JP2010065250A - Method for producing composite body, and composite body - Google Patents

Abstract

Disclosed is a composite in which the surface of metal particles is coated with a mesoporous material.
The surface of a metal particle is a mesoporous material by a method comprising a step of generating a mesoporous material on the surface of the metal particle using a surfactant as a template and a step of removing the surfactant by solvent extraction. A composite coated with is produced. According to this method, a composite in which pores of the mesoporous material penetrate in a direction substantially perpendicular to the surface of the metal particles can be preferably produced.
[Selection figure] None

Description

  The present invention relates to a composite of metal particles and a mesoporous material and a method for producing the same.

  A mesoporous material typified by mesoporous silica is a material having pores having a diameter of 1 to 50 nm. A typical mesoporous material has a structure in which uniform pores having a uniform diameter of several nanometers and a cylindrical shape are regularly arranged like a honeycomb. A combination of a material having such pores (nanospaces) and a material having catalytic activity is expected to provide a high-performance catalyst.

  Patent Document 1 discusses the synthesis of a new composite catalyst in which solid fine particles such as metal oxides are directly embedded in a mesoporous material. Specifically, it is described that a composite catalyst using titanium oxide as solid fine particles can decompose nonylphenol at high speed and with molecular selectivity. Since ordinary titanium oxide does not show molecular selectivity, it is considered that it is a result of showing a molecular selective adsorption function by complexing with a mesoporous material. In this composite catalyst, a mesoporous material is formed from a surfactant mold and then baked to remove the mold. Further, in the method for producing a composite catalyst containing solid fine particles specifically disclosed herein, there is no problem that the catalyst performance of the solid fine particles is greatly deteriorated by firing.

On the other hand, metal particles are used as a catalyst for various purposes such as environmental conservation applications including purification of automobile exhaust gas, and chemical applications such as petroleum refining, petrochemistry, medicines, fragrances and foods. In chemical applications, various compounds have been synthesized by various chemical reactions such as hydrogenation, dehydrogenation, oxidation, carbonylation, hydroformylation and the like. Many methods for synthesizing compounds have been established industrially, but many are still under development, and development for industrialization is underway. When substrate selectivity is required, sequential reactions and side reactions occur, synthesis may be difficult even if the catalyst is improved, and a method of controlling the reaction field of metal particles with a mesoporous material is conceivable.
JP-A-2005-314208 S. Hitz and R.M. Princes, J.M. Catal. , 168, 194-206 (1997)

  However, when a composite in which metal particles are directly embedded in a mesoporous material is synthesized according to the method of Patent Document 1, thermal shrinkage may occur due to thermal history, and cracks and voids may be formed at the interface between the mesoporous material and the metal particles. The inventors have found that. In addition, in the case where the mesoporous material or the metal particle is a substance that is unstable to heat, the structural change, decomposition, or disappearance may occur due to firing, so that when the composite is used as a catalyst, the catalytic performance inherent to the metal particle is We also found out that it may not be demonstrated.

  Non-Patent Document 1 discloses a method of removing a surfactant mold by solvent extraction when forming a porous body called MCM-41. However, Non-Patent Document 1 does not describe a composite in which solid fine particles of metal oxide or metal particles are directly embedded in a porous body.

  An object of the present invention is to provide a composite in which the surface of a metal particle is coated with a mesoporous material and in which the problems due to the thermal history are eliminated.

  The present invention provides a method for producing a composite in which the surface of metal particles is coated with a mesoporous material, the step of generating a mesoporous material on the surface of the metal particles using a surfactant as a template, and the surface activity And a step of removing the agent by solvent extraction.

  Moreover, this invention is a composite_body | complex by which the surface of the metal particle manufactured by said method is coat | covered with the mesoporous material, for example. Alternatively, the composite is a composite in which the surface of the metal particles is coated with a mesoporous material, and the pores of the mesoporous material penetrate in a direction substantially perpendicular to the surface of the metal particles.

