JP3440505B2 - Method for producing ceric oxide - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing ceric oxide, and more particularly, to a method for producing ceric oxide which has a small decrease in specific surface area even in a high temperature region and is stable. The present invention relates to providing ceric oxide having a color tone close to white. 2. Description of the Related Art Conventionally, ceric oxide has been used in large quantities as an exhaust gas purifying catalyst, silicone rubber filler, abrasive, etc. For example, in the field of catalysts, ceric oxide absorbs oxygen in an oxidizing atmosphere, Utilizing the characteristic of ceric oxide that releases oxygen in a reducing atmosphere, HC, CO, N
The purification rate of O _x has been improved, and the silicone rubber filler is used as an additive for improving heat resistance without lowering the rubber strength. Such conventional ceric oxide is usually, for example, a method of adding oxalic acid or ammonium bicarbonate to a cerium nitrate solution or a hydrochloride solution, filtering the obtained precipitate, washing, drying and calcining. Being manufactured. However, the conventional ceric oxide prepared by the method, and the like, although having a specific surface area of about 100 m ² / g, specific surface area at 800 ° C. firing 10 m ² /
g or less, and when used in addition to silicone rubber, the color of the rubber becomes yellowish due to the high yellowness of ceric oxide. In addition, since the polishing ability of ceric oxide used as an abrasive greatly depends on mechanochemical parts (surface activity), it is necessary to increase the specific surface area in a normal firing temperature range of about 800 to 1000 ° C. Is desired. [0003] In order to further improve the performance and the like used in the above-mentioned applications, ceric oxide has the following characteristics: a higher specific surface area and a lowering of the specific surface area at high temperatures. It is required to be stable and to bring the color tone closer to white. As a result of various studies to solve the above-mentioned problems, the present inventor has found that cerium carbonate can be brought into a temperature range of 60 to 100 ° C. under a high humidity of 80% or more relative humidity. A method for producing ceric oxide characterized by performing humidification heat treatment to obtain cerium monooxycarbonate, followed by firing. First, cerium carbonate as a raw material will be described. Cerium carbonate is commercially available and can be used in the present invention. An example of producing cerium carbonate is as follows. That is, first, a cerium nitrate aqueous solution and an ammonium bicarbonate aqueous solution are mixed to obtain a cerium carbonate precipitate. At this time, the mixing order may be such that an aqueous solution of ammonium bicarbonate is added to the aqueous solution of cerium nitrate, or an aqueous solution of cerium nitrate is added to and mixed with the aqueous solution of ammonium bicarbonate. The concentration of the cerium nitrate aqueous solution is preferably in the range of 30 to 200 g / l, particularly preferably 100 to 150 g / l. The mixing ratio of the cerium nitrate aqueous solution and the ammonium bicarbonate aqueous solution is preferably in a range of 1: 1.4 to 3 by weight ratio of cerium nitrate and ammonium bicarbonate contained in each aqueous solution. The cerium carbonate obtained at this time is trivalent cerium and is Ce ₂ (CO ₃ ) ₃ .xH ₂ O (x = 1 to 8). Next, in the present invention, the cerium carbonate or the commercially available cerium carbonate obtained as described above is subjected to a humidifying heat treatment in a temperature range of 60 to 100 ° C. and a high humidity of 80% or more in relative humidity. By this treatment, acicular or spherical cerium monooxycarbonate [Ce ₂
O (CO ₃ ) ₂ .xH ₂ O (x = 1 to 6)] is produced. The above-mentioned humidification heat treatment can be performed by a thermo-hygrostat, a dryer in which steam is introduced, or the like, and the treatment time is desirably 1 hour or more. If the temperature of the humidification and drying treatment is lower than 60 ° C., it may be because the water of crystallization is difficult to desorb,
If cerium monooxycarbonate is not generated and if the temperature exceeds 100 ° C, desorption of surface water occurs before desorption of water of crystallization,
The production ratio of cerium monooxycarbonate decreases,
Since it becomes a basic carbonate such as e (OH) (CO ₃ ) .xH ₂ O, the temperature must be within the above-mentioned range. On the other hand, if the relative humidity is less than 80%, the surface water is desorbed before the crystallization water is desorbed, or an amorphous portion appears from cerium carbonate as in a normal drying treatment, which is not preferable. Next, ceric oxide is obtained by calcining the produced cerium monooxycarbonate.
