JP4565424B2 - Exhaust gas purification catalyst - Google Patents
Exhaust gas purification catalyst Download PDFInfo
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- JP4565424B2 JP4565424B2 JP2001156620A JP2001156620A JP4565424B2 JP 4565424 B2 JP4565424 B2 JP 4565424B2 JP 2001156620 A JP2001156620 A JP 2001156620A JP 2001156620 A JP2001156620 A JP 2001156620A JP 4565424 B2 JP4565424 B2 JP 4565424B2
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- exhaust gas
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- 239000003054 catalyst Substances 0.000 title claims description 170
- 238000000746 purification Methods 0.000 title claims description 107
- 229930195733 hydrocarbon Natural products 0.000 claims description 111
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- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 claims description 15
- 239000011148 porous material Substances 0.000 claims description 15
- 210000002421 cell wall Anatomy 0.000 claims description 13
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims description 13
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- BMMGVYCKOGBVEV-UHFFFAOYSA-N oxo(oxoceriooxy)cerium Chemical compound [Ce]=O.O=[Ce]=O BMMGVYCKOGBVEV-UHFFFAOYSA-N 0.000 claims description 7
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- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 claims description 4
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- QEFYFXOXNSNQGX-UHFFFAOYSA-N neodymium atom Chemical compound [Nd] QEFYFXOXNSNQGX-UHFFFAOYSA-N 0.000 claims description 2
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- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 6
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- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
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- JSKIRARMQDRGJZ-UHFFFAOYSA-N dimagnesium dioxido-bis[(1-oxido-3-oxo-2,4,6,8,9-pentaoxa-1,3-disila-5,7-dialuminabicyclo[3.3.1]nonan-7-yl)oxy]silane Chemical compound [Mg++].[Mg++].[O-][Si]([O-])(O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2)O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2 JSKIRARMQDRGJZ-UHFFFAOYSA-N 0.000 description 2
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- 238000011144 upstream manufacturing Methods 0.000 description 2
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- IXSUHTFXKKBBJP-UHFFFAOYSA-L azanide;platinum(2+);dinitrite Chemical compound [NH2-].[NH2-].[Pt+2].[O-]N=O.[O-]N=O IXSUHTFXKKBBJP-UHFFFAOYSA-L 0.000 description 1
- 238000001354 calcination Methods 0.000 description 1
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- VXNYVYJABGOSBX-UHFFFAOYSA-N rhodium(3+);trinitrate Chemical compound [Rh+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O VXNYVYJABGOSBX-UHFFFAOYSA-N 0.000 description 1
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Images
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- Exhaust Gas After Treatment (AREA)
- Exhaust Gas Treatment By Means Of Catalyst (AREA)
Description
【０００１】
【発明の属する技術分野】
本発明は、排気ガス浄化触媒に係り、更に詳細には、炭化水素（ＨＣ）を効率よく浄化する排気ガス浄化触媒に関する。
【０００２】
【従来の技術】
近年、内燃機関のエンジン始動時の低温域で大量に排出されるＨＣ（コールドＨＣ）の浄化を目的とし、ＨＣ吸着材として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。
かかる触媒は、三元触媒が活性化し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を一時的に吸着、保持し、その後、排気ガス温度の上昇により三元触媒が活性化した時に、ＨＣを徐々に脱離し、しかも浄化するものである。
吸着材から脱離するＨＣの浄化触媒としては、従来よりロジウム（Ｒｈ）、白金（Ｐｔ）及びパラジウム（Ｐｄ）等の貴金属種を同一層に共存させた仕様や、Ｒｈ層とＰｄ層を塗り分けた仕様のものなどが提案されている。例えば、特開平２−５６２４７号公報には、ゼオライトを主成分とする第一層の上に、Ｐｔ，Ｐｄ及びＲｈ等の貴金属を主成分とする第二層を設けた排気ガス浄化用触媒が提案されている。
【０００３】
かかるＨＣ吸着材を用いた発明としては、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号公報及び特開平７−１０２９５７号公報等に開示されているものがある。
