JP2016059851A - Ammonia synthesis catalyst, production process therefor, and ammonia synthesis process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ammonia synthesis catalyst that can allow an efficient ammonia synthesis under a low temperature condition and under a low pressure condition.SOLUTION: Provided is an ammonia synthesis catalyst having a transition metal with ammonia synthesis activity supported on a zeolite particle comprising an aluminosilicate skelton and including a mesoporous structure. The zeolite particle includes a meso-porous structure comprising a micro-pore having an average major diameter of 0.2 to 0.5 nm and a meso-pore having an average major diameter of 4 to 5 nm, and the bulk density preferably is 0.5 to 2.0 g/cm.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an ammonia synthesis catalyst capable of promoting ammonia synthesis, a method for producing the catalyst, and an ammonia synthesis method.

  Ammonia is a raw material for artificial fertilizers such as ammonium sulfate and urea fertilizers that are indispensable for grain production. The Harbor Bosch method is known as a basic technology for ammonia synthesis. The Harbor Bosch method is a technology that synthesizes ammonia by directly reacting nitrogen and hydrogen with a double-promoted iron catalyst. Since it was industrially completed in the 1910s, it has evolved into human life. It is heavily used as a technology that supports

Double promoting iron catalyst is mainly composed of Fe ₃ O _4. Regarding the composition of the double promoted iron catalyst, taking the double promoted iron catalyst manufactured by BASF as an example, the composition is: Fe ₃ O ₄ 94.3%, K ₂ O 0.8%, Al ₂ O ₃ 2.3%, others ( CaO, MgO, SiO ₂ ) 2.6%. The iron oxide contained in the composition exemplified above is reduced by hydrogen during the ammonia synthesis process to produce metallic iron, and exhibits catalytic activity.

  The Harbor Bosch method is carried out under reaction conditions of a reaction temperature of 400 to 600 ° C. and a reaction pressure of about 20 to 100 MPa. In order to satisfy this reaction condition, the synthesis method is carried out batchwise using a high-pressure reaction vessel. Therefore, it is difficult to produce ammonia continuously. In order to increase the catalytic activity, the reaction temperature must be at least 400 ° C.

  A synthesizer that satisfies the above temperature and pressure conditions tends to be large because it requires highly durable piping equipment and a compressor. Further, since the synthesis method is performed under high temperature conditions, the heat energy loss is large. Therefore, a method capable of synthesizing ammonia under a low temperature condition or a low pressure condition is desired rather than the Harbor Bosch method.

  In Patent Document 1, as an ammonia synthesis method that can be performed under a lower temperature condition than the Harbor Bosch method, the catalyst component is any metal element of Mo, W, Re, Fe, Co, Ru, Os, or Fe. A method is disclosed in which a transition metal composed of any one of a combination of Ru and Ru, Ru and Re, or Fe and Mo is used in a substantially metallic state. In the method using the above catalyst component, ammonia can be synthesized at 200 to 300 ° C.

  As an ammonia synthesis method that can be performed under a low temperature condition or a low pressure condition, in addition to the above, an ammonia synthesis method using a Group 8 or Group 9 transition metal such as Fe, Ru, Os, Co or the like as a catalyst component (patent) Documents 2 to 4) and methods using ruthenium as a catalyst for ammonia synthesis (Patent Documents 5 to 8) have also been proposed.

  Patent Documents 9 and 10 disclose ammonia synthesis methods using a group 8 or 6B transition metal nitride or Co-Mo composite nitride as a catalyst as a method for synthesizing ammonia at 300 to 500 ° C. The Patent Document 11 includes at least one from the group of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Mn, and Cu. Disclosed is a method for producing ammonia from nitrogen and water vapor by plasma contact using a catalyst containing a catalytically active component selected from two transition metals in a support material.

  The method using the above catalyst component does not require a high-pressure process, and the reaction of the raw material component can proceed even at normal pressure. Ru et al. Are attracting attention as a second-generation ammonia synthesis catalyst. However, the catalytic activity of Ru alone is very small, and it is necessary to use a carrier or a promoter compound to exert its ability.

  Magnesium oxide, aluminum oxide, graphite, cerium, magnesia, and the like are used as carriers that promote the catalytic activity of Ru, Fe, and the like. When an oxide compound such as aluminum oxide is used as a carrier, a large amount of an accelerator compound such as an alkali metal, alkali metal compound, or alkaline earth metal compound having a large electronegativity is added to improve the electron donating ability of the catalyst component. And improve the catalytic activity. However, it is desirable to synthesize ammonia more efficiently under low temperature conditions or low pressure conditions.