The firing temperature is preferably from 300 to 650 ° C, more preferably from 300 to 550 ° C, and the firing time is preferably from 1 to 4 hours. If the firing temperature is lower than 300 ° C., even if the firing time is lengthened, it is difficult to completely change to CeO ₂ , and if it exceeds 550 ° C., the specific surface area of the obtained CeO ₂ is relatively small, which is not desirable. The ceric oxide obtained in the present invention is:
It has a large specific surface area of 140 m ² / g or more, and has a characteristic of a small decrease in the specific surface area even at a high temperature, especially at 700 ° C. or more, and has a high whiteness. The shape is also acicular, spherical, cubic or the like. In the case of spherical or cubic, the diameter and one side are 20 μm or less, respectively, and in the case of a needle, the thickness is 10 μm or less, the length is 60 μm, and the aspect ratio is 3 μm. Although the above is normal, it is not limited to this value.
The ceric oxide obtained by the production method of the present invention can be used as it is, but when used as an exhaust gas cleaning catalyst, it is mixed with zirconium oxide, aluminum oxide, alkaline earth metal oxide, or silicone. When used as a rubber filler, it is mixed with titanium dioxide, aluminum oxide, etc., and when used as an abrasive, it may be used as a mixture with rare earth metal oxides and fluorides, aluminum oxide, zirconium oxide and other common abrasives. it can. Examples will be described in detail below with reference to examples and comparative examples. Example 1 A high-purity cerium nitrate solution (manufactured by Tohoku Metal Chemical Co., Ltd., purity 99.95%) was dissolved in water, and 1 liter of a 50 g / liter cerium nitrate aqueous solution at 35 ° C. in terms of ceric oxide CeO _2. Then, 1 liter of an aqueous solution of ammonium bicarbonate having a concentration of 150 g / liter was added and mixed to obtain 2300 g of a hexagonal plate-like precipitate of cerium carbonate. The obtained precipitate is put in a thermo-hygrostat at 85 ° C. and a relative humidity of 95%.
% To 8 hours humidification dried under acicular Monookishi cerium carbonate Ce ₂ O (CO ₃₎ to give the ₂ · H ₂ O1700g. This was calcined at 400 ° C. for 2 hours to obtain ceric oxide. Table 1 shows the properties of the obtained ceric oxide and the value of the specific surface area changed by refiring the ceric oxide at 800 ° C. for 5 hours. The yellowness (YI value) shown in Table 1 is a value measured as follows. Yellowness indicates the degree of separation from white in the yellow direction, and ideal white has almost zero yellowness. As the yellow color increases and the distance from the ideal white color increases, the numerical value of the yellowness increases. When measuring the yellowness, the obtained fired product was crushed in a nylon pot (nylon ball) for about 2 hours, and the average particle size d ₅₀ = 2.0.
Make powder of ± 0.2 μm and 22 μm or less. Approximately 5 g of this crushed powder was produced using a color difference meter (manufactured by Tokyo Denshoku Co., Ltd.
× 15t) without any pressure, and measured by measuring each value of XYZ to obtain a YI value (yellowness) according to ASTM E313. The YI values shown in Table 1 were measured three times for each sample, three times for each sample, and each was measured three times and displayed as an average value of nine times in total. Comparative Example 1 The cerium carbonate precipitate in Example 1 was directly calcined at 400 ° C. for 2 hours without humidifying and drying treatment to obtain ceric oxide. Other conditions are the same as in the first embodiment. Table 1 shows the properties of the obtained ceric oxide and the specific surface area after recalcination at 800 ° C. for 5 hours. Comparative Example 2 The hexagonal plate-like precipitate of cerium carbonate obtained in Example 1 was placed in an autoclave and subjected to a hydrothermal treatment at 120 ° C. for 8 hours. The main products obtained are hexagonal plate-like and spherical basic cerium carbonate (Ce (OH) (CO ₃ ) .2H
₂ O), the production amount of cerium monooxycarbonate is 5
%. The mixture was calcined at 400 ° C. for 2 hours to obtain ceric oxide shown in Table 1. Also, this 8
Table 1 also shows the specific surface area after recalcination at 00 ° C. for 5 hours. Comparative Example 3 The hexagonal plate-like precipitate of cerium carbonate obtained in Example 1 was placed in a thermo-hygrostat introduced with steam, and humidified and heated at 50 ° C. and 95% relative humidity for 8 hours. Was. as a result,
Cerium monooxycarbonate was not obtained, and remained hexagonal plate-like cerium carbonate. This was calcined at 400 ° C. for 2 hours to obtain ceric oxide shown in Table 1, and further baked at 800 ° C.
