JPH0566176B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a perovskite catalyst, and more particularly to a method for easily producing a perovskite catalyst having excellent catalytic activity. (Prior Art) Perovskite catalysts made of oxides of alkaline earth metals or rare earth elements and transition metals have been known and have been widely studied as various catalysts having excellent properties. Although such perovskite catalysts are used as powders, they are often supported on structural carriers. As a method for supporting the catalyst on the structural support, a method has been adopted in which perovskite catalyst powder is dispersed in a binder and then supported on the structural support. This method requires steps such as dispersing the powder in a binder and coating it on a structural support, which is complicated, and the use of a binder inevitably reduces the effective area of the perovskite catalyst. However, there was a problem that the original catalytic activity of the perovskite catalyst could not be fully demonstrated. In order to solve these problems, research has been carried out on a method of directly forming a perovskite catalyst on a structured carrier, such as a porous honeycomb carrier. (Problems to be Solved by the Invention) The method for forming a perovskite catalyst directly on the above-mentioned structural support is to form an aqueous solution of a water-soluble salt of each of an alkaline earth metal or a rare earth element and a transition metal to form a perovskite catalyst. This is a method in which a perovskite-type catalyst is formed on a structured carrier by impregnating it into a structured carrier, followed by drying and calcination.
The thermal decomposition of each water-soluble salt generates toxic gases such as NOx gas (if the water-soluble salt is nitrate) and SOx gas (if the water-soluble salt is sulfate), causing various problems. There is. Therefore, an object of the present invention is to provide a method for producing a perovskite catalyst that does not generate toxic gases as described above, and this object has been achieved by the present invention described below. (Means for Solving the Problems) That is, the present invention has the general formula ABO ₃ (A is an alkaline earth metal or a rare earth element, B is Co,
A method for producing a perovskite catalyst, in which a perovskite catalyst represented by a transition metal selected from the group consisting of Ni, Mn, and Fe is supported on a structural support, in which an aqueous solution of a water-soluble salt of A and a water-soluble salt of B is provided. This is a method for producing a perovskite type catalyst, which is characterized in that colloidal oxides and/or hydroxides are mixed and precipitated from a colloidal oxide and/or hydroxide, and then the resulting precipitate is impregnated into a structural support and then fired. Next, to explain the present invention in detail, the rare earth elements used in the production of the perovskite catalyst of the present invention are rare earth elements such as lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, and gadolinium. Alkaline earth metals such as strontium and barium can also be used in place of part or all of the rare earth elements. In the present invention, these alkaline earth metals or rare earth elements are used as di- to tetravalent water-soluble salts. These water-soluble salts include chlorides, nitrates,
Any water-soluble compound such as sulfate or acetate may be used, and these compounds can be used alone or as a mixture. The transition metals used in the present invention are iron, cobalt, nickel, or manganese, and in the present invention, these transition metals are used as divalent or trivalent water-soluble salts. These water-soluble salts include chlorides, nitrates,
Any water-soluble compound such as sulfate or acetate may be used, and these compounds can be used alone or as a mixture. In the present invention, it is preferable to use a water-soluble salt of an alkaline earth metal or rare earth element as described above and a water-soluble salt of a transition metal in a metal molar ratio of about 1:1. It is preferred that at least one or a portion of the water-soluble salts of the elements and the water-soluble salts of the transition metals be used as divalent metals. In the present invention, it is necessary to precipitate colloidal oxides and/or hydroxides from aqueous solutions of water-soluble salts of alkaline earth metals or transition metals and water-soluble salts of transition metals as described above. There is a method in which a colloidal mixed oxide and/or hydroxide sol is produced from these mixed salt aqueous solutions using an anion exchange resin, and a method in which the above mixed aqueous salt solutions are neutralized with an alkali agent. Methods such as precipitating colloidal oxides and/or hydroxides can be used, but
Since the former method is expensive and difficult to form a concentrated sol, the latter method is more preferred. Which method is used to mix and precipitate the oxides and/or hydroxides of water-soluble salts of alkaline earth metals or rare earth elements and water-soluble transition metals from an aqueous solution by neutralizing them with an alkaline agent? For example, (1) a water-soluble salt of an alkaline earth metal or a transition metal and a water-soluble salt of a transition metal are dissolved in water to prepare an aqueous solution, and an alkali agent or its aqueous solution is added thereto. How to neutralize. (2) A method in which the above aqueous solutions are injected into an aqueous solution of an alkaline agent, either separately or in a mixture. (3) A method in which a water-soluble salt of an alkaline earth metal or rare earth element and a water-soluble salt of a transition metal are added separately or simultaneously to an aqueous solution of an alkaline agent. (4) A method according to (1) to (3) above, in which a water-soluble salt of an alkaline earth metal or rare earth element, a water-soluble salt of a transition metal, or an aqueous solution thereof are sequentially added to an aqueous solution of an alkaline agent. In short, oxides and/or hydroxides of alkaline earth metals or rare earth elements and oxides and/or hydroxides of transition metals can be used.
Alternatively, any method may be used as long as it can be obtained in a uniformly mixed state with the hydroxide. The alkaline agent used in such a mixed precipitation method may be any alkaline agent such as sodium hydroxide, potassium hydroxide, sodium carbonate, or ammonia water. The amount of alkaline agent used may be any amount that can neutralize the water-soluble salt of the alkaline earth metal or rare earth element and transition metal, but it is preferable to use an excess amount of the alkaline agent. In addition, the slurry concentration of oxides and/or hydroxides of alkaline earth metals or rare earth elements and transition metals generated by these neutralizations is about 2 to 8
Approximately % by weight is suitable. In the present invention, it is preferable that divalent metal ions in the slurry thus obtained be oxidized to trivalent metal ions in the slurry. Oxidizing agents used include hydrogen peroxide, oxygen,
Any oxidizing agent such as sodium chlorate may be used, but
Preferred are oxidizing agents that do not produce impurities upon oxidation, such as hydrogen peroxide or oxygen gas. The amount of the oxidizing agent used may be the amount necessary for oxidizing the divalent metal to trivalent metal ions, but
It is preferable to use a certain amount of excess in order to complete oxidation and refinement of precipitates. Such oxidation may be carried out by using the slurry as it is, or by removing unnecessary cations and anions, such as cations such as sodium ions and potassium ions, chloride ions, and various anions from the slurry in advance. You can go after that. When the slurry is used as it is for oxidation, after the oxidation is completed, the various unnecessary ions mentioned above are removed as much as possible by filtering the slurry, washing with water, etc. The thus obtained slurry, which is a precursor of a perovskite catalyst, is redissolved with an appropriate amount of water to form a colloid. In addition, to further increase dispersion stability, it is possible to add phosphoric acid, polyphosphoric acid, phosphates, polyphosphates, etc. as a dispersant in the range of 0.2 to 2% by weight to create a slurry with high dispersion stability. can. Dispersants to be used include phosphates such as sodium orthophosphate and sodium metaphosphate, monophosphoric acids such as phosphoric acid excluding cations such as sodium, polyphosphates or sodium such as sodium pyrophosphate and sodium hexametaphosphate, etc. It is possible to use polyphosphoric acid from which cations have been removed, and of course they may be used alone or as a mixture. In the present invention, the slurry of the oxide and/or hydroxide thus obtained is impregnated into a structural support for the catalyst. The structural carrier may have any shape as long as it is porous; for example, a porous honeycomb carrier, which has been widely used as a conventional structural carrier, is preferred. The amount of the slurry impregnated into such a structural support varies depending on the porosity of the structural support and cannot be unconditionally defined, but in general, it is
The solid content is 1 to 10 parts by weight per 100 parts by weight. Impregnation may be performed multiple times until a predetermined amount of impregnation is achieved. The structure carrier impregnated in this way is exposed to normal atmosphere,
about 600-1000, preferably under a non-reducing atmosphere
The perovskite type catalyst, which is the object of the present invention, can be obtained by firing at a temperature of about 800°C, preferably about 800°C, for about 5 minutes to 1 hour. (Function/Effect) According to the present invention as described above, a perovskite type catalyst with extremely high catalytic activity is used without using any binder and without generating any toxic gas using particularly expensive equipment. It can be easily provided without. Next, the present invention will be specifically explained with reference to Examples. In the text, percentages are based on weight unless otherwise specified. Example 1 32.6 g of lanthanum oxide La ₂ O ₃ was added to 60% nitric acid aqueous solution 43
Cobalt nitrate in this aqueous solution is completely dissolved in cc.
Dissolve 58.2 g of CO ₍ NO ₃ ) 2.6H ₂ O and add water to make a total volume of 300 c.c. On the other hand, prepare a solution of 38 g of sodium hydroxide dissolved in 200 c.c. of water and 100 c.c. of a 15% aqueous solution of hydrogen peroxide, and place the above three in a container equipped with a stirrer and previously filled with 500 c.c. Inject the solutions simultaneously. During this time, the pH of the slurry liquid is maintained at around 9 and the temperature is maintained at 30°C. After the precipitation reaction and oxidation reaction were completed, excess sodium hydroxide aqueous solution was added to adjust the pH to 10, and then to 80.
Heat and ripen at ℃ for 1 hour. The obtained black and colored product is filtered and washed with water to remove impurities such as unnecessary cations and anions, then an appropriate amount of water is added and dissolved in a homomixer, and the entire amount is mixed into a slurry of 400 c.c. Then, 0.8 g of sodium hexametaphosphate was added as a dispersant. In the above colloidal slurry, 400 cells/
A coradilite honeycomb with a diameter of 20 mm and a height of 10 mm was impregnated, dried after removing excess slurry, and fired at 850°C for 30 ^minutes . The supported amount was 5.4% of the honeycomb. The catalytic activity of the porous honeycomb carrier thus obtained was 3 ml of propane/
min., and air at 300 ml/min., by burning a mixed gas using a conventional fixed bed flow reactor. The results are shown in Figure 1 (SV=
7200H ^-1 ). Example 2 A colloidal product was prepared in the same manner as in Example 1 except that instead of lanthanum oxide, mixed rare earth element REX 70 manufactured by Santoku Metal Co., Ltd. or mixed rare earth element 29.0 g manufactured by Nissan Rare Earth Element Co., Ltd. was used. Got slurry. Table 1 shows the compositions of the two types of mixed rare earth elements used in this example. Further, it was supported on the same honeycomb as in Example 1 and fired at 800°C for 30 minutes. The supported amount was 5.4% of the honeycomb. The catalytic activity was evaluated in the same manner as in Example 1, and the results when mixed rare earth elements manufactured by Santoku Metals Co., Ltd. were used are shown in FIG.

