JP2004016931A - Exhaust gas purification catalyst - Google Patents

Exhaust gas purification catalyst Download PDF

Info

Publication number
JP2004016931A
JP2004016931A JP2002175795A JP2002175795A JP2004016931A JP 2004016931 A JP2004016931 A JP 2004016931A JP 2002175795 A JP2002175795 A JP 2002175795A JP 2002175795 A JP2002175795 A JP 2002175795A JP 2004016931 A JP2004016931 A JP 2004016931A
Authority
JP
Japan
Prior art keywords
layer
nox
exhaust gas
catalyst
powder
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
JP2002175795A
Other languages
Japanese (ja)
Inventor
Yasunari Hanaki
花木 保成
Hironori Wakamatsu
若松 広憲
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nissan Motor Co Ltd
Original Assignee
Nissan Motor Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nissan Motor Co Ltd filed Critical Nissan Motor Co Ltd
Priority to JP2002175795A priority Critical patent/JP2004016931A/en
Publication of JP2004016931A publication Critical patent/JP2004016931A/en
Pending legal-status Critical Current

Links

Images

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas purification catalyst having a high NOx purification ratio in a wide cleaning temperature region, especially a low temperature region and capable of efficiently purifying not only NOx in an oxygen excessive region discharged from an internal combustion engine but also CO and HC even if an exhaust gas is in a low temperature region. <P>SOLUTION: An inner layer containing an NOx adsorbent for adsorbing NOx in an exhaust gas and a surface layer comprising an NOx purification layer for reducing and purifying NOx discharged from the NOx adsorbent of the inner layer are provided. An isolation means, which comprises a heat-resistant porous inorganic material and temporarily holds NOx discharged from the inner layer to delay the arrival thereof to the surface layer, is interposed between the inner and outer layers. <P>COPYRIGHT: (C)2004,JPO

