JP6854477B2 - Method for producing perovskite-type composite oxide - Google Patents

Description

The present invention relates to a method for producing a perovskite-type composite oxide that can be used as a catalyst for purifying exhaust gas, a catalyst for combustion of natural gas, or an adsorbent for harmful substances such as nitrogen oxides.

_{Nitrogen oxides (NO x} ), carbon monoxide (CO), hydrocarbons (HC) and the like are contained in the exhaust gas from internal combustion engines such as automobile engines. These substances can be removed by an exhaust gas purification catalyst capable of oxidizing CO and HC and _{reducing NO x at the same time.} A typical example of an exhaust gas purification catalyst is a three-way catalyst in which a noble metal such as platinum (Pt), rhodium (Rh), or palladium (Pd) is supported on a porous metal oxide carrier such as γ-alumina. Are known.

However, such precious metals are expensive and have small reserves, so it is possible that they will be in short supply in the future. Therefore, a new exhaust gas purification catalyst for reducing the usage fee of precious metals has been proposed.

For example, Patent Document 1 proposes to use porous silica having only mesopores of 1 to 5 nm as a porous metal oxide carrier. In such an exhaust gas purification catalyst, the movement of the noble metal supported in the mesopores is suppressed, the grain growth due to long-term use is prevented, and the noble metal maintains a highly dispersed state, thereby achieving high catalytic activity. Can be maintained.

Further, Patent Document 2 describes a catalyst component containing a noble metal and _{a perovskite represented by the chemical formula ABO 3} (A = La, Sr, Ce, Ba, Ca, B = Co, Fe, Ni, Cr, Mn, Mg). It has been proposed to mix and use a catalyst component which is a type composite oxide. By using such a perovskite-type composite oxide in combination, it is possible to enhance the combustion of fine particle carbon substances and hydrocarbons in the exhaust gas in the low temperature region and the absorption / decomposition action of _{NO x.} Here, as a method for preparing a perovskite-type composite oxide, a method has been proposed in which a metal citric acid complex is heated at 350 ° C. or higher in a vacuum or an inert gas and then calcined in an oxidizing atmosphere.

As described above, the perovskite-type composite oxide can provide a catalytic activity superior to that of the noble metal catalyst in terms of low-temperature catalytic activity. In general, a perovskite-type composite oxide is prepared by precipitating a precursor of a perovskite-type composite oxide from a solution containing a salt of a metal constituting the perovskite-type composite oxide by a coprecipitation method, and the precursor is dried and fired. Manufactured by However, in recent years, as the problem of environmental pollution has become more serious, the purification standards for exhaust gas have become stricter, and the perovskite-type composite oxide synthesized by this method has insufficient catalytic activity.

Japanese Unexamined Patent Publication No. 2000-24503 Japanese Unexamined Patent Publication No. 8-229404

When a perovskite-type composite oxide is produced by the coprecipitation method, the particles of the obtained perovskite-type composite oxide are sintered between the particles during firing at a temperature of 800 ° C. or higher, resulting in a large particle size of several μm. Have. Since such particles have a small surface area, sufficient catalytic activity has not been obtained.

The present invention has been made in view of the above problems, and provides a method for producing a perovskite-type composite oxide in the form of fine particles in a single phase with extremely few by-products without performing a calcination treatment.

The present inventors have made extensive studies to solve the above-mentioned problems. As a result, the raw material aqueous solution containing a predetermined ion is brought into a supercritical state under a predetermined temperature and pressure condition, and the raw material aqueous solution is subjected to hydrothermal treatment, whereby the perovskite type composite oxide is not calcined. We have found that it can be produced in the form of fine particles, and have completed the present invention. Specifically, the present invention provides the following.

(1) The first invention of the present invention is a group consisting of La at the A site and Fe, Al, Mn, Ni, Co, Pd, Pt, Sc, Ti, Nb, Ta, W and Mo at the B site. _{A method for producing a perovskite-type composite oxide represented by the chemical formula ABO 3} containing one or more types of ions selected from the above, wherein a raw material aqueous solution containing a raw material metal ion having a pH of 5 or more and 11.5 or less is prepared at 425 ° C. This is a method for producing a perovskite-type composite oxide, which is heated at 650 ° C. or lower and pressurized at 22 MPa or more and 60 MPa or less to bring it into a supercritical state, and hydrothermally heats the raw material aqueous solution.

_{(2) The second invention of the present invention is represented by the chemical formula ABO 3} containing La at the A site and one or more ions selected from the group consisting of Fe, Al, Mn, Ni and Co at the B site. A method for producing a perovskite-type composite oxide, which comprises heating a raw material aqueous solution containing a raw material metal ion having a pH of 5 or more and 11.5 or less at 425 ° C. or higher and 650 ° C. or lower and pressurizing it at 22 MPa or higher and 60 MPa or lower. This is a method for producing a perovskite-type composite oxide in which the raw material aqueous solution is subjected to hydrothermal treatment to bring it into a supercritical state.

(3) The third invention of the present invention is the method for producing a perovskite-type composite oxide in which the pH of the raw material aqueous solution is 6 or more and 11 or less in the first or second invention.

(4) The fourth invention of the present invention is the method for producing a perovskite-type composite oxide via lanthanum oxyhydroxide (LaOOH) as a reaction intermediate in any one of the first to third inventions.

(5) A fifth aspect of the present invention is the method for producing a perovskite-type composite oxide in which the perovskite-type composite oxide is particles having an average particle size of 1000 nm or less in any one of the first to fourth inventions. Is.

(6) The sixth invention of the present invention is the method for producing a perovskite-type composite oxide in which the aqueous solution of the raw material is hydroheat-treated in a batch reactor in any one of the first to fifth inventions.

(7) The seventh invention of the present invention is the method for producing a perovskite-type composite oxide in which the raw material aqueous solution is subjected to hydrothermal treatment in a flow reactor in any one of the first to fifth inventions.

According to the present invention, it is possible to produce a perovskite-type composite oxide in the form of fine particles in a single phase with extremely few by-products without performing a calcination treatment.

It is a schematic diagram of a batch reactor. It is a schematic diagram of a distribution type reactor system.

Hereinafter, a specific embodiment of the present invention (hereinafter, referred to as “the present embodiment”) will be described in detail. The present invention is not limited to the following embodiments, and can be carried out with appropriate modifications within the scope of the object of the present invention.

≪1. Perovskite type composite oxide ≫
The perovskite-type composite oxide according to the present embodiment _{contains La at the A site of the perovskite-type structure represented by the chemical formula ABO 3} , and Fe, Al, Mn, Ni, Co, Pd, Pt, Sc, at the B site. It is a composite oxide containing one or more selected from the group consisting of Ti, Nb, Ta, W and Mo.

Perovskite is a general term for composite oxides represented by the chemical formula ABO _3. A 12-coordinated cation having a relatively large ionic radius is arranged at the A site, a 6-coordinated cation having a relatively small ionic radius is arranged at the B site, and oxygen is arranged at the O site. In the perovskite-type composite oxide according to the present embodiment, La is arranged at the A site, and Fe, Al, Mn, Ni, Co, Pd, Pt, Sc, Ti, Nb, Ta, W and Mo are arranged at the B site. One or more selected from the group consisting of O is arranged at the O site.

La is placed at the A site. In addition to La ions, the A site includes, for example, Ce ion, Nd ion, Ba ion, Sr ion, Ca ion, Pb ion, Bi ion, Gd ion, Nd ion, Y ion, K ion, Na ion, etc. It can be partially replaced by cations that are coordinated and have an ion radius of 0.9 A or more and 1.4 A or less.

The content of La ions is not particularly limited, and is preferably 0.6 or more, preferably 0.7 or more, with respect to the total content of all ions arranged at the A site, for example. More preferably, it is more preferably 0.8 or more, and particularly preferably 0.9 or more.

The content of ions arranged at the A site other than La ions is not particularly limited, and can be appropriately adjusted as long as the composite oxide maintains the perovskite structure. The total content of the ions arranged at the A site other than the La ion is, for example, preferably 0.4 or less in terms of molar ratio with respect to the total content of all the ions arranged at the A site, and is 0. It is more preferably 0.3 or less, further preferably 0.2 or less, and particularly preferably 0.1 or less.

At the B site, one or more selected from the group consisting of Fe, Al, Mn, Ni, Co, Pd, Pt, Sc, Ti, Nb, Ta, W and Mo is arranged. The total content of one or more ions selected from the group consisting of Fe, Al, Mn, Ni, Co, Pd, Pt, Sc, Ti, Nb, Ta, W and Mo is not particularly limited, for example. , The molar ratio is preferably 0.4 or more, more preferably 0.6 or more, and further preferably 0.8 or more with respect to the total content of all the ions arranged at the B site. It is preferably 0.9 or more, and particularly preferably 0.9 or more.

