JP2004251266A

JP2004251266A - Ceramic honeycomb filter type and exhaust gas purifying method

Info

Publication number: JP2004251266A
Application number: JP2003093677A
Authority: JP
Inventors: Hirohisa Suwabe; 博久諏訪部; Takashi Takakura; 隆高倉; Satoru Makita; 哲牧田; Hiroshi Funahashi; 博舟橋
Original assignee: Hino Motors Ltd; Hitachi Metals Ltd
Current assignee: Hino Motors Ltd; Proterial Ltd
Priority date: 2002-03-29
Filing date: 2003-03-31
Publication date: 2004-09-09
Anticipated expiration: 2023-03-31
Also published as: JP3867976B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a honeycomb filter capable of easily causing combustion by a catalyst substance of fine particles, preventing the deposit of fine particles on the honeycomb filter, avoiding a problem of the breakage and melting loss of the filter, and reducing an increase in pressure loss stably over a long time. <P>SOLUTION: This ceramic honeycomb filter has such structure that exhaust gas passes through a thin hole formed in a bulkhead of a honeycomb structural body by sealing a flow passage of the porous ceramic honeycomb structural body. A catalyst substance is held in at least the bulkhead and the sealing part. At least one exhaust gas flow-in side sealing part is arranged apart from an exhaust gas flow-in side end face. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、自動車エンジンの排気ガス浄化装置、特にディーゼルエンジンからの排気ガス中の微粒子を除去するための浄化装置に使用するに適したセラミックハニカムフィルタ及び排気ガス浄化方法に関する。
【０００２】
【従来技術】
近年、ディーゼルエンジンの排気ガス中から炭素を主成分とする微粒子を除去するため、セラミックハニカム構造体の複数の流路を両端部で交互に目封止したセラミックハニカムフィルタ（以下、「セラミックハニカムフィルタ」を略して「ハニカムフィルタ」という）が使用されるようになってきた。
【０００３】
図３は、ハニカムフィルタ１１の模式斜視図であり、図４は、図３に示すハニカムフィルタ１１の模式断面図の一部である。図３及び図４に示すように、通常、ハニカムフィルタ１１は、流路方向に垂直な断面が略円状又は略楕円状で、外周壁２０と、この外周壁２０の内周側で隔壁３０により囲まれた多数の流路を有する多孔質セラミックハニカム構造体（以下、「多孔質セラミックハニカム構造体」を略して「ハニカム構造体」という）１０の流入側端面１２、及び流出側端面１３において流路を目封止部５０、５２で交互に目封止している。
【０００４】
ハニカムフィルタ１１での排気ガス浄化の仕組みについて図４でさらに詳しく説明する。図４において、ハニカムフィルタ１１の流入側端面１２で開口している流路４１に流入した排気ガス（矢印９０で示す）は、この流路４１の流出側端面に目封止部５２が形成されていることから、隔壁３０に形成された細孔（図示せず）を通過した上で、隣接する流出側端面１３で開口している流路４３から排出される（矢印９２で示す）。このとき、排気ガス中に含まれる微粒子などは、隔壁３０に形成された細孔に捕集され、排気ガスが浄化される。この細孔に捕集された微粒子が一定量以上になると細孔の目詰まりが発生し、ハニカムフィルタの圧力損失が上昇するため、エンジンの出力低下につながり好ましくない。このため、ハニカムフィルタとしての機能を停止させて、バーナーや電気ヒーターにより捕集された微粒子を燃焼させ、ハニカムフィルタの再生が行われる。この、バーナーや電気ヒーターにより微粒子を燃焼除去する際には、捕集された微粒子が多い程、ハニカムフィルタ内の温度を均一に制御することが困難であり、特に高濃度に微粒子が堆積した箇所の温度が上昇し易く、燃焼に伴い発生する熱応力によりハニカムフィルタが破損することがあった。また、場合によっては隔壁を構成するセラミック材料の溶融温度以上にハニカムフィルタの温度が上昇し、隔壁に溶損が発生するという問題もあった。一方、ハニカムフィルタの最高温度を、破損や、溶損が起きないように抑えようとすると、微粒子の燃え残りが発生し、燃え残り微粒子により、再生処理を行ってもハニカムフィルタの圧力損失を低減することができないという問題があった。
【０００５】
上記問題を解決し、ハニカムフィルタの再生を容易に行うため、例えば特許文献１に記載の発明では、ハニカム構造体のセルの流入側に加熱手段を設け、排気ガスの流入側に位置した閉塞部（目封止部）とセルの排気ガス流入側端面との間に空間を設けた排気ガス浄化用構造物が開示されている。この従来技術によれば、閉塞部とセルの排気ガス流入側端面に設けられた空間に付着する微粒子の量が多くなることから、流入側に設けられた加熱手段による熱量を下流側まで有効に伝えられ、特に下流域の微粒子の燃焼、再生が容易になるとしている。
また、特許文献２に記載の発明には、隔壁表面に担持した白金族金属及びアルカリ土類金属酸化物を含んでなる触媒の作用により微粒子の燃焼が始まる温度を低下させ、この微粒子を連続的に除去するフィルタが開示されている。この従来技術によれば、ディーゼルエンジンの作動条件下で得られる排気ガス温度程度の低い温度条件であってもフィルタの連続的再生が達成でき、微粒子による目詰まりが避けられるとしている。
【０００６】
【特許文献１】
特公平３−６８２１０号公報
【特許文献２】
特公平７−１０６２９０号公報
【特許文献３】
特開２００２−１２２０１５号公報
【０００７】
【発明が解決しようとする課題】
しかしながら、上記従来技術には以下のような問題があった。
特許文献１に記載のハニカムフィルタは、ハニカム構造体のセルの流入側に加熱手段を設け、微粒子の燃焼が容易になるようにしているが、加熱手段はセルの流入側のみに配置されており、流路方向に長いハニカムフィルタ内部の温度を流入側から流出側まで均一に制御することは難しかった。このため、微粒子の捕集量が多くなると、微粒子の自己発熱により、局所的な温度上昇箇所が発生し、破損や溶損に至ることもあった。また、配置した加熱手段の制御を精密に行う必要があり、エネルギー費も必要となることから、排気ガス浄化装置全体がコスト高になるという欠点も有していた。
一方、特許文献２に記載の白金族金属及びアルカリ土類金属酸化物を含んでなる触媒等が担持されたフィルタでは、触媒物質の作用により排気ガス中の微粒子を連続的に低温で燃焼除去させているが、微粒子の目詰まりによるフィルタの圧力損失の上昇を防止出来ない場合もあった。これは、フィルタに担持される触媒物質には活性温度領域があり、特に大都市の渋滞領域での走行を中心とした使用環境では、触媒活性下限温度である約３００℃を下まわるような排気温度での運転状態が続くようになる場合があることから、触媒物質による微粒子の燃焼除去が良好に行われないためである。
このような問題を解決するため特許文献３に記載の発明では、ディーゼルエンジンの運転状態に応じて、触媒物質を担持させたフィルタ上への微粒子の堆積量を推定した上で、フィルタの上流側に燃料を未燃のまま噴射して、前記触媒物質上で、燃料の酸化反応を促し、その反応熱によりフィルタの内部温度を前記触媒物質の活性下限温度以上に維持し、堆積した微粒子を燃焼させる排気浄化方法が開示されている。また、このフィルタの上流側に燃料を未燃のまま噴射する以外に、同じく未燃の炭化水素ガスを噴射する方法も知られている。このため、ディーゼルエンジンの運転状態に係わらず、常に触媒物質が安定した活性状態に維持されて、フィルタに捕集された微粒子が滞りなく良好に燃焼除去できるとされている。しかしながら、この特許文献３に記載されている排気浄化方法を採用しても、微粒子の目詰まりにより、圧力損失が早期に上昇し、使用できなくなると言う問題の発生することがあった。
【０００８】
本発明は、上記問題に鑑みてなされたもので、ハニカムフィルタに担持した触媒物質の作用により排気ガス中の微粒子を連続的に燃焼、再生させるセラミックハニカムフィルタにおいて、微粒子のハニカムフィルタへの堆積による圧力損失の上昇を確実に回避しうるようにして、フィルタの破損や溶損の問題を回避し、長期に亘り安定して使用できるセラミックハニカムフィルタ及びその排気ガスの浄化方法を得ることにある。
【０００９】
【課題を解決するための手段】
本発明者らは、特許文献３に記載の排気浄化方法における、触媒物質が担持されたハニカムフィルタの圧力損失上昇の原因について、詳細な調査を行ったところ、図５に示すように、微粒子７０が流入側目封止部５０の端部を中心に多く堆積することにより、流路４０の開口端部を閉塞させ、ハニカムフィルタの圧力損失を上昇させていることを突きとめた。更に、この微粒子のハニカムフィルタの排気ガス流入側への堆積について、詳細な調査を行ったところ、ディーゼルエンジンの運転状態に応じて、触媒物質を担持させたフィルタ上への微粒子の堆積量を推定した上で、フィルタの上流側に適宜に燃料及び／又は炭化水素ガスを未燃のまま噴射させた際の、ハニカムフィルタ内に生じる流路方向温度分布が原因であることを突き止めた。この場合のハニカムフィルタ内の流路方向温度分布は、図６に示すように、排気ガス流入側端面の温度が最も低く、フィルタ内部に入るに従い上昇し、ある位置より排気ガス流出側では、ほぼ一定となり流出側端面の温度に収束していた。従って、ハニカムフィルタの排気ガス流入側に担持された触媒物質は触媒活性温度まで昇温されていないことから触媒の活性度が低くなり、この部分での微粒子の燃焼が容易に行われないこと、また流入側目封止部端面５１が排気ガス流入方向に対して垂直に配置されているため、排気ガス中の微粒子が目封止部端面５１に強固に凝着、堆積し易い構造になっていることにより、この部分に堆積した微粒子が時間の経過と共に徐々に大きくなり、流入側目封止部端面５１の周囲の流路４０開口端部を閉塞させたことが、ハニカムフィルタの圧力損失を上昇させた原因であった。
この時、本来フィルタ内部温度を上昇させることを目的として行われる未燃の燃料及び／又は炭化水素ガス噴射時に、図６に示すような流路方向の温度分布が発生するのは、噴射された未燃の燃料及び／又は炭化水素ガスの酸化反応はフィルタ表面に担持された触媒物質により促進されるが、未燃の燃料及び／又は炭化水素ガスの酸化反応が触媒物質により促進されていないためフィルタの流入側端部の温度は排気ガス温度以上にはなり得ないからである。即ち、排気ガスがフィルタの流路内を進行することによって初めて、排気ガス中の未燃の燃料及び／又は炭化水素ガスがフィルタ表面に担持された触媒物質との作用により酸化燃焼による反応熱を生成し、排気ガス温度を上昇させるとともにハニカムフィルタの温度を上昇させ、温度上昇した排気ガスにより更にその下流側のハニカムフィルタ温度を上昇させることによる。さらにハニカムフィルタの温度上昇は、触媒物質と作用反応する排気ガス中の未燃燃料及び／又は炭化水素ガスの減少と共に起こりにくくなるため、ハニカムフィルタの排気ガス流入側端面からの或る位置より排気ガス流出側では、略一定温度に収束する。
【００１０】
そこで、本発明者は鋭意検討を行った結果、ディーゼルエンジンの運転状態に応じて、触媒物質を担持させたフィルタ上への微粒子の堆積量を推定した上で、フィルタの上流側に燃料及び／又は炭化水素ガスを未燃のまま噴射して、前記触媒物質上で、未燃の燃料及び／又は炭化水素ガスの酸化反応を促し、その反応熱によりフィルタの内部温度を前記触媒物質の活性下限温度以上に維持し、堆積した微粒子を燃焼させる際に、フィルタ中で最も微粒子が堆積しやすい流入側目封止部端面を触媒物質の活性下限温度近くまで昇温できる部位に配置すれば、流入側目封止部端面に堆積する微粒子を容易に燃焼除去することが出来ると考え、本発明に想到した。
すなわち、本発明のセラミックハニカムフィルタは、多孔質セラミックハニカム構造体の流路を目封止することによりハニカム構造体の隔壁に形成された細孔に排気ガスを通過させる構造のセラミックハニカムフィルタにおいて、前記隔壁及び／または目封止部の少なくとも一部に触媒物質が担持されているとともに、少なくとも一つの排気ガス流入側目封止部が排気ガス流入側端面より離れて配置されていることを特徴とする。
前記排気ガスは、前記排気ガス流入側端面より離れて配置された排気ガス流入側目封止部５０より排気ガス流入側に存在する隔壁３１中の細孔内を少なくとも通過することが好ましい。
前記排気ガス流入側目封止部端面は、内燃機関運転中の少なくともある期間、即ち運転状態に応じてフィルタ上への微粒子の堆積量を推定した上で、フィルタ上流への未燃燃料及び／又は炭化水素ガスを噴射する際に、前記流入側目封止部に担持された触媒物質の活性下限温度以上に維持される位置に配置されていることが好ましい。さらに排気ガス流入側目封止部端面は、セラミックハニカムフィルタの流入側端面から該セラミックハニカムフィルタ全長の０．７倍以下の長さの区間に配置されていると良い。
尚、前記セラミックハニカムフィルタに担持される触媒物質は、白金族金属を含んでなることが好ましく、また、排気ガス流入側の隔壁３１に担持された触媒物質の活性度が、排気ガス流出側の隔壁３２に担持された触媒物質の活性度に比べて高いことが好ましい。
さらに、本発明の排気ガス浄化方法は、多孔質セラミックハニカム構造体の流路を目封止することによりハニカム構造体の隔壁に形成された細孔に排気ガスを通過させる構造であって、前記隔壁及び／または目封止部の少なくとも一部に触媒物質が担持されているとともに、少なくとも一つの排気ガス流入側目封止部が排気ガス流入側端面より離れて配置されているセラミックハニカムフィルタの上流側に、適宜に未燃の燃料及び／又は炭化水素ガスを噴射してセラミックハニカムフィルタの排気ガス流入側目封止部及びその流出側の領域の少なくとも一部の温度を前記触媒物質の活性下限温度以上に維持することを特徴とする。
【００１１】
本発明に関わるセラミックハニカムフィルタは図１及び図７〜図１１に示すような構造からなる。
図１はハニカムフィルタ１１の一例の模式断面図である。ハニカムフィルタ１１は、流路方向垂直断面が略円状又は略楕円状で、外周壁２０と、この外周壁２０の内周側で隔壁３０により囲まれた多数の流路４０を有する多孔質セラミックハニカム構造体１０の流路４０の所望部位に目封止部５０、５２により交互に目封止している。そして、少なくとも一つの排気ガス流入側の目封止部端面５１は、セラミックハニカムフィルタの流入側端面１２に対して、排気ガス流出側に離れて配置されており、隔壁及び／または目封止部の少なくとも一部には触媒物質６０が担持されている。
このような構造を有するハニカムフィルタにおいて排気ガスは、流入側端面１２で開口している流路４１、及び４２から流入する。このうち流路４２から流入した排気ガス９１は、流入側目封止部５０があることから、隔壁３１中に形成された細孔（図示せず）を通過して隣接する流路４１に排出され、この流路４１に流入側端面１２から流入した排気ガス９０と合流後、流路４１を流出側端面１３に向かって進行し、隔壁３２に形成された細孔（図示せず）を通過して隣接する流路である流出側端面１３で開口している流路４３から排出（矢印９２で示す）される。この間、排気ガス中の微粒子は、流路４１〜４３、及び隔壁３１〜３２を通過する際に、触媒物質の作用により燃焼、無害化され、浄化された排気ガスが排出される。
【００１２】
次に、本発明における作用効果につき説明する。
本発明のセラミックハニカムフィルタは、図１、図７〜図１１に示すように、多孔質セラミックハニカム構造体の流路を目封止することによりハニカム構造体の隔壁に形成された細孔に排気ガスを通過させる構造のセラミックハニカムフィルタにおいて、前記隔壁及び／または目封止部の少なくとも一部に触媒物質が担持されているとともに、少なくとも一つの排気ガス流入側目封止部５０が排気ガス流入側端面１２より離れて配置されている。このため、内燃機関運転中にハニカムフィルタ上への微粒子の堆積量がある一定値以上になったと推定された場合に、ハニカムフィルタの温度を上昇させる目的で行う、フィルタ上流への未燃の燃料及び／又は炭化水素ガス噴射時においては、フィルタ内で未燃の燃料及び／又は炭化水素ガスが触媒物質による酸化反応により反応熱を生成することから、フィルタ内の温度分布は、図７の模式図のようになり、微粒子７０が凝着、堆積しやすい流入側目封止部端面５１がハニカムフィルタ内の温度の高い部位に配置される。従って、当該部位に担持された触媒物質の活性度が高められているため、流入側目封止部端面５１での微粒子の燃焼が容易に行われ、流入側目封止部端面５１への微粒子７０堆積を防ぐことができる。
一方、流入側目封止部５０より排気ガス流出側の隔壁３２は、図７の模式図に示すように、流入側目封止部と同様、ハニカムフィルタ内の温度の高い部位に配置されるため、当該部位に担持された触媒物質の活性度は高い状態にあり、微粒子の酸化燃焼が容易に行われるため、流入側に開口した流路４１から流入した排気ガスが隔壁３２に形成された細孔内を通過して隣接した流路４３に排出される際に、排気ガス中の微粒子が燃焼、浄化される。
以上述べたように、内燃機関運転中にハニカムフィルタへの微粒子の堆積量がある一定値以上になったと推定された場合に、ハニカムフィルタの温度を上昇させる目的で行う、フィルタ上流への未燃の燃料及び／又は炭化水素ガス噴射時において、微粒子の浄化作用がハニカムフィルタ内各所、即ち、流入側目封止部５０、流入側目封止部より排気ガス流入側の隔壁３１、及び流入側目封止部より排気ガス流出側の隔壁３２を含む箇所、で行われることから、本発明のセラミックハニカムフィルタによれば、従来のハニカムフィルタで認められた図５に示すような、流路４０の開口端部での微粒子堆積による流路閉塞により、圧力損失が上昇する現象は発生しにくく、微粒子が触媒物質の作用により有効に燃焼され、フィルタの破損や溶損の問題を回避すると共に、長期に亘り圧力損失を上昇させることなく使用することができる。
更に、内燃機関運転中にハニカムフィルタへの微粒子の堆積量がある一定値以上になったと推定された場合に、ハニカムフィルタの温度を上昇させる目的で行う、フィルタ上流への未燃の燃料及び／又は炭化水素ガス噴射の際には、セラミックハニカムフィルタ内の温度は図７に示すような分布となる。このような温度分布が発生すると、時間の経過と共に、流入側目封止部５０及び流入側目封止部５０より排気ガス流出側の隔壁３２から、流入側目封止部５０より排気ガス流入側の隔壁３１への熱伝導により、隔壁３１の温度が上昇し、セラミックハニカムフィルタの流入側端面１２の温度も上昇して、流入側目封止部５０より排気ガス流入側の隔壁３１に担持された触媒物質の活性度が上昇し、より確実に微粒子の燃焼が容易に行われ、流入側目封止部端面５１への微粒子７０堆積を防ぐことができる。
