Electrochemical device and method for producing organic substance

Abstract

An electrochemical device 10 electrochemically synthesizes a carbonyl compound, and 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 electrolysis unit 21 has a first redox species, the reaction unit 31 has a second redox species, and the first redox species has a standard oxidation-reduction potential more positive than that of the second redox species.

Description

Electrochemical device and method for producing organic material

[0001] The present invention relates to an electrochemical device capable of electrochemically synthesizing a carbonyl compound from carbon monoxide, and a method for producing a carbonyl compound using the electrochemical device.

[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 and carbon monoxide obtained by reducing carbon dioxide, with the aim of curbing global warming and replacing fossil fuels.

[0003] For example, a conventional electrochemical cell has been disclosed that includes 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 that separates the cathode chamber from the anode chamber, and a connecting path that connects the cathode chamber to the anode chamber. In such an electrochemical cell, carbon dioxide is reduced to carbon monoxide at the second electrode, and the generated carbon monoxide is discharged into the anode chamber via the connecting path, where valuable materials such as carbonyl compounds are produced from the carbon monoxide and the reaction substrate.

[0004] Various improvements have been made to electrochemical cells for producing carbonyl compounds, and for example, Patent Document 1 discloses that the electrolyte filled in the anode chamber contains a redox species, a catalyst, and a reaction substrate such as methanol, which is a raw material for the carbonyl compound. Patent Document 1 shows that the above configuration enables electrochemical synthesis of carbonyl compounds with high selectivity.

[0005] International Publication No. 2023 / 038091

[0006] However, in electrochemical cells for synthesizing carbonyl compounds, catalyst degradation in the anode chamber can occur due to overvoltage. Furthermore, containing a reaction substrate such as methanol in the anode chamber can cause problems such as deformation of the ion exchange membrane due to the reaction substrate, elution of the cathode binder, and deposition of cathode salt in the anode electrolyte. Therefore, the present inventors have attempted to provide a reaction section for synthesizing carbonyl compounds separate from the electrochemical cell. While providing a separate reaction section can prevent the above problems, further improvement of the reaction efficiency is required for practical application.

[0007] Therefore, an object of the present invention is to provide an electrochemical device that has a reaction section separate from an electrochemical cell and that can synthesize carbonyl compounds with high selectivity while utilizing electrochemical reactions, even if carbonyl compounds are produced in the reaction section.

[0008] The present invention provides the following [1] to [9]: [1] An electrochemical device for electrochemically synthesizing at least one carbonyl compound selected from the group consisting of organic carbonates and organic oxalates from carbon monoxide, 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 electrolysis unit contains a first redox species, the reaction unit contains a second redox species, and the standard redox potential of the first redox species is more positive than the standard redox potential of the second redox species. [2] The electrochemical device according to [1] above, wherein an oxide of the first redox species is in a gaseous state and is supplied to the reaction unit through the first connecting path, and wherein liquid-phase reactions occur in both the first electrolysis unit and the reaction unit. [3] The electrochemical device according to [1] above or [2] above, wherein the first electrolysis unit contains an aqueous electrolyte. [4] The electrochemical device according to any one of [1] to [3] above, wherein the first redox species is at least one selected from the group consisting of fluoride, bromide, and chloride. [5] The electrochemical device according to any one of [1] to [4] above, wherein the second redox species is at least one selected from the group consisting of bromide, chloride, metal complex, and organic redox species. [6] The electrochemical device according to any one of [1] to [5] above, comprising a second electrolysis section having the second electrode and a second connecting path connecting the second electrolysis section to a reaction section, the second connecting path supplying carbon monoxide generated in the second electrolysis section to the reaction section. [7] The electrochemical device according to any one of [1] to [6] above, wherein the reaction section contains a reactant. [8] The electrochemical device according to [7] above, wherein the reactant is an alcohol-based compound. [9] A method for producing an organic substance using the electrochemical device according to any one of [1] to [8] above, comprising: oxidizing a reduced product of the first redox species to an oxide at the first electrode; supplying the oxide to the reaction section via the first connecting path; oxidizing the second redox species with the oxide at the reaction section; and producing the carbonyl compound from carbon monoxide and the oxide of the second redox species.

[0009] According to the present invention, even if a reaction section is provided separately from an electrochemical cell and a carbonyl compound is produced in the reaction section, the carbonyl compound can be synthesized with high selectivity while utilizing an electrochemical reaction.

[0010] 1 is a schematic diagram showing an electrochemical device according to a first embodiment, a schematic diagram showing an electrochemical device according to a second embodiment, and a schematic diagram showing an electrochemical device according to a third embodiment.

[0011] The electrochemical device and the method for producing a carbonyl compound using the electrochemical device of the present invention will be described below with reference to the drawings. In the following description, elements having the same configuration are designated by the same reference numerals.

[0012] 1 shows an electrochemical device 10 according to a first embodiment of the present invention. The electrochemical device 10 is an apparatus for electrochemically synthesizing a carbonyl compound from carbon monoxide. The electrochemical device 10 includes 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 connecting path 41.

[0013] (First Electrolysis Unit) The first electrode 11 is an anode and is disposed in a first electrolysis unit 21 that constitutes an anode chamber. The first electrolysis unit 21 is filled with an electrolytic solution (also referred to as a first electrolytic solution 21A). The first electrolytic solution 21A may fill the entire anode chamber, or may fill only a portion of the anode chamber as long as the first electrode 11 is in contact with the electrolytic solution, with a space above the anode chamber that is not filled with the electrolytic solution. The first electrolysis unit 21 contains a first redox species. The first electrode 11 oxidizes a reduction product A1 of the first redox species to an oxide B1, as described below.

[0014] In this embodiment, the first electrolytic solution 21A is an aqueous electrolyte solution. The aqueous electrolyte solution uses water as a solvent and contains a first redox species and water. The first redox species is preferably dissolved in water in the aqueous electrolyte solution to form an electrolyte. In this embodiment, using an aqueous electrolyte solution as the first electrolytic solution 21A can prevent the first electrode 11, the ion exchange membrane 15 described below, and the like from being deteriorated by organic compounds. In addition, in this embodiment, the first electrolytic unit 21 is filled with an electrolyte solution, and a liquid-phase reaction occurs in which the first redox species is oxidized in the electrolyte solution. Therefore, as described below, an oxide B1 of the first redox species that becomes a gas easily escapes from the first electrolytic solution 21A and is easily supplied to the reaction unit 31.

[0015] The first redox species is preferably one capable of generating halogen ions in the first electrolytic solution 21A, and specific examples include halides such as fluoride, chloride, and bromide. Examples of halides include halide salts and hydrogen halides. While a combination of halide salts and hydrogen halides may be used, it is preferable to use at least a halide salt. By using a halide salt, the first electrolytic unit 21 can easily generate a halogen, which is the oxide B1. Examples of halogens that can be generated include fluorine, chlorine, and bromine.