Further, the B site preferably contains one or more ions selected from the group consisting of Fe, Al, Mn, Ni and Co. The total content of one or more ions selected from the group consisting of Fe, Al, Mn, Ni and Co is not particularly limited, and for example, with respect to the total content of all ions arranged at the B site. The molar ratio is preferably 0.4 or more, more preferably 0.6 or more, further preferably 0.8 or more, and particularly preferably 0.9 or more.

Total content of ions located at B sites other than one or more ions selected from the group consisting of Fe, Al, Mn, Ni, Co, Pd, Pt, Sc, Ti, Nb, Ta, W and Mo. The above is not particularly limited, and can be appropriately adjusted as long as the composite oxide maintains the perovskite structure. As the content of ions arranged at B sites other than one or more ions selected from the group consisting of Fe, Al, Mn, Ni, Co, Pd, Pt, Sc, Ti, Nb, Ta, W and Mo. Is, for example, preferably 0.6 or less, more preferably 0.4 or less, and 0.2 or less, based on the content of all the ions arranged at the B site. Is more preferable, and 0.1 or less is particularly preferable.

As the ions arranged at the O site, the O ion can be partially replaced with, for example, anions such as F ion, Cl ion, N ion, and S ion.

The content of O ions is not particularly limited, and for example, it is preferably 0.6 or more, preferably 0.7 or more, in terms of molar ratio with respect to the total content of all ions arranged at the O site. More preferably, it is more preferably 0.8 or more, and particularly preferably 0.9 or more.

The total content of the ions arranged at the O sites other than the O ions is not particularly limited, and can be appropriately adjusted as long as the composite oxide maintains the perovskite structure. The total content of all the ions arranged at the O site other than the O ion is preferably 0.4 or less in terms of molar ratio with respect to the content of all the ions arranged at the O site. It is more preferably 0.3 or less, further preferably 0.2 or less, and particularly preferably 0.1 or less.

The perovskite-type composite oxide is not particularly limited as long as it has a perovskite-type crystal structure, and for example, those having defects at the A site, the B site, or the O site can be obtained. Due to the presence of such defects, the total number of moles of all the ions arranged at the A site (the total number of moles of all the ions arranged at the A site) with respect to the total number of moles of all the ions arranged at the B site. To obtain a non-stoichiometric composition in which the total number of moles of all the ions arranged at the / B site) deviates from the equivalent ratio of 1.0, for example, 0.8 to 1.2. You can also.

The form of the perovskite-type composite oxide is not particularly limited, and in addition to the nanoparticles and fine particles, bulk and thin films can be obtained by subjecting the nanoparticles or fine particles to a predetermined treatment such as firing. You can also.

≪2. Manufacturing method of perovskite type composite oxide ≫
In the method for producing a perovskite-type composite oxide according to the present embodiment, a raw material aqueous solution containing at least La and Fe having a pH of 5 or more and 11.5 or less is heated to 425 ° C or more and 650 ° C or less and 22 MPa or more and 60 MPa or less. This is a method in which an aqueous solution of a raw material is subjected to hydrothermal treatment by pressurizing it to a supercritical state.

The supercritical state is a state in which the temperature and pressure of a substance exceed the critical point. For example, in the case of water, the critical points are a temperature of 374 ° C. and a saturated vapor pressure of 22.1 MPa. In the supercritical state, water can strictly control the reaction equilibrium and reaction rate in the system by adjusting only the temperature and pressure without adding an acid, an alkali, or an organic solvent. Therefore, water in a supercritical state (hereinafter, also referred to as "supercritical water") is expected to be used as an environment-friendly reaction crystallization solvent. Furthermore, in the supercritical region, the solubility of metal oxides can be set to an extremely low value compared to normal hydrothermal synthesis conditions, and the hydrothermal reaction rate increases significantly. Therefore, nano-sized metal oxides Suitable for high-speed synthesis of fine particles.

Hereinafter, a method for producing the perovskite-type composite oxide LaFeO ₃ will be described with reference to more specific examples, but the present invention is not limited to the following examples, and the raw material metal ions contained in the raw material aqueous solution are used. By modifying it, various perovskite-type composite oxides can be produced.

The method for preparing the raw material aqueous solution is not particularly limited, and examples thereof include a method in which an aqueous solution containing La and an aqueous solution containing Fe are prepared, and these are mixed with a basic aqueous solution or an acidic aqueous solution to adjust the pH. Be done.

More specifically, a La-containing aqueous solution prepared by dissolving the La source in water and an Fe-containing aqueous solution prepared by dissolving the Fe source in water are mixed to obtain a mixed solution of a metal salt, and then this mixing is performed. A basic aqueous solution or an acidic aqueous solution can be added to the solution to adjust the pH to 5 or more and 11.5 or less to prepare a raw material aqueous solution.

In _{this example of producing LaFeO 3} , a raw material aqueous solution containing La and Fe is used as the raw material metal ion, but the raw material aqueous solution can be appropriately adjusted according to the chemical species of the perovskite type composite oxide to be produced. .. For example, _{when producing LaAlO 3} , a raw material aqueous solution containing La and Fe as raw material metal ions _{can be used, and when producing LaMnO 3} , a raw material aqueous solution containing La and Mn as raw material metal ions can be used.

Further, in the case of producing a perovskite-type composite oxide containing a plurality of ions at the A site or the B site, a plurality of raw material metal ions are mixed. For example, when synthesizing a compound in which the A site of the perovskite type composite oxide is substituted with an ion other than La ion or a compound in which B site is substituted with an ion other than Fe ion, a La-containing aqueous solution and an Fe-containing aqueous solution are used. At the time of mixing, in addition to those aqueous solutions, an aqueous solution containing other raw material metal ions can be mixed.

The source of the raw material metal ions, which are essential components, is not particularly limited as long as it is a compound containing those metal ions and soluble in supercritical water, but for example, hydroxides, oxides, and halides (chlorides). Inorganic acid salts such as substances, fluorides, bromides, iodides, etc.), nitrates, carbonates, sulfates, etc. can be used. In addition, organic acid salts such as acetate, oxalate and lactate can also be used. Of these, nitrates are preferable because they are easily available and an aqueous solution can be easily prepared.

The concentration of the raw material metal ions in the raw material solution is not particularly limited, but the total content of the metal ions arranged at the A site and the total content of the metal ions arranged at the B site are 0.001 M or more and 5 M, respectively. The following is preferable. When the metal ion content is 0.001 M or more, a perovskite-type composite oxide having a sufficient yield can be obtained. Further, when the content of the metal ion is 5 M or less, the aggregation of the obtained particles can be suppressed.

When the O-site is partially replaced with nitrogen (N) to obtain an oxynitride, for example, ammonia, amine or the like can be appropriately added to the raw material aqueous solution as a nitrogen source.

When the O-site is partially replaced with sulfur (S) to obtain an acid sulfide, for example, thiourea, potassium sulfide, sodium sulfide, carbon disulfide, sulfur and the like can be appropriately added as a sulfur source.

The mixing ratio of the raw material metal ions contained in the raw material aqueous solution is not particularly limited, and can be adjusted so that the composition ratio is substantially the same as that of the target perovskite-type composite oxide.

The compound in which the A site of the perovskite type composite oxide is substituted with an ion other than La ion and the B site are Fe, Al, Mn, Ni, Co, Pd, Pt, Sc, Ti, Nb, Ta, W and Mo. When synthesizing a compound substituted with an ion other than one or more ions selected from the group consisting of, each site may not be sufficiently substituted depending on the ion to be substituted and the synthesis conditions. In such a case, the ratio of ions in the raw material aqueous solution can be increased or decreased to control the ratio of ions in the obtained perovskite-type composite oxide. For example, the total number of moles of all ions arranged at A site relative to the total number of moles of all ions arranged at B site (total number of moles of all ions arranged at A site / arranged at B site). The total number of moles of all ions) is preferably adjusted to 0.7 or more and 1.4 or less, and more preferably 0.9 or more and 1.2 or less.

The pH of the raw material aqueous solution is adjusted to 5 or more and 11.5 or less. Although details will be described later, by setting the pH to 5 or more and 11.5 or less, lanthanum oxyhydroxide (LaOOH), which is a reaction intermediate, can be produced at 405 to 425 ° C. during hydrothermal treatment. Further, from the viewpoint of more efficiently producing lanthanum oxide (LaOOH), the pH of the raw material aqueous solution is preferably 6 or more and 10 or less, and more preferably 7 or more and 9 or less. By producing lanthanum oxyhydroxide as a reaction intermediate under such conditions, a perovskite-type fine particle-like perovskite-type composite oxide can be finally produced with a small amount of by-products and in a single phase.

