Method for producing ammonia

Abstract

To provide a method for producing ammonia capable of producing ammonia without using samarium.SOLUTION: A method for producing ammonia includes producing ammonia from nitrogen using (1) a nitrogen-activating complex, (2) a proton source, (3) an electron source, and (4) a Lewis acid that does not contain samarium as a constituent element.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to a method for producing ammonia. Specifically, the disclosed technology relates to an ammonia production method that can produce ammonia without using samarium, which is a rare earth. [Background technology]

[0002] Ammonia is an important chemical raw material used as a basic material for fertilizers and chemical products, and in recent years has been attracting attention for its use in co-firing coal-fired power plants and as an energy carrier. German researchers Haber and Bosch succeeded in mass-producing ammonia chemically more than 100 years ago using an iron-based catalyst. This Haber-Bosch process produces ammonia by reacting nitrogen in the air with hydrogen in fossil fuels, as shown in the reaction formula below. N2+3H2→ 2NH3 However, the above reaction is carried out under high temperature and pressure conditions (400 to 600°C, 100 to 200 atm). In addition, the hydrogen used is derived from fossil fuels and emits carbon dioxide, a greenhouse gas.

[0003] A method of obtaining hydrogen by electrolysis of water using renewable energy has also been proposed. However, the production of ammonia requires large equipment made of special materials, and requires a large amount of energy.

[0004] Nishibayashi et al. found that it is possible to produce ammonia using a specific Mo complex catalyst at room temperature and pressure using water as a proton source (Patent Documents 1 and 2 and Non-Patent Document 1). Nishibayashi et al. also improved the activity of the catalyst by introducing an electron-withdrawing group into a specific Mo complex catalyst (Patent Document 3 and Non-Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2010-195703 A [Patent Document 2] JP 2013-159568 A [Patent Document 3] International Publication No. 2022 / 025054 [Non-patent literature]

[0006] [Non-Patent Document 1] Y.Ashida, K.Arashiba, K.Nakajima, and Y.Nishibayashi., Molybdenum-Catalysed Ammonia Production with Samarium Diiodide and Alcohols or Water, Nature, 2019, 568, 536-540 [Non-Patent Document 2] Y.Ashida, T.Mizushima, K.Arashiba, A.Egi, H.Tanaka, K.Yoshizawa, and Y.Nishibayashi., Catalytic Production of Ammonia from Dinitrogen Employing Molybdenum Complexes Bearing N-Heterocyclic Carbene-Based PCP-Type Pincer Ligands, Nature Synthesis, 2023, 2, 635-644 Summary of the Invention [Problem to be solved by the invention]

[0007] By the way, to produce ammonia from nitrogen, protons (H + ) and electrons (e -) must be supplied. Here, even if one tries to use H2O as a proton source and an electron source, it is usually difficult because the OH bond in H2O is very strong. In contrast, in the above-mentioned conventional technology, H2O is coordinated to SmI2 to weaken the OH bond in H2O, and protons (H + ) and electrons (e - As a result, in the presence of the Mo complex, ammonia is produced from nitrogen through the following ammonia production reaction: PCET reaction SmI2+H2O→SmI2(H2O)→SmI2(OH)+H + +e - Ammonia production reaction (in the presence of Mo complex catalyst) N2+6SmI2+6H2O→2NH3+6SmI2(OH)

[0008] However, the above-described ammonia production method requires three times the molar amount of a reducing agent containing samarium, a rare earth, relative to the amount of ammonia produced, and therefore there is room for improvement in terms of cost, etc.

[0009] One of the objects of the disclosed technique is to provide an ammonia production method capable of producing ammonia without using samarium. [Means for solving the problem]

[0010] As a result of intensive research, the present inventors have found that ammonia can be produced from nitrogen without using samarium by using a nitrogen activating complex, a proton source, an electron source, and a Lewis acid that does not contain samarium as a constituent element, and have completed the disclosed technology. According to the disclosed technique, the following ammonia production method and the like can be provided. 1. A method for producing ammonia from nitrogen using (1) a nitrogen activating complex, (2) a proton source, (3) an electron source, and (4) a Lewis acid that does not contain samarium as a constituent element. 2. The method for producing ammonia according to 1, further comprising reducing the nitrogen-activating complex. 3. The method for producing ammonia according to 1 or 2, wherein the Lewis acid is a Lewis acid that exhibits a pH of 2.0 to 8.3 when reacted with water. 4. The method for producing ammonia according to any one of 1 to 3, wherein the Lewis acid is a Lewis acid that does not contain chlorine as a constituent element. 5. The method for producing ammonia according to any one of 1 to 3, wherein the Lewis acid is one or more selected from the group consisting of boron compounds, neodymium compounds, ytterbium compounds, lanthanum compounds, hafnium compounds, iron compounds, aluminum compounds, gallium compounds, scandium compounds, indium compounds, silver compounds, copper compounds, yttrium compounds, titanium compounds, zinc compounds, and manganese compounds. 6. The method for producing ammonia according to any one of 1 to 5, wherein the Lewis acid is one or more selected from the group consisting of trispentafluorophenylborane, yttrium (III) trifluoromethanesulfonate, scandium (III) triflate, neodymium (III) triflate, ytterbium (III) triflate, lanthanum (III) triflate, boron trifluoride diethyl ether complex (BF3·Et2O), manganese (II) trifluoromethanesulfonate, 2,4-(CF3)2-C6H3)3B, B(Mesityl)2F, FeCl3, GaCl3, YbCl3·6H2O, hafnium (IV) triflate, and AlCl3. 7. The method for producing ammonia according to any one of 1 to 6, wherein the complex that activates nitrogen is a molybdenum complex. 8. The method for producing ammonia according to any one of 1 to 7, wherein the proton source includes one or more selected from the group consisting of water and alcohols. 9. The method for producing ammonia according to any one of 1 to 8, wherein the electron source includes one or more selected from the group consisting of a reducing agent and an electrode. 10. The method for producing ammonia according to any one of 1 to 9, wherein the electron efficiency in ammonia production is 10% or more. Effect of the Invention

