JP2014176779A - Exhaust gas purification catalyst and method for producing the same - Google Patents
Exhaust gas purification catalyst and method for producing the same Download PDFInfo
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- 239000003054 catalyst Substances 0.000 title claims abstract description 96
- 238000004519 manufacturing process Methods 0.000 title claims description 10
- 238000000746 purification Methods 0.000 title description 11
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- 239000000843 powder Substances 0.000 claims abstract description 62
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- 238000010298 pulverizing process Methods 0.000 claims abstract description 34
- 239000007787 solid Substances 0.000 claims abstract description 26
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- 238000000034 method Methods 0.000 claims description 11
- 229910052751 metal Inorganic materials 0.000 claims description 8
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- 230000000694 effects Effects 0.000 abstract description 10
- 239000007789 gas Substances 0.000 description 29
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- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 10
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- HSJPMRKMPBAUAU-UHFFFAOYSA-N cerium(3+);trinitrate Chemical compound [Ce+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O HSJPMRKMPBAUAU-UHFFFAOYSA-N 0.000 description 2
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- 235000011114 ammonium hydroxide Nutrition 0.000 description 1
- 125000000129 anionic group Chemical group 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
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- JSKIRARMQDRGJZ-UHFFFAOYSA-N dimagnesium dioxido-bis[(1-oxido-3-oxo-2,4,6,8,9-pentaoxa-1,3-disila-5,7-dialuminabicyclo[3.3.1]nonan-7-yl)oxy]silane Chemical compound [Mg++].[Mg++].[O-][Si]([O-])(O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2)O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2 JSKIRARMQDRGJZ-UHFFFAOYSA-N 0.000 description 1
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- UJVRJBAUJYZFIX-UHFFFAOYSA-N nitric acid;oxozirconium Chemical compound [Zr]=O.O[N+]([O-])=O.O[N+]([O-])=O UJVRJBAUJYZFIX-UHFFFAOYSA-N 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 239000008213 purified water Substances 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 238000005245 sintering Methods 0.000 description 1
- 239000011949 solid catalyst Substances 0.000 description 1
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 238000001238 wet grinding Methods 0.000 description 1
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Abstract
Description
本発明は、排気ガス浄化用触媒、及びその製造方法に関する。 The present invention relates to an exhaust gas purification catalyst and a method for producing the same.
触媒担体に触媒材料を担持させる際には、触媒材料を粉砕しスラリー状にして触媒担体にコーティングする方法が一般的に採用されている。触媒全体の活性は触媒粉末の表面積に依存し、その表面積が大きいほど活性が高いことが知られている。そのため、触媒材料を粉砕する工程では、触媒粉末の粒子径をある程度小さくすることが求められる。 When the catalyst material is supported on the catalyst carrier, a method is generally employed in which the catalyst material is pulverized into a slurry and coated on the catalyst carrier. It is known that the activity of the entire catalyst depends on the surface area of the catalyst powder, and the higher the surface area, the higher the activity. Therefore, in the step of pulverizing the catalyst material, it is required to reduce the particle diameter of the catalyst powder to some extent.
一方、直噴ガソリンエンジンの高出力化あるいは自動車の高速走行の増加などを背景に、近年の自動車の排気ガスの温度は６００〜７００℃の高温となっている。しかし、従来の触媒は、耐熱性が低く、排気ガスの熱によって触媒粒子がシンタリングし、比表面積が低下することによって浄化性能が低下するという問題がある。特に触媒粉末の粒子径が小さくなるほど排気ガスの熱によるシンタリングを起こしやすい。 On the other hand, against the backdrop of increasing the output of a direct-injection gasoline engine or increasing the high-speed driving of automobiles, the temperature of exhaust gas in automobiles in recent years has become as high as 600 to 700 ° C. However, the conventional catalyst has low heat resistance, and there is a problem that the purification performance is lowered by the catalyst particles being sintered by the heat of the exhaust gas and the specific surface area being lowered. In particular, as the particle size of the catalyst powder becomes smaller, sintering due to the heat of the exhaust gas tends to occur.
上記触媒の耐熱性を得るには、耐熱性のある材料の開発や、粒子径の選択が必要である。先行技術として、特許文献１には、耐熱性を得るために、平均粒子径２０ｎｍ以下の複合金属酸化物を担体に均一に分散させて担持することが記載されている。具体的には、平均粒子径が２００ｎｍのセリア−ジルコニア固溶体（Ｃｅ／Ｚｒ＝５０／５０（モル比））からなる複合金属酸化物凝集体を、直径５０μｍのジルコニア製マイクロビーズを用いて水溶液中で１２０分間粉砕及び混合して、平均粒子径が１５ｎｍの均質なＣＺコロイド粒子が均一分散しているゾル溶液を得ること、このゾル溶液をアルミナ多孔質担体に加え、蒸発乾固法によって担持させること、さらに、そのアルミナ多孔質担体に白金を蒸発乾固法によって担持させることが記載されている。
In order to obtain the heat resistance of the catalyst, it is necessary to develop a material having heat resistance and to select a particle size. As a prior art,
特許文献２には、熱処理により予めシンタリングされたアルミナ粒子にＣｅＯ２−ＺｒＯ２固溶体粒子を担持させた複合酸化物を排気ガス浄化触媒に用いること、アルミナ粒子の平均粒子径を１００ｎｍ以下とすること、大気中１０００℃での熱処理後のＣｅＯ２−ＺｒＯ２固溶体粒子の平均粒子径を１〜２０ｎｍとすることが記載されている。その複合酸化物の製法は、硝酸セリウム水溶液とオキシ硝酸ジルコニウム水溶液と過酸化水素水とアルミナ粉末とを撹拌混合し、これにアンモニア水を滴下し、得られた沈殿物を濾過・洗浄し、仮焼成後、本焼成を行なうというものである。
In
触媒粒子の粒子径を小さくすると、その活性が高くなるが、上述の如く耐熱性は必ずしも高くならない。触媒粒子は粒子径が小さくなるほど表面エネルギーが大きくなり、その結果、熱によって凝集しやすくなるためである。 When the particle diameter of the catalyst particles is reduced, the activity is increased, but the heat resistance is not necessarily increased as described above. This is because the catalyst particles have a surface energy that increases as the particle size decreases, and as a result, the catalyst particles tend to aggregate due to heat.
