JP6941315B2 - Method for producing perovskite-type composite oxide - Google Patents

Description

The present invention relates to a method capable of easily producing a highly active perovskite-type composite oxide having a large specific surface area.

Some perovskite-type composite oxides exhibit very useful properties such as high catalytic activity, high dielectric constant, low dielectric loss, and superconducting properties. Moreover, since the perovskite-type composite oxide has a dense crystal structure and is excellent in heat resistance and conductivity, it is useful as an industrial material such as a catalyst, a piezoelectric material, a ferroelectric substance, and a magnetic material.

The perovskite-type composite oxide was once produced by mixing powders of each oxide and then firing at a high temperature of 1000 ° C. or higher. However, after firing at a high temperature, there is a problem that the specific surface area decreases due to the growth and binding of particles, and the catalytic activity and the like decrease. Therefore, a citric acid complex method has been developed in which a solution of nitrate and citric acid of each constituent metal element is prepared and the citric acid complex obtained from the solution is fired at a relatively low temperature of 700 ° C.

However, the citric acid complex method has a problem that the concentration of each component in the citric acid complex solution is extremely low, it takes a long time to evaporate the solvent and take out the solid content, and the composition uniformity is low. Therefore, in the invention of Patent Document 1, a salt of each constituent metal is mixed with ethylene glycol or the like, and the mixture is dried and then fired. According to the present invention, a perovskite-type composite oxide having a specific surface area of 12 m ² / g and 11 m ^{2 / g can be produced at a relatively low firing temperature.}

Further, although Patent Document 2 does not describe the specific surface area, the citrate complex is intended to improve the dispersity of the noble metal element in the composite oxide and improve the catalytic activity and adsorption activity of the perovskite-type composite oxide. Is described to be fired at a temperature of 700 to 950 ° C. after being heated in a vacuum or an inert gas.

As an invention for producing a perovskite-type composite oxide having a high specific surface area, Patent Document 3 states that the precursor slurry is wet-ground until its average particle size is 1.0 μm or less, and the specific surface area is about 30 m. It has been shown that perovskite-type composite oxides up to ^{2 / g can be produced.}

Further, although increasing the specific surface area is not an issue, Patent Document 4 states that the pH of a suspension containing a hydroxide or hydrate obtained by adding a salt of each constituent metal to an alkaline aqueous solution. The invention describes the invention of producing fine perovskite-type composite oxide particles having an average particle diameter of 5 nm or more and 50 nm by performing hydrothermal treatment after preparing the above.

In Patent Document 5, in order to produce a perovskite-type composite oxide powder in which the variation in the primary particle size is reduced, maleic acid, tartaric acid, 1, 2, 3, 4 are added to a slurry of a compound containing each constituent metal element. It is described that an organic acid having an even number of carboxy groups and all carboxy groups being paired, such as butanetetracarboxylic acid, or an acid anhydride thereof is added.

Japanese Unexamined Patent Publication No. 4-254419 Japanese Unexamined Patent Publication No. 6-100319 Japanese Unexamined Patent Publication No. 2014-118330 JP-A-2007-84390 JP-A-2015-166302

As described above, techniques for producing a perovskite-type composite oxide having a high specific surface area have been developed. However, the specific surface area obtained by the invention of Patent Document 1 is insufficient, and there is room for improvement. Further, in the invention of Patent Document 3, ^{a perovskite-type composite oxide having a high specific surface area of about 30 m 2} / g is produced, but the average particle size of the solid content contained in the precursor slurry is 1.0 μm or less. Must be wet ground to. In this way, crushing to the nanometer level requires a great deal of energy and time, and the finer the crushing, the greater the van der Waals force between the particles and the aggregation, so the use of a surfactant is also necessary. It will be. If a surfactant is contained in the slurry, extra energy and time are required for drying and firing the precursor, and the overall production efficiency is lowered. In addition, the citric acid complex method using nitrate as a raw material has a problem that it takes time and effort to prepare a citric acid complex.

