JPWO2006051825A1 - Method for producing noble metal particulate carrier - Google Patents

Abstract

The method for producing a noble metal fine particle carrier of the present invention includes a step of preparing a colloid solution containing noble metal fine particles as a colloid, and a step of supporting the noble metal fine particles on a substrate using the colloid solution. In the step of supporting the noble metal fine particles on the substrate, a voltage is applied to the colloid solution while the colloid solution and the substrate are in contact with each other.

Description

  The present invention relates to a method for producing a noble metal fine particle carrier having noble metal fine particles supported on a substrate.

  Noble metals are utilized as catalysts by being supported on various substrates such as carbon-based materials, ceramics, metal oxide-based materials, metal-based materials and the like. For example, by supporting a noble metal on a porous substrate, it is used as a catalyst for purifying exhaust gas of automobiles. There is also a photocatalyst co-catalyst aimed at increasing the activity of the photocatalyst material by supporting a noble metal on the photocatalyst material.

  In the fuel cell field, there is an electrode catalyst in which a noble metal is supported on a carbon-based material. A reforming catalyst in which a noble metal is supported on an inorganic oxide substrate is used for reforming a hydrocarbon compound to generate hydrogen.

  Examples of the method for supporting the noble metal on the substrate include the following techniques.

  One is a method in which noble metal ions are reduced and supported directly on the surface of the substrate as disclosed in JP-A-9-47659 and JP-A-2003-320249. In this method, the substrate is brought into contact with a solution containing a noble metal salt or a noble metal complex, and then noble metal particles are directly deposited on the surface of the substrate while reducing the noble metal ions by adding a reducing agent. In addition to the addition of a reducing agent, as disclosed in JP-A No. 2000-157874, there are a heat reduction with a reducing gas and a reduction method by ultraviolet light irradiation.

  The other is a method in which noble metal fine particles are prepared in advance and then fixed to a substrate. Specifically, as disclosed in Japanese Patent Application Laid-Open No. 2004-100040 by the present inventors, a method in which a colloid solution containing noble metal fine particles as a colloid is brought into contact with the substrate to naturally adsorb the noble metal fine particles on the surface of the substrate. It is. Further, as disclosed in Japanese Patent Application Laid-Open No. 2002-305001, there is a method of promoting adsorption of noble metal fine particles to a substrate by changing the pH of a colloid solution.

  As described above, in the method of directly reducing noble metal ions on the substrate surface, it is difficult to control the particle size and dispersibility of the noble metal fine particles. For this reason, noble metal fine particles grow greatly on the surface of the substrate or grow in a film shape, so that the expected catalytic ability may not be obtained. Another problem is that impurities such as amino groups, nitro groups, and chlorine ions tend to remain on the surface of the support.

  On the other hand, in the method in which the colloidal noble metal fine particles are naturally adsorbed on the substrate, it is necessary to increase the concentration of the colloid solution in order to increase the amount of the noble metal fine particles supported on the substrate. However, since the precious metal fine particles have low dispersion power, it is often difficult to increase the concentration of the precious metal colloid solution.

  Certainly, as disclosed in Japanese Patent Application Laid-Open No. 2002-305001, the surface of the noble metal fine particles is coated with a protective colloid, thereby improving the dispersion stability of the noble metal fine particles and increasing the concentration of the colloid solution. There is also technology. However, the noble metal fine particles with protective colloid have a drawback that the catalytic ability is lowered because the reaction surface is reduced by the protective colloid. Although there is a measure to remove the protective colloid by carrying out a heat treatment after supporting the noble metal fine particles with protective colloid on the substrate, the increase in the number of steps is unavoidable. Is difficult to remove completely.

  Further, in order to promote the loading of the noble metal fine particles by controlling the pH of the colloidal solution, it is necessary to add hydrochloric acid or the like, so that there is a disadvantage that impurities remain on the carrier.

  An object of the present invention is to provide a method for producing a noble metal fine particle carrier capable of efficiently carrying the noble metal fine particles on a substrate.

  That is, the present invention provides a method for producing a noble metal fine particle carrier, in which a noble metal fine particle is supported on a substrate while a voltage is applied to the colloid solution while the substrate is in contact with a colloidal solution containing the noble metal fine particles as a colloid. .

