Ammonia production method and production apparatus

Abstract

An ammonia production method according to the present invention is a method for producing ammonia from nitrogen atoms by the action of electrons suppled from a power source in the presence of a complex and a proton source. As the complex, a molybdenum complex (1) supported on a Merrifield resin can be used for example. As the proton source, an electrolyte membrane, or a solution to be used in a cathode vessel, or both of an electrolyte membrane and a solution to be used in a cathode vessel can be used.

Description

[Technical field]

[0001] The present invention relates to a method and an apparatus for producing ammonia. [Background technology]

[0002] In a method for producing ammonia from nitrogen molecules, when a molybdenum complex is used as a catalyst, there is a report of using samarium iodide (II) as a reducing agent and alcohols or water as a proton source (Non-Patent Document 1). It has been reported that ammonia was produced using a molybdenum complex supported on a polystyrene resin (Non-Patent Document 2). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Nature 2019, vol. 568(7753), pp. 536-540 [Non-Patent Document 2] Chem. Lett. 2019, vol. 48, pp. 693-695 Summary of the Invention [Problem to be solved by the invention]

[0004] In a method for producing ammonia from nitrogen molecules, when a molybdenum complex is used as a catalyst, from the viewpoint of supplying electrons to the reaction system, it is necessary to use samarium iodide(II) as a reducing agent in Non-Patent Document 1, and it is necessary to use decamethylcobaltocene as a reducing agent in Non-Patent Document 2. From the viewpoint of practical application, it has been an issue that it is not easy to recover and recycle these reducing agents.

[0005] The present invention has been made to solve the above-mentioned problems, and a main object of the present invention is to provide a method for electrochemically producing ammonia while avoiding the use of a reducing agent. [Means for solving the problem]

[0006] In order to achieve the above object, the present inventors have fabricated an ammonia production device in which a molybdenum complex is disposed near an electrode so that electrons and protons required for the production of ammonia from nitrogen molecules can be rapidly supplied to the molybdenum complex, and have found that ammonia can be produced by electrons supplied from a power source without using a reducing agent such as samarium iodide (II) or decamethylcobaltocene, thereby completing the present invention. There have been no reports of a method for producing ammonia from nitrogen molecules using a molybdenum complex as a catalyst to produce ammonia by electrons supplied from a power source without using a reducing agent.

[0007] That is, the method for producing ammonia of the present invention is a method for producing ammonia from nitrogen molecules using electrons supplied from a power source in the presence of a complex and a proton source, The complex is (A) a molybdenum complex having 2,6-bis(dialkylphosphinomethyl)pyridine as a PNP ligand (wherein the two alkyl groups may be the same or different, and at least one hydrogen atom of the pyridine ring may be substituted with an alkyl group, an alkoxy group or a halogen atom); (B) a molybdenum complex having 1,3-bis(dialkylphosphinomethyl)benzimidazol-2-ylidene as a PCP ligand (wherein the two alkyl groups may be the same or different, and at least one hydrogen atom of the benzene ring may be substituted with an alkyl group, an alkoxy group or a halogen atom); (C) a molybdenum complex having a bis(dialkylphosphinoethyl)arylphosphine as a PPP ligand, where the two alkyl groups may be the same or different, or (D)trans-Mo(N2)2(R 5 R 6 R 7 P) 4 (However, R 5 and R 6 are aryl groups which may be the same or different, R 7 is an alkyl group, and two R 7may be linked to each other to form an alkylene chain), The proton source is the electrolyte membrane, the solution used in the cathode chamber, or both the electrolyte membrane and the solution used in the cathode chamber; A method for producing ammonia.

[0008] The ammonia production apparatus of the present invention comprises: an apparatus main body including a membrane electrode assembly having a structure in which an ion exchange membrane is sandwiched between a cathode and an anode, a pair of current collectors sandwiching the membrane electrode assembly, an anode tank disposed on the current collector side in contact with the anode, a cathode tank disposed on the current collector side in contact with the cathode, and a nitrogen gas supply unit that supplies nitrogen gas to the cathode tank; a power supply device connected to the pair of current collectors outside the device body; Equipped with The cathode contains, as a catalyst, (A) a molybdenum complex having 2,6-bis(dialkylphosphinomethyl)pyridine as a PNP ligand (wherein the two alkyl groups may be the same or different, and at least one hydrogen atom of the pyridine ring may be substituted with an alkyl group, an alkoxy group or a halogen atom); (B) a molybdenum complex having 1,3-bis(dialkylphosphinomethyl)benzimidazol-2-ylidene as a PCP ligand (wherein the two alkyl groups may be the same or different, and at least one hydrogen atom of the benzene ring may be substituted with an alkyl group, an alkoxy group or a halogen atom); (C) a molybdenum complex having a bis(dialkylphosphinoethyl)arylphosphine as a PPP ligand, where the two alkyl groups may be the same or different, or (D) a trans-Mo(N2)2(R 5 R 6 R 7 P) 4 (However, R 5 and R 6 are aryl groups which may be the same or different, R 7 is an alkyl group, and two R 7may be linked to each other to form an alkylene chain), The anode comprises a catalyst for producing protons from water. It is something. Effect of the Invention

[0009] According to the ammonia production method of the present invention, ammonia can be simply produced from nitrogen molecules by electrons supplied from a power source in the presence of a molybdenum complex and an ion exchange membrane without using a reducing agent. Furthermore, in the ammonia production apparatus of the present invention, protons are generated from water in the anode tank by the action of a catalyst contained in the anode. The protons pass through the anode and the ion exchange membrane and move to the cathode. In the cathode tank, the protons that have moved, nitrogen gas supplied to the cathode tank, and electrons supplied to the cathode from the power supply device react with each other by the action of the molybdenum complex contained in the cathode to produce ammonia. The ammonia production apparatus of the present invention is suitable for carrying out the ammonia production method of the present invention. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view of an ammonia production apparatus 10. [Diagram 2] FIG. 2 is an explanatory diagram of a cathode chamber 27 and its peripheral devices. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Preferred embodiments of the method and apparatus for producing ammonia according to the present invention are described below.

