WO2021132335A1 - Solid solution nanoparticles, method for producing same, dispersion liquid of solution solid nanoparticles, and catalyst - Google Patents

Abstract

The solid solution nanoparticles according to the present invention have a compositional makeup represented by formula Pt_xM1_yM2_1-x-y (0<x<1, 0<y<1, x+y<1). M1 represents Ru or Ir. When M1 represents Ru, M2 represents at least one selected from the group consisting of Ir, Rh, Ag, Cu, and Au. When M1 represents Ir, M2 represents at least one selected from the group consisting of Rh, Pd, Ag, Cu, and Au. Pt, M1, and M2 form a solid solution.

Description

Solid solution nanoparticles, their production method, dispersion of solid solution nanoparticles and catalyst

The present invention relates to solid solution nanoparticles, a method for producing the same, a dispersion of solid solution nanoparticles, and a catalyst.

Precious metal nanoparticles such as Pt nanoparticles are known to exhibit different optical, electrical, and chemical properties than bulk nanoparticles, and are known to exhibit electronic, magnetic, catalytic, pharmaceutical, cosmetic, or cosmetic materials. It is used in various fields as a food material.

As described in Patent Documents 1-4, catalysts are one of the most well-known uses of precious metal nanoparticles.

Patent Document 5 describes that noble metal nanoparticles are used as an antioxidant.

Patent Document 6 describes that noble metal nanoparticles are used as a material for a contrast medium.

International Publication No. 2002/040152 Japanese Unexamined Patent Publication No. 2007-90331 Japanese Unexamined Patent Publication No. 2009-11912 Japanese Unexamined Patent Publication No. 2014-155919 Japanese Unexamined Patent Publication No. 2008-156440 Special Table 2016-507726

Among the precious metal nanoparticles, Pt nanoparticles are highly useful because they exert various effects. It is conceivable to alloy a noble metal other than Pt with Pt in order to improve the desired effect.

However, except for specific combinations such as PtRh, many combinations of noble metal elements do not show a complete total rate solid-state alloy phase diagram. For example, PtIr forms a total solid solution at high temperatures, but is immiscible over a wide composition range of 1370 ° C. or lower. Similarly, PtRu and IrRu also have an immiscible composition range of about 15 atom% in the entire temperature range. Therefore, even if noble metal nanoparticles are synthesized by a conventional reduction method using a solution containing a plurality of noble metal salts, only a mixture of simple noble metal nanoparticles can be obtained.

If solid solution type metal nanoparticles that cannot be predicted from the alloy phase diagram can be obtained, it can be expected that the desired effect of the metal nanoparticles in existing applications will be improved. It is expected that new physical properties will be developed and the applications of metal nanoparticles based on the new physical properties will be expanded.

An object of the present invention is to provide a novel solid solution nanoparticles, a method for producing the same, a dispersion liquid of the solid solution nanoparticles, and a catalyst using the solid solution nanoparticles.

The present invention
It has a composition represented by the formula Pt _x M1 _y M2 _1-xy (0 <x <1, 0 <y <1, x + y <1).
M1 is Ru or Ir and
When M1 is Ru, M2 is at least one selected from the group consisting of Ir, Rh, Ag, Cu and Au.
When M1 is Ir, M2 is at least one selected from the group consisting of Rh, Pd, Ag, Cu and Au.
Pt, M1 and M2 form a solid solution,
Provided are solid solution nanoparticles.

In another aspect, the present invention
Provided is a catalyst containing the solid solution nanoparticles of the present invention.

In yet another aspect, the present invention
With solvent
With the solid solution nanoparticles of the present invention dispersed in the solvent,
Provided is a dispersion liquid of solid solution nanoparticles provided with.

In yet another aspect, the present invention
A method for producing solid solution nanoparticles having a composition represented by the formula Pt _x M1 _y M2 _1-xy (0 <x <1, 0 <y <1, x + y <1).
It involves adding a solution containing a Pt salt, a salt of M1 and a salt of M2 to a liquid reducing agent heated to a temperature in the range of 150 ° C. or higher and 250 ° C. or lower for reaction.
The salt of M1 is a Ru salt or an Ir salt.
When the salt of M1 is Ru salt, the salt of M2 contains at least one selected from the group consisting of Ir salt, Rh salt, Ag salt, Cu salt and Au salt.
When the salt of M1 is an Ir salt, the salt of M2 contains at least one selected from the group consisting of Rh salt, Pd salt, Ag salt, Cu salt and Au salt.
Provided is a method for producing solid solution nanoparticles.

According to the present invention, it is possible to provide a novel solid solution nanoparticles, a method for producing the same, a dispersion liquid of the solid solution nanoparticles, and a catalyst using the solid solution nanoparticles.

FIG. 1 is a TEM image of PtRuIr solid solution nanoparticles supported on _{ZrO 2 of Example 1.} FIG. 2A is a HAADF-STEM image of PtRuIr solid solution nanoparticles supported on _{ZrO 2 of Example 1.} FIG. 2B shows the result of elemental mapping of Pt in Example 1. FIG. 2C shows the result of elemental mapping of Ir in Example 1. FIG. 2D shows the result of elemental mapping of Ru in Example 1. FIG. 3A is a STEM image of PtRuIr solid solution nanoparticles subjected to EDX ray analysis. FIG. 3B is a graph showing the results of EDX ray analysis. FIG. 4 is a TEM image of Pt nanoparticles supported on _{ZrO 2 of Reference Example 1.} FIG. 5 is a TEM image of Ru nanoparticles supported on _{ZrO 2 of Reference Example 2.} FIG. 6 is a TEM image of Ir nanoparticles supported on _{ZrO 2 of Reference Example 3.} FIG. 7 is a TEM image of Pd nanoparticles supported on _{ZrO 2 of Reference Example 4.} FIG. 8 is a graph showing the evaluation of the methane oxidation activity of the catalysts of Examples, Reference Examples and Comparative Examples. FIG. 9 is a graph showing the evaluation of the methane oxidation activity of the catalysts of Examples 1 to 6. FIG. 10 is a triangular graph showing the relationship between the methane conversion rate at 400 ° C. and the composition of the solid solution nanoparticles. FIG. 11A is a graph showing the time course of methane oxidation activity at 400 ° C. FIG. 11B is a graph showing the time course of methane oxidation activity at 400 ° C. FIG. 12 is a graph showing the time course of the methane oxidation activity of the catalysts of Examples 3, 5 and 7 at 400 ° C. FIG. 13A is a graph showing the measurement results of _{NH 3-TPD.} FIG. 13B is a graph showing the measurement results of _{CO 2-TPD.} FIG. 14 is a TEM image of PtIrPd solid solution nanoparticles of Example 8. FIG. 15 is an X-ray diffraction pattern of the PtIrPd solid solution nanoparticles of Example 8. FIG. 16 is a TEM image of PtIrPdRh solid solution nanoparticles of Example 9. FIG. 17 is an X-ray diffraction pattern of the PtIrPdRh solid solution nanoparticles of Example 9.

Conventionally, it has been known to support Pt on a carrier as a means for adjusting the catalytic activity of Pt. This has the advantage that the specific surface area of Pt can be increased and the catalytic activity can be changed by the interaction between Pt and the carrier.

Patent Documents 1 to 4 disclose catalysts using a plurality of precious metals. These catalysts are produced by impregnating a carrier with an aqueous solution containing a plurality of noble metal salts, and then calcining the carrier in air at 550 to 600 ° C. for 3 to 6 hours. This method is called the impregnation method. According to the impregnation method, it is presumed that the plurality of noble metals constituting the catalyst exist in the state of simple noble metal particles without alloying, or form noble metal particles having a variable and non-uniform composition. Therefore, the catalyst produced by the impregnation method cannot sufficiently exert the effect of alloying.

