JP2010005590A - Catalyst for purifying exhaust gas - Google Patents

Catalyst for purifying exhaust gas Download PDF

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JP2010005590A
JP2010005590A JP2008170808A JP2008170808A JP2010005590A JP 2010005590 A JP2010005590 A JP 2010005590A JP 2008170808 A JP2008170808 A JP 2008170808A JP 2008170808 A JP2008170808 A JP 2008170808A JP 2010005590 A JP2010005590 A JP 2010005590A
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catalyst layer
layer
gas flow
length
exhaust gas
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JP4751917B2 (en
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Tomoaki Sunada
智章 砂田
Toshitaka Tanabe
稔貴 田邊
Naoki Takahashi
直樹 高橋
Hirohisa Tanaka
裕久 田中
Mari Uenishi
真里 上西
Masashi Taniguchi
昌司 谷口
Shingo Sakagami
新吾 坂神
Masaaki Kawai
将昭 河合
Hirotaka Ori
浩隆 小里
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Daihatsu Motor Co Ltd
Cataler Corp
Toyota Motor Corp
Toyota Central R&D Labs Inc
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Daihatsu Motor Co Ltd
Cataler Corp
Toyota Motor Corp
Toyota Central R&D Labs Inc
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Priority to PCT/IB2009/006122 priority patent/WO2010001226A1/en
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst for purifying an exhaust gas which can effectively exhibit performance for purifying both NOx and HC. <P>SOLUTION: The catalyst for purifying the exhaust gas comprises a honeycomb base material 1 having a gas stream passage 10 through which exhaust gas passes, a lower catalyst layer 2 formed on the surface of the honeycomb base material 1, and the upper catalyst layer 3 formed on the surface of the lower catalyst layer 2. The upper catalyst layer 3 carries Rh. The lower catalyst layer 2 is composed of a Pd-carrying layer 21 and a Pt-carrying layer 22. The length of the upper catalyst layer 3 in the gas flow direction is shorter than the length of the lower catalyst layer 2 in the gas flow direction. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

本発明は、三元触媒として有用な排ガス浄化用触媒に関する。   The present invention relates to an exhaust gas purifying catalyst useful as a three-way catalyst.

自動車の排ガス中のＨＣ、ＣＯ及びＮＯｘを浄化する触媒として、三元触媒が広く用いられている。この三元触媒は、例えば、特許文献１（特開昭６３−２３６５４１号公報）に開示されているように、基材に、Ｐｔ（白金）、Ｐｄ（パラジウム）、Ｒｈ（ロジウム）などの貴金属を担持したものであり、ＨＣ及びＣＯを酸化して浄化すると共に、ＮＯｘを還元して浄化する。これらの反応は、酸化成分と還元成分がほぼ同量で存在する雰囲気下で最も効率よく進行する。このため、三元触媒を搭載した車両においては、理論空燃比（ストイキ）近傍で燃焼されるように空燃比の制御が行われる。   Three-way catalysts are widely used as catalysts for purifying HC, CO, and NOx in automobile exhaust gas. For example, as disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 63-236541), this three-way catalyst has a base material such as Pt (platinum), Pd (palladium), or Rh (rhodium). HC and CO are oxidized and purified, and NOx is reduced and purified. These reactions proceed most efficiently in an atmosphere where the oxidizing component and reducing component are present in approximately the same amount. For this reason, in a vehicle equipped with a three-way catalyst, the air-fuel ratio is controlled so that it is burned in the vicinity of the stoichiometric air-fuel ratio (stoichiometric).

ところで、近年、有限資源の節約のため、貴金属の使用の低減が求められている。貴金属の中でもＲｈは採掘量に限りがあり、高コストである。そのため、特許文献２（特開２００４−２９８８１３号公報）及び特許文献３（特開２００１−７９４０３号公報）に開示されているように、Ｒｈを有効に活用するために、触媒層を２層化し、上層にＲｈを配置することでＲｈの活性を高めていた。詳しくは、特許文献２では、上層にＲｈ、下層にＰｔを配置しており、特許文献３では、上層にＲｈ及びＰｔの少なくとも一方、下層にＰｄを配置していた。   By the way, in recent years, reduction of the use of precious metals has been demanded in order to save limited resources. Among precious metals, Rh has a limited amount of mining and is expensive. Therefore, as disclosed in Patent Document 2 (Japanese Patent Laid-Open No. 2004-298913) and Patent Document 3 (Japanese Patent Laid-Open No. 2001-79403), in order to effectively use Rh, the catalyst layer is divided into two layers. The activity of Rh was increased by arranging Rh in the upper layer. Specifically, in Patent Document 2, Rh is disposed in the upper layer and Pt is disposed in the lower layer, and in Patent Document 3, at least one of Rh and Pt is disposed in the upper layer, and Pd is disposed in the lower layer.

Ｒｈは、ＮＯｘ還元浄化活性が高く、Ｐｔ、ＰｄはＨＣ、ＣＯの酸化浄化活性が高い。上層にＲｈを配置することで、ＮＯｘの浄化性能が向上する。   Rh has high NOx reduction purification activity, and Pt and Pd have high HC and CO oxidation purification activity. By arranging Rh in the upper layer, the NOx purification performance is improved.

しかしながら、特許文献２、３に開示されているように、触媒層を上層と下層で２層化した場合には、下層が上層に被覆されるため、上層に比べて、下層へのガス拡散性が低下し、下層の触媒活性が抑えられる。   However, as disclosed in Patent Documents 2 and 3, when the catalyst layer is divided into two layers, the upper layer and the lower layer, the lower layer is covered with the upper layer. Decreases, and the catalytic activity of the lower layer is suppressed.

特許文献２では、下層にＰｔが配置されているため、ＰｔのＨＣ浄化性能が抑えられる。特許文献３では、下層にＰｄが配置されているため、ＰｄのＨＣ浄化性能が抑えられる。特に、特許文献３の実施例１、４では、上層にＲｈとＰｔとが共存しているため、ＲｈとＰｔとが合金化し、ＰｔのＨＣ浄化性能が低下してしまう。
特開昭６３−２３６５４１号公報 特開２００４−２９８８１３号公報 特開２００１−７９４０３号公報 In Patent Document 2, since Pt is disposed in the lower layer, the HC purification performance of Pt is suppressed. In Patent Document 3, since Pd is disposed in the lower layer, the HC purification performance of Pd is suppressed. In particular, in Examples 1 and 4 of Patent Document 3, since Rh and Pt coexist in the upper layer, Rh and Pt are alloyed and the HC purification performance of Pt is lowered.
JP 63-236541 A Japanese Patent Laid-Open No. 2004-289813 JP 2001-79403 A

本発明はかかる事情に鑑みてなされたものであり、ＮＯｘ浄化性能とＨＣ浄化性能を共に有効に発揮することができる排ガス浄化用触媒を提供することを課題とする。   This invention is made | formed in view of this situation, and makes it a subject to provide the catalyst for exhaust gas purification which can exhibit both NOx purification performance and HC purification performance effectively.

