Ammonia decomposition catalyst and its manufacturing method, ammonia decomposition method, hydrogen production method, and hydrogen production device

Abstract

The present invention provides a non-noble metal ammonia decomposition catalyst that exhibits ammonia decomposition activity, a method for producing the same, a method for decomposing ammonia, a method for producing hydrogen, and a hydrogen production device. The ammonia decomposition catalyst includes a composite oxide and non-precious metal particles supported on the composite oxide. x Mg 1-x O y (wherein A is at least one element selected from the group consisting of alkali metal elements and alkaline earth metal elements excluding Mg; 0

Description

[Technical Field]

[0001] The present invention relates to an ammonia decomposition catalyst and a method for producing the same, a method for decomposing ammonia, a method for producing hydrogen, and a hydrogen production device. [Background technology]

[0002] In recent years, the use of hydrogen energy has been attracting attention as one means of achieving a carbon-neutral, decarbonized society. However, hydrogen is a gas at room temperature and has a low volumetric energy density, making it difficult to store and transport. While it is possible to liquefy hydrogen for storage and transportation, it must be kept at extremely low temperatures, which poses the problem of boil-off. However, by converting hydrogen into ammonia, it is possible to store and transport hydrogen under mild conditions.

[0003] Ammonia is one of the hydrogen carriers, and has the following characteristics: it does not contain carbon atoms, it is easily liquefied, so it has high volumetric and weight energy density, and existing facilities can be used for storage and transportation. Ru, for example, is known as an ammonia decomposition catalyst for extracting hydrogen by decomposing ammonia.

[0004] Although the prior art Patent Document 1 is not a technology related to an ammonia decomposition catalyst, it describes a compound having the general formula L consisting of an oxide of a metal element L and an oxide of a metal element N. n N 1-n The present invention discloses a technology relating to an ammonia synthesis catalyst in which particles of at least one metal selected from the group consisting of Co, Fe, and Ni are supported on a composite oxide having a composition of O. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] WO2021 / 153738 publication Summary of the Invention [Problem to be solved by the invention]

[0006] Conventionally well-known Ru exhibits excellent ammonia decomposition activity, but it is an expensive and rare noble metal element and is not suitable for large-scale industrial use. Therefore, the development of an ammonia decomposition catalyst using non-noble metals is required.

[0007] The present invention has been made in view of such problems, and aims to provide an ammonia decomposition catalyst that exhibits ammonia decomposition activity in a non-noble metal system, a method for producing the ammonia decomposition catalyst, a method for decomposing ammonia using the ammonia decomposition catalyst, a method for producing hydrogen using the ammonia decomposition catalyst, and a hydrogen production apparatus using the ammonia decomposition catalyst.

Means for Solving the Problems

[0008] One aspect of the present invention is including a composite oxide and non-noble metal particles supported on the composite oxide, the composite oxide is A x Mg 1-x O y (where A is an alkaline metal element selected from the group consisting of alkaline earth metal elements excluding alkaline metal elements and Mg, x is 0 < x ≦ 0.1, and y is the number of oxygen atoms necessary for the composite oxide to maintain electrical neutrality), the non-noble metal constituting the non-noble metal particles is Co, Ni, Fe, or an alloy thereof, in an ammonia decomposition catalyst.

[0009] Another aspect of the present invention is A x Mg 1-x O y a preparation step of preparing a composite oxide represented by the composition of (where A is an alkaline metal element selected from the group consisting of alkaline earth metal elements excluding alkaline metal elements and Mg, x is 0 < x ≦ 0.1, and y is the number of oxygen atoms necessary for the composite oxide to maintain electrical neutrality), a heat treatment step of impregnating the composite oxide with a non-precious metal precursor containing at least one non-precious metal selected from the group consisting of Co, Ni, and Fe to obtain an impregnated body, and heat treating the impregnated body in an inert gas atmosphere to obtain a heat-treated product; a reduction step of subjecting the heat-treated product to a hydrogen reduction treatment in a reducing atmosphere containing hydrogen at a reduction temperature of 300°C or higher and 800°C or lower; The present invention relates to a method for producing an ammonia decomposition catalyst.

[0010] Yet another aspect of the present invention is a method for producing a semiconductor device comprising: The present invention relates to a method for decomposing ammonia, which comprises bringing ammonia into contact with the ammonia decomposition catalyst or the ammonia decomposition catalyst obtained by the method for producing an ammonia decomposition catalyst, to decompose the ammonia.

[0011] Yet another aspect of the present invention is a method for producing a semiconductor device comprising: The present invention also relates to a method for producing hydrogen, which comprises bringing ammonia into contact with the ammonia decomposition catalyst or the ammonia decomposition catalyst obtained by the method for producing an ammonia decomposition catalyst, thereby decomposing the ammonia and producing hydrogen.

[0012] Yet another aspect of the present invention is a method for producing a semiconductor device comprising: The present invention relates to a hydrogen production device using the ammonia decomposition catalyst. [Effects of the Invention]

[0013] The ammonia decomposition catalyst has the above-described structure. Therefore, the ammonia decomposition catalyst can exhibit ammonia decomposition activity without using a noble metal. Therefore, the ammonia decomposition catalyst is suitable for large-scale industrial use.

[0014] The method for producing an ammonia decomposition catalyst has the above-described configuration. Therefore, according to the method for producing an ammonia decomposition catalyst, the ammonia decomposition catalyst that exhibits ammonia decomposition activity can be produced without using a noble metal.

[0015] The above-mentioned ammonia decomposition method uses the above-mentioned ammonia decomposition catalyst, and therefore can decompose ammonia without using any noble metals.

[0016] The hydrogen production method uses the ammonia decomposition catalyst, and therefore can decompose ammonia and produce hydrogen without using a noble metal.

[0017] The hydrogen production device uses the ammonia decomposition catalyst, and therefore can decompose ammonia and produce hydrogen without using any precious metals. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a graph showing the ammonia decomposition activity measured at different reaction temperatures in a 20 mass% Co / Al0.01Mg0.99Oy catalyst (reduced at 700°C) in an experimental example. [Figure 2] FIG. 2 is a graph showing the ammonia decomposition activity at a reaction temperature of 450° C. in a 20 mass% Co / AlO.OlMgO.99Oy catalyst (reduced at 700° C.) of an experimental example. [Figure 3] FIG. 3 is a graph showing the ammonia decomposition activity measured at different reaction temperatures in a 20 mass% Co / Al0.01Mg0.99Oy catalyst (reduced at 500° C.) of an experimental example. [Figure 4] FIG. 4 is a graph showing the ammonia decomposition activity at a reaction temperature of 450° C. in a 20 mass% Co / AlO.OlMgO.99Oy catalyst (reduced at 500° C.) of an experimental example. [Figure 5] FIG. 5 is a graph showing the ammonia decomposition activity measured at different reaction temperatures in a 20 mass% Co / BaxMg1-xOy catalyst (reduced at 700° C.) of an experimental example. [Figure 6] FIG. 6 is a graph showing the ammonia decomposition activity of the 20 mass% Co / BaxMg1-xOy catalyst (reduced at 700°C) in the experimental example when the reaction temperature was 450°C. [Figure 7]FIG. 7 shows the HAADF-STEM image and EDX analysis results obtained for the 20 mass% Co / BaO.sub.0.01MgO.sub.99Oy catalyst (reduced at 700°C) of the experimental example, in which (a) is an HAADF-STEM image, (b) is an elemental map of Co, (c) is an elemental map of Ba, (d) is an elemental map of Mg, and (e) is an overlay elemental map obtained by superimposing the elemental maps (b) to (d). [Figure 8] FIG. 8 shows an HAADF-STEM image and the results of EDX analysis obtained for a 20 mass% Co / SrMgO catalyst (reduced at 700°C) of an experimental example, in which (a) is an HAADF-STEM image, (b) is an elemental map of Mg, (c) is an elemental map of Sr, (d) is an elemental map of Co, and (e) is an overlay elemental map obtained by superimposing the elemental maps (b) to (d). [Figure 9] FIG. 9 shows the results of measuring CO2-TPD spectra for the 20 mass% Co / AlO_O1MgO_99Oy catalyst (A=Ba, Sr, K, Li, reduced at 700°C) of the experimental example, 20 mass% Co / MgO (reduced at 700°C), and MgO. [Figure 10] FIG. 10 is a graph showing the change over time in ammonia decomposition activity when an ammonia exposure step was performed after a reduction step for 20 mass% Co / Ba0.01Mg0.99Oy (reduced at 500° C.) of an experimental example. DETAILED DESCRIPTION OF THE INVENTION