For example, when the main component of hydrocarbons in exhaust gas is methane, such as combustion exhaust gas of natural gas, methane has high chemical stability, so oxidative decomposition of hydrocarbons (removal of methane) proceeds sufficiently. It's not easy to get it done. Further, there is also a problem that the activity of the catalyst decreases with time due to the precipitation of a reaction inhibitor such as sulfur oxide (SOx) derived from the sulfur compound contained in the fuel on the surface of the catalyst.

The present inventors have found that solid solution nanoparticles in which metals that normally do not dissolve in solid solution are solid-solved can be produced, and that the solid solution nanoparticles can be used as a novel catalyst. The present invention is based on this new finding.

In detail, the present invention reveals that by mixing and alloying Pt with various metals, it is possible to adjust the catalytic activity of Pt on a nanoscale, which was difficult in the past. This demonstrates the new industrial applicability of Pt as a catalyst. The following embodiments show one aspect of Pt in which such catalytic activity is adjusted at the nano level.

(Embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments.

The solid solution nanoparticles of the present embodiment have a composition represented by the following formula (1).

Pt _x M1 _y M2 _1-xy ... (1)

In the formula (1), x and y satisfy 0 <x <1, 0 <y <1 and x + y <1. M1 is Ru or Ir. When M1 is Ru, M2 is at least one selected from the group consisting of Ir, Rh, Ag, Cu and Au. When M1 is Ir, M2 is at least one selected from the group consisting of Rh, Pd, Ag, Cu and Au. Pt, M1 and M2 form a solid solution. In other words, Pt, M1 and M2 are in solid solution with each other at the atomic level. In the solid solution nanoparticles, a region in which each element is uniformly distributed is included. It is preferable that each element is uniformly distributed throughout the solid solution nanoparticles.

A solid solution is one form included in the concept of alloy, and means a state in which constituent elements are mixed at the atomic level. In general, the term "alloy" means an alloy in a broad sense that includes not only solid solutions but also non-solid solutions. The local alloy composition is uniform in a solid solution, whereas it is not uniform in a non-solid solution system. The physical characteristics of alloys generally differ depending on whether a plurality of metal elements are mixed as a solid solution alloy as a whole at the atomic level or simply form a non-solid solution type alloy.

The solid solution nanoparticles of this embodiment can be precious metal nanoparticles. Generally, Cu is not classified as a noble metal, but is treated as a noble metal in the present specification.

As a method for confirming that the noble metal nanoparticles are a solid solution, element mapping by energy dispersive X-ray analysis (EDX) using a scanning transmission electron microscope (STEM), EDX ray analysis, and X-ray diffraction (XRD) are performed. Structural analysis and the like can be mentioned.

The average particle size of the solid solution nanoparticles of the present embodiment may be in the range of 0.5 nm or more and 100 nm or less, or may be in the range of 1 nm or more and 10 nm or less. When the average particle size is small enough, the solid solution nanoparticles can exhibit high activity. The average particle size can be calculated from the electron microscope image of the solid solution nanoparticles. In the electron microscope image, the particle size (major axis) of a plurality of solid solution nanoparticles (for example, 100) is measured. The average value of the measured particle sizes represents the average particle size of the solid solution nanoparticles.

In the formula (1), x representing the content ratio of Pt satisfies, for example, 0.01 ≦ x ≦ 0.98. In the formula (1), y representing the content ratio of M1 satisfies, for example, 0.01 ≦ y ≦ 0.98. In the formula (1), (1-xy) representing the content ratio of M2 satisfies 0.01 ≦ (1-xy) ≦ 0.98. In other words, the respective content ratios of Pt, M1 and M2 are in the range of, for example, 1 mol% or more and 98 mol% or less based on the solid solution nanoparticles (100 mol%). The respective content ratios of Pt, M1 and M2 may be in the range of 5 mol% or more and 90 mol% or less, or may be in the range of 10 mol% or more and 80 mol% or less.

The solid solution nanoparticles of this embodiment contain Pt as an essential component. Pt nanoparticles can be used in various applications such as electronic materials, magnetic materials, catalytic materials, pharmaceutical materials, cosmetic materials, food materials and the like. However, Pt is expensive. Therefore, if the function and activity equal to or higher than those of the Pt nanoparticles can be achieved while lowering the Pt content ratio, the solid solution nanoparticles having excellent economic efficiency can be provided. As will be described later, the solid solution nanoparticles of the present embodiment exhibit catalytic activity exceeding that of Pt nanoparticles. However, catalytic activity is only one function of solid solution nanoparticles.

In equation (1), M1 can be Ru. Ru is cheaper than Pt and is suitable as a substitute element for Pt in solid solution nanoparticles.

The activity of Ru alone (catalytic activity) is usually lower than that of Pt. Therefore, Ru nanoparticles themselves are unlikely to be a substitute for Pt nanoparticles.

In equation (1), M1 may be Ir. Although Ir is an expensive precious metal like Pt, it often exhibits higher activity than Ru, and is suitable as a material for the solid solution nanoparticles of the present embodiment. By including Ir, the solid solution nanoparticles can exhibit higher activity.

In the formula (1), M1 may be Ru and M2 may be Ir. In this case, both the advantages of the combination of Pt and Ir and the advantages of the combination of Pt and Ru are obtained.

M2 may consist of 1 type, 2 types, 3 types, 4 types or 5 types of metal elements. When M2 is composed of one kind of metal element, the solid solution nanoparticles of the present embodiment are ternary solid solution nanoparticles. That is, in the formula (1), when M1 is Ru, M2 is Ir, Rh, Ag, Cu or Au. When M1 is Ir, M2 is Rh, Pd, Ag, Cu or Au. Compared with the quaternary system or the quaternary system, the production of the ternary solid solution nanoparticles is easy.

M1 is Ru, if M2 is composed of two metal elements, consisting of ^{_{M2 = M a p2 M b q2}} ( where, M ^a and M ^b are different from each other, Ir, Rh, Ag, Cu and Au It is selected from the group and is represented by p2 = 0.01 to 0.99, q2 = 0.99 to 0.01, p2 + q2 = 1).

M1 is Ir, if M2 is composed of two metal elements, consisting of ^{_{M2 = M a p2 M b q2}} ( where, M ^a and M ^b are different from each other, Rh, Pd, Ag, Cu and Au It is selected from the group and is represented by p2 = 0.01 to 0.99, q2 = 0.99 to 0.01, p2 + q2 = 1).

M1 is Ru, if M2 consists of three metal _{^{elements, M2 = M a p3 M b}} q3 M c r3 ( wherein, M ^a, M ^b and M ^c are different from one another, Ir, Rh, Ag , Cu and Au, p3 = 0.01 to 0.98, q3 = 0.01 to 0.98, r3 = 0.01 to 0.98, p3 + q3 + r3 = 1).

When M1 is Ir and M2 is composed of three kinds of metal elements, M2 = M ^a _p3 M ^b _q3 M ^c _r3 (in the formula, M ^a , M ^b and M ^c are different from each other, and Rh, Pd, Ag. , Cu and Au, p3 = 0.01 to 0.98, q3 = 0.01 to 0.98, r3 = 0.01 to 0.98, p3 + q3 + r3 = 1).

M1 is Ru, if M2 is composed of four metal elements, M2 = in _{^{M a p4 M b q4 M c}} r4 M d s4 ( ^{wherein, M a, M b, M} c and M ^d are different from each other , Ir, Rh, Ag, Cu and Au, p4 = 0.01 to 0.97, q4 = 0.01 to 0.97, r4 = 0.01 to 0.97, s4 = 0 It is represented by 0.01 to 0.97, p4 + q4 + r4 + s4 = 1).

