JP4654101B2 - EXHAUST GAS PURIFICATION CATALYST, ITS MANUFACTURING METHOD, AND EXHAUST GAS PURIFICATION INTEGRATED STRUCTURE TYPE CATALYST - Google Patents
EXHAUST GAS PURIFICATION CATALYST, ITS MANUFACTURING METHOD, AND EXHAUST GAS PURIFICATION INTEGRATED STRUCTURE TYPE CATALYST Download PDFInfo
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Description
本発明は、排気ガス浄化用触媒、その製造方法、及び排気ガス浄化用一体構造型触媒に関し、より詳しくは、内燃機関、ボイラー等の排気ガスに含まれるＨＣ、ＣＯ、ＳＯＦ、ＮＯｘ等に対して優れた浄化能力を有し、また、低コストでありながら、高温の環境下においても安定した浄化能力を発現しうる排気ガス浄化用触媒、その製造方法、及び排気ガス浄化用一体構造型触媒に関するものである。 The present invention relates to an exhaust gas purification catalyst, a manufacturing method thereof, and an exhaust gas purification monolithic catalyst, and more particularly to HC, CO, SOF, NOx, etc. contained in exhaust gas of an internal combustion engine, a boiler, etc. Exhaust gas purification catalyst that has an excellent purification capacity and is low in cost and can exhibit a stable purification capacity even in a high temperature environment, a method for producing the same, and an integral structure type catalyst for exhaust gas purification It is about.
内燃機関、ボイラーは、その構造、種類に応じて、燃料、潤滑剤等に由来した様々な有害物質を排出する。これら有害物質としては炭化水素（ＨＣ）、一酸化炭素（ＣＯ）、窒素酸化物（ＮＯｘ）のほかに、ディーゼルエンジンなどから排出される煤（スート）に代表される粒子状物質（ｐａｒｔｉｃｕｌａｔｅ ｍａｔｔｅｒ：以下、ＰＭという事がある）があり、前記ＨＣにはベンゼン、トルエン、炭素鎖長の長い炭化水素など有機溶剤に可溶な成分である可溶性有機成分（ｓｏｌｕｂｌｅ ｏｒｇａｎｉｃ ｆｒａｃｔｉｏｎ：以下、ＳＯＦと言うことがある）が含まれる。 Internal combustion engines and boilers emit various harmful substances derived from fuels, lubricants, etc., depending on their structure and type. In addition to hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx), these harmful substances include particulate matter typified by soot discharged from diesel engines and the like: Hereinafter, the HC may be a soluble organic component (hereinafter referred to as SOF), which is a component soluble in an organic solvent such as benzene, toluene, or a hydrocarbon having a long carbon chain length. Is included).
近年、各種内燃機関からの排気ガスによる環境汚染が社会的問題となり、その浄化のために種々の手法が提案されている。これら排気ガス中の有害成分を浄化する一つの方法として、排気ガスを触媒に接触させ、浄化する接触処理法が実用化されている。
このうちガソリン機関の排気ガス浄化用触媒としては、ＨＣ、ＳＯＦ、ＣＯなどの有害成分を酸化して浄化する酸化触媒、ＮＯｘなどの有害成分を一時的に吸蔵した後に加熱したり、燃料などの未燃炭化水素、尿素、アンモニアなどの還元剤を供給することにより還元除去する還元触媒、ＨＣ、ＣＯ、ＮＯｘを同時に酸化・還元処理して浄化する三元触媒が知られている。
In recent years, environmental pollution due to exhaust gas from various internal combustion engines has become a social problem, and various methods have been proposed for purification. As one method for purifying harmful components in these exhaust gases, a contact treatment method for purifying exhaust gases by contacting them with a catalyst has been put into practical use.
Among these, exhaust gas purification catalysts for gasoline engines include oxidation catalysts that oxidize and purify harmful components such as HC, SOF, and CO, heat after temporarily storing harmful components such as NOx, and fuel There are known reduction catalysts that reduce and remove by supplying a reducing agent such as unburned hydrocarbon, urea, ammonia, etc., and three-way catalysts that purify by oxidizing and reducing HC, CO, and NOx simultaneously.
また、ディーゼル機関から排出されるスートを排気ガスから濾し取り、スートが溜まった時点で燃料などの未燃炭化水素やＮＯ２を供給し、加熱処理して、スートを酸化（燃焼）処理する方法が検討され、排気ガス中の粒子状物質を濾し取るためのフィルター（Ｄｉｅｓｅｌ Ｐａｒｔｉｃｕｌａｔｅ Ｆｉｌｔｅｒ、以下、ＤＰＦと言うことがある）、ＤＰＦを触媒化した触媒化フィルター（ｃａｔａｌｙｚｅｄ ｓｏｏｔ ｆｉｌｔｅｒ、以下、ＣＳＦという事がある）が知られている。 Also, a method of filtering soot discharged from a diesel engine from exhaust gas, supplying unburned hydrocarbons such as fuel and NO 2 when the soot accumulates, heat-treating, and oxidizing (combusting) the soot And a filter for filtering particulate matter in exhaust gas (Diesel Particulate Filter, hereinafter referred to as DPF), a catalyzed filter (catalyzed soot filter, hereinafter referred to as CSF). Is known).
これら排気ガス浄化用の触媒は、排気ガスが流出する際の圧力損失を小さく抑えることができ、しかも接触効率を大きく確保できるように、担体の表面に触媒組成物を被覆した触媒として、通常は排気ガスの流路に設置される。
このうち自動車に搭載される排気ガス浄化用触媒は、比較的温度の低い床下に設置されるものと、エンジンから排出された直後、高温の排気ガスに触れる位置に設置される直下型と言われるものとがある。直下型では排気ガスの温度は１０００℃を超える場合があることから、排気ガス浄化用触媒には、このように高温で苛酷な条件においても安定して排気ガスを浄化できる性能が要求される。
These exhaust gas purifying catalysts are usually used as catalysts having a catalyst composition coated on the surface of a carrier so that the pressure loss when exhaust gas flows out can be kept small, and the contact efficiency can be kept large. It is installed in the exhaust gas flow path.
Among these, exhaust gas purification catalysts mounted on automobiles are said to be installed under the floor where the temperature is relatively low, and directly below, where the exhaust gas purification catalyst is installed at a position where it comes into contact with the hot exhaust gas immediately after being discharged from the engine. There is a thing. Since the exhaust gas temperature may exceed 1000 ° C. in the direct type, the exhaust gas purifying catalyst is required to have a performance capable of stably purifying the exhaust gas even under severe conditions at such a high temperature.
このような排気ガス浄化用触媒の担体としては、金属の波板やセラミックスで成形されたハニカム状のフロースルー型担体や、ＤＰＦ、ＣＳＦに多く用いられるハニカムの一端が閉じて市松模様になったウォールフロー型担体の一体構造型担体が知られている。また、太い繊維状物からなるフェルト様の不燃性構造体や、数ミリから数センチの直径の球状物、柱状物などからなる成型担体が知られている（本発明では、これらを総称して構造型担体と言い、フロースルー型担体、ウォールフロー型担体などの一体構造型担体と区別する）。 As such an exhaust gas purifying catalyst carrier, a honeycomb flow-through carrier formed of metal corrugated plates or ceramics, or one end of a honeycomb often used for DPF or CSF was closed to form a checkered pattern. An integral structure type carrier of a wall flow type carrier is known. In addition, a felt-like noncombustible structure made of a thick fibrous material, a spherical carrier having a diameter of several millimeters to several centimeters, a molded carrier made of a columnar material, etc. are known (in the present invention, these are generically called This is called a structural carrier, and is distinguished from a monolithic carrier such as a flow-through carrier and a wall flow carrier).
排気ガス浄化に寄与する活性金属としては、白金、パラジウム、ロジウムなどの貴金属、ニッケル、鉄他の遷移金属、セリウム、ランタン他の希土類金属やその酸化物が知られている。また、これら活性金属は、表面積を大きくし強度を高めるために、β−アルミナ、γ−アルミナなどのアルミナやゼオライトなどの担体に担持される。なお、ゼオライトには、ＭＦＩ型、β型等の種類があり、内部のカチオンをＣｅ、Ｆｅなどの金属イオンで交換されることがある。触媒組成物は、その求められる機能に応じて、活性金属、担体の種類と量が選択され、触媒製造時に、アルカリ金属、アルカリ土類金属が添加されることがある。 As active metals contributing to exhaust gas purification, noble metals such as platinum, palladium and rhodium, transition metals other than nickel, iron, cerium, lanthanum and other rare earth metals and oxides thereof are known. These active metals are supported on a support such as alumina such as β-alumina and γ-alumina and zeolite in order to increase the surface area and increase the strength. There are various types of zeolite such as MFI type and β type, and the internal cation may be exchanged with metal ions such as Ce and Fe. In the catalyst composition, the type and amount of the active metal and the carrier are selected according to the required function, and an alkali metal or an alkaline earth metal may be added during the production of the catalyst.
ディーゼル機関からの排気ガス浄化用触媒の場合、特に活性金属種である白金、パラジウムなどの貴金属が酸化活性の面で重要な役割を果たし、担持母材の多層化や、セリアに代表される酸素の吸蔵・放出材等との組み合わせが重要な要素であるとされている（例えば、特許文献１参照）。 In the case of exhaust gas purification catalysts from diesel engines, precious metals such as platinum and palladium, which are active metal species, play an important role in terms of oxidation activity. The combination with the occlusion / release material is an important element (see, for example, Patent Document 1).
