JP5376919B2 - Exhaust gas purification catalyst - Google Patents
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本発明は、各貫通孔を通過する排ガスの流圧を調節することで触媒担持層に担持された貴金属をより効率よく活用しうる排ガス浄化触媒、に関する。 The present invention relates to an exhaust gas purification catalyst capable of more efficiently utilizing a noble metal supported on a catalyst support layer by adjusting the flow pressure of exhaust gas passing through each through hole.
従来より、触媒貴金属として排ガス浄化用触媒に使用される白金、ロジウム、パラジウムなどは埋蔵量が少なく高価であったが、近年発展途上国等での需要が急増しており、他の資源と同様にこれらの価格も高騰している。一方、近年の環境意識の高まりから各国の排ガス規制は年々強化される傾向にあり、排ガス浄化用触媒の排ガス浄化性能に対する要求も厳しさを増している。 Conventionally, platinum, rhodium, palladium, etc. used as catalysts for exhaust gas purification as catalyst precious metals have been low in reserves and expensive, but demand in developing countries has increased rapidly in recent years, and as with other resources These prices are also rising. On the other hand, exhaust gas regulations in each country tend to be strengthened year by year due to the recent increase in environmental awareness, and the demand for exhaust gas purification performance of exhaust gas purification catalysts is also becoming stricter.
かかる理由より、少ない貴金属量でより優れた排ガス浄化性能を発揮しうる触媒の開発が求められている。例えば、特開２００６−１８１４８７号公報では、担体表面にバリア層を設け、当該バリア層に固定層を介して貴金属粒子を配置することで、貴金属の使用を抑え、触媒活性を高めた触媒が提案されている。 For this reason, development of a catalyst capable of exhibiting better exhaust gas purification performance with a small amount of noble metal has been demanded. For example, Japanese Patent Application Laid-Open No. 2006-181487 proposes a catalyst in which a barrier layer is provided on the surface of a carrier and noble metal particles are arranged on the barrier layer via a fixed layer, thereby suppressing the use of the noble metal and increasing the catalytic activity. Has been.
本願発明は、上記事情を鑑みてなされたものであり、少ない貴金属量で従来よりも優れた排ガス浄化性能を発揮しうる触媒構成を有する排ガス浄化触媒を提供することにある。 This invention is made | formed in view of the said situation, and it is providing the exhaust gas purification catalyst which has a catalyst structure which can exhibit the exhaust gas purification performance superior to the past with little noble metal amount.
排ガス浄化用触媒は、排ガスとの接触面積が大きいこと、圧力圧損が小さいことなどが要求されるため、排ガス流れに対し垂直の断面が多数の貫通孔から成る担体基材を用いて構成されるのが一般的である。 The exhaust gas purification catalyst is required to have a large contact area with the exhaust gas and a small pressure pressure loss. Therefore, the exhaust gas purification catalyst is configured by using a carrier base material having a plurality of through-holes perpendicular to the exhaust gas flow. It is common.
このような排ガス浄化用触媒の担体基材は、多数の貫通孔を有する形状となるようにコージェライトなどの耐熱性セラミックスを成形することで調整することができる。あるいは、金属箔からなる波板と平板を重ねてロール状に巻き回すことで多数の貫通孔を有する形状に成形することができる（以下、本明細書においては、便宜的にかかる多数の貫通孔を有する担体基材を「ハニカム構造体」と総称する）。一般的な排ガス浄化用触媒は、このような担体基材上に触媒貴金属等をコーティングするための触媒担持層が配置されている。 The carrier substrate of such an exhaust gas purifying catalyst can be adjusted by molding heat-resistant ceramics such as cordierite so as to have a shape having a large number of through holes. Alternatively, it can be formed into a shape having a large number of through-holes by overlapping a corrugated sheet and a flat plate made of metal foil in a roll shape (hereinafter referred to as a large number of through-holes for convenience in this specification). The carrier base material having the above is generically called “honeycomb structure”). In a general exhaust gas purifying catalyst, a catalyst support layer for coating a catalyst noble metal or the like is disposed on such a carrier substrate.
触媒担持層は、ウォッシュコート法又はゾル−ゲル法によりアルミナ等を含むスラリーで基材をコーティングすることにより形成するのが一般的であり、この場合、触媒担持層は存在する貫通孔の内壁全面に形成され、その厚みは通常均一なものとなる。換言すると、従来技術におけるハニカム構造体内の各貫通孔は、ほぼ均一の開口面積を有している。 The catalyst support layer is generally formed by coating the base material with a slurry containing alumina or the like by a wash coat method or a sol-gel method. In this case, the catalyst support layer is formed on the entire inner wall of the through hole in which the catalyst support layer exists. The thickness is usually uniform. In other words, each through hole in the honeycomb structure in the prior art has a substantially uniform opening area.
