JP7023457B2 - Ammonia synthesis catalyst and ammonia synthesis method using the catalyst - Google Patents

Description

The present invention relates to a catalyst for synthesizing ammonia and an ammonia synthesizing method using the catalyst.

The Haber-Bosch method, which is a typical ammonia synthesis method, uses a double promoted iron catalyst containing several mass% of Al ₂ O ₃ and K ₂ O in Fe ₃ O ₄ as this catalyst. This is a method for producing ammonia by directly reacting a mixed gas of nitrogen and hydrogen under high temperature and high pressure conditions. This technology is still used industrially in the manufacturing process as it was when it was completed.

On the other hand, a method of synthesizing ammonia at a temperature lower than the reaction temperature of the Haber-Bosch method is being studied. A catalyst capable of synthesizing ammonia by contacting with nitrogen and hydrogen has been studied, and a transition metal has been studied as a catalytically active ingredient thereof. Of these, a method in which ruthenium (Ru) is supported on various carriers as a catalytically active ingredient and used as a catalyst for ammonia synthesis has been proposed as an efficient method (for example, Patent Document 1).

It is known that catalysts using transition metals such as Ru can synthesize ammonia under milder conditions than the reaction conditions used in the Haber-Bosch process because of their extremely high activity. .. For example, it is known that the reaction proceeds at a reaction temperature of 200 to 400 ° C. and a reaction pressure of about 1.1 MPa from atmospheric pressure under low temperature and low pressure.

There is a compound called "myenite-type compound" which is calcium aluminosilicate having CaO, Al ₂ O ₃ , and SiO ₂ as constituents and has a crystal structure of the same type as mayenite. The representative composition of the mayenite-type compound is represented by 12CaO ・_7Al2O3 , and _two oxygen atoms are included as “free oxygen” in the space in the cage formed by the crystal skeleton thereof. Has a structure.
According to the present inventor, a catalyst in which a transition metal is supported as a catalytically active component in a mayenite compound (hereinafter referred to as C12A7 electride) in which free oxygen in the mayenite-type compound is substituted with electrons has high activity as a catalyst for ammonia synthesis. Found to have. (Patent Document 2).
Furthermore, the present inventor has found that a supported metal catalyst using a compound such as a metal amide compound or a metal hydride has high activity as a catalyst for ammonia synthesis. (Patent Documents 3 and 4).
These catalysts have sufficient reaction activity even under low temperature and low pressure reaction conditions as compared with the reaction conditions of the Haber-Bosch method.

Japanese Unexamined Patent Publication No. 2006-231229 International Publication No. 2012/077658 International Publication No. 2016/088896 International Publication No. 2017/082265

Ammonia synthesis by the Haber-Bosch method, which mainly uses a double-accelerated iron catalyst, has been put into practical use, but there is a problem that the burden on the equipment and cost is large because it requires high temperature and high pressure conditions.
As the supported metal catalyst as described in Patent Document 1, a carbonaceous carrier such as activated carbon or an inorganic oxide carrier is usually used. However, these supported metal catalysts have low reaction activity and have insufficient performance for practical use.
That is, there is a demand for a catalyst for ammonia synthesis that has sufficient reaction activity even under conditions of lower temperature and lower pressure than the reaction conditions of the Haber-Bosch method.

The catalysts described in Patent Documents 2 to 3 have sufficient reaction activity even under low temperature and low pressure reaction conditions, but can be produced by a simpler method as compared with these catalysts, and are used for ammonia synthesis with high reaction activity. A catalyst is required.
The catalyst described in Patent Document 4 can be produced by a simpler method than the catalysts described in Patent Documents 2 to 3 while having sufficient reaction activity even under low temperature and low pressure reaction conditions. There is a demand for a catalyst for ammonia synthesis in which the catalytic activity does not decrease even after repeated synthesis reactions.

The present inventor has provided the catalyst for ammonia synthesis of the present invention, which can achieve both improvement and stabilization of catalytic performance by supporting and supporting a transition metal on a metal hydride containing an alkaline earth metal oxide. The finding led to the present invention.

That is, the gist of the present invention is
[1] A catalyst for ammonia synthesis comprising a transition metal and a metal carrier containing the transition metal carrier, wherein the carrier is a metal hydride represented by the following general formula (1) and MgO. A catalyst for ammonia synthesis, which comprises any one of alkaline earth metal oxides selected from the group consisting of SrO and BaO.
XH _n ... (1)
(In the above general formula (1), X represents at least one selected from Group 2 atoms, Group 3 atoms, or lanthanoid atoms in the periodic table, and n represents a number represented by 2 ≦ n ≦ 3. )
[2] The catalyst for ammonia synthesis according to [1], wherein X in the general formula (1) is at least one selected from Mg, Ca, Sr, Ba, Sc, Y, or a lanthanoid atom.
[3] The catalyst for ammonia synthesis according to [1] or [2], wherein the transition metal is at least one selected from Ru, Co, or Fe.
[4] The catalyst for ammonia synthesis according to any one of [1] to [3], wherein the amount of the transition metal supported on the carrier is 1.0% by mass or more and 30% by mass or less.
[5] The catalyst for ammonia synthesis according to any one of [1] to [4], wherein the content of the alkaline earth metal oxide with respect to the carrier is 0.5 mol% or more and 8 mol% or less.
[6] A method for producing ammonia, characterized in that a raw material gas containing hydrogen and nitrogen is brought into contact with the catalyst for ammonia synthesis according to any one of [1] to [5] to synthesize ammonia. Ammonia production method.
[7] The method for producing ammonia according to [6], wherein the reaction temperature at the time of contact with the catalyst for ammonia synthesis is 100 ° C. or higher and 600 ° C. or lower.
[8] The method for producing ammonia according to [6] or [7], wherein the reaction pressure at the time of contact with the catalyst for ammonia synthesis is 10 kPa or more and 20 MPa or less.
[9] The method for producing ammonia according to any one of [6] to [8], wherein the raw material gas has a water content of 100 ppm or less.
[10] Any of [6] to [9], wherein the ratio of hydrogen to nitrogen (H ₂ / N ₂ (volume / volume)) when contacted with the ammonia synthesis catalyst is 0.4 or more. The method for producing ammonia according to.

The catalyst for ammonia synthesis of the present invention is suitable as a catalyst for ammonia synthesis because it has a high ammonia synthesis activity even at a low reaction temperature and a low reaction pressure, and the catalytic activity does not decrease even if the synthesis reaction is repeated. .. By producing ammonia using the catalyst for synthesizing ammonia of the present invention, ammonia can be synthesized with less energy, and the catalytic activity does not decrease even if the synthesis reaction is repeated. Ammonia can be produced with the stability of. That is, the catalyst for ammonia synthesis of the present invention can achieve both improvement and stabilization of catalytic performance, and not only exhibits catalytic performance more than twice that of the conventional transition metal particle / calcium hydride catalyst, but also its catalytic performance. Does not deteriorate over time.

It is a graph which shows the time-dependent change of the ammonia synthesis rate in Example 1 and Comparative Example 1. It is a graph which shows the time-dependent change of the ammonia synthesis rate in Examples 1-6. It is a figure which shows the dependence of the BaO molar ratio of a catalytic activity (ammonia synthesis rate). 3 is an SEM photograph of the catalyst before and after the ammonia synthesis reaction in Example 1. 5 is an XPS spectrum of an ammonia synthesis catalyst in Example 1. It is a figure which shows the X-ray diffraction pattern of the ammonia synthesis catalyst in Example 5. It is a graph which shows the time-dependent change of the ammonia synthesis rate in Examples 1, 7-10. It is a figure which shows the dependence of Ru carrying amount of catalytic activity (ammonia synthesis rate). It is a graph which shows the time-dependent change of the ammonia synthesis rate in Examples 1, 11 and 12. It is a graph which shows the time-dependent change of the ammonia synthesis rate in Examples 1 and 13.