そこで、本発明は、従来より両立が困難とされている触媒の活性向上と耐熱性向上との両立を図ることを課題とする。 Then, this invention makes it a subject to aim at coexistence with the activity improvement and heat resistance improvement of the catalyst which has been made difficult to achieve conventionally.
本発明者は、上記課題を解決するために、触媒粉末をビーズミルで湿式粉砕するときの導入エネルギーの大きさ、並びにＸ線回折における回折ピークの半価幅に着目した。 In order to solve the above-mentioned problems, the present inventor paid attention to the magnitude of the energy introduced when wet-grinding the catalyst powder with a bead mill and the half width of the diffraction peak in X-ray diffraction.
ここに提示する排気ガス浄化用触媒は、Ｃｅ含有複合酸化物と触媒金属を有する排気ガス浄化用触媒であって、上記Ｃｅ含有複合酸化物は、メディアン粒子径が２０ｎｍ以上２００ｎｍ以下であり、１０００℃の温度に２４時間保持したときのＸ線回折法における（２２０）面の回折ピークの半価幅が０．９５゜以上１．２５゜以下であることを特徴とする。 The exhaust gas purifying catalyst presented here is an exhaust gas purifying catalyst having a Ce-containing composite oxide and a catalytic metal, and the Ce-containing composite oxide has a median particle diameter of 20 nm or more and 200 nm or less, The half width of the diffraction peak of the (220) plane in the X-ray diffraction method when held at a temperature of ° C for 24 hours is from 0.95 ° to 1.25 °.
回折ピークの半価幅はＣｅ含有複合酸化物の結晶化度の指標となり、その半価幅の値が大きいほど結晶化度が小さい（結晶子が小さい）ことが知られている。１０００℃の温度に２４時間保持したときの上記半価幅が０．９５゜以上１．２５゜以下であるということは、結晶化度が小さい、すなわち、結晶成長が抑制されている（耐熱性が高い）ということである。また、上記Ｃｅ含有複合酸化物は、排気ガスの浄化においてＯＳＣ（酸素吸蔵放出能）を有することが知られている。本発明に係るＣｅ含有複合酸化物はメディアン粒子径が２０ｎｍ以上２００ｎｍ以下である（微粒子である）から、ＯＳＣに優れ、触媒の活性向上に有利になる。 The half width of the diffraction peak serves as an index of the crystallinity of the Ce-containing composite oxide, and it is known that the larger the half width, the smaller the crystallinity (the smaller the crystallite). When the half width is 0.95 ° or more and 1.25 ° or less when held at a temperature of 1000 ° C. for 24 hours, the crystallinity is small, that is, crystal growth is suppressed (heat resistance Is high). Further, it is known that the Ce-containing composite oxide has OSC (oxygen storage / release capability) in purification of exhaust gas. Since the Ce-containing composite oxide according to the present invention has a median particle diameter of 20 nm to 200 nm (fine particles), it is excellent in OSC and advantageous in improving the activity of the catalyst.
好ましいのは、上記触媒金属の少なくとも一部が上記Ｃｅ含有複合酸化物に固溶していることである。これにより、Ｃｅ含有複合酸化物のＯＳＣが高くなり、また、固溶した触媒金属が排気ガスの浄化に効果的に働く。 It is preferable that at least a part of the catalyst metal is dissolved in the Ce-containing composite oxide. As a result, the OSC of the Ce-containing composite oxide is increased, and the solid catalyst metal effectively works to purify the exhaust gas.
次に、ここに提示する排気ガス浄化用触媒の製造方法は、上記Ｃｅ含有複合酸化物と触媒金属を有する排気ガス浄化用触媒を製造する方法であり、
Ｃｅ含有複合酸化物粉末が懸濁したスラリーを調製する工程と、
上記スラリー中の上記Ｃｅ含有複合酸化物粉末をビーズミルによって粉砕する工程とを備え、
上記粉砕によって得られたＣｅ含有複合酸化物粉末を用いて触媒金属を含有する排気ガス浄化用触媒を製造する方法において、
上記スラリー調製工程においては、固形分としてメディアン粒子径１００ｎｍ以上３００ｎｍ以下のＣｅ含有複合酸化物粉末を１０質量％以上３０質量％以下含有し、分散剤を上記固形分量に対する割合で２質量％よりも多く且つ２０質量％以下含有するスラリーを調製し、
上記粉砕工程においては、上記ビーズの粒子径を０．０１５ｍｍ以上０．０５ｍｍ以下とし、粉砕のために導入する上記固形分単位質量当たり且つ１時間当たりのエネルギー量を０．５ｋＷ／ｄｒｙ・ｋｇ以上４．０ｋＷ／ｄｒｙ・ｋｇ以下として、Ｃｅ含有複合酸化物粉末をメディアン粒子径が２０ｎｍ以上２００ｎｍ以下になるように粉砕することを特徴とする。
Next, a method for producing an exhaust gas purification catalyst presented here is a method for producing an exhaust gas purification catalyst having the Ce-containing composite oxide and a catalyst metal,
Preparing a slurry in which Ce-containing composite oxide powder is suspended;
Crushing the Ce-containing composite oxide powder in the slurry with a bead mill,
In the method for producing an exhaust gas purifying catalyst containing a catalytic metal using the Ce-containing composite oxide powder obtained by the pulverization,
In the slurry preparation step, a Ce-containing composite oxide powder having a median particle diameter of 100 nm to 300 nm as a solid content is contained in an amount of 10% by mass to 30% by mass, and the dispersant is more than 2% by mass with respect to the solid content. Preparing a slurry containing at most 20% by mass,
In the pulverization step, the particle diameter of the beads is set to 0.015 mm or more and 0.05 mm or less, and the amount of energy per unit solid mass introduced for pulverization and per hour is 0.5 kW / dry · kg or more. The Ce-containing composite oxide powder is pulverized so as to have a median particle diameter of 20 nm to 200 nm at 4.0 kW / dry · kg or less.