[0019] The ammonia decomposition catalyst and its manufacturing method, ammonia decomposition method, hydrogen production method, and hydrogen production apparatus of the present disclosure will be described in detail below using embodiments. Note that the ammonia decomposition catalyst and its manufacturing method, ammonia decomposition method, hydrogen production method, and hydrogen production apparatus of the present disclosure are not limited to the examples shown in the following embodiments. Furthermore, the lower and upper limits of the numerical ranges shown below can be combined arbitrarily (omitted below).

[0020] (Ammonia decomposition catalyst) The ammonia decomposition catalyst of this embodiment (hereinafter sometimes abbreviated as "this catalyst") contains a composite oxide and non-noble metal particles.

[0021] In this catalyst, the composite oxide serves as a carrier for supporting non-noble metal particles. The composite oxide can, for example, exhibit a particulate shape.

[0022] The composite oxide is A x Mg 1-x O y and is represented by the composition. However, in this compositional formula, x satisfies 0 < x ≤ 0.1. y is the number of oxygen atoms necessary for the composite oxide to maintain electrical neutrality. A is an alkaline metal element that is at least one element selected from the group consisting of alkaline earth metal elements excluding alkaline metal elements and Mg.

[0023] From the viewpoint of improving the ratio of the surface of the non-noble metal particles in contact with the alkaline metal element, etc., x is preferably 0.001 or more, more preferably 0.002 or more, still more preferably 0.003 or more, even more preferably 0.004 or more, even still more preferably 0.005 or more. Also, from the viewpoint of preventing the surface of the non-noble metal particles from being excessively covered by the oxide of the alkaline metal element, etc., x is preferably 0.09 or less, more preferably 0.08 or less, still more preferably 0.07 or less, even more preferably 0.06 or less, even still more preferably 0.05 or less.

[0024] Since y is the number of oxygen atoms necessary for the composite oxide to maintain electrical neutrality, it varies depending on the type of alkaline metal element, etc. Here, since x does not take 0, y < 1, and since it is an oxide and contains O, 0 < y. Usually, the range of 0.95 < y < 1 can be taken, and in particular, the range of 0.97 < y < 0.998 can be taken.

[0025] The alkali metal element constituting the alkali metal element may specifically be at least one selected from the group consisting of K, Na, Rb, Li, and Cs, and preferably at least one selected from the group consisting of K, Na, and Rb from the viewpoint of improving ammonia decomposition activity, more preferably K or Na, and even more preferably K. The alkaline earth metal element constituting the alkali metal element may specifically be at least one selected from the group consisting of Ba, Sr, Ca, Be, and Ra, and preferably at least one selected from the group consisting of Ba, Sr, and Ca from the viewpoint of high thermal stability such as melting point and boiling point, more preferably Ba or Sr from the viewpoint of improving ammonia decomposition activity, and even more preferably Ba from the viewpoint of exceptionally high ammonia decomposition activity.

[0026] In the composite oxide, the alkali metal element is preferably at least one selected from the group consisting of Ba, K, Sr, and Ca, from the viewpoint of being able to exhibit high ammonia decomposition activity in a low temperature range (e.g., 350°C or higher and 550°C or lower), and more preferably Ba, from the viewpoint of exhibiting particularly high ammonia decomposition activity compared to K, Sr, and Ca.

[0027] As can be seen from the above composition formula, the above-mentioned composite oxide can be said to be composed of an oxide of an alkali metal element (excluding MgO) and MgO. In the above composition formula, the alkali metal element is, as mentioned above, at least one element selected from the group consisting of alkali metal elements and alkaline earth metal elements. Therefore, the oxide of an alkali metal element can be specifically an alkali metal oxide, an alkaline earth metal oxide, a composite oxide containing an alkali metal and an alkaline earth metal, a composite oxide containing two or more different alkali metals, or a composite oxide containing two or more different alkaline earth metals, and these can be used alone or in combination.

[0028] Examples of the oxide of an alkali metal element include BaO, KO, SrO, CaO, NaO, RbO, LiO, and CsO. The oxide of an alkali metal element is preferably BaO, KO, SrO, or CaO, from the viewpoint of exhibiting high ammonia decomposition activity in a low temperature range (e.g., 350°C or higher and 550°C or lower), and more preferably BaO, from the viewpoint of exhibiting particularly high ammonia decomposition activity compared to KO, SrO, or CaO.

[0029] In the composite oxide, the oxide of the alkali metal element may or may not be solid-dissolved in MgO. The composite oxide preferably contains an oxide of the alkali metal element that is not solid-dissolved in MgO. When the oxide of the alkali metal element is solid-dissolved in MgO, the oxide of the alkali metal element is present inside the MgO, which reduces the amount of the oxide of the alkali metal element in contact with the non-precious metal particles, making it difficult to exhibit the electron-donating effect. In contrast, the oxide of the alkali metal element that is not solid-dissolved in MgO is present outside the MgO, which increases the amount of the oxide of the alkali metal element in contact with the non-precious metal particles, making it easier to exhibit the electron-donating effect. Therefore, when the composite oxide contains an oxide of the alkali metal element that is not solid-dissolved in MgO, there is an advantage in that it is easier to improve the ammonia decomposition activity. Whether or not the composite oxide contains oxides of alkali metal elements that are not dissolved in MgO can be determined by combining observation using HAADF-STEM images (high-angle dark-field scanning transmission electron microscope images) with element mapping using EDX analysis (energy-dispersive X-ray fluorescence spectroscopy analysis).

[0030] In the present catalyst, the non-noble metal particles are supported on a composite oxide, and it is preferable that the non-noble metal particles are distributed at least on the surface of the composite oxide from the viewpoints of increasing the opportunity for contact with ammonia, ammonia decomposition activity, etc.

[0031] Furthermore, the oxide of the alkali metal element that constitutes part of the composite oxide can be distributed on the surface of the composite oxide, on both the surface of the composite oxide and the surface of the non-precious metal particles, or on the surface of the non-precious metal particles. In other words, in ammonia decomposition, unlike in ammonia synthesis, ammonia decomposition activity can be exhibited even when the oxide of the alkali metal element does not cover the entire surface of the non-precious metal particles. This is thought to be because the reaction steps promoted by electron donation are different in ammonia synthesis and ammonia decomposition. Thus, in this catalyst, it is not necessarily necessary for the oxide of the alkali metal element to cover the entire surface of the non-precious metal particles.

