WO2016143490A1

WO2016143490A1 - Gold hydroxo anion complex solution

Info

Publication number: WO2016143490A1
Application number: PCT/JP2016/055027
Authority: WO
Inventors: 宏昭櫻井; 健司古賀; 木内　正人; 哲郎神
Original assignee: 国立研究開発法人産業技術総合研究所
Priority date: 2015-03-09
Filing date: 2016-02-22
Publication date: 2016-09-15
Also published as: JPWO2016143490A1; JP6441454B2

Abstract

Provided is a method for producing a gold hydroxo anion complex solution which comprises: a step 1 of preparing a reaction liquid in which a hydrolysis reaction of a gold compound is proceeded in the presence of conjugate bases of a weak acid in a solution of pH 8 or more in which a trivalent gold compound that does not include halide ions is suspended or dispersed in water; and a step 2 of mixing the reaction liquid with a weak acid.

Description

Gold hydroxo anion complex solution

The present invention relates to a gold hydroxo anion complex solution and a method for producing the same, and a method for producing a gold nanoparticle carrier using the gold hydroxo anion complex solution.

In recent years, applications of gold nanoparticle catalysts in which gold is supported as a nanoparticle on the surface of a support such as an oxide are being studied in various fields. For example, indoor air purification such as carbon monoxide oxidation removal, atmospheric environment conservation such as NOx reduction, fuel cell related reactions such as selective oxidation of carbon monoxide in hydrogen, reactions for chemical processes such as propylene oxide synthesis reaction from propylene, etc. Is a typical application field. In these cases, it is necessary to change the type of the carrier according to the type of reaction to be applied. However, by attaching gold to the surface of the carrier as hemispherical nanoparticles of 10 nm or less, preferably 5 nm or less, Even in this case, the performance can be improved. For this reason, selection of the preparation method for exhibiting performance is especially important.

For catalysts that have been used for a long time, such as platinum catalysts and palladium catalysts, the carrier is immersed in a solution of a precious metal compound such as chloroplatinic acid in a solvent such as water, and the solvent is removed by a method such as evaporation to dryness. In many cases, it is prepared by a so-called impregnation method in which chloroplatinic acid is dispersed and supported on the surface of the carrier and calcined and reduced to form platinum fine particles. In the case of platinum, it is possible to support platinum nanoparticles having a particle size of 5 nm or less by this method. According to this method, a wide variety of catalysts can be easily prepared by combining a noble metal compound and a carrier, and mass production is easy.

However, in the case of gold, a highly active catalyst cannot be obtained by a normal impregnation method. For example, even when prepared by an impregnation method similar to that for a platinum catalyst using chloroauric acid, the particle size of gold becomes as large as about 30 nm. It has been pointed out that this is because chloride ions contained in the raw material chloroauric acid result in particles that have become agglomerated and agglomerated during the thermal decomposition. Furthermore, even after the thermal decomposition treatment, the remaining chloride ions cause poisoning of the active sites for many catalytic reactions, so that the activity becomes extremely low due to a double negative factor together with the aggregation of gold.

For this reason, gold has been treated as an inactive element as a catalyst until a method for preparing a gold catalyst by a coprecipitation method or a precipitation method is established. In the coprecipitation method that succeeded in making gold a highly active catalyst for the first time, although chloroauric acid is used as a raw material, it is neutralized by adding a base and precipitated together with a precursor of a carrier oxide. was in the form of gold hydroxide Au (OH) ₃ which does not contain, followed by washing with water of the coprecipitate at this stage, to remove chloride ions, to obtain a highly active gold catalysts and then drying and firing. The operation of washing the coprecipitate is particularly important, and it has been reported that the presence of chloride ions even in a trace amount of about 300 ppm increases the particle size of gold during firing. For this reason, the washing operation needs to be repeated using a large amount of water, but in order to obtain a highly active catalyst with a large surface area, the carrier oxide also needs to be made into fine particles. In many cases, separation of water and precipitates takes a long time when using either the decantation method or the centrifugal separation method, and washing must be repeated until no chloride ions are detected. Is a very time-consuming operation.

Further, since the gold remaining in the liquid phase is washed away by the washing operation, it is a big problem that the amount of gold finally supported on the surface is smaller than the amount of gold supported under the charging conditions. With a gold / titanium oxide catalyst, a catalyst having a high activity for CO oxidation can be prepared by using a precipitation method in the vicinity of pH 7. For example, even if it is prepared with a charge amount of 3% by weight of gold, the actual gold after preparation is prepared. / The gold contained in titanium oxide is about 1.5% by mass, and only about 50% of the charged amount is supported. Further, since the carrier capable of supporting gold by the precipitation method is limited to basic to amphoteric oxides, it cannot support gold on acidic oxides such as silica and silica-alumina.

Further, in the following Patent Document 1, Non-Patent Document 1, etc., after impregnating titanium oxide with chloroauric acid and further impregnating with sodium carbonate, gold hydroxide is precipitated in the pores, washed with water, A method is described in which gold / titanium oxide showing high activity is dried by drying. However, in this method, chloride ions cannot be completely removed by washing with water, and many chloride ions are detected as compared with the precipitation method, and the activity is reduced when firing at about 400 ° C.

On the other hand, a method has been reported in which gold acetate is used as a gold compound not containing chloride ions, and Au / TiO ₂ is prepared under the same preparation conditions as in a conventional precipitation method (see Non-Patent Document 2 below). In this method, the amount of gold lost by washing was reduced by using gold acetate, and the gold loading rate was improved, but the catalytic activity was inferior to the case of using chloroauric acid as a raw material.

As described above, the liquid phase gold nanoparticle preparation process has various drawbacks, and therefore, gold nanoparticle catalyst preparation methods using a gas phase method or a solid phase method have been studied. A typical example of the gas phase method is a gas phase grafting method in which dimethylgold acetylacetonate complex (CH ₃ ) ₂ Au (acac) is vaporized and supported in a vacuum line. There is a solid phase mixing method in which the same complex is mixed and pulverized in a carrier and a mortar, and a sublimated gold precursor is supported on the surface with high dispersion. In these methods, the gold raw material itself does not contain chloride ions and is supported on various supports such as acidic oxides, activated carbon, polymers, and porous polymer complexes that cannot be supported by the conventional liquid phase method. Is possible. However, the gold complex of the precursor is expensive, and the sublimable gold complex is harmful to the human body and needs to be handled so as not to be sucked, and mass production is not always easy in terms of equipment.

As a method for solving various problems of the liquid phase gold nanoparticle preparation process as described above, for example, the method disclosed in Patent Document 2 can be mentioned.

US2007 / 0219090A1 WO2012 / 144532

According to the technique disclosed in Patent Document 2, in a method for preparing a gold nanoparticle catalyst using a liquid phase method, a gold compound containing no halide ions such as chloride ions is used as a raw material, and this is efficiently supported. In addition, a highly active gold nanoparticle-supported catalyst can be produced by a simple preparation method.

However, in the technique disclosed in Patent Document 2, it is necessary to set the pH of the gold hydroxo anion complex solution used for the preparation of the gold nanoparticle catalyst to 8 or more in order to dissolve the raw material gold acetate. . In order to adjust the particle size of the supported gold nanoparticles, it is necessary to change the amount of gold supported or the heat treatment temperature after loading, and it is impossible to control the particle size depending on the solution. Met. Further, for example, it may not always be preferable to select a weakly alkaline carrier such as silica or zeolite as the carrier for supporting the gold hydroxo anion complex solution.
Under such circumstances, the present invention provides a gold hydroxo anion complex solution that can easily control the particle size of gold nanoparticles and can be used for the production of gold nanoparticle catalysts at a lower pH than before. The main purpose. Furthermore, the main object of the present invention is to provide a method for producing the gold hydroxo anion complex solution and a method for producing a gold nanoparticle carrier using the gold hydroxo anion complex solution.

