JP5772593B2 - CuPd alloy nanoparticles, composition and composition for catalyst, and method for producing CuPd alloy nanoparticles - Google Patents

Description

Cross-reference of related applications

  This application claims the priority of Japanese Patent Application No. 2009-117386 filed on May 14, 2009, the entire description of which is specifically incorporated herein by reference.

  The present invention relates to an alloy nanoparticle comprising Cu and Pd, a composition for a catalyst using the nanoparticle, and a method for producing the nanoparticle.

  For the photocatalyst and the electrode of the fuel cell, it is necessary to use an expensive metal such as Pt or Pd as the catalyst. Although these Pt group metals are very highly active, they are problematic in that they are vulnerable to poisoning from oxygen and carbon monoxide and voltage drop. At present, attempts are being made to improve the performance of metal catalysts by reducing the proportion of metal costs in the catalyst cost and improving the poisoning resistance by using alloys of different metals together.

  Nanoparticles of such alloys are produced by pyrolysis of metal salts as raw materials (Chemistry of Materials, 1990, 2,564-567 (Non-patent Document 1), Chemistry of Materials, 1993, 5, 254-256 (Non-patent Document 2). ), Or a high temperature method using polyhydric alcohol (Chem. Lett., 1993, 1611-1614 (Non-patent Document 3), Langmuir, 1994, 10, 4574-4580 (Non-patent Document 4)). ing.

JP 2004-263222 A

Chemistry of Materials, 1990,2,564-567 Chemistry of Materials, 1993,5,254-256 Chem. Lett., 1993, 1611-1614 Langmuir, 1994,10,4574-4580

  The entire descriptions of Patent Document 1 and Non-Patent Documents 1 to 4 are specifically incorporated herein by reference.

  As described above, conventional CuPd alloy nanoparticles can be prepared by thermal decomposition using a high-boiling organic solvent or polyvalent alcohol synthesized with polyhydric alcohol as a solvent and reducing agent at a high temperature for a long time. The alcohol method is known.

In the above pyrolysis method, copper acetate and palladium acetate are used as raw materials and dissolved in a high boiling point organic solvent (for example, 2-ethoxyethanol (also reducing agent), methyl isobutyl ketone, xylene, bromobenzene) and a protective agent. After mixing the polyvinylpyrrolidone (PVP), the raw metal salt is thermally decomposed by refluxing for about 2 hours (110-156 ° C.) to synthesize CuPd nanoparticles. However, there are cases where Cu ₂ O nanoparticles are by-produced together with CuPd nanoparticles (Non-patent Document 1), but there are reports that only CuPd nanoparticles were obtained (Non-patent Document 2).

  The polyhydric alcohol method is synthesized using copper sulfate and palladium acetate as raw materials and PVP as a protective agent. CuPd nanoparticles can be obtained by dissolving the metal salt, PVP, and NaOH (pH adjustment) in glycol, which is a solvent and a reducing agent, and refluxing at 198 ° C. for 3 hours (Non-patent Documents 3 and 4).

  Thus, both the pyrolysis method and the polyhydric alcohol method require treatment at a high temperature exceeding 110 ° C.

  CuPd alloy nanoparticles produced by these methods are heterogeneous alloy nanoparticles containing small domains of constituent metals and uneven mixing. Inhomogeneous alloy nanoparticles have problems such as low electrical or chemical properties and inability to obtain stable catalytic properties. In addition, each method has a problem that the production efficiency is low and the production cost is high.

  Patent Document 1 describes a method for preparing a colloid of a metal containing a noble metal using a protective agent, describes palladium as the noble metal, and describes copper as a metal other than the noble metal. However, there is no description of examples of colloids composed of an alloy of palladium and copper, and it cannot be confirmed that CuPd alloy nanoparticles are prepared by the method described in Patent Document 1.

  An object of the present invention is to provide CuPd alloy nanoparticles having sufficient catalytic activity and toxicity resistance even when used as a photocatalyst or an electrode catalyst of a fuel cell, and a method for producing the same. Another object of the present invention is to provide a composition for a catalyst using the CuPd alloy nanoparticles.

