JP3925015B2

JP3925015B2 - Internal combustion engine exhaust gas purification device, purification method, and purification catalyst

Info

Publication number: JP3925015B2
Application number: JP32364299A
Authority: JP
Inventors: 雅人金枝; 幸二郎奥出; 秀宏飯塚; 更成永山; 寿生山下; 雄一北原; 修黒田
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1999-11-15
Filing date: 1999-11-15
Publication date: 2007-06-06
Anticipated expiration: 2019-11-15
Also published as: JP2001137666A

Description

【０００１】
【発明の属する技術分野】
本発明は、自動車エンジン等の内燃機関から排出される燃焼排ガスなどのように、窒素酸化物（以下、ＮＯｘという）を含有する排ガスからＮＯｘを効率良く浄化する排ガス浄化装置，排ガス浄化触媒及び浄化方法に係わる。
【０００２】
【従来の技術】
近年、自動車用内燃機関において空燃比を燃料希薄とするリーンバーンエンジンが注目されている。しかし、リーンバーンエンジンの排ガスは、Ｏ₂濃度が該排ガスに含まれる還元成分を完全燃焼するのに必要な化学量論比を超える酸化雰囲気（以下、酸化雰囲気）となる。このような酸化雰囲気下においては、従来の三元触媒は充分なＮＯｘ浄化性能を示さない。従って、酸化雰囲気下においてＮＯｘ，ＨＣ及びＣＯの中で特にＮＯｘを効果的に浄化する触媒の開発が望まれている。
【０００３】
リーンバーンエンジン用の排ガス浄化装置として、ＷＯ９３／０７３６３及びＷＯ９３／０８３８３には、排ガス通路に燃料希薄燃焼時に排ガス中のＮＯｘを吸収し、排ガス中の酸素濃度が低下すると吸収したＮＯｘを放出するＮＯｘ吸収剤を設置することが記載されている。
【０００４】
また、特開平10−212933号公報には、排気通路に燃料希薄燃焼時に排ガス中のＮＯｘを化学吸着し燃料過剰燃焼時に吸着したＮＯｘを接触還元するＮＯｘ吸着還元触媒を設置することが示されている。
【０００５】
【発明が解決しようとする課題】
本発明は、希薄燃焼時に排ガス中のＮＯｘを捕捉し、理論空燃比および燃料過剰燃焼時に捕捉したＮＯｘを還元する排ガス浄化触媒を備えた排ガス浄化装置において、該触媒によるＮＯｘ浄化性能を高めることにある。特に５００℃のような高温域を含む広い温度範囲で高いＮＯｘ浄化性能を発現し、また高温８００℃に加熱されたあと或いはＳＯｘによって被毒されたあとでも高いＮＯｘ浄化性能を保有するようにすることにある。
【０００６】
【課題を解決するための手段】
本発明の触媒は、多孔質担体上に触媒活性成分としてＲｈ，Ｐｔ，Ｐｄの少なくとも一種と、アルカリ金属と、ＢとＰから選ばれた少なくとも一種と、Ｍｎ，Ｃｕ，Ｃｏ，Ｎｉ，Ｓｉ及びＴｉから選ばれた少なくとも１種と、を有することを特徴とする。ここで触媒活性成分とは、排ガスを浄化するために作用する成分を意味する。
【０００７】
アルカリ金属は排ガス中のＮＯｘを捕捉する役割を持つ。担体に担持されるアルカリ金属は一種でもよいが、二種以上担持されていると更に活性が向上する。またアルカリ土類金属を加えると、活性が向上する。二種以上を組み合わせることにより触媒に新たな活性点が生じ、ＮＯｘ捕捉能力が高まるためではないかと考える。
【０００８】
アルカリ金属の担持量は多孔質担体１.９mol部に対して金属元素換算で、一種類当り０.０５mol部以上３mol 部以下が好ましい。ここでmol 部とは、各成分のmol数換算での含有比率を表したものであり、例えばＡ成分１.９mol 部に対してＢ成分の担持量が３mol 部ということは、Ａ成分の絶対量の多少に関わらず、mol数換算でＡが１.９に対しＢが３の割合で担持されていることを意味する。アルカリ金属担持量が一種類当り０.０５mol部より少ない場合には、アルカリ金属担持による活性向上効果は必ずしも十分とはなり得ず、一方３mol 部より多いとアルカリ金属の比表面積が低下するようになる。アルカリ金属に加えて更にアルカリ土類金属を担持する場合、アルカリ金属の場合と同様の理由により、その担持量は多孔質担体１.９mol部に対して金属元素換算で、一種類当り０.０５mol部以上３mol 部以下が好ましい。
【０００９】
またＲｈ，Ｐｔ，Ｐｄの少なくとも一種を触媒中に含むことにより、触媒のＮＯｘ浄化性能，耐熱性能，耐ＳＯｘ性能が向上する。担持されるＲｈ，Ｐｔ，Ｐｄは一種でもよいが二種以上担持されていると更に活性が向上する。貴金属同士が相互作用を及ぼしあっているためと考える。
【００１０】
貴金属の担持量は多孔質担体１.９mol部に対して金属元素換算で少なくとも一種を各々、Ｐｔの場合は０.００２mol部以上０.０５mol部以下、Ｒｈの場合は０.０００３mol部以上０.０１mol部以下、Ｐｄの場合は０.００１部以上０.２ mol 部以下とすることが望ましい。貴金属の担持量が上記範囲に示す量より少ないと貴金属添加効果は小さく、上記範囲に示す量より多いと貴金属自身の比表面積が小さくなり、やはり貴金属添加効果が小さくなる。
【００１１】
ＢおよびＰは単体または酸化物の形態、もしくはアルカリ金属，Ａｌから選ばれた少なくとも一種との複合酸化物の形態で存在し、酸化雰囲気下においてNOxを捕捉する働き、及び還元剤であるＣＯ，炭化水素等を触媒表面上に引きつける役割を持つものと考えられ、更に触媒の耐熱性，耐ＳＯｘ性を向上させる働きがある。触媒調製時のＢ又はＰを混ぜる順序、或いは焼成温度等をコントロールすることにより、酸化物の形態や複合酸化物の形態で存在させることができる。
【００１２】
ＢまたはＰ担持量は多孔質担体１.９mol部に対して元素換算で、少なくともどちらか一方を各々０.０１mol部以上２mol 部以下とすることが好ましい。ＢまたはＰ担持量が０.０１mol部より少ないとＢ，Ｐ担持効果は不十分となり、２mol部より多いと触媒の比表面積が低下するため好ましくない。
【００１３】
また多孔質担体は基材上に担持しても良く、その場合基材１Ｌに対し多孔質担体の担持量を０.３mol以上４mol 以下とするとＮＯｘ浄化性能にとって好ましい。多孔質担体担持量が０.３mol部より少ないと多孔質担体担持効果は不十分となり、４mol 部より多いと多孔質担体自体の比表面積が低下するため好ましくない。
【００１４】
上記成分に加えて、希土類金属の少なくとも１種を担持させると、よりＮＯｘ浄化性能及び高温耐久性能が向上する。この場合、多孔質担体１.９mol部に対して金属元素換算で、希土類金属の少なくとも１種を０.０２mol部以上１mol 部以下含むことが好ましい。０.０２mol部より少ないと希土類金属添加効果が不十分であり、１mol 部より多いと触媒の比表面積が低下するため好ましくない。希土類金属としてはＬａ，Ｎｄ，Ｃｅが好ましい。
【００１５】
また、Ｍｎ，Ｃｏ，Ｎｉ，Ｃｕ，Ｔｉ，Ｓｉの少なくとも１種を担持させることにより、ＮＯｘ浄化率が向上し、耐熱性能，耐ＳＯｘ性能も向上する。特にＭｎはアルカリ金属，アルカリ土類金属と相互作用をすることにより耐熱性能が向上し、またＴｉ，Ｓｉはアルカリ金属，アルカリ土類金属と複合化し、耐SOx性能が向上すると考えられる。Ｍｎ，Ｃｏ，Ｎｉ，Ｃｕ，Ｔｉ，Ｓｉの担持量はその少なくとも一種を、多孔質担体１.９mol部に対して元素換算で、０.０１mol部以上２mol部以下の範囲とすることが好ましい。
【００１６】
