JP3595874B2 - Zirconium-cerium composite oxide and method for producing the same - Google Patents

Description

【００５９】
【表２】

【００６０】
比較例１
硝酸ジルコニウム水溶液（酸化ジルコニウムとして２４ｇ含有）に、硝酸セリウム水溶液（酸化セリウムとして７４ｇ含有）及び硝酸ランタン水溶液（酸化ランタンとして２ｇ）を添加して混合液を調製し、さらに硫酸アンモニウム２ｇ添加した。この混合液に、２５重量％アンモニア水をｐＨが１０．２となるまで添加して沈殿物を生成させた。沈殿物を固液分離し、得られた固形分を大気中６６０℃で３時間焼成した。この複合酸化物の結晶相は、２種類の立方晶、すなわち複合酸化物の立方晶と酸化セリウム単体の立方晶とが混在していた。実施例１と同様にして、得られた複合酸化物の各物性を調べた。その結果を表３に示す。
【００６１】
比較例２
水酸化ジルコニウム水溶液（酸化ジルコニウムとして８４ｇ含有）に、硝酸セリウム水溶液（酸化セリウムとして１１６ｇ含有）を添加して混合液を調製した。混合液に、２５重量％アンモニア水をｐＨが１０．２となるまで添加して沈殿物を生成させた。沈殿物を固液分離し、得られた固形分を大気中６６０℃で３時間焼成した。この複合酸化物の結晶相は、２種類の立方晶、すなわち複合酸化物の立方晶と酸化セリウム単体の立方晶とが混在していた。実施例１と同様にして、得られた複合酸化物の各物性を調べた。その結果を表３に示す。
【００６２】
【表３】

【００６３】
試験例１
実施例１、比較例１及び比較例２で得られた複合酸化物について、加熱・冷却サイクル（熱処理サイクル）試験を４回繰り返した。各試料について加熱・冷却サイクル１回ごとにＸ線回折分析を行った。その結果をそれぞれ図１〜３に示す。また、各試料について、加熱・冷却サイクル１回ごとにＯＳＣを測定した。その結果を図４に示す。
【００６４】
図１〜３から、比較例１及び２の複合酸化物では、熱処理サイクルを繰り返すことによって、セリア（１１１）面に相当するピークの強度が強くなり、ジルコニア−セリア系固溶体の立方晶（１１１）面に相当するピークの強度が低下していることがわかる。これは、セリアのシンタリングが進行し、触媒性能が低下していることを示すものである。これに対し、実施例１の複合酸化物は、熱処理サイクルを繰り返しても、ジルコニア−セリア系固溶体の立方晶が優位であり、純粋なセリアの生成が阻止され、安定化していることがわかる。
【００６５】
また、図４より、比較例１及び２の複合酸化物では、熱処理サイクルを繰り返すことによって、酸素吸着量が大幅に低下していることがわかる。これに対し、実施例１では、そのような低下が認められず、比較的安定した性能を発揮できることがわかる。
【００６６】
試験例２
実施例５で得られた複合酸化物について、試験例１と同様の加熱・冷却サイクル（熱処理サイクル）試験を行った。その結果を図５に示す。また、試験例１と同様に、加熱・冷却サイクル１回ごとにＯＳＣを測定した。その結果を図６に示す。
【００６７】
図５より、実施例５の複合酸化物は、実施例１と同様、熱処理サイクルを繰り返しても、ジルコニア−セリア系固溶体の立方晶が優位であり、純粋なセリアの生成が阻止され、安定化していることがわかる。また、図６より、実施例５では、酸素吸着量の大幅な低下が認められず、比較的安定した性能を発揮できることがわかる。
【図面の簡単な説明】
【図１】実施例１の複合酸化物について熱処理サイクル試験を行ったときのＸ線回折分析の結果を示す図である。
【図２】比較例１の複合酸化物について熱処理サイクル試験を行ったときのＸ線回折分析の結果を示す図である。
【図３】比較例２の複合酸化物について熱処理サイクル試験を行ったときのＸ線回折分析の結果を示す図である。
【図４】実施例１、比較例１及び比較例２の各複合酸化物について熱処理サイクル試験を行ったときのＯＳＣ測定結果を示す図である。
【図５】実施例５の複合酸化物について熱処理サイクル試験を行ったときのＸ線回折分析の結果を示す図である。
【図６】実施例５の複合酸化物について熱処理サイクル試験を行ったときのＯＳＣ測定結果を示す図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a novel zirconium-cerium composite oxide and a method for producing the same. Further, the present invention relates to an exhaust gas purifying catalyst material containing the above composite oxide.