Japanese Patent Publication No.51-47674 Japanese Patent Publication No.54-37592 Japanese Patent Publication No.59-16816 International Publication No. 96/38222 Japanese Patent Laid-Open No. 2-256666 Japanese Patent Laid-Open No. 9-239272 Japanese Unexamined Patent Publication No. 2004-35399 Japanese Unexamined Patent Publication No. 2006-231229 Japanese Unexamined Patent Publication No. 2000-264625 JP 2008-13435 Gazette JP 2001-151507 A

  An object of the present invention is to provide an ammonia synthesis catalyst that exhibits excellent catalytic activity under low-temperature conditions or low-pressure conditions, and to provide a method capable of synthesizing ammonia with high efficiency using the catalyst.

The present invention is an ammonia synthesis catalyst in which a transition metal having an ammonia synthesis activity is supported on zeolite particles having an aluminosilicate skeleton and having a mesoporous structure. The ammonia synthesis catalyst has an aluminosilicate skeleton, has a mesoporous structure having micropores with an average major axis of 0.2 to 0.5 nm and mesopores with an average major axis of 4 to 5 nm, and a bulk density of 0.5 to 2.0 g / cm. A transition metal having ammonia synthesis activity is supported on the zeolite particles ³ .

The present invention comprises a mesoporous structure having an aluminosilicate skeleton and having micropores with an average major axis of 0.2 to 0.5 nm and mesopores with an average major axis of 4 to 5 nm, and a bulk density of 0.5 to 2.0 g / cm ³ . The present invention includes a method for producing an ammonia synthesis catalyst including a supporting step of supporting a transition metal having ammonia synthesis activity on a certain zeolite particle.

  The production method includes a dispersion step of dispersing a silicic acid raw material, an aluminate raw material, a nonionic surfactant, and an ionic surfactant in a basic aqueous liquid, and heat-treating the dispersion solution obtained in the dispersion step. A heat treatment step for producing zeolite particles containing a nonionic surfactant and an ionic surfactant, washing the zeolite particles with water, and heating the zeolite particles to produce a nonionic surfactant and an ionic surfactant. It is preferable to include a surfactant removing step for removing the agent and a supporting step for supporting a transition metal having ammonia synthesis activity on the zeolite particles.

The present invention comprises a mesoporous structure having an aluminosilicate skeleton and having micropores with an average major axis of 0.2 to 0.5 nm and mesopores with an average major axis of 4 to 5 nm, and a bulk density of 0.5 to 2.0 g / cm ³ . This includes an ammonia synthesis method in which ammonia is synthesized by reacting hydrogen and nitrogen using an ammonia synthesis catalyst in which a transition metal having ammonia synthesis activity is supported on a zeolite particle. In the above ammonia synthesis method, it is preferable to synthesize ammonia under reaction conditions satisfying at least one of a temperature condition of 250 to 350 ° C. and a pressure condition of 0.1 to 1 MPa.

  The present invention exhibits excellent catalytic activity under low temperature conditions and low pressure conditions. Also, it is possible to provide a method capable of synthesizing ammonia with high efficiency using an ammonia synthesis catalyst.

It is a table | surface which shows the example of the addition amount of the raw material of the zeolite particle used for this invention. It is a table | surface which shows the structural example of the zeolite particle used for this invention. It is a schematic diagram of an example of an ammonia synthesis apparatus to which the ammonia synthesis method of the present invention is applied.

[Ammonia synthesis catalyst]
The ammonia synthesis catalyst of the present invention is obtained by supporting a transition metal having ammonia synthesis activity on predetermined zeolite particles.

[Zeolite particles]
The predetermined zeolite particles of the present invention function as a carrier for supporting a transition metal having ammonia synthesis activity. The purity of the zeolite particles is 95 to 100% by mass, and may contain a small amount of impurities that could not be completely eliminated in the production process.

  The zeolite particles used in the present invention have an aluminosilicate skeleton having a relatively large lattice gap. The basic structure of the aluminosilicate skeleton is a tetrahedral structure in which oxygen occupies each vertex and Si is located in the center. By sharing oxygen at the apex of the tetrahedral structure, the tetrahedral structure is connected, and a part of the Si is substituted with Al to form an aluminosilicate skeleton. Since the structure is negatively charged as a whole of the crystal lattice, charge compensation is performed by containing a cation such as an alkali metal ion such as K, Cs, or Na.

  When an ammonia synthesis catalyst having the above structure is used for an ammonia synthesis reaction using nitrogen and hydrogen as raw materials, hydrogen can be temporarily taken into lattice gaps of the aluminosilicate skeleton of the catalyst support. As a result, the contact between the transition metal, which is the supported component, and hydrogen is suppressed, and poisoning of the catalyst component such as the transition metal can be suppressed. That is, this invention can suppress the deactivation of the catalyst by poisoning, and can exhibit the outstanding catalyst activity stably. Therefore, ammonia can be synthesized with high efficiency.