また、上記触媒のみでも炭化水素およびＣＯの除去性能があるが、その性能が不十分な場合、その触媒の前段または後段または両方に炭化水素およびＣＯの燃焼触媒を設置して内燃機関からの燃焼排ガスを浄化するのも好ましい方法である。
【００１７】
本発明による排ガス浄化触媒の形状は、用途に応じ各種の形状で適用できる。コージェライト，ステンレス等の各種材料からなるハニカム構造体に各種成分を担持した触媒粉末をコーティングして得られるハニカム形状を始めとし、ペレット状，板状，粒状，粉末状等として適用できる。
【００１８】
排ガス浄化触媒の調製方法は、含浸法，混練法，共沈法，ゾルゲル法，イオン交換法，蒸着法等の物理的調製方法や化学反応を利用した調製方法等いずれも適用可能である。
【００１９】
排ガス浄化触媒の出発原料としては、硝酸化合物，酢酸化合物，錯体化合物，水酸化物，炭酸化合物，有機化合物などの種々の化合物や金属及び金属酸化物を用いることができる。
【００２０】
多孔質担体としては、アルミナのほかにチタニア，シリカ，シリカ−アルミナ，ジルコニア，マグネシア等の金属酸化物や複合酸化物等を用いることができる。本発明の触媒は、ハニカム構造等の基体にコーティングして用いることができる。基体はコージェライトが最適であるが、金属製のものを用いても良好な結果を得ることができる。
【００２１】
【発明の実施の形態】
図１は本発明の排ガス浄化装置の一実施態様を示す全体構成図である。
【００２２】
本発明の排ガス浄化装置はリーンバーン可能なエンジン９９，エアフローセンサー２，スロットバルブ３等を擁する吸気系，酸素濃度センサー（orＡ／Ｆセンサー）７，排ガス温度センサー８，触媒出口ガス温度センサー９，排ガス浄化触媒１０等を擁する排気系及び制御ユニット（ＥＣＵ）１１等から構成される。
【００２３】
ＥＣＵは入出力インターフェイスとしてのＩ／Ｏ，ＬＳＩ，演算処理装置ＭＰＵ，多数の制御プログラムを記憶させた記憶装置ＲＡＭ及びＲＯＭ，タイマーカウンター等により構成される。
【００２４】
以上の排気浄化装置は以下のように機能する。エンジンへの吸入空気はエアクリーナー１によりろ過された後エアフローセンサー２により計量され、スロットバルブ３を経て、さらにインジェクター５から燃料噴射を受け混合気としてエンジン９９に供給される。エアフローセンサー信号その他のセンサー信号はＥＣＵ(Engine Control Unit）へ入力される。
【００２５】
ＥＣＵでは内燃機関の運転状態及び排ガス浄化触媒の状態を評価して運転空燃比を決定し、インジェクター５の噴射時間等を制御して混合気の燃料濃度を所定値に設定する。シリンダーに吸入された混合気はＥＣＵ１１からの信号で制御される点火プラグ６により着火され燃焼する。燃焼排ガスは排気浄化系に導かれる。排気浄化系には排ガス浄化触媒１０が設けられ、ストイキ運転時にはその三元触媒機能により排ガス中のＮＯｘ，ＨＣ，ＣＯを浄化し、また、リーン運転時にはＮＯｘ捕捉能によりＮＯｘを浄化すると同時に併せ持つ燃焼機能により、ＨＣ，ＣＯを浄化する。さらにＥＣＵの判定及び制御信号により、リーン運転時には排ガス浄化触媒のＮＯｘ浄化能力を常時判定して、ＮＯｘ浄化能力が低下した場合燃焼の空燃比等をリッチ側にシフトして触媒のＮＯｘ捕捉能を回復させる。以上の操作により本装置ではリーン運転，ストイキ（含むリッチ）運転の全てのエンジン燃焼条件下における排ガスを効果的に浄化する。
【００２６】
以下、具体的な例で本発明を説明するが、本発明はこれらの実施例により制限されるものではない。
【００２７】
「参考例１」
アルミナ粉末とアルミナの前駆体からなり硝酸酸性に調製したスラリーをコージェライト製ハニカム（４００セル／ｉｎｃ２）にコーティングした後、乾燥焼成して、ハニカムの見掛けの容積１リットルあたり１.９molのアルミナをコーティングしたアルミナコートハニカムを得た。該アルミナコートハニカムに、ジニトロジアンミンＰｔ硝酸溶液と硝酸Ｒｈ溶液の混合溶液を含浸した後、２００℃で乾燥、続いて６００℃で焼成した。次に、硝酸Ｎａ溶液にＨ₃ＢＯ₃を溶かした溶液、または硝酸Ｎａ溶液とリン酸溶液の混合溶液をそれぞれ該Ｐｔ，Ｒｈ担持ハニカムに含浸し、２００℃で乾燥、続いて６００℃で焼成した。以上により、アルミナ１.９molに対して、元素換算でＲｈ０.００２２mol，Ｐｔ０.０１４mol，Ｎａ０.８mol，Ｂ０.１molを含有する参考触媒１、及びアルミナ１.９molに対して、元素換算でＲｈ０.００２２mol，Ｐｔ０.０１４mol，Ｎａ０.８mol，Ｐ０.１mol を含有する参考触媒２を得た。以下この触媒をそれぞれ０.８Ｎａ０.１Ｂ−ＲｈＰｔ／Ａｌ₂Ｏ₃及び０.８Ｎａ０.１Ｐ−ＲｈＰｔ／Ａｌ₂Ｏ₃のように表記する。他の触媒についても同様の表記とする。
【００２８】
同様にして、Ｂ，Ｐ，Ｒｈ，Ｐｔ，Ａｌ₂Ｏ₃の担持量は変えず、Ｎａの代りにＬｉ，Ｋ，Ｒｂ，Ｃｓをそれぞれ０.８mol担持した参考触媒３〜１０、またＢ，Ｐ，Ｒｈ，Ｐｔ，Ａｌ₂Ｏ₃の担持量は変えず、ＢまたはＰの少なくとも１種と、アルカリ金属，アルカリ土類金属を２種以上含む参考触媒１１〜２２，Ｂ，Ｐ，Ｒｈ，Ａｌ₂Ｏ₃の担持量は変えず、ＢまたはＰの少なくとも１つと、アルカリ金属の少なくとも１つとアルカリ土類金属を含む参考触媒２３〜４１を得た。更に参考触媒１と同様にして、Ｂ及びＰを含まず、アルミナ１.９molに対して、金属換算でＲｈ０.００２２mol，Ｐｔ０.０１４mol、及び０.８molのＮａ，Ｌｉ，Ｋ，Ｒｂ，Ｃｓ，Ｍｇ，Ｃａ，Ｓｒ，Ｂａを担持した比較例触媒１〜９，Ｂ，Ｐを含まず、Ｒｈ，Ｐｔ，Ａｌ₂Ｏ₃の担持量は変えず、アルカリ金属，アルカリ土類金属の少なくとも１つを含む比較例触媒１０〜２４を得た。
【００２９】
［試験例１］
（試験方法）
上記触媒に対して、次の条件でＮＯｘ浄化性能試験を行った。容量６ｃ.ｃ.のハニカム触媒を石英ガラス製反応管中に固定した。この反応管を電気炉中に導入し、反応管に導入されるガス温度が３００℃，４００℃，５００℃となるように加熱制御した。反応管に導入されるガスは、自動車のエンジンが理論空燃比で運転されているときの排ガスを想定したモデルガス（以下ストイキモデルガス）と、自動車のエンジンがリーンバーン運転を行っているときの排ガスを想定したモデルガス（以下、リーンモデルガス）を３分毎に切り替えて導入した。ストイキモデルガスの組成は、ＮＯｘ：１０００ppm，Ｃ₃Ｈ₆：６００ppm,ＣＯ：０.５％，ＣＯ₂：５％，Ｏ₂：０.５％，Ｈ₂：０.３％，Ｈ₂Ｏ：１０％，Ｎ₂：残部とした。リーンモデルガスの組成は、ＮＯｘ：６００ppm，Ｃ₃Ｈ₆：５００ppm, ＣＯ：０.１％，ＣＯ₂：１０％，Ｏ₂：５％，Ｈ₂Ｏ：１０％，Ｎ₂：残部とした。この時、触媒出入口の総ＮＯｘ量を測定し、ＮＯｘ浄化率を次式により算出した。
【００３０】
ＮＯｘ浄化率(％)＝((リーンに切り替え後４分間に触媒に流入した総ＮＯｘ量)−(リーンに切り替え後４分間に触媒から流出した総ＮＯｘ量))÷（リーンに切り替え後４分間に触媒に流入した総ＮＯｘ量）×１００
以上のようにＮＯｘ浄化率を求める試験を試験例１とする。
【００３１】
（試験結果）
参考触媒１〜４１，比較例触媒１〜２４を、試験例１により評価した結果を表１に示す。なお、ストイキ燃焼運転時のＮＯｘ浄化率は３００℃で常に９０％以上、４００℃では１００％であり、三元性能も十分に具備している。参考触媒の性能はリーン燃焼運転とストイキ燃焼運転を複数回繰り返しても各運転中のＮＯｘ浄化率は不変であった。また、リーン燃焼運転においてＨＣ及びＣＯ浄化率は９０％以上であった。Ｒｈ，Ｐｔ，Ｐｄの少なくとも１種と、アルカリ金属と、ＢまたはＰから選ばれる少なくとも１種を有する参考触媒は、高温領域である５００℃を含め全測定温度範囲において比較例触媒よりも明らかにＮＯｘ浄化率が高い。
【００３２】
【表１（１）】

