Metal-metal oxide composite particles and method for producing same

Abstract

The present invention provides novel metal-metal oxide composite particles and a method for producing the same.　Specifically, the present invention provides a method for producing metal-metal oxide composite particles, the method comprising a step for reacting, using a flow reactor, one or more precursor fluids that contain one or more metal elements in the form of ions or molecules, and a supercritical fluid or a subcritical fluid that contains an oxidizing agent and a reducing agent, the oxidizing agent being water.

Description

Metal-metal oxide composite particles and method for producing the same

[0001] The present invention relates to metal-metal oxide composite particles and a method for producing the same.

[0002] Metal-metal oxide composite catalysts, in which a noble metal is supported on a metal oxide support, are widely used industrially as, for example, excellent catalysts for purifying exhaust gases. As a method for producing the composite catalyst, for example, an impregnation method is known (for example, Patent Document 1).

[0003] Japanese Patent Application Publication No. 2019-084467

[0004] In the impregnation method, a metal oxide support is impregnated with a metal salt solution, and the metal is adsorbed onto the support surface to form a composite catalyst. However, the state of metal support is affected by the concentration of the metal salt solution, drying conditions, type of salt, coexisting components, etc., so it is usually difficult to control the state of support. Even if support is possible, the composite is merely adsorbed on each other's surface, and since a long calcination process is required using a pre-made support, it is also disadvantageous in terms of obtaining a non-equilibrium substance.

[0005] In response to this, the present inventors have hypothesized that unique interfacial structures and non-equilibrium materials can be obtained by simultaneously synthesizing a metal and a metal oxide. However, while metals are generally synthesized using a reduction reaction, metal oxides are synthesized using an oxidation reaction, and it is difficult to simultaneously cause an oxidation reaction and a reduction reaction. Therefore, such simultaneous synthesis has not yet been realized, let alone conceived.

[0006] The present invention has been made in view of the above-mentioned current state of the prior art, and a main object of the present invention is to provide novel metal-metal oxide composite particles and a method for producing the same.

[0007] The present inventors have conducted extensive research to achieve the above-mentioned object. As a result, they have found that metal-metal oxide composite particles can be obtained by reacting, using a flow reactor, one or more precursor fluids containing one or more metal elements in an ionic or molecular state with a supercritical fluid or subcritical fluid containing an oxidizing agent and a reducing agent. Based on this finding, the present inventors have conducted further research and have completed the present invention. That is, the present invention encompasses the following features.

[0008] Item 1. A method for producing metal-metal oxide composite particles, comprising the step of reacting, using a flow reactor, one or more precursor fluids containing one or more metal elements in an ionic or molecular state with a supercritical fluid or subcritical fluid containing an oxidizing agent and a reducing agent, wherein the oxidizing agent is water.

[0009] Item 2. The method according to Item 1, wherein the metal constituting the metal-metal oxide composite particles contains at least one metal selected from the group consisting of Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Tc, Ru, Rh, Pd, Ag, In, Sn, W, Re, Os, Ir, Pt, Au, Ga, Pb, and Bi.

[0010] Item 3. The method according to Item 1 or 2, wherein the metal oxide constituting the metal-metal oxide composite particles contains at least one selected from the group consisting of Li, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Cs, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, and Bi.

[0011] Item 4. The method according to any one of Items 1 to 3, wherein the metal-metal oxide composite particles contain two or more metal elements.

[0012] Item 5. The method according to any one of Items 1 to 4, wherein the reducing agent is at least one selected from the group consisting of an alcohol, an aldehyde, and an organic acid.

[0013] Item 6. The method according to Item 5, wherein the reducing agent comprises at least one selected from the group consisting of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, ethylene glycol, triethylene glycol, tetraethylene glycol, diethylene glycol, formaldehyde, acetaldehyde, propanal, butanal, pentanal, hexanal, glyoxal, glyceraldehyde, benzaldehyde, citric acid, and ascorbic acid.

[0014] Item 7. The method according to any one of Items 1 to 6, wherein the reaction temperature is 300°C or higher.

[0015] Item 8. The method according to any one of Items 1 to 7, wherein the reaction is carried out under a pressure of 10 MPa or more.

[0016] Item 9. The method according to any one of Items 1 to 8, wherein the particle diameter of the metal-metal oxide composite particles is 1000 nm or less.

[0017] Item 10. The method according to any one of Items 1 to 9, wherein the particle diameter of the metal constituting the metal-metal oxide composite particles is 100 nm or less.

[0018] Item 11. The method according to any one of Items 1 to 10, wherein the particle diameter of the metal oxide constituting the metal-metal oxide composite particles is 1000 nm or less.

[0019] Item 12. Metal-metal oxide composite particles obtained by the production method according to any one of Items 1 to 11.

[0020] Item 13. A catalyst containing the metal-metal oxide composite particles according to Item 12.

[0021] Item 14. The catalyst according to Item 13, which is a carbon monoxide oxidation catalyst.

[0022] Item 15. Metal-metal oxide composite particles, wherein the metal constituting the metal-metal oxide composite particles is an alloy containing at least two or more metal elements selected from the group consisting of Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Tc, Ru, Rh, Pd, Ag, In, Sn, W, Re, Os, Ir, Pt, Au, Ga, Pb, and Bi, The metal oxide constituting the metal-metal oxide composite particles is a composite metal oxide and / or solid solution containing at least two or more metal elements selected from the group consisting of Li, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Cs, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, and Bi.

[0023] According to the method of the present invention, novel metal-metal oxide composite particles and a method for producing the same can be provided.

[0024] Schematic diagrams of Examples 1 and 2 are shown. XRD patterns of the Pt—Ce oxide composite nanoparticles obtained in Examples 1 and 2 are shown. From top to bottom, the patterns are Example 2, Example 1, and CeO ２ TEM images of the Pt-Ce oxide composite nanoparticles obtained in Example 1 (left) and Example 2 (right) are shown. The white arrows indicate Pt metal particles. The XRD pattern of the Pt-Zr oxide composite nanoparticles obtained in Comparative Example 1 is shown. From the top, Comparative Example 1, CeO ２ 1 shows the XRD patterns of Pt-Zr oxide composite nanoparticles obtained in Examples 3 and 4. From the top, they are Example 4, Example 3, Pt only, and ZrO. ２ (tetragonal) only and ZrO ２This shows the XRD pattern of only the Pt-Zr oxide composite nanoparticles (monoclinic). This shows a TEM image of the Pt-Zr oxide composite nanoparticles obtained in Example 4. This shows the STEM-EDX results of the Pt-Zr oxide composite nanoparticles obtained in Examples 3 and 4. The upper left shows a HAADF-STEM image, the upper right shows Pt, the lower left shows O, and the lower right shows Zr. This shows a schematic diagram of Examples 5 and 6. This shows the XRD patterns of the Pt-Ti oxide composite nanoparticles obtained in Examples 5 and 6. From top to bottom, the images are those of Example 5, Example 6, and TiO. ２ 4 shows the XRD patterns of only Pt and only Pt. TEM images (top row) of Pt-Ti oxide composite nanoparticles obtained in Example 5 (left) and Example 6 (right) are shown. The white arrow indicates a Pt metal particle. The results of composition analysis by X-ray fluorescence analysis (XRF) are also shown (bottom row). The results of STEM-EDX of the Pt-Ti oxide composite nanoparticles obtained in Examples 5 and 6 are shown. The left image shows an HAADF-STEM image, the center image shows Ti, and the right image shows Pt. The results of STEM-EDX of the Rh-CeLaDyW oxide composite nanoparticles obtained in Example 7 are shown. The results of STEM-EDX of the Rh-ZrNdCeRe oxide composite nanoparticles obtained in Example 8 are shown. The XRD patterns of the metal-metal oxide composite particles obtained in Examples 9 to 13 are shown. From top to bottom, they are: Example 13, Example 12, Example 11, Example 10, Example 9, CeO ２, Pt only, and Pd only. For the XRD patterns of the metal-metal oxide composite particles obtained in Examples 9 to 13, enlarged views are shown for the diffraction angle 2θ range of 22° to 35°. A TEM image of the CrMnFeCoNiCuPd-CeCrMnFeCoNiCu oxide composite nanoparticles obtained in Example 9 is shown. The white arrow indicates a metal nanoparticle. A TEM image of the InSnPt-CeEuGdTb oxide composite nanoparticles obtained in Example 10 is shown. The white arrow indicates a metal nanoparticle. A TEM image of the AuCu-CeHoErYbLu oxide composite nanoparticles obtained in Example 11 is shown. The white arrow indicates a metal nanoparticle. A TEM image of the PtWReMoZn-CeWReMoZn oxide composite nanoparticles obtained in Example 12 is shown. The white arrow indicates a metal nanoparticle. 1 shows a TEM image of the PdGaPb-CeGaPb oxide composite nanoparticles obtained in Example 13. The white arrow indicates the metal nanoparticles. This is a graph showing the results of Test Example 1. The circles indicate the Pt-Ce oxide composite particles obtained in Example 14, the black squares indicate the Pt-Ce oxide composite particles obtained in Comparative Example 2, and the white squares indicate the Pt-Ce oxide composite particles obtained in Comparative Example 3. The horizontal axis of the graph indicates the reaction temperature (°C), and the vertical axis indicates the amount of carbon dioxide produced.

