Ammonia decomposition catalyst, method for producing same, and method for producing hydrogen

Abstract

One embodiment of the present invention relates to an ammonia decomposition catalyst which contains cobalt (A), barium (B), and cerium (C), wherein the content of an alkali metal in the catalyst is 0.01 mol or less with respect to 1 mol of the cobalt (A).

Description

Ammonia decomposition catalyst, method for producing the same, and method for producing hydrogen

[0001] The present invention relates to an ammonia decomposition catalyst, a method for producing the same, and a method for producing hydrogen by decomposing ammonia into nitrogen and hydrogen using the ammonia decomposition catalyst.

[0002] Hydrogen is expected to be a new energy source for reducing carbon dioxide emissions. Ammonia, which can be transported and stored at a lower cost than hydrogen, is considered a promising substance for hydrogen storage and transport because it can produce hydrogen through decomposition reactions. Catalysts using precious metals such as ruthenium as active metals are known to exhibit high activity in ammonia decomposition, but because such precious metals are very expensive, research is being conducted on ammonia decomposition catalysts that do not use precious metals.

[0003] Patent Document 1 discloses a catalyst comprising one or more elements selected from nickel, cobalt, and iron, one or more elements selected from strontium and barium, one or more elements selected from rare earth elements, and magnesium, wherein the magnesium content is 10% to 65% by mass in terms of magnesium oxide relative to the total mass of the catalyst, and a method for producing hydrogen by contacting the catalyst with a raw material gas containing ammonia.

[0004] Patent Document 2 discloses an ammonia decomposition catalyst containing one or more rare earth elements selected from cobalt, cerium, yttrium, and lanthanum, one or more alkaline earth metal elements selected from barium and strontium, zirconium, and one or more calcium compounds selected from calcium carbonate, calcium oxide, and calcium hydroxide, wherein the cobalt, rare earth elements, alkaline earth metal elements, and zirconium are included as metals or oxides.

[0005] Non-patent document 1 discloses an ammonia decomposition catalyst comprising cobalt, barium, and cerium.

[0006] Japanese Patent No. 6883289, International Publication No. 2022 / 070597

[0007] Cobalt catalysts for COx-free hydrogen production: Effect of catalyst type on ammonia decomposition in gliding discharge plasma reactor, Journal of CO2 Utilization 82 (2024) 102755

[0008] In view of the above-mentioned prior art, the present invention aims to provide an ammonia decomposition catalyst that can exhibit improved catalytic activity at relatively low temperatures, a method for producing the same, and a method for producing hydrogen using the same.

[0009] The present invention includes the following embodiments: [1] An ammonia decomposition catalyst comprising cobalt (A), barium (B), and cerium (C), wherein the alkali metal content in the catalyst is 0.01 moles or less per mole of cobalt (A). [2] The content of barium (B) is 0.01 to 0.15 moles in terms of barium oxide (BaO) per mole of cobalt (A), and the content of cerium (C) is 0.01 to 0.15 moles in terms of barium oxide (BaO) per mole of cobalt (A). ２ The catalyst according to [1], wherein the amount is 0.2 to 0.8 moles in terms of cobalt (A). [3] The catalyst according to [1], further comprising magnesium (D). [4] The content of barium (B) is 0.01 to 0.15 moles in terms of barium oxide (BaO) per mole of cobalt (A), and the content of cerium (C) is 0.01 to 0.15 moles in terms of barium oxide (BaO) per mole of cobalt (A). ２The catalyst according to [3], wherein the magnesium (D) content is 0.2 to 0.5 moles in terms of cobalt (A), and the magnesium (D) content is 0.02 to 1.60 moles in terms of magnesium oxide (MgO) per mole of cobalt (A). [5] The catalyst according to [1], further comprising calcium (E). [6] The barium (B) content is 0.01 to 0.15 moles in terms of barium oxide (BaO) per mole of cobalt (A), and the cerium (C) content is 0.02 to 1.60 moles in terms of cerium oxide (CeO) per mole of cobalt (A). ２ The catalyst according to [5], wherein the calcium (E) content is 0.2 to 0.5 moles in terms of cobalt (A), and the calcium (E) content is 0.05 to 1.00 moles in terms of calcium oxide (CaO) per mole of cobalt (A). [7] The barium (B) content is 0.01 to 0.13 moles in terms of barium oxide (BaO) per mole of cobalt (A), and the cerium (C) content is 0.05 to 1.00 moles in terms of cerium oxide (CeO) per mole of cobalt (A). ２[1] The catalyst according to [1], wherein the amount is 0.2 to 0.7 moles when converted to 0.5. [8] The catalyst according to any one of [1] to [7], wherein the alkali metal is sodium and / or potassium. [9] The catalyst according to any one of [1] to [8], wherein the ammonia conversion rate (%) by the catalyst satisfies the following relationship (1) under atmospheric pressure: Conversion rate (%) > 0.6458T - 202.25 (1), and T is the temperature (°C) of the catalyst in the range of 400 to 550°C.

[10] A method for producing the catalyst according to any one of [1] to [9] by coprecipitation, comprising the step of dropping an alkaline solution containing a sodium salt and / or a potassium salt into an acid solution containing a cobalt (A) salt, a barium (B) salt, and a cerium (C) salt.