[0016] Examples of metal halide salts include metal halide salts, and among these, alkali metal halide salts are preferred, such as lithium halide salts, sodium halide salts, potassium halide salts, and cesium halide salts. Ammonium halides such as ammonium chloride and ammonium bromide are also included. Specific examples of halide salts include metal fluoride salts such as lithium fluoride, potassium fluoride, sodium fluoride, potassium fluoride, and cesium fluoride; metal chloride salts such as lithium chloride, potassium chloride, sodium chloride, potassium chloride, and cesium chloride; and metal bromide salts such as lithium bromide, potassium bromide, sodium bromide, potassium bromide, and cesium bromide. Among these, from the viewpoint of increasing the selectivity of the target product, lithium fluoride, lithium chloride, lithium bromide, lithium bromide, sodium fluoride, sodium chloride, sodium bromide, potassium fluoride, potassium chloride, and potassium bromide are more preferred, and among these, potassium fluoride, sodium chloride, and sodium bromide are even more preferred. Examples of hydrogen halides include hydrogen fluoride, hydrogen chloride, and hydrogen bromide. From the viewpoint of increasing the standard oxidation-reduction potential, the first redox species is preferably either a fluoride or a chloride, and more preferably a fluoride. Furthermore, as the first redox species, a species other than a halide can be used as long as its oxide becomes a gas, such as methyl nitrate.

[0017] The standard redox potential of the first redox species is more positive than the standard redox potential of the second redox species described below. The difference between the standard redox potential of the first redox species and the standard redox potential of the second redox species described below is not particularly limited, but by making it a certain value or greater, the second redox species is more likely to be oxidized by the oxide B1 of the first redox species in the reaction section 31 described below. The difference between the standard redox potential of the first redox species and the standard redox potential of the second redox species described below is preferably 0.1 V or greater, more preferably 0.2 V or greater, and even more preferably 0.3 V or greater. The difference in standard redox potential is not particularly limited, and may be, for example, 3 V or less, or 2.5 V or less in practice.

[0018] The first redox species has a high standard redox potential, which makes it easier for the oxide B1 of the first redox species to oxidize the second redox species in the reaction section 31. Furthermore, the options for the second redox species are broadened, allowing various compounds to be used as the second redox species. On the other hand, by setting the standard redox potential to a certain level or lower, the first redox species is more easily oxidized in the first electrolysis section 21. From the above perspectives, the standard redox potential of the first redox species is preferably 0.5 to 3 V, more preferably 0.5 to 2 V. The standard redox potential is based on the standard hydrogen electrode (SHE). The standard redox potential of the first redox species is the potential when the activity of the chemical species involved in the reduction reaction when the oxide B1 is reduced to the reduced product A1 is 1 and in equilibrium. The standard redox potential of the second redox species is similarly defined for the reduction reaction when the oxide B2 is reduced to the reduced product A2.

[0019] In the first electrolysis unit 21, the concentration of the first redox species in the first electrolytic solution 21A is not particularly limited, but is, for example, 0.1 to 10 M, preferably 0.3 to 8 M, and more preferably 0.6 to 6 M. The first redox species may be used singly or in combination of two or more. When two or more species are used in combination, it is preferable that the standard redox potentials of all the first redox species be more positive than the standard redox potential of the second redox species described below. The temperature in the first electrolysis unit 21 is not particularly limited, but may be a temperature at which the oxide B1 of the first redox species produced becomes gaseous. The temperature in the first electrolysis unit 21 may be, for example, approximately 0 to 95°C. However, when bromide is used as the first redox species, the temperature is preferably 30°C or higher, more preferably 50°C or higher, so that the bromine oxide B1 can be easily supplied to the reaction unit 31 in a gaseous state.

[0020] The first electrolytic solution 21A may be water to which a first redox species has been added, but may also contain water and a component other than the first redox species (e.g., an electrolyte other than the first redox species) as appropriate. Note that the components (water, first redox species, etc.) constituting the first electrolytic solution 21A may be supplied to the first electrolytic unit 21 in any manner as long as they are introduced into the first electrolytic unit 21. For example, they may be introduced through an inlet (not shown) of the first electrolytic unit 21. Furthermore, the first electrolytic solution 21A may be partially or completely replaced as the reaction in the first electrolytic unit 21 progresses.

[0021] The first electrolysis unit 21 is connected to the reaction unit 31 by a first connecting path 41. The first redox species oxide B1 produced in the first electrolysis unit 21 is supplied to the reaction unit 31 via the first connecting path 41. The first connecting path 41 is a conduit or the like connecting the first electrolysis unit 21 and the reaction unit 31, and may be provided with a flow rate adjustment mechanism or the like to adjust the flow rate. The first connecting path 41 may be provided with a check valve or the like so that gas is supplied from the first electrolysis unit 21 to the reaction unit 31, while gas is not supplied from the reaction unit 31 to the first electrolysis unit 21. The first redox species oxide B1 may be supplied, for example, by bubbling into the reaction liquid of the reaction unit 31, which will be described later.

[0022] (Second Electrolysis Section) The electrochemical device 10 includes an electrochemical cell 14, which includes a first electrolysis section 21 that constitutes the anode chamber described above and a second electrolysis section 22 that constitutes the cathode chamber. The second electrode 12 is a cathode and is preferably disposed in the second electrolysis section 22 that constitutes the cathode chamber. The second electrolysis section 22 is a region in which introduced carbon dioxide is electrochemically reduced. The second electrode 12 includes a second catalyst (carbon dioxide reduction catalyst) that promotes a reduction reaction that reduces carbon dioxide to carbon monoxide. Details of the second catalyst and the second electrode 12 will be described later. Furthermore, the electrochemical cell 14 may appropriately include a reference electrode disposed in the first electrolysis section 21, the second electrolysis section 22, or the like.

[0023] The second electrolysis unit 22 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 an optional 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 second electrolysis unit 22 continuously or intermittently. Carbon dioxide is preferably supplied to the second electrolysis unit 22 as carbon dioxide alone, but may also be supplied to the second electrolysis unit 22 using an inert gas, such as helium, as a carrier gas. The carbon dioxide supply source is not particularly limited, and may be a gas cylinder or the like. 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.

[0024] In this embodiment, the second electrolysis unit 22 is filled with an electrolytic solution (hereinafter also referred to as the second electrolytic solution 22A). The second electrolytic solution 22A is preferably an aqueous electrolyte solution. In the second electrolytic unit 22, carbon dioxide is supplied to the second electrolytic solution 22A, and the carbon dioxide in the electrolytic solution 22A is reduced at the second electrode 12. The aqueous electrolyte solution used is preferably one in which an electrolyte is dissolved in water. The electrolyte is not particularly limited, but may be appropriately selected from the compounds listed in the first redox species, and preferably a halide is used. The halide is preferably a metal halide salt. In this embodiment, using an aqueous electrolyte solution as the second electrolytic solution 22A can prevent the second electrode 12, the ion exchange membrane 15 described below, and the like from being deteriorated by organic compounds.

[0025] The electrolyte used in the second electrolysis unit 22 may be the same as the first redox species used in the first electrolysis unit 21. Therefore, when fluoride is used in the first electrolysis unit 21, fluoride may also be used in the second electrolysis unit 22. When chloride is used in the first electrolysis unit 21, chloride may also be used in the second electrolysis unit 22. Furthermore, when bromide is used in the first electrolysis unit 21, bromide may also be used in the second electrolysis unit 22. Of course, the electrolyte used in the second electrolysis unit 22 may be different from the first redox species used in the first electrolysis unit 21. The electrolyte used in the second electrolysis unit 22 is more preferably lithium fluoride, lithium chloride, lithium bromide, sodium fluoride, sodium chloride, sodium bromide, potassium fluoride, potassium chloride, or potassium bromide, and among these, potassium fluoride, sodium chloride, and sodium bromide are even more preferable. The electrolyte used in the second electrolysis unit 22 may be one type alone or two or more types may be used in combination. In the second electrolysis unit 22, the concentration of the electrolyte in the electrolytic solution is not particularly limited, but is, for example, 0.1 to 10 M, preferably 0.3 to 8 M, and more preferably 0.6 to 5 M. The temperature in the second electrolysis unit 22 is not particularly limited, but may be the same as that of the first electrolysis unit 21, for example, about 0 to 95°C. However, when bromide is used as the first redox species, the temperature is preferably 30°C or higher, and more preferably 50°C or higher.

