JP3839860B2 - Exhaust gas purification catalyst and exhaust gas purification method - Google Patents
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【０００１】
【発明の属する技術分野】
本発明は、内燃機関から排出される排ガスを浄化する排ガス浄化用触媒及び排ガス浄化方法に関し、さらに詳しくは、酸素過剰の排ガス、すなわち排ガス中に含まれる一酸化炭素（ＣＯ）、水素（Ｈ2 ）及び炭化水素（ＨＣ）等の還元性成分を完全に酸化するのに必要な酸素量より過剰の酸素を含む排ガス中の、窒素酸化物（ＮＯx ）を効率良く還元浄化できる排ガス浄化用触媒及び排ガス浄化方法に関する。
【０００２】
【従来の技術】
従来より、自動車の排ガス浄化用触媒として、ＣＯ及びＨＣの酸化とＮＯx の還元とを行って排ガスを浄化する三元触媒が用いられている。このような三元触媒としては、例えばコーディエライトなどからなる耐熱性基材にγ−アルミナからなる多孔質担体層を形成し、その多孔質担体層に白金（Ｐｔ）、ロジウム（Ｒｈ）、パラジウム（Ｐｄ）などの触媒貴金属を担持させたものが広く知られている（例えば特公昭５６−２７２９５号公報など）。
【０００３】
一方、近年、地球環境保護の観点から、自動車などの内燃機関から排出される排ガス中の二酸化炭素（ＣＯ2 ）が問題とされ、その解決策として酸素過剰雰囲気において希薄燃焼させるいわゆるリーンバーンが有望視されている。このリーンバーンにおいては、燃料の使用量が低減されるため燃費が向上し、また燃焼排ガスであるＣＯ2 の発生を抑制することができる。
【０００４】
これに対し、従来の三元触媒は、空燃比が理論空燃比（ストイキ）の混合気が燃焼した排ガス中のＣＯ，ＨＣ，ＮＯx を同時に酸化・還元し、浄化するものであって、リーンバーン時の排ガスの酸素過剰雰囲気下におけるＮＯx の還元除去に対しては充分な浄化性能を示さない。このため、酸素過剰雰囲気下においても効率よくＮＯx を浄化しうる排ガス浄化用触媒及び排ガス浄化システムの開発が望まれている。
【０００５】
そこで本願出願人は、先にカリウム（Ｋ）やナトリウム（Ｎａ）に代表されるアルカリ金属とＰｔとを担持した排ガス浄化用触媒を用いた排ガス浄化方法を提案している（特開平６−３１１３９号公報）。また、リチウム（Ｌｉ）、Ｎａ、Ｋ及びセシウム（Ｃｓ）などのアルカリ金属と、鉄（Ｆｅ）、ニッケル（Ｎｉ）、コバルト（Ｃｏ）及びマグネシウム（Ｍｇ）の群から選ばれた少なくとも一種の金属と、バリウム（Ｂａ）と、Ｐｔ及び／又はＰｄとを担持した排ガス浄化用触媒も提案している（特開平６−１４２４５８号公報）。
【０００６】
これらの排ガス浄化用触媒によれば、排ガス中の還元性成分を酸化するのに必要な化学量論比を超える酸素過剰雰囲気（リーン雰囲気）において、窒素酸化物（ＮＯx ）がアルカリ金属などの所謂ＮＯx 吸収材に吸収される。つまりアルカリ金属などがＮＯ x と反応して硝酸塩を生成することでＮＯx が吸収されると考えられている。
【０００７】
そして吸収されたＮＯx は、酸素濃度が化学当量点（理論空燃比：ストイキ）あるいはそれ以下（リッチ雰囲気）となったときに放出され、排ガス中に含まれるＨＣやＣＯなどの還元性成分と反応して還元浄化される。
したがってリーンバーンエンジンに供給する混合気を定期的にストイキ又はリッチ側にしてやることにより、ＮＯx 吸収材に吸収されていたＮＯx を還元浄化することができ、ＮＯx 吸収材は次のリーン雰囲気において再びＮＯx を吸収する。これにより、リーン側においてもＮＯx の良好な浄化性能が得られる。
【０００８】
