JP2011224555A - Catalyst for decomposing ammonia and method for producing the catalyst, and method for producing hydrogen using the catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst which contains as an active component a non-noble metal having high practicality in terms of cost, and which has high activity.SOLUTION: The catalyst for decomposing ammonia contains nickel and additives being a metal oxide and/or a compound oxide of at least one metal element selected from the group comprising the metal elements of groups 2-5 and groups 12-15 of the long-form periodic table. The ratio (S2/S1) of the calculated specific surface area (S2) of nickel to the specific surface area (S1) of the catalyst is 0.50-0.85.

Description

  The present invention relates to an ammonia decomposition catalyst, a method for producing the same, and a method for producing hydrogen using the catalyst.

  Hydrogen production technology by ammonia decomposition has been proposed for a long time, but it is rarely put into practical use. For example, a technique for decomposing ammonia generated from a coke oven to obtain hydrogen has been proposed (Patent Document 1). The catalyst essentially requires a platinum group, and its high cost is a practical problem. On the other hand, non-noble metal catalysts have been proposed in order to overcome the problems of noble metal catalysts containing a platinum group as an essential component. As a non-noble metal catalyst, a catalyst using at least one metal or compound selected from a copper group element, a chromium group element and an iron group element and nickel as a catalyst component has been proposed (Patent Document 2). The catalyst is obtained by improving the catalyst performance by combining nickel, cobalt, copper, chromium, and other components, compared to a catalyst composed of nickel alone. A catalyst combining rare earth and nickel has also been proposed (Patent Document 3).

  These catalysts are prepared by impregnating a support having a high specific surface area with a solution of each catalyst component, and by using an oxide surface having a high specific surface area, the catalyst component is dispersed and supported on the surface. The active point is physically increased to improve the activity of the catalyst as a whole.

JP 05-329372 A Japanese Patent Laid-Open No. 02-198638 Japanese Patent Laid-Open No. 02-198639

  In a catalyst system in which the number of catalytic active points is increased by using a support having a high specific surface area, the catalytic active point is reduced and the catalytic activity is reduced as the specific surface area of the support material is reduced due to thermal deterioration. It becomes. Further, even if a large amount of the catalyst component is impregnated and supported on the carrier component in order to increase the catalyst active point, the particles composed of the catalyst component are likely to aggregate, and as a result, the catalyst active specific surface area does not increase. Therefore, even if the content of the catalyst component impregnated in the carrier component is increased, the activity improvement corresponding to the increase in the content cannot be obtained, and the catalyst activity is lowered due to the increase in content, and a catalyst having sufficient catalytic activity is produced. It was difficult to do. There is a need to develop a highly active catalyst that overcomes the problems found in such conventional catalysts and that is also practical in terms of cost.

  The catalyst for decomposing ammonia of the present invention that has solved the above problems is at least one metal oxide selected from the group consisting of nickel and metal elements of groups 2 to 5 and 12 to 15 of the long-period periodic table And / or an additive substance which is a composite oxide, and the ratio (S2 / S1) of the calculated specific surface area (S2) of nickel to the specific surface area (S1) of the catalyst is 0.50 to It is characterized by 0.85. The additive is preferably at least one metal oxide and / or composite oxide selected from the group consisting of alumina, silica, zirconia, alkaline earth metal oxides, and lanthanoid metal oxides. The catalyst preferably contains 55 to 95% by mass of nickel with respect to the total amount of the catalyst.

  The embodiment of the method for producing an ammonia decomposition catalyst according to the present invention comprises dissolving a water-soluble salt of nickel and a water-soluble salt of an additive substance precursor in water, and generating a precipitate of nickel and the additive substance precursor with an alkaline compound. Then, filtration, washing, drying, and heat treatment: an aqueous solution is prepared by adding a nickel salt to water, an alkaline compound is added to the aqueous solution to precipitate fine particles containing nickel, and a fine particle dispersion is prepared. The fine particle-dispersed sol solution of the additive substance is added while stirring the dispersion to produce a precipitate composed of nickel-containing fine particles and additive substance fine particles, and then the precipitate is filtered, washed, dried, and heat-treated. Embodiments are preferred. The present invention also includes a hydrogen production method in which ammonia is decomposed to obtain hydrogen using the ammonia decomposition catalyst.

