JP6656037B2 - Ammonia synthesis catalyst and method for synthesizing ammonia using the catalyst - Google Patents

Description

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

Ammonia has heretofore been widely produced at the industrial level by the Haberbosch process. In the Haberbosch method, ammonia is obtained by reacting hydrogen and nitrogen at 400 to 600 ° C. and a high pressure of 20 to 100 MPa using a double-promoted iron catalyst (Non-Patent Document 1).
There is also an example in which ammonia synthesis at lower temperature and lower pressure is realized by using a catalyst using ruthenium as an active metal (Patent Document 1). Further, in a catalyst using ruthenium as an active metal, there is an example in which a high activity is realized by using a carrier containing a lanthanoid oxide such as ceria or an alkaline earth metal (Patent Document 2 and Non-Patent Documents 2 to 4). ). As described above, in the catalyst used in the conventional Haberbosch method, it is said that high activation can be realized by using a catalyst in which magnesia and a lanthanoid or an alkaline earth metal coexist.

On the other hand, recently, the inventors have proposed a method for synthesizing ammonia using a catalyst installed in an electric field (Patent Document 3). In this method of synthesizing ammonia by the electric field catalytic reaction, a small scale or low temperature is applied by applying a voltage that does not cause discharge to a catalyst provided between a pair of electrodes (hereinafter, sometimes simply referred to as “electric field application”). It is possible to obtain the effect of promoting ammonia synthesis even under conditions such as low pressure, which are disadvantageous in terms of energy efficiency in the conventional Haberbosch synthesis. In addition, since it is possible to flexibly cope with the start and stop of the reaction, it can be suitably used in combination with intermittent power supply, for example, a power generation facility using renewable energy having power generation fluctuation. In such a reaction method, the catalyst needs to have a certain conductivity, and Patent Document 3 discloses a catalyst using a Ce _0.5 Zr _0.5 O ₂ composite oxide as a carrier.

JP-A-2-258066 JP-A-6-79177 JP 2014-141361 A

"Catalyst Handbook" Kodansha Published December 10, 2008 pp. 68 Journal of Fuel Chemistry and Technology Vol. 40, pp. 848-854, 2012 Catalysis Letters Vol. 106 pp. 107-110, 2006 Catalysis Letters Vol. 141 pp. 1275-1281,2111

  However, the ammonia synthesis process such as the Haberbosch process is a high energy consumption process, and there is still a demand for improvement in energy efficiency by improving the activity of the catalyst. In particular, in the ammonia synthesis method using an electric field catalytic reaction, there is a problem that the reaction efficiency of the catalyst is low, so that the energy efficiency is inferior to the Haberbosch method. In the field-catalyzed reaction, a magnesia carrier that is effective in the conventional Haberbosch method, or a catalyst using an oxide composed of lanthanoids such as lanthanum oxide and ceria as a carrier, a discharge occurs because the insulating property of the catalyst is too high, The effect of promoting the synthesis of ammonia by applying an electric field cannot be obtained, and most of the input electric energy is used for ionizing molecules in the gas, resulting in a significant decrease in energy efficiency. Therefore, there is a need for a catalyst for ammonia synthesis that can effectively utilize the effect of applying an electric field and achieve high activity.

  The present inventors have conducted intensive studies in view of the above problems, and found that in ammonia synthesis, particularly ammonia synthesis by an electric field catalytic reaction, the activity was significantly improved by using a catalyst containing a composite oxide having a pyrochlore structure and / or an apatite structure. And found that the invention was completed.

The present invention is described below.
[1] An ammonia synthesis catalyst comprising at least a catalytically active component and a composite oxide, wherein a composite oxide having a pyrochlore structure and / or an apatite structure is used as the composite oxide.
[2] The catalyst for ammonia synthesis according to [1], wherein a catalyst is provided between a pair of electrodes, and a voltage that does not cause a discharge is applied between the electrodes in the presence of hydrogen and nitrogen to synthesize ammonia. .
[3] The catalyst for ammonia synthesis according to [1] or [2], wherein the composite oxide having a pyrochlore structure and / or an apatite structure is a composite oxide containing a lanthanoid.
[4] The ammonia synthesis catalyst according to any one of [1] to [3], further including at least one element selected from an alkali metal, an alkaline earth metal, and a lanthanoid as a cocatalyst. The catalyst for ammonia synthesis as described above.
[5] The catalyst according to any one of [1] to [4], wherein the catalytically active component contains at least one element selected from ruthenium, iron, cobalt, nickel, platinum, palladium, rhodium, and iridium. A catalyst for ammonia synthesis according to 1.
[6] A method in which a catalyst is provided between a pair of electrodes, and ammonia is synthesized by applying a voltage that does not cause a discharge between the electrodes in the presence of hydrogen and nitrogen, the method comprising the steps of [1] to [5]. A method for synthesizing ammonia, comprising using the catalyst for ammonia synthesis according to any one of the above.

