JPH1085601A - Ammonia decomposition catalyst, its production and method for decomposing ammonia - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an ammonia decomposition catalyst capable of efficiently decomposing ammonia at a relatively low temp. and capable of efficiently producing a gaseous hydrogen-nitrogen mixture by carrying Ru and an alkali metal on a carrier and specifying the halogen content of the resultant catalyst. SOLUTION: A gaseous hydrogen-nitrogen mixture having a ratio of 3:1 used as atmospheric gas in a process for bright-annealing stainless steel or nickel, a process for brazing stainless steel, etc., is produced at a low cost by decomposing amonia with an ammonia decomposition catalyst obtd. by carrying Ru and an alkali metal on a carrier and regulating the halogen content of the resultant catalyst to ⊖100wt.ppm. The alkali metal is preferably at least one of Na, K, Rb and Cs. The pref. Ru and alkali metal contents of the catalyst are preferably 0.1-5wt.% and 1-30wt.%, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ammonia decomposition catalyst capable of efficiently decomposing ammonia at a relatively low temperature to produce a mixed gas containing hydrogen and nitrogen, a method for preparing the same, and a method using the same. The present invention relates to a method for decomposing ammonia.

[0002]

[Prior Art] Stainless steel, nickel, nickel
In a bright annealing process of copper or a nickel-chromium alloy or a brazing process of stainless steel, a 3: 1 mixed gas of hydrogen and nitrogen is used as an atmosphere gas. Since this mixing ratio corresponds to the composition of the mixed gas generated when ammonia is decomposed, a relatively small and inexpensive gas for decomposing ammonia to produce a mixed gas containing hydrogen and nitrogen is produced. A method is needed.

As a catalyst for decomposing ammonia, conventionally, Fe
₂ O ₃ —Al ₂ O ₃ , NiO—SiO ₂ .Al ₂ O ₃ , Ni
O-MgO, such as Pt-Al ₂ O ₃ are known. The decomposition reaction of ammonia is a volume expansion type endothermic reaction that generates three molecules of hydrogen and one molecule of nitrogen from two molecules of ammonia. From the viewpoint of reaction equilibrium, a low-pressure high-temperature reaction is desirable. Therefore, the ammonia decomposition catalyst also
The pressure is near atmospheric pressure, but the temperature is between 700 ° C and 1100
It is used under high temperature conditions of ° C.

[0004] Also, CATALYSIS Sciennce and Technolog
y Vol. 1, p118, 1981, reported that platinum group elements such as Pt, Pd, Rh, and Ru are effective alone for decomposing ammonia, but the decomposition temperature is also 1350 in this case.
It is a high temperature range up to ℃.

[0005]

Since the above-mentioned catalytic reaction must be operated at a high temperature, the catalyst life is 1 year to 2 years.
It needs to use expensive heat-resistant material such as SUS310S as the material of the device. Nitrogen is generated under high temperature, the material life is shortened by nitriding, and a large amount of energy is required to maintain high temperature. As a result, all of the equipment costs, maintenance costs, and operation costs were expensive, and the utility was poor.

[0006] JP-A-5-329370 and JP-A-5-329372 disclose ammonia under a decomposition condition in which the pressure is about the vapor pressure of liquid ammonia (10 kg / cm ² abs. At 26 ° C) and the temperature is up to 700 ° C. As a catalyst for decomposing ammonia, an ammonia decomposition catalyst in which Co or Ni, La and a platinum group element are supported on a carrier has been proposed. However, the method using these Co- or Ni-La-platinum group element-based catalysts is not practical because the cost is high for measures against high temperatures and the like.

On the other hand, as a catalyst for producing ammonia for synthesizing ammonia from hydrogen and nitrogen, see JP-A-2-2580.
No. 66 discloses a ruthenium compound containing no chlorine (eg, ruthenium carbonyl complex or ruthenium nitrate)
Is supported on a carrier, hydrogen is reduced to prepare a metal Ru catalyst, and a catalyst in which an alkali metal compound is supported is proposed. Also, an ammonia production catalyst in which Ru, Os or Co and an alkali metal are supported on activated carbon or porous carbon is known (see Japanese Patent Publication No. 54-37592). However, since these catalysts are for synthesizing ammonia, they are not suitable for decomposing ammonia which is a reverse reaction.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object thereof is to efficiently decompose ammonia at a relatively low temperature to produce a mixed gas of hydrogen and nitrogen. It is an object of the present invention to provide an ammonia decomposing catalyst capable of producing the same, a method for preparing the same and an ammonia decomposing method using the same.

[0009]

According to the present invention, in order to solve the above-mentioned problems, the present invention is characterized in that, in claim 1, Ru and an alkali metal are supported on a carrier, and the halogen content is 1% of the weight of the catalyst.
Provided is an ammonia decomposition catalyst having a concentration of not more than 00 ppm by weight. The alkali metal is Na, K, Rb, or C
It is preferably at least one selected from s.
In this ammonia decomposition catalyst, the Ru content is in the range of 0.1% to 5% by weight of the catalyst weight, and the alkali metal content is in the range of 1% to 30% by weight of the catalyst weight. Is preferred.