【００３３】
【表１（２）】

【００３４】
【表１（３）】

【００３５】
「参考例２」
参考例１と同様の方法で、アルミナ１.９molに対して元素換算で０.８molのＮａ，Ｌｉ，Ｋ及び０.１molのＢ及びＰｔ０.０１４mol，Ｐｄ０.０１４molを担持した参考触媒４２〜４４、またアルミナ１.９molに対して元素換算で０.８molのＮａ，Ｌｉ，Ｋ及び０.１molのＰ及びＰｔ０.０１４mol，Ｐｄ０.０１４molを担持した参考触媒４５〜４７を得た。
【００３６】
同様に０.１molのＢ，０.８molのＮａ，Ｌｉ，Ｋ及びＲｈ０.００２２mol，Ｐｄ0.014mol を担持した参考触媒４８〜５０、また０.１molのＰ，０.８molのＮａ，Ｌｉ，Ｋ及びＲｈ０.００２２mol，Ｐｄ０.０１４mol を担持した参考触媒５１〜５３を得た。
【００３７】
同様に参考触媒２０，２１にそれぞれＰｄ０.０１４molを担持した参考触媒５４，５５を得た。
【００３８】
同様に０.８molのＮａ，Ｌｉ，Ｋ及びＰｔ０.０１４mol，Ｐｄ０.０１４molを担持した比較例触媒２５〜２７、また０.８molのＮａ，Ｌｉ，Ｋ及びＲｈ0.0022mol，Ｐｄ０.０１４molを担持した比較例触媒２８〜３０を得た。
【００３９】
［試験例２］
（試験方法）
参考触媒１，６，９，１２，１６，１９，２０，２１，４０，４２〜５５，比較例触媒１〜５，２１，２４〜３０を８００℃で５ｈ焼成し、その後は試験例１の方法で試験を行った。
【００４０】
（試験結果）
参考触媒１，６，９，１２，１６，１９，２０，２１，４０，４２〜５５，比較例触媒１〜５，２１，２４〜３０を、試験例２により評価した結果を表２に示す。アルカリ金属を含む触媒について、Ｂ及びＰから選ばれた少なくとも一種及びＲｈ，Ｐｔ，Ｐｄから選ばれた少なくとも一種を含む参考触媒の方が、高温領域である５００℃を含め全測定温度範囲において比較例触媒よりも明らかにＮＯｘ浄化率が高く、耐熱性能に優れている。
【００４１】
【表２（１）】

【００４２】
【表２（２）】

【００４３】
「実施例３」
参考例１と同様の方法で、参考触媒５４，５５にそれぞれＭｎ，Ｃｏ，Ｎｉ，Ｃｕを添加した触媒、実施例触媒５６〜６３を調製した。試験例２で各触媒の評価を行った。Ｍｎ，Ｃｏ，Ｎｉ，Ｃｕの担持量はアルミナ１.９molに対し金属元素換算で０.２molとした。
【００４４】
（試験結果）
実施例触媒５６〜６３を試験例２により評価した結果を表３に示す。表２に示した比較例触媒１〜５，２１，２４〜３０に対し、Ｍｎ，Ｃｏ，Ｎｉ，Ｃｕを添加した実施例触媒の活性は高く、耐熱性能に優れている。
【００４５】
【表３】

【００４６】
「実施例４」
参考例１と同様の方法で実施例触媒５６，６０にそれぞれＴｉ，Ｓｉを含む実施例触媒６４〜６７を調製した。Ｔｉ，Ｓｉの担持量はアルミナ１.９molに対し元素換算で０.１molとした。
【００４７】
［試験例３］
（試験方法）
試験例１において、反応管中にＳＯ₂添加リーンガスのみを１.５ｈ流通させた。リーンガスへのＳＯ₂添加量は０.０１％とした。この後、試験例１の方法でＮＯｘ浄化率を測定した。
【００４８】
（試験結果）
実施例触媒６４〜６７，比較例触媒１，２１を、試験例３により評価した結果を表４に示す。実施例触媒６４〜６７は、比較例触媒１，２１よりもＮＯｘ浄化率が高く、耐ＳＯｘ性能に優れている。
【００４９】
【表４】

【００５０】
「実施例５」
参考例１と同様の方法で実施例触媒６４，６６にそれぞれＣｅ，Ｌａ，Ｎｄをアルミナ１.９molに対し金属元素換算で０.２mol添加した実施例触媒６８〜７３を調製した。試験は試験例２と同様とした。
【００５１】
（試験結果）
試験例２により評価したＮＯｘ浄化率を表５に示す。実施例触媒６８〜７３は表２に示した比較例触媒１〜５，２１，２４〜３０よりも明らかにＮＯｘ浄化率が高く、耐熱性能に優れている。
【００５２】
【表５】