  According to the present invention, by adding the operation of applying a voltage to the colloidal solution, the amount of noble metal fine particles supported on the substrate is greatly increased as compared with the case where no voltage is applied to the colloidal solution. Accordingly, it is not essential to increase the concentration of the colloidal solution by coating the noble metal fine particles with the protective colloid. When no precious metal particles with protective colloids are not used, there is no need to perform a step of removing the protective colloids by heat treatment, etc. I can expect. However, precious metal fine particles with protective colloid can also be used in the production method of the present invention.

  The protective colloid refers to a hydrocolloid added to increase the stability of the hydrophobic colloid to the electrolyte in a broad sense. However, in the present specification, the protective colloid is used in the sense of an organic polymer hydrocolloid. Also in the above-mentioned Japanese Patent Application Laid-Open No. 2002-305001, polyvinyl pyrrolidone, polyvinyl sulfonic acid and the like are used as protective polymers.

  In addition, since a colloid solution is prepared in advance and the substrate is brought into contact with the colloid solution to support the noble metal particles, the phenomenon that the noble metal particles grow greatly on the substrate surface does not occur, and the particle size and dispersibility are controlled. Cheap. That is, the noble metal fine particles can be uniformly distributed on the substrate surface in a nano-sized state with a particle size of several nanometers to several tens of nanometers, which contributes to an improvement in catalytic performance. Further, since the time required for supporting the noble metal fine particles on the substrate can be greatly shortened as compared with natural adsorption, an improvement in productivity can be expected. Further, since the ratio of the amount of noble metal supported on the substrate to the amount of noble metal contained in the colloidal solution can be increased, it contributes to the reduction of raw material costs.

  By the way, although the reason why the amount of noble metal particles supported can be increased or the time required for the supporting process can be shortened by applying a voltage to the colloidal solution is not necessarily clear, the present inventors consider as follows. ing. That is, due to the generation of an electric field in the colloidal solution, some electrical action works between the substrate and the noble metal fine particles, increasing the collision probability between the two, and as a result, the amount of noble metal fine particles supported on the substrate is increased. As it increases, the loading process is completed in a short time. However, it is considered that both the base and the noble metal fine particles are electrically neutral, and the noble metal fine particles are supported on the base by van der Waals force.

FIG. 1 is a schematic diagram for explaining an example of a method for producing a noble metal fine particle carrier according to the present invention. FIG. 2 is a schematic view for explaining another example of the method for producing a noble metal fine particle carrier according to the present invention. FIG. 3A is a schematic cross-sectional view illustrating a noble metal fine particle carrier according to the present invention. FIG. 3B is a schematic cross-sectional view illustrating another example of the noble metal fine particle carrier according to the present invention.

  Hereinafter, embodiments of the present invention will be described in detail.

(About the substrate)
As the substrate for supporting the noble metal fine particles, a substrate made of one inorganic material selected from the group consisting of carbon materials, ceramics, metal oxide materials and metal materials can be used. The substrate made of an inorganic material can be used in the form of, for example, a powder (inorganic powder) or a film (inorganic film) formed on a suitable support.

  A typical carbon-based material is conductive carbon. For example, a support formed by supporting noble metal fine particles on a conductive carbon powder such as carbon black is attracting attention as a catalyst for an electrode of a fuel cell. Examples of ceramics include porous ceramics. For example, a support formed by supporting noble metal fine particles on porous alumina ceramics is used as a catalyst for purifying exhaust gas of automobiles. An example of the metal oxide material is titanium oxide. Titanium oxide is used as a photocatalyst by itself, but the catalytic activity can be enhanced by supporting noble metal fine particles. In addition, when the noble metal fine particles are supported on the titanium oxide thin film formed on the substrate by a known film forming method such as sputtering or CVD, the method of the present invention can be employed. In the case of a metal-based material, the present invention is useful in a form where it is difficult to use the electrode itself as a metal powder.

  Another example of the substrate for supporting the noble metal fine particles is glass. Glass can be used in the form of beads, powder or fibers. A support formed by supporting precious metal fine particles on a glass substrate has uses such as a catalyst for decomposing a harmful substance contained in wastewater and a catalyst for air cleaning.