  ADVANTAGE OF THE INVENTION According to this invention, the composite body with which the surface of the metal particle is coat | covered with the mesoporous material can be provided. In particular, when the composite is a catalyst, the composite can exhibit sufficient catalytic performance.

<Composite>
The composite of the present invention is a composite in which the surface of metal particles is coated with a mesoporous material. In the composite of the present invention, a part of the surface of the metal particles may not be covered with the mesoporous material, but the surface of the metal particle is preferably substantially completely covered with the mesoporous material, It is preferably completely covered with a mesoporous material.

  Although it does not specifically limit as a metal which comprises a metal particle, Nickel, cobalt, iron, manganese, ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, gold | metal | money etc. are mentioned. A composite or mixture of these metals may also be used. Of these, noble metals such as ruthenium, rhodium, palladium, silver, osmium, iridium, platinum and gold exhibiting a catalytic function are preferable. The metal constituting the metal particles may be one type or two or more types. Also, metal particles supported on a carrier may be used.

  Since the catalytic activity is higher when the surface area per mass of the metal particles is larger, the average particle size of the metal particles is preferably smaller, specifically 5000 nm or less is preferable, 3000 nm or less is more preferable, 1000 nm or less is more preferable, and 500 nm. The following are particularly preferred: Further, from the viewpoint of enhancing the stability of the metal particles, the average particle size of the metal particles is preferably larger than the pore diameter of the mesoporous material, specifically 3 nm or more, more preferably 10 nm or more, and more preferably 50 nm or more. Preferably, 100 nm or more is particularly preferable. In addition, an average particle diameter means a median diameter. This average particle diameter can be measured with a transmission electron microscope (TEM) or the like. When the average particle diameter of the metal particles is smaller than the pore diameter of the mesoporous material, a support may be used.

  In particular, in the case of metal particles, even if the average particle size is large, the catalytic activity is enhanced if the aggregate is a microcrystal. Therefore, the crystallite diameter of the metal particles is preferably small, specifically 20 nm or less, more preferably 10 nm or less, still more preferably 5 nm or less, and particularly preferably 3 nm or less. The crystallite diameter of the metal particles can be measured from the Scherrer equation using an X-ray diffractometer.

  Examples of mesoporous materials include mesoporous silica, mesoporous alumina, mesoporous titania, and mesoporous zirconia. Among these, mesoporous silica that can be easily synthesized is preferable. The mesoporous material may be one type, two or more types, or two or more types of composite materials.

  Since the content of the metal particles in the composite is preferably large in order to sufficiently exert the catalytic function, the lower limit is specifically preferably 0.1% by mass or more, and preferably 1% by mass or more. Is preferably 10% by mass or more, more preferably 20% by mass or more, particularly preferably 40% by mass or more, and most preferably 60% by mass or more. On the other hand, the content of the metal particles in the composite is preferably smaller as the upper limit from the viewpoint of material cost and the stability of the metal particles in the composite. Specifically, 98 mass% or less is preferable, 95 mass% or less is more preferable, 90 mass% or less is further more preferable, 80 mass% or less is especially preferable, and 70 mass% or less is the most preferable.

The pore characteristics of the composite can be appropriately adjusted by controlling the pore characteristics of the mesoporous material to be formed. The specific surface area of the composite is preferably from 10m ² / g~500m ² / g, more preferably 50m ² / g~100m ² / g. The pore volume of the composite is preferably 0.1 ml / g to 2.0 ml / g, more preferably 0.2 ml / g to 1.5 ml / g. This specific surface area is determined by the BET method using nitrogen gas adsorption. The pore diameter of the composite (pore diameter of the mesoporous material) is preferably 1 to 50 nm, and more preferably 2 to 10 nm. The pore diameter can be calculated by BJH plotting data obtained by the nitrogen gas adsorption method. However, the pore diameter of the composite is preferably larger than the average particle diameter of the metal particles.

