JP3924341B2 - Method for catalytic reduction of nitrogen oxides - Google Patents
Method for catalytic reduction of nitrogen oxides Download PDFInfo
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- JP3924341B2 JP3924341B2 JP01150897A JP1150897A JP3924341B2 JP 3924341 B2 JP3924341 B2 JP 3924341B2 JP 01150897 A JP01150897 A JP 01150897A JP 1150897 A JP1150897 A JP 1150897A JP 3924341 B2 JP3924341 B2 JP 3924341B2
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Description
【0001】
【発明の属する技術分野】
本発明は、排ガスに含まれる窒素酸化物を触媒の存在下に還元剤を用いて接触還元する方法に関し、詳しくは、工場や自動車等、特に、リーンバーンガソリン自動車やディーゼルエンジン車両から排出される排ガス中の有害な窒素酸化物を還元剤として炭化水素を用いて、窒素酸化物に対する還元剤の比率(モル比)を小さくしながら、安定に且つ効率よく還元除去することができる窒素酸化物の接触還元方法に関する。
【0002】
【従来の技術】
従来、排ガス中に含まれる窒素酸化物は、窒素酸化物を酸化した後、アルカリに吸収させる方法や、アンモニア、水素、一酸化炭素、炭化水素等の還元剤を用いて、窒素に変換する方法等によって除去されている。
【0003】
しかしながら、前者の方法によれば、生成するアルカリ廃液を処理して、公害の発生を防止する方策が必要である。他方、後者の方法によれば、還元剤としてアンモニアを用いるときは、これが排ガス中の硫黄酸化物と反応して塩類を生成し、その結果、触媒の還元活性が低下する問題がある。また、水素、一酸化炭素、炭化水素等を還元剤として用いる場合でも、これらが低濃度に存在する窒素酸化物よりも高濃度に存在する酸素と反応するので、窒素酸化物を低減するためには、多量の還元剤を必要とするという問題がある。
【0004】
このため、最近では、還元剤の不存在下に窒素酸化物を触媒にて直接分解する方法も提案されているが、しかし、従来、知られているそのような触媒は、窒素酸化物の分解活性が低いために、実用に供し難いという問題がある。
【0005】
また、炭化水素や含酸素化合物を還元剤として用いる新たな窒素酸化物接触還元用触媒として、H型ゼオライトやCuイオン交換ZSM−5等が提案されており、なかでも、H型ZSM−5(SiO2 /Al2 O3 モル比=30〜40)が最適であるとされている。しかしながら、このようなH型ZSM−5でも、未だ十分な還元活性を有するものとはいい難く、特に、ガス中に水分が含まれるとき、ゼオライト構造体中のアルミニウムが脱アルミニウムして、性能が急激に低下するので、一層高い還元活性を有し、更に、ガスが水分を含有する場合にも、すぐれた耐久性を有する窒素酸化物接触還元用触媒が要望されている。
【0006】
【発明が解決しようとする課題】
そこで、銀又は銀酸化物を無機酸化物に担持させてなる触媒も提案されているが、そのような触媒は、酸化活性が高く、窒素酸化物に対する選択反応性が低いために、窒素酸化物の除去率が低い。また、触媒が窒素酸化物の分解活性を有する温度域が450〜600℃のように高いので、排ガス中の窒素酸化物を有効に分解するには、排ガスを予め加熱することが必要であって、実用化には問題がある。更に、銀又は銀酸化物を無機酸化物に担持させてなる触媒は、硫黄酸化物の共存下での触媒活性の劣化が著しいという問題もある(特開平5−317647号公報)。そのうえ、従来の窒素酸化物接触還元用触媒は、一般に、耐熱性が十分ではなく、用途によっては、一層の耐熱性が強く要望されている。
【0007】
本発明は、上述したような事情に鑑みてなされたものであって、その目的とするところは、炭化水素を還元剤として用いて、窒素酸化物を触媒の存在下に接触還元する方法であって、窒素酸化物に対する還元剤の比率(モル比)を低くしながら、酸素や硫黄酸化物や水分の共存下においても、排ガス中の窒素酸化物を安定して且つ効率よく接触還元することができる窒素酸化物の接触還元方法を提供することにある。
【0008】
【課題を解決するための手段】
本発明は、排ガスに含まれる窒素酸化物を触媒の存在下に還元剤を用いて接触還元する方法において、第1段階として、炭化水素からなる還元剤と窒素酸化物とを含む排ガスを担体にリン酸、周期律表第Ib、VIIa及びVIII族元素のリン酸塩、塩化物及び硫酸塩から選ばれる少なくとも1種を担持させてなる第1の触媒に接触させ、第2段階として、銀、酸化銀及びアルミン酸銀から選ばれる第2の触媒に接触させることを特徴とする。
【0009】
【発明の実施の形態】
本発明の方法によれば、第1段階として、炭化水素からなる還元剤と窒素酸化物とを含む排ガスを担体にリン酸、リン酸塩、塩化物及び硫酸塩から選ばれる少なくとも1種(単に、リン酸等ということがある。)を担持させてなる第1の触媒に接触させることによって、上記還元剤を窒素酸化物との反応性にすぐれる化合物、例えば、含酸素有機化合物や、より低分子量の炭化水素に転換させ、これらを第2段階において、第2の触媒の存在下に還元剤として窒素酸化物に作用させる。
【0010】
上記リン酸塩、塩化物及び硫酸塩は、それぞれ周期律表第Ib、VIIa及びVIII族元素のリン酸塩、塩化物及び硫酸塩である。従って、リン酸塩の具体例としては、例えば、リン酸銀、リン酸銅、リン酸マンガン、リン酸鉄、リン酸コバルト、リン酸ニッケル等を挙げることができる。塩化物の具体例としては、例えば、塩化銀、塩化銅、塩化マンガン、塩化鉄、塩化コバルト、塩化ニッケル等を挙げることができる。また、硫酸塩の具体例としては、例えば、硫酸銀、硫酸銅、硫酸マンガン、硫酸鉄、硫酸コバルト、硫酸ニッケル等を挙げることができる。
【0011】
上記第1の触媒は、γ−アルミナ等の適宜の担体に含浸法等の適宜の方法によって、リン酸等を担持させてなるものである。例えば、γ−アルミナにリン酸等を含浸させた後、空気中、200〜500℃程度の温度で焼成することによって、γ−アルミナにリン酸等を担持させてなる触媒を得ることができる。
