JP2012011373A - Catalyst for decomposing ammonia, method for producing the catalyst, and method for decomposing ammonia and method for producing hydrogen using the catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst which can efficiently decompose ammonia into hydrogen and nitrogen under the condition that high-concentrated steam exists in a gas, and uses nonnoble metals, highly practical in terms of cost, as active constituents.SOLUTION: The catalyst for decomposing ammonia which decomposes ammonia into hydrogen and nitrogen in the presence of steam comprises at least one element (component A) selected from the elements of groups 6-10 of the long-form periodic table, and an oxide and/or complex oxide of at least one element (component B) selected from the elements of groups 2-5 and groups 12-15 of the long-form periodic table.

Description

  The present invention relates to an ammonia decomposition catalyst, a method for producing the same, and an ammonia decomposition method using the catalyst in the presence of water vapor.

  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).

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

Many of the catalysts for ammonia decomposition that have been proposed heretofore relate to ammonia decomposition under dry gas conditions that do not contain water vapor, and little consideration has been given to the influence of coexisting water vapor on ammonia decomposition activity.
On the other hand, since the water vapor contained in the reaction gas has a reaction inhibiting effect on the ammonia decomposition reaction, even if the conventionally proposed ammonia decomposition catalyst is directly applied to the ammonia decomposition reaction in the coexistence of water vapor, It may be difficult to effectively decompose.
In addition, even if a large amount of catalyst component is impregnated and supported on the support component for the purpose of increasing the catalyst active point, the catalyst component particles aggregate, and as a result, the catalyst active surface does not increase and a catalyst having sufficient catalytic activity cannot be obtained. Sometimes.

  An object of the present invention is to provide a catalyst capable of effectively decomposing ammonia even when water vapor is contained in ammonia gas without using a noble metal element that has practical problems in terms of cost.

  The catalyst for decomposing ammonia of the present invention that has solved the above problems is a catalyst that decomposes ammonia into nitrogen and hydrogen in the presence of water vapor, and is at least one of the groups 6 to 10 in the long-period periodic table. And an oxide and / or composite oxide of at least one element (B component) selected from the group consisting of groups 2 to 5 and groups 12 to 15 of the long-period periodic table It is characterized by that. The calculated specific surface area (S2) of the component A is preferably 0.15 to 0.85 (S2 / S1) with respect to the specific surface area (S1) of the catalyst. The B component oxide and / or composite oxide is preferably at least one selected from the group consisting of alumina, silica, titania, hafnia, zirconia, zinc oxide, alkaline earth metal oxides, and lanthanoid metal oxides. is there. The catalyst preferably contains 55 to 95% by mass of component A based on the total amount of the catalyst.

  In the embodiment of the method for producing an ammonia decomposition catalyst of the present invention, the water-soluble salt of the component A and the water-soluble salt of the component B are dissolved in water, and a precipitate is formed with an alkaline compound. Filtering, washing, drying, and heat treatment: preparing an aqueous solution by adding the water-soluble salt of component A to water, adding an alkaline compound to the aqueous solution, and precipitating fine particles containing component A to prepare a fine particle dispersion Then, the fine particle-dispersed sol solution containing the component B is added while stirring the fine particle dispersion to produce a precipitate composed of the fine particles containing the component A and the fine particles containing the component B. An embodiment in which the precipitate is filtered, washed with water, dried, and heat-treated is preferable.

  In the present invention, an ammonia decomposition method for decomposing ammonia into nitrogen and hydrogen in the presence of water vapor using the above catalyst for decomposing ammonia; a hydrogen production method for decomposing ammonia into nitrogen and hydrogen in the presence of water vapor; 1 to 40% by volume, 1 to 99% by volume of ammonia, 0 to 50% by volume of hydrogen, and ammonia in a gas containing nitrogen (a total volume of water vapor, ammonia, hydrogen and nitrogen is 100% by volume) into nitrogen and hydrogen Also included is a method for producing hydrogen that decomposes.

  The catalyst for decomposing ammonia according to the present invention effectively exhibits catalytic action without being greatly affected by the reaction inhibition effect even when the raw material gas contains water vapor, and effectively decomposes ammonia into hydrogen and nitrogen. Is possible. Further, the catalyst of the present invention is characterized in that the specific surface area of the component A which is an active component is increased on the surface of the catalyst. Even if the A component has the same content in the catalyst, the specific surface area of the A component can be kept high, so that ammonia can be efficiently decomposed into hydrogen and nitrogen. Therefore, ammonia can be decomposed at a lower cost than a conventionally used noble metal catalyst.