According to the present invention, there is also provided in claim 4, in preparing the ammonia decomposition catalyst, a Ru supporting step of impregnating the carrier with a water-soluble ruthenium halide, and the halogen content is 100 ppm by weight or less of the weight of the catalyst. As described above, the present invention provides a method for preparing an ammonia decomposition catalyst, which includes a halogen removing step of removing halogen from a carrier by washing with water and an alkali metal supporting step of supporting an alkali metal on the carrier.

In a fifth aspect of the present invention, the halogen removing step comprises a step of impregnating the carrier with a water-soluble ruthenium halide in the Ru supporting step, and then fixing Ru on the carrier and making the halogen water-soluble. A washing step of washing the Ru-immobilized carrier obtained in the immobilizing step with water to remove halogen.

[0012] In claim 6, the immobilizing step comprises:
It is preferable to include a reduction step of reducing the Ru-supported carrier obtained in the Ru-supporting step with a water-soluble reducing agent. The water-soluble reducing agent is NaBH ₄ , KBH ₄ , or LiA.
It is preferably at least one selected from lH ₄ .

Alternatively, in claim 8, the immobilization step preferably includes a neutralization step of neutralizing the Ru-supported carrier obtained in the Ru-supporting step with an aqueous alkali solution.

Alternatively, in the ninth aspect, the immobilization step includes a neutralization step of neutralizing the Ru-supported carrier obtained in the Ru-supporting step with an aqueous alkali solution and a reduction step of reducing the Ru-supported carrier with a water-soluble reducing agent. Is preferred.

In the tenth aspect, it is preferable that the alkali metal supporting step impregnates the carrier with an aqueous solution containing an alkali metal nitrate or carbonate.
The alkali metal is preferably at least one selected from Na, K, Rb, and Cs.

The present invention provides, in claim 12, an ammonia decomposition catalyst prepared by any of the above-described methods for preparing an ammonia decomposition catalyst (hereinafter, referred to as “the present preparation method”).

[0017] In the present invention, the ammonia-containing gas and the ammonia decomposition catalyst according to the first or twelfth aspect of the present invention may be used in a pressure range of 0.1 MPa to 1.0 MPa and a temperature of 500 ° C to 700 ° C. The present invention provides a method for decomposing ammonia, comprising a catalytic decomposition step of contacting within the range of

[0018]

Embodiments of the present invention will be described below in detail. In the present catalyst, basically, Ru and an alkali metal are supported on a carrier, and the content of halogen such as chlorine is set to 100 ppm by weight or less of the weight of the catalyst. It is known that Ru alone catalytically decomposes ammonia, but when an alkali metal is allowed to coexist with the Ru catalyst, and when the content of halogen mixed in the process of catalyst preparation is 100 ppm by weight or less of the catalyst weight, It was found that the ammonia decomposition activity of the catalyst was remarkably improved, and a practical catalyst capable of efficiently decomposing ammonia at a low pressure of about atmospheric pressure, particularly at a relatively low temperature of 700 ° C. or less, for example, 500 ° C., was obtained.

In the present catalyst, the Ru content is in the range of 0.1% by weight to 5% by weight of the catalyst weight. If the amount is less than 0.1% by weight, practical catalytic activity cannot be obtained. If the amount exceeds 5% by weight, the decomposition rate of ammonia increases, but the disadvantage of using a large amount of expensive Ru increases in practice. Loses sex. In this respect, the Ru content is more preferably in the range of 0.3% to 3% by weight.

The alkali metal contained in the catalyst has the effect of improving the activity of Ru for decomposing ammonia. Examples of the alkali metal include, for example, Na, K, Rb, Cs or a mixture of two or more thereof.

The content of the alkali metal is 1 to the weight of the catalyst.
It is preferable to be within the range of 30% by weight to 30% by weight. When two or more kinds of alkali metals are used, the total content may be within the above range. When the content of the alkali metal is less than 1% by weight, the effect of improving the catalyst activity is difficult to appear, and when the content exceeds 30% by weight, there is a limit in the support capacity of the carrier, and it does not contribute to the improvement of the ammonia decomposition activity. Absent. From this viewpoint, the content of the alkali metal is more preferably in the range of 3% by weight to 25% by weight.

In the present catalyst, it is important that the halogen content is suppressed to 100 ppm by weight or less of the weight of the catalyst. Halogen such as chlorine inhibits the ammonia decomposition reaction of the catalyst and shortens the catalyst life. By suppressing the halogen content to 100 ppm by weight or less, the present catalyst becomes a practical catalyst having a high space velocity and a high decomposition rate of an ammonia decomposition reaction at a low pressure and a low temperature and a long catalyst life.