[0012] The method for producing ammonia according to the present embodiment is a method for producing ammonia from nitrogen molecules using electrons supplied from a power source in the presence of a complex and a proton source. In this method, the catalyst is selected from the group consisting of (A) a molybdenum complex having 2,6-bis(dialkylphosphinomethyl)pyridine as a PNP ligand (wherein the two alkyl groups may be the same or different, and at least one hydrogen atom of the pyridine ring may be substituted with an alkyl group, an alkoxy group, or a halogen atom), (B) a molybdenum complex having 1,3-bis(dialkylphosphinomethyl)benzimidazol-2-ylidene as a PCP ligand (wherein the two alkyl groups may be the same or different, and at least one hydrogen atom of the benzene ring may be substituted with an alkyl group, an alkoxy group, or a halogen atom), (C) a molybdenum complex having bis(dialkylphosphinoethyl)arylphosphine as a PPP ligand (wherein the two alkyl groups may be the same or different), or (D) trans-Mo(N2)2(R 5 R 6 R 7 P) 4 (However, R 5 and R 6 are aryl groups which may be the same or different, R 7 is an alkyl group, and two R 7 may be linked to each other to form an alkylene chain), is used.

[0013] In the molybdenum complex (A), the alkyl group may be, for example, a linear or branched alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, or a structural isomer thereof, or may be a cyclic alkyl group such as a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, or a cyclohexyl group. The alkyl group preferably has 1 to 12 carbon atoms, and more preferably has 1 to 6 carbon atoms. The alkoxy group may be, for example, a linear or branched alkoxy group such as a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a pentoxy group, a hexyloxy group, a benzyloxy group, or a structural isomer thereof, or may be a cyclic alkoxy group such as a cyclopropoxy group, a cyclobutoxy group, a cyclopentoxy group, or a cyclohexyloxy group. The alkoxy group preferably has 1 to 12 carbon atoms. When the alkoxy group is a benzyloxy group, at least one hydrogen atom on the benzene ring of the benzyloxy group may be substituted with a resin. Examples of halogen atoms include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

[0014] The molybdenum complex (A) is, for example, a compound represented by the formula (A1), (A2) or (A3): [ka] (In the formula, R 1 and R 2 R are alkyl groups which may be the same or different, X is an iodine atom, a bromine atom or a chlorine atom, and at least one hydrogen atom on the pyridine ring may be substituted with an alkyl group, an alkoxy group or a halogen atom. Examples of the alkyl group, the alkoxy group and the halogen atom include the same as those already exemplified. 1 and R 2As the aryl group, a bulky alkyl group (such as a tert-butyl group or an isopropyl group) is preferable. The hydrogen atom on the pyridine ring is preferably not substituted, or the hydrogen atom at the 4-position is preferably substituted with a linear, cyclic or branched alkyl group having 1 to 12 carbon atoms or an alkoxy group. A more preferable alkoxy group is a benzyloxy group in which at least one hydrogen atom on the benzene ring is substituted with a resin, and examples of the resin include chloromethyl resin (e.g., polymer-bonded 5-[4-(chloromethyl)phenyl]pentyl]styrene, polymer-bonded 4-(benzyloxy)benzyl chloride, polymer-bonded 4-methoxybenzhydryl chloride), (chloromethyl)polystyrene, Merrifield resin, JandaJel-Cl (trademark), and the like. Of these, (chloromethyl)polystyrene, Merrifield resin, and JandaJel-Cl (trademark) are preferable.

[0015] The molybdenum complex (B) is represented by the following formula (B1) or (B2): [ka] (In the formula, R 1 and R 2 R are alkyl groups which may be the same or different, X is an iodine atom, a bromine atom or a chlorine atom, and at least one hydrogen atom on the benzene ring may be substituted with an alkyl group, an alkoxy group or a halogen atom. Examples of the alkyl group, the alkoxy group and the halogen atom include the same as those already exemplified. 1 and R 2 R is preferably a bulky alkyl group (e.g., a tert-butyl group or an isopropyl group). It is preferable that the hydrogen atoms on the benzene ring are not substituted, or that the hydrogen atoms at the 5- and 6-positions are substituted with a linear, cyclic or branched alkyl group having 1 to 12 carbon atoms. 3 and R 4 At least one of the groups is preferably substituted with a trifluoromethyl group, and it is more preferable that both of the groups are substituted with trifluoromethyl groups.

[0016] The molybdenum complex (C) is, for example, a molybdenum complex represented by the formula (C1): [ka] (In the formula, R 1 and R 2 are alkyl groups which may be the same or different, R 5 is an aryl group, and X is an iodine atom, a bromine atom, or a chlorine atom). Examples of the alkyl group include the same as those already exemplified. Examples of the aryl group include a phenyl group, a tolyl group, a xylyl group, a naphthyl group, and groups in which at least one hydrogen atom on the ring of these groups is substituted with an alkyl group or a halogen atom. Examples of the alkyl group and the halogen atom include the same as those already exemplified. 1 and R 2 R is preferably a bulky alkyl group (e.g., a tert-butyl group or an isopropyl group). 5 As the alkyl group, for example, a phenyl group is preferable.

[0017] The molybdenum complex of (D) is represented by the formula (D1) or (D2): [ka] (In the formula, R 5 and R 6 are aryl groups which may be the same or different, R 7 is an alkyl group, and n is 2 or 3. Examples of the alkyl group and aryl group include the same as those already exemplified. In formula (D1), R 5 and R 6 is an aryl group (e.g., a phenyl group) and R 7 is preferably an alkyl group having 1 to 4 carbon atoms (e.g., a methyl group). 5 and R 6 It is preferred that n is an aryl group (eg, a phenyl group) and n is 2.

