Method for producing a carrier for ammonia synthesis catalyst and method for producing ammonia synthesis catalyst

Abstract

To provide a method capable of simply manufacturing an ammonia synthesis catalyst carrier including hydride containing oxide having a perovskite type structure.SOLUTION: A method for manufacturing an ammonia synthesis catalyst carrier comprises the steps of: dispersing TiH2 particles into a solution obtained by dissolving the hydroxide or nitrate of an alkali earth metal element in a solvent so that the content of the alkali earth metal element in a carrier is within a range of 1-10 mass% by metal conversion and carrying the alkali earth metal element on the surface of the TiH2 particle by removing the solvent; and obtaining the carrier consisting of the TiH2 particles including hydride containing oxide ATiO3-xHx [where in the formula, A represents the alkali earth metal element, and 0<x≤1] having a perovskite type structure and formed on the surface by calcining the TiH2 particles having the alkali earth metal element carried on the surface in an inert atmosphere or a reducing atmosphere.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a carrier for an ammonia synthesis catalyst and a method for producing an ammonia synthesis catalyst, and more specifically, to a method for producing a carrier for an ammonia synthesis catalyst comprising TiH2 particles having a perovskite-type structure and a hydride-containing oxide formed on its surface, and to a method for producing an ammonia synthesis catalyst in which a noble metal is supported on the ammonia synthesis catalyst carrier. [Background technology]

[0002] In recent years, ammonia has attracted attention as a component that can be applied to applications such as hydrogen energy carriers. While the Haber-Bosch process, using iron-based catalysts, has traditionally been used industrially to synthesize ammonia, recent research has focused on developing various types of ammonia synthesis catalysts with the aim of synthesizing ammonia under milder conditions than the Haber-Bosch process.

[0003] For example, International Publication No. 2015 / 136954 (Patent Document 1) contains hydride (H - An ammonia synthesis catalyst has been disclosed in which a perovskite-type oxyhydride powder containing ) is used as a support, and a metal or metal compound exhibiting catalytic activity for ammonia synthesis is supported on the support. However, hydride (H - When synthesizing perovskite-type oxyhydride powders containing ), the alkali metal or alkaline earth metal hydrides, which are one of the raw materials, are unstable in the atmosphere. Therefore, synthesis must be carried out in a vacuum or inert gas atmosphere, making it unsuitable for large-scale industrial production.

[0004] Furthermore, Japanese Patent Publication No. 2017-148810 (Patent Document 2) discloses a method for producing an ammonia synthesis catalyst, which includes the steps of mixing a support made of a semiconductor containing a transition element with a metal, and calcining the mixture obtained in the mixing step in the presence of air to obtain an ammonia synthesis catalyst. However, this ammonia synthesis catalyst did not contain hydride, and its ammonia synthesis catalytic activity was insufficient. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2015 / 136954 [Patent Document 2] Japanese Patent Publication No. 2017-148810 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The present invention has been made in view of the problems of the prior art described above, and aims to provide a method for easily producing a support for ammonia synthesis catalysts and a catalyst for ammonia synthesis having a hydride-containing oxide with a perovskite structure. [Means for solving the problem]

[0007] As a result of diligent research to achieve the above objective, the present inventors have discovered that a carrier for ammonia synthesis catalysts and an ammonia synthesis catalyst having a perovskite-type hydride-containing oxide can be easily produced by dispersing TiH2 particles in a solution of hydroxide or nitrate of an alkaline earth metal element in a solvent, then removing the solvent to support the alkaline earth metal element on the surface of the TiH2 particles, and then calcining the TiH2 particles with the alkaline earth metal element supported on their surface in an inert or reducing atmosphere, thereby completing the present invention.

[0008] In other words, the method for producing a carrier for ammonia synthesis catalysts of the present invention is In the middle Ba The content of the metal is within the range of 1 to 10% by mass. Ba After dispersing TiH2 particles in a solution of hydroxide or nitrate dissolved in a solvent, the solvent is removed, thereby forming the surface of the TiH2 particles. Ba The process of supporting and The aforementioned Ba By firing the TiH2 particles, which have the material supported on their surface, in an inert atmosphere or a reducing atmosphere, The aforementioned TiH 2 TiH 2 Area S of the 111 main peaks 111 Area S of the peak observed around 2θ = 31.5° with respect to . 110 The proportion [S 110 / S 111 The ratio is 0.5-20%, Ba / TiH 2 Carrier The process of obtaining This method is characterized by including [a certain element].

[0009] In the method for producing a carrier for ammonia synthesis catalyst of the present invention 、 It is preferable that the firing temperature be within the range of 300 to 600°C.

[0010] Furthermore, the method for producing the ammonia synthesis catalyst of the present invention is A step of producing an ammonia synthesis catalyst carrier by the method for producing an ammonia synthesis catalyst carrier of the present invention, The aforementioned Ba The surface of TiH2 particles on which the above is supported or Ba / TiH 2 Carrier on the surface Ru The process of supporting and This method is characterized by including [a certain element].

