Ammonia synthesis materials and ammonia production systems

Abstract

To provide an ammonia synthesis material that does not contain noble metals or rare earths, or can suppress the amount of these used, and can synthesize ammonia at a low temperature of 400°C or less.SOLUTION: The ammonia synthesis material 10 contains an ordered alloy containing Fe and Ni in the surface layer part 11 constituting the surface 10A of the ammonia synthesis material 10.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an ammonia synthesis material used in the synthesis of ammonia by the reaction of nitrogen and hydrogen. , Nitrogen The present invention relates to an ammonia production system for producing ammonia by reacting oxygen with hydrogen. [Background technology]

[0002] Patent Document 1 discloses an ammonia synthesis catalyst made of iron-based alloy flakes containing vanadium, which can replace the Haber-Bosch process catalyst that synthesizes ammonia by directly reacting nitrogen and hydrogen at high temperatures of 400°C to 600°C. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-53606 Summary of the Invention [Problem to be solved by the invention]

[0004] However, if the ammonia synthesis temperature is high, the energy consumption during ammonia production becomes large and the ammonia production process becomes complicated. For this reason, it is desirable that the ammonia synthesis temperature be low, at 400°C or less.

[0005] Furthermore, if the ammonia synthesis material used to synthesize ammonia is expensive, the cost of producing ammonia will increase. Therefore, it is desirable that the ammonia synthesis material be inexpensive by not containing precious metals or rare earths, or by using only small amounts of these metals.

[0006] The ammonia synthesis material is a material that promotes the ammonia synthesis reaction, and includes catalysts that do not change themselves before and after the ammonia synthesis reaction, and materials that change themselves before and after the ammonia synthesis reaction.

[0007] In view of the above, the present invention provides an ammonia synthesis material that does not contain precious metals or rare earths or that can minimize the amount of precious metals or rare earths used, and that can synthesize ammonia at low temperatures of 400°C or less. ,oh The objective of this invention is to provide an ammonia production system capable of synthesizing ammonia at low temperatures of 400°C or less. [Means for solving the problem]

[0008] To achieve the above object, the invention described in claim 1 is an ammonia synthesis material used for synthesizing ammonia by reacting nitrogen and hydrogen, and includes an ordered alloy containing Fe and Ni. This makes it possible to provide an ammonia synthesis material that does not contain precious metals or rare earths, or that can minimize the amount of precious metals or rare earths used, and that enables ammonia synthesis at low temperatures of 400°C or less.

