Nanocomposite materials, catalyst materials, and methods for manufacturing nanocomposite materials

Abstract

To provide a nano-composite material in which pores are regularly arranged.SOLUTION: The nano-composite material is a pores-regularly arranged nano-composite material that contains a noble metal, at least one of an alkali metal and an alkaline earth metal, and porous alumina, and in which the noble metal is contained inside the porous alumina, the alkali metal and the alkaline earth metal are supported on the porous alumina containing the noble metal inside, and the mode value in the pore size distribution is diameter 1 to 200 nm.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a technology of nanocomposite materials used for, for example, catalyst materials and adsorption materials for producing ammonia.

Background Art

[0002] Among aluminas, transition aluminas typified by γ-alumina are preferred as carriers for catalyst materials and adsorption materials because they have a high specific surface area in addition to surface characteristics. As methods for increasing the specific surface area of transition aluminas, in addition to particle refinement and morphology control, pore formation is known. By compounding a noble metal species such as platinum with porous alumina, it is possible to prevent aggregation and outflow of the noble metal species, and a suitable material as a catalyst material or an adsorption material can be synthesized.

[0003] For example, Patent Document 1 discloses a technique for synthesizing porous alumina containing platinum by a freeze-drying method. Porous alumina can maximize the specific surface area by regularly arranging and packing pores with a uniform pore diameter on the nanometer scale in the densest manner. As a method for synthesizing such porous alumina with a high specific surface area, there is a method in which an amphiphilic organic molecule is self-organized and then the amphiphilic organic molecule is removed to form pores.

[0004] However, the porous alumina synthesized by this method has a problem that the porous structure collapses and the specific surface area decreases due to the collapse during the process of compounding with a noble metal species.

[0005] Therefore, in Non-Patent Document 1 and Non-Patent Document 2, a method has been proposed to prevent the occurrence of collapse of the porous structure and decrease in specific surface area by adding a noble metal species together with an amphiphilic organic molecule to the precursor solution of porous alumina.

[0006] In addition to precious metals, composite materials formed by combining alkali metals or alkaline earth metals with alumina are known to chemically adsorb nitrogen oxides (NOx) in the gas phase by forming nitrates or nitrites with the alkali metals or alkaline earth metals. Such composite materials are called NSR catalysts (NOx Storage-Reduction Catalysts), and are particularly used for the purpose of purifying automobile exhaust gases.

[0007] Therefore, for example, it is conceivable that alkali metals and alkaline earth metals, in addition to precious metal species, could be compounded with alumina using the technologies described in Patent Document 1, Non-Patent Document 1, and Non-Patent Document 2. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Patent No. 5019526 [Non-patent literature]

[0009] [Non-Patent Document 1] Physical Chemistry Chemical Physics 2011, 13, 2488-2491. A facile route to ordered mesoporous-alumina-supported catalysts, and their catalytic activities for CO oxidation [Non-Patent Document 2] Nature Communications 2017, 8, 16100. Thermally stable single atom Pt / m-Al2O3 for selective hydrogenation and CO oxidation [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] However, when using Patent Document 1, Non-Patent Document 1, and Non-Patent Document 2, it is conceivable that alkali metals or alkaline earth metals, in addition to precious metal species, may be added to alumina to affect the porous structure (for example, the pores may be irregularly arranged). Taking these circumstances into consideration, the present invention provides a nanocomposite material in which the pores are regularly arranged. [Means for solving the problem]

[0011] The nanocomposite material according to the present invention is a nanocomposite material having regularly arranged pores, comprising a noble metal, at least one of an alkali metal and an alkaline earth metal, and porous alumina, wherein the noble metal is contained within the porous alumina, and the alkali metal and alkaline earth metal are supported on the porous alumina containing the noble metal, and the mode of the pore size distribution is a diameter of 1 to 200 nm. [Effects of the Invention]

[0012] According to a preferred embodiment of the present invention, the nanocomposite material has regularly arranged pores. Therefore, it is possible to increase the specific surface area. Consequently, it exhibits high performance as a catalyst material, for example, when producing ammonia from nitrogen oxides (NOx). [Brief explanation of the drawing]

[0013] [Figure 1] The diffraction pattern according to Example 1 is shown. [Figure 2] The diffraction pattern according to Example 2 is shown. [Figure 3] The diffraction pattern for Example 3 is shown. [Figure 4] The diffraction pattern according to Example 4 is shown. [Figure 5] The diffraction pattern according to Example 5 is shown. [Figure 6] The diffraction pattern according to Example 6 is shown. [Figure 7] The diffraction pattern according to Example 7 is shown. [Figure 8]Shows the diffraction pattern according to Comparative Example 1.

Mode for Carrying Out the Invention

[0014] <Nanocomposite Material> The nanocomposite material according to the present invention contains a noble metal (nanoparticle), at least one of an alkali metal and an alkaline earth metal, and porous alumina.

[0015] The nanocomposite material according to the present invention is suitably used, for example, as a catalyst material for producing ammonia from nitrogen oxides (NOx). For example, after adsorbing nitrogen oxides (NOx) to the nanocomposite material (catalyst material), ammonia is produced by reducing the nitrogen oxides with a reducing gas.