【００５３】
「実施例６」
参考例１と同様の方法で、実施例触媒６８，７１についてＢまたはＰ含有量を変化させた触媒を調製した。試験は試験例１と同様とした。
【００５４】
（試験結果）
実施例触媒６８，７１についてＢまたはＰ含有量を変化させた触媒を、試験例１により評価したときの４００℃でのＮＯｘ浄化率を表６に示す。上記触媒はＢまたはＰの担持量が各々元素換算で０.０１mol〜２mol のときＮＯｘ浄化率が８０％を超え、高いＮＯｘ浄化率を示す。
【００５５】
【表６】

【００５６】
「実施例７」
参考例１と同様の方法で実施例触媒６８，７１について、それぞれＮａ，Ｌｉ，Ｋ含有量を変化させた触媒を調製した。試験は試験例１と同様とした。
【００５７】
（試験結果）
試験例１により評価した４００℃でのＮＯｘ浄化率の結果を表７に示す。それぞれの触媒においてＮａ，Ｌｉ，Ｋの担持量が各々０.０５mol以上３mol 以下のとき４００℃のＮＯｘ浄化率が８０％を超え、高いＮＯｘ浄化率を示す。
【００５８】
【表７】

【００５９】
「実施例８」
参考例１と同様の方法で実施例６８，７１のＲｈ，Ｐｔ，Ｐｄ含有量を変化させた触媒を調製した。試験は試験例１と同様とした。
【００６０】
（試験結果）
試験例１により評価した４００℃でのＮＯｘ浄化率を表８に示す。Ｒｈ，Ｐｔ，Ｐｄの担持量が金属換算でそれぞれ、Ｐｔの場合０.００２mol以上０.０５mol以下，Ｒｈの場合０.０００３mol以上０.０１mol以下，Ｐｄの場合０.００１mol以上０.２mol以下のとき４００℃のＮＯｘ浄化率が８０％を超え、高いＮＯｘ浄化率が得られる。
【００６１】
【表８】

【００６２】

【００６３】

【００６４】
「実施例９」
参考例１と同様の方法で実施例触媒６８〜７３のＣｅ，Ｌａ，Ｎｄ添加量を変化させた触媒を調製した。試験は試験例２と同様とした。
【００６５】
（試験結果）
試験例２により評価した４００℃でのＮＯｘ浄化率を表９に示す。Ｃｅ，Ｌａ，Ｎｄの担持量が金属換算で０.０２mol以上１mol 以下のとき８００℃，５ｈ耐熱後の４００℃のＮＯｘ浄化率が８０％を超え、高いＮＯｘ浄化率が得られる。
【００６６】
【表９】

【００６７】
「実施例１０」
参考例１と同様の方法で実施例触媒５６〜６３のＭｎ，Ｃｏ，Ｎｉ，Ｃｕ添加量を変化させた触媒を調製した。試験は試験例２と同様とした。
【００６８】
（試験結果）
試験例２により評価した４００℃でのＮＯｘ浄化率を表１０に示す。Ｍｎ，Ｃｏ，Ｎｉ，Ｃｕの担持量が金属換算で０.０１mol以上２mol 以下のとき８００℃，５ｈ耐熱後の４００℃のＮＯｘ浄化率が８０％を超え、高いＮＯｘ浄化率が得られる。
【００６９】
【表１０】

【００７０】
「実施例１１」
参考例１と同様の方法で実施例触媒６４，６６に関してはＴｉ添加量を、実施例触媒６５，６７に関してはＳｉ添加量を変化させた触媒を調製した。
【００７１】
（試験結果）
試験例３により評価した４００℃でのＮＯｘ浄化率を表１１に示す。Ｔｉ，Ｓｉの担持量が元素換算で０.０１mol以上２mol 以下のときＳＯｘ被毒後の400℃のＮＯｘ浄化率が５０％を超え、高いＮＯｘ浄化率が得られる。
【００７２】
【表１１】

【００７３】
「実施例１２」
参考例１と同様の方法で実施例触媒６４，６６においてＡｌ₂Ｏ₃コーティング量を変化させた触媒を調製した。
【００７４】
（試験結果）
試験例１により評価した４００℃でのＮＯｘ浄化率を表１２に示す。例えば、Ａｌ₂Ｏ₃コーティング量がＡｌ₂Ｏ₃換算でハニカム容積１Ｌに対して０.１molの場合、ＮａＬｉＫＰｄＢＭｎＴｉ−ＲｈＰｔ／０.１Ａｌ₂Ｏ₃と表記した。
【００７５】
Ａｌ₂Ｏ₃コーティング量がＡｌ₂Ｏ₃換算でハニカム容積１Ｌに対して０.３mol以上４ mol以下のとき４００℃のＮＯｘ浄化率が８０％を超え、高いＮＯｘ浄化率が得られる。
【００７６】
【表１２】

【００７７】
「実施例１３」
炭化水素およびＣＯの燃焼触媒として、参考例１と同様の方法でＲｈ，Ｐｔのみを担持した触媒を調製した。Ｒｈ，Ｐｔの含有量は金属換算でアルミナ１.９molに対して、Ｒｈ０.００２mol，Ｐｔ０.０１molとした。試験は試験例１と同様とし、実施例触媒６４，６６について、その前段または後段に該炭化水素およびＣＯの燃焼触媒を設置した場合、また全く該炭化水素およびＣＯの燃焼触媒を設置しない場合についてその炭化水素及びＣＯ除去率を測定した。
【００７８】
なお、Ｃ₃Ｈ₆浄化率及びＣＯ浄化率はそれぞれ次式により算出した。
【００７９】
Ｃ₃Ｈ₆浄化率(％)＝((リーンに切り替え後４分間に触媒に流入した総Ｃ₃Ｈ₆ 量)−(リーンに切り替え後４分間に触媒から流出した総Ｃ₃Ｈ₆量))÷（リーンに切り替え後４分間に触媒に流入した総Ｃ₃Ｈ₆量）×１００
ＣＯ浄化率(％)＝((リーンに切り替え後４分間に触媒に流入した総ＣＯ量) −(リーンに切り替え後４分間に触媒から流出した総ＣＯ量))÷(リーンに切り替え後４分間に触媒に流入した総ＣＯ量）×１００
測定温度は４００℃とした。
【００８０】
（試験結果）
試験例１と同様の方法により評価した４００℃でのＣ₃Ｈ₆浄化率，ＣＯ浄化率を表１３に示す。実施例触媒６４，６６の前段または後段に炭化水素およびＣＯの燃焼触媒を設置すると炭化水素，ＣＯ除去性能が向上する。
【００８１】
【表１３】

