Composite material, method for producing same, and method for producing ammonia

Abstract

This composite material has a first structure or a second structure including a carbon material, particles containing iron group elements, and compounds containing alkali metal elements (alkali metal and / or alkaline earth metal). In the first structure, a large number of particles containing iron group elements and compounds containing alkali metal elements are dispersed in the carbon skeleton of the carbon material, the particles containing iron group elements contain iron group metal particles having a passivated particle surface, and the compounds containing alkali metal elements are present at least as oxides containing alkali metal elements and / or carbonates containing alkali metal elements. In the second structure, a large number of particles containing iron group elements are dispersed in the carbon skeleton of the carbon material, a large number of compounds containing alkali metal elements are collectively present on the surface of the particles containing iron group elements, the particles containing iron group elements contain iron group metal particles, and the compounds containing alkali metal elements are present at least as oxides containing alkali metal elements.

Description

Composite material, method for producing the same, and method for producing ammonia CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Japanese Application No. 2024-102027, filed on June 25, 2024, the contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a composite material and a method for producing the same, as well as a method for producing ammonia.

[0003] Conventionally, composite materials having a plurality of metal elements on the surface of an oxide have been known.

[0004] For example, Non-Patent Document 1 discloses a composite material having MgO, Co particles supported on the surface of the MgO, and BaO covering the surface of the Co particles. ２ and calcined at 700°C, then impregnated with Co(II) acetylacetonate hydrate into MgO, heated to 500°C, and then subjected to hydrogen reduction at 700°C for 1 hour or at 500°C for 72 hours. This resulted in the reduction of Co oxide on the MgO surface to metallic Co and BaCO ３ Ba(OH) ２ Hydrogenolysis into Co particles and Ba(OH) ２ The document also describes that the composite material activated by hydrogen reduction under the above conditions is used as a catalyst material for ammonia synthesis to produce ammonia.

[0005] ACS Catalysis, (US), 2021, Vol. 11, No. 21, p. 13050-13061.

[0006] However, conventional composite materials have room for improvement in the following respect: Conventional composite materials require reduction treatment at an ultra-high temperature of 700°C for a short time, such as 1 hour, or at a high temperature of 500°C for a long time, such as 72 hours, for activation.

[0007] The present disclosure has been made in view of the above-mentioned problems, and aims to provide a composite material that exhibits activity through reduction treatment at a low temperature and in a short time, as compared with conventional composite materials, and a method for producing ammonia using the same.

[0008] One aspect of the present disclosure is a composite material having a first structure or a second structure including a carbon material, particles containing an iron group element, and a compound containing an alkali metal element, which is at least one element selected from the group consisting of alkali metal elements and alkaline earth metal elements; the first structure is a structure in which a large number of particles containing the iron group element and compounds containing the alkali metal element are dispersed in a carbon skeleton constituting the carbon material, and the particles containing the iron group element include at least iron group metal particles having passivated particle surfaces, and the compounds containing the alkali metal element exist at least as oxides containing the alkali metal element and / or carbonates containing the alkali metal element; and the second structure is a structure in which a large number of particles containing the iron group element are dispersed in a carbon skeleton constituting the carbon material, and a large number of compounds containing the alkali metal element are present on the surfaces of the particles containing the iron group element, and the particles containing the iron group element include at least iron group metal particles, and the compounds containing the alkali metal element exist at least as oxides containing the alkali metal element.

[0009] Another aspect of the present disclosure resides in a method for producing a composite material, the method comprising: a precursor preparation step of preparing a precursor composed of an organometallic complex containing an iron group element, an alkali metal element which is at least one element selected from the group consisting of alkali metal elements and alkaline earth metal elements, and an organic compound; a pyrolysis step of thermally decomposing the organic compound in the precursor under an inert gas atmosphere; and a passivation step of passivating the particle surfaces of at least iron group metal particles contained in the obtained pyrolysate.

[0010] Yet another aspect of the present disclosure is a method for producing a composite material, comprising: subjecting the composite material having the first structure to a reduction treatment, thereby obtaining the composite material having the second structure.

[0011] Yet another aspect of the present disclosure is a method for producing ammonia, comprising the steps of: reducing the composite material having the first structure; and then contacting the composite material with hydrogen and nitrogen; or contacting the composite material having the second structure with hydrogen and nitrogen.

[0012] The composite material has the above-described configuration. Therefore, when the composite material has the first structure, it can be activated by a reduction treatment before use at a reduction temperature of less than 500°C for a reduction time of 24 hours or less. Furthermore, when the composite material has the second structure, it can be activated by a reduction treatment during production at a reduction temperature of less than 500°C for a reduction time of 24 hours or less. Therefore, the composite material can exhibit activity by a reduction treatment at a low temperature and in a short time, compared to conventional composite materials made of an MgO support supporting Co particles whose surfaces are covered with BaO.

[0013] The method for producing the composite material has the above-described configuration, and therefore, the method for producing the composite material can provide the composite material that exhibits activity through reduction treatment at a lower temperature and in a shorter time than conventional composite materials.

[0014] The method for producing ammonia has the above-described configuration. Therefore, according to the method for producing ammonia, ammonia can be produced with a high ammonia yield even under mild conditions such as temperatures below 500°C and pressure below 10 MPa.

[0015] FIG. 1 shows the NH ３ Yield (NH ３ yield (hereinafter omitted) (%) and NH ３ Synthesis rate (NH ３ synthesis rate (omitted below) (mmol g ｃａｔ －１ h －１ 2 is a graph showing the temperature dependence of NH３ Yield (%) and NH ３ Synthesis rate (mmolg ｃａｔ －１ h －１ 3 is a graph showing the temperature dependence of NH 3 obtained in Experimental Example 1 using Fe / C composite materials containing different types of alkali metal elements and alkaline earth metal elements (after reduction treatment, the molar amount of citric acid is three times that of citric acid). ３ Yield (%) and NH ３ Synthesis rate (mmolg ｃａｔ －１ h －１ 4 is a graph showing the temperature dependence of NH ３ Yield (%) and NH ３ Synthesis rate (mmolg ｃａｔ －１ h －１ 5 is a graph showing the temperature dependence of (Ba / Co) at 350° C. obtained in Experimental Example 1. ０．３ / C composite material ３ Yield (%) and NH ３ Synthesis rate (mmolg ｃａｔ －１ h －１ 6 is a graph showing the pressure dependence of (Ba / Co) under ammonia synthesis conditions of 350°C and 1.0 MPa obtained in Experimental Example 1. ０．３ / C composite material ３ Yield (%) and NH ３ Synthesis rate (mmolg ｃａｔ －１ h －１ 7 is a graph showing the change over time of the (Ba / Co) prepared by the sol-gel method obtained in Experimental Example 1. ０．３ Ba and Co were impregnated onto activated carbon at the same molar ratio (Ba / Co) under different treatment conditions. ０．３ / AC composite material NH ３ Yield (%) and NH ３ Synthesis rate (mmolg ｃａｔ －１ h －１8 is a graph showing the temperature dependence of (Ba / Co) before reduction treatment obtained in Experimental Example 1. ０．３ 9 shows the results of HAADF-STEM images (high-angle dark-field scanning transmission electron microscope images) and EDX analysis (energy dispersive X-ray spectroscopy analysis) of a (Ba / Co) / C composite material, where (a) is an HAADF-STEM image, (b) is an HAADF-STEM image taken at a higher magnification than (a), (c) is an EDX map obtained by superimposing the EDX maps of (d), (e), and (f), (d) is an EDX map of Co K, (e) is an EDX map of C K, (f) is an EDX map of Ba L, and (g) is an EDX map of O K. FIG. 9 shows the results of HAADF-STEM images (high-angle dark-field scanning transmission electron microscope images) and EDX analysis (energy dispersive X-ray spectroscopy analysis) of a (Ba / Co) / C composite material after reduction treatment, obtained in Experimental Example 1. ０．３ 10 shows HAADF-STEM images and EDX analysis results of the (Ba / Co) / C composite material, where (a) is an HAADF-STEM image, (b) to (f) are EDX maps corresponding to (a), (b) is an EDX map obtained by superimposing the EDX maps of (c), (d), and (e), (d) is an EDX map of Co K, (d) is an EDX map of Ba L, (e) is an EDX map of C K, (f) is an EDX map of O K, and (g) is an atomic resolution HAADF-STEM image of Co particles. ０．３ (a) is a bright-field STEM image of the Ba / Co composite material before reduction treatment and shows the distribution of Co particles. ０．３ (b) is a bright-field STEM image of the Ba / Co composite material; (b) is the Co particle distribution corresponding to (a); (c) and (d) are the (Ba / Co) composite material after reduction treatment. ０．３ 11 shows a bright-field STEM image of the Ba / Co composite material obtained in Experimental Example 1, and (e) shows the Co particle distribution corresponding to (c) and (d). ０．３ The results of an investigation into the chemical states of Co and Ba in the / C composite materials, where (a) shows the normalized Co K-edge XANES (X-ray absorption near edge structure) spectra of composite materials with and without passivation, reduction, use, and air exposure, and a reference Co-based material, and (b) shows the normalized Ba L spectra of each composite material shown in (a) and a reference Ba-based material. ３12 shows the pore size distributions obtained from the adsorption branch of the adsorption / desorption isotherms of the Co / C composite materials of different alkali metal elements and alkaline earth metal elements, as a function of the BET specific surface area (S ＢＥＴ ), the total pore volume (V) calculated by the BJH method ｐ ) and average pore diameter (d ａｖｅ 13 shows the TPR patterns (H ２ by CH ４ 14 shows the signal of the product (m / z=16) obtained in Experimental Example 1, which has different molar ratios of Ba to Co (Ba / Co). ｘ / C (x = 0.03, 0.3, 0.5) composite materials ３ Yield (%) and NH ３ Synthesis rate (mmolg ｃａｔ －１ h －１ 15 is a graph showing the temperature dependence of (Ba / Co) obtained in Experimental Example 1 at different reduction treatment temperatures. ０．３ / C composite material ３ Yield (%) and NH ３ Synthesis rate (mmolg ｃａｔ －１ h －１ 16 is a graph showing the temperature dependence of (Ba / Co) obtained in Experimental Example 1 with different reduction treatment times. ０．３ / C composite material ３ Yield (%) and NH ３ Synthesis rate (mmolg ｃａｔ －１ h －１ 17 is a graph showing the temperature dependence of the (Cs / Fe) alloy obtained in Experimental Example 2, which is made of pellets or powder and is produced by preparing the precursor in the precursor preparation step as pellets or powder. ０．３ / C<2> Composite Material NH ３ Yield (%) and NH ３ Synthesis rate (mmolg ｃａｔ－１ h －１ 18 is a graph showing the temperature dependence of the (Ba / Co) alloy obtained in Experimental Example 2, which is made of pellets or powder and is produced by preparing the precursor in the precursor preparation step as pellets or powder. ０．３ / C composite material ３ Yield (%) and NH ３ Synthesis rate (mmolg ｃａｔ －１ h －１ ) is a graph showing the temperature dependence of

[0016] The composite material and its manufacturing method, as well as the method for manufacturing ammonia according to the present disclosure, are described in detail below using embodiments. Note that the composite material and its manufacturing method, as well as the method for manufacturing ammonia according to the present disclosure, are not limited by the examples in the following embodiments. Furthermore, the lower and upper limits of the numerical ranges shown below can be arbitrarily combined, including the values ​​described in the experimental examples (omitted below).

