JP2010094667A - Ammonia-decomposition catalyst, method of producing the same, and method of treating ammonia - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst capable of producing highly pure hydrogen by efficiently decomposing ammonia into nitrogen and hydrogen in a broad ammonia concentration range at a relatively low temperature and at a high space velocity without using noble metal, a method of producing the same, and a method of treating ammonia. <P>SOLUTION: The ammonia decomposition catalyst includes at least one species selected from the group consisting of molybdenum, tungsten, and vanadium. The ammonia decomposition catalyst is produced for example, by preparing an oxide comprising a specific transition metal and subsequently treating the oxide with an ammonia gas or with a mixed gas of nitrogen and hydrogen at a temperature of 300 to 800°C. By treating a gas comprising ammonia using the ammonia-decomposition catalyst, ammonia therein is decomposed into nitrogen and hydrogen, and hydrogen can be obtained. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a catalyst for decomposing ammonia into nitrogen and hydrogen, a method for producing the catalyst, and an ammonia treatment method using the catalyst.

  Since ammonia has an odorous property, particularly an irritating malodor, it is necessary to treat it when the gas contains an odor threshold value or more. Therefore, various ammonia treatment methods have been conventionally studied. For example, a method in which ammonia is brought into contact with oxygen and oxidized into nitrogen and water, and a method in which ammonia is decomposed into nitrogen and hydrogen have been proposed.

  For example, Patent Document 1 discloses that, for example, a platinum-alumina catalyst, a manganese-alumina catalyst, a cobalt-alumina catalyst, and the like are used to oxidize ammonia generated from a coke oven to nitrogen and water, and ammonia generated from the coke oven is used. In decomposing into nitrogen and hydrogen, for example, an ammonia treatment method using an iron-alumina catalyst, a nickel-alumina catalyst, or the like is disclosed. However, this ammonia treatment method is not preferable because NOx is often produced as a by-product and a new NOx treatment facility is required.

  Patent Document 2 discloses that nickel or nickel oxide is deposited on a metal oxide carrier such as alumina, silica, titania, zirconia in decomposing ammonia generated from a process of treating organic waste into nitrogen and hydrogen. An ammonia treatment method using a catalyst that is supported and further added with at least one of an alkaline earth metal and a lanthanoid element in the form of a metal or an oxide is disclosed. However, this ammonia treatment method has a low ammonia decomposition rate and is not practical.

  Further, Patent Document 3 discloses an ammonia treatment method using a catalyst in which an alkali metal or an alkaline earth metal basic compound is added to ruthenium on an alumina support in decomposing ammonia generated from a coke oven into nitrogen and hydrogen. It is disclosed. This ammonia treatment method uses ruthenium, which is a rare noble metal, as an active metal species, despite the advantage that ammonia can be decomposed at a lower temperature than a conventional catalyst such as iron-alumina. It has a big problem in cost and is not practical.

  In addition, it has been studied to use hydrogen recovered by decomposition of ammonia as a hydrogen source for a fuel cell. In this case, it is necessary to obtain high-purity hydrogen. When trying to obtain high-purity hydrogen using the ammonia decomposition catalysts proposed so far, there is a problem that a very high reaction temperature is required or a large amount of an expensive catalyst needs to be used. .

  In order to solve such a problem, as a catalyst capable of decomposing ammonia at a relatively low temperature (about 400 to 500 ° C.), for example, Patent Document 4 discloses an iron-ceria complex, and Patent Document 5 discloses Nickel-lanthanum oxide / alumina, nickel-yttria / alumina, nickel-ceria / alumina ternary composites are disclosed, and Non-Patent Document 1 discloses an iron-ceria / zirconia ternary composite. ing.

However, any of these catalysts has a low ammonia concentration in the processing gas (specifically, 5% by volume in Patent Document 4 and 50% by volume in Patent Document 5), or a space velocity based on ammonia. (Specifically, Patent Document 4 is 642 h ⁻¹ , Patent Document 5 is 1,000 h ⁻¹ , Non-Patent Document 1 is 430 h ⁻¹ ), and the ammonia decomposition rate is measured. Even if the ammonia decomposition rate is 100% at a relatively low temperature, the catalyst performance is not necessarily high.

  As described above, each of the conventional ammonia decomposition catalysts has a problem that it is not possible to obtain high-purity hydrogen by efficiently decomposing ammonia at a relatively low temperature and at a high space velocity.

