JP4218364B2 - Method for producing metal oxide - Google Patents

Description

【００６４】
各耐久試験後の各触媒について、表２に示すモデルガスを、リッチガス１秒間及びリーンガス１秒間の条件で交互に繰り返し全流量20Ｌ／分で流しながら20℃／分の速度で昇温し、その間のHC，CO及びNO_x の浄化率を連続的に測定した。そして各有害成分の50％が浄化される温度（Ｔ₅₀）を算出し、結果を図２及び図３に示す。なお図２及び図３における棒グラフの頂点の数字は、実際のＴ₅₀の値である。
【００６５】
【表２】

【００６６】
また実施例２及び比較例２の触媒を評価装置に配置し、表１に示したモデルガスを、リッチガス１分間及びリーンガス４分間の条件で交互に繰り返し流しながら、1000℃で５時間保持するリッチリーン耐久試験を行った。全流量は20Ｌ／分である。またこれとは別に、大気中にて 850℃で５時間保持するエアー耐久試験を行った。
【００６７】
各耐久試験後の各触媒について、表２に示したモデルガスを、リッチガス１秒間及びリーンガス１秒間の条件で交互に繰り返し全流量20Ｌ／分で流しながら20℃／分の速度で昇温し、その間のHC，CO及びNO_x の浄化率を連続的に測定した。そして各有害成分の50％が浄化される温度（Ｔ₅₀）を算出し、結果を図４及び図５に示す。なお図４及び図５における棒グラフの頂点の数字は、実際のＴ₅₀の値である。
【００６８】
図２及び図３より、実施例１の触媒は比較例１の触媒に比べて各耐久試験後にも低温域から高い浄化能を示し、これはCeO₂−ZrO₂粉末の細孔容積及び平均二次粒子径の差に起因していると考えられる。すなわち実施例１の触媒は、コート層のガス拡散性に優れているため、コート層の下層に担持されているPtも有効に利用されたと考えられる。
【００６９】
また図４及び図５より、実施例２の触媒は比較例２の触媒に比べて各耐久試験後にも低温域から高い浄化能を示し、これは図１に示すように実施例２の触媒の方が細孔容積が大きく、平均二次粒子径も大きいことに起因していると考えられる。すなわち実施例２の触媒は、コート層のガス拡散性に優れているため、コート層の下層に担持されているRhも有効に利用されたと考えられる。
【００７０】
（実施例３）
第１工程：
３リットルのビーカ中において、硝酸セリウム水溶液589.71ｇ（CeO₂として28重量％）と、オキシ硝酸ジルコニウム水溶液 437.3ｇ（ZrO₂として18重量％）と、30％過酸化水素水 199.5ｇと、界面活性剤（「レオコン」ライオン社製）12ｇと、を1200ｇのイオン交換水と混合し、プロペラ撹拌器及びホモジナイザで撹拌しながら、25％アンモニア水溶液 340ｇを添加し、酸化物前駆体の沈殿物を得た。
【００７１】
第２工程以下は実施例１と同様にして、本実施例のCeO₂−ZrO₂固溶体粉末を調製した。
【００７２】
得られたCeO₂−ZrO₂固溶体粉末の、細孔径が 0.1μｍ以下の細孔の細孔容積は 0.3cc／ｇであり、平均二次粒子径は６μｍであった。なお細孔容積は水銀ポロシメータにより測定し、平均二次粒子径はレーザー回折／散乱式粒度分布測定装置により測定した。
【００７３】
（実施例４）
第１工程：
３リットルのビーカ中において、硝酸セリウム水溶液589.71ｇ（CeO₂として28重量％）と、オキシ硝酸ジルコニウム水溶液 437.3ｇ（ZrO₂として18重量％）と、30％過酸化水素水 199.5ｇと、30％過酸化水素水 199.5ｇと、を1200ｇのイオン交換水と混合し、25％アンモニア水溶液３ｇを添加して、プロペラ撹拌器で撹拌した。これを 120℃で２時間加圧熟成した。この溶液をプロペラ撹拌器で撹拌しながら、25％アンモニア水溶液 340ｇを添加し、酸化物前駆体の沈殿物を得た。
【００７４】
第２工程以下は実施例１と同様にして、本実施例のCeO₂−ZrO₂固溶体粉末を調製した。
【００７５】
得られたCeO₂−ZrO₂固溶体粉末の、細孔径が 0.1μｍ以下の細孔の細孔容積は 0.2cc／ｇであり、平均二次粒子径は６μｍであった。なお細孔容積は水銀ポロシメータにより測定し、平均二次粒子径はレーザー回折／散乱式粒度分布測定装置により測定した。
【００７６】
＜試験・評価＞
実施例３及び実施例４のCeO₂−ZrO₂固溶体粉末の細孔分布を水銀ポロシメータにより測定し、結果を図６に示す。
【００７７】
図６より、実施例４のCeO₂−ZrO₂固溶体粉末の細孔分布は、実施例３に比べて微細な範囲に集中していることがわかる。これは、詳細な理由は不明であるが、微量のアンモニア水の添加と加圧熟成により、均一な核の生成が生じたことに起因していると考えられる。
【００７８】
そして図６より、実施例４のCeO₂−ZrO₂固溶体粉末は、細孔径が0.01μｍ以上かつ0.05μｍ以下の細孔の細孔容積が 0.1cc／ｇ以上であり、かつその細孔容積が、細孔径が0.01μｍ以上かつ 0.1μｍ以下の細孔の細孔容積の70％以上を占めていることが明らかである。
【００７９】
【発明の効果】
すなわち本発明で得られた金属酸化物によれば、細孔容積と平均二次粒子径が従来より大きいためガス拡散性に優れ、その金属酸化物を用いた排ガス浄化用触媒によれば、コート層の下層に担持されている触媒成分と排ガスとの接触機会が増し浄化能が向上する。
【図面の簡単な説明】
【図１】実施例２及び比較例２のZrO₂粉末の細孔分布を示すグラフである。
【図２】実施例１及び比較例１の触媒のリッチリーン耐久試験後の50％浄化温度を示すグラフである。
【図３】実施例１及び比較例１の触媒のエアー耐久試験後の50％浄化温度を示すグラフである。
【図４】実施例２及び比較例２の触媒のリッチリーン耐久試験後の50％浄化温度を示すグラフである。
【図５】実施例２及び比較例２の触媒のエアー耐久試験後の50％浄化温度を
【図６】実施例３及び実施例４のCeO₂−ZrO₂固溶体粉末の細孔分布を示すグラフである。[0001]
BACKGROUND OF THE INVENTION
  The present invention is used as a catalyst carrier for an exhaust gas purification catalyst of an automobile.Method for producing metal oxideAbout.Manufactured in the present inventionIn addition to this, the metal oxide can also be used as a catalyst support for a diesel particulate oxidation catalyst, a solid electrolyte, an electrode material, ceramic dispersion strengthened particles, an ultraviolet shielding material, and the like.
[0002]
[Prior art]