[0017] (Composite Material) The composite material of the present embodiment (hereinafter sometimes abbreviated as "the present composite material") has a first structure and a second structure each including a carbon material, particles containing an iron-group element, and a compound containing an alkali metal element, which is at least one element selected from the group consisting of alkali metal elements and alkaline earth metal elements.

[0018] In this composite material, the carbon material is the portion that forms the main body of the composite material. The carbon material has a carbon skeleton formed by bonding multiple carbon atoms. Specifically, the carbon skeleton can be formed by three-dimensionally bonding multiple carbon atoms, and may be formed only from carbon atoms, or may have hydrogen, an iron group element, an alkali metal element, or the like bonded to it. The carbon material can function as a carrier (support) that supports particles containing an iron group element and a compound containing an alkali metal element. In other words, the composite material can also be said to have a carbon material as a support, and particles containing an iron group element and a compound containing an alkali metal element supported on the carbon material.

[0019] In this composite material, the first structure is a structure in which a large number of particles containing an iron group element and a compound containing an alkali metal element are dispersed in the carbon skeleton constituting the carbon material. The first structure can also be said to be a structure in which the particles containing an iron group element and the compound containing an alkali metal element are uniformly distributed in the carbon skeleton constituting the carbon material.

[0020] In the first structure, the particles containing an iron group element and the compound containing an alkali metal element may be present inside or outside the carbon skeleton (inside the carbon skeleton or outside (on the surface) of the carbon skeleton, hereinafter omitted), or may be present only inside the carbon skeleton, or may be present only outside the carbon skeleton. Specifically, for example, in the first structure, the particles containing an iron group element may be dispersed in large numbers inside and outside the carbon skeleton, and the compounds containing an alkali metal element may be dispersed in large numbers at least within the carbon skeleton. Also, in the first structure, the particles containing an iron group element may be dispersed in large numbers inside and outside the carbon skeleton, and the compounds containing an alkali metal element may be dispersed in large numbers at least outside the carbon skeleton.

[0021] When the present composite material has the first structure, the particles containing an iron group element include at least iron group metal particles whose particle surfaces are passivated. The iron group metal particles whose particle surfaces are passivated are iron group metal particles having a passivation film formed on the particle surfaces of the iron group metal particles, the passivation film being made of an oxide and / or carbonate of the iron group metal that constitutes the iron group metal particles. When the present composite material has the first structure, the particles containing an iron group element may also include iron group metal particles whose particle surfaces are not passivated (iron group metal particles in a metallic state), iron group oxide particles, etc., so long as they include at least iron group metal particles whose particle surfaces are passivated.

[0022] Furthermore, when the present composite material has the first structure, the compound containing an alkali metal element can exist as an oxide containing an alkali metal element and / or a carbonate containing an alkali metal element.

[0023] In this composite material, the second structure is a structure in which a large number of particles containing an iron group element are dispersed in the carbon skeleton constituting the carbon material, and a large number of compounds containing an alkali metal element are concentrated on the surfaces of the particles containing the iron group element. The second structure can also be described as a structure in which the particles containing an iron group element are uniformly distributed in the carbon skeleton constituting the carbon material, and the compounds containing an alkali metal element are more distributed on the surfaces of the particles containing the iron group element than around the particles containing the iron group element.

[0024] In the second structure, the particles containing the iron group element may be present inside or outside the carbon skeleton, or may be present only inside the carbon skeleton, or may be present only outside the carbon skeleton. Furthermore, the compound containing the alkali metal element may be present around the particles containing the iron group element, as long as it is present in large numbers on the surface of the particles containing the iron group element. In addition, in the second structure, a portion of the alkali metal element may be present in a metallic state.

[0025] When the composite material has the second structure, the particles containing an iron group element include at least iron group metal particles. In this case, the iron group metal particles are iron group metal particles whose particle surfaces are not passivated (iron group metal particles in a metallic state). When the composite material has the second structure, the particles containing an iron group element are preferably composed of iron group metal particles from the viewpoint of high activation, etc.

[0026] When the composite material has the second structure, the compound containing an alkali metal element can exist as an oxide containing an alkali metal element.

[0027] Specific examples of the iron-group metal particles include Co particles, Fe particles, Ni particles, Co alloy particles, Fe alloy particles, and Ni alloy particles. Examples of Co alloy particles include particles made of an alloy of Co and Fe and / or Ni. Examples of Fe alloy particles include particles made of an alloy of Fe and Ni and / or Co. Examples of Ni alloy particles include particles made of an alloy of Ni and Co and / or Fe. From the viewpoints of ammonia production activity when the composite material is used as a catalyst material for ammonia synthesis (described in detail below) and simplification of the manufacturing process of the composite material, the iron-group metal particles are preferably Co particles, Fe particles, or Ni particles, more preferably Co particles or Fe particles, and even more preferably Co particles. Examples of iron-group metal particles having a passivated particle surface include the above-mentioned iron-group metal particles having a passivated particle surface. The iron group metal particles and the iron group metal particles having passivated particle surfaces can each be composed of one or more of the above-mentioned particles.

[0028] Specific examples of the iron group oxide particles include Co oxide particles, Fe oxide particles, Ni oxide particles, oxide particles containing Co and Fe and / or Ni, oxide particles containing Fe and Ni and / or Co, and oxide particles containing Ni and Co and / or Fe. From the viewpoints of ammonia production activity when the composite material is reduced and used as a catalyst, and simplification of the manufacturing process for the composite material, the iron group oxide particles are preferably Co oxide particles, Fe oxide particles, Ni oxide particles, etc. The iron group oxide particles can be composed of one or more of the above-mentioned particles.

[0029] The oxide containing an alkali metal element is an oxide containing at least one alkali metal element selected from the group consisting of alkali metal elements and alkaline earth metal elements. The alkali metal element is specifically at least one selected from the group consisting of Li, Na, K, Rb, and Cs. Preferably, from the viewpoint of suppressing carbon skeleton loss, at least one selected from the group consisting of Na, K, Rb, and Cs. More preferably, from the viewpoint of high activation, at least one selected from the group consisting of K and Cs. The alkaline earth metal element is specifically at least one selected from the group consisting of Be, Mg, Ca, Sr, Ba, and Ra. Preferably, from the viewpoint of suppressing carbon skeleton loss, at least one selected from the group consisting of Mg, Ca, Sr, and Ba. More preferably, from the viewpoint of high specific surface area, at least one selected from the group consisting of Ba and Sr. Even more preferably, from the viewpoint of high activation, Ba. The oxide containing an alkaline metal element may be, specifically, any of 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, and a composite oxide containing two or more different alkaline earth metals, and these may be used alone or in combination. Examples of the oxide containing an alkaline metal element include Li ２ O, Na ２ O.K. ２ O, Rb ２ O, Cs ２ Examples of the oxides include O, MgO, CaO, SrO, and BaO.

[0030] The carbonate containing an alkali metal element is a carbonate containing at least one alkali metal element selected from the group consisting of alkali metal elements and alkaline earth metal elements. The alkali metal element is, specifically, at least one selected from the group consisting of Li, Na, K, Rb, and Cs. Preferably, from the viewpoint of suppressing carbon skeleton loss, it is at least one selected from the group consisting of Na, K, Rb, and Cs. More preferably, from the viewpoint of high activation, it is at least one selected from the group consisting of K and Cs. The alkaline earth metal element is, specifically, at least one selected from the group consisting of Be, Mg, Ca, Sr, Ba, and Ra. Preferably, from the viewpoint of suppressing carbon skeleton loss, it is at least one selected from the group consisting of Mg, Ca, Sr, and Ba. More preferably, from the viewpoint of high specific surface area, it is at least one selected from the group consisting of Ba and Sr. Even more preferably, from the viewpoint of high activation, it is Ba. The carbonate containing an alkali metal element may be, specifically, any of alkali metal carbonates, alkaline earth metal carbonates, composite carbonates containing an alkali metal and an alkaline earth metal, composite carbonates containing two or more different alkali metals, and composite carbonates containing two or more different alkaline earth metals, and these may be used alone or in combination. Examples of carbonates containing an alkali metal element include Li ２ CO ３ , K. ２ CO ３ , Cs ２ CO ３ , BaCO ３ , CaCO ３ , SrCO ３ Examples include:

[0031] When the composite material has the second structure, it has been reduced during production and can therefore exhibit activity in that state. When the composite material has the first structure, it has not been reduced during production and can therefore exhibit activity by reduction before use. That is, in the composite material, the first structure represents the structure before reduction, and the second structure represents the structure after the first structure has been reduced. The composite material can be activated by reduction at a temperature below 500°C for a reduction time of 24 hours or less. Therefore, compared to the conventional composite material described above, which is made of an MgO support carrying Co particles whose surfaces are covered with BaO, the composite material can exhibit activity by reduction at a low temperature and in a short time.

[0032] This is presumably due to the following reasons. Specifically, when the above-mentioned conventional composite material (MgO support supporting Co particles whose surfaces are covered with BaO) is activated by reduction treatment, the strong interaction between the oxide of the support and the iron-group oxide particles present on the oxide surface requires high energy to reduce the iron-group oxide to iron-group metal. Therefore, the above-mentioned conventional composite material requires reduction treatment at an ultra-high temperature of 700°C for a short time, such as 1 hour, or at a high temperature of 500°C for a long time, such as 72 hours. In contrast, when the present composite material is activated by reduction treatment, the weak interaction between the carbon material and the iron-group element facilitates reduction to iron-group metal. Furthermore, in the present composite material, the oxide containing an alkali-based metal element is surrounded by carbon atoms (C) in the carbon skeleton constituting the carbon material, forming a stable structure, making it difficult to generate carbonates containing alkali-based metal elements. Therefore, even with the first structure, the proportion of alkali metal elements present as carbonates in the composite material can be kept low, and the energy required for hydrogenation and thermal decomposition of carbonates containing alkali metal elements into oxides containing alkali metal elements can be reduced, compared to conventional composite materials such as those described in Non-Patent Document 1. Therefore, the present composite material can exhibit activity through reduction treatment at a low temperature and in a short time, compared to the above-mentioned conventional composite materials.

[0033] This composite material can be used as a catalyst material (a catalyst material made from this composite material can also be called a composite catalyst) as it is when it has the second structure, or by subjecting it to a reduction treatment when it has the first structure, and can be suitably used at least as a catalyst material for ammonia synthesis. In this case, the following advantages are obtained.

[0034] Ammonia synthesis reaction (3H ２ +N ２ →2NH ３ ) is a reaction in which, at equilibrium, the lower the temperature and pressure, the higher the ammonia yield. If a catalytic material that exhibits a high ammonia yield under mild temperature and pressure conditions, such as <500°C and <10 MPa, could be developed, it could potentially lead to the development of a new ammonia synthesis process. However, the iron-based catalytic materials currently used in the industrial ammonia synthesis process (the Haber-Bosch process) require high temperatures and pressures to maximize their performance, and do not exhibit sufficient activity under such mild conditions. Therefore, there is a need for catalytic materials that exhibit high ammonia production activity under mild conditions, such as <500°C and <10 MPa.

[0035] The above-mentioned conventional MgO-supported catalyst, which supports Co particles whose surfaces are covered with BaO, can significantly increase its ammonia production activity by activating it at an ultra-high temperature for a short time of 1 hour at 700°C, or by activating it at a high temperature for a long time of 72 hours at 500°C. However, to further improve the efficiency of the entire process and enhance competitiveness, it is necessary to create a highly active catalyst material that can reduce the reduction temperature and time for activation.