JP-A 64-56301 JP 2004-195454 A JP-A-1-119341 JP 2001-300314 A Japanese Patent Laid-Open No. 2-198639

Masahiro Hamada and three others, “Ammonia Decomposition Characteristics of Rare Earth Oxide-Iron Complex”, Proceedings of the 18th Rare Earth Discussion Meeting “Rare Earth”, Organizer: Japan Rare Earth Society, Date: May 10-11, 2001 Japan, Chuo University, p. 122-123

  Under the circumstances described above, the problem to be solved by the present invention is that ammonia is used at a relatively low temperature in a wide ammonia concentration range from a low concentration to a high concentration without using a noble metal that has practical problems in terms of cost. Another object of the present invention is to provide a catalyst that can be efficiently decomposed into nitrogen and hydrogen at a high space velocity to obtain high purity hydrogen, a method for producing the catalyst, and an ammonia treatment method.

  As a result of various studies, the present inventors have found that if an oxide containing a specific transition metal (excluding a noble metal) is treated with ammonia gas or a nitrogen-hydrogen mixed gas at a predetermined temperature, the ammonia is relatively reduced. The present invention was completed by finding that a catalyst capable of efficiently decomposing nitrogen and hydrogen at a low temperature and at a high space velocity to obtain high purity hydrogen was obtained.

  That is, the present invention is a catalyst for decomposing ammonia into nitrogen and hydrogen, and the catalytically active component contains at least one selected from the group consisting of molybdenum, tungsten and vanadium (hereinafter referred to as “component A”). An ammonia decomposition catalyst is provided. In the ammonia decomposition catalyst of the present invention, the catalytically active component preferably further contains at least one selected from the group consisting of cobalt, nickel, manganese and iron (hereinafter referred to as “component B”). More preferably, the A component and the B component are in the form of a composite oxide. The catalytically active component may further contain at least one selected from the group consisting of alkali metals, alkaline earth metals and rare earth metals (hereinafter referred to as “C component”). Furthermore, some or all of the catalytically active components may be treated with ammonia gas or a nitrogen-hydrogen mixed gas.

  In the present invention, after preparing an oxide containing an A component or an oxide containing an A component and a B component, the oxide is converted into ammonia gas or nitrogen-hydrogen at a temperature of 300 to 800 ° C. Provided is a method for producing an ammonia decomposition catalyst, which comprises treating with a mixed gas. In addition, you may add the compound of C component after preparing the said oxide. In the ammonia decomposition catalyst obtained by this production method, a part or all of the catalytically active component is changed to a nitride containing an A component or a nitride containing an A component and a B component.

  Furthermore, the present invention is an ammonia treatment method characterized in that the ammonia-decomposing catalyst as described above is used to treat a gas containing ammonia to obtain hydrogen by decomposing the ammonia into nitrogen and hydrogen. I will provide a.

  According to the present invention, ammonia is efficiently decomposed into nitrogen and hydrogen at a relatively low temperature and at a high space velocity in a wide ammonia concentration range from a low concentration to a high concentration without using noble metals. Provided are a catalyst capable of obtaining pure hydrogen, a method for easily producing the catalyst, and a method for obtaining hydrogen by decomposing ammonia into nitrogen and hydrogen using the catalyst.

≪Ammonia decomposition catalyst≫
The ammonia decomposition catalyst of the present invention (hereinafter sometimes referred to as “the catalyst of the present invention”) is a catalyst that decomposes ammonia into nitrogen and hydrogen, and the catalytically active component is selected from the group consisting of molybdenum, tungsten, and vanadium. It contains at least one kind (hereinafter referred to as “component A”).

  In addition to the component A, the catalytically active component preferably further contains at least one selected from the group consisting of cobalt, nickel, manganese and iron (hereinafter referred to as “component B”). In this case, the component A and the component B are more preferably in the form of a complex oxide.

  In addition to the A component or in addition to the A component and the B component, the catalytically active component is further at least one selected from the group consisting of alkali metals, alkaline earth metals and rare earth metals (hereinafter “ "C component") may be contained.

  Part or all of the catalytically active component may be treated with ammonia gas or a nitrogen-hydrogen mixed gas.

<A component>
The catalytically active component contains at least one selected from the group consisting of molybdenum, tungsten and vanadium as the A component. Of these components A, molybdenum and tungsten are preferable, and molybdenum is more preferable.

  The starting material for the component A is not particularly limited as long as it is usually used as a starting material for the catalyst, but is preferably an inorganic compound such as an oxide, chloride, ammonium salt, alkali metal salt; And organic acid salts such as acetate and oxalate; organometallic complexes such as acetylacetonate complex and metal alkoxide; and the like.

