JP3760717B2 - Low temperature harmful gas purification catalyst - Google Patents
Low temperature harmful gas purification catalyst Download PDFInfo
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- JP3760717B2 JP3760717B2 JP2000054522A JP2000054522A JP3760717B2 JP 3760717 B2 JP3760717 B2 JP 3760717B2 JP 2000054522 A JP2000054522 A JP 2000054522A JP 2000054522 A JP2000054522 A JP 2000054522A JP 3760717 B2 JP3760717 B2 JP 3760717B2
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- metal
- temperature
- gas purification
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Images
Description
【０００１】
【発明の属する技術分野】
本発明は低温有害ガス浄化触媒に関するものであり、より詳しくは、空気中のアルデヒド類や排ガス中のＮＯｘ、ＣＯ等を低温であっても浄化することが可能な低温有害ガス浄化触媒に関するものである。
【０００２】
【従来の技術】
近年、人間を取り巻く環境に存在し得る成分であって人体に影響を及ぼす可能性のある有害ガスの存在が問題視されるようになってきており、例えば建築資材等から空気中に発散するアルデヒド類や、排ガス中の有害成分であるＮＯｘやＣＯをより低温で確実に浄化することが可能な技術の開発が望まれている。
【０００３】
このような背景の下で、有害ガスを浄化するための各種の触媒が開発されており、例えば特開平８−２４６５３号公報には、γ−アルミナ、チタニア、ジルコニア等の多孔質無機酸化物に白金属金属を含浸法、沈澱法、ゾル−ゲル法等によって担持せしめた第１の触媒と多孔質無機酸化物に銀化合物を担持せしめた第２の触媒とを備えた排ガス浄化触媒が記載されている。しかしながら、特開平８−２４６５３号公報に記載の排ガス浄化触媒であっても、１５０〜６５０℃で排ガス中の窒素酸化物を還元できるにとどまり、排ガス中の有害成分であるＮＯｘやＣＯをエンジン始動時（コールドスタート時）のように排ガス温度が低い時からより確実に浄化するためには十分なものではなかった。
【０００４】
また、特開平８−５２３５１号公報には、チタニアを主成分とする担体に主触媒活性金属成分として白金族金属、助触媒成分として酸化ホウ素を含浸法で担持せしめた揮発性有機塩素化合物分解用触媒が開示されている。しかしながら、特開平８−５２３５１号公報に記載の触媒は４００〜５００℃で揮発性有機塩素化合物を分解するものであり、空気中や排ガス中の有害成分を低温で浄化するためには十分なものではなかった。
【０００５】
一方、チタニアに白金を担持せしめた触媒は、ＮＯｘの分解やＣＯの酸化反応に触媒活性を示し、その触媒活性が光の照射により促進されるいわゆる光触媒としての機能が知られている。しかしながら、かかる光触媒に対しては光を照射しないと十分な触媒活性が得られないため、空気中や排ガス中の有害成分の浄化のように必ずしも光を照射できる状態にあるとは限らない場合には適用が困難であった。
【０００６】
また、本発明者らによる国際公開第ＷＯ９９／１０１６７号公報には、活性炭等の多孔質炭素や多孔質シリカ等の多孔質金属酸化物に貴金属金属等を超臨界流体を用いて担持せしめた金属担持物が記載されている。しかしながら、この国際公開第ＷＯ９９／１０１６７号公報においては、空気中のアルデヒド類や排ガス中のＮＯｘ、ＣＯ等を低温で浄化するための低温有害ガス浄化触媒としてかかる金属担持物を用いることについては何ら開示も示唆もなされていなかった。
【０００７】
【発明が解決しようとする課題】
本発明は、上記従来技術の有する課題に鑑みてなされたものであり、空気中のアルデヒド類や排ガス中のＮＯｘ、ＣＯ等といった有害ガスを常温あるいは従来よりも低温であってもより確実に浄化することが可能な低温有害ガス浄化触媒を提供することを目的とする。
【０００８】
【課題を解決するための手段】
本発明者らは、上記目的を達成すべく鋭意研究を重ねた結果、金属酸化物及び炭素質材料からなる群から選択される少なくとも一種の物質とそれに担持される金属微粒子とからなる触媒において金属微粒子を平均粒径５ｎｍ以下という超微粒子とすることによって、驚くべきことに常温であっても空気中のアルデヒド類を十分に浄化することが可能となり、また２００℃以下という低温であっても排ガス中のＮＯｘ及びＣＯを十分に浄化することが可能となることを見出し、本発明を完成するに至った。
【０００９】
すなわち、本発明は、金属酸化物及び炭素質材料からなる群から選択される少なくとも一種の物質と、５ｎｍ以下の平均粒径を有する金属超微粒子とからなることを特徴とする低温有害ガス浄化触媒である。
【００１０】
なお、上記本発明の触媒により常温であっても空気中のアルデヒド類が十分に浄化され、また２００℃以下という低温であっても排ガス中のＮＯｘ及びＣＯが十分に浄化される理由は定かではないが、金属が極めて微細な粒子として担持されていることからその触媒活性が特異的に増長され、更にかかる金属の触媒活性と金属酸化物又は炭素質材料の触媒活性との相乗効果によって達成されていると本発明者らは考えている。
【００１１】
また、本発明にかかる金属酸化物としては、Ti,Al,Si,Ce,Zr,Fe,Mn,Ni,Zn,Cuからなる群から選択される少なくとも一種の金属の単独酸化物又は複合酸化物からなる１０００μｍ以下の平均粒径を有する粒子が好ましく、
炭素質材料としては、活性炭、黒鉛、活性チャー、コークス、ハードカーボン及びソフトカーボンからなる群から選択される少なくとも一種の炭素質材料からなる１０００μｍ以下の平均粒径を有する粒子が好ましく、
金属超微粒子は、Pt,Pd,Rh,Ru,Ir,Os,Au,Ag,Cu,Fe,Niからなる群から選択される少なくとも一種の金属の超微粒子である。このような金属超微粒子と金属酸化物又は炭素質材料との組み合わせによれば、有害ガスの浄化がより効率良く進行する傾向にある。
【００１２】
また、本発明の触媒は、１．０１３×１０６Ｐａ（１０ａｔｍ）以上の圧力下でかつその圧力下における沸点以上の温度に維持された高温高圧流体を用いて前記物質に前記金属超微粒子を担持せしめたものである。このような高温高圧流体を用いることによって金属が５ｎｍ以下（好ましくは２ｎｍ以下）という超微細な粒子サイズでかつ均一な圧力下で均一に分散して担持されるため、触媒活性がより向上する傾向にある。
【００１３】
更に、本発明の触媒は、超臨界流体を用いて前記物質に前記金属超微粒子を担持せしめたものであることがより好ましい。このように超臨界流体を用いることによって金属が５ｎｍ以下（好ましくは２ｎｍ以下）という超微細な粒子サイズでかつ金属単体として均一に分散して担持されるため、触媒活性が更に向上する傾向にある。
【００１４】
また、本発明の触媒においては、前記金属酸化物が光増感作用を有する金属酸化物でありかつ前記金属超微粒子が２ｎｍ以下の平均粒径を有する貴金属超微粒子であることが好ましい。このように光の照射によって触媒活性が促進されるいわゆる光増感作用を有する金属酸化物に２ｎｍ以下の平均粒径を有する貴金属超微粒子を担持せしめることにより、驚くべきことに光を照射しない状態であっても有害ガスの触媒反応に対して高い触媒活性を示すようになることを本発明者らが見出したものである。かかる知見は従前のいわゆる光触媒に関する当業者の常識を覆すものであり、光の照射なしで光触媒の触媒活性を増長させる手法として極めて有用な手法である。
【００１５】