The present invention will be described in detail below.
<Catalyst for ammonia synthesis>
The catalyst for ammonia synthesis of the present invention contains a transition metal and a carrier supporting the transition metal, and the carrier consists of a metal hydride represented by the following general formula (1) and a group consisting of MgO, SrO, and BaO. It is characterized by comprising any one of the selected alkaline earth metal oxides.

XH _n ... (1)

(In the above general formula (1), X represents at least one selected from Group 2 atoms, Group 3 atoms, or lanthanoid atoms in the periodic table, and n represents a number represented by 2 ≦ n ≦ 3. )

(Metal hydride)
The carrier used in the present invention contains a hydride of the metal element X.
In the general formula (1), X represents at least one selected from Group 2 atoms, Group 3 atoms, or lanthanoid atoms in the periodic table.
The atom used for X is not particularly limited, but may be one kind or may contain two or more kinds of elements. When two or more kinds of elements are contained, it is not particularly limited, but it is preferable that atoms of the same group or lanthanoid atoms are contained.

The group 2 atom of the periodic table (hereinafter, simply referred to as a group 2 atom and may be abbreviated as AE) is not particularly limited, but is preferably Mg, Ca, Sr, Ba, and more preferably. It is Ca and Sr because it has high activity when used as a catalyst for ammonia synthesis, and more preferably Ca because it has high activity when used as a catalyst for ammonia synthesis.

The Group 3 atom (hereinafter referred to as Group 3 atom) in the periodic table is not particularly limited, but is preferably Y because it is an element having a larger abundance.
The lanthanoid atom is not particularly limited, but is preferably La, Ce, Pr, Nd, Sm, Eu, Pr, Yb because it is a more general-purpose material, and more preferably the abundance is compared. It has a large amount of La, Ce, Nd, and Sm, and more preferably La, Ce because it has high activity when used as a catalyst for ammonia synthesis.

When X is a lanthanoid atom, it may contain a plurality of lanthanoid atoms, and specifically, it may be a misch metal. Mischmetal is a common name for an alloy containing a plurality of rare earth elements (rare earths), and is generally known as an alloy containing a large amount of Ce as a component thereof.
The Group 3 atom and the lanthanoid atom may be collectively abbreviated as RE below.
The X is preferably a Group 2 atom or a lanthanoid atom having a large amount of elements and high activity when used as a catalyst for ammonia synthesis, and more preferably a second group in that the abundance of elements is large. It is a group atom.
Further, the X is preferably Ca, Mg, Sr, Ba, Y, or a lanthanoid atom, and more preferably Ca, Mg, Sr, Ba, Y, La, Ce, Pr, Nd, Sm, Eu, Pr. , Yb, and more preferably Ca.

N in the general formula (1) represents a numerical value of 2 ≦ n ≦ 3.
When X is a Group 2 atom, the n is not particularly limited, but is preferably 2.
When X is a Group 3 atom or a lanthanoid atom, the n usually represents an arbitrary numerical value of 2 to 3, and is preferably 2 or 3.

The AE and RE usually form an ion-bonded hydride. In the ion-bonded hydride, hydrogen exists as a hydride ion (H ^- ion), and when it comes into contact with water or an acid, hydrogen (H ₂ ) and a hydroxide ion (OH- ⁾ are generated.
As the hydride of RE (hereinafter referred to as REH _n ), a dihydride which is a general hydride and a trihydride which is a high-density hydride are known. Then, a high-density metal hydride having a value between the dihydride and the trihydride can be formed, and the value between the dihydride and the trihydride can be continuously changed. ..

As long as the effect of the present invention is not impaired, the X may further contain an atom other than X, and specifically, at least one kind of alkali metal atom may be contained.

The metal hydride used in the present invention is not particularly limited, and may be used by using a commercially available reagent or an industrial raw material, or by synthesizing and using a corresponding metal by a known method such as heating in a hydrogen atmosphere. good.

(Alkaline earth metal oxide)
The carrier used in the present invention contains the alkaline earth metal oxide. The alkaline earth metal oxide is any one selected from the group consisting of MgO, SrO, and BaO. BaO is preferred.
As MgO, SrO, and BaO, commercially available products such as BaO powder (specific surface area: 1.0 m ² / g) manufactured by high-purity chemicals may be used as they are, and they may be used after being dried before use. May be good.
In addition, barium hydroxide (Ba (OH) ₂ ) or the like that can generate BaO (as a precursor of BaO) may be used in pretreatment or the like.
Further, a Ba compound or the like capable of producing metal Ba may be used in pretreatment or the like.

Although the action and effect of a specific alkaline earth metal oxide such as BaO in the catalyst of the present invention has not been clarified yet, it is suggested that oxygen defect BaO may be formed in the vacuum heat treatment step described later.

(Transition metal)
The transition metal used in the present invention is not particularly limited, but is usually a transition metal of Group 6, 7, 8, 9, and 10 of the periodic table, and is preferably Group 6; It is a Group 8 or Group 9 transition metal, more preferably a Group 8 or Group 9 metal.
The specific metal element is not particularly limited, but is usually Cr, Mo, Mn, Re, Fe, Ru, Os, Co, Rh, Ni, Pd, Pt, and is preferably bonded to nitrogen. It is Mo, Re, Fe, Ru, Os, Co in terms of high energy, and more preferably Ru, Co in that it has ammonia synthesis activity when a catalyst for ammonia synthesis is used as a catalyst for ammonia synthesis. Alternatively, it is Fe, and more preferably Ru in that it has the highest catalytic activity.
Each of the above elements may be used alone or in combination of two or more. Further, intermetallic compounds of these elements, for example, Co ₃ Mo ₃ N, Fe ₃ Mo ₃ N, Ni ₂ Mo ₃ N, Mo ₂ N and the like can also be used. It is preferable to use each element alone or in combination of two or more kinds, and more preferably, it is advantageous in terms of cost to use them alone.

(Composition of catalyst for ammonia synthesis)
The molar ratio content of the alkaline earth metal oxide in the carrier used for the catalyst for synthesizing ammonia of the present invention is not particularly limited, but is the total amount of the metal hydride and the alkaline earth metal oxide. On the other hand, it is usually 0.5 mol% or more, preferably 1 mol% or more, more preferably 2 mol% or more, and usually 10 mol% or less, preferably 5 mol% or less, more preferably 4 mol% or less. If it is at least the lower limit value, the effect of the present invention is obtained, and if it is at least the upper limit value, the catalytic activity is conversely lowered.

The amount of the transition metal supported on the carrier containing the metal hydride and the alkaline earth metal oxide in the catalyst for ammonia synthesis of the present invention is not particularly limited, but is usually relative to the total amount of the catalyst. , 0.5 wt% or more, preferably 2 wt% or more, more preferably 5 wt% or more, usually 20 wt% or less, preferably 15 wt% or less, more preferably 10 wt% or less. If it is at least the lower limit value, the effect of the present invention can be obtained, and if it is at least the upper limit value, the effect of the present invention corresponding to the amount of support and the cost can be obtained.

The specific surface area of the catalyst for ammonia synthesis of the present invention is not particularly limited, but is usually 0.1 m ² / g or more, preferably 1 m ² / g or more, and preferably 3 m ² / g or more.

