JPH0818841B2 - Method for producing complex oxide precursor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a precursor having high catalytic activity as a combustion catalyst and capable of producing composite perovskite type oxide fine particles at a relatively low temperature at a relatively low cost.

[0002]

2. Description of the Related Art La-Sr-Co based perovskite oxides have high oxidation catalytic performance comparable to noble metals such as Pt and Pd, and are excellent in heat resistance as compared with these noble metals, and are therefore expected as high temperature combustion catalyst materials. ing. However, in the classical solid-phase reaction method in which each single-component powder is mixed and baked, the target perovskite phase is not generated unless it is baked at a high temperature of 1000 ° C. or higher, and as a result, the specific surface area decreases and There was a problem that a good catalytic activity could not be obtained. As a method that can solve this, a method of passing through a liquid phase such as a coprecipitation method or a sol-gel method is considered to be advantageous, and recently, as a method of obtaining an active powder that can be synthesized at low temperature by Yamazoe et al. The citric acid complex method has been proposed.

[0003]

However, there have been problems in the conventional method of passing through a liquid phase. That is, both the coprecipitation method in which the powder is precipitated by adjusting the pH of the solution in which each metal salt is dissolved and the sol-gel method in which each metal alkoxide is hydrolyzed have different precipitation conditions and hydrolysis conditions for each component. The homogeneity of the powder used in the strict sense is not achieved, and it is difficult to obtain a perovskite with a high specific surface area that can be fired at a low temperature. Also, the latter has a high price of alkoxide, and it is doubtful whether it will be suitable for the cost performance of the catalyst material. The citric acid complex method by Yamazoe et al. Can be said to be an excellent method that can alleviate these problems, but the component concentration in the precursor solution is extremely low, and it takes a long time to evaporate the solvent and extract the solid content. However, due to the difference in the solubility of each starting material in the final concentration step, some composition segregation is unavoidable, and there is a problem in composition uniformity in a strict sense. An object of the present invention is to solve the above problems, and to provide a method capable of forming a perovskite crystal phase having excellent catalytic activity at a lower temperature and more easily producing a homogeneous precursor. .

[0004]

The present invention solves such a problem in synthesizing a perovskite type complex oxide represented by La _1-x Sr _x CoO system which exhibits high performance as an oxidation catalyst. In order to obtain a uniform precursor without segregation by dissolving each metal salt in a solvent in the presence of polyhydric alcohol as desired, active perovskite-type composite oxides can be obtained by firing at low temperature. It has been found that can be synthesized. That is, in the present invention, the A site is La, C
At least one element selected from e and Gd and the B site are Mn. A precursor of a complex perovskite type oxide represented by the general formula ABO ₃ occupied by at least one element selected from Fe, Co, Ni and Cu , or a metal element of the A site of the complex perovskite type oxide. a method of manufacturing a precursor of the following half was replaced with Sr Sr substitution composite perovskite oxide, said composite perovskite
One or more elements selected from polyhydric alcohols and polyhydric alcohol derivatives in the form of a metal salt in the form of a metal salt, and one or more of the elements constituting the tor oxide or the Sr-substituted complex perovskite oxide. or mixed, or the solvent for dissolving these
A method for producing a composite oxide precursor, which comprises mixing in the presence .

The precursor of the present invention comprises a composite perovskite type oxide (hereinafter simply referred to as ABO ₃ ) or an Sr-substituted composite perovskite type oxide (hereinafter referred to as Sr-substituted ABO) represented by ABO ₃ by firing. Say ₃ )
If the above is obtained, the details of the structure are not limited, but the metal composition of the precursor is preferably equal to the metal composition of the both oxides. The structure of Sr-substituted ABO ₃ is ABO
It is obtained by substituting one or more atoms of the A site of ₃ with Sr, and is, for example, A _1-X Sr _X
It can be represented by BO ₃ (0 <X ≦ 0.5).

The metal element constituting the A and / or B site includes one or more elemental species used as a starting material in the form of a metal salt. The salt form may be one element or more. But it can be configured. Further, the metal salt may be used for at least one of the A or B sites, but in the present invention, it is preferable that the elements constituting the A and B sites, or Sr is in the form of a salt, Particularly, nitrate is preferable. The A
The metal element of the starting material forming the B-site and / or the B-site is not limited to the salt form, and simple metals, metal alkoxides, and the like can be used within the range not deviating from the object of the present invention. For example, Sr can be used as a simple metal or as an alkoxide. Examples of the metal salt include organic acid salts such as acetates and oxalates, inorganic salts such as chlorides, sulfates and nitrates, and commonly available double salts and complex salts. These salts may be hydrated salts having structured water or anhydrous salts. In addition, the metal salt used in the present invention is easily available, has high solubility in a solvent, and can be effectively coordinated with a polyhydric alcohol, which is the greatest feature of the present invention, and can be complexed. Therefore, nitrate is most preferred.