【0012】
上記リン酸等の担体への担持率、即ち、リン酸等と担体の合計重量に対するリン酸等の割合は、触媒が置かれる反応条件等にもよるが、通常、0.05〜5重量%の範囲であり、好ましくは、0.1〜3重量%の範囲である。リン酸等の担体への担持率が0.05重量%よりも少ないときは、炭化水素からなる還元剤を含酸素有機化合物や低分子量炭化水素に転換する能力が不十分であって、第2段階において、窒素酸化物を効率よく接触還元することができない。しかし、担持率が5重量%よりも多いときも、第2段階において、窒素酸化物を効率よく接触還元することができない。
【0013】
第1段階において、炭化水素からなる還元剤と窒素酸化物とを含む排ガスをこのような第1の触媒に接触させる際の空間速度は、通常、10000〜1000000hr-1の範囲である。
【0014】
本発明の方法によれば、還元剤として、炭化水素が用いられる。具体例として、例えば、メタン、エタン、プロパン、ブタン、ペンタン、ヘキサン、ヘプタン、オクタン、ノナン、デカン等のアルカン類、エチレン、プロピレン、イソブチレン、1−ブテン、2−ブテン等のアルケン類、ベンゼン、トルエン、キシレン等の芳香族炭化水素類、ガソリン、灯油、軽油、重油等の鉱油系炭化水素、これらの2種以上の混合物等を挙げることができる。特に、本発明においては、上記したなかでも、プロパン、ブタン等の低級アルカン類、エチレン、プロピレン、イソブチレン、1−ブテン、2−ブテン等の低級アルケン類や、軽油等が好ましく用いられる。これら炭化水素は、単独で用いてもよく、又は必要に応じて二種以上併用してもよい。
【0015】
更に、本発明によれば、リーンバーンガソリン自動車の排ガスに含まれる炭素数6までの低級アルケン類、低級アルカン類又はこれらの混合物からなる低級脂肪族炭化水素類は、還元剤の炭化水素成分として好ましく用いられる。なかでも、エチレン、プロピレン、ブチレン等のアルケン類、プロパン、ブタン等のアルカン類、これらの混合物を主成分とする炭化水素が好ましく用いられる。
【0016】
上記還元剤である炭化水素は、用いる具体的な炭化水素によって異なるが、通常、排ガス中の窒素酸化物に対するモル比にて、0.1〜5程度の範囲にて用いられる。炭化水素の使用量が窒素酸化物に対するモル比にて、0.1未満であるときは、窒素酸化物に対して十分な還元活性を得ることができず、他方、モル比が5を越えるときは、未反応の炭化水素の排出量が多くなるために、窒素酸化物の接触還元処理の後に、これを回収するための後処理が必要となる。
【0017】
本発明の方法によれば、このように、好ましくは、排ガス中の窒素酸化物に対して所定のモル比の炭化水素からなる還元剤を第1の触媒に接触させることによって、上記還元剤を窒素酸化物との選択反応性にすぐれる含酸素有機化合物や低分子量炭化水素に効率よく変換し、第2段階において、これらを還元剤として用いて、窒素酸化物と共に第2の触媒に接触させることによって、窒素酸化物に対する還元剤の使用量を小さくしつつ、安定に且つ効率よく、窒素酸化物を還元除去することができる。
【0018】
本発明の方法において、第2の触媒は、銀、酸化銀又はアルミン酸銀から選ばれるものであるが、なかでも、触媒活性の高いアルミン酸銀が好ましく用いられる。これらの第2の触媒のうち、銀及び酸化銀は、通常、比表面積の大きい酸化物、例えば、アルミナ、シリカ、シリカ−アルミナ、ジルコニア、チタニア、ゼオライト等の固体酸担体に担持させて用いられる。これらの担体のなかでは、特に、担持効果にすぐれるアルミナが好ましく用いられる。
【0019】
アルミナのなかでも、特開平7−171347号公報に記載されているように、アルカリ金属及びアルカリ土類金属の含有量が0.5重量%以下であり、径60オングストローム以下の細孔から形成される細孔容積が0.06cm3 /g以上、径80オングストローム以下の細孔から形成される細孔容積が0.1cm3 /g以上であるアルミナが特に好ましく用いられる。このような細孔容積を有する多孔質のアルミナは、還元剤の適度な酸化を促進し、これに担持されている銀又は酸化銀と協同して、窒素酸化物を効果的に接触還元することができる。
【0020】
このように、銀又は酸化銀からなる第2の触媒は、従来、知られている成形方法によって、それ自体にて、又は担体に担持させた後、ハニカム状、球状等の種々の形状に成形することができる。この成形の際に、成形助剤、成形体補強体、無機繊維、有機バインダー等を適宜配合してもよい。また、第2の触媒は、予め成形された不活性な基材上にウオッシュ・コート法等によって被覆担持させることもできる。上記基材としては、例えば、コージェライトのような粘土からなるハニカム構造体に担持させることができる。
【0021】
銀又は酸化銀の担体への担持量は、銀換算にて、0.1〜5重量%の範囲であり、特に、0.5〜3重量%の範囲であることが好ましい。担持量が0.1重量%よりも少ないときは、窒素酸化物の還元活性が十分でなく、他方、5重量%よりも多いときは、酸化活性が高すぎて、選択性に劣ることとなる。
【0022】
本発明においては、第2の触媒としては、アルミン酸銀からなる触媒が好ましく用いられる。このアルミン酸銀からなる第2の触媒も、通常、比表面積の大きい酸化物、例えば、アルミナ、シリカ、シリカ−アルミナ、ジルコニア、チタニア、ゼオライト等の固体酸担体に担持させて用いられ、このような触媒は、例えば、次に示す(1)から(4)のいずれかの方法に従って調製することができる。
【0023】
(1)固体酸担体を分散させたスリラー中に硝酸銀等の水溶性銀塩を投入し、スラリーのpHを銀水酸化物の生成しない8.0近傍に維持して、固体酸のイオン交換サイトに銀イオンを固定する。ここに、固体酸としてアルミナを用いた場合は、このようにして、銀イオンを固定した固体酸を、その銀イオンを固定するのに十分な塩素イオンを含有する水溶液、例えば、塩酸水溶液中に浸漬することによって、塩化銀を生成させた後、過剰の塩素イオンを水洗等によって除去することによって、先ず、塩化銀を担持した固体酸触媒を調製する。
【0024】
次いで、これを空気等のような酸化雰囲気下、好ましくは、水蒸気の存在下に、600〜900℃程度、好ましくは、700〜800℃程度の温度にて加熱焼成することによって、アルミン酸銀を生成させれば、アルミン酸銀を担持させてなる固体酸触媒を得ることができる。
【0025】