これらのうち、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、その後流路を切換え、下流の三元触媒が活性化した後、排気ガスの一部をＨＣ吸着触媒に通じ、脱離したＨＣを後段の三元触媒で徐々に浄化するシステムが提案されている。
【０００４】
また、特開平７−１４４１１９号公報では、コールド時に前段の三元触媒に熱を奪わせ中段のＨＣ吸着触媒の吸着効率を向上し、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吸着触材を介して後段の三元触媒に反応熱を伝熱し易くし、後段の三元触媒の浄化を促進するシステムを提案している。
更に、特開平６−１４２１４５７号公報には、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し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。
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の流路を切換えによって、ＨＣ吸着材の昇温を緩慢にし、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。
また、特開平７−１０２９５７号公報には、後段の酸化・三元触媒の浄化性能を向上するため、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が提案されている。
【０００５】
【発明が解決しようとする課題】
しかしながら、吸着材としてゼオライトを用いる場合、良好なコールドＨＣ吸着性能を実現するには、排気ガス中のＨＣ種組成とゼオライトの有する細孔径との間に相関があるので、最適な細孔径と分布、骨格構造を持つゼオライトを使用する必要がある。
従来は、ＭＦＩ型ゼオライトをメインに、他の細孔径を有するゼオライト（例えば、ＵＳＹ）を単独で、あるいはこれらを混合して細孔径分布を調整していたが、耐久後にはゼオライト種によって細孔径の歪みや吸着・脱離特性が異なってしまうため、排気ガスＨＣ種の吸着が不十分であるという問題点があった。
【０００６】
また、従来のＨＣ吸着材層と浄化触媒層を設けた排気ガス浄化用触媒では、内燃機関の始動直後の排気ガス低温域において、ＨＣ吸着材に吸着したコールドＨＣが、排気ガス温度の上昇する前に脱離して浄化できず、更に、吸着ＨＣが脱離する際、浄化触媒層の雰囲気は酸素不足状態になるため、理論空燃比域での浄化に有効な三元触媒では、ＨＣ、一酸化炭素（ＣＯ）及び窒素酸化物（ＮＯｘ）のバランスの良い浄化ができなくなり、吸着ＨＣの浄化が十分にできないという問題点があった。
【０００７】
このため、排気流路の切換えによって、三元触媒が十分に活性化した後に吸着ＨＣを脱離させ、三元触媒で浄化する方法や電熱ヒーターによって三元触媒の早期活性化を図る方法、外部から空気を導入して三元触媒の活性化開始を早める方法なども検討されているが、システム構成が煩雑化し、しかも十分なコールドＨＣの低減効果が得られない、コストが高い、長期間の使用に耐えられない、などの問題点があった。
【０００８】
本発明は、このような従来技術の有する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、コールドＨＣの浄化効率に優れ、しかも簡易な構成で製造の容易な排気ガス浄化触媒を提供することにある。
【０００９】
【課題を解決するための手段】
本発明者らは、上記課題を解決すべく鋭意検討を重ねた結果、一端が閉塞されたセルを有する触媒担体を用い、特定の層構造を形成することなどにより、上記課題が解決されることを見出し、本発明を完成するに至った。
【００１０】
即ち、本発明の排気ガス浄化触媒は、内燃機関の冷間始動時に排出される炭化水素を効率良く浄化する排気ガス浄化触媒であって、
延在方向の一端が閉塞された一端閉塞セルを一部に有するハニカム構造型担体に、炭化水素吸着材層と、浄化触媒成分層を形成して成ることを特徴とする。
【００１１】
また、本発明の排気ガス浄化触媒の好適形態では、上記ハニカム構造型担体は、隣接する上記一端閉塞セル同士の閉塞端が逆転して配置されている閉塞セル対部分を有することを特徴とする。
この場合、上記ハニカム構造型担体のセル全部が上記一端閉塞セルで構成され、隣接する上記一端閉塞セル同士では、それぞれの閉塞端が逆転して配置されていることが望ましい。
【００１２】
更に、本発明の排気ガス浄化触媒の他の好適形態は、上記一端閉塞セルの壁部内に、炭化水素吸着材又は浄化触媒成分を含有させて成ることを特徴とする。
【００１３】
また、本発明の排気ガス浄化触媒の更に他の好適形態は、少なくとも上記一端閉塞セルの壁部に、上記炭化水素吸着材層又は浄化触媒成分層を積層して成り、上記閉塞セル対部分では、一方の一端閉塞セルの壁部に該炭化水素吸着材層が、他方の一端閉塞セルの壁部に該浄化触媒成分層が積層されていることを特徴とする。
【００１４】
更にまた、本発明の排気ガス浄化触媒の他の好適形態は、少なくとも上記一端閉塞セルの壁部に、上記炭化水素吸着材層及び浄化触媒成分層の双方を積層して成ることを特徴とする。
この場合、上記閉塞セル対部分を有し、この閉塞セル対部分では、一方のセルの壁部と他方のセルの壁部とにおける上記炭化水素吸着材層及び浄化触媒成分層の積層順が逆転していてもよい。
【００１５】
【作用】
本発明においては、一端が閉塞されたセル（「一端閉塞セル」という）を有するハニカム構造型担体を用い、かかる担体にＨＣ吸着材層と浄化触媒成分層を形成することにした。
このような構成を有する本発明の排気ガス浄化触媒では、一端閉塞セルのセル流路を通過する排気ガスは、流入したセル流路の出口が目詰めによって塞がれているため、開口率の大きいセル壁内を通過して、出口が開いている隣接したセル流路から流出する。この際、ＨＣ吸着材層内を通過するガス量は増加するが、通過する流速（拡散速度）が遅くなり、しかも隣接する一端閉塞セル同士の閉塞端がセルの延在方向において逆転配置されている閉塞セル対部分を有するか、又は特にセル全部が該閉塞セル対で構成されている場合には、排気ガスが交互目詰めしたセル流路を行き交うため、ＨＣ吸着材層に吸着したＨＣの滞留時間を長くでき、コールドＨＣの保持力が向上するとともに、脱離遅延化が図れるので、浄化効率を向上できる。
なお、本明細書において、「浄化効率」又は「脱離浄化効率」は、主に吸着材から脱離する吸着ＨＣ（コールドＨＣ）の浄化効率のことを意味する。
【００１６】
また、本発明においては、セル壁内にＨＣ吸着材又は浄化触媒成分を含有させてもよく、ＨＣ吸着材を含有させた場合には、セル壁を通過するガス流速を制御して吸着ＨＣの脱離を遅延化することができ、一方、浄化触媒成分を含有させた場合には、浄化触媒成分と吸着ＨＣとの接触頻度を増大できるので、浄化効率をいっそう向上できる。
更に、本発明では、ＨＣ吸着材層と浄化触媒成分層との積層配置を制御することにより、上記ハニカム構造型担体を通過する排気ガスが、ＨＣ吸着材層及び浄化触媒成分層に対し、ＨＣ吸着材層−浄化触媒成分層、又は浄化触媒成分層−ＨＣ吸着材層の順で接触するようにすることができ、ＨＣ吸着材層−浄化触媒成分層の順にすれば、吸着ＨＣの脱離を有効に遅延させ、浄化触媒成分層−ＨＣ吸着材層の順とすれば、浄化触媒成分層を迅速に活性化できる。
【００１７】
【発明の実施の形態】
以下、本発明の排気ガス浄化触媒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示す。
上述の如く、本発明の排気ガス浄化触媒は、一端閉塞セルを一部に有するハニカム構造型担体と、これに形成したＨＣ吸着材層と浄化触媒成分層を有する。
【００１８】
ここで、上記ハニカム構造型担体としては、隣接する一端閉塞セル同士であって、その閉塞端がセルの延在方向において相互に逆転配置されているセル対（「閉塞セル対」という）を有することが好ましく、更には、かかる閉塞セル対で全部のセルが構成されている、いわゆるウォールフロー型ハニカム担体やチェッカードハニカムと称されるものであることが更に好ましい。
このような閉塞セル対の採用により、上述したように、吸着ＨＣの滞留時間を長時間化でき、ＨＣの浄化効率を十分に向上させることができるようになる。
【００１９】
