction substrates contained in the electrolytic solution, and the oxidant derived from the electrolyte. The generated carbonyl compounds may be discharged from the electrochemical cell together with the electrolytic solution. Alternatively, the electrolytic solution discharged from the electrochemical cell may be circulated and resupplied to the cathode chamber, as shown in the eighteenth embodiment, to form a circulation system. In the case of a circulation system, the carbon dioxide concentration in the electrolytic solution may be increased in a reservoir or the like, as shown in the eighteenth embodiment, before being resupplied to the cathode chamber.

[0265] The configuration of the electrochemical cell described in the third aspect can also be applied to the other aspects. Specifically, in the first and second aspects, the configuration of the electrolyte inside the electrochemical cell, the distance between electrodes, the current density, and the like may be the same as those described in the third aspect. For example, in the first and second aspects, when the electrochemical cell is a single-compartment electrochemical cell not separated by a separator (ion exchange membrane), the electrolyte filled in the single-compartment electrochemical cell may have the configuration described in the third aspect (e.g., the thirteenth embodiment). In addition, when the electrochemical cell is separated into an anode chamber and a cathode chamber by a separator (ion exchange membrane), the configuration of the electrolyte in at least the anode chamber may have the configuration described in the third aspect, as described in the sixteenth embodiment.

[0266] The present invention will be explained in more detail by way of examples, but the present invention is not limited to these examples in any way.

[0267] The following Examples 1A to 4A correspond to the first aspect of the present invention. [Example 1A] (Preparation of catalyst) 38.0 mg of poly(4-vinylpyridine) (P4VP, weight average molecular weight 60,000) was dispersed in 50 ml of ethanol to obtain a P4VP dispersion. 20 mM Co(II)(NO ３ ) ２ 1.8 ml of the ethanol solution (6.5 mg, Co = 2 mg) and 54 mg of Ketjen Black (ECP600JD, manufactured by Lion Specialty Chemicals Co., Ltd.) were mixed with the P4VP dispersion and dried to obtain a powder (first catalyst raw material mixture). The cobalt content in the first catalyst raw material mixture was 2 mass %. The obtained powder was calcined in an argon atmosphere at 300°C for 3 hours to obtain a first catalyst. Also, 30 mg of PdCl ２ (manufactured by Aldrich Co.) and 30 mg of Ketchum Black were dispersed in 50 ml of ethanol, the solvent was removed using an evaporator, and the resulting mixture was dried at 150° C. for 30 minutes to obtain a second catalyst.

[0268] (Fabrication of Membrane-Electrode Assembly) 2 mg of the first catalyst and 10 μl of a 30 mass % dispersion of a catalyst additive (Nafion) were dispersed in isopropanol and applied to carbon paper. This was then dried by heating at 80°C for 1 hour to obtain a first electrode. Using carbon paper as the second electrode, the resulting first and second electrodes were laminated on an ion transport membrane made of Nafion (trade name), and heat-pressed at 59 MPa and 413 K to produce a membrane-electrode assembly having a first electrode 11 and a second electrode 12 on each side of a first ion exchange membrane 15.

[0269] (Fabrication of Carbon Dioxide Reduction Device) Next, a membrane-electrode assembly was set in the center of the cell to obtain an electrochemical cell consisting of a two-compartment diaphragm cell partitioned into a first electrolysis section 21 and a second electrolysis section (electrolysis reaction section) 22A by a first ion exchange membrane 15, as shown in Fig. 4. In the electrochemical cell, the first electrolysis section 21 and the electrolysis reaction section 22A were connected with a Teflon (registered trademark) tube to form a first connecting path 41A, thereby obtaining a carbon dioxide reduction device 10D according to the fourth embodiment.

[0270] (Synthesis of Organic Compounds) The electrolysis reaction section 22A was filled with methanol (reaction substrate) containing 0.2 mol / L of LiBr (manufactured by Aldrich) as an oxidation-reduction substance, and 1 g / L of the second catalyst was further mixed therein. ２ A pressure of 1 atm was passed through the electrolytic reaction unit 22A, and a current of 10 mA was passed between the first electrode and the second electrode at 273 K, and the product produced in the first electrolysis unit 21 was bubbled through the first connecting path 41A into the electrolysis reaction unit 22A. Analysis of the products in the first electrolysis unit 21 and the electrolysis reaction unit 22A by gas chromatography (GC) confirmed that carbon monoxide was produced in the first electrolysis unit 21 and dimethyl carbonate was produced in the electrolysis reaction unit 22A.