Since ceria has an oxygen storage / release capacity (OSC), it is widely used as a promoter for exhaust gas purification catalysts that purify exhaust gas from internal combustion engines. In order to increase OSC, it is desirable to increase the specific surface area, so ceria is used as a powder.
[0003]
However, since the exhaust gas purifying catalyst is used at a high temperature, it is necessary that the purifying activity at a high temperature is high. For this reason, ceria is required to have no reduction in specific surface area when used at a high temperature, that is, excellent heat resistance, even when used as a powder having a high specific surface area.
[0004]
In view of this, it has been conventionally proposed that a rare earth element oxide other than zirconia or cerium is dissolved in ceria. For example, Japanese Patent Laid-Open No. 04-055315 discloses an oxidation in which a ceria precursor and a zirconia precursor are co-precipitated from a mixed aqueous solution of a water-soluble salt of cerium (Ce) and a water-soluble salt of zirconium (Zr) and heat-treated. A method for producing a cerium fine powder is disclosed. According to this production method, the coprecipitate is heat treated to give CeO.₂And ZrO₂Becomes a complex oxide, and an oxide solid solution that is solid-solved with each other is formed.
[0005]
JP-A 09-221304 discloses that the average diameter of the crystallite is small and high by adding a surfactant when the oxide precursor is precipitated from an aqueous solution in which the metal salt of Ce and Zr is dissolved. A method for producing a ceria-zirconia solid solution having a solid solubility and high OSC is disclosed.
[0006]
Thus, by adding a surfactant when the oxide precursor is precipitated, a plurality of types of precipitated particles are uniformly taken into the micelles of the surfactant. As the neutralization, aggregation and aging proceed in the micelles, the formation of solid solution particles proceeds in a small space in which a plurality of components are uniformly contained and concentrated. Furthermore, the dispersibility of the precipitated fine particles is improved by the dispersing effect of the surfactant, the segregation is reduced and the contact degree is increased. As a result, the solid solubility increases and the average diameter of the crystallites can be reduced.
[0007]
Furthermore, Japanese Patent Publication No. 2001-524918 discloses a zirconia that optimally adjusts the particle size distribution, pore volume, etc. by adding a surfactant when the oxide precursor is precipitated from an aqueous solution of a metal salt. Alternatively, a method for producing ceria-zirconia solid solution or the like is disclosed.
[0008]
[Patent Document 1]
JP 04-055315
[Patent Document 2]
JP 09-221304 A
[Patent Document 3]
Special table 2001-524918
[0009]
[Problems to be solved by the invention]
However, in the method of adding a surfactant when precipitating the oxide precursor from the aqueous solution of the metal salt, the secondary particle size of the resulting oxide powder may be reduced and the pore volume may be reduced, When used as a catalyst carrier, the characteristics may not be fully expressed.