また、ＨＣ吸着材層及び浄化触媒成分層は、従来の排気ガス浄化触媒と同様に、セルの内壁に被着・積層されるが、本発明においては、両層の配置を調整することにより、排気ガスとの接触順を変化させることができ、それぞれ好適な効果を得ることができる。
【００２０】
本発明の触媒におけるＨＣ吸着材層及び浄化触媒成分層の配置例を図１〜図３に示す。図１〜図３は、ウォールフロー型ハニカム担体を用いて成る本発明の触媒例を示す部分断面図である。
図１において、この触媒部位では、上段、中段及び下段の順で端部が交互に目詰めされ、セルの左端、右端及び左端が閉塞されている。そして、中段のセルでは、その内壁表面に対して浄化触媒成分層１０、ＨＣ吸着材層２０の順で両層が積層されており、この中段セルと隣接する上段セル及び下段セルでは、それぞれの内壁に対してＨＣ吸着材層２０、浄化触媒成分層１０の順で積層されており、中段セルでの積層順とは逆順になっている。
【００２１】
このような構造を有する触媒において、左方から中段セルに流入した排気ガスは、矢印で示すように、まずＨＣ吸着材層２０と接触し、次いで浄化触媒成分層１０と接触した後、セル壁を通過し、それぞれ上段セル及び下段セルのＨＣ吸着材層２０、浄化触媒成分層１０に接触し、更に右端の開口端から流出して行く。
このように、この触媒構造では、排気ガスは順次ＨＣ吸着材層と浄化触媒成分層とに吸着−保持−浄化の一連の過程を繰り返すことができ、しかもセル壁がガス拡散を阻害するので脱離を遅延させることができるため、吸着ＨＣの浄化効率を向上させることができる。
【００２２】
図２に示す触媒構造は、中段セルにおける触媒成分層１０とＨＣ吸着材層２０の積層順が図１の触媒構造と逆順になっている以外は、図１の触媒構造と同様の構成を有する。
この触媒構造では、排気ガスは、矢印で示したように、まず浄化触媒成分層１０と接触し、その後にＨＣ吸着材層２０と接触する。ＨＣ吸着材層間にガス拡散を阻害するセル壁を挟むことで、吸着ＨＣの脱離遅延が図れ、浄化効率を向上できる。
【００２３】
図３に示す触媒構造では、上段〜下段のセルに被着されているのは、浄化触媒成分層１０又はＨＣ吸着材層２０のいずれか一方であり、中段セルがＨＣ吸着材層１０なのに対し、上段セル及び下段セルは浄化触媒成分層２０であり、隣接するセル同士では被着されている層の種類が逆転している。
この触媒構造でも、排気ガスは最初にＨＣ吸着材層と接触するので、吸着ＨＣの脱離を有効に遅延させることができる。
【００２４】
なお、本発明の排気ガス浄化触媒においては、セル壁内にＨＣ吸着材又は浄化触媒成分を含有（担持）させることが可能であり、これにより、浄化効率を向上することができる。
そして、ＨＣ吸着材を担持した場合には、セル壁を通過するガス流速を制御して吸着ＨＣの脱離を遅延化することができ、一方、浄化触媒成分を担持した場合には、浄化触媒成分と吸着ＨＣとの接触頻度を増大できるので、浄化効率をいっそう向上できる。
このようなセル壁内にＨＣ吸着材又は浄化触媒成分を担持した触媒構造の例を図４及び図５に示す。
【００２５】
かかるＨＣ吸着材又は浄化触媒成分のセル壁中への担持方法については、特に限定されるものではないが、ＨＣ吸着材については、平均粒子径が２ｍｍ以下のＨＣ吸着材を含むスラリーにウォールフロー型ハニカム担体を浸漬し、その後に乾燥・焼成することなどにより行うことができる。
一方、浄化触媒成分、代表的には貴金属については、平均粒子径が２ｍｍ以下のアルミナなどの無機酸化物を含むスラリーにウォールフロー型ハニカム担体を浸漬し、更に貴金属を含む溶液に浸漬した後、乾燥・焼成することなどにより行うことができる。また、貴金属を担持した無機酸化物を製造した後、これを平均粒子径２ｍｍ以下に粉砕して用いてもよい。
【００２６】
次に、本発明の排気ガス浄化触媒に用いるハニカム構造型担体やＨＣ吸着材、触媒成分の材質や性質などにつき説明する。
まず、ハニカム構造型担体、代表的には、ウォールフロー型ハニカム担体については、炭化ケイ素（ＳｉＣ）製やコーディエライト製のものを好適に用いることができる。また、ＳｉＣ製のものの場合には、その気孔径が５〜３０μｍ、気孔率が３５〜５０％、気孔容積が０．８〜１．４ｃｍ３／ｇであることが好ましい。
気孔径や気孔率、気孔容積が上記範囲内であると、排ガスの通過抵抗が大きくなっても運転性が悪化せず、また通過抵抗が小さくても十分な効果が得られる。
一方、コーディエライト製のものの場合には、その気孔径が５〜５０μｍ、気孔率が２０〜５０％、気孔容積が０．３〜０．６ｃｍ３／ｇであることが好ましく、気孔径や気孔率、気孔容積が上記範囲内にあると良好な理由は、上記同様である。
【００２７】
また、ＨＣ吸着材層を形成するＨＣ吸着材としては、Ｓｉ／２Ａｌ比が１０〜１０００のＨ型β−ゼオライト、又はこのβ−ゼオライトと、ＭＦＩ、Ｙ型、ＵＳＹ、モルデナイト若しくはフェリエライト及びこれらの混合物を用いることができる。かかる材料を採用すれば、細孔径の分布を広くできるので、ＨＣの吸着効率を更に向上できる。
【００２８】
一方、浄化触媒成分層を形成する触媒成分としては、パラジウム、白金又はロジウム及びこれらの混合物を用いることができるが、かかる貴金属と、セリウム、ジルコニウム又はランタン及びこれらの混合物を金属換算で１〜１０モル％含むアルミナと、ジルコニウム、ネオジウム、プラセオジウム又はランタン及びこれらの混合物を金属換算で１〜５０モル％含むセリウム酸化物とを併用して、浄化触媒成分層を形成することが好ましい。
このような材料を選定することにより、吸着ＨＣが脱離する際にセリウム酸化物が酸素を放出するため、浄化触媒層の脱離浄化効率を向上できる。
また、上述した触媒成分層には、更に、セリウム、ジルコニウム又はランタン及びこれらの混合物を金属換算で１〜４０モル％含むジルコニウム酸化物を添加することができ、これにより、浄化触媒層の脱離浄化効率を更に向上できる。
【００２９】
なお、本発明の触媒における触媒成分層は、上述の貴金属と、アルカリ金属及び／又はアルカリ土類金属とを用いて形成することも可能であり、この場合には、浄化触媒層の耐熱性が改善され、脱離浄化効率も向上できる。
【００３０】
【実施例】
以下、本発明を実施例及び比較例により更に詳細に説明するが、本発明はこれら実施例に限定されるものではない。
【００３１】
（実施例１）
β−ゼオライト粉末（Ｈ型、Ｓｉ／２Ａｌ＝２５）２１２５ｇ、シリカゾル（固形分２０％）１８７５ｇ、純水３０００ｇ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。このスラリー液をモノリス担体（２００セル／１０ミル、触媒容量１．３Ｌ）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。このときの塗布量として、焼成後に２５０ｇ／Ｌになるまでコーティング作業を繰り返し、触媒−ａを得た。
【００３２】
Ｃｅ３ｍｏｌ％を含むアルミナ粉末（Ａｌ９７ｍｏｌ％）に、硝酸パラジウム水溶液を含浸し又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重量％であった。
また、Ｌａ１ｍｏｌ％とＺｒ３２ｍｏｌ％含有セリウム酸化物粉末（Ｃｅ６７ｍｏｌ％）に、硝酸パラジウム水溶液を含浸し又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重量％であった。
【００３３】
上記Ｐｄ担持アルミナ粉末（粉末ａ）３１４ｇ、Ｐｄ担持セリウム酸化物粉末（粉末ｂ）３１４ｇ、硝酸酸性アルミナゾル３２０ｇ（ベーマイトアルミナ１０重量％に１０重量％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３２ｇ）及び炭酸バリウム５１．５ｇ（ＢａＯとして４０ｇ）を純水２０００ｇ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−ａ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、コート層重量７０ｇ／Ｌを塗布し、触媒−ｂを得た。
【００３４】
Ｚｒ３ｍｏｌ％を含むアルミナ粉末（Ａｌ９７ｍｏｌ％）に、硝酸ロジウム水溶液を含浸し又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重量％であった。