一般に触媒組成物中の貴金属量を多くするほど排気ガス浄化能力を向上しうるが、貴金属の増量はコストアップにつながり、安価な触媒をユーザーに向けて安定的に供給することが困難となる。ところが、環境問題に直面した自動車業界などからは、排気ガス浄化性能の向上に関する期待が近年一段と増している。このように、排気ガス浄化用触媒の開発には、コストアップを抑えた上で浄化能力を向上しなければならないという、相反した課題を有している。
このような状況下、触媒組成物中の貴金属量を増やすことなく排気ガス浄化能力を向上でき、１０００℃を超えるような高温で過酷な条件においても安定して排気ガスを浄化できる排気ガス浄化用触媒及び排気ガス浄化用一体構造型触媒が切望されていた。
Under such circumstances, the exhaust gas purification capacity can be improved without increasing the amount of noble metal in the catalyst composition, and the exhaust gas can be stably purified even under severe conditions at high temperatures exceeding 1000 ° C. An integral structure type catalyst for purifying a catalyst and exhaust gas has been desired.
本発明の目的は、上記従来の課題に鑑み、内燃機関、ボイラー等の排気ガスに含まれるＨＣ、ＣＯ、ＳＯＦ、ＮＯｘ等に対して優れた浄化能力を有し、また、低コストでありながら、高温の環境下においても安定して浄化能力を発現しうる排気ガス浄化用触媒、その製造方法、排気ガス浄化用一体構造型触媒を提供することにある。また、特に、ＨＣ、ＮＯｘ、ＣＯを同時に削減する事が可能な三元系触媒について好適な触媒技術を提供することにある。 In view of the above-described conventional problems, an object of the present invention is to have an excellent purifying ability for HC, CO, SOF, NOx, etc. contained in exhaust gas of an internal combustion engine, a boiler, etc., and at a low cost. An object of the present invention is to provide an exhaust gas purifying catalyst that can stably exhibit purifying performance even in a high temperature environment, a method for producing the exhaust gas purifying catalyst, and an exhaust gas purifying integrated structure type catalyst. It is another object of the present invention to provide a catalyst technology suitable for a three-way catalyst that can reduce HC, NOx, and CO at the same time.
本発明者らは、このような上記課題を解決するために鋭意研究を重ねた結果、ウイスカー状無機母材上に金属触媒成分が針状に担持された繊維状の無機母材―金属触媒複合物を排気ガス浄化用触媒として用いることにより、高価な貴金属触媒成分の使用量が削減でき、この無機母材―金属触媒複合物は、金属触媒成分と特定の無機母材とを含むスラリーを焼成して得られ、１１００℃の高温に１２時間加熱された後も無機母材、金属触媒成分共に長時間高温に晒される前の形状を保ち、安定した触媒性能を維持できることを見出し、本発明を完成するに至った。 As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a fibrous inorganic base material-metal catalyst composite in which a metal catalyst component is supported in a needle shape on a whisker-like inorganic base material. The amount of expensive noble metal catalyst component used can be reduced by using the product as an exhaust gas purification catalyst. This inorganic matrix-metal catalyst composite fires a slurry containing the metal catalyst component and a specific inorganic matrix. It was found that the inorganic base material and the metal catalyst component can maintain the shape before being exposed to a high temperature for a long time even after being heated to a high temperature of 1100 ° C. for 12 hours, and stable catalyst performance can be maintained. It came to be completed.
すなわち、本発明の第１の発明によれば、金属触媒成分（Ａ）がウイスカー状無機母材（Ｂ）上に担持された繊維状の無機母材―金属触媒複合物を含有する排気ガス浄化用触媒であって、金属触媒成分（Ａ）が、無機母材（Ｂ）の少なくとも表層部中で、長さが１００ｎｍ以上の針状形態をなして存在し、かつ金属触媒成分（Ａ）、無機母材（Ｂ）の直径がいずれも実質的に１００ｎｍ以下であり、かつアスペクト比が２以上であることを特徴とする排気ガス浄化用触媒が提供される。 That is, according to the first invention of the present invention, the exhaust gas purification containing the fibrous inorganic base material-metal catalyst composite in which the metal catalyst component (A) is supported on the whisker-like inorganic base material (B). The metal catalyst component (A) is present in an acicular form having a length of 100 nm or more in at least the surface layer portion of the inorganic base material (B), and the metal catalyst component (A), Provided is an exhaust gas purification catalyst characterized in that the inorganic base material (B) has a diameter of substantially 100 nm or less and an aspect ratio of 2 or more.
また、本発明の第２の発明によれば、第１の発明において、金属触媒成分（Ａ）が、白金、パラジウム、又はロジウムから選ばれる一種以上であることを特徴とする排気ガス浄化用触媒が提供される。 According to the second invention of the present invention, in the first invention, the catalyst for exhaust gas purification, wherein the metal catalyst component (A) is one or more selected from platinum, palladium, or rhodium. Is provided.
また、本発明の第３の発明によれば、第１、又は２の発明において、金属触媒成分（Ａ）の直径が、実質的に５０ｎｍ以下であり、無機母材（Ｂ）の直径が、実質的に２０ｎｍ以下であることを特徴とする排気ガス浄化用触媒が提供される。 According to the third invention of the present invention, in the first or second invention, the diameter of the metal catalyst component (A) is substantially 50 nm or less, and the diameter of the inorganic base material (B) is An exhaust gas purifying catalyst characterized by being substantially 20 nm or less is provided.
また、本発明の第４の発明によれば、第１〜３のいずれかの発明において、金属触媒成分（Ａ）が、１１００℃の高温で１２時間加熱後も繊維形状を保つことを特徴とする排気ガス浄化用触媒が提供される。 Moreover, according to the fourth invention of the present invention, in any one of the first to third inventions, the metal catalyst component (A) is characterized by maintaining the fiber shape even after heating at a high temperature of 1100 ° C. for 12 hours. An exhaust gas purifying catalyst is provided.
また、本発明の第５の発明によれば、第１〜４のいずれかの発明において、無機母材（Ｂ）が、Ａｌ２Ｏ３を主要構成単位とする無機物質であることを特徴とする排気ガス浄化用触媒が提供される。 According to a fifth invention of the present invention, in any one of the first to fourth inventions, the inorganic base material (B) is an inorganic substance having Al 2 O 3 as a main structural unit. An exhaust gas purifying catalyst is provided.
また、本発明の第６の発明によれば、第１〜５のいずれかの発明において、無機母材（Ｂ）が、希土類元素から選ばれる一種以上を含むことを特徴とする排気ガス浄化用触媒が提供される。 According to a sixth aspect of the present invention, in any one of the first to fifth aspects, the inorganic base material (B) contains one or more selected from rare earth elements. A catalyst is provided.
さらに、本発明の第７の発明によれば、第６の発明において、希土類元素の含有量が、無機母材（Ｂ）に対して０．５〜２０重量％であることを特徴とする排気ガス浄化用触媒が提供される。 Furthermore, according to the seventh invention of the present invention, in the sixth invention, the exhaust gas is characterized in that the rare earth element content is 0.5 to 20 wt% with respect to the inorganic base material (B). A gas purification catalyst is provided.
一方、本発明の第８の発明によれば、第１〜７のいずれかの発明に係り、金属触媒成分（Ａ）と無機母材（Ｂ）とを水系媒体中で混合してスラリーを調製した後、該スラリーを、ウイスカー状無機母材（Ｂ）上に担持される金属触媒成分（Ａ）がその表層部中で針状形態をなして存在するに十分な程度に、焼成することにより、金属触媒成分（Ａ）、無機母材（Ｂ）共、直径が実質的に１００ｎｍ以下である繊維状の無機母材―金属触媒複合物を形成させることを特徴とする排気ガス浄化用触媒の製造方法が提供される。 On the other hand, according to the eighth aspect of the present invention relates to any one of aspects 1-7, metal catalyst component (A) and the inorganic base material and (B) are mixed in an aqueous medium to the slurry preparation Then, the slurry is fired to such an extent that the metal catalyst component (A) supported on the whisker-like inorganic base material (B) is present in a needle-like form in the surface layer portion. An exhaust gas purifying catalyst characterized by forming a fibrous inorganic base material-metal catalyst composite having a diameter of substantially 100 nm or less for both the metal catalyst component (A) and the inorganic base material (B). A manufacturing method is provided.
一方、本発明の第９の発明によれば、第１〜７のいずれかの発明に係り、排気ガス浄化用触媒を、一体構造型担体の表面に被覆してなる排気ガス浄化用一体構造型触媒が提供される。 On the other hand, according to the ninth aspect of the present invention, the first to relate to any one of the 7, the exhaust gas purifying catalyst, integral structure monolithic structure type for and formed by the exhaust gas purifying coating to the surface of the support A catalyst is provided.
また、本発明の第１０の発明によれば、第９の発明において、金属触媒成分（Ａ）の量が、一体構造型担体に対して０．０１〜１０ｇ／Ｌであることを特徴とする排気ガス浄化用一体構造型触媒が提供される。 According to a tenth aspect of the present invention, in the ninth aspect , the amount of the metal catalyst component (A) is 0.01 to 10 g / L with respect to the monolithic support. An integral structure type catalyst for exhaust gas purification is provided.