[0032] The non-precious metals constituting the non-precious metal particles are Co, Ni, Fe, or alloys thereof, i.e., Co, Co alloy, Ni, Ni alloy, Fe, or Fe alloy. Therefore, the non-precious metal particles can be specifically Co particles, Ni particles, Fe particles, Co alloy particles, Ni alloy particles, Fe alloy particles, etc., and these can be used alone or in combination. Examples of Co alloys include alloys of Co and Ni and / or Fe. Examples of Ni alloys include alloys of Ni and Co and / or Fe. Examples of Fe alloys include alloys of Fe and Ni and / or Co.

[0033] The non-precious metal constituting the non-precious metal particles is preferably Co or a Co alloy, more preferably Co, from the viewpoints of ammonia decomposition activity, the ability to maintain a small particle size after hydrogen reduction treatment, etc. The non-precious metal particles may have a passivated particle surface.

[0034] In this catalyst, the amount of non-precious metal particles supported can be preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, from the viewpoint of increasing the number of active sites. The amount of non-precious metal particles supported can be preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, from the viewpoint of suppressing particle aggregation and enlargement. The amount of non-precious metal particles supported can be calculated using the formula: 100 × (mass of non-precious metal particles) / (mass of non-precious metal particles when present as oxides on the surface and in the interior + mass of composite oxide).

[0035] Because the present catalyst has the above-described structure, it can exhibit ammonia decomposition activity without using a noble metal, and is therefore suitable for large-scale industrial use.

[0036] In the present catalyst described above, the oxide of the alkali metal element is part of the components that make up the composite oxide, and it is preferable that as many alkali metal elements as possible exist in the form of an oxide. This is because it is easier to improve ammonia decomposition activity. This is thought to be because the oxide of the alkali metal element has high electron donating properties, making it easier to donate electrons to the N atom via the non-precious metal particles supported on the composite oxide, weakening the bond between the non-precious metal particle and the N atom and promoting the formation of the N-N bond, which is the rate-determining step.

[0037] However, because oxides of alkali metal elements are highly basic, they react with carbon dioxide and water in the atmosphere to form carbonates and hydroxides of alkali metal elements. For example, because the carbonate state of Ba is very stable, it easily becomes BaCO3 or Ba(OH)2 in the atmosphere. Carbonates and hydroxides of alkali metal elements have lower electron donating properties than the oxides of alkali metal elements that make up the composite oxide. In particular, carbonates of alkali metal elements have lower electron donating properties than hydroxides of alkali metal elements. Therefore, from the perspective of improving ammonia decomposition activity, it is desirable to minimize the amount of carbonates and hydroxides of alkali metal elements contained in this catalyst. Hydrogen reduction and ammonia exposure after hydrogen reduction, as described below, are effective in reducing the amount of carbonates and hydroxides of alkali metal elements, which can effectively decompose the carbonates and hydroxides of alkali metal elements. The decomposition mechanism of carbonates of alkali metal elements is thought to be as follows: carbonate of alkali metal element → hydroxide of alkali metal element → oxide of alkali metal element.

[0038] As long as the present catalyst contains at least the above-described composite oxide and non-precious metal particles and exhibits ammonia decomposition activity, there are no particular limitations on whether or not it contains substances other than the composite oxide and non-precious metal particles. However, as described above, from the perspective of having as many alkali metal elements as possible present in the oxide state and improving ammonia decomposition activity, it is preferable that the present catalyst does not contain detectable carbonates of alkali metal elements, which have low electron donating properties. To obtain an ammonia decomposition catalyst in which no detectable carbonates of alkali metal elements are present, exposure to ammonia after hydrogen reduction, as described below, is particularly effective. Note that the detection of carbonates of alkali metal elements can be performed by using infrared absorption spectroscopy to confirm the presence or absence of peaks derived from carbonates of alkali metal elements.

[0039] While it is ideal and desirable for the catalyst to contain no detectable alkali metal carbonates, taking into account the possibility of residual alkali metal carbonates remaining during production, handling, and storage, it is acceptable for the catalyst to contain alkali metal carbonates and / or alkali metal hydroxides as long as they exhibit ammonia decomposition activity. In this case, from the viewpoint of ensuring ammonia decomposition activity, the content of alkali metal oxides constituting part of the composite oxide is preferably greater than the combined content of alkali metal carbonates and alkali metal hydroxides. From the viewpoint of minimizing the decrease in electron donating ability, the content of alkali metal carbonates is more preferably less than the content of alkali metal hydroxides. The content of alkali metal oxides, alkali metal carbonates, and alkali metal hydroxides in the catalyst can be quantified by detecting products produced during heating using thermal desorption spectroscopy or by measuring the carbon and nitrogen content using CHN elemental analysis.

[0040] The carbonate of an alkaline metal element may be, for example, an alkali metal carbonate, an alkaline earth metal carbonate, a composite carbonate containing an alkali metal and an alkaline earth metal, a composite carbonate containing two or more different alkali metals, or a composite carbonate containing two or more different alkaline earth metals, and may contain one or more of these. Examples of carbonates of alkaline metal elements include BaCO3, K2CO3, SrCO3, CaCO3, Na2CO3, Rb2CO3, Li2CO3, and Cs2CO3. The hydroxide of an alkaline metal element may be, for example, an alkali metal hydroxide, an alkaline earth metal hydroxide, a composite hydroxide containing an alkali metal and an alkaline earth metal, a composite hydroxide containing two or more different alkali metals, or a composite hydroxide containing two or more different alkaline earth metals, and may contain one or more of these. Examples of hydroxides of alkaline metal elements include Ba(OH)2, KOH, Sr(OH)2, Ca(OH)2, NaOH, RbOH, LiOH, and CsOH.

[0041] The alkali metal element of this catalyst is Ba, and in the spectrum measured by infrared absorption spectroscopy, the absorbance of the peak assigned to BaCO3 and the peak at 2000 cm -1 The ratio of the absorbance to the absorbance may be less than 0.01.

[0042] According to this configuration, it is possible to ensure that BaCO3 is sufficiently decomposed by the hydrogen reduction treatment, and therefore the ammonia decomposition activity of the present catalyst can be ensured.

[0043] The peak attributed to (or derived from) BaCO3 is at a wavenumber of 1443 cm -1 The peak that appears at 2000cm -1 The absorbance at 2000 cm is significant in that it shows the infrared absorption spectrum of the catalyst itself, without the influence of absorption peaks derived from carbonate species. -1 Specifically, the ratio of the absorbance of the peak attributable to BaCO3 to the absorbance of the peak attributable to BaCO3 is calculated by subtracting the background from the absorption spectrum after measurement. -1 It can be calculated using the formula:

[0044] The catalyst can be configured so that the maximum value of the CO2 desorption peak is present at 200°C or higher in the CO2-TPD spectrum measured by temperature programmed desorption spectroscopy using CO2 gas as a probe molecule.

[0045] Because CO2 exhibits weak acidity, when a temperature-programmed desorption (TPD) spectrum is applied to a catalyst using CO2 gas as a probe molecule, it adsorbs to basic sites on the catalyst surface. Therefore, in the CO2-TPD spectrum measured by the temperature-programmed desorption (TPD) spectrum (horizontal axis: temperature, vertical axis: intensity corresponding to the mass of CO2 desorbed at the corresponding temperature), a large amount of CO2 desorption indicates the presence of many basic sites on the catalyst. Furthermore, the stronger the basicity, the stronger the CO2 adsorption to the site, and therefore, a higher temperature is required to desorb the CO2 adsorbed on such sites. Therefore, a higher CO2 desorption temperature indicates a catalyst with more basic sites. As shown in the experimental examples below, in the CO2-TPD spectrum, catalysts consisting of only MgO without alkali metal doping or MgO with non-precious metal particles have a maximum CO2 desorption peak near 180 °C. Catalysts with a higher maximum CO2 desorption peak at a higher temperature indicate a stronger basicity. As will be shown in the experimental examples described later, a catalyst having such a basicity that the maximum value of the CO2 desorption peak is present at 200°C or higher, preferably 230°C or higher, exhibits high ammonia decomposition activity.