As the carrier in the present catalyst, those commonly used as carriers for gas phase reaction catalysts can be appropriately used. Examples thereof include alumina, silica, silica-alumina, activated carbon, titania, and magnesia. Depending on the choice of the support, the initial activity of the obtained catalyst may decrease, and in this respect, a particularly suitable support is alumina.

Next, one embodiment of the method for preparing the present catalyst (the present preparing method) according to claim 5 will be described below. In the following embodiment, the halogen removing step includes a fixing step of fixing Ru to the carrier and making the halogen water-soluble, and a washing step of removing the water-solubilized halogen by washing with water.

(Preparation method A) This preparation method A corresponds to claim 6, wherein the immobilization step comprises a reduction step. A-: Ru supporting step . An aqueous solution of water-soluble ruthenium chloride (RuCl ₃ .3H ₂ O) is prepared as a Ru source, and this is impregnated into sized activated alumina as a support to obtain a wet Ru-supported support. A-: Halogen removal step . This step includes the following two steps. A--1: Reduction step . The Ru-support is reduced by adding NaBH ₄ which is a water-soluble reducing agent. This reduces ruthenium chloride, which is soluble in water,
Is fixed to the carrier as a water-insoluble metal or a partial oxide or hydroxide, and chlorine is transferred to the aqueous phase as a water-soluble compound or chloride ion. A--2: Cleaning step . The Ru-immobilized carrier obtained in the previous step is sufficiently washed with water until substantially no trace of chloride ions is observed in the carrier. It is preferable to use warm water for washing. By this washing step, the chlorine content of the present catalyst is reduced to 100 ppm by weight or less of the catalyst weight. A-: Alkali metal supporting step . The alkali metal salt of cesium nitrate (CsN
Impregnated with an aqueous solution of O ₃ ) and dried. As a result, Ru and the alkali metal are supported on the carrier, and a "catalyst precursor A" containing no chlorine is obtained.

The catalyst precursor A is, for example, 100 ° C. to 6 ° C.
H at a temperature of 00 ° C_Two, NH_Three, N_TwoReducing heat gas such as O
When the catalyst A is brought into contact with the catalyst, the activated present catalyst A is obtained.
This activation treatment is performed, for example, in a reactor filled with precursor A.
At a pressure of 0.1 MPa to 1.0 MPa and a temperature of 5
In the range of 00 ° C to 700 ° C, ammonia for decomposition
It can also be carried out by flowing Agus.
Therefore, the special activity of the catalyst precursor A due to the reducing hot gas
Is not always necessary, the catalyst precursor A
Even when used for ammonia decomposition, it is converted to this catalyst A on the spot.
And high NH _ThreeDecompose ammonia efficiently with decomposition rate
Thus, a mixed gas of hydrogen and nitrogen can be obtained. Follow
Therefore, in the present specification, substantially no halogen is contained.
The catalyst precursor is also included in the “present catalyst”.

(Preparation method B) This preparation method B corresponds to claim 8, and the immobilization step comprises a neutralization step. B-: Ru supporting step . The description is omitted because it is the same as A-. B-: halogen removal step . This step includes the following two steps. B--1: Neutralization step . Ru obtained in the Ru loading step
The carrier is neutralized by immersion in an aqueous alkaline solution (for example, aqueous ammonia). Thereby, ruthenium chloride supported on the carrier is decomposed into ruthenium oxide (aqueous) insoluble in water and chloride ions, and Ru is fixed on the carrier,
Chlorine remains in the aqueous phase as ions. B--2: Washing step . The description is omitted because it is the same as A--2. B-: alkali metal supporting step . The description is omitted because it is the same as A-. This allows Ru and the alkali metal to be supported on the carrier, and does not contain chlorine.
Is obtained.

If the catalyst precursor B is treated in the same manner as the catalyst precursor A, the activated catalyst B is obtained. Therefore, if the catalyst precursor B is used as it is for ammonia decomposition, it can be converted into the present catalyst B in situ to efficiently decompose ammonia at a high NH ₃ decomposition rate and obtain a mixed gas of hydrogen and nitrogen. it can.

In the above preparation method B, the halogen removal step
The operation is simple because no water-soluble reducing agent such as aBH ₄ is used. The alkali used in the neutralization step is not limited to ammonia water, and any alkali aqueous solution such as sodium hydroxide, potassium hydroxide, and calcium hydroxide can be used.