Description

【0001】
【発明の属する技術分野】
本発明は、内燃機関の排気浄化装置に係わり、さらに詳細には、流入する排気の空燃比がリーンのときに排気中のNOx を吸着し、流入する排気の空燃比がリッチ及び/又はストイキのときに吸着したNOx を放出するNOx吸着剤と、放出したNOxを還元浄化するNOx浄化触媒を備えた排気ガス浄化触媒に関するものである。
【0002】
【従来の技術】
上記のような内燃機関の排気浄化装置としては、流入する排気空燃比がリーンのときに排気中のNOx(窒素酸化物)を吸収し、流入する排気空燃比がリッチになると吸収したNOxを放出して還元浄化するNOx吸収還元触媒が知られている。この種のNOx吸収還元触媒を使用した排気浄化装置の例としては、例えば特許第2600492号に記載されたものがある。
【0003】
上記特許に係わる排気浄化装置は、リーン空燃比運転を行う機関の排気通路にNOx吸収還元触媒を配置し、機関のリーン空燃比運転中にNOx吸収還元触媒に排気中のNOx を吸収させ、NOx吸収還元触媒のNOx吸収量が増大したときに機関を短時間理論空燃比以下の空燃比(すなわちリッチ空燃比)で運転するリッチスパイク操作を行うことにより、NOx吸収還元触媒から吸収したNOxを放出させると共に、放出されたNOxを還元浄化している。すなわち、機関の運転空燃比がリッチになると、リーン空燃比運転時に較べて排気中の酸素濃度が急激に低下するとともに排気中の未燃HC、CO成分の量が急激に増大する。このため、リッチスパイク操作により機関運転空燃比がリッチ空燃比に切り換えられると、NOx吸収還元触媒からNOxが放出され、NOx吸収還元触媒上で排気中の未燃HC、CO成分と反応し還元される。
【0004】
また、上記特許公報には、NOx吸収還元触媒の上流側排気通路に三元触媒を配置して機関始動時に機関から排出されるHC、CO成分を浄化するようにした構成が開示されている。当該三元触媒は機関排気マニホルド近傍に配置され機関からの高温の排気が通過するため、機関始動後短時間で昇温し三元触媒の活性化温度に到達する。従って,機関始動後暖機完了までの時間が短縮されるため、この間に比較的多量に機関から排出されるHC、COを低減することができる。
【0005】
ディーゼルエンジン等においては、排気管途中に触媒を設置して、内燃機関より排出されるNOxを浄化している。かかるNOx浄化触媒としては、ゼオライト系触媒やアルミナ系触媒等の種々の触媒が知られているが、いずれもNOx浄化作用を示す温度域が限られている。このため、浄化温度域の異なる複数の触媒を組み合わせてNOx浄化温度域を拡大させることが提案されている。例えば、特開平6−134258号公報には、モルデナイトに担持するコバルトの量を変えて、最高活性が得られる反応温度が異なる複数の触媒を用いた触媒装置が開示されている。なお、複数の触媒は、通常、高温活性触媒は排気流路の上流側に、低温活性触媒は排気流路の下流側に配置される。
【0006】
また、特開平6−307231号公報には、複数のNOx浄化触媒を、排気ガスの流れ方向に直列に、かつ炭化水素に対する酸化活性能力が下流側に向かって順次大きくなるように配置した触媒装置が開示されている。
【0007】
【発明が解決しようとする課題】
上記特許第2600492号に記載されたようなNOx吸収還元触媒では、白金Pt、パラジウムPd、ロジウムRh等の貴金属触媒成分の他に、アルカリ、アルカリ土類金属に代表されるようなNOx吸収物質を使用している。しかし、当該特許に記載されているように、リーン空燃比運転中にリッチスパイク運転を行い排気空燃比をリッチ空燃比にすると排気中のHC、CO成分の量が急激に増大するが、HC、CO成分はNOx吸収還元触媒の触媒成分に付着しやすい性質があるため、NOx吸収還元触媒に流入する排気中のHC、CO成分が急激に増大すると付着したHCやCOによって触媒成分表面が覆われてしまい、触媒としての機能が低下する問題、すなわちHC被毒やCO被毒が生じてしまい、NOx吸収還元触媒のNOx浄化能力が低下する問題がある。
【0008】
このHC被毒やCO被毒といった現象は、触媒の活性が低い低温度域において顕著である。酸素過剰雰囲気下で吸収したNOxをリッチ雰囲気下でNOx吸収還元触媒から放出し、同触媒上で還元浄化しようとしても、HC被毒やCO被毒、特に還元ガス中に含まれるCOによりNOx吸収還元触媒が被毒され、NOx吸収還元触媒からNOxが十分に放出されないため、NOx吸収還元触媒のNOx吸着力回復せず、従って、NOx浄化率が大幅に低下してしまうといった問題が発生することがあった。また、複数の触媒を使用しても、それぞれのNOx浄化量がわずかなため、NOx浄化率が大幅に低下してしまうという問題点があった。このような背景から、本発明者らは、高温域ではNOxの浄化に非常な有用な還元剤(COやHC)が低温域ではNOxの浄化を妨げるため、NOx浄化率が大きく向上しないことに着目した。
【0009】
本発明は、従来技術が有するこのような課題に鑑みてなされたものであり、その目的とするところは、内燃機関から排出される酸素過剰領域のNOxを効率よく浄化すると共に、排気ガスが低温域であってもCO及びHCを効率良く浄化することができる排気ガス浄化触媒を提供することにある。また、本発明は、広い浄化温度域、特に低温域において一定以上の高いNOx浄化率を示す排気ガス浄化触媒を提供することを目的としている。
【0010】
【課題を解決するための手段】
本発明に係わる排気ガス浄化触媒は、内燃機関の排気通路に配置する排気ガス浄化触媒であって、排気中のNOxを少なくともNO‐吸着種として吸着するNOx吸着剤を含有する内層と、該内層の前記NOx吸着剤から放出されるNOxを還元浄化するNOx浄化層からなる表層を有すると共に、耐熱性多孔質無機材料からなり、内層から放出されたNOxを一時的に保持して表層側への到達を遅延させる隔離手段が前記表層と内層の間に介在している構成としたことを特徴しており、排気ガス浄化触媒におけるこのような構成を上記課題を解決するための手段としている。このとき、上記内層をPt、Pd及びRhから選ばれる少なくとも1種の貴金属と酸素吸蔵成分からなるNOx吸着剤を含有するものに替えることができる。
【0011】
また、本発明に係わる排気ガス浄化触触媒においては、隣接するセルの両端部が交互に目詰めされたウォールフロー型ハニカム担体を使用し、当該担体のセル壁を上記隔離手段として利用し、担体セル壁の排気ガス上流側面に、上記内層成分を含む上流側層を形成し、担体セル壁の排気ガス下流側面に上記表層成分を含む下流側層を形成したものとすることも可能である。
【0012】
【発明の実施の形態】
以下、本発明に係わる排気ガス浄化触媒の実施形態について詳細に説明する。なお、本明細書において、「%」は特記しない限り質量百分率を意味するものとする。
【0013】
本発明に係わる排気ガス浄化触触媒は、NO‐吸着種としてNOxを吸着するNOx吸着剤を含む内層と、このNOx吸着剤から放出されるNOxを還元浄化するNOx浄化層からなる表層を有し、これら内外層の間に隔離手段を介在させたものであり、当該排気ガス浄化触媒によれば、リッチ雰囲気下でCO被毒を受けず、しかも低温域においてもNOxが放出可能なNOx吸着剤を使用し、かつ、リッチ及び/又はストイキ雰囲気下で、NOx吸着剤から放出されたNOxを浄化することができる。
すなわち、リーン空燃比で運転されNOx吸着剤に流入する排気がリーン空燃比である場合には、排気中の多くのNOxがNO‐として吸着することにより、HCやCOが排気ガス中に多量に含まれる場合でも、触媒上でNO‐吸着種の結合が切断されれば容易にNOxを放出することができる。言い換えると、HC被毒やCO被毒の影響を受け難く、したがってNOx浄化層をNOx吸着剤の上側に配置した触媒構造とすることにより、低温域においても、また、リッチガス中にCOが含まれている状態においても、高いNOx浄化性能を保つことができることになる。
【0014】
さらに、NOx吸着剤からなる内層と、前記内層のNOx吸着剤から放出するNOxを還元浄化するNOx浄化層からなる表層の間に、耐熱性多孔質無機材料からなる両層間の隔離手段を備えているので、両端が開放された通常のオープンセル型の担体に当該触媒を塗布した場合、排気ガスは一旦触媒の内層方向に浸透、分散したのち、内層方向から表層方向に向けて拡散していくことになり、内層と表層の間の隔離手段が細孔を備えていることから、その細孔内での反応ガス拡散が生じやすくなり、いわゆるバッファーの役割を果たすものと考えられる。したがって、排気ガスの条件が急激に変化する場合において、内層のNOx吸着剤に吸着したNOxが脱離し、NOx浄化層に拡散していく際、この隔離手段によりNOxの拡散速度が緩やかなものとなり、反応速度がそれほど大きくない低温域(200℃以下)においても高いNOx浄化性能が保持されることになる。
【0015】
隔離手段による遅延作用は、HCやCOなどの還元剤に対しても有効であって、隔離手段の細孔内で乱流、再拡散を生じさせることができるため、還元剤が触媒担体層に長く留まることでき、結果として、反応速度がそれほど大きくない低温域(200℃以下)でのNOx浄化性能を高く保つことができる。なお、このような隔離手段としては、その耐熱性、成形性、コスト、入手のし易さなどの観点から、コージェライト、SiC(炭化ケイ素)、アルミナ、シリカ、ジルコニア、チタニア及びゼオライトなどの耐熱性多孔質無機材料が好適に用いられる。
【0016】
上記表層中のNOx吸着剤としては、その中に少なくともチタン及び/又はジルコニウム酸化物が含まれるものを使用することができる。すなわち、NOx吸着剤中に、このような成分が含まれることにより、NOxが非常に放出しやすくなる。また、吸着剤中に三元成分を添加することにより、吸着および吸着したNOxの放出特性が向上することが判っているので、Pt、Pd及びRhなどの貴金属触媒成分をさらに添加するのが望ましい。なお、これら酸化物としては、チタンやジルコニウムを含む他の元素との複合酸化物であってもよい。
【0017】
また、上記NOx吸着剤においては、多孔質担体を使用することもできる。その材質としては、特に限定されるものではないが、例えばアルミナ、シリカ、シリカアルミナやチタニア等を挙げることができ、とりわけ耐熱性及び貴金属分散性に優れたアルミナを用いることが好ましい。
【0018】
内層に含まれるNOx吸着剤として、Pt、Pd及びRhから選ばれる少なくとも1種の貴金属と酸素吸蔵成分からなるNOx吸着剤を使用しても同様の効果が得られる。貴金属および酸素吸蔵成分をNOx吸着剤として使用することにより、HCやCO、特にCOが排気ガス中に多量に含まれる場合でも、容易にNOxを放出することができ、同様にHC被毒やCO被毒の影響を受けにくいNOx吸着剤となる。これは、NOx吸着成分として貴金属および酸素吸蔵成分を利用することにより、NOxが脱離しやすいNO‐の形で吸着することによるものと考えられる。したがって、低温域においても、またリッチガス中にCOが含まれている状態においても、高いNOx浄化性能が確保されることになる。
【0019】
この場合、上記酸素吸蔵成分としては、セリウム酸化物を用いることができる。このセリウム酸化物についても、セリウム成分が含まれて折さえすれば、他の元素との複合酸化物であってもよい。貴金属およびセリウム成分、例えばPt/CeOをNOx吸着剤として使用することにより、HCやCOが排気ガス中に多量に含まれている場合でも、特にCOが多量に含まれる場合であっても、より容易にNOxを放出することができるようになる。
【0020】
このときのセリウム酸化物の含有量としては、CeO2換算で10〜500g/Lの範囲とすることが望ましい。すなわち、CeO2換算で10g/Lより少ない場合には、十分なNOx吸着量を得ることができず、500g/Lよりも多くしたとしても、NOx吸着量がほとんど飽和に達し、それ以上の効果が得られなくなることによる。
【0021】
一方、表層としてのNOx浄化層には、ロジウムと共に、ジルコニア酸化物を含有させることができる。このNOx浄化層がロジウムと、ジルコニア酸化物を含有することにより、NOx吸着触媒から放出したNOxの浄化性能が大きく向上する。
【0022】
NOx吸着剤から放出されたNOxは、拡散層(隔離手段)を経てNOx浄化層を通過することになるが、このとき、拡散層では短時間のうちに高濃度のNOxとなって放出されたNOxを徐々にNOx浄化層へ供給する働きをしているが、この働きに拘わらず低濃度化しきれずに高濃度のNOxとなって放出されたNOxを浄化する貴金属として、ロジウムが好ましい。また、ロジウムとともに使用しているジルコニウム酸化物をロジウムの担持基材として使用することにより、さらにNOx浄化性能が向上する。
【0023】
このとき、空間速度や温度等の条件変動に素早く対応するためには、ロジウム(Rh)の含有量は触媒体積当たり0.1〜50g/L、ジルコニウム酸化物の含有量は5〜100g/Lとすることが好ましい。なお、ジルコニウム酸化物は、上記のように担体として用いていることが好ましい。また、他の元素との複合酸化物を用いることも可能である。
【0024】
なお、Rhの含有量を上記範囲としたのは、0.1g/L未満では十分な触媒活性が得られないことがあり、逆に50g/Lを超えると触媒活性が飽和する傾向があることによる。また、ジルコニウム酸化物については、その含有量が5g/L未満ではロジウムの触媒性能の改質効果が十分に得られず、逆に100g/Lを超えると触媒活性が飽和する傾向があることによる。
【0025】
また、上記NOx浄化触媒には、多孔質担体が使用され、その材質は特に限定されるものではないが、例えばアルミナ、シリカ、シリカアルミナやチタニア等を挙げることができ、特に耐熱性及び貴金属分散性に優れるアルミナを用いることが好ましい。
【0026】
本発明に係わる排気ガス浄化触触媒においては、NOx吸着剤から放出されたNOxを一時的に保持してNOx浄化層への到達を遅延させるために用いる上記隔離手段として、隣接するセルの両端部が交互に目詰めされたウォールフロー型ハニカム担体を利用することができる。すなわち、ウォールフロー型ハニカム担体のセル壁面の排気ガス上流側に上記内層に相当する上流側層を形成し、セル壁の排気ガス下流側面に上記表層に相当する下流側層を形成したものとすることにより、当該セル壁が隔離手段として機能し、セル壁内の細孔がバッファーの役割を果たすことから、オープンセル型のハニカム担体に内層及び表層を形成した排気ガス浄化触触媒の場合と基本的に同様の作用効果が得られることになる。
【0027】
ウォールフロー型ハニカム担体は、隣接するセルの両端部が交互目詰めになっており、排気ガスは担体のセル壁を通過する。そのため、上流壁側にはディーゼルエンジンから排出されるPM(Particulate Mattter)分や、SOF(Soluble Oganic Fraction)分がトラップされることになるが、上流壁側に、例えばPt/CeOのようなNOx吸着剤を使用することにより、触媒の酸化活性によって比較的低温でのPM燃焼を行うことができ、触媒の熱劣化の観点からも効果的である。
【0028】
なお、PMの燃焼に際しては、例えば、定常走行時には任意に設定した時間で、あるいはエンジンの運転履歴からPM分のトラップ量を推測したり、触媒担体の前後に配置した排気差圧センサなどを用いてPMトラップ量がある値に達したことを検知したときなどに、トラップされたPM分を燃焼可能な状態(温度、酸素濃度)になるようにエンジン制御を行うことにより、自動的にPM除去を行うことができる。そして、このとき当該排気ガス浄化触触媒においては、上流側層の触媒の酸化活性が強いことから、PM分の着火が比較的低温で進行するため、エンジン制御に必要なエネルギーのロスが少なくて済むという利点がある。さらに、上流側に塗布した触媒は、R/S(リッチスパイク)時のCOを選択的に除去する作用をも有しているため、還元力の強い水素を下流側触媒に透過することができ、下流壁側のNOx浄化層において低温からNOx浄化を行うこともできる。
【0029】
なお、ウォールフロー型ハニカム担体の素材としては、隔離手段と同様に、コージェライト、SiC、アルミナ、シリカ、ジルコニア、チタニア及びゼオライトなどの耐熱性多孔質無機材料からなるものとすることができる。
【0030】
【実施例】
以下、本発明を実施例によりさらに詳細に説明するが、本発明はこれら実施例のみに限定されるものではない。
【0031】
(実施例1)
(1)内層:NOx吸着剤の調製
酸化セリウム粉末にジニトロジアンミン白金溶液を含浸し、乾燥後空気中400℃で1時間焼成して、Pt担持酸化セリウム粉末NA1を得た。この粉末のPt濃度は4.0%であった。
この粉末NA1を282.5g、活性アルミナ粉末を217.5g、水500gを磁性ボールミルに投入し、混合粉砕してスラリーを得た。このスラリーをコージェライト質モノリス担体(1.2L、900セル)に付着させ、空気流にてセル内の余剰のスラリーを取り除いて、130℃で乾燥した後、400℃で1時間焼成し、コート層250g/LのNOx吸着層を塗布した触媒NAC1を得た。この触媒NAC1のNOx吸着層におけるセリウム量は、CeO換算で134.2g/Lであった。
【0032】
(2)隔壁層(隔離手段)の調製
次に、活性アルミナ粉末を300g、75%の水分量含むベーマイトを75g、水300g/Lを磁性ボールミルに投入し、混合粉砕してスラリーI1を得た。このスラリーI1を上記触媒NAC1に付着させ、空気流にてセル内の余剰のスラリーを取り除いて,130℃で乾燥した後、400℃で1時間焼成した。このとき、隔壁層のコート量は20g/Lであり、総コート層は270g/Lであった。
【0033】
(3)表層:NOx浄化層の調製
硝酸ジルコニウム溶液を活性アルミナ粉末に含浸し、乾燥後空気中600℃で1時間焼成してジルコニウム担持アルミナ粉末を得た。硝酸ロジウム溶液を前記粉末に含浸し、乾燥後空気中400℃で1時間焼成して、Rh・Zr担持アルミナ粉末(粉末NR1)を得た。この粉末のジルコニウム濃度はZrO換算で20%、Rh濃度は2.8%であった。
一方、硝酸セリウム溶液を活性アルミナ粉末に含浸し、乾燥後空気中600℃で1時間焼成してセリウム担持アルミナ粉末を得た。ジニトロジアミン白金溶液を前記粉末に含浸し、乾燥後空気中400℃で1時間焼成して、Pt・セリア担持アルミナ粉末(粉末NR2)を得た。この粉末のCe濃度は3%、Pt濃度は2.8%であった。
そして、上記粉末NR1を100g、NR2を100g、水200gを磁性ボールミルに投入し、混合粉砕してスラリーを得た。このスラリーを上記のコージェライト質モノリス担体(1.2L、900セル)に付着させ、空気流にてセル内の余剰のスラリーを取り除いて、130℃で乾燥した後、400℃で1時間焼成し、NOx浄化層のコート量100g/L、総コート量370g/Lの排ガス浄化用触媒NC1を得た。
このようにして、図1に示すように、オープンセル型のモノリス担体の上に、Ptとセリウム酸化物からなるNOx吸着剤を含む内層2と、この上にアルミナからなる隔壁層(隔離手段)3を介して形成された表層4、すなわちRh,Ptを含むNOx浄化層を備えた排気ガス浄化触触媒1を得た。
【0034】
(実施例2)
内層におけるNOx吸着剤の調製において、酸化セリウムの代わりにCe0.94Pr0.06を使用した以外は、実施例1と同様にして、実施例2に係わる排気ガス浄化触媒を調製した。
【0035】
(実施例3)
内層におけるNOx吸着剤の調製において、酸化セリウムの代わりにCe0.85Pr0.15を使用した以外は、実施例1と同様にして実施例3に係わる触媒を調製した。
【0036】
(実施例4)
内層におけるNOx吸着剤の調製において、酸化セリウムの代わりにCe0.66Pr0.34を使用した以外は、実施例1と同様にして実施例4に係わる触媒を調製した。
【0037】
(実施例5)
内層におけるNOx吸着剤の調製において、酸化セリウムの代わりにCe0.75Zr0.25を使用した以外は、実施例1と同様にして実施例5に係わる触媒を調製した。
【0038】
(実施例6)
(1)内層:NOx吸着剤の調製
Ce0.75Zr0.25粉末にジニトロジアンミン白金溶液を含浸し、乾燥後、空気中400℃で1時間焼成して、Pt担持Ce0.75Zr0.25粉末NA2を得た。この粉末のPt濃度は4.0%であった。また、Ce0.94Pr0.06粉末にジニトロジアンミン白金溶液を含浸し、乾燥後、空気中400℃で1時間焼成して、Pt担持Ce0.94Pr0.06粉末NA3を得た。この粉末のPt濃度は4.00%であった。
そして、上記粉末NA2を141.25g、粉末NA3を141.25g、活性アルミナ粉末を217.5g、水500gを磁性ボールミルに投入し、混合粉砕してスラリーを得た。このスラリーをコージェライト質モノリス担体(1.2L、900セル)に付着させ、空気流にてセル内の余剰のスラリーを取り除いて130℃で乾燥した後、400℃で1時間焼成し、コート層250g/LのNOx吸着層を塗布した触媒NAC2を得た。
【0039】
(2)隔壁層及び表層の調製
このNAC2に実施例1と同様にして隔離層およびNOx浄化層を設け、図1に示すように、総コート層370g/Lの排ガス浄化用触媒を得た。
【0040】
(実施例7)
(1)内層:NOx吸着剤の調製
酸化チタン粉末にジニトロジアンミン白金溶液を含浸し、乾燥後空気中400℃で1時間焼成して、Pt担持酸化チタン粉末NA4を得た。この粉末のPt濃度は4.0%であった。また、Ce0.94Pr0.06 粉末にジニトロジアンミン白金溶液を含浸し、乾燥後空気中400℃で1時間焼成して、Pt担持Ce0.94Pr0.06粉末NA3を得た。この粉末のPt濃度は4.0%であった。
そして、上記粉末NA3を141.25g、粉末NA4を141.25g、活性アルミナ粉末を217.5g、水500gを磁性ボールミルに投入し、混合粉砕してスラリーを得た。このスラリーをコージェライト質モノリス担体(1.2L、900セル)に付着させ、空気流にてセル内の余剰のスラリーを取り除いて、130℃で乾燥した後、400℃で1時間焼成し、コート層250g/LのNOx吸着層を塗布した触媒NAC3を得た。
【0041】
(2)隔壁層及び表層の調製
このNAC3に実施例1と同様にして隔離層およびNOx浄化層を設け、総コート層370g/Lの排ガス浄化用触媒を得た。
【0042】
(実施例8)
(1)内層:NOx吸着剤の調製
ベーマイト粉末を硝酸セリウム溶液中で解膠し、24時間攪拌したのち、pH7.5に調製して沈殿物を得た。沈殿物をろ過し、150℃で12時間乾燥後、400℃で2時間焼成し、その後さらに、800℃で2時間焼成することにより、アルミナ上にセリウムが高分散度で存在するCe担持アルミナ粉末NA5を得た。この粉末のCe濃度は10%であった。粉末NA5に、さらに酢酸セリウムを含浸担持し、乾燥後400℃で1時間焼成し、Ce担持アルミナ粉末NA6を得た。この粉末のCe濃度は30%であった。このようにして得たCe担持アルミナ粉末NA6にジニトロジアンミン白金溶液を含浸し、乾燥後、空気中400℃で1時間焼成して、PtおよびCe担持アルミナ粉末NA7を得た。この粉末のPt濃度は4.0%であった。
そして、上記粉末NA7を282.5g、活性アルミナ粉末を217.5g、水500gを磁性ボールミルに投入し、混合粉砕してスラリーを得た。このスラリーをコージェライト質モノリス担体(1.2L、900セル)に付着させ、空気流にてセル内の余剰のスラリーを取り除いて130℃で乾燥した後、400℃で1時間焼成し、コート層250g/LのNOx吸着層を塗布した触媒NAC4を得た。
【0043】
(2)隔壁層及び表層の調製
このNAC4に実施例1と同様にして、隔離層およびNOx浄化層を設け、総コート層70g/Lの排ガス浄化用触媒を得た。
【0044】
(実施例9)
(1)内層:NOx吸着剤の調製
酸化セリウム粉末にジニトロジアンミン白金溶液を含浸し、乾燥後、空気中400℃で1時間焼成して、Pt担持酸化セリウム粉末NA1を得た。この粉末のPt濃度は4.0%であった。また、 酸化セリウム粉末に硝酸パラジウム溶液を含浸し、乾燥後空気中400℃で1時間焼成して、Pd担持酸化セリウム粉末NA8を得た。この粉末のPd濃度は4.0%であった。
そして、上記粉末NA1を188.3g、粉末NA8を94.2g、活性アルミナ粉末を217.5g、水500gを磁性ボールミルに投入し、混合粉砕してスラリーを得た。このスラリーをコージェライト質モノリス担体(1.2L、900セル)に付着させ、空気流にてセル内の余剰のスラリーを取り除いて130℃で乾燥した後、400℃で1時間焼成し、コート層250g/LのNOx吸着層を塗布した触媒NAC3(上記実施例7と同じ記号ですが、NAC5でしょうか?)を得た。
【0045】
(2)隔壁層及び表層の調製
このNAC3に実施例1と同様にして、隔離層およびNOx浄化層を設け、総コート層370g/Lの排ガス浄化用触媒を得た。
【0046】
(実施例10)
(1)内層:NOx吸着剤の調製
Ce0.94Pr0.06 粉末にジニトロジアンミン白金溶液を含浸し、乾燥後空気中400℃で1時間焼成して、Pt担持Ce0.94Pr0.06 粉末NA3を得た。この粉末のPt濃度は4.0%であった。また、 酸化セリウム粉末に硝酸パラジウム溶液を含浸し、乾燥後空気中400℃で1時間焼成して、Pd担持酸化セリウム粉末NA8を得た。この粉末のPd濃度は4.0%であった。
そして、上記粉末NA3を188.3g、粉末NA8を94.2g、活性アルミナ粉末を217.5g、水500gを磁性ボールミルに投入し、混合粉砕してスラリーを得た。このスラリーをコージェライト質モノリス担体(1.2L、900セル)に付着させ、空気流にてセル内の余剰のスラリーを取り除いて130℃で乾燥した後、400℃で1時間焼成し、コート層250g/LのNOx吸着層を塗布した触媒NAC3を得た(これも上記実施例7と同じ記号です。NAC6でしょうか?)。
【0047】
(2)隔壁層及び表層の調製
このNAC3に、実施例1と同様にして隔離層およびNOx浄化層を設け、総コート層370g/Lの排ガス浄化用触媒を得た。
【0048】
(実施例11)
隔壁層の活性アルミナをTiOに代えた以外は、実施例1と同様にして実施例11に係わる触媒を調製した。
【0049】
(実施例12)
隔壁層の活性アルミナをSiOに代えた以外は、実施例1と同様にして実施例12に係わる触媒を調製した。
【0050】
(実施例13)
隔壁層の活性アルミナをβ−ゼオライトに代えた以外は、実施例1と同様にして実施例13に係わる触媒を調製した。
【0051】
(実施例14)
隔壁層の活性アルミナをA型−ゼオライトに代えた以外は、実施例1と同様にして実施例14に係わる触媒を調製した。
【0052】
(実施例15)
隔壁層の活性アルミナをフェリエライトに代えた以外は、実施例1と同様にして実施例15に係わる触媒を調製した。
【0053】
(実施例16)
表層におけるNOx浄化層の調製において、ジルコニア担持アルミナの代わりにカルシウムを含有するジルコニウム酸化物(Ca0.2Zr0.8)を用いたこと以外は、実施例1と同様にして実施例16に係わる触媒を調製した。
【0054】
<ウォールフロー型担体の調製>
以下に、交互目詰め担体、すなわち隣接するセルの両端部が交互に目詰めされたウォールフロー(フィルタ)タイプの触媒調製要領について説明する。
まず、平均気孔率30%、平均細孔径20μmのコージェライト製ハニカム担体の片面に、耐熱性セメントを互いに接しないように、チェッカーボード状(市松模様)に上端面の約5mm程度の深さを塞ぐように注入し、乾燥後、以下に示す成分組成の上流側コート層を上記各実施例と同様の要領で付着させる。これによって、上流側コート層が互いに接しないようにチェッカーボード状に付着されることになる。次に、耐熱セメントを塗布した端面5mm分を切断して各セルを貫通させたのち、上流側コート層を付着させた各セルを耐熱セメントで同様に塞ぎ、以下に示す成分組成の下流側コート層を付着させる。そして最後に、耐熱性セメントを最初に塞いだセルに再び注入し、乾燥させることによって交互目詰めウォールフロー型担体が得られる。
【0055】
(実施例17)
(1)上流側層:NOx吸着剤の調製
実施例1で使用した粉末NA1を282.5g、活性アルミナ粉末を217.5g、水500gを磁性ボールミルに投入し、混合粉砕してスラリーを得た。このスラリーを上記した交互目詰めウォールフロー型担体の排ガス流れ方向に対して上流側の壁面に付着させ、空気流にてセル内の余剰のスラリーを取り除いて130℃で乾燥した後、400℃で1時間焼成し、コート層250g/LのNOx吸着層を塗布した。
【0056】
(2)下流側層:NOx浄化層の調製
硝酸ジルコニウム溶液を活性アルミナ粉末に含浸し、乾燥後空気中600℃で1時間焼成してジルコニウム担持アルミナ粉末を得た。硝酸リジウム溶液を前記粉末に含浸し、乾燥後空気中400℃で1時間焼成して、Rh・Zr担持アルミナ粉末(粉末NR1)を得た。この粉末のジルコニウム濃度は10%、Rh濃度は2.8%であった。
次に、硝酸セリウム溶液を活性アルミナ粉末に含浸し、乾燥後空気中600℃で1時間焼成してセリウム担持アルミナ粉末を得た。ジニトロジアミン白金溶液を前記粉末に含浸し、乾燥後空気中400℃で1時間焼成して、Pt・セリア担持アルミナ粉末(粉末NR2)を得た。この粉末のセリウム濃度は3%、Pt濃度は2.8%であった。
そして、上記粉末NR1を100g、NR2を100g、活性アルミナ200g、水400gを磁性ボールミルに投入し、混合粉砕してスラリーを得た。このスラリーを上記交互目詰めウォールフロー型担体の排ガス流れ方向に対して下流側の壁面に付着させ、空気流にてセル内の余剰のスラリーを取り除いて130℃で乾燥した後、400℃で1時間焼成し、コート層200g/LのNOx浄化層を塗布した。
このようにして、図2に示すように、ウォールフロー型モノリス担体のセル壁5の上流側面に、Ptとセリウム酸化物からなるNOx吸着剤を含む上流側層6を備え、セル壁の下流側面に下流側層7としてRh,Ptを含むNOx浄化層を備えた排気ガス浄化触触媒10を得た。
【0057】
(実施例18)
(1)上流側層:NOx吸着剤の調製
実施例6の内層に使用した粉末NA2,NA3,活性アルミナ及び水からなるスラリーを交互目詰めウォールフロー型担体の排ガス流れ方向に対して上流側の壁面に付着させ、空気流にてセル内の余剰のスラリーを取り除いて130℃で乾燥した後、400℃で1時間焼成し、コート層250g/LのNOx吸着層を塗布した。
【0058】
(2)下流側層:NOx浄化層の調製
硝酸ジルコニウム溶液を活性アルミナ粉末に含浸し、乾燥後空気中600℃で1時間焼成してジルコニウム担持アルミナ粉末を得た。硝酸リジウム溶液を前記粉末に含浸し、乾燥後空気中400℃で1時間焼成して、Rh・Zr担持アルミナ粉末(粉末NR1)を得た。この粉末のジルコニウム濃度は20%、Rh濃度は2.8%であった。