  The catalyst for decomposing ammonia according to the present invention includes at least one element (A component) of Group 6 to 10 of the long period periodic table, and groups 2 to 5 and 12 to 15 of the long period periodic table. It is a catalyst containing an oxide and / or composite oxide of at least one selected element (component B).

  The component A uses at least one element of groups 6 to 10 of the long periodic table, preferably at least one selected from the group consisting of iron, cobalt and nickel, more preferably cobalt. Or nickel. The state of the component A may be any of a metal, an oxide, and a mixture thereof, and is preferably a metal state.

  The content rate of A component in a catalyst is 55-95 mass% with respect to the said catalyst, Preferably it is 60-90 mass%, More preferably, it is 65-85 mass%. If the content of the A component is less than 55% by mass, sufficient ammonia decomposition activity may not be obtained. If it exceeds 95% by mass, the B component is insufficient with respect to the A component, and the A component aggregates under the reaction conditions. There is a risk that the heat resistance will decrease.

  The B component is an oxide and / or composite oxide of at least one element selected from the group consisting of groups 2 to 5 and 12 to 15 of the long period periodic table, preferably alumina, silica, zirconia, It is at least one oxide selected from the group consisting of alkaline earth metal oxides and lanthanoid metal oxides and / or composite oxides thereof. 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 calculated specific surface area (S2) of the component A 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. is there. When the calculated specific surface area of the component A 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 the component A is preferably as large as possible, but 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. Hereinafter, it is more preferably 150 m ² / g or less.

  The calculated specific surface area (S2) of the A component is calculated by subtracting the specific surface integral derived from the B component oxide from the specific surface area of the catalyst. The B component oxide is obtained by, for example, dissolving a water-soluble salt of the B component in water and adding an alkaline compound used for the preparation of the catalyst to obtain a precipitate (for example, a hydroxide) of the B component. Similarly to the catalyst preparation procedure, the B component precipitate (for example, hydroxide) is filtered, washed with water, dried and reduced to prepare the B component oxide. About the obtained B component oxide, a specific surface area (S (b)) is measured by the BET method using nitrogen gas. Calculation of the A component by subtracting the specific surface integral (S (b) × mass content of the B component oxide in the catalyst) derived from the B component oxide contained in the catalyst from the specific surface area (S1) of the catalyst. A specific surface area (S2) can be obtained.

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.

  In the ammonia decomposition catalyst of the present invention, the ratio (S2 / S1) of the calculated specific surface area (S2) of the component A to the specific surface area (S1) of the catalyst is preferably 0.15 or more, more preferably 0.20 or more, More preferably, it is 0.22 or more, 0.85 or less is preferable, More preferably, it is 0.80 or less, More preferably, it is 0.75 or less. If the ratio (S2 / S1) is less than 0.15, the calculated specific surface area of the component A in the catalyst may be small and sufficient activity may not be obtained, and if it exceeds 0.85, the heat resistance decreases and the durability is low. May decrease. When nickel is used as the A component, the catalyst activity is slightly inferior to other A components (for example, cobalt). Therefore, the ratio (S2 / S1) is preferably 0.50 or more. Preferably it is 0.55 or more, More preferably, it is 0.60 or more.

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.
The catalyst for decomposing ammonia according to the present invention effectively exhibits catalytic action without being greatly affected by the reaction inhibition effect even when the raw material gas contains water vapor, and effectively decomposes ammonia into hydrogen and nitrogen. Is possible. Therefore, it is preferably used for an ammonia decomposition method in which ammonia in an ammonia-containing gas in which water vapor coexists is decomposed into nitrogen and hydrogen; a hydrogen production method in which ammonia in an ammonia-containing gas in which water vapor coexists is decomposed to produce hydrogen. Can do.

