JP2004132193A - Catalyst system for exhaust emission control - Google Patents
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【０００１】
【発明の属する技術分野】
本発明は、自動車用エンジンなどの内燃機関から排出される排気ガスを浄化するための触媒システムに係わり、特に内燃機関の始動直後の排気ガス中に含まれる炭化水素（以下、「ＨＣ」と称する）を効率良く浄化することができる排気ガス浄化用触媒システムに関するものである。
【０００２】
【従来の技術】
近年、内燃機関の始動時における低温域で大量に排出されるＨＣ（コールドＨＣ）の浄化を目的に、ＨＣ吸着材にゼオライトを用いたＨＣ吸着型三元触媒（ＨＣ吸着機能付き三元触媒）が開発されている。
このようなＨＣ吸着型三元触媒は、三元触媒がまだ十分に活性化していないエンジン始動時の低温域において、大量に排出されるＨＣをＨＣ吸着材によって一時的に吸着・保持したのち、排気ガス温度の上昇によって三元触媒が活性化した時に、吸着したＨＣを徐々に脱離し、浄化しようとするものであり、このようなＨＣ吸着型三元触媒がコールドＨＣの浄化処理に有効であると考えられてきた。しかし、ＨＣ吸着型三元触媒が備えている浄化触媒成分あるいはこの触媒の下流側に備えた浄化触媒が十分に活性化する前に、ＨＣ吸着材の昇温によって、当該吸着材に一旦貯蔵されたコールドＨＣが脱離してしまうことから、効率良く浄化することができなかった。
【０００３】
すなわち、従来の合成ゼオライトを主体としたＨＣ吸着材を用いた排ガス浄化用触媒、特に上記のようなＨＣ吸着型三元触媒においては、排ガス中に含まれる水分がゼオライト細孔内の酸点に対する化学吸着を阻害するため、エンジン始動直後の三元触媒が活性化する前に排出されるコールドＨＣの吸着は、ゼオライトの分子篩作用を利用した物理吸着によるものが支配的である。しかし、物理吸着したＨＣは、ゼオライト細孔内での保持力が弱いため、排ガス温度の上昇や排ガス流量の増加などの外的（物理的）な要因によって、容易に脱離するものと推測される。このため、排ガス流路の下流にＨＣ吸着型三元触媒を設置しても、コールドＨＣの吸着及び脱離現象は生じるものの、吸着ＨＣの脱離開始と浄化触媒の活性化とのタイミングが一致せず、吸着ＨＣの脱離浄化処理を効率良く実行するのは極めて困難であった。
【０００４】
従来においては、コールドＨＣの分子径に適した細孔径を有するゼオライトを選択することによって、比較的効率よくコールドＨＣを吸着することは可能であったが、このように物理吸着したＨＣをゼオライト細孔内に長時間留めておくことができないために、浄化触媒が充分に活性化する前に脱離が始まってしまい、所望の浄化処理効率を得ることができないのが実情であった。
【０００５】
さらに、従来においては、ゼオライト骨格構造の耐熱性の向上を図るため、ゼオライト骨格を構成しているシリカ（ＳｉＯ２）及びアルミナ（Ａｌ２Ｏ３）のうちのＡｌを酸溶液で処理して脱離する処理（脱Ａｌ処理）が行われている。しかし、このような脱Ａｌ処理を施したゼオライトは、耐熱性が向上する反面、骨格構造中の酸点であるＡｌのカチオンサイトが減少するため、酸特性が著しく低下し、ゼオライト細孔内に物理吸着したＨＣを保持する特性に著しく欠けるという問題があった。
【０００６】
このため、このようなＨＣ吸着材を用いた排気ガス浄化システムとしては、例えば特開平６−７４０１９号公報、特開平７−１４４１１９号公報、特開平６−１４２４５７号公報、特開平５−５９９４２号公報、特開平７−１０２９５７号公報、特開平９−８５０５６号公報、特開平７−９６１８３号公報、特開平１１−８１９９９号公報等に開示されているものがある。
【０００７】
すなわち、特開平６−７４０１９号公報には、排気流路にバイパスを設け、エンジン始動直後のコールド時に排出されるＨＣをバイパス流路に配置したＨＣ吸着材に一旦吸着させ、その後流路を切り換え、下流の三元触媒が活性化した後に排気ガスの一部をＨＣ吸着触媒に通じ、吸着材から脱離したＨＣを徐々に後段の三元触媒で浄化するシステムが提案されている。
【０００８】
特開平７−１４４１１９号公報においては、コールド時に前段の三元触媒に熱を奪わせて中段のＨＣ吸着触媒の吸着効率を向上する一方、前段の三元触媒が活性化した後は、タンデム配置した中段のＨＣ吸着触媒を介して後段の三元触媒に反応熱を伝熱し易くし、後段の三元触媒による浄化を促進するシステムが提案されている。
【０００９】
また、特開平６−１４２１４５７号公報では、低温域で吸着したＨＣが脱離する際に、脱離ＨＣを含む排気ガスを熱交換器で予熱することによって三元触媒での浄化を促進するコールドＨＣ吸着除去システムが提案されている。
【００１０】
一方、特開平５−５９９４２号公報には、触媒配置とバルブによる排気ガス流路の切り換えによって、ＨＣ吸着材の昇温を緩慢にし、これによって吸着材によるコールドＨＣの吸着効率を向上するシステムが提案されている。
【００１１】
また、特開平７−１０２９５７号公報では、後段の酸化・三元触媒の浄化性能を向上させるために、前段の三元触媒と中段のＨＣ吸着材の間に空気を供給し、後段の酸化・三元触媒の活性化を促進するシステムを提案している。
【００１２】
さらに、特開平９−８５０５６号公報には、ゼオライトからなるＨＣ吸着材とＰｔ−Ｒｈ系触媒成分を含む前段触媒と、ゼオライトからなるＨＣ吸着材とＰｄ系触媒成分と酸化セリウムを含む後段触媒とを同じ容器に充填し、これらの間に２次エアーを供給することによって後段触媒の浄化促進するシステムが提案されている。
【００１３】
そして、特開平７−９６１８３号公報では、ゼオライトと接触する触媒層（ＰｄとＡｌ２Ｏ３が主成分）の高温下での劣化抑制の観点から、吸着材層と触媒層との間に多孔質バリヤ層を設ける一方、下層吸着材層の吸着能の低下を抑制する観点から、Ｐｄ担持Ａｌ２Ｏ３粒子の平均粒子径が１５〜２５μｍ、耐火性無機質粒子の平均粒子径が５〜１５μｍのものを用いることを提案している。
【００１４】
さらに、特開平１１−８１９９９号公報では、コールド時に吸着材に捕捉されたＨＣの脱離を緩慢にするために、ＨＣ吸着触媒の温度上昇を十分に遅延させるべく、上流三元触媒と下流吸着触媒との間を結ぶ排気通路における管体の肉厚を厚くしたり、担体などを設置したりすることによって、上記排気通路の熱容量を排気マニホールドの熱容量より大きくする方法が提案されている。
【００１５】
【発明が解決しようとする課題】
しかしながら、上記した特開平５−５９９４２号公報や特開平６−７４０１９号公報記載のシステムにおいては、車種や走行パターンなどの諸条件の相違によってコールドＨＣの吸着や脱離時間が大きく変動するため、切り換えバルブの作動タイミングを最適に制御することが困難であり、ＨＣ吸着材からのＨＣ脱離と、後段三元触媒の活性化とのタイミングを常に一致させることができず、浄化処理の効率を十分に向上させることができないという問題がある。