  The above zeolite particles have micropores and mesopores. In the catalyst field, IUPAC defines pores with a diameter of 2 nm or less as micropores, pores with a diameter of 2 to 50 nm as mesopores, and pores with a diameter of 50 nm or more as macropores. In the present invention, the average major axis of each micropore of the zeolite particles is preferably 0.2 to 0.5 nm, and the average major axis of each mesopore is preferably 4 to 5 nm.

  The `` average major axis '' between the micropores and mesopores of the zeolite particles used in the present invention is the measurement of the major axis of each pore visible on the particle surface, the pores having a major axis of 2 nm or less are micropores, and the major axis is 2 nm. The average major axis of the micropores and the average major axis of the mesopores are calculated with the pores exceeding 4 being mesopores. The zeolite particles used in the present invention have an average major axis of the micropores and an average major axis of the mesopores within the above predetermined range. In addition, the measuring method of a long diameter is possible by SEM etc., for example.

  The shape and ratio of the micropores and mesopores formed in the zeolite particles are adjusted by the amount of nonionic surfactant or ionic surfactant added as a structure-directing agent during the production of the ammonia synthesis catalyst. it can.

  Zeolite particles having micropores and mesopores can ensure a wide specific surface area compared to zeolite particles having only micropores. Moreover, the more mesopores, the easier it is to generate active sites and the catalytic activity of the zeolite particles can be improved. However, zeolite particles with too many mesopores have a weak structure and low toughness. When a catalyst using such zeolite particles is pelletized and filled into a reactor, the catalyst cannot easily withstand thermal expansion associated with a temperature change in the reactor and collapses, so that the catalytic activity tends to decrease.

Zeolite particles used in the present invention are present from the viewpoint of improving catalytic activity and ensuring toughness, with a proportion of micropores having an average major axis of 0.2 to 0.5 nm and mesopores having an average major axis of 4 to 5 nm at a predetermined bulk density. Coexisting zeolite particles are used. The bulk density of the support used in the present invention is preferably 0.5 to 2.0 g / cm ^3, more preferably 0.7~1.5g / cm ^3, further to be 0.8~1.2g / cm ³ preferable. When the bulk density is less than 0.5 g / cm ³ , the toughness becomes insufficient. When it is larger than 2.0 g / cm ³ , the catalytic activity becomes insufficient.

  In the present invention, the bulk density of the zeolite particles is determined as a value obtained by measuring the mass of the zeolite particles filled in the measurement container using a known measuring apparatus and dividing the mass by the capacity of the measurement container. As a known measuring apparatus, Hosokawa Micron Powder Tester PT-X can be mentioned.

The larger the specific surface area of the zeolite particles by the BET method, the more transition metals can be supported. From the viewpoint of ease of production, it is preferably 1 to 10 m ² / g, more preferably 1 to 5 m ² / g. When the specific surface area is less than 1 m ² / g, the amount of transition metal supported becomes small, so that the catalytic activity cannot be sufficiently improved. In the ammonia synthesis catalyst of the present invention, a large amount of a predetermined transition metal is supported on the zeolite particles. By supporting a transition metal having an ammonia synthesis activity under a reaction condition that satisfies at least one of a temperature condition of 250 to 350 ° C. and a pressure condition of 0.1 to 1 MPa, the present invention stably exhibits high catalytic activity. And contributes to highly efficient ammonia synthesis.

  Specific examples of the zeolite particles include mordenite, A type zeolite, Y type zeolite, X type zeolite, L type zeolite, erionite, beta zeolite, ZSM-5 zeolite and the like.

[Transition metals]
In the ammonia synthesis catalyst of the present invention, a transition metal having ammonia synthesis activity is supported on the predetermined zeolite particles. As such a transition metal, one having a catalytic activity for promoting ammonia synthesis under a reaction condition satisfying at least one of a temperature condition of 250 to 350 ° C. and a pressure condition of 0.1 to 1 MPa is preferable. Specific examples include Group 8 transition metal elements such as Fe, Ru and Os, and Group 9 transition metal elements such as Co and Ir. In addition, Mo of a Group 6 transition metal element and Re of a Group 7 transition metal element may be supported. The transition metal used in the present invention may be used singly or in combination of two or more.

Examples of transition metal compounds that serve as the transition metal source include triruthenium dodecacarbonyl (Ru ₃ (CO) ₁₂ ), dichlorotetraskis (triphenylphosphine) ruthenium (II) (RuCl ₂ (PPh ₃ ) ₄ ), Dichlorotris (triphenylphosphine) ruthenium (II) (RuCl ₂ (PPh ₃ ) ₃ ), tris (acetylacetonato) ruthenium (III) (Ru (acac) ₃ ), pentacarbonyl iron iodide (Fe (CO) ₄ Examples thereof include inorganic metal compounds or organometallic complexes that are easily thermally decomposed, such as I ₂ ). The transition metal compounds exemplified above may be used singly or in combination of two or more.