The present inventors have intensively studied to solve the above problems. As a result, a reaction solution in which the hydrolysis reaction of the gold compound was advanced in the presence of a conjugate base of a weak acid in a solution having a pH of 8 or higher in which a trivalent gold compound not containing halide ions was suspended or dispersed in water. Suitable for the production of gold nanoparticle catalyst at a lower pH (less than 8) by the method for producing a gold hydroxo anion complex solution comprising the step 1 for preparing a solution and the step 2 for mixing the reaction solution and a weak acid. It was found that a gold hydroxo anion complex solution that can be used in the present invention is obtained. According to the conventional knowledge, it has been considered in Patent Document 2 that the pH needs to be set to at least 8 or more, so this result is very unexpected. Further, in such a production method, a gold hydroxo anion complex solution that can be suitably used for the production of a gold nanoparticle catalyst is obtained not only at a pH of less than 8, but also at a pH of 8 or more, and a mixing ratio of weak acids. It was also found that the particle size of the gold nanoparticles supported can be easily controlled by changing the pH of the solution. The present invention has been completed by further studies based on such findings.

That is, this invention provides the invention of the aspect hung up below.
Item 1. Preparation of a reaction solution in which a hydrolysis reaction of a gold compound proceeds in a solution of pH 8 or higher in which a trivalent gold compound not containing halide ions is suspended or dispersed in water in the presence of a conjugate base of a weak acid Step 1 to perform,
Step 2 of mixing the reaction solution and a weak acid;
A method for producing a gold hydroxo anion complex solution.
Item 2. Item 2. The method for producing a gold hydroxo anion complex solution according to Item 1, wherein the weak acid in Step 2 is at least one selected from the group consisting of carboxylic acid, phosphoric acid, and carbonic acid.
Item 3. The trivalent gold compound containing no halide ions in the step 1 is at least one selected from the group consisting of gold carboxylate, gold oxide, gold hydroxide, and a double oxide of gold and an alkali metal. Item 3. A method for producing a gold hydroxo anion complex solution according to

Item

1 or 2, which is a seed.
Item 4. Item 1 to 3 wherein the conjugate base of the weak acid in Step 1 is at least one selected from the group consisting of a carboxylate anion, carbonate ion, hydrogen carbonate ion, phosphate ion, and borate ion. A method for producing a gold hydroxo anion complex solution according to any one of the above.
Item 5. Item 5. The method for producing a gold hydroxo anion complex solution according to any one of Items 1 to 4, wherein, in the step 2, the pH of the gold hydroxo anion complex solution is adjusted to less than 8 with the weak acid.
Item 6. A step A of impregnating a carrier with the gold hydroxo anion complex solution produced by the method for producing a gold hydroxo anion complex solution according to any one of Items 1 to 5,
Removing water from the carrier impregnated with the gold hydroxo anion complex solution and performing a heat treatment; and
A method for producing a gold nanoparticle carrier.
Item 7. The carrier is at least one selected from the group consisting of metal oxides, porous silicates, porous metal complexes, porous polymer beads, carbon materials, ceramic honeycombs, and metal honeycombs. 6. A method for producing a gold nanoparticle carrier according to 6.
Item 8. At least one ligand is OH ^- an A, includes a hydroxo anionic complex of 3 Ataikin square planar structure containing no halogen anion as a ligand, the conjugate base of a weak acid that does not coordinate to gold A gold hydroxo anion complex solution comprising a transparent solution having a pH of less than 8 and containing no halogen anion.
Item 9. Item 9. The gold hydroxo anion complex solution according to Item 8, which is an impregnating solution for producing a gold nanoparticle carrier.

According to the method for producing a gold hydroxo anion complex solution of the present invention, a trivalent gold compound not containing a halide ion is suspended or dispersed in water at a pH of 8 or higher in the presence of a conjugate base of a weak acid. In the prior art, for example, a gold nanoparticle having a pH of less than 8 is prepared by including a step 1 for preparing a reaction solution in which a hydrolysis reaction of a gold compound proceeds and a step 2 for mixing the reaction solution and a weak acid. A gold hydroxo anion complex solution that does not contain halide ions such as chloride ions, which have been thought to be unusable for the production of catalysts, can be suitably produced. Further, in the method for producing a gold hydroxo anion complex solution of the present invention, a gold hydroxo anion complex solution that can be used for producing a gold nanoparticle catalyst not only at a pH of less than 8 but also at a pH of 8 or more is suitable. Can be manufactured. Furthermore, according to this invention, the manufacturing method of the gold | metal | money nanoparticle support body by which the particle diameter was controlled using the said gold hydroxo anion complex solution and the said gold hydroxo anion complex solution can also be provided.

C. F. B. Jr. , R. E. It is a graph which shows the relationship between the halogen ion concentration, pH, and the composition of a gold complex in the solution as described in Mesmer, Tsuji The Hydrology of Cations, Wiley, 1976. It is a graph which shows the relationship between the particle diameter of the gold | metal | money in the gold nanoparticle cerium oxide support body obtained by the Example and the comparative example, and the pH of the gold hydroxo anion complex solution used for preparation of a gold nanoparticle support body. CO conversion rate (%) in the case of performing CO oxidation reaction using the gold nanoparticle cerium oxide support obtained in Examples and Comparative Examples, and the gold hydroxo anion complex used for the preparation of the gold nanoparticle support It is a graph which shows the relationship with pH of a solution. It is the figure which plotted about the relationship between the particle diameter of gold | metal | money and CO oxidation activity from the data of FIG. 2 and FIG. In the figure, the horizontal axis represents the reciprocal of the particle diameter (nm) of gold, and the vertical axis represents the CO conversion rate (%). It is a measurement result of the powder X-ray diffraction of the gold | metal | money nanoparticle beta zeolite support body obtained by the Example and the comparative example, and the H-type beta zeolite which is not carrying | supporting a gold nanoparticle. It is the result of having evaluated the activity with respect to the water-splitting hydrogen generation reaction which uses methanol as a sacrificial agent using the gold nanoparticle titanium oxide support body obtained by the Example and the comparative example as a photocatalyst. It is the result of having evaluated the activity with respect to the water-splitting hydrogen generation reaction which uses glycerin as a sacrificial agent using the gold nanoparticle titanium oxide support body obtained in the Example as a photocatalyst.

1. Method for Producing Gold Hydroxo Anion Complex Solution The method for producing a gold hydroxo anion complex solution of the present invention comprises a solution having a pH of 8 or more in which a trivalent gold compound not containing a halide ion is suspended or dispersed in water. It comprises a step 1 for preparing a reaction solution in which a hydrolysis reaction of a gold compound proceeds in the presence of a conjugate base of a weak acid, and a step 2 for mixing the reaction solution and a weak acid. Hereinafter, the manufacturing method of the gold hydroxo anion complex solution of this invention is explained in full detail.

(Process 1)
Raw Material Compound As the raw material used in Step 1 of the present invention, a gold compound containing trivalent gold not containing halide ions is used. In general, chloroauric acid is often used as a raw material for the production of gold nanoparticle catalysts. However, in the case of using chloroauric acid, in order to obtain a highly dispersed and highly active catalyst, residual chloride ions are used. Need to be removed. For this reason, a process process becomes complicated and there exists a problem that the utilization factor of gold is low.

Moreover, there is a report of 47 ppm as an analytical value of chloride ion for the precipitation / precipitation method Au / TiO ₂ (Au 1.5 mass%) which is a gold reference catalyst of World Gold Council (M. Azar et al., Journal). of Catalysis 239 (2006) 307-312), it is difficult to reduce chloride ions by a conventional preparation method using ordinary chloroauric acid.

In the present invention, a trivalent gold compound not containing halide ions is used as a raw material, and a gold hydroxo anion complex solution in which the gold compound is uniformly dissolved is prepared by the method described later, and this is used to impregnate the solution. By producing a gold nanoparticle catalyst, it is possible to eliminate the problems caused by the presence of halide ions and obtain a highly dispersed and highly active catalyst. In addition, if the gold compound as a raw material contains 0.01% by mass of impurity halide ions and remains in the gold catalyst after preparation, if the amount of gold supported is 1.5% by mass, the halide Ions are 3 ppm or less at maximum, and chloride ions can be greatly reduced as compared with conventional methods.

