JPWO2015049959A1 - Method for producing alloy nanoparticles, alloy nanoparticles produced using the same, and catalyst comprising the same - Google Patents

Abstract

The present invention provides a method for efficiently producing composite noble metal nanoparticles by simple processing with low energy and low environmental load. The present invention adds a metal ion reducing bacterium and an electron donor to a raw material solution containing a plurality of types of noble metal ions, and reduces the noble metal ions by the metal ion reducing bacterium, so that a plurality of ions are contained in one particle. A method for producing composite noble metal nanoparticles, comprising a bioreduction step of depositing composite noble metal nanoparticles containing seed noble metals.

Description

  The present invention relates to a method for producing composite noble metal nanoparticles, composite noble metal nanoparticles produced using the same, and a catalyst containing the same.

In recent years, most gasoline vehicles are equipped with an exhaust gas purification system using a three-way catalytic converter. This three-way catalytic converter converts carbon monoxide (CO), nitrogen oxide (NO _x ), and unburned hydrocarbons into carbon dioxide, nitrogen, and water to purify exhaust gas from a gasoline engine.

  The catalytic converter has a honeycomb (monolith) structure as a basic structure, and a catalytic coating is applied to the surface of the honeycomb structure. When performing catalyst coating, first, the surface of the honeycomb is covered with a thin film of a washcoat (catalyst carrier holding material), and the catalyst is covered on the washcoat. As the catalyst, for example, noble metal-based fine particles containing platinum group metals (PGM: Platinum Group Metals) such as platinum (Pt), palladium (Pd), and rhodium (Rh) are used.

  As a conventional method for producing an exhaust gas purification catalyst using noble metal-based fine particles, for example, a method is known in which a colloidal solution containing noble metal-based fine particles is mixed and heated (fired) at a high temperature (for example, patents). Literature 1: JP 2011-143339 A). However, such a method has a problem that the number of steps is complicated and a lot of energy is consumed for heating, and special equipment that can withstand high temperatures is required.

  In addition, several methods for synthesizing bimetallic nanoparticles (for example, core-shell structured metal nanoparticles in which Pt is deposited on the surface of a nucleus made of Pd) using chemicals such as ascorbic acid have been reported. (For example, Non-Patent Document 1: Byungkwon Lim et al., Pd-Pt Bimetallic Nanodendrites with High Activity for Oxygen Reduction, Science, 324, 1302, 2009). However, this method also has a problem that the number of steps is large and complicated.

  On the other hand, when an iron-reducing bacterium is added to a solution containing a platinum group element and an electron donor in an anaerobic atmosphere, a single species of platinum group is formed on the microbial cell surface of the iron-reducing bacterium by the metal ion reducing power of the iron-reducing bacterium. It is known that nanoparticles composed of elements are deposited (for example, Patent Document 2: JP 2010-162442 A, Patent Document 3: JP 2011-113788 A). However, a method for producing nanoparticles (composite noble metal nanoparticles) containing a plurality of types of noble metals in one particle using a microorganism such as iron-reducing bacteria has not been known so far.

JP 2011-143339 A JP 2010-162442 A JP 2011-113788 A

Byungkwon Lim et al., Pd-Pt Bimetallic Nanodendrites with High Activity for Oxygen Reduction, Science, 324, 1302, 2009

  As described above, the conventional method for producing an exhaust gas purifying catalyst using noble metal-based fine particles has a problem that the number of steps is complicated and the production efficiency is low.

  Accordingly, an object of the present invention is to provide a method for efficiently producing composite noble metal nanoparticles by a simple process of low energy and low environmental load.

In the present invention, a metal ion reducing bacterium and an electron donor are added to a raw material solution containing a plurality of kinds of noble metal ions,
By reducing the noble metal ions by metal ion reducing bacteria,
A method for producing composite noble metal nanoparticles, comprising a bioreduction step of depositing composite noble metal nanoparticles containing a plurality of types of noble metals in one particle.