[0002]
[Prior art]
In a three-way catalyst capable of simultaneously removing hydrocarbons, carbon monoxide and nitrogen oxides in exhaust gas discharged from an internal combustion engine of an automobile or the like, a platinum group element such as platinum, rhodium or palladium is used as a catalytically active component. Cerium oxide having redox properties has been used to improve catalytic activity.
[0003]
However, it is known that a catalyst containing a platinum group element and cerium oxide has a significantly reduced oxidation-reduction characteristic at a high temperature of 800 ° C. or higher, so that its catalytic performance tends to be deteriorated.
[0004]
In order to maintain the oxidation-reduction properties of cerium oxide at high temperatures, a method has been proposed in which a rare earth metal other than cerium and / or an oxide of zirconium is added to suppress crystallization thereof (for example, see Japanese Patent Application Laid-Open 64-58347, JP-A-63-116741, etc.). It is also disclosed that cerium oxide and zirconium oxide are prepared in advance as a composite oxide and used (for example, JP-A-62-168544, JP-A-1-281144, JP-A-4-284875, etc.). ).
[0005]
Also disclosed is a method for improving the stability of specific surface area and the oxidation-reduction characteristics of a composite oxide containing cerium oxide and zirconium oxide in order to enhance the function of the exhaust gas treatment catalyst as a promoter or a catalyst carrier (for example, disclosed). JP-A-4-55315, JP-A-2698302, JP-A-5-286772, JP-A-9-278444 and the like. Nowadays, as environmental protection measures for the global environment are progressing, due to stricter regulations on exhaust gas, the durability temperature for the stability of the specific surface area required for the co-catalyst and the catalyst carrier and the deterioration temperature of the oxidation-reduction characteristics are reduced. It has been improved to 1000 ° C.
[0006]
[Problems to be solved by the invention]
However, the stability of the specific surface area of these conventional cerium oxide-zirconium oxide composite oxides is about 20 m ² / g after heat treatment at 1000 ° C., and the oxidation-reduction characteristics show that even the composite oxides not heat-treated have an oxygen adsorption amount. it is _0.1mmol-O 2 / g approximately.
[0007]
When the vehicle is traveling under certain conditions (for example, in 10 mode traveling in Japan), most of the total amount of unpurified hydrocarbons is discharged at a temperature lower than the temperature at which the catalyst starts to function. The temperature at which this catalyst begins to function is called T ₅₀ (the temperature at which the purification rate reaches 50% of the maximum purification rate). Attempts have been made to reduce the time it takes for the catalyst to heat up by bringing the catalyst closer to the engine. According to this measure, the endurance temperature required for the catalyst exceeds 1000 ° C., and the catalyst is exposed to repeated heat cycles of rapid heating and cooling to room temperature. For this reason, it is necessary to develop a new catalyst material that can satisfy these requirements.
[0008]
On the other hand, as a method for uniformly integrating cerium oxide and zirconium oxide, there is generally a method of adding an aqueous solution containing cerium ions and an aqueous solution containing zirconium ions or a base to recover a complex salt precipitate (particularly). Kaihei 9-278444).
[0009]
However, since the composite salt precipitate obtained by the above method is a gel-like bulky hydroxide having a high water content, an extra filtration or solid-liquid separation step for removing impurities is required. Therefore, not only does the processing speed per operation inevitably slow, but also the heat energy required for heat conversion to oxides becomes enormous. Thus, it is difficult to say that the conventional manufacturing method is suitable for manufacturing on an industrial scale.
[0010]
Accordingly, the present invention has been made in view of the problems of the related art, and has a main object of, in particular, to provide a zirconium-cerium-based composite oxide having excellent thermal stability and oxidation-reduction properties. .