【００１６】
一方、特開平７−１４４１１９号公報や特開平６−１４２１４５７号公報に記載されたシステムでは、ＨＣ吸着材の後段に配置した三元触媒の熱による活性化の促進が不十分となり易く、浄化処理を必ずしも効率良く行うことができないという難点があり、特開平７−１０２９５７号公報や特開平９−８５０５６号公報に提案されたシステムにおいても、２次空気を供給することによる後段の酸化・三元触媒の活性化促進効果にもおのずと限界があり、浄化処理効率の向上幅は必ずしも十分なものとは言えない。
【００１７】
そして、特開平７−９６１８３号公報には、ゼオライト層と触媒層との間にバリヤ層を設けることによる触媒層の劣化抑制が提案されているが、その効果は必ずしも十分とは言えず、三元触媒による脱離ＨＣの浄化処理効率を十分なものとすることができない。
また、特開平１１−８１９９９号公報記載のシステムでは、排気通路の熱容量を大きくして吸着材層の温度上昇を遅らせ、もってコールド時に吸着材に捕捉されたＨＣの脱離が緩慢なものとなるようにしているが、同時に、後段三元触媒の活性化開始も遅れることから、脱離と浄化開始のタイミングを十分に一致させることができず、浄化処理効率を十分に向上させることができないという問題がある。
【００１８】
以上のように、上記公報に開示された各浄化システムにおいては、バルブ切り換え、予熱や空気供給による浄化触媒の活性化促進、吸着材からのＨＣ離脱の緩慢化などによるＨＣ脱離と浄化開始のタイミングを一致させるようにしており、それなりの効果はあるにしても、両者のタイミングを十分に一致させるには到っておらず、いずれのシステムにおいてもＨＣ吸着型三元触媒の浄化触媒成分、あるいはその後段に備えた浄化触媒が活性化する前に、ＨＣ吸着材に一旦吸着されたコールドＨＣが脱離してしまうことがないとは言えず、コールドＨＣを必ずしも効率良く浄化することができないという問題点があり、従来の排気ガス浄化システムにおける課題となっていた。
【００１９】
本発明は、ＨＣ吸着型三元触媒を備えた従来の排気ガス浄化システムにおける上記課題に鑑みてなされたものであって、ＨＣ吸着材層からのＨＣの脱離を遅延化して、触媒成分による浄化開始とのタイミングを十分に一致させることができ、コールドＨＣの浄化効率の向上が可能な排気ガス浄化用触媒システムを提供することを目的としている。
【００２０】
【課題を解決するための手段】
本発明の排気ガス浄化用触媒システムは、排気ガス流路の上流側に三元触媒を配置し、ゼオライトを含有するＨＣ吸着材層と、触媒金属を含有する浄化触媒成分層を担体の多角形セル内にこの順序に積層して成るＨＣ吸着型三元触媒を上記三元触媒の下流側に複数個配置したシステムであって、上記複数個のＨＣ吸着型三元触媒における担体セルの辺数が排気ガス流路の下流側に向けて増加している構成としたことを特徴としている。
【００２１】
【発明の実施の形態】
以下、本発明の排気ガス浄化用触媒システムについて詳細に説明する。
本発明の排気ガス浄化用触媒システムは、排気ガス流路の上流側に三元触媒、その下流側に複数個のＨＣ吸着型三元触媒を配置して成る触媒システムであって、上記ＨＣ吸着型三元触媒が担体の多角形セル内に、ゼオライトを含有するＨＣ吸着材層と触媒金属を含有する浄化触媒成分層とをこの順序に積層した多層構造を有し、これら複数個のＨＣ吸着型三元触媒の担体セルの辺数が排気ガス流路の下流側に向けて増加するように配列されていることから、排気ガス流路の上流側に配置した三元触媒が活性化する前に排出されるコールドＨＣが下流側に配置した複数のＨＣ吸着型三元触媒で分担して吸着されることになり、コールドＨＣの吸着効率の向上と吸着したＨＣの脱離遅延化が図れる。
【００２２】
すなわち、排気ガス流路の前段側と後段側とで昇温プロファイルが異なる２個以上のＨＣ吸着型三元触媒によってコールドＨＣを分担して吸着すること、望ましくは、例えば前段、すなわち最上流のＨＣ吸着型三元触媒でコールドＨＣ排出量の５０％以上を一旦吸着することにより、後段側触媒の吸着負荷が軽減され、前段で未浄化のまま脱離するＨＣを後段側触媒中のゼオライトで効率良く再吸着できるため、システム全体の吸着効率の向上が達成される。
さらに、最上流の三元触媒の活性化開始を速め、その下流に配置したＨＣ吸着型三元触媒に流入するコールドＨＣ量を、該ＨＣ吸着型三元触媒に含有されるゼオライトの飽和吸着容量の７０％以下、望ましくは５０％以下の範囲で捕捉（物理吸着）させることによって、温度が上昇あるいはガス流量が増大した場合にも、ゼオライト細孔内のＨＣ分子の拡散衝突が緩和されるため、脱離の遅延化が図れるものと考えられる。
【００２３】
そして、排気ガス流路に配置された複数のＨＣ吸着型三元触媒が、上流から下流に行くに従って触媒成分を塗布する担体が角（辺）の増えた多角形セル形状（例えば、四角形セルから六角形セル）になるようにしてあるので、これによってコーナー部の角度が大きくなり、スラリーの塗布形状、とりわけ第１層であるＨＣ吸着材層の塗布厚さが平均化され、塗布形態が吸着−保持特性に優れた形状となる。すなわち、塗布量に対して吸着表面積が増すと共に、塗布厚さの極度に薄い部分がなくなることから、急激な加熱によって吸着ＨＣを早期に放出してしまうようなことがなくなる。
したがって、コールドＨＣの吸着効率が向上すると共に、吸着ＨＣの脱離が遅延化され、浄化触媒成分層の温度上昇が緩慢で活性化し難い下流側でも、ＨＣの浄化処理効率が著しく改善されることになる。
【００２４】
なお、三元触媒の下流側に配置される複数個のＨＣ吸着型三元触媒における担体セル形状の具体的配置としては、最上流に位置するＨＣ吸着型三元触媒に用いる担体のセル形状を四角形とし、これよりも下流側の触媒には六角形セルを備えた担体を使用することができる。
すなわち、四角形−六角形（２個配置の場合）、四角形−六角形−六角形（３個配置の場合）、四角形−六角形−六角形−六角形（４個配置の場合）などが考えられるが、下流側触媒ほど温度が低くなり、徒にこれら触媒の数を増したとしても排ガス浄化に実質的に寄与しない触媒を増したに過ぎない結果となることが多いので、四角形及び六角形セルの担体をそれぞれ使用した２個のＨＣ吸着型三元触媒をこの順序に配置することが望ましい。
【００２５】
本発明の排気ガス浄化用触媒システムにおける好適形態としては、上流から下流に行くにしたがって、ＨＣ吸着型三元触媒の触媒成分を塗布する担体のセル形状が角の増えた多角形になり、さらに担体の幾何学的表面積（ＧＳＡ）が増大したものとすることが望ましく、これによって排気ガスとの接触効率が向上することから、前段のＨＣ吸着型三元触媒で未吸着となったコールドＨＣや未浄化のまま排出されるコールドＨＣが後段側のＨＣ吸着型三元触媒によって効率良く吸着されるようになる。このため、後段ＨＣ吸着型三元触媒に流入してくる難吸着性のＨＣ種も効率良く吸着され、浄化触媒層による脱離ＨＣの浄化処理効率が一層改善されることになる。
【００２６】