一般的なコーティング法により形成された触媒担持層を有する担体基材内を通過する排ガスの流れについて本発明者が調査したところ、排ガスは、ハニカム構造体内を均一に流れるのではなく、特定の部分を中心に流れていることが分かった。ここで、一般的なコーティング方法に拠った場合、通過する排ガスの流圧の如何に関わらず、触媒担持層上には触媒金属がほぼ均一に担持されており、その結果、排ガスの流圧が低い貫通孔上に存在する貴金属は、流圧が高い部分と比べ、有効活用されていないと考えられる。しかし、排ガスの流圧が高い部分に集中的に貴金属を担持させると、その部分で貴金属の密度が高まり、シンタリングなどが生じ易くなり、その結果浄化性能が低下することが考えられる。 When the present inventor investigated the flow of exhaust gas passing through a carrier substrate having a catalyst support layer formed by a general coating method, the exhaust gas does not flow uniformly in the honeycomb structure, but a specific portion. It turned out that it is flowing around. Here, when a general coating method is used, the catalyst metal is supported almost uniformly on the catalyst support layer regardless of the flow pressure of the exhaust gas passing through. As a result, the flow pressure of the exhaust gas is reduced. It is considered that the noble metal existing on the low through-hole is not effectively utilized compared with the portion where the fluid pressure is high. However, if the noble metal is intensively supported on the portion where the exhaust gas flow pressure is high, the density of the noble metal is increased in the portion, and sintering or the like is likely to occur, resulting in a decrease in purification performance.
そこで、本発明者らは、触媒貴金属の中でも、通過する排ガスの流圧が低い貫通孔の内壁を構成する触媒担持層に担持されている触媒貴金属の利用効率を高めることで、上記課題を解決できると考え、本発明を完成するに至った。 Therefore, the present inventors have solved the above problem by increasing the utilization efficiency of the catalyst noble metal supported on the catalyst support layer constituting the inner wall of the through hole in which the flow pressure of the exhaust gas passing therethrough is low among the catalyst noble metals. The present invention has been completed.
即ち、本発明は、以下の発明を包含する。
［１］排ガスの流れ方向に対し複数の貫通孔を有する担体基材と、当貫通孔の内壁面に形成された１又は複数の触媒担持層と、当該触媒担持層に担持された貴金属と、を有する排ガス浄化触媒であって、
通過する排ガスの流圧が全貫通孔間で均一となるように触媒担持層の厚みが調節されている、排ガス浄化用触媒。
［２］全貫通孔のうち、通過する排ガスの流圧が相対的に高い貫通孔の内壁部を構成している触媒担持層の厚みを前記流圧に応じて増大させるか、そして／あるいは
全貫通孔のうち、通過する排ガスの流圧が相対的に低い貫通孔の内壁部を構成している触媒担持層の厚みを前記流圧に応じて減少させることにより、前記触媒担持層の厚みの調節が行われる、［１］の排ガス浄化用触媒。
［３］排ガス流れ方向から見て中央部に位置する貫通孔の開口面積が、その外側に位置する貫通孔の開口面積よりも小さい、［１］又は［２］の排ガス浄化用触媒。
［４］貫通孔の開口面積が、排ガス流れ方向から見て、外側から中央部にかけて段階的に減少している、［１］〜［３］のいずれかの排ガス浄化用触媒。
［５］前記触媒の軸方向から見て下流部に位置する貫通孔の開口面積が、上流部に位置する貫通孔の開口面積よりも大きい、［１］〜［４］の排ガス浄化用触媒。
［６］前記複数の触媒担持層のうち最上層にのみ前記貴金属が担持されており、当該最上層以外の層の厚みを増減することにより触媒担持層の厚みが調節されている、［１］〜［５］の排ガス浄化用触媒。
That is, the present invention includes the following inventions.
[1] A carrier base material having a plurality of through holes in the exhaust gas flow direction, one or more catalyst support layers formed on the inner wall surface of the through holes, a noble metal supported on the catalyst support layers, An exhaust gas purification catalyst having
An exhaust gas purifying catalyst in which the thickness of the catalyst support layer is adjusted so that the flow pressure of the exhaust gas passing therethrough is uniform among all through holes.
