JP2012200674A - Ruthenium-supported catalyst fiber and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst fiber having high strength and a sintering-resistant property, and a method for producing the same.SOLUTION: The invention relates to silica-based composite oxide fiber composed of an oxide phase (first phase) mainly made of a silica ingredient and a metal oxide phase (second phase) composed of a metal other than silica. The proportion of presence of one or more metallic elements of the metal oxides constituting the metal phase (second phase) slantingly increases toward the surface of the fiber. The metal oxide phase (second phase) is formed of particles of the constituent metal. Mesopores having an average diameter of 2-30 nm and extending from the surface of the fiber toward the interior of the fiber are formed among the particles of the constituent metal. Particles of metallic ruthenium (Ru) having an average diameter of 0.5-25.0 nm are supported in the mesopores.

Description

  The present invention relates to a catalyst fiber in which ruthenium particles are supported in mesopores (pores) formed in a silica-based composite oxide fiber having excellent mechanical properties, and a method for producing the catalyst fiber.

  Ruthenium is an element having excellent catalytic ability, and is known to be a catalyst for various oxidation-reduction reactions in heterogeneous systems, and for the formation of carbon-carbon bonds, cyclization reactions, and radical reactions in homogeneous systems.

  Among them, in heterogeneous systems, there are many examples that are industrially employed such as hydrogen reduction catalysts, reforming catalysts such as hydrocarbons, CO removal catalysts, and catalysts for producing chlorine. For this reason, not only the initial catalyst activity but also the overall performance improvement such as maintaining the activity and resistance to the catalyst poison, etc., it is preferable that the catalyst preparation process is short, and it is desirable that a high-performance catalyst can be easily prepared. ing.

A metal ruthenium-supported catalyst shows activity in a reduction reaction, and is often used as a highly active catalyst for hydrogen reduction, for example. One of them, the Sabatier reaction, is a reaction in which CO ₂ is reduced with hydrogen to form water and CH ₄ as shown in the following reaction formula 1.
CO ₂ + 4H ₂ → CH ₄ + 2H ₂ O (Scheme 1)

  This reaction is attracting attention as a practical reaction for constructing an air regeneration system, which is very important in establishing life support technology in a closed space such as the International Space Station. However, in order to carry out this reaction with high efficiency, it is necessary to set the reaction system to 300 ° C. or higher, and temperature control is also necessary because the reaction itself is an exothermic reaction. As described above, there are problems in terms of safety and cost when performing in a closed space where energy and materials are limited, and development of a catalyst that can lower the temperature and increase the efficiency of this reaction is desired.

Previous studies have shown that when TiO ₂ is used as the ruthenium support, it acts as a highly active catalyst for the Sabatier reaction. However, since TiO ₂ which is the object of research in many cases is a powder, when actually used as a catalyst, a structure supporting TiO ₂ powder is required. For example, Non-Patent Document 1 is used by mixing with ceramic wool, and Non-Patent Document 2 is used by being supported on an alumina ball. However, in such a case, the TiO ₂ powder may fall off with use, so that it cannot be put into practical use in outer space where dust is likely to cause a system trouble. Therefore, it is desired that the metal carrier itself has a high strength structure.

  Patent Document 1 describes a silica-based composite oxide fiber that has excellent mechanical properties and can be used as a catalyst carrier, and a method for producing a catalyst fiber using the same. If a high-strength fibrous catalyst is used, the above problem can be solved.

International Publication WO2008 / 114597

Proceedings of the 54th Space Science and Technology Conference of the Japan Aerospace Society 2F0P “Study on Low Temperature Carbon Dioxide Reduction by Sabachie Reaction” Proceedings of the 49th Space Science and Technology Conference of the Japan Aerospace Society 1C02 “Technical Proof of Air Regeneration and Water Splitting System”

  However, most of the ruthenium supported ruthenium catalyst prepared by this method exists in the state of the compound used as the raw material, oxide, or hydroxide, so that it can be used as a catalyst for reduction reaction such as Sabatier reaction. A process of reduction to metallic ruthenium is required, and sintering of ruthenium particles is a concern during reduction. Further, in the metal ruthenium-supported catalyst fiber thus prepared, the metal ruthenium particles are generated at the place where the ruthenium compound used as the raw material is adsorbed. Therefore, when the provided ruthenium compound concentration is high, the ruthenium is a fine fiber. A large amount other than the hole is supported, and ruthenium sintering is likely to occur, which may cause a decrease in catalytic activity. As a method for supporting metal particles, a method of mixing metal particles and a carrier is known. However, in this method, the metal particles are also supported on the surface of the carrier, and the sintering resistance is not high.