また、他の好適形態としては、上流から下流に行くにしたがって、触媒成分を塗布する担体のセル形状を角の増えた多角形状とすると共に、セルの角部（コーナー部）と平坦部とのＨＣ吸着材層塗布量の差を小さくすることが望ましい。
すなわち、複数個のＨＣ吸着型三元触媒を配置した排ガス浄化システムにおいては、一般に、上流から下流に行くにしたがって、触媒出口の排気組成が徐々に変化し、下流側の排気ガス中には吸着し難く脱離し易いＨＣ種が残っているため、下流側触媒ほど、ＨＣ吸着材層の塗布形態が吸着−保持特性に優れた形状にすることが望ましい。このため、上記のようにセルの角部と平坦部とのＨＣ吸着材層塗布量の差を小さくすることによって、ＨＣ吸着材層の塗布形態が吸着−保持特性に優れた形状となり、吸着ＨＣの脱離が遅延化し、浄化触媒層の温度上昇が緩慢で活性化し難い下流側でも、ＨＣの浄化処理効率を著しく改善できることになる。
【００２７】
本発明の排気ガス浄化用触媒システムにおけるさらに他の好適形態としては、排気ガス流路の上流から下流に行くにしたがって、ＨＣ吸着型三元触媒において触媒成分を塗布する担体のセル形状を角数の増えた多角形セル形状とし、さらに、下流に行くほどＨＣ吸着材層の塗布量を増やすようになすことができ、これによってＨＣ吸着材層の形態が吸着−保持特性に優れた形状となって吸着ＨＣの脱離が遅延化され、浄化触媒層の温度上昇が緩慢で活性化し難い下流側でも、ＨＣの浄化処理効率がさらに一層改善されることになる。
【００２８】
そして、本発明の排気ガス浄化用触媒システムの別の好適形態においては、上記ＨＣ吸着型三元触媒の表層である浄化触媒成分層に、白金（Ｐｔ），パラジウム（Ｐｄ）及びロジウム（Ｒｈ）から成る群より選ばれた少なくとも１種の金属と、セリウム（Ｃｅ），ジルコニウム（Ｚｒ）及びランタン（Ｌａ）から成る群より選ばれた少なくとも１種を金属換算で１〜１０モル％含むアルミナと、ジルコニウム（Ｚｒ），ネオジウム（Ｎｄ），プラセオジウム（Ｐｒ），イットリウム（Ｙ）及びランタン（Ｌａ）から成る群より選ばれた少なくとも１種を金属換算で１〜５０モル％含むセリウム酸化物を含有させることができ、これによって活性成分であるＰｔ及びＰｄの経時劣化が抑制され、脱離ＨＣの浄化処理効率を高く維持することができると共に、三元触媒としても高い浄化性能が得られることになる。
【００２９】
また、さらなる好適形態としては、上記浄化触媒成分層に、更にセリウム（Ｃｅ），ネオジウム（Ｎｄ），プラセオジウム（Ｐｒ），イットリウム（Ｙ）及びランタン（Ｌａ）から成る群より選ばれた少なくとも１種を金属換算で１〜４０モル％含むジルコニウム酸化物を含有させることが望ましく、これによって活性成分であるＲｈの経時劣化が抑制でき、脱離ＨＣの高い浄化処理効率を維持することができ、三元触媒としてもさらに高い浄化性能を得ることができる。
【００３０】
上記排気ガス浄化用触媒システムのさらなる好適形態としては、上記浄化触媒成分層に、更にアルカリ金属及びアルカリ土類金属から選ばれた少なくとも１種の金属を含有させることが望ましく、これによって、還元雰囲気における浄化活性の向上と共に活性成分の経時劣化の抑制を図ることができ、脱離ＨＣの高い浄化処理効率が維持できると共に、三元触媒としても高い浄化性能が得られることになる。しかも、これらアルカリ金属及びアルカリ土類金属を水に難溶性あるいは不溶性の化合物を用いて浄化触媒成分層に含有させることによって、スラリー中の水分の移動に伴ってスラリー中に溶出した金属イオンのゼオライト細孔内へ浸入を抑制することができ、初期から耐久後まで高い吸着効率を維持できることになる。
【００３１】
【実施例】
以下、本発明を実施例に基づいてさらに具体的に説明する。なお、当該実施例において、「％」は特記しない限り質量百分率を表すものとする。
【００３２】
（触媒１）
ＳｉＯ２／Ａｌ２Ｏ３比が４０のβ−ゼオライト粉末２２５７ｇ、シリカゾル（固形分２０％）１２１５ｇ、純水１０００ｇを磁性ボールミルに投入し、混合粉砕してスラリー液を得た。このスラリー液をコージェライト製担体（セル形状：四角形、セル数：４６．５個／ｃｍ２，セル壁厚み：０．０１５ｃｍ，ＧＳＡ：２４．１ｃｍ２／ｃｍ３，担体容量：１．０Ｌ）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乾燥し、４００℃で１時間焼成した。そして、このゼオライトを含有する吸着材層のコート量が３５０ｇ／Ｌになるまでコーティング作業を繰り返すことによって、触媒−ａ１を得た。
【００３３】
次に、３モル％のＣｅを含むアルミナ粉末（Ａｌ：９７モル％）に、硝酸パラジウム水溶液を含浸あるいは高速撹拌中で噴霧し、１５０℃で２４時間乾燥した後、４００℃で１時間、次いで、６００℃で１時間焼成し、Ｐｄ担持アルミナ粉末（粉末ａ）を得た。この粉末ａのＰｄ濃度は４．０％であった。
また、１モル％のＬａと３２モル％のＺｒを含有するセリウム酸化物粉末（Ｃｅ：６７モル％）に、硝酸パラジウム水溶液を含浸あるいは高速撹拌中で噴霧し、１５０℃で２４時間乾燥した後、４００℃で１時間、次いで、６００℃で１時間焼成し、Ｐｄ担持セリウム酸化物粉末（粉末ｂ）を得た。この粉末ｂのＰｄ濃度は２．０％であった。
そして、上記Ｐｄ担持アルミナ粉末（粉末ａ）４００ｇ、Ｐｄ担持セリウム酸化物粉末（粉末ｂ）１４１ｇ、硝酸酸性アルミナゾル２４０ｇ（ベーマイトアルミナ１０％に１０％の硝酸を添加することによって得られたゾルで、Ａｌ２Ｏ３換算で２４ｇ）及び炭酸バリウム１００ｇ（ＢａＯとして６７ｇ）を純水２０００ｇと共に磁性ボールミルに投入し、混合粉砕してスラリー液を得た。このスラリー液を上記コート触媒−ａ１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乾燥し、４００℃で１時間焼成して、コート層重量６６．５ｇ／Ｌを塗布した触媒−ｂを得た。
【００３４】
次に、３モル％のＺｒを含むアルミナ粉末（Ａｌ：９７モル％）に、硝酸ロジウム水溶液を含浸或いは高速撹拌中で噴霧し、１５０℃で２４時間乾燥した後、４００℃で１時間、次いで、６００℃で１時間焼成し、Ｒｈ担持アルミナ粉末（粉末ｃ）を得た。この粉末ｃのＲｈ濃度は２．０％であった。
また、３モル％のＣｅを含むアルミナ粉末（Ａｌ：９７モル％）に、ジニトロジアンミン白金水溶液を含浸或いは高速撹拌中で噴霧し、１５０℃で２４時間乾燥した後、４００℃で１時間、次いで、６００℃で１時間焼成し、Ｐｔ担持アルミナ粉末（粉末ｄ）を得た。この粉末ｄのＰｔ濃度は３．０％であった。
さらに、１モル％のＬａと２０モル％のＣｅを含有するジルコニウム酸化物粉末に、ジニトロジアンミン白金水溶液を含浸或いは高速撹拌中で噴霧し、１５０℃で２４時間乾燥した後、４００℃で１時間、次いで、６００℃で１時間焼成し、Ｐｔ担持アルミナ粉末（粉末ｅ）を得た。この粉末ｅのＰｔ濃度は３．０％であった。