ここに、ビーズの粒子径を０．０１５ｍｍ以上０．０５ｍｍ以下と小さくすることにより、Ｃｅ含有複合酸化物粉末をメディアン粒子径が２０ｎｍ以上２００ｎｍ以下になるまで粉砕することが容易になる。そして、ビーズ径を小さくし、且つ粉砕のために導入する単位時間当たりのエネルギー量を０．５ｋＷ／ｄｒｙ・ｋｇ以上４．０ｋＷ／ｄｒｙ・ｋｇ以下としたことにより、ビーズがＣｅ含有複酸化物粒子に衝突するエネルギーが小さくなる。そのため、個々のＣｅ含有複酸化物粒子が粉砕されるときに、その結晶の歪が大きくならない。すなわち、当該粒子の表面エネルギーの増大が抑えられる。その結果、得られるＣｅ含有複酸化物粉末は粒子径が小さいにも拘わらず、熱による結晶成長や凝集を生じ難くなる。つまり、本発明に係る方法によれば、活性が高く且つ耐熱性が高い排気ガス浄化用触媒が得られる。 Here, by reducing the particle diameter of the beads to 0.015 mm or more and 0.05 mm or less, the Ce-containing composite oxide powder can be easily pulverized until the median particle diameter becomes 20 nm or more and 200 nm or less. Then, by reducing the bead diameter and setting the amount of energy per unit time introduced for pulverization to be 0.5 kW / dry · kg or more and 4.0 kW / dry · kg or less, the beads are converted to a Ce-containing composite oxide. The energy that collides with the particles is reduced. Therefore, when the individual Ce-containing double oxide particles are pulverized, the distortion of the crystals does not increase. That is, an increase in the surface energy of the particles can be suppressed. As a result, although the obtained Ce-containing double oxide powder has a small particle diameter, it is difficult to cause crystal growth and aggregation due to heat. That is, according to the method of the present invention, an exhaust gas purification catalyst having high activity and high heat resistance can be obtained.
また、固形分量に対する分散剤の割合を２質量％よりも多くしたから、上記ビーズによる粉砕によってＣｅ含有複合酸化物粉末の粒子数が増大してもその分散が確保され、一旦粉砕された粒子の再凝集が防止される。さらに、固形分量に対する分散剤の割合を２０質量％以下としたから、Ｃｅ含有複合酸化物粉末の粉砕に要する時間が長くなることが避けられる。 In addition, since the ratio of the dispersing agent to the solid content is more than 2% by mass, even if the number of particles of the Ce-containing composite oxide powder is increased by pulverization with the beads, the dispersion is ensured. Reaggregation is prevented. Furthermore, since the ratio of the dispersant to the solid content is 20% by mass or less, it is possible to avoid an increase in the time required for pulverizing the Ce-containing composite oxide powder.
好ましいのは、上記Ｃｅ含有複合酸化物粉末の粉砕にポリカルボン酸アンモニウムを主成分とする分散剤を用いることである。これにより、ビーズミルでのＣｅ含有複合酸化物粉末の分散が良好になり、所期の粉砕に有利になる。 It is preferable to use a dispersant containing ammonium polycarboxylate as a main component for grinding the Ce-containing composite oxide powder. As a result, the dispersion of the Ce-containing composite oxide powder in the bead mill becomes good, which is advantageous for desired pulverization.
上記導入エネルギー量はビーズミルのロータ周速及び／又はビーズ径によって調節することができる。 The amount of energy introduced can be adjusted by the rotor peripheral speed of the bead mill and / or the bead diameter.
本発明に係る排気ガス浄化用触媒によれば、メディアン粒子径が２０ｎｍ以上２００ｎｍであり、１０００℃の温度に２４時間保持したときのＸ線回折法における（２２０）面の回折ピークの半価幅が０．９５゜以上１．２５゜以下であるＣｅ含有複合酸化物を含有するから、触媒活性及び耐熱性の向上に有利になる。 According to the exhaust gas purifying catalyst of the present invention, the half width of the diffraction peak of the (220) plane in the X-ray diffraction method when the median particle diameter is 20 nm or more and 200 nm and held at a temperature of 1000 ° C. for 24 hours. Is contained in the Ce-containing composite oxide having an angle of 0.95 ° or more and 1.25 ° or less, which is advantageous in improving catalyst activity and heat resistance.
