JP2008150231A - Composite oxide powder and method for producing the same - Google Patents
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本発明は、排ガス浄化用触媒の触媒担体として有用な複合酸化物粉末及びその製造方法に関する。 The present invention relates to a composite oxide powder useful as a catalyst carrier for an exhaust gas purification catalyst and a method for producing the same.
従来、自動車のような内燃機関から排出される有害成分を浄化するための排ガス浄化用触媒として様々な触媒が開発されており、このような排ガス浄化用触媒としては、例えば排ガス中の一酸化炭素（ＣＯ）及び炭化水素（ＨＣ）の酸化と窒素酸化物（ＮＯｘ）の還元とを同時に行って浄化する三元触媒が用いられている。そして、このような三元触媒としては、例えばコーディエライト等からなる耐熱性ハニカム基材にアルミナ、ジルコニア、セリア等の金属酸化物からなる担体層（触媒担体）を形成し、その担体層に白金（Ｐｔ）やロジウム（Ｒｈ）といった貴金属を担持させたものが広く知られている。 Conventionally, various catalysts have been developed as exhaust gas purification catalysts for purifying harmful components discharged from an internal combustion engine such as an automobile. Examples of such exhaust gas purification catalysts include carbon monoxide in exhaust gas. A three-way catalyst that purifies by simultaneously oxidizing (CO) and hydrocarbon (HC) and reducing nitrogen oxide (NOx) is used. As such a three-way catalyst, for example, a carrier layer (catalyst carrier) made of a metal oxide such as alumina, zirconia, or ceria is formed on a heat-resistant honeycomb substrate made of cordierite or the like, and the carrier layer is formed on the carrier layer. Those supporting noble metals such as platinum (Pt) and rhodium (Rh) are widely known.
しかしながら、近年の排ガス規制の強化に伴い、排ガス浄化用触媒に用いられる触媒担体として、より耐熱性が高く、高温耐久試験後においても比表面積が大きいものが要求されていた。 However, with the recent tightening of exhaust gas regulations, catalyst carriers used for exhaust gas purification catalysts have been required to have higher heat resistance and a large specific surface area even after a high temperature durability test.
このような課題を解決するために、例えば、特開２００２−２２０２２８号公報（特許文献１）には、セリウム化合物が溶解した水溶液又は水を含む溶液に含まれる酸基と等量以上の塩基を添加することでセリア前駆体の沈殿を析出させ、その後焼成することを特徴とする酸化物粉末の製造方法が開示され、明細書中において、前記前駆体の沈殿は、水又は水を含む溶液を分散媒とした懸濁状態又は系内に水が十分に存在する状態で熟成（水熱処理）されることが記載されている。 In order to solve such a problem, for example, Japanese Patent Application Laid-Open No. 2002-220228 (Patent Document 1) includes a base equivalent to or more than an acid group contained in an aqueous solution in which a cerium compound is dissolved or a solution containing water. Disclosed is a method for producing an oxide powder characterized in that a precipitate of ceria precursor is precipitated by addition, followed by calcination. In the specification, precipitation of the precursor includes water or a solution containing water. It is described that aging (hydrothermal treatment) is performed in a suspended state as a dispersion medium or in a state where water is sufficiently present in the system.
しかしながら、特許文献１に記載のような酸化物粉末の製造方法により得られる酸化物粉末においても耐熱性の点で未だ必ずしも十分なものではなく、このような酸化物粉末を触媒担体として用いた排ガス浄化用触媒は、高温耐久試験後の触媒性能の点で未だ必ずしも十分なものではなかった。
本発明は、上記従来技術の有する課題に鑑みてなされたものであり、優れた耐熱性を有し、触媒担体として用いた場合に貴金属の粒成長を十分に抑制し、触媒性能を十分に維持することが可能な複合酸化物粉末、並びにその複合酸化物粉末の製造方法を提供することを目的とする。 The present invention has been made in view of the above-described problems of the prior art, has excellent heat resistance, and when used as a catalyst carrier, sufficiently suppresses the growth of noble metal grains and sufficiently maintains catalyst performance. It is an object of the present invention to provide a composite oxide powder that can be used, and a method for producing the composite oxide powder.
本発明者らは、上記目的を達成すべく鋭意研究を重ねた結果、２種以上の金属化合物を含有する溶液から、塩基の存在下で複合酸化物前駆体を沈殿せしめ、その後、水熱処理した後に焼成する複合酸化物粉末の製造方法において、水熱処理を高剪断速度の下で行うことにより驚くべきことに優れた耐熱性を有し、触媒担体として用いた場合に貴金属の粒成長を十分に抑制し、触媒性能を十分に維持することが可能な複合酸化物粉末が得られることを見出し、本発明を完成するに至った。 As a result of intensive studies to achieve the above object, the present inventors precipitated a complex oxide precursor from a solution containing two or more metal compounds in the presence of a base, and then hydrothermally treated. In the manufacturing method of the composite oxide powder to be fired later, it has surprisingly excellent heat resistance by performing hydrothermal treatment at a high shear rate, and when it is used as a catalyst carrier, the grain growth of the noble metal is sufficiently achieved. The present inventors have found that a composite oxide powder that can be suppressed and sufficiently maintain the catalyst performance can be obtained, and the present invention has been completed.
