Dehydrogenation / carbon dioxide hydrogenation catalyst, and hydrogen gas production method and carbon dioxide hydrogenation method each using same

Abstract

Provided is a dehydrogenation / carbon dioxide hydrogenation catalyst characterized by comprising an iridium complex represented by formula (3) and having a ligand bound to a polymer support. (In formula (3), pc represents a portion of the polymer support; m and n each independently represent a positive integer or 0; X and Y each independently represent a positive integer of 1 to 6; R1's each independently represent a hydrogen atom or a methyl group; R2's each independently represent a hydrogen atom or a methyl group; P represents a molecule or an ion of any one of H2O, chlorine (Cl), bromine (Br) and acetonitrile (CH3CN); and C represents any one of a hydroxide ion (OH-), a sulfate ion (SO4 2-), a chlorine ion (Cl-), a bromine ion (Br-), a nitrate ion (NO3 -) and a trifluoromethanesulfonate ion (CF3SO3 -).)

Description

Dehydrogenation / carbon dioxide hydrogenation catalyst, method for producing hydrogen gas using the same, and method for carbon dioxide hydrogenation

[0001] The present invention relates to a dehydrogenation / carbon dioxide hydrogenation catalyst that produces compounds such as formic acid from carbon dioxide and hydrogen, or that selectively decomposes compounds such as formic acid to produce carbon dioxide and hydrogen, and a method for producing hydrogen gas and a method for carbon dioxide hydrogenation that use the same.

[0002] Hydrogen has attracted attention as a next-generation energy source, and various technologies for storing, transporting, and utilizing hydrogen are being developed. For example, attempts have been made to convert electrical energy into hydrogen, and then convert the hydrogen into other materials (hydrogen carriers) for storage, transportation, etc. As such hydrogen carriers, formic acid has been proposed, along with liquid hydrogen, ammonia, and methylcyclohexane.

[0003] Formic acid can be selectively decomposed to carbon dioxide and hydrogen using a catalyst, and conversely, formic acid can be synthesized from hydrogen and carbon dioxide using a catalyst. Many catalysts are available for the dehydrogenation of formic acid and the hydrogenation of carbon dioxide to produce formic acid. However, homogeneous catalysts using complexes are said to have a faster formic acid decomposition rate or formic acid production rate per catalyst than heterogeneous catalysts using solids such as precious metals.

[0004] Ruthenium complexes are known as homogeneous catalysts that can be used for the decomposition and synthesis of formic acid, for example, as disclosed in Patent Document 1.

[0005] Japanese Patent Application Laid-Open No. 2019-218579

[0006] In practice, it is preferable to carry out the decomposition and synthesis of formic acid in a continuous flow reaction rather than in a batch process, and in the case of a homogeneous catalyst using a metal complex, it is necessary to immobilize the catalyst on an inorganic support or a polymer support to form an immobilized catalyst. Generally, the catalyst can be supported on a support such as silica or a polymer by forming a bond with the ligand of the metal complex that serves as the catalyst.

[0007] On the other hand, with immobilized catalysts in which these metal complexes are immobilized on a support, approximately 20 to 30% of the metal complex is leached out after each reaction. As a result, the catalytic activity is significantly reduced to less than half after several uses. Therefore, there is a need for a supported catalyst for formic acid production / decomposition that can efficiently decompose and synthesize formic acid even in a flow system.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a dehydrogenation / carbon dioxide hydrogenation catalyst suitable for decomposing and synthesizing compounds such as formic acid in a flow system, and a method for producing hydrogen gas and a method for carbon dioxide hydrogenation using the same.

[0009] We propose an immobilized catalyst in which the ligand of a metal complex, a homogeneous complex catalyst, is incorporated into the polymer backbone using an amino or hydroxyl group, and also in which the ligand is incorporated into the polymer side chain. While maintaining the high activity of the homogeneous complex catalyst, this catalyst functions as a solid-phase catalyst, enabling continuous, continuous reactions in the dehydrogenation of formic acid and the production of formic acid and formate from hydrogen and carbon dioxide. At the same time, this facilitates catalyst recovery after the reaction. Furthermore, this catalyst can be effectively used not only in the continuous system but also in the batch system.

[0010] The dehydrogenation / carbon dioxide hydrogenation catalyst according to the present invention is characterized by comprising an iridium complex represented by the following formula (3) having a ligand bound to a polymer support. (In the above formula (3), pc represents a portion of the polymer carrier, m and n each independently represent a positive integer or 0, X and Y each independently represent a positive integer from 1 to 6, and R １ are each independently a hydrogen atom or a methyl group, and R ２ are each independently hydrogen or a methyl group, and P is H ２ O, chlorine (Cl), bromine (Br), and acetonitrile (CH ３ CN), where C is a hydroxide ion (OH － ), sulfate ions (SO ４ ２－ ), chloride ions (Cl － ), bromine ion (Br－ ), nitrate ions (NO ３ － ), and trifluoromethanesulfonate (CF ３ SO ３ － ) is one of the ions

[0011] In the above-mentioned invention, the dehydrogenation / carbon dioxide hydrogenation catalyst may further comprise a polymer support represented by the following formula (1): (In the above formula (1), pc represents a portion of the polymer carrier, X is a positive integer from 1 to 6, and R １ are each independently hydrogen or a methyl group.

[0012] In the above-mentioned invention, the dehydrogenation / carbon dioxide hydrogenation catalyst may further comprise a ligand represented by the following formula (2) bound to the polymer support: (In the above formula (2), pc represents a portion of the polymer carrier, X and Y each independently represent a positive integer from 1 to 6, and R １ are each independently a hydrogen atom or a methyl group, and R ２ are each independently hydrogen or a methyl group.