[0026] The second electrolysis unit 22 is connected to the reaction unit 31 by a second connecting path 42, and carbon monoxide generated in the second electrolysis unit 22 is supplied to the reaction unit 31 via the second connecting path 42, as described below. Carbon monoxide may be supplied as a gas to the reaction unit 31 through the second connecting path 42. That is, the electrochemical device 10 is preferably a gas-phase supply type device in which carbon monoxide and the first redox species oxide B1 are both supplied as gas from the electrochemical cell 14 to the reaction unit 31. The second connecting path 42 is a conduit or the like connecting the second electrolysis unit 22 and the reaction unit 31, and may be provided with a flow rate adjustment mechanism or the like to adjust the flow rate. Furthermore, the second connecting path 42 may be provided with a check valve or the like, so that gas is supplied from the second electrolysis unit 22 to the reaction unit 31, but gas is not supplied from the reaction unit 31 to the second electrolysis unit 22. Carbon monoxide may be supplied, for example, by bubbling into the reaction solution in the reaction unit 31. Furthermore, carbon monoxide may be supplied to the reaction section 31 together with carbon dioxide that has not reacted in the second electrolysis section 22 .

[0027] (Ion Exchange Membrane) The electrochemical cell 14 may further include an ion exchange membrane 15. The ion exchange membrane 15 is located between the second electrode 12 and the first electrode 11, and separates a first electrolysis section 21 (anode chamber) from a second electrolysis section 22 (cathode chamber). The first electrode 11 and the second electrode 12 may be disposed on either side of the ion exchange membrane 15 and joined together to form a membrane-electrode assembly, or the first electrode 11 and the second electrode 12 may be disposed at a position separated from the ion exchange membrane 15 without being joined to the ion exchange membrane 15, as shown in FIG. 1 .

[0028] A solid membrane is used as the ion exchange membrane 15, and examples thereof include 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. When the ion exchange membrane 15 is a cation exchange membrane, cations such as protons permeate from the first electrolysis unit 21 side to the second electrolysis unit 22 side, and the reaction of formula (ii-1) described below can easily occur on the second electrolysis unit 22 side. When the ion exchange membrane 15 is an anion exchange membrane, anions such as hydroxide ions permeate from the second electrolysis unit 22 side to the first electrolysis unit 21 side, and the reaction of formula (ii-2) described below can easily occur on the second electrolysis unit 22 side.

[0029] 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.

[0030] 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).

[0031] 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. By applying the voltage, the first redox species is oxidized from a reduction product A1 to an oxide B1 at the first electrode 11, as shown in formula (i). The oxide B1 is typically a gas such as a halogen, and the oxide B1 obtained by oxidation in the first electrolysis unit 21 is supplied to the reaction unit 31 via the first connection path 41, as will be described later. aX ｒｅｄ → bX ｏｘ + ce － (i) In formula (i), X ｒｅｄ is the reduced product A1 of the first redox species, and X ｒｅｄ is the oxide B1 of the first redox species. a, b, and c are coefficients appropriately selected depending on the type of the first redox species. When the first redox species is a halide, formula (i) is as shown in (i-1) below. 2X － →X ２ + 2e － (i-1) In the above formula (i-1), X is a halogen atom that constitutes the first redox species.

[0032] When a voltage is applied between the electrodes, a reduction reaction occurs on the second electrode 12 side, in which carbon dioxide is reduced to carbon monoxide. The reaction at the second electrode (second electrolysis section) is typically represented by the following formula (ii-1) or formula (ii-2). The following formula (ii-1) is a reaction that generally proceeds under acidic conditions, and the following formula (ii-2) is a reaction that generally proceeds under basic conditions. CO ２ +2H ＋ +2e － →CO+H ２ O (ii-1) CO ２ +H ２ O + 2e － →CO + 2OH － (ii-2)

[0033] (Reaction Section) The reaction section 31 is composed of a reactor separate from the second electrolysis section 22 and the first electrolysis section 21. That is, the reaction section 31 is a reaction system separate from the reaction system composed of the second electrolysis section 22 and the reaction system composed of the first electrolysis section 21. The reaction section 31 contains a second redox species. Here, the standard redox potential of the first redox species contained in the first electrolysis section 21 is more positive than the standard redox potential of the second redox species. Therefore, as described above, the oxide B1 of the first redox species is supplied from the first electrolysis section 21 to the reaction section 31. However, due to the difference in standard redox potential, in the reaction section 31, the reduced product A2 of the second redox species is oxidized to the oxide B2 as shown in formula (iii) below. Furthermore, the oxide B1 supplied with the first redox species is reduced to the reduced product A1. fY ｒｅｄ + gX ｏｘ → hY ｏｘ + iX ｒｅｄ (iii) X ｏｘ , X ｒｅｄ is as above. Y ｒｅｄ is the reduction product of the second redox species A2, Y ｏｘ is the oxide B2 of the second redox species, and f, g, h, and i are coefficients appropriately selected depending on the types of the first and second redox species.

[0034] The second redox species has a lower standard oxidation-reduction potential than the first redox species. Specific examples include halides such as chloride and bromide, metal complexes, and organic redox species. The type of second redox species is appropriately changed depending on the type of first redox species. For example, when fluoride is used as the first redox species, the second redox species may be selected from chlorides, bromides, metal complexes, and organic redox species. When chloride is used as the first redox species, the second redox species may be selected from bromides, metal complexes, and organic redox species. When bromide is used as the first redox species, the second redox species may be selected from metal complexes and organic redox species.

[0035] The chlorides and bromides used as the second redox species may be alkali metal halide salts, ammonium halide, or hydrogen halide, but it is preferable to use at least metal halide salts as the halide. Furthermore, bromide is preferred as the halide, from the viewpoint that the oxide B2 of the second redox species becomes a liquid and is easily retained in the reaction section 31. Specific examples of chlorides and bromides that can be used include the chlorides and bromides listed above for the first redox species. However, from the viewpoint of increasing the selectivity of the target product, lithium chloride, lithium bromide, sodium chloride, sodium bromide, potassium chloride, and potassium bromide are more preferred, and among these, sodium chloride and sodium bromide are even more preferred, with sodium bromide being even more preferred. When the first redox species and the second redox species are halides, the reaction represented by the above formula (iii) is as shown in the following formula (iii-1). 2Y － + X ２ → Y ２ + 2X － (iii-1) In formula (iii-1), X is a halogen atom constituting the first redox species, and Y is a halogen atom constituting the second redox species.

[0036] Examples of metal complexes used as the second redox species include cobalt complexes and copper complexes. Specific examples include bipyridine-cobalt complexes such as tris(2,2'-bipyridine)cobalt (Co(bpy) complex) and bis(2,2'-bipyridyl)dichlorocobalt, and bipyridine-copper complexes such as bis(2,2'-bipyridyl)dichlorocopper complex. The metal complex may be a complex salt having a counter anion. The type of counter anion is not particularly limited; for example, for cobalt complexes, hexafluorophosphate, tetrafluoroboric acid, etc. may be used.