For 5 hours, and the change in specific surface area was determined. [Table 1] Example 2 A hexagonal plate-like cerium carbonate was obtained under the same conditions as in Example 1 except that an aqueous cerium nitrate solution was added to and mixed with an aqueous ammonium bicarbonate solution. 2300 g of this precipitate was subjected to a humidifying heat treatment at 95 ° C. and a relative humidity of 95% for 8 hours in a steam introduction dryer to obtain acicular cerium monooxycarbonate C.
e ₂ O (CO ₃₎ to give the ₂ · H ₂ O1700g. This is 3
It was calcined at 00 ° C. for 4 hours to obtain ceric oxide having the characteristics shown in Table 2. This was further calcined at 800 ° C. for 5 hours to determine the change in specific surface area. The value is shown in Table 2. Comparative Example 4 The hexagonal plate-like precipitate of cerium carbonate obtained in Example 2 was directly calcined at 300 ° C. for 4 hours without humidifying heat treatment.
Cerium oxide having the characteristics shown in Table 2 was obtained, and the same recalcination treatment as in Example 2 was performed. [Table 2] Example 3 A hexagonal plate-like precipitate of cerium carbonate prepared in the same manner as in Example 1 was placed in a thermo-hygrostat at 60 ° C. and a relative humidity of 90%.
Humidification and drying treatment for 12 hours, and acicular cerium monooxycarbonate Ce ₂ O (CO ₃ ) ₂ .3H ₂ O 180
0 g was obtained. 500 g of the obtained cerium monooxycarbonate
Table 3 shows the properties of the ceric oxide obtained by calcining at 2 ° C. for 2 hours and the specific surface area when the ceric oxide was calcined again at 800 ° C. for 5 hours. Comparative Example 5 A hexagonal plate-like precipitate of cerium carbonate prepared in the same manner as in Example 1 was placed in a thermo-hygrostat at 60 ° C. and a relative humidity of 70%.
Was subjected to a humidification drying treatment for 12 hours, but no cerium monooxycarbonate was obtained, and the hexagonal cerium carbonate remained. Table 3 shows the properties of the ceric oxide obtained by firing this cerium carbonate at 500 ° C. for 2 hours and the specific surface area when the cerium oxide was fired again at 800 ° C. for 5 hours. [Table 3] Example 4 A hexagonal plate-like precipitate of cerium carbonate prepared in the same manner as in Example 2 was placed in a drier in which steam was introduced.
8 hours humidification and drying at 80% relative humidity,
1700 g of acicular cerium monooxycarbonate was obtained. The obtained cerium monooxycarbonate Ce ₂ O (CO ₃ ) ₂ .H
Table 4 shows the properties of ceric oxide obtained by calcining ₂ O at 500 ° C. for 2 hours and the specific surface area when ceric oxide was calcined again at 800 ° C. for 5 hours. Comparative Example 6 A hexagonal plate-like precipitate of cerium carbonate prepared in the same manner as in Example 2 was placed in a dryer into which steam had been introduced.
The humidification and drying treatment was performed for 8 hours at a relative humidity of 70%, but no cerium monooxycarbonate was obtained and the hexagonal plate-like cerium carbonate remained. 500 g of this cerium carbonate
Table 4 shows the properties of the ceric oxide obtained by calcining at 2 ° C. for 2 hours and the specific surface area when the ceric oxide was calcined again at 800 ° C. for 5 hours. Comparative Example 7 A hexagonal plate-like precipitate of cerium carbonate prepared in the same manner as in Example 2 was placed in a drier having a vat filled with water at the bottom, and steam at 110 ° C. and a relative humidity of 85% was placed. The humidification and drying treatment was performed under pressure for 8 hours. The main product at this time is hexagonal plate-like and spherical basic cerium carbonate salt. In addition, about 20% of unreacted cerium carbonate keeping the hexagonal plate-like shape is recognized, and the desired cerium monooxycarbonate is formed. The amount was about 5% of the whole. 500 ° C.
Table 4 shows the characteristics of the ceric oxide obtained by firing for 2 hours at, and the specific surface area when the cerium oxide was refired at 800 ° C for 5 hours. [Table 4] The ceric oxide obtained according to the present invention has the following advantages: a) a large specific surface area; and b) a decrease in specific surface area at high temperatures. C) It exhibits a color tone close to white. There are many effects. Further, according to the production method of the present invention, the ceric oxide of the present invention having the above characteristics can be easily produced with good reproducibility. Therefore, ceric oxide obtained in the present invention is an exhaust gas cleaning catalyst,
It is particularly suitable for ceric oxide, such as a silicone rubber filler, which requires heat stability.

Claims (1)

(57) [Claims 1] Cerium carbonate is subjected to a humidifying heat treatment at a high humidity of 80% or more in a temperature range of 60 to 95 ° C. to form cerium monooxycarbonate, followed by firing. A method for producing ceric oxide.