(2)例えば、硝酸アルミニウム等のような固体酸の前駆体である水溶性塩と硝酸銀等のような水溶性銀塩を均一に混合した水溶液を調製し、この水溶液を塩素イオンの存在下で中和する等の方法によって、沈殿物を生成させ、次いで、この沈殿物を濾過、水洗、リパルプを繰り返して行なった後、乾燥し、焼成して、固体酸を生成させると同時に塩化銀をその固体酸に担持させる。
【0026】
次いで、これを上述したと同様にして、酸化雰囲気下、好ましくは、水蒸気の存在下に、600〜900℃程度、好ましくは、700〜800℃程度の温度にて加熱焼成することによって、アルミン酸銀を生成させれば、アルミン酸銀を担持させてなる固体酸触媒を得ることができる。
【0027】
(3)硝酸アルミニウムのような水溶性アルミニウム塩と硝酸銀のような水溶性銀塩の水溶液に水和アルミナを浸漬し、上記アルミニウム塩と銀塩とをアルミナの細孔に含浸させた後、噴霧乾燥機のような適当な手段にて乾燥させ、この後、これを前述したように、酸化雰囲気下、好ましくは、水蒸気の存在下に、600〜900℃程度、好ましくは、700〜800℃程度の温度にて加熱焼成することによって、アルミン酸銀を生成させれば、アルミン酸銀を担持させてなる固体酸触媒を得ることができる。
【0028】
(4)更に、別の方法として、アルミン酸ナトリウムのようなアルミン酸アルカリ金属塩とその1〜4倍当量の硝酸銀の水溶液を噴霧乾燥によって均一に混合すると共に乾燥させ、得られた粒状物を水分の不存在下に300〜800℃の温度にて共融させることによって、アルミン酸銀を得、これを水洗し、過剰の硝酸銀と硝酸ナトリウムを除去すれば、アルミン酸銀の高純度品を得ることができる。このアルミン酸銀とアルミナ等の固体酸とをボールミル等を用いて湿式にて均一に混合粉砕した後、乾燥させれば、アルミン酸銀を担持させたアルミナを得ることができる。
【0029】
第2の触媒の調製においても、固体酸担体としては、特に、アルミナが好ましく用いられ、このアルミナのなかでも、前述したように、アルカリ金属及びアルカリ土類金属の含有量が0.5重量%以下であり、径60オングストローム以下の細孔から形成される細孔容積が0.06cm3 /g以上、径80オングストローム以下の細孔から形成される細孔容積が0.1cm3 /g以上であるアルミナが特に好ましく用いられる。このような細孔容積を有する多孔質のアルミナは、還元剤の適度な酸化を促進し、これに担持されているアルミン酸銀と協同して、窒素酸化物を効果的に接触還元することができる。
【0030】
第2の触媒において、固体酸担体へのアルミン酸銀の担持量は、銀換算にて、0.01〜10重量%の範囲であることが好ましい。アルミン酸銀の担持量が銀換算にて10重量%を越えるときは、得られる触媒の酸化力が高すぎて、選択性に劣り、他方、担持量が銀換算にて0.01重量%よりも少ないときは、触媒活性が十分でない。特に、本発明においては、アルミン酸銀の担持量は、0.1〜5重量%の範囲であることが好ましい。担持量がこの範囲にあるときは、窒素酸化物の接触還元反応の空間速度依存性が極めて小さいというすぐれた特性をも得ることができる。
【0031】
第2段階において、窒素酸化物と共に還元剤を含む排ガスをこのような第2の触媒に接触させる際の空間速度は、通常、5000〜100000hr-1の範囲である。第2段階において用いる第2の触媒は、第1段階において用いる第1の触媒に比べて、酸化活性が小さく、窒素酸化物との選択性にすぐれるので、高い脱硝率を得るには、空間速度は小さいことが好ましいが、通常、実用上、上記の範囲の空間速度が採用される。
【0032】
本発明の方法によれば、第1段階及び第2段階における反応温度は、150〜600℃の範囲であり、好ましくは、250〜550℃の範囲である。必要に応じて、第1段階及び第2段階において、反応温度を変えてもよい。
【0033】
本発明によれば、上述したように、第1段階において、炭化水素からなる還元剤と窒素酸化物とを含む排ガスを比較的、部分酸化活性が高いが、完全酸化能の低い第1の触媒に接触させて、上記還元剤を含酸素有機化合物や低分子量炭化水素に効率よく部分酸化して、窒素酸化物との選択反応性にすぐれる還元剤とし、第2段階において、これら還元剤の存在下に窒素酸化物の選択還元活性にすぐれる第2の触媒に排ガスを接触させることによって、窒素酸化物に対する還元剤の使用比率(モル比)を小さくしても、酸素や硫黄酸化物や水分の存在下においても、窒素酸化物を安定して且つ効率よく還元分解することができる。
【0034】
【実施例】
以下に各段階のための触媒の調製例と共に実施例を挙げて本発明を説明するが、本発明はこれら実施例により何ら限定されるものではない。
【0035】
(1)第1の触媒の調製
調製例1
γ−アルミナ(住友化学工業(株)製KHA−24)のペレットを粉砕して得たアルミナ粉末60gとアルミナゾル(日産化学工業(株)製520)6gと適量の水とを混和し、得られた混合物をジルコニアボール100gを粉砕媒体として遊星ミルで5分間湿式粉砕して、ウオッシュ・コート用スラリーを調製した。このスラリーをセル数400セル/平方インチのコージェライト基材に塗布して、γ−アルミナを約170g/Lの割合で担持させた。これを空気中、500℃で3時間焼成して、γ−アルミナを担持させた担体(コージェライト)を調製した。
【0036】
一方、リン酸水溶液(85重量%濃度)3.6gをイオン交換水に溶解させ、液量を30mLとし、これに上記アルミナを担持させたコージェライト担体を浸漬して、γ−アルミナ担持担体にリン酸を十分に含浸させた。
次いで、上記アルミナ担持担体をリン酸水溶液から分離し、表面に付着した過剰の水溶液を除去した後、100℃で12時間乾燥させ、更に、空気中、500℃で焼成して、γ−アルミナにリン酸を2.0重量%の担持量で担持させてなる触媒(A−1)を得た。
【0037】
調製例2
塩化ニッケル(NiCl3 )2.10gをイオン交換水に溶解させ、液量を30mLとした水溶液を調製した。以下、調製例1と同様にして、γ−アルミナに塩化ニッケルをニッケルとして2.0重量%の担持量で担持させてなる触媒(A−2)を得た。
【0038】
調製例3
硫酸ニッケル(NiSO4 ・ 6H2 O)4.33gをイオン交換水に溶解させ、液量を30mLとした水溶液を調製した。以下、調製例1と同様にして、γ−アルミナに硫酸ニッケルをニッケルとして2.0重量%の担持量で担持させてなる触媒(A−3)を得た。
【0039】
調製例4