[0025] In this specification, the expressions "contain" and "comprise" include any of "contain," "comprise," "consist only of," "consist essentially only of," and "consist only of."

[0026] In this specification, the expression "A to B" indicating a range of values ​​means "greater than or equal to A and less than or equal to B."

[0027] In this specification, the term "metal element" refers to metal elements in a broad sense, and is a concept that includes so-called metalloid elements.

[0028] In this specification, the "metal" constituting the metal-metal oxide composite particles means a zero-valent metal obtained by reducing a metal ion, and is a concept that encompasses simple metals, alloys, intermetallic compounds, ordered alloys, phase-separated alloys, and solid solutions. In this specification, the "metal" constituting the metal-metal oxide composite particles may be a solid solution in which light elements such as hydrogen, carbon, and nitrogen are contained within a metal lattice, or may be a hydride, carbide, or nitride in which these light elements are regularly contained.

[0029] In this specification, the "metal oxide" constituting the metal-metal oxide composite particles broadly refers to a compound containing a metal element and an oxygen element, and is a concept that includes metal oxide solid solutions. The valence of the metal element constituting the metal oxide may be any oxidation number that each element can have, such as monovalent, divalent, trivalent, tetravalent, pentavalent, or hexavalent.

[0030] In this specification, the term "supercritical state" refers to a state in which the temperature is equal to or higher than the temperature at the critical point (critical temperature) and the pressure is equal to or higher than the pressure at the critical point (critical pressure). Alternatively, the supercritical state refers to the point at which the dielectric constant of water, which is about 80 at room temperature, decreases to about 2 to 5.

[0031] In this specification, the term "subcritical state" refers to a state in which the temperature is slightly lower than the critical temperature or the pressure is slightly lower than the critical pressure, near the critical point. Alternatively, the subcritical state refers to the point at which the dielectric constant of water, which is about 80 at room temperature, decreases to about 40.

[0032] 1. Method for Producing Metal-Metal Oxide Composite Particles The method for producing metal-metal oxide composite particles of the present invention comprises a step of reacting, using a flow reactor, one or more precursor fluids containing one or more metal elements in an ionic or molecular state with a supercritical fluid or subcritical fluid containing an oxidizing agent and a reducing agent.

[0033] The production method of the present invention, which includes the reaction step, can simultaneously synthesize a metal and a metal oxide and produce metal-metal oxide composite particles. No examples of obtaining metal-metal oxide composite particles by simultaneously synthesizing a metal and a metal oxide have been reported to date.

[0034] In the manufacturing method of the present invention, in the reaction step, a reaction to obtain a metal by reducing one or more metal elements contained in the precursor fluid (hereinafter sometimes referred to as "first metal elements") and a reaction to obtain a metal oxide by oxidizing one or more metal elements contained in the precursor fluid (hereinafter sometimes referred to as "second metal elements") proceed simultaneously, and as a result, a metal and a metal oxide can be obtained simultaneously from a single precursor fluid.

[0035] Furthermore, the production method of the present invention allows for the simultaneous synthesis of metals and metal oxides, thereby enabling the production of composite materials containing special nano-interfaces or various non-equilibrium substances.In this regard, composite catalysts obtained by conventional impregnation or physical adsorption methods cannot be used to produce catalysts containing non-equilibrium substances because they require a calcination process.

[0036] Furthermore, conventional methods often require a surface protective agent to synthesize catalysts consisting of non-equilibrium substances or precisely controlled metal nanoparticles, which poses the problem of inactivating the catalyst surface due to the protective agent adsorbed to the surface. The production method of the present invention does not require a surface protective agent, and therefore, catalytic inactivation can be avoided. Furthermore, in the metal-metal oxide composite particles obtained by the production method of the present invention, the metal or metal oxide is uniformly dispersed, which makes it easy to avoid particle aggregation.

[0037] Furthermore, in the production method of the present invention, by adjusting synthesis conditions such as the reducing agent / oxidizing agent ratio, pH, temperature, pressure, concentration, and flow rate, it is possible to control the structure and particle size of the metal and oxide, and to synthesize new materials that cannot be obtained by conventional methods.

[0038] The present invention will be described in detail below.

[0039] 1-1. Metal-Metal Oxide Composite Particles The metal-metal oxide composite particles obtained by the present invention are composite particles containing a metal and a metal oxide. The metal in the metal-metal oxide composite particles contains one or more metal elements (first metal elements) contained in the precursor fluid, and the metal oxide in the metal-metal oxide composite particles contains one or more metal elements (second metal elements) contained in the precursor fluid.

[0040] The metal-metal oxide composite particles may contain only one type of metal element as the metal element, or may contain two or more types of metal elements. In either case, there have been no known examples of obtaining metal-metal oxide composite particles by simultaneously synthesizing a metal and a metal oxide.

[0041] The metal element (first metal element) constituting the metal in the metal-metal oxide composite particle and the metal element (second metal element) constituting the metal oxide in the metal-metal oxide composite particle may be the same or different from each other. Between the first metal element and the second metal element, not even one metal element may be the same, some metal elements may be the same, or all metal elements may be the same.

[0042] In the metal-metal oxide composite particles, the metal and the metal oxide are composited. Examples of the composite form include a metal supported on a metal oxide, or a metal oxide supported on a metal. The production method of the present invention makes it easier to obtain metal-metal oxide composite particles in which a metal is supported on a metal oxide.

[0043] The metal-metal oxide composite particles may also have a structure in which metal particles are partially buried in the metal oxide, a nanostructure in which metal particles are encapsulated in the metal oxide, etc. Furthermore, the metal-metal oxide composite particles may also have a structure in which metal particles are dispersed in the metal oxide as clusters consisting of several atoms.

[0044] The metal-metal oxide composite particles are not particularly limited and can be fine particles. In particular, from the viewpoint of catalytic activity, the metal-metal oxide composite particles are preferably microparticles or nanoparticles, and more preferably nanoparticles.

[0045] The particle size of the metal-metal oxide composite particles is not particularly limited, but from the viewpoint of catalytic activity, it is preferably 1000 nm or less, more preferably 1 nm to 500 nm, and even more preferably 1 nm to 50 nm. The particle size can be determined using a transmission electron microscope (TEM) or a scanning transmission electron microscope (STEM).

[0046] The shape of the metal-metal oxide composite particles is not particularly limited, and may be any of spherical, approximately spherical, rod-like, cylindrical, disc-like, rectangular, cubic, tetrahedral, octahedral, truncated octahedral, block-like, and pellet-like.

[0047] From the viewpoint of catalytic activity, it is preferable that the metal-metal oxide composite particles obtained in the present invention have no surface protective agent on their surfaces.

[0048] Metal The metal constituting the metal-metal oxide composite particles contains the first metal element.

[0049] The metal constituting the metal-metal oxide composite particles can be a simple metal when the first metal element is a single type, or can be an alloy including a solid solution, a core-shell type, a separated type, an ordered alloy, or an intermetallic compound when the first metal element is a single type.

[0050] The metal constituting the metal-metal oxide composite particles can be crystalline or amorphous.

[0051] The crystalline phase of the metal (e.g., alloy) constituting the metal-metal oxide composite particles can be a stable phase or a metastable phase. The manufacturing method of the present invention is also advantageous in that it can produce metal particles with a metastable structure that cannot be produced by conventional techniques.

[0052] The metal constituting the metal-metal oxide composite particles may be a single atom of the first metal element, in which case the single atom is useful as a single atom catalyst.