[0013] In the above invention, the polymer carrier represented by the formula (1) may be polyethyleneimine, polystyrene, or a copolymer of ethyleneimine and styrene.

[0014] The dehydrogenation / carbon dioxide hydrogenation catalyst according to the present invention is characterized by comprising an iridium complex represented by the following formula (6) having a ligand bound to a polymer support: (In the above formula (6), pc represents a portion of the polymer carrier, m and n each independently represent a positive integer or 0, X2 and Y2 each independently represent an integer from 0 to 6, Z2 and W2 each independently represent a positive integer from 1 to 6, and R １ are each independently a hydrogen atom or a methyl group, and R ２ are each independently hydrogen or a methyl group, and P is H ２ O, chlorine (Cl), bromine (Br), and acetonitrile (CH３ CN), where C is a hydroxide ion (OH － ), sulfate ions (SO ４ ２－ ), chloride ions (Cl － ), bromine ion (Br － ), nitrate ions (NO ３ － ), and trifluoromethanesulfonate (CF ３ SO ３ － ) is one of the ions

[0015] In the above-mentioned invention, the dehydrogenation / carbon dioxide hydrogenation catalyst may further comprise a polymer support represented by the following formula (4): (In the above formula (4), pc represents a portion of the polymer carrier, and X2 is an integer of 0 to 6.)

[0016] In the above-mentioned invention, the dehydrogenation / carbon dioxide hydrogenation catalyst may further contain a ligand represented by the following formula (5) bound to the polymer support: (In the above formula (5), pc represents a portion of the polymer carrier, X2 and Y2 each independently represent an integer of 0 to 6, Z2 and W2 each independently represent a positive integer of 1 to 6, and R １ are each independently a hydrogen atom or a methyl group, and R ２ are each independently hydrogen or a methyl group.

[0017] In the above-mentioned invention, the polymer carrier represented by the formula (4) may be polyacrylic acid, polymethacrylic acid, polymaleic acid, or a copolymer of at least two selected from the group consisting of acrylic acid, methacrylic acid, and maleic acid.

[0018] Furthermore, the hydrogen gas production method according to the present invention is a hydrogen gas production method for generating a gas containing hydrogen and carbon dioxide and having a total pressure of 0.1 MPa or more and 200 MPa or less from a solution containing formic acid, and is characterized by using the above-mentioned catalyst.

[0019] Furthermore, the method for hydrogenating carbon dioxide according to the present invention is a method for hydrogenating carbon dioxide in which formic acid or a formate is produced from a gas containing hydrogen and carbon dioxide and having a total pressure of 0.1 MPa or more and 200 MPa or less, and is characterized by using the above-mentioned catalyst.

[0020] 1 is a graph showing the results of the amount of gas produced according to the present invention. FIG. 2 is a graph showing the results of the rotation speed versus the number of repetitions of a catalyst according to the present invention. FIG. 3 is a graph showing the results of measuring the initial formic acid decomposition rate versus the iridium loading weight and PEI weight ratio according to the present invention. FIG. 4 is a graph showing the results of the amount of gas produced according to the present invention. FIG. 5 is a graph showing the results of the catalyst turnover number versus the reaction time according to the present invention. FIG. 6 is a graph showing the results of the catalyst turnover number versus the reaction time according to the present invention. FIG. 7 is a graph showing the results of Example 7. FIG. 8 is a graph showing the results of Example 9. FIG. 9 is a diagram showing the results of a reference example. FIG. 10 is an explanatory diagram showing a batch-type hydrogen production test. FIG. 11 is an explanatory diagram showing the results of Example 14. FIG. 12 is an explanatory diagram showing a flow-type hydrogen production test. FIG. 13 is a graph showing the results of Example 15.

[0021] Representative examples of the present invention will be described in detail below.

[0022] A dehydrogenation / carbon dioxide hydrogenation catalyst according to one embodiment of the present invention comprises an iridium complex having a ligand bound to a polymer support and represented by the following formula (3): In formula (3), pc represents a portion of the polymer support, m and n each independently represent a positive integer or 0 (preferably 1 to 3, more preferably 1 to 2, and even more preferably 1), X and Y each independently represent a positive integer of 1 to 6 (preferably 1 to 4, more preferably 1 to 2), and R １ are each independently hydrogen or a methyl group (preferably hydrogen), and R ２ are each independently hydrogen or a methyl group (preferably hydrogen), and P is H ２ O, chlorine (Cl), bromine (Br), and acetonitrile (CH ３ CN), where C is a hydroxide ion (OH － ), sulfate ions (SO ４ ２－ ), chloride ions (Cl－ ), bromine ion (Br － ), nitrate ions (NO ３ － ), and trifluoromethanesulfonate (CF ３ SO ３ － ) is an ion of either

[0023]

[0024] Here, the iridium complex represented by the above formula (3) includes a salt of the iridium complex represented by formula (3). For example, when m and n are 1, the iridium complex represented by formula (3) is a salt of an iridium complex having C as a counter anion. The bonding site of the polymer support is not particularly limited and may be the end of the main chain of the polymer constituting the polymer support or a side chain of the polymer. Furthermore, each pc in formula (3) may represent a portion of the same polymer support or a portion of a different polymer support. Representing a portion of a different polymer support indicates a structure in which different polymer supports are crosslinked. This makes the polymer support more likely to become a gel or solid. Furthermore, the ligand bonded to the polymer support refers, for example, to the portion of formula (2) in formula (3) above. When the iridium complex represented by formula (3) above is included, it functions as a dehydrogenation / carbon dioxide hydrogenation catalyst.

[0025] The content of the iridium complex represented by the above formula (3) in the dehydrogenation / carbon dioxide hydrogenation catalyst is not particularly limited, but can be set to 0.04 to 0.10% by weight.

