JP2004275883A - Waste gas purification catalyst - Google Patents
Waste gas purification catalyst Download PDFInfo
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- JP2004275883A JP2004275883A JP2003070436A JP2003070436A JP2004275883A JP 2004275883 A JP2004275883 A JP 2004275883A JP 2003070436 A JP2003070436 A JP 2003070436A JP 2003070436 A JP2003070436 A JP 2003070436A JP 2004275883 A JP2004275883 A JP 2004275883A
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- 239000003054 catalyst Substances 0.000 title claims abstract description 169
- 238000000746 purification Methods 0.000 title abstract description 23
- 239000002912 waste gas Substances 0.000 title abstract 5
- 229910000510 noble metal Inorganic materials 0.000 claims abstract description 57
- 230000003197 catalytic effect Effects 0.000 claims description 48
- 230000002093 peripheral effect Effects 0.000 abstract description 24
- 230000008021 deposition Effects 0.000 abstract 2
- 239000007789 gas Substances 0.000 description 137
- 239000000758 substrate Substances 0.000 description 18
- 229910001220 stainless steel Inorganic materials 0.000 description 16
- 239000010935 stainless steel Substances 0.000 description 16
- 239000007864 aqueous solution Substances 0.000 description 15
- 229910052697 platinum Inorganic materials 0.000 description 12
- 229910052703 rhodium Inorganic materials 0.000 description 12
- 230000000694 effects Effects 0.000 description 7
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 7
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 6
- 239000000654 additive Substances 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 3
- 230000000996 additive effect Effects 0.000 description 3
- 229910002091 carbon monoxide Inorganic materials 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 229930195733 hydrocarbon Natural products 0.000 description 3
- 150000002430 hydrocarbons Chemical class 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- 229910052763 palladium Inorganic materials 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- 230000004913 activation Effects 0.000 description 2
- QVQLCTNNEUAWMS-UHFFFAOYSA-N barium oxide Chemical compound [Ba]=O QVQLCTNNEUAWMS-UHFFFAOYSA-N 0.000 description 2
- 238000002485 combustion reaction Methods 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 239000002002 slurry Substances 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 241000282326 Felis catus Species 0.000 description 1
- 229910021536 Zeolite Inorganic materials 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 229910000420 cerium oxide Inorganic materials 0.000 description 1
- 229910052878 cordierite Inorganic materials 0.000 description 1
- 239000008367 deionised water Substances 0.000 description 1
- 229910021641 deionized water Inorganic materials 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 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 1
- HNPSIPDUKPIQMN-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Al]O[Al]=O HNPSIPDUKPIQMN-UHFFFAOYSA-N 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 239000003779 heat-resistant material Substances 0.000 description 1
- 229910052809 inorganic oxide Inorganic materials 0.000 description 1
- 229910052746 lanthanum Inorganic materials 0.000 description 1
- FZLIPJUXYLNCLC-UHFFFAOYSA-N lanthanum atom Chemical compound [La] FZLIPJUXYLNCLC-UHFFFAOYSA-N 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- VUZPPFZMUPKLLV-UHFFFAOYSA-N methane;hydrate Chemical compound C.O VUZPPFZMUPKLLV-UHFFFAOYSA-N 0.000 description 1
- 238000000034 method Methods 0.000 description 1