[0037] Examples of organic redox species include organic compounds such as quinone derivatives and anthraquinone derivatives. In this specification, quinone derivatives include quinone and its derivatives, and anthraquinone derivatives include anthraquinone and its derivatives. Examples of quinone derivatives include benzoquinones having a benzoquinone skeleton, specifically parabenzoquinone, 2-tert-butyl-1,4-benzoquinone, 2,3,5,6-tetrachloro-1,4-benzoquinone, methyl-p-benzoquinone, methoxybenzoquinone, 2-chloro-5-methyl-1,4-benzoquinone, 2,5-dibromo-3,6-dihydroxy-p-quinone, 2,5-dichloro-1,4-benzoquinone, and 2,6-dichloro-1,4-benzoquinone. Examples of suitable redox species include quinone, tetrafluoro-1,4-benzoquinone, fluoranil, 5-isopropyl-2-methyl-1,4-benzoquinone, 2-(10-hydroxydecyl)-5,6-dimethoxy-3-methyl-1,4-benzoquinone, 2-bromo-1,4-benzoquinone, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, 2,3-dimethoxy-5-methyl-1,4-benzoquinone, and 5-isopropyl-2-methyl-1,4-benzoquinone. Among these, parabenzoquinone, 2-tert-butyl-1,4-benzoquinone, and 2,3,5,6-tetrachloro-1,4-benzoquinone are preferred. The second redox species is oxidized and reduced in reaction section 31. When a quinone derivative is used, the quinone derivative may be a hydroquinone. That is, in the reaction section 31, the oxide B2 of the second redox species is a benzoquinone, and the reduced product A2 of the second redox species is a hydroquinone. Hydroquinones are compounds having a hydroquinone skeleton, and specific examples include reduced products corresponding to the specific examples of benzoquinones listed above. For example, the reduced product corresponding to parabenzoquinone is hydroquinone.

[0038] Examples of the anthraquinone derivative include various anthraquinones having an anthraquinone skeleton, and specific examples thereof include 2-ethylanthraquinone, 2-chloroanthraquinone, anthraquinone, anthraquinone-2-carboxylic acid, 2-methylanthraquinone, 2-tert-butylanthraquinone, 1,4-dichloroanthraquinone, 1-nitroanthraquinone, 2-phenylanthraquinone, 2-vinylanthraquinone, 2-bromoanthraquinone, 1-bromoanthraquinone, 1,8-dichloroanthraquinone, and 1,4,5,8-tetrachloroanthraquinone. Examples include chloroanthraquinone, 2,6-dibromoanthraquinone, anthraquinone-2-carbonyl chloride, 1,4-diamino-2,3-dichloroanthraquinone, 1,5-diaminoanthraquinone, 1-amino-2-methylanthraquinone, 1-hydroxy-4-toluidinoanthraquinone, 1,4-bis(methylamino)anthraquinone, 1-acetamido-4-hydroxyanthraquinone, and anthraquinone-2,3-dicarboxylic acid. Of these, 2-ethylanthraquinone and 2-chloroanthraquinone are preferred.

[0039] The second redox species is oxidized and reduced in reaction section 31. When an anthraquinone derivative is used, the anthraquinone derivative may be an anthrahydroquinone. That is, in reaction section 31, the oxide B2 of the second redox species may be an anthraquinone, and the reduced product A2 of the second redox species may be an anthrahydroquinone. An anthrahydroquinone is a compound having an anthrahydroquinone skeleton, and specific examples thereof include reduced products corresponding to the specific examples of anthraquinones described above.

[0040] When the first redox species is a halide and the second redox species is a quinone derivative or an anthraquinone derivative, the reaction represented by the above formula (iii) is as shown in the following formula (iii-2): ２ Q + X ２ → Q+2H ＋ + 2X －(iii-2) In formula (iii-2), X is a halogen atom constituting the first redox species, Q is a benzoquinone or an anthraquinone, and H ２ Q is a hydroquinone or an anthrahydroquinone.

[0041] The standard redox potential of the second redox species is not particularly limited, but is preferably 0.5 to 3 V, more preferably 0.5 to 2 V, from the viewpoint of facilitating the synthesis of carbonyl compounds with high selectivity. In the reaction section 31, the concentration of the second redox species in the reaction solution is not particularly limited, but is, for example, 0.001 to 3 M, preferably 0.01 to 1 M, and more preferably 0.05 to 0.5 M. The concentration of the second redox species in the reaction solution may be lower than the concentration of the first redox species in the second electrolysis section 22. The second redox species may be used alone, or two or more types may be used in combination. When two or more types are used in combination, it is preferable that the standard redox potentials of all the second redox species be lower than the standard redox potential of the first redox species described above.

[0042] As described above, the reaction section 31 is also connected to the second electrolysis section 22 via the second connecting path 42. Therefore, carbon monoxide is also supplied to the reaction section 31 from the second electrolysis section 22. The reaction section 31 also contains a reaction substrate, which is a raw material for the carbonyl compound. Therefore, in the reaction section 31, the reaction substrate and carbon monoxide react in the presence of the second redox species, oxide B2, to synthesize the carbonyl compound, as shown in the following formula (iv). Furthermore, oxide B2 is reduced to a reduction product A2 as the reaction between the reaction substrate and carbon monoxide occurs. Note that, although an example in which the reaction substrate is an alcohol-based compound is shown below, the reaction substrate is not limited to an alcohol-based compound. CO + 2ROH + Y ｏｘ →CO(OR) ２ +Y ｒｅｄ +2H ＋ (iv) In the formula (iv), Y ｏｘ , Y ｒｅｄ is as described above, and R is as described below.

[0043] As described above, in this embodiment, the first electrolysis unit 21 contains the first redox species having a higher standard oxidation-reduction potential than the second redox species, the reaction unit 31 contains the second redox species, and the first redox species oxidized at the first electrode is supplied to the reaction unit 31 via the first connecting path 41. Therefore, the second redox species is oxidized in the reaction unit 31, and in the reaction unit 31, the action of the oxide of the second redox species enables the synthesis of a carbonyl compound, which is a target compound, from carbon monoxide and a reaction substrate with high selectivity.

[0044] In a preferred embodiment, the reaction section 31 contains a first catalyst. The first catalyst may be a catalyst that promotes a reaction in which a carbonyl compound (target product) is synthesized from carbon monoxide and a reaction substrate in the presence of an oxide of a redox species (mainly, an oxide B2 of the second redox species). Details of the first catalyst will be described later.

[0045] The second redox species may be dispersed or dissolved in the reaction liquid. Similarly, the first catalyst may be dispersed or dissolved in the reaction liquid. In the reaction section 31, the reaction liquid may be formed by adding the second redox species, or the second redox species and the first catalyst, to the reaction substrate. As described above, a liquid-phase reaction is carried out in the reaction section 31, thereby efficiently oxidizing the second redox species and synthesizing the carbonyl compound. The reactor 31 may be packed into a portion of the reaction section, and for example, there may be a space above the reaction section 31 that is not filled with the reaction liquid. Furthermore, as long as the first catalyst contacts the reaction liquid in the reaction section 31, it does not have to be dispersed or dissolved in the reaction liquid, and the reaction section 31 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. 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, preferably 10 to 200°C. However, in order to efficiently proceed with the carbonylation reaction, it is preferable to set the temperature to a value equal to or lower than the boiling point of the oxide B2 (e.g., a halogen) of the second redox species. For example, when a bromide is used as the second redox species, the temperature is preferably 57°C or lower, and more preferably 50°C or lower.