また、本発明の第１１の発明によれば、第９または１０の発明において、無機母材―金属触媒複合物の量が、一体構造型担体に対して１０〜４００ｇ／Ｌであることを特徴とする排気ガス浄化用一体構造型触媒が提供される。 According to the eleventh aspect of the present invention, in the ninth or tenth aspect , the amount of the inorganic base material-metal catalyst composite is 10 to 400 g / L with respect to the monolithic support. An integral structure type catalyst for purifying exhaust gas is provided.
さらに、本発明の第１２の発明によれば、第９〜１１のいずれかの発明において、さらに、酸素吸蔵・放出材を含むことを特徴とする排気ガス浄化用一体構造型触媒が提供される。 Furthermore, according to a twelfth aspect of the present invention, there is provided the exhaust gas purifying integrated structure type catalyst according to any one of the ninth to eleventh aspects, further comprising an oxygen storage / release material. .
本発明の排気ガス浄化用触媒は、排気ガス中のＨＣ、ＮＯｘ、ＣＯなどに対して優れた浄化能力を発揮すると共に、これら有害成分を同時に除去できることから、特に内燃機関から排出される排気ガス浄化用の三元系触媒として良好である。また、１０００℃を超える高温での耐久性能にも優れていることから、内燃機関に対して直下型の一体構造型触媒として設置することが可能となる。
さらに、本発明の触媒は、貴金属の使用量が少なくて済むため低コストで製造する事ができ、排気ガス浄化装置を安定的に生産し供給することができる。
The exhaust gas purifying catalyst of the present invention exhibits an excellent purifying ability for HC, NOx, CO, etc. in the exhaust gas and can remove these harmful components at the same time. Good as a three-way catalyst for purification. Moreover, since it is excellent in durability performance at a high temperature exceeding 1000 ° C., it can be installed as a direct-type monolithic catalyst for an internal combustion engine.
Furthermore, the catalyst of the present invention can be manufactured at low cost because the amount of noble metal used is small, and an exhaust gas purification device can be stably produced and supplied.
以下、本発明の排気ガス浄化用触媒、その製造方法、及び排気ガス浄化用一体構造型触媒について、図面を用いて詳細に説明する。 Hereinafter, the exhaust gas purifying catalyst, the manufacturing method thereof, and the exhaust gas purifying monolithic catalyst of the present invention will be described in detail with reference to the drawings.
１．排気ガス浄化用触媒
本発明の排気ガス浄化用触媒は、金属触媒成分（Ａ）がウイスカー状無機母材（Ｂ）上に担持された繊維状の無機母材―金属触媒複合物を含有する排気ガス浄化用触媒であって、金属触媒成分（Ａ）が、無機母材（Ｂ）の少なくとも表層部中で、長さが１００ｎｍ以上の針状形態をなして存在し、かつ金属触媒成分（Ａ）、無機母材（Ｂ）の直径がいずれも実質的に１００ｎｍ以下であり、かつアスペクト比が２以上であることを特徴とする。
1. Exhaust gas purification catalyst The exhaust gas purification catalyst of the present invention is an exhaust gas containing a fibrous inorganic base material-metal catalyst composite in which a metal catalyst component (A) is supported on a whisker-like inorganic base material (B). A catalyst for gas purification, wherein the metal catalyst component (A) is present in an acicular form having a length of 100 nm or more in at least the surface layer portion of the inorganic base material (B), and the metal catalyst component (A ), The inorganic base material (B) has a diameter of substantially 100 nm or less and an aspect ratio of 2 or more.
なお、ここで複合物、無機母材、金属触媒の形状を示す“繊維状”とは直径の大小によらず、針状、ウイスカー状のほか、数本の繊維が合体して太くなった状態、さらに多数の繊維がランダムに集合したフェルト状態であっても良い。また、触媒金属、無機母材は、柱状、針状、ウイスカー状、繊維状など広い意味でアスペクト比を有する形状を取ることができる。望ましいアスペクト比は２以上であり、より望ましくは１０以上である。以下、本発明においては、触媒金属については針状、無機母材についてはウイスカー状、複合物については繊維状という。さらに、これらの形状を包括する場合にも繊維状ということがある。 Here, “fibrous” indicating the shape of the composite, inorganic base material, and metal catalyst is a state where needles and whiskers are combined, and several fibers are combined and thick regardless of the diameter. Further, a felt state in which a large number of fibers are randomly gathered may be used. Further, the catalyst metal and the inorganic base material can take a shape having an aspect ratio in a broad sense such as a columnar shape, a needle shape, a whisker shape, and a fiber shape. A desirable aspect ratio is 2 or more, more desirably 10 or more. Hereinafter, in the present invention, the catalyst metal is referred to as a needle shape, the inorganic base material is referred to as a whisker shape, and the composite is referred to as a fiber shape. Furthermore, when including these shapes, it may be fibrous.
（金属触媒成分）
本発明において金属触媒成分は、排気ガスの浄化に対して活性を有するものであれば、特に限定されず、遷移金属、希土類金属、貴金属などのいずれでもよい。
具体的には、鉄、ニッケル、コバルト、ジルコニウム、銅などの遷移金属、セリウム、ランタン、プラセオジム、ネオジウムなどの希土類金属、金、銀、白金、パラジウム、ロジウム等の貴金属から一種以上を適宜選択できる。特に好ましい金属触媒成分は、白金、パラジウム、又はロジウムから選ばれる１種以上の貴金属である。金属触媒成分の原料は、通常、硝酸塩、硫酸塩、炭酸塩、酢酸塩等の形態で使用される。
金属触媒成分の量は、遷移金属、希土類金属、貴金属の種類、無機母材や担体の種類などによって異なるが、貴金属であれば、無機母材や担体の容積当り、０．０１〜１０ｇ／Ｌ、特に０．１〜１０ｇ／Ｌである事が好ましい。金属触媒成分の量が１０ｇ／Ｌを超えると、触媒の生産コストが上昇してしまい、０．０１ｇ／Ｌ未満では、排気ガスの浄化性能が低下する。
(Metal catalyst component)
In the present invention, the metal catalyst component is not particularly limited as long as it has activity for purification of exhaust gas, and may be any of transition metal, rare earth metal, noble metal and the like.
Specifically, one or more kinds of transition metals such as iron, nickel, cobalt, zirconium, and copper, rare earth metals such as cerium, lanthanum, praseodymium, and neodymium, and noble metals such as gold, silver, platinum, palladium, and rhodium can be appropriately selected. . Particularly preferred metal catalyst components are one or more noble metals selected from platinum, palladium, or rhodium. The raw material for the metal catalyst component is usually used in the form of nitrate, sulfate, carbonate, acetate or the like.
The amount of the metal catalyst component varies depending on the type of transition metal, rare earth metal, noble metal, type of inorganic base material and support, and in the case of noble metal, 0.01 to 10 g / L per volume of the inorganic base material and support. In particular, it is preferably 0.1 to 10 g / L. When the amount of the metal catalyst component exceeds 10 g / L, the production cost of the catalyst increases, and when it is less than 0.01 g / L, the exhaust gas purification performance decreases.
金属触媒成分が繊維状の無機母材上に担持された無機母材−金属触媒複合物にあっては、金属触媒成分の形状は針状であり、その直径が実質的に１００ｎｍ以下であることが望ましく、５０ｎｍ以下、最も好ましくは４０ｎｍ以下である。また、針状の金属触媒成分の長さは、実質的に１００ｎｍ以上であることが望ましく、好ましくは３００ｎｍ以上である。
なお、本発明においてサイズを表す表現として用いる「実質的に」とは、直径、および長さの平均値を指すか、そのサイズを取りうる構成要素の多くが当該サイズを有する部位を保ちえる状態であることを意味する。以下、無機母材においても同様の意味で用いる。
In the inorganic base material-metal catalyst composite in which the metal catalyst component is supported on the fibrous inorganic base material, the shape of the metal catalyst component is needle-like and the diameter is substantially 100 nm or less. Is preferably 50 nm or less, and most preferably 40 nm or less. The length of the acicular metal catalyst component is desirably substantially 100 nm or more, and preferably 300 nm or more.
In the present invention, “substantially” used as an expression representing a size refers to an average value of a diameter and a length, or a state in which many components capable of taking the size can maintain a portion having the size. It means that. Hereinafter, the same meaning also applies to the inorganic base material.
（無機母材）
本発明において、原料として用いられる無機母材は、少なくともＡｌ２Ｏ３、ＳｉＣ、ＳｉＯ２、ＴｉＯ２等、熱的に安定な構成単位からなる無機物質、または焼成後にウイスカー状になりうる前駆体である。特にＡｌ２Ｏ３、又はＳｉＣを構成単位とする無機物質が望ましく、このような無機物質としては、繊維状ベーマイトや、ＳｉＣナノファイバー（前駆体を含む）などがある。
(Inorganic base material)
In the present invention, the inorganic base material used as a raw material is an inorganic substance composed of a thermally stable structural unit such as at least Al 2 O 3 , SiC, SiO 2 , or TiO 2 , or a precursor that can become a whisker after firing It is. In particular, an inorganic substance having Al 2 O 3 or SiC as a structural unit is desirable, and examples of such an inorganic substance include fibrous boehmite and SiC nanofiber (including a precursor).