  In the ammonia decomposition catalyst of the present invention, even when the content of nickel as an active component is increased, the calculated specific surface area (S2) of nickel is 0.50 to the specific surface area (S1) of the catalyst. 0.85 (S2 / S1) and the calculated specific surface area (S2) of nickel can be kept high. Therefore, without using a noble metal catalyst that has practical problems in terms of cost, it exhibits high activity for the ammonia decomposition reaction and can efficiently decompose ammonia into hydrogen and nitrogen.

  The catalyst according to the present invention is a catalyst used for producing hydrogen by decomposing ammonia. The catalyst contains nickel and an additive substance that is at least one metal oxide and / or composite oxide selected from the group consisting of metal elements of groups 2 to 5 and 12 to 15 of the long-period periodic table.

  The nickel state may be any of a metal, an oxide, and a mixture thereof, and is preferably a metal state. The content of nickel in the catalyst is preferably 55 to 95 mass%, more preferably 60 to 90 mass% with respect to the total mass (total 100 mass%) of nickel (metal conversion) and additive substances (oxide conversion). %, More preferably 67 to 85% by mass. If the nickel content is less than 55% by mass, sufficient ammonia decomposition activity may not be obtained. If the nickel content exceeds 95% by mass, the amount of nickel is insufficient with respect to the amount of nickel, and the agglomeration of nickel proceeds and heat resistance decreases There is a fear.

  The additive substance is at least one metal oxide and / or composite oxide selected from the group consisting of long-period periodic table 2-5 and group 12-15 metal elements, preferably alumina, silica, It is at least one metal oxide and / or composite oxide selected from the group consisting of zirconia, alkaline earth metal oxides, and lanthanoid metal oxides. The complex oxide is not a simple physical mixture of individual metal oxides, but each constituent metal element is complexed at the atomic level as exemplified by ceria / zirconia solid solution, silica / alumina, etc. It refers to a material that exhibits different characteristics in terms of structure and physical properties compared to a simple physical mixture of materials.

  In the ammonia decomposition catalyst of the present invention, the ratio (S2 / S1) of the calculated specific surface area (S2) of nickel to the specific surface area (S1) of the catalyst is 0.50 or more, preferably 0.55 or more, more preferably 0. .60 or more, 0.85 or less, preferably 0.80 or less, more preferably 0.75 or less. When the ratio (S2 / S1) is less than 0.50, the calculated specific surface area of nickel in the catalyst is small and sufficient activity may not be obtained, and when it exceeds 0.85, the heat resistance decreases and the durability decreases. There is a case.

  The calculated specific surface area (S2) of nickel is calculated by subtracting the specific surface integral derived from the additive substance from the specific surface area of the catalyst. The powder consisting only of the additive substance is prepared in the same manner as the catalyst preparation procedure from the additive substance precursor. The specific surface area (S (b)) is measured by the BET method using nitrogen gas for the obtained powder consisting only of the additive substance. Calculated specific surface area (S2) of the nickel by subtracting the specific surface integral (S (b) × mass content of the additive substance in the catalyst) derived from the additive substance contained in the catalyst from the specific surface area (S1) of the catalyst Can be obtained.

In the ammonia decomposition catalyst of the present invention, the calculated specific surface area (S2) of nickel is preferably 20 m ² / g or more, more preferably 25 m ² / g or more, and further preferably 30 m ² / g or more. . When the calculated specific surface area of nickel is 20 m ² / g or more, the catalytic activity of the ammonia decomposition catalyst is further improved. The calculated specific surface area (S2) of nickel is preferably as large as possible. However, there is a limit to the value that can be increased by improving the catalyst preparation method and the like. In practice, it is preferably 250 m ² / g or less, more preferably 200 m ² / g or less. More preferably, it is 150 m ² / g or less.

The specific surface area of the ammonia decomposition catalyst of the present invention (S1) is preferably from 10 to 500 m ² / g, more preferably 20~450m ² / g, more preferably, 25~400m ² / g, more preferably, 30 -350 m < ² > / g. When the specific surface area (S1) of the catalyst is 10 m ² / g or more, the catalyst performance is further improved, and when it is 500 m ² / g or less, the strength of the catalyst is good. The specific surface area of the ammonia decomposition catalyst is measured by the BET method using nitrogen gas.

  The shape of the catalyst for decomposing ammonia according to the present invention may be various shapes such as powder, sphere, pellet, saddle type, cylindrical type, plate shape, honeycomb shape and the like.