[0026] The dehydrogenation / carbon dioxide hydrogenation catalyst preferably further contains a polymer support represented by the following formula (1): By containing the polymer support represented by the following formula (1), optimal acidity and basicity in the formic acid decomposition or production reaction can be maintained, making it easier to maintain high activity for a long period of time. (In the above formula (1), pc represents a portion of the polymer carrier, X represents a positive integer of 1 to 6 (preferably 1 to 4, more preferably 1 to 2), and R １are each independently hydrogen or a methyl group (preferably hydrogen).

[0027] The content of the polymer support represented by formula (1) in the dehydrogenation / carbon dioxide hydrogenation catalyst is not particularly limited, but can be 50 to 99% by weight. Furthermore, the weight ratio of the polymer support content represented by formula (1) (e.g., polyethyleneimine) to the iridium content in the dehydrogenation / carbon dioxide hydrogenation catalyst is not particularly limited, but is preferably 25 to 500, more preferably 50 to 450, and even more preferably 75 to 300.

[0028] The dehydrogenation / carbon dioxide hydrogenation catalyst preferably further contains a ligand represented by the following formula (2) bonded to the polymer support. The ligand represented by the following formula (2) is covalently bonded to the polymer support via a nitrogen atom. The bonding site of the polymer support is not particularly limited, and may be the end of the main chain of the polymer constituting the polymer support, or a side chain of the polymer. Furthermore, each pc in formula (2) may represent a part of the same polymer support, or may represent a part of a different polymer support. Representing a part of a different polymer support indicates a structure in which different polymer supports are crosslinked. This makes the polymer support more likely to become a gel or solid. By containing a ligand represented by the following formula (2), when an iridium complex elutes during the reaction, the ligand can capture the iridium complex and suppress the elution of iridium. As a result, the catalyst's life is likely to be extended. (In the above formula (2), pc represents a portion of the polymer carrier, X and Y each independently represent a positive integer of 1 to 6 (preferably 1 to 4, more preferably 1 to 2), and R １ are each independently hydrogen or a methyl group (preferably hydrogen), and R ２ are each independently hydrogen or a methyl group (preferably hydrogen).

[0029] The content of the ligand represented by the above formula (2) bound to the polymer support in the dehydrogenation / carbon dioxide hydrogenation catalyst is not particularly limited, but can be 1 to 50% by weight.

[0030] A dehydrogenation / carbon dioxide hydrogenation catalyst according to one embodiment of the present invention comprises an iridium complex having a ligand bound to a polymer support and represented by the following formula (6): In formula (6), pc represents a portion of the polymer support, m and n each independently represent a positive integer or 0 (preferably 1 to 3, more preferably 1 to 2, and even more preferably 1), X2 and Y2 each independently represent an integer from 0 to 6 (preferably 1 to 6, more preferably 1 to 4, and even more preferably 1 to 2), Z2 and W2 each independently represent a positive integer from 1 to 6 (preferably 1 to 4, more preferably 1 to 2), and R １ are each independently hydrogen or a methyl group (preferably hydrogen), and R ２ are each independently hydrogen or a methyl group (preferably hydrogen), and P is H ２ O, chlorine (Cl), bromine (Br), and acetonitrile (CH ３ CN), where C is a hydroxide ion (OH － ), sulfate ions (SO ４ ２－ ), chloride ions (Cl － ), bromine ion (Br － ), nitrate ions (NO ３ － ), and trifluoromethanesulfonate (CF ３ SO ３ － ) is an ion of either

[0031]

[0032] Here, the iridium complex represented by the above formula (6) includes a salt of the iridium complex represented by formula (6). For example, when m and n are 1, the iridium complex represented by formula (6) is a salt of an iridium complex having C as a counter anion. The bonding site of the polymer support is not particularly limited and may be the end of the main chain of the polymer constituting the polymer support or a side chain of the polymer. Furthermore, each pc in formula (6) may represent a portion of the same polymer support or a portion of a different polymer support. Representing a portion of a different polymer support indicates a structure in which different polymer supports are crosslinked. This makes the polymer support more likely to become a gel or solid. Furthermore, the ligand bonded to the polymer support refers, for example, to the portion of formula (5) in formula (6) above. When the iridium complex represented by formula (6) above is included, it functions as a dehydrogenation / carbon dioxide hydrogenation catalyst.

[0033] The content of the iridium complex represented by the above formula (6) in the dehydrogenation / carbon dioxide hydrogenation catalyst is not particularly limited, but can be set to 0.04 to 0.10% by weight.

[0034] The dehydrogenation / carbon dioxide hydrogenation catalyst preferably further contains a polymer support represented by the following formula (4): By containing the polymer support represented by the following formula (4), optimal acidity and basicity in the formic acid decomposition or production reaction can be maintained, making it easier to maintain high activity for a long period of time. (In the above formula (4), pc represents a portion of the polymer carrier, and X2 represents an integer of 0 to 6 (preferably 1 to 6, more preferably 1 to 4, and even more preferably 1 to 2).)

[0035] The content of the polymer support represented by formula (4) in the dehydrogenation / carbon dioxide hydrogenation catalyst is not particularly limited, but can be 1 to 50 wt %. Furthermore, the ratio of the polymer support content represented by formula (4) (e.g., polyacrylic acid) to the iridium content in the dehydrogenation / carbon dioxide hydrogenation catalyst is not particularly limited, but is preferably 25 to 500, more preferably 50 to 450, and even more preferably 75 to 300.