  Further, the substrate on which the noble metal fine particles are supported may be made of a polymer material. An example of such a polymer material is an anion exchange resin. An anion exchange resin has a feature that a functional group having a positive charge is fixed on the surface, and a noble metal colloid having a negative charge is easily supported.

(Precious metal fine particles)
Examples of the noble metal fine particles supported on the substrate include those containing as a main component one selected from the group consisting of gold, silver, platinum, palladium, iridium, ruthenium, rhenium, osmium and rhodium. It is desirable that the noble metal fine particles are substantially composed of only the noble metal. Further, fine particles made of an alloy or mixture of two or more kinds of noble metals selected from the above group can be supported on the substrate. It is also possible to support the first noble metal fine particles (for example, platinum fine particles) and the second noble metal fine particles (for example, gold fine particles) on the same substrate. When importance is attached to high catalytic ability, it is recommended to use noble metal particles consisting essentially of platinum alone.

  “Contained as a main component” means a component that is contained most in mass%. “Substantially” means that impurities that are inevitably mixed in and impurities that are difficult to remove industrially may be included.

  The noble metal fine particles may have a surface coated with a protective colloid, or may have no protective colloid. The protective colloid is, for example, a polymer compound such as polyvinyl alcohol or polyvinyl pyrrolidone. When preparing a colloidal solution, noble metal fine particles with protective colloid can be formed by using a solvent in which these polymer compounds are dissolved.

  When the noble metal fine particles are coated with the protective colloid, the dispersion stability in the solvent is improved, so that the concentration can be increased. However, since the catalytic activity is lowered by the protective colloid, it is necessary to carry out a heat treatment for removing the protective colloid after it is supported on the substrate.

  On the other hand, the precious metal fine particles not covered with the protective colloid have high catalytic ability, but have a weak point that the dispersion stability in the solvent is low, and the aggregation is likely to occur when the concentration is increased. However, according to the method of the present invention, a sufficient loading amount can be achieved even when a relatively low concentration colloidal solution is used. In consideration of the point that the step of removing the protective colloid is unnecessary, in the present invention, it is desirable that noble metal fine particles having no protective colloid on the surface are supported on the substrate.

  If noble metal fine particles having substantially no protective colloid on the surface are used, only the reducing agent (for example, citric acid) used when forming the noble metal fine particles is present on the surface of the noble metal fine particles. Therefore, no amino group, nitro group, or chlorine ion is present on the surface of the noble metal fine particles. For this reason, the noble metal fine particles are kept highly active.

(About preparation of colloidal solution)
A colloid solution containing noble metal fine particles as a colloid can be prepared by adding a reducing agent to a preliminary solution in which a noble metal source is dissolved in an appropriate solvent to prepare a raw material solution, and stirring this raw material solution while boiling (colloid). Solution preparation step). The reason why the reduction reaction proceeds while removing dissolved oxygen from the raw material solution by boiling is because dissolved oxygen inhibits the reduction reaction. Moreover, aggregation becomes difficult to occur by boiling.

  Examples of the reducing agent include alcohols, citric acids, carboxylic acids, ketones, ethers, aldehydes, and esters. Examples of alcohols include methanol and ethanol, examples of citric acids include citric acid and sodium citrate, and examples of carboxylic acids include acetic acid and fumaric acid. Two or more of these may be used in combination. The use of citric acids such as sodium citrate is recommended to produce noble metal particles with a small particle size. Further, when citric acids are used as the reducing agent, a colloid solution containing a relatively high concentration of noble metal fine particles having no protective colloid can be prepared.

  As the noble metal source, a noble metal salt such as a noble metal chloride, nitrate or sulfate, or a noble metal complex can be used. When two or more kinds of noble metal sources are used in combination, a colloidal solution containing noble metal fine particles of the alloy as a colloid can be prepared. Further, when a platinum salt is used as the noble metal salt, it is preferable because noble metal fine particles having a particle diameter as small as several nm can be formed.

  The solvent used for preparing the colloidal solution may be any solvent that can dissolve the noble metal source and the reducing agent, and examples thereof include water and alcohols. Examples of alcohols include methanol and ethanol. Water is particularly preferable.

(Supporting precious metal particles on the substrate)
After preparing the colloidal solution, the substrate is brought into contact with the colloidal solution. If the substrate has a powder or fiber form, an appropriate amount is weighed and mixed into the colloidal solution. When the substrate has the form of a film, the support on which the film is formed is immersed in the colloidal solution. Then, the colloid solution is sufficiently agitated while applying a voltage to support the noble metal fine particles as a colloid on the substrate (supporting step).

