JP2005125282A - Catalyst particle and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To properly produce in a liquid phase a catalyst particle consisting of a base particle having a nano-meter order primary particle size and made of one kind of a single fine particle or a solid solution fine particle of two or more kinds, and one or more kinds of metals covering at least a part of the surface of the base particle. <P>SOLUTION: The base particle 1 having the nano-meter order primary particle size and made of one kind of the single fine particle or the solid solution fine particle of two or more kinds and a metal precursor 3 are mixed with a solvent 4. By exposing the solvent 4 in which the base particle 1 and the metal precursor 3 are mixed to an ultrasonic wave, a metal coating layer 2 consisting of the metal fine particle having the nano-meter order particle size or several atomic layers, the metal of which is obtained by the reduction of the metal precursor 3, is precipitated on the surface of the base particle 1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to catalyst particles used for automobile exhaust purification, fuel cell use, and environmental purification, and particularly relates to nanometer order catalyst particles.

  For example, noble metals such as Pt, Pd, and Rh are used as catalysts for purifying harmful components such as HC, CO, and NOx contained in automobile exhaust gas. In order to increase the contact area with the exhaust gas, these noble metals for catalyst are supported as particles on the surface of a carrier such as alumina to purify harmful components.

  In recent years, exhaust gas regulations for automobiles and the like are becoming stricter, and it is desired for exhaust gas purification catalysts to purify harmful components with higher efficiency.

  Similarly, it is necessary to further improve the purification performance and function of a catalyst for a fuel cell (for example, a catalyst such as a reaction between hydrogen and oxygen or a methanol reforming catalyst) or a catalyst for environmental purification. Development of catalysts is expected.

  As one of the measures for improving the efficiency of the noble metal catalyst, it is conceivable to make the noble metal particles fine and increase the contact area with harmful components. However, in the conventional loading method, only noble metal particles of submicron order (about several hundred nm) can be obtained, which hinders further improvement of the specific surface area of the catalyst. For this reason, nanometer order ( The appearance of a noble metal fine particle catalyst of nano order (about 100 nm or less) is desired.

  Therefore, in the background as described above, the development of nano-order noble metal particles having a large contact area is progressing with the aim of further increasing the activation.

For example, a method of supporting nano-order metal fine particles on γAl ₂ O ₃ using a sputtering method has been proposed (see, for example, Patent Document 1). Further, a method has been proposed in which fine particles of 20 nm or less are supported on a carrier such as Al ₂ O ₃ by using an electron beam simultaneous irradiation method (see, for example, Patent Document 2).

  However, in each of the above-described patent documents, nano-order noble metal fine particles can be supported on a carrier, but the configuration (shape, specificity, etc.) of the surface of the noble metal fine particles is not particularly limited.

  Furthermore, in general, a purification catalyst exhibits a specific decomposition activity only for a specific type of harmful substance, and does not exhibit a universal activity for a plurality of types of harmful substances. Absent.

  For this reason, when it is necessary to effectively treat exhaust gas containing many kinds of harmful substances, a method of using a combination of many kinds of catalysts according to the kinds of harmful substances can be considered. 1 and Patent Document 2 do not mention contents and effects related to the combination.

  In addition, for example, the presence of a cocatalyst is indispensable for simultaneously purifying a plurality of harmful substances such as HC, CO, and NOx, but there are very few examples of research on the structure of the cocatalyst and the combination with the catalyst. .

  From the above, it can be said that the catalyst design at the thin film level or the atomic level is necessary to develop a nanocomposite catalyst with higher activity. In response to such a demand, a catalyst particle having higher activity and capable of exhibiting activity against a plurality of types of substances has been proposed (see Patent Document 3).

This includes a single particle having a primary particle size of nanometer order or two or more solid solution fine particles, and one or more metals or their derivatives covering at least a part of the surface of the basic particle. The catalyst particles and the method for producing the same are provided.
Special table 2000-510042 gazette JP 2000-15098 A Japanese Patent Laid-Open No. 2003-80077

  However, the method for producing catalyst particles described in Patent Document 3 is a method in the gas phase in which the structure is easily controlled, and it is difficult to scale up the production apparatus when mass production is considered. Therefore, it is difficult to say that the production method is satisfactory enough. Therefore, there is an urgent need to develop a production method in a liquid phase that is excellent in mass productivity.