そして、上記Ｒｈ担持アルミナ粉末（粉末ｃ）１１８ｇ、Ｐｔ担持アルミナ粉末（粉末ｄ）１１８ｇ、Ｐｔ担持ジルコニウム酸化物粉末（粉末ｅ）１１８ｇ、硝酸酸性アルミナゾル１６０ｇを磁性ボールミルに投入し、混合粉砕してスラリー液を得た。このスラリー液を上記コート触媒−ｂ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乾燥し、４００℃で１時間焼成して、コート層重量３７ｇ／Ｌを塗布したＨＣ吸着型三元触媒１を得た。
当該触媒１の貴金属担持量は、Ｐｔ：０．７１ｇ／Ｌ、Ｐｄ：１．８８ｇ／Ｌ、Ｒｈ：０．２４ｇ／Ｌであった。
【００３５】
（触媒２）
触媒担体として、セル形状が四角形、セル数：３１．０個／ｃｍ２、セル壁厚み：０．０２５ｃｍ、ＧＳＡ：１９．０ｃｍ２／ｃｍ３、担体容量：１．０Ｌのコージェライト製担体を用いたこと以外は、上記触媒１と同様の操作を繰り返し、ＨＣ吸着材層及び浄化触媒成分層を積層して、本例に係わるＨＣ吸着型三元触媒２を得た。
【００３６】
（触媒３）
触媒担体として、セル形状が六角形、セル数：６２．０個／ｃｍ２、セル壁厚み：０．０１１ｃｍ、ＧＳＡ：２７．２ｃｍ２／ｃｍ３、担体容量：１．０Ｌのコージェライト製担体を用いたこと以外は、上記触媒１と同様の操作を繰り返し、ＨＣ吸着材層及び浄化触媒成分層を積層して、本例に係わるＨＣ吸着型三元触媒３を得た。
【００３７】
（触媒４）
触媒担体として、セル形状が六角形、セル数：７１．３個／ｃｍ２、セル壁厚み：０．０１１ｃｍ、ＧＳＡ：２８．４ｃｍ２／ｃｍ３、担体容量：１．０Ｌのコージェライト製担体を用いたこと以外は、上記触媒１と同様の操作を繰り返し、ＨＣ吸着材層及び浄化触媒成分層を積層して、本例に係わるＨＣ吸着型三元触媒４を得た。
【００３８】
（触媒５）
触媒担体として、セル形状が六角形、セル数：９３．０個／ｃｍ２、セル壁厚み：０．００８ｃｍ、ＧＳＡ：３３．４ｃｍ２／ｃｍ３、担体容量：１．０Ｌのコージェライト製担体を用いたこと以外は、上記触媒１と同様の操作を繰り返して、ＨＣ吸着材層及び浄化触媒成分層を積層し、本例に係わるＨＣ吸着型三元触媒５を得た。
【００３９】
（触媒６）
触媒担体として、セル形状が六角形、セル数：１０７．０個／ｃｍ２、セル壁厚み：０．０１１ｃｍ、ＧＳＡ：３４．０ｃｍ２／ｃｍ３、担体容量：１．０Ｌのコージェライト製担体を用いたこと以外は、上記触媒１と同様の操作を繰り返し、ＨＣ吸着材層及び浄化触媒成分層を積層して、本例に係わるＨＣ吸着型三元触媒６を得た。
【００４０】
（触媒７）
触媒担体として、セル形状が四角形、セル数：９３．０個／ｃｍ２、セル壁厚み：０．０１０ｃｍ、ＧＳＡ：３４．５ｃｍ２／ｃｍ３、担体容量：１．０Ｌのコージェライト製担体を用いたこと以外は、上記触媒１と同様の操作を繰り返して、ＨＣ吸着材層及び浄化触媒成分層を積層し、本例に係わるＨＣ吸着型三元触媒７を得た。
【００４１】
（触媒８）
触媒担体として、セル形状が四角形、セル数：１３９．５個／ｃｍ２、セル壁厚み：０．００５ｃｍ、ＧＳＡ：４３．６ｃｍ２／ｃｍ３、担体容量：１．０Ｌのコージェライト製担体を用いたこと以外は、上記触媒１と同様の操作を繰り返して、ＨＣ吸着材層及び浄化触媒成分層を積層し、本例に係わるＨＣ吸着型三元触媒８を得た。
【００４２】
（触媒９）
触媒担体として、セル形状が三角形、セル数：１９．０個／ｃｍ２、セル壁厚み：０．００５ｃｍ、ＧＳＡ：１１．１ｃｍ２／ｃｍ３、担体容量：１．０Ｌのコージェライト製担体を用いたこと以外は、上記触媒１と同様の操作を繰り返し、ＨＣ吸着材層及び浄化触媒成分層を積層して、本例に係わるＨＣ吸着型三元触媒９を得た。
【００４３】
以上によって得られたＨＣ吸着型三元触媒１〜９の仕様をそれぞれ表１に示す。
【００４４】
【表１】
下記条件による耐久後の上記ＨＣ吸着型三元触媒１〜９をそれぞれ選択して組み合わせ、図１に示す排気ガス浄化用触媒システムの触媒位置１及び２に配置し、下記の条件のもとにＨＣ特性評価を行い、ＨＣ吸着率と脱離ＨＣ浄化率を測定した。その結果を表２に示す。
【００４６】
耐久条件
・エンジン排気量 ３０００ｃｃ
・燃料 ガソリン（日石ダッシュ）
・耐久温度 ６５０℃
・耐久時間 ５０時間
車両性能試験
・エンジン 日産自動車株式会社製 直列４気筒 ２．０Ｌ
・評価方法 北米排ガス試験法のＬＡ４−ＣＨのＡ−ｂａｇ
【００４７】
【表２】
【発明の効果】
以上説明してきたように、本発明の排気ガス浄化用触媒システムは、排気ガス流路の上流側に三元触媒を配置すると共に、その下流側に複数のＨＣ吸着型三元触媒を配置して成る触媒システムにおいて、これら複数個のＨＣ吸着型三元触媒の担体セルの辺数が排気ガス流路の下流側に向けて増加するように配列したものであるから、上流側の三元触媒が活性化する前に排出されるコールドＨＣが下流側に配置された複数のＨＣ吸着型三元触媒により分担して吸着されると共に、下流側のＨＣ吸着型三元触媒における、特にＨＣ吸着材層の塗布形態が吸着−保持特性に優れた形状となることから、コールドＨＣの吸着効率の向上と吸着されたＨＣの脱離遅延化が可能になり、吸着ＨＣの脱離と浄化開始とのタイミングが一致するようになり、コールドＨＣの浄化効率を大幅に向上させ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】本発明の排気ガス浄化用触媒システムの構成例を示す概略図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a catalyst system for purifying exhaust gas discharged from an internal combustion engine such as an automobile engine, and particularly to a hydrocarbon (hereinafter, referred to as “HC”) contained in exhaust gas immediately after the start of the internal combustion engine. The present invention relates to an exhaust gas purifying catalyst system capable of efficiently purifying the catalyst.
[0002]
[Prior art]
In recent years, an HC adsorption type three-way catalyst (three-way catalyst with an HC adsorption function) using zeolite as an HC adsorbent for the purpose of purifying a large amount of HC (cold HC) discharged in a low temperature range at the time of starting an internal combustion engine. Is being developed.