硫酸ニッケル(NiSO4 ・ 6H2 O)10.83gをイオン交換水に溶解させ、液量を30mLとした水溶液を調製した。以下、調製例1と同様にして、γ−アルミナに硫酸ニッケルをニッケルとして5.0重量%の担持量で担持させてなる触媒(A−4)を得た。
【0040】
調製例5
硫酸ニッケル(NiSO4 ・ 6H2 O)0.43gをイオン交換水に溶解させ、液量を30mLとした水溶液を調製した。以下、調製例1と同様にして、γ−アルミナに硫酸ニッケルをニッケルとして0.2重量%の担持量で担持させてなる触媒(A−5)を得た。
【0041】
調製例6
硫酸マンガン(MnSO4 ・ 5H2 O)4.24gをイオン交換水に溶解させ、液量を30mLとした水溶液を調製した。以下、調製例1と同様にして、γ−アルミナに硫酸マンガンをマンガンとして2.0重量%の担持量で担持させてなる触媒(A−6)を得た。
【0042】
調製例7
硝酸銀(AgNO3 )1.52gをイオン交換水に溶解させ、液量を30mLとした水溶液を調製した。以下、調製例1と同様にして、γ−アルミナに硝酸銀を銀として2.0重量%の担持量で担持させた。この後、この触媒を1重量%濃度の塩酸に浸漬して、硝酸銀を塩化銀とし、塩化銀を銀として2.0重量%の担持量で担持させてなる触媒(A−7)を得た。
【0043】
調製例8
リン酸銀(Ag3 PO4 )3.06gを10重量%濃度のリン酸水溶液に溶解させ、液量を30mLとした。調製例1と同じアルミナを担持させたコージェライト担体を上記リン酸銀を含むリン酸水溶液に浸漬して、γ−アルミナ担持担体にリン酸銀を十分に含浸させた。
次いで、上記アルミナ担持担体をリン酸銀水溶液から分離し、表面に付着した過剰の水溶液を除去した後、100℃で12時間乾燥させ、更に、空気中、500℃で焼成して、γ−アルミナにリン酸銀を銀として2.0重量%の担持量で担持させてなる触媒(A−8)を得た。
【0044】
(2)第2の触媒の調製
調製例9
硝酸アルミニウム(Al(NO3 )3 ・9H2 O)8.69g、硝酸銀1.58g及び水和アルミナ(水澤化学工業(株)製)100gを適当量の水と混和して、ペースト状物を調製した。これを加熱式混練機を用いて混練乾燥させた後、500℃で3時間加熱焼成して、担持量2.5重量%にて銀を担持させてなるアルミナ粉末触媒を得た。
【0045】
このアルミナ粉末触媒60gとシリカゾル(日産化学工業(株)製スノーテックスN)6gとを適当量の水と混和し、これをジルコニアボール100gを粉砕媒体として遊星ミルで5分間湿式粉砕して、ウオッシュ・コート用スラリーを調製した。このスラリーをセル数200セル/平方インチのコージェライト基材に塗布して、触媒を約150g/Lの割合で担持させた。この触媒をB−1という。
【0046】
調製例10
硝酸アルミニウム(Al(NO3 )3 ・9H2 O)8.69g、硝酸銀3.94g及び水和アルミナ(水澤化学工業(株)製)100gを適当量の水と混和して、ペースト状物を調製した。これを加熱式混練機を用いて混練乾燥させた後、水分10重量%を含む空気雰囲気下、800℃で3時間加熱焼成して、銀重量換算にて担持量2.5重量%にてアルミン酸銀を担持させてなるアルミナ粉末触媒を得た。
【0047】
このアルミナ粉末触媒60gとシリカゾル(日産化学工業(株)製スノーテックスN)6gとを適当量の水と混和し、これをジルコニアボール100gを粉砕媒体として遊星ミルで5分間湿式粉砕して、ウオッシュ・コート用スラリーを調製した。このスラリーをセル数200セル/平方インチのコージェライト基材に塗布して、触媒を約150g/Lの割合で担持させた。この触媒をB−2という。
【0048】
実施例1〜10(評価試験)
以上のようにして調製した第1の触媒(A−1〜8)を第1段階に用いると共に、第2の触媒(B−1〜2)を第2段階に用いて、下記の試験条件にて、窒素酸化物含有ガスの窒素酸化物接触還元を行ない、窒素酸化物の除去率をケミカルルミネッセンス法にて求めた。結果を表1及び表2に示す。
【0049】
【0050】
比較例1及び2(評価試験)
触媒として第1の触媒又は第2の触媒のいずれか一方のみを用いた以外は、実施例と同様にして、窒素酸化物含有ガスの窒素酸化物接触還元を行ない、窒素酸化物の除去率をケミカルルミネッセンス法にて求めた。結果を表1に示す。
第1の触媒のみを用いた場合、窒素酸化物の除去率が非常に低い。第2の触媒のみを用いた場合も、本発明の方法に比べて、反応温度域全般において、窒素酸化物の除去率が低い。
【0051】
【表1】
【0052】
【表2】
【0053】
表1及び表2に示す結果から明らかなように、本発明の方法によれば、従来の方法に比べて、酸素や硫黄酸化物や水分の共存下においても、窒素酸化物に対する還元剤の使用比率(モル比)を小さくして、排ガス中の窒素酸化物を安定して且つ高い除去率にて還元除去することができる。
【0054】
【発明の効果】
以上のように、本発明の方法によれば、酸素や硫黄酸化物や水分の共存下においても、多量の還元剤を用いることなく、排ガス中の窒素酸化物を安定して且つ効率よく接触還元することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for catalytic reduction of nitrogen oxides contained in exhaust gas using a reducing agent in the presence of a catalyst, and more specifically, discharged from factories and automobiles, particularly lean burn gasoline automobiles and diesel engine vehicles. Using hydrocarbons with harmful nitrogen oxides in exhaust gas as reducing agents, nitrogen oxides that can be reduced and removed stably and efficiently while reducing the ratio (molar ratio) of reducing agents to nitrogen oxides The present invention relates to a catalytic reduction method.