  1 shows an example of a catalyst production method (coprecipitation method) according to the present invention. In addition, as long as there exists an effect of this invention, it is not limited to the following catalyst manufacturing methods. As a method for producing the catalyst of the present invention, for example, (1) an aqueous solution is prepared by adding a nickel salt to water, and an alkaline compound is added to the aqueous solution to precipitate nickel-containing fine particles (for example, nickel hydroxide fine particles). To prepare a fine particle dispersion. While stirring this fine particle dispersion, a fine particle-dispersed sol solution of the additive substance is added to generate a precipitate composed of nickel-containing fine particles (for example, nickel hydroxide fine particles) and additive substance fine particles. Thereafter, the precipitate is removed by filtration, washed with water, dried, and heat-treated (for example, heat-treated in a reducing atmosphere) to obtain a catalyst; (2) Water-soluble salt of additive precursor and water-soluble nickel After the salt is added to water and mixed well, an alkaline compound is added to form a precipitate of fine particles (eg, hydroxide fine particles) containing nickel and an additive precursor. Thereafter, the precipitate is taken out by filtration, filtered, washed with water, dried, and heat-treated (for example, heat-treated in a reducing atmosphere) to obtain a catalyst; (3) An alkaline aqueous solution to which an alkaline compound is added is prepared. A mixed aqueous solution containing a water-soluble salt of an additive precursor and a water-soluble salt of nickel is added to an agitated alkaline aqueous solution, and fine particles containing nickel (for example, nickel hydroxide fine particles) and fine particles of an additive precursor are added. A precipitate is formed. Thereafter, the precipitate is taken out by filtration, washed with water, dried, and heat-treated (for example, heat-treated in a reducing atmosphere) to obtain a catalyst.

  In the above manufacturing method, the heat treatment includes firing in an air atmosphere; heat treatment in an inert gas atmosphere such as nitrogen or argon; and reduction in a reducing gas atmosphere containing a reducing gas such as hydrogen. The catalyst is preferably subjected to a reduction treatment when used. As a reduction method, a normal method of contacting with a reducing gas such as hydrogen gas can be employed. When the reduction treatment using hydrogen gas is performed, the reduction is performed at 300 to 750 ° C., preferably 400 to 650 ° C., for 30 minutes to 2 hours. During hydrogen production, if the source gas contains oxygen gas, the ammonia combustion reaction proceeds along with the ammonia decomposition reaction. The catalyst temperature immediately rises due to the ammonia combustion reaction, and the catalyst is reduced by the hydrogen generated by the ammonia decomposition. The Therefore, when the source gas contains oxygen gas, the ammonia decomposition catalyst may be used without being subjected to reduction treatment before use.

  As the nickel raw material, any compound can be used as long as it finally produces metallic nickel by reduction treatment. Preferably, nickel nitrate hexahydrate and nickel acetate, which are water-soluble compounds, are used. Tetrahydrate, nickel chloride hexahydrate.

  As the additive material, any compound can be used as long as it finally generates a metal oxide and / or composite oxide by heat treatment, and various metal nitrates, preferably water-soluble compounds. , Acetates, chlorides, sulfates can be used.

  Examples of the alkaline compound include ammonia compounds such as ammonia, ammonium carbonate, and tetramethylammonium hydroxide; alkali metal hydroxides such as potassium hydroxide; and the like.

  The hydrogen production method using the catalyst for ammonia decomposition according to the present invention produces hydrogen by decomposing ammonia gas using the catalyst. The source gas is ammonia gas, but other gases can be added as long as they do not hinder the effects of the present invention, such as nitrogen, argon, helium, carbon monoxide, and oxygen. In particular, when the source gas contains oxygen, ammonia decomposition can be performed by an autothermal reformer that burns part of the ammonia gas or hydrogen produced by the ammonia decomposition reaction and uses the combustion heat as the reaction heat of the ammonia decomposition reaction. it can. In this case, the molar ratio of oxygen to ammonia (oxygen / ammonia) needs to be less than 0.75. Further, from the viewpoint of achieving both the amount of hydrogen obtained by ammonia decomposition and the combustion heat by the combustion reaction, the molar ratio (oxygen / ammonia) is preferably 0.05 or more, more preferably 0.1 or more, and even more preferably 0. .12 or more, preferably 0.5 or less, more preferably 0.3 or less.