  The composite noble metal nanoparticles are preferably an alloy composed of a plurality of kinds of the noble metals. The noble metal is preferably selected from platinum group metals and gold. The platinum group metal is preferably selected from platinum, palladium and rhodium. Moreover, it is preferable that the temperature of the said bioreduction process is normal temperature.

After the bioreduction process,
It is preferable to include a separation step of separating the metal ion-reducing bacteria and the composite noble metal nanoparticles by destroying the cells by ultrasonic destruction or chemical destruction.

  The present invention also relates to composite noble metal nanoparticles produced by the production method described above. The composite precious metal nanoparticles preferably have an average particle size of 1 to 100 nm.

  The present invention also relates to a catalyst comprising the above composite noble metal nanoparticles.

  According to the production method of the present invention, composite noble metal nanoparticles can be efficiently produced by a simple process with low energy and low environmental load. In addition, the composite noble metal nanoparticles produced by the production method of the present invention are significantly superior in catalytic function compared to nanoparticles made of a single metal, and can be suitably used as a catalyst.

2 is a photographed image taken by a transmission electron micrograph of a metal ion reducing bacterium in Example 1. It is the elements on larger scale of the picked-up image of FIG. FIG. 3 is a mapping diagram of Rh (rhodium) based on EDX elemental analysis of composite noble metal nanoparticles in the same range as FIG. 2. FIG. 3 is a mapping diagram of Pd (palladium) based on EDX elemental analysis of composite noble metal nanoparticles in the same range as FIG. 2. It is a mapping figure of Pt (platinum) based on the EDX elemental analysis of the composite noble metal nanoparticle in the same range as FIG. FIG. 3 is a mapping diagram of C (carbon) based on EDX elemental analysis of composite noble metal nanoparticles in the same range as FIG. 2. FIG. 3 is a mapping diagram of N (nitrogen) based on EDX elemental analysis of composite noble metal nanoparticles in the same range as FIG. 2. FIG. 3 is a mapping diagram of O (oxygen) based on EDX elemental analysis of composite noble metal nanoparticles in the same range as FIG. 2. 4 is a graph showing the chemical reaction rate (relative value) of each nanoparticle in Test Example 1.

<Method for producing composite noble metal nanoparticles>
The present invention relates to a method for producing composite noble metal nanoparticles. Composite noble metal nanoparticles are nanoparticles containing a plurality of types of noble metals in one particle.

  The composite noble metal nanoparticles are preferably an alloy composed of plural kinds of noble metals. An alloy is different from a pure metal composed of a single metal element, and is composed of a plurality of metal elements or a metal-like material composed of at least one metal element and at least one non-metal element. . Alloys include solid solutions in which metals are dissolved in other metals, eutectic alloys in which multiple types of metals are independent at the crystal level, and intermetallic compounds in which multiple types of metals are bonded at a certain rate at the atomic level. Is included. However, the composite noble metal nanoparticles of the present invention are not limited to alloys, metal nanoparticles having a structure in which a core of a certain metal is covered with another metal layer (core-shell structure), and a composite of a plurality of types of noble metal particles. It may be a body.

  The noble metal is preferably selected from platinum group metals and gold (Au). Examples of the platinum group metal include platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), and iridium (Ir). The platinum group metal is preferably selected from Pt, Pd and Rh used in industrial catalysts.

  Specific noble metal combinations included in the composite noble metal nanoparticles include, for example, (1) Pt, Pd and Rh, (2) Pt and Pd, (3) Pt and Rh, or (4) Au and Pd. Can be mentioned.

[Bioreduction process]
The method for producing the composite noble metal nanoparticles of the present invention includes:
A metal ion reducing bacterium and an electron donor (for example, sodium formate) are added to a raw material solution containing ions of plural kinds of noble metals,
It basically includes a bioreduction process in which composite noble metal nanoparticles are precipitated by reducing the noble metal ions by metal ion reducing bacteria.