本発明に係る排気ガス浄化用触媒の製造方法によれば、メディアン粒子径１００ｎｍ以上３００ｎｍ以下のＣｅ含有複合酸化物粉末を１０質量％以上３０質量％以下含有し、固形分量に対する割合で分散剤を２質量％よりも多く且つ２０質量％以下含有するスラリーを調製し、ビーズの粒子径を０．０１５ｍｍ以上０．０５ｍｍ以下とし、粉砕のために導入する固形分単位質量当たり且つ１時間当たりのエネルギー量を０．５ｋＷ／ｄｒｙ・ｋｇ以上４．０ｋＷ／ｄｒｙ・ｋｇ以下として、スラリー中のＣｅ含有複合酸化物粉末をメディアン粒子径が２０ｎｍ以上２００ｎｍ以下になるようにビーズミルで粉砕するから、活性が高く且つ耐熱性が高い排気ガス浄化用触媒が得られる。 According to the method for producing an exhaust gas purifying catalyst according to the present invention, a Ce-containing composite oxide powder having a median particle diameter of 100 nm or more and 300 nm or less is contained in an amount of 10% by mass or more and 30% by mass or less, and the dispersant is contained at a ratio to the solid content. A slurry containing more than 2% by mass and not more than 20% by mass is prepared, and the bead particle size is 0.015 mm or more and 0.05 mm or less, and energy per unit of solid content introduced for pulverization and energy per hour The amount is 0.5 kW / dry · kg or more and 4.0 kW / dry · kg or less, and the Ce-containing composite oxide powder in the slurry is pulverized by a bead mill so that the median particle diameter is 20 nm or more and 200 nm or less. An exhaust gas purifying catalyst having high heat resistance is obtained.
以下、本発明を実施するための形態を図面に基づいて説明する。以下の好ましい実施形態の説明は、本質的に例示に過ぎず、本発明、その適用物或いはその用途を制限することを意図するものではない。 Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The following description of the preferred embodiments is merely exemplary in nature and is not intended to limit the invention, its application, or its use.
（触媒粉末の調製）
触媒材料（Ｃｅ含有複合酸化物粉末）としてＲｈドープＣｅＺｒ系複合酸化物粉末を準備した。これは、Ｚｒを主成分とするＣｅＺｒ系複合酸化物にＲｈがドープ（固溶）している粉末であり、さらにＮｄを含有する（ＲｈドープＣｅＺｒＮｄ複合酸化物）。Ｒｈを除く組成はＣｅＯ２：ＺｒＯ２：Ｎｄ２Ｏ３＝２３：６７：１０（質量％）であり、Ｒｈドープ量は０．１質量％である。触媒材料は、共沈法で調製し、乾燥及び焼成を行なった後、メディアン粒子径が約２００ｎｍとなるようにディスパーザで予備粉砕した。
(Preparation of catalyst powder)
As a catalyst material (Ce-containing composite oxide powder), an Rh-doped CeZr-based composite oxide powder was prepared. This is a powder in which Rh is doped (solid solution) in a CeZr-based composite oxide containing Zr as a main component, and further contains Nd (Rh-doped CeZrNd composite oxide). The composition excluding Rh is CeO 2 : ZrO 2 : Nd 2 O 3 = 23: 67: 10 (mass%), and the Rh doping amount is 0.1 mass%. The catalyst material was prepared by a coprecipitation method, dried and calcined, and then preliminarily pulverized with a disperser so that the median particle diameter was about 200 nm.
上記予備粉砕後の触媒材料５０ｇを分散剤２．５ｇと共に精製水に加えホモジナイザーを用いて攪拌することによってスラリー５００ｇを調製した。分散剤としては、サンノプコ社製「ノプコスパース５６００（主成分；ポリカルボン酸アンモニウム，アニオン性）を用いた。このスラリーの固形分濃度は１０質量％、この固形分量に対する分散剤の割合は５質量％（スラリー全量に対する割合は０．５質量％）である。 A slurry of 500 g was prepared by adding 50 g of the pre-ground catalyst material together with 2.5 g of the dispersant to purified water and stirring using a homogenizer. As the dispersant, “Nopcosperth 5600 (main component; ammonium polycarboxylate, anionic)” manufactured by San Nopco Co. was used. The solid content concentration of this slurry was 10% by mass, and the ratio of the dispersant to this solid content was 5% by mass. (The ratio to the total amount of the slurry is 0.5% by mass).
上記スラリーを寿工業社製「デュアルアペックスミルＤＡＭ−０１５」（スラリー循環方式のセパレータ付きビーズミル，ミル有効容積；０．１７Ｌ，ロータ外径４４ｍｍ，ロータ羽数；２０枚，ミル容器、ロータ、セパレータ及びビーズの材質；ジルコニア，ビーズ径（直径）；０．０１５ｍｍ）に供給し、スラリー中の触媒材料の粉砕を行なった。ビーズ投入量は４００ｇとし、ロータ周速を変える（１２ｍ／ｓ、１０ｍ／ｓ、６ｍ／ｓ、３ｍ／ｓ）ことによって、粉砕のための導入エネルギー量Ｓを変化させた。 “Dual Apex Mill DAM-015” manufactured by Kotobuki Industries Co., Ltd. (bead mill with slurry circulation type separator, mill effective volume: 0.17 L, rotor outer diameter 44 mm, number of rotor blades: 20 sheets, mill container, rotor, separator And bead material: zirconia, bead diameter (diameter): 0.015 mm), and the catalyst material in the slurry was pulverized. The amount of introduced energy S for pulverization was changed by changing the rotor peripheral speed (12 m / s, 10 m / s, 6 m / s, 3 m / s) to 400 g of beads.
導入エネルギー量Ｓは、ミル内にスラリー及びビーズを入れてミルを駆動したときの動力（消費電力）から、ミル内にスラリーのみを入れビーズを入れないでミルを駆動したときの動力を差し引いた値を粉砕動力Ｐ（ｋＷ）、スラリーの固形分量をＫ（ｋｇ）、粉砕処理に要した時間をｔ（ｈ）としたとき、次式で表される。 The amount of energy introduced S was subtracted from the power (power consumption) when the mill was driven with the slurry and beads placed in the mill, and the power when the mill was driven with only the slurry in the mill and no beads. When the value is pulverization power P (kW), the solid content of the slurry is K (kg), and the time required for the pulverization process is t (h), it is expressed by the following equation.