The average particle size of the transition metal is not limited as long as it is a size that can be supported on the zeolite particles, but is preferably 5 to 500 nm, more preferably 50 to 300 nm. In the present invention, the particle size means a 50% particle size (D ₅₀ ) in a volume-based cumulative particle size distribution obtained by measuring the particle size distribution by a laser diffraction method.

  The amount of the transition metal supported on the carrier varies depending on the combination of the carrier and the transition metal to be supported, but is at least 1 to 10% by mass, more preferably 2 to 7% with respect to 100 mass g of zeolite particles as the carrier. % By mass.

  In the ammonia synthesis catalyst of the present invention, in addition to the above zeolite particles and transition metals, a promoter may be contained for the purpose of improving the ammonia synthesis activity. Moreover, as long as the effect of this invention is not inhibited, you may contain another component.

[Method for producing ammonia synthesis catalyst]
The method for producing an ammonia synthesis catalyst of the present invention comprises a dispersion step of dispersing raw material components in a solvent, a heat treatment step of producing zeolite particles from a dispersion solution obtained by the dispersion step, and a surfactant contained in the zeolite particles. It is preferable to include a surfactant removing step to be removed. In addition, as long as the effect of this invention is not inhibited, the other process may be included.

[Dispersion process]
A silicic acid raw material, an aluminate raw material, a nonionic surfactant, and an ionic surfactant are added to the basic aqueous liquid. The basic aqueous liquid to which the raw materials are added is stirred using sodium carbonate, sodium hydroxide, or the like, thereby forming a slurry-like dispersion solution in which the silicic acid raw material and the aluminate raw material are uniformly dispersed. Further, bubbles are formed so as to be surrounded by the nonionic surfactant or the ionic surfactant in the dispersion solution.

  The nonionic surfactant and the ionic surfactant function as a structure-directing agent for the zeolite particles. The bubbles surrounded by the nonionic surfactant are relatively small and later define the micropores. The bubbles surrounded by the ionic surfactant are relatively large and later define mesopores. Therefore, by adjusting the addition amount of the nonionic surfactant or the ionic surfactant, the abundance ratio of micropores and mesopores can be defined, and zeolite particles having a desired bulk density can be obtained.

  The total content of the silicic acid compound and aluminate dispersed in the basic aqueous liquid is appropriately adjusted to a concentration at which the raw material dispersion becomes a slurry. Preferably, it is 300-500 g / L. The total amount of the nonionic surfactant and the ionic surfactant is 5 to 10 mass g / mol with respect to the total number of moles of silicon and aluminum contained in the silicic acid raw material and the aluminate raw material. It is preferable to satisfy.

  As the silicic acid raw material, either an organic silicic acid compound or an inorganic silicic acid compound may be used. Examples of the organic silicate compound include silicate esters such as tetraethyl orthosilicate, tetramethyl orthosilicate, and tetraisopropyl orthosilicate. Examples of the inorganic silicate compound include silicate metal salts such as sodium silicate and potassium silicate, colloidal silica, gel silica, water glass, silicon oxide and the like. Preferably, sodium silicate is used. The silicic acid compound may be used alone or in combination of two or more.

  As the aluminate raw material, either an organic aluminum compound or an inorganic aluminum compound may be used. Examples of the organoaluminum compound include aluminum alkoxides such as aluminum isopropoxide and aluminum butoxide. Examples of the inorganic aluminum compound include aluminum salts of various acids such as aluminum nitrate, aluminum sulfate, aluminum chloride, and aluminum acetate, aluminum hydroxide, and aluminum oxide. Preferably, aluminum nitrate is used. The silicic acid compound may be used alone or in combination of two or more. It is preferable to use the silicic acid compound and aluminate prepared in a powder form so that they can be easily mixed uniformly in an aqueous liquid.

  The nonionic surfactant functions as a template for forming micropores. As the nonionic surfactant, polyoxyalkylene alkyl ethers, polyoxyalkylene fatty acid esters, polyoxyalkylene sorbitan fatty acid esters, polyoxyalkylene alkylphenyl ethers, and the like can be used.

  Preferably, the hydrophilic portion has one or more polyoxyethylene chains, and the hydrophobic portion is one or more selected from polyoxypropylene chains, alkyl chains, polyoxybutylene chains and substituted aryl chains. A block copolymer containing is used. Specific examples include nonaethylene glycol monohexadecyl ether and polyoxyethylene sorbitan monostearate.

  Examples of commercially available nonionic surfactants include PLURONIC (trade name, manufactured by BASF), TETRONIC (trade name, manufactured by BASF), TRITON (trade name, manufactured by Union Carbide), and TERGITOL (Union Carbide, Inc.). Product name) is preferred. One nonionic surfactant may be used, or two or more nonionic surfactants may be used in combination.

  The ionic surfactant functions as a template for forming mesopores. As the ionic surfactant, any of an anionic surfactant, a cationic surfactant, and an amphoteric ionic surfactant may be used.