[2] Among all the through holes, the thickness of the catalyst support layer constituting the inner wall portion of the through hole in which the flow pressure of the exhaust gas passing therethrough is relatively high is increased according to the flow pressure and / or By reducing the thickness of the catalyst supporting layer constituting the inner wall portion of the through hole in which the flow pressure of the exhaust gas passing therethrough is relatively low among the through holes, the thickness of the catalyst supporting layer is reduced. The exhaust gas purifying catalyst according to [1], wherein adjustment is performed.
[3] The exhaust gas purifying catalyst according to [1] or [2], wherein an opening area of a through hole located in a central portion when viewed from an exhaust gas flow direction is smaller than an opening area of a through hole located outside the through hole.
[4] The exhaust gas purifying catalyst according to any one of [1] to [3], wherein the opening area of the through hole is reduced stepwise from the outside to the center as viewed from the exhaust gas flow direction.
[5] The exhaust gas purifying catalyst according to [1] to [4], wherein an opening area of the through hole located in the downstream portion when viewed from the axial direction of the catalyst is larger than an opening area of the through hole located in the upstream portion.
[6] The noble metal is supported only on the uppermost layer among the plurality of catalyst supporting layers, and the thickness of the catalyst supporting layer is adjusted by increasing or decreasing the thickness of the layers other than the uppermost layer. [1] The catalyst for exhaust gas purification of [5].
本発明によれば、全貫通孔のうち、通過する排ガスの流圧が相対的に高い貫通孔の内壁部を構成している１又は複数の触媒担持層の厚みを前記流圧の高さに応じて増大することで、通過する排ガスの流圧が全体的に均一となる。その結果、排ガスが全ての貫通孔の隅々にまで行きわたり、触媒担持層に担持された貴金属が最大限有効活用され、最終的に排ガス浄化性能が向上することとなる。 According to the present invention, among all the through holes, the thickness of the one or more catalyst support layers constituting the inner wall portion of the through hole in which the flow pressure of the exhaust gas passing therethrough is relatively high is set to the height of the flow pressure. By increasing accordingly, the flow pressure of the exhaust gas passing therethrough becomes uniform as a whole. As a result, exhaust gas reaches every corner of all through holes, the noble metal supported on the catalyst support layer is utilized to the maximum extent, and exhaust gas purification performance is finally improved.
尚、触媒担持層の厚みを増減させる方法のほか、ハニカム構造体を調製する段階でその格子自体の大きさを所望のサイズに調節することも考えられる。しかしながら、メタルハニカムを例に説明すると、メタルハニカム構造体は上述のように通常金属箔からなる波板と平板を重ねてロール状に巻き回すことで製造されるため、形成される貫通孔はほぼ一定の径を有することとなり、本発明のように流圧に応じて貫通孔の径を変化させる場合、複雑な製法が要求される。また、仮に可能だとしてもコスト面で問題がある。 In addition to the method of increasing / decreasing the thickness of the catalyst support layer, it is conceivable to adjust the size of the lattice itself to a desired size at the stage of preparing the honeycomb structure. However, taking a metal honeycomb as an example, a metal honeycomb structure is usually manufactured by winding a corrugated sheet and a flat plate made of metal foil in a roll shape as described above. When the diameter of the through hole is changed according to the flow pressure as in the present invention, a complicated manufacturing method is required. Even if it is possible, there is a problem in cost.
本発明の排ガス浄化触媒は、排ガスの流れ方向に対し複数の貫通孔を有する担体基材と、当貫通孔の内壁面に形成された１又は複数の触媒担持層と、当該触媒担持層に担持された貴金属と、を有する排ガス浄化触媒であって、通過する排ガスの流圧が全貫通孔間で均一となるように触媒担持層の厚みが調節されていること、を特徴とする。 The exhaust gas purifying catalyst of the present invention includes a carrier base material having a plurality of through holes in the exhaust gas flow direction, one or more catalyst support layers formed on the inner wall surface of the through holes, and supported on the catalyst support layer. An exhaust gas purifying catalyst comprising a noble metal, wherein the thickness of the catalyst support layer is adjusted so that the flow pressure of the exhaust gas passing therethrough is uniform between all through holes.