次に、硝酸セリウム溶液を活性アルミナ粉末に含浸し、乾燥後空気中600℃で1時間焼成してセリウム担持アルミナ粉末を得た。ジニトロジアミン白金溶液を前記粉末に含浸し、乾燥後空気中400℃で1時間焼成して、Pt・セリア担持アルミナ粉末(粉末NR2)を得た。この粉末のセリウム濃度は3%、Pt濃度は2.8%であった。
そして、上記粉末NR1を100g、NR2を100g、活性アルミナ200g、水400gを磁性ボールミルに投入し、混合粉砕してスラリーを得た。このスラリーを上記交互目詰めウォールフロー型担体の排ガス流れ方向に対して下流側の壁面に付着させ、空気流にてセル内の余剰のスラリーを取り除いて130℃で乾燥した後、400℃で1時間焼成し、コート層200g/LのNOx浄化層を塗布した。このようにして、図2と同様の排ガス浄化用触媒を得た。
【0059】
(実施例19)
(1)上流側層:NOx吸着剤の調製
実施例7の内層に使用した粉末NA3,NA4,活性アルミナ及び水からなるスラリーを交互目詰めウォールフロー型担体の排ガス流れ方向に対して上流側の壁面に付着させ、空気流にてセル内の余剰のスラリーを取り除いて130℃で乾燥した後、400℃で1時間焼成し、コート層250g/LのNOx吸着層を塗布した。
【0060】
(2)下流側層:NOx浄化層の調製
上記実施例18と同様のスラリーを用いて、交互目詰めウォールフロー型担体の排ガス流れ方向に対して下流側の壁面にコート量200g/LのNOx浄化層を塗布し、図2に示すような排ガス浄化用触媒を得た。
【0061】
(実施例20)
(1)上流側層:NOx吸着剤の調製
上記実施例18と同様に、交互目詰めウォールフロー型担体の排ガス流れ方向に対して上流側の壁面に、コート層250g/LのNOx吸着層を塗布した。
【0062】
(2)下流側層:NOx浄化層の調製
硝酸ロジウム溶液をカルシウムを含有するジルコニウム酸化物(Ca0.2Zr0.8)粉末に含浸し、乾燥後空気中400℃で1時間焼成して、Rh担持カルシウム含有ジルコニウム酸化物粉末(粉末NR3)を得た。この粉末のRh濃度は2.8%であった。
次に、硝酸セリウム溶液を活性アルミナ粉末に含浸し、乾燥後空気中600℃で1時間焼成してセリウム担持アルミナ粉末を得た。ジニトロジアミン白金溶液を前記粉末に含浸し、乾燥後空気中400℃で1時間焼成して、Pt・セリア担持アルミナ粉末(粉末NR3)を得た。この粉末のセリウム濃度は3%、Pt濃度は2.8%であった。
そして、上記粉末NR3を100g、NR2を100g、活性アルミナ200g、水400gを磁性ボールミルに投入し、混合粉砕してスラリーを得た。このスラリーを交互目詰めウォールフロー型担体の排ガス流れ方向に対して下流側の壁面に付着させ、空気流にてセル内の余剰のスラリーを取り除いて130℃で乾燥した後、400℃で1時間焼成し、コート層200g/LのNOx浄化層を塗布し、図2に示すような排ガス浄化用触媒を得た。
【0063】
(実施例21)
(1)上流側層:NOx吸着剤の調製
上記実施例18と同様のスラリーを用い、交互目詰めウォールフロー型担体の排ガス流れ方向に対して上流側の壁面に、コート層250g/LのNOx吸着層を塗布した。
【0064】
(2)下流側層:NOx浄化層の調製
硝酸ロジウム溶液をカルシウムを含有するジルコニウム酸化物(Ca0.2Zr0.8)粉末に含浸し、乾燥後空気中400℃で1時間焼成して、Rh担持カルシウム含有ジルコニウム酸化物粉末(粉末NR3)を得た。この粉末のRh濃度は1.4%であった。
そして、上記粉末NR3を200g、活性アルミナ200g、水400gを磁性ボールミルに投入し、混合粉砕してスラリーを得た。このスラリーを交互目詰めウォールフロー型担体の排ガス流れ方向に対して下流側の壁面に付着させ、空気流にてセル内の余剰のスラリーを取り除いて130℃で乾燥した後、400℃で1時間焼成し、コート量200g/LのNOx浄化層を塗布し、図2に示すような排ガス浄化用触媒を得た。
【0065】
(実施例22)
(1)上流側層:NOx吸着剤の調製
Ce0.75Zr0.25粉末にジニトロジアンミン白金溶液を含浸し、乾燥後、空気中400℃で1時間焼成して、Pt担持Ce0.75Zr0.25粉末NA2を得た。この粉末のPt濃度は5.0%であった。また、Ce0.94Pr0.06粉末にジニトロジアンミン白金溶液を含浸し、乾燥後、空気中400℃で1時間焼成して、Pt担持Ce0.94Pr0.06粉末NA3を得た。この粉末のPt濃度は5.00%であった。
そして、上記粉末NA2を141.25g、粉末NA3を141.25g、活性アルミナ粉末を217.5g、水500gを磁性ボールミルに投入し、混合粉砕してスラリーを得た。このスラリーを交互目詰めウォールフロー型担体の排ガス流れ方向に対して上流側の壁面に付着させ、空気流にてセル内の余剰のスラリーを取り除いて130℃で乾燥した後、400℃で1時間焼成し、コート層250g/LのNOx吸着層を塗布した。
【0066】
(2)下流側層:NOx浄化層の調製
硝酸ジルコニウム溶液を活性アルミナ粉末に含浸し、乾燥後空気中600℃で1時間焼成してジルコニウム担持アルミナ粉末を得た。硝酸ロジウム溶液を前記粉末に含浸し、乾燥後空気中400℃で1時間焼成して、Rh・Zr担持アルミナ粉末(粉末NR1)を得た。この粉末のジルコニウム濃度は10%、Rh濃度は2.8%であった。
次に、硝酸セリウム溶液を活性アルミナ粉末に含浸し、乾燥後空気中600℃で1時間焼成してCe担持アルミナ粉末を得た。ジニトロジアミン白金溶液を前記粉末に含浸し、乾燥後空気中400℃で1時間焼成して、Pt・セリア担持アルミナ粉末(粉末NR2)を得た。この粉末のCe濃度は3%、Pt濃度は2.8%であった。
さらに、硝酸ロジウム溶液をカルシウムを含有するジルコニウム酸化物(Ca0.2Zr0.8)粉末に含浸し、乾燥後空気中400℃で1時間焼成して、Rh担持カルシウム含有ジルコニウム酸化物粉末(粉末NR3)を得た。この粉末のGh濃度は2.8%であった。
そして、上記粉末NR1を100g、NR2を100g、水200gを磁性ボールミルに投入し、混合粉砕してスラリーを得た。このスラリーを交互目詰めウォールフロー型担体の排ガス流れ方向に対して下流側の壁面に付着させ、空気流にてセル内の余剰のスラリーを取り除いて130℃で乾燥した後、400℃で1時間焼成し、コート層100g/LのNOx浄化層を塗布した。
さらに、上記粉末NR3を100g、水100gを磁性ボールミルに投入し、混合粉砕してスラリーを得た。このスラリーを交互目詰めウォールフロー型担体の排ガス流れ方向に対して下流側の壁面において、コート層100g/LのNOx浄化層を塗布した上に付着させ、空気流にてセル内の余剰のスラリーを取り除いて130℃で乾燥した後、400℃で1時間焼成し、コート層50g/L、トータル150g/LのNOx浄化層を塗布した。このようにして、図2に示すような排ガス浄化用触媒を得た。
【0067】
(実施例23)
(1)上流側層:NOx吸着剤の調製
酸化セリウム粉末にジニトロジアンミン白金溶液を含浸し、乾燥後空気中400℃で1時間焼成して、Pt担持酸化セリウム粉末NA1を得た。この粉末のPt濃度は4.0%であった。また、 酸化セリウム粉末に硝酸パラジウム溶液を含浸し、乾燥後空気中400℃で1時間焼成して、Pd担持酸化セリウム粉末NA8を得た。この粉末のPd濃度は4.0%であった。
そして、上記粉末NA1を188.3g、粉末NA8を94.2g、活性アルミナ粉末を217.5g、水500gを磁性ボールミルに投入し、混合粉砕してスラリーを得た。このスラリーを交互目詰めウォールフロー型担体の排ガス流れ方向に対して上流側の壁面に付着させ、空気流にてセル内の余剰のスラリーを取り除いて130℃で乾燥した後、400℃で1時間焼成し、コート層250g/LのNOx吸着層を塗布した。
【0068】
(2)下流側層:NOx浄化層の調製
上記実施例18と同様のスラリーを用いて、交互目詰めウォールフロー型担体の排ガス流れ方向に対して下流側の壁面にコート量200g/LのNOx浄化層を塗布し、図2に示すような排ガス浄化用触媒を得た。
【0069】
[耐久試験]
上記によって得られた各触媒を排気量4000ccのエンジンの排気系に装着し、表1に示すように、国内レギュラーガソリンを使用し、触媒入口温度を700℃として、50時間運転し、耐久試験を実施した。
【0070】
【表1】
【0071】
[性能評価試験]
上記条件による耐久後の各触媒を排気量2000ccのエンジンの排気系に装着して、表2に示すように、リーン(A/F=18)40sec→リッチ(A/F=11.0)2secの運転を行い、この区間における排気浄化率を求めた。その結果を表3(オープンセル型ハニカム担体)、及び表4(ウォールスルー型ハニカム担体)に示す。なお、触媒入口温度は200℃に設定した。
【0072】
【表2】
【0073】
【表3】
【0074】
【表4】
【0075】
【発明の効果】
以上、説明してきたように、本発明に係わる排気ガス浄化触媒は、オープンセル型ハニカム担体の内層側あるいはウォールスルー型ハニカム担体の排気ガス流上流側にNOx吸着剤含有層を備える一方、オープンセル型ハニカム担体の表層側あるいはウォールスルー型ハニカム担体の排気ガス流下流側にはNOx浄化層を形成し、さらにオープンセル型ハニカム担体を用いた場合には上記内外層の間に耐熱性多孔質無機材料からなる隔離手段を設けてなるものであるから、内層あるいは上流層の吸着剤は、排気ガス中にHCやCO量が多量に含まれる場合でもNOxを容易に放出することができ、放出されたNOxの表層あるいは下流側層への拡散が隔離手段あるいはウォールスルー型ハニカム担体セル壁によって遅延することから、反応速度がさほど大きくない低温域においても高いNOx浄化率を保持することができるという極めて優れた効果がもたらされる。
【図面の簡単な説明】
【図1】本発明に係わる排気ガス浄化触媒の一実施形態として、オープンセル型ハニカム担体のセル壁面に形成した内外層とその間の隔離手段からなる触媒構造例を示す断面図である。
【図2】本発明に係わる排気ガス浄化触媒の他の実施形態として、ウォールスルー型ハニカム担体のセル壁両面に形成した上流側及び下流側層からなる触媒構造例を示す断面図である。
【 符号の説明】
1,10 排気ガス浄化触媒
2 内層
3 隔壁層(隔離手段)
4 表層
5 ウォールスルー型ハニカム担体セル壁
6 上流側層
7 下流側層
[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, and more particularly, to adsorbing NOx in exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean, so that the air-fuel ratio of the inflowing exhaust gas is rich and / or stoichiometric. The present invention relates to an exhaust gas purifying catalyst including a NOx adsorbent that releases sometimes adsorbed NOx and a NOx purifying catalyst that reduces and purifies the released NOx.
[0002]
[Prior art]
The exhaust gas purifying apparatus for an internal combustion engine as described above absorbs NOx (nitrogen oxide) in the exhaust gas when the inflowing exhaust air-fuel ratio is lean, and releases the absorbed NOx when the inflowing exhaust air-fuel ratio becomes rich. There is known a NOx absorption reduction catalyst that performs reduction and purification. An example of an exhaust gas purifying apparatus using this type of NOx absorption reduction catalyst is disclosed in, for example, Japanese Patent No. 2640092.
[0003]
The exhaust gas purifying apparatus according to the above patent has a NOx absorption reduction catalyst disposed in an exhaust passage of an engine that performs a lean air-fuel ratio operation, and causes the NOx absorption reduction catalyst to absorb NOx in the exhaust gas during the lean air-fuel ratio operation of the engine. When the amount of NOx absorbed by the absorption reduction catalyst increases, the NOx absorbed from the NOx absorption reduction catalyst is released by performing a rich spike operation of operating the engine for a short time at an air-fuel ratio equal to or lower than the stoichiometric air-fuel ratio (that is, a rich air-fuel ratio). At the same time, the released NOx is reduced and purified. That is, when the operating air-fuel ratio of the engine becomes rich, the oxygen concentration in the exhaust gas sharply decreases and the amount of unburned HC and CO components in the exhaust gas sharply increases as compared with the lean air-fuel ratio operation. Therefore, when the engine operating air-fuel ratio is switched to the rich air-fuel ratio by the rich spike operation, NOx is released from the NOx absorption-reduction catalyst, and is reacted with unburned HC and CO components in the exhaust on the NOx absorption-reduction catalyst to be reduced. You.
[0004]
Further, the above-mentioned patent publication discloses a configuration in which a three-way catalyst is disposed in an exhaust passage on the upstream side of a NOx absorption reduction catalyst to purify HC and CO components discharged from the engine when the engine is started. Since the three-way catalyst is disposed near the engine exhaust manifold and passes high-temperature exhaust gas from the engine, the temperature rises shortly after the engine starts and reaches the activation temperature of the three-way catalyst. Accordingly, since the time from the start of the engine to the completion of warm-up is shortened, a relatively large amount of HC and CO discharged from the engine during this period can be reduced.
[0005]
In a diesel engine or the like, a catalyst is provided in the middle of an exhaust pipe to purify NOx emitted from an internal combustion engine. As such a NOx purification catalyst, various catalysts such as a zeolite-based catalyst and an alumina-based catalyst are known, but all have a limited temperature range in which the NOx purification action is exhibited. Therefore, it has been proposed to expand the NOx purification temperature range by combining a plurality of catalysts having different purification temperature ranges. For example, JP-A-6-134258 discloses a catalyst device using a plurality of catalysts having different reaction temperatures at which the highest activity is obtained by changing the amount of cobalt supported on mordenite. The plurality of catalysts are usually arranged such that the high-temperature active catalyst is arranged on the upstream side of the exhaust passage and the low-temperature active catalyst is arranged on the downstream side of the exhaust passage.
[0006]
Japanese Patent Application Laid-Open No. 6-307231 discloses a catalyst device in which a plurality of NOx purification catalysts are arranged in series in the flow direction of exhaust gas so that the oxidizing activity for hydrocarbons increases gradually toward the downstream side. Is disclosed.
[0007]
[Problems to be solved by the invention]
In the NOx absorption reduction catalyst described in the above-mentioned Japanese Patent No. 2600492, in addition to a noble metal catalyst component such as platinum Pt, palladium Pd, and rhodium Rh, a NOx absorption material represented by an alkali or an alkaline earth metal is used. I'm using However, as described in the patent, when a rich spike operation is performed during the lean air-fuel ratio operation and the exhaust air-fuel ratio is set to the rich air-fuel ratio, the amounts of HC and CO components in the exhaust rapidly increase. Since the CO component has a property of easily adhering to the catalyst component of the NOx absorption reduction catalyst, if the HC and CO components in the exhaust gas flowing into the NOx absorption reduction catalyst rapidly increase, the surface of the catalyst component is covered by the attached HC and CO. As a result, there is a problem that the function as a catalyst decreases, that is, HC poisoning and CO poisoning occur, and the NOx purification ability of the NOx absorption reduction catalyst decreases.
[0008]
Such phenomena as HC poisoning and CO poisoning are remarkable in a low temperature range where the activity of the catalyst is low. NOx absorbed in an oxygen-excess atmosphere is released from a NOx-absorbing reduction catalyst in a rich atmosphere, and even if an attempt is made to reduce and purify on the same catalyst, NOx is absorbed by HC poisoning and CO poisoning, particularly CO contained in reducing gas. Since the reduction catalyst is poisoned and NOx is not sufficiently released from the NOx absorption-reduction catalyst, the NOx adsorption power of the NOx absorption-reduction catalyst is not restored, and thus the problem that the NOx purification rate is significantly reduced occurs. was there. Further, even when a plurality of catalysts are used, there is a problem that the NOx purification rate is significantly reduced because the respective NOx purification amounts are small. From such a background, the present inventors have determined that a NOx purification rate is not significantly improved because a reducing agent (CO or HC) which is very useful for NOx purification in a high temperature range hinders NOx purification in a low temperature range. I paid attention.
[0009]
The present invention has been made in view of the above-mentioned problems of the related art. It is an object of the present invention to efficiently purify NOx in an oxygen-excess region exhausted from an internal combustion engine and reduce the temperature of exhaust gas at a low temperature. An object of the present invention is to provide an exhaust gas purifying catalyst capable of efficiently purifying CO and HC even in a low-temperature region. Another object of the present invention is to provide an exhaust gas purification catalyst that exhibits a high or higher NOx purification rate in a wide purification temperature range, particularly in a low temperature range.
[0010]
[Means for Solving the Problems]
An exhaust gas purifying catalyst according to the present invention is an exhaust gas purifying catalyst disposed in an exhaust passage of an internal combustion engine, and is configured to reduce NOx in exhaust gas to at least NO. 2 -Having an inner layer containing a NOx adsorbent that adsorbs as an adsorbent, and a surface layer composed of a NOx purification layer for reducing and purifying NOx released from the NOx adsorbent of the inner layer, and comprising a heat-resistant porous inorganic material; Isolation means for temporarily holding NOx released from the inner layer and delaying the arrival at the surface layer side is interposed between the surface layer and the inner layer. Such a configuration is a means for solving the above-mentioned problem. At this time, the inner layer can be replaced with one containing at least one noble metal selected from Pt, Pd and Rh and a NOx adsorbent composed of an oxygen storage component.
[0011]
Further, in the exhaust gas purifying catalyst according to the present invention, a wall flow type honeycomb carrier in which both ends of adjacent cells are alternately plugged is used, and the cell walls of the carrier are used as the isolation means, It is also possible to form an upstream layer containing the inner layer component on the exhaust gas upstream side surface of the cell wall, and to form a downstream layer containing the surface layer component on the exhaust gas downstream side surface of the carrier cell wall.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the exhaust gas purifying catalyst according to the present invention will be described in detail. In this specification, “%” means percent by mass unless otherwise specified.