  From the viewpoint of forming mesopores, an anionic surfactant having a carboxylic acid group, a sulfonic acid group or a phosphoric acid group as a hydrophilic group is particularly preferred. Examples include sodium di (2-ethylhexyl) sulfosuccinate, sodium alkyl naphthalene sulfonate fatty acid, monoalkyl sulfate, alkyl polyoxyethylene sulfate, alkyl benzene sulfonate, monoalkyl phosphate, and the like.

  Examples of the cationic surfactant include those having an ammonium group, a phosphonium group or an arsonium group as a hydrophilic group. Examples include quaternary ammonium compounds such as tetraalkylammonium salts, alkyltrimethylammonium salts, dialkyldimethylammonium salts, alkylbenzyldimethylammonium salts, tetraalkylphosphonium alkyltrimethylammonium salts, dialkyldimethylammonium salts, alkylbenzyldimethylammonium salts, etc. Is mentioned.

  More specifically, quaternary ammonium such as octyltrimethylammonium chloride, octyltrimethylammonium bromide, octyltrimethylammonium hydroxide, decyltrimethylammonium chloride, decyltrimethylammonium bromide, decyltrimethylammonium hydroxide, n-hexadecyltrimethylammonium bromide, etc. A halogen salt or hydroxide of can be preferably used.

  Examples of the zwitterionic surfactant include amine oxide and carboxybetaine, and examples thereof include alkyldimethylamine oxide and alkylcarboxybetaine. 1 type may be used for said ionic surfactant and it may use 2 or more types together.

  Each of the above raw materials is dispersed in a basic aqueous liquid. By making the aqueous liquid basic, the silicate compound and aluminate are easily converted into silicate ions and aluminate ions, respectively. Examples of the alkali agent added to obtain a basic aqueous liquid include metal hydroxides such as sodium hydroxide, potassium hydroxide and aluminum hydroxide, water-soluble amine compounds such as aqueous ammonia, trimethylamine and triethylamine, and tetrahydroxide. Examples include organic ammonium compounds such as alkyl ammonium. Preferably, sodium hydroxide, potassium hydroxide, etc. are used.

  In the above dispersion step, other additives such as a pH adjuster may be contained as long as the effects of the present invention are not impaired, and means for promoting dispersion / dissolution of the raw material components may be appropriately added.

  The addition order of each raw material may be simultaneous, and after dispersing a silicic acid raw material and an aluminate raw material in a basic aqueous liquid, a nonionic surfactant and an ionic surfactant may be added. However, once the aluminosilicate skeleton is formed by the silicic acid raw material and the aluminate raw material, it becomes extremely difficult to define micropores and mesopores thereafter. Therefore, it is preferable that the nonionic surfactant and the ionic surfactant are added before the aluminosilicate skeleton starts to be formed. From the above viewpoint, it is preferable that the nonionic surfactant and the ionic surfactant are immediately added after the silicic acid raw material and the aluminate raw material are sufficiently dispersed in the basic aqueous liquid. During the addition of the nonionic surfactant and the ionic surfactant, the temperature of the dispersion solution is preferably 25 to 100 ° C, more preferably 60 to 90 ° C.

[Heat treatment process]
By heat-treating the dispersion, an aluminosilicate skeleton is formed and zeolite particles can be generated. The zeolite particles contain a nonionic surfactant or an ionic surfactant in their pores. By agitation before hydrothermal synthesis, the nonionic surfactant is contained in the pores in a state of surrounding small bubbles. Further, the ionic surfactant is contained in the pores in a state of surrounding large bubbles.

  The reaction temperature of hydrothermal synthesis is preferably 80 to 200 ° C, more preferably 100 to 200 ° C, and further preferably 160 to 180 ° C. The reaction pressure is preferably 0.3 to 1 MPa. The reaction time is preferably 1 to 5 hours, more preferably 2 to 4 hours. When the range of the above preferable reaction conditions is exceeded, there are cases where zeolite particles of a type suitable for the present invention cannot be formed.

  After completion of hydrothermal synthesis, the obtained zeolite particles are separated from the aqueous liquid by a method such as filtration and solid-liquid separation, and then washed with water to remove organic ions, metal ions, and the like of the surfactant. Further, the zeolite particles are dried to remove the nonionic surfactant and the ionic surfactant contained in the pores of the zeolite particles. As the drying method, heat treatment is preferable. In this case, the heating conditions are preferably a temperature increase rate of 1 to 20 ° C./min, a heating temperature of 400 to 600 ° C., and a heating time of 1 to 10 hours.

  The present invention is provided with a mesoporous structure having micropores having an average major axis of 0.4 to 0.5 nm and mesopores having an average major axis of 4 to 5 nm by further drying after removing the nonionic surfactant and the ionic surfactant. Predetermined zeolite particles can be obtained. The heating temperature during drying is preferably 350 to 500 ° C, and more preferably 400 to 500 ° C.

