Ammonia synthesis catalyst

Abstract

To provide a complex oxide that can improve ammonia synthetic activity.SOLUTION: A supported metal material in which metal particles M are supported on a complex oxide consisting of an oxide of a metal element L and an oxide of a metal element N, where (A) the complex oxide is shown by a composition of the following general formula (1), and is the following (a) to (d), LnN1-n (1), (a) the metal element L is selected from the group consisting of Ba and Sr, (b) the metal element N is selected from the group consisting of Mg and Be, (c) n is 0.001 or more and 0.300 or less, (d) the oxide of the metal element L and the oxide of the metal element N do not form a solid solution, oxide particles of the metal element L are deposited on the surface of oxide particles of the metal element N, (B) the metal particles M are one kind or more selected from the group consisting of Fe, Co, Ni, (C) the metal particles M are supported on the oxide of the metal element L deposited on the surface of the oxide of the metal element N, and the oxide particles of the metal element L are deposited on the surface of the metal particles M.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a composite oxide useful for the synthesis of ammonia under mild conditions, a metal support using the same, an ammonia synthesis catalyst, a method for producing the composite oxide, a method for producing the metal support, and a method for producing ammonia.

Background Art

[0002] Ammonia is an important raw material in the modern chemical industry. More than 80% of the produced ammonia is used to manufacture chemical fertilizers for crops. Furthermore, ammonia has attracted much attention as a carrier of energy and hydrogen. The reasons are (1) its high hydrogen content (17.6 wt%), (2) its high energy density (12.8 GJ / m 3 ), and (3) no carbon dioxide is generated when decomposed to produce hydrogen. If it becomes possible to efficiently produce ammonia from renewable energy such as solar energy and wind power, global problems related to energy and food crises will be alleviated.

[0003] Currently, the Haber-Bosch process used to produce ammonia consumes a large amount of energy, accounting for about 1-2% of the world's energy consumption. In this method, about 60% of the consumed energy is recovered and secured as the enthalpy of ammonia. However, most of the remaining energy is lost during the production of hydrogen from natural gas, the synthesis of ammonia, and the separation of gases. Since ammonia synthesis by the Haber-Bosch process is carried out at very high temperatures (>450 °C) and pressures (>20 MPa), there is a need to reduce the large amount of energy used in this method. To suppress global energy consumption, a catalyst capable of synthesizing ammonia under milder conditions (lower temperature and pressure) than the iron-based catalyst used in the Haber-Bosch process is required.

[0004] In recent years, a method for producing ammonia under low-pressure conditions of about 1 MPa (10 atmospheres) has been known. The ruthenium catalyst used for ammonia production is generally supported on a carrier. For example, Patent Document 1 discloses that when a rare earth oxide is used as a carrier for supporting ruthenium, the amount of ruthenium used can be reduced and the reaction temperature can be lowered. However, in the ammonia production method of Patent Document 1, the ammonia yield when producing ammonia under lower-pressure conditions was not sufficient. Therefore, the present inventors reported the development of a ruthenium catalyst using La 0.5 Ce 0.5 O 1.75 as a carrier, which exhibits excellent properties even under low-pressure conditions (Non-Patent Document 4).

[0005] Furthermore, the present inventors have developed binary composite oxides composed of two metal elements and metal-supported materials (catalysts for ammonia synthesis) supporting catalysts such as ruthenium thereon (Patent Document 5, Patent Document 6). As catalysts for ammonia synthesis using the binary composite oxides (carriers) disclosed in this document, the following are disclosed.

[0006] Ru / Ce 0.85 La 0.15 O x _(500°C, 600°C, 650°C, 700°C) reduction, Ru / Ce 0.67 La 0.33 O x _(500°C, 600°C, 650°C, 700°C) reduction, Ru / Ce 0.33 La 0.67 O x _(500°C, 600°C, 650°C, 700°C) reduction, Ru / Ce 0.15 La 0.85 O x _(500°C, 600°C, 650°C, 700°C) reduction, Ru / Ce 0.5 La 0.5 O x _(500°C, 650°C, 800°C) reduction, Ru / Ce 0.5 Zr 0.5 O x _700°C reduction, Ru / Ce 0.5 Pr 0.5O x _(Reduction at 500 °C, 600 °C, 650 °C, 700 °C, 800 °C), Ru / La 0.5 Pr 0.5 O x _(Reduction at 450 °C, 500 °C, 600 °C, 650 °C, 700 °C), Ru / Ba 0.1 La 0.9 O x _(Reduction at 500 °C, 700 °C, 800 °C, 900 °C), Ru / Ba 0.1 Ce 0.9 O x _(Reduction at 500 °C, 700 °C), Co / Ba 0.05 La 0.95 O x _(Reduction at 500 °C, 600 °C, 700 °C, 800 °C), Co / Ba 0.01 La 0.99 O x _Reduction at 700 °C, Co / Ba 0.03 La 0.97 O x _Reduction at 700 °C, Co / Ba 0.1 La 0.9 O x _Reduction at 700 °C.

[0007] Furthermore, this document also describes 8.4 wt% Ba / 4.5 wt% Ru / MgO reduced at 500 °C and 700 °C (Examples 80 and 81). These oxides were obtained by impregnating a Ru solution on the carrier MgO, followed by calcination, and further loading Ba using Ba(OH)₂·8H₂O.

[0008] In addition to Patent Document 1 and Non-Patent Document 4, ammonia synthesis catalysts with ruthenium supported on various rare earth oxide carriers are disclosed in various patent documents. Representative ones include Patent Documents 2 - 4 and Non-Patent Documents 1 - 3. Patent Document 2 and Patent Document 4 disclose lanthanoid oxides, Patent Document 3 discloses praseodymium oxide, and Non-Patent Document 1 discloses Ce oxide as carriers. Non-Patent Document 2 discloses a Ru / CeO₂-La₂O₃-based catalyst prepared by coprecipitating the hydroxides of Ru, Ce, and La, followed by drying and activation.

[0009] In the prior art documents including Patent Documents 1, 2, 4 and Non-Patent Document 1, it is described that in the ruthenium catalyst used for ammonia synthesis, Ru exists as particles on the surface of the carrier. When it exists as particles, there are reports that its average diameter is larger than 5 nm (see Non-Patent Document 2), and there are also reports that it is less than 2 nm (Non-Patent Document 4). Further, in Patent Document 3, it is described that Ru has an eggshell structure. On the other hand, regarding the carrier, in Non-Patent Document 3, when evaluating the ammonia synthesis activity of a Y(La)-M-O (M is Ca, Sr, Ba) catalyst supporting Ru, for the carrier oxide before supporting Ru, it is described that the specific surface area of the carrier oxide with a calcination temperature of 450 °C is large, and the specific surface area of the carrier with the calcination temperature raised to 650 °C decreased. In view of the fact that Ru is expensive, ammonia synthesis catalysts supporting transition metal compounds other than Ru, such as Co, on the carrier have also been proposed (for example, see Non-Patent Document 5 and Non-Patent Document 6). However, in Non-Patent Document 6, Co-BaO / C in which cobalt is supported on barium oxide is disclosed, but the ammonia synthesis activity was low. Further, in Non-Patent Document 5, calcium amide is used instead of an oxide (Co / Ba-Ca(NH2)2)), but the ammonia yield at 1 MPa of the catalyst supporting the Co was inferior to that of the catalyst supporting Ru.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Non-Patent Literature

[0011]

Non-Patent Literature 1

Non-Patent Literature 2

Non-Patent Literature 3

Non-Patent Literature 4

Non-Patent Literature 5

Non-Patent Literature 6

Summary of the Invention

Problems to be Solved by the Invention

[0012] Generally, a high synthesis activity is required for the synthesis catalyst. Regarding the catalysts for ammonia synthesis under development, those with high activity that enable higher yields are still in demand. Among binary catalysts, for example, Co / BaLaOx Catalysts such as this had a sufficiently high ammonia synthesis activity, but further improvement in activity was desired.

[0013] An object of the present invention is to provide a composite oxide that exhibits higher ammonia synthesis activity than conventional binary composite oxides containing rare earths, such as BaLaOx, when, for example, cobalt is supported thereon. Another object of the present invention is to provide a metal support and a catalyst for ammonia synthesis that exhibit such high ammonia synthesis activity. Still another object of the present invention is to provide a method for producing such a composite oxide or metal support and a method for producing ammonia.

Means for Solving the Problems

[0014] In order to solve the above problems, the present inventors have found that by using a combination of two types of Group 2 elements having specific properties as metal oxides constituting a composite oxide, the ammonia synthesis activity is high when used as a catalyst, and have made the following invention.

[0015] 〔1〕 A composite oxide comprising an oxide of a metal element L and an oxide of a metal element N, having a composition represented by the following general formula (1) and characterized by the following (a) to (d) L n N 1-n (1) (a) The metal element L is an oxide of an element selected from any of the following (i) to (iii), (i) A Group 1 element, (ii) A Group 2 element, (iii) A Group 1 element and a Group 2 element, (b) The metal element N consists of a Group 1 or Group 2 element other than the metal element L, (c) The n is 0.001 or more and 0.300 or less, (d) The oxide of the metal element L and the oxide of the metal element N do not form a solid solution, and the oxide particles of the metal element L are deposited on the surface of the oxide particles of the metal element N.

[0016] 〔2〕(a) The metal element L represents a metal element that is a strongly basic element with a value of the partial negative charge (-δ OA ) of oxygen in the oxide state being 0.56 or more and 0.70 or less, (b) The metal element N represents a metal element that is a weakly basic element with a value of the partial negative charge (-δ OB ) of oxygen in the oxide state being 0.35 or more and 0.55 or less. The composite oxide according to 〔1〕.

[0017] 〔3〕 A binary composite oxide composed of the metal element A contained in the metal element L and the metal element B contained in the metal element N, wherein the general formula (1) is represented by the composition of the following general formula (2), and the following (a) to (d) are satisfied. The composite oxide according to 〔1〕 or 〔2〕 A n B 1-n (2) (a) The metal element A represents a Group 2 element that is a strongly basic element with a value of the partial negative charge (-δ OA ) of oxygen in the oxide state being 0.56 or more and 0.70 or less, (b) The metal element B represents a Group 2 element that is a weakly basic element with a value of the partial negative charge (-δ OB ) of oxygen in the oxide state being 0.35 or more and 0.55 or less, (c) The n is 0.001 or more and 0.300 or less, (d) The oxide of the metal element A and the oxide of the metal element B do not form a solid solution, and the oxide particles of the metal element A are deposited on the surface of the oxide particles of the metal element B.

[0018] 〔4〕 A composite oxide composed of the oxide of the metal element L and the oxide of the metal element N, which is represented by the composition of the following general formula (3), and the following (a) to (d) are satisfied. The composite oxide L n N 1-n O x (3) (a) The metal element L is an oxide of an element selected from any of the following (i) to (iii), (i) A Group 1 element, (ii) A Group 2 element, (iii) Group 1 elements and Group 2 elements, (b) The metal element N consists of a Group 1 element or a Group 2 element other than the metal element L, (c) The n is 0.001 or more and 0.300 or less, (d) The oxide of the metal element L and the oxide of the metal element N do not form a solid solution, and the oxide particles of the metal element L are deposited on the surface of the oxide particles of the metal element N.

[0019] [5] (a) The metal element L represents a metal element that is a strongly basic element with a value of the partial negative charge (-δ OA ) of oxygen in the oxide state being 0.56 or more and 0.70 or less, (b) The metal element N represents a metal element that is a weakly basic element with a value of the partial negative charge (-δ OB ) of oxygen in the oxide state being 0.35 or more and 0.55 or less. The composite oxide according to [4].

[0020] [6] A binary composite oxide composed of the metal element A contained in the metal element L and the metal element B contained in the metal element N, wherein the general formula (3) is represented by the composition of the following general formula (4), and the following (a) to (d): The composite oxide according to [4] or [5], characterized in that A n B 1-n O x (4) (a) The metal element A represents a Group 2 element that is a strongly basic element with a value of the partial negative charge (-δ OA ) of oxygen in the oxide state being 0.56 or more and 0.70 or less, (b) The metal element B represents a Group 2 element that is a weakly basic element with a value of the partial negative charge (-δ OB ) of oxygen in the oxide state being 0.35 or more and 0.55 or less, (c) The n is 0.001 or more and 0.300 or less, (d) The oxide of the metal element A and the oxide of the metal element B do not form a solid solution, and the oxide particles of the metal element A are deposited on the surface of the oxide particles of the metal element B, (e) The composite oxide according to [4] and [5], wherein x is the number of oxygen atoms necessary for the composite oxide to maintain electrical neutrality.