[0046] Therefore, if this catalyst satisfies the requirement that the maximum value of the CO2 desorption peak be at 200°C or higher in the CO2-TPD spectrum measured by the temperature-programmed desorption method using CO2 gas as the probe molecule, it is certain that the catalyst will exhibit high ammonia decomposition activity.

[0047] For other configurations and effects, reference can be made to the descriptions in the sections "(Method for producing an ammonia decomposition catalyst)," "(Method for decomposing an ammonia)," "(Method for producing hydrogen)," and "(Hydrogen production apparatus)" described below, as needed.

[0048] (Method of manufacturing an ammonia decomposition catalyst) The method for producing an ammonia decomposition catalyst of this embodiment (hereinafter sometimes abbreviated as "this production method") is a method for producing the ammonia decomposition catalyst of this embodiment.

[0049] This manufacturing method has a preparation step, a heat treatment step, and a reduction step.

[0050] In this manufacturing method, the preparation step is to prepare a composite oxide represented by the composition of A x Mg 1-x O y (where A is an alkaline metal element selected from the group consisting of alkaline earth metal elements excluding alkaline metal elements and Mg, x is 0 < x ≤ 0.1, and y is the number of oxygen atoms required for the composite oxide to maintain electrical neutrality). Since the details of the composition of the composite oxide are as described above, the description is omitted.

[0051] The composite oxide can be obtained, for example, by mixing an aqueous mixed solution of a water-soluble salt of an alkaline metal element and MgO, stirring, drying, and firing the obtained powder.

[0052] Examples of the water-soluble salt of the alkaline metal element include nitrates, sulfates, hydroxides, acetates, chlorides, carbonates, etc. of the alkaline metal element. These can be used alone or in combination of two or more. The molar ratio of Mg to the alkaline metal element can be appropriately adjusted by changing the charged amount of the raw materials in the aqueous mixed solution to a predetermined molar ratio.

[0053] The calcination can be carried out, for example, in an oxygen-containing atmosphere such as air, at a calcination temperature of 300°C to 800°C for a calcination time of 1 hour to 48 hours. The calcination temperature is preferably 325°C or higher, more preferably 350°C or higher, even more preferably 375°C or higher, and even more preferably 400°C or higher, from the viewpoint of sufficiently reacting the salt of the alkali metal element with oxygen to form an oxide. The calcination temperature is preferably 750°C or lower, more preferably 700°C or lower, even more preferably 650°C or lower, and even more preferably 600°C or lower, from the viewpoint of preventing excessive reduction in the surface area of ​​the composite oxide due to sintering. The calcination time is preferably 2 hours or higher, more preferably 3 hours or higher, and even more preferably 4 hours or higher, from the viewpoint of sufficiently reacting the salt of the alkali metal element with oxygen to form an oxide. The firing time can be set to preferably 24 hours or less, more preferably 12 hours or less, and even more preferably 8 hours or less, from the viewpoint of preventing an excessive decrease in the surface area of ​​the composite oxide due to sintering.

[0054] In this production method, the heat treatment step is a step in which an impregnated body obtained by impregnating a composite oxide with a non-precious metal precursor containing at least one non-precious metal selected from the group consisting of Co, Ni, and Fe is heat-treated in an inert gas atmosphere to obtain a heat-treated product.

[0055] The non-precious metal precursor impregnated into the composite oxide is the raw material for the non-precious metal particles supported on the composite oxide. Details of the non-precious metal contained in the non-precious metal precursor are as described above, and therefore will not be described here.

[0056] Examples of the non-precious metal precursor include organometallic compounds containing a non-precious metal. Specific examples of the non-precious metal precursor include, when the non-precious metal is Co, cobalt(II) acetylacetonate, cobalt(III) acetylacetonate, cobalt acetate, cobalt citrate, etc., when the non-precious metal is Ni, nickel(II) acetylacetonate, nickel acetate, nickel citrate, etc., when the non-precious metal is Fe, and iron(III) acetylacetonate, iron acetate, etc.

[0057] Impregnation of a composite oxide with a non-precious metal precursor can be carried out, for example, by immersing and stirring the composite oxide in a solution containing the non-precious metal precursor. The solvent for the solution can be selected from a variety of solvents, depending on the type of non-precious metal precursor. However, when the non-precious metal precursor is an organometallic compound containing a non-precious metal, it is advantageous to use an organic solvent. Examples of organic solvents include tetrahydrofuran (THF), methanol, ethanol, hexane, and toluene. These can be used alone or in combination. Furthermore, the resulting impregnated body can be dried, if necessary, using an evaporator or the like under reduced pressure in a low-temperature atmosphere (e.g., 20°C to 35°C).

[0058] Examples of inert gases for forming the inert gas atmosphere include nitrogen gas (N2 gas), argon gas (Ar gas), and helium gas (He gas), and these can be used alone or in combination of two or more. From the viewpoints of impurity content, gas price, etc., the inert gas for forming the inert gas atmosphere is preferably nitrogen gas or argon gas, and more preferably argon gas.

[0059] The heat treatment temperature can be set to preferably 300° C. or higher, more preferably 400° C. or higher, and even more preferably 450° C. or higher, from the viewpoint of reducing organic residue remaining on the surface of the heat-treated product after the heat treatment. The heat treatment temperature can be set to preferably 700° C. or lower, more preferably 600° C. or lower, and even more preferably 550° C. or lower, from the viewpoint of suppressing the formation of a solid solution between the non-precious metal and the composite oxide and suppressing the aggregation of the non-precious metal itself during the heat treatment process.

[0060] The heat treatment time is preferably 2 hours or more, more preferably 3 hours or more, and even more preferably 4 hours or more, from the viewpoint of reducing organic residue remaining on the surface of the heat-treated product after the heat treatment. The heat treatment time is preferably 10 hours or less, more preferably 8 hours or less, and even more preferably 6 hours or less, from the viewpoint of suppressing the formation of a solid solution between the non-precious metal and the composite oxide and the aggregation of the non-precious metal itself during the heat treatment.

[0061] The amount of non-precious metal particles carried can be adjusted appropriately by, for example, the amount of non-precious metal precursor impregnated into the composite oxide.

[0062] In this production method, the reduction step is a step in which the heat-treated product is subjected to hydrogen reduction treatment in a reducing atmosphere containing hydrogen at a reduction temperature of 300°C or higher and 800°C or lower.

[0063] Specific examples of the reducing atmosphere containing hydrogen include a hydrogen atmosphere, a hydrogen-inert gas mixed atmosphere (e.g., a hydrogen-nitrogen mixed atmosphere, a hydrogen-argon mixed atmosphere, etc.), etc. From the viewpoint of reducing power, the reducing atmosphere containing hydrogen is preferably a hydrogen atmosphere.

[0064] The reduction temperature may be preferably 325°C or higher, more preferably 350°C or higher, and even more preferably 400°C or higher, from the viewpoints of reducing non-precious metal oxides to their metallic state, forming alkali metal elements in an oxide state, and removing organic residues in the catalyst. The reduction temperature may be preferably 750°C or lower, more preferably 700°C or lower, even more preferably 650°C or lower, even more preferably 600°C or lower, and even more preferably 550°C or lower, from the viewpoints of suppressing aggregation of non-precious metal particles. Furthermore, from the viewpoint of forming a large number of fine non-precious metal particles, the reduction temperature may be 500°C or lower, even more preferably less than 500°C, even more preferably 475°C or lower, and even more preferably 450°C or lower.