Ｓ＝Ｐ×ｔ／Ｋ（ｋＷｈ／ｄｒｙ−ｋｇ） S = P × t / K (kWh / dry-kg)
触媒材料をその粒子径測定値が飽和するまで（粉砕による粒子径の低下がなくなるまで）粉砕したときの導入エネルギー量を単位時間（１時間）当たりの導入エネルギー量に換算すると、ロータ周速１２ｍ／ｓでは４．０ｋＷ／ｄｒｙ−ｋｇ、１０ｍ／ｓでは２．４ｋＷ／ｄｒｙ−ｋｇ、６ｍ／ｓでは０．８ｋＷ／ｄｒｙ−ｋｇ、３ｍ／ｓでは０．４ｋＷ／ｄｒｙ−ｋｇであった。 When the amount of energy introduced when the catalyst material is pulverized until the measured particle size is saturated (until the particle size decreases due to pulverization) is converted into the amount of energy introduced per unit time (1 hour), the rotor peripheral speed is 12 m. It was 4.0 kW / dry-kg at / s, 2.4 kW / dry-kg at 10 m / s, 0.8 kW / dry-kg at 6 m / s, and 0.4 kW / dry-kg at 3 m / s.
（Ｘ線回折ピークの半価幅）
上記の各ロータ周速での粉砕によって得られた触媒粉末、並びに未粉砕触媒粉末についてアルミナ粉末と混合してＸ線回折分析を行ない、（２２０）面の回折ピークの半価幅を次のシェラーの式から求めた。λは特性Ｘ線ＣｕＫαの波長（１．５４Å)、βは(２２０)面の半価幅（ラジアン）、θはブラッグ角である。触媒粉末とアルミナ粉末とは１０：９０（質量比）で混合した。
(Half width of X-ray diffraction peak)
The catalyst powder obtained by pulverization at each rotor peripheral speed and the unpulverized catalyst powder were mixed with alumina powder and subjected to X-ray diffraction analysis, and the half-value width of the diffraction peak on the (220) plane was determined as the following Scherrer It was obtained from the formula of λ is the wavelength (1.54Ｘ) of the characteristic X-ray CuKα, β is the half width (radian) of the (220) plane, and θ is the Bragg angle. The catalyst powder and the alumina powder were mixed at 10:90 (mass ratio).
結晶子径Ｄ(２２０)＝０．９λ／(β・cosθ) Crystallite diameter D (220) = 0.9λ / (β · cosθ)
図１は熱処理を施していないフレッシュ触媒粉末の回折ピーク位置・半価幅と単位時間当たりの導入エネルギー量との関係を示す。図２はＯ２を２％、Ｈ２Ｏを１０％含み残部がＮ２よりなるガス中で触媒粉末を１０００℃の温度に２４時間保持した後（熱エージング後）の同関係を示す。図１及び図２において、「粉砕品」は上記粉砕によって得られた触媒粉末のことであり、「未粉砕品」は未粉砕触媒粉末のことである。 FIG. 1 shows the relationship between the diffraction peak position and half-value width of fresh catalyst powder not subjected to heat treatment and the amount of energy introduced per unit time. FIG. 2 shows the same relationship after keeping the catalyst powder at a temperature of 1000 ° C. for 24 hours in a gas composed of 2% O 2 and 10% H 2 O and the balance N 2 (after thermal aging). In FIG. 1 and FIG. 2, “pulverized product” refers to the catalyst powder obtained by the above pulverization, and “unground product” refers to the unpulverized catalyst powder.
図１と図２とを比較すると、単位時間当たりの導入エネルギー量が０．４ｋＷ／ｄｒｙ−ｋｇである粉砕品では、エージングによって半価幅が増大し、他の触媒粉末ではエージングによって半価幅が小さくなっている。 When FIG. 1 and FIG. 2 are compared, the half-value width increases due to aging in the pulverized product having an introduced energy amount per unit time of 0.4 kW / dry-kg, and the half-value width due to aging in other catalyst powders. Is getting smaller.
単位時間当たりの導入エネルギー量が０．４ｋＷ／ｄｒｙ−ｋｇであるときは、ビーズの衝突エネルギーが小さいことから、得られる触媒粒子の結晶子の表面エネルギーが高くならない。そのため、熱が加わっても触媒粉末が凝集せずに熱安定なアルミナ粒子上で分散化された状態が保たれやすく、さらには加熱によってアルミナ粒子に一部固溶した状態になって粒子の分散性が高くなり易い。その結果、半価幅が増大したと推測される。これに対して、単位時間当たりの導入エネルギー量が大きい他の粉砕品では、ビーズの衝突エネルギーが大きいため、結晶子自体の表面エネルギーも高くなり、粉砕の過程で既に触媒粉末が凝集していると推測される。そのため、熱が加わると、結晶成長する触媒粒子の割合が大きくなり、半価幅が小さくなると推察される。 When the amount of energy introduced per unit time is 0.4 kW / dry-kg, since the collision energy of the beads is small, the surface energy of the crystallites of the obtained catalyst particles does not increase. Therefore, even when heat is applied, the catalyst powder does not agglomerate and is easily dispersed on the heat-stable alumina particles, and further, the particles are dispersed in the alumina particles by heating and become partly dissolved. Tend to be high. As a result, it is estimated that the half width has increased. On the other hand, in other pulverized products with a large amount of energy introduced per unit time, since the collision energy of the beads is large, the surface energy of the crystallite itself also increases, and the catalyst powder has already aggregated during the pulverization process. It is guessed. For this reason, when heat is applied, it is assumed that the proportion of catalyst particles for crystal growth increases and the half width decreases.