更に、本発明の触媒においては、前記金属酸化物が酸化チタンでありかつ前記金属超微粒子が２ｎｍ以下の平均粒径を有する白金超微粒子であることが特に好ましい。このような組み合わせとすることによって、常温でかつ光を照射しない状態であっても空気中のアルデヒド類の分解反応に対して非常に高い触媒活性を示す「常温空気浄化用触媒」、あるいは、２００℃以下という低温でかつ光を照射しない状態であっても排ガス中のＮＯｘの分解反応及びＣＯの酸化反応に対して高い触媒活性を示す「低温排ガス浄化用触媒」が得られる傾向にある。
【００１６】
【発明の実施の形態】
以下、本発明の好適な実施形態について詳細に説明する。
【００１７】
本発明の低温有害ガス浄化触媒は、金属酸化物及び炭素質材料からなる群から選択される少なくとも一種の物質と、５ｎｍ以下の平均粒径を有する金属超微粒子とからなることを特徴とするものである。
【００１８】
すなわち、本発明の触媒は、金属酸化物及び炭素質材料からなる群から選択される少なくとも一種の物質と５ｎｍ以下の平均粒径を有する金属超微粒子とが共存したものである。その共存の形態は、上記物質を担体としてその担体に金属超微粒子を担持せしめたものでも、両者が混合したもの等でもよいが、前者の方が触媒活性がより高くなる傾向にあるため好ましい。また、上記物質が粒子の形態であると、触媒活性がより高くなる傾向にあるため好ましい。
【００１９】
このような金属酸化物としては、貴金族元素（Pt, Pd, Rh, Ru, Au等）、卑金属元素（Y, La, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ca, Mg, Al, K, Ti, Cr, Mn, Fe, Co, Ni, Cu, Ga, Rb, Sr, Zr, Nb, Mo, In, Sn, Cs, Ba, Ta, W等）、メタロイド元素（Si, Ge, As, Sb等）の酸化物が挙げられ、中でもTi,Al,Si,Ce,Zr,Fe,Mn,Ni,Zn,Cuからなる群から選択される少なくとも一種の金属の単独酸化物又は複合酸化物が好ましく、酸化チタン、アルミナ、酸化ケイ素、酸化セリウム、ゼオライト、ジルコニア、酸化鉄、酸化マンガン、酸化ニッケル、酸化亜鉛、酸化銅がより好ましい。なお、本発明にかかる金属酸化物は、ゼオライト、酸化チタン−ジルコニア、酸化セリウム−ジルコニアのように複数の金属元素を含有していてもよく、更に非金属元素を含んでいてもよい。また、ここでは「金属」の範疇に「半金属」も含めることとする。
【００２０】
このような金属酸化物を使用することにより、その物質自体も触媒として作用し、特に後述する金属超微粒子との相乗効果によって低温における有害ガスの浄化が十分に達成される。
【００２１】
本発明にかかる金属酸化物は、好ましくは１０００μｍ以下、より好ましくは１００μｍ〜１０ｎｍ、特に好ましくは１０μｍ〜１０ｎｍ、の平均粒径を有する粒子である。平均粒径が１０００μｍを超えると粒子の表面積が低下し、十分な触媒活性が得られない傾向にある。また、金属酸化物の比表面積は１〜１０００ｍ2／ｇ程度であることが好ましく、平均粒径が比較的大きい場合は多孔質粒子であることが好ましい。
【００２２】
また、炭素質材料としては、活性炭、黒鉛、活性チャー、コークス、ハードカーボン（難黒鉛化炭素）、ソフトカーボン（易黒鉛化炭素）が好ましい。このような炭素質材料を使用した場合も、その物質自体が触媒として作用し、特に後述する金属超微粒子との相乗効果によって低温における有害ガスの浄化が十分に達成される。
【００２３】
本発明にかかる炭素質材料は、好ましくは１０００μｍ以下、より好ましくは１００μｍ〜１０ｎｍ、特に好ましくは１０μｍ〜１０ｎｍ、の平均粒径を有する粒子である。平均粒径が１０００μｍを超えると粒子の表面積が低下し、十分な触媒活性が得られない傾向にある。また、炭素質材料の比表面積は１〜４０００ｍ2／ｇ程度であることが好ましく、多孔質粒子であることが好ましい。
【００２４】
上記本発明にかかる物質の形状は特に制限はなく、粉末状、ペレット状、モノリス状、板状、繊維状等の形状を使用条件に応じて選択することができる。
【００２５】
本発明の触媒は、上記物質に金属超微粒子を共存せしめたものである。このような金属としては、、Pt,Pd,Rh,Ru,Ir,Os,Au,Ag,Cu,Mn,Fe,Niが挙げられ、中でも貴金属元素（Pt,Pd,Rh,Ru,Ir,Os,Au,Ag）が好ましく、白金族元素（Pt,Pd,Rh,Ru,Ir,Os）がより好ましい。このような金属の超微粒子を前記物質と共存させて使用することにより、金属超微粒子の触媒作用と前記物質の触媒作用との相乗効果によって低温における有害ガスの浄化が十分に達成される。
【００２６】
本発明にかかる金属超微粒子は平均粒径が５ｎｍ以下であることが必要であり、より好ましくは２ｎｍ以下、特に好ましくは１ｎｍ以下の平均粒径を有する超微粒子である。このように本発明の触媒においては、金属酸化物又は炭素質材料に担持される金属微粒子を平均粒径５ｎｍ以下という超微粒子とすることによって、驚くべきことに常温であっても空気中のアルデヒド類を十分に浄化することが可能となり、また２００℃以下という低温であっても排ガス中のＮＯｘ及びＣＯを十分に浄化することが可能となる。
【００２７】
なお、本発明にかかる金属超微粒子は、金属酸化物等の金属化合物を一部に含有していてもよいが、より触媒活性が強まることから金属単体であることが好ましい。上記本発明の触媒により常温であっても空気中のアルデヒド類が十分に浄化され、また２００℃以下という低温であっても排ガス中のＮＯｘ及びＣＯが十分に浄化される理由は定かではないが、金属が極めて微細な粒子として担持されていることからその触媒活性が特異的に増長され、更にかかる金属の触媒活性と金属酸化物又は炭素質材料の触媒活性との相乗効果によって達成されていると本発明者らは考えている。
【００２８】
本発明の触媒中の金属超微粒子の含有率は、触媒の全重量を基準にして０．０１〜２０重量％であることが好ましく、０．０５〜５重量％であることがより好ましく、０．２〜２重量％であることが特に好ましい。金属超微粒子の含有率が０．０１重量％未満では、金属超微粒子による触媒作用が十分に得られない傾向にある。
【００２９】
また、本発明の触媒においては、前記金属酸化物が光増感作用を有する金属酸化物でありかつ前記金属超微粒子が２ｎｍ以下の平均粒径を有する貴金属超微粒子であることが好ましい。このような光増感作用を有する金属酸化物としては、酸化チタン、酸化ニッケル、酸化亜鉛、酸化銅、酸化鉄、酸化セリウム、酸化ニオブ、酸化タングステンが挙げられ、酸化チタンが特に好ましい。このように光の照射によって触媒活性が促進されるいわゆる光増感作用を有する金属酸化物に２ｎｍ以下の平均粒径を有する貴金属超微粒子を担持せしめることにより、驚くべきことに光を照射しない状態であっても有害ガスの触媒反応に対して高い触媒活性（*1）を示すようになることを本発明者らが見出したものである。かかる知見は従前のいわゆる光触媒に関する当業者の常識を覆すものであり、光の照射なしで光触媒の触媒活性を増長させる手法として極めて有用な手法である。なお、ここでいう高い触媒活性（*1）とは、例えば反応速度定数を触媒活性の指標とした場合に、以下の関係：
｛（光照射しない時の反応速度定数）／（光照射した時の反応速度定数）｝×100≧５０
を満たすような場合をいう。
【００３０】
更に、本発明の触媒においては、前記金属酸化物が酸化チタンでありかつ前記金属超微粒子が２ｎｍ以下の平均粒径を有する白金超微粒子であることが特に好ましい。このような組み合わせとすることによって、常温（好ましくは−２０〜８０℃）でかつ光を照射しない状態であっても空気中のアルデヒド類の分解反応に対して非常に高い触媒活性を示す「常温空気浄化用触媒」、あるいは、２００℃以下という低温でかつ光を照射しない状態であっても排ガス中のＮＯｘの分解反応及びＣＯの酸化反応に対して高い触媒活性を示す「低温排ガス浄化用触媒」が得られる傾向にある。
【００３１】
上記物質に金属超微粒子を共存せしめる方法としては、以下に説明するいわゆる高温高圧法かいわゆる超臨界法が特に好ましい。
【００３２】