[11] The manufacturing method according to

[10] , further comprising the steps of washing the coprecipitation of the acid solution and the alkaline solution with water, and calcining the coprecipitation after washing.

[12] A method for producing hydrogen, comprising the step of contacting a catalyst according to any one of [1] to [9] with a raw material gas containing ammonia.

[13] The manufacturing method according to

[12] , wherein the raw material gas contains ammonia in an amount of 10 to 100% by volume.

[14] The manufacturing method according to

[12] or

[13] , wherein the temperature of the catalyst when it comes into contact with the raw material gas is in the range of 300 to 900°C.

[0010] An ammonia decomposition catalyst according to one aspect of the present invention exhibits an improved ammonia conversion rate at relatively low temperatures.

[0011] These graphs show the relationship between the ammonia conversion rate and catalyst layer temperature of the ammonia decomposition catalysts in Examples 1-7 and Comparative Examples 1-2. These graphs show the relationship between the ammonia conversion rate and catalyst layer temperature of the ammonia decomposition catalysts in Examples 8-11 and Comparative Examples 3-5. These graphs show the relationship between the ammonia conversion rate and catalyst layer temperature of the ammonia decomposition catalysts in Examples 12-16 and Comparative Example 6.

[0012] [First Embodiment] (1) Co-Ba-Ce Ammonia Decomposition Catalyst The ammonia decomposition catalyst according to the first embodiment of the present invention comprises cobalt (A), barium (B), and cerium (C), and the alkali metal content in the ammonia decomposition catalyst is 0.01 moles or less per mole of cobalt (A).

[0013] The chemical forms of cobalt (A), barium (B), and cerium (C) in the ammonia decomposition catalyst may be elemental metals, alloys, oxides, nitrides, complex oxides, carbides, hydroxides, or combinations thereof. Preferably, the chemical forms of cobalt (A), barium (B), and cerium (C) are elemental metals, oxides, nitrides, complex oxides, or combinations thereof. Furthermore, the chemical forms of cobalt (A), barium (B), and cerium (C) may be the same or different.

[0014] The cobalt (A) content in the ammonia decomposition catalyst is calculated assuming that all elements (A) exist as elemental metals. Furthermore, the barium (B) and cerium (C) content in the ammonia decomposition catalyst is calculated assuming that all elements (B) and (C) exist as oxides (BaO, CeO). ２ It is calculated assuming that it exists as ).

[0015] The barium (B) content in the ammonia decomposition catalyst is 0.01 to 0.15 moles, 0.01 to 0.14 moles, 0.01 to 0.13 moles, 0.017 to 0.126 moles, or 0.02 to 0.12 moles of barium oxide (BaO) per mole of cobalt (A) in the ammonia decomposition catalyst.

[0016] The cerium (C) content in the ammonia decomposition catalyst is such that, relative to 1 mole of cobalt (A) in the ammonia decomposition catalyst, there is cerium oxide (CeO2). ２ In terms of mol / L conversion, this corresponds to 0.2–0.8 mol, 0.2–0.7 mol, 0.2–0.5 mol, 0.25–0.80 mol, 0.25–0.70 mol, 0.25–0.50 mol, or 0.260–0.693 mol.

[0017] The content of alkali metal in the ammonia decomposition catalyst is 0.01 mol or less, 0.008 mol or less, 0.006 mol or less, 0.004 mol or less, 0.002 mol or less, or 0 mol per 1 mol of cobalt (A) in the ammonia decomposition catalyst. Preferably, the alkali metal is sodium and / or potassium, and the ammonia decomposition catalyst does not contain any alkali metals other than sodium and potassium.

[0018] Alkali metals reduce catalytic activity. However, the ammonia decomposition catalyst according to the present embodiment can exhibit improved catalytic activity (ammonia conversion rate) by setting the alkali metal content to 0.01 mol or less. In addition, the ammonia decomposition catalyst contains barium having electron-donating properties and cerium that improves the dispersibility of cobalt as an active metal by inhibiting the sintering (grain growth) of cobalt, and these factors are also considered to contribute to the improvement of catalytic activity.

[0019] The ammonia conversion rate (%) achieved by the ammonia decomposition catalyst satisfies the following relational expression (1) under atmospheric pressure: Conversion rate (%) > 0.6458T - 202.25 (1), wherein T is the temperature (°C) of the ammonia decomposition catalyst in the range of 400 to 550°C or 420 to 480°C.

[0020] (2) Method for producing ammonia decomposition catalyst The ammonia decomposition catalyst according to the present embodiment is produced by a coprecipitation method. The method for producing an ammonia decomposition catalyst by a coprecipitation method comprises a step of dropping an alkaline solution containing a sodium salt and / or a potassium salt as a coprecipitant into an acid solution containing an acid salt of cobalt (A), an acid salt of barium (B), and an acid salt of cerium (C) (dropping step). The temperature of the acid solution and the alkaline solution in the dropping step is preferably 20 to 60°C, 30 to 50°C, or 35 to 45°C.