[0010] Also, claims 5 The invention described in the above is an ammonia production system for producing ammonia by reacting nitrogen and hydrogen, and includes a reaction vessel in which ammonia is synthesized by reacting nitrogen and hydrogen, and a reaction vessel disposed inside the reaction vessel, as claimed in claims 1 to 5. 4 and the ammonia synthesis material according to any one of the above. This enables ammonia synthesis at a low temperature of 400°C or less. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram showing a cross-sectional structure of an ammonia synthesis material according to an embodiment of the present invention. FIG. [Figure 2] 1 is a schematic diagram showing a cross-sectional structure of an ammonia synthesis material according to an embodiment of the present invention. FIG. [Figure 3] FIG. 1 is a schematic diagram showing the lattice structure of an FeNi ordered alloy. [Figure 4] FIG. 1 is a schematic diagram showing the lattice structure of FeNiN, an ordered FeNi nitride. [Figure 5]1 is a schematic diagram showing the lattice structure of (FeNi)2N of FeNi ordered nitride. [Figure 6] FIG. 1 is a schematic diagram showing a face-centered cubic lattice. [Figure 7] FIG. 1 is a schematic diagram showing the arrangement of Fe and Ni for each degree of order S ranging from S=0 to S=1. [Figure 8A] FIG. 1 is a diagram showing the calculation results of the partial electronic density of states of the Fe orbital of an FeNi ordered alloy. [Figure 8B] FIG. 10 is a diagram showing the calculation results of the partial electronic density of states of the Fe orbital of an FeNi disordered alloy. [Figure 9] FIG. 1 shows the calculation results of the partial electronic density of states of the Fe orbital of an FeNi ordered alloy, an ordered nitride (FeNi) 2 N, and an ordered nitride FeNiN. [Figure 10] 1 is a diagram showing the detected positions and diffraction intensities of diffraction peaks representing each crystal plane in an X-ray diffraction pattern of FeNiN with an order degree of 1.0 at an X-ray wavelength of 0.1744 nm. [Figure 11] 1 is a diagram showing the detected positions and diffraction intensities of diffraction peaks representing each crystal plane in an X-ray diffraction pattern of (FeNi) 2 N with an order degree of 1.0 at an X-ray wavelength of 0.1744 nm. [Figure 12] 1 is a diagram showing the detected positions and diffraction intensities of diffraction peaks representing each crystal plane in an X-ray diffraction pattern of L10-FeNi with an order degree of 1.0 at an X-ray wavelength of 0.1744 nm. [Figure 13] 1 is an X-ray diffraction pattern of a sample of Example 1. [Figure 14] FIG. 1 is a graph showing the relationship between the diffraction intensity ratio at an X-ray wavelength of 0.1744 nm and the degree of order S of FeNiN. [Figure 15] 1 is an X-ray diffraction pattern of a sample of Example 2. [Figure 16] 1 is an X-ray diffraction pattern of a sample of Example 3. [Figure 17] 1 is an X-ray diffraction pattern of a sample of Comparative Example 2. [Figure 18] 1 shows X-ray diffraction patterns of the samples of Example 3 and Comparative Example 2 in the range of 20° to 45°. [Figure 19] FIG. 1 is a graph showing the relationship between the diffraction intensity ratio at an X-ray wavelength of 0.1744 nm and the degree of order S of FeNi. [Figure 20] FIG. 1 is a diagram showing the measurement results of the ion current of mass number 17 at each temperature in the ammonia synthesis evaluation test of Examples 1 to 3 and Comparative Examples 1 and 2. [Figure 21] FIG. 10 is a graph showing the measurement results of the amount of ammonia produced at each temperature in the ammonia synthesis evaluation test of Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In each drawing, the same or equivalent parts are designated by the same reference numerals.

[0013] [Ammonia synthesis materials] Ammonia synthesis materials are materials used to synthesize ammonia by reacting nitrogen and hydrogen. The ammonia synthesis material contains an ordered alloy containing Fe and Ni in the surface portion of the ammonia synthesis material. The ordered alloy containing Fe and Ni has an ordered structure of Fe and Ni. Examples of ordered alloys containing Fe and Ni include FeNi ordered alloys and FeNi ordered nitrides. Hereinafter, FeNi ordered nitrides will also be referred to as ordered nitrides. The ammonia synthesis material is in the form of particles or films, as shown in the examples of Figures 1 and 2, respectively.

[0014] 1, the ammonia synthesis material 10 has a granular shape and includes a surface layer portion 11 that constitutes a surface 10A of the ammonia synthesis material 10, and a core portion 12 that is covered by the surface layer portion 11. The entire surface of the core portion 12 is covered by the surface layer portion 11.

[0015] 2, the ammonia synthesis material 20 is in a state of being fixed in contact with the surface 30A of the base material 30, and has a surface layer portion 21 that constitutes the surface 20A of the ammonia synthesis material 20, and a core portion 22 that is covered by the surface layer portion 21. A part of the surface of the core portion 22 is in contact with the surface 30A of the base material 30, and another part of the surface of the core portion 22 is covered by the surface layer portion 21.

[0016] 1 and 2, the surface layer portions 11 and 21 contain an ordered alloy containing Fe and Ni. The core portions 12 and 22 may contain an ordered alloy containing Fe and Ni, or may be made of a material that does not contain an ordered alloy containing Fe and Ni. For example, the surface layer portions 11 and 21 may be made of an ordered alloy containing Fe and Ni, and the core portions 12 and 22 may be made of an FeNi disordered alloy.

[0017] The ammonia synthesis reaction occurs on the surface of the ammonia synthesis material. Therefore, it is important that the surface portion of the ammonia synthesis material contains an ordered alloy containing Fe and Ni. Note that the entire ammonia synthesis material may contain an ordered alloy containing Fe and Ni.

[0018] The ammonia synthesis material is used as particles having a particle size of 0.3 to 200 nm, or as a compact formed into a shape other than particles.