[0016] The porous alumina used in the nanocomposite material is particulate porous alumina (mesoporous alumina) having a crystal structure. This porous alumina is produced by drying and sintering a precursor solution containing monomers and oligomer species of alumina and its hydrates and amphiphilic organic molecules by a process described later. During sintering, the amphiphilic organic molecules disappear and a porous structure with pores regularly arranged is formed.

[0017] The average particle size of the porous alumina is, for example, 0.01 to 500 μm, preferably 0.1 to 100 μm, and more preferably 0.5 to 50 μm. By setting the average particle size of the porous alumina within the above range, it is possible to achieve both efficient gas diffusion and easy handling of the material. The average particle size of the porous alumina is the volume-based cumulative average particle size (median diameter) measured by a particle size distribution measuring device.

[0018] The precious metals are contained within the porous alumina. Hereafter, porous alumina containing precious metals will be referred to as "precious metal-containing porous alumina." Specifically, precious metal-containing porous alumina refers to a state in which particulate precious metals are embedded within the spherical particles of porous alumina, forming a composite. Therefore, some of the precious metal nanoparticles are exposed within the porous structure, while others are embedded within the alumina framework.

[0019] In this invention, precious metals may be contained in porous alumina as pure precious metals, as precious metal compounds containing precious metals, or both. In the following description, the term "precious metal" includes both pure precious metals and precious metals in precious metal compounds.

[0020] The precious metals (elemental precious metals) contained within the porous alumina are one or more of the following: gold, silver, platinum, palladium, rhodium, iridium, ruthenium, osmium, and rhenium. When the precious metals are contained within the porous alumina as precious metal compounds, the precious metal compounds are either these elemental precious metals or oxides. From the viewpoint of improving catalytic activity, one or more of the precious metals from platinum, palladium, rhodium, and iridium are preferred, and one or more of the precious metals from platinum and rhodium are even more preferred. Note that multiple types of each precious metal may be contained within the porous alumina.

[0021] The average particle size of the precious metal is, for example, 0.1 to 100 nm, preferably 10 to 50 nm. By keeping the average particle size of the precious metal and precious metal compounds within the above range, it is possible to achieve both the oxidation reaction characteristics of the circulating gas and the durability of the catalyst.

[0022] The average particle size of the precious metal is the mode (mode diameter) determined by measuring the particle size of a predetermined number of particles (e.g., 100 particles) using a transmission electron microscope.

[0023] The content of precious metals (precious metal elements in the nanocomposite material) is 0.01 to 20% by mass of the total nanocomposite material, preferably 0.05 to 15.0% by mass, and more preferably 0.1 to 10.0% by mass. By keeping the precious metal content within the above range, catalytic activity can be improved. Furthermore, the amount of expensive precious metals used can be reduced.

[0024] Alkali metals and alkaline earth metals are incorporated into nanocomposite materials in a state where they are supported on porous alumina containing precious metals. The alkali metals and alkaline earth metals supported on the porous alumina containing precious metals are coated onto the already formed porous structure and are mainly present on the surface of the porous alumina and precious metals.

[0025] In the present invention, alkali metals and alkaline earth metals are typically supported on precious metal-containing porous alumina as compounds containing at least one of the alkali metal and alkaline earth metal (hereinafter referred to as "alkali metal-alkaline earth metal compounds"). However, configurations in which the alkali metal and alkaline earth metal are supported on precious metal-containing porous alumina as individual elements are not excluded from the present invention.

[0026] The alkali metal and alkaline earth metal compounds supported on porous alumina containing precious metals are, for example, oxides, peroxides, carbonates, and hydroxides of alkali metals and alkaline earth metals.

[0027] Furthermore, in alkali metal / alkaline earth metal compounds, when multiple types of alkali metals and alkaline earth metals are included, two or more types may be selected from alkali metals alone, two or more types may be selected from alkaline earth metals alone, or one or more types may be selected from alkali metals and one or more types from alkaline earth metals. Furthermore, one type of alkali metal / alkaline earth metal compound may be supported on porous alumina containing precious metals, or multiple types may be supported on porous alumina containing precious metals.

[0028] The alkali metals used in alkali metal and alkaline earth metal compounds are one or more of lithium, sodium, potassium, rubidium, cesium, and francium. From the viewpoint of improving the reduction efficiency of nitrogen oxides, one or more of lithium, potassium, sodium, and cesium are preferred, and one or more of potassium and sodium are even more preferred.

[0029] The alkaline earth metals used in alkali metal and alkaline earth metal compounds are one or more of beryllium, magnesium, calcium, strontium, barium, and radium. From the viewpoint of improving the reduction efficiency of nitrogen oxides, one or more of magnesium, calcium, strontium, and barium are preferred, and one or more of calcium and barium are even more preferred.