[0002]
[Prior art]
Conventionally, nitrogen oxides contained in exhaust gas are oxidized by nitrogen oxides and absorbed by alkali, or converted to nitrogen using a reducing agent such as ammonia, hydrogen, carbon monoxide, hydrocarbons, etc. Etc. have been removed.
[0003]
However, according to the former method, a measure for treating the generated alkaline waste liquid to prevent the occurrence of pollution is necessary. On the other hand, according to the latter method, when ammonia is used as a reducing agent, it reacts with sulfur oxides in the exhaust gas to generate salts, resulting in a problem that the reduction activity of the catalyst is lowered. In addition, even when hydrogen, carbon monoxide, hydrocarbons, etc. are used as reducing agents, these react with oxygen present at a higher concentration than nitrogen oxide present at a lower concentration. Has the problem of requiring a large amount of reducing agent.
[0004]
For this reason, recently, a method of directly decomposing nitrogen oxides with a catalyst in the absence of a reducing agent has also been proposed. However, conventionally known such catalysts are not capable of decomposing nitrogen oxides. Since the activity is low, there is a problem that it is difficult to put to practical use.
[0005]
Further, H-type zeolite, Cu ion exchange ZSM-5, and the like have been proposed as new nitrogen oxide catalytic reduction catalysts using hydrocarbons or oxygen-containing compounds as reducing agents. Among them, H-type ZSM-5 ( The SiO 2 / Al 2 O 3 molar ratio = 30 to 40) is said to be optimal. However, even with such H-type ZSM-5, it is difficult to say that it still has sufficient reduction activity. In particular, when the gas contains moisture, the aluminum in the zeolite structure is dealuminated and the performance is reduced. There is a need for a catalyst for catalytic reduction of nitrogen oxides that has a higher reduction activity because it rapidly decreases, and also has excellent durability even when the gas contains moisture.
[0006]
[Problems to be solved by the invention]
Therefore, a catalyst in which silver or silver oxide is supported on an inorganic oxide has also been proposed. However, such a catalyst has high oxidation activity and low selective reactivity with respect to nitrogen oxide. The removal rate is low. Moreover, since the temperature range in which the catalyst has a nitrogen oxide decomposition activity is as high as 450 to 600 ° C., it is necessary to heat the exhaust gas in advance in order to effectively decompose the nitrogen oxide in the exhaust gas. There is a problem in practical use. Furthermore, a catalyst in which silver or silver oxide is supported on an inorganic oxide also has a problem that the catalytic activity is significantly deteriorated in the presence of sulfur oxide (Japanese Patent Laid-Open No. 5-317647). In addition, conventional nitrogen oxide catalytic reduction catalysts generally do not have sufficient heat resistance, and there is a strong demand for further heat resistance depending on the application.
[0007]
The present invention has been made in view of the circumstances as described above, and its object is to use a hydrocarbon as a reducing agent to perform catalytic reduction of nitrogen oxides in the presence of a catalyst. Thus, nitrogen oxides in exhaust gas can be stably and efficiently reduced even in the presence of oxygen, sulfur oxides and moisture while reducing the ratio (molar ratio) of the reducing agent to nitrogen oxides. Another object of the present invention is to provide a method for catalytic reduction of nitrogen oxides.
[0008]
[Means for Solving the Problems]
The present invention relates to a method for catalytically reducing nitrogen oxides contained in exhaust gas using a reducing agent in the presence of a catalyst. As a first step, exhaust gas containing a reducing agent comprising hydrocarbon and nitrogen oxides is used as a carrier. Contacting with a first catalyst supporting at least one selected from phosphoric acid, phosphates, chlorides and sulfates of Group Ib, VIIa and Group VIII elements of the periodic table, and silver, It is made to contact with the 2nd catalyst chosen from silver oxide and silver aluminate.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
According to the method of the present invention, as the first stage, at least one selected from phosphoric acid, phosphate, chloride and sulfate (simply, simply using an exhaust gas containing a reducing agent consisting of hydrocarbon and nitrogen oxide as a carrier) Or the like, phosphoric acid, etc.) by contacting with a first catalyst carrying the above-mentioned reducing agent, a compound having excellent reactivity with nitrogen oxides, such as an oxygen-containing organic compound, They are converted to low molecular weight hydrocarbons, which in the second stage act on nitrogen oxides as a reducing agent in the presence of the second catalyst.
[0010]
The phosphates, chlorides and sulfates are phosphates, chlorides and sulfates of Group Ib, VIIa and VIII elements of the periodic table, respectively. Accordingly, specific examples of the phosphate include silver phosphate, copper phosphate, manganese phosphate, iron phosphate, cobalt phosphate, nickel phosphate, and the like. Specific examples of the chloride include silver chloride, copper chloride, manganese chloride, iron chloride, cobalt chloride, nickel chloride and the like. Specific examples of the sulfate include silver sulfate, copper sulfate, manganese sulfate, iron sulfate, cobalt sulfate, and nickel sulfate.
[0011]
The first catalyst is obtained by supporting phosphoric acid or the like on an appropriate carrier such as γ-alumina by an appropriate method such as an impregnation method. For example, after impregnating γ-alumina with phosphoric acid or the like, a catalyst in which phosphoric acid or the like is supported on γ-alumina can be obtained by firing in air at a temperature of about 200 to 500 ° C.
[0012]
The loading ratio of the phosphoric acid and the like on the carrier, that is, the ratio of phosphoric acid and the like to the total weight of the phosphoric acid and the carrier depends on the reaction conditions in which the catalyst is placed, but is usually 0.05 to 5% by weight. The range is preferably 0.1 to 3% by weight. When the loading ratio of phosphoric acid or the like on the carrier is less than 0.05% by weight, the ability to convert the reducing agent composed of hydrocarbons into oxygen-containing organic compounds or low molecular weight hydrocarbons is insufficient. In the stage, nitrogen oxides cannot be efficiently catalytically reduced. However, even when the loading ratio is more than 5% by weight, the nitrogen oxide cannot be efficiently catalytically reduced in the second stage.
[0013]
In the first stage, the space velocity when the exhaust gas containing a reducing agent composed of hydrocarbon and nitrogen oxide is brought into contact with such a first catalyst is usually in the range of 10,000 to 1,000,000 hr −1 .