Such an HC adsorption type three-way catalyst temporarily adsorbs and holds a large amount of HC by an HC adsorbent in a low temperature region at the time of engine start in which the three-way catalyst has not been sufficiently activated. When the three-way catalyst is activated by a rise in the exhaust gas temperature, the adsorbed HC is gradually desorbed and purified, and such an HC-adsorbing three-way catalyst is effective for the purification process of cold HC. It has been thought that there is. However, before the purification catalyst component provided in the HC adsorption type three-way catalyst or the purification catalyst provided downstream of the catalyst is sufficiently activated, the catalyst is temporarily stored in the adsorbent by raising the temperature of the HC adsorbent. Since the cold HC was desorbed, it could not be efficiently purified.
[0003]
That is, in a conventional exhaust gas purifying catalyst using an HC adsorbent mainly composed of a synthetic zeolite, particularly in the above-described HC adsorption type three-way catalyst, the moisture contained in the exhaust gas is reduced with respect to the acid sites in the zeolite pores. In order to inhibit the chemical adsorption, the adsorption of cold HC discharged immediately after the start of the engine before the activation of the three-way catalyst is dominated by the physical adsorption utilizing the molecular sieve action of zeolite. However, it is presumed that the physically adsorbed HC is easily desorbed due to external (physical) factors such as an increase in the temperature of the exhaust gas and an increase in the flow rate of the exhaust gas because the holding power in the zeolite pores is weak. You. For this reason, even if the HC adsorption type three-way catalyst is installed downstream of the exhaust gas flow path, although the adsorption and desorption phenomena of the cold HC occur, the timing of the start of the desorption of the adsorbed HC and the activation of the purification catalyst coincide. Without this, it was extremely difficult to efficiently perform the desorption purification process of the adsorbed HC.
[0004]
In the past, it was possible to adsorb cold HC relatively efficiently by selecting a zeolite having a pore size suitable for the molecular diameter of cold HC. Since the catalyst cannot be kept in the pores for a long time, desorption starts before the purification catalyst is sufficiently activated, and the desired purification efficiency cannot be obtained.
[0005]
Furthermore, conventionally, in order to improve the heat resistance of the zeolite skeleton structure, Al of silica (SiO 2 ) and alumina (Al 2 O 3 ) constituting the zeolite skeleton is treated with an acid solution to remove Al. A release process (de-Al treatment) is performed. However, zeolite that has been subjected to such Al removal treatment has improved heat resistance, but has a reduced number of Al cation sites, which are acid sites in the skeletal structure. There is a problem that the property of retaining physically adsorbed HC is remarkably lacking.
[0006]
For this reason, an exhaust gas purification system using such an HC adsorbent is disclosed in, for example, JP-A-6-74019, JP-A-7-144119, JP-A-6-142457, and JP-A-5-59942. JP-A-7-102957, JP-A-9-85056, JP-A-7-96183, JP-A-11-81999 and the like.
[0007]
In JP-A-6-74019, a bypass is provided in an exhaust passage, and HC discharged at the time of cold immediately after starting the engine is once adsorbed by an HC adsorbent disposed in the bypass passage, and then the passage is switched. There has been proposed a system in which a part of exhaust gas is passed to an HC adsorption catalyst after a downstream three-way catalyst is activated, and HC desorbed from an adsorbent is gradually purified by a subsequent three-way catalyst.
[0008]
In Japanese Patent Application Laid-Open No. Hei 7-144119, while the former three-way catalyst is deprived of heat during cold to improve the adsorption efficiency of the middle-stage HC adsorption catalyst, the tandem arrangement is performed after the former-stage three-way catalyst is activated. A system has been proposed that facilitates the transfer of reaction heat to the subsequent three-way catalyst via the middle-stage HC adsorption catalyst and promotes purification by the latter three-way catalyst.
[0009]
In Japanese Patent Application Laid-Open No. 6-142457, when HC adsorbed in a low-temperature region is desorbed, a cold gas that promotes purification by a three-way catalyst by preheating exhaust gas containing desorbed HC in a heat exchanger. An HC adsorption removal system has been proposed.
[0010]
On the other hand, Japanese Patent Application Laid-Open No. 5-59942 discloses a system in which the temperature of the HC adsorbent is slowly increased by switching the exhaust gas flow path by disposing the catalyst and a valve, thereby improving the efficiency of adsorbing cold HC by the adsorbent. Proposed.
[0011]
Also, in Japanese Patent Application Laid-Open No. 7-102957, in order to improve the purification performance of the latter oxidation / three-way catalyst, air is supplied between the former three-way catalyst and the middle-stage HC adsorbent, and the latter oxidation / three-way catalyst is supplied. A system that promotes activation of the three-way catalyst is proposed.
[0012]
Further, Japanese Patent Application Laid-Open No. 9-85056 discloses a first-stage catalyst containing an HC adsorbent made of zeolite and a Pt-Rh-based catalyst component, and a second-stage catalyst containing an HC adsorbent made of zeolite, a Pd-based catalyst component, and cerium oxide. Has been proposed in which the same catalyst is filled in the same container, and secondary air is supplied between the two to promote purification of the second-stage catalyst.
[0013]
In JP-A-7-96183, from the viewpoint of suppressing deterioration of a catalyst layer (mainly composed of Pd and Al 2 O 3 ) in contact with zeolite at high temperatures, a porous layer is provided between the adsorbent layer and the catalyst layer. While providing the porous barrier layer, the average particle diameter of the Pd-supported Al 2 O 3 particles is 15 to 25 μm, and the average particle diameter of the refractory inorganic particles is 5 to 15 μm from the viewpoint of suppressing the lowering of the adsorbing ability of the lower adsorbent layer. It is proposed to use those.
[0014]
Further, in Japanese Patent Application Laid-Open No. 11-81999, in order to slow the desorption of HC trapped in the adsorbent during cold operation, the upstream three-way catalyst and the downstream adsorber are required to sufficiently delay the temperature rise of the HC adsorption catalyst. A method has been proposed in which the heat capacity of the exhaust passage is made larger than the heat capacity of the exhaust manifold by increasing the wall thickness of the pipe in the exhaust passage connecting to the catalyst or installing a carrier or the like.
[0015]
[Problems to be solved by the invention]
However, in the systems described in JP-A-5-59942 and JP-A-6-74019 described above, the adsorption and desorption time of cold HC greatly fluctuates due to differences in various conditions such as a vehicle type and a running pattern. It is difficult to optimally control the operation timing of the switching valve, and the timing of desorption of HC from the HC adsorbent and the activation of the latter three-way catalyst cannot always be made to coincide with each other. There is a problem that it cannot be sufficiently improved.
[0016]
On the other hand, in the systems described in JP-A-7-144119 and JP-A-6-142457, the activation of the three-way catalyst disposed downstream of the HC adsorbent by heat tends to be insufficient, and the purification treatment is easily performed. However, the system proposed in Japanese Patent Application Laid-Open No. 7-102957 and Japanese Patent Application Laid-Open No. 9-85056 also has a drawback that it is not always possible to carry out the oxidation / ternary reaction at the subsequent stage by supplying secondary air. The effect of promoting the activation of the catalyst is naturally limited, and the improvement in purification efficiency is not always sufficient.
[0017]
Japanese Patent Application Laid-Open No. 7-96183 proposes that a barrier layer be provided between the zeolite layer and the catalyst layer to suppress the deterioration of the catalyst layer, but the effect is not necessarily sufficient. The purification efficiency of the desorbed HC by the source catalyst cannot be made sufficient.
Further, in the system described in Japanese Patent Application Laid-Open No. H11-81999, the heat capacity of the exhaust passage is increased to delay the temperature rise of the adsorbent layer, so that the desorption of HC trapped by the adsorbent at the time of cold is slow. However, at the same time, the activation of the latter three-way catalyst is also delayed, so that the timing of desorption and the start of purification cannot be sufficiently matched, and the purification treatment efficiency cannot be sufficiently improved. There's a problem.