[0011] According to the disclosed technique, it is possible to provide an ammonia production method capable of producing ammonia without using samarium. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram showing an example of an ammonia production apparatus for carrying out an ammonia production method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The ammonia synthesis catalyst, the ammonia production apparatus, and the ammonia production method of the present disclosure will be described in detail below. In this specification, "x to y" represents a numerical range of "not less than x and not more than y." The upper and lower limit values ​​described in relation to the numerical ranges can be combined in any combination. In addition, among the individual embodiments of the aspects of the disclosed technology described below, it is possible to combine two or more embodiments that are not mutually contradictory, and an embodiment combining two or more embodiments is also an embodiment of the aspects of the disclosed technology.

[0014] An ammonia production method according to one embodiment of the disclosed technique produces ammonia from nitrogen using (1) a nitrogen-activating complex, (2) a proton source, (3) an electron source, and (4) a Lewis acid that does not contain samarium as a constituent element. According to this embodiment, an effect is obtained in which ammonia can be produced without using samarium, which is a rare earth.

[0015] The reason why the above effect is obtained is presumed to be that the dissociation of protons from the proton source is promoted by the Lewis acid. That is, by coordinating with HO, the OH bond of HO can be weakened. In addition, by using a Lewis acid, it is possible to use alcohols and the like as a proton source, not limited to HO. As an example, the reaction in which the Lewis acid is trispentafluorophenylborane {(C6F5)3B} and the proton source is water is shown below by a reaction formula. Addition reaction of a proton source to a Lewis acid (C6F5)3B+H2O→{(C6F5)3B-H2O} Ammonia formation reaction (in the presence of nitrogen-activating complexes) N2+6{(C6F5)3B-H2O}+6e - →2NH3+6{(C6F5)3B(OH)} -

[0016] Furthermore, as shown in the above "Addition reaction of a proton source to a Lewis acid", unlike the case of using a reducing agent containing samarium, this addition reaction does not require the use of electrons (e - Therefore, various proton sources and various electron sources can be combined with high versatility as required, allowing ammonia to be produced with a high degree of freedom.

[0017] (1) Nitrogen Activation Complex As used herein, "activating nitrogen" refers to activating a proton (H + ) and electrons (e - ) (which can also be said to "promote the production of ammonia"). The nitrogen-activating complex can also be called an "ammonia-production catalyst." The complex that activates nitrogen is not particularly limited as long as it can activate nitrogen, and a complex that corresponds to the solubility in an organic solvent and, when a reducing agent is used in combination, the reactivity with the reducing agent can be appropriately used.

[0018] In one embodiment, the nitrogen-activating complex comprises a metal ion. In one embodiment, the metal ions are Mo ions, Re ions, Mn ions, Co ions, Fe ions, Cr ions, Os ions, Ti ions, V ions, Ru ions, Pt ions, Ir ions, or W ions, which provides an effect of suitably activating nitrogen. In one embodiment, the metal ion is a Mo ion. Complexes containing Mo ions are also referred to as "molybdenum complexes."

[0019] In one embodiment, the nitrogen-activating complex comprises a metal ion and a ligand that includes an aromatic ring structure. The aromatic ring structure contained in the ligand may be one aromatic ring, or may be a fused ring formed by condensing two or more aromatic rings. An aromatic ring structure consisting of a fused ring formed by condensing two or more aromatic rings is also called an "aromatic polycyclic structure." In one embodiment, the aromatic ring structure has 1-10, 1-8, 1-6, or 1-5 aromatic rings.

[0020] In one embodiment, the aromatic ring constituting the aromatic ring structure has 5 to 10, 5 to 8, or 5 to 6 ring-forming atoms. In one embodiment, the aromatic ring structure is composed of one or more rings selected from the group consisting of 5-membered rings and 6-membered rings. In one embodiment, the aromatic ring structure consists exclusively of one or more six-membered rings.