[0021] Preferably, the acid salt of cobalt (A), the acid salt of barium (B), and the acid salt of cerium (C) are each cobalt nitrate hydrate (Co(NO ３ ) ２ ·6H ２ O), barium nitrate (Ba(NO ３ ) ２), and cerium nitrate hydrate (Ce(NO) ３ ) ３ 6H ２ O) Preferably, the sodium salt of the alkaline solution used as a coprecipitant is sodium carbonate, and the potassium salt is potassium carbonate.

[0022] The method for producing an ammonia decomposition catalyst further includes a step of heating the acid solution to which an alkaline solution has been added dropwise after the dropwise addition step, and allowing it to mature while stirring (maturation step), and a step of filtering the solution after the maturation step to remove the coprecipitate (solid component) of the acid solution and the alkaline solution. The temperature during heating is preferably 40 to 80°C or 50 to 70°C.

[0023] A method for producing an ammonia decomposition catalyst further includes a step of washing the coprecipitation of an acid solution and an alkaline solution with water (washing step) and a step of calcining the washed coprecipitation (calcination step). The water used in the washing step is preferably distilled water or pure water (or ultrapure water). In the calcination step, the washed coprecipitation is calcined under air at a temperature of 400 to 700°C or 500 to 600°C.

[0024] The method for producing the ammonia decomposition catalyst may include multiple washing steps, and may also include a step of drying the coprecipitate after the washing steps.

[0025] [Second Embodiment] (1) Co-Ba-Ce-Mg Ammonia Decomposition Catalyst The ammonia decomposition catalyst according to the second embodiment of the present invention comprises cobalt (A), barium (B), and cerium (C), and further comprises magnesium (D). The alkali metal content in the ammonia decomposition catalyst is 0.01 moles or less per mole of cobalt (A).

[0026] The chemical forms of cobalt (A), barium (B), cerium (C), and magnesium (D) may be elemental metals, alloys, oxides, nitrides, composite oxides, carbides, hydroxides, or combinations thereof. Preferably, the chemical forms of cobalt (A), barium (B), cerium (C), and magnesium (D) are elemental metals, oxides, nitrides, composite oxides, or combinations thereof. Furthermore, the chemical forms of cobalt (A), barium (B), cerium (C), and magnesium (D) may be the same or different.

[0027] The cobalt (A) content in the ammonia decomposition catalyst is calculated assuming that all elements (A) exist as elemental metals. Furthermore, the barium (B), cerium (C), and magnesium (D) content in the ammonia decomposition catalyst is calculated assuming that all elements (B), (C), and (D) exist as oxides (BaO, CeO). ２ It is calculated assuming that it exists as MgO.

[0028] The barium (B) content in the ammonia decomposition catalyst is 0.01 to 0.15 moles, 0.01 to 0.14 moles, 0.01 to 0.13 moles, or 0.017 to 0.126 moles of barium oxide (BaO) per mole of cobalt (A) in the ammonia decomposition catalyst.

[0029] The cerium (C) content in the ammonia decomposition catalyst is such that, relative to 1 mole of cobalt (A) in the ammonia decomposition catalyst, there is cerium oxide (CeO2). ２ In terms of mol / mol ratio, this corresponds to 0.2–0.8 mol, 0.2–0.7 mol, 0.2–0.5 mol, 0.25–0.80 mol, 0.25–0.70 mol, 0.25–0.50 mol, 0.26–0.69 mol, 0.3–0.4 mol, or 0.336–0.365 mol.

[0030] The magnesium (D) content in the ammonia decomposition catalyst is 0.02 to 1.60 moles, 0.02 to 1.40 moles, 0.02 to 1.20 moles, or 0.021 to 1.109 moles of magnesium oxide (MgO) per mole of cobalt (A) in the ammonia decomposition catalyst.

[0031] The alkali metal content in the ammonia decomposition catalyst is 0.01 moles or less, 0.008 moles or less, 0.0062 moles or less, 0.006 moles or less, 0.004 moles or less, 0.002 moles or less, or 0 moles per mole of cobalt (A) in the ammonia decomposition catalyst. Preferably, the alkali metal is sodium and / or potassium, and the ammonia decomposition catalyst does not contain alkali metals other than sodium and potassium.

[0032] The ammonia decomposition catalyst can exhibit improved catalytic activity by reducing the alkali metal content to 0.01 moles or less. Furthermore, the ammonia decomposition catalyst contains barium, which has electron-donating properties, and cerium, which improves the dispersibility of cobalt as an active metal by suppressing cobalt sintering (grain growth). These factors are also thought to contribute to the improved catalytic activity.

[0033] The conversion rate (%) of ammonia by the ammonia decomposition catalyst satisfies the following relationship (1) under atmospheric pressure: Conversion rate (%) > 0.6458T - 202.25 (1) where T is the temperature (°C) of the ammonia decomposition catalyst in the range of 400 to 550°C or 420 to 480°C.

[0034] Alternatively, the conversion rate (%) of ammonia by the ammonia decomposition catalyst satisfies the following relationship under atmospheric pressure: Conversion rate (%) > 0.6667T - 210 (2), where T is the temperature (°C) of the ammonia decomposition catalyst in the range of 400 to 550°C or 420 to 480°C.