[0046] (Reaction Substrate) The reaction substrate contained in the reaction section 31 is a compound that serves as a raw material for obtaining a carbonyl compound (target product) by reacting with carbon monoxide. The reaction substrate is changed depending on the type of target product to be produced. The target product is not particularly limited as long as it is a carbonyl compound, and is at least one selected from organic carbonates and organic oxalates, and it is preferable to use an alcohol-based compound as the reaction substrate.

[0047] (Alcohol-Based Compound) An alcohol-based compound is a reaction substrate that reacts with carbon monoxide in the reaction section 31 to produce an organic carbonate, an organic oxalate, 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 a liquid. A liquid alcohol-based compound can be easily filled into the reaction section 31 as a reaction liquid without using a reaction solvent, which will be described later. An 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] When an alcohol-based compound is used as the reaction substrate, a reaction (also referred to as a first reaction) in which an organic carbonate 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 a second reaction) in which an organic oxalate 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.

[0052] The first reaction is a carbonylation reaction in which an organic carbonate is produced. For example, the organic carbonate ((RO)) is produced by the reaction shown in formula (iv) above. ２ When ROH is represented by the general formula (1-1), an organic carbonate is produced by the reaction shown in the following formula (iv-1): In addition, in formula (iv-1), Y ｏｘ , Y ｒｅｄ and R 11 is the same as above.

[0053] Specific preferred organic carbonates 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.

[0054] The second reaction is a reaction in which carbon monoxide and an alcohol compound produce an organic oxalate represented by the following formula (2): For example, the organic oxalate represented by formula (2) may be synthesized by the reaction represented by formula (v) below. In formula (2), R is the same as above, but the two Rs in one molecule may be the same or different. In addition, in formula (v), Y ｏｘ , Y ｒｅｄ , and R is the same as above.

[0055] When ROH is represented by the general formula (1-1), an organic oxalate represented by the following formula (2-1) is produced by the reaction represented by the following formula (v-1). (In the formula (2-1), Y ｏｘ , Y ｒｅｄ , R １１ is the same as above.) (In formula (vi), X and R １１ is the same as above.)

[0056] Specific preferred organic oxalates 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.

[0057] When the above-mentioned reaction substrate is a solid or gas, or when it is necessary to improve the solubility of the first redox species or the second redox species, the reaction substrate (reaction liquid) filled into 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 into 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.

[0058] 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.

[0059] In the reaction section 31, by-products are also generated along with the target product. The by-products are components derived from the first redox species, typically hydrogen halide. The by-products may be appropriately removed from the reaction section 31. The by-products removed from the reaction section 31 may be supplied to the first electrolysis section 21 as the first redox species by a known supply mechanism. Preferably, the by-products derived from the first redox species, such as hydrogen halide, are removed from the reaction section 31 together with the target product obtained in the reaction section 31, unreacted reaction substrate, the second redox species, etc., and purified in a purification device such as a distillation device. The purified by-products, such as hydrogen halide, may then be supplied to the first electrolysis section 21 as the first redox species. The by-products, such as hydrogen halide, may be appropriately neutralized and supplied to the first electrolysis section 21, for example, as a metal halide salt. In this way, by supplying the by-products to the first electrolysis section 21, the first redox species is circulated between the first electrolysis section 21 and the reaction section 31, thereby reducing raw material loss. In addition, unreacted reaction substrates and second redox species may also be removed from the reaction section 31, purified in the purification device as described above, and then returned to the reaction section 31.

[0060] In the first embodiment described above, the reactant substrates serving as raw materials for the carbonyl compound are not contained in the electrochemical cell 14, but are contained in the reaction unit 31 provided separately from the electrochemical cell 14. This prevents problems such as deformation of the ion exchange membrane due to the reactant substrate, precipitation of electrolytic salt, or elution of the binder in the electrochemical cell. Furthermore, since there is no need to contain a catalyst for synthesizing the carbonyl compound in the first electrolysis unit 21, it is also possible to prevent catalyst deterioration in the first electrolysis unit 21 due to overvoltage. Furthermore, by synthesizing the carbonyl compound using the first and second redox species as described above, the target product can be synthesized with high selectivity.

[0061] Next, the first catalyst used in the reaction section 31, the second catalyst used in the second electrode 12, and the configurations of the first and second electrodes 11, 12 will be described in more detail.

[0062] (First Catalyst) The first catalyst used in the reaction section 31 preferably promotes a chemical reaction that synthesizes a carbonyl compound, the target product, from carbon monoxide and a reaction substrate in the presence of an oxide of a redox species, and preferably contains a metal element, and particularly preferably contains a metal element selected from elements of Groups 8 to 11. Using an element of Groups 8 to 11 as the catalyst facilitates electrochemical synthesis of a carbonyl compound, in particular an organic carbonate, from carbon monoxide with high selectivity.

[0063] Specific examples of Group 8 to Group 11 elements used in the first 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, Ag, and Ir being more preferred. Use of each of the above elements facilitates the synthesis of an organic carbonate, an organic oxalate, or both from carbon monoxide with high selectivity. From these perspectives, Au and Pd are more preferred as the metal element contained in the catalyst, with Pd being particularly preferred.

[0064] The metal element used in the first 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 the 4th period, but may also be a metal element other than the 4th period. 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 high selectivity in synthesizing carbonyl compounds while reducing the amount of precious metal used.

[0065] From the viewpoint of improving selectivity, when two or more metal elements are used in combination, the first catalyst preferably contains at least two metal elements selected from Groups 8 to 11. 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.

[0066] The first 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 organic carbonates, can be produced from carbon monoxide with high conversion efficiency. Among these, metal salts are preferred.

[0067] <<Active particle-containing catalyst>> The active particles in the active particle-containing catalyst have catalytic activity to promote the reaction when carbon monoxide is electrochemically synthesized into a carbonyl compound. 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.

[0068] In the first catalyst, the active particles are, for example, in the form of fine particles. Although not particularly limited, they are preferably nano-order particles, preferably having an average particle diameter of 100 nm or less, more preferably 1 nm to 40 nm. By having the above particle diameter and nanostructuring the active particles, 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 then calculating the diameter from the area of ​​each particle when it is assumed to be a circle.

[0069] 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 examples include carbon, silica, aluminum oxide, and zirconium oxide. 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 porous carbon, silica, or 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.

[0070] 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 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.

[0071] 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.

[0072] 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 support, a metal precursor, 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 component derived from the nitrogen-containing compound in the active particle-containing catalyst preferably has a nitrogen-containing aromatic ring structure. The component derived from the nitrogen-containing compound preferably forms a bond such as a coordinate bond with the metal element derived from the metal derivative in the nitrogen-containing metal catalyst. 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.

[0073] <<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 the 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. The metal precursor or the mixture containing the metal precursor and the support, which is the raw material for the active particle-containing catalyst, is hereinafter also referred to as the first 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 the metal precursor and the support, and the first catalyst raw material may contain the metal precursor, the support, and the nitrogen-containing compound.