The polyhydric alcohol and its derivative used in the present invention are not particularly limited in the structure as long as they satisfy the above-mentioned conditions, but usually, a monomer having a degree of polymerization of 1 to a polymer having several hundreds. You can choose from. As a specific example, as the dihydric alcohol, ethylene glycol, propylene glycol, trimethylene glycol,
Examples include butanediol and pentanediol, examples of trivalent alcohols include glycerin, examples of tetravalent alcohols include erythritol, examples of pentavalent alcohols include pencit, and examples of hexavalent alcohols are hexite. Etc. are used, and they are used alone or in combination. Examples of the polyhydric alcohol derivative include esterified products and etherified products, which may be partially esterified, etherified, and the like, and specific examples include the alcohol derivatives described above. For example, as the ester of the dihydric alcohol, ethylene glycol monomethyl ester, ethylene glycol monoethyl ester, propylene monoethyl ester, 1,3-butanediol monoethyl ester, etc., 2
Examples of ethers of polyhydric alcohols include monomethoxyethyl glycol, monoethoxyethyl glycol, monoethoxypropylene glycol, and monoethoxy-1,3-butanediol. Esters of trihydric alcohols include glycerin monomethyl ester, glycerin dimethyl ester, and glycerin monoester. Examples of ethers of trihydric alcohols such as ethyl ester include monomethoxyglycerin and monoethoxyglycerin, which are used alone or in combination. In the present invention, the polyhydric alcohols and polyhydric alcohol derivatives may be used alone or in combination of two kinds. In the present invention, a polyhydric alcohol having two hydroxyl groups (dihydric alcohol) and its derivative are most effective in a small amount.

In the present invention, the amount of the polyhydric alcohol and / or its derivative added depends on the number of metal atoms in the system, that is, to constitute the precursor in the reaction system for producing the precursor of the present invention. 0.1 to 30 times mol, more preferably 0.5 to 10 times, the number of all metal atoms of the metal element.
It is desirable that the molar amount is twice. In this case, if the amount is 0.1 times or less, the effect cannot be exhibited. Further, when the amount is 30 times or more, the effect is not improved, the drying property is rather deteriorated, and adverse effects due to carbon residue after firing are likely to occur.

The precursor of the present invention is a solvent that dissolves the above-mentioned metal salts and the like and polyhydric alcohols and / or their derivatives, if desired, such as water (normal water other than the structural water of the above-mentioned metal salts), organic It is formed by mixing in the presence of a solvent, but its form may be a solution state, a solution obtained by evaporating to dryness, or a case where it is calcined.

In this case, in the present invention, the solvent for dissolving the metal salt and the polyhydric alcohol and / or the derivative thereof is not essential, but the coordination and conjugation are promoted and the precursor is improved by improving the solubility of these. It is useful because it can be used for concentration adjustment and the like when used as a coating solution. Examples of the organic solvent include alcohols such as ethanol, acetone, toluene, tetrahydrofuran and the like.

In the present invention, the precursor is calcined to form ABO ₃ or Sr-substituted ABO _3, which can be formed by a conventionally known means. For example,
A method in which the calcined precursor powder is put into a mold and shaped into a desired shape, a porous substrate that serves as a carrier is immersed in a solution of the precursor, or the solution is spray-coated and supported, and after firing, a catalyst material And the like. The firing temperature is
It is a low temperature of usually 1000 ° C or lower, preferably 700 ° C or lower, and the specific surface area after firing at 700 ° C is usually 10 m ² / g.
That is all.

Examples of ABO ₃ formed from the precursor of the present invention include LaCoO ₃ , LaMnO ₃ , LaCuO ₃ ,
LaMn _0.6 Cu _0.4 O _{3 and the} like, and Sr-substituted AB
As O ₃ , La _1-X Sr _X CoO ₃ (0 <X ≦ 0.
5, preferably 0.1 ≦ X ≦ 0.3), La _0.8 Sr
_0.2 MnO ₃ , La _0.8 Sr _0.2 Mn _0.6 Cu _0.4 O ₃
Etc.

[0013]

According to the present invention, the metal atoms constituting the A and B sites are mixed and reacted in the form of at least a salt with a polyhydric alcohol or its derivative in the presence of water to react the metal atom with the polyhydric alcohol or its derivative. And are coordinated, and due to the coordination effect, a precursor with high homogeneity on the molecular order is formed.As a result, low temperature synthesis is possible, so single phase, high specific surface area, catalytic activity It is possible to produce an excellent composite oxide.