[0019] An FeNi ordered alloy is an FeNi alloy with a regular arrangement of Fe and Ni atoms. Examples of FeNi ordered alloys include FeNi, Fe3Ni, and FeNi3. FeNi ordered alloys include those with an L10 ordered structure and those with an L12 ordered structure. Both Fe3Ni and FeNi3 have an L12 ordered structure. FeNi ordered alloys, particularly those with an L10 ordered structure, exhibit a high ammonia synthesis efficiency. This L10 ordered structure is based on a face-centered cubic lattice. As shown in Figure 3, Ni layers with multiple Ni atoms aligned along the (001) plane and Fe layers with multiple Fe atoms aligned along the (001) plane are alternately stacked along the

[0001] axis. The

[0001] axis is perpendicular to the (001) plane. The Ni atoms in the Ni layers are located at the vertices and the center of the faces of the face-centered cubic lattice unit cell. The Fe in the Fe layer is present at the center of the face of the unit cell of the face-centered cubic lattice.

[0020] Ordered nitrides are FeNi nitrides in which the atomic arrangement of Fe and Ni is regular. Ordered nitrides include FeNiN and (FeNi)2N.

[0021] As shown in Figures 4 and 5, both the ordered nitrides FeNiN and (FeNi)2N have an ordered structure of Fe and Ni. Like the L10-type ordered structure, this ordered structure is based on a face-centered cubic lattice, and is composed of Ni layers with multiple Ni atoms in the direction along the (001) plane and Fe layers with multiple Fe atoms in the direction along the (001) plane, alternately stacked in the

[0001] axis direction. The Ni atoms in the Ni layers are located at the vertices and the center of the faces of the unit cell of the face-centered cubic lattice. The Fe atoms in the Fe layers are located at the center of the faces of the unit cell of the face-centered cubic lattice.

[0022] As shown in Figure 4, in the ordered nitride FeNiN, N exists in the Fe layer at the center of the edges of the face-centered cubic unit cell and at the center of the unit cell. As shown in Figure 5, in the ordered nitride (FeNi)2N, N exists only at the center of the face-centered cubic unit cell in the Fe layer.

[0023] The ammonia synthesis material may contain only one of the ordered FeNi alloy, the ordered nitride FeNiN, and the ordered nitride (FeNi) 2 N, or may contain two or more of them.

[0024] The degree of order S of each of the FeNi ordered alloy and the ordered nitride may be greater than 0, preferably greater than 0.5, and more preferably greater than 0.9. The degree of order S indicates the degree of order in the atomic arrangement of Fe and Ni. If the degree of order S is greater than 0, it is believed that ammonia synthesis is possible.

[0025] In the face-centered cubic lattice shown in Figure 6, the uppermost layer in the direction of the

[0001] axis of the face-centered cubic lattice is the I site, and the intermediate layer located between the uppermost layer and the lowermost layer is the II site. In this case, if the ratio of metal A existing in the I site is x and the ratio of metal B existing in the I site is 1-x, then the ratio of metal A and metal B existing in the I site is A. x B 1-x Similarly, if the ratio of metal B existing in the II site is x and the ratio of metal A existing in the II site is 1-x, then the ratio of metal A and metal B existing in the II site is A 1-x B x where x satisfies 0.5≦x≦1. In this case, the degree of order S is defined as S=2x−1.

[0026] If metal A is Ni and metal B is Fe, with Ni represented in white and Fe represented in black, the degree of order S can be expressed as shown in Figure 7, ranging from S=0 to S=1. Note that all white indicates 100% Ni and 0% Fe, and all black indicates 0% Ni and 100% Fe. Also, half white and half black indicates 50% Ni and 50% Fe. Note that in FeNi ordered nitrides, N exists in the II site.

[0027] The above ammonia synthesis material does not contain precious metals or rare earths, and is therefore inexpensive. Note that the above ammonia synthesis material may contain precious metals or rare earths. Even in this case, the above ammonia synthesis material allows the amount of these elements used to be kept low, making it possible to provide the ammonia synthesis material at low cost. Furthermore, as will be described later, the above ammonia synthesis material allows ammonia synthesis at low temperatures of 400°C or less.

[0028] [Method for producing ammonia synthesis material] The ordered nitride FeNiN is obtained by nitriding an FeNi disordered alloy, in which the atomic arrangement of Fe and Ni is random and not regular, by performing a nitriding treatment on the FeNi. The incorporation of N into the FeNi disordered alloy creates regularity in the atomic arrangement of Fe and Ni. FeNi disordered alloys manufactured by thermal plasma methods, flame spraying, coprecipitation, or the like are used. The nitriding treatment involves heat treatment in an atmosphere containing N, such as an NH3 gas atmosphere, at a predetermined temperature, such as 200 to 500°C, for a predetermined time.