[0053] Alternatively, the metal constituting the metal-metal oxide composite particles can be a cluster of several atoms of the first metal element, and in this case too, the metal can exhibit excellent catalytic activity.

[0054] The first metal element is not particularly limited as long as it is a metal element. Among them, from the viewpoint of obtaining a metal (e.g., a metal element, an alloy, etc.), the first metal element is preferably an element of Groups 6 to 15, more preferably an element of Groups 7 to 14, and even more preferably an element of Groups 8 to 11. More specifically, from the viewpoint of obtaining a metal (for example, a metal element, an alloy, or the like), the first metal element is preferably at least one selected from the group consisting of Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Tc, Ru, Rh, Pd, Ag, In, Sn, W, Re, Os, Ir, Pt, Au, Ga, Pb, and Bi, more preferably at least one selected from the group consisting of Mn, Fe, Co, Ni, Cu, Tc, Ru, Rh, Pd, Ag, In, Sn, Re, Os, Ir, Pt, Au, Ga, Pb, and Bi, and even more preferably at least one selected from the group consisting of Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, In, Sn, Os, Ir, Pt, Au, Ga, Pb, and Bi.

[0055] When the metal constituting the metal-metal oxide composite particles contains two or more metal elements (first metal elements), the combination of metal elements constituting the metal is preferably at least two or more selected from the group consisting of Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Tc, Ru, Rh, Pd, Ag, In, Sn, W, Re, Os, Ir, Pt, Au, Ga, Pb and Bi from the viewpoint of catalytic activity, and is preferably Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt or A combination of Au with at least one metal element selected from the group consisting of Mg, Ca, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Sr, Y, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, and Bi is more preferred.

[0056] When the metal constituting the metal-metal oxide composite particles is an alloy, it is preferably an alloy consisting of a noble metal (e.g., Ru, Rh, Pd, Ag, Os, Ir, Pt, Au, etc.) and a non-noble metal from the viewpoint of metal price. On the other hand, when the metal constituting the metal-metal oxide composite particles is an alloy, it is preferably a high-entropy alloy in which five or more elements are solid-solved from the viewpoint of thermal stability and activity.

[0057] Each metal element constituting the metal constituting the metal-metal oxide composite particles can be present in an amount of 0.1 mol% or more relative to the total amount of each metal element (100 mol%). For example, when composed of two metal elements, the two metal elements can be present in a total of 0.1 mol% to 99 mol%, preferably 0.5 mol% to 95 mol%, more preferably 1 mol% to 90 mol%. When composed of three metal elements, the three metal elements can be present in a total of 0.1 mol% to 98 mol%, preferably 0.5 mol% to 90 mol%, more preferably 1 mol% to 80 mol%. When composed of four metal elements, the four metal elements can be present in a total of 0.1 mol% to 97 mol%, preferably 0.5 mol% to 85 mol%, more preferably 1 to 70 mol%. When composed of five metal elements, the five metal elements can be present in a total of 0.1 mol% to 96 mol%, preferably 0.5 mol% to 80 mol%, more preferably 1 mol% to 60 mol%.

[0058] The particle size of the metal constituting the metal-metal oxide composite particles is not particularly limited, but from the viewpoint of catalytic activity, it is preferably 100 nm or less, more preferably 0.5 nm to 50 nm, and even more preferably 1 nm to 10 nm.

[0059] The shape of the metal constituting the metal-metal oxide composite particles is not particularly limited, and may be any of spherical, approximately spherical, rod-like, cylindrical, disc-like, rectangular, cubic, tetrahedral, octahedral, truncated octahedral, block, and pellet-like.

[0060] From the viewpoint of catalytic activity, it is preferable that the metal constituting the metal-metal oxide composite particles obtained in the present invention does not have a surface protective agent on its surface.

[0061] Metal Oxide The metal oxide constituting the metal-metal oxide composite particles contains the second metal element.

[0062] When the second metal element is two or more types, the metal oxide constituting the metal-metal oxide composite particle can be a composite metal oxide and / or a solid solution.

[0063] The metal oxide constituting the metal-metal oxide composite particles can be crystalline or amorphous.

[0064] The crystalline phase of the metal oxide constituting the metal-metal oxide composite particles can be either a stable phase or a metastable phase. The production method of the present invention is also advantageous in that it can produce metal oxide particles with a metastable structure that cannot be produced by conventional techniques.

[0065] The second metal element is not particularly limited as long as it is a metal element. Among them, from the viewpoint of obtaining a metal oxide, the second metal element is preferably an element of Groups 1 to 15, more preferably an element of Groups 2 to 10 and 12 to 14, and even more preferably an element of Groups 2 to 9 and 13 to 14. More specifically, from the viewpoint of obtaining a metal oxide, the second metal element is Li, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sc, Ba, La, Ce, Pr, Nd, P At least one selected from the group consisting of Mg, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb and Bi is preferred, and Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Ga, Ge, Sr, Y, Zr, Nb, M At least one element selected from the group consisting of O, Tc, Ru, Rh, Pd, Cd, In, Sn, Ce, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Hg, Tl, and Pb is more preferred, and Mg, Al, Si, Ca, Sc, Ti, and V are also preferred. , Cr, Mn, Fe, Co, Ga, Ge, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, In, Sn, Ce, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Tl, and at least one selected from the group consisting of Pb is more preferred.

[0066] When the metal oxide constituting the metal-metal oxide composite particles contains two or more metal elements (second metal elements), the combination of metal elements constituting the metal oxide may be selected from the following in terms of catalytic activity: Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, and At least two or more metal elements selected from the group consisting of Ce, Ti, Zr, Si or Al and Mg, Ca, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Sr, Y, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb and Bi are preferred, and a combination of at least one metal element selected from the group consisting of Ce, Ti, Zr, Si or Al and Mg, Ca, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Sr, Y, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb and Bi is more preferred. On the other hand, from the viewpoint of thermal stability and activity, when the oxide constituting the metal-metal oxide composite particle is a composite oxide, it is preferably a high-entropy oxide (solid solution) in which five or more elements are solid-solved.

[0067] As a combination of the first metal element and the second metal element, from the viewpoint of catalyst design to be used for various reactions, (I) at least one metal element selected from the group consisting of Ni, Cu, Ru, Ir, Pt, Rh, and Pd, and a few metal elements selected from the group consisting of Zr, Ce, La, Al, Nd, Re, Si, Mg, Mn, Fe, Co, V, Cr, Nb, Mo, Sn, Hf, Ta, W, Re, Bi, Pr, Pm, Sm, Eu, Gd, Tb, Ho, Er, Tm, Yb, Lu, and Dy, (II) a combination of a noble metal element with Ce, Ti, Zr, Si or Al; (III) a combination of a noble metal element and one or more other metal elements with Ce, Ti, Zr, Si or Al; (IV) a combination of a noble metal element with Ce, Ti, Zr, Si or Al and one or more other metal elements; and (V) a combination of a noble metal element and one or more other metal elements with Ce, Ti, Zr, Si or Al and one or more other metal elements.

[0068] The particle size of the metal oxide constituting the metal-metal oxide composite particles is not particularly limited, but from the viewpoint of catalytic activity, it is preferably 1000 nm or less, more preferably 1 nm to 500 nm, and even more preferably 5 nm to 100 nm.

[0069] The shape of the metal oxide constituting the metal-metal oxide composite particles is not particularly limited, and may be any of spherical, approximately spherical, rod-like, cylindrical, disc-like, rectangular parallelepiped, cubic, tetrahedral, octahedral, truncated octahedral, block, and pellet-like.

[0070] From the viewpoint of catalytic activity, the metal oxide constituting the metal-metal oxide composite particles obtained by the present invention preferably does not have a surface protective agent on its surface. Examples of surface protective agents include polymers such as poly(N-vinyl-2-pyrrolidone) (PVP) and polyethylene glycol (PEG), amines such as oleylamine, and carboxylic acids such as oleic acid and hexanoic acid.

[0071] Other Components The metal-metal oxide composite particles obtained in the present invention may or may not further contain hydroxides of the metal elements contained in the precursor fluid.