また、Ｃｅ３ｍｏｌ％を含むアルミナ粉末（Ａｌ９７ｍｏｌ％）に、ジニトロジアンミン白金水溶液を含浸し又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４．０重量％であった。
【００３５】
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）１７７ｇ、Ｌａ１モル％とＣｅ２０モル％を含有するジルコニウム酸化物粉末１７５ｇ、硝酸酸性アルミナゾル３００ｇ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、コート層重量５０ｇ／Ｌを塗布し、触媒を得た。触媒の貴金属担持量は、Ｐｔ０．７１ｇ／Ｌ、Ｐｄ１．８８ｇ／Ｌ、Ｒｈ０．２４ｇ／Ｌであった。
こうして得た触媒の排気ガス上流側と下流側のセル開口部を交互に目詰めし、図１に示す構造を有する本例の触媒Ｎｏ．１を得た。
本例の触媒の成分組成及び構造、用いた担体の性質などを表１及び表２にまとめて示す。
【００３６】
（実施例２）
上記Ｐｄ担持アルミナ粉末（粉末ａ）４３２ｇ、Ｐｄ担持セリウム酸化物粉末（粉末ｂ）３１４ｇ、硝酸酸性アルミナゾル１４０ｇ（ベーマイトアルミナ１０重量％に１０重量％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３２ｇ）及び炭酸バリウム５１．５ｇ（ＢａＯとして４ｇ）を純水２０００ｇ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。このスラリー液をモノリス担体（１２００セル／２ミル、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、コート層重量８０ｇ／Ｌを塗布し、触媒−ｅを得た。
【００３７】
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ｈ）１７７ｇ、Ｌａ１モル％とＣｅ２０モル％を含有するジルコニウム酸化物粉末１７５ｇ、硝酸酸性アルミナゾル３００ｇ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、コート層重量５０ｇ／Ｌを塗布し、触媒を得た。
こうして得た触媒の貴金属担持量は、Ｐｔ０．２４ｇ／Ｌ、Ｐｄ２．３５ｇ／Ｌ、Ｒｈ０．２４ｇ／Ｌであった。
得られた触媒のセル開口部を実施例１と同様に交互に目詰めし、図１に示す構造を有する本例の触媒Ｎｏ．２を得た。
本例の触媒の成分組成及び構造、用いた担体の性質などを表１及び表２にまとめて示す。
【００３８】
（実施例３〜１９）
表１及び表２に示す成分組成や担体、触媒構造（図１〜図５に示す構造に相当）を採用して実施例１と同様の操作を繰り返し、各例の触媒である触媒Ｎｏ．３〜Ｎｏ．１９を得た。
なお、表１及び表２中、触媒Ｎｏ．２０としたものは、後述する触媒性能の評価に用いる通常の三元触媒である。
【００３９】
（比較例１〜５）
表１及び表２に示す成分組成や担体、触媒構造を採用して実施例１と同様の操作を繰り返し、各例の触媒である触媒Ｎｏ．２１〜Ｎｏ．２５を得た。
なお、触媒構造１’〜５’については、これら比較例ではセル開口部の交互目詰めを実施していないが、これ以外については触媒構造１〜５と同じ構成を有する。
【００４０】
【表１】
【表２】
（実施例２０〜３８）
上述のようにして得られた触媒Ｎｏ．１〜Ｎｏ．１９と、触媒Ｎｏ．２０を用いて、図６に示すような排気ガス浄化システムを構築した。
この場合、表３に示すように、触媒位置１には触媒Ｎｏ．２０を配置し、触媒位置２には触媒Ｎｏ．１〜Ｎｏ．１９を配置した。
【００４３】
（比較例６〜１０）
触媒Ｎｏ．１の代わりに触媒Ｎｏ．２１〜Ｎｏ．２５を用いた以外は、実施例２０と同様の構成を採用し、各例の排気ガス浄化システムを構築した。表３に触媒位置を示す。
【００４４】
［性能評価］
以上で得られた実施例２０〜３８、及び比較例６〜１０の排気ガス浄化システムにつき、下記の条件で性能評価を実施した。得られた結果を表３に併記する。
なお、この性能評価では、上流（位置１）の三元触媒が活性化する前に排出されるコールドＨＣの浄化率のことを脱離ＨＣ浄化率と称することにする。
【００４５】
（評価方法）
耐久条件
エンジン排気量 ３０００ｃｃ
燃料 ガソリン（日石ダッシュ）
触媒入口ガス温度 ６５０℃
耐久時間 １００時間
車両性能試験
エンジン排気量 日産自動車株式会社製 直列４気筒 ２．０Ｌエンジン
評価方法 北米排ガス試験法のＬＡ４−ＣＨのＡ−ｂａｇ
【００４６】
【表３】
表３に示すように、本発明の範囲に属する実施例２０〜３８の浄化システムは、本発明範囲外の比較例６〜１０の浄化システムに比し、ＨＣ吸着率及び脱離浄化効率が良好で、特に両者のバランスが良いことが分かる。
なお、現時点においては、ＨＣ吸着率及び脱離ＨＣ浄化効率の観点から、実施例１１の触媒を用いた実施例３０が最も良好であると言い得る。
【００４８】
以上、本発明を好適実施例により詳細に説明したが、本発明はこれら実施例に限定されるものではなく、本発明の要旨の範囲内において種々の変形が可能である。
例えば、本発明の骨子の１つは、ＨＣ吸着材層に吸着したＨＣが放出される際の滞留時間を長くすることにあるので、かかる滞留時間の適切な長時間化を実現できるのであれば、一端閉塞セルを有する担体、代表的にはウォールフロー型の担体を用いる必要はなく、担体の材質などを適宜に調整することによっても本発明が意図する効果を得られる可能性がある。
【００４９】
【発明の効果】
以上説明してきたように、本発明によれば、一端が閉塞されたセルを有する触媒担体を用い、特定の層構造を形成することなどとしたため、コールドＨＣの浄化効率に優れ、しかも簡易な構成で製造の容易な排気ガス浄化触媒を提供することができる。
【図面の簡単な説明】
【図１】ウォールフロー型ハニカム担体を用いて成る本発明の触媒例を示す部分断面図である。
【図２】ウォールフロー型ハニカム担体を用いて成る本発明の触媒例を示す部分断面図である。
【図３】ウォールフロー型ハニカム担体を用いて成る本発明の触媒例を示す部分断面図である。
【図４】セル壁内にＨＣ吸着材又は浄化触媒成分を担持した本発明の触媒構造の例を示す部分断面図である。
【図５】セル壁内にＨＣ吸着材又は浄化触媒成分を担持した本発明の触媒構造の例を示す部分断面図である。
【図６】本発明の触媒を用いて成る排気ガス浄化システムの一例を示すシステム構成図である。
【符号の説明】
１０ ＨＣ吸着材層
２０ 浄化触媒成分層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification catalyst, and more particularly, to an exhaust gas purification catalyst that efficiently purifies hydrocarbons (HC).
[0002]
[Prior art]
In recent years, HC adsorption type three-way catalyst (three-way catalyst with HC adsorption function) using zeolite as the HC adsorbent for the purpose of purifying HC (cold HC) discharged in a large amount in the low temperature range at the start of the internal combustion engine ) Has been developed.
Such a catalyst temporarily adsorbs and holds a large amount of exhausted HC in a low temperature range at the time of engine start where the three-way catalyst is not activated, and then when the three-way catalyst is activated due to an increase in exhaust gas temperature. HC is gradually desorbed and purified.