(Shape of catalyst for ammonia synthesis)
The shape of the catalyst for synthesizing ammonia of the present invention is not particularly limited, and may be any shape such as a lump, a powder, and a film, but is usually a powder. The particle size of the powdery ammonia synthesis catalyst is not particularly limited, but is usually 1 nm or more and 100 nm or less.
The particle size of the transition metal in the catalyst for synthesizing ammonia of the present invention is not particularly limited, but is usually 1 nm or more and 100 nm or less. It is preferably 10 nm or less, more preferably 5 nm or less, which is advantageous in that the number of step sites which are active sites of nitrogen dissociation increases when used as a catalyst for ammonia synthesis.

The dispersity of the alkaline earth metal oxide in the carrier of the catalyst for synthesizing ammonia of the present invention is not particularly limited, but for example, the alkaline earth metal oxide particles (regions) in the carrier are usually 10 nm or more. It is 20 μm or less. It is desirable that alkaline earth metal oxides are dispersed on the surface of the catalyst for ammonia synthesis, but it is not desirable to completely cover the surface.

(Manufacturing method of catalyst for ammonia synthesis)
The catalyst for ammonia synthesis of the present invention is produced by supporting the transition metal on the carrier containing the metal hydride and the alkaline earth metal oxide. The production method is not particularly limited, but usually, the carrier is supported on a transition metal or a compound that is a precursor of the transition metal (hereinafter referred to as a transition metal compound).

As the metal hydride used as a raw material for the catalyst for ammonia synthesis of the present invention, a commercially available reagent or an industrial raw material may be used, or a metal obtained from a corresponding metal by a known method may be used. Usually, metal hydrides are obtained by heating the corresponding metal in a hydrogen atmosphere.
For example, calcium hydride (CaH ₂ ) can be obtained by heating metallic calcium to about 400 ° C. in a hydrogen atmosphere.
Further, for example, cerium hydride (CeH ₂ ) can be obtained by heating metallic cerium to about 700 to 800 ° C. in a hydrogen atmosphere.

The method for preparing a carrier by mixing the alkaline earth metal oxide with the metal hydride used in the present invention is not particularly limited, and a known method can be used. Specifically, for example, a method such as a physical mixing method, a CVD method (chemical vapor deposition method), or a sputtering method can be used. Since the metal hydride easily reacts with water and has low solubility in an organic solvent, the alkaline earth metal oxide in a powder state is mixed with the metal hydride in a powder state by a physical mixing method. The method is preferred. The physical mixing method is a method in which the carrier and the transition metal compound are solid-mixed and then heated in an inert gas stream such as nitrogen, argon or helium, or under vacuum. As the solid mixing method, for example, a device and a method for mixing and pulverizing two or more known solids are used. In that case, the heating temperature is usually preferably 400 ° C. or lower, which is higher than the decomposition temperature of the transition metal compound. The heating time is preferably 2 hours or more.

The carrier obtained above may be used as it is to support the transition metal in the transition metal supporting step described later, or at about 200 to 500 ° C. for several hours, for example, 340 ° C. for 2 hours in a hydrogen atmosphere. After performing the pretreatment for heating, the transition metal may be supported in the transition metal supporting step described later.
The carrier A catalyst produced by using a sample preheated in a hydrogen atmosphere can obtain high activity immediately after the start of the reaction, for example, when used in an ammonia synthesis reaction.

The method is not particularly limited as the carrier used in the present invention, and known methods can be used. Usually, a method is used in which a transition metal compound that is a carrier of a transition metal and can be converted into a transition metal by reduction, thermal decomposition, or the like is supported on the carrier and then converted into a transition metal.

The transition metal compound is not particularly limited, but an inorganic compound or an organic transition metal complex of a transition metal that is easily thermally decomposed can be used. Specifically, transition metal complexes, transition metal oxides, transition metal salts such as nitrates and hydrochlorides, and the like can be used.
For example, examples of the Ru compound include ruthenium dodecacarbonyl [Ru ₃ (CO) ₁₂ ], dichlorotetrakis (triphenylphosphine) ruthenium (II) [RuCl ₂ (PPh ₃ ) ₄ ], and dichlorotris (triphenylphosphine) ruthenium (II). ) [RuCl ₂ (PPh ₃ ) ₃ ], Tris (acetylacetonato) ruthenium (III) [Ru (acac) ₃ ], Ruthenosen [Ru (C _{5H 5 )} ], Ruthenium nitrosyl nitrate [Ru (NO) (NO) ₃ ) ₃ ], potassium rutheniumate, ruthenium oxide, ruthenium nitrate, ruthenium chloride and the like can be mentioned. Tris (acetylacetonato) ruthenium (III) [Ru (acac) ₃ ] is preferred.

Examples of Fe compounds include pentacarbonyl iron [Fe (CO) ₅ ], dodecacarbonyl triiron [Fe ₃ (CO) ₁₂ ], nonacarbonyl iron [Fe ₂ (CO) ₉ ], and tetracarbonyl iron iodide [Fe (CO). ) ₄ I ₂ ], tris (acetylacetonato) iron (III) [Fe (acac) ₃ ], ferrocene [Fe _{(C5 H 5) 2 ] ,} iron oxide, iron nitrate, iron chloride (FeCl ₃ ), etc. Can be mentioned.

Examples of Co compounds include cobalt octacarbonyl [Co ₂ (CO) ₈ ], tris (acetylacetonato) cobalt (III) [Co (acac) ₃ ], cobalt (II) acetylacetonato [Co (acac) ₂ ], Cobalt sen [Co (C ₅ H ₅ ) ₂ ], cobalt oxide, cobalt nitrate, cobalt chloride and the like can be mentioned.
Among these transition metal compounds, [Ru ₃ (CO) ₁₂ ], [Fe (CO) ₅ ], [Fe ₃ (CO) ₁₂ ], [Fe ₂ (CO) ₉ ], [Co ₂ (CO) ₈ ] And the like, the transition metal is supported by heating the carbonyl complex of the transition metal after being carried. Therefore, in producing the catalyst for ammonia synthesis of the present invention, the reduction treatment described later can be omitted. preferable.

The amount of the transition metal compound used is not particularly limited, and an amount for achieving a desired supported amount can be appropriately used, but usually, it is usually 2 wt% or more with respect to the mass of the carrier used. It is preferably 10 wt% or more, more preferably 20 wt% or more, usually 50 wt% or less, preferably 40 wt% or less, and more preferably 30 wt% or less.

As a method for supporting the transition metal compound on a carrier, specifically, for example, a physical mixing method, a CVD method (chemical vapor deposition method), a sputtering method, or the like can be used.

The physical mixing method is a method in which the carrier and the transition metal compound are solid-mixed and then heated in an inert gas stream such as nitrogen, argon or helium, or under vacuum. The heating temperature at this time is not particularly limited, but is usually 200 ° C. or higher and 600 ° C. or lower. The heating time is not particularly limited, but usually 2 hours or more is desirable.