[0029] An FeNi ordered alloy can be obtained by denitrifying the ordered nitride FeNiN to remove all of the N contained in the FeNiN. The denitrification treatment involves heat treatment in an atmosphere capable of denitrification, such as an H2 gas atmosphere, at a predetermined temperature, such as 100 to 400°C, for a predetermined time.

[0030] The ordered nitride (FeNi)2N can be obtained by lowering the temperature or shortening the time of the denitrification treatment compared to the denitrification treatment used to produce an FeNi ordered alloy, so that some of the N remains.

[0031] [Ammonia production system] The ammonia production system includes a reaction vessel in which ammonia is synthesized by a reaction between nitrogen and hydrogen, and the above-mentioned ammonia synthesis material disposed inside the reaction vessel. The ammonia synthesis material is disposed in a state supported by support members. Examples of a supported state include a state in which the ammonia synthesis material is disposed on the support members, a state in which the ammonia synthesis material is sandwiched between support members, a state in which the ammonia synthesis material is housed in the support members, etc.

[0032] The ammonia production system also includes a gas supply unit that supplies a raw material gas containing nitrogen and hydrogen to the inside of the reaction vessel, and a heating unit that heats the inside of the reaction vessel.

[0033] [Method for producing ammonia] An ammonia production method is carried out using the ammonia production system described above. The ammonia production method includes a synthesis step of supplying nitrogen and hydrogen to the inside of the reaction vessel in which the ammonia synthesis material is disposed, and synthesizing ammonia by reacting the nitrogen and hydrogen.

[0034] In this step, the inside of the reaction vessel is heated by a heating unit. The heating temperature at this time, i.e., the ammonia synthesis temperature, is a low temperature of 100°C or higher and 400°C or lower, and can also be lower than 350°C.

[0035] In this step, the synthesis pressure of ammonia, which is the pressure inside the reaction vessel, is atmospheric pressure (i.e., 1 atmosphere = 0.1 MPa). The synthesis pressure may be other pressures greater than 0 and equal to or less than 10 atmospheres (i.e., 1 MPa). Other pressures include pressures lower than atmospheric pressure.

[0036] The ammonia synthesis reaction is presumed to occur as follows: When nitrogen and hydrogen are supplied to the inside of a reaction vessel, electrons are supplied from the ammonia synthesis material to nitrogen molecules near the surface of the ammonia synthesis material, making it easier to break the triple bonds of the nitrogen molecules. The broken nitrogen atoms are adsorbed onto the surface of the synthesis material. Similarly, hydrogen molecules are also easily broken, and the broken hydrogen atoms are adsorbed onto the surface of the ammonia synthesis material. The adsorbed nitrogen atoms react with hydrogen atoms to synthesize ammonia.

[0037] When an FeNi ordered alloy is used as an ammonia synthesis material, the FeNi ordered alloy remains unchanged before and after the ammonia synthesis reaction. The FeNi ordered alloy functions as a catalyst to promote the ammonia synthesis reaction.

[0038] On the other hand, when an FeNiN ordered nitride is used as an ammonia synthesis material, the FeNiN ordered nitride not only promotes the above-described ammonia synthesis reaction, but also causes nitrogen atoms in the FeNiN ordered nitride to react with hydrogen atoms, thereby synthesizing ammonia.

[0039] Here, the reason why the ammonia synthesis material of this embodiment can be used to synthesize ammonia by reacting nitrogen with hydrogen will be explained.

[0040] Figures 8A and 8B show the calculation results of the partial electronic density of states of the Fe orbitals of an FeNi ordered alloy and an FeNi disordered alloy, respectively, obtained from the literature (Li-Yun Tian et al. Scientific Reports 10 14766 (2020)). In each of Figures 8A and 8B, the upper half shows the partial electronic density of states of the up-spin side, and the lower half shows the partial electronic density of states of the down-spin side. As can be seen by comparing Figures 8A and 8B, in the area surrounded by the dashed ellipse in Figure 8A, the partial electronic density of states of the down-spin side is steep, and electron localization is high.