[0011]
[Means for Solving the Problems]
The present inventors have conducted intensive studies and as a result, found that a composite oxide obtained by a specific production method expresses unique properties, and finally completed the present invention.
[0012]
That is, the present invention relates to the following zirconium-cerium-based composite oxide and a method for producing the same.
[0013]
1. A composite oxide containing zirconium and cerium,
(1) 95% by volume or more of the crystal phase is a cubic crystal of a zirconia-ceria-based solid solution, and (2) after repeating the step of heat-treating the composite oxide at 1000 ° C. and then cooling to room temperature at least twice. However, the cubic crystal ratio is 75% by volume or more, a zirconium-cerium-based composite oxide (first invention).
[0014]
2. A composite oxide containing zirconium and cerium,
(1) Even after the initial oxygen adsorption amount is 800 μmol-O ₂ / g-CeO ₂ or more, and (2) the step of heat-treating the composite oxide at 1000 ° C. and then cooling to room temperature is repeated twice or more. A zirconium-cerium-based composite oxide having an oxygen adsorption amount of 70% or more of the initial oxygen adsorption amount (second invention).
[0015]
3. A method for producing a zirconium-cerium-based composite oxide, comprising mixing a basic zirconium sulfate with a solution containing cerium ions, and then adding a base to the mixed solution to form a precipitate.
[0016]
Furthermore, the present invention relates to an exhaust gas purifying catalyst material containing the zirconium-cerium-based composite oxide described in the above item 1 or 2.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
The zirconium-cerium-based composite oxide of the first invention is a composite oxide containing zirconium and cerium, wherein (1) 95% by volume or more of a crystal phase is a cubic crystal of a zirconia-ceria-based solid solution, and ( 2) The cubic crystal ratio is at least 75% by volume even after the step of heat-treating the composite oxide at 1000 ° C. and then cooling to room temperature is repeated twice or more (especially three or more times).
[0018]
95% by volume or more, preferably 99% by volume or more of the crystal phase in the composite oxide is a cubic crystal of a zirconia-ceria-based solid solution. By setting the cubic ratio to 95% by volume or more, excellent performance as a catalyst material or the like can be exhibited.
[0019]
Further, even after repeating the step of heat-treating the composite oxide at 1000 ° C. and then cooling to room temperature twice or more, the cubic crystal ratio is at least 75% by volume, preferably at least 80% by volume. Therefore, for example, a composite oxide which is within the above range of the cubic ratio when the above step is repeated twice is included in the present invention.
[0020]
Specifically, in the above step, 5 g of the above composite oxide is placed in a crucible and heat-treated in an electric furnace preheated to 1000 ° C. in an oxidizing atmosphere at 1000 ° C. for 3 hours. It is left to cool to room temperature (about 18 ° C.) in it. This heating / cooling cycle is repeated two or more times (hereinafter, the same applies to the second invention and Examples).
[0021]
The zirconium-cerium-based composite oxide of the second invention is a composite oxide containing zirconium and cerium, wherein (1) the initial oxygen adsorption amount is 800 μmol-O ₂ / g-CeO ₂ or more, and (2) After the heat treatment of the composite oxide at 1000 ° C. and cooling to room temperature are repeated twice or more (especially three or more times), the composite oxide has an oxygen adsorption amount of 70% or more of the initial oxygen adsorption amount. And
[0022]
The initial oxygen adsorption amount is 800 μmol-O ₂ / g-CeO ₂ or more, preferably 1000 μmol-O ₂ / g-CeO ₂ or more.
[0023]
Even after the step of heat-treating the composite oxide at 1000 ° C. and cooling to room temperature is repeated twice or more, the composite oxide has an oxygen adsorption amount of 70% or more, preferably 80% or more of the initial oxygen adsorption amount. That is, in the second invention, the deterioration rate of the oxygen adsorption amount is preferably less than 30%.