ここで、無機母材は、その直径が実質的に５０ｎｍ以下であることが望ましく、より好ましくは２０ｎｍ以下、最も好ましくは１０ｎｍ以下である。無機母材の直径の下限については、特に限定されるものでは無いが、２ｎｍ以上の無機母材を用いた場合で本発明の効果が確認されている。なお、前駆体の場合は、通常は鎖状の高分子化合物の集合体であるため、直径を規定することはできない。 Here, the inorganic base material desirably has a diameter of substantially 50 nm or less, more preferably 20 nm or less, and most preferably 10 nm or less. The lower limit of the diameter of the inorganic base material is not particularly limited, but the effect of the present invention has been confirmed when an inorganic base material of 2 nm or more is used. In the case of a precursor, since it is usually an assembly of chain polymer compounds, the diameter cannot be defined.
無機母材は、熱的な安定性を得る点から希土類を含む無機物質である事が望ましい。このような無機物質と希土類の好ましい組み合わせとしては、無機物質としてＡｌ２Ｏ３単位を有する繊維状ベーマイト、希土類としてランタンの組み合わせがあげられる。なお、ここでランタンは、ランタンアルミネート、酸化ランタンなどの化合物でもよく、ランタンそのものとして無機物質に含まれていても良いが、繊維状ベーマイトに結晶内に取り込まれていることが望ましい。
なお、繊維状ベーマイトへのランタンの添加方法は、例えば、硝酸ランタン等のランタン塩の溶液と繊維状ベーマイトを混合攪拌し、乾燥焼成することによって得ることができる。ここで、繊維状ベーマイトに添加されるランタンの量は０．５〜２０重量％とし、１〜１０重量％がより好ましい。ランタンが０．５重量％未満では充分な加熱耐久性の向上が得られず、２０重量％を超えると繊維状ベーマイトに結晶学的変化が起こり、活性アルミナとしての特性が変化してしまう恐れがある。
The inorganic base material is preferably an inorganic substance containing a rare earth from the viewpoint of obtaining thermal stability. As a preferable combination of such an inorganic substance and a rare earth, a fibrous boehmite having an Al 2 O 3 unit as an inorganic substance and a combination of lanthanum as a rare earth can be given. Here, the lanthanum may be a compound such as lanthanum aluminate or lanthanum oxide, and may be contained in the inorganic substance as lanthanum itself, but it is desirable that the lanthanum is incorporated into the crystalline boehmite.
In addition, the addition method of lanthanum to fibrous boehmite can be obtained, for example, by mixing and stirring a solution of lanthanum salt such as lanthanum nitrate and fibrous boehmite, followed by drying and baking. Here, the amount of lanthanum added to the fibrous boehmite is 0.5 to 20% by weight, and more preferably 1 to 10% by weight. If lanthanum is less than 0.5% by weight, sufficient improvement in heat durability cannot be obtained, and if it exceeds 20% by weight, crystallographic changes may occur in the fibrous boehmite and the properties as activated alumina may change. is there.
本発明において、無機母材として好ましい繊維状ベーマイトは、主として分子式がＡｌ２Ｏ３・１．０５〜３．０Ｈ２Ｏで表される。アルミナの結晶水が１．０５より少ないベーマイトは、形状が板状になることがあり、結晶水が３．０を越えるベーマイトは極めて小さな繊維の凝集体であるため好ましくない。無機母材として好ましい繊維状ベーマイトは、主として分子式がＡｌ２Ｏ３・１．３〜３．０Ｈ２Ｏで表されるものである。 In the present invention, the preferred fibrous boehmite as the inorganic base material has a molecular formula mainly represented by Al 2 O 3 .1.05-3.0H 2 O. Boehmite with a crystal water of less than 1.05 in alumina may have a plate shape, and boehmite with a crystal water exceeding 3.0 is not preferable because it is an aggregate of very small fibers. The preferred fibrous boehmite as the inorganic base material is one whose molecular formula is mainly represented by Al 2 O 3 · 1.3 to 3.0H 2 O.
また、繊維状ベーマイトは、直径が実質的に５０ｎｍ以下、特に３〜５０ｎｍの範囲にあるものが好ましい。繊維の長さは特に限定されないが、１００ｎｍよりも長いものが好ましく、例えば、１００〜１００００ｎｍの範囲にあるものが好ましい。繊維状ベーマイトの直径と長さは、得られる焼成物の細孔構造とも密接に関係している。すなわち、短い繊維のベーマイトから得られる焼成物の細孔容積は小さく、長い繊維の場合は細孔容積が大きい。また、細い繊維のベーマイトから得られる焼成物の比表面積は大きく、太い繊維の場合は比表面積が小さい。 The fibrous boehmite preferably has a diameter of substantially 50 nm or less, particularly 3 to 50 nm. Although the length of a fiber is not specifically limited, A thing longer than 100 nm is preferable, For example, the thing in the range of 100-10000 nm is preferable. The diameter and length of the fibrous boehmite are closely related to the pore structure of the obtained fired product. That is, the pore volume of the fired product obtained from boehmite of short fibers is small, and the pore volume is large in the case of long fibers. Moreover, the specific surface area of the baked product obtained from boehmite having fine fibers is large, and the specific surface area is small in the case of thick fibers.
このような繊維状ベーマイトからなるアルミナ水和物は、たとえば、国際公開特許（ＷＯ９７／３２８１７号公報）に記載された方法によって調製することができる。具体的には、アルミナ原料の水懸濁液に、酸を加えたのち９０〜１５０℃の温度で水熱処理を行い、繊維状ベーマイトが分散したアルミナゾルを調製する。
上記アルミナ原料としては、少なくとも部分的に再水和性を有するρおよび／またはχ結晶構造を示すアルミナが用いられる。中でもギブサイト、バイヤライト等のアルミナ三水和物を急速高温加熱により脱水して得られたもので、比表面積が５０〜５００ｍ２／ｇの範囲にあり、かつ部分的に再水和性を有するアルミナが好ましい。
このようにして得られる繊維状ベーマイトは、通常、水に分散したゾル状であるが、このゾルに前記触媒金属成分を混合し、このスラリーを乾燥・焼成すると、繊維状ベーマイトの表面に触媒金属成分が針状に担持され安定したウイスカー状構造を形成する。
Alumina hydrate composed of such fibrous boehmite can be prepared, for example, by the method described in International Patent Publication (WO97 / 32817). Specifically, after adding an acid to an aqueous suspension of an alumina raw material, hydrothermal treatment is performed at a temperature of 90 to 150 ° C. to prepare an alumina sol in which fibrous boehmite is dispersed.
As the alumina raw material, alumina having a ρ and / or χ crystal structure having at least a partial rehydration property is used. Above all, it is obtained by dehydrating alumina trihydrate such as gibbsite and bayerite by rapid high-temperature heating, has a specific surface area in the range of 50 to 500 m 2 / g, and has partial rehydration properties. Alumina is preferred.
The fibrous boehmite thus obtained is usually in the form of a sol dispersed in water. When the catalyst metal component is mixed with the sol, and the slurry is dried and fired, the catalyst metal is formed on the surface of the fibrous boehmite. The components are supported in a needle shape to form a stable whisker-like structure.
一方、ＳｉＣナノファイバーは、化学気相析出法（ＣＶＤ法）、ケイ素系ポリマーの熱分解による方法（プレカーサー法）などにより調製される。このようなものに、ＳｉＣウィスカー、Ｓｉ−Ｃ−Ｏ系繊維などが知られている。ＣＶＤ法は、原料ガスを高温で反応させ、炭素やタングステンなどの繊維にＳｉＣを化学的に成長する方法である。また、プレカーサー法は、ケイ素系ポリマーのポリカルボシラン（Ｐｏｌｙｃａｒｂｏｓｉｌａｎｅ：ＰＣＳ）を出発物質として、溶融紡糸、不融化、熱処理（焼成）という３つの工程を経て製造する方法である。本発明では、ＰＣＳを用いるプレカーサー法の適用が好ましい。
一方、ＳｉＣナノファイバーでは、前駆体の焼成後に直径が実質的に５０ｎｍ以下、特に３〜５０ｎｍの範囲になるものが好ましい。繊維の長さは特に限定されないが、実質的に１００ｎｍよりも長いものが好ましく、例えば、１００〜１００００ｎｍの範囲にあるものが好ましい。
On the other hand, SiC nanofibers are prepared by a chemical vapor deposition method (CVD method), a method based on thermal decomposition of a silicon-based polymer (precursor method), or the like. As such, SiC whiskers, Si—C—O fibers, and the like are known. The CVD method is a method in which a raw material gas is reacted at a high temperature to chemically grow SiC on a fiber such as carbon or tungsten. In addition, the precursor method is a method in which a silicon-based polymer polycarbosilane (PCS) is used as a starting material to be manufactured through three steps of melt spinning, infusibilization, and heat treatment (firing). In the present invention, it is preferable to apply a precursor method using PCS.
On the other hand, it is preferable that the SiC nanofiber has a diameter of substantially 50 nm or less, particularly 3 to 50 nm after firing of the precursor. Although the length of a fiber is not specifically limited, The thing substantially longer than 100 nm is preferable, for example, the thing in the range of 100-10000 nm is preferable.
（複合物）
本発明において複合物は、ウイスカー状無機母材上に、金属触媒成分が針状に担持された繊維状の無機母材―金属触媒複合物であり、この無機母材―金属触媒複合物は、熱的に極めて安定である。
(Composite)
In the present invention, the composite is a fibrous inorganic base material-metal catalyst composite in which a metal catalyst component is supported in a needle shape on a whisker-like inorganic base material. This inorganic base material-metal catalyst composite is: It is extremely stable thermally.
