Supported catalyst, method for producing hydrogen, method for producing carbon dioxide, hydrogen production device, and carbon dioxide production device

Abstract

Provided is a supported catalyst comprising a carrier and a transition metal complex, wherein the carrier contains one or more selected from the group consisting of (A) and (B) below, and the transition metal complex is supported on the carrier. (A): polyacrylic acid resin having a crosslinking degree of 0-40 mass%, (B): activated carbon

Description

Supported catalyst, hydrogen production method, carbon dioxide production method, hydrogen production device, and carbon dioxide production device

[0001] The present disclosure relates to a supported catalyst, a method for producing hydrogen, a method for producing carbon dioxide, a hydrogen production device, and a carbon dioxide production device.

[0002] Formic acid has been attracting attention as a next-generation hydrogen carrier. Various efforts are being made in Japan toward the realization of a hydrogen-based society. Recently, a method for obtaining hydrogen and carbon dioxide by dehydrogenating formic acid using an iridium or ruthenium catalyst has been reported (Patent Document 1, Non-Patent Document 1). Furthermore, it has been reported that the same volumes of hydrogen and carbon dioxide can be obtained from formic acid at a maximum pressure of 157 MPa without the use of a compressor (Patent Document 2, Non-Patent Document 2). Overseas, practical power generation using fuel cells using a mixed gas containing hydrogen and carbon dioxide obtained from formic acid has begun (Non-Patent Document 3).

[0003] Patent No. 6502091 Patent No. 7370040

[0004] Formic Acid as a Hydrogen Carrier for Fuel Cells Toward a Sustainable Energy System, Hajime Kawanami, Yuichi Himeda, Gabor Laurenczy, Advances in Inorganic Chemistry (Edited by Rudi van Eldik, Colin D. Hubbard), Vol. 70, 395-427, 2017Ligand Design for Catalytic Dehydrogenation of Formic Acid to Produce High-pressure Hydrogen Gas under Base-free Conditions Hajime Kawanami,* Masayuki Iguchi, Yuichiro Himeda, Inorganic Chemistry, 2020, 59, 4191-4199.Fuelling the hydrogen economy: Scale-up of an integrated formic acid-to-power system, Robbert van Putten, Tim Wissink, Tijn Swinkels, Evgeny A. Pidko, International Journal of Hydrogen Energy, 2019, 44, 53, 28533-28541.

[0005] The present inventors noted that the catalysts described in Patent Documents 1 and 2, as well as Non-Patent Document 1, are all homogeneous complex catalysts, necessitating batch-wise reactions. When a formic acid solution is used as a raw material, the formic acid is decomposed into hydrogen and carbon dioxide gas by dehydrogenation, but the water in the formic acid solution remains unreacted in the reaction vessel. Therefore, if the reaction is carried out in a single reaction vessel for a long period of time, water accumulates and eventually saturates the reaction vessel. Furthermore, although the complex catalyst remains dissolved in the reaction solution, its amount is only on the order of a few millimoles per liter of reaction solution. To recover and reuse the complex catalyst, however, a process for completely removing the water is required, which is not practical from the perspective of production efficiency. However, if the complex catalyst contains an extremely expensive noble metal such as iridium or ruthenium as the central metal, recovering and reusing the complex catalyst is useful. Therefore, to solve the problem of water accumulation in the reaction vessel during homogeneous formic acid dehydrogenation, it is necessary to use formic acid that is as close to 100% as possible. However, the proton source required for hydrogen generation is protons derived from formic acid, which slows the reaction. Furthermore, when high-concentration formic acid is used, reduction of the catalyst itself occurs, resulting in significant catalyst deterioration and a decrease in the rate of hydrogen generation.

[0006] Therefore, the present inventors have investigated the development of heterogeneous immobilized catalysts in which homogeneous complex catalysts are supported on polymer supports. However, in the case of such immobilized catalysts, the catalytic activity may be reduced due to immobilization compared to homogeneous complex catalysts.

[0007] The present disclosure has been made in consideration of these circumstances and provides a supported catalyst and catalytic reaction system that, when using a supported catalyst carrying a homogeneous transition metal complex to efficiently produce hydrogen and carbon dioxide from formic acid, suppresses a decrease in catalytic activity compared to unsupported homogeneous transition metal complexes and enables the recovery and reuse of the catalyst. The present disclosure also provides a method for producing hydrogen and a method for producing carbon dioxide using the supported catalyst. Furthermore, the present disclosure provides a hydrogen production apparatus for implementing the hydrogen production method of the present disclosure. Additionally, the present disclosure provides a carbon dioxide production apparatus for implementing the carbon dioxide production method of the present disclosure.

[0008] The present disclosure relates to a supported catalyst comprising a support and a transition metal complex, wherein the support comprises one or more selected from the group consisting of the following (A) and (B), and the transition metal complex is supported on the support: (A) a polyacrylic acid resin having a crosslinking degree of 0 to 40% by mass; and (B) activated carbon.

[0009] According to the present disclosure, there is provided a supported catalyst that, when using a supported catalyst carrying a homogeneous transition metal complex to efficiently produce hydrogen and carbon dioxide from formic acid, suppresses a decrease in catalytic activity compared to an unsupported homogeneous transition metal complex and enables recovery and reuse of the catalyst. The present disclosure also provides a method for producing hydrogen and a method for producing carbon dioxide using the supported catalyst. Furthermore, the present disclosure provides a hydrogen production apparatus for implementing the hydrogen production method of the present disclosure. Additionally, the present disclosure provides a carbon dioxide production apparatus for implementing the carbon dioxide production method of the present disclosure.

[0010] FIG. 1 is an explanatory diagram showing a batch type reaction vessel according to an embodiment of the present disclosure. FIG. 2 is an explanatory diagram showing a semi-batch type reaction vessel according to an embodiment of the present disclosure. FIG. 3 is an explanatory diagram showing a flow type reaction vessel according to an embodiment of the present disclosure. FIG. 4 is an explanatory diagram showing a flow type reaction vessel according to an embodiment of the present disclosure. FIG. 5 is an explanatory diagram showing evaluation results of a supported catalyst in Example 1. FIG. 6 is an explanatory diagram showing evaluation results of a supported catalyst in Example 10.

[0011] The present disclosure will be described in detail below, but is not limited to the following description. The expressions "XX or more and YY or less" and "XX to YY" that represent a numerical range mean a numerical range including the lower and upper limits, which are the endpoints, unless otherwise specified. When a numerical range is described in stages, the upper and lower limits of each numerical range can be combined in any way.

[0012] The present disclosure relates to a supported catalyst comprising a support and a transition metal complex, wherein the support comprises one or more selected from the group consisting of the following (A) and (B), and the transition metal complex is supported on the support: (A) a polyacrylic acid resin having a crosslinking degree of 0 to 40% by mass; and (B) activated carbon.

[0013] The present inventors discovered a phenomenon known as the boomerang phenomenon, whereby a supported catalyst includes a support containing one or more selected from the group consisting of a polyacrylic acid resin having a crosslinking degree of 0 to 40% by mass and activated carbon. When the transition metal complex contained in the support generates hydrogen and carbon dioxide from formic acid, the transition metal complex is liberated from the support in the presence of formic acid and functions as a homogeneous complex catalyst. When the formic acid is converted to hydrogen and carbon dioxide and the formic acid concentration reaches nearly zero, the transition metal complex is re-adsorbed onto the support. This phenomenon is known as the boomerang phenomenon. As a result of extensive research, the present disclosure was completed. By re-adsorbing the transition metal complex onto the support as described above, the transition metal complex adsorbed onto the support can be easily separated from the solution, leaving only water in the post-reaction solution, allowing the transition metal complex adsorbed onto the support to be reused. The supported catalyst of the present disclosure can be used as a hydrogen generation catalyst. The supported catalyst of the present disclosure can also be used as a carbon dioxide generation catalyst.

[0014] Although the mechanism by which the supported catalyst of the present disclosure functions as described above is unclear, the present inventors speculate as follows. Specifically, the polyacrylic acid resin has weak acidity, and the carboxylic acid moiety coordinates to the transition metal complex, causing the transition metal complex to adsorb to the polyacrylic acid resin. That is, the transition metal complex is preferably coordinated to the carboxylic acid moiety of the polyacrylic acid resin. Furthermore, the degree of crosslinking of the polyacrylic acid resin is 0 to 40% by mass. With a degree of crosslinking within this range, the polyacrylic acid resin is in a gel state, but the degree of crosslinking is relatively low, making it prone to water absorption. That is, the polyacrylic acid resin is preferably in a gel state. Meanwhile, formic acid is more acidic than the polyacrylic acid resin. Therefore, in the formic acid solution, the polyacrylic acid resin coordinated to the transition metal complex is replaced by formic acid, which is released from the support as a transition metal complex coordinated with formic acid and dissolves in the solution. When the formic acid coordinated to the transition metal complex undergoes dehydrogenation, the formic acid is converted to hydrogen and carbon dioxide, and the formic acid is consumed. As dehydrogenation progresses, the formic acid coordinated to the transition metal complex is eventually lost, and the carboxylic acid moiety of the polyacrylic acid resin coordinates to the transition metal complex again and is adsorbed onto the carrier. Furthermore, even if the carboxylic acid moiety of the polyacrylic acid resin coordinates to the transition metal complex, dehydrogenation does not occur because there is no hydrogen at the α-position of the carboxylic acid. From the above, it is presumed that the effects of the present disclosure can be obtained.