[0021] The ring-forming atoms of the aromatic ring constituting the aromatic cyclic structure may be only carbon atoms, or may include carbon atoms and atoms other than carbon atoms (heteroatoms: for example, nitrogen atoms, oxygen atoms, sulfur atoms, boron atoms, phosphorus atoms, etc.). Specific examples of the aromatic ring constituting the aromatic ring structure include a benzene ring, a pyridine ring, a pyridazine ring, a pyrimidine ring, and a pyrazine ring. The aromatic ring structure may contain, for example, quinoline, quinoxaline, etc. as a partial structure constituting the aromatic ring structure.

[0022] In one embodiment, the aromatic cyclic structure of the ligand carries one or more substituents or has no substituents. In one embodiment, the aromatic ring structure of the ligand bears one or more substituents.

[0023] The substituent that the aromatic ring structure may have is not particularly limited, and examples thereof include electron-withdrawing groups. Electron-withdrawing groups, also known as electron-withdrawing groups or electron-accepting groups, refer to substituents that attract electrons from the bonding electron side compared to hydrogen atoms due to the mesomeric effect or inductive effect in the electron theory (which is a theory that attempts to interpret as unified as possible by focusing on changes in the electron density and bonding state of reactants).

[0024] Examples of electron-withdrawing groups include substituents whose mesomeric effect is electron-donating but whose inductive effect is electron-withdrawing, more specifically, fluorine atom, chlorine atom, bromine atom, iodine atom, -CH2Cl, -CH=CHNO2, etc. Examples of electron-withdrawing groups include substituents whose mesomeric effect and inductive effect are electron-withdrawing, more specifically, quaternary ammonium groups with an anion as a counter ion, trifluoromethyl groups, perfluoroalkyl groups, trichloromethyl groups, cyano groups, nitro groups, formyl groups, carboxylic acid groups, carbonyl (C 1-6 Alkyl) group, carbonyl (C 1-6 alkoxy) group, carbonyl (Ar 6-10 aryl) group, carbonylamino group, carbonyl (C 1-6 alkyl)amino group, carbonyldi(C 1-6 alkyl)amino group, sulfonic acid group, sulfonylamino group, sulfonyl (C 1-6 alkyl)amino group, sulfonyldi(C 1-6 alkyl)amino group, Ar 6-10 Examples of the alkyl group include an aryl group.

[0025] Among the electron-withdrawing groups exemplified above, -NH3 cation, -N trimethyl cation, -N triethyl cation, -N dimethylphenyl cation, -(CF2)9CF3 and -(CF2)11 CF3, a fluorine atom, a chlorine atom and a trifluoromethyl group are preferred, and a fluorine atom, a chlorine atom and a trifluoromethyl group are particularly preferred.

[0026] The substituent that the aromatic ring structure may have is not limited to the electron-withdrawing groups exemplified above, and may be any substituent including a substituent other than an electron-withdrawing group. The substituent that the aromatic ring structure may have may be given for the purpose of improving the electronic state, solubility, and stability of the compound of the complex, for example. In addition, the aromatic ring structure may not have a substituent.

[0027] Examples of the substituent other than the electron-withdrawing group include a hydrocarbon group other than the electron-withdrawing group. Examples of the hydrocarbon group other than the electron-withdrawing group include an alkyl group having 1 to 6 carbon atoms. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, an i-propyl group, an i-butyl group, an s-butyl group, a t-butyl group, an i-pentyl group, a neopentyl group, a t-pentyl group, a 1,1-dimethylpropyl group, an i-hexyl group, and a cyclohexyl group.

[0028] The ligand of the nitrogen activating complex has an electron-withdrawing group, which provides an effect of excellent catalytic activity during ammonia synthesis. In addition, the ligand of the nitrogen activating complex contains an aromatic ring structure, particularly an aromatic polycyclic structure, which also provides an effect of excellent catalytic activity during ammonia synthesis.

[0029] In one embodiment, the ligand is a pincer type, which allows the ligand to coordinate to the metal ion from three directions, thus improving the stability of the catalyst.

[0030] In one embodiment, the coordination atoms of the ligand are three or more atoms selected from the group consisting of nitrogen atom (N), carbon atom (C), phosphorus atom (P), sulfur atom (S), arsenic atom (As), boron atom (B) and silicon atom (Si). This provides an effect of improving the stability of the ammonia synthesis catalyst.

[0031] In one embodiment, the complex is represented by formula (A): [ka]

[0032] During the ceremony, M is the metal ion; Z 1 ~Z 3 each represents a carbon atom, a nitrogen atom, or a boron atom, L 1 and L 2 each represents a single bond or a divalent group, Z 4 and Z 5 is a group containing a coordination atom, X is a ligand; p is an integer of 0 to 5. When p is 2 or more, the two or more Xs may be different from each other or may be the same. p varies depending on the valence of the metal ion. In formulas (1) and (2), the bond between M and X is shown as one dotted line, but is not limited to one (single bond) and may be a double bond or a triple bond. Rg1 is an aromatic ring structure.

