JP2018052787A - A hollow silica particle internally containing molybdenum oxide nanoparticles, a process for producing the same, and a catalyst containing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hollow silica particle internally containing molybdenum oxide nanoparticles and advantageously available as a yoke shell type catalyst, and a process for producing the particle.SOLUTION: A process for producing a hollow silica particle comprises a mixing step in which a polymer having a carboxyl group and molybdenum source are mixed in basic solution, a reduction step in which molybdenum oxide nanoparticles are formed from the molybdenum source by adding a reductant to the basic solution, a shell formation step in which a silica shell internally containing a polymer and a molybdenum oxide nanoparticles is formed by adding a silica source to the basic solution, and a removal step in which the hollow silica particle internally containing the molybdenum oxide nanoparticles is obtained by removing the polymer from inside the silica shell.SELECTED DRAWING: Figure 1

Description

  The present invention relates to hollow silica particles encapsulating molybdenum oxide nanoparticles and a method for producing the same. Moreover, this invention relates to the catalyst containing the said hollow silica particle.

  In general, heterogeneous catalysts are used for various reactions in which an active metal (or metal oxide) is supported on a support. On the other hand, a yoke shell type (hollow core shell type) catalyst having a metal as a core and a refractory metal oxide such as silica alumina as a shell can suppress deterioration due to agglomeration of active metals and simultaneously performs two kinds of reactions. There are advantages that can be made. For this reason, research on yoke-shell catalysts has been vigorously advanced.

  For example, Non-Patent Document 1 discloses a result of synthesizing a benzimidazole derivative in a high yield by simultaneously performing coupling and hydrogenation using a yoke shell type catalyst having palladium as a core and silica alumina as a shell. It is shown. Non-Patent Document 2 discloses that a yoke shell type material having gold or platinum as a core and titanium oxide as a shell is useful as a photocatalyst for generating hydrogen from a water-methanol solution.

  Further, as a yoke shell type catalyst having a core as a metal oxide, for example, Patent Document 1 discloses a photocatalyst having a titanium oxide as a core and a silica as a shell.

International Publication No. 2007/063615

Acta Chem. Sinica, 71, 334-338 (2013) Chemical Engineering Journal, 257, 112-121 (2014)

  An object of the present invention is to provide hollow silica particles that encapsulate molybdenum oxide nanoparticles and can be suitably used as a yoke shell type catalyst. Moreover, an object of this invention is to provide the manufacturing method which can manufacture easily the hollow silica particle which included the molybdenum oxide nanoparticle. Furthermore, an object of the present invention is to provide a catalyst that includes hollow silica particles encapsulating molybdenum oxide nanoparticles and can be suitably used as a catalyst for various reactions such as an epoxidation reaction.

  One aspect of the present invention relates to a method for producing hollow silica particles encapsulating molybdenum oxide nanoparticles. This manufacturing method includes a mixing step of mixing a polymer having a carboxyl group and a molybdenum source in a basic solution, and a reducing step of forming molybdenum oxide nanoparticles from the molybdenum source by adding a reducing agent to the basic solution. Adding a silica source to the basic solution to form a silica shell that encapsulates the polymer and molybdenum oxide nanoparticles; and removing the polymer from the silica shell to encapsulate the molybdenum oxide nanoparticles. Removing hollow silica particles to be obtained.

  According to such a production method, hollow silica particles encapsulating molybdenum oxide nanoparticles can be easily formed. In the hollow silica particles, molybdenum oxide is encapsulated in the silica shell as nanoparticles, so that the active species are prevented from leaking out of the system when used as a catalyst, and stable catalyst performance can be maintained. The hollow silica particles can be used repeatedly as a catalyst because catalyst deterioration due to aggregation of active species is sufficiently suppressed.

  In one embodiment, the molybdenum source may include hexaammonium heptamolybdate.

  In one embodiment, the polymer may include polyacrylic acid.

  In one embodiment, the silica source may contain tetraalkoxysilane. An alkyltrialkoxysilane may further be contained.

  In one embodiment, the pH of the basic solution may be 9-12.