In the present invention, as the trivalent gold compound not containing halide ions, for example, gold compounds shown in the following items (1) to (4) can be preferably used.
(1) Gold carboxylate: Au (CH ₃ COO) ₃ , Au (C ₂ H ₅ COO) ₃ or the like (basic salt Au (OH) (CH ₃ COO) ₂ , Au (OH) ₂ ( CH ₃ COO) etc. may be included)
(2) Gold oxide: Au ₂ O ₃
(3) Gold hydroxide: Au (OH) ₃
(4) Gold and alkali metal double oxide: NaAuO ₂ , KAuO _2, etc.

Preparation of reaction solution In step 1 of the present invention, first, the above-described trivalent gold compound not containing halide ions is used as a raw material, and this is suspended or dispersed in water at pH 8 or more, preferably pH 10 or more. In the solution, the hydrolysis reaction of the gold compound proceeds in the presence of a conjugated base of a weak acid to obtain a reaction solution. The concentration of the gold compound in the reaction solution is not particularly limited as long as a uniform dispersion can be formed, but it is usually in the range of about 0.001 to 10% by mass.

Specifically, the conjugate base of the weak acid present in the solution means A ⁻ represented by the following ionization formula of the weak acid HA.

In the present invention, the conjugate base of the weak acid can be used without particular limitation as long as it meets the above definition. Specific examples of such weak acid conjugate bases include carboxylate anions, carbonate ions, hydrogen carbonate ions, phosphate ions, and borate ions. As the carboxylate anion, monocarboxylate ions such as formate ion, acetate ion, propionate ion, lactate ion, butyrate ion; oxalate ion, succinate ion, malate ion, tartrate ion, fumarate And dicarboxylic acid ions such as acid ions; and tricarboxylic acid ions such as citrate ions.

In order to prepare a reaction solution having a pH of 8 or more containing a conjugate base of a weak acid in which a gold compound is suspended or dispersed in water, a salt of a weak acid and a strong base is previously dissolved in water so that the pH becomes 8 or more. A trivalent gold compound may be added to an aqueous solution adjusted to 1 or a salt of a weak acid and a strong base is added to a solution in which a trivalent gold compound is suspended or dispersed in water to adjust the pH to 8 or more. It is good. In these cases, the amount of the salt of the weak acid and the strong base may be such that the pH of the solution in which the gold compound is suspended or dispersed in water is 8 or more. In addition, when gold acetate or the like is used as the gold compound, acetate ions that are conjugate bases of weak acids are generated from the gold compound itself, and thus pH adjustment may be performed using a strong base such as NaOH.

When the pH of the solution is 8 or more, a uniform solution can be obtained. However, if the pH value in step 1 is lower than this, precipitation of gold hydroxide Au (OH) ₃ is likely to occur, and the uniform solution Is difficult to get.

Examples of the salt of a weak acid and a strong base used for adjusting the pH to 8 or more include, for example, alkali metal ions (K ⁺ , Na ⁺ etc.), alkaline earth metal ions (Ca ²⁺ , It is sufficient to use a salt of a weak acid containing Ba ²⁺ or the like and generating the above-mentioned conjugate base, and it is particularly preferable to use a salt of a weak acid containing an alkali metal ion as a cation component.

In addition, although there is no limitation in particular about the upper limit of pH, it should just be about 14 or less normally.

A solution with a pH of 8 or more containing a conjugate base of a weak acid, in which the trivalent gold compound prepared by the above method is suspended or dispersed in water, the gold compound is gradually hydrolyzed, and the solution continues for a long time even at room temperature. , The gold compound is completely dissolved as a gold hydroxo anion complex, and a transparent homogeneous solution (reaction solution) is obtained. Usually, in order to shorten the preparation time of the transparent solution, it is preferable to heat to 80 ° C. or higher, and it is particularly preferable to boil and reflux. Moreover, even if it is uniformly dispersed using an ultrasonic cleaner or the like before heating, a uniform aqueous solution of gold compound cannot be obtained immediately, but depending on the concentration, a colloidal solution of the gold compound can be obtained. The time required for hydrolysis can be shortened. However, if ultrasonic dispersion is excessively performed, black precipitates may be mixed with the product.

When using gold hydroxide, gold oxide or the like as the gold compound, compared to using gold acetate, it takes a long time to obtain a transparent solution under the same conditions, but no matter which reaction condition is used, If the reaction is performed until the raw material powder remains undissolved and the colloid disappears, a desired transparent solution can be obtained. Even when the raw powder remains undissolved, a clear solution in which the gold compound is dissolved can be obtained by separating the supernatant.

As an example of a specific solution preparation method, for example, when gold acetate is used as a gold compound and sodium carbonate is used for pH adjustment, gold acetate is added to deionized water, and an aqueous sodium carbonate solution is added thereto to adjust pH 8 As described above, when boiling to reflux, a brown colloidal solution turns into a yellow transparent solution in a few minutes, and a colorless and transparent reaction solution is obtained in about 10 minutes.

After completion of the reaction, a uniform transparent reaction solution can be obtained by returning to room temperature. Using this reaction solution, Step 2 described later is performed, and then a gold nanoparticle carrier (gold nanoparticle catalyst) can be prepared. If the reaction solution is allowed to stand for about a day, a small amount of black precipitate may be separated, but it is also possible to use a solution from which the precipitate has been removed by filtration using a membrane filter or the like.

The reaction solution (transparent solution) prepared by the above-described method is a solution in which a gold hydroxo anion complex that does not contain halide ions such as chloride ions is uniformly dissolved, which causes coarsening of the gold particles. Does not contain halide ions that are poisonous to catalytic reactions. For this reason, according to the method of mixing the reaction solution with a weak acid in Step 2 to be described later, impregnating the obtained solution into a support, and then performing a heat treatment, a highly active catalyst uniformly supporting gold nanoparticles is obtained. Can be easily obtained. As in the technique disclosed in the above-mentioned Patent Document 2, a highly active catalyst in which gold nanoparticles are uniformly supported can be easily obtained by a method in which the support is impregnated with the reaction solution and then heat-treated. However, in this method, there is a limitation that the pH of the solution impregnated on the carrier needs to be set to 8 or more.

The reaction liquid containing the gold hydroxo anion complex includes a trivalent gold hydroxo anion complex having a planar quadrangular structure in which at least one ligand is OH ⁻ and does not contain a halogen anion, It is a clear solution having a pH of 8 or more, which contains a weak acid conjugate base that is not coordinated to gold and does not contain a halogen anion.

This reaction solution is a solution in which a gold hydroxo anion complex that does not contain a halide ion such as chloride ion is uniformly dissolved, which causes coarsening of the gold particles and becomes a poison for the catalytic reaction. In order not to contain halide ions, after mixing with a weak acid in Step 2, the resulting mixture is impregnated into a support and heat treated, whereby a highly active catalyst uniformly supporting gold nanoparticles is obtained. Can be easily obtained. Further, since a weak acid conjugate base is present, the solution has a buffering action and the pH is stable even after the weak acid is added in Step 2. Thereby, it is considered that the gold complex in the solution interacts with the carrier under a certain condition, and helps to generate uniform gold nanoparticles.

As the trivalent gold hydroxo anion complex contained in this reaction solution, for example, those satisfying the following conditions (1) to (4) can be preferably used.
(1) The following formula:

A gold complex having a planar rectangular structure represented by
(2) Gold is trivalent and is an anionic complex having a negative charge as a whole due to the coordination of anionic ligands a, b, c, d.
(3) at least one of the ligands a, b, c and d is OH ⁻ ;
(4) The ligands a, b, c and d are all not halogen anions,

In the above-described gold hydroxo anion complex, any ligand other than OH ⁻ among the ligands a, b, c, and d may be any anion ligand that is not a halogen anion. For example, acetate ion CH ₃ COO ⁻ , carbonate ion CO ₃ ^{2− and the} like can be exemplified.