[0010]
For example, in a catalyst for exhaust gas purification in which a coat layer is formed from a catalyst carrier powder on a honeycomb substrate and a catalyst component such as a noble metal is supported on the coat layer, there is a problem that the catalyst component in the lower layer portion in the coat layer cannot be effectively used. is there. This is because the exhaust gas hardly diffuses to the lower layer when passing through the coat layer, which is considered to be caused by the small pore volume.
[0011]
The present invention has been made in view of such circumstances, and its main object is to provide a metal oxide having a large pore volume and extremely useful as a catalyst support.
[0012]
[Means for Solving the Problems]
  The present invention solves the above-mentioned problems.Method for producing metal oxideThe features ofAl , Zr , Ti , Si as well as Ce A first step of obtaining a precipitate of an oxide precursor by adding an alkaline substance to an aqueous solution in which a compound containing a metal element selected from the above is dissolved, a second step of washing the precipitate, and a washed precipitate A third step of stirring in water together with the surfactant and a fourth step of firing the precipitate after the third step to obtain a metal oxide powder are sequentially performed.
[0015]
  In the production method of the present invention, the surfactant is desirably added so as to be 2 to 40% by weight with respect to the obtained metal oxide powder. The metal element is Zr or Ce and Zr,Obtained in the present inventionMetal oxide is ZrO₂Or CeO₂−ZrO₂It is desirable to be a solid solution.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Al used as a catalyst carrier for exhaust gas purification catalysts₂O_Three, ZrO₂, CeO₂−ZrO₂In a conventional metal oxide such as a solid solution, the pore volume of pores having a pore diameter of 0.1 μm or less was in a relatively small range of 0 to 0.2 cc / g. Therefore, the gas diffusibility in the coat layer is low, and it is difficult to effectively use the catalyst component supported in the lower layer of the coat layer. The pore volume means the total volume of each pore. The secondary particles are formed by aggregation of the primary particles, and the average secondary particle diameter corresponds to the actual average particle diameter of the metal oxide powder.
[0018]
  Obtained in the present inventionThe metal oxide has a pore volume of 0.2 cc / g or more of pores having a pore diameter of 0.1 μm or less. By forming a coat layer from this metal oxide powder, it becomes a coat layer with excellent gas diffusivity, and the contact opportunity between the catalyst component and the exhaust gas increases in the lower layer. Therefore, the catalyst component can be used effectively, and the purification performance is improved.
[0019]
  Obtained in the present inventionIn the metal oxide powder, when the pore volume of pores having a pore diameter of 0.1 μm or less is smaller than 0.2 cc / g, sufficient gas diffusibility cannot be obtained. If the average secondary particle size is too large, the coating layer becomes brittle and may cause problems such as peeling during use, so that the average secondary particle size is preferably 30 μm or less.
[0020]
  Obtained in the present inventionMetal oxide is Al₂O_Three, ZrO₂, TiO₂, SiO₂, CeO₂Or a composite oxide composed of any plural kinds selected from these. For example ZrO₂Or CeO₂−ZrO₂It is particularly preferable to use a solid solution. ZrO₂In this case, for example, by using a catalyst supporting Rh, since the gas diffusibility is high, the steam reforming reaction activity is greatly improved, and the catalyst can be used as a hydrogen production catalyst having high production ability. Also CeO₂−ZrO₂In the case of a solid solution, high OSC is expressed due to high gas diffusivity, and it is extremely useful as a three-way catalyst.
[0021]
  In the production method of the present invention,First, in the first step,Al , Zr , Ti , Si as well as Ce Metal elements selected fromThe precipitate of the oxide precursor is formed by adding an alkaline substance to the aqueous solution in which the compound containing is dissolved.
[0022]
  Examples of aqueous solutions in which compounds containing metal elements that form oxides are dissolved include Al, Zr, Ti, Si, and Ce.Chosen fromAn aqueous solution of a water-soluble compound containing a metal can be used. For example, when the metal is Ce or Zr, cerium (III) nitrate, cerium (IV) ammonium nitrate, cerium (III) chloride, cerium sulfate (III), An aqueous solution of cerium (IV) sulfate, zirconium oxynitrate, zirconium oxychloride, or the like can be used.
[0023]
Moreover, as an alkaline substance, what shows alkalinity as aqueous solution can be used. Ammonia, which can be easily separated during heating, is particularly desirable. However, other alkaline substances such as alkali metal hydroxides can be used because they can be easily removed by washing with water. The alkaline substance is preferably added as an aqueous solution, which may be gradually added dropwise or mixed all at once. In order to prevent segregation of precipitates, it is desirable to add an aqueous solution in which a metal element is dissolved with stirring.