[0036] The dehydrogenation / carbon dioxide hydrogenation catalyst preferably further contains a ligand represented by the following formula (5) bound to the polymer support. The ligand represented by the following formula (5) is covalently bonded to the polymer support via an amide bond. The binding site of the polymer support is not particularly limited, and may be the end of the main chain of the polymer constituting the polymer support, or a side chain of the polymer. Furthermore, each pc in formula (5) may represent a portion of the same polymer support, or may represent a portion of a different polymer support. Representing a portion of a different polymer support indicates a structure in which different polymer supports are crosslinked. This makes the polymer support more likely to become a gel or solid. By containing a ligand represented by the following formula (5), when an iridium complex elutes during the reaction, the ligand can capture the iridium complex and suppress the elution of iridium. As a result, the catalyst's life is likely to be extended. (In the above formula (5), pc represents a portion of the polymer carrier, X2 and Y2 each independently represent an integer of 0 to 6 (preferably 1 to 6, more preferably 1 to 4, and even more preferably 1 to 2), Z2 and W2 each independently represent a positive integer of 1 to 6 (preferably 1 to 4, and even more preferably 1 to 2), and R １ are each independently hydrogen or a methyl group (preferably hydrogen), and R ２ are each independently hydrogen or a methyl group (preferably hydrogen).

[0037] The content of the ligand represented by the above formula (5) bound to the polymer support in the dehydrogenation / carbon dioxide hydrogenation catalyst is not particularly limited, but can be 1 to 50% by weight.

[0038] Furthermore, by using the above-described catalyst, a gas containing hydrogen and carbon dioxide and having a total pressure of 0.1 MPa or more and 200 MPa or less can typically be produced from a solution containing formic acid. At this time, production can be performed in a batch system or a flow system. Furthermore, formic acid or a formate can be produced from a gas containing hydrogen and carbon dioxide and having a total pressure of 0.1 MPa or more and 200 MPa or less. At this time, production can be performed in a batch system or a flow system.

[0039] [Polymer Support] As described above, the polymer support used in the supported complex catalyst (dehydrogenation / carbon dioxide hydrogenation catalyst) is represented by the above formula (1) or formula (4) and also has the function of maintaining optimal acid / base concentrations when decomposing / producing formic acid. Therefore, affinity with water is also important. Examples include polyalkyleneimine and polyalkylenecarboxylic acid. Specifically, polyethyleneimine, polybutyleneimine, polyacrylic acid, polymethacrylic acid, polymaleic acid, etc. are preferably used. Furthermore, copolymers containing these polyalkyleneimine and polyalkylenecarboxylic acid are also preferably used. Other polymer supports can also be used, such as polystyrene, or copolymers of the above polymers with polystyrene, such as copolymers of ethyleneimine and styrene. Furthermore, copolymers of at least two selected from the group consisting of acrylic acid, methacrylic acid, and maleic acid can be used.

[0040] [Metal Complex] The central metal used in the supported complex catalyst can be one or more of iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, platinum, copper, silver, gold, and zinc, cadmium, mercury from Group VIII of the short periodic table, and Group IB of Group IIB.Preferably, one or more of iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, platinum from Group VIII, more preferably one or more of nickel, ruthenium, rhodium, palladium, iridium, platinum, and most preferably one or more of ruthenium, rhodium, palladium, iridium.Preferably, metal fine particles can be used.

[0041] [Formic Acid Concentration] The present catalyst can efficiently produce hydrogen and carbon dioxide from formic acid even at low concentrations. Therefore, although the concentration range is not particularly limited, using a higher concentration of formic acid allows for more efficient extraction of hydrogen and carbon dioxide from formic acid per unit volume. However, economically, more dilute formic acid is available at lower cost and is not classified as a hazardous material, so safety measures in accordance with the Fire Service Act are not required. Therefore, on the high-concentration side, hydrogen and carbon dioxide can be efficiently produced from formic acid by using a formic acid aqueous solution of preferably 78% by mass or less, more preferably 85% by mass or less, even more preferably 90% by mass or less, and most preferably 99.8% by mass or less. The lower limit of the concentration range is not particularly limited, but a formic acid aqueous solution of 0.1% by mass or more is preferred. However, a formic acid aqueous solution of 1% by mass or more, and most preferably 5% by mass or more, can be used to efficiently produce hydrogen and carbon dioxide. From the above, the formic acid concentration is not particularly limited, but can be, for example, 1% by mass to 78% by mass, preferably 3% by mass to 78% by mass, 5% by mass to 85% by mass, 5% by mass to 90% by mass, or 5% by mass to 99.8% by mass.

[0042] [Purity of Formic Acid] The present catalyst can be used to suitably carry out the reaction even in a mixed solution containing an aqueous solution of formic acid and other compounds. Specific examples of other compounds include methanol, ethanol, propanol, isopropanol, diethyl ether, tetrahydrofuran, dioxane, acetone, methyl ethyl ketone, acetic acid, propionic acid, dimethylformamide, diethylformamide, dimethyl sulfoxide, chloroform, dichloromethane, trichloroethane, hexane, and pentane. Even when these compounds are present, hydrogen and carbon dioxide can be suitably produced from formic acid.

[0043] However, since the presence of compounds other than formic acid can degrade performance, it is preferable to keep the concentrations of the following compounds that may be contained in the aqueous solution of formic acid below a predetermined level: That is, by keeping the concentrations of fluorine (fluoride ions), chlorine (chloride ions), bromine (bromine ions), and iodine (iodide ions) each at 1 ppm by mass or less, the reaction can be carried out favorably.

[0044] [Gas Pressure Range] The pressure of hydrogen and carbon dioxide is not particularly limited, and the reaction can be carried out, for example, at a total pressure of 0.1 MPa or more, with hydrogen at 0.05 MPa and carbon dioxide at 0.05 MPa or more. Preferably, the total pressure of hydrogen and carbon dioxide is 1 MPa or more, more preferably 5 MPa or more, and even more preferably 8 MPa or more. The total pressure can be, for example, 1 to 200 MPa, 5 to 200 MPa, or 8 to 200 MPa. When gases other than hydrogen and carbon dioxide are included, their pressures are not particularly limited and can be set appropriately.