[0014]
According to the method of the present invention, a hydrocarbon is used as the reducing agent. Specific examples include, for example, alkanes such as methane, ethane, propane, butane, pentane, hexane, heptane, octane, nonane and decane, alkenes such as ethylene, propylene, isobutylene, 1-butene and 2-butene, benzene, Aromatic hydrocarbons such as toluene and xylene, mineral oil-based hydrocarbons such as gasoline, kerosene, light oil and heavy oil, and mixtures of two or more of these. In particular, in the present invention, among the above, lower alkanes such as propane and butane, lower alkenes such as ethylene, propylene, isobutylene, 1-butene and 2-butene, and light oil are preferably used. These hydrocarbons may be used alone or in combination of two or more as required.
[0015]
Further, according to the present invention, lower aliphatic hydrocarbons comprising lower alkenes, lower alkanes or mixtures thereof having up to 6 carbon atoms contained in the exhaust gas of lean burn gasoline vehicles are used as the hydrocarbon component of the reducing agent. Preferably used. Among these, alkenes such as ethylene, propylene and butylene, alkanes such as propane and butane, and hydrocarbons mainly composed of a mixture thereof are preferably used.
[0016]
The hydrocarbon as the reducing agent varies depending on the specific hydrocarbon used, but is usually used in a range of about 0.1 to 5 in terms of a molar ratio to nitrogen oxide in the exhaust gas. When the amount of hydrocarbon used is less than 0.1 in terms of molar ratio to nitrogen oxides, sufficient reduction activity cannot be obtained for nitrogen oxides, while when the molar ratio exceeds 5. Since the discharge amount of unreacted hydrocarbons increases, after the nitrogen oxide catalytic reduction treatment, a post-treatment for recovering it is necessary.
[0017]
According to the method of the present invention, preferably, the reducing agent is made to contact the first catalyst with a reducing agent composed of hydrocarbons having a predetermined molar ratio with respect to nitrogen oxides in the exhaust gas. Efficient conversion into oxygen-containing organic compounds and low molecular weight hydrocarbons with excellent selective reactivity with nitrogen oxides, and in the second stage, these are used as a reducing agent and brought into contact with the second catalyst together with nitrogen oxides Thus, the nitrogen oxide can be reduced and removed stably and efficiently while reducing the amount of the reducing agent used with respect to the nitrogen oxide.
[0018]
In the method of the present invention, the second catalyst is selected from silver, silver oxide, or silver aluminate. Among them, silver aluminate having high catalytic activity is preferably used. Of these second catalysts, silver and silver oxide are usually used by being supported on a solid acid carrier such as an oxide having a large specific surface area, for example, alumina, silica, silica-alumina, zirconia, titania, zeolite, and the like. . Among these carriers, alumina having excellent loading effect is particularly preferably used.
[0019]
Among alumina, as described in JP-A-7-171347, the content of alkali metal and alkaline earth metal is 0.5% by weight or less, and it is formed from pores having a diameter of 60 angstroms or less. that a pore volume of 0.06 cm 3 / g or more, a pore volume formed from the following pore diameters 80 Å are particularly preferably used alumina is 0.1 cm 3 / g or more. Porous alumina having such a pore volume promotes appropriate oxidation of the reducing agent and effectively catalytically reduces nitrogen oxides in cooperation with silver or silver oxide supported thereon. Can do.
[0020]
As described above, the second catalyst made of silver or silver oxide is formed into various shapes such as a honeycomb shape and a spherical shape by itself or by supporting the second catalyst by a known forming method. can do. In the molding, a molding aid, a molded body reinforcing body, inorganic fibers, an organic binder, and the like may be appropriately blended. In addition, the second catalyst can be coated and supported by a wash coat method or the like on a previously formed inert base material. For example, the base material can be supported on a honeycomb structure made of clay such as cordierite.
[0021]
The amount of silver or silver oxide supported on the carrier is in the range of 0.1 to 5% by weight in terms of silver, and particularly preferably in the range of 0.5 to 3% by weight. When the supported amount is less than 0.1% by weight, the reduction activity of nitrogen oxides is not sufficient, while when it is more than 5% by weight, the oxidation activity is too high and the selectivity is poor. .
[0022]
In the present invention, a catalyst made of silver aluminate is preferably used as the second catalyst. The second catalyst made of silver aluminate is also usually used by being supported on a solid acid carrier such as an oxide having a large specific surface area, for example, alumina, silica, silica-alumina, zirconia, titania, zeolite, etc. Such a catalyst can be prepared, for example, according to any one of the following methods (1) to (4).
[0023]
(1) A water-soluble silver salt such as silver nitrate is introduced into a chiller in which a solid acid carrier is dispersed, and the pH of the slurry is maintained at around 8.0 where no silver hydroxide is formed, so that an ion exchange site for the solid acid is obtained. Fix silver ions to the surface. Here, when alumina is used as the solid acid, the solid acid in which the silver ions are fixed in this manner is added to an aqueous solution containing enough chlorine ions to fix the silver ions, for example, an aqueous hydrochloric acid solution. First, a solid acid catalyst supporting silver chloride is prepared by removing silver ions by immersing and then removing excess chlorine ions by washing with water or the like.
[0024]
Next, the silver aluminate is heated and fired at a temperature of about 600 to 900 ° C., preferably about 700 to 800 ° C. in an oxidizing atmosphere such as air, preferably in the presence of water vapor. If produced, a solid acid catalyst in which silver aluminate is supported can be obtained.
[0025]
(2) For example, an aqueous solution in which a water-soluble salt that is a precursor of a solid acid such as aluminum nitrate and a water-soluble silver salt such as silver nitrate is uniformly mixed is prepared, and this aqueous solution is added in the presence of chloride ions. A precipitate is formed by a method such as neutralization, and then this precipitate is repeatedly filtered, washed with water, and repulped, then dried and calcined to produce a solid acid and at the same time silver chloride is Supported on solid acid.
[0026]
Then, in the same manner as described above, the aluminate is heated and fired at a temperature of about 600 to 900 ° C., preferably about 700 to 800 ° C. in an oxidizing atmosphere, preferably in the presence of water vapor. If silver is produced, a solid acid catalyst in which silver aluminate is supported can be obtained.
[0027]
(3) Immerse hydrated alumina in an aqueous solution of a water-soluble aluminum salt such as aluminum nitrate and a water-soluble silver salt such as silver nitrate, impregnate the aluminum salt and silver salt in the pores of the alumina, and spray After drying by an appropriate means such as a dryer, as described above, this is about 600 to 900 ° C., preferably about 700 to 800 ° C. in an oxidizing atmosphere, preferably in the presence of water vapor. If silver aluminate is produced by heating and firing at a temperature of 1, a solid acid catalyst in which silver aluminate is supported can be obtained.