As a purification catalyst for HC desorbed from the adsorbent, conventionally, noble metal species such as rhodium (Rh), platinum (Pt) and palladium (Pd) coexist in the same layer, and the Rh layer and the Pd layer are applied. The thing of the divided specification is proposed. For example, JP-A-2-56247 discloses an exhaust gas purifying catalyst in which a second layer mainly composed of noble metals such as Pt, Pd and Rh is provided on a first layer mainly composed of zeolite. Proposed.
[0003]
Examples of the invention using such an HC adsorbent include, for example, JP-A-6-74019, JP-A-7-144119, JP-A-6-142457, JP-A-5-59942, and JP-A-7-102957. There are some which are disclosed in the Gazette.
Of these, Japanese Patent Laid-Open No. 6-74019 discloses that a bypass is provided in the exhaust passage, and HC discharged during cold immediately after engine start is once adsorbed by the HC adsorbent disposed in the bypass passage, and then the passage After the downstream three-way catalyst is activated, a system is proposed in which a part of the exhaust gas is passed through the HC adsorption catalyst, and the desorbed HC is gradually purified by the latter three-way catalyst.
[0004]
Further, in Japanese Patent Application Laid-Open No. 7-144119, the first three-way catalyst is deprived of heat during cold to improve the adsorption efficiency of the middle HC adsorption catalyst, and after the first three-way catalyst is activated, a tandem arrangement is provided. We have proposed a system that facilitates the transfer of reaction heat to the latter three-way catalyst via the middle HC adsorption contact material and promotes purification of the latter three-way catalyst.
Further, Japanese Patent Laid-Open No. 6-142457 discloses a cold HC that preheats exhaust gas containing desorbed HC with a heat exchanger and promotes purification with a three-way catalyst when HC adsorbed in a low temperature region is desorbed. Adsorption removal systems have been proposed.
On the other hand, Japanese Patent Application Laid-Open No. 5-59942 proposes a system that slows the temperature rise of the HC adsorbent and improves the cold HC adsorption efficiency by switching the catalyst arrangement and the exhaust gas flow path by the valve. .
Japanese Patent Laid-Open No. 7-102957 discloses that in order to improve the purification performance of the downstream oxidation / three-way catalyst, air is supplied between the upstream three-way catalyst and the middle HC adsorbent, and the subsequent oxidation / Systems that promote the activation of three-way catalysts have been proposed.
[0005]
[Problems to be solved by the invention]
However, when zeolite is used as the adsorbent, there is a correlation between the HC species composition in the exhaust gas and the pore diameter of the zeolite in order to achieve good cold HC adsorption performance. It is necessary to use a zeolite having a framework structure.
Conventionally, the pore size distribution was adjusted mainly by MFI type zeolite and zeolite having other pore sizes (for example, USY) alone or by mixing them. There is a problem in that the exhaust gas HC species are not sufficiently adsorbed because the distortion and the adsorption / desorption characteristics differ.
[0006]
Further, in the conventional exhaust gas purification catalyst provided with the HC adsorbent layer and the purification catalyst layer, the cold HC adsorbed on the HC adsorbent increases in the exhaust gas temperature in the exhaust gas low temperature region immediately after the start of the internal combustion engine. Since the atmosphere of the purification catalyst layer becomes oxygen-deficient when the adsorbed HC is desorbed before it can be desorbed, the three-way catalyst effective for purification in the stoichiometric air-fuel ratio region has HC, There is a problem that carbon oxide (CO) and nitrogen oxide (NOx) cannot be purified with good balance and adsorbed HC cannot be sufficiently purified.
[0007]
For this reason, by switching the exhaust flow path, the adsorbed HC is desorbed after the three-way catalyst is sufficiently activated, and the three-way catalyst is purified, or the three-way catalyst is activated early with an electric heater, Although the method of introducing the air from the catalyst to accelerate the activation of the three-way catalyst has also been studied, the system configuration becomes complicated, and a sufficient cold HC reduction effect cannot be obtained. There were problems such as inability to use.
[0008]
The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to provide an exhaust gas purification catalyst that is excellent in the purification efficiency of cold HC and that is easy to manufacture with a simple configuration. It is to provide.
[0009]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventors can solve the above problems by forming a specific layer structure using a catalyst carrier having a cell closed at one end. As a result, the present invention has been completed.
[0010]
That is, the exhaust gas purification catalyst of the present invention is an exhaust gas purification catalyst that efficiently purifies hydrocarbons discharged at the time of cold start of an internal combustion engine,
It is characterized in that a hydrocarbon adsorbent layer and a purification catalyst component layer are formed on a honeycomb structure-type carrier partially having one end closed cell in which one end in the extending direction is closed.
[0011]
In a preferred embodiment of the exhaust gas purification catalyst of the present invention, the honeycomb structure type carrier has a closed cell pair portion in which the closed ends of the adjacent one closed cells are reversed. .
In this case, it is desirable that all the cells of the honeycomb structure type carrier are constituted by the one end closed cells, and the closed ends of the adjacent one end closed cells are arranged in reverse.
[0012]
Furthermore, another preferred embodiment of the exhaust gas purification catalyst of the present invention is characterized in that a hydrocarbon adsorbent or a purification catalyst component is contained in the wall portion of the one end closed cell.
[0013]
Further, another preferred embodiment of the exhaust gas purification catalyst of the present invention is formed by laminating the hydrocarbon adsorbent layer or the purification catalyst component layer at least on the wall portion of the one end closed cell, and in the closed cell pair portion. The hydrocarbon adsorbent layer is laminated on the wall of one end closed cell, and the purification catalyst component layer is laminated on the wall of the other end closed cell.
[0014]
Furthermore, another preferred embodiment of the exhaust gas purifying catalyst of the present invention is characterized in that both the hydrocarbon adsorbent layer and the purifying catalyst component layer are laminated on at least the wall of the one end closed cell. .
In this case, the closed cell pair portion is provided, and in this closed cell pair portion, the stacking order of the hydrocarbon adsorbent layer and the purification catalyst component layer on the wall portion of one cell and the wall portion of the other cell is reversed. You may do it.
[0015]
[Action]
In the present invention, a honeycomb structure type carrier having a cell closed at one end (referred to as “one end closed cell”) is used, and an HC adsorbent layer and a purification catalyst component layer are formed on the carrier.
In the exhaust gas purification catalyst of the present invention having such a configuration, the exhaust gas passing through the cell flow path of the one-end closed cell has an opening ratio because the outlet of the flowed cell flow path is blocked by clogging. Passes through large cell walls and out of adjacent cell channels with open outlets. At this time, the amount of gas passing through the HC adsorbent layer increases, but the flow velocity (diffusion speed) passing through becomes slow, and the closed ends of adjacent one closed cells are reversely arranged in the cell extending direction. In particular, when all the cells are composed of the closed cell pairs, the exhaust gas travels through the alternately packed cell flow paths, so that the HC adsorbed on the HC adsorbent layer The residence time can be increased, the retention of cold HC can be improved, and the desorption can be delayed, so that the purification efficiency can be improved.
In the present specification, “purification efficiency” or “desorption purification efficiency” mainly means the purification efficiency of adsorbed HC (cold HC) desorbed from the adsorbent.
