JP4385130B2 - INORGANIC COMPOSITE CONTAINING TITANIUM OXIDE, AND METHOD FOR PRODUCING PROPYLENE OXIDE USING THE COMPOSITE AS CATALYST - Google Patents

Description

   The present invention relates to a novel inorganic compound composite containing a special titanium oxide structure, and a method for producing propylene oxide by propylene oxidation using the composite as a catalyst.

In recent years, composites of titanium oxide and other inorganic compounds have been used in a wide range of fields such as photocatalysts, catalysts, catalyst materials, cosmetics, paints, and electronic materials. Conventionally, as a method of complexing titanium oxide with an inorganic carrier, as a precursor of titanium oxide, there is one Ti atom at the center, and a chlorine atom, a methoxy group, an ethoxy group, an iso-, n-propoxy group, etc. around it. A substance having a functional group bonded thereto, for example, titanium chloride (TiCl ₄ ) or titanium tetraisopropoxide (Ti (i-OC ₃ H ₇ ) ₄ ) is dissolved or dispersed in a solvent such as alcohols, and the resultant is inorganic. After contacting with the carrier, a method of changing to titanium oxide or a precursor thereof by a method such as heating or hydrolysis has been adopted. Typical methods include an impregnation method (for example, see Non-Patent Document 1) and a sol-gel method (for example, see Non-Patent Document 2).

In addition, a titanium atom is introduced into the skeleton of a zeolitic material, such as zeolite (general abbreviation TS-1) having a structure in which part of silicon in the skeleton of silicalite-1 having an MFI structure is replaced with titanium. There is also a method in which one titanium atom is combined with an inorganic carrier in a state where one titanium atom is isolated. In addition, an example in which a titanium atom is introduced into a silica-based mesoporous material called MCM-41, which is an abbreviation commonly used in technical literature or the like, is also known (see, for example, Non-Patent Documents 3 and 4). .
However, in the above method, even though it is possible to create an isolated titanium species composed of one titanium atom surrounded by silicon atoms and oxygen atoms, a special structure composed of two or more titanium atoms is formed. It is difficult to create a target structure selectively even if it is produced on an inorganic support such as silica by chance, while the target structure may occur by chance within the probable range. There was a problem that there was. Therefore, for example, a titanium oxide catalyst having a special structure useful for the synthesis of propylene oxide by a gas phase oxidation reaction using molecular oxygen (O ₂ ) of propylene as an oxidizing agent has not been known yet.

Chemical Communications, 2001 (15), p 1356-1357. Chem. Mater. 1999, 11, p1253-1258 Issued by CMC, “Synthesis and Application of Functional Zeolite” p154-160 Chem. Rev. , 97, p2373 (1997)

  This invention is made | formed in view of the above-mentioned actual condition in a prior art. That is, an object of the present invention is to provide a titanium oxide-based inorganic composite comprising a special structure having high activity and durability, and suitable for use in various fields. Another object of the present invention is to provide a titanium oxide-based reaction catalyst having a long activity and a relatively high yield and selectivity when producing propylene oxide by direct oxidation of propylene.

  As a result of intensive studies on the structure of titanium oxide-based inorganic composites used in a wide range of fields, the present inventors combined a precursor of titanium oxide having a specific local structure with an inorganic compound such as a carrier. After that, by applying external energy or the like to decompose the titanium precursor, an inorganic composite of a titanium oxide and an inorganic compound that retains the unique local structure of the titanium precursor can be obtained. The inorganic composite was found to be useful as a catalyst for producing propylene oxide, and the present invention was completed.

That is, the inorganic composite of the titanium oxide and the inorganic compound of the present invention is characterized by comprising a titanium oxide having a cyclic structure in which two or more titanium atoms are alternately bonded to oxygen atoms and the inorganic compound. Is.
In addition, in the method for producing an inorganic composite of the present invention, a titanium compound having a cyclic structure in which two or more titanium atoms are alternately bonded to oxygen atoms is bonded to an inorganic compound, and then external energy is applied or a reactive agent is used. A method for producing an inorganic composite of a titanium oxide and an inorganic compound having a cyclic structure in which two or more titanium atoms are alternately bonded to oxygen atoms, wherein the titanium compound is decomposed by addition.

The method for producing propylene oxide of the present invention uses propylene and oxygen as a catalyst by using an inorganic complex composed of a titanium compound and an inorganic compound having a cyclic structure in which two or more titanium atoms are alternately bonded to oxygen atoms in one molecule. It is characterized by reacting the contained gas in a gas phase.
The propylene oxide production apparatus of the present invention is a flow-type propylene oxide production apparatus for producing propylene oxide by gas phase reaction of propylene and an oxygen-containing gas, wherein two or more titanium atoms are oxygen atoms in one molecule. And using a reaction tube equipped with a catalyst packed bed filled with an inorganic composite composed of a titanium compound and an inorganic compound having an annular structure alternately bonded to each other and a space layer held at or near the reaction temperature at the rear part. Features.