[0021] [7] Ba n Mg 1-n O x (where 0.001 ≦ n ≦ 0.300), the composite oxide according to [1] to [6].

[0022] [8] Ba n Mg 1-n O x (where 0.01 ≦ n ≦ 0.10), the composite oxide according to [7].

[0023] [9] The composite oxide according to [7] or [8], wherein the amount of carbonate contained in the composite oxide is 10 mol% or less based on Ba.

[0024]

[10] A metal-supported material, wherein at least one type of metal particle M selected from the group consisting of cobalt, iron, and nickel is supported on the composite oxide according to [1] to [9].

[0025] [10-1] A composition comprising the metal particle M and the composite oxide according to [1] to [3], wherein each element is recognized as an aggregate of particles, and a metal element L having a particle size of 10% or less of the particle size of the metal particle M is observed to be distributed on the particles of the metal particle M, between the metal particle M and the metal oxide N, and on the metal oxide N. [10-2] The metal-supported material according to [10-1], wherein the distribution of the metal element L particles is observed to be uniformly distributed. [10-3] The metal-supported material according to [10-1] to [10-2], wherein the particles of the metal element L are also distributed in the intermediate layer between the metal particle M and the metal element N. [10-4] The metal-supported material according to [10-1] to [10-3], wherein the composite oxide is the composite oxide according to [6], the metal element A is selected from the metal element L, and the metal element B is selected from the metal element N.

[0026] 〔11〕 The metal-supported material according to

[10] , wherein the metal particles M are supported on the oxide of the metal element L deposited on the surface of the oxide of the metal element N, and oxide particles of the metal element L are deposited on the surface of the metal particles M.

[0027] 〔12〕 The metal-supported material according to

[10] , wherein oxide particles of the metal element N are distributed between the oxide particles of the metal element L and the metal particles M. 〔12-1〕 The metal-supported material according to

[11] or

[12] , wherein the composite oxide is the composite oxide according to [6], the metal element A is selected from the metal element L, and the metal element B is selected from the metal element N.

[0028] 〔13〕 The metal-supported material according to

[10] , wherein the metal particles M are cobalt particles.

[0029] 〔14〕 A catalyst for ammonia synthesis, characterized in that the metal-supported material according to

[10] is used.

[0030] 〔15〕 A method for producing the metal-supported material according to

[10] , comprising the following steps (a) to (d). (a) An impregnation step of impregnating an N-precursor containing the metal element N with an L-precursor containing the metal element L; (b) A composite oxide firing step of firing the mixture at a temperature of 500 °C or higher to obtain a carrier made of a composite oxide; (c) A loading step of impregnating the composite oxide with a precursor of a compound containing the metal particles M to obtain a loaded carrier; (d) A supported material firing step of firing the loaded carrier at a temperature of 400 °C or higher.

[0031] 〔15-1〕 A method for producing the metal-supported material according to

[15] , wherein the metal element A is selected from the metal element L, the metal element B is selected from the metal element N, and the following steps (a) to (d) are included. (a) An impregnation step of impregnating a B-precursor containing the metal element B with an A-precursor solution containing the metal element A; (b) A composite oxide firing step of firing the mixture at a temperature of 500 °C or higher to obtain a carrier made of a composite oxide; (c) An impregnation step of impregnating the composite oxide with a precursor solution of a compound containing the metal particles M to obtain an impregnated carrier; (d) A fired product firing step of firing the impregnated carrier at a temperature of 400 °C or higher. 〔15-2〕 The method for producing a metal-supported material according to 〔15〕 or 〔15-1〕, characterized in that the step (b) is carried out in air. 〔15-3〕 The method for producing a metal-supported material according to 〔15〕 or 〔15-1〕, characterized in that the step (d) is carried out in argon.

[0032] 〔16〕 The method for producing a metal-supported material according to any one of 〔15〕 to 〔15-3〕, further comprising a step (e). (e) A reduction step of firing the metal-supported material obtained in (d) at 500 °C or higher in the presence of hydrogen.

[0033] 〔17〕 A method for producing ammonia by bringing hydrogen and nitrogen into contact with a catalyst, characterized in that the catalyst is the ammonia synthesis catalyst described in 〔14〕.

Advantages of the Invention

[0034] According to the present invention, for example, when cobalt is supported, it is possible to provide a composite oxide showing higher ammonia synthesis activity than a conventional binary composite oxide containing rare earths, for example, Ru / BaLaOx. Further, according to the present invention, it is possible to provide a metal-supported material and an ammonia synthesis catalyst showing such high ammonia synthesis activity. Furthermore, according to the present invention, it is possible to provide a method for producing such a composite oxide and a metal-supported material, and a method for producing ammonia.

Brief Description of the Drawings

[0035]

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DETAILED DESCRIPTION OF THE INVENTION

[0036] <Composite oxide> The composite oxide of the present invention is a composite oxide composed of an oxide of a metal element L and an oxide of a metal element N, and is represented by the composition of the following general formula (1) and has the following (a) to (d). A composite oxide characterized by L n N 1-n (1) is. Here, the metal element L is an oxide of an element selected from any of the following (i) to (iii). (i) Group 1 element, (ii) Group 2 element (iii) Group 1 element and Group 2 element. In the present invention, the "metal element L" includes not only one type of element (Group 1 element or Group 2 element) but also two types of elements (Group 1 element and Group 2 element). The Group 1 element as the metal element L is a metal so-called alkali metal, and examples include Li, Na, K, Rb, and Cs. The Group 2 element is a metal so-called alkaline earth metal, and examples include Be, Mg, Ca, Sr, Ba, and Ra. In addition, as the metal element L, the Group 1 element and the Group 2 element may be used simultaneously. The selection of these elements is made in consideration of basicity. Furthermore, the partial negative charge described later can be calculated and used. When using a Group 1 metal and a Group 2 metal, the ratio is preferably in the range of 0.1:1.9 to 1.9:0.1, more preferably in the range of 0.8:1.2 to 1.2:0.8, and particularly preferably 1:1. It can be used with. From the point that the ammonia synthesis activity of the metal support described later is high, the metal element L is preferably a Group 2 element alone or a composite oxide of a Group 1 element and a Group 2 element.

[0037] As the metal element N, an oxide of a Group 1 or Group 2 element other than the metal element L is used. The metal element L is used in a small amount relative to the metal element N. The metal element N relative to the total amount of the metal element L is usually used in an amount of 0.001 or more and 0.300 or less, preferably 0.01 or more and 0.100 or less. The ratio of the metal element L affects the morphology during catalyst production and also affects the catalytic activity. The oxide of the metal element L and the oxide of the metal element N do not form a solid solution, and the metal element L is observed on the metal element N. In this specification, this state may be referred to as the metal element L or the oxide of the metal element L being deposited on the metal element N or the oxide of the metal element N.

[0038] In the composite oxide used in the present invention, when the metal element A is selected from the metal element L and the metal element B is selected from the metal element L and this is a binary composite oxide, the general formula (1) is represented by the following general formula (2). A n B 1-n (2) (a) The metal element A is an alkaline earth metal which is a Group 2 element, and is a strongly basic element having a value of the partial negative charge (-δ OA ) of oxygen in the state of the oxide being 0.56 or more and 0.70 or less. (b) The metal element B is an alkaline earth metal other than the metal element A, and represents a Group 2 element which is a weakly basic element having a value of the partial negative charge (-δ OB ) of oxygen in the state of the oxide being 0.35 or more and 0.55 or less. (c) The addition ratio of the metal element A relative to the whole is 0.001 or more and 0.300 or less, and in this range, the morphology has a good influence on the catalytic activity. (d) Also, in this specification, the state where the oxide particles of the metal element A are observed on the surface of the oxide particles of the metal element B without forming a solid solution between the oxide of the metal element A and the oxide of the metal element B is expressed as "deposited".

[0039] The complex oxide represented by the following general formula (1) can be written as in formula (3) in another notation. That is, the complex oxide used in the present invention is a complex oxide composed of an oxide of metal element L and an oxide of metal element N, and is represented by the composition of the following general formula (3), and is a complex oxide characterized by the following (a) to (d). L n N 1-n O x (3) (a) The metal element L is an oxide of an element selected from any of the following (i) to (iii), (i) a Group 1 element, (ii) a Group 2 element, (iii) a Group 1 element and a Group 2 element, (b) The metal element N consists of a Group 1 element or a Group 2 element other than the metal element L, (c) The n is 0.001 or more and 0.300 or less, (d) The oxide of the metal element L and the oxide of the metal element N do not form a solid solution, and the oxide particles of the metal element L are deposited on the surface of the oxide particles of the metal element N, (e) The x is the number of oxygen atoms necessary for the complex oxide to maintain electrical neutrality. The complex oxide of the present invention, when the above general formula (2) is written in another notation, is a binary complex oxide composed of metal element A and metal element B represented by the composition of the following general formula (4). A n B 1-n O x (4) (Here, A, B, n, and x are as described in the above general formula (2).)

[0040] <Basicity> The complex oxide used in the present invention does not form a solid solution with the oxide of metal element L and the oxide of metal element N. The metal element L is preferably a strongly basic element in which the value of the partial negative charge (-δ OA ) of oxygen in the state of the oxide is 0.56 or more and 0.70 or less, and the metal element N is the partial negative charge (-δ OBIt is preferable that the metal element is a weakly basic element with a value of between 0.35 and 0.55.

[0041] When the metal element A is selected from the metal elements L and the metal element B is selected from the metal elements N to form a binary composite oxide, (a) The metal element A represents a Group 2 element which is a strongly basic element with a value of the partial negative charge (-δ OA ) of oxygen in the oxide state between 0.56 and 0.70, (b) The metal element B represents a Group 2 element which is a weakly basic element with a value of the partial negative charge (-δ OB ) of oxygen in the oxide state between 0.35 and 0.55, (c) The n is between 0.001 and 0.300, (d) The oxide of the metal element A and the oxide of the metal element B do not form a solid solution, and the oxide particles of the metal element A are deposited on the surface of the oxide particles of the metal element B, (e) The x is the number of oxygen atoms required for the composite oxide to maintain electrical neutrality.

[0042] The metal element A is a strongly basic element with a value of the partial negative charge (-δ O ) of oxygen in the oxide state between 0.56 and 0.70. -δ OA A value of 0.60 or more is more preferable, and a value of 0.65 or more is most preferable. Specifically, the metal element A can be selected from Ba (barium), Sr (strontium), and Ca (calcium).

[0043] The metal element B is a weakly basic element with a value of the partial negative charge (-δ O ) of oxygen in the oxide state between 0.35 and 0.55. -δ OB A value of 0.40 or more is more preferable. Also, -δ OB A value of 0.50 or less is more preferable, and a value of 0.45 or less is most preferable. Specifically, the metal element B can be selected from Mg (magnesium) and Be (beryllium). -δ OA and -δ OBThe difference from is preferably 0.10 to 0.40, more preferably 0.15 to 0.35, and most preferably 0.20 to 0.30.

[0044] In the present invention, since the metal element A contained in the composite oxide is a strong basic element that exhibits high basicity in the oxide state, it is possible to improve the activity of the ammonia synthesis catalyst. The outline of the mechanism will be described below.

[0045] The metal element A is a strongly basic metal element. Electrons are generated from the base points of the composite oxide (support) of such an element, and this is back-donated to the nitrogen molecule via the transition metal particles that are the catalyst supported on the composite oxide, weakening the nitrogen triple bond. The inventors consider this stage to be the rate-determining step of the ammonia synthesis reaction, and due to the above series of electron movements, the energy for breaking the triple bond of the nitrogen molecule is reduced, and the ammonia synthesis activity of the metal support (catalyst) is improved.

[0046] The basicity (Lewis basicity) of a metal oxide is related to the high electron-donating ability. That is, it is considered that a substance with a higher electron-donating ability exhibits stronger basicity. Basically, in an oxide, oxygen acts as an electron donor, so the amount of charge that oxygen in the oxide has, that is, the partial negative charge of oxygen, is useful as an index of basicity. In fact, in a non-patent document (Sanderson, "Inorganic Chemistry (Part 1)", Hirokawa Shoten (1975), page 276, Table 12.7), it is shown that the value of the partial negative charge of oxygen correlates well with the acid-base properties exhibited by the oxide.