[0015] Activated carbon, like polyacrylic acid resin, is a porous material primarily composed of carbon and has weak acidity. The surface of activated carbon has coordinating functional groups such as carboxyl groups, phenolic hydroxyl groups, carbonyl groups, and hydroxyl groups, and exhibits weaker acidity than formic acid. Therefore, as with polyacrylic acid resin, these functional groups present on the surface of activated carbon coordinate or bond to transition metal complexes and are adsorbed. That is, it is preferable that the transition metal complex is coordinated to the coordinating functional groups of activated carbon. In a formic acid solution, formic acid coordinates to the transition metal complex, and the formic acid-coordinated transition metal complex is liberated from the support and dissolved in the solution. When the formic acid coordinated to the transition metal complex undergoes dehydrogenation, the formic acid is consumed. As a result, the functional groups on the surface of the activated carbon coordinate and are adsorbed again. It is believed that this is how the effects of the present disclosure are achieved.

[0016] (Carrier) The supported catalyst includes a carrier. The carrier includes one or more selected from the group consisting of (A) and (B) below. The content of the carrier in the supported catalyst is not particularly limited, but can be, for example, 50 to 99% by mass. (A) Polyacrylic acid resin with a crosslinking degree of 0 to 40% by mass (B) Activated carbon

[0017] (Polyacrylic acid resin) The polyacrylic acid resin is, for example, polyacrylic acid or a crosslinked product of polyacrylic acid and a crosslinking agent. Here, the polyacrylic acid may be, for example, a polymer of one or more monomers selected from the group consisting of acrylic acid, acrylic esters, and acrylamides. It may also be a copolymer of a monomer containing one or more selected from the group consisting of acrylic acid, acrylic esters, and acrylamides in a range of 10 mol% to 100 mol%, with the remainder being other monomers described below. In this case, since the polyacrylic acid is not crosslinked, it can be said to be a polyacrylic acid resin with a crosslinking degree of 0%. Among these, the polyacrylic acid resin is preferably a polymer of acrylic acid. It is preferable to use a radical initiator or polymerization initiator such as azobisisobutyronitrile to synthesize the polyacrylic acid resin.

[0018] The content of one or more selected from the group consisting of acrylic acid, acrylic acid esters, and acrylamides is not particularly limited, but is preferably in the range of 10 mol % or more and 90 mol % or less, more preferably 20 mol % or more and 80 mol % or less, and most preferably 30 mol % or more and 80 mol % or less.

[0019] Examples of the crosslinked product of polyacrylic acid and a crosslinking agent include a reaction product of one or more monomers selected from the group consisting of acrylic acid, acrylic acid esters, and acrylamides with a crosslinking agent described below. The amount of the crosslinking agent is not particularly limited as long as the degree of crosslinking is 0 to 40% by mass, but is preferably in the range of more than 0 mol% to 50 mol% or less.

[0020] The acrylic acid ester is not particularly limited, but examples thereof include methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and hydroxyethyl acrylate. Of these, hydroxyethyl acrylate is preferred. The acrylamide is not particularly limited, but examples thereof include acrylamide, N-methylacrylamide, N-ethylacrylamide, and N-isopropylacrylamide. Acrylic acid esters and acrylamides can exhibit hydrophobic properties.

[0021] The degree of crosslinking of the polyacrylic acid resin is not particularly limited as long as the structure of the polyacrylic acid resin can be maintained in the reaction solution, but is generally 0 to 40% by mass, preferably 0 to 30% by mass, more preferably 0 to 16% by mass, and even more preferably 5 to 14% by mass. Within the above range, the support is easily separated from the solution, and the transition metal complex adsorbed or supported on the support is easily liberated from the support. Furthermore, from the viewpoint of easily improving catalytic activity, the degree of crosslinking of the polyacrylic acid resin may be 2 to 30% by mass, preferably 5 to 35% by mass, more preferably 8 to 33% by mass, and even more preferably 25 to 35% by mass. The degree of crosslinking of the polyacrylic acid resin can be increased by increasing the amount of crosslinking agent relative to the monomer, and can be decreased by decreasing the amount of crosslinking agent. The content of the polyacrylic acid resin in the support is not particularly limited, but can be, for example, 80 to 100% by mass.

[0022] There is a relationship between the degree of crosslinking of polyacrylic acid resin and the amount of ion-exchanged water absorbed by the polyacrylic acid resin. In order to efficiently adsorb and release transition metal complexes onto a resin support, it is necessary to incorporate water from the medium into the support. Therefore, the amount of ion-exchanged water absorbed by the polyacrylic acid resin is preferably in the range of 100 g to 100,000 g per 1 g of polyacrylic acid resin, but is preferably in the range of 100 g to 10,000 g, more preferably 100 g to 1,000 g, and particularly preferably 150 g to 1,000 g. When the amount of water absorption is within the above range, the degree of crosslinking is said to be 0 to 40% by mass. The measurement of the amount of water absorption is described in Japanese Industrial Standards (JIS) K7223 and can be calculated using the following formula: Water absorption W = ((mass of sample after absorbing water b) - (mass of sample before absorbing water c)) / (mass of sample before absorbing water a)

[0023] (Crosslinking Agent) The crosslinking agent is not particularly limited, and examples thereof include divinyl compounds and trivinyl compounds such as N,N'-methylenebisacrylamide, ethylene glycol dimethacrylate, butylene dimethacrylate, nonapropylene glycol dimethacrylate, and trimethylpropane trimethacrylate. Among these, N,N'-methylenebisacrylamide is preferred. Furthermore, it is preferable that the crosslinking agent does not have a functional group, such as a sulfo group, that is more acidic than formic acid. If the crosslinking agent has a functional group that is more acidic than formic acid, the resulting polyacrylic acid resin will also have a functional group that is more acidic than formic acid. In this case, the adsorption force to the transition metal complex is increased, which may make it difficult for the transition metal complex to be released.

[0024] (Other Monomers) In order to adjust the physical properties of the carrier, such as hydrophilicity, water absorption, and pH responsiveness, methacrylic acid esters or methacrylamides can be used as other monomers. For example, one or more monomers selected from the group consisting of methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, and hydroxyethyl methacrylate, and methacrylamides such as methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, and N-isopropylmethacrylamide may be used. These monomers can exhibit hydrophobic properties. The content of the other monomer is not particularly limited, but may be, for example, 0 mol% to 30 mol%. Furthermore, it is preferable that the other monomer does not have a sulfo group. When the other monomer has a functional group, such as a sulfo group, that is more acidic than formic acid, the resulting polyacrylic acid resin has a functional group that is more acidic than formic acid. In this case, the adsorption force to the transition metal complex is increased, which may make it difficult for the transition metal complex to be released.

[0025] (Activated Carbon) Activated carbon is not particularly limited, but examples include activated carbon derived from minerals such as coal, petroleum pitch, and tar; activated carbon derived from plants such as coconut shells, wood, and bamboo; and activated carbon derived from resins such as phenolic resin, melamine resin, polyimide resin, and polyester resin. Specifically, activated carbon manufactured by Wako Pure Chemical Industries, Ltd. (synthesized by a chemical activation method, in which zinc chloride is added to and impregnated into wood material, and carbonized at a temperature of 500 to 700°C in an air-free environment) is preferred. Examples of the form of activated carbon include powdered activated carbon, granular activated carbon, crushed activated carbon, and fibrous activated carbon. It is also preferable that the activated carbon does not have a functional group, such as a sulfo group, that is more acidic than formic acid. In this case, the adsorption force for transition metal complexes is increased, which may make the transition metal complexes less likely to be liberated. The specific surface area of ​​the activated carbon is not particularly limited, but is preferably 1,000 to 10,000 m. ２ The content of activated carbon in the carrier is not particularly limited, but can be, for example, 80 to 100 mass %.

[0026] (Central Metal of Transition Metal Complex) The transition metal complex is supported on a carrier. The transition metal complex is not particularly limited as long as it is a complex that can be adsorbed and desorbed on a carrier, but is preferably a complex having one or more metals selected from the group consisting of chromium, manganese, iron, cobalt, nickel, copper, zinc, molybdenum, ruthenium, rhodium, palladium, silver, tungsten, rhenium, osmium, iridium, platinum, and gold as the central metal, more preferably a complex having one or more metals selected from the group consisting of iridium, ruthenium, and rhodium as the central metal, and even more preferably a complex having iridium as the central metal. When the above metal is the central metal of the transition metal complex, hydrogen can be easily produced from formic acid.