Therefore, an object of the present invention is to provide a method capable of easily producing a highly active perovskite-type composite oxide having a large specific surface area.

The present inventors have conducted intensive studies to solve the above problems. As a result, by adding a specific dicarboxylic acid compound to the solution of the raw material compound instead of citric acid conventionally used as an additive to the precursor, the precursor slurry is not finely pulverized. The present invention has been completed by finding that a perovskite-type composite oxide having a large specific surface area can be easily produced.
Hereinafter, the present invention will be shown.

[1] A method for producing a perovskite-type composite oxide.
A step of dissolving at least a metal compound containing each metal element component constituting the perovskite type composite oxide and a dicarboxylic acid compound having a hydroxyl group and / or an amino group in the molecule in a solvent to obtain a solution.
A step of preparing a precursor of the perovskite-type composite oxide from the solution, and
A method comprising a step of calcining the precursor to obtain the perovskite-type composite oxide.

[2] The method according to the above [1], wherein the precursor is heat-treated at 500 ° C. or higher and lower than 650 ° C.

[3] The method according to the above [1] or [2], wherein the dicarboxylic acid compound is malic acid and / or aspartic acid.

[4] The above-mentioned [1] to [3], wherein the metal compound is at least one selected from hydroxides, oxyhydroxides, carbonates, phosphates and organic acid salts. Method.

[5] The perovskite-type composite oxide represents _{at least one element selected from the general formula ABO 3-x} (in the formula, A is a rare earth element and an alkaline earth metal element; B is manganese, iron, cobalt). , At least one element selected from the group consisting of nickel, copper, ruthenium, rhodium, palladium, iridium, platinum and titanium; 0≤x≤0.5). 1] The method according to any one of [4].

According to the method of the present invention, a perovskite-type composite oxide can be easily produced without performing a treatment requiring high energy such as finely pulverizing the solid content of the raw material metal compound or the precursor slurry. Moreover, the specific surface area of the perovskite-type composite oxide produced by the method of the present invention is large. Therefore, the present invention is industrially excellent as a technique capable of efficiently producing a perovskite-type composite oxide having excellent various properties.

Hereinafter, a method for producing a perovskite-type composite oxide according to the present invention will be described for each step.

1. 1. Preparation step of precursor solution In this step, at least a metal compound containing each metal element component constituting the perovskite type composite oxide and a dicarboxylic acid compound having a hydroxyl group and / or an amino group in the molecule are dissolved in a solvent. To obtain the solution.

The perovskite-type composite oxide is a composite oxide having a crystal structure similar to that of _{perovskite CaTIO 3,} and is represented by the _{general formula ABO 3-x.} The metal elements constituting the A site are alkaline earth metal elements selected from calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra); lanthanum (La), cerium (Ce), and placeodium. (Pr), Neogym (Nd), Samarium (Sm), Europium (Eu), Gadrinium (Gd), Disprosium (Dy), Holmium (Ho), Elbium (Er), Tulum (Tm), Itterbium (Yb), Rutetium Rare earth metal elements such as (Lu); at least one metal element selected from other metal elements such as magnesium (Mg), scandium (Sc), ittrium (Y), and preferably alkaline earth metals. At least one metallic element selected from.

The metal elements constituting the B site include chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), niobium (Nb), molybdenum (Mo), and the like. Selected from the group consisting of ruthenium (Ru), rhodium (Rh), palladium (Pd), antimony (Sb), iridium (Ir), platinum (Pt), titanium (Ti), lead (Pb), and bismuth (Bi). At least one metal element selected from the group consisting of manganese, iron, cobalt, nickel, copper, ruthenium, rhodium, palladium, iridium, platinum and titanium is preferable. ..

In the above formula, x indicates an oxygen defect, and is usually 0 ≦ x ≦ 0.5, preferably 0 ≦ x ≦ 0.2.