The present invention for solving the above problems is as follows.
[1]
The crystal structure is B2 type or L12 type, the average particle size is 1 to ₂₀₀ nm, and is represented by Cu _x Pd _(1-x) (in the case of B2 type, 0.3 <x <0. is 7, if the L1 ₂ type is 0.7 ≦ x ≦ 0.98), CuPd alloy nanoparticles.
[2]
CuPd alloy nanoparticles according to [1], wherein the degree of ordering represented by the following formula (1) is 95% or more.
(1- (m−M) / M) × 100% (1)
m: Lattice constant of CuPd alloy nanoparticles M: Bulk lattice constant in which Cu atoms and Pd atoms are regularly arranged
[3]
A composition comprising the CuPd alloy nanoparticles according to [1] or [2] and a protective polymer.
[4]
The composition for catalysts which carry | supported the CuPd nanoalloy particle in any one of [1]-[3] on the support | carrier.
[5]
The catalyst composition according to [4], wherein the carrier is an inorganic compound.
[6]
The catalyst composition according to [5] or [6], wherein the catalyst is for a water-splitting hydrogen generation reaction, a water-splitting oxygen generation reaction, or an organic matter decomposition reaction.
[7]
Prepare a dispersion or solution of Cu ions and Pd ions in the presence of a protective polymer in water or an aqueous solution,
A method for producing CuPd nanoparticles, comprising: adding a reducing agent for the Cu ions and Pd ions to the obtained dispersion or solution to reduce Cu ions and Pd ions to prepare CuPd nanoparticles.
[8]
The molar ratio of Cu ions and Pd ions in the dispersion or solution is in the range of more than 0.3: less than 0.7 to less than 0.7: more than 0.3.
The reduction temperature is set to 10 ° C. or higher, and CuPd nanoparticles having a crystal structure of B2 type and Cu _x Pd _(1-x) (provided that 0.3 <x <0.7) are prepared [7]. The manufacturing method as described in.
[9]
The molar ratio of Cu ions to Pd ions in the dispersion or solution is in the range of 0.01: 0.99 to 0.99: 0.01,
The reduction temperature is set to less than 10 ° C., and CuPd nanoparticles having a crystal structure of fcc type and Cu _x Pd _(1-x) (where 0.01 ≦ x ≦ 0.99) are prepared [7] The manufacturing method as described in.
[10]
The molar ratio of Cu ions to Pd ions in the dispersion or solution is in the range of 0.7: 0.3 to 0.98: 0.02,
The reduction temperature of 10 ° C. or higher, the crystal structure is L1 ₂ type, and Cu _x represented by Pd _{(1-x) (where,} 0.7 ≦ x ≦ 0.98) to prepare a CuPd nanoparticles [7 ] The manufacturing method of description.
[11]
The production method according to any one of [8] to [10], wherein the reducing agent is a compound containing hydrogen.
[12]
A CuPd nanoparticle is produced by the method according to [8] or [10], and the produced CuPd nanoparticle is exposed to a hydrogen atmosphere to obtain a CuPd nanoparticle having improved crystal structure regularity. A method for producing CuPd nanoparticles with improved regularity.
[13]
The degree of ordering represented by the following formula (1) of CuPd nanoparticles produced by the method according to [8] or [10] is less than 98%,
The production method according to [13], wherein the degree of ordering represented by the following formula (1) of CuPd nanoparticles having improved crystal structure regularity is 99% or more.
(1- (m−M) / M) × 100% (1)
m: Lattice constant of CuPd alloy nanoparticles M: Bulk lattice constant in which Cu atoms and Pd atoms are regularly arranged
[14]
[12] or [13], wherein the exposure treatment to the hydrogen atmosphere is performed at a temperature of 0 to 200 ° C. and a hydrogen pressure of 1 Pa to 10 MPa.
[15]
The manufacturing method according to any one of [12] to [14], wherein the exposure treatment to the hydrogen atmosphere is performed in multiple stages at different temperatures.
[16]
The exposure treatment to the hydrogen atmosphere comprises a first stage at a temperature in the range of 30 to 150 ° C. and a second stage at a temperature in the range of 40 to 250 ° C., and the temperature of the first stage and the second stage. The production method according to any one of [12] to [14], wherein the difference is in the range of 10 to 100 ° C.

According to the present invention, highly ordered CuPd alloy nanoparticles are provided. Specifically, CuPd alloy nanoparticles having a regular type B2 or L1 ₂ type crystal structure is provided. Conventionally, CuPd alloy nanoparticles such rule type B2 and L1 ₂ type crystal structure were not known.

Further according to the invention, CuPd alloy nanoparticles of the rule type B2 or L1 ₂ type crystal structure, and further can prepare CuPd alloy nanoparticles having an fcc-type crystal structure with high production efficiency, the production of CuPd nanoparticles Law is provided.

  Since the CuPd alloy nanoparticles provided by the present invention can be produced at a lower cost than Pt and Pd and have high durability, application to photocatalysts, fuel cell electrode catalysts, and the like can be expected.

The crystal structure of fcc-type CuPd nanoalloy particles with irregular atomic arrangement and the atomic model of B2-type CuPd nanoalloy particles with regular atomic arrangement are shown. The transmission electron micrograph (upper stage) of the CuPd nanoalloy particles obtained in Examples 1 and 2 and the average particle diameter (lower stage) estimated from 200 particles in the photographs are shown. The analysis result of the powder XRD diffraction peak of the CuPd nanoalloy particle obtained in Examples 1 and 2 is shown. The change of the powder XRD diffraction pattern at the time of carrying out the hydrogen atmosphere exposure process of the CuPd nanoalloy particle obtained in Example 1 and 2 is shown. The CuPd nanoalloy particles obtained in Example 2 and the TEM images when the CuPd nanoalloy particles are exposed to a hydrogen atmosphere (two types) are shown. Showing of H ₂ pressure an In-situ X-ray powder diffraction pattern of the synthesized CuPd nanoparticles in Example 2. The result of the photohydrolysis hydrogen generation reaction obtained in Example 3 is shown. The result of the carbon monoxide poisoning test obtained in Example 3 is shown. The powder X-ray-diffraction pattern about the sample which gave the hydrogen treatment (2) to the particle | grains obtained in Example 2 and the analysis result by the Rietveld method are shown. A peak peculiar to the B2 structure is observed at the position indicated by the arrow. TEM of a sample just prepared in Example 2 and a sample subjected to hydrogen treatment (1) (100 ° C., 2 MPa H ₂ ) and a sample subjected to hydrogen treatment (2) (100 ° C., 150 ° C., 2 MPa H ₂ ) Show the image. Newly prepared B2 CuPd nanoparticles (B2-CuPd) and ordered B2 CuPd alloy nanoparticles with hydrogen treatment (2) (2MPa hydrogen, 373K, 240 hours and 2MPa hydrogen, 423K, 24 hours) (B2- The result of the photohydrolysis hydrogen generation experiment of the catalyst which supported CuPd after H2 treat. (2)) is shown. A catalyst carrying bare Pd (bare-Pd) which does not contain a protective agent prepared by a photoprecipitation method is also described for reference.

[CuPd alloy nanoparticles]
The present invention relates to CuPd alloy nanoparticles, which have a crystal structure of B2 type or L12 type, an average particle diameter of 1 to ₂₀₀ nm, and represented by Cu _x Pd _(1-x) . However, in the case of type B2 is 0.3 <x <0.7, in the case of L1 ₂ type is 0.7 ≦ x ≦ 0.98.

CuPd alloy nanoparticles of the present invention, either the crystal structure is of type B2, or L1 ₂ type. CuPd alloy nanoparticles having a crystal structure of B2 type are represented by Cu _x Pd _(1-x) and 0.3 <x <0.7. When x is 0.3 or less, it becomes an irregular fcc type and the poisoning resistance to carbon monoxide becomes weak. Becomes L1 ₂ or irregular fcc type is 0.7 or more, poisoning resistance to carbon monoxide is weak when it becomes irregular fcc-type as compared with the type B2. x is 0.3 <x <0.7, but preferably 0.4 <x <0.6. The B2-type crystal structure is based on a body-centered cubic structure, in which the eight vertices of the cube are Cu and Pd is placed at the position of the body center. Cu and Pd can be interchanged.