[0045] [Ratio of Hydrogen to Carbon Dioxide] It is preferable to use hydrogen and carbon dioxide at an appropriate ratio, since too much hydrogen may produce methane or methanol. However, since carbon dioxide also functions as a solvent even when present in large excess, the ratio of carbon dioxide to hydrogen is not particularly limited. Hydrogen is preferably present in a range of 10 mass ppm or more (0.001 mass%) to 50 mass% or less relative to carbon dioxide, and from the viewpoint of efficiency, it is preferably used in a range of 1 mass% to 50 mass% or less, more preferably 10 mass% to 50 mass% or less, and even more preferably 20 mass% to 50 mass%.

[0046] [Gas Purity] Gases other than hydrogen and carbon dioxide can be used as long as they are inert to the reaction, such as helium, nitrogen, argon, xenon, methane, ethane, and propane. These gases can be used in a range of 10 ppm by mass (0.001% by mass) to 50% by mass relative to hydrogen and carbon dioxide. While lower amounts are preferable in terms of efficiency, the range is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 1% by mass or less. For example, the range can be 10 ppm by mass to 20% by mass, 10 ppm by mass to 10% by mass, or 10 ppm by mass to 1% by mass.

[0047] [Reaction Temperature] When producing formic acid from hydrogen and carbon dioxide, the reaction temperature can be suitably adjusted as needed as long as it is at or above the critical temperature of the mixed gas of hydrogen and carbon dioxide. Therefore, the reaction temperature has a range, but can be adjusted as needed within the range of, for example, 0°C to 150°C, more preferably 10°C to 150°C, even more preferably 10°C to 100°C, and most preferably 50°C to 100°C.

[0048] [Reaction Time] The reaction time when obtaining formic acid from hydrogen and carbon dioxide is not particularly limited, but since the reaction rate differs depending on the substance, it can be adjusted appropriately depending on the purpose. In either the batch or flow reaction, the target substance can be obtained by adjusting the reaction time to, for example, 1 minute to 72 hours, but the target compound can be obtained preferably in 10 minutes to 72 hours, more preferably in 30 minutes to 48 hours, and most preferably in 1 hour to 24 hours.

[0049] [Reaction Vessel] The reaction vessel may be of a flow type, but may also be of a batch type.

[0050] As described above, in the dehydrogenation reaction of formic acid and the reaction of producing formic acid and formate from hydrogen and carbon dioxide, an immobilized catalyst composed of a polymer support having amino or carboxylic acid functional groups, a ligand having amino groups, and an iridium complex having amino groups can be used. Conventional methods involve the elution of the iridium complex during the reaction, resulting in a very short catalyst life. However, when using this immobilized catalyst, the iridium complex that elutes during the reaction is captured by another ligand, significantly reducing the elution of iridium. Furthermore, the functional groups on the polymer support can maintain optimal acidity and basicity for the formic acid decomposition or production reaction, making it easier to maintain high activity for long periods of time. Therefore, the use of this catalyst can create a system that uses formic acid as a hydrogen carrier in the construction of a future hydrogen society.

[0051] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these. The conversion rate and yield of the reaction will be determined later.

[0052] Example 1 Synthesis of Immobilized Catalyst 4,4'-Dichloro-2,2'-bipyridine (0.32 g, 1.43 mmol) and water (1.02 mL) were added to 1.06 g of polyethyleneimine (PEI, branched, Mw: 25,000, Mn: 10,000), and the mixture was heated at 130°C for 24 hours. The resulting pale yellow solid was washed with chloroform and then with water until chlorine was no longer detected, yielding 1.36 g of a pale yellow solid. This solid (0.6 g) was dispersed in water, and triaqua(pentamethylcyclopentadienyl)iridium(III) sulfate (11.6 mg, 13.0 μmol) was dissolved therein. The mixture was stirred at room temperature for 3 days to support iridium. The resulting solid was separated using a centrifuge and then dried under reduced pressure to synthesize an immobilized catalyst (Cp*IrBPY / PEI, formula (A), 0.6 g). In formula (A), n, n', and n'' represent the degree of polymerization.

[0053] Example 2: Evaluation of formic acid decomposition performance of immobilized catalyst A magnetic stirrer and 13.5 mg of immobilized catalyst (Cp*IrBPY / PEI, iridium content 3.2 wt%) were placed in a 30 mL stainless steel autoclave, followed by 17.5 mL of water and formic acid (98% or higher, 2.5 mL) and heating to 80°C in a water bath. The production rate of the generated gas was measured using a wet gas meter. After gas generation was completed, additional formic acid (98% or higher, 1 mL) was added and the production rate measurement was repeated. The generated gas was collected in a sampling bag, and the composition was measured using a gas chromatograph.

[0054] As shown in Figure 1, the amount of gas generated was slightly small only the first time, but from the second time onwards, approximately 2.6 L of gas was detected, and almost 100% of the formic acid was decomposed and converted into carbon dioxide and hydrogen.

[0055] As shown in FIG. 2, the number of formic acid molecules catalyzed by iridium metal per hour is approximately 7000 h －１ Even after seven cycles, there was almost no decrease in the catalyst turnover rate. Furthermore, when the composition of the produced gas was examined by gas chromatography, it was found to be 50% hydrogen, 50% carbon dioxide, and no carbon monoxide was detected.