  The inorganic composite of the present invention is a stable composite composed of a titanium compound and an inorganic compound in a special bond form, and is useful as a chemical reaction catalyst, etc., and is particularly directly epoxidized by a gas phase oxidation reaction of propylene. When used as a reaction catalyst for producing propylene oxide, the catalytic activity is maintained for a long time, and propylene oxide can be obtained with a relatively high selectivity and high yield.

   The inorganic composite of the present invention comprises a titanium oxide having a cyclic structure in which two or more titanium atoms are alternately bonded to oxygen atoms and an inorganic compound, that is, two or more titanium atoms in one molecule. A titanium compound having at least one cyclic structure bonded through an oxygen atom as a structural unit and an inorganic compound are chemically or physically bonded.

  In order to produce the inorganic composite of the present invention, a cyclic structure (hereinafter also referred to as “titanium multinuclear structure”) in which two or more titanium atoms are alternately bonded to oxygen atoms in advance as a precursor of titanium oxide. A titanium compound having a unique local structure is used, and among them, a four-membered ring structure represented by the following formula (1) or (2) in which two titanium atoms are arranged through oxygen atoms (hereinafter referred to as “titanium 2”). A titanium compound such as a titanium complex having a “nuclear structure” as a structural unit is preferably used.

In these titanium dinuclear structures, the atoms around the titanium atoms [bonds (A) to (H) in the formula] are arranged with atoms such as oxygen, hydrogen, or carbon, respectively.
Titanium dinuclear structures include those having a four-coordinate structure represented by formula (1) and those having a six-coordinate structure represented by formula (2), in which titanium atoms are arranged through oxygen atoms. It has an annular structure. Examples of the compound having a 4-coordinate structure represented by the formula (1) include titanium peroxocitrate ammonium (chemical formula: (NH ₄ ) ₄ [Ti ₂ (C ₆ H ₄ O ₇ ) ₂ (O ₂ ) ₂ ] or ( NH ₄ ) ₈ [Ti ₄ (C ₆ H ₄ O ₇ ) ₄ (O ₂ ) ₄ ]) or a derivative thereof is exemplified. The structure of this compound is shown in FIG. As shown in FIG. 1, titanium forms a diamond-shaped ring structure through an oxygen atom, oxygen is bonded to the positions of (A) and (C) in formula (1), and (B), (D ) Is coordinated with the peroxo ion O ₂ ²⁻ . In addition, a carbon atom or the like is bonded to a cross-linked oxygen atom.
In addition, as an example of a binuclear complex having a six-coordinate structure represented by the formula (2), Na ₄ (THF) ₈ [Ti ₂ (μ−O) disclosed in Inorganica Chimica Acta 332 (2002) p41 to 46 is used. ) ₂ (calix [4] arene) ₂ ], etc., which has a molecular structure in which two titanium and two oxygens are alternately arranged in a ring as shown in the formula (2) and FIG. is there.
Furthermore, the titanium compound used in the present invention is not limited to those described above, and an oxo-titanium complex disclosed in JP-A-7-252277 can also be used.

  After supporting or binding the titanium compound having the titanium multinuclear structure as a precursor to an inorganic compound such as a carrier, the precursor is decomposed by applying external energy or a reactive agent to form a titanium multinuclear structure. An inorganic composite in which the retained titanium oxide is formed on the inorganic compound can be obtained. FIG. 3 illustrates an inorganic composite in which a titanium binuclear structure is formed on an inorganic compound containing silica and alumina, and a reaction mechanism presumed that the inorganic composite activates oxygen molecules.

By supporting such a multinuclear structure titanium compound on an inorganic compound such as an inorganic carrier and chemically changing it to a titanium oxide, a titanium oxide having a multinuclear structure similar to the precursor is generated on the inorganic compound, A composite of a titanium oxide and an inorganic carrier can be obtained. However, when a precursor consisting of a single titanium atom having no conventional polynuclear structure, such as titanium tetraisopropoxide, is used, a similar structure is accidentally formed. Even if it is predicted to be formed, it is not possible to selectively obtain a composite of titanium oxide and an inorganic carrier having a desired multinuclear structure.
Advantages of generating this titanium multinuclear structure on an inorganic compound are that a reaction mechanism characteristic of complex catalysts in solution can be performed on an inorganic support, and intermediate products necessary for the estimated reaction mechanism are generated. What can be done is exemplified. For example, in order to establish the reaction mechanism shown in Catalysis Communications 4 (2003) p385-391, a titanium oxide having a four-membered ring structure in which two titanium atoms are bonded in a rhombus shape through oxygen atoms; When a complex of zeolite is required, but the raw material is a mononuclear structure titanium compound in which only one titanium atom is contained in the unit structure, two titanium atoms are bonded in a diamond shape through oxygen atoms. A four-membered ring structure is produced only by chance, and a desired complex can be selectively obtained only by preparing a characteristic rhombus-shaped binuclear titanium complex as a precursor.