[0072] 1-2. Precursor Fluid The precursor fluid used in the present invention contains one or more metal elements in an ionic or molecular state. Preferably, the precursor fluid contains one or more metal elements in a solvated ionic or molecular state. That is, in the production method of the present invention, the one or more metal elements do not constitute metal-metal oxide composite particles before the reaction step described below. In the production method of the present invention, one or more metal elements present in an ionic or molecular state are precipitated as the metal and metal oxide that constitute the metal-metal oxide composite particles in the reaction step described below. Note that the metal element being in a molecular state means, for example, a state in which a zero-valent carbonyl complex is solvated.

[0073] Metal element The "one or more metal elements" are preferably those exemplified as the "first metal element" and the "second metal element" above, and are preferably the "first metal element" and the "second metal element" above.

[0074] The precursor fluid may contain only one type of metal element as the metal element, or may contain two or more types of metal elements. When the precursor fluid contains only one type of metal element as the metal element, metal-metal oxide composite particles having a simple metal as the metal are easily obtained. When the precursor fluid contains two or more types of metal elements as the metal elements, metal-metal oxide composite particles having an alloy as the metal are easily obtained, and metal-metal oxide composite particles having a composite metal oxide and / or solid solution as the metal oxide are easily obtained.

[0075] When a precursor fluid contains only one type of metal element, by carrying out the manufacturing method of the present invention using this, it is possible to simultaneously obtain a metal and a metal oxide containing the same type of metal element from a single precursor fluid. Conventional techniques have not been able to simultaneously obtain a metal and a metal oxide containing the same type of metal element unless they are oxidized after production. When the precursor fluid contains Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Tc, Ru, Rh, Pd, Ag, In, Sn, W, Re, Os, Ir, Pt, Au, Ga, In, Sn, Pb, and Bi, it is easy to obtain metal-metal oxide composite particles having a metal and a metal oxide each containing the same type of metal element.

[0076] When a precursor fluid contains two or more metal elements, a metal and a metal oxide containing different metal elements can be simultaneously obtained from a single precursor fluid by carrying out the production method of the present invention using the precursor fluid. Also, when a precursor fluid contains two or more (preferably three or more, more preferably four or more) metal elements as metal elements, a metal (alloy) containing two or more metal elements and a metal oxide (composite metal oxide) and / or solid solution containing two or more metal elements can be simultaneously obtained from a single precursor fluid by carrying out the production method of the present invention using the precursor fluid.

[0077] The concentration of the first metal element in the precursor fluid is not particularly limited, but from the viewpoint of yield, it is preferably about 0.0001 mol / L to 10 mol / L, more preferably about 0.0025 mol / L to 5 mol / L, and even more preferably about 0.01 mol / L to 5 mol / L. Note that when multiple metal elements are used as the first metal element, the concentration of the first metal element means the total concentration of each element.

[0078] The concentration of the second metal element in the precursor fluid is not particularly limited, but from the viewpoint of yield, it is preferably about 0.001 mol / L to 1000 mol / L, more preferably about 0.025 mol / L to 500 mol / L, and even more preferably about 0.1 mol / L to 500 mol / L. When multiple metal elements are used as the second metal element, the concentration of the second metal element means the total concentration of each element.

[0079] The content of the second metal element in the precursor fluid is not particularly limited, but from the viewpoint of obtaining composite particles, it is preferably 0.001 mol to 1000 mol, more preferably 0.1 mol to 500 mol, even more preferably 1 mol to 100 mol, and particularly preferably 10 mol to 100 mol, relative to 1 mol of the first metal element.

[0080] The precursor fluid is not particularly limited as long as it is a fluid, and may be in any form, for example, a solution, a dispersion (suspension), a slurry, or a paste.

[0081] The precursor fluid contains water, an organic solvent, or a mixture thereof as a solvent for dispersing or dissolving the metal element. Examples of organic solvents include polar solvents such as alcohols (methanol, ethanol, isopropanol, etc.), polyols (ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, glycerin, etc.), polyethers (polyethylene glycol, etc.), acetonitrile, acetone, dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran (THF), and dimethyl sulfoxide (DMSO); nonpolar solvents such as hexane and diethyl ether; and mixtures thereof.

[0082] The content of water in the precursor fluid is not particularly limited, but is preferably 50 mass parts by volume, more preferably 90 volume%, and even more preferably 100 volume%, relative to 100 volume% of the total amount of the solvent.

[0083] The pH of the precursor fluid is not particularly limited and may be acidic, neutral, or alkaline. The pH can be adjusted appropriately using an acid or a base in consideration of the solubility of the metal element.

[0084] The method for producing the precursor fluid is not particularly limited, and examples thereof include a method of dissolving a metal compound in a solvent. The metal compound is not particularly limited as long as it contains a first metal element and / or a second metal element. Examples include organic acid salts of the metal elements, such as sulfates, nitrates, and acetates, carbonates, halides (fluorides, chlorides, bromides, and iodides), perchlorates, hydroxides, and complexes. Among these, halides, nitrates, and complexes are preferred from the viewpoint of water solubility. The valence of the metal in the metal compound may be zero, monovalent, divalent, trivalent, tetravalent, pentavalent, or hexavalent. Furthermore, when a nonpolar solvent is used, examples of the metal compound include acetates, acetylacetonato salts, carbonyl salts, and organometallic complexes of the metal elements, such as cyclopentadienyl complexes. In the method for producing the precursor fluid, it is preferable to completely dissolve the metal compound by applying energy, such as ultrasound or heat, to the metal compound.

[0085] The temperature of the precursor fluid is not particularly limited, but before the reaction, it is preferably less than 300° C., more preferably less than 200° C., even more preferably less than 100° C., and particularly preferably less than 50° C. In this case, it is easy to avoid the metal element from precipitating before the reaction.

[0086] The pressure of the precursor fluid is not particularly limited, but before the reaction, it is preferably atmospheric pressure before introduction into the flow reactor, and when introduced into the reactor, it is preferably at a pressure similar to that of the back pressure valve for liquid delivery.

[0087] 1-3. Supercritical Fluid or Subcritical Fluid The supercritical fluid or subcritical fluid used in the present invention is not particularly limited as long as it contains an oxidizing agent and a reducing agent and is a fluid in a supercritical state or a subcritical state.

[0088] In the production method of the present invention, the use of a supercritical fluid or a subcritical fluid makes it possible to easily dissolve or disperse a non-polar substance.

[0089] Oxidant In the supercritical or subcritical fluid, the oxidant is water.

[0090] The content of the oxidizing agent in the supercritical fluid or subcritical fluid is not particularly limited, and is, for example, preferably 1 to 99% by volume, more preferably 50 to 95% by volume, even more preferably 60 to 90% by volume, and particularly preferably 70 to 80% by volume, relative to the total volume of the fluid.

[0091] Reducing Agent In the supercritical fluid or subcritical fluid, the reducing agent is not particularly limited as long as it is a compound having a reducing action. The reducing agent is, for example, an organic reducing agent or an inorganic reducing agent. Among them, as the reducing agent, from the viewpoint of obtaining a metal, an organic reducing agent is preferable, an alcohol, an aldehyde, or an organic acid (particularly, a carboxylic acid) is more preferable, and an alcohol is even more preferable.

[0092] Specific examples of the organic reducing agent include alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, ethylene glycol, triethylene glycol, tetraethylene glycol, and diethylene glycol; aldehydes such as formaldehyde, acetaldehyde, propanal, butanal, pentanal, hexanal, glyoxal, glyceraldehyde, and benzaldehyde; and organic acids such as citric acid and ascorbic acid. Of these, ethanol, ethylene glycol, and ascorbic acid are preferred as the organic reducing agent.

[0093] Specific examples of inorganic reducing agents include borohydride salts such as sodium borohydride and ammonium borohydride, and hydrazines such as hydrazine and hydrazine carbonate. Of these, sodium borohydride and hydrazine are preferred as inorganic reducing agents.

[0094] The content of the reducing agent in the supercritical fluid or subcritical fluid is not particularly limited, and is, for example, preferably 0.1 to 99% by volume, more preferably 5 to 50% by volume, even more preferably 10 to 40% by volume, and particularly preferably 20 to 30% by volume, relative to the total volume of the fluid.

[0095] Other Components The supercritical fluid or subcritical fluid may further contain an organic solvent. Examples of organic solvents that can be contained in the supercritical fluid or subcritical fluid include the same organic solvents that can be contained in the precursor fluid.

[0096] The content of the organic solvent in the supercritical fluid or subcritical fluid is not particularly limited, and can be, for example, 1% by volume or more relative to the total volume of the fluid.