[0047] Here, for the oxides of individual metal elements, the partial negative charge of oxygen (-δ O ) can use the values listed in Table 12.7 of a non-patent document (Sanderson, "Inorganic Chemistry (Part 1)", Hirokawa Shoten (1975), page 276), and those for which the values are not listed can be calculated by the above calculation of the partial negative charge of oxygen. The following table shows the values of the partial negative charge of oxygen (-δ O ) for the oxides of Group 2 elements.

[0048]

Table 1

[0049] On the other hand, for the entire composite oxide, the calculation method of the partial negative charge of oxygen was referred to Non-Patent Document (Sanderson, "Inorganic Chemistry (Part 1)", Hirokawa Shoten (1975), page 122, Table 6.7, pages 126-128). First, the composition ratio of each element in the composite oxide is determined. For example, for "Ce 0.5 La 0.5 O 1.75 ", if it is La, the value is 0.5. Let this value be ni (where i is the corresponding element). Also, let the electronegativity of each element be χi. Then, the geometric mean of the electronegativities of all the atoms constituting the composite oxide is obtained by (Π(χi ni ))^(1 / Σni). Next, in order to obtain it from the change in the electronegativity of oxygen, the difference between the geometric mean and the electronegativity of oxygen (5.21) is taken. Finally, it is divided by the change in electronegativity (-4.75) when one oxygen atom acquires one electron from the change in the electronegativity of oxygen. By the above calculation, the partial negative charge of oxygen exhibited by the composite oxide can be calculated.

[0050] Summarizing the above, the value of the partial negative charge of oxygen in the composite oxide is represented by the following formula (A) when the composition ratio of each element contained in the composite oxide is ni (where i represents all the elements in the composite oxide containing at least A, B, and O), and the electronegativity of each element is χi (where i represents all the elements in the composite oxide containing at least A, B, and O). ((Π(χi ni ))^(1 / Σni) - 5.21) / -4.75 ·· Formula (A)

[0051] When determining the partial negative charge of oxygen in the composite oxide, among the elements forming the composite, (a) it may be determined by the partial negative charge of oxygen in the state of the oxide, or (b) when the composition ratio of each element contained in the composite oxide is ni (where i represents all the elements in the composite oxide containing A, B, and O), and the Sanderson electronegativity of each element is χi (where i represents all the elements in the composite oxide containing A, B, and O), it may also be determined by the following formula (A). ((Π(χi ni))^(1 / Σni)―5.21) / -4.75 ·· Formula (A) When the composite oxide forms a uniform composite oxide, it is preferably carried out by the method (b). On the other hand, when the composite oxide forms a non-uniform composite oxide, it is preferably carried out by the method (a). In that case, the result of the element with the largest absolute value among the partial negative charges of oxygen of the individual elements is used. In the composite oxide of the present invention, since the oxide of metal element A and the oxide of metal element B are phase-separated without forming a solid solution, the value of the partial negative charge of oxygen in the composite oxide is preferably calculated by the method (a) above.

[0052] The value of the partial negative charge of oxygen in the composite oxide is preferably 0.35 or more, more preferably 0.40 or more. When the value of the partial negative charge of oxygen in the composite oxide is 0.35 or more, the ammonia synthesis activity tends to increase.

[0053] <Removal of carbonate and hydroxide> Metal elements L (alkali metals) and N (alkaline earth metals) are oxides and have strong basicity, and easily react with carbon dioxide and water in the atmosphere to form metal carbonates and hydroxides. However, these metal carbonates and hydroxides reduce the basicity of the composite oxide and cause a decrease in the ammonia synthesis activity of the catalyst. For example, Ba becomes BaCO3 or Ba(OH)2 in the atmosphere, which reduces the ammonia synthesis activity. Therefore, the amount of metal carbonate and hydroxide contained in the ammonia synthesis catalyst should be as small as possible. In order to reduce the metal carbonate and hydroxide, it is preferable to perform a reduction treatment under heating conditions as described later, thereby decomposing the metal carbonate and hydroxide contained in the catalyst and preventing a decrease in basicity. The amount of carbonate contained in the metal support is not particularly limited as long as it does not inhibit the ammonia synthesis activity. For example, it is 10 mol% or less, preferably 1 mol% or less, more preferably 0.1 mol% or less, and still more preferably 0.01 mol% or less with respect to metal element A.

[0054] As a method for quantifying the amount of carbonate present as a metal carbonate, a method is to heat the catalyst under a hydrogen flow, detect hydrocarbons such as methane generated by the hydrogenation of carbonate species using a mass spectrometer or a flame ionization detector (FID), a thermal conductivity detector (TCD), etc., and convert this.

[0055] In addition, infrared absorption spectroscopy, which has high sensitivity to metal carbonates, can also be used. By irradiating infrared light on the catalyst and measuring the absorption intensity of the peak at the wave number that carbonate characteristically absorbs, the amount of carbonate contained in the catalyst can be quantified. For example, as the peak positions that can be used for the quantification of BaCO₃, there are around 3000 cm -1 nearby, 2450 cm -1 nearby, 1750 cm -1 nearby, 1480 cm -1 nearby, 1060 cm -1 nearby, etc.

[0056] The following table shows the melting points of oxides such as Ba and Sr, which have large partial negative charge values of oxygen among Group 2 elements, and Cs and K, which are alkali metals.

[0057]

Table 2

[0058] From the H2-TPR measurement results described later, it is considered that the following reaction occurs. BaCO₃ + 4H₂ → BaO + CH₄ + 2H₂O (5) Also, although the oxide of Ba has a high melting point, as described above, it passes through a hydroxide with a low melting point during heat treatment in a hydrogen atmosphere. Therefore, fluidity is obtained by melting the hydroxide. At this time, since both Ba and the metal element B exist as strongly basic compounds, they repel each other, or due to surface tension, or for some other reason, as a result, the Ba compound flows onto the metal particles, and a state is generated in which Ba hydroxide is distributed in a particulate form on the surface of the metal particles. After the reaction, it becomes an oxide, loses fluidity, and shrinks in volume, and is fixed in the state with voids, thereby exhibiting high activity. In the present invention, the state of further existing in a particulate form on the metal surface is referred to as a "distributed" or "deposited" state.

[0059] Thus, since the original basicity of the element is strong and it is easy to reduce the carbonate that inhibits it, Ba is particularly preferable as the metal element A from the viewpoint of being able to increase the ammonia synthesis activity.

[0060] The oxide of the metal element B is a main component of the composite oxide and exhibits weak basicity (including slightly weak basicity; the same applies in the following description). In the binary composite oxide Ba n La 1-n O x described in the prior art documents, although the values of the partial negative charges of the oxide parts of both Ba and La, which are two metal elements, are high (Ba is 0.67 and La is 0.56), in the present invention, the value of the partial negative charge of the oxide of the metal element B is as low as 0.35 or more and 0.55 or less.

[0061] <deposited> In the present invention, the oxide of the metal element L and the oxide of the metal element N are phase-separated without forming a solid solution, and the oxide of the metal element L is deposited on the surface of the metal element N oxide particles, and moreover, it is deposited on the surface of the metal particles on which the oxide of the metal element L is supported. Therefore, even if the basicity of the oxide of the metal element N is weak, if the basicity of the oxide of the metal element L is strong, the ammonia synthesis activity is increased by the oxide of the metal element L. Therefore, even if the oxide of the metal element N is lower than before, it will exhibit high ammonia synthesis activity.

[0062] As the oxide of metal element N, it is preferable that the specific surface area (SSA) is larger. This is because when the specific surface area of the oxide of metal element N, which is the main component of the composite oxide, is large, fine nanoparticles such as Co can be firmly fixed, and the number of active sites of these nanoparticles increases, resulting in higher ammonia synthesis activity. Therefore, from the perspective of the magnitude of the specific surface area, Mg (magnesium) is particularly preferable as metal element N. Although metal element N is the main component as the composite oxide, when used as a catalyst as a supported material with a transition metal, the oxide of metal element N plays a major role as a carrier.

[0063] From the above perspective, as the composite oxides of formula (1) and formula (2), Ba n Mg 1-n O x (where 0.001 ≦ n ≦ 0.300) is preferable.

[0064] Here, for Ba n Mg 1-n O x Regarding Ba, the composition ratio of Ba (that is, the value of n) is preferably within the range of 0.01 ≦ n ≦ 0.10. As shown in the examples described later, when it is within the range of 0.01 ≦ n ≦ 0.10, the ammonia synthesis activity (yield, yield) tends to be higher.

[0065] <Metal support> The metal-supported material of the present invention is one in which particles of transition metals excluding Group 4 (hereinafter sometimes referred to as transition metal particles) are supported on the composite oxide of the present invention. From the viewpoint of high catalytic activity, the transition metal is preferably at least one selected from the group consisting of Ru, Fe, Co, Ni, Rh, Pd, Os, Ir, and Pt, and more preferably Ru, Co, or a mixture of Fe and Co. Among these, Co is particularly preferable because of the high ammonia synthesis activity when combined with the composite oxide of the present invention. The quantitative ratio of the transition metal to the composite oxide can be determined in consideration of the catalytic activity and the cost of the transition metal. For example, the ratio of the transition metal to the entire metal-supported material is preferably in the range of 0.1 to 50% by weight, and more preferably in the range of 5.0 to 30% by weight.

[0066] The transition metal M of the present invention does not form a solid solution with either the oxide of the metal element L or the oxide of the metal element N. In particular, it is preferable that a structure in which oxide particles of the metal element L are deposited and covered on the particles of the transition metal M is further deposited on the surface of the oxide particles of the metal element N, which is the main component. That is, it is preferable that the transition metal M is in a so-called core / shell relationship with the metal element N as the shell. It is preferable that the transition metal M is entirely covered with the oxide particles of the metal element L and is supported on the oxide particles of the metal element N, which is the carrier, via the oxide of the metal element L. Such a structure is considered to be because metal L is supported on metal N, and then transition metal M is supported, and the oxide of metal L having fluidity covers transition metal M during high-temperature reduction treatment. If the amount of metal L is too large relative to the amount of the metal element N as the carrier or too large relative to the amount of the transition metal, the layer becomes too thick, and nitrogen and hydrogen cannot reach the surface of the transition metal, which is the active site, which is not preferable. Also, if firing is performed at a high temperature exceeding 700°C or for a long time, the oxide particles of metal L aggregate, and again, nitrogen and hydrogen cannot reach the surface of the transition metal, which is the active site, which is not preferable.

[0067] The composite oxide of the present invention is in a mixed state of an oxide of metal element L and an oxide of metal element N. In particular, it preferably has a laminated structure in which oxide particles of metal element L are deposited on the surface of oxide particles of metal element N, which is the main component. It is most preferable that the two have a so-called core / shell relationship. Furthermore, metal element L may not be present inside the catalyst carrier, and metal element L is preferably present on the carrier surface. In particular, the composite oxide of the present invention is in a mixed state of an oxide of metal element A and an oxide of metal element B. In particular, it preferably has a laminated structure in which oxide particles of metal element A are deposited on the surface of oxide particles of metal element B, which is the main component. It is most preferable that the two have a so-called core / shell relationship. Furthermore, metal element A may not be present inside the catalyst carrier, and metal element A is preferably present on the carrier surface.

[0068] Since the oxide of metal element L and the oxide of metal element N are in a mixed state (phase-separated) without solid solution, when the metal-supported material (catalyst) described later is formed, the transition metal particles directly contact the oxide of metal element L on the surface of the composite oxide. Since the oxide of metal element L (for example, Ba) is strongly basic, it is presumed that when the transition metal particles directly contact these oxides, the number of active sites showing high activity increases, and the ammonia synthesis activity increases. On the other hand, in the case of Co, the basicity of the cation is important, and the oxide of metal element A such as Ba has higher ammonia synthesis activity when the partial negative charge of oxygen is larger.

[0069] The particle size ratio A / M of the oxide particles of metal element A to the metal particles M is usually preferably 20% or less, more preferably 10% or less, and even more preferably 5% or less. In order to change this particle size, the ratio of metal element A to the transition metal M is adjusted. If this particle size ratio is too large or too small, it tends to be difficult to obtain the expected catalytic activity.

[0070] Also, the value of the Co dispersion (D ads ) determined by the H2 pulse chemisorption method and the value of the Co dispersion (D TEM ) predicted from the average particle size of the Co particles obtained from the TEM image, the ratio of 0 < Dads / D TEM It is preferably 1. The Co dispersion represents the ratio of the number of Co atoms exposed on the surface of the metal support to the total number of all Co atoms contained in the metal support. The Co dispersion can be determined from the hydrogen adsorption amount of the metal support carrying Co.