[0024]
CeO₂−ZrO₂When producing a solid solution, it is necessary to pay attention to the valence of cerium. In the case of tetravalent cerium, CeO₂ZrO₂However, in the case of trivalent cerium, CeO₂ZrO₂For example, it is desirable to coexist hydrogen peroxide in an aqueous solution. In this way, cerium (III) forms a complex with hydrogen peroxide and is oxidized to cerium (IV).₂ZrO₂Can be easily dissolved.
[0025]
The amount of hydrogen peroxide added is desirably ¼ or more of cerium ions. If the amount of hydrogen peroxide added is less than 1/4 of cerium ion, CeO₂And ZrO₂Insufficient solid solution. The excessive addition of hydrogen peroxide has no particular adverse effect, but it is disadvantageous in terms of economy, has no merit, and is preferably in the range of 1/2 to 2 times that of cerium ions. In addition, the addition timing in particular of hydrogen peroxide is not restrict | limited, It may be before the addition of an alkaline substance, and can also be added simultaneously or after it. Hydrogen peroxide is a particularly desirable oxidizing agent because it does not require post-treatment, but in some cases, other oxidizing agents such as oxygen gas, peroxides such as ozone, perchloric acid and permanganic acid can be used. .
[0026]
Further, an aqueous solution in which a compound containing a metal element to be an oxide is dissolved is added.^Threesec^-1Or more, preferably 10^Foursec^-1It is also preferable to add the alkaline substance while stirring at a high shear rate as described above. Since the components in the precipitated fine particles, which are neutralized products, cannot avoid a certain degree of segregation, the segregation can be made uniform and the dispersibility can be improved by vigorous stirring. For example, when co-precipitated from an aqueous solution of cerium salt and zirconium salt, the same kind of precipitated particles are likely to be a group because the pH at which they precipitate is different. Therefore, high-speed stirring at a high shear rate destroys a group of precipitated fine particles of the same type, and CeO₂Precursor and ZrO₂Since the contact degree of the precursor is improved, the precipitated particles are well mixed. Therefore CeO₂−ZrO₂The solid solubility of the solid solution can be improved and the average diameter of the crystallite can be reduced. Shear rate is 10^Threesec^-1If it is less than 1, the solid solution promoting effect is not sufficient. The shear rate V is expressed by V = v / D. Here, v is a speed difference (m / sec) between the rotor and the stator of the stirrer, and D is a gap (m) between the rotor and the stator.
[0027]
In the conventional coprecipitation method, a compound containing a metal element that becomes an oxide, an alkaline substance, and a surfactant coexist in an aqueous solution. For this reason, there has been a problem that the property of the surfactant is changed by the pH change when the alkaline substance is added, and the effect of adding the surfactant is impaired.
[0028]
Therefore, in the production method of the present invention, the precipitate of the oxide precursor is washed in the second step, and the washed precipitate is stirred in water together with the surfactant in the third step. Since the alkaline substance and free acid are washed away from the oxide precursor by washing in the second step, the surfactant is not exposed to pH change in the third step. Therefore, the effect of adding the surfactant is maximized, and a metal oxide having a pore volume of 0.1 cc / g or more and a pore volume of 0.2 cc / g or more can be produced by firing in the fourth step.
[0029]
The action of the surfactant is not clear, but is presumed as follows. That is, in the state just neutralized with the alkaline substance, the metal element that becomes an oxide precipitates in a very fine hydroxide or oxide state having a particle size of several nm or less. Then, the aggregation of the primary particles proceeds to some extent during the cleaning in the second step and becomes secondary particles.
[0030]
By adding the surfactant in the third step, the secondary particles are taken into the micelles of the surfactant, and the particles grow in the concentrated small space by aggregating and aging in the micelles. Progresses. Furthermore, the dispersibility of the secondary particles is improved by the dispersing effect of the surfactant. By these actions, it is considered that a metal oxide powder having a pore diameter of 0.1 袖 m or less and a pore volume of 0.2 cc / g or more can be produced.
[0031]
The addition amount of the surfactant in the third step is in a range of 2 to 40% by weight with respect to the obtained metal oxide powder, that is, metal oxide powder: surfactant = 98 to 60: 2 to 40 in a weight ratio. The range of is preferable. If the added amount of the surfactant is less than 2% by weight, the effect of the addition is small. If the added amount exceeds 40% by weight, the dispersibility of the oxide precursor is reduced due to the aggregation of the surfactants, and firing in the fourth step Sometimes the amount of heat generated by the combustion of the surfactant increases, so that the metal oxide aggregates and the specific surface area decreases.
[0032]
The amount of water in the third step is preferably about the same as the amount of water in the first step, but is not particularly limited as long as it can be stirred. The stirring speed in the third step is 1000 sec.^-1It is preferable to make it above, and it is preferable to stir at a temperature of 10 to 30 ° C. for 5 minutes or more. If the shearing force by stirring is too large, heat will be generated or the apparatus will be exhausted excessively. If the shearing force is too small, the surfactant may not be sufficiently dispersed. Further, if the temperature during stirring is lower than this range, the stirring time becomes longer, and if the temperature is higher than this range, heat generation or exhaustion of the apparatus occurs.