[0041] When FeNi alloying is performed, there is electron donation from Ni (10 valence electrons) to Fe (8 valence electrons). Furthermore, when the FeNi alloy is ordered, as shown in the area enclosed by the dashed ellipse in Figure 8A, the partial electronic density of states of the Fe d orbital, especially on the down-spin side, increases, and the localization of electrons increases. For this reason, the FeNi ordered alloy has a π-like structure in the triple bond of the nitrogen molecule. * It is easy to donate electrons to antibonding orbitals and break the nitrogen triple bond. Therefore, it is thought that using an FeNi ordered alloy makes it easier to synthesize ammonia.

[0042] Figure 9 shows the calculation results for the partial electronic density of states of the Fe orbitals of an L10 FeNi ordered alloy, an ordered nitride (FeNi)2N, and an ordered nitride FeNiN. The calculations were performed using the abinitio quantum mechanics program CASTEP, based on density functional theory included in Materials Studio 2019 (manufactured by Daikin Industries, Ltd.), under the following calculation conditions: Method: plane-wave pseudootentials, Functional: GGA-PBE, Energy cutoff: 570 eV, Pseudootentials: OTFG Ultrasoft, k-point set: 6 × 6 × 7 (for FeNiN), 7 × 7 × 7 (for (FeNi)2N, FeNi ordered alloy). As FeNi becomes more nitrided, the peak position of the partial electronic density of states on the down-spin side tends to shift to lower energy, increasing the electron density near the Fermi level. This increase in electron density near the Fermi level is due to the π-like structure of the nitrogen triple bond. * This means that the nitrogen triple bond is more easily broken in ordered nitrides than in FeNi ordered alloys. In addition, the high electron density near the Fermi level means that the nitride itself is unstable. The nitrogen state in ordered nitrides is more likely to become unstable, making it easier for the nitrogen atoms in the nitrides to react with hydrogen atoms and synthesize ammonia. For these reasons, using ordered nitrides makes it possible to synthesize ammonia, and ammonia synthesis can be achieved at lower temperatures than with FeNi ordered alloys. [Example]

[0043] (Examples 1 to 3 and Comparative Examples 1 and 2) The methods and results of ammonia synthesis evaluation tests conducted by the present inventors for each of the samples of Examples 1 to 3 and Comparative Examples 1 and 2 will be described.

[0044] [Sample preparation] The sample of Comparative Example 1 is a powder of FeN reagent (manufactured by Kojundo Chemical Co., Ltd., purity 99.9%). The sample of Comparative Example 2 is a powder of FeNi disordered alloy (i.e., Al-FeNi), which is synthesized by a thermal plasma method and then reduced with hydrogen.

[0045] The sample of Example 1 is a powder containing ordered nitrides FeNiN and (FeNi)N. The sample of Example 1 was obtained by subjecting an FeNi disordered alloy synthesized by the same thermal plasma method as the sample of Comparative Example 2 to a nitriding treatment by heating in an NH gas atmosphere at 325°C for 30 hours.

[0046] The sample of Example 2 is a powder containing ordered nitrides FeNiN, (FeNi)N, and an FeNi ordered alloy. The sample of Example 2 was obtained by subjecting a sample synthesized in the same manner as the sample of Example 1 to denitrification treatment in a H gas atmosphere at 200°C for 1 minute.

[0047] The sample of Example 3 is an FeNi ordered alloy having an L10 ordered structure. The sample of Example 3 was obtained by subjecting a sample synthesized in the same manner as the sample of Example 1 to a denitrification treatment at 250°C for 8 hours in a H2 gas atmosphere.

[0048] The FeNi ratio of each sample of Examples 1 to 3 and Comparative Example 2 was analyzed using a scanning electron microscope energy dispersive X-ray fluorescence analyzer (i.e., SEM-EDS). As a result, the FeNi ratio of each sample was Fe:Ni=49.7:50.3 at%, with an error of ±0.3 at%.