In the above formula, the value of n indicates the valence of the negative charge determined by the type of anion ligand, and the total valence of the anion ligands a, b, c, d is the valence of gold. The value obtained by subtracting 3 is the value of n.

Examples of such a gold hydroxo anion complex include the following compounds.

For the gold hydroxo anion complexes of the above formulas, [Au (OH) ₄ ] ⁻ , [Au (OH) ₂ (CH ₃ COO) ₂ ] ⁻ , [Au (OH) ₃ (CO ₃ )] ^{2 -} it can be referred to as such.

These gold complexes do not need to be a single species in the impregnation solution, and may be a mixture. For example, a solution containing 90% of [Au (OH) ₄ ] ⁻ and 10% of [Au (OH) ₃ (CH ₃ COO)] ⁻ as a gold hydroxo anion complex may be used.

(Process 2)
In this invention, the process 2 which mixes the reaction liquid and weak acid which were obtained at the process 1 is performed. For example, according to the technique of the above-mentioned Patent Document 2, it is necessary to produce a gold nanoparticle carrier by impregnating a carrier with a solution having a pH of 8 or higher. However, according to the production method of the present invention, in step 2, the pH is 8 Since the above-described step of mixing the reaction solution and the weak acid is performed, it is possible to produce a gold nanoparticle support by impregnating the support with a solution having a pH lower than that of the reaction solution.

As described above, as in Patent Document 2, according to the conventional knowledge, it was considered that the pH of the gold hydroxo anion complex solution to be impregnated into the support had to be set to at least 8 or more, and this result was very unexpected. It was something. The gold complex ion species in the reaction solution obtained in step 1 is considered to be [Au (OH) ₄ ] ⁻ . For example, when [AuCl ₄ ] ⁻ ions in chloroauric acid are changed to alkaline, Cl ⁻ ligands are sequentially replaced by OH 2 ⁻ ligands and approach [Au (OH) ₄ ] ^−. ^- it is known that tends to remain as a ligand. For example, since gold acetate originally does not contain Cl ⁻ , the dominant species at about pH 11 is considered to be [Au (OH) ₄ ] ⁻ . When this solution is acidified by adding HCl at room temperature, a yellow solution is immediately formed and Cl ^- is readily re-coordinated to Au. That is, in the Au (III) —OH—Cl— system, it can be said that precipitation hardly occurs although it depends on the Au concentration. On the other hand, in the Au (III) —OH— system without Cl—, as shown in FIG. 1, when the pH of the [Au (OH) ₄ ] ⁻ solution is lowered, it precipitates as Au (OH) ₃ . (C.F.B.Jr., R.E. Mesmer, The Hydrology of Cations, Wiley, 1976). Thus, for example, prepared from such gold acetate [Au (OH) _4] ^- solution is stable precisely under alkaline conditions, was considered to be impossible to prepare in the vicinity of pH 7. However, as a result of repeated studies by the inventor, a gold hydroxo anion complex solution obtained by preparing a reaction solution having a pH of 8 or higher in Step 1 and then mixing the reaction solution and a weak acid in Step 2 described above. It has been found that a gold nanoparticle carrier can be suitably produced by impregnating a carrier with a gold hydroxo anion complex solution having a pH of less than 8, for example.

In addition, in the process of confirming this phenomenon, the present inventor also examined mixing a strong acid such as nitric acid, but when a strong acid was used, a gold hydroxo anion complex solution having the same pH was prepared. Even so, it has been clarified that a gold nanoparticle carrier having a small gold particle diameter and a high CO addition rate cannot be suitably produced.

The reason why a stable complex solution can be obtained even near pH 7 by addition of a weak acid is not clear, but the following mechanism can be considered, for example. The addition of a weak acid causes the solution to have a strong pH buffering action and stabilizes the pH, and an anion such as acetate ion, which is a conjugate base generated by dissociation of the added weak acid, coordinates to a trivalent gold ion. This is thought to stabilize. In addition, when a weak acid having two or more carboxyl groups such as oxalic acid is used, the carboxylate of the conjugate base is multidentate to form a chelate complex, so compared with the case of using a monocarboxylic acid. It is thought to be a more stable complex.

The weak acid to be mixed in step 2, typically pK _a appreciable weak acids may be used an acid in the range of 1-7. The structure is not particularly limited, but preferably includes carboxylic acid, phosphoric acid, carbonic acid and the like. Preferred carboxylic acids include monocarboxylic acids such as formic acid, acetic acid, propionic acid, lactic acid and butyric acid; dicarboxylic acids such as oxalic acid, succinic acid, malic acid, tartaric acid and fumaric acid; and tricarboxylic acids such as citric acid. . The use of dicarboxylic acid or tricarboxylic acid is preferable because the above-mentioned chelate complex can be formed. However, it is known that a hydroxocarboxylic acid having both a carboxyl group and a hydroxyl group such as citric acid has the ability to reduce a chloroauric acid ion to produce a gold colloid (gold particle diameter of 10 nm or more). For this reason, the trivalent gold hydroxo anion complex that does not contain chloride ions obtained in Step 1 is likely to produce colloidal gold in the acidic region at pH 7 or less, and obtain small gold nanoparticles of 10 nm or less. Tends to be difficult. In addition, oxalic acid is known to act as a reducing agent that generates metallic gold from gold ions at the same time that it is oxidized to CO _2. Such a reducing action occurs at a pH of 7 or less. It is easy and the produced | generated gold | metal | money tends to become a coarse particle. A weak acid may be used individually by 1 type, and may be used in combination of 2 or more types.

Moreover, the amount of the weak acid mixed is not particularly limited, and may be adjusted so that the pH corresponds to the gold particle diameter in the target gold nanoparticle carrier. At this time, for example, when the substance added to the gold compound in step 1 is sodium carbonate and the weak acid added to the solution in step 2 is acetic acid, the cation is Na ⁺ and H ⁺ , and the anion is CO ₃ ^2- As a buffer solution composed of CH ₃ COO ⁻ , the pH can be estimated from the amount ratio of each component. Actually, ions derived from a gold compound are added to this, but it is known that, for example, when the gold compound is gold acetate, the influence on the pH is not great. Thus, by setting the pH in advance, the gold particle diameter of the prepared gold nanoparticle carrier can be easily controlled. Further, even when the carrier is not sufficiently resistant to alkalinity, the amount of the weak acid may be adjusted so as to obtain a desired pH. The pH of the gold hydroxo anion complex solution obtained in step 2 is not particularly limited, and can be adjusted to, for example, less than pH 8, which has been conventionally considered difficult, or can be adjusted to pH 8 or more. From the viewpoint of reducing the gold particle size in the gold nanoparticle carrier prepared from the gold hydroxo anion complex solution, the pH is preferably about pH 6 or more, more preferably about pH 6.5 or more. The upper limit of the pH is not particularly limited, but is usually about 14 or less.

The gold hydroxo anion complex solution obtained in step 2 is used as an impregnating solution for producing a gold nanoparticle carrier.

2. Method for Producing Gold Nanoparticle Carrier A method for producing a gold nanoparticle carrier according to the present invention is the step A of impregnating a carrier with the gold hydroxo anion complex solution produced by the method for producing a gold hydroxo anion complex solution described above. And a step B of removing water from the carrier impregnated with the gold hydroxo anion complex solution and performing a heat treatment. Hereinafter, the manufacturing method of the gold nanoparticle carrier (gold nanoparticle catalyst) of the present invention will be described in detail.

(Step A) Impregnation on carrier In step A, the carrier is impregnated with the gold hydroxo anion complex solution produced by the method for producing a gold hydroxo anion complex solution described above.