  In view of the above problems, the present invention provides a base particle which is a kind of single particle or a two or more kinds of solid solution fine particles having a primary particle size on the order of nanometers, and one or more metals covering at least a part of the surface of the base particle. It is an object to enable appropriate production of catalyst particles comprising:

  In order to achieve the above object, according to the first aspect of the present invention, there is provided a base particle (1) which is one kind of single particle having a primary particle size of nanometer order or two or more kinds of solid solution particles, and a metal precursor (3 ) In the solvent (4) and irradiating the solvent (4) in which the base particles (1) and the metal precursor (3) are mixed with ultrasonic waves, the surface of the base particles (1) The metal precursor (3) is a reduced metal and is characterized by depositing a metal coating layer (2) consisting of nanometer-order metal fine particles or several atomic layers.

  The present invention was obtained as a result of experimental studies, and the base particles (1) and the metal precursor (3) were mixed in the solvent (4), and these were irradiated with ultrasonic waves, The metal coating layer (2) made of the metal reduced by the metal precursor (3) can be deposited on the surface of the base particle (1) with good dispersibility.

  Here, the form of the metal coating layer (2) is nanometer-order metal fine particles, or a few atomic layers of metal.

  In general, in the method for producing a purification catalyst, a method of metallization by impregnating a support with a noble metal in an ionic state and calcining is common, but in the production method of the present invention, calcining is performed. The metal precursor (3) can be metallized at normal temperature and deposited on the surface of the base particles (1).

  Thus, according to the production method of the present invention, a base particle that is one kind of single particle or two or more solid solution fine particles having a primary particle size on the order of nanometers and at least a part of the surface of the base particle are coated. The catalyst particle which consists of 1 or more types of metal to perform can be manufactured appropriately in a liquid phase.

  Here, as in the invention described in claim 2, as the base particle (1) in the method for producing catalyst particles according to claim 1, Ce, Zr, Al, Ti, Si, Mg, W, Fe , Sr, Y can be used alone, or a metal oxide composed of two or more solid solutions can be used.

  In addition, as in the invention described in claim 3, the metal precursor (3) in the method for producing catalyst particles according to claim 1 or claim 2 is a metal oxide, a metal chloride, a metal ammonium salt, Those selected from metal nitrates and their derivatives can be used.

  In addition, as in the invention according to claim 4, the metal coating layer (2) in the method for producing catalyst particles according to claims 1 to 3 is made of a transition metal, and Pt, One or more simple substances selected from Pd, Rh, Ir, Ru, Au, Ag, Re, Os, Co, Ni, Fe, Cu, Mn, Cr, V, Mo, and W, or two or more solid solutions Can be.

  Moreover, in invention of Claim 5, in the manufacturing method of the catalyst particle of Claims 1-4, in the solvent (4) in which the said base particle (1) and a metal precursor (3) are mixed, It is characterized by adding a reducing agent.

  In order to reduce the metal precursor (3), it is preferable to add a reducing agent as described above and perform ultrasonic irradiation.

  Here, as in the invention described in claim 6, the reducing agent in the method for producing catalyst particles according to claim 5 is selected from alcohols, amines, sugars and surfactants. be able to.

  Further, as in the invention according to claim 7, in the method for producing catalyst particles according to claim 5 or 6, the ratio of the reducing agent is 0.01 wt% or more in the liquid phase. Is preferred.

  As in the invention described in claim 8, in the method for producing catalyst particles described in claims 1-7, it is preferable that the frequency of the ultrasonic wave is 20 kHz or more and 300 kHz or less.

  In addition, the code | symbol in the bracket | parenthesis of each said means is an example which shows a corresponding relationship with the specific means as described in embodiment mentioned later.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram schematically showing catalyst particles according to an embodiment of the present invention. In FIG. 1, 1 is a base particle, and this base particle 1 is one kind of single particle or two or more kinds of solid solution fine particles having a primary particle diameter of nanometer order (hereinafter referred to as nano order).

  Here, the primary particle diameter of the base particle 1 is the diameter of one base particle 1, and the primary particle diameter being nano-order usually means that the primary particle diameter is 100 nm or less. In this example, the primary particle diameter of the base particle 1 is about 1 nm to 50 nm.

  In addition, as the base particle 1, one kind of single particle is a kind of fine particle made of an element or compound such as one kind of ceramic or metal, and two or more kinds of solid solution fine particles are two or more kinds of ceramic or metal. A fine particle in which an element or a compound is in a solid solution.