[0036] This composite material exhibits high ammonia production activity even under mild conditions such as temperatures below 500°C and pressures below 10 MPa due to the simultaneous presence of numerous oxides containing alkali metal elements such as K and alkaline earth metal elements such as Ba, which function as promoters, on the surfaces of iron-group metal particles dispersed in the carbon skeleton of the carbon material. Furthermore, the use of a carbon material in this composite material facilitates the reduction of iron-group oxides to iron-group metals. Furthermore, the addition of a specific promoter suppresses destruction of the carbon skeleton due to methanation reactions in the presence of hydrogen gas, thereby demonstrating high stability. Therefore, even though this composite material contains a carbon material, it is possible to suppress deactivation due to methanation during ammonia synthesis and exhibit high durability. From these perspectives, this composite material is suitable for use as a catalyst material for ammonia synthesis.

[0037] As described above, the present composite material can be used at least as a catalyst material for ammonia synthesis, but the present composite material is not limited to being a catalyst material for ammonia synthesis and can also be used as other catalyst materials, etc. For example, the present composite material can also be used as a catalyst material for ammonia decomposition, a catalyst material for Fischer-Tropsch synthesis, an electrode catalyst material in electrochemical cells, etc.

[0038] In this composite material, the iron group element may contain at least Co, and the alkali metal element may contain at least Ba. With this configuration, when used as a catalyst material for ammonia synthesis, high ammonia production activity is easily obtained. In this case, preferably, from the viewpoint of ensuring the above-mentioned effects, the iron group element is Co, and the alkali metal element is Ba.

[0039] In this case, in the first structure, the Co-containing metal particles having passivated particle surfaces can exist inside or outside the carbon skeleton, and the Ba-containing compound can exist as Ba oxide (BaO) inside the carbon skeleton rather than outside (on the surface). In the second structure, the Co-containing metal particles can exist inside or outside the carbon skeleton, and the Ba-containing compound can exist as Ba oxide (BaO) at least in a state where a large number of Ba particles are gathered on the surface of the Co-containing metal particles.

[0040] In this composite material, the iron group element can include at least Fe, and the alkali metal element can include at least K and / or Cs. This configuration also makes it easier to obtain high ammonia production activity when used as a catalyst material for ammonia synthesis. In this case, from the viewpoint of ensuring the above-mentioned effects, it is preferable that the iron group element is Fe, and the alkali metal element is K and / or Cs, and more preferably, from the viewpoint of electronegativity that contributes to the electron donating ability to Fe, it is preferable that the iron group element is Fe, and the alkali metal element is K.

[0041] In this case, in the first structure, the metal particles containing Fe whose particle surfaces are passivated can exist inside or outside the carbon skeleton, and the compound containing K is K carbonate [K ２ CO ３ In this second structure, the metal particles containing Fe can be present inside or outside the carbon skeleton, and the compound containing K can be present as K oxide [K ２ O] and K hydroxide [K(OH) ２ ] can be present at least in a state where a large number of K atoms are gathered on the surface of the Fe-containing metal particles. In particular, since the temperature at which decomposition of oxides and hydroxides of K occurs is low, some K may exist in a metallic state. Similarly, in the first structure in the above case, the Fe-containing metal particles whose particle surfaces are passivated can exist inside or outside the carbon skeleton, and the Cs-containing compound can exist as Cs carbonate [Cs ２ CO ３In this second structure, the Fe-containing metal particles can be present inside or outside the carbon skeleton, and the Cs-containing compound can be present as Cs oxide [Cs ２ O] and Cs hydroxide [Cs(OH) ２ In particular, since the temperature at which decomposition of Cs into oxides or hydroxides occurs is low, some Cs may exist in a metallic state.

[0042] The present composite material can have a BET specific surface area as follows: Specifically, when the present composite material has the first structure and the iron group element contains Co, the BET specific surface area after reduction treatment under the conditions of maintaining the material at 485°C or less for 4 hours in a hydrogen atmosphere containing 75% by volume of hydrogen gas can be 30 m ２ In this case, the BET specific surface area is preferably 75 m / g or more from the viewpoint of high activity. ２ / g or more, more preferably 100m ２ / g or more, more preferably 125m ２ / g or more.

[0043] In addition, when the composite material has the first structure and the iron group element contains Fe, the BET specific surface area after reduction treatment under the condition of maintaining the material at 450°C or less for 4 hours in a hydrogen atmosphere containing 75% by volume of hydrogen gas is 50 m ２ In this case, the BET specific surface area is preferably 80 m / g or more from the viewpoint of high activity. ２ / g or more, more preferably 100m ２ / g or more, more preferably 150m ２ / g or more, and even more preferably 200m ２ / g or more, and even more preferably 250m ２ / g or more, and even more preferably 300m ２ / g or more.

[0044] In addition, when the composite material has the second structure, the BET specific surface area is 30 m ２In this case, the BET specific surface area is preferably 75 m / g or more from the viewpoint of high activity. ２ / g or more, more preferably 100m ２ / g or more, more preferably 125m ２ / g or more.

[0045] When the BET specific surface area of ​​the composite material is within the above-mentioned range, the increase in the surface area of ​​the composite material can increase the number of highly active sites, and when used as a catalyst material for ammonia synthesis, high ammonia production activity is easily obtained. The BET specific surface area can be measured in accordance with JIS 8830:2013. Nitrogen gas is used as the adsorption gas. The measurement temperature is liquid nitrogen temperature.

[0046] In the present composite material, the particles containing an iron group element can be on the nano-order (nano-size). Specifically, when the present composite material has the second structure, the average particle size of the particles containing an iron group element can be preferably 3 nm or more from the viewpoint of ensuring stability by suppressing sintering during the reaction. On the other hand, when the present composite material has the second structure, the average particle size of the particles containing an iron group element can be preferably 30 nm or less, more preferably 20 nm or less, and even more preferably 15 nm or less from the viewpoint of increasing the number of active sites. The average particle size of the particles containing an iron group element is the arithmetic mean of the maximum diameters measured for 100 particles containing any iron group element extracted from a bright-field STEM (scanning transmission electron microscope) image of the present composite material having the second structure. Note that, compared to the particles containing an iron group element, the compound containing an alkali metal element may or may not be in the form of particles. Furthermore, in the present composite material, the compound containing an alkali metal element is present in large numbers on the surfaces of the particles containing an iron group element, and therefore is smaller in size than the particles containing an iron group element.

[0047] The present composite material can have a peak in the mesopore region of its pore size distribution, with pore diameters of 2 nm to 50 nm. This configuration has the advantage of making it easier to increase the BET specific surface area of ​​the present composite material and to achieve high activity. Note that mesopores are pores with a pore diameter of 2 nm to 50 nm. From the viewpoint of making it easier to obtain a high BET specific surface area, the peak is preferably present in a range of pore diameters of 40 nm or less, more preferably pore diameters of 30 nm or less, even more preferably pore diameters of 25 nm or less, and even more preferably pore diameters of 20 nm or less.

[0048] The pore size distribution of the present composite material can be determined by pore analysis using the BJH (Barrett-Joyner-Halenda) method for the adsorption isotherm of the present composite material prepared using nitrogen gas as the adsorption gas. The pore size distribution is expressed as follows: the horizontal axis represents the pore diameter d ｐ , the vertical axis is the total pore volume V of the composite material ｐ is the pore diameter d ｐ dV differentiated by ｐ / dd ｐ In addition to mesopores, the composite material may also have micropores (pore diameter less than 2 nm) and macropores (pore diameter greater than 50 nm).

[0049] In this composite material, the molar ratio of alkali metal element to iron group element can be preferably 0.01 or more, more preferably 0.03 or more, even more preferably 0.05 or more, and even more preferably 0.1 or more, from the viewpoint of easily obtaining high ammonia generation activity when used as a catalytic material for ammonia synthesis. Furthermore, the molar ratio of alkali metal element to iron group element can be preferably 1.0 or less, more preferably 0.8 or less, even more preferably 0.6 or less, and even more preferably 0.5 or less, from the viewpoint of easily obtaining high ammonia generation activity when used as a catalytic material for ammonia synthesis, and from the viewpoint of stability of the oxide containing alkali metal element. The molar ratio of alkali metal element to iron group element can be easily measured by X-ray fluorescence analysis. When a light element such as Li is contained, inductively coupled plasma atomic emission spectrometry is suitable.

[0050] The shape of the present composite material is not particularly limited. The present composite material can have a desired shape depending on the application, etc. For example, the present composite material may be in the form of a powder or a molded body. When the present composite material is in the form of a molded body, it can exhibit superior activity (ammonia activity, etc.) compared to when the present composite material is in the form of a powder.

[0051] For other configurations and effects, the descriptions in the sections "(Method for producing a composite material)" and "(Method for producing ammonia)" described below can be referred to as needed.

[0052] (Method for Producing Composite Material) The method for producing a composite material of this embodiment (hereinafter sometimes abbreviated as "this method") is a method for producing the present composite material.

[0053] First Embodiment of the Present Manufacturing Method The present manufacturing method according to the first embodiment includes at least a precursor preparation step, a thermal decomposition step, and a passivation step.

[0054] In this production method, the precursor preparation step is a step of preparing a precursor composed of an organometallic complex containing an iron group element, an alkali metal element which is at least one element selected from the group consisting of alkali metal elements and alkaline earth metal elements, and an organic compound.

[0055] The iron group element and alkali metal element are as described above. The organic compound is not particularly limited as long as it is water-soluble and capable of forming an organometallic complex with an iron group element and an alkali metal element. Examples of organic compounds include citric acid, malic acid, tartaric acid, urea, ethylene glycol, and polyvinylpyrrolidone. These can be used alone or in combination of two or more. Of these, citric acid is preferable from the viewpoint of dispersibility of the iron group element. When the organic compound is citric acid, the organometallic complex is specifically a metal-citric acid complex containing a metal composed of an iron group element and an alkali metal element and citric acid.

[0056] A precursor composed of an organometallic complex can be synthesized by the sol-gel method using a mixed aqueous solution containing, for example, a water-soluble salt of an iron-group element, a water-soluble salt of an alkali metal element, and an organic compound. The mixed aqueous solution can be prepared, for example, by mixing a first aqueous solution containing a water-soluble salt of an iron-group element and a water-soluble salt of an alkali metal element but not containing an organic compound with a second aqueous solution containing an organic compound but not containing a water-soluble salt of an iron-group element or a water-soluble salt of an alkali metal element. The precursor prepared by the sol-gel method can also be prepared in powder form by drying a gel and thoroughly pulverizing it. The precursor can also be prepared in the form of a compact. A compact precursor can be formed, for example, by compacting a powder precursor, or by crushing the powder after compacting and, if necessary, classifying the powder. Examples of the shape of the compact include pellets.

[0057] Because this composite material contains a relatively high carbon content, it is easier to powder than materials with a relatively low carbon content. Therefore, it is relatively difficult to later mold this composite material obtained in powder form into a molded body such as a pellet. However, if the precursor is prepared as a molded body in advance in the precursor preparation step before the pyrolysis step, it becomes relatively easy to manufacture this composite material composed of a molded body.

[0058] Examples of water-soluble salts of iron-group elements include nitrates, sulfates, hydroxides, acetates, chlorides, and carbonates of iron-group elements. These can be used alone or in combination of two or more. Examples of water-soluble salts of alkali metal elements include nitrates, sulfates, hydroxides, acetates, chlorides, and carbonates of alkali metal elements. These can be used alone or in combination of two or more. The organic compound is as described above. The molar ratio of the alkali metal element to the iron-group element can be adjusted appropriately by changing the amounts of raw materials charged in the mixed aqueous solution so as to achieve a predetermined molar ratio.