前記課題を解決するため、請求項１に係る発明は、排ガスが流通するガス流路を有する基材と、該基材の表面に形成された下触媒層と、該下触媒層の表面に形成された上触媒層と、を有する排ガス浄化用触媒において、前記上触媒層は、Ｒｈを担持してなり、前記下触媒層は、Ｐｄ又は／及びＰｔを担持してなり、前記上触媒層の前記ガス流路に沿ったガス流れ方向の長さは、前記下触媒層の前記ガス流れ方向の長さよりも短いことを特徴とする。   In order to solve the above problems, the invention according to claim 1 is a substrate having a gas flow path through which exhaust gas flows, a lower catalyst layer formed on the surface of the substrate, and formed on the surface of the lower catalyst layer. In the exhaust gas purifying catalyst having the upper catalyst layer, the upper catalyst layer carries Rh, the lower catalyst layer carries Pd or / and Pt, The length of the gas flow direction along the gas flow path is shorter than the length of the lower catalyst layer in the gas flow direction.

請求項２に係る発明は、前記下触媒層の前記ガス流れ方向の長さに対する前記上触媒層の前記ガス流れ方向の長さの比率は５０〜９０％であることを特徴とする。   The invention according to claim 2 is characterized in that a ratio of a length of the upper catalyst layer in the gas flow direction to a length of the lower catalyst layer in the gas flow direction is 50 to 90%.

請求項３に係る発明は、前記上触媒層は、前記下触媒層の前記ガス流れ方向の下流側端部を含む部分の表面に配設されていることを特徴とする。   The invention according to claim 3 is characterized in that the upper catalyst layer is disposed on a surface of a portion including a downstream end portion of the lower catalyst layer in the gas flow direction.

請求項４に係る発明は、前記下触媒層は、前記ガス流れ方向の上流側でＰｄを担持してなるＰｄ担持層と、前記Ｐｄ担持層よりも前記ガス流れ方向の下流側でＰｔを担持してなるＰｔ担持層とからなることを特徴とする。   In the invention according to claim 4, the lower catalyst layer carries a Pd carrying layer carrying Pd on the upstream side in the gas flow direction, and carries Pt on the downstream side in the gas flow direction from the Pd carrying layer. It is characterized by comprising a Pt support layer.

前記請求項１に係る発明においては、上触媒層でＲｈを担持し、下触媒層でＰｄ又は／及びＰｔを担持している。Ｒｈは、Ｐｄ又は／及びＰｔと分層されているため、ＲｈがＰｄ又は／及びＰｔと合金化することはなく、Ｐｄ又は／及びＰｔのＨＣ浄化性能が低下するおそれもない。   In the first aspect of the invention, the upper catalyst layer carries Rh, and the lower catalyst layer carries Pd or / and Pt. Since Rh is separated from Pd or / and Pt, Rh does not alloy with Pd or / and Pt, and the HC purification performance of Pd or / and Pt does not deteriorate.

また、上触媒層にはＲｈが担持されている。ＲｈはＮＯｘ浄化性能に優れており、ガス流路に接する上層に配置することで、ガス流路を流れる排ガスの上触媒層への拡散性が高くなり、排ガス中のＮＯｘと接触しやすくなり、ＲｈのＮＯｘ浄化性能を有効に発揮することができる。   Further, Rh is supported on the upper catalyst layer. Rh is excellent in NOx purification performance, and by disposing it in the upper layer in contact with the gas flow path, the diffusibility of the exhaust gas flowing in the gas flow path to the upper catalyst layer becomes high, and it becomes easier to contact NOx in the exhaust gas, The NOx purification performance of Rh can be effectively exhibited.

また、上触媒層のガス流れ方向の長さは、下触媒層の前記ガス流れ方向の長さよりも短い。このため、下触媒層の一部が、上触媒層に被覆されず、ガス流路に露出する。ゆえに、下触媒層へ排ガスが拡散しやすくなり、Ｐｄ又は／及びＰｔのＨＣ浄化性能及びＣＯ浄化性能を有効に発揮することができる。   The length of the upper catalyst layer in the gas flow direction is shorter than the length of the lower catalyst layer in the gas flow direction. For this reason, a part of lower catalyst layer is not coat | covered with an upper catalyst layer, but is exposed to a gas flow path. Therefore, the exhaust gas easily diffuses into the lower catalyst layer, and the HC purification performance and CO purification performance of Pd or / and Pt can be effectively exhibited.

前記請求項２に係る発明によれば、下触媒層のガス流れ方向の長さに対する上触媒層のガス流れ方向の長さの比率は５０〜９０％である。このため、上触媒層の長さを保持しつつ、下触媒層もある程度の長さでガス流路に露出させることができる。ゆえに、上触媒層に担持されているＲｈのＮＯｘ浄化性能と、下触媒層に担持されているＰｄ又は／及びＰｔのＨＣ浄化性能を、共に効果的に発揮させることができる。   According to the second aspect of the present invention, the ratio of the length of the upper catalyst layer in the gas flow direction to the length of the lower catalyst layer in the gas flow direction is 50 to 90%. For this reason, it is possible to expose the lower catalyst layer to the gas flow path with a certain length while maintaining the length of the upper catalyst layer. Therefore, both the NOx purification performance of Rh supported on the upper catalyst layer and the HC purification performance of Pd or / and Pt supported on the lower catalyst layer can be effectively exhibited.

また、下触媒層にセリアなどの酸素吸放出材を含む場合には、下触媒層がガス流路に表出することにより、ガス流路を流れる排ガスの空燃比（Ａ／Ｆ）の変動が緩和される。ゆえに、下触媒層及び上触媒層が、安定した浄化性能を発揮することができる。   Further, when the lower catalyst layer includes an oxygen storage / release material such as ceria, the lower catalyst layer is exposed to the gas flow path, thereby causing fluctuations in the air-fuel ratio (A / F) of the exhaust gas flowing through the gas flow path. Alleviated. Therefore, the lower catalyst layer and the upper catalyst layer can exhibit stable purification performance.

前記請求項３に係る発明によれば、上触媒層は、下触媒層におけるガス流れ方向の下流側端部を含む部分の表面に配設されている。基材の下流側は、上流側に比べて、低温である。このため、下流側に、Ｒｈを担持してなる上触媒層を配設することにより、Ｒｈの高温時の熱劣化を抑制することができる。   According to the third aspect of the present invention, the upper catalyst layer is disposed on the surface of the lower catalyst layer including the downstream end in the gas flow direction. The downstream side of the substrate is at a lower temperature than the upstream side. For this reason, the thermal degradation at the time of the high temperature of Rh can be suppressed by arrange | positioning the upper catalyst layer which carry | supports Rh in the downstream.