[0033]
As the surfactant, any of an anionic type, a cationic type and a nonionic type can be used, and among them, a shape in which the micelle to be formed can form a narrow space inside, for example, a spherical micelle is easily formed. A surfactant is desirable. A surfactant having a critical micelle concentration (cmc) of 0.1 mol / liter or less is desirable, and a surfactant having a concentration of 0.01 mol / liter or less is desirable. The critical micelle concentration (cmc) is the lowest concentration at which a surfactant forms micelles.
[0034]
Examples of these surfactants include anionic surfactants such as alkylbenzene sulfonic acid and its salt, α-olefin sulfonic acid and its salt, alkyl sulfate ester salt, alkyl ether sulfate ester salt, phenyl ether sulfate ester salt, Methyl taurate, sulfosuccinate, ether sulfate, alkyl sulfate, ether sulfonate, saturated fatty acid and its salt, unsaturated fatty acid such as oleic acid and its salt, other carboxylic acid, sulfonic acid, sulfuric acid, phosphorus Acids, phenol derivatives, etc .;
Nonionic surfactants such as polyoxyethylene polypropylene alkyl ether, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene polystyryl phenyl ether, polyoxyethylene polyoxypolypropylene alkyl ether, polyoxyethylene poly Polyhydric alcohols such as oxypropylene glycol, glycol, glycerin, sorbitol, mannitol, pentaerythritol, sucrose, fatty acid partial ester of polyhydric alcohol, polyoxyethylene fatty acid partial ester of polyhydric alcohol, polyoxyethylene fatty acid of polyhydric alcohol Ester, polyoxyethylenated castor oil, polyglycene fatty acid ester, fatty acid diethanolamide, polyoxyethylene alkyl Min, triethanolamine fatty acid partial esters, trialkylamine oxide and the like;
Cationic surfactants, fatty acid primary amine salt, fatty acid secondary amine salt, fatty acid tertiary amine salt, tetraalkylammonium salt, trialkylbenzylammonium salt, alkylpyrodinium salt, 2-alkyl-1- Quaternary ammonium salts such as alkyl-1-hydroxyethylimidazolinium salts, N, N-dialkylmorpholinium salts, polyethylene polyamines, fatty acid amide salts, etc .;
At least one selected from betaine compounds and the like that are amphoteric surfactants can be used.
[0035]
In a 4th process, the metal element in a precipitate is made into an oxide by baking the precipitate of the oxide precursor after a 3rd process. The firing atmosphere may be any of an oxidizing atmosphere, a reducing atmosphere, and a neutral atmosphere. The reason why the metal element in the precipitate becomes an oxide is that oxygen contained in water or the like of the aqueous solution used as a raw material is involved, and the metal element in the precipitate is oxidized during firing. Therefore, a metal oxide can be obtained even when fired in a reducing atmosphere. The firing temperature is preferably 150 to 800 ° C. When the firing temperature is lower than 150 ° C, it takes a long time for firing. When the firing temperature is higher than 800 ° C, the specific surface area decreases.
[0036]
Moreover, it is also preferable to perform a precipitate washing step between the third step and the fourth step. As a result, the surfactant can be removed, and heat generation due to combustion of the surfactant during firing can be avoided.
[0037]
  An exhaust gas purifying catalyst can be produced by supporting at least a noble metal on the obtained metal oxide powder.The noble metal is at least one selected from Pt, Rh, Pd, Ir, etc., and can be supported by an adsorption support method, an impregnation support method, etc. as in the past, as an oxidation catalyst, a hydrogen generation catalyst, a three-way catalyst, etc. Can be used. At least one NO selected from alkali metals, alkaline earth metals, and rare earth metals_x NO is stored with a precious metal_x It can also be an occlusion reduction catalyst. The amount of precious metal supported per liter of catalyst volume is preferably in the range of 0.1 to 20 g._x The loading amount of the occlusion material is preferably in the range of 0.05 mol to 2 mol.
[0038]
  In additionObtainedWhen producing an exhaust gas purification catalyst from metal oxide powder, first a coat layer is formed and then noble metal or NO_x A catalyst component such as an occlusion material may be supported, or a coating layer may be formed from a catalyst powder in which a catalyst component is previously supported on a metal oxide powder.
[0039]
【Example】
Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.
[0040]
Example 1
First step:
In a 3 liter beaker, 442.29 g of cerium nitrate aqueous solution (CeO₂281.3% by weight) and 601.3 g of zirconium oxynitrate aqueous solution (ZrO₂189.5%) and 309.5% aqueous hydrogen peroxide (199.5g) were mixed with 1200g ion-exchanged water and stirred with a propeller stirrer. A precipitate was obtained.