  By using the catalyst for ammonia synthesis according to the present invention, it is possible to greatly improve the rate of ammonia generation in the synthesis of ammonia, particularly in the synthesis of ammonia by an electric field catalytic reaction, as compared with the conventional case.

Hereinafter, the catalyst for ammonia synthesis and the method for synthesizing ammonia according to the present invention will be described in detail, but the scope of the present invention is not limited to these descriptions, and a range other than the following examples does not impair the spirit of the present invention. Can be appropriately changed and implemented.
In this embodiment, an example of an ammonia synthesis catalyst and an ammonia synthesis method which are one embodiment of the present invention will be described.

[Ammonia synthesis catalyst]
The catalyst for ammonia synthesis is not particularly limited as long as it contains a catalytically active component and a composite oxide having a pyrochlore structure and / or an apatite structure.

Examples of the catalytically active component include ruthenium, iron, cobalt, nickel, platinum, palladium, rhodium, iridium, and the like. Ruthenium, iron, cobalt, and nickel are preferred, and ruthenium and iron are particularly preferred.
The content of the catalytically active component is not particularly limited as long as it has the effect of the present invention, but is preferably 0.01 to 40% by weight, more preferably 0.1 to 30% by weight, based on the ammonia synthesis catalyst. ~ 25 wt% is more preferred.

As the composite oxide having a pyrochlore _{structure, La 2 Zr 2 O 7,} Nd 2 Zr 2 O 7, Sm 2 Zr 2 O 7, Gd 2 Zr 2 O 7, La 2 Ti 2 O 7, Nd 2 Ti 2 O ₇ , Sm ₂ Zr ₂ O ₇ , Gd ₂ Zr ₂ O _7, La ₂ Ce ₂ O ₇ , Ca ₂ Nb ₂ O ₇ , Sr ₂ Nb ₂ O ₇ , Ba ₂ Nb ₂ O ₇ , Bi ₂ Ti ₂ O ₇ and the _like, preferably _{La 2 Zr 2 O 7, Nd} 2 Zr 2 O 7, Sm 2 Zr 2 O 7, Gd 2 Zr 2 O 7, La 2 Ce 2 O 7 _{is, La 2 Zr 2 O 7,} Nd ₂ Zr ₂ O ₇ is particularly preferred.
As the composite oxide having an apatite _{structure, La 10 Si 6 O 27,} Nd 10 Si 6 O 27, Sm 10 Si 6 O 27, La 10 Ge 6 O 27, Nd 10 Ge 6 O 27, Sm 10 Ge 6 O _{27, and the} like. La ₁₀ Si ₆ O ₂₇ , Nd ₁₀ Si ₆ O ₂₇ , and Sm ₁₀ Si ₆ O ₂₇ are preferable, and La ₁₀ Si ₆ O ₂₇ is particularly preferable.

The method for preparing the composite oxide is not particularly limited, and includes the following methods. For example, a metal salt is dissolved in a glycol solution containing an excess of oxycarboxylic acid to form a metal oxycarboxylic acid complex. When this solution is heated, a polyester polymer gel is obtained. A composite oxide powder can be obtained by thermally decomposing the obtained polymer gel at a high temperature (complex polymerization method). In addition, a method of mixing and baking solid raw materials such as oxides and carbonates of the elements constituting the composite oxide (solid-state reaction method), a method of mixing one element of the composite oxide into another oxide A method of impregnating an aqueous solution containing a salt of an element, drying and calcining (impregnation method), mixing an aqueous solution containing a salt of a constituent element of the composite oxide, adjusting the pH, obtaining a precipitate, drying the precipitate, There is a firing method (coprecipitation method) and the like. Preferably, a complex polymerization method, a solid phase reaction method, and a coprecipitation method are used. In these methods, the firing temperature is preferably from 800 to 1200C, and more preferably from 900 to 1200C from the viewpoint of reproducibility and specific surface area. The specific surface area of these composite oxides is preferably ^{0.5~50m 2 / g, 5~50m 2 /} g is more preferable.