前記請求項４に係る発明によれば、下触媒層が、上流側のＰｄ担持層と、下流側のＰｔ担持層とからなる。下触媒層に含まれているＰｄ又は／及びＰｔは、排ガス中の酸素を消費して、排ガス中のＨＣ及びＣＯを酸化浄化する。このため、下流側の酸素濃度が、上流側よりも低くなる。そこで、酸素濃度が高い上流側に、酸素濃度が高い雰囲気で高温時の耐久性が高いＰｄ担持層を配設し、下流側にＰｔ担持層を配設している。これにより、Ｐｔ担持層が、下流側の酸素濃度が低く比較的低温の雰囲気に配置されるため、Ｐｔの熱劣化が抑制されて、下触媒層全体の耐久性が向上する。   According to the fourth aspect of the present invention, the lower catalyst layer includes the upstream Pd carrying layer and the downstream Pt carrying layer. Pd and / or Pt contained in the lower catalyst layer consumes oxygen in the exhaust gas and oxidizes and purifies HC and CO in the exhaust gas. For this reason, the oxygen concentration on the downstream side is lower than that on the upstream side. Therefore, a Pd support layer having high durability at high temperatures in an atmosphere having a high oxygen concentration is disposed on the upstream side where the oxygen concentration is high, and a Pt support layer is disposed on the downstream side. As a result, the Pt-supporting layer is disposed in a relatively low temperature atmosphere with a low oxygen concentration on the downstream side, so that thermal deterioration of Pt is suppressed and the durability of the entire lower catalyst layer is improved.

本発明の排ガス浄化用触媒は、ガス流路を有する基材と、基材の表面に形成された下触媒層と、下触媒層の表面に形成された上触媒層とをもつ。基材は、ガス流路を有する構造を備えており、例えば、ハニカム形状、フォーム形状などのものを用いることができる。基材の材質は特に限定されず、コージェライト、ＳｉＣなどのセラミックス製のもの、あるいは金属製のものなど公知のものを用いることができる。   The exhaust gas purifying catalyst of the present invention has a base material having a gas flow path, a lower catalyst layer formed on the surface of the base material, and an upper catalyst layer formed on the surface of the lower catalyst layer. The substrate has a structure having a gas flow path, and for example, a honeycomb shape, a foam shape, or the like can be used. The material of the substrate is not particularly limited, and known materials such as cordierite, ceramics such as SiC, or metals can be used.

下触媒層は、基材の表面に形成されている。ここで、基材がハニカム形状である場合には、複数のガス流路を区画しているハニカム基材の隔壁の表面に下触媒層が形成されている。下触媒層は、基材のガス流れ方向の全体に形成されているとよい。   The lower catalyst layer is formed on the surface of the substrate. Here, when the substrate has a honeycomb shape, a lower catalyst layer is formed on the surface of the partition wall of the honeycomb substrate that defines a plurality of gas flow paths. The lower catalyst layer may be formed on the entire gas flow direction of the substrate.

下触媒層は、担体と、担体に担持され貴金属触媒としてのＰｄ又は／及びＰｔとからなる。下触媒層は、Ｐｄ又は／及びＰｔは担持しているが、Ｒｈは担持していないことが望ましい。Ｐｄ又は／及びＰｔは、ＨＣ及びＣＯの酸化浄化反応を促進する。   The lower catalyst layer is composed of a support and Pd or / and Pt as a noble metal catalyst supported on the support. The lower catalyst layer preferably supports Pd or / and Pt but not Rh. Pd or / and Pt promote the oxidative purification reaction of HC and CO.

下触媒層は、ガス流れ方向の上流側にＰｄを担持してなるＰｄ担持層と、Ｐｄ担持層よりも下流側でＰｔを担持してなるＰｔ担持層とからなることが好ましい。この場合には、高温で酸素濃度が高い上流側に、酸素濃度が高い雰囲気下で高温時の耐久性に優れたＰｄが配置され、Ｐｔの劣化を抑制でき、下触媒相全体の耐久性を向上させることができる。   The lower catalyst layer is preferably composed of a Pd-carrying layer that carries Pd on the upstream side in the gas flow direction and a Pt-carrying layer that carries Pt on the downstream side of the Pd-carrying layer. In this case, Pd having excellent durability at high temperature in an atmosphere with high oxygen concentration is arranged on the upstream side where oxygen concentration is high at high temperature, so that deterioration of Pt can be suppressed, and the durability of the entire lower catalyst phase can be reduced. Can be improved.

基材のガス流れ方向の長さに対する、Ｐｄ担持層のガス流れ方向の長さの比率は２０〜４５％であることが好ましい。該比率が２０％未満の場合には、高熱時の耐久性が比較的低いＰｔを担持したＰｔ担持層が、高温の上流側に近接し、Ｐｔが熱劣化するおそれがあり、４５％を越える場合には、上流側のＰｄ濃度が低くなるため、暖機性能が低下するおそれがある。   The ratio of the length of the Pd-supported layer in the gas flow direction to the length of the base material in the gas flow direction is preferably 20 to 45%. If the ratio is less than 20%, the Pt carrying layer carrying Pt having relatively low durability when heated is close to the high temperature upstream side, and Pt may be thermally deteriorated, exceeding 45%. In this case, since the upstream Pd concentration is low, the warm-up performance may be reduced.

下触媒層のＰｄ担持層のＰｄ担持量は、０．２５〜５．０ｇ／Ｌ（リットル）であることが好ましい。０．２５ｇ／Ｌ未満の場合には、ＨＣ及びＣＯの酸化活性が低下するおそれがあり、５．０ｇ／Ｌを超える場合には、効果が飽和するとともにコストの増加を招く。   The Pd carrying amount of the Pd carrying layer of the lower catalyst layer is preferably 0.25 to 5.0 g / L (liter). If it is less than 0.25 g / L, the oxidation activity of HC and CO may decrease. If it exceeds 5.0 g / L, the effect is saturated and the cost is increased.

下触媒層のＰｔ担持層のＰｔ担持量は、０．２５〜５．０ｇ／Ｌであることが好ましい。０．２５ｇ／Ｌ未満の場合には、ＨＣ及びＣＯの酸化活性が低下するおそれがあり、５．０ｇ／Ｌを超える場合には、効果が飽和するとともにコストの増加を招く。   The Pt carrying amount of the Pt carrying layer of the lower catalyst layer is preferably 0.25 to 5.0 g / L. If it is less than 0.25 g / L, the oxidation activity of HC and CO may decrease. If it exceeds 5.0 g / L, the effect is saturated and the cost is increased.