図２によれば、単位時間当たりの導入エネルギー量が変わっても回折ピーク位置は殆ど変わらないが、半価幅はビーズミルによる粉砕触媒粉末の方が未粉砕触媒粉末よりも大きく、ビーズミルによる粉砕によって触媒粉末の結晶成長が抑制されていることがわかる。そして、粉砕された触媒粉末をみると、単位時間当たりの導入エネルギー量が少なくなるほど半価幅が大きくなっている。なお、図２の近似曲線はＲ２＝0.7698の相関式ｙ＝−０．０２５ｌｎ(ｘ)＋１．００４による。 According to FIG. 2, the diffraction peak position hardly changes even when the amount of energy introduced per unit time changes, but the half-value width is larger in the pulverized catalyst powder by the bead mill than in the unpulverized catalyst powder. It can be seen that the crystal growth of the catalyst powder is suppressed. When looking at the pulverized catalyst powder, the half-value width increases as the amount of energy introduced per unit time decreases. The approximate curve in FIG. 2 is based on the correlation equation y = −0.025ln (x) +1.004 with R 2 = 0.7698.
（排気ガス浄化用触媒の調製）
上記ビーズミルによって粉砕して得た単位時間当たりの導入エネルギー量が４．０ｋＷ／ｄｒｙ−ｋｇ、２．４ｋＷ／ｄｒｙ−ｋｇ及び０．８ｋＷ／ｄｒｙ−ｋｇの実施例に係る各触媒粉末（フレッシュ）、並びに単位時間当たりの導入エネルギー量を６．０ｋＷ／ｄｒｙ−ｋｇとした比較例に係る触媒粉末（フレッシュ）について、それぞれアルミナ粉末と１０：９０の質量比で混合し、その混合物を担体に担持させることによって実施例及び比較例の各排気ガス浄化用触媒を得た。比較例の触媒粉末の組成は、実施例の触媒粉末と同じである。
(Preparation of exhaust gas purification catalyst)
Each catalyst powder (fresh) according to Examples having an energy introduction amount per unit time of 4.0 kW / dry-kg, 2.4 kW / dry-kg and 0.8 kW / dry-kg obtained by pulverization by the bead mill. In addition, catalyst powder (fresh) according to a comparative example in which the amount of energy introduced per unit time was 6.0 kW / dry-kg was mixed with alumina powder at a mass ratio of 10:90, and the mixture was supported on a carrier. Thus, the exhaust gas purifying catalysts of Examples and Comparative Examples were obtained. The composition of the catalyst powder of the comparative example is the same as that of the catalyst powder of the example.
実施例の各触媒粉末のメディアン粒子径（Ｄ５０）は、単位時間当たりの導入エネルギー量が４．０ｋＷ／ｄｒｙ−ｋｇのとき３４ｎｍ、２．４ｋＷ／ｄｒｙ−ｋｇのとき３５ｎｍ、０．８ｋＷ／ｄｒｙ−ｋｇのとき３６ｎｍであった。また、比較例の触媒粉末のメディアン粒子径（Ｄ５０）は４０ｎｍであった。粒子径の測定には堀場製作所製ナノ粒子解析装置（動的光散乱法）ＳＺ−１００を用いた。 The median particle diameter (D50) of each catalyst powder in the examples is 34 nm when the amount of energy introduced per unit time is 4.0 kW / dry-kg, 35 nm when the amount of energy is 2.4 kW / dry-kg, and 0.8 kW / dry. At -kg, it was 36 nm. Moreover, the median particle diameter (D50) of the catalyst powder of the comparative example was 40 nm. For the measurement of the particle diameter, a nanoparticle analyzer (dynamic light scattering method) SZ-100 manufactured by HORIBA, Ltd. was used.
担体としては、セル壁厚さ３．５mil（８．８９×１０−２ｍｍ）、１平方インチ（６４５．１６ｍｍ２）当たりのセル数６００のコージェライト製ハニカム担体（容量１００ｍＬ）を用いた。触媒粉末の担持量は担体１Ｌ当たり１００ｇである。 As the carrier, a cordierite honeycomb carrier (capacity: 100 mL) having a cell wall thickness of 3.5 mil (8.89 × 10 −2 mm) and 600 cells per square inch (645.16 mm 2 ) was used. The supported amount of catalyst powder is 100 g per liter of support.
（触媒性能の評価）
実施例及び比較例の各排気ガス浄化用触媒についてベンチエージングを行なった。すなわち、触媒をエンジンの排気管に取り付け、触媒入口での温度が９００℃の排気ガスに触媒を５０時間晒した。このとき、エンジン回転数及び空燃比を（アイドル回転数，Ａ／Ｆ＝１４．７において１分間）→（３５６０ｒｐｍ，Ａ／Ｆ＝１３．５において２分間）→（３３００ｒｐｍ，Ａ／Ｆ＝１４．７において２分間）の３モードで順に変化させた。エンジン運転期間中、エンジンオイルを吸気マニホールドに３０ｍＬ／ｈで添加し続けるようにした。
(Evaluation of catalyst performance)
Bench aging was performed on each of the exhaust gas purifying catalysts of Examples and Comparative Examples. That is, the catalyst was attached to the exhaust pipe of the engine, and the catalyst was exposed to exhaust gas having a temperature of 900 ° C. at the catalyst inlet for 50 hours. At this time, the engine speed and the air-fuel ratio are set to (idle speed, 1 minute at A / F = 14.7) → (2 minutes at 3560 rpm, A / F = 13.5) → (3300 rpm, A / F = 14 (7 minutes for 2 minutes). During the engine operation period, engine oil was continuously added to the intake manifold at 30 mL / h.
