JP2004321894A

JP2004321894A - Exhaust gas cleaning catalyst and method for producing the same

Info

Publication number: JP2004321894A
Application number: JP2003118112A
Authority: JP
Inventors: Masaki Nakamura; 雅紀中村; Katsuo Suga; 克雄菅
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 2003-04-23
Filing date: 2003-04-23
Publication date: 2004-11-18

Abstract

<P>PROBLEM TO BE SOLVED: To produce an exhaust gas cleaning catalyst which by itself can realize HC (hydrocarbon) adsorption cleaning at low temperatures and NO<SB>X</SB>removal in a low-temperature and lean regions and is improved in an NO<SB>x</SB>removal capacity, and to provide a method for producing the same. <P>SOLUTION: The exhaust gas cleaning catalyst is prepared by laminating at least three layers of an HC adsorption cleaning layer, an interior adsorption cleaning layer, and an exterior adsorption cleaning layer on an integral support in the above order. The HC adsorption cleaning layer contains a Pt-bearing ceria and zeolite, the internal adsorption cleaning layer contains Ce, Pt, or the like, and the external adsorption cleaning layer contains an alkali metal, or the like, Ce, Rh, Pt, or the like, and the total Ce content (calculated as CeO<SB>2</SB>) of the internal and external adsorption cleaning layers is 40 to 100 g/L of the catalyst. The method for producing the same comprises preparing a slurry containing ceria bearing Pt, or the like, for every layer, and applying, drying, and baking to every slurry. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、排気ガス浄化触媒及びその製造方法に係り、更に詳細には、１５０℃以下の低温での炭化水素（ＨＣ）吸着浄化性能、１５０〜２５０℃の低温及び酸素過剰雰囲気下（リーン域）での窒素酸化物（ＮＯｘ）吸着浄化性能に優れた排気ガス浄化触媒及びその製造方法に関する。
【０００２】
【従来の技術】
従来からリーン域のＮＯｘを浄化する触媒は種々提案されており、例えば、白金とランタンを多孔質担体に担持した触媒（例えば、特許文献１参照。）に代表されるように、リーン域でＮＯｘを吸着し、ストイキからリッチ域の時にＮＯｘを放出させて浄化する触媒が知られている。
また、エンジン始動時等の低排温時にＨＣを浄化する触媒としては、例えば、ゼオライトを含む触媒が知られている（例えば、特許文献２参照。）。
【０００３】
【特許文献１】
特開平５−１６８８６０号公報
【特許文献２】
特開平１１−４７５９６号公報
【０００４】
【発明が解決しようとする課題】
しかしながら、リーンバーンエンジンやディーゼルエンジンでは、低温でのＨＣ吸着浄化、リーン域でのＮＯｘ浄化のために上記のような触媒を２個配置する必要があり、貴金属使用量の増加や排圧の上昇などの多くの問題点が存在した。本発明のように、２つの触媒の機能を１つの触媒で満たせるようにすれば、上記のような問題は解決できると考えられ、具体的には、ＨＣ吸着材であるゼオライト層の上に貴金属とＮＯｘ吸着材であるアルカリを含む層を積層し、下層において、低温でのＨＣの吸着、上層において、ＮＯｘの吸着、浄化及び下層で吸着したＨＣの浄化を行わせるという触媒が挙げられる。
しかし、このような触媒は、それぞれの触媒層が薄くなるため、それぞれの機能が十分に発揮できないという問題がある。
【０００５】
本発明者らが細かく解析すると、上層のＮＯｘ浄化を行う層からのＮＯｘ脱離、浄化が十分に行われていないことがわかった。これは、触媒入口温度が２５０℃以下であると、より顕著であり、この温度範囲でも十分にＮＯｘを脱離、浄化するためにはＨ_２が必要であることも明らかになった。近年、低燃費化のためエンジンの燃焼効率が上がり、低排温化が進むにつれて、この問題は益々大きくなりつつある。
【０００６】
本発明は、このような知見に鑑みてなされたものであり、その目的とするところは、１５０℃以下の低温での炭化水素（ＨＣ）吸着浄化、１５０〜２５０℃の低温及びリーン域での窒素酸化物（ＮＯｘ）浄化を１つの触媒で実現でき、ＮＯｘ浄化性能を向上した排気ガス浄化触媒及びその製造方法を提供することにある。
【０００７】
【課題を解決するための手段】
本発明者らは、上記目的を達成すべく鋭意検討を重ねた結果、ＨＣ吸着浄化層に、ゼオライトと白金等の貴金属を担持したセリア材を共存させ、更に吸着浄化内層及び吸着浄化外層に、所定量のセリウムを存在させることなどにより、上記目的が達成できることを見出し、本発明を完成するに至った。
【０００８】
即ち、本発明の排気ガス浄化触媒は、一体構造型担体に、ＨＣを吸着・浄化するＨＣ吸着浄化層、ＮＯｘを吸着・浄化し且つＨＣを浄化する吸着浄化内層、及びＮＯｘを吸着・浄化し且つＨＣを浄化する吸着浄化外層の少なくとも３つの触媒層をこの順で積層して成る。
上記ＨＣ吸着浄化層が、ゼオライトと、白金（Ｐｔ）及び／又はパラジウム（Ｐｄ）と、セリア材とを含有し、かかるセリア材にはＰｔ及び／又はＰｄが担持されており、上記吸着浄化内層が、アルカリ金属及び／又はアルカリ土類金属と、セリウム（Ｃｅ）と、Ｐｔ及び／又はＰｄと、アルミナとを含有し、上記吸着浄化外層が、アルカリ金属及び／又はアルカリ土類金属と、Ｃｅと、ロジウム（Ｒｈ）と、Ｐｔ及び／又はＰｄと、アルミナとを含有し、上記吸着浄化内層及び外層のＣｅ量の合計がＣｅＯ_２換算で、この触媒１Ｌ当り４０〜１００ｇ／Ｌであって、低温でのＨＣ吸着浄化能、低温及び酸素過剰雰囲気下でのＮＯｘ吸着浄化能を併有する排気ガス浄化触媒である。
【０００９】
また、本発明の排気ガス浄化触媒の製造方法は、上述の如き排気ガス浄化触媒を製造する方法であって、下記の工程▲１▼〜▲４▼を含むものである。
▲１▼セリア材にＰｔ及び／又はＰｄを含有するアルカリ性水溶液を含浸させてＰｔ及び／又はＰｄ担持粉末を作成し、次いで、この粉末とゼオライトを用いてＨＣ吸着浄化層を形成するためのＨＣ吸着浄化層スラリーを作成する工程。
▲２▼アルミナにＣｅとアルカリ金属及び／又はアルカリ土類金属を担持した粉末を作成し、次いで、この粉末にＰｔ及び／又はＰｄを含有するアルカリ性水溶液を含浸させてＰｔ及び／又はＰｄ担持粉末を作成し、これら粉末を用いて吸着浄化内層を形成するための内層スラリーを作成する工程。
▲３▼アルミナにＣｅとアルカリ金属及び／又はアルカリ土類金属を担持した粉末を作成し、次いで、この粉末にＰｔ及び／又はＰｄを含有するアルカリ性水溶液を含浸させてＰｔ及び／又はＰｄ担持粉末を作成し、一方、アルミナに硝酸ロジウム水溶液を含浸させてＲｈ担持粉末を作成し、これら粉末を用いて吸着浄化外層を形成するための外層スラリーを作成する工程。
▲４▼その後、一体構造型担体に、▲１▼〜▲３▼工程で得られたＨＣ吸着浄化層スラリー、内層スラリー及び外層スラリーをこの順で、コートし、乾燥し、焼成して、ＨＣ吸着浄化層、吸着浄化内層及び吸着浄化外層を積層形成する工程。
【００１０】
【発明の実施の形態】
以下、本発明の排気ガス浄化触媒について詳細に説明する。なお、本明細書において、「％」は特記しない限り質量百分率を表すものとする。
【００１１】
上述の如く、本発明の排気ガス浄化触媒は、一体構造型担体に、ＨＣを吸着・浄化するＨＣ吸着浄化層、ＮＯｘを吸着・浄化し且つＨＣを浄化する吸着浄化内層、及びＮＯｘを吸着・浄化し且つＨＣを浄化する吸着浄化外層の少なくとも３つの触媒層をこの順で積層して構成され、低温でのＨＣ吸着浄化能、低温及び酸素過剰雰囲気下でのＮＯｘ吸着浄化能を併有する。
ここで、一体構造型担体としては、例えばコーディエライトなどのセラミックスやフェライト系ステンレスなどの金属等の耐熱性材料から成るモノリス担体やハニカム担体が用いられる。
【００１２】