The ammonia decomposition reaction has a reaction temperature of 300 to 900 ° C., preferably 400 to 700 ° C., and a reaction pressure of 0.002 to 2 MPa, preferably 0.004 to 1 MPa. The space velocity at the time of introduction of the reaction gas (source gas) is 1,000 to 500,000 hr ⁻¹ , preferably 1,000 to 200,000 hr ⁻¹ .

  Moreover, when using a catalyst, it can also pre-process in advance. By performing pretreatment under suitable treatment conditions, the state of the catalyst can be made close to that during the reaction, and by performing this pretreatment, operation in a steady reaction state can be performed from the beginning. As pretreatment, for example, nitrogen gas is allowed to flow through the catalyst for a certain period of time under reaction conditions.

  The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to the following examples, and may be appropriately modified and implemented within a range that can meet the purpose described above and below. All of which are within the scope of the present invention.

Production Example 1
34.9 g of nickel nitrate hexahydrate and 25.7 g of aluminum nitrate nonahydrate were dissolved in 500 mL of pure water to prepare a mixed aqueous solution of nickel nitrate and aluminum nitrate (aqueous solution A1). Separately, an aqueous solution B1 in which 42.7 g of ammonium carbonate was dissolved in 1.0 L of pure water was prepared. The aqueous solution A1 was dropped into the aqueous solution B1 that was vigorously stirred at room temperature to form a precipitate. Thereafter, the precipitate was collected by filtration, washed with water, and dried at 150 ° C. overnight. The dried precipitate was pulverized, filled into a tube furnace, and reduced at 650 ° C. for 1 hour using 10 vol% hydrogen gas (diluted with nitrogen) to obtain catalyst 1 composed of nickel and alumina. The obtained catalyst 1 had a nickel content of 67% by mass and an alumina content of 33% by mass.

Production Example 2
81.4 g of nickel nitrate hexahydrate and 23.4 g of aluminum nitrate nonahydrate were dissolved in 500 mL of pure water to prepare a mixed aqueous solution of nickel nitrate and aluminum nitrate (aqueous solution A2). Separately, an aqueous solution B2 in which 327 g of a 25 mass% tetramethylammonium hydroxide aqueous solution was dissolved in 1.5 L of pure water was prepared. The aqueous solution A2 was added dropwise to the aqueous solution B2 vigorously stirred at room temperature to generate a precipitate. Thereafter, the precipitate was collected by filtration, washed with water, and dried at 150 ° C. overnight. The dried precipitate was pulverized, filled into a tubular furnace, and reduced at 450 ° C. for 1 hour using 10 vol% hydrogen gas (diluted with nitrogen) to obtain catalyst 2 composed of nickel and alumina. The obtained catalyst 2 had a nickel content of 84 mass% and an alumina content of 16 mass%.

Production Example 3
34.9 g of nickel nitrate hexahydrate and 21.8 g of magnesium nitrate hexahydrate were dissolved in 500 mL of pure water to prepare a mixed aqueous solution of nickel nitrate and magnesium nitrate (aqueous solution A3). Separately, an aqueous solution B3 in which 57.6 g of potassium hydroxide was dissolved in 1.0 L of pure water was prepared. The aqueous solution A3 was dropped into the aqueous solution B3 that was vigorously stirred at room temperature to form a precipitate. The precipitate was filtered, washed thoroughly with water, and dried overnight at 150 ° C. The dried precipitate was further baked at 650 ° C. for 3 hours in a baking furnace. The fired solid was pulverized, filled into a tube furnace, and reduced at 650 ° C. for 1 hour using 10 vol% hydrogen gas (diluted with nitrogen) to obtain catalyst 3 composed of nickel and magnesia. The obtained catalyst 3 had a nickel content of 67% by mass and a magnesia content of 33% by mass.

Production Example 4
An aqueous solution in which γ-alumina (manufactured by Strem Chemicals Inc.) powder dried overnight at 150 ° C. is pulverized, and 24.8 g of nickel nitrate hexahydrate is dissolved in 50 mL of pure water in 20 g of the powder. And heated with stirring to evaporate the water to obtain a dried product. The obtained dried product was further dried at 150 ° C. overnight, then pulverized and filled into a tubular furnace, and reduced at 450 ° C. for 1 hour using 10% by volume hydrogen gas (diluted with nitrogen) to obtain nickel and γ-alumina. A catalyst 4 consisting of The resulting catalyst 4 had a nickel content of 20% by mass.