[0065] The reduction time is preferably 30 minutes or more, more preferably 1 hour or more, from the viewpoints of reducing non-precious metal oxides to their metallic state, forming alkali metal elements in an oxide state, and removing organic residues in the catalyst, etc. The reduction time is preferably 48 hours or less, more preferably 24 hours or less, and even more preferably 12 hours or less, from the viewpoints of suppressing aggregation of non-precious metal particles, etc.

[0066] According to this production method, an ammonia decomposition catalyst exhibiting ammonia decomposition activity can be obtained through the above-described preparation step, heat treatment step, and reduction step. However, this production method may further include the following ammonia exposure step, if necessary.

[0067] The ammonia exposure step is a step in which the reduction temperature is 300°C or higher and 500°C or lower, and the catalyst obtained after hydrogen reduction is exposed to a gas containing ammonia at a temperature of 350°C or higher and 550°C or lower.

[0068] By carrying out the exposure step after the reduction step, the temperature required to activate the ammonia decomposition catalyst can be kept low. This is thought to be because the decomposition of carbonates of alkali metal elements that remain undecomposed when reduced (with hydrogen) at low temperatures proceeds even at low temperatures by reacting with ammonia, increasing the electron-donating ability of the alkali metal elements and promoting the formation of N-N bonds, which is the rate-determining step in ammonia decomposition.

[0069] When the exposure step is included, the reduction temperature in the reduction step can be preferably 325° C. or higher, more preferably 350° C. or higher, and even more preferably 400° C. or higher, from the viewpoints of reducing non-precious metal oxides to a metallic state, removing organic residues in the catalyst, etc. The reduction temperature in the reduction step can be preferably lower than 500° C., more preferably 475° C. or lower, and even more preferably 450° C. or lower, from the viewpoints of suppressing aggregation of non-precious metal particles, etc.

[0070] The temperature at the time of exposure to the ammonia-containing gas (hereinafter sometimes referred to as the exposure temperature) can be set to preferably 360°C or higher, more preferably 375°C or higher, and even more preferably 400°C or higher, from the viewpoint of promoting the reaction between ammonia and a carbonate of an alkali metal element. The exposure temperature can be set to preferably less than 550°C, more preferably 530°C or lower, even more preferably 520°C or lower, even more preferably 500°C or lower, and even more preferably less than 500°C, from the viewpoint of suppressing excessive external heat input during the exposure process.

[0071] The pressure when exposed to the ammonia-containing gas (hereinafter sometimes referred to as the exposure pressure) is preferably atmospheric pressure or higher from the viewpoint of simplifying the equipment and operation. The exposure pressure can also be increased to atmospheric pressure or higher from the viewpoint of promoting the reaction between ammonia and a carbonate of an alkaline metal element. In this case, the exposure pressure can be preferably 0.1 MPa (G) or higher, more preferably 0.5 MPa (G) or higher. From the viewpoint of simplifying the equipment and operation and preventing ammonia from coagulating or liquefying when ammonia is contained at a high concentration, the exposure pressure can be preferably 1.0 MPa (G) or lower, more preferably 0.8 MPa (G) or lower.

[0072] The time for exposure to the ammonia-containing gas (hereinafter sometimes referred to as the exposure time) can be preferably 1 hour or more, more preferably 3 hours or more, and even more preferably 6 hours or more, from the viewpoint of promoting the reaction between ammonia and the carbonate of an alkaline metal element, etc. The exposure time can be preferably 72 hours or less, more preferably 48 hours or less, and even more preferably 24 hours or less, from the viewpoint of suppressing the consumption of ammonia, etc.

[0073] Specific examples of the ammonia-containing gas include ammonia, ammonia-inert gas mixtures (e.g., ammonia-nitrogen mixtures, ammonia-argon mixtures, etc.), etc. The ammonia-containing gas is preferably ammonia, from the viewpoints of promoting the reaction between ammonia and a carbonate of an alkali metal element, and enabling easy transition from the exposure step to the ammonia decomposition and hydrogen production steps.

[0074] For other configurations and effects, the descriptions in the above-mentioned "(Ammonia decomposition catalyst)" and the below-mentioned "(Ammonia decomposition method)", "(Hydrogen production method)", and "(Hydrogen production apparatus)" can be referred to as needed.

[0075] (Method for decomposing ammonia) The method for decomposing ammonia according to this embodiment (hereinafter sometimes abbreviated as "the present ammonia decomposition method") is a method for decomposing ammonia by bringing ammonia into contact with the ammonia decomposition catalyst according to this embodiment or the ammonia decomposition catalyst obtained by the method for producing an ammonia decomposition catalyst according to this embodiment.

[0076] Since the present ammonia decomposition method uses the above-mentioned ammonia decomposition catalyst, it is possible to decompose ammonia without using a noble metal.

[0077] In this ammonia decomposition method, the reaction temperature during ammonia decomposition can be preferably 300°C or higher, more preferably 350°C or higher, and even more preferably 400°C or higher, from the viewpoint of improving the ammonia decomposition rate. The reaction temperature during ammonia decomposition can be preferably 700°C or lower, more preferably 600°C or lower, and even more preferably 500°C or lower, from the viewpoint of suppressing excessive external heat input. Furthermore, the reaction pressure during ammonia decomposition can be preferably atmospheric pressure or higher, more preferably 0.1 MPa(G) or higher, and even more preferably 0.3 MPa(G) or higher, from the viewpoint of simplifying equipment and operations, and from the viewpoint of preventing ammonia aggregation and liquefaction when ammonia is contained at a high concentration, from the viewpoint of simplifying equipment and operations, and from the viewpoint of preventing ammonia aggregation and liquefaction when ammonia is contained at a high concentration, and the reaction pressure during ammonia decomposition can be preferably 1.0 MPa(G) or lower, more preferably 0.8 MPa(G) or lower.

[0078] Although the ammonia decomposition catalyst described above has ammonia decomposition activity, in order to ensure ammonia decomposition, the ammonia decomposition catalyst can be pretreated by hydrogen reduction or the like before use in the present ammonia decomposition method. The hydrogen reduction treatment is as described above.

[0079] For other configurations and effects, the descriptions in the above-mentioned "(Ammonia decomposition catalyst)" and "(Method for producing an ammonia decomposition catalyst)" and the below-mentioned "(Hydrogen production method)" and "(Hydrogen production apparatus)" can be referred to as needed.

[0080] (Hydrogen production method) The hydrogen production method of this embodiment (hereinafter sometimes abbreviated as "this hydrogen production method") is a production method in which ammonia is brought into contact with the ammonia decomposition catalyst of this embodiment or the ammonia decomposition catalyst obtained by the method for producing an ammonia decomposition catalyst of this embodiment to decompose the ammonia and produce hydrogen.

[0081] Since the present hydrogen production method uses the above-mentioned ammonia decomposition catalyst, it is possible to decompose ammonia and produce hydrogen without using any noble metals.