[0041]
Second step:
The resulting precipitate was centrifuged to discard the supernatant, and the same amount of the supernatant from which ion-exchanged water was discarded was added and stirred, and then centrifuged again. This operation was further performed twice to wash the precipitate.
[0042]
Third step:
Finally, the precipitate after discarding the supernatant was again transferred to a 3-liter beaker, and 1800 g of ion-exchanged water was added, followed by stirring using a propeller stirrer and a homogenizer. Thereto were added 5 g of a cationic surfactant (manufactured by “Armac” Lion) and 5 g of an anionic surfactant (“Armoflow” Lion), and the mixture was further stirred for 5 minutes.
[0043]
This dispersion was centrifuged and the precipitate was washed in the same manner as in the second step.
[0044]
Fourth step:
Finally, the precipitate after discarding the supernatant is calcined at 400 ° C for 5 hours in the air using a degreasing furnace, and further calcined at 700 ° C for 5 hours in CeO.₂−ZrO₂A solid solution powder was prepared.
[0045]
Obtained CeO₂−ZrO₂The pore volume of the pores having a pore size of 0.1 μm or less in the solid solution powder was 0.3 cc / g, and the average secondary particle size was 6 μm. The pore volume was measured with a mercury porosimeter, and the average secondary particle size was measured with a laser diffraction / scattering particle size distribution analyzer.
[0046]
Catalytic:
Obtained CeO₂−ZrO₂The solid solution powder was impregnated with a predetermined amount of a Pt—P salt aqueous solution having a predetermined concentration, evaporated and dried, and then fired in the atmosphere at 300 ° C. for 3 hours to carry Pt. The amount of Pt supported is 1% by weight. This Pt-supported CeO₂−ZrO₂Solid solution powder, aluminum nitrate and alumina sol as binder are mixed with ion-exchanged water to prepare a slurry, which is washed on a cordierite 35cc honeycomb substrate (3 mil, 400 cells) and fired at 500 ° C for 1 hour. A coat layer was formed. The coating amount is 150 g per liter of honeycomb substrate, and the amount of Pt supported is 1.5 g per liter of honeycomb substrate.
[0047]
(Comparative Example 1)
In a 3 liter beaker, 442.29 g of cerium nitrate aqueous solution (CeO₂281.3% by weight) and 601.3 g of zirconium oxynitrate aqueous solution (ZrO₂189.5%), 199.5 g of 30% hydrogen peroxide solution, 12 g of surfactant (“Leocon” Lion) 12 g are mixed with 1200 g of ion-exchanged water, and stirred with a propeller stirrer, 25% ammonia 319.9 g of an aqueous solution was added to obtain an oxide precursor precipitate.
[0048]
The obtained precipitate is calcined in a degreasing furnace at 400 ° C. for 5 hours in the atmosphere without washing, and further calcined in the atmosphere at 700 ° C. for 5 hours to obtain CeO.₂−ZrO₂A solid solution powder was prepared.
[0049]
Obtained CeO₂−ZrO₂The pore volume of the pores having a pore diameter of 0.1 μm or less in the solid solution powder was 0.05 cc / g, and the average secondary particle diameter was 8 μm.
[0050]
This CeO₂−ZrO₂A catalyst of Comparative Example 1 was prepared in the same manner as in Example 1 except that solid solution powder was used.
[0051]
(Example 2)
First step:
In a 3 liter beaker, 278 g of zirconium oxynitrate aqueous solution (ZrO₂18% by weight) was mixed with 1800 g of ion-exchanged water, and 67 g of 25% aqueous ammonia solution was added while stirring with a propeller stirrer to obtain a precipitate of an oxide precursor.
[0052]
Second step:
The resulting precipitate was centrifuged to discard the supernatant, and the same amount of the supernatant from which ion-exchanged water was discarded was added and stirred, and then centrifuged again. This operation was further performed twice to wash the precipitate.
[0053]
Third step:
Finally, the precipitate after discarding the supernatant was again transferred to a 3-liter beaker, and 1800 g of ion-exchanged water was added, followed by stirring using a propeller stirrer and a homogenizer. Thereto was added 5 g of an anionic surfactant (manufactured by “Armoflow” Lion), and the mixture was further stirred for 5 minutes.
[0054]
This dispersion was centrifuged and the precipitate was washed in the same manner as in the second step.
[0055]
Fourth step:
Finally, the precipitate after discarding the supernatant is baked at 400 ° C for 5 hours in the air using a degreasing furnace, and further baked at 800 ° C for 5 hours in the air.₂A powder was prepared.
[0056]
Obtained ZrO₂The pore distribution of the powder was measured with a mercury porosimeter, and the results are shown in FIG. The average secondary particle diameter measured in the same manner as in Example 1 was 7 μm.