すなわち、本発明の複合酸化物粉末の製造方法は、２種以上の金属酸化物により構成される複合酸化物粉末の製造方法であって、
２種以上の金属化合物を含有する溶液から、塩基の存在下で複合酸化物前駆体を沈殿せしめる工程と、
前記複合酸化物前駆体を沈殿せしめた溶液を、１０００ｓｅｃ−１以上の剪断速度の下で、８０〜２５０℃の温度で水熱処理した後に焼成することによって、前記複合酸化物粉末を得る工程と、
を含むことを特徴とする方法である。
That is, the method for producing a composite oxide powder of the present invention is a method for producing a composite oxide powder composed of two or more metal oxides,
Precipitating a complex oxide precursor from a solution containing two or more metal compounds in the presence of a base;
A step of obtaining the composite oxide powder by hydrothermally treating the solution in which the composite oxide precursor is precipitated at a temperature of 80 to 250 ° C. under a shear rate of 1000 sec −1 or more;
It is the method characterized by including.
また、本発明の複合酸化物粉末の製造方法においては、前記金属酸化物が少なくとも酸化セリウムを含むことが好ましい。 In the method for producing a composite oxide powder of the present invention, it is preferable that the metal oxide contains at least cerium oxide.
本発明の複合酸化物粉末は、前記複合酸化物粉末の製造方法により得られたものであることを特徴とするものである。 The composite oxide powder of the present invention is obtained by the method for producing a composite oxide powder.
本発明の排ガス浄化用触媒は、複合酸化物粉末を含む担体と、前記担体に担持された貴金属とを含むことを特徴とするものである。 The exhaust gas purifying catalyst of the present invention is characterized in that it contains a carrier containing composite oxide powder and a noble metal supported on the carrier.
なお、本発明の複合酸化物粉末の製造方法によって優れた耐熱性を有し、触媒担体として用いた場合に貴金属の粒成長を十分に抑制し、触媒性能を十分に維持することが可能な複合酸化物粉末が得られる理由は必ずしも定かではないが、本発明者らは以下のように推察する。すなわち、複合酸化物前駆体を沈殿せしめた溶液を水熱処理した場合には、複合酸化物前駆体の溶解や再析出が促進され、その結果、得られる複合酸化物粉末の耐熱性が向上する。また、このような水熱処理を高剪断速度の下で行うと、複合酸化物前駆体の溶解や再析出がむらなく進行し、複合酸化物前駆体の微粒子がより均質に成長するものと本発明者らは推察する。そして、本発明の複合酸化物粉末の製造方法においては、複合酸化物前駆体を沈殿せしめた溶液を、高剪断速度の下で水熱処理した後に焼成することによって、２種以上の金属酸化物により構成される複合酸化物粉末を得る。このように、複合酸化物前駆体の微粒子をより均質に成長させた後に焼成することによって、得られる複合酸化物粉末を構成する２種以上の金属酸化物の固溶が促進され、そのため、得られる複合酸化物粉末の耐熱性がより向上するものと本発明者らは推察する。 It should be noted that the composite oxide powder of the present invention has excellent heat resistance, and when used as a catalyst carrier, a composite capable of sufficiently suppressing noble metal grain growth and sufficiently maintaining catalyst performance. The reason why the oxide powder is obtained is not necessarily clear, but the present inventors speculate as follows. That is, when the solution in which the composite oxide precursor is precipitated is subjected to hydrothermal treatment, dissolution and reprecipitation of the composite oxide precursor are promoted, and as a result, the heat resistance of the obtained composite oxide powder is improved. Further, when such hydrothermal treatment is performed at a high shear rate, the dissolution and reprecipitation of the composite oxide precursor proceed evenly and the fine particles of the composite oxide precursor grow more uniformly. They guess. In the method for producing the composite oxide powder of the present invention, the solution in which the composite oxide precursor is precipitated is subjected to hydrothermal treatment at a high shear rate and then fired to obtain two or more metal oxides. A composite oxide powder is obtained. In this way, by firing the fine particles of the composite oxide precursor more uniformly and then firing, the solid solution of two or more kinds of metal oxides constituting the obtained composite oxide powder is promoted. The present inventors speculate that the heat resistance of the resulting composite oxide powder is further improved.
本発明によれば、優れた耐熱性を有し、触媒担体として用いた場合に貴金属の粒成長を十分に抑制し、触媒性能を十分に維持することが可能な複合酸化物粉末、並びにその複合酸化物粉末の製造方法を提供することが可能となる。 According to the present invention, a composite oxide powder having excellent heat resistance, capable of sufficiently suppressing grain growth of noble metal and sufficiently maintaining catalyst performance when used as a catalyst carrier, and composites thereof It becomes possible to provide the manufacturing method of oxide powder.
以下、本発明をその好適な実施形態に即して詳細に説明する。 Hereinafter, the present invention will be described in detail with reference to preferred embodiments thereof.
本発明の複合酸化物粉末の製造方法は、２種以上の金属酸化物により構成される複合酸化物粉末の製造方法であって、
２種以上の金属化合物を含有する溶液から、塩基の存在下で複合酸化物前駆体を沈殿せしめる工程と、
前記複合酸化物前駆体を沈殿せしめた溶液を、１０００ｓｅｃ−１以上の剪断速度の下で、８０〜２５０℃の温度で水熱処理した後に焼成することによって、前記複合酸化物粉末を得る工程と、
を含むことを特徴とする方法である。
The method for producing a composite oxide powder of the present invention is a method for producing a composite oxide powder composed of two or more metal oxides,
Precipitating a complex oxide precursor from a solution containing two or more metal compounds in the presence of a base;
A step of obtaining the composite oxide powder by baking the solution in which the composite oxide precursor is precipitated at a temperature of 80 to 250 ° C. under a shear rate of 1000 sec −1 or more and then baking.
It is the method characterized by including.