[0271] Example 2A First and second catalysts and a membrane-electrode assembly were prepared in the same manner as in Example 1A. Also, in the same manner as in Example 1A, the membrane-electrode assembly was set in the center of the cell, and an electrochemical cell consisting of a two-compartment diaphragm cell partitioned into a first electrolysis section 21 and a second electrolysis section 22 by a first ion exchange membrane 15 was obtained, as shown in FIG. 1 . In addition to the electrochemical cell, a reactor constituting a reaction section 31 was prepared. The first electrolysis section 21 and the reaction section 31, and the second electrolysis section 22 and the reaction section 31 were connected with Teflon (registered trademark) tubes to form a first connecting path 41 and a second connecting path 42, thereby obtaining a carbon dioxide reduction device 10 according to the first embodiment (see FIG. 1 ).

[0272] The second electrolysis section 21 was filled with an aqueous electrolyte solution in which 0.2 M LiCl was dissolved, and the reaction section 31 was filled with methanol in which 1 g / L of the second catalyst was dispersed. ２ A pressure of 1 atm was passed through the electrolytic solution, and a current of 10 mA was passed between the first electrode and the second electrode at 273 K, and the products produced in the first electrolysis unit 21 and the second electrolysis unit 22 were bubbled with gas into the reaction unit 31 via the first connecting path 41 and the second connecting path 42. When the products in the first electrolysis unit 21 and the first reaction unit 31 were analyzed by gas chromatography (GC), it was confirmed that carbon monoxide was produced in the first electrolysis unit 21 and dimethyl carbonate was produced in the reaction unit 31.

[0273] Example 3A First and second catalysts and a membrane-electrode assembly were prepared in the same manner as in Example 1A. A three-compartment diaphragm cell was used instead of a two-compartment diaphragm cell, and the first, second, and third chambers were designated as the first electrolysis section 21, the second electrolysis section 22, and the reaction section 31, respectively. The membrane-electrode assembly was inserted between the first and second chambers, and a Nafion membrane (second ion exchange membrane 25) was inserted between the second and third chambers. The first and third chambers, and the second and third chambers, were connected by Teflon (registered trademark) tubes, respectively, to form a first connecting path 41 and a second connecting path 42, thereby obtaining a carbon dioxide reduction device 10B (see FIG. 2) according to the second embodiment.

[0274] The second electrolysis section 22 was filled with an aqueous electrolyte solution containing 0.2 M LiCl dissolved therein, and the reaction section 31 was filled with methanol containing 1 g / L of the second catalyst dispersed therein.２ A pressure of 1 atm was passed through the electrolytic solution, and a current of 10 mA was passed between the first electrode and the second electrode at 273 K, and the products produced in the first electrolysis unit 21 and the second electrolysis unit 22 were bubbled into the reaction unit 31 via the first connecting path 41 and the second connecting path 42. When the products in the first electrolysis unit 21 and the reaction unit 31 were analyzed by gas chromatography (GC), it was confirmed that carbon monoxide was produced in the first electrolysis unit 21 and dimethyl carbonate was produced in the reaction unit 31.

[0275] [Example 4A] In Example 2A, 0.2M Na ２ CO ３ The carbon dioxide reduction device 10C according to the third embodiment (see FIG. 3) was fabricated by mixing the above. ２ A pressure of 1 atm was passed through the first electrolysis unit 21 and the second electrolysis unit 22, and a current of 10 mA was passed between the first electrode and the second electrode at 273 K, and the products generated in the first electrolysis unit 21 and the second electrolysis unit 22 were bubbled into the reaction unit 31 via the first connecting path 41 and the second connecting path 42. After a predetermined time had elapsed, the reaction liquid obtained in the reaction unit 31 was circulated to perform solid-liquid separation, and the obtained solid was introduced into the second electrolysis unit 22. Thereafter, CO was subsequently introduced into the first electrolysis unit 21. ２ A pressure of 1 atm was passed through the first electrode and the second electrode at 273 K, and a current of 10 mA was continuously passed between the first electrode and the second electrode. When the products in the first electrolysis section 21 and the first reaction section 31 were analyzed by gas chromatography (GC), it was confirmed that carbon monoxide was produced in the first electrolysis section 21 and dimethyl carbonate was produced in the reaction section 31.