[0033] Z 1 ~Z 3 are the atoms forming Rg1. Examples of the divalent group include alkylene groups having 1 to 4 carbon atoms, such as a methylene group or an ethylene group, and arylene groups, such as a phenylene group. In the group containing a coordinating atom, the coordinating atom may be N, C, P, S, As, B or Si as described above. Examples of groups containing a coordinating atom include a hydrocarbon ring containing a coordinating atom, a heterocycle containing a coordinating atom, >PR2, >NR2, >AsR2, etc. R is an alkyl group, an aryl group such as a phenyl group, or an aliphatic hydrocarbon ring group such as an adamantyl group.

[0034] In one embodiment, the coordination atoms of the ligand are two phosphorus atoms and one carbon atom (PCP type, as shown in formula (A) Z 4 Z 2 Z5 ), two phosphorus atoms and one nitrogen atom (PNP type), two arsenic atoms and one nitrogen atom (AsNAs type), two phosphorus atoms and one boron atom (PBP type), two sulfur atoms and one carbon atom (SCS type), three nitrogen atoms (NNN type), two phosphorus atoms and one silicon atom (PSiP type), or three phosphorus atoms (PPP type).

[0035] In one embodiment, the aromatic cyclic structure (Rg1) in formula (A) consists of one aromatic ring. In one embodiment, the aromatic cyclic structure (Rg1) in formula (A) is an aromatic polycyclic structure.

[0036] In one embodiment, the nitrogen activating complex has a tertiary phosphine ancillary ligand.

[0037] In one embodiment, the complex is represented by the following formula (1) or the following formula (2): [ka]

[0038] In formula (1) and formula (2), M is the metal ion; X is a ligand; R 1 ~R 4 are each independently an alkyl group having 1 to 6 carbon atoms, p is an integer of 0 to 5. When p is 2 or more, the two or more Xs may be different from each other or may be the same. p varies depending on the valence of the metal ion. In formulas (1) and (2), the bond between M and X is shown as one dotted line, but is not limited to one (single bond) and may be a double bond or a triple bond. The ring represented by the dashed line is the aromatic ring structure. The aromatic ring structure may bear one or more substituents or may be unsubstituted.

[0039] In one embodiment, X are the same as each other. Ligands represented by X include halogen atoms, nitrogen atoms, and the like.

[0040] R 1 ~R 4 Examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, a trifluoromethyl group, an ethyl group, an i-propyl group, an i-butyl group, an s-butyl group, a t-butyl group, an i-pentyl group, a neopentyl group, a t-pentyl group, a 1,1-dimethylpropyl group, an i-hexyl group, and a cyclohexyl group. R 1 ~R 4 The alkyl group preferably has 2 to 6 carbon atoms, and more preferably has 3 to 6 carbon atoms. In one embodiment, R 1 ~R 4 are identical to each other.

[0041] In one embodiment, the complex is represented by formula (1A) or formula (2A):

[0042] [ka]

[0043] In formula (1A) and formula (2A), M is the metal ion; X 1 ~X 3 are each independently an iodine atom, a bromine atom, or a chlorine atom, R 1 ~R 4 are each independently an alkyl group having 1 to 6 carbon atoms, The ring represented by the dashed line is the aromatic ring structure. The aromatic ring structure may bear one or more substituents or may be unsubstituted. In one embodiment, X 1 ~X 3 are identical to each other.

[0044] In one embodiment, the aromatic ring structure in formula (1), formula (2), formula (1A) and formula (2A) is composed of one aromatic ring. In one embodiment, the aromatic cyclic structures in Formula (1), Formula (2), Formula (1A) and Formula (2A) are aromatic polycyclic structures.

[0045] As a complex that activates nitrogen, for example, the complexes described in WO 2022 / 025054, JP 2010-195703 A and JP 2013-159568 A may be used.

[0046] (2) Proton source The proton source is not particularly limited as long as it is a substance capable of supplying a proton to a nitrogen-activating complex (in a state in which nitrogen is activated) under the action of a Lewis acid. In one embodiment, the proton source comprises one or more selected from the group consisting of water and alcohols, such as methanol, ethanol, propanol, butanol, trifluoroethanol, phenol, ethylene glycol, and the like. In one embodiment, the proton source comprises water.

[0047] (3) Electron source The electron source can be anything that can reduce the nitrogen activating complex. To be more specific, "reducing the nitrogen activating complex" means reducing the central element (metal ion) of the nitrogen activating complex. This promotes the production of ammonia. In one embodiment, the electron source comprises one or more selected from the group consisting of a reducing agent and an electrode. The reducing agent is not particularly limited, but from the viewpoint of further promoting the production of ammonia, for example, a compound having an oxidation-reduction potential of -0.40 (V vs. SCE) or less and soluble in an organic solvent is preferred ("SCE" means saturated calomel electrode). Also, from the viewpoint of further promoting the synthesis reaction of ammonia, the reduction potential of the reducing agent is preferably more noble than the competing reaction of hydrogen production by reduction of a proton source, and is preferably more noble than -2.0 (V vs. SCE). Specific examples of the reducing agent include metallocene compounds such as chromocene, decamethylchromocene, cobaltocene, and decamethylcobaltocene, potassium graphite (KC8), alkali metals, and alkaline earth metals. When an electrode is used, the nitrogen-activating complex may receive electrons directly from the electrode, or may receive electrons from the electrode via a mediator (electron mediator). The electron mediator is not particularly limited, and examples thereof include metallocene compounds such as chromocene, decamethylchromocene, cobaltocene, and decamethylcobaltocene. The reducing agent and mediator are preferably those that do not contain samarium as a constituent element.