CuPd alloy nanoparticles crystal structure is a L1 ₂ type is indicated by _{Cu x Pd (1-x)} , and is 0.7 ≦ x ≦ 0.98. When x exceeds 0.98, an irregular fcc structure is formed, and the poisoning resistance to CO decreases. When x is less than 0.7, a B2-type crystal structure is obtained as described above. L1 ₂ type crystal structure is a face-centered cubic structure to the basic, a structure in which Cu is placed vertices eight cubic Pd, the face-centered. Depending on the composition, the position of one metal may be replaced with one metal.

The CuPd alloy nanoparticles of the present invention are CuPd nanoparticles with improved crystal structure regularity. Specifically, the degree of ordering represented by the following formula (1) is 98% or more. Is preferably 99.0% or more, more preferably 99.5% or more, and most preferably 100% or more.
(1- (m−M) / M) × 100% (1)
m: Lattice constant of CuPd alloy nanoparticles M: Bulk lattice constant in which Cu atoms and Pd atoms are regularly arranged

  The bulk lattice constant M in which Cu atoms and Pd atoms are regularly arranged as a basis for calculating the degree of ordering can be obtained by experiments such as powder or single crystal X-ray diffraction. Or the estimated value L of M can also be calculated based on the metal bond radius value of Cu atom and Pd atom shown in the chemical handbook. Moreover, the crystal structure and lattice constant m of CuPd alloy nanoparticles can be obtained by performing powder X-ray diffraction and analyzing the obtained diffraction pattern.

For example, the estimated value L of the lattice constant of a B2 type A _x B _(1-x) alloy (0.3 <x <0.7) at room temperature is the metal bond radius of A and B (Chemical Handbook 5th edition, Fundamentals II, p .887), and when the metal bond radii of A and B are a and b, respectively, they are roughly expressed as follows.
L = 2 × (a × x + b × (1-x)) / √3
The lattice constant m of the B2 type A _x B _(1-x) alloy nanoparticles just prepared is the bulk lattice constant M in which A and B atoms are regularly arranged (M is an estimated value L calculated by the above formula) Is greater than). As will be described later, by hydrogen treatment, the interaction between metal atoms can be strengthened, and the lattice constant of the A _x B _(1-x) alloy nanoparticles can be decreased from m and can be made comparable to M.

In Example 2, the degree of ordering of the just synthesized Cu _0.5 Pd _0.5 nanoparticles is (1- (3.036-2.99) /2.99) × 100 = 98.5%
However, 100% was achieved by hydrogen treatment.
The lattice constant of CuPd nanoparticles can be determined by analyzing a powder X-ray diffraction pattern as shown in FIG. 3 or FIG. 6 by the Rietveld method or the like.

  The average particle diameter of the CuPd alloy nanoparticles of the present invention is 1 to 200 nm, preferably 1 to 100 nm, more preferably 1 to 20 nm, still more preferably 1 to 10 nm, and still more preferably 1 to 5 nm. The smaller the average particle size of the CuPd alloy nanoparticles, the higher the activity when used as a catalyst, which is preferable. Therefore, the smaller the average particle size of the CuPd alloy nanoparticles, the better. In the present invention, the average particle diameter of the CuPd alloy nanoparticles may be any 200 photographed in a photograph obtained by observation of particles with a transmission electron microscope (for example, JEM-2000FX), as described in Examples. It is a value estimated from individual particles.

  The CuPd alloy nanoparticles of the present invention are particles having a small average particle diameter and improved regularity of the crystal structure. Therefore, when used as a catalyst, it exhibits high catalytic activity and is excellent in poisoning resistance.

[Composition]
The present invention relates to a composition comprising the CuPd alloy nanoparticles of the present invention and a protective polymer. The CuPd alloy nanoparticles of the present invention have an average particle size of 1 to 200 nm, and in the most preferred case, the average particle size is in the range of 1 to 5 nm. Therefore, in order to maintain this particle size, it is preferable to use a means for protecting each nanoparticle from aggregation or the like. In the present invention, a protective polymer is used as a means for that purpose.

  The protective polymer is preferably a water-soluble polymer, and specifically, a polymer having a cyclic amide structure such as PVP is suitable. However, the present invention is not limited to this, and for example, polyvinyl alcohol, polyvinyl ether, polyacrylate, poly (mercaptomethylenethrylene-N-vinyl-2-pyrrolidone), polyacrylonitrile is used depending on the type of alloy particles to be protected. You can also.

  The composition of the present invention can also contain a solvent in addition to the CuPd alloy nanoparticles and the protective polymer. The solvent is preferably an aqueous solvent, for example, water alone or a mixed solvent of water and an organic solvent having an affinity for water. The organic solvent used for the mixed solvent may be appropriately selected according to the type of the organic polymer, and for example, polyhydric alcohols such as propanol, ethylene glycol, and glycerin can be used.

  The composition ratio of the CuPd alloy nanoparticles, the protective polymer and the solvent in the composition of the present invention is such that the concentration of the CuPd alloy nanoparticles is in the range of 1 to 99% by mass, preferably 20 to 99% by mass. The concentration can range from 1 to 99% by weight, preferably from 1 to 10% by weight. However, it selects so that the sum total of a CuPd alloy nanoparticle, a protection polymer, and a solvent may be 100 mass%. It is not intended to be limited to these ranges.

[Composition for catalyst]
The present invention also relates to a catalyst composition in which the CuPd nanoalloy particles of the present invention are supported on a support.

The support is not particularly limited, and a carrier used for a normal solid carrier can be used. Such a carrier can be, for example, an inorganic compound. Examples of inorganic compounds include metal oxides (TiO ₂ , SrTiO ₃ , WO ₃ , TaON, ZnO, NiO, Cu ₂ O), metal sulfides (ZnS, CdS, HgS), metal selenides (CdSe), or It is possible to mention their derivatives. The support can have various shapes as in the case of an ordinary catalyst support, and can be a powder, a granule, a granule, a molded body (for example, a honeycomb structure), or the like.