  Such base particles 1 can be made of a metal oxide, specifically, one kind of simple substance selected from Ce, Zr, Al, Ti, Si, Mg, W, Fe, Sr, Y, or Two or more kinds of solid solutions can be employed.

  A method for producing the base particle 1 which is such a nano-order fine particle is not particularly limited, but includes a coprecipitation method, a sol-gel method, a hydrothermal synthesis method, a plating method, an atmospheric pressure plasma method, a vacuum evaporation method, and the like. Can be given.

  In addition, the properties and composition ratios of the two or more solid solutions are not particularly limited, and the properties and composition ratios of the two or more solid solutions are set in order to improve the purification performance such as temperature characteristics and durability characteristics. What is necessary is just to adjust suitably.

  In this embodiment, at least a part of the surface of the base particle 1 is covered with a metal coating layer 2 made of one or more metals. Here, the one or more metals may be precious metals having a catalytic function.

  The metal coating layer 2 is attached to the surface of the base particle 1 as nano-sized metal fine particles, for example, ultrafine particles having a particle diameter of less than 50 nm, or is formed on the surface of the base particle 1 as a coating layer consisting of several atomic layers. It is attached.

  Thus, when the metal coating layer 2 composed of ultrafine particles or several atomic layers is formed on the nano-order base particles 1, highly active catalyst particles can be realized. This reason is described in Patent Document 3 (Japanese Patent Laid-Open No. 2003-80077) described above.

  And such a metal coating layer 2 consists of a metal which reduced the metal precursor by the ultrasonic assist reduction method mentioned later.

  The metal precursor is selected from metal oxides, metal chlorides, metal ammonium salts, metal nitrates and derivatives thereof.

  If these compounds are used, the structure is not particularly limited. When Pt is used as an example, platinum acid is used as a metal oxide, platinum chloride is used as a metal chloride, tetraamminedichloroplatinum is used as a metal ammonium salt, Examples of the metal nitrate include dinitrodiamine platinum.

  And the metal coating layer 2 which deposits on the base particle 1 by reducing such a metal precursor consists of transition metals, specifically, Pt, Pd, Rh, Ir, Ru, Au, Ag, Re, , Os, Co, Ni, Fe, Cu, Mn, Cr, V, Mo, and W. One or more simple substances or two or more solid solutions.

  In the present embodiment, the base particle 1 can also have catalytic activity, and the base particle 1 and the metal coating layer 2 can be selected so as to exhibit catalytic activity against different substances. Therefore, one type of catalyst particle can exhibit activity against a plurality of types of substances.

  Although the detailed mechanism is not well understood, in practice, the catalytic function can be synergistically enhanced, and catalyst particles having high decomposition activity can be realized for a plurality of toxic substances.

Specifically, the combination of the base particles 1 coated with the metal coating layer 2 that can be expected to have a synergistic effect on the catalyst function includes CeO ₂ fine particles coated with Pt and CeO ₂ —ZrO ₂ coated with Pt. Examples thereof include solid solution fine particles, TiO ₂ fine particles coated with Au, and carbon particles coated with Pt.

  Thus, according to the present embodiment, it is possible to provide catalyst particles that have higher activity and can exhibit activity against a plurality of types of substances.

  Such catalyst particles of this embodiment can be produced by an ultrasonic assisted reduction method. FIG. 2 is a diagram for explaining the ultrasonic assisted reduction method which is the manufacturing method of this embodiment.

  The catalyst particles of the present embodiment are broadly obtained by mixing the base particles 1 and the metal precursor 3 in the solvent 4 and irradiating the solvent 4 in which the base particles 1 and the metal precursor 3 are mixed with ultrasonic waves. It is produced by depositing on the surface of the base particle 1 a metal coating layer 2 which is a metal reduced by the metal precursor 3 and consists of metal fine particles of nanometer order or several atomic layers.

  Specifically, as shown in FIG. 2A, the solvent 4 is put in a container 10 such as a beaker, and the base particles 1 and the metal precursor 3 are mixed in the solvent 4. And this container 10 is set to the ultrasonic generator (sono reactor) 20, and an ultrasonic wave is irradiated as shown by a figure.

Here, the principle of the ultrasonic assisted reduction method will be described with reference to FIGS. 2B to 2E for an example in which CeO ₂ is used as the base particle 1 and PtCl ₂ is used as the metal precursor 3. In addition, as the solvent 4, organic solvents, such as water and ethanol, etc. can be used.