[0028]
(4) Further, as another method, an alkali metal aluminate salt such as sodium aluminate and an aqueous solution of 1 to 4 equivalents of silver nitrate are uniformly mixed by spray drying and dried. By eutectic melting at a temperature of 300 to 800 ° C. in the absence of moisture, silver aluminate is obtained, and this is washed with water to remove excess silver nitrate and sodium nitrate. Obtainable. If this silver aluminate and a solid acid such as alumina are uniformly mixed and pulverized by a wet method using a ball mill or the like and then dried, alumina carrying silver aluminate can be obtained.
[0029]
Also in the preparation of the second catalyst, alumina is particularly preferably used as the solid acid carrier. Among the alumina, as described above, the content of alkali metal and alkaline earth metal is 0.5% by weight. or less, a pore volume formed from the following pore diameters 60 angstroms 0.06 cm 3 / g or more, with a pore volume formed from the following pore diameters 80 angstroms 0.1 cm 3 / g or more A certain alumina is particularly preferably used. Porous alumina having such a pore volume promotes appropriate oxidation of the reducing agent and can effectively reduce nitrogen oxides in cooperation with silver aluminate supported on the alumina. it can.
[0030]
In the second catalyst, the amount of silver aluminate supported on the solid acid carrier is preferably in the range of 0.01 to 10% by weight in terms of silver. When the supported amount of silver aluminate exceeds 10% by weight in terms of silver, the resulting catalyst has too high oxidizing power and is inferior in selectivity, while the supported amount is from 0.01% by weight in terms of silver. Is too low, the catalytic activity is not sufficient. In particular, in the present invention, the supported amount of silver aluminate is preferably in the range of 0.1 to 5% by weight. When the loading is within this range, it is possible to obtain excellent characteristics that the space velocity dependence of the catalytic reduction reaction of nitrogen oxides is extremely small.
[0031]
In the second stage, the space velocity when the exhaust gas containing a reducing agent together with nitrogen oxides is brought into contact with such a second catalyst is usually in the range of 5000 to 100,000 hr −1 . The second catalyst used in the second stage has a lower oxidation activity than the first catalyst used in the first stage and is excellent in selectivity with nitrogen oxides. Although the speed is preferably small, a space speed in the above-mentioned range is usually employed in practice.
[0032]
According to the method of the present invention, the reaction temperature in the first stage and the second stage is in the range of 150 to 600 ° C, preferably in the range of 250 to 550 ° C. If necessary, the reaction temperature may be changed in the first stage and the second stage.
[0033]
According to the present invention, as described above, in the first stage, the first catalyst having a relatively high partial oxidation activity but a low complete oxidation ability of the exhaust gas containing the reducing agent composed of hydrocarbon and nitrogen oxide is relatively high. The reducing agent is efficiently partially oxidized to an oxygen-containing organic compound or a low molecular weight hydrocarbon to obtain a reducing agent having excellent selective reactivity with nitrogen oxides. Even if the use ratio (molar ratio) of the reducing agent to the nitrogen oxide is reduced by bringing the exhaust gas into contact with the second catalyst having excellent selective reduction activity of the nitrogen oxide in the presence, oxygen, sulfur oxide, Even in the presence of moisture, nitrogen oxides can be stably and efficiently reduced and decomposed.
[0034]
【Example】
EXAMPLES The present invention will be described below with examples together with preparation examples of catalysts for each step, but the present invention is not limited to these examples.
[0035]
(1) Preparation Example 1 of First Catalyst
It is obtained by mixing 60 g of alumina powder obtained by pulverizing pellets of γ-alumina (KHA-24 manufactured by Sumitomo Chemical Co., Ltd.), 6 g of alumina sol (520 manufactured by Nissan Chemical Industries, Ltd.) and an appropriate amount of water. The obtained mixture was wet pulverized with a planetary mill for 5 minutes using 100 g of zirconia balls as a pulverization medium to prepare a wash coat slurry. This slurry was applied to a cordierite substrate having 400 cells / square inch, and γ-alumina was supported at a rate of about 170 g / L. This was calcined in air at 500 ° C. for 3 hours to prepare a carrier (cordierite) supporting γ-alumina.
[0036]
On the other hand, 3.6 g of phosphoric acid aqueous solution (85% by weight concentration) is dissolved in ion-exchanged water to make a liquid volume of 30 mL, and the cordierite carrier carrying the alumina is immersed in this, to the γ-alumina carrier. The phosphoric acid was sufficiently impregnated.
Next, the above alumina-supported carrier is separated from the phosphoric acid aqueous solution, and after removing the excess aqueous solution adhering to the surface, it is dried at 100 ° C. for 12 hours, and further calcined in air at 500 ° C. to give γ-alumina. A catalyst (A-1) obtained by supporting phosphoric acid at a supported amount of 2.0% by weight was obtained.
[0037]
Preparation Example 2
Nickel chloride (NiCl 3 ) 2.10 g was dissolved in ion-exchanged water to prepare an aqueous solution with a liquid volume of 30 mL. Thereafter, in the same manner as in Preparation Example 1, a catalyst (A-2) obtained by supporting 2.0% by weight of nickel chloride as nickel on γ-alumina was obtained.
[0038]
Preparation Example 3
An aqueous solution having a volume of 30 mL was prepared by dissolving 4.33 g of nickel sulfate (NiSO 4 .6H 2 O) in ion-exchanged water. Thereafter, in the same manner as in Preparation Example 1, a catalyst (A-3) obtained by loading γ-alumina with nickel sulfate as nickel at a loading amount of 2.0% by weight was obtained.
[0039]
Preparation Example 4
An aqueous solution was prepared by dissolving 10.83 g of nickel sulfate (NiSO 4 .6H 2 O) in ion-exchanged water to a liquid volume of 30 mL. Thereafter, in the same manner as in Preparation Example 1, a catalyst (A-4) obtained by loading γ-alumina with nickel sulfate as nickel at a loading amount of 5.0% by weight was obtained.
[0040]
Preparation Example 5
An aqueous solution in which 0.43 g of nickel sulfate (NiSO 4 .6H 2 O) was dissolved in ion-exchanged water to a liquid volume of 30 mL was prepared. Thereafter, in the same manner as in Preparation Example 1, a catalyst (A-5) obtained by loading nickel sulfate on γ-alumina with a loading amount of 0.2 wt% was obtained.