  In the bioreduction step, composite noble metal nanoparticles are precipitated by reducing noble metal ions contained in the raw material solution using metal ion reducing bacteria. Specifically, for example, by mixing a raw material solution containing a noble metal, an electron donor (for example, sodium formate), and a suspension of metal ion reducing bacteria in an anaerobic atmosphere at room temperature, the platinum group in the liquid is mixed. Metal ions are reduced and platinum group metals are deposited in the cells.

(Raw material solution)
The raw material solution is not particularly limited as long as it contains a noble metal ion. For example, a solution containing a plurality of types of noble metal compounds (for example, a solution of platinum chloride, palladium chloride and rhodium chloride, or palladium chloride and gold chloride) Can be used. Further, as the raw material solution, for example, a leaching noble liquid (solution containing a noble metal as a main component) obtained from a catalyst-containing washcoat containing a noble metal can also be used.

  Although pH of a raw material solution is not specifically limited, It is preferable that it is the same as that of the culture | cultivation conditions of a metal ion reduction bacterium, for example, is pH 6-pH7.

(Metal ion reducing bacteria)
A metal ion reducing bacterium is a bacterium having the ability to reduce metal ions. The metal ion reducing bacterium has a function of receiving metal from an electron donor (using electrons generated by oxidizing an organic substance) to reduce metal ions to a metal and deposit them. For example, facultative anaerobic bacteria that inhabit the bottom mud of the natural water environment. In industrial applications, it is a great merit that it can secure safety, not pathogenic bacteria, and has a low nutrient cost for culture and quick growth (it can supply cells quickly at low cost).

  Examples of metal ion-reducing bacteria include Shewanella algae (hereinafter referred to as “S. algae”): ATCC (American Type Culture Collection) 51181 strain, Shewanella oneidensis: ATCC 700550 strain, etc. Genus (Representative species: Geobacter metalreducens: Geobacter metalreduction: TCC53774 strain), Desulfomonas spp. DSM (Deutsche Sammlung von Mikroorganismen und Zellkulturen) 7343), Perovacter genus (representative species: Pelobacter venetianus: Perovacter venetianus: ATCC 2394 strain), Ferrimonas balmonica: Ferrimonas valerica: DSM97 , Sulfurospirillum genus (representative species: Sulfurospirillum bannesii: Sulfurospirillum varnesii: ATCC 700032 strain), Worinella genus (representative species: Warinella suschinogenes: Wolinella succinogenes: ATCC 29543 strain), desulfobibrio genus (representative species) lfovivrio desulfuricans: Desulfoburibrio desulfuricans: ATCC 29577), Geotricus genus (representative species: Geothrix fermentans: Fermentans: ATCC 700665 strain), Deferbacter genus derfermter genus (Deferrter terbium deferrter terbium) , Geovibrio genus (representative species: Geovibrio ferrireducens: Geovibrio ferrireducence: ATCC 51996 strain), Pyrobaculum genus (representative species: Pyrobaculum islandicum: Thermoproteus islandicam: DSM4184 strain, representative genus Thermotoga m aritima: Thermotoga maritima: DSM3109 strain), Alkaeglobus genus (representative species: Archaeoglobus fulgidus: Alkaeglobus fulgidus: ATCC 49558 strain), Pyrococcus genus (representative species: Pyrococcus furiosus strain 35, Pyrococcus pirodianthus 35 AT (Representative species: Pyrodicium abyssi: Pyrodictium abyssi: DSM6158 strain). Preferred is the genus Shivanella, and particularly preferred is S. aureus. algae. These metal ion reducing bacteria are anaerobic bacteria (facultative anaerobic bacteria).

The metal ion reducing bacterium used in the present invention can be grown and maintained using a medium suitable for the bacterium. The pH of the medium for growth and maintenance is preferably pH 6 to pH 7. The medium preferably contains an electron donor and an electron acceptor. Specific examples of the medium include citric acid having a pH of 7.0 and containing sodium lactate (32 mol / m ³ ) as an electron donor and Fe (III) ions (56 mol / m ³ ) as an electron acceptor. A ferric medium (ATCC No. 1931) can be used.