  The amount of CuPd nanoalloy particles supported on the carrier is not particularly limited, and can be, for example, in the range of 0.1 to 20% by mass, and preferably in the range of 0.5 to 1% by mass in view of catalyst activity and performance. is there. However, depending on the type and conditions of the catalytic reaction to be used, a supported amount outside the above range can be selected.

  In the method for producing the catalyst composition of the present invention, CuPd nanoalloy particles prepared by the method described later can be supported on a carrier by a conventional method (for example, an immersion method). After the loading, it can be dried and subjected to an activation treatment (for example, hydrogen treatment) if necessary.

  The catalytic reaction in the case of using the catalyst composition of the present invention as a catalyst can be, for example, a water-splitting hydrogen generation reaction, a water-splitting oxygen generation reaction, or an organic matter decomposition reaction. However, it is not the intention limited to these.

The water-splitting hydrogen generation reaction and the water-splitting oxygen generation reaction may be carried out, for example, by mixing or contacting a semiconductor powder or plate-like product carrying the Cu _x Pd _(1-x) nanoparticles of the present invention with water, and then contacting the This is performed by irradiating light or visible light.

The organic matter decomposition reaction is performed, for example, by mixing or contacting with a solution containing an organic matter that decomposes into a powder of a semiconductor supporting the Cu _x Pd _(1-x) nanoparticles of the present invention or processed into a plate shape, and ultraviolet light or visible light. It is performed by irradiating light.

  The catalyst composition of the present invention uses a CuPd alloy in which Cu is introduced into Pd, which is a Pt group metal, but the catalyst is more active than the case where Pt or Pd is used as a single metal. And since it introduces Cu, it is less expensive than the case of Pd alone. Furthermore, since the CuPd alloy nanoparticles have improved regularity of the crystal structure, the poisoning resistance is also improved.

[Method for producing CuPd nanoparticles]
The present invention relates to a method for producing CuPd nanoparticles.
The production method of the present invention comprises:
A step of preparing a dispersion or solution of Cu ions and Pd ions in the presence of a protective polymer in water or an aqueous solution, and a reducing agent for the Cu ions and Pd ions is added to the obtained dispersion or solution. And a step of preparing CuPd nanoparticles by reducing Cu ions and Pd ions.

<Process for preparing dispersion or solution>
As the Cu ion source, a compound containing copper can be used, and it is appropriate that the compound has excellent solubility in water or an aqueous solution. Examples of such compounds include inorganic copper-containing compounds such as copper acetate, copper chloride, copper sulfate, copper chloride, copper nitrate and hydrates thereof, and complexes containing Cu.

  As the Pd ion source, a compound containing palladium can be used, and it is appropriate that the compound has excellent solubility in water or an aqueous solution. Examples of such compounds include inorganic palladium-containing compounds such as palladium acetate, palladium chloride, palladium nitrate and hydrates thereof, and complexes containing palladium.

  As the protective polymer, those mentioned in the description of the composition can be used as they are. The role of the protective polymer includes preventing aggregation between alloy particles produced in the subsequent reduction step and controlling the size of the produced alloy particles. The particle size can be controlled by adjusting the ratio of metal to polymer. For example, when the amount of the protective polymer in the solution is relatively increased, the particle size of the alloy particles to be precipitated becomes small. By utilizing this phenomenon, the particle size of the alloy particles can be controlled. In addition, the particle size of the alloy particle to precipitate can also be adjusted by adjusting the density | concentration of the metal containing compound (for example, salt) used as Cu ion source and Pd ion source.

  In preparing the dispersion or solution, water or an aqueous solution can be used as a solvent. The aqueous solution can be a mixture of water and an organic solvent mentioned in the description of the composition. In the case of using a mixture of water and an organic solvent, the kind of the organic solvent and the mixing ratio of the organic solvent and water can be appropriately adjusted in consideration of the solubility of the metal raw material and the protective agent.

  The dispersion or solution can be prepared by adding a protective polymer, a Cu ion source, and a Pd ion source to the solvent and dissolving or dispersing them. There are no restrictions on the order of addition of the protective polymer and the Cu ion source and Pd ion source. It can also be prepared by appropriately mixing a solution in which the protective polymer is dispersed or dissolved, a solution in which the Cu ion source is dissolved, and a solution in which the Pd ion source is dissolved.

The concentration of the protective polymer, the concentration of Cu ions, and the concentration of Pd ions in the dispersion or solution are, for example, in the range of 1 × 10 ^{−4 to} 5 mass% for the protective polymer and 3 × 10 ^{−7 to} 5 for Cu ions. × 10 ^-1 wt% range, and Pd ions can be in the range of 3 × 10 ^-7 to 5 × 10 ^-1 wt%.

<Reduction process>
A reducing agent for Cu ions and Pd ions is added to the dispersion or solution obtained in the above step. As the reducing agent, it is appropriate to use a compound whose standard reduction potential is more negative than hydrogen (0 eV) at room temperature from the viewpoint of strong ability to reduce Cu ions and Pd ions to metal. Examples of such a reducing agent include MBH ₄ , MEt ₃ BH (M = Na, K), sodium cyanoborohydride NaBH ₃ CN, lithium borohydride LiBH ₄ , lithium triethylborohydride LiBHEt ₃ , and borane complex. Examples thereof include BH ₃ · L, triethylsilane Et ₃ SiH, sodium bis (2-methoxyethoxy) aluminium hydride (Red-Al). However, some of these reducing agents are dangerous because they react explosively with water and cannot be used in an aqueous solution. In that case, it is appropriate to use a solvent other than water (for example, an aprotic polar solvent such as tetrahydrofuran, N, N-dimethylformamide, dimethylsulfoxide) as the solvent.

  The amount of the reducing agent used is appropriately determined in consideration of the amount of Cu contained in the metal raw material, for example, within a range from the equivalent of the total amount of Cu ions and Pd ions to be reduced to 50 times equivalent or less. Can do.

  CuPd nanoparticles are prepared by reducing Cu ions and Pd ions with the reducing agent. The temperature of reduction is determined in consideration of the crystal structure of the alloy to be prepared by reduction, and is suitably in the range of 0 to 110 ° C., for example. The relationship between the crystal structure of the alloy and the reduction temperature will be described later.