[0276] The following Examples 1B to 30B are examples corresponding to the second aspect of the present invention. [Example 1B] (Preparation of second catalyst) 140 mg of PdCl ２ (Aldrich) was dissolved in 50 ml of an aqueous ammonium solution (26 wt %, Wako). 20 g of silica was dispersed in the resulting solution as a metal compound, and the solvent was then evaporated using an evaporator. The resulting solid was heat-treated at 200°C for 3 hours in an air atmosphere to obtain a second catalyst.

[0277] (Preparation of Electrochemical System) An electrode (anode) made of carbon paper (product name "Sigracet 29 BC", manufactured by SGL Carbon) and a reference electrode made of Ag / AgCl were placed in the anode chamber of a two-compartment diaphragm electrolysis cell, and an electrode (cathode) made of Pt was set in the cathode chamber, and the anode chamber and cathode chamber were separated by a Nafion ion exchange membrane. Then, 2 g of the second catalyst was filled in the anode chamber, and 30 ml of a methanol solution in which 0.2 M LiBr was dissolved as a redox species was filled in the anode chamber as an electrolyte. The cathode chamber was filled with 30 ml of a methanol solution of 0.2 M LiBr. CO (1 atm) was supplied to the anode chamber at room temperature (23°C), and a voltage of +1 V was applied between the electrodes to cause a reaction. The components of the reaction solution were then analyzed by gas chromatography, and the faradaic efficiency was calculated by comparing the results with the current value. The faradaic efficiencies were calculated for organic carbonates and organic oxalates. The results are shown in Table 1. In Table 1, the compound produced in the largest amount on a molar basis is listed as the target compound, and the faradaic efficiency of that target compound is also shown. The faradaic efficiencies shown are those measured 1 minute and 30 minutes after the start of CO supply.

[0278] [Examples 2B to 12B] In the production of the second catalyst, the same procedure as in Example 1 was carried out, except that the type of metal compound used as the support was changed as shown in Table 1. [Examples 13B to 15B] In the production of the second catalyst, PdCl was used as the metal precursor. ２ Instead of HAuCl ４The same procedure as in Example 1 was repeated, except that a second catalyst (manufactured by Aldrich) was used and the type of metal compound used as the support was changed as shown in Table 1. [Example 16B] The same procedure as in Example 1 was repeated, except that a reaction chamber was prepared separately from the electrochemical cell, 2 g of the second catalyst was filled in the reaction chamber instead of the anode chamber, the reaction chamber and the anode chamber were connected, and a diaphragm pump was used to circulate the electrolyte between the reaction chamber and the anode chamber. [Examples 17B and 18B] The same procedure as in Example 16 was repeated, except that the type of metal compound used as the support was changed as shown in Table 1 in the production of the second catalyst. [Example 19B] The same procedure as in Example 1 was repeated, except that a reaction chamber was prepared separately from the electrochemical cell, 2 g of the second catalyst and 30 ml of methanol were filled in the reaction chamber, LiCl was used instead of LiBr as the redox species, and the reaction chamber and the anode chamber were connected, and gas generated from the anode chamber was supplied to the reaction chamber. [Examples 20B and 21B] In the production of the second catalyst, the same procedures as in Example 16B were carried out except that the type of the metal compound serving as the support was changed as shown in Table 1.