【００８２】
【発明の効果】
本発明によれば、酸素が過剰に存在する雰囲気下においても有害物質、特に窒素酸化物を高効率で浄化することができ、さらに耐熱性能，耐ＳＯｘ性能にも優れているため、高い浄化性能を長期間維持することができる。
【図面の簡単な説明】
【図１】本発明の排ガス浄化装置の一実施態様を示す構成図である。
【符号の説明】
１…エアクリーナー、２…エアフローセンサー、３…スロットバルブ、５…インジェクター、６…点火プラグ、７…酸素濃度センサー(またはＡ／Ｆセンサー)、８…排ガス温度センサー、９…触媒出口ガス温度センサー、１０…排ガス浄化触媒、１１…ＥＣＵ、９９…エンジン。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification apparatus, an exhaust gas purification catalyst, and purification that efficiently purify NOx from exhaust gas containing nitrogen oxides (hereinafter referred to as NOx), such as combustion exhaust gas discharged from an internal combustion engine such as an automobile engine. Related to the method.
[0002]
[Prior art]
2. Description of the Related Art In recent years, a lean burn engine in which an air-fuel ratio is lean in an automobile internal combustion engine has attracted attention. However, the exhaust gas of the lean burn engine becomes an oxidizing atmosphere (hereinafter referred to as an oxidizing atmosphere) in which the O ₂ concentration exceeds the stoichiometric ratio necessary for complete combustion of the reducing component contained in the exhaust gas. Under such an oxidizing atmosphere, the conventional three-way catalyst does not exhibit sufficient NOx purification performance. Therefore, development of a catalyst that effectively purifies NOx in NOx, HC and CO under an oxidizing atmosphere is desired.
[0003]
As exhaust gas purification devices for lean burn engines, WO93 / 07363 and WO93 / 08383 absorb NOx in exhaust gas during lean fuel combustion in the exhaust gas passage, and release the absorbed NOx when the oxygen concentration in the exhaust gas decreases. The installation of an absorbent is described.
[0004]
Japanese Laid-Open Patent Publication No. 10-212933 discloses that an NOx adsorption reduction catalyst that chemically adsorbs NOx in exhaust gas during lean fuel combustion and catalytically reduces NOx adsorbed during excessive fuel combustion is installed in the exhaust passage. Yes.
[0005]
[Problems to be solved by the invention]
The present invention is to improve NOx purification performance of an exhaust gas purification apparatus equipped with an exhaust gas purification catalyst that captures NOx in exhaust gas during lean combustion and reduces NOx captured during stoichiometric air-fuel ratio and excessive fuel combustion. is there. In particular, a high NOx purification performance is exhibited in a wide temperature range including a high temperature region such as 500 ° C., and a high NOx purification performance is maintained even after being heated to a high temperature of 800 ° C. or poisoned by SOx. There is.
[0006]
[Means for Solving the Problems]
The catalyst of the present invention comprises at least one of Rh, Pt, Pd as a catalytically active component on a porous carrier, an alkali metal, at least one selected from B and P , Mn, Cu, Co, Ni, Si, and And at least one selected from Ti . Here, the catalytically active component means a component that acts to purify the exhaust gas.
[0007]
The alkali metal has a role of capturing NOx in the exhaust gas. The alkali metal supported on the carrier may be one kind, but the activity is further improved when two or more kinds are supported. In addition, the activity is improved by adding an alkaline earth metal. It is thought that combining two or more types may cause a new active point in the catalyst and increase the NOx trapping ability.
[0008]
The supported amount of alkali metal is preferably 0.05 mol part or more and 3 mol part or less per one kind in terms of metal element with respect to 1.9 mol part of the porous carrier. Here, the mol part represents the content ratio of each component in terms of the number of moles. For example, the loading amount of B component relative to 1.9 mol part of A component is 3 mol parts. It means that A is 1.9 and B is supported in a ratio of 3 in terms of mol, regardless of the amount. When the amount of alkali metal supported is less than 0.05 mol part per type, the activity improvement effect by alkali metal support cannot necessarily be sufficient, while when it exceeds 3 mol part, the specific surface area of alkali metal is lowered. Become. When an alkaline earth metal is further supported in addition to the alkali metal, the supported amount is 0.05 mol per kind in terms of metal element with respect to 1.9 mol parts of the porous carrier for the same reason as in the case of the alkali metal. The amount is preferably from 3 parts to 3 mol.
[0009]
Further, by containing at least one of Rh, Pt, and Pd in the catalyst, the NOx purification performance, heat resistance performance, and SOx resistance performance of the catalyst are improved. The supported Rh, Pt, and Pd may be one kind, but if two or more kinds are supported, the activity is further improved. This is because noble metals interact with each other.
[0010]
The amount of noble metal supported is at least one metal element equivalent in terms of 1.9 mol parts of the porous carrier, 0.002 mol parts to 0.05 mol parts in the case of Pt, and 0.0003 mol parts to 0.003 mol parts in the case of Rh. In the case of Pd, the content is preferably 0.001 part or more and 0.2 mol part or less. When the amount of the noble metal supported is less than the amount shown in the above range, the effect of adding the noble metal is small.
[0011]
B and P are present in the form of a simple substance or an oxide, or in the form of a complex oxide with at least one selected from alkali metals and Al, function to trap NOx in an oxidizing atmosphere, and CO, which is a reducing agent, It is considered to have a role of attracting hydrocarbons and the like on the catalyst surface, and further has a function of improving the heat resistance and SOx resistance of the catalyst. By controlling the order of mixing B or P at the time of catalyst preparation, or the calcination temperature, it can be present in the form of an oxide or complex oxide.
[0012]
The amount of B or P supported is preferably 0.01 mol part or more and 2 mol part or less for at least one of them in terms of element with respect to 1.9 mol part of the porous carrier. If the amount of B or P supported is less than 0.01 mol part, the effect of supporting B or P is insufficient, and if it exceeds 2 mol part, the specific surface area of the catalyst decreases, which is not preferable.
[0013]
Further, the porous carrier may be supported on a base material. In that case, it is preferable for NOx purification performance that the amount of the porous carrier supported is 0.3 mol or more and 4 mol or less with respect to 1 L of the base material. When the amount of the porous carrier supported is less than 0.3 mol part, the effect of supporting the porous carrier is insufficient, and when it exceeds 4 mol part, the specific surface area of the porous carrier itself is lowered, which is not preferable.
[0014]
In addition to the above components, when at least one rare earth metal is supported, the NOx purification performance and the high temperature durability performance are further improved. In this case, it is preferable to contain 0.02 mol part or more and 1 mol part or less of at least one rare earth metal in terms of metal element with respect to 1.9 mol part of the porous carrier. If the amount is less than 0.02 mol part, the effect of rare earth metal addition is insufficient, and if it exceeds 1 mol part, the specific surface area of the catalyst is lowered, which is not preferable. As the rare earth metal, La, Nd, and Ce are preferable.
[0015]
Further, by supporting at least one of Mn, Co, Ni, Cu, Ti, and Si, the NOx purification rate is improved, and the heat resistance performance and SOx resistance performance are also improved. In particular, Mn is considered to improve heat resistance by interacting with alkali metal and alkaline earth metal, and Ti and Si are combined with alkali metal and alkaline earth metal to improve SOx resistance. It is preferable that at least one of the supported amounts of Mn, Co, Ni, Cu, Ti, Si is in the range of 0.01 mol part or more and 2 mol part or less in terms of element with respect to 1.9 mol part of the porous carrier.
[0016]
In addition, the above catalyst alone has hydrocarbon and CO removal performance, but if the performance is insufficient, a combustion catalyst of hydrocarbon and CO is installed in the front stage, the rear stage or both of the catalyst, and combustion from the internal combustion engine is performed. It is also a preferable method to purify the exhaust gas.
[0017]