When preparing CuPd nanoparticles having a crystal structure of B2 type, the molar ratio of Cu ions to Pd ions in the dispersion or solution is more than 0.3: less than 0.7 to less than 0.7: 0 And a reduction temperature of 10 ° C. or higher. When reduction is performed under these conditions, CuPd nanoparticles having a crystal structure of B2 type and represented by Cu _x Pd _(1-x) can be prepared. An alloy having an ordered structure tends to be difficult to form when the reduction temperature is low. Therefore, the reduction temperature is set to 10 ° C. or higher, preferably 20 ° C. or higher, more preferably 30 ° C. or higher. The upper limit of reduction temperature is 100 degreeC, for example, Preferably it is 80 degreeC. The value of x varies with the size of the nanoparticles. Small sized nanoparticles can be obtained by increasing the amount of protective polymer or decreasing the amount of reducing agent, or both.

If the crystal structure is prepared CuPd nanoparticles is L1 ₂ type, the molar ratio of Cu ions and Pd ions of the dispersion or solution in 0.7: 0.3 to .98: 0.02 of the range, and reduction temperature, and 10 ° C. or higher, the crystal structure is L1 ₂ type, and can be prepared CuPd nanoparticles represented by _{Cu x Pd (1-x)} . An alloy having an ordered structure tends to be difficult to form when the reduction temperature is low. Therefore, the reduction temperature is set to 10 ° C. or higher, preferably 20 ° C. or higher, more preferably 30 ° C. or higher. The upper limit of reduction temperature is 100 degreeC, for example, Preferably it is 80 degreeC.

If the case crystal structure to prepare CuPd nanoparticles are type B2 and crystal structure to prepare CuPd nanoparticles is L1 ₂ type, it is preferable that the reducing agent is a compound containing hydrogen. In the above, all of the compounds mentioned as examples of the compound whose standard reduction potential is more negative than hydrogen (0 eV) at room temperature are compounds containing hydrogen. When a compound containing hydrogen is used as a reducing agent, hydrogen atoms enter the gaps between metal atoms during the reduction process, weakening the bond between metals, promoting rearrangement of metal atoms, and further improving the ordered structure. There is a tendency to stabilize. In addition, by using a hydrogen-containing compound as a reducing agent, there is an advantage that the regularity in exposure to a hydrogen atmosphere described later easily occurs. In the present invention, by using a compound containing hydrogen of a metal hydride such as reducing agents, hydrogen from the synthesis can be obtained efficiently B2 type alloys and L1 ₂ type by the action on the metal.

According to the production method of the present invention, water can be used as a solvent, and alloy nanoparticles can be produced at a relatively low temperature and in a short operation. Further, in the method of the present invention, the type B2 or L1 ₂ type CuPd nanoparticles it is ordered alloy nanoparticles which are constituent elements Cu and Pd arranged in alternately or several intervals can be prepared.

When preparing CuPd nanoparticles having a crystal structure of fcc type using an inorganic hydride having a strong reducing power as a reducing agent, the molar ratio of Cu ions to Pd ions in the dispersion or solution is 0.01: 0. .99 to 0.99: 0.01, and the reduction temperature is less than 10 ° C. When reduction is performed under these conditions, CuPd nanoparticles having a crystal structure of fcc type and represented by Cu _x Pd _(1-x) (provided that 0.01 <x <0.99) can be prepared. . The fcc type alloy tends to be difficult to be formed when the reduction temperature is high, and therefore the reduction temperature is less than 10 ° C., preferably 5 ° C. or less, more preferably 0 ° C. or less. The lower limit of the reduction temperature is, for example, −10 ° C.

<Hydrogen atmosphere exposure treatment>
The present invention, the crystal structure by the above method to produce CuPd nanoparticles are type B2 or L1 ₂ type, by exposing the CuPd nanoparticles produced in a hydrogen atmosphere, CuPd nanoparticles regularity of the crystal structure is improved And a method for producing CuPd nanoparticles with improved crystal structure regularity.

CuPd nanoparticle crystal structure produced by the above method is type B2 or L1 ₂ type, the degree of ordering represented by the following formula (1) is less than 99%. In contrast, by exposure to a hydrogen atmosphere, degree of ordering represented by the following formula (1) of at least 99%, CuPd nanoparticles regularity of the crystal structure is type B2 or L1 ₂ type with improved Can be obtained.
(1- (m−M) / M) × 100% (1)
m: Lattice constant of CuPd alloy nanoparticles M: Bulk lattice constant in which Cu atoms and Pd atoms are regularly arranged

  The exposure treatment to the hydrogen atmosphere is carried out at a predetermined temperature and hydrogen pressure after removing water (eg, drying) as a solvent from the mixture of CuPd nanoparticles and protective polymer obtained by the above method. Can do. The temperature can be, for example, in the range of 0 to 200 ° C., and the hydrogen pressure can be in the range of 1 Pa to 10 MPa. The conditions for the hydrogen atmosphere exposure treatment are preferably in the range of 50 to 150 ° C. and the hydrogen pressure in the range of 1 MPa to 5 MPa. The treatment time can be appropriately set according to the temperature and pressure, and can be, for example, in the range of 1 to 1000 hours, or in the range of 1 to 10 hours. However, it is not intended to be limited to this range.

Further, the hydrogen atmosphere exposure treatment can be performed in multiple stages at different temperatures, and the treatment temperature is preferably increased at each stage. The multi-stage treatment is, for example, a first stage at a temperature in the range of 30 to 150 ° C, preferably in the range of 50 to 150 ° C, more preferably in the range of 70 to 130 ° C and in the range of 40 to 250 ° C, preferably 80. The second stage at a temperature in the range of ~ 200 ° C, more preferably in the range of 120-180 ° C, and the temperature difference between the first stage and the second stage is in the range of 10-100 ° C, preferably 20-90 It can be in the range of ° C, more preferably in the range of 30-80 ° C. By performing the hydrogen atmosphere exposure treatment in multiple stages with different temperatures, the degree of ordering can be further increased, and as a result, when used in combination with a photowater decomposition catalyst such as TiO ₂ , high photowater decomposition performance is exhibited. There is an advantage that.