下触媒層のＰｄ担持層の担体は、アルミナ、セリア、セリア−ジルコニア複合酸化物、及び、ランタン、イットリウム、ネオジウム、プラセオジウムの酸化物を前記複合酸化物に添加したものなどを用いることができる。下触媒層のＰｔ担持層の担体は、アルミナ、セリア、セリア−ジルコニア複合酸化物、及び、ランタン、イットリウム、ネオジウム、プラセオジウムの酸化物を前記複合酸化物に添加したものなどを用いることができる。   As the carrier for the Pd-supporting layer of the lower catalyst layer, alumina, ceria, ceria-zirconia composite oxide, and lanthanum, yttrium, neodymium, and praseodymium oxide added to the composite oxide can be used. As the carrier for the Pt-supporting layer of the lower catalyst layer, alumina, ceria, ceria-zirconia composite oxide, and lanthanum, yttrium, neodymium, praseodymium oxide added to the composite oxide can be used.

下触媒層の厚みは、１０〜２０μｍであることが好ましい。１０μｍ未満の場合には、下触媒層に含まれるＰｄ又は／及びＰｔの触媒活性が低下するおそれがあり、２０μｍを越える場合には、下触媒層の深部でのＰｄ又は／及びＰｔへの排ガスの拡散性が低下するおそれがある。   The thickness of the lower catalyst layer is preferably 10 to 20 μm. If it is less than 10 μm, the catalytic activity of Pd and / or Pt contained in the lower catalyst layer may be reduced. If it exceeds 20 μm, the exhaust gas to Pd or / and Pt in the deep part of the lower catalyst layer There is a possibility that the diffusibility of the material may decrease.

下触媒層を形成するにあたっては、下触媒層用の担体粉末を含むスラリーを基材にウォッシュコートした後に、それにＰｄ又は／及びＰｔを担持してもよいし、担体粉末に予めＰｄ又は／及びＰｔを担持させた触媒粉末を含むスラリーを、下触媒層をもつ基材にウォッシュコートしてもよい。   In forming the lower catalyst layer, after the slurry containing the carrier powder for the lower catalyst layer is wash-coated on the base material, Pd or / and Pt may be supported on the substrate, or Pd or / and A slurry containing catalyst powder supporting Pt may be wash-coated on a substrate having a lower catalyst layer.

下触媒層が上流側のＰｄ担持層と下流側のＰｔ担持層とに分離されている場合には、Ｐｄ担持層を形成するにあたって、Ｐｄ担持層用担体粉末を含むスラリーの中に、基材の上流側端部から所定の長さまでの部分を浸漬した後、Ｐｄを担持させる。Ｐｄを担持した触媒粉末を含むスラリーについても同様とする。Ｐｔ担持層を形成するに当たっては、Ｐｔ担持層用担体粉末を含むスラリーの中に、基材の下流側端部から所定の長さまでの部分を浸漬する。Ｐｔを担持した触媒粉末を含むスラリーについても同様とする。   In the case where the lower catalyst layer is separated into the upstream Pd support layer and the downstream Pt support layer, the base material is added to the slurry containing the carrier powder for the Pd support layer in forming the Pd support layer. After immersing a part from the upstream side end portion to a predetermined length, Pd is supported. The same applies to the slurry containing the catalyst powder supporting Pd. In forming the Pt-supporting layer, a portion from the downstream end of the substrate to a predetermined length is immersed in the slurry containing the carrier powder for the Pt-supporting layer. The same applies to the slurry containing the catalyst powder supporting Pt.

下触媒層の表面には、上触媒層が形成されている。上触媒層のガス流れ方向の長さは、下触媒層のガス流れ方向の長さよりも短い。下触媒層のガス流れ方向の長さに対する上触媒層のガス流れ方向の長さの比率は１００％以下であり、好ましくは５０〜９０％であり、望ましくは６０〜８５％である。該比率が５０％未満の場合には、上触媒層の長さが下触媒層の長さに比べて短すぎ、上触媒層に担持されているＲｈのＮＯｘ浄化活性が低下するおそれがある。９０％を越える場合には、下触媒層の多くの部分が上触媒層で被覆されて、下触媒層へのガス拡散性が低下するおそれがある。   An upper catalyst layer is formed on the surface of the lower catalyst layer. The length of the upper catalyst layer in the gas flow direction is shorter than the length of the lower catalyst layer in the gas flow direction. The ratio of the length of the upper catalyst layer in the gas flow direction to the length of the lower catalyst layer in the gas flow direction is 100% or less, preferably 50 to 90%, and desirably 60 to 85%. When the ratio is less than 50%, the length of the upper catalyst layer is too short compared to the length of the lower catalyst layer, and there is a possibility that the NOx purification activity of Rh supported on the upper catalyst layer is lowered. If it exceeds 90%, a large part of the lower catalyst layer is covered with the upper catalyst layer, and gas diffusibility to the lower catalyst layer may be reduced.

下触媒層のガス流れ方向の長さに対する上触媒層のガス流れ方向の長さの比率が６０〜８５％であることにより、下触媒層に担持されているＰｄ又は／及びＰｔのＨＣ酸化活性と、上触媒層に担持されているＲｈのＮＯｘ還元活性とをバランスよく効果的に発揮させることができる。   The ratio of the length of the upper catalyst layer in the gas flow direction to the length of the lower catalyst layer in the gas flow direction is 60 to 85%, so that the HC oxidation activity of Pd and / or Pt supported on the lower catalyst layer And the NOx reduction activity of Rh supported on the upper catalyst layer can be effectively exhibited in a balanced manner.

上触媒層は、下触媒層のガス流れ方向の下流側端部を含む部分の表面に配設されているとよい。この場合、下触媒層における下流側端部を含む部分は上触媒層により被覆され、上流側の部分はガス流路に露出する。   The upper catalyst layer may be disposed on the surface of the portion including the downstream end portion of the lower catalyst layer in the gas flow direction. In this case, the portion including the downstream end portion in the lower catalyst layer is covered with the upper catalyst layer, and the upstream portion is exposed to the gas flow path.

上触媒層は、担体と、担体に担持されている触媒貴金属であるＲｈとからなる。上触媒層には、Ｒｈが担持されているが、Ｐｄ及びＰｔのいずれも担持していないことが望ましい。上触媒層のＲｈ担持量は、０．１〜１．２ｇ／Ｌであることが好ましい。０．１ｇ／Ｌ未満の場合には、ＮＯｘの還元活性が低下するおそれがあり、１．２ｇ／Ｌを超える場合には、効果が飽和するとともにコストの増加を招く。   The upper catalyst layer is composed of a support and Rh, which is a catalyst noble metal supported on the support. The upper catalyst layer supports Rh, but it is desirable that neither Pd nor Pt be supported. The amount of Rh supported on the upper catalyst layer is preferably 0.1 to 1.2 g / L. If it is less than 0.1 g / L, the reduction activity of NOx may be reduced. If it exceeds 1.2 g / L, the effect is saturated and the cost is increased.