Further, a part of the La site of the lanthanum oxide can be replaced with a cation other than the La ion. For example, Bi ion, Gd ion, Nd ion, Y ion, Al ion, Ga ion, Fe ion, Mn ion, Ni ion, Co ion, Sc ion, Ce ion, or La ion having the same valence as La ion. When Nd ions, Ba ions, Sr ions, and Ca ions having similar ion radii are contained in the raw material aqueous solution, a part of La sites of lanthanum oxyhydroxide, which is an intermediate product, can be replaced. In such a case, a perovskite-type composite oxide in which La at the A site is partially substituted can be synthesized.

The pH of the raw material aqueous solution can be adjusted by using a basic solution or an acidic solution. The basic solution is ^{not particularly limited as long as it can supply hydroxide ions (OH −} ), and is, for example, an alkali metal such as potassium hydroxide, sodium hydroxide or barium hydroxide, or alkaline earth. An aqueous solution of metal hydroxide or aqueous ammonia can be used. The acidic solution is ^{not particularly limited as long as it can supply hydrogen ions (H +} ), and for example, an aqueous solution of nitric acid, hydrochloric acid, sulfuric acid, oxalic acid, acetic acid, hydrofluoric acid or the like can be used.

The raw material aqueous solution may contain, for example, an organic solvent, a complexing agent, a dispersant, a pH buffer, an oxidizing agent, etc., in addition to each metal ion, as long as it does not contradict the object of the present invention.

Then, the raw material aqueous solution prepared in this manner is heated at 425 ° C. or higher and 650 ° C. or lower and pressurized at 22 MPa or higher to bring it into a supercritical state, and the raw material aqueous solution is subjected to hydrothermal treatment.

In such hydrothermal treatment, lanthanum oxyhydroxide (LaOOH) is produced as a reaction intermediate. As described above, when the temperature is 425 ° C. or higher and the pressure is 22 MPa or higher, the raw material aqueous solution can be brought into a supercritical state. In the hydrothermal reaction in such a supercritical state, when the pH of the raw material aqueous solution is 5 or more and 11.5 or less, lanthanum oxyhydroxide (LaOOH), which is a reaction intermediate, can be produced.

For example, _{in the case of synthesizing LaFeO 3} , when the temperature of the raw material aqueous solution containing La and Fe is raised from room temperature, lanthanum oxyhydroxide (LaOOH) and iron oxide (Fe ₂ O) are heated at 410 to 420 ° C. ₃ ) is produced as an intermediate product. Then, when the temperature is further raised to 425 ° C. or higher, these react to form a perovskite-type composite oxide of _{LaFeO 3 in a single phase.} For example, in the case of synthesizing La (Fe, Ni) O ₃ , nickel oxide (NiO) is produced as an intermediate product in addition to lanthanum oxyhydroxide (LaOOH) and iron oxide (Fe ₂ O _3). To do. In the synthesis of a perovskite-type composite oxide containing lanthanum at the A site, the reaction proceeds in this way via lanthanum oxyhydroxide (LaOOH).

As described above, the pH of the raw material aqueous solution is 5 or more and 11.5 or less. When the pH of the raw material aqueous solution is 5 or more, _{the formation of lanthanum oxide hydroxide (for example, La 2} (OH) _5.1 (NO ₃ ) _0.9 , La (OH) ₂ (NO ₃ )) is prevented. be able to. This lanthanum oxide does not easily react with compounds of B-site ions such as iron oxide (Fe ₂ O ₃ ), and once formed, it can remain as it is, so that the yield of perovskite-type composite oxide is reduced. Further, when the pH is 11 or less, _{the formation of lanthanum hydroxide (La (OH) 3} ) can be prevented. This lanthanum hydroxide also _{does not easily react with iron oxide (Fe 2} O ₃ ), and once formed, it can remain as it is, so that the yield of the perovskite-type composite oxide is reduced.

The reaction temperature is not particularly limited as long as it is 425 ° C. or higher and 650 ° C. or lower. As described above, when the reaction temperature is 425 ° C. or higher, the raw material aqueous solution is brought into a supercritical state, and _{intermediate products such as lanthanum oxide (LaOOH) and iron oxide (Fe 2} O ₃ ) are mixed with perovskite. It can be changed to a type composite oxide. Further, when the reaction temperature is 650 ° C. or lower, it is possible to suppress the corrosion of the reaction vessel and the generation of impurities generated due to the corrosion.

The reaction temperature is preferably, for example, 430 ° C. or higher. When the reaction temperature is 430 ° C. or higher, intermediate products such as lanthanum oxyhydroxide and iron oxide can be reacted more efficiently to produce a perovskite-type composite oxide. On the other hand, the reaction temperature is preferably, for example, 640 ° C. or lower. When the reaction temperature is 640 ° C. or lower, corrosion of the reaction vessel can be efficiently suppressed.

The reaction pressure (pressure in the system) is not particularly limited as long as it is 22 MPa or more and 60 MPa or less. As described above, when the reaction pressure is 22 Mpa or more, the raw material aqueous solution can be brought into a supercritical state. Further, when the reaction pressure is 60 MPa or less, it is possible to suppress the corrosion of the reaction vessel and the generation of impurities generated due to the corrosion.

The reaction pressure is preferably, for example, 50 MPa or less. When the reaction pressure is 50 MPa or less, corrosion of the reaction vessel can be suppressed more efficiently.

The reaction time is not particularly limited, but is preferably 0.005 seconds or longer, more preferably 0.01 seconds or longer, further preferably 0.05 seconds or longer, and 0.1. It is particularly preferable that it is seconds or more. When the reaction time is 0.005 seconds or more, a perovskite-type composite oxide can be formed. The reaction time is preferably 10 hours or less, more preferably 5 hours or less, further preferably 2 hours or less, and particularly preferably 1 hour or less. When the reaction time is 10 hours or less, the reaction cycle can be increased and the productivity can be increased. The "reaction time" means from the time when the heating of the raw material aqueous solution is started to the time when the heating of the raw material aqueous solution is stopped.

The reaction vessel is not particularly limited as long as it can provide a pressure-controlled system, and for example, a pressure-resistant closed vessel or a vessel capable of controlling the internal pressure can be used. Further, the type of reaction is not particularly limited, and for example, either a batch type or a distribution type can be used.

The batch method is a method in which raw materials are charged into a reaction vessel or a reaction device and taken out after a predetermined time (for example, until equilibrium or a certain reaction rate is reached). As a specific embodiment of the batch type, for example, an aqueous solution of a raw material is placed in a pressure-resistant, heat-resistant container that can be sealed even at high temperature and high pressure, and put into a preheated shaking type heating and stirring device, and the solvent is supercritical water. There is a method of performing hydrothermal treatment by changing to.

FIG. 1 is a schematic diagram of a batch reactor. The batch reactor 1 is composed of, for example, a pressure-resistant and heat-resistant sealed pressure-resistant container 11 and a heater 12 arranged so as to surround the pressure-resistant container 11. The raw material aqueous solution L is charged inside the pressure-resistant container 11. The heater 12 heats the raw material aqueous solution L inside the pressure-resistant container 11 to a high temperature and high pressure state, the raw material aqueous solution L becomes a supercritical state, and a perovskite-type composite oxide is produced.

The distribution method refers to a method in which raw materials are continuously supplied into a reactor (reaction unit) to carry out a reaction and then continuously extracted. As a specific embodiment of the distribution type, for example, the raw material aqueous solution is continuously supplied into the reactor (reaction part), the raw material aqueous solution is subjected to hydrothermal treatment in the reactor (reaction part), and the perovskite type is applied from the reactor (reaction part). A method of continuously discharging the post-reaction liquid containing the composite oxide can be mentioned.

FIG. 2 is a schematic diagram of a distribution reactor system. The flow reactor system 2 includes a pipe 21 for supplying distilled water, a pipe 22 for supplying an aqueous solution of raw materials, a pipe 23 for a hydrothermal reaction, heaters 24a and 24b, a cooler 25, and a pressure reducing valve (discharge). Part) 26. The pipe 21 for supplying distilled water and the pipe 22 for supplying the raw material aqueous solution are connected to the pipe 23 for hydrothermal reaction, respectively. Further, the pipe 21 for supplying distilled water and the pipe 23 for hydrothermal reaction are surrounded by heaters 24a and 24b, respectively. Inside the connected pipe, the internal pressure is controlled to be 22 MPa or more.