[0049] [Evaluation of the crystal phase and order of the sample] The inventors performed crystal structure analysis using anomalous X-ray scattering with synchrotron X-rays of 7.11 keV and 0.1744 nm wavelength for each of the samples of Examples 1 to 3 and Comparative Example 2 to evaluate the crystalline phase and the presence or absence of ordering. When X-rays under the above conditions were used, the detected positions (2θ [deg.]) and diffraction intensities of diffraction peaks representing each crystal plane in the X-ray diffraction pattern of FeNiN with an ordering degree of S = 1.0 were found to be as shown in FIG. 10 . Furthermore, the detected positions (2θ [deg.]) and diffraction intensities of diffraction peaks representing each crystal plane in the X-ray diffraction pattern of (FeNi)2N with an ordering degree of S = 1.0 were found to be as shown in FIG. 11 . Furthermore, the detected positions (2θ [deg.]) and diffraction intensities of diffraction peaks representing each crystal plane in the X-ray diffraction pattern of FeNi having an L10-type ordered structure with an ordering degree of S = 1.0 were found to be as shown in FIG. 12 .

[0050] From the X-ray diffraction pattern of the sample of Example 1 shown in FIG. 13, it was confirmed that the sample of Example 1 contained 98.7 wt % of FeNiN and 1.3 wt % of (FeNi)2N.

[0051] When X-rays under the above conditions are used, it has been found that in the X-ray diffraction pattern of FeNiN having an ordered structure of Fe and Ni, a diffraction peak representing FeNiN110 is detected in the range of 2θ = 35.9 ± 0.5°. The diffraction peak representing FeNiN110 represents the long-period regularity of Fe and Ni. The presence of this diffraction peak representing FeNiN110 was confirmed in the X-ray diffraction pattern of the sample of Example 1.

[0052] Furthermore, a specific relationship has been found between the degree of order (S) of FeNiN and the diffraction intensity ratio, which is the ratio of the diffraction intensity of FeNiN110 to that of FeNiN111 in the X-ray diffraction pattern of FeNiN, as shown in Figure 14. This specific relationship was determined from simulation results of the diffraction intensity for each order state using RIETAN-FP, as described in the literature (F. Izumi and K. Momma, Solid State Phenom., 130, 15-20 (2007)). The anomalous scattering terms f' and f'' of the atomic scattering factors are −5.3363 and 0.471 for Fe, −1.7208 and 0.6404 for Ni, and 0.0368 and 0.0237 for N, respectively. The X-ray diffraction pattern of FeNiN with a degree of order (S) of 0 also shows a diffraction peak of FeNiN110, with a diffraction intensity ratio of 2.5%. Therefore, when the diffraction intensity ratio is greater than 2.5%, it can be determined that the degree of order S is greater than 0 and that the material has an ordered structure of Fe and Ni (ie, FeNi order).

[0053] The diffraction intensity ratio calculated from the X-ray diffraction pattern of the sample of Example 1 was 13.17. The degree of ordering S of FeNiN of the sample of Example 1 was calculated using this calculated diffraction intensity ratio and the relationship shown in Fig. 14, and was found to be S = 0.97. Therefore, the sample of Example 1 has an ordered structure of Fe and Ni.

[0054] From the X-ray diffraction pattern of the sample of Example 2 shown in FIG. 15, it was confirmed that the sample of Example 2 contained 96.4 wt% FeNiN, 3.3 wt% (FeNi)N, and 0.3 wt% FeNi. Furthermore, when the diffraction intensity ratio was calculated from the X-ray diffraction pattern of the sample of Example 2, the diffraction intensity ratio was 12.58. Using this calculated diffraction intensity ratio and the relationship shown in FIG. 14, the degree of ordering S of the FeNiN of the sample of Example 2 was calculated to be S = 0.93. Therefore, the FeNiN of the sample of Example 2 has an ordered structure of Fe and Ni.

[0055] The sample of Example 1 and the sample of Example 2 contained only trace amounts of (FeNi)2N, so the degree of ordering S could not be determined. However, these samples were obtained by nitriding a disordered FeNi alloy, so it is presumed that (FeNi)2N has an ordered structure of Fe and Ni. Furthermore, the sample of Example 2 contained only a trace amount of FeNi, so it was not possible to confirm the diffraction peak representing L10-FeNi001, which will be described later. However, the sample of Example 2 was obtained by nitriding a disordered FeNi alloy, so it is presumed that the FeNi contained in the sample of Example 2 has an ordered L10 structure.