One of the features of the method of the present invention is that a metal compound containing each metal element component constituting the perovskite-type composite oxide, which is the target compound, is dissolved in a solvent to prepare a solution. Therefore, as the raw material metal compound, a compound containing each metal element component and soluble in a solvent is selected. Examples of such raw material metal compounds include simple metals, oxides, alkoxides, chlorides, hydroxides, oxyhydroxides, carbonate sulfates, nitrates, phosphates and organic acid salts. At least one selected from hydroxides, oxyhydroxides, carbonates, phosphates and organic acid salts is preferable because complex formation with the dicarboxylic acid compound used in the above is facilitated. Examples of the organic acid salt include formic acid salt, acetate, oxalate and the like.

The amount of each metal compound used is adjusted according to the molar ratio of each metal in the target perovskite-type composite oxide.

In the present invention, a dicarboxylic acid compound having a hydroxyl group and / or an amino group and two carboxy groups in the molecule is also dissolved in the solution of the raw material metal compound. Although the action and effect of the dicarboxylic acid compound are not always clear, a perovskite-type composite oxide precursor that is easily fired at a relatively low temperature is formed by forming a complex with each metal ion generated by dissolving the raw material metal compound. It is thought that.

The number of hydroxyl groups and amino groups in the dicarboxylic acid compound is not particularly limited and may be appropriately selected, but the dicarboxylic acid compound preferably has one hydroxyl group or one amino group in the molecule. Further, as the dicarboxylic acid compound, only one kind may be used, or two or more kinds may be used in combination. Further, in order to improve the water solubility, an alkali metal salt such as a sodium salt or a potassium salt may be used as the dicarboxylic acid compound.

Examples of the dicarboxylic acid compound include malic acid, hydroxycyclohexanedicarboxylic acid, 2-hydroxy-2-butendicarboxylic acid, and hydroxyterephthalic acid as those having one hydroxyl group, and those having one amino group. , Aspartic acid, glutamate, pyrrolidinedicarboxylic acid, imidazoledicarboxylic acid. As the dicarboxylic acid compound, malic acid and / or aspartic acid is preferable.

The amount of the dicarboxylic acid compound used may be appropriately adjusted, but for example, it is preferably 60 parts by mass or more and 120 parts by mass or less with respect to 100 parts by mass of the metal compound. If the ratio is too small, the specific surface area of the perovskite-type composite oxide obtained due to insufficient complex formation between the dicarboxylic acid compound and the metal may be reduced. On the other hand, if the ratio is too large, the amount of organic matter increases during the firing of the precursor, and it becomes necessary to raise the firing temperature, which may reduce the specific surface area of the perovskite-type composite oxide that is also obtained. The ratio is more preferably 65 parts by mass or more, further preferably 70 parts by mass or more, further preferably 75 parts by mass or more, still more preferably 110 parts by mass or less or 100 parts by mass or less, and 95 parts by mass or less. More preferably, 90 parts by mass or less is even more preferable.

In the present invention, it is preferable to use water as the solvent. As the water, it is preferable to use water that does not contain a metal component or has a very small amount of the metal component, such as ultrapure water, pure water, distilled water, and ion-exchanged water.

When it is difficult to dissolve both the metal compound and the dicarboxylic acid compound only in water, a mixed solvent of water and a water-miscible organic solvent may be used as the solvent. The water-miscible organic solvent refers to an organic solvent that can be miscible with water indefinitely, for example, a lower alcohol solvent such as methanol, ethanol, isopropanol; a lower nitrile solvent such as acetonitrile; a lower ketone solvent such as acetone; dimethylformamide or An amide solvent such as dimethylacetamide; a sulfoxide solvent such as dimethylsulfoxide can be mentioned. When a water-miscible organic solvent is used in combination, the ratio of the water-miscible organic solvent to the mixed solvent with water is preferably 50% by mass or less, preferably 40% by mass or less, 30% by mass or less, or 20% by mass or less. More preferably, 10% by mass or less or 5% by mass or less is even more preferable.