以上は、内燃機関運転中にハニカムフィルタへの微粒子の堆積量がある一定値以上になったと推定された場合に、ハニカムフィルタの温度を上昇させる目的で行う、フィルタ上流への未燃の燃料及び／又は炭化水素ガス噴射時において、ハニカムフィルタ内の流入側目封止部５０を含む、その下流側の領域の温度を触媒の活性度が高まるようにする例を用いて説明したが、噴射する未燃の燃料及び／又は炭化水素ガスの量を調整することにより、ハニカムフィルタ内の流入側目封止部５０を含む、その下流側の領域の温度を微粒子の自己燃焼が起こる６００℃以上の温度に加熱し、触媒の力を借りずに微粒子を燃焼させても同様に、微粒子７０が凝着、堆積しやすい流入側目封止部端面５１での微粒子の燃焼が容易に行われ、流入側目封止部端面５１への微粒子７０の堆積を防ぐことができる。
また、内燃機関運転中にハニカムフィルタ上への微粒子の堆積量がある一定値以下の場合で、ハニカムフィルタ上流側に未燃の燃料及び／又は炭化水素ガスを噴射する必要のない、内燃機関からの排気ガス温度が、触媒活性下限温度以上に高い場合は、ハニカムフィルタ各所に担持された触媒物質が活性となることにより、排気ガス中の微粒子は触媒物質により燃焼反応が促進されるため、ハニカムフィルタに流入する排気ガス９０、９１は、ハニカムフィルタの流路及び隔壁を通過される際に浄化され、排気ガス９２として排出される。
ここで、図１に示すように排気ガス流入側目封止部５０すべてが、ハニカムフィルタの排気ガス流入側端面１２より離れて配置される必要はなく、図１０に示すように、本発明の目的を達成できる程度に配置すれば良い。即ち、少なくとも７０％以上の排気ガス流入側目封止部５０が排気ガス流入側端面１２より離れていれば、微粒子の堆積による圧力損失上昇を防ぐ効果が大きくなる。排気ガス流入側目封止部５０のうちハニカムフィルタの排気ガス流入側端面１２より離れて配置されている目封止部が７０％未満である場合は、セラミックハニカムフィルタ内の温度の高い部位に配置される排気ガス流入側目封止部５０の割合が少なくなるため、即ちセラミックハニカムフィルタ内の温度の低い部位に配置される目封止部の割合が増えるため、低温の目封止部端面に微粒子が堆積しやすくなり、本発明のハニカムフィルタの圧力損失の上昇を防ぐ効果が小さくなるからである。
本発明において、排気ガス流入側目封止部５０がセラミックハニカムフィルタ内の温度の高い部位に配置されれば微粒子の燃焼が容易に行われ、微粒子の堆積による圧力損失の上昇が起こりにくくなることを考慮すると、排気ガス流入側目封止部５０は、図８に示すように排気ガス流入側目封止部端面５１が流入側端面１２から同一の位置に配置されなくても良く、また、図９に示すように、排気ガス流入側目封止部５０及び流出側目封止部５０の長さは全て同一でなくても良いのである。また、本発明の効果が得られるのであれば、排気ガス流出側目封止部５０は、同一の位置に配置されなくても良い。
また、図１１に示すように、外周壁周辺の流路両端を目封止するような構造のセラミックハニカムフィルタの場合には、外周壁周辺の両端が目封止された流路には、排気ガスが流入しないことから、この流路が断熱空間として作用し、セラミックハニカムフィルタ内で排気ガスと触媒により発生した熱が、外周壁を経由して、ハニカムフィルタを把持している把持部材、更には金属容器を経由して、外気へ放出されることを防ぐことができるため、セラミックハニカムフィルタ内の温度を均一にできることから好ましい。
また、排気ガス流出側の目封止部が、排気ガス流入側の目封止部と同様にセラミックハニカムフィルタ流出側端面より離れて配置されている場合、或いは流出側端面より突出して配置されている場合でも、同様の効果が得られる。
【００１３】
本発明のセラミックハニカムフィルタにおいて、前記排気ガスは、前記排気ガス流入側端面より離れて配置された排気ガス流入側目封止部５０より排気ガス流入側に存在する隔壁３１中の細孔内を少なくとも通過することが好ましいのは、流入側目封止部５０より排気ガス流入側の隔壁３１は、図７の模式図に示すように、流入側目封止部に比べて温度の低い部位に配置されるものの、当該部位に担持された触媒物質は流入側端部に比べ温度が高く、触媒物質の活性度は流入側端部に比べて高められていることから、流路４２に流入した排気ガスが隔壁３１に形成された細孔内を通過して隣接する流路４１に排出される際に、排気ガス中の微粒子が燃焼、浄化される。
本発明のハニカムフィルタの排気ガス流入側目封止部端面は、内燃機関運転中の少なくともある期間、即ちハニカムフィルタ上への微粒子の堆積量がある一定値以上になったと推定された場合に、ハニカムフィルタの温度を上昇させる目的で行う、フィルタ上流への未燃の燃料及び／又は炭化水素ガス噴射時において、前記隔壁に担持された触媒物質の活性化下限温度以上に維持される位置に配置されていることが好ましいのは、本発明の目的が排気ガス流入側目封止部端面に、微粒子が凝着、堆積して、排気ガス流入側通路を閉塞させることを防ぐことにあることから、排気ガス流入側目封止部端面５１が、前記隔壁に担持された触媒物質の活性下限温度以上に維持される位置に配置された場合、触媒物質の作用により微粒子を確実に燃焼除去できるためである。また排気ガス流入側目封止部端面５１を触媒物質の活性下限温度以上に維持される位置に配置するとは、排気ガス流入側目封止部端面５１を必ずしも触媒物質の活性下限温度以上に維持される位置のみではなく、その活性下限温度近傍の温度以上の位置に配置すれば良い。
ここで、触媒物質の活性下限温度とは触媒が活性化する温度をいう。
本発明のセラミックハニカムフィルタの流入側目封止部端面５１は、セラミックハニカムフィルタ流入側端面１２から該セラミックハニカムフィルタ全長の０．７倍の長さの区間に配置されていると好ましいのは、流入側端面１２から該セラミックハニカムフィルタ全長の０．７倍の長さの区間を越えて配置すると、セラミックハニカムフィルタの全体の長さには制約があるため、排気ガス流入側目封止部より流出側の隔壁３２の面積が、隔壁３１に比べて少なくなるため、ハニカムフィルタ全体の初期圧力損失が上昇することもあるからである。また、ハニカムフィルタ上流に未燃の燃料及び／又は炭化水素ガスを噴射した際の、触媒物質によるフィルタ温度上昇効果を十分得るためには、流入側目封止部５０は流入側端面１２から１ｍｍ以上に離れて配置されていることがさらに好ましい。また、更に好ましい流入側目封止部端面５１の配置区間は、セラミックハニカムフィルタ流入側端面１２から該セラミックハニカムフィルタ全長の０．１〜０．４倍の長さの区間である。
【００１４】
次に、本発明のセラミックハニカムフィルタに担持される触媒物質が、白金族金属を含んでなることが好ましいのは、白金族金属を含む触媒物質が、ハニカムフィルタの上流に噴射された未燃燃料及び／又は炭化水素ガスのハニカムフィルタ上での燃焼反応を促進し、反応熱の生成が促進されることにより、フィルタ内の温度が上昇し易くなり、触媒物質の活性度が上昇するのと共に、排気ガス中に含まれる微粒子の浄化反応とりわけ酸化反応を促進するからである。ここで、白金族金属を含む触媒物質による排気ガス中に含まれる微粒子の除去反応は以下のように行われる。排気ガス中の微粒子は、活性状態にある白金族金属を含む触媒物質と接触すると、例えば排気ガス中の微粒子の主成分である炭素Ｃが酸素Ｏ_２との反応により酸化され二酸化炭素ＣＯ_２に変換燃焼され、無害化されため、長期に亘り圧力損失を上昇させることなく使用することができる。尚、白金族金属を含む触媒物質は、たとえば、Ｐｔ、Ｐｄ、Ｒｕ、Ｒｈ又はその組合せ、白金族金属酸化物等が含まれるが、アルカリ土類金属酸化物や希土類酸化物、或いはベース金属触媒、典型的にはランタン、セシウム、バナジウム（Ｌａ／Ｃｓ／Ｖ_２Ｏ_３）類等を含んでも良い。また、触媒物質には、公知のγアルミナ等の活性アルミナからなる高比表面積材料が含まれると、触媒物質と排気ガスとの接触面積を大きくすることができ、排気ガスの浄化効率を高めることができることから好ましい。
【００１５】
また、セラミックハニカムフィルタの排気ガス流入側の隔壁３１に担持された触媒物質の活性度が、排気ガス流出側の隔壁３２に担持された触媒物質の活性度に比べて高いことが好ましいのは、隔壁３１において、ハニカムフィルタの上流に噴射された未燃の燃料及び／または炭化水素ガスのハニカムフィルタ上での燃焼反応が促進され、反応熱の生成がより促進されることにより、隔壁３１の領域において、フィルタ内の温度が上昇し易くなるため、流入側目封止部端面５１に担持された触媒物質の活性度が上昇し、この部分への微粒子の堆積を防ぐことができ、フィルタの圧力損失の上昇を防ぐことができるのと共に、流入側目封止部５０より排気ガス流入側の隔壁３１に担持された触媒物質による、例えば排気ガス中の微粒子の主成分である炭素ＣのＣＯ_２への変換率が高くなり、流路４２での排気ガス中の微粒子の酸化燃焼反応が効率よく行われるため、長期に亘り圧力損失を上昇させることなく使用することができるからである。ここで、排気ガス流入側の隔壁３１に担持された触媒物質の活性度が、排気ガス流出側の隔壁３２に担持された触媒物質の活性度に比べて高いというのは、例えば流入側目封止部５０より排気ガス流入側である隔壁３１に担持された触媒物質中の白金族金属を含む触媒物質の含有量や、助触媒物質であるアルカリ土類金属酸化物、希土類酸化物、或いはベース金属触媒の含有量を、排気ガス流出側の隔壁３２に担持された触媒物質に比べて多く担持させ、担持された触媒全体として見た時に、触媒の性能が高いことを意味する。
例えば、流入側目封止部５０より排気ガス流入側の隔壁３１に担持された触媒物質中の白金属金属含有量を、排気ガス流出側の隔壁３２に担持された触媒物質中の白金属金属含有量を多くすることにより、長期に亘り圧力損失が上昇しないセラミックハニカムフィルタが得られる。
また、流入側目封止部５０より排気ガス流入側である隔壁３１には、酸化触媒である、Ｐｔ、Ｐｄ、Ｒｕ、Ｒｈ等の白金族金属を含む触媒物質の含有量を多く担持し、排気ガス流出側の隔壁３２には、助触媒であるベース金属触媒、典型的にはランタン、セシウム、バナジウム（Ｌａ／Ｃｓ／Ｖ_２Ｏ_３）類よりなる触媒物質及び白金族金属を含む触媒物質を多く担持させることにより、微粒子の燃焼が効率よく行われるため、長期に亘り圧力損失が上昇しにくいセラミックハニカムフィルタが得られる。
本発明の排気ガス浄化方法は、多孔質セラミックハニカム構造体の流路を目封止することによりハニカム構造体の隔壁に形成された細孔に排気ガスを通過させる構造であって、少なくとも前記隔壁に触媒物質が担持されているとともに、少なくとも一つの排気ガス流入側目封止部が排気ガス流入側端面より離れて配置されているセラミックハニカムフィルタの上流側に、適宜に燃料及び／または炭化水素ガスを未燃のまま噴射して、前記触媒物質上で燃料及び／または炭化水素ガスの酸化反応を促進し、その反応熱によりセラミックハニカムフィルタの少なくとも排気ガス流入側目封止部から流出側の領域の温度を前記触媒物質の活性下限温度以上に維持していることから、内燃機関からの排気ガス温度が低い状態にあっても、ハニカムフィルタの上流側に燃料及び／または炭化水素ガスを未燃のまま噴射して、該燃料及び／または炭化水素ガスをハニカムフィルタの隔壁及び目封止部に担持された触媒物質の作用により燃焼させ、ハニカムフィルタ内で排気ガスが高温化されて、ハニカムフィルタに担持された触媒物質の活性下限温度以上まで強制的に維持されるため、排気ガス中の微粒子が滞りなく良好に除去される。しかも、排気ガス流入側目封止部がハニカムフィルタの排気ガス流入側端面に形成されている従来構造のハニカムフィルタに比べ、微粒子が堆積して流路を塞ぐ問題の発生し易い排気ガス流入側目封止部５０が排気ガス流入側端面より離れて配置されているため、担持されている触媒物質が活性下限温度以上に維持され、排気ガス中の微粒子の燃焼除去が効率よく行われ、微粒子の堆積することを防ぐことができ、長期に亘り圧力損失を上昇させることがない。
【００１６】
次に本発明に用いられる多孔質セラミックハニカム構造体について説明する。
本発明に用いられる多孔質セラミックハニカム構造体の隔壁及び目封止材を構成する材料としては、本発明が主にディーゼルエンジンの排気ガス中の微粒子を除去するためのフィルタとして使用されるため、耐熱性に優れた材料を使用することが好ましく、コージェライト、アルミナ、ムライト、窒化珪素、炭化珪素及びＬＡＳからなる群から選ばれた少なくとも１種を主結晶とするセラミック材料を用いることが好ましい。中でも、コージェライトを主結晶とするセラミックハニカムフィルタは、安価で耐熱性、耐食性に優れ、また低熱膨張であることから最も好ましい。
前記ハニカム構造体の隔壁の気孔率は５０〜８０％であることが好ましい。排気ガスが隔壁に形成された細孔を通過することから、隔壁の気孔率が５０％未満であると、ハニカムフィルタの圧力損失が上昇し、エンジンの出力低下につながるからであり、隔壁の気孔率が８０％を超えると、隔壁の強度が低下するため、使用時の熱衝撃や機械的振動により破損することがあるからである。また、前記ハニカム構造体の目封止材の気孔率は、隔壁の気孔率に比べて、低い場合、同程度の場合、或いは高い場合いずれの場合でも良いが、隔壁の気孔率より高い場合は、排気ガスが目封止材中の細孔内部を通過することも可能となるため、排気ガス流入側目封止部の排気ガス流入側端面５１への微粒子の堆積が起こりにくくなることから好ましい。
本発明に係るセラミックハニカムフィルタの隔壁厚は０．１〜０．５ｍｍが好ましく、隔壁のピッチは１．２ｍｍ以上が好ましい。隔壁厚が０．１ｍｍ未満では、隔壁が細孔を有する高気孔率の多孔質体であることからハニカム構造体の強度が低下し、好ましくない。一方、隔壁厚が０．５ｍｍを超えると、如何に隔壁が高気孔率であっても、排気ガスに対する隔壁の通気抵抗が大きくなるため、フィルタの圧力損失が大きくなるからである。より好ましい隔壁厚さは、０．２〜０．４ｍｍである。また、隔壁のピッチが１．３ｍｍ未満であると、ハニカム構造体の入口の開口面積が小さくなることから、フィルタ入口の圧力損失が大きくなるためである。
【００１７】
次に本発明のセラミックハニカムフィルタの製造方法一例を図２を用いて説明する。ハニカム構造体の排気ガス流入側端面に図２に示すように市松模様に樹脂製スラリー導入通路８１を設けた樹脂製のマスク８０を装着し、図２のＡ部拡大図の矢印で示すようにスラリー導入通路８１を通してスラリー状の目封止材５３を導入、ハニカム構造体の流路の一部に充填する。その後、スラリー状の目封止材５３中に含まれる水分はハニカム構造体の隔壁に吸水され目封止材が隔壁に着肉して行き保形性が得られるようになると、固化していないスラリーを排出し、樹脂製マスクを除去後、固化した目封止材の乾燥を行う。このとき樹脂製スラリー導入通路８１内に存在するスラリー状の目封止材は隔壁からの吸水が無いことから固化しないため、スラリ−導入通路の長さを調整することにより、排気ガス流入側目封止部のハニカム構造体流入側端面からの形成位置を決定することができる。一方、流出側の端面は、公知の技術により端部に目封止部を形成し、その後、目封止材の焼成を行い、隔壁と目封止材を一体化せしめる。
なお、その他の方法としては、注射針状の管をハニカム構造体の端部から流路の所定位置まで挿入し、この管を通して所定位置に所定量のペースト状の目封止材を導入後、乾燥、焼成させる方法や、セラミックチップをハニカム構造体の内部に埋め込み、焼成させる方法等を採用し、隔壁と目封止材を一体化することができる。
【００１８】
【発明の実施の形態】
以下、発明の実施の形態を詳細に説明する。
（実施例１）
カオリン、タルク、シリカ、水酸化アルミ、アルミナなどの粉末を調整して、質量比で、ＳｉＯ_２：４７〜５３％、Ａｌ_２Ｏ_３：３２〜３８％、ＭｇＯ：１２〜１６％及びＣａＯ、Ｎａ_２Ｏ、Ｋ_２Ｏ、ＴｉＯ_２ _、Ｆｅ_２Ｏ_３、ＰｂＯ、Ｐ_２Ｏ_５などの不可避的に混入する成分を全体で２．５％以下を含むようなコージェライト生成原料粉末に、成形助剤と造孔剤を添加し、規定量の水を注入して更に十分な混合を行い、ハニカム構造に押出成形可能な坏土を調整した。
そして、公知の押出成形用金型を用い押出成形し、外周壁と、この外周壁の内周側で隔壁により囲まれた断面が四角形状の流路を有するハニカム構造の成形体を作製し、乾燥後焼成を行い、直径２６７ｍｍ、全長Ｌ３００ｍｍ、隔壁のピッチ１．５ｍｍで、隔壁厚さ０．３ｍｍの隔壁構造を有し、隔壁の気孔率が６５％のハニカム構造体を作製した。
【００１９】
次に、図２に示すようにハニカム構造体の排気ガス流入側端面に市松模様にスラリー導入通路８１を設けた樹脂製のマスク８０を装着し、スラリー導入通路を通してスラリー状の目封止材を導入、ハニカム構造体の流路の一部に充填した。
その後、目封止材が隔壁に着肉し保形性が得られた後、樹脂製マスクを除去し、目封止材５３の乾燥を行った。ここで、排気ガス流入側目封止部がハニカムフィルタ端面から５通りの位置に形成されるようにスラリー導入通路８１の長さを調整した。一方、ハニカム構造体の排気ガス流出側端面の目封止部は、端面にマスキングフィルムを接着剤で貼り付けた後、市松模様となるように穿孔し、続いて、スラリー状の目封止材を端面より導入して目封止部を形成した。次いで、バッチ式焼成炉を用いて温度制御しつつ目封止材の焼成を行い、図１に模式図を示すような試験ＮＯ．１〜６のハニカムフィルタ１１を得た。
得られたハニカムフィルタに対して排気ガス流入側目封止部の排気ガス流入側端面５１とハニカムフィルタ端面１２の間の距離Ｘ（ｍｍ）を測定した。Ｘの測定は、排気ガス流入側端面から直径約０．８ｍｍ長さ２００ｍｍの金属棒を差込、ハニカムフィルタからでた金属棒の長さを読みとることで測定した。測定は、１ケのハニカムフィルタにつき任意の２０箇所の目封止部について行い、平均値を算出した。これら試験ＮＯ．１〜６のハニカムフィルタの排気ガス流入側目封止部の排気ガス流入側端面５１とハニカムフィルタ端面１２の間の距離Ｘ（ｍｍ）及びＸ／（ハニカムフィルタの全長Ｌ）の値を表１に示す。
【００２０】
前記のハニカムフィルタに対して、Ｐｔ、酸化セリウム、及び活性アルミナからなる触媒物質を隔壁表面及び隔壁中の細孔内部、更には目封止部表面及び目封止部中の細孔内部に担持させた。担持量はＰｔ量で２ｇ／Ｌ（ハニカムフィルタ容積１Ｌに対して２ｇ担持の意味）とした。
【００２１】
上記のように作製した試験ＮＯ．１〜６のセラミックハニカムフィルタを圧力損失試験装置（図示せず）に設置し、空気流量７．５Ｎｍ^３／ｍｉｎの条件で空気を流入し、流入側端面と流出側端面の差圧を測定し、各セラミックハニカムフィルタの初期圧力損失を評価した。このとき、排気ガス流入側目封止部の端面がハニカムフィルタと同一面に配置されている試験ＮＯ．１のセラミックハニカムフィルタの初期圧力損失を１として、試験ＮＯ．２〜６の初期圧力損失を表１に示した。上記のように形成したセラミックハニカムフィルタの圧力損失を以下のように測定した。更に、ディーゼルエンジンの排気管に上記試験ＮＯ．１〜６のハニカムフィルタを配置し、市街地走行を模したパターン走行条件で耐久試験を行った。この際、排気ガス温度が触媒物質の活性下限温度を下まわるような運転状態が続くような場合も発生させ、微粒子がフィルタ上に僅かに堆積するような条件を作り出した上で、この運転状態に応じて、触媒物質を担持させたフィルタ上への微粒子の堆積量を推定し、堆積量が一定値以上なったと判断された時点で、フィルタの上流側に燃料を未燃のまま噴射して、フィルタの強制的再生を行った。そして、１０，０００ｋｍ走行に相当する時間経過まで試験が継続できたものを判定合格（○）とし、継続できなかったものを判定不合格（×）とし、判定合格だったものについては、１０，０００ｋｍ走行に相当する時間経過後のハニカムフィルタの圧力損失を初期圧力損失と同様に測定し、初期圧力損失と比較して、圧力損失比：（試験後の圧力損失）／（初期圧力損失）を算出した。
【００２２】
【表１】