上触媒層の担体は、アルミナ、ジルコニア、ジルコニア−セリア複合酸化物、及び、ランタン、イットリウム、ネオジウム、プラセオジウムの酸化物を前記複合酸化物に添加したものなどを用いることができる。   As the support for the upper catalyst layer, alumina, zirconia, zirconia-ceria composite oxide, and lanthanum, yttrium, neodymium, and praseodymium oxide added to the composite oxide can be used.

上触媒層の厚みは、１０〜２０μｍであることが好ましい。１０μｍ未満の場合には、上触媒層に含まれるＲｈの触媒活性が低下するおそれがあり、２０μｍを越える場合には、下触媒層の上触媒層に被覆されている部分への排ガスの拡散性が低下するおそれがある。   The thickness of the upper catalyst layer is preferably 10 to 20 μm. If it is less than 10 μm, the catalytic activity of Rh contained in the upper catalyst layer may be reduced. If it exceeds 20 μm, the diffusibility of exhaust gas to the portion covered by the upper catalyst layer of the lower catalyst layer May decrease.

上触媒層を形成するにあたっては、上触媒層用の担体粉末を含むスラリーを下触媒層を形成した基材にウォッシュコートした後に、それに少なくともＲｈを担持してもよいし、担体粉末に予めＲｈを担持させた触媒粉末を含むスラリーを、下触媒層を形成した基材にウォッシュコートしてもよい。   In forming the upper catalyst layer, the slurry containing the carrier powder for the upper catalyst layer is wash-coated on the substrate on which the lower catalyst layer is formed, and then at least Rh may be supported on the slurry, or the carrier powder may be preloaded with Rh. A slurry containing the catalyst powder supporting the catalyst may be wash-coated on the substrate on which the lower catalyst layer is formed.

上触媒層又は／及び下触媒層に含まれる担体には、ガス流路を流れる排ガス中の酸素を吸放出し得る酸素吸放出材として機能するものがある。酸素吸放出材としては、セリア、セリア−ジルコニア複合酸化物などがあげられる。   Some carriers contained in the upper catalyst layer and / or the lower catalyst layer function as an oxygen storage / release material capable of absorbing and releasing oxygen in the exhaust gas flowing through the gas flow path. Examples of the oxygen storage / release material include ceria and ceria-zirconia composite oxide.

本発明の排ガス浄化用触媒は、三元触媒として有用に用いることができる。   The exhaust gas purifying catalyst of the present invention can be usefully used as a three-way catalyst.

本発明について、実施例及び比較例を用いて具体的に説明する。   The present invention will be specifically described using examples and comparative examples.

（実施例１）
本例の排ガス浄化用触媒は、図１に示すように、排ガスが流通するガス流路１０を有するハニカム基材１と、ハニカム基材１の表面に形成された下触媒層２と、下触媒層２の表面に形成された上触媒層３とを有している。 Example 1
As shown in FIG. 1, the exhaust gas purifying catalyst of this example includes a honeycomb base material 1 having a gas flow path 10 through which exhaust gas flows, a lower catalyst layer 2 formed on the surface of the honeycomb base material 1, and a lower catalyst. And an upper catalyst layer 3 formed on the surface of the layer 2.

図２に示すように、ハニカム基材１は、長さ（Ｌ１）１０５ｍｍの円筒体であり、コーディエライト製である。図３，図４に示すように、ハニカム基材１には、長手方向に延びる多数の六角形断面のセル１１が隔壁１２で区画されている。各セル１１を構成する隔壁１２の表面には、下触媒層２及び上触媒層３が形成されており、その表面の空間部にガス流路１０が形成されている。   As shown in FIG. 2, the honeycomb substrate 1 is a cylindrical body having a length (L1) of 105 mm and is made of cordierite. As shown in FIGS. 3 and 4, in the honeycomb substrate 1, a large number of hexagonal cross-sectional cells 11 extending in the longitudinal direction are partitioned by partition walls 12. A lower catalyst layer 2 and an upper catalyst layer 3 are formed on the surface of the partition wall 12 constituting each cell 11, and a gas flow path 10 is formed in a space portion on the surface.

図１に示すように、下触媒層２は、Ｐｄを担持してなるＰｄ担持層２１と、Ｐｔを担持してなるＰｔ担持層２２とから構成されている。Ｐｄ担持層２１は、ガス流路１０を流れるガスの流れ方向の基材１の上流側端部１ａから２０ｍｍまでの部分に配置されている。Ｐｔ担持層２２は、Ｐｄ担持層２１の下流側端部２１ｂから、基材１の下流側端部１ｂまでの８５ｍｍの部分に配置されている。したがって、図３に示すように、基材１の上流側では、下触媒層２のＰｄ担持層２１のみの単層が配設され、図４に示すように、基材１の下流側では、下触媒層２のＰｔ担持層２２と上触媒層３の２層が配設されている。   As shown in FIG. 1, the lower catalyst layer 2 includes a Pd carrying layer 21 carrying Pd and a Pt carrying layer 22 carrying Pt. The Pd carrying layer 21 is disposed at a portion from the upstream end 1a of the base material 1 in the gas flow direction through the gas flow path 10 to 20 mm. The Pt-carrying layer 22 is disposed at a portion of 85 mm from the downstream end 21 b of the Pd carrying layer 21 to the downstream end 1 b of the substrate 1. Therefore, as shown in FIG. 3, a single layer of only the Pd support layer 21 of the lower catalyst layer 2 is disposed on the upstream side of the base material 1, and as shown in FIG. 4, on the downstream side of the base material 1, Two layers of a Pt support layer 22 of the lower catalyst layer 2 and an upper catalyst layer 3 are disposed.

上触媒層３は、Ｒｈを担持している。上触媒層３のガス流れ方向の長さＬ３は、８５ｍｍであり、基材１の下流側端部１ｂから上流側に向けて８５ｍｍまでの部分に配置されている。したがって、下触媒層２の上流側端部２ａから２０ｍｍまでの部分は、ガス流路１０に露出している。   The upper catalyst layer 3 carries Rh. The length L3 of the upper catalyst layer 3 in the gas flow direction is 85 mm, and is arranged in a portion from the downstream end 1b of the base material 1 to 85 mm toward the upstream side. Accordingly, a portion from the upstream end 2 a of the lower catalyst layer 2 to 20 mm is exposed to the gas flow path 10.

下触媒層２の厚みは１５μｍであり、上触媒層３の厚みは１２μｍである。   The thickness of the lower catalyst layer 2 is 15 μm, and the thickness of the upper catalyst layer 3 is 12 μm.