  In the composite of the present invention, it is preferable that the pores of the mesoporous material pass through in a direction substantially perpendicular to the surface of the metal particles. However, there may be holes that do not penetrate, and there may be holes that penetrate from the surface of the metal particles in a direction that is not substantially perpendicular. It can be confirmed by TEM observation that the holes of the mesoporous material penetrate in the direction substantially perpendicular to the surface of the metal particles.

  In the composite of the present invention, changes in the crystal phase of metal particles (phase transition), particle growth, fusion between metal particles, reduction in surface area, and the like are suppressed, and metal particles can be stabilized. This technique can be used in all fields where metal particles are used. In particular, it can be suitably used in the catalyst field where stabilization of metal particles as an active component is important.

<Method for producing composite>
The composite as described above can be preferably produced by having a step of generating a mesoporous material on the surface of metal particles using a surfactant as a template and a step of removing the surfactant by solvent extraction. The metal particles may be in the state of a dispersion, for example.

  Moreover, it is preferable to have the process which makes an organic acid contact the surface of a metal particle. By forming the mesoporous material after bringing the organic acid into contact with the surface of the metal particles, the surface of the metal particles is easily coated with the mesoporous material, and the entire surface of the metal particles is completely coated with the mesoporous material. Becomes easier to obtain.

  As the organic acid, carboxylic acid, sulfonic acid, phenols, thiols and the like can be used. Examples of carboxylic acids include saturated aliphatic acids such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, etc. Monocarboxylic acids; saturated aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid; oleic acid, linoleic acid, linolenic acid, arachidonic acid, docosahexaenoic acid, eicosapentaenoic acid, fumaric acid, maleic acid Unsaturated carboxylic acids such as lactic acid, malic acid, citric acid and the like; aromatic carboxylic acids such as benzoic acid, phthalic acid, isophthalic acid, terephthalic acid and salicylic acid. Examples of the sulfonic acid include methanesulfonic acid and benzenesulfonic acid. Examples of phenols include phenol, cresol, picric acid, naphthol, catechol, resorcinol, and pyrogallol. Examples of thiols include benzenethiol. Among these, carboxylic acid and sulfonic acid are preferable, carboxylic acid is more preferable, carboxylic acid having 8 to 16 carbon atoms is further preferable, capric acid and lauric acid are particularly preferable, and lauric acid is most preferable. The organic acid may be one type or two or more types.

  As a method for bringing the organic acid into contact with the metal particles, the organic acid may be added to and mixed with a solution or dispersion in which the metal particles are dissolved or dispersed in a solvent. By bringing the organic acid into contact with the metal particles, the organic acid interacts with the metal particles, and the metal particles are easily coated with the mesoporous material. The contact between the metal particles and the organic acid can be performed at 40 to 70 ° C. for about 1 to 48 hours, for example. The longer the contact, the more organic acid will interact with the metal particles and the metal particles will be more easily coated with the mesoporous material.

  As the solvent, water or an organic solvent can be used. Examples of organic solvents include alcohols such as ethanol, 1-propanol, 2-propanol, n-butanol, t-butanol; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone; heptane, hexane, cyclohexane, etc. Aliphatic hydrocarbons: aromatic hydrocarbons such as benzene, toluene and xylene; ethers such as diethyl ether, tetrahydrofuran and dioxane; amides such as dimethylformamide and dimethylacetamide; dimethyl sulfoxide. 1 type may be sufficient as an organic solvent, and 2 or more types may be sufficient as it. When two or more organic solvents are used, the solvent is preferably in a uniform state, but may be in a non-uniform state.

  A mixed solvent of water and an organic solvent can also be used. The organic solvent contained in the mixed solvent is preferably an alcohol or a ketone. 2-70 mass% is preferable and, as for the content rate of the water in a mixed solvent, 5-50 mass% is more preferable. The mixed solvent is preferably in a uniform state, but may be in a non-uniform state.

  In order to produce a mesoporous material on the surface of metal particles using a surfactant as a template, for example, a reaction for producing the mesoporous material in a solution or dispersion of metal particles may be performed. For example, a sol-gel method using a surfactant as a template can be used for the reaction of the mesoporous material. In the sol-gel method, the size, shape, and packing structure of the pores can be controlled by changing the type of surfactant.