[0074] 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 first catalyst raw material.

[0075] 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 metal nitrates and metal chlorides used in the metal precursor are the same as the metal salts used as the first catalyst described below, and therefore, further explanation is omitted. The metal salt may also be a hydrate.

[0076] The metal content derived from the metal precursor in the first 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 first catalyst raw material. By setting the content within the above range, the metal is contained in the catalyst without agglomerating, and an appropriate number of catalytic active sites are formed. This makes it easier to increase the selectivity when synthesizing carbonyl compounds, and also increases the reaction efficiency.

[0077] The content of the support in the first 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 components derived from the active particles and 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 first 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.

[0078] The temperature at which the first 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.

[0079] The first catalyst raw material to be heat-treated is preferably in powder, particulate, or pellet form. If the first catalyst raw material is in powder or particulate form, the catalyst obtained by heat treatment can also be in powder or particulate form. Furthermore, the first catalyst raw material to be heat-treated more preferably consists of a metal precursor and a support, or a metal precursor, a support, and a nitrogen-containing compound. The first catalyst raw material may be obtained, for example, by preparing a diluted solution of the first catalyst raw material and drying the diluted solution. In the diluted solution of the first catalyst raw material, each component (the metal precursor and the support, or the metal precursor, the nitrogen-containing compound, and the support) is preferably dispersed or dissolved in a dilution solvent. By dispersing or dissolving each component in the dilution solvent, a first catalyst raw material in which each component is homogeneously mixed can be obtained. The dilution solvent used to dilute the first catalyst raw material may be water or an organic solvent, with water being preferred.

[0080] Metal Salts Examples of metal salts used as the first 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 palladium chloride (PdCl ２ ), ruthenium chloride (RuCl ３ ), iridium chloride (IrCl ３ ), platinum chloride (PtCl ４ ), gold chloride (AuCl ３ ) and the like. ４ Among these, palladium chloride, tetrachloroauric acid, and iridium chloride are preferred, and palladium chloride is more preferred.

[0081] The metal salt used as the first 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 first catalyst may be used alone or in combination of two or more types.

[0082] (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 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 first electrode are as described above.

[0083] 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).

[0084] As described above, the first electrode may not contain a catalyst as long as it can oxidize the reduced product A1 of the redox species to the oxide B1, or may contain a catalyst (also referred to as a "third catalyst"). 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.

[0085] (Second Catalyst) The second catalyst is a reduction catalyst capable of reducing carbon dioxide to carbon monoxide. The second catalyst is not particularly limited as long as it is a catalyst capable of reducing carbon dioxide to a reduced product such as carbon monoxide, and may, for example, contain a metal element. The metal element may be the metal itself or a metal compound. Examples of the metal element in the metal 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.

[0086] The metal element used in the second 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.

[0087] The second 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 second 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 second 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.

[0088] The second catalyst is also preferably a catalyst containing nitrogen 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, as described below. 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 "second catalyst raw material mixture"), and is particularly preferably a catalyst obtained by heat-treating a second catalyst raw material mixture containing a metal derivative, a nitrogen-containing compound, and a carbon compound. Specific examples of nitrogen-containing compounds include pyridine derivatives, imidazole derivatives, pyrazole derivatives, and triazole derivatives. These compounds may be used alone or in combination of two or more. The metal element in the metal derivative is as described above. The metal derivative preferably contains a metal ion. Furthermore, the metal derivative 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, with metal nitrates being preferred. The heat treatment is typically calcination. The heat treatment may be carried out, for example, at 150 to 550° C., preferably 200 to 470° C. By carrying out the heat treatment at such a low temperature as described above, it is possible to leave ring structures derived from the nitrogen-containing compound, such as a pyridine ring structure, an imidazole ring structure, a pyrazole ring structure, and a triazole ring structure, in the nitrogen-containing metal catalyst.

[0089] 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 nitrogen-containing compound such as a metal derivative and 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 ketjen black, being more preferred. The nitrogen-containing metal catalyst is preferably in powder or particulate form. In powder or particulate form, it is easier to support it on an electrode base material, as described below. In addition, the contact area with carbon dioxide is likely to be larger, making it easier to improve the conversion efficiency to carbon monoxide.

[0090] In addition to the above, the second 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. The second catalyst may be used alone or in combination of two or more.

[0091] (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 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 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 used as the electrode substrate for the second electrode are as described above.

[0092] The second catalyst may be supported on an electrode substrate. The method for supporting the second catalyst on the electrode substrate is not particularly limited. The second 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 second 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.

[0093] The second 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 a cation-conductive compound, an anion-conductive compound, and a fluorine compound other than the cation-conductive compound and the anion-conductive compound. The method for supporting the second catalyst on the electrode substrate is not particularly limited, but examples include a method in which a diluted solution obtained by diluting the second catalyst and components other than the catalyst, such as a catalyst additive added as needed, with a dilution solvent is applied to 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.

[0094] Second Embodiment Next, a second embodiment of the present invention will be described. The second embodiment differs from the first embodiment in that the electrochemical device 10A is a flow cell type. Differences between the second embodiment and the first embodiment will be described below. In this embodiment, the first electrolytic solution 21A filled in the first electrolysis unit 21 may be circulated. Specifically, as shown in FIG. 2 , a first cell 51 for circulating the first electrolytic solution 21A may be provided separately from the electrochemical cell 14. Furthermore, the second electrolytic solution 22A filled in the second electrolytic unit 22 may also be circulated. Specifically, a second cell 52 for circulating the second electrolytic solution 22A may be provided separately from the electrochemical cell 14.

[0095] The first electrolysis unit 21 and the first cell 51 are connected to each other by circulation paths 51A, 51B, and the first electrolytic solution 21A circulates between the first electrolytic unit 21 and the first cell 51. As a result, the first redox species is oxidized at the first electrode 11 while the first electrolytic solution 21A is flowed by convection F1, and an oxide B1 of the first redox species is efficiently produced. The first connecting path 41 is connected to the first cell 51, and the first electrolysis unit 21 is thereby connected to the reaction unit 31 via the first connecting path 41 and the first cell 51. The oxide B1 produced in the first electrolysis unit 21 is preferably supplied in a gaseous state to the reaction unit 31 via the first connecting path 41.

[0096] The second electrolysis unit 22 and the second cell 52 are connected to each other by circulation paths 52A, 52B, and the second electrolytic solution 22A circulates between the second electrolytic unit 22 and the second cell 52. As a result, the second electrolytic solution 22A reduces the carbon dioxide contained therein to carbon monoxide at the second electrode 12 while flowing due to convection F2. Therefore, carbon dioxide is efficiently reduced to carbon monoxide. The inlet 23 is provided in the second cell 52, and carbon dioxide is supplied to the second electrolytic solution 22A in the second cell 52. The second connecting path 42 is connected to the second cell 52, and the second electrolytic unit 22 is connected to the reaction unit 31 via the second connecting path 42 and the second cell 52. The carbon monoxide produced in the second electrolytic unit 22 is supplied in a gaseous state to the reaction unit 31 via the second connecting path 42. In the present embodiment, the first electrolytic solution 21A may be caused to flow along the convection F1 by a pump such as a diaphragm pump, a syringe pump, or a peristaltic pump, or may be caused to flow by a known means other than a pump, such as by gravity, to form the convection F1. The same applies to the second electrolytic solution 22A.