  Accordingly, the present invention provides a catalyst fiber in which metal ruthenium is selectively supported in the pores of the silica-based composite oxide fiber, which does not require a reduction treatment after loading, and can prevent ruthenium sintering. It aims at providing the manufacturing method.

  In order to achieve the above object, as a result of intensive studies, the present inventors have irradiated a ruthenium-containing solution containing a sacrificial agent and ruthenium while irradiating the silica-based composite oxide fiber with light. It has been found that catalyst fibers in which metal ruthenium is supported in pores can be produced. That is, the present invention mainly relates to a modified polycarbosilane having a structure in which a polycarbosilane having a main chain skeleton represented by Chemical Formula 1 and having a number average molecular weight of 200 to 10,000 is modified with an organometallic compound, or the modified polycarbosilane. A first step of obtaining a spinning dope, which is a mixture of a silane and an organometallic compound, a second step of obtaining a spun fiber from the spinning dope, and heat-treating the spun fiber in an oxidizing atmosphere, thereby infusible fiber A third step of obtaining a silica-based composite oxide fiber by firing the infusible fiber in an oxidizing atmosphere, and a treatment on the surface side of the silica-based composite oxide fiber. The silica-based composite oxide fiber is contacted with a ruthenium-containing solution containing a sacrificial agent and ruthenium in a fifth step of removing silica in the vicinity of the surface to form mesopores. A method for producing a catalyst fiber comprising: the sixth step of irradiating light, a while.

（但し、式中のＲは水素原子、低級アルキル基又はフェニル基を示す。）

(However, R in the formula represents a hydrogen atom, a lower alkyl group or a phenyl group.)

  The present invention also provides a silica-based composite oxide fiber comprising a composite oxide phase of an oxide phase (first phase) mainly composed of a silica component and a metal oxide phase (second phase) made of a metal other than silica. And the presence ratio of at least one or more metal elements of the metal oxide constituting the metal oxide phase (second phase) increases in a gradient toward the fiber surface, and the metal oxide phase ( In the second phase), the metal constituting it is formed in particles, mesopores having an average pore diameter of 2 to 30 nm from the fiber surface to the inside of the fiber are formed between the particles, and the average particle diameter is in the mesopores. The catalyst fiber is characterized in that metal ruthenium particles of 0.5 to 25.0 nm are supported.

  As described above, according to the present invention, the ruthenium in a metal state is selected in the pores of the silica-based composite oxide fiber, which does not require a reduction treatment after loading and can prevent ruthenium sintering. Supported catalyst fiber and a method for producing the same can be provided.

It is a figure which shows typically the catalyst fiber which concerns on this invention. 2 is a STEM photograph of titania / silica fibers obtained in Production Example 1. (A) It is the ESCA measurement spectrum of the ruthenium carrying | support titania / silica fiber obtained in Example 1, and (B) the ruthenium carrying titania / silica fiber obtained in the comparative example 1. 2 is a STEM photograph of the ruthenium-supporting titania / silica fiber obtained in Example 1.

  The catalyst fiber according to the present invention is one in which ruthenium (Ru) particles are supported in mesopores formed on the catalyst fiber by further processing the catalyst fiber described in Patent Document 1.

  In the catalyst fiber according to the present invention, the oxide phase (first phase) mainly composed of the silica component may be amorphous or crystalline. The first phase may contain a metal element or metal oxide that can form a solid solution or a eutectic compound with silica. An example of a metal element that can form a solid solution with silica is titanium. Examples of the metal element of the metal oxide that can form a solid solution with silica include aluminum, zirconium, yttrium, lithium, sodium, barium, calcium, boron, zinc, nickel, manganese, magnesium, and iron.

  The oxide phase (first phase) forms the internal phase of the catalyst fiber according to the present invention, and plays an important role in bearing the mechanical properties. The ratio of the first phase to the entire catalyst fiber is preferably 98 to 40% by mass. In order to effectively form mesopores on the surface of the catalyst fiber and to exhibit high mechanical properties, it is preferable to control the presence ratio of the first phase within the range of 50 to 95% by mass.