[0018] In the method for producing ammonia according to the present embodiment, the ion exchange membrane used as the proton source is preferably a proton-conductive polymer electrolyte membrane. Examples of such polymer electrolyte membranes include Neocepta (registered trademark) from Astom Corporation, Selemion (registered trademark) from AGC Corporation, Aciplex (registered trademark) from Asahi Kasei Corporation, Fumasep (registered trademark) from Fumatech Corporation, fumapem (registered trademark) from Fumatech Corporation, Nafion (registered trademark) from DuPont Corporation, Aquivion (registered trademark) from Solvay Corporation, Flemion (registered trademark) from AGC Corporation, and Gore-Tex (registered trademark) from Gore-Tex Corporation. As the ion exchange membrane 22, Aciplex (registered trademark) from Asahi Kasei Corporation, Nafion (registered trademark) from DuPont Corporation, Aquivion (registered trademark) from Solvay Corporation, and Flemion (registered trademark) from AGC Corporation are preferred, with Nafion (registered trademark) being more preferred.

[0019] In the method for producing ammonia according to the present embodiment, nitrogen gas is preferably used as the nitrogen molecules. It is more preferable that the nitrogen gas is used in a form in which the flow rate is controlled using a nitrogen cylinder, a regulator, and a mass flow controller.

[0020] In the method for producing ammonia according to the present embodiment, the reaction temperature is preferably room temperature (0 to 40° C.). The reaction atmosphere does not need to be a pressurized atmosphere, and may be a normal pressure atmosphere. The reaction time is not particularly limited, but may usually be set within a range of several minutes to several tens of hours.

[0021] Next, an ammonia production apparatus for carrying out the ammonia production method of this embodiment will be described below. Here, an ammonia production apparatus 10 is shown as an example. Fig. 1 is a cross-sectional view of the ammonia production apparatus 10, and Fig. 2 is an explanatory diagram of a cathode tank 27 and its peripheral devices.

[0022] The ammonia producing apparatus 10 includes an apparatus main body 20 and a power supply unit 30. The apparatus main body 20 includes a membrane electrode assembly 21, a pair of current collectors 25, 25, an anode tank 26, and a cathode tank 27. The power supply unit 30 is disposed outside the apparatus main body 20 and is connected to the anode 23 and the cathode 24 in the apparatus main body 20.

[0023] The membrane electrode assembly 21 has a structure in which both sides of an ion exchange membrane 22 are sandwiched between an anode 23 and a cathode 24. In this embodiment, the anode 23 refers to an electrode into which a current flows from a power supply device 30, and the cathode 24 refers to an electrode from which a current flows out to the power supply device 30. Electrochemically, the anode 23 is an electrode in which an oxidation reaction occurs, and the cathode 24 is an electrode in which a reduction reaction occurs, and ammonia is produced in a cathode tank 27 on the cathode 24 side.

[0024] The ion exchange membrane 22 is a member used as a proton source when producing ammonia, and is preferably a proton-conductive polymer electrolyte membrane. Specific examples of such a polymer electrolyte membrane have already been given.

[0025] Although not shown, the anode 23 includes a gas diffusion layer and a catalyst layer. The gas diffusion layer is disposed on the current collector 25 side of the anode 23.

[0026] The gas diffusion layer in this embodiment may be, for example, carbon paper, carbon cloth, or carbon felt. Examples of carbon paper include TGP-H-060, TGP-H-090, TGP-H-120, TGP-H-060H, TGP-H-090H, and TGP-H-120H from Toray Industries, Inc., EC-TP1-030T, EC-TP1-060T, EC-TP1-090T, and EC-TP1-120T from Electrochem, and 22BB, 28BC, 36BB, and 39BB from SIGRACET. Examples of carbon cloth include EC-CC1-060, EC-CC1-060T, and EC-CCC-060 from Electrochem Corporation, and Torayca (registered trademark) cloth from Toray Industries, Inc., and examples of carbon felt include CO6142, CO6151B, CO6343, CO6343B, CO6347B, CO6644B, CO1302, CO1303, CO5642, CO7354, CO7359B, CK6244C, CK6273C, and CK6261C. Examples of carbon felt include H1410 and H2415 from Freudenberg.

[0027] The gas diffusion layer in the anode 23 of this embodiment is preferably carbon paper, and more preferably TGP-H-060, TGP-H-090, TGP-H-060H, TGP-H-090H, EC-TP1-060T, or EC-TP1-090T.

[0028] The catalyst layer in the anode 23 is a layer containing a catalyst, and is disposed on the ion exchange membrane 22 side of the anode 23. As the catalyst, any known catalyst can be used without particular limitation as long as it promotes the reaction of generating protons from water. As the catalyst, for example, an iridium (IV) oxide powder catalyst, platinum, gold, silver, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, and other metals and alloys thereof can be mentioned. Among these, as the catalyst, an iridium (IV) oxide powder catalyst and platinum are preferable. In addition to the catalyst, the catalyst layer includes a catalyst carrier and an electrolyte.

[0029] The catalyst carrier supports a catalyst, and examples of the catalyst carrier include carbon black such as channel black, furnace black, thermal black, acetylene black, and Ketjen black, activated carbon obtained by carbonizing and activating various materials containing carbon atoms, carbonaceous materials such as coke, natural graphite, artificial graphite, and graphitized carbon, metal mesh such as nickel or titanium, and metal foam. Of these, the catalyst carrier is preferably carbon black, Ketjen black, nickel metal mesh, titanium metal mesh, and metal foam, because they have a high specific surface area and excellent electronic conductivity, and more preferably titanium metal mesh and metal foam, because they are more durable.

[0030] The electrolyte is responsible for the proton conduction in the catalyst layer, and examples thereof include fluorine-based sulfonic acid polymers, hydrocarbon-based sulfonic acid polymers, and partially fluorinated hydrocarbon-based sulfonic acid polymers, such as DuPont's Nafion (registered trademark), Solvay's Aquivion (registered trademark), AGC's Flemion (registered trademark), and Asahi Kasei's Aciplex (registered trademark). Preferred electrolytes are Nafion, Aquivion, Flemion, and Aciplex. These electrolytes may be used in combination, and from the viewpoint of voltage characteristics in the high current region, it is preferred to include a perfluoro acid polymer such as Nafion.