図１の写真は、本発明に係る繊維状の無機母材―金属触媒複合物を１１００℃のオーブン中で、１２時間放置し、その後の無機母材―金属触媒複合物の外観を走査型透過電子顕微鏡で観察したもの（倍率：×１００ｋ）である。図３は無機母材のみの電子顕微鏡写真であるが、図１を見ると、原料として用いた無機母材（繊維状ベーマイト）が、略一方向に整列し、部分的に複数本の無機母材が合体して太くなったウイスカー状態で、金属触媒を針状に担持している様子がわかる。本発明において複合物は、このように１１００℃の高温に１２時間加熱された後も無機母材、金属触媒成分が共に繊維状を保ちうるものであることが望ましい。
なお、この写真を一見すると、表層部では無機母材の上に金属触媒が載っているだけのようであるが、本発明の無機母材−金属触媒複合物は、無機母材上に単に金属触媒が担持されている状態に限らず、無機母材が組成中、あるいは結晶中に金属触媒を取り込んだ状態で有っても良い。
The photograph in FIG. 1 shows that the fibrous inorganic base material-metal catalyst composite according to the present invention is allowed to stand in an oven at 1100 ° C. for 12 hours, and then the appearance of the inorganic base material-metal catalyst composite is scanned and transmitted. It is what was observed with the electron microscope (magnification: x100k). FIG. 3 is an electron micrograph of only the inorganic base material. When FIG. 1 is viewed, the inorganic base material (fibrous boehmite) used as a raw material is aligned in approximately one direction, and a plurality of inorganic base materials are partially formed. It can be seen that the metal catalyst is supported in a needle shape in a whisker state in which the materials are combined and thickened. In the present invention, it is desirable that the composite is such that both the inorganic base material and the metal catalyst component can maintain a fibrous shape even after being heated to a high temperature of 1100 ° C. for 12 hours.
At first glance, it seems that the metal catalyst is only placed on the inorganic base material in the surface layer portion, but the inorganic base material-metal catalyst composite of the present invention is simply a metal on the inorganic base material. Not only the state in which the catalyst is supported, but the inorganic base material may be in the composition or in the state in which the metal catalyst is incorporated in the crystal.
また、繊維の方向は、一方向であってもランダム方向であっても構わないが、通常は焼成によって略一方向に揃った状態で得られることが多い。繊維の長さやフェルトの幅は、特に限定されないが、繊維が長くフェルトの幅が広いほど金属触媒を効果的に担持できるので好ましい。 Further, the direction of the fiber may be one direction or random direction, but usually it is often obtained in a state of being aligned in approximately one direction by firing. The length of the fiber and the width of the felt are not particularly limited. However, the longer the fiber and the wider the width of the felt, the more preferable because the metal catalyst can be effectively supported.
このように、本発明においては、ウイスカー状無機母材に金属触媒成分が針状に担持されたときに、金属触媒成分の含有量が従来の量より少なくても優れた排気ガス浄化性能を発現する。金属触媒成分が無機母材に針状に担持されることにより、排気ガス浄化性能が向上する理由は定かでは無いが、その理由の一つとしては、無機母材の形状を極細の繊維状にすることにより、粒状である場合に比べて比表面積が著しく増大し、金属触媒成分がより多くの排気ガスと接触する事が可能になるためでは無いかと考えられる。
また、他の理由としては、金属触媒成分、無機母材が所謂ナノサイズにまで微細化されていることで、量子サイズ効果により電子状態が変化し、近年注目されている所謂ナノ材料同様に、当該金属触媒成分が新規で特異な性質を発現し、金属触媒成分の量を減らしても排気ガス浄化性能が向上するのでは無いかと考えられる。
また、金属をナノサイズまで微細化した場合、一般に融点が低下する事が知られているが、本発明において金属触媒成分は長時間高温に晒された状態であっても、金属は繊維形状を維持して安定した排気ガス浄化性能を発揮することは、これまで知られていない。
As described above, in the present invention, when the metal catalyst component is supported in the form of needles on the whisker-like inorganic base material, excellent exhaust gas purification performance is exhibited even if the content of the metal catalyst component is less than the conventional amount. To do. The reason why the exhaust gas purification performance is improved by supporting the metal catalyst component on the inorganic base material in a needle shape is not certain, but one of the reasons is that the shape of the inorganic base material is made into an extremely fine fiber shape. This is considered to be because the specific surface area is remarkably increased as compared with the case of being granular, and the metal catalyst component can come into contact with more exhaust gas.
Another reason is that the metal catalyst component and the inorganic base material are miniaturized to a so-called nano-size, and the electronic state changes due to the quantum size effect. It is considered that the metal catalyst component exhibits novel and unique properties, and the exhaust gas purification performance is improved even if the amount of the metal catalyst component is reduced.
In addition, it is known that when the metal is refined to a nano size, the melting point generally decreases, but in the present invention, even if the metal catalyst component is exposed to a high temperature for a long time, the metal has a fiber shape. It has not been known so far to maintain and exhibit stable exhaust gas purification performance.
本発明の排気ガス浄化用触媒には、前記原料の他、触媒性能を改善するために、アルカリ金属、アルカリ土類金属などを適宜添加することができる。また、ゼオライト等の吸着剤、セリアやセリア−ジルコニア複合酸化物などの酸素吸蔵・放出材（ｏｘｇｅｎ ｓｔｏｒａｇｅ ｃｏｍｐｏｎｅｎｔ：以下、ＯＳＣ材と言うことがある）などを適宜組み合わせて、より高度な機能を有する排気ガス浄化用触媒とする事が可能である。
ＯＳＣ材の量は、その種類、担体の種類などによって異なるが、セリア−ジルコニア複合酸化物であれば、担体の容積当り、０．０１〜１０ｇ／Ｌ、特に０．１〜１０ｇ／Ｌである事が好ましい。このように、本発明を酸化触媒として用いる場合は、ＯＳＣ材と併用することで、ＯＳＣ材から放出される酸素によりＨＣ、ＳＯＦ等の酸化作用が促進される。
In addition to the above raw materials, an alkali metal, alkaline earth metal or the like can be appropriately added to the exhaust gas purifying catalyst of the present invention in order to improve the catalyst performance. In addition, adsorbents such as zeolite, oxygen storage / release materials (hereinafter referred to as OSC materials) such as ceria and ceria-zirconia composite oxides, etc., are combined in an appropriate manner to provide more advanced functions. It can be used as an exhaust gas purification catalyst.
The amount of the OSC material varies depending on the type, the type of the carrier, etc., but in the case of a ceria-zirconia composite oxide, it is 0.01 to 10 g / L, particularly 0.1 to 10 g / L, per volume of the carrier. Things are preferable. Thus, when the present invention is used as an oxidation catalyst, the combined use with the OSC material promotes the oxidizing action of HC, SOF, etc. by the oxygen released from the OSC material.
本発明の排気ガス浄化用触媒は、担体表面に上記複合物が被覆された構造型触媒として用いることが望ましい。ここで担体の形状は特に限定されるものではなく、円柱状、円筒状、球状、ハニカム状、シート状などから選択可能である。構造型担体のサイズは特に制限されないが、円柱状、円筒状、球状のいずれかであれば、例えば数ミリから数センチの直径のものが使用できる。 The exhaust gas purifying catalyst of the present invention is desirably used as a structural catalyst in which the above composite is coated on the surface of the carrier. Here, the shape of the carrier is not particularly limited, and can be selected from a columnar shape, a cylindrical shape, a spherical shape, a honeycomb shape, a sheet shape, and the like. The size of the structure-type carrier is not particularly limited, and a structural carrier having a diameter of, for example, several millimeters to several centimeters can be used as long as it is in a columnar shape, a cylindrical shape, or a spherical shape.
本発明の排気ガス浄化用触媒は、熱的に安定であり、例えば金属触媒成分として貴金属を用いた場合、多くの貴金属がシンタリングを始める１０００℃を越える高温に長時間晒された状態であっても、貴金属成分のみならず、無機母材においても焼結、凝集による粗大粒子の発生が見られず、繊維形状を保つ事ができる。 The exhaust gas purifying catalyst of the present invention is thermally stable. For example, when noble metal is used as a metal catalyst component, many noble metals are exposed to a high temperature exceeding 1000 ° C. at which sintering begins for a long time. However, the generation of coarse particles due to sintering and aggregation is not observed not only in the noble metal component but also in the inorganic base material, and the fiber shape can be maintained.
プラチナ、ロジウム、パラジウムは１５００℃を越える融点を持つが、従来の排気ガス浄化用触媒のように微細化された状態では、通常の排気ガス雰囲気においてシンタリング（粒成長）を起こし、表面積を減少して触媒活性を低下させていた。これに対して、本発明における無機母材−金属触媒複合物は、このような苛酷な条件下でも、無機母材、金属触媒成分とも、それ以前の形状を保つだけでなく、ナノクラスのサイズを維持でき優れた耐久性を有する事は驚くべきことである。 Platinum, rhodium, and palladium have melting points in excess of 1500 ° C, but when they are miniaturized like conventional exhaust gas purifying catalysts, they cause sintering in the normal exhaust gas atmosphere, reducing the surface area. As a result, the catalytic activity was lowered. In contrast, the inorganic matrix-metal catalyst composite in the present invention not only maintains the previous shape of both the inorganic matrix and the metal catalyst component under such severe conditions, but also has a nano-class size. It is surprising that it can be maintained and has excellent durability.