  Another aspect of the present invention relates to a hollow silica particle comprising a silica shell and molybdenum oxide nanoparticles encapsulated in the silica shell.

  In one embodiment, the silica shell may be porous and the average pore size may be 2-7 nm.

In one embodiment, the surface area of the hollow silica particles may be 20 to 300 m ² / g.

  In one embodiment, the hollow silica particles may have an average particle size of 50 to 1000 nm.

  Yet another aspect of the present invention relates to a catalyst comprising the above hollow silica particles.

  In one embodiment, the catalyst may be a catalyst for an epoxidation reaction using olefin as a raw material.

  According to the present invention, hollow silica particles that include molybdenum oxide nanoparticles and can be suitably used as a yoke shell type catalyst are provided. Moreover, according to this invention, the manufacturing method which can manufacture easily the hollow silica particle which included the molybdenum oxide nanoparticle is provided. In addition, according to the present invention, there is provided a catalyst that includes hollow silica particles encapsulating molybdenum oxide nanoparticles and can be suitably used as a catalyst for various reactions such as an epoxidation reaction.

2 is a diagram showing an SEM observation image of catalyst a-1 prepared in Example 1. FIG. 2 is a diagram showing a TEM observation image of catalyst a-2 prepared in Example 1. FIG. 6 is a view showing a TEM observation image of catalyst b-2 prepared in Comparative Example 2. FIG.

  Hereinafter, preferred embodiments of the present invention will be described.

<Manufacturing method>
The production method according to the present embodiment includes a mixing step of mixing a polymer having a carboxyl group and a molybdenum source in a basic solution, adding a reducing agent to the basic solution, and removing molybdenum oxide nanoparticles from the molybdenum source. A reduction step to form, a shell forming step to form a silica shell encapsulating the polymer and molybdenum oxide nanoparticles by adding a silica source to the basic solution, and a molybdenum oxide by removing the polymer from the silica shell A removal step of obtaining hollow silica particles enclosing the nanoparticles.

  According to this production method, hollow silica particles encapsulating molybdenum oxide nanoparticles (hereinafter referred to as “hollow silica particles”) can be easily formed. The hollow silica particles obtained by this production method can be suitably used as a catalyst for various reactions such as an epoxidation reaction. In addition, since the hollow silica particles are encapsulated in the silica shell as molybdenum oxide nanoparticles, when used as a catalyst, the active species are prevented from leaking out of the system, and stable catalytic performance is achieved. Can be maintained. The hollow silica particles can be used repeatedly as a catalyst because catalyst deterioration due to aggregation of active species is sufficiently suppressed.

  Hereinafter, each process of the manufacturing method which concerns on this embodiment is explained in full detail.

(Mixing process)
In the mixing step, a polymer having a carboxyl group and a molybdenum source are mixed in a basic solution. In the basic solution after mixing, the polymer may form a colloidal aggregate.

  The solvent of the basic solution is not particularly limited, but it is desirable that the molybdenum source is a solvent that can be dissolved, and that the polymer can form a colloidal aggregate. Such a solvent may be, for example, a water-alcohol mixed solvent. Specific examples of the water-alcohol mixed solvent include a water-ethanol mixed solvent.

  The pH of the basic solution may be 9 to 12, for example, and preferably 10 to 11. By setting the pH within the above range, the formation of a silica shell described later can be efficiently advanced. The pH of the basic solution may be adjusted with ammonia, for example.

  In this embodiment, it is considered that the molybdenum source is included in the colloidal aggregate because the carboxyl group of the polymer interacts with the molybdenum source. From the viewpoint that the interaction with the molybdenum source is remarkably obtained, the polymer is preferably a polymer having a plurality of carboxyl groups in the molecular chain. As such a polymer, polyacrylic acid can be suitably used.

  When polyacrylic acid is used as the polymer, the weight average molecular weight of polyacrylic acid is preferably 500 or more, and more preferably 1000 or more. Thereby, polyacrylic acid tends to easily form a colloidal aggregate. Moreover, it is preferable that the weight average molecular weight of polyacrylic acid is 10,000 or less, and it is more preferable that it is 6000 or less. Thereby, there exists a tendency for a silica shell to become easy to form in the below-mentioned process. In addition, the weight average molecular weight of polyacrylic acid shows the value measured by using polyacrylic acid as a standard substance by gel permeation chromatography (GPC).