  Specifically, examples of the molybdenum source include molybdenum oxide, ammonium molybdate, sodium molybdate, potassium molybdate, rubidium molybdate, cesium molybdate, lithium molybdate, molybdenum 2-ethylhexylate, and bis (acetylacetonato). ) Oxomolybdenum and the like, and ammonium molybdate is preferred. Examples of the tungsten source include tungsten oxide, ammonium tungstate, sodium tungstate, potassium tungstate, rubidium tungstate, lithium tungstate, tungsten ethoxide, and the like, and ammonium tungstate is preferable. Examples of the vanadium source include vanadium oxide, ammonium vanadate, sodium vanadate, lithium vanadate, bis (acetylacetonato) oxovanadium, vanadium oxytriethoxide, vanadium oxytriisopropoxide, and vanadic acid. Ammonium is preferred.

  The A component is an essential element of the catalytically active component, and the content of the A component is preferably 20 to 90% by mass, and more preferably 40 to 70% by mass with respect to 100% by mass of the catalytically active component.

<B component>
The catalytically active component preferably contains at least one selected from the group consisting of cobalt, nickel, manganese and iron as the B component. Of these B components, cobalt and nickel are preferable, and cobalt is more preferable.

  The starting material for the component B is not particularly limited as long as it is usually used as a starting material for the catalyst, but is preferably an inorganic material such as an oxide, hydroxide, nitrate, sulfate, or carbonate. Compound; Organic acid salt such as acetate and oxalate; Organometallic complex such as acetylacetonato complex and metal alkoxide; and the like.

  Specifically, examples of the cobalt source include cobalt oxide, cobalt hydroxide, cobalt nitrate, cobalt sulfate, ammonium cobalt sulfate, cobalt carbonate, cobalt acetate, cobalt oxalate, cobalt citrate, cobalt benzoate, and 2-ethylhexyl acid. Examples include cobalt and lithium cobalt oxide, and cobalt nitrate is preferable. Examples of the nickel source include nickel oxide, nickel hydroxide, nickel nitrate, nickel sulfate, nickel carbonate, nickel acetate, nickel oxalate, nickel citrate, nickel benzoate, nickel 2-ethylhexylate, and bis (acetylacetonate). Nickel etc. are mentioned, Nickel nitrate is preferable. Examples of the manganese source include manganese oxide, manganese nitrate, manganese sulfate, manganese carbonate, manganese acetate, manganese citrate, manganese 2-ethylhexylate, potassium permanganate, sodium permanganate, cesium permanganate and the like. Manganese nitrate is preferred. Examples of the iron source include iron oxide, iron hydroxide, iron nitrate, iron sulfate, iron acetate, iron oxalate, iron citrate, and iron methoxide, and iron nitrate is preferable.

  The content of the component B is preferably 0 to 50% by mass and more preferably 10 to 40% by mass with respect to 100% by mass of the catalytically active component.

When the A component and the B component are used in combination, as a starting material of the A component and the B component, for example, a mixture of an oxide of the A component and an oxide of the B component, or a composite of the A component and the B component An oxide can be used. Specific examples of the composite oxide of the A component and the B component are not particularly limited, and examples thereof include CoMoO ₄ , NiMoO ₄ , MnMoO ₄ , and CoWO ₄ .

<C component>
The catalytically active component may contain at least one selected from the group consisting of alkali metals, alkaline earth metals, and rare earth metals as the C component. Of these C components, alkali metals and alkaline earth metals are preferred, and alkali metals are more preferred.

  The starting material of component C is not particularly limited as long as it is usually used as a starting material for the catalyst, but is preferably an oxide, hydroxide, nitrate, sulfate, carbonate, acetate. And oxalate.

  The content of the component C is preferably 0 to 50% by mass, more preferably 0.2 to 20% by mass with respect to 100% by mass of the catalytically active component.

<Physical properties>
The specific surface area of the catalyst of the present invention is preferably 1 to 300 m ² / g, more preferably 5 to 260 m ² / g, still more preferably 18 to ²⁰⁰ m ² / g.

<Catalyst shape>
In the catalyst of the present invention, the catalytically active component may be used as it is, or the catalytically active component may be supported on a carrier by a conventionally known method. The support is not particularly limited, and examples thereof include metal oxides such as alumina, silica, titania, zirconia, and ceria.

  The catalyst of the present invention may be molded into a desired shape using a conventionally known method. The shape of the catalyst is not particularly limited, and examples thereof include granular, spherical, pellet-shaped, crushed, saddle-shaped, ring-shaped, honeycomb-shaped, monolith-shaped, net-shaped, columnar, cylindrical, and the like.