  The content of the composite oxide having a pyrochlore and / or apatite structure is preferably 60 to 99.99 wt%, more preferably 70 to 99.9 wt%, and more preferably 75 to 99 wt% based on the catalyst for ammonia synthesis. Is more preferred.

The catalyst for ammonia synthesis in the present invention may further contain a co-catalyst. The promoter is not particularly limited as long as it is generally used for a catalyst for ammonia synthesis. As an example, potassium, sodium, rubidium, alkali metals such as cesium, magnesium, calcium, strontium, alkaline earth metals such as barium, lanthanum, cerium, praseodymium, neodymium, samarium, rare earths such as yttrium can be used, potassium , Sodium, cesium, calcium, strontium, barium, lanthanum, cerium and neodymium are preferred, and cesium, barium, lanthanum, cerium and neodymium are particularly preferred.
The form of these cocatalysts is not particularly limited, and they can be contained as forms such as metals, oxides, hydroxides, and carbonates.

The method for preparing the ammonia synthesis catalyst is not particularly limited, and a method generally used for preparing this type of catalyst can be used. For example, (1) a method of mixing a solution containing a Ru precursor and a composite oxide to carry out impregnation, (2) a method of mixing a solution containing a Ru precursor and a cocatalyst precursor and a composite oxide to carry out impregnation, (3) a method in which a solution containing a Ru precursor and a co-catalyst is mixed with a composite oxide and precipitated by an acid or a base to form a support, and (4) a Ru precursor is supported on the composite oxide by the method described above. After that, a method of further impregnating and supporting a solution containing the promoter precursor is exemplified. The shape of these catalysts is not particularly limited, and may be in the form of a powder, or a molded product obtained by molding a powder or the like into a fixed shape such as a columnar shape, a ring shape, a spherical shape by an extrusion molding method or a tablet molding method. Or, it may be an irregularly shaped body or the like which is crushed after being formed into a fixed shape.
After supporting the Ru precursor or the cocatalyst precursor, it may be calcined at a temperature of about 200 to 600 ° C. in air. Before the reaction, the reduction treatment may be performed at a temperature in the range of 50 to 600 ° C. under a gas flow containing hydrogen.

[Synthesis method of ammonia]
In the ammonia synthesis method of the present invention, when synthesizing ammonia by flowing a raw material gas through a reactor described below and applying a voltage that does not cause discharge between a pair of electrodes, the ammonia is synthesized using the ammonia synthesis catalyst described above. Is a method of synthesizing

  Note that discharge in this specification means that nitrogen, hydrogen, and the like in a source gas passed between electrodes cause dielectric breakdown due to an applied voltage, ionization and electron emission occur, and a current flows. When a discharge occurs, a light emission phenomenon can often be observed at the same time. The applied voltage in the present invention is a voltage at which dielectric breakdown occurs, that is, a voltage lower than the dielectric breakdown voltage.

  The reactor used in the present invention includes a pair of electrodes, a voltage applying means for applying a voltage between the electrodes, an ammonia synthesis catalyst installed between the electrodes, a raw material gas inlet and a generated ammonia-containing gas outlet. Consists of The reactor may further include a catalyst support for holding the catalyst in a preferred position.

  The pair of electrodes may be made of a conductive material and have any shape and arrangement capable of forming an electric field in the space containing the catalyst. As an example of the electrode material, iron, stainless steel, titanium, and Hastelloy (registered trademark) can be used, and stainless steel is preferable in terms of corrosion resistance and cost. As an example of the shape of the electrode, a rod-shaped electrode, a cylindrical electrode, a plate-shaped electrode, a mesh-shaped electrode, and the like can be used. From the viewpoint of gas flowability and volumetric efficiency of the device, a rod-shaped electrode, a cylindrical electrode, and a mesh-shaped electrode can be used. Is preferred. As an example of the arrangement of the electrodes, in addition to a method of arranging a pair of electrodes in the flow direction of the flow type reactor and arranging the catalyst, a pair of electrodes composed of a rod electrode and a cylindrical electrode arranged concentrically. There is a method of disposing a catalyst between them.