[0071] Specifically, assuming that one Co atom adsorbs one H atom, the ratio (H / Co) of the number of hydrogen atoms H corresponding to the number of Co atoms exposed on the surface of the metal support to the total number of Co atoms Co supported on the metal support is the Co dispersion. In the present invention, the Co dispersion based on this hydrogen adsorption amount is denoted as D ads and represented as such. By comparing metal supports carrying the same amount (same number of atoms) of Co, it can be considered that the higher the Co dispersion, the larger the number of catalytically active sites.

[0072] Also, assuming that the form of the Co particles is cubic, it is known that the value of the Co dispersion can be geometrically determined using the average particle diameter (d, unit: nm) of Co obtained by TEM observation (see the literature "Dictionary of Catalysts"). The calculation method can be represented by the general formula (8). The average particle diameter of Co can be calculated by randomly extracting 100 to 150 Co particles from the TEM image, measuring their respective particle diameters, and then averaging them. In the present invention, the value of the Co dispersion obtained based on the general formula (4) is denoted as D TEM and represented as such. D TEM = 0.732 / d (8)

[0073] Therefore, D ads / D TEM being less than 1 means that a part of the Co particles, mainly near the interface between the particles and the composite oxide (support), or the particle surface is covered with the oxide of metal element B, preventing the adsorption of H atoms on the Co particle surface.

[0074] TOF (catalyst rotation frequency) represents the number of reactions that proceed per unit time on one active site on the catalyst surface. In this application, it is described as the number of ammonia molecules generated per second per atom of surface Co, which is the active site.

[0075] The average particle diameter of Co supported on the composite oxide is preferably 100 nm or less, more preferably 50 nm or less, and still more preferably 20 nm or less. The smaller the particle diameter of Co, the more advantageous it is because the number of active sites increases when used as an ammonia synthesis catalyst. The lower limit of the average particle diameter of Co is not particularly limited, but for example, it is 0.5 nm or more, and 1 nm or more.

[0076] The metal support of the present invention is fine particles with an average particle diameter of 100 nm or less of supported metallic cobalt. As a result, it exhibits a very high ammonia synthesis rate under mild ammonia synthesis conditions (300 to 500 °C, 0.1 to 20 MPa).

[0077] In this specification, for the sake of brevity, the metal support represented by "Ba 0.01 Mg 0.99 O 1.00 " supporting Co is represented as "Co / Ba 0.01 Mg 0.99 O1", and the reduced metal support is represented as "Co / Ba 0.01 Mg 0.99 O x ". The same expression will be used for other supports. Here, x means that with reduction, 1.00, which is the molar ratio of oxygen during firing, has decreased to x. In this specification, when simply described as ABO x , it means that the quantitative ratio of A and B is not specified, and it does not mean A 1.00 B 1.00 O x .

[0078] In the general formula (2) representing the proportion of oxygen O in the composite oxide, x is the number of oxygen atoms necessary for the composite oxide to maintain electrical neutrality. Although x depends on the types of elements A and B, generally it is in the range of 0.5 < x ≤ 2, and particularly in the range of 0.9 < x ≤ 1.

[0079] <Effect of Reduction Temperature on Ammonia Synthesis Activity> The catalyst of the present invention is activated by subjecting it to a hydrogen reduction pretreatment at a high temperature. This is because Co is reduced. Also, at this time, a characteristic structure in which the oxide of metal element A is deposited on the surface of Co particles appears. Generally, when the reduction pretreatment is at a high temperature, a decrease in specific surface area accompanied by sintering of the carrier and coarsening of the metal particle size occur, leading to a decrease in catalyst activity.

[0080] Figures 4 and 5 are graphs showing the ammonia synthesis activity of the catalysts produced by changing the reduction temperature in the examples (Co / BaMgO x ) described later. From this graph, it can be seen that as the reduction temperature increases, the ammonia synthesis activity increases, and the ammonia synthesis rate is the highest when reduced at 700 °C and 800 °C. When reduced at 900 °C, the ammonia production rate is slightly lower compared to 800 °C.

[0081] Figure 6 shows the XRD pattern of Co / BaMgO in the examples described later. x As can be seen from this figure, before reduction, peaks due to BaCO3 were observed. When the reduction temperature is increased to 700 °C or higher, the peaks of BaCO3 disappear, indicating that BaCO3 is decomposed. Also, it can be seen that when the reduction temperature is increased, the peaks of Co increase.

[0082] Also, as shown in Figure 12, it was found that the catalyst reduced at 500 °C for 72 hours exhibits performance comparable to that of the catalyst reduced at 700 °C for 1 hour. From this, it can be seen that for the catalyst of the present invention, high activity can be obtained with a long time at low temperature reduction or a short time at high temperature reduction.

[0083] The TOF (turnover frequency of the catalyst) tends to increase as the reduction temperature rises.

[0084] That is, when the reduction temperature is higher than 800 °C, the reasons for the decrease in the ammonia production rate are considered to be that the specific surface area decreases due to the sintering and enlargement of the carrier particles and the progress of Co sintering, and the surface of the Co particles is excessively covered with the oxide of metal element A, resulting in a decrease in the number of active sites.

[0085] By using a metal support carrying Co as a catalyst, ammonia can be produced by reacting nitrogen and hydrogen. The synthesis method of ammonia itself is not particularly limited. For example, ammonia can be produced by supplying a raw material gas composed of hydrogen gas and nitrogen gas into a reaction vessel filled with the catalyst. The reaction temperature is preferably 300 to 550 °C, more preferably 300 to 500 °C, and even more preferably 300 to 450 °C.

[0086] When ammonia synthesis is carried out using the catalyst of the present invention, the reaction pressure is preferably low pressure of 0.1 to 20 MPa, more preferably 0.1 to 15 MPa, and still more preferably 0.1 to 10 MPa. As shown in FIGS. 10 and 11, it can be seen that the catalyst supporting Co has improved activity even under high-pressure reaction conditions compared with the catalyst supporting Ru. This is because Co is less susceptible to hydrogen poisoning compared with Ru, and thus the activity is less likely to decrease even under high pressure. That is, in the case of Ru, the interaction between the hydrogen atoms adsorbed on the surface and Ru becomes stronger under high pressure, and the desorption of hydrogen atoms is remarkably difficult to occur, and the active sites on the Ru surface are blocked, and the ammonia synthesis reaction initiated by the adsorption of nitrogen molecules to the active sites is difficult to occur. Since Co has a weaker interaction with hydrogen than Ru, such a phenomenon is less likely to occur, and it has the property that the ammonia synthesis activity is less likely to decrease even at high pressures. Since the ammonia synthesis reaction generally tends to increase the ammonia yield as the pressure is higher according to the thermodynamic equilibrium, it is expected that a higher yield can be obtained under high-pressure conditions of about 10 MPa, for example, by using the catalyst for ammonia synthesis according to the present invention. In addition, since Co is present more widely by 10,000 times or more in the earth's crust abundance compared with Ru, it has higher versatility and lower cost than Ru.

[0087] When a metal-supported material supporting Co is used as a catalyst, it is preferable from the viewpoint of catalyst activity that the composite oxide serving as a carrier contains Ba. By this combination, even when Co, which is cheaper than Ru, is used, sufficient ammonia synthesis activity can be exhibited. Also, even when the reaction pressure is high, it is less susceptible to poisoning by hydrogen than the Ru catalyst. Therefore, the reaction pressure is most preferably 1 to 10 MPa.

[0088] <Method for producing composite oxide and metal-supported material> Next, the method for producing the composite oxide and metal-supported material of the present invention will be described. The composite oxide of the present invention can be produced by the following method. (a) An impregnation step of impregnating an L precursor containing a metal element L into an N precursor containing the metal element N, (b) Firing the mixture at a temperature of 500 °C or higher to obtain a carrier made of a composite oxide, including a composite oxide firing step. The metal-supported material of the present invention can be further produced by the following method with respect to the composite oxide obtained in (a) and (b) above. (c) An impregnation step of impregnating the composite oxide with a precursor of a compound containing the metal particles M to obtain an impregnated carrier. (d) A supported material firing step of firing the impregnated carrier at a temperature of 400 °C or higher.

[0089] Hereinafter, step (a) will be described. Step (a) corresponds to the method for producing the composite oxide of the present invention. The composite oxide is a step of mixing and impregnating an L precursor containing a metal element L and an N precursor containing a metal element N to obtain a mixture (precursor of the composite oxide). The precursor of the composite oxide can be prepared by various methods such as the precipitation method and the complex polymerization method. For example, a neutralization precipitation method can be used in which a precipitating agent such as ammonia, sodium hydroxide, or cesium hydroxide is reacted with nitrates, chlorides, acetates, carbonates, or sulfates of A and B to obtain a hydroxide.

[0090] The precursor of the composite oxide can also be obtained by individually preparing and mixing those containing one or more of the elements of the metal element L and the metal element N. In this way, a compound containing the metal element L and a compound containing the metal element N are mixed to obtain a mixture.

[0091] Next, step (b) will be described. This step is a step of firing the mixture obtained in step (a). Thereby, the generated mixture (composite oxide precursor) is changed into a composite oxide with a high specific surface area by firing. The firing is preferably performed at a low temperature of about 200 to 400 °C for about 1 to 10 hours, at an intermediate temperature of about 400 to 600 °C for about 1 to 10 hours, and at a high temperature of about 600 to 700 °C for about 1 to 10 hours. The firing temperature of the final step is most preferably 700 °C. This firing can be performed at any oxygen concentration as long as it is in an atmosphere containing oxygen, such as in air or a mixed gas of oxygen with an inert gas.

[0092] Hereinafter, step (c) will be described. In step (c), the composite oxide obtained in step (b) is stirred together with a solvent in which a transition metal particle source such as cobalt, iron, or nickel is dissolved, so that the transition metal particle source is impregnated into the composite oxide. Then, the solvent is removed by heating, followed by decomposition of the transition metal particle source, to obtain a pre-reduction supported product in which transition metal particles are supported in fine particle form on the composite oxide carrier.

[0093] As the transition metal particle source of cobalt (cobalt source), various compounds containing Co can be used. For example, organometallic compounds such as cobalt(II) acetylacetonate can be mentioned. Among these, cobalt(II) acetylacetonate is particularly preferred from the viewpoint of high ammonia synthesis activity. It is also possible to use other cobalt sources capable of supporting cobalt on the composite oxide, such as cobalt nitrate, cobalt chloride, cobalt nitrosyl nitrate, and the like.

[0094] When using an organometallic compound such as cobalt(II) acetylacetonate as a cobalt source, it is advantageous to use an organic solvent as the solvent. Examples of organic solvents include tetrahydrofuran (THF), methanol, ethanol, hexane, toluene, and the like. These solvents can be used without any particular pretreatment if they are general commercial products, but it is more preferable to use those that have been purified, dehydrated, etc. The solid content concentrations of the composite oxide and the cobalt source per liter of the solvent are generally preferably about 1 to 30 g / liter and 0.1 to 3 g / liter, respectively, and more preferably about 10 to 30 g / liter and 0.1 to 0.3 g / liter, respectively. Stirring can be carried out at room temperature, and the stirring time is preferably 1 to 24 hours, and more preferably 6 to 12 hours. The removal of the solvent can be carried out by heating by various methods, but it is preferably carried out under reduced pressure and in a low-temperature atmosphere using, for example, an evaporator. The decomposition of the cobalt source is carried out by heating in an inert atmosphere, such as a helium, argon, or nitrogen atmosphere. It can also be carried out in an atmosphere containing hydrogen. The heating is carried out at a temperature of about 200 to 600 °C for about 1 to 12 hours. A more preferable heating temperature is about 300 to 500 °C, and a more preferable heating time is about 3 to 6 hours.

[0095] As the ruthenium source, various compounds containing Ru can be used. Preferably, organometallic compounds such as tritolylruthenium dodecacarbonyl and ruthenium acetylacetonate can be used. It is also possible to use other ruthenium sources that can support ruthenium on the composite oxide, such as ruthenium chloride and ruthenium nitrosyl nitrate.

[0096] The following describes step (d). Next, the pretreated supported material (impregnated carrier) thus obtained is subjected to a reduction treatment. The reduction treatment is performed for the purpose of reducing transition metal particles and reducing carbonates described later for the purpose of destroying them. The reduction temperature is from 400°C to 800°C, preferably 600 to 700°C. When the reduction temperature is higher than 500°C, usually the reduction time is from 10 minutes to 40 hours, preferably about 30 minutes to 5 hours. When the reduction temperature is low, the reduction time is from 48 hours to 120 hours, preferably from 60 hours to 100 hours. The reduction treatment is performed in the presence of a reducing gas such as hydrogen gas.