次に、本例の排ガス浄化用触媒の製造方法について説明する。まず、Ｐｔ担持層形成用の担体としてのＣｅＯ２―ＺｒＯ２―Ｙ２Ｏ３―Ｌａ２Ｏ３複合酸化物粉末（ＣｅＯ２：３０質量％、ＺｒＯ２：６０質量％、Ｙ２Ｏ３：５質量％、Ｌａ２Ｏ３：５質量％）を用意し、貴金属触媒溶液としてのジニトロジアミンＰｔ溶液を含浸した後、蒸発乾固してＰｔを１．４質量％担持したＰｔ／担体粉末を調製した。 Next, a method for producing the exhaust gas purifying catalyst of this example will be described. First, CeO 2 —ZrO 2 —Y 2 O 3 —La 2 O 3 composite oxide powder (CeO 2 : 30% by mass, ZrO 2 : 60% by mass, Y 2 O 3 : as a carrier for forming a Pt support layer: 5 mass%, La 2 O 3 : 5 mass%), impregnated with a dinitrodiamine Pt solution as a noble metal catalyst solution, evaporated to dryness, and Pt / support powder carrying 1.4 mass% of Pt. Prepared.

このＰｔ／担体粉末６０質量部と、Ａｌ２Ｏ３−Ｌａ２Ｏ３複合酸化物（Ａｌ２Ｏ３：９６質量％、Ｌａ２Ｏ３：４質量％）２５重量部と、ＢａＳＯ４を１５重量部バインダとしてのアルミナゾル（Ａｌ２Ｏ３：１０質量％）３重量部（アルミナの絶対量）と、蒸留水とを混合してＰｔ担持層用スラリーを調製した。これにコージェライト製のハニカム基材１（直径１０３ｍｍ、全長１０５ｍｍ）の下流側端部１ｂから上流側へ８５ｍｍの部分までを浸漬し、引き上げて余分なスラリーを吹き払った後、乾燥、焼成してＰｔ担持層２２を形成した。Ｐｔ担持層２２は、ハニカム基材１の１Ｌ当たり１０３ｇ形成され、Ｐｔはハニカム基材１の１Ｌ当たり０．４５ｇ担持されている。 60 parts by mass of this Pt / carrier powder, 25 parts by weight of Al 2 O 3 —La 2 O 3 composite oxide (Al 2 O 3 : 96% by mass, La 2 O 3 : 4% by mass), and 15% of BaSO 4 A slurry for Pt support layer was prepared by mixing 3 parts by weight (absolute amount of alumina) of alumina sol (Al 2 O 3 : 10% by mass) as a part by weight binder and distilled water. The honeycomb base material 1 made of cordierite (diameter: 103 mm, total length: 105 mm) is dipped from the downstream end 1b to the upstream portion of 85 mm, pulled up to blow off excess slurry, and then dried and fired. Thus, the Pt support layer 22 was formed. The Pt support layer 22 is formed in an amount of 103 g per liter of the honeycomb substrate 1, and 0.45 g of Pt is supported per liter of the honeycomb substrate 1.

次に、Ｐｄ担持層形成用の担体として、ＣｅＯ２―ＺｒＯ２―Ｌａ２Ｏ３―Ｐｒ６Ｏ１１複合酸化物粉末（ＣｅＯ２：６０質量％、ＺｒＯ２：４０質量％、Ｌａ２Ｏ３：３質量％、Ｐｒ６Ｏ１１：７質量％）を用意し、貴金属触媒溶液としての硝酸Ｐｄ水溶液を含浸した後、蒸発乾固して、Ｐｄを担持したＰｄ／担体粉末を調製した。 Next, CeO 2 —ZrO 2 —La 2 O 3 —Pr 6 O 11 composite oxide powder (CeO 2 : 60% by mass, ZrO 2 : 40% by mass, La 2 O 3 as a carrier for forming a Pd-supporting layer. : 3% by mass, Pr 6 O 11 : 7% by mass), impregnated with a Pd nitrate aqueous solution as a noble metal catalyst solution, and evaporated to dryness to prepare Pd / carrier powder supporting Pd.

このＰｄ／担体粉末９質量部と、Ａｌ２Ｏ３−Ｌａ２Ｏ３複合酸化物（Ａｌ２Ｏ３：９６質量％、Ｌａ２Ｏ３：４質量％）３重量部と、ＢａＳＯ４を３重量部、バインダとしてのアルミナゾル（Ａｌ２Ｏ３：１０質量％）２重量部（アルミナの絶対量）と、蒸留水とを混合してＰｄ担持層用スラリーを調製した。このＰｄ担持層用スラリーに、上記のＰｔ担持層２２を形成したハニカム基材１の上流側端部１ａから下流側へ２０ｍｍの部分までを漬浸し、引き上げて余分なスラリーを吹き払った後、乾燥、焼成してＰｄ担持層２１を形成した。Ｐｄ担持層２１は、ハニカム基材１の１Ｌ当たり１７ｇ形成され、Ｐｄはハニカム基材１の１Ｌ当たり０．９ｇ担持されている。 9 parts by weight of this Pd / carrier powder, 3 parts by weight of Al 2 O 3 —La 2 O 3 complex oxide (Al 2 O 3 : 96% by weight, La 2 O 3 : 4% by weight), and 3 parts of BaSO 4 2 parts by weight of alumina sol (Al 2 O 3 : 10% by mass) as a binder (absolute amount of alumina) and distilled water were mixed with each other to prepare a slurry for a Pd-supporting layer. In this slurry for Pd carrying layer, the honeycomb substrate 1 on which the above Pt carrying layer 22 is formed is soaked from the upstream end 1a to the downstream part up to 20 mm, and pulled up to blow off excess slurry. The Pd carrying layer 21 was formed by drying and firing. The Pd support layer 21 is formed in an amount of 17 g per liter of the honeycomb substrate 1, and 0.9 g of Pd is supported per liter of the honeycomb substrate 1.

次に、上触媒層形成用の担体として、ＣｅＯ２―ＺｒＯ２―Ｙ２Ｏ３―Ｎｄ２Ｏ３複合酸化物粉末（ＣｅＯ２：２０質量％、ＺｒＯ２：６０質量％、Ｙ２Ｏ３：８質量％、Ｎｄ２Ｏ３：１２質量％）を用意し、貴金属触媒溶液としての硝酸Ｒｈ水溶液を含浸した後、蒸発乾固してＲｈを担持したＲｈ／担体粉末を調製した。 Next, CeO 2 —ZrO 2 —Y 2 O 3 —Nd 2 O 3 composite oxide powder (CeO 2 : 20% by mass, ZrO 2 : 60% by mass, Y 2 O 3 as a carrier for forming the upper catalyst layer) : 8% by mass, Nd 2 O 3 : 12% by mass) were impregnated with an aqueous Rh nitrate solution as a noble metal catalyst solution, and then evaporated to dryness to prepare Rh / carrier powder carrying Rh.