  The catalyst support may be of any shape and material as long as the catalyst is fixed between the electrodes and does not adversely affect the reaction. As an example, a plate of quartz wool, glass wool, granular silica, alumina, zirconia, magnesia or the like provided with holes for gas flow can be arranged before and after the catalyst.

  The voltage applying means is not particularly limited as long as a voltage can be applied between the pair of electrodes. For example, a commercially available high voltage power supply can be used. As the high-voltage power supply, a DC power supply, an AC power supply, or an ultrashort pulse generator can be used, but it is preferable to use a DC power supply for forming an electric field.

  The raw material gas may be a gas containing hydrogen atoms and nitrogen atoms, which is a raw material for ammonia, and the molar ratio of hydrogen atoms / nitrogen atoms in the raw material gas is preferably from 0.01 to 10 and more preferably. Is 0.1 or more and 3.0 or less. If the molar ratio of hydrogen atoms / nitrogen atoms is less than 0.01, the rate of ammonia production is undesirably greatly reduced due to the restriction of equilibrium. Conversely, if it is greater than 3, the applied voltage becomes undesirably high.

  A mixture gas in which components containing a hydrogen atom and a nitrogen atom are present as separate components may be used, or a mixture containing both a hydrogen atom and a nitrogen atom in the same component may be used. May be used. From the viewpoint of availability, economy, and catalyst durability, it is preferable to use a nitrogen molecule as a gas containing a nitrogen atom and a hydrogen molecule as a gas containing a hydrogen atom, and to introduce a mixed gas thereof into the catalyst layer as a source gas. .

  As the raw material gas supply means, a method of introducing an arbitrary gas necessary for the reaction into the reactor can be provided. As an example, when synthesizing ammonia from nitrogen gas and hydrogen gas, a nitrogen gas cylinder, an industrial nitrogen generator, or the like can be used as a nitrogen supply source. Examples of the hydrogen supply source include a hydrogen gas cylinder, a hydrocarbon, and the like. A hydrogen-containing gas obtained by reforming a hydrogen-containing compound described above, a hydrogen-containing gas obtained by alkaline water electrolysis or steam electrolysis, or the like can be used.

  The ammonia synthesis in the present invention may be performed at normal pressure, but is more effective when performed under pressure. Specifically, it is advantageous when the pressure in the reactor is 102 kPa to 40 MPa, preferably 102 kPa to 5 MPa to synthesize ammonia.

Further, the ammonia synthesis according to the method of the present invention may be performed by heating using a heating device. As an example, ammonia can be synthesized at a catalyst layer temperature of 20 to 600C, preferably 20 to 450C, and more preferably 20 to 400C. As the temperature rises, the catalytic activity increases and the amount of produced ammonia also increases. However, if the temperature is higher than 600 ° C., the ammonia synthesis reaction is disadvantageously thermodynamically disadvantageous. In addition, the reaction at a low temperature is thermodynamically advantageous, but the catalytic activity is low.Therefore, in the above temperature range, an appropriate reaction temperature may be set in consideration of the activity and economy of the catalyst used. .
In the obtained gas containing ammonia, if necessary, only ammonia may be separated by a known method. Further, a recycle process may be included in which the source gas is further separated from the remaining gas and reused as the source gas.

  Hereinafter, the present invention will be described specifically with reference to examples. However, the present invention is not limited by the following examples, and the present invention is implemented with appropriate modifications within a range that is compatible with the gist of the present invention. It is also possible and they are all included in the technical scope of the present invention.