The method of impregnating the carrier with the solution containing the gold hydroxo anion complex is not particularly limited, and may be a method of immersing the carrier in the solution by using the solution in excess of the volume of the carrier, or The impregnation may be carried out by an incipient wetness method in which an amount of a solution corresponding to the pore volume of the support is dropped onto the support. In these cases, it is necessary to adjust the concentration of the gold hydroxo anion complex solution in advance so that the target amount of gold is supported.

Next, moisture is removed and the gold hydroxo anion complex is immobilized on the surface of the carrier. The method for removing moisture is not particularly limited, and any method such as evaporation to dryness by heating on a hot plate, reduced-pressure drying with a rotary evaporator, freeze-drying method, etc. can be applied.

At this time, the presence of CO ₃ ²⁻ or CH ₃ COO ⁻ , which is a conjugate base of a weak acid, together with alkali metal ions, alkaline earth metal ions, etc., the solution has a buffering action and the pH is stabilized. Thereby, it is considered that the gold complex in the solution interacts with the carrier under a certain condition, and helps to generate uniform gold nanoparticles.

On the other hand, when a weak acid conjugate base is not present, it is considered that after the solution is impregnated on the surface of the carrier, the solution is concentrated in the process of removing moisture, and the pH gradually increases, resulting in a strong base condition. During this time, the state of adsorption of the gold complex on the surface of the carrier changes, which causes non-uniform gold nanoparticles to be generated, and also causes damage to the surface of the carrier oxide due to strong alkalinity.

The carrier is not particularly limited as long as it is usually used as a carrier for a noble metal catalyst. Metal oxides as shown below; porous silicates such as zeolites, mesoporous silicates, clays; porous metal complexes (MOF); porous polymer beads; carbon nanotubes, activated carbon Examples thereof include carbon materials such as ceramic honeycombs and metal honeycombs. Which carrier is used depends on the target catalytic reaction and the conditions of use. However, taking the oxidation reaction of carbon monoxide as an example, good adhesion to gold nanoparticles and formation of active sites at the bonding interface are possible. It is preferable to use a metal oxide from the viewpoints of ease and heat resistance.

Examples of such metal oxide carriers include beryllium, magnesium, aluminum, silicon, calcium, scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, germanium, strontium, yttrium, An oxide containing a metal element such as zirconium, cadmium, indium, tin, barium, or a lanthanoid element can be used. These metal oxides may be single metal oxides containing only one of the above metal elements, or complex oxides containing two or more metal elements.

Among these metal oxides, metal oxides or composite oxides containing one or more metal elements such as titanium, manganese, iron, cobalt, nickel, zinc, zirconium, lanthanum, and cerium are particularly preferable. The above-mentioned single metal metal oxide and composite oxide can be mixed and used as necessary. In addition, beryllium, magnesium, calcium, strontium, and barium of the periodic group 2 elements may include hydroxides, basic carbonates, and the like in addition to the corresponding oxides depending on the manufacturing method. In the present invention, the “oxide” supporting gold in the form of nanoparticles may contain these hydroxides, basic carbonates, and the like.

In the present invention, when a gold hydroxo anion complex solution having a pH of less than 8 as described above is used, a carrier (for example, silica, zeolite, mesoporous silicate, etc.) that can be easily dissolved in an alkaline aqueous solution can be suitably used as the carrier. .

In the gold nanoparticle carrier of the present invention, the gold content is not particularly limited as long as it can be prepared so that gold can be held in a nanoparticle state. For example, a gold nanoparticle carrier having a gold content of about 0.1 to 60% by mass based on the total amount of gold nanoparticles and the carrier can be prepared by appropriately selecting the type of carrier and the preparation method.

The form of the gold nanoparticle carrier of the present invention can be appropriately selected according to the purpose of use. For example, it can be used in the form of powder, or can be used after being formed into granules or pellets. In addition, a support carrying gold nanoparticles on a support can be immobilized and used as a shape of the support. The shape of the support is not particularly limited as long as the carrier supporting gold nanoparticles on the surface can be fixed, and may be any shape such as a flat plate shape, a block shape, a fiber shape, a net shape, a bead shape, and a honeycomb shape. For example, when used as a honeycomb, a carrier prepared in a powder form can be used by adhering to the surface of the honeycomb, or a carrier is fixed in advance on the surface of the honeycomb, and the carrying method of the present invention is applied. Gold nanoparticles can also be directly supported on the surface. The material of the support is not particularly limited as long as it is stable under the conditions for supporting the gold nanoparticles and under the reaction conditions. For example, various ceramics can be used.

The specific surface area of the carrier in the state where the gold nanoparticles are supported is preferably about 1 to 2000 m ² / g, more preferably about 5 to 1000 m ² / g, as measured by the BET method. In order to obtain such a gold nanoparticle carrier, for example, a carrier having a specific surface area in the above-described range may be used as a carrier for supporting gold nanoparticles.

(Step B) Generation of gold nanoparticles by heat treatment In step A, gold is supported as metal nanoparticles by heating after immobilizing the gold hydroxo anion complex on the surface of the carrier. There is no particular limitation on the heating atmosphere, and the heat treatment can be performed in various atmospheres such as an oxygen-containing atmosphere, a reducing gas atmosphere, and an inert gas atmosphere. For example, as the oxygen-containing atmosphere, an air atmosphere, a mixed gas atmosphere in which oxygen is diluted with nitrogen, helium, argon, or the like can be used. As the reducing gas, for example, about 1 to 10% by volume of hydrogen gas or carbon monoxide gas diluted with nitrogen gas can be used. For example, nitrogen, helium, argon, or the like can be used as the inert gas.

The heat treatment temperature is not higher than the heat resistance temperature of the carrier and is usually about 100 to 600 ° C. In order to obtain stable and fine gold particles, it is preferably about 200 to 400 ° C. The heat treatment time is not particularly limited, but may be heated for about 5 minutes or more after reaching the predetermined heat treatment temperature in the above temperature range.

Next, it is preferable to wash the carrier after the heat treatment described above. On the support after the heat treatment, conjugate bases of weak acids such as acetate ions and carbonate ions remain in the form of alkali metal salts, alkaline earth metal salts and the like. These salts do not cause as much poisoning as halogen anions, but if the salts remain on the surface, they cause a decrease in activity by physically blocking the active site. For this reason, it is preferable to remove the remaining salts by washing the carrier after heat treatment with water.

The washing method is not particularly limited. For example, washing with deionized water on a filter paper using a suction filter; placing the carrier powder and deionized water in a beaker and removing the supernatant A decantation method of washing while exchanging; a method of washing usually performed, such as a method of washing while separating the precipitate and water using a centrifuge, can be appropriately applied.

After washing with water, a carrier carrying gold nanoparticles can be obtained by drying. The drying temperature may be any temperature that is lower than the temperature at which gold nanoparticles are produced by heat treatment, and is usually a temperature between room temperature and 150 ° C.

3. Gold nanoparticle carrier According to the above-described method, a carrier in which gold nanoparticles are uniformly supported can be obtained using a trivalent gold compound containing no halide ions as a raw material.

The gold nanoparticle carrier obtained by the method of the present invention is one in which gold nanoparticles are uniformly supported on a carrier and does not contain halide ions that become poisonous substances for the catalytic reaction. It has high activity for the reaction. Therefore, indoor air purification such as carbon monoxide oxidation removal, atmospheric environment conservation such as NOx reduction, fuel cell related reactions such as selective oxidation of carbon monoxide in hydrogen, reactions for chemical processes such as propylene oxide synthesis reaction from propylene It can be effectively used as a thermal catalyst in various fields where gold nanoparticle catalysts are conventionally used.

The gold nanoparticle carrier can also be used effectively as a photocatalyst. By supporting a noble metal as a cocatalyst on a photocatalyst represented by titanium oxide, water decomposition reaction, hydrogen generation reaction from organic substance-containing aqueous solution, CO ₂ photoreduction reaction as a model reaction of artificial photosynthesis, oxidation of pollutants It is known to show high activity in air purification and water purification by decomposition, various organic synthesis reactions under light irradiation, and the like. Pt is most widely used as a noble metal serving as a promoter, but Au is also known to be useful. In addition, as photocatalysts other than titanium oxide, strontium titanate, tungsten oxide, zinc oxide, zirconium oxide, tantalum oxide, and the like are also known. Obtainable.