Here, if it is a transition metal compound that is converted into a transition metal by thermal decomposition, the transition metal is usually carried at this stage and becomes the catalyst for ammonia synthesis of the present invention.
When a compound other than the transition metal compound converted into the transition metal by thermal decomposition is used, the transition metal compound is usually reduced to obtain the catalyst for ammonia synthesis of the present invention.
The method for reducing the transition metal compound (hereinafter referred to as reduction treatment) is not particularly limited as long as the object of the present invention is not impaired, but for example, a method for reducing the transition metal compound in an atmosphere containing a reducing gas or the transition metal compound can be used. A method of adding a reducing agent such as NaBH ₄ , NH ₂ NH ₂ or formalin to the containing solution to precipitate it on the surface of the metal hydride can be mentioned, but the method is preferably carried out in an atmosphere containing a reducing gas. Examples of the reducing gas include hydrogen, ammonia, methanol (steam), ethanol (steam), methane, ethane and the like.
Further, during the reduction treatment, a component other than the reducing gas, which does not inhibit the object of the present invention, particularly the ammonia synthesis reaction, may coexist in the reaction system. Specifically, in the reduction treatment, in addition to the reducing gas such as hydrogen, a gas such as argon or nitrogen that does not inhibit the reaction may coexist, and it is preferable that nitrogen coexists.
When the reduction treatment is carried out in a gas containing hydrogen, it can be carried out in parallel with the production of ammonia described later by coexisting nitrogen with hydrogen. That is, when the catalyst for ammonia synthesis of the present invention is used as the catalyst for ammonia synthesis described later, the transition metal compound supported on the metal hydride is placed in the reaction conditions of the ammonia synthesis reaction. The transition metal compound may be reduced and converted into a transition metal.

The temperature at the time of the reduction treatment is not particularly limited, but is usually 200 ° C. or higher, preferably 300 ° C. or higher, usually lower than the decomposition temperature of the metal hydride carrier, and preferably 600 ° C. or lower. .. This is because the growth of the transition metal occurs sufficiently and in a preferable range by performing the reduction treatment within the temperature range.
The pressure during the reduction treatment is not particularly limited, but is usually 0.01 MPa or more and 10 MPa. If the pressure during the reduction treatment is the same as the ammonia synthesis conditions described later, complicated operations are not required, which is advantageous in terms of production efficiency.
The time of the reduction treatment is not particularly limited, but when it is carried out under normal pressure, it is usually 1 hour or more, preferably 2 hours or more.
Further, when the reaction pressure is high, for example, 1 MPa or more, 1 hour or more is preferable.

In the method for producing an ammonia synthesis catalyst of the present invention, as in the above example, a carrier containing the metal hydride and the alkaline earth metal oxide is first prepared, and then the transition metal is supported. In addition to the method of producing the metal hydride, there is also a method of supporting the transition metal on the metal hydride and then incorporating the alkaline earth metal oxide.

When a transition metal compound that is converted into a transition metal by thermal decomposition is used, the alkaline earth metal oxide, the metal hydride, and the transition metal compound are mixed in any order, and then nitrogen and argon are used. There is also a method of heating in an inert gas stream such as helium or under vacuum. From the viewpoint of simple manufacturing method, this three-component mixing method is preferable. Among them, from the viewpoint of improving the dispersibility between the alkaline earth metal oxide and the metal hydride, a solid mixing device such as a Menou dairy pot or a solid mixer containing the alkaline earth metal oxide is used. , The metal hydride is added and solid-mixed, then the transition metal compound is added, and after solid-solid mixing, heating is performed in an inert gas stream such as nitrogen, argon or helium, or under vacuum. preferable.

When a compound other than the transition metal compound converted into the transition metal by thermal decomposition is used, the transition metal compound contained in the solid mixture is reduced by a usual method in the same manner as the above-mentioned reduction treatment method. , The catalyst for ammonia synthesis of the present invention.

As the components other than the metal hydride and the transition metal, SiO ₂ , Al ₂ O ₃ , ZrO ₂ , MgO, activated carbon, graphite, SiC and the like may be further contained as the carrier of the metal hydride.

The catalyst for ammonia synthesis of the present invention can be used as a molded body by using a usual molding technique. Specific examples thereof include granules, spheres, tablets, rings, macaroni, four leaves, dice, and honeycomb shapes. It can also be used after being coated on a suitable support.

When the catalyst for ammonia synthesis of the present invention is used, its reaction activity is not particularly limited, but when the reaction temperature is 340 ° C. and the reaction pressure is 0.1 MPa as an example, the reaction activity is 0.5 mmol / g. It is preferably h or more, more preferably 1.0 mmol / g · h or more because it is suitable for practical production conditions, and more preferably 2.0 mmol / g · h or more for more efficient production. It is more preferable because it is suitable for the conditions, and more preferably 3.0 mmol / g · h or more because it is suitable for the production conditions with higher efficiency.

The method for producing ammonia using the catalyst for synthesizing ammonia of the present invention will be described below.

<Ammonia production method>
The method for producing ammonia of the present invention (hereinafter, may be referred to as the method for producing ammonia of the present invention) uses the catalyst for synthesizing ammonia of the present invention as a catalyst, and reacts hydrogen and nitrogen on the catalyst to synthesize ammonia. The method.
The specific production method is not particularly limited as long as it is a method in which hydrogen and nitrogen are brought into contact with each other on the catalyst to synthesize ammonia, and production can be appropriately performed according to a known production method.

In the method for producing ammonia of the present invention, usually, when hydrogen and nitrogen are brought into contact with each other on the catalyst, the catalyst is heated to produce ammonia.
The reaction temperature in the production method of the present invention is not particularly limited, but is usually 200 ° C. or higher, preferably 250 ° C. or higher, more preferably 300 ° C. or higher, usually 600 ° C. or lower, preferably 500 ° C. or lower. Yes, more preferably 450 ° C. or lower. Since ammonia synthesis is an exothermic reaction, the low temperature region is more advantageous for ammonia production in terms of chemical equilibrium theory, but it is preferable to carry out the reaction in the above temperature range in order to obtain a sufficient ammonia production rate.
_In the production method of the present invention, the molar ratio of nitrogen and hydrogen brought into contact with the catalyst is not particularly limited, but is usually ₀ . 4 or more, preferably 0.5 or more, more preferably 1 or more, usually 10 or less, preferably 5 or less.

The reaction pressure in the production method of the present invention is not particularly limited, but is usually 0.01 MPa or more, preferably 0.1 MPa or more, usually 20 MPa or less, preferably 15 MPa or less, more preferably the pressure of the mixed gas containing nitrogen and hydrogen. Is 10 MPa or less. Further, considering practical use, it is preferable to carry out the reaction under a pressurized condition of atmospheric pressure or higher.

In the production method of the present invention, before contacting nitrogen and hydrogen with the catalyst, water and oxides adhering to the catalyst are removed by a method using a dehydrating material, a deep cold separation method, hydrogen gas and the like. It is preferable to do so. Examples of the removal method include reduction treatment.
In the production method of the present invention, in order to obtain a better ammonia yield, it is preferable that the water content in nitrogen and hydrogen used in the production method of the present invention is small, and the content is not particularly limited, but usually nitrogen. The total water content in the mixed gas of hydrogen and hydrogen is preferably 100 ppm or less, preferably 50 ppm or less.

In the production method of the present invention, the type of the reaction vessel is not particularly limited, and a reaction vessel that can be usually used for the ammonia synthesis reaction can be used. As a specific reaction type, for example, a batch type reaction type, a closed circulation system reaction type, a distribution system reaction type, or the like can be used. Of these, the distribution reaction type is preferable from a practical point of view. Further, any one type of reactor filled with a catalyst, a method of connecting a plurality of reactors, or a method of a reactor having a plurality of reaction layers in the same reactor can be used.
Since the reaction for synthesizing ammonia from hydrogen and nitrogen is an exothermic reaction accompanied by volume shrinkage, it is industrially preferable to remove the heat of reaction in order to increase the yield of ammonia, and it is accompanied by a commonly used heat removing means. A known reactor may be used. For example, specifically, a method of connecting a plurality of reactors filled with a catalyst in series and installing an intercooler at the outlet of each reactor to remove heat may be used.