[0082] In this hydrogen production method, the reaction temperature during ammonia decomposition can be preferably 300°C or higher, more preferably 350°C or higher, and even more preferably 400°C or higher, from the viewpoint of improving the ammonia decomposition rate. The reaction temperature during ammonia decomposition can be preferably 700°C or lower, more preferably 600°C or lower, and even more preferably 500°C or lower, from the viewpoint of suppressing excessive external heat input. Furthermore, the reaction pressure during ammonia decomposition can be preferably atmospheric pressure or higher, more preferably 0.1 MPa(G) or higher, and even more preferably 0.3 MPa(G) or higher, from the viewpoint of simplifying equipment and operations, and from the viewpoint of preventing ammonia aggregation and liquefaction when ammonia is contained at a high concentration. The reaction pressure during ammonia decomposition can be preferably 1.0 MPa(G) or lower, more preferably 0.8 MPa(G) or lower, from the viewpoint of simplifying equipment and operations, and from the viewpoint of preventing ammonia aggregation and liquefaction when ammonia is contained at a high concentration.

[0083] Although the ammonia decomposition catalyst has ammonia decomposition activity, in order to ensure the generation of hydrogen by ammonia decomposition, the ammonia decomposition catalyst can be pretreated by hydrogen reduction or the like before use in the present hydrogen production method. The hydrogen reduction treatment is as described above.

[0084] For other configurations and effects, the descriptions in the above-mentioned "(Ammonia decomposition catalyst)", "(Method for producing ammonia decomposition catalyst)", "(Method for decomposing ammonia)", and the below-mentioned "(Hydrogen production apparatus)" can be referred to as needed.

[0085] (Hydrogen production equipment) The hydrogen production apparatus of this embodiment (hereinafter sometimes abbreviated as "the present hydrogen production apparatus") is an apparatus that produces hydrogen using the ammonia decomposition catalyst of this embodiment or an ammonia decomposition catalyst obtained by the method for producing an ammonia decomposition catalyst of this embodiment.

[0086] Since the present hydrogen production device uses the above-mentioned ammonia decomposition catalyst, it is possible to decompose ammonia and produce hydrogen without using any precious metals.

[0087] Specifically, the hydrogen production device can be configured, for example, to supply ammonia from the upstream side of a reaction section having an ammonia decomposition catalyst, and recover hydrogen-containing gas from the downstream side of the reaction section. Other than the ammonia decomposition catalyst, known configurations can be appropriately adopted for the configuration of the hydrogen production device.

[0088] For other configurations and effects, the descriptions in the above "(Ammonia decomposition catalyst)", "(Method for producing ammonia decomposition catalyst)", "(Method for decomposing ammonia)", and "(Method for producing hydrogen)" can be referred to as needed.

[0089] <Experimental Example> The ammonia decomposition catalyst and its production method, ammonia decomposition method, hydrogen production method, and hydrogen production device of the present disclosure will be described in more detail below using experimental examples.

[0090] 1. Catalyst Preparation In this experimental example, the following catalyst was prepared. A supporting 20 mass% Co particles 0.01 Mg 0.99 O y (A = Li, Na, K, Rb, Cs, Ca, Sr, Ba) 0.01 Mg 0.99 O y It may be written as Ba supported with 20% by mass of Co particles x Mg 1-x O y (where x = 0, 0.005, 0.01, 0.02, or 0.05) x Mg 1-x O y It may be written as When x=0, the support is MgO that is not doped with the alkali metal element A and is not a composite oxide, so the catalyst in this case, i.e., 20 mass% Co / MgO, is a comparative example (referred to as "Undoped" in Figs. 1 to 4 and 9 described later).

[0091] 20 mass% Co / A 0.01 Mg 0.99 O y , 20 mass% Co / Ba x Mg 1-x O yThe catalyst was prepared by sequential impregnation as follows. Specifically, MgO was added to an aqueous solution containing a water-soluble salt of a given alkaline metal element, stirred for 1 hour, and then evaporated to dryness under reduced pressure using an evaporator. The resulting powder was calcined in an air stream at 500°C for 5 hours to obtain the given composite oxide as a support. The water-soluble salts of the alkaline metal elements used were LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2, Sr(OH)2, and Ba(OH)2, respectively.

[0092] The Co precursor, cobalt(II) acetylacetonate dihydrate (Co(CH3COCHCOCH3)2·2H2O), was dissolved in 150 mL of tetrahydrofuran (THF) to achieve a Co loading of 20% by mass. The desired composite oxide was added to the solution containing the Co precursor, and the suspension was stirred overnight using a magnetic stirrer. The THF was then removed using an evaporator, and the suspension was dried overnight at 80°C. The resulting impregnated material was then heat-treated under an Ar flow at 500°C for 5 hours to remove the ligands. The resulting heat-treated material was then pelletized under pressure and sized to 250-500 μm.

[0093] Next, 0.1 g of the sized heat-treated product was packed into a quartz reaction tube with an outer diameter of 10 mm and an inner diameter of 7 mm to form a catalyst layer, and the front and rear of this catalyst layer were fixed with quartz wool. This reaction tube was installed in a fixed-bed flow reactor. 60 mL min -1 The catalyst layer was subjected to hydrogen reduction treatment by passing H2 through the catalyst layer, raising the temperature of the catalyst layer at 10°C / min, and holding the catalyst layer at a predetermined reduction temperature (500°C or 700°C) for 1 hour.

[0094] From the above, 20 mass% Co / A by reduction at 700℃ or 500℃ 0.01 Mg 0.99 O y (A = Li, Na, K, Rb, Cs, Ca, Sr, or Ba), 20 mass% Co / Ba by reduction at 700℃ x Mg 1-x O y(x = 0, 0.005, 0.01, 0.02, or 0.05), where y represents the number of oxygen atoms required for each composite oxide to maintain electrical neutrality.

[0095] 2. Evaluation of catalyst ammonia decomposition activity After the hydrogen reduction treatment of the catalyst layer, the catalyst layer was cooled to 300°C while He was supplied and purged. Then, NH3 (15 mL / min) was supplied as a reaction gas at a space velocity SV (9000 mL g cat -1 h -1 ) The reaction temperature was set to 300°C to 700°C. The gas concentration at the catalyst layer outlet was analyzed by gas chromatography to determine the ammonia conversion (NH3 conversion). In preparing the catalyst and evaluating the ammonia decomposition activity, all gases supplied to the reaction tube were supplied so that the pressure of the catalyst layer atmosphere was 1 atm. The results are shown in Figures 1 to 6.

[0096] As shown in Figures 1 and 2, 20 mass% Co / A composites were prepared by doping various alkali metal elements A onto an MgO support. 0.01 Mg 0.99 O y All of the catalysts (reduced at 700°C) were able to demonstrate ammonia decomposition activity without the use of a noble metal such as Ru.

[0097] 20 mass% Co / A doped with alkali metal element A on MgO support 0.01 Mg 0.99 O yThe catalysts (reduced at 700°C) showed improved ammonia decomposition activity compared to a catalyst (undoped) in which the MgO support was not doped with alkali metal element A, except for those in which Li was used as alkali metal element A. A significant improvement in ammonia decomposition activity was observed when Ba, Sr, K, or Ca was used as alkali metal element A, and a particularly significant improvement in ammonia decomposition activity was observed when Ba was used. Note that the reason why no improvement in ammonia decomposition activity was observed when Li was used as alkali metal element A is thought to be because Li dissolved in the crystal structure of MgO, reducing the contact rate with Co particles.

[0098] As shown in Figures 3 and 4, 20 mass% Co / A films were prepared by doping various alkali metal elements A onto an MgO support. 0.01 Mg 0.99 O y As with the above, all of the catalysts (reduced at 500°C) were able to demonstrate ammonia decomposition activity without the use of a noble metal such as Ru.