[0024]
The second invention preferably further satisfies the requirements of the first invention. That is, (1) 95% by volume or more of the crystal phase is a cubic crystal of a zirconia-ceria-based solid solution, and (2) a step of cooling the composite oxide to room temperature after heat treatment at 1000 ° C. twice or more ( Even after repeating (especially three or more times), the cubic crystal ratio is preferably 75% by volume or more.
[0025]
The first invention and the second invention (hereinafter collectively referred to as “the present invention”) further have a specific surface area (BET method) after heat treatment of the composite oxide at 1100 ° C. of 10 m ² / g or more, particularly 20 m ² / g. It is preferably at least ² / g. In particular, it is preferable that the specific surface area after the heat treatment at 1100 ° C. for 3 hours has the above value.
[0026]
The composition ratio in the present invention may be appropriately set according to the use of the final product or the like, but is usually 30 to 90% by weight as zirconium oxide and 10 to 70% by weight as cerium oxide, preferably 40 to 70% as zirconium oxide. The weight percentage and the cerium oxide may be 30 to 60 weight%.
[0027]
In the present invention, another metal (third metal) may be included as needed. For example, scandium, yttrium, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium and other rare earth metals, titanium, hafnium, vanadium, chromium, manganese, iron, Cobalt, nickel, copper, zinc, molybdenum, tungsten, indium, tin, antimony, phosphorus and the like can be mentioned. These can be used alone or in combination of two or more. In the present invention, among these, at least one of rare earth metals (excluding cerium), titanium and hafnium is particularly preferred. In this case, it is more preferable to include at least one of lanthanum, praseodymium and neodymium. By adding these third metals, the control of the crystal phase or the thermal cycle stability of the oxidation-reduction characteristics can be more reliably improved.
[0028]
The content of the third metal may be appropriately set according to the type of the third metal to be used, the use of the final product, and the like. It may be 15% by weight, more preferably 5 to 14% by weight.
[0029]
Further, in the present invention, sulfur can be contained in a sulfuric acid form (SO ₄ ). Thereby, especially the oxidation-reduction characteristics can be further enhanced. The content of the sulfated sulfur can be appropriately changed depending on the composition of the composite oxide, the use of the final product, and the like, but is usually not more than 3% by weight in the composite oxide, preferably 0.05 to 1%. It may be set to 0.5% by weight.
[0030]
The method for producing the composite oxide of the present invention can be carried out, for example, by mixing a solution containing basic zirconium sulfate and cerium ions and then adding a base to the mixture to form a precipitate. .
[0031]
The basic zirconium sulfate is not particularly limited, for example _{ZrOSO 4 · ZrO 2, 5ZrO 2} · 3SO 3, 7ZrO hydrates of the compounds represented by ₂ · 3SO ₃ and the like. These can be used alone or in combination of two or more.
[0032]
In general, these basic salts are obtained as aggregated particles having a particle size of 0.1 to several tens μm as an aggregate of fine particles having a small solubility and a particle size of several tens of angstroms by optical measurement, which are known in the art. Or a commercially available product can be used. For example, those described in "Gmelin Handbuch, TEIL 42; Zirkonium (ISBN 3-540-93242-9, 334-353, 1958)" and the like can also be used.
[0033]
The solution containing cerium ions is not particularly limited as long as cerium ions (generally represented by Ce ³⁺ and Ce ⁴⁺ ) are stably present. For example, a solution in which a cerium salt is dissolved in an appropriate solvent can be used. . As the cerium salt, for example, inorganic acid salts such as cerium nitrate, sulfate and chloride, and organic acid salts such as cerium acetate and oxalate can be used. More specifically, cerium (III) nitrate, cerium (IV) nitrate, cerium (III) chloride, cerium (IV) sulfate, ammonium (III) nitrate and the like can be mentioned.
[0034]
The solvent is not particularly limited as long as it can dissolve a cerium salt, a zirconium salt or the like, but usually, water, alcohols (eg, methanol, ethanol, etc.) can be used. The concentration of the solution can be changed as appropriate depending on the composition ratio of the composite oxide and the like, but is usually about 1 to 25% by weight, preferably 10 to 20% by weight.