[0031] Although not shown, the cathode 24 includes a gas diffusion layer and a catalyst layer. The gas diffusion layer is disposed on the current collector 25 side of the cathode 24. Specific examples of such a gas diffusion layer have already been described.

[0032] The gas diffusion layer in the cathode 24 of this embodiment is preferably carbon paper, more preferably TGP-H-060, TGP-H-090, TGP-H-060H, TGP-H-090H, EC-TP1-060T, or EC-TP1-090T, and even more preferably TGP-H-060H, TGP-H-090H, EC-TP1-060T, or EC-TP1-090T.

[0033] The catalyst layer in the cathode 24 is a layer containing a catalyst, and is disposed on the ion exchange membrane 22 side of the cathode 24. The catalyst is one that promotes a reaction that produces ammonia from nitrogen, protons, and electrons, specifically, any of the molybdenum complexes (A) to (D) described above. The molybdenum complex (A) may be the molybdenum complex represented by (A1), (A2), or (A3) described above. The molybdenum complex (B) may be the molybdenum complex represented by (B1) or (B2) described above. The molybdenum complex (C) may be the molybdenum complex represented by (C1) described above. The molybdenum complex (D) may be the molybdenum complex represented by (D1) or (D2) described above. The catalyst layer includes a catalyst carrier and an electrolyte in addition to the catalyst. The same catalyst carrier and electrolyte as those of the anode 23 may be used.

[0034] The anode chamber 26 is a chamber arranged on the anode 23 side, and the cathode chamber 27 is a chamber arranged on the cathode 24 side.

[0035] Examples of the solution used in the tank in this embodiment include water, ionic liquid, methanol, isopropyl alcohol, N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide, N-methylpyrrolidone, diethylamine, hexamethylphosphonic acid triamide, acetic acid, acetonitrile, methylene chloride, trifluoroethanol, nitromethane, sulfolane, pyridine, tetrahydrofuran, dimethoxyethane, propylene carbonate, etc. Among these, water, ionic liquid, tetrahydrofuran, and dimethoxyethane are preferred.

[0036] Specifically, a supporting electrolyte may be added to the water used as the solution in the tank in this embodiment. The supporting electrolyte is not particularly limited as long as it is a compound that dissociates in water to form ions. Examples of the supporting electrolyte include HCl, HNO3, H2SO4, HClO4, NaCl, Na2SO4, NaClO4, KCl, K2SO4, KClO4, NaOH, LiOH, KOH, alkyl ammonium salts, alkyl imidazolium salts, alkyl piperidinium salts, and alkyl pyrrolidinium salts. These supporting electrolytes may be used alone or in combination of two or more. Of these, the solutions used in the tank in this embodiment are preferably water, purified water, and an aqueous sulfuric acid solution (water containing H2SO4).

[0037] Examples of the ionic liquid used as the solution in the tank in this embodiment include diethyl-methyl-(2-methoxyethyl)ammonium-bis(trifluoromethanesulfonyl)imide, diethyl-methyl-(2-methoxyethyl)ammonium-tetrafluoroborate, N-methyl-N-propylpiperidinium-bis(trifluoromethanesulfonyl)imide, trimethyl-propylammonium-bis(trifluoromethanesulfonyl)imide, methyl-propylpyrrolidium-bis(trifluoromethanesulfonyl)imide, butyl-methylpyrrolidium-bis(trifluoromethanesulfonyl)imide, Examples of the ionic liquid include 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide, butylpyridinium-tetrafluoroborate, butylpyridinium-trifluoromethanesulfonate, 1-ethylpyridinium hexafluoroborate, 1-methyl-1-propylpiperidinium hexafluorophosphate, 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide, 1-butyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate, 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate, and combinations thereof. These ionic liquids may be used alone or in combination of two or more. Among these, 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide and 1-butyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate are preferred.

[0038] It is also possible to add an acid such as sulfuric acid or trifluoromethanesulfonic acid to the ionic liquid before use. Preferred ionic liquids to which an acid is added include 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butyl-1-methylpiperidinium bis(trifluoromethanesulfonyl)imide, and 1-butyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate.

[0039] The electrolyte contained in the solution used in the tank in this embodiment may be any substance that dissolves in the solution and exhibits ion conductivity, and examples of such electrolytes include cations such as protons, lithium ions, sodium ions, potassium ions, imidazolium ions, pyridinium ions, quaternary ammonium ions, phosphonium ions, pyrrolidinium ions, and phosphonium ions, either singly or in combination, and anions such as chloride ions, bromide ions, iodide ions, tetrafluoroborate, trifluoro(trifluoromethyl)borate, dimethylphosphate ions, diethylphosphate ions, hexafluorophosphate, tris(pentafluoroethyl)trifluorophosphate, trifluoroacetate, methylsulfate, trifluoromethanesulfonate, bis(trifluoromethanesulfonyl)imide, perchlorate ions, sulfate ions, and nitrate ions, either singly or in combination. The electrolytes may be used alone or in combination of two or more.

[0040] Examples of the imidazolium ion in the electrolyte include 1-allyl-3-methylimidazolium ion, 1-butyl-3-methylimidazolium ion, 1-butyl-2,3-dimethylimidazolium ion, 1-butyl-3-methylimidazolium ion, 1-butyl-2,3-dimethylimidazolium ion, 1-butyl-3-methylimidazolium ion, 1,3-dimethylimidazolium ion, 2,3-dimethyl-1-propylimidazolium ion, 1-decyl-3-methylimidazolium ion, 1,3-dimethylimidazolium ion, 1-decyl-3-methylimidazolium ion, 1-ethyl-3-methylimidazolium ion, 1-ethyl-2,3-dimethylimidazolium ion, 1-ethyl ... midazolium ion, 3-ethyl-1-vinylimidazolium ion, 1-ethyl-3-methylimidazolium ion, 1-hexyl-3-methylimidazolium ion, 1-(2-hydroxyethyl)-3-methylimidazolium ion, 1-hexyl-3-methylimidazolium ion, 1-(2-hydroxyethyl)-3-methylimidazolium ion, 1-hexyl-3-methylimidazolium ion, 1-methyl-3-propylimidazolium ion, 1-methyl-3-n-octylimidazolium ion, 1-methyl-3-propylimidazolium ion, 1-methyl-3-pentylimidazolium ion, 1-methyl-3-n-octylimidazolium ion, 1-methyl-3-propylimidazolium ion, and the like.