  Further, the catalyst of the present invention may be used by coating the surface of the structure in layers. The structure is not particularly limited. For example, a structure made of a ceramic such as cordierite, mullite, silicon carbide, alumina, silica, titania, zirconia, and ceria; a structure made of a metal such as ferritic stainless steel Body; and the like. The shape of the structure is not particularly limited, and examples thereof include a honeycomb shape, a corrugated shape, a net shape, a columnar shape, and a cylindrical shape.

≪Method for producing ammonia decomposition catalyst≫
Hereinafter, preferred specific examples of the method for producing the ammonia decomposition catalyst of the present invention will be shown, but the present invention is not limited to the following production method as long as the object of the present invention is achieved.

(1) A component oxide, a mixture of an A component oxide and a B component oxide, a composite oxide of A component and B component, a mixture obtained by adding an oxide of C component to these, or these A method of using, as a catalyst, a calcined product obtained by calcining a mixture obtained by adding an aqueous solution of the component C to a dried product;
(2) A method in which the fired product of (1) is further treated (nitrided) with ammonia gas or a nitrogen-hydrogen mixed gas at a temperature of 300 to 800 ° C;
(3) A method in which an aqueous solution of a salt containing the component A is calcined to form an oxide, and the oxide is used as a catalyst;
(4) A method of further processing (nitriding) the oxide of (3) at a temperature of 300 to 800 ° C. with ammonia gas or a nitrogen-hydrogen mixed gas;
(5) A method in which an aqueous solution of a salt containing an A component and a salt containing a B component is baked into an oxide, and the oxide is used as a catalyst;
(6) A method of further treating (nitriding) the oxide of (5) with ammonia gas or a nitrogen-hydrogen mixed gas at a temperature of 300 to 800 ° C;
(7) A method in which an acid aqueous solution of a salt containing the component A is neutralized with an aqueous alkali metal solution or ammonia water to obtain an oxide, and the oxide is used as a catalyst;
(8) A method of further processing (nitriding) the oxide of (7) at a temperature of 300 to 800 ° C. with ammonia gas or a nitrogen-hydrogen mixed gas;
(9) A method in which an acid aqueous solution of a salt containing an A component and a salt containing a B component is neutralized with an aqueous alkali metal solution or aqueous ammonia to obtain an oxide, and the oxide is used as a catalyst;
(10) A method of further processing (nitriding) the oxide of (9) at a temperature of 300 to 800 ° C. with ammonia gas or a nitrogen-hydrogen mixed gas.

  The method for producing an ammonia decomposition catalyst according to the present invention (hereinafter sometimes referred to as “the production method of the present invention”) comprises preparing an oxide containing A component or an oxide containing A component and B component; The oxide is treated (nitrided) with ammonia gas or a nitrogen-hydrogen mixed gas at a temperature of 300 to 800 ° C. In addition, you may add the compound of C component after preparing the said oxide.

  The temperature of the nitriding treatment is usually 300 to 800 ° C, preferably 400 to 750 ° C, more preferably 500 to 720 ° C. When ammonia gas is used, the concentration is preferably 10 to 100% by volume, more preferably 50 to 100% by volume. When a nitrogen-hydrogen mixed gas is used, the concentration of nitrogen is preferably 2 to 95% by volume, more preferably 20 to 90% by volume. The concentration of hydrogen is preferably 5 to 98% by volume, more preferably 10 to 80% by volume.

  In either case of ammonia gas or nitrogen-hydrogen mixed gas, the gas flow rate (volume) is preferably 80 to 250 times, more preferably 100 to 200 times the volume of the catalyst per minute.

  Prior to nitriding treatment, it is more preferable to raise the temperature to 300 to 400 ° C. while flowing nitrogen. In this case, the flow rate (volume) of nitrogen is preferably 50 to 120 times, more preferably 60 to 100 times the volume of the catalyst per minute.

  The ratio of the catalytically active component changed to nitride by the nitriding treatment can be confirmed by examining the crystal structure of the catalyst by X-ray diffraction. Although it is preferable that all of the catalytically active component is changed to nitride, it is not always necessary, and even if a part of the catalytically active component is changed to nitride, it has sufficient catalytic activity. . The ratio of nitride in the catalyst (ratio when the sum of integrated values of oxide peaks and nitride peaks in the X-ray diffraction pattern is 100%) is preferably 3% or more, more preferably 5% That's it.