  The electrode material for applying a voltage to the colloidal solution may be any material that conducts electricity, and stainless steel, aluminum, carbon, or the like can be used. The area of the electrodes and the distance between the electrodes may be adjusted according to the size of the substrate and the amount of colloidal solution used. It is desirable to use a plate-like electrode in that a turbulent flow is likely to occur when the colloidal solution is stirred, and a sufficient stirring effect can be obtained. The applied voltage may be either direct current or alternating current. There is no particular limitation on the waveform, and for example, a pulse component may be included in the DC component or the AC component. Note that if the applied voltage is too high, it is not preferable in terms of work safety, and is preferably 100 V or less.

  The arrangement of the electrodes for applying a voltage to the colloidal solution is not particularly problematic when the substrate is a powder, and it is only necessary to arrange an electrode pair consisting of an anode and a cathode in a container containing the colloidal solution. . On the other hand, when a substrate such as a film formed on a support is used and a DC voltage is applied to the colloidal solution, attention must be paid to the positional relationship between the electrode and the substrate. Specifically, a substrate is disposed between an anode and a cathode disposed in the colloid solution, and stirring is performed while applying a DC voltage to the colloid solution while keeping the posture of the substrate constant. In this way, it is possible to selectively carry the noble metal fine particles on a specific region of the substrate. That is, the noble metal fine particles can be selectively supported on the surface on which the film is formed.

  For example, as shown in FIG. 2, in the case where noble metal fine particles are supported on a film 11 (for example, a titanium oxide film) formed on one main surface of a plate-like support 12, the film 11 is oriented in the direction of the cathode 5b. A support 13 with a film is arranged between the anode 5a and the cathode 5b so as to face. Then, with the position of the support 13 with the film fixed, a DC voltage is applied to the colloidal solution 21 and the colloidal solution 21 is stirred by the magnetic stirrer 7. In this way, the noble metal fine particles are selectively carried on the film 11, and the noble metal fine particles are hardly carried on the back surface of the support 12 on which the film 11 is not formed.

  Further, when an alternating voltage is applied to the colloidal solution, noble metal fine particles can be uniformly supported on the entire substrate by disposing the substrate between the electrodes 5a and 5b. What is necessary is just to adjust the frequency of an alternating voltage in the range of several dozen Hz-several hundred Hz, for example. Even when a DC voltage is applied, the same effect as when an AC voltage is applied can be obtained by supporting the noble metal fine particles on the substrate while changing the positional relationship between the electrodes 5a and 5b and the substrate. Can be obtained.

  A colloid solution containing precious metal fine particles as a colloid was prepared as follows.

  First, ion-exchanged and ultrafiltered pure water was boiled and refluxed to remove dissolved oxygen. Next, as a noble metal salt, this pure water was added to hexachloroplatinic acid hexahydrate, which is a chloride of platinum, to prepare an aqueous hexachloroplatinic acid solution. Moreover, the above-mentioned pure water was added to sodium citrate to prepare a sodium citrate aqueous solution.

  Subsequently, a hexachloroplatinic acid aqueous solution was added to pure water that had been boiled and refluxed to remove dissolved oxygen, and then boiled and refluxed for 30 minutes, and a sodium citrate aqueous solution was further added. After the addition, boiling reflux was continued to promote the platinum reduction reaction. The reaction was stopped 2 hours after the start of the reduction reaction, and the reaction solution was rapidly cooled to room temperature.

  The cooled reaction solution was passed through a column packed with ion exchange resin MB-1 (manufactured by Organo Corporation), and metal ions and reducing agent remaining in the reaction solution were removed to obtain a stable platinum colloid solution. Here, the molar ratio of platinum and sodium citrate was changed as appropriate, so that the colloid solution No. 1 to 5 (see Table 1). The colloid solution No. 4 and no. No. 5 performs the platinum reduction reaction described above in two stages to increase the particle size of the fine particles (colloid).