  An example of the manufacturing method of the catalyst concerning this invention is shown. In addition, as long as there exists an effect of this invention, it is not limited to the following catalyst manufacturing methods. As the method for producing the catalyst of the present invention, for example, (1) an aqueous solution is prepared by adding a water-soluble salt of an A component (for example, cobalt) to water, and an alkaline compound is added to this aqueous solution to contain fine particles containing an A component ( For example, component A hydroxide fine particles) are precipitated to prepare a fine particle dispersion. While stirring this fine particle dispersion, fine particles containing B component (for example, fine particles of B component oxide) dispersed sol solution are added, and fine particles containing A component (for example, hydroxide fine particles of A component) And a fine particle containing B component (for example, B component oxide fine particle). 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 component B and component A (for example, cobalt) Is added to water and mixed well, and then an alkaline compound is added to form a precipitate of fine particles (for example, hydroxide fine particles) containing the A component and the B component. Thereafter, this precipitate is removed by filtration, 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 B component and a water-soluble salt of A component (for example, cobalt) is added to the stirred alkaline aqueous solution, and fine particles containing A component (for example, hydroxide fine particles of A component) And a fine particle containing B component (for example, B component hydroxide fine particle). 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 raw material of the component A, any compound can be used as long as it can generate a mixture of metals, oxides and the like by heat treatment (preferably reduction treatment), but preferably it is water-soluble. The compounds are nitrates, acetates and chlorides. Examples of the water-soluble salt of the component A include a water-soluble salt of cobalt such as cobalt nitrate hexahydrate; a water-soluble salt of nickel such as nickel nitrate hexahydrate;

  The raw material of the B component can be any compound as long as it finally generates an oxide and / or a composite oxide by heat treatment, preferably various metal nitrates that are water-soluble compounds, Acetates, chlorides and sulfates can be used. Examples of the water-soluble salt of the component B include water-soluble salts of aluminum such as aluminum nitrate nonahydrate; water-soluble salts of magnesium such as magnesium nitrate hexahydrate; and cerium nitrate such as cerium nitrate hexahydrate. Water-soluble salts; water-soluble salts of zirconium such as zirconium oxynitrate; Examples of the B component fine particles include alumina sol; silica sol; and the like.

  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 catalyst for decomposing ammonia according to the present invention exhibits an effective catalytic action without being greatly affected by the reaction inhibition effect even when the raw material gas contains water vapor. Therefore, it can be suitably used for producing hydrogen by decomposing ammonia in an ammonia-containing gas in which water vapor coexists. In this case, the reaction gas (raw material gas) is 1 to 40% by volume of water vapor, 1 to 99% by volume of ammonia, 0 to 50% by volume of hydrogen, and nitrogen (the total capacity of water vapor, ammonia, hydrogen and nitrogen is 100%). %) Is preferred. In this reaction gas (raw material gas), ammonia is present in an amount of 1 to 99% by volume, preferably 5 to 98% by volume, and water vapor is 1 to 40% by volume, preferably 2 to 30% by volume.

  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 (SV) when the reaction gas (raw material gas) is introduced 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.

  According to the present invention, ammonia can be decomposed even with a gas containing ammonia containing water vapor. Furthermore, hydrogen can be obtained by decomposing the ammonia.

  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 of first catalyst>
Production Example 1
24.74 g of cobalt nitrate hexahydrate and 110.57 g of aluminum nitrate nonahydrate were dissolved in 500 mL (milliliter) of pure water to prepare a mixed aqueous solution of cobalt nitrate and aluminum nitrate (aqueous solution A1). . Separately, an aqueous solution B1 in which 101.2 g of ammonium carbonate was dissolved in 1.5 L (liter) of pure water was prepared. The aqueous solution A1 was added at once to the aqueous solution B1 vigorously stirred at room temperature, and the stirring was further continued for 1 hour 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 650 ° C. for 1 hour using 10% by volume hydrogen gas (diluted with nitrogen) to obtain catalyst 1. The obtained catalyst 1 had a cobalt content of 25% by mass. The specific surface area (S1) of the catalyst 1 measured by the BET method using nitrogen gas was 241.3 m ² / g.

Further, in order to calculate the calculated specific surface area (S2) of cobalt, which is the A component of the catalyst 1, powder 1 consisting only of alumina, which is the B component, was prepared. Specifically, 105.0 g of aluminum nitrate nonahydrate was first dissolved in 500 mL of pure water (aqueous solution a1). Separately, an aqueous solution (aqueous solution b1) in which 80.6 g of ammonium carbonate was dissolved in 1.5 L of pure water was prepared. The aqueous solution a1 was added at once to the aqueous solution b1 vigorously stirred at room temperature, and the stirring was continued for another hour to form a precipitate. Thereafter, the precipitate was collected by filtration, washed with water, and dried at 150 ° C. overnight. The dried precipitate 1 is pulverized, filled into a tube furnace, reduced at 650 ° C. for 1 hour using 10% by volume hydrogen gas (diluted with nitrogen), and powder 1 consisting only of alumina as the B component of catalyst 1 Got. The specific surface area of the powder 1 measured by the BET method using nitrogen gas was 285.5 m ² / g.