Production Example 5
23.3 g of nickel nitrate hexahydrate, 25.0 g of aluminum nitrate nonahydrate, and 7.6 g of lanthanum nitrate hexahydrate are dissolved in 500 mL of pure water, and nickel nitrate, aluminum nitrate, and nitric acid are dissolved. A mixed aqueous solution of lanthanum was prepared (aqueous solution A4). Separately, an aqueous solution B4 in which 39.6 g of ammonium carbonate was dissolved in 1.0 L of pure water was prepared. The aqueous solution A4 was dropped into the aqueous solution B4 that was vigorously stirred at room temperature to form a precipitate. Thereafter, the precipitate was collected by filtration, washed with water, and dried at 150 ° C. overnight. The dried precipitate was pulverized, filled into a tube furnace, and reduced at 650 ° C. for 1 hour using 10 vol% hydrogen gas (diluted with nitrogen) to obtain catalyst 5 composed of nickel, alumina, and lanthanum oxide. . The contents of nickel, alumina, and lanthanum oxide in the obtained catalyst 5 were 43% by mass, 31% by mass, and 26% by mass, respectively.

Production Example 6
105.0 g of aluminum nitrate nonahydrate was dissolved in 500 mL of pure water (aqueous solution A5). Separately, an aqueous solution B5 in which 80.6 g of ammonium carbonate was dissolved in 1.5 L of pure water was prepared. The aqueous solution A5 was dropped into the aqueous solution B5 that was vigorously stirred at room temperature to form a precipitate. Thereafter, the precipitate was collected by filtration, washed with water, and dried at 150 ° C. overnight. The dried precipitate was pulverized, filled into a tubular furnace, and reduced at 650 ° C. for 1 hour using 10 vol% hydrogen gas (diluted with nitrogen) to obtain powder 1 made of alumina.

Production Example 7
93.8 g of aluminum nitrate nonahydrate was dissolved in 500 mL of pure water (aqueous solution A6). Separately, an aqueous solution B6 in which 684 g of a 25 mass% tetramethylammonium hydroxide aqueous solution was dissolved in 1.5 L of pure water was prepared. The aqueous solution A6 was added dropwise to the aqueous solution B6 vigorously stirred at room temperature to generate a precipitate. Thereafter, the precipitate was collected by filtration, washed with water, and dried at 150 ° C. overnight. The dried precipitate was pulverized, filled into a tube furnace, and reduced at 450 ° C. for 1 hour using 10 vol% hydrogen gas (diluted with nitrogen) to obtain powder 2 made of alumina.

Production Example 8
102.6 g of magnesium nitrate hexahydrate was dissolved in 500 mL of pure water (aqueous solution A7). Separately, an aqueous solution B7 in which 112.2 g of potassium hydroxide was dissolved in 2 L of pure water was prepared. The aqueous solution A7 was added dropwise to the aqueous solution B7 that was vigorously stirred at room temperature to form a precipitate. The precipitate was filtered, washed thoroughly with water, and dried overnight at 150 ° C. The dried precipitate was further baked at 650 ° C. for 3 hours in a baking furnace. The fired solid was pulverized, filled into a tube furnace, and reduced at 650 ° C. for 1 hour using 10 vol% hydrogen gas (diluted with nitrogen) to obtain a powder 3 made of magnesia.

Production Example 9
After γ-alumina (manufactured by Strem Chemicals Inc.) used in Production Example 4 was pulverized, the powder was filled into a tube furnace and reduced at 450 ° C. for 1 hour using 10 vol% hydrogen gas (diluted with nitrogen). Thus, powder 4 made of γ-alumina was obtained.

Production Example 10
25.0 g of aluminum nitrate nonahydrate and 7.6 g of lanthanum nitrate hexahydrate were dissolved in 500 mL of pure water to prepare a mixed aqueous solution of aluminum nitrate and lanthanum nitrate (aqueous solution A8). Separately, an aqueous solution B8 in which 24.3 g of ammonium carbonate was dissolved in 1.0 L of pure water was prepared. The aqueous solution A8 was dropped into the aqueous solution B8 that was vigorously stirred at room temperature to form a precipitate. Thereafter, the precipitate was collected by filtration, washed with water, and dried at 150 ° C. overnight. The dried precipitate was pulverized, filled into a tube furnace, and reduced at 650 ° C. for 1 hour using 10 vol% hydrogen gas (diluted with nitrogen) to obtain a powder 5 made of alumina and lanthanum oxide.