本発明で使用する担体基材には、当業界で一般的に使用されているハニカム担体基材等の、多数の貫通孔を有する担体基材を使用することができ、セラミックス製のものでも金属製のものでもよい。限定しないが、担体基材に使用可能なセラミックスとして、アルミナ、シリカ、コージェライト、ジルコニア、シリカ−アルミナ、アルミナ−ジルコニア、アルミナ−チタニア、シリカ−チタニア、シリカ−ジルコニア、チタニア−ジルコニア、ムライト等が挙げられる。 As the carrier substrate used in the present invention, a carrier substrate having a large number of through-holes such as a honeycomb carrier substrate generally used in the industry can be used. It may be made of. Although not limited, ceramics that can be used for the carrier substrate include alumina, silica, cordierite, zirconia, silica-alumina, alumina-zirconia, alumina-titania, silica-titania, silica-zirconia, titania-zirconia, mullite, and the like. Can be mentioned.
いわゆるメタルハニカム体についても、従来のものを利用することができる。ここで、メタルハニカム体は上述の通り金属製の平箔及び波箔を用いて構成される。当該メタルハニカム体を構成する金属箔の性質は、熱容量が低く、且つ耐熱性、耐圧性等に優れているものが好ましい。従って、ステンレス鋼、耐熱鋼等が好ましいが、これらの材料に限定されない。ステンレス鋼の例としては、フェライト系ステンレス、オーステナイト系ステンレス等の鋼材があり、本発明においてはこれらを箔状に圧延して用いることができる。 Conventional so-called metal honeycomb bodies can also be used. Here, as described above, the metal honeycomb body is configured using a metal flat foil and corrugated foil. The metal foil constituting the metal honeycomb body preferably has a low heat capacity and excellent heat resistance, pressure resistance, and the like. Accordingly, stainless steel, heat resistant steel, and the like are preferable, but are not limited to these materials. Examples of stainless steel include steel materials such as ferritic stainless steel and austenitic stainless steel. In the present invention, these can be rolled into a foil shape and used.
前記担体基材は、排ガス流れ方向から見て、多数の貫通孔を有している。これらの貫通孔の内壁には、触媒担持層が形成される。触媒担持層は、アルミナ等のセラミックスを含むスラリーを調製し、担体基材の貫通孔の内壁に付着させた後に乾燥し焼成することで形成することができる（ウォッシュコート法）。当該方法で使用するセラミックスとしては、アルミナ、シリカ、コージェライト、ジルコニア、シリカ−アルミナ、アルミナ−ジルコニア、アルミナ−チタニア、シリカ−チタニア、シリカ−ジルコニア、チタニア−ジルコニア、ムライト、等が挙げられるスラリーに予め触媒貴金属を含めることもできるが、コスト及び触媒性能の観点からは、触媒貴金属を含まないスラリーを用いて触媒担持層の厚みを調節することが好ましい。 The carrier substrate has a large number of through-holes when viewed from the exhaust gas flow direction. A catalyst support layer is formed on the inner walls of these through holes. The catalyst-carrying layer can be formed by preparing a slurry containing ceramics such as alumina, adhering it to the inner wall of the through hole of the support substrate, and drying and firing (wash coat method). Examples of ceramics used in the method include slurries including alumina, silica, cordierite, zirconia, silica-alumina, alumina-zirconia, alumina-titania, silica-titania, silica-zirconia, titania-zirconia, mullite, and the like. Although a catalyst noble metal can be included in advance, it is preferable to adjust the thickness of the catalyst support layer using a slurry containing no catalyst noble metal from the viewpoint of cost and catalyst performance.
複数の触媒担持層を設ける場合、排ガスの流圧が相対的に多い貫通孔における触媒担持層に、貴金属を含まない層（以下、「貴金属非含有層」と称する）を配置し、その厚みを調整することによっても前記流圧を均一化することができる。当該貴金属非含有層は、触媒貴金属を含まない、アルミナ等の一般的なスラリーのみを使用することで調製することができる。従って、貴金属非含有層を配置した場合、従来のものと比較して低廉な手段で排ガス浄化性能の向上を達成することが可能である。 When providing a plurality of catalyst-carrying layers, a layer not containing a noble metal (hereinafter referred to as a “noble metal-free layer”) is disposed in the catalyst-carrying layer in the through hole where the flow pressure of the exhaust gas is relatively large, The flow pressure can be made uniform also by adjusting. The noble metal-free layer can be prepared by using only a general slurry such as alumina that does not contain a catalyst noble metal. Therefore, when the noble metal non-containing layer is arranged, it is possible to achieve an improvement in the exhaust gas purification performance by a cheaper means compared to the conventional one.