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- BMMGVYCKOGBVEV-UHFFFAOYSA-N oxo(oxoceriooxy)cerium Chemical compound [Ce]=O.O=[Ce]=O BMMGVYCKOGBVEV-UHFFFAOYSA-N 0.000 description 1
- RVTZCBVAJQQJTK-UHFFFAOYSA-N oxygen(2-);zirconium(4+) Chemical compound [O-2].[O-2].[Zr+4] RVTZCBVAJQQJTK-UHFFFAOYSA-N 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 239000010970 precious metal Substances 0.000 description 1
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- 229910001868 water Inorganic materials 0.000 description 1
- 238000004804 winding Methods 0.000 description 1
- 229910052727 yttrium Inorganic materials 0.000 description 1
- VWQVUPCCIRVNHF-UHFFFAOYSA-N yttrium atom Chemical compound [Y] VWQVUPCCIRVNHF-UHFFFAOYSA-N 0.000 description 1
- 239000010457 zeolite Substances 0.000 description 1
- 229910001928 zirconium oxide Inorganic materials 0.000 description 1
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- Exhaust Gas Treatment By Means Of Catalyst (AREA)
- Catalysts (AREA)
Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は、排ガス浄化用触媒に関し、詳しくは、触媒の着火性にすぐれた排ガス浄化用触媒に関する。
【０００２】
【従来の技術】
近年の環境問題への関心の高まりにともない、自動車のエンジン等の内燃機関からの排気ガス対策が重要視されてきている。すなわち、排気ガスをそのまま排出すると、公害や環境の悪化といった問題を引き起こすためである。このため、これらの排気ガスは排ガス浄化用触媒等を用いて浄化された後に大気中に排出されている。
【０００３】
この排ガス浄化用触媒を用いた排気ガス浄化システムは、他の方法に比べ、排気ガスを発生するエンジン等の内燃機関にそれほどの負担をかけることなく、大幅なエミッションの低減が可能であるために広く採用されている。
【０００４】
排ガス浄化用触媒は、一般的には、耐熱性を有する担体基材の表面に耐熱性無機酸化物等よりなる多孔質の担持層を形成した触媒担体に、触媒貴金属を担持した構造を有している。また、排気ガスの浄化を行う触媒貴金属の担持量を部分的に増加させることで浄化効率を向上させることも提案されている。（たとえば、特許文献１〜６参照。）
排ガス浄化用触媒は、触媒貴金属の作用により、排気ガスに含まれる有害な窒素酸化物（ＮＯｘ）、炭化水素（ＨＣ）および一酸化炭素（ＣＯ）を無害な窒素、二酸化炭素、水に変換している。
【０００５】
触媒貴金属による排気ガスの浄化性能は温度の影響を強く受けることが知られており、一般に３００℃以上の温度において浄化が行われる。このため、エンジン始動直後におけるように、排気ガス温度が低い時には、貴金属触媒の触媒活性が低く、排気ガスの浄化がむずかしいという問題があった。
【０００６】
【特許文献１】
特開２０００−２０２３０４号公報
【特許文献２】
特開平９−３１７４５４号公報
【特許文献３】
特開平９−９４４号公報
【特許文献４】
特開平６−２０５９８９号公報
【特許文献５】
特開昭６１−１８５３３８号公報
【特許文献６】
特開昭５８−１９３７４０号公報
【０００７】
【発明が解決しようとする課題】
本発明は上記実状に鑑みてなされたものであり、エンジン始動直後のような低温域においても有効な浄化活性を示す、すなわち、触媒貴金属の着火性能に優れた排気ガス浄化用触媒を提供することを課題とする。
【０００８】
【課題を解決するための手段】
上記課題を解決するために本発明者らは、排ガス浄化用触媒について検討を重ねた結果、排ガス浄化用触媒において排気ガスのガス流の流量の多い部分に触媒貴金属を多量に担持させることで上記課題を解決できることを見出した。
【０００９】
すなわち、本発明の排ガス浄化用触媒は、軸方向に排ガスが通過する複数のセルを有する触媒担体と、触媒担体に担持された触媒貴金属と、を有する排ガス浄化用触媒において、軸方向に垂直な断面の中心部における触媒貴金属の担持量が中心部以外の周縁部における担持量の３倍以上となるように全長にわたって担持されていることを特徴とする。
【００１０】
本発明の排ガス浄化用触媒は、排気ガスのガス流の流量の多い部分（排気ガスのガス流速の早い部分）に担持された多量の触媒貴金属が排気ガスにより触媒活性を発揮できる温度まですぐに加熱される。また、それ以外の部分にも、十分な量の触媒貴金属が担持されているため、高い排ガス浄化性能を示す。すなわち、本発明の排ガス浄化用触媒は、高い排ガス浄化性能を維持しながら着火性にすぐれた排ガス浄化用触媒となっている。
【００１１】
【発明の実施の形態】
本発明の排ガス浄化用触媒は、軸方向に垂直な断面の中心部における触媒貴金属の担持量が中心部以外の周縁部における担持量の３倍以上となるように全長にわたって担持されている。
【００１２】
軸方向に垂直な断面の中心部は、排ガスの流量および流速の最も大きな部分であることから、排ガス浄化用触媒が最も排気ガスと接触する部分となっている。すなわち、中心部が最も排気ガスにより加熱されやすい部分となっている。すなわち、本発明の排ガス浄化用触媒は、この最も加熱される部分に多量の触媒貴金属を担持しているので、多量の触媒貴金属は、すぐに触媒活性温度にまで温度が上昇する。このため、本発明の排ガス浄化用触媒は、エンジン始動直後から高い浄化性能を発揮する。
【００１３】
また、中心部における触媒貴金属の担持量がそれ以外の部分の３倍以上となることで、すぐれた着火性能を発揮できるようになる。担持量が３倍未満では、エンジン始動直後の排ガス浄化性能が十分に得られない。
【００１４】
本発明の排ガス浄化用触媒は、中心部に高担持量で触媒貴金属の担持を行うことを全長にわたって行っている。全長にわたって高担持を行うことで、高い排ガス浄化性能が維持できる。すなわち、中心部は、排気ガスが最も多く流れる部分であるため、中心部においては触媒貴金属の担持量が多いことが求められ、高担持の長さが短くなると触媒貴金属量が不足し、排気ガスの浄化が不十分となる。
【００１５】
本発明の排ガス浄化用触媒において、中心部とは、軸方向に垂直な断面における触媒担体の軸心部近傍である。通常の排ガス浄化用触媒は、管路内に同軸的に取り付けられた状態で使用され、管路内を流れる排気ガスは管路の軸心近傍において最も流速が速くなっている。すなわち、本発明の排ガス浄化用触媒において、中心部のセルに、最も流速の速い排気ガスが通過するようになっている。また、中心部が軸心部近傍となることで、中心部の熱が周縁部に均等に伝導するようになり、周縁部の触媒貴金属の触媒活性に周方向でのムラが生じなくなる。
【００１６】
また、本発明の排ガス浄化用触媒において、軸方向に垂直な断面における中心部の外周形状は、特に限定されるものではない。触媒担体の軸方向に垂直な断面の外周形状に相似な形状であることが好ましい。中心部の外周形状としては、たとえば、円、楕円、正方形、長方形、三角形等の形状をあげることができる。周方向の位相が限定されない円形が好ましい。
【００１７】