(Preparation method C) This preparation method C corresponds to claim 9, and the immobilization step comprises a neutralization step and a reduction step. C-: Ru supporting step . The description is omitted because it is the same as A-. C-: halogen removal step . This step includes the following three steps. C-1: neutralization step . Ru obtained in the Ru loading step
The carrier is neutralized by immersion in an aqueous alkaline solution (for example, aqueous ammonia). Thereby, ruthenium chloride supported on the carrier is decomposed into ruthenium oxide (aqueous) insoluble in water and chloride ions, and Ru is fixed on the carrier,
Chlorine remains in the aqueous phase as ions. C--2: reduction step . Next, NaBH ₄ which is a water-soluble reducing agent is added to the Ru-immobilized carrier for reduction. As a result, the (aqueous) ruthenium oxide is reduced and insolubilized on the carrier as a water-insoluble metallic Ru. C--3: washing step . The description is omitted because it is the same as A--2. C-: an alkali metal supporting step . The description is omitted because it is the same as A-. As a result, Ru and the alkali metal are supported on the carrier, and the “catalyst precursor C” containing no chlorine is used.
Is obtained.

If the catalyst precursor C is treated in the same manner as the catalyst precursor A, the activated catalyst C is obtained. Therefore, if the catalyst precursor C is used as it is for ammonia decomposition as in the case of the catalyst precursors A and B, the catalyst precursor C is converted into the present catalyst C in situ and efficiently decomposes ammonia at a high NH ₃ decomposition rate, Mixed gas of nitrogen and nitrogen can be obtained.

The above preparation method C comprises a halogen removal step,
First, Ru is fixed to the carrier by neutralization, and then insolubilized by reduction.
Not only is economically advantageous due to reduced flow-out of the catalyst, but also has the advantage of increasing the retention of Ru in the catalyst and thus improving the catalytic activity.

Next, each step of the present preparation method will be described in detail. This preparation method employs an aqueous impregnation method as a method for supporting Ru and an alkali metal on a carrier.
Ru can be supported on a carrier as an aqueous solution of a water-soluble compound by an impregnation method. As the water-soluble ruthenium compound, for example, a ruthenium complex such as water-soluble ruthenium oxide, ruthenium nitrate, or ruthenium carbonyl, which does not contain a catalyst poison, can also be used. However, it is economically advantageous to use ruthenium (III) chloride, which is readily available in the process of converting a Ru ingot to a water-soluble mixture. For this purpose, chlorine derived from the Ru raw material must be removed during the preparation of the present catalyst. The present inventors have found a method for preparing the present catalyst which does not substantially reduce the catalytic activity even when ruthenium chloride is used, thereby achieving the present invention.

Ru Supporting Step : This step is used in any of the above-mentioned Preparation Methods A, B and C, in which Ru is impregnated on a carrier (such as activated alumina) as a water-soluble aqueous ruthenium chloride solution to be supported. It is a process. The concentration of the aqueous ruthenium chloride aqueous solution used for the impregnation is not particularly limited. For example, ruthenium chloride (RuCl _3.
It is preferable to use an aqueous solution in which 3H ₂ O) is dissolved in a range of 0.1 weight / vol% to 5 weight / vol%. The amount of the carrier to be used is 30 weight / vol% with respect to the ruthenium chloride aqueous solution.
It is preferable to set it to ６０60 weight / volume%. The impregnation method is not particularly limited, but it is preferable that the carrier is dried after immersion or spray impregnation so that the carrier is uniformly impregnated with the ruthenium chloride aqueous solution.

Halogen removing step : This step is performed between the Ru supporting step and the alkali metal supporting step. This halogen removal step comprises an immobilization step and a washing step. This immobilization step comprises a reduction step in the preparation method A, a neutralization step in the preparation method B, and a preparation method C Consists of two steps, a neutralization step and a reduction step. Here, the halogen removing step will be described in detail according to the preparation method C including the two-step immobilizing step.

[0036]Neutralization processIn the Ru supporting step,
The carrier supporting the water-soluble ruthenium chloride is converted to an alkali
It is poured into an aqueous solution, and ruthenium chloride is converted to Ru (O
H) _ThreeConverted to ruthenium (water) oxide and fixed
You. The alkali used for immobilization is ammonia water,
Of sodium, potassium hydroxide or calcium hydroxide
Ru, which is hardly soluble in ruthenium chloride aqueous solution such as aqueous solution
If any (hydr) oxide can be precipitated,
May be. At this time, chlorine contained in ruthenium chloride
Elutes into the aqueous phase as an alkali counterion.

This neutralization step is for preventing expensive Ru from flowing into the aqueous phase in a subsequent washing step or the like. Therefore, it is preferable that the addition amount of the alkaline aqueous solution be stoichiometrically excessive relative to the concentration of chlorine present in the carrier. This ensures that Ru is fixed as (hydr) oxide in the carrier, and chlorine is transferred to the aqueous phase as chloride ions.

The reduction step; but supported ruthenium chloride on a carrier is of course water soluble in Ru loading step, a carrier in the form of (water) ruthenium oxide, such as Ru (OH) ₃ in the neutralization step These Ru compounds are still slightly soluble in water even when fixed to
It may be lost as u ions. Therefore, in order to maintain the Ru loading rate in the carrier and improve the catalyst efficiency,
Preferably, an insolubilization treatment is performed. This insolubilization can be performed by reduction. For the reduction, a water-soluble reducing agent,
For example, NaBH ₄ , KBH ₄ , or LiAlH ₄ is preferably used. By this reduction, soluble (aqueous) ruthenium oxide is converted to hardly soluble ruthenium oxide (Ru ₂ O ₃ ) or metallic Ru while being supported on a carrier.