[0097] When strongly basic Ba is included, it is known that BaO reacts with carbon dioxide in the air and easily forms barium carbonate (Ba(CO3)) and barium hydroxide (Ba(OH)2). When carbonates and hydroxides are formed in this way, the partial negative charge of oxygen in BaO significantly decreases, and high basicity cannot be obtained. Therefore, in order to exhibit high ammonia synthesis activity, it is necessary to destroy these carbonates and hydroxides by appropriate treatment. For example, as a method of destroying Ba carbonate to form BaO, heat treatment (reduction treatment) under hydrogen gas flow is effective. This reaction is represented by the following formula. BaCO3 + 4H2 → BaO + CH4 + 2H2O (5)

[0098] By heating the catalyst in a hydrogen atmosphere, dissociation of hydrogen occurs on the surface of the supported metal species, and hydrogen species with strong reducing power are generated. By the action of these hydrogen species, Ba carbonate is destroyed and changed to BaO. As a method of destroying Ba carbonate, it can be exemplified to hold the catalyst under hydrogen flow at a temperature of 550°C or higher for about 1 hour. Preferred conditions are about 600°C to 800°C. Also, Ba carbonate can be destroyed by holding the catalyst under hydrogen flow at a low temperature for a long time. Preferred conditions are about 48 hours at 500°C, about 72 hours at 450°C, and 120 hours or more at 400°C.

[0099] By using such a method, the carbonate of Ba can be destroyed. In order to exhibit the basic properties of Ba, it is desirable to reduce the proportion of Ba present as carbonate as much as possible. The proportion of Ba present as carbonate in the catalyst is preferably 10 mol% or less, more preferably 1 mol% or less, still more preferably 0.1 mol% or less, and particularly preferably 0.01 mol% or less, based on the total amount of Ba contained in the catalyst.

[0100] As the calcination temperature in step (d), 700 to 800 °C is most preferable. If the calcination temperature in this step is too high, excessive sintering of the support and the active metal will proceed during the reduction treatment, and the particle size will increase, resulting in a decrease in the number of active sites and a reduction in catalyst performance. On the other hand, if the calcination temperature in this step is too high, the specific surface area of the support will decrease, so the dispersion state of the active metal will be poor, and the particle size will increase, resulting in a decrease in the number of active sites and a reduction in catalyst performance. Regarding the relationship between the calcination temperature and the reduction temperature, as described above, from the viewpoint of ammonia synthesis activity, it is preferable to calcine the support at a temperature equal to or higher than the reduction treatment temperature.

[0101] Figure 35 illustrates the above situation. Figure 35 explains the differences due to differences in the manufacturing method of the metal-supported Co / BaMgOx. The inventors have disclosed Ba / Ru / MgO in prior research (see Examples 80 and 81 of WO2019 / 059190). However, if the manufacturing method at this time is carried out in the present application, the following will occur. That is, Co is supported on Ba as shown in Figure 35(1), and after further supporting barium as (2), for example, when high-temperature reduction is carried out at 700 °C, the structure of (2) is formed. That is, the transition metal Co is deposited on the support MgO, and barium oxide is deposited thereon, but according to the cross-section (3), Co and MgO are in direct contact.

[0102] On one hand, when producing a metal-supported material by the method of the present invention, the following occurs. That is, since BaO is supported on MgO and then Co is supported, it becomes (4). Then, when (4) is reduced at, for example, 700 °C, (5) is generated. This is because during the high-temperature reduction treatment, the supported Ba compound obtains fluidity and moves to cover Co. Therefore, when observing the cross-section (6), MgO and Co do not directly contact each other, and Co is arranged with MgO via the Ba compound. Since barium oxide covers Co with an appropriate density, nitrogen and hydrogen can reach Co which is the active site.

[0103] The metal-supported material according to the present invention thus obtained has better handleability and stability during the reaction compared to the metal-supported materials used as ammonia synthesis catalysts so far.

[0104] In addition, when Ba or the like is contained in the composite oxide, even if the catalyst is in an oxidized state during production, when exposed to the atmosphere, it is likely to absorb CO2 and become a carbonate. Therefore, after decomposing BaCO3 by the above reduction treatment, it is preferably handled so as not to be exposed to CO2 until the catalyst is used. For example, it is preferable to store the catalyst by sealing it in a container filled with an inert gas or the like. However, even if a part of the carrier becomes a carbonate, by hydrogenating and decomposing, the carbonate can be reduced and the ammonia synthesis activity can be restored.

[0105] Since the metal-supported material loaded in the synthesis reactor and used as a catalyst is inevitably replaced regularly and is assumed to be used over a long period of time, a metal-supported material that is easy to handle and has excellent stability is required. The metal-supported material of the present invention is advantageous in this regard.

Examples

[0106] Next, the present invention will be further described by way of examples. Needless to say, the present invention is not limited to these examples.

[0107] <Measurement of Ammonia Synthesis Activity> The ammonia synthesis activity of the metal-supported material was measured using a fixed-bed flow reactor. The metal-supported material pretreated by the methods described in the examples and comparative examples was allowed to cool to 300 °C while flowing Ar through it. While maintaining the temperature of the metal-supported material layer at 300 °C, the pressure was increased to 1.0 MPa or 3.0 MPa by the back pressure valve at the reaction tube outlet while supplying Ar. The supply of Ar was stopped, and while maintaining the pressure, H2 and N2 were each flowed at 90 mL min -1 , 30 mL min -1 (space velocity 72 L h -1 g -1 ) and transferred to the reaction atmosphere. According to the height of the NH3 synthesis activity, 200 mL of a sulfuric acid aqueous solution of 1 - 100 mM (1, 5, 10, 25, 100 mM) was added to a three-necked flask connected to a conductivity meter, and a mixed gas containing hydrogen (purity, 99.995%, manufactured by Fukuoka Oxygen), nitrogen (purity, 99.995%, manufactured by Fukuoka Oxygen), and NH3 flowing out from the reaction tube outlet was bubbled into the sulfuric acid aqueous solution. Also, when removing impurities such as moisture and oxygen, a gas purifier (gas purification filter MC50 - 904F, manufactured by SAES) was used to make the purity 99.99999999 or higher. At this time, the amount of ammonia generated in the outlet gas was quantified by measuring the change in conductivity caused by the reaction between NH3 and sulfuric acid. Next, the temperature of the metal-supported material layer was raised until it reached 350 °C, 400 °C, or 450 °C. When the temperature of the metal-supported material layer stabilized at 350 °C, 400 °C, or 450 °C, it was left for 10 minutes, and the amount of ammonia generated was quantified by the same method as described above.

[0108] <Powder X-ray diffraction> The powder X-ray diffraction pattern of the metal-supported material (catalyst) was measured using a SmartLab x-ray diffractometer (Rigaku).

[0109] <Specific surface area (SSA) measurement> The specific surface area of the metal-supported material was determined by the BET method from the nitrogen adsorption amount at 77 K using a BEL-sorp mini (Nippon Bell). Before the measurement, vacuum heating at 300 °C was performed for 2 hours as a pretreatment.

[0110] 1. Co / Ba0.01 Mg 0.99 O x _Reduction at 700 °C and Co / Ba 0.05 La 0.95 O x _Comparison of Reduction at 700 °C (Example 1) <Co / Ba 0.01 Mg 0.95 O x _Reduction at 700 °C > <Preparation of Composite Oxide> Ba 0.01 Mg 0.99 O x The composite oxide was synthesized as follows. Ba(OH)2 (Wako Pure Chemical Industries) was dissolved in purified water to obtain an aqueous Ba(OH)2 solution, and 200 mL of a precursor solution containing 0.000625 mol of Ba was prepared. 2.5 g of MgO (UBE Materials) was added thereto, and the mixture was stirred at 320 rpm with a magnetic stirrer while stirring was continued at room temperature for 1 hour. After the suspension was evaporated to dryness using a rotary evaporator, the obtained powder was dried overnight using an oven set at 80 °C. The dried powder was pulverized in a mortar, and the obtained powder was heated in an electric furnace at 700 °C for 5 hours in an air atmosphere to obtain Ba 0.01 Mg 0.99 O x was obtained.

[0111] <Loading of Co> Co was loaded onto the carrier Ba 0.01 Mg 0.99 O x by an impregnation method. A 200 mL eggplant flask was prepared with a solution of cobalt(II) acetylacetonate (Wako Pure Chemical Industries), which is a Co precursor, dissolved in tetrahydrofuran (THF) (Wako Pure Chemical Industries). 1 g of the carrier was added thereto, and stirring was performed at room temperature for 18 hours or more. The amount of cobalt(II) acetylacetonate and the carrier used was appropriately adjusted so that the amount of Co contained in the catalyst after heating under the following argon atmosphere would be 20% by weight. After the stirred suspension was dried under reduced pressure at 35 °C and 0.3 atm using a rotary evaporator, it was dried at 80 °C for 18 hours using an oven. The obtained powder was 80 mL min -1The acetylacetonate ligand in the precursor was removed by heating at 500 °C for 5 hours using a tubular electric furnace under argon flow. By the above operation, Co / Ba 0.01 Mg 0.99 O x supported metal was obtained.

[0112] <Hydrogen reduction pretreatment> For the Co / Ba 0.01 Mg 0.99 O x obtained above, hydrogen reduction pretreatment (also simply referred to as "pretreatment") was carried out by the following method. The powder of the supported metal was pressed at 20 MPa for 5 minutes to produce a disk, and then this disk was ground in a mortar and classified by a sieve to produce pellets. The size of the pellets was adjusted to 250 - 500 μm in diameter. Using 100 mg of the pellets, a catalyst reaction tube made of Inconel (trademark) with a diameter of 7 mm was filled, and the front and back of the catalyst layer were fixed with quartz wool. This reaction tube was installed in a fixed-bed flow-type reactor for ammonia synthesis activity measurement, and 60 mL min -1 of H2 was passed through the reaction tube filled with the pellets, and heated at 700 °C for 1 hour to obtain Co / Ba 0.01 Mg 0.99 O x _700 °C reduction.

[0113] (Comparative Example 1) <Co / Ba 0.05 La 0.95 O x _700 °C reduction> The Co / Ba of Example 101 in Patent Document 6 (International Publication No. 2019 / 216304) 0.05 La 0.95 O x _700 °C reduction was used as a comparative example. Co / Ba 0.05 La 0.95 O x _700 °C reduction was produced by the method described in this document.

[0114] For the supported metals of Example 1 and Comparative Example 1, ammonia synthesis was carried out at reaction pressures of 1 MPa and various temperatures (300 °C, 350 °C, 400 °C, 450 °C), and the ammonia synthesis activity was measured by the method described above. The results are shown in the following table.

[0115]

Table 3

[0116] Also, the results are shown in FIG. 1. On the right side of the vertical axis of this figure is the ammonia synthesis rate, on the left side of the vertical axis is the ammonia yield, and the horizontal axis is the reaction temperature. From this figure, it can be seen that at any reaction temperature, the metal support of Example 1 exceeds that of the metal support of Comparative Example 1 in terms of ammonia synthesis rate and yield. Also, it can be seen that the higher the reaction temperature for ammonia synthesis, the higher the ammonia synthesis activity (synthesis rate, yield).

[0117] 2. Examination of Ba addition amount (Examples 1 to 6, Comparative Example 2) In Example 1, the ratio of the number of moles of Ba to the total number of moles of Ba and Mg was variously changed (0 mol% (Comparative Example 2), 0.5 mol% (Example 2), 1 mol% (Example 1), 2 mol% (Example 3), 3 mol% (Example 4), 5 mol% (Example 5), 10 mol% (Example 6)) to produce a metal support.

[0118] For the metal supports of Examples 1 to 6 and Comparative Example 2, ammonia synthesis was carried out at a reaction pressure of 1 MPa and various temperatures (300 °C, 350 °C, 400 °C, 450 °C), and the ammonia synthesis activity was measured by the method described above. The results are shown in the following table.

[0119]

Table 4

[0120] Also, the results are shown in FIGS. 2 and 3. From these figures, it was found that as the Ba addition amount increases, the ammonia synthesis activity improves, but the ammonia synthesis activity reaches its maximum at an addition amount of 1 mol%, and when the addition amount is increased further, the ammonia synthesis activity gradually decreases. Also, from FIG. 3, it can be seen that the Ba addition amount with high ammonia synthesis activity is within the range of 0.5 to 3 mol%.