First, as shown in FIG. 2B, when the base particles 1 and the metal precursor 3 are mixed in the solvent 4, CeO ₂ and Pt ²⁺ ions Cl ⁻ ions are dispersed in the solvent. . In FIG. 2, Pt ²⁺ ions are shown as small black circles, and Cl ⁻ ions are shown as slightly larger circles with a cross mark inside.

Then, as shown in FIG. 2 (c), the reducing agent contained in the solvent 4, the active sites of the CeO ₂ surface by the Pt ²⁺ ions as a nucleus is metallized by reduction, the CeO ₂ surface Pt metal is deposited as the metal coating layer 2.

Then, the precipitation of the Pt metal 2 proceeds. At this time, as shown in FIG. 2D, cavities (bubbles) K are generated on the CeO ₂ surface by the ultrasonic waves.

The presence of the cavity K causes the Pt metal 2 to be dispersed and precipitated on the CeO ₂ surface, and the crystal growth of the Pt metal 2 is suppressed by the impact of the disappearance of the cavity K. In FIG. 2D, the cavity K is indicated by a slightly smaller white circle and a jagged mark. The jagged cavity K shows a ruptured state.

  In the ultrasonic assisted reduction method, such a mechanism is presumed. As a result, as shown in FIG. 2E, the metal precursor 3 is a reduced metal having a nanometer size on the surface of the base particle 1. Catalyst particles are produced by depositing a metal coating layer 2 composed of order metal fine particles or several atomic layers.

  Thus, in the present embodiment, the catalyst particles of the present embodiment can be appropriately manufactured by the ultrasonic assisted reduction method.

  Here, as described above, a reducing agent may be added as a means for activating ultrasonic assisted reduction. Such a reducing agent is not particularly limited, and examples thereof include alcohols, amines, saccharides, and surfactants.

  Specifically, the alcohols include ethanol, propanol, the amines include diethanolamine, the saccharides include sucrose, and the surfactant includes an alkaline surfactant.

  Further, the addition amount of the reducing agent is not particularly limited as long as it is 0.01 wt% (wt%) or more with respect to the solvent 4, that is, 0.01 wt% or more in the liquid phase. .

  However, by controlling the ratio of the reducing agent, it is possible to control the metal particle size that is reduced and deposited, and it is desirable to select the ratio of the reducing agent to the desired metal particle size.

  When the ratio of the reducing agent is large, the reaction becomes faster, so that the growth of the metal particles is promoted and the metal particle size is increased. On the other hand, when the ratio of the reducing agent is small, the growth of the metal particles is slow and the precipitation to other active sites is promoted more than the growth, so that the metal particle size tends to be small.

  In the ultrasonic assisted reduction method, the frequency of the ultrasonic wave to be irradiated is not particularly limited, but is preferably 20 to 300 kHz. The optimum frequency differs depending on the metal precursor. Generally, for metal precursors that dissolve in the liquid phase, a high frequency is used, and for metal precursors that are insoluble in the liquid phase, It is desirable to use a low frequency.

  As described above, according to the present embodiment, the base particle 1 which is a kind of simple particles having a primary particle size of nanometer order or two or more kinds of solid solution particles, and the metal precursor 3 are contained in the solvent 4. And by irradiating the solvent 4 in which the base particles 1 and the metal precursor 3 are mixed with ultrasonic waves, the surface of the base particles 1 is a metal obtained by reducing the metal precursor 3 and having a metal on the nanometer order. There is provided a method for producing catalyst particles mainly characterized by depositing a metal coating layer 2 composed of fine particles or several atomic layers.

  By mixing the base particle 1 and the metal precursor 3 in the solvent 4 and irradiating them with ultrasonic waves, the surface of the base particle 1 has nano-particles or a number of nanoparticles made of metal reduced by the metal precursor 3. The atomic metal coating layer 2 can be deposited with good dispersibility.

  Further, in general, in a method for producing a purification catalyst, a method of metallization by impregnating a support with a noble metal in an ionic state and calcination is common, but in the production method of the present embodiment, calcination is performed. The metal precursor 3 can be metallized at room temperature and deposited on the surface of the base particle 1 without doing so.

  As described above, according to the manufacturing method of the present embodiment, the base particle 1 which is one kind of single particle or two or more kinds of solid solution fine particles having a primary particle size on the order of nanometers, and at least one of the surfaces of the base particle 1 is used. The catalyst particle which consists of 1 or more types of metal which coat | covers a part can be manufactured appropriately in a liquid phase. Therefore, a manufacturing method suitable for mass production is provided.