[0041] Examples of the pyridinium ion in the electrolyte include a 1-butylpyridinium ion, a 1-butyl-4-methylpyridinium ion, a 1-ethyl-3-methylpyridinium ion, and a 1-ethyl-3-(hydroxymethyl)pyridinium ion.

[0042] Examples of the quaternary ammonium ion in the electrolyte include triethylpentylammonium ion, diethyl(methyl)propylammonium ion, methyltri-n-octylammonium ion, trimethylpropylammonium ion, cyclohexyltrimethylammonium ion, diethyl(2-methoxyethyl)-methylammonium ion, ethyl(2-methoxyethyl)-dimethylammonium ion, ethyl(3-methoxypropyl)dimethyl-ammonium ion, ethyl(dimethyl)(2-phenylethyl)-ammonium ion, tetramethylammonium ion, tetraethylammonium ion, triethylpentylammonium ion, tetra-n-butylammonium ion, diethyl(methyl)propylammonium ion, methyltri-n-octylammonium ion, trimethylpropylammonium ion, cyclohexyltrimethylammonium ion, diethyl(2-methoxyethyl)-methylammonium ion, ethyl(2-methoxyethyl)-dimethylammonium ion, ethyl(3-methoxypropyl)dimethyl-ammonium ion, and ethyl(dimethyl)(2-phenylethyl)-ammonium ion.

[0043] Examples of the phosphonium ion in the electrolyte include a tributylmethylphosphonium ion and a tributylethylphosphonium ion.

[0044] Examples of the pyrrolidinium ion in the electrolyte include a 1-allyl-1-methylpyrrolidinium ion, a 1-butyl-1-methylpyrrolidinium ion, a 1-methyl-1-propylpyrrolidinium ion, and a 1-(2-methoxyethyl)-1-methylpyrrolidinium ion.

[0045] The solution used in the anode tank 26 is preferably water, purified water, or an aqueous sulfuric acid solution (water containing H2SO4), and the solution used in the cathode tank 27 is preferably an ionic liquid, water, or an aqueous sulfuric acid solution (water containing H2SO4), of which 1-butyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate, 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide, or an aqueous sulfuric acid solution (water containing H2SO4) is more preferred.

[0046] In the anode chamber 26, if the solution and electrolyte used in the chamber are non-aqueous, water may be added to carry out this embodiment. The water used in the anode chamber 26 is converted into oxygen, protons, and electrons by the catalytic action of the anode 23 (2H2O→O2+4e - +4H + The protons move through the ion exchange membrane 22 to the cathode 24, and the electrons move through the current collector 25 on the cathode 24 side to the power supply 30. The generated oxygen can be released to the atmosphere while being partially dissolved in the solution in the anode tank 26, or the oxygen can be forcibly expelled by bubbling nitrogen gas into the solution in the anode tank 26.

[0047] Nitrogen gas is supplied to the cathode tank 27. As shown in FIG. 2, nitrogen gas is supplied from a nitrogen cylinder 31 at a flow rate controlled by a regulator 32 and a mass flow controller 33, and is supplied by bubbling the nitrogen gas through a gas pipe 34 into the solution in the cathode tank 27. In the cathode 24, the above-mentioned molybdenum complex causes the nitrogen gas supplied to the cathode tank 27, protons that have migrated from the anode 23 through the ion exchange membrane 22 or protons derived from the solution used in the cathode tank 27, and electrons supplied from the power supply unit 30 to react with each other to generate ammonia (N2+6e - +6H +→2NH3). The mixed gas consisting of ammonia produced in the cathode 24, by-produced hydrogen, and unreacted nitrogen is sent from the cathode tank 27 through a gas pipe 35 to a dilute sulfuric acid aqueous solution tank 36 for collecting ammonia. When the mixed gas passes through the dilute sulfuric acid aqueous solution tank 36, the ammonia is collected in the dilute sulfuric acid aqueous solution, or in the solution used in the cathode tank 27, or in both cases. The by-produced hydrogen and nitrogen are safely discharged to the outside through a draft device 37. Putty or a sealant is used at the connection between the gas pipes 34, 35 and the cathode tank 27 to prevent gas leakage.

[0048] It goes without saying that the present invention is not limited to the above-described embodiment, and can be embodied in various forms within the technical scope of the present invention. EXAMPLES

[0049] EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to the following examples in any way.

[0050] [Experimental Example 1] 1. Preparation of ammonia production apparatus 10 First, the anode 23 was prepared as follows. The catalyst ink used for the anode 23 was prepared using platinum-supported carbon (Tanaka Kikinzoku Kogyo Co., Ltd., platinum content: 46.5 wt%, product name "TEC10E50E"), deionized water, ethanol (Fujifilm Wako Pure Chemical Industries, Ltd.), and Nafion dispersion solution as an electrolyte (Fujifilm Wako Pure Chemical Industries, Ltd., product name "5% Nafion Dispersion Solution DE521 CS type"). The platinum-supported carbon, deionized water, ethanol, and Nafion dispersion solution were added in this order to a glass vial, and the resulting dispersion solution was irradiated with ultrasonic waves using an ultrasonic homogenizer Smurt NR-50M manufactured by Microtech Nithion Co., Ltd. at an output of 40% for 30 minutes to prepare the catalyst ink. Next, this catalyst ink was applied to a carbon paper (Toray Industries, product name "TGP-H-090H", 2.9 cm x 2.9 cm square) fixed to a hop plate at 80°C. The amount of application was 1 cm per 1 cm of the applied surface. 2 The amount of platinum per unit area was adjusted to 2.4 mg. In this manner, an anode 23 containing a platinum catalyst (20 mg) was produced.