In the method for producing ammonia of the present invention, the catalyst for ammonia synthesis obtained by the method for producing ammonia of the present invention can be used alone or in combination with other known catalysts that can be usually used for ammonia synthesis. ..

Hereinafter, the present invention will be described in more detail based on examples. Ammonia synthesis activity was evaluated by dissolving the amount of NH ₃ produced by a gas chromatograph or by dissolving the produced NH ₃ in a sulfuric acid aqueous solution and quantifying the solution by an ion chromatograph to determine the ammonia production rate.

(BET specific surface area measurement method)
The BET specific surface area was measured by adsorbing nitrogen gas on the surface of an object at a liquid nitrogen temperature and using an adsorption / desorption isotherm based on the adsorption / desorption of nitrogen gas at -196 ° C. The analysis conditions are as follows.

[Measurement condition]
Measuring device: High-speed specific surface / pore distribution measuring device BELSORP-mini 2 (manufactured by Microtrac BEL)
Adsorbed gas: Nitrogen 99.99995 by volume
Adsorption temperature: Liquid nitrogen temperature -196 ° C

(Ion chromatogram analysis)
Ammonia gas discharged from the reaction vessel was dissolved in a 5 mM sulfuric acid aqueous solution, and the captured ammonium ions (NH ⁴⁺ ) were analyzed by ion chromatography. The analysis conditions are as follows.

[Measurement condition]
Equipment: Prominence manufactured by Shimadzu Corporation
Detector: Electrical conductivity detector CDD-10Avp (manufactured by Shimadzu Corporation)
Column: Column IC-C4 for ion chromatogram (manufactured by Shimadzu Corporation)
Eluent: 3.0 mM oxalic acid + 2.0 mM 18-crown-6-ether aqueous solution Flow rate: 1.0 mL / min
Column temperature: 40 ° C

(Example 1)
(Preparation of catalyst for ammonia synthesis)
0.009 g of BaO (manufactured by High Purity Chemical Co., Ltd., purity 99.9%) is physically mixed with 0.081 g of CaH ₂ powder (manufactured by Aldrich, purity 99.9%) in a glove box with an Ar atmosphere to serve as a carrier. A mixture of CaH ₂ and BaO containing 3 mol% BaO (“ _97CaH 2-3BaO”) was prepared, and 0.041 g of Ru (acac) ₃ powder (manufactured by Aldrich, purity 99.7%) was added to 97CaH ₂ . It was physically mixed with -3BaO and sealed in a quartz glass tube. Next, the quartz glass tube was heated at 260 ° C. for 1 hour in a nitrogen gas atmosphere, and then heated at 260 ° C. for 1 hour and 340 ° C. for 5 hours in a hydrogen gas atmosphere. As a result, a catalyst for ammonia synthesis (hereinafter referred to as Ru / 97CaH _2-3BaO ) in which 10 wt% of metal Ru was supported on CaH ₂ / BaO was obtained. The BET surface area of this ammonia synthesis catalyst was 20 m ² / g. Below, ammonia synthesis was carried out using the catalyst for ammonia synthesis.

(Ammonia synthesis reaction)
A reaction (hereinafter referred to as ammonia synthesis reaction) was carried out in which nitrogen gas (N ₂ ) and hydrogen gas (H ₂ ) were reacted on a catalyst to generate ammonia (NH ₃ ). 0.1 g of the Ru / 97CaH _2-3BaO was packed in a glass tube, and the ammonia synthesis reaction was carried out with a fixed-bed flow reactor. The water concentration of both the raw materials N ₂ gas and H ₂ gas was 1 ppm or less. The flow rate of the raw material gas was set to N ₂ : 15 mL / min and H ₂ : 45 mL / min, for a total of 60 mL / min, and the reaction was carried out at a pressure of 0.1 mPa and a reaction temperature of 340 ° C.

(Ammonia production rate)
The gas discharged from the fixed-bed flow reactor was bubbled in a 0.005 M sulfuric acid aqueous solution, ammonia in the gas was dissolved, and the generated ammonium ions were quantified by the above method by an ion chromatograph. The production rates of ammonia at 340 ° C. were 7.7 mmol / g · h and 9.5 mmol / g · h, 10.0 mmol / g · h, respectively, at 1 hour, 20 hours, and 50 hours, respectively. The results are shown in Table 1.

(Long-term stability of catalyst)
Using 10 wt% Ru / 97CaH _2-3BaO of Example 1 as a catalyst, an ammonia synthesis reaction was continuously carried out for 250 hours under the same reaction conditions, and the long-term stability of the catalyst was evaluated. The results are shown in FIG. It was found that the catalyst of this example stably produced ammonia even in the reaction for 250 hours, and the reaction activity was hardly reduced.

(Structural changes before and after catalytic reaction)
For the ammonia synthesis catalyst 10 wt% Ru / 97CaH _2-3BaO of this implementation, structural changes were observed before the ammonia synthesis reaction and after the 100-hour reaction. A SEM electron microscope (SEM) photograph is shown in FIG.

(XPS measurement of vacuum-heat-treated carrier)
The XPS of the obtained sample was measured with the vacuum heat treatment time of the 97CaH 2-3BaO carrier of this example being ₂ hours and 50 hours. The results are shown in FIG. For comparison, the XPS of the raw material BaO (manufactured by high-purity chemicals) was measured and the results are shown in FIG. BaO containing oxygen defects was produced at the stage of heat treatment for 2 hours.
Vacuum heat treatment conditions: 340 ° C
XPS measurement conditions: Equipment (manufactured by Shimadzu Corporation, ESCA 3200), X-ray source (MgKα ray, 30 kV, 8 mA)

(Example 2)
(Preparation of catalyst for ammonia synthesis)
Metal Ru was added to 99CaH _2-1BaO by the same method as in Example 1 except that 99CaH _2-1BaO containing 1 mol% of BaO was used instead of 97CaH _2-3BaO containing 3 mol% BaO in Example 1. A%-supported catalyst for ammonia synthesis (hereinafter referred to as Ru / 99CaH _2-1BaO ) was obtained.

(Ammonia synthesis reaction)
Reaction to generate ammonia (NH ₃ ) by the same method and conditions as in Example 1 except that 10 wt% Ru / _{99CaH 2-1BaO} was used instead of 10 wt% Ru / 97CaH 2-3BaO in Example 1. (Hereinafter, ammonia synthesis reaction) was carried out.

(Ammonia production rate)
The production rate of ammonia at 340 ° C. was measured by the same method as in Example 1. The production rates of ammonia at 340 ° C. were 8.5 mmol / g · h, 9.4 mmol / g · h, and 8.6 mmol / g · h, respectively, at 1 hour, 20 hours, and 50 hours. The results are shown in Table 1.

(Long-term stability of catalyst)
Using 10 wt% Ru / 99CaH _2-1BaO of this example as a catalyst, the ammonia synthesis reaction was continuously carried out for 60 hours under the same reaction conditions, and the long-term stability of the catalyst was evaluated. The results are shown in FIG. It was found that the catalyst of this example stably produced ammonia even in the reaction for 60 hours, and the reaction activity was hardly reduced.

(Example 3)
(Preparation of catalyst for ammonia synthesis)
Metal Ru was added to 98CaH _2-2BaO by the same method as in Example 1 except that 98CaH _{2-2BaO containing 2 mol} % of BaO was used instead of 97CaH 2-3BaO containing 3 mol% BaO in Example 1. A%-supported catalyst for ammonia synthesis (hereinafter referred to as Ru / 98CaH _-2 -BaO) was obtained.