[0035]
Further, when a third metal is contained in the composite oxide, ions of the metal may be contained in the mixed solution. For example, a solution or mixture of a compound containing a third metal (for example, an inorganic acid salt such as a sulfate, a nitrate, or a chloride of a third metal, or an organic acid salt such as an acetate or an oxalate) containing cerium ions as it is The compound may be mixed with a liquid, or a solution of the compound may be prepared in advance, and the solution may be mixed with the solution, the mixed solution, or the basic zirconium sulfate.
[0036]
Further, when sulfated sulfur is contained in the composite oxide, a solution containing sulfate ions may be added or sulfate ions of basic zirconium sulfate may be retained. When a solution containing sulfate ions is added, a compound containing sulfate ions (for example, sulfuric acid or a sulfate such as ammonium sulfate, sodium sulfate, potassium sulfate, aluminum sulfate, or the like) is added to the solution, or added in advance. A solution of the components may be prepared, and this solution may be blended with the solution or basic zirconium sulfate. As a method for retaining the sulfate ion of the basic zirconium sulfate, for example, the pH may be changed when a hydroxide is formed by adding a base to control the sulfate ion so as not to be desorbed.
[0037]
The mixing ratio of the basic zirconium sulfate and the solution containing cerium ions can be determined by appropriately adjusting the concentration of the solution and the like so as to have the above-mentioned composition ratio. The temperature of the mixed solution is usually 80 ° C. or lower, preferably 20 to 50 ° C.
[0038]
Next, after mixing basic zirconium sulfate and a solution containing cerium ions, a base is added to the mixed solution to form a precipitate.
[0039]
The base is not particularly limited, and known alkali agents such as sodium hydroxide, potassium hydroxide, sodium carbonate, ammonium carbonate, and ammonia can be used. In the present invention, it is particularly preferable to use a strong alkali such as sodium hydroxide and potassium hydroxide. Further, these bases are preferably added as an aqueous solution. In this case, the concentration of the aqueous solution is not particularly limited as long as the pH can be adjusted, but may be generally about 5 to 50% by weight, preferably 20 to 25% by weight.
[0040]
In the present invention, the content of sulfated sulfur in the composite oxide can be particularly controlled by changing the amount of the base (ie, pH). The pH of the mixed solution may be usually 12 or more and less than 14. The amount of the base to be added may be appropriately set within this range according to the desired content.
[0041]
The generated precipitate can be collected by filtration, washing with water, etc., according to a recovery method employed in a known coprecipitation method or the like, and then by a known solid-liquid separation method. The collected precipitate may be dried if necessary. Drying may be either natural drying or heat drying.
[0042]
In the present invention, the precipitate may be further baked if necessary. The firing conditions are not particularly limited, but usually firing may be performed at 400 ° C. or higher in an oxidizing atmosphere or air. The upper limit of the firing temperature is not particularly limited as long as a desired composite oxide is obtained. The firing time may be appropriately set according to the firing temperature or the like, and may be generally about 1 to 8 hours after the temperature of the fired product reaches the set temperature. After the firing, a known pulverization treatment, classification treatment, or the like may be performed as necessary.
[0043]
The exhaust gas purifying catalyst material of the present invention contains the zirconium-cerium-based composite oxide of the present invention, and can be used, for example, as a catalyst, a co-catalyst, a catalyst carrier and the like. In particular, it is useful as a co-catalyst for assisting the action of a noble metal (eg, platinum, rhodium, palladium, iridium, etc.) which is an active component for purifying exhaust gas immediately below an engine. In addition, it can be suitably used as an OSC (oxygen adsorption) component corresponding to monitoring of OBD-II regulations.
[0044]
[Action]
In the production method of the present invention, by adding a base to a mixed solution containing basic zirconium sulfate and cerium ions. The neutralization reaction of the hydroxide ion (OH ⁻ ) supplied by the sulfate and base in the basic zirconium sulfate and the neutralization reaction of the cerium ion and the hydroxide ion proceed simultaneously.
[0045]
At this time, the cerium ions are selectively present in the vicinity of the sulfate sites of the basic zirconium sulfate due to the chemical affinity with the sulfate ions, and the surface of the basic zirconium sulfate (or zirconium hydroxide depending on the progress of the neutralization reaction). Is also hydroxylated. This phenomenon generally follows the principle of late precipitation or co-precipitation.