Examples of the inorganic compound used in the present invention include, but are not limited to, a metal compound, a carbon material, a silicon compound, a zeolite compound, or a mesoporous material. More specifically, examples of metal compounds include lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, strontium, barium, scandium, yttrium, titanium, zirconium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten. , Manganese, technetium, rhenium, iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium, platinum, copper, silver, gold, zinc, cadmium, mercury, aluminum, gallium, indium, thulium, germanium, tin, lead Lanthanum, cerium, praseodymium, samarium, europium oxide, chloride, carbonate, sulfate, nitrate, sulfide and the like. Among these, magnesium, calcium, strontium, barium, titanium, zirconium, aluminum, niobium, zinc, cerium, lanthanum oxide, and carbonate can be preferably used. For example, any crystal structure can be used as long as it has various crystal structures such as an alpha type and a gamma type even with the same atomic composition such as aluminum oxide (chemical formula: Al ₂ O ₃ ). These compounds may be composite compounds containing two or more metal elements. Examples of the carbon material include activated carbon, graphite, fullerene, carbon nanotube, and diamond. Examples of the silicon compound include silicon dioxide, silica gel, silicon nitride, silicon carbide, and silicalite. Zeolite compounds are A type, X type, Y type, mordenite, beta, ZSM-5, ZSM-11, AlPO ^- n (n is a positive integer), SAPO ^- n (n is a positive integer). Examples of mesoporous materials include materials called MCM-41, SBA-15, and FSM-16 as abbreviations commonly used widely in science and technology literature. It is not limited.

  A well-known method can be used to support the titanium compound having the above titanium multinuclear structure on an inorganic compound such as an inorganic carrier. Specifically, impregnation method, vapor deposition method, liquid phase adsorption method, sol gel Law, etc., but is not limited thereto. Of these, the impregnation method preferably used will be described in more detail. First, the titanium compound is dissolved in a solvent to disperse the powder and pellets of the inorganic compound as a carrier and sufficiently stirred, and the solvent is removed by a method such as reduced pressure and heating to bond the inorganic carrier and the titanium compound. As the solvent, an appropriate solvent is used so that the compound can be easily dissolved in accordance with the titanium compound, and easily compatible with the inorganic carrier. Examples thereof include water, alcohols, ethers, esters, petroleum solvents. And the like. The inorganic carrier may be subjected to a known pretreatment suitable for the loading method used. Examples of pretreatment include, but are not limited to, heating, drying, gas treatment and the like. In addition, the above carbon material is exemplified by changing surface characteristics by a known treatment method such as oxygen treatment or steam treatment, if necessary. However, it is not essential to perform these pretreatments.

In the present invention, the decomposition of the titanium compound having a multinuclear structure is performed by applying energy from the outside such as heat, electromagnetic waves, radiation, or adding a reactant. A known method can be used for decomposing energy such as heat, electromagnetic waves, and radiation from the outside. For example, as a safe and easy method, heating using a furnace such as an electric furnace, gas furnace, or image furnace, infrared irradiation, visible light irradiation, ultraviolet light irradiation, microwave irradiation, X-ray irradiation, laser Irradiation, electron beam irradiation, alpha ray irradiation, beta ray irradiation, gamma ray irradiation, and the like, but are not limited thereto. In addition, the wavelengths of light such as infrared rays, ultraviolet rays, and microwaves, and electromagnetic waves are not limited. The atmosphere at the time of decomposition is exemplified by vacuum, air, oxygen, nitrogen, argon, helium, carbon dioxide, carbon monoxide, water vapor, and a mixed gas thereof, but is not limited thereto. Further, the total amount of heat, electromagnetic waves and radiation energy applied is desirably an amount sufficient to decompose most of the precursor and change it into titanium oxide. When heat is selected as the external energy, the heating temperature is not particularly limited, but a preferable temperature is 100 to 1500 ° C, more preferably 300 to 800 ° C. A preferable heating time is 1 second to 10 days, more preferably 10 seconds to 10 hours.
Examples of the reactive agent include acidic substances such as hydrochloric acid, nitric acid and sulfuric acid, and basic substances such as sodium hydroxide, aqueous ammonia and sodium carbonate. Use an appropriate amount of a substance suitable for decomposing the titanium precursor to be used. Is preferred. When using a reactive agent, it is preferable to remove the reactive agent by a method such as heating or washing after completion of the reaction.

