Sub-nanoparticle inclusion complex and its manufacturing method

Abstract

To provide a sub-nanoparticle inclusion complex that promote the spread of sub-nanoparticle in industries such as catalysts from a cost perspective, and to provide a method for producing the same, and particularly to provide a sub-nanoparticle inclusion complex that is suitable for use in organic solvent, suppresses agglomeration and has small particle size distribution.SOLUTION: The sub-nanoparticle inclusion complex of the present invention is characterized in that the sub-nanoparticles are included in branched polyethyleneimine having a number average molecular weight of 500 to 12,000 and having a fatty acid ionically bonded thereto.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to sub-nanoparticle inclusion bodies and methods for their production. [Background technology]

[0002] In recent years, the catalytic activity of nanoparticles composed of precious metal elements such as platinum and gold has attracted attention. Meanwhile, the synthesis of sub-nanoparticles, which have fewer atoms and are smaller in size than nanoparticles, has been reported. These sub-nanoparticles, approximately 1 nm in size, are composed of only a few dozen atoms or less, and exhibit large and discrete band gaps due to quantum size effects, as well as unique geometric structures specific to the elements. These sub-nanoparticles possess aspects that cannot be captured by the conventional concept of nanoparticles, which has been discussed based on simple structural features such as size and shape. They are therefore expected to exhibit catalytic activity and reaction selectivity superior to that of nanoparticles.

[0003] The present inventors have explored and developed a method for producing subnanoparticles using phenylazomethine dendrimers as templates (Non-Patent Documents 1 and 2, Patent Documents 1 to 5). Phenylazomethine dendrimers form metal salt complexes in a stepwise manner, preferentially starting with the innermost imine due to an electron density gradient in which the electron density of imines increases from the terminal imines toward the center. This enables precise heterometallic integration, including single-component systems such as platinum salts, binary systems using two metal salts, where different metal species are integrated in each layer, and even multi-component systems with three, four, or five metal salts. Dendrimer complexes with a specified number and composition of metal salts can be prepared. By reducing these metal salt-coordinated dendrimer complexes, precisely controlled metal subnanoparticles with extremely narrow particle size distribution can be formed. It has been reported that these platinum and other sub-nanoparticles exhibit oxygen reduction catalytic activity per equivalent that is far higher than that of conventional nanoparticles, and the present inventors are investigating the use of platinum sub-nanoparticle supports, templated using phenylazomethine dendrimers, as catalysts for hydrocarbon oxidation reactions.

[0004] Currently, catalysts for purifying automobile exhaust gases and fuel cells are primarily made of precious metals such as platinum, palladium, and rhodium. However, these materials face challenges such as price fluctuations and high costs, prompting calls for alternatives from major companies. Furthermore, the global chemical market involving catalytic technology is extremely large, and the resulting social and economic impacts are immeasurable. Therefore, if catalyst development can advance beyond precious metals such as platinum, it could potentially solve the problem of rare element depletion. In particular, if inexpensive, highly catalytically active sub-nanoparticle catalysts centered on copper can be developed, they could be used in a variety of applications, including the development of catalysts for purifying automobile exhaust gases and fuel cell catalysts, as well as the development of catalysts for the chemical conversion of lower alkanes into alcohols, which are considered a next-generation resource gas.

[0005] Phenylazomethine dendrimers have the advantage of being able to precisely control the number of atoms, but their synthesis costs are currently high, and there has been a need for technology that can cost-effectively promote their widespread use in industries such as sub-nanoparticle catalysts.

[0006] Branched polyethyleneimines, like phenylazomethine dendrimers, have multiple complex-forming sites, and the synthesis of complexes using them as templates and nano- to sub-nano-sized metal particles by their reduction has been reported (Non-Patent Documents 3-5). However, unlike phenylazomethine dendrimers, they do not have a regular electron density gradient in which the electron density of the imines increases from the terminal imines toward the center, and the synthesized particles have a wide particle size distribution. There are structural challenges in precisely controlling the number of metal elements, as with phenylazomethine dendrimers. Non-Patent Document 3 describes the formation of a complex by adding copper sulfate to a solution of branched polyethyleneimine with a molecular weight of 10 K. Although the relationship between the concentration and the absorption wavelength suggests pentadentate coordination, the relationship between the equivalent number and the absorption wavelength has not been clarified.

[0007] Non-Patent Document 4 describes the stabilization of large gold nanoparticles with branched polyethyleneimine. Branched polyethyleneimine has a large molecular weight of 25,000 and is synthesized by reducing HAuCl4 in a PEI aqueous solution. There is no disclosure about the synthesis of subnanoparticles.

[0008] Non-Patent Document 5 describes that graphene oxide (GO) and branched polyethyleneimine (PEI) with a molecular weight of 600 were mixed and supported in pure water, and platinum salt and cobalt salt were added to the GO-PEI support in water, followed by reduction with sodium borohydride to obtain an alloy with a particle size of 2.3 nm. [Prior art documents] [Non-patent literature]

[0009] [Non-Patent Document 1] K. Yamamoto et al. Angew. Chem. Int. Ed. 2015, 54, 9810-9815. [Non-patent document 2] K. Yamamoto et al. Sci. Adv. 2017, 3, e1700101. [Non-patent document 3] J. Organomet. Chem. 2019,898, 120881 [Non-patent document 4] Colloids and Surfaces A: Physicochem. Eng. Aspects 2013,419, 80-86 [Non-patent document 5] RSC Adv., 2014, 4, 41152-41158 [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-23166 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-18610 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-159588 [Patent Document 4] Japanese Patent Application Publication No. 2017-087151 [Patent Document 5] International Publication No. 2018 / 159505 Summary of the Invention [Problem to be solved by the invention]

[0011] Polyethyleneimine is cheaper than conventional dendrimers, and sub-nanoparticles templated using it are expected to be widely used in industry. However, to achieve this, it is necessary to establish a synthesis method that can precisely control the number of metal atoms in the sub-nanoparticle range, that is, a method that controls the number of atoms to a narrower distribution than a random statistical distribution. To achieve this, a protective effect that suppresses aggregation is necessary. Furthermore, conventional catalytic reactions often use organic solvents, and their application is required.