先ず、２種以上の金属化合物を含有する溶液から、塩基の存在下で複合酸化物前駆体を沈殿せしめる工程について説明する。 First, a step of precipitating a composite oxide precursor from a solution containing two or more metal compounds in the presence of a base will be described.
本発明にかかる金属化合物は、複合酸化物粉末を構成する２種以上の金属酸化物の原料となるものである。このような金属化合物としては、以下説明する金属酸化物の構成元素である金属の塩が挙げられる。また、このような塩としては、例えば、硝酸塩、酢酸塩、塩化物、硫酸塩、亜硫酸塩、無機錯塩が挙げられる。 The metal compound concerning this invention becomes a raw material of 2 or more types of metal oxide which comprises composite oxide powder. Examples of such a metal compound include a metal salt which is a constituent element of a metal oxide described below. Examples of such salts include nitrates, acetates, chlorides, sulfates, sulfites, and inorganic complex salts.
本発明にかかる金属酸化物は、酸化ジルコニウム、酸化アルミニウム、酸化チタン、酸化鉄、希土類元素酸化物、アルカリ金属酸化物及びアルカリ土類金属酸化物からなる群から選択される２種以上の金属酸化物である。希土類元素酸化物としては、セリウム、ランタン、ネオジム、イットリウム、プラセオジム等の酸化物が挙げられ、アルカリ金属酸化物としては、リチウム、ナトリウム、カリウム、セシウム等の酸化物が挙げられ、アルカリ土類金属酸化物としては、バリウム、ストロンチウム、カルシウム、マグネシウム等の酸化物が挙げられる。 The metal oxide according to the present invention includes two or more metal oxides selected from the group consisting of zirconium oxide, aluminum oxide, titanium oxide, iron oxide, rare earth element oxide, alkali metal oxide, and alkaline earth metal oxide. It is a thing. Examples of rare earth element oxides include oxides such as cerium, lanthanum, neodymium, yttrium, and praseodymium. Examples of alkali metal oxides include oxides such as lithium, sodium, potassium, and cesium, and alkaline earth metals. Examples of the oxide include oxides such as barium, strontium, calcium, and magnesium.
また、本発明においては、得られる複合酸化物粉末が排ガス浄化用触媒の触媒担体等として有用なものとなるという観点から、このような金属酸化物が少なくとも酸化セリウムを含むことが好ましい。さらに、酸化セリウムと組み合わせて用いる金属酸化物としては特に限定されないが、得られる複合酸化物粉末が排ガス浄化用触媒の触媒担体等として有用なものとなるという観点から、酸化ジルコニウム、酸化イットリウム、酸化ランタン、酸化プラセオジムが好ましく、酸化ジルコニウムがより好ましい。なお、本発明の複合酸化物粉末における金属酸化物の組成比は特に制限されず、前記金属化合物の配合量を調節することによって適宜調整することができる。 In the present invention, it is preferable that such a metal oxide contains at least cerium oxide from the viewpoint that the obtained composite oxide powder is useful as a catalyst carrier of an exhaust gas purifying catalyst. Further, the metal oxide used in combination with cerium oxide is not particularly limited, but from the viewpoint that the obtained composite oxide powder is useful as a catalyst carrier of an exhaust gas purification catalyst, zirconium oxide, yttrium oxide, oxidation Lanthanum and praseodymium oxide are preferred, and zirconium oxide is more preferred. In addition, the composition ratio of the metal oxide in the composite oxide powder of the present invention is not particularly limited, and can be appropriately adjusted by adjusting the blending amount of the metal compound.
本発明においては、前記２種以上の金属化合物を含有する溶液を用いる。このような溶液としては、前記金属化合物を水、アルコール等の溶媒に溶解した溶液が好適に用いられる。また、このような溶液のｐＨは、特に限定されるものではないが、溶液中で金属イオンがより安定に存在するという観点から、溶液のｐＨが１．０〜６．０であることが好ましい。 In the present invention, a solution containing the two or more metal compounds is used. As such a solution, a solution obtained by dissolving the metal compound in a solvent such as water or alcohol is preferably used. Further, the pH of such a solution is not particularly limited, but the pH of the solution is preferably 1.0 to 6.0 from the viewpoint that metal ions exist more stably in the solution. .
そして、本発明においては、前記２種以上の金属化合物を含有する溶液から、塩基の存在下で複合酸化物前駆体を沈殿せしめる。具体的には、このような溶液に含まれる酸基と等量以上の塩基を添加することで、複合酸化物前駆体の沈殿せしめることができる。このように等量以上の塩基で中和することにより、複合酸化物前駆体の析出反応が促進される。塩基としては、アンモニア、炭酸アンモニウム、水酸化ナトリウム、水酸化カリウム、炭酸ナトリウム等を用いることができる。これらの中でも、焼成時に揮散するという観点から、アンモニア、炭酸アンモニウムが特に好ましい。なお、これらの塩基は水、アルコール等の溶媒に溶解させて塩基性溶液として用いることが好ましい。また、このような塩基性溶液のｐＨは９以上であることが好ましい。 In the present invention, the complex oxide precursor is precipitated from the solution containing the two or more metal compounds in the presence of a base. Specifically, the composite oxide precursor can be precipitated by adding an amount of base equal to or more than the acid group contained in such a solution. By neutralizing with an equal amount or more of the base in this way, the precipitation reaction of the composite oxide precursor is promoted. As the base, ammonia, ammonium carbonate, sodium hydroxide, potassium hydroxide, sodium carbonate, or the like can be used. Among these, ammonia and ammonium carbonate are particularly preferable from the viewpoint of volatilization during firing. These bases are preferably dissolved in a solvent such as water or alcohol and used as a basic solution. Moreover, it is preferable that the pH of such a basic solution is 9 or more.