The amount of the solvent used may be appropriately adjusted within a range in which the metal compound and the dicarboxylic acid compound can be sufficiently dissolved. For example, the total concentration of the metal compound and the dicarboxylic acid compound in the solution is 2% by mass or more and 20% by mass. % Or less is preferable. If the concentration is too low, excessive energy may be required to remove the solvent. On the other hand, if the concentration is too high, both the metal compound and the dicarboxylic acid compound may not be sufficiently dissolved, resulting in insufficient complex formation, and the specific surface area of the perovskite-type composite oxide obtained may be reduced. obtain. The concentration is more preferably 4% by mass or more or 5% by mass or more, further preferably 6% by mass or more or 7% by mass or more, still more preferably 15% by mass or less, still more preferably 10% by mass or less.

In addition to the metal compound and the dicarboxylic acid compound, components for promoting complex formation and firing may be added and dissolved in the above solution.

In order to prepare a solution, the above metal compound, the above dicarboxylic acid compound and a solvent may be mixed. In order to increase the mixing efficiency, the mixture may be stirred or heated at about 40 ° C. or higher and 60 ° C. or lower. Alternatively, the pH may be adjusted by adding an acid or a base. As the acid or base for adjusting the pH, it is preferable to use one that does not contain a metal element that constitutes a perovskite-type composite oxide.

2. Precursor Preparation Step In this step, a precursor of the perovskite-type composite oxide, which is the target compound, is prepared from the obtained metal compound / dicarboxylic acid compound solution. Generally, when preparing a precursor of a perovskite-type composite oxide from a solution of each constituent metal element component, a coprecipitation method, a sol-gel method, or the like is used. However, especially in the coprecipitation method, it is difficult to control the composition due to the difference in the solubility of each constituent metal element component, and a homogeneous precursor may not be obtained in some cases. Therefore, in the present invention as well, a known method such as the coprecipitation method or the sol-gel method may be used for the preparation of the precursor, but for each metal in the perovskite type composite oxide for the purpose of using each metal compound. It is preferred to prepare a completely amorphous precursor by adjusting according to the molar ratio and directly concentrating and drying the resulting solution. The method of directly concentrating and drying the solution to obtain a precursor can also be understood as a kind of sol-gel method.

The method for concentrating and drying the solution is not particularly limited, and a known method may be used. For example, the solvent may be distilled off by heating, and at that time, the pressure may be reduced to suppress the temperature and improve the efficiency. Further, for energy saving, a spray drying method or a thin film drying method may be used.

3. 3. Firing step In this step, the perovskite-type composite oxide, which is the target compound, is obtained by calcining the precursor. Since the precursor obtained in the present invention is completely amorphous, it can be calcined at a relatively low temperature, and a perovskite-type composite oxide having a high specific surface area can be obtained.

The specific firing temperature may be appropriately adjusted within the range in which a perovskite-type composite oxide can be obtained, and can be, for example, 500 ° C. or higher and lower than 650 ° C. The temperature is more preferably 550 ° C. or higher, more preferably 620 ° C. or lower, and even more preferably 600 ° C. or lower.

4. Perovskite-type composite oxide The perovskite-type composite oxide produced by the method of the present invention is obtained by firing at a relatively low temperature, and therefore has a large specific surface area and high performance. The specific surface area, for example, at 30 m ² / g or more, more preferably at least 40 m ² / g, more 45 m ² / g is more preferred. The upper limit of the specific surface area is not particularly limited, but if it is excessively large, the strength may not be sufficient, so 100 m ² / g or less is more preferable.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited by the following examples as well as the present invention, and appropriate modifications are made to the extent that it can be adapted to the gist of the above and the following. Of course, it is possible to carry out, and all of them are included in the technical scope of the present invention.
First, a method for evaluating the produced composite oxide will be described.