[0011] In the method for producing the ammonia synthesis catalyst of the present invention, Ba / TiH 2 Carrier After obtaining the TiH2 particles, Ru It is preferable to have it supported. [Effects of the Invention]

[0012] According to the present invention, it is possible to easily manufacture a support for ammonia synthesis catalysts and a catalyst for ammonia synthesis having a hydride-containing oxide with a perovskite structure. [Brief explanation of the drawing]

[0013] [Figure 1] These are scanning electron microscope images of the carriers obtained in Example 3, Example 5, Comparative Example 1, and Comparative Example 4. [Figure 2] This graph shows the powder X-ray diffraction patterns of each support obtained in Examples 1-5 and Comparative Examples 1-4. (a) is the powder X-ray diffraction pattern over the entire range of 2θ, (b) is the powder X-ray diffraction pattern around 2θ = 24°, and (c) is the powder X-ray diffraction pattern around 2θ = 31.5°. [Figure 3] These graphs show the powder X-ray diffraction patterns of each support obtained in Comparative Examples 5 to 7. (a) is the powder X-ray diffraction pattern over the entire range of 2θ, (b) is the powder X-ray diffraction pattern around 2θ = 24°, and (c) is the powder X-ray diffraction pattern around 2θ = 31.5°. [Figure 4] This graph shows the powder X-ray diffraction patterns of each support obtained in Examples 5-6 and Comparative Example 8. [Figure 5] This graph shows the powder X-ray diffraction patterns of each support obtained in Examples 7-10. [Modes for carrying out the invention]

[0014] The present invention will be described in detail below with reference to its preferred embodiments.

[0015] [Method for manufacturing a carrier for ammonia synthesis catalyst] First, the method for manufacturing a carrier for an ammonia synthesis catalyst of the present invention will be described. The method for manufacturing a carrier for an ammonia synthesis catalyst of the present invention is such that the content of the alkaline earth metal element in the carrier is within the range of 1 to 10% by mass in terms of metal. After dispersing TiH2 particles in a solution obtained by dissolving a hydroxide or nitrate of an alkaline earth metal element in a solvent, the solvent is removed to support the alkaline earth metal element on the surface of the TiH2 particles (alkaline earth metal supporting step), and the TiH2 particles having the alkaline earth metal element supported on the surface are fired in an inert atmosphere or a reducing atmosphere to obtain a carrier composed of TiH2 particles having a perovskite-type structure hydride-containing oxide ATiO 3-x H x 〔In the above formula, A represents an alkaline earth metal element, and 0 < x ≦ 1〕, and a step of obtaining a carrier composed of TiH2 particles having the perovskite-type structure hydride-containing oxide formed on the surface (firing step).

[0016] (Alkaline earth metal supporting step) The alkaline earth metal supporting step according to the present invention is a step of supporting an alkaline earth metal element on the surface of TiH2 particles. Specifically, after dispersing TiH2 particles in a solution obtained by dissolving a hydroxide or nitrate of an alkaline earth metal element in a solvent, the solvent is removed to support the alkaline earth metal element on the surface of the TiH2 particles.

[0017] In the present invention, as the alkaline earth metal source, a hydroxide or nitrate of an alkaline earth metal element is used. Thereby, the perovskite-type structure hydride-containing oxide ATiO 3-x H x is formed, and a highly active ammonia synthesis catalyst can be obtained. Further, from the viewpoint that the perovskite-type structure hydride-containing oxide ATiO 3-x H x is easily formed and a more highly active ammonia synthesis catalyst can be obtained, a hydroxide of an alkaline earth metal element is preferable.

[0018] On the other hand, when an alkaline earth metal compound other than hydroxides and nitrates of alkaline earth metal elements (for example, an acetate of an alkaline earth metal element) is used as the alkaline earth metal source, the hydride-containing oxide ATiO2 with the perovskite structure is obtained. 3-x H x This makes it difficult to generate the necessary compounds and obtain highly active ammonia synthesis catalysts.

[0019] The alkaline earth metal element is preferably Ca, Sr, or Ba, and the hydride-containing oxide ATiO2 has a perovskite-type structure. 3-x H x Ba is preferred because it facilitates the formation of a more highly active ammonia synthesis catalyst. Furthermore, one or more alkaline earth metal elements may be used individually or in combination.