  Hereinafter, examples of catalyst fine particles according to the present invention will be described together with comparative examples. The catalyst targeted in the present invention is nano-order catalyst fine particles, which are widely used for exhaust gas purification, environmental purification, fuel cell, and the like. Needless to say, the present invention is applicable in the field and is not limited to the embodiments.

CeO ₂ fine particles having a primary particle diameter of several tens of nanometers as base particles, PtCl ₂ as a metal precursor, and water as a solvent were mixed and dispersed uniformly using a rotor or the like.

  Subsequently, ethanol was mixed as a reducing agent, and ultrasonic waves were applied using a sonoreactor to reduce and precipitate Pt as a metal. As the conditions, the irradiation frequency of ultrasonic waves was 24 kHz, the irradiation time was 1 hour, and the water bath temperature was 20 ° C.

CeO ₂ fine particles having a primary particle diameter of several tens of nanometers as base particles, PtCl ₂ as a metal precursor, and water as a solvent were mixed and dispersed uniformly using a rotor or the like.

  Subsequently, diethanolamine was mixed as a reducing agent, and ultrasonic waves were applied using a sonoreactor to reduce and precipitate Pt as a metal. As the conditions, the irradiation frequency of ultrasonic waves was 24 kHz, the irradiation time was 1 hour, and the water bath temperature was 20 ° C.

CeO ₂ fine particles having a primary particle size of several tens of nanometers as base particles, PtO ₂ as a metal precursor, and water as a solvent were mixed and dispersed uniformly using a rotor or the like.

  Subsequently, ethanol was mixed as a reducing agent, and ultrasonic waves were applied using a sonoreactor to reduce and precipitate Pt as a metal. As the conditions, the irradiation frequency of ultrasonic waves was 24 kHz, the irradiation time was 1 hour, and the water bath temperature was 20 ° C.

CeO ₂ fine particles having a primary particle diameter of several tens of nanometers as base particles, PtO ₂ as a metal precursor, and ethanol as a solvent were mixed and dispersed uniformly using a rotor or the like.

  Subsequently, ultrasonic waves were used to reduce and precipitate Pt as a metal using a sonoreactor. As the conditions, the irradiation frequency of ultrasonic waves was 24 kHz, the irradiation time was 1 hour, and the water bath temperature was 20 ° C.

CeO ₂ fine particles having a primary particle diameter of several tens of nanometers as base particles, ammonium tetrachloroplatinate as a metal precursor, were mixed in water as a solvent, and uniformly dispersed using a rotor or the like.

  Subsequently, ethanol was mixed as a reducing agent, and ultrasonic waves were applied using a sonoreactor to reduce and precipitate Pt as a metal. As the conditions, the irradiation frequency of ultrasonic waves was 24 kHz, the irradiation time was 1 hour, and the water bath temperature was 20 ° C.

CeO ₂ fine particles having a primary particle diameter of several tens of nanometers as base particles, ammonium tetrachloroplatinate as a metal precursor, were mixed in water as a solvent, and uniformly dispersed using a rotor or the like.

  Subsequently, ethanol was mixed as a reducing agent, and ultrasonic waves were applied using a sonoreactor to reduce and precipitate Pt as a metal. As the conditions, the ultrasonic irradiation frequency was 300 kHz, the irradiation time was 1 hour, and the water bath temperature was 20 ° C.

CeO ₂ fine particles having a primary particle diameter of several tens of nanometers as base particles, PtCl ₂ and RhCl ₃ / 3H ₂ O as metal precursors were mixed in water as a solvent, and uniformly dispersed using a rotor or the like.

  Subsequently, ethanol was mixed as a reducing agent, and ultrasonic waves were applied using a sonoreactor to reduce and deposit Pt and Rh as metals. As the conditions, the irradiation frequency of ultrasonic waves was 24 kHz, the irradiation time was 1 hour, and the water bath temperature was 20 ° C.

CeO ₂ .ZrO ₂ solid solution fine particles having a primary particle diameter of several nanometers as base particles, PtCl ₂ and RhCl ₃ / 3H ₂ O as metal precursors are mixed in water as a solvent, and uniform using a rotor or the like. Dispersed.