The particle diameter of the gold nanoparticles supported on the gold nanoparticle support is not particularly limited, but preferably 100 nm or less, more preferably 10 nm or less, and even more preferably 5 nm or less. The lower limit of the particle diameter of the gold nanoparticles is usually about 1 nm. The particle diameter of the gold nanoparticles is a volume average value measured by a powder X-ray diffraction method, and more specifically a value measured by the method used in the examples. However, since the particle diameter smaller than 2 nm cannot be measured by the powder X-ray diffraction method, it is necessary to separately perform other measurements such as observation with a transmission electron microscope to obtain the particle diameter.

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. However, the present invention is not limited to the examples.

<Example 1>
96 mg of brown powder of gold acetate [Au (CH ₃ COO) ₃ , manufactured by Alfa Aesar, purity 99.99% as described in the manufacturer's certificate of analysis] in 100 mL of an aqueous solution of sodium carbonate (0.1 mol / L) Then, while stirring with a magnetic stirrer, the mixture was heated on a hot plate to maintain the boiling reflux state, and the brown color almost disappeared about 10 minutes after boiling. In 1 hour after boiling, the heating was stopped and the temperature was returned to room temperature to obtain a colorless and transparent solution (pH 11.5). Next, to 20 mL of the obtained solution, an aqueous acetic acid solution (0.1 mol / L) was added and stirred so as to have the pH shown in Table 1, and each gold hydroxo anion complex solution was obtained.

On the other hand, 1.0 g of yellow powder of cerium oxide (manufactured by 1st rare element, Grade A) was placed in a PFA dish, and the gold hydroxo anion complex solution obtained by the above method was added and mixed. The amount of the solution was 20 mL as a gold hydroxo anion complex solution before adding acetic acid to 1 g of cerium oxide, and the total amount including the volume increase due to addition was added to the solution to which acetic acid was added. Next, the PFA dish was heated to about 40 ° C. to evaporate the water and evaporated to dryness, and then transferred to a crucible and baked in a muffle furnace at 350 ° C. for 1 hour, whereby gold nanoparticles were converted to cerium oxide. A black to gray powder (Au / CeO ₂ support) supported on the substrate was obtained.

Next, in order to remove the remaining soluble salts, it was washed with deionized water, and then dried at 100 ° C. to obtain a carrier having gold nanoparticles supported on cerium oxide. The amount of gold supported on the obtained support was 1.0% by mass. The obtained carrier was stored in a glass screw tube bottle.

(Measurement of gold particle diameter)
It was confirmed by powder X-ray diffraction (XRD) measurement that gold nanoparticles were supported on cerium oxide. Using the Rigaku Ultima IV as the XRD apparatus, the volume average particle diameter of gold was calculated from the half width of the Au (111) diffraction line by the following Scherrer equation. The calculation results by the following formula are shown in Table 1 and FIG.

D = Kλ / (Bcosθ)
D: Size of crystallite (corresponding to volume average particle diameter)
K: Scherrer constant (K = 0.849 was used in the above formula)
λ: CuKα X-ray wavelength 0.154 nm
B: Diffraction line width (In the above formula, the angle obtained by subtracting 0.18 ° of the device width from the half-value width of Au (111) measured) was used.
θ: Bragg angle of Au (111) 19.1 °

(Measurement of CO conversion)
The gold nanoparticle support obtained by the above method was subjected to an oxidation reaction of carbon monoxide at room temperature (23 ° C.) using a fixed bed flow reactor by the following method, and the catalytic activity was evaluated.

First, a quartz reaction tube having an inner diameter of 6 mm was filled with 20 mg of carrier powder mixed with 0.5 g of quartz sand. A mixed gas of CO (1%) + O ₂ (20%) + He (balance gas) was passed through this reaction tube at 100 mL / min, and the gas at the outlet of the reaction tube was analyzed with a photoacoustic analyzer (PAS). Table 1 and FIG. 3 show values obtained by calculating the CO conversion rate from the concentration analysis values of CO and CO ₂ after stabilization.

<Example 2>
In Example 1, each gold hydroxo was prepared in the same manner as in Example 1 except that an aqueous citric acid solution (0.1 mol / L) was added to the obtained colorless and transparent solution so as to have the pH shown in Table 1. An anion complex solution was obtained. Next, a gold nanoparticle carrier was produced in the same manner as in Example 1, and the catalytic activity was evaluated. Further, the particle diameter of gold was also measured in the same manner as in Example 1. The results are shown in Table 1 and FIGS.

<Example 3>
In Example 1, each gold hydroxo was prepared in the same manner as in Example 1 except that an aqueous oxalic acid solution (0.1 mol / L) was added to the obtained colorless and transparent solution to have the pH shown in Table 1. An anion complex solution was obtained. Next, a gold nanoparticle carrier was produced in the same manner as in Example 1, and the catalytic activity was evaluated. Further, the particle diameter of gold was also measured in the same manner as in Example 1. The results are shown in Table 1 and FIGS.

<Comparative Example 1>
In Example 1, each gold hydrosodium was treated in the same manner as in Example 1 except that an aqueous nitric acid solution (0.1 mol / L) was added to the obtained colorless and transparent solution so as to have the pH shown in Table 1. An ion complex solution was obtained. Next, a gold nanoparticle carrier was produced in the same manner as in Example 1, and the catalytic activity was evaluated. Further, the particle diameter of gold was also measured in the same manner as in Example 1. The results are shown in Table 1 and FIGS.

<Comparative example 2>
In Example 1, each gold hydroxo anion complex solution was obtained in the same manner as in Example 1 except that no acetic acid aqueous solution was added to the colorless and transparent solution obtained. Next, a gold nanoparticle carrier was produced in the same manner as in Example 1, and the catalytic activity was evaluated. Further, the particle diameter of gold was also measured in the same manner as in Example 1. The results are shown in Table 1 and FIGS. The difference in pH in Comparative Example 2 is an experimental error.

As shown in Table 1 and FIGS. 2 and 3, when nitric acid is added, the particle size of gold exceeds 10 nm, whereas in acetic acid, citric acid, and oxalic acid, the solution pH is 7 to 8 and 10 nm or less. Small gold could be supported, and with acetic acid, the particle size of gold at 20 nm or less could be controlled by changing the pH from 10 to 4.5. Also in the catalytic activity of CO oxidation, the addition of nitric acid results in a low CO conversion of 2% or less, whereas acetic acid, citric acid and oxalic acid have a high CO conversion of 3.5% or more at a solution pH of 7 or more. In particular, when oxalic acid was added and the pH was adjusted to 7-8, the catalytic activity was higher than that of the comparative example 2 where no weak acid was added.

FIG. 4 shows the relationship between the particle size of gold and the CO oxidation catalyst activity. Regarding the CO oxidation reaction by the gold nanoparticle catalyst, it has been reported that the gold nanoparticle of 2 nm or more has a higher catalytic activity as the particle diameter is smaller (the reporter has a difference for less than 2 nm). . The interface between the gold nanoparticles and the support is considered to be the active point, and the catalytic activity is proportional to the interface length. In relation to the particle size of gold, the reciprocal of the particle size of gold is proportional to the catalytic activity. From FIG. 4, it is clear that a lot of data is distributed near a straight line indicating a proportional relationship. Note that the data at two points surrounded by a broken line (in the case of pH 5.8 with citric acid addition and pH 5.6 with oxalic acid addition) are greatly deviated from the linear relationship, and the particle size (each 16.2 nm). The activity was much higher than expected from 96.3 nm). This is presumably because the obtained particle diameter is a volume average value by the X-ray diffraction method, and the average value is increased by mixing a small number of coarse particles. Even if the volume average value is 15 nm or more, when a large number of particles are 10 nm or less, a high CO conversion can be expected.