[0035] (2) Method for Producing the Ammonia Decomposition Catalyst The ammonia decomposition catalyst of this embodiment is produced by the coprecipitation method. The method for producing the ammonia decomposition catalyst by the coprecipitation method includes a step of dropping an alkaline solution containing a sodium salt and / or a potassium salt as a coprecipitant to an acid solution containing a cobalt (A) salt, a barium (B) salt, a cerium (C) salt, and a magnesium (D) salt. The temperatures of the acid solution and the alkaline solution in the dropping step are preferably 20 to 60°C, 30 to 50°C, or 35 to 45°C.

[0036] Preferably, the salts of cobalt (A), barium (B), cerium (C), and magnesium (D) are each cobalt nitrate hydrate (Co(NO)). ３ ) ２ 6H ２ O), barium nitrate (Ba(NO) ３ ) ２ ), cerium nitrate hydrate (Ce(NO) ３ ) ３ 6H ２ O), and magnesium nitrate hydrate (Mg(NO) ３ ) ２ 6H ２ O) Preferably, the sodium salt of the alkaline solution used as a coprecipitant is sodium carbonate, and the potassium salt is potassium carbonate.

[0037] The method for producing an ammonia decomposition catalyst further includes a step of heating the acid solution to which an alkaline solution has been added dropwise after the dropwise addition step, and allowing it to mature while stirring (maturation step), and a step of filtering the solution after the maturation step to remove the coprecipitate (solid component) of the acid solution and the alkaline solution. The temperature during heating is preferably 40 to 80°C or 50 to 70°C.

[0038] A method for producing an ammonia decomposition catalyst further includes a step of washing the coprecipitation of an acid solution and an alkaline solution with water (washing step) and a step of calcining the washed coprecipitation (calcination step). The water used in the washing step is preferably distilled water or pure water (or ultrapure water). In the calcination step, the washed coprecipitation is calcined under air at a temperature of 400 to 700°C or 500 to 600°C.

[0039] The method for producing the ammonia decomposition catalyst may include multiple washing steps, and may also include a step of drying the coprecipitate after the washing steps.

[0040] [Third Embodiment] (1) Co-Ba-Ce-Ca Ammonia Decomposition Catalyst The ammonia decomposition catalyst according to the third embodiment of the present invention comprises cobalt (A), barium (B), and cerium (C), and further comprises calcium (E). The alkali metal content in the ammonia decomposition catalyst is 0.01 moles or less per mole of cobalt (A).

[0041] The chemical forms of cobalt (A), barium (B), cerium (C), and calcium (E) may be elemental metals, alloys, oxides, nitrides, composite oxides, carbides, hydroxides, or combinations thereof. Preferably, the chemical forms of cobalt (A), barium (B), cerium (C), and calcium (E) are elemental metals, oxides, nitrides, composite oxides, or combinations thereof. Furthermore, the chemical forms of cobalt (A), barium (B), cerium (C), and calcium (E) may be the same or different.

[0042] The cobalt (A) content in the ammonia decomposition catalyst is calculated assuming that all elements (A) exist as elemental metals. Furthermore, the barium (B), cerium (C), and calcium (E) content in the ammonia decomposition catalyst is calculated assuming that all elements (B), (C), and (E) exist as oxides (BaO, CeO). ２ It is calculated assuming that it exists as CaO.

[0043] The barium (B) content in the ammonia decomposition catalyst is 0.01 to 0.15 moles, 0.01 to 0.14 moles, 0.01 to 0.13 moles, or 0.018 to 0.119 moles of barium oxide (BaO) per mole of cobalt (A) in the ammonia decomposition catalyst.

[0044] The cerium (C) content in the ammonia decomposition catalyst is such that, relative to 1 mole of cobalt (A) in the ammonia decomposition catalyst, there is cerium oxide (CeO2). ２In terms of mol / L (per mol), these are 0.2–0.8 mol, 0.2–0.7 mol, 0.2–0.5 mol, 0.25–0.80 mol, 0.25–0.70 mol, 0.25–0.50 mol, 0.26–0.69 mol, 0.3–0.4 mol, or 0.344–0.374 mol.

[0045] The calcium (E) content in the ammonia decomposition catalyst is 0.02 to 1.60 moles, 0.02 to 1.40 moles, 0.02 to 1.20 moles, 0.05 to 1.00 moles, or 0.079 to 0.807 moles in terms of calcium oxide (CaO) per mole of cobalt (A) in the ammonia decomposition catalyst.

[0046] The alkali metal content in the ammonia decomposition catalyst is 0.01 moles or less, 0.008 moles or less, 0.006 moles or less, 0.0057 moles or less, 0.004 moles or less, 0.002 moles or less, or 0 moles, relative to 1 mole of cobalt (A) in the ammonia decomposition catalyst.

[0047] Preferably, the alkali metal is sodium and / or potassium, and the ammonia decomposition catalyst does not contain alkali metals other than sodium and potassium.

[0048] The ammonia decomposition catalyst can exhibit improved catalytic activity by reducing the alkali metal content to 0.01 moles or less. Furthermore, the ammonia decomposition catalyst contains barium, which has electron-donating properties, and cerium, which suppresses cobalt sintering (grain growth) and improves the dispersibility of cobalt as the active metal. These factors are also thought to contribute to the improved catalytic activity.