For example, S.M. algae has a pH of 7.0, ferric citrate medium (ATCC No. 2) containing sodium lactate (32 mol / m ³ ) as an electron donor and Fe (III) ions (56 mol / m ³ ) as an electron acceptor. 1931) can be grown and maintained in batch cultures under anaerobic atmosphere. In this example, the iron ion salt is citrate, but may be appropriately selected depending on the medium used and the type of metal ion reducing bacteria used. S. algae can also be aerobically cultured. Examples of the medium used for aerobic culture include TSB (tryptosoy broth) liquid medium (pH 7.2).

  S. algae is an industrial product that can safely supply cells at a low cost, safely and at low cost, since biosafety is safe at "level 1" and the cost of nutrients for culturing is kept low and growth is fast. It is a microorganism suitable for application.

  On the other hand, the pH of the medium for the bioreduction step (for example, a mixed solution of the raw material solution and the suspension of metal ion reducing bacteria) is preferably pH 6 to pH 7.

  Moreover, it is preferable that the temperature of the said bioreduction process is normal temperature (for example, 5-35 degreeC), More preferably, it is 20-30 degreeC. After the addition of the metal ion reducing bacteria, basically, if left unattended, the noble metal ions are reduced and the composite noble metal nanoparticles are deposited in the cells (particularly in the vicinity of the cell membrane). In the present invention, composite noble metal nanoparticles can be produced by such a low energy and low environmental load simple treatment. However, operations such as stirring may be performed as necessary.

The number of metal ion reducing bacteria used in this step is not particularly limited. In general, the greater the number of cells, the shorter the processing time. The number of bacteria (cell concentration) in the mixed solution of the suspension of metal ion reducing bacteria and the raw material solution is preferably from 1.0 × 10 ¹⁴ cells / m ^{3 to} 1.0 × 10 ¹⁶ cells / m ³ . preferably ^{1.0 × 10 15 cells / m 3} ~8.0 × 10 15 cells / m 3.

  In preparing a suspension of metal ion-reducing bacteria, for example, a metal ion-reducing bacterial culture that has reached the end of exponential growth is first collected in a glove box that has been anaerobic with nitrogen gas, and collected by a centrifuge. To do. The collected bacterial solution is adjusted to a predetermined concentration using water (including distilled water, ion-exchanged water, pure water, etc.).

  An electron donor is preferably added to the mixed solution of the raw material solution and the suspension of metal ion reducing bacteria. Examples of the electron donor include organic acid salts. Examples of the organic acid salt include C1-C7 carboxylate (formate, acetate, etc.), aromatic carboxylate (aliphatic carboxylate (fatty acid salt), benzoate, etc.), oxocarboxylic acid, etc. Acid salts (such as pyruvate) and other carboxylates (such as lactate). Examples of electron donors other than organic acid salts include alcohols (such as ethanol), unsaturated aromatics (such as toluene phenol), and hydrogen gas (molecular hydrogen). In addition, carbon number of alcohol and unsaturated fatty acid becomes like this. Preferably it is 1-7.

  A suitable electron donor varies depending on the type of metal ion reducing bacterium to be used, and may be appropriately selected. For example, S.M. For algae, an organic acid salt can be suitably used as an electron donor. The initial concentration of the electron donor in the mixed solution is preferably 10 to 1000 mM, more preferably 20 to 200 mM.

  The treatment time of the bioreduction process is not particularly limited, but considering the treatment efficiency, the concentration of noble metal in the raw material solution and the number of metal ion reducing bacteria used are adjusted to increase the production efficiency of composite noble metal nanoparticles. It may be adjusted so that In addition, from the viewpoint of general production efficiency, it is preferable that the processing time of the batch operation is 3 hours or less.