M1 is Ir, if M2 is composed of four metal elements, M2 = in _{^{M a p4 M b q4 M c}} r4 M d s4 ( ^{wherein, M a, M b, M} c and M ^d are different from each other , Rh, Pd, Ag, Cu and Au, p4 = 0.01 to 0.97, q4 = 0.01 to 0.97, r4 = 0.01 to 0.97, s4 = 0 It is represented by 0.01 to 0.97, p4 + q4 + r4 + s4 = 1).

M1 is Ru, if M2 consists of five _{^{metal, M2 = M a p5 M b}} q5 M c r5 M d s5 M e t5 ( ^{where, M a, M b, M} c, M d and M ^e is different from each other and is selected from the group consisting of Ir, Rh, Ag, Cu and Au, p5 = 0.01 to 0.96, q5 = 0.01 to 0.96, r5 = 0.01 to 0. It is represented by 96, s5 = 0.01 to 0.96, t5 = 0.01 to 0.96, p5 + q5 + r5 + s5 + t5 = 1).

M1 is Ir, if M2 consists of five _{^{metal, M2 = M a p5 M b}} q5 M c r5 M d s5 M e t5 ( ^{where, M a, M b, M} c, M d and M ^e is different from each other and is selected from the group consisting of Rh, Pd, Ag, Cu and Au, p5 = 0.01 to 0.96, q5 = 0.01 to 0.96, r5 = 0.01 to 0. It is represented by 96, s5 = 0.01 to 0.96, t5 = 0.01 to 0.96, p5 + q5 + r5 + s5 + t5 = 1).

In the solid solution nanoparticles of the present embodiment, the content ratio of Pt can be in the range of 10 mol% or more and 30 mol% or less.

For example, when solid solution nanoparticles are used as a catalyst, Pt is considered to be the main component that influences the catalytic activity. Therefore, it is predicted that if the Pt content ratio is lowered, the catalytic activity is also lowered. However, surprisingly, catalysts containing solid solution nanoparticles exhibit the highest methane oxidative degradation activity when the Pt content is reduced. Specifically, the catalytic activity tends to increase as the Pt content ratio decreases to 50 mol%, 40 mol%, and 30 mol%. Regarding the lower limit, the catalytic activity tends to increase as the Pt content ratio increases to 5 mol% and 10 mol%. This becomes clear from the examples described later.

The solid solution nanoparticles of the present embodiment can be suitably used as various catalysts.

Examples of catalytic reactions include chemical reactions such as reduction reaction, oxidation reaction, dehydrogenation reaction, and coupling reaction. The catalyst of this embodiment can be used in a process or apparatus involving these catalytic reactions. Specific applications of the catalyst include environmental applications including purification of exhaust gas, electrode applications, and chemical process applications. In environmental applications, catalysts are used in at least one reaction selected from the group consisting of nitrogen oxide reduction reactions, carbon monoxide oxidation reactions, hydrocarbon oxidation reactions, and volatile organic compound (VOC) oxidation reactions. To. In electrode applications, catalysts are used in at least one reaction selected from the group consisting of hydrogen oxidation reactions, oxygen reduction reactions, and water electrolysis reactions. In chemical process applications, catalysts are used in at least one reaction selected from the group consisting of hydrogenation reactions of unsaturated hydrocarbons and dehydrogenation reactions of saturated or unsaturated hydrocarbons. In particular, the catalyst of the present embodiment can be suitably used for purifying the exhaust gas discharged from the heat engine, generating hydrogen in the fuel cell, and removing the volatile organic compounds.

Among the exhaust gas, methane may be the main component of hydrocarbons in the exhaust gas, such as the combustion exhaust gas of natural gas. Methane has a greenhouse effect about 25 times that of carbon dioxide. Therefore, it is recommended to reduce the release of methane into the atmosphere as much as possible from the viewpoint of global environmental protection. The catalyst of this embodiment is suitable for oxidative decomposition of hydrocarbons, particularly methane. Although the chemical stability of methane is high, the catalyst of the present embodiment exhibits high activity, so that the oxidative decomposition of methane can proceed sufficiently at a relatively low temperature. In addition, the catalyst of the present embodiment is also excellent in durability against reaction inhibitors such as _{sulfur oxides (SO x).} Examples of heat engines that use natural gas as fuel include gas turbines. The catalyst of this embodiment is suitable for a purification device for combustion exhaust gas of a gas turbine.

The catalyst of the present embodiment may further include a carrier supporting solid solution nanoparticles. By supporting the solid solution nanoparticles on the carrier, aggregation of the solid solution nanoparticles can be suppressed. In addition, the electronic interaction from the carrier can promote the adsorption and activation of the reaction molecule on the surface of the solid solution nanoparticles. Depending on the carrier, it is also possible to electronically interact with the solid solution nanoparticles to further improve the catalytic activity of the solid solution nanoparticles.

The structure of the carrier is not particularly limited. The carrier is typically particles. The shape of the particles is not particularly limited, and particles having various shapes such as spherical, elliptical spherical, and scaly can be used.

The material of the carrier is not particularly limited. Examples of the carrier material include oxides, nitrides, carbides, carbon materials, and metal materials. Oxides include silica, alumina, ceria, titania, zirconia, niobia, silica-alumina, titania-zirconia, ceria-zirconia, tin oxide, tungsten trioxide, molybdenum trioxide, tantalum pentaoxide, and strontium titanate. Can be mentioned. The oxide may be a metal oxide. Examples of the nitride include boron nitride, silicon nitride, gallium nitride, indium nitride, aluminum nitride, zirconium nitride, vanadium nitride, tungsten nitride, molybdenum nitride, titanium nitride, and niobium nitride. The nitride may be a metal nitride. Examples of the carbide include silicon carbide, gallium carbide, indium carbide, aluminum carbide, zirconium carbide, vanadium carbide, tungsten carbide, molybdenum carbide, titanium carbide, niobium carbide, and boron carbide. The carbide may be a metal carbide. Examples of the carbon material include activated carbon, carbon black, graphite, carbon nanotubes, and activated carbon fiber. Examples of the metal material include pure metals such as iron, copper and aluminum, and alloys such as stainless steel. One kind or a combination of two or more kinds selected from these carriers can be used.

Among the above, metal oxide particles such as zirconia particles can be suitably used as a carrier. The metal oxide has a large specific surface area and is excellent in heat resistance, chemical stability, mechanical strength, and dispersibility.

The carrier may contain at least one selected from the group consisting of _{SnO 2} , WO ₃ , MoO ₃ , Ta ₂ O ₅ , and Nb ₂ O _5. Since these materials have _{excellent durability against SO x,} they may have the effect of maintaining the activity of the catalyst for a long period of time. The carrier may contain any of these materials as a main component, or may be substantially composed of these materials. The "main component" means the component contained most in the mass ratio. By "substantially consisting of ...", it means that no material other than a specific material is intentionally added except for unavoidable impurities.

The solid solution nanoparticles may be used as a catalyst without being supported on a carrier. When the solid solution nanoparticles are used as a catalyst in the solution, the solid solution nanoparticles may be protected with a protective agent.

Next, a method for producing solid solution nanoparticles will be described. The method described below allows mixing at the atomic level, even with immiscible metal combinations in the phase diagram.

The solid solution nanoparticles having the composition represented by the formula (1) are produced through a step of adding a solution containing a Pt salt, a salt of M1 and a salt of M2 to a liquid reducing agent heated to a predetermined temperature T and reacting them. .. The composition of the solid solution nanoparticles can be controlled by adjusting the ratio of the metal salt as the raw material.