<Example 4>
In the same manner as in Example 1, 96 mg of gold acetate was dissolved in 100 mL of an aqueous sodium carbonate solution (0.1 mol / L) to obtain a solution having a pH of 10.8. The pH of the gold hydroxo anion complex solution obtained by adding 1.2 mL of acetic acid (0.1 mol / L) to 1.0 mL of this solution for pH adjustment was 7.1. A gold / silica carrier was obtained in the same manner as the loading on cerium oxide in Example 1 except that this solution was added to 50 mg of silica (Nippon Aerosil, Aerosil 200) powder in a crucible. The amount of gold supported on the obtained support was 1.0% by mass. About the gold / silica carrier, the particle diameter (volume average value) of gold was measured using a powder X-ray diffractometer (Ultima IV manufactured by Rigaku Corporation). The results are shown in Table 2.

<Example 5>
A gold / silica carrier was prepared in the same manner as in Example 4 except that 0.4 mL of citric acid (0.1 mol / L) was added instead of acetic acid, and the pH of the solution was adjusted to 7.4. The amount of gold supported on the obtained support was 1.0% by mass. In the same manner as in Example 4, the gold particle diameter (volume average value) was measured. The results are shown in Table 2.

<Example 6>
A gold / silica support was prepared in the same manner as in Example 4 except that 0.6 mL of oxalic acid (0.1 mol / L) was added instead of acetic acid, and the pH of the solution was 7.1. The amount of gold supported on the obtained support was 1.0% by mass. In the same manner as in Example 4, the gold particle diameter (volume average value) was measured. The results are shown in Table 2.

<Comparative Example 3>
A gold / silica carrier was prepared in the same manner as in Example 4 except that 96 mg of gold acetate was dissolved in 100 mL of an aqueous sodium carbonate solution (0.1 mol / L) in the same manner as in Example 1 and then no weak acid was added. . The amount of gold supported on the obtained support was 1.0% by mass. In the same manner as in Example 4, the gold particle diameter (volume average value) was measured. The results are shown in Table 2.

As shown in Table 2, in the case of supporting gold nanoparticles on silica using a gold hydroxo anion complex solution, in Examples 4 to 6 in which the pH was adjusted to 7 to 8 using a weak acid, the pH was adjusted. Compared to Comparative Example 3 used at 10.8, smaller gold nanoparticles could be supported.

<Example 7>
In the same manner as in Example 1, 48 mg of gold acetate was dissolved in 50 mL of an aqueous sodium carbonate solution (0.05 mol / L) to obtain a solution having a pH of 11.1. The pH of the gold hydroxo anion complex solution obtained by adding 2.8 mL of acetic acid (0.1 mol / L) for pH adjustment to 5.0 mL of this solution was 7.4. Except that this solution was added to 0.25 g of an H-type β zeolite (HSZ980HOA manufactured by Tosoh) powder having a SiO ₂ / Al ₂ O ₃ (mol / mol) ratio of 500 taken in a PFA dish, the same as in Example 1. Thus, a gold / β zeolite support was obtained. The amount of gold supported on the obtained support was 1.0% by mass. The powder X-ray diffraction measurement was performed in the same manner as in Example 1, and it was confirmed whether or not the crystal structure of the zeolite was retained after supporting gold. From the full width at half maximum, the volume average particle diameter of gold was calculated according to Scherrer's formula. The results are shown in Table 3 and FIG.

<Example 8>
A gold / β zeolite support was prepared in the same manner as in Example 7 except that 0.9 mL of citric acid (0.1 mol / L) was added instead of acetic acid, and the pH of the solution was adjusted to 7.4. The amount of gold supported on the obtained support was 1.0% by mass. In the same manner as in Example 4, powder X-ray diffraction was measured, and the particle size (volume average value) of gold was calculated. The results are shown in Table 3 and FIG.

<Example 9>
A gold / β zeolite support was prepared in the same manner as in Example 7 except that 1.3 mL of oxalic acid (0.1 mol / L) was added instead of acetic acid, and the pH of the solution was 7.6. The amount of gold supported on the obtained support was 1.0% by mass. In the same manner as in Example 4, powder X-ray diffraction was measured, and the particle size (volume average value) of gold was calculated. The results are shown in Table 3 and FIG.

<Comparative example 4>
A gold / β zeolite support was prepared in the same manner as in Example 7 except that 48 mg of gold acetate was dissolved in 50 mL of an aqueous sodium carbonate solution (0.05 mol / L) in the same manner as in Example 7 and then no weak acid was added. did. The amount of gold supported on the obtained support was 1.0% by mass. In the same manner as in Example 4, powder X-ray diffraction was measured, and the particle size (volume average value) of gold was calculated. The results are shown in Table 3 and FIG.

As shown in FIG. 5, the Au / β zeolites of Examples 7, 8, and 9 prepared by adding a weak acid showed a diffraction line at the same angle as that of the original Hβ zeolite, although the strength was weak, and retained the crystals. ing. On the other hand, in Comparative Example 4 impregnated with pH 11.1 without adding weak acid, the diffraction line indicating the crystal structure of the zeolite becomes very weak and at the same time, a halo is observed in the vicinity of 2θ = 22 °, causing crystal destruction. Suggests what happened.

Table 3 summarizes the results of the presence or absence of retention of the crystal structure of the zeolite and the particle size of the supported gold. In either case, although gold nanoparticles of 10 nm or less can be supported, it is very effective to add a weak acid to the gold hydroxo complex solution to make the pH around 7.5 in order to maintain the crystal structure. Indicated.

Of the Au / SiO ₂ and Au / β zeolite obtained by the method described above, the gold nanoparticle carriers of Example 5, Comparative Example 3, Example 7, and Comparative Example 4 were selected and the following method was used at 100 ° C. Glucose oxidation reaction was performed and the catalytic activity was evaluated. In order to examine the catalytic activity of only the carrier used for these gold nanoparticle carriers, the catalytic activity was also evaluated for SiO ₂ as Comparative Example 5 and Hβ zeolite as Comparative Example 6. The results are shown in Table 4.

(Measurement of glucose oxidation activity)
A stirrer and 10 mg of support powder were put into a 10 mL capacity screw-tube test tube, and an aqueous glucose solution (a total amount of 15 mg glucose dissolved in 3 mL water) was added. The reaction was carried out at 100 ° C. for 4 hours while stirring with a heat-resistant magnetic stirrer (HP40163, ISIS Co., Ltd., a general domestic distributor in Japan) installed in a thermostat and sealed with a lid with Teflon-coated packing. After the reaction solution is cooled to room temperature, it is oxidized by using an enzymatic method analysis kit (F-kit No. 428191, JK International Co., Ltd., Global Farmer Biofarm Co., Ltd.). The amount of gluconic acid as a product was quantified, and the yield was calculated.

As is apparent from Table 4, gluconic acid was hardly generated with the carrier alone, whereas a high yield of gluconic acid was obtained by supporting the gold nanoparticles. In the case of Au / SiO ₂ , the difference in yield of gluconic acid was not great depending on whether or not the weak acid was added in Step 2, but in Comparative Example 3 where no weak acid was added, the color of the solution after the reaction was colored magenta. It was shown that the supported Au was easily detached as a colloid. In the case of addition of citric acid in Example 5, the liquid color after the reaction was completely colorless. In both Example 7 and Comparative Example 4 of the Au / β zeolite, the solution after the reaction showed only a slight reddish purple coloration, and no difference was observed. When the glucose yield was compared, a large difference was observed, and in Example 7 in which acetic acid was added, a yield two times or more higher than that in Comparative Example 4 in which acetic acid was not added was obtained. From these comparisons, when the gold hydroxo complex anion solution added with a weak acid in Step 2 is used, favorable effects can be seen such that gold nanoparticles can be supported more stably and the catalytic activity becomes higher. It became clear.