  As the surfactant, a cationic surfactant, an amphoteric surfactant, and the like can be used, and a cationic surfactant is preferable. The surfactant may be one kind or two or more kinds.

  Examples of the cationic surfactant include quaternary ammonium salts and alkylpyridinium salts. Preferably, it is an alkyl quaternary ammonium salt represented by the following general formula (1).

(R ¹ NR ² R ³ ₂ ) ⁺ X ⁻ (1)
In the formula (1), R ¹ is C _n H _{2n + 1} or (CH ₂ ) _m C _p F _{2p + 1} , R ² is methyl, ethyl or benzyl, R ³ is methyl or ethyl, X is halogen or hydroxyl group, n is an integer of 8 to 20, m is an integer of 2 to 6, and p is an integer of 2 to 18. The halogen for X is preferably a chlorine or bromine atom.

  Examples of alkyl quaternary ammonium salts include n-dodecyltrimethylammonium chloride, n-dodecyltrimethylammonium bromide, benzyldimethyltetradecylammonium chloride, hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, 3-perfluorooctylpropyl Examples include trimethylammonium chloride, 3-perfluorooctylpropyltrimethylammonium bromide, 3-perfluorohexylpropyltrimethylammonium chloride, and 6-perfluorooctylhexyltrimethylammonium chloride.

  The concentration of the surfactant in the solvent may be a concentration equal to or higher than the critical micelle concentration in the solvent used, preferably 0.0001 mol / l or more, and more preferably 0.001 mol / l or more. When the surfactant is dissolved in the solvent at a concentration equal to or higher than the critical micelle concentration, the surfactant forms micelles, and the micelles become a filling structure, thereby producing a template having a mesoporous structure. When the raw materials for the mesoporous material coexist, the mesoporous material may be generated even at a critical micelle concentration or lower, and therefore an appropriate concentration is appropriately selected.

  Further, a mesoporous material having larger pores can be obtained by adding a substance that expands the micelles of the surfactant (hereinafter referred to as an expanding agent). The expansion agent may be added before the mesoporous material is formed, and is more preferably before or after the addition of the surfactant. The swelling agent may be added in a state dissolved or dispersed in a solvent in advance, or may be added directly to the synthesis solution.

  As the swelling agent, a substance having hydrophobicity is preferable because it penetrates into the hydrophobic part of the micelle of the surfactant. Among them, aromatic compounds, hydrocarbon compounds, alcohols having a large hydrophobic group, etc. are more preferred, such as mesitylene, carbon. Particularly preferred are alkanes having 2 to 20 carbon atoms and alcohols having 4 or more carbon atoms. Examples of the alkane having 2 to 20 carbon atoms include n-tridecane. The amount of the expanding agent to be added should be less than the amount that destroys the mold having a mesoporous structure, and is preferably 1000% by mass or less, more preferably 5 to 200% by mass with respect to the surfactant.

  Next, in the presence of surfactant micelles, the raw material of the mesoporous material is added to the solvent, and if necessary, the catalyst is added, so that the sol-gel reaction proceeds in the gap between the micelles, and the gel skeleton of the mesoporous material is generated To do. The pH of the solvent before adding the mesoporous material is not particularly limited as long as the pH is suitable for synthesizing the mesoporous material. The mesoporous material can be synthesized under both acidic and basic conditions, but is preferably pH 4 or lower, and more preferably pH 3 or lower as long as it is acidic. In basic synthesis, pH 9 or higher is preferable, and pH 10 or higher is more preferable. The pH can be adjusted, for example, by adding an acidic compound such as hydrochloric acid, nitric acid or sulfuric acid, or a basic compound such as ammonia, sodium hydroxide or potassium hydroxide. The time for adjusting the pH may be before the mesoporous material is produced. The formation of the porous body can be performed, for example, at 20 to 80 ° C. for about 2 to 10 hours. Or it can also carry out at 100-200 degreeC using an autoclave.