[0059] The thermal decomposition step is a step in which the organic compound in the precursor is thermally decomposed in an inert gas atmosphere. In this thermal decomposition step, it is important to perform the thermal decomposition of the organic compound in an inert gas atmosphere. In the sol-gel method, a gel-like substance is usually fired in an oxygen-containing atmosphere such as air. However, if the precursor is fired and thermally decomposed in an oxygen-containing atmosphere, the organic compound is burned and lost, making it impossible to form the carbon skeleton that constitutes the carbon material in this composite material. Therefore, in the thermal decomposition step, the organic compound is thermally decomposed in an inert gas atmosphere.

[0060] The inert gas for forming the inert gas atmosphere is, for example, nitrogen gas (N ２Examples of the inert gas include nitrogen 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.

[0061] The thermal decomposition of the organic compound is preferably carried out in the inert gas atmosphere at a thermal decomposition temperature of 300° C. or higher and 700° C. or lower. By setting the thermal decomposition temperature to 300° C. or higher in an inert gas atmosphere, the formation of the carbon skeleton constituting the carbon material can be ensured. On the other hand, by setting the thermal decomposition temperature to 700° C. or lower in an inert gas atmosphere, there are advantages such as suppressing aggregation due to sintering of the iron-group metal particles, improving the BET specific surface area of ​​the composite material, making it easier to achieve high activity, and enabling the formation of a stable carbon skeleton while suppressing excessive graphitization.

[0062] From the above viewpoint, the thermal decomposition temperature can be preferably 500° C. or higher, more preferably 550° C. or higher, and even more preferably 575° C. or higher. From the above viewpoint, the thermal decomposition temperature can be preferably 750° C. or lower, more preferably 700° C. or lower, and even more preferably 650° C. or lower.

[0063] The pyrolysis time may be preferably 1 hour or more, more preferably 3 hours or more, and even more preferably 5 hours or more from the viewpoint of removing excess carbon, etc. The pyrolysis time may be preferably 10 hours or less, more preferably 8 hours or less, and even more preferably 6 hours or less from the viewpoint of suppressing destruction of the carbon skeleton, etc.

[0064] Specifically, the thermal decomposition of the organic compound can be carried out by calcining the organic compound under the inert gas atmosphere. The calcination can be carried out once or multiple times. The thermal decomposition of the organic compound can be carried out, for example, by calcining the organic compound once, or by calcining the organic compound at a temperature lower than the main calcination temperature followed by main calcination (substantial thermal decomposition). The calcination can be carried out, for example, under the inert gas atmosphere at a calcination temperature of 200°C to 300°C for a calcination time of 1 hour to 10 hours. The main calcination can be carried out, for example, under the inert gas atmosphere at a main calcination temperature of 300°C to 700°C for a main calcination time of 1 hour to 10 hours. When performing calcination and main calcination, the total time of the calcination and main calcination can be set to 10 hours or less, from the viewpoint of preventing destruction of the carbon skeleton.

[0065] The thermal decomposition step produces a thermal decomposition product having a carbon skeleton and containing iron-group metal particles and an alkali metal compound dispersed in the carbon skeleton. The carbon skeleton may contain some iron-group oxide particles for manufacturing reasons.

[0066] In this manufacturing method, the passivation step is a step of passivating the surfaces of iron-group metal particles contained in the obtained pyrolyzate. In particular, when exposed to the atmosphere, iron-group metals rapidly oxidize and generate heat, leading to destruction of the carbon skeleton. To prevent this, at least the surfaces of the iron-group metal particles formed in the pyrolyzate are passivated. Specifically, the obtained pyrolyzate is held in a gas atmosphere containing a trace amount of oxygen and a gas other than oxygen gas as a base, such as an atmosphere containing carbon dioxide, argon, nitrogen, or helium, to form a passive film (e.g., an iron-group oxide film, an iron-group carbonate film, etc.) on at least the surfaces of the iron-group metal particles. The passivation treatment time can be, for example, from 10 minutes to 1 hour if the treatment amount is on the order of a few grams, but can be appropriately set depending on the treatment amount. The passivation treatment temperature can be, for example, from 5°C to 50°C.

[0067] When the present production method is carried out up to the passivation step described above, the pyrolyzed product after the passivation step becomes the present composite material. In other words, the composite material obtained in this manner has the first structure described above, and can be activated by a separate reduction treatment before use.

[0068] The present production method can further include a reduction step in which the thermal decomposition product obtained after the passivation step is reduced. In this case, the material obtained by reducing the thermal decomposition product after the passivation step is the present composite material. In other words, the composite material obtained in this manner is a composite material having the second structure described above, and since it has already undergone the reduction step as one of the steps in the present production method, it can exhibit activity without being subjected to a separate reduction treatment before use, etc.

[0069] The reduction treatment can be carried out in a reducing atmosphere containing hydrogen at a reduction temperature of 300° C. or higher and lower than 500° C. for a reduction time of 1 hour or higher and 24 hours or lower.

[0070] The reduction temperature may be set to preferably 350° C. or higher, more preferably 400° C. or higher, even more preferably 425° C. or higher, still more preferably 450° C. or higher, from the viewpoint of stable formation and high activation of the carbon skeleton constituting the carbon material. The reduction temperature may be set to preferably 498° C. or lower, more preferably 495° C. or lower, and even more preferably 490° C. or lower, from the viewpoint of suppressing structural changes in the carbon skeleton constituting the carbon material.

[0071] The reduction 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 improving the degree of reduction of the iron group elements, etc. The reduction time is preferably 8 hours or less, more preferably 6 hours or less, and even more preferably 5 hours or less from the viewpoint of preventing sintering of the iron group metal particles, etc.

[0072] The pressure during the reduction treatment is preferably around atmospheric pressure, about 0.1 MPa, but the composite material can also be treated under pressure conditions exceeding 0.1 MPa.

[0073] According to this production method, it is possible to produce the present composite material that is activated by reduction treatment at a reduction temperature of less than 500° C. for a reduction time of 24 hours or less. Therefore, according to this production method, it is possible to obtain the present composite material that exhibits high activity by reduction treatment at a low temperature and in a short time, compared to conventional composite materials made of an MgO support that supports Co particles whose surfaces are covered with BaO.

[0074] Furthermore, this manufacturing method uses a simple sol-gel method, which does not require complicated processes or a controlled environment, and does not require time-consuming processes such as ball milling, which is advantageous in improving the productivity of this composite material.

[0075] Furthermore, this production method not only makes it possible to obtain a composite material that exhibits activity even under mild reaction conditions of temperature and pressure, but also makes it possible to lower the temperatures during preparation of the composite material and the reduction treatment (activation treatment), which has the advantage of reducing the production costs of the composite material and the ammonia synthesis costs when the composite material is used in ammonia synthesis.

[0076] -Second embodiment of the present manufacturing method- The present manufacturing method according to the second embodiment is a manufacturing method in which the present composite material having the above-mentioned first structure is subjected to a reduction treatment to obtain the present composite material having the above-mentioned second structure.

[0077] The composite material having the first structure can be prepared, for example, by going through the precursor preparation step, the thermal decomposition step, and the passivation step described above in the "first embodiment of the present production method." The reduction treatment can be carried out under the conditions of the reduction step described above in the "first embodiment of the present production method."

[0078] For other configurations and effects, the descriptions in "(Composite material)" and the descriptions in "(Method for producing ammonia)" described below can be referenced as needed. In addition, the descriptions in "First embodiment of the present production method" can be referenced as needed in "Second embodiment of the present production method," and the descriptions in "Second embodiment of the present production method" can be referenced as needed in "First embodiment of the present production method."

[0079] (Method for Producing Ammonia) The method for producing ammonia according to this embodiment (hereinafter sometimes abbreviated as "the present ammonia production method") is a method for producing ammonia using the present composite material as a catalyst material.

[0080] The method for producing ammonia includes a step of reducing the composite material having a first structure and then contacting the composite material with hydrogen and nitrogen, or a step of contacting the composite material having a second structure with hydrogen and nitrogen.

[0081] According to this ammonia production method, ammonia can be produced with a high ammonia yield even under mild conditions such as temperatures below 500°C and pressures below 10 MPa.

[0082] Regarding the detailed configuration of the present composite material having the first structure, the present composite material having the second structure, the reduction conditions of the present composite material having the first structure, and other configurations and effects, the descriptions in "(Composite material)" and "(Method for manufacturing composite material)" can be referred to as needed.

[0083] (Experimental Examples) The composite material and its manufacturing method, as well as the method for manufacturing ammonia according to the present disclosure, will be described in more detail below using experimental examples. Note that in these experimental examples, detailed experiments were conducted assuming the use of the composite material as a catalyst material for ammonia synthesis, but the use of the composite material is not limited to a catalyst material for ammonia synthesis. The composite material can be applied to a variety of uses in various fields where active materials are required while reducing the activation temperature and the activation time.

[0084] Experimental Example 1 1. Preparation of the Present Composite Material The following were prepared as raw materials for various composite materials. Water-soluble salts of iron-group elements When preparing a Co-based composite material containing Co as the iron-group element, cobalt nitrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) When preparing an Fe-based composite material containing Fe as the iron-group element, iron nitrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Water-soluble salts of alkali-based metal elements Lithium nitrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Potassium nitrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Cesium nitrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Calcium nitrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Strontium nitrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Barium nitrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Organic compound Citric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0085] Appropriate amounts of a water-soluble salt of a predetermined iron group element and an appropriate amount of a water-soluble salt of a predetermined alkali metal element were dissolved in a sufficient amount of deionized water at room temperature. Next, a calculated amount of citric acid as an organic compound was separately dissolved in a sufficient amount of deionized water so that the molar ratio of the iron group element to the alkali metal element was the predetermined molar ratio. Next, after complete dissolution, the two aqueous solutions were mixed in a 1 L beaker to obtain a mixed aqueous solution containing the water-soluble salt of the iron group element, the water-soluble salt of the alkali metal element, and citric acid.

[0086] Using this mixed aqueous solution, a precursor composed of an organometallic complex containing an iron-group element, an alkali metal element, and an organic compound was synthesized by a sol-gel method. Specifically, the mixed aqueous solution was held in a mantle heater and mixed thoroughly under vigorous stirring to form a metal-citric acid complex containing a metal composed of an alkali metal element and an iron-group element and citric acid in the solution. After three hours, the temperature of the mantle heater was raised to 80°C, and vigorous stirring was continued until gelation occurred. The resulting gel-like substance was then dried in an oven at 80°C and thoroughly pulverized to form a powdered precursor. This resulted in the preparation of a precursor composed of a metal-citric acid complex containing a metal composed of a predetermined iron-group element and an alkali metal element and citric acid.

[0087] Next, citric acid, an organic compound in the obtained precursor, was thermally decomposed under an inert gas atmosphere. Specifically, the obtained precursor was collected in a quartz boat, pre-baked at 300°C for 5 hours under an Ar atmosphere, and then further baked at 600°C for 5 hours under an Ar atmosphere to obtain a thermally decomposed product. The obtained thermally decomposed product was cooled to room temperature. By the above thermal decomposition, citric acid (CA) in the precursor was thermally decomposed (CA → C + CO ２ + CO + H ２ As a result, a pyrolyzed product is obtained which has a carbon skeleton and contains iron-group metal particles and a compound of an alkali metal element dispersed in the carbon skeleton.

[0088] Next, in order to prevent rapid oxidation of the iron group metal, the surfaces of the iron group metal particles contained in the obtained pyrolyzed product were passivated. Specifically, the obtained pyrolyzed product was passivated in an atmosphere containing carbon dioxide. Here, the pyrolyzed product was subjected to a passivation treatment in an atmosphere containing 100% CO ２ The passivation treatment was carried out under flow for 30 minutes.