[0013]
The exhaust gas purifying catalyst according to the present invention has NO 2 A surface layer consisting of an inner layer containing a NOx adsorbent for adsorbing NOx as an adsorbing species and a NOx purification layer for reducing and purifying NOx released from the NOx adsorbent, with an isolation means interposed between these inner and outer layers According to the exhaust gas purifying catalyst, a NOx adsorbent which is not poisoned by CO in a rich atmosphere and can release NOx even in a low temperature range is used, and a rich and / or stoichiometric atmosphere is used. Below, the NOx released from the NOx adsorbent can be purified.
That is, when the engine is operated at the lean air-fuel ratio and the exhaust gas flowing into the NOx adsorbent has the lean air-fuel ratio, a large amount of NOx in the exhaust gas is NO. 2 -Allows adsorption of NO or NO on the catalyst even when HC and CO are contained in a large amount in exhaust gas. 2 NOx can be released easily if the bond of the adsorbed species is broken. In other words, it is hardly affected by HC poisoning and CO poisoning. Therefore, by using a catalyst structure in which the NOx purification layer is disposed above the NOx adsorbent, even in a low temperature range, CO is contained in the rich gas. In this state, high NOx purification performance can be maintained.
[0014]
Further, a separation means is provided between the inner layer made of a heat-resistant porous inorganic material, between an inner layer made of a NOx adsorbent and a surface layer made of a NOx purification layer for reducing and purifying NOx released from the NOx adsorbent of the inner layer. Therefore, when the catalyst is applied to a normal open cell type carrier with both ends open, the exhaust gas once permeates and disperses in the inner layer direction of the catalyst, and then diffuses from the inner layer direction to the surface layer direction. That is, since the separating means between the inner layer and the surface layer has pores, it is considered that the reaction gas is easily diffused in the pores and plays a role of a so-called buffer. Therefore, when the condition of the exhaust gas changes rapidly, when the NOx adsorbed by the NOx adsorbent in the inner layer is desorbed and diffused into the NOx purification layer, the diffusion speed of NOx is reduced by the isolation means. Even in a low temperature range (200 ° C. or lower) where the reaction rate is not so high, high NOx purification performance is maintained.
[0015]
The delay effect of the separating means is also effective for reducing agents such as HC and CO, and can cause turbulence and re-diffusion in the pores of the separating means. As a result, the NOx purification performance in a low temperature range (200 ° C. or lower) where the reaction rate is not so large can be kept high. In addition, from the viewpoints of heat resistance, moldability, cost, availability, and the like, such an isolating means includes heat-resistant materials such as cordierite, SiC (silicon carbide), alumina, silica, zirconia, titania, and zeolite. A porous inorganic material is preferably used.
[0016]
As the NOx adsorbent in the surface layer, an adsorbent containing at least titanium and / or zirconium oxide therein can be used. That is, when such a component is contained in the NOx adsorbent, NOx is very easily released. Further, it has been known that the addition of a ternary component to the adsorbent improves the adsorption and the release characteristics of the adsorbed NOx. Therefore, it is desirable to further add a noble metal catalyst component such as Pt, Pd and Rh. . Note that these oxides may be composite oxides with other elements including titanium and zirconium.
[0017]
In the NOx adsorbent, a porous carrier can be used. Although the material is not particularly limited, for example, alumina, silica, silica alumina, titania and the like can be mentioned, and it is particularly preferable to use alumina having excellent heat resistance and noble metal dispersibility.
[0018]
Similar effects can be obtained by using a NOx adsorbent comprising at least one noble metal selected from Pt, Pd and Rh and an oxygen storage component as the NOx adsorbent contained in the inner layer. By using a noble metal and an oxygen storage component as a NOx adsorbent, NOx can be easily released even when HC and CO, especially CO are contained in a large amount in exhaust gas, and similarly HC poisoning and CO It is a NOx adsorbent that is not easily affected by poisoning. This is because NOx is easily desorbed by using a noble metal and an oxygen storage component as NOx adsorption components. 2 This is probably due to adsorption in the form of-. Therefore, high NOx purification performance is ensured even in a low temperature range and in a state where CO is contained in the rich gas.
[0019]
In this case, cerium oxide can be used as the oxygen storage component. This cerium oxide may be a composite oxide with another element as long as it contains a cerium component and is broken. Noble metal and cerium components such as Pt / CeO 2 By using as a NOx adsorbent, NOx can be more easily released even when HC or CO is contained in a large amount in the exhaust gas, especially when CO is contained in a large amount. Become like
[0020]
At this time, the content of the cerium oxide is desirably in the range of 10 to 500 g / L in terms of CeO2. That is, when the amount is less than 10 g / L in terms of CeO2, a sufficient NOx adsorption amount cannot be obtained, and even if the amount is more than 500 g / L, the NOx adsorption amount almost reaches saturation, and a further effect is obtained. It is because it cannot be obtained.
[0021]
On the other hand, the NOx purification layer as the surface layer can contain zirconia oxide together with rhodium. Since the NOx purification layer contains rhodium and zirconia oxide, the purification performance of NOx released from the NOx adsorption catalyst is greatly improved.
[0022]
The NOx released from the NOx adsorbent passes through the NOx purification layer via the diffusion layer (separation means). At this time, the diffusion layer releases high-concentration NOx in a short time. Although it functions to gradually supply NOx to the NOx purification layer, rhodium is preferable as a noble metal that purifies NOx released as high-concentration NOx that cannot be reduced to a low concentration regardless of this function. In addition, by using the zirconium oxide used together with rhodium as a rhodium support substrate, the NOx purification performance is further improved.
[0023]
At this time, in order to quickly respond to changes in conditions such as space velocity and temperature, the content of rhodium (Rh) is 0.1 to 50 g / L per catalyst volume, and the content of zirconium oxide is 5 to 100 g / L. It is preferable that Note that zirconium oxide is preferably used as a carrier as described above. It is also possible to use a composite oxide with another element.
[0024]
The reason for setting the Rh content to the above range is that if the content is less than 0.1 g / L, sufficient catalytic activity may not be obtained, whereas if it exceeds 50 g / L, the catalytic activity tends to be saturated. by. When the content of zirconium oxide is less than 5 g / L, the effect of reforming the catalytic performance of rhodium cannot be sufficiently obtained, and when it exceeds 100 g / L, the catalytic activity tends to be saturated. .
[0025]
In addition, a porous carrier is used for the NOx purification catalyst, and the material is not particularly limited. Examples thereof include alumina, silica, silica alumina, and titania. It is preferable to use alumina having excellent properties.
[0026]
In the exhaust gas purifying catalyst according to the present invention, as the above-mentioned isolating means used to temporarily hold NOx released from the NOx adsorbent and delay arrival at the NOx purifying layer, both ends of adjacent cells are used. Can be used. That is, the upstream layer corresponding to the inner layer is formed on the exhaust gas upstream side of the cell wall surface of the wall flow type honeycomb carrier, and the downstream layer corresponding to the surface layer is formed on the exhaust gas downstream side surface of the cell wall. Thereby, the cell wall functions as an isolating means, and pores in the cell wall play a role of a buffer. Therefore, the catalyst is basically the same as the case of the exhaust gas purifying catalyst in which the inner layer and the surface layer are formed on the open cell type honeycomb carrier. Thus, the same operation and effect can be obtained.
[0027]
In the wall flow type honeycomb carrier, both ends of adjacent cells are alternately plugged, and the exhaust gas passes through the cell walls of the carrier. Therefore, PM (Particulate Matter) and SOF (Soluble Organic Fraction) components discharged from the diesel engine are trapped on the upstream wall side. For example, Pt / CeO is discharged on the upstream wall side. 2 By using such a NOx adsorbent, PM combustion can be performed at a relatively low temperature by the oxidation activity of the catalyst, which is effective also from the viewpoint of thermal deterioration of the catalyst.
[0028]
During the combustion of PM, for example, at a arbitrarily set time during steady running, or by estimating the trap amount for PM from the operation history of the engine, or using an exhaust differential pressure sensor disposed before and after the catalyst carrier. Automatically removes PM by controlling the engine so that the trapped PM can be burned (temperature, oxygen concentration) when it detects that the trapped PM amount has reached a certain value. It can be performed. At this time, in the exhaust gas purifying catalyst, since the oxidation activity of the catalyst in the upstream layer is strong, the ignition of the PM proceeds at a relatively low temperature, so that energy loss required for engine control is small. There is an advantage that it is done. Furthermore, since the catalyst applied on the upstream side also has an action of selectively removing CO during R / S (rich spike), hydrogen having a strong reducing power can be transmitted to the downstream side catalyst. Also, NOx purification can be performed from a low temperature in the NOx purification layer on the downstream wall side.
[0029]
The material of the wall flow type honeycomb carrier can be made of a heat-resistant porous inorganic material such as cordierite, SiC, alumina, silica, zirconia, titania, and zeolite, as in the case of the isolation means.
[0030]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.
[0031]
(Example 1)
(1) Inner layer: Preparation of NOx adsorbent
The cerium oxide powder was impregnated with a dinitrodiammine platinum solution, dried and calcined in air at 400 ° C. for 1 hour to obtain Pt-supported cerium oxide powder NA1. The Pt concentration of this powder was 4.0%.
282.5 g of this powder NA1, 217.5 g of activated alumina powder, and 500 g of water were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry. This slurry was adhered to a cordierite-based monolithic carrier (1.2 L, 900 cells), excess slurry in the cells was removed with an air stream, dried at 130 ° C., baked at 400 ° C. for 1 hour, and coated. A catalyst NAC1 coated with a 250 g / L NOx adsorption layer was obtained. The amount of cerium in the NOx adsorption layer of this catalyst NAC1 is CeO 2 It was 134.2 g / L in conversion.
[0032]
(2) Preparation of partition layer (isolation means)
Next, 300 g of activated alumina powder, 75 g of boehmite containing 75% of water and 300 g / L of water were charged into a magnetic ball mill, and mixed and pulverized to obtain a slurry I1. The slurry I1 was attached to the catalyst NAC1, the excess slurry in the cell was removed by an air flow, dried at 130 ° C., and fired at 400 ° C. for 1 hour. At this time, the coating amount of the partition layer was 20 g / L, and the total coating layer was 270 g / L.
[0033]
(3) Surface layer: Preparation of NOx purification layer
The activated alumina powder was impregnated with the zirconium nitrate solution, dried, and fired in air at 600 ° C. for 1 hour to obtain a zirconium-supported alumina powder. The powder was impregnated with a rhodium nitrate solution, dried and calcined in air at 400 ° C. for 1 hour to obtain a Rh.Zr-supported alumina powder (powder NR1). The zirconium concentration of this powder is ZrO 2 The conversion was 20%, and the Rh concentration was 2.8%.
Separately, the activated alumina powder was impregnated with a cerium nitrate solution, dried and calcined at 600 ° C. for 1 hour in the air to obtain a cerium-supported alumina powder. The powder was impregnated with a dinitrodiamine platinum solution, dried and calcined at 400 ° C. for 1 hour in the air to obtain Pt / ceria-supported alumina powder (powder NR2). The Ce concentration of this powder was 3%, and the Pt concentration was 2.8%.