すなわち、高温高圧法とは、１．０１３×１０6Ｐａ（１０ａｔｍ）以上、より好ましくは１．５２０×１０6Ｐａ（１５ａｔｍ）以上、の圧力下でかつその圧力下における沸点以上の温度に維持された高温高圧流体を用いて前記物質に前記金属超微粒子を担持せしめる方法である。より具体的には、金属及び／又は金属前駆体と溶媒とを含む溶液をその溶媒が上記の高温高圧流体になる状態で担体に接触させることにより担体表面に金属及び／又は金属前駆体を担持させる方法であり、その後に必要に応じて後述する焼成処理及び／又は還元処理を施すことによって本発明の触媒が得られる。このような高温高圧流体は、液体に近い溶解能力と、気体に近い拡散性及び粘性を有する傾向にあるため、担体の孔の深部や非常に微細な口径の孔にも、金属を迅速にかつ均一に微細な状態で浸透させることができる。なお、上記の溶解能力は、温度、圧力、エントレーナー（添加物）等によって調整できる。従って、このような高温高圧流体を用いることによって金属が５ｎｍ以下（好ましくは２ｎｍ以下）という超微細な粒子サイズでかつ均一な圧力下で均一に分散して担持されるため、触媒活性がより向上する傾向にある。
【００３３】
また、超臨界法とは、本発明者らによる国際公開番号ＷＯ９９／１０１６７号公報に記載の超臨界流体を用いて前記物質に前記金属超微粒子を担持せしめる方法である。より具体的には、金属及び／又は金属前駆体と溶媒とを含む溶液をその溶媒が超臨界流体になる状態で担体に接触させることにより担体表面に金属及び／又は金属前駆体を担持させる方法であり、その後に必要に応じて後述する焼成処理及び／又は還元処理を施すことによって本発明の触媒が得られる。ここで、超臨界流体とは臨界温度以上に加熱された流体を意味する。したがって、溶媒が超臨界流体になる状態とは、溶媒の臨界温度以上に溶媒が加熱された状態を意味する。圧力に関しては特に制限はないが、臨界圧力以上とすることが好ましい。このような超臨界流体は、液体と同等の溶解能力と、気体に近い拡散性及び粘性を有するため、担体の孔の深部や非常に微細な口径の孔にも、金属を迅速にかつ均一に微細な状態で浸透させることができる。なお、上記の溶解能力は、温度、圧力、エントレーナー（添加物）等によって調整できる。従って、このように超臨界流体を用いることによって金属が５ｎｍ以下（好ましくは２ｎｍ以下）という超微細な粒子サイズでかつ金属単体として均一に分散して担持されるため、触媒活性が更に向上する傾向にある。
【００３４】
なお、上記のようにして金属及び／又は金属前駆体を担体に担持せしめた後、必要に応じて窒素もしくは空気中での焼成処理、及び／又は、水素もしくは一酸化炭素もしくは炭化水素（メタン、アセトアルデヒド等）含有雰囲気中での還元処理を施すことが好ましい。このような焼成処理、還元処理の条件は特に制限されないが、例えば２００〜８００℃の温度で１〜１０時間加熱するといった条件が採用される。
【００３５】
また、金属前駆体としては、金属のハロゲン化物、硝酸塩、炭酸塩、アセチルアセトナート、テトラアンミン塩、アルコキシド等が用いられる。
【００３６】
更に、このような高温高圧流体又は超臨界流体となる溶媒としては特に制限はないが、例えば、メタン、エタン、プロパン、ブタン、エチレン、プロピレン等の炭化水素；メタノール、エタノール、イソプロパノール等のモノオール；エチレングリコール、プロピレングリコール等のグリコール；アセトン、アセチルアセトン等のケトン；ジメチルエーテル等のエーテル；二酸化炭素；水；アンモニア；塩素；クロロホルム；フレオン類等を挙げることができる。また、金属及び／又は金属前駆体の流体への溶解度を高めるために、メタノール、エタノール、プロパノール等のアルコール；アセトン、エチルメチルケトン、アセチルアセトン等のケトン；ベンゼン、トルエン、キシレン等の芳香族炭化水素等をエントレーナーとして用いることができる。
【００３７】
本発明の触媒の使用方法は特に制限されず、例えば処理対象となる有害ガスを含む気体と触媒とをバッチ式あるいは連続的に接触させることによって触媒による有害ガスの浄化が達成される。処理対象となる有害ガスとしては、空気中のＶＯＣ類(Volatile Organic Chemicals)、特にアルデヒド類、アミン類、メルカプタン類；空気中及び排ガス中のＮＯｘ、ＣＯ、ＨＣ、ＳＯｘ；またＳＶＯＣ類(Semi Volatile Organic Chemicals)として挙げられるフタル酸エステル類、アルキルフェノール類、クロロフェノール類が挙げられる。
【００３８】
また、本発明の触媒を使用する場合の反応条件は特に制限されないが、前述の通り従来より低温において有害ガスの浄化を行なえようになるため、触媒による浄化処理可能温度の下限が従来より下がることとなる。なお、効率良く浄化できる温度領域は使用する触媒と処理対象となる有害ガスとの組み合わせにより相違するため、実際の処理温度はその組み合わせに応じて好ましくは−２０℃〜５００℃の間で適宜選択される。例えば、空気中のアルデヒド類を対象とする場合は好ましくは０〜８０℃の処理温度で浄化することが可能となり、また、排ガス中のＮＯｘ及びＣＯを対象とする場合は好ましくは１５０〜２００℃の処理温度で浄化することが可能となる。
【００３９】
【実施例】
以下、実施例及び比較例に基づいて本発明をより具体的に説明するが、本発明は以下の実施例に限定されるものではない。
【００４０】
実施例１
白金アセチルアセトナート５００ｍｇをアセトン５ｍｌに溶解させ、これをオートクレーブ中に導入し、更にチタニア粉末（Sachtleben Chemie GMBH製、UV100）１ｇ及びドライアイス３０ｇを入れ、オートクレーブを密閉した後に温度１５０℃、圧力３００ｋｇ／ｃｍ2に加熱加圧して２時間保持し、二酸化炭素を超臨界流体とした状態でチタニア粉末に白金アセチルアセトナートを担持せしめた。次いで、このチタニア粉末を、１０５℃にて１時間保持して乾燥し、チタニア上に白金を担持した表１に示す触媒（白金量1.3wt%）を得た。
【００４１】
なお、担体粒子及び担持されている金属の平均粒径はTEM観察、SEM観察あるいはX線回折から求めた。X線回折により粒子径を求める場合は、理学電機製X線回折装置RAD-Bを使用し、下記手法により実施した。
【００４２】
すなわち、触媒を硝子製試料セルに詰め、グラファイトモノクロメータで単色化したCuKαを線源とし、反射式ディフラクトメータ法によって広角X線回折強度曲線を測定した。そして、粒子径（格子面に垂直方向の結晶の厚さ）Lcを、その格子面による回折線の半値幅β、波長λ、Bragg角θに基づいて以下のScherrerの式：
Lc＝Ｋλ／βcosθ
(但し、Ｋ＝0.90)
により求めた。
【００４３】
実施例２
白金アセチルアセトナート５００ｍｇをアセトン５ｍｌに溶解させ、これをオートクレーブ中に導入し、更に実施例１と同様のチタニア粉末１ｇ及び水５ｇを入れ、オートクレーブを密閉した後に温度２００℃、圧力１５気圧（１．５２０×１０6Ｐａ）に加熱加圧して１週間保持し、水を高温高圧流体とした状態でチタニア粉末に白金アセチルアセトナートを担持せしめた。次いで、このチタニア粉末を、１０５℃にて１時間保持して乾燥し、チタニア上に白金を担持した表１に示す触媒（白金量0.05wt%）を得た。
【００４４】
実施例３〜７
白金の担持量を表１に示す量にした以外は実施例２と同様にして表１に示す触媒（白金量0.2〜7.0wt%）を得た。
【００４５】
比較例１
実施例１で用いたチタニア粉末を、白金を担持することなくそのまま用いた。
【００４６】
比較例２
実施例１と同様のチタニア粉末１ｇを白金アンミン塩水溶液（白金含有量１．３２ｇ／ｌ、田中貴金属社製）１０ｍｌ中に浸漬し、チタニア粉末に白金のアンミン塩を担持せしめた。次いで、このチタニア粉末を、２５０℃にて５時間保持して乾燥した後、空気中５００℃にて２時間焼成し、更に水素中３００℃にて３時間保持して還元せしめ、チタニア上に白金を担持した表１に示す触媒（白金量1.3wt%）を得た。
【００４７】
実施例８
白金アセチルアセトナートに代えてパラジウムアセチルアセトナート５００ｍｇを使用した以外は実施例１と同様にしてチタニア上にパラジウムを担持した表１に示す触媒（パラジウム量1.3wt%）を得た。