First, a solution containing a Pt salt, a salt of M1 and a salt of M2 is prepared. The solution is typically an aqueous solution. The salt of M1 is Ru salt or Ir salt. When the salt of M1 is Ru salt, the salt of M2 contains at least one selected from the group consisting of Ir salt, Rh salt, Ag salt, Cu salt and Au salt. When the salt of M1 is an Ir salt, the salt of M2 contains at least one selected from the group consisting of Rh salt, Pd salt, Ag salt, Cu salt and Au salt. The Pt salt, the salt of M1 and the salt of M2 can be water-soluble, respectively.

Examples of the Pt salt, Ru salt, Ir salt, Rh salt, Pd salt, Ag salt, Cu salt and Au salt include the following salts.
Pt: K ₂ PtCl ₄ , (NH ₄ ) ₂ K ₂ PtCl ₄ , (NH ₄ ) ₂ PtCl ₆ , Na ₂ PtCl ₆ , [Pt (NO ₂ ) ₂ (NH ₃ ) ₂ ]
Ru: _{Ruthenium halides such as RuCl 3} , RuBr ₃ , Ruthenium nitrate Ir: Iridium chloride, iridium acetylacetonate, potassium iridium cyanate, potassium iridium Rh: rhodium acetate, rhodium nitrate, rhodium chloride Pd: K ₂ PdCl ₄ , Na ₂ PdCl ₄ , K ₂ PdBr ₄ , Na ₂ PdBr ₄ , Palladium nitrate Ag: Silver nitrate, Silver acetate Cu: Copper sulfate, cuprous chloride, cupric chloride, copper acetate, copper nitrate Au: gold chloride acid, odor Chemical acid, gold acetate

First, the Pt salt, the salt of M1 and the salt of M2 are weighed and added to water to prepare a solution. Acids or alkalis may be added to the water to adjust the pH of the solution. The temperature of the solution is, for example, room temperature (20 ° C. ± 15 ° C.).

Next, if necessary, add the carrier to the solution. The timing of adding the carrier to the solution is not particularly limited. When the reaction for forming the solid solution nanoparticles is allowed to proceed while the carrier is present in the solution, the solid solution nanoparticles can be directly supported on the carrier without using a protective agent such as a polymer.

Next, the liquid reducing agent and the solution are mixed to obtain a reaction solution. In one example, the liquid reducing agent and the solution are mixed by spraying the solution onto the liquid reducing agent heated to a predetermined temperature T. The reaction is allowed to proceed over a predetermined time t while maintaining the reaction solution at a predetermined temperature T. Instead of spraying, the solution may be added dropwise to the liquid reducing agent. Then, the reaction solution is allowed to cool to perform solid-liquid separation, whereby solid solution nanoparticles having a desired composition can be obtained.

The predetermined temperature T is, for example, in the range of 150 ° C. or higher and 250 ° C. or lower. The predetermined time t is, for example, in the range of 1 minute or more and 12 hours or less. Examples of the liquid reducing agent include polyhydric alcohols such as ethylene glycol, glycerin, diethylene glycol, and triethylene glycol. One or both of the liquid reducing agent and the solution may be preheated and mixed.

The reaction solution may contain a protective agent. The protective agent has a role of suppressing the aggregation of solid solution nanoparticles. Protective agents include polymers, amines, and carboxylic acids. Polymers include poly (N-vinyl-2-pyrrolidone) (PVP) and polyethylene glycol (PEG). Examples of the amine include oleylamine. Examples of the carboxylic acid include oleic acid.

It is also possible to support the solid solution nanoparticles on the carrier after the fact by mixing the solid solution nanoparticles and the particles of the carrier. Mixing may be carried out using a solvent. When a solvent is used, filtration, drying, and molding operations may be performed, if necessary.

The solid-liquid separation process may be omitted. That is, the solid solution nanoparticles may be provided in the form of a dispersion. The dispersion liquid contains a solvent and solid solution nanoparticles dispersed in the solvent. Depending on the application, it is desirable to provide solid solution nanoparticles in the form of a dispersion.

Hereinafter, the present invention will be described in more detail by way of examples.

<< Example 1: PtRuIr solid solution nanoparticles >>
Dilute hydrochloric acid was prepared by adding 0.117 ml of hydrochloric acid to 40 ml of water. The pH of dilute hydrochloric acid was 1.64 and the temperature was 24.7 ° C. 0.1025 mmol of K ₂ PtCl ₄ was dissolved in 8 ml of dilute hydrochloric acid to obtain a Pt salt aqueous solution. 0.205 mmol of RuCl ₃ · nH ₂ O was dissolved in 8 ml of dilute hydrochloric acid to obtain an aqueous Ru salt solution. 0.205 mmol of IrCl ₄ · nH ₂ O was dissolved in 8 ml of dilute hydrochloric acid to obtain an aqueous Ir salt solution. A Pt salt aqueous solution, a Ru salt aqueous solution and an Ir salt aqueous solution were mixed to obtain a mixed solution of a noble metal salt. Using an ultrasonic homogenizer, 1920 mg of ZrO ₂ powder (RC-100, manufactured by Daiichi Rare Element Co., Ltd.) was dispersed in 16 ml of dilute hydrochloric acid to obtain a ZrO ₂ dispersion. The mixture of noble metal salt added to the ZrO ₂ dispersion with stirring ZrO ₂ dispersion, to obtain a raw material solution. Stirring of the raw material solution was continued for 15 minutes.

On the other hand, an aqueous NaOH solution was prepared by dissolving 1.3 mmol of NaOH in 2 ml of water. The pH of the triethylene glycol was adjusted to 7 by slowly adding an aqueous NaOH solution to 400 ml of triethylene glycol. Then, the triethylene glycol was heated to 232 ° C.

The raw material solution was sprayed on the heated triethylene glycol over 19 minutes. The temperature of triethylene glycol at the time of spraying was 229 to 232 ° C. After the spraying was completed, the reaction solution containing triethylene glycol and the raw material solution was stirred over 10 minutes while maintaining the temperature at 232 ° C. After allowing the reaction solution to cool, the precipitate was separated by centrifugation and washed with water. Then, the separated solid matter was vacuum dried. As a result, PtRuIr solid solution nanoparticles supported on _{ZrO 2 were obtained.}

[Composition analysis, TEM observation]
The composition of PtRuIr solid solution nanoparticles was identified using a fluorescent X-ray analyzer. The results are shown in Table 1. PtRuIr solid solution nanoparticles supported on _{ZrO 2} were observed by a transmission electron microscope. The obtained TEM image is shown in FIG.

The amount of Pt supported was 1.08 wt%, which was almost the same as the target value (1 wt%). The composition ratio (atom%) of the PtRuIr solid solution nanoparticles was Pt: Ru: Ir = 22: 40: 38, which was almost in line with the target of 1: 2: 2. HfO ₂ is an impurity inevitably contained in zirconia particles.

In FIG. 1, the large particles are ZrO ₂ particles. The small particles attached to the surface of the _{ZrO 2 particles are PtRuIr solid solution nanoparticles.} The PtRuIr solid solution nanoparticles were uniformly attached to the surface of the _{ZrO 2 particles.} The average particle size of the PtRuIr solid solution nanoparticles was 2.2 ± 0.4 nm. In the notation of "A ± Bnm", A represents the average particle size and B represents the standard deviation.

[Elemental mapping and line analysis]
_{The PtRuIr solid solution nanoparticles supported on ZnO 2} of Example 1 were subjected to elemental mapping and line analysis by energy dispersive X-ray analysis (EDX). The image by HAADF-STEM (High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy) and the result of element mapping are shown in FIGS. 2A to 2D. FIG. 2A shows a HAADF-STEM image. 2B, 2C and 2D show elemental mapping data for Pt, Ir and Ru, respectively. The results of the line analysis are shown in FIGS. 3A and 3B. FIG. 3B shows the results of line analysis of PtRuIr solid solution nanoparticles appearing in the STEM image of FIG. 3A.