≪Ammonia treatment method≫
The ammonia treatment method of the present invention is characterized in that a gas containing ammonia is treated using the ammonia decomposition catalyst as described above, and the ammonia is decomposed into nitrogen and hydrogen to obtain hydrogen. The “gas containing ammonia” to be treated is not particularly limited, but includes not only ammonia gas and ammonia-containing gas but also gas containing a substance that generates ammonia by thermal decomposition such as urea. There may be. Moreover, the gas containing ammonia may contain other components as long as it does not become a catalyst poison.

The flow rate of the “gas containing ammonia” per catalyst is a space velocity, preferably 1,000 to 200,000 h ⁻¹ , more preferably 2,000 to 150,000 h ⁻¹ , more preferably 3,000 to 3,000. 100,000h- ¹ . Here, the flow rate of the “gas containing ammonia” per catalyst means the volume of the “gas containing ammonia” passing through the catalyst per unit time per volume occupied by the catalyst when the catalyst is charged into the reactor. Means.

  Reaction temperature becomes like this. Preferably it is 180-950 degreeC, More preferably, it is 300-900 degreeC, More preferably, it is 400-800 degreeC. The reaction pressure is preferably 0.002 to 2 MPa, more preferably 0.004 to 1 MPa.

  According to the ammonia treatment method of the present invention, high-purity hydrogen can be obtained by separating nitrogen and hydrogen obtained by decomposing ammonia into nitrogen and hydrogen using a conventionally known method. it can.

  Hereinafter, the present invention will be described more specifically with reference to experimental examples.However, the present invention is not limited by the following experimental examples, and appropriate modifications are made within a range that can meet the purpose described above and below. Any of these can be carried out and are included in the technical scope of the present invention.

  An X-ray diffractometer (product name “RINT-2400”, manufactured by Rigaku Corporation) was used for the X-ray diffraction measurement. CuKα (0.154 nm) was used as the X-ray source. The measurement conditions were an X-ray output of 50 kV, 300 mA, a divergence slit of 1.0 mm, a divergence length limit slit of 10 mm, a scan speed of 5 degrees per minute, and a sampling width of 0. The scanning was performed at 02 degrees and a scanning range of 5 to 90 degrees.

«Experimental example 1»
80.00 g of cobalt nitrate hexahydrate was dissolved in 400.00 g of distilled water. Separately, 48.53 g of ammonium molybdate was gradually added and dissolved in 250 g of boiling distilled water. After mixing both aqueous solutions, it was heated and stirred and evaporated to dryness. The obtained solid was dried at 120 ° C. for 10 hours, calcined at 350 ° C. for 5 hours under a nitrogen stream, and calcined at 500 ° C. for 3 hours under an air stream. It was confirmed to be α-CoMoO ₄ by X-ray diffraction measurement.

Furthermore, 0.5-1.0 mL of α-CoMoO ₄ was charged into a reaction tube made of SUS316, and the temperature was raised to 400 ° C. while flowing 30-50 mL / min of nitrogen gas (hereinafter referred to as “nitrogen”). Next, while flowing ammonia gas (hereinafter abbreviated as “ammonia”) at 50 to 100 mL / min, the temperature was raised to 700 ° C., and the treatment was held at 700 ° C. for 5 hours (nitriding treatment). CoMoO ₄ ”).

«Experimental example 2»
80.00 g of cobalt nitrate hexahydrate was dissolved in 400.00 g of distilled water. Separately, 48.53 g of ammonium molybdate was gradually added and dissolved in 250 g of boiling distilled water. After mixing both aqueous solutions, it was heated and stirred and evaporated to dryness. The obtained solid was dried at 120 ° C. for 10 hours, calcined at 350 ° C. for 5 hours under a nitrogen stream, and calcined at 500 ° C. for 3 hours under an air stream. It was confirmed to be α-CoMoO ₄ by X-ray diffraction measurement.

Next, 0.089 g of cesium nitrate was dissolved in 3.23 g of distilled water. This aqueous solution was dropped into 6.00 g of α-CoMoO ₄ and uniformly infiltrated, dried at 90 ° C. for 10 hours, and confirmed to be α-CoMoO ₄ by X-ray diffraction measurement.

Furthermore, 0.5-1.0 mL of α-CoMoO ₄ containing Cs was charged into a reaction tube made of SUS316, and the temperature was raised to 400 ° C. while flowing 30-50 mL / min of nitrogen. Next, while flowing ammonia at 50 to 100 mL / min, the temperature was raised to 700 ° C., and a treatment (nitriding treatment) was performed at 700 ° C. for 5 hours to display an ammonia decomposition catalyst (hereinafter, “1% Cs—CoMoO ₄ ”). Obtained).