【００４８】
実施例９
白金アセチルアセトナートに代えてパラジウムアセチルアセトナート５００ｍｇを使用した以外は実施例２と同様にしてチタニア上にパラジウムを担持した表１に示す触媒（パラジウム量1.3wt%）を得た。
【００４９】
実施例１０〜１３
白金アセチルアセトナートに代えて、
実施例１０：ロジウムアセチルアセトナート５００ｍｇ
実施例１１：ルテニウムアセチルアセトナート５００ｍｇ
実施例１２：鉄アセチルアセトナート５００ｍｇ
実施例１３：ニッケルアセチルアセトナート５００ｍｇ
を使用した以外は実施例１と同様にしてチタニア上にロジウム、ルテニウム、鉄又はニッケルを担持した表１に示す触媒（金属担持量は全て1.3wt%）を得た。
【００５０】
実施例１４
白金アセチルアセトナートに代えて塩化金酸５００ｍｇを使用した以外は実施例２と同様にしてチタニア上に金を担持した表１に示す触媒（金量0.5wt%）を得た。
【００５１】
実施例１５
チタニア粉末に代えてγ−アルミナ粉末（日揮ユニバーサル社製）１ｇを使用した以外は実施例１と同様にしてγ−アルミナ上に白金を担持した表２に示す触媒（白金量1.3wt%）を得た。
【００５２】
比較例３
チタニア粉末に代えてγ−アルミナ粉末（日揮ユニバーサル社製）１ｇを使用した以外は比較例２と同様にしてγ−アルミナ上に白金を担持した表２に示す触媒（白金量1.3wt%）を得た。
【００５３】
実施例１６〜１８
チタニア粉末に代えて、
実施例１６：酸化ケイ素粉末（富士シリシア社製）１ｇ
実施例１７：酸化セリウム粉末（和光純薬社製）１ｇ
実施例１８：活性炭（比表面積１５００m2/g、キャタラー社製）１ｇ
を使用した以外は実施例１と同様にして酸化ケイ素、酸化セリウム又は活性炭上に白金を担持した表２に示す触媒（白金量は全て1.3wt%）を得た。
【００５４】
比較例４〜７
実施例１５〜１８で用いたγ−アルミナ粉末（比較例４）、酸化ケイ素粉末（比較例５）、酸化セリウム粉末（比較例６）又は活性炭（比較例７）を、白金を担持することなくそのまま用いた。
【００５５】
［アセトアルデヒド浄化性能試験］
実施例１〜１８及び比較例１〜７の触媒をそれぞれ０．１ｇ、モデルガスとして２０ｐｐｍアセトアルデヒド含有ガス（Ｏ2２０％／Ｎ2バランス）を１０リットル用いて、以下の条件下でガスを触媒に連続的に接触させ、アセトアルデヒド濃度の経時的変化から各触媒によるアセトアルデヒド浄化性能を評価した。
【００５６】
評価装置としては循環閉鎖系の装置を使用し、２０ｐｐｍアセトアルデヒド含有ガス１０リットルを流速５リットル／ｍｉｎで循環させて触媒に接触させ、１０分毎にサンプリングしてガスクロマトグラフィーにてアセトアルデヒドの濃度を測定した。なお、装置内には光が照射しないように遮光した状態とし、温度は２０℃に維持した。
【００５７】
得られたアセトアルデヒドの残存濃度の経時的変化を時間に対して対数表示し、その傾きから触媒活性の指標として反応速度定数を求めた。得られた結果を表１及び表２に示す。また、実施例１の触媒と比較例２の触媒については、アセトアルデヒドの残存濃度と時間との関係を図１に示す。
【００５８】
【表１】
【表２】
表１及び表２に示した結果から明らかなように、本発明の触媒（実施例１〜１８）によれば、常温でかつ光を照射しない状態であっても空気中のアルデヒド類の分解反応に対して非常に高い触媒活性を示すことが確認された。かかる本発明の触媒によって達成される触媒活性は、金属超微粒子を担持していない比較例１、４〜７の触媒のみならず、金属微粒子の粒径が５ｎｍより大きい比較例２〜３の触媒に比べても顕著に高い活性であった。
【００６１】
従って、かかる効果は、金属酸化物粒子又は炭素質材料粒子の触媒作用と金属超微粒子の触媒作用との相乗効果を伴うものであり、当業者の予想を遥かに超えた効果であることが確認された。
【００６２】
次に、実施例４の触媒を用いて、温度を０℃及び６０℃に維持した以外は前記試験と同様にして反応速度定数を得た。得られた反応速度定数を表３に示す。
【００６３】
【表３】
表３に示した結果から明らかなように、本発明の触媒（実施例４）による触媒活性は、０℃という非常に低い温度においても十分に高く、６０℃になると更に顕著に高くなることが確認された。
【００６５】
次に、実施例１、比較例１及び比較例２の触媒を用いて、キセノンランプ（ウシオ電機製、型番ＵＩ−５０１Ｃ）によって触媒に光を照射しながらガスと接触させた以外は前記試験と同様にして反応速度定数を得た。得られた反応速度定数を表４に示す。
【００６６】
【表４】
表４に示した結果から明らかなように、本発明の触媒（実施例１）においては、本来はいわゆる光触媒として知られている組成（チタニア＋白金）であるにも拘わらず、チタニアに担持されている白金の平均粒径が小さい（１ｎｍ以下）と、驚くべきことに光を照射しない状態であってもアセトアルデヒドの分解反応に対して非常に高い触媒活性を示していることが確認された。そして、本発明の触媒による触媒活性の水準は、光を照射しない状態で白金の平均粒径が大きい（１０ｎｍ）比較例２の触媒に光を照射した場合と同程度であり、光を照射した状態では更に顕著に高いものであった。
【００６８】
［排ガス浄化性能試験〜昇温評価による初期活性試験〜］
実施例１、比較例２及び比較例３の触媒をそれぞれ粒子径１ｍｍ〜２ｍｍのペレット形状にしたもの１ｇ、モデル排ガスとして以下の組成：
ＣＯ：７０００ｐｐｍ
ＮＯｘ：１２００ｐｐｍ
Ｃ3Ｈ6（ＴＨＣ）：１６００ｐｐｍＣ１（メタン換算）
Ｏ2：６４６０ｐｐｍ
ＣＯ2：１０％
Ｈ2Ｏ：５％
Ｎ2：バランス
を有するガスを用いて、以下の条件下でガスを触媒にワンパスで接触させ、ＮＯｘ，ＣＯ，ＴＨＣの濃度の経時的変化を求めた。
【００６９】
（測定条件）
測定温度領域：５０℃→３５０℃
昇温速度：１２℃／ｍｉｎ
ガス流速：３５００ｍｌ／ｍｉｎ
ＳＶ：２１００００／ｈｒ。
【００７０】
実施例１、比較例２及び比較例３の触媒を用いた場合のそれぞれの結果（ＮＯｘ，ＣＯ，ＴＨＣの濃度の経時的変化）を図２〜図４に示す。また、各ガスが５０％浄化されるようになる温度（５０％浄化温度）を表５に示す。
【００７１】
【表５】
図２〜図４及び表５に示した結果から明らかなように、本発明の触媒（実施例１）によれば、常温からＮＯｘの分解反応及びＣＯの酸化反応に対する触媒活性があり、１５０〜２００℃という低温領域で十分に高い触媒活性を示すようになることが確認された。また、本発明の触媒（実施例１）によれば、ＴＨＣの分解反応に対しても従来の触媒に比べて触媒活性が低温側にシフトすることが確認された。
【００７３】
【発明の効果】
以上説明したように、本発明の低温有害ガス浄化触媒によれば、空気中のアルデヒド類や排ガス中のＮＯｘ、ＣＯ等といった有害ガスを常温あるいは従来よりも低温であってもより確実に浄化することが可能となる。
【００７４】
従って、本発明の低温有害ガス浄化触媒は、常温で空気中のアルデヒド類等の有害ガスを浄化するための「常温空気浄化用触媒」、あるいは、２００℃以下という低温で排ガス中のＮＯｘ、ＣＯ等の有害ガスを浄化するための「低温排ガス浄化用触媒」として非常に有用である。
【図面の簡単な説明】
【図１】アセトアルデヒド浄化試験における実施例１と比較例２の結果を示すグラフである。
【図２】排ガス浄化試験における実施例１の結果を示すグラフである。
【図３】排ガス浄化試験における比較例２の結果を示すグラフである。
【図４】排ガス浄化試験における比較例３の結果を示すグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a low-temperature noxious gas purification catalyst, and more particularly to a low-temperature noxious gas purification catalyst capable of purifying aldehydes in air and NOx, CO, etc. in exhaust gas even at a low temperature. is there.