[0041]
Preparation Example 6
4.24 g of manganese sulfate (MnSO 4 .5H 2 O) was dissolved in ion exchange water to prepare an aqueous solution having a liquid volume of 30 mL. Thereafter, in the same manner as in Preparation Example 1, a catalyst (A-6) was obtained in which manganese sulfate was supported on γ-alumina as a manganese in a supported amount of 2.0% by weight.
[0042]
Preparation Example 7
An aqueous solution having a liquid volume of 30 mL was prepared by dissolving 1.52 g of silver nitrate (AgNO 3 ) in ion-exchanged water. Thereafter, in the same manner as in Preparation Example 1, γ-alumina was loaded with silver nitrate as silver at a loading amount of 2.0% by weight. Thereafter, the catalyst was immersed in hydrochloric acid having a concentration of 1% by weight to obtain a catalyst (A-7) in which silver nitrate was converted to silver chloride and silver chloride was converted to silver and supported at a supported amount of 2.0% by weight. .
[0043]
Preparation Example 8
3.06 g of silver phosphate (Ag 3 PO 4 ) was dissolved in a 10% by weight aqueous phosphoric acid solution to make the volume 30 mL. The same cordierite carrier supporting alumina as in Preparation Example 1 was immersed in the phosphoric acid aqueous solution containing silver phosphate, and the γ-alumina carrier was sufficiently impregnated with silver phosphate.
Next, the alumina-supported carrier is separated from the aqueous silver phosphate solution, after removing the excess aqueous solution adhering to the surface, dried at 100 ° C. for 12 hours, and further calcined in air at 500 ° C. to obtain γ-alumina. A catalyst (A-8) was obtained in which silver phosphate was supported at 2.0% by weight as silver phosphate.
[0044]
(2) Preparation Example 9 of Second Catalyst
Aluminum nitrate (Al (NO 3) 3 · 9H 2 O) 8.69g, silver nitrate 1.58g and hydrated alumina (manufactured by Mizusawa Industrial Chemicals, Ltd.) was admixed with a suitable amount of water 100 g, the paste-like product Prepared. This was kneaded and dried using a heating kneader, and then heated and calcined at 500 ° C. for 3 hours to obtain an alumina powder catalyst in which silver was supported at a supported amount of 2.5% by weight.
[0045]
60 g of this alumina powder catalyst and 6 g of silica sol (Snowtex N manufactured by Nissan Chemical Industries, Ltd.) are mixed with an appropriate amount of water, and this is wet crushed with a planetary mill for 5 minutes using 100 g of zirconia balls as a grinding medium, and washed. -A slurry for coating was prepared. This slurry was applied to a cordierite substrate having 200 cells / square inch, and the catalyst was supported at a rate of about 150 g / L. This catalyst is referred to as B-1.
[0046]
Preparation Example 10
Aluminum nitrate (Al (NO 3) 3 · 9H 2 O) 8.69g, silver nitrate 3.94g and hydrated alumina (manufactured by Mizusawa Industrial Chemicals, Ltd.) was admixed with a suitable amount of water 100 g, the paste-like product Prepared. This was kneaded and dried using a heating kneader, and then heated and fired at 800 ° C. for 3 hours in an air atmosphere containing 10% by weight of water, and the aluminum content was 2.5% by weight in terms of silver weight. An alumina powder catalyst with silver acid supported thereon was obtained.
[0047]
60 g of this alumina powder catalyst and 6 g of silica sol (Snowtex N manufactured by Nissan Chemical Industries, Ltd.) are mixed with an appropriate amount of water, and this is wet crushed with a planetary mill for 5 minutes using 100 g of zirconia balls as a grinding medium, and washed. -A slurry for coating was prepared. This slurry was applied to a cordierite substrate having 200 cells / square inch, and the catalyst was supported at a rate of about 150 g / L. This catalyst is referred to as B-2.
[0048]
Examples 1 to 10 (evaluation test)
The first catalyst (A-1 to 8) prepared as described above is used in the first stage, and the second catalyst (B-1 to 2) is used in the second stage. The nitrogen oxide-containing gas was subjected to nitrogen oxide catalytic reduction, and the nitrogen oxide removal rate was determined by the chemical luminescence method. The results are shown in Tables 1 and 2.
[0049]
[0050]
Comparative examples 1 and 2 (evaluation test)
Except that only one of the first catalyst and the second catalyst was used as the catalyst, the nitrogen oxide-containing gas was subjected to nitrogen oxide catalytic reduction in the same manner as in the examples, and the nitrogen oxide removal rate was improved. It calculated | required with the chemical luminescence method. The results are shown in Table 1.
When only the first catalyst is used, the nitrogen oxide removal rate is very low. Even when only the second catalyst is used, the nitrogen oxide removal rate is low in the entire reaction temperature range as compared with the method of the present invention.
[0051]
[Table 1]
[0052]
[Table 2]
[0053]
As is apparent from the results shown in Tables 1 and 2, according to the method of the present invention, compared with the conventional method, the use of a reducing agent for nitrogen oxides even in the presence of oxygen, sulfur oxides and moisture. By reducing the ratio (molar ratio), nitrogen oxides in the exhaust gas can be reduced and removed stably at a high removal rate.
[0054]
【The invention's effect】
As described above, according to the method of the present invention, even in the presence of oxygen, sulfur oxides, and moisture, nitrogen oxides in exhaust gas can be stably and efficiently catalytically reduced without using a large amount of reducing agent. can do.
Claims (4)
Priority Applications (4)
Application Number | Priority Date | Filing Date | Title |
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JP01150897A JP3924341B2 (en) | 1997-01-24 | 1997-01-24 | Method for catalytic reduction of nitrogen oxides |
EP97300816A EP0788829B1 (en) | 1996-02-08 | 1997-02-07 | Catalyst and method for catalytic reduction of nitrogen oxides |
DE69730764T DE69730764T2 (en) | 1996-02-08 | 1997-02-07 | Catalyst and process for the catalytic reduction of nitrogen oxides |
US08/796,884 US6045765A (en) | 1996-02-08 | 1997-02-07 | Catalyst and method for catalytic reduction of nitrogen oxides |
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JP01150897A JP3924341B2 (en) | 1997-01-24 | 1997-01-24 | Method for catalytic reduction of nitrogen oxides |
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JP3924341B2 true JP3924341B2 (en) | 2007-06-06 |
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JP6061406B2 (en) * | 2014-04-03 | 2017-01-18 | 株式会社豊田中央研究所 | PM oxidation catalyst, exhaust gas purification filter and exhaust gas purification method using the same |
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