[0012] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a sub-nanoparticle inclusion complex that will promote the widespread use of sub-nanoparticle catalysts and the like in industries from a cost perspective, and a method for producing the same, and in particular, a sub-nanoparticle inclusion complex that is suitable for use in organic solvents, inhibits aggregation, and has a narrow particle size distribution. [Means for solving the problem]

[0013] As a result of extensive research to solve the above problems, the present inventors discovered that metal subnanoparticles with a narrow particle size distribution can be obtained using an inexpensive template, branched polyethyleneimine, which has a large number of nitrogen atoms in the polymer chain, similar to dendrimers, and that particle aggregation can be suppressed by introducing fatty acids, which are fat-soluble functional groups, and thus completed the present invention.

[0014] That is, the sub-nanoparticle clathrate of the present invention is characterized in that sub-nanoparticles are encapsulated in branched polyethyleneimine having a number average molecular weight of 500 to 12,000 and having a fatty acid ionically bonded thereto. The present invention also provides a sub-nanoparticle support in which the sub-nanoparticle inclusion complex is supported on a carrier, and an oxidation reaction catalyst comprising the sub-nanoparticle inclusion complex.

[0015] The method for producing a subnanoparticle inclusion complex in which subnanoparticles are encapsulated in branched polyethyleneimine according to the present invention is characterized by comprising the following steps: A step of coordinating a reducing metal element in a pentadentate configuration to a nitrogen site in a branched polyethyleneimine having a number average molecular weight of 500 to 12,000 to produce an aggregate of the metal element; and a step of reducing the aggregate of metal elements in the presence of a reducing agent while the aggregate is dissolved in an organic solvent, thereby producing sub-nanoparticles of the metal elements; This production method may further include a step of mixing the sub-nanoparticle inclusion complex with a fatty acid in a liquid, and ionically bonding the fatty acid to the branched polyethyleneimine. [Effects of the Invention]

[0016] The subnanoparticle inclusion complex of the present invention uses a branched polyethyleneimine template, which is less expensive than conventional dendrimers, and by introducing fatty acids, which are fat-soluble functional groups, aggregation is suppressed, resulting in subnanoparticles with a narrow particle size distribution. The number of atoms can be controlled depending on the molecular weight of the branched polyethyleneimine. This subnanoparticle inclusion complex forms fat-soluble micelles by introducing fatty acids, making it suitable for catalytic reactions in organic solvents. When used as a catalyst, aggregation of the subnanoparticles is suppressed even during catalytic reactions, allowing for repeated use and long-term continuous operation. [Brief explanation of the drawings]