[Supporting process]
Subsequently, a transition metal is supported on the obtained zeolite particles. As a supporting method, a conventionally known impregnation method, vapor deposition method, or the like can be applied.

  In the case of applying the impregnation method, the above-mentioned zeolite particles finely divided to have an average particle diameter of 5 to 300 nm are added to a dispersion solution in which a transition metal compound as a transition metal source is dispersed in an organic solvent. The addition amount of the transition metal compound as a transition metal source is preferably 0.1 to 40 parts by mass and more preferably 1 to 30 parts by mass with respect to 100 parts by mass of the zeolite particles. When the amount is less than 0.1 parts by mass, the amount of transition metal supported in the resulting ammonia synthesis catalyst is reduced, and sufficient catalytic activity cannot be obtained. When it exceeds 40 parts by mass, the transition metal that cannot be supported remains in the dispersion solution. The organic solvent is not particularly limited as long as it can uniformly disperse the zeolite particles and the transition metal source, and specific examples include hexane and heptane.

  The dispersion is heat-treated in an inert gas stream or under vacuum to remove the solvent, and then dried to obtain a catalyst precursor in which zeolite particles are impregnated with a transition metal compound. The treatment temperature is preferably 50 to 200 ° C., and the treatment time is preferably 30 minutes to 5 hours.

  The obtained catalyst precursor is subjected to reduction treatment by heating in an inert gas stream or in vacuum. A preferred treatment temperature is 30 to 80 ° C. Thus, the transition metal is supported on the aluminosilicate skeleton of the zeolite particles, and the ammonia synthesis catalyst of the present invention can be obtained.

The obtained ammonia synthesis catalyst is formed into pellets, granules, spheres, tablets, etc., and applied to the ammonia synthesis method described below. However, pelletization is not essential. The ammonia synthesis catalyst uses zeolite particles having a mesoporous structure having micropores having an average major axis of 0.2 to 0.5 nm and mesopores having an average major axis of 4 to 5 nm and having a bulk density of 0.5 to 2.0 g / cm ^3. Therefore, the toughness is good. Therefore, the ammonia synthesis catalyst of the present invention is less likely to collapse during the ammonia synthesis reaction and has little deterioration. Therefore, it has excellent catalytic activity over a long period.

[Ammonia synthesis method]
The ammonia synthesis method of the present invention is a method of synthesizing ammonia by directly reacting hydrogen and nitrogen using the above-described predetermined ammonia synthesis catalyst. In the synthesis method of the present invention, ammonia can be synthesized under a reaction condition that satisfies at least one of a temperature condition of 250 to 350 ° C. and a pressure condition of 0.1 to 1 MPa. The reaction rate during synthesis is 20 to 300 μmolg ⁻¹ h ⁻¹ , preferably 60 to 300 μmolg ⁻¹ h ⁻¹ .

  In the ammonia synthesis method of the present invention, ammonia can be efficiently synthesized by bringing hydrogen and nitrogen into contact with the predetermined ammonia synthesis catalyst. The ammonia synthesis catalyst used in the present invention uses a zeolite particle having a predetermined mesoporous structure as a carrier, and therefore, reaction conditions satisfying at least one of a temperature condition of 250 to 350 ° C. and a pressure condition of 0.1 to 1 MPa. It is possible to carry a large amount of a supported metal that exhibits good catalytic activity. Therefore, the ammonia synthesis method of the present invention is suitable when the reaction is performed under reaction conditions that satisfy at least one of temperature conditions of 250 to 350 ° C. and pressure conditions of 0.1 to 1 MPa.

  FIG. 3 is a schematic diagram of an example of an ammonia synthesis apparatus to which the ammonia synthesis method of the present invention is applied. In FIG. 3, 1 is an ammonia synthesizer, 2 is a reactor, and 3 is a catalyst layer. The catalyst layer 3 of the reactor 2 is filled with pellets obtained by molding the predetermined ammonia synthesis catalyst of the present invention. Hydrogen and nitrogen are passed through the reactor 2 to react hydrogen and nitrogen to synthesize ammonia. Usually, hydrogen and nitrogen are passed through the reactor 2 as a mixed gas. The molar ratio of hydrogen to nitrogen in the mixed gas is preferably 1: 3. The aeration rate of the mixed gas reactor is preferably 30 to 180 ml / min.

  The temperature condition in the reactor is preferably 250 to 350 ° C, more preferably 280 to 330 ° C. The pressure condition is preferably 0.1 to 1 MPa. The temperature condition and the pressure condition may satisfy at least one, and more preferably satisfy both. The ammonia synthesis catalyst of the present invention suitably exhibits its catalytic activity under the above reaction conditions, and can effectively advance the ammonia synthesis reaction. The synthesized ammonia can be recovered through a conventionally known cooling step or adsorption step.