[0027] (Shape of Complex) An example of the transition metal complex is a transition metal complex represented by the following formula (1). The transition metal complex represented by the following formula (1) facilitates efficient production of hydrogen from formic acid. In the following formula (1), M represents a central metal, A⌒B represents a bidentate ligand coordinated to M, A and B each independently represent a nitrogen atom, a carbon atom, an oxygen atom, a sulfur atom, or a phosphorus atom, L represents an aromatic ligand, Z represents any ligand or vacant site, and [C ｎ－ ] represents an anion, and m and n are each independently a positive integer or 0. Here, n being 0 indicates that the transition metal complex has no anion. Furthermore, m / n represents the molar ratio of anions to cationic moieties. For example, when m is 1 and n is 2, this indicates that 1 / 2 mole of anions is present per mole of cationic moieties. The same applies to m / n in formulas other than (1). Note that A and B may be the same or different. It is preferable that A and B each independently represent a nitrogen atom, an oxygen atom, or a carbon atom.

[0028] The aromatic ligand is not particularly limited, but examples thereof include benzene-based aromatic ligands, annulene-based aromatic ligands, heterocyclic aromatic ligands, troponoid-based aromatic ligands, bicycloaromatic ligands, homoaromatic ligands, and ionic ligands. Examples of ionic aromatic ligands include cyclopentadienyl anions and tripyrinium ions. Pentamethylcyclopentadienyl ligands or p-cymene ligands, all of which are substituted with methyl groups, are preferred. The aromatic ring of the aromatic ligand may have one or more substituents.

[0029] The anion [C ｎ－ ] is not particularly limited, but may be hexafluorophosphate ion (PF ６ － ), difluorophosphate ion (F ２ P.O. ２ － ), tetrafluoroborate ion (BF ４ － ), bis(fluorosulfonyl)imide ion, bis(trifluoromethanesulfonyl)imide ion, hydroxide ion (OH － ), halide ions such as acetate ion, carbonate ion, phosphate ion, sulfate ion, nitrate ion, fluoride ion, chloride ion, bromide ion, and iodide ion; hypohalite ions such as hypofluorite ion, hypochlorite ion, hypobromite ion, and hypoiodite ion; halite ions such as fluorite ion, chlorite ion, bromite ion, and iodite ion; halogen ions such as fluorate ion, chlorate ion, bromate ion, and iodate ion; perhalogen ions such as perfluorate ion, perchlorate ion, perbromate ion, and periodate ion; trifluoromethanesulfonate ion (OSO ２ CF ３ － ), and tetrakispentafluorophenylborate ion [B(C ６ F ５ ) ４ －]. Among them, sulfate ions are preferred. Sulfate ions are water-soluble, resistant to oxidation and reduction, and easily detached. Therefore, they function as stable anions and tend to exhibit stable activity. Furthermore, from the viewpoint of stability and water solubility, one or more selected from the group consisting of chloride ions, bromide ions, and nitrate ions are also preferred.

[0030] The transition metal complex represented by the formula (1) is preferably a transition metal complex represented by any one of the following formulas (2) to (6): In the following formulas (2) to (6), M represents a central metal, L represents an aromatic ligand, Z represents an arbitrary ligand or a vacant site, and [C ｎ－ ] represents an anion, and m and n are each independently a positive integer or 0. Here, n being 0 means that the transition metal complex does not have an anion. Here, C coordinated to M represents carbon. Furthermore, N and O coordinated to M represent nitrogen and oxygen, respectively.

[0031] The transition metal complex represented by formula (1) is more preferably a transition metal complex (organic iridium complex) represented by the following formula (7) or (8): In formulas (7) and (8), A⌒B represents a bidentate ligand coordinated to iridium, A and B represent a nitrogen atom, a carbon atom, an oxygen atom, a sulfur atom, or a phosphorus atom, A and B are the same atom, Z represents any ligand or vacant site, [C ｎ－ ] represents any anion, and m and n each independently represent a positive integer or 0. Here, n being 0 means that the transition metal complex does not have an anion. It is preferable that A and B each independently represent a nitrogen atom, an oxygen atom, or a carbon atom.

[0032] In the transition metal complex represented by any one of the above formulas (1) to (8), when Z represents a ligand, examples of the ligand include water molecules, hydride ions, alkoxide ions, hydroxide ions, halide ions, carbonate ions, trifluoromethanesulfonate ions, sulfate ions, nitrate ions, formate ions, and acetate ions. Examples of alkoxide ions include alkoxide ions derived from methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, isobutyl alcohol, and tert-butyl alcohol. Among these, water molecules are preferred. Water molecules stabilize the transition metal complex by coordination, while being easily exchanged for other ligands, and high catalytic activity can be expected.

[0033] The bidentate ligand in the organic iridium complex represented by the formula (7) and the organic iridium complex represented by the formula (8) is preferably a bidentate ligand represented by any one of the following formulas (9) to (12): ７ ~X ３１ each independently represents a nitrogen atom, a carbon atom, an oxygen atom, or sulfur. ｈ (h is an integer of 7 to 31) is an oxygen atom or a sulfur atom, ｈ R bonded to ｊ (j is an integer between 7 and 31) does not exist. １ ~Y ８ each independently represents a nitrogen atom or a carbon atom.

[0034] R ７ ~R ３２each independently represents a hydrogen atom, a hydroxy group, a nitro group, a halogen group, a carboxy group, an oxyanion group, or a sulfo group, or an alkyl group having 1 to 6 carbon atoms (preferably 1 to 3) which may have one or more substituents, an alkoxy group having 1 to 6 carbon atoms (preferably 1 to 3), an alkylthio group having 1 to 6 carbon atoms (preferably 1 to 3), an amino group, an alkylamino group having 1 to 6 carbon atoms (preferably 1 to 3), an alkyldiamino group having 1 to 6 carbon atoms, an amide group, an ester group, or a phenyl group. Among these, an alkylamino group having 1 to 6 carbon atoms, an alkyldiamino group having 1 to 6 carbon atoms, a hydroxy group, or an oxyanion group (-O － ) is preferred. The alkylamino group having 1 to 6 carbon atoms is not particularly limited, but examples thereof include linear alkylamino groups such as methylamino, ethylamino, and isopropylamino groups, and groups having a nitrogen-containing ring structure such as piperidyl. The nitrogen-containing ring structure may be, for example, a 4- to 7-membered ring structure, with a 6-membered ring structure being preferred. Among the alkylamino groups having 1 to 6 carbon atoms, alkylamino groups having 1 to 3 carbon atoms are preferred. Furthermore, the alkyldiamino group having 1 to 6 carbon atoms is not particularly limited, but hexane-1,6-diamine is particularly preferred. R ７ ~R ３２ In the formula (12), adjacent substituents may form a ring. The elements forming the ligand are bonded by a single bond or a double bond. The heterocycle may be an aromatic ring or a non-aromatic ring. In the formula (12), Q represents oxygen, sulfur, or selenium (preferably oxygen), and Z represents any ligand or vacant site. In the formula (12), R ３２ and Y ８ The sandwiched N can form a covalent bond with iridium.

[0035] The content of the transition metal complex in the supported catalyst is not particularly limited, but is preferably 0.1 to 40% by mass, or 1 to 20% by mass. This range tends to provide favorable catalytic activity. The supported catalyst may contain the free bidentate ligand in addition to the bidentate ligand constituting the transition metal complex. That is, the supported catalyst may contain the bidentate ligand as a molecule. This makes it easier to recover the free transition metal complex. When the supported catalyst contains the bidentate ligand as a molecule, the content of the bidentate ligand in the supported catalyst is not particularly limited, but is preferably 0.1 to 40% by mass, or 1 to 20% by mass. The free bidentate ligand may be the same as or different from the bidentate ligand constituting the transition metal complex.

[0036] <Methods for Producing Hydrogen and Carbon Dioxide> The present disclosure relates to a method for producing hydrogen from a solution containing formic acid, the method including: an elution step of contacting a supported catalyst of the present disclosure with a solution containing formic acid to elute a transition metal complex; and a dehydrogenation step of dehydrogenating the formic acid in the solution containing formic acid using the transition metal complex as a catalyst. As described above, the transition metal complex can be eluted by contacting the supported catalyst of the present disclosure with a solution containing formic acid. Then, the eluted transition metal complex is used as a catalyst to dehydrogenate the formic acid in the solution containing formic acid, thereby producing hydrogen from the solution containing formic acid. In this process, carbon dioxide is obtained simultaneously with hydrogen. Therefore, the method for producing hydrogen of the present disclosure can also be used as a method for producing carbon dioxide. Specifically, the present disclosure relates to a method for producing carbon dioxide by producing carbon dioxide from a solution containing formic acid, the method including: an elution step of contacting a supported catalyst of the present disclosure with a solution containing formic acid to elute a transition metal complex; and a dehydrogenation step of dehydrogenating the formic acid in the solution containing formic acid using the transition metal complex as a catalyst.

[0037] The solvent used for the solution containing formic acid may be any solvent capable of dissolving formic acid. For example, one or more solvents selected from water, methanol, ethanol, propanol, hexanol, acetonitrile, and acetic acid, or a mixture of these solvents, may be used. Preferably, water or a mixed solvent of water / methanol, water / ethanol, or water / acetonitrile may be used. In particular, it is preferable to use a solvent containing water as a proton source required for the dehydrogenation reaction. That is, the solution containing formic acid is preferably an aqueous solution containing formic acid. Formic acid may be formic acid itself or a formic acid derivative such as ethyl formate, propyl formate, or hexyl formate. The content of formic acid in the aqueous solution is preferably 1 to 100% by mass.