[0121] 3. Investigation of Reduction Temperature (Examples 7 - 11) In Example 1, the Co loading was set to 20 wt%, and the reduction temperature was varied (500 °C (Example 7), 650 °C (Example 8), 700 °C (Example 9), 800 °C (Example 10), 900 °C (Example 11)) to produce metal - supported materials.

[0122] For the metal - supported materials of Examples 7 - 11, ammonia synthesis was carried out at a reaction pressure of 1 MPa and various temperatures (300 °C, 350 °C, 400 °C, 450 °C), and the ammonia synthesis activity was measured by the method described above. The results are shown in the following table.

[0123]

Table 5

[0124] Also, the results are shown in Figures 4 and 5. From this figure, it was found that the ammonia synthesis activity was relatively low when the reduction temperature was 500 °C, but it became high at 650 °C or higher.

[0125] Figure 6 shows the XRD patterns of the metal - supported materials in Example 7 (reduction temperature 500 °C), Example 9 (reduction temperature 700 °C), and Example 10 (reduction temperature 800 °C). In the figure, "fresh" is the sample before the reduction treatment. As can be seen from this figure, BaCO3 has decomposed by the reduction treatment. When the reduction temperature is increased to about 700 °C, the peak of BaCO3 is no longer observed, indicating that BaCO3 has decomposed. Also, when the reduction temperature is increased to 800 °C, it can be seen that the peak of metallic Co, which has not been observed until then, appears. This is considered to be because the peak of metallic Co, which was not observed due to the highly dispersed Co particles, appears due to the aggregation of the somewhat dispersed Co particles by the high - temperature reduction treatment.

[0126] The following table shows various parameters of the metal support at a reaction temperature of 350°C in Example 7 (reduction temperature: 500°C), Example 9 (reduction temperature: 700°C), Example 10 (reduction temperature: 800°C), and Comparative Example 2 (without Ba, reduction temperature: 700°C). From this table, it can be seen that although the specific surface area (SSA) decreases with an increase in the reduction temperature, the ammonia synthesis activity improves.

[0127]

Table 6

[0128] 4. Investigation of Co loading amount (Example 12, Example 1, Example 15) In Example 1, the Co loading amount was varied (5 wt% (Example 12), 10 wt% (Example 13), 20 wt% (Example 1), 30 wt% (Example 15)) to produce metal supports.

[0129] For the metal supports of Example 12, Example 1, and Example 15, ammonia synthesis was carried out at a reaction pressure of 1 MPa and various temperatures (300°C, 350°C, 400°C, 450°C), and the ammonia synthesis activity was measured by the method described above. The results are shown in the following table.

[0130]

Table 7

[0131] Also, the results are shown in Figures 7 and 8. From these figures, it was found that the ammonia synthesis activity increases as the Co loading amount increases, and the ammonia synthesis activity is almost maximum at 20 wt%.

[0132] (Comparative Examples 1, 4, 5) As comparative examples, Co / Ba 0.05 La 0.95 O x (Comparative Example 1), Ru / CeO x , (Comparative Example 4), Cs + / Ru / MgO x (Comparative Example 5) were prepared. Ru / CeOx , (Comparative Example 4) was prepared by the following method. Ru was supported on CeO2 by an impregnation method. Ru3(CO) 12 (Furya Metal) dissolved in tetrahydrofuran (THF) (Wako Pure Chemical Industries) solution was prepared in a 200 mL eggplant flask, and 5 g of CeO2 (Daiichi Rare Element Chemical Industries) was added thereto, and stirring was carried out at room temperature for 18 hours or more. Note that the amount of Ru3(CO) 12 and the amount of the carrier were appropriately adjusted so that the amount of Ru contained in the catalyst after heating in an argon atmosphere was 5 wt%. After the stirred suspension was dried under reduced pressure at 35 °C and 0.3 atm using a rotary evaporator, it was dried at 80 °C for 18 hours using an oven. The obtained powder was heated at 500 °C for 5 hours under an argon flow of 80 mL min -1 using a tubular electric furnace to remove the carbonyl ligand in the precursor. Ru / CeO2 was obtained by the above operations. The reduction treatment was carried out at 400 °C.

[0133] Cs + / Ru / MgO x (Comparative Example 5) was prepared by the method described in a non-patent document (F. Rosowski, A. Hornung, O. Hinrichsen, D. Herein, M. Muhler and G. Ertl, Appl. Catal., A, 1997, 151, 443-460.). Note that the supported amount of Ru was 5 wt% and Cs / Ru was 1 / 1 (mol / mol). The reduction treatment was carried out at 500 °C.

[0134] For the metal-supported materials of Comparative Examples 3 to 5, ammonia synthesis was carried out at various temperatures (300 °C, 350 °C, 400 °C, 450 °C) and pressures (0.1 MPa, 1.0 MPa, 3.0 MPa), and the ammonia synthesis activity was measured by the method described above. The results are shown in the following table.

[0135]

Table 8

[0136] The results are shown in Fig. 10 (reaction temperature: 350 °C) and Fig. 11 (reaction temperature: 400 °C). The results of Example 3 (Co / Ba 0.01 Mg 0.99 O x ) are also shown in the figure. From this figure, it can be seen that the metal supports of the examples have higher ammonia synthesis activity than those of Comparative Examples 1, 4, and 5.

[0137] 6. Influence of pretreatment conditions (reduction conditions) (Example 1, Example 17, Comparative Example 6) In Example 1, the temperature and time of the hydrogen reduction pretreatment were changed to 500 °C and 72 hours to prepare a metal support (Example 17). As a comparative example, 5 wt% Ru / MgO (Comparative Example 6) was prepared in the same manner as Comparative Example 4 except that the carrier was MgO (UBE material).

[0138] For the metal supports of Example 1, Example 17, and Comparative Example 6, ammonia synthesis was carried out at a reaction pressure of 1 MPa and various temperatures (300 °C, 350 °C, 400 °C, 450 °C), and the ammonia synthesis activity was measured by the method described above. The results are shown in the following table.

[0139]

Table 9

[0140] The results are also shown in Fig. 12. From this figure, it was found that even under low-pressure reduction conditions, the ammonia synthesis activity was improved by long-time reduction.

[0141] 7. Influence of Co precursor (Example 1, Example 18) In Example 1, a metal support was prepared in the same manner as Example 1 except that Co(NO3)2·6H2O (Wako Pure Chemical Industries, Ltd.) was used instead of Co acetylacetonate (II) (Co(acac)) as the Co precursor, purified water was used instead of THF, and the atmosphere during firing was Air (Example 18).

[0142] For the metal supports of Example 1 and Example 18, ammonia synthesis was carried out at a reaction pressure of 1 MPa and various temperatures (300 °C, 350 °C, 400 °C, 450 °C), and the ammonia synthesis activity was measured by the method described above. The results are shown in the following table.

[0143]

Table 10

[0144] Also, the results are shown in Fig. 13. From this figure, it was found that the ammonia synthesis activity was improved with Co(acac) as the Co precursor rather than Co nitrate.

[0145] Fig. 14 shows the XRD of the metal supports in Example 1 (Co(acac)) and Example 17 (Co nitrate). As can be seen from this figure, no peak derived from metallic Co was observed in the metal support with Co(acac) as the precursor, but a peak derived from metallic Co was observed in the metal support with nitrate as the precursor. From this, it is presumed that Co was more highly dispersed in the metal support with Co(acac) as the precursor than in the metal support with Co nitrate as the precursor, and as a result, the ammonia synthesis activity was improved.

[0146] 8. SV study (Example 1) In Example 1, Co(NO3)2·6H2O (Wako Pure Chemical Industries, Ltd.) was used instead of Co acetylacetonate (II) (Co(acac)), which is the Co precursor, to prepare a metal support (Example 18).

[0147] For the metal support of Example 1, ammonia synthesis was carried out at a reaction pressure of 1 MPa, various temperatures (300 °C, 350 °C, 400 °C, 450 °C) and various SVs (18 L / h -1 g -1 、36 L / h -1 g -1 、72 L / h -1 g -1 ), and the ammonia synthesis activity was measured by the method described above. The results are shown in the following table.

[0148]

Table 11

[0149] Also, the results are shown in FIGS. 15 and 16. From this figure, it was found that as the value of SV increases, the ammonia synthesis rate increases (FIG. 15), but the ammonia yield decreases (FIG. 16).

[0150] 9. Investigation of carrier characteristics (Example 1, Comparative Example 7, Comparative Example 1) (5wt%Ru / Ba 0.1 La 0.45 Ce 0.45 Ox: Comparative Example 7) In Comparative Example 1, instead of CeO2, Ba 0.1 La 0.45 Ce 0.45 was used, and the Ru content was appropriately adjusted to 5wt%Ru / Ba 0.1 La 0.45 Ce 0.45Ox (Comparative Example 7) was prepared. The carrier was synthesized as follows using the reverse homogeneous precipitation method according to the method described in Example 6 of Patent Document 6 (International Publication No. 2019 / 216304). La(NO3)3·6H2O (Wako Pure Chemical Industries) was dissolved in purified water to obtain an aqueous La(NO3)3 solution. Ce(NO3)3·6H2O (Kanto Chemical) was dissolved in purified water to obtain an aqueous Ce(NO3)3 solution. Ba(NO3)2·6H2O (Wako Pure Chemical Industries) was dissolved in purified water to obtain an aqueous Ba(NO3)2 solution. The aqueous La(NO3)3 solution, the aqueous Ce(NO3)3 solution, and the aqueous Ba(NO3)2 solution were mixed to prepare 250 mL of a carrier precursor solution containing a total of 0.0625 mol of La, Ce, and Ba. 250 mL of 28% aqueous NH3 solution (Wako Pure Chemical Industries) was added to a 1000 mL beaker, and while stirring at 320 rpm with a magnetic stirrer, the above carrier precursor solution was added all at once, and stirring was carried out for 1 hour. Then, it was left standing for 12 hours, and the precipitate (1) was separated by suction filtration. The separated filtrate was collected in a 2 L beaker. 350 mL of ion-exchanged water was added to the separated precipitate (1), and the precipitate was washed by stirring for 30 minutes, and the precipitate (1) was separated by suction filtration. This washing operation was performed 3 times. All the ion-exchanged water used for washing was recovered, and the filtrate and the washing liquid were added to a 2 L beaker and mixed. By leaving this mixed solution standing for 12 hours, a white precipitate (2) was generated, and the generated precipitate (2) was recovered by suction filtration. Precipitate (1) and precipitate (2) were mixed and dried at 80 °C for 15 hours using an oven. The dried precipitate was pulverized in a mortar, and the obtained powder was heated at 700 °C for 5 h in an air atmosphere using an electric furnace to obtain Ba 0.1 La 0.45 Ce 0.45 O x was obtained.

[0151] For the metal-supported materials of Example 1, Comparative Example 1, and Comparative Example 7, ammonia synthesis was carried out at a reaction pressure of 1 MPa and a reaction temperature of 350 °C, and the ammonia synthesis activity was measured by the method described above. The results are shown in the following table.

[0152]

Table 12

[0153] From this table, 20 wt% Co / Ba of Example 1 0.01 Mg 0.99 Ox has a large specific surface area (SSA), and it is presumed that this contributes to the improvement of ammonia synthesis activity.

[0154] 10. Activity at low temperature (Example 1, Comparative Example 9, Comparative Example 10) As a comparative example, Ru / Ba 0.1 La 0.45 Ce 0.45 O x (700 °C, 1 h, red) (Comparative Example 9) was produced by the method described in Example 6 of Patent Document 6 (International Publication No. 2019 / 216304). Also, Ru / La 0.5 Ce 0.5 O x (650 °C, 1 h, red) (Comparative Example 10) was produced by the method described in Example 1 of Patent Document 6 (International Publication No. 2019 / 216304).

[0155] For Example 1, ammonia synthesis was carried out at various temperatures (150 °C, 200 °C, 250 °C) and various pressures (0.1 MPa, 1.0 MPa, 3.0 MPa), and the ammonia synthesis activity was measured by the method described above. Also, for the metal supports of Comparative Example 9 and Comparative Example 10, ammonia synthesis (pressure 1.0 MPa) was carried out at various temperatures (150 °C, 200 °C, 250 °C), and the ammonia synthesis activity was measured by the method described above. The results are shown in the following table.