  The hydrogen atmosphere exposure time in the multistage treatment can be set as appropriate. For example, the first stage hydrogen atmosphere exposure time is, for example, in the range of 1 to 500 hours, preferably in the range of 100 to 400 hours, and in the second stage of hydrogen. The atmospheric exposure time is, for example, in the range of 0.1 to 200 hours, preferably in the range of 1 to 100 hours.

Degree of ordering was prepared by the above method is less than 95%, by preferably subjecting less than 98%, the CuPd nanoparticles to a hydrogen atmosphere exposure process and more preferably a crystalline structure type B2 or L1 ₂ type is less than 99% The degree of ordering is higher than that before the hydrogen atmosphere exposure treatment, and the regularity of the crystal structure is improved. The ordering degree is 98.5% or more, preferably 99% or more, more preferably 100% or more. can be obtained CuPd nanoparticles is L1 ₂ type. Furthermore, a degree of ordering of 100% or more may be obtained due to the nanosize effect that the lattice constant is smaller than that of the bulk. In particular, when a hydrogen-containing compound is used as the reducing agent in the above method, since the hydrogen atoms enter the gaps between the metal atoms during the reduction process, it is easy to improve the degree of ordering by the hydrogen atmosphere exposure treatment. There is an advantage.

  Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1
・ Synthesis of irregular fcc-type CuPd nanoparticles
7.5 × 10 ⁻⁴ mol of copper acetate was dissolved in 100 ml of ion exchange water, and 7.5 × 10 ⁻⁴ mol of palladium acetate was dissolved in 50 ml of acetone. These solutions were mixed with 1.5 × 10 ⁻¹ mol of poly [N-vinyl-2-pyrrolidone] (NW = 48000), and ion-exchanged water was added to prepare a 300 ml solution, which was cooled to 0 ° C. When 7.5 × 10 ⁻³ mol of NaBH ₄ dissolved in 100 ml of ion exchange water was added all at once, a dark brown colloidal solution was obtained. After stirring for 30 minutes, reprecipitation using acetone, water, and diethyl ether was repeated three times to remove the solvent and the by-product inorganic compound to obtain CuPd nanoparticles. As a result of elemental analysis of the CuPd nanoparticles, the metal (copper and palladium) content was 11.7% by mass, and the remainder was poly [N-vinyl-2-pyrrolidone]. The breakdown of the metals copper and palladium was determined by ICP emission analysis to be 50:50 in molar ratio (atomic ratio) from the composition of the raw materials.

(Hydrogen atmosphere exposure treatment (hereinafter referred to as hydrogen treatment))
The CuPd nanoparticles obtained above were put in a stainless steel container and connected to a stainless steel vacuum line. The sample was heated and degassed at room temperature for 30 minutes or more and at 373 K for 30 minutes or more, and then held for 3 hours by applying a hydrogen pressure of 0.1 MPa, or held for 6 hours by applying a hydrogen pressure of 2 MPa. After the holding, the hydrogen was evacuated for about 30 minutes with the temperature kept constant, and allowed to cool to room temperature.

Example 2
・ Synthesis of ordered B2 type CuPd nanoparticles
7.5 × 10 ⁻⁴ mol of copper acetate was dissolved in 100 ml of ion exchange water, and 7.5 × 10 ⁻⁴ mol of palladium acetate was dissolved in 50 ml of acetone. These solutions and 1.5 × 10 ⁻¹ mol of poly [N-vinyl-2-pyrrolidone] (NW = 48000) were mixed, and ion-exchanged water was added to prepare a 300 ml solution, which was heated to 30 ° C. When 7.5 × 10 ⁻³ mol of NaBH ₄ dissolved in 100 ml of ion exchange water is added at once, a dark brown colloidal solution is obtained. After stirring for 50 minutes, reprecipitation with acetone, water, and diethyl ether was repeated three times to remove the solvent and by-product inorganic compounds. As a result of elemental analysis of the CuPd nanoparticles, the metal (copper and palladium) content was 18.6% by mass, and the remainder was poly [N-vinyl-2-pyrrolidone]. The breakdown of copper and palladium of the metal was determined to be 52:48 in terms of molar ratio (atomic ratio) from ICP emission analysis.

(Hydrogen atmosphere exposure treatment (hereinafter referred to as hydrogen treatment) (1))
The CuPd nanoparticles obtained above were put in a stainless steel container and connected to a stainless steel vacuum line. The sample was heated and degassed at room temperature for 30 minutes or more and at 373 K for 30 minutes or more, and then held for 3 hours by applying a hydrogen pressure of 0.1 MPa, or held for 6 hours by applying a hydrogen pressure of 2 MPa. After the holding, the hydrogen was evacuated for about 30 minutes with the temperature kept constant, and allowed to cool to room temperature.

(Hydrogen atmosphere exposure treatment (hydrogen treatment) (2))
The CuPd nanoparticles obtained above were put in a stainless steel container and connected to a stainless steel vacuum line. After heating and degassing the sample for 30 minutes or more at room temperature and 30 minutes or more at 373 K, after applying a hydrogen pressure of 2 MPa at 373 K and holding for 240 hours, the temperature was continuously raised to 423 K and a hydrogen pressure of 2 MPa was Applied and held for 24 hours. After the holding, the hydrogen was evacuated for about 30 minutes with the temperature kept constant, and allowed to cool to room temperature.

Test example 1
(1) Observation with transmission electron microscope The reduced CuPd nanoparticles obtained in Examples 1 and 2 were observed with JEM-2000FX. The results are shown in FIG. The average particle diameter is estimated from 200 particles in the obtained photograph (upper figure) and shown in the lower figure. CuPd (0 ° C.) is the result of Example 1, and CuPd (30 ° C.) is the result of Example 2.

(2) Powder X-ray diffraction measurement The reduced CuPd nanoparticles obtained in Examples 1 and 2 were subjected to diffraction measurement at a wavelength of Cu Kα by RINT-2000 / PC. The results are shown in FIG. CuPd (0 ° C.) is the result of Example 1, and CuPd (30 ° C.) is the result of Example 2.