[0049] The conversion rate (%) of ammonia by the ammonia decomposition catalyst satisfies the following relationship (1) under atmospheric pressure: Conversion rate (%) > 0.6458T - 202.25 (1) where T is the temperature (°C) of the ammonia decomposition catalyst in the range of 400 to 550°C or 420 to 480°C.

[0050] Preferably, the conversion rate (%) of ammonia by the ammonia decomposition catalyst satisfies the following relationship (3) under atmospheric pressure: Conversion rate (%) > T - 365 (3). T is the temperature (°C) of the ammonia decomposition catalyst, which is in the range of 400 to 550°C or 420 to 480°C.

[0051] (2) Method for Producing the Ammonia Decomposition Catalyst The ammonia decomposition catalyst of this embodiment is produced by the coprecipitation method. The method for producing the ammonia decomposition catalyst by the coprecipitation method includes a step of dropping an alkaline solution containing a sodium salt and / or a potassium salt as a coprecipitant to an acid solution containing a cobalt (A) salt, a barium (B) salt, a cerium (C) salt, and a calcium (E) salt. The temperatures of the acid solution and the alkaline solution in the dropping step are preferably 20 to 60°C, 30 to 50°C, or 35 to 45°C.

[0052] Preferably, the salts of cobalt (A), barium (B), cerium (C), and calcium (E) are each cobalt nitrate hydrate (Co(NO)). ３ ) ２ 6H ２ O), barium nitrate (Ba(NO) ３ ) ２ ), cerium nitrate hydrate (Ce(NO) ３ ) ３ 6H ２ O), and calcium nitrate hydrate (Ca(NO) ３ ) ２ 4H ２ O) Preferably, the sodium salt of the alkaline solution used as a coprecipitant is sodium carbonate, and the potassium salt is potassium carbonate.

[0053] The method for producing an ammonia decomposition catalyst further includes a step of heating the acid solution to which an alkaline solution has been added dropwise after the dropwise addition step, and allowing it to mature while stirring (maturation step), and a step of filtering the solution after the maturation step to remove the coprecipitate (solid component) of the acid solution and the alkaline solution. The temperature during heating is preferably 40 to 80°C or 50 to 70°C.

[0054] A method for producing an ammonia decomposition catalyst further includes a step of washing the coprecipitation of an acid solution and an alkaline solution with water (washing step) and a step of calcining the washed coprecipitation (calcination step). The water used in the washing step is preferably distilled water or pure water (or ultrapure water). In the calcination step, the washed coprecipitation is calcined under air at a temperature of 400 to 700°C or 500 to 600°C.

[0055] The method for producing the ammonia decomposition catalyst may include multiple washing steps, and may also include a step of drying the coprecipitate after the washing steps.

[0056] [Fourth Embodiment] (1) Co-Ba-Ce Ammonia Decomposition Catalyst The ammonia decomposition catalyst according to the fourth embodiment of the present invention contains only cobalt (A), barium (B), and cerium (C) as active components and support components, and does not contain other active components and support components such as magnesium (D) or calcium (E). Furthermore, the alkali metal content in the ammonia decomposition catalyst is 0.01 moles or less per mole of cobalt (A). Points that overlap with the first embodiment are omitted from the explanation.

[0057] The barium (B) content in the ammonia decomposition catalyst is 0.01 to 0.15 moles, 0.01 to 0.14 moles, 0.01 to 0.13 moles, or 0.020 to 0.120 moles of barium oxide (BaO) per mole of cobalt (A) in the ammonia decomposition catalyst.

[0058] The cerium (C) content in the ammonia decomposition catalyst is such that, relative to 1 mole of cobalt (A) in the ammonia decomposition catalyst, there is cerium oxide (CeO2). ２ In terms of mol / L conversion, this corresponds to 0.2–0.8 mol, 0.2–0.7 mol, 0.2–0.5 mol, 0.25–0.80 mol, 0.25–0.70 mol, 0.25–0.50 mol, 0.26–0.69 mol, 0.3–0.4 mol, or 0.260–0.693 mol.

[0059] The alkali metal content in the ammonia decomposition catalyst is 0.01 moles or less, 0.008 moles or less, 0.006 moles or less, 0.0049 moles or less, 0.004 moles or less, 0.002 moles or less, or 0 moles per mole of cobalt (A) in the ammonia decomposition catalyst. Preferably, the alkali metal is sodium and / or potassium, and the ammonia decomposition catalyst does not contain alkali metals other than sodium and potassium.

[0060] The conversion rate (%) of ammonia by the ammonia decomposition catalyst satisfies the following relationship (1) under atmospheric pressure: Conversion rate (%) > 0.6458T - 202.25 (1) where T is the temperature (°C) of the ammonia decomposition catalyst in the range of 400 to 550°C or 420 to 480°C.

[0061] Alternatively, the conversion rate (%) of ammonia by the ammonia decomposition catalyst satisfies the following relationship under atmospheric pressure: Conversion rate (%) > 0.75T - 260 (4) where T is the temperature (°C) of the ammonia decomposition catalyst in the range of 400 to 550°C or 420 to 480°C.

[0062] The method for producing the ammonia decomposition catalyst of this embodiment is the same as that of the first embodiment, and therefore, a detailed explanation will be omitted.