[0017] [Figure 1] (a) shows the absorption spectrum at each equivalent when CuSO4 is added dropwise to an aqueous solution of Epomin R (SP-006), a commercially available branched polyethyleneimine (PEI), and (b) shows the absorption spectrum at each equivalent when CuSO4 is added dropwise to an aqueous solution of Epomin (R) (SP-018). The inset shows an enlarged view around a wavelength of 620 nm, and (c) shows the relationship between absorbance at 620 nm and the number of copper sulfate equivalents. [Figure 2](a) shows the absorption spectrum at each equivalent when CuBr2 acetonitrile solution (30 mM) was added dropwise to (SP-018) acetonitrile solution (30 μM), (b) shows an enlarged view around a wavelength of 720 nm, and (c) shows the relationship between absorbance at 720 nm and the number of copper sulfate equivalents. [Figure 3] (a) shows the absorption spectrum at each equivalent when CuBr2 acetonitrile solution (30 mM) was added dropwise to Epomin(R) (SP-200) acetonitrile solution (30 μM), (b) is an enlarged view around a wavelength of 735 nm, and (c) shows the relationship between absorbance at 735 nm and the number of copper sulfate equivalents. [Figure 4] (a) shows the absorption spectrum at each equivalent when a PtBr2 acetonitrile solution (10 mM) is dropped into an (SP-018) acetonitrile solution (10 μM), (b) is an enlarged view around a wavelength of 281 nm, and (c) shows the relationship between the absorbance at 281 nm and the number of copper sulfate equivalents. [Figure 5] (a) shows the absorption spectrum at each equivalent when a PtBr2 acetonitrile solution (10 mM) is dropped into an (SP-200) acetonitrile solution (10 μM), (b) is an enlarged view around a wavelength of 282 nm, and (c) shows the relationship between the absorbance at 282 nm and the number of copper sulfate equivalents. [Figure 6] (a) shows the absorption spectrum at each equivalent when CuBr2 and PtBr2 acetonitrile solutions (CuBr2: 30 mM, PtBr2: 10 mM) are dropped into an (SP-200) acetonitrile solution (30 μM), (b) is an enlarged view around a wavelength of 731 nm, and (c) shows the relationship between absorbance at 731 nm and the number of copper sulfate equivalents. [Figure 7] (a) shows the absorption spectrum at each equivalent when SnCl2 2-acetoxy-1-methoxypropane solution (30 mM) was added dropwise to (SP-018) 2-acetoxy-1-methoxypropane solution (30 μM), (b) is an enlarged view around a wavelength of 250 nm, and (c) shows the relationship between absorbance at 250 nm and the number of copper sulfate equivalents. [Figure 8]This is a scanning transmission electron microscope (STEM) image of a sample in which a Cu@PEI complex (PEI:SP-200) was reduced with sodium borohydride in an aqueous solution. [Figure 9] (a) Particle size distribution of Cu clusters in a KB-supported sample prepared by reducing a Cu@PEI complex (PEI:SP-018) with sodium borohydride in an organic solvent. (b) Scanning transmission electron microscope (STEM) image of the Cu clusters. [Figure 10] The following clusters were prepared by reducing Cu, Pt, and PtCu@PEI complex (PEI:SP-018) with sodium borohydride in an organic solvent: (1) KB-supported copper cluster KB / Cu10, (2) KB-supported platinum cluster KB / Pt10, and (3) KB-supported platinum-copper cluster KB / Pt5Cu5. The left and center images are scanning transmission electron microscope (STEM) images, and the right is an energy dispersive X-ray spectroscopy (EDS) spectrum chart. [Figure 11] The following morphological observations are shown for SiO2-supported samples prepared by reducing Cu, Pt, and PtCu@PEI complexes (PEI:SP-018) with sodium borohydride in an organic solvent: (1) SiO2-supported Cu cluster SiO2 / Cu10, (2) SiO2-supported Pt cluster SiO2 / Pt10, and (3) SiO2-supported PtCu cluster Si / Pt5Cu5. The left and center images are scanning transmission electron microscope (STEM) images, and the right is an energy dispersive X-ray spectroscopy (EDS) spectrum chart. [Figure 12] The samples were obtained by reducing an aggregate of metal salts and lauric acid (LA) without using PEI using sodium borohydride. (a) shows the results of morphological observation of a Pt10@LA aggregate. (b) shows the results of morphological observation of a Cu10@LA aggregate. The left, center, and right insets are scanning transmission electron microscope (STEM) images, and the center and right are energy dispersive X-ray spectroscopy (EDS) spectrum charts. [Figure 13]Pt10@SP-018 clusters were untreated (no flocculant), or treated with PVP, stearic acid (SA), or lauric acid (LA), and then loaded onto a carrier. The particle size distribution (left), scanning transmission electron microscope (STEM) images (center and right inset), and energy dispersive X-ray spectroscopy (EDS) spectrum chart (right) are shown. [Figure 14] (a) Untreated Cu10@SP-018 clusters, (b) lauric acid (LA)-treated Cu10@SP-018 clusters, are supported on a support. The particle size distribution (left), scanning transmission electron microscope (STEM) images (center and right inset), and energy dispersive X-ray spectroscopy (EDS) spectrum chart (right) are shown for the samples. [Figure 15] (a) shows the particle size distribution (left), scanning transmission electron microscope (STEM) images (center and right inset), and energy dispersive X-ray spectroscopy (EDS) spectrum chart (right) of samples in which untreated Pt5Cu5@SP-018 clusters are supported on a support, and (b) shows lauric acid (LA)-treated Pt5Cu5@SP-018 clusters are supported on a support. [Figure 16] (a) Untreated Cu52@SP-200 clusters, (b) lauric acid (LA)-treated Cu52@SP-200 clusters, are supported on a support. The particle size distribution (left), scanning transmission electron microscope (STEM) images (center and right inset), and energy dispersive X-ray spectroscopy (EDS) spectrum chart (right) are shown for the samples. [Figure 17] (a) shows the particle size distribution (left), scanning transmission electron microscope (STEM) images (center and right inset), and energy dispersive X-ray spectroscopy (EDS) spectrum chart (right) of samples in which untreated Pt52@SP-200 clusters are supported on a support, and (b) shows Pt52@SP-200 clusters that have been treated with lauric acid (LA). [Figure 18] (a) shows the particle size distribution (left), scanning transmission electron microscope (STEM) images (center and right inset), and energy dispersive X-ray spectroscopy (EDS) spectrum chart (right) of samples in which untreated Pt26Cu26@SP-200 clusters are supported on a support, and (b) shows lauric acid (LA)-treated Pt26Cu26@SP-200 clusters are supported on a support. [Figure 19] Pt52@SP-200 complexes were prepared at SP-200 concentrations of 3 μM (a), 10 μM (b), and 30 μM (c). After reduction, the lauric acid (LA)-treated Pt52@SP-200 clusters were supported on a carrier. The particle size distribution (left), scanning transmission electron microscope (STEM) images (center and right inset), and energy dispersive X-ray spectroscopy (EDS) spectrum chart (right) are shown. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present invention will be described in detail. The sub-nanoparticle inclusion complex of the present invention is a complex in which sub-nanoparticles are included in branched polyethyleneimine to which a fatty acid is ionically bonded.

[0019] In the subnanoparticle inclusion complex of the present invention, the branched polyethyleneimine is a polymer having a branched structure, particularly a hyperbranched structure, containing primary, secondary, and tertiary amines, with a main chain consisting of repeating units of ethylene groups and amino groups, and having repeating units of the structures -(CH2)2-NH-, -(CH2)2-N<.

[0020] The lower limit of the number average molecular weight (Mn) of the branched polyethyleneimine is 500 or more, preferably 600 or more. The upper limit is 12,000 or less, preferably 10,000 or less. If the number average molecular weight is within this range, the number of nitrogen atoms contained in the coordination sites can be set to correspond to the number of sub-nanoparticles, and the number of nitrogen atoms contained can be freely changed. The maximum number of metal elements contained in the pentadentate coordination is 3 for a branched polyethyleneimine with a molecular weight of 600, 6 for a branched polyethyleneimine with a molecular weight of 1,200, 10 for a branched polyethyleneimine with a molecular weight of 1,800, and 52 for a branched polyethyleneimine with a molecular weight of 10,000.