[0002]
[Prior art]
In recent years, the presence of harmful gases that can be present in the environment surrounding humans and can affect the human body has been regarded as a problem. For example, aldehydes emitted from the building materials into the air Development of technology capable of reliably purifying NOx and CO, which are harmful components in exhaust gas, at lower temperatures is desired.
[0003]
Under such a background, various catalysts for purifying harmful gases have been developed. For example, JP-A-8-24653 discloses porous inorganic oxides such as γ-alumina, titania and zirconia. An exhaust gas purification catalyst comprising a first catalyst in which a white metal metal is supported by an impregnation method, a precipitation method, a sol-gel method, etc. and a second catalyst in which a silver compound is supported on a porous inorganic oxide is described. ing. However, even the exhaust gas purification catalyst described in JP-A-8-24653 can only reduce nitrogen oxides in the exhaust gas at 150 to 650 ° C., and starts NOx and CO which are harmful components in the exhaust gas. It was not enough to clean up more reliably when the exhaust gas temperature was low, such as at the time of cold start.
[0004]
JP-A-8-52351 discloses a method for decomposing a volatile organochlorine compound in which a support mainly composed of titania is loaded with a platinum group metal as a main catalytic active metal component and boron oxide as a promoter component by an impregnation method. A catalyst is disclosed. However, the catalyst described in JP-A-8-52351 decomposes volatile organic chlorine compounds at 400 to 500 ° C. and is sufficient to purify harmful components in the air and exhaust gas at low temperatures. It wasn't.
[0005]
On the other hand, a catalyst in which platinum is supported on titania is known to have a function as a so-called photocatalyst that exhibits catalytic activity in NOx decomposition and CO oxidation reaction, and that catalytic activity is promoted by light irradiation. However, since sufficient catalytic activity cannot be obtained unless light is irradiated to such a photocatalyst, it is not always possible to irradiate light as in the purification of harmful components in air or exhaust gas. Was difficult to apply.
[0006]
In addition, in International Publication No. WO99 / 10167 published by the present inventors, a metal in which a noble metal is supported on a porous metal oxide such as porous carbon such as activated carbon or porous silica using a supercritical fluid. The support is described. However, in this International Publication No. WO99 / 10167, there is nothing about using such a metal support as a low-temperature harmful gas purification catalyst for purifying aldehydes in the air, NOx, CO, etc. in exhaust gas at a low temperature. There was no disclosure or suggestion.
[0007]
[Problems to be solved by the invention]
The present invention has been made in view of the above-mentioned problems of the prior art, and more reliably purifies harmful gases such as aldehydes in the air and NOx, CO, etc. in the exhaust gas even at room temperature or at a temperature lower than conventional ones. An object of the present invention is to provide a low-temperature noxious gas purification catalyst that can be used.
[0008]
[Means for Solving the Problems]
As a result of intensive studies to achieve the above object, the present inventors have found that a metal in a catalyst comprising at least one substance selected from the group consisting of metal oxides and carbonaceous materials and metal fine particles supported thereon. By making the fine particles into ultrafine particles having an average particle size of 5 nm or less, it is surprisingly possible to sufficiently purify aldehydes in the air even at room temperature, and exhaust gas even at a low temperature of 200 ° C. or less. The present inventors have found that it is possible to sufficiently purify NOx and CO therein, and have completed the present invention.
[0009]
That is, the present invention is a low-temperature noxious gas purification catalyst comprising at least one substance selected from the group consisting of metal oxides and carbonaceous materials, and ultrafine metal particles having an average particle diameter of 5 nm or less. It is.
[0010]
The reason why the catalyst of the present invention sufficiently purifies aldehydes in the air even at room temperature and sufficiently purifies NOx and CO in the exhaust gas even at a low temperature of 200 ° C. or lower is clear. However, since the metal is supported as very fine particles, its catalytic activity is specifically increased, and is further achieved by the synergistic effect of the catalytic activity of such a metal and the catalytic activity of a metal oxide or carbonaceous material. The present inventors believe that this is the case.
[0011]
The metal oxide according to the present invention includes a single oxide or a composite oxide of at least one metal selected from the group consisting of Ti, Al, Si, Ce, Zr, Fe, Mn, Ni, Zn, and Cu. Particles having an average particle size of 1000 μm or less consisting of
As the carbonaceous material, particles having an average particle diameter of 1000 μm or less made of at least one carbonaceous material selected from the group consisting of activated carbon, graphite, activated char, coke, hard carbon and soft carbon are preferable,
Metal ultrafine particlesThe child is, Pt, Pd, Rh, Ru, Ir, Os, Au, Ag, Cu, FUltrafine particles of at least one metal selected from the group consisting of e and NiIs. According to such a combination of ultrafine metal particles and metal oxide or carbonaceous material, the purification of harmful gases tends to proceed more efficiently.
[0012]
Further, the catalyst of the present invention has 1.013 × 106The metal ultrafine particles are supported on the substance using a high-temperature and high-pressure fluid maintained at a pressure of Pa (10 atm) or higher and at a temperature higher than the boiling point under the pressure.TheBy using such a high-temperature and high-pressure fluid, the metal has an ultrafine particle size of 5 nm or less (preferably 2 nm or less) and is uniformly dispersed and supported under a uniform pressure, so that the catalytic activity tends to be further improved. It is in.
[0013]
Furthermore, the catalyst of the present invention is more preferably one in which the metal ultrafine particles are supported on the substance using a supercritical fluid. By using a supercritical fluid in this way, the metal has an ultrafine particle size of 5 nm or less (preferably 2 nm or less) and is uniformly dispersed and supported as a single metal, so that the catalytic activity tends to be further improved. .
[0014]
In the catalyst of the present invention, the metal oxide is preferably a metal oxide having a photosensitizing action, and the metal ultrafine particles are precious metal ultrafine particles having an average particle diameter of 2 nm or less. In this way, the metal oxide having a so-called photosensitizing action whose catalytic activity is promoted by light irradiation is loaded with noble metal ultrafine particles having an average particle diameter of 2 nm or less, and surprisingly no light is irradiated. However, the present inventors have found that high catalytic activity is exhibited for the catalytic reaction of harmful gases. Such knowledge overturns the conventional knowledge of those skilled in the art regarding so-called photocatalysts, and is extremely useful as a technique for increasing the catalytic activity of photocatalysts without light irradiation.
[0015]
Furthermore, in the catalyst of the present invention, it is particularly preferable that the metal oxide is titanium oxide and the metal ultrafine particles are platinum ultrafine particles having an average particle diameter of 2 nm or less. By using such a combination, a “room temperature air purification catalyst” that exhibits a very high catalytic activity for the decomposition reaction of aldehydes in the air even at a room temperature and without light irradiation, or 200 There is a tendency to obtain a “low temperature exhaust gas purifying catalyst” that exhibits high catalytic activity for NOx decomposition reaction and CO oxidation reaction in exhaust gas even at a low temperature of less than or equal to ° C. and without light irradiation.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail.
[0017]
The low-temperature noxious gas purification catalyst of the present invention comprises at least one substance selected from the group consisting of metal oxides and carbonaceous materials, and metal ultrafine particles having an average particle diameter of 5 nm or less. It is.