In such a reactor system, the distilled water L2 is heated to 425 ° C. or higher and 620 ° C. or lower by a heater 24a arranged so as to surround the distilled water supply pipe 21, and becomes a supercritical state. It is supplied to 23. On the other hand, the raw material aqueous solution L1 is supplied to the hydrothermal reaction pipe 23 through the pipe 22 for supplying the raw material aqueous solution at room temperature, for example. The raw material aqueous solution instantly becomes supercritical at the place where the heated distilled water and the raw material aqueous solution are mixed. After that, it is heated by a heater 24b arranged so as to surround the circumference of the water-heat reaction pipe 23, and the reaction of the metal source contained in the raw material aqueous solution proceeds to generate a perovskite-type composite oxide. The raw material aqueous solution containing the perovskite-type composite oxide thus produced is cooled and the reaction is stopped instantly. The cooled post-reaction liquid is discharged from the reactor system 2 through the pressure reducing valve to recover the perovskite-type composite oxide.

In this way, in the flow-type reactor system, the raw material aqueous solution is rapidly heated and raised by mixing the raw material aqueous solution and water that has been preheated to a supercritical state, and a high degree of supersaturation is instantly given to the nano. A perovskite-type composite oxide of a size can be efficiently produced.

In addition, by indirectly cooling the reaction solution with cooling water and stopping the reaction instantly, uniform nucleation is caused, and the particle size, crystal structure, composition and morphology of the perovskite-type composite oxide particles produced are precisely determined. Can be controlled.

As described above, the supercritical hydrothermal synthesis method by the flow method has the advantages that the temperature, pressure and reaction time in the system can be strictly controlled, and the raw material aqueous solution can be rapidly heated and cooled. Have. The particle size of the obtained particles is preferable in that it becomes fine.

The obtained perovskite-type composite oxide has, as by-products, for example, La ₂ (OH) _5.1 (NO ₃ ) _0.9 , La (OH) ₂ (NO ₃ ), Fe ₂ O ₃ , and so on. Fe (OH) _{3 and the} like may be slightly contained. These can be easily removed, for example, by treating with water or a weak acid. Therefore, for example, the method for producing a perovskite-type composite oxide according to the present embodiment can further include a washing step.

The obtained perovskite-type composite oxide is used as, for example, a semiconductor material effective for deodorization, water purification, antibacterial, and antifouling, an antibacterial tile, an antibacterial film in a medical field, and the like, in addition to the above-mentioned three-way catalyst for automobiles. be able to. It can also be used as an electronic material such as a normal dielectric material or a conductor, or as a magnetic material.

The particle size and dispersity of the perovskite-type composite oxide particles can be appropriately controlled by the pH, pressure, temperature, metal source, etc. of the raw material aqueous solution. As described above, when used in a three-way catalyst application, the smaller the particle size, the more preferable, but the required particle size differs depending on the application.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

[Synthesis of LaFeO ₃ ]
Lanthanum nitrate _{(La (NO 3) 3 ·} 6H 2 O, 99% purity, manufactured by Kanto Kagaku) was dissolved in distilled water to prepare a aqueous solution of lanthanum of 0.1 M. Moreover, iron nitrate _{(Fe (NO 3) 3 ·} 9H 2 O, 99% purity, manufactured by Kanto Kagaku) was dissolved in distilled water to prepare an aqueous solution of iron 0.1 M. These aqueous solutions were mixed in an equimolar proportion of lantern and iron. Then, while vigorously stirring this aqueous solution, a 5 M potassium hydroxide aqueous solution was added dropwise until the pH reached a predetermined pH and mixed to obtain a raw material aqueous solution. This aqueous solution changed to a suspension when the pH was in the alkaline range.

A predetermined amount of the raw material aqueous solution was put into a heat-resistant and pressure-resistant metal container having an internal volume of 5 cm ³ , sealed, and put into an electric furnace preheated to a predetermined temperature. Here, assuming that the temperature of the electric furnace is 374 ° C. or higher, which is the critical point of water, the pressure inside the container is determined depending on the amount of water charged because it is inside the closed container. Therefore, the water in the container can be brought into a supercritical state by controlling the input amount so that the water of the charged raw material aqueous solution is 374 ° C. or higher and 22.1 MPa or higher. After a predetermined time had passed, the metal container was taken out of the electric furnace and placed in a container filled with water for quenching. Here, the reaction temperature was set to the set temperature of the electric furnace, and the reaction time was set to the time of charging into the electric furnace.

The lid of the cooled metal container was removed, the product in the container was taken out, and washing with distilled water was repeated 5 times by ultrasonic cleaning and centrifugation. The product after washing was heated to 60 ° C. and dried. The product phase of the obtained powder was identified by powder X-ray diffraction measurement (XRD: X'pertPro manufactured by PANalytical). In addition, the particle size was measured with a transmission electron microscope (TEM: HF-2200 manufactured by Hitachi, Ltd.). In addition, local composition analysis (EDS) of the particles was performed by an energy dispersive spectroscope associated with the TEM.

Table 1 shows the pH of each of the raw material aqueous solutions of Examples 1 to 12 and Comparative Examples 1 to 23, the pressure in the metal container (MPa), the set temperature of the electric furnace (° C.), and the reaction time (minutes). In addition, the particle size of _{LaFeO 3} measured from the product phases and TEM images of Examples 1 to 12 and Comparative Examples 1 to 23 is shown.

(Examples 1 to 3 and Comparative Examples 1 to 2)
In Comparative Example 1, Example 1, Example 2, Example 3, and Comparative Example 2, the pH of the raw material aqueous solution was set to 4, 6, 8, 11 or 12, respectively, the pressure in the metal container was set to 30 MPa, and the electric furnace was set. Hydrothermal synthesis was carried out under the conditions of a temperature of 430 ° C. and a reaction time of 30 minutes.

X-ray diffraction measurements of the powders obtained in Examples 1 to 3 and Comparative Examples 1 and 2 were performed. When the pH of the raw material aqueous solution was 6 to 11 (Examples 1 to 3), LaFeO ₃ (JCPDS card: 01-078-4249) was produced. On the other hand, when the pH is 4 (Comparative Example 1), in addition to _{LaFeO 3 , La 2} (OH) _5.1 (NO ₃ ) _0.9 (JCPDS card: 00-026-1145) and iron oxide (III) (Fe ₂ O ₃ , JCPDS card: 01-076-8403) was generated. When the pH was 12 (Comparative Example 2), La (OH) ₃ (JCPDS card: 01-077-3934) and an amorphous phase of iron hydroxide were produced in _{addition to LaFeO 3.}

The particle size _{of LaFeO 3} of Examples 1 to 3 was measured by TEM observation. _{LaFeO 3} of Example 1 had a cubic shape and a particle size of 30 to 70 nm. _{LaFeO 3} of Example 2 had a cubic shape and a particle size of 100 to 1000 nm. _{LaFeO 3} of Example 3 had a cubic shape and a particle size of 200 to 700 nm. As a result of EDS composition analysis, the La / Fe atomic ratio was 0.8 to 1.2.

(Comparative Examples 3 to 7)
In Comparative Examples 3 to 7, the pH of the raw material aqueous solution was 4, 6, 8, 11 and 12, respectively, and the water heat was set under the conditions of a pressure of 30 MPa in a metal container, a set temperature of an electric furnace of 410 ° C., and a reaction time of 5 minutes. Synthesis was performed.

In Comparative Examples 3 to 7, LaFeO ₃ was not obtained at any pH. It is considered that this is because the reaction temperature is low.

The X-ray diffraction measurement of the powder obtained in Comparative Examples 3 to 7 was performed. When the pH of the raw material aqueous solution is 6 to 11 (Comparative Examples 4 to 6), lanthanum oxide (LaOOH, JCPDS card: 01-077-2349) and iron oxide (III) (Fe ₂ O ₃ , JCPDS card) : 01-076-8403) was generated. On the other hand, when the pH is 4 (Comparative Example 3), La ₂ (OH) _5.1 (NO ₃ ) _0.9 (JCPDS card: 00-026-1145) and iron oxide (III) (Fe ₂ O). _3. JCPDS card: 01-076-8403) was generated. When the pH was 12 (Comparative Example 7), La (OH) ₃ (JCPDS card: 01-077-3934) and an amorphous phase of iron hydroxide were produced.

Comparative Example 3, Comparative Example 4, Comparative Example 5, Comparative Example 6 and Comparative Example 7 use the same raw material aqueous solutions as in Comparative Example 1, Example 1, Example 2, Example 3 and Comparative Example 2, respectively. Compared to them, the set temperature of the electric furnace is low and the reaction time is short. That is, Comparative Example 3, Comparative Example 4, Comparative Example 5, Comparative Example 6 and Comparative Example 7 are elevated in the reactions of Comparative Example 1, Example 1, Example 2, Example 3 and Comparative Example 2, respectively. It corresponds to the one completed by quenching the reaction at 410 ° C. in the middle of warming. That is, the products obtained in Comparative Example 3, Comparative Example 4, Comparative Example 5, Comparative Example 6 and Comparative Example 7 are the corresponding Comparative Example 1, Example 1, Example 2, Example 3 and Comparative Example 2. It is considered to correspond to the intermediate product of.