  The metal oxide constituting the metal oxide phase (second phase) plays an important role in forming mesopores on the surface layer of the catalyst fiber according to the present invention. The proportion of the second phase constituting the surface layer part of the catalyst fiber is preferably 2 to 60% by mass, and in order to exhibit its effect sufficiently and at the same time to develop high strength, it is within the range of 5 to 50% by mass. It is preferable to control.

  The metal oxide composing the metal oxide phase (second phase) is a semiconductor material that is excited when irradiated with light having a wavelength corresponding to the band gap to form an electron-hole pair. Need to be, titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), cobalt (Co), copper (Cu), zinc (Zn), barium (Ba), strontium (Sr), Cadmium (Cd), lead (Pb), iron (Fe), nickel (Ni), aluminum (Al), gallium (Ga), germanium (Ge), indium (In), tin (Sn), zirconium (Zn) and It is at least one oxide or composite oxide of tungsten (W). Of these, titania, barium titanate, strontium titanate, zirconia, and the like are preferably used.

  In the catalyst fiber according to the present invention, the inclination of the abundance ratio of at least one metal element of the metal oxide constituting the second phase is preferably present at a depth of 500 nm from the surface of the catalyst fiber.

  In the catalyst fiber according to the present invention, the size of the mesopores is controlled by the particle size of the metal oxide constituting the second phase. In order to use mesopores as a chemical reaction field, the mesopores have an average pore diameter of 2 to 30 nm, preferably 5 to 20 nm. The average pore diameter of mesopores can be measured using a gas adsorption method.

  In the catalyst fiber according to the present invention, metal ruthenium particles are supported in the mesopores. Whether the supported ruthenium particles exist in a metallic state can be measured by ESCA. The average particle diameter of the ruthenium particles is 0.5 to 25 nm, preferably 1 to 15 nm, and more preferably 1 to 5 nm. The average particle diameter can be measured using TEM. The size of the ruthenium particles is limited by the pore size of the mesopores. The mass of the supported ruthenium particles is preferably 0.01 to 2.0 mass%, more preferably 0.1 to 0.5 mass%, based on the catalyst fiber. The mass of the supported ruthenium particles can be measured by ICP-AES.

In the catalyst fiber according to the present invention, the number of the ruthenium particles supported in the mesopore is preferably 6 × 10 ¹³ particles / m ² or more per unit surface area in the mesopore. The number of ruthenium particles can be calculated by counting visually from the STEM photograph.

  The catalyst fiber according to the present invention is preferably produced by the following first to sixth steps.

(First step)
In the first step, first, a modified polycarbosilane having a number average molecular weight of 1,000 to 50,000 used as a starting material for silica-based composite oxide fibers is produced. The method for producing this modified polycarbosilane is similar to the method described in JP-A-56-74126, but it is necessary to carefully control the bonding state of the functional groups described therein. This is outlined below.

  The modified polycarbosilane, which is a starting material, is composed of a polycarbosilane having a main chain skeleton represented by Chemical Formula 2 and having a number average molecular weight of 200 to 10,000, and a general formula M (OR ′) n or MR ″ m ( M is a metal element, R ′ is an alkyl group or phenyl group having 1 to 20 carbon atoms, R ″ is acetylacetonate, and m and n are integers greater than 1.) And is derived from.

（但し、式中のＲは水素原子、低級アルキル基又はフェニル基を示す。）

(However, R in the formula represents a hydrogen atom, a lower alkyl group or a phenyl group.)

  In order to produce a catalyst fiber having a gradient composition according to the present invention, it is necessary to select a slow reaction condition such that only a part of the organometallic compound forms a bond with polycarbosilane. For that purpose, it is necessary to make it react in inert gas at the temperature of 280 degrees C or less, Preferably, it is 250 degrees C or less. Under these reaction conditions, even if the organometallic compound reacts with polycarbosilane, it binds as a monofunctional polymer (that is, binds in a pendant form) and does not significantly increase the molecular weight. The modified polycarbosilane in which the organometallic compound is partially bonded plays an important role in improving the compatibility between the polycarbosilane and the organometallic compound.

  When many functional groups of two or more functional groups are bonded, a crosslinked structure of polycarbosilane is formed and a marked increase in molecular weight is observed. In this case, a sudden exotherm and a rise in melt viscosity occur during the reaction. On the other hand, when only one functional group reacts as described above and an unreacted organometallic compound remains, conversely, a decrease in melt viscosity is observed.