従来技術によれば、ＨＣを吸着する触媒とリーン時のＮＯｘを浄化する触媒のすくとも２種の触媒が必要となり、これにより、排圧上昇が生じて燃費に悪影響を及ぼし、また少なくとも触媒２個分の貴金属量が必要となり資源枯渇を招くが、本発明の排気ガス浄化触媒は、上述した複合機能を１個の触媒に集約した触媒であり、このような問題を改善することができる。
【００１３】
また、本発明の排気ガス浄化触媒のＨＣ吸着浄化層は、ゼオライトとＰｔ及びＰｄの一方又は双方を担持したセリア材とを含有し、吸着浄化内層は、アルカリ金属及びアルカリ土類金属の一方又は双方と、Ｃｅと、Ｐｔ及びＰｄの一方又は双方と、アルミナとを含有し、吸着浄化外層は、アルカリ金属及びアルカリ土類金属の一方又は双方と、Ｃｅと、Ｒｈと、Ｐｔ及びＰｄの一方又は双方と、アルミナとを含有する。
ここで、「セリア材」とは、少なくともＣｅを含有する酸化物のことをいう。
【００１４】
かかるＨＣ吸着浄化層において、ゼオライトは、１５０℃以下の低温でＨＣの吸着や浄化を行い、ＰｔやＰｄを担持したセリア材は、水（Ｈ_２Ｏ）とゼオライトのＨＣ浄化で発生した一酸化炭素（ＣＯ）からＣＯシフト反応によって、ＮＯｘ浄化に有効な水素（Ｈ_２）を生成する。
一方、かかる吸着浄化内層及び外層において、アルミナは高表面積基材として触媒成分を担持し、アルカリ金属やアルカリ土類金属が形成する化合物（ＮＯｘ吸着材）はＮＯｘの吸着を行い、Ｐｔ、Ｐｄ及びＲｈはＮＯｘ浄化やＨＣ浄化を行うが、特にＲｈはＮＯｘ浄化に優れた性能を示し、セリア材は上述したＨ_２生成によるＮＯｘの脱離や浄化の機能を向上させる。
これにより、１５０℃以下の低温でのＨＣ吸着や浄化が可能となり、１５０〜２５０℃の低温でのＮＯｘ浄化性能を向上させることができる。
【００１５】
更に、本発明の排気ガス浄化触媒は、吸着浄化内層及び外層のＣｅ量の合計がＣｅＯ_２換算で、この触媒１Ｌ当り４０〜１００ｇ／Ｌであることを要する。
４０ｇ／Ｌ未満では、ＣＯシフト反応を十分に進行させることができない可能性があり、１００ｇ／Ｌを超えると、ＨＣ、ＣＯ、Ｈ_２などの還元材を酸化する機能の方が強く発現し、ＮＯｘの脱離が行われなくなる可能性がある。
【００１６】
本発明の排気ガス浄化触媒においては、吸着浄化内層のＣｅ量が吸着浄化外層のＣｅ量より多いことが好ましく、吸着浄化内層のＣｅ量と吸着浄化外層のＣｅ量の比がＣｅＯ_２換算で６：４〜８：２であることが更に好ましい。
吸着浄化内層のＣｅ量より吸着浄化外層のＣｅ量が多いと、上述の還元材を酸化して消費してしまい、ＮＯｘの脱離や浄化に悪影響を及ぼす可能性がある。Ｃｅが吸着浄化外層にあると、ＮＯｘの浄化に必要な上述の還元材を酸化してしまうため、Ｃｅは理想的には吸着浄化外層には含有されないことが望ましい。
しかし、含有されない場合は、硫黄化合物（Ｓ）被毒解除に有効なＨ_２は、ＰｔやＰｄを担持したセリア材によって生成することから、Ｓ被毒によってＮＯｘ浄化性能に悪影響が及ぶ可能性が高い。
このような観点から、上述の比率で吸着浄化内層及び外層に含有させることが好ましく、これにより、内層及び外層の双方において、ＮＯｘの吸着、脱離及び浄化ができるようになり、更にＳ被毒解除性能も向上する。
【００１７】
また、本発明の排気ガス浄化触媒においては、吸着浄化外層に含まれるアルカリ金属及びアルカリ土類金属の一方又は双方の量が、吸着浄化内層に含まれるアルカリ金属及びアルカリ土類金属の一方又は双方の量より対応するそれぞれの酸化物換算で、多いことが好ましい。
本発明の触媒は２５０℃以下の低温で使用するので、ＮＯｘ吸着性能を最大限発揮するためである。また、Ｓ被毒解除も吸着浄化外層側ほど起こり易いので、Ｓ被毒解除に関しても有効なアルカリ金属やアルカリ土類金属の配置となる。
【００１８】
更に、本発明の排気ガス浄化触媒においては、吸着浄化内層及び外層のアルカリ金属及びアルカリ土類金属の一方又は双方の金属が、マグネシウム（Ｍｇ）、カルシウム（Ｃａ）、ストロンチウム（Ｓｒ）、バリウム（Ｂａ）又はナトリウム（Ｎａ）及びこれらの任意の組合せに係る金属を含有することが望ましく、これら金属が形成する化合物の一部又は全部が、炭酸バリウムマグネシウム（ＢａＭｇ（ＣＯ_３）_２）であることが特に望ましい。
【００１９】
本発明の触媒は２５０℃以下の低温で使用するので、上記アルカリ金属やアルカリ土類金属を含有する化合物より弱いアルカリ（例えば、希土類などが挙げられる。）では、ＮＯｘの吸着ができず、また、強いアルカリ（例えば、カリウム（Ｋ）やセシウム（Ｃｓ）などが挙げられる。）では、これらが吸着したＮＯｘが脱離することができず、ＮＯｘ浄化性能に悪影響を及ぼす可能性がある。
このようなＮＯｘ吸着材としては、ＢａやＮａを含有する化合物が好適であるが、Ｎａはその化合物（例えば、炭酸ナトリウム（Ｎａ_２ＣＯ_３）が挙げられる。）が、水溶性であるため、触媒作成時にゼオライトを含有するＨＣ吸着浄化層に溶け出してしまい、ＨＣ吸着性能に悪影響を及ぼす可能性が高い。
【００２０】
一方、Ｓ被毒解除を考慮した場合には、ＮＯｘ吸着材の安定性が非常に重要な課題となり、この点はＮＯｘ浄化性能に関しても同様であるが、そのためには、複合化という手段を用いることが有効である。現時点において、本発明の触媒を用いる温度範囲において好適なＮＯｘ浄化性能を発揮し、且つ複合化することができる良好なものとして、例えばＢａＭｇ（ＣＯ_３）_２が挙げられる。また、複合化することは、ゼオライトへの吸着材の溶け出しを考慮した場合にも有効である。
このように吸着材を複合化することにより、Ｓ被毒を抑制、ＮＯｘ浄化性能の低下を抑制、及びゼオライトへの溶け出しを防止などの多くの問題点を解決することができる。
【００２１】
また、本発明の排気ガス浄化触媒のＨＣ吸着浄化層において、ＰｔやＰｄを担持したセリア材に、更にアルカリ土類金属を含有させることが望ましい。
ＮＯｘ吸着材をＨＣ吸着浄化層に含有させることにより、ＮＯｘ浄化性能を向上させることが可能となり、ゼオライト以外のＰｔやＰｄを担持したセリア材にアルカリ土類金属を担持させることにより、ゼオライトへ溶け出し、及びその結果発生する細孔閉塞が防止されＨＣ吸着性能を維持することができる。
【００２２】
更に、本発明の排気ガス浄化触媒のＨＣ吸着浄化層において、ＰｔやＰｄを担持したセリア材に、更にジルコニウム（Ｚｒ）を含有させることが好ましく、セリア材中のＣｅとＺｒとの含有比率が、それぞれＣｅＯ_２、ＺｒＯ_２換算の重量比で７０：３０〜８０：２０であることが更に好ましく、その重量比が７５：２５であることが特に好ましい。
セリア材の安定性を向上させるためにジルコニウムと複合化させることは有効であり、また、Ｈ_２生成機能の劣化を抑制することもできる。現時点における、その好適形態は上述のＣｅ−Ｚｒ複合酸化物である。
【００２３】
次に、本発明の排気ガス浄化触媒の製造方法につき詳細に説明する。
この製造方法は、上述した本発明の排気ガス浄化触媒を製造する方法であり、上記ＨＣ吸着浄化層、吸着浄化内層及び吸着浄化外層を形成するためのＨＣ吸着浄化層スラリー、内層スラリー及び外層スラリーを調製し、これらスラリーをハニカム担体などの一体構造型担体に順次塗布し、乾燥及び焼成等を行う方法であり、具体的には、下記の▲１▼〜▲４▼の工程を含む。
【００２４】
▲１▼セリア材にＰｔ及びＰｄの一方又は双方を含有するアルカリ性水溶液を含浸させて、Ｐｔ及びＰｄの一方又は双方を担持する粉末を作成し、次いで、この粉末とゼオライトを用いてＨＣ吸着浄化層スラリーを作成する工程。
▲２▼アルミナにＣｅとアルカリ金属及びアルカリ土類金属の一方又は双方を担持した粉末を作成し、次いで、この粉末にＰｔ及びＰｄの一方又は双方を含有するアルカリ性水溶液を含浸させてＰｔ及びＰｄの一方又は双方を担持する粉末を作成し、これら粉末を用いて内層スラリーを作成する工程。
▲３▼アルミナにＣｅとアルカリ金属及びアルカリ土類金属の一方又は双方を担持した粉末を作成し、次いで、この粉末にＰｔ及びＰｄの一方又は双方を含有するアルカリ性水溶液を含浸させてＰｔ及びＰｄの一方又は双方を担持した粉末を作成し、一方、アルミナに硝酸ロジウム水溶液を含浸させてＲｈ担持粉末を作成し、これら粉末を用いて外層スラリーを作成する工程。
▲４▼しかる後、ハニカム担体などの一体構造型担体に、▲１▼〜▲３▼工程で得られたＨＣ吸着浄化層スラリー、内層スラリー及び外層スラリーをこの順で、コートし、乾燥し、焼成して、ＨＣ吸着浄化層、吸着浄化内層及び吸着浄化外層を積層形成する工程。
【００２５】
▲１▼工程、▲２▼工程及び▲３▼工程において、ＰｔやＰｄをセリア材に担持させるのは、このような粉末がＨＣ吸着浄化層において、上述したようにＨ_２生成に寄与するからである。
また、ＨＣ吸着浄化層にアルカリ土類金属を含有させる場合には、▲１▼工程において、まず、セリア材にアルカリ土類金属を担持させることが望ましい。このように、ゼオライト以外のセリア材に担持させることによって、ゼオライトの細孔がＮＯｘ吸着材によって閉塞されることが防止され、ＨＣ吸着性能を維持でき、また、ＮＯｘ浄化性能を向上することが可能となる。
【００２６】
【実施例】
以下、本発明を実施例及び比較例により更に詳細に説明するが、本発明はこれら実施例に限定されるものではない。
【００２７】
（実施例１）
酢酸セリウム水溶液と酢酸バリウム水溶液とを混合、攪拌し、この中にアルミナを投入し、１時間室温で攪拌し、１２０℃で一昼夜乾燥した後、６００℃で１時間焼成し、２種担持粉末を得た。これを粉末Ａとした（粉末ＡのＢａ担持濃度はＢａＯとして７．３％、Ｃｅ担持濃度はＣｅＯ_２として２０％）。
粉末Ａに２％のテトラアンミンＰｔ水酸塩溶液（ｐＨ＝１０．５）を含浸させ、１２０℃で一昼夜乾燥した後、４００℃で１時間焼成し、Ｐｔ担持粉末を得た。これを粉末Ｂとした（粉末ＢのＰｔ担持濃度は１．０４％）。