The shape of the exhaust gas purifying catalyst according to the present invention can be applied in various shapes depending on applications. The present invention can be applied to a honeycomb structure obtained by coating a honeycomb structure made of various materials such as cordierite and stainless steel with a catalyst powder carrying various components, as well as pellets, plates, granules, and powders.
[0018]
As the method for preparing the exhaust gas purification catalyst, any of a physical preparation method such as an impregnation method, a kneading method, a coprecipitation method, a sol-gel method, an ion exchange method, and a vapor deposition method and a preparation method using a chemical reaction can be applied.
[0019]
As starting materials for the exhaust gas purification catalyst, various compounds such as nitric acid compounds, acetic acid compounds, complex compounds, hydroxides, carbonic acid compounds, organic compounds, metals, and metal oxides can be used.
[0020]
As the porous carrier, in addition to alumina, metal oxides such as titania, silica, silica-alumina, zirconia, and magnesia, composite oxides, and the like can be used. The catalyst of the present invention can be used by coating on a substrate such as a honeycomb structure. Cordierite is optimal for the substrate, but good results can be obtained even if a metal substrate is used.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is an overall configuration diagram showing an embodiment of an exhaust gas purification apparatus of the present invention.
[0022]
The exhaust gas purifying apparatus of the present invention comprises a lean burnable engine 99, an air flow sensor 2, an intake system having a slot valve 3, etc., an oxygen concentration sensor (or A / F sensor) 7, an exhaust gas temperature sensor 8, a catalyst outlet gas temperature sensor 9, The exhaust system includes an exhaust gas purification catalyst 10 and the like, and a control unit (ECU) 11 and the like.
[0023]
The ECU includes an I / O as an input / output interface, an LSI, an arithmetic processing unit MPU, a storage device RAM and ROM storing a number of control programs, a timer counter, and the like.
[0024]
The above exhaust purification device functions as follows. The intake air to the engine is filtered by the air cleaner 1 and then measured by the air flow sensor 2. The fuel is injected from the injector 5 through the slot valve 3 and supplied to the engine 99 as an air-fuel mixture. The airflow sensor signal and other sensor signals are input to an ECU (Engine Control Unit).
[0025]
The ECU evaluates the operating state of the internal combustion engine and the state of the exhaust gas purification catalyst to determine the operating air-fuel ratio, and controls the injection time of the injector 5 to set the fuel concentration of the air-fuel mixture to a predetermined value. The air-fuel mixture sucked into the cylinder is ignited and burned by a spark plug 6 controlled by a signal from the ECU 11. The combustion exhaust gas is led to an exhaust purification system. An exhaust gas purification catalyst 10 is provided in the exhaust gas purification system. During stoichiometric operation, the three-way catalyst function purifies NOx, HC, CO in the exhaust gas, and during lean operation, NOx is purified by NOx trapping capability and combustion is combined with it. Purifies HC and CO by function. Further, the ECU's determination and control signals always determine the NOx purification capacity of the exhaust gas purification catalyst during lean operation, and if the NOx purification capacity decreases, the combustion air / fuel ratio, etc. is shifted to the rich side to increase the NOx trapping capacity of the catalyst. Let me recover. With the above operation, the present apparatus effectively purifies exhaust gas under all engine combustion conditions of lean operation and stoichiometric (including rich) operation.
[0026]
EXAMPLES Hereinafter, although this invention is demonstrated with a specific example, this invention is not restrict | limited by these Examples.
[0027]
"Reference Example 1"
A cordierite honeycomb (400 cells / inc2) is coated with a slurry made of alumina powder and an alumina precursor and prepared to be nitric acid, and then dried and fired to obtain 1.9 mol of alumina per liter of apparent volume of the honeycomb. A coated alumina coated honeycomb was obtained. The alumina-coated honeycomb was impregnated with a mixed solution of a dinitrodiammine Pt nitric acid solution and a nitric acid Rh solution, dried at 200 ° C., and then fired at 600 ° C. Next, the Pt / Rh supporting honeycomb is impregnated with a solution of H ₃ BO ₃ dissolved in a sodium nitrate solution or a mixed solution of sodium nitrate solution and phosphoric acid solution, dried at 200 ° C., and then fired at 600 ° C. did. From the above, with respect to 1.9 mol of alumina, the reference catalyst 1 containing Rh 0.0022 mol, Pt 0.014 mol, Na 0.8 mol, and B 0.1 mol in terms of element and 1.9 mol of alumina in terms of element Rh Reference catalyst 2 containing 0022 mol, Pt 0.014 mol, Na 0.8 mol, P 0.1 mol was obtained. Hereinafter referred to as the catalyst, respectively 0.8Na0.1B-RhPt / Al ₂ O ₃ and _{_{0.8Na0.1P-RhPt / Al 2 O 3}} . The same notation is used for other catalysts.
[0028]
Similarly, the supported amounts of B, P, Rh, Pt, and Al ₂ O ₃ were not changed, and reference catalysts 3 to 10 each supporting 0.8 mol of Li, K, Rb, and Cs instead of Na, and B, The supported amounts of P, Rh, Pt, and Al ₂ O ₃ are not changed, and the reference catalysts 11 to 22 , B, P, Rh, and B containing at least one of B or P and two or more of alkali metals and alkaline earth metals are used. The supported amount of Al ₂ O ₃ was not changed, and reference catalysts 23 to 41 containing at least one of B or P, at least one alkali metal, and alkaline earth metal were obtained. Further, in the same manner as in Reference Catalyst 1 , B and P are not contained, and 1.9 mol of alumina is Rh 0.0022 mol, Pt 0.014 mol, and 0.8 mol Na, Li, K, Rb, Cs, Comparative catalysts 1-9, Mg, Ca, Sr, and Ba supported, Mg, Ca, Sr, Ba are not included, Rh, Pt, Al ₂ O ₃ loading is not changed, and at least one of alkali metals and alkaline earth metals Comparative Examples 10-24 containing
[0029]
[Test Example 1]
(Test method)
A NOx purification performance test was performed on the catalyst under the following conditions. A honeycomb catalyst having a capacity of 6 cc was fixed in a reaction tube made of quartz glass. This reaction tube was introduced into an electric furnace, and the temperature of the gas introduced into the reaction tube was controlled to be 300 ° C, 400 ° C, and 500 ° C. The gas introduced into the reaction tube is model gas (hereinafter referred to as stoichiometric model gas) that assumes exhaust gas when the automobile engine is operated at the stoichiometric air-fuel ratio, and when the automobile engine is performing lean burn operation. Model gas assuming exhaust gas (hereinafter referred to as lean model gas) was introduced by switching every 3 minutes. The composition of the stoichiometric model gas is NOx: 1000 ppm, C ₃ H ₆ : 600 ppm, CO: 0.5%, CO ₂ : 5%, O ₂ : 0.5%, H ₂ : 0.3%, H ₂ O : 10%, N ₂ : The balance. The composition of the lean model gas was NOx: 600 ppm, C ₃ H ₆ : 500 ppm, CO: 0.1%, CO ₂ : 10%, O ₂ : 5%, H ₂ O: 10%, N ₂ : balance . At this time, the total NOx amount at the catalyst inlet / outlet was measured, and the NOx purification rate was calculated by the following equation.
[0030]
NOx purification rate (%) = ((total NOx amount flowing into the catalyst in 4 minutes after switching to lean) − (total NOx amount flowing out of the catalyst in 4 minutes after switching to lean)) ÷ (4 minutes after switching to lean) Total NOx amount flowing into the catalyst) x 100
The test for obtaining the NOx purification rate as described above is referred to as Test Example 1.
[0031]
(Test results)
Table 1 shows the results of evaluation of Reference Catalysts 1 to 41 and Comparative Catalysts 1 to 24 in Test Example 1. Note that the NOx purification rate during stoichiometric combustion operation is always 90% or more at 300 ° C. and 100% at 400 ° C., and the three-way performance is sufficiently provided. Regarding the performance of the reference catalyst , the NOx purification rate during each operation was unchanged even when the lean combustion operation and the stoichiometric combustion operation were repeated a plurality of times. In the lean combustion operation, the HC and CO purification rates were 90% or more. The reference catalyst having at least one selected from Rh, Pt, and Pd, an alkali metal, and B or P is clearly more than the comparative example catalyst in the entire measured temperature range including 500 ° C. that is a high temperature range. NOx purification rate is high.
[0032]
[Table 1 (1)]