The reaction rate according to the ammonia synthesis method of the present invention is 20 to 300 μmol g ⁻¹ h ⁻¹ , preferably 60 to 300 μmol g ⁻¹ h ⁻¹ . In the present invention, the predetermined ammonia synthesis catalyst is less deteriorated and maintains the above reaction rate for a long time. By using the ammonia synthesis method of the present invention, the ammonia synthesis reaction can be carried out continuously for at least 1 to 8 hours. it can.

  In the ammonia synthesis method of the present invention, ammonia synthesis can be carried out under reaction conditions satisfying at least one of a temperature condition of 250 to 350 ° C. and a pressure condition of 0.1 to 1 MPa. Therefore, it is not necessary to provide the ammonia synthesizer with equipment for meeting high temperature and high pressure conditions, and the burden of maintenance can be reduced.

  The present invention will be further described below using examples. However, the present invention is not limited to the following examples.

<Manufacture of ammonia synthesis catalyst>
In a resin beaker, 252 g of ion-exchanged water and 11.0 g of polyethylene glycol (molecular weight 6000, manufactured by Tokyo Chemical Industry Co., Ltd.) are dissolved. Next, 2.5 g of sodium hydroxide (Katayama Chemical Co., Ltd.) is added and dissolved sufficiently. Further, 14.3 g of sodium aluminate (manufactured by Sumitomo Chemical Co., Ltd., NaOH: 26.1% by mass, Al ₂ O ₃ : 18.5% by mass, water: 55.4% by mass) was added and stirred well, and hydrous silicate powder (Nippon Silica Industry Co., Ltd.) 41.9 g of SiO ₂ : 93.3% by mass, water: 6.7% by mass). Subsequently, 2.0 g of an ionic surfactant (sodium di (2-ethylhexylsulfosuccinate)) and 2.0 g of a nonionic surfactant (polyoxyethylene sorbitan monostearate, trade name: Tween 60, manufactured by Tokyo Chemical Industry Co., Ltd.) are added. Mix using a shaker at 60 ° C. for 20 minutes until the raw material is homogeneously dispersed to obtain a raw material slurry.

  The obtained raw slurry is put into a stainless steel autoclave having a capacity of 500 ml, and heated at 170 ° C. for 71 hours with sufficient stirring. Water is removed from the precipitated product by heat treatment using a centrifuge (3000 rpm). The product is washed thoroughly with distilled water. The product is heated to 400 ° C. for 1 hour and dried to obtain a white fired product. The fired product is referred to as fired product A.

  In the measurement of the diffraction pattern of the fired product A by the X-ray diffraction method, the X-ray diffraction pattern of the mordenite-type zeolite can be confirmed. Moreover, it can confirm that the baked product A is a porous block-shaped nanoparticle by observation with a scanning electron microscope.

50 particles are randomly selected from the fired product A, and the major axis and particle size of the pores that can be confirmed on the surface of each particle are measured. The average major axis of the micropores and the average major axis of the mesopores of each particle are calculated by defining the pores on the surface of each particle as micropores having a major axis of 2 nm or less and those having a major axis exceeding 2 nm as mesopores. In that case, the average major axis of the micropores of each particle of the fired product A is 0.2 to 0.5 nm, and the average major axis of the mesopores is 4 to 5 nm. The particle size of the 50 particles is 60 nm. The average specific surface area according to the BET method is 5 m ² / g. The specific surface area can be measured using a flow type specific surface area automatic measuring device FlowSorb III 2310 or the like.

  The calcined products B to H are obtained in the same manner as the production step of the calcined product A except that the silicic acid raw material, the aluminate raw material, the ionic surfactant, and the nonionic surfactant are added in the amounts shown in FIG. . FIG. 2 shows the identification results of the fired products A to H, the mesopore average major axis, the micropore average major axis, the average particle size, the bulk density, and the specific surface area.

<Manufacture of ammonia synthesis catalyst>
[Example 1]
Ru ₃ (CO) ₁₂ is dissolved in hexane, the Ru ₃ (CO) ₁₂ solution and the zeolite particles of the calcined product A are added, and the mixture is stirred and dispersed in the solution. Thereafter, the solution containing the zeolite particles of the calcined product A and Ru ₃ (CO) ₁₂ is heat-treated at 200 ° C. for 30 minutes in a vacuum, and the solvent is removed and dried to obtain a catalyst precursor. The catalyst precursor is further reduced by heat treatment at a treatment temperature of 400 ° C. and a treatment time of 3 hours, and Ru is supported on cesium aluminosilicate to obtain the ammonia synthesis catalyst of Example 1.