  In the production of the catalyst fiber according to the present invention, it is desirable to select conditions for intentionally leaving the unreacted organometallic compound. In the present invention, mainly the modified polycarbosilane and an unreacted organometallic compound or an organometallic compound of about 2 to 3 trimmers are used as starting materials, but only the modified polycarbosilane alone, If a very low molecular weight modified polycarbosilane component is included, it can be used as a starting material as well. The obtained modified polycarbosilane or the modified polycarbosilane and a low molecular weight organometallic compound are mixed to obtain a spinning dope.

(Second step)
A stock solution is prepared by melting the spinning solution of the modified polycarbosilane obtained in the first step or the modified polycarbosilane and a low molecular weight organometallic compound (hereinafter sometimes referred to as a precursor). Is filtered to remove substances that are harmful when spinning, such as microgels and impurities, and this is spun by a commonly used apparatus for spinning synthetic fibers. The temperature of the spinning dope during spinning varies depending on the softening temperature of the raw material modified polycarbosilane, but a temperature range of 50 to 200 ° C. is advantageous. In the above spinning apparatus, a humidification heating cylinder may be provided below the nozzle as necessary. The fiber diameter is adjusted by changing the discharge amount from the nozzle and the winding speed of a high-speed winding device installed at the lower part of the spinning machine. Alternatively, the fiber discharged from the nozzle may be directly molded into a felt shape by a melt blow method or a spun bond method.

  In addition to the melt spinning, the modified polycarbosilane obtained in the first step, or the spinning stock solution of the modified polycarbosilane and the low molecular weight organometallic compound, for example, benzene, toluene, xylene or other modified polycarbosilane and low A molecular weight organometallic compound is dissolved in a solvent that can be melted to prepare a stock solution. In some cases, this is filtered to remove harmful substances such as macrogels and impurities. Spinning can be performed by a dry spinning method using a spinning device, and the winding speed can be controlled to obtain a target fiber.

  In the second step, if necessary, a spinning cylinder is attached to the synthetic fiber spinning device, and the atmosphere in the spinning cylinder is a mixed atmosphere with at least one gas of benzene, toluene, xylene, or the like, or , Air, inert gas, hot air, hot inert gas, steam, ammonia gas, hydrocarbon gas, and organosilicon compound gas to control the solidification of the spinning fiber in the spinning cylinder be able to.

(Third step)
In the third step, the spun fiber obtained in the second step is preheated in an oxidizing atmosphere under the action of tension or no tension to infusibilize the spun fiber. The third step is performed for the purpose of preventing the fibers from melting and adhering to the adjacent fibers during the firing in the fourth step. The treatment temperature and treatment time vary depending on the composition and are not particularly limited, but in general, the treatment temperature is 50 to 400 ° C., and the treatment time is several hours to 30 hours. The oxidizing atmosphere may contain water, nitrogen oxide, ozone, or the like that enhances the oxidizing power of the spun fiber. Further, the oxygen partial pressure in the oxidizing atmosphere may be changed intentionally. Depending on the proportion of low molecular weight substances contained in the starting material used in the first step, the softening temperature of the spun fiber may be lower than 50 ° C. In that case, at the temperature lower than the above treatment temperature in advance, the fiber surface You may give the process which accelerates | stimulates oxidation of this.

  In the catalyst fiber according to the present invention, during the second step and the third step, the transition (bleed out) of the low molecular weight compound contained in the starting material to the fiber surface proceeds, and the target inclination It is thought that the foundation of the composition is formed.

(4th process)
In the fourth step, the infusible fiber obtained in the third step is calcined in an oxidizing atmosphere under the action of tension or no tension, preferably at 500 to 1800 ° C., whereby an oxide phase mainly composed of a silica component. (1st phase) and the metal oxide phase (2nd phase) which consists of metals other than a silica, and the abundance ratio of at least 1 or more metal element of the metal oxide which comprises a 2nd phase Increases in a slope toward the fiber surface, and the second phase produces silica-based composite oxide fibers in which the metal constituting the second phase is formed in the form of particles. The firing temperature in the fourth step affects the particle size of the metal constituting the second phase. That is, when the firing temperature is increased, the particle size of the metal constituting the second phase is increased. Since the size of the mesopores is controlled by the size of the metal particles constituting the second phase, the selection of the firing temperature is performed according to the size of the target mesopores. In the fourth step, the organic component contained in the infusible fiber is basically oxidized, but depending on the conditions to be selected, it may remain in the fiber as carbon or carbide. Even in such a state, when the target function is not hindered, it is used as it is. However, when the target function is hindered, further oxidation treatment is performed. In that case, the processing temperature and processing time which do not cause a problem in the target gradient composition and crystal structure must be selected.