[0056] [Example 3] An immobilized catalyst (Cp*IrBPY / PEI) was obtained in the same manner as in Example 1, except that the amount of raw materials added was changed so that the iridium content was 2.5 wt%, 5.5 wt%, 10 wt%, 25 wt%, or 50 wt%. A magnetic stirrer and a predetermined amount of immobilized catalyst (Cp*IrBPY / PEI) having different iridium contents were placed in a 30 mL stainless steel autoclave, followed by 17.5 mL of water and 2.5 mL of formic acid (98% or higher) and heating to 80°C in a water bath. The production rate of the generated gas was measured using a wet gas meter. The generated gas was collected in a sampling bag, and the composition was measured using a gas chromatograph.

[0057] Figure 3 shows the results of measuring the initial formic acid decomposition rate using immobilized catalysts with varying weight ratios of PEI (polyethyleneimine) to Ir supported using the above method. It was found that the initial formic acid decomposition (dehydrogenation) rate increased as the weight ratio of PEI to Ir supported increased. Furthermore, when the gas composition was examined by gas chromatography, it was found to be 50% hydrogen, 50% carbon dioxide, and no carbon monoxide was detected.

[0058] Example 4 The immobilized catalyst (Cp*IrBPY / PEI) having a predetermined iridium content obtained in the experiment of Example 1 was placed in a 30 mL stainless steel autoclave, followed by the addition of 17.5 mL of water and 2.5 mL of formic acid (98% or higher), and heating to 80°C in a water bath.

[0059] The amount of iridium contained in the aqueous solution after the seventh reaction was measured by inductively coupled plasma atomic emission spectroscopy, and it was confirmed that 0.74 mass% of iridium had been eluted. This indicated that almost no iridium had been eluted. The catalytic activity was measured using this solution containing eluted iridium. The results are shown in Figure 4.

[0060] As shown in Figure 4, gas was generated from formic acid. The catalyst turnover time (TOF) was 6000 h －１From the above, it was found that the iridium complex structure of the active center was maintained. In other words, it was speculated that simple iridium was not eluted, but that part of the polyethyleneimine skeleton was cleaved by hydrogen, resulting in the elution of the iridium complex structure. The gas produced was collected in a sampling bag and its composition was measured using a gas chromatograph, but no carbon monoxide was detected. Furthermore, a dehydrogenation reaction from formic acid was carried out under similar conditions without adding a catalyst, but the amount of gas produced was below the detection limit of the gas meter.

[0061] 5 and 6 show the catalyst turnover rate versus reaction time when a catalyst represented by formula (A) and a catalyst represented by formula (B) were used, respectively. As a result, the catalyst represented by formula (A) having a structure supported on the polymer support PEI exhibited a high TOF value, while the catalyst represented by formula (B) not having a structure supported on the polymer support PEI exhibited a low TOF value. From this, it was inferred that the substance eluted into the aqueous solution in Example 4 was a trace amount of active catalyst, and that the structure of the iridium complex supported on PEI was a catalyst eluted from the immobilized catalyst (Cp*IrBPY / PEI) by decomposing the PEI skeleton.

[0062] [Example 5: Evaluation of high-pressure gas generation performance of immobilized catalyst] A magnetic stirrer and 13.5 mg of immobilized catalyst (Cp*IrBPY / PEI, iridium content 3.2 wt%) were placed in a 30 mL stainless steel autoclave, followed by the addition of 17.5 mL of water and formic acid (98% or higher, 2.5 mL) and heating to 80°C in a water bath. The pressure increase rate due to the generated gas was measured using a pressure sensor. After the pressure increase reached a steady state, the decomposition rate of formic acid was measured using liquid chromatography, and the decomposition rate was found to be 90% by mass. After gas generation was completed, additional formic acid (98% or higher, 1 mL) was added and the generation rate measurement was repeated. The generated gas was collected in a sampling bag, and the composition was measured using a gas chromatograph.

[0063] As a result of carrying out the above-mentioned method, it was found that a pressure of 60 MPa was generated. Furthermore, when the composition of the generated gas was examined by gas chromatography, it was found to be 50% by mass of hydrogen, 50% by mass of carbon dioxide, and no carbon monoxide was detected.

[0064] [Example 6: Evaluation of Repeated High-Pressure Gas Generation Performance of Immobilized Catalyst] High-pressure gas was generated in the same manner as in Example 5. After the reaction was completed, 2.5 mL of formic acid was added and a pressure increase test was conducted again. As a result, there was no change in the pressure increase rate even after three repetitions. Furthermore, the formic acid decomposition rate for each run was constant at 90 mass %. When the product gas recovered after the reaction was examined, no carbon monoxide was detected. Furthermore, after three reactions were completed, the amount of iridium contained in the reaction solution filtered to remove the immobilized catalyst was examined, and 0.42 mass % was found to be eluted. Furthermore, when the dehydrogenation reaction of formic acid was examined using this eluted solution, the TOF value was 5000 h －１ That was about it.

[0065] The above results show that the catalyst exhibits stable activity even under high pressures of 50 MPa or higher. Catalyst decomposition was also suppressed, and although some elution was observed, the stability remained unchanged.

[0066] Example 7 Five types of iridium-supported polymers (Cp*IrBPY / PEI) with different iridium contents were obtained in the same manner as in Example 1, except that the amount of polyethyleneimine was 1.0 g, the amount of 4,4'-dichloro-2,2'-bipyridine was 0.3 g, and the amounts of triaqua(pentamethylcyclopentadienyl)iridium(III) sulfate were 0.10 mg (0.22 μmol), 0.50 mg (1.1 μmol), 2.0 mg (4.4 μmol), 5.5 mg (12.1 μmol), and 51.1 mg (112.4 μmol), respectively. The catalytic activity of these iridium-supported polymers was investigated, and the results are shown in FIGS. 7 and 8 . The catalytic activity was investigated using the same method as in Example 2.