２．排気ガス浄化用触媒の製造方法
本発明の排気ガス浄化用触媒は、金属触媒成分と無機母材とを水系媒体中で混合してスラリーを調製した後、該スラリーを、ウイスカー状無機母材上に担持される金属触媒が針状に存在するに十分な程度に、焼成することにより、直径が実質的に１００ｎｍ以下である繊維状の無機母材―金属触媒複合物を形成させることにより製造される。
2. Manufacturing method of exhaust gas purifying catalyst The exhaust gas purifying catalyst of the present invention is prepared by mixing a metal catalyst component and an inorganic base material in an aqueous medium to prepare a slurry, which is then placed on a whisker-like inorganic base material. It is manufactured by forming a fibrous inorganic base material-metal catalyst composite having a diameter of substantially 100 nm or less by firing to such an extent that the metal catalyst supported on the substrate is present in a needle shape. The
ここで、スラリーは、無機母材、金属触媒成分、水系媒体を所定の比率で混合して調製されるが、本発明においては、無機母材１００重量部に対して、金属触媒成分０．０１〜２５重量部とを混合することが好ましい。水系媒体はスラリー中で無機母材と金属触媒成分が均一に分散できる量を用いれば良い。この際、必要に応じてｐＨ調整のための酸、アルカリを、粘性の調整やスラリー分散性を向上するための界面活性剤、分散用樹脂等を配合する事ができる。また、スラリーの混合方法としては、ボールミルなどによる粉砕混合が適用可能であるが、他の粉砕、もしくは混合方法を適用しても良い。
なお、焼成条件は、ウイスカー状無機母材上に金属触媒成分が針状に存在して担持された繊維状の複合物が得られるのに十分な程度であればよく、特に限定されない。焼成温度は、３００〜１２００℃が好ましく、４００〜８００℃がより好ましい。加熱手段については、電気炉やガス炉等の公知の加熱手段によって行う事ができる。
Here, the slurry is prepared by mixing an inorganic base material, a metal catalyst component, and an aqueous medium in a predetermined ratio. In the present invention, the metal catalyst component 0.01 is added to 100 parts by weight of the inorganic base material. It is preferable to mix ˜25 parts by weight. What is necessary is just to use the quantity which can disperse | distribute an inorganic base material and a metal catalyst component uniformly in a slurry for an aqueous medium. At this time, an acid or an alkali for adjusting the pH, a surfactant for improving the viscosity or improving the slurry dispersibility, a dispersing resin, or the like can be blended as necessary. Further, as a mixing method of the slurry, pulverization and mixing by a ball mill or the like can be applied, but other pulverization or mixing methods may be applied.
The firing condition is not particularly limited as long as it is sufficient to obtain a fibrous composite in which a metal catalyst component is present in a needle shape on a whisker-like inorganic base material. The firing temperature is preferably 300 to 1200 ° C, more preferably 400 to 800 ° C. About a heating means, it can carry out by well-known heating means, such as an electric furnace and a gas furnace.
無機母材としてはＳｉＣナノファイバーであっても良い。ＳｉＣナノファイバーの製法は、その前駆体（ＰＣＳ）に金属触媒成分を混合し、これを紡糸してから、不融化し、焼成する。プレカーサー法において、不融化処理は、溶融紡糸したポリマー繊維中の分子同士を架橋し、その後の熱処理工程において、繊維が溶融せずに形状を保持する処理である。不融化の条件は特に限定されないが、放射線などにより酸素を含まない雰囲気下で処理すればＳｉＣ系繊維が得られ、空気または酸素雰囲気下で熱酸化することでＳｉ−Ｃ−Ｏ系繊維が得られる。 The inorganic base material may be SiC nanofiber. The manufacturing method of SiC nanofiber mixes a metal catalyst component with the precursor (PCS), spins it, infusibilizes, and fires. In the precursor method, the infusibilization treatment is a treatment in which molecules in the melt-spun polymer fiber are cross-linked, and the shape is maintained without melting the fiber in the subsequent heat treatment step. Conditions for infusibilization are not particularly limited, but SiC fiber can be obtained by treatment in an atmosphere not containing oxygen by radiation or the like, and Si-C-O fiber can be obtained by thermal oxidation in an air or oxygen atmosphere. It is done.
なお、本発明の構造型触媒は、上記のようにスラリーを構造型担体に塗工し加熱することによって得られるが、予めスラリーそのものを焼成することによって焼成触媒組成物を得た後、別途粉砕してから構造型担体に担持させて触媒を得ることもできる。 The structural catalyst of the present invention can be obtained by applying the slurry to the structural carrier and heating as described above, but after obtaining the calcined catalyst composition by calcining the slurry in advance, it is separately pulverized. Then, the catalyst can be obtained by supporting it on a structural support.
３．排気ガス浄化用一体構造型触媒
本発明の排気ガス浄化用一体構造型触媒は、排気ガスが流通可能な一体構造型担体表面に上記の無機母材―金属触媒複合物が被覆された触媒である。
3. Integrated structure type catalyst for exhaust gas purification The integrated structure type catalyst for exhaust gas purification of the present invention is a catalyst in which the above-mentioned inorganic base material-metal catalyst composite is coated on the surface of an integrated structure type carrier through which exhaust gas can flow. .
ここで、一体構造型担体は、特に限定されるものではなく、公知の一体構造型担体の中から選択可能である。このような一体構造型担体としては、フロースルー型担体や、ＤＰＦに用いられるウォールフロー型担体があり、これら担体の材質としては金属、セラミックスがある。この他にも、細い繊維状物を編んだシート状構造体、比較的太い繊維状物からなるフェルト様の不燃性構造体が使用できる。これら一体構造型担体は、金属触媒成分の担持量が大きく、また排ガスとの接触面積が大きいので他の構造型担体よりも処理能力が高い。
一体構造型担体の全体形状は任意であり、円柱型、四角柱型、六角柱型など適用する排気系の構造に応じて適宜選択できる。さらに開口部の孔数についても処理すべき排気ガスの種類、ガス流量、圧力損失あるいは除去効率などを考慮して適正な孔数が決められるが、通常、自動車用排気ガス浄化用途としては１平方インチ当たり１０〜１５００個程度である。
Here, the monolithic structure type carrier is not particularly limited, and can be selected from known monolithic structure type carriers. As such an integral structure type carrier, there are a flow-through type carrier and a wall flow type carrier used for a DPF, and materials of these carriers include metals and ceramics. In addition, a sheet-like structure knitted from a fine fibrous material, or a felt-like non-combustible structure made of a relatively thick fibrous material can be used. Since these monolithic structural carriers have a large amount of supported metal catalyst components and a large contact area with the exhaust gas, they have a higher processing capacity than other structural carriers.
The overall shape of the monolithic structure type carrier is arbitrary, and can be appropriately selected according to the structure of the exhaust system to be applied, such as a columnar, quadrangular, or hexagonal column. In addition, the number of holes in the opening can be determined in consideration of the type of exhaust gas to be processed, gas flow rate, pressure loss or removal efficiency, etc. About 10 to 1500 per inch.
このようなフロースルー型担体、ウォールフロー型担体のようなハニカム形状の担体では、その構造的特徴がセル密度であらわされるが、本発明においてはセル密度１．６〜２３２．５ｃｅｌ／ｃｍ ２ （１０〜１５００ｃｅｌ／ｉｎｃｈ２ ）、より好ましくは５４．３〜１３９．５ｃｅｌ／ｃｍ ２ （３５０〜９００ｃｅｌ／ｉｎｃｈ２ ）の担体を用いる事ができる。セル密度が１．６ｃｅｌ／ｃｍ ２ （１０ｃｅｌ／ｉｎｃｈ２ ）以上であれば、内燃機関の排気ガスの圧力損失を生じることなく内燃機関の性能を損う事がない。また、セル密度が２３２．５ｃｅｌ／ｃｍ ２ （１５００ｃｅｌ／ｉｎｃｈ２ ）以下であれば、排気ガスと触媒の接触面積を確保する事ができ、充分な排気ガスの浄化機能が得られる。
なお、本発明ではこのようなフロースルー型担体、ウォールフロー型担体などの一体構造型担体上に触媒組成物が被覆されたものを、以下、一体構造型触媒と言うことがある。
In such a honeycomb-shaped carrier such as a flow-through carrier and a wall-flow carrier, the structural feature is expressed by the cell density. In the present invention, the cell density is 1.6 to 232.5 cel / cm 2 ( 10 to 1500 cel / inch 2 ) , more preferably 54.3 to 139.5 cel / cm 2 ( 350 to 900 cel / inch 2 ) . If the cell density is 1.6 cel / cm 2 ( 10 cel / inch 2 ) or more, the pressure loss of the exhaust gas of the internal combustion engine does not occur and the performance of the internal combustion engine is not impaired. If the cell density is 232.5 cel / cm 2 ( 1500 cel / inch 2 ) or less, the contact area between the exhaust gas and the catalyst can be secured, and a sufficient exhaust gas purification function can be obtained.
In the present invention, a catalyst in which a catalyst composition is coated on an integral structure type carrier such as a flow-through type carrier or a wall flow type carrier is hereinafter sometimes referred to as an integral structure type catalyst.