When the method of the present invention is used, as described above, a titanium compound having a titanium multinuclear structure, for example, a titanium compound having a structure in which two titanium atoms are arranged in a rhombus via an oxygen atom, is used as a precursor. After the compound is supported on the surface of the inorganic carrier, the titanium compound is decomposed to produce titanium oxide with a characteristic local structure consisting of the same titanium multinuclear structure as the titanium compound used as the precursor on the inorganic carrier. A composite of the titanium oxide and the inorganic carrier thus produced can be easily produced.
Furthermore, the inventive concept and technique leading to the formation of the inorganic composite in the present invention will be clarified with reference to FIG. (1) in FIG. 4 is a schematic diagram of a titanium compound having a titanium binuclear structure (characteristic local structure). (2) is a diagram schematically showing an operation in which the titanium compound of (1) is supported on an inorganic carrier and then decomposed by heat, electromagnetic waves or radiation. (3) is a view schematically showing that the surrounding ligand is removed by the decomposition operation after decomposition, and titanium oxide having a characteristic local structure is generated on the surface of the inorganic carrier.

  Inorganic composites comprising titanium oxide and inorganic compounds obtained by the present invention are durable and have improved chemical properties of titanium oxides, so photocatalysts, catalyst materials, cosmetics, paints and electronic materials In particular, when used as a catalyst in the production of propylene oxide by epoxidation reaction by direct oxidation of propylene with molecular oxygen, the catalytic activity lasts for a long time, and the yield is relatively high. Propylene oxide can be obtained with high selectivity.

Next, a method for producing propylene oxide by vapor phase epoxidation reaction of propylene using the inorganic composite of the present invention as a catalyst will be described.
As the raw material gas, a gas containing propylene and oxygen as essential components, and further containing an inert gas such as helium, argon, nitrogen, carbon dioxide as a dilution gas is used as necessary. In order to prevent the risk of explosion due to the reaction temperature or reaction pressure, it is preferable to appropriately mix an inert gas in consideration of the explosion limit of the mixed gas. Although reaction temperature is not specifically limited, Preferred temperature is 100-500 degreeC, More preferably, it is 150-350 degreeC. The pressure can be any of atmospheric pressure, pressurization, and decompression, but atmospheric pressure or pressurization conditions are preferable, and a preferable pressure is 1 to 200 atm, and more preferably 1 to 50 atm. The flow rate of the raw material gas is not particularly limited, but is preferably 0.1 to 1000 mL / min, more preferably 1 to 100 mL / min, with respect to 1 g of the catalyst weight.

As the reaction apparatus, a known reaction mode in which a solid catalyst such as a flow type or a batch type or a powder catalyst is generally used can be applied, but a tubular flow type reactor is preferably used. The material of the reaction apparatus is preferably made of an inert material having high heat resistance such as quartz or stainless steel, and may be a material treated with a known inert material such as coating. In this reaction apparatus, a reaction tube provided with a catalyst packed bed of the above-described inorganic complex of titanium oxide and an inorganic compound and a space layer that can be kept at the reaction temperature or a temperature close thereto at the rear part is used. In order to prevent movement and outflow of the catalyst, it is desirable that the catalyst packed bed and the space layer be partitioned by a partition made of an inert material and shape that does not disturb the gas flow. The space layer is a layer in which the mixed product gas after contact with the catalyst stays for a long time, and is kept at the reaction temperature or a temperature close to it, preferably 100 to 500 ° C, more preferably 150 to 350 ° C. Although the temperature difference between the catalyst layer and the rear space layer is not particularly limited, the value of (catalyst layer temperature) − (space layer temperature) is exemplified as a preferable range, and particularly preferably −50 to 50 It is the range of ° C. Further, the preferable volume of the rear space layer is a volume capable of heating the mixed product gas after contact with the catalyst to some extent for a long time, and the value obtained by dividing the space layer volume by the raw material gas flow rate (gas residence time) is not particularly limited. Is preferably 5 seconds to 60 minutes or more, and particularly preferably 10 seconds to 10 minutes.
FIG. 8 shows a conceptual diagram for further clarifying the structure of the tubular flow reactor. The supply gas first reaches the catalyst packed bed and comes into contact with the catalyst, and then passes through a partition of a material and shape that does not hinder the gas flow and reaches the rear space layer. Here, the product, unreacted raw materials, etc. reach the outside of the tube after staying for a long time. The tube is maintained at the reaction temperature by a heater or the like.
In addition, a fluidized bed catalytic reactor, which is one of flow-type reactors, can also be preferably used for this reaction. In this case as well, similarly, the gas in contact with the catalyst is at or near the reaction temperature, preferably It is desirable that the temperature is kept at 100 to 500 ° C, more preferably 150 to 350 ° C. In this case, the volume obtained by subtracting the catalyst volume provided for the reaction from the internal volume of the reactor is the space layer volume, and the value obtained by dividing the space layer volume by the raw material gas flow rate (gas residence time) is not particularly limited. Like the above fixed bed apparatus, it is preferable that the structure stays for a long time, preferably 5 seconds to 60 minutes, or more, particularly preferably 10 seconds to 10 minutes.