【発明が解決しようとする課題】
上記の公報には、空燃比（Ａ／Ｆ）＝１８のリーン雰囲気において、入りガス温度６５０℃で５０時間の耐久試験後、１０・１５モードで走行して浄化率を評価している。この評価試験では、排ガス浄化用触媒のさらされる温度域は２５０〜３００℃であり、この範囲であれば優れた浄化性能を有している。
【０００９】
ところが近年のエンジンの高性能化や高速道路の普及などを考慮すると、排ガス浄化用触媒は例えば４００〜５００℃となるような、さらに高温にさらされる機会が多くなる。このため、排ガス浄化用触媒にはさらなる高温耐久性が求められている。
そこで本願発明者らは、ＮＯx 吸収材としてアルカリ金属を用いた排ガス浄化用触媒について高温耐久性を調査した。その結果、９００℃程度の過度の高温にさらされた場合にはアルカリ金属が蒸散し、ＮＯx 浄化率が低下することが明らかとなったのである。
【００１０】
本発明はこのような事情に鑑みてなされたものであり、高温にさらされた場合でもアルカリ金属の蒸散を防止し、低温から高温まで高いＮＯx 浄化性能を維持することを目的とする。
【００１１】
【課題を解決するための手段】
上記課題を解決する本発明の排ガス浄化用触媒の特徴は、排ガス中の酸素濃度が排ガス中の還元性成分を酸化するのに必要な化学量論比を超える酸素過剰雰囲気において排ガス中のＮＯx を吸収し、排ガス中の酸素濃度が化学量論比以下である化学当量点あるいは還元性雰囲気において吸収したＮＯx を還元性成分により還元浄化する排ガス浄化用触媒であって、
多孔質酸化物と、多孔質酸化物に担持されたＺｒ又はＳｉと、触媒貴金属及びアルカリ金属とからなり、Ｚｒはアルカリ金属に対するモル比で０．０５〜２含まれ、Ｓｉはアルカリ金属に対するモル比で０．００３〜１含まれることにある。
【００１２】
また本発明の排ガス浄化方法の特徴は、排ガス中の酸素濃度が排ガス中の還元性成分を酸化するのに必要な化学量論比を超える酸素過剰雰囲気において排ガス中のＮＯx を吸収し、排ガス中の酸素濃度が化学量論比以下である化学当量点あるいは還元性雰囲気において吸収したＮＯx を還元性成分により還元浄化する排ガス浄化方法であって、
多孔質酸化物と、多孔質酸化物に担持されたＺｒ又はＳｉと、触媒貴金属及びアルカリ金属とからなり、Ｚｒはアルカリ金属に対するモル比で０．０５〜２含まれ、Ｓｉはアルカリ金属に対するモル比で０．００３〜１含まれる排ガス浄化用触媒に排ガスを接触させ、排ガス中のＮＯx を還元浄化させることにある。
【００１３】
第３発明の排ガス浄化用触媒は、第１発明の排ガス浄化用触媒においてアルカリ金属はＣｓであることを特徴とする。
さらに第４発明の排ガス浄化方法は、第２発明の排ガス浄化方法において排ガス浄化用触媒中に含まれるアルカリ金属はＣｓであることを特徴とする。
【００１４】
【発明の実施の形態】
本発明の排ガス浄化用触媒及び排ガス浄化方法では、リーン雰囲気の排ガス中のＮＯx がアルカリ金属に吸収され、リッチ雰囲気となったときに放出されて排ガス中のＨＣやＣＯ等の還元性成分と反応し還元浄化される。
ここで例えばＣｓを多孔質酸化物に担持させた場合には、Ｃｓは８００℃以上の高温にさらされることにより遊離して多孔質酸化物外へ蒸散してしまう。そこで本発明では、アルカリ金属とともにＺｒ及びＳｉの少なくとも一方を複合担持している。この場合、アルカリ金属は高温においてＺｒ又はＳｉとの複合化合物として存在していると考えられ、蒸散が防止され多孔質酸化物上に安定して存在し続けることができる。
【００１５】
一方、この複合化合物は、触媒貴金属の触媒作用が奏される３００〜５００℃付近では結合力が弱まり、ＮＯのアタックなどによりアルカリ金属のＮＯx 吸収能が復活するものと考えられ、Ｚｒ又はＳｉの存在によるアルカリ金属のＮＯx吸収能への影響はほとんどない。