[0038] The method for contacting the supported catalyst with the solution containing formic acid is not particularly limited, but for example, in the case of a batch system, a method in which the supported catalyst is packed into a reaction vessel and the solution containing formic acid is introduced into the vessel can be mentioned. Furthermore, in the case of a flow system, a method in which the supported catalyst is packed into a column and the solution containing formic acid is introduced into the column can be mentioned. Specific methods will be described later. The temperature in the elution step is not particularly limited, but is preferably, for example, 0 to 100°C, more preferably 4 to 100°C, and even more preferably 10 to 100°C. The time period for the elution step is not particularly limited, but is preferably, for example, 1 second to 24 hours.

[0039] The temperature in the dehydrogenation step is not particularly limited, but is preferably, for example, 0 to 100°C, more preferably 4 to 100°C, and even more preferably 10 to 100°C. The pressure in the dehydrogenation step is not particularly limited, but is preferably normal pressure or higher and 200 MPa or lower. The time for the dehydrogenation step is not particularly limited, but for example, a residence time of 1 minute to 24 hours is preferred in the case of a batch system, and a residence time of 1 second to 8 hours is preferred in the case of a flow system. The above-mentioned methods for producing hydrogen and carbon dioxide can be carried out by any of a batch system, a semi-batch system, and a flow system.

[0040] <Apparatus for Implementing Hydrogen Production Method and Apparatus for Implementing Carbon Dioxide Production Method> Another aspect of the present disclosure is a hydrogen production apparatus for implementing the production method of the present disclosure, the hydrogen production apparatus including a reaction layer having therein the supported catalyst of the present disclosure, a formic acid introduction channel for introducing a formic acid solution into the reaction layer, and a gas discharge channel for discharging hydrogen from the reaction layer. As with the above-described hydrogen production method, the hydrogen production apparatus of the present disclosure can also be used as a carbon dioxide production apparatus. That is, another aspect of the present disclosure is a carbon dioxide production apparatus for implementing the production method of the present disclosure, the apparatus including a reaction layer having therein the supported catalyst of the present disclosure, a formic acid introduction channel for introducing a formic acid solution into the reaction layer, and a gas discharge channel for discharging carbon dioxide from the reaction layer.

[0041] The apparatus of this embodiment is shown in FIG. 1 . FIG. 1 is an explanatory diagram showing a batch-type reaction vessel according to one embodiment of the present disclosure. A reaction vessel 103 serving as a reaction bed is provided therein with a supported catalyst 106 according to the present disclosure. The reaction vessel 103 has a formic acid inlet channel for introducing a formic acid solution into the reaction vessel. In FIG. 1 , the formic acid solution is introduced into the reaction vessel 103 through the formic acid inlet channel from a vessel 101 filled with the formic acid solution by a liquid feed pump 102. The reaction vessel 103 can be adjusted to a predetermined temperature by a temperature-control jacket 107 serving as a heater. As a result, when the formic acid solution is introduced into the reaction vessel 103 adjusted to a predetermined temperature, dehydrogenation of formic acid proceeds in the reaction solution 104, generating a product gas 105 containing hydrogen and carbon dioxide. The generated product gas 105 is transferred to a product gas collection vessel 109 via a pressure relief valve 108. That is, the apparatus includes a gas exhaust channel for discharging hydrogen and carbon dioxide from the reaction bed. On the other hand, after the reaction to obtain product gas 105 containing hydrogen and carbon dioxide from reaction solution 104, the remaining reaction solution is transferred to a reaction solution recovery container via exhaust pressure valve 110. That is, the apparatus preferably includes a reaction solution discharge path for discharging the reaction solution from the reaction layer. As a result, the supported catalyst 106 remains inside reaction container 103, and hydrogen can be produced by repeating the above operation.

[0042] Another aspect of the present disclosure is a hydrogen production device for carrying out the production method of the present disclosure, the hydrogen production device including a complex catalyst introduction layer having a supported catalyst of the present disclosure therein, a complex catalyst recovery layer having a carrier therein, a reaction layer, and a liquid flow path connecting the complex catalyst introduction layer, the complex catalyst recovery layer, and the reaction layer. The device also includes a formic acid introduction path for introducing a solution containing formic acid into at least one of the complex catalyst introduction layer and the complex catalyst recovery layer, and a gas discharge path for discharging hydrogen from the reaction layer. The carrier included in the complex catalyst recovery layer further includes one or more selected from the group consisting of (A) and (B) below: (A) a polyacrylic acid resin having a crosslinking degree of 0 to 40 mass%; (B) activated carbon. The device also preferably includes a reaction solution discharge path for discharging a reaction solution from at least one of the complex catalyst introduction layer and the complex catalyst recovery layer.

[0043] Similar to the hydrogen production method described above, the hydrogen production apparatus of the present disclosure can also be used as a carbon dioxide production apparatus. That is, another aspect of the present disclosure is a carbon dioxide production apparatus for carrying out the production method of the present disclosure, the carbon dioxide production apparatus including a complex catalyst introduction layer having the supported catalyst of the present disclosure therein, a complex catalyst recovery layer having a carrier therein, a reaction layer, and a liquid flow path connecting the complex catalyst introduction layer, the complex catalyst recovery layer, and the reaction layer. The apparatus also includes a formic acid introduction path for introducing a solution containing formic acid into at least one of the complex catalyst introduction layer and the complex catalyst recovery layer, and a gas discharge path for discharging carbon dioxide from the reaction layer. Furthermore, the carrier included in the complex catalyst recovery layer includes one or more selected from the group consisting of (A) and (B) below. (A) Polyacrylic acid resin having a crosslinking degree of 0 to 40% by mass; (B) Activated carbon.

[0044] The apparatus of this embodiment is shown in FIGS. 2 to 4. FIG. 2 is an explanatory diagram showing a semi-batch reaction vessel according to one embodiment of the present disclosure. A first carrier column 201 serving as a complex catalyst introduction layer includes a supported catalyst of the present disclosure as a first carrier 202 therein. The first carrier column 201 has a formic acid introduction channel. That is, a formic acid solution 208 is introduced into the first carrier column 201 through the formic acid introduction channel via a switching valve V1-1 by a liquid feed pump. When the formic acid solution (a solution containing formic acid) 208 is introduced into the first carrier column 201, the transition metal complex supported on the first carrier 202 dissolves in the introduced formic acid solution. That is, the complex catalyst introduction layer is a layer in which the transition metal complex is introduced into the formic acid solution. Thereafter, the formic acid solution in which the transition metal complex has been dissolved is introduced into a reaction vessel 203 serving as a reaction layer via switching valves V1-2, V1-3, and V1-4. The first carrier column 201 and the reaction vessel 203 are connected by a liquid flow path. The reaction vessel 203 is equipped with a heater (not shown) and can be adjusted to a predetermined temperature. This allows formic acid to be dehydrogenated in the formic acid solution containing the transition metal complex dissolved therein, i.e., the reaction solution 204, and generates a product gas 205 containing hydrogen and carbon dioxide.

[0045] The generated product gas 205 is transferred as product gas 209 via the switching valve V1-8. That is, the apparatus includes a gas discharge channel for discharging hydrogen and carbon dioxide from the reaction layer. Meanwhile, after the reaction to obtain product gas 205 containing hydrogen and carbon dioxide from the reaction solution 204, a transition metal complex is dissolved in the remaining reaction solution. This reaction solution is introduced into a second carrier column 206 serving as a complex catalyst recovery layer via switching valves V1-4, V1-5, and V1-6. ​​That is, the reaction vessel 203 and the second carrier column 206 are connected by a liquid flow path. The second carrier column 206 is provided with a carrier serving as a second carrier 207 therein. Therefore, the transition metal complex contained in the introduced reaction solution is adsorbed onto the carrier. Thereafter, a reaction solution 210 as a residue in which the transition metal complex is adsorbed onto the carrier is recovered via the switching valve V1-7. That is, the apparatus preferably includes a reaction solution discharge channel for discharging the reaction solution from the complex catalyst recovery layer. As a result of the above operation, the first carrier column 201 is provided with a first carrier 202 from which a transition metal complex has been eluted, and the second carrier column 206 is provided with a supported catalyst of the present disclosure as a second carrier. Here, the second carrier column 206 has a formic acid inlet channel similar to the first carrier column 201. Therefore, by using the second carrier column 206 as a complex catalyst introduction layer and the first carrier column 201 as a complex catalyst recovery layer, the same operation as above can be performed to generate a product gas 205 containing hydrogen and carbon dioxide. In other words, the eluted transition metal complex can be easily recovered and reused. In this case, the apparatus preferably includes a reaction solution outlet channel for discharging the reaction solution from the complex catalyst introduction layer.