本発明においては、全貫通孔のうち、通過する排ガスの流圧が相対的に高い貫通孔の内壁部を構成している触媒担持層の厚みが前記流圧の高さに応じて増大される。あるいは、通過する排ガスの流圧が相対的に低い貫通孔の内壁部を構成している触媒担持層の厚みを前記流圧に応じて減少させてもよい。 In the present invention, among all the through holes, the thickness of the catalyst supporting layer constituting the inner wall portion of the through hole in which the flow pressure of the exhaust gas passing therethrough is relatively high is increased according to the height of the flow pressure. . Or you may reduce the thickness of the catalyst support layer which comprises the inner wall part of the through-hole in which the flow pressure of the exhaust gas which passes is relatively low according to the said flow pressure.
排ガスの流圧は、限定しないが、一般的な流圧計を用いて決定することができる。「相対的に」と記載したとおり、触媒担持層の厚みの増減は、各貫通孔間の排ガスの流圧を比較検討し、通過する排ガスの流圧が低いために触媒貴金属の機能が十分に発揮されないと予測される、一定の領域内の貫通孔の触媒担持層の厚みを減少することで行われる。また、流圧が高い一定の領域内の貫通孔は、その触媒担持層の厚みを減少してもよい。このように触媒担持層の厚みを、排ガスの流圧に応じて一定領域毎に調節することで、通過する排ガスの流圧の均一化、延いては触媒性能の向上を達成することができる。 The flow pressure of the exhaust gas is not limited, but can be determined using a general flow pressure gauge. As described as “relatively”, the increase or decrease in the thickness of the catalyst support layer is a comparison of the exhaust gas flow pressure between the through-holes. This is done by reducing the thickness of the catalyst-carrying layer of the through-holes in a certain region that is predicted not to be exhibited. Moreover, the through-hole in a fixed area | region with a high fluid pressure may reduce the thickness of the catalyst support layer. In this way, by adjusting the thickness of the catalyst support layer for each predetermined region according to the flow pressure of the exhaust gas, it is possible to achieve a uniform flow pressure of the exhaust gas that passes through, and thus improve the catalyst performance.
本発明の触媒を搭載する実機によって異なるが、概して、排ガスは、排ガス流れ方向から見て担体基材の中央部において流圧が高いことから、当該中央部の触媒担持層の厚みを増大させることが好ましい。また、触媒の軸方向長さにおける上流部も排ガスの流圧が高いことが多いため、当該上流部の触媒担持層の厚みを増大させるのも好ましい。 Although it differs depending on the actual machine on which the catalyst of the present invention is mounted, in general, the exhaust gas has a high fluid pressure at the center portion of the carrier base material when viewed from the exhaust gas flow direction, so that the thickness of the catalyst support layer at the center portion is increased. Is preferred. Further, since the upstream portion of the catalyst in the axial length often has a high exhaust gas flow pressure, it is also preferable to increase the thickness of the catalyst support layer in the upstream portion.
触媒担持層の厚さは、排ガス流れ方向から見て、中央部から外周部にかけて、あるいは上流部から下流部にかけて段階的に変化させてもよい。触媒担持層の厚さは複数段階、例えば２〜３段階変化されることがある。しかしながら、多数回コーティングを繰り返して厚みを調節することはコストの観点からは好ましくないため、２段階程度変化させるのが望ましい。 The thickness of the catalyst support layer may be changed stepwise from the center to the outer periphery or from the upstream to the downstream as viewed from the exhaust gas flow direction. The thickness of the catalyst support layer may be changed in a plurality of steps, for example, 2 to 3 steps. However, since it is not preferable from the viewpoint of cost to adjust the thickness by repeating coating many times, it is preferable to change the thickness by about two steps.
本発明の触媒と実際に搭載する車両等の状況によって異なるが、以下の実施例２に示すように、排ガス流れ方向から見て中央部に位置し、且つ触媒の軸方向長さにおける上流部に位置する触媒担持層の厚みを増大させるのが好ましい（図２を参照のこと）。 Although it differs depending on the situation of the catalyst of the present invention and the vehicle actually mounted, as shown in Example 2 below, it is located in the center portion when viewed from the exhaust gas flow direction and in the upstream portion in the axial length of the catalyst. It is preferred to increase the thickness of the catalyst support layer located (see FIG. 2).