When the results of Comparative Example 4, Comparative Example 5 and Comparative Example 6 are compared with the results of Examples 1, 2 and 3 in comparison, the LaFeO ₃ production mechanism of Examples 1 to 3 is first intermediate. It is considered that lanthanum oxide is produced as a product, and then LaFeO _{3 is produced by further raising the temperature.}

(Examples 4 to 6, Comparative Examples 8 to 9)
In Comparative Example 8, Example 4, Example 5, Example 6 and Comparative Example 9, the pH of the raw material aqueous solution was set to 4, 6, 8, 11 and 13, respectively, the pressure in the metal container was set to 22 MPa, and the electric furnace was set. Hydrothermal synthesis was carried out under the conditions of a temperature of 460 ° C. and a reaction time of 15 minutes.

X-ray diffraction measurements of the powders obtained in Examples 4 to 6 and Comparative Examples 8 to 9 were performed. When the pH of the raw material aqueous solution was 6 to 11 (Examples 4 to 6), LaFeO ₃ (JCPDS card: 01-078-4249) was produced. On the other hand, when the pH is 4 (Comparative Example 8), in addition to _{LaFeO 3 , La 2} (OH) _5.1 (NO ₃ ) _0.9 (JCPDS card: 00-026-1145), iron oxide (III) (Fe ₂ O ₃ , JCPDS card: 01-076-8403) was generated. When the pH was 12 (Comparative Example 9), La (OH) ₃ (JCPDS card: 01-077-3934) and an amorphous phase of iron hydroxide were produced in _{addition to LaFeO 3.}

The particle size _{of LaFeO 3} of Examples 4 to 6 was measured by TEM observation. _{LaFeO 3} of Example 4 had a cubic shape and a particle size of 50 to 120 nm. _{LaFeO 3} of Example 5 had a cubic shape and a particle size of 200 to 800 nm. _{LaFeO 3} of Example 6 had a cubic shape and a particle size of 300 to 500 nm. As a result of EDS composition analysis, the La / Fe atomic ratio was 0.7 to 1.1.

(Comparative Examples 10 to 14)
In Comparative Examples 10 to 14, the pH of the raw material aqueous solution was 4, 6, 8, 11 and 13, respectively, and the water heat was set under the conditions of a pressure of 22 MPa in a metal container, a set temperature of an electric furnace of 420 ° C., and a reaction time of 5 minutes. Synthesis was performed.

In Comparative Examples 10 to 14, LaFeO ₃ was not obtained at any pH. It is considered that this is because the reaction temperature is low.

The X-ray diffraction measurement of the powder obtained in Comparative Examples 10 to 14 was performed. When the pH of the raw material aqueous solution is 6 to 11 (Comparative Examples 11 to 13), lanthanum oxide (LaOOH, JCPDS card: 01-077-2349) and iron oxide (III) (Fe ₂ O ₃ , JCPDS card) : 01-076-8403) was generated. On the other hand, when the pH is 4 (Comparative Example 10), La ₂ (OH) _5.1 (NO ₃ ) _0.9 (JCPDS card: 00-026-1145) and iron oxide (III) (Fe ₂ O). _3. JCPDS card: 01-076-8403) was generated. When the pH was 13 (Comparative Example 14), La (OH) ₃ (JCPDS card: 01-077-3934) and an amorphous phase of iron hydroxide were produced.

Comparative Example 10, Comparative Example 11, Comparative Example 12, Comparative Example 13 and Comparative Example 14 used the same raw material aqueous solutions as in Comparative Example 8, Example 4, Example 5, Example 6 and Comparative Example 9, respectively. Compared to them, the set temperature of the electric furnace is low and the reaction time is short. That is, Comparative Example 10, Comparative Example 11, Comparative Example 12, Comparative Example 13 and Comparative Example 14 were elevated in the reactions of Comparative Example 8, Example 4, Example 5, Example 6 and Comparative Example 9, respectively. It corresponds to the one in which the reaction was completed by quenching at 420 ° C. in the middle of warming. That is, the products obtained in Comparative Example 10, Comparative Example 11, Comparative Example 12, Comparative Example 13 and Comparative Example 14 are the corresponding Comparative Example 8, Example 4, Example 5, Example 6, and Comparative Example 9. It is considered to correspond to the intermediate product of.

Comparing the results of Comparative Example 11, Comparative Example 12 and Comparative Example 13 with the results of Examples 4, 5 and 6, the LaFeO ₃ production mechanism of Examples 4 to 6 was first intermediate. It is considered that lanthanum oxide is produced as a product, and then LaFeO _{3 is produced by further raising the temperature.}

(Examples 7 to 9, Comparative Examples 15 to 16)
In Comparative Example 15, Example 7, Example 8, Example 9, and Comparative Example 16, the pH of the raw material aqueous solution was set to 4, 7, 8, 9 and 12, respectively, the pressure in the metal container was set to 50 MPa, and the electric furnace was set. Hydrothermal synthesis was carried out under the conditions of a temperature of 500 ° C. and a reaction time of 10 minutes.

X-ray diffraction measurements of the powders obtained in Examples 7 to 9 and Comparative Examples 15 to 16 were performed. When the pH of the raw material aqueous solution was 7 to 9 (Examples 7 to 9), LaFeO ₃ (JCPDS card: 01-078-4249) was produced. On the other hand, when the pH is 4 (Comparative Example 15), in addition to _{LaFeO 3 , La 2} (OH) _5.1 (NO ₃ ) _0.9 (JCPDS card: 00-026-1145) and iron oxide (III) (Fe ₂ O ₃ , JCPDS card: 01-076-8403) was generated. When the pH was 12 (Comparative Example 16), La (OH) ₃ (JCPDS card: 01-077-3934) and an amorphous phase of iron hydroxide were produced in _{addition to LaFeO 3.}

The particle size _{of LaFeO 3} of Examples 7 to 9 was measured by TEM observation. _{LaFeO 3} of Examples 7 to 9 had a cubic shape and a particle size of 200 to 600 nm. As a result of EDS composition analysis, the La / Fe atomic ratio was 0.9 to 1.1.

(Comparative Examples 17 to 21)
In Comparative Examples 17 to 21, the pH of the raw material aqueous solution was 4, 7, 8, 9 and 12, respectively, and the water heat was set under the conditions of a pressure of 50 MPa in a metal container, a set temperature of an electric furnace of 410 ° C., and a reaction time of 5 minutes. Synthesis was performed.

In Comparative Examples 17 to 21, LaFeO ₃ was not obtained at any pH. It is considered that this is because the reaction temperature is low.

X-ray diffraction measurements of the powders obtained in Comparative Examples 17 to 21 were performed. When the pH of the raw material aqueous solution is 7 to 9 (Comparative Examples 17 to 21), lanthanum oxide (LaOOH, JCPDS card: 01-077-2349) and iron oxide (III) (Fe ₂ O ₃ , JCPDS card) : 01-076-8403) was generated. On the other hand, when the pH is 4 (Comparative Example 17), La ₂ (OH) _5.1 (NO ₃ ) _0.9 (JCPDS card: 00-026-1145) and iron oxide (III) (Fe ₂ O). _3. JCPDS card: 01-076-8403) was generated. When the pH was 12 (Comparative Example 21), La (OH) ₃ (JCPDS card: 01-077-3934) and an amorphous phase of iron hydroxide were produced.

Comparative Example 17, Comparative Example 18, Comparative Example 19, Comparative Example 20 and Comparative Example 21 used the same raw material aqueous solutions as in Comparative Example 15, Example 7, Example 8, Example 9 and Comparative Example 16, respectively. Compared to them, the set temperature of the electric furnace is low and the reaction time is short. That is, Comparative Example 17, Comparative Example 18, Comparative Example 19, Comparative Example 20, and Comparative Example 21 were elevated in the reactions of Comparative Example 15, Example 7, Example 8, Example 9, and Comparative Example 16, respectively. It corresponds to the one in which the reaction was completed by quenching at 410 ° C. in the middle of warming. That is, the products obtained in Comparative Example 17, Comparative Example 18, Comparative Example 19, Comparative Example 20 and Comparative Example 21 are the corresponding Comparative Example 15, Example 7, Example 8, Example 9 and Comparative Example 16. It is considered to correspond to the intermediate product of.

