JP4751917B2 - Exhaust gas purification catalyst - Google Patents
Exhaust gas purification catalyst Download PDFInfo
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- JP4751917B2 JP4751917B2 JP2008170808A JP2008170808A JP4751917B2 JP 4751917 B2 JP4751917 B2 JP 4751917B2 JP 2008170808 A JP2008170808 A JP 2008170808A JP 2008170808 A JP2008170808 A JP 2008170808A JP 4751917 B2 JP4751917 B2 JP 4751917B2
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- 238000000746 purification Methods 0.000 title claims description 31
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- 239000000463 material Substances 0.000 claims description 23
- 239000002356 single layer Substances 0.000 claims description 3
- 239000007789 gas Substances 0.000 description 82
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Substances [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 60
- KDLHZDBZIXYQEI-UHFFFAOYSA-N palladium Substances [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 57
- 239000010948 rhodium Substances 0.000 description 40
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- 229910052760 oxygen Inorganic materials 0.000 description 11
- 229910021193 La 2 O 3 Inorganic materials 0.000 description 10
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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 3
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- PLDDOISOJJCEMH-UHFFFAOYSA-N neodymium oxide Inorganic materials [O-2].[O-2].[O-2].[Nd+3].[Nd+3] PLDDOISOJJCEMH-UHFFFAOYSA-N 0.000 description 1
- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 description 1
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- B01D53/34—Chemical or biological purification of waste gases
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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 near 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
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
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。
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く、前記下触媒層は、少なくとも前記ガス流れ方向の前記基材の上流側端部に、Pdを担持してなるPd担持層をもち、前記基材の前記上流側端部を含む上流側部分では、前記下触媒層の前記Pd担持層のみの単層が配設されていることを特徴とする。
In order to solve the above problems, the invention according to
請求項2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
請求項3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71%以下であることを特徴とすることを特徴とする。
The invention according to
請求項4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。
請求項5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。
The invention according to claim 4 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% .
In the invention according to claim 5, 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、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 second 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3に係る発明によれば、HC浄化特性が更に向上する(図7参照)。 According to the third aspect of the present invention, the HC purification characteristics are further improved (see FIG. 7) .
前記請求項4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 fourth 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5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 fifth aspect of the present invention, the lower catalyst layer is composed of 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 and ceramics such as SiC, or metal materials 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 disposed 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 contained in the slurry containing the Pd support layer carrier powder when 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, 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
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
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
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
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
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
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
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
(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。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、71%である。その他は、実施例1と同様である。
(Example 2)
In this example, the
(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
(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
(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
(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
<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。 Each exhausted catalyst is installed in the exhaust system of an inline 4-cylinder 2.4L engine 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% with respect 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 highest, 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.
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 (5)
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く、
前記下触媒層は、少なくとも前記ガス流れ方向の前記基材の上流側端部に、Pdを担持してなるPd担持層をもち、
前記基材の前記上流側端部を含む上流側部分では、前記下触媒層の前記Pd担持層のみの単層が配設されている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,
Length of the gas flow direction along said gas flow path of the upper catalyst layer, rather short than the gas flow direction length of the lower catalyst layer,
The lower catalyst layer has a Pd-supporting layer formed by supporting Pd at least at the upstream end of the base material in the gas flow direction,
An exhaust gas purifying catalyst , wherein a single layer of only the Pd-supporting layer of the lower catalyst layer is disposed in an upstream portion including the upstream end portion of the base material .
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