[0030] The total content of alkali metals and alkaline earth metals (alkali metal elements and alkaline earth metal elements in the nanocomposite material) is 0.1 to 50% by mass of the entire nanocomposite material, preferably 0.5 to 40% by mass, and more preferably 1 to 30% by mass. By keeping the content of alkali metals and alkaline earth metals within the above range, it is possible to improve the reduction efficiency of nitrogen oxides while maintaining a uniformly arranged pore structure.

[0031] The average particle size of the nanocomposite material according to the present invention (a composite material containing porous alumina, noble metal nanoparticles, and alkali metals / alkaline earth metals) is, for example, 0.01 to 500 μm, preferably 0.1 to 100 μm, and more preferably 0.5 to 50 μm. The average particle size of the nanocomposite material is the volume-based cumulative average particle size (median diameter) measured by a particle size distribution analyzer.

[0032] The specific surface area of ​​nanocomposite materials is, for example, 100 to 350 m². 2 The amount is / g, preferably 120-330m 2 / g, and more preferably 150-300m 2The specific surface area is / g. Nanocomposite materials with a specific surface area within the above range can, for example, adsorb gases (e.g., nitrogen oxides) with high efficiency. The specific surface area of ​​the nanocomposite material is measured by the BET multipoint method.

[0033] The mode of the pore size distribution of nanocomposite materials is, for example, 1 to 200 nm in diameter, preferably 1 to 50 nm, and more preferably 2 to 20 nm in diameter. Nanocomposite materials with a mode of pore size distribution within the above range can, for example, adsorb gases (e.g., nitrogen oxides) with high efficiency.

[0034] The pore volume of nanocomposite materials is, for example, 0.2 to 1.5 cm³. 3 The value is / g, preferably 0.3 to 1.2 cm 3 The density is / g, and more preferably 0.5-0.9cm 3 The value is / g. Nanocomposite materials with average pore diameter and pore volume within the above range can, for example, adsorb gases (e.g., nitrogen oxides) with high efficiency.

[0035] The mode of the pore size distribution in nanocomposite materials is measured, for example, by the NLDFT method using gas adsorption. Similarly, the pore volume of nanocomposite materials is measured, for example, by gas adsorption.

[0036] The nanocomposite material according to the present invention exhibits at least one of a diffraction peak and a scattering peak corresponding to a lattice plane spacing of 1 to 200 nm, obtained by irradiation with X-rays. The diffraction peak is measured by X-ray diffraction. The scattering peak is measured by small-angle X-ray scattering. Specifically, in the X-ray diffraction measurement, one or more diffraction peaks corresponding to a lattice plane spacing of 1 to 200 nm are observed, and in the small-angle X-ray scattering measurement, one or more scattering peaks corresponding to a lattice plane spacing of 1 to 200 nm are observed.

[0037] For X-ray generating tubes, Fe is preferable because its characteristic X-ray wavelength is long, the diffraction or scattering peak appears at high angles, making detection easy, and its intensity is sufficient for the detector. However, tubes using other elements (e.g., Cu) are also acceptable. The presence of these diffraction and scattering peaks reveals the regular arrangement of pores in the porous structure.

[0038] In nanocomposite materials in which one or more diffraction or scattering peaks corresponding to lattice plane spacings of 1 to 200 nm are observed, a high specific surface area and uniform gas diffusion behavior within the pores can be expected due to the presence of a regular arrangement of pores with uniform pore sizes in the porous structure.

[0039] <Method for manufacturing nanocomposite materials> The following describes an example of a method for manufacturing nanocomposite materials. The nanocomposite material according to the present invention is generally manufactured by synthesizing porous alumina containing a precious metal (precious metal-containing porous alumina) and supporting alkali metals or alkaline earth metals on the precious metal-containing porous alumina.

[0040] <1> Preparation of Precursor Solution A precious metal-containing precursor solution (hereinafter simply referred to as "precursor solution") is a solution containing an alumina source, a precious metal source, an amphiphilic organic molecule, an acid, and a solvent.

[0041] As the alumina source (aluminum compound) used in the precursor solution, a transition alumina (alumina with a crystal structure other than α) such as γ-alumina is used upon calcination. Specifically, examples of alumina sources include aluminum hydroxide, aluminum nitrate, aluminum sulfate, aluminum chloride (including hydrate), and aluminum alkoxide, but aluminum alkoxide is preferred. Examples of aluminum alkoxides include aluminum (tri-sec-butoxide), aluminum (tri-n-butoxide), aluminum (tri-tert-butoxide), aluminum (tri-iso-propoxide), aluminum (tri-ethoxide), and aluminum (tri-phenoxide). Among these, aluminum chloride (including hydrate), aluminum (tri-sec-butoxide), and aluminum (tri-n-butoxide) are preferred from the viewpoint of reactivity to hydrolysis, availability, and raw material cost, and aluminum (tri-sec-butoxide) is particularly preferred.

[0042] Examples of precious metal sources included in the precursor solution include one or more oxides, hydroxides, chlorides, carbonates, acetates, nitrates, oxalates, phosphates, and chloride complexes from among gold, silver, platinum, palladium, rhodium, iridium, ruthenium, osmium, and rhenium. From the viewpoint of improving catalytic activity, it is preferable to use one or more precious metal sources from among platinum, palladium, rhodium, and iridium.