  As a raw material of the mesoporous material, an alkoxide of an element (an element other than oxygen) constituting the mesoporous material can be used. For example, when producing mesoporous silica, tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, or the like can be used as a raw material. The raw material of the mesoporous material may be one type or two or more types.

  After the formation reaction of the mesoporous material, it is necessary to remove the swelling agent and the surfactant used as a template. In the present invention, this removal is performed by solvent extraction. The solvent extraction can be performed, for example, by extraction at 20 to 90 ° C., 10 minutes to 96 hours (preferably 1 hour to 30 hours), 1 to 10 times (preferably 2 to 8 times).

  As the extraction solvent, for example, a polar solvent such as ion-exchanged water, alcohol, ether, acetonitrile, dimethyl sulfoxide, dimethylformamide, or a solvent having a strong extraction force such as supercritical carbon dioxide can be used. In the case of using a polar solvent, the addition of an acid or nitrate further increases the solvent extraction ability. Examples of the acid include nitric acid, sulfuric acid, hydrochloric acid, formic acid, acetic acid, formic acid and propionic acid, but formic acid, acetic acid and propionic acid are preferred. Examples of nitrates include ammonium nitrate, sodium nitrate, and potassium nitrate. These acids and nitrates are preferably added in a small amount to a polar solvent, preferably 0.001 mol% or more, more preferably 0.01 mol% or more, and preferably 1 mol% or less, more preferably 0.5 mol% or less. Thereby, the composite_body | complex which has a mesoporous material which has a mesopore which reaches the surface of a metal particle from the outside can be obtained.

  The extraction solvent present in the pores of the mesoporous material can be removed as appropriate. Examples of the method include drying. When drying, if the drying temperature is too high, the structural change, decomposition, and disappearance of the metal particles may occur. Therefore, it is preferable to determine the temperature in consideration of this point. Specifically, it is preferably below the temperature at which solvent extraction is performed. When a solvent having a high boiling point is used, for example, when the drying temperature must be increased, it is preferable to perform drying under reduced pressure.

  In the composite thus obtained, the surfaces of the metal particles are tightly coated with a mesoporous material. Moreover, the hole of the mesoporous material penetrates in a substantially vertical direction from the surface of the metal particle. This can be confirmed by a large number of streak patterns oriented in a substantially vertical direction from the surface of the metal particles appearing in the layer of the mesoporous material covering the metal particles by TEM observation.

  Hereinafter, the present invention will be described in more detail with reference to examples in which palladium particles are used as metal particles and mesoporous silica is used as a mesoporous material. However, the present invention is not limited to these examples.

<Preparation of aqueous dispersion of palladium particles>
In 50 g of 88 mass% valeric acid aqueous solution, 1.0549 g of palladium acetate (corresponding to 0.5 g of Pd) was completely dissolved, and this solution was put into an autoclave and purged with nitrogen, and then 0.6 MPa of propylene was introduced at room temperature. For 24 hours. The slurry under pressure was centrifuged and replaced with 50% acetone aqueous solution until the smell of valeric acid disappeared to obtain an aqueous dispersion of palladium particles.

<Example 1>
2.81 mg of lauric acid was dissolved in an aqueous dispersion of palladium particles (corresponding to 0.17 g of Pd) and stirred at 55 ° C. for about 2 hours. On the other hand, 0.0812 g of hexadecyltrimethylammonium bromide as a surfactant was dissolved in 4.35 g of ion exchange water while heating. To this solution, an aqueous dispersion of palladium particles in which the above lauric acid was dissolved was added, and ammonia water was further added to adjust the pH to 11.8.

  While the resulting dispersion was vigorously stirred, 0.306 g of tetraethoxysilane was added all at once and stirred for 1 hour. The product was filtered, washed with ion exchanged water, and dried overnight at 70 ° C. The obtained dried product was added to a 0.1 M acetic acid-ethanol solution, stirred at 80 ° C. for 2 hours, filtered, and washed with ethanol. Finally, it was dried at 80 ° C. overnight.