(Preparation of composite oxide)
Each composite oxide was prepared by the following method. The composite oxide was used in Examples and Comparative Examples.
<La ₁₀ Si ₆ O ₂₇ >
Lanthanum oxide and silicon dioxide are weighed and mixed so that La: Si = 10: 6, calcined at 1100 ° C. for 10 hours in an air atmosphere, and wet-ground in ethanol to obtain La ₁₀ Si ₆ O ₂₇ powder. Was. The specific surface area of La ₁₀ Si ₆ O ₂₇ measured by the BET method was 10.7 m ² / g. The powder XRD measurement confirmed that the obtained composite oxide had an apatite structure.
<La ₂ Zr ₂ O ₇ >
Lanthanum oxide and zirconium oxide are weighed and mixed so that La: Zr = 1: 1, calcined at 1100 ° C. for 10 hours in an air atmosphere, and wet-ground in ethanol to obtain La ₂ Zr ₂ O ₇ powder. Was. The specific surface area of La ₂ Zr ₂ O ₇ measured by the BET method was 13.9 m ² / g. By powder XRD measurement, it was confirmed that the obtained composite oxide had a pyrochlore structure.
<CaZrO ₃ >
Calcium carbonate and zirconium oxide were weighed and mixed so that Ca: Zr = 1: 1, calcined at 1100 ° C. for 10 hours in an air atmosphere, and wet-pulverized in ethanol to obtain CaZrO ₃ powder. The specific surface area of CaZrO ₃ measured by the BET method was 14.8 m ² / g. By powder XRD measurement, it was confirmed that the obtained composite oxide had a perovskite structure.
_<Ce 0.5 _Zr 0.5 _O 2>
Cerium oxide and zirconium oxide are weighed and mixed so that Ce: Zr = 1: 1, fired at 1100 ° C. for 10 hours in an air atmosphere, and wet-ground in ethanol to obtain Ce _0.5 Zr _0.5 O _2. A powder was obtained. The specific surface area of Ce _0.5 Zr _0.5 O ₂ measured by the BET method was 29.0 m ² / g. By powder XRD measurement, it was confirmed that the obtained composite oxide had a cubic structure.

[Specific surface area measurement]
The specific surface area was measured using Macsorb Model-1210 manufactured by Mountech Co., Ltd. as a BET specific surface area meter.
[X-ray diffraction measurement]
The measurement was performed using Cu-Kα radiation (X-ray output: 45 kV-40 mA, Kα1 ray wavelength: 1.5406 °) using X'pert PRO MPD manufactured by Spectris.

(Example 1)
The acetone solution of the tris (acetylacetonato) ruthenium complex was impregnated and supported so that the tris (acetylacetonato) ruthenium complex (in terms of Ru metal) was 7 parts by weight with respect to 100 parts by weight of La ₁₀ Si ₆ O ₂₇ . After the obtained sample was dried at 120 ° C. for 10 hours, it was fired at 450 ° C. for 2 hours in an air atmosphere to obtain a Ru / La ₁₀ Si ₆ O ₂₇ catalyst. As a result of the XRD measurement, it was confirmed that the composite oxide maintained the apatite structure even after the preparation of the catalyst.
0.2 g of the catalyst was charged into a quartz tube reactor having an outer diameter of 10 mm and an inner diameter of 6 mm, and the catalyst layer was placed between a pair of SUS304 porous flat plate electrodes having the same size as the inner diameter.
A mixed gas of hydrogen gas and nitrogen gas was introduced into the reactor and pressurized to 0.8 MPaG. Using a commercially available high-voltage power supply (Matsusada Precision's HAR-20N7.5), apply a voltage of 2 mA in a constant current mode in a constant current mode, apply a voltage, and use a heating device so that the catalyst layer temperature becomes 300 ° C. or 350 ° C. The reaction was carried out for 30 minutes while warming. The molar ratio of hydrogen atoms / nitrogen atoms in the introduced gas was set to 1, and an ammonia synthesis reaction was performed at a total gas flow rate of 240 ml / min. Table 1 shows the results.
The ammonia generation rate is determined by capturing the ammonia contained in the gas after passing through the catalyst layer in a 0.1 M boric acid aqueous solution and quantifying the ammonium ion concentration in the solution by cation chromatography, so that the ammonia generation rate during the reaction time is determined. It was calculated as the average value of the speed.

(Example 2)
A catalyst was prepared in the same manner as in Example 1 except that La ₂ Zr ₂ O ₇ was used instead of La ₁₀ Si ₆ O ₂₇ to obtain a Ru / La ₂ Zr ₂ O ₇ catalyst. The obtained catalyst reacted in the same manner as in Example 1, and the ammonia generation rate was calculated. Table 1 shows the results.
In addition, as a result of confirming the crystal structure of the catalyst by XRD measurement, it was confirmed that the composite oxide maintained a pyrochlore structure even after preparation of the catalyst.