[0021] The number average molecular weight (Mn) of polyethyleneimine can be determined by gel permeation chromatography (GPC), ebulliometry, etc. In the present invention, the number average molecular weight (Mn) used is a value measured by ebulliometry.

[0022] Among the primary amines, secondary amines, and tertiary amines in the branched polyethyleneimine, the proportion of tertiary amines is preferably 5 to 50 mol%, more preferably 10 to 45 mol%. The combined proportion of primary amino groups and secondary amino groups is preferably 50 mol% or more, more preferably 60 mol% or more. Here, the proportions of primary amines, secondary amines, and tertiary amines can be measured by NMR analysis, titration, etc.

[0023] The viscosity of the branched polyethyleneimine is not particularly limited, but is preferably 500 to 150,000 mPa·s at 25°C with a resin content of 98% by mass or more. The amine value of the branched polyethyleneimine is not particularly limited, but is preferably 18 to 20 mmol / g solid.

[0024] The branched polyethyleneimine can be produced by a known method, for example, by polymerizing ethyleneimine. As branched polyethyleneimines, for example, Epomin® SP-006 (number average molecular weight: about 600), SP-012 (number average molecular weight: about 1200), SP-018 (number average molecular weight: about 1800), and SP-200 (number average molecular weight: about 10000) manufactured by Nippon Shokubai Co., Ltd. are commercially available and can be used.

[0025] In the subnanoparticle clathrate of the present invention, the fatty acid is not particularly limited, but one having 12 to 18 carbon atoms is preferred. The fatty acid may be linear or branched, but linear is preferred. The fatty acid is preferably a monocarboxylic acid, and the hydrocarbon moiety is preferably a linear alkyl group. Specific examples include lauric acid, myristic acid, palmitic acid, and stearic acid.

[0026] The subnanoparticle clathrate of the present invention is obtained by ionically bonding a fatty acid to a branched polyethyleneimine. By introducing a fatty acid, which is a fat-soluble functional group, aggregation of metal subnanoparticles is suppressed by micelle formation. Using the branched polyethyleneimine ionically bonded to a fatty acid as a template, particles with a sharp particle size distribution, with a peak particle size corresponding to the number of subnanoparticles, can be synthesized. Furthermore, the compound can be made suitable for use in organic solvents used in catalytic reactions, etc.

[0027] The following is a conceptual diagram of an example of a sub-nanoparticle inclusion complex in which sub-nanoparticles are encapsulated in branched polyethyleneimine ionically bonded to a fatty acid. The branched polyethyleneimine is an aggregate formed by coordinating 10 copper atoms to branched polyethyleneimine with a molecular weight of 1800, which is then reduced to form a sub-nanoparticle inclusion complex; the cluster of black dots in the center represents the sub-nanoparticles.

[0028] [ka]

[0029] The branched polyethyleneimine having a fatty acid ionically bonded thereto can be obtained, for example, by mixing the branched polyethyleneimine with a fatty acid, or by obtaining an inclusion complex in which subnanoparticles are enclosed in the branched polyethyleneimine in an organic solvent, and then mixing the fatty acid into the solution. In the branched polyethyleneimine to which a fatty acid is ionically bonded, the molar ratio of the branched polyethyleneimine to the fatty acid is preferably 1 / 3 to 1 / 100, more preferably 1 / 10 to 1 / 52.

[0030] Subnanoparticles are encapsulated in branched polyethyleneimine ionically bonded to a fatty acid. Conventionally, nanoparticles of platinum and other metals synthesized by reduction under conditions such as simple concentration control or the addition of a carrier have been known to have over 1,000 elements. In contrast, in the present invention, the term "subnano" refers to a particle diameter within the range of, for example, 0.5 to 2 nm, particularly within the range of 0.8 to 1.8 nm. It also encompasses particle groups containing such particles, with a peak of 3.5 nm or less, preferably 3.0 nm or less, in the particle size distribution measured by electron microscopy. Polyhedral atomic groups formed by the direct bonding of several atoms, some or all of which are directly bonded, are generally referred to as clusters, and subnanoparticles are clusters in this sense. It has been confirmed that subnanoparticles synthesized using branched polyethyleneimine as a template can be formed into clusters with a narrow particle size distribution by ionically bonding fatty acids.

[0031] The number of elements in the sub-nanoparticles is, for example, 3 or more, or 6 or more, and, for example, 60 or less, or 52 or less.

[0032] The metal element in the sub-nanoparticles is not particularly limited, and examples thereof include titanium, vanadium, iron, cobalt, nickel, copper, zinc, gallium, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, indium, tin, antimony, hafnium, tantalum, tungsten, osmium, iridium, platinum, gold, and bismuth. Among these, copper, tin, nickel, and alloys of these metals with noble metals are preferred from the viewpoint of industrial applications such as catalysts.

[0033] Subnanoparticles can be either simple substances or alloys. Phenylazomethine dendrimers, a conventional template, are endowed with the ability to control the number of atoms through differences in imine basicity, but branched polyethyleneimine, a versatile polymer, has three amine groups with different basicities (differences in carbon-nitrogen bonds). This provides a pseudo-control function that allows for the control of the number of atoms. Since the number of the three types of amine groups in branched polyethyleneimine can be calculated from structural data, adding an appropriate metal salt forms a branched polyethyleneimine complex with a controlled number of atoms that is narrower than the random statistical distribution. Therefore, it is possible to obtain alloy subnanoparticles in which the number of individual metal elements is controlled.