Examples Hereinafter, the present invention will be described more specifically with reference to examples and the like, but the present invention is not limited to these examples.

Titanium peroxocitrate tetrahydrate (chemical formula: (NH ₄ ) ₄ [Ti ₂ (), which is a binuclear titanium compound having a structure in which two titanium atoms are arranged in a diamond shape in a ring shape through oxygen. _{C 6 H 4 O 7) 2} (O 2) 2] · 4H 2 O or _{(NH 4) 8 [Ti 4} (C 6 H 4 O 7) 4 (O 2) 4] · 8H 2 O) ( trade name : Tasfine, manufactured by Furuuchi Chemical Co., Ltd.) A homogeneous solution in which 0.6 g was dissolved in 50 mL of distilled water was obtained. Silicon dioxide powder (Caractect Q-30, manufactured by Fuji Silysia Chemical Ltd., physical property values (values described in the catalog)): surface area 100 m ² / g, average pore diameter 30 nm, pore volume 1.0 mL / g, particles 9.8 g (diameter 75 to 500 μm) was dispersed to form a slurry. After sufficiently stirring this, it dried under reduced pressure at 80 degreeC, water was removed, and the powder containing the titanium precursor which consists of a titanium compound and silicon dioxide was produced | generated.
The powder containing the produced titanium precursor was fired at 600 ° C. in air for 3 hours to obtain an inorganic composite powder. The obtained inorganic composite consisted of a weight composition ratio of 2% titanium oxide and 98% silicon dioxide, and this was designated as sample A-2.
Similarly, inorganic composites each having a different titanium dioxide content were prepared, and the titanium oxide content was 7% by weight (sample A-7) and the titanium oxide content was 15% by weight (sample A-15). An inorganic composite was prepared.
(Comparative Example 1)

Instead of the titanium peroxoammonium citrate tetrahydrate used in Example 1, mononuclear titanium tetraisopropoxide (chemical formula: Ti (iso-C ₃ H ₇ O) ₄ ) different from the binuclear structure was used. A composite was prepared.
First, 0.35 mL of titanium tetraisopropoxide was mixed with ethanol to obtain a uniform solution. Silicon dioxide powder dried at 150 ° C. in the solution (Caractect Q-30, manufactured by Fuji Silysia Chemical Ltd., physical property values (values described in the catalog): surface area 100 m ² / g, average pore diameter 30 nm, pore volume 1 (4.9 mL / g, particle diameter 75 to 500 μm) was dispersed to form a slurry. Next, aqueous ammonia was added dropwise to the slurry to hydrolyze titanium tetraisopropoxide and left to stand for aging. After aging, the gelled slurry was transferred to an evaporating dish and the residual solvent was removed by heating. The powder containing the hydrolyzate of titanium tetraisopropoxide produced was fired in air at 600 ° C. for 3 hours to obtain a composite powder. The titanium oxide content of the obtained inorganic composite was 2% as in Example 1, and this was designated as Sample B-2.

X-ray absorption measurement of the four types of complexes obtained in Example 1 and Comparative Example 1, TS-1, rutile titanium oxide, anatase titanium oxide, and titanium peroxocitrate ammonium tetrahydrate as standard substances Went. This measurement was performed by the transmission method or the fluorescence method at the High Energy Accelerator Research Organization, Synchrotron Radiation Facility.
The four types of composites prepared in both cases were pre-heated at 300 ° C. in air and sealed in a polyethylene film bag together with helium gas to eliminate the influence of outside air. XANES and EXAFS analysis was performed from the obtained absorption spectrum.

FIG. 5 shows the XANES spectrum. In FIG. 5, spectrum A is titanium peroxocitrate tetrahydrate, spectrum B is TS-1, spectrum C is rutile titanium oxide, spectrum D is anatase titanium oxide, and spectrum E is sample A- of Example 1. 2. Spectrum F is Sample B-2 of Comparative Example 1.
TS-1 of B has one sharp pre-edge peak observed and can be attributed to a tetrahedral structure in which oxygen is tetracoordinated to titanium from the state of titanium in the known TS-1. In the rutile titanium oxide of C, three characteristic pre-edge peaks were observed. The anatase type titanium oxide of D showed three pre-edge peaks, but showed a spectrum clearly different from the rutile type. The titanium precursor complex of A showed a pre-edge different from rutile, anatase and TS-1.
The sample of Example 1 of E shows a pre-edge peak very similar to the titanium complex of the raw material, and the whole spectrum is similar to the titanium complex of the titanium oxide precursor, and is different from the standard material other than the titanium complex. It was also confirmed. In contrast, the sample of Comparative Example 1 showed a slightly different spectrum from the sample of Example 1, but no clear difference could be confirmed.