(Comparative Example 1)
A catalyst was prepared in the same manner as in Example 1 except that CaZrO ₃ was used instead of La ₁₀ Si ₆ O ₂₇ to obtain a Ru / CaZrO ₃ catalyst. The obtained catalyst reacted in the same manner as in Example 1, and the ammonia generation rate was calculated. Table 1 shows the results.
In addition, as a result of confirming the crystal structure of the catalyst by XRD measurement, it was confirmed that the composite oxide maintained the perovskite structure even after preparation of the catalyst.

(Example 3)
An acetone solution of a tris (acetylacetonato) ruthenium complex, an aqueous solution of cerium acetate monohydrate and La ₁₀ Si ₆ O ₂₇ were mixed with 100 parts by weight of La ₁₀ Si ₆ O _{27 to} prepare a tris (acetylacetonato) ruthenium complex ( 7 parts by weight (Ru metal conversion) and 8 parts by weight of cerium acetate (CeO ₂ conversion) were mixed and impregnated and supported. The obtained sample was dried and calcined at 450 ° C. for 2 hours in the air to obtain a CeO ₂ —Ru / La ₁₀ Si ₆ O ₂₇ catalyst. The obtained catalyst reacted in the same manner as in Example 1, and the ammonia generation rate was calculated. Table 1 shows the results.
In addition, as a result of confirming the crystal structure of the catalyst by XRD measurement, it was confirmed that the composite oxide maintained the apatite structure even after preparation of the catalyst.

(Example 4)
A catalyst was prepared in the same manner as in Example 3 except that La ₂ Zr ₂ O ₇ was used instead of La ₁₀ Si ₆ O ₂₇ to obtain a CeO ₂ —Ru / La ₂ Zr ₂ O ₇ catalyst. The obtained catalyst reacted in the same manner as in Example 1, and the ammonia generation rate was calculated. Table 1 shows the results.
In addition, as a result of confirming the crystal structure of the catalyst by XRD measurement, it was confirmed that the composite oxide maintained the pyrochlore structure even after preparation of the catalyst.

(Comparative Example 2)
A catalyst was prepared in the same manner as in Example 3 except that CaZrO ₃ was used instead of La ₁₀ Si ₆ O ₂₇ to obtain a CeO ₂ —Ru / CaZrO ₃ catalyst. The obtained catalyst reacted in the same manner as in Example 1, and the ammonia generation rate was calculated. Table 1 shows the results.
In addition, as a result of confirming the crystal structure of the catalyst by XRD measurement, it was confirmed that the composite oxide maintained the perovskite structure even after preparation of the catalyst.

(Comparative Example 3)
A catalyst was prepared in the same manner as in Example 3 except that Ce _0.5 Zr _0.5 O ₂ was used instead of La ₁₀ Si ₆ O ₂₇ , and CeO ₂ —Ru / Ce _0.5 Zr _{0. 5} O ₂ catalyst was obtained. The obtained catalyst reacted in the same manner as in Example 1, and the ammonia generation rate was calculated. Table 1 shows the results.
In addition, as a result of confirming the crystal structure of the catalyst by XRD measurement, it was confirmed that the composite oxide had a cubic crystal structure even after preparation of the catalyst.

(Example 5)
A tris (acetylacetonato) ruthenium complex, an aqueous solution of cesium hydroxide and an aqueous solution of cesium hydroxide and La ₁₀ Si ₆ O ₂₇ were mixed with 100 parts by weight of La ₁₀ Si ₆ O ₂₇ to obtain a tris (acetylacetonato) ruthenium complex (in terms of Ru metal). 7 parts by weight and 12 parts by weight of cesium hydroxide (in terms of Cs metal) were mixed and impregnated and supported. After drying the obtained sample, it was baked in air at 450 ° C. for 2 hours to obtain a Cs-Ru / La ₁₀ Si ₆ O ₂₇ catalyst. The obtained catalyst reacted in the same manner as in Example 1, and the ammonia generation rate was calculated. Table 1 shows the results.
In addition, as a result of confirming the crystal structure of the catalyst by XRD measurement, it was confirmed that the composite oxide maintained the apatite structure even after preparation of the catalyst.