Test Example 1: Measurement of specific surface area The produced perovskite-type composite oxide sample was placed in a measurement cell and pretreated at 150 ° C. for 1 hour under reduced pressure. Next, using a fully automatic specific surface area measuring device (model "Nova-4200e" manufactured by Kantachrome Co., Ltd.), the temperature was maintained at the liquid nitrogen temperature in a nitrogen gas stream, and the adsorption isotherm was measured. The specific surface area was calculated using the BET adsorption isotherm when the parallel relative pressure P / P _{0 of the adsorbed gas was in the range of 0.05 to 0.30.}

Test Example 2: Powder X-ray Diffraction Measurement The manufactured perovskite type composite oxide sample is crushed in a mortar, and the obtained powder is filled in a sample plate to be filled with a powder X-ray diffractometer (model "Ultima IV" manufactured by Rigaku Co., Ltd.). ) Was used for powder X-ray diffraction measurement. The measurement conditions are as follows.
Radioactive source: CuKα Operating axis: 2θ / θ
Measurement type: Continuous voltage: 40 kV
Current: 40mA Start angle: 10 °
End angle: 80 ° Sampling width: 0.02 °
Scan speed: 20 ° / min

Example 1
Strontium acetate 0.5 hydrate (5.64 g), manganese acetate tetrahydrate (6.44 g), and L-aspartic acid (10.48 g) are dissolved in ion-exchanged water (250 mL) and then rotary. The powder was obtained by drying at 70 ° C. for about 1 hour using an evaporator. Further, the powder obtained to remove other components such as acetic acid was dried at 190 ° C. for 1 hour to obtain a precursor. When the obtained precursor was subjected to powder X-ray diffraction measurement, no peak derived from crystals was confirmed, and it was amorphous. Subsequently, the precursor was calcined at 550 ° C. for 5 hours in an air atmosphere to obtain a composite oxide. The obtained composite oxide was Sr46.08% and Mn27.33% by elemental analysis, and was identified as a perovskite-type composite oxide crystal of _{SrMnO 3 by X-ray diffraction analysis.} Further, the specific surface area was 47 m ² / g.

Example 2
A composite oxide was obtained in the same manner as in Example 1 above except that L-aspartic acid was changed to malic acid (10.56 g). The obtained composite oxide was Sr48.33% and Mn28.82% by elemental analysis, and was identified as a perovskite-type composite oxide crystal of _{SrMnO 3 by X-ray diffraction analysis.} Further, the specific surface area was 42 m ² / g.

Example 3
After dissolving barium acetate (6.71 g), manganese acetate tetrahydrate (6.44 g), and malic acid (10.56 g) in ion-exchanged water (250 mL), use a rotary evaporator at about 70 ° C. It was dried for 1 hour to obtain a powder. Further, the powder obtained to remove other components such as acetic acid was dried at 190 ° C. for 1 hour to obtain a precursor. When the obtained precursor was subjected to powder X-ray diffraction measurement, no peak derived from crystals was confirmed, and it was amorphous. Subsequently, the precursor was calcined at 500 ° C. for 5 hours in an air atmosphere to obtain a composite oxide. The obtained composite oxide was Ba56.49% and Mn21.93% by elemental analysis, and was identified as a perovskite-type composite oxide crystal of _{BaMnO 3 by X-ray diffraction analysis.} Further, the specific surface area was 30 m ² / g.

Comparative Example 1
A composite oxide was produced in the same manner except that L-aspartic acid was changed to citric acid (10.08 g) in Example 1. When the obtained composite oxide was subjected to X-ray diffraction analysis, it was identified as a mixed crystal of _{SrmnO 3} and SrCO _{3 which are perovskite-type composite oxides.}

As described above, it was clarified that when citric acid was used, the perovskite type composite oxide could not be satisfactorily produced at a relatively low firing temperature of 550 ° C. The specific surface area of the oxide was 27 m ² / g.