中心部における触媒貴金属の担持量は、３ｇ／Ｌ−ｃａｔ以上であることが好ましい。ここで、ｇ／Ｌ−ｃａｔとは、触媒担体容積１Ｌあたりの触媒貴金属の担持量を示すものである。触媒貴金属の担持量が３ｇ／Ｌ−ｃａｔ以上となることで、本発明の排ガス浄化用触媒がすぐれた着火性能と排気ガスの浄化性能を有するようになる。担持量が３ｇ／Ｌ−ｃａｔ未満では、触媒貴金属量が不足し、十分な浄化性能が得られない。
【００１８】
中心部は、軸方向に垂直な断面の断面積の１／５０以上の断面積を有することが好ましい。中心部が少なくとも１／５０の断面積を有することで、触媒貴金属の担持量を増加させることの効果が得られるようになる。中心部の断面積が１／５０未満では触媒貴金属量が不足し十分な効果が得られない。すなわち、中心部が１／５０の断面積を有することで、本発明の排ガス浄化用触媒がすぐれた着火性能と排気ガスの浄化性能を有するようになる。
【００１９】
中心部は、１ｃｍ２以上の断面積を有することが好ましい。中心部が１ｃｍ２以上の断面積を有することで、触媒貴金属の担持量を増加させることの効果が得られるようになる。中心部が１ｃｍ２未満では、触媒貴金属量が不足し十分な効果が得られない。すなわち、中心部が１ｃｍ２以上の断面積を有することで、本発明の排ガス浄化用触媒がすぐれた着火性能と排気ガスの浄化性能を有するようになる。
【００２０】
軸方向に垂直な断面が略円形を有することが好ましい。本発明の排ガス浄化用触媒が略円形の断面を有することで、排気ガスの中心部での流量および流速が大きくなる。この結果、本発明の排ガス浄化用触媒において、貴金属触媒を高担持した効果が得られるようになる。なお、略円形とは、真円形および楕円形を示す。
【００２１】
本発明の排ガス浄化用触媒は、軸方向に排ガスが通過する複数のセルを有する触媒担体と、触媒担体に担持された触媒貴金属と、を有する。
【００２２】
触媒担体は、耐熱性材料よりなる触媒担体基材と、触媒担体基材上に形成された耐熱性多孔質体よりなる担持層と、を有することが好ましい。
【００２３】
触媒担体基材は、軸方向に排ガスが通過する管状通路を有する部材である。すなわち、その内部を排ガスが通過する管状通路を有する構造とすることで、排ガス浄化用触媒の排ガスとの接触面積が大きくなる。排ガスとの接触面積が大きくなると、触媒金属と排ガスとがより接触することとなり、排ガス浄化用触媒の排ガスの浄化能が向上する。このような排ガス浄化用触媒としては、たとえば、モノリスハニカム担体等の触媒担体基材をあげることができる。また、触媒担体基材は、従来の排ガス浄化用触媒に用いられる材質を用いられることができ、たとえば、コーディエライトなどの耐熱性セラミックスや、ステンレス等の耐熱性金属などの材質を用いることができる。
【００２４】
担持層が、耐熱性多孔質体よりなることで、排ガス浄化用触媒の触媒担体としての表面積が確保できる。担持層を形成する材質は、特に限定されるものではなく、従来公知の排ガス浄化用触媒において担持層に用いられている材質を用いることができる。たとえば、アルミナをあげることができる。
【００２５】
また、担持層は、従来公知の添加物が添加されていてもよい。たとえば、セリウム酸化物、ジルコニウム酸化物、バリウム酸化物、イットリウム、ランタン、ゼオライト等をあげることができる。これらの添加物の添加量についても、特に限定されるものではない。また、中心部と周縁部とにおける添加物の添加量を変化させてもよい。
【００２６】
触媒貴金属は、Ｐｔ、Ｐｄ、Ｒｈの少なくとも一種よりなることが好ましい。すなわち、触媒金属をＰｔ、ＰｄおよびＲｈの少なくとも一種とすることで、ＨＣ、ＣＯおよびＮＯｘの浄化を行うことができる。本発明においては、触媒貴金属を複数種の貴金属としたときには、複数種の貴金属の合計の担持量を触媒担体への担持量とする。
【００２７】
本発明の排気ガス浄化用触媒は、排気ガスが内部を流れる管路に略同軸的な状態で、設置されることが好ましい。管路に略同軸的に取り付けられることで、触媒担体の軸心部近傍を中心部とすることができる。
【００２８】
本発明の排ガス浄化用触媒は、触媒貴金属を中心部に高担持量で担持することができる製造方法であれば、特に限定されない。
【００２９】
本発明の排ガス浄化用触媒は、排気ガスのガス流の流量の多い部分（排気ガスのガス流速の早い部分）に担持された多量の触媒貴金属が排気ガスにより触媒活性を発揮できる温度まですぐに加熱される。また、それ以外の部分にも、十分な量の触媒貴金属が担持されているため、高い排ガス浄化性能を示す。すなわち、本発明の排ガス浄化用触媒は、高い排ガス浄化性能を維持しながら着火性にすぐれた排ガス浄化用触媒となっている。
【００３０】
【実施例】
以下、実施例を用いて本発明を説明する。
【００３１】
本発明の実施例として、排ガス浄化用触媒を製造した。
【００３２】
（試料１）
まず、アルミナ粉末１００重量部を脱イオン水１５０重量部に分散させ、ついでアルミナ換算で５重量部のアルミナゾルを添加し、湿式粉砕してアルミナスラリーを調製した。
【００３３】
調製されたアルミナスラリーを、セル数が１００セルのウォールフローのガス流通セルを有する直径１００ｍｍ×軸方向の長さ２０ｍｍの円筒状のステンレスよりなる触媒担体基材に塗布し、２００℃で１時間乾燥し、ついで４００℃で１時間焼成して担持層を形成した。なお、触媒担体基材は、ステンレス板とステンレス製波板とを重ねた状態で巻回して製造されている。
【００３４】
つづいて、Ｐｔ換算で８ｇ／ＬでＰｔを含有するＰｔ水溶液およびＲｈ換算で１．６ｇ／ＬでＲｈを含有するＲｈ水溶液を調製した。そして、担持層が形成されたステンレス担体をＰｔ水溶液に浸漬し、乾燥焼成した。その後、ステンレス担体をＲｈ水溶液に浸漬し、乾燥焼成した。ＰｔおよびＲｈの担持量は、Ｐｔ：１．０ｇ／Ｌ−ｃａｔ、Ｒｈ：０．２ｇ／Ｌ−ｃａｔであった。
【００３５】
そして、担体と同心の直径５０ｍｍの円の部分（中心部）に、さらにＰｔ：４．０ｇ／Ｌ−ｃａｔおよびＲｈ：０．８ｇ／Ｌ−ｃａｔを担持させた。この触媒貴金属の更なる担持により、中心部のＰｔおよびＲｈの担持量は、Ｐｔ：５．０ｇ／Ｌ−ｃａｔ、Ｒｈ：１．０ｇ／Ｌ−ｃａｔとなった。
【００３６】
この、中心部への触媒貴金属の担持は、まず、Ｐｔ換算で３２ｇ／ＬでＰｔを含有するＰｔ水溶液を調製した。担体を軸を垂直となるように設置し、中心部にＰｔ水溶液を流し込み、中心部に対応したセルの担持層にのみＰｔ水溶液を含浸させ、乾燥焼成した。Ｒｈ換算で６．４ｇ／ＬでＲｈを含有するＲｈ水溶液を調製した。Ｐｔ水溶液のときと同様に、Ｒｈの担持を行った。
【００３７】
以上の手段により、本試料の排ガス浄化用触媒が製造された。
【００３８】
本試料の排ガス浄化用触媒の構成を図１に示した。なお、図１（ａ）は、排ガス浄化用触媒の軸方向に垂直な断面であり、（ｂ）は軸と同一平面における断面を示した図である。また、図１において図示された排ガス浄化用触媒は、外筒の軸心の中空部に嵌入されている。
【００３９】
本試料の排ガス浄化用触媒は、ステンレスよりなる担体基材の表面に担持層が形成された円筒状の触媒担体にＰｔおよびＲｈが担持されている。そして、触媒担体の軸に垂直な断面において、触媒担体の軸心と同心の半径２５ｍｍの円の内部である中心部にはＰｔが５．０ｇ／Ｌ−ｃａｔ、Ｒｈが１．０ｇ／Ｌ−ｃａｔの担持量で、それ以外の部分（周縁部）にはＰｔが１．０ｇ／Ｌ−ｃａｔ、Ｒｈが０．２ｇ／Ｌ−ｃａｔの担持量で担持されている。本試料の排ガス浄化用触媒は、触媒担体の軸に垂直ないずれの断面においても、中心部および周縁部の触媒貴金属の担持量に変化はない。
【００４０】
（試料２）
中心部を直径２０ｍｍの円形状とした以外は、試料１と同様に排ガス浄化用触媒の製造を行った。
【００４１】
本試料の排ガス浄化用触媒は、ステンレスよりなる担体基材の表面に担持層が形成された円筒状の触媒担体にＰｔおよびＲｈが担持されている。そして、触媒担体の軸に垂直な断面において、触媒担体の軸心と同心の半径１０ｍｍの円の内部である中心部にはＰｔが５．０ｇ／Ｌ−ｃａｔ、Ｒｈが１．０ｇ／Ｌ−ｃａｔの担持量で、それ以外の部分（周縁部）にはＰｔが１．０ｇ／Ｌ−ｃａｔ、Ｒｈが０．２ｇ／Ｌ−ｃａｔの担持量で担持されている。本試料の排ガス浄化用触媒は、触媒担体の軸に垂直ないずれの断面においても、中心部および周縁部の触媒貴金属の担持量に変化はない。
【００４２】
（試料３）
中心部にＰｄを担持させた以外は、試料１と同様に排ガス浄化用触媒の製造を行った。なお、中心部以外の部分には、Ｐｄは担持されていない。