Then, 100 g of the powder NR1, 100 g of NR2, and 200 g of water were charged into a magnetic ball mill, and mixed and pulverized to obtain a slurry. The slurry was attached to the cordierite-based monolithic carrier (1.2 L, 900 cells), excess slurry in the cells was removed by an air stream, dried at 130 ° C., and calcined at 400 ° C. for 1 hour. Thus, an exhaust gas purifying catalyst NC1 having a NOx purification layer coating amount of 100 g / L and a total coating amount of 370 g / L was obtained.
In this manner, as shown in FIG. 1, an inner layer 2 containing a NOx adsorbent composed of Pt and cerium oxide, and a partition layer composed of alumina thereon (separation means), on an open cell type monolithic carrier Thus, an exhaust gas purifying catalytic catalyst 1 having a surface layer 4 formed through the NO. 3, that is, a NOx purifying layer containing Rh and Pt was obtained.
[0034]
(Example 2)
In the preparation of the NOx adsorbent in the inner layer, instead of cerium oxide, Ce 0.94 Pr 0.06 O 2 The exhaust gas purifying catalyst according to Example 2 was prepared in the same manner as in Example 1 except that was used.
[0035]
(Example 3)
In the preparation of the NOx adsorbent in the inner layer, instead of cerium oxide, Ce 0.85 Pr 0.15 O 2 A catalyst according to Example 3 was prepared in the same manner as in Example 1, except for using.
[0036]
(Example 4)
In the preparation of the NOx adsorbent in the inner layer, instead of cerium oxide, Ce 0.66 Pr 0.34 O 2 A catalyst according to Example 4 was prepared in the same manner as in Example 1, except for using.
[0037]
(Example 5)
In the preparation of the NOx adsorbent in the inner layer, instead of cerium oxide, Ce 0.75 Zr 0.25 O 2 A catalyst according to Example 5 was prepared in the same manner as in Example 1, except that was used.
[0038]
(Example 6)
(1) Inner layer: Preparation of NOx adsorbent
Ce 0.75 Zr 0.25 O 2 The powder is impregnated with a dinitrodiammine platinum solution, dried, and calcined in air at 400 ° C. for 1 hour to obtain Pt-supported Ce. 0.75 Zr 0.25 O 2 Powder NA2 was obtained. The Pt concentration of this powder was 4.0%. Also, Ce 0.94 Pr 0.06 O 2 The powder is impregnated with a dinitrodiammine platinum solution, dried, and calcined in air at 400 ° C. for 1 hour to obtain Pt-supported Ce. 0.94 Pr 0.06 O 2 Powder NA3 was obtained. The Pt concentration of this powder was 4.00%.
Then, 141.25 g of the powder NA2, 141.25 g of the powder NA3, 217.5 g of the activated alumina powder, and 500 g of water were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry. The slurry was adhered to a cordierite-based monolithic carrier (1.2 L, 900 cells), excess slurry in the cells was removed with an air stream, dried at 130 ° C., and baked at 400 ° C. for 1 hour to form a coating layer. A catalyst NAC2 coated with a 250 g / L NOx adsorption layer was obtained.
[0039]
(2) Preparation of partition layer and surface layer
This NAC2 was provided with an isolation layer and a NOx purification layer in the same manner as in Example 1, and as shown in FIG. 1, an exhaust gas purification catalyst having a total coat layer of 370 g / L was obtained.
[0040]
(Example 7)
(1) Inner layer: Preparation of NOx adsorbent
The titanium oxide powder was impregnated with a dinitrodiammine platinum solution, dried and calcined at 400 ° C. for 1 hour in the air to obtain Pt-supported titanium oxide powder NA4. The Pt concentration of this powder was 4.0%. Also, Ce 0.94 Pr 0.06 O 2 The powder is impregnated with a dinitrodiammine platinum solution, dried and calcined at 400 ° C. for 1 hour in air to obtain Pt-supported Ce. 0.94 Pr 0.06 O 2 Powder NA3 was obtained. The Pt concentration of this powder was 4.0%.
Then, 141.25 g of the powder NA3, 141.25 g of the powder NA4, 217.5 g of the activated alumina powder, and 500 g of water were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry. This slurry was adhered to a cordierite-based monolithic carrier (1.2 L, 900 cells), excess slurry in the cells was removed with an air stream, dried at 130 ° C., baked at 400 ° C. for 1 hour, and coated. A catalyst NAC3 coated with a 250 g / L NOx adsorption layer was obtained.
[0041]
(2) Preparation of partition layer and surface layer
This NAC3 was provided with an isolation layer and a NOx purification layer in the same manner as in Example 1, and an exhaust gas purification catalyst having a total coat layer of 370 g / L was obtained.
[0042]
(Example 8)
(1) Inner layer: Preparation of NOx adsorbent
The boehmite powder was peptized in a cerium nitrate solution, stirred for 24 hours, and then adjusted to pH 7.5 to obtain a precipitate. The precipitate is filtered, dried at 150 ° C. for 12 hours, calcined at 400 ° C. for 2 hours, and further calcined at 800 ° C. for 2 hours, whereby Ce-carrying alumina powder in which cerium exists on alumina with a high degree of dispersion is provided. NA5 was obtained. The Ce concentration of this powder was 10%. Cerium acetate was further impregnated and supported on the powder NA5, dried and calcined at 400 ° C. for 1 hour to obtain Ce-supported alumina powder NA6. The Ce concentration of this powder was 30%. The thus-obtained Ce-supported alumina powder NA6 was impregnated with a dinitrodiammine platinum solution, dried, and calcined at 400 ° C. for 1 hour in the air to obtain Pt and Ce-supported alumina powder NA7. The Pt concentration of this powder was 4.0%.
Then, 282.5 g of the powder NA7, 217.5 g of activated alumina powder, and 500 g of water were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry. The slurry was adhered to a cordierite-based monolithic carrier (1.2 L, 900 cells), excess slurry in the cells was removed with an air stream, dried at 130 ° C., and baked at 400 ° C. for 1 hour to form a coating layer. A catalyst NAC4 coated with a 250 g / L NOx adsorption layer was obtained.
[0043]
(2) Preparation of partition layer and surface layer
This NAC4 was provided with an isolation layer and a NOx purification layer in the same manner as in Example 1 to obtain an exhaust gas purification catalyst having a total coat layer of 70 g / L.
[0044]
(Example 9)
(1) Inner layer: Preparation of NOx adsorbent
The cerium oxide powder was impregnated with a dinitrodiammine platinum solution, dried and calcined at 400 ° C. for 1 hour in the air to obtain Pt-supported cerium oxide powder NA1. The Pt concentration of this powder was 4.0%. The cerium oxide powder was impregnated with a palladium nitrate solution, dried and calcined at 400 ° C. for 1 hour in the air to obtain Pd-supported cerium oxide powder NA8. The Pd concentration of this powder was 4.0%.
Then, 188.3 g of the powder NA1, 94.2 g of the powder NA8, 217.5 g of the activated alumina powder, and 500 g of water were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry. The slurry was adhered to a cordierite-based monolithic carrier (1.2 L, 900 cells), excess slurry in the cells was removed with an air stream, dried at 130 ° C., and baked at 400 ° C. for 1 hour to form a coating layer. A catalyst NAC3 coated with a 250 g / L NOx adsorption layer (same symbol as in the above Example 7, but NAC5?) Was obtained.
[0045]
(2) Preparation of partition layer and surface layer
This NAC3 was provided with an isolation layer and a NOx purification layer in the same manner as in Example 1, and an exhaust gas purification catalyst having a total coat layer of 370 g / L was obtained.
[0046]
(Example 10)
(1) Inner layer: Preparation of NOx adsorbent
Ce 0.94 Pr 0.06 O 2 The powder is impregnated with a dinitrodiammine platinum solution, dried and calcined at 400 ° C. for 1 hour in air to obtain Pt-supported Ce. 0.94 Pr 0.06 O 2 Powder NA3 was obtained. The Pt concentration of this powder was 4.0%. The cerium oxide powder was impregnated with a palladium nitrate solution, dried and calcined at 400 ° C. for 1 hour in the air to obtain Pd-supported cerium oxide powder NA8. The Pd concentration of this powder was 4.0%.
Then, 188.3 g of the powder NA3, 94.2 g of the powder NA8, 217.5 g of the activated alumina powder, and 500 g of water were charged into a magnetic ball mill, and mixed and pulverized to obtain a slurry. The slurry was adhered to a cordierite-based monolithic carrier (1.2 L, 900 cells), excess slurry in the cells was removed with an air stream, dried at 130 ° C., and baked at 400 ° C. for 1 hour to form a coating layer. A catalyst NAC3 coated with a 250 g / L NOx adsorption layer was obtained (this is also the same symbol as in Example 7 above, is it NAC6?).
[0047]
(2) Preparation of partition layer and surface layer
This NAC3 was provided with an isolation layer and a NOx purification layer in the same manner as in Example 1, and an exhaust gas purification catalyst having a total coat layer of 370 g / L was obtained.
[0048]
(Example 11)
Activated alumina of partition wall layer is made of TiO 2 A catalyst according to Example 11 was prepared in the same manner as in Example 1, except that the catalyst was replaced with:
[0049]
(Example 12)
The activated alumina of the partition layer is made of SiO 2 A catalyst according to Example 12 was prepared in the same manner as in Example 1 except that the catalyst was replaced with.
[0050]
(Example 13)
A catalyst according to Example 13 was prepared in the same manner as in Example 1, except that the activated alumina of the partition layer was changed to β-zeolite.
[0051]
(Example 14)
A catalyst according to Example 14 was prepared in the same manner as in Example 1, except that the activated alumina of the partition layer was changed to A-type zeolite.
[0052]
(Example 15)
A catalyst according to Example 15 was prepared in the same manner as in Example 1, except that the activated alumina in the partition layer was changed to ferrierite.
[0053]
(Example 16)
In the preparation of the NOx purification layer on the surface, zirconium oxide containing calcium (Ca 0.2 Zr 0.8 O 2 ) Was prepared in the same manner as in Example 1 except that the catalyst of Example 16 was used.
[0054]
<Preparation of wall flow type carrier>
In the following, an alternately plugged support, that is, a wall flow (filter) type catalyst preparation procedure in which both ends of adjacent cells are alternately plugged will be described.
First, on one side of a cordierite honeycomb carrier having an average porosity of 30% and an average pore diameter of 20 μm, a depth of about 5 mm at an upper end surface in a checkerboard shape (checkered pattern) is formed so that heat-resistant cement does not contact each other. After pouring and drying, an upstream coat layer having the following component composition is adhered in the same manner as in the above examples. As a result, the upstream coat layers are attached in a checkerboard shape so as not to contact each other. Next, after cutting 5 mm of the end face to which the heat-resistant cement was applied and penetrating each cell, each cell to which the upstream coat layer was adhered was similarly closed with heat-resistant cement, and the downstream coat of the component composition shown below was used. Apply layer. And finally, the heat-resistant cement is again injected into the cell which was first closed and dried to obtain an alternately plugged wall flow type carrier.
[0055]
(Example 17)
(1) Upstream layer: Preparation of NOx adsorbent
282.5 g of the powder NA1 used in Example 1, 217.5 g of the activated alumina powder, and 500 g of water were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry. This slurry is attached to the wall surface on the upstream side with respect to the exhaust gas flow direction of the alternately-filled wall flow type carrier, and the excess slurry in the cell is removed by an air flow and dried at 130 ° C., and then dried at 400 ° C. It was baked for 1 hour, and a 250 g / L NOx adsorption layer of a coat layer was applied.
[0056]
(2) Downstream layer: Preparation of NOx purification layer
The activated alumina powder was impregnated with the zirconium nitrate solution, dried, and fired in air at 600 ° C. for 1 hour to obtain a zirconium-supported alumina powder. The powder was impregnated with the iridium nitrate solution, dried and calcined in air at 400 ° C. for 1 hour to obtain a Rh.Zr-supported alumina powder (powder NR1). The zirconium concentration of this powder was 10%, and the Rh concentration was 2.8%.
Next, the activated alumina powder was impregnated with a cerium nitrate solution, dried and calcined at 600 ° C. for 1 hour in the air to obtain a cerium-supported alumina powder. The powder was impregnated with a dinitrodiamine platinum solution, dried and calcined at 400 ° C. for 1 hour in the air to obtain Pt / ceria-supported alumina powder (powder NR2). The cerium concentration of this powder was 3%, and the Pt concentration was 2.8%.
Then, 100 g of the powder NR1, 100 g of NR2, 200 g of activated alumina, and 400 g of water were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry. This slurry is adhered to the wall surface on the downstream side in the exhaust gas flow direction of the alternately-filled wall flow type carrier, excess slurry in the cell is removed by an air flow, dried at 130 ° C, and then dried at 400 ° C. The coating was baked for a period of time, and a 200 g / L NOx purification layer was applied.
In this way, as shown in FIG. 2, the upstream side of the cell wall 5 of the wall flow type monolith carrier is provided with the upstream layer 6 containing the NOx adsorbent composed of Pt and cerium oxide, and the downstream side of the cell wall is provided. Then, an exhaust gas purifying catalyst 10 provided with a NOx purifying layer containing Rh and Pt as the downstream layer 7 was obtained.