  Subsequently, ethanol was mixed as a reducing agent, and ultrasonic waves were applied using a sonoreactor to reduce and deposit Pt and Rh as metals. As the conditions, the irradiation frequency of ultrasonic waves was 24 kHz, the irradiation time was 1 hour, and the water bath temperature was 20 ° C.

(Comparative Example 1)
Other methods for producing Pt-coated CeO ₂ fine particles include a coprecipitation method. The manufacturing method in this case is as follows. A predetermined amount of a water-soluble salt of Ce and Pt (for example, chloride, nitrate, sulfate, etc.) is dissolved in a water-soluble solvent such as pure water or ethanol.

  To the resulting aqueous solution, an alkaline solution such as ammonia or sodium hydroxide is gradually added dropwise so that the pH is 7 or more. At this time, the concentration of the alkaline solution (0.1 N or less) is preferably as thin as possible. As soon as the alkaline solution is dropped, a precipitate of Ce and Pt hydroxide is formed.

  The obtained hydroxide precipitate is rubbed with filter paper, washed with pure water 2 to 3 times, and filtered to obtain a mixed powder of Ce and Pt hydroxide.

The obtained powder is calcined in the air (the calcining temperature is about 300 to 1000 ° C., but preferably about 400 to 600 ° C.) to obtain a composite powder made of CeO ₂ and Pt. At this time, since Pt is a substance that is very easily reduced, it is easily reduced at a high temperature and deposited as a metal even in the atmosphere.

The powder thus obtained is a powder uniformly mixed in a nanometer size, but it is merely a mixture of CeO ₂ and Pt particles, and their binding force is smaller than that of the above example. Moreover, it is extremely difficult to control the particle diameter and the compounding ratio (composition ratio), and there are many impurities.

  The composite powder thus obtained is uniaxially pressed (applied pressure is 1 to 1000 MPa, but if the pressure is too high, the surface area is reduced, so about 1 to 10 MPa is preferable). Is made.

In this Comparative Example 1, using the above coprecipitation method, CeCl ₃ · xH ₂ O cocatalyst feed, the PtCl ₄ · 5H ₂ O as a catalyst material, the weight ratio of CeO _2: Pt = 100: 10 of the Pt-coated CeO ₂ fine particles were prepared.

(Observation of surface properties)
In order to confirm the particle diameter and the like of the catalyst fine particles produced in the above Examples and Comparative Examples, TEM observation and measurement of the metal surface by the CO pulse method were performed, and the Pt particle diameter was analyzed.

In Example 1, it was confirmed that about 2 nm of Pt was deposited on CeO ₂ particles having a primary particle diameter of 10 to 30 nm. On the other hand, in Comparative Example 1, CeO ₂ particles having a primary particle diameter of about 50 nm and Pt of about several nm were confirmed, but unlike Example 1, CeO ₂ and Pt existed alone. It was.

(Evaluation of purification performance of toxic substances)
In order to confirm that the above examples exhibit high activity against toxic gases, the purification performance was evaluated using the catalyst fine particle pellets produced in the first to fifth examples and the comparative example 1.

  After preparing a φ5 mm pellet composed of the particles of Examples 1 to 8 and Comparative Example 1, it was pulverized from φ0.85 mm to 1.7 mm with a sieve, and 5 cc of the pulverized granule was set in a quartz glass tube.

  Under conditions of 50 ° C. to 400 ° C. in an infrared image furnace, propylene gas is allowed to flow from the inlet side of the glass tube, and the gas amount and gas components coming out from the outlet side of the glass tube are analyzed by gas chromatography. The temperature at which propylene gas was purified by 50% (purification temperature) was measured. This is called the initial purification temperature.

  Furthermore, in order to evaluate the stability of the catalyst particles at a high temperature, the same measurement was carried out after being left in a furnace at 1000 ° C. for 24 hours. The purification temperature obtained by this measurement will be referred to as the purification temperature after aging. The lower the purification temperature, the better the purification performance.

  The results of measuring the purification temperature for each of Examples 1 to 8 and Comparative Example 1 were as follows.

  In Example 1, the initial purification temperature was 163 ° C., and the purification temperature after aging was 195 ° C.

  In Example 2, the initial purification temperature was 157 ° C., and the purification temperature after aging was 188 ° C.

  In Example 3, the initial purification temperature was 172 ° C., and the purification temperature after aging was 205 ° C.

  In Example 4, the initial purification temperature was 168 ° C., and the purification temperature after aging was 198 ° C.

  In Example 5, the initial purification temperature was 170 ° C., and the purification temperature after aging was 200 ° C.