ベンチエージング後の排気ガス浄化用触媒から担体容量約２５ｍＬのコアサンプルを切り出した。このコアサンプルをモデルガス流通反応装置に取り付け、ＨＣ、ＣＯ及びＮＯｘの浄化に関する各ライトオフ温度Ｔ５０（℃）を測定した。すなわち、触媒に流入するモデルガスの温度を１００℃から漸次上昇させていき、その触媒から流出するガスのＨＣ及びＣＯ各々の濃度変化を検出した。Ｔ５０（℃）は、ＨＣ、ＣＯ及びＮＯｘ各成分の浄化率が５０％に達したときの触媒入口ガス温度である。 A core sample having a carrier volume of about 25 mL was cut out from the exhaust gas purifying catalyst after bench aging. This core sample was attached to a model gas flow reactor, and each light-off temperature T50 (° C.) relating to purification of HC, CO and NOx was measured. That is, the temperature of the model gas flowing into the catalyst was gradually increased from 100 ° C., and changes in the concentrations of HC and CO in the gas flowing out from the catalyst were detected. T50 (° C.) is the catalyst inlet gas temperature when the purification rate of each component of HC, CO and NOx reaches 50%.
モデルガスは、Ａ／Ｆ＝１４．７±０．９とした。すなわち、Ａ／Ｆ＝１４．７のメインストリームガスを定常的に流しつつ、所定量の変動用ガスを１Ｈｚでパルス状に添加することにより、Ａ／Ｆを±０．９の振幅で強制的に振動させた。空間速度ＳＶは６００００ｈ−１、昇温速度は３０℃／分である。 The model gas was A / F = 14.7 ± 0.9. That is, the A / F is forced at an amplitude of ± 0.9 by adding a predetermined amount of fluctuation gas in a pulse form at 1 Hz while constantly flowing the main stream gas of A / F = 14.7. Vibrated. The space velocity SV is 60000 h −1 , and the heating rate is 30 ° C./min.
結果を図３に示す。ＨＣ、ＣＯ及びＮＯｘ（窒素酸化物）のいずれ関しても、単位時間当たりの導入エネルギー量が４．０ｋＷ／ｄｒｙ−ｋｇ以下の各実施例は、導入エネルギー量が６．０ｋＷ／ｄｒｙ−ｋｇである比較例よりも、ライトオフ温度が１０℃以上低くなっている。また、単位時間当たりの導入エネルギー量が少なくなるほどライトオフ温度が低くなっている。 The results are shown in FIG. For any of HC, CO, and NOx (nitrogen oxide), each of the examples in which the amount of energy introduced per unit time is 4.0 kW / dry-kg or less is 6.0 kW / dry-kg. The light-off temperature is 10 ° C. or more lower than a certain comparative example. In addition, the light-off temperature decreases as the amount of energy introduced per unit time decreases.
（分散剤添加量について）
スラリーにおける分散剤（ノプコスパース５６００）の添加量が触媒粉末（上記ＲｈドープＣｅＺｒ系複合酸化物）の粒子径（Ｄ１０，Ｄ５０，Ｄ９０）に及ぼす影響を上記ビーズミルを用いて調べた。ビーズ径は０．０１５ｍｍ、スラリー量は５００ｇ、触媒材料の量（固形分量）は５０ｇ、ロータ周速は１２ｍ／ｓとした。その結果を図４〜図７に示す。
(About the amount of dispersant added)
The effect of the added amount of the dispersant (Nopcosper 5600) in the slurry on the particle diameter (D10, D50, D90) of the catalyst powder (the Rh-doped CeZr composite oxide) was examined using the bead mill. The bead diameter was 0.015 mm, the amount of slurry was 500 g, the amount of catalyst material (solid content) was 50 g, and the rotor peripheral speed was 12 m / s. The results are shown in FIGS.
図４に示すように、固形分量に対する分散剤量の割合が２質量％であるときは、粉砕時間が長くなるに伴って触媒粉末の粒子径が増大する傾向が見られる。ビーズによる触媒粉末の粉砕によって粒子表面積がトータルで増大していくところ、その表面積の増大に対して分散剤が不足し、一旦粉砕された微粒子が再凝集していると考えられる。 As shown in FIG. 4, when the ratio of the amount of the dispersant to the solid content is 2% by mass, the particle diameter of the catalyst powder tends to increase as the pulverization time becomes longer. When the total surface area of the particles is increased by the pulverization of the catalyst powder with beads, it is considered that the dispersant is insufficient for the increase in the surface area, and the finely pulverized fine particles are re-aggregated.
図５〜図７に示すように、固形分量に対する分散剤量の割合が５質量％、１０質量％、２０質量％であるときは、粉砕時間が長くなるに伴って触媒粉末の粒子径が小さくなっており、微粒子の再凝集は見られない。但し、分散剤量が多くなると、微粒子化に要する粉砕時間が長くなる傾向が見られる。 As shown in FIGS. 5 to 7, when the ratio of the amount of the dispersant to the solid content is 5% by mass, 10% by mass, and 20% by mass, the particle size of the catalyst powder becomes smaller as the pulverization time becomes longer. Thus, no reaggregation of the fine particles is observed. However, when the amount of the dispersing agent is increased, the pulverization time required for micronization tends to be longer.
従って、固形分量に対する分散剤量の割合は、粒子径が不安定になることを避けるために、２質量％よりも大きくすることが好ましく、また、粉砕時間が長くなることを避けるために、２０質量％以下にすることが好ましい、ということができる。 Accordingly, the ratio of the amount of the dispersant to the solid content is preferably larger than 2% by mass in order to avoid unstable particle size, and 20% in order to avoid an increase in the grinding time. It can be said that it is preferable to set it to mass% or less.