(5th process)
In the fifth step, the surface side of the silica-based composite oxide fiber obtained in the fourth step is treated to remove silica in the vicinity of the surface, and mesopores are formed on the fiber surface. There is no restriction | limiting in particular in the method of removing this silica, A physical method and a chemical method can be used. Examples thereof include a method of evaporating silica under reduced pressure and high temperature, and a method of eluting silica using an acid. In particular, silica is removed by immersing the silica-based composite oxide fiber obtained in the fourth step in a 2% by mass hydrogen fluoride aqueous solution for about 10 minutes or in a 10% by mass sodium hydroxide aqueous solution for about 12 hours. Is preferred.

(6th process)
In the sixth step, the ruthenium-containing solution (electrodeposition solution) containing the sacrificial agent and ruthenium is irradiated with light while bringing the silica-based composite oxide fiber into contact with the ruthenium in the mesopores of the silica-based composite oxide fiber. The catalyst fibers are produced by supporting the particles. Irradiating light having energy equal to or higher than the band gap of the metal oxide constituting the second phase while bringing the silica-based composite oxide fiber into contact with a ruthenium-containing solution obtained by adding a sacrificial agent to a liquid containing ruthenium. By doing so, ruthenium particles can be selectively supported on the reduction site of the metal oxide (non-light-irradiated surface, that is, inside the mesopore).

Ruthenium compounds in the ruthenium-containing solution include ruthenium chlorides such as RuCl ₃ and RuCl ₃ hydrate, chlororuthenates such as K ₃ RuCl ₆ , [RuCl ₆ ] ³⁻ and K ₂ RuCl ₆ , [RuCl ₅ (H ₂ O) ₄ ] ²⁻ , [RuCl ₂ (H ₂ O) ₄ ] ⁺ and other chlororuthenate hydrates, ruthenium acid salts such as K ₂ RuO ₄ , Ru ₂ OCl ₄ and Ru ₂ OCl ₅ Ruthenium oxychlorides such as Ru ₂ OCl ₆ , ruthenium oxychloride salts such as K ₂ Ru ₂ OCl ₁₀ and Cs ₂ Ru ₂ OCl ₄ , [Ru (NH ₃ ) ₆ ] ²⁺ , [Ru (NH ₃ ) ₆ ] ³⁺ , [Ru (NH ₃ ) ₅ H ₂ O] ²⁺ and other ruthenium ammine complexes, [Ru (NH ₃ ) ₅ Cl] ²⁺ , [Ru (NH ₃ ) Ruthenium such as chlorides, bromides, RuBr ₃ , RuBr ₃ hydrates of ruthenium ammine complexes such as ₆ ] Cl ₂ , [Ru (NH ₃ ) ₆ ] Cl ₃ , [Ru (NH ₃ ) ₆ ] Br ₃ Bromides, other ruthenium organic amine complexes, ruthenium acetylacetonate complexes, ruthenium carbonyl complexes such as Ru (CO) ₅ , Ru ₃ (CO) ₁₂ , [Ru ₃ O (OCOCH ₃ ) ₆ (H ₂ O) ₃ ] OCOCH _trihydrate, Ru 2 _(RCOO) 4 ruthenium organic acid salt such as Cl (R = alkyl group of 1-3 carbon atoms), _{K 2} [RuCl ₅ NO)], _{[Ru (NH 3) 5 (NO} ) ] Cl _{3, [Ru (OH) (NH 3)} 4 (NO) ] _{(NO 3) 2, Ru (} NO) (NO 3) 3 ruthenium nitrosyl complexes such as ruthenium And compounds such as phosphine complex. Preferred ruthenium compounds, RuCl _3, RuCl ruthenium chloride such as ₃ hydrate, RuBr _3, RuBr ₃ ruthenium bromide such as halogenated ruthenium compounds such as hydrates and the like. More preferred is ruthenium chloride hydrate.