The molybdenum source may be a molybdenum compound that is soluble in a basic solution and can form molybdenum oxide (MoO _x ) by reduction. Examples of the molybdenum source include paramolybdic acid, phosphomolybdic acid, 12 silicomolybdic acid, ammonium salts thereof, halides (for example, chloride, bromide, etc.), mineral salts (for example, nitrate, sulfate, phosphoric acid). Salt), carboxylate (for example, carbonate, oxalate, etc.) and the like. Further, molybdenum carbide may be used as the molybdenum source. The molybdenum source may be subjected to the mixing step as a hydrate of the molybdenum compound.

As the molybdenum source, hexaammonium heptamolybdate (Mo ₇ O ₂₄ (NH ₄ ) ₆ ) is particularly preferred because of its excellent water solubility and the ease of forming molybdenum oxide nanoparticles in the steps described below. Can be used. Hexamethylene ammonium heptamolybdate, for example hydrates _{(Mo 7 O 24 (NH 4} ) 6 · 4H 2 O) may be subjected to the mixing process as may be subjected to a mixing process as an aqueous solution.

  The amount of the molybdenum source used for the mixing step is preferably 5 parts by mass or more and more preferably 10 parts by mass or more with respect to 100 parts by mass of the polymer. By increasing the amount of the molybdenum source relative to the polymer, the amount of molybdenum oxide nanoparticles included in the hollow silica particles tends to increase. The amount of the molybdenum source is preferably 100 parts by mass or less, more preferably 50 parts by mass or less with respect to 100 parts by mass of the polymer. By reducing the amount of the molybdenum source relative to the polymer, the molybdenum oxide nanoparticles can be efficiently encapsulated in the silica shell.

  In the mixing step, for example, the first solution in which the polymer is dissolved may be mixed with the second solution in which the molybdenum source is dissolved. Specifically, for example, the mixing step may be performed by adding and mixing an aqueous solution of a molybdenum source and an alcohol to a polymer solution in which a polymer is dissolved in aqueous ammonia. Moreover, you may implement a mixing process by adding a polymer to ammonia aqueous solution containing a molybdenum source, and then adding ethanol.

(Reduction process)
In the reduction step, a reducing agent is added to the basic solution after the mixing step. In this embodiment, the molybdenum source is reduced by the addition of a reducing agent, and molybdenum oxide nanoparticles are formed.

The reducing agent may be any reducing agent that can reduce the molybdenum source in a basic solution. Examples of the reducing agent include sodium borohydride (NaBH ₄ ), potassium borohydride (KBH ₄ ), lithium aluminum hydride (LiAlH ₄ ), hydrazine (N ₂ H ₄ ), and ammonia borane (H ₃ NBH ₃ ). Sodium formate (HCOONa) and the like can be used.

  It is preferable that the addition amount of a reducing agent is 100-400 mol% with respect to the molybdenum atom contained in a molybdenum source. By making the addition amount of the reducing agent 100 mol% or more with respect to molybdenum atoms, molybdenum is sufficiently reduced, and molybdenum oxide nanoparticles can be efficiently formed. Moreover, by making the addition amount of the reducing agent 400 mol% or less with respect to the molybdenum atom, it is possible to suppress the molybdenum oxide from forming an aggregate having a nano size or more, and to efficiently form molybdenum oxide nanoparticles. .

  In the basic solution after the reduction step, it is considered that polymer-molybdenum oxide nanoparticle aggregates in which molybdenum oxide nanoparticles are encapsulated in colloidal aggregates of polymers are formed.

(Shell formation process)
In the shell formation step, a silica source is added to the basic solution after the reduction step to form a silica shell enclosing the polymer and molybdenum oxide nanoparticles. In this embodiment, polymer-molybdenum oxide nanoparticle aggregates are formed in the basic solution after the reduction step, and the silica source is hydrolyzed and polycondensed on the outer peripheral surface of the aggregates. A silica shell is formed.