Production Example 11
52.5 g of nickel nitrate hexahydrate, 3.1 g of lanthanum nitrate hexahydrate, and 14.19 g of Zircosol (registered trademark) ZN (manufactured by Daiichi Rare Element Chemical Co., Ltd., zirconium oxynitrate aqueous solution: oxidation) 25 wt% as zirconium) was dissolved in 720 mL of pure water to prepare a mixed aqueous solution of nickel nitrate, lanthanum nitrate, and zirconium oxynitrate (aqueous solution A9). Separately, an aqueous solution B9 in which 63.0 g of potassium carbonate was dissolved in 360 mL of pure water was prepared. The aqueous solution A9 was dropped into the aqueous solution B9 that was vigorously stirred at room temperature to form a precipitate. Thereafter, the precipitate was collected by filtration, washed with water, and dried at 110 ° C. The precipitate after drying was pulverized and calcined at 600 ° C. for 3 hours in a nitrogen atmosphere to obtain oxides of nickel, lanthanum and zirconia. Further, it was filled in a tubular furnace and reduced at 600 ° C. for 1 hour using 10 vol% hydrogen gas (diluted with nitrogen) to obtain a catalyst 6. The specific surface area (S1) of the catalyst 6 measured by the BET method using nitrogen gas was 84.5 m ² / g. The resulting catalyst 6 had a nickel content of 74% by mass.

In addition, in order to calculate the calculated specific surface area (S2) of nickel of the catalyst 6, a powder 6 made only of lanthanum zirconia as an additive substance was prepared. Specifically, first, 4.3 g of lanthanum nitrate hexahydrate and 19.7 g of zircozole ZN were dissolved in 240 mL of pure water to prepare a mixed aqueous solution of lanthanum nitrate and zirconium oxynitrate (aqueous solution a9). Separately, an aqueous solution b9 in which 21.5 g of potassium carbonate was dissolved in 120 mL of pure water was prepared. The aqueous solution a9 was dropped into the aqueous solution b9 that was vigorously stirred at room temperature to form a precipitate. Thereafter, the precipitate was collected by filtration, washed with water, and dried at 110 ° C. The precipitate after drying was pulverized and calcined at 600 ° C. for 3 hours in a nitrogen atmosphere to obtain an oxide of lanthanum and zirconia. Further, it was filled in a tubular furnace and reduced at 600 ° C. for 1 hour using 10 vol% hydrogen gas (diluted with nitrogen) to obtain a powder 6. The specific surface area of the powder 6 measured by the BET method using nitrogen gas was 108.8 m ² / g.

<Method for measuring specific surface area of catalyst>
The specific surface area of the catalyst was measured by the BET method using nitrogen gas.

<Calculation method of specific surface area of nickel>
The calculated specific surface area of nickel was calculated by subtracting the specific surface integral derived from the additive substance from the specific surface area of the catalyst. The specific surface area derived from the additive substance in the catalyst was determined as follows. Specifically, using only the additive precursor used in each production example, a powder consisting only of the additive substance was prepared in the same manner as the catalyst preparation procedure in the production example. The specific surface area (S (b)) was measured by the BET method using nitrogen gas for the obtained powder consisting only of the additive substance. The specific surface area derived from the additive substance in the catalyst was calculated from the following formula.
Specific surface area derived from additive substance in catalyst = (S (b) × mass content of additive substance in catalyst)

<Ammonia decomposition reaction>
Using a 10 mmφ SUS316 reaction tube, 0.8 mL of the catalyst 1 to 6 prepared in the production example was charged, and ammonia decomposition reaction was performed in the presence of water vapor. Under normal pressure, SV = 21,000 hr ⁻¹ , the reaction tube was heated in an electric furnace, and the ammonia decomposition rate at each electric furnace set temperature was measured. The ammonia decomposition reaction was carried out with the composition of the inlet gas supplied to the catalyst being 48.3% by volume of ammonia, 17.3% by volume of steam and the balance nitrogen.
The ammonia decomposition rate was calculated from the ammonia flow rate V1 and nitrogen flow rate V2 supplied to the inlet and the gas flow rate V3 after trapping water vapor and unreacted ammonia contained in the catalyst layer outlet gas by the following formula. In addition, as a pretreatment of the catalyst, 10% hydrogen diluted with nitrogen was reduced at 450 ° C. for 1 hour while flowing at 100 ml per minute, and then an ammonia decomposition reaction was carried out in the presence of water vapor. The reaction results are shown in Table 2.
Ammonia decomposition rate (%) = 100 × (V3−V2) × 0.5 / V1