[0063] [Fifth Embodiment] (1) Method for Producing Hydrogen The fifth embodiment of the present invention relates to a method for producing hydrogen using an ammonia decomposition catalyst according to the first to fourth embodiments.

[0064] The hydrogen production method includes a step (contact step) of contacting one of the ammonia decomposition catalysts of the first to fourth embodiments, or a combination thereof, with a raw material gas containing ammonia. The raw material gas contains ammonia in the range of 10 to 100% by volume, 30 to 100% by volume, 50 to 100% by volume, 70 to 100% by volume, or 90 to 100% by volume. In addition to ammonia, the raw material gas may also contain inert gases (noble gases, nitrogen, etc.), carbon monoxide, water vapor, etc.

[0065] The reaction mode for carrying out the hydrogen production method is not particularly limited, but may include fixed-bed, fluidized-bed, or moving-bed reactors. For example, fixed-bed reactors include catalyst-packed-bed reactors and catalyst-film reactors. The reactor may be heated by any method, such as heating with an electric heater or heating by gas combustion. For example, the ammonia decomposition catalyst is provided as a catalyst layer in the reactor.

[0066] In the contact process, the temperature of the ammonia decomposition catalyst when it comes into contact with the raw material gas is in the range of 200-1000°C, 300-900°C, 300-800°C, 400-800°C, 400-600°C, 400-500°C, or 420-470°C.

[0067] While not limited to these, the total pressure of the raw material gas in the reactor is 0.001 to 3 MPa, 0.05 to 1 MPa, or 0.05 to 0.2 MPa, and the pressure of the raw material gas in the reactor, as a partial pressure of ammonia, is 0.001 to 3 MPa, 0.05 to 1 MPa, or 0.05 to 0.2 MPa.

[0068] While not limited to these, the contact time between the raw material gas and the catalyst may be set to, for example, 1,000 to 100,000 [Ncc / g / h], 2,000 to 100,000 [Ncc / g / h], or 3,000 to 100,000 [Ncc / g / h] as expressed in equation (5) below (the amount of raw material gas supplied is expressed as the volume of ammonia gas at standard conditions supplied per unit time (Ncc)). SV [Ncc / g / h] = (Raw material supply amount [Ncc / h]) / (Catalyst mass [g]) Equation (5)

[0069] In a hydrogen production method, the product obtained by the ammonia decomposition reaction only needs to contain hydrogen, and may also contain other components. For example, in a typical ammonia decomposition, three molecules of hydrogen and one molecule of nitrogen are produced from two molecules of ammonia. Therefore, if the raw material gas does not contain nitrogen and hydrogen, the product will contain nitrogen and hydrogen in a volume ratio of 1:3. In addition, the product may also contain unreacted or by-product ammonia in addition to hydrogen.

[0070] [Example 1] MgO support ammonia decomposition catalyst (Preparation of ammonia decomposition catalyst) Cobalt nitrate hexahydrate Co(NO) ３ ) ２ 6H ２ O (manufactured by Fujifilm Wako Pure Chemical Industries) 22.2g, barium nitrate Ba (NO ３ ) ２ (Manufactured by Fujifilm Wako Pure Chemical Industries) 2.9g, Cerium nitrate hexahydrate Ce(NO) ３ ) ３ 6H ２ O (manufactured by Fujifilm Wako Pure Chemical Industries) 12.2 g, and magnesium nitrate hexahydrate Mg (NO ３ ) ２ 6H ２ 25.4 g of O (manufactured by Fujifilm Wako Pure Chemical Industries) was added to 430 ml of distilled water, heated to 40°C, and stirred to prepare an acid solution. The composition of each component (expressed as the molar ratio of each component to Co) is as shown in Table 1. Potassium carbonate K was added as a precipitating agent to this acid solution. ２ CO ３ 37.9 g of (manufactured by Fujifilm Wako Pure Chemical Industries) was added to 550 ml of distilled water, and a solution (alkaline solution) heated to 40°C was added dropwise over 40 minutes to obtain a suspension (dropwise addition step). The suspension was heated from 40°C to 60°C over 15 minutes while stirring, then stirred at 60°C for 1 hour to allow it to mature, and then filtered. For washing, the obtained solid components (coprecipitate) were suspended in 2500 ml of distilled water heated to 40°C, stirred, and filtered (washing operation). This washing operation was repeated four times to finally reduce the conductivity of the filtrate to 400 μS / cm. After that, the filtrate was heated to 80°C, dried for 12 hours, and calcined under air at 550°C for 2 hours to obtain Co-BaO-CeO ２ A calcined powder of -MgO (ammonia decomposition catalyst) was prepared. For use in the catalyst activity test, 2% by mass of graphite was added to the calcined powder and mixed, and a 2.2 g / ml molded body was obtained using a press. The molded body was then pulverized to a size of 335–850 μm for the activity test.