  As the silica source, tetraalkoxysilane is preferably used. Examples of the tetraalkoxysilane include tetraethoxysilane (TEOS), tetramethoxysilane (TMOS), tetraisopropoxysilane (TPOS), and tetrabutoxysilane (TBOS). Of these, tetraethoxysilane (TEOS) and tetramethoxysilane (TMOS) are preferably used from the viewpoint of availability.

  As the silica source, other silica sources may be further used together with tetraalkoxysilane. Other silica sources include known silica sources that are used as organosilane coupling agents. Other silica sources include methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES), ethyltrimethoxysilane (ETMS), phenyltriethoxysilane (PhTES), triethoxychlorosilane (TECS), triethoxyfluorosilane (TEFS), octyltriethoxysilane (C8TES), trialkoxysilane such as dodecyltrimethoxysilane (C12TMS), dialkoxysilane such as dimethyldiethoxysilane (DMDES), diphenyldimethoxysilane (DPhDMS), hexamethyldisiloxane ( HMDSO), tetramethyldisiloxane (TMDSO), tetramethylcyclotetrasiloxane (TMCTS), 1,2-bis (triethoxysilyl) ethane (BTEE), 1,4-bi Etc. (triethoxysilyl) benzene (BTEB) can be exemplified.

  In this embodiment, it is preferable to use alkyltrialkoxysilane together with tetraalkoxysilane as the silica source. Thereby, the silica shell can be made porous. In this embodiment, the pore diameter of the silica shell can be adjusted by changing the number of carbon atoms of the alkyl group of the alkyltrialkoxysilane.

  The number of carbon atoms of the alkyl group of the alkyltrialkoxysilane may be appropriately changed according to the desired pore diameter, and may be, for example, 1-30, preferably 8-18.

  The amount of alkyltrialkoxysilane used is not particularly limited. The porosity of the silica shell can be adjusted by changing the amount of alkyltrialkoxysilane used. The molar ratio of alkyltrialkoxysilane to tetraalkoxysilane may be, for example, 40 mol% or less, and preferably 20 mol% or less. When an excessive amount of alkyltrialkoxysilane is added, a silica lump is easily formed. However, if the molar ratio is above, formation of this silica lump is sufficiently suppressed, and desired hollow silica particles can be obtained efficiently. The molar ratio of alkyltrialkoxysilane to tetraalkoxysilane may be, for example, 0 mol%, 1 mol% or more, and preferably 5 mol% or more.

  The addition amount of the silica source is preferably 500 parts by mass or more, more preferably 1000 parts by mass or more, with the total amount of the polymer blended in the mixing step being 100 parts by mass. By making the addition amount of the silica source 500 parts by mass or more, the outer peripheral surface of the polymer-molybdenum oxide nanoparticle aggregate can be sufficiently covered with the silica shell. Further, the addition amount of the silica source is preferably 2500 parts by mass or less, more preferably 2000 parts by mass or less, with the total amount of the polymer blended in the mixing step being 100 parts by mass. When there is too much addition amount of a silica source, there exists a tendency for a silica shell to become thick and to become difficult to exhibit the effect as a catalyst. By making the addition amount of the silica source 2000 parts by mass or less, hollow silica particles more suitable as a catalyst for epoxidation reaction and the like can be obtained.

  You may implement a shell formation process by dripping a silica source to a basic solution, without diluting, for example. Moreover, you may implement a shell formation process by preparing the solution (silica source solution) which dissolved the silica source, and dripping a silica source solution in a basic solution, for example.

  The solvent of a silica source solution should just be a hydrophilic solvent, and is not specifically limited. As the solvent for the silica source solution, for example, alcohols such as methanol and ethanol, acetone, acetonitrile and the like are preferably used. The density | concentration of a silica source solution is not specifically limited, For example, it may be 1-99.9 mass%, Preferably it is 10-99.9 mass%.