Comparing the results of Comparative Example 18, Comparative Example 19 and Comparative Example 20 with the results of Examples 7, 8 and 9, the LaFeO ₃ production mechanism of Examples 7 to 9 was first intermediate. It is considered that lanthanum oxide is produced as a product, and then LaFeO _{3 is produced by further raising the temperature.}

(Examples 10 to 12, Comparative Examples 22 to 23)
In Comparative Example 22, Example 10, Example 11, Example 12, and Comparative Example 23, the pH of the raw material aqueous solution was set to 4, 6, 8, 11 or 12, respectively, the pressure in the metal container was set to 30 MPa, and the electric furnace was set. Hydrothermal synthesis was carried out under the conditions of a temperature of 600 ° C. and a reaction time of 5 minutes.

X-ray diffraction measurements of the powders obtained in Examples 10-12 and Comparative Examples 22-23 were performed. When the pH of the raw material aqueous solution was 6 to 11 (Examples 10 to 12), LaFeO ₃ (JCPDS card: 01-078-4249) was produced. On the other hand, when the pH is 4 (Comparative Example 22), in addition to _{LaFeO 3 , La 2} (OH) _5.1 (NO ₃ ) _0.9 (JCPDS card: 00-026-1145) and iron oxide (III) (Fe ₂ O ₃ , JCPDS card: 01-076-8403) was generated. When the pH was 12 (Comparative Example 23), La (OH) ₃ (JCPDS card: 01-077-3934) and an amorphous phase of iron hydroxide were produced in _{addition to LaFeO 3.}

The particle size _{of LaFeO 3} of Examples 10 to 12 was measured by TEM observation. _{LaFeO 3} of Example 10 had a cubic shape and a particle size of 100 to 300 nm. _{LaFeO 3} of Example 11 had a cubic shape and a particle size of 200 to 500 nm. _{LaFeO 3} of Example 12 had a cubic shape and a particle size of 200 to 700 nm. As a result of EDS composition analysis, the La / Fe atomic ratio was 0.7 to 1.2.

(Example 13)
Supercritical hydrothermal synthesis was carried out in a flow reactor using the same raw material aqueous solution as in Example 2. A reactor system having the configuration shown in FIG. 2 was configured. The raw material aqueous solution is supplied into a pipe pressurized to a pressure higher than the critical pressure of the reactor while stirring, and supercritical water heated to a critical point or higher is merged in the pressurized pipe to combine a mixed aqueous solution of lantern and iron. The water inside was instantly put into a supercritical state. The time to pass through the hydrothermal reaction pipe after merging is the time to maintain the supercritical state, which is determined by the length and flow velocity of the hydrothermal reaction pipe. _{LaFeO 3} was obtained as a result of a synthetic experiment in which the transport speed of the mixed aqueous solution was 2 mL / min, the transport speed of the heated water was 10 mL / min, and the pipe length of the pipe for the hydrothermal reaction was 40 cm.

As a result of TEM observation, the obtained LaFeO ₃ had a cubic shape and a particle size of 20 to 40 nm. As a result of EDS composition analysis, the La / Fe atomic ratio was 0.9 to 1.1.

_{As described above, it was found that even when the flow reactor is used, LaFeO 3} can be efficiently synthesized by suppressing the production of by-products in the supercritical hydrothermal synthesis, as in the case of using the batch reactor. .. _{Further, LaFeO 3} synthesized by using this flow reactor was a very fine particle having a particle size of 20 to 40 nm. It is considered that fine particles were obtained because the reaction time was as short as 1.8 seconds and rapid heating and rapid cooling were realized.

[La (Fe, Ni) Synthesis of _{O 3]}
(Examples 14 to 16, Comparative Examples 24 to 25)
Lanthanum nitrate _{(La (NO 3) 3 ·} 6H 2 O, 99% purity, manufactured by Kanto Kagaku) was dissolved in distilled water to prepare an aqueous solution of 0.1M lanthanum. Moreover, iron nitrate _{(Fe (NO 3) 3 ·} 9H 2 O, 99% purity, manufactured by Kanto Kagaku) was dissolved in distilled water to prepare an aqueous solution of iron 0.1 M. Furthermore, nickel nitrate _{(Ni (NO 3) 2 ·} 6H 2 O, 98% purity, manufactured by Kanto Kagaku) was dissolved in distilled water to prepare an aqueous solution of 0.1M nickel. These aqueous solutions were mixed at a ratio of lanthanum: iron: nickel in a molar ratio of 2: 1: 1. Then, while vigorously stirring this aqueous solution, a 5 M aqueous potassium hydroxide solution was added dropwise until the pH reached a predetermined pH to obtain a raw material aqueous solution. Powders were prepared and analyzed in the same manner as in Example 1 except for the raw material aqueous solution.

Table 2 shows the pH of each of the raw material aqueous solutions of Examples 14 to 16 and Comparative Examples 24 to 25, the pressure in the metal container (MPa), the set temperature of the electric furnace (° C.), and the reaction time (minutes). Also shows the particle size of Examples 14-16 and Comparative Examples 24-25 La as measured from each of the product phase and TEM images (Fe, Ni) _{O 3.}

X-ray diffraction measurements of the powders obtained in Examples 14 to 16 and Comparative Examples 24 to 25 were performed. When the pH of the raw material aqueous solution was 6 to 11 (Examples 14 to 16), La (Fe, Ni) O ₃ (JCPDS card: 01-077-4279) was produced. On the other hand, when the pH is 4 (Comparative Example 24), in addition to La (Fe, Ni) O ₃ , La ₂ (OH) _5.1 (NO ₃ ) _0.9 (JCPDS card: 00-026- 1145), iron (III) oxide (Fe ₂ O ₃ , JCPDS card: 01-076-8403), and nickel oxide (II) (NiO, JCPDS card: 00-044-1159) were also produced. When the pH is 12 (Comparative Example 25), in addition to La (Fe, Ni) O ₃ , La (OH) ₃ (JCPDS card: 01-077-3934), non-mixture of iron hydroxide and nickel hydroxide A crystalline phase was also produced.

The TEM observation was measured particle size of the La (Fe, Ni) _{O 3} of Examples 14-16. La (Fe, Ni) O ₃ of Examples 14 to 16 had a cubic shape and a particle size of 30 to 50 nm. Further, the composition analysis of the particles of La (Fe, Ni) O ₃ revealed that the La / (Fe + Ni) atomic ratio was 0.8 to 1.1 and the Fe / Ni atomic ratio was 0.9 to 1.1.

Comparing Example 14 and Example 7, Example 15 and Example 8, and Example 16 and Example 9, which have the same synthesis conditions except whether or not the raw material aqueous solution contains Ni, they contain Ni. In Examples 14, 15 and 16, the particle size of the perovskite-type composite oxide particles is significantly reduced. From this, it can be said that substituting Ni with a part of Fe is effective in reducing the particle size of the particles. This tendency to reduce the particle size was the same even when the Fe / Ni atomic ratios were 0.25 and 0.75.

(Example 17)
Supercritical hydrothermal synthesis was carried out in a flow reactor using the same raw material aqueous solution as in Example 15. A reactor system having the configuration shown in FIG. 2 was configured. The raw material aqueous solution is supplied into a pipe pressurized to a pressure higher than the critical pressure of the reactor while stirring, and supercritical water heated to a critical point or higher is merged in the pressurized pipe to combine a mixed aqueous solution of lantern and iron. The water inside was instantly put into a supercritical state. The time to pass through the hydrothermal reaction pipe after merging is the time to maintain the supercritical state, which is determined by the length and flow velocity of the hydrothermal reaction pipe. _{La (Fe, Ni) O 3} was obtained as a result of conducting a synthesis experiment with the transport speed of the mixed aqueous solution being 2 mL / min, the transport speed of the heated water being 10 mL / min, and the pipe length of the pipe for hydrothermal reaction being 40 cm. ..

TEM observation was performed results, obtained La (Fe, Ni) _{O 3} is a cubic shape, a particle size of 10 to 40 nm. As a result of EDS composition analysis, the La / Fe atomic ratio was 0.9 to 1.1.

Thus, even when a flow reactor, as in the case of using a batch-type reactor, by suppressing the formation of by-products in the supercritical hydrothermal synthesis La (Fe, Ni) O ₃ efficiency It turned out that it can be synthesized well. _{Moreover, La (Fe, Ni) O} 3 were synthesized using the flow reactor was very fine particles and the particle size 10 to 40 nm. It is considered that fine particles were obtained because the reaction time was as short as 1.8 seconds and rapid heating and rapid cooling were realized.