[0046]
In the present invention, by utilizing this characteristic reaction, a precipitate in which zirconium and cerium are uniformly integrated can be efficiently obtained. Further, in this reaction process, sulfate ions contained in basic zirconium sulfate are desorbed from zirconium and then combined with cerium ions (or cerium hydroxide) due to the difference in chemical affinity between zirconium and cerium and sulfate ions. Or chemisorbed). This phenomenon is evident from the fact that the content of sulfated sulfur in the composite oxide has a large effect not on the thermal stability of the specific surface area caused by zirconium oxide but on the oxidation-reduction properties caused by cerium oxide. .
[0047]
【The invention's effect】
In the production method of the present invention, in particular, since basic zirconium sulfate is used as the zirconium precursor, a highly chemically uniform zirconium-cerium-based composite oxide can be produced with good reproducibility, and efficiently. Suitable for industrial scale production.
[0048]
Since the zirconium-cerium-based composite oxide of the present invention has a structure with high chemical uniformity, it has excellent thermal stability and oxidation-reduction properties. Accordingly, excellent heat stability and oxidation-reduction characteristics can be maintained, especially even in a heating-cooling cycle.
[0049]
Therefore, when this is used as an exhaust gas purifying catalyst material (catalyst, co-catalyst, catalyst carrier, etc.) in an internal combustion engine, the crystal structure changes even in the heating-cooling cycle by stopping, starting, accelerating, and stopping the engine. Almost no excellent redox properties can be obtained stably.
[0050]
【Example】
Examples and comparative examples are shown below to further clarify the features of the present invention. However, the present invention is not limited to these examples. Each physical property was measured by the following method. The zirconium in the examples contains hafnium (1.3 to 2.5% by weight as hafnium oxide) as an unavoidable impurity.
(1) Composition ratio of composite oxide It was examined by ICP-emission spectroscopy.
(2) Using an oxygen adsorption apparatus “Multitask TPD (TPD-1-AT)” (manufactured by Nippon Bell), the measurement was performed by the oxygen pulse method at 600 ° C.
(3) Deterioration rate of OSC (OSC)
As shown by the following equation, the difference between the initial oxygen adsorption amount (OSC ₀ ) of the composite oxide and the oxygen adsorption amount (OSC ₂ ) after repeating the heating-cooling cycle twice is divided by the initial oxygen adsorption amount. I asked.
[0051]
OSC (%) = [(OSC ₀ −OSC ₂ ) / OSC ₀ ] × 100
(4) Cubic Crystal Ratio in Crystal Phase As shown by the following formula, the sum of the intensities (Ia + Ib) of the cubic crystal plane (111) of the cubic crystal of the composite oxide and the pure cerium oxide alone represents the cubic crystal of the composite oxide. It was determined by dividing the intensity (Ia) of the crystal plane (111). In addition, each intensity | strength was measured using the device "Geigerflex RAD-2C" (made by Rigaku).
[0052]
Cubic ratio (% by volume) = [Ia / (Ia + Ib)] × 100
(5) Using a sulfuric acid sulfur content analyzer “HORIBA EMIA-520” (manufactured by HORIBA, Ltd.), it was measured by a plasma combustion-infrared absorption method.
[0053]
Example 1
Basic zirconium sulfate (containing 86 g as zirconium oxide) is dispersed in 1000 g of water, and an aqueous cerium nitrate solution (containing 88 g as cerium oxide), an aqueous lanthanum nitrate solution (containing 18 g as lanthanum oxide) and an aqueous praseodymium nitrate solution (containing 8 g as praseodymium oxide) Was added to prepare a mixed solution.
[0054]
Next, a 25% by weight aqueous sodium hydroxide solution was added until the pH of the mixed solution became 13.5 to obtain a precipitate. The generated precipitate was collected by solid-liquid separation and the solid content was calcined at 660 ° C. in the air for 3 hours.