多孔質酸化物としては、アルミナ、チタニア、シリカ−アルミナ、ゼオライトなどの高比表面積を有する耐熱性無機酸化物が挙げられる。なかでも活性アルミナは高耐熱性、高比表面積を有するために好ましい。触媒の形状は、ガスと触媒貴金属との接触効率が高ければ特に制限されず、ペレット状、ハニカム状などとすることができる。そして多孔質酸化物自体からその形状に形成してもよく、コーディエライトやメタルなどから形成されたモノリス基材に多孔質酸化物をコートして用いることもできる。
【００１６】
触媒貴金属としては、従来と同様にＰｔ、Ｒｈ、Ｐｄなどを用いることができる。その担持量は、ハニカム担体の１リットル当たり、Ｐｔ及びＰｄの場合は０．１〜１０ｇが好ましく、１〜５ｇが特に好ましい。またＰｄの場合は０．０１５〜２ｇが好ましく、０．０１〜１ｇが特に好ましい。触媒貴金属の担持量がこの範囲より少ないと良好な活性が得られず、この範囲を超えて担持しても効果が飽和するとともに高価となる。
【００１７】
なお、触媒貴金属を多孔質酸化物に担持させるには、その塩化物や硝酸塩等を用いて、含浸法、噴霧法、スラリー混合法などを利用して従来と同様に担持させることができる。
アルカリ金属としては、Ｌｉ、Ｎａ、Ｋ、Ｒｂ、Ｃｓが挙げられ、なかでも高温で特に蒸散し易いＣｓが特に推奨される。このアルカリ金属の担持量は、ハニカム担体の１リットル当たり０．０１〜０．５モルの範囲とすることが好ましい。０．０１モル／Ｌより少ないと十分なＮＯx 吸収能が得られずＮＯx 浄化性能に劣り、０．５モル／Ｌを超えて担持してもＮＯx 吸収能が飽和し、アルカリ金属が触媒貴金属の表面を被覆してしまうために触媒活性が低下する。０．０５〜０．３モル／Ｌの範囲が特に好ましい。
【００１８】
Ｚｒの担持量は、アルカリ金属に対するモル比で０．０５〜２とされる。０．０５より少ないとアルカリ金属の蒸散を抑制する効果が十分に得られず、２を超えて担持しても効果が飽和するとともにアルカリ金属のＮＯx 吸収能を低下させるので好ましくない。アルカリ金属に対するモル比で０．８〜１．２の範囲が特に好ましい。
【００１９】
またＳｉの担持量は、アルカリ金属に対するモル比で０．００３〜１とされる。０．００３より少ないとアルカリ金属の蒸散を抑制する効果が十分に得られず、１を超えて担持しても効果が飽和するとともにアルカリ金属のＮＯx 吸収能を低下させるので好ましくない。アルカリ金属に対するモル比で０．００８〜０．１の範囲が特に好ましい。
【００２０】
ＺｒとＳｉはいずれか一方を担持してもよいし、両方を共存させることもできる。共存させる場合の担持量は、Ｚｒ及びＳｉはそれぞれ上記の範囲と同様である。なおＺｒ及び／又はＳｉの担持法は、通常の含浸法で担持させてもよいし、アルカリ金属と固溶させて担持させることもできる。
【００２１】
【実施例】
以下、実施例及び比較例により本発明をさらに具体的に説明する。なお、以下の例において「部」は特にことわらない限り「重量部」を示す。
＜触媒の調製＞
アルミナ粉末１００部と、アルミナゾル（アルミナ含有率１０重量％）７０部と、４０重量％硝酸アルミニウム水溶液１５部及び水３０部を混合し、コーティング用スラリーを調製した。
【００２２】
このスラリーにコーディエライト質ハニカム担体を浸漬し、引き上げた後余分なスラリーを吹き払い、乾燥後６００℃で１時間焼成してアルミナコート層を形成した。コート量はハニカム担体の体積１リットル当たり１２０ｇである。このアルミナコート層をもつハニカム担体を、ジニトロジアンミン白金水溶液に浸漬し、引き上げて余分な水滴を吹き払った後２５０℃で乾燥してＰｔを担持した。次いで硝酸ロジウム水溶液に浸漬し、引き上げて余分な水滴を吹き払った後２５０℃で乾燥してＲｈを担持させた。Ｐｔ及びＲｈの担持量は表１に示すとおりである。