[0057]
(Example 18)
(1) Upstream layer: Preparation of NOx adsorbent
A slurry composed of powders NA2, NA3, activated alumina and water used for the inner layer of Example 6 was adhered to the wall surface on the upstream side with respect to the exhaust gas flow direction of the alternately plugged wall flow type carrier, and the air flow in the cell was performed. After removing excess slurry and drying at 130 ° C., it was baked at 400 ° C. for 1 hour to apply a 250 g / L NOx adsorption layer of a coat layer.
[0058]
(2) Downstream layer: Preparation of NOx purification layer
The activated alumina powder was impregnated with the zirconium nitrate solution, dried, and fired in air at 600 ° C. for 1 hour to obtain a zirconium-supported alumina powder. The powder was impregnated with the iridium nitrate solution, dried and calcined in air at 400 ° C. for 1 hour to obtain a Rh.Zr-supported alumina powder (powder NR1). The zirconium concentration of this powder was 20%, and the Rh concentration was 2.8%.
Next, the activated alumina powder was impregnated with a cerium nitrate solution, dried and calcined at 600 ° C. for 1 hour in the air to obtain a cerium-supported alumina powder. The powder was impregnated with a dinitrodiamine platinum solution, dried and calcined at 400 ° C. for 1 hour in the air to obtain Pt / ceria-supported alumina powder (powder NR2). The cerium concentration of this powder was 3%, and the Pt concentration was 2.8%.
Then, 100 g of the powder NR1, 100 g of NR2, 200 g of activated alumina, and 400 g of water were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry. This slurry is adhered to the wall surface on the downstream side in the exhaust gas flow direction of the alternately-filled wall flow type carrier, excess slurry in the cell is removed by an air flow, dried at 130 ° C, and then dried at 400 ° C. The coating was baked for a period of time, and a 200 g / L NOx purification layer was applied. Thus, an exhaust gas purifying catalyst similar to that of FIG. 2 was obtained.
[0059]
(Example 19)
(1) Upstream layer: Preparation of NOx adsorbent
The slurry composed of the powders NA3, NA4, activated alumina and water used for the inner layer of Example 7 was attached to the wall surface on the upstream side with respect to the exhaust gas flow direction of the alternately plugged wall flow type carrier, and the inside of the cell was air-flowed. After removing excess slurry and drying at 130 ° C., it was baked at 400 ° C. for 1 hour to apply a 250 g / L NOx adsorption layer of a coat layer.
[0060]
(2) Downstream layer: Preparation of NOx purification layer
Using the same slurry as in Example 18 above, a 200 g / L NOx purification layer was applied to the wall surface on the downstream side in the exhaust gas flow direction of the alternately packed wall flow type carrier, as shown in FIG. An exhaust gas purifying catalyst was obtained.
[0061]
(Example 20)
(1) Upstream layer: Preparation of NOx adsorbent
In the same manner as in Example 18, a 250 g / L NOx adsorption layer was applied to the wall surface on the upstream side in the exhaust gas flow direction of the alternately packed wall flow type carrier.
[0062]
(2) Downstream layer: Preparation of NOx purification layer
The rhodium nitrate solution is converted to a zirconium oxide containing calcium (Ca 0.2 Zr 0.8 O 2 ) The powder was impregnated, dried and calcined in the air at 400 ° C for 1 hour to obtain Rh-supported calcium-containing zirconium oxide powder (powder NR3). The Rh concentration of this powder was 2.8%.
Next, the activated alumina powder was impregnated with a cerium nitrate solution, dried and calcined at 600 ° C. for 1 hour in the air to obtain a cerium-supported alumina powder. The powder was impregnated with a dinitrodiamine platinum solution, dried and calcined in air at 400 ° C. for 1 hour to obtain a Pt / ceria-supported alumina powder (powder NR3). The cerium concentration of this powder was 3%, and the Pt concentration was 2.8%.
Then, 100 g of the powder NR3, 100 g of NR2, 200 g of activated alumina, and 400 g of water were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry. This slurry is adhered to the wall surface on the downstream side with respect to the exhaust gas flow direction of the alternately-filled wall flow type carrier, the excess slurry in the cell is removed by an air flow, dried at 130 ° C, and then at 400 ° C for 1 hour. After baking, a 200 g / L NOx purification layer was applied to the coat layer to obtain an exhaust gas purification catalyst as shown in FIG.
[0063]
(Example 21)
(1) Upstream layer: Preparation of NOx adsorbent
Using the same slurry as in Example 18 above, a 250 g / L NOx adsorption layer was coated on the wall surface of the alternately-filled wall flow type carrier on the upstream side in the exhaust gas flow direction.
[0064]
(2) Downstream layer: Preparation of NOx purification layer
The rhodium nitrate solution is converted to a zirconium oxide containing calcium (Ca 0.2 Zr 0.8 O 2 ) The powder was impregnated, dried and calcined in the air at 400 ° C for 1 hour to obtain Rh-supported calcium-containing zirconium oxide powder (powder NR3). The Rh concentration of this powder was 1.4%.
Then, 200 g of the powder NR3, 200 g of activated alumina, and 400 g of water were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry. This slurry is adhered to the wall surface on the downstream side with respect to the exhaust gas flow direction of the alternately-filled wall flow type carrier, the excess slurry in the cell is removed by an air flow, dried at 130 ° C, and then at 400 ° C for 1 hour. After baking, a 200 g / L NOx purification layer was applied to obtain an exhaust gas purification catalyst as shown in FIG.
[0065]
(Example 22)
(1) Upstream layer: Preparation of NOx adsorbent
Ce 0.75 Zr 0.25 O 2 The powder is impregnated with a dinitrodiammine platinum solution, dried, and calcined in air at 400 ° C. for 1 hour to obtain Pt-supported Ce. 0.75 Zr 0.25 O 2 Powder NA2 was obtained. The Pt concentration of this powder was 5.0%. Also, Ce 0.94 Pr 0.06 O 2 The powder is impregnated with a dinitrodiammine platinum solution, dried, and calcined in air at 400 ° C. for 1 hour to obtain Pt-supported Ce. 0.94 Pr 0.06 O 2 Powder NA3 was obtained. The Pt concentration of this powder was 5.00%.
Then, 141.25 g of the powder NA2, 141.25 g of the powder NA3, 217.5 g of the activated alumina powder, and 500 g of water were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry. This slurry is adhered to the wall surface on the upstream side with respect to the exhaust gas flow direction of the alternately packed wall flow type carrier, excess slurry in the cell is removed by an air flow, dried at 130 ° C, and then at 400 ° C for 1 hour. It was baked and a 250 g / L NOx adsorption layer was applied.
[0066]
(2) Downstream layer: Preparation of NOx purification layer
The activated alumina powder was impregnated with the zirconium nitrate solution, dried, and fired in air at 600 ° C. for 1 hour to obtain a zirconium-supported alumina powder. The powder was impregnated with a rhodium nitrate solution, dried and calcined in air at 400 ° C. for 1 hour to obtain a Rh.Zr-supported alumina powder (powder NR1). The zirconium concentration of this powder was 10%, and the Rh concentration was 2.8%.
Next, the activated alumina powder was impregnated with a cerium nitrate solution, dried, and calcined at 600 ° C. for 1 hour in the air to obtain Ce-supported alumina powder. The powder was impregnated with a dinitrodiamine platinum solution, dried and calcined at 400 ° C. for 1 hour in the air to obtain Pt / ceria-supported alumina powder (powder NR2). The Ce concentration of this powder was 3%, and the Pt concentration was 2.8%.
Further, the rhodium nitrate solution is converted to a zirconium oxide containing calcium (Ca 0.2 Zr 0.8 O 2 ) The powder was impregnated, dried and calcined in the air at 400 ° C for 1 hour to obtain Rh-supported calcium-containing zirconium oxide powder (powder NR3). The Gh concentration of this powder was 2.8%.
Then, 100 g of the powder NR1, 100 g of NR2, and 200 g of water were charged into a magnetic ball mill, and mixed and pulverized to obtain a slurry. This slurry is adhered to the wall surface on the downstream side with respect to the exhaust gas flow direction of the alternately-filled wall flow type carrier, the excess slurry in the cell is removed by an air flow, dried at 130 ° C, and then at 400 ° C for 1 hour. It was baked, and a 100 g / L NOx purification layer was applied.
Further, 100 g of the powder NR3 and 100 g of water were charged into a magnetic ball mill, and mixed and pulverized to obtain a slurry. This slurry is applied on a wall surface on the downstream side of the flow direction of the exhaust gas of the alternately plugged wall flow type carrier, on which a NOx purification layer of 100 g / L is applied and adhered, and the excess slurry in the cell is air-flowed. After drying at 130 ° C. and baking at 400 ° C. for 1 hour, a NOx purification layer of 50 g / L of the coating layer and 150 g / L in total was applied. Thus, an exhaust gas purifying catalyst as shown in FIG. 2 was obtained.
[0067]
(Example 23)
(1) Upstream layer: Preparation of NOx adsorbent
The cerium oxide powder was impregnated with a dinitrodiammine platinum solution, dried and calcined in air at 400 ° C. for 1 hour to obtain Pt-supported cerium oxide powder NA1. The Pt concentration of this powder was 4.0%. The cerium oxide powder was impregnated with a palladium nitrate solution, dried and calcined at 400 ° C. for 1 hour in the air to obtain Pd-supported cerium oxide powder NA8. The Pd concentration of this powder was 4.0%.
Then, 188.3 g of the powder NA1, 94.2 g of the powder NA8, 217.5 g of the activated alumina powder, and 500 g of water were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry. This slurry is adhered to the wall surface on the upstream side with respect to the exhaust gas flow direction of the alternately packed wall flow type carrier, excess slurry in the cell is removed by an air flow, dried at 130 ° C, and then at 400 ° C for 1 hour. It was baked and a 250 g / L NOx adsorption layer was applied.
[0068]
(2) Downstream layer: Preparation of NOx purification layer
Using the same slurry as in Example 18 above, a 200 g / L NOx purification layer was applied to the wall surface on the downstream side in the exhaust gas flow direction of the alternately packed wall flow type carrier, as shown in FIG. An exhaust gas purifying catalyst was obtained.
[0069]
[An endurance test]
Each of the catalysts obtained above was mounted on an exhaust system of an engine with a displacement of 4000 cc. As shown in Table 1, the catalyst was operated for 50 hours at a catalyst inlet temperature of 700 ° C. using domestic regular gasoline, and an endurance test was performed. Carried out.
[0070]
[Table 1]
[0071]
[Performance evaluation test]
Each catalyst after the endurance under the above conditions was mounted on an exhaust system of an engine with a displacement of 2000 cc, and as shown in Table 2, lean (A / F = 18) 40 sec → rich (A / F = 11.0) 2 sec , And the exhaust gas purification rate in this section was determined. The results are shown in Table 3 (open cell type honeycomb carrier) and Table 4 (wall-through type honeycomb carrier). The catalyst inlet temperature was set to 200 ° C.
[0072]
[Table 2]
[0073]
[Table 3]
[0074]
[Table 4]
[0075]
【The invention's effect】
As described above, the exhaust gas purifying catalyst according to the present invention includes the NOx adsorbent-containing layer on the inner layer side of the open-cell type honeycomb carrier or on the exhaust gas flow upstream side of the wall-through type honeycomb carrier. A NOx purification layer is formed on the surface layer side of the honeycomb honeycomb carrier or on the downstream side of the exhaust gas flow of the wall-through honeycomb carrier, and when an open cell honeycomb carrier is used, a heat-resistant porous inorganic material is interposed between the inner and outer layers. Since the separation means made of the material is provided, the adsorbent in the inner layer or the upstream layer can easily release NOx even when the exhaust gas contains a large amount of HC or CO, and is released. The diffusion of NOx into the surface layer or downstream layer is delayed by the isolation means or the wall of the wall-through type honeycomb carrier cell. There results an extremely excellent effect that it is possible to maintain a high NOx purification rate even at a low temperature region not so large.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing, as an embodiment of an exhaust gas purifying catalyst according to the present invention, an example of a catalyst structure including inner and outer layers formed on a cell wall surface of an open-cell type honeycomb carrier and isolation means therebetween.
FIG. 2 is a cross-sectional view showing an example of a catalyst structure comprising upstream and downstream layers formed on both surfaces of a cell wall of a wall-through type honeycomb carrier as another embodiment of the exhaust gas purifying catalyst according to the present invention.
[Explanation of symbols]
1,10 Exhaust gas purification catalyst
2 Inner layer
3 partition layer (isolation means)
4 Surface layer
5 Wall-through type honeycomb carrier cell wall
6 upstream layer
7 Downstream layer