[0020] Furthermore, in the present invention, the hydride-containing oxide ATiO2 of the perovskite-type structure is used. 3-x H x From the viewpoint of forming a highly active ammonia synthesis catalyst, it is preferable to use water or a mixed solvent of water and ethanol as the solvent, and the hydride-containing oxide ATiO with the perovskite structure is formed on the surface of the TiH2 particles. 3-x H x From the viewpoint of uniform formation and obtaining a more highly active ammonia synthesis catalyst, it is more preferable to use a mixed solvent of water and ethanol. Furthermore, the mixing ratio of water to ethanol in this mixed solvent is preferably in the range of 10 / 90 to 90 / 10, and more preferably in the range of 30 / 70 to 70 / 30. If the water / ethanol (volume ratio) is below the lower limit, the amount of water in the mixed solvent is small, and it may not be possible to sufficiently dissolve the hydroxide or nitrate of the alkaline earth metal element. On the other hand, if it exceeds the upper limit, the amount of ethanol in the mixed solvent is small, and the hydride-containing oxide ATiO of the perovskite-type structure may not dissolve. 3-x H x In some cases, the formation of [the substance] may not be sufficiently promoted.

[0021] In the alkaline earth metal loading process according to the present invention, first, TiH2 particles are dispersed in the solution in which the hydroxide and nitrate of the alkaline earth metal element are dissolved. There are no particular restrictions on the TiH2 particles, but the hydride-containing oxide ATiO2 with the perovskite structure formed on the surface of the TiH2 particles 3-x H x From the viewpoint of obtaining a more highly active ammonia synthesis catalyst by reducing the specific surface area, TiH2 particles with an average crystallite diameter in the range of 1 to 100 nm are preferred, and TiH2 particles with an average crystallite diameter in the range of 5 to 40 nm are more preferred.

[0022] Furthermore, in the alkaline earth metal supporting step according to the present invention, the amount of solubility (solubility concentration) of hydroxides and nitrates of the alkaline earth metal elements and the amount of dispersion (dispersion concentration) of TiH2 particles in the solvent are set so that the content of alkaline earth metal elements in the resulting ammonia synthesis catalyst carrier is within the range of 1 to 10% by mass (preferably 3 to 10% by mass, more preferably 5 to 10% by mass) in terms of metal. When the content of alkaline earth metal elements in the carrier falls below the lower limit, the hydride-containing oxide ATiO2 of the perovskite structure is formed. 3-x H x If the catalyst is not sufficiently formed, the activity of the ammonia synthesis catalyst decreases. On the other hand, if the upper limit is exceeded, a carbonate of an alkaline earth metal element is generated, which is a hydride-containing oxide ATiO2 with a perovskite-type structure. 3-x H x Because it is coated, the activity of the ammonia synthesis catalyst decreases.

[0023] In the alkaline earth metal loading step according to the present invention, next, the solvent is removed from the dispersion liquid in which the TiH2 particles are dispersed. Thereby, the alkaline earth metal element is supported on the surface of the TiH2 particles. The method for removing the solvent is not particularly limited, but a method of evaporating the solvent by heating is preferred. The heating temperature in this case is preferably 100 to 350°C, more preferably 200 to 300°C. When the heating temperature is less than the lower limit, the solvent tends not to evaporate sufficiently. On the other hand, when it exceeds the upper limit, TiH2 may react with oxygen in the air and decompose, and the hydride may be lost. The heating time is preferably 0.5 to 10 hours, more preferably 1 to 5 hours.

[0024] (Firing step) The firing step according to the present invention is a step of firing the TiH2 particles supporting the alkaline earth metal element in an inert atmosphere or a reducing atmosphere. Thereby, TiH2 reacts with the hydroxide or nitrate of the alkaline earth metal element on the surface of the TiH2 particles, and the hydride-containing oxide ATiO 3-x H x 〔In the above formula, A represents an alkaline earth metal element, and 0 < x ≤ 1〕 is easily formed, and the carrier for an ammonia synthesis catalyst of the present invention can be obtained simply.

[0025] In the firing step according to the present invention, firing is performed in an inert atmosphere or a reducing atmosphere. Examples of the reducing gas in the reducing atmosphere include hydrogen, carbon monoxide, hydrocarbons (e.g., CH4), etc. Examples of the inert gas in the inert atmosphere and the inert gas mixed with the reducing gas in the reducing atmosphere include nitrogen, argon, helium, etc. Among such firing atmospheres, from the viewpoint of suppressing the desorption of hydride from the perovskite-type structure hydride-containing oxide ATiO 3-x H x and obtaining a more highly active ammonia synthesis catalyst, a reducing atmosphere is preferred, and a reducing atmosphere containing hydrogen is more preferred.

[0026] Furthermore, in the firing process according to the present invention, the firing temperature is preferably in the range of 300 to 600°C, more preferably in the range of 300 to 500°C, and particularly preferably in the range of 300 to 400°C. If the firing temperature falls below the lower limit, the TiH2 and the hydroxide or nitrate of the alkaline earth metal element do not react sufficiently, and the hydride-containing oxide ATiO with the perovskite structure is formed on the surface of the TiH2 particles. 3-x H x Because the ammonia synthesis catalyst is not easily and sufficiently formed, the activity of the ammonia synthesis catalyst tends to decrease. On the other hand, if the upper limit is exceeded, a portion of the TiH2 is decomposed into Ti, and the activity of the ammonia synthesis catalyst tends to decrease. Furthermore, the calcination time is preferably 1 to 10 hours, and more preferably 2 to 5 hours.