[Synthesis of La (Fe, Mn) O _3]
(Examples 18 to 20, Comparative Examples 26 to 27)
Lanthanum nitrate _{(La (NO 3) 3 ·} 6H 2 O, 99% purity, manufactured by Kanto Kagaku) was dissolved in distilled water to prepare an aqueous solution of 0.1M lanthanum. Moreover, iron nitrate _{(Fe (NO 3) 3 ·} 9H 2 O, 99% purity, manufactured by Kanto Kagaku) was dissolved in distilled water to prepare an aqueous solution of iron 0.1 M. Further, manganese nitrate _{(Mn (NO 3) 2 ·} 6H 2 O, 98% purity, manufactured by Kanto Kagaku) was diluted in distilled water to prepare an aqueous solution of 0.1M manganese. These aqueous solutions were mixed at a ratio of lantern: iron: manganese molar ratio of 2: 1: 1. Then, while vigorously stirring this aqueous solution, a 5 M aqueous potassium hydroxide solution was added dropwise until the pH reached a predetermined pH to obtain a raw material aqueous solution. Powders were prepared and analyzed in the same manner as in Example 1 except for the raw material aqueous solution.

Table 3 shows the pH of each of the raw material aqueous solutions of Examples 18 to 20 and Comparative Examples 26 to 27, the pressure in the metal container (MPa), the set temperature of the electric furnace (° C.), and the reaction time (minutes). Also shows the particle size of Examples 18 to 20 and Comparative Examples 26-27 La as measured from each of the product phase and TEM images (Fe, Mn) _{O 3.}

X-ray diffraction measurements of the powders obtained in Examples 18 to 20 and Comparative Examples 26 to 27 were performed. When the pH of the raw material aqueous solution was 6 to 11 (Examples 18 to 20), La (Fe, Mn) O ₃ was produced. On the other hand, when the pH is 4 (Comparative Example 26), in addition to La (Fe, Mn) O ₃ , La ₂ (OH) _5.1 (NO ₃ ) _0.9 (JCPDS card: 00-026- 1145), iron (III) oxide (Fe ₂ O ₃ , JCPDS card: 01-076-8403), and manganese oxide (Mn ₂ O ₃ , Mn O) were also produced. When the pH is 12 (Comparative Example 27), in addition to La (Fe, Mn) O ₃ , La (OH) ₃ (JCPDS card: 01-077-3934), non-mixture of iron hydroxide and manganese hydroxide A crystalline phase was also produced.

Was measured La (Fe, Mn) the particle size of _{O 3} in Examples 18 to 20 by TEM observation. La (Fe, Mn) O ₃ of Examples 18 to 20 were all single crystals and had a particle size of 200 to 500 nm. Further, the composition analysis of the particles of La (Fe, Mn) O ₃ revealed that the La / (Fe + Mn) atomic ratio was 0.7 to 1.1 and the Fe / Mn atomic ratio was 0.9 to 1.1.

Comparing Example 18 and Example 7, Example 19 and Example 8, and Example 20 and Example 9, which have the same synthesis conditions except whether or not the raw material aqueous solution contains Mn, they contain Mn. In Examples 18, 19 and 20, the surface irregularities of the perovskite-type composite oxide are large. From this, it can be said that substituting Mn with a part of Fe is effective in increasing the surface area. This tendency of increasing the surface area was the same even when the Fe / Mn atomic ratios were 0.25 and 0.75.

(Example 21)
Supercritical hydrothermal synthesis was carried out in a flow reactor using the same raw material aqueous solution as in Example 19. A reactor system having the configuration shown in FIG. 2 was configured. The raw material aqueous solution is supplied into a pipe pressurized to a pressure higher than the critical pressure of the reactor while stirring, and supercritical water heated to a critical point or higher is merged in the pressurized pipe to combine a mixed aqueous solution of lantern and iron. The water inside was instantly put into a supercritical state. The time to pass through the hydrothermal reaction pipe after merging is the time to maintain the supercritical state, which is determined by the length and flow velocity of the hydrothermal reaction pipe. The conveying speed of the mixed aqueous solution 2 mL / min, a transporting speed of the heated water 10 mL / min, a result of the pipe length of piping for hydrothermal reaction was conducted synthesis experiment as 40cm, La (Fe, Mn) O 3 is a single-phase Obtained.

As a result of TEM observation, the obtained La (Fe, Mn) O ₃ was a single crystal particle having a particle size of 10 to 30 nm. As a result of EDS composition analysis, the La / Mn atomic ratio was 0.9 to 1.1, and the Fe / Mn atomic ratio was 0.9 to 1.1. Further, the surface of the obtained particles similar to the result of Example 18 was particles having large irregularities and a large surface area.

Thus, even when a flow reactor, as in the case of using the batch reactor, La by suppressing the formation of by-products in the supercritical hydrothermal synthesis (Fe, Mn) O ₃ efficiency It turned out that it can be synthesized well. _{Moreover, La (Fe, Mn) O} 3 were synthesized using the flow reactor was very fine particles and the particle size 10 to 30 nm. It is considered that fine particles were obtained because the reaction time was as short as 1.8 seconds and rapid heating and rapid cooling were realized.

[Synthesis of _{LaAlO 3]}
(Examples 22 to 24, Comparative Examples 28 to 34)
In Examples 22 to 24 and Comparative Examples 28 to 34, aluminum nitrate _{(Al (NO 3) 3 ·} 9H 2 O, 98% purity instead of iron nitrate _{(Fe (NO 3) 3 ·} 9H 2 O), Kanto Chemical The powder was prepared and analyzed in the same manner as in Examples 1 to 3 and Comparative Examples 1 to 7, except that (manufactured by) was used.

Table 4 shows the pH of each of the raw material aqueous solutions of Examples 22 to 24 and Comparative Examples 28 to 34, the pressure in the metal container (MPa), the set temperature of the electric furnace (° C.), and the reaction time (minutes). Also shows the particle size of Examples 22 to 24 and Comparative Examples 28 to 34 LaAlO ₃ was measured from each of the product phase and TEM images.

When the reaction temperature was 430 ° C. and the pH of the raw material aqueous solution was 6 to 11 (Examples 22 to 24), LaAlO ₃ (JCPDS card: 01-070-4115) was produced. On the other hand, when the reaction temperature is 430 ° C. and the pH is 4 (Comparative Example 28), La ₂ (OH) _5.1 (NO _{3 ) 0.9} (JCPDS card: 00-026) in _{addition to LaAlO 3.} -1145) and aluminum oxide (Al ₂ O ₃ ) were also produced. When the pH was 12 (Comparative Example 29), La (OH) ₃ (JCPDS card: 01-077-3934) and an amorphous phase presumed to be aluminum hydroxide were produced in _{addition to LaAlO 3.}

The particle size _{of LaAlO 3} of Examples 22 to 24 was measured by TEM observation. _{LaAlO 3} of Example 22 was a single crystal particle having a particle size of 40 to 100 nm. _{LaAlO 3} of Example 23 was a single crystal particle having a particle size of 150 to 800 nm. _{LaAlO 3} of Example 24 was a single crystal particle having a particle size of 400 to 800 nm. As a result of EDS composition analysis, the La / Al atomic ratio was 0.8 to 1.2.

On the other hand, in Comparative Examples 30 to 34 having a reaction temperature of 410 ° C., LaAlO ₃ could not be obtained at any pH. This is probably because the reaction temperature is low.

When the pH of the raw material aqueous solution was 6 to 11 (Comparative Examples 31 to 33), lanthanum oxide (LaOOH, JCPDS card: 01-077-2349) and aluminum oxide (Al ₂ O ₃ ) were produced. On the other hand, when the pH is 4 (Comparative Example 30), La ₂ (OH) _5.1 (NO ₃ ) _0.9 (JCPDS card: 00-026-1145) and aluminum oxide (Al ₂ O ₃ ) are used. Generated. When the pH was 12 (Comparative Example 34), La (OH) ₃ (JCPDS card: 01-077-3934) and an amorphous phase presumed to be aluminum hydroxide were produced.

Comparative Example 30, Comparative Example 31, Comparative Example 32, Comparative Example 33 and Comparative Example 34 use the same raw material aqueous solutions as in Comparative Example 28, Example 22, Example 23, Example 24 and Comparative Example 29, respectively. Compared to them, the set temperature of the electric furnace is low and the reaction time is short. That is, Comparative Example 30, Comparative Example 31, Comparative Example 32, Comparative Example 33, and Comparative Example 34 are elevated in the reactions of Comparative Example 28, Example 22, Example 23, Example 24, and Comparative Example 29, respectively. It corresponds to the one completed by quenching the reaction at 410 ° C. in the middle of warming. That is, the products obtained in Comparative Example 30, Comparative Example 31, Comparative Example 32, Comparative Example 33 and Comparative Example 34 are the corresponding Comparative Example 28, Example 22, Example 23, Example 24 and Comparative Example 29. It is considered to correspond to the intermediate product of.