In order to clarify the difference between the samples of Example 1 and Comparative Example 1, EXAFS analysis was performed. FIG. 6 shows the result of extracting the EXAFS vibration from the X-ray absorption spectrum and performing the Fourier transform. Spectrum A is Sample A-2 of Example 1, and Spectrum B is Sample B-2 of Comparative Example 1. The peak in the vicinity of 1.5 mm indicated by a line in the figure is attributed to a tetracoordinate Ti—O bond. A clear difference between the two is a peak in the vicinity of 2.7 mm indicated by an arrow in the figure, which appears clearly in the spectrum A, whereas the intensity in the spectrum B is very small and unclear. This 2.7２ peak is attributed to the distance between Ti atoms in the Ti—O—Ti bond. In the sample of Comparative Example 1, no clear peak is observed at a distance of 2.7 mm, because the structure at a distance of about 2.7 mm from the center titanium around the titanium atom is messy, and the titanium atom is rhombus via oxygen. This is because it does not have a regular cyclic cluster structure bonded to the. On the other hand, in the sample of Example 1, the peak due to the Ti—O—Ti bond is clearly confirmed, and it is also seen that the XANES spectrum is similar to the precursor complex used as the raw material. It can be concluded that Ti atoms form a ring structure arranged in a diamond shape through oxygen.
From the above examination results, titanium oxide produced on the SiO ₂ surface is different from rutile, anatase and TS-1, and is also different from a catalyst prepared using titanium tetraisopropoxide as a precursor, and two Ti atoms are It was clarified that a ring-shaped cluster structure arranged in a diamond shape was formed through oxygen.

Furthermore, the coordination number and coordination atom of the titanium atom were obtained by performing curve fitting analysis on the EXAFS spectrum shown in FIG. For this structural analysis, REX2000 (Rigaku software) was used, and for the theoretical parameters used for the analysis, McKale parameters built in the software were used.
First, in order to examine the validity of applying the above theoretical parameters, the spectrum of a metal titanium foil as a standard material was analyzed. The range of the radial distribution distance (R range) that determines the spectrum to be extracted as the analysis target from the spectrum obtained by multiplying the EXAFS vibration extracted from the obtained raw spectrum by the cube of the wave number and then Fourier-transformed is 1.7-3. The wave number range that determines the fitting range of the spectrum obtained by inverse Fourier transform of .4 angstrom was selected to be 3.0 to 12 (angstrom) ^-1 . As a result, the coordination number between Ti and Ti is
The result was that the child bolt and the Debye-Waller factor were 0.091 angstroms. The R factor indicating the degree of convergence of the analysis value was a very good value of 1.0%. According to the literature (Chemical Handbook Basic Edition (II) revised 4th edition, published by Maruzen), metal titanium has a hexagonal close-packed structure, and the coordination number between Ti and Ti is 12. Since it is known that the coordination number is calculated to be a little smaller in the theoretical parameters, the coordination number obtained by the calculation was appropriate. In addition, the lattice constant (a = 2.950 angstrom) of metallic titanium described in the above literature and the value of the interatomic distance obtained by the analysis are very close, and the validity of the theoretical parameters was confirmed also in the interatomic distance. Therefore, it was concluded that it is appropriate to use this theoretical parameter for the analysis of titanium-based materials.

Next, the spectrum A) in FIG. 6, which is a spectrum of a composite prepared from a binuclear titanium complex, was analyzed using theoretical parameters whose validity was confirmed. The Fourier filter range (R range) was 1.0 to 3.3 angstroms, and the wave number range for determining the fitting range of the spectrum obtained by inverse Fourier transform was 4.0 to 11 (angstroms) ⁻¹ . As a result, for Ti-O, the coordination number is 3.7 and the interatomic distance is 1.9.
And between Ti and Ti, the coordination number is 0.79 and the interatomic distance is
It was. Further, the R factor indicating the convergence of the analysis value was 17%, which was a numerical value that caused no problem in the actual sample analysis. Using this result, considering the fact that the coordination number is an integer in an ideal state, and that the coordination number is calculated slightly smaller when theoretical parameters are used, the coordination between Ti-O As a result of approximating the number 4 and the coordination number between Ti and Ti to 1 and deriving an appropriate structure from the analysis results, the tetracoordinate titanium atoms present on the support are bonded to the rhombus via oxygen. As shown in FIG. 7, it was confirmed that the structure was an annular structure in which titanium and oxygen were alternately bonded. From the above curve fitting analysis, the existence of the novel complex shown in claims 1 to 4 and the effectiveness of the preparation method of the complex shown in claims 5 to 7 were clearly shown.