【００２３】
排気ガス流入側目封止部の端面がハニカムフィルタ端面と同一面に配置されている比較例である試験ＮＯ．１のセラミックハニカムフィルタは、約５，０００ｋｍ走行後に排圧が急上昇し、再生不能になったため試験を中断したため、判定は不合格（×）であった。これに対して、本発明例である試験ＮＯ．２〜６のセラミックハニカムフィルタは排気ガス流入側目封止部端面がセラミックハニカムフィルタ排気ガス流入側端面より流出側に離れて配置され、隔壁及び目封止部に触媒物質が担持されていることから、フィルタ上流に未燃燃料を噴射した際であっても、微粒子がハニカムフィルタの排気ガス流入側に堆積し、流路を閉塞させにくいため、１０，０００ｋｍ走行に相当する時間の耐久試験においても問題なく判定合格（○）が得られた。このうち試験ＮＯ．２〜５のセラミックハニカムフィルタはハニカムフィルタ流入側端面と排気ガス流入側目封止部の排気ガス流入側端面との距離Ｘがハニカムフィルタ全長Ｌの０．７以下であることから、試験ＮＯ．１のセラミックハニカムフィルタに対する初期圧力損失の上昇は僅かであり、エンジンの出力低下につながらないことからより好ましいことがわかる。特に、試験ＮＯ．２〜３のセラミックハニカムフィルタは、ハニカムフィルタ流入側端面と排気ガス流入側目封止部の排気ガス流入側端面との距離Ｘがハニカムフィルタ全長Ｌの０．１〜０．４であることから、初期圧力損失は試験ＮＯ．１のセラミックハニカムフィルタと同様であり、且つ１０，０００ｋｍ走行に相当する時間の耐久試験後においても圧力損失の上昇は小さく、圧力損失比は１．２未満であり、より長期間の使用に耐えうることが判った。
【００２４】
（実施例２）
実施例と同様の方法により直径２６７ｍｍ、長さ３００ｍｍ、隔壁のピッチ１．５ｍｍで、隔壁厚さ０．３ｍｍの隔壁構造を有し、隔壁の気孔率が６５％のハニカム構造体を作製した後、目封止を行い、ハニカムフィルタ流入側端面からの排気ガス流入側目封止部形成位置Ｘが４９．８ｍｍ及び９６．３ｍｍである図１に模式図を示す試験ＮＯ．７〜８のハニカムフィルタ５０を得た。
【００２５】
前記のハニカムフィルタに対して、Ｐｔ、酸化セリウム、及び活性アルミナからなる触媒物質を排気ガス流入側目封止部よりも排気ガス流出側の隔壁表面及び隔壁中の細孔内部、更には目封止部表面及び目封止部中の細孔内部に担持させた。このときの触媒物質中の担持量はＰｔで１ｇ／Ｌとした。一方、前記触媒物質よりＰｔ濃度を高めた触媒物質を排気ガス流入側目封止部より排気ガス流入側である隔壁表面及び隔壁中の細孔内部に担持させた。このときの触媒物質の担持量はＰｔで４ｇ／Ｌとした。
【００２６】
上記のように形成したセラミックハニカムフィルタの耐久試験を実施例１と同様に測定し、１０，０００ｋｍ走行に相当する時間経過後の判定を行い、１０、０００ｋｍ走行に相当する時間経過後のハニカムフィルタの圧力損失を測定し、初期圧力損失と比較して、圧力損失比：（試験後の圧力損失）／（初期圧力損失）を算出した。
【００２７】
【表２】