  Examples of the sacrificial agent include electron donors such as formic acid, sodium hydride, hydrazine, and alcohol. Alcohol is preferable, and methanol and ethanol are preferable from the viewpoint of economy and safety of handling. More preferably it is.

  The concentration of ruthenium in the ruthenium-containing solution can be adjusted according to the target loading, and is not particularly limited as long as the ruthenium compound can be dissolved in the ruthenium-containing solution, and is 1.0 to 50.0 ppm. It is preferable that it is the range of this, and it is still more preferable that it is the range of 5.0-15.0 ppm. If it is less than 1.0 ppm, it is difficult to obtain the desired catalyst activity, and even if it exceeds 50.0 ppm, it is difficult to obtain a further increase in activity, which is uneconomical.

  The concentration of the sacrificial agent in the ruthenium-containing solution can be adjusted according to the type of ruthenium compound and the irradiation time of light, and is particularly limited as long as the ruthenium compound does not become insoluble in the ruthenium-containing solution by adding the sacrificial agent. There is no. The higher the sacrificial agent concentration, the shorter the irradiation time can be expected.

As described above, the wavelength of the irradiated light is not particularly limited as long as the light has energy equal to or higher than the energy corresponding to the band gap of the metal oxide constituting the second phase. For example, when the second phase is anatase type titania, the band gap is 3.2 eV, and therefore, energy corresponding to this, that is, a wavelength of 387 nm or less can be used. The light intensity is not particularly limited, but the light intensity in the range of 2.5 mW / cm ^{2 to} 7.0 mW / cm ² is preferable because stable catalytic activity can be expected to increase. Since this range can be easily achieved with a commercially available lamp, it is also economical.

  In the following, the high-performance catalyst fiber composed of the silica-based composite oxide fiber according to the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples at all. Changes can be made without departing from the spirit of the present invention.

(Reference Example 1: Production of polycarbosilane)
A three-neck flask with a capacity of 5 liters was charged with 2.5 liters of anhydrous toluene and 400 g of metallic sodium, heated to the boiling point of toluene under a nitrogen gas stream, and 1 liter of dimethyldichlorosilane was added dropwise over 1 hour. After completion of the dropwise addition, the mixture was heated to reflux for 10 hours to produce a precipitate. The precipitate was filtered and washed with methanol and then with water to obtain 420 g of white powder of polydimethylsilane. In a three-necked flask equipped with a water-cooled refluxing apparatus, 250 g of the obtained polydimethylsilane was put and reacted by heating at 420 ° C. for 30 hours under a nitrogen gas stream to obtain polycarbosilane having a number average molecular weight of 1200.

(Production Example 1)
To 50 g of polycarbosilane synthesized by the method of Reference Example 1, 100 g of toluene and 50 g of tetrabutoxytitanium were added, preheated at 100 ° C. for 1 hour, and then slowly heated to 150 ° C. to distill off the toluene. Then, after reacting for 5 hours as it was, the temperature was further raised to 250 ° C. and reacted for 5 hours to synthesize modified polycarbosilane. To this modified polycarbosilane, 5 g of tetrabutoxytitanium was intentionally added for the purpose of coexistence of a low molecular weight organometallic compound to obtain a mixture (spinning stock solution) of the modified polycarbosilane and the low molecular weight organometallic compound.

  After the resulting mixture of modified polycarbosilane and low molecular weight organometallic compound was dissolved in toluene, it was charged into a glass spinning device, the interior was thoroughly purged with nitrogen, and the temperature was raised to distill off the toluene. Then, melt spinning was performed at 180 ° C. The obtained spun fiber was heated to 150 ° C. stepwise in air and infusible, and then fired in air at 900 to 1300 ° C. for 1 hour to obtain titania / silica fiber. The silica on the fiber surface was removed by immersing the fiber in a 2% by mass hydrogen fluoride aqueous solution for 10 minutes to obtain a titania / silica fiber (average diameter: 10 μm) having a mesopore structure. FIG. 2 shows a STEM photograph of titania / silica fibers having a mesopore structure at a firing temperature of 1200 ° C.

  As a result of X-ray diffraction, the titania / silica fiber obtained in Production Example 1 was composed of amorphous silica and anatase titania. As a result of the fluorescent X-ray analysis, silica was 78% by mass and titania was 22% by mass. Further, when the distribution state of the constituent atoms was measured by EPMA (X-ray microanalyzer), Ti / Si (molar ratio) = 0.90 to 0.94 in the region of 1 μm from the outermost periphery of the fiber, from the outermost periphery. Ti / Si (molar ratio) = 0.12 to 0.15 in the region of 3 to 4 μm, Ti / Si (molar ratio) = 0.03 to 0.04 in the center, and titanium is directed toward the fiber surface. It was confirmed that the composition had an increasing gradient composition.