【００４３】
まず、試料１と同様に、ステンレスよりなる担体基材の表面に担持層を形成し、Ｐｔ：１．０ｇ／Ｌ−ｃａｔ、Ｒｈ：０．２ｇ／Ｌ−ｃａｔで担持した。
【００４４】
その後、Ｐｄ換算で３２ｇ／ＬでＰｄを含有するＰｄ水溶液を調製した。そして、このＰｄ水溶液を上記触媒担体の中心部に含浸させ、乾燥焼成した。この処理によるＰｄの担持量は、４．０ｇ／Ｌ−ｃａｔであった。
【００４５】
本試料の排ガス浄化用触媒は、ステンレスよりなる担体基材の表面に担持層が形成された円筒状の触媒担体にＰｔ、ＲｈおよびＰｄが担持されている。そして、触媒担体の軸に垂直な断面において、触媒担体の軸心と同心の半径２５ｍｍの円の内部である中心部にはＰｔが１．０ｇ／Ｌ−ｃａｔ、Ｒｈが０．２ｇ／Ｌ−ｃａｔ、Ｐｄが４．０ｇ／Ｌ−ｃａｔの担持量で、それ以外の部分（周縁部）にはＰｔが１．０ｇ／Ｌ−ｃａｔ、Ｒｈが０．２ｇ／Ｌ−ｃａｔの担持量で担持されている。本試料の排ガス浄化用触媒は、触媒担体の軸に垂直ないずれの断面においても、中心部および周縁部の触媒貴金属の担持量に変化はない。
【００４６】
（試料４）
中心部にＰｔを担持させた以外は、試料１と同様に排ガス浄化用触媒の製造を行った。
【００４７】
まず、試料１と同様に、ステンレスよりなる担体基材の表面に担持層を形成し、Ｐｔ：１．０ｇ／Ｌ−ｃａｔ、Ｒｈ：０．２ｇ／Ｌ−ｃａｔで担持した。
【００４８】
その後、Ｐｔ換算で３２ｇ／ＬでＰｔを含有するＰｔ水溶液を調製した。そして、このＰｔ水溶液を上記触媒担体の中心部に含浸させ、乾燥焼成した。この処理によるＰｔの担持量は４．０ｇ／Ｌ−ｃａｔであった。
【００４９】
本試料の排ガス浄化用触媒は、ステンレスよりなる担体基材の表面に担持層が形成された円筒状の触媒担体にＰｔおよびＲｈが担持されている。そして、触媒担体の軸に垂直な断面において、触媒担体の軸心と同心の半径２５ｍｍの円の内部である中心部にはＰｔが５．０ｇ／Ｌ−ｃａｔ、Ｒｈが０．２ｇ／Ｌ−ｃａｔの担持量で、それ以外の部分（周縁部）にはＰｔが１．０ｇ／Ｌ−ｃａｔ、Ｒｈが０．２ｇ／Ｌ−ｃａｔの担持量で担持されている。本試料の排ガス浄化用触媒は、触媒担体の軸に垂直ないずれの断面においても、中心部および周縁部の触媒貴金属の担持量に変化はない。
【００５０】
（試料５）
中心部を直径１０ｍｍの円形状とした以外は、試料１と同様に排ガス浄化用触媒の製造を行った。
【００５１】
本試料の排ガス浄化用触媒は、ステンレスよりなる担体基材の表面に担持層が形成された円筒状の触媒担体にＰｔおよびＲｈが担持されている。そして、触媒担体の軸に垂直な断面において、触媒担体の軸心と同心の半径５ｍｍの円の内部である中心部にはＰｔが５．０ｇ／Ｌ−ｃａｔ、Ｒｈが１．０ｇ／Ｌ−ｃａｔの担持量で、それ以外の部分（周縁部）にはＰｔが１．０ｇ／Ｌ−ｃａｔ、Ｒｈが０．２ｇ／Ｌ−ｃａｔの担持量で担持されている。本試料の排ガス浄化用触媒は、触媒担体の軸に垂直ないずれの断面においても、中心部および周縁部の触媒貴金属の担持量に変化はない。
【００５２】
（試料６）
中心部へのＰｔおよびＲｈの担持量を変化させた以外は、試料１と同様に排ガス浄化用触媒の製造を行った。
【００５３】
まず、試料１と同様に、ステンレスよりなる担体基材の表面に担持層を形成し、Ｐｔ：１．０ｇ／Ｌ−ｃａｔ、Ｒｈ：０．２ｇ／Ｌ−ｃａｔで担持した。
【００５４】
そして、Ｐｔ換算で８ｇ／ＬでＰｔを含有するＰｔ水溶液を調製した。このＰｔ水溶液を上記触媒担体の中心部に含浸させ、乾燥焼成した。Ｒｈ換算で１．６ｇ／ＬでＲｈを含有する水溶液を調製し、Ｐｔと同様に中心部に担持させた。この処理によるＰｔの担持量は１．０ｇ／Ｌ−ｃａｔ、Ｒｈの担持量は０．２ｇ／Ｌ−ｃａｔであった。
【００５５】
本試料の排ガス浄化用触媒は、ステンレスよりなる担体基材の表面に担持層が形成された円筒状の触媒担体にＰｔおよびＲｈが担持されている。そして、触媒担体の軸に垂直な断面において、触媒担体の軸心と同心の半径２５ｍｍの円の内部である中心部にはＰｔが２．０ｇ／Ｌ−ｃａｔ、Ｒｈが０．４ｇ／Ｌ−ｃａｔの担持量で、それ以外の部分（周縁部）にはＰｔが１．０ｇ／Ｌ−ｃａｔ、Ｒｈが０．２ｇ／Ｌ−ｃａｔの担持量で担持されている。本試料の排ガス浄化用触媒は、触媒担体の軸に垂直ないずれの断面においても、中心部および周縁部の触媒貴金属の担持量に変化はない。
【００５６】
（評価）
各試料の排ガス浄化用触媒の評価として、触媒の着火温度を測定した。着火温度の測定は、４サイクルエンジン（１２５ｃｃ）を有するスクーターに実際に取り付け、ＥＣ−４０（ＩＳＯ ６４６０）に規定の条件で稼働させたときの着火温度を測定することでなされた。測定結果を図２および表１に示した。
【００５７】
なお、着火温度の測定は、具体的には、触媒への入りガス温度と触媒の床内温度を測定しながら、ＥＣ−４０モードで走行させた。そして、触媒の床内温度が入りガス温度よりも高くなった点を着火温度として判定し、測定した。
【００５８】
【表１】
図および表より、試料１〜４の排ガス浄化用触媒は、触媒の着火温度が大幅に低下していることがわかる。試料１〜４の排ガス浄化用触媒は、中心部の触媒貴金属の担持量が周縁部の担持量より多量となっている。そして、この中心部は排気ガスのガス流が最も速く流れる部分である。このため、多量の排気ガスが中心部のセルの内部を通過し、排気ガスがセルの内壁に形成された担持層および触媒貴金属を加熱する。排気ガスの流速の速い中心部は周縁部よりも加熱されやすいため、中心部に担持された触媒貴金属はすぐに触媒活性温度に到達する。そして、試料１〜４の排ガス浄化用触媒は、中心部に多量の触媒貴金属を担持しており、中心部のセルを通過する排気ガスの浄化を十分に行うことができる。このため、試料１〜４の排ガス浄化用触媒は、エンジン始動直後のような低温域においても高い浄化性能を発揮できる。
【００６０】
試料５の排ガス浄化用触媒は、中心部の断面積が小さいため、十分な着火性能が発揮できなかった。また、試料６の排ガス浄化用触媒は、触媒貴金属の担持量が少ないため、十分な着火性能が発揮できなかった。
【００６１】
（試料７）
中心部の形状を正方形とした以外は、試料１と同様に排ガス浄化用触媒の製造を行った。
【００６２】
本試料の排ガス浄化用触媒は、ステンレスよりなる担体基材の表面に担持層が形成された円筒状の触媒担体にＰｔおよびＲｈが担持されている。そして、触媒担体の軸に垂直な断面において、重心が触媒担体の軸心と一致した一辺の長さが２５ｍｍの正方形の内部である中心部にはＰｔが５．０ｇ／Ｌ−ｃａｔ、Ｒｈが１．０ｇ／Ｌ−ｃａｔの担持量で、それ以外の部分（周縁部）にはＰｔが１．０ｇ／Ｌ−ｃａｔ、Ｒｈが０．２ｇ／Ｌ−ｃａｔの担持量で担持されている。本試料の排ガス浄化用触媒は、触媒担体の軸に垂直ないずれの断面においても、中心部および周縁部の触媒貴金属の担持量に変化はない。
【００６３】
本試料の排ガス浄化用触媒の構成を図３に示した。
【００６４】
本試料は、中心部が正方形を有するように形成されているが、中心部の触媒貴金属の担持量が周縁部の５倍であり、かつ十分な断面積を有しているため、上記試料１〜４と同様に触媒着火性にすぐれた排ガス浄化用触媒となっている。
【００６５】
【発明の効果】
本発明の排ガス浄化用触媒は、排気ガスのガス流の流量の多い部分（排気ガスのガス流速の早い部分）に担持された多量の触媒貴金属が排気ガスにより触媒活性を発揮できる温度まですぐに加熱される。また、それ以外の部分にも、十分な量の触媒貴金属が担持されているため、高い排ガス浄化性能を示す。すなわち、本発明の排ガス浄化用触媒は、高い排ガス浄化性能を維持しながら着火性にすぐれた排ガス浄化用触媒となっている。
【図面の簡単な説明】
【図１】試料１の排ガス浄化用触媒の構成を示した図である。
【図２】試料１〜６の排ガス浄化用触媒の触媒着火温度の測定結果を示した図である。
【図３】試料７の排ガス浄化用触媒の構成を示した図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purifying catalyst, and more particularly to an exhaust gas purifying catalyst excellent in ignitability of the catalyst.