【００２８】
試験ＮＯ．７〜８のセラミックハニカムフィルタは排気ガス流入側目封止部端面がセラミックハニカムフィルタ排気ガス流入側端面より流出側に配置され、隔壁及び目封止部に触媒物質が担持され、更には流入側目封止部よりも排気ガス流入側のＰｔ担持量が高く、排気ガス流入側の触媒物質の活性度が排気ガス流出側に比べて高くなっていることから、１０，０００ｋｍ走行に相当する時間の耐久試験においても問題なく判定合格（○）が得られ、また、実施例１に示す試験ＮＯ．２〜３のセラミックハニカムフィルタに対して１０，０００ｋｍ走行に相当する時間の耐久試験後においても圧力損失の上昇は小さく、圧力損失比が小さくなっていることから、より長期間に亘って使用が可能である。
【００２９】
（実施例３）
実施例と同様の方法により直径２６７ｍｍ、長さ３００ｍｍ、隔壁のピッチ１．５ｍｍで、隔壁１１ｂの厚さ０．３ｍｍの隔壁構造を有し、隔壁の気孔率が６５％のハニカム構造体を作製した後、目封止を行い、ハニカムフィルタ流入側端面からの排気ガス流入側目封止部形成位置Ｘが４９．８ｍｍ及び９６．３ｍｍである図１に示すような試験ＮＯ．９〜１０のハニカムフィルタ５０を得た。
【００３０】
前記のハニカムフィルタに対して、Ｐｔ、酸化セリウム、及び活性アルミナからなる触媒物質１を流入側目封止部より排気ガス流入側である隔壁及び隔壁内の細孔中にに担持させた。その後、ランタン、セシウム、バナジウム類よりなる触媒物質を加えた触媒物質３を排気ガス流入側目封止部よりも排気ガス流出側の隔壁表面及び隔壁中の細孔内部、更には目封止部表面及び目封止部中の細孔内部に担持させた。これにより、流入側目封止部より排気ガス流入側の隔壁に担持された触媒物質を排気ガス流出側の隔壁に担持した触媒物質よりも活性度を高くした。
【００３１】
上記のように形成したセラミックハニカムフィルタの耐久試験を実施例１と同様に測定し、１０，０００ｋｍ走行に相当する時間経過後の判定を行い、１０，０００ｋｍ走行に相当する時間経過後のハニカムフィルタの圧力損失を測定し、試験前の圧力損失と比較して、圧力損失比：（試験後の圧力損失）／（試験前の圧力損失比）を算出した。
【００３２】
【表３】

【００３３】
試験ＮＯ．９〜１０のセラミックハニカムフィルタは排気ガス流入側目封止部端面がセラミックハニカムフィルタ排気ガス流入側端面より流出側に配置され、隔壁及び目封止部にＰｔ、酸化セリウム、及び活性アルミナからなる触媒物質が担持されると共に、流入側目封止部よりも排気ガス流入側にランタン、セシウム、バナジウム類よりなる触媒物質が担持されており、排気ガス流入側の触媒物質の活性度が排気ガス流出側に比べて高くなっていることから、１０，０００ｋｍ走行に相当する時間の耐久試験においても問題なく判定合格（○）が得られ、また、実施例１に示す試験ＮＯ．２〜３のセラミックハニカムフィルタに対して耐久試験後の１０，０００ｋｍ走行に相当する時間の耐久試験後においても圧力損失の上昇は小さく、圧力損失比が小さくなっていることから、より長期間に亘って使用が可能である。
【００３４】
【発明の効果】
以上詳細に説明のとおり、ハニカムフィルタに担持した触媒物質により微粒子を連続的に燃焼させるセラミックハニカムフィルタにおいて、排気ガス流入側目封止部端面がセラミックハニカムフィルタの排気ガス流入側端面より流出側に配置されていることから、ディーゼルエンジンの運転状態に応じて、触媒物質を担持させたフィルタ上への微粒子の堆積量を推定した上で、フィルタの上流側に適宜に燃料及び／または炭化水素ガスを未燃のまま噴射させた際であっても、微粒子の触媒物質による燃焼が起こりやすく、かつ微粒子のハニカムフィルタへの堆積による流路の閉塞が起こりにくく、フィルタの破損や溶損の問題を回避すると共に、長期に亘り安定して圧力損失の増加の少ないハニカムフィルタ及び排気ガス浄化方法を得ることができる。
【図面の簡単な説明】
【図１】実施の形態でのハニカムフィルタの模式断面図である。
【図２】ハニカム構造体に目封止材を導入している状況を示す模式断面図である。
【図３】従来のハニカムフィルタの斜視図である。
【図４】図３のハニカムフィルタの模式断面図である。
【図５】ハニカムフィルタに堆積する微粒子を模式的に示したハニカムフィルタの断面図である。
【図６】従来のセラミックハニカムフィルタの模式断面図と長手方向の温度変化を示した図である。
【図７】本発明のセラミックハニカムフィルタの模式断面図と長手方向の温度変化を示した図である。
【図８】本発明のセラミックハニカムフィルタの模式断面図である。
【図９】本発明のセラミックハニカムフィルタの模式断面図である。
【図１０】本発明のセラミックハニカムフィルタの模式断面図である。
【図１１】本発明のセラミックハニカムフィルタの模式断面図である。
【符号の説明】
１０：ハニカム構造体
１１：ハニカムフィルタ
１２：流入側端面
１３：流出側端面
２０：外周壁
３０：隔壁
３１：流入側目封止部より流入側の隔壁
３２：流入側目封止部より流出側の隔壁
４０：流路
４１：流入側端面で開口している流路
４２：流入側端面で開口している流路
４３：排気ガス流出側に開口した流路
５０：流入側目封止部
５１：流入側目封止部端面
５２：流出側目封止部
５３：目封止材
６０：触媒物質
７０：微粒子
８０：マスク
８１：スラリー導入通路
９０：排気ガスの流入
９１：排気ガスの流入
９２：排気ガスの流出
Ｘ：目封止部形成位置[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a ceramic honeycomb filter and an exhaust gas purifying method suitable for use in an exhaust gas purifying apparatus for an automobile engine, particularly a purifying apparatus for removing particulates in exhaust gas from a diesel engine.
[0002]
[Prior art]
In recent years, in order to remove fine particles mainly composed of carbon from exhaust gas of a diesel engine, a ceramic honeycomb filter (hereinafter, referred to as a “ceramic honeycomb filter”) in which a plurality of channels of a ceramic honeycomb structure are alternately plugged at both ends. ”For short) and“ honeycomb filters ”).
[0003]
FIG. 3 is a schematic perspective view of the honeycomb filter 11, and FIG. 4 is a part of a schematic cross-sectional view of the honeycomb filter 11 shown in FIG. As shown in FIGS. 3 and 4, the honeycomb filter 11 generally has a substantially circular or substantially elliptical cross section perpendicular to the flow path direction, and has an outer peripheral wall 20 and a partition 30 on the inner peripheral side of the outer peripheral wall 20. A porous ceramic honeycomb structure (hereinafter abbreviated as “porous ceramic honeycomb structure”) having a large number of flow paths surrounded by a honeycomb structure (hereinafter referred to as “honeycomb structure”) 10 has an inflow-side end surface 12 and an outflow-side end surface 13. The flow path is plugged alternately with plugging