[0033]
[Table 1 (2)]

[0034]
[Table 1 (3)]

[0035]
"Reference Example 2"
In the same manner as in Reference Example 1, reference catalysts 42 to 44 supporting 0.8 mol of Na, Li, K and 0.1 mol of B, Pt 0.014 mol, and Pd 0.014 mol in terms of element with respect to 1.9 mol of alumina. Reference catalysts 45 to 47 carrying 0.8 mol of Na, Li, K, 0.1 mol of P, 0.014 mol of Pt, and 0.014 mol of Pd in terms of element with respect to 1.9 mol of alumina were obtained.
[0036]
Similarly, 48 to 50 of the reference catalyst carrying 0.1 mol of B, 0.8 mol of Na, Li, K and Rh of 0.0022 mol and Pd of 0.014 mol, 0.1 mol of P, 0.8 mol of Na, Li and K And Reference Catalysts 51 to 53 carrying Rh 0.0022 mol and Pd 0.014 mol were obtained.
[0037]
Afforded Reference catalyst 54 and 55 carrying the Pd0.014mol each Likewise reference catalysts 20,21.
[0038]
Similarly, Comparative Catalysts 25-27 carrying 0.8 mol of Na, Li, K and Pt 0.014 mol, Pd 0.014 mol, and 0.8 mol of Na, Li, K and Rh 0.0022 mol, Pd 0.014 mol were carried. Comparative catalyst 28-30 was obtained.
[0039]
[Test Example 2]
(Test method)

Reference catalysts

1, 6, 9, 12, 16, 19, 20, 21, 40, 42 to 55, and comparative example catalysts 1 to 5, 21, and 24 to 30 were calcined at 800 ° C. for 5 hours. The method was tested.
[0040]
(Test results)
Table 2 shows the results of evaluation of

Reference Catalysts

1, 6, 9, 12, 16, 19, 20, 21, 40, 42 to 55 and Comparative Catalysts 1 to 5, 21, and 24 to 30 according to Test Example 2. . For a catalyst containing an alkali metal, a reference catalyst containing at least one selected from B and P and at least one selected from Rh, Pt, Pd is compared in the entire measurement temperature range including 500 ° C. which is a high temperature region. The NOx purification rate is clearly higher than that of the example catalyst, and the heat resistance is excellent.
[0041]
[Table 2 (1)]

[0042]
[Table 2 (2)]

[0043]
"Example 3"
In the same manner as in Reference Example 1 , catalysts obtained by adding Mn, Co, Ni, and Cu to Reference Catalysts 54 and 55, and Example Catalysts 56 to 63 were prepared. In Test Example 2, each catalyst was evaluated. The supported amount of Mn, Co, Ni, and Cu was 0.2 mol in terms of metal element with respect to 1.9 mol of alumina.
[0044]
(Test results)
Table 3 shows the results of evaluation of Example Catalysts 56 to 63 in Test Example 2. The comparative example catalysts 1 to 5, 21, and 24 to 30 shown in Table 2 have high activity and excellent heat resistance performance of the example catalysts to which Mn, Co, Ni, and Cu are added.
[0045]
[Table 3]

[0046]
Example 4
In the same manner as in Reference Example 1 , Example catalysts 64 to 67 containing Ti and Si in Example catalysts 56 and 60 were prepared. The supported amount of Ti and Si was 0.1 mol in terms of element with respect to 1.9 mol of alumina.
[0047]
[Test Example 3]
(Test method)
In Test Example 1, only the lean gas containing SO _{2 was} passed through the reaction tube for 1.5 hours. The amount of SO ₂ added to the lean gas was 0.01%. Thereafter, the NOx purification rate was measured by the method of Test Example 1.
[0048]
(Test results)
Table 4 shows the results of evaluation of Example Catalysts 64 to 67 and Comparative Example Catalysts 1 and 21, according to Test Example 3. The example catalysts 64 to 67 have a higher NOx purification rate than the comparative example catalysts 1 and 21, and are superior in SOx resistance performance.
[0049]
[Table 4]

[0050]
"Example 5"
In the same manner as in Reference Example 1 , Example Catalysts 68 to 73 were prepared by adding 0.2 mol of Ce, La, and Nd to 1.9 mol of alumina in terms of metal element to Example Catalysts 64 and 66, respectively. The test was the same as in Test Example 2.
[0051]
(Test results)
Table 5 shows the NOx purification rate evaluated in Test Example 2. The example catalysts 68 to 73 clearly have a higher NOx purification rate than the comparative example catalysts 1 to 5, 21 and 24 to 30 shown in Table 2, and are excellent in heat resistance.
[0052]
[Table 5]

[0053]
"Example 6"
In the same manner as in Reference Example 1 , catalysts having different B or P contents were prepared for Example Catalysts 68 and 71. The test was the same as in Test Example 1.
[0054]
(Test results)
Table 6 shows the NOx purification rate at 400 ° C. when the catalysts of Example Catalysts 68 and 71 having different B or P contents were evaluated according to Test Example 1. The above catalyst exhibits a high NOx purification rate with a NOx purification rate exceeding 80% when the supported amount of B or P is 0.01 mol to 2 mol in terms of elements.
[0055]
[Table 6]

[0056]
"Example 7"
Catalysts with different Na, Li, and K contents were prepared for Example Catalysts 68 and 71 in the same manner as in Reference Example 1 . The test was the same as in Test Example 1.
[0057]
(Test results)
Table 7 shows the results of the NOx purification rate at 400 ° C. evaluated by Test Example 1. When the supported amounts of Na, Li and K are 0.05 mol or more and 3 mol or less in each catalyst, the NOx purification rate at 400 ° C. exceeds 80%, and a high NOx purification rate is exhibited.
[0058]
[Table 7]

[0059]
"Example 8"
Catalysts having different Rh, Pt, and Pd contents in Examples 68 and 71 were prepared in the same manner as in Reference Example 1 . The test was the same as in Test Example 1.
[0060]
(Test results)
Table 8 shows the NOx purification rate at 400 ° C. evaluated by Test Example 1. The amount of Rh, Pt, Pd supported in terms of metal is 0.002 mol to 0.05 mol in the case of Pt, 0.0003 mol to 0.01 mol in the case of Rh, and 0.001 mol to 0.2 mol in the case of Pd. When the NOx purification rate at 400 ° C. exceeds 80%, a high NOx purification rate is obtained.
[0061]
[Table 8]

[0062]

[0063]

[0064]
"Example 9"
Catalysts were prepared in the same manner as in Reference Example 1 , except that the amounts of Ce, La, and Nd added to Example catalysts 68 to 73 were changed. The test was the same as in Test Example 2.
[0065]
(Test results)
Table 9 shows the NOx purification rate at 400 ° C. evaluated by Test Example 2. When the supported amount of Ce, La, and Nd is 0.02 mol or more and 1 mol or less in terms of metal, the NOx purification rate at 800 ° C. and 400 ° C. after 5 hours of heat resistance exceeds 80%, and a high NOx purification rate is obtained.
[0066]
[Table 9]

[0067]
"Example 10"
In the same manner as in Reference Example 1 , catalysts were prepared by changing the amounts of Mn, Co, Ni, and Cu added in Example catalysts 56 to 63. The test was the same as in Test Example 2.
[0068]
(Test results)
Table 10 shows the NOx purification rate at 400 ° C. evaluated by Test Example 2. When the supported amount of Mn, Co, Ni, Cu is 0.01 mol or more and 2 mol or less in terms of metal, the NOx purification rate at 800 ° C. and 400 ° C. after 5 hours of heat resistance exceeds 80%, and a high NOx purification rate is obtained.
[0069]
[Table 10]

[0070]
"Example 11"
In the same manner as in Reference Example 1 , a catalyst was prepared in which the Ti addition amount was changed for the example catalysts 64 and 66 and the Si addition amount was changed for the example catalysts 65 and 67.
[0071]
(Test results)
Table 11 shows the NOx purification rate at 400 ° C. evaluated by Test Example 3. When the loading amount of Ti and Si is 0.01 mol or more and 2 mol or less in terms of element, the NOx purification rate at 400 ° C. after SOx poisoning exceeds 50%, and a high NOx purification rate is obtained.
[0072]
[Table 11]