[0071] (Activity Test of Ammonia Decomposition Catalyst) The catalytic activity (ammonia conversion rate) of the ammonia decomposition catalyst was evaluated by performing an ammonia decomposition reaction using a fixed-bed flow reactor. Specifically, 1.0 ml of ammonia decomposition catalyst was packed into a reaction tube (forming a catalyst layer), and the catalyst layer was reduced at a temperature of 600°C for 2 hours under atmospheric pressure while 50 vol% hydrogen diluted with nitrogen was flowed into the reaction tube at a flow rate of 170 N ml / min as the flow gas. After this reduction treatment, the temperature inside the reaction tube was lowered, and the flow gas was switched to 100 vol% ammonia. The ammonia decomposition reaction was carried out at a flow rate of 100 N ml / min under atmospheric pressure, with the temperature of the catalyst layer set to 437°C (contact step between ammonia and ammonia decomposition catalyst). Subsequently, the heating temperature of the reaction tube was changed so that the temperature of the catalyst layer reached 446°C and 458°C, and the ammonia decomposition reaction was carried out. The ammonia conversion rate (%) was estimated using the formula {1 - (ammonia flow rate at the outlet of the reaction tube / ammonia flow rate at the inlet of the reaction tube)} × 100. The results are shown in Table 2 and Figure 1.

[0072] (Compositional analysis of ammonia decomposition catalyst) 0.01 g of calcined powder (ammonia decomposition catalyst) used during catalyst preparation was dissolved in 0.5 ml of 11.3-12.0 mol / L hydrochloric acid, and water (pure water) was added to dilute it to prepare a sample solution so that the weight of the aqueous solution was 50 g. After further diluting the sample solution 10 times with water, the content (analytical concentration (ppm)) of Co, Ce, Mg, K (precipitant), and Ba was quantified using inductively coupled plasma atomic emission spectrometry (ICP emission spectrometer (Thermo Fisher Scientific iCAP 6500)). (However, Co, Na, and K were quantified as elemental metals, and Ba, Ce, and Mg were quantified as oxides (BaO, CeO, respectively) ２ The components were quantified in terms of MgO. The content of each component (component concentration (mass%)) was calculated from the formula: analytical concentration (ppm) × 5 = component concentration (mass%), and the component molar concentration (mol / kg) was determined by: component concentration (mass%) × 10 / component atomic weight. The molar ratio (analytical composition ratio) of each component was calculated from the ratio of the component molar concentration of the target element (Ba, Ce, Mg, K, Na) to the component molar concentration of Co (number of moles of target element / number of moles of Co). The results are shown in Table 1.

[0073] [Examples 2-7 and Comparative Examples 1-2] Examples 2-7 and Comparative Examples 1-2 were prepared using the same method as in Example 1, with cobalt nitrate hexahydrate Co(NO) nitrate as the raw material. ３ ) ２ 6H ２ O, Barium nitrate Ba (NO ３ ) ２ , cerium nitrate hexahydrate Ce(NO ３ ) ３ 6H ２ O, and magnesium nitrate hexahydrate Mg(NO) ３ ) ２ 6H ２ Using O, adjust the quantity (g) so that the composition ratio (molar ratio) of the preparation is as shown in Table 1, and potassium carbonate K as the precipitating agent. ２ CO ３ or sodium carbonate (Na) ２ CO ３ Using this method, the conductivity of the filtrate is adjusted to the values ​​listed in Table 1, and finally Co-BaO-CeO ２ -MgO calcined powder (ammonia decomposition catalyst) was prepared. The compositional analysis and activity test of the obtained ammonia decomposition catalyst were carried out in the same manner as in Example 1. In Comparative Example 1, the washing operation was performed only once, so the alkali metal (K) content in the ammonia decomposition catalyst was relatively high. In Comparative Example 2, Ce(NO) ３ ) ３ 6H ２ A Co-BaO-MgO ammonia decomposition catalyst was prepared without using oxygen. The results are shown in Tables 1 and 2, and Figure 1. In Figure 1, the dashed line represents equation (1): conversion rate (%) = 0.6458T-202.25.

[0074]

[0075]

[0076] [Examples 8-11 and Comparative Examples 3-5] CaO-supported ammonia decomposition catalyst (Preparation of ammonia decomposition catalyst) Examples 8-11 and Comparative Examples 3-5 were prepared using the same method as in Example 1, with cobalt nitrate hexahydrate Co(NO) nitrate as the raw material. ３ ) ２ 6H ２ O, Barium nitrate Ba (NO３ ) ２ , cerium nitrate hexahydrate Ce(NO ３ ) ３ ·6H ２ O, and calcium nitrate tetrahydrate Ca(NO ３ ) ２ ·4H ２ O were used, the amounts (g) were adjusted to achieve the charging composition ratio (molar ratio) described in Table 3, and potassium carbonate K ２ CO ３ or sodium carbonate Na ２ CO ３ was used as a precipitant, the electrical conductivity of the filtrate was adjusted to the value described in Table 3, and finally a calcined powder of Co-BaO-CeO ２ -CaO (ammonia decomposition catalyst) was prepared. Composition analysis and activity tests of the obtained ammonia decomposition catalyst were also performed in the same manner as in Example 1. In Comparative Example 5, without using Ba(NO ３ ) ２ and Ce(NO ３ ) ３ ·6H ２ O as raw materials, a Co-CaO ammonia decomposition catalyst was finally prepared. The results are shown in Table 3, Table 4, and Figure 2. The broken line in Figure 2 represents formula (1): conversion rate (%) = 0.6458T - 202.25.