Results of Comparative Example 31, Comparative Example 32 and Comparative Example 33, Example 22, when the results of Example 23 and Example 24 versus discussed, generation mechanism of LaAlO ₃ of Example 22 to 24, first intermediate It is considered that lanthanum oxide is produced as a product, and then LaAlO _{3 is produced by further raising the temperature.}

[Synthesis of _{LaMnO 3]}
(Examples 25 to 27, Comparative Examples 35 to 41)
In Examples 1-3 and Comparative Examples 1-7, manganese nitrate _{(Mn (NO 3) 2 ·} 6H 2 O in place of iron nitrate _{(Fe (NO 3) 3 ·} 9H 2 O), 98% purity, Kanto Chemical The powder was prepared and analyzed in the same manner as in Examples 1 to 3 and Comparative Examples 1 to 7 except that the above was used.

Table 5 shows the pH of each of the raw material aqueous solutions of Examples 25 to 27 and Comparative Examples 35 to 41, the pressure in the metal container (MPa), the set temperature of the electric furnace (° C.), and the reaction time (minutes). Also shows the particle size of Examples 25 to 27 and Comparative Examples 35 to 41 La as measured from each of the product phase and TEM images (Fe, Mn) _{O 3.}

When the reaction temperature was 430 ° C. and the pH of the raw material aqueous solution was 6 to 11 (Examples 25 to 27), LaMnO ₃ (JCPDS card: 01-076-9086) was produced. On the other hand, when the reaction temperature is 430 ° C. and the pH is 4 (Comparative Example 35), La ₂ (OH) _5.1 (NO _{3 ) 0.9} (JCPDS card: 00-026-1145) in _{addition to LaMnO 3.} ) And manganese oxide (Mn ₂ O ₃ , Mn O) were produced. When the pH was 12 (Comparative Example 37), La (OH) ₃ (JCPDS card: 01-077-3934) and an amorphous phase presumed to be manganese hydroxide were generated in _{addition to LaMnO 3.} ..

The particle size _{of LaMnO 3} of Examples 25 to 27 was measured by TEM observation. _{LaMnO 3} of Example 25 was a single crystal particle having a particle size of 40 to 100 nm. _{LaMnO 3} of Example 26 was a single crystal particle having a particle size of 200 to 1000 nm. _{LaMnO 3} of Example 27 was a single crystal particle having a particle size of 300 to 700 nm. As a result of EDS composition analysis, the La / Mn atomic ratio was 0.8 to 1.1.

On the other hand, in Comparative Examples 37 to 41 at a reaction temperature of 410 ° C., LaMnO ₃ was not obtained at any pH. It is considered that this is because the reaction temperature is low.

When the pH of the raw material aqueous solution is 6 to 11 (Comparative Examples 38 to 40), lanthanum oxide (LaOOH, JCPDS card: 01-077-2349) and manganese oxide (Mn ₂ O ₃ , Mn O) are produced. It was. On the other hand, when the pH is 4 (Comparative Example 37), La ₂ (OH) _5.1 (NO ₃ ) _0.9 (JCPDS card: 00-026-1145) and manganese oxide (Mn ₂ O ₃ , Mn O). ) Was generated. When the pH was 12 (Comparative Example 41), La (OH) ₃ (JCPDS card: 01-077-3934) and an amorphous phase presumed to be manganese hydroxide were produced.

Comparative Example 37, Comparative Example 38, Comparative Example 39, Comparative Example 40 and Comparative Example 41 used the same raw material aqueous solutions as Comparative Example 35, Example 25, Example 26, Example 27 and Comparative Example 36, respectively. Compared to them, the set temperature of the electric furnace is low and the reaction time is short. That is, Comparative Example 37, Comparative Example 38, Comparative Example 39, Comparative Example 40, and Comparative Example 41 were elevated in the reactions of Comparative Example 35, Example 25, Example 26, Example 27, and Comparative Example 36, respectively. It corresponds to the one completed by quenching the reaction at 410 ° C. in the middle of warming. That is, the products obtained in Comparative Example 37, Comparative Example 38, Comparative Example 39, Comparative Example 40 and Comparative Example 41 are the corresponding Comparative Example 35, Example 25, Example 26, Example 27 and Comparative Example 36. It is considered to correspond to the intermediate product of.

When the results of Comparative Example 38, Comparative Example 39 and Comparative Example 40 are compared with the results of Examples 25, 26 and 27, the LaMnO ₃ production mechanism of Examples 25 to 27 is first intermediate. It is considered that lanthanum oxide is produced as a product, and then LaMnO _{3 is produced by further raising the temperature.}

[Synthesis of (La, Sr) FeO _3]
(Example 28, Comparative Example 42)
Lanthanum nitrate _{(La (NO 3) 3 ·} 6H 2 O, 99% purity, manufactured by Kanto Kagaku) was dissolved in distilled water to prepare an aqueous solution of 0.1M lanthanum. Further, strontium nitrate (Sr (NO ₃ ) ₂ ) was dissolved in distilled water to prepare a 0.1 M strontium aqueous solution. Furthermore, iron nitrate _{(Fe (NO 3) 3 ·} 9H 2 O, 99% purity, manufactured by Kanto Kagaku) was dissolved in distilled water to prepare an aqueous solution of iron 0.1 M. These aqueous solutions were mixed at a ratio of lanthanum: strontium: iron in a molar ratio of 0.6: 0.4: 1. Then, while vigorously stirring this aqueous solution, a 5 M potassium hydroxide aqueous solution was added dropwise until the predetermined pH reached 8, to obtain a raw material aqueous solution. Powders were prepared and analyzed under the same supercritical water heat conditions as in Examples 1 to 2, Comparative Examples 1 and 2, and Comparative Examples 4 to 9, respectively, except for the aqueous solution of the raw material (Example 28 and Example 28, respectively). It is referred to as Comparative Example 42).

As a result of performing X-ray diffraction measurement of the powder obtained in Example 28, an XRD pattern of a perovskite type structure was observed. Moreover, as a result of TEM observation, the obtained powder was cubic single crystal particles having a diameter of 50 to 750 nm. Furthermore, the powder obtained from the EDS local analysis contains La, Sr, Fe and O, with a La / Sr atomic ratio of 0.8 to 1.1 and a (La + Sr) / Fe atomic ratio of 0.8. It was ~ 1.1.

As a result of performing X-ray diffraction measurement of the powder obtained in Comparative Example 42, the XRD pattern of the perovskite type structure was not observed. On the other hand, the XRD pattern of lanthanum oxide (LaOOH) was observed, and compounds containing other La such as _{La 2} (OH) _5.1 (NO ₃ ) _0.9 and La (OH) _{3 were not observed.} .. From this, it was confirmed that lanthanum oxyhydroxide was used as an intermediate product when synthesizing a perovskite compound in which a part of La at the A site was replaced with Sr.

Single-use reactor 11 Pressure-resistant container 12 Heater 2 Flow reactor system 21 Distilled water supply piping 22 Raw material aqueous solution supply piping 23 Hydrothermal reaction piping 24a, 24b Heater 25 Cooler 26 Pressure reducing valve (discharge part)

Claims (6)

A method for producing a perovskite-type composite oxide having a composition represented by the chemical formulas LaFeO ₃ , La (Fe, Ni) O ₃ , La (Fe, Mn) O ₃ , LaAlO ₃ , or LaMnO _3.
A raw material aqueous solution containing a raw material metal ion having a pH of 5 or more and 11.5 or less is heated at 425 ° C or more and 650 ° C or less and pressurized at 22 MPa or more and 60 MPa or less to bring it into a supercritical state, and the raw material aqueous solution is subjected to hydrothermal treatment. A method for producing a perovskite-type composite oxide. The method for producing a perovskite-type composite oxide according to claim 1, wherein the pH of the raw material aqueous solution is 6 or more and 11 or less. The method for producing a perovskite-type composite oxide according to claim 1 or 2 , wherein lanthanum oxyhydroxide (LaOOH) is used as a reaction intermediate. The method for producing a perovskite-type composite oxide according to any one of claims 1 to 3 , wherein the perovskite-type composite oxide is particles having an average particle size of 1000 nm or less. The method for producing a perovskite-type composite oxide according to any one of claims 1 to 4 , wherein the aqueous solution of the raw material is subjected to hydrothermal treatment in a batch reactor. The method for producing a perovskite-type composite oxide according to any one of claims 1 to 4 , wherein the aqueous solution of the raw material is subjected to hydrothermal treatment in a flow reactor.

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