[0097] The pH of the precursor fluid is not particularly limited and may be acidic, neutral, or alkaline. The pH can be adjusted appropriately using an acid or a base in consideration of the solubility of the metal element.

[0098] The method for producing a supercritical fluid or subcritical fluid is not particularly limited, and examples thereof include a method in which a dispersion or suspension obtained by dispersing or dissolving a reducing agent in water, which is an oxidizing agent, is pressurized and heated to bring the dispersion or suspension into a supercritical or subcritical state.

[0099] The temperature of the supercritical fluid or subcritical fluid is not particularly limited, but before the reaction, it is preferably 300° C. or higher, more preferably 400° C. or higher, even more preferably 410° C. or higher, and particularly preferably 450° C. or higher. In this case, the yield of metal-metal oxide composite particles is further improved.

[0100] The pressure of the supercritical fluid or subcritical fluid is not particularly limited, but is preferably 10 MPa or more, more preferably 15 MPa or more, even more preferably 20 MPa or more, and particularly preferably 25 MPa or more before the reaction, which further improves the yield of the metal-metal oxide composite particles.

[0101] 1-4. Steps Reaction Step The production method of the present invention includes a step of reacting the precursor fluid with the supercritical fluid or subcritical fluid using a flow reactor.

[0102] The flow reactor used in the present invention is not particularly limited, and a wide variety of known flow reactors equipped with a flow path, a liquid transfer pump, a mixing section, a heater, a pressure pump, a back pressure valve, a cooler, etc. can be used.

[0103] The production method of the present invention can be carried out, for example, by continuously supplying the precursor fluid and the supercritical fluid or subcritical fluid to the mixing section using a liquid pump or the like. Each fluid may be supplied in its entirety at once, or in small amounts in multiple batches. Furthermore, as the precursor fluid, a single precursor fluid containing one or more metal elements may be supplied, or two or more precursor fluids containing one or more metal elements may be supplied simultaneously or sequentially. In the mixing section, the precursor fluid may be supplied to the supercritical fluid or subcritical fluid, or vice versa.

[0104] The supercritical fluid or subcritical fluid does not need to be in a supercritical or subcritical state before being supplied to the mixing section, but is preferably preheated and pressurized to be in a supercritical or subcritical state before being supplied to the mixing section. On the other hand, the precursor fluid is preferably not in a supercritical or subcritical state before being supplied to the mixing section. However, this is not a limitation, and it is sufficient for the supercritical fluid or subcritical fluid to be in a supercritical or subcritical state at the start of the reaction.

[0105] The metal-metal oxide composite particles obtained in the present invention can be continuously discharged from a discharge part, and then appropriately recovered by a known recovery method such as drying under reduced pressure, centrifugation, or filtration.

[0106] Reaction Conditions The reaction is preferably carried out at a high temperature, although not limited thereto. Specifically, the reaction temperature is preferably 300°C or higher, more preferably 400°C or higher, even more preferably 410°C or higher, and particularly preferably 450°C or higher.

[0107] The reaction is preferably carried out under high pressure, although not particularly limited thereto. More specifically, the reaction is preferably carried out under a pressure of 10 MPa or more, more preferably under a pressure of 15 MPa or more, even more preferably under a pressure of 20 MPa or more, and particularly preferably under a pressure of 25 MPa or more.

[0108] The temperature and pressure of each fluid and the temperature and pressure of the reaction field are preferably adjusted appropriately by using, for example, a heater, a pressure pump, and a back pressure valve provided in the flow reactor.

[0109] The pH of the reaction field is not particularly limited and may be acidic, neutral, or alkaline. The pH can be adjusted, for example, by supplying a fluid containing an acid or a base in addition to the above fluid. In the above reaction, although not particularly limited, from the viewpoint of obtaining the desired metal-metal oxide composite particles, it is preferable to adjust the pH of the precursor fluid and the supercritical fluid or subcritical fluid to neutral to alkaline (e.g., pH 7 to 14) by supplying an aqueous solution containing a base such as sodium hydroxide. For example, the pH can be 8, 9, 10, 11, 12, 13, or 14. The acid or base may be supplied at any timing before, simultaneously with, or after mixing the precursor fluid and the supercritical fluid or subcritical fluid.

[0110] The flow rate of the precursor fluid is not particularly limited, and is usually about 1 mL / min to 100 mL / min.

[0111] The flow rate of the supercritical fluid or subcritical fluid is not particularly limited, and is usually about 10 mL / min to 1000 mL / min.

[0112] The ratio of the flow rate of the precursor fluid to the flow rate of the supercritical fluid or subcritical fluid (precursor fluid / supercritical fluid or subcritical fluid) is not particularly limited, and is usually about 0.01 to 1.

[0113] The reaction time is not particularly limited and is usually about 0.1 to 1 second. Here, the reaction time means the time until the reaction progresses to produce some or all of the metal-metal oxide composite particles. According to the method of the present invention, continuous liquid transfer makes it possible to easily produce a large amount of metal-metal oxide composite particles in a short time.

[0114] The reaction can be carried out under air or, to prevent side reactions, under a non-oxidizing atmosphere, such as Ar or N ２ In an inert gas atmosphere such as H ２The reaction can also be carried out under a reducing atmosphere such as

[0115] Additives In the production method of the present invention, additives can also be used within the range that does not impair the effects of the present invention. As the additives, a wide range of additives used in known methods for producing metal particles and metal oxide particles can be used, and examples thereof include inorganic salts such as sodium chloride and bromine chloride. However, from the viewpoint of catalytic activity, it is preferable not to use a surface protective agent.

[0116] In the production method of the present invention, a support can also be used as long as the effects of the present invention are not impaired. Supports that can be used include a wide variety of supports used in known methods for producing metal particles and metal oxide particles, such as carbon materials, metal oxides such as silica, alumina, ceria, and zirconia. According to the method of the present invention, metal particles or metal oxide particles supported on a support can be obtained without adding a support.

[0117] Cooling Step After the reaction, the production method of the present invention can include a cooling step. From the viewpoint of reducing the particle size of the metal-metal oxide composite particles and obtaining metal-metal oxide composite particles having a metastable structure, it is preferable to include a cooling step. Cooling may be performed simply by air cooling, or may be performed using a cooler (chiller). Examples of coolers include a refrigerant circulation device using a refrigerant such as water. From the viewpoint of obtaining particles with a small particle size, rapid cooling is more preferable.

[0118] 2. Catalyst The production method of the present invention makes it easy to obtain metal-metal oxide composite particles having a novel nanostructure including a unique interface. Therefore, the metal-metal oxide composite particles obtained by the production method of the present invention are useful as catalysts. Preferably, catalysts containing the metal-metal oxide composite particles obtained by the production method of the present invention can have catalytic activity and durability that are unparalleled in conventional catalysts.

[0119] EXAMPLES Hereinafter, examples and comparative examples will be shown to further clarify the features of the present invention, but the present invention is not limited to the following examples.

[0120] [Synthesis of Pt—Ce Oxide Composite Nanoparticles] Example 1 A 25 vol% aqueous ethanol solution was heated to 450° C. while being pressurized at 25 MPa to obtain supercritical ethanol water. ３ , 2.16 M, 0.267 mL, 0.577 mmol) with potassium tetrachloroplatinate(II) (K ２ PtCl ４ A precursor fluid was obtained by dissolving Pt-Ce oxide composite nanoparticles (1.9 mg, 4.58 μmol) in the mixture. In the flow reactor, supercritical ethanol water was supplied to the mixing section at 80 mL / min, and the pH of the mixing section was adjusted to 12 by supplying a sodium hydroxide solution (NaOH, 1.79 M, 50.0 mL, 89.3 mmol) at 8 mL / min. The precursor aqueous solution was then supplied at 8 mL / min to cause the reaction. The reaction temperature was 450°C and the pressure was 25 MPa. After the reaction was allowed to proceed for 0.05 to 1.0 seconds, the mixture was rapidly cooled to 15°C using a cooler (Figure 1). The precipitated Pt-Ce oxide composite nanoparticles were recovered by centrifugation.

[0121] Example 2 The same procedure as in Example 1 was carried out, except that the pH of the mixing section was changed to 13 (FIG. 1).

[0122] The XRD patterns of the Pt-Ce oxide composite nanoparticles obtained in Examples 1 and 2 are shown in Figure 2. In both cases, cerium oxide CeO ２ The formation of CeO was confirmed, while the formation of Pt was not detected. ２ This is thought to be because Pt, which is contained in only about 1 mass % of the alloy, cannot be detected by XRD.