  From the results shown in FIG. 3, different diffraction patterns were observed in the XRD patterns of the sample produced at the synthesis temperature of 0 ° C. (Example 1) and the sample produced at the synthesis temperature of 30 ° C. (Example 2). It was found that CuPd nanoparticles having an irregular fcc type structure in Example 1 and an ordered B2 type structure in Example 2 were obtained.

  In FIG. 4, the result of having performed the X-ray-diffraction measurement about the sample which performed the hydrogen treatment to the particle | grains obtained in Example 1 and 2 is shown. As a result, the particles obtained in Example 2 were subjected to hydrogen treatment (1), particularly at 373 K for 3 hours at a hydrogen pressure of 0.1 MPa, the diffraction position shifted to the high angle side, and the interatomic distance was shortened. It was found that alloy nanoparticles with aligned metal arrays were obtained.

  Since no significant change was observed in the powder X-ray diffraction pattern when treated with 0.1 MPa for 3 hours and when treated with 2 MPa for 6 hours, it is assumed that there was no significant change in the lattice constant of these samples. Next, FIG. 5 shows TEM images of the sample just prepared and the sample subjected to hydrogen treatment (1). In the TEM image of FIG. 5, the contrast in the TEM image of the sample treated for 3 hours at 373 K with a hydrogen pressure of 0.1 MPa was more uniform than that of the sample just prepared. The sample treated with hydrogen pressure of 2MPa at 373K for 6 hours is more uniform. This indicates that hydrogen treatment improves not only the structure inside the particles but also the regularity on the surface. It is considered that the catalytic activity is improved by hydrogen because the regularity of the structure inside and on the surface of the particles is improved.

  Further, as shown in FIG. 4, the diffraction position of the particles obtained in Example 1 was also shifted to the high angle side by the hydrogen treatment for 6 hours at a hydrogen pressure of 2 MPa. This result shows that hydrogen treatment enhances the interaction between metal atoms even in an irregular fcc-type CuPd alloy. As a result, although the results are not shown, the hydrogen treatment has a function of enhancing the catalytic activity even for the irregular fcc type CuPd alloy.

  FIG. 9 is a powder X-ray diffraction pattern using synchrotron radiation and a result of analysis by the Rietveld method for a sample obtained by subjecting the particles obtained in Example 2 to hydrogen treatment (2). A peak peculiar to the B2 structure is observed at the position indicated by the arrow. This is because crystals grow inside the grains and the crystallite size increases. As a result of the analysis, the lattice constant was determined to be 2.97 cm.

FIG. 10 shows a sample just prepared in Example 2, a sample subjected to hydrogen treatment (1) (100 ° C., 2 MPa H ₂ ), and a sample subjected to hydrogen treatment (2) (100 ° C., 150 ° C., 2 MPa). A TEM image of H ₂ ) is shown.

(3) Calculation of degree of ordering The degree of ordering of CuPd nanoparticles synthesized in Example 2 (before hydrogen treatment) and hydrogen treatment (1) of CuPd nanoparticles after hydrogen treatment (pressurization of hydrogen at 0.1 MPa at 373 K) The degree of ordering was obtained by calculating the lattice constant of CuPd nanoparticles from the H ₂ pressurized In-situ powder X-ray diffraction pattern shown in FIG. 6 by the Rietveld method or the like. The lattice constant m of CuPd nanoparticles before hydrogen treatment was 3.036, and the lattice constant m of CuPd nanoparticles after hydrogen treatment was 2.99. As a result, the degree of ordering of CuPd nanoparticles before hydrogen treatment was (1- (3.036-2.99) /2.99) × 100 = 98.5%, whereas CuPd nanoparticles after hydrogen treatment (1) The degree of ordering was (1- (2.99-2.99) /2.99) × 100 = 100%. The degree of ordering of the CuPd nanoparticles after hydrogen treatment (2) was (1- (2.97-2.99) /2.99) × 100 = 101%. The degree of ordering is 100% or more is a phenomenon caused by the nano-size effect observed in particles in the nanometer region where the lattice is compressed to reduce the surface energy.

Example 3
Activity test for water splitting hydrogen generation The sample containing 1 mg of alloy particles (total amount of metal) obtained in Example 2 was dissolved in 20 ml of ion-exchanged water and subjected to ultrasonic treatment for 15 minutes. 1 g of TiO ₂ (P25) powder was added to the alloy nanoparticle aqueous solution, and ultrasonic treatment was further performed for 15 minutes. The obtained suspension was filtered to prepare a CuPd nanoparticle-supported TiO ₂ catalyst. As a reference sample, TiO ₂ supporting Pd nanoparticles with a diameter of 6.3 ± 1.0 nm was prepared.

(Photohydrolysis hydrogen generation test)
10 vol.% Methanol aqueous solution was added to 100 mg of the supported catalyst obtained above (regular B2 type CuPd alloy nanoparticles obtained in Example 2 (before and after hydrogen treatment (1)) and Pd nanoparticles supported catalyst). In addition, 250 ml of reaction solution was prepared. This solution was installed in a closed circulation device manufactured by Makuhari RI Chemical, and the amount of hydrogen generated after irradiation with a xenon lamp was quantified with a gas chromatograph GC-8A manufactured by Shimadzu Corporation. The results are shown in FIG. In FIG. 7, the result of the Pd-supported catalyst used as the catalyst for the photowater decomposition reaction is also described for reference.

  The catalyst carrying the ordered B2-type CuPd alloy nanoparticles (0.1 MPa hydrogen, 373 K, 3 hours and 2 MPa hydrogen, 373 K, 6 hours) subjected to the hydrogen treatment (1) prepared in Example 2 was just synthesized (hydrogen It was found that the hydrogen generation activity by photowater decomposition was improved 1.3 times and 1.7 times compared to the B2 structure CuPd supported catalyst (before treatment) (FIG. 7). Furthermore, it was found that the ordered B2-type CuPd alloy nanoparticle-supported catalyst after the hydrogen treatment (1) shows higher activity than the Pd-supported catalyst used as a catalyst for the photo-water decomposition reaction.