[0027] In the ammonia synthesis catalyst support obtained in this manner, from the viewpoint of obtaining a more highly active ammonia synthesis catalyst, the area S of the 111 main peak of TiH2, determined based on the powder X-ray diffraction pattern, is 111 The hydride-containing oxide ATiO with the perovskite structure relative to the above-mentioned perovskite-type structure 3-x H x Area S of the 110 main peaks 110 The proportion [S 110 / S 111 It is preferable that the ratio is within the range of 0.5 to 20%, more preferably within the range of 3 to 20%, and even more preferably within the range of 10 to 20%.

[0028] Furthermore, in the ammonia synthesis catalyst support, the area S of the 111 main peak of TiH2, which is determined based on the powder X-ray diffraction pattern, 111 Area S of the 110+102 main peaks for alkaline earth metal carbonates. 110 The proportion [S 110+102 / S 111 It is preferable that ] be 4% or less, and more preferably 3% or less. 110+102 / S 111 When this value exceeds the aforementioned upper limit, the activity of the ammonia synthesis catalyst tends to decrease.

[0029] [Method for producing ammonia synthesis catalyst] Next, the method for producing the ammonia synthesis catalyst of the present invention will be described. The method for producing the ammonia synthesis catalyst of the present invention comprises a step of producing an ammonia synthesis catalyst carrier by the method for producing an ammonia synthesis catalyst carrier of the present invention (carrier manufacturing step), and the surface of TiH2 particles on which the alkaline earth metal element is supported on the surface or the hydride-containing oxide ATiO2 with a perovskite structure. 3-x H x The method includes a step of supporting a precious metal on the surface of TiH2 particles formed on the surface (precious metal supporting step).

[0030] (Precious metal loading process) The noble metal loading process according to the present invention involves the surface of TiH2 particles on which the alkaline earth metal element is supported, or the surface of the hydride-containing oxide ATiO2 with a perovskite structure. 3-x H x This is a process in which a noble metal is supported on the surface of TiH2 particles formed on the surface.

[0031] In the noble metal loading process according to the present invention, the noble metal may be loaded onto the surface of TiH2 particles on which the alkaline earth metal element obtained in the alkaline earth metal loading process is loaded (in this case, an ammonia synthesis catalyst can be obtained by subsequently performing calcination), or the perovskite-type hydride-containing oxide ATiO obtained in the calcination process 3-x H x A noble metal may be supported on the surface of TiH2 particles with a perovskite-type structure, but the hydride-containing oxide ATiO 3-x H x From the viewpoint of preventing the precious metal from becoming embedded and reducing catalytic activity, the hydride-containing oxide ATiO with the perovskite structure obtained in the calcination process 3-x H x It is preferable to support a noble metal on the surface of TiH2 particles that have a surface formed on them.

[0032] There are no particular restrictions on the method of supporting the precious metal; for example, the surface of TiH2 particles on which the alkaline earth metal element is supported on the surface of a precious metal solution prepared by dissolving a precious metal precursor in a solvent, or the surface of a hydride-containing oxide ATiO2 with a perovskite structure. 3-x H x Conventional known methods for supporting precious metals can be employed, such as a method in which the solvent is removed after dispersing TiH2 particles formed on the surface, thereby supporting the precious metal on the surface of the TiH2 particles.

[0033] The aforementioned noble metal is not particularly limited as long as it is a noble metal used in ammonia synthesis catalysts, but ruthenium (Ru) is preferred from the viewpoint of obtaining a more highly active ammonia synthesis catalyst. In addition, as a precursor of the noble metal, a complex (for example, Ru3(CO)) is preferred. 12 Examples of noble metals include ruthenium complexes such as Ru(acac)3, RuCl2(PPh3)4, RuCl2(PPh3)3, and Ru(C5H5), chlorides (e.g., RuCl3), nitrates (e.g., ruthenium nitrate), alkali metal salts of ruthenic acid (e.g., potassium ruthenate), alkali metal salts of ruthenium cyanide (e.g., potassium ruthenium cyanide), and ruthenium nitrosylnitrate. As for the solvent, there are no particular restrictions as long as it is a solvent used when supporting noble metals, and examples include tetrahydrofuran (THF), acetone, dimethyl ether, ethanol, and water.

[0034] Furthermore, in the noble metal loading step according to the present invention, the amount of noble metal loaded per 100 parts by mass of the carrier in the obtained ammonia synthesis catalyst is set to the range of 0.1 to 10 parts by mass (preferably 0.2 to 5 parts by mass, more preferably 0.5 to 3 parts by mass) by setting the amount of dissolution (dispersion concentration) of the carrier in the solvent.