  The platinum fine particles contained as a colloid in the obtained colloid solution were measured for particle diameter by observation with a transmission electron microscope (TEM). Specifically, an appropriate amount of the colloidal solution was dropped on a sheet and dried to prepare a particle size measurement sample, and the particle size measurement sample was observed by TEM. The particle diameter of platinum fine particles appearing in the TEM image was estimated, and the average particle diameter was derived. As a result, the average particle size was in the range of 1.1 to 5.5 nm. Further, it was confirmed that 80% or more of the platinum fine particles were distributed within a range of ± 30% of the average particle diameter, and the particle diameters were uniform. Table 1 shows the average particle diameter in each colloid solution and the abundance ratio (%) distributed within a range of ± 30% of the average particle diameter.

  The noble metal fine particles obtained in this way are characterized by their uniform particle sizes. Thus, if a colloidal solution containing noble metal fine particles having a uniform particle size as a colloid is used, the distribution of the noble metal fine particles on the substrate surface can be easily made uniform.

  Furthermore, instead of platinum chloride, chloroauric acid, which is a gold chloride, was used to obtain a stable colloidal solution in the same manner. With respect to the gold fine particles contained as a colloid in this colloid solution, the same measurement as in the case of platinum was performed to measure the particle size distribution. The results are shown in Table 2.

  From the above, it was confirmed that 80% or more of the gold fine particles were distributed within a range of ± 30% of the average particle size, and the particle size was uniform. Moreover, although both the platinum fine particles and the gold fine particles varied somewhat depending on the amount of the reducing agent used, the average particle size was 100 nm or less.

(Preliminary examination of substrate)
Preliminary studies were made on substrates to which the method of the present invention can be applied.
The platinum colloid solution (No. 1) described above is put in a beaker, and a DC voltage is applied between the two electrodes 5a and 5b by a DC power source while stirring with a magnetic stirrer and a rotor, thereby supporting platinum fine particles on various substrates. I let you. The electrodes 5a and 5b are both stainless steel plates, and have an electrode area of 5 cm ² and an interelectrode distance of 1.5 cm.

  As a result, it was confirmed that platinum fine particles can be supported on glass beads (porous body), glass beads (no pores), glass powder, glass fiber, carbon powder, titanium oxide powder and anion exchange resin.

(Example 1)
Example 1 is an example using platinum as a noble metal and titanium oxide powder as a substrate. A description will be given with reference to FIG.

First, colloidal solution No. 1 prepared as described above. Concentrated colloidal solution (platinum concentration 1500 mg / L) 100 mL boiled 3 and 1000 mg of titanium oxide powder (particle size: about 7 nm, ST-01, manufactured by Ishihara Sangyo) in container 4 (200 mL beaker) And mixed to obtain a mixed solution 22. At this time, the mixed solution 22 was suspended in black. While this mixed solution 22 is being stirred by the magnetic stirrer 7 and the rotor 6, a direct current power source 3 applies a direct current voltage of 50 V between the two electrodes 5a and 5b for 2 hours to carry platinum fine particles on the titanium oxide powder. The process was carried out. The two electrodes 5a and 5b are both stainless steel plates, the electrode area is 5 cm ² , and the distance between the electrodes is 1.5 cm.

  After completion of the above supporting step, the upper part of the mixed solution was transparent, and the platinum fine particles were adsorbed and supported on the titanium oxide powder, and precipitated at the bottom of the beaker.

  The titanium oxide powder carrying the platinum fine particles was taken out, dried and subjected to plasma emission (ICP) analysis. In the ICP analysis in this case, titanium oxide powder carrying platinum fine particles was dissolved in aqua regia and atomized, and the element was identified and quantified from the emission wavelength and emission intensity of the element. From the quantitative value, the mass of platinum supported on the titanium oxide powder (platinum supported amount) was calculated. From this, the loading rate of the platinum fine particles carried on the titanium oxide powder was calculated to be 12.3% by mass. Here, this loading rate was defined as the following equation (Equation 1).

(Equation 1)
Platinum fine particle supporting rate (%) = [platinum supporting amount / (titanium oxide amount + platinum supporting amount)] × 100

  Further, the ratio of the mass of platinum contained in the mixed solution (determined by ICP analysis) to the mass of platinum supported on the titanium oxide powder was determined to be about 95% by mass.

  From this result, it can be determined that by applying a voltage, most of the platinum fine particles in the mixed solution were supported on the titanium oxide powder.