[0048] As described above, the technology of Patent Document 1 weakens the OH bond in H2O by coordinating SmI2 to H2O, and supplies both protons and electrons via SmI2 by the PCET reaction. In other words, the proton supply path to the nitrogen-activating complex (in a nitrogen-activated state) and the electron supply path are not independent of each other (both paths have a common intermediate point, SmI2). In contrast, in this embodiment, the proton supply path to the nitrogen activating complex (in an activated nitrogen state) and the electron supply path can be made independent of each other. That is, protons from the proton source can be supplied to the nitrogen activating complex (in an activated nitrogen state) by the action of a Lewis acid on the proton source (for example, coordination of a Lewis acid). On the other hand, electrons from the electron source can be supplied to the nitrogen activating complex (in an activated nitrogen state) independently of the above-mentioned proton supply path (both paths do not have a common waypoint). In this respect, the present embodiment is essentially different from the technique of Patent Document 1, and various proton sources and various electron sources can be combined with high versatility, allowing ammonia to be produced with a high degree of freedom.

[0049] (4) Lewis acids that do not contain samarium as a constituent element The Lewis acid may be an atom, molecule, or ion having an empty electron orbital capable of accepting at least one electron pair, and may also be said to be an electron pair acceptor. The Lewis acid can promote dissociation of a proton from a proton source (for example, weakening the OH bond in water, etc.). In this embodiment, the Lewis acid used does not contain samarium as a constituent element. In one embodiment, the Lewis acid not containing samarium as a constituent element is at least one selected from the group consisting of boron compounds, neodymium compounds, ytterbium compounds, lanthanum compounds, hafnium compounds, iron compounds, aluminum compounds, gallium compounds, scandium compounds, indium compounds, silver compounds, copper compounds, yttrium compounds, titanium compounds, zinc compounds, and manganese compounds.

[0050] In one embodiment, the boron compound is represented by formula (3):

[0051] [ka]

[0052] In formula (3), R11 ~R 13 are each independently selected from the group consisting of a substituted or unsubstituted phenyl group, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, an alkyl group, a perfluoroalkyl group, and a triflate group (-OSO2CF3, sometimes referred to as "OTf"). The alkyl group and the perfluoroalkyl group have 1 to 10, 1 to 8, 1 to 5, 1 to 3 or 1 to 2 carbon atoms, for example.

[0053] In one embodiment, the boron compound is represented by formula (4):

[0054] [ka]

[0055] In formula (4), R 14 ~R 16 each represents a substituent. a to c each represents an integer of 0 to 5. R 14 ~R 16 The substituent may be, for example, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, an alkyl group, a perfluoroalkyl group, or a triflate group. The alkyl group and the perfluoroalkyl group have 1 to 10, 1 to 8, 1 to 5, 1 to 3 or 1 to 2 carbon atoms, for example.

[0056] Specific examples of the boron compound include the following compounds:

[0057] [ka]

[0058] Specific examples of boron compounds include boron trifluoride diethyl ether complex (BF3·Et2O), (2,4-(CF3)2-C6H3)3B, B(Mesityl)2F, BF3, BCl3, and BBr3.

[0059] An example of the neodymium compound is neodymium(III) triflate.

[0060] Examples of ytterbium compounds include ytterbium(III) triflate, YbCl3·6H2O, and the like.

[0061] An example of the lanthanum compound is lanthanum(III) triflate.

[0062] An example of the hafnium compound is hafnium(IV) triflate.

[0063] An example of the iron compound is FeCl3.

[0064] Examples of aluminum compounds include AlF3, AlCl3, and AlBr3.

[0065] Examples of gallium compounds include GaF3, GaCl3, and gallium (III) isopropoxide.

[0066] Examples of scandium compounds include scandium(III) triflate, ScF3, ScCl3, and the like.

[0067] Examples of indium compounds include InF3, InCl3, and InBr3.

[0068] An example of the silver compound is silver trifluoromethanesulfonate.

[0069] An example of the copper compound is copper(II) trifluoromethanesulfonate.

[0070] An example of the yttrium compound is yttrium (III) trifluoromethanesulfonate.

[0071] Examples of titanium compounds include TiCl4 and titanium (IV) isopropoxide.

[0072] An example of the zinc compound is zinc(II) trifluoromethanesulfonate.

[0073] An example of the manganese compound is manganese(II) trifluoromethanesulfonate.