[0016]
In the present invention, the cell wall may contain an HC adsorbent or a purification catalyst component. When the HC adsorbent is contained, the flow rate of the adsorbed HC is controlled by controlling the flow rate of gas passing through the cell wall. Desorption can be delayed, and on the other hand, when the purification catalyst component is contained, the contact frequency between the purification catalyst component and the adsorbed HC can be increased, so that the purification efficiency can be further improved.
Furthermore, in the present invention, by controlling the stacking arrangement of the HC adsorbent layer and the purification catalyst component layer, the exhaust gas passing through the honeycomb structure type carrier is reduced in the amount of HC with respect to the HC adsorbent layer and the purification catalyst component layer. The adsorbent layer-purified catalyst component layer or the purified catalyst component layer-HC adsorbent layer can be contacted in this order. If the HC adsorbent layer-purified catalyst component layer is ordered, the adsorbed HC is desorbed. Is effectively delayed and the order of the purification catalyst component layer-HC adsorbent layer is followed, the purification catalyst component layer can be activated quickly.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the exhaust gas purification catalyst of the present invention will be described in detail. In the present specification, “%” indicates a mass percentage unless otherwise specified.
As described above, the exhaust gas purification catalyst of the present invention has a honeycomb structure-type carrier partially having a closed cell at one end, and an HC adsorbent layer and a purification catalyst component layer formed thereon.
[0018]
Here, the honeycomb structure-type carrier has a pair of cells adjacent to each other at one closed end, and the closed ends are mutually reversed in the cell extending direction (referred to as “closed cell pair”). It is more preferable that all the cells are constituted by such closed cell pairs, so-called wall flow type honeycomb carrier or checkered honeycomb.
By employing such a closed cell pair, as described above, the residence time of the adsorbed HC can be extended, and the HC purification efficiency can be sufficiently improved.
[0019]
In addition, the HC adsorbent layer and the purification catalyst component layer are deposited and laminated on the inner wall of the cell similarly to the conventional exhaust gas purification catalyst, but in the present invention, by adjusting the arrangement of both layers, The order of contact with the exhaust gas can be changed, and suitable effects can be obtained respectively.
[0020]
Examples of arrangement of the HC adsorbent layer and the purification catalyst component layer in the catalyst of the present invention are shown in FIGS. 1 to 3 are partial cross-sectional views showing examples of the catalyst of the present invention using a wall flow type honeycomb carrier.
In FIG. 1, in this catalyst part, the end portions are alternately clogged in the order of the upper stage, the middle stage, and the lower stage, and the left end, right end, and left end of the cell are closed. In the middle cell, the purification catalyst component layer 10 and the HC adsorbent layer 20 are laminated in that order on the inner wall surface. In the upper cell and the lower cell adjacent to the middle cell, The HC adsorbent layer 20 and the purification catalyst component layer 10 are laminated on the inner wall in this order, which is the reverse of the lamination order in the middle cell.
[0021]
In the catalyst having such a structure, the exhaust gas flowing into the middle cell from the left side first comes into contact with the HC adsorbent layer 20 and then comes into contact with the purification catalyst component layer 10 as shown by the arrow, and then the cell wall. , Contact the HC adsorbent layer 20 and the purification catalyst component layer 10 of the upper cell and the lower cell, respectively, and further flow out from the opening end on the right end.
Thus, in this catalyst structure, the exhaust gas can be sequentially repeated through the HC adsorbent layer and the purification catalyst component layer through the adsorption-retention-purification process, and the cell walls obstruct gas diffusion, so that the exhaust gas is removed. Since the separation can be delayed, the purification efficiency of the adsorbed HC can be improved.
[0022]
The catalyst structure shown in FIG. 2 has the same configuration as the catalyst structure of FIG. 1 except that the stacking order of the catalyst component layer 10 and the HC adsorbent layer 20 in the middle cell is reverse to the catalyst structure of FIG. .
In this catalyst structure, the exhaust gas first contacts the purification catalyst component layer 10 and then contacts the HC adsorbent layer 20 as indicated by arrows. By sandwiching a cell wall that hinders gas diffusion between HC adsorbent layers, desorption delay of adsorbed HC can be achieved, and purification efficiency can be improved.
[0023]
In the catalyst structure shown in FIG. 3, the upper to lower cells are attached to either the purification catalyst component layer 10 or the HC adsorbent layer 20, whereas the middle cell is the HC adsorbent layer 10. The upper cell and the lower cell are the purification catalyst component layer 20, and the types of the deposited layers are reversed between adjacent cells.
Even in this catalyst structure, since the exhaust gas first comes into contact with the HC adsorbent layer, desorption of the adsorbed HC can be effectively delayed.
[0024]
In the exhaust gas purification catalyst of the present invention, it is possible to contain (support) an HC adsorbent or a purification catalyst component in the cell wall, thereby improving purification efficiency.
When the HC adsorbent is supported, the flow rate of gas passing through the cell wall can be controlled to delay the desorption of the adsorbed HC, whereas when the purification catalyst component is supported, the purification catalyst. Since the contact frequency between the component and the adsorbed HC can be increased, the purification efficiency can be further improved.
Examples of the catalyst structure in which the HC adsorbent or the purification catalyst component is supported in such a cell wall are shown in FIGS.
[0025]
The method for supporting the HC adsorbent or the purification catalyst component in the cell wall is not particularly limited, but for the HC adsorbent, the wall flow is applied to the slurry containing the HC adsorbent having an average particle diameter of 2 mm or less. This can be done by immersing the mold honeycomb carrier, followed by drying and firing.
On the other hand, for the purification catalyst component, typically a noble metal, the wall flow type honeycomb carrier is immersed in a slurry containing an inorganic oxide such as alumina having an average particle diameter of 2 mm or less, and further immersed in a solution containing the noble metal, It can be performed by drying and baking. Moreover, after manufacturing the inorganic oxide which carry | supported the noble metal, you may grind | pulverize and use this for the average particle diameter of 2 mm or less.
[0026]
Next, the honeycomb structure type carrier, the HC adsorbent, the material and properties of the catalyst component used for the exhaust gas purification catalyst of the present invention will be described.
First, as the honeycomb structure type carrier, typically, the wall flow type honeycomb carrier, those made of silicon carbide (SiC) or cordierite can be suitably used. Moreover, in the case of a product made of SiC, the pore diameter is preferably 5 to 30 μm, the porosity is 35 to 50%, and the pore volume is 0.8 to 1.4 cm 3 / g.
When the pore diameter, the porosity, and the pore volume are within the above ranges, the drivability does not deteriorate even when the passage resistance of the exhaust gas increases, and a sufficient effect can be obtained even when the passage resistance is small.
On the other hand, in the case of cordierite, the pore diameter is preferably 5 to 50 μm, the porosity is 20 to 50%, and the pore volume is preferably 0.3 to 0.6 cm 3 / g. The reason why the porosity and pore volume are in the above ranges is the same as described above.
[0027]
Further, as the HC adsorbent forming the HC adsorbent layer, H-type β-zeolite having a Si / 2Al ratio of 10 to 1000, or this β-zeolite, and MFI, Y-type, USY, mordenite or ferrierite, and these Can be used. By adopting such a material, the pore size distribution can be widened, so that the HC adsorption efficiency can be further improved.