[0055]
The crystal phase of the obtained composite oxide was a single cubic crystal, and the initial oxygen adsorption amount was 412 μmol-O ₂ / g (940 μmol-O ₂ / g-CeO ₂ ). The composition ratio was 42.9% by weight of zirconium oxide, 43.8% by weight of cerium oxide, 9.1% by weight of lanthanum oxide and 4.1% by weight of praseodymium oxide. The sulfated sulfur content was 0.1% by weight. The cubic crystal ratio after the heating-cooling cycle was 100% by volume, and the rate of deterioration of the amount of adsorbed oxygen was 7%. The BET specific surface area after heat treatment at 1100 ° C. for 3 hours was 22 m ² / g, and the amount of adsorbed oxygen was 840 μmol-O ₂ / g-CeO ₂ .
[0056]
Examples 2 to 5
A composite oxide was prepared in the same manner as in Example 1, except that basic zirconium sulfate, cerium nitrate aqueous solution, lanthanum nitrate aqueous solution, and praseodymium nitrate were blended in the ratio (g) shown in Table 1. The cubic crystal ratio of each of the obtained composite oxides was 95% by volume or more.
[0057]
Composition ratio of each composite oxide, sulfated sulfur content, initial oxygen adsorption amount, cubic ratio after heating-cooling cycle and deterioration rate of oxygen adsorption amount, and oxygen adsorption amount after heat treatment at 1100 ° C. for 3 hours Table 2 shows the BET specific surface area.
[0058]
[Table 1]

[0059]
[Table 2]

[0060]
Comparative Example 1
An aqueous cerium nitrate solution (containing 74 g as cerium oxide) and an aqueous lanthanum nitrate solution (2 g as lanthanum oxide) were added to an aqueous zirconium nitrate solution (containing 24 g as zirconium oxide) to prepare a mixed solution, and 2 g of ammonium sulfate was further added. To this mixture, 25% by weight aqueous ammonia was added until the pH became 10.2, to generate a precipitate. The precipitate was subjected to solid-liquid separation, and the obtained solid content was calcined at 660 ° C. in the air for 3 hours. The crystal phase of this composite oxide was a mixture of two types of cubic crystals, namely, a cubic crystal of the composite oxide and a cubic crystal of cerium oxide alone. In the same manner as in Example 1, each physical property of the obtained composite oxide was examined. Table 3 shows the results.
[0061]
Comparative Example 2
An aqueous cerium nitrate solution (containing 116 g as cerium oxide) was added to an aqueous zirconium hydroxide solution (containing 84 g as zirconium oxide) to prepare a mixed solution. A 25% by weight aqueous ammonia solution was added to the mixture until the pH reached 10.2 to form a precipitate. The precipitate was subjected to solid-liquid separation, and the obtained solid content was calcined at 660 ° C. in the air for 3 hours. The crystal phase of this composite oxide was a mixture of two types of cubic crystals, namely, a cubic crystal of the composite oxide and a cubic crystal of cerium oxide alone. In the same manner as in Example 1, each physical property of the obtained composite oxide was examined. Table 3 shows the results.
[0062]
[Table 3]

[0063]
Test example 1
The heating / cooling cycle (heat treatment cycle) test was repeated four times for the composite oxides obtained in Example 1, Comparative Example 1 and Comparative Example 2. X-ray diffraction analysis was performed on each sample for each heating / cooling cycle. The results are shown in FIGS. The OSC of each sample was measured for each heating / cooling cycle. The result is shown in FIG.
[0064]
From FIGS. 1 to 3, in the composite oxides of Comparative Examples 1 and 2, the intensity of the peak corresponding to the ceria (111) plane was increased by repeating the heat treatment cycle, and the cubic (111) zirconia-ceria solid solution was obtained. It can be seen that the intensity of the peak corresponding to the plane has decreased. This indicates that sintering of ceria has progressed and the catalytic performance has been reduced. On the other hand, it can be seen that the cubic crystal of the zirconia-ceria-based solid solution is dominant in the composite oxide of Example 1 even when the heat treatment cycle is repeated, and that the formation of pure ceria is prevented and stabilized.