[0034] The alloy sub-nanoparticles using three types of amine groups with different reactivities are not particularly limited as long as they are made of two or more metal elements, but examples include those made of two or three elements.Specific examples include combinations of two or three elements, such as copper and a noble metal, and examples of noble metals include platinum, palladium, gold, and rhodium.

[0035] The sub-nanoparticle inclusion complex of the present invention can be supported on a carrier to form a sub-nanoparticle support. By supporting the sub-nanoparticles on a carrier, aggregation of the sub-nanoparticles can be suppressed, and a decrease in catalytic activity can be effectively suppressed.

[0036] The shape of the support on which the sub-nanoparticle clathrate is supported is not particularly limited and can be appropriately selected depending on the type of catalyst bed, and may be various shapes such as granular, fibrous, granular, film-like, plate-like, etc. Considering that the surface area per unit weight is large and it is suitable for catalysts, granular (powder-like) shapes are preferred.

[0037] Examples of the support include carbon materials, such as carbon black (e.g., ketjen black, oil furnace black, gas black, acetylene black, lamp black, thermal black, channel black), activated carbon, amorphous (microcrystalline) carbon such as carbon fiber, nanocarbons such as fullerene, nanotube, graphene, and graphene oxide, three-dimensional crystals such as graphite, and graphitized mesoporous carbon. These carbon materials may be porous substances, and the subnanoparticle inclusion bodies can be supported on the pore surfaces. In addition, inorganic materials can be used as the carrier, such as silica gel, alumina, titania, magnesia, zirconia, iron oxide, copper oxide, glass, silica sand, talc, mica, clay, and wollastonite.

[0038] The amount of sub-nanoparticles supported on the carrier is not particularly limited, but considering that a higher amount is needed to increase the reaction efficiency with the substrate when used as a catalyst, it is preferably 0.5 wt% or more, more preferably 1 wt% or more. There is no particular upper limit, but considering that cluster aggregation is less likely to occur, it is preferably 20 wt% or less, more preferably 10 wt% or less.

[0039] The sub-nanoparticle inclusion complex of the present invention can be used as a catalyst either as a solution in which it is dissolved in an organic solvent, or in the form of a support in which the sub-nanoparticle inclusion complex is supported on a support. For example, it can be suitably used as an oxidation reaction catalyst. Examples of the oxidation reaction include the oxygen oxidation reaction of organic compounds, the oxygen oxidation reaction of alcohols, and the oxygen oxidation reaction of alkanes. Oxygen oxidation reactions of organic compounds are carried out in the presence of oxygen using the organic compound as a substrate. Examples of organic compounds that can be used include aromatic and aliphatic hydrocarbon compounds. While such catalytic reactions are typically carried out in organic solvents, the sub-nanoparticle clathrate of the present invention forms fat-soluble micelles through the introduction of fatty acids, making it suitable for catalytic reactions in organic solvents. When used as a catalyst, it suppresses aggregation of the sub-nanoparticles even during catalytic reactions, allowing for multiple repeated use and long-term continuous operation.

[0040] The method for producing a subnanoparticle inclusion complex in which subnanoparticles are encapsulated in branched polyethyleneimine is not particularly limited, but preferably includes the following steps: A step (A) of coordinating a reducing metal element in a pentadentate configuration to a nitrogen site in a branched polyethyleneimine having a number average molecular weight of 500 to 12,000 to produce an aggregate of the metal element; and A step (B) of reducing the aggregate of metal elements in the presence of a reducing agent while the aggregate is dissolved in an organic solvent to produce sub-nanoparticles of the metal elements. The method may further comprise a step (C) of mixing the sub-nanoparticle inclusion complex with a fatty acid in a liquid to ionically bond the fatty acid to the branched polyethyleneimine.

[0041] <Process (A)> In step (A) of producing an aggregate of metal elements, a solution containing branched polyethyleneimine is prepared as the first step. The solvent is not particularly limited as long as it can dissolve the branched polyethyleneimine, the metal salt to be accumulated, and the reducing agent. Examples include aprotic solvents and protic solvents. Among these, aprotic solvents are preferred. The aprotic solvent may be any of aprotic medium-polarity solvents, aprotic high-polarity solvents, and aprotic low-polarity solvents, but aprotic medium-polarity solvents are preferred. These organic solvents may be used alone or in combination of two or more.

[0042] Examples of aprotic medium-polar solvents include nitriles such as acetonitrile and propionitrile; halogenated hydrocarbons such as dichloromethane, dichloroethane, chloroform (trichloromethane), and carbon tetrachloride; ethers such as diethyl ether, tetrahydrofuran, 1,4-dioxane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and triethylene glycol dimethyl ether; ketones such as acetone, 2-butanone, methyl ethyl ketone, isobutyl methyl ketone, diisobutyl ketone, and cyclohexanone; and esters such as ethyl acetate, butyl acetate, propylene glycol monomethyl ether acetate, methyl decanoate, methyl laurate, and diisobutyl adipate. Examples of aprotic highly polar solvents include N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, sulfolane, dihexamethylphosphoric triamide, 1,3-dimethyl-2-imidazolidinone, N,N'-dimethylpropyleneurea, and 1-methyl-2-pyrrolidinone. Examples of aprotic low-polarity solvents include aromatic hydrocarbons such as benzene, toluene, and xylene, and aliphatic hydrocarbons such as pentane, hexane, cyclohexane, and octane. Examples of protic solvents include alcohols such as methanol, ethanol, 2-propanol, 1-butanol, 1,1-dimethyl-1-ethanol, hexanol, and decanol; carboxylic acids such as formic acid and acetic acid; and nitromethane.

[0043] The concentration of the branched polyethyleneimine in the organic solvent solution before mixing with the metal salt is not particularly limited, but is preferably 3 to 200 μmol / L, more preferably 10 to 100 μmol / L.