【００２３】
次に、Ｃｓ、Ｚｒ及びＳｉの水溶性化合物の水溶液を用意し、表１に示す担持量となるように混合した混合溶液に上記のＰｔ−Ｒｈ担持担体をそれぞれ浸漬し、引き上げて余分な水滴を吹き払って乾燥後６００℃で１時間焼成して、表１に示す９種類の触媒を調製した。
【００２４】
【表１】
【００２５】
【表２】
熱処理後の各触媒を評価装置に配置し、ガス流量３０Ｌ／ｍｉｎにて表３に示すストイキ雰囲気のガスとリーン雰囲気のガスを２分間ずつ交互に流して、入りガス温度が３００℃、４００℃及び５００℃のときのＮＯx 浄化率を測定した。また熱処理後の各触媒中のＣｓの量を測定し、熱処理前のＣｓ量に対する残存率を測定した。なお、各触媒の容積は３５ｃｃである。結果を表４に示す。
【００２６】
【表３】
【表４】
表４より、各実施例は比較例３に比べて低温域〜高温域で高いＮＯx 浄化率を示し、ＮＯx 浄化性能に優れている。これはＺｒ又はＳｉをＣｓと共存させたことによる効果であることが明らかである。また比較例１、２のように、Ｚｒ又はＳｉの担持量が所定範囲を外れた場合には、上記効果が得られないこともわかる。
【００２８】
つまり比較例３では、Ｚｒ及びＳｉが含まれないために熱処理後のＣｓの残存率が低くなっている。また比較例１ではＺｒの含有量が少ないために、熱処理後のＣｓの残存率が低い。したがって比較例１及び比較例３では、ＮＯx 浄化率が実施例に比べて低くなっている。そして比較例２では、Ｚｒの含有量が多いため熱処理後のＣｓの残存率は高いものの、過剰のＺｒがＣｓのＮＯx 吸収能を低下させるためＮＯx 浄化率が実施例に比べて低くなっている。
【００２９】
一方、各実施例では適切な範囲のＺｒ又はＳｉが含まれているために、熱処理後のＣｓの残存率が７６％以上と高くＣｓの蒸散が抑止されている。したがって熱処理後にもＣｓのＮＯx 吸蔵能が高く維持され、これにより高いＮＯx 浄化率が得られている。
【００３０】
【発明の効果】
すなわち本発明の排ガス浄化用触媒及び排ガス浄化方法によれば、高温時のアルカリ金属の蒸散が防止されているので、低温域から高温域まで高いＮＯx 浄化率が得られ、高温耐久性に優れている。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purifying catalyst and an exhaust gas purifying method for purifying exhaust gas discharged from an internal combustion engine. More specifically, the present invention relates to an exhaust gas containing excess oxygen, that is, carbon monoxide (CO), hydrogen (H 2 ) contained in the exhaust gas. ) And hydrocarbons (HC) and other exhaust gas purifying catalysts capable of efficiently reducing and purifying nitrogen oxides (NO x ) in exhaust gas containing oxygen in excess of the amount of oxygen necessary for complete oxidation. And an exhaust gas purification method.