The dark white portion appearing in FIGS. 2B to 2D corresponds to the portion of small particles in FIG. 2A. These results indicate that PtRuIr solid solution nanoparticles were uniformly formed on _{the ZnO 2 particles.} The results of the line analysis of FIGS. 3A and 3B show that Pt, Ir and Ru are not present separately from each other, but that Pt, Ir and Ru are uniformly distributed throughout the particles. .. That is, the data in FIGS. 2A-2D, 3A and 3B show that Pt, Ir and Ru are solid-solved at the atomic level in the PtRuIr nanoparticles.

<< Examples 2 to 6: PtRuIr solid solution nanoparticles >>
PtRuIr solid solution nanoparticles of Examples 2 to 6 having different composition ratios were prepared by the same method as in Example 1 except that the charging ratios of Pt salt, Ru salt and Ir salt were changed. The target composition in each example was as follows. The target value of the amount of Pt supported in each example was 1 wt%.

Example 2: Pt _0.2 Ru _0.6 Ir _0.2
Example 3: Pt _0.2 Ru _0.2 Ir _0.6
Example 4: Pt _0.25 Ru _0.25 Ir _0.5
Example 5: Pt _0.3 Ru _0.3 Ir _0.3
Example 6: Pt _0.6 Ru _0.2 Ir _0.2

<< Reference Example 1: Pt nanoparticles >>
0.205 mmol of K ₂ PtCl ₄ was dissolved in 20 ml of water to obtain a Pt salt aqueous solution. 3960 mg of ZrO ₂ powder was dispersed in 30 ml of water to obtain a ZrO ₂ dispersion. The Pt salt solution was added to ZrO ₂ dispersion with stirring ZrO ₂ dispersion, to obtain a raw material solution. Stirring of the raw material solution was continued for 15 minutes.

The raw material solution was sprayed on 300 ml of triethylene glycol heated to 232 ° C. over 19 minutes. The temperature of triethylene glycol at the time of spraying was 228 to 233 ° C. After the spraying was completed, the reaction solution containing triethylene glycol and the raw material solution was stirred over 10 minutes while maintaining the temperature at 230 ° C. After allowing the reaction solution to cool, the precipitate was separated by centrifugation and washed with water. Then, the separated solid matter was vacuum dried. As a result, Pt nanoparticles supported on _{ZrO 2 were obtained.} The amount of Pt supported was 1.02 wt%, which was almost the same as the target value (1 wt%).

FIG. 4 is a TEM image of Pt nanoparticles supported on _{ZrO 2 of Reference Example 1.} In FIG. 4, the large particles are ZrO ₂ particles. The small particles attached to the surface of the _{ZrO 2 particles are Pt nanoparticles.} The average particle size of the Pt nanoparticles was 2.9 ± 0.8 nm.

<< Reference example 2: Ru nanoparticles >>
Dilute hydrochloric acid was prepared by adding 0.088 ml of hydrochloric acid to 30 ml of water. 0.07689 mmol of RuCl ₃ · nH ₂ O was dissolved in 8 ml of dilute hydrochloric acid to obtain an aqueous Ru salt solution. Using an ultrasonic homogenizer, 1462.45 mg of ZrO ₂ powder was dispersed in 12 ml of dilute hydrochloric acid to obtain a ZrO ₂ dispersion. The Ru salt solution was added to ZrO ₂ dispersion with stirring ZrO ₂ dispersion, to obtain a raw material solution. Stirring of the raw material solution was continued for 15 minutes.

On the other hand, 1 mmol of NaOH was dissolved in 2 ml of water to prepare an aqueous NaOH solution. The pH of the triethylene glycol was adjusted to 7 by slowly adding an aqueous NaOH solution to 300 ml of triethylene glycol. Then, the triethylene glycol was heated to 232 ° C.

The raw material solution was sprayed on the heated triethylene glycol over 13 minutes. The temperature of triethylene glycol at the time of spraying was 229 to 232 ° C. After the spraying was completed, the reaction solution containing triethylene glycol and the raw material solution was stirred over 10 minutes while maintaining the temperature at 230 ° C. After allowing the reaction solution to cool, the precipitate was separated by centrifugation and washed with water. Then, the separated solid matter was vacuum dried. As a result, Ru nanoparticles supported on _{ZrO 2 were obtained.} The amount of Ru carried was 0.43 wt%, which was almost the same as the target value (0.5 wt%).

FIG. 5 is a TEM image of Ru nanoparticles supported on _{ZrO 2 of Reference Example 2.} In FIG. 5, the large particles are ZrO ₂ particles. The small particles attached to the surface of the _{ZrO 2 particles are Ru nanoparticles.} The average particle size of the Ru nanoparticles was 4.2 ± 0.8 nm.

<< Reference Example 3: Ir Nanoparticles >>
0.07689 mmol of IrCl ₄ · nH ₂ O was dissolved in 18 ml of water to obtain an aqueous Ir salt solution. 1462.45 mg of ZrO ₂ powder was dispersed in 12 ml of water to obtain a ZrO ₂ dispersion. The Ir salt solution was added to ZrO ₂ dispersion with stirring ZrO ₂ dispersion, to obtain a raw material solution. Stirring of the raw material solution was continued for 15 minutes.

The raw material solution was sprayed on 300 ml of triethylene glycol heated to 232 ° C. over 12 minutes. The temperature of triethylene glycol at the time of spraying was 228 to 232 ° C. After the spraying was completed, the reaction solution containing triethylene glycol and the raw material solution was stirred over 10 minutes while maintaining the temperature at 230 ° C. After allowing the reaction solution to cool, the precipitate was separated by centrifugation and washed with water. Then, the separated solid matter was vacuum dried. As a result, Ir nanoparticles supported on _{ZrO 2 were obtained.} The amount of Ir carried was 1.1 wt%, which was almost the same as the target value (1 wt%).

FIG. 6 is a TEM image of Ir nanoparticles supported on _{ZrO 2 of Reference Example 3.} In FIG. 6, the large particles are ZrO ₂ particles. The small particles attached to the surface of the _{ZrO 2 particles are Ir nanoparticles.} The average particle size of the Ir nanoparticles was 1.3 ± 0.3 nm.

<< Reference Example 4: Pd nanoparticles >>
0.3759 mmol of K ₂ PdCl ₄ was dissolved in 20 ml of water to obtain an aqueous Pd salt solution. 3960 mg of ZrO ₂ powder was dispersed in 30 ml of water to obtain a ZrO ₂ dispersion. The Pd salt solution was added to ZrO ₂ dispersion with stirring ZrO ₂ dispersion, to obtain a raw material solution. Stirring of the raw material solution was continued for 15 minutes.

The raw material solution was sprayed on 300 ml of triethylene glycol heated to 232 ° C. over 22 minutes. The temperature of triethylene glycol at the time of spraying was 228 to 233 ° C. After the spraying was completed, the reaction solution containing triethylene glycol and the raw material solution was stirred over 10 minutes while maintaining the temperature at 230 ° C. After allowing the reaction solution to cool, the precipitate was separated by centrifugation and washed with water. Then, the separated solid matter was vacuum dried. As a result, Pd nanoparticles supported on _{ZrO 2 were obtained.} The amount of Pd supported was 1.06 wt%, which was almost the same as the target value (1 wt%).

FIG. 7 is a TEM image of Pd nanoparticles supported on _{ZrO 2 of Reference Example 4.} In FIG. 7, the large particles are ZrO ₂ particles. The small particles attached to the surface of the _{ZrO 2 particles are Pd nanoparticles.} The average particle size of the Pd nanoparticles was 3.9 ± 0.8 nm.