[Table] Example 3 Same as Example 1 except that 50.2 g of manganese nitrate Mn (NO ₃ ) ₂・4H ₂ O was used instead of 58.2 g of cobalt nitrate Co (NO ₃ ) ₂・6H ₂ O. A colloidal slurry of LaMnO ₃ precursor was obtained. Also, Example 1
It was supported on the same honeycomb as above and fired at 800°C for 30 minutes. The amount of honeycomb supported was 4.5%. The catalytic activity was evaluated in the same manner as in Example 1, and the results were used in the first
Shown in the figure. Example 4 LaNiO ₃ was prepared in the same manner as in Example 1 except that 58.2 g _of nickel nitrate Ni (NO ₃ ) 2.6H _{2 O} was used instead of 58.2 g of cobalt nitrate Co (NO ₃ ) 2.6H ₂ O. A colloidal slurry of the precursor was obtained. Also, Example 1
It was supported on the same honeycomb as above and fired at 1000°C for 30 minutes. The amount of honeycomb supported was 4.4%. The catalytic activity was evaluated in the same manner as in Example 1, and the results were used in the first
Shown in the figure. Example 5 A colloidal slurry of a LaMnO ₃ precursor was obtained in the same manner as in Example 3, except that 100 g of 28% aqueous ammonia was used instead of 38 g of sodium hydroxide. Thereafter, the catalytic activity was evaluated in the same manner, and the results are shown in FIG. Comparative Example 1 A black and colored product was obtained in the same manner as in Example 1. After that, it is filtered and washed with water to remove unnecessary cations, anions, and other impurities, and thoroughly dried at 100°C. This dried product was calcined at 850°C for 60 minutes to obtain a LaCoO ₃ perovskite type fine powder. 2 g of this powder was sufficiently dispersed in 2 g of alumina sol #200 manufactured by Nissan Chemical Co., Ltd. and 2 g of water, and then further diluted with 6 g of water.
% supported and the catalytic activity was measured, and the results are shown in FIG. Comparative Example 2 After obtaining a black and colored product in the same manner as in Example 3, it is filtered, washed with water to remove unnecessary impurities such as cations and anions, and thoroughly dried at 100°C. This dried product was calcined at 800°C for 60 minutes to obtain a fine perovskite powder with LaMnO ₃ . This powder was supported on a honeycomb in the same manner as in Comparative Example 1, and the catalytic activity was measured. The results are shown in FIG.