[Separation process]
The method for producing composite noble metal nanoparticles of the present invention preferably further includes a separation step of separating the metal ion-reducing bacteria and the composite noble metal nanoparticles after the bioreduction step.

  The metal ion-reducing bacteria and the composite noble metal nanoparticles can be separated by various known methods after, for example, separating the cells from the liquid by centrifugation or filtration. Separation of the composite noble metal nanoparticles from the microbial cells is preferably carried out by destroying the microbial cells by ultrasonic destruction or chemical destruction using an alkaline solution (NaOH aqueous solution or the like). On the other hand, a method of removing organic substances such as bacterial cells by firing or the like is not desirable because composite noble metal nanoparticles made of noble metal alloys or the like may be bonded to increase the particle diameter.

  The average particle size of the composite noble metal nanoparticles produced by the above production method is preferably 1 to 100 nm, more preferably 1 to 10 nm. Thereby, the reaction surface area at the time of using as a catalyst can be enlarged, and the catalyst which has high activity can be obtained. In addition, with the conventional method, it has been particularly difficult to obtain nanoparticles of 10 nm or less. Note that the average particle diameter here is, for example, an average particle diameter obtained from a high-resolution STEM image.

<Catalyst>
Since the composite noble metal nanoparticles of the present invention are easy to manufacture and have excellent catalytic activity, automobile exhaust gas removal catalysts (three-way catalysts, etc.), factory exhaust gas treatment catalysts, chemical synthesis industries It can be used for many applications such as catalysts and catalysts for fuel cells. In particular, it can be used as a catalyst for redox reaction.

  The composite noble metal nanoparticles of the present invention can be used as a catalyst by various known methods, and for example, can be used as a three-way catalyst by being supported on the surface of a washcoat (catalyst carrier holding material).

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

  In the following examples, the suspension of metal ion-reducing bacteria was prepared by first collecting the metal ion-reducing bacteria culture solution that had reached the end of exponential growth in a glove box that was anaerobic with nitrogen gas, and centrifuge. Bacteria were collected using a separator. Next, the collected bacterial solution was resuspended with ion-exchanged water and adjusted to a predetermined concentration.

[Example 1]
In this example, a noble metal leaching noble liquid recovered from a catalyst washcoat or the like was used as a raw material solution for composite noble metal nanoparticles. Thus, in the case of producing composite noble metal nanoparticles by reusing the catalyst washcoat, the entire process is further simplified and the production efficiency is increased.

  The material of the washcoat is generally used as a catalyst carrier such as a porous inorganic oxide (alumina, titania, zirconia, silica-alumina, etc.) in order to increase the catalytic ability (surface area where the reaction occurs) of the converter. Inorganic oxides) are used, and in particular, activated alumina is often used. Activated alumina often contains rare earth elements such as lanthanum and cerium and alkaline earth elements such as barium.

(Preparation of raw material solution)
First, a powdered catalyst-containing washcoat recovered from a used automobile catalytic converter (Al: 29%, Ce: 14%, Fe: 0.97%, La: 5.9%, Pd: 0.24%, Pt: 0.40%, Rh: 0.083%). In addition, each metal content rate in a catalyst containing washcoat is the value calculated | required by measuring the metal concentration in a solution by inductively coupled plasma (ICP: Inductively Coupled Plasma) emission spectroscopy after making it melt | dissolve with aqua regia. .

Next, an operation for separating Al occupying about 60% of the catalyst-containing washcoat from the platinum group metal was performed. Specifically, the catalyst washcoat powder was added to a 4 kmol / m ³ aqueous sodium hydroxide solution so that the initial solid-liquid mixing ratio was 58.8 kg / m ³ . Thereafter, using an autoclave, batch operation for 3 hours was performed at a temperature of 160 ° C. and a pressure of 5.8 atm. And the leaching residue was recovered by filtration.