Washing step : After the above-mentioned fixing step, R
The water-soluble chlorine attached to the u-support is removed by washing with water. This water washing may be performed continuously in running water, or may be performed batchwise several times. It is preferable to use warm water in order to reliably perform dechlorination. Washing is completed when chlorine ions are substantially no longer detected in the washing wastewater.

In the halogen removing step, neutralization and reduction performed prior to the washing step are important as steps for insolubilizing Ru to prevent loss and for reliably removing chlorine as a water-soluble ionic form from the carrier. . As in the preparation method A or B, only one of the neutralization step and the reduction step may be employed. However, unless particularly difficult, it is preferable to employ both steps sequentially. In this case, the reduction step can precede the neutralization step, but from the viewpoint of preventing Ru loss, the neutralization step and the reduction step are more preferably performed as in Preparation Method C.

Alkali metal supporting step : This step is necessary in any of the preparation methods A, B and C.
In this step, in order to support the alkali metal, the Ru-supported carrier is impregnated with an aqueous solution of an alkali metal salt.
The alkali metal salt that can be used here may be any as long as it contains no halogen, is water-soluble, and can release the alkali metal in a reducing hot gas. In this respect, preferred alkali metal salts are water-soluble nitrates or carbonates of at least one alkali metal selected from Na, K, Rb, and Cs. The impregnation amount of the alkali metal salt is adjusted so that the alkali metal is in the range of 1% by weight to 30% by weight of the catalyst weight.

The catalyst precursor obtained by each of the above preparation methods is preferably subjected to a reducing hot gas treatment for the purpose of activation. By this hot gas treatment step, when a ruthenium oxide compound such as (water) ruthenium oxide is present in the catalyst precursor, the ruthenium oxide compound is reduced to a metallic Ru, and an alkali metal salt is reduced to a metallic alkali metal. By imparting catalytic activity, the present catalyst having high ammonia decomposition efficiency can be obtained.

The reducing heat gas which can be used in this step
For example, H_Two, NH_Three, N _TwoO etc.
Can be. Generally H_TwoGas is preferred, but NH_ThreeAlso
The catalyst precursor is used for decomposition as it can be used
Contact with hot ammonia gas
In this case, the present catalyst can also be generated.

In this hot gas treatment step, the carrier supporting Ru and the alkali metal is placed in a stream of reducing gas in a stream of 400 g.
It is preferable that the temperature is kept at 1 to 600 ° C for 1 to 8 hours. In practice, it is preferable to gradually or stepwise raise the temperature from about 100 ° C. to about 600 ° C. in 3 to 6 hours. By this hot gas treatment step, the present catalyst having excellent ammonia decomposition efficiency and decomposition rate can be obtained.

Next, a method for decomposing ammonia using the present catalyst will be described. Ammonia decomposition method : The ammonia decomposition method of the present invention comprises:
Basically, an ammonia-containing gas is brought into contact with the present catalyst at an elevated temperature to generate 3 mol of hydrogen and 1 mol of nitrogen from 2 mol of ammonia as shown in the following formula. 2NH ₃ → 3H ₂ + N ₂

This ammonia decomposition reaction can be carried out using an ordinary gas-solid contact reactor using a corrosion-resistant material such as stainless steel. This reaction is an equilibrium reaction, a reaction that is endothermic and increases in volume. Therefore, by applying low pressure and high temperature conditions to the reaction system, the reaction can proceed in the decomposition direction.

When this catalyst is used, the pressure is 0.1 MPa
Ammonia can be efficiently decomposed in the range of 1.0 to 1.0 MPa and the temperature in the range of 500 ° C to 700 ° C.
Although the reaction proceeds even if the pressure is less than 0.1 MPa, it is not advantageous because a decompression facility is required.
Exceeding the range is not preferable because the equilibrium of the reaction is biased toward the ammonia generation side. If the temperature is less than 500 ° C., the decomposition rate is insufficient, and if it exceeds 700 ° C., an expensive heat-resistant apparatus is required, and the life of the catalyst is adversely affected.

Since the cracked gas obtained by the ammonia cracking method of the present invention contains hydrogen and nitrogen at a molar ratio of 3: 1, it is possible to use stainless steel, nickel, nickel
It can be used as a bright annealing finishing gas such as copper or a nickel-chromium alloy. This decomposition gas may contain a small amount of NH ₃ , H ₂ O, NO _x , CO _2, etc. as impurities. When these impurities become obstacles, they can be easily removed by adsorption with zeolite, activated carbon or the like in the recovery step following the catalytic cracking step.