（ビーズ径について）
ビーズ径が触媒粉末（上記ＲｈドープＣｅＺｒ系複合酸化物）の粒子径（Ｄ１０，Ｄ５０，Ｄ９０）に及ぼす影響を上記ビーズミルを用いて調べた。スラリー量は５００ｇ、触媒材料の量（固形分量）は５０ｇ、固形分量に対する分散剤量の割合は５質量％、ロータ周速は１２ｍ／ｓとした。その結果を図８〜図１１に示す。
(Bead diameter)
The effect of the bead diameter on the particle diameter (D10, D50, D90) of the catalyst powder (the Rh-doped CeZr-based composite oxide) was examined using the bead mill. The amount of the slurry was 500 g, the amount of the catalyst material (solid content) was 50 g, the ratio of the dispersant amount to the solid content was 5 mass%, and the rotor peripheral speed was 12 m / s. The results are shown in FIGS.
図８〜図１１によれば、ビーズ径が小さくなるほど触媒材料の微粒子化が図れ、且つ微粒子化に要する粉砕時間が短くなることがわかる。よって、生産効率及び省エネにも有利になる。また、ビーズ径が小さくなるほど、個々のビーズの触媒材料に対する衝突エネルギーが小さくなるため、触媒材料の結晶構造の歪みが少なくなる。すなわち、得られる触媒粉末の表面エネルギーが大きくならないから、その耐熱性が高くなる（結晶成長ないしは凝集をしにくくなる。）。従って、触媒材料の微粒子化、生産効率、省エネ、耐熱性向上の観点から、ビーズ径は小さいこと、特に０．０１５ｍｍ以上０．０５ｍｍ以下であることが好ましい。 8 to 11, it can be seen that as the bead diameter becomes smaller, the catalyst material can be made finer and the pulverization time required for making finer becomes shorter. Therefore, it becomes advantageous for production efficiency and energy saving. Also, as the bead diameter decreases, the collision energy of the individual beads against the catalyst material decreases, and therefore the distortion of the crystal structure of the catalyst material decreases. That is, since the surface energy of the obtained catalyst powder does not increase, its heat resistance increases (it becomes difficult for crystal growth or aggregation). Therefore, it is preferable that the bead diameter is small, particularly 0.015 mm or more and 0.05 mm or less, from the viewpoints of making the catalyst material finer, producing efficiency, energy saving, and improving heat resistance.
なし None
Claims (4)
上記Ｃｅ含有複合酸化物は、メディアン粒子径が２０ｎｍ以上２００ｎｍ以下であり、１０００℃の温度に２４時間保持したときのＸ線回折法における（２２０）面の回折ピークの半価幅が０．９５゜以上１．２５゜以下であることを特徴とする排気ガス浄化用触媒。 An exhaust gas purifying catalyst having a Ce-containing composite oxide and a catalytic metal,
The Ce-containing composite oxide has a median particle diameter of 20 nm or more and 200 nm or less, and a half-value width of a diffraction peak on the (220) plane in the X-ray diffraction method when held at a temperature of 1000 ° C. for 24 hours is 0.95. An exhaust gas purifying catalyst characterized by having an angle of from ° to 1.25 °.
上記触媒金属の少なくとも一部が上記Ｃｅ含有複合酸化物に固溶していることを特徴とする排気ガス浄化用触媒。 In claim 1,
An exhaust gas purifying catalyst, characterized in that at least a part of the catalyst metal is dissolved in the Ce-containing composite oxide.
上記スラリー中の上記Ｃｅ含有複合酸化物粉末をビーズミルによって粉砕する工程とを備え、
上記粉砕によって得られたＣｅ含有複合酸化物粉末を用いて触媒金属を含有する排気ガス浄化用触媒を製造する方法において、
上記スラリー調製工程においては、固形分としてメディアン粒子径１００ｎｍ以上３００ｎｍ以下のＣｅ含有複合酸化物粉末を１０質量％以上３０質量％以下含有し、分散剤を上記固形分量に対する割合で２質量％よりも多く且つ２０質量％以下含有するスラリーを調製し、
上記粉砕工程においては、上記ビーズの粒子径を０．０１５ｍｍ以上０．０５ｍｍ以下とし、粉砕のために導入する上記固形分単位質量当たり且つ１時間当たりのエネルギー量を０．５ｋＷ／ｄｒｙ・ｋｇ以上４．０ｋＷ／ｄｒｙ・ｋｇ以下として、Ｃｅ含有複合酸化物粉末をメディアン粒子径が２０ｎｍ以上２００ｎｍ以下になるように粉砕することを特徴とする排気ガス浄化用触媒の製造方法。 Preparing a slurry in which Ce-containing composite oxide powder is suspended;
Crushing the Ce-containing composite oxide powder in the slurry with a bead mill,
In the method for producing an exhaust gas purifying catalyst containing a catalytic metal using the Ce-containing composite oxide powder obtained by the pulverization,
In the slurry preparation step, a Ce-containing composite oxide powder having a median particle diameter of 100 nm to 300 nm as a solid content is contained in an amount of 10% by mass to 30% by mass, and the dispersant is more than 2% by mass with respect to the solid content. Preparing a slurry containing at most 20% by mass,
In the pulverization step, the particle diameter of the beads is set to 0.015 mm or more and 0.05 mm or less, and the amount of energy per unit solid mass introduced for pulverization and per hour is 0.5 kW / dry · kg or more. A method for producing an exhaust gas purifying catalyst, wherein the Ce-containing composite oxide powder is pulverized to 4.0 kW / dry · kg or less so that the median particle diameter is 20 nm or more and 200 nm or less.
上記分散剤がポリカルボン酸アンモニウムを主成分とすることを特徴とする排気ガス浄化用触媒の製造方法。 In claim 3,
A method for producing an exhaust gas purifying catalyst, characterized in that the dispersant contains ammonium polycarboxylate as a main component.
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| JP2007268470A (en) * | 2006-03-31 | 2007-10-18 | Mazda Motor Corp | Method for manufacturing catalytic material, catalytic material and exhaust gas cleaning catalyst using the same |
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