[0018]
As described above, in each of the purification systems disclosed in the above-mentioned publications, switching of valves, promotion of activation of the purification catalyst by preheating or air supply, slowing of desorption of HC from the adsorbent, and the like, start of HC desorption and purification are started. The timing is made to match, and although there is a certain effect, the two timings are not sufficiently matched, and the purification catalyst component of the HC adsorption type three-way catalyst is used in any system. Alternatively, it cannot be said that the cold HC once adsorbed on the HC adsorbent does not desorb before the purification catalyst provided in the subsequent stage is activated, and it is not always possible to efficiently purify the cold HC. There is a problem, which has been a problem in the conventional exhaust gas purification system.
[0019]
The present invention has been made in view of the above-mentioned problems in a conventional exhaust gas purification system including an HC adsorption type three-way catalyst, and delays the desorption of HC from an HC adsorbent layer to reduce the amount of HC components. An object of the present invention is to provide an exhaust gas purifying catalyst system that can sufficiently match the timing with the start of purification and that can improve the purification efficiency of cold HC.
[0020]
[Means for Solving the Problems]
In the exhaust gas purifying catalyst system of the present invention, a three-way catalyst is disposed on the upstream side of the exhaust gas flow path, and a HC adsorbent layer containing zeolite and a purifying catalyst component layer containing catalytic metal are formed into a polygonal carrier. A system in which a plurality of HC adsorption type three-way catalysts stacked in this order in a cell are arranged downstream of the three-way catalyst, wherein the number of sides of the carrier cell in the plurality of HC adsorption type three-way catalysts Are increased toward the downstream side of the exhaust gas flow path.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the exhaust gas purifying catalyst system of the present invention will be described in detail.
The exhaust gas purifying catalyst system of the present invention is a catalyst system comprising a three-way catalyst disposed upstream of an exhaust gas flow path and a plurality of HC adsorption type three-way catalysts disposed downstream thereof. The three-way catalyst has a multilayer structure in which a HC adsorbent layer containing zeolite and a purification catalyst component layer containing catalytic metal are stacked in this order in a polygonal cell of the carrier, and a plurality of these HC adsorbents are adsorbed. Since the number of sides of the carrier cells of the three-way catalyst is arranged so as to increase toward the downstream side of the exhaust gas passage, the three-way catalyst disposed upstream of the exhaust gas passage is not activated. The cold HC discharged to the exhaust pipe is shared and adsorbed by the plurality of HC adsorption-type three-way catalysts disposed on the downstream side, so that the adsorption efficiency of the cold HC can be improved and the desorption of the adsorbed HC can be delayed.
[0022]
That is, the cold HC is shared and adsorbed by two or more HC adsorbing three-way catalysts having different temperature rising profiles on the upstream side and the downstream side of the exhaust gas flow path. By temporarily adsorbing 50% or more of the cold HC emission by the HC adsorption type three-way catalyst, the adsorption load of the downstream catalyst is reduced, and the HC which is desorbed without purification in the upstream is removed by the zeolite in the downstream catalyst. Since the re-adsorption can be performed efficiently, the adsorption efficiency of the entire system can be improved.
Further, the activation of the most upstream three-way catalyst is accelerated, and the amount of cold HC flowing into the HC adsorption three-way catalyst disposed downstream thereof is reduced by the saturated adsorption capacity of zeolite contained in the HC adsorption three-way catalyst. By trapping (physical adsorption) in a range of 70% or less, desirably 50% or less, the diffusion collision of HC molecules in the zeolite pores is reduced even when the temperature is increased or the gas flow rate is increased. It is considered that the desorption can be delayed.
[0023]
Then, a plurality of HC adsorption-type three-way catalysts arranged in the exhaust gas flow path form a polygonal cell shape (for example, from a square cell to a carrier) on which a carrier to which a catalyst component is applied increases from upstream to downstream. (Hexagonal cells), thereby increasing the angle of the corners, averaging the slurry coating shape, especially the coating thickness of the HC adsorbent layer as the first layer, and the -A shape with excellent holding characteristics is obtained. That is, the adsorbed surface area is increased with respect to the applied amount, and the extremely thin portion of the applied thickness is eliminated, so that the adsorbed HC is not released early due to rapid heating.
Therefore, the adsorption efficiency of the cold HC is improved, and the desorption of the adsorbed HC is delayed, so that the purification efficiency of the HC is significantly improved even on the downstream side where the temperature of the purification catalyst component layer is slow and difficult to activate. become.
[0024]
As a specific arrangement of the carrier cell shape in the plurality of HC adsorption type three-way catalysts arranged downstream of the three-way catalyst, the cell shape of the carrier used for the HC adsorption type three-way catalyst located at the most upstream position is used. A catalyst having a hexagonal cell can be used for the catalyst downstream of this.
That is, a square-hexagon (in the case of two arrangements), a square-hexagon-hexagon (in the case of three arrangements), a square-hexagon-hexagon-hexagon (in the case of four arrangements) and the like are conceivable. However, the lower the temperature of the downstream catalyst, the more the number of these catalysts increases, the more often the result is that the number of catalysts that does not substantially contribute to exhaust gas purification is often increased. It is desirable to arrange two HC adsorption type three-way catalysts each using the above carrier in this order.
[0025]
As a preferred mode in the exhaust gas purifying catalyst system of the present invention, as going from upstream to downstream, the cell shape of the carrier for applying the catalyst component of the HC adsorption type three-way catalyst becomes a polygon with increased corners, It is desirable that the geometric surface area (GSA) of the support be increased, thereby improving the contact efficiency with the exhaust gas. Cold HC discharged without being purified is efficiently adsorbed by the latter HC adsorption type three-way catalyst. For this reason, the hardly adsorbable HC species flowing into the latter HC adsorption type three-way catalyst are also adsorbed efficiently, and the purification treatment efficiency of the desorbed HC by the purification catalyst layer is further improved.
[0026]
Further, as another preferred embodiment, the cell shape of the carrier on which the catalyst component is applied is made to be a polygonal shape with an increased corner as going from the upstream to the downstream, and the corner of the cell (corner portion) and the flat portion are formed. It is desirable to reduce the difference in the amount of HC adsorbent layer applied.
That is, in an exhaust gas purification system in which a plurality of HC adsorption type three-way catalysts are arranged, generally, the exhaust gas composition at the catalyst outlet gradually changes from upstream to downstream, and adsorbed in exhaust gas on the downstream side. Since HC species that are difficult to be removed and easily desorbed remain, it is desirable that the application form of the HC adsorbent layer is formed to have a more excellent adsorption-retention characteristic in the downstream catalyst. For this reason, as described above, by reducing the difference in the amount of the HC adsorbent layer applied between the corner portion and the flat portion of the cell, the application form of the HC adsorbent layer becomes a shape having excellent adsorption-retention characteristics, and the adsorbed HC Is delayed, and the purification efficiency of HC can be significantly improved even on the downstream side where the temperature rise of the purification catalyst layer is slow and it is difficult to activate.
[0027]
As still another preferred embodiment of the exhaust gas purifying catalyst system of the present invention, as the exhaust gas flow path goes from upstream to downstream, the cell shape of the carrier on which the catalyst component is applied in the HC adsorption type three-way catalyst is squared. And the amount of application of the HC adsorbent layer can be increased toward the downstream, so that the form of the HC adsorbent layer becomes a shape having excellent adsorption-retention characteristics. Thus, the desorption of the adsorbed HC is delayed, and the purification efficiency of the HC is further improved even on the downstream side where the temperature rise of the purification catalyst layer is slow and is difficult to activate.