触媒担持層の厚さの調節は、上記スラリーの成分、濃度、又はコーティングの回数を変更することで実施可能である。その結果、形成される貫通孔の内径、ひいては貫通孔の開口面積も調節されうる。材料コストの観点からは、貴金属非含有層の厚みを調節するのが好ましい。貫通孔の開口面積の減少は、コーティング前の貫通孔の開口面積に対するコーティング後の開口面積の比率（開口率）により相対的に評価することもできる。 The thickness of the catalyst support layer can be adjusted by changing the composition, concentration, or number of coatings of the slurry. As a result, the inner diameter of the formed through hole, and thus the opening area of the through hole can be adjusted. From the viewpoint of material cost, it is preferable to adjust the thickness of the noble metal-free layer. The decrease in the opening area of the through hole can be relatively evaluated by the ratio (opening ratio) of the opening area after coating to the opening area of the through hole before coating.
触媒担持層の厚さの調節は、限定しないが、以下のように実施することができる。例えば、排ガス流れ方向から見て、特定の貫通孔、例えば担体基材の中央部に存在する貫通孔の内壁を構成する触媒担持層の厚みを調節する場合、アルミナ等のスラリーを担体基材の入りガス側から全貫通孔に流して乾燥・焼成させ、任意に厚みを増したい所定の貫通孔にのみ再度スラリーを流して乾燥・焼成を行うことで、所望の厚みを有する触媒担持層が形成されうる。 Although adjustment of the thickness of a catalyst carrying layer is not limited, it can be implemented as follows. For example, when adjusting the thickness of a catalyst support layer that constitutes the inner wall of a specific through hole, for example, the through hole existing in the center of the support substrate, as viewed from the exhaust gas flow direction, a slurry such as alumina is added to the support substrate. A catalyst-carrying layer with a desired thickness is formed by flowing the slurry through all the through holes from the inlet gas side, drying and firing, and then allowing the slurry to flow again only through the predetermined through holes where the thickness is to be increased. Can be done.
一方、貫通孔のうち、入りガス側から担体基材の軸方向長さの特定の部分までをコーティングする場合、セラミックスの濃度を高めてスラリーの粘度を増大させるとともに、所定の範囲のみをコーティングするのに十分な量のスラリーを準備する。ハニカム形状の断面が地面に対し平行となり、且つ入りガス側が上となるように基材を据えた後、前記高粘度スラリーを入りガス側から所定の貫通孔に流すことで、所定の範囲にある貫通孔の内壁のみがコーティングされ、それ以外の部分（出ガス側）がコーティングされないようにすることができる。 On the other hand, when coating from the inlet gas side to a specific part of the axial length of the carrier substrate in the through hole, the ceramic concentration is increased to increase the viscosity of the slurry, and only a predetermined range is coated. A sufficient amount of slurry is prepared. After setting the base material so that the honeycomb-shaped cross-section is parallel to the ground and the incoming gas side is up, the high-viscosity slurry is allowed to flow from the incoming gas side to a predetermined through hole, thereby being in a predetermined range. Only the inner wall of the through-hole can be coated, and the other part (outgas side) can be prevented from being coated.
触媒担持層の形成後、当該層の最表面上に所望の貴金属を担持するか、又は予め当該層の最上層を触媒貴金属を含むスラリーで形成しておくことで、本発明の触媒を製造することができる。使用する触媒貴金属は、限定しないが、アルミナ粉末などの酸化物担体粉末に予め貴金属を担持させた触媒粉末を調製してスラリー化したものをコーティングすることで担持することができる。 After the formation of the catalyst support layer, a desired noble metal is supported on the outermost surface of the layer, or the uppermost layer of the layer is formed in advance with a slurry containing the catalyst noble metal to produce the catalyst of the present invention. be able to. Although the catalyst noble metal to be used is not limited, the catalyst noble metal can be supported by coating a slurry obtained by preparing a catalyst powder in which a noble metal is previously supported on an oxide carrier powder such as alumina powder.
実施例１
本実施例においては、排ガス流れ方向から見て、ハニカム構造体の中央部から外周部にかけて三段階で厚みが減少した触媒担持層が配置されている排ガス浄化触媒を調製する。尚、触媒貴金属は最上層を構成するスラリーにのみ含め、それ以外の層（貴金属非含有層）を構成するスラリーには含めない。
Example 1
In this embodiment, an exhaust gas purification catalyst is prepared in which a catalyst support layer having a thickness reduced in three stages from the center to the outer periphery of the honeycomb structure as viewed from the exhaust gas flow direction is prepared. The catalyst noble metal is included only in the slurry constituting the uppermost layer, and is not included in the slurry constituting the other layer (noble metal-free layer).
最初に、アルミナバインダー、アルミナを混合し、貴金属非含有層用のスラリーを調製した（スラリー１）。 First, an alumina binder and alumina were mixed to prepare a slurry for a noble metal-free layer (slurry 1).