  Furthermore, the catalyst carrying the ordered B2 type CuPd alloy nanoparticles (2MPa hydrogen, 373K, 240 hours and 2MPa hydrogen, 423K, 24 hours) subjected to the hydrogen treatment (2) prepared in Example 2 is also 10 vol.%. Of methanol was added to prepare a 250 ml reaction solution. This solution was installed in a closed circulation device manufactured by Makuhari RI Chemical, and the amount of hydrogen generated after irradiation with a xenon lamp was quantified with a gas chromatograph GC-8A manufactured by Shimadzu Corporation. The results are shown in FIG. FIG. 11 also describes a catalyst supporting bare Pd that does not contain a protective agent prepared by a commonly used photoprecipitation method as a reference. The ordered B2-type CuPd alloy nanoparticle-supported catalyst after the hydrogen treatment (2) showed more than twice as high activity as the B2-type CuPd alloy nanoparticle-supported catalyst just prepared. From this result, it was found that hydrotreating (2) is more effective than hydrotreating (1) to obtain nanoparticles exhibiting a highly active photohydrolysis catalyst. In addition, it was found that the catalyst using B2 type CuPd subjected to the hydrogen treatment (2) has higher activity than the catalyst supporting bare Pd generally used as a photocatalyst. Further, the catalyst using bare Pd showed high activity for 30 minutes after light irradiation, but the activity decreased thereafter. Since methanol is used as a sacrificial reducing agent in the examples, formaldehyde is generated by light irradiation. When naked Pd is used, the activity is lost due to formaldehyde poisoning, but the catalyst using the CuPd nanoparticles provided in the present invention did not show any deterioration in performance due to such poisoning. This result indicates that CuPd nanoparticles are also resistant to formaldehyde poisoning.

  The fcc-type CuPd alloy nanoparticle-supported catalyst prepared by hydrogen treatment in Example 1 has not been subjected to a photohydrolysis hydrogen generation test. However, as described above, by hydrogen treatment, even in an irregular fcc-type CuPd alloy, metal atoms It is considered that the catalytic activity such as photo-water splitting reaction is increased.

(Carbon monoxide poisoning test)
The samples obtained in Examples 1 and 2 (both 2MPa hydrogen, 373K, 6 hour hydrogen-treated (1) product) were left for 30 minutes under one atmosphere of carbon monoxide and poisoned with carbon monoxide. . The results are shown in FIG.

  Hydrogen generation amount after carbon monoxide poisoning (after 15 hours) The degree of performance deterioration due to carbon monoxide (CO) poisoning is 1/2 for irregular fcc-type CuPd (Example 1) compared to Pd. In B2 type CuPd, it was 1/3 (Example 2), and an improvement was observed in the poisoning resistance. The rate of activity decrease due to CO adsorption was -47% (Pd), -24% (irregular fcc-type CuPd, Example 1), and -14% (ordered B2-type CuPd, Example 2)).

  The present invention is useful in fields related to CuPd alloy nanoparticles such as a photocatalyst promoter and a fuel cell electrode catalyst.

Claims (11)

The crystal structure is B2 type , the average particle size is 1 to 200 nm, and is represented by Cu _x Pd _(1-x) (provided that 0.4 <x < 0.6 ), represented by the following formula (1) CuPd alloy nanoparticles having a degree of ordering of 99% or more .
(1- (m−M) / M) × 100% (1)
m: lattice constant of CuPd alloy nanoparticles
M: Bulk lattice constant in which Cu atoms and Pd atoms are regularly arranged A composition comprising the CuPd alloy nanoparticles according to claim 1 and a protective polymer. The composition for catalysts which carry | supported the CuPd alloy nanoparticle of Claim 1 on the support | carrier. 4. The catalyst composition according to claim 3 , wherein the support is an inorganic compound. The catalyst composition according to claim 3 or 4 , wherein the catalyst is for a water-splitting hydrogen generation reaction, a water-splitting oxygen generation reaction, or an organic matter decomposition reaction. Preparing a dispersion or solution of Cu ions and Pd ions in the presence of a protective polymer in water or an aqueous solution,
To the obtained dispersion or solution, a reducing agent for Cu ions and Pd ions is added to reduce Cu ions and Pd ions to prepare CuPd alloy nanoparticles ,
Exposing the CuPd alloy nanoparticles to a hydrogen atmosphere;
A method for producing CuPd alloy nanoparticles according to claim 1, comprising:
The reducing agent is MBH ₄ (M = Na, K), MEt ₃ BH (M = Na, K), sodium cyanoborohydride, lithium borohydride, lithium triethylborohydride, borane complex, triethylsilane and hydrogen. A method for producing CuPd alloy nanoparticles, which is at least one selected from the group consisting of sodium bis (2-methoxyethoxy) aluminum chloride. The dispersion or solution in a molar ratio of Cu ions and Pd ions than 0.4: less than from 0.6 to 0.6: in the range greater than 0.4, and
Claims wherein the reduction temperature is 10 ° C or higher, the crystal structure is B2 type, and Cu _x Pd _(1-x) (where 0.4 <x < 0.6 ) CuPd alloy nanoparticles are prepared. 6. The production method according to 6 . The degree of ordering represented by the following formula (1) of the CuPd alloy nanoparticles before the exposure treatment to the hydrogen atmosphere is less than 99% ,
The manufacturing method according to claim 6 or 7 , wherein the degree of ordering represented by the following formula (1) of the CuPd alloy nanoparticles having improved crystal structure regularity when exposed to the hydrogen atmosphere is 99% or more.
(1- (m−M) / M) × 100% (1)
m: Lattice constant of CuPd alloy nanoparticles M: Bulk lattice constant in which Cu atoms and Pd atoms are regularly arranged The manufacturing method according to claim 8 , wherein the exposure treatment to the hydrogen atmosphere is performed at a temperature of 0 to 200 ° C. and a hydrogen pressure of 1 Pa to 10 MPa. The manufacturing method according to claim 8 or 9 , wherein the exposure treatment to the hydrogen atmosphere is performed in multiple stages at different temperatures. The exposure treatment to the hydrogen atmosphere comprises a first stage at a temperature in the range of 30 to 150 ° C. and a second stage at a temperature in the range of 40 to 250 ° C., and the temperature of the first stage and the second stage. The manufacturing method according to any one of claims 8 to 10, wherein the difference is in a range of 10 to 100 ° C.