«Experimental example 3»
Experimental example 2 except that in Example 2, 0.089 g of cesium nitrate was dissolved in 3.23 g of distilled water, an aqueous solution in which 0.18 g of cesium nitrate was dissolved in 3.21 g of distilled water was used. In the same manner as in No. 2, an ammonia decomposition catalyst (hereinafter referred to as “2% Cs—CoMoO ₄ ”) was obtained. The state after uniformly infiltrating cesium nitrate and drying at 90 ° C. for 10 hours was confirmed to be α-CoMoO ₄ by X-ray diffraction measurement.

<< Experimental Example 4 >>
Experimental Example 2 except that in Example 2, 0.089 g of cesium nitrate was dissolved in 3.23 g of distilled water, an aqueous solution in which 0.46 g of cesium nitrate was dissolved in 3.20 g of distilled water was used. In the same manner as in No. 2, an ammonia decomposition catalyst (hereinafter referred to as “5% Cs—CoMoO ₄ ”) was obtained. The state after uniformly infiltrating cesium nitrate and drying at 90 ° C. for 10 hours was confirmed to be α-CoMoO ₄ by X-ray diffraction measurement.

<< Experimental Examples 5-7 >>
In Example 1, except that the amounts of cobalt nitrate hexahydrate and ammonium molybdate were appropriately changed, the molar ratio of cobalt to molybdenum (Co / Mo) was changed to Example 5 except that the amounts of cobalt nitrate hexahydrate and ammonium molybdate were changed. Then, an ammonia decomposition catalyst having 1.05 (hereinafter referred to as “Co / Mo = 1.05”), and in Experimental Example 6, an ammonia decomposition catalyst having 1.10 (hereinafter “Co / Mo = 1.10”). In Example 7, an ammonia decomposition catalyst with 0.90 (hereinafter referred to as “Co / Mo = 0.90”) was obtained. Incidentally, under a nitrogen stream, then calcined 5 hours at 350 ° C., under an air stream, the state after firing for 3 hours at 500 ° C., the X-ray diffraction measurement, respectively, it was confirmed that the α-CoMoO _4.

<< Experimental Example 8 >>
In Experimental Example 1, an ammonia decomposition catalyst (hereinafter referred to as “NiMoO ₄ ”) was obtained in the same manner as Experimental Example 1, except that the cobalt nitrate hexahydrate was changed to nickel nitrate hexahydrate. Incidentally, under a nitrogen stream, then calcined 5 hours at 350 ° C., confirmed that an air stream, the state after firing for 3 hours at 500 ° C., the X-ray diffraction measurement, a NiMoO ₄ showing the ₄ type alpha-CoMoO did.

<< Experimental Example 9 >>
In Experimental Example 8, the state after calcination at 350 ° C. for 5 hours in a nitrogen stream and after calcination at 500 ° C. for 3 hours in an air stream is NiMoO ₄ showing α-CoMoO ₄ type by X-ray diffraction measurement. After confirming this, an aqueous solution in which 0.075 g of cesium nitrate was dissolved in 1.55 g of distilled water was dropped into NiMoO ₄ showing the α-CoMoO ₄ type, and the solution was uniformly infiltrated and stirred at 90 ° C. for 10 hours. After drying, an ammonia decomposition catalyst (hereinafter referred to as “1% Cs—NiMoO ₄ ”) was obtained in the same manner as in Experimental Example 8 except that nitriding treatment was performed. The state before the nitriding treatment was confirmed to be NiMoO ₄ indicating α-CoMoO ₄ type by X-ray diffraction measurement.

<< Experimental Examples 10 and 11 >>
In Experimental Example 9, instead of an aqueous solution in which 0.075 g of cesium nitrate was dissolved in 1.55 g of distilled water, an aqueous solution in which 0.15 g of cesium nitrate was dissolved in 1.55 g of distilled water was used in Experimental Example 10. In Experimental Example 11, an ammonia decomposition catalyst (hereinafter referred to as “2% Cs—NiMoO”) was prepared in the same manner as in Experimental Example 9 except that an aqueous solution in which 0.40 g of cesium nitrate was dissolved in 1.55 g of distilled water was used. ₄ ”) and an ammonia decomposition catalyst (hereinafter referred to as“ 5% Cs—NiMoO ₄ ”).

Incidentally, a pre-stage of the conditions of the nitriding treatment, respectively, by X-ray diffraction measurement, it was confirmed that the NiMoO ₄ showing the ₄ type alpha-CoMoO.