[0067] As a result, it was found that the initial formic acid dehydrogenation reaction rate (initial r on the vertical axis of Figure 7) increased with increasing iridium content (Ir cat. amount on the horizontal axis of Figure 7) (Figure 7). On the other hand, it was found that the catalyst turnover rate per mole of iridium (TOF on the vertical axis of Figure 8) increased with decreasing iridium content (Ir cat. amount on the horizontal axis of Figure 8) (Figure 8). Furthermore, the formic acid conversion using each catalyst was 99% or higher in all cases.

[0068] Example 8 In order to determine the optimal ratio of polyethyleneimine to iridium, immobilized catalysts were synthesized using the same method as in Example 1, varying the ratio of polyethyleneimine content to iridium content. Specifically, immobilized catalysts were synthesized with ratios of polyethyleneimine content to iridium content of 2, 4, 10, 18, 40, 100, 200, and 450. Then, using the same method as in Example 2, the initial rate of formic acid dehydrogenation was measured. The results are shown in FIG. 9. The initial rate of formic acid dehydrogenation (initial gas generation rate on the vertical axis in FIG. 9) increased up to a value of 100 for the ratio of polyethyleneimine content to iridium content (PEI / Ir complex on the horizontal axis in FIG. 9). However, it was found that the initial rate of formic acid dehydrogenation slowed down as the ratio of polyethyleneimine content to iridium content increased to 200 and 450. Furthermore, when the gas composition was examined by gas chromatography, it was found to be 50% hydrogen, 50% carbon dioxide, and less than 1 ppm of carbon monoxide.

[0069] Example 9: Iridium catalyst supported on various carriers Next, the results using various carriers other than polyethyleneimine are shown. First, polyacrylic acid (average molecular weight 100,000, 100 mg) was added to the ligand (50 milligrams) shown in formula (7) below, followed by N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride and heating to 80°C. The resulting solid was separated and thoroughly washed with water. Then, 10 mL of water and triaqua(pentamethylcyclopentadienyl)iridium(III) sulfate were added, and the mixture was stirred at 40°C under a nitrogen atmosphere for 3 days. The resulting yellow solid was separated. The structure of the yellow solid was estimated to be formula (8) below. This is a polymer compound in which polyacrylic acid is crosslinked by amide bonds.

[0070]

[0071] Example 10: Iridium catalysts supported on various carriers Under the same conditions as in Example 9, a reaction with polyacrylic acid was carried out using the ligand shown in the following formula (9) instead of the ligand shown in the above formula (7), and triaqua(pentamethylcyclopentadienyl)iridium(III) sulfate was added to the resulting solid, which was then stirred at 40°C under a nitrogen atmosphere for 3 days to obtain a yellow solid. The structure of the resulting solid was estimated to be that of the following formula (10).

[0072]

[0073] Example 11: Evaluation of formic acid decomposition performance of immobilized catalyst A magnetic stirrer and 13.5 mg of the immobilized catalyst represented by formula (8) or formula (10) were placed in a 30 mL stainless steel autoclave, followed by the addition of 17.5 mL of water and formic acid (98% or higher, 2.5 mL) and heating to 80°C in a water bath. The rate of gas production was measured using a wet gas meter. After gas production was completed, additional formic acid (98% or higher, 1 mL) was added and the measurement of the production rate was repeated. The gas produced was collected in a sampling bag, and its composition was measured using a gas chromatograph.

[0074] The amount of gas generated using the above method was approximately 2.6 L when the immobilized catalyst represented by the formula (8) was used, and approximately 2.5 L when the immobilized catalyst represented by the formula (10) was used. The composition of the gas was 50 mass % carbon dioxide, 50 mass % hydrogen, and carbon monoxide was 1 mass ppm or less. Furthermore, the TOF value, which is the number of formic acid molecules catalyzed by iridium metal per hour, was approximately 5000 h －１ As a result of repeating the procedure five times in the same manner as in Example 2, almost no decrease in the TOF value was observed.

[0075] Example 12 Iridium Catalyst Supported on Various Carriers Polyacrylic acid crosslinked to 0% to 14% by methylenebisacrylamide was synthesized instead of polyacrylic acid, and a yellow solid was obtained in the same manner as in Example 9, except for using this polyacrylic acid.

[0076] Example 13 Iridium Catalyst Supported on Various Carriers A yellow solid was obtained in the same manner as in Example 9, except that a copolymer of methacrylic acid and polyacrylic acid was synthesized and used instead of polyacrylic acid.

[0077] Example 14: Production of Hydrogen and Carbon Dioxide from Formic Acid at Various Formic Acid Concentrations, Batch Method A hydrogen production test was conducted using various formic acid concentrations under the same conditions as in Example 2. The hydrogen production test method is shown in Figure 11. The formic acid concentrations were 0.5 M, 1 M, 2.75 M, 5 M, 10 M, 15 M, and 20 M. Here, M represents mol / L. A 50 mL pressure-resistant vessel with a glass inner liner was used as the reaction vessel. A catalyst (20 mg, iridium content: 33.7 μmol) was placed in the vessel, and 5 mL of each formic acid was added at 80°C to carry out the reaction. The results are shown in Figure 12. It was found that the highest efficiency was achieved at concentrations between 5 and 10% by mass.

[0078] Example 15: Hydrogen and Carbon Dioxide Production from Formic Acid at Various Formic Acid Concentrations, Flow-Through Method. A powder of 256 mg of catalyst (Cp*IrBPY / PEI) diluted with an equal amount of Celite was packed into a tubular reactor (inner diameter 10 mm × length 100 mm), and 5 mL of formic acid at each concentration was passed through at a flow rate of 15 mL / h. Figure 13 shows the hydrogen production test method. Formic acid concentrations were 1 M, 3 M, 5 M, 10 M, and 20 M. Here, M represents mol / L. The results are shown in Figure 14. Measurement of the initial gas generation rate revealed that the higher the concentration, the greater the generation rate in the flow-through method.