Next, leaching of the platinum group metal with aqua regia (a liquid in which concentrated hydrochloric acid and concentrated nitric acid were mixed at a volume ratio of 3: 1) was performed on the recovered leaching residue. Concentrated hydrochloric acid is a 35 w / v% aqueous HCl solution, and concentrated nitric acid is a 60 w / v% HNO ₃ aqueous solution. The mixing ratio of the leach residue to the aqua regia (initial solid-liquid mixing ratio) was 25 kg / m ³ . The operation was performed for 3 hours at a temperature of 90 ° C. and atmospheric pressure. The concentration of each platinum group metal in the leached noble liquid was measured by inductively coupled plasma (ICP) emission spectroscopy, and after 2 hours, most of the platinum group metal (Pd, Pt, Rh) leached into the leached noble liquid. Confirmed that.

Next, potassium dihydrogen phosphate (KH ₂ PO ₄ ) in an amount of 5 or more times the sum of the number of moles of heavy metal components (Al, Fe, Ce, La) in the leached noble liquid is added to the obtained leached noble liquid. ) Was added, and a sodium hydroxide solution was further added to adjust the pH to around 6. By this pH adjustment step, most of heavy metal components other than platinum group metals can be removed by precipitation, and coprecipitation of platinum group metals accompanying this precipitation hardly occurs.

(Bioreduction process)
A bioreduction process of platinum group metals (Pt, Pd, Rh) was performed by a batch operation using the pH-adjusted leached noble solution obtained as described above as a raw material solution.

That is, a leaching noble solution, an electron donor (sodium formate), and a suspension of metal ion reducing bacteria were mixed. Examples of metal ion reducing bacteria include S. cerevisiae. algae (ATCC 51181 strain) was used. The main operating conditions of the bioreduction process are: cell concentration: 5.0 × 10 ¹⁵ cells / m ³ , electron donor (formate) initial concentration: 100 mol / m ³ , solution pH 6, room temperature, anaerobic environment, operating time : 2h.

  In FIG. 1, the picked-up image by the transmission electron microscope (STEM) photograph of the metal ion reduction bacteria after the bioreduction process in Example 1 is shown. The white spots in the cells of the elliptical metal ion reducing bacteria are composite noble metal nanoparticles. FIG. 2 shows a partially enlarged view of the photographed image of FIG. The particle diameter of the composite noble metal nanoparticles observed in the high resolution STEM image was about 1.5 to 4 nm.

  Moreover, the mapping figure of each element (Rh, Pd, Pt, C, N, O) based on the EDX elemental analysis of the composite noble metal nanoparticle in the same range as FIG. 2 is shown in FIGS. The position of the composite noble metal nanoparticle shown in FIG. 2 and the position of each element (Rh, Pd, Pt) shown in FIGS. Moreover, the big difference of a composition ratio was not recognized by the center part and edge part of the nanoparticle. Moreover, in FIG. 2, the crystal lattice stripe of a nanoparticle is recognized. From these things, the composite noble metal nanoparticles obtained in Example 1 are considered to be an alloy composed of three kinds of elements (Rh, Pd, Pt). On the other hand, as shown in FIGS. 6 to 8, C, N, and O that are constituent elements of the fungus body are generally distributed regardless of the position of the composite noble metal nanoparticles.

[Example 2]
(Preparation of raw material solution)
An aqueous solution containing equimolar amounts (0.5 mol / m ³ ) of Au ions and Pd ions was prepared by using a solution of palladium chloride and gold chloride as a raw material solution.

(Bioreduction process)
The raw material solution, the electron donor (sodium formate), and the suspension of metal ion reducing bacteria were mixed. Examples of metal ion reducing bacteria include S. cerevisiae. Oneidensis (ATCC 700550 strain) was used. The main operating conditions of the bioreduction process are: cell concentration: 5.0 × 10 ¹⁵ cells / m ³ , electron donor (formate) initial concentration: 50 mol / m ³ , solution pH 7, room temperature, anaerobic environment, operating time : 2h.