[0035] In the precious metal loading process according to the present invention, the surface of TiH2 particles on which the alkaline earth metal element is supported, or the hydride-containing oxide ATiO with the perovskite structure, is then... 3-x H xThe solvent is removed from the dispersion containing TiH2 particles with the surface formed on it. This allows the noble metal to be supported on the surface of the TiH2 particles. There are no particular limitations on the method of removing the solvent, but a method of evaporating the solvent by heating is preferred. In this case, the heating temperature is preferably 0 to 100°C, and more preferably 20 to 50°C. If the heating temperature is below the lower limit, the solvent tends not to evaporate sufficiently, on the other hand, if it exceeds the upper limit, the hydride-containing oxide ATiO 3-x H x It may decompose by reacting with oxygen in the atmosphere. Furthermore, the heating time is preferably 0.5 to 5 hours, and more preferably 1 to 3 hours.

[0036] In the method for producing the ammonia synthesis catalyst of the present invention, the hydride-containing oxide ATiO2 has a perovskite-type structure. 3-x H x The ammonia synthesis catalyst, in which a noble metal is supported on the surface of TiH2 particles with a surface formed thereon, may be subjected to a drying treatment as needed. There are no particular restrictions on the drying temperature, but 50 to 150°C is preferred, and 70 to 130°C is more preferred. The drying time is preferably 6 to 48 hours, and more preferably 12 to 24 hours.

[0037] (Catalyst pretreatment process) Furthermore, the ammonia synthesis catalyst obtained according to the present invention may be subjected to heat treatment (catalyst pretreatment) in an inert atmosphere or a reducing atmosphere as needed before use. Examples of reducing gases in the reducing atmosphere include hydrogen, carbon monoxide, hydrocarbons (e.g., CH4), etc. Examples of inert gases in the inert atmosphere and inert gases mixed with reducing gases in the reducing atmosphere include nitrogen, argon, helium, etc. Among such heating atmospheres, the hydride-containing oxide ATiO2 of the perovskite structure is used. 3-x H x A reducing atmosphere is preferred, and a hydrogen-containing reducing atmosphere is more preferred, from the viewpoint that the elimination of hydride from the catalyst is suppressed, resulting in a more highly active ammonia synthesis catalyst.

[0038] Furthermore, the heating temperature in the catalyst pretreatment is preferably in the range of 300 to 600°C, more preferably in the range of 300 to 500°C, and particularly preferably in the range of 300 to 400°C. The heating time is preferably 1 to 10 hours, and more preferably 2 to 5 hours.

[0039] Furthermore, in the method for producing the ammonia synthesis catalyst of the present invention, if the noble metal loading step is performed after the alkaline earth metal loading step, this catalyst pretreatment step can be replaced with the calcination step. [Examples]

[0040] The present invention will be described more specifically below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0041] (Example 1) <Carrier preparation> To prepare a Ba solution, Ba(OH)2·8H2O was dissolved in a water / ethanol mixed solvent (volume ratio: 3 / 2) so that the Ba content in the support was 1.6% by mass in terms of metal. TiH2 particles (manufactured by Aldrich, average crystallite size: 40 nm) were added to the Ba solution and stirred for 10 minutes. The resulting dispersion was heated on a hot plate at 230°C for 2 hours to evaporate the solvent, and the resulting powder was calcined at 350°C for 3 hours under a 10% H2 / 90% N2 flow to obtain a Ba / TiH2 support in which Ba was supported on TiH2 particles.

[0042] <Catalyst preparation> The amount of Ru supported per 100 parts by mass of the carrier is 1 part by mass of Ru3(CO) 12 The Ru solution prepared by dissolving in tetrahydrofuran was mixed with the support material and stirred for 5 hours. The resulting dispersion was heated at 27°C for 2 hours to evaporate the solvent, and the resulting powder was dried at 80°C for 18 hours to obtain a Ru-Ba / TiH2 catalyst in which Ru was supported on the support material.

[0043] (Example 2) A Ba / TiH2 support was prepared in the same manner as in Example 1, except that the amount of Ba(OH)2·8H2O was changed so that the Ba content in the support was 2.4% by mass in terms of metal, and a Ru-Ba / TiH2 catalyst was obtained.

[0044] (Example 3) A Ba / TiH2 support was prepared in the same manner as in Example 1, except that the amount of Ba(OH)2·8H2O was changed so that the Ba content in the support was 4.0% by mass in terms of metal, and a Ru-Ba / TiH2 catalyst was obtained.

[0045] (Example 4) A Ba / TiH2 support was prepared in the same manner as in Example 1, except that the amount of Ba(OH)2·8H2O was changed so that the Ba content in the support was 5.7% by mass in terms of metal, and a Ru-Ba / TiH2 catalyst was obtained.

[0046] (Example 5) A Ba / TiH2 support was prepared in the same manner as in Example 1, except that the amount of Ba(OH)2·8H2O was changed so that the Ba content in the support was 8.2% by mass in terms of metal equivalent, and a Ru-Ba / TiH2 catalyst was obtained.