[0279] [Example 22B] In the production of a second catalyst, the metal compounds shown in Table 1 were used, and the obtained second catalyst was further treated with H ２ [Example 23B] In the production of the second catalyst, the metal compounds listed in Table 1 were used, and the obtained second catalyst was further subjected to a reduction treatment using CO gas at room temperature (23°C), except that the same procedure was carried out as in Example 16B. [Example 24B] In the production of the second catalyst, the metal compounds listed in Table 1 were used, and the obtained second catalyst was further subjected to a reduction treatment using H ２ Example 25B was carried out in the same manner as in Example 16B, except that the reduction treatment was carried out using a gas. [Example 25B] In the production of the second catalyst, the metal compound (silica) shown in Table 1 was pretreated with lithium nitrate. The pretreatment was carried out using PdCl ２Before adding the metal compound to the solution, 5.3 g of lithium nitrate was added to 20 g of silica, mixed, and heated at 500°C. [Example 26B] The second catalyst was produced in the same manner as in Example 16B, except that the metal compound (silica) listed in Table 1 was pretreated with magnesium nitrate. The pretreatment was also carried out in the same manner as in Example 25B, except that magnesium nitrate was used instead of lithium nitrate. [Example 27B] The second catalyst was produced in the same manner as in Example 16B, except that the metal compound (silica) listed in Table 1 was pretreated with sodium nitrate. The pretreatment was also carried out in the same manner as in Example 25B, except that sodium nitrate was used instead of lithium nitrate. [Example 28B] The second catalyst was produced in the same manner as in Example 18B, except that the metal compound (alumina) listed in Table 1 was pretreated with lithium nitrate. The pretreatment was also carried out in the same manner as in Example 25B, except that the metal compound was changed. [Example 29B] The second catalyst was produced in the same manner as in Example 18B, except that the metal compound (alumina) listed in Table 1 was pretreated with magnesium nitrate. The pretreatment was carried out in the same manner as in Example 28B, except that magnesium nitrate was used instead of lithium nitrate. [Example 30B] In the production of a second catalyst, the metal compound (alumina) shown in Table 1 was pretreated with sodium nitrate, and the pretreatment was carried out in the same manner as in Example 18B. The pretreatment was carried out in the same manner as in Example 28B, except that sodium nitrate was used instead of lithium nitrate.

[0280] [Comparative Example 1B] The second catalyst was produced in the same manner as in Example 1B, except that no metal compound was added. [Comparative Example 2B] The second catalyst was produced in the same manner as in Example 1B, except that 20 g of Ketjen Black was used instead of 20 g of silica. [Comparative Example 3B] The second catalyst was produced in the same manner as in Example 1B, except that 20 g of Ketjen Black was used instead of 20 g of silica, and PdCl was used as the metal precursor. ２ Instead of HAuCl ４ The procedure of Example 1B was repeated except that Aldrich was used instead.

[0281] DMC stands for dimethyl carbonate. DMO stands for dimethyl oxalate.

[0282] In each example, in a system for producing carbonyl compounds from carbon monoxide using a redox species, a second catalyst for producing carbonyl compounds was used that contained a catalytically active species and a metal compound supporting the catalytically active species, thereby enabling the synthesis of carbonyl compounds with high selectivity. In contrast, in the comparative examples, the second catalyst did not contain a support, or a support other than a metal compound was used, and therefore the carbonyl compounds could not be synthesized with high selectivity.

[0283] The following Examples 1C to 11C are examples corresponding to the third aspect of the present invention. [Example 1C] (Catalyst Preparation) A first catalyst was obtained in the same manner as in Example 1A. 60 mg of Pd(NO3)2.2H2O (manufactured by Aldrich Co.) and 60 mg of Ketchum Black (product name "EC-300J" (Fuel Cell Store)), BET specific surface area 800 m ２The first catalyst (Pd—C) was dispersed in 50 ml of ion-exchanged water, dried, and then heated at 300°C for 1 hour to obtain a second catalyst (Pd—C). (Electrode Preparation) 24 mg of the first catalyst was mixed with 120 μL of a 10% by mass dispersion of a catalyst additive (Nafion), dispersed in 4800 μL of acetone, sprayed onto carbon paper, and dried to obtain a cathode. 24 mg of the second catalyst was mixed with 120 μL of a 10% by mass dispersion of a catalyst additive (PTFE), dispersed in 4800 μL of acetone, sprayed onto carbon paper, and dried to obtain an anode. (Electrolyte) A 0.1 M NaBr methanol solution was prepared as the electrolyte. (Cell Fabrication) A 4 mm thick frame (made of ABS) with tube holes (supply and discharge ports) was prepared, and the cathode and anode were sandwiched facing each other between 0.5 mm thick Teflon (registered trademark) sheets (packing) cut to the same size, and sealed with epoxy resin to prepare the electrochemical cell shown in FIG. 13 . In the electrochemical cell, the distance between the electrodes was 35 mm. (Electrochemical Cell Evaluation) 50 ml of the above electrolyte solution was placed in a solvent bottle, and carbon dioxide was bubbled through at 50 mL / min for 15 minutes to prepare an electrolyte solution with 7.9 g / L of dissolved carbon dioxide. A current of 20 mA / cm was applied between the cathode and anode. ２ A current of 1000 kJ / cm was passed through the electrolyte to cause an electrochemical reaction. The resulting electrolyte was analyzed by gas chromatography to obtain the selectivity of the target compound.