[0014]

Example 1 43.3 g (0.1 mol) of lanthanum nitrate hexahydrate, 29.1 g (0.1 mol) of cobalt nitrate hexahydrate, and 100 g (1.6 mol) of ethylene glycol and ethanol. 15
0 g was mixed at room temperature, 100 g of distilled water was added thereto, and the mixture was sufficiently stirred to obtain a transparent magenta solution as the precursor of the present invention. After distilling off most of the solvent under heating and reduced pressure, 1
It was dried at 00 ° C. to obtain a carmel-like solid substance. This was baked at 500 ° C. for 2 hours in an oxygen atmosphere to obtain a black powder composite oxide. When the crystal phase of this powder was examined by X-ray diffraction, it was found to be single-phase LaCoO ₃ .
The specific surface area after firing at 700 ° C. under the same conditions is 12
It was m ² / g.

Example 2 34.6 g (0.08 mol) of lanthanum nitrate hexahydrate and 29.1 g (0.1 mol) of cobalt nitrate hexahydrate were added with 50 g (1.6 mol) of ethylene glycol and 1,2. 30 g of 3-butanediol (0.33 mol) and 150 g of ethanol
1.75% strontium metal in the solution
g (0.02 mol) dissolved in 20 g of 1,3-butanediol was mixed, and then 100 g of distilled water was added and sufficiently stirred to obtain a transparent magenta solution as the precursor of the present invention. It was Most of the solvent was distilled off under heating and reduced pressure, followed by drying at 100 ° C. to obtain a carmel-like solid.
This was fired in an oxygen atmosphere at 500 ° C. for 2 hours to obtain a La _0.8 S r _0.2 CoO ₃ single-phase black powder composite oxide. The specific surface area after firing at 700 ° C. under the same conditions was 11 m ² / g.

Example 3 34.6 g (0.08 mol) of lanthanum nitrate hexahydrate, 29.1 g (0.1 mol) of cobalt nitrate hexahydrate and 4.2 g (0.02 mol) of anhydrous strontium nitrate. 1,3-
A solution prepared by dissolving and mixing 100 g (1.1 mol) of butanediol and 100 g of ethanol at room temperature was obtained as the precursor of the present invention. Porous alumina beads having a specific surface area of 190 m ² / g (particle diameter 1 to 2 mm) were obtained in this solution. Was dipped under heating at 80 ° C. for 2 hours, taken out, dried, and calcined in an oxygen atmosphere at 800 ° C. for 1 hour to obtain blue porous beads carrying La _0.8 St _0.2 CoO ₃ . The specific surface area of the beads was 170 m ² / g, which was almost the same as that of the carrier. The La _0.8 St _0.2 CoO ₃ -supported alumina beads were set in a fixed bed catalyst calcination device, and 10 ml of methane was added.
/ Min, air was simultaneously flown at 990 ml / min, and a firing experiment was carried out. T10 (temperature at which the combustion rate of methane reaches 10%) = 420 ° C., T90 (temperature at which the combustion rate of methane reaches 90%) = 640 It showed a high catalytic activity as high as ℃ and platinum and palladium supported catalysts.

[0017]

INDUSTRIAL APPLICABILITY According to the present invention, a complex oxide having a high homogeneity, a high specific surface area and a high catalytic activity can be obtained only by providing a very simple step of mixing a metal salt and a polyhydric alcohol or a derivative thereof. A precursor that can be produced only by firing can be produced. Since this precursor can be used in various forms, for example, a solution, a powder, etc., it has a wide range of applications and is advantageous. Further, the method of the present invention is energy-saving and has a simple manufacturing process, so that labor can be saved and the cost of the catalyst product can be reduced.

Claims (2)

[Claims] 1. The A site is at least one element selected from La, Ce, and Gd, and the B site is Mn. Fe, C
o, Ni, metals of at least one precursor of a composite perovskite oxide represented by the general formula ABO ₃ in which the element occupies or <br/> the A site of the complex perovskite-type oxide, selected from Cu A method for producing a precursor of an Sr-substituted composite perovskite type oxide in which half or less of elements are replaced with Sr, the composite perovskite type oxide or the
Mixing one or more of the elements constituting the Sr-substituted complex perovskite oxide in the form of a metal salt with one or more selected from polyhydric alcohols and polyhydric alcohol derivatives .
Luke or method for producing a composite oxide precursor, characterized in that these are mixed in the presence of a solvent which dissolves. 2. At least one kind of metal salt used is a nitrate, and at least one kind of polyhydric alcohol or polyhydric alcohol derivative is a compound having two hydroxyl groups in one molecule, and its addition amount is within the system. The method for producing a composite oxide precursor according to claim 1, wherein the amount is 0.1 to 30 times the molar amount of all the metal atoms.