また、本発明の排気ガス浄化用一体構造型触媒は、一体構造型担体がセル密度１．６〜２３２．５ｃｅｌ／ｃｍ ２ （１０〜１５００ｃｅｌ／ｉｎｃｈ２ ）であれば、複合物の被覆量は１０〜４００ｇ／Ｌ、特に３０〜３００ｇ／Ｌである事が好ましい。被覆量が４００ｇ／Ｌを超えると、自動車の排気ガス流路に配置すると排気ガスの圧損を生じてしまい、１０ｇ／Ｌ未満では、排気ガスの浄化性能が不十分となる。
また、金属触媒成分が白金族金属の場合、その担持量は、前記一体構造型担体に対して０．０１〜１０ｇ／Ｌ、特に０．１〜１０ｇ／Ｌである事が好ましい。触媒の担持量が１０ｇ／Ｌを超えると、生産コストが上昇してしまい、０．０１ｇ／Ｌ未満では、排気ガスの浄化性能が低下する。
In addition, the integral structure type catalyst for exhaust gas purification of the present invention has a composite covering amount of the integral structure type carrier if the cell density is 1.6 to 232.5 cel / cm 2 ( 10 to 1500 cel / inch 2 ). It is preferable that it is 10-400 g / L, especially 30-300 g / L. When the coating amount exceeds 400 g / L, the pressure loss of the exhaust gas occurs when it is disposed in the exhaust gas flow path of the automobile, and when it is less than 10 g / L, the exhaust gas purification performance becomes insufficient.
When the metal catalyst component is a platinum group metal, the supported amount is preferably 0.01 to 10 g / L, particularly 0.1 to 10 g / L with respect to the monolithic structure type carrier. If the supported amount of the catalyst exceeds 10 g / L, the production cost increases, and if it is less than 0.01 g / L, the exhaust gas purification performance decreases.
４．排気ガス浄化用一体構造型触媒の製造
本発明の排気ガス浄化用一体構造型触媒は、前記の方法で金属触媒成分またはその前駆体と、前記無機母材またはその前駆体とを水系媒体と共に混合してスラリー状混合物にしてから、一体構造型担体へスラリー状混合物を塗工して、乾燥、焼成する事により製造される。
4). Manufacture of monolithic structure type catalyst for exhaust gas purification The monolithic structure type catalyst for exhaust gas purification of the present invention mixes a metal catalyst component or a precursor thereof and the inorganic base material or a precursor thereof together with an aqueous medium by the above method. Then, the slurry mixture is made, and then the slurry mixture is applied to the monolithic structure type carrier, dried and fired.
すなわち、まず、無機物質、金属触媒成分、水系媒体を所定の比率で混合してスラリー状混合物を得る。本発明においては、無機母材１００重量部に対して、金属触媒成分を０．０１〜２５重量部混合することが好ましい。水系媒体は、スラリー中で無機母材と金属触媒成分が均一に分散できる量を用いれば良い。
この際、必要に応じてｐＨ調整のための酸、アルカリを、粘性の調整やスラリー分散性向上のための界面活性剤、分散用樹脂等を配合する事ができる。スラリーの混合方法としては、ボールミルなどによる粉砕混合が適用可能であるが、他の粉砕、もしくは混合方法を適用しても良い。
That is, first, an inorganic substance, a metal catalyst component, and an aqueous medium are mixed at a predetermined ratio to obtain a slurry mixture. In the present invention, it is preferable to mix 0.01 to 25 parts by weight of the metal catalyst component with respect to 100 parts by weight of the inorganic base material. What is necessary is just to use the quantity which can disperse | distribute an inorganic base material and a metal catalyst component uniformly in a slurry for an aqueous medium.
At this time, if necessary, an acid or alkali for adjusting pH, a surfactant for adjusting viscosity or improving slurry dispersibility, a dispersing resin, or the like can be blended. As a mixing method of the slurry, pulverization and mixing by a ball mill or the like can be applied, but other pulverization or mixing methods may be applied.
次に、一体構造型担体へスラリー状混合物を塗工する。塗工方法は、特に限定されないが、ウオッシュコート法が好ましい。塗工した後、乾燥、焼成を行う事により触媒組成物が担持された一体構造型触媒が得られる。なお、乾燥温度は、１００〜３００℃が好ましく、１００〜２００℃がより好ましい。また、焼成温度は、３００〜１２００℃が好ましく、４００〜８００℃、特に４００〜６００℃が好ましい。加熱手段については、電気炉やガス炉等の公知の加熱手段によって行う事ができる。 Next, the slurry-like mixture is applied to the monolithic structure type carrier. A coating method is not particularly limited, but a wash coat method is preferable. After coating, drying and firing are performed to obtain a monolithic structure type catalyst carrying the catalyst composition. In addition, 100-300 degreeC is preferable and, as for drying temperature, 100-200 degreeC is more preferable. Moreover, 300-1200 degreeC is preferable and baking temperature is 400-800 degreeC, Especially 400-600 degreeC is preferable. About a heating means, it can carry out by well-known heating means, such as an electric furnace and a gas furnace.
前記特許文献１には、一体構造型担体（基材）上に無機酸化物からなる第１層を形成し、次に、該第１層上に無機繊維材からなる第２層を網目状に形成するとともに、少なくとも該第１層に触媒成分を担持することによる排気ガス浄化用触媒の製造方法が開示されている。ところが、この方法では、第２層を網目状にするために、アルミナ繊維であれば直径が１００〜１０００ｎｍと比較的太い無機繊維を用いるため、予め一体構造型担体上に無機酸化物からなる第１層を形成しておかねばならない。ところが、本発明においては、比較的細い無機母材（前駆体）を用い、この上に金属触媒成分が針状に担持された直径が１００ｎｍ以下の複合物とするもので、発明として構成が全く異なるものである。 In Patent Document 1, a first layer made of an inorganic oxide is formed on a monolithic structure type carrier (base material), and then a second layer made of an inorganic fiber material is formed on the first layer in a mesh shape. A method for producing an exhaust gas purifying catalyst by forming and at least supporting a catalyst component on the first layer is disclosed. However, in this method, in order to make the second layer into a network, inorganic fibers having a diameter of 100 to 1000 nm are used in the case of alumina fibers. One layer must be formed. However, in the present invention, a comparatively thin inorganic base material (precursor) is used, and a metal catalyst component is supported in a needle shape on this to form a composite having a diameter of 100 nm or less. Is different.
本発明では、上記の方法で無機母材−金属触媒複合物を含む被覆層を形成した後、その上、またはその下にＯＳＣ材、すなわちゼオライト等の吸着剤、セリアやセリア−ジルコニア複合酸化物などの酸素吸蔵・放出材をコートして２層化することもできる。これにより、ＯＳＣ材から放出される酸素によりＨＣ、ＳＯＦ等の酸化作用が促進され、より高度な機能を有する排気ガス浄化用触媒とする事が可能である。
なお、これら吸着剤、酸素吸蔵・放出材は、無機母材−金属触媒複合物を含む被覆層に配合されていても良い。
In the present invention, after the coating layer containing the inorganic base material-metal catalyst composite is formed by the above method, an OSC material, that is, an adsorbent such as zeolite, ceria or ceria-zirconia composite oxide is formed thereon or under the coating layer. It is also possible to coat with an oxygen storage / release material such as 2 layers. Thereby, the oxidation action of HC, SOF, etc. is promoted by oxygen released from the OSC material, and it is possible to obtain an exhaust gas purification catalyst having a higher function.
These adsorbents and oxygen storage / release materials may be blended in a coating layer containing an inorganic base material-metal catalyst composite.
以下、本発明の実施例、比較例を示すが、本発明は、この実施例に限定して解釈されるものではない。 Examples of the present invention and comparative examples are shown below, but the present invention is not construed as being limited to these examples.
（実施例１）
＜焼成触媒組成物の製造＞
無機母材として繊維状ベーマイト（Ｌａ添加量：５重量％）、金属触媒成分としてプラチナ硝酸塩とロジウム硝酸塩を用い、これに水系媒体を加えてからボールミルを用いて混合しスラリーを得た。なお、各成分の使用量は、原料無機母材に対する金属触媒成分合計量が０．５重量％となり、水系媒体はスラリー中で無機母材と金属触媒成分が均一に分散できる量とした。このスラリーを乾燥し、５００℃で１時間焼成し、焼成触媒組成物を得た。
得られた焼成触媒組成物を１１００℃のオーブン中で１２時間放置し、その後の焼成触媒組成物の外観を走査型透過電子顕微鏡で観察し、加熱耐久性を評価した。走査型透過電子顕微鏡による写真（倍率：×１００ｋ）を図１に示す。図３は原料として用いた無機母材の電子顕微鏡写真である。この実施例１の触媒組成、形状、サイズは表１のとおりであった。なお、原料及び加熱耐久性試験後の無機母材、および加熱耐久性試験後の金属触媒成分の直径、および長さは、電子顕微鏡下において目視で測定した平均値である。
Example 1
<Production of calcined catalyst composition>
Fibrous boehmite (La addition amount: 5% by weight) was used as the inorganic base material, platinum nitrate and rhodium nitrate were used as the metal catalyst components, and an aqueous medium was added thereto, followed by mixing using a ball mill to obtain a slurry. The amount of each component used was such that the total amount of the metal catalyst component relative to the raw material inorganic base material was 0.5% by weight, and the aqueous medium was such an amount that the inorganic base material and the metal catalyst component could be uniformly dispersed in the slurry. This slurry was dried and calcined at 500 ° C. for 1 hour to obtain a calcined catalyst composition.