[0097] However, in this embodiment, the first connecting path 41 and the second connecting path 42 may be connected to the first electrolysis unit 21 and the second electrolysis unit 22, respectively, without being connected to the first cell 51 and the second cell 52. Similarly, the inlet 23 may be provided in the second electrolysis unit 22, without being provided in the second cell 52.

[0098] In this embodiment as well, the reactant substrates serving as raw materials for the carbonyl compound are not contained in the electrochemical cell 14 but are contained in the reaction unit 31 provided separately from the electrochemical cell 14, thereby preventing problems such as deformation of the ion exchange membrane due to the reactant substrate, precipitation of electrolytic salt in the electrochemical cell, or elution of the binder. Furthermore, since it is not necessary to contain a catalyst for synthesizing the carbonyl compound in the first electrolysis unit 21, it is also possible to prevent catalyst deterioration in the first electrolysis unit 21 due to overvoltage. Furthermore, in this embodiment as well, the use of the first and second redox species allows the target compound, the carbonyl compound, to be synthesized from carbon monoxide and the reactant substrate with high selectivity.

[0099] <Third Embodiment> Next, a third embodiment of the present invention will be described. Figure 3 shows an electrochemical device 10B according to a third embodiment of the present invention. The electrochemical device 10B according to this embodiment differs from the first embodiment in that the reaction section 31 and the first electrolysis section 21 are further connected via a second ion exchange membrane 25. Differences between the first embodiment and the third embodiment will be described below.

[0100] In this embodiment, the reaction section 31 and the first electrolysis section 21 are separated by a second ion exchange membrane 25, and therefore, the electrochemical cell 14B in this embodiment is separated into three regions, the second electrolysis section 22, the first electrolysis section 21, and the reaction section 31, by two ion exchange membranes.

[0101] Details of the ion exchange membrane that can be used for the second ion exchange membrane 25 are as described for the ion exchange membrane 15. However, it is preferable to use the same type of ion exchange membrane as the ion exchange membrane 15 for the second ion exchange membrane 25. Therefore, if the 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. Note that FIG. 3 shows an embodiment in which the first electrode 11 and the second electrode 12 are disposed on both sides of the ion exchange membrane 15 and joined to form a membrane-electrode assembly, but the first electrode 11 and the second electrode 12 may also be disposed at positions separated from the ion exchange membrane 15 without being joined to the ion exchange membrane 15, as shown in FIG. 1.

[0102] In this embodiment, as in the first embodiment, the first redox species is oxidized from a reduction product A1 to an oxide B1 at the first electrode 11, and the oxide B1 is supplied to the reaction unit 31 via the first connecting path 41. Furthermore, in the reaction unit 31, the reduction product A2 of the second redox species is oxidized to an oxide B2 by the oxide B1 of the first redox species, as shown in formula (iii). Furthermore, a reduction reaction occurs at the second electrode 12 in which carbon dioxide is reduced to carbon monoxide, and the carbon monoxide is supplied to the reaction unit 31 via the second connecting path 42. Therefore, in the reaction unit 31, carbon monoxide and the reaction substrate are reacted in the presence of the oxide B2 of the second redox species, as shown in formula (iv) and the like, to obtain the target product, a carbonyl compound.

[0103] 3, 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 first electrolysis section 21. 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.

[0104] Furthermore, in the third embodiment, anions or cations move between the first electrolysis section 21 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. 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 further through the ion exchange membrane 15 to the first electrolysis section 21 and further to the second electrolysis section 22. Therefore, the protons (H ＋ ) concentration decreases, and the reaction in the reaction section 31 easily proceeds. Furthermore, protons (H ＋ ) is easily supplied, and reduction in the second electrolysis section 22 is easily promoted.

[0105] On the other hand, for example, when the first and second ion exchange membranes 15 and 25 are anion exchange membranes, hydroxide ions (OH － ) moves through the ion exchange membrane 15 and the second ion exchange membrane 25 to the first electrolysis section 21 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 (first electrolysis section 21 or reaction section 31), which facilitates the reduction reaction in second electrolysis section 22 to proceed.

[0106] Furthermore, when the first redox species is a halide and the second ion exchange membrane 25 is an anion exchange membrane, halogen ions derived from the first redox species generated in the first reactant 31 can migrate to the first electrolysis unit 21 via the second ion exchange membrane 25 (anion exchange membrane). Specifically, when the concentration of halogen ions (i.e., the first redox species) in the reaction unit 31 becomes higher than the concentration of halogen ions (i.e., the first redox species) in the first electrolysis unit 21, the halogen ions (first redox species) can migrate. Therefore, the first redox species can circulate between the first electrolysis unit 21 and the reaction unit 31 via the first connecting path 41 and the second ion exchange membrane 25. In addition, halogen ions derived from the second redox species may also be present in the reaction section 31, but the concentration of the second redox species in the reaction section is low, for example, lower than the concentration of the first redox species in the first electrolysis section 21, so that halogen ions derived from the second redox species hardly move to the first electrolysis section 21.

[0107] Furthermore, in this embodiment, when the second ion exchange membrane 25 is a cation exchange membrane and the first redox species is a metal halide salt, metal ions (preferably alkali metal ions such as sodium and lithium) may migrate from the first electrolysis unit 21 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 a halogen ion. Therefore, in this embodiment, a metal halide salt may be produced as a by-product in the reaction unit 31. Note that the above-described aspects of the third embodiment may also be applied when the electrochemical device is of a flow cell type. For example, in the aspect of the second embodiment, the first cell 51 or the first electrolysis unit 21 may be connected to the first electrolysis unit 21 via the second ion exchange membrane 25.

[0108] <Modifications> The present invention is not limited to the configurations of the above-described embodiments, and may have any configuration as long as it does not deviate from the gist of the present invention. For example, it is also possible to adopt the configurations shown in the following first to fourth modifications.

[0109] <First Modification> In each of the above embodiments, an ion exchange membrane is provided between the second electrode and the first electrode, and the electrochemical cell is divided into first and second electrolysis sections to form a two-chamber structure. However, the ion exchange membrane may be omitted. In this case, the electrolysis section formed by the electrochemical cell may be a single-chamber structure without being divided by an ion exchange membrane, consisting of a single electrolysis section (first electrolysis section). The second connecting channel may be omitted, while a connecting channel (first connecting channel) connecting the single electrolysis section (first electrolysis section) to the reaction section may be provided. In this modification, the first electrolysis section is also filled with an electrolytic solution. The electrolytic solution may be an aqueous electrolyte solution, and may be an electrolytic solution containing water and a first redox species, as described for the first electrolytic solution in the first embodiment. The first redox species is as described above, and the concentration of the first redox species in the electrolytic solution is also as described for the first electrolysis section 21 in the first embodiment. The first electrode and the second electrode are preferably disposed inside the first electrolysis unit so as to be in contact with the electrolytic solution.

[0110] In this modification, carbon dioxide is introduced into the electrolysis unit through an inlet, and the carbon dioxide is reduced to carbon monoxide at the first electrode. Meanwhile, at the first electrode, the reduced product A1 of the first redox species is oxidized to an oxide B1, thereby obtaining the oxide B1. Both the carbon monoxide and the oxide B1 obtained in the first electrolysis unit are discharged as gases through the first connecting path to the reaction unit. In this modification, as in the first embodiment, the second redox species is oxidized by the first redox species in the reaction unit, and a carbonyl compound is synthesized from the carbon monoxide and the reaction substrate in the presence of the oxide of the second redox species.