portions

50 and 52.
[0004]
The mechanism of exhaust gas purification by the honeycomb filter 11 will be described in more detail with reference to FIG. In FIG. 4, the exhaust gas (indicated by an arrow 90) flowing into the flow path 41 opened at the inflow side end face 12 of the honeycomb filter 11 has a plugged portion 52 formed at the outflow side end face of the flow path 41. Therefore, after passing through the pores (not shown) formed in the partition 30, it is discharged from the flow path 43 opened at the adjacent outflow side end face 13 (indicated by an arrow 92). At this time, fine particles and the like contained in the exhaust gas are trapped in the pores formed in the partition wall 30, and the exhaust gas is purified. If the amount of the fine particles trapped in the pores exceeds a certain amount, the pores are clogged, and the pressure loss of the honeycomb filter increases. For this reason, the function as the honeycomb filter is stopped, and the fine particles collected by the burner or the electric heater are burned, so that the honeycomb filter is regenerated. When burning and removing fine particles by a burner or an electric heater, it is difficult to uniformly control the temperature in the honeycomb filter as the amount of collected fine particles is large, particularly in a portion where fine particles are deposited at a high concentration. The temperature of the honeycomb filter was liable to rise, and the honeycomb filter was sometimes damaged by thermal stress generated by combustion. In some cases, the temperature of the honeycomb filter rises to a temperature higher than the melting temperature of the ceramic material forming the partition walls, and there is a problem that the partition walls are damaged by melting. On the other hand, if the maximum temperature of the honeycomb filter is controlled so as not to cause breakage or erosion, unburned fine particles will be generated, and the unburned fine particles will reduce the pressure loss of the honeycomb filter even when regenerating. There was a problem that you can not.
[0005]
In order to solve the above problem and facilitate the regeneration of the honeycomb filter, for example, in the invention described in Patent Document 1, a heating unit is provided on the inflow side of the cells of the honeycomb structure, and the closing portion located on the inflow side of the exhaust gas is provided. An exhaust gas purifying structure in which a space is provided between a (plugged portion) and an end face on the exhaust gas inflow side of the cell is disclosed. According to this conventional technique, since the amount of fine particles adhering to the space provided at the closing portion and the end face on the exhaust gas inflow side of the cell increases, the amount of heat by the heating means provided on the inflow side can be effectively reduced to the downstream side. According to the report, it is said that the combustion and regeneration of fine particles in the downstream area will be particularly easy.
Further, in the invention described in Patent Document 2, the temperature at which the burning of the fine particles is started is reduced by the action of a catalyst containing a platinum group metal and an alkaline earth metal oxide supported on the surface of the partition wall, and the fine particles are continuously discharged. There is disclosed a filter that removes the noise. According to this conventional technique, continuous regeneration of the filter can be achieved even under a temperature condition as low as the exhaust gas temperature obtained under the operating conditions of a diesel engine, and clogging by particulates is avoided.
[0006]
[Patent Document 1]
Japanese Patent Publication No. 3-68210
[Patent Document 2]
Japanese Patent Publication No. 7-106290
[Patent Document 3]
JP 2002-12015 A
[0007]
[Problems to be solved by the invention]
However, the above prior art has the following problems.
The honeycomb filter described in Patent Document 1 is provided with a heating means on the inflow side of the cell of the honeycomb structure to facilitate the burning of the fine particles, but the heating means is arranged only on the inflow side of the cell. In addition, it has been difficult to uniformly control the temperature inside the honeycomb filter that is long in the flow path direction from the inflow side to the outflow side. For this reason, when the collection amount of the fine particles increases, a local temperature rise may occur due to the self-heating of the fine particles, which may lead to breakage or melting. In addition, it is necessary to precisely control the arranged heating means, and energy cost is also required. Therefore, there is a disadvantage that the cost of the entire exhaust gas purifying apparatus is increased.
On the other hand, in the filter described in Patent Document 2 carrying a catalyst or the like containing a platinum group metal and an alkaline earth metal oxide, fine particles in exhaust gas are continuously burned and removed at a low temperature by the action of a catalytic substance. However, in some cases, an increase in pressure loss of the filter due to clogging of the fine particles cannot be prevented. This is because the catalyst substance carried on the filter has an active temperature range, and particularly in an operating environment centered on traveling in a congested area in a large city, the exhaust gas falls below the catalyst active lower limit temperature of about 300 ° C. This is because, in some cases, the operating state at the temperature may be continued, so that the combustion and removal of the fine particles by the catalytic substance are not performed favorably.
In order to solve such a problem, according to the invention described in Patent Document 3, the amount of particulates deposited on the filter supporting the catalyst substance is estimated in accordance with the operation state of the diesel engine, and then the upstream side of the filter is The fuel is injected in an unburned state to promote oxidation reaction of the fuel on the catalyst substance, and the reaction heat maintains the internal temperature of the filter at or above the activation lower limit temperature of the catalyst substance to burn the accumulated particulates. An exhaust purification method is disclosed. A method of injecting unburned hydrocarbon gas in addition to injecting unburned fuel upstream of the filter is also known. For this reason, it is said that the catalyst substance is always maintained in a stable and active state regardless of the operation state of the diesel engine, and the fine particles trapped by the filter can be satisfactorily burned off without any delay. However, even if the exhaust gas purification method described in Patent Document 3 is adopted, there is a problem that the pressure loss rises early due to the clogging of the fine particles, and the device cannot be used.
[0008]
The present invention has been made in view of the above problems, and in a ceramic honeycomb filter that continuously burns and regenerates fine particles in exhaust gas by the action of a catalyst substance carried on the honeycomb filter, the fine particles are deposited on the honeycomb filter. An object of the present invention is to provide a ceramic honeycomb filter that can be used stably for a long period of time and a method for purifying exhaust gas of the filter so as to avoid a problem of filter breakage and erosion by surely avoiding an increase in pressure loss.
[0009]
[Means for Solving the Problems]
The present inventors have conducted a detailed investigation on the cause of the increase in pressure loss of the honeycomb filter supporting the catalytic substance in the exhaust gas purification method described in Patent Document 3, and found that the fine particles 70 shown in FIG. It has been found that a large amount of is deposited around the end of the inflow-side plugged portion 50, thereby closing the open end of the flow passage 40 and increasing the pressure loss of the honeycomb filter. Furthermore, a detailed investigation was conducted on the accumulation of these particulates on the exhaust gas inflow side of the honeycomb filter. Based on the operating conditions of the diesel engine, the amount of the particulates deposited on the filter supporting the catalyst substance was estimated. Then, it was found that the cause was a temperature distribution in the flow channel direction generated in the honeycomb filter when fuel and / or hydrocarbon gas was appropriately injected unburned upstream of the filter. As shown in FIG. 6, the temperature distribution in the flow path direction in the honeycomb filter in this case has the lowest temperature at the end face of the exhaust gas inflow side and rises as it enters the inside of the filter. It became constant and converged to the temperature of the outflow side end face. Therefore, since the catalyst material carried on the exhaust gas inflow side of the honeycomb filter has not been heated to the catalyst activation temperature, the activity of the catalyst becomes low, and the combustion of fine particles in this portion is not easily performed. In addition, since the inflow side plugging portion end face 51 is arranged perpendicular to the exhaust gas inflow direction, the structure is such that fine particles in the exhaust gas are firmly adhered to the plugging portion end face 51 and easily deposited. As a result, the fine particles deposited on this portion gradually increase with the passage of time, and closing the opening end of the flow passage 40 around the inflow-side plugging portion end face 51 reduces the pressure loss of the honeycomb filter. It was the cause that raised it.
At this time, when the unburned fuel and / or hydrocarbon gas is injected for the purpose of raising the internal temperature of the filter, the temperature distribution in the flow path direction as shown in FIG. The oxidation reaction of unburned fuel and / or hydrocarbon gas is promoted by the catalyst material carried on the filter surface, but the oxidation reaction of unburned fuel and / or hydrocarbon gas is not promoted by the catalyst material. This is because the temperature at the inlet end of the filter cannot be higher than the exhaust gas temperature. That is, only when the exhaust gas travels in the flow path of the filter, unburned fuel and / or hydrocarbon gas in the exhaust gas reacts with the catalytic substance carried on the filter surface to generate reaction heat by oxidative combustion. The temperature of the honeycomb filter is increased at the same time as the temperature of the exhaust gas generated, and the temperature of the honeycomb filter on the downstream side is further increased by the exhaust gas having the increased temperature. Further, since the temperature rise of the honeycomb filter is less likely to occur with the decrease of the unburned fuel and / or the hydrocarbon gas in the exhaust gas that reacts with the catalytic substance, the exhaust gas is exhausted from a certain position from the exhaust gas inflow side end face of the honeycomb filter. On the gas outflow side, the temperature converges to a substantially constant temperature.
[0010]
Therefore, the present inventor has conducted intensive studies and, based on the operating state of the diesel engine, estimated the amount of fine particles deposited on the filter supporting the catalyst substance, and then added fuel and / or Alternatively, hydrocarbon gas is injected in a non-burned state to promote an oxidation reaction of unburned fuel and / or hydrocarbon gas on the catalyst substance, and the heat of the reaction lowers the internal temperature of the filter to the lower limit of activity of the catalyst substance. When maintaining the temperature above the temperature and burning deposited particulates, if the end face of the inflow-side plugging portion where the particulates are most likely to be deposited in the filter is placed in a location where the temperature can be raised to near the activity lower limit temperature of the catalytic substance, The present inventors thought that fine particles deposited on the end face of the side plugging portion could be easily removed by burning, and arrived at the present invention.
That is, the ceramic honeycomb filter of the present invention is a ceramic honeycomb filter having a structure in which exhaust gas passes through pores formed in partition walls of the honeycomb structure by plugging a flow path of the porous ceramic honeycomb structure, A catalyst substance is carried on at least a part of the partition wall and / or the plugging portion, and at least one exhaust gas inflow side plugging portion is disposed apart from an exhaust gas inflow side end face. And
It is preferable that the exhaust gas passes at least through pores in the partition wall 31 existing on the exhaust gas inflow side from the exhaust gas inflow side plugging portion 50 disposed apart from the exhaust gas inflow side end face.
The end face of the plugged portion on the exhaust gas inflow side estimates the amount of particulates deposited on the filter at least during a certain period during operation of the internal combustion engine, that is, after estimating the amount of the unburned fuel and / or Alternatively, when the hydrocarbon gas is injected, the catalyst material is preferably arranged at a position maintained at a temperature equal to or higher than the activity lower limit temperature of the catalyst substance carried on the inflow-side plugging portion. Further, the end face of the plugged portion on the exhaust gas inflow side is preferably arranged in a section having a length of 0.7 times or less the entire length of the ceramic honeycomb filter from the inflow side end face of the ceramic honeycomb filter.
The catalyst material carried on the ceramic honeycomb filter preferably contains a platinum group metal, and the activity of the catalyst material carried on the partition wall 31 on the exhaust gas inflow side is such that the activity on the exhaust gas outflow side is high. It is preferable that the activity is higher than the activity of the catalyst substance supported on the partition walls 32.
Further, the exhaust gas purifying method of the present invention has a structure in which exhaust gas passes through pores formed in partition walls of the honeycomb structure by plugging a flow path of the porous ceramic honeycomb structure, The catalyst substance is carried on at least a part of the partition wall and / or the plugged portion, and at least one exhaust gas inflow side plugged portion is disposed apart from the exhaust gas inflow side end face. Unburned fuel and / or hydrocarbon gas is appropriately injected into the upstream side to adjust the temperature of at least a part of the exhaust gas inlet side plugging portion of the ceramic honeycomb filter and the area of the outlet side thereof to the activity of the catalyst substance. It is characterized by maintaining the temperature at or above the lower limit temperature.
[0011]
The ceramic honeycomb filter according to the present invention has a structure as shown in FIGS. 1 and 7 to 11.
FIG. 1 is a schematic sectional view of an example of the honeycomb filter 11. The honeycomb filter 11 is a porous ceramic having a substantially circular or substantially elliptical cross section perpendicular to the flow path direction and having an outer peripheral wall 20 and a number of flow paths 40 surrounded by partition walls 30 on the inner peripheral side of the outer peripheral wall 20. Plugging