Production of propylene oxide using propylene and molecular oxygen as raw materials, using the inorganic composite obtained in Example 1 as a catalyst, 1.0 g of the composite powder (Sample A-2) obtained in Example 1 as a catalyst, This was physically mixed with 3.0 g of quartz sand and filled into a quartz reaction tube. This reaction tube is provided with a catalyst packed bed followed by a 25 mL space. The temperature was raised to a reaction temperature of 285 ° C. while circulating helium in the reaction tube, and after confirming the stability of the temperature, the reaction was started by switching to a mixed gas of 10 mL of propylene per minute and 10 mL of oxygen per minute. In this case, the time for the gas after the reaction to stay in the space behind the catalyst layer is 1.25 minutes. The reaction pressure was 3.5 atm (pressure gauge indicated value). After confirming that the temperature and pressure were stable at 295 ° C. after 25 minutes, the product was analyzed using an on-line gas chromatograph. As a result, the conversion of propylene was 9.21%, the yield of propylene oxide was 3.20%, and the selectivity for propylene oxide was 34.7%.
(Comparative Example 2)

Propylene oxide production reaction and product analysis were performed in the same manner as in Example 2 except that the composite powder (Sample B-2) obtained in Comparative Example 1 was used as a catalyst. As a result, the conversion of propylene was 4.36%, the yield of propylene oxide was 1.16%, and the selectivity for propylene oxide was 26.7%. From comparison between Example 2 and Comparative Example 2, titanium peroxocitrate ammonium tetrahydrate having a binuclear structure was used as the precursor of the composite titanium oxide, and the structure of the titanium oxide contained in the composite was 2 The effect of the cyclic cluster structure in which Ti atoms are arranged in a diamond shape through oxygen was confirmed.
(Comparative Example 3)

Titanium oxide powder obtained by heating and calcining at 600 ° C. for 3 hours without supporting ammonium peroxocitrate tetrahydrate on silicon dioxide was used as a catalyst. This powder was confirmed by X-ray diffraction to contain both rutile and anatase crystalline phases. Its BET surface area was 6.34 m ² / g.
When this catalyst was used for the reaction and analysis under the same conditions as in Example 1, the conversion of propylene was 2.25%, the yield of propylene oxide was 0.48%, and the selectivity of propylene oxide was 21.5%. there were. From these results, it was confirmed that titanium oxide alone does not exhibit sufficient catalytic performance and is effective in forming a composite with an inorganic carrier such as silicon dioxide.

  The reaction was conducted in the same manner as in Example 2 except that the amount of catalyst was changed to a mixture of 2.0 g of composite (sample A-2) catalyst powder and 2.0 g of quartz sand, and the product was analyzed. It was. As a result, the conversion of propylene was 21.4%, the yield of propylene oxide was 8.0%, and the selectivity for propylene oxide was 37.4%.

  The reaction was conducted in the same manner as in Example 2 except that the reaction temperature was changed to 290 ° C. in Example 2, and the product was analyzed. As a result, the conversion of propylene was 9.0%, and propylene oxide The yield was 2.5%, and the selectivity for propylene oxide was 28.3%.

  In Example 1, the silicon dioxide carrier has different physical properties (Caract Q-3, manufactured by Fuji Silysia Chemical Ltd., physical property values (values announced by the manufacturer): surface area 500 m 2 / g, average pore diameter 3 nm, pore volume 0. A composite (sample C-2) was obtained in the same manner as in Example 1 except that the volume was changed to 3 mL / g and the particle diameter was 75 to 500 μm. When this was used as a catalyst and reacted in the same manner as in Example 2, the obtained product was analyzed. As a result, the conversion of propylene was 20.2%, the yield of propylene oxide was 6.2%, and the selection of propylene oxide. A value of 30.5% was obtained. From these results, it was found that the physical properties of silicon dioxide, which is a carrier of the composite, do not have a great influence on the reaction results when applied to a catalyst.