[0056] The X-ray diffraction pattern of the sample of Example 3 shown in Figure 16 and the X-ray diffraction pattern of the sample of Comparative Example 2 shown in Figure 17 contain peaks representing an FeNi alloy. It has been found that, when X-rays under the above conditions are used, in an X-ray diffraction pattern in which FeNi has an L10-type ordered structure, a diffraction peak representing L10-FeNi001 is detected in the range of 2θ = 28.2 ± 0.5°, and a diffraction peak representing L10-FeNi110 is detected in the range of 2θ = 40.3 ± 0.5°. The presence or absence of these diffraction peaks can be used to determine the presence or absence of an L10-type ordered structure (i.e., FeNi ordering).

[0057] It was confirmed that the X-ray diffraction pattern of the sample of Example 3 shown in FIGS. 16 and 18 contains diffraction peaks representing L10-FeNi001 and L10-FeNi110. Therefore, the sample of Example 3 has an L10-type ordered structure. On the other hand, the X-ray diffraction pattern of the sample of Comparative Example 2 shown in FIGS. 17 and 18 does not contain diffraction peaks representing L10-FeNi001 and L10-FeNi110. Therefore, the sample of Comparative Example 2 does not have an L10-type ordered structure.

[0058] Furthermore, it has been found that there is a predetermined relationship shown in FIG. 19 between the degree of order (S) of FeNi and the diffraction intensity ratio, which is the ratio of the diffraction intensity of L10-FeNi001 to the diffraction intensity of L10-FeNi111 in the X-ray diffraction pattern of FeNi. This predetermined relationship, similar to the relationship between the degree of order (S) of FeNi and the diffraction intensity ratio described above, was determined from the simulation results of the diffraction intensity for each order state using RIETAN-FP. This diffraction intensity ratio was calculated from the X-ray diffraction pattern of the sample of Example 3, and was found to be 1.35. Using this calculated diffraction intensity ratio and the relationship shown in FIG. 19, the degree of order (S) of FeNi in the sample of Example 3 was calculated to be S = 0.57.

[0059] [Ammonia synthesis evaluation test] The test equipment used in the evaluation test was a TG-MS device, which is a thermogravimetric measuring device with a quadrupole mass spectrometer attached. The heating furnace of the test equipment corresponds to the reaction vessel.

[0060] A platinum-rhodium pan containing a predetermined amount of sample was placed inside the heating furnace of the test equipment. Then, with a source gas containing nitrogen gas and hydrogen gas continuously flowing through the furnace, the interior of the furnace was maintained at 40°C for 60 minutes, and then the temperature was increased to 500°C at a rate of 10°C / min. The predetermined amount was 3.0±0.3 mg. The ratio of nitrogen gas to hydrogen gas in the source gas was N2:H2 = 96.2 mol%:3.8 mol%. The internal pressure of the heating furnace was atmospheric pressure.

[0061] To investigate the temperature at which ammonia generation begins during this temperature rise, the ion current of mass number 17, which indicates ammonia generation, was measured using a quadrupole mass spectrometer. The ion current measurement results shown in Figure 20 are the results after subtracting the ion current value at 100°C in each sample measurement as the background current value. The background current value for each was 9.6 x 10 -12 A, error 8.5×10 -13From this result, the ammonia generation starting temperature was determined. In the ion current measurement results shown in Figure 20, the temperature at which an increase in the ion current value of 10% or more compared to the background was observed was defined as the ammonia generation starting temperature. The ammonia generation starting temperature for each sample was as shown in Table 1.

[0062] [Table 1]

[0063] In the sample of Comparative Example 2, no increase in ion current value was observed, and ammonia was not produced. It was confirmed that the ammonia production starting temperature was lower than 400°C in all of the samples of Examples 1, 2, and 3. It was confirmed that the ammonia production starting temperature of the samples of Examples 1 and 2 was lower than 220°C, and that the ammonia production starting temperature of the samples of Examples 1 and 2 was lower than that of the sample of Example 3. It was confirmed that the ammonia production starting temperature of the sample of Example 2 was lower than that of the sample of Example 1.

[0064] Example 4 The inventors synthesized FeNi by coprecipitation and nitrided it in the same manner as the sample in Example 1 to produce FeNiN powder. The FeNi ratio was analyzed using SEM-EDS, revealing a Fe:Ni ratio of 48.3:51.7 at%, with an error of ±0.6 at%. 100 mg of this FeNiN powder was weighed and loaded into an Inconel reaction tube reactor with an inner diameter of 7 mm. The FeNiN powder was subjected to a denitrification treatment at 200°C for 6 hours in a 100% hydrogen gas atmosphere, yielding a sample made of an FeNi ordered alloy with an L10 ordered structure.