【００２８】
酢酸ジルコニウム水溶液中にアルミナを投入し、１時間室温で攪拌し、１２０℃で一昼夜乾燥した後、９００℃で１時間焼成して粉末を得、得られた粉末に６％の硝酸ロジウム水溶液を含浸させ、１２０℃で一昼夜乾燥した後、４００℃で１時間焼成し、Ｒｈ担持粉末を得た。これを粉末Ｃとした（粉末ＣのＲｈ担持濃度は２．４％、Ｚｒの担持濃度はＺｒＯ_２として３％）。
粉末Ａに２％のテトラアンミンＰｔ水酸塩溶液（ｐＨ＝１０．５）を含浸させ、１２０℃で一昼夜乾燥した後、４００℃で１時間焼成し、Ｐｔ担持粉末を得た。これを粉末Ｄとした（粉末ＤのＰｔ担持濃度は３．４１％）。
酸化セリウムに２％のテトラアンミンＰｔ水酸塩溶液（ｐＨ＝１０．５）を含浸させ、１２０℃で一昼夜乾燥した後、４００℃で１時間焼成し、Ｐｔ担持粉末を得た。これを粉末Ｅとした（粉末ＥのＰｔ担持濃度は３．２％）。
【００２９】
ベータゼオライトを６２７．５ｇ、粉末Ｅを９２．６ｇ、シリカゾルを１７９．９ｇ、水９００ｇを磁性ボールミルに投入し、混合粉砕して、ＨＣ吸着浄化層スラリーを得た。
粉末Ｂを７６７．８ｇ、粉末Ａを５０．５ｇ、酸化Ｃｅを４７．８ｇ、アルミナゾル３３．９ｇ、水９００ｇを磁性ボールミルに投入し、混合粉砕して、内層スラリーを得た。
粉末Ｃを２７２．０ｇ、粉末Ｄを４０３．９ｇ、粉末Ａを８４．８、酸化セリウムを８１．１ｇ、アルミナゾルを５８．１ｇ、水９００ｇを磁性ボールミルに投入し、混合粉砕して、外層スラリーを得た。
【００３０】
ＨＣ吸着浄化層スラリーをコーデェライト質モノリス担体（１．２Ｌ、４００セル）に付着させ、空気流にてセル内の余剰のスラリーを取り除いて１３０℃で乾燥した後、４００℃で１時間焼成し、コート層１７２．１ｇ／Ｌの触媒を得た。これを触媒ａとした。
内層スラリーを触媒ａに付着させ、空気流にてセル内の余剰のスラリーを取り除いて１３０℃で乾燥した後、４００℃で１時間焼成し、コート層１６７．５ｇ／Ｌの触媒を得た。これを触媒ｂとした。
外層スラリーを触媒ｂに付着させ、空気流にてセル内の余剰のスラリーを取り除いて１３０℃で乾燥した後、４００℃で１時間焼成し、コート層９７．６ｇ／Ｌの本例の排気ガス浄化触媒を得た。
【００３１】
（実施例２）
粉末Ａに１２％の硝酸パラジウム溶液を含浸させ、１２０℃で一昼夜乾燥した後、４００℃で１時間焼成し、Ｐｄ担持粉末を得た。これを粉末Ｆとした（粉末ＦのＰｄ担持濃度は１．０４％）。
粉末Ａに１２％の硝酸パラジウム溶液を含浸させ、１２０℃で一昼夜乾燥した後、４００℃で１時間焼成し、Ｐｄ担持粉末を得た。これを粉末Ｇとした（粉末ＦのＰｄ担持濃度は３．４１％）。
酸化セリウムに１２％の硝酸パラジウム溶液を含浸させ、１２０℃で一昼夜乾燥した後、４００℃で１時間焼成し、Ｐｄ担持粉末を得た。これを粉末Ｈとした（粉末ＨのＰｄ担持濃度は３．２％）。
【００３２】
ベータゼオライトを６２７．５ｇ、粉末Ｅを６９．４ｇ、粉末Ｈを２３．２ｇ、シリカゾルを１７９．９ｇ、水９００ｇを磁性ボールミルに投入し、混合粉砕して、ＨＣ吸着浄化層スラリーを得た。
粉末Ｂを５７５．８ｇ、粉末Ｆを１９２．０ｇ、粉末Ａを５０．５ｇ、酸化Ｃｅを４７．８ｇ、アルミナゾル３３．９ｇ、水９００ｇを磁性ボールミルに投入し、混合粉砕して、内層スラリーを得た。
粉末Ｃを２７２．０ｇ、粉末Ｄを３０２．９ｇ、粉末Ｇを１０１．０ｇ、粉末Ａを８４．８、酸化Ｃｅを８１．１ｇ、アルミナゾルを５８．１ｇ、水９００ｇを磁性ボールミルに投入し、混合粉砕して、外層スラリーを得た。
【００３３】
ＨＣ吸着浄化層スラリーをコーデェライト質モノリス担体（１．２Ｌ、４００セル）に付着させ、空気流にてセル内の余剰のスラリーを取り除いて１３０℃で乾燥した後、４００℃で１時間焼成し、コート層１７２．１ｇ／Ｌの触媒を得た。これを触媒ｃとした。
内層スラリーを触媒ｃに付着させ、空気流にてセル内の余剰のスラリーを取り除いて１３０℃で乾燥した後、４００℃で１時間焼成し、コート層１６７．５ｇ／Ｌの触媒を得た。これを触媒ｄとした。
外層スラリーを触媒ｄに付着させ、空気流にてセル内の余剰のスラリーを取り除いて１３０℃で乾燥した後、４００℃で１時間焼成し、コート層９７．６ｇ／Ｌの本例の排気ガス浄化触媒を得た。
【００３４】
（実施例３）
粉末Ａの酢酸バリウム水溶液を酢酸カルシウム水溶液に変えた（この粉末のＣａ担持濃度はＣａＯとして、２．６５％）以外は実施例１と同様の操作を繰り返し、本例の排気ガス浄化触媒を得た。
【００３５】
（実施例４）
粉末Ａの酢酸バリウム水溶液を酢酸ストロンチウム水溶液に変えた（この粉末のＳｒ担持濃度はＳｒＯとして、４．９１％）以外は実施例１と同様の操作を繰り返し、本例の排気ガス浄化触媒を得た。
【００３６】
（実施例５）
粉末Ａの酢酸バリウム水溶液を酢酸ナトリウム水溶液に変えた（この粉末のＮａ担持濃度はＮａ_２Ｏとして、２．９９％）以外は実施例１と同様の操作を繰り返し、本例の排気ガス浄化触媒を得た。
【００３７】
（実施例６）
粉末Ａの酢酸バリウム水溶液を酢酸バリウムと酢酸マグネシウムの混合溶液に変えた（この粉末のＢａ担持濃度はＢａＯとして、７．３％、Ｍｇ担持濃度はＭｇＯとして、２．３％）以外は実施例１と同様の操作を繰り返し、本例の排気ガス浄化触媒を得た。
【００３８】
（実施例７）
粉末Ａの酢酸バリウム水溶液を酢酸バリウムと酢酸ナトリウムの混合溶液に変えた（この粉末のＢａ担持濃度はＢａＯとして、７．３％、Ｎａ担持濃度はＮａ_２Ｏとして、３．４８％）以外は実施例１と同様の操作を繰り返し、本例の排気ガス浄化触媒を得た。
【００３９】
（実施例８）
粉末Ａの酢酸バリウム水溶液を酢酸バリウムと酢酸ストロンチウムの混合溶液に変えた（この粉末のＢａ担持濃度はＢａＯとして、７．３％、Ｓｒ担持濃度はＳｒＯとして、５．８５％）以外は実施例１と同様の操作を繰り返し、本例の排気ガス浄化触媒を得た。
【００４０】
（実施例９）
内層スラリーの粉末ＢのＣｅ担持濃度をＣｅＯ_２として２５％、粉末ＡのＣｅ担持濃度をＣｅＯ_２として２５％、外層スラリーの粉末ＤのＣｅ担持濃度をＣｅＯ_２として１５％、粉末ＡのＣｅ担持濃度をＣｅＯ_２として１５％とした以外は実施例６と同様の操作を繰り返し、本例の排気ガス浄化触媒を得た。
【００４１】
（実施例１０）
内層スラリーの粉末ＢのＢａ担持濃度をＢａＯとして３％、粉末ＡのＢａ担持濃度をＢａＯとして３％、外層スラリーの粉末ＤのＢａ担持濃度をＢａＯとして２０％、粉末ＡのＢａ担持濃度をＢａＯとして２０％とした以外は実施例６と同様の操作を繰り返し、本例の排気ガス浄化触媒を得た。
【００４２】
（実施例１１）
酸化セリウムに酢酸バリウム水溶液を含浸させ、１２０℃で一昼夜乾燥した後、６００℃で１時間焼成して粉末を得、得られた粉末に２％のテトラアンミンＰｔ水酸塩溶液（ｐＨ＝１０．５）を含浸させ、１２０℃で一昼夜乾燥した後、４００℃で１時間焼成し、Ｐｔ担持粉末を得た。これを粉末Ｉとした（粉末ＩのＰｔ担持濃度は３．２％、Ｂａ担持濃度はＢａＯとして７．６％）。ＨＣ吸着浄化層スラリーの粉末Ｅの代わりに粉末Ｉを用いた以外は実施例１０と同様の操作を繰り返し、本例の排気ガス浄化触媒を得た。
【００４３】
（実施例１２）
ＣｅＯ_２（７５％）−ＺｒＯ_２（２５％）の複合酸化物に２％のテトラアンミンＰｔ水酸塩溶液（ｐＨ＝１０．５）を含浸させ、１２０℃で一昼夜乾燥した後、４００℃で１時間焼成し、Ｐｔ担持粉末を得た。これを粉末Ｊとした（粉末ＪのＰｔ担持濃度は３．２％）。ＨＣ吸着浄化層スラリーの粉末Ｅの代わりに粉末Ｊを用いた以外は実施例１０と同様の操作を繰り返し、本例の排気ガス浄化触媒を得た。
【００４４】
（比較例１）
ベータゼオライトを７２０．１ｇ、シリカゾルを１７９．９ｇ、水９００ｇを磁性ボールミルに投入し、混合粉砕して、ＨＣ吸着浄化層スラリーを得、これを代わりに使用した以外は実施例１と同様の操作を繰り返し、本例の排気ガス浄化触媒を得た。
【００４５】
（比較例２）
粉末Ａの酢酸バリウム水溶液を酢酸カリウム水溶液に変えた（この粉末のＫ担持濃度はＫ_２Ｏとして、４．５１％）以外は実施例１と同様の操作を繰り返し、本例の排気ガス浄化触媒を得た。
【００４６】
（比較例３）
粉末Ａの酢酸バリウム水溶液を酢酸セシウム水溶液に変えた（この粉末のＣｓ担持濃度はＣｓ_２Ｏとして、１３．４１％）以外は実施例１と同様の操作を繰り返し、本例の排気ガス浄化触媒を得た。
【００４７】
（比較例４）
粉末Ａの酢酸バリウム水溶液を酢酸ランタン水溶液に変えた（この粉末のＬａ担持濃度はＬａ_２Ｏ_３として、１５．５３％）以外は実施例１と同様の操作を繰り返し、本例の排気ガス浄化触媒を得た。
【００４８】
（比較例５）
粉末ＡのＣｅ担持濃度をＣｅＯ_２として１０％とした以外は実施例１と同様の操作を繰り返し、本例の排気ガス浄化触媒を得た。
【００４９】
（比較例６）
内層スラリーの粉末ＢのＣｅ担持濃度をＣｅＯ_２として２５％、粉末ＡのＣｅ担持濃度をＣｅＯ_２として２５％、外層スラリーの粉末ＤのＣｅ担持濃度をＣｅＯ_２として３％、粉末ＡのＣｅ担持濃度をＣｅＯ_２として３％とした以外は実施例１と同様の操作を繰り返し、本例の排気ガス浄化触媒を得た。
【００５０】
（比較例７）
内層スラリーの粉末ＢのＣｅ担持濃度をＣｅＯ_２として１３％、粉末ＡのＣｅ担持濃度をＣｅＯ_２として１３％、外層スラリーの粉末ＤのＣｅ担持濃度をＣｅＯ_２として４０％、粉末ＡのＣｅ担持濃度をＣｅＯ_２として４０％とした以外は実施例１と同様の操作を繰り返し、本例の排気ガス浄化触媒を得た。
【００５１】
上記各例の排気ガス浄化触媒の仕様を表１に示す。なお、表１中の第一層、第二層及び第三層は、それぞれＨＣ吸着浄化層、吸着浄化内層及び吸着浄化外層を表すものである。
【００５２】
【表１】