[0028]
In another preferred embodiment of the exhaust gas purifying catalyst system of the present invention, platinum (Pt), palladium (Pd) and rhodium (Rh) are added to the purifying catalyst component layer, which is the surface layer of the HC adsorption three-way catalyst. At least one metal selected from the group consisting of cerium (Ce), zirconium (Zr) and lanthanum (La); Cerium oxide containing at least one selected from the group consisting of zirconium (Zr), neodymium (Nd), praseodymium (Pr), yttrium (Y) and lanthanum (La) in an amount of 1 to 50 mol% in terms of metal. As a result, the deterioration with time of the active components Pt and Pd can be suppressed, and the purification treatment efficiency of the desorbed HC can be kept high. Rutotomoni, so that high purification performance can be obtained as a three-way catalyst.
[0029]
In a further preferred embodiment, the purification catalyst component layer further comprises at least one selected from the group consisting of cerium (Ce), neodymium (Nd), praseodymium (Pr), yttrium (Y) and lanthanum (La). Of zirconium oxide containing 1 to 40 mol% in terms of metal in terms of metal, whereby the deterioration with time of the active component Rh can be suppressed, and the purification efficiency of desorbed HC can be maintained at a high level. Even higher purification performance can be obtained as a raw catalyst.
[0030]
As a further preferred form of the exhaust gas purifying catalyst system, it is desirable that the purifying catalyst component layer further contains at least one metal selected from alkali metals and alkaline earth metals. As a result, it is possible to suppress the deterioration of the active component over time, to maintain the high purification efficiency of the desorbed HC, and to obtain high purification performance as a three-way catalyst. In addition, by including these alkali metals and alkaline earth metals in the purification catalyst component layer using a compound that is hardly soluble or insoluble in water, zeolite of metal ions eluted in the slurry with the movement of water in the slurry. Intrusion into the pores can be suppressed, and high adsorption efficiency can be maintained from the initial stage to after the endurance.
[0031]
【Example】
Hereinafter, the present invention will be described more specifically based on examples. In the examples, “%” represents mass percentage unless otherwise specified.
[0032]
(Catalyst 1)
A magnetic ball mill was charged with 2257 g of β-zeolite powder having a SiO 2 / Al 2 O 3 ratio of 40, 1215 g of silica sol (solid content: 20%), and 1000 g of pure water, and mixed and pulverized to obtain a slurry liquid. This slurry liquid is applied to a cordierite carrier (cell shape: square, number of cells: 46.5 cells / cm 2 , cell wall thickness: 0.015 cm, GSA: 24.1 cm 2 / cm 3 , carrier volume: 1.0 L) Then, excess slurry in the cell was removed by an air flow, dried, and fired at 400 ° C. for 1 hour. Then, the coating operation was repeated until the coating amount of the zeolite-containing adsorbent layer reached 350 g / L, whereby Catalyst-a1 was obtained.
[0033]
Next, an aqueous solution of palladium nitrate is impregnated or sprayed with high-speed stirring on alumina powder containing 3 mol% of Ce (Al: 97 mol%), dried at 150 ° C. for 24 hours, then at 400 ° C. for 1 hour, The mixture was calcined at 600 ° C. for 1 hour to obtain Pd-supported alumina powder (powder a). The Pd concentration of this powder a was 4.0%.
A cerium oxide powder (Ce: 67 mol%) containing 1 mol% La and 32 mol% Zr is impregnated with an aqueous solution of palladium nitrate or sprayed at high speed and dried at 150 ° C. for 24 hours. The mixture was calcined at 400 ° C. for 1 hour and then at 600 ° C. for 1 hour to obtain Pd-supported cerium oxide powder (powder b). The Pd concentration of this powder b was 2.0%.
Then, 400 g of the above-mentioned Pd-supported alumina powder (powder a), 141 g of Pd-supported cerium oxide powder (powder b), 240 g of nitric acid acidic alumina sol (a sol obtained by adding 10% nitric acid to 10% boehmite alumina, 24 g in terms of Al2O3) and 100 g of barium carbonate (67 g as BaO) were put into a magnetic ball mill together with 2000 g of pure water, and mixed and pulverized to obtain a slurry liquid. This slurry liquid was adhered to the above-mentioned coated catalyst-a1, the excess slurry in the cell was removed by an air stream, dried, and baked at 400 ° C. for 1 hour to apply a coat layer weight of 66.5 g / L. -B was obtained.
[0034]
Next, an aqueous rhodium nitrate solution is impregnated or sprayed with high-speed stirring on alumina powder containing 3 mol% of Zr (Al: 97 mol%), dried at 150 ° C. for 24 hours, then at 400 ° C. for 1 hour, The mixture was calcined at 600 ° C. for 1 hour to obtain a Rh-supported alumina powder (powder c). The Rh concentration of this powder c was 2.0%.
Also, an aqueous solution of dinitrodiammine platinum is impregnated or sprayed with high-speed stirring on alumina powder (Al: 97 mol%) containing 3 mol% Ce, dried at 150 ° C. for 24 hours, then at 400 ° C. for 1 hour, The mixture was calcined at 600 ° C. for 1 hour to obtain Pt-supported alumina powder (powder d). The Pt concentration of this powder d was 3.0%.
Further, a zirconium oxide powder containing 1 mol% La and 20 mol% Ce is impregnated with an aqueous solution of dinitrodiammine platinum or sprayed with high-speed stirring, dried at 150 ° C. for 24 hours, and then dried at 400 ° C. for 1 hour. Then, the mixture was calcined at 600 ° C. for 1 hour to obtain Pt-supported alumina powder (powder e). The Pt concentration of this powder e was 3.0%.
Then, 118 g of the above-described Rh-supported alumina powder (powder c), 118 g of Pt-supported alumina powder (powder d), 118 g of Pt-supported zirconium oxide powder (powder e), and 160 g of nitric acid-acidified alumina sol were put into a magnetic ball mill, mixed and pulverized. A slurry liquid was obtained. This slurry liquid was adhered to the above-mentioned coat catalyst-b, excess slurry in the cell was removed by an air stream, dried, baked at 400 ° C. for 1 hour, and coated with a coat layer weight of 37 g / L. Three-way catalyst 1 was obtained.
The noble metal supported amounts of the catalyst 1 were Pt: 0.71 g / L, Pd: 1.88 g / L, and Rh: 0.24 g / L.
[0035]
(Catalyst 2)
As the catalyst carrier, a cordierite carrier having a square cell shape, the number of cells: 31.0 cells / cm 2 , the cell wall thickness: 0.025 cm, the GSA: 19.0 cm 2 / cm 3 , and the carrier volume: 1.0 L. The same operation as that of the above-mentioned catalyst 1 was repeated except that it was used, and the HC adsorbent layer and the purification catalyst component layer were laminated to obtain the HC adsorption type three-way catalyst 2 according to this example.
[0036]
(Catalyst 3)
As a catalyst carrier, a cordierite carrier having a hexagonal cell shape, 62.0 cells / cm 2 , cell wall thickness: 0.011 cm, GSA: 27.2 cm 2 / cm 3 , and a carrier volume: 1.0 L The same operation as that of the above-mentioned catalyst 1 was repeated, except that the catalyst adsorbent was used, and the HC adsorbent layer and the purification catalyst component layer were laminated to obtain the HC adsorption type three-way catalyst 3 according to this example.