[0074] In one embodiment, the Lewis acid not containing samarium as a constituent element is one or more selected from the group consisting of trispentafluorophenylborane, yttrium(III) trifluoromethanesulfonate, scandium(III) triflate, neodymium(III) triflate, ytterbium(III) triflate, lanthanum(III) triflate, boron trifluoride diethyl ether complex (BF3·Et2O), manganese(II) trifluoromethanesulfonate, (2,4-(CF3)2-C6H3)3B, B(Mesityl)2F, FeCl3, GaCl3, YbCl3·6H2O, hafnium(IV) triflate, and AlCl3.

[0075] Lewis acids (those that do not contain samarium as a constituent element) exhibit a specific pH when reacted with water. The pH may be, for example, 1.5 or more, 1.6 or more, 1.7 or more, 1.8 or more, 1.9 or more, more than 1.9, 2.0 or more, 2.2 or more, 2.4 or more, 2.6 or more, 2.8 or more, 3.0 or more, or 3.2 or more, and may be 10.0 or less, 9.8 or less, 9.6 or less, 9.4 or less, 9.2 or less, 9.0 or less, 8.8 or less, 8.6 or less, 8.5 or less, less than 8.5, 8.4 or less, or 8.3 or less. This allows ammonia to be produced efficiently. In one embodiment, the pH is preferably 1.5 to 10.0, 1.6 to 9.5, 1.7 to 9.0, 1.8 to 8.8, 1.9 to 8.5, more than 1.9 and less than 8.5, more than 1.9 and 8.4 or less, or further preferably 2.0 to 8.3, which allows ammonia to be produced more efficiently. Incidentally, "efficient generation of ammonia" may mean high electron efficiency, which will be described later.

[0076] In one embodiment, the Lewis acid (Lewis acid not containing samarium as a constituent element) is a Lewis acid not containing chlorine as a constituent element. By using a Lewis acid not containing chlorine as a constituent element, the catalytic performance of the nitrogen activating complex is well exhibited, and ammonia is produced more efficiently.

[0077] In one embodiment, 1 to 180 moles of a proton source and 1 to 180 moles of a Lewis acid not containing samarium as a constituent element are allowed to coexist per mole of the nitrogen-activating complex. In one embodiment, when a reducing agent is used as the electron source, the reducing agent is allowed to coexist in an amount of 1 to 180 moles per mole of the complex that activates nitrogen.

[0078] In the method for producing ammonia, nitrogen, a complex activating nitrogen, a proton source, an electron source, and a Lewis acid not containing samarium as a constituent element are allowed to coexist, but it is not necessary to allow samarium iodide (SmI2) to coexist in this reaction system. However, in one embodiment, samarium iodide may be allowed to coexist in this reaction system. When the reaction system contains samarium iodide, for example, the amount of samarium iodide relative to 1 mole of Lewis acid may be 1 mole or less, 0.5 moles or less, 0.1 moles or less, 0.05 moles or less, or 0.01 moles or less.

[0079] In one embodiment, the ammonia production reaction in the ammonia production process is described as follows. Nitrogen (N2) reacts with a nitrogen-activating complex (catalyst). This activates the nitrogen (the nitrogen atom is activated by a proton (H + ) and electrons (e - ) is easily accepted. On the other hand, the addition reaction of the proton source to the Lewis acid proceeds, and the proton (H + ) becomes more easily dissociated. Also, electrons (e -) is supplied. The activated nitrogen is charged with a proton (H + ) and electrons (e - ) to produce ammonia (NH3). After ammonia (NH3) is produced, the nitrogen-activating complex (catalyst) reacts with new nitrogen (N2), and the above reaction is repeated.

[0080] FIG. 1 is a schematic diagram showing an example of an ammonia production apparatus for carrying out the ammonia production method. The illustrated ammonia production apparatus has a reaction apparatus. The reaction apparatus is made of a material with excellent chemical resistance, and a Schlenk line or the like is used, which can carry out a reaction without problems even in the presence of an organic solvent or ammonia. A stirrer (not shown) is connected to the reaction chamber, and the reaction is promoted by stirring the solvent. For example, 1,2-dimethoxyethane (DME) or THF can be used as the solvent. In addition, a supply pipe (not shown) for supplying nitrogen (N2) into the reaction chamber is connected, and a nitrogen atmosphere is always maintained inside the reaction chamber. An exhaust pipe (not shown) for discharging the generated ammonia (NH3) is connected to the reaction chamber. The ammonia discharged from the exhaust pipe is diffused and passed through a separation device using, for example, cryogenic separation, so that the raw material nitrogen is separated and ammonia is purified. The separated nitrogen is reused as a raw material.

[0081] Next, an example of an ammonia production method using the above-mentioned ammonia production apparatus will be described. First, deoxygenated THF, a nitrogen activating complex, a Lewis acid, and deoxygenated water are placed in the reactor. The reaction is carried out by stirring the mixture with a stirrer at room temperature while supplying nitrogen (N2) from a supply pipe into the reactor. When the reaction proceeds in the reactor, electrons can be supplied from the above-mentioned electron source to the nitrogen activating complex (reducing the nitrogen activating complex). The generated ammonia (NH3) is discharged from an exhaust pipe and purified by removing the raw material nitrogen in a separator. When the reaction is stopped, an aqueous potassium hydroxide solution is added to the reactor to liberate the ammonia in the solution, and the dissolved ammonia is also recovered. The remaining solution is then reused by distilling it separately.