【００５３】
［性能評価］
（試験例１）
排気量４５００ｃｃのエンジンの排気系に上記各例の触媒を装着して、軽油（Ｓ＝１０ｐｐｍ以下）を使用し、触媒入口温度を６５０℃とし、５０時間運転して耐久させた。
排気量２５００ｃｃのディーゼルエンジンの排気系に上記耐久後の各例の触媒を装着して、１１モードを走り、排気浄化率（１１モード−ＨＣ転化率）を求めた。
【００５４】
（試験例２）
排気量４５００ｃｃのエンジンの排気系に上記各例の触媒を装着して、軽油（Ｓ＝１０ｐｐｍ以下）を使用し、触媒入口温度を６５０℃とし、５０時間運転して耐久させた。
その後、軽油（Ｓ＝４００ｐｐｍ）を使用し、触媒入口温度２５０℃とし、３時間運転してＳ被毒処理を行った後、軽油（Ｓ＝１０ｐｐｍ以下）を使用し、触媒入口温度を６５０℃とし、３０分運転してＳ脱離処理を行った。
排気量２５００ｃｃのディーゼルエンジンの排気系に上記耐久後の各例の触媒を装着して、リーン（Ａ／Ｆ＝３０）４０秒、次いで、リッチ（Ａ／Ｆ＝１１）４秒の運転を行い、この区間における排気浄化率（Ｓ被毒処理前ＮＯｘ転化率及びＳ被毒・脱離処理後ＮＯｘ転化率）を求めた。触媒入口温度は２５０℃とした。得られた結果を表２に示す。
【００５５】
【表２】