[0044] In the next step, the metal salt is mixed with an organic solvent solution to obtain an aggregate in which the metal element is accumulated at the nitrogen site of the branched polyethyleneimine. The method for mixing the metal salt with the branched polyethyleneimine solution is not particularly limited, but examples thereof include adding the metal salt solution dropwise to the branched polyethyleneimine solution. The metal salt solution may be prepared, for example, using the organic solvent described above to have a high concentration relative to the branched polyethyleneimine solution.

[0045] When a branched polyethyleneimine and a metal salt are mixed, the metal element coordinates to the complex-forming site of the branched polyethyleneimine and is incorporated into the branched polyethyleneimine. The metal element is surrounded by a tertiary amine and primary and secondary amines branched therefrom, and is regularly pentadentately coordinated by five nitrogen atoms. Therefore, the metal element can be arranged by controlling the equivalent ratio of the branched polyethyleneimine to the metal salt. The metal salt solution is added to the branched polyethyleneimine solution, preferably so that the complex formation is saturated.

[0046] The metal element in the metal salt accumulated on the branched polyethyleneimine is the same as that described above as the metal species of the subnanoparticles. The counter anion or ligand in the metal salt is not particularly limited as long as it is soluble in the organic solvent of the branched polyethyleneimine solution, and examples thereof include halogen ions such as chloride ion, bromide ion, iodide ion, and trifluoroacetate ion, as well as trifluoromethanesulfonic acid, acetic acid, acetylacetone, acetonitrile, salen, cyclopentadiene, and tetrafluoroborate ion.

[0047] <Process (B)> By reducing this metal element aggregate of branched polyethyleneimine, sub-nanoparticles of the metal element can be produced. The reduction of the metal element aggregate of branched polyethyleneimine can be carried out in an organic solvent such as those described above, for example, using a reducing agent that has a reducing effect on metal salts and can reduce them to a zero-valent state.

[0048] The reducing agent is not particularly limited as long as it dissolves in an organic solvent in the solution of the metal element aggregate of branched polyethyleneimine, and examples thereof include sodium borohydride, sodium cyanoborohydride, hydrogen, hydrazines, lithium aluminum hydride, diisobutylaluminum hydride, lithium borohydride, tetra-n-butylammonium borohydride, methylammonium borohydride, lithium triethylborohydride, borane complexes, sodium triacetoxyborohydride, zinc borohydride, lithium tributylborohydride, potassium tributylborohydride, Schwartz reagent, Stryker reagent, tributyltin hydride, sodium hydride, lithium hydride, calcium hydride, benzophenone ketyl radicals, metal naphthalenides, and hydrogen peroxide.

[0049] By reducing the metal element aggregate of branched polyethyleneimine in this manner, subnanoparticles having a size corresponding to the number of accumulated metal elements can be prepared as those encapsulated in branched polyethyleneimine. As examples of branched polyethyleneimine aggregates and subnanoparticle inclusion complexes, two conceptual examples are shown: one in which 10 copper atoms are coordinated to branched polyethyleneimine with a molecular weight of 1,800 to form an aggregate, which is then reduced to form a subnanoparticle inclusion complex; and the other in which 52 copper atoms are coordinated to branched polyethyleneimine with a molecular weight of 10,000 to form an aggregate, which is then reduced to form a subnanoparticle inclusion complex.

[0050] [ka]

[0051] [ka]

[0052] [ka]

[0053] [ka]

[0054] <Process (C)> The sub-nanoparticle clathrate and the fatty acid are mixed in a liquid. The liquid is not particularly limited as long as it can dissolve them. For example, the aforementioned organic solvent can be used as is, and the fatty acid can be added to the organic solvent solution of the sub-nanoparticle clathrate. This ionically bonds the fatty acid to the branched polyethyleneimine.

[0055] The support of the present invention can be obtained by supporting the sub-nanoparticle inclusion complex on a carrier as described above. Supporting on a carrier can be performed, for example, by contacting the carrier with a solution of the sub-nanoparticle inclusion complex dissolved in an organic solvent by mixing with the carrier dispersion, impregnation, coating, dropping, etc., and then drying. A pulverization treatment may be performed as necessary. [Example]

[0056] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples. In the following, the following branched polyethyleneimine was used. Epomin(R) SP-006 Nippon Shokubai Co., Ltd. Number average molecular weight 600 Epomin(R) SP-018 Nippon Shokubai Co., Ltd. Number average molecular weight 1800 Epomin(R) SP-200 Nippon Shokubai Co., Ltd. Number average molecular weight 10,000

[0057] The theoretical copper encapsulation number was determined by titration, in which copper sulfate (CuSO4) was added dropwise to an SP-006 aqueous solution. Figure 1(a) shows the absorption spectrum for each equivalent of CuSO4 added to an SP-006 aqueous solution, and (b) shows the absorption spectrum for each equivalent of SP-018. The ultraviolet absorption (273 nm) is the electron transfer absorption band due to electron transfer between copper and the ligand (amine), while the visible absorption (620 nm) is the ligand field absorption band due to electron transfer of the dd orbital of copper split by the ligand field. A calibration curve was created from the absorbance at 620 nm and the copper sulfate equivalent number (Figure 1(c)). The estimated saturated equivalents for SP-006 (number-average molecular weight 600) and SP-018 (number-average molecular weight 1800) were determined to be 3 and 10, respectively, confirming the complex structure. However, Cu@branched polyethyleneimine did not form clusters even when reduced with sodium borohydride in aqueous solution, as shown in the TEM photograph in Figure 8 .