[0047] (Example 6) A Ba / TiH2 support was prepared in the same manner as in Example 5, except that Ba(NO3)2 was used instead of Ba(OH)2·8H2O, and a Ru-Ba / TiH2 catalyst was obtained.

[0048] (Example 7) A Ba / TiH2 support was prepared in the same manner as in Example 5, except that only water was used instead of the water / ethanol mixed solvent, and a Ru-Ba / TiH2 catalyst was obtained.

[0049] (Example 8) A Ba / TiH2 support was prepared in the same manner as in Example 5, except that TiH2 particles with an average crystallite size of 90 nm (manufactured by Kojun Chemical Laboratory Co., Ltd.) were used instead of TiH2 particles with an average crystallite size of 40 nm, and a Ru-Ba / TiH2 catalyst was obtained.

[0050] (Example 9) A Ru-Ba / TiH2 catalyst was obtained in the same manner as in Example 5, except that the Ba / TiH2 support was prepared by calcining under a 100% N2 flow instead of a 10% H2 / 90% N2 flow.

[0051] (Example 10) A Ru-Ba / TiH2 catalyst was obtained in the same manner as in Example 5, except that the calcination temperature was changed to 550°C to prepare the Ba / TiH2 support.

[0052] (Comparative Example 1) A TiH2 support was prepared in the same manner as in Example 1, except that Ba(OH)2·8H2O was not used, and a Ru-TiH2 catalyst was obtained.

[0053] (Comparative Example 2) A Ba / TiH2 support was prepared in the same manner as in Example 1, except that the amount of Ba(OH)2·8H2O was changed so that the Ba content in the support was 0.8% by mass in terms of metal, and a Ru-Ba / TiH2 catalyst was obtained.

[0054] (Comparative Example 3) A Ba / TiH2 support was prepared in the same manner as in Example 1, except that the amount of Ba(OH)2·8H2O was changed so that the Ba content in the support was 10.7% by mass in terms of metal, and a Ru-Ba / TiH2 catalyst was obtained.

[0055] (Comparative Example 4) A Ba / TiH2 support was prepared in the same manner as in Example 1, except that the amount of Ba(OH)2·8H2O was changed so that the Ba content in the support was 12.4% by mass in terms of metal, and a Ru-Ba / TiH2 catalyst was obtained.

[0056] (Comparative Example 5) A TiO2 support was prepared in the same manner as in Example 1, except that TiO2 particles (manufactured by Aldrich Corporation) were used instead of TiH2 particles (manufactured by Aldrich Corporation, average crystallite size: 40 nm), and Ba(OH)2·8H2O was not used. Furthermore, a Ru-TiO2 catalyst was obtained.

[0057] (Comparative Example 6) A Ba / TiO2 support was prepared in the same manner as in Example 3, except that TiO2 particles (manufactured by Aldrich) were used instead of TiH2 particles (manufactured by Aldrich, average crystallite size: 40 nm), and a Ru-Ba / TiO2 catalyst was obtained.

[0058] (Comparative Example 7) A Ba / TiO2 support was prepared in the same manner as in Example 5, except that TiO2 particles (manufactured by Aldrich) were used instead of TiH2 particles (manufactured by Aldrich, average crystallite size: 40 nm), and a Ru-Ba / TiO2 catalyst was obtained.

[0059] (Comparative Example 8) A Ba / TiH2 support was prepared in the same manner as in Example 5, except that Ba(OCOCH3)2 was used instead of Ba(OH)2·8H2O, and a Ru-Ba / TiH2 catalyst was obtained.

[0060] <Scanning electron microscope observation> Each support obtained in the examples and comparative examples was observed using a scanning electron microscope (SEM). Figure 1 shows SEM images of the supports obtained in Example 3, Example 5, Comparative Example 1, and Comparative Example 4.

[0061] <Powder X-ray diffraction measurement> The X-ray diffraction patterns of each support obtained in the examples and comparative examples were measured using a powder X-ray diffractometer. The results are shown in Figures 2 to 5. Note that in the X-ray diffraction patterns shown in Figures 2 to 5, the peak observed around 2θ = 31.5° is BaTiO 3-x H x The peak originates from [source], and the peak observed around 2θ=24° originates from BaCO3.

[0062] Furthermore, based on the X-ray diffraction patterns of each obtained support, the area S of the 111 main peak of TiH2 was determined. 111 BaLiO 3-x H x Area S of the 110 main peaks 110 The proportion [S 110 / S 111〕and the area S of the 111 main peak of TiH2 111 The area S of the 110 + 102 main peaks of BaCO3 relative to 110+102 The ratio [S 110+102 / S 111 〕was determined, and the abundance ratios of BaTiO 3-x [[ID=M10]]H x and BaCO3 relative to TiH2 were quantified, and the results are shown in Table 1.