[0284] (Examples 2C to 6C, Comparative Example 1C) The same procedure as in Example 1 was carried out, except that the current density and electrolyte concentration were set as shown in Table 1. (Comparative Example 2C) The same procedure as in Example 1C was carried out, except that the electrolyte was changed from NaBr to LiBr and the electrolyte concentration was set as shown in Table 2. (Examples 7C, 8C, Comparative Example 3C) The same procedure as in Example 1C was carried out, except that the electrolytic solution was changed to an ethanol solution of LiBr and the current density and electrolyte concentration were set as shown in Table 2. (Examples 9C to 11C) The same procedure as in Example 3C was carried out, except that bromine was mixed into the NaBr methanol solution to achieve the concentration shown in Table 3.

[0285]

[0286] In the above Examples 1C to 11C and Comparative Examples 1A to 1C, the selectivity was evaluated according to the following criteria: [Criteria] A: Selectivity of 40% or more B: Selectivity of 30 to 39% C: Selectivity of less than 30%

[0287] The results of Examples 1C to 8C and Comparative Examples 1A to 1C are shown in Table 2. As shown in Table 2, the electrolyte concentration was set to 0.3 M or less and the current density was set to 20 mA / cm ２ In each of the above Examples, carbonyl compounds were produced with high selectivity. In contrast, in Comparative Examples 1C to 3C, in which the electrolyte concentration was higher than 0.3 M, carbonyl compounds could not be produced with high selectivity.

[0288]

[0289] The results of Examples 2C, 9C to 11C, in which all conditions except the bromine concentration were the same, are shown in Table 3. As shown in Table 3, when the electrolyte concentration was 0.3 M or less and the current density was 20 mA / cm ２ In each of the above examples, it can be seen that the selectivity for obtaining the target product can be increased by keeping the halogen concentration (bromine concentration) at a certain value or less.

[0290] DESCRIPTION OF SYMBOLS 10, 10B to 10H Carbon dioxide reduction device (electrochemical reaction device) 11, 11B, 62, 81 First electrode (cathode) 12, 12B, 61, 82 Second electrode (anode) 15 First ion exchange membrane 19, 69, 89 Power source 21, 21A, 21B First electrolysis section 22 Second electrolysis section 22A Electrolysis reaction section (second electrolysis section) 25 Second ion exchange membrane 31, 63X, 100 Reaction section 32, 32A Purification device 36 Supply channel (supply mechanism) 41, 41A, 41B First connecting channel 42 Second connecting channel 45 Separation mechanism 60, 80, 80A to 80E Electrochemical cell 60X Anode chamber (second electrolysis section) 60Y Cathode chamber (first electrolysis section) 63, 63A, 93 Electrolyte 63B Reaction liquid 65, 84 First catalyst 64, 85 Second catalyst 70, 70A to 70C Electrochemical system (electrochemical reaction device) 71 Reaction chamber (first reaction section) 75, 76 Separation membrane 90, 90A to 90E Electrochemical reaction device 95 Reservoir section 101 Separation layer (separation membrane) F Convection