[0043] As platinum sources, for example, inorganic platinum compounds such as chloroplatinic acid (including hydrate), dinitrodiammineplatin, hexahydroxyplatinic acid, platinum monochloride, platinum dicchloride, tetraammineplatinate dichloride, potassium tetrachloroplatinate, and potassium hexachloroplatinate can be used, as well as organic platinum compounds such as bis(acetylacetonato)platinum, dichloro(cyclohexane)platinum dimer, dichloro(η-ethylene)Pt dimer, dichloro(η-cycloocta-1,5-diene)platinum, tetrakis(triphenylphosphite)platinum, cis-dichlorobis(triphenylphosphine)platinum, bis(benzonitrile)dichloroplatinum, trans-d-cyclohexanediaminedichloroplatinum, and trans-l-cyclohexanediaminedichloroplatinum can be used. These may be used individually or in combination of multiple types. Among these, chloroplatinic acid (including hydrate) or bis(acetylacetonate)platinum is particularly preferred from the viewpoint of solubility in the solvent during the preparation of the precursor solution.

[0044] Examples of palladium sources include palladium chloride, palladium acetate, tetrakistriphenylphosphine palladium, tris(dibenzylideneacetone)dipalladium, and allyl palladium chloride dimer. Examples of ligands include bis[2-(diphenylphosphino)phenyl] ether (DPEphos), triphenylphosphine, 1,1'-bis(diphenylphosphino)ferrocene (dppf), 4,5'-bis(diphenylphosphino)-9,9'-dimethylxanthene (xanthophos), and 1,3-di-tert-butylimidazolium. These may be used individually or in combination.

[0045] Examples of rhodium sources include rhodium chloride, dirhodium tetraacetate dihydrate, rhodium acetate, rhodium isobutyrate, rhodium 2-ethylhexanoate, rhodium benzoate, and rhodium octanoate. These may be used individually or in combination.

[0046] Examples of iridium sources include iridium chloride, iridium sulfate, iridium nitrate, iridium nitrite, ammonium hexachloroiridiate, hexachloroiridiate n-hydrate, chlorocarbonylbis(triphenylphosphine)iridium, and sodium iridium chloride n-hydrate. These can be used individually or in combination.

[0047] As the amphiphilic organic molecule used in the precursor solution, one or more of the following can be used: polyethylene oxide-polypropylene oxide-polyethylene oxide block copolymer (trade name: Pluronic®), alkylammonium salt, polystyrene-polyethylene oxide block copolymer, etc. Among these, from the viewpoint of forming a regularly arranged porous structure, at least one of polyethylene oxide-polypropylene oxide-polyethylene oxide block copolymer and polystyrene-polyethylene oxide block copolymer is particularly preferred, and Pluronic P123 and F127 are even more preferred.

[0048] The pore size of porous alumina varies greatly depending on the type of amphiphilic organic molecule. When polyethylene oxide-polypropylene oxide-polyethylene oxide block copolymer is used as the amphiphilic organic molecule, the mode of the pore size distribution is 2-30 nm. Furthermore, when polystyrene-polyethylene oxide block copolymer is used as the amphiphilic organic molecule, the mode of the pore size distribution is 25-200 nm (see: "Bulletin of the Chemical Society of Japan, 2019, 92, 1859-1866.", "Dalton Transactions, 2021, 50, 7191-7197.").

[0049] Inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid, as well as organic acids such as carboxylic acids and sulfonic acids, can be used as the acids in the precursor solution. Among these, it is particularly preferable to include at least one of hydrochloric acid and nitric acid from the viewpoint of forming a regularly arranged porous structure.

[0050] As solvents used in the precursor solution, alcohols, ethers, water, ketones, etc., can be used. In particular, various alcohols can be used, including ethanol, methanol, n-butanol, sec-butanol, tert-butanol, n-propanol, and iso-propanol. Among these, ethanol is particularly preferred from the viewpoint of forming a regular porous structure by optimizing the evaporation rate of the solvent.

[0051] The content of the alumina source (aluminum compound) in the precursor solution is 5 to 25% by mass, preferably 8 to 20% by mass, and more preferably 10 to 15% by mass.

[0052] The content of the precious metal source is 0.01 to 0.20% by mass of the precursor solution, preferably 0.03 to 0.20% by mass, and more preferably 0.05 to 0.10% by mass.

[0053] The content of amphiphilic organic molecules is 1 to 20% by mass of the precursor solution, preferably 2 to 15% by mass, and more preferably 3 to 10% by mass.

[0054] The acid content is 0.1 to 3.0% by mass of the precursor solution, preferably 0.3 to 2.0% by mass, and more preferably 0.5 to 1.5% by mass.

[0055] The solvent content is 50 to 93% by mass of the precursor solution, preferably 60 to 90% by mass, and more preferably 70 to 80% by mass.

[0056] An example of a specific method for preparing the precursor solution is as follows (1)-(3).