[0156]

Table 13

[0157] Also, the results are shown in FIGS. 17 and 18. From FIG. 17, it was found that under low-temperature conditions, the Co-supported catalyst shows higher activity than the Ru-supported catalyst. Also, from FIG. 18, it was found that the ammonia synthesis activity improves with an increase in pressure even under low-temperature conditions.

[0158] 11. Study on Ru-Supported Catalysts (Example 21, Comparative Examples 11 to 14) (Example 21) <Ru / Ba 0.01 Mg 0.99 O x _Reduction at 700 °C> In Example 1, the same operations as in Example 1 were performed except that Co acetylacetonate (II) was used as the Ru precursor Ru3(CO) 12 (Furya Metal), and Ru / Ba 0.05 Mg 0.95 O x _Reduction at 700 °C was obtained.

[0159] 11. Study on Fe-Supported Catalysts (Example 22, Comparative Examples 15, 16) (Example 22) <Fe / Ba 0.01 Mg 0.99 O x _Reduction at 700 °C> In Example 1, the same operations as in Example 1 were performed except that Co acetylacetonate (II) was used as the Fe precursor iron(III) acetylacetonate (Dojindo Laboratories), and Fe / Ba 0.01 Mg 0.99 O x _Reduction at 700 °C was obtained.

[0160] (Comparative Examples 15, 16) As comparative examples, except that Ru was changed to Fe and the amount of Ba was changed, 20 wt% Fe / Ba 0.1 La 0.45 CeO x (Reduction at 700 °C for 1 hour) (Comparative Example 15) was prepared. Also, 5 wt% Ru / MgO (Comparative Example 16) was prepared in the same manner as in Comparative Example 6.

[0161] For the metal supports of Example 22, Comparative Example 15, and Comparative Example 16, ammonia synthesis was carried out at a reaction pressure of 1 MPa and various temperatures (300 °C, 350 °C, 400 °C, 450 °C), and the ammonia synthesis activity was measured by the method described above. The results are shown in the following table.

[0162]

Table 14

[0163] Also, the results are shown in Fig. 20. From this figure, it was found that the metal support carrying Fe has higher ammonia synthesis activity than 5wt% Ru / MgO or 20wt% Fe / Ba 0.1 La 0.45 CeO x (reduced at 700°C for 1 hour).

[0164] 12. Investigation of pretreatment conditions: Fe-supported catalysts (Example 23, Example 24, Comparative Example 16) In Example 22, the pretreatment conditions were variously changed (H2+N2, reduced at 500°C for 72 hours (Example 23), H2 only, reduced at 700°C for 1 hour (Example 24)) to produce metal supports.

[0165] For the metal supports of Example 23, Example 24, and Comparative Example 16, ammonia synthesis was carried out at a reaction pressure of 1 MPa and various temperatures (300°C, 350°C, 400°C, 450°C), and the ammonia synthesis activity was measured by the method described above. The results are shown in the following table.

[0166]

Table 15

[0167] Also, the results are shown in Fig. 21. From this figure, it was found that the ammonia synthesis activity is greatly improved depending on the pretreatment conditions.

[0168] 13. Investigation of Co-Fe catalysts (Examples 25 to 27) In Example 7 (20wt% Co / Ba 0.05 Mg 0.95 O x ), the Fe precursor of Example 22 was added to the Co precursor to prepare a mixing ratio to produce a metal support (Example 25).

[0169] For the metal supports of Example 7, Example 22, and Example 25, ammonia synthesis was carried out at various temperatures (300 °C, 350 °C, 400 °C, 450 °C), and the ammonia synthesis activity was measured by the method described above. The results are shown in the following table.

[0170]

Table 16

[0171] Further, the results are shown in Fig. 22. From this figure, it was found that the ammonia synthesis activity of Co alone is higher than that of Fe alone or the Fe-Co mixed catalyst.

[0172] 14. H2-TPR measurement results (Example 1, Comparative Example 2) Example 1 (Co / Ba 0.05 Mg 0.95 O x _700 °C reduction), Comparative Example 2 (Co / MgO x ) were subjected to H2-TPR (H-Temperature Programmed Reduction) measurement. H2-TPR is a method in which the temperature of a solid is continuously increased at a constant rate under the flow of hydrogen gas (H2) diluted with an inert gas such as argon, and the consumption rate of hydrogen gas and the production rate of reaction products are measured, and a mass spectrometer is used as a detector. The results are shown in Figs. 23 and 24.

[0173] From Fig. 23, it can be seen that the Co / BaMgO of Example 1 x absorbs hydrogen with a molecular weight of 2 at just above 500 °C and releases methane with a molecular weight of 16. It can also be seen that water with a molecular weight of 18 is released at just above 600 °C. On the other hand, from Fig. 24, it can be seen that the Co / MgO of Comparative Example 2 x has no such absorption and release. From these facts, it can be seen that in Example 1, the reduction reaction of the following formula (5) occurs with respect to Ba. BaCO3 + 4H2 → BaO + CH4 + 2H2O (5)

[0174] From these results, it is suggested that BaCO3 and Ba(OH)2 are formed on the surface of the Co / BaMgOx catalyst. However, by heat treatment under hydrogen, at a temperature slightly above 500 °C, H2 reacts with BaCO3 to decompose it into Ba(OH)2 and CH4, and at a temperature slightly above 600 °C, Ba(OH)2 decomposes into BaO and H2O. That is, by performing heat treatment under hydrogen, BaCO3 and Ba(OH)2 formed on the surface become BaO, so it is considered that the catalytic activity is improved.

[0175] Figure 25 is an electron micrograph of the catalyst of Example 1. (1) is an HAADF-STEM image. The following can be considered from the elemental mapping images of (2) to (5). The part that shines the brightest white in (1) is Co, and the part that shines in a light gray color next is the part where magnesium oxide is present. Looking at (5), it can be seen that the barium oxide particles are distributed uniformly on Co / MgO in a particle shape smaller than the Co particles. The particle size of the barium oxide particles is at most about 10% of the particle size of the Co particles. Since the order of catalyst preparation is to support barium hydroxide on the magnesium oxide support and then support cobalt on it, it is considered that the barium oxide particles move onto the cobalt particles under the catalyst production conditions, and since the barium compound was already uniformly distributed on the surface of the magnesium oxide before cobalt loading, Ba is also likely to be present near the interface between magnesium oxide and cobalt. According to the overlay image of (5), it can be seen that Ba exists as a nano-order core (Co particle) / shell (barium oxide) structure covering the periphery of Co. In this catalyst, the surface cobalt atoms close to barium oxide receive strong electron donation, so it shows high ammonia synthesis activity. This supports the above consideration.

[0176] Figure 34 is an electron micrograph of the catalyst of Example 17. (1) is an HAADF-STEM image. (2) to (5) are elemental mapping images, and the following can be considered from a comparison with Figure 25. In the case of reduction at 500 °C for 72 hours (Figure 34), since the reduction temperature is lower than that at 700 °C for 1 hour (Figure 25), a nano-order core (Co particles) / shell (barium oxide) structure can be seen, but the particle size of barium oxide is small and the mobility of barium oxide onto the cobalt particles is somewhat low. However, considering the fact that the reduction treatment was carried out over a long time, the decomposition of barium carbonate and hydroxide is considered to have progressed more than in the case of reduction at 500 °C for 1 hour (Example 7). On the other hand, since the reduction temperature is low, the cobalt particle size is small, and also because the reduction treatment was carried out over a long time, the reduction degree of cobalt is higher than that in the case of reduction at 500 °C for 1 hour (Example 7), and the number of surface cobalt atoms in the metallic state contributing to ammonia synthesis increases. Therefore, the catalyst of Example 17 exhibits ammonia synthesis activity comparable to that of the catalyst of Example 1.

[0177] As in Examples 33 and 34 described later, in the case of double addition of Group 1 element + Group 2 element, an improvement in ammonia synthesis activity was observed more than in Example 17. This is because a Group 1 element, which is a stronger basic element than the oxide of the Group 2 element, is incorporated into the shell structure of barium oxide, and the surface cobalt atoms close to the shell receive a very strong electron donation.

[0178] 15. Ammonia synthesis activity of catalysts in which Ba is changed to other Group 2 elements (Sr, Ca) (Examples 26 to 27) In Example 1, Sr(OH)2 and Ca(OH)2 were used instead of Ba(OH)2 as the raw material, and 20 wt% Co / Sr 0.01 Mg 0.99 O x (Example 26) and 20 wt% Co / Ca 0.01 Mg 0.99 O x(Example 27) was prepared. For these metal supports, ammonia synthesis was carried out at various temperatures (300 °C, 350 °C, 400 °C, 450 °C), and the ammonia synthesis activity was measured by the method described above. The ammonia synthesis conditions were a reaction pressure of 1.0 MPa, for the reaction gas, H2 / N2 = 90 / 30 cc / min (total flow rate was 120 cc / min), and the catalyst amount was 0.1 g (SV = 72 L h -1 g -1 ). The results are shown in the following table.

[0179]

Table 17

[0180] Also, the results are shown in Fig. 26. From this figure, for Group 2 elements other than Ba (Sr, Ca), the activity is also higher than that of only MgO, and the effect of improving the ammonia synthesis activity by addition was recognized.

[0181] 16. Addition of Group 1 elements instead of Group 2 elements (Examples 28 - 31) In Example 1, instead of Ba(OH)2 as the raw material, KNO3, KOH, LiNO3, and LiOH were used, and composite oxides were produced at various reduction temperatures, and 20 wt% Co / K 0.03 Mg 0.97 O x (Example 28), 20 wt% Co / K 0.03 Mg 0.97 O x (Example 29), 20 wt% Co / Li 0.03 Mg 0.97 O x (Example 30), 20 wt% Co / Li 0.03 Mg 0.97 O x (Example 31) was prepared. For these metal supports, ammonia synthesis was carried out at various temperatures (300 °C, 350 °C, 400 °C, 450 °C), and the ammonia synthesis activity was measured by the method described above. The results are shown in Fig. 27. From this figure, for the system with K added using KOH, some effect of improving ammonia activity was observed, but it was found that the ammonia synthesis activity was not as significantly high as that of Group 2 elements.

[0182] 17. Double addition of Group 1 element + Group 2 element (Examples 32 to 34) In Example 1, in addition to Ba(OH)2 as the raw material, CsOH, RbOH, and KOH were used to produce a composite oxide, which was pretreated under reduction conditions of 700°C for 1 hour, and 20 wt% Co / Cs 0.01 Ba 0.01 Mg 0.98 O x _Reduced at 700°C for 1 h (Example 32), 20 wt% Co / Rb 0.01 Ba 0.01 Mg 0.98 O x _Reduced at 700°C for 1 h (Example 33), 20 wt% Co / K 0.01 Ba 0.01 Mg 0.98 O x _Reduced at 700°C for 1 h (Example 34) were prepared. Ammonia synthesis was carried out on these metal supports at various temperatures (300°C, 350°C, 400°C, 450°C), and the ammonia synthesis activity was measured by the method described above. The results are shown in the following table.

[0183]

Table 18

[0184] Also, the results are shown in Fig. 28. From this figure, when 1 mol% of the Group 1 element was added and the pretreatment conditions were fixed at 700°C for 1 h, the activity was slightly lower than that when no Group 1 element was added (only Ba), but the ammonia synthesis activity comparable to that of the case of only Ba was obtained. However, since the ammonia synthesis activity was the highest in the case of only Ba, no improvement in ammonia synthesis activity was observed by adding (double adding) the Group 1 element.

[0185] 18. Double addition of Group 1 element + Group 2 element (Investigation of reduction conditions 1) (Examples 35 to 36) In Example 30, the amount of KOH as the raw material was increased and the reduction conditions were changed to 20 wt% Co / K 0.03 Ba 0.01 Mg0.96 O x _Reduction at 500 °C for 72 h (Example 35), 20 wt% Co / K 0.03 Ba 0.01 Mg 0.96 O x _Reduction at 700 °C for 1 h (Example 36) was prepared. For these metal supports, ammonia synthesis was carried out at various temperatures (300 °C, 350 °C, 400 °C, 450 °C), and the ammonia synthesis activity was measured by the method described above. The results are shown in the following table.

[0186]

Table 19

[0187] Also, the results are shown in Figure 29. From this figure, in the case of 3 mol% K + 1 mol% Ba, no effect on the improvement of ammonia synthesis activity was observed even after reduction at low temperature for a long time.