[0089] As described above, a composite material containing a carbon material, an iron-group element, and an alkali metal element was prepared. Specifically, the molar ratio of the alkali metal element X (X = any one of Li, K, Cs, Ca, Sr, and Ba) to Co was kept constant (0.3) (X / Co). ０．３ The molar ratio of the alkali metal element X (X = Li, K, Cs, Ca, or Ba) to Fe was constant (0.3) (X / Fe). ０．３ Similarly, a Ba / Co composite material was prepared by changing the molar ratio of Ba to Co (Ba / Co). ｘ / C (where x = 0.03, 0.3, 0.5) composite material, no passivation treatment was performed (Ba / Co) ０．３ For comparison, a Co / C composite material containing Co but not containing an alkali metal element was also prepared.

[0090] In addition, "(X / X1)" shown in this experimental example ｘ In the notation of "X / X2", X2 represents the material of the support, X1 represents an iron group element, and X represents an alkali metal element, (X / X1) ｘindicates that the molar ratio X / X1 of the X element to the X1 element is x. Furthermore, when only the iron-group element X1 is listed without specifying the alkali-based metal element X or the molar ratio x, this means that the alkali-based metal element X is not included. Furthermore, when multiple iron-group elements are listed as the X1 element, this means that the listed multiple iron-group elements are included. In this case, the numerical subscripts shown to the lower right of each iron-group element indicate the molar ratio of each iron-group element. Furthermore, when multiple alkali-based metal elements are listed as the X element, this means that the listed multiple alkali-based metal elements are included.

[0091] 2. Preparation of composite material using activated carbon as a carrier For comparison, (Ba / Co) ０．３ Ba and Co were supported on activated carbon (AC) in the same molar ratio as in the Ba / Co composite material. ０．３ A Ba(NO) / AC composite material was prepared. Specifically, commercially available activated carbon (manufactured by TCI) was pretreated at 600°C for 5 hours, and then at 900°C for 5 hours in an Ar atmosphere. The temperature was increased at a rate of 1°C / min. The activated carbon was then subjected to ultrasonic treatment in water to obtain a good dispersion. ３ ) ２ and Co(NO ３ ) ２ 6H ２ An aqueous solution of 0 was added and stirred overnight. The water was then evaporated using a rotary evaporator, and the mixture was dried in an oven at 80°C. The resulting dried product was then thoroughly pulverized and thermally decomposed in an Ar atmosphere in the same manner as above. For comparison with the present composite material, milder temperature conditions were used, different from the commonly used high-temperature treatment. The (Ba / Co) obtained in this manner was ０．３ The Ba / Co / AC composite material was subjected to reduction treatment in an Ar gas atmosphere at 485°C for 4 hours. The composite material thus obtained was called (Ba / Co) ０．３ / AC-Ar-485°C / 4h composite material. ０．３ / AC composite material, ２ The composite material obtained was subjected to a reduction treatment at 485°C for 4 hours in a gas atmosphere. ０．３ / AC-H ２ -485 ° C / 4h composite material. Also, (Ba / Co) ０．３ / AC composite material, ２ The composite material obtained was subjected to a reduction treatment at 500°C for 48 hours in a gas atmosphere. ０．３ / AC-H ２ This is referred to as the -500°C / 48h composite material.

[0092] The composite material prepared above was activated by reduction treatment, and ammonia synthesis was carried out using this as a catalyst material. The ammonia synthesis reaction was carried out using a fixed-bed flow-type reactor.

[0093] Specifically, 100 mg of the composite material was placed in a stainless steel reactor (diameter 10 mm, inner diameter 7 mm), and the outlet of the reactor was connected to an IR analyzer. The composite material was then activated by reduction prior to ammonia synthesis. The reduction conditions were as follows: when Co was used as the iron group element, H ２ and N ２ In a mixed gas atmosphere (volume ratio: H ２ / N ２ The conditions were: 0.1 MPa, 485°C (heating rate 4°C / min), 1000 kJ / min, total flow rate 240 mL / min), and 485°C for 4 hours. ２ and N ２ In a mixed gas atmosphere (volume ratio: H ２ / N ２ The conditions were: 0.1 MPa, 450°C (heating rate 4°C / min), 0.3 MPa, total flow rate 240 mL / min, and 4 hours. When Co and Fe were used, the same conditions as for Co were used.

[0094] After the reduction treatment, the reactor was cooled to 200°C with the same gas flow as in the reduction treatment, and then the total gas flow rate was reduced to 120 mL / min (H ２ / N ２ =3, weight space velocity WHSV=72,000mLg ｃａｔ －１ h －１), the pressure was increased to 1.0 MPa, and the ammonia synthesis rate was measured in the temperature range of 200°C to 400°C. At each temperature, the reaction conditions were kept constant for 30 minutes until stability was achieved, and then measurements were carried out for 1 hour. After the ammonia synthesis reaction, the used composite material was stored in a 100% CO atmosphere to avoid rapid oxidation by the atmosphere. ２ The passivation treatment was carried out under flow for 30 minutes.

[0095] The ammonia synthesis rate was calculated by measuring the ammonia concentration in the outlet gas flowing out from the outlet of the reaction tube using an IR analyzer and using the following formulas: Ammonia yield = (ammonia concentration / 100 × 2) / (1 + ammonia concentration / 100) × 100 Ammonia synthesis rate (mmol / g / h) = Nitrogen supply rate (mmol / h) × 2 × ammonia yield / 100 / catalyst weight (g)

[0096] 4. Evaluation of Material Properties The material properties of the prepared composite materials were evaluated as follows.

[0097] 4.1 High-Angle Dark-Field Scanning Transmission Electron Microscopy (HAADF-STEM), Energy Dispersive X-ray Analysis (EDX), and X-ray Absorption Fine Structure (XAFS) Measurements. HAADF-STEM images and EDX analysis were performed on the composite materials. 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 pre- and post-reduction samples were ground at room temperature and dispersed in ethanol. The dispersion was dropped onto a carbon-coated copper grid (TEM grid) and dried under vacuum at room temperature for 24 hours. For STEM observations without air exposure, the samples were reduced in a quartz reactor under the same conditions as above, then opened in an Ar-filled glove box without passivation or air exposure. The samples were then ground and deposited on a TEM grid and transferred to a special holder.

[0098] At the BL11S2 beamline of the Aichi Synchrotron Light Center of the Japan Science and Technology Foundation, we performed measurements at the Co K absorption edge and Ba L ３XAFS measurements of the absorption edge were carried out. The composite materials before and after the reaction were mixed with a calculated appropriate amount of boron nitride (BN) powder, thoroughly pulverized, and then pelletized. For XAFS measurements without exposure to air, the sample was reduced in a quartz reactor under the same conditions as above, opened in a glove box filled with Ar, mixed with an appropriate amount of BN powder, thoroughly pulverized, and then pelletized. The pellets were placed in oxygen-blocking plastic bags, sealed with Ar, and transferred to the beamline. The Co K absorption edge and Ba L ３ The absorption edge XANES spectra were measured in transmittance mode with two ion chambers.

[0099] 4.2 X-ray Diffraction Measurement (XRD Measurement) XRD measurements of the composite materials were performed as required using an X-ray diffractometer (Rigaku Corporation, "MiniFlex") equipped with CuKα radiation, and the XRD patterns were analyzed using SmartLab Studio II software.

[0100] 4.3 Average particle size of particles containing iron group elements The maximum diameters of 100 particles containing any iron group element extracted from the bright-field STEM image of the composite material were measured, and the average particle size of the particles containing iron group elements was calculated as the arithmetic mean value of the obtained maximum diameters.

[0101] 4.4 Measurement of BET specific surface area and pore size distribution The composite materials reduced under the specified reduction conditions as described above were degassed under vacuum at 300°C for 3 hours. Next, the BET specific surface area of ​​each composite material was measured at liquid nitrogen temperature using a BELSORP-miniX (manufactured by Microtrac-Bell) with nitrogen gas as the adsorption gas. The BET specific surface area was measured at a relative P / P of 0.05 to 0.3. ０ The total pore volume of the composite material, V ｐ The pore size distribution was determined from the adsorption branch of the adsorption / desorption isotherm by the BJH method.

[0102] 4.5 Temperature-Programmed Reduction Measurement (TPR Measurement) To investigate the reduction behavior of the composite material, ２The TPR measurement was carried out using a BELCAT-II device (Microtrac BEL Co., Ltd.) under a flow of 1000 kJ / L. For the composite material before use, 50 mg of the composite material was placed in a reactor and heated to 1000 kJ / L. ２ The temperature was raised from room temperature to 800°C at a rate of 10°C / min with a gas flow of 30 mL / min. ２ -N ２ Mixture of gases (volume ratio: H ２ / N ２ The sample was treated with a flow rate of 3 mL / min (total of 120 mL / min), and the temperature of the fixed bed was raised from room temperature to 485°C over 2 hours. The sample was then held at that temperature for 4 hours under the same mixed gas flow, then cooled to 50°C and held in Ar gas for 10 minutes. After this reduction treatment and stabilization of the detector (quadrupole mass spectrometer "BEL-MS", manufactured by Microtrac BEL), the temperature was raised using the same procedure as for the composite material before use.

[0103] 5. Results and Discussion 5.1 Ammonia production activity of the present composite material A series of (X / Co) ０．３ The Co / C composite material (where X=Li, K, Cs, Ca, Sr, or Ba) and the comparative Co / C composite material were subjected to NH ３ Yield and NH ３ The synthesis rate was measured. ２ and N ２ In a mixed gas atmosphere (volume ratio: H ２ / N ２ The reduction treatment was carried out under the conditions of (a) pressure (300 psi, total flow rate 240 mL / min), 0.1 MPa, and 485°C for 4 hours. The results are shown in Figure 1.

[0104] As shown in Figure 1, (X / Co) ０．３ It was confirmed that all of the (X / Co) composite materials had ammonia production activity. ０．３ When comparing the Ba / Co composite materials, in particular, ０．３ The remaining (X / Co) ０．３The Ba / Co composite material showed higher ammonia production activity than the Ba / Co composite material (where X = Li, K, Cs, Ca, or Sr). ０．３ The / C composite material is, for example, a NH ３ The synthesis rate is 33.8 mmol g ｃａｔ －１ h －１ This shows a high activity compared to other carbon-based catalysts reported so far. From this result, it was confirmed that when the iron group element is Co, high ammonia production activity can be easily obtained by using Ba as the alkali metal element.

[0105] Next, a series of (X / Fe) samples prepared as described above according to this manufacturing method were ０．３ The citric acid molar ratio of the iron group element and the alkali metal element was 5 times that of the iron group element / C composite material (where X = Li, K, Cs, Ca, or Ba), and the NH ３ Yield and NH ３ The synthesis rate was measured. ２ and N ２ In a mixed gas atmosphere (volume ratio: H ２ / N ２ The reduction treatment was carried out under the conditions of (a) 0.1 MPa, (b) 450°C, (c) 0.3, (d) 240 mL / min total flow rate, and (e) 0.1 MPa for 4 hours. The results are shown in Figure 2.