[0028]
On the other hand, palladium, platinum or rhodium and a mixture thereof can be used as the catalyst component for forming the purification catalyst component layer. However, such noble metal, cerium, zirconium or lanthanum and a mixture thereof are converted to 1 to 10 in terms of metal. It is preferable to form a purification catalyst component layer by using alumina containing mol% in combination with cerium oxide containing 1 to 50 mol% of zirconium, neodymium, praseodymium or lanthanum and a mixture thereof in terms of metal.
By selecting such a material, the cerium oxide releases oxygen when the adsorbed HC is desorbed, so that the desorption purification efficiency of the purification catalyst layer can be improved.
Further, zirconium oxide containing 1 to 40 mol% of cerium, zirconium or lanthanum and a mixture thereof in terms of metal can be added to the above-described catalyst component layer, thereby removing the purification catalyst layer. The purification efficiency can be further improved.
[0029]
The catalyst component layer in the catalyst of the present invention can also be formed using the above-mentioned noble metal and an alkali metal and / or alkaline earth metal. In this case, the heat resistance of the purification catalyst layer is high. It is improved and the desorption purification efficiency can be improved.
[0030]
【Example】
EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to these Examples.
[0031]
Example 1
β-zeolite powder (H type, Si / 2Al = 25) 2125 g, silica sol (solid content 20%) 1875 g, and pure water 3000 g were charged into a magnetic ball mill, mixed and ground to obtain a slurry liquid. This slurry was adhered to a monolith support (200 cells / 10 mil, catalyst capacity 1.3 L), excess slurry in the cells was removed by air flow, dried, and calcined at 400 ° C. for 1 hour. The coating operation was repeated until the coating amount was 250 g / L after firing to obtain catalyst-a.
[0032]
Alumina powder containing 3 mol% of Ce (Al 97 mol%) is impregnated with an aqueous palladium nitrate solution or sprayed with high-speed stirring, dried at 150 ° C. for 24 hours, calcined at 400 ° C. for 1 hour, and then 600 ° C. for 1 hour. A Pd-supported alumina powder (powder a) was obtained. The Pd concentration of this powder a was 4.0% by weight.
Further, cerium oxide powder containing 1 mol% La and 32 mol% Zr (Ce 67 mol%) was impregnated with an aqueous palladium nitrate solution or sprayed with high-speed stirring, dried at 150 ° C. for 24 hours, then at 400 ° C. for 1 hour, then 600 Firing at 1 ° C. for 1 hour gave Pd-supported cerium oxide powder (powder b). The Pd concentration of this powder b was 2.0% by weight.
[0033]
314 g of the above Pd-supported alumina powder (powder a), 314 g of Pd-supported cerium oxide powder (powder b), 320 g of nitric acid acidic alumina sol (a sol obtained by adding 10 wt% nitric acid to 10 wt% boehmite alumina) 2 O 3 in terms of in 32 g) and barium carbonate 51.5g of (40 g as BaO) were charged pure water 2000g into a magnetic ball mill to obtain a slurry which mixing and grinding. This slurry liquid was attached to the coat catalyst-a, the excess slurry in the cell was removed by air flow, dried, baked at 400 ° C. for 1 hour, a coat layer weight of 70 g / L was applied, and catalyst-b Got.
[0034]
Alumina powder containing Zr 3 mol% (Al 97 mol%) is impregnated with an aqueous rhodium nitrate solution or sprayed with high-speed stirring, dried at 150 ° C. for 24 hours, calcined at 400 ° C. for 1 hour, and then calcined at 600 ° C. for 1 hour. Rh-supported alumina powder (powder c) was obtained. The Rh concentration of this powder c was 2.0% by weight.
In addition, alumina powder containing 3 mol% of Ce (Al 97 mol%) was impregnated with dinitrodiammine platinum aqueous solution or sprayed with high-speed stirring, dried at 150 ° C. for 24 hours, then at 400 ° C. for 1 hour, and then at 600 ° C. for 1 hour. Calcination for a period of time gave Pt-supported alumina powder (powder d). The powder d had a Pt concentration of 4.0% by weight.
[0035]
118 g of the above Rh-supported alumina powder (powder c), 177 g of Pt-supported alumina powder (powder d), 175 g of zirconium oxide powder containing La 1 mol% and Ce 20 mol%, and 300 g of nitric acid acidic alumina sol were put into a magnetic ball mill, and mixed and pulverized. Thus, a slurry liquid was obtained. This slurry liquid was adhered to the above-mentioned coated catalyst-b, excess slurry in the cell was removed by air flow, dried, calcined at 400 ° C. for 1 hour, and coated layer weight 50 g / L was applied to obtain a catalyst. It was. The amount of noble metal supported by the catalyst was Pt 0.71 g / L, Pd 1.88 g / L, and Rh 0.24 g / L.
In this example, the catalyst openings of the present example having the structure shown in FIG. 1 was obtained.
Tables 1 and 2 collectively show the component composition and structure of the catalyst of this example, the properties of the carrier used, and the like.
[0036]
(Example 2)
432 g of the above Pd-supported alumina powder (powder a), 314 g of Pd-supported cerium oxide powder (powder b), 140 g of nitric acid acidic alumina sol (sol obtained by adding 10 wt% nitric acid to 10 wt% boehmite alumina) 2 O 3 in terms of in 32 g) and barium carbonate 51.5g of (4g as BaO) were charged pure water 2000g into a magnetic ball mill to obtain a slurry which mixing and grinding. This slurry liquid was attached to a monolith carrier (1200 cells / 2 mil, 1.0 L), excess slurry in the cells was removed by air flow, dried, fired at 400 ° C. for 1 hour, coat layer weight 80 g / L was applied to obtain catalyst-e.
[0037]
118 g of the above Rh-supported alumina powder (powder c), 177 g of Pt-supported alumina powder (powder h), 175 g of zirconium oxide powder containing 1 mol% of La and 20 mol% of Ce, and 300 g of nitric acid acidic alumina sol were put into a magnetic ball mill and mixed and pulverized. Thus, a slurry liquid was obtained. This slurry liquid was adhered to the above-mentioned coated catalyst-b, excess slurry in the cell was removed by air flow, dried, calcined at 400 ° C. for 1 hour, and coated layer weight 50 g / L was applied to obtain a catalyst. It was.
The amount of noble metal supported on the catalyst thus obtained was Pt 0.24 g / L, Pd 2.35 g / L, and Rh 0.24 g / L.
The cell openings of the obtained catalyst were alternately packed in the same manner as in Example 1, and the catalyst No. 1 of this example having the structure shown in FIG. 2 was obtained.
Tables 1 and 2 collectively show the component composition and structure of the catalyst of this example, the properties of the carrier used, and the like.
[0038]
(Examples 3 to 19)
By adopting the component composition, carrier, and catalyst structure shown in Tables 1 and 2 (corresponding to the structures shown in FIGS. 1 to 5), the same operations as in Example 1 were repeated, and catalyst No. 3-No. 19 was obtained.
In Tables 1 and 2, the catalyst No. What was set to 20 is a normal three-way catalyst used for evaluation of the catalyst performance described later.