[Brief explanation of drawings]

FIG. 1 shows the activity of the catalysts obtained in Examples and Comparative Examples. 1: Examples 1, 2; Examples 2, 3; Example 3,
4; Examples 4, 5; Examples 5, 6; Comparative example 1,
7; Comparative example 2.

Claims (1)

[Claims] 1. A perovskite catalyst represented by the general formula ABO ₃ (A is an alkaline earth metal or rare earth element, and B is a transition metal selected from the group consisting of Co, Ni, Mn, and Fe). In a method for producing a perovskite catalyst in which A and B are supported on a structural support, colloidal oxides and/or hydroxides are mixed and precipitated from an aqueous solution of a water-soluble salt of A and a water-soluble salt of B, and then the resulting precipitate is mixed and precipitated. A method for producing a perovskite catalyst, which comprises impregnating a structural carrier and then firing the catalyst. 2. The method for producing a perovskite catalyst according to claim 1, wherein the structural carrier is a porous honeycomb carrier. 3. The method for producing a perovskite catalyst according to claim 1, wherein the oxide and/or hydroxide is oxidized in a liquid phase at the same time as the precipitation or after the precipitation and then impregnated into the structural support. 4. The method for producing a perovskite catalyst according to claim 1, wherein a phosphate or polyphosphate is added as a dispersant to the slurry of the oxide and/or hydroxide.