このように複合酸化物前駆体を沈殿せしめる方法としては、様々な方法があり、例えば、塩基性溶液を瞬時に添加し強撹拌して沈殿を析出させる方法、過酸化水素等を加えることで酸化物前駆体の沈殿し始めるｐＨを調節した後、塩基性溶液で沈殿を析出させる方法、塩基性溶液を添加する際に中和にかかる時間を十分に長く（好ましくは１０分以上）して徐々に沈殿を析出させる方法、塩基性溶液を添加する際にｐＨをモニターしながら段階的に中和する又は所定のｐＨに保つような緩衝溶液を添加しつつ沈殿を析出させる方法が挙げられる。 There are various methods for precipitating the composite oxide precursor as described above. For example, a method in which a basic solution is added instantaneously and vigorously stirred to precipitate a precipitate, and hydrogen peroxide is added to oxidize. After adjusting the pH at which the precursor of the precursor begins to precipitate, a method of precipitating the precipitate with a basic solution, and gradually adding a sufficiently long time (preferably 10 minutes or more) when adding the basic solution And a method of precipitating the precipitate while adding a buffer solution that neutralizes stepwise while monitoring the pH when the basic solution is added, or maintains a predetermined pH.
次に、前記複合酸化物前駆体を沈殿せしめた溶液を、１０００ｓｅｃ−１以上の剪断速度の下で、８０〜２５０℃の温度で水熱処理した（水熱処理工程）後に焼成すること（焼成工程）によって、前記複合酸化物粉末を得る工程について説明する。 Next, the solution in which the composite oxide precursor is precipitated is hydrothermally treated at a temperature of 80 to 250 ° C. under a shear rate of 1000 sec −1 or more (hydrothermal treatment step) (baking step). The step of obtaining the composite oxide powder will be described.
本発明にかかる水熱処理工程においては、前記複合酸化物前駆体を沈殿せしめた溶液を、１０００ｓｅｃ−１以上の剪断速度の下で水熱処理する。かかる剪断速度が１０００ｓｅｃ−１未満では、複合酸化物前駆体の溶解や再析出にむらが生じ、得られる複合酸化物粉末の耐熱性が不十分となる。また、得られる複合酸化物粉末の耐熱性を更に向上させるという観点から、かかる剪断速度が５０００ｓｅｃ−１以上であることが好ましく、１００００ｓｅｃ−１以上であることがより好ましい。なお、かかる剪断速度の上限は特に制限されないが、用いる装置上の制約という観点から３００００ｓｅｃ−１以下であることが好ましい。 In the hydrothermal treatment step according to the present invention, the solution in which the composite oxide precursor is precipitated is hydrothermally treated under a shear rate of 1000 sec −1 or more. When the shear rate is less than 1000 sec −1 , unevenness of dissolution and reprecipitation of the composite oxide precursor occurs, and the resulting composite oxide powder has insufficient heat resistance. Further, from the viewpoint of further heat resistance of the composite oxide powder obtained improvement, it is preferred that such shear rate is 5000Sec -1 or more, and more preferably 10000 sec -1 or more. The upper limit of the shear rate is not particularly limited, but is preferably 30000 sec −1 or less from the viewpoint of restrictions on the apparatus to be used.
また、ここで用いる装置は、このような高剪断速度で攪拌できるものであればよく特に制限されないが、ホモジナイザが好適に用いられる。なお、剪断速度は、このような装置におけるロータとステータの速度差、及びロータとステータの間隙から、下記計算式：
（剪断速度）＝（ロータとステータの速度差）／（ロータとステータの間隙）
を用いて算出することができる。
The apparatus used here is not particularly limited as long as it can stir at such a high shear rate, but a homogenizer is preferably used. The shear rate is calculated from the following formula based on the speed difference between the rotor and the stator and the gap between the rotor and the stator in such an apparatus:
(Shear rate) = (Speed difference between rotor and stator) / (Gap between rotor and stator)
Can be used to calculate.
本発明にかかる水熱処理工程における水熱処理温度は、８０〜２５０℃の範囲であることが必要である。溶液温度が８０℃未満では、複合酸化物前駆体の溶解や再析出の促進効果が不十分となり、得られる複合酸化物粉末の耐熱性が不十分となる。他方、溶液温度が２５０℃を超える場合には、１０気圧以上に耐えうる合成装置が必要となり、設備コストが高くなるため、本発明の主な用途である触媒担体の製造方法には適さない。 The hydrothermal treatment temperature in the hydrothermal treatment step according to the present invention needs to be in the range of 80 to 250 ° C. When the solution temperature is less than 80 ° C., the effect of promoting the dissolution and reprecipitation of the composite oxide precursor becomes insufficient, and the resulting composite oxide powder has insufficient heat resistance. On the other hand, when the solution temperature exceeds 250 ° C., a synthesizer that can withstand 10 atm or more is required, which increases the equipment cost, and is not suitable for the catalyst carrier production method that is the main application of the present invention.