[0018]
That is, the catalyst of the present invention is one in which at least one substance selected from the group consisting of metal oxides and carbonaceous materials coexists with ultrafine metal particles having an average particle size of 5 nm or less. The coexistence form may be the above-mentioned substance as a carrier, with the carrier carrying ultrafine metal particles, or a mixture of both, but the former is preferred because the catalytic activity tends to be higher. Further, it is preferable that the substance is in the form of particles because the catalytic activity tends to be higher.
[0019]
Such metal oxides include noble metal elements (Pt, Pd, Rh, Ru, Au, etc.), base metal elements (Y, La, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho, Er , Tm, Yb, Lu, Ca, Mg, Al, K, Ti, Cr, Mn, Fe, Co, Ni, Cu, Ga, Rb, Sr, Zr, Nb, Mo, In, Sn, Cs, Ba, Ta , W, etc.) and oxides of metalloid elements (Si, Ge, As, Sb, etc.), among others, selected from the group consisting of Ti, Al, Si, Ce, Zr, Fe, Mn, Ni, Zn, Cu At least one metal single oxide or composite oxide is preferable, and titanium oxide, alumina, silicon oxide, cerium oxide, zeolite, zirconia, iron oxide, manganese oxide, nickel oxide, zinc oxide, and copper oxide are more preferable. The metal oxide according to the present invention may contain a plurality of metal elements such as zeolite, titanium oxide-zirconia, and cerium oxide-zirconia, and may further contain a non-metal element. Here, “metal” is included in the category of “metal”.
[0020]
By using such a metal oxide, the substance itself also acts as a catalyst, and in particular, purification of harmful gases at a low temperature is sufficiently achieved by a synergistic effect with metal ultrafine particles described later.
[0021]
The metal oxide according to the present invention is a particle having an average particle diameter of preferably 1000 μm or less, more preferably 100 μm to 10 nm, particularly preferably 10 μm to 10 nm. When the average particle diameter exceeds 1000 μm, the surface area of the particles decreases, and sufficient catalytic activity tends not to be obtained. The specific surface area of the metal oxide is 1-1000 m.2/ G is preferable, and when the average particle size is relatively large, porous particles are preferable.
[0022]
As the carbonaceous material, activated carbon, graphite, activated char, coke, hard carbon (non-graphitizable carbon), and soft carbon (graphitizable carbon) are preferable. Even when such a carbonaceous material is used, the substance itself acts as a catalyst, and the purification of harmful gases at a low temperature is sufficiently achieved especially by a synergistic effect with the ultrafine metal particles described later.
[0023]
The carbonaceous material according to the present invention is a particle having an average particle diameter of preferably 1000 μm or less, more preferably 100 μm to 10 nm, and particularly preferably 10 μm to 10 nm. When the average particle diameter exceeds 1000 μm, the surface area of the particles decreases, and sufficient catalytic activity tends not to be obtained. The specific surface area of the carbonaceous material is 1 to 4000 m.2/ G, preferably porous particles.
[0024]
The shape of the substance according to the present invention is not particularly limited, and a powder shape, a pellet shape, a monolith shape, a plate shape, a fiber shape, or the like can be selected according to use conditions.
[0025]
The catalyst of the present invention is one in which ultrafine metal particles coexist in the above-mentioned substance. Examples of such metals include Pt, Pd, Rh, Ru, Ir, Os, Au, Ag, Cu, Mn, Fe, and Ni. Among them, noble metal elements (Pt, Pd, Rh, Ru, Ir, Os, etc.) , Au, Ag), and platinum group elements (Pt, Pd, Rh, Ru, Ir, Os) are more preferable. By using such metal ultrafine particles in the presence of the substance, purification of harmful gases at low temperatures can be sufficiently achieved by the synergistic effect of the catalytic action of the metal ultrafine particles and the catalytic action of the substance.
[0026]
The ultrafine metal particles according to the present invention are required to have an average particle size of 5 nm or less, more preferably 2 nm or less, particularly preferably 1 nm or less. As described above, in the catalyst of the present invention, the metal fine particles supported on the metal oxide or carbonaceous material are made ultrafine particles having an average particle size of 5 nm or less, and surprisingly, aldehydes in the air even at room temperature. Can be sufficiently purified, and even at a low temperature of 200 ° C. or lower, NOx and CO in the exhaust gas can be sufficiently purified.
[0027]
In addition, although the metal ultrafine particle concerning this invention may contain metal compounds, such as a metal oxide, in part, since a catalytic activity becomes stronger, it is preferable that it is a metal simple substance. Although the aldehydes in the air are sufficiently purified by the catalyst of the present invention even at room temperature, and the reason why NOx and CO in exhaust gas are sufficiently purified even at a low temperature of 200 ° C. or less is not clear. Furthermore, since the metal is supported as extremely fine particles, its catalytic activity is specifically increased, and is further achieved by a synergistic effect of the catalytic activity of the metal and the catalytic activity of the metal oxide or carbonaceous material. The present inventors think.
[0028]
The content of the ultrafine metal particles in the catalyst of the present invention is preferably 0.01 to 20% by weight, more preferably 0.05 to 5% by weight, based on the total weight of the catalyst. It is particularly preferably 2 to 2% by weight. When the content of the ultrafine metal particles is less than 0.01% by weight, the catalytic action by the ultrafine metal particles tends to be insufficient.
[0029]
In the catalyst of the present invention, the metal oxide is preferably a metal oxide having a photosensitizing action, and the metal ultrafine particles are precious metal ultrafine particles having an average particle diameter of 2 nm or less. Examples of the metal oxide having such a photosensitizing action include titanium oxide, nickel oxide, zinc oxide, copper oxide, iron oxide, cerium oxide, niobium oxide, and tungsten oxide, and titanium oxide is particularly preferable. In this way, the metal oxide having a so-called photosensitizing action whose catalytic activity is promoted by light irradiation is loaded with noble metal ultrafine particles having an average particle diameter of 2 nm or less, and surprisingly no light is irradiated. However, the present inventors have found that high catalytic activity (* 1) is exhibited with respect to the catalytic reaction of harmful gases. Such knowledge overturns the conventional knowledge of those skilled in the art regarding so-called photocatalysts, and is extremely useful as a technique for increasing the catalytic activity of photocatalysts without light irradiation. In addition, high catalyst activity (* 1) here is the following relationship, when a reaction rate constant is made into the parameter | index of catalyst activity, for example:
{(Reaction rate constant without light irradiation) / (Reaction rate constant with light irradiation)} × 100 ≧ 50
The case that satisfies
[0030]
Furthermore, in the catalyst of the present invention, it is particularly preferable that the metal oxide is titanium oxide and the metal ultrafine particles are platinum ultrafine particles having an average particle diameter of 2 nm or less. By using such a combination, even at a normal temperature (preferably -20 to 80 ° C.) and in a state where no light is irradiated, “normal temperature” which exhibits a very high catalytic activity for the decomposition reaction of aldehydes in the air. "Air purifying catalyst" or "low temperature exhaust gas purifying catalyst having high catalytic activity for NOx decomposition reaction and CO oxidation reaction in exhaust gas even at a low temperature of 200 ° C or lower and not irradiated with light" "Tends to be obtained.
[0031]
As a method for allowing the ultrafine metal particles to coexist with the above substance, a so-called high-temperature high-pressure method or a so-called supercritical method described below is particularly preferable.
[0032]
That is, the high-temperature high-pressure method is 1.013 × 106Pa (10 atm) or more, more preferably 1.520 × 106In this method, the metal ultrafine particles are supported on the substance using a high-temperature and high-pressure fluid maintained at a pressure of Pa (15 atm) or higher and at a temperature equal to or higher than the boiling point under the pressure. More specifically, the metal and / or metal precursor is supported on the surface of the support by bringing the solution containing the metal and / or metal precursor and the solvent into contact with the support in a state where the solvent becomes the above high-temperature and high-pressure fluid. The catalyst of this invention is obtained by performing the baking process and / or reduction process which are mentioned later as needed after that. Such high-temperature and high-pressure fluids tend to have dissolution ability close to liquid, diffusivity and viscosity close to gas, so that the metal can be quickly and deeply inserted into the deep holes of the carrier and holes with very fine diameters. It can penetrate in a fine and uniform state. In addition, said melt | dissolution capability can be adjusted with temperature, a pressure, an entrainer (additive), etc. Therefore, by using such a high-temperature and high-pressure fluid, the metal is supported in an ultrafine particle size of 5 nm or less (preferably 2 nm or less) and uniformly dispersed under a uniform pressure, so that the catalytic activity is further improved. Tend to.