  The dripping time of the silica source (or silica source solution) may be, for example, 5 to 60 minutes. By setting the dropping time to 5 minutes or longer, the polymer-molybdenum oxide nanoparticle aggregate tends to be covered with the silica shell. Moreover, by making the dropping time within 60 minutes, formation of silica aggregates can be suppressed, and inhibition of the catalytic reaction by the silica aggregates can be avoided.

  In the present embodiment, organic-inorganic composite particles including polymer-molybdenum oxide nanoparticle aggregates and a silica shell covering the aggregates are formed by the shell forming step.

(Removal process)
In the removing step, the polymer is removed from the silica shell. By removing the polymer in the core from the organic-inorganic composite particles formed in the shell formation step, hollow silica particles enclosing molybdenum oxide nanoparticles can be obtained.

  The removal of the polymer can be performed by separating the organic-inorganic composite particles from the basic solution and baking them.

  The method for separating the organic-inorganic composite particles from the basic solution is not particularly limited, and may be a separation means such as filtration or centrifugation. The separated organic / inorganic composite particles are usually fired after drying.

  The firing temperature for firing the organic-inorganic composite particles may be any temperature that can remove the polymer. The firing temperature is preferably 300 ° C. or higher, and more preferably 400 ° C. or higher. Thereby, the polymer is sufficiently removed, and the inside of the silica shell can be easily made hollow. Further, the firing temperature is preferably 700 ° C. or lower, and more preferably 600 ° C. or lower. Thereby, thermal decomposition and aggregation of molybdenum oxide nanoparticles can be avoided, and hollow silica particles with higher catalytic activity can be obtained.

  The firing of the organic / inorganic composite particles may be performed in an atmosphere containing oxygen. Firing may be performed, for example, in air, or in an atmosphere in which oxygen is diluted with an inert gas such as He, Ne, Ar, Kr, or the like.

  In the present embodiment, hollow silica particles encapsulating molybdenum oxide nanoparticles are obtained by the above method. The hollow silica particles can be suitably used as a catalyst for epoxidation reaction or the like. Further, the hollow silica particles can be stored for a long period of time while maintaining the catalyst performance by storing them under a reduced pressure atmosphere or in dry air.

  The hollow silica particles produced by the production method according to this embodiment will be described in detail below.

<Hollow silica particles>
The hollow silica particle according to the present embodiment includes a silica shell and molybdenum oxide nanoparticles encapsulated in the silica shell.

  The hollow silica particles can be suitably used as a catalyst for various reactions such as an epoxidation reaction. When hollow silica particles are used as a catalyst, molybdenum oxide, which is an active species, is encapsulated in the silica shell, so that leakage of the active species out of the system is suppressed, and stable catalyst performance can be maintained for a long period of time. Moreover, since molybdenum oxide nanoparticles are encapsulated in each of the plurality of hollow silica particles, catalyst deterioration due to excessive aggregation of the nanoparticles is sufficiently suppressed. For this reason, the hollow silica particle which concerns on this embodiment can also be used as a catalyst repeatedly.

  The silica shell may be porous. The average pore diameter of the silica shell is not particularly limited, and may be appropriately changed according to the reaction substrate or product size of the reaction to which the hollow silica particles are applied. Moreover, the selectivity of the reaction can be improved by adjusting the average pore diameter of the silica shell. For example, when applying hollow silica particles to an olefin epoxidation reaction, the average pore diameter of the silica shell is preferably 2 to 7 nm.

  In the hollow silica particles according to this embodiment, a plurality of molybdenum oxide nanoparticles may be included in the silica shell. Content of the molybdenum atom in a hollow silica particle is not specifically limited, You may change suitably according to desired catalyst performance.

The molybdenum content in the hollow silica particles may be, for example, 1 to 30% by mass, preferably 5 to 20% by mass in terms of MoO ₃ . As a result, the hollow silica particles have particularly suitable catalytic activity as a catalyst for the epoxidation reaction. The molybdenum content in terms of MoO ₃ in the hollow silica particles can be measured by inductively coupled plasma optical emission spectrometry (ICP).