Production Example 2
Catalyst 2 was prepared in the same manner as in Production Example 1 except that the amounts of cobalt nitrate hexahydrate, aluminum nitrate nonahydrate and ammonium carbonate used in Production Example 1 were changed to 66.6 g, 48.9 g and 81.5 g. Obtained. The obtained catalyst 2 had a cobalt content of 67% by mass. The specific surface area (S1) of the catalyst 1 measured by the BET method using nitrogen gas was 121.7 m ² / g.
Further, in order to calculate the calculated specific surface area (S2) of cobalt, which is the A component of the catalyst 2, a powder 2 consisting only of alumina, which is the B component, was prepared in the same manner as in Production Example 1. The specific surface area of the powder 2 measured by the BET method using nitrogen gas was 285.5 m ² / g.

Production Example 3
Catalyst 3 was prepared in the same manner as in Production Example 1 except that the amounts of cobalt nitrate hexahydrate, aluminum nitrate nonahydrate and ammonium carbonate used in Production Example 1 were changed to 81.5 g, 28.1 g and 75.3 g. Obtained. The obtained catalyst 3 had a cobalt content of 81.2% by mass. The specific surface area (S1) of the catalyst 1 measured by the BET method using nitrogen gas was 75.4 m ² / g.
Further, in order to calculate the calculated specific surface area (S2) of cobalt, which is the A component of the catalyst 3, a powder 3 consisting only of alumina, which is the B component, was prepared in the same manner as in Production Example 1. The specific surface area of the powder 3 measured by the BET method using nitrogen gas was 285.5 m ² / g.

Production Example 4
Γ-alumina (Sumitomo Chemical Co., Ltd.) powder dried overnight at 150 ° C. was pulverized, and 5 g of the powder was added to 100 mL of pure water and dispersed by stirring. While stirring pure water in which γ-alumina was dispersed, 99.2 g of cobalt nitrate hexahydrate was added little by little. Next, the cobalt nitrate aqueous solution in which γ-alumina was dispersed was heated with stirring to evaporate the water, thereby obtaining a dried product. The obtained dried product was further dried at 150 ° C. overnight, pulverized and filled into a tubular furnace, and reduced at 450 ° C. for 1 hour using 10% by volume hydrogen gas (nitrogen dilution) to obtain catalyst 4. . The obtained catalyst 4 had a cobalt content of 80% by mass. The specific surface area (S1) of the catalyst 4 measured by the BET method using nitrogen gas was 61.1 m ² / g.
Further, in order to calculate the calculated specific surface area (S2) of cobalt, which is the A component of the catalyst 4, γ-alumina (manufactured by Sumitomo Chemical Co., Ltd.) powder, which is the B component, is pulverized, and then the powder is put into a tubular furnace. Filling and reduction treatment at 450 ° C. for 1 hour using 10 vol% hydrogen gas (diluted with nitrogen) gave a powder 4 made of γ-alumina. The specific surface area of the powder 4 measured by the BET method using nitrogen gas was 291.4 m ² / g.

Production Example 5
29.1 g of cobalt nitrate hexahydrate and 102.4 g of magnesium nitrate hexahydrate were dissolved in 500 mL of pure water to prepare a mixed aqueous solution of cobalt nitrate and magnesium nitrate (aqueous solution A2). Separately, an aqueous solution B2 in which 140.1 g of potassium hydroxide was dissolved in 2 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. The precipitate was filtered, washed thoroughly with water, and dried overnight at 150 ° C. The dried precipitate was pulverized, filled into a tubular furnace, and reduced at 450 ° C. for 1 hour using 10% by volume hydrogen gas (diluted with nitrogen) to obtain catalyst 5. The obtained catalyst 5 had a cobalt content of 26.8% by mass. The specific surface area (S1) of the catalyst 5 measured by the BET method using nitrogen gas was 188.3 m ² / g.