[0033]
The supercritical method is a method for supporting the metal ultrafine particles on the substance using a supercritical fluid described in International Publication No. WO99 / 10167 by the present inventors. More specifically, a method of supporting a metal and / or metal precursor on the surface of a carrier by bringing a solution containing a metal and / or a metal precursor and a solvent into contact with the carrier in a state where the solvent becomes a supercritical fluid. Thereafter, the catalyst of the present invention is obtained by performing a baking treatment and / or a reduction treatment, which will be described later, as necessary. Here, the supercritical fluid means a fluid heated to a critical temperature or higher. Therefore, the state in which the solvent becomes a supercritical fluid means a state in which the solvent is heated to a temperature higher than the critical temperature of the solvent. Although there is no restriction | limiting in particular regarding a pressure, It is preferable to set it as a critical pressure or more. Such supercritical fluids have the same dissolving ability as liquids, diffusivity and viscosity close to gas, so that the metal can be quickly and evenly distributed in the deep holes of the carrier and holes with very fine diameters. It can be penetrated in a fine state. In addition, said melt | dissolution capability can be adjusted with temperature, a pressure, an entrainer (additive), etc. Accordingly, by using the supercritical fluid in this way, the metal is supported in an ultrafine particle size of 5 nm or less (preferably 2 nm or less) and uniformly dispersed and supported as a single metal, so that the catalytic activity tends to be further improved. It is in.
[0034]
In addition, after the metal and / or metal precursor is supported on the support as described above, if necessary, a calcination treatment in nitrogen or air, and / or hydrogen, carbon monoxide, or hydrocarbon (methane, It is preferable to perform a reduction treatment in an atmosphere containing acetaldehyde or the like. The conditions for such baking treatment and reduction treatment are not particularly limited. For example, a condition of heating at a temperature of 200 to 800 ° C. for 1 to 10 hours is employed.
[0035]
As the metal precursor, metal halides, nitrates, carbonates, acetylacetonates, tetraammine salts, alkoxides and the like are used.
[0036]
Furthermore, there are no particular limitations on the solvent that becomes such a high-temperature and high-pressure fluid or supercritical fluid. For example, hydrocarbons such as methane, ethane, propane, butane, ethylene, and propylene; monools such as methanol, ethanol, and isopropanol Glycols such as ethylene glycol and propylene glycol; ketones such as acetone and acetylacetone; ethers such as dimethyl ether; carbon dioxide; water; ammonia; chlorine; chloroform; In order to increase the solubility of metals and / or metal precursors in fluids, alcohols such as methanol, ethanol, and propanol; ketones such as acetone, ethyl methyl ketone, and acetylacetone; aromatic hydrocarbons such as benzene, toluene, and xylene Etc. can be used as entrainers.
[0037]
The method of using the catalyst of the present invention is not particularly limited, and purification of harmful gas by the catalyst can be achieved, for example, by bringing the gas containing the harmful gas to be treated into contact with the catalyst batchwise or continuously. Examples of harmful gases to be treated include VOCs in the air (Volatile Organic Chemicals), especially aldehydes, amines, mercaptans; NOx, CO, HC, SOx in air and exhaust gas; and SVOCs (Semi Volatile Phthalates, alkylphenols and chlorophenols mentioned as Organic Chemicals).
[0038]
In addition, the reaction conditions in the case of using the catalyst of the present invention are not particularly limited. However, as described above, since the harmful gas can be purified at a lower temperature than before, the lower limit of the temperature at which the catalyst can be purified can be lowered. It becomes. In addition, since the temperature range that can be efficiently purified differs depending on the combination of the catalyst used and the harmful gas to be treated, the actual treatment temperature is preferably appropriately selected between −20 ° C. and 500 ° C. depending on the combination. Is done. For example, when targeting aldehydes in the air, it is possible to purify at a treatment temperature of preferably 0 to 80 ° C., and when targeting NOx and CO in exhaust gas, preferably 150 to 200 ° C. It becomes possible to purify at the processing temperature.
[0039]
【Example】
EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.
[0040]
Example 1
500 mg of platinum acetylacetonate is dissolved in 5 ml of acetone and introduced into an autoclave. Further, 1 g of titania powder (Sachtleben Chemie GMBH, UV100) and 30 g of dry ice are added. / Cm2The mixture was heated and pressurized to 2 hours and held for 2 hours, and platinum acetylacetonate was supported on titania powder in a state where carbon dioxide was used as a supercritical fluid. Next, the titania powder was dried by holding at 105 ° C. for 1 hour to obtain a catalyst (platinum amount 1.3 wt%) shown in Table 1 carrying platinum on titania.
[0041]
The average particle size of the carrier particles and the supported metal was obtained from TEM observation, SEM observation or X-ray diffraction. When the particle diameter was determined by X-ray diffraction, an X-ray diffractometer RAD-B manufactured by Rigaku Corporation was used and the following method was used.
[0042]
That is, a wide-angle X-ray diffraction intensity curve was measured by a reflective diffractometer method using CuKα packed in a glass sample cell and monochromatized with a graphite monochromator as a radiation source. Then, the particle diameter (the thickness of the crystal perpendicular to the lattice plane) Lc is determined based on the half-value width β, the wavelength λ, and the Bragg angle θ of the diffraction line by the lattice plane as follows:
Lc = Kλ / βcosθ
(However, K = 0.90)
Determined by
[0043]
Example 2
500 mg of platinum acetylacetonate was dissolved in 5 ml of acetone, and this was introduced into an autoclave. Further, 1 g of titania powder and 5 g of water as in Example 1 were added, and after sealing the autoclave, the temperature was 200 ° C., the pressure was 15 atm (1 .520 × 106Pa) was heated and pressurized for 1 week, and platinum acetylacetonate was supported on titania powder in a state where water was used as a high-temperature and high-pressure fluid. Next, this titania powder was dried by holding at 105 ° C. for 1 hour to obtain a catalyst (platinum amount 0.05 wt%) shown in Table 1 carrying platinum on titania.
[0044]
Examples 3-7
A catalyst (platinum amount 0.2 to 7.0 wt%) shown in Table 1 was obtained in the same manner as in Example 2 except that the amount of platinum supported was changed to the amount shown in Table 1.
[0045]
Comparative Example 1
The titania powder used in Example 1 was used as it was without supporting platinum.
[0046]
Comparative Example 2
1 g of titania powder similar to that in Example 1 was immersed in 10 ml of an aqueous platinum ammine salt solution (platinum content: 1.32 g / l, manufactured by Tanaka Kikinzoku Co., Ltd.), and the platinum ammine salt was supported on the titania powder. Next, the titania powder was dried by holding at 250 ° C. for 5 hours, then calcined in air at 500 ° C. for 2 hours, further held in hydrogen at 300 ° C. for 3 hours to reduce, and platinum on the titania. The catalyst shown in Table 1 (platinum content: 1.3 wt%) on which was supported was obtained.
[0047]
Example 8
Except that 500 mg of palladium acetylacetonate was used in place of platinum acetylacetonate, the catalyst shown in Table 1 (palladium amount 1.3 wt%) having palladium supported on titania was obtained in the same manner as in Example 1.
[0048]
Example 9
Except that 500 mg of palladium acetylacetonate was used instead of platinum acetylacetonate, the catalyst shown in Table 1 (palladium amount 1.3 wt%) in which palladium was supported on titania was obtained in the same manner as in Example 2.
[0049]
Examples 10-13
Instead of platinum acetylacetonate,
Example 10: Rhodium acetylacetonate 500 mg
Example 11: Ruthenium acetylacetonate 500 mg
Example 12: Iron acetylacetonate 500mg
Example 13: Nickel acetylacetonate 500 mg
In the same manner as in Example 1 except that was used, the catalyst shown in Table 1 carrying rhodium, ruthenium, iron or nickel on titania was obtained (all metal loadings were 1.3 wt%).
[0050]
Example 14
Except that 500 mg of chloroauric acid was used in place of platinum acetylacetonate, a catalyst (gold amount 0.5 wt%) shown in Table 1 carrying gold on titania was obtained in the same manner as in Example 2.