[0063] <NH3 synthesis> 0.200 g of the obtained catalyst was charged into a reaction tube and installed in a fixed-bed flow-type reactor. While supplying a mixed gas of hydrogen and nitrogen (75 vol% H2 / 25 vol% N2) to this catalyst at a flow rate of 80 ml / min and a pressure of 0.1 MPa, first, the catalyst was heated at 400 °C for 2 hours for pretreatment, and then the temperature was lowered to 350 °C to start the ammonia synthesis reaction. One hour after the start of the synthesis reaction, the ammonia concentration in the catalyst effluent gas was measured using an infrared spectrometer installed at the outlet of the reactor, and the ammonia synthesis rate per 1 g of the catalyst was determined. The results are shown in Table 1.

[0064]

Table 1

[0065] As is clear from the results shown in Fig. 1, the TiH2 support obtained in Comparative Example 1 was found to be particles on the order of several μm.

[0066] On the other hand, in the Ba / TiH2 supports obtained in Examples 3 and 5, as shown in Fig. 1, nanoparticles on the order of 100 nm were formed on the surface of the TiH2 particles. In particular, in the Ba / TiH2 support obtained in Example 5, it was confirmed that the entire surface of the TiH2 particles was covered with nanoparticles on the order of 100 nm. Further, as shown in Fig. 2, in the powder X-ray diffraction spectra of the Ba / TiH2 supports obtained in Examples 1 to 5, BaTiO 3-x H xA peak derived from it (near 2θ = 31.5°) was observed. From this result, in the Ba / TiH₂ carrier obtained in Example 5, it was found that the surface of the TiH₂ particles was covered with BaTiO 3-x H x nanoparticles at the 100 nm level. Therefore, it was found that the Ba / TiH₂ carrier obtained in Example 5 has a core-shell structure with TiH₂ particles as the core and BaTiO 3-x H x as the shell.

[0067] On the other hand, in the Ba / TiH₂ carrier obtained in Comparative Example 4, as shown in Fig. 1, it was confirmed that columnar crystals were formed on the surface of the TiH₂ particles in addition to nanoparticles at the 100 nm level. Further, as shown in Fig. 2, in the powder X-ray diffraction spectrum of the Ba / TiH₂ carrier obtained in Comparative Example 4, a peak derived from BaCO₃ (near 2θ = 24°) was observed. From this result, it is considered that the columnar crystals formed on the surface of the TiH₂ particles of the Ba / TiH₂ carrier obtained in Comparative Example 4 are BaCO₃.

[0068] As shown in Table 1, for Ru-Ba / TiH₂ catalysts (Examples 1 to 5 and Comparative Examples 1 to 4) prepared using the same TiH₂ particles (average crystallite size: 40 nm), Ba salt (Ba(OH)₂·8H₂O) and solvent (water / ethanol mixed solvent), in an identical firing atmosphere (10% H₂ / 90% N₂) and firing temperature (350 °C), when the Ba content was 8.2 mass% or less, as the Ba content increased, S 110 / S 111 increased and the NH₃ synthesis rate also improved (Examples 1 to 5 and Comparative Examples 1 to 2). On the other hand, when the Ba content was 10.7 mass% or more, as the Ba content increased, both S 110 / S 111 and the NH₃ synthesis rate decreased (Comparative Examples 3 to 4). From these results, it is considered that the formation of BaTiO 3-x H x contributes to the improvement of NH₃ synthesis activity.

[0069] Also, as shown in Table 1, S 110+102 / S111 For the case of 111 , when the Ba content rate was 4.0 mass% or less, it was 0% (Examples 1 to 3 and Comparative Examples 1 to 2). However, when the Ba content rate became 5.7 mass% or more, as the Ba content rate increased, S 110+102 / S 111 also increased (Examples 4 to 5 and Comparative Examples 3 to 4). In particular, the Ru-Ba / TiH2 catalyst obtained in Comparative Example 3 had the same S 110 / S 111 as that of the Ru-Ba / TiH2 catalyst obtained in Example 5. However, compared with the Ru-Ba / TiH2 catalyst obtained in Example 5, S 110+102 / S 111 was large and the NH3 synthesis rate decreased. From these results, in the Ru-Ba / TiH2 catalyst obtained in Comparative Example 3, it is considered that the NH3 synthesis rate decreased because BaCO3 with low NH3 synthesis activity covered BaTiO 3-x H x .

[0070] As shown in Table 1, in the Ru-Ba / TiO2 catalysts (Comparative Examples 5 to 7) prepared using TiO2 particles instead of TiH2 particles, as the Ba content rate increased, the NH3 synthesis rate improved. However, the NH3 synthesis rate of the Ru-Ba / TiO2 catalyst (Ba content rate: 8.2 mass%) obtained in Comparative Example 7 was about 17% of that of the Ru-Ba / TiH2 catalyst with the same Ba content rate (Example 5). Also, as shown in FIG. 3, in the powder X-ray diffraction spectra of the Ba / TiO2 carriers obtained in Comparative Examples 5 to 7, peaks (near 2θ = 31.5°) derived from BaTiO 3-x H x were not observed. From these results, it was found that the formation of BaTiO 3-x H x is necessary for the improvement of NH3 synthesis activity, and the presence of TiH2 containing hydride is indispensable for the formation of BaTiO 3-x H x .