Claims (12)

内燃機関の排気通路に配置する排気ガス浄化触媒であって、排気中のNOxを少なくともNO‐吸着種として吸着するNOx吸着剤を含有する内層と、該内層の前記NOx吸着剤から放出されるNOxを還元浄化するNOx浄化層からなる表層を有すると共に、耐熱性多孔質無機材料からなり、内層から放出されたNOxを一時的に保持して表層側への到達を遅延させる隔離手段が前記表層と内層の間に介在していることを特徴とする排気ガス浄化触媒。An exhaust gas purifying catalyst disposed in an exhaust passage of an internal combustion engine, wherein the inner layer contains a NOx adsorbent that adsorbs NOx in exhaust gas at least as NO 2 -adsorbed species, and is released from the NOx adsorbent in the inner layer. An isolation means having a surface layer composed of a NOx purification layer for reducing and purifying NOx, comprising a heat-resistant porous inorganic material, and temporarily holding NOx released from the inner layer to delay the arrival at the surface layer is provided by the surface layer. An exhaust gas purifying catalyst characterized by being interposed between a catalyst and an inner layer. 前記隔離手段が、コージェライト、SiC、アルミナ、シリカ、ジルコニア、チタニア及びゼオライトから選ばれる少なくとも1種の耐熱性多孔質無機材料からなることを特徴とする請求項2に記載の排気ガス浄化触媒。The exhaust gas purifying catalyst according to claim 2, wherein the separating means is made of at least one kind of heat-resistant porous inorganic material selected from cordierite, SiC, alumina, silica, zirconia, titania, and zeolite. 内燃機関の排気通路に配置する排気ガス浄化触媒であって、隣接するセルの両端部が交互に目詰めされたウォールフロー型ハニカム担体のセル壁面の排気ガス上流側に排気中のNOxを少なくともNO‐吸着種として吸着するNOx吸着剤を含有する上流側層が形成され、セル壁面の排気ガス下流側に前記上流側層のNOx吸着剤から放出されるNOx を還元浄化するNOx浄化層からなる下流側層が形成されていることを特徴とする排気ガス浄化触媒。An exhaust gas purifying catalyst disposed in an exhaust passage of an internal combustion engine, wherein at least NOx in exhaust gas is exhausted to an exhaust gas upstream side of a cell wall surface of a wall flow type honeycomb carrier in which both ends of adjacent cells are alternately plugged. 2- An upstream layer containing a NOx adsorbent that is adsorbed as an adsorbent is formed, and a NOx purification layer for reducing and purifying NOx released from the NOx adsorbent of the upstream layer is formed downstream of exhaust gas on the cell wall surface. An exhaust gas purification catalyst comprising a downstream layer. ウォールフロー型ハニカム担体が、コージェライト、SiC、アルミナ、シリカ、ジルコニア、チタニア及びゼオライトから選ばれる少なくとも1種の耐熱性多孔質無機材料からなることを特徴とする請求項3に記載の排気ガス浄化触媒。The exhaust gas purification according to claim 3, wherein the wall flow type honeycomb carrier is made of at least one kind of heat-resistant porous inorganic material selected from cordierite, SiC, alumina, silica, zirconia, titania, and zeolite. catalyst. NOx吸着剤中に、少なくともチタン及びジルコニウム酸化物の一方を含んでいることを特徴とする請求項1〜4のいずれか1つの項に記載の排気ガス浄化触媒。The exhaust gas purifying catalyst according to any one of claims 1 to 4, wherein the NOx adsorbent contains at least one of titanium and zirconium oxide. 内燃機関の排気通路に配置する排気ガス浄化触媒であって、Pt、Pd及びRhから選ばれる少なくとも1種の貴金属と酸素吸蔵成分からなるNOx吸着剤を含有する内層と、該内層の前記NOx吸着剤から放出されるNOxを還元浄化するNOx浄化層からなる表層を有すると共に、耐熱性多孔質無機材料からなり、内層から放出されたNOxを一時的に保持して表層側への到達を遅延させる隔離手段が前記表層と内層の間に介在していることを特徴とする排気ガス浄化触媒。An exhaust gas purifying catalyst disposed in an exhaust passage of an internal combustion engine, comprising: an inner layer containing a NOx adsorbent comprising at least one noble metal selected from Pt, Pd and Rh and an oxygen storage component, and the NOx adsorbing of the inner layer. It has a surface layer composed of a NOx purification layer that reduces and purifies NOx released from the agent, and is made of a heat-resistant porous inorganic material, and temporarily holds NOx released from the inner layer to delay its arrival at the surface layer side. An exhaust gas purifying catalyst, wherein an isolation means is interposed between the surface layer and the inner layer. 前記隔離手段が、コージェライト、SiC、アルミナ、シリカ、ジルコニア、チタニア及びゼオライトから選ばれる少なくとも1種の耐熱性多孔質無機材料からなることを特徴とする請求項6に記載の排気ガス浄化触媒。The exhaust gas purifying catalyst according to claim 6, wherein the separating means is made of at least one kind of heat-resistant porous inorganic material selected from cordierite, SiC, alumina, silica, zirconia, titania, and zeolite. 内燃機関の排気通路に配置する排気ガス浄化触媒であって、隣接するセルの両端部が交互に目詰めされたウォールフロー型ハニカム担体のセル壁面の排気ガス上流側にPt、Pd及びRhから選ばれる少なくとも1種の貴金属と酸素吸蔵成分からなるNOx吸着剤を含有する上流側層が形成され、セル壁面の排気ガス下流側に前記上流側層のNOx吸着剤から放出されるNOx を還元浄化するNOx浄化層からなる下流側層が形成されていることを特徴とする排気ガス浄化触媒。An exhaust gas purifying catalyst disposed in an exhaust passage of an internal combustion engine, wherein Pt, Pd, and Rh are selected on the exhaust gas upstream side of the cell wall surface of a wall flow type honeycomb carrier in which both ends of adjacent cells are alternately plugged. An upstream layer containing a NOx adsorbent comprising at least one noble metal and an oxygen storage component is formed, and NOx released from the NOx adsorbent in the upstream layer is reduced and purified downstream of exhaust gas on the cell wall. An exhaust gas purification catalyst comprising a downstream layer formed of a NOx purification layer. ウォールフロー型ハニカム担体が、コージェライト、SiC、アルミナ、シリカ、ジルコニア、チタニア及びゼオライトから選ばれる少なくとも1種の耐熱性多孔質無機材料からなることを特徴とする請求項8に記載の排気ガス浄化触媒。The exhaust gas purification according to claim 8, wherein the wall flow type honeycomb carrier is made of at least one kind of heat-resistant porous inorganic material selected from cordierite, SiC, alumina, silica, zirconia, titania, and zeolite. catalyst. NOx吸着剤中に、酸素吸蔵成分として少なくともセリウム酸化物を含んでいることを特徴とする請求項6〜9のいずれか1項に記載の排気ガス浄化触媒。The exhaust gas purifying catalyst according to any one of claims 6 to 9, wherein the NOx adsorbent contains at least cerium oxide as an oxygen storage component. CeO換算で10〜500g/Lのセリウム酸化物を含んでいることを特徴とする請求項10に記載の排気ガス浄化触媒。Exhaust gas purifying catalyst according to claim 10, characterized in that it contains cerium oxide of 10 to 500 g / L in terms of CeO 2. 前記NOx浄化層がロジウムと共に、ジルコニウム酸化物を含有し、ロジウム含有量が0.1〜50g/L、ジルコニア酸化物の含有量が5〜100g/Lであることを特徴とする請求項1〜11のいずれか1つの項に記載の排気ガス浄化触媒。The said NOx purification layer contains a zirconium oxide with rhodium, The rhodium content is 0.1-50 g / L, and the content of a zirconia oxide is 5-100 g / L, The claim 1 characterized by the above-mentioned. 12. The exhaust gas purifying catalyst according to any one of the eleventh to eleventh aspects.
JP2002175795A 2002-06-17 2002-06-17 Exhaust gas purification catalyst Pending JP2004016931A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP2002175795A JP2004016931A (en) 2002-06-17 2002-06-17 Exhaust gas purification catalyst