[0106] In addition, a series of (X / Fe) alloys prepared as described above according to this manufacturing method were ０．３ Among the / C composite materials (where X = either K or Cs), those prepared by using three times the molar amount of citric acid relative to the total molar amount of iron group elements and alkali metal elements were subjected to NH ３ Yield and NH ３ The synthesis rate was measured. ２ and N ２ In a mixed gas atmosphere (volume ratio: H ２ / N ２The reduction treatment was carried out under the conditions of (X / X1) = 3, total flow rate 240 mL / min), 0.1 MPa, and 450°C for 4 hours. The results are shown in Figure 3. Note that the sample prepared with three times the molar amount of citric acid is labeled "(X / X1)" in this experimental example to distinguish it from the sample prepared with five times the molar amount of citric acid. ｘ In the notation " / X2", "<2>" is added after X2, which indicates the material of the carrier.

[0107] As shown in FIG. 2, (X / Fe) ０．３ / C composite materials, (X / Co) ０．３ It was confirmed that both of the (X / Fe) and (X / C) composite materials have ammonia production activity. ０．３ When comparing the X / Fe composite materials, in particular, ０．３ / C composite material (where X = either K or Cs) is the remaining (X / Fe) ０．３ The results confirmed that when the iron group element is Fe, high ammonia production activity can be easily achieved by using K or Cs as the alkali metal element.

[0108] Furthermore, as shown in FIG. 3, the molar amount of citric acid was three times the total molar amount of the iron group element and the alkali metal element (X / Fe). ０．３ The / C<2> composite material (where X=K or Cs) was prepared by adding 5 times the molar amount of citric acid to the total molar amount of the iron group element and the alkali metal element (X / Fe). ０．３It was confirmed that the composite material exhibited higher ammonia generation activity than a ZnO / C composite material (where X = either K or Cs). From these results, it can be said that by adjusting the molar amount of an organic compound such as citric acid to less than 5 times, preferably 4 times or less, and more preferably 3 times or less, the total molar amount of an iron-group element and an alkali-based metal element in the precursor preparation step during the production of the composite material, it is possible to improve the ammonia generation activity compared to when the molar amount of an organic compound such as citric acid is adjusted to 5 times or more the total molar amount of an iron-group element and an alkali-based metal element. Thus, it was confirmed that the ammonia generation activity can be improved by optimizing the total molar amount of an iron-group element and an alkali-based metal element and the molar amount of an organic compound in the precursor preparation step during the production of the composite material.

[0109] Next, a series of (X / CoFe)0.3 or 0.1 / C composite materials (where X=K, Ba, or both) prepared according to this manufacturing method were subjected to NH ３ Yield and NH ３ The synthesis rate was measured. The molar ratio of Co to Fe in each composite material was Co: 0.83, Fe: 0.17 (Co ０．８３ Fe ０．１７ ), or Co: 0.20, Fe: 0.80 (Co ０．２０ Fe ０．８０ Each composite material is expressed as H ２ and N ２ In a mixed gas atmosphere (volume ratio: H ２ / N ２ The reduction treatment was carried out under the conditions of (a) 0.1 MPa, (b) 485°C, (c) 0.1 MPa, (d) 0.1 MPa, (e) 485°C, (f) 4 hours. The results are shown in Figure 4.

[0110] As shown in Figure 4, the (X / CoFe)0.3 or 0.1 / C composites also exhibited the same properties as the (X / Co) ０．３ / C composite material and (X / Fe) ０．３It was confirmed that both of them had ammonia production activity, similar to the (X / CoFe)0.3 or 0.1 / C composite material. In addition, when comparing the (X / CoFe)0.3 or 0.1 / C composite materials, the (K / Co ０．２０ Fe ０．８０ ) ０．３ The remaining (X / CoFe) ０．１ The results confirmed that when the particles containing an iron-group element are composite metal particles containing Co and Fe as iron-group elements, specifically CoFe, using K as the alkali metal element makes it easier to obtain high ammonia generation activity.

[0111] Next, (Ba / Co) ０．３ For the / C composite material, NH ３ The effect of reaction pressure on the synthesis rate was measured using a weight hourly space velocity (WHSV): 72,000 mL / g ｃａｔ －１ h －１ The investigation was carried out under the conditions of reaction pressure: 0.1 to 3.0 MPa, and reaction temperature: 350°C. The results are shown in Figure 5. As shown in Figure 5, ３ The synthesis rate increased rapidly with increasing reaction pressure, reaching 64 mmol g at 3.0 MPa. ｃａｔ －１ h －１ reached a high value.

[0112] In addition, under mild conditions of a reaction temperature of 350°C and a reaction pressure of 1.0 MPa, ３ (Ba / Co) for the continuous synthesis of ０．３ The long-term durability (stability) of the SiO2 / C composite material was confirmed, and the results are shown in Figure 6.

[0113] As shown in FIG. 6, (Ba / Co) ０．３The MgO / C composite material exhibited very stable ammonia production activity for at least 100 hours. These results confirmed that this composite material, even one containing a carbon material, exhibits high durability and stability. Furthermore, since this composite material can be activated by reduction treatment at a temperature below 500°C for a reduction time of 24 hours or less, it can be said that it can exhibit activity by reduction treatment at a lower temperature and in a shorter time than the composite material described in Non-Patent Document 1, which consists of an MgO support supporting Co particles whose surfaces are covered with BaO.

[0114] Next, the present composite material produced by the present production method and a Ba / Co composite produced by impregnation method, in which Ba and Co are supported on activated carbon, were compared. ０．３ The ammonia production activity of the ZnO / AC composite was compared, and the results are shown in Figure 7.

[0115] As shown in FIG. 7, (Ba / Co) ０．３ / AC-Ar-485℃ / 4h composite material, (Ba / Co) ０．３ / AC-H ２ -485°C / 4h composite material, and (Ba / Co) ０．３ / AC-H ２ -500℃ / 48h composite material (Ba / Co) ０．３ It can be seen that the ammonia generation activity is extremely low in both cases compared to the / C-485°C / 4h composite material. This indicates that the composite material produced by this manufacturing method is completely different from composite materials in which iron-group metals such as Co and Fe, alkaline earth metals such as Ba, or alkali metals such as K are supported on the surface of activated carbon. Furthermore, this manufacturing method can be said to be useful in that it allows for the easy production of highly active composite materials compared to multi-stage impregnation methods, which require long periods of time.

[0116] 5.2 Elucidation of the microstructure of this composite material 5.2.1 Before reduction treatment Using high-angle anisotropy dark-field scanning transmission electron microscopy (HAADF-STEM) and EDX maps obtained by energy dispersive X-ray spectroscopy (EDX analysis), (Ba / Co) ０．３ The microstructure of the SiO2 / C composite material was investigated. The sample used was before reduction treatment by hydrogen reduction. The results are shown in Figure 8.

[0117] As shown in FIG. 8, it can be seen that Co, an iron-group element, in this sample is particulate. As described above, since the thermal decomposition product has been subjected to passivation treatment, it can be said that these particles are Co particles with passivated particle surfaces (Co particles having CoO on their surfaces). It can be seen that these Co particles with passivated particle surfaces are uniformly (homogenously) dispersed (distributed) inside and on the surface (external) of the carbon skeleton constituting the carbon material. It can also be seen that Ba, an alkali-based metal element in this sample, exists in the form of an oxide (specifically, BaO), and this BaO is uniformly (homogenously) dispersed (distributed) inside and on the surface (external) of the carbon skeleton. In other words, it was confirmed that the composite material before reduction treatment has a first structure in which a large number of Co particles with passivated particle surfaces and BaO are dispersed in the carbon skeleton constituting the carbon material. Although not shown, a similar tendency was observed when Fe was used as the iron-group element, but in this case, when K was used as the alkali-based metal element, some of the K was converted to K. ２ CO ３ It was suggested that the hydroxyl group exists mainly outside the carbon skeleton in this state.

[0118] 5.2.2 After reduction treatment Using HAADF-STEM and EDX map by EDX analysis, (Ba / Co) ０．３ The microstructure of the SiO2 / C composite was investigated. Note that the sample used here was prepared without exposure to air after hydrogen reduction. The results are shown in Figure 9.

[0119] As shown in Figure 9, the Co particles, whose particle surfaces were passivated, became metallic after the reduction treatment and existed as metallic Co particles. It was also found that these Co particles were uniformly dispersed (distributed) inside and on the surface (exterior) of the carbon skeleton constituting the carbon material. It was also found that the Ba element, an alkali metal element in this sample, remained in the oxide state (specifically, BaO) even after the reduction treatment. It was also found that much of the BaO, which was uniformly dispersed in the carbon skeleton before the reduction treatment, migrated to the surface of the Co particles and was concentrated on the surface of the Co particles in a denser state than the surrounding area of ​​the Co particles. In other words, it was confirmed that the composite material after the reduction treatment had a second structure in which a large number of metallic Co particles were dispersed in the carbon skeleton constituting the carbon material and a large number of BaO particles were concentrated on the surface of the Co particles.

[0120] In this experimental example, during the thermal decomposition of the precursor under an Ar gas atmosphere, the Ba ions and Co ions in the metal-citric acid complex are strongly coordinated with the carbon in the citric acid. If passivation is not performed after the thermal decomposition, the heat generated during the rapid oxidation of Co is large, and part of the carbon skeleton is destroyed, resulting in the formation of Co. ３ O ４ and BaCO ３ The reduction treatment temperature of less than 500°C produces Co ３ O ４ is completely reduced to BaCO ３ The temperature is not high enough to decompose Co. ３ O ４ and BaCO ３ When the composite material after passivation is subjected to reduction treatment, the CoO formed on the surface of the Co particles becomes metallic Co, which is a reduction product, and BaO is present in large amounts on the surface of the Co particles. ３ has been virtually non-existent since the beginning.

[0121] Next, in FIG. 10, (Ba / Co) ０．３ 10(a) and 10(b) show bright-field STEM images and Co particle distribution of the (Ba / Co) / C composite before reduction treatment. ０．３In the Ba / C composite material, the Co particles have an average particle size in the range of 2 to 3 nm. ０．３ In the Co / C composite material, the Co particles had a wide particle size distribution of 2 to 35 nm, with an average particle size of 11 nm. Based on XRD and STEM-EDX analyses, it is presumed that during the reduction process, methanation destroyed part of the carbon skeleton that constitutes the carbon material, causing the nearby Co particles to aggregate, resulting in the increase in the average particle size of the Co particles due to the reduction process.

[0122] However, although not shown, compared to the results of a Co / C composite material produced in a similar manner, BaO is dispersed (Ba / Co). ０．３ The Co / C composite material had a smaller average particle size of Co particles after reduction than the Co / C composite material without BaO. Furthermore, larger aggregates of Co particles were observed in the reduced Co / C composite material. These findings suggest that in this composite material, oxides containing alkali metal elements such as BaO play a role in suppressing further aggregation of iron-group metal particles by migrating over the carbon skeleton and iron-group metal particles such as Co particles. Furthermore, in this sol-gel production method, even if iron-group elements are uniformly dispersed in the carbon skeleton, if alkali metal elements are not present, methanation is highly catalyzed by the iron-group elements during reduction, which likely leads to aggregation of iron-group metal particles. Therefore, in this composite material, oxides containing alkali metal elements are important not only for controlling the size and distribution of iron-group metal particles during reduction and reaction, but also for suppressing methanation of the carbon skeleton that constitutes the carbon material.

[0123] Although not shown, the (Ba / Co) ratio before and after the reduction treatment ０．３When comparing the SiO2 / C composites, none of them showed a graphite peak, only a turbostratic carbon peak. This is thought to be because in this experimental example, the precursor was pyrolyzed at 600°C, which is not sufficient to graphitize the carbon derived from the carbon source, citric acid, and most of the carbon remained in an amorphous state.