  In Example 6, the initial purification temperature was 165 ° C., and the purification temperature after aging was 193 ° C.

  In Example 7, the initial purification temperature was 160 ° C., and the purification temperature after aging was 195 ° C.

  In Example 8, the initial purification temperature was 157 ° C., and the purification temperature after aging was 190 ° C.

  In Comparative Example 1, the initial purification temperature was 200 ° C., and the purification temperature after aging was 250 ° C.

  Compared to Comparative Example 1, in Examples 1 to 8, the initial purification temperature is low, and it is confirmed that the purification performance is greatly improved.

  Further, when Example 1 in which the metal precursor is PtCl 2, Example 3 in which the metal precursor is PtO 2, and Example 5 in which the metal precursor is ammonium tetrachloroplatinate are compared, the metal precursor (Pt The purification performance varies slightly depending on the raw materials.

  Also, the purification characteristics slightly change depending on the frequency of the ultrasonic wave, the ratio of the reducing agent, and the type of the reducing agent, and the detailed cause is not well understood, but it is considered that the optimum conditions differ depending on the Pt raw material.

  In addition, as is clear from the evaluation results of the examples and comparative examples, when purification at the same temperature is considered, it can be said that the catalyst according to this example functions in a small amount compared to the existing one, which reduces the cost. Can also be expected to contribute.

  As described above, the present invention is a technique for producing nanocomposite particles at room temperature by using an ultrasonic-assisted reduction method to precipitate and reduce a metal element in a liquid phase.

  Specifically, the base particles 1 having a primary particle size on the order of nanometers and the metal precursor 3 are mixed in the solvent 4 and are irradiated with ultrasonic waves, whereby the base particles 1 This is a method of realizing nanocomposite particles by reducing and depositing metal coating layer 2 composed of metric metal fine particles or several atomic layers.

  Although the detailed mechanism is not clear, when the ultrasonic-assisted reduction method of the present invention is used, the metal element can be reduced and deposited on the base particles 1 with good dispersibility, and there is no need to calcinate at a high temperature. Nanocomposite particles can be realized. In addition, this can ensure high-performance decomposition activity with a small amount of catalyst, and can be expected to contribute to cost reduction.

It is a figure which shows typically the catalyst particle which concerns on embodiment of this invention. It is a figure for demonstrating the ultrasonic-assisted reduction method which is the manufacturing method of embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Base particle, 2 ... Metal coating layer, 3 ... Metal precursor, 4 ... Solvent.

Claims (8)

A base particle (1) which is a kind of single particle having a primary particle size of nanometer order or two or more kinds of solid solution particles, and a metal precursor (3) are mixed in a solvent (4),
By irradiating ultrasonic waves to the solvent (4) in which the base particles (1) and the metal precursor (3) are mixed,
The surface of the base particle (1) is characterized in that a metal coating layer (2) comprising a metal fine particle of nanometer order or several atomic layers, which is a metal reduced by the metal precursor (3), is deposited. A method for producing catalyst particles. The base particle (1) is a single oxide selected from Ce, Zr, Al, Ti, Si, Mg, W, Fe, Sr, and Y, or a metal oxide composed of two or more solid solutions. The method for producing catalyst particles according to claim 1, wherein the method is characterized in that: 3. The catalyst particle according to claim 1, wherein the metal precursor (3) is selected from metal oxides, metal chlorides, metal ammonium salts, metal nitrates, and derivatives thereof. Production method. The metal coating layer (2) is made of a transition metal, and is made of Pt, Pd, Rh, Ir, Ru, Au, Ag, Re, Os, Co, Ni, Fe, Cu, Mn, Cr, V, The method for producing catalyst particles according to any one of claims 1 to 3, wherein the catalyst particles are one or more selected from Mo and W, or two or more solid solutions. The method for producing catalyst particles according to any one of claims 1 to 4, wherein a reducing agent is added to the solvent (4) in which the base particles (1) and the metal precursor (3) are mixed. . The method for producing catalyst particles according to claim 5, wherein the reducing agent is selected from alcohols, amines, saccharides, and surfactants. The method for producing catalyst particles according to claim 5 or 6, wherein the ratio of the reducing agent is 0.01 wt% or more in the liquid phase. The method for producing catalyst particles according to any one of claims 1 to 7, wherein the frequency of the ultrasonic wave is 20 kHz or more and 300 kHz or less.

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