また、このような水熱処理工程における水熱処理時間は、剪断速度や水熱処理温度に応じて適宜調整することができるが、３０〜１０００分の範囲であることが好ましく、６０〜３００分の範囲であることがより好ましい。水熱処理時間が前記下限未満では、複合酸化物前駆体の溶解や再析出の促進効果が不十分となる傾向にあり、他方、前記上限を超えると、水熱処理による効果が飽和状態となり、生産性が低下することになる傾向にある。 Further, the hydrothermal treatment time in such a hydrothermal treatment step can be appropriately adjusted according to the shear rate and the hydrothermal treatment temperature, but is preferably in the range of 30 to 1000 minutes, and in the range of 60 to 300 minutes. More preferably. If the hydrothermal treatment time is less than the lower limit, the effect of promoting the dissolution and reprecipitation of the composite oxide precursor tends to be insufficient. On the other hand, if the upper limit is exceeded, the effect of the hydrothermal treatment becomes saturated, and the productivity Tends to decrease.
本発明にかかる焼成工程においては、前記水熱処理工程後の溶液を焼成することによって、本発明の複合酸化物粉末を得る。このような焼成工程は、大気中で行えばよく、その温度は３００〜１２００℃の範囲であることが好ましく、５００〜１０００℃の範囲であることがより好ましい。焼成温度が前記下限未満では、実質上、触媒担体としての安定性に欠ける傾向にあり、他方、前記上限を超えると、高温・酸化雰囲気により触媒担体としての性能低下を伴い易くなる傾向にある。また、焼成時間は１〜２０時間の範囲であることが好ましく、３〜１０時間の範囲であることがより好ましい。 In the firing step according to the present invention, the composite oxide powder of the present invention is obtained by firing the solution after the hydrothermal treatment step. Such a baking process may be performed in air | atmosphere, and it is preferable that the temperature is the range of 300-1200 degreeC, and it is more preferable that it is the range of 500-1000 degreeC. When the calcination temperature is less than the lower limit, the stability as a catalyst carrier tends to be substantially lacking. On the other hand, when the upper limit is exceeded, the performance as a catalyst carrier tends to decrease due to a high temperature / oxidation atmosphere. The firing time is preferably in the range of 1 to 20 hours, more preferably in the range of 3 to 10 hours.
以上説明した本発明の複合酸化物粉末の製造方法により、優れた耐熱性を有する本発明の複合酸化物粉末を得ることができる。また、このような本発明の複合酸化物粉末を触媒担体として用いた場合には、貴金属の粒成長を十分に抑制し、触媒性能を十分に維持することが可能となる。 The composite oxide powder of the present invention having excellent heat resistance can be obtained by the method for producing the composite oxide powder of the present invention described above. Further, when such a composite oxide powder of the present invention is used as a catalyst carrier, it becomes possible to sufficiently suppress the noble metal grain growth and maintain the catalyst performance sufficiently.
次に、本発明の排ガス浄化用触媒について説明する。すなわち、本発明の排ガス浄化用触媒は、前記本発明の複合酸化物粉末を含む担体と、前記担体に担持された貴金属とを含むことを特徴とするものである。このように、本発明の排ガス浄化用触媒は、前記本発明の複合酸化物粉末を含む担体に貴金属を担持させたものであるため、高温耐久試験後においても貴金属の粒成長が十分に抑制され、優れた触媒性能を発揮することができる。 Next, the exhaust gas purifying catalyst of the present invention will be described. That is, the exhaust gas purifying catalyst of the present invention is characterized by comprising a carrier containing the composite oxide powder of the present invention and a noble metal supported on the carrier. As described above, since the exhaust gas purifying catalyst of the present invention is obtained by supporting a noble metal on the carrier containing the composite oxide powder of the present invention, the grain growth of the noble metal is sufficiently suppressed even after the high temperature durability test. Can exhibit excellent catalytic performance.
本発明にかかる貴金属としては、白金（Ｐｔ）、ロジウム（Ｒｈ）、パラジウム（Ｐｄ）、イリジウム（Ｉｒ）、ルテニウム（Ｒｕ）等が挙げられ、三元活性が高いという観点から、Ｐｔ、Ｒｈ、Ｐｄが好ましい。 Examples of the noble metal according to the present invention include platinum (Pt), rhodium (Rh), palladium (Pd), iridium (Ir), ruthenium (Ru) and the like. From the viewpoint of high ternary activity, Pt, Rh, Pd is preferred.
このような貴金属の担持量としては、前記複合酸化物粉末１００質量部当たり０．０１〜１０質量部であることが好ましく、０．１〜４質量部であることがより好ましい。前記貴金属の担持量が前記下限未満ではＨＣ、ＣＯ及びＮＯｘの浄化率が低下する傾向にあり、他方、前記上限を超えると、貴金属により得られる効果が飽和するとともにコストが増大する傾向にある。 The amount of such noble metal supported is preferably 0.01 to 10 parts by mass, more preferably 0.1 to 4 parts by mass, per 100 parts by mass of the composite oxide powder. If the loading amount of the noble metal is less than the lower limit, the purification rate of HC, CO and NOx tends to decrease. On the other hand, if the amount exceeds the upper limit, the effect obtained by the noble metal tends to be saturated and the cost tends to increase.