(Comparative Example 1)
When only voltage application was not performed under the same experimental conditions as in Example 1, the mixed solution remained suspended in black even after 2 hours of stirring. This indicates that the state in which the platinum fine particles are dispersed is maintained, and the adsorption / support on the titanium oxide powder is insufficient. The titanium oxide powder carrying the platinum fine particles was dried and then subjected to ICP analysis in the same manner as in Example 1. As a result, the platinum fine particle carrying rate was 1.2% by mass.

  From the results of Example 1 and Comparative Example 1, it was possible to increase the support ratio of platinum fine particles by 10 times or more by applying a voltage to the mixed solution (platinum colloid solution mixed with titanium oxide powder).

(Example 2)
Example 2 is an example in which the platinum concentration was changed from that of Example 1 and carbon powder was used as the substrate. First, the colloid solution No. 1 shown in Table 1 was used. 150 mL of 1 (platinum concentration 135 mg / L) and 76.5 mg of carbon powder (particle size: about 30 nm, Vulcan XC-72R, manufactured by Cabot) were mixed in a container (200 mL beaker) to obtain a mixed solution. At this time, the mixed solution was suspended in black. While stirring this mixed solution with a stirrer, a DC voltage of 50 V was applied between the two electrodes 5a and 5b by the DC power source 3 for 3 hours to support the platinum fine particles on the carbon powder. The experimental conditions are the same as in Example 1 above. As a result, similarly to Example 1 described above, after the voltage was applied, the upper part of the mixed solution became transparent, and the platinum fine particles were adsorbed and supported on the carbon powder and precipitated at the bottom of the beaker.

(Comparative Example 2)
This is a case where no voltage was applied to the mixed solution under the same experimental conditions as in Example 2. Even after stirring for 3 hours, the mixed solution remained suspended in black. This indicates that the adsorption of platinum fine particles on the carbon powder is insufficient, and the platinum fine particles are maintained in a dispersed state in the mixed solution.

(Example 3)
Example 3 is an example using a film as a substrate. This will be described with reference to FIG.
The colloidal solution No. used in Example 2 200 mL of 1 (platinum concentration 135 mg / L) is put in a container (beaker), and the titanium oxide film produced on the glass substrate having an area of 25 cm ² is immersed in the colloid solution as described in FIG. The attached glass substrate was disposed so as to be positioned between the two electrodes 5a and 5b. While stirring this colloidal solution with the magnetic stirrer 7 and the rotor 6, a DC voltage 50V was applied between the electrodes 5a and 5b for 1 hour by the DC power source 3 to support the platinum fine particles on the titanium oxide film. At this time, the stirring speed was set to such an extent that the glass substrate with the titanium oxide film did not fall down. Other conditions are the same as in the first embodiment.

(Comparative Example 3)
Under the same experimental conditions as in Example 3, no voltage was applied to the colloidal solution, and only the glass substrate with a titanium oxide film was immersed. After immersion for 1 hour, the surface of the titanium oxide film was rinsed lightly with ultrapure water to obtain a titanium oxide film carrying platinum fine particles.

  For comparison between Example 3 and Comparative Example 3, the support state of platinum fine particles was examined by immersing these two platinum fine particle carriers in hydrogen peroxide water. When platinum fine particles are supported on the film surface, the hydrogen peroxide solution should be decomposed into water and oxygen by the catalytic ability of platinum, and oxygen bubbles should be generated from the film surface.

  When the titanium oxide films of Example 3 and Comparative Example 3 were compared, a large amount of oxygen bubbles were confirmed from the film surface of Example 3 as compared to Comparative Example 3. That is, the amount of platinum fine particles supported was increased by applying a voltage to the colloidal solution.

Example 4
Example 4 is an example using a particulate anion exchange resin as a substrate. First, the colloid solution No. 1 in Table 1 was used. 1 was boiled and concentrated to obtain a mixed solution by mixing 250 mL of a colloid solution having a platinum concentration of 350 mg / L and 100 g of an anion exchange resin (Amberlite IRA400J CL, manufactured by Organo). While stirring this mixed solution with a stirrer, a DC voltage of 50 V was applied for 5 hours from a DC power source, and platinum fine particles were supported on the anion exchange resin. The two electrodes 5a and 5b were stainless steel plates, the electrode area was 5 cm ² , and the distance between the electrodes was 3 cm. After completion of the supporting step, the anion exchange resin was taken out, washed with pure water, and then dried at 50 ° C. to obtain a support in which platinum fine particles were supported on the anion exchange resin.