このＲｈ／担体粉末５０質量部と、Ａｌ２Ｏ３−Ｌａ２Ｏ３複合酸化物（Ａｌ２Ｏ３：９６質量％、Ｌａ２Ｏ３：４質量％）２５重量部と、バインダとしてのアルミナゾル（Ａｌ２Ｏ３：１０質量％）３重量部（アルミナの絶対量）と、蒸留水とを混合して上触媒層用スラリーを調製した。この上触媒層用スラリーに、上記のハニカム基材１表面のＰｄ担持層２１及びＰｔ担持層２２の表面の、ハニカム基材１の下流側端部１ｂから上流側へ８５ｍｍの部分までを漬浸し、引き上げて余分なスラリーを吹き払った後、乾燥、焼成して、Ｒｈを担持してなる上触媒層３を形成した。上触媒層３は、ハニカム基材１の１Ｌ当たり７８ｇ形成され、Ｒｈはハニカム基材１の１Ｌ当たり０．１３ｇ担持されている。 50 parts by mass of this Rh / carrier powder, 25 parts by weight of Al 2 O 3 —La 2 O 3 composite oxide (Al 2 O 3 : 96% by mass, La 2 O 3 : 4% by mass), and alumina sol as a binder (Al 2 O 3 : 10 mass%) 3 parts by weight (absolute amount of alumina) and distilled water were mixed to prepare a slurry for the upper catalyst layer. In this upper catalyst layer slurry, the surface of the Pd-supporting layer 21 and the Pt-supporting layer 22 on the surface of the above-mentioned honeycomb substrate 1 is soaked up to 85 mm from the downstream end 1b of the honeycomb substrate 1 to the upstream side. The upper catalyst layer 3 carrying Rh was formed by lifting and blowing off excess slurry, followed by drying and firing. The upper catalyst layer 3 is formed in an amount of 78 g per liter of the honeycomb substrate 1, and Rh is supported by 0.13 g per liter of the honeycomb substrate 1.

（実施例２）
本例においては、上触媒層３が、下触媒層２の下流側端部２ｂから上流側に向けて７５ｍｍの長さまでの部分に形成されている点が、実施例１と相違する。その他は、実施例１と同様である。 (Example 2)
In this example, the upper catalyst layer 3 is different from the first example in that the upper catalyst layer 3 is formed in a portion from the downstream end 2b of the lower catalyst layer 2 to a length of 75 mm toward the upstream side. Others are the same as in the first embodiment.

（実施例３）
本例においては、上触媒層３が、下触媒層２の下流側端部２ｂから上流側に向けて６５ｍｍの長さまでの部分に形成されている点が、実施例１と相違する。その他は、実施例１と同様である。 (Example 3)
In this example, the upper catalyst layer 3 is different from the first example in that the upper catalyst layer 3 is formed in a portion from the downstream end 2b of the lower catalyst layer 2 to a length of 65 mm toward the upstream side. Others are the same as in the first embodiment.

（実施例４）
本例においては、図５に示すように、上触媒層３が、下触媒層２の下流側端部２ｂから上流側に向けて５５ｍｍの長さまでの部分に形成されている点が、実施例１と相違する。その他は、実施例１と同様である。 Example 4
In this example, as shown in FIG. 5, the upper catalyst layer 3 is formed in a portion from the downstream end portion 2b of the lower catalyst layer 2 to a length of 55 mm toward the upstream side. 1 and different. Others are the same as in the first embodiment.

（実施例５）
本例においては、上触媒層３が、下触媒層２の下流側端部２ｂから上流側に向けて９５ｍｍの長さまでの部分に形成されている点が、実施例１と相違する。その他は、実施例１と同様である。 (Example 5)
In this example, the upper catalyst layer 3 is different from the first example in that the upper catalyst layer 3 is formed in a portion from the downstream end 2b of the lower catalyst layer 2 to a length of 95 mm toward the upstream side. Others are the same as in the first embodiment.

（比較例１）
本比較例においては、図６に示すように、上触媒層３が、下触媒層２の下流側端部２ｂから上流側に向けて１０５ｍｍの長さの部分に形成されている。即ち、上触媒層３は、下触媒層２の全体を被覆している。 (Comparative Example 1)
In this comparative example, as shown in FIG. 6, the upper catalyst layer 3 is formed in a portion having a length of 105 mm from the downstream end 2b of the lower catalyst layer 2 toward the upstream side. That is, the upper catalyst layer 3 covers the entire lower catalyst layer 2.

＜実験＞
前記実施例１〜５及び比較例１の触媒をＶ型８気筒４．３Ｌエンジンの排気系にそれぞれ装着し、ガソリンを用いて、定常条件、Ａ／Ｆ（空燃比）＝１４．０とＡ／Ｆ＝１５．０との間を１Ｈｚで振動させ、触媒の中心温度１０００℃の条件にて、５０時間の耐久試験を施した。 <Experiment>
The catalysts of Examples 1 to 5 and Comparative Example 1 were respectively mounted on the exhaust system of a V-type 8-cylinder 4.3L engine, and gasoline was used under steady conditions, A / F (air-fuel ratio) = 14.0 and A An endurance test of 50 hours was performed under the condition that the center temperature of the catalyst was 1000 ° C. while vibrating at 1 Hz between /F=15.0.

直列４気筒の２．４Ｌエンジンの排気系に耐久試験後の各触媒をそれぞれ搭載し、触媒入りガス温度が５５０℃になるまで理論空燃比（Ａ／Ｆ＝１４．２）で燃焼させ、その間に排出されたＮＯｘ量及びＨＣ量を測定した。測定結果を図７に示した。図７には、上触媒層の長さの短い順に測定結果を配列させた。図７の中、Ｅ１〜Ｅ５及びＣ１は、実施例１〜５及び比較例１を示す。   The exhaust system of the in-line 4-cylinder 2.4L engine is loaded with each of the catalysts after the endurance test and burned at the stoichiometric air-fuel ratio (A / F = 14.2) until the temperature of the gas containing the catalyst reaches 550 ° C. The amount of NOx and the amount of HC discharged were measured. The measurement results are shown in FIG. In FIG. 7, the measurement results are arranged in ascending order of the length of the upper catalyst layer. In FIG. 7, E1 to E5 and C1 indicate Examples 1 to 5 and Comparative Example 1.

図７より、上触媒層の長さを長くするほど、触媒のＨＣ排出量が増加し、一方でＮＯｘ排出量が減少した。このことから、上触媒層の長さを長くするほど、上触媒層に担持されているＲｈのＮＯｘ還元浄化活性が高くなることがわかる。これは、上触媒層の長さが長いほど、排ガスの上触媒層に対する空間速度（ＳＶ）が小さくなるため、排ガスの上触媒層へのガス拡散性が高くなるからであると考えられる。また、上触媒層の長さが長いほど、下触媒層が上触媒層に被覆される長さが長くなり、下触媒層へのガス拡散性が低く、下触媒層に担持されているＰｔ及びＰｄのＨＣ酸化浄化活性が低くなることがわかる。   From FIG. 7, as the length of the upper catalyst layer was increased, the HC emission amount of the catalyst increased, while the NOx emission amount decreased. From this, it can be seen that the longer the length of the upper catalyst layer, the higher the NOx reduction purification activity of Rh supported on the upper catalyst layer. This is presumably because the longer the upper catalyst layer, the smaller the space velocity (SV) with respect to the upper catalyst layer of the exhaust gas, and the higher the gas diffusibility to the upper catalyst layer of the exhaust gas. Further, as the length of the upper catalyst layer is longer, the length of the lower catalyst layer covered by the upper catalyst layer is longer, the gas diffusibility to the lower catalyst layer is lower, and Pt and It can be seen that the HC oxidation purification activity of Pd decreases.