[0002]
[Prior art]
2. Description of the Related Art With an increase in interest in environmental issues in recent years, measures against exhaust gas from an internal combustion engine such as an automobile engine have been emphasized. That is, if the exhaust gas is directly discharged, problems such as pollution and deterioration of the environment are caused. For this reason, these exhaust gases are discharged into the air after being purified using an exhaust gas purifying catalyst or the like.
[0003]
Compared with other methods, the exhaust gas purification system using this exhaust gas purification catalyst can significantly reduce emissions without imposing a significant burden on internal combustion engines such as engines that generate exhaust gas. Widely adopted.
[0004]
Exhaust gas purifying catalysts generally have a structure in which a catalytic noble metal is supported on a catalyst carrier in which a porous carrier layer made of a heat-resistant inorganic oxide or the like is formed on the surface of a heat-resistant carrier substrate. ing. It has also been proposed to improve the purification efficiency by partially increasing the supported amount of catalytic noble metal for purifying exhaust gas. (For example, see Patent Documents 1 to 6.)
Exhaust gas purifying catalysts convert harmful nitrogen oxides (NOx), hydrocarbons (HC) and carbon monoxide (CO) contained in exhaust gas into harmless nitrogen, carbon dioxide and water by the action of catalytic noble metals. ing.
[0005]
It is known that the purification performance of exhaust gas by a catalytic noble metal is strongly affected by temperature, and purification is generally performed at a temperature of 300 ° C. or higher. Therefore, when the exhaust gas temperature is low, such as immediately after the start of the engine, there is a problem that the catalytic activity of the noble metal catalyst is low and purification of the exhaust gas is difficult.
[0006]
[Patent Document 1]
JP 2000-202304 A [Patent Document 2]
JP-A-9-317454 [Patent Document 3]
Japanese Patent Application Laid-Open No. 9-944 [Patent Document 4]
JP-A-6-205989 [Patent Document 5]
JP-A-61-185338 [Patent Document 6]
JP-A-58-193740
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and provides an exhaust gas purification catalyst that exhibits an effective purification activity even in a low-temperature region such as immediately after starting an engine, that is, has excellent ignition performance of a catalytic noble metal. As an issue.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventors have conducted repeated studies on an exhaust gas purifying catalyst. We found that we could solve the problem.
[0009]
That is, the exhaust gas purifying catalyst of the present invention is a catalyst carrier having a plurality of cells through which exhaust gas passes in the axial direction, and a catalyst noble metal supported on the catalyst carrier, and an exhaust gas purifying catalyst having an axially perpendicular direction. The catalyst is supported over the entire length such that the amount of the catalytic noble metal carried at the center of the cross section is at least three times the amount carried at the peripheral portion other than the center.
[0010]
The exhaust gas purifying catalyst of the present invention can be used immediately at a temperature at which a large amount of catalytic noble metal carried on a portion where the flow rate of the exhaust gas is high (a portion where the gas flow rate of the exhaust gas is fast) can exhibit catalytic activity by the exhaust gas. Heated. In addition, since a sufficient amount of catalytic noble metal is supported on other portions, high exhaust gas purification performance is exhibited. That is, the exhaust gas purifying catalyst of the present invention is an exhaust gas purifying catalyst having excellent ignitability while maintaining high exhaust gas purifying performance.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
The exhaust gas purifying catalyst of the present invention is supported over the entire length such that the amount of the catalytic noble metal carried at the center of the cross section perpendicular to the axial direction is at least three times the amount carried at the periphery other than the center.
[0012]
The central portion of the cross section perpendicular to the axial direction is the portion where the flow rate and the flow rate of the exhaust gas are the largest, so that the exhaust gas purifying catalyst is the portion that contacts the exhaust gas most. That is, the central portion is the portion that is most easily heated by the exhaust gas. That is, since the exhaust gas purifying catalyst of the present invention carries a large amount of catalytic noble metal in the most heated portion, the temperature of the large amount of catalytic noble metal immediately rises to the catalyst activation temperature. Therefore, the exhaust gas purifying catalyst of the present invention exhibits high purification performance immediately after starting the engine.
[0013]
In addition, when the amount of the catalytic noble metal carried in the central portion is three times or more that of the other portions, excellent ignition performance can be exhibited. If the carrying amount is less than three times, sufficient exhaust gas purification performance immediately after engine start cannot be obtained.
[0014]
In the exhaust gas purifying catalyst of the present invention, the catalytic noble metal is carried in a large amount in the central portion over the entire length. By performing high loading over the entire length, high exhaust gas purification performance can be maintained. That is, since the central portion is a portion through which the exhaust gas flows most, it is required that the catalytic noble metal carry a large amount in the central portion. Purification becomes insufficient.
[0015]
In the exhaust gas purifying catalyst of the present invention, the central portion is near the axis of the catalyst carrier in a cross section perpendicular to the axial direction. An ordinary exhaust gas purifying catalyst is used in a state of being coaxially mounted in a pipeline, and the exhaust gas flowing in the pipeline has the highest flow velocity near the axis of the pipeline. That is, in the exhaust gas purifying catalyst of the present invention, the exhaust gas with the highest flow rate passes through the central cell. In addition, since the central portion is near the axial center portion, heat at the central portion is evenly conducted to the peripheral portion, so that the catalytic activity of the catalytic noble metal at the peripheral portion does not become uneven in the circumferential direction.
[0016]
Further, in the exhaust gas purifying catalyst of the present invention, the outer peripheral shape of the central portion in the cross section perpendicular to the axial direction is not particularly limited. It is preferable that the shape is similar to the outer peripheral shape of the cross section perpendicular to the axial direction of the catalyst carrier. As the outer peripheral shape of the central portion, for example, a shape such as a circle, an ellipse, a square, a rectangle, and a triangle can be given. A circular shape in which the circumferential phase is not limited is preferable.
[0017]
The supported amount of the catalytic noble metal in the central portion is preferably 3 g / L-cat or more. Here, g / L-cat indicates the amount of supported catalyst noble metal per 1 L of catalyst carrier volume. When the supported amount of the catalytic noble metal is 3 g / L-cat or more, the exhaust gas purifying catalyst of the present invention has excellent ignition performance and exhaust gas purifying performance. If the supported amount is less than 3 g / L-cat, the catalytic noble metal amount will be insufficient, and sufficient purification performance cannot be obtained.