[0049]

The present invention will be described in more detail with reference to the following examples.
I do. Example 1 This example corresponds to Preparation A
Thus, the immobilization step comprises a reduction step. Preparation of catalyst : A-Ru supporting step. Water-soluble chloride lute in about 80 ml of water
Numium (RuCl_Three・ 3H_Two O) Dissolve 1 g and add
Activated alumina 3 sized to a particle size of 0.5 mm to 1.0 mm
8 g was charged and left standing for about 1 hour to obtain a Ru-supported carrier. A--1 reduction step. On this Ru-supporting carrier,
Sodium chloride (NaBH_Four) Add 0.5g while stirring
And reduction was performed. This NaBH_FourOf Ru is used
2 molar times of A--2 washing step. Then add 100ml of water and heat
After filtration, the resultant was washed with warm water three times or more to perform dechlorination. A-Alkali metal loading step. Approximately 80 ml of water
The above dechlorinated carrier was added to an aqueous solution in which 8.5 g of sodium was dissolved.
After charging, let stand for about 1 hour, dry on a warm bath,
Dry in a warm air dryer at 20 ° C for 12 hours and remove chlorine
Catalyst precursor A was obtained. A-Activation step. To evaluate the performance as a catalyst
Then, an activation treatment was performed using hydrogen gas. The catalyst described above
Precursor A was heated in a stream of hydrogen at 100 ° C. for 1 hour,
Step by step to 600 ° C and heat at 600 ° C for 3 hours
Then, hydrogen treatment was performed to obtain the present catalyst A of Example 1. this
The residual chlorine in the catalyst was 46 ppm by weight.

Ammonia decomposition test : 2.2 ml of the catalyst of Example 1 was charged into a stainless steel reaction tube having an inner diameter of 7.5 mm, and liquid ammonia was vaporized at a reaction pressure of 0.1 MPa and a reaction temperature of 500 ° C. Ammonia gas from 36 ml / min to 360 ml / min (space velocity 1000 H ^-1
Was circulated by equivalent) to ~10000H ^-1, the residual ammonia gas concentration in the outlet gas of the reaction tube (volume%) TCD-GC
Was measured by The results were obtained using the catalyst preparation conditions, reaction pressure,
N obtained from temperature, space velocity, and residual ammonia gas concentration
Table 1 shows the H ₃ decomposition rate (%) and the H ₂ concentration (% by volume) in the decomposition gas.

Example 2 This example illustrates the preparation method B
The immobilization step comprises a neutralization step. Preparation of catalyst : B-Ru supporting step. In the same manner as A- of Example 1,
A Ru-supported carrier was obtained. B-1 Neutralization step. This Ru-supported carrier is 0.2
Volume of ammonia water, decant and drain the aqueous phase,
This operation is repeated three times to fix Ru on the carrier and
Most of the chlorine was removed as ions. B--2 washing step. Next, the same as A--2 in Example 1
Washing and dechlorination were performed in the same manner. B-Alkali metal loading step. Same as A- in Example 1.
Thus, a chlorine-free catalyst precursor B was obtained. B-activation step. To evaluate the performance as a catalyst
Then, hydrogen treatment was performed in the same manner as in Example 1 A-.
Thus, the present catalyst B was obtained. The residual chlorine of this catalyst is 60 weight p
pm.Ammonia decomposition test : Evaluation test in the same manner as in Example 1.
Was done. Table 1 shows the results.

(Example 3) Preparation of catalyst : In this example, the amount of cesium nitrate used in the alkali metal supporting step of Example 2 (8.5 g) was 4.25 g, and the Cs content in the catalyst was 10% by weight. % To 5
The same treatment as in Example 2 was carried out except that the content was changed to% by weight.
The present catalyst B of Example 3 was obtained. The residual chlorine of this catalyst is 60
It was ppm by weight. Ammonia decomposition test : An evaluation test was performed in the same manner as in Example 1. The results are shown in FIG.

Example 4 This example corresponds to the preparation method C, and the immobilization step consists of a neutralization step and a reduction step. Preparation of catalyst : C-Ru loading step. A Ru-supported carrier was obtained in the same manner as in A- of Example 1. C-1 neutralization step. 1% by weight of the Ru-supported carrier
, And the aqueous phase was discharged by decantation to fix Ru on the carrier and remove most of the chlorine as ions. C-2 reduction step. Sodium borohydride (NaBH ₄ ) (0.5 g) was added to the Ru-immobilized carrier with stirring to effect reduction. The amount of NaBH ₄ used is Ru
2 molar times of C--3 washing step. Next, washing and dechlorination were performed in the same manner as in A--2 of Example 1. C-Alkali metal loading step. In the same manner as in Example 3, the above-mentioned dechlorinated carrier was put into an aqueous solution in which 4.25 g of cesium nitrate was dissolved in about 80 ml of water, allowed to stand for about 1 hour, dried on a warm bath, and further heated at 120 ° C. with hot air. After drying in a dryer for 12 hours, a chlorine-free catalyst precursor C was obtained. C-activation step. In order to evaluate the performance as a catalyst, hydrogen treatment was carried out in the same manner as A- of Example 1 to obtain the present catalyst C of Example 4. The residual chlorine of this catalyst is 40 weight p
pm. Ammonia decomposition test : An evaluation test was performed in the same manner as in Example 1. The results are shown in FIG.