[0057]
Catalytic:
Obtained ZrO₂The powder was impregnated with a predetermined amount of an aqueous rhodium nitrate solution having a predetermined concentration, evaporated and dried, and then fired in the atmosphere at 300 ° C. for 3 hours to carry Rh. The amount of Rh supported is 1% by weight. This Pt supported ZrO₂The powder and aluminum nitrate and alumina sol as binder are mixed with ion-exchanged water to prepare a slurry, which is washed on a cordierite 35cc honeycomb substrate (3 mil, 400 cells) and fired at 500 ° C. for 1 hour. A coat layer was formed. The coating amount is 40 g per liter of honeycomb substrate, and the amount of Rh supported is 0.4 g per liter of honeycomb substrate.
[0058]
(Comparative Example 2)
In a 3 liter beaker, 278 g of zirconium oxynitrate aqueous solution (ZrO₂18% by weight) was mixed with 1800 g of ion-exchanged water, and 67 g of 25% aqueous ammonia solution was added while stirring with a propeller stirrer to obtain a precipitate of an oxide precursor.
[0059]
The obtained precipitate is calcined in a degreasing furnace at 400 ° C. for 5 hours in the air without washing, and further calcined in the air at 800 ° C. for 5 hours to obtain ZrO.₂A powder was prepared.
[0060]
Obtained ZrO₂The pore distribution of the powder was measured with a mercury porosimeter, and the results are shown in FIG. V on the vertical axis in FIG. 1 means the pore diameter. This ZrO measured in the same manner as in Example 1₂The average secondary particle diameter of the powder was 8 μm.
[0061]
This ZrO₂A catalyst of Comparative Example 2 was prepared in the same manner as Example 2 except that powder was used.
[0062]
<Test and evaluation>
The catalyst of Example 1 and Comparative Example 1 is placed in the evaluation apparatus, and the model gas shown in Table 1 is kept at 900 ° C. for 5 hours while being repeatedly flowed under the conditions of rich gas for 1 minute and lean gas for 4 minutes. A test was conducted. The total flow rate is 20 L / min. Separately from this, an air durability test was conducted in the atmosphere at 900 ° C. for 5 hours.
[0063]
[Table 1]

[0064]
For each catalyst after each endurance test, the model gas shown in Table 2 was heated up at a rate of 20 ° C./min while flowing at a total flow rate of 20 L / min alternately under conditions of rich gas for 1 sec and lean gas for 1 sec. HC, CO and NO_x The purification rate was measured continuously. And the temperature at which 50% of each harmful component is purified (T₅₀) And the results are shown in FIGS. The numbers at the vertices of the bar graphs in FIGS. 2 and 3 are the actual T₅₀Is the value of
[0065]
[Table 2]

[0066]
In addition, the catalysts of Example 2 and Comparative Example 2 were placed in the evaluation apparatus, and the model gas shown in Table 1 was kept flowing at 1000 ° C. for 5 hours while alternately flowing repeatedly under conditions of rich gas for 1 minute and lean gas for 4 minutes. A lean endurance test was conducted. The total flow rate is 20 L / min. Separately from this, an air durability test was conducted in the air at 850 ° C. for 5 hours.
[0067]
For each catalyst after each endurance test, the model gas shown in Table 2 was heated at a rate of 20 ° C./min while repeatedly flowing at a total flow rate of 20 L / min under the conditions of rich gas for 1 second and lean gas for 1 second. HC, CO and NO in the meantime_x The purification rate was measured continuously. And the temperature at which 50% of each harmful component is purified (T₅₀) And the results are shown in FIGS. The numbers at the vertices of the bar graphs in FIGS. 4 and 5 are the actual T₅₀Is the value of
[0068]
2 and 3, the catalyst of Example 1 shows higher purification performance from the low temperature range after each endurance test than the catalyst of Comparative Example 1, which is CeO.₂−ZrO₂This is considered to be due to the difference in the pore volume and average secondary particle size of the powder. That is, since the catalyst of Example 1 is excellent in gas diffusibility of the coat layer, it is considered that Pt supported on the lower layer of the coat layer was also effectively used.
[0069]
4 and 5, the catalyst of Example 2 shows higher purification performance from the low temperature range after each endurance test than the catalyst of Comparative Example 2, which is the same as that of the catalyst of Example 2 as shown in FIG. 1. This is probably because the pore volume is larger and the average secondary particle size is larger. That is, since the catalyst of Example 2 is excellent in gas diffusibility of the coat layer, it is considered that Rh supported on the lower layer of the coat layer was also effectively used.
[0070]
(Example 3)
First step:
In a 3 liter beaker, 589.71 g of cerium nitrate aqueous solution (CeO₂As 28% by weight) and 437.3 g of zirconium oxynitrate aqueous solution (ZrO₂189.5%), 199.5 g of 30% hydrogen peroxide, and 12 g of a surfactant (manufactured by Leocon Lion) are mixed with 1200 g of ion-exchanged water and stirred with a propeller stirrer and homogenizer. Then, 340 g of a 25% aqueous ammonia solution was added to obtain a precipitate of an oxide precursor.