«Experimental example 12»
A reaction tube made of SUS316 was charged with 0.5 to 1.0 mL of commercially available molybdenum oxide (MoO ₃ ), and heated to 400 ° C. while flowing nitrogen of 30 to 50 mL / min. Next, while flowing ammonia at 50 to 100 mL / min, the temperature is raised to 700 ° C. and a treatment (nitriding treatment) is performed at 700 ° C. for 5 hours to obtain an ammonia decomposition catalyst (hereinafter referred to as “MoO ₃ ”). It was.

«Experimental example 13»
An aqueous solution obtained by dissolving 0.21 g of cesium nitrate in 1.62 g of distilled water is dropped into 7.00 g of commercially available molybdenum oxide (MoO ₃ ) and uniformly infiltrated, and dried at 120 ° C. for 10 hours. Then, it was calcined at 350 ° C. for 5 hours, and calcined at 500 ° C. for 3 hours in an air stream.

Furthermore, 0.5 to 1.0 mL of the fired product was charged into a reaction tube made of SUS316, and the temperature was raised to 400 ° C. while flowing 30 to 50 mL / min of nitrogen. Next, while flowing ammonia at 50 to 100 mL / min, the temperature was raised to 700 ° C., and a treatment (nitriding treatment) was performed at 700 ° C. for 5 hours to display an ammonia decomposition catalyst (hereinafter “2% Cs—MoO ₃ ”). Obtained).

<< Experimental Examples 14 and 15 >>
In Experimental Example 13, instead of an aqueous solution in which 0.21 g of cesium nitrate was dissolved in 1.62 g of distilled water, an aqueous solution in which 0.54 g of cesium nitrate was dissolved in 1.62 g of distilled water was used in Experimental Example 14. In Experimental Example 15, an ammonia decomposition catalyst (hereinafter referred to as “5% Cs—MoO”) was prepared in the same manner as in Experimental Example 13, except that an aqueous solution in which 1.14 g of cesium nitrate was dissolved in 1.62 g of distilled water was used. ₃ ”) and an ammonia decomposition catalyst (hereinafter referred to as“ 10% Cs—MoO ₃ ”).

<< Experimental Example 16 >>
9.49 g of cobalt nitrate hexahydrate was dissolved in 41.18 g of distilled water, and an aqueous ammonium metatungstate solution (abbreviation “MW-2”, manufactured by Nippon Inorganic Chemical Industries, Ltd .; containing 50% by mass as tungsten oxide) 15 .13 g was added. After mixing both solutions, they were heated and stirred and evaporated to dryness. The obtained solid was dried at 120 ° C. for 10 hours, calcined at 350 ° C. for 5 hours under a nitrogen stream, and calcined at 500 ° C. for 3 hours under an air stream.

Furthermore, 0.5 to 1.0 mL of the fired product was charged into a reaction tube made of SUS316, and the temperature was raised to 400 ° C. while flowing 30 to 50 mL / min of nitrogen. Next, while flowing ammonia at 50 to 100 mL / min, the temperature is raised to 700 ° C., and a treatment (nitriding treatment) is performed at 700 ° C. for 5 hours to obtain an ammonia decomposition catalyst (hereinafter referred to as “CoWO ₄ ”). It was.

<< Experimental Example 17 >>
Manganese nitrate hexahydrate (13.36 g) was dissolved in distilled water (67.08 g). Separately, 8.22 g of ammonium molybdate was gradually added and dissolved in 41.04 g of boiling distilled water. After mixing both aqueous solutions, it was heated and stirred and evaporated to dryness. The obtained solid was dried at 120 ° C. for 10 hours, calcined at 350 ° C. for 5 hours under a nitrogen stream, and calcined at 500 ° C. for 3 hours under an air stream. It was confirmed to be α-MnMoO ₄ by X-ray diffraction measurement.

Furthermore, 0.5 to 1.0 mL of the fired product was charged into a reaction tube made of SUS316, and the temperature was raised to 400 ° C. while flowing 30 to 50 mL / min of nitrogen. Next, while flowing ammonia at 50 to 100 mL / min, the temperature is raised to 700 ° C. and a treatment (nitriding treatment) is performed at 700 ° C. for 5 hours to obtain an ammonia decomposition catalyst (hereinafter referred to as “MnMoO ₄ ”). It was.

<< Experimental Example 18 >>
11.81 g of calcium nitrate tetrahydrate was dissolved in 60.10 g of distilled water. Separately, 8.83 g of ammonium molybdate was gradually added and dissolved in 45.06 g of boiling distilled water. After mixing both aqueous solutions, it was heated and stirred and evaporated to dryness. The obtained solid was dried at 120 ° C. for 10 hours, calcined at 350 ° C. for 5 hours under a nitrogen stream, and calcined at 500 ° C. for 3 hours under an air stream.