<Test Example 1>
Pd / Au alloy nanoparticles of Example 2 (produced by the above biopreparation and supported on bacterial cells), Au nanoparticles (produced by biopreparation and supported on bacterial cells), and commercially available Pd The chemical reaction rate was measured about the nanoparticle (Product name: Palladium carrying activated carbon catalyst, Wako Pure Chemical Industries Ltd. make). The Au nanoparticles are nanoparticles produced in the same manner as in Example 2 except that the composition of Au ions contained in the raw material solution is 1 mol / m ³ .

  The relative value of the chemical reaction rate was obtained by comparing the catalytic ability (reaction rate) in the model chemical reaction (4-nitrophenol reductive decolorization reaction, room temperature).

  FIG. 9 is a graph showing the chemical reaction rate (relative value) of each nanoparticle in Test Example 1. As shown in FIG. 9, the chemical reaction rate of the Pd / Au alloy nanoparticles of Example 2 is about three times that of Au nanoparticles and commercially available Pd nanoparticles, and the composite noble metal nanoparticles of the present invention have high activity. You can see that

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

[0001]
Technical field [0001]
The present invention relates to a method for producing alloy nanoparticles, an alloy nanoparticle produced using the method, and a catalyst including the same.
Background art [0002]
In recent years, most gasoline vehicles are equipped with an exhaust gas purification system using a three-way catalytic converter. This three-way catalytic converter converts carbon monoxide (CO), nitrogen oxide (NOx), and unburned hydrocarbons into carbon dioxide, nitrogen, and water to purify exhaust gas from a gasoline engine.
[0003]
The catalytic converter has a honeycomb (monolith) structure as a basic structure, and a catalytic coating is applied to the surface of the honeycomb structure. When performing catalyst coating, first, the surface of the honeycomb is covered with a thin film of a washcoat (catalyst carrier holding material), and the catalyst is covered on the washcoat. As the catalyst, for example, noble metal-based fine particles containing platinum group metals (PGM: Platinum Group Metals) such as platinum (Pt), palladium (Pd), and rhodium (Rh) are used.
[0004]
As a conventional method for producing an exhaust gas purification catalyst using noble metal-based fine particles, for example, a method is known in which a colloidal solution containing noble metal-based fine particles is mixed and heated (fired) at a high temperature (for example, patents). Literature 1: JP 2011-143339 A). However, such a method has a problem that the number of steps is complicated and a lot of energy is consumed for heating, and special equipment that can withstand high temperatures is required.
[0005]
In addition, bimetallic nanoparticles (for example, metal nanoparticles having a core-shell structure in which Pt is deposited on the surface of a nucleus made of Pd using a chemical such as ascorbic acid)

Claims (9)

In a raw material solution containing ions of a plurality of types of precious metals, metal ion reducing bacteria and an electron donor are added,
By reducing the noble metal ions by metal ion reducing bacteria,
A method for producing composite noble metal nanoparticles, comprising a bioreduction step of precipitating composite noble metal nanoparticles containing a plurality of kinds of the noble metals in one particle.   The manufacturing method according to claim 1, wherein the composite noble metal nanoparticles are an alloy made of a plurality of types of the noble metals.   The manufacturing method according to claim 1, wherein the noble metal is selected from a platinum group metal and gold.   The method according to claim 3, wherein the platinum group metal is selected from platinum, palladium, and rhodium.   The manufacturing method according to any one of claims 1 to 3, wherein the temperature of the bioreduction step is normal temperature. After the bioreduction process,
The method according to any one of claims 1 to 5, further comprising a separation step of separating the metal ion-reducing bacteria and the composite noble metal nanoparticles by destroying the cells by ultrasonic destruction or chemical destruction. Production method.   Composite noble metal nanoparticles produced by the production method according to claim 1.   The composite noble metal nanoparticles according to claim 7, wherein the average particle diameter is 1 to 100 nm.   A catalyst comprising the composite noble metal nanoparticles according to claim 7 or 8.