  The composite of Example 1 (Pd content: 65% by mass) was obtained by the above method. The TEM measurement result of the composite of Example 1 is shown in FIG. 1, and the results of measuring the crystallite diameter determined from X-ray diffraction are shown in Table 1.

<Comparative Example 1>
The same operation as in Example 1 was performed until a dried product was obtained. The obtained dried product was baked at 540 ° C. for 6 hours to remove the surfactant. Thereafter, hydrogen reduction was performed using N ₂ / H ₂ gas. The gas flow rates were N ₂ gas 180 ml / min and H ₂ gas 20 ml / min. The temperature was raised from room temperature to 300 ° C. over 1.5 hours, held at 300 ° C. for 3 hours, and then allowed to cool to room temperature.

  The composite of Comparative Example 1 (Pd content: 65% by mass) was obtained by the above method. The TEM measurement result of the composite of Comparative Example 1 is shown in FIG. 3, and the results of measuring the crystallite diameter determined from X-ray diffraction are shown in Table 1.

  As shown in FIG. 1, in the composite obtained in Example 1 subjected to the solvent extraction, the mesoporous material was coated on the palladium particles, and the pores of the mesoporous silica were seen from the surface of the palladium particles so as to look like streaks. It penetrated in a nearly vertical direction. Moreover, the crystal | crystallization of the palladium particle was not growing by removal of surfactant. On the other hand, in Comparative Example 1 in which the firing was performed as shown in FIG. 2, gaps were scattered between the palladium particles and the mesoporous material, and unlike FIG. 1, the streaks were not seen and the holes of the mesoporous silica were scattered. there were. Moreover, the crystal | crystallization of the palladium particle was growing by removal of surfactant.

<Catalyst performance evaluation>
Hydrogenation of trans-cinnamaldehyde (CAD) was performed using the Pd particles obtained by filtering and drying the aqueous dispersion of palladium particles and the composites obtained in Example 1 and Comparative Example 1 as catalysts. A scheme showing the hydrogenation reaction of trans-cinnamaldehyde is shown below.

  Specifically, in a 25 ml round bottom flask, 5 mmol of CAD was dissolved in 5 ml of toluene, 0.1 g of catalyst was added, and the mixture was reacted at room temperature with stirring in a hydrogen atmosphere. The reaction product was analyzed by gas chromatography. The results are shown in Table 2.

  When Pd particles were used as a catalyst, POL was selectively produced. On the other hand, when the composite of Example 1 was used as a catalyst, PAD was selectively produced and the reaction rate was improved. On the other hand, when the composite of the composite of Comparative Example 1 was used as a catalyst, the CAD hydrogenation reaction did not proceed. This is presumably because the crystals of palladium particles grew by firing in the production process of the composite of Comparative Example 1.

4 is a TEM measurement result of the composite of Example 1. 3 is a TEM measurement result of the composite of Comparative Example 1.

Claims (6)

  A method for producing a composite in which the surface of metal particles is coated with a mesoporous material, the step of generating a mesoporous material on the surface of the metal particles using a surfactant as a template, and solvent extraction of the surfactant The manufacturing method of a composite_body | complex which has a process removed by this.   The manufacturing method of the composite_body | complex of Claim 1 which further has the process of making an organic acid contact the surface of the said metal particle.   The method for producing a composite according to claim 1 or 2, wherein a method of producing a mesoporous material on the surface of the metal particles using a surfactant as a template is a sol-gel method.   The composite_body | complex manufactured by the method in any one of Claim 1 to 3.   The composite according to claim 4, wherein the holes of the mesoporous material penetrate in a direction substantially perpendicular to the surface of the metal particles.   A composite in which the surface of a metal particle is covered with a mesoporous material, wherein the pores of the mesoporous material penetrate in a direction substantially perpendicular to the surface of the metal particle.