[0123] TEM images of the Pt-Ce oxide composite nanoparticles obtained in Examples 1 and 2 are shown in Figure 3. In both cases, homogeneous cerium oxide (CeO) with large particle diameters was observed. ２ Nanoparticles can be confirmed, and CeO ２ It was confirmed that extremely small Pt nanoparticles were formed on the nanoparticles, and that they were composited together.

[0124] Comparative Example 1 The above reaction was carried out using a batch reactor. Specifically, an aqueous solution of cerium (III) chloride (CeCl３ , 2.16 M, 0.267 mL, 0.577 mmol) with potassium tetrachloroplatinate(II) (K ２ PtCl ４ A precursor fluid was obtained by dissolving 25% ethanol (1.9 mg, 4.58 μmol) in the ethanol solution. The precursor fluid and 25 vol% ethanol aqueous solution were mixed in a batch reactor and heated to 500°C at a temperature increase rate of 30°C / min under a pressure of 25 MPa. The mixture was then cooled to room temperature at a temperature decrease rate of 10°C / min. The precipitated particles were collected by centrifugation.

[0125] The XRD pattern of the particles recovered in Comparative Example 1 is shown in Figure 4. Cerium oxide CeO ２ and Pt were observed, confirming that metal-metal oxide composite particles were not formed by the batch method.

[0126] A TEM image of the particles recovered in Comparative Example 1 is shown in Figure 5. In Figure 5, dark-colored Pt metal particles and light-colored Ce oxide particles were observed in different positions, confirming that metal-metal oxide composite particles were not formed in the batch method. It is thought that in the batch method, the timing at which the metal precipitates and the timing at which the metal oxide precipitates are different, preventing composite formation.

[0127] [Synthesis of Pt—Zr oxide composite particles] Example 3 A 25 vol % ethanol aqueous solution was heated to 435° C. while pressurizing it at 25 MPa to obtain supercritical ethanol water. ４ , 187.9 mg) and potassium tetrachloroplatinate (II) (K ２ PtCl ４ A precursor fluid with a neutral pH was obtained by dissolving 2.3 mg of Pt-Zr oxide in 50 mL of water. In a flow reactor, supercritical ethanol water was supplied to the mixing section at 80 mL / min, and the precursor fluid was supplied thereto at 8 mL / min to cause a reaction. The temperature of the reaction system was 435°C, and the pressure was 25 MPa. After reacting for 0.05 to 1.0 seconds, the mixture was rapidly cooled to 15°C using a cooler (Figure 6). The precipitated Pt-Zr oxide composite nanoparticles were recovered by centrifugation.

[0128] Example 4 The same procedure as in Example 3 was carried out except that the reaction temperature was changed to 450°C (Fig. 6).

[0129] The XRD patterns of the Pt-Zr oxide composite nanoparticles obtained in Examples 3 and 4 are shown in Figure 7. In both cases, zirconium oxide ZrO ２ The formation of ZrO was confirmed, while the formation of Pt was not detected. ２ This is thought to be because Pt, which is contained in only about 1 mass % of the alloy, cannot be detected by XRD.

[0130] TEM images of the Pt-Zr oxide composite nanoparticles obtained in Example 4 are shown in Figure 8. In both cases, homogeneous and extremely small zirconium oxide ZrO ２ Nanoparticles can be seen, and zirconium oxide (ZrO) ２ It was confirmed that smaller Pt nanoparticles were formed on the nanoparticles, and that they were composited together.

[0131] The results of STEM-EDX analysis of the Pt-Zr oxide composite nanoparticles obtained in Example 4 are shown in Figure 9. It was confirmed in Figure 9 that Zr and O co-localize, and that Pt exists in the region where they exist. From these results, it was confirmed that zirconium oxide ZrO ２ It was shown that metal Pt was supported on the nanoparticles to form a composite.

[0132] [Synthesis of Pt-Ti Oxide Composite Nanoparticles] Example 5 A 25 vol% aqueous ethanol solution was heated to 390°C while being pressurized at 25 MPa to obtain supercritical ethanol water. ４ , 4.13 M, 0.20 mL) with potassium tetrachloroplatinate(II) (K ２ PtCl ４A precursor fluid was obtained by dissolving 2.2 mg of Pt-Ti oxide composite nanoparticles in the supercritical ethanol solution. In the flow reactor, supercritical ethanol water was supplied to the mixing section at 80 mL / min, and then the precursor aqueous solution was supplied at 8 mL / min to cause a reaction. The temperature of the reaction system was 390°C, and the pressure was 25 MPa. After reacting for 0.05 to 1.0 seconds, the mixture was rapidly cooled to 15°C using a cooler (Figure 10). The precipitated Pt-Ti oxide composite nanoparticles were collected by centrifugation.

[0133] Example 6 The same procedure as in Example 1 was carried out except that the reaction temperature was changed to 490°C (Fig. 10).

[0134] The XRD patterns of the Pt-Ti oxide composite nanoparticles obtained in Examples 5 and 6 are shown in Figure 11. In both cases, titanium oxide TiO ２ The formation of anatase type TiO was confirmed, whereas the formation of Pt was not detected. ２ This is thought to be because Pt, which is contained in only about 1 mass % of the alloy, cannot be detected by XRD.

[0135] TEM images of the Pt-Ti oxide composite nanoparticles obtained in Examples 5 and 6 are shown in Figure 12. In both cases, uniform titanium oxide TiO ２ Nanoparticles can be confirmed, and TiO ２ It was confirmed that extremely small Pt nanoparticles were formed on the nanoparticles, and that they were composited together.

[0136] The results of composition analysis by X-ray fluorescence analysis (XRF) are shown in Figure 12. From the results, it was confirmed that the composition of the metal-metal oxide composite particles was approximately 1 mass % Pt metal and approximately 98 mass % Ti oxide.

[0137] The results of STEM-EDX analysis of the Pt-Ti oxide composite nanoparticles obtained in Examples 5 and 6 are shown in Figure 13. From the results in Figure 13, it is clear that titanium oxide TiO ２ It was confirmed that the nanoparticles were loaded with metallic Pt to form a composite. The average particle size of Pt was 8.2±3.3 nm, and the average particle size of titanium oxide (TiO ２ The average particle size was 3.3±1.1 nm.

[0138] [Synthesis of Rh-CeLaDyW Oxide Composite Nanoparticles] Example 7 A 25 vol% aqueous ethanol solution was heated to 350°C while pressurizing it at 25 MPa to obtain supercritical ethanol water. ３ ・7H ２ 0, 0.5 M aqueous solution, 1.2 ml), lanthanum(III) chloride heptahydrate (LaCl ３ ・7H ２ 0, 0.5 M aqueous solution, 0.9 ml) dysprosium(III) chloride hexahydrate (DyCl ３ ・6H ２ 0, 0.5M aqueous solution, 0.2 ml), sodium tungstate dihydrate (Na ２ WO ４ ・2H ２ 0, 0.5 M aqueous solution, 0.6 ml), rhodium(III) chloride trihydrate (RhCl ３ ・3H ２ A precursor fluid was obtained by mixing two solutions (3.4 ml of a 0.1 M aqueous solution of Rh-Ce-La-Dy-W oxide) and adding an aqueous HCl solution (0.1 M) to make a total volume of 95 ml. In a flow reactor, supercritical ethanol water was supplied to the mixing section at 50 mL / min, and the pH of the mixing section was adjusted by supplying an aqueous sodium hydroxide solution (NaOH, 25 M) at 10 mL / min. The precursor aqueous solution was then supplied at 30 mL / min to cause a reaction. The reaction system temperature was 350°C and the pressure was 25 MPa. After reacting for 0.05 to 1.0 seconds, the mixture was rapidly cooled to 20°C using a cooler. The precipitated Rh-Ce-La-Dy-W oxide composite nanoparticles were collected by filtration.

[0139] The results of STEM-EDX analysis of the Rh-CeLaDyW oxide composite nanoparticles obtained in Example 7 are shown in Fig. 14. From the results in Fig. 14, it was confirmed that metallic Rh was supported on the composite oxide nanoparticles of Ce, La, W, and Dy to form a composite.