[0018]
The central portion preferably has a cross-sectional area of 1/50 or more of a cross-sectional area of a cross section perpendicular to the axial direction. When the central portion has a cross-sectional area of at least 1/50, the effect of increasing the supported amount of the catalytic noble metal can be obtained. If the cross-sectional area at the center is less than 1/50, the amount of catalyst noble metal is insufficient, and a sufficient effect cannot be obtained. That is, when the central portion has a 1/50 cross-sectional area, the exhaust gas purifying catalyst of the present invention has excellent ignition performance and exhaust gas purifying performance.
[0019]
The central portion preferably has a cross-sectional area of 1 cm 2 or more. When the central portion has a cross-sectional area of 1 cm 2 or more, the effect of increasing the supported amount of the catalytic noble metal can be obtained. If the central portion is less than 1 cm 2 , the amount of the catalyst noble metal is insufficient, and a sufficient effect cannot be obtained. That is, when the central portion has a cross-sectional area of 1 cm 2 or more, the exhaust gas purifying catalyst of the present invention has excellent ignition performance and exhaust gas purifying performance.
[0020]
Preferably, the cross section perpendicular to the axial direction has a substantially circular shape. Since the exhaust gas purifying catalyst of the present invention has a substantially circular cross section, the flow rate and the flow velocity of the exhaust gas at the central portion are increased. As a result, in the exhaust gas purifying catalyst of the present invention, the effect of highly supporting the noble metal catalyst can be obtained. The term “substantially circular” refers to a true circle and an ellipse.
[0021]
The exhaust gas purifying catalyst of the present invention includes a catalyst carrier having a plurality of cells through which exhaust gas passes in an axial direction, and a catalyst precious metal carried on the catalyst carrier.
[0022]
The catalyst carrier preferably has a catalyst carrier substrate made of a heat-resistant material and a carrier layer made of a heat-resistant porous body formed on the catalyst carrier substrate.
[0023]
The catalyst carrier substrate is a member having a tubular passage through which exhaust gas passes in the axial direction. That is, by having a structure having a tubular passage through which the exhaust gas passes, the contact area of the exhaust gas purifying catalyst with the exhaust gas increases. When the contact area with the exhaust gas increases, the catalytic metal and the exhaust gas come into more contact, and the exhaust gas purifying ability of the exhaust gas purifying catalyst improves. Examples of such an exhaust gas purifying catalyst include a catalyst carrier substrate such as a monolith honeycomb carrier. The catalyst carrier substrate may be made of a material used for a conventional exhaust gas purifying catalyst. For example, a material such as a heat-resistant ceramic such as cordierite or a heat-resistant metal such as stainless steel may be used. it can.
[0024]
Since the support layer is made of a heat-resistant porous body, the surface area of the catalyst for exhaust gas purification as a catalyst carrier can be secured. The material for forming the support layer is not particularly limited, and a material used for a support layer in a conventionally known exhaust gas purifying catalyst can be used. For example, alumina can be used.
[0025]
Further, the carrier layer may be added with a conventionally known additive. For example, cerium oxide, zirconium oxide, barium oxide, yttrium, lanthanum, zeolite, and the like can be given. The amounts of these additives are not particularly limited. Further, the additive amount of the additive in the central portion and the peripheral portion may be changed.
[0026]
The catalytic noble metal is preferably made of at least one of Pt, Pd and Rh. That is, HC, CO, and NOx can be purified by using at least one of Pt, Pd, and Rh as the catalyst metal. In the present invention, when the catalyst noble metal is a plurality of noble metals, the total supported amount of the plurality of noble metals is defined as the supported amount on the catalyst carrier.
[0027]
The exhaust gas purifying catalyst of the present invention is preferably installed substantially coaxially with a pipe through which exhaust gas flows. By being attached substantially coaxially to the pipe, the vicinity of the axial center of the catalyst carrier can be used as the center.
[0028]
The exhaust gas purifying catalyst of the present invention is not particularly limited as long as it is a production method capable of supporting a catalytic noble metal at a high amount in the center.
[0029]
The exhaust gas purifying catalyst of the present invention can be used immediately at a temperature at which a large amount of catalytic noble metal carried on a portion where the flow rate of the exhaust gas is high (a portion where the gas flow rate of the exhaust gas is fast) can exhibit catalytic activity by the exhaust gas. Heated. In addition, since a sufficient amount of catalytic noble metal is supported on other portions, high exhaust gas purification performance is exhibited. That is, the exhaust gas purifying catalyst of the present invention is an exhaust gas purifying catalyst having excellent ignitability while maintaining high exhaust gas purifying performance.
[0030]
【Example】
Hereinafter, the present invention will be described using examples.
[0031]
As an example of the present invention, an exhaust gas purifying catalyst was manufactured.
[0032]
(Sample 1)
First, 100 parts by weight of alumina powder was dispersed in 150 parts by weight of deionized water, and then 5 parts by weight of alumina sol in terms of alumina was added and wet-milled to prepare an alumina slurry.
[0033]
The prepared alumina slurry was applied to a cylindrical catalyst support substrate made of stainless steel having a diameter of 100 mm and a length of 20 mm in the axial direction having a gas flow cell having a wall flow of 100 cells, and then at 200 ° C. for 1 hour. It was dried and then fired at 400 ° C. for 1 hour to form a carrier layer. The catalyst carrier substrate is manufactured by winding a stainless steel plate and a corrugated stainless steel plate in an overlapping state.
[0034]
Subsequently, a Pt aqueous solution containing 8 g / L of Pt in terms of Pt and an Rh aqueous solution containing 1.6 g / L of Rh in terms of Rh were prepared. Then, the stainless steel carrier on which the supporting layer was formed was immersed in a Pt aqueous solution, and dried and fired. Thereafter, the stainless steel carrier was immersed in an aqueous Rh solution and dried and fired. The supported amounts of Pt and Rh were Pt: 1.0 g / L-cat and Rh: 0.2 g / L-cat.
[0035]
Then, Pt: 4.0 g / L-cat and Rh: 0.8 g / L-cat were further carried on a circular portion (center portion) having a diameter of 50 mm concentric with the carrier. By further supporting the catalytic noble metal, the supported amounts of Pt and Rh at the center became 5.0 g / L-cat for Pt and 1.0 g / L-cat for Rh.
[0036]
In order to carry the catalytic noble metal on the central portion, first, a Pt aqueous solution containing Pt was prepared at 32 g / L in terms of Pt. The carrier was placed so that the axis was vertical, a Pt aqueous solution was poured into the center, the Pt aqueous solution was impregnated only into the cell supporting layer corresponding to the center, and dried and fired. An Rh aqueous solution containing Rh at 6.4 g / L in terms of Rh was prepared. Rh was carried in the same manner as in the case of the Pt aqueous solution.
[0037]
By the above means, the exhaust gas purifying catalyst of this sample was manufactured.
[0038]
FIG. 1 shows the configuration of the exhaust gas purifying catalyst of this sample. 1A is a cross section perpendicular to the axial direction of the exhaust gas purifying catalyst, and FIG. 1B is a diagram showing a cross section on the same plane as the axis. Further, the exhaust gas purifying catalyst illustrated in FIG. 1 is fitted into a hollow portion of a shaft center of an outer cylinder.