続いて、硝酸白金溶液、セリウム酸化物を混合し、２５０℃で３時間乾燥した後、５００℃で２時間焼成することで、粉末１を調製した後、硝酸パラジウム溶液、ジルコニア酸化物を混合し、２５０℃で３時間乾燥後、５００℃で２時間焼成して粉末２を調製した。これらの粉末１及び２を、アルミナ、硫酸バリウム、アルミナバインダーと混合することで、最終組成が白金１．５ｇ／Ｌ、ロジウム０．４ｇ／Ｌ、セリウム酸化物１３５ｇ／Ｌ、ジルコニア酸化物５０ｇ／Ｌ、アルミナ７５ｇ／Ｌのスラリーを調製した（スラリー２）。
Subsequently, a platinum nitrate solution and a cerium oxide were mixed, dried at 250 ° C. for 3 hours, and then fired at 500 ° C. for 2 hours to prepare a
モノリスハニカム担体基材を準備し、図１に示すような中央部Ａにある各貫通孔に対しスラリー１を流し込み、乾燥・焼成させることで、コーティング前と比較して貫通孔の開口率が約８０％となるように貴金属非含有層を設けた。
A monolith honeycomb carrier base material is prepared, and the
続いて、前記貴金属非含有層を形成した貫通孔の周囲に位置する貫通孔（図１のＢ部に相当）に対し、Ａ部と同様にスラリー１を使用して、開口率が約９０％の貴金属非含有層を形成させた。この時点では、Ｃ部（Ｂ部の外周部に相当）を除く全ての貫通孔内にスラリー１による貴金属非含有層が形成されている。
Subsequently, the
Ａ部とＢ部に異なる厚みの貴金属非含有層が形成されているモノリスハニカム担体全体をスラリー２中に浸漬させた。浸漬後、乾燥・焼成を行うことにより、複数の触媒担持層を有する触媒１が調製された。触媒担持層形成前の貫通孔の開口率を１００％とした場合、最終的な貫通孔の開口率は、Ａ部７０％、Ｂ部８０％、Ｃ部９０％となった。尚、Ａ部は排ガス流れ方向から見た場合基材断面積のうち１０％を占めており、Ｂ部は基材断面積のうち４０％を占めている。
The entire monolith honeycomb carrier in which noble metal-free layers having different thicknesses were formed in the A part and the B part was immersed in the slurry 2. After the immersion, drying and firing were performed to prepare a
実施例２
本実施例においては、排ガス流れ方向から見た場合に、ハニカム構造体の中央部に位置している貫通孔のうち、入りガス側部分に触媒担持層が配置されている排ガス浄化触媒を調製する（図２を参照のこと）。
Example 2
In this embodiment, an exhaust gas purification catalyst is prepared in which a catalyst-supporting layer is disposed on the inlet gas side portion of the through hole located in the central portion of the honeycomb structure when viewed from the exhaust gas flow direction. (See Figure 2).
図２に示すＤ部の貫通孔の開口率が、未処理の貫通孔の開口率（１００％）と比較して８０％となるように、基材の入りガス側を下向きにし、下方から所望の高さになるまで中央部に位置する貫通孔にスラリー（実施例１で使用したもの）を注入した後、基材をそのまま放置することで余剰のスラリーを重力により除去した。続いて、実施例１と同様に乾燥・焼成工程を経ることで、触媒非含有層がＤ部にのみ形成された。 Desirable from below, with the inlet gas side of the base material facing downward so that the opening ratio of the through-holes in part D shown in FIG. 2 is 80% compared to the opening ratio of untreated through-holes (100%) After injecting the slurry (used in Example 1) into the through-hole located in the central part until the height reached, the excess slurry was removed by gravity by leaving the substrate as it was. Subsequently, a catalyst-free layer was formed only in part D by passing through the drying / firing process in the same manner as in Example 1.
続いて、モノリスハニカム担体全体をスラリー２中に浸漬させた。浸漬後、乾燥・焼成を行うことにより、図２に示すような触媒２が調製された。未処理の貫通孔の開口率を１００％とした場合、最終的な貫通孔の開口率は、Ｄ部７０％、Ｅ部９０％となった。尚、Ｄ部は、基材の全長の４０％の長さを有しており、そして排ガス流れ方向から見た場合基材断面積のうち２５％を占めている。 Subsequently, the entire monolith honeycomb carrier was immersed in the slurry 2. The catalyst 2 as shown in FIG. 2 was prepared by performing drying and baking after immersion. When the opening ratio of the untreated through hole was 100%, the final opening ratio of the through hole was 70% for the D portion and 90% for the E portion. Note that the portion D has a length of 40% of the entire length of the base material, and occupies 25% of the cross-sectional area of the base material when viewed from the exhaust gas flow direction.