[0054]

[Table 1]

(Comparative Example 1) A catalyst of Comparative Example 1 was prepared in the same manner as in Example 1 except that the alkali metal supporting step of Example 1 was omitted and the Cs content in the catalyst was reduced to zero. I got The residual chlorine of this catalyst was 50 ppm by weight. An evaluation test was performed on this catalyst in the same manner as in Example 1. Table 2 shows the results.

(Comparative Example 2) This comparative example is a case in which halogen removal is performed by a reducing hot gas treatment without using cleaning. Preparation of catalyst : R-Ru supporting step. A Ru-supported carrier was obtained in the same manner as in A- of Example 1. R-Alkali metal loading step. After dissolving 8.5 g of cesium nitrate in about 80 ml of water, impregnating the impregnated with the above-mentioned Ru-supported carrier, filtering, drying on a warm bath, and further in a hot air drier at 120 ° C. for 12 hours After drying, a Ru / alkali metal-carrying support was obtained. R-halogen removal step. This Ru / alkali metal-supported carrier was heated in a hydrogen stream at 100 ° C. for 1 hour, then gradually heated to 600 ° C., and heated at 600 ° C. for 3 hours to perform a reducing hot gas treatment. Was obtained. The residual chlorine of this catalyst was 4,800 ppm by weight. Ammonia decomposition test : An evaluation test was performed in the same manner as in Example 1. Table 2 shows the results.

Comparative Example 3 This comparative example is an example using a commercially available ammonia decomposition catalyst. Preparation of catalyst : A pellet of a commercially available catalyst (N-135, manufactured by JGC Chemicals Co., Ltd.) in which Ni (about 15% by weight) was supported on a carrier Al ₂ O ₃ was crushed and sized to 0.5 mm to 1.0 mmφ. 2.2 ml of the mixture was filled into a stainless steel reaction tube having an inner diameter of 7.5 mm, and heated at 100 ° C. for 1 hour in a hydrogen stream, and then gradually heated to 600 ° C. and heated at 600 ° C. for 3 hours. Hydrogenation was performed to obtain a catalyst of Comparative Example 3. Ammonia decomposition test : An evaluation test was performed in the same manner as in Example 1. Table 2 shows the results.

[0058]

[Table 2]

[0059] From the results in Table 1, the catalyst according to Preparation A of Example 1 (reduction fixation), low decomposition temperature of 500 ° C., at a high space velocity that 5000H ^-1 ~8000H ^-1, 99.7% base And a high ammonia decomposition rate was obtained, indicating that the catalyst was an excellent ammonia decomposition catalyst.

The catalyst obtained by the preparation method B (neutralization fixing method) of Example 2 also obtained a high ammonia decomposition rate on the order of 99.7% under the same decomposition conditions as in Example 1, and was an excellent ammonia decomposition catalyst. It can be seen that it is.

The catalyst of Example 3 was prepared in the same manner as in Example 2 except that the content of Cs was reduced to half.
This catalyst has an ammonia decomposition rate of 99% even at a space velocity of 5000 H ^-1 irrespective of the small amount of Cs used.
It is a catalyst that can be used practically enough.

The catalyst according to the preparation method C (neutralization reduction fixation method) of Example 4 has the same Ru content (1% by weight) and Cs content (5% by weight) as in Example 3, but in the halogen removal step. Both neutralization and reduction are performed, whereby the ammonia decomposition rate is improved from that of Example 3 particularly at a space velocity of 5000 H ⁻¹ , and the residual ammonia concentration is also reduced,
It can be seen that the catalyst is extremely efficient regardless of the amount of Cs used.

On the other hand, the catalyst of Comparative Example 1 shown in Table 2 was Ru
The content (1% by weight) and the halogen removal step were the same as in Example 1, but the ammonia decomposition rate was 9 at a low space velocity of 2000 H ^-1 because no alkali metal was supported.
It is as low as 3%, and finally reaches 99% at a lower space velocity of 1000H ^-1 . From this result, it is understood that the alkali metal enhances the ammonia decomposition efficiency of the catalyst.

Comparative Example 2 shows that Ru content (1% by weight) and Cs
The content (10% by weight) is the same as in Example 1, but the halogen removing step is performed not by washing but by reducing hot gas treatment. Therefore, the residual chlorine concentration in the catalyst was 4800.
As high as ppm by weight, the ammonia decomposition efficiency is low.