Example 1
2.41 g of titania / silica fiber obtained in Production Example 1 was placed in a glass container having a length of 550 mm × width of 380 mm × height of 25 mm and a thickness of 3.3 mm, and 24.9 mg of ruthenium (III) chloride / n hydrate was added. It was dissolved in a mixed solvent of 50 g of ultrapure water and 750 g of ethanol, immersed in an electrodeposition solution (ruthenium concentration: 12.0 ppm), and irradiated with black light at an intensity of 5.5 mW / cm ² for 4 hours (electrodeposition reaction). After irradiation, the fiber was taken out from the glass container, washed with water, and further dried to obtain a catalyst fiber according to Example 1. In ESCA, a peak of 280.7 eV derived from Ru (Metal) was shown (FIG. 3A). From this, it was found that the supported ruthenium is in a metal state. From the results of ICP-AES, the amount of ruthenium supported by the catalyst fiber according to Example 1 was 0.4% by mass (vs. catalyst fiber). Moreover, it was found from the STEM photograph (FIG. 4) that the supported ruthenium exists only in the mesopores on the surface of the catalyst fiber. Ruthenium in the mesopore has excellent sintering resistance. Each ruthenium had a particle size of about 1 to 3 nm and was supported on the titania layer in a highly dispersed state, and showed an ideal structure as a catalyst.

(Comparative Example 1)
A catalyst fiber according to Comparative Example 1 was obtained in the same manner as in Example 1 except that ethanol as a sacrificial agent was not added and 800 g of ultrapure water was used as a solvent. ESCA showed a peak at 282.1 eV, which is considered to be derived from Ru ³⁺ and Ru ⁴⁺ (FIG. 3B). From this, it was found that a salt of an ionic species was formed instead of a metal state.

Claims (6)

A modified polycarbosilane having a structure in which a polycarbosilane having a main chain skeleton represented by Chemical Formula 1 and having a number average molecular weight of 200 to 10,000 is modified with an organometallic compound, or the modified polycarbosilane and an organometallic compound, A first step of obtaining a spinning dope that is a mixture of
A second step of obtaining a spun fiber from the spinning dope;
A third step of obtaining an infusible fiber by heat-treating the spun fiber in an oxidizing atmosphere;
A fourth step of obtaining a silica-based composite oxide fiber by firing the infusible fiber in an oxidizing atmosphere;
A fifth step of forming mesopores by removing the silica in the vicinity of the surface by treating the surface side of the silica-based composite oxide fiber;
A sixth step of irradiating the ruthenium-containing solution containing the sacrificial agent and ruthenium with light while contacting the silica-based composite oxide fiber;
A method for producing a catalyst fiber, comprising:

(However, R in the formula represents a hydrogen atom, a lower alkyl group or a phenyl group.)   The method for producing a catalyst fiber according to claim 1, wherein the sacrificial agent is methanol or ethanol.   The method for producing a catalyst fiber according to claim 1 or 2, wherein a concentration of the ruthenium in the ruthenium-containing solution is 1.0 to 50.0 ppm. 5. The method for producing a catalyst fiber according to claim 1, wherein the light intensity is 2.5 to 7.0 mW / cm ² . A silica-based composite oxide fiber comprising a composite oxide phase of an oxide phase (first phase) mainly composed of a silica component and a metal oxide phase (second phase) comprising a metal other than silica,
The presence ratio of at least one or more metal elements of the metal oxide constituting the metal oxide phase (second phase) increases in a slope toward the fiber surface, and the metal oxide phase (second phase) The metal constituting it is formed into particles, and mesopores having an average pore diameter of 2 to 30 nm from the fiber surface to the inside of the fiber are formed between the particles, and the average particle diameter is 0.5 to 4 in the mesopores. A catalyst fiber, wherein metal ruthenium (Ru) particles of 25.0 nm are supported. 7. The catalyst fiber according to claim 6, wherein the number of the metal ruthenium particles supported in the mesopore is 6 × 10 ¹³ particles / m ² or more per unit surface area in the mesopore.

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