[0111] <Second Modification> In each of the above embodiments, the first electrolysis unit 21 is filled with an aqueous electrolyte solution. However, it is not necessarily required to fill it with an aqueous electrolyte solution. It may be filled with a non-aqueous electrolyte solution using an organic solvent such as an alcohol solvent or a nitrile solvent. Similarly, the second electrolysis unit 22 may be filled with a non-aqueous electrolyte solution instead of an aqueous electrolyte solution. Furthermore, the second electrolysis unit 22 does not necessarily have to be a liquid-phase reaction unit. Instead of being filled with an electrolyte solution, gaseous carbon dioxide may contact the second electrode 12 and be reduced to carbon monoxide by a gas-phase reaction at the second electrode 12. However, in this case, the gaseous carbon dioxide may contain moisture or may be supplied together with a carrier gas as described above.

[0112] <Third Modification> In each of the above embodiments, carbon monoxide is generated in the second electrolysis unit 22 and supplied to the reaction unit 31 via the second connecting path 42. However, the carbon monoxide supplied to the reaction unit 31 is not limited to carbon monoxide generated in the second electrolysis unit 22, and carbon monoxide may be supplied to the reaction unit 31 from another carbon monoxide supply source. The other carbon monoxide supply source may be a carbon monoxide cylinder or carbon monoxide generated in another electrochemical cell. In this case, the second connecting path 42 may be omitted, and the second electrode 12 may not contain a second catalyst for reducing carbon dioxide. However, both carbon monoxide generated in the second electrolysis unit 22 and carbon monoxide from the other carbon monoxide supply source may be supplied to the reaction unit 31.

[0113] 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.

[0114] Example 1 A first 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 first electrolysis section of a two-chamber diaphragm-type electrochemical cell, a second electrode (cathode) made of Pt was set in the second electrolysis section, and the first electrolysis section and the second electrolysis section were separated by a Nafion ion exchange membrane. Then, 50 ml and 50 ml of a 1.0 M KF aqueous solution were filled in the first electrolysis section and the second electrolysis section, respectively. KF was used as the first redox species or electrolyte. Furthermore, 3 mg of PdCl was placed in a reaction section provided separately from the electrochemical cell as a first catalyst. ２The vessel was filled with 30 ml of a methanol solution containing 0.1 M NaCl as a second redox species, and the first electrolysis unit and the reaction unit were connected with a Teflon (registered trademark) tube to form a first connecting path, resulting in the electrochemical device shown in FIG. 1 (however, the second connecting path was omitted). A 50 mA current was passed between the first and second electrodes, and CO (1 atm) was supplied to the reaction unit to cause a reaction. The components of the reaction solution were then analyzed by gas chromatography, and the selectivity was calculated by comparing the current value. The temperatures of the electrolytes (KF aqueous solution) in the first electrolysis unit 21 and the second electrolysis unit 22 were set to 25°C, and the temperature of the reaction solution (NaCl methanol solution) in the reaction unit 31 was set to 25°C. The selectivity was calculated for dimethyl carbonate (DMC), an organic carbonate. The results are shown in Table 1.

[0115] Examples 2 to 5 The same procedures as in Example 1 were carried out, except that the redox species shown in Table 1 were used instead of NaCl as the second redox species.

[0116] Examples 6 to 9 were carried out in the same manner as in Example 1, except that NaCl was used instead of KF as the first redox species and the electrolyte of the second electrolysis section, and the redox species shown in Table 1 were used instead of NaCl as the second redox species.

[0117] Examples 10 to 12 were carried out in the same manner as in Example 1, except that NaBr was used instead of KF as the electrolyte of the first redox species and the second electrolysis unit, and that the redox species shown in Table 1 was used instead of NaCl as the second redox species. The temperature of the electrolytic solution (KF aqueous solution) in the first electrolysis unit 21 and the second electrolysis unit 22 was set to 50°C.

[0118] Comparative Example 1 The same procedure as in Example 1 was carried out, except that NaCl was used instead of KF as the first redox species and the electrolyte of the second electrolysis section.

[0119] Quinone derivative: Hydroquinone Co complex: Tris(2,2'-bipyridine)cobalt complex Cu complex: Bis(2,2'-bipyridyl)dichlorocopper complex

[0120] In the above Examples 1 to 12, the first electrolysis unit contained a first redox species having a higher standard oxidation-reduction potential than the second redox species, and the reaction unit contained a second redox species. The first redox species oxidized at the first electrode was supplied to the reaction unit via the first connecting path. Therefore, the second redox species was oxidized in the reaction unit, and the target compound, a carbonyl compound, was synthesized with high selectivity from carbon monoxide and the reaction substrate in the reaction unit due to the action of the oxide of the second redox species. In contrast, in Comparative Example 1, the first electrolysis unit and the reaction unit contained redox species having the same standard oxidation-reduction potential, so the redox species were not oxidized in the reaction unit, and the target compound, a carbonyl compound, was not synthesized with high selectivity from carbon monoxide and the reaction substrate.

[0121] REFERENCE SIGNS LIST 10, 10A, 10B Electrochemical device 11 First electrode 12 Second electrode 15 Ion exchange membrane 19 Power source 21 First electrolysis section 21A First electrolytic solution 22 Second electrolysis section 22A Second electrolytic solution 23 Inlet 25 Second ion exchange membrane 31 Reaction section 41 First connecting path 42 Second connecting path 51 First cell 52 Second cell

Claims

An electrochemical device for electrochemically synthesizing at least one carbonyl compound selected from the group consisting of organic carbonates and organic oxalates from carbon monoxide, comprising: a first electrode, a second electrode, a first electrolysis unit having the first electrode, a reaction unit, and a first connection path connecting the first electrolysis unit and the reaction unit; An electrochemical device, wherein the first electrolysis section contains a first redox species, the reaction section contains a second redox species, and the standard redox potential of the first redox species is more positive than the standard redox potential of the second redox species.

2. The electrochemical device according to claim 1, wherein the oxide of the first redox species is a gas and is supplied to the reaction section through the first connecting path, and both the first electrolysis section and the reaction section perform liquid-phase reactions.

3. The electrochemical device according to claim 1, wherein the first electrolysis section contains an aqueous electrolyte solution.

3. The electrochemical device according to claim 1, wherein the first redox species is at least one species selected from the group consisting of fluoride, bromide, and chloride.

3. The electrochemical device according to claim 1, wherein the second redox species is at least one species selected from the group consisting of bromides, chlorides, metal complexes, and organic redox species.

3. The electrochemical device according to claim 1, further comprising: a second electrolysis section having the second electrode; and a second connecting path connecting the second electrolysis section and the reaction section, wherein the second connecting path supplies carbon monoxide generated in the second electrolysis section to the reaction section.

3. The electrochemical device according to claim 1, wherein the reaction section contains a reaction substrate.

8. The electrochemical device according to claim 7, wherein the reaction substrate is an alcohol-based compound. 　 A method for producing an organic substance using the electrochemical device according to claim 1 or 2, oxidizing a reduced product of the first redox species to an oxide at the first electrode; The oxide is supplied to the reaction section through the first connecting path, In the reaction section, the second redox species is oxidized by the oxide; and A method for producing an organic substance, comprising producing the carbonyl compound from carbon monoxide and an oxide of the second redox species.

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