Further, in order to calculate the calculated specific surface area (S2) of cobalt, which is the A component of the catalyst 5, powder 5 consisting only of magnesia, which is the B component, was prepared. Specifically, 102.6 g of magnesium nitrate hexahydrate was first dissolved in 500 mL of pure water (aqueous solution a2). Separately, an aqueous solution b2 in which 112.2 g of potassium hydroxide was dissolved in 2 L of pure water was prepared. The aqueous solution a2 was dropped into the aqueous solution b2 that was vigorously stirred at room temperature to generate a precipitate. The precipitate was filtered, washed thoroughly with water, and dried overnight at 150 ° C. 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 a powder 5 made of magnesia. The specific surface area of the powder 5 measured by the BET method using nitrogen gas was 173.7 m ² / g.

Production Example 6
Catalyst 6 was prepared in the same manner as in Production Example 5 except that the amounts of cobalt nitrate hexahydrate, magnesium nitrate hexahydrate and potassium hydroxide used in Production Example 5 were changed to 53.8 g, 62.2 g and 120.0 g. Got. The obtained catalyst 6 had a cobalt content of 52.7% by mass. The specific surface area (S1) of the catalyst 6 measured by the BET method using nitrogen gas was 158.1 m ² / g.
Further, in order to calculate the calculated specific surface area (S2) of cobalt, which is the A component of the catalyst 6, a powder 6 consisting only of magnesia, which is the B component, was prepared in the same manner as in Production Example 5. The specific surface area of the powder 6 measured by the BET method using nitrogen gas was 173.7 m ² / g.

Production Example 7
Catalyst 7 was prepared in the same manner as in Production Example 5 except that the amounts of cobalt nitrate hexahydrate, magnesium nitrate hexahydrate and potassium hydroxide used in Production Example 5 were changed to 72.8 g, 35.0 g and 108.4 g. Got. The obtained catalyst 7 had a cobalt content of 72.8% by mass. The specific surface area (S1) of the catalyst 7 measured by the BET method using nitrogen gas was 123.6 m ² / g.
Further, in order to calculate the calculated specific surface area (S2) of cobalt, which is the A component of the catalyst 7, a powder 7 consisting only of magnesia, which is the B component, was prepared in the same manner as in Production Example 5. The specific surface area of the powder 7 measured by the BET method using nitrogen gas was 173.7 m ² / g.

Production Example 8
Basic magnesium carbonate (Wako Pure Chemical Industries, Ltd.) was calcined at 750 ° C. for 2 hours to prepare magnesia. 5 g of the magnesia powder was added to 100 mL of pure water and dispersed by stirring. While vigorously stirring pure water in which magnesia was dispersed, 74.4 g of cobalt nitrate hexahydrate was added little by little. Next, the aqueous cobalt nitrate solution in which magnesia was dispersed was heated with stirring to evaporate the water, thereby obtaining a dried product. The obtained dried product was further dried overnight at 150 ° C., pulverized and filled into a tubular furnace, and reduced at 450 ° C. for 1 hour using 10 vol% hydrogen gas (diluted with nitrogen) to obtain catalyst 8. . The obtained catalyst 8 had a cobalt content of 60% by mass. The specific surface area (S1) of the catalyst 8 measured by the BET method using nitrogen gas was 84.4 m ² / g.

Further, in order to calculate the calculated specific surface area (S2) of cobalt, which is the A component of the catalyst 8, a powder 8 consisting only of magnesia, which is the B component, was prepared. Specifically, basic magnesium carbonate (manufactured by Wako Pure Chemical Industries, Ltd.) is calcined at 750 ° C. for 2 hours to produce magnesia, the magnesia powder is pulverized and then filled into a tubular furnace, and 10 volume% hydrogen gas Using nitrogen dilution, reduction treatment was performed at 450 ° C. for 1 hour to obtain a powder 8 made only of magnesia. The specific surface area of the powder 8 measured by the BET method using nitrogen gas was 56.3 m ² / g.

Production Example 9
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 A3). Separately, an aqueous solution B3 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 A3 was added at once to the aqueous solution B3 vigorously stirred at room temperature, and the stirring was continued for another hour 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% by volume hydrogen gas (diluted with nitrogen) to obtain catalyst 9. The resulting catalyst 9 had a nickel content of 83.8% by mass. The specific surface area (S1) of the catalyst 9 measured by the BET method using nitrogen gas was 177.5 m ² / g.