portions

50 and 52 are alternately plugged at desired portions of the flow channel 40 of the honeycomb structure 10. The at least one end face 51 of the plugged portion on the exhaust gas inflow side is arranged on the exhaust gas outflow side with respect to the inflow side end face 12 of the ceramic honeycomb filter, and the partition wall and / or the plugged portion is provided. The catalyst material 60 is supported on at least a part of the.
In the honeycomb filter having such a structure, the exhaust gas flows from the

flow paths

41 and 42 that are open at the inflow side end face 12. Among them, the exhaust gas 91 flowing from the flow channel 42 passes through the fine holes (not shown) formed in the partition wall 31 and is discharged to the adjacent flow channel 41 because of the presence of the inflow-side plugging portion 50. Then, after merging with the exhaust gas 90 flowing from the inflow side end face 12 into the flow path 41, the gas flows through the flow path 41 toward the outflow side end face 13, and passes through a fine hole (not shown) formed in the partition wall 32. Then, it is discharged (shown by an arrow 92) from the flow channel 43 which is open at the outflow side end face 13 which is the adjacent flow channel. During this time, the fine particles in the exhaust gas are burned and made harmless by the action of the catalyst substance when passing through the flow paths 41 to 43 and the partition walls 31 to 32, and the purified exhaust gas is discharged.
[0012]
Next, the function and effect of the present invention will be described.
As shown in FIGS. 1 and 7 to 11, the ceramic honeycomb filter of the present invention exhausts gas into pores formed in partition walls of the honeycomb structure by plugging channels of the porous ceramic honeycomb structure. In a ceramic honeycomb filter having a structure that allows gas to pass through, at least a part of the partition wall and / or the plugging portion carries a catalytic substance, and at least one exhaust gas inflow side plugging portion 50 has an exhaust gas inflow side. It is arranged away from the side end surface 12. For this reason, when it is estimated that the amount of particulates deposited on the honeycomb filter during operation of the internal combustion engine has reached a certain value or more, unburned fuel upstream of the filter is performed for the purpose of raising the temperature of the honeycomb filter. And / or at the time of injection of hydrocarbon gas, unburned fuel and / or hydrocarbon gas in the filter generates reaction heat due to an oxidation reaction by a catalytic substance. As shown in the figure, the inflow-side plugging portion end face 51 where the fine particles 70 are likely to adhere and accumulate is arranged at a high temperature portion in the honeycomb filter. Therefore, since the activity of the catalyst substance carried on the site is increased, the burning of the fine particles on the inflow-side plugging portion end face 51 is easily performed, and the fine particles on the inflow-side plugging portion end face 51 70 deposition can be prevented.
On the other hand, the partition wall 32 on the exhaust gas outflow side from the inflow side plugging portion 50 is arranged at a high temperature part in the honeycomb filter similarly to the inflow side plugging portion, as shown in the schematic diagram of FIG. Therefore, the activity of the catalyst material carried on the portion is in a high state, and the oxidizing combustion of the fine particles is easily performed, so that the exhaust gas flowing from the flow path 41 opened on the inflow side is formed on the partition wall 32. When the particles pass through the pores and are discharged to the adjacent flow channel 43, the fine particles in the exhaust gas are burned and purified.
As described above, during the operation of the internal combustion engine, if it is estimated that the amount of particulates deposited on the honeycomb filter has reached a certain value or more, the unburned upstream of the filter is performed for the purpose of raising the temperature of the honeycomb filter. When the fuel and / or hydrocarbon gas is injected, the purification action of the fine particles is performed in various places in the honeycomb filter, that is, the inflow side plugging portion 50, the partition wall 31 on the exhaust gas inflow side from the inflow side plugging portion, and the inflow side. According to the ceramic honeycomb filter of the present invention, since it is performed at a portion including the partition wall 32 on the exhaust gas outflow side from the plugged portion, the flow passage 40 as shown in FIG. The phenomenon that the pressure loss increases due to the blockage of the flow path due to the accumulation of fine particles at the open end of the filter is unlikely to occur. While avoiding problems, it can be used without increasing the pressure loss for a long time.
Further, when it is estimated that the amount of particulates deposited on the honeycomb filter during the operation of the internal combustion engine has reached a certain value or more, unburned fuel and / or unburned fuel upstream of the filter is used for raising the temperature of the honeycomb filter. Alternatively, when the hydrocarbon gas is injected, the temperature in the ceramic honeycomb filter has a distribution as shown in FIG. When such a temperature distribution occurs, as time passes, the exhaust gas flows from the inflow side plugging portion 50 and the partition wall 32 on the exhaust gas outflow side from the inflow side plugging portion 50. Due to the heat conduction to the partition wall 31 on the side, the temperature of the partition wall 31 rises, and the temperature of the inflow side end face 12 of the ceramic honeycomb filter also rises. The activity of the catalyst material thus increased increases, and the burning of the fine particles is easily performed more reliably, so that the fine particles 70 can be prevented from being deposited on the end face 51 of the inflow-side plugging portion.
The above is performed for the purpose of raising the temperature of the honeycomb filter when it is estimated that the accumulation amount of the fine particles on the honeycomb filter has become a certain value or more during the operation of the internal combustion engine. At the time of hydrocarbon gas injection, the temperature of the downstream region including the inflow-side plugging portion 50 in the honeycomb filter is described using an example in which the activity of the catalyst is increased. By adjusting the amount of unburned fuel and / or hydrocarbon gas, the temperature of the downstream region including the inlet-side plugging portion 50 in the honeycomb filter is set to 600 ° C. or more at which the self-burning of the fine particles occurs. Similarly, even if the particles are heated to a temperature and the particles are burned without using the power of the catalyst, the particles are easily burned at the inlet-side plugging portion end face 51 where the particles 70 are easily adhered and deposited. Side plugging part It is possible to prevent the deposition of fine particles 70 to the surface 51.
In addition, when the amount of fine particles deposited on the honeycomb filter during operation of the internal combustion engine is equal to or less than a certain value, there is no need to inject unburned fuel and / or hydrocarbon gas upstream of the honeycomb filter. If the exhaust gas temperature is higher than the catalyst activity lower limit temperature, the catalytic substance carried in each part of the honeycomb filter becomes active, and the particulate matter in the exhaust gas promotes the combustion reaction by the catalytic substance.