The surface area of the hollow silica particles is not particularly limited, and is preferably 20 to 300 m ² / g. By having such a surface area, the reaction substrate is efficiently adsorbed when the catalytic reaction is used, and the catalytic reaction is promoted. In addition, in this specification, the surface area of a hollow silica particle shows the value computed by the BET (Brunauer-Emmett-Teller) method from the nitrogen adsorption isotherm.

  The average particle diameter of the hollow silica particles is not particularly limited, and may be, for example, 50 to 1000 nm, and preferably 100 to 300 nm. By having such an average particle diameter, the number of molybdenum oxide nanoparticles contained in one hollow silica particle is limited, so that aggregation of molybdenum oxide nanoparticles is suppressed and the catalytic activity is further improved. Tend. In addition, in this specification, the average particle diameter of a hollow silica particle shows the average particle diameter of 100 particles chosen at random among the hollow silica particles observed by SEM.

<Catalyst>
The catalyst according to this embodiment includes the hollow silica particles. This catalyst can be suitably used for various reactions in which molybdenum oxide has catalytic ability.

  In the catalyst according to this embodiment, molybdenum oxide is encapsulated in the silica shell as nanoparticles, so that leakage of active species out of the system is suppressed, and stable catalyst performance can be maintained for a long period of time. Moreover, since molybdenum oxide nanoparticles are encapsulated in each of the plurality of hollow silica particles, catalyst deterioration due to excessive aggregation of the nanoparticles is sufficiently suppressed. For this reason, the catalyst which concerns on this embodiment can be repeatedly used for various reaction.

  The catalyst according to the present embodiment may be one using hollow silica particles as they are, or may be a combination of hollow silica particles and other catalyst components. In addition, the catalyst according to the present embodiment may be one in which hollow silica particles are filled in a reactor, or may be one in which hollow silica particles are bonded together with a binder or the like.

  Examples of the reaction to which the catalyst according to this embodiment can be applied include an epoxidation reaction using an olefin as a raw material, an acetalization reaction of a ketone compound or an aldehyde compound, an esterification reaction of a carboxylic acid compound and an alcohol, and the like.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment.

  For example, one aspect of the present invention may be an epoxy compound production method including a step of oxidizing an olefin using a catalyst containing the hollow silica particles to obtain an epoxy compound. In this production method, by using the catalyst containing the hollow silica particles, stable catalyst performance is maintained for a long time, and an epoxy compound can be produced efficiently.

  Another aspect of the present invention may relate to a reaction apparatus including a reactor filled with a catalyst containing the hollow silica particles. In such a reaction apparatus, leakage of catalytically active species from the reactor is suppressed, so that the frequency of catalyst replacement can be reduced and the reaction can be carried out efficiently.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment.

  EXAMPLES Hereinafter, although an Example demonstrates this invention more concretely, this invention is not limited to an Example.

[Example 1: Preparation of catalyst a-1]
A polyacrylic acid aqueous solution (PAA; molecular weight 5,000, 50% by mass, Acros Organics) 0.24 g and 28% ammonia water 4.5 mL were put in a 200 mL eggplant flask and at room temperature until the polyacrylic acid was completely dissolved. Stir. 20 mg / mL hexamethylene ammonium heptamolybdate solution prepared here _{(Mo 7 O 24 (NH 4} ) 6 · 4H 2 O, Wako Pure Chemical) 2 mL, sequentially adding ethanol 90 mL, and stirred at room temperature for 10 minutes. Thereafter, 0.9 mL of an aqueous solution of sodium borohydride (NaBH ₄ , Nacalai Tesque) prepared to 20 mg / mL was added and stirred at room temperature for 30 minutes.

Next, a solution prepared by mixing 1.6 mL of tetraethyl orthosilicate (TEOS; 95%, Nacalai Tesque) and 0.2 mL of dodecyltrimethoxysilane (C ₁₂ TMS; 93%, Tokyo Chemical Industry) was added dropwise over 10 minutes. Stir at room temperature for 6 hours. The produced precipitate was separated from the solution by centrifugation, washed with 50 mL of ethanol and 50 mL of distilled water, and dried at 70 ° C. overnight. After drying, the powder was pulverized in an agate mortar and then fired in the atmosphere at 500 ° C. for 6 hours using an electric furnace to obtain a white powder (catalyst a-1).