<< Comparative Example 1: Preparation of nanoparticles by impregnation method >>
2.94 g of ZrO ₂ powder was dispersed in 50 ml of water to obtain a ZrO ₂ dispersion. The ZrO ₂ dispersion was stirred at room temperature for 30 minutes. 0.666 g of Pt (NO ₂ ) ₂ (NH ₃ ) ₂ solution (Pt content: 4.595 wt%) and 1.043 g of Ru (NO) (NO ₃ ) ₃ solution (Ru content: 1.50 wt%) %) And 0.375 g of Ir (NO ₃ ) ₄ solution (Ir content: 7.91 wt%) were mixed to obtain a mixed solution. ZrO ₂ dispersion was mixed solution slowly added dropwise to ZrO ₂ dispersion while stirring to obtain a raw material solution. Stirring of the raw material solution was continued for 1 hour.

The solvent was removed from the raw material solution in a hot water bath at 50 ° C. using an evaporator. The remaining powder was collected, placed in a dryer, and dried in air at 110 ° C. for 12 hours. The dried powder was crushed in a mortar, placed in an electric furnace, and baked in air at 600 ° C. for 5 hours. As a result, PtRuIr / ZrO ₂ particles of Comparative Example 1 were obtained.

[Evaluation of methane oxidation activity]
The methane oxidation activity when the nanoparticles of Example 5, Reference Examples 1 to 4 and Comparative Example 1 were used as a catalyst was investigated. Methane oxidative activity means the catalytic ability to oxidatively decompose methane. Hereinafter, the catalyst using the nanoparticles of the example will be referred to as "catalyst of the example". A catalyst using nanoparticles of the reference example is referred to as a "catalyst of the reference example". A catalyst using nanoparticles of the comparative example is referred to as a "catalyst of the comparative example".

The methane oxidation activity of the catalysts of Example 5, Reference Examples 1 to 4 and Comparative Example 1 was evaluated using a fixed bed flow type reactor. First, a pellet-shaped 50 mg catalyst was filled in a quartz reaction tube having an inner diameter of 7 mm using quartz wool. _{A reaction gas (CH 4} : 0.1%, O ₂ : 10%, SO ₂ : 5 volppm, H ₂ O: 3%, He: balance) that simulates the combustion exhaust gas of natural gas by connecting the reaction tube to the gas supply device. Gas) was supplied towards the catalyst.

As a pretreatment before measurement, the catalyst was heated to 600 ° C. in the above reaction gas and held for 1 hour. Then, the temperature of the catalyst was lowered to 200 ° C., and the reaction gas was supplied at a flow rate of 100 ml / min. The temperature of the catalyst was increased by 50 ° C. from 200 ° C. to 600 ° C. The temperature of the catalyst was maintained at each temperature for 20 minutes, and the concentration of methane in the reaction gas that passed through the catalyst in a steady state was measured. The methane conversion rate (%) was calculated from the measured concentration. The results are shown in FIG. The "methane conversion rate" on the vertical axis indicates the ratio of oxidatively decomposed methane. The higher the methane conversion rate, the higher the methane-oxidizing activity of the catalyst.

The methane conversion rate of the catalyst of Example 5 at 400 ° C. was 41% (FIG. 8). The methane conversion rate of the catalyst of Comparative Example 1 at 400 ° C. was 29%. When the rate constant k was calculated based on the following formula, the rate constant of the catalyst of Example 5 was 4.71 × 10 ^-5 mol / min / g-cat. The rate constant of the catalyst of Comparative Example 1 was 3.06 × 10 ^-5 mol / min / g-cat. The rate constant of the catalyst of Example 5 was about 1.5 times the rate constant of the catalyst of Comparative Example 1.

k =-(F / W) ln (1-x)
F: Molar flow velocity of methane (= (0.1 / 100) × 100/22400)
W: Weight of catalyst (50 mg)
x: Conversion rate

The PtRuIr catalyst of Example 5 (Pt _0.3 Ru _0.3 Ir _0.3 / ZnO ₂ ) showed a high activity equal to or higher than that of the Pd catalyst of Reference Example 4. In the low temperature range of 350 to 500 ° C., the activity of the PtRuIr catalyst of Example 5 exceeded that of the catalyst of Comparative Example 1. The activity of the PtRuIr catalyst of Example 5 was significantly higher than that of the Pt catalyst, Ru catalyst and Ir catalyst of Reference Examples 1 to 3. For example, at 400 ° C., the methane conversion rates of the Pt catalyst, Ru catalyst and Ir catalyst of Reference Examples 1 to 3 were less than 10%. On the other hand, the methane conversion rate of the catalyst of Example 5 at 400 ° C. was about 40%.

"400 ° C" is, for example, a temperature sufficiently lower than the temperature of the exhaust gas of a general gas turbine. Therefore, it can be said that a catalyst capable of exhibiting sufficient activity at 400 ° C. is suitable for use in removing methane from the exhaust gas of a gas turbine.

The methane-oxidizing activity of the PtRuIr catalysts of Examples 1 to 4 and 6 was also examined by the same method. The results are shown in FIG.

In Examples 1 to 6, the total supported amount (wt%) of the noble metal is different from each other. In Examples 1 to 6, the amount of Pt supported is equal at 1 wt%. For example, when the activity at 400 ° C. (methane conversion rate) was compared, the activity of the PtRuIr catalyst of Example 1 (Pt _0.2 Ru _0.4 Ir _0.4 ) was the highest. The activity of the PtRuIr catalyst of Example 6 (Pt _0.6 Ru _0.2 Ir _0.2 ) was the lowest. The amount of Pt supported in Example 1 and the amount of Pt supported in Example 6 are approximately 1 wt% and equal. When the Pt content was relatively low, the PtRuIr catalyst showed high activity.

The methane-oxidizing activity of Ru nanoparticles alone is very low (Fig. 8). Nevertheless, it is surprising that the PtRuIr catalyst of Example 1 (Pt _0.2 Ru _0.4 Ir _0.4 ) and the PtRuIr catalyst of Example 2 (Pt _0.2 Ru _0.6 Ir _0.2 ) showed very high activity.

Even when the composition of the PtRuIr solid solution nanoparticles is changed while the total amount of the noble metal supported is unified to a predetermined ratio (for example, 4 wt%), the PtRuIr catalyst having various compositions has the same tendency as that of the above example. Presumed to show.

FIG. 10 is a triangular graph showing the relationship between the methane conversion rate at 400 ° C. and the composition of the solid solution nanoparticles. When the composition ratio of Pt-Ru-Ir was 0.2: 0.4: 0.4 (Example 1), the PtRuIr catalyst showed the highest activity (77.3%). As can be seen from FIGS. 9 and 10, when the content ratio of Pt in the PtRuIr solid solution nanoparticles was in an appropriate range, the catalyst using the PtRuIr solid solution nanoparticles showed high activity. From FIGS. 9 and 10, the catalytic activity tended to increase as the Pt content ratio decreased to 50 mol%, 40 mol%, and 30 mol%. Regarding the lower limit, the catalytic activity tended to increase as the Pt content ratio increased to 5 mol% and 10 mol%. Therefore, the upper limit of the Pt content ratio in the PtRuIr solid solution nanoparticles is, for example, 50 mol%, 40 mol% or 30 mol%. The lower limit of the Pt content ratio in the PtRuIr solid solution nanoparticles is, for example, 5 mol% or 10 mol%. The content ratio of Pt in the PtRuIr solid solution nanoparticles may be in the range of 10 mol% or more and 30 mol% or less.