Comparative Example 3 is an example of a commercially available Ni-based catalyst and does not contain Ru. The ammonia decomposition rate of this catalyst was 7 at a decomposition temperature of 500 ° C. and a space velocity of 2000 H ⁻¹ .
It is in the range of 5%, and even if the decomposition temperature is raised to 550 ° C, 9
In the range of 3%, it is clear that the catalyst of the present invention obtains a higher ammonia decomposition rate under the condition of lower temperature and higher space velocity.

[0066]

According to the ammonia decomposition catalyst of the present invention, Ru and an alkali metal are supported on a carrier and the halogen content is 100 ppm by weight or less of the weight of the catalyst. When used, ammonia can be decomposed at a relatively low pressure and low temperature with a high space velocity and a high decomposition rate.

The process for preparing the ammonia decomposition catalyst of the present invention is characterized in that the carrier is impregnated with a water-soluble ruthenium halide.
u supporting step, a halogen removing step of removing the halogen by washing with water, and an alkali metal supporting step of supporting the alkali metal on the carrier are sequentially included. The halogen content can be less than 100 ppm by weight.

Since the halogen removing step includes a fixing step for fixing Ru to the carrier and a washing step for washing the Ru fixed carrier with water, the flow-out of Ru is prevented, and the efficient ammonia decomposition catalyst is prevented. Is obtained.

In the method for decomposing ammonia according to the present invention, the ammonia-containing gas and the above-mentioned ammonia decomposing catalyst are mixed at a pressure of 0.1 MPa to 1.0 MPa and a temperature of 500 ° C.
Since it includes a catalytic cracking step of contacting at a temperature of 700 ° C., an ammonia cracking gas composed of hydrogen and nitrogen can be easily obtained without requiring a special high-temperature and high-pressure reactor.

Claims (13)

[Claims] 1. Ru (ruthenium) and an alkali metal are supported on a carrier, and the halogen content is 100 parts by weight of the catalyst.
Ammonia decomposition catalyst of not more than ppm by weight. 2. The method according to claim 1, wherein the alkali metal is Na, K, R
The ammonia decomposition catalyst according to claim 1, wherein the catalyst is at least one selected from b and Cs. 3. The content of Ru is from 0.1% by weight to the weight of the catalyst.
The ammonia cracking catalyst according to claim 1, wherein the amount is in the range of 5% by weight and the content of the alkali metal is in the range of 1% to 30% by weight of the catalyst weight. 4. The process for preparing the ammonia decomposition catalyst according to claim 1, wherein the carrier is impregnated with a water-soluble ruthenium halide, and the carrier is adjusted so that the halogen content is not more than 100 ppm by weight of the catalyst. A method for preparing an ammonia decomposition catalyst, comprising: a halogen removing step of removing halogen from water by washing with water; and an alkali metal supporting step of supporting an alkali metal on a carrier. 5. The immobilizing step in which, in the halogen removing step, a carrier is impregnated with a water-soluble ruthenium halide in the Ru supporting step, and then the Ru is immobilized on the carrier and the halogen is solubilized. R obtained by
5. The method for preparing an ammonia decomposition catalyst according to claim 4, comprising a step of washing the u-fixed carrier with water to remove halogen. 6. The method for preparing an ammonia decomposition catalyst according to claim 5, wherein the immobilization step includes a reduction step of reducing the Ru-supported carrier obtained in the Ru-supporting step with a water-soluble reducing agent. 7. The water-soluble reducing agent is NaBH ₄ , K
At least one selected from BH ₄ and LiAlH ₄
The method for preparing an ammonia decomposition catalyst according to claim 6, which is a seed. 8. The method for preparing an ammonia decomposition catalyst according to claim 5, wherein the immobilizing step includes a neutralizing step of neutralizing the Ru-supported carrier obtained in the Ru-supporting step with an aqueous alkali solution. 9. The method according to claim 5, wherein the immobilizing step includes a neutralizing step of neutralizing the Ru-supported carrier obtained in the Ru-supporting step with an aqueous alkali solution and a reducing step of reducing the Ru-supported carrier with a water-soluble reducing agent. Method for preparing an ammonia decomposition catalyst. 10. The method for preparing an ammonia decomposition catalyst according to claim 4, wherein the alkali metal supporting step impregnates the carrier with an aqueous solution containing a nitrate or carbonate of an alkali metal. 11. The method according to claim 11, wherein the alkali metal is Na, K, R
The method for preparing an ammonia decomposition catalyst according to claim 10, wherein the catalyst is at least one selected from b and Cs. 12. An ammonia decomposition catalyst prepared by the method for preparing an ammonia decomposition catalyst according to any one of claims 4 to 11. 13. An ammonia-containing gas and the ammonia cracking catalyst according to claim 1 or 12 at a pressure of 0.1 MPa to 1.0 MPa and a temperature of 500 ° C.
An ammonia decomposition method including a catalytic decomposition step of contacting at a temperature of 700 ° C.