[0057] (1) After adding an amphiphilic organic molecule to the solvent, a noble metal source is added. (2) Add the aluminum source to the solvent to prepare a dispersion. Add the acid dropwise over a predetermined time (e.g., 10 minutes or more) while stirring the dispersion. Stir the dispersion for a predetermined time (e.g., 3 hours). (3) A precursor solution is prepared by adding the dispersion from (2) to the solution prepared in (1).

[0058] <2> Synthesis of porous alumina containing precious metals One example of a method for synthesizing porous alumina containing precious metals is as follows (1)(2).

[0059] (1) The precursor (powder) of precious metal-containing porous alumina is recovered from the precursor solution. First, the solvent and water are removed from the precursor solution by drying. The method of drying the precursor solution is not particularly limited, but examples include one or more combinations of any known method such as spray drying, freeze-drying, heat drying, hot air drying, vacuum drying, and natural drying. Among these, spray drying is particularly preferred in terms of productivity and reproducibility. The precursor solution is dried and the precursor (powder) of precious metal-containing porous alumina is recovered.

[0060] (2) Precious metal-containing porous alumina is synthesized by calcining the recovered precursor. Calcining the precursor removes the amphiphilic organic molecules that served as templates for the pores, resulting in porous material, while thermal decomposition of the precious metal source and crystallization of the alumina occur. Calcining of the precursor is carried out by holding it at a desired temperature (e.g., 800-900°C) under a nitrogen stream for a predetermined time (e.g., 1-3 hours), and then holding it at the same temperature under an oxygen stream for a further predetermined time (e.g., 2-3 hours). It is preferable to raise the temperature gradually (e.g., 1-3°C per minute) until the desired temperature is reached under a nitrogen stream.

[0061] <3> Supporting of alkali metals and alkaline earth metals At least one of an alkali metal and an alkaline earth metal is supported on a synthesized porous alumina containing precious metals as an alkali metal-alkaline earth metal compound.

[0062] The alkali metals and alkaline earth metals used in this invention are as described above.

[0063] To support alkali metals and alkaline earth metals on porous alumina containing precious metals, compounds such as acetates, nitrates, carbonates, hydroxides, halides, oxides, and hydrides (hereinafter referred to as "precursor compounds") containing at least one of the alkali metals and alkaline earth metals are used. Among these, at least one of acetates and nitrates is preferred from the viewpoint of solubility and thermal decomposition temperature. The precursor compounds are converted into alkali metal / alkaline earth metal compounds by thermal decomposition upon heating.

[0064] An example of a method for supporting alkali metals and alkaline earth metals on porous alumina containing precious metals is as follows (1)-(3). For example, alkali metals and alkaline earth metals are supported on porous alumina containing precious metals by impregnation.

[0065] (1) Disperse the precious metal-containing porous alumina in distilled water, and add an aqueous solution of the precursor compound dropwise while stirring vigorously.

[0066] An aqueous solution of the precursor compound is added dropwise so that the content of alkali metal and alkaline earth metal elements in the nanocomposite material is, for example, 0.1 to 50% by mass, preferably 0.5 to 40% by mass, and more preferably 1 to 30%. By adding the aqueous solution of the precursor compound dropwise so that the mass ratio of alumina to alkali metal / alkaline earth metal compound in the precious metal-containing porous alumina is within the above range, the nitrogen oxide storage characteristics and reduction efficiency can be improved.

[0067] (2) Heat the dispersion from (1) under reduced pressure to remove distilled water and obtain a powder. For example, remove distilled water from the dispersion by vacuum distillation at 30-80°C.

[0068] (3) The powder obtained in (2) is dried and then calcined to obtain the nanocomposite material according to the present invention. The powder obtained in (2) is dried, for example, at 80 to 120°C for 6 to 20 hours. The dried powder is then calcined, for example, in a tubular furnace at 400 to 700°C for 2 to 5 hours.

[0069] Nanocomposite materials are manufactured by the above manufacturing method. The manufacturing method according to the present invention has the advantage of being able to produce nanocomposite materials in a short period of time and with high productivity compared to, for example, a method in which a precursor solution is spread in a container such as a petri dish and dried at a predetermined temperature for several days.

[0070] By manufacturing nanocomposite materials using the above manufacturing method, the mode of the pore size distribution becomes a diameter of 1 to 200 nm. Furthermore, nanocomposite materials with a mode of pore size distribution of 1 to 200 nm can facilitate the smooth diffusion and absorption of nitrogen oxides in the gas phase. In addition, the pore size distribution of the nanocomposite material can be controlled depending on the type of amphiphilic organic molecule selected and the synthesis conditions, and the balance between the diffusion of nitrogen oxides within the pores and the specific surface area of ​​the nanocomposite material can also be adjusted.

[0071] In the nanocomposite material according to the present invention, by supporting at least one of an alkali metal and an alkaline earth metal on porous alumina containing a precious metal, it is possible to improve the amount of nitrogen oxide adsorption while also improving the reduction efficiency of nitrogen oxides.