[0058] Next, the complex structure of metal M (Cu, Pt, PtCu)@branched polyethyleneimine was identified by titration. First, titration was performed using a metal salt (CuBr2, PtBr2) blank. 30 mM CuBr2 was added to acetonitrile (AN) as a solvent, and the absorbance was measured at a wavelength of 635 nm to create a calibration curve. 30 mM PtBr2 was also added to acetonitrile (AN) as a solvent, and the absorbance was measured at a wavelength of 332 nm to create a calibration curve. As expected, the absorbance increased linearly with increasing metal salt equivalents.

[0059] On the other hand, in a titration in which CuBr2 acetonitrile solution (30 mM) was added dropwise to SP-018 acetonitrile solution (30 μM) (Figure 2(a) and (b)), the estimated saturation equivalent of 10 and the complex structure were identified from the calibration curve of absorbance at 720 nm and copper sulfate equivalent (Figure 2(c)).

[0060] In titration, CuBr2 acetonitrile solution (30 mM) was added dropwise to SP-200 acetonitrile solution (30 μM) (Figure 3(a) and (b)). From the calibration curve of absorbance at 735 nm versus copper sulfate equivalents (Figure 3(c)), the estimated saturation equivalent of 52 and the complex structure were identified.

[0061] In titration, a PtBr2 acetonitrile solution (10 mM) was added dropwise to a SP-018 acetonitrile solution (10 μM) (Figures 4(a) and (b)). From the calibration curve of absorbance at 281 nm versus copper sulfate equivalents (Figure 4(c)), an estimated saturation equivalent of 10 and the complex structure were identified.

[0062] In titration, a PtBr2 acetonitrile solution (10 mM) was added dropwise to a SP-200 acetonitrile solution (10 μM) (Figures 5(a) and (b)). From the calibration curve of absorbance at 282 nm versus copper sulfate equivalents (Figure 5(c)), the estimated saturation equivalent of 52 and the complex structure were identified.

[0063] In titration, CuBr2 and PtBr2 acetonitrile solutions (CuBr2: 30 mM, PtBr2: 10 mM) were added dropwise to SP-200 acetonitrile solution (30 μM) (Figures 6(a) and (b)). From the calibration curve of absorbance at 731 nm versus copper sulfate equivalents (Figure 6(c)), the estimated saturation equivalent of 52 and the complex structure were identified.

[0064] In titration, SnCl2 2-acetoxy-1-methoxypropane solution (30 mM) was added dropwise to SP-018 2-acetoxy-1-methoxypropane solution (30 μM) (Figures 7(a) and (b)). From the calibration curve of absorbance at 250 nm versus copper sulfate equivalents (Figure 7(c)), the estimated saturation equivalent of 10 and the complex structure were identified.

[0065] When the Cu@branched polyethyleneimine complex (SP-200) was reduced with sodium borohydride in aqueous solution, a pattern resembling a single copper atom was observed in the STEM image, but no Cu clusters were detected (Figure 8).

[0066] Therefore, we attempted to synthesize metal clusters in an organic solvent system. Following the method for synthesizing sub-nanoparticles using dendrimers as templates developed by the inventors, we synthesized metal@SP-018 clusters supported on the carriers Ketjen Black (KB) or silica (Si). To SP-018 (acetonitrile solution, concentration 30 μM), (1) 10 equivalents of CuBr2 (acetonitrile solution, concentration 3 mM), (2) 10 equivalents of PtBr2 (acetonitrile solution, concentration 3 mM), or (3) 5 equivalents of PtBr2 and 5 equivalents of CuBr2 were added dropwise. 10 , Pt 10 , or Pt5Cu5@SP-018 complex was obtained. The reducing agent, sodium borohydride NaBH4 (methanol solution, concentration 0.3 M), was added to obtain Cu, Pt, or PtCu clusters encapsulated by SP-018. Ketjen black (KB) or silica (SiO2) supports were added to obtain Ketjen black-supported clusters (KB / M) and silica-supported clusters (SiO2 / M). Figure 9(a) shows the particle size distribution of the Cu clusters, and Figure 9(b) shows a STEM image of the Cu clusters. Figure 10 shows (1) KB-supported copper cluster KB / Cu. 10 (2) KB-supported platinum cluster KB / Pt 10 , (3) KB-supported platinum-copper cluster KB / Pt5Cu5 cluster morphology observation results, and Figure 11 shows (1) SiO2-supported Cu cluster SiO2 / Cu 10 (2) Si-supported Pt cluster Si / Pt 10 (3) Morphological observation of SiO2-supported PtCu clusters (SiO2 / Pt5Cu5) is shown. Subnanoparticles consisting of approximately 10 metal atoms were synthesized, but the particle size distribution was still inhomogeneous. Table 1 shows the loading rate of metal clusters on the carrier, determined by ICP (Inductively Coupled Plasma) emission spectroscopy.

[0067] [Table 1]

[0068] Next, xanthene oxidation was carried out according to the following scheme, and silica-supported Cu10 ,Pt 10 The catalytic activity of the Pt5Cu5@SP-018 metal clusters was evaluated. 1 The conversion rate was calculated from the area ratio of XO / (XT+XO+XH) by HNMR (CDCl3). The results are shown in Table 2. 10 ,Pt 10 ,Pt5Cu5@SP-018 metal clusters (3), (4), and (5) are the same as the comparative samples (1), (2), and R 1 , R 2 showed higher catalytic activity than

[0069] [ka]

[0070] [Table 2]

[0071] Next, the effect of anti-aggregation agents on Cu, Pt, and PtCu@SP-018 clusters was verified by particle size distribution. Figure 12 shows a sample in which an association of a metal salt and lauric acid was reduced with sodium borohydride without using branched polyethyleneimine. (a) Pt 10 @LA aggregate, (b)Cu 10 The results of morphological observation of the LA aggregate are shown below. Clusters could not be synthesized from the aggregate of metal and lauric acid. Pt 10 In the Cu@LA aggregate, only traces of PtMα or Lα peaks were detected in the copper cluster-like structure. 10 In the @LA aggregate, no CuKα peak was detected in the copper cluster-like structure, and the copper atoms formed aggregated particles.