[0099] 20 mass% Co / A doped with alkali metal element A on MgO support 0.01 Mg 0.99 O y The catalysts (reduced at 700°C) showed improved ammonia decomposition activity compared to an undoped catalyst (in which the MgO support was not doped with alkali metal element A), except for those using Li or Cs as alkali metal element A. When Ba was used as alkali metal element A, a significant improvement in ammonia decomposition activity was observed. The reason why no improvement in ammonia decomposition activity was observed when Li or Cs was used as alkali metal element A is thought to be that Li dissolved in the MgO crystal structure, reducing the contact rate with the Co particles, and that the low melting point of Cs oxide and hydroxide caused them to melt during the reduction process and segregate within the catalyst, reducing the contact rate with the Co particles.

[0100] As shown in Figures 2 and 3, except for the catalyst doped with Ba as the alkali metal element A, the catalysts reduced at 700°C showed improved ammonia decomposition activity compared to the catalyst reduced at 500°C. This is thought to be because the high-temperature reduction accelerates the decomposition of Ba, which existed as carbonate before the reduction, into hydroxides and oxides, thereby enhancing the electron-donating effect of Ba and facilitating the N-N bond formation, which is the rate-determining step. Furthermore, these results suggest that the Ba-doped catalysts suppress the decline in ammonia decomposition activity and achieve high ammonia decomposition activity, even at low reduction temperatures. This is thought to be because the Ba carbonate remaining on the catalyst during low-temperature reduction is decomposed into oxides by reaction with ammonia, resulting in an enhanced electron-donating effect of Ba, which accelerates the rate-determining step of ammonia decomposition.

[0101] As shown in Figures 5 and 6, 20 mass% Co / A 0.01 Mg 0.99 O y In the catalyst (reduced at 700°C), the doping amount of Ba, an alkaline metal element, showed the highest ammonia decomposition activity when x in the chemical composition was 0.01, and thereafter, as the value of x increased, the ammonia decomposition activity tended to decrease. From this result, it can be said that the value of x in the chemical composition should be greater than 0, and at most 0.1, taking into account the ammonia decomposition activity and the type of alkaline metal element A, and is sufficiently sufficient.

[0102] 3. Investigation of catalyst microstructure 20 mass% Co / Ba 0.01 Mg 0.99 O y Catalyst (reduced at 700°C), 20 mass% Co / Sr 0.01 Mg 0.99 O yThe catalysts (reduced at 700°C) were subjected to high-angle dark-field scanning transmission electron microscopy (HAADF-STEM) and energy-dispersive X-ray fluorescence (EDX) analysis. Specifically, HAADF-STEM images and EDX analysis were performed using a wide-voltage, ultra-high-sensitivity atomic-resolution electron microscope (JEOL, "JEM-ARM200CF") operating at 120 kV. The reduced samples were ground at room temperature and then dispersed in ethanol. The dispersion was then dropped onto a carbon-coated copper grid (TEM grid) and vacuum-dried at room temperature for 24 hours. The results are shown in Figures 7 and 8.

[0103] 20 mass% Co / Ba 0.01 Mg 0.99 O y If MgO and BaO form a solid solution in the catalyst (reduced at 700°C), Mg and Ba should appear in the same location on the elemental map. However, as shown in Figure 7, Mg and Ba have biases for each element. This result indicates that MgO and BaO do not form a solid solution.

[0104] In addition, 20 mass% Co / Sr 0.01 Mg 0.99 O y Even in the catalyst (reduced at 700°C), 20 mass% Co / Ba 0.01 Mg 0.99 O y As with the catalyst (reduced at 700°C), it is clear that MgO and SrO do not form a solid solution.

[0105] These results show that the inclusion of an oxide of an alkali metal element that is not dissolved in MgO in the composite oxide of the catalyst is advantageous for improving ammonia decomposition activity. This is thought to be because the oxide of an alkali metal element that is not dissolved in MgO is present outside the MgO, increasing the amount of the oxide of the alkali metal element in contact with the non-precious metal particles, making it easier for the electron-donating effect to be exerted.

[0106] 4. Evaluation of basicity of catalysts by CO2-TPD 20 mass% Co / A 0.01 Mg 0.99 O y The CO2-TPD spectra were measured by temperature-programmed desorption using CO2 gas as a probe molecule for the catalyst (A = Ba, Sr, K, Li, reduced at 700°C), 20 mass% Co / MgO (reduced at 700°C), and MgO. Specifically, 100 mg of catalyst was reduced by holding it at 700°C for 1 hour under a 50 mL / min H2 flow, followed by holding it under a 50 mL / min He flow for 1 hour to remove adsorbed hydrogen species remaining on the catalyst surface. Next, the catalyst was allowed to cool to 50°C while He was still flowing, and then a CO2 / He mixed gas containing 4.97 vol% CO2 was flowed at 50°C for 30 minutes to adsorb CO2 onto the catalyst. The flow gas was then switched to He to remove any remaining CO2 in the system, and the catalyst was heated at a heating rate of 10°C min under He flow. -1 The CO2 contained in the eluted He was detected by mass spectrometry while heating at 1000 K. The CO2-TPD spectrum obtained is shown in Figure 9. 0.01 Mg 0.99 O y The catalysts are simply represented by the alkali metal element A used. 20 mass% Co / MgO is represented as "Undoped." MgO is represented as "Without Co."

[0107] In the CO2-TPD spectrum shown in Figure 9, it can be seen that the higher the ammonia decomposition activity of the catalyst, the higher the maximum value of the CO2 desorption peak shifts to the higher temperature side. In other words, the higher the ammonia decomposition activity of the catalyst, the stronger its basicity.

[0108] More specifically, in the CO2-TPD spectrum shown in Figure 9, the catalyst consisting of only MgO and the catalyst in which Co particles are supported on MgO have a maximum CO2 desorption peak near 180°C, and catalysts whose CO2 desorption peak has a maximum at a higher temperature exhibit stronger basicity. From these results, it can be said that catalysts with such a strong basicity that the CO2 desorption peak has a maximum at 200°C or higher, preferably 230°C or higher, in the CO2-TPD spectrum exhibit high ammonia decomposition activity.

[0109] 5. Change in catalyst ammonia decomposition activity over time 20 mass% Co / Ba 0.01 Mg 0.99 O y During the preparation of the catalyst (500°C reduction), the catalyst layer was subjected to hydrogen reduction treatment under the condition that it was kept at a reduction temperature of 500°C for 1 hour, and then kept at 500°C under a 100% ammonia supply, and the change in the ammonia decomposition activity of the catalyst over time was measured. This experiment simulated the case where an ammonia exposure step was carried out after the reduction step. The results are shown in Figure 10. In Figure 10, the notation "700°C red" indicates the case where an ammonia exposure step was not carried out after the reduction step. 0.01 Mg 0.99 O y (700℃ reduction).

[0110] As shown in Figure 10, the ammonia conversion rate gradually increases immediately after the start of ammonia supply, and after 400 minutes, an ammonia conversion rate equivalent to that obtained when hydrogen reduction treatment was performed at 700°C was obtained. This result shows that by performing the exposure step after the reduction step, the temperature required to activate the ammonia decomposition catalyst can be kept low. This is thought to be because the decomposition of remaining carbonates of alkali metal elements progresses, resulting in an increased electron-donating effect of the alkali metal elements and promoting the formation of N-N bonds, which is the rate-determining step in ammonia decomposition.

[0111] The present disclosure is not limited to the above embodiments and above experimental examples, and various modifications are possible without departing from the gist thereof. Further, each configuration shown in the above embodiments and above experimental examples can be arbitrarily combined. Further, each of the claims described in the claims at the time of filing can be arbitrarily combined with each other.