[0077]

[0078]

[0079] [Examples 12 to 16 and Comparative Example 6] CeO ２ Support-supported ammonia decomposition catalyst (Preparation of ammonia decomposition catalyst) Examples 12 to 16 and Comparative Example 6 were prepared by the same method as Example 1, using cobalt nitrate hexahydrate Co(NO ３ ) ２ ·6H ２ O, barium nitrate Ba(NO ３ ) ２ , and cerium nitrate hexahydrate Ce(NO ３ ) ３ ·6H ２ O were used, the amounts (g) were adjusted to achieve the charging composition ratio (molar ratio) described in Table 5, and potassium carbonate K ２CO ３ or sodium carbonate (Na) ２ CO ３ Using this method, the conductivity of the filtrate is adjusted to the values ​​listed in Table 5, and finally Co-BaO-CeO ２ A calcined powder (ammonia decomposition catalyst) was prepared. The compositional analysis and activity test of the obtained ammonia decomposition catalyst were carried out in the same manner as in Example 1. In Comparative Example 6, Ba (NO) was used as the raw material. ３ ) ２ It is not used, and ultimately Co-CeO ２ An ammonia decomposition catalyst was prepared. The results are shown in Tables 5 and 6, and Figure 3. The dashed line in Figure 3 represents equation (1): conversion rate (%) = 0.6458T-202.25.

[0080]

[0081]

[0082] As shown in Figures 1 to 3, the ammonia decomposition catalysts of Examples 1 to 16 contain cobalt (A), barium (B), and cerium (C), with an alkali metal content of 0.01 moles or less per mole of cobalt (A). This configuration resulted in the ammonia decomposition catalysts of Examples 1 to 16 exhibiting improved catalytic activity (ammonia conversion rate) at relatively lower temperatures compared to the ammonia decomposition catalysts of Comparative Examples 1 to 6. In other words, the ammonia decomposition catalysts of Examples 1 to 16 achieved a predetermined ammonia conversion rate (e.g., 90%) at temperatures approximately 20 to 80°C lower than those of the ammonia decomposition catalysts of Comparative Examples 1 to 6.

Claims

1. An ammonia decomposition catalyst comprising cobalt (A), barium (B), and cerium (C), wherein the alkali metal content in the catalyst is 0.01 moles or less per mole of cobalt (A).

2. The barium (B) content is 0.01 to 0.15 moles in terms of barium oxide (BaO) per mole of cobalt (A), and the cerium (C) content is 0.01 to 0.15 moles in terms of barium oxide (BaO) per mole of cobalt (A). ２ The catalyst according to claim 1, wherein the amount is 0.2 to 0.8 moles when converted to a fractional amount.

3. The catalyst according to claim 1, further comprising magnesium (D).

4. The barium (B) content is 0.01 to 0.15 moles in terms of barium oxide (BaO) per mole of cobalt (A), and the cerium (C) content is 0.01 to 0.15 moles in terms of barium oxide (BaO) per mole of cobalt (A). ２ The catalyst according to claim 3, wherein the amount of magnesium (D) is 0.2 to 0.5 moles in terms of cobalt (A), and the content of magnesium (D) is 0.02 to 1.60 moles in terms of magnesium oxide (MgO) per mole of cobalt (A).

5. The catalyst according to claim 1, further comprising calcium (E).

6. The barium (B) content is 0.01 to 0.15 moles in terms of barium oxide (BaO) per mole of cobalt (A), and the cerium (C) content is 0.01 to 0.15 moles in terms of barium oxide (BaO) per mole of cobalt (A). ２ The catalyst according to claim 5, wherein the amount of calcium (E) is 0.2 to 0.5 moles in terms of cobalt (A), and the content of calcium (E) is 0.05 to 1.00 moles in terms of calcium oxide (CaO) per mole of cobalt (A).

7. The barium (B) content is 0.01 to 0.13 moles of barium oxide (BaO) per mole of cobalt (A), and the cerium (C) content is 0.01 to 0.13 moles of cerium oxide (CeO) per mole of cobalt (A). ２ The catalyst according to claim 1, wherein the amount is 0.2 to 0.7 moles when converted to 0.5g.

8. The catalyst according to claim 1, wherein the alkali metal is sodium and / or potassium.

9. The catalyst according to claim 1, wherein the ammonia conversion rate (%) by the catalyst satisfies the following relationship under atmospheric pressure: Conversion rate (%) > 0.6458T - 202.25 (1), where T is the temperature (°C) of the catalyst in the range of 400 to 550°C.

10. A method for producing a catalyst according to any one of claims 1 to 9 by coprecipitation, comprising the step of dropping an alkaline solution containing a sodium salt and / or a potassium salt to an acid solution containing a cobalt (A) salt, a barium (B) salt, and a cerium (C) salt.

11. The manufacturing method according to claim 10, further comprising the steps of washing the coprecipitate of the acid solution and the alkaline solution with water, and calcining the coprecipitate after washing.

12. A method for producing hydrogen, comprising the step of contacting a catalyst according to any one of claims 1 to 9 with a raw material gas containing ammonia.

13. The manufacturing method according to claim 12, wherein the raw material gas contains ammonia in an amount of 10 to 100% by volume.

14. The manufacturing method according to claim 12, wherein the temperature of the catalyst when it comes into contact with the raw material gas is in the range of 300 to 900°C.

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