[0072] Figure 13 shows the Pt 10@SP-018 clusters were left untreated (no flocculant), or treated with PVP, stearic acid (SA), or lauric acid (LA), and the particle size distribution and morphology of the samples were observed. Treatment with stearic acid (SA) and lauric acid (LA) resulted in small particle sizes and their distribution, demonstrating good anti-flocculation effects.

[0073] Figure 14 shows (a) untreated Cu 10 @SP-018 cluster, (b) Cu treated with lauric acid (LA) 10 Figure 15 shows (a) an untreated Pt5Cu5@SP-018 cluster, (b) a lauric acid (LA)-treated Pt5Cu5@SP-018 cluster, and (c) a Pt5Cu5@SP-018 cluster treated with LA. Figure 16 shows (a) an untreated Cu 52 @SP-200 cluster, (b) Cu treated with lauric acid (LA) 52 @SP-200 clusters, and Fig. 17 shows (a) untreated Pt 52 @SP-200 cluster, (b) Pt treated with lauric acid (LA). 52 @SP-200 clusters, and Fig. 18 shows (a) untreated Pt 26 Cu 26 @SP-200 cluster, (b) Pt treated with lauric acid (LA). 26 Cu 26 The results of particle size distribution and morphology observations of samples in which SP-200 clusters were supported on a carrier are shown. Lauric acid (LA) treatment resulted in smaller particle sizes and distributions than untreated samples, demonstrating a good anti-aggregation effect. In Figure 18, the untreated sample had Cu and Pt single atoms scattered within the SP-200 molecules or formed large nanoparticles.

[0074] Next, Pt 52 @SP-200+LA 52 The optimal preparation concentration of SP-200 was examined to obtain the best cluster aggregation prevention effect. LA-untreated Pt 52 @SP-200 clusters aggregated after being supported on the carrier when the preparation concentration of SP-200 was 30 μM or less. 52The clusters were not synthesized well. 52 The cluster was successfully synthesized under the following conditions: 20 mL of PtBr2 (3 mM, acetonitrile) was added to 100 mL of SP-200 (60 μM, acetonitrile), and the mixture was stirred overnight. 52 12 mL of sodium borohydride (0.3 mM, solvent: methanol) was added to obtain the Pt@SP-200 complex. 52 Got the @SP-200 cluster.

[0075] The acetonitrile solution of SP-200 was diluted to a concentration of 1000 ppm. 52 @SP-200+LA 52 PtBr2 (3 mM in acetonitrile) was added to SP-200 (3, 10, 30 μM in acetonitrile), and the mixture was stirred overnight. 52 Sodium borohydride (0.3 mM, solvent: methanol) was added to obtain the Pt@SP-200 complex. 52 Lauric acid (10 mM, solvent: acetonitrile) was added to obtain the Pt@SP-200 cluster. 52 @SP-200+LA 52 Got a cluster.

[0076] Figure 19 shows the results of Pt at a concentration of 3 μM (a), 10 μM (b), and 30 μM (c) of SP-200. 52 The lauric acid-treated Pt@SP-200 complex was prepared and treated with lauric acid (LA) after reduction. 52 The results of particle size distribution and morphology observation of the sample in which @SP-200 clusters were supported on a carrier are shown. (a) Pt 52 @SP-200 (3 μM) + 52LA has an average particle size of 2.24 nm, (b) Pt 52 @SP-200 (10 μM) + 52LA has an average particle size of 2.76 nm, (c) Pt 52 @SP-200 (30 μM) + 52LA had an average particle size of 2.89 nm, and aggregation was suppressed by LA treatment.

[0077] Next, a xanthene oxidation reaction was carried out according to the above scheme, and the catalytic activity of the Cu@SP-018 / LA cluster was evaluated. 1 The conversion rate was calculated from the area ratio of XO / (XT + XO + XH) by HNMR (CDCl3). TON is the number of moles of XO produced per mole of XT per hour on average. The results are shown in Table 3. 10 The @SP-018 / 10LA cluster exhibited higher catalytic activity than the control samples, both on and off silica.

[0078] [Table 3]

Claims

1. The sub-nanoparticle clathrate is formed by encapsulating sub-nanoparticles made of metal and having a particle size in the range of 0.5 to 2 nm in branched polyethyleneimine having a number average molecular weight of 500 to 12,000 and having a fatty acid ionically bonded thereto.

2. A sub-nanoparticle support, in which the sub-nanoparticle inclusion complex according to claim 1 is supported on a carrier.

3. An oxidation reaction catalyst comprising the sub-nanoparticle inclusion complex according to claim 1.

4. A method for producing a subnanoparticle inclusion complex in which subnanoparticles are encapsulated in branched polyethyleneimine, comprising the following steps: a step of coordinating a reducing metal element in a pentadentate configuration to a nitrogen site in a branched polyethyleneimine having a number average molecular weight of 500 to 12,000 to produce an aggregate of the metal element; a step of reducing the aggregate of the metal element in the presence of a reducing agent while the aggregate is dissolved in an organic solvent, thereby generating sub-nanoparticles of the metal element having a particle size in the range of 0.5 to 2 nm, and forming the sub-nanoparticle inclusion complex; and A step of mixing the sub-nanoparticle inclusion complex with a fatty acid in a liquid to ionically bond the fatty acid to the branched polyethyleneimine.

Images