[0071]
The second and subsequent steps are the same as in Example 1, and the CeO of this example₂−ZrO₂A solid solution powder was prepared.
[0072]
Obtained CeO₂−ZrO₂The pore volume of the pores having a pore size of 0.1 μm or less in the solid solution powder was 0.3 cc / g, and the average secondary particle size was 6 μm. The pore volume was measured with a mercury porosimeter, and the average secondary particle size was measured with a laser diffraction / scattering particle size distribution analyzer.
[0073]
(Example 4)
First step:
In a 3 liter beaker, 589.71 g of cerium nitrate aqueous solution (CeO₂As 28% by weight) and 437.3 g of zirconium oxynitrate aqueous solution (ZrO₂189.5%), 309.5% hydrogen peroxide water 199.5g, 30% hydrogen peroxide water 199.5g, and 1200g ion-exchanged water, added 3% 25% aqueous ammonia solution, propeller stirrer Stir with. This was subjected to pressure aging at 120 ° C. for 2 hours. While stirring this solution with a propeller stirrer, 340 g of a 25% aqueous ammonia solution was added to obtain a precipitate of an oxide precursor.
[0074]
The second and subsequent steps are the same as in Example 1, and the CeO of this example₂−ZrO₂A solid solution powder was prepared.
[0075]
Obtained CeO₂−ZrO₂The pore volume of the pores having a pore size of 0.1 μm or less in the solid solution powder was 0.2 cc / g, and the average secondary particle size was 6 μm. The pore volume was measured with a mercury porosimeter, and the average secondary particle size was measured with a laser diffraction / scattering particle size distribution analyzer.
[0076]
<Test and evaluation>
CeO of Example 3 and Example 4₂−ZrO₂The pore distribution of the solid solution powder was measured with a mercury porosimeter, and the results are shown in FIG.
[0077]
From FIG. 6, CeO of Example 4₂−ZrO₂It can be seen that the pore distribution of the solid solution powder is concentrated in a fine range as compared with Example 3. Although the detailed reason is unknown, it is considered that this is caused by the generation of uniform nuclei due to the addition of a small amount of aqueous ammonia and pressure aging.
[0078]
And from FIG. 6, the CeO of Example 4₂−ZrO₂Solid solution powder has a pore volume of 0.01 cc / g or more and a pore volume of 0.1 cc / g or more and a pore volume of 0.01 μm or more and 0.1 μm or less. It is clear that it accounts for more than 70% of the pore volume.
[0079]
【The invention's effect】
  IeObtained in the present inventionAccording to the metal oxide, since the pore volume and the average secondary particle diameter are larger than the conventional one, the gas diffusibility is excellent, and according to the exhaust gas purification catalyst using the metal oxide, it is supported on the lower layer of the coat layer. The opportunity for contact between the catalyst component and the exhaust gas is increased, and the purification performance is improved.
[Brief description of the drawings]
FIG. 1 ZrO of Example 2 and Comparative Example 2₂It is a graph which shows pore distribution of powder.
FIG. 2 is a graph showing a 50% purification temperature after a rich lean endurance test of the catalyst of Example 1 and Comparative Example 1.
FIG. 3 is a graph showing 50% purification temperature after an air durability test of the catalysts of Example 1 and Comparative Example 1.
4 is a graph showing a 50% purification temperature after a rich lean endurance test of catalysts of Example 2 and Comparative Example 2. FIG.
FIG. 5 shows the 50% purification temperature after the air durability test of the catalysts of Example 2 and Comparative Example 2.
FIG. 6: CeO of Example 3 and Example 4₂−ZrO₂It is a graph which shows the pore distribution of solid solution powder.

Claims (5)

Al , Zr , Ti , Si as well as Ce A first step of obtaining a precipitate of an oxide precursor by adding an alkaline substance to an aqueous solution in which a compound containing a metal element selected from:
  A second step of washing the precipitate;
  A third step of stirring the precipitate after washing in water with a surfactant;
  A method for producing a metal oxide, comprising sequentially performing a fourth step of baking the precipitate after the third step to obtain a metal oxide powder. The surfactant is 2 to 2 to the metal oxide powder obtained. 40 The manufacturing method of the metal oxide of Claim 1 added so that it may become weight%. The method for producing a metal oxide according to claim 1, wherein the metal element is zirconium or cerium and zirconium. The stirring in the third step is 1000sec ^-1 The manufacturing method of the metal oxide in any one of Claims 1-3 performed with the above shear rate. The critical micelle concentration of the surfactant is  0.1 It is below mol / liter, The manufacturing method of the metal oxide in any one of Claims 1-4.

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