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP2002175795A JP2004016931A (en) 2002-06-17 2002-06-17 Exhaust gas purification catalyst

Publications (1)

Publication Number Publication Date
JP2004016931A true JP2004016931A (en) 2004-01-22

Family

ID=31174349

Family Applications (1)

Application Number Title Priority Date Filing Date
JP2002175795A Pending JP2004016931A (en) 2002-06-17 2002-06-17 Exhaust gas purification catalyst

Country Status (1)

Country Link
JP (1) JP2004016931A (en)

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2006231204A (en) * 2005-02-24 2006-09-07 Toyota Motor Corp Catalyst for cleaning exhaust gas
WO2007026806A1 (en) * 2005-08-31 2007-03-08 Ngk Insulators, Ltd. Honeycomb catalyst body and process for producing the same
WO2008010576A1 (en) * 2006-07-20 2008-01-24 Toyota Jidosha Kabushiki Kaisha Catalyst for exhaust gas purification
JP2008510605A (en) * 2004-08-21 2008-04-10 ユミコア・アクチエンゲゼルシャフト・ウント・コムパニー・コマンディットゲゼルシャフト Catalyst coated particle filter, process for its production and use thereof
JP2009183865A (en) * 2008-02-06 2009-08-20 Toyota Motor Corp Exhaust gas treatment catalyst
JP2009255034A (en) * 2008-03-27 2009-11-05 Ibiden Co Ltd Honeycomb structure and apparatus of treating exhaust gas
WO2010058834A1 (en) * 2008-11-21 2010-05-27 日産自動車株式会社 Particulate substance removing material, particulate substance removing filter catalyst using particulate substance removing material, and method for regenerating particulate substance removing filter catalyst
JP2010540217A (en) * 2007-09-28 2010-12-24 ユミコア・アクチエンゲゼルシャフト・ウント・コムパニー・コマンディットゲゼルシャフト Removal of particles from exhaust gas of internal combustion engines operated mainly with stoichiometric mixtures
JP2011038405A (en) * 2009-08-06 2011-02-24 Honda Motor Co Ltd Exhaust emission control device of internal combustion engine
WO2011042990A1 (en) * 2009-10-09 2011-04-14 イビデン株式会社 Honeycomb filter
JP2011526203A (en) * 2008-06-27 2011-10-06 ビー・エイ・エス・エフ、コーポレーション NOx adsorption catalyst with excellent low-temperature performance
US8133841B2 (en) 2005-08-31 2012-03-13 Ngk Insulators, Ltd. Honeycomb catalytic structure, precoated support for producing honeycomb catalytic structure, and process for producing honeycomb catalytic structure
JP2013500857A (en) * 2009-08-05 2013-01-10 ビーエーエスエフ ソシエタス・ヨーロピア Gasoline engine exhaust gas treatment system

Cited By (22)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2008510605A (en) * 2004-08-21 2008-04-10 ユミコア・アクチエンゲゼルシャフト・ウント・コムパニー・コマンディットゲゼルシャフト Catalyst coated particle filter, process for its production and use thereof
JP2006231204A (en) * 2005-02-24 2006-09-07 Toyota Motor Corp Catalyst for cleaning exhaust gas
WO2007026806A1 (en) * 2005-08-31 2007-03-08 Ngk Insulators, Ltd. Honeycomb catalyst body and process for producing the same
US8133841B2 (en) 2005-08-31 2012-03-13 Ngk Insulators, Ltd. Honeycomb catalytic structure, precoated support for producing honeycomb catalytic structure, and process for producing honeycomb catalytic structure
JP4814887B2 (en) * 2005-08-31 2011-11-16 日本碍子株式会社 Honeycomb catalyst body and manufacturing method thereof
US7887761B2 (en) 2005-08-31 2011-02-15 Ngk Insulators, Ltd. Honeycomb catalyst and manufacturing method thereof
JP2008023451A (en) * 2006-07-20 2008-02-07 Toyota Motor Corp Catalyst for purifying exhaust gas
WO2008010576A1 (en) * 2006-07-20 2008-01-24 Toyota Jidosha Kabushiki Kaisha Catalyst for exhaust gas purification
US7846865B2 (en) 2006-07-20 2010-12-07 Toyota Jidosha Kabushiki Kaisha Catalyst for purifying exhaust gas
KR101006220B1 (en) * 2006-07-20 2011-01-07 도요타 지도샤(주) Catalyst for exhaust gas purification
JP2010540217A (en) * 2007-09-28 2010-12-24 ユミコア・アクチエンゲゼルシャフト・ウント・コムパニー・コマンディットゲゼルシャフト Removal of particles from exhaust gas of internal combustion engines operated mainly with stoichiometric mixtures
JP2009183865A (en) * 2008-02-06 2009-08-20 Toyota Motor Corp Exhaust gas treatment catalyst
JP2009255034A (en) * 2008-03-27 2009-11-05 Ibiden Co Ltd Honeycomb structure and apparatus of treating exhaust gas
JP2011526203A (en) * 2008-06-27 2011-10-06 ビー・エイ・エス・エフ、コーポレーション NOx adsorption catalyst with excellent low-temperature performance
JP5445465B2 (en) * 2008-11-21 2014-03-19 日産自動車株式会社 Particulate matter purification material, particulate matter purification filter catalyst using particulate matter purification material, and method for regenerating particulate matter purification filter catalyst
US9222382B2 (en) 2008-11-21 2015-12-29 Nissan Motor Co., Ltd. Particulate matter purifying material, filter catalyst for purifying particulate matter using particulate matter purifying material, and method of regenerating filter catalyst for purifying particulate matter
WO2010058834A1 (en) * 2008-11-21 2010-05-27 日産自動車株式会社 Particulate substance removing material, particulate substance removing filter catalyst using particulate substance removing material, and method for regenerating particulate substance removing filter catalyst
RU2468862C1 (en) * 2008-11-21 2012-12-10 Ниссан Мотор Ко., Лтд. Purifying from disperse particles material, filter-catalyst for purification from disperse particles with application of purifying from disperse particles material and method of regenerating filter-catalyst for purification from disperse particles
JP2013500857A (en) * 2009-08-05 2013-01-10 ビーエーエスエフ ソシエタス・ヨーロピア Gasoline engine exhaust gas treatment system
JP2011038405A (en) * 2009-08-06 2011-02-24 Honda Motor Co Ltd Exhaust emission control device of internal combustion engine
US8617476B2 (en) 2009-10-09 2013-12-31 Ibiden Co., Ltd. Honeycomb filter and urea SCR device
WO2011042990A1 (en) * 2009-10-09 2011-04-14 イビデン株式会社 Honeycomb filter

Similar Documents

Publication Publication Date Title
KR101652537B1 (en) Nox adsorber catalyst with superior low temperature performance
JP3859940B2 (en) Exhaust gas purification catalyst and method for producing the same
JP3904802B2 (en) Exhaust gas purification catalyst and method for producing the same
JP3489048B2 (en) Exhaust gas purification catalyst
WO2014192219A1 (en) Exhaust gas purification catalyst and production method thereof
US10226754B2 (en) Lean NOx trap with enhanced high and low temperature performance
JP2003200049A (en) Catalyst for exhaust gas purification
EP1188908A2 (en) Exhaust gas purifying system
JP4390000B2 (en) NOx adsorption device
US8980209B2 (en) Catalyst compositions, catalytic articles, systems and processes using protected molecular sieves
JP2004016931A (en) Exhaust gas purification catalyst
JP2004275814A (en) Exhaust gas purifying catalyst, its manufacturing method and exhaust gas purifying apparatus
JP2006255539A (en) Exhaust gas purifying device
JP2011220123A (en) Exhaust purification catalyst
JP2002191988A (en) Catalyst for cleaning exhaust gas
JP2004322022A (en) Catalyst for cleaning exhaust gas
JP4058588B2 (en) Exhaust gas purification catalyst
JP2003135970A (en) Exhaust gas cleaning catalyst
JP2004016850A (en) Exhaust gas cleaning catalyst, production method and exhaust gas cleaning system
JP2008229546A (en) Catalyst for purifying exhaust gas and its manufacturing method
JP2008274807A (en) Exhaust emission control device
JP2002018242A (en) Exhaust gas cleaning apparatus of engine
JP2002168117A (en) Exhaust emission control system
JP2003343252A (en) Exhaust gas purifying system
JP2003200063A (en) Catalyst for exhaust gas purification, method for manufacturing the same and exhaust gas purification system