[0072] The nanocomposite material according to the present invention is capable of maintaining a regularly arranged pore structure. Therefore, it can maintain a high specific surface area. [Examples]

[0073] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0074] <Example 1> Example 1 is a nanocomposite material in which barium is supported on porous alumina containing platinum. The mass ratio of platinum, barium, and porous alumina (platinum:barium:porous alumina) is 1:10:100.

[0075] Example 1 is as follows: <1> - <3> It was prepared according to the instructions.

[0076] <1> Preparation of platinum-containing porous alumina precursor solution (1) 15 g of Pluronic P123 (polyethylene oxide-polypropylene oxide-polyethylene oxide block copolymer) was weighed into a stoppered Erlenmeyer flask, 120 mL of ethanol was added, and then 0.135 g of chloroplatinic acid hexahydrate was added, and the mixture was stirred with a magnetic stirrer and a stirring bar.

[0077] (2) Add 60 mL of ethanol and 24.6 g of aluminum (tri-sec-butoxide) to a three-necked flask to prepare a dispersion. While continuing to stir the dispersion, add concentrated hydrochloric acid (14.5 mL) dropwise over more than 10 minutes and stir for 3 hours.

[0078] (3) The dispersion from (2) was added to the solution from (1) to prepare a platinum-containing porous alumina precursor solution.

[0079] <2> Synthesis of platinum-containing porous alumina (1) A platinum-containing porous alumina precursor solution was introduced into a spray dryer (Yamato Scientific ADL311), and the water containing ethanol was removed by hot air drying along with the spraying of the precursor solution. The inlet temperature of the spray dryer was set to 170°C. After that, the platinum-containing porous alumina precursor was recovered using a cyclone separator.

[0080] (2) The precursor recovered by the cyclone separator was calcined in a tubular furnace to remove the Pluronic P123 that had formed the mold for the pores, thereby creating a porous structure, as well as to perform thermal decomposition of the platinum compound (hexahydrate chlorplatinic acid) and crystallization of alumina. The calcination was carried out by raising the temperature to 850°C at a rate of 2°C per minute under a nitrogen stream, holding it at the same temperature for 1 hour, and then holding it at the same temperature for another 2 hours under an oxygen stream.

[0081] <3> Barium support on platinum-containing porous alumina

[0082] As described above, barium is supported on platinum-containing porous alumina as a barium compound (in Example 1, this is a barium compound produced by the thermal decomposition of barium acetate, such as barium carbonate, barium oxide, and barium hydroxide).

[0083] Specifically, the barium compound was loaded onto platinum-containing porous alumina by an impregnation loading method.

[0084] (1) Platinum-containing porous alumina was dispersed in distilled water, and barium acetate aqueous solution was added dropwise while vigorously stirring. The barium acetate aqueous solution was added dropwise so that the mass ratio of platinum-containing porous alumina to barium in the barium acetate aqueous solution (platinum-containing porous alumina:barium) was 101:10.

[0085] (2) After shaking the dispersion from (1) for 1 hour, the dispersion was transferred to a round-bottom flask, and the distilled water was removed under reduced pressure at 60°C using a rotary evaporator to recover the powder. The powder was further dried at 110°C for more than 10 hours, and then calcined in a tubular furnace at 500°C for 3 hours (heating rate: 10°C per minute, under a dry air stream) to obtain a nanocomposite material consisting of platinum-containing porous alumina on which a barium compound was supported.

[0086] The average particle size of platinum (nanoparticles) in the platinum-containing porous alumina was 24 nm. The average particle size of the platinum was determined by transmission electron microscopy using a JEOL JEM-2010 microscope, measuring the size of 100 precious metal nanoparticles, and determining the mode (mode diameter) of the particle size.

[0087] <Example 2> Example 2 is a nanocomposite material in which calcium is supported on porous alumina containing platinum. The mass ratio of platinum, calcium, and porous alumina (platinum:calcium:porous alumina) is 1:10:100.

[0088] The procedure is the same as in Example 1, except that an aqueous solution of calcium acetate monohydrate was used instead of an aqueous solution of barium acetate.

[0089] In Example 2, as well, calcium is supported on platinum-containing porous alumina as a calcium compound by impregnation and support.

[0090] <Example 3> Example 3 is a nanocomposite material in which magnesium is supported on porous alumina containing platinum. The mass ratio of platinum, magnesium, and porous alumina (platinum:magnesium:porous alumina) is 1:10:100.

[0091] The procedure is the same as in Example 1, except that an aqueous solution of magnesium acetate tetrahydrate was used instead of an aqueous solution of barium acetate.

[0092] In Example 3, too, magnesium is supported on platinum-containing porous alumina as a magnesium compound by impregnation support.

[0093] <Example 4> Example 4 is a nanocomposite material in which strontium is supported on porous alumina containing platinum. The mass ratio of platinum, strontium, and alumina was 1:10:100.

[0094] The procedure is the same as in Example 1, except that an aqueous solution of strontium acetate 0.5 hydrate was used instead of an aqueous solution of barium acetate.