[0039]
In the exhaust gas purifying catalyst of this sample, Pt and Rh are supported on a cylindrical catalyst carrier having a carrier layer formed on the surface of a carrier substrate made of stainless steel. Then, in a cross section perpendicular to the axis of the catalyst carrier, Pt is 5.0 g / L-cat and Rh is 1.0 g / L- at a central portion inside a circle having a radius of 25 mm concentric with the axis of the catalyst carrier. Cat is loaded, and Pt is loaded on other portions (peripheral portions) at a loading of 1.0 g / L-cat and Rh is loaded at a loading of 0.2 g / L-cat. In the exhaust gas purifying catalyst of this sample, the carrying amount of the catalytic noble metal in the center portion and the peripheral portion does not change in any cross section perpendicular to the axis of the catalyst carrier.
[0040]
(Sample 2)
An exhaust gas purifying catalyst was produced in the same manner as in Sample 1, except that the center portion was formed in a circular shape having a diameter of 20 mm.
[0041]
In the exhaust gas purifying catalyst of this sample, Pt and Rh are supported on a cylindrical catalyst carrier having a carrier layer formed on the surface of a carrier substrate made of stainless steel. Then, in a cross section perpendicular to the axis of the catalyst carrier, Pt is 5.0 g / L-cat and Rh is 1.0 g / L- at the center of a circle having a radius of 10 mm concentric with the axis of the catalyst carrier. Cat is loaded, and Pt is loaded on other portions (peripheral portions) at a loading of 1.0 g / L-cat and Rh is loaded at a loading of 0.2 g / L-cat. In the exhaust gas purifying catalyst of this sample, the carrying amount of the catalytic noble metal in the center portion and the peripheral portion does not change in any cross section perpendicular to the axis of the catalyst carrier.
[0042]
(Sample 3)
An exhaust gas purifying catalyst was manufactured in the same manner as in Sample 1, except that Pd was supported at the center. Note that Pd is not carried on portions other than the central portion.
[0043]
First, similarly to Sample 1, a support layer was formed on the surface of a support substrate made of stainless steel, and Pt was supported at 1.0 g / L-cat and Rh was supported at 0.2 g / L-cat.
[0044]
Thereafter, a Pd aqueous solution containing Pd at 32 g / L in terms of Pd was prepared. Then, this Pd aqueous solution was impregnated into the center of the catalyst support, and dried and fired. The amount of Pd carried by this treatment was 4.0 g / L-cat.
[0045]
In the exhaust gas purifying catalyst of the present sample, Pt, Rh and Pd are supported on a cylindrical catalyst carrier having a carrier layer formed on the surface of a carrier substrate made of stainless steel. Then, in a cross section perpendicular to the axis of the catalyst carrier, Pt is 1.0 g / L-cat and Rh is 0.2 g / L- at a central portion inside a circle having a radius of 25 mm concentric with the axis of the catalyst carrier. cat and Pd carry 4.0 g / L-cat, and other parts (periphery) carry Pt at 1.0 g / L-cat and Rh carry 0.2 g / L-cat. Have been. In the exhaust gas purifying catalyst of this sample, the carrying amount of the catalytic noble metal in the center portion and the peripheral portion does not change in any cross section perpendicular to the axis of the catalyst carrier.
[0046]
(Sample 4)
An exhaust gas purifying catalyst was manufactured in the same manner as in Sample 1, except that Pt was supported at the center.
[0047]
First, similarly to Sample 1, a support layer was formed on the surface of a support substrate made of stainless steel, and Pt was supported at 1.0 g / L-cat and Rh was supported at 0.2 g / L-cat.
[0048]
Then, a Pt aqueous solution containing Pt at 32 g / L in terms of Pt was prepared. Then, this Pt aqueous solution was impregnated into the center of the catalyst support, and dried and fired. The carried amount of Pt by this treatment was 4.0 g / L-cat.
[0049]
In the exhaust gas purifying catalyst of this sample, Pt and Rh are supported on a cylindrical catalyst carrier having a carrier layer formed on the surface of a carrier substrate made of stainless steel. Then, in a cross section perpendicular to the axis of the catalyst carrier, Pt is 5.0 g / L-cat and Rh is 0.2 g / L- at a central portion inside a circle having a radius of 25 mm concentric with the axis of the catalyst carrier. Cat is loaded, and Pt is loaded on other portions (peripheral portions) at a loading of 1.0 g / L-cat and Rh is loaded at a loading of 0.2 g / L-cat. In the exhaust gas purifying catalyst of this sample, the carrying amount of the catalytic noble metal in the center portion and the peripheral portion does not change in any cross section perpendicular to the axis of the catalyst carrier.
[0050]
(Sample 5)
An exhaust gas purifying catalyst was produced in the same manner as in Sample 1, except that the center was a circular shape having a diameter of 10 mm.
[0051]
In the exhaust gas purifying catalyst of this sample, Pt and Rh are supported on a cylindrical catalyst carrier having a carrier layer formed on the surface of a carrier substrate made of stainless steel. Then, in a cross section perpendicular to the axis of the catalyst carrier, Pt is 5.0 g / L-cat and Rh is 1.0 g / L- at a central portion inside a circle having a radius of 5 mm concentric with the axis of the catalyst carrier. Cat is loaded, and Pt is loaded on other portions (peripheral portions) at a loading of 1.0 g / L-cat and Rh is loaded at a loading of 0.2 g / L-cat. In the exhaust gas purifying catalyst of this sample, the carrying amount of the catalytic noble metal in the center portion and the peripheral portion does not change in any cross section perpendicular to the axis of the catalyst carrier.
[0052]
(Sample 6)
An exhaust gas purifying catalyst was produced in the same manner as in Sample 1, except that the amounts of Pt and Rh carried on the center were changed.
[0053]
First, similarly to Sample 1, a support layer was formed on the surface of a support substrate made of stainless steel, and Pt was supported at 1.0 g / L-cat and Rh was supported at 0.2 g / L-cat.
[0054]
Then, a Pt aqueous solution containing Pt at 8 g / L in terms of Pt was prepared. This Pt aqueous solution was impregnated into the center of the catalyst support and dried and fired. An aqueous solution containing Rh at 1.6 g / L in terms of Rh was prepared and supported on the center similarly to Pt. The carried amount of Pt by this treatment was 1.0 g / L-cat, and the carried amount of Rh was 0.2 g / L-cat.
[0055]
In the exhaust gas purifying catalyst of this sample, Pt and Rh are supported on a cylindrical catalyst carrier having a carrier layer formed on the surface of a carrier substrate made of stainless steel. Then, in a cross section perpendicular to the axis of the catalyst carrier, Pt is 2.0 g / L-cat and Rh is 0.4 g / L- at a central portion inside a circle having a radius of 25 mm concentric with the axis of the catalyst carrier. Cat is loaded, and Pt is loaded on other portions (peripheral portions) at a loading of 1.0 g / L-cat and Rh is loaded at a loading of 0.2 g / L-cat. In the exhaust gas purifying catalyst of this sample, the carrying amount of the catalytic noble metal in the center portion and the peripheral portion does not change in any cross section perpendicular to the axis of the catalyst carrier.