[0140] [Synthesis of Rh-ZrNdCeRe Oxide Composite Nanoparticles] Example 8 A 25 vol% aqueous ethanol solution was heated to 250°C while pressurizing it at 25 MPa to obtain supercritical ethanol water. In addition, zirconium (III) acetate tetrahydrate (Zr(CH ３ COO) ３・4H ２ 0, 0.224 M aqueous solution, 1.4 ml), neodymium(III) chloride (NdCl ３ ・6H ２ 0.5M aqueous solution, 0.5 ml), sodium perrhenate(VII) (NaReO ４ , 0.1 M aqueous solution, 4.1 ml), cerium(III) chloride heptahydrate (CeCl ３ ・7H ２ 0, 0.5 M aqueous solution, 0.9 ml), rhodium(III) chloride trihydrate (RhCl ３ ・3H ２ A precursor fluid was obtained by mixing two solutions (4.5 ml of a 0.1 M aqueous solution of ethanol) and adding an aqueous HCl solution (0.1 M) to make a total volume of 95 ml. In a flow reactor, supercritical ethanol water was supplied to the mixing section at 50 mL / min, and the pH of the mixing section was adjusted by supplying an aqueous sodium hydroxide solution (NaOH, 25 M) at 1.0 mL / min. The precursor aqueous solution was then supplied at 20 mL / min to cause a reaction. The temperature of the reaction system was 250°C, and the pressure was 25 MPa. After reacting for 0.05 to 1 second, the mixture was rapidly cooled to 20°C using a cooler. The precipitated Rh-ZrNdCeRe oxide composite nanoparticles were collected by filtration.

[0141] The results of STEM-EDX analysis of the Rh—ZrNdCeRe oxide composite nanoparticles obtained in Example 8 are shown in Fig. 15. From the results in Fig. 15, it was confirmed that metallic Rh was supported on the composite oxide nanoparticles of Zr, Nd, Ce, and Re to form a composite.

[0142] [Synthesis of CrMnFeCoNiCuPd-CeCrMnFeCoNiCu Oxide Composite Nanoparticles] Example 9 A 25 vol% aqueous ethanol solution was heated to 350°C while being pressurized at 25 MPa to obtain supercritical ethanol water. ３ ・7H ２ 0, 0.5M aqueous solution, 5.32 ml), potassium tetrachloropalladate(II) (K ２ PdCl ４ , 0.1 M aqueous solution, 2.07 ml), chromium(III) chloride hexahydrate (CrCl ３ ・6H ２0, 0.1 M aqueous solution, 0.15 ml), manganese(II) chloride tetrahydrate (MnCl ２ ・4H ２ 0, 0.1M aqueous solution, 0.15 ml), iron(II) chloride (FeCl ２ , 0.1M aqueous solution, 0.15 ml), cobalt(II) chloride (CoCl ２ , 0.5M aqueous solution, 0.03 ml), nickel(II) chloride (NiCl ２ , 0.5 M aqueous solution, 0.03 ml), and copper(II) chloride dihydrate (CuCl ２ ・2H ２ A precursor fluid was obtained by mixing Pd-CeCrMnFeCoNiCuP ... In this specification, the expression "CrMnFeCoNiCuPd-CeCrMnFeCoNiCu oxide" means that, in the metals, some or all of Cr, Mn, Fe, Co, Ni, Cu, and Pd may exist as a solid solution with one another, and in the metal oxide, it means that some or all of Ce, Cr, Mn, Fe, Co, Ni, and Cu may exist as a solid solution with one another, and the same applies hereinafter.

[0143] [Synthesis of InSnPt-CeEuGdTb Oxide Composite Nanoparticles] Example 10 A 25 vol% aqueous ethanol solution was heated to 350°C while being pressurized at 25 MPa to obtain supercritical ethanol water. ３ ・7H ２ 0, 0.5M aqueous solution, 3.40 ml), potassium tetrachloroplatinate(II) (K ２ PtCl ４, 0.1M aqueous solution, 2.16 ml), indium(III) chloride tetrahydrate (InCl ３ ・4H ２ 0, 0.1 M aqueous solution, 0.27 ml), tin(II) chloride (SnCl ２ , 0.5M aqueous solution, 0.05 ml), europium(III) chloride (EuCl ３ ・6H ２ 0, 0.5 M aqueous solution, 0.49 ml), gadolinium(III) chloride (GdCl ３ ・6H ２ 0, 0.5 M aqueous solution, 0.49 ml), and terbium(III) chloride hexahydrate (TbCl ３ ・6H ２ A precursor fluid was obtained by mixing two InSnPt-CeEuGdTb oxide composite nanoparticles (0.49 ml) and adding a 0.1 M aqueous HCl solution to make a total volume of 95 ml. In a flow reactor, supercritical ethanol water was supplied to the mixing section at 100 mL / min, and a sodium hydroxide aqueous solution (NaOH, 25 M) was supplied thereto at 5 mL / min to adjust the pH of the mixing section. The precursor aqueous solution was then supplied at 15 mL / min to cause a reaction. The reaction temperature was 350°C and the pressure was 25 MPa. After reacting for 0.05 to 1.0 seconds, the mixture was rapidly cooled to 20°C using a cooler. The precipitated InSnPt-CeEuGdTb oxide composite nanoparticles were collected by filtration.

[0144] [Synthesis of AuCu-CeHoErYbLu Oxide Composite Nanoparticles] Example 11 A 25 vol% aqueous ethanol solution was heated to 350°C while being pressurized at 25 MPa to obtain supercritical ethanol water. ３ ・7H ２ O, 0.5M aqueous solution, 3.91ml), HAuCl ４ ・3H ２ O, 0.5M aqueous solution, 0.38ml), copper(II) chloride dihydrate (CuCl ２ ・2H ２ O, 0.5M aqueous solution, 0.16ml), holmium(III) chloride (HoCl ３ ・6H ２ 0, 0.5M aqueous solution, 0.24 ml), erbium(III) chloride (ErCl ３ ・6H２ 0, 0.5 M aqueous solution, 0.24 ml), ytterbium(III) chloride (YbCl ３ ・6H ２ 0, 0.5 M aqueous solution, 0.24 ml), and terbium(III) chloride hexahydrate (TbCl ３ ・6H ２ A precursor fluid was obtained by mixing two solutions of AuCu-CeHoErYbLu oxide composite nanoparticles (0.5M aqueous solution, 0.24 ml) and adding an aqueous HCl solution (0.1 M) to make a total volume of 95 ml. In a flow reactor, supercritical ethanol water was supplied to the mixing section at 100 mL / min, and the pH of the mixing section was adjusted by supplying an aqueous sodium hydroxide solution (NaOH, 25 M) at 5 mL / min. The precursor aqueous solution was then supplied at 15 mL / min to cause a reaction. The reaction temperature was 350°C and the pressure was 25 MPa. After reacting for 0.05 to 1.0 seconds, the mixture was rapidly cooled to 20°C using a cooler. The precipitated AuCu-CeHoErYbLu oxide composite nanoparticles were collected by filtration.

[0145] [Synthesis of PtWReMoZn-CeWReMoZn Oxide Composite Nanoparticles] Example 12 A 25 vol% aqueous ethanol solution was heated to 350°C while being pressurized at 25 MPa to obtain supercritical ethanol water. ３ ・7H ２ 0, 0.5M aqueous solution, 4.99 ml), potassium tetrachloroplatinate(II) (K ２ PtCl ４ , 0.1M aqueous solution, 2.22 ml), sodium tungstate(VI) dihydrate (Na ２ WO ４ ・2H ２ 0.5M aqueous solution, 0.03 ml), sodium perrhenate(VII) (NaReO ４ , 0.1M aqueous solution, 0.14 ml), sodium molybdate (VI) (Na ２ MoO ４ ・2H ２ 0, 0.5 M aqueous solution, 0.03 ml), and zinc(II) chloride (ZnCl ２A precursor fluid was obtained by mixing two solutions of PtWReMoZn—CeWReMoZn (0.5 M aqueous solution, 0.03 mL) and adding an aqueous HCl solution (0.1 M) to make a total volume of 95 mL. In a flow reactor, supercritical ethanol water was supplied to the mixing section at 100 mL / min, and the pH of the mixing section was adjusted by supplying an aqueous sodium hydroxide solution (NaOH, 25 M) at 5 mL / min. The precursor aqueous solution was then supplied at 15 mL / min to cause a reaction. The reaction system temperature was 350°C and the pressure was 25 MPa. After reacting for 0.05 to 1.0 seconds, the mixture was rapidly cooled to 20°C using a cooler. The precipitated PtWReMoZn-CeWReMoZn oxide composite nanoparticles were collected by filtration.