[0095] In Example 4, as well, strontium is supported on platinum-containing porous alumina as a strontium compound by impregnation support.

[0096] <Example 5> Example 5 is a nanocomposite material, similar to Example 1, in which barium is supported on porous alumina containing platinum.

[0097] The procedure is the same as in Example 1, except that 0.101 g of platinum acetylacetonate was used instead of hexahydrate chlorplatinic acid as the precious metal source.

[0098] In Example 5, as well, barium is supported on platinum-containing porous alumina as a barium compound by impregnation support.

[0099] <Example 6> Example 6 is a nanocomposite material in which barium is supported on porous alumina containing palladium. The mass ratio of palladium, barium, and porous alumina is 1:10:100.

[0100] The procedure is the same as in Example 1, except that 0.085 g of palladium chloride was used instead of hexahydrate chlorplatinic acid as the precious metal source, and 0.1 mL of concentrated hydrochloric acid was added to dissolve the palladium chloride in the ethanol solution.

[0101] In Example 6, as well, barium is supported on palladium-containing porous alumina as a barium compound by impregnation support.

[0102] <Example 7> Example 7 is a nanocomposite material in which barium is supported on porous alumina containing rhodium, and the mass ratio of rhodium, barium, and porous alumina is 1:10:100.

[0103] The procedure is the same as in Example 1, except that 0.131 g of rhodium chloride was used instead of hexahydrate chlorplatinate as the precious metal source.

[0104] In Example 7, as well, barium is supported on rhodium-containing porous alumina as a barium compound by impregnation support.

[0105] <Comparative Example 1> Comparative Example 1 is a material in which both platinum (nanoparticles) and barium are supported on commercially available γ-alumina (manufactured by Strem Chemicals). Comparative Example 1 was prepared as follows (1)-(4).

[0106] (1) γ-alumina was pretreated at 500°C for 2 hours in a stream of dry air. (2) Using an ethanol solution of hexachloroplatinic acid hexahydrate, the γ-alumina and platinum from (1) were mixed so that the mass ratio was 100:1. (3) After evaporating the ethanol to dryness, the platinum-supported γ-alumina was prepared by calcining it at 600°C for 3 hours in a stream of dry air. (4) Barium species were supported on the platinum-supported γ-alumina obtained in (3) in the same manner as in Example 1. The mass ratio of platinum-supported γ-alumina to barium atoms was 101:10.

[0107] Examples and comparative examples are as follows: <1> - <3> We conducted an evaluation regarding this.

[0108] <1> Mode of pore size distribution Samples (Examples 1-7, Comparative Example 1) were heated under reduced pressure at 110°C for 6 hours to remove adsorbed water and other substances. Nitrogen adsorption isotherms were then measured using Quantachrome's Autosorb-1 or Autosorb-iQ. The pore size distribution was calculated from the adsorption isotherms using the NLDFT method (software: Quantachrome's AS1Win; NLDFT kernel: N2 at 77K on Carbon, slit pore, NLDFT equilibrium model), and the mode of the pore size distribution was identified.

[0109] <2> X-ray diffraction measurement X-ray diffraction measurements were performed on the samples (Examples 1-7, Comparative Example 1) using a RIGAK RINT 2100 (Fe source, scanning angle: 0.6 to 12 degrees, scanning speed: 2 degrees per minute) to confirm whether diffraction peaks corresponding to lattice plane spacings of 1 to 200 nm could be detected. Figures 1-8 show the diffraction patterns for Examples 1-7 and Comparative Example 1.

[0110] <3> Ammonia production test from nitrogen oxides (NOx) The tests were conducted using a fixed-bed flow reactor. 100 mg of each sample (Examples 1, 2, and Comparative Example 1) was placed inside a quartz reaction tube, and both ends were secured with quartz wool. The gas flow rate was fixed at 100 mL / min throughout the test.

[0111] As a pretreatment step, the sample temperature was set to 500°C and held for 1 hour in a nitrogen gas stream containing 10% oxygen to remove any remaining moisture and organic matter.

[0112] Next, as a NOx adsorption step, the sample temperature was set to 300°C and held for 1 hour in a nitrogen gas stream containing 1000 ppm nitric oxide (NO) and 10% oxygen. Subsequently, as an ammonia production step, the sample was held for 1 hour in a nitrogen gas stream containing 1% hydrogen.

[0113] In subsequent tests, the pretreatment step was omitted, and only the NOx adsorption step and the ammonia production step were repeatedly tested. The amount of NOx adsorbed and the amount of ammonia produced were quantified using a Thermo Fisher Scientific Nicolet iS 20 infrared spectrophotometer and a PIKE Technologies multiple reflection gas cell.

[0114] Table 1 shows the mode of the pore size distribution and the lattice plane spacing indicated by the diffraction peaks obtained by X-ray diffraction measurements.

