KR0149935B1 - Manufacturing method of cecium oxide - Google Patents

Abstract

The present invention relates to that, in particular, method of manufacturing a suitable cerium oxide (CeO ₂₎ to have a high specific surface area even at a high temperature for the production of the cerium oxide is used as a catalyst for automobile exhaust gas, Ce (OH) ₄ or CeO ₂ A first step of adding an acidic medium to the solution to dissolve it; a second step of digestion at a temperature of 100 to 150 ° C. to a gel state; and distilled water added to the gel to form colloidal particles. The third step of the sol (Sol) state, and a method for producing a cerium oxide (CeO ₂ ) characterized by the addition of a basic medium to precipitate cerium ions, washing and drying the precipitate.

Description

Method of producing cerium oxide

The accompanying drawings show a manufacturing process of the present invention.

The present invention relates to a method for producing cerium oxide (CeO ₂ ), and more particularly to a manufacturing method suitable for having a high specific surface area even at high temperatures.

It is well known that cerium oxide can be used as a filler, a binder, a dispersant, especially a catalyst or a carrier for catalysts for automobile exhaust purification.

For example, a paper on the synthesis of methanol from CO + H ₂ in a catalyst in which a platinum group catalyst is supported on cerium oxide (Meriaudeau et al, CRAcad. Sc. Parist 297-Serie II-471-1983) and residual gas treatment Mention may be made of the catalysts used in (Japanese Patent Application No. 76-62616).

For example, internal combustion engines such as automobiles emit exhaust gases such as unburned hydrocarbons, carbon monoxide, and nitrogen oxides (typically referred to as NOx, mainly nitrogen monoxide (NO) and nitrogen dioxide (NO ₂ )). Catalysts and operating parts for internal combustion engines have been developed.

Successful conversion of exhaust gas components is very demanding, as it requires the rapid reduction of nitrogen oxides (NO, etc.) to nitrogen while oxidizing the containing carbon monoxide to harmless carbon dioxide.

In general, the oxidation reaction is promoted by sufficient oxygen, while the reduction reaction is interrupted thereby.

In order to satisfy these operating conditions, so-called three-way catalysts have been developed in a number of ways over other catalysts.

The exhaust gas purification catalyst mainly consists of a carrier and a catalytically active seed.

Precious metals such as platinum (Pt), palladium (Pd) and rhodium (Rh) are mainly used as catalytically active materials. Group VIII such as cerium (Ce) and lanthanum (La) are used to accelerate and stabilize the catalytic activity of these precious metals. Compounds selected from compounds of elements, compounds of alkaline earth metals such as sodium (Na), potassium (K) and cesium (Cs) are generally used, among which oxides of cerium are particularly useful.

The oxides of cerium generally improve the effect of oxygen storage, promote the conversion reaction of water vapor (CO + H ₂ O = CO ₂ + H ₂ ), enhance the dispersibility of precious metals, and improve the thermal stability of activated alumina at high temperatures. It is known to have an effect.

For this reason, the effective use of trickle oxides is a very important issue in itself.

In addition, cerium oxide improves the heat resistance of activated alumina and acts as a catalyst to increase activity, thereby reducing the amount of precious metal used, and in particular, since cerium oxide regulates the amount of oxygen, the oxidation / reduction reaction of the catalyst is properly controlled. Among the catalysts for automobile exhaust purification, addition to the three-way catalyst is essential.

It is also well known that the effectiveness of a catalyst generally increases as the surface of the catalyst and the reactant contact with each other. In order to increase the catalytic efficiency, the catalyst particles are as fine as possible and separated from each other.

That is, they must have a monodisperse particle form.

Thus, the basic role of the carrier is to keep the catalyst particles or crystals as dispersed as possible in contact with the reactants.

In order to exhibit excellent catalytic reactivity for the above reasons, it is preferable to use a second cerium oxide having a specific surface as large as possible.

The current trend of automotive catalysts is the improvement of high temperature specific surface area values in an effort to improve the purification rate at high temperatures, for example due to attempts to install catalysts near automotive engines, due to rising exhaust gas temperatures and increasingly stringent environmental regulations. This is important.

Most of the cerium oxides produced by the known methods show rapidly decreasing specific surface area values for operating temperatures above 500 ° C. The US is made from oxalates and carbonate salts commercialized with conventional cerium oxides for catalysts. Molycorp's cerium oxide has a specific surface area (BET value) of 800 m < 2 >

In the US Patent (4,356, 106) proposed by Molycorp (Molycorp), the cerium hydroxide is placed in the crucible and heated to 300 ℃ or more in a muffle furnace in the air to obtain a dry dispersible cerium compound, which is in the hot water or Agitated in normal temperature water to form a sol (Sol) as a colloidal phase or treating cerium hydroxide with high purity with an acidic medium and drying to obtain cerium oxide (IV) hydrate, which was heated at high temperature in a muffle to obtain a dispersible powder and dispersion To obtain a colloidal sol.

The above-mentioned method also includes problems such as the selection of a strong reactor for corrosion resistance at high temperature and the continuous process using the same, which makes it difficult to mass-produce.

In addition, the high temperature (800-900 ° C.) specific surface value may be manufactured to 10 m 2 / g or more by patents Rheone-Poulenc of Co., Ltd., 91-10126 to 91-10132, but problems appear in the process.

That is, in France, France, to obtain a second cerium oxide, cerium hydroxide is dissolved with nitric acid to obtain a cerium nitrate solution, which is hydrolyzed in hot water at 100 ° C., and then colloidal through a autoclave. Is getting.