[0082] The reaction temperature and pressure in the ammonia production reaction are not particularly limited. In the method for producing ammonia according to this embodiment, the ammonia production reaction can be suitably carried out even at room temperature and normal pressure. In one embodiment, the reaction temperature is 0 to 100°C. In one embodiment, the reaction pressure is 0.1 to 200 atmospheres in terms of absolute pressure.

[0083] In one embodiment, the electronic efficiency in ammonia production is greater than 0%, 1% or more, 2% or more, 3% or more, 4% or more, 5% or more, 7% or more, 10% or more, 15% or more, 20% or more, 25% or more, 30% or more, 35% or more, 40% or more, 45% or more, 50% or more, 55% or more, 60% or more, 65% or more, 70% or more, 75% or more, 80% or more, 85% or more, or 90% or more. The upper limit is not particularly limited, and may be, for example, 100% or less, 99% or less, 98% or less, 97% or less, 96% or less, 95% or less, 94% or less, or 93% or less. The electron efficiency is a percentage of the actual amount of ammonia produced relative to the amount of ammonia produced (theoretical value) on the assumption that all of the supplied electrons (e.g., electrons supplied from a reducing agent or an electrode) are used for ammonia production, and can be determined, for example, by the method described in the Examples. When a reducing agent is used as the electron source, the electron efficiency can be expressed as "reducing agent efficiency", and when an electrode is used as the electron source, the electron efficiency can be expressed as "Faraday efficiency". EXAMPLES

[0084] Examples of the disclosed technology are described below, but the disclosed technology is not limited to these examples.

[0085] Example 1 To a Schlenk tube under N2 flow, 10 mL of tetrahydrofuran (THF) was added as a solvent. Next, 1 μmol of a compound represented by the following formula (5) as a nitrogen activating complex, 180 μmol of a compound represented by the following formula (6) (trispentafluorophenylborane, B(C6F5)3) as a Lewis acid, 180 μmol of H2O as a proton source, and 180 μmol of decamethylchromocene as a reducing agent were added to the Schlenk flask, and the reaction was carried out for 18 hours at 25°C and 1 atm (absolute pressure). A trap for dilute sulfuric acid aqueous solution A was installed downstream of the Schlenk flask to trap gaseous ammonia produced during the reaction.

[0086] [ka]

[0087] After 18 hours, 5 mL of a 30% by mass aqueous potassium hydroxide solution was added to the Schlenk flask, and a distillation operation was performed while heating to 45° C., thereby recovering ammonia in the reaction liquid in a separately prepared dilute aqueous sulfuric acid solution B.

[0088] The amount of ammonia present in the dilute sulfuric acid aqueous solution A and B was measured by ion chromatography, and the total amount of ammonia produced was calculated by adding up these values, which was 40.0 μmol. The electronic efficiency was calculated from this total amount of ammonia produced by the following method.

[0089] How to calculate electronic efficiency Since the ammonia production reaction is a three-electron reaction, 1 mole of ammonia is produced for every 3 moles of reducing agent (3 moles of electrons). Therefore, if all of the electrons derived from the reducing agent were used to produce ammonia, the theoretical amount of ammonia produced would be 180 μmol / 3 = 60 μmol. The electron efficiency was calculated as a percentage by dividing the total amount of ammonia produced actually measured by this theoretical amount of ammonia produced.

[0090] Example 2 Ammonia was produced in the same manner as in Example 1, except that Y(OTf)3 was used as the Lewis acid instead of B(C6F5)3, and the electron efficiency was determined.

[0091] Example 3 Ammonia was produced in the same manner as in Example 1, except that Sc(OTf)3 was used as the Lewis acid instead of B(C6F5)3, and the electron efficiency was determined.

[0092] Example 4 Ammonia was produced in the same manner as in Example 1, except that Nd(OTf)3 was used as the Lewis acid instead of B(C6F5)3, and the electron efficiency was determined.

[0093] Example 5 Ammonia was produced in the same manner as in Example 1, except that Yb(OTf)3 was used as the Lewis acid instead of B(C6F5)3, and the electron efficiency was determined.

[0094] Example 6 Ammonia was produced in the same manner as in Example 1, except that La(OTf)3 was used as the Lewis acid instead of B(C6F5)3, and the electronic efficiency was determined.

[0095] Example 7 Ammonia was produced in the same manner as in Example 1, except that boron trifluoride diethyl ether complex (BF3·Et2O) was used as the Lewis acid instead of B(C6F5)3, and the electron efficiency was determined.

[0096] Example 8 Ammonia was produced in the same manner as in Example 1, except that Mn(OTf)2 was used as the Lewis acid instead of B(C6F5)3, and the electron efficiency was determined.