逆に、上触媒層の長さが短いほど、下触媒層に担持されているＰｔ及びＰｄのＨＣ酸化浄化活性が低くなった。これは、上触媒層の長さが短いほど、下触媒層の露出量が増えて、排ガス中のＨＣの燃焼活性が高いＰｔへのガス拡散性が大きくなるためであると考えられる。   Conversely, the shorter the length of the upper catalyst layer, the lower the HC oxidation purification activity of Pt and Pd supported on the lower catalyst layer. This is presumably because the shorter the upper catalyst layer, the more the lower catalyst layer is exposed and the greater the gas diffusivity to Pt, which has a higher combustion activity of HC in the exhaust gas.

また、上触媒層の長さが８０ｍｍ、即ち下触媒層の長さに対する上触媒層の長さが７６％で、ＨＣ排出量及びＮＯｘ排出量の双方が低くなった。このことから、上触媒層の長さが、５０〜９０％であり、望ましくは６０〜８５％の場合に、ＨＣ及びＮＯｘの浄化活性をバランスよく発揮させることができることがわかる。   Further, the length of the upper catalyst layer was 80 mm, that is, the length of the upper catalyst layer was 76% relative to the length of the lower catalyst layer, and both the HC emission amount and the NOx emission amount were low. From this, it can be seen that when the length of the upper catalyst layer is 50 to 90%, preferably 60 to 85%, the purification activity of HC and NOx can be exhibited in a balanced manner.

一方、比較例では、下触媒層の長さに対する上触媒層の長さの比率が１００％であり、ＨＣ排出量は最も多くなったが、ＮＯｘ排出量は最も低くなった。このことから、上触媒層のＲｈによるＮＯｘ浄化活性は高くなったが、下触媒層のＰｔ及びＰｄによるＨＣ浄化活性が低く抑えられたことがわかる。   On the other hand, in the comparative example, the ratio of the length of the upper catalyst layer to the length of the lower catalyst layer was 100%, and the HC emission amount was the largest, but the NOx emission amount was the lowest. From this, it can be seen that the NOx purification activity due to Rh in the upper catalyst layer has increased, but the HC purification activity due to Pt and Pd in the lower catalyst layer has been kept low.

実施例１の排ガス浄化用触媒のガス流れ方向の断面図である。2 is a cross-sectional view in the gas flow direction of the exhaust gas purifying catalyst of Example 1. FIG. 実施例１の排ガス浄化用触媒の斜視図である。1 is a perspective view of an exhaust gas purification catalyst of Example 1. FIG. 図２のＡ−Ａ矢視線断面図である。FIG. 3 is a cross-sectional view taken along line AA in FIG. 2. 図２のＢ−Ｂ矢視線断面図である。It is a BB arrow line sectional view of Drawing 2. 実施例２の排ガス浄化用触媒のガス流れ方向の断面図である。6 is a cross-sectional view in the gas flow direction of an exhaust gas purifying catalyst of Example 2. FIG. 比較例１の排ガス浄化用触媒のガス流れ方向の断面図である。2 is a cross-sectional view in the gas flow direction of an exhaust gas purification catalyst of Comparative Example 1. FIG. 上触媒層の長さとＨＣ排出量及びＮＯｘ排出量との関係を示す線図である。It is a diagram which shows the relationship between the length of an upper catalyst layer, HC discharge | emission amount, and NOx discharge | emission amount.

符号の説明Explanation of symbols

１：ハニカム基材、２：下触媒層、３：上触媒層、１０：ガス流路、２１：Ｐｄ担持層、２２：Ｐｔ担持層。 1: honeycomb substrate, 2: lower catalyst layer, 3: upper catalyst layer, 10: gas flow path, 21: Pd carrying layer, 22: Pt carrying layer.

Claims (4)

排ガスが流通するガス流路を有する基材と、該基材の表面に形成された下触媒層と、該下触媒層の表面に形成された上触媒層と、を有する排ガス浄化用触媒において、
前記上触媒層は、Ｒｈを担持してなり、前記下触媒層は、Ｐｄ又は／及びＰｔを担持してなり、
前記上触媒層の前記ガス流路に沿ったガス流れ方向の長さは、前記下触媒層の前記ガス流れ方向の長さよりも短いことを特徴とする排ガス浄化用触媒。 In an exhaust gas purifying catalyst having a base material having a gas flow path through which exhaust gas flows, a lower catalyst layer formed on the surface of the base material, and an upper catalyst layer formed on the surface of the lower catalyst layer,
The upper catalyst layer carries Rh, and the lower catalyst layer carries Pd or / and Pt,
The exhaust gas purifying catalyst, wherein a length of the upper catalyst layer in the gas flow direction along the gas flow path is shorter than a length of the lower catalyst layer in the gas flow direction. 前記下触媒層の前記ガス流れ方向の長さに対する前記上触媒層の前記ガス流れ方向の長さの比率は５０〜９０％であることを特徴とする請求項１記載の排ガス浄化用触媒。   The exhaust gas purifying catalyst according to claim 1, wherein a ratio of a length of the upper catalyst layer in the gas flow direction to a length of the lower catalyst layer in the gas flow direction is 50 to 90%. 前記上触媒層は、前記下触媒層の前記ガス流れ方向の下流側端部を含む部分の表面に配設されていることを特徴とする請求項１又は請求項２に記載の排ガス浄化用触媒。   3. The exhaust gas purifying catalyst according to claim 1, wherein the upper catalyst layer is disposed on a surface of a portion including a downstream end portion of the lower catalyst layer in the gas flow direction. . 前記下触媒層は、前記ガス流れ方向の上流側でＰｄを担持してなるＰｄ担持層と、前記Ｐｄ担持層よりも前記ガス流れ方向の下流側でＰｔを担持してなるＰｔ担持層とからなることを特徴とする請求項１乃至請求項３のいずれか１項に記載の排ガス浄化用触媒。   The lower catalyst layer includes a Pd carrying layer carrying Pd on the upstream side in the gas flow direction, and a Pt carrying layer carrying Pt on the downstream side in the gas flow direction from the Pd carrying layer. The exhaust gas-purifying catalyst according to any one of claims 1 to 3, wherein
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