<Example 10>
In the same manner as in Example 1, 115 mg of gold acetate was dissolved in 120 mL of an aqueous sodium carbonate solution (0.1 mol / L) to obtain a solution having a pH of 10.8. Next, to 20 mL of the obtained solution, an aqueous citric acid solution (0.1 mol / L) was added and stirred so as to achieve the pH shown in Table 5, and each gold hydroxo anion complex solution was obtained. This solution was added to 1.0 g of titanium oxide (P25 manufactured by Nippon Aerosil Co., Ltd.) powder taken in a PFA dish. Next, after heating to about 40 ° C. to evaporate the water and evaporating it to dryness, it is transferred to a crucible and baked at 350 ° C. for 1 hour in a muffle furnace, whereby a blue-violet gold / titanium oxide support (Au / TiO ₂ ) was obtained. Subsequently, in order to remove the remaining soluble salts, it was washed with deionized water and then dried at 100 ° C. The amount of gold supported on the obtained support was 1.0% by mass. The obtained carrier was stored in a glass screw tube bottle. Next, in the same manner as in Example 1, powder X-ray diffraction was measured. Similar to Example 1, the volume average particle diameter of gold was calculated from the half-width of the diffraction line by the Scherrer equation. At this time, the Au (111) diffraction line overlaps with the peak of titanium oxide, so Au (111) 311) Calculation was performed using diffraction lines. The CO oxidation activity was also measured in the same manner as in Example 1. The results are shown in Table 5.

<Comparative Example 7>
Titanium oxide (P25 manufactured by Nippon Aerosil Co., Ltd.) was prepared by adding water to 0.5 mL of a 0.1 mol / L aqueous solution of chloroauric acid prepared in advance to make 10 mL, and taking this solution (pH 2.5) into a PFA dish. Added to 1.0 g of powder. Next, the PFA dish is heated to about 40 ° C. to evaporate water to evaporate to dryness, and then transferred to a crucible and baked in a muffle furnace at 350 ° C. for 1 hour, thereby supporting a gold / titanium oxide carrier. (Au / TiO ₂ ) was obtained. The amount of gold supported on the obtained support was 1.0% by mass. The obtained carrier was stored in a glass screw tube bottle. Similarly to Example 10, the volume average particle diameter of gold was calculated from the half-width of the diffraction line by the Scherrer equation, and the CO oxidation activity was also measured in the same manner as in Example 10. The results are shown in Table 5.

As is clear from Table 5, when the amount of citric acid added was small and the pH increased, the gold particle size decreased and the CO conversion increased. In Comparative Example 7, when chloroauric acid was directly supported without using a gold hydroxo complex, the particle size of gold exceeded 40 mn, and no catalytic activity for CO conversion was observed. It was revealed that by using a solution obtained by adding citric acid to the gold hydroxo complex of Example 10, a catalyst having high CO conversion activity can be obtained while controlling the particle size of the gold nanoparticles.

(Measurement of photocatalytic activity)
Using a reactor equipped with a magnetic stirrer and a 100 W high-pressure mercury lamp (HL100G manufactured by SEN Special Light Source Co., Ltd.), the photocatalytic reaction activity of the support powder for the water-splitting hydrogen generation reaction using methanol as a sacrificial agent was evaluated. In a test tube used as a reaction tube (P-18M manufactured by Nidec Rika Glass Co., Ltd., an internal volume of 35.4 mL measured by filling the inside with water), a stirrer and 10 mg of support powder were placed, and a methanol aqueous solution (50 vol%) was added. ) 8 mL was added. Next, a rubber W cap is put on, a Teflon tube is inserted into the liquid from the gap, and nitrogen gas is bubbled from there for 10 minutes to remove dissolved oxygen in the liquid and the air above the test tube is also nitrogen. Replaced. Next, the Teflon tube was pulled out and sealed at the same time with a W cap, and further parafilm was wound to prevent air from entering. The needle of a gas tight syringe was pierced into the W cap, 0.2 mL of the internal gas was sampled, and analyzed by TCD gas chromatograph (Molecular Sieve 13X column) to confirm that almost no oxygen remained. Next, turn on the high-pressure mercury lamp in advance and stabilize it sufficiently. Then, set the reaction tube on the magnetic stirrer, stir the reaction solution so that the carrier powder is suspended, UV-visible light was irradiated from the side of the test tube to initiate the reaction. The reaction tube was taken out every 15 minutes, 0.2 mL of gas was sampled with a gas tight syringe, and H ₂ , O ₂ , and N ₂ were analyzed by TCD gas chromatography. The amount of H ₂ generation was calculated from the relative molar sensitivity obtained in advance from the obtained peak area ratio. The result of plotting the H ₂ generation amount against the light irradiation time is shown in FIG.

Further, the photocatalytic reaction activity of the support powder for the water-splitting hydrogen generation reaction using glycerin as a sacrificial agent in the same procedure as above except that 8 mL of glycerin aqueous solution (0.5 wt%) was used instead of the methanol aqueous solution Went. The results are shown in FIG.

As shown in FIG. 6, by using a solution obtained by adding citric acid to the gold hydroxo complex of Example 10, a gold nanoparticle support showing photocatalytic activity in a hydrogen generation reaction using methanol as a sacrificial agent is obtained. It turned out that activity becomes higher than the case where it prepares by the comparative example 7 which is a conventional method. Furthermore, it was found that the activity increases when the pH of the preparation liquid is increased and the gold particle size is controlled to be small. Further, as shown in FIG. 7, when glycerin is used as the sacrificial agent, it has been clarified that a sufficient hydrogen generation rate can be obtained even with a much smaller amount than the methanol sacrificial agent.

Claims

Preparation of a reaction solution in which a hydrolysis reaction of a gold compound proceeds in a solution of pH 8 or higher in which a trivalent gold compound not containing halide ions is suspended or dispersed in water in the presence of a conjugate base of a weak acid Step 1 to perform,
Step 2 of mixing the reaction solution and a weak acid;
A method for producing a gold hydroxo anion complex solution.
The method for producing a gold hydroxo anion complex solution according to claim 1, wherein the weak acid in the step 2 is at least one selected from the group consisting of carboxylic acid, phosphoric acid, and carbonic acid.
The trivalent gold compound containing no halide ions in the step 1 is at least one selected from the group consisting of gold carboxylate, gold oxide, gold hydroxide, and a double oxide of gold and an alkali metal. The manufacturing method of the gold hydroxo anion complex solution of Claim 1 or 2 which is a seed | species.
The conjugate base of the weak acid in the step 1 is at least one selected from the group consisting of a carboxylate anion, carbonate ion, hydrogen carbonate ion, phosphate ion, and borate ion. 4. A method for producing a gold hydroxo anion complex solution according to any one of 3 above.
The method for producing a gold hydroxo anion complex solution according to any one of claims 1 to 4, wherein in the step 2, the pH of the gold hydroxo anion complex solution is adjusted to less than 8 with the weak acid.
A step A of impregnating a carrier with the gold hydroxo anion complex solution produced by the method for producing a gold hydroxo anion complex solution according to any one of claims 1 to 5;
Removing water from the carrier impregnated with the gold hydroxo anion complex solution and performing a heat treatment; and
A method for producing a gold nanoparticle carrier.
The support is at least one selected from the group consisting of metal oxides, porous silicates, porous metal complexes, porous polymer beads, carbon materials, ceramic honeycombs, and metal honeycombs. Item 7. A method for producing a gold nanoparticle carrier according to Item 6.
At least one ligand is OH - an A, includes a hydroxo anionic complex of 3 Ataikin square planar structure containing no halogen anion as a ligand, the conjugate base of a weak acid that does not coordinate to gold A gold hydroxo anion complex solution comprising a transparent solution having a pH of less than 8 and containing no halogen anion.
The gold hydroxo anion complex solution according to claim 8, which is an impregnation liquid for producing a gold nanoparticle carrier.