[0002]
[Prior art]
Conventionally, a three-way catalyst that purifies exhaust gas by oxidizing CO and HC and reducing NO x has been used as an exhaust gas purification catalyst for automobiles. As such a three-way catalyst, for example, a porous carrier layer made of γ-alumina is formed on a heat-resistant substrate made of cordierite or the like, and platinum (Pt), rhodium (Rh), A catalyst on which a catalytic noble metal such as palladium (Pd) is supported is widely known (for example, Japanese Patent Publication No. 56-27295).
[0003]
On the other hand, in recent years, from the viewpoint of protecting the global environment, carbon dioxide (CO 2 ) in exhaust gas discharged from internal combustion engines such as automobiles has been a problem, and so-called lean burn that makes lean combustion in an oxygen-excess atmosphere is promising as a solution. Is being viewed. In this lean burn, the amount of fuel used is reduced, so that the fuel consumption is improved and the generation of CO 2 as combustion exhaust gas can be suppressed.
[0004]
In contrast, conventional three-way catalyst, there is the air-fuel ratio is CO in the exhaust gas air-fuel mixture is burned in the theoretical air-fuel ratio (stoichiometric), HC, simultaneously oxidizing and reducing NO x, to purify, lean do not exhibit sufficient purification performance for reduction and removal of the nO x in an oxygen excess atmosphere of the exhaust gas during the burn. Therefore, it is desired to develop an exhaust gas purification catalyst and an exhaust gas purification system that can efficiently purify NO x even in an oxygen-excess atmosphere.
[0005]
Therefore, the applicant of the present application has previously proposed an exhaust gas purification method using an exhaust gas purification catalyst carrying Pt and an alkali metal typified by potassium (K) or sodium (Na) (JP-A-6-31139). Issue gazette). Further, at least one metal selected from the group consisting of alkali metals such as lithium (Li), Na, K, and cesium (Cs), and iron (Fe), nickel (Ni), cobalt (Co), and magnesium (Mg) In addition, an exhaust gas purifying catalyst supporting barium (Ba) and Pt and / or Pd is also proposed (Japanese Patent Laid-Open No. Hei 6-142458).
[0006]
According to these exhaust gas-purifying catalysts, nitrogen oxides (NO x ), such as alkali metals, in an oxygen-excess atmosphere (lean atmosphere) that exceeds the stoichiometric ratio required to oxidize reducing components in the exhaust gas. It is absorbed by the so-called NO x absorbent. That alkali metal is considered to NO x is absorbed by generating nitrate reacts with NO x.
[0007]
The absorbed NO x is released when the oxygen concentration reaches the chemical equivalent point (theoretical air-fuel ratio: stoichiometric) or lower (rich atmosphere), and the reducing components such as HC and CO contained in the exhaust gas. It reacts and is reduced and purified.
By give proper mixture supplied to a lean burn engine regularly stoichiometric or rich side Therefore, it is possible to reduce and purify NO x which had been absorbed in the absorption of NO x material, absorption of NO x material next lean atmosphere again to absorb the NO x in. Thereby, good purification performance of NO x can be obtained even on the lean side.
[0008]
[Problems to be solved by the invention]
The above publication evaluates the purification rate by running in a 10.15 mode after a 50 hour endurance test at an inlet gas temperature of 650 ° C. in a lean atmosphere with an air-fuel ratio (A / F) = 18. In this evaluation test, the temperature range to which the exhaust gas purifying catalyst is exposed is 250 to 300 ° C., and if it is within this range, excellent purification performance is obtained.
[0009]
However, considering the recent high performance of engines and the widespread use of highways, the exhaust gas purifying catalyst is exposed to higher temperatures such as 400 to 500 ° C., for example. For this reason, further high temperature durability is calculated | required by the catalyst for exhaust gas purification.