However, the above-described process by autoclave requires a lot of equipment since high temperature pressurization is required. In the process by hydrolysis, the yield decreases because the loss of about 10-20% of cerium ions occurs, thus controlling the semen process. Is difficult.

Therefore, there is a difficulty in adjusting the acidity of the reaction medium, the concentration of cerium, the oxidation state and the ratio thereof to the conditions.

The present invention has been made in order to solve the above-mentioned problems, and it is possible to continuously produce by thermally immersing in a simple facility at low temperature, and in particular, a cerium oxide suitable for improving the specific surface area value at high temperature according to the rise of exhaust gas temperature. The purpose is to provide.

Hereinafter, the present invention will be described.

The present invention is a first step of dissolving Ce (OH ₄ ) or CeO ₂ powder using an acidic medium, a second step of digestion at a temperature of 100 ~ 150 ℃ to a gel (Gel) state, and Distilled water was added to one gel to form a sol (Sol), which is a shape group of colloidal particles, and a basic medium was added to precipitate cerium ions. The precipitate was washed with water and dried to obtain cerium oxide (CeO ₂ ).

The present invention can also be subjected to a basic step of adding a medium, washing with water and drying after the second step of gelling is completed by warming again (that is, repeating the warming step) and then gelling again. The surface area is further increased.

The accompanying drawings show the manufacturing process diagram of the present invention, will be described in detail accordingly.

The starting material Ce (OH) ₄ or CeO ₂ was dissolved in an acidic medium, and in particular, nitric acid was dissolved to have a constant initial acidity and a normal concentration of 0.5N to 5N. As in a), the heater 1 is embedded and placed in a tank equipped with the stirrer 2 and digested at a temperature of 100 to 150 ° C. to a gel state of Ce (NO ₃ ) ₄ · _X H ₂ O. Then, distilled water was added to form a sol (Sol) of a colloidal particle having a free acidity of 0.1 N to 0.5 N, as shown in (b), followed by using a precipitant as a basic medium in (c). Cerium ions are completely precipitated and the precipitate is washed and dried to obtain cerium oxide (CeO ₂ ) having a high specific surface area.

In the present invention, after the step (b) of obtaining the sol state in the above-described process, the process is returned to the first process, followed by a warming process (gel state) as shown in (d), and distilled water is added as shown in (e) again to obtain the sol state. The basic medium can be added, washed and dried as shown in (f).

In this way, the high temperature specific surface area can be further improved by repeating the warming step and the step of obtaining the sol.

The following is described according to the embodiment.

Example 1

A starting material of Ce (OH) ₄ or CeO ₂ type having a purity of 99% or more was used as a starting material.

100 g of Ce (OH) ₄ powder is added to 200 ml of 60% industrial nitric acid in a 1 l Teflon beaker, dissolved in an aqueous solution, stirred and warmed to a gel state.

The heating temperature at this time was performed at 100-150 degreeC.

In the gelled state, 800 ml of distilled water was added to form a sol, and then precipitated to pH = 9, where cerium ions were completely precipitated with 10 N ammonia solution, followed by heat treatment of the precipitate obtained by washing with water. Specific surface area values were measured.

As a result, the specific surface area of the product after heat treatment at 800 ° C. for 2 to 4 hours was 23 to 26 m 2 / g, and especially at 900 ° C., having a value of 16 m 2 / g.

The specific surface area value at this time was measured using an AUTOSORB-1 type of analytical equipment of QUANTACHROME.

Example 2

Of Example 1, but a row in the same manner starting material of high purity (99%) Ce (OH) CeO ₂ purity of 95% (rare earth ions other than the 4% Ce) was used instead of _4, the raw material level.

As a result, the specific surface area value of the final product heat-treated at 800 ° C. for 2 to 4 hours was slightly lower than that of Example 1 of about 15 to 20 m 2 / g.

Example 3

In the same manner as in Example 1, but using a 100g Ce (OH) ₄ and 300ml of 60% industrial nitric acid to change the NO ₃ / CeO ₃ ratio, the specific surface area value at high temperatures (800 ~ 900 ℃) There was no significant change.

Example 4

After performing in the same manner as in Example 1 to the sol (Sol) state, and then again digestion, that is, through a two-time impregnation process to make a gel (Gel) state by adding distilled water to colloid and then The specific surface area value was measured by precipitating to pH = 9 with 10N aqueous ammonia solution and then heat treating the precipitate.

As a result, the specific surface area after heat treatment of the product at 800 ° C. for 2 to 4 hours was 27 m 2 / g or more, and 17 m 2 / g was maintained even when the product was heat treated at 900 ° C.

Claims (2)

The first step was obtained by dissolving an acidic medium in Ce (OH) ₄ or CeO ₂ to obtain a second solution of cerium nitrate, and digestion at a temperature of 100 to 150 ° C. to form Ce (OH) ₄ · _X H ₂ O. 2nd process which makes a gel state, 3rd process which makes said gel the sol state which is a colloid particle formation group which shows free acidity of 0.1-0.5 N by adding distilled water, and the said sol A method of producing cerium oxide (CeO ₂ ) for the activity of the catalyst for purification of exhaust gas or catalyst carrier, characterized in that cerium ions are precipitated by adding an ammonia solution in a (Sol) state, and the precipitate is washed and dried. The cerium oxide for the activity of the catalyst or catalyst carrier for exhaust gas purification according to claim 1, wherein after the third step is finished, the second step and the third step are repeated and the cerium ions are precipitated, washed and dried. Method for preparing (CeO ₂ ).