(Comparative Example 4)
Under the same experimental conditions as in Example 4, no voltage was applied to the mixed solution, and the supporting step was performed only by stirring. After the supporting step, the same cleaning and drying treatment as in Example 4 was performed to obtain a supporting body.

[Activity comparison by hydrogen peroxide (H ₂ O ₂ ) decomposition characteristics]
The platinum fine particle carriers of Example 4 and Comparative Example 4 produced as described above were compared in activity based on the decomposition characteristics of H ₂ O ₂ .

After putting 15 mL of hydrogen peroxide solution having a concentration of 30% by mass into an Erlenmeyer flask, it was kept in a hot water bath at a temperature of 50 ° C. for 5 minutes. Subsequently, 50 mg of platinum fine particle support was placed in an Erlenmeyer flask and quickly plugged with a rubber stopper. A flow meter is connected to the Erlenmeyer flask via a rubber stopper and a glass tube. Using the time when the platinum fine particle support was put into the Erlenmeyer flask as a reference, the amount of generated oxygen was measured in chronological order until 15 minutes passed every 15 seconds. Then, three points with the highest generation amount were selected and totaled (total 45 seconds), and the oxygen generation amount (mL / min) per unit time was calculated from the total generation amount. Table 3 shows the oxygen generation amount (mL / min) per unit time as H ₂ O ₂ decomposition characteristics.

It was found that the platinum fine particle support of Example 4 had H ₂ O ₂ decomposition characteristics far superior to the platinum fine particle support of Comparative Example 4. This can be said to be because the application of a voltage to the mixed solution during the carrying step promotes the carrying of platinum fine particles on the substrate and the amount of platinum fine particles carried on the substrate increases.

  According to the present invention, as shown in FIG. 3A, a noble metal fine particle carrier 1 in which a large number of noble metal fine particles 2 are supported on a powder substrate 10, or a large number of noble metals on a film-like substrate 11 as shown in FIG. 3B. A noble metal fine particle carrier 1 ′ carrying fine particles 2 can be obtained. FIGS. 3A and 3B both show cross-sectional views of the noble metal fine particle carrier 1, 1 '.

Claims (12)

  A method for producing a noble metal fine particle carrier, wherein the noble metal fine particles are supported on the substrate while applying a voltage to the colloid solution in a state where the colloid solution containing the noble metal fine particles as a colloid is in contact with the substrate.   The method for producing a noble metal fine particle carrier according to claim 1, wherein the substrate is made of an inorganic material having a powder or film form.   The method for producing a noble metal fine particle carrier according to claim 2, wherein the inorganic material is carbon or titanium oxide.   The method for producing a noble metal fine particle carrier according to claim 1, wherein the substrate is made of glass having a form of beads, powder or fibers.   The method for producing a noble metal fine particle carrier according to claim 1, wherein the substrate is made of a polymer material.   The method for producing a noble metal fine particle carrier according to claim 5, wherein the polymer material is an anion exchange resin.   2. The method for producing a noble metal fine particle carrier according to claim 1, wherein the noble metal fine particle contains, as a main component, one selected from the group consisting of gold, silver, platinum, palladium, iridium, ruthenium, rhenium, osmium and rhodium.   The method for producing a noble metal fine particle carrier according to claim 1, wherein the noble metal fine particles are substantially made of platinum and have no protective colloid on the surface.   The method for producing a noble metal fine particle carrier according to claim 1, wherein the colloidal solution is prepared from a raw material solution containing a noble metal source and a reducing agent.   The method for producing a noble metal fine particle carrier according to claim 9, wherein an average particle diameter of the noble metal fine particles contained in the colloidal solution is 100 nm or less.   The method for producing a noble metal fine particle carrier according to claim 10, wherein 80% or more of the noble metal fine particles contained in the colloidal solution are distributed within a range of ± 30% from an average particle diameter.   The method for producing noble metal fine particles according to claim 1, wherein a position of the substrate is fixed between an anode and a cathode disposed in the colloid solution, and a DC voltage is applied to the colloid solution.

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