(Ammonia synthesis reaction)
Reaction to generate ammonia (NH ₃ ) by the same method and conditions as in Example 1 except that 10 wt% Ru / _{98CaH 2-2BaO} was used instead of 10 wt% Ru / 97CaH 2-3BaO in Example 1. (Hereinafter, ammonia synthesis reaction) was carried out.

(Ammonia production rate)
The production rate of ammonia at 340 ° C. was measured by the same method as in Example 1. The production rate of ammonia at 340 ° C. was 8.3 mmol / g · h, 10 mmol / g · h, and 10 mmol / g · h, respectively, at 1 hour, 20 hours, and 50 hours. The results are shown in Table 1.

(Long-term stability of catalyst)
Using 10 wt% Ru / 98CaH _-2 -BaO of this example as a catalyst, the ammonia synthesis reaction was continuously carried out for 60 hours under the same reaction conditions, and the long-term stability of the catalyst was evaluated. The results are shown in FIG. It was found that the catalyst of this example stably produced ammonia even in the reaction for 60 hours, and the reaction activity was hardly reduced.

(Example 4)
(Preparation of catalyst for ammonia synthesis)
Metal Ru was added to _{96CaH 2 -4 BaO by the same method as in Example 1 except that 96CaH 2 -4} BaO containing 4 mol% of BaO was used instead of 97 CaH 2-3 BaO containing 3 mol% BaO in Example 1. A%-supported catalyst for ammonia synthesis (hereinafter referred to as Ru / 96CaH _2-4BaO ) was obtained.

(Ammonia synthesis reaction)
Reaction to generate ammonia (NH ₃ ) by the same method and conditions as in Example 1 except that _{10 wt% Ru / 96CaH 2 -4BaO} was used instead of 10 wt% Ru / 97CaH 2-3BaO in Example 1. (Hereinafter, ammonia synthesis reaction) was carried out.

(Ammonia production rate)
The production rate of ammonia at 340 ° C. was measured by the same method as in Example 1. The production rates of ammonia at 340 ° C. were 5.6 mmol / g · h, 7.9 mmol / g · h, and 7.9 mmol / g · h, respectively, at 1 hour, 20 hours, and 50 hours. The results are shown in Table 1.

(Long-term stability of catalyst)
Using 10 wt% Ru / 96CaH _2-4BaO of this example as a catalyst, the ammonia synthesis reaction was continuously carried out for 60 hours under the same reaction conditions, and the long-term stability of the catalyst was evaluated. The results are shown in FIG. It was found that the catalyst of this example stably produced ammonia even in the reaction for 60 hours, and the reaction activity was hardly reduced.

(Example 5)
(Preparation of catalyst for ammonia synthesis)
Metal Ru was added to 95CaH _2-5BaO by the same method as in Example 1 except that 95CaH _2-5BaO containing 5 mol% of BaO was used instead of 97CaH _2-3BaO containing 3 mol% BaO in Example 1. A%-supported catalyst for ammonia synthesis (hereinafter referred to as Ru / 95CaH _2-5BaO ) was obtained.

(Ammonia synthesis reaction)
Reaction to generate ammonia (NH ₃ ) by the same method and conditions as in Example 1 except that 10 wt% Ru / _{95CaH 2-5BaO} was used instead of 10 wt% Ru / 97CaH 2-3BaO in Example 1. (Hereinafter, ammonia synthesis reaction) was carried out.

(Ammonia production rate)
The production rate of ammonia at 340 ° C. was measured by the same method as in Example 1. The production rates of ammonia at 340 ° C. were 5.5 mmol / g · h, 6.4 mmol / g · h, and 6.9 mmol / g · h, respectively, at 1 hour, 20 hours, and 50 hours. The results are shown in Table 1.

(Long-term stability of catalyst)
Using 10 wt% Ru / 95CaH _2-5BaO of this example as a catalyst, the ammonia synthesis reaction was continuously carried out for 60 hours under the same reaction conditions, and the long-term stability of the catalyst was evaluated. The results are shown in FIG. It was found that the catalyst of this example stably produced ammonia even in the reaction for 60 hours, and the reaction activity was hardly reduced.

(XRD measurement of vacuum-heat-treated carrier)
The XRD of the sample obtained by vacuum heat-treating the _95CaH 2-5BaO carrier was measured. The results are shown in FIG. For comparison, the XRD of the raw material BaO (manufactured by high-purity chemicals) was measured and the results are shown in FIG.
Vacuum heat treatment conditions: 340 ° C., 2 hours XPD measurement conditions: Equipment (made by Bruker, D8 ADVANCE), X-rays (Cu Kα, 45 kV, 360 mA)

(Example 6)
(Preparation of catalyst for ammonia synthesis)
Metal Ru was added to 93CaH _2-7BaO by the same method as in Example 1 except that 93CaH 2-7BaO containing 7 mol% of BaO was used instead of _{97CaH 2-3BaO} containing 3 mol% BaO in Example 1. A%-supported catalyst for ammonia synthesis (hereinafter referred to as Ru / 93CaH _2-7BaO ) was obtained.

(Ammonia synthesis reaction)
Reaction to generate ammonia (NH ₃ ) by the same method and conditions as in Example 1 except that 10 wt% Ru / _{93CaH 2-7BaO} was used instead of 10 wt% Ru / 97CaH 2-3BaO in Example 1. (Hereinafter, ammonia synthesis reaction) was carried out.

(Ammonia production rate)
The production rate of ammonia at 340 ° C. was measured by the same method as in Example 1. The production rates of ammonia at 340 ° C. were 2.7 mmol / g · h and 3.0 mmol / g · h and 4.6 mmol / g · h, respectively, at 1 hour, 20 hours, and 50 hours. The results are shown in Table 1.

(Long-term stability of catalyst)
Using 10 wt% Ru / 93CaH _2-7BaO of this example as a catalyst, the ammonia synthesis reaction was continuously carried out for 60 hours under the same reaction conditions, and the long-term stability of the catalyst was evaluated. The results are shown in FIG. It was found that the catalyst of this example stably produced ammonia even in the reaction for 60 hours, and the reaction activity was hardly reduced.

(Comparative Example 1)
(Preparation of catalyst for ammonia synthesis)
Ammonia in which 10 wt% of metal Ru was supported _{on CaH 2 by the same method as in Example 1 except that CaH 2 containing} no BaO was used instead of 97CaH 2-3BaO containing 3 mol% BaO in Example 1. A catalyst for synthesis (hereinafter referred to as Ru / CaH ₂ ) was obtained.

(Ammonia synthesis reaction)
Reaction to generate ammonia (NH ₃ ) by the same method and conditions as in Example 1 except that 10 wt% Ru / CaH ₂ was used instead of 10 wt% Ru / 97CaH _2-3BaO of Example 1 (hereinafter). , Ammonia synthesis reaction).

(Ammonia production rate)
The production rate of ammonia at 340 ° C. was measured by the same method as in Example 1. The production rates of ammonia at 340 ° C. were 6.7 mmol / g · h and 6.6 mmol / g · h and 5.6 mmol / g · h, respectively, at 1 hour, 20 hours and 50 hours. The results are shown in Table 1.

(Long-term stability of catalyst)
Using 10 wt% Ru / CaH ₂ of Comparative Example 1 as a catalyst, an ammonia synthesis reaction was continuously carried out for 110 hours under the same reaction conditions, and the long-term stability of the catalyst was evaluated. The results are shown in FIG. It was found that the catalyst of this comparative example had a reduced reaction activity from the start to 100 hours.