【００５６】
表２より、本発明の範囲に属する実施例１〜１２の排気ガス浄化触媒は、本発明外の比較例１〜７よりも、Ｓ被毒解除性能とＮＯｘ浄化性能の双方に優れていることが分かる。
また、現時点では、ＮＯｘ浄化性能、ＨＣ浄化性能、Ｓ被毒解除性能の全てが優れているという観点から、実施例１０が最も良好な結果をもたらすものと思われる。
【００５７】
【発明の効果】
以上説明してきたように、本発明によれば、ＨＣ吸着浄化層に、ゼオライトとＰｔ等の貴金属を担持したセリア材を共存させ、更に吸着浄化内層及び吸着浄化外層に、所定量のＣｅを存在させることなどとしたため、１５０℃以下の低温でのＨＣ吸着浄化、１５０〜２５０℃の低温及びリーン域でのＮＯｘ浄化を１つの触媒で実現でき、ＮＯｘ浄化性能を向上した排気ガス浄化触媒及びその製造方法を提供することができる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purification catalyst and a method for producing the same, and more particularly, to a hydrocarbon (HC) adsorption purification performance at a low temperature of 150 ° C. or lower, a low temperature of 150 to 250 ° C., and an oxygen-excess atmosphere (lean region). The present invention relates to an exhaust gas purifying catalyst excellent in nitrogen oxide (NOx) adsorption purifying performance and a method for producing the same.
[0002]
[Prior art]
Conventionally, various catalysts for purifying NOx in a lean region have been proposed. For example, as represented by a catalyst in which platinum and lanthanum are supported on a porous carrier (for example, see Patent Document 1), NOx in a lean region is represented. There is known a catalyst that adsorbs NOx and releases NOx when stoichiometric is in a rich region to purify NOx.
Further, as a catalyst for purifying HC at the time of low exhaust temperature at the time of starting the engine or the like, for example, a catalyst containing zeolite is known (for example, see Patent Document 2).
[0003]
[Patent Document 1]
JP-A-5-168860
[Patent Document 2]
JP-A-11-47596
[0004]
[Problems to be solved by the invention]
However, in a lean burn engine or a diesel engine, it is necessary to arrange two catalysts as described above for HC adsorption purification at a low temperature and NOx purification in a lean region. There were many problems. If the functions of the two catalysts can be satisfied by one catalyst as in the present invention, it is considered that the above problem can be solved. Specifically, the noble metal is placed on the zeolite layer as the HC adsorbent. And a layer comprising a layer containing an alkali that is a NOx adsorbent, wherein the lower layer adsorbs HC at a low temperature, the upper layer adsorbs and purifies NOx, and purifies the HC adsorbed in the lower layer.
However, such a catalyst has a problem in that the respective catalyst layers cannot be sufficiently exhibited because each catalyst layer becomes thin.
[0005]
Detailed analysis by the present inventors has revealed that NOx desorption and purification from the upper layer that performs NOx purification are not sufficiently performed. This is more remarkable when the catalyst inlet temperature is 250 ° C. or less. In order to sufficiently desorb and purify NOx even in this temperature range, H is required. ₂ It became clear that it was necessary. In recent years, as the combustion efficiency of the engine has increased due to the reduction in fuel consumption and the exhaust temperature has been reduced, this problem has been increasing.
[0006]
The present invention has been made in view of such findings, and has as its object to purify hydrocarbon (HC) adsorption and purification at a low temperature of 150 ° C. or lower, and at a low temperature of 150 to 250 ° C. and in a lean region. An object of the present invention is to provide an exhaust gas purifying catalyst capable of purifying nitrogen oxides (NOx) with one catalyst and having improved NOx purifying performance, and a method of manufacturing the same.
[0007]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to achieve the above object, and as a result, a ceria material carrying a noble metal such as zeolite and platinum coexists in the HC adsorption purification layer, and further, in the adsorption purification inner layer and the adsorption purification outer layer, It has been found that the above object can be achieved by the presence of a predetermined amount of cerium, and the present invention has been completed.
[0008]
That is, the exhaust gas purifying catalyst of the present invention has an integral structure type carrier, which is an HC adsorbing and purifying layer for adsorbing and purifying HC, an adsorbing and purifying inner layer for adsorbing and purifying NOx and purifying HC, and adsorbing and purifying NOx. In addition, at least three catalyst layers of an adsorption purification outer layer for purifying HC are laminated in this order.
The HC adsorption and purification layer contains zeolite, platinum (Pt) and / or palladium (Pd), and a ceria material, and the ceria material carries Pt and / or Pd. Contains an alkali metal and / or an alkaline earth metal, cerium (Ce), Pt and / or Pd, and alumina, and the adsorption and purification outer layer contains an alkali metal and / or an alkaline earth metal, Ce , Rhodium (Rh), Pt and / or Pd, and alumina, and the total amount of Ce in the inner and outer layers of the adsorption purification is CeO. ₂ In terms of conversion, the catalyst is 40 to 100 g / L per liter of the catalyst, and is an exhaust gas purifying catalyst having both the ability to purify HC at low temperature and the ability to purify NOx at low temperature and in an atmosphere containing excess oxygen.
[0009]
Further, the method for producing an exhaust gas purifying catalyst of the present invention is a method for producing an exhaust gas purifying catalyst as described above, and includes the following steps (1) to (4).
{Circle around (1)} Ct material is impregnated with an alkaline aqueous solution containing Pt and / or Pd to prepare Pt and / or Pd-supported powder, and then HC is used to form an HC adsorption purification layer using this powder and zeolite. A step of preparing an adsorption purification layer slurry.
(2) A powder in which Ce and an alkali metal and / or an alkaline earth metal are supported on alumina is prepared, and then this powder is impregnated with an alkaline aqueous solution containing Pt and / or Pd to form a powder supporting Pt and / or Pd. And forming an inner layer slurry for forming an adsorption purification inner layer using these powders.
(3) A powder in which Ce and an alkali metal and / or an alkaline earth metal are supported on alumina is prepared, and then this powder is impregnated with an aqueous alkaline solution containing Pt and / or Pd to obtain a powder supporting Pt and / or Pd. On the other hand, impregnating alumina with an aqueous rhodium nitrate solution to produce Rh-supported powders, and using these powders to produce an outer layer slurry for forming an adsorption purification outer layer.
{Circle around (4)} Thereafter, the HC-adsorbing / purifying layer slurry, the inner layer slurry and the outer layer slurry obtained in steps (1) to (3) are coated on the monolithic carrier in this order, dried, and calcined to form HC A step of laminating an adsorption purification layer, an adsorption purification inner layer, and an adsorption purification outer layer.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the exhaust gas purifying catalyst of the present invention will be described in detail. In addition, in this specification, "%" represents a mass percentage unless otherwise specified.
[0011]
As described above, the exhaust gas purifying catalyst of the present invention has an integrated structure-type carrier in which an HC adsorbing / purifying layer that adsorbs and purifies HC, an inner layer that adsorbs and purifies NOx, and an adsorbing and purifying inner layer that adsorbs and purifies HC. At least three catalyst layers of an outer purification layer for purifying and purifying HC are laminated in this order, and have both an ability to purify HC at low temperature and an ability to adsorb and purify NOx at low temperature and in an oxygen-excess atmosphere.
Here, as the monolithic carrier, for example, a monolith carrier or a honeycomb carrier made of a heat-resistant material such as ceramics such as cordierite or a metal such as ferritic stainless steel is used.
[0012]
According to the prior art, at least two types of catalysts are required: a catalyst for adsorbing HC and a catalyst for purifying NOx during lean operation. This causes an increase in exhaust pressure, which adversely affects fuel economy. The amount of noble metal for each individual is required, which leads to resource depletion. However, the exhaust gas purifying catalyst of the present invention is a catalyst in which the above-described composite function is integrated into one catalyst, and such a problem can be solved.
[0013]
Further, the HC adsorption purification layer of the exhaust gas purification catalyst of the present invention contains zeolite and a ceria material supporting one or both of Pt and Pd, and the adsorption purification inner layer contains one or both of an alkali metal and an alkaline earth metal. It contains both, Ce, one or both of Pt and Pd, and alumina, and the adsorption purification outer layer contains one or both of an alkali metal and an alkaline earth metal, Ce, Rh, and one of Pt and Pd. Or it contains both and alumina.
Here, the “ceria material” refers to an oxide containing at least Ce.
[0014]
In such an HC adsorption purification layer, zeolite adsorbs and purifies HC at a low temperature of 150 ° C. or less, and the ceria material supporting Pt or Pd is water (H). ₂ O) and hydrogen (H) effective for NOx purification by CO shift reaction from carbon monoxide (CO) generated by HC purification of zeolite. ₂ ).
On the other hand, in the inner and outer layers of the adsorption purification, alumina supports a catalyst component as a high surface area substrate, and a compound formed by an alkali metal or an alkaline earth metal (NOx adsorbent) adsorbs NOx, and Pt, Pd and Rh performs NOx purification and HC purification. In particular, Rh exhibits excellent performance in NOx purification. ₂ The function of desorbing and purifying NOx by generation is improved.
This makes it possible to adsorb and purify HC at a low temperature of 150 ° C. or lower, and improve NOx purification performance at a low temperature of 150 to 250 ° C.
[0015]
Further, in the exhaust gas purifying catalyst of the present invention, the total amount of Ce in the inner layer and the outer layer ₂ In terms of conversion, it is required to be 40 to 100 g / L per 1 L of the catalyst.
If it is less than 40 g / L, the CO shift reaction may not be able to proceed sufficiently. If it exceeds 100 g / L, HC, CO, H ₂ Thus, the function of oxidizing the reducing agent such as the above may be more strongly expressed, and the desorption of NOx may not be performed.
[0016]
In the exhaust gas purifying catalyst of the present invention, the Ce amount of the inner layer of the adsorption purification is preferably larger than the Ce amount of the outer layer of the adsorption purification, and the ratio of the amount of Ce in the inner layer of the adsorption purification and the amount of Ce in the outer layer of the adsorption purification is CeO. ₂ More preferably, it is 6: 4 to 8: 2 in conversion.
If the amount of Ce in the outer layer of adsorption purification is larger than the amount of Ce in the inner layer of adsorption purification, the above-described reducing agent is oxidized and consumed, which may adversely affect the desorption and purification of NOx. If Ce is present in the outer adsorption purification layer, it oxidizes the above-described reducing agent necessary for NOx purification. Therefore, it is ideally desirable that Ce is not contained in the outer adsorption purification layer.
However, when it is not contained, H which is effective for detoxification of sulfur compound (S) is effective. ₂ Is generated by a ceria material carrying Pt or Pd, and therefore, there is a high possibility that S poisoning will adversely affect the NOx purification performance.
From such a viewpoint, it is preferable that the above-described ratio is contained in the inner layer and the outer layer of the adsorption purification, so that both the inner layer and the outer layer can adsorb, desorb and purify NOx, and furthermore, the S poisoning. Release performance is also improved.
[0017]
In the exhaust gas purifying catalyst of the present invention, the amount of one or both of the alkali metal and the alkaline earth metal contained in the outer layer of the adsorption purification is one or both of the alkali metal and the alkaline earth metal contained in the inner layer of the adsorption purification. Is preferably larger in terms of the corresponding oxide than the amount of.
This is because the catalyst of the present invention is used at a low temperature of 250 ° C. or lower, so that the NOx adsorption performance is maximized. In addition, since the removal of S poison is more likely to occur on the outer side of the adsorption purification layer, an effective arrangement of alkali metals and alkaline earth metals is also provided for the removal of S poison.
[0018]
Further, in the exhaust gas purifying catalyst of the present invention, one or both of the alkali metal and the alkaline earth metal of the inner layer and the outer layer of the adsorption purification are magnesium (Mg), calcium (Ca), strontium (Sr), barium ( Ba) or sodium (Na) and a metal according to any combination thereof is desirably contained, and some or all of the compounds formed by these metals are composed of barium magnesium carbonate (BaMg (CO ₃ ) ₂ ) Is particularly desirable.
[0019]
Since the catalyst of the present invention is used at a low temperature of 250 ° C. or lower, NOx cannot be adsorbed with an alkali (for example, rare earth or the like) weaker than the compound containing an alkali metal or an alkaline earth metal. In the case of a strong alkali (for example, potassium (K), cesium (Cs), etc.), NOx adsorbed by these cannot be desorbed, which may adversely affect NOx purification performance.
As such a NOx adsorbent, a compound containing Ba or Na is preferable, and Na is a compound of the compound (for example, sodium carbonate (Na ₂ CO ₃ ). ) Is water-soluble, so that it is likely to dissolve into the zeolite-containing HC-adsorbing / purifying layer during the preparation of the catalyst, adversely affecting the HC-adsorbing performance.
[0020]
On the other hand, in consideration of the release of S poisoning, the stability of the NOx adsorbent becomes a very important issue, and this point is the same as for the NOx purification performance. It is effective. At present, as a good material that exhibits suitable NOx purification performance in the temperature range using the catalyst of the present invention and can be combined, for example, BaMg (CO ₃ ) ₂ Is mentioned. Further, the compounding is effective also in consideration of the dissolution of the adsorbent into the zeolite.
By combining the adsorbent in this way, it is possible to solve many problems such as suppressing S poisoning, suppressing reduction in NOx purification performance, and preventing leaching into zeolite.
[0021]
Further, in the HC adsorption purification layer of the exhaust gas purification catalyst of the present invention, it is desirable that the ceria material supporting Pt or Pd further contain an alkaline earth metal.
By including the NOx adsorbent in the HC adsorption purification layer, it is possible to improve the NOx purification performance, and by dissolving the zeolite by supporting an alkaline earth metal on a ceria material supporting Pt or Pd other than zeolite. And the resulting pore blockage is prevented, and the HC adsorption performance can be maintained.
[0022]
Further, in the HC adsorption purification layer of the exhaust gas purification catalyst of the present invention, it is preferable that the ceria material supporting Pt or Pd further contain zirconium (Zr), and the content ratio of Ce and Zr in the ceria material is reduced. , Respectively CeO ₂ , ZrO ₂ It is more preferable that the weight ratio is 70:30 to 80:20 in terms of reduced weight, and it is particularly preferable that the weight ratio is 75:25.