[0051]
Example 15
Except for using 1 g of γ-alumina powder (manufactured by JGC Universal) instead of titania powder, the catalyst shown in Table 2 (platinum amount 1.3 wt%) supporting platinum on γ-alumina was used in the same manner as in Example 1. Obtained.
[0052]
Comparative Example 3
A catalyst (platinum amount 1.3 wt%) shown in Table 2 carrying platinum on γ-alumina was used in the same manner as in Comparative Example 2 except that 1 g of γ-alumina powder (manufactured by JGC Universal) was used instead of titania powder. Obtained.
[0053]
Examples 16-18
Instead of titania powder,
Example 16: Silicon oxide powder (manufactured by Fuji Silysia) 1 g
Example 17: 1 g of cerium oxide powder (manufactured by Wako Pure Chemical Industries, Ltd.)
Example 18: Activated carbon (specific surface area 1500 m2/ g, manufactured by Cataler) 1g
In the same manner as in Example 1 except that was used, a catalyst shown in Table 2 (platinum amount was 1.3 wt%) in which platinum was supported on silicon oxide, cerium oxide or activated carbon was obtained.
[0054]
Comparative Examples 4-7
The γ-alumina powder (Comparative Example 4), silicon oxide powder (Comparative Example 5), cerium oxide powder (Comparative Example 6) or activated carbon (Comparative Example 7) used in Examples 15 to 18 was supported without platinum. Used as is.
[0055]
[Acetaldehyde purification performance test]
0.1 g of each of the catalysts of Examples 1 to 18 and Comparative Examples 1 to 7, and 20 ppm acetaldehyde-containing gas (
[0056]
As an evaluation device, a circulating closed system is used, 10 liters of a 20 ppm acetaldehyde-containing gas is circulated at a flow rate of 5 liters / min, brought into contact with the catalyst, sampled every 10 minutes, and the concentration of acetaldehyde is measured by gas chromatography. It was measured. The apparatus was shielded from light so that it was not irradiated with light, and the temperature was maintained at 20 ° C.
[0057]
The change with time of the residual concentration of the obtained acetaldehyde was logarithmically expressed with respect to time, and the reaction rate constant was determined from the slope as an index of catalyst activity. The obtained results are shown in Tables 1 and 2. FIG. 1 shows the relationship between the residual concentration of acetaldehyde and time for the catalyst of Example 1 and the catalyst of Comparative Example 2.
[0058]
[Table 1]
[Table 2]
As is clear from the results shown in Tables 1 and 2, according to the catalysts of the present invention (Examples 1 to 18), the decomposition reaction of aldehydes in the air even at room temperature and in a state where no light is irradiated. It was confirmed that the catalyst activity was very high. The catalytic activity achieved by the catalyst of the present invention is not limited to the catalysts of Comparative Examples 1 and 4 to 7 that do not carry ultrafine metal particles, but also the catalysts of Comparative Examples 2 to 3 in which the particle size of the metal fine particles is larger than 5 nm. The activity was significantly higher than
[0061]
Therefore, such an effect is accompanied by a synergistic effect of the catalytic action of the metal oxide particles or carbonaceous material particles and the catalytic action of the ultrafine metal particles, and it is confirmed that the effect is far beyond the expectation of those skilled in the art. It was done.
[0062]
Next, using the catalyst of Example 4, a reaction rate constant was obtained in the same manner as in the above test except that the temperature was maintained at 0 ° C. and 60 ° C. The obtained reaction rate constants are shown in Table 3.
[0063]
[Table 3]
As is clear from the results shown in Table 3, the catalytic activity of the catalyst of the present invention (Example 4) is sufficiently high even at a very low temperature of 0 ° C., and becomes significantly higher at 60 ° C. confirmed.
[0065]
Next, using the catalyst of Example 1, Comparative Example 1 and Comparative Example 2, the test was performed except that the catalyst was irradiated with light by a xenon lamp (USHIO, model number UI-501C) while irradiating the catalyst with light. The reaction rate constant was obtained in the same manner. The obtained reaction rate constants are shown in Table 4.
[0066]
[Table 4]
As is apparent from the results shown in Table 4, the catalyst of the present invention (Example 1) is supported on titania, although it is originally known as a so-called photocatalyst (titania + platinum). When the average particle diameter of platinum is small (1 nm or less), it was surprisingly confirmed that even in a state where light is not irradiated, the catalyst exhibits very high catalytic activity for the acetaldehyde decomposition reaction. And the level of the catalyst activity by the catalyst of this invention is comparable as the case where light is irradiated to the catalyst of the comparative example 2 with which the average particle diameter of platinum is large (10 nm) in the state which does not irradiate light, and light was irradiated. The condition was significantly higher.
[0068]
[Exhaust gas purification performance test-Initial activity test by temperature rise evaluation-]
1 g of the catalyst of Example 1, Comparative Example 2 and Comparative Example 3 in the form of pellets each having a particle diameter of 1 mm to 2 mm, the following composition as a model exhaust gas:
CO: 7000 ppm
NOx: 1200ppm
CThreeH6(THC): 1600ppmC1 (methane conversion)
O2: 6460ppm
CO2: 10%
H2O: 5%
N2:balance
The gas was brought into contact with the catalyst in one pass under the following conditions, and the change with time in the concentrations of NOx, CO, and THC was determined.
[0069]
(Measurement condition)
Measurement temperature range: 50 ° C → 350 ° C
Temperature increase rate: 12 ° C / min
Gas flow rate: 3500 ml / min
SV: 210000 / hr.
[0070]
The respective results (changes in NOx, CO, and THC concentrations over time) when the catalysts of Example 1, Comparative Example 2, and Comparative Example 3 were used are shown in FIGS. Table 5 shows the temperatures at which each gas is purified by 50% (50% purification temperature).
[0071]
[Table 5]
As is apparent from the results shown in FIGS. 2 to 4 and Table 5, according to the catalyst of the present invention (Example 1), there is catalytic activity for NOx decomposition reaction and CO oxidation reaction from room temperature. It was confirmed that the catalyst activity was sufficiently high in a low temperature region of 200 ° C. In addition, according to the catalyst of the present invention (Example 1), it was confirmed that the catalytic activity shifts to a lower temperature side than the conventional catalyst for the decomposition reaction of THC.
[0073]
【The invention's effect】
As described above, according to the low-temperature harmful gas purification catalyst of the present invention, harmful gases such as aldehydes in the air and NOx, CO, etc. in the exhaust gas are more reliably purified even at room temperature or at a temperature lower than conventional. It becomes possible.
[0074]
Therefore, the low temperature harmful gas purification catalyst of the present invention is a “normal temperature air purification catalyst” for purifying harmful gases such as aldehydes in the air at room temperature, or NOx, CO in exhaust gas at a low temperature of 200 ° C. or less. It is very useful as a “low-temperature exhaust gas purification catalyst” for purifying harmful gases such as.
[Brief description of the drawings]
FIG. 1 is a graph showing the results of Example 1 and Comparative Example 2 in an acetaldehyde purification test.
FIG. 2 is a graph showing the results of Example 1 in an exhaust gas purification test.
FIG. 3 is a graph showing the results of Comparative Example 2 in an exhaust gas purification test.
FIG. 4 is a graph showing the results of Comparative Example 3 in an exhaust gas purification test.
Claims (15)
１．０１３×１０６Ｐａ（１０ａｔｍ）以上の圧力下でかつ該圧力下における沸点以上の温度に維持された高温高圧流体を用いて前記物質に前記金属超微粒子を担持せしめたものであり、
前記金属超微粒子が、 Pt,Pd,Rh,Ru,Ir,Os,Au,Ag,Cu,Fe,Ni からなる群から選択される少なくとも一種の金属の超微粒子であることを特徴とする低温有害ガス浄化触媒。Consisting of at least one substance selected from the group consisting of metal oxides and carbonaceous materials, and ultrafine metal particles having an average particle size of 5 nm or less,
Der that allowed carrying the metal ultrafine particles to the substance with 1.013 × 10 6 Pa (10atm) or more under pressure in and high-temperature high-pressure fluid is maintained at a temperature higher than the boiling point at the pressure under is,
The metal ultrafine particles are at least one kind of metal ultrafine particles selected from the group consisting of Pt, Pd, Rh, Ru, Ir, Os, Au, Ag, Cu, Fe, and Ni. Gas purification catalyst.
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