また、本発明の排ガス浄化用触媒を製造する方法は特に制限されず、例えば、前記複合酸化物粉末に前記貴金属のイオンを含有する水溶液（例えば、ジニトロジアンミン白金水溶液、硝酸ロジウム水溶液）を所定量含浸させ、これを蒸発乾固もしくは選択担持により濾過させた後、２５０〜５００℃程度で０．５〜５時間焼成する方法や、上記本発明の排ガス浄化用触媒担体を脱イオン水中に分散させ、これに前記貴金属のイオンを含有する水溶液を所定量添加して十分に撹拌した後、これを蒸発乾固せしめ、その後に２５０〜５００℃程度で０．５〜５時間焼成する方法を採用することができる。 The method for producing the exhaust gas purifying catalyst of the present invention is not particularly limited. For example, a predetermined amount of an aqueous solution (for example, dinitrodiammine platinum aqueous solution or rhodium nitrate aqueous solution) containing the noble metal ions in the composite oxide powder is used. After impregnating and filtering this by evaporation to dryness or selective loading, the method of calcining at about 250 to 500 ° C. for 0.5 to 5 hours or the above-described exhaust gas purification catalyst carrier of the present invention is dispersed in deionized water. Then, after adding a predetermined amount of the aqueous solution containing the noble metal ions and stirring it sufficiently, it is evaporated to dryness, and then baked at about 250 to 500 ° C. for 0.5 to 5 hours. be able to.
また、本発明の排ガス浄化用触媒の形態も特に制限されず、例えば、定法によりペレット化してペレット触媒としても、本発明の排ガス浄化用触媒を主成分とするスラリーをコーディエライトや金属箔からなるハニカム基材にコートし焼成してモノリス触媒としてもよい。 Further, the form of the exhaust gas purifying catalyst of the present invention is not particularly limited. For example, a pellet containing the exhaust gas purifying catalyst of the present invention as a main component is prepared from cordierite or metal foil. The resulting honeycomb substrate may be coated and fired to form a monolith catalyst.
以下、実施例及び比較例に基づいて本発明をより具体的に説明するが、本発明は以下の実施例に限定されるものではない。 EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.
（実施例１）
先ず、硝酸セリウム水溶液（ＣｅＯ２として２８質量%含む）２３３ｇ、オキシ硝酸ジルコニウム水溶液（ＺｒＯ２として１８質量%含む）１５２ｇ、硝酸イットリウム１４ｇ及びノニオン系界面活性剤（ライオン社製、商品名：レオコン）１０ｇを含有する混合水溶液２０００ｇに２５質量％濃度のアンモニア水２００ｇを添加し、室温で１０分間攪拌して共沈殿物を析出させた。次に、攪拌を継続しながらこの溶液を９５℃まで加熱し、プロペラ攪拌の他にホモジナイザを用いて、１００００ｓｅｃ−１の剪断速度の下で１時間の水熱処理を施した。その後、ホモジナイザ攪拌を止め、水熱処理後の溶液を室温まで冷却した。そして、冷却後の溶液から遠心分離機を用いて上澄み液を除去した後に、脱脂炉中にて４００℃で５時間焼成して、複合酸化物粉末を得た。
(Example 1)
First, 233 g of a cerium nitrate aqueous solution (containing 28% by mass as CeO 2 ), 152 g of a zirconium oxynitrate aqueous solution (containing 18% by mass as ZrO 2 ), 14 g of yttrium nitrate and a nonionic surfactant (product name: Leocon, manufactured by Lion Corporation) To 2000 g of a mixed aqueous solution containing 10 g, 200 g of ammonia water having a concentration of 25% by mass was added and stirred at room temperature for 10 minutes to precipitate a coprecipitate. Next, the solution was heated to 95 ° C. while stirring was continued, and hydrothermal treatment was performed for 1 hour under a shear rate of 10,000 sec −1 using a homogenizer in addition to propeller stirring. Thereafter, the homogenizer stirring was stopped, and the hydrothermally treated solution was cooled to room temperature. And after removing supernatant liquid from the cooled solution using a centrifuge, it baked at 400 degreeC in the degreasing furnace for 5 hours, and obtained complex oxide powder.
（実施例２）
水熱処理における剪断速度が５０００ｓｅｃ−１となるようにした以外は実施例１と同様にして複合酸化物粉末を得た。
(Example 2)
A composite oxide powder was obtained in the same manner as in Example 1 except that the shear rate in hydrothermal treatment was set to 5000 sec −1 .
（実施例３）
水熱処理における溶液温度を１２０℃とした以外は実施例１と同様にして複合酸化物粉末を得た。
(Example 3)
A composite oxide powder was obtained in the same manner as in Example 1 except that the solution temperature in hydrothermal treatment was 120 ° C.
（実施例４）
水熱処理における溶液温度を１２０℃とし、剪断速度が５０００ｓｅｃ−１となるようにした以外は実施例１と同様にして複合酸化物粉末を得た。
Example 4
A composite oxide powder was obtained in the same manner as in Example 1, except that the solution temperature in hydrothermal treatment was 120 ° C. and the shear rate was 5000 sec −1 .
（比較例１）
水熱処理においてプロペラによりゆるやかに攪拌（剪断速度：１０ｓｅｃ−１以下）するようにした以外は実施例１と同様にして比較用の複合酸化物粉末を得た。
(Comparative Example 1)
A comparative composite oxide powder was obtained in the same manner as in Example 1 except that the mixture was gently stirred with a propeller in a hydrothermal treatment (shear rate: 10 sec −1 or less).
（比較例２）
共沈殿物を析出させた溶液を加熱せずに１００００ｓｅｃ−１の剪断速度の下で１時間攪拌した以外は実施例１と同様にして比較用の複合酸化物粉末を得た。
(Comparative Example 2)
A composite oxide powder for comparison was obtained in the same manner as in Example 1 except that the solution in which the coprecipitate was precipitated was stirred for 1 hour at a shear rate of 10,000 sec −1 without heating.
（比較例３）
水熱処理における剪断速度が５００ｓｅｃ−１となるようにした以外は実施例１と同様にして複合酸化物粉末を得た。
(Comparative Example 3)
A composite oxide powder was obtained in the same manner as in Example 1 except that the shear rate in hydrothermal treatment was 500 sec −1 .