It is effective to form a composite with zirconium in order to improve the stability of the ceria material. ₂ Deterioration of the generation function can also be suppressed. At present, the preferred form is the above-mentioned Ce-Zr composite oxide.
[0023]
Next, the method for producing the exhaust gas purifying catalyst of the present invention will be described in detail.
This production method is a method for producing the above-described exhaust gas purification catalyst of the present invention, and includes an HC adsorption purification layer slurry, an inner layer slurry and an outer layer slurry for forming the HC adsorption purification layer, the adsorption purification inner layer and the adsorption purification outer layer. Is prepared, and these slurries are sequentially applied to a carrier having an integral structure such as a honeycomb carrier, followed by drying and firing, and specifically includes the following steps (1) to (4).
[0024]
{Circle around (1)} Ceria material is impregnated with an alkaline aqueous solution containing one or both of Pt and Pd to prepare a powder carrying one or both of Pt and Pd, and then HC adsorption purification using this powder and zeolite. A step of forming a layer slurry.
{Circle around (2)} A powder in which Ce and one or both of an alkali metal and an alkaline earth metal are supported on alumina is prepared, and then this powder is impregnated with an alkaline aqueous solution containing one or both of Pt and Pd to form Pt and Pd. Preparing powder supporting one or both of the above, and preparing an inner layer slurry using these powders.
{Circle around (3)} A powder is prepared by supporting Ce and one or both of an alkali metal and an alkaline earth metal on alumina, and then this powder is impregnated with an alkaline aqueous solution containing one or both of Pt and Pd to form Pt and Pd. A step of preparing a powder carrying one or both of the above, and impregnating alumina with an aqueous rhodium nitrate solution to prepare a Rh-supported powder, and preparing an outer layer slurry using these powders.
(4) Thereafter, the HC adsorption purification layer slurry, the inner layer slurry, and the outer layer slurry obtained in the steps (1) to (3) are coated on a monolithic carrier such as a honeycomb carrier in this order, and dried. Baking to form a stacked layer of an HC adsorption purification layer, an adsorption purification inner layer, and an adsorption purification outer layer.
[0025]
In the step (1), the step (2) and the step (3), the Pt or Pd is supported on the ceria material because such powder is used in the HC adsorption purification layer as described above. ₂ This is because it contributes to generation.
In addition, when the alkaline earth metal is contained in the HC adsorption purification layer, it is desirable that the ceria material first support the alkaline earth metal in the step (1). As described above, by being supported on a ceria material other than zeolite, pores of zeolite can be prevented from being blocked by the NOx adsorbent, HC adsorption performance can be maintained, and NOx purification performance can be improved. It becomes.
[0026]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.
[0027]
(Example 1)
A cerium acetate aqueous solution and a barium acetate aqueous solution are mixed and stirred. Alumina is put therein, stirred at room temperature for 1 hour, dried at 120 ° C. all day and night, and calcined at 600 ° C. for 1 hour to obtain two kinds of supported powder. Obtained. This powder was used as powder A (Ba concentration of powder A was 7.3% as BaO, Ce concentration was CeO ₂ 20%).
The powder A was impregnated with a 2% tetraammine Pt hydroxide solution (pH = 10.5), dried at 120 ° C. for 24 hours, and calcined at 400 ° C. for 1 hour to obtain a Pt-supported powder. This was designated as Powder B (Pt carrying concentration of Powder B was 1.04%).
[0028]
Alumina was put into an aqueous solution of zirconium acetate, stirred at room temperature for 1 hour, dried at 120 ° C. for 24 hours, and calcined at 900 ° C. for 1 hour to obtain a powder. The obtained powder was impregnated with a 6% rhodium nitrate aqueous solution. After drying at 120 ° C. for 24 hours, it was baked at 400 ° C. for 1 hour to obtain a Rh-supported powder. This was used as powder C (the concentration of Rh supported on powder C was 2.4%, and the supported concentration of Zr was ZrO ₂ 3%).
The powder A was impregnated with a 2% tetraammine Pt hydroxide solution (pH = 10.5), dried at 120 ° C. for 24 hours, and calcined at 400 ° C. for 1 hour to obtain a Pt-supported powder. This was designated as Powder D (Pt carrying concentration of Powder D was 3.41%).
Cerium oxide was impregnated with a 2% tetraammine Pt hydroxide solution (pH = 10.5), dried at 120 ° C. for 24 hours, and calcined at 400 ° C. for 1 hour to obtain a Pt-supported powder. This was designated as Powder E (Pt carrying concentration of Powder E was 3.2%).
[0029]
627.5 g of beta zeolite, 92.6 g of powder E, 179.9 g of silica sol, and 900 g of water were charged into a magnetic ball mill, mixed and pulverized to obtain a slurry for the HC adsorption purification layer.
767.8 g of powder B, 50.5 g of powder A, 47.8 g of Ce oxide, 33.9 g of alumina sol, and 900 g of water were charged into a magnetic ball mill and mixed and pulverized to obtain an inner layer slurry.
272.0 g of powder C, 403.9 g of powder D, 84.8 g of powder A, 81.1 g of cerium oxide, 58.1 g of alumina sol, and 900 g of water were charged into a magnetic ball mill, mixed and pulverized, and mixed with an outer layer slurry. Got.
[0030]
The HC adsorption purification layer slurry is attached to a cordierite-based monolithic carrier (1.2 L, 400 cells), excess slurry in the cells is removed by an air flow, dried at 130 ° C., and calcined at 400 ° C. for 1 hour. Thus, a catalyst having a coat layer of 172.1 g / L was obtained. This was designated as catalyst a.
The inner layer slurry was adhered to the catalyst a, the excess slurry in the cell was removed with an air stream, dried at 130 ° C., and fired at 400 ° C. for 1 hour to obtain a catalyst of 167.5 g / L of a coat layer. This was designated as catalyst b.
The outer layer slurry is adhered to the catalyst b, the excess slurry in the cell is removed by an air stream, dried at 130 ° C., and then baked at 400 ° C. for 1 hour to obtain 97.6 g / L of the exhaust gas of the present example of the coat layer. A purification catalyst was obtained.
[0031]
(Example 2)
Powder A was impregnated with a 12% palladium nitrate solution, dried at 120 ° C. for 24 hours, and calcined at 400 ° C. for 1 hour to obtain a Pd-supported powder. This was designated as Powder F (Pd carrying concentration of Powder F was 1.04%).
Powder A was impregnated with a 12% palladium nitrate solution, dried at 120 ° C. for 24 hours, and calcined at 400 ° C. for 1 hour to obtain a Pd-supported powder. This was designated as Powder G (Pd-supporting concentration of Powder F was 3.41%).
Cerium oxide was impregnated with a 12% palladium nitrate solution, dried at 120 ° C. for 24 hours, and calcined at 400 ° C. for 1 hour to obtain a Pd-supported powder. This was designated as Powder H (Pd carrying concentration of Powder H was 3.2%).
[0032]
627.5 g of beta zeolite, 69.4 g of powder E, 23.2 g of powder H, 179.9 g of silica sol, and 900 g of water were charged into a magnetic ball mill, mixed and pulverized to obtain an HC adsorption purification layer slurry.
575.8 g of powder B, 192.0 g of powder F, 50.5 g of powder A, 47.8 g of Ce oxide, 33.9 g of alumina sol, and 900 g of water were charged into a magnetic ball mill, mixed and pulverized, and the inner layer slurry was formed. Obtained.
272.0 g of powder C, 302.9 g of powder D, 101.0 g of powder G, 84.8 g of powder A, 81.1 g of Ce oxide, 58.1 g of alumina sol, and 900 g of water were charged into a magnetic ball mill, The mixture was pulverized to obtain an outer layer slurry.
[0033]
The HC adsorption purification layer slurry is attached to a cordierite-based monolithic carrier (1.2 L, 400 cells), excess slurry in the cells is removed by an air flow, dried at 130 ° C., and calcined at 400 ° C. for 1 hour. Thus, a catalyst having a coat layer of 172.1 g / L was obtained. This was designated as catalyst c.
The inner layer slurry was adhered to the catalyst c, the excess slurry in the cell was removed by an air stream, dried at 130 ° C., and fired at 400 ° C. for 1 hour to obtain a catalyst of 167.5 g / L of a coat layer. This was designated as catalyst d.
The outer layer slurry is adhered to the catalyst d, the excess slurry in the cell is removed by an air flow, dried at 130 ° C., and then baked at 400 ° C. for 1 hour, and the exhaust gas of the present example having a coat layer of 97.6 g / L is obtained. A purification catalyst was obtained.
[0034]
(Example 3)
The same operation as in Example 1 was repeated except that the aqueous barium acetate solution of the powder A was changed to an aqueous calcium acetate solution (the concentration of Ca supported in the powder was 2.65% as CaO) to obtain the exhaust gas purification catalyst of the present example. Was.
[0035]
(Example 4)
The same operation as in Example 1 was repeated except that the barium acetate aqueous solution of the powder A was changed to a strontium acetate aqueous solution (the Sr carrying concentration of this powder was 4.91% as SrO), to obtain the exhaust gas purification catalyst of the present example. Was.
[0036]
(Example 5)
The aqueous barium acetate solution of powder A was changed to an aqueous sodium acetate solution (the Na carrying concentration of this powder was Na ₂ The same operation as in Example 1 was repeated except for O (2.99%) to obtain an exhaust gas purifying catalyst of this example.
[0037]
(Example 6)
The barium acetate aqueous solution of powder A was changed to a mixed solution of barium acetate and magnesium acetate (the Ba carrying concentration of this powder was 7.3% as BaO, and the Mg carrying concentration was 2.3% as MgO). The same operation as in Example 1 was repeated to obtain an exhaust gas purifying catalyst of this example.
[0038]
(Example 7)
The aqueous barium acetate solution of powder A was changed to a mixed solution of barium acetate and sodium acetate (Ba concentration of this powder was BaO as 7.3%, and Na concentration was Na. ₂ The same operation as in Example 1 was repeated except for O (3.48%) to obtain an exhaust gas purifying catalyst of this example.
[0039]
(Example 8)
The barium acetate aqueous solution of powder A was changed to a mixed solution of barium acetate and strontium acetate (Ba carrying concentration of this powder is 7.3% as BaO, Sr carrying concentration is 5.85% as SrO). The same operation as in Example 1 was repeated to obtain an exhaust gas purifying catalyst of this example.
[0040]
(Example 9)
The Ce supported concentration of the powder B of the inner layer slurry was CeO ₂ 25%, and the Ce loading concentration of powder A is CeO ₂ 25%, the Ce supported concentration of the powder D of the outer layer slurry was CeO ₂ 15%, and the Ce loading concentration of powder A was CeO ₂ The same operation as in Example 6 was repeated except that the value was set to 15% to obtain an exhaust gas purification catalyst of this example.
[0041]
(Example 10)
The Ba carrying concentration of the powder B of the inner layer slurry is 3% as BaO, the Ba carrying concentration of the powder A is 3% as BaO, the Ba carrying concentration of the powder D of the outer slurry is 20% as BaO, and the Ba carrying concentration of the powder A is BaO. The same operation as in Example 6 was repeated except that the value was set to 20% to obtain an exhaust gas purification catalyst of this example.
[0042]
(Example 11)
Cerium oxide was impregnated with an aqueous barium acetate solution, dried at 120 ° C. for 24 hours, and calcined at 600 ° C. for 1 hour to obtain a powder. The obtained powder was mixed with a 2% tetraammine Pt hydroxide solution (pH = 10.5). ), Dried at 120 ° C. for 24 hours, and calcined at 400 ° C. for 1 hour to obtain a Pt-supported powder. This was used as Powder I (Pt carrying concentration of Powder I was 3.2%, Ba carrying concentration was 7.6% as BaO). The same operation as in Example 10 was repeated except that the powder I was used instead of the powder E of the HC adsorption purification layer slurry, to obtain an exhaust gas purification catalyst of this example.
[0043]
(Example 12)
CeO ₂ (75%)-ZrO ₂ (25%) composite oxide was impregnated with 2% tetraammine Pt hydroxide solution (pH = 10.5), dried at 120 ° C. all day and night, and calcined at 400 ° C. for 1 hour to obtain a Pt-supported powder. Was. This was designated as Powder J (Pt carrying concentration of Powder J was 3.2%). The same operation as in Example 10 was repeated except that powder J was used instead of powder E of the HC adsorption purification layer slurry, to obtain an exhaust gas purification catalyst of this example.
[0044]
(Comparative Example 1)
The same operation as in Example 1 was carried out except that 720.1 g of beta zeolite, 179.9 g of silica sol, and 900 g of water were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry for an HC adsorption purification layer, which was used instead. Was repeated to obtain an exhaust gas purifying catalyst of this example.
[0045]
(Comparative Example 2)
The aqueous barium acetate solution of the powder A was changed to an aqueous potassium acetate solution. ₂ The same operation as in Example 1 was repeated except for 4.51% as O) to obtain an exhaust gas purifying catalyst of this example.
[0046]
(Comparative Example 3)
The barium acetate aqueous solution of powder A was changed to a cesium acetate aqueous solution (the Cs carrying concentration of this powder was Cs ₂ Except for 13.41% as O), the same operation as in Example 1 was repeated to obtain an exhaust gas purifying catalyst of this example.
[0047]
(Comparative Example 4)
The barium acetate aqueous solution of the powder A was changed to a lanthanum acetate aqueous solution (the La carrying concentration of this powder was La ₂ O ₃ (Except for 15.53%), the same operation as in Example 1 was repeated to obtain an exhaust gas purifying catalyst of this example.
[0048]
(Comparative Example 5)
The Ce loading concentration of powder A was CeO ₂ The same operation as in Example 1 was repeated except that the value was set to 10% to obtain an exhaust gas purification catalyst of this example.
[0049]
(Comparative Example 6)
The Ce supported concentration of the powder B of the inner layer slurry was CeO ₂ 25%, and the Ce loading concentration of powder A is CeO ₂ 25%, the Ce supported concentration of the powder D of the outer layer slurry was CeO ₂ 3%, and the Ce loading concentration of powder A was CeO ₂ The same operation as that of Example 1 was repeated except that the value was set to 3% to obtain an exhaust gas purification catalyst of this example.
[0050]
(Comparative Example 7)
The Ce supported concentration of the powder B of the inner layer slurry was CeO ₂ 13%, and the Ce loading concentration of powder A was CeO ₂ 13%, the Ce supported concentration of powder D of the outer layer slurry was CeO ₂ 40%, and the Ce loading concentration of powder A was CeO ₂ The same operation as in Example 1 was repeated except that the value was set to 40% to obtain an exhaust gas purification catalyst of this example.
[0051]
Table 1 shows the specifications of the exhaust gas purifying catalyst of each of the above examples. The first, second, and third layers in Table 1 represent an HC adsorption purification layer, an adsorption purification inner layer, and an adsorption purification outer layer, respectively.
[0052]
[Table 1]