[0039]
(Comparative Examples 1-5)
By adopting the component composition, carrier and catalyst structure shown in Tables 1 and 2, the same operation as in Example 1 was repeated, and the catalyst No. 21-No. 25 was obtained.
In addition, about catalyst structure 1'-5 ', although the alternate opening of the cell opening part is not implemented in these comparative examples, it has the same structure as catalyst structure 1-5 except this.
[0040]
[Table 1]
[Table 2]
(Examples 20 to 38)
Catalyst No. obtained as described above was obtained. 1-No. 19 and catalyst no. 20 was used to construct an exhaust gas purification system as shown in FIG.
In this case, as shown in Table 3, the catalyst No. 20 is arranged, and catalyst position 2 is located at catalyst position 2. 1-No. 19 was placed.
[0043]
(Comparative Examples 6 to 10)
Catalyst No. In place of catalyst No. 1 21-No. Except for using 25, the same configuration as in Example 20 was adopted, and the exhaust gas purification system of each example was constructed. Table 3 shows the catalyst positions.
[0044]
[Performance evaluation]
For the exhaust gas purification systems of Examples 20 to 38 and Comparative Examples 6 to 10 obtained above, performance evaluation was performed under the following conditions. The results obtained are also shown in Table 3.
In this performance evaluation, the purification rate of the cold HC discharged before the upstream (position 1) three-way catalyst is activated is referred to as a desorption HC purification rate.
[0045]
(Evaluation methods)
Endurance engine displacement 3000cc
Fuel Gasoline (Nisseki Dash)
Catalyst inlet gas temperature 650 ° C
Endurance time 100 hours Vehicle performance test Engine displacement Nissan Motor Co., Ltd. Inline 4-cylinder 2.0L engine evaluation method North American exhaust gas test method LA4-CH A-bag
[0046]
[Table 3]
As shown in Table 3, the purification systems of Examples 20 to 38 belonging to the scope of the present invention have better HC adsorption rate and desorption purification efficiency than the purification systems of Comparative Examples 6 to 10 outside the scope of the present invention. It can be seen that the balance between the two is particularly good.
At this time, it can be said that Example 30 using the catalyst of Example 11 is the best from the viewpoint of the HC adsorption rate and desorption HC purification efficiency.
[0048]
As mentioned above, although this invention was demonstrated in detail by the preferable Example, this invention is not limited to these Examples, A various deformation | transformation is possible within the range of the summary of this invention.
For example, one of the gist of the present invention is to lengthen the residence time when HC adsorbed on the HC adsorbent layer is released, so that the residence time can be appropriately increased. It is not necessary to use a carrier having a closed end cell, typically a wall flow type carrier, and the effect intended by the present invention may be obtained by appropriately adjusting the material of the carrier.
[0049]
【The invention's effect】
As described above, according to the present invention, the catalyst carrier having a cell closed at one end is used to form a specific layer structure, etc., so that it is excellent in the purification efficiency of cold HC and has a simple configuration. Thus, an exhaust gas purification catalyst that is easy to manufacture can be provided.
[Brief description of the drawings]
FIG. 1 is a partial cross-sectional view showing an example of a catalyst of the present invention using a wall flow type honeycomb carrier.
FIG. 2 is a partial cross-sectional view showing an example of the catalyst of the present invention using a wall flow type honeycomb carrier.
FIG. 3 is a partial cross-sectional view showing an example of the catalyst of the present invention using a wall flow type honeycomb carrier.
FIG. 4 is a partial cross-sectional view showing an example of a catalyst structure of the present invention in which an HC adsorbent or a purification catalyst component is supported in a cell wall.
FIG. 5 is a partial cross-sectional view showing an example of the catalyst structure of the present invention in which an HC adsorbent or a purification catalyst component is supported in a cell wall.
FIG. 6 is a system configuration diagram showing an example of an exhaust gas purification system using the catalyst of the present invention.
[Explanation of symbols]
10 HC adsorbent layer 20 Purification catalyst component layer
Claims (14)
延在方向の一端が閉塞された一端閉塞セルを一部に有するハニカム構造型担体に、炭化水素吸着材層と、浄化触媒成分層を形成して成ることを特徴とする排気ガス浄化触媒。An exhaust gas purification catalyst that efficiently purifies hydrocarbons discharged at the time of cold start of an internal combustion engine,
An exhaust gas purification catalyst comprising a hydrocarbon adsorbent layer and a purification catalyst component layer formed on a honeycomb structure-type carrier partially including one end-clogged cell with one end closed in the extending direction.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2001156620A JP4565424B2 (en) | 2001-05-25 | 2001-05-25 | Exhaust gas purification catalyst |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2001156620A JP4565424B2 (en) | 2001-05-25 | 2001-05-25 | Exhaust gas purification catalyst |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JP2002346396A JP2002346396A (en) | 2002-12-03 |
| JP4565424B2 true JP4565424B2 (en) | 2010-10-20 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2001156620A Expired - Fee Related JP4565424B2 (en) | 2001-05-25 | 2001-05-25 | Exhaust gas purification catalyst |
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Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2012166128A (en) * | 2011-02-10 | 2012-09-06 | Jfe Engineering Corp | Dehumidifier |
| US10934910B2 (en) | 2017-03-27 | 2021-03-02 | Cataler Corporation | Exhaust gas cleaning catalyst |
| JP2020142165A (en) * | 2019-03-04 | 2020-09-10 | 東京濾器株式会社 | filter |
Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH02102957A (en) * | 1988-10-13 | 1990-04-16 | Toyota Motor Corp | Elastic energy accumulating device |
| JPH06182219A (en) * | 1992-08-05 | 1994-07-05 | Corning Inc | Device and method for denaturation of gas mixture |
| JPH1076141A (en) * | 1996-09-02 | 1998-03-24 | Toyota Motor Corp | Catalyst for purification of exhaust gas |
| JPH10202111A (en) * | 1997-01-21 | 1998-08-04 | Toyota Motor Corp | Catalyst for purifying diesel exhaust gas |
| JP2005500147A (en) * | 1999-08-13 | 2005-01-06 | ジョンソン、マッセイ、パブリック、リミテッド、カンパニー | Catalyst wall flow filter |
-
2001
- 2001-05-25 JP JP2001156620A patent/JP4565424B2/en not_active Expired - Fee Related
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH02102957A (en) * | 1988-10-13 | 1990-04-16 | Toyota Motor Corp | Elastic energy accumulating device |
| JPH06182219A (en) * | 1992-08-05 | 1994-07-05 | Corning Inc | Device and method for denaturation of gas mixture |
| JPH1076141A (en) * | 1996-09-02 | 1998-03-24 | Toyota Motor Corp | Catalyst for purification of exhaust gas |
| JPH10202111A (en) * | 1997-01-21 | 1998-08-04 | Toyota Motor Corp | Catalyst for purifying diesel exhaust gas |
| JP2005500147A (en) * | 1999-08-13 | 2005-01-06 | ジョンソン、マッセイ、パブリック、リミテッド、カンパニー | Catalyst wall flow filter |
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| Publication number | Publication date |
|---|---|
| JP2002346396A (en) | 2002-12-03 |
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