[An endurance test]
Next, the durability of the catalysts of Example 1, Example 5, Reference Examples 1 to 4 and Comparative Example 1 was examined. Specifically, using the reactor and reaction gas described above, the time course of methane oxidation activity at 400 ° C. was investigated until 30 hours had passed. The amount of catalyst was changed from 50 mg to 200 mg. The pretreatment was performed by the same method as described above. The results are shown in FIGS. 11A and 11B.

As shown in FIG. 11A, the activity of the catalyst (Pd nanoparticles) of Reference Example 4 decreased significantly with the passage of time. This result indicates that Pd was poisoned by _{SO 2.}

The activity of the catalysts of Example 1, Example 5, and Comparative Example 1 was substantially constant over the test period of 30 hours, respectively. This result indicates that the PtRuIr catalyst is less susceptible to sulfur poisoning. Moreover, the activity of the catalysts of Examples 1 and 5 was much higher than that of the catalyst of Comparative Example 1.

As shown in FIG. 11B, the activity of the catalysts of Reference Examples 1 to 3 decreased slightly with the passage of time. However, the activity of the catalysts of Reference Examples 1 to 3 was low from the initial stage. Comparing the rate of decrease based on the initial activity, the rate of decrease in the activity of the catalysts of Reference Examples 1 to 3 was large. This indicates that Pt, Ru and Ir are also subject to sulfur poisoning, though not as much as Pd. Since the activity of the catalyst of Example 1 was hardly reduced, it is considered that the PtRuIr catalyst newly acquired excellent durability against sulfur poisoning by forming a solid solution of Pt, Ru and Ir.

<< Example 7: PtRuIr solid solution nanoparticles / SnO ₂ >>
The same method as in Example 5 except that 1438.5 mg of SnO _{2 powder was used instead of ZrO 2} powder and the amount of metal salt charged was adjusted so that the total amount of metal after support was 4.1 wt%. Obtained PtRuIr solid solution nanoparticles supported on SnO _2. That is, the composition of the PtRuIr solid solution nanoparticles in Example 7 is Pt _0.3 Ru _0.3 Ir _0.3 .

[An endurance test]
The durability of the following four types of catalysts was investigated. Specifically, using the reactor and reaction gas described above, the time course of methane oxidation activity at 400 ° C. was investigated until 100 hours had passed. The results are shown in FIG.

Example 3 catalyst (Pt _0.2 Ru _0.2 Ir _0.6 / ZrO ₂ ) 200 mg
50 mg of catalyst of Example 5 (Pt _0.3 Ru _0.3 Ir _0.3 / ZrO ₂₎
Example 7 catalyst (Pt _0.3 Ru _0.3 Ir _0.3 / SnO ₂ ) 200 mg
Example 7 catalyst (Pt _0.3 Ru _0.3 Ir _0.3 / SnO ₂ ) 50 mg

FIG. 12 is a graph showing the time course of the methane oxidation activity of the catalysts of Examples 3, 5 and 7 at 400 ° C. The initial activity (0 to 50 hours) of 200 mg of the catalyst of Example 3 using ZrO ₂ as a carrier was superior to the initial activity of 200 mg of the catalyst of Example 7 using _{SnO 2 as a carrier.} However, after 100 hours, the activity of the catalyst of Example 7 exceeded that of the catalyst of Sample 1. That is, _{the catalyst using SnO 2} as a carrier was excellent in durability.

The composition of the PtRuIr solid solution nanoparticles in the catalyst of Example 5 is the same as the composition of the PtRuIr solid solution nanoparticles in the catalyst of Example 7. The activity of 50 mg of the catalyst of Example 5 decreased immediately after the start of the test, and then remained around 40%. On the other hand, 50 mg of the catalyst of Example 7 maintained the initial activity (60%) even after the lapse of 100 hours. That is, _{the catalyst using SnO 2} as a carrier was excellent in durability.

[Acid point and base point of carrier]
The acid and basic properties of the surfaces of the ZrO ₂ particles and SnO ₂ particles as carriers were measured by the thermal desorption method (TPD). In the measurement of acid sites, ammonia is a base probe molecules are adsorbed on the carrier, to determine the amount of ammonia desorbed when the temperature was continuously increased (NH ₃ -TPD). In the measurement of the base point, carbon dioxide, which is an acid probe molecule, was used for the measurement (CO _2- TPD). Specifically, pretreatment and measurement were performed under the following conditions.

(Preprocessing)
100 mg of ZrO ₂ particles or SnO ₂ particles were filled in a reaction tube as a sample, the temperature was raised to 600 ° C. while flowing Ar, and Ar treatment was carried out over 30 minutes. Then, after switching to 100% O ₂ and performing the treatment for 30 minutes, switching to Ar and performing the treatment for 30 minutes. The sample was then cooled to 100 ° C. (NH _3- TPD) or 50 ° C. (CO _2-TPD). NH ₃ at a concentration of 0.5 vol% for 1 hour at -TPD at 100 ° C. was circulated NH ₃ / Ar mixed gas containing NH ₃ and was adsorbed NH ₃ in the sample. In CO _2- TPD, a CO ₂ / Ar mixed gas containing 0.5 vol% concentration of CO ₂ was circulated at 50 ° C. for 1 hour to adsorb _{CO 2 to the sample.} Then, it was switched to Ar, and the physically adsorbed species was desorbed from the sample over 30 minutes.

(Measurement)
The sample was heated from _{100 ° C. (NH 3} ) or 50 ° C. (CO ₂ ) to 600 ° C. at a rate of 10 ° C./min while flowing Ar at a flow rate of 40 ml / min. In NH _3- TPD, the MS signal having a mass number of 16 which is a fragment of _{NH 3 was measured.} In CO _2- TPD, an MS signal having a mass number of 44 corresponding to _{CO 2 was measured.} The results are shown in FIGS. 13A and 13B.

FIG. 13A is a graph showing the measurement results of _{NH 3-TPD.} FIG. 13B is a graph showing the measurement results of _{CO 2-TPD.} The horizontal axis shows the temperature of the sample. The vertical axis shows the MS signal intensity. As shown in FIGS. 13A and 13B, ZrO ₂ showed desorption of _{NH 3} and CO ₂ over a wide temperature range. That is, ZrO ₂ had both an acid point and a base point. On the other hand, SnO ₂ showed desorption of _{NH 3} over a wide temperature range, but showed almost no desorption of _{CO 2. No CO 2} signal was detected above 200 ° C. That is, there were almost no base points in _{SnO 2.} From these results, it is considered that the reason why the decrease in the methane conversion rate is gradual when _{SnO 2} is used as a carrier is that SO ₄ ^2- is difficult to be adsorbed on _{SnO 2.} The effect of the catalyst can be maintained for a long period of time by using a carrier in which no _{CO 2} signal is detected at 200 ° C. or higher when CO _{2-TPD measurement is performed.}

<< Example 8: PtIrPd solid solution nanoparticles >>
Using an ultrasonic homogenizer, 0.3 mmol of K ₂ PtCl ₄ , 0.3 mmol of IrCl ₄ · nH ₂ O, and 0.3 mmol of K ₂ PdCl ₄ were dissolved in 40 ml of water. As a result, a raw material liquid containing a noble metal salt was obtained.

9 mmol of PVP was added to 300 ml of triethylene glycol and heated. The raw material solution was sprayed on the heated triethylene glycol over 15 minutes. The temperature of triethylene glycol at the time of spraying was 228 to 233 ° C. After the spraying was completed, the reaction solution containing triethylene glycol and the raw material solution was stirred over 10 minutes while maintaining the temperature at 230 ° C. After allowing the reaction solution to cool, the precipitate was separated by centrifugation. The supernatant was colorless and transparent. As a result, 736.89 mg of PtIrPd solid solution nanoparticles were obtained.