[0051] The proportion of Nafion (hereinafter, abbreviated as ionomer) which is a proton conductive ionomer in the above-mentioned catalyst ink will be described. In preparing the catalyst ink, the proportion (wt%) of the ionomer calculated from the following formula was set to 28 wt%. Ionomer ratio (wt%) = [Ionomer solid content (weight) / [{Platinum-supported carbon (weight) + ionomer solid content (weight)}] × 100 Specifically, when the ionomer was Nafion, the amount of platinum-supported carbon was 100.0 mg, the amount of Nafion dispersion solution was 837 μL, the amount of deionized water was 0.6 mL, and the amount of ethanol was 5 mL. The Nafion solid content in the Nafion dispersion solution (837 μL) was 38.9 mg.

[0052] Next, the cathode 24 was prepared as follows. Before preparing the cathode 24, a composition of Ketjen Black and Nafion (hereinafter referred to as composition 1) was prepared as follows. Ketjen Black (535 mg, manufactured by Lion Corporation, product name "EC600JD") and Nafion dispersion solution (8.37 mL, manufactured by Fujifilm Wako Pure Chemical Industries, product name "5% Nafion Dispersion Solution DE521 CS type") were mixed in a screw tube, and the obtained dispersion solution was irradiated with ultrasonic waves for 30 minutes using an ultrasonic homogenizer Smurt NR-50M manufactured by Microtech Nithion Co., Ltd. with an output of 40%, and then the ethanol of the Nafion dispersion solution was distilled off using an evaporator, thereby obtaining 919 mg (99% yield) of composition 1 of Ketjen Black and Nafion in the form of black powder.

[0053] The catalyst ink used for the cathode is a molybdenum complex (1) represented by the following formula supported on Merrifield resin (9.1 mg, the number of moles per molybdenum is 6.6 μmol by ICP emission spectroscopy) and composition 1 (51.8 mg) crushed in a mortar to form a mixture of the molybdenum complex supported on the resin, Ketjen Black and Nafion, and then a dispersion of the mixture and an ionic liquid (1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide, 300 μL) was applied to carbon paper (Toray Industries, Inc., product name "TGP-H-090H", 2.9 cm x 2.9 cm square). In this way, the cathode 24 was prepared. The molybdenum complex (1) can be synthesized by the method described in the non-patent document Chem.Lett. 2019, Vol. 48, pp. 693-695. [ka]

[0054] Next, the membrane electrode assembly 21 was produced as follows. A DuPont Nafion 212 membrane (registered trademark) (film thickness 50 μm, 5 cm × 4 cm square) was prepared as the ion exchange membrane 22. An anode 23 was placed on one side of the ion exchange membrane 22, and a cathode 24 was placed on the other side to obtain the membrane electrode assembly 21. The anode 23 and the cathode 24 were both placed so that their catalyst-coated surfaces were in contact with the ion exchange membrane 22.

[0055] Stainless steel current collectors 25, 25 with 25 circular holes of 2.5 mm in diameter were attached to both sides of the obtained membrane electrode assembly 21. Then, an anode tank 26 was attached to the anode side current collector 25 via a Teflon (registered trademark) gasket, and a cathode tank 27 was attached to the cathode side current collector 25 via a Teflon gasket. In addition, a power supply unit 30 was connected to both current collectors 25, 25. In this manner, an ammonia production apparatus 10 was assembled.

[0056] 2. Ammonia production Using the ammonia production apparatus 10 assembled as described above, ammonia was produced under the following conditions. Temperature of device body 20: 25 to 28°C (room temperature) Voltage and current measurements were also made using a power supply 30: VersaSTAT 4 manufactured by Princeton Applied Research. Anode chamber 26: Purified water (8 mL) Cathode cell 27: 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (8 mL) Measurement conditions: constant potential measurement was performed at -2.3 V for 50 minutes.

[0057] Ammonia was quantified using a Thermo Scientific Dionex ion chromatography (IC) system, Dionex Integrion manufactured by Thermo. The amount of ammonia in the water of the dilute sulfuric acid aqueous solution tank for ammonia collection and in the ionic liquid in the cathode tank were quantified. In order to eliminate the burden on the column and suppressor of the equipment, the ammonia in the ionic liquid was first extracted into the aqueous layer with purified water and then analyzed.

[0058] The results are shown in Table 1. In Experimental Example 1, the amount of ammonia produced was 0.703 μmol, the amount of electricity used was 64.6 C, and the conversion efficiency was 0.32%. The amount of ammonia produced per 1 μmol of the complex was 106.5 nmol.

[0059] [Experimental Example 2] An ammonia production apparatus 10 was produced in the same manner as in Experimental Example 1 described above, except that the catalyst added to the cathode 24 was changed from a molybdenum complex to titanocene dichloride. Specifically, the cathode 24 was produced as follows. That is, titanocene dichloride (46.5 mg) and the above-mentioned composition 1 (92.4 mg) were ground in a mortar to obtain a mixture with the complex, Ketjen Black, and Nafion, and then a dispersion of the mixture (39 mg) and an ionic liquid (1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide, 300 μL) was applied to carbon paper to obtain the cathode 24.

[0060] Using this ammonia production apparatus 10, ammonia production was attempted in the same manner as in Experimental Example 1. The results are shown in Table 1. In Experimental Example 2, the amount of ammonia produced was 0.523 μmol, the amount of electricity used was 81.3 C, and the conversion efficiency was 0.19%. The amount of ammonia produced per 1 μmol of complex was 9.9 nmol.

[0061] [Experimental Example 3] An ammonia production apparatus 10 was produced in the same manner as in Experimental Example 1 described above, except that no catalyst was added to the cathode 24. Using this ammonia production apparatus 10, an attempt was made to produce ammonia in the same manner as in Experimental Example 1. The results are shown in Table 1. In Experimental Example 3, the amount of ammonia produced was 0.121 μmol, and ammonia derived from the components of the ammonia production apparatus 10 was confirmed.