Therefore, the inventors of the present application investigated the high temperature durability of the exhaust gas purification catalyst using an alkali metal as the NO x absorbent. As a result, it has been clarified that when exposed to an excessively high temperature of about 900 ° C., the alkali metal evaporates and the NO x purification rate decreases.
[0010]
The present invention has been made in view of such circumstances, and an object of the present invention is to prevent alkali metal transpiration even when exposed to high temperatures and to maintain high NO x purification performance from low temperatures to high temperatures.
[0011]
[Means for Solving the Problems]
Features of the exhaust gas purifying catalyst of the present invention for solving the above-mentioned problems, NO x in the exhaust gas in an oxygen-rich atmosphere in excess of the stoichiometric ratio required for the oxygen concentration in the exhaust gas to oxidize the reducing components in the exhaust gas An exhaust gas purifying catalyst that reduces and purifies NO x absorbed in a reducing atmosphere at a chemical equivalent point where the oxygen concentration in the exhaust gas is less than the stoichiometric ratio or in a reducing atmosphere,
It consists of a porous oxide, Zr or Si supported on the porous oxide , a catalyst noble metal and an alkali metal, and Zr is contained in a molar ratio of 0.05 to 2 with respect to the alkali metal, and Si is a mole with respect to the alkali metal. It is contained in 0.003 to 1 by ratio.
[0012]
Further, the exhaust gas purification method of the present invention is characterized in that NO x in the exhaust gas is absorbed in an oxygen-excess atmosphere in which the oxygen concentration in the exhaust gas exceeds the stoichiometric ratio necessary for oxidizing the reducing component in the exhaust gas. An exhaust gas purification method for reducing and purifying NO x absorbed in a chemical equivalent point where the oxygen concentration is less than or equal to the stoichiometric ratio or in a reducing atmosphere with a reducing component,
It consists of a porous oxide, Zr or Si supported on the porous oxide , a catalyst noble metal and an alkali metal, and Zr is contained in a molar ratio of 0.05 to 2 with respect to the alkali metal, and Si is a mole with respect to the alkali metal. The exhaust gas is brought into contact with an exhaust gas purifying catalyst contained in a ratio of 0.003 to 1 to reduce and purify NO x in the exhaust gas.
[0013]
The exhaust gas purifying catalyst of the third invention is characterized in that the alkali metal is Cs in the exhaust gas purifying catalyst of the first invention.
Furthermore, the exhaust gas purification method of the fourth invention is characterized in that the alkali metal contained in the exhaust gas purification catalyst in the exhaust gas purification method of the second invention is Cs.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The exhaust gas purifying catalyst and the exhaust gas purifying method of the present invention, NO x in the exhaust gas of lean atmosphere is absorbed by the alkali metal, and reducing component of HC and CO, etc. is released in the exhaust gas when it becomes a rich atmosphere It reacts and is reduced and purified.
Here, for example, when Cs is supported on the porous oxide , the Cs is liberated by being exposed to a high temperature of 800 ° C. or more and is evaporated away from the porous oxide. Accordingly, in the present invention, at least one of Zr and Si is supported in combination with the alkali metal. In this case, it is considered that the alkali metal exists as a complex compound with Zr or Si at a high temperature, and transpiration is prevented and the alkali metal can continue to exist stably on the porous oxide.
[0015]
On the other hand, the complex compound is at 300 to 500 around ℃ catalytic action of the catalyst noble metal is exerted weakened binding force, NO x absorption capability of the alkali metal is believed to revive the like attack NO, Zr or Si Almost no influence is exerted on the NO x absorption capacity of alkali metals.
Examples of the porous oxide include heat-resistant inorganic oxides having a high specific surface area such as alumina, titania, silica-alumina, and zeolite. Of these, activated alumina is preferred because of its high heat resistance and high specific surface area. The shape of the catalyst is not particularly limited as long as the contact efficiency between the gas and the catalyst noble metal is high, and may be a pellet shape, a honeycomb shape, or the like. The porous oxide itself may be formed into that shape, or a monolith substrate made of cordierite or metal may be coated with the porous oxide .