(Example 6)
A catalyst was prepared in the same manner as in Example 5 except that La ₂ Zr ₂ O ₇ was used instead of La ₁₀ Si ₆ O ₂₇ to obtain a Cs-Ru / La ₂ Zr ₂ O ₇ catalyst. The obtained catalyst reacted in the same manner as in Example 1, and the ammonia generation rate was calculated. Table 1 shows the results.
In addition, as a result of confirming the crystal structure of the catalyst by XRD measurement, it was confirmed that the composite oxide maintained the pyrochlore structure even after preparation of the catalyst.

(Comparative Example 4)
In Example _5, except for using CaZrO ₃ in place of La ₁₀ Si _{6 O 27} performs a catalyst prepared in the same manner to obtain a Cs-Ru / CaZrO ₃ catalyst. The obtained catalyst reacted in the same manner as in Example 1, and the ammonia generation rate was calculated. Table 1 shows the results.
In addition, as a result of confirming the crystal structure of the catalyst by XRD measurement, it was confirmed that the composite oxide maintained the perovskite structure even after preparation of the catalyst.

(Example 7)
In Example 5, the ammonia generation rate was calculated in the same manner except that the molar ratio of hydrogen atoms / nitrogen atoms in the introduced gas was changed to 3, and the total gas flow rate was changed to 60 ml / min. Table 1 shows the results.

(Comparative Example 5)
In Comparative Example 4, the ammonia generation rate was calculated in the same manner except that the molar ratio of hydrogen atoms / nitrogen atoms in the introduced gas was changed to 3, and the total gas flow rate was changed to 60 ml / min. Table 1 shows the results.

(Example 8)
The ammonia generation rate was calculated in the same manner as in Example 5, except that no voltage was applied without supplying electricity. Table 2 shows the results.

(Comparative Example 6)
In Comparative Example 4, the ammonia generation rate was calculated in the same manner except that no voltage was applied without energization. Table 2 shows the results.

※アンモニア生成速度：触媒１ｇあたり１時間でのアンモニア生成量（マイクロモル）

* Ammonia production rate: Amount of ammonia produced per gram of catalyst per hour (micromol)

※アンモニア生成速度：触媒１ｇあたり１時間でのアンモニア生成量（マイクロモル）

* Ammonia production rate: Amount of ammonia produced per gram of catalyst per hour (micromol)

  As shown in Tables 1 and 2, it was revealed that the inclusion of the composite oxide of the present invention in the catalyst exhibited higher activity than the conventional catalyst.

  By using the catalyst for ammonia synthesis according to the present invention, ammonia can be synthesized more efficiently than conventional catalysts for ammonia synthesis, and the energy efficiency can be increased. Therefore, storage of renewable energy during oversupply, ammonia supply system for fertilizer in remote areas using renewable energy, and ammonia synthesis device for on-board NOx reduction, which were conventionally difficult to apply in terms of efficiency and economy For example, in performing ammonia synthesis using an electric field catalytic reaction, it can be used as a suitable catalyst.

Claims (7)

An ammonia synthesis catalyst used to provide a catalyst between the electrodes and apply a voltage between the electrodes in the presence of a gas containing a hydrogen atom and a nitrogen atom to synthesize ammonia,
A catalyst for ammonia synthesis comprising at least a catalytically active component and a composite oxide, wherein a composite oxide having a pyrochlore structure and / or an apatite structure is used as the composite oxide. The catalyst for ammonia synthesis according to claim 1, wherein the catalyst is provided between a pair of electrodes . The catalyst for ammonia synthesis according to claim 1 or 2, wherein the voltage does not cause discharge. The catalyst for ammonia synthesis according to any one of claims 1 to 3, wherein the composite oxide having a pyrochlore structure and / or an apatite structure is a composite oxide containing a lanthanoid. The ammonia synthesis catalyst according to any one of claims 1 to 4 , wherein the ammonia synthesis catalyst further contains at least one element selected from an alkali metal, an alkaline earth metal, and a lanthanoid as a cocatalyst. Catalyst. The ammonia according to any one of claims 1 to 5 , wherein the catalytically active component contains at least one element selected from ruthenium, iron, cobalt, nickel, platinum, palladium, rhodium, and iridium. Catalyst for synthesis. The catalyst provided between the pair of electrodes, a method of synthesizing ammonia by applying a voltage that does not cause a discharge between the electrodes in the presence of a gas containing hydrogen and nitrogen atoms, one of the claims 1-6 A method for synthesizing ammonia, comprising using the catalyst for ammonia synthesis according to claim 1.