[0079] Comparative Example 1 An iridium complex represented by the following formula (11) or an iridium complex represented by the following formula (12) was placed in a 30 mL stainless steel autoclave, followed by the addition of 17.5 mL of water and 2.5 mL of formic acid (98% or higher), and heating to 80°C in a water bath. The generated gas was measured using a wet gas meter. The gas was collected in a sampling bag, and the composition was measured using a gas chromatograph. No carbon monoxide was detected in either case of the iridium complex used.

[0080]

[0081] Reference Example In the same manner as in Example 1, 0.05 g, 0.10 g, 0.20 g, or 0.30 g of 4,4'-dichloro-2,2'-bipyridine and 1.02 mL of water were added to 1.0 g of polyethyleneimine (branched type, Mw: 2,5000, Mn: 10,000), and the mixture was heated at 130°C for 24 hours. The state of the resulting polymer was observed, and the results are shown in Table 1. Furthermore, a photograph of the polymer obtained at that time is shown in Figure 10.

[0082] Table 1 shows the state of the polymer obtained by crosslinking polyethyleneimine with 4,4'-dichloro-2,2'-bipyridine.

[0083] Table 1 reveals that by adding approximately 10% by weight or more of 4,4'-dichloro-2,2'-bipyridine to 1.0 g of polyethyleneimine, the 4,4'-dichloro-2,2'-bipyridine acts as a crosslinking agent, allowing the polyethyleneimine to be handled as a gel or solid.

Claims

1. A dehydrogenation / carbon dioxide hydrogenation catalyst comprising an iridium complex represented by the following formula (3) having a ligand bound to a polymer support: (In the above formula (3), p c represents a portion of the polymer carrier, m and n each independently represent a positive integer or 0, X and Y each independently represent a positive integer from 1 to 6, and R １ are each independently a hydrogen atom or a methyl group; R ２ are each independently hydrogen or a methyl group, and P is H ２ O, chlorine (Cl), bromine (Br), and acetonitrile (CH ３ CN), where C is a hydroxide ion (OH － ), sulfate ion (SO ４ ２－ ), chloride ion (Cl － ), bromine ion (Br － ), nitrate ion (NO ３ － ), and trifluoromethanesulfonate (CF ３ SO ３ － ) is one of the ions

2. 2. The dehydrogenation / carbon dioxide hydrogenation catalyst according to claim 1, further comprising a polymer support represented by the following formula (1): (In the above formula (1), p represents a portion of the polymer carrier, X is a positive integer from 1 to 6, and R １ are each independently a hydrogen atom or a methyl group.

3. 2. The dehydrogenation / carbon dioxide hydrogenation catalyst of claim 1, further comprising a ligand of formula (2) bound to the polymer support: (In the above formula (2), pc represents a portion of the polymer carrier, X and Y each independently represent a positive integer from 1 to 6, and R １ are each independently a hydrogen atom or a methyl group; R ２ are each independently a hydrogen atom or a methyl group.

4. 3. The dehydrogenation / carbon dioxide hydrogenation catalyst according to claim 2, wherein the polymer support represented by formula (1) is polyethyleneimine, polystyrene, or a copolymer of ethyleneimine and styrene.

5. A dehydrogenation / carbon dioxide hydrogenation catalyst comprising an iridium complex represented by the following formula (6) having a ligand bound to a polymer support: (In the above formula (6), pc represents a portion of the polymer carrier, m and n each independently represent a positive integer or 0, X2 and Y2 each independently represent an integer from 0 to 6, Z2 and W2 each independently represent a positive integer from 1 to 6, and R １ are each independently hydrogen or a methyl group, R ２ are each independently hydrogen or a methyl group, and P is H ２ O, chlorine (Cl), bromine (Br), and acetonitrile (CH ３ CN), where C is a hydroxide ion (OH － ), sulfate ion (SO ４ ２－ ), chloride ion (Cl － ), bromine ion (Br － ), nitrate ion (NO ３ － ), and trifluoromethanesulfonate (CF ３ SO ３ － ) is one of the ions

6. The dehydrogenation / carbon dioxide hydrogenation catalyst according to claim 5, further comprising a polymer support represented by the following formula (4): (In the above formula (4), p c represents a portion of the polymer carrier, and X2 is an integer from 0 to 6.)

7. 6. The dehydrogenation / carbon dioxide hydrogenation catalyst of claim 5, further comprising a ligand of formula (5) bound to the polymer support: (In the above formula (5), pc represents a portion of the polymer carrier, X2 and Y2 each independently represent an integer of 0 to 6, Z2 and W2 each independently represent a positive integer of 1 to 6, and R １ are each independently a hydrogen atom or a methyl group; R ２ are each independently a hydrogen atom or a methyl group.

8. 7. The dehydrogenation / carbon dioxide hydrogenation catalyst according to claim 6, wherein the polymer support represented by formula (4) is polyacrylic acid, polymethacrylic acid, polymaleic acid, or a copolymer of at least two acids selected from the group consisting of acrylic acid, methacrylic acid, and maleic acid.

9. A method for producing hydrogen gas, which generates a gas containing hydrogen and carbon dioxide and having a total pressure of 0.1 MPa or more and 200 MPa or less from a solution containing formic acid, comprising: A method for producing hydrogen gas, comprising using the catalyst according to any one of claims 1 to 8.

10. A method for hydrogenating carbon dioxide, which produces formic acid or a formate from a gas containing hydrogen and carbon dioxide and having a total pressure of 0.1 MPa or more and 200 MPa or less, comprising the steps of: A method for hydrogenating carbon dioxide, comprising using the catalyst according to any one of claims 1 to 8.

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