[0115] [Table 1]

[0116] As can be seen from Table 1, in Examples 1-7, the mode of the pore size distribution was in the range of 1 to 200 nm in diameter, and diffraction peaks corresponding to lattice plane spacings of 1 to 200 nm were observed. In other words, it was confirmed that the pores in Example 1-7 were regularly arranged. In Example 1-7, it is thought that the pores are regularly arranged by the self-assembly of amphiphilic organic molecules that chemically interact with the alumina source, followed by the removal of the amphiphilic organic molecules by calcination.

[0117] In contrast, no diffraction peaks corresponding to the lattice plane spacing were observed in Comparative Example 1. This indicates that the pores in Comparative Example 1 are not arranged regularly.

[0118] Table 2 shows the results of ammonia production tests from nitrogen oxides (NOx). Table 2 shows the amount of NOx adsorbed, the amount of ammonia produced from NOx, and the ammonia yield (ammonia production amount / NOx adsorbed amount). The NOx adsorbed amount and NH3 production amount per unit mass were calculated from the catalyst weight after the ammonia production tests.

[0119] [Table 2]

[0120] As shown in Table 2, in Examples 1 and 2, the ammonia yield did not decrease even after the second use, and in Example 2 in particular, it increased with each use. In contrast, in Comparative Example 1, the ammonia yield decreased drastically after the second use.

[0121] As can be understood from the above explanation, the nanocomposite material according to the present invention makes it possible to repeatedly produce ammonia with high efficiency.

[0122] Furthermore, no N2O was observed in Examples 1 and 2.

[0123] In this context, a technology has been proposed to reduce nitrogen oxides (NOx) in exhaust gas to nitrogen using a catalytic material (NSR catalyst). It is known that ammonia is produced as an intermediate product, and N2O is also generated. However, since N2O has a greenhouse effect approximately 300 times greater than CO2, it is preferable to produce as little N2O as possible. Furthermore, the amount of N2O produced can increase depending on the catalytic material used.

[0124] The nanocomposite material according to the present invention makes it possible to produce ammonia from nitrogen oxides (NOx) (in other words, reduce nitrogen oxides to ammonia) while sufficiently reducing the amount of N2O produced. Specifically, in the nanocomposite material according to the present invention, the concentration of N2O produced together with ammonia is below the measurable concentration range.

[0125] The nanocomposite material according to the present invention is particularly suitable for use as a catalyst material in the production of ammonia. The method of producing ammonia using the nanocomposite material is arbitrary. For example, as in the ammonia production test described above, ammonia may be produced by adsorbing NOx onto the nanocomposite material by flowing in nitrogen gas containing NOx, followed by a switch to a reducing gas, or ammonia may be produced by simultaneously flowing in nitrogen gas and a reducing gas.

[0126] The nanocomposite material according to the present invention can be used for purposes other than as a catalyst material for ammonia production. For example, it can be used as an NSR catalyst, NOx adsorbent, oxidation catalyst, and the like.

Claims

1. A nanocomposite material having regularly arranged pores, comprising a precious metal, at least one of an alkali metal and an alkaline earth metal, and porous alumina, The aforementioned precious metal has an average particle size of 10 to 50 nm and is contained within the porous alumina. The alkali metals and alkaline earth metals are supported on the porous alumina containing the noble metals internally. The mode in the pore size distribution is a diameter of 1 to 200 nm. Nanocomposite materials.

2. At least one of the diffraction peaks and scattering peaks corresponding to lattice plane spacings of 1 to 200 nm, obtained by irradiating with X-rays, is observed. The nanocomposite material according to claim 1.

3. The aforementioned precious metal is one or more of platinum, palladium, rhodium, and iridium. The nanocomposite material according to claim 1 or claim 2.

4. The content of the aforementioned precious metal is 0.01 to 20.0% by mass of the entire nanocomposite material, with the total mass being 100%. A nanocomposite material according to any one of claims 1 to 3.

5. The alkali metal is one or more selected from lithium, potassium, sodium, and cesium. The alkaline earth metal is one or more selected from calcium, magnesium, strontium, and barium. A nanocomposite material according to any one of claims 1 to 4.

6. The content of the alkali metals and alkaline earth metals is 0.1 to 50.0% by mass of the nanocomposite material as 100% by mass. A nanocomposite material according to any one of claims 1 to 5.

7. A catalyst material for producing ammonia from nitrogen oxides, comprising the nanocomposite material according to any one of claims 1 to 6.

8. A method for producing a nanocomposite material according to any one of claims 1 to 6, A first step involves recovering a precursor of porous alumina containing a precious metal by removing the solvent and water from a precursor solution containing a precious metal source, an alumina source, an amphiphilic organic molecule, an acid, and a solvent. A second step involves calcining the recovered precursor to synthesize porous alumina containing the precious metal, The process includes a third step of supporting at least one of an alkali metal and an alkaline earth metal on porous alumina containing the aforementioned precious metal, In the second step, the precursor is calcined by holding it at 800-900°C under a nitrogen stream and then further holding it under an oxygen stream. Manufacturing method.

9. At least one of polyethylene oxide-polypropylene oxide-polyethylene oxide block copolymer and polystyrene-polyethylene oxide block copolymer is used as the amphiphilic organic molecule. The manufacturing method according to claim 8.

Images