[0056]
(Evaluation)
As the evaluation of the exhaust gas purifying catalyst of each sample, the ignition temperature of the catalyst was measured. The ignition temperature was measured by measuring the ignition temperature when actually mounted on a scooter having a 4-cycle engine (125 cc) and operated under the conditions specified in EC-40 (ISO 6460). The measurement results are shown in FIG.
[0057]
Specifically, the ignition temperature was measured by running in the EC-40 mode while measuring the temperature of the gas entering the catalyst and the temperature in the bed of the catalyst. Then, the point at which the temperature in the catalyst bed became higher than the incoming gas temperature was determined as the ignition temperature and measured.
[0058]
[Table 1]
From the figure and the table, it can be seen that the ignition temperatures of the catalysts of the exhaust gas purifying catalysts of Samples 1 to 4 are significantly reduced. In the exhaust gas purifying catalysts of Samples 1 to 4, the supported amount of the catalytic noble metal in the central portion is larger than the supported amount in the peripheral portion. This central portion is the portion where the gas flow of the exhaust gas flows fastest. For this reason, a large amount of exhaust gas passes through the inside of the central cell, and the exhaust gas heats the carrier layer and the catalytic noble metal formed on the inner wall of the cell. Since the central part where the flow rate of the exhaust gas is fast is more easily heated than the peripheral part, the catalytic noble metal carried in the central part immediately reaches the catalytic activation temperature. The exhaust gas purifying catalysts of Samples 1 to 4 carry a large amount of catalytic noble metal at the center, and can sufficiently purify the exhaust gas passing through the cell at the center. Therefore, the exhaust gas purifying catalysts of Samples 1 to 4 can exhibit high purification performance even in a low temperature range immediately after the start of the engine.
[0060]
The exhaust gas purifying catalyst of Sample 5 was unable to exhibit sufficient ignition performance because of the small cross-sectional area at the center. In addition, the exhaust gas purifying catalyst of Sample 6 did not exhibit sufficient ignition performance because the amount of the noble metal catalyst carried was small.
[0061]
(Sample 7)
An exhaust gas purifying catalyst was produced in the same manner as in Sample 1, except that the shape of the central portion was square.
[0062]
In the exhaust gas purifying catalyst of this sample, Pt and Rh are supported on a cylindrical catalyst carrier having a carrier layer formed on the surface of a carrier substrate made of stainless steel. Then, in a cross section perpendicular to the axis of the catalyst carrier, Pt is 5.0 g / L-cat, Rh is Pt in the center of the inside of a square having a side length of 25 mm whose center of gravity coincides with the axis of the catalyst carrier. 1.0 g / L-cat is supported, and Pt is supported on the other part (peripheral portion) at 1.0 g / L-cat and Rh is supported at 0.2 g / L-cat. In the exhaust gas purifying catalyst of this sample, the carrying amount of the catalytic noble metal in the center portion and the peripheral portion does not change in any cross section perpendicular to the axis of the catalyst carrier.
[0063]
FIG. 3 shows the structure of the exhaust gas purifying catalyst of this sample.
[0064]
This sample is formed so that the center has a square shape. However, the amount of the catalyst noble metal carried in the center is five times that of the peripheral portion, and the sample has a sufficient cross-sectional area. As in Nos. 1 to 4, the catalyst is an exhaust gas purifying catalyst having excellent catalytic ignition properties.
[0065]
【The invention's effect】
The exhaust gas purifying catalyst of the present invention can be used immediately at a temperature at which a large amount of catalytic noble metal carried on a portion where the flow rate of the exhaust gas is high (a portion where the gas flow rate of the exhaust gas is fast) can exhibit catalytic activity by the exhaust gas. Heated. In addition, since a sufficient amount of catalytic noble metal is supported on other portions, high exhaust gas purification performance is exhibited. That is, the exhaust gas purifying catalyst of the present invention is an exhaust gas purifying catalyst excellent in ignitability while maintaining high exhaust gas purifying performance.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an exhaust gas purifying catalyst of Sample 1. FIG.
FIG. 2 is a view showing measurement results of catalyst ignition temperatures of exhaust gas purifying catalysts of samples 1 to 6.
FIG. 3 is a diagram showing a configuration of an exhaust gas purifying catalyst of Sample 7.
Claims (5)
軸方向に垂直な断面の中心部における該触媒貴金属の担持量が該中心部以外の周縁部における担持量の３倍以上となるように全長にわたって担持されていることを特徴とする排ガス浄化用触媒。A catalyst carrier having a plurality of cells through which exhaust gas passes in the axial direction, and a catalyst noble metal supported on the catalyst carrier,
An exhaust gas purifying catalyst characterized in that the catalyst is supported over its entire length such that the amount of the catalyst noble metal carried at the center of the cross section perpendicular to the axial direction is at least three times the amount carried at the periphery other than the center. .
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| Application Number | Priority Date | Filing Date | Title |
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| JP2003070436A JP2004275883A (en) | 2003-03-14 | 2003-03-14 | Waste gas purification catalyst |
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| JP2003070436A JP2004275883A (en) | 2003-03-14 | 2003-03-14 | Waste gas purification catalyst |
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2009528477A (en) * | 2006-02-28 | 2009-08-06 | ジョンソン、マッセイ、パブリック、リミテッド、カンパニー | Exhaust mechanism for spark ignition internal combustion engine |
| JP2013154300A (en) * | 2012-01-30 | 2013-08-15 | Toyota Motor Corp | Honeycomb structure |
| JP2013244438A (en) * | 2012-05-24 | 2013-12-09 | Toyota Motor Corp | Catalytic converter |
| JP2015024381A (en) * | 2013-07-26 | 2015-02-05 | マツダ株式会社 | Catalyst for exhaust gas purification |
| WO2016039302A1 (en) * | 2014-09-10 | 2016-03-17 | 株式会社キャタラー | Exhaust gas purification catalyst |
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2003
- 2003-03-14 JP JP2003070436A patent/JP2004275883A/en active Pending
Cited By (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2009528477A (en) * | 2006-02-28 | 2009-08-06 | ジョンソン、マッセイ、パブリック、リミテッド、カンパニー | Exhaust mechanism for spark ignition internal combustion engine |
| JP2013127251A (en) * | 2006-02-28 | 2013-06-27 | Johnson Matthey Plc | Exhaust system for spark-ignited internal combustion engine |
| JP2013154300A (en) * | 2012-01-30 | 2013-08-15 | Toyota Motor Corp | Honeycomb structure |
| JP2013244438A (en) * | 2012-05-24 | 2013-12-09 | Toyota Motor Corp | Catalytic converter |
| JP2015024381A (en) * | 2013-07-26 | 2015-02-05 | マツダ株式会社 | Catalyst for exhaust gas purification |
| WO2016039302A1 (en) * | 2014-09-10 | 2016-03-17 | 株式会社キャタラー | Exhaust gas purification catalyst |
| CN106714963A (en) * | 2014-09-10 | 2017-05-24 | 株式会社科特拉 | Exhaust gas purification catalyst |
| JPWO2016039302A1 (en) * | 2014-09-10 | 2017-07-20 | 株式会社キャタラー | Exhaust gas purification catalyst |
| CN106714963B (en) * | 2014-09-10 | 2020-01-03 | 株式会社科特拉 | Catalyst for exhaust gas purification |
| US10688476B2 (en) | 2014-09-10 | 2020-06-23 | Cataler Corporation | Exhaust gas purification catalyst |
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