＜耐熱性及び触媒性能の評価＞
（i）複合酸化物粉末の耐熱性の評価
先ず、実施例１〜４及び比較例１〜３で得られた複合酸化物粉末にそれぞれ大気中にて１０００℃の温度条件で５時間熱処理して高温耐久試験を行った。そして、高温耐久試験後の複合酸化物粉末における比表面積及び平均一次粒子径を測定して、複合酸化物粉末の耐熱性を評価した。すなわち、比表面積を吸着等温線からＢＥＴ等温吸着式を用いてＢＥＴ比表面積として算出した。また、平均一次粒子径をＸ線回折（ＸＲＤ）により測定した。
<Evaluation of heat resistance and catalyst performance>
(I) Evaluation of heat resistance of composite oxide powder First, the composite oxide powders obtained in Examples 1 to 4 and Comparative Examples 1 to 3 were each heat-treated at 1000 ° C. for 5 hours in the air. A high temperature durability test was conducted. And the specific surface area and average primary particle diameter in the complex oxide powder after a high temperature endurance test were measured, and the heat resistance of the complex oxide powder was evaluated. That is, the specific surface area was calculated as the BET specific surface area from the adsorption isotherm using the BET isotherm adsorption equation. Moreover, the average primary particle diameter was measured by X-ray diffraction (XRD).
（ii）排ガス浄化用触媒の触媒性能の評価
先ず、実施例１〜４及び比較例１〜３で得られた複合酸化物粉末をそれぞれジニトロジアミン白金の硝酸水溶液（白金濃度：４質量％）に浸漬し、濾過及び洗浄した後に、１１０℃の温度条件で乾燥し、更に大気中にて５００℃の温度条件で３時間焼成して、前記複合酸化物粉末にＰｔが担持された排ガス浄化用触媒を得た。そして、このようにして得られた粉末状の排ガス浄化用触媒を、冷間等方圧加圧法（ＣＩＰ法）を採用して１ｔ／ｃｍ２の圧力で圧粉成形した後、０．５〜１ｍｍの大きさに粉砕し、ペレット状の触媒とした。なお、得られた排ガス浄化用触媒におけるＰｔの担持量は１質量％であった。
(Ii) Evaluation of catalytic performance of exhaust gas purification catalyst First, the composite oxide powders obtained in Examples 1 to 4 and Comparative Examples 1 to 3 were each converted to a nitric acid aqueous solution (platinum concentration: 4% by mass) of dinitrodiamine platinum. After being immersed, filtered and washed, dried under a temperature condition of 110 ° C. and further calcined in the atmosphere at a temperature condition of 500 ° C. for 3 hours, and the exhaust gas purification catalyst in which Pt is supported on the composite oxide powder Got. The powdery exhaust gas purifying catalyst thus obtained is compacted at a pressure of 1 t / cm 2 using a cold isostatic pressing method (CIP method), and then 0.5 to The catalyst was pulverized to a size of 1 mm to obtain a pellet-shaped catalyst. The amount of Pt supported in the obtained exhaust gas purification catalyst was 1% by mass.
次に、得られたペレット状の触媒をそれぞれ用いて高温耐久試験を行った。すなわち、反応容器に触媒を仕込み、反応容器中に触媒３ｇあたりの流量が５００ｃｃ／分となるようにして、ＣＯ（５％）、ＣＯ２（１０％）、Ｎ２（バランス）からなるリッチガスとＯ２（５％）、ＣＯ２（１０％）、Ｎ２（バランス）からなるリーンガスとを５分おきに交互に流入させて１０００℃の温度条件で５時間処理することによって複合酸化物粉末（触媒担体）上の貴金属を粒成長させた。 Next, the high temperature durability test was done using each of the obtained pellet-shaped catalysts. That is, a catalyst is charged in a reaction vessel, and the flow rate per 3 g of catalyst is 500 cc / min in the reaction vessel, and a rich gas composed of CO (5%), CO 2 (10%), and N 2 (balance) A complex oxide powder (O 2 (5%), CO 2 (10%), N 2 (balance) and lean gas alternately flow every 5 minutes and treated at 1000 ° C. for 5 hours. Noble metal on the catalyst support) was grown.
次いで、高温耐久試験後の触媒の触媒性能を以下の方法によって評価した。すなわち、先ず、前処理として高温耐久試験後の触媒に、表１に示す定常ガスに表１に示すリッチ変動ガス及びリーン変動ガスを１秒おきに交互に導入した変動雰囲気の前処理ガスを、５００℃の温度条件で１５分間流通させた。次に、前処理後の触媒に、表１に示す定常ガスに表１に示すリッチ変動ガス及びリーン変動ガスを１秒おきに交互に導入した変動雰囲気の混合ガスを触媒１ｇあたり７０００ｃｃ／分の流量で、入りガス温度を１００℃から５００℃まで昇温させながら（昇温速度１２℃／分）流通させた。そして、触媒を流通した生成ガスに含まれる全炭化水素濃度（ＴＨＣ濃度）を測定し、５００℃におけるＴＨＣ浄化率（％）〔（生成ガス中の全炭化水素）／（混合ガス中の全炭化水素）〕が５０％となる温度、すなわちＴＨＣ５０％浄化温度を測定した。 Next, the catalyst performance of the catalyst after the high temperature durability test was evaluated by the following method. That is, first, as a pretreatment, a pretreatment gas having a fluctuating atmosphere in which the rich fluctuating gas and the lean fluctuating gas shown in Table 1 are alternately introduced into the stationary gas shown in Table 1 every 1 second as the catalyst after the high temperature durability test It was circulated for 15 minutes at a temperature of 500 ° C. Next, a mixed gas having a varying atmosphere in which the rich fluctuating gas and the lean fluctuating gas shown in Table 1 are alternately introduced into the stationary gas shown in Table 1 every other second is added to the pre-treated catalyst at 7000 cc / min per gram of the catalyst. With the flow rate, the inlet gas temperature was increased from 100 ° C. to 500 ° C. (temperature increase rate: 12 ° C./min). Then, the total hydrocarbon concentration (THC concentration) contained in the product gas flowing through the catalyst is measured, and the THC purification rate (%) at 500 ° C. [(total hydrocarbons in the product gas) / (total carbonization in the mixed gas] Hydrogen)] is 50%, that is, the THC 50% purification temperature is measured.