[0037]
(Catalyst 4)
As a catalyst carrier, a cordierite carrier having a hexagonal cell shape, 71.3 cells / cm 2 , cell wall thickness: 0.011 cm, GSA: 28.4 cm 2 / cm 3 , and a carrier volume: 1.0 L The same operation as in the above catalyst 1 was repeated, except that the HC adsorbent layer and the purification catalyst component layer were laminated to obtain an HC adsorption type three-way catalyst 4 according to this example.
[0038]
(Catalyst 5)
As a catalyst carrier, a cordierite carrier having a hexagonal cell shape, the number of cells: 93.0 cells / cm 2 , a cell wall thickness: 0.008 cm, a GSA: 33.4 cm 2 / cm 3 , and a carrier volume: 1.0 L The same operation as in the above-mentioned catalyst 1 was repeated, except that the HC adsorbent layer and the purification catalyst component layer were laminated to obtain the HC adsorption type three-way catalyst 5 according to this example.
[0039]
(Catalyst 6)
As a catalyst carrier, a cordierite carrier having a hexagonal cell shape, 107.0 cells / cm 2 , cell wall thickness: 0.011 cm, GSA: 34.0 cm 2 / cm 3 , and a carrier volume: 1.0 L The same operation as in the above-mentioned catalyst 1 was repeated, except that the HC adsorbent layer and the purification catalyst component layer were laminated to obtain the HC adsorption type three-way catalyst 6 according to this example.
[0040]
(Catalyst 7)
As the catalyst carrier, a cordierite carrier having a square cell shape, 93.0 cells / cm 2 , cell wall thickness: 0.010 cm, GSA: 34.5 cm 2 / cm 3 , and a carrier volume: 1.0 L is used. The same operation as that of the above-mentioned catalyst 1 was repeated, except that the HC adsorbent layer and the purification catalyst component layer were stacked to obtain the HC adsorption type three-way catalyst 7 according to this example.
[0041]
(Catalyst 8)
As a catalyst carrier, a cordierite carrier having a square cell shape, 139.5 cells / cm 2 , cell wall thickness: 0.005 cm, GSA: 43.6 cm 2 / cm 3 , and a carrier volume: 1.0 L is used. The same operation as that of the above-mentioned catalyst 1 was repeated except that the HC adsorbent layer and the purification catalyst component layer were laminated to obtain an HC adsorption type three-way catalyst 8 according to this example.
[0042]
(Catalyst 9)
As a catalyst carrier, a cordierite carrier having a triangular cell shape, the number of cells: 19.0 cells / cm 2 , the cell wall thickness: 0.005 cm, the GSA: 11.1 cm 2 / cm 3 , and the carrier volume: 1.0 L. The same operation as that of the above-mentioned catalyst 1 was repeated, except that the HC adsorbent layer and the purification catalyst component layer were stacked to obtain an HC adsorption type three-way catalyst 9 according to this example.
[0043]
Table 1 shows the specifications of the HC adsorption type three-way catalysts 1 to 9 obtained as described above.
[0044]
[Table 1]
The HC adsorption three-way catalysts 1 to 9 after the endurance under the following conditions are selected and combined respectively, and arranged at catalyst positions 1 and 2 of the exhaust gas purifying catalyst system shown in FIG. 1 under the following conditions. The HC characteristics were evaluated, and the HC adsorption rate and the desorbed HC purification rate were measured. Table 2 shows the results.
[0046]
Endurance conditions and engine displacement 3000cc
・ Fuel Gasoline (Nisseki dash)
・ Endurance temperature 650 ℃
・ Endurance time 50 hours Vehicle performance test ・ Engine Nissan Motor Co., Ltd. In-line 4-cylinder 2.0L
・ Evaluation method A-bag of LA4-CH of North American exhaust gas test method
[0047]
[Table 2]
【The invention's effect】
As described above, the exhaust gas purifying catalyst system of the present invention has the three-way catalyst arranged upstream of the exhaust gas passage and the plurality of HC adsorption type three-way catalysts arranged downstream thereof. Since the number of sides of the carrier cells of the plurality of HC adsorption type three-way catalysts is arranged to increase toward the downstream side of the exhaust gas flow path, the upstream three-way catalyst Cold HC discharged before activation is shared and adsorbed by a plurality of HC adsorption-type three-way catalysts arranged on the downstream side. Since the application form of the coating has excellent adsorption-retention characteristics, it is possible to improve the adsorption efficiency of the cold HC and delay the desorption of the adsorbed HC, and to determine the timing of the desorption of the adsorbed HC and the start of purification. Will match, Excellent effect is brought about that the purification efficiency of the field HC can be greatly improved.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a configuration example of an exhaust gas purifying catalyst system of the present invention.
Claims (7)
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| JP2002294868A JP4016420B2 (en) | 2002-10-08 | 2002-10-08 | Exhaust gas purification catalyst system |
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| JP2002294868A JP4016420B2 (en) | 2002-10-08 | 2002-10-08 | Exhaust gas purification catalyst system |
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2007052479A1 (en) * | 2005-11-04 | 2007-05-10 | Ngk Insulators, Ltd. | Honeycomb structure and honeycomb catalyst |
| US8375701B2 (en) | 2008-07-30 | 2013-02-19 | Ford Global Technologies, Llc | Hydrocarbon retaining and purging system |
| CN103046985A (en) * | 2011-10-13 | 2013-04-17 | 现代自动车株式会社 | Exhaust gas purifying filter, system of regenerating gasoline particulate filter, and method thereof |
| CN108035789A (en) * | 2017-11-21 | 2018-05-15 | 中国第汽车股份有限公司 | Gasoline car multistage ternary catalyzing unit performance on-line monitoring system and method |
| CN110898853A (en) * | 2019-12-19 | 2020-03-24 | 太原理工大学 | Catalyst for preparing cyclohexanone by phenol hydrogenation and preparation method thereof |
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2002
- 2002-10-08 JP JP2002294868A patent/JP4016420B2/en not_active Expired - Fee Related
Cited By (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2007052479A1 (en) * | 2005-11-04 | 2007-05-10 | Ngk Insulators, Ltd. | Honeycomb structure and honeycomb catalyst |
| US7695798B2 (en) | 2005-11-04 | 2010-04-13 | Ngk Insulators, Ltd. | Honeycomb structure and honeycomb catalyst |
| JP5376805B2 (en) * | 2005-11-04 | 2013-12-25 | 日本碍子株式会社 | Honeycomb structure and honeycomb catalyst body |
| US8375701B2 (en) | 2008-07-30 | 2013-02-19 | Ford Global Technologies, Llc | Hydrocarbon retaining and purging system |
| CN103046985A (en) * | 2011-10-13 | 2013-04-17 | 现代自动车株式会社 | Exhaust gas purifying filter, system of regenerating gasoline particulate filter, and method thereof |
| US20130095002A1 (en) * | 2011-10-13 | 2013-04-18 | Kia Motors Corporation | Exhaust gas purifying filter, system of regenerating gasoline particulate filter, and method thereof |
| CN103046985B (en) * | 2011-10-13 | 2017-06-13 | 现代自动车株式会社 | Exhaust emission control filter, the system and method for making the regeneration of diesel particulate filter device |
| CN108035789A (en) * | 2017-11-21 | 2018-05-15 | 中国第汽车股份有限公司 | Gasoline car multistage ternary catalyzing unit performance on-line monitoring system and method |
| CN110898853A (en) * | 2019-12-19 | 2020-03-24 | 太原理工大学 | Catalyst for preparing cyclohexanone by phenol hydrogenation and preparation method thereof |
| CN110898853B (en) * | 2019-12-19 | 2022-05-17 | 太原理工大学 | Catalyst for preparing cyclohexanone by phenol hydrogenation and preparation method thereof |
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| JP4016420B2 (en) | 2007-12-05 |
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