[0065]
Further, from FIG. 4, it can be seen that in the composite oxides of Comparative Examples 1 and 2, the amount of adsorbed oxygen is significantly reduced by repeating the heat treatment cycle. On the other hand, in Example 1, such a decrease was not recognized, and it can be seen that relatively stable performance can be exhibited.
[0066]
Test example 2
The same heating / cooling cycle (heat treatment cycle) test as in Test Example 1 was performed on the composite oxide obtained in Example 5. The result is shown in FIG. Also, as in Test Example 1, the OSC was measured for each heating / cooling cycle. FIG. 6 shows the result.
[0067]
As shown in FIG. 5, the cubic crystal of the zirconia-ceria-based solid solution is superior to the composite oxide of Example 5, even when the heat treatment cycle is repeated. You can see that it is. In addition, FIG. 6 shows that in Example 5, a significant decrease in the amount of adsorbed oxygen was not observed, and relatively stable performance could be exhibited.
[Brief description of the drawings]
FIG. 1 is a view showing a result of an X-ray diffraction analysis when a heat treatment cycle test is performed on the composite oxide of Example 1.
FIG. 2 is a view showing a result of an X-ray diffraction analysis when a heat treatment cycle test is performed on the composite oxide of Comparative Example 1.
FIG. 3 is a view showing a result of an X-ray diffraction analysis when a heat treatment cycle test is performed on the composite oxide of Comparative Example 2.
FIG. 4 is a view showing OSC measurement results when a heat treatment cycle test was performed on each of the composite oxides of Example 1, Comparative Examples 1 and 2.
FIG. 5 is a diagram showing the results of X-ray diffraction analysis when a heat treatment cycle test was performed on the composite oxide of Example 5.
FIG. 6 is a view showing an OSC measurement result when a heat treatment cycle test is performed on the composite oxide of Example 5.

Claims (10)

A composite oxide containing zirconium and cerium,
(1) 95% by volume or more of the crystal phase is a cubic crystal of a zirconia-ceria-based solid solution, and (2) after repeating the step of heat-treating the composite oxide at 1000 ° C. and then cooling to room temperature at least twice. However, the cubic crystal ratio is 75% by volume or more, a zirconium-cerium-based composite oxide. A composite oxide containing zirconium and cerium,
(1) Even after the initial oxygen adsorption amount is 800 μmol-O ₂ / g-CeO ₂ or more, and (2) the step of heat-treating the composite oxide at 1000 ° C. and then cooling to room temperature is repeated twice or more. A zirconium-cerium-based composite oxide having an oxygen adsorption amount of 70% or more of the initial oxygen adsorption amount. A composite oxide containing zirconium and cerium,
(1) Even after the initial oxygen adsorption amount is 800 μmol-O ₂ / g-CeO ₂ or more, and (2) the step of heat-treating the composite oxide at 1000 ° C. and then cooling to room temperature is repeated twice or more. 2. The zirconium-cerium-based composite oxide according to claim 1, having an oxygen adsorption amount of 70% or more of the initial oxygen adsorption amount. The zirconium-cerium composite oxide according to any one of claims 1 to 3, wherein a specific surface area of the composite oxide after heat treatment at 1100 ° C is 10 m ² / g or more. The zirconium-cerium-based composite oxide according to any one of claims 1 to 4, wherein a composition ratio is 30 to 90% by weight as zirconium oxide and 10 to 70% by weight as cerium oxide. The zirconium-cerium-based composite oxide according to any one of claims 1 to 5, further comprising a rare earth metal (excluding cerium), at least one of titanium and hafnium. The zirconium-cerium-based composite oxide according to any one of claims 1 to 6, further comprising sulfur in a sulfated form in a range not exceeding 3% by weight. After mixing a basic zirconium sulfate and a solution containing cerium ions, a base is added to the mixed solution, and a pH is adjusted to 12 or more and less than 14 to form a precipitate, thereby producing a zirconium-cerium composite. A method for producing an oxide. 9. The production method according to claim 8, wherein the mixture contains at least one ion of rare earth metals (excluding cerium), titanium and hafnium. An exhaust gas purifying catalyst material comprising the zirconium-cerium-based composite oxide according to claim 1.

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