[Example 2-6, Comparative Example 1-6]
The ammonia synthesis catalysts of Example 2-6 and Comparative Example 1-6 can be manufactured under the same conditions as in Example 1 except that the materials shown in Tables 1 and 2 are selected for the fired product and the transition metal source. As γ-Al ₂ O ₃ shown in Table 2, 5% Ru alumina powder AA-4501 manufactured by NECCHEMCAT can be used. As activated carbon, NECCHEMCAT 5% Ru carbon powder (water-containing product) A type can be used.

<Ammonia synthesis>
The ammonia synthesis catalyst of Example 1-6 and Comparative Example 1-6 was molded into a disk-shaped pellet having a diameter of 2 cm, 0.3 g was packed in a U-shaped glass tube, and the inner volume of the glass tube with the glass tube was closed by 200 ml. Install in the circulatory system. As a pretreatment, H ₂ 200 Torr was introduced into the closed circulation system and allowed to flow at 400 ° C. for 3 hours, and then a N ₂ / H ₂ mixed gas having a molar ratio of 1: 3 was passed through the closed circulation system to perform an ammonia synthesis reaction. . The reaction conditions are a reaction temperature of 400 ° C. and a reaction pressure of 1 MPa. Tables 1 and 2 list the reaction rates of Example 1-6 and Comparative Example 1-6, respectively.

The reaction rates described in Table 1 and Table 2 were determined based on the relationship between the surface area of the mesoporous material disclosed in Document 1-4 and the reaction rate. Documents 1-4 discuss the catalytic reaction using a mesoporous material having a simple oxide or composite oxide as a skeleton component as a catalyst carrier.
[Reference 1]
Y. Takahara, D. Lu, JN Kondo and K. Domen, “Synthesis and application for overall water splitting of transition metal-mixed mesoporous Ta oxide”, Proc. SSP2000, Solid State Ionics, 151 (1-4), 305- 311 (2002).
[Reference 2]
B. Lee, D. Lu, JN Kondo and K. Domen, “Effect of cations addition for the highly ordered mesoporous niobium oxide”, Stud. Surf. Sci. Catal., Proc. IMMS, 146, 323-327 (2003) .
[Reference 3]
JN Kondo, M. Uchida, K. Nakajima, D. Lu, M. Hara and K. Domen, “Synthesis, mesostructure and photocatalysis of a highly ordered and stably stable mesoporous ternary (Ma-Ta) oxide”, Chem. Mater. , 16 (22), 4304-4310 (2004).
[Reference 4]
Y. Takahara, JN Kondo, T. Takata, D. Lu and K. Domen, "Mesoporous Ta oxide: (1) characterization and photocatalytic activity for overall water decomposition", Chem. Mater., 13 (4), 1194-1199 (2001).

1 Ammonia synthesis device 2 Reactor 3 Catalyst layer

Claims (6)

  An ammonia synthesis catalyst obtained by supporting a transition metal having ammonia synthesis activity on zeolite particles having an aluminosilicate skeleton and having a mesoporous structure. Zeolite particles having an aluminosilicate skeleton, having a mesoporous structure having micropores having an average major axis of 0.2 to 0.5 nm and mesopores having an average major axis of 4 to 5 nm, and having a bulk density of 0.5 to 2.0 g / cm ³ 2. The ammonia synthesis catalyst according to claim 1, wherein a transition metal having ammonia synthesis activity is supported. Zeolite particles having an aluminosilicate skeleton, having a mesoporous structure having micropores having an average major axis of 0.2 to 0.5 nm and mesopores having an average major axis of 4 to 5 nm, and having a bulk density of 0.5 to 2.0 g / cm ³ And a method for producing an ammonia synthesis catalyst, comprising a supporting step of supporting a transition metal having ammonia synthesis activity.   A dispersion step of dispersing a silicic acid raw material, an aluminate raw material, a nonionic surfactant, and an ionic surfactant in a basic aqueous liquid, and heat-treating the dispersion solution obtained in the dispersion step to be nonionic A heat treatment step for producing zeolite particles containing a surfactant and an ionic surfactant, and washing and heating the zeolite particles to remove the nonionic surfactant and the ionic surfactant from the zeolite particles. 4. The method for producing an ammonia synthesis catalyst according to claim 3, comprising a surfactant removing step and a loading step of loading a transition metal having ammonia synthesis activity on the zeolite particles. Zeolite particles having an aluminosilicate skeleton, having a mesoporous structure having micropores having an average major axis of 0.2 to 0.5 nm and mesopores having an average major axis of 4 to 5 nm, and having a bulk density of 0.5 to 2.0 g / cm ³ An ammonia synthesis method in which ammonia is synthesized by reacting hydrogen and nitrogen using an ammonia synthesis catalyst in which a transition metal having ammonia synthesis activity is supported.   6. The ammonia synthesis method according to claim 5, wherein ammonia is synthesized under a reaction condition that satisfies at least one of a temperature condition of 250 to 350 ° C. and a pressure condition of 0.1 to 1 MPa.