[0071] Furthermore, as shown in Table 1, when Ba(NO3)2 (Example 6) or Ba(OCOCH3)2 (Comparative Example 8) were used as the Ba salt, the NH3 synthesis rate decreased to 31% (Example 6) and 3% (Comparative Example 8) compared to when Ba(OH)2·8H2O was used (Example 5). Also, as shown in Table 1, the Ba / TiH2 support obtained in Example 6 showed a lower S content compared to the Ba / TiH2 support obtained in Example 5. 110 / S 111 The percentage was 14%, and in the Ba / TiH2 support obtained in Comparative Example 8, as shown in Figure 4, BaTiO 3-x H x No peak originating from (around 2θ=31.5°) was observed. These results suggest that BaTiO is necessary for improving NH3 synthesis activity. 3-x H x The generation of BaTiO is required. 3-x H x It was found that the presence of TiH2 containing hydride is essential for the formation of BaTiO 3-x H x This suggests that the hydroxide state of Ba is necessary for its formation, and it was found that Ba(OH)2·8H2O is particularly suitable as a Ba salt.

[0072] Furthermore, when water alone was used as the solvent (Example 7), when TiH2 particles with an average crystallite size of 90 nm were used (Example 8), and when calcination was performed under 100% N2N2 flow (Example 9), as shown in Figure 5, BaTiO 3-x H x A peak originating from (around 2θ=31.5°) was observed, and as shown in Table 1, the S content was equivalent to that obtained when a water / ethanol mixed solvent was used as the solvent, TiH2 particles with an average crystallite size of 40 nm were used, and calcination was performed under a 10% H2 / 90% N2 flow (Example 5). 110 / S 111 Although it had the properties of BaTiO, the NH3 synthesis rate decreased. This is because, in Example 7, since the solvent does not contain ethanol, BaTiO was formed on the surface of the TiH2 particles. 3-x H x In Example 8, the formation was not uniform, and BaTiO 3-x Hx The specific surface area of ​​the material decreased, and in Example 9, because it was fired in an atmosphere that did not contain H2, BaTiO 3-x H x This is presumed to be due to the partial detachment of hydride. Furthermore, when calcined at 550°C (Example 10), the NH3 synthesis rate decreased compared to when calcined at 350°C (Example 5), as shown in Table 1. This is because, in Example 10, S 110 / S 111 The size of the particles was reduced, which is thought to be due to the decomposition of some of the TiH2 into Ti during firing at 550°C. From these results, it was found that in the process of supporting Ba on the surface of TiH2 particles, it is preferable to use a solvent containing ethanol and TiH2 particles with an average crystallite diameter of 50 nm or less, and to fire them at a temperature of 300 to 400°C in an atmosphere containing H2. [Industrial applicability]

[0073] As described above, the present invention makes it possible to easily obtain a support for an ammonia synthesis catalyst having a hydride-containing oxide with a perovskite structure. Therefore, the method for producing an ammonia synthesis catalyst of the present invention is useful as a method for easily producing a highly active ammonia synthesis catalyst because the method for producing the support for the ammonia synthesis catalyst is simple.

Claims

1. A solution of Ba hydroxide or nitrate dissolved in a solvent is prepared so that the Ba content in the carrier is within the range of 1 to 10% by mass in terms of metal, and TiH ２ After dispersing the particles, the solvent is removed, thereby reducing the TiH ２ A step of supporting the Ba on the surface of the particles, The TiH on which the Ba is supported on its surface ２ A step to obtain a Ba / TiH2 support in which Ba is supported on TiH2 particles by firing the particles in an inert atmosphere or a reducing atmosphere, wherein the ratio of the area of ​​the peak S110 observed around 2θ = 31.5° to the area S111 of the main peak of TiH2 [S110 / S111], determined based on the powder X-ray diffraction pattern, is 0.5 to 20%. A method for producing a carrier for an ammonia synthesis catalyst, characterized by containing the following:

2. A method for producing a carrier for an ammonia synthesis catalyst according to claim 1, characterized in that the firing temperature is within the range of 300 to 600°C.

3. A step of producing a carrier for an ammonia synthesis catalyst by the method of claim 1 or 2, TiH with the aforementioned Ba supported on its surface ２ A step of supporting Ru on the surface of the particles or on the surface of the Ba / TiH2 carrier. A method for producing an ammonia synthesis catalyst, characterized by containing [the specified ingredient].

4. After obtaining the Ba / TiH2 carrier, the TiH ２ A method for producing an ammonia synthesis catalyst according to claim 3, characterized in that Ru is supported on the surface of the particles.

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