Claims

1. The device comprises a first electrode, a second electrode, a first electrolytic section having the first electrode, a second electrolytic section having the second electrode, a first ion exchange membrane located between the first electrode and the second electrode, a reaction section, a first connecting path connecting the first electrolytic section and the reaction section, and a second connecting path connecting the second electrolytic section and the reaction section. The second electrolytic section contains a redox substance, and the reaction section contains at least one reaction substrate selected from the group consisting of alcohol compounds and amine compounds. The first electrode includes a first catalyst that promotes the reaction of reducing carbon dioxide to a first reduced product, The second electrode oxidizes the reduced product A of the redox substance to oxide B, The first connecting path allows the first reduced product generated in the first electrolytic section to flow out to the reaction section. The second connecting passage allows the oxide B to flow out to the reaction section. An electrochemical reactor having a second catalyst that causes the reaction unit to produce at least one organic substance selected from the group consisting of carbonate compounds, oxalate compounds, isocyanate compounds, and urea compounds using the first reduced product and the oxide B.

2. The electrochemical reaction apparatus according to claim 1, wherein the oxidation-reduction substance is at least one of a halogenated salt or a hydrogen halide.

3. The electrochemical reaction apparatus according to claim 1, wherein the oxidation-reduction substance is a metal halide salt.

4. The electrochemical reaction apparatus according to claim 1, wherein the oxidation-reduction substance is at least one selected from the group consisting of lithium chloride, lithium bromide, sodium chloride, sodium bromide, potassium chloride, and potassium bromide.

5. The electrochemical reaction apparatus according to claim 1, comprising an apparatus for purifying by-products removed from the earlier reaction section.

6. The electrochemical reaction apparatus according to claim 5, wherein the purifying apparatus is either a distillation apparatus or a solid-liquid separation apparatus.

7. The electrochemical reaction apparatus according to claim 1, further comprising a supply mechanism for supplying by-products generated in the reaction section to the second electrolytic section.

8. The electrochemical reaction apparatus according to claim 7, wherein the supply mechanism supplies at least one of a metal halide salt or a hydrogen halide as the by-product.

9. The electrochemical reaction apparatus according to claim 1, further comprising a second ion exchange membrane separating the second electrolytic unit and the reaction unit.

10. The electrochemical reaction apparatus according to claim 1, wherein the first reduced product contains carbon monoxide.

11. The electrochemical reaction apparatus according to claim 10, wherein the first connecting circuit is equipped with a separation mechanism for separating carbon monoxide and carbon dioxide.

12. The electrochemical reaction apparatus according to claim 1, wherein the first connecting passage allows the first reducing agent to flow out to the reaction section as a gas, and the second connecting passage allows the oxide B to flow out to the reaction section as a gas.

13. The electrochemical reaction apparatus according to claim 1, wherein the second connecting path allows the halogen, which is oxide B, to flow out to the reaction section as a gas.

14. The electrochemical reaction apparatus according to claim 1, wherein the second catalyst comprises a catalytic active species containing at least one metal element selected from the group consisting of elements from Group 8 to Group 11, and a metal compound on which the catalytic active species is supported.

15. The electrochemical reaction apparatus according to claim 1, wherein the second electrode does not contain a catalyst.

16. The electrochemical reaction apparatus according to claim 1, wherein the carbon dioxide is obtained from the exhaust gas of a power plant, steel mill, cement factory, or waste incinerator.

17. The electrochemical reaction apparatus according to claim 1, wherein the reaction substrate is supplied to the reaction section and convection is formed so that it is discharged from the reaction section together with the organic matter generated in the reaction section.

18. A method for producing organic matter using an electrochemical reaction apparatus according to any one of claims 1 to 17, In the first electrode, carbon dioxide is reduced to a first reduced product, In the second electrode, the reduced product A of the redox substance is oxidized to oxide B, The first reduced product generated at the first electrode is allowed to flow out to the reaction section via the first connecting path. The oxide B is allowed to flow out to the reaction section via the second connecting passage, and A method for producing an organic substance, wherein the reaction unit generates the organic substance using the first reduced product and the oxide B.

19. A method for producing a carbonyl compound, comprising reducing carbon dioxide to carbon monoxide and electrochemically synthesizing at least one carbonyl compound selected from the group consisting of organic carbonates and organic oxalates from the carbon monoxide obtained by reduction, using an electrochemical reactor according to any one of claims 1 to 17.