  As can be seen from Table 2, even if the catalyst preparation is a coprecipitation method, the catalyst according to the present invention in which a large amount of nickel is present on the surface is not necessarily produced. Further, even if a catalyst having a large specific surface area is used, nickel is not necessarily dispersed widely over the catalyst surface. That is, it can be easily understood that even if S2 / S1 is slightly different, a significant difference is caused in the ammonia decomposition rate, and the element of S2 / S1 has a great influence on the catalyst.

<Ammonia decomposition reaction in the presence of oxygen>
Using a 10 mmφ SUS316 reaction tube, 0.8 mL of Catalysts 3 and 4 prepared in Production Examples 3 and 4 were charged, and ammonia decomposition reaction was performed in the presence of oxygen. Under normal pressure, SV = 36,000 hr ⁻¹ , the reaction tube was heated in an electric furnace, and the ammonia decomposition rate at an electric furnace set temperature of 350 ° C. was measured. The ammonia decomposition reaction was carried out with the composition of the inlet gas supplied to the catalyst being 29 volume% ammonia, 4.9 volume% oxygen, and the balance nitrogen.
The ammonia decomposition rate is determined by collecting the ammonia flow rate F1 supplied to the inlet, unreacted ammonia in the catalyst outlet gas with an aqueous boric acid solution for a certain period of time, and quantifying the ammonia concentration contained in the collected liquid with a cation chromatograph. The ammonia flow rate F2 in the outlet gas was determined by analysis and calculated by the following formula. In addition, as a pretreatment of the catalyst, 10% hydrogen diluted with nitrogen was reduced at 450 ° C. for 1 hour while flowing at 100 ml per minute, and then an ammonia decomposition reaction was carried out in the presence of water vapor. The reaction results are shown in Table 3.
Ammonia decomposition rate (%) = 100− {100 × (F2 / F1)}

  The present invention relates to the decomposition of ammonia, and hydrogen can be efficiently obtained from ammonia by using the present invention. The present invention can be widely applied to hydrogen production technology.

Claims (6)

A catalyst comprising nickel and an additive substance which is at least one metal oxide and / or composite oxide selected from the group consisting of metal elements of groups 2 to 5 and 12 to 15 of the long periodic table ,
A catalyst for ammonia decomposition, wherein the ratio (S2 / S1) of the calculated specific surface area (S2) of nickel and the specific surface area (S1) of the catalyst is 0.50 to 0.85.   The ammonia-decomposing material according to claim 1, wherein the additive substance is at least one metal oxide and / or composite oxide selected from the group consisting of alumina, silica, zirconia, alkaline earth metal oxides, and lanthanoid metal oxides. catalyst.   The catalyst for ammonia decomposition according to claim 1 or 2, wherein nickel is contained in an amount of 55 to 95 mass% with respect to the total amount of the catalyst. It is a manufacturing method of the catalyst for ammonia decomposition | disassembly of any one of Claims 1-3,
A water-soluble salt of nickel and a water-soluble salt of an additive precursor are dissolved in water, and a precipitate of nickel and the additive precursor is generated by an alkaline compound, followed by filtration, washing, drying, and heat treatment. A process for producing an ammonia decomposition catalyst. It is a manufacturing method of the catalyst for ammonia decomposition | disassembly of any one of Claims 1-3,
A nickel salt is added to water to prepare an aqueous solution, an alkaline compound is added to the aqueous solution to precipitate fine particles containing nickel to prepare a fine particle dispersion, and the fine particle dispersion sol of the additive substance is stirred while stirring the fine particle dispersion. A method for producing an ammonia decomposition catalyst, comprising: adding a solution to form a precipitate comprising nickel-containing fine particles and additive substance fine particles; and filtering, washing, drying, and heat-treating the precipitate.   A method for producing hydrogen, comprising decomposing ammonia by using the catalyst according to claim 1 to obtain hydrogen.