[Composition analysis, TEM observation]
The composition of PtIrPd solid solution nanoparticles was identified using a fluorescent X-ray analyzer. The results are shown in Table 2. PtIrPd solid solution nanoparticles were observed with a transmission electron microscope. The obtained TEM image is shown in FIG.

The composition ratio (atom%) of the PtIrPd solid solution nanoparticles was Pt: Ir: Pd = 32: 35: 32, which was almost in line with the target of 1: 1: 1. The quantitative result (wt%) is a value calculated on the assumption that the balance other than the precious metal is PVP.

FIG. 14 is a TEM image of the PtIrPd solid solution nanoparticles of Example 8. As shown in FIG. 14, nano-sized PtIrPd solid solution nanoparticles were obtained. The average particle size of the PtIrPd solid solution nanoparticles was 4.4 ± 0.9 nm. The average particle size was calculated by measuring the particle size (major axis) of the particles (100 particles) in the TEM image and calculating the average. A in the notation A ± Bnm represents the average particle size, and B represents the standard deviation. "Major axis" means the longest distance between two points on the outer edge of a particle.

[X-ray diffraction measurement]
Powder X-ray diffraction measurement of PtIrPd solid solution nanoparticles of Example 8 was carried out. FIG. 15 is an X-ray diffraction pattern of the PtIrPd solid solution nanoparticles of Example 8. X-ray diffraction measurement was performed at room temperature using CuKα rays. The X-ray diffraction pattern showed a single fcc pattern. This indicates that the sample is a solid solution rather than a mixture of Pt, Ir and Pd. When multiple types of single noble metal nanoparticles are simply physically mixed, or when multiple types of single noble metals are phase-separated in a single particle, the lattice constant of each single noble metal is Since they are different, a plurality of fcc patterns having different peak positions are observed. However, in the case of a solid solution in which all elements are uniformly mixed at the atomic level, the lattice constant is determined by the composition ratio of each element and the atomic radius to a single value, so that only a single fcc pattern is observed.

<< Example 9: PtIrPdRh solid solution nanoparticles >>
Using an ultrasonic homogenizer, 0.25mmol of _{K 2 PtCl 4, IrCl 4 ·} nH 2 O of 0.25mmol, K ₂ PdCl ₄ of 0.25mmol, and RhCl ₃ · 3H ₂ O of 0.25mmol in 40ml water Was dissolved in. As a result, a raw material liquid containing a noble metal salt was obtained.

2 mmol of PVP was added to 300 ml of triethylene glycol and heated. The raw material liquid was sprayed on the heated triethylene glycol over 16 minutes. The temperature of triethylene glycol at the time of spraying was 229 to 232 ° C. After the spraying was completed, the reaction solution containing triethylene glycol and the raw material solution was stirred over 10 minutes while maintaining the temperature at 230 ° C. After allowing the reaction solution to cool, the precipitate was separated by centrifugation. The supernatant had a light brown color. As a result, 105.19 mg of PtIrPdRh solid solution nanoparticles were obtained.

[Composition analysis, TEM observation]
The composition of PtIrPdRh solid solution nanoparticles was identified using a fluorescent X-ray analyzer. The results are shown in Table 3. PtIrPdRh solid solution nanoparticles were observed with a transmission electron microscope. The obtained TEM image is shown in FIG.

The composition ratio (atom%) of the PtIrPdRh solid solution nanoparticles was Pt: Ir: Pd: Rh = 21: 24: 28: 27, which was almost in line with the target of 1: 1: 1: 1. The quantitative result (wt%) is a value calculated on the assumption that the balance other than the precious metal is PVP.

FIG. 16 is a TEM image of the PtIrPdRh solid solution nanoparticles of Example 9. As shown in FIG. 16, nano-sized PtIrPdRh solid solution nanoparticles were obtained. The average particle size of the PtIrPdRh solid solution nanoparticles was 3.9 ± 1.2 nm.

[X-ray diffraction measurement]
Powder X-ray diffraction measurement of PtIrPdRh solid solution nanoparticles of Example 9 was carried out. FIG. 17 is an X-ray diffraction pattern of the PtIrPdRh solid solution nanoparticles of Example 9. The X-ray diffraction pattern showed a single fcc pattern. This indicates that the sample is a solid solution rather than a mixture of Pt, Ir, Pd and Rh. When multiple types of single noble metal nanoparticles are simply physically mixed, or when multiple types of single noble metals are phase-separated in a single particle, the lattice constant of each single noble metal is Since they are different, a plurality of fcc patterns having different peak positions are observed. However, in the case of a solid solution in which all elements are uniformly mixed at the atomic level, the lattice constant is determined by the composition ratio of each element and the atomic radius to a single value, so that only a single fcc pattern is observed.

The solid solution nanoparticles of the present invention are useful as electronic materials, magnetic materials, catalyst materials, pharmaceutical materials, cosmetic materials or food materials.

Claims (15)

1. It has a composition represented by the formula Pt _x M1 _y M2 _1-xy (0 <x <1, 0 <y <1, x + y <1).
   M1 is Ru or Ir and
   When M1 is Ru, M2 is at least one selected from the group consisting of Ir, Rh, Ag, Cu and Au.
   When M1 is Ir, M2 is at least one selected from the group consisting of Rh, Pd, Ag, Cu and Au.
   Pt, M1 and M2 form a solid solution,
   Solid solution nanoparticles.
2. When M1 is Ru, M2 is Ir, Rh, Ag, Cu or Au.
   When M1 is Ir, M2 is Rh, Pd, Ag, Cu or Au.
   The solid solution nanoparticles according to claim 1.
3. M1 is Ru,
   The solid solution nanoparticles according to claim 1 or 2.
4. M2 is Ir,
   The solid solution nanoparticles according to any one of claims 1 to 3.
5. M1 is Ru,
   M2 is Ir,
   The solid solution nanoparticles according to any one of claims 1 to 4.
6. A catalyst containing the solid solution nanoparticles according to any one of claims 1 to 5.
7. Further comprising a carrier carrying the solid solution nanoparticles,
   The catalyst according to claim 6.
8. The carrier is particles of metal oxide.
   The catalyst according to claim 7.
9. _{When the CO 2-} TPD measurement of the carrier was performed at a heating rate of 10 ° C./min, no _{CO 2} signal was detected at 200 ° C. or higher.
   The catalyst according to claim 7 or 8.
10. The carrier comprises at least one selected from the group consisting of _{SnO 2} , WO ₃ , MoO ₃ , Ta ₂ O ₅ , and Nb ₂ O _5.
    The catalyst according to any one of claims 7 to 9.
11. A catalyst for oxidative decomposition of hydrocarbons,
    The catalyst according to any one of claims 6 to 10.
12. The hydrocarbon contains methane,
    The catalyst according to claim 11.
13. With solvent
    The solid solution nanoparticles according to any one of claims 1 to 5 dispersed in the solvent.
    A dispersion of solid solution nanoparticles.
14. A method for producing solid solution nanoparticles having a composition represented by the formula Pt _x M1 _y M2 _1-xy (0 <x <1, 0 <y <1, x + y <1).
    It involves adding a solution containing a Pt salt, a salt of M1 and a salt of M2 to a liquid reducing agent heated to a temperature in the range of 150 ° C. or higher and 250 ° C. or lower for reaction.
    The salt of M1 is a Ru salt or an Ir salt.
    When the salt of M1 is Ru salt, the salt of M2 contains at least one selected from the group consisting of Ir salt, Rh salt, Ag salt, Cu salt and Au salt.
    When the salt of M1 is an Ir salt, the salt of M2 contains at least one selected from the group consisting of Rh salt, Pd salt, Ag salt, Cu salt and Au salt.
    A method for producing solid solution nanoparticles.
15. The solution further comprises a carrier,
    The method for producing solid solution nanoparticles according to claim 14.

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