Comparative Example 2
A composite oxide was obtained in the same manner except that the firing temperature was changed to 650 ° C. in Comparative Example 1. The obtained composite oxide was Sr45.10% and Mn29.06% by elemental analysis, and was identified as a perovskite-type composite oxide crystal of _{SrMnO 3 by X-ray diffraction analysis.} Furthermore, the specific surface area was 18 m ² / g.

As shown in this result, when citric acid was used, the firing temperature had to be relatively high in order to obtain a perovskite-type composite oxide, and therefore only crystals having a small specific surface area could be obtained.

Comparative Example 3
Strontium nitrate (22.12 g), manganese nitrate hexahydrate (2.87 g), and citric acid (15.4 g) were dissolved in ion-exchanged water (50 mL). Next, ethylene glycol (25.0 mL) was added and stirred to obtain a pale yellow transparent solution. Using an evaporator, the solution was concentrated at 60 ° C. to obtain a yellow transparent solution. Using a hot stirrer, the obtained solution was gradually heated to 190 ° C. with stirring to obtain a dark brown gel. Further, the powder was obtained by heating to 250 ° C. and then 300 ° C. for thermal decomposition. The powder obtained using an automatic mortar was crushed for 1 hour and then baked at 650 ° C. The powder after firing was washed with water and then vacuum dried to obtain a composite oxide. The obtained composite oxide was Sr45.25% and Mn27.65% by elemental analysis, and was identified as a perovskite-type composite oxide crystal of _{SrMnO 3 by X-ray diffraction analysis.} Further, the specific surface area was 25 m ² / g.

As shown in the above results, a perovskite-type composite oxide crystal having a relatively large specific surface area could be obtained even at a firing temperature of 650 ° C. by a conventional method using citric acid and nitrate as a starting material compound. However, in the above-mentioned conventional method, a complicated operation is required for forming the citric acid complex as described above.

Comparative Example 4
Strontium carbonate (2.95 g) and manganese oxide (1.42 g) were mixed in an alumina mortar, then ethanol was added and wet mixed to obtain a precursor. The obtained precursor was calcined at 1300 ° C. for 5 hours to obtain a composite oxide. The obtained composite oxide was identified as a perovskite-type composite oxide crystal of _{BaMnO 3} by X-ray diffraction analysis. Furthermore, the specific surface area was 2 m ² / g. As described above, when a specific dicarboxylic acid is not used, the production of the perovskite-type composite oxide requires a calcination treatment at a high temperature, and only a product having a small specific surface area can be obtained.

Claims (6)

A method for producing a perovskite-type composite oxide.
At least, to obtain an organic acid salt containing the respective metal element component constituting the perovskite-type composite oxide, a solution dissolved in a solvent and a dicarboxylic acid compound having an amino group in the molecule,
A step of preparing a precursor of the perovskite-type composite oxide from the solution, and
Method characterized by comprising the step of obtaining the perovskite complex oxide form shrink the precursor. The method according to claim 1, wherein the precursor is heat-treated at 500 ° C. or higher and lower than 650 ° C. The method according to claim 1 or 2 , wherein the dicarboxylic acid compound of 60 parts by mass or more and 120 parts by mass or less is used with respect to 100 parts by mass of the organic acid salt. The method according to any one of claims 1 to 3 which is the dicarboxylic acid compound there aspartate. The method according to any one of claims 1 to 4 , wherein the organic acid salt is at least one selected from formic acid salt, acetate and oxalate. The perovskite-type composite oxide represents _{at least one element selected from the general formula ABO 3-x} (in the formula, A is a rare earth element and an alkaline earth metal element; B is manganese, iron, cobalt, nickel, Claims 1 to 5 which represent at least one element selected from the group consisting of copper, ruthenium, rhodium, palladium, iridium, platinum and titanium; 0≤x≤0.5). The method described in any of.