Further, in order to calculate the calculated specific surface area (S2) of nickel which is the A component of the catalyst 9, a powder 9 consisting only of alumina which is the B component was prepared. Specifically, 93.8 g of aluminum nitrate nonahydrate was first dissolved in 500 mL of pure water (aqueous solution a3). Separately, an aqueous solution (b3) 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 a3 was added at once to the aqueous solution b3 vigorously stirred at room temperature, and the stirring was continued for another hour 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 450 ° C. for 1 hour using 10% by volume hydrogen gas (diluted with nitrogen) to obtain a powder 9 consisting only of alumina. The specific surface area of the powder 9 measured by the BET method using nitrogen gas was 341.7 m ² / g.

Production Example 10
61.1 g of nickel nitrate hexahydrate and 53.8 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 A4). Separately, an aqueous solution B4 in which 118 g of potassium hydroxide was dissolved in 1.5 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. The precipitate was filtered, washed thoroughly with water, and dried overnight at 150 ° C. 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 10. The resulting catalyst 10 had a nickel content of 59.3 mass%. The specific surface area (S1) of the catalyst 10 measured by the BET method using nitrogen gas was 118.5 m ² / g.

Further, in order to calculate the calculated specific surface area (S2) of nickel which is the A component of the catalyst 10, a powder 10 consisting only of magnesia which is the B component was prepared. 102.6 g of magnesium nitrate hexahydrate was dissolved in 500 mL of pure water (aqueous solution a4). Separately, an aqueous solution b4 in which 112.2 g of potassium hydroxide was dissolved in 2 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. The precipitate was filtered, washed thoroughly with water, and dried overnight at 150 ° C. 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 10 made of magnesia. The specific surface area of the powder 10 measured by the BET method using nitrogen gas was 58.2 m ² / g.

Production Example 11
66.9 g of cobalt nitrate hexahydrate, 15.4 g of cerium nitrate hexahydrate and 2.37 g of zirconium oxynitrate are dissolved in 500 mL of pure water, and a mixed aqueous solution of cobalt nitrate, cerium nitrate and zirconium oxynitrate (Aqueous solution A5) was prepared. Separately, an aqueous solution B5 in which 56.1 g of ammonium carbonate was dissolved in 1.5 L of pure water was prepared. The aqueous solution A5 was added to the aqueous solution B5 vigorously stirred at room temperature all at once, and the stirring was continued for another hour 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% by volume hydrogen gas (diluted with nitrogen) to obtain catalyst 11. The obtained catalyst 11 had a cobalt content of 64.1% by mass. The specific surface area (S1) of the catalyst 11 measured by the BET method using nitrogen gas was 75.7 m ² / g.

Further, in order to calculate the calculated specific surface area (S2) of cobalt, which is the A component of the catalyst 11, a powder 11 consisting only of ceria and zirconia, which is the B component, was prepared. Specifically, 17.4 g of cerium nitrate hexahydrate and 2.67 g of zirconium oxynitrate were first dissolved in 500 mL of pure water to prepare a mixed aqueous solution of cerium nitrate and zirconium oxynitrate (aqueous solution a5). Separately, an aqueous solution b5 in which 13.4 g of ammonium carbonate was dissolved in 1.5 L of pure water was prepared. The aqueous solution a5 was added at once to the aqueous solution b5 vigorously stirred at room temperature, and the stirring was continued for another hour 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 a powder 11 consisting only of ceria and zirconia. The specific surface area of the powder 11 measured by the BET method using nitrogen gas was 145.1 m ² / g.

Production Example 12
49.5 g of cobalt nitrate hexahydrate was dissolved in 1 L of pure water (aqueous solution A6). Separately, 14.24 g of SNOWTEX (registered trademark) N (Nissan Chemical Industries, Ltd. silica sol: 20.3% by mass of silica) in ammonia water diluted to 300 mL by adding pure water to 25.6 mL of 25 mass% ammonia water. Aqueous solution B6 was added, and the aqueous solution B6 was added dropwise to the aqueous solution A6 to generate a precipitate. The precipitate was filtered, washed thoroughly with water, and dried overnight at 150 ° C. 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 12. The obtained catalyst 12 had a cobalt content of 77.6% by mass. The specific surface area (S1) of the catalyst 12 measured by the BET method using nitrogen gas was 118.2 m ² / g.