Exhaust gases

90 and 91 flowing into the filter are purified when passing through the flow path and the partition of the honeycomb filter, and are exhausted as an exhaust gas 92.
Here, it is not necessary that all the exhaust gas inflow side plugging portions 50 are arranged away from the exhaust gas inflow side end face 12 of the honeycomb filter as shown in FIG. 1, and as shown in FIG. What is necessary is just to arrange so that an objective can be achieved. That is, if at least 70% or more of the exhaust gas inflow side plugging portion 50 is separated from the exhaust gas inflow side end face 12, the effect of preventing an increase in pressure loss due to the accumulation of fine particles becomes large. When less than 70% of the plugged portions of the exhaust gas inflow side plugged portion 50 that are arranged apart from the exhaust gas inflow side end face 12 of the honeycomb filter are located at a high temperature portion in the ceramic honeycomb filter. Since the ratio of the disposed exhaust gas inflow side plugged portions 50 is reduced, that is, the ratio of the plugged portions disposed in the low-temperature portion in the ceramic honeycomb filter is increased, the low-temperature plugged portion end face is increased. This is because particles easily accumulate in the honeycomb filter, and the effect of preventing an increase in pressure loss of the honeycomb filter of the present invention is reduced.
In the present invention, if the exhaust gas inflow side plugging portion 50 is arranged at a high temperature portion in the ceramic honeycomb filter, the burning of the fine particles is easily performed, and the pressure loss due to the deposition of the fine particles is less likely to occur. In consideration of the above, in the exhaust gas inflow side plugging portion 50, as shown in FIG. 8, the exhaust gas inflow side plugging portion end face 51 may not be arranged at the same position from the inflow side end face 12, and As shown in FIG. 9, the lengths of the exhaust gas inflow side plugging portions 50 and the outflow side plugging portions 50 do not have to be all the same. Also, as long as the effects of the present invention can be obtained, the exhaust gas outlet side plugging portions 50 need not be arranged at the same position.
Further, as shown in FIG. 11, in the case of a ceramic honeycomb filter having a structure in which both ends of the flow path around the outer peripheral wall are plugged, exhaust gas is supplied to the flow path whose both ends around the outer peripheral wall are plugged. Since the gas does not flow, this flow path acts as an adiabatic space, and the heat generated by the exhaust gas and the catalyst in the ceramic honeycomb filter passes through the outer peripheral wall, and a gripping member that grips the honeycomb filter, Can be prevented from being released to the outside air via a metal container, and is therefore preferable because the temperature in the ceramic honeycomb filter can be made uniform.
Further, when the plugged portion on the exhaust gas outflow side is arranged apart from the ceramic honeycomb filter outlet side end surface similarly to the plugged portion on the exhaust gas inflow side, or is arranged so as to protrude from the outlet side end surface. , The same effect can be obtained.
[0013]
In the ceramic honeycomb filter of the present invention, the exhaust gas flows through pores in the partition wall 31 existing on the exhaust gas inflow side from the exhaust gas inflow side plugging portion 50 disposed apart from the exhaust gas inflow side end face. It is preferable that the partition wall 31 at least on the exhaust gas inflow side than the inflow side plugging portion 50 is located at a position where the temperature is lower than that of the inflow side plugging portion, as shown in the schematic diagram of FIG. Although disposed, the temperature of the catalyst material carried on the site is higher than that of the inflow-side end, and the activity of the catalyst material is higher than that of the inflow-side end. When the exhaust gas passes through the pores formed in the partition wall 31 and is discharged to the adjacent flow path 41, the fine particles in the exhaust gas are burned and purified.
The end face of the plugged portion on the exhaust gas inflow side of the honeycomb filter of the present invention is at least during a certain period during the operation of the internal combustion engine, that is, when it is estimated that the amount of particulates deposited on the honeycomb filter has reached a certain value or more, At the time of injecting unburned fuel and / or hydrocarbon gas upstream of the filter, which is performed for the purpose of raising the temperature of the honeycomb filter, the honeycomb filter is disposed at a position maintained at a temperature equal to or higher than the activation lower limit temperature of the catalyst material carried on the partition walls. It is preferable that the object of the present invention is to prevent fine particles from adhering and accumulating on the end face of the plugged portion on the exhaust gas inflow side to block the exhaust gas inflow side passage. When the end face 51 of the plugged portion on the exhaust gas inflow side is arranged at a position maintained at a temperature equal to or higher than the minimum activation temperature of the catalyst material carried on the partition wall, the action of the catalyst material reliably burns the fine particles. This is because that can be removed by. In addition, to dispose the end face 51 of the exhaust gas inlet side plugging portion at a position that is maintained at a temperature equal to or higher than the lower limit temperature of the catalytic substance means that the end face 51 of the plugged portion of the exhaust gas inlet side is necessarily maintained at a temperature equal to or higher than the lower limit temperature of the catalytic substance. It may be arranged not only at the position where the heat treatment is performed but also at a position higher than the temperature near the lower limit temperature of the activity.
Here, the activity lower limit temperature of the catalyst substance means a temperature at which the catalyst is activated.
It is preferable that the inflow side plugged portion end face 51 of the ceramic honeycomb filter of the present invention is disposed in a section having a length of 0.7 times the entire length of the ceramic honeycomb filter from the ceramic honeycomb filter inflow side end face 12, If the ceramic honeycomb filter is disposed beyond the section having a length of 0.7 times the entire length of the ceramic honeycomb filter from the inflow side end face 12, there is a restriction on the entire length of the ceramic honeycomb filter. This is because the area of the partition wall 32 on the outflow side is smaller than that of the partition wall 31, so that the initial pressure loss of the entire honeycomb filter may increase. Further, in order to sufficiently obtain the effect of increasing the filter temperature by the catalytic substance when unburned fuel and / or hydrocarbon gas is injected upstream of the honeycomb filter, the inflow-side plugging portion 50 is 1 mm from the inflow-side end face 12. More preferably, they are arranged apart from each other. Further, a more preferred section of the inflow side plugged portion end face 51 is a section having a length from the ceramic honeycomb filter inflow side end face 12 of 0.1 to 0.4 times the entire length of the ceramic honeycomb filter.
[0014]
Next, the catalyst material supported on the ceramic honeycomb filter of the present invention preferably contains a platinum group metal because the catalyst material containing the platinum group metal is injected into the unburned fuel injected upstream of the honeycomb filter. And / or promotes the combustion reaction of the hydrocarbon gas on the honeycomb filter, and promotes the generation of reaction heat, so that the temperature in the filter is easily increased, and the activity of the catalyst material is increased, This is because it promotes the purification reaction of the fine particles contained in the exhaust gas, especially the oxidation reaction. Here, the removal reaction of the fine particles contained in the exhaust gas by the catalytic substance containing the platinum group metal is performed as follows. When the fine particles in the exhaust gas come into contact with a catalytic substance containing a platinum group metal in an active state, for example, carbon C, which is the main component of the fine particles in the exhaust gas, becomes oxygen O₂Is oxidized by the reaction with₂It is converted to harmless and detoxified, so that it can be used for a long time without increasing the pressure loss. The catalyst material containing a platinum group metal includes, for example, Pt, Pd, Ru, Rh or a combination thereof, a platinum group metal oxide, and the like, but includes an alkaline earth metal oxide, a rare earth oxide, or a base metal catalyst. , Typically lanthanum, cesium, vanadium (La / Cs / V₂O₃) May be included. In addition, when the catalyst material contains a material having a high specific surface area made of known activated alumina such as γ-alumina, the contact area between the catalyst material and the exhaust gas can be increased, and the purification efficiency of the exhaust gas can be increased. Is preferred because
[0015]
Further, it is preferable that the activity of the catalyst substance carried on the partition wall 31 on the exhaust gas inflow side of the ceramic honeycomb filter is higher than the activity of the catalyst substance carried on the partition wall 32 on the exhaust gas outflow side. In the partition wall 31, the combustion reaction of the unburned fuel and / or hydrocarbon gas injected upstream of the honeycomb filter on the honeycomb filter is promoted, and the generation of reaction heat is further promoted. In this case, since the temperature inside the filter easily rises, the activity of the catalyst material carried on the inflow side plugging portion end face 51 increases, and the accumulation of fine particles on this portion can be prevented, and the pressure of the filter can be reduced. In addition to preventing the loss from increasing, the main component of fine particles in the exhaust gas, for example, due to the catalyst material carried on the partition wall 31 on the exhaust gas inflow side from the inflow side plugging portion 50 CO of certain carbon C₂This is because the conversion rate to the gas becomes high, and the oxidation and combustion reaction of the fine particles in the exhaust gas in the flow path 42 is efficiently performed, so that the gas can be used for a long time without increasing the pressure loss. Here, the fact that the activity of the catalyst substance carried on the partition wall 31 on the exhaust gas inflow side is higher than the activity of the catalyst substance carried on the partition wall 32 on the exhaust gas outflow side means, for example, that the inflow side plugging is performed. The content of the catalyst material containing the platinum group metal in the catalyst material supported on the partition wall 31 on the exhaust gas inflow side from the stop portion 50, the alkaline earth metal oxide, the rare earth oxide, or the base material as the promoter material This means that the content of the metal catalyst is higher than that of the catalyst material supported on the partition wall 32 on the exhaust gas outlet side, and the performance of the catalyst is high when the supported catalyst as a whole is viewed.
For example, the content of the white metal in the catalyst material supported on the partition 31 on the exhaust gas inflow side from the inflow side plugging portion 50 is determined by the content of the white metal in the catalyst material supported on the partition 32 on the exhaust gas outflow side. By increasing the content, a ceramic honeycomb filter in which the pressure loss does not increase over a long period of time can be obtained.
Further, the partition wall 31 on the exhaust gas inflow side from the inflow side plugging portion 50 carries a large content of a catalytic substance containing a platinum group metal such as Pt, Pd, Ru, Rh or the like, which is an oxidation catalyst. On the partition wall 32 on the exhaust gas outlet side, a base metal catalyst as a promoter, typically lanthanum, cesium, vanadium (La / Cs / V₂O₃By supporting a large amount of the catalytic substance of the type (1) and the catalytic substance containing a platinum group metal, the combustion of the fine particles is carried out efficiently, so that a ceramic honeycomb filter in which the pressure loss hardly increases for a long time can be obtained.
The exhaust gas purification method of the present invention has a structure in which exhaust gas passes through pores formed in partition walls of a honeycomb structure by plugging flow paths of a porous ceramic honeycomb structure, and at least the partition walls And a catalyst and / or a hydrocarbon, as appropriate, on the upstream side of the ceramic honeycomb filter in which at least one exhaust gas inflow side plugging portion is arranged at a distance from the end surface of the exhaust gas inflow side. By injecting the gas unburned, the oxidation reaction of fuel and / or hydrocarbon gas is promoted on the catalyst substance, and the heat of the reaction causes at least the exhaust gas inlet side plugging portion of the ceramic honeycomb filter to the outlet side of the ceramic honeycomb filter. Since the temperature of the region is maintained at a temperature equal to or higher than the activity lower limit temperature of the catalyst substance, even when the temperature of the exhaust gas from the internal combustion engine is low, the honeycomb filter may be used. The fuel and / or hydrocarbon gas is injected unburned to the upstream side of the filter, and the fuel and / or hydrocarbon gas is burned by the action of the catalytic substance carried on the partition walls and plugging portions of the honeycomb filter. Since the exhaust gas is heated to a high temperature in the honeycomb filter and is forcibly maintained at a temperature equal to or higher than the activity lower limit temperature of the catalyst material carried on the honeycomb filter, fine particles in the exhaust gas are removed without interruption. In addition, compared to the honeycomb filter having the conventional structure in which the exhaust gas inlet side plugging portion is formed on the exhaust gas inlet side end face of the honeycomb filter, the exhaust gas inlet side where the problem that particles accumulate and block the flow path is likely to occur. Since the plugging portion 50 is arranged at a distance from the end face on the exhaust gas inflow side, the supported catalyst substance is maintained at a temperature equal to or higher than the activation lower limit temperature, and the burning and removal of fine particles in the exhaust gas are performed efficiently. Can be prevented, and the pressure loss does not increase over a long period of time.
[0016]
Next, the porous ceramic honeycomb structure used in the present invention will be described.
As a material constituting the partition wall and plugging material of the porous ceramic honeycomb structure used in the present invention, the present invention is mainly used as a filter for removing particulates in exhaust gas of a diesel engine, It is preferable to use a material having excellent heat resistance, and it is preferable to use a ceramic material having a main crystal of at least one selected from the group consisting of cordierite, alumina, mullite, silicon nitride, silicon carbide, and LAS. Among them, a ceramic honeycomb filter using cordierite as a main crystal is most preferable because it is inexpensive, has excellent heat resistance and corrosion resistance, and has low thermal expansion.
The porosity of the partition walls of the honeycomb structure is preferably 50 to 80%. Since the exhaust gas passes through the pores formed in the partition wall, if the porosity of the partition wall is less than 50%, the pressure loss of the honeycomb filter increases, leading to a decrease in engine output. If the ratio exceeds 80%, the strength of the partition wall is reduced, and the partition wall may be damaged by thermal shock or mechanical vibration during use. In addition, the porosity of the plugging material of the honeycomb structure is lower than the porosity of the partition, if the same, or may be higher, but if the porosity is higher than the porosity of the partition Since the exhaust gas can also pass through the inside of the pores in the plugging material, it is preferable because the accumulation of fine particles on the exhaust gas inflow side end face 51 of the exhaust gas inflow side plugging portion is less likely to occur. .
The partition wall thickness of the ceramic honeycomb filter according to the present invention is preferably 0.1 to 0.5 mm, and the pitch of the partition walls is preferably 1.2 mm or more. If the partition wall thickness is less than 0.1 mm, the strength of the honeycomb structure is reduced because the partition wall is a porous material having high porosity having pores, which is not preferable. On the other hand, if the partition wall thickness exceeds 0.5 mm, the pressure loss of the filter becomes large because the partition wall has high ventilation resistance to exhaust gas, no matter how high the porosity of the partition wall. A more preferred partition wall thickness is 0.2 to 0.4 mm. Further, when the pitch of the partition walls is less than 1.3 mm, the opening area of the inlet of the honeycomb structure becomes small, so that the pressure loss at the filter inlet becomes large.
[0017]
Next, an example of a method for manufacturing a ceramic honeycomb filter of the present invention will be described with reference to FIG. As shown in FIG. 2, a resin mask 80 provided with a resin slurry introduction passage 81 in a checkered pattern is attached to the end face on the exhaust gas inflow side of the honeycomb structure as shown in FIG. The plugging material 53 in the form of slurry is introduced through the slurry introduction passage 81 to fill a part of the flow channel of the honeycomb structure. After that, the water contained in the plugging material 53 in a slurry state is not solidified when the partition walls of the honeycomb structure absorb water and the plugging material is deposited on the partition walls to obtain shape retention. After discharging the slurry and removing the resin mask, the solidified plugging material is dried. At this time, the plugging material in the slurry existing in the resin slurry introduction passage 81 does not solidify because there is no water absorption from the partition walls. Therefore, by adjusting the length of the slurry introduction passage, the exhaust gas inlet side The formation position of the sealing portion from the honeycomb structure inflow side end surface can be determined. On the other hand, a plugging portion is formed at the end of the end surface on the outflow side by a known technique, and thereafter, the plugging material is baked to integrate the partition wall and the plugging material.
In addition, as another method, an injection needle-shaped tube is inserted from the end of the honeycomb structure to a predetermined position of the flow path, and after a predetermined amount of paste-like plugging material is introduced into the predetermined position through the tube, A method of drying and firing, a method of embedding and firing a ceramic chip in the inside of the honeycomb structure, and the like are adopted, and the partition and the plugging material can be integrated.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the invention will be described in detail.
(Example 1)
By adjusting powder such as kaolin, talc, silica, aluminum hydroxide, alumina, etc.₂ : 47-53%, Al₂O₃: 32 to 38%, MgO: 12 to 16% and CaO, Na₂O, K₂O, TiO₂ _,Fe₂O₃, PbO, P₂O₅A molding aid and a pore-forming agent are added to a cordierite-forming raw material powder containing a total of 2.5% or less of components inevitably mixed, such as the above, and a sufficient amount of water is injected by injecting a specified amount of water. Was performed to prepare a clay that can be extruded into a honeycomb structure.
Then, extrusion molding is performed using a known extrusion molding die, and an outer peripheral wall, and a cross-section surrounded by a partition wall on the inner peripheral side of the outer peripheral wall, to produce a honeycomb structure molded body having a rectangular flow path, After drying, baking was performed to prepare a honeycomb structure having a partition wall structure having a diameter of 267 mm, a total length of L 300 mm, a partition wall pitch of 1.5 mm, a partition wall thickness of 0.3 mm, and a partition wall porosity of 65%.
[0019]
Next, as shown in FIG. 2, a resin mask 80 provided with a checkerboard-shaped slurry introduction passage 81 is attached to the end face on the exhaust gas inflow side of the honeycomb structure, and a slurry plugging material is passed through the slurry introduction passage. Introduced and filled a part of the channel of the honeycomb structure.
Then, after the plugging material was deposited on the partition walls to obtain shape retention, the resin mask was removed, and the plugging material 53 was dried. Here, the length of the slurry introduction passage 81 was adjusted so that the exhaust gas inflow side plugged portion was formed at five positions from the end face of the honeycomb filter. On the other hand, the plugged portion on the end face on the exhaust gas outflow side of the honeycomb structure is formed by attaching a masking film to the end face with an adhesive, and then piercing in a checkered pattern, followed by a slurry plugging material. Was introduced from the end face to form a plugged portion. Next, the plugging material was fired while controlling the temperature using a batch-type firing furnace, and the test sample No. shown in FIG. 1 to 6 honeycomb filters 11 were obtained.
The distance X (mm) between the exhaust gas inflow side end face 51 of the exhaust gas inflow side plugging portion and the honeycomb filter end face 12 was measured for the obtained honeycomb filter. X was measured by inserting a metal rod having a diameter of about 0.8 mm and a length of 200 mm from the end face on the exhaust gas inflow side, and reading the length of the metal rod coming out of the honeycomb filter. The measurement was performed on arbitrary 20 plugged portions of one honeycomb filter, and an average value was calculated. These test nos. Table 1 shows the distance X (mm) between the exhaust gas inflow side end face 51 of the exhaust gas inflow side plugging portion of each of the honeycomb filters 1 to 6 and the honeycomb filter end face 12 and the value of X / (overall length L of the honeycomb filter). Shown in
[0020]
With respect to the honeycomb filter, a catalyst material comprising Pt, cerium oxide, and activated alumina is supported on the surface of the partition wall and inside the pores in the partition wall, and further on the surface of the plugging portion and inside the pores in the plugging portion. I let it. The supported amount was 2 g / L in Pt amount (meaning that 2 g was supported for 1 L of honeycomb filter volume).
[0021]
The test NO. The ceramic honeycomb filters Nos. 1 to 6 were installed in a pressure loss test device (not shown), and the air flow rate was 7.5 Nm.³Air was flowed under the condition of / min, and the differential pressure between the inflow side end face and the outflow side end face was measured to evaluate the initial pressure loss of each ceramic honeycomb filter. At this time, in the test No. 1 in which the end face of the plugged portion on the exhaust gas inflow side was arranged on the same plane as the honeycomb filter. Assuming that the initial pressure loss of the ceramic honeycomb filter of Test No. 1 was 1, the test NO. Table 1 shows the initial pressure losses of 2 to 6. The pressure loss of the ceramic honeycomb filter formed as described above was measured as follows. Further, the test NO. The endurance test was performed under the pattern running conditions simulating the running in an urban area, with 1 to 6 honeycomb filters arranged. At this time, a case where an operating condition in which the exhaust gas temperature is lower than the activation lower limit temperature of the catalytic substance continues may occur, and a condition that the particulates slightly accumulate on the filter is created. In accordance with the estimated amount of particulates deposited on the filter carrying the catalyst substance, when it is determined that the deposited amount has reached a certain value or more, fuel is injected unburned to the upstream side of the filter , Forced regeneration of the filter. If the test could be continued until the time corresponding to 10,000 km of travel, the test was judged as pass (合格), the test that could not be continued was judged as failed (×), and if the test was not passed, the test was judged as 10,000. The pressure loss of the honeycomb filter after a lapse of time equivalent to 000 km traveling is measured in the same manner as the initial pressure loss, and compared with the initial pressure loss, the pressure loss ratio: (pressure loss after test) / (initial pressure loss) Calculated.
[0022]
[Table 1]