[0097] Example 9 Ammonia was produced in the same manner as in Example 1, except that 2,4-((CF3)2-C6H3)3B was used as the Lewis acid instead of B(C6F5)3, and the electron efficiency was determined.

[0098] Example 10 Ammonia was produced in the same manner as in Example 1, except that B(Mesityl)2F was used as the Lewis acid instead of B(C6F5)3, and the electron efficiency was determined.

[0099] Example 11 Ammonia was produced in the same manner as in Example 1 except that FeCl3 was used as the Lewis acid instead of B(C6F5)3, and the electron efficiency was determined.

[0100] Example 12 Ammonia was produced in the same manner as in Example 1 except that GaCl3 was used as the Lewis acid instead of B(C6F5)3, and the electron efficiency was determined.

[0101] Example 13 Ammonia was produced in the same manner as in Example 1, except that YbCl3·6H2O was used as the Lewis acid instead of B(C6F5)3, and the electron efficiency was determined.

[0102] Example 14 Ammonia was produced in the same manner as in Example 1, except that Hf(OTf) was used as the Lewis acid instead of B(C(C(F)) and 1,2-dimethoxyethane (DME) was used as the solvent instead of THF, and the electron efficiency was determined.

[0103] Example 15 Ammonia was produced in the same manner as in Example 1, except that 45 μmol of Yb(OTf) was used as the Lewis acid instead of 180 μmol of B(C6F5)3, ethylene glycol (EG) was used as the proton source instead of water, and decamethylcobaltocene was used as the reducing agent instead of decamethylchromocene, and the electronic efficiency was determined.

[0104] Example 16 Ammonia was produced in the same manner as in Example 1, except that 45 μmol of La(OTf) was used as the Lewis acid instead of 180 μmol of B(C6F5)3, ethylene glycol (EG) was used as the proton source instead of water, and decamethylcobaltocene was used as the reducing agent instead of decamethylchromocene, and the electronic efficiency was determined.

[0105] (Example 17) Ammonia was produced in the same manner as in Example 1, except that 45 μmol of AlCl was used instead of 180 μmol of B(C6F5)3 as the Lewis acid, ethylene glycol (EG) was used instead of water as the proton source, and decamethylcobaltocene was used instead of decamethylchromocene as the reducing agent, and the electron efficiency was determined.

[0106] Comparative Example 1 The same procedure as in Example 1 was conducted except that the use of Lewis acid was omitted, and no ammonia production was confirmed (total amount of ammonia produced was 0 μmol).

[0107] For each Lewis acid used in the examples, the pH was measured when the Lewis acid was reacted with water. Specifically, 0.1 mmol of the Lewis acid was dissolved in 10 mL of water, and the pH was measured at 25° C. using a pH meter.

[0108] The above results are shown in Table 1.

[0109] [Table 1]

Claims

1. A method for producing ammonia from nitrogen, comprising (1) a nitrogen-activating complex, (2) a proton source, (3) an electron source, and (4) a Lewis acid that does not contain samarium as a constituent element.

2. A method for producing ammonia according to claim 1, comprising reducing the nitrogen-activating complex.

3. The method for producing ammonia according to claim 1 or 2, wherein the Lewis acid is a Lewis acid that exhibits a pH of 2.0 to 8.3 when reacted with water.

4. The ammonia production method according to claim 1 or 2, wherein the Lewis acid is a Lewis acid that does not contain chlorine as a constituent element.

5. The method for producing ammonia according to claim 1 or 2, wherein the Lewis acid is one or more selected from the group consisting of boron compounds, neodymium compounds, ytterbium compounds, lanthanum compounds, hafnium compounds, iron compounds, aluminum compounds, gallium compounds, scandium compounds, indium compounds, silver compounds, copper compounds, yttrium compounds, titanium compounds, zinc compounds, and manganese compounds.

6. The Lewis acid is tris(pentafluorophenyl)borane, yttrium(III) trifluoromethanesulfonate, scandium(III) triflate, neodymium(III) triflate, ytterbium(III) triflate, lanthanum(III) triflate, boron trifluoride diethyl ether complex (BF ３ ·Et ２ O), manganese(II) trifluoromethanesulfonate, 2,4-(CF ３ ) ２ -C ６ H ３ ), B, B(Mesityl) ３ F, FeCl ２ , GaCl ３ , YbCl ３ , YbCl ３ ·6H ２ O, hafnium(IV) triflate and AlCl ３ ; The method for producing ammonia according to claim 1 or 2, which is one or more selected from the group consisting of

7. The ammonia production method according to claim 1 or 2, wherein the nitrogen-activating complex is a molybdenum complex.

8. The ammonia production method according to claim 1 or 2, wherein the proton source comprises one or more selected from the group consisting of water and alcohol.

9. The ammonia production method according to claim 1 or 2, wherein the electron source comprises one or more selected from the group consisting of a reducing agent and an electrode.

10. The ammonia production method according to claim 1 or 2, wherein the electron efficiency in ammonia production is 10% or more.

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