[0112] The features of the present disclosure are shown as follows. Item 1. Comprising a composite oxide and non-noble metal particles supported on the composite oxide, The composite oxide is A x Mg 1-x O y (wherein A is an alkaline metal element selected from the group consisting of alkaline earth metal elements excluding alkaline metal elements and Mg, x is 0 < x ≤ 0.1, and y is the number of oxygen atoms necessary for the composite oxide to maintain electrical neutrality), The non-noble metal constituting the non-noble metal particles is Co, Ni, Fe, or an alloy thereof, An ammonia decomposition catalyst. Item 2. The alkaline metal element is at least one selected from the group consisting of Ba, K, Sr, and Ca, The ammonia decomposition catalyst according to Item 1. Item 3. The composite oxide contains an oxide of the alkaline metal element not dissolved in MgO, The ammonia decomposition catalyst according to Item 1 or Item 2. Item 4. Containing a carbonate of the alkaline metal element and / or a hydroxide of the alkaline metal element, The content of the oxide of the alkaline metal element constituting a part of the composite oxide is greater than the total content of the carbonate of the alkaline metal element and the hydroxide of the alkaline metal element, The ammonia decomposition catalyst according to any one of Items 1 to 3. Item 5. the content of the carbonate of the alkali metal element is less than the content of the hydroxide of the alkali metal element; Item 5. The ammonia decomposition catalyst according to item 4. Section 6. No carbonate of the alkali metal element is detected; Item 4. The ammonia decomposition catalyst according to any one of items 1 to 3. Section 7. the alkali metal element is Ba, In the spectrum measured by infrared absorption spectroscopy, the absorbance of the peak assigned to BaCO3 and the absorbance at 2000 cm -1 The ratio of the absorbance of Item 6. The ammonia decomposition catalyst according to any one of items 1 to 5. Section 8. In the CO2-TPD spectrum measured by the temperature-programmed desorption method using CO2 gas as a probe molecule, the maximum value of the CO2 desorption peak exists above 200°C. Item 8. The ammonia decomposition catalyst according to any one of items 1 to 7. Section 9. A x Mg 1-x O y (wherein A is an alkali metal element which is at least one element selected from the group consisting of alkali metal elements and alkaline earth metal elements excluding Mg, and x is 0 <x≦0.1、前記yは前記複合酸化物が電気的に中性を保つのに必要な酸素原子の数)を準備する準備工程と、a heat treatment step of impregnating the composite oxide with a non-precious metal precursor containing at least one non-precious metal selected from the group consisting of Co, Ni, and Fe to obtain an impregnated body, and heat treating the impregnated body in an inert gas atmosphere to obtain a heat-treated product; a reduction step of subjecting the heat-treated product to a hydrogen reduction treatment in a reducing atmosphere containing hydrogen at a reduction temperature of 300°C or higher and 800°C or lower; A method for producing an ammonia decomposition catalyst. Section 10. The reduction temperature is 300°C or higher and 500°C or lower, The method further includes an ammonia exposure step of exposing the catalyst obtained after hydrogen reduction to a gas containing ammonia at a temperature of 350°C or higher and 550°C or lower. Item 10. A method for producing an ammonia decomposition catalyst according to item 9. Section 11. Item 11. A method for decomposing ammonia, comprising contacting ammonia with the ammonia decomposition catalyst according to any one of items 1 to 8 or the ammonia decomposition catalyst obtained by the method for producing an ammonia decomposition catalyst according to item 9 or 10, to decompose the ammonia. Section 12. Item 11. A method for producing hydrogen, comprising contacting ammonia with the ammonia decomposition catalyst according to any one of Items 1 to 8 or the ammonia decomposition catalyst obtained by the method for producing an ammonia decomposition catalyst according to Item 9 or 10 to decompose the ammonia and produce hydrogen. Section 13. Item 9. A hydrogen production device using the ammonia decomposition catalyst according to any one of items 1 to 8.

Claims

1. A composite oxide and non-precious metal particles supported on the composite oxide, The composite oxide is A ｘ Mg １－ｘ O ｙ (wherein A is an alkali metal element which is at least one element selected from the group consisting of alkali metal elements and alkaline earth metal elements excluding Mg, x is 0<x≦0.1, and y is the number of oxygen atoms necessary for the composite oxide to maintain electrical neutrality), The non-noble metal constituting the non-noble metal particles is Co, Ni, Fe, or an alloy thereof. Ammonia decomposition catalyst.

2. The alkali metal element is at least one selected from the group consisting of Ba, K, Sr, and Ca. The ammonia decomposition catalyst according to claim 1.

3. the composite oxide contains an oxide of the alkali metal element that is not solid-solved in MgO; The ammonia decomposition catalyst according to claim 1.

4. containing a carbonate of the alkali metal element and / or a hydroxide of the alkali metal element, the content of the oxide of the alkali metal element that constitutes a part of the composite oxide is greater than the total content of the carbonate of the alkali metal element and the hydroxide of the alkali metal element; The ammonia decomposition catalyst according to claim 1.

5. the content of the carbonate of the alkali metal element is less than the content of the hydroxide of the alkali metal element; The ammonia decomposition catalyst according to claim 4.

6. No carbonate of the alkali metal element is detected; The ammonia decomposition catalyst according to claim 1.

7. the alkali metal element is Ba, In the spectrum measured by infrared absorption spectroscopy, BaCO ３ and the absorbance of the peak assigned to 2000 cm －１ the ratio of the absorbance to the absorbance is less than 0.01; The ammonia decomposition catalyst according to claim 1.

8. CO as a probe molecule ２ CO measured by thermal desorption spectroscopy using gas ２ - In the TPD spectrum, CO ２ The maximum value of the desorption peak is at 200 ° C or higher. The ammonia decomposition catalyst according to claim 1.

9. A ｘ Mg １－ｘ O ｙ a preparation step of preparing a composite oxide represented by the following composition (wherein A is an alkali metal element which is at least one element selected from the group consisting of alkali metal elements and alkaline earth metal elements excluding Mg, x is 0<x≦0.1, and y is the number of oxygen atoms necessary for the composite oxide to maintain electrical neutrality); a heat treatment step of impregnating the composite oxide with a non-precious metal precursor containing at least one non-precious metal selected from the group consisting of Co, Ni, and Fe, and heat treating the resulting impregnated body in an inert gas atmosphere to obtain a heat-treated product; a reduction step of subjecting the heat-treated product to a hydrogen reduction treatment in a reducing atmosphere containing hydrogen at a reduction temperature of 300°C or higher and 800°C or lower; A method for producing an ammonia decomposition catalyst.

10. The reduction temperature is 300°C or higher and 500°C or lower, The catalyst obtained after the hydrogen reduction step may further include an ammonia exposure step of exposing the catalyst to an ammonia-containing gas at a temperature of 350°C or higher and 550°C or lower. The method for producing the ammonia decomposition catalyst according to claim 9.

11. A method for decomposing ammonia, comprising contacting ammonia with the ammonia decomposition catalyst according to claim 1 or the ammonia decomposition catalyst obtained by the method for producing an ammonia decomposition catalyst according to claim 9 to decompose the ammonia.

12. A method for producing hydrogen, comprising contacting ammonia with the ammonia decomposition catalyst according to claim 1 or the ammonia decomposition catalyst obtained by the method for producing an ammonia decomposition catalyst according to claim 9 to decompose the ammonia and produce hydrogen.

13. A hydrogen production device using the ammonia decomposition catalyst according to claim 1.

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