Further, in order to calculate the calculated specific surface area (S2) of cobalt, which is the A component of the catalyst 12, a powder 12 made only of silica, which is the B component, was prepared. Specifically, Snowtex N (silica sol manufactured by Nissan Chemical Industries, Ltd .: containing 20.3% by mass of silica) was weighed into a 50 g glass beaker and dried at 150 ° C. overnight. The solid obtained by drying was pulverized, filled into a tubular furnace, and reduced at 450 ° C. for 1 hour using 10% by volume hydrogen gas (diluted with nitrogen) to obtain a powder 12 made only of silica. The specific surface area of the powder 12 measured by the BET method using nitrogen gas was 220.8 m ² / g.

Production Example 13
34.9 g of cobalt nitrate hexahydrate and 27.3 g of aluminum nitrate nonahydrate were dissolved in 1 L of pure water (aqueous solution A7). Separately, 21.5 g of Snowtex N (Nissan Chemical Co., Ltd. silica sol: containing 20.3% by mass of silica) was added to 34.5 mL of 25% by mass of ammonia water and pure water diluted to 300 mL. An aqueous solution B7 was prepared, and the aqueous solution B7 was dropped into the aqueous solution A7 to generate a precipitate. The precipitate was filtered, washed thoroughly with water, and dried overnight at 150 ° C. The dried precipitate was pulverized, filled into a tubular furnace, and reduced at 450 ° C. for 1 hour using 10% by volume hydrogen gas (diluted with nitrogen) to obtain catalyst 13. The obtained catalyst 13 had a cobalt content of 46.7% by mass. The specific surface area (S1) of the catalyst 13 measured by the BET method using nitrogen gas was 122.8 m ² / g.

Further, in order to calculate the calculated specific surface area (S2) of cobalt, which is the A component of the catalyst 13, a powder 13 made only of silica / alumina, which is the B component, was prepared. 37.5 g of aluminum nitrate nonahydrate was dissolved in 1 L of pure water (aqueous solution a7). Separately, 29.6 g of Snowtex N (Nissan Chemical Co., Ltd. silica sol: containing 20.3% by mass of silica) was added to 22.6 mL of 25% by mass of ammonia water and pure water diluted to 300 mL. An aqueous solution b7 was prepared, and the aqueous solution b7 was dropped into the aqueous solution a7 to generate a precipitate. The precipitate was filtered, washed thoroughly with water, and dried overnight at 150 ° C. The dried precipitate was pulverized, filled into a tube furnace, and reduced at 450 ° C. for 1 hour using 10% by volume hydrogen gas (diluted with nitrogen) to obtain a powder 13 consisting only of silica / alumina. The specific surface area of the powder 13 measured by the BET method using nitrogen gas was 150.8 m ² / g.

Production Example 14
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 overnight at 150 ° C., 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 catalyst 14. . The resulting catalyst 14 had a nickel content of 20% by mass. The specific surface area (S1) of the catalyst 14 measured by the BET method using nitrogen gas was 157.4 m ² / g.
Further, in order to calculate the calculated specific surface area (S2) of nickel which is the A component of the catalyst 14, after pulverizing the γ-alumina (made by Strem Chemicals Inc.) powder which is the B component, the powder is put into a tubular furnace. Filled and reduced using 450% hydrogen gas (diluted with nitrogen) at 450 ° C. for 1 hour to obtain a powder 14 made of γ-alumina. The specific surface area of the powder 14 measured by the BET method using nitrogen gas was 187.1 m ² / g.

Production Example 15
99.0 g of cobalt nitrate hexahydrate was dissolved in 500 mL of pure water (aqueous solution A8). Separately, an aqueous solution B8 in which 65.3 g of ammonium carbonate was dissolved in 1.5 L of pure water was prepared, and the aqueous solution A8 was added to the aqueous solution B8 vigorously stirred at room temperature all at once, and stirring was further continued for 1 hour to precipitate. Product was produced. 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% by volume hydrogen gas (diluted with nitrogen) to obtain catalyst 15. The obtained catalyst 15 had a cobalt content of 100% by mass. The specific surface area (S1) of the catalyst 15 measured by the BET method using nitrogen gas was 4.5 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.