[0062] [Consideration] It was found that in Experimental Example 1, in which a molybdenum complex was used as the cathode catalyst, 10 times more ammonia was generated than in Experimental Example 2, in which titanocene dichloride was used as the cathode catalyst. In Experimental Example 3, in which no catalyst was added to the cathode, substantially no ammonia was generated. Note that Experimental Example 1 corresponds to an embodiment of the present invention, and Experimental Examples 2 and 3 correspond to comparative examples. [Table 1]

[0063] [Experimental Example 4] The catalyst added to the cathode 24 is a molybdenum complex (2). [ka] The ammonia production apparatus 10 was produced in the same manner as in the above-mentioned Experimental Example 1, except that the ionic liquid used in the cathode tank and the catalyst layer was changed to 1-butyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate. Specifically, the cathode 24 was produced as follows. That is, the molybdenum complex (2) (6.0 mg, 6.6 μmol) and the above-mentioned composition 1 (51.8 mg) were ground in a mortar to obtain a mixture of the complex, Ketjen Black, and Nafion, and then a dispersion of the mixture and the ionic liquid (1-butyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate, 300 μL) was applied to carbon paper to obtain the cathode 24.

[0064] Using this ammonia production apparatus 10, ammonia production was attempted in the same manner as in Experimental Example 1. The results are shown in Table 2. In Experimental Example 4, the amount of ammonia produced was 0.540 μmol, the amount of electricity used was 103.6 C, and the conversion efficiency was 0.15%. The amount of ammonia produced per 1 μmol of complex was 81.8 nmol.

[0065] [Experimental Example 5] The catalyst added to the cathode 24 is a molybdenum complex (3). [ka] Except for changing the above, the ammonia production apparatus 10 was produced in the same manner as in the above-mentioned Experimental Example 4. Specifically, the molybdenum complex (3) (5.8 mg, 6.6 μmol) and the above-mentioned composition 1 (51.8 mg) were used.

[0066] Using this ammonia production apparatus 10, ammonia production was attempted in the same manner as in Experimental Example 1. The results are shown in Table 2. In Experimental Example 5, the amount of ammonia produced was 1.003 μmol, the amount of electricity used was 114.1 C, and the conversion efficiency was 0.25%. The amount of ammonia produced per 1 μmol of complex was 152.0 nmol. Experimental Examples 4 and 5 correspond to examples of the present invention. [Table 2]

[0067] [Experimental Example 6] 1. Preparation of ammonia production apparatus 10 The anode 23 was prepared as follows. The anode 23 of Experimental Example 6 was prepared in the same manner as the anode 23 of Experimental Example 1, except that the size and coating amount of the carbon paper (manufactured by Toray Industries, product name "TGP-H-090H", 2.7 cm x 2.7 cm square) were changed. The coating amount was 1 cm per 1 cm of the coated surface. 2 The amount of platinum per anode was set to 1.0 mg. Specifically, the anode 23 was a carbon paper coated with a platinum catalyst (7.3 mg) on ​​one side.

[0068] Next, the cathode 24 was prepared as follows. First, the above-mentioned molybdenum complex (3) (5.8 mg) was dissolved in 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (1.0 mL) to prepare a catalyst ink. Next, the above-mentioned catalyst ink (50 μL) was applied to carbon paper (manufactured by Toray Industries, Inc., product name "TGP-H-090H", 2.7 cm x 2.7 cm square) to prepare the cathode 24 of Experimental Example 6. Specifically, the cathode 24 is a carbon paper coated on one side with the molybdenum complex represented by formula (3) (0.29 mg, 0.33 μmol) and the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (50 μL).

[0069] Next, the membrane electrode assembly 21 was prepared as follows. As the ion exchange membrane 22, a DuPont Nafion 212 membrane (film thickness 50 μm, 5 cm × 4 cm square) was prepared. The anode 23 prepared above was placed on one side of the ion exchange membrane 22, and the cathode 24 prepared above was placed on the other side, and then the anode 23 and the cathode 24 were thermocompressed under the conditions of upper and lower plate temperatures of 132° C., load of 5.4 kN, and compression time of 240 seconds to obtain the membrane electrode assembly 21 of Experimental Example 6. The anode 23 and the cathode 24 were both placed so that the catalyst-coated surfaces were in contact with the ion exchange membrane 22.

[0070] Stainless steel current collectors 25, 25 with 25 circular holes of 2.5 mm in diameter were attached to both sides of the obtained membrane electrode assembly 21. Then, an anode tank 26 was attached to the anode side current collector 25 via a Teflon gasket, and a cathode tank 27 was attached to the cathode side current collector 25 via a Teflon gasket. In addition, a power supply unit 30 was connected to both current collectors 25, 25. In this manner, the ammonia production apparatus 10 of Experimental Example 6 was assembled.

[0071] 2. Ammonia production Using the ammonia production apparatus 10 assembled as described above, ammonia was produced under the following conditions. Temperature of device body 20: 25 to 28°C (room temperature) Voltage and current measurements were also made using a power supply 30: VersaSTAT 4 manufactured by Princeton Applied Research. Anode chamber 26: 0.02 mol / L sulfuric acid aqueous solution (6 mL) Cathode cell 27: 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (6 mL) Measurement conditions: constant potential measurement was performed at -2.3 V for 60 minutes.

[0072] Ammonia was quantified using a Thermo Scientific Dionex ion chromatography (IC) system, Dionex Integrion, manufactured by Thermo Corp. The amount of ammonia in the water of the dilute sulfuric acid aqueous solution tank for ammonia capture and in the ionic liquid in the cathode tank was quantified.