[0023]
Test No. 1 is a comparative example in which the end face of the plugged portion on the exhaust gas inflow side is arranged on the same plane as the end face of the honeycomb filter. As for the ceramic honeycomb filter of No. 1, the exhaust pressure rapidly increased after traveling about 5,000 km, and the test was interrupted because the regeneration became impossible. On the other hand, in the test NO. In the ceramic honeycomb filters of Nos. 2 to 6, the end face of the plugged portion on the exhaust gas inflow side is disposed farther to the outflow side from the end face on the inflow side of the exhaust gas of the ceramic honeycomb filter, and the partition wall and the plugged portion carry a catalytic substance. Therefore, even when unburned fuel is injected upstream of the filter, the particulates accumulate on the exhaust gas inflow side of the honeycomb filter and are unlikely to block the flow path, so in a durability test for a time equivalent to 10,000 km traveling, Also, the test passed (なく) without any problem. Test No. In Test Nos. 2 to 5, the distance X between the honeycomb filter inlet side end face and the exhaust gas inlet side end face of the exhaust gas inlet side plugging portion was 0.7 or less of the entire length L of the honeycomb filter. The increase in the initial pressure loss with respect to the ceramic honeycomb filter of No. 1 is slight, and does not lead to a decrease in the output of the engine. In particular, the test NO. In the ceramic honeycomb filters 2 to 3, the distance X between the honeycomb filter inflow side end face and the exhaust gas inflow side end face of the exhaust gas inflow side plugging portion is 0.1 to 0.4 of the entire length L of the honeycomb filter. , The initial pressure loss was measured in Test NO. The same as the ceramic honeycomb filter of No. 1, and the pressure loss rise is small even after the durability test for a time corresponding to 10,000 km running, and the pressure loss ratio is less than 1.2. It turned out to be.
[0024]
(Example 2)
After manufacturing a honeycomb structure having a partition structure having a diameter of 267 mm, a length of 300 mm, a partition pitch of 1.5 mm, a partition thickness of 0.3 mm, and a partition wall porosity of 65% in the same manner as in the example, In FIG. 1, the positions of the exhaust gas inflow side plugging portion formation position X from the honeycomb filter inflow side end surface are 49.8 mm and 96.3 mm. Seven to eight honeycomb filters 50 were obtained.
[0025]
For the honeycomb filter, a catalytic material comprising Pt, cerium oxide, and activated alumina was filled with a catalytic substance consisting of Pt, cerium oxide, and activated alumina on the surface of the partition wall on the exhaust gas outflow side with respect to the exhaust gas inflow side plugging portion, inside the pores in the partition wall, and further plugged. It was carried on the surface of the stopper and inside the pores in the plugged portion. At this time, the supported amount in the catalyst substance was 1 g / L in Pt. On the other hand, a catalyst material having a Pt concentration higher than that of the catalyst material was carried on the surface of the partition wall on the exhaust gas inflow side from the plugged portion on the exhaust gas inflow side and inside the pores in the partition wall. At this time, the supported amount of the catalyst substance was 4 g / L in Pt.
[0026]
The durability test of the ceramic honeycomb filter formed as described above was measured in the same manner as in Example 1, and the judgment was made after the passage of time corresponding to 10,000 km traveling. The honeycomb filter after the passage of time corresponding to 10,000 km traveling was performed. Was measured and compared with the initial pressure loss to calculate a pressure loss ratio: (pressure loss after test) / (initial pressure loss).
[0027]
[Table 2]

[0028]
Test No. In the ceramic honeycomb filters 7 to 8, the end face of the plugged portion of the exhaust gas inflow side is disposed on the outflow side from the end face of the exhaust gas inflow side of the ceramic honeycomb filter, and the partition wall and the plugged portion carry a catalytic substance. Since the amount of Pt carried on the exhaust gas inflow side is higher than that of the plugged portion, and the activity of the catalyst substance on the exhaust gas inflow side is higher than that on the exhaust gas outflow side, the time corresponding to 10,000 km traveling is obtained. In the endurance test, no problem was found in the test. Even after a durability test for a time equivalent to 10,000 km traveling for a few ceramic honeycomb filters, the rise in pressure loss is small and the pressure loss ratio is small, so that the filter can be used for a longer period of time. It is possible.
[0029]
(Example 3)
A honeycomb structure having a partition wall structure having a diameter of 267 mm, a length of 300 mm, a partition wall pitch of 1.5 mm, a partition wall 11b having a thickness of 0.3 mm, and a porosity of the partition walls of 65% was produced in the same manner as in the example. After that, plugging is performed, and the test NO. As shown in FIG. 1 where the positions X where the exhaust gas inflow side plugging portions are formed from the honeycomb filter inflow side end face are 49.8 mm and 96.3 mm. 9 to 10 honeycomb filters 50 were obtained.
[0030]
The catalyst material 1 composed of Pt, cerium oxide, and activated alumina was supported on the above-described honeycomb filter in the partition wall on the exhaust gas inflow side from the inflow side plugging portion and in the pores in the partition wall. After that, a catalyst material 3 to which a catalyst material composed of lanthanum, cesium, and vanadium is added is used. It was carried on the surface and inside the pores in the plugged portion. Thereby, the activity of the catalyst material carried on the partition wall on the exhaust gas inflow side from the inflow side plugging portion is higher than that of the catalyst material carried on the partition wall on the exhaust gas outflow side.
[0031]
The durability test of the ceramic honeycomb filter formed as described above was measured in the same manner as in Example 1, and the judgment was made after the passage of time corresponding to 10,000 km traveling, and the honeycomb filter after the passage of time corresponding to 10,000 km traveling. Was measured and compared with the pressure loss before the test to calculate a pressure loss ratio: (pressure loss after the test) / (pressure loss ratio before the test).
[0032]
[Table 3]

[0033]
Test No. In the ceramic honeycomb filters 9 to 10, the end face of the plugged portion of the exhaust gas inflow side is disposed on the outflow side from the end face of the exhaust gas inflow side of the ceramic honeycomb filter, and the partition walls and the plugged portion are made of Pt, cerium oxide, and activated alumina. A catalyst material is supported, and a catalyst material composed of lanthanum, cesium, and vanadium is supported on the exhaust gas inflow side with respect to the inflow side plugged portion. Since it is higher than the outflow side, a pass (○) was obtained without any problem even in a durability test for a time equivalent to traveling 10,000 km, and the test NO. Even after a durability test for a time corresponding to 10,000 km after the durability test, the rise in pressure loss is small and the pressure loss ratio is small for a few ceramic honeycomb filters. It can be used all over.
[0034]
【The invention's effect】
As described in detail above, in a ceramic honeycomb filter in which fine particles are continuously burned by a catalyst material carried on the honeycomb filter, the end face of the plugged portion on the exhaust gas inflow side is closer to the outflow side than the end face on the exhaust gas inflow side of the ceramic honeycomb filter. Since it is arranged, the amount of particulates deposited on the filter carrying the catalyst substance is estimated in accordance with the operation state of the diesel engine, and then the fuel and / or hydrocarbon gas is appropriately placed upstream of the filter. Even when the fuel is injected unburned, combustion of the fine particles by the catalytic substance is liable to occur, and the flow path is not easily blocked by the deposition of the fine particles on the honeycomb filter. Obtaining a honeycomb filter and an exhaust gas purifying method that avoids and stably reduces pressure loss over a long period of time It can be.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of a honeycomb filter according to an embodiment.
FIG. 2 is a schematic cross-sectional view showing a state where a plugging material is introduced into a honeycomb structure.
FIG. 3 is a perspective view of a conventional honeycomb filter.
FIG. 4 is a schematic sectional view of the honeycomb filter of FIG.
FIG. 5 is a cross-sectional view of a honeycomb filter schematically showing fine particles deposited on the honeycomb filter.
FIG. 6 is a schematic cross-sectional view of a conventional ceramic honeycomb filter and a diagram showing a temperature change in a longitudinal direction.
FIG. 7 is a schematic cross-sectional view of a ceramic honeycomb filter of the present invention and a diagram showing a temperature change in a longitudinal direction.
FIG. 8 is a schematic sectional view of a ceramic honeycomb filter of the present invention.
FIG. 9 is a schematic sectional view of a ceramic honeycomb filter of the present invention.
FIG. 10 is a schematic sectional view of a ceramic honeycomb filter of the present invention.
FIG. 11 is a schematic sectional view of a ceramic honeycomb filter of the present invention.
[Explanation of symbols]
10: Honeycomb structure
11: Honeycomb filter
12: Inflow side end face
13: Outflow side end face
20: Outer wall
30: Partition wall
31: Partition wall on the inflow side from the inflow side plugged portion
32: Partition wall on the outflow side from the inflow side plugged portion
40: Channel
41: Flow path open at the inflow side end face
42: Flow path open at the inflow side end face
43: Flow path opened to exhaust gas outflow side
50: inflow side plugged portion
51: End face of inflow side plugged portion
52: Outflow-side plugged portion
53: Plugging material
60: Catalyst substance
70: fine particles
80: Mask
81: Slurry introduction passage
90: Inflow of exhaust gas
91: Inflow of exhaust gas
92: Outflow of exhaust gas
X: Plugging part formation position

Claims

In a ceramic honeycomb filter having a structure in which exhaust gas passes through pores formed in partition walls of the honeycomb structure by plugging a flow path of the porous ceramic honeycomb structure, the partition walls and / or the plugged portions may be provided. A ceramic honeycomb filter, wherein a catalyst substance is supported on at least a part of the ceramic honeycomb filter, and at least one exhaust gas inflow side plugging portion is disposed apart from an end surface of the exhaust gas inflow side.

The exhaust gas passes at least through pores in a partition wall present on an exhaust gas inflow side from an exhaust gas inflow side plugging portion disposed apart from the exhaust gas inflow side end face. The ceramic honeycomb filter according to the above.

The end face of the exhaust gas inlet-side plugged portion is arranged at a position maintained at least at the activity lower limit temperature of the catalyst substance carried on the inlet-side plugged portion during at least a certain period during operation of the internal combustion engine. The ceramic honeycomb filter according to claim 1 or 2, wherein:

The exhaust gas inflow side plugging portion end face is disposed in a section having a length of 0.7 times or less the total length of the ceramic honeycomb filter from the inflow side end face of the ceramic honeycomb filter. The ceramic honeycomb filter according to any one of the above.

The ceramic honeycomb filter according to any one of claims 1 to 4, wherein the catalyst material supported on the ceramic honeycomb filter includes a platinum group metal.

6. The activity of the catalyst substance carried on the partition wall on the exhaust gas inflow side of the ceramic honeycomb filter is higher than the activity of the catalyst substance carried on the partition wall on the exhaust gas outflow side. The ceramic honeycomb filter according to any one of the above.

A structure in which exhaust gas passes through pores formed in partition walls of the honeycomb structure by plugging a flow path of the porous ceramic honeycomb structure, wherein at least one of the partition walls and / or plugged portions is provided. While the catalyst material is carried on the portion, at least one exhaust gas inflow side plugging portion is located upstream of the ceramic honeycomb filter which is arranged apart from the exhaust gas inflow side end face, and unburned fuel and And / or injecting a hydrocarbon gas to lower the temperature of at least a part of the exhaust gas inflow side plugged portion of the ceramic honeycomb filter and the region on the outflow side of the exhaust gas inflow side plugged portion to the activation lower limit temperature of the catalyst substance. An exhaust gas purification method characterized by maintaining the above.