[0046] FIG. 3 is an explanatory diagram showing a flow-type reaction vessel according to one embodiment of the present disclosure. A first carrier column 301 serving as a complex catalyst introduction layer includes a first carrier 302 containing a supported catalyst of the present disclosure. The first carrier column 301 also includes a formic acid introduction channel. Specifically, a formic acid solution 308 is delivered by a liquid delivery pump, and the formic acid solution 308 is introduced into the first carrier column 301 through the formic acid introduction channel via a switching valve V2-1. When the formic acid solution 308 is introduced into the first carrier column 301, the transition metal complex supported on the first carrier 302 dissolves in the introduced formic acid solution. The formic acid solution containing the dissolved transition metal complex is then introduced into a reaction vessel 303 serving as a reaction vessel via a switching valve V2-2. The first carrier column 301 and the reaction vessel 303 are connected by a liquid flow channel. The reaction vessel 303 is equipped with a heater (not shown) and can be adjusted to a predetermined temperature. As a result, dehydrogenation of formic acid progresses in the formic acid solution in which the transition metal complex is dissolved, that is, in the reaction solution 304, and a product gas 305 containing hydrogen and carbon dioxide is generated.

[0047] The generated product gas 305 is transferred as product gas 309 via the switching valve V2-5. That is, the apparatus includes a gas discharge channel for discharging hydrogen and carbon dioxide from the reaction layer. Meanwhile, after the reaction to obtain product gas 305 containing hydrogen and carbon dioxide from the reaction solution 304, a transition metal complex is dissolved in the remaining reaction solution. This reaction solution is introduced into a second carrier column 306 serving as a complex catalyst recovery layer via the switching valve V2-3. That is, the reaction vessel 303 and the second carrier column 306 are connected by a liquid flow path. The second carrier column 306 is provided with a carrier serving as a second carrier 307 therein. Therefore, the transition metal complex contained in the introduced reaction solution is adsorbed onto the carrier. Thereafter, a reaction solution 310 as a residue in which the transition metal complex is adsorbed onto the carrier is recovered via the switching valve V2-4. That is, the apparatus preferably includes a reaction solution discharge channel for discharging the reaction solution from the complex catalyst recovery layer. As a result of the above operation, the first carrier column 201 is provided with the first carrier 202 from which the transition metal complex has been eluted, and the second carrier column 206 is provided with the supported catalyst of the present disclosure as the second carrier. In other words, the eluted transition metal complex can be easily recovered and reused.

[0048] FIG. 4 is an explanatory diagram showing a flow-type reaction vessel according to one embodiment of the present disclosure. A first carrier column 401 serving as a complex catalyst introduction layer includes a first carrier 402 containing a supported catalyst of the present disclosure. The first carrier column 401 also includes a formic acid introduction channel. Specifically, a formic acid solution 408 is delivered by a liquid delivery pump, and the formic acid solution 408 is introduced into the first carrier column 401 through the formic acid introduction channel via a switching valve V3-1. When the formic acid solution 408 is introduced into the first carrier column 401, the transition metal complex supported on the first carrier 402 dissolves in the introduced formic acid solution. The formic acid solution containing the dissolved transition metal complex is then introduced into a reaction vessel 403 serving as a reaction vessel via a switching valve V3-2. The first carrier column 401 and the reaction vessel 403 are connected by a liquid flow channel. The reaction vessel 403 is equipped with a heater (not shown) and can be adjusted to a predetermined temperature. As a result, dehydrogenation of formic acid progresses in the formic acid solution in which the transition metal complex is dissolved, that is, in the reaction solution 404, and a product gas 405 containing hydrogen and carbon dioxide is generated.

[0049] The generated product gas 405 is transferred as product gas 409. That is, the apparatus includes a gas exhaust channel for discharging hydrogen and carbon dioxide from the reaction layer. Meanwhile, after the reaction to obtain product gas 405 containing hydrogen and carbon dioxide from reaction solution 404, a transition metal complex is dissolved in the remaining reaction solution. This reaction solution is introduced into second carrier column 406, which serves as a complex catalyst recovery layer, via switching valve V3-6. That is, the reaction vessel 403 and the second carrier column 406 are connected by a liquid flow path. The second carrier column 406 has a carrier therein, which serves as a second carrier 407. Therefore, the transition metal complex contained in the introduced reaction solution is adsorbed onto the carrier. Thereafter, reaction solution 410, which serves as a residue in which the transition metal complex is adsorbed onto the carrier, is recovered via switching valve V3-7. That is, the apparatus preferably includes a reaction solution exhaust channel for discharging the reaction solution from the complex catalyst recovery layer. As a result of the above operation, the first carrier column 401 contains the first carrier 402 from which the transition metal complex has been eluted, and the second carrier column 406 contains the supported catalyst of the present disclosure as the second carrier. In other words, the eluted transition metal complex can be easily recovered and reused.

[0050] The present invention will be explained in more detail below with reference to examples, but is not limited to these examples as long as they do not depart from the gist of the invention.

[0051] Example 1 (Method for synthesizing supported catalyst) The method for synthesizing the supported catalyst is described below. 1.22 g of N,N'-methylenebisacrylamide was mixed with 3.1 mL of acrylic acid, and radical polymerization was carried out at 80°C using 21.7 mg of AIBN (azobisisobutyronitrile), synthesizing a 14% by mass crosslinked polyacrylic acid resin. The water absorption per gram of the resulting polyacrylic acid resin was 432 g. 70 mg of (N,N-[2,2'-bipyridine]-4,4'-diyl)bis(hexane-1,6-diamine) was added to 0.5 g of the resulting polyacrylic acid resin and allowed to adsorb, yielding a compound represented by the following formula (13). Then, 13 mg of Triaqua[(1,2,3,4,5-)-1,2,3,4,5-pentamethyl-2,4-cyclopentadien-1-yl]iridium(2+) sulfate was added to prepare a supported catalyst 1 represented by the following formula (14). In formulas (13) and (14), Ra represents hydrogen, m is an integer of approximately 1 million, n represents 16% relative to m, o represents 1.1% relative to m, and p represents 1.9% relative to m.

[0052] (Supported Catalyst Evaluation Method 1) The configuration of the batch reaction vessel used in Example 1 is shown in Figure 1. The components are described as follows: vessel 101 (volume 1000 mL) containing a formic acid solution, liquid feed pump 102, reaction vessel 103 (volume 30 mL), reaction solution 104, product gas 105 (hydrogen and carbon dioxide), supported catalyst 106, temperature control jacket 107, exhaust pressure valve 108, product gas collection vessel 109 (volume 5000 mL), exhaust pressure valve 110, and reaction liquid collection vessel 111 (volume 1000 mL). Note that supported catalyst 1 was used as supported catalyst 106.

[0053] The experimental method is described below. 20 mg of supported catalyst 1 was placed in a 30 mL stainless steel reaction vessel 103 equipped with a pressure sensor and a temperature sensor, and a heat transfer medium (water) was circulated through a temperature-control jacket 107 to adjust the reaction vessel 103 to 80°C. Next, 20 mL of a 1 M formic acid solution was introduced into the reaction vessel 103 using a liquid transfer pump 102 from a resin vessel 101 containing the formic acid solution. After introduction, dehydrogenation of the formic acid in the reaction solution 104 proceeded using the supported catalyst 1, and approximately 0.9 L of product gas 105 containing hydrogen and carbon dioxide was generated at room temperature and atmospheric pressure. While monitoring the pressure inside the reaction vessel 103, gas that reached a pressure of 0.1 MPa or higher was collected in a gas sampling bag serving as a product gas collection vessel 109 via a pressure relief valve 108. When the pressure of the product gas was 0.1 MPa or higher, the gas was collected using a stainless steel pressure vessel instead of a gas sampling bag.

[0054] From the obtained gas volume, the TOF (catalyst turnover rate) value was 63,813 h －１ The TOF was calculated using the following formula: TOF value (h －１ ) = amount of hydrogen gas produced from formic acid (mol) / (amount of iridium 2.5 μmol) / reaction time (h)

[0055] After the reaction, the reaction solution in which the supported catalyst 1 was dispersed was removed from the reaction vessel 103. The resulting reaction solution was filtered using a membrane filter to separate the supported catalyst from the reaction solution. When the amount of iridium contained in the reaction solution was analyzed by ICP, the iridium concentration was below the detection limit (0.01 mass ppm). In other words, the transition metal complex eluted in the reaction solution was recovered in almost 100% on the support and became the supported catalyst 1. In other words, the boomerang phenomenon was confirmed. Furthermore, when the formic acid concentration in the separated reaction solution was analyzed by ion chromatography, it was below the detection limit.

[0056] The supported catalyst 1 filtered and recovered through the membrane filter was washed with water and dried, and then placed back into the reaction vessel shown in FIG. 1. The supported catalyst was evaluated using the method described above. The TOF value was 63,085 h －１This procedure was repeated up to five times, resulting in the results shown in Figure 5. As can be seen, no deterioration of the supported catalyst was observed even after repeated use.