  The reactors used in the reactions of Examples and Comparative Examples have a space of 25 mL behind the catalyst packed bed and are kept at the same temperature as the reaction temperature, so that the gas in contact with the catalyst stays in the reaction tube for 1.25 minutes. However, the space behind it was filled with quartz sand so that most of the space was blocked so as not to hinder the flow of gas, and the effective volume of the space layer was reduced to reduce the gas residence time to less than 3 seconds. did. Then, a mixture of 1.0 g of a composite containing 2% of titanium oxide prepared in Example 1 and 3.0 g of inert quartz sand was used as a catalyst, the supply gas was 10 mL of propylene per minute, 5 mL of oxygen per minute, The reaction was carried out at a reaction temperature of 295 ° C. and a reaction pressure of 3.5 atm. As a result, propylene conversion was 0.6%, propylene oxide yield was 0%, and propylene oxide selectivity was 0%. Further, the reaction activity was measured in the same manner at a temperature of 300 ° C. As a result, the propylene conversion was 0.7%, the propylene oxide yield was 0%, and the propylene oxide selectivity was 0%. Further, at 300 ° C., the gas composition was 10 mL of propylene per minute, 10 mL of oxygen per minute, and 5 mL of helium per minute. As a result, propylene conversion was 1.2%, propylene oxide yield was 0%, and propylene oxide selectivity was 0%. Furthermore, as a result of setting the gas composition to 10 mL of propylene per minute and 10 mL of oxygen at 300 ° C., the propylene conversion was 1.9%, the propylene oxide yield was 0.04%, and the propylene oxide selectivity was 1.9%. As a result, the effectiveness of the reactor having a space behind the catalyst packed bed and in which the gas after contacting the catalyst stays for a relatively long time was shown.

1.0 g of the composite powder (sample A-2) obtained in Example 1 was used as a catalyst, which was physically mixed with 3.0 g of quartz sand and filled into a quartz reaction tube. The reaction was switched to a mixed gas of 5 mL of propylene per minute, 10 mL of oxygen per minute and 5 mL of helium. In this case, the time for the gas after the reaction to stay in the space behind the catalyst layer is 1.25 minutes. The reaction pressure was 3.5 atm (pressure gauge indicated value). After confirming that the temperature and pressure were stable at 293 ° C. after 25 minutes, the product was analyzed using an online gas chromatograph.
As a result, the conversion of propylene was 7.8%, the yield of propylene oxide was 3.0%, and the selectivity for propylene oxide was 38.5%. The raw material was continuously supplied under the same conditions, and the reaction was continued. After 465 minutes, the product was analyzed in the same manner as 25 minutes later. As a result, the conversion of propylene was 9.2%, and the yield of propylene oxide was 3. .4%, propylene oxide selectivity is 36.9%. Compared with the result after 25 minutes, the propylene conversion and the yield of propylene oxide were slightly increased. From this, it was confirmed that this catalyst can maintain stable performance for a long time without decreasing its activity even in a long-time reaction.

Since the inorganic composite of the present invention is superior in activity and durability compared to a composite containing titanium oxide alone, it can be applied to the field of use of conventional titanium oxide-based composites, particularly direct oxidation of propylene. it is useful as propylene Oki shea de fabrication catalyst by.

The example of the binuclear structure (upper part) which consists of the tetracoordinate structure of titanium contained in the inorganic composite of this invention and the chemical structure (lower part) of titanium peroxocitrate are shown. Examples of a binuclear structure composed of a six-coordinate structure of titanium contained in the inorganic composite of the present invention (upper stage) and Na ₄ (THF) ₈ [Ti ₂ (μ-O) ₂ (calix [4] arene) ₂ ] Chemical structure (bottom) is shown. An example of a bond with silica and alumina having a titanium binuclear structure, which is the main part of the inorganic composite of the present invention, and an example of its reaction mechanism are shown. It is a conceptual diagram which shows the formation process of the inorganic composite_body | complex of this invention. It is a XANES spectrum figure of the inorganic composite of one example of this invention, and another compound. It is an EXAFS spectrum figure of the inorganic composite_body | complex obtained in Example 1 and Comparative Example 1 of this invention. 2 is a main part of the chemical structure derived from curve fitting analysis of the titanium oxide binuclear structure obtained in Example 1. FIG. It is the schematic which shows one example of the propylene oxide manufacturing apparatus of this invention.

Claims (5)

Propylene oxide production for producing propylene oxide by gas phase reaction of propylene and oxygen-containing gas consisting of titanium oxide and inorganic compound having a cyclic structure in which two or more titanium atoms are alternately bonded to oxygen atoms catalyst. The catalyst for producing propylene oxide according to claim 1, wherein the cyclic structure is a four-membered ring structure in which two titanium atoms are bonded through an oxygen atom. The catalyst for producing propylene oxide according to claim 1 or 2, wherein the inorganic compound is at least one selected from a silicon compound, a carbon material, and a zeolite compound. A method for producing propylene oxide, comprising using the catalyst according to any one of claims 1 to 3 to cause gas phase reaction between propylene and an oxygen-containing gas. In the flow-type propylene oxide manufacturing apparatus which manufactures propylene oxide by carrying out the gas phase reaction of propylene and oxygen-containing gas, the catalyst packed bed filled with the catalyst according to any one of claims 1 to 3, and the reaction temperature in the rear part thereof Or an apparatus for producing propylene oxide, characterized in that a reaction tube having a space layer maintained at a temperature close to that is used.