The obtained calcined catalyst composition was left in an oven at 1100 ° C. for 12 hours, and the appearance of the calcined catalyst composition thereafter was observed with a scanning transmission electron microscope to evaluate the heat durability. A photograph taken with a scanning transmission electron microscope (magnification: x100k) is shown in FIG. FIG. 3 is an electron micrograph of an inorganic base material used as a raw material. The catalyst composition, shape, and size of Example 1 were as shown in Table 1. The diameters and lengths of the raw materials and the inorganic base material after the heat durability test and the metal catalyst component after the heat durability test are average values measured visually under an electron microscope.
（比較例１）
＜焼成触媒組成物の製造＞
無機母材として粒状γ−アルミナ（Ｌａ添加量：５重量％）を用いた以外は実施例１と同様にして、焼成触媒組成物を製造した。まず、金属触媒成分として所定量のプラチナ硝酸塩とロジウム硝酸塩を採り、これに無機母材と水系媒体を加えて、ボールミルで混合しスラリーを得た。なお、各成分の使用量は、原料無機母材に対する金属触媒成分合計量が０．５重量％となり、水系媒体はスラリー中で無機母材と金属触媒成分が均一に分散できる量とした。このスラリーを乾燥し、５００℃で１時間焼成し、焼成触媒組成物を得た。
次に、得られた焼成触媒組成物を１１００℃のオーブン中で、１２時間放置し、加熱耐久性を評価した。加熱耐久性試験後の焼成触媒組成物の走査型透過電子顕微鏡による写真（倍率：×１００ｋ）を図２に示す。その触媒組成、形状、サイズは表１のとおりであった。なお、原料無機母材のサイズは、電子顕微鏡下において目視で測定した平均値である。
(Comparative Example 1)
<Production of calcined catalyst composition>
A calcined catalyst composition was produced in the same manner as in Example 1 except that granular γ-alumina (La addition amount: 5% by weight) was used as the inorganic base material. First, a predetermined amount of platinum nitrate and rhodium nitrate were taken as metal catalyst components, an inorganic base material and an aqueous medium were added thereto, and mixed with a ball mill to obtain a slurry. The amount of each component used was such that the total amount of the metal catalyst component relative to the raw material inorganic base material was 0.5% by weight, and the aqueous medium was such an amount that the inorganic base material and the metal catalyst component could be uniformly dispersed in the slurry. This slurry was dried and calcined at 500 ° C. for 1 hour to obtain a calcined catalyst composition.
Next, the obtained calcined catalyst composition was left in an oven at 1100 ° C. for 12 hours to evaluate the heat durability. FIG. 2 shows a photograph (magnification: × 100 k) of the calcined catalyst composition after the heat durability test, taken with a scanning transmission electron microscope. The catalyst composition, shape, and size were as shown in Table 1. In addition, the size of the raw material inorganic base material is an average value measured visually under an electron microscope.
表１から、本発明の触媒組成物は、長時間高温下に晒されても金属触媒が粒成長せず無機母材、金属触媒成分とも加熱耐久性試験前の形状を保ちうる事がわかる。これに対して、比較例の触媒組成物は、長時間高温下に晒されると金属触媒が粒成長してしまう事がわかる。 From Table 1, it can be seen that the catalyst composition of the present invention does not grow as a metal catalyst even when exposed to a high temperature for a long time, and the inorganic base material and the metal catalyst component can maintain the shape before the heat durability test. On the other hand, it can be seen that when the catalyst composition of the comparative example is exposed to a high temperature for a long time, the metal catalyst grows.
＜一体構造型触媒の製造＞
次に、前記の金属触媒成分と無機母材を含むスラリーを用いて、ウォッシュコート法により下記一体構造型担体に被覆し、一体構造型触媒を製造した。被覆量は、金属触媒成分の量が、最終的に一体構造型担体に対して１ｇ／Ｌとなり、無機母材−金属触媒複合物の量が、一体構造型担体に対して１００ｇ／Ｌとなる量とした。
［一体構造型担体］
・一体構造型担体の種類：フロースルー型担体
・一体構造型担体の容量：９００ｃｃ
・一体構造型担体の材質：コージェライト
・一体構造型担体のセル密度：６２ｃｅｌ／ｃｍ ２ （４００ｃｅｌ／ｉｎｃｈ２ ）
<Production of the monolithic structure type catalysts>
Next, using the slurry containing the metal catalyst component and the inorganic base material, the following monolithic structure type carrier was coated by a wash coat method to produce an monolithic structure type catalyst. With respect to the coating amount, the amount of the metal catalyst component is finally 1 g / L with respect to the monolithic structure type carrier, and the amount of the inorganic matrix-metal catalyst composite is 100 g / L with respect to the monolithic structure type carrier. The amount.
[Integrated structure type carrier]
・ Type of monolithic carrier: Flow-through carrier ・ Capacity of monolithic carrier: 900cc
-Material of monolithic structure type carrier: cordierite-Cell density of monolithic structure type carrier: 62 cel / cm 2 ( 400 cel / inch 2 )
＜触媒性能評価＞
実施例１、および比較例１で得られた各一体構造型触媒について、以下の条件で排気ガス中のＨＣ、ＮＯｘ、ＣＯの濃度を測定し、触媒性能を評価した。
・測定モード：ＦＴＰモード
・排気ガスの測定機器：ＨＯＲＩＢＡ社製 ＭＥＸＡ９０００
・評価エンジン：１．８Ｌ ガソリンエンジン
上記条件における排気ガス中のＨＣ、ＮＯｘ、ＣＯの濃度変化を対比し、グラフに表すと図４のようになった。なお、ＨＣについてはＦＴＰモード試験の基準に従い測定した、ｎｏｎ−ｍｅｔｈａｎｅ ｈｙｄｒｏｃａｒｂｏｎ（以下、ＮＭＨＣという）の結果である。グラフは、比較例２におけるＮＭＨＣ、ＮＯｘ、ＣＯの排出量（重量）に対する、実施例２の排出量の割合を示している。
グラフから、実施例１の触媒は、比較例１の触媒に対して、浄化能力がＮＭＨＣについては２１％、ＮＯｘについては２７％優れていることが分かる。
<Catalyst performance evaluation>
For each monolithic structure type catalyst obtained in Example 1 and Comparative Example 1, the concentration of HC, NOx and CO in the exhaust gas was measured under the following conditions to evaluate the catalyst performance.
・ Measurement mode: FTP mode ・ Exhaust gas measurement device: MEXA9000 manufactured by HORIBA
Evaluation engine: 1.8L gasoline engine FIG. 4 shows a graph comparing the concentration changes of HC, NOx, and CO in the exhaust gas under the above conditions. In addition, about HC, it is the result of non-methane hydrocarbon (henceforth NMHC) measured according to the standard of FTP mode test. The graph shows the ratio of the emission amount of Example 2 to the emission amount (weight) of NMHC, NOx, and CO in Comparative Example 2.
From the graph, it can be seen that the catalyst of Example 1 is 21% better for NMHC and 27% better for NOx than the catalyst of Comparative Example 1.
Claims (12)
金属触媒成分（Ａ）が、無機母材（Ｂ）の少なくとも表層部中で、長さが１００ｎｍ以上の針状形態をなして存在し、かつ金属触媒成分（Ａ）、無機母材（Ｂ）の直径がいずれも実質的に１００ｎｍ以下であり、かつアスペクト比が２以上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 containing a fibrous inorganic base material-metal catalyst composite in which a metal catalyst component (A) is supported on a whisker-like inorganic base material (B),
The metal catalyst component (A) is present in a needle-like form having a length of 100 nm or more in at least the surface layer portion of the inorganic base material (B), and the metal catalyst component (A) and the inorganic base material (B) The exhaust gas purifying catalyst is characterized in that the diameter of each is substantially 100 nm or less and the aspect ratio is 2 or more.
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| KR101402210B1 (en) * | 2010-12-30 | 2014-06-27 | 주식회사 엘지화학 | Platinium-palladium composite catalyst having a new structure and method for manufacturing the same |
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| MX2017009912A (en) * | 2015-01-29 | 2018-06-20 | Basf Corp | Platinum group metal (pgm) catalysts for automotive emissions treatment. |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH07204517A (en) * | 1994-01-13 | 1995-08-08 | Matsushita Electric Ind Co Ltd | Ceramic sheet having catalytic function and production thereof |
| JP2000225349A (en) * | 1999-02-02 | 2000-08-15 | Otsuka Chem Co Ltd | Filter |
| JP2004074116A (en) * | 2002-08-22 | 2004-03-11 | Denso Corp | Catalyst body |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH07204517A (en) * | 1994-01-13 | 1995-08-08 | Matsushita Electric Ind Co Ltd | Ceramic sheet having catalytic function and production thereof |
| JP2000225349A (en) * | 1999-02-02 | 2000-08-15 | Otsuka Chem Co Ltd | Filter |
| JP2004074116A (en) * | 2002-08-22 | 2004-03-11 | Denso Corp | Catalyst body |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR101402210B1 (en) * | 2010-12-30 | 2014-06-27 | 주식회사 엘지화학 | Platinium-palladium composite catalyst having a new structure and method for manufacturing the same |
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