[Example 2: Preparation of catalyst a-2]
A catalyst a-2 was obtained in the same manner as in Example 1 except that the dropping time of the silica source (mixed solution of TEOS and C ₁₂ TMS) was changed to 1 hour.

[Example 3: Preparation of catalyst a-3]
A catalyst a-3 was obtained in the same manner as in Example 1 except that the mixing ratio of TEOS, which is a silica source, and C ₁₂ TMS was changed to 1.2 mL: 0.6 mL (volume ratio).

[Example 4: Preparation of catalyst a-4]
A catalyst a-4 was obtained in the same manner as in Example 1 except that the silica source was changed to only 1.8 mL of TEOS.

[Comparative Example 1: Preparation of catalyst b-1]
Prepared in the same procedure as in Example 1 except that MoO ₃ powder (99.9% or more, average particle size 13-80 nm, manufactured by US Research Nanomaterials) was used instead of hexaammonium heptamolybdate. Catalyst b-1 was obtained.

[Comparative Example 2: Preparation of catalyst b-2]
A catalyst b-2 was prepared in the same manner as in Example 1 except that 0.12 g of polyethyleneimine (PEI; molecular weight 1,800, 100% by weight, Alfa Aesar) was used instead of polyacrylic acid. Got.

[Comparative Example 3: Preparation of catalyst b-3]
A catalyst b-3 was prepared in the same manner as in Example 1, except that 0.12 g of polyvinylpyrrolidone (PVP; molecular weight 40,000, 100% by weight, Nacalai Tesque) was used instead of polyacrylic acid. Got.

<SEM observation>
About each catalyst prepared in Examples 1-4 and Comparative Examples 1-3, the scanning electron microscope (SEM) observation was performed and the shape of the primary particle was observed. 1 is a view showing an observation image of catalyst a-1 prepared in Example 1. FIG. As shown in FIG. 1, monodispersed spherical silica particles were observed from the observed image of the catalyst a-1. Similarly, monodispersed spherical silica particles were observed from the observed images of the catalysts a-2 to a-4. On the other hand, in the observed images of the catalysts b-1 to b-3 of Comparative Examples 1 to 3, spherical silica particles could not be observed, and a spherical silica shell could not be formed.

  Moreover, the average particle diameter of catalyst a-1 to a-4 of Examples 1-4 was calculated | required from the result of SEM observation. The results are as shown in Table 1.

<Measurement of surface area>
About each catalyst prepared in Examples 1-4 and Comparative Examples 1-3, the surface area was computed by BET (Brunauer-Emmett-Teller) method from the nitrogen adsorption isotherm. The results are shown in Table 1. The specific measurement conditions were as follows.
Before the measurement, the sample was treated at 300 ° C. for 3 hours under vacuum (1 × 10 ⁻⁴ Pa or less) to remove water molecules that were physically adsorbed. For nitrogen adsorption / desorption measurement, BELSORP-maxII manufactured by Microtrac Bell Co., Ltd. was used, and measurement was performed at a liquid nitrogen temperature (−196 ° C.).

<TEM observation>
Each catalyst prepared in Examples 1 to 4 and Comparative Examples 1 to 3 was observed with a transmission electron microscope (TEM). 2 is a diagram showing an observation image of catalyst a-1 prepared in Example 1. FIG. As shown in FIG. 1, from the observation image of catalyst a-1, spherical silica particles having a hollow structure were confirmed, and it was confirmed that molybdenum oxide nanoparticles were encapsulated in the silica particles. Similarly, from the observed images of the catalysts a-2 to a-4, spherical silica particles having a hollow structure and molybdenum oxide nanoparticles encapsulated in the silica particles were confirmed.