[0124] Next, (Ba / Co) ０．３ The chemical states of Co and Ba in the Co / C composite material were investigated for each of the following cases: with passivation, no reduction, and unused (Fresh, (i) Passivated); without passivation, no reduction, and unused (Fresh, (ii) Not passivated); with passivation, reduction, and passivated after use (Used, (iii) Passivated); and with passivation, reduction, and no air exposure after use (Used, (iv) No air). The investigation was carried out by the above-mentioned X-ray absorption fine structure measurement (XAFS measurement). The results are shown in Figure 11. In Figure 11, CoO, Co ３ O ４ , Co foil, BaO, BaCO ３ is the reference sample.

[0125] As shown in FIG. 11, if the thermal decomposition product is not passivated after the thermal decomposition of the organic compound in the precursor under an inert gas atmosphere (spectrum (ii) in the figure), Co particles and Ba are rapidly oxidized, resulting in Co ３ O ４ , BaCO ３ This was also confirmed by XRD measurement (not shown). After thermal decomposition, the passivated and reduced (Ba / Co) ０．３ / C composite material and (Ba / Co) reduced without passivation after pyrolysis. ０．３ The reduction was carried out under the conditions described above.

[0126] In contrast, when the thermal decomposition product is passivated and not reduced after the thermal decomposition of the organic compound in the precursor under an inert gas atmosphere (spectrum (i) in the figure), (Ba / Co) ０．３ The Co / C composite material contains CoO and BaO. This composite material can be activated by reducing CoO to metallic Co through a reduction treatment. The reduction of CoO to metallic Co can be confirmed by the Co K-edge XANES spectrum (spectrum (iv) in the figure) obtained without exposure to air after reduction.

[0127] In addition, when the organic compound in the precursor was thermally decomposed under an inert gas atmosphere, the thermal decomposition product was passivated, used after reduction, and then taken out into the air after passivation treatment (spectrum (iii) in the figure), (Ba / Co) ０．３ Although the / C composite material was passivated after use, some of the Co on the surface of the Co particles was oxidized, and a strong peak of CoO was observed. ３ In addition, when the thermal decomposition product was subjected to passivation treatment after thermal decomposition of the organic compound in the precursor under an inert gas atmosphere and then measured without exposure to air after reduction (spectrum (iv) in the figure), (Ba / Co) ０．３ The BaCO / C composite material shows a strong Co peak. ３ From these results, it can be seen that (Ba / Co) ０．３ It was confirmed that the Co / C composite material was passivated against pyrolysis products, and when reduced, almost all of the CoO was reduced to metallic Co, and Ba remained as BaO. This result was in good agreement with the HAADF-STEM image and EDX analysis results shown in Figure 9.

[0128] Next, in FIG. 12, (Ba / Co) ０．３ / C composite material, (Ca / Co) ０．３ / C composite material, (K / Co) ０．３ / C composite material, (Sr / Co) ０．３ / C composite material, (Cs / Co) ０．３The pore size distributions of the carbon / carbon composite materials obtained from their adsorption / desorption isotherms are shown in the figure. ＢＥＴ ), the total pore volume (V) calculated by the BJH method ｐ ) and average pore diameter (d ａｖｅ 12 also shows the experimental results when the composite material has the second structure.

[0129] As shown in FIG. 12, (Ba / Co) ０．３ It was confirmed that the Ba / Co composite material had mesopores in addition to micropores and macropores. ０．３ This was also supported by the fact that the adsorption / desorption isotherm of the (K / Co) composite material belonged to the Type IV category with an H3 type hysteresis loop according to the IUPAC classification. ０．３ / C composite material, (Ca / Co) ０．３ / C composite material, (Sr / Co) ０．３ / C composite material, (Cs / Co) ０．３ It was confirmed that the K / Co composite material mainly had macropores. ０．３ / C composite material, (Ca / Co) ０．３ / C composite material, (Sr / Co) ０．３ / C composite material, (Cs / Co) ０．３ This was also supported by the fact that the adsorption / desorption isotherm of the SiO2 / C composite material does not have the above-mentioned hysteresis loop and is classified as Type II.

[0130] Also, (Ba / Co) ０．３ / C composite material, (Ca / Co) ０．３ / C composite material, (K / Co) ０．３ / C composite material, (Cs / Co) ０．３ The total pore volume of the / C composite material is V ｐ are almost the same values, but the BET specific surface area and average pore diameter d ａｖｅ Specifically, there was a significant difference in (Ba / Co) ０．３ / C composite material, (K / Co) ０．３ / C composite material, (Cs / Co) ０．３ / C composite material is (Ca / Co) ０．３Compared with the / C composite material, the BET specific surface area is larger and the average pore diameter d ａｖｅ was small. (Ca / Co) ０．３ The (Ca / Co) / C composite material does not have a peak in the pore size distribution in the mesopore region and is composed mainly of macropores and some mesopores. ０．３ It is believed that the BET specific surface area of ​​the (Ba / Co) composite material is smaller than that of the other materials. ０．３ The / C composite material has a peak in the pore size distribution in the mesopore region, and is composed mainly of mesopores, which is thought to be why it has a larger BET specific surface area than the other materials.

[0131] The BET specific surface areas of Co / C composite materials and Fe / C composite materials containing different types of alkali metal elements and alkaline earth metal elements are summarized in Table 1. The BET specific surface areas shown in Table 1 are the BET specific surface areas of the composite materials having the first structure after reduction treatment under the above-mentioned predetermined conditions.

[0132]

[0133] Next, in FIG. ２ and N ２ In a mixed gas atmosphere (volume ratio: H ２ / N ２ = 3, total flow rate 240 mL / min), 0.1 MPa, 485 ° C. for 4 hours, reduction treatment (Ba / Co) ０．３ / C composite material, (Ca / Co) ０．３ / C composite material, (K / Co) ０．３ / C composite material, (Sr / Co) ０．３ / C composite material, CH of Co / C composite material ４ The resulting (m / z = 16) TPR pattern is shown. Note that in the figure, (Ba / Co) ０．３ / C composite materials are called "Ba / Co" and (Ca / Co) ０．３ / C composite materials are called "Ca / Co" and (K / Co) ０．３ / C composite materials are called "K / Co" and (Sr / Co) ０．３ The Sr / C composite material is abbreviated as "Sr / Co" and the Co / C composite material is abbreviated as "Co".

[0134] According to FIG. 13, the reduced (Ba / Co) ０．３ / C composite material, (Ca / Co) ０．３ / C composite material, (K / Co) ０．３ / C composite material, (Sr / Co) ０．３ All of the / C composite materials exhibited CH ４ On the other hand, in the Co / C composite, CH ４ No peaks indicating the formation of carbon were observed, indicating that most of the carbon was lost by the reduction treatment. These results confirm that the reduced Co / C composite materials containing different types of alkali metal and alkaline earth metal elements exhibited little carbon loss due to methanation of the carbon skeleton at low temperatures below 500°C and had a relatively stable carbon skeleton that was highly resistant to methanation.

[0135] 5.3 Effect of the composition of iron-group elements and alkali-based metal elements in the composite material on ammonia production activity According to the above-mentioned experimental results, it has been confirmed that in a Co-based composite material containing Co as an iron-group element, when Ba is contained as an alkali-based metal element, higher activity can be obtained than when other alkali-based metal elements are used.

[0136] Therefore, (Ba / Co) having high ammonia production activity ０．３ The Ba / Co molar ratio was varied based on the Ba / C composite material. ０．０３ / C composite material, (Ba / Co) ０．５ The influence of the Ba and Co compositions on the ammonia production activity was investigated using the H / C composite materials. ２ and N ２ In a mixed gas atmosphere (volume ratio: H ２ / N ２ The reduction treatment was carried out under the conditions of (a) 0.1 MPa, (b) 485°C, (c) 0.1 MPa, (d) 0.1 MPa, (e) 485°C, (f) 4 hours. The results are shown in Figure 14.

[0137] As shown in FIG. 14, the ammonia production activity is (Ba / Co) ０．０３ / C composite material <(Ba / Co) ０．５ / C composite material <(Ba / Co) ０．３ / C. As mentioned above, in Co / C composite materials that do not contain BaO, the Co particles aggregate due to sintering, resulting in a decrease in ammonia generation activity. In contrast, Co-based composite materials that contain even a small amount of BaO can exhibit high ammonia generation activity. This is because BaO can suppress the aggregation of Co particles due to sintering. On the other hand, although the ammonia generation activity increases as the molar ratio of Ba to Co increases, a tendency was observed in which the ammonia generation activity decreases as the molar ratio of Ba to Co increases.

[0138] 5.4 Investigation of the reduction temperature of this composite material (Ba / Co) ０．３ The effect of reduction temperature on the activity of the (Ba / Co) / C composite material was investigated. ０．３ For the / C composite material, H ２ and N ２ In a mixed gas atmosphere (volume ratio: H ２ / N ２ The composite materials were reduced at four different temperatures (400°C, 450°C, 485°C, and 500°C) under 0.1 MPa for 4 hours, with a total flow rate of 240 mL / min. These four composite materials were then subjected to reduction treatment under four different temperatures (400°C, 450°C, 485°C, and 500°C) under a pressure of 0.1 MPa for 4 hours. ０．３ / C-400℃ composite material, (Ba / Co) ０．３ / C-450℃ composite material, (Ba / Co) ０．３ / C-485℃ composite material, (Ba / Co) ０．３ / C-500℃ composite material.

[0139] Ammonia synthesis was carried out using each composite material after the reduction treatment. In order to confirm the stability of the composite material at higher reaction temperatures, the reaction temperature was set to 300°C to 450°C and the reaction pressure was set to 1 MPa. The results are shown in Figure 15. As shown in Figure 15, the (Ba / Co) ０．３ It is found that the SiC / C composite material can be activated by reduction at low temperatures below 500°C.

[0140] More specifically, (Ba / Co) ０．３The Ba / C-485°C composite material was the most active, reaching equilibrium at a reaction temperature of 450°C. ０．３ / C-500°C composite material is (Ba / Co) ０．３ Compared to the / C-485°C composite material, the activity was slightly lower in the reaction temperature range of 300°C to 350°C, but the activity became even lower at reaction temperatures of 400°C and above. ２ According to the results of the TPR measurement, the methanation initiation temperature was high, and it is presumed that this is because a part of the carbon skeleton constituting the carbon material was graphitized due to the high reduction temperature of 500°C. ０．３ The / C-400°C composite material was the least active. ２ - According to the results of TPR measurement, (Ba / Co) reduced at other reduction temperatures ０．３ The carbon loss was larger than that of the (Ba / Co) / C composite material, which is presumed to be due to the fact that the carbon skeleton constituting the carbon material was not sufficiently stabilized due to the presence of amorphous carbon and oxygen-containing groups. ０．３ The activity of the Ba / C-450°C composite material increased linearly up to a reaction temperature of 450°C, and the Ba / Co ０．３ The activity of the / C-400°C composite material increased sharply at a reaction temperature of 450°C. This is presumably because both the composite materials reduced at the reduction treatment temperatures of 450°C and 400°C still had room for further reduction, and when the reaction temperature reached 450°C during the reaction, further reduction occurred, resulting in a rapid increase in activity.

[0141] 5.5 Examination of reduction time of this composite material (Ba / Co) ０．３ The effect of reduction time on the activity of the (Ba / Co) / C composite material was investigated. ０．３ For the / C composite material, H ２ and N ２ In a mixed gas atmosphere (volume ratio: H ２ / N ２The four composite materials were reduced at 0.1 MPa and 485°C for four different reduction times (2 h, 4 h, 8 h, and 16 h), with a total flow rate of 240 mL / min and a pressure of 0.1 MPa. ０．３ / C-2h composite material, (Ba / Co) ０．３ / C-4h composite material, (Ba / Co) ０．３ / C-8h composite material, (Ba / Co) ０．３ / C-16h composite material.