<Method for calculating specific surface area of component A>
The calculated specific surface area (S2) of the A component was calculated by subtracting the specific surface area (Sb) derived from the B component oxide from the specific surface area (S1) of the catalyst. The specific surface area derived from the B component oxide in the catalyst was determined as follows. Specifically, the B component water-soluble salt used in each production example is dissolved in water, and the alkaline compound used in the production example is added thereto to prepare a B component precipitate (eg, hydroxide). did. Thereafter, the B component precipitate (for example, hydroxide) was filtered, washed with water, dried and reduced in the same manner as the catalyst preparation procedure in the production example to prepare the B component oxide. About the obtained oxide, the specific surface area (S (b)) was measured by BET method using nitrogen gas. The specific surface area derived from the B component oxide in the catalyst was calculated from the following formula.
Specific surface area derived from B component oxide in catalyst = (S (b) × mass content of B component oxide in the catalyst)

<Ammonia decomposition reaction in the presence of water vapor>
Using a 10 mmφ SUS316 reaction tube, 0.8 mL of catalyst 1-15 prepared in Production Examples 1-15 was charged and ammonia decomposition reaction (reaction examples 1-15) 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

<Ammonia decomposition reaction in the presence of water vapor and oxygen>
Using a 10 mmφ SUS316 reaction tube, 0.8 mL of Catalysts 2, 11, and 14 prepared in Production Examples 2, 11, and 14 were charged, the reaction tube was heated in an electric furnace, and ammonia in the presence of water vapor and oxygen A decomposition reaction was performed. Under normal pressure, SV = 50,000 hr ^−1, and the ammonia decomposition rate at an electric furnace set temperature of 150 ° C. was measured. The ammonia decomposition reaction was carried out with the composition of the inlet gas supplied to the catalyst being 48.4 vol% ammonia, 17 vol% water vapor, 7.2 vol% 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 an ammonia decomposition catalyst that can efficiently decompose ammonia into hydrogen and nitrogen even in the presence of water vapor, and has high practicality in terms of cost. By using the ammonia decomposition catalyst according to the present invention, Even in the presence, hydrogen can be efficiently obtained from ammonia. The present invention can be widely applied to hydrogen production technology.

Claims (9)

A catalyst that decomposes ammonia into nitrogen and hydrogen in the presence of water vapor,
At least one element (A component) of group 6-10 of long-period periodic table and at least one element (B) selected from the group consisting of groups 2-5 and 12-15 of long-period periodic table A catalyst for decomposing ammonia, comprising a component) oxide and / or composite oxide.   The catalyst for ammonia decomposition according to claim 1, wherein the calculated specific surface area (S2) of the component A is 0.15 to 0.85 (S2 / S1) with respect to the specific surface area (S1) of the catalyst.   The B component oxide and / or composite oxide is at least one oxide selected from the group consisting of alumina, silica, titania, hafnia, zirconia, zinc oxide, alkaline earth metal oxides, and lanthanoid metal oxides. The catalyst for decomposing ammonia according to claim 1 or 2, which is a composite oxide thereof.   The catalyst for ammonia decomposition | disassembly of any one of Claims 1-3 which contains 55-95 mass% of said A components with respect to the catalyst whole quantity. It is a manufacturing method of the catalyst for ammonia decomposition | disassembly of any one of Claims 1-4,
The water-soluble salt of the component A and the water-soluble salt of the component B are dissolved in water, and a precipitate is formed with an alkaline compound, and then the precipitate is filtered, washed with water, dried, and heat-treated. A method for producing an ammonia decomposition catalyst. It is a manufacturing method of the catalyst for ammonia decomposition | disassembly of any one of Claims 1-4,
A water-soluble salt of the component A is added to water to prepare an aqueous solution, an alkaline compound is added to the aqueous solution to precipitate fine particles containing the component A to prepare a fine particle dispersion, and the fine particle dispersion is stirred while stirring the fine particle dispersion. A fine particle-dispersed sol solution containing the B component is added to form a precipitate composed of the fine particles containing the A component and the fine particles containing the B component, and then the precipitate is filtered, washed, dried, and heat-treated. A method for producing a catalyst for decomposing ammonia.   A method for decomposing ammonia, comprising decomposing ammonia into nitrogen and hydrogen in the presence of water vapor using the catalyst according to any one of claims 1 to 4.   A method for producing hydrogen comprising decomposing ammonia into nitrogen and hydrogen in the presence of water vapor using the catalyst according to any one of claims 1 to 4.   Using the catalyst according to any one of claims 1 to 4, steam is 1 to 40% by volume, ammonia is 1 to 99% by volume, hydrogen is 0 to 50% by volume, and nitrogen (steam, ammonia, hydrogen and A method for producing hydrogen, comprising decomposing ammonia in a gas containing 100% by volume of nitrogen into nitrogen and hydrogen.