  On the other hand, in the catalysts b-1 to b-3 of Comparative Examples 1 to 3, spherical silica particles having a hollow structure could not be confirmed. FIG. 3 is a view showing an observation image of the catalyst b-2 of Comparative Example 2. As shown in FIG. 3, in the catalyst b-2, spherical silica particles having a hollow structure were not confirmed, and it was confirmed that molybdenum oxide nanoparticles were present free from the silica lump.

[Comparative Example 4: Preparation of catalyst b-4]
Hexamethylene ammonium heptamolybdate _{(Mo 7 O 24 (NH 4} ) 6 · 4H 2 O, Wako Pure Chemical) in 200mL eggplant flask containing distilled water 50mL was dissolved 0.139 g, fumed silica (Wako Pure Chemical) 1. 0 g was added and stirred at room temperature for 2 hours. After stirring, water was evaporated and dried by an evaporator and dried at 100 ° C. overnight. After drying, the obtained powder was pulverized in an agate mortar and then calcined in the atmosphere at 500 ° C. for 6 hours to obtain catalyst b-4 in which molybdenum oxide was supported on amorphous silica.

<Epoxidation reaction>
Using each catalyst prepared in Examples 1 to 4 and Comparative Examples 1 to 4, an epoxidation reaction was performed according to the following procedure.
After placing 75 mg of catalyst, 5 mL of 1,2-dichloroethane, 116 mg of cyclooctene, and 176 mg of t-butyl hydroperoxide (TBHP; 5.5 mol / L in dekane, Aldrich) in a 50 mL capacity Pyrex (registered trademark) reactor Using an oil bath, the temperature was maintained at 80 ° C., and the reaction was performed for 8 hours while stirring. During the reaction, sampling was performed at any time, and the product was quantified using gas chromatography. Table 2 shows the conversion rate of cyclooctene and the selectivity of cyclooctene oxide (epoxy compound) obtained by the reaction.

<Repeated test of epoxidation reaction>
After completion of the epoxidation reaction, the catalyst was recovered by centrifugation. Using this recovered catalyst, an olefin epoxidation reaction was performed again. This repeated reaction was performed up to 5 times, and the conversion rate of cyclooctene and the selectivity of the epoxide compound in each reaction were determined. The results are shown in Table 3. In Table 3, the conversion rate of cyclooctene is shown as a relative value with the conversion rate in the first reaction as 100.

  From the above results, it was confirmed that the catalysts a-1 to a-4 of Examples 1 to 4 showed high reactivity and selectivity for the olefin epoxidation reaction and could maintain them for a long period of time.

Claims (13)

A mixing step of mixing a polymer having a carboxyl group and a molybdenum source in a basic solution;
A reducing step of adding a reducing agent to the basic solution to form molybdenum oxide nanoparticles from the molybdenum source;
A shell forming step of adding a silica source to the basic solution to form a silica shell containing the polymer and the molybdenum oxide nanoparticles;
Removing the polymer from the silica shell to obtain hollow silica particles encapsulating the molybdenum oxide nanoparticles;
A process for producing hollow silica particles.   The manufacturing method according to claim 1, wherein the molybdenum source contains hexaammonium heptamolybdate.   The manufacturing method of Claim 1 or 2 with which the said polymer contains polyacrylic acid.   The manufacturing method as described in any one of Claims 1-3 in which the said silica source contains tetraalkoxysilane.   The production method according to claim 4, wherein the silica source further contains an alkyltrialkoxysilane.   The production method according to any one of claims 1 to 5, wherein the pH of the basic solution is 9 to 12. Silica shell,
Molybdenum oxide nanoparticles encapsulated in the silica shell;
Hollow silica particles comprising:   The hollow silica particle according to claim 7, wherein the silica shell is porous.   The hollow silica particles according to claim 8, wherein the silica shell has an average pore diameter of 2 to 7 nm. The hollow silica particle as described in any one of Claims 7-9 whose surface area is 20-300 m < ² > / g.   The hollow silica particles according to any one of claims 7 to 10, wherein the average particle diameter is 50 to 1000 nm.   The catalyst containing the hollow silica particle as described in any one of Claims 7-11.   The catalyst of Claim 12 which is a catalyst of the epoxidation reaction which uses an olefin as a raw material.