[0142] Ammonia synthesis was carried out using each composite material after the reduction treatment. In order to confirm the stability of the composite material at higher reaction temperatures, the reaction temperature was set to 300°C to 450°C and the reaction pressure was set to 1 MPa. The results are shown in Figure 16. As shown in Figure 16, the (Ba / Co) ０．３ It was confirmed that the Al / C composite material was activated within a short reduction time of 24 hours even at a low temperature of less than 500°C.

[0143] In the above-described Experimental Example 1, a precursor composed of a metal-citric acid complex containing a metal composed of a predetermined iron-group element and an alkali-based metal element and citric acid was prepared as a powder in the precursor preparation step. In contrast, in this Experimental Example 2, the precursor was prepared as a molded body, and the difference between them was confirmed.

[0144] Specifically, a powdery precursor composed of a metal-citric acid complex containing a metal composed of a predetermined iron-group element and an alkali-based metal element and citric acid was obtained in the same manner as in Experimental Example 1 (hereinafter, this will be simply referred to as precursor powder). The obtained precursor powder was then placed in a cylindrical metal mold and compacted by applying pressure from above using a hydraulic press to produce a disk-shaped compact. This compact was then crushed using a mortar and pestle and sieved using a sieve to produce precursor pellets with a diameter of 250 to 500 μm.

[0145] Next, in the same manner as in Experimental Example 1, citric acid, which was an organic compound in the obtained precursor pellets, was thermally decomposed in an inert gas atmosphere to obtain a pellet-shaped pyrolyzate.

[0146] Next, in the same manner as in Experimental Example 1, the surfaces of the iron group metal particles contained in the obtained pellet-shaped pyrolyzate were passivated to prevent rapid oxidation of the iron group metal.

[0147] As a result, a composite material in the form of pellets containing a carbon material, an iron-group element, and an alkali metal element was prepared. Specifically, the molar ratio of Cs to Fe was kept constant (0.3) (Cs / Fe). ０．３ / C<2> composite material (pellet), the molar ratio of Ba to Co was kept constant (0.3) (Ba / Co) ０．３ For comparison, a Cs / Fe composite material (pellet) was prepared in the same manner as in Experimental Example 1, with the molar ratio of Cs to Fe kept constant (0.3) (Cs / Fe). ０．３ / C<2> composite material (powder), with a constant Ba to Co molar ratio of 0.3 (Ba / Co) ０．３ A carbon / carbon composite material (powder) was prepared.

[0148] All of the composite materials prepared above were H ２ and N ２ In a mixed gas atmosphere (volume ratio: H ２ / N ２ The composite materials were then subjected to reduction treatment under the conditions of a reaction temperature of 300 to 400°C and a reaction pressure of 1.0 MPa at 0.1 MPa under a pressure of 450°C. ３ Yield and NH ３ The synthesis rate was measured, and the results are shown in Figures 17 and 18.

[0149] As shown in Figures 17 and 18, (Cs / Fe) ０．３ / C<2> composite material, and (Ba / Co) ０．３ Both the P / C composites showed better ammonia production activity in pellet form than in powder form. This is because pelletization facilitates gas diffusion and heat transfer within the composite, thereby improving the reaction activity per mass of the composite.

[0150] In this experimental example, the precursor pellets were prepared by crushing and sieving the pressure-molded body, and the pellet size was set to a diameter of 250 to 500 μm. However, the molding method and pellet size are not limited to these, and the molding method can be appropriately selected depending on the desired shape and pellet size.

[0151] The present disclosure is not limited to the above-described embodiments and experimental examples, and various modifications are possible within the scope of the gist thereof. Furthermore, the configurations shown in the above-described embodiments and experimental examples can be combined in any manner. Furthermore, the claims set forth in the scope of the claims as originally filed can be combined in any manner.

[0152] The features of the present disclosure are as follows: Item 1. A composite material having a first structure or a second structure including a carbon material, particles containing an iron group element, and a compound containing an alkali metal element, which is at least one element selected from the group consisting of alkali metal elements and alkaline earth metal elements, wherein the first structure is a structure in which a large number of particles containing the iron group element and compounds containing the alkali metal element are dispersed in a carbon skeleton constituting the carbon material, and the particles containing the iron group element include at least iron group metal particles having passivated particle surfaces, and the compounds containing the alkali metal element are present at least as oxides containing the alkali metal element and / or carbonates containing the alkali metal element, and the second structure is a structure in which a large number of particles containing the iron group element are dispersed in a carbon skeleton constituting the carbon material, and a large number of compounds containing the alkali metal element are present on the surfaces of the particles containing the iron group element, and the particles containing the iron group element include at least iron group metal particles, and the compounds containing the alkali metal element are present at least as oxides containing the alkali metal element. Item 2. The composite material according to Item 1, which is usable as at least a catalyst material for ammonia synthesis. Item 3. The composite material according to Item 1 or 2, wherein the iron group element includes at least Co, and the alkali metal element includes at least Ba. Item 4. The composite material according to Item 1 or 2, wherein the iron group element includes at least Fe, and the alkali metal element includes at least K and / or Cs. Item 5. A composite material having the first structure, wherein the iron group element includes Co, and wherein a BET specific surface area after reduction treatment under conditions of maintaining at 485°C or less for 4 hours in a hydrogen atmosphere containing 75% by volume of hydrogen gas is 30 m ２ Item 6. The composite material according to any one of Items 1 to 3, wherein the composite material has the first structure, the iron group element includes Fe, and the BET specific surface area after reduction treatment is maintained under the conditions of being held in a hydrogen atmosphere containing 75% by volume of hydrogen gas at 450°C or less for 4 hours is 50 m ２Item 7. The composite material according to any one of Items 1, 2, and 4, wherein the BET specific surface area is 30 m / g or more. ２Item 8. The composite material according to any one of Items 1 to 6, wherein the pore diameter distribution of the composite material has a peak in a mesopore region of pore diameters of 2 nm to 50 nm. Item 9. A method for producing a composite material, comprising: a precursor preparation step of preparing a precursor composed of an organometallic complex containing an iron group element, an alkali metal element which is at least one element selected from the group consisting of alkali metal elements and alkaline earth metal elements, and an organic compound; a pyrolysis step of thermally decomposing the organic compound in the precursor in an inert gas atmosphere; and a passivation step of passivating the particle surfaces of at least iron group metal particles contained in the obtained pyrolyzate. Item 10. The method for producing a composite material according to Item 9, wherein in the pyrolysis step, the organic compound is thermally decomposed in an inert gas atmosphere of nitrogen gas or argon gas at a pyrolysis temperature of 300°C to 700°C. Item 11. Item 12. The method for producing a composite material according to any one of Items 9 to 11, further comprising a reduction step of reducing the thermal decomposition product obtained after the passivation step. Item 13. The method for producing a composite material according to Item 12, further comprising: in the reduction step, the reduction is carried out in a reducing atmosphere containing hydrogen at a reduction temperature of 300°C or higher and lower than 500°C for a reduction time of 1 hour to 24 hours. Item 14. The method for producing a composite material according to any one of Items 9 to 13, further comprising: in the precursor preparation step, the precursor is prepared as a molded body. Item 15. The method for producing a composite material, further comprising: reducing the composite material according to any one of Items 1 to 8, which has the first structure, to obtain the composite material according to any one of Items 1 to 8, which has the second structure.Item 16. A method for producing ammonia, comprising the steps of: reducing the composite material having the first structure according to any one of Items 1 to 8; and then contacting the composite material with hydrogen and nitrogen; or contacting the composite material having the second structure according to any one of Items 1 to 8 with hydrogen and nitrogen.

Claims

a first structure or a second structure including a carbon material, particles including an iron-group element, and a compound including an alkali metal element, which is at least one element selected from the group consisting of alkali metal elements and alkaline earth metal elements; The first structure is The carbon material has a structure in which a large number of particles containing an iron group element and a compound containing an alkali metal element are dispersed in a carbon skeleton constituting the carbon material, and the particles containing an iron group element include at least iron group metal particles having a passivated particle surface, the compound containing an alkali metal element is present at least as an oxide containing the alkali metal element and / or a carbonate containing the alkali metal element, The second structure is a structure in which a large number of particles containing the iron group element are dispersed in a carbon skeleton constituting the carbon material, and a large number of compounds containing the alkali metal element are present and gathered on the surfaces of the particles containing the iron group element; and the particles containing an iron group element include at least iron group metal particles, the compound containing an alkali metal element is present at least as an oxide containing the alkali metal element; Composite material. 　 It can be used as a catalyst material for at least ammonia synthesis. The composite material of claim 1. 　 The iron group element includes at least Co, The alkali metal element includes at least Ba. The composite material according to claim 1 or claim 2. 　 the iron group element includes at least Fe, The alkali metal element includes at least K and / or Cs. The composite material according to claim 1 or claim 2. 　 having the first structure, The iron group element includes Co, The BET specific surface area after reduction treatment under the condition of holding for 4 hours at 485°C or less in a hydrogen atmosphere containing 75% by volume of hydrogen gas is 30 m ２ / g or more, The composite material according to claim 1 or claim 2. 　 having the first structure, The iron group element includes Fe, The BET specific surface area after reduction treatment under the condition of holding for 4 hours at 450°C or less in a hydrogen atmosphere containing 75% by volume of hydrogen gas is 50 m ２ / g or more, The composite material according to claim 1 or claim 2. 　 The second structure is provided. BET specific surface area is 30m ２ / g or more, The composite material according to claim 1 or claim 2. 　 The pore size distribution of the composite material has a peak in a mesopore region with a pore diameter of 2 nm or more and 50 nm or less. The composite material according to claim 1 or claim 2. 　 a precursor preparation step of preparing a precursor composed of an organometallic complex containing an iron group element, an alkali metal element which is at least one element selected from the group consisting of alkali metal elements and alkaline earth metal elements, and an organic compound; a thermal decomposition step of thermally decomposing the organic compound in the precursor under an inert gas atmosphere; and a passivation step of passivating the particle surfaces of at least the iron group metal particles contained in the obtained pyrolyzate. Composite material manufacturing methods. 　 In the thermal decomposition step, The thermal decomposition of the organic compound is carried out in an inert gas atmosphere of nitrogen gas or argon gas at a thermal decomposition temperature of 300° C. or higher and 700° C. or lower. A method for producing the composite material according to claim 9. the organic compound is citric acid; the organometallic complex is a metal-citrate complex containing a metal composed of the iron group element and the alkali metal element and the citric acid; A method for producing the composite material according to claim 9 or 10. 　 A reduction step of reducing the thermal decomposition product after the passivation step, A method for producing the composite material according to claim 9 or 10. 　 In the reduction step, The reduction treatment is carried out under conditions of a reducing atmosphere containing hydrogen, a reduction temperature of 300°C or higher and lower than 500°C, and a reduction time of 1 hour or higher and 24 hours or lower. A method for producing the composite material according to claim 12. 　 In the precursor preparation step, The precursor is provided as a shaped body. A method for producing the composite material according to claim 9 or 10. 　 The composite material according to claim 1 having the first structure is subjected to a reduction treatment, Obtaining the composite material of claim 1 having the second structure. Composite material manufacturing methods. 　 After subjecting the composite material having the first structure according to claim 1 to a reduction treatment, the composite material is brought into contact with hydrogen and nitrogen; or A method for producing ammonia, comprising the step of contacting hydrogen and nitrogen with the composite material according to claim 1 having the second structure.

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