（iii）評価結果
実施例１〜４及び比較例１〜３で得られた複合酸化物粉末における、高温耐久試験後の比表面積及び平均一次粒子径の測定値を表２に示す。また、実施例１〜４及び比較例１〜３で得られた複合酸化物粉末を用いた排ガス浄化用触媒における高温耐久試験後のＴＨＣ５０％浄化温度を表２に示す。さらに、実施例１〜４及び比較例１〜３における水熱処理条件を表２に示す。
(Iii) Evaluation Results Table 2 shows measured values of the specific surface area and average primary particle diameter after the high temperature durability test in the composite oxide powders obtained in Examples 1 to 4 and Comparative Examples 1 to 3. Table 2 shows the THC 50% purification temperature after the high temperature endurance test in the exhaust gas purification catalysts using the composite oxide powders obtained in Examples 1 to 4 and Comparative Examples 1 to 3. Furthermore, Table 2 shows the hydrothermal treatment conditions in Examples 1 to 4 and Comparative Examples 1 to 3.
表２に示した結果から明らかなように、本発明の複合酸化物粉末（実施例１〜４）においては、高温耐久試験後における比表面積が大きく、また一次粒子径が小さかった。したがって、本発明の複合酸化物粉末の製造方法によれば、優れた耐熱性を有する複合酸化物粉末が得られることが確認された。また、本発明の複合酸化物粉末（実施例１〜４）を触媒担体として用いた排ガス浄化用触媒においては、高温耐久試験後におけるＴＨＣ５０％浄化温度が低かった。したがって、本発明の複合酸化物粉末の製造方法によれば、触媒担体として用いた場合に貴金属の粒成長を十分に抑制し、触媒性能を十分に維持することが可能な複合酸化物粉末が得られることが確認された。 As is clear from the results shown in Table 2, in the composite oxide powders (Examples 1 to 4) of the present invention, the specific surface area after the high temperature durability test was large and the primary particle diameter was small. Therefore, according to the method for producing a composite oxide powder of the present invention, it was confirmed that a composite oxide powder having excellent heat resistance was obtained. Further, in the exhaust gas purification catalyst using the composite oxide powder of the present invention (Examples 1 to 4) as a catalyst carrier, the THC 50% purification temperature after the high temperature durability test was low. Therefore, according to the method for producing a composite oxide powder of the present invention, when used as a catalyst support, a composite oxide powder capable of sufficiently suppressing noble metal grain growth and sufficiently maintaining catalyst performance is obtained. It was confirmed that
以上説明したように、本発明によれば、優れた耐熱性を有し、触媒担体として用いた場合に貴金属の粒成長を十分に抑制し、触媒性能を十分に維持することが可能な複合酸化物粉末、並びにその複合酸化物粉末の製造方法を提供することが可能となる。 As described above, according to the present invention, the composite oxidation has excellent heat resistance, can sufficiently suppress the noble metal grain growth, and can sufficiently maintain the catalyst performance when used as a catalyst carrier. It is possible to provide a product powder and a method for producing the composite oxide powder.
Claims (4)
２種以上の金属化合物を含有する溶液から、塩基の存在下で複合酸化物前駆体を沈殿せしめる工程と、
前記複合酸化物前駆体を沈殿せしめた溶液を、１０００ｓｅｃ−１以上の剪断速度の下で、８０〜２５０℃の温度で水熱処理した後に焼成することによって、前記複合酸化物粉末を得る工程と、
を含むことを特徴とする複合酸化物粉末の製造方法。 A method for producing a composite oxide powder composed of two or more metal oxides,
Precipitating a complex oxide precursor from a solution containing two or more metal compounds in the presence of a base;
A step of obtaining the composite oxide powder by baking the solution in which the composite oxide precursor is precipitated at a temperature of 80 to 250 ° C. under a shear rate of 1000 sec −1 or more and then baking.
A method for producing a composite oxide powder comprising:
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
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| JP2009263150A (en) * | 2008-04-23 | 2009-11-12 | Toyota Central R&D Labs Inc | Compound oxide powder, method and apparatus for producing the same and catalyst for cleaning exhaust gas |
| JP2012223667A (en) * | 2011-04-15 | 2012-11-15 | Toyota Motor Corp | Columnar ceria catalyst |
| JP2014105133A (en) * | 2012-11-28 | 2014-06-09 | Japan Fine Ceramics Center | Method for producing ceria-zirconia composite oxide material and ceria-zirconia composite oxide material obtained thereby |
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| JP2014105133A (en) * | 2012-11-28 | 2014-06-09 | Japan Fine Ceramics Center | Method for producing ceria-zirconia composite oxide material and ceria-zirconia composite oxide material obtained thereby |
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| JP5030573B2 (en) | 2012-09-19 |
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