[0053]
[Performance evaluation]
(Test Example 1)
The catalyst of each of the above examples was mounted on the exhaust system of an engine with a displacement of 4500 cc, and light oil (S = 10 ppm or less) was used, the catalyst inlet temperature was set to 650 ° C., and the operation was performed for 50 hours to endurance.
The catalyst of each example after the above-mentioned durability was mounted on an exhaust system of a diesel engine having a displacement of 2500 cc, and the engine was run in 11 modes to determine an exhaust gas purification rate (11 mode-HC conversion rate).
[0054]
(Test Example 2)
The catalyst of each of the above examples was mounted on the exhaust system of an engine with a displacement of 4500 cc, and light oil (S = 10 ppm or less) was used, the catalyst inlet temperature was set to 650 ° C., and the operation was performed for 50 hours to endurance.
After that, light polish (S = 400 ppm) was used, the catalyst inlet temperature was set to 250 ° C., and the system was operated for 3 hours to perform S poisoning treatment. The operation was performed for 30 minutes to perform the S desorption process.
The catalyst of each example after the above-mentioned durability was attached to the exhaust system of a diesel engine with a displacement of 2500 cc, and the operation was performed for 40 seconds in a lean (A / F = 30) and then for 4 seconds in a rich (A / F = 11). The exhaust gas purification rate (NOx conversion rate before S poisoning processing and NOx conversion rate after S poisoning / desorption processing) in this section was determined. The catalyst inlet temperature was 250 ° C. Table 2 shows the obtained results.
[0055]
[Table 2]