[0057] (Supported Catalyst Evaluation Method 2) Next, the concentration of the transition metal complex eluted from the supported catalyst in the aqueous solution, the rate of gas generation from formic acid, and the amount of gas generated from formic acid were investigated using the same method as described in the Supported Catalyst Evaluation Method 1 section, except that the amount of supported catalyst 1 was 18 mg and the amount of formic acid solution was 10 mL. The results are shown in Figure 6. The concentration of the transition metal complex in the aqueous solution was calculated from the absorbance at 350 nm using an ultraviolet-visible absorption spectrum. The gas generation rate and amount were calculated using a gas meter. As a result, the transition metal complex began to elute immediately after the addition of formic acid and reached a maximum concentration within several minutes. Thereafter, the concentration of the transition metal complex in the aqueous solution decreased over time, reaching almost zero after one hour. In conjunction with the behavior of this transition metal complex, the gas generation rate from formic acid also reached a maximum value near the maximum concentration of the transition metal complex, and then the generation rate decreased and reached zero after one hour. Furthermore, the UV spectrum of the eluted transition metal complex matched the spectrum of the complex catalyst represented by the following formula (16), which revealed that the transition metal complex represented by the following formula (16) had been eluted. This has the same structure as the transition metal complex contained in the supported catalyst represented by the above formula (14). Furthermore, elution of the ligand represented by the following formula (15) was not confirmed by UV, NMR, etc. of the solution.

[0058] Reference Example 1 Using only the transition metal complex represented by the above formula (16) as a catalyst, the same reaction as in Example 1 was carried out. As a result, the TOF value was 61,854 h －１ and was almost the same as that of Supported Catalyst 1. This indicates that even the supported catalysts carrying the complex catalyst exhibited almost the same level of activity as the unsupported homogeneous complex catalyst.

[0059] <Examples 1-1 to 1-3> In Example 1, synthesis was performed using Triaqua[(1,2,3,4,5-)-1,2,3,4,5-pentamethyl-2,4-cyclopentadien-1-yl]iridium(2+) chloride, Triaqua[(1,2,3,4,5-)-1,2,3,4,5-pentamethyl-2,4-cyclopentadien-1-yl]iridium(2+) bromide, or Triaqua[(1,2,3,4,5-)-1,2,3,4,5-pentamethyl-2,4-cyclopentadien-1-yl]iridium(2+) nitrate instead of Triaqua[(1,2,3,4,5-)-1,2,3,4,5-pentamethyl-2,4-cyclopentadien-1-yl]iridium(2+) sulfate, and supported catalysts 1-1 to 1-3 were obtained. Supported catalysts 1-1 to 1-3 have a structure in which the sulfate ions in supported catalyst 1 represented by the above formula (14) are replaced with chloride ions, bromide ions, or nitrate ions, respectively.

[0060] Example 2 Supported catalyst 2 was prepared and evaluated in the same manner as in Example 1, except that the amount of N,N'-methylenebisacrylamide added as a crosslinking agent was reduced to 0.78 g. The degree of crosslinking of the polyacrylic acid resin in the supported catalyst was 10% by mass. The amount of water absorbed per gram of the resulting polyacrylic acid resin was 315 g. In this case, the TOF value was 62,787 h －１ This was a slight increase compared to Example 1. Furthermore, the boomerang phenomenon was observed.

[0061] Example 3 Supported catalyst 3 was prepared and evaluated in the same manner as in Example 1, except that the crosslinking agent N,N'-methylenebisacrylamide was not used. In this case, the TOF value was 51,932 h －１ This was a slight decrease compared to Example 1. Furthermore, the boomerang phenomenon was observed.

[0062] Examples 4 to 8 Supported catalysts 4 to 8 were prepared and evaluated in the same manner as in Example 1, except that the amount of N,N'-methylenebisacrylamide crosslinking agent added was 0.07 g, 0.22 g, 0.53 g, 2.95 g, and 4.60 g. The crosslinking degrees of the polyacrylic acid resin in the supported catalysts were 1 mass%, 3 mass%, 7 mass%, 30 mass%, and 40 mass%, respectively. The water absorption amounts per gram of the resulting polyacrylic acid resins were 858 g, 364 g, 326 g, 261 g, and 153 g, respectively. The TOF values ​​were 1,932 h －１ , 37,028h －１ , 51,517h －１ , 61,177h －１ , and 25,759h －１ Furthermore, the boomerang phenomenon was observed in all the examples.

[0063] Comparative Example 1 Supported catalyst 9 was prepared and evaluated in the same manner as in Example 1, except that the amount of N,N'-methylenebisacrylamide crosslinking agent added was increased to 6.9 g. The degree of crosslinking of the polyacrylic acid resin in the supported catalyst was 50% by mass. The amount of water absorption per gram of the resulting polyacrylic acid resin was 89 g. In this case, the TOF value was 3,551 h －１ It was.

[0064] Comparative Example 2 A supported catalyst 10 was prepared and evaluated in the same manner as in Example 1, except that methacrylic acid was used instead of acrylic acid as the raw material. In this case, the TOF value was 2,546 h －１ It was.

[0065] Comparative Example 3 Supported catalyst 11 was prepared and evaluated in the same manner as in Comparative Example 2, except that the crosslinking agent N,N'-methylenebisacrylamide was not used. In this case, the TOF value was 5,160 h －１ As is clear from Comparative Examples 2 and 3, the activity of the catalyst using methacrylic acid as a raw material was low.

[0066] The results of Comparative Examples 1 to 3 above show that when the degree of crosslinking of the polyacrylic acid resin was increased too much, or when the carrier did not contain polyacrylic acid resin, the TOF value was low. Analysis of these cases using ultraviolet-visible absorption spectroscopy revealed that the transition metal complex did not elute into the reaction solvent, and the boomerang effect was not observed. In other words, it was found that the reaction occurring in the polymer was the cause of the significant drop in TOF value when these catalysts were used.

[0067] Comparative Examples 4 to 7 Supported catalysts 12 to 15 were prepared and evaluated in the same manner as in Example 1, except that α-alumina (manufactured by Kojundo Chemical Co., Ltd.), activated alumina (manufactured by Wako Pure Chemical Industries, Ltd.), γ-alumina (manufactured by Mizusawa Industrial Chemicals, Inc.), and an ion (anion) exchange resin (Diaion CR-20, manufactured by Mitsubishi Chemical Corporation) were used instead of the polyacrylic acid resin. As a result, the recovery rates of the transition metal complexes were 2%, 1%, 2%, and 2.5%, respectively. Comparative Examples 4 to 7 show that when these supports were used, it was possible to adsorb the transition metal complexes onto the supports, but the transition metal complexes dissolved in the formic acid solution could not be re-adsorbed onto the supports. In other words, the boomerang phenomenon was not observed.

[0068] In each example and comparative example, the catalyst recovery rate was calculated by measuring the amount of transition metal contained in the aqueous solution before the reaction and the amount of transition metal contained in the aqueous solution after the reaction using ICP emission spectrometry, and then calculating according to the following formula: Transition metal recovery rate % = (amount of transition metal contained before the reaction - amount of transition metal contained after the reaction) / amount of transition metal contained before the reaction × 100

[0069] Example 9 A supported catalyst 16 was prepared and evaluated in the same manner as in Example 1, except that activated carbon (manufactured by Wako Pure Chemical Industries, Ltd.) was used instead of polyacrylic acid resin. As a result, the recovery rate of the transition metal complex was 98%. This indicates that activated carbon can also be used as a support that functions in the same way as polyacrylic acid resin. When evaluated in the same manner as in Example 1, the TOF was 8,264 h －１ It was.

[0070] Example 10 (Supported Catalyst Evaluation Method 3) The configuration of the semi-batch reaction vessel used in Example 10 is shown in Figure 2. The components are described as follows: first carrier column 201 (including first carrier 202 with a complex catalyst adsorbed thereon, volume 10 mL), second carrier column 206 (including second carrier 207, volume 10 mL), reaction vessel 203 (stainless steel autoclave, volume 50 mL), and switching valves V1-1 to V1-8.

[0071] The experimental method is described below. Supported catalyst 1 (1.0 g) was packed into a 10 mL first carrier column 201. Furthermore, the polyacrylic acid resin (1.0 g) obtained in Example 1 was packed into a second carrier column 206. Next, at room temperature, an aqueous formic acid solution (10 mL, 76% by mass) serving as the formic acid solution 208 was passed through the first carrier column 201 at a rate of 0.1 mL / min via a switching valve V1-1 using a liquid pump (not shown). The transition metal complex adsorbed and supported on the first carrier 202 was dissolved in the injected aqueous formic acid solution. Then, an aqueous formic acid solution (reaction solution 204) was injected into the reaction vessel 203 via switching valves V1-2, V1-3, and V1-4. When the reaction vessel 203 was heated to 80°C while stirring at 1000 rpm, dehydrogenation of formic acid progressed, product gas 205 containing hydrogen and carbon dioxide was generated, and the pressure inside the reaction vessel 203 reached 0.1 MPa or higher. The generated product gas 205 was separately filled into a gas collection tube or bag as product gas 209 via switching valve V1-8. The above reaction was carried out for 6 hours, and the reaction progressed until the generation of product gas 205 ceased. Then, when the formic acid in the reaction solution 204 had almost completely disappeared, the remaining reaction solution 204 was injected into the second carrier column 206 via switching valves V1-4, V1-5, and V1-6. ​​In the second carrier column 206, the dissolved transition metal complex was adsorbed onto the second carrier 207. Thereafter, the reaction solution 210, which was the residue of the transition metal complex adsorbed onto the carrier, was recovered via switching valve V1-7.