[0065] Using this sample, an ammonia synthesis evaluation test was conducted under conditions of 10 atmospheres, N2: 30 sccm, H2: 90 sccm (SV72 L / h·g). The gas before and after the reaction was then passed through 1 mM sulfuric acid water, and the amount of ammonia produced was quantified by calculating the change in conductivity measured with a conductivity meter before and after the reaction. The temperature measurement points were 200°C, 250°C, 300°C, 350°C, and 400°C. After waiting 10 minutes at each temperature, conductivity measurements were conducted for 40 minutes to determine the amount of ammonia produced.

[0066] Figure 21 shows the test results. Ammonia generation occurred at 200°C and reached a maximum at 250°C. The amount of ammonia generation decreased at 300°C and 350°C, and then increased again at 400°C. The decrease in ammonia generation at 300°C and 350°C is thought to be due to a decrease in the degree of order, as the FeNi order-disorder transition temperature is 320°C. The increase in ammonia generation at 400°C is thought to be due to the low atomic diffusion coefficient of FeNi, which maintains the ordered phase to some extent and activity, even though 400°C is above the order-disorder transition temperature. Furthermore, the activation of nitrogen molecular motion due to heat may have made it easier for nitrogen molecular bonds to break.

[0067] As described above, it was confirmed that the use of an FeNi ordered alloy material makes it possible to generate ammonia at low temperatures below 400°C, even under a pressure of 10 atmospheres.

[0068] The present invention is not limited to the above-described embodiments and examples, and can be modified as appropriate within the scope of the claims, and also includes various modified examples and modifications within the equivalent scope. [Explanation of symbols]

[0069] 10, 20 Ammonia synthesis materials 11, 21 Surface layer 12, 22 Core section 30 Base material

Claims

1. An ammonia synthesis material used in the synthesis of ammonia by the reaction of nitrogen and hydrogen, An ordered alloy containing Fe and Ni, The ordered alloy containing Fe and Ni has a lattice structure based on a face-centered cubic lattice, and has an L1 structure in which Ni layers in which a plurality of Ni atoms exist in the direction along the (001) plane and Fe layers in which a plurality of Fe atoms exist in the direction along the (001) plane are alternately stacked in the [001] axis direction. ０ The ammonia synthesis material is an ordered FeNi alloy having an ordered structure of the type.

2. An ammonia synthesis material used in the synthesis of ammonia by the reaction of nitrogen and hydrogen, comprising: An ordered alloy containing Fe and Ni, The ordered alloy containing Fe and Ni has an ordered structure of Fe and Ni, and has a lattice structure based on a face-centered cubic lattice, in which Ni layers in which a plurality of Ni atoms exist in a direction along the (001) plane and Fe layers in which a plurality of Fe atoms exist in a direction along the (001) plane are alternately stacked in the [001] axial direction, and N exists in the Fe layers. This is an ammonia synthesis material.

3. An ammonia synthesis material used in the synthesis of ammonia by the reaction of nitrogen and hydrogen, comprising: An ordered alloy containing Fe and Ni, The ordered alloy containing Fe and Ni has a lattice structure based on a face-centered cubic lattice, in which Ni layers in which a plurality of Ni atoms exist in a direction along the (001) plane and Fe layers in which a plurality of Fe atoms exist in a direction along the (001) plane are alternately stacked in the [001] axis direction. ０ and FeNiN and (FeNi) which are FeNi ordered nitrides having an ordered structure of Fe and Ni and a lattice structure based on a face-centered cubic lattice, in which Ni layers in which a plurality of Ni atoms exist in a direction along the (001) plane and Fe layers in which a plurality of Fe atoms exist in a direction along the (001) plane are alternately stacked in the [001] axis direction, and N exists in the Fe layers. ２ N.

4. 4. The ammonia synthesis material according to claim 1, wherein the ordered alloy containing Fe and Ni is present in a portion constituting a surface of the ammonia synthesis material.

5. An ammonia production system for producing ammonia by reacting nitrogen and hydrogen, a reaction vessel in which ammonia is synthesized by reacting nitrogen and hydrogen; and the ammonia synthesis material according to any one of claims 1 to 4, disposed inside the reaction vessel.

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