[0073] In Experimental Example 6, the amount of ammonia produced was 0.390 μmol, the amount of electricity used was 21.8 C, and the conversion efficiency was 0.52%. The amount of ammonia produced per 1 μmol of complex was 1180 nmol. In comparison with Example 5, which used the same molybdenum complex (3), the amount of ammonia produced per 1 μmol of complex per 50 minutes was 983.3 nmol, which was about 6 times higher.

[0074] [Experimental Example 7] Except for changing the solution used in the catalyst ink when preparing the cathode 24 to dichloromethane (1.0 mL) and changing the solution used in the cathode tank 27 to a 0.02 mol / L sulfuric acid aqueous solution (6 mL), the ammonia production apparatus 10 was prepared in the same manner as in the above-mentioned Experimental Example 6, and ammonia production was carried out. The amount of ammonia produced was 0.20 μmol, the amount of electricity used was 105.1 C, and the conversion efficiency was 0.06%. The amount of ammonia produced per 1 μmol of complex was 606.1 nmol. In comparison with Example 5 using the same molybdenum complex (3), the amount of ammonia produced per 1 μmol of complex per 50 minutes was 505.1 nmol, which was about three times higher. It should be noted that Experimental Examples 6 and 7 correspond to examples of the present invention.

[0075] This application claims priority from Japanese Patent Application No. 2019-162176, filed on September 5, 2019, the entire contents of which are incorporated herein by reference. [Industrial Applicability]

[0076] The present invention can be used in a method for producing ammonia.

Claims

1. A method for producing ammonia from nitrogen molecules in the presence of a complex and a proton source using electrons supplied from a power source, comprising: The complex is (A) a molybdenum complex having 2,6-bis(dialkylphosphinomethyl)pyridine as a PNP ligand (wherein the two alkyl groups may be the same or different, and at least one hydrogen atom of the pyridine ring may be substituted with an alkyl group, an alkoxy group or a halogen atom); (B) a molybdenum complex having 1,3-bis(dialkylphosphinomethyl)benzimidazol-2-ylidene as a PCP ligand (wherein the two alkyl groups may be the same or different, and at least one hydrogen atom on the benzene ring may be substituted with an alkyl group, an alkoxy group or a halogen atom); (C) a molybdenum complex having a bis(dialkylphosphinoethyl)arylphosphine (wherein the two alkyl groups may be the same or different) as a PPP ligand, or (D) a trans-Mo(N 2 ) 2 (R 5 R 6 R 7 P) 4 (However, R 5 and R 6 are aryl groups which may be the same or different, R 7 is an alkyl group, and two R 7 may be linked to each other to form an alkylene chain), The proton source is the electrolyte membrane, the solution used in the cathode chamber, or both the electrolyte membrane and the solution used in the cathode chamber; A method for producing ammonia.

2. The molybdenum complex (A) is represented by the following formula (A1), (A2) or (A3): 【Chemistry 1】 (In the formula, R 1 and R 2 are alkyl groups which may be the same or different, X is an iodine atom, a bromine atom or a chlorine atom, and at least one hydrogen atom on the pyridine ring may be substituted with an alkyl group, an alkoxy group or a halogen atom. The method for producing ammonia according to claim 1 .

3. The molybdenum complex (B) is represented by the following formula (B1) or (B2): 【Chemistry 2】 (In the formula, R 1 and R 2 are alkyl groups which may be the same or different, X is an iodine atom, a bromine atom or a chlorine atom, at least one hydrogen atom on the benzene ring may be substituted with an alkyl group, an alkoxy group or a halogen atom, R 3 and R 4 at least one of which is substituted with a trifluoromethyl group; The method for producing ammonia according to claim 1 .

4. The molybdenum complex (C) is represented by the formula (C1): 【Chemistry 3】 (In the formula, R 1 and R 2 are alkyl groups which may be the same or different, R 5 is an aryl group, and X is an iodine atom, a bromine atom, or a chlorine atom; The method for producing ammonia according to claim 1 .

5. The molybdenum complex (D) is represented by the formula (D1) or (D2): 【Chemistry 4】 (In the formula, R 5 and R 6 are aryl groups which may be the same or different, R 7 is an alkyl group, and n is 2 or 3; The method for producing ammonia according to claim 1 .

6. As the nitrogen molecules, nitrogen gas at normal pressure is used. The method for producing ammonia according to any one of claims 1 to 5.

7. an apparatus main body including a membrane electrode assembly having a structure in which an ion exchange membrane is sandwiched between a cathode and an anode, a pair of current collectors sandwiching the membrane electrode assembly, an anode tank disposed on the current collector side in contact with the anode, a cathode tank disposed on the current collector side in contact with the cathode, and a nitrogen gas supply unit that supplies nitrogen gas to the cathode tank; a power supply device connected to the pair of current collectors outside the device body; Equipped with The cathode contains, as a catalyst, (A) a molybdenum complex having 2,6-bis(dialkylphosphinomethyl)pyridine as a PNP ligand (wherein the two alkyl groups may be the same or different, and at least one hydrogen atom of the pyridine ring may be substituted with an alkyl group, an alkoxy group or a halogen atom); (B) a molybdenum complex having 1,3-bis(dialkylphosphinomethyl)benzimidazol-2-ylidene as a PCP ligand (wherein the two alkyl groups may be the same or different, and at least one hydrogen atom on the benzene ring may be substituted with an alkyl group, an alkoxy group or a halogen atom); (C) a molybdenum complex having a bis(dialkylphosphinoethyl)arylphosphine (wherein the two alkyl groups may be the same or different) as a PPP ligand, or (D) a trans-Mo(N 2 ) 2 (R 5 R 6 R 7 P) 4 (However, R 5 and R 6 are aryl groups which may be the same or different, R 7 is an alkyl group, and two R 7 may be linked to each other to form an alkylene chain), The anode comprises a catalyst for producing protons from water. Ammonia production plant.

8. The solution used in the anode bath is water or an aqueous sulfuric acid solution (H 2 SO 4 The solution used in the cathode bath is water, an aqueous sulfuric acid solution (H 2 SO 4 water containing the compound (I) or an ionic liquid; The ammonia production apparatus according to claim 7.

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