[0072] The formic acid concentration of the recovered reaction solution was analyzed by ion chromatography, and the result was that the formic acid concentration was below the detection limit (0.1 ppm by mass). Next, the amount of iridium contained in the recovered reaction solution was analyzed using ICP, and the result was that the iridium concentration was below the detection limit (0.01 ppm by mass). From the above, it was confirmed that almost 100% of the formic acid was decomposed and almost 100% of the iridium was recovered.

[0073] Subsequently, similar to the above process, an aqueous formic acid solution (10 mL, 76% by mass) as the formic acid solution 208 was passed through the second carrier column 206 on which the transition metal complex had been adsorbed via the switching valve V1-6, and then injected into the reaction vessel 203 via the switching valves V1-7, V1-5, and V1-4. When the aqueous formic acid solution (reaction solution 204) injected into the reaction vessel 203 was heated to 80°C while stirring at 1000 rpm, dehydrogenation of formic acid proceeded, a product gas 205 containing hydrogen and carbon dioxide was generated, and the pressure inside the reaction vessel 203 reached 0.1 MPa or more. The generated product gas 205 was separately filled into a gas collection tube or bag as a product gas 209 via the switching valve V1-8. After the above reaction was carried out for 6 hours, the reaction proceeded and the product gas 205 no longer generated. Then, when the formic acid in the reaction solution 204 had almost disappeared, the remaining reaction solution 204 was injected into the first carrier column 201 via the switching valves V1-4, V1-3, and V1-1. In the first carrier column 201, the dissolved transition metal complex was adsorbed onto the first carrier 202. Thereafter, the reaction solution 210 as a residue in which the transition metal complex was adsorbed onto the carrier was recovered via the switching valve V1-7.

[0074] The formic acid concentration of the recovered reaction solution was analyzed by ion chromatography, and the formic acid concentration was found to be below the detection limit (0.1 mass ppm). Next, the amount of iridium contained in the recovered reaction solution was analyzed using ICP, and the iridium concentration was found to be below the detection limit (0.01 mass ppm). From the above, it was confirmed that almost 100% of the formic acid was decomposed and almost 100% of the iridium was recovered. In other words, the boomerang phenomenon was confirmed.

[0075] The above process was repeated two more times, but the concentrations of both formic acid and the transition metal complex in the recovered reaction solution were below the detection limit. In other words, no deterioration of the supported catalyst was observed even after repeated use.

[0076] In the first experiment, that is, the experiment in which the formic acid solution 208 was first passed through the first carrier column 201, the catalyst turnover rate estimated from the gas generation rate was 61,230 h －１ The results of further repeated operations are shown in FIG. 7 . Four repeated experiments revealed no catalyst deterioration and a stable gas generation rate. The second experiment was a series of experiments following the first experiment, in which a formic acid solution was first passed through the second carrier column 206, and finally the transition metal complex was adsorbed onto the first carrier 202. The third experiment was a series of experiments following the second experiment, in which a formic acid solution was first passed through the first carrier column 201, and finally the transition metal complex was adsorbed onto the second carrier 207. The fourth experiment was a series of experiments following the third experiment, in which a formic acid solution was first passed through the second carrier column 206, and finally the transition metal complex was adsorbed onto the first carrier 202.

[0077] Examples 11-1 to 11-25 Next, supported catalysts 17 to 41 were prepared and evaluated under the same conditions as in Example 1, except that after obtaining the compound represented by formula (13), the compounds listed in Table 1 were adsorbed. The evaluation results are shown in Table 1. As a result, in Examples 11-1 to 11-25, the transition metal complex eluted in the reaction solution was recovered in almost 100% on the support. In other words, the boomerang phenomenon was confirmed. The adsorbed compounds and transition metal complexes in the supported catalysts in Table 1 are the following compounds.

[0078] Compound 1a′ is represented by the formula (17) Ａ is a hydrogen atom, and compound 1b' is a compound represented by the formula (17) Ａ is a methyl group, and compound 1c′ is a compound represented by the formula (17) Ａ is an ethyl group, and compound 1d′ is a compound represented by the formula (17) Ａ is an isopropyl group.

[0079] Compound 1a is represented by the formula (18) Ａ is a hydrogen atom, and compound 1b' is a compound represented by the formula (18) Ａ is a methyl group, and compound 1c′ is a compound represented by the formula (18) Ａ is an ethyl group, and compound 1d′ is a compound represented by the formula (18) Ａ is an isopropyl group.

[0080] Compound 1e′ is a compound represented by formula (19).

[0081] Compound 1e is a compound represented by formula (20).

[0082] Compound 3a′ is represented by the formula (21) Ｂ is a hydrogen atom, and compound 3b′ is a compound represented by the formula (21) Ｂ is a methyl group, and compound 3c′ is a compound represented by the formula (21) Ｂ is an ethyl group, and compound 3d′ is a compound represented by the formula (21) Ｂ is an isopropyl group.

[0083] Compound 3a is represented by the formula (22) Ｂ is a hydrogen atom, and compound 3b is a compound represented by the formula (22) Ｂ is a methyl group, and compound 3c is a compound represented by the formula (22) Ｂ is an ethyl group, and compound 3d is a compound represented by the formula (22) Ｂ is an isopropyl group.

[0084] Compound 4a′ is represented by the formula (23) Ｃ is a hydrogen atom, and compound 4b′ is a compound represented by the formula (23) Ｃ is a methyl group, and compound 4c′ is a compound represented by the formula (23) Ｃ is an ethyl group, and compound 4d′ is a compound represented by the formula (23) Ｃ is an isopropyl group.

[0085] Compound 4a is represented by the formula (24) Ｃ is a hydrogen atom, and compound 4b is a compound represented by the formula (24) Ｃ is a methyl group, and compound 4c is a compound represented by the formula (24) Ｃ is an ethyl group, and compound 4d is a compound represented by the formula (24) Ｃ is an isopropyl group.

[0086] Compound 5a′ is represented by the formula (25) Ｄ is a hydrogen atom, and compound 5b′ is a compound represented by the formula (25) Ｄ is a methyl group, and compound 5c′ is a compound represented by the formula (25) Ｄ is an ethyl group, and compound 5d′ is a compound represented by the formula (25) Ｄ is an isopropyl group.

[0087] Compound 5a is represented by the formula (26) Ｄ is a hydrogen atom, and compound 5b is a compound represented by the formula (26) Ｄ is a methyl group, and compound 5c is a compound represented by the formula (26) Ｄ is an ethyl group, and compound 5d is a compound represented by the formula (26) Ｄ is an isopropyl group.

[0088] Compound 7a′ is a compound represented by the formula (27) Ｅ is a hydrogen atom, and compound 7b′ is a compound represented by the formula (27) Ｅ is a methyl group.

[0089] Compound 7a is represented by the formula (28) Ｅ is a hydrogen atom, and compound 7b is a compound represented by the formula (28) Ｅ is a methyl group.

[0090] Compound 10a′ is represented by the formula (29) Ｆ is a hydrogen atom and R Ｇis a phenyl group, and compound 10b′ is a compound represented by the formula (29) Ｆ is a methyl group and R Ｇ is a phenyl group, and compound 10c′ is a compound represented by the formula (29) Ｆ is a hydroxy group and R Ｇ is a phenyl group, and compound 10d′ is a compound represented by the formula (29) Ｆ is a methoxy group and R Ｇ is a phenyl group, and compound 10e′ is a compound represented by the formula (29) Ｆ is a dimethylamino group and R Ｇ is a phenyl group.

[0091] Compound 10a is represented by the formula (30) Ｆ is a hydrogen atom and R Ｇ is a phenyl group, and compound 10b is a compound represented by the formula (30) Ｆ is a methyl group and R Ｇ is a phenyl group, and compound 10c is a compound represented by the formula (30) Ｆ is a hydroxy group and R Ｇ is a phenyl group, and compound 10d is a compound represented by the formula (30) Ｆ is a methoxy group and R Ｇ is a phenyl group, and compound 10e is a compound represented by the formula (30) Ｆ is a dimethylamino group and R Ｇ is a phenyl group.

[0092] Compound 11 is a compound represented by formula (31).

[0093] Compounds 1a to 1e, 3a to 3d, 4a to 4d, 5a to 5d, 7a and 7b, as well as compounds 10a to 10e and 11 were synthesized based on the description in Non-Patent Document 2. In the table, "-" indicates that the data was not measured.