The relationship between the _NH3 production rate (reaction time 50 hr) of Examples 1 to 6 in Table 1 and the BaO-CaH ₂ molar ratio in the carrier is shown in FIG. It was found that the catalytic activity depends on the BaO-CaH ₂ molar ratio.

(Example 7)
(Preparation of catalyst for ammonia synthesis)
Ammonia synthesis in which 2 wt% of metal Ru was supported on 97CaH _2-3BaO by the same method as in Example 1 except that the supported amount of 2 wt% Ru was used instead of the supported amount of 10 wt% Ru in Example 1. A catalyst for use (hereinafter, ₂ wt% Ru / 97CaH 2-3BaO) was obtained.

(Ammonia synthesis reaction)
Reaction to generate ammonia (NH ₃ ) by the same method and conditions as in Example 1 except that ₂ wt% Ru / _97CaH 2-3BaO was used instead of 10 wt% Ru / 97CaH 2-3BaO in Example 1. (Hereinafter, ammonia synthesis reaction) was carried out.

(Ammonia production rate)
The production rate of ammonia at 340 ° C. was measured by the same method as in Example 1. The production rate of ammonia at 340 ° C. was 5.1 mmol / g · h, 5.1 mmol / g · h, 4.1 mmol / g · h, respectively, at 1 hour, 20 hours, and 50 hours. The results are shown in Table 2.

(Long-term stability of catalyst)
Using ₂ wt% Ru / 97CaH 2-3BaO of this example as a catalyst, the ammonia synthesis reaction was continuously carried out for 60 hours under the same reaction conditions, and the long-term stability of the catalyst was evaluated. The results are shown in FIG. It was found that the catalyst of this example stably produced ammonia in the reaction for 20 hours, and the reaction activity hardly decreased.

(Example 8)
(Preparation of catalyst for ammonia synthesis)
Ammonia synthesis in which 4 wt% of metal Ru was supported on 97CaH _2-3BaO by the same method as in Example 1 except that the supported amount of 4 wt% Ru was used instead of the supported amount of 10 wt% Ru in Example 1. A catalyst for use (hereinafter, 4 wt% Ru / 97CaH _2-3BaO ) was obtained.

(Ammonia synthesis reaction)
Reaction to generate ammonia (NH ₃ ) by the same method and conditions as in Example 1 except that 4 wt% Ru / _{97CaH 2-3BaO} was used instead of 10 wt% Ru / 97CaH 2-3BaO in Example 1. (Hereinafter, ammonia synthesis reaction) was carried out.

(Ammonia production rate)
The production rate of ammonia at 340 ° C. was measured by the same method as in Example 1. The production rates of ammonia at 340 ° C. were 6.6 mmol / g · h and 6.5 mmol / g · h and 5.1 mmol / g · h, respectively, at 1 hour, 20 hours and 50 hours. The results are shown in Table 2.

(Long-term stability of catalyst)
Using 4 wt% Ru / 97CaH _2-3BaO of this example as a catalyst, the ammonia synthesis reaction was continuously carried out for 60 hours under the same reaction conditions, and the long-term stability of the catalyst was evaluated. The results are shown in FIG. It was found that the catalyst of this example stably produced ammonia in the reaction for 20 hours, and the reaction activity hardly decreased.

(Example 9)
(Preparation of catalyst for ammonia synthesis)
Ammonia synthesis in which 5 wt% of metal Ru was supported on 97CaH _2-3BaO by the same method as in Example 1 except that the supported amount of 5 wt% Ru was used instead of the supported amount of 10 wt% Ru in Example 1. A catalyst for use (hereinafter, 5 wt% Ru / 97CaH _2-3BaO ) was obtained.

(Ammonia synthesis reaction)
Reaction to generate ammonia (NH ₃ ) by the same method and conditions as in Example 1 except that 5 wt% Ru / _{97CaH 2-3BaO} was used instead of 10 wt% Ru / 97CaH 2-3BaO in Example 1. (Hereinafter, ammonia synthesis reaction) was carried out.

(Ammonia production rate)
The production rate of ammonia at 340 ° C. was measured by the same method as in Example 1. The production rates of ammonia at 340 ° C. were 7.9 mmol / g · h, 8.6 mmol / g · h, and 8.4 mmol / g · h, respectively, at 1 hour, 20 hours, and 50 hours. The results are shown in Table 2.

(Long-term stability of catalyst)
Using 5 wt% Ru / 97CaH _2-3BaO of this example as a catalyst, the ammonia synthesis reaction was continuously carried out for 60 hours under the same reaction conditions, and the long-term stability of the catalyst was evaluated. The results are shown in FIG. It was found that the catalyst of this example stably produced ammonia even in the reaction for 50 hours, and the reaction activity was hardly reduced.

(Example 10)
(Preparation of catalyst for ammonia synthesis)
Ammonia synthesis in which 15 wt% of metal Ru was supported on 97CaH _2-3BaO by the same method as in Example 1 except that the supported amount of 15 wt% Ru was used instead of the supported amount of 10 wt% Ru in Example 1. A catalyst for use (hereinafter referred to as 15 wt% Ru / 97CaH _2-3BaO ) was obtained.

(Ammonia synthesis reaction)
Reaction to generate ammonia (NH ₃ ) by the same method and conditions as in Example 1 except that 15 wt% Ru / _{97CaH 2-3BaO} was used instead of 10 wt% Ru / 97CaH 2-3BaO in Example 1. (Hereinafter, ammonia synthesis reaction) was carried out.

(Ammonia production rate)
The production rate of ammonia at 340 ° C. was measured by the same method as in Example 1. The production rates of ammonia at 340 ° C. were 5.5 mmol / g · h, 6.2 mmol / g · h, and 6.9 mmol / g · h, respectively, at 1 hour, 20 hours, and 50 hours. The results are shown in Table 2.

(Long-term stability of catalyst)
Using 15 wt% Ru / 97CaH _2-3BaO of this example as a catalyst, the ammonia synthesis reaction was continuously carried out for 60 hours under the same reaction conditions, and the long-term stability of the catalyst was evaluated. The results are shown in FIG. It was found that the catalyst of this example stably produced ammonia even in the reaction for 50 hours, and the reaction activity was hardly reduced.

表２における実施例１、７～１０のＮＨ_３生成速度（反応時間５０ｈｒ）とＲｕの担持量との関係を図８に示す。触媒活性がＢａＯ－ＣａＨ_２モル比に依存していることがわかった。

FIG. 8 shows the relationship between the _NH3 production rate (reaction time 50 hr) and the amount of Ru carried in Examples 1 and 7 to 10 in Table 2. It was found that the catalytic activity depends on the BaO-CaH ₂ molar ratio.

(Example 11)
(Preparation of catalyst for ammonia synthesis)
Metal Ru was added to 97CaH _2-3SrO by the same method as in Example 1 except that 97CaH _2-3SrO containing 3 mol% SrO was used instead of 97CaH _2-3BaO containing 3 mol% BaO in Example 1. A%-supported catalyst for ammonia synthesis (hereinafter referred to as Ru / 97CaH _2-3SrO ) was obtained.

(Ammonia synthesis reaction)
Reaction to generate ammonia (NH ₃ ) by the same method and conditions as in Example 1 except that 10 wt% Ru / _{97CaH 2-3SrO} was used instead of 10 wt% Ru / 97CaH 2-3BaO in Example 1. (Hereinafter, ammonia synthesis reaction) was carried out.