比較例１
実施例と同じモノリスハニカム担体基材を用い、実施例１と同様の条件で当該担体全体にスラリー２を適用することで、触媒貴金属を含む一層の触媒担持層が形成された。
Comparative Example 1
Using the same monolith honeycomb carrier base material as in the example and applying the slurry 2 to the entire carrier under the same conditions as in Example 1, one catalyst supporting layer containing a catalyst noble metal was formed.
（浄化性能測定）
上記触媒を排気量４．３Ｌのエンジンにて、触媒床温１０５０℃で４０時間耐久させた後、排気量２．２Ｌのエンジンを有する実機車両へ搭載した。運転モードをＬＡ♯４モードに設定して当該車両を走行させ、当該触媒のＮＯｘエミッション効果を測定した。ＮＯｘエミッションについての結果を図３に示す。
(Purification performance measurement)
The catalyst was endured for 40 hours at a catalyst bed temperature of 1050 ° C. with an engine with a displacement of 4.3 L, and then mounted on an actual vehicle having an engine with a displacement of 2.2 L. The vehicle was driven with the operation mode set to LA # 4 mode, and the NOx emission effect of the catalyst was measured. The results for NOx emissions are shown in FIG.
図３に示したとおり、実施例１及び２の触媒は、比較例１の触媒と触媒貴金属量が同量であるのにも関わらず、比較例１の触媒よりもＮＯｘエミッションが一割程度低下した。 As shown in FIG. 3, the NOx emissions of the catalysts of Examples 1 and 2 were reduced by about 10% compared to the catalyst of Comparative Example 1, even though the catalyst noble metal amount was the same as that of Comparative Example 1. did.
本発明の排ガス浄化触媒によれば、触媒貴金属量を増大させることなく排ガス浄化性能を向上させることができる。本発明は、コート層厚を排ガスの流圧に合わせて適宜増減させることのみでかかる効果を達成できるとともに、既存のあらゆるハニカム触媒に適用することができることから従来の触媒と比較して好適である。 According to the exhaust gas purification catalyst of the present invention, the exhaust gas purification performance can be improved without increasing the amount of the catalyst noble metal. The present invention can achieve such an effect only by appropriately increasing or decreasing the coat layer thickness in accordance with the flow pressure of the exhaust gas, and can be applied to any existing honeycomb catalyst. Therefore, the present invention is more suitable than conventional catalysts. .
Claims (2)
全貫通孔のうち、通過する排ガスの流圧が相対的に高い貫通孔の内壁部を構成している触媒担持層の厚みを前記流圧に応じて増大させるか、そして／あるいは
全貫通孔のうち、通過する排ガスの流圧が相対的に低い貫通孔の内壁部を構成している触媒担持層の厚みを前記流圧に応じて減少させることにより触媒担持層の厚みが調節されており、
排ガス流れ方向から見て中央部に位置する貫通孔の開口面積がその外側に位置する貫通孔の開口面積よりも小さく、
貫通孔の開口面積が、排ガス流れ方向から見て、外側から中央部にかけて段階的に減少しており、且つ
前記触媒の軸方向から見て下流部に位置する貫通孔の開口面積が、上流部に位置する貫通孔の開口面積よりも大きい、排ガス浄化用触媒。 Exhaust gas comprising a carrier substrate having a plurality of through holes in the exhaust gas flow direction, one or more catalyst support layers formed on the inner wall surface of the through holes, and a noble metal supported on the catalyst support layers. A purification catalyst,
Of all the through holes, the thickness of the catalyst support layer constituting the inner wall of the through hole where the flow pressure of the exhaust gas passing therethrough is relatively high is increased according to the flow pressure, and / or
The thickness of the catalyst support layer is adjusted by reducing the thickness of the catalyst support layer that constitutes the inner wall of the through hole in which the flow pressure of the exhaust gas passing through is relatively low among all the through holes. Has been
The opening area of the through hole located in the center portion when viewed from the exhaust gas flow direction is smaller than the opening area of the through hole located outside thereof,
The opening area of the through hole is reduced stepwise from the outside to the center as seen from the exhaust gas flow direction, and
An exhaust gas purifying catalyst, wherein an opening area of a through hole located in a downstream portion when viewed from the axial direction of the catalyst is larger than an opening area of a through hole located in an upstream portion .
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