[0094] Examples of the inventions grasped from the above disclosure are as follows. [1] A supported catalyst comprising a support and a transition metal complex, wherein the support comprises one or more selected from the group consisting of the following (A) and (B), and the transition metal complex is supported on the support: (A) a polyacrylic acid resin having a crosslinking degree of 0 to 40 mass %; (B) activated carbon. [2] The supported catalyst according to [1], wherein the polyacrylic acid resin is polyacrylic acid, or a crosslinked product of polyacrylic acid and a crosslinking agent. [3] The supported catalyst according to [1] or [2], wherein the transition metal complex is a transition metal complex represented by the following formula (1): (In formula (1), M represents a central metal, A⌒B represents a bidentate ligand coordinated to the M, A and B each independently represent a nitrogen atom, a carbon atom, an oxygen atom, a sulfur atom, or a phosphorus atom, L represents an aromatic ligand, Z represents an arbitrary ligand or a vacant site, [C ｎ－ ] represents an anion, and m and n each independently represent a positive integer or 0.) [4] The supported catalyst according to [3], wherein the transition metal complex is a transition metal complex represented by the following formula (7) or the following formula (8): (In formulas (7) and (8), A⌒B represents a bidentate ligand coordinated to iridium, A and B each independently represent a nitrogen atom, a carbon atom, an oxygen atom, a sulfur atom, or a phosphorus atom, A and B are the same atom, Z represents any ligand or vacant site, [C ｎ－ ] represents any anion, and m and n each independently represent a positive integer or 0. [5] In formula (1), [C ｎ－] represents sulfate ions. [6] The supported catalyst according to any one of [1] to [5], wherein the supported catalyst is a catalyst for generating hydrogen or a catalyst for generating carbon dioxide. [7] A method for producing hydrogen from a solution containing formic acid, comprising: an elution step of contacting the supported catalyst according to any one of [1] to [6] with a solution containing formic acid to elute the transition metal complex; and a dehydrogenation step of dehydrogenating the formic acid in the solution containing formic acid using the transition metal complex as a catalyst. [8] A hydrogen production device for carrying out the production method according to [7], comprising: a reaction layer having the supported catalyst therein; a formic acid inlet channel for introducing a formic acid solution into the reaction layer; and a gas outlet channel for discharging hydrogen from the reaction layer. [9] A hydrogen production device for carrying out the production method according to [7], the hydrogen production device comprising: a complex catalyst introduction layer having the supported catalyst therein; a complex catalyst recovery layer having a carrier therein; a reaction layer; a liquid flow path connecting the complex catalyst introduction layer, the complex catalyst recovery layer, and the reaction layer; a formic acid introduction path for introducing a solution containing formic acid into at least one of the complex catalyst introduction layer and the complex catalyst recovery layer; and a gas discharge path for discharging hydrogen from the reaction layer, wherein the carrier provided in the complex catalyst recovery layer comprises one or more selected from the group consisting of (A) and (B) below. (A) a polyacrylic acid resin having a crosslinking degree of 0 to 40% by mass, (B) activated carbon

[10] A method for producing carbon dioxide from a solution containing formic acid, comprising: an elution step of contacting a solution containing formic acid with the supported catalyst according to any one of [1] to [6] to elute a transition metal complex; and a dehydrogenation step of dehydrogenating the formic acid in the solution containing formic acid using the transition metal complex as a catalyst.

[11] A carbon dioxide production apparatus for carrying out the production method according to

[10] , comprising: a reaction layer having the supported catalyst therein; a formic acid introduction channel for introducing a formic acid solution into the reaction layer; and a gas discharge channel for discharging carbon dioxide from the reaction layer.

[12] A carbon dioxide production apparatus for carrying out the production method according to

[10] , comprising: a complex catalyst introduction layer having the supported catalyst therein; a complex catalyst recovery layer having a carrier therein; a reaction layer; a liquid flow path connecting the complex catalyst introduction layer, the complex catalyst recovery layer, and the reaction layer; a formic acid introduction path for introducing a solution containing formic acid into at least one of the complex catalyst introduction layer and the complex catalyst recovery layer; and a gas discharge path for discharging carbon dioxide from the reaction layer, wherein the carrier provided in the complex catalyst recovery layer comprises one or more selected from the group consisting of (A) and (B) below: (A) a polyacrylic acid resin having a crosslinking degree of 0 to 40% by mass; (B) activated carbon.

[0095] 101: container, 102: liquid feed pump, 103: reaction vessel, 104: reaction solution, 105: product gas, 106: supported catalyst, 107: temperature control jacket, 108: exhaust pressure valve, 109: product gas collection vessel, 110: exhaust pressure valve, 111: reaction solution collection vessel, 201: first carrier column, 202: first carrier, 203: reaction vessel, 204: reaction solution, 205: product gas, 206: second carrier column, 207: second carrier, 208: formic acid solution, 209: product gas, 210: reaction solution, 301: first carrier column, 302: first carrier, 303: reaction vessel, 304: reaction solution, 305: product gas, 306: second carrier column, 307: second carrier, 308: formic acid solution, 309: product gas, 310: reaction solution, 401: first carrier column, 402: first carrier, 403: reaction vessel, 404: reaction solution, 405: product gas, 406: second carrier column, 407: second carrier, 408: formic acid solution, 409: product gas, 410: reaction solution, V1-1 to V1-8: switching valves V2-1 to V2-5: switching valves V3-1 to V3-2: switching valves V3-6 to V3-7: switching valves

Claims

1. A supported catalyst comprising a support and a transition metal complex, wherein the support comprises one or more selected from the group consisting of the following (A) and (B), and the transition metal complex is supported on the support: (A) a polyacrylic acid resin having a crosslinking degree of 0 to 40% by mass; (B) activated carbon.

2. The supported catalyst according to claim 1, wherein the polyacrylic acid resin is polyacrylic acid or a crosslinked product of polyacrylic acid and a crosslinking agent.

3. The supported catalyst according to claim 1 or 2, wherein the transition metal complex is a transition metal complex represented by the following formula (1): (In formula (1), M represents a central metal, A⌒B represents a bidentate ligand coordinated to the M, A and B each independently represent a nitrogen atom, a carbon atom, an oxygen atom, a sulfur atom, or a phosphorus atom, L represents an aromatic ligand, Z represents an arbitrary ligand or a vacant site, [C ｎ－ ] represents an anion, and m and n each independently represent a positive integer or 0.

4. The supported catalyst according to claim 3, wherein the transition metal complex is a transition metal complex represented by the following formula (7) or (8): (In formulas (7) and (8), A⌒B represents a bidentate ligand coordinated to iridium, A and B each independently represent a nitrogen atom, a carbon atom, an oxygen atom, a sulfur atom, or a phosphorus atom, A and B are the same atom, Z represents any ligand or vacant site, [C ｎ－ ] represents any anion, and m and n each independently represent a positive integer or 0.

5. In formula (1), [C ｎ－ 4. The supported catalyst of claim 3, wherein ] represents a sulfate ion.

6. The supported catalyst according to any one of claims 1 to 5, wherein the supported catalyst is a catalyst for producing hydrogen or a catalyst for producing carbon dioxide.

7. A method for producing hydrogen by generating hydrogen from a solution containing formic acid, comprising: an elution step of contacting the supported catalyst according to any one of claims 1 to 6 with a solution containing formic acid to elute the transition metal complex; and a dehydrogenation step of dehydrogenating the formic acid in the solution containing formic acid using the transition metal complex as a catalyst.

8. A hydrogen production device for carrying out the production method according to claim 7, comprising: a reaction layer having the supported catalyst therein; a formic acid introduction path for introducing a formic acid solution into the reaction layer; and a gas discharge path for discharging hydrogen from the reaction layer.

9. A hydrogen production device for carrying out the production method according to claim 7, comprising: a complex catalyst introduction layer having the supported catalyst therein; a complex catalyst recovery layer having a carrier therein; a reaction layer; a liquid flow path connecting the complex catalyst introduction layer, the complex catalyst recovery layer, and the reaction layer; a formic acid introduction path for introducing a solution containing formic acid into at least one of the complex catalyst introduction layer and the complex catalyst recovery layer; and a gas discharge path for discharging hydrogen from the reaction layer, wherein the carrier provided in the complex catalyst recovery layer comprises one or more selected from the group consisting of (A) and (B) below: (A) a polyacrylic acid resin having a crosslinking degree of 0 to 40% by mass; (B) activated carbon.

10. A method for producing carbon dioxide by generating carbon dioxide from a solution containing formic acid, comprising: an elution step of contacting a solution containing formic acid with the supported catalyst according to any one of claims 1 to 6 to elute a transition metal complex; and a dehydrogenation step of dehydrogenating the formic acid in the solution containing formic acid using the transition metal complex as a catalyst.

11. A carbon dioxide production apparatus for carrying out the production method according to claim 10, comprising: a reaction layer having the supported catalyst therein; a formic acid introduction path for introducing a formic acid solution into the reaction layer; and a gas discharge path for discharging carbon dioxide from the reaction layer.

12. A carbon dioxide production apparatus for carrying out the production method according to claim 10, comprising: a complex catalyst introduction layer having the supported catalyst therein; a complex catalyst recovery layer having a carrier therein; a reaction layer; a liquid flow path connecting the complex catalyst introduction layer, the complex catalyst recovery layer, and the reaction layer; a formic acid introduction path for introducing a solution containing formic acid into at least one of the complex catalyst introduction layer and the complex catalyst recovery layer; and a gas discharge path for discharging carbon dioxide from the reaction layer, wherein the carrier provided in the complex catalyst recovery layer comprises one or more selected from the group consisting of (A) and (B) below: (A) a polyacrylic acid resin having a crosslinking degree of 0 to 40% by mass; (B) activated carbon.

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