[0056]
Table 2 shows that the exhaust gas purifying catalysts of Examples 1 to 12 belonging to the scope of the present invention are superior to both the S poisoning release performance and the NOx purifying performance than Comparative Examples 1 to 7 other than the present invention. I understand.
At the present time, from the viewpoint that the NOx purification performance, the HC purification performance, and the S poisoning release performance are all excellent, it is considered that the tenth embodiment provides the best result.
[0057]
【The invention's effect】
As described above, according to the present invention, the HC adsorption purification layer is made to coexist with a ceria material carrying a noble metal such as zeolite and Pt, and furthermore, a predetermined amount of Ce exists in the adsorption purification inner layer and the adsorption purification outer layer. As a result, it is possible to realize NOx purification at a low temperature of 150 ° C. or lower and NOx purification at a low temperature of 150 to 250 ° C. and in a lean region with a single catalyst. A manufacturing method can be provided.

Claims

At least three of an HC adsorption / purification layer that adsorbs and purifies HC, an inner layer that adsorbs and purifies NOx, and purifies HC, and an outer adsorption purification layer that adsorbs and purifies NOx, and purifies HC are formed on the monolithic carrier. An exhaust gas purifying catalyst comprising a stack of two catalyst layers in this order and having both a HC adsorption purification ability at a low temperature and a NOx adsorption purification ability at a low temperature and in an oxygen-excess atmosphere.
The HC adsorption purification layer contains zeolite, platinum and / or palladium and a ceria material, and the ceria material supports platinum and / or palladium,
The adsorption purification inner layer contains an alkali metal and / or an alkaline earth metal, cerium and platinum and / or palladium and alumina,
The adsorption purification outer layer contains an alkali metal and / or an alkaline earth metal, cerium, rhodium, platinum and / or palladium and alumina,
A total of CeO ₂ in terms of the cerium amount of adsorption purification inner and outer layers, the exhaust gas purifying catalyst which is a catalyst 1L per 40 to 100 g / L.

The exhaust gas purification catalyst according to claim 1, wherein the amount of cerium in the inner layer of the adsorption purification is larger than the amount of cerium in the outer layer of the adsorption purification.

The ratio of cerium amount of adsorption purification outer cerium amount of adsorption purification inner layer calculated as CeO ₂ in 6: 4 to 8: 2 in the exhaust gas purifying catalyst according to claim 1 or 2, characterized in that.

The amount of the alkali metal and / or alkaline earth metal in the outer layer of adsorption purification is larger than the amount of alkali metal and / or alkaline earth metal in the inner layer of adsorption purification in terms of the oxide. The exhaust gas purifying catalyst according to any one of the above items.

The alkali metal and / or alkaline earth metal of the inner layer and the outer layer of the adsorption purification layer contains at least one metal selected from the group consisting of magnesium, calcium, strontium, barium, and sodium. 4. The exhaust gas purification catalyst according to any one of the items 4 to 5.

The exhaust gas purifying catalyst according to any one of claims 1 to 5, wherein a part or all of the compound formed by the alkali metal and / or the alkaline earth metal is barium magnesium carbonate.

The exhaust gas purification catalyst according to any one of claims 1 to 6, wherein the ceria material supporting platinum and / or palladium of the HC adsorption purification layer further contains an alkaline earth metal.

The exhaust gas purification catalyst according to any one of claims 1 to 7, wherein the ceria material supporting platinum and / or palladium of the HC adsorption purification layer further contains zirconium.

The exhaust gas purifying catalyst according to claim 8, wherein the content ratio of cerium and zirconium in the ceria material is 70:30 to 80:20 in terms of oxide weight.

In producing the exhaust gas purifying catalyst according to any one of claims 1 to 9,
{Circle around (1)} A ceria material is impregnated with an alkaline aqueous solution containing platinum and / or palladium to prepare a platinum- and / or palladium-supported powder, and then the HC and the zeolite are used to form an HC adsorption / purification layer. Make the adsorption purification layer slurry,
(2) A powder in which cerium and an alkali metal and / or an alkaline earth metal are supported on alumina is prepared, and then this powder is impregnated with an alkaline aqueous solution containing platinum and / or palladium to obtain a powder supporting platinum and / or palladium. The inner layer slurry for forming the adsorption purification inner layer using these powders,
(3) A powder in which cerium and an alkali metal and / or an alkaline earth metal are supported on alumina is prepared, and then the powder is impregnated with an alkaline aqueous solution containing platinum and / or palladium to obtain a powder supporting platinum and / or palladium. On the other hand, alumina is impregnated with an aqueous solution of rhodium nitrate to prepare a rhodium-supported powder, and an outer layer slurry for forming an adsorption and purification outer layer using these powders is prepared.
(4) Thereafter, the HC-adsorbing / purifying layer slurry, the inner layer slurry and the outer layer slurry obtained in the steps (1) to (3) are coated on the monolithic carrier in this order, dried, and fired. Forming a stack of an HC adsorption purification layer, an adsorption purification inner layer and an adsorption purification outer layer,
A method for producing an exhaust gas purifying catalyst, comprising:

In the step (1), a powder in which an alkali metal and / or an alkaline earth metal is supported on a ceria material is prepared, and then the powder is impregnated with an alkaline aqueous solution containing platinum and / or palladium to obtain platinum and / or palladium. The method for producing an exhaust gas purifying catalyst according to claim 10, wherein the supporting powder is prepared.