[0073]
"Example 12"
In the same manner as in Reference Example 1 , catalysts having different Al ₂ O ₃ coating amounts were prepared in Example Catalysts 64 and 66.
[0074]
(Test results)
Table 12 shows the NOx purification rate at 400 ° C. evaluated by Test Example 1. For example, when the Al ₂ O ₃ coating amount is 0.1 mol in terms of Al ₂ O ₃ with respect to 1 L of honeycomb volume, it is expressed as NaLiKPdBMnTi—RhPt / 0.1Al ₂ O ₃ .
[0075]
When the Al ₂ O ₃ coating amount is 0.3 mol or more and 4 mol or less with respect to 1 L of honeycomb volume in terms of Al ₂ O ₃ , the NOx purification rate at 400 ° C. exceeds 80%, and a high NOx purification rate is obtained.
[0076]
[Table 12]

[0077]
"Example 13"
As a hydrocarbon and CO combustion catalyst, a catalyst carrying only Rh and Pt was prepared in the same manner as in Reference Example 1 . The contents of Rh and Pt were Rh 0.002 mol and Pt 0.01 mol with respect to 1.9 mol of alumina in terms of metal. The test is the same as in Test Example 1, and when the hydrocarbon and CO combustion catalysts are installed before or after the Example Catalysts 64 and 66, or when the hydrocarbon and CO combustion catalysts are not installed at all. The hydrocarbon and CO removal rates were measured.
[0078]
The C ₃ H ₆ purification rate and the CO purification rate were calculated by the following equations, respectively.
[0079]
C ₃ H ₆ purification rate (%) = ((total C ₃ H ₆ flowing into the catalyst in 4 minutes after switching to lean) Amount)-(total amount of C ₃ H ₆ flowing out of the catalyst in 4 minutes after switching to lean)) ÷ (total amount of C ₃ H ₆ flowing into the catalyst in 4 minutes after switching to lean) × 100
CO purification rate (%) = ((total amount of CO flowing into the catalyst in 4 minutes after switching to lean)-(total amount of CO flowing out of the catalyst in 4 minutes after switching to lean)) ÷ (4 minutes after switching to lean) Total CO flowed into the catalyst) x 100
The measurement temperature was 400 ° C.
[0080]
(Test results)
Table 13 shows the C ₃ H ₆ purification rate and CO purification rate at 400 ° C. evaluated by the same method as in Test Example 1. If a hydrocarbon and CO combustion catalyst is installed in the upstream or downstream of Example Catalysts 64 and 66, the hydrocarbon and CO removal performance is improved.
[0081]
[Table 13]

[0082]
【The invention's effect】
According to the present invention, harmful substances, particularly nitrogen oxides, can be purified with high efficiency even in an atmosphere where oxygen is excessively present, and furthermore, the heat resistance performance and the SOx resistance performance are excellent. Can be maintained for a long time.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an embodiment of an exhaust gas purification apparatus of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Air cleaner, 2 ... Air flow sensor, 3 ... Slot valve, 5 ... Injector, 6 ... Spark plug, 7 ... Oxygen concentration sensor (or A / F sensor), 8 ... Exhaust gas temperature sensor, 9 ... Catalyst exit gas temperature sensor DESCRIPTION OF SYMBOLS 10 ... Exhaust gas purification catalyst, 11 ... ECU, 99 ... Engine.

Claims

In the exhaust gas purification apparatus in which the exhaust gas purification catalyst is installed in the engine exhaust gas flow path in which the exhaust gas having a lean air-fuel ratio and the exhaust gas having a rich or stoichiometric air / fuel ratio flows alternately, the exhaust gas purification catalyst includes a porous carrier and the carrier. A catalytically active component supported on the catalyst, wherein the catalytically active component is at least one selected from Rh, Pt, Pd, an alkali metal, at least one selected from B and P , Mn, Cu, Co, Ni, An exhaust gas purifying device for an internal combustion engine, comprising at least one selected from Si and Ti .

2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the catalytically active component further contains an alkaline earth metal.

The exhaust gas purifying apparatus for an internal combustion engine according to claim 1 or 2, wherein the porous carrier is supported on a base material.

4. An exhaust gas purification apparatus for an internal combustion engine according to claim 1 , wherein the catalytically active component further contains at least one rare earth metal.

An exhaust gas purification apparatus for an internal combustion engine according to claim 1,
An exhaust gas purification apparatus for an internal combustion engine, characterized in that a combustion catalyst for burning hydrocarbons and carbon monoxide is disposed in at least one of a front stage and a rear stage of the exhaust gas purification catalyst.

In a method for purifying exhaust gas by alternately flowing exhaust gas having a lean air-fuel ratio and exhaust gas having a rich or stoichiometric air-fuel ratio to an exhaust gas purification catalyst installed in an exhaust gas flow path of an internal combustion engine, the exhaust gas purification catalyst is porous. And a catalytically active component supported on the carrier, wherein the catalytically active component is at least one selected from Rh, Pt, and Pd, an alkali metal, and B or P , and Mn, Cu And an exhaust gas purification method for an internal combustion engine, comprising: at least one selected from Co, Ni, Si and Ti .

The exhaust gas purification method for an internal combustion engine according to claim 6, wherein the catalytically active component further contains an alkaline earth metal.

8. The exhaust gas purification method for an internal combustion engine according to claim 6 , wherein the catalytically active component further contains at least one rare earth metal.

At least one of Rh, Pt and Pd on the surface of the porous carrier, an alkali metal, at least one selected from B and P, and at least one selected from Mn, Cu, Co, Ni, Si and Ti; Have
With respect to 1.9 mol parts of the porous carrier, at least one of Rh, Pt, and Pd is converted into metal elements, Rh is 0.0003 mol part to 0.01 mol part and Pt is 0.002 mol part to 0.05 mol. Pd is contained in the range of 0.001 mol part or more and 0.2 mol part or less, and the alkali metal is contained in the range of 0.05 mol part or more and 3 mol part or less per type in terms of metal element. one hints in terms of element within the range of 2mol portion than 0.01mol unit, Mn, Cu, Co, 0 . 01 mol or more parts 2 mol unit Ni, at least one element selected from Si and Ti in terms of element Within the following range,
The Rh, Pt, Pd and alkali metals in the form of metals or oxides, the B and P in the form of simple substances or oxides or complex oxides with other elements other than B and P, the Mn, Cu, Co , Ni, Si, and Ti in the form of a metal, oxide, or simple substance, an exhaust gas purification catalyst for an internal combustion engine.

10. The porous support according to claim 9 , further comprising an alkaline earth metal on the porous support, and 0.05 mol part or more and 3 mol part or less per one kind of alkaline earth metal in terms of metal element with respect to 1.9 mol part of the support. An exhaust gas purifying catalyst for an internal combustion engine, characterized in that the catalyst contains an alkaline earth metal in the form of a metal or an oxide.

The exhaust gas purification of an internal combustion engine according to claim 9 or 10 , wherein the porous carrier is supported on a base material, and the porous carrier is contained in a range of 0.3 mol to 4 mol with respect to the base material 1L. catalyst.

12. The method according to claim 9 , further comprising at least one rare earth metal on the porous carrier, wherein at least one rare earth metal is added to the 1.9 mol part of the porous carrier as a metal element. An exhaust gas purification catalyst for an internal combustion engine, which is contained in a range of 0.02 mol part or more and 1 mol part or less in terms of conversion, and contains the rare earth metal in the form of a metal or an oxide.