[0188] 19. Double addition of Group 1 element + Group 2 element (Investigation of reduction conditions 2) (Example 37) In Example 30, without changing the amount of raw material KOH, the reduction conditions were changed to prepare 20 wt% Co / K 0.01 Ba 0.01 Mg 0.98 O x _Reduction at 500 °C for 72 h (Example 37) was prepared. For these metal supports, ammonia synthesis was carried out at various temperatures (300 °C, 350 °C, 400 °C, 450 °C), and the ammonia synthesis activity was measured by the method described above. The results are shown in the following table.

[0189]

Table 20

[0190] Also, the results are shown in Figure 30. From this figure, in the case of 1 mol% K + 1 mol% Ba, it was found that the activity improved when reduced at low temperature for a long time. In the figure, near the reaction temperature of 450 °C, the influence of equilibrium appears, and it is presumed that they all have the same degree of ammonia synthesis activity.

[0191] 20. Double addition of Group 1 element + Group 2 element (Investigation of reduction conditions 3) (Example 38) In Example 29, the reduction conditions were changed to prepare 20 wt% Co / Rb 0.01 Ba 0.01 Mg 0.98 O x _reduced at 500 °C for 72 h (Example 38). Ammonia synthesis was carried out on these metal supports at various temperatures (300 °C, 350 °C, 400 °C, 450 °C), and the ammonia synthesis activity was measured by the method described above. The results are shown in the following table.

[0192]

Table 21

[0193] Also, the results are shown in Figure 31. From this figure, it was found that in the case of 1 mol% Rb + 1 mol% Ba, the activity is improved when reduced at a low temperature for a long time. In the figure, the influence of equilibrium appears near the reaction temperature of 450 °C, and it is presumed that the ammonia synthesis activities are all of the same degree.

[0194] 21. Replace Co with Ni (Investigation of reaction pressure 1) (Example 39) In Example 1, the same operation as in Example 1 was carried out except that cobalt acetylacetonate (II) was replaced with nickel acetylacetonate (II) (Kishida Chemical), which is a Ni precursor, to obtain Ni / Ba 0.01 Mg 0.99 O x _reduced at 700 °C for 1 h (Example 35). Ammonia synthesis was carried out on this metal support (Example 39) and the metal supports of Example 1 and Example 22 at 1.0 MPa and various temperatures (300 °C, 350 °C, 400 °C, 450 °C), and the ammonia synthesis activity was measured by the method described above. The results are shown in the following table.

[0195]

Table 22

[0196] Also, the results are shown in Fig. 32. From this figure, it was found that the Ni-supported catalyst has higher ammonia synthesis activity than the Fe-supported catalyst at 450°C.

[0197] 22. Replacing Co with Ni (Investigation of reaction pressure 2) (Example 40) For the metal supports of Example 1, Example 22, and Example 40, ammonia synthesis was carried out under the condition of 3.0 MPa, and the ammonia synthesis activity was measured by the method described above. The results are shown in the following table.

[0198]

Table 23

[0199] Also, the results are shown in Fig. 33. From this figure, it was found that both the Ni-supported catalyst and the Fe-supported catalyst show relatively high activity even at 3 MPa. However, it seems that the Ni-supported catalyst is slightly affected by poisoning.

[0200] 23. Reduction degree of Co To compare the influence of the hydrogen reduction treatment on the reduction state of Co in the catalyst, X-ray absorption near-edge structure (XANES) spectra of the Co K absorption edge of Co / BaMgOx were measured. For the catalyst before the reduction treatment and the standard sample as the comparison target, samples for XANES spectrum measurement were prepared by the following method. The catalyst and the standard sample before the reduction treatment and boron nitride powder were ground and mixed in the air, and the mixed powder was pressed into a disk shape with a diameter of 10 mm. At this time, the ratio of each catalyst and standard sample to boron nitride and the thickness of the disk were appropriately adjusted so that the concentration of Co in the measurement target was optimized with respect to the absorbance of the X-ray transmitted during the spectrum measurement.

[0201] For the catalyst after the reduction treatment, samples for XANES spectrum measurement were prepared by the following method. The catalyst was filled into a sample tube and connected to a fixed-bed flow-type reaction apparatus. While flowing hydrogen, it was heated at a predetermined temperature for 1 hour for the reduction treatment. After the reduction treatment, the catalyst was allowed to cool to room temperature while supplying an inert gas (Ar) to the sample tube. The sample tube of this reaction apparatus is equipped with cocks on both the gas inlet and outlet sides. By closing these cocks after cooling, the catalyst can be held without being exposed to the atmosphere even when removed from the reaction apparatus. Using this sample tube, the reduced catalyst was transferred to a glove box filled with an inert gas. After grinding and mixing the reduced catalyst and boron nitride powder in the glove box, the mixed powder was press-molded into a disk shape with a diameter of 10 mm. At this time, the ratio of each catalyst to boron nitride and the thickness of the disk were appropriately adjusted so that the concentration of Co in the measurement target was optimized with respect to the absorbance of the X-ray transmitted during the spectrum measurement.

[0202] The formed disk was triple-encapsulated in an oxygen-barrier resin bag in the glove box. As a result, even when the resin bag is taken out of the glove box into the atmosphere, the spectrum can be measured while the catalyst is not affected by re-oxidation by oxygen.

[0203] The XANES spectra of each prepared measurement sample were measured at BL01B1 of the large synchrotron radiation facility (SPring-8). Using an ion chamber as the detector, the spectrum measured by the transmission method was analyzed using X-ray absorption spectrum analysis software (Athena, Demeter 0.9.26).

[0204] Figure 36 shows the XANES spectra of the normalized catalyst and the standard sample. When the spectral shapes of the unreduced catalyst and the standard sample were compared, it was found that, whether Ba was included or not, the energy position and shape of the XANES spectrum of the unreduced catalyst were in good agreement with those of oxide (II) (CoO). Therefore, it was suggested that Co existed as CoO in the unreduced catalyst. Also, by performing the reduction treatment, the spectral shape of the XANES spectrum approached that of Co foil. This means that Co in the catalyst changed to the metallic state by the reduction treatment.

[0205] Therefore, linear combination fitting was performed on the normalized XANES spectra of each catalyst after the reduction treatment, using the spectra of metallic Co foil and Co oxide (II) of the standard sample as a reference, to determine the ratio (degree of reduction) of metallic Co contained in the catalyst. As a result, for the Co / BaMgOx catalyst, the Co reduction degree after reduction at 500 °C for 1 hour was 71%, and the Co reduction degree after reduction at 700 °C for 1 hour (the catalyst of Example 1) was 93%. It became clear that as the reduction treatment temperature increased, the ratio of Co oxide, which is inactive for ammonia synthesis, decreased, while the ratio of metallic Co, which is active for ammonia synthesis, increased.

Claims

1. A metal-supported material in which metal particles M are supported on a composite oxide composed of an oxide of metal element L and an oxide of metal element N, (A) The composite oxide is represented by the composition of the following general formula (1) and has the following (a) to (d): L ｎ N １－ｎ (1) (a) The metal element L is selected from the group consisting of Ba and Sr. (b) The metal element N is selected from the group consisting of Mg and Be. (c) The n is 0.001 or more and 0.300 or less. (d) The oxide of the metal element L and the oxide of the metal element N do not form a solid solution, and the oxide particles of the metal element L are deposited on the surface of the oxide particles of the metal element N. (B) The metal particles M are one or more selected from the group consisting of Fe, Co, and Ni. (C) A metal-supported material in which the metal particles M are supported on the oxide of the metal element L deposited on the surface of the oxide of the metal element N, and oxide particles of the metal element L are deposited on the surface of the metal particles M.

2. (a) The metal element L represents a metal element that is a strongly basic element with a value of the partial negative charge (-δ ＯＡ ) of oxygen in the oxide state being 0.56 or more and 0.70 or less. (b) The metal element N represents a metal element that is a weakly basic element with a value of the partial negative charge (-δ ＯＢ ) of oxygen in the oxide state being 0.35 or more and 0.55 or less. The metal-supported material according to claim 1, characterized in that.

3. The composite oxide is a binary composite oxide composed of a metal element A contained in the metal element L and a metal element B contained in the metal element N, and the general formula (1) is represented by the composition of the following general formula (2) and has the following (a) to (d). The metal-supported material according to claim 1, characterized in that A ｎ B １－ｎ (2) (a) The metal element A represents a Group 2 element which is a strongly basic element with a value of the partial negative charge (-δ ＯＡ ) of oxygen in the oxide state being 0.56 or more and 0.70 or less. (b) The metal element B represents a Group 2 element which is a weakly basic element with the value of the partial negative charge (-δ ＯＢ ) of oxygen in the oxide state being 0.35 or more and 0.55 or less, (c) The n is 0.001 or more and 0.300 or less. (d) The oxide of the metal element A and the oxide of the metal element B do not form a solid solution, and the oxide particles of the metal element A are deposited on the surface of the oxide particles of the metal element B.

4. A metal-supported material in which metal particles M are supported on a composite oxide composed of an oxide of metal element L and an oxide of metal element N, (A) The composite oxide is represented by the composition of the following general formula (3) and has the following (a) to (d): L ｎ N １－ｎ O ｘ (3) (a) The metal element L is selected from the group consisting of Ba and Sr. (b) The metal element N is selected from the group consisting of Mg and Be. (c) The n is 0.001 or more and 0.300 or less. (d) The oxide of the metal element L and the oxide of the metal element N do not form a solid solution, and the oxide particles of the metal element L are deposited on the surface of the oxide particles of the metal element N. (B) The metal particles M are one or more selected from the group consisting of Fe, Co, and Ni. (C) A metal-supported material in which the metal particles M are supported on the oxide of the metal element L deposited on the surface of the oxide of the metal element N, and oxide particles of the metal element L are deposited on the surface of the metal particles M.

5. (a) The metal element L represents a metal element that is a strongly basic element with a value of the partial negative charge (-δ ＯＡ ) of oxygen in the oxide state being 0.56 or more and 0.70 or less. (b) The metal element N represents a metal element that is a weakly basic element with a value of the partial negative charge (-δ ＯＢ ) of oxygen in the oxide state being 0.35 or more and 0.55 or less. The metal-supported material according to claim 4, characterized in that.

6. The composite oxide is a binary composite oxide composed of metal element A contained in metal element L and metal element B contained in metal element N. The general formula (3) is represented by the composition of the following general formula (4) and is characterized by the following (a) to (d). The metal support according to claim 4 A ｎ B １－ｎ O ｘ (4) (a) The metal element A represents a Group 2 element which is a strongly basic element having a value of the partial negative charge (-δ ＯＡ ) of oxygen in the oxide state of 0.56 or more and 0.70 or less. (b) The metal element B represents a Group 2 element which is a weakly basic element with the value of the partial negative charge (-δ ＯＢ ) of oxygen in the oxide state being 0.35 or more and 0.55 or less. (c) n is 0.001 or more and 0.300 or less, (d) The oxide of the metal element A and the oxide of the metal element B do not form a solid solution, and the oxide particles of the metal element A are deposited on the surface of the oxide particles of the metal element B, (e) x is the number of oxygen atoms necessary for the composite oxide to maintain electrical neutrality. A metal support characterized by this

7. wherein the composite oxide is Ba ｎ Mg １－ｎ O ｘ (where 0.001 ≦ n ≦ 0.300), and the metal support according to claim 1 or 4, characterized in that.

8. wherein the composite oxide is Ba ｎ Mg １－ｎ O ｘ (where 0.01 ≦ n ≦ 0.10), the metal support according to claim 7.

9. The amount of carbonate contained in the composite oxide is 10 mol% or less with respect to Ba. The metal support according to claim 7

10. The metal support according to claim 1, wherein oxide particles of the metal element N are distributed between the oxide particles of the metal element L and the metal particles M

11. The metal support according to claim 1, wherein the metal particles M are cobalt particles

12. A catalyst for ammonia synthesis, characterized by using the metal support according to claim 1

13. A method for producing a metal support according to claim 1, characterized by including the following steps (a) to (d). (a) An impregnation step of impregnating an N precursor containing the metal element N with an L precursor containing the metal element L to obtain a mixture, (b) A composite oxide firing step of firing the mixture at a temperature of 500°C or higher to obtain a carrier made of a composite oxide, (c) A supporting step of impregnating the composite oxide with a precursor of a compound containing the metal particles M to obtain an impregnated carrier, (d) A support firing step of firing the impregnated carrier at a temperature of 400°C or higher, (e) A reduction step of firing the metal support obtained in (d) at 500°C or higher in the presence of hydrogen.

14. A method for producing ammonia by bringing hydrogen and nitrogen into contact with a catalyst, wherein the catalyst is the catalyst for ammonia synthesis according to claim 12

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