Furthermore, 0.5 to 1.0 mL of the fired product was charged into a reaction tube made of SUS316, and the temperature was raised to 400 ° C. while flowing 30 to 50 mL / min of nitrogen. Next, while flowing ammonia at 50 to 100 mL / min, the temperature is raised to 700 ° C. and a treatment (nitriding treatment) is performed at 700 ° C. for 5 hours to obtain an ammonia decomposition catalyst (hereinafter referred to as “CaMoO ₄ ”). It was.

<< Experimental Example 19 >>
13.92 g of magnesium nitrate hexahydrate was dissolved in 70.02 g of distilled water. Separately, 9.58 g of ammonium molybdate was gradually added and dissolved in 48.03 g of boiling distilled water. After mixing both aqueous solutions, it was heated and stirred and evaporated to dryness. The obtained solid was dried at 120 ° C. for 10 hours, calcined at 350 ° C. for 5 hours under a nitrogen stream, and calcined at 500 ° C. for 3 hours under an air stream.

Furthermore, 0.5 to 1.0 mL of the fired product was charged into a reaction tube made of SUS316, and the temperature was raised to 400 ° C. while flowing 30 to 50 mL / min of nitrogen. Next, while flowing ammonia at 50 to 100 mL / min, the temperature is raised to 700 ° C. and a treatment (nitriding treatment) is performed at 700 ° C. for 5 hours to obtain an ammonia decomposition catalyst (hereinafter referred to as “MgMoO ₄ ”). It was.

≪Ammonia decomposition reaction≫
Using each catalyst obtained in Experimental Examples 1 to 19 and ammonia having a purity of 99.9% by volume or more, an ammonia decomposition reaction was performed to decompose the ammonia into nitrogen and hydrogen.

The ammonia decomposition rate was measured under the conditions of an ammonia space velocity of 6,000 h ⁻¹ , a reaction temperature of 400 ° C., 450 ° C., or 500 ° C., and a reaction pressure of 0.101325 MPa (normal pressure) (calculated by the following formula). did). The results are shown in Table 1.

As is clear from Table 1, each of the ammonia decomposition catalysts of Experimental Examples 1 to 19 has a high concentration of ammonia having a purity of 99.9% by volume or more at a relatively low temperature of 400 to 500 ° C., and 6, It can be efficiently decomposed into nitrogen and hydrogen at a high space velocity of 000 h ⁻¹ . Moreover, since the ammonia catalysts of Experimental Examples 1 to 11 are complex oxides of molybdenum as the A component and cobalt or nickel as the B component, the ammonia decomposition rate is relatively high. Furthermore, the ammonia decomposition catalysts of Experimental Examples 2 to 4 have a very high ammonia decomposition rate because cesium as the C component is added to the composite oxide of molybdenum as the A component and cobalt as the B component. .

  The present invention relates to the decomposition of ammonia, and makes a great contribution in the environmental field in which ammonia-containing gas is treated and non-brominated, and in the energy field in which ammonia is decomposed into nitrogen and hydrogen to obtain hydrogen. It is what makes.

Claims (8)

  A catalyst for decomposing ammonia into nitrogen and hydrogen, wherein the catalytically active component contains at least one selected from the group consisting of molybdenum, tungsten and vanadium (hereinafter referred to as “component A”). Ammonia decomposition catalyst.   The ammonia decomposition catalyst according to claim 1, wherein the catalytically active component further contains at least one selected from the group consisting of cobalt, nickel, manganese and iron (hereinafter referred to as "component B").   The ammonia decomposition catalyst according to claim 1 or 2, wherein the A component and the B component are in the form of a composite oxide.   The catalyst active component further contains at least one selected from the group consisting of alkali metals, alkaline earth metals, and rare earth metals (hereinafter referred to as “C component”). The ammonia decomposition catalyst as described.   The ammonia decomposition catalyst according to any one of claims 1 to 4, wherein a part or all of the catalytically active component is treated with ammonia gas or a nitrogen-hydrogen mixed gas.   After preparing an oxide containing an A component or an oxide containing an A component and a B component, the oxide is treated with ammonia gas or a nitrogen-hydrogen mixed gas at a temperature of 300 to 800 ° C. A process for producing an ammonia decomposition catalyst characterized by the above.   The method for producing an ammonia decomposition catalyst according to claim 6, further comprising adding a compound of component C after preparing the oxide.   A gas containing ammonia is treated using the ammonia decomposition catalyst according to any one of claims 1 to 5, and the ammonia is decomposed into nitrogen and hydrogen to obtain hydrogen. Ammonia treatment method.