(Ammonia production rate)
The production rate of ammonia at 340 ° C. was measured by the same method as in Example 1. The production rates of ammonia at 340 ° C. were 7.5 mmol / g · h, 8.4 mmol / g · h, and 8.6 mmol / g · h, respectively, at 1 hour, 20 hours, and 50 hours. The results are shown in Table 3.

(Long-term stability of catalyst)
Using 10 wt% Ru / 97CaH _2-3SrO of this example as a catalyst, the ammonia synthesis reaction was continuously carried out for 60 hours under the same reaction conditions, and the long-term stability of the catalyst was evaluated. The results are shown in FIG. It was found that the catalyst of this example stably produced ammonia even in the reaction for 60 hours, and the reaction activity was hardly reduced.

(Example 12)
(Preparation of catalyst for ammonia synthesis)
Metal Ru was added to 97CaH _2-3MgO by the same method as in Example 1 except that 97CaH _2-3MgO containing 3 mol% MgO was used instead of 97CaH _2-3BaO containing 3 mol% BaO in Example 1. A%-supported catalyst for ammonia synthesis (hereinafter referred to as Ru / 97CaH _2-3MgO ) was obtained.

(Ammonia synthesis reaction)
Reaction to generate ammonia (NH ₃ ) by the same method and conditions as in Example 1 except that 10 wt% Ru / 97CaH _2-3 MgO was used instead of 10 wt% Ru / 97CaH _2-3BaO in Example 1. (Hereinafter, ammonia synthesis reaction) was carried out.

(Ammonia production rate)
The production rate of ammonia at 340 ° C. was measured by the same method as in Example 1. The production rates of ammonia at 340 ° C. were 9.9 mmol / g · h, 9.4 mmol / g · h, and 8.9 mmol / g · h, respectively, at 1 hour, 20 hours, and 50 hours. The results are shown in Table 3.

(Long-term stability of catalyst)
Using 10 wt% Ru / 97CaH _2-3MgO of this example as a catalyst, the ammonia synthesis reaction was continuously carried out for 60 hours under the same reaction conditions, and the long-term stability of the catalyst was evaluated. The results are shown in FIG. It was found that the catalyst of this example stably produced ammonia even in the reaction for 60 hours, and the reaction activity was hardly reduced.

(Example 13)
(Preparation of catalyst for ammonia synthesis)
A mixture of CaH ₂ and BaO (“ _97CaH 2-3BaO”) prepared by the same method as in Example 1 was sealed in a quartz glass tube, heated at 340 ° C. for 2 hours in a hydrogen gas atmosphere, and pretreated. _97CaH 2-3BaO was obtained. A catalyst for ammonia synthesis in which 10 wt% of metal Ru was supported on _97CaH 2-3BaO * by the same method as in Example 1 except that the pretreated _97CaH 2-3BaO (“ _97CaH 2-3BaO *”) was used. (Hereinafter, Ru / 97CaH ₂ -BaO *) was obtained.

(Ammonia synthesis reaction)
Ammonia (NH ₃ ) is produced by the same method and conditions as in Example 1 except that 10 wt% Ru / _{97CaH 2-3BaO} * is used instead of 10 wt% Ru / 97CaH 2-3BaO in Example 1. The reaction (hereinafter referred to as ammonia synthesis reaction) was carried out.

(Ammonia production rate)
The production rate of ammonia at 340 ° C. was measured by the same method as in Example 1. The production rate of ammonia at 340 ° C. was 10.1 mmol / g · h, 11.2 mmol / g · h, and 10.6 mmol / g · h, respectively, at 1 hour, 20 hours, and 50 hours. The results are shown in Table 3.

(Long-term stability of catalyst)
Using 10 wt% Ru / _97CaH 2-3BaO * of this example as a catalyst, the ammonia synthesis reaction was continuously carried out for 60 hours under the same reaction conditions, and the long-term stability of the catalyst was evaluated. The results are shown in FIG. It was found that the catalyst of this example stably produced ammonia even in the reaction for 60 hours, and the reaction activity was hardly reduced.

It is considered that the effect of the catalyst for ammonia synthesis of the present invention is that the presence of BaO or BaO containing oxygen defects maintained the action brought about by the dynamic role of hydride ions (H ^- ions) contained in the metal hydrogen compound for a long time. That is, when the ammonia synthesis catalyst carrying a transition metal such as Ru on a metal hydride is heated, the H ^- ions in the ammonia synthesis catalyst are desorbed as neutral hydrogen, and the defective sites are occupied by electrons. F center is generated. Since the valence of metal ions generated from the metal hydride used in the present invention is usually +2 or +3, these crystals have a larger lattice energy than ionic crystals such as alkali metals. There is. Further, compared with oxygen ions and halogen ions, hydride ions are characterized in that their ionic radii can be significantly changed depending on the environment. Therefore, the energy level of the electron at the F center in these hydride crystals is significantly reduced by the relaxation of the structure around the F center as seen in alkali metal oxides and halides when hydride ions are replaced with electrons. It is presumed that it will be kept high without decreasing. It is considered that this lowers the work function of the ammonia synthesis catalyst itself, thereby efficiently donating electrons to the supported metal species and promoting the catalytic activity of the metal species. Then, it is considered that the activity effect of the metal hydride can be maintained for a long time due to the presence of BaO or oxygen defect-containing BaO in the vicinity of the metal hydrogen compound.
Further, it is generally known that the oxygen-deficient-containing BaO has a low work function, and it is possible that the donation of electrons from the oxygen-deficient-containing BaO to Ru also contributes to the high catalytic activity of the present invention. be.

Claims (9)

Transition metals and
A catalyst for ammonia synthesis comprising a metal carrier including the carrier supporting the transition metal.
The transition metal is at least one selected from Ru, Co, or Fe.
The carrier
The metal hydride represented by the following general formula (1) and
A catalyst for ammonia synthesis, which comprises any one alkaline earth metal oxide selected from the group consisting of MgO, SrO, and BaO.
XH _n ... (1)
(In the above general formula (1), X represents at least one selected from Group 2 atoms, Group 3 atoms, or lanthanoid atoms in the periodic table, and n represents a number represented by 2 ≦ n ≦ 3. ) The catalyst for ammonia synthesis according to claim 1, wherein X in the general formula (1) is at least one selected from Mg, Ca, Sr, Ba, Sc, Y, or a lanthanoid atom. The catalyst for ammonia synthesis according to claim 1 or 2 , wherein the amount of the transition metal supported on the carrier is 0.5% by mass or more and 20% by mass. The catalyst for ammonia synthesis according to any one of claims 1 to 3 , wherein the content of the alkaline earth metal oxide with respect to the carrier is 0.5 mol% or more and 10 mol% or less. A method for producing ammonia, which comprises contacting a raw material gas containing hydrogen and nitrogen with the catalyst for ammonia synthesis according to any one of claims 1 to 3 to synthesize ammonia. Manufacturing method. The method for producing ammonia according to claim 5 , wherein the reaction temperature at the time of contact with the catalyst for ammonia synthesis is 100 ° C. or higher and 600 ° C. or lower. The method for producing ammonia according to claim 5 or 6 , wherein the reaction pressure at the time of contact with the catalyst for ammonia synthesis is 10 kPa or more and 20 MPa or less. The method for producing ammonia according to any one of claims 5 to 7 , wherein the water content of the raw material gas is 100 ppm or less. The invention according to any one of claims 5 to 8 , wherein the ratio of hydrogen to nitrogen (H ₂ / N ₂ (volume / volume)) when contacted with the catalyst for ammonia synthesis is 0.4 or more. Ammonia production method.

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