[0146] [Synthesis of PdGaPb-CeGaPb Oxide Composite Nanoparticles] Example 13 A 25 vol% aqueous ethanol solution was heated to 350°C while being pressurized at 25 MPa to obtain supercritical ethanol water. ３ ・7H ２ 0, 0.5M aqueous solution, 5.25 ml), potassium tetrachloropalladate(II) (K ２ PdCl ４ , 0.1M aqueous solution, 2.63 ml), gallium(II) chloride (GaCl ２ , 0.5 M aqueous solution, 0.03 ml), and lead(II) acetate dihydrate (Pb(CH ３ COO) ２ ・2H ２ A precursor fluid was obtained by mixing a 0.5M aqueous solution of PdGaPb and a 0.1M aqueous solution of HCl (0.03 ml) and adding it to a total volume of 95 ml. In a flow reactor, supercritical ethanol water was supplied to the mixing section at 100 mL / min, and the pH of the mixing section was adjusted by supplying a 25M sodium hydroxide aqueous solution (NaOH) at 5 mL / min. The precursor aqueous solution was then supplied at 15 mL / min to react. The reaction temperature was 350°C and the pressure was 25 MPa. After reacting for 0.05 to 1.0 seconds, the mixture was rapidly cooled to 20°C using a cooler. The precipitated PdGaPb-CeGaPb oxide composite nanoparticles were collected by filtration.

[0147] The XRD patterns of the metal-metal oxide composite nanoparticles obtained in Examples 9 to 13 are shown in Figures 16 and 17. In all of the composite particles, cerium oxide (CeO ２ The formation of CeO ２ The peak shifts to the lower angle side compared to the peak of only CeO. ２ It was confirmed that the solid solution

[0148] 18 to 22 show TEM images of the metal-metal oxide composite nanoparticles obtained in Examples 9 to 13. In all composite particles, uniform metal oxide nanoparticles with large particle diameters were observed, and it was confirmed that extremely small metal nanoparticles were formed on the metal oxide particles and that these were composited together.

[0149] [Synthesis of Pt—Ce Oxide Composite Nanoparticles] Example 14 Subcritical ethanol water was obtained by heating a 25 vol% ethanol aqueous solution to 350° C. while pressurizing it at 25 MPa. ３ , 2.16 M, 0.267 mL, 0.577 mmol) with potassium tetrachloroplatinate(II) (K ２ PtCl ４ A precursor fluid was obtained by dissolving a potassium hydroxide solution (KOH, 0.712 M, 50.0 ml, 35.6 mmol) in the mixture. In the flow reactor, supercritical ethanol water was supplied to the mixing section at 80 mL / min, and then a potassium hydroxide solution (KOH, 0.712 M, 50.0 ml, 35.6 mmol) was supplied at 8 mL / min. The precursor solution was then supplied at 8 mL / min and reacted. The reaction temperature was 350°C and the pressure was 25 MPa. After reacting for 0.05 to 1.0 seconds, the mixture was rapidly cooled to 15°C using a cooler. The precipitated Pt-Ce oxide composite nanoparticles were recovered by centrifugation.

[0150] [Synthesis of Pt—Ce Oxide Composite by Impregnation and Calcination Method] Comparative Example 2 A Pt—Ce oxide composite was synthesized by the impregnation and calcination method. Specifically, commercially available cerium (IV) oxide (CeO ２ , 500 mg), potassium tetrachloroplatinate (II) (K ２ PtCl４ , 10.74 mg) was added to the solution, and the mixed solution, with Pt at 1 wt % relative to CeO2, was stirred at room temperature for 1 hour. After that, water was removed by distillation at 60°C using a rotary evaporator, and the mixture was further dried at 60°C for 12 hours and calcined in air at 350°C for 2 hours to obtain a Pt-Ce oxide composite.

[0151] [Synthesis of Pt—Ce Oxide Composite by Liquid Phase Reduction] Comparative Example 3 A Pt—Ce oxide composite was synthesized by the liquid phase reduction method. ２ PtCl ４ , 10.74 mg) aqueous solution was subjected to ultrasonic treatment. In addition, commercially available cerium (IV) oxide (CeO ２ After mixing these solutions, the Pt nanoparticles were mixed with CeO while stirring at 100°C for 2 hours. ２ After cooling, the Pt—Ce oxide composite was recovered by centrifugation and dried.

[0152] [Carbon monoxide (CO) oxidation catalyst activity test] Test Example 1 A CO oxidation reaction was carried out using the Pt—Ce oxide composite obtained in Example 14, Comparative Example 2, or Comparative Example 3 as a catalyst. He gas, O ２ / He gas, CO / He gas mixture (0.6% CO / He: 2 sccm (CO: 2000 ppm), 10% O ２ A gas mixture of 33.3 sccm CO / He (2000 ppm CO, 64.7 sccm He) was introduced into the catalyst-filled reactor at a flow rate of 100 ml / min, and the temperature was increased from room temperature to 300°C at a rate of 2°C / min. While the temperature was increased, carbon monoxide (CO) and carbon dioxide (CO) were measured by gas chromatography (Agilent 490 Micro GC). ２ The amount of ) produced was measured.

[0153] Reaction temperature and CO ２ The relationship between the amount of CO produced and the temperature is shown in Figure 23. In Comparative Examples 2 and 3, CO was produced at temperatures between 200°C and 250°C.２ In Example 14, CO was not generated in the low temperature range (50°C to 100°C). ２ At around 150°C, almost all of the CO is converted to CO ２ It was confirmed that the metal-metal oxide composite particles obtained by the production method of the present invention exhibit extremely high CO oxidation catalytic activity.

Claims

1. A method for producing metal-metal oxide composite particles, comprising the step of reacting, using a flow reactor, one or more precursor fluids containing one or more metal elements in an ionic or molecular state with a supercritical fluid or subcritical fluid containing an oxidizing agent and a reducing agent, wherein the oxidizing agent is water.

2. The method according to claim 1, wherein the metal constituting the metal-metal oxide composite particles contains at least one metal selected from the group consisting of Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Tc, Ru, Rh, Pd, Ag, In, Sn, W, Re, Os, Ir, Pt, Au, Ga, Pb, and Bi.

3. The method according to claim 1, wherein the metal oxide constituting the metal-metal oxide composite particles contains at least one element selected from the group consisting of Li, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Cs, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, and Bi.

4. The method according to claim 1, wherein the metal-metal oxide composite particles contain two or more metal elements.

5. The method of claim 1, wherein the reducing agent is at least one selected from the group consisting of alcohols, aldehydes, and organic acids.

6. The method of claim 5, wherein the reducing agent comprises at least one selected from the group consisting of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, ethylene glycol, triethylene glycol, tetraethylene glycol, diethylene glycol, formaldehyde, acetaldehyde, propanal, butanal, pentanal, hexanal, glyoxal, glyceraldehyde, benzaldehyde, citric acid, and ascorbic acid.

7. The method of claim 1, wherein the reaction temperature is 300°C or higher.

8. The method according to claim 1, wherein the reaction is carried out under a pressure of 10 MPa or more.

9. The method according to claim 1, wherein the particle size of the metal-metal oxide composite particles is 1000 nm or less.

10. The method according to claim 1, wherein the particle diameter of the metal constituting said metal-metal oxide composite particles is 100 nm or less.

11. The method according to claim 1, wherein the particle diameter of the metal oxide constituting the metal-metal oxide composite particles is 1000 nm or less.

12. Metal-metal oxide composite particles obtained by the manufacturing method according to any one of claims 1 to 11.

13. A catalyst containing the metal-metal oxide composite particles according to claim 12.

14. The catalyst of claim 13, which is a carbon monoxide oxidation catalyst.

15. Metal-metal oxide composite particles, wherein the metal constituting the metal-metal oxide composite particles is an alloy containing at least two or more metal elements selected from the group consisting of Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Tc, Ru, Rh, Pd, Ag, In, Sn, W, Re, Os, Ir, Pt, Au, Ga, Pb, and Bi; The metal oxide constituting the metal-metal oxide composite particles is a composite metal oxide and / or solid solution containing at least two or more metal elements selected from the group consisting of Li, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Cs, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, and Bi.

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