[0016]
As the catalyst noble metal, Pt, Rh, Pd and the like can be used as in the conventional case. The supported amount is preferably 0.1 to 10 g, particularly preferably 1 to 5 g in the case of Pt and Pd per liter of the honeycomb carrier . In the case of Pd, 0.015 to 2 g is preferable, and 0.01 to 1 g is particularly preferable. If the supported amount of the catalyst noble metal is less than this range, good activity cannot be obtained, and even if the supported amount exceeds this range, the effect is saturated and expensive.
[0017]
In order to support the catalyst noble metal on the porous oxide, it can be supported in the same manner as before by using the chloride, nitrate, etc., using an impregnation method, a spray method, a slurry mixing method, or the like.
Examples of the alkali metal include Li, Na, K, Rb, and Cs. Among them, Cs that is easy to evaporate at a high temperature is particularly recommended. The amount of alkali metal supported is preferably in the range of 0.01 to 0.5 mol per liter of the honeycomb carrier . If the amount is less than 0.01 mol / L, sufficient NO x absorption ability cannot be obtained and the NO x purification performance is poor. Even if it exceeds 0.5 mol / L, the NO x absorption ability is saturated, and the alkali metal is absorbed. Since the surface of the catalytic noble metal is coated, the catalytic activity is lowered. A range of 0.05 to 0.3 mol / L is particularly preferable.
[0018]
The amount of Zr supported is 0.05 to 2 in molar ratio to the alkali metal. If it is less than 0.05, the effect of suppressing alkali metal transpiration cannot be sufficiently obtained, and even if it is supported in excess of 2, the effect is saturated and the NO x absorption capacity of the alkali metal is lowered, which is not preferable. A range of 0.8 to 1.2 in terms of molar ratio to alkali metal is particularly preferred.
[0019]
The Si loading is 0.003 to 1 in terms of a molar ratio to the alkali metal. The effect of suppressing less than 0.003 and the evaporation of the alkali metal can not be sufficiently obtained, undesirably reduces the absorption of NO x capacity of the alkali metal with the effect be supported by more than one is saturated. A range of 0.008 to 0.1 in terms of molar ratio to alkali metal is particularly preferred.
[0020]
Zr and Si may carry either one or both may coexist. In the case of coexistence, Zr and Si are each in the same range as above. The Zr and / or Si loading method may be carried by a normal impregnation method, or may be carried in a solid solution with an alkali metal.
[0021]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. In the following examples, “parts” means “parts by weight” unless otherwise specified.
<Preparation of catalyst>
A slurry for coating was prepared by mixing 100 parts of alumina powder, 70 parts of alumina sol (alumina content 10% by weight), 15 parts of 40% by weight aluminum nitrate aqueous solution and 30 parts of water.
[0022]
A cordierite honeycomb carrier was immersed in this slurry, pulled up, and then the excess slurry was blown off. After drying, the slurry was fired at 600 ° C. for 1 hour to form an alumina coat layer. The coating amount is 120 g per liter of honeycomb carrier volume. The honeycomb carrier having the alumina coat layer was dipped in a dinitrodiammine platinum aqueous solution, pulled up to blow off excess water droplets, and then dried at 250 ° C. to carry Pt. Next, it was immersed in an aqueous rhodium nitrate solution, pulled up to blow off excess water droplets, and then dried at 250 ° C. to carry Rh. The amounts of Pt and Rh supported are as shown in Table 1.
[0023]
Next, an aqueous solution of a water-soluble compound of Cs, Zr, and Si is prepared, and the above Pt-Rh-supported carriers are respectively immersed in mixed solutions mixed so as to have the supported amounts shown in Table 1, and are pulled up to remove excess water droplets. Nine types of catalysts shown in Table 1 were prepared by blowing off and drying and calcining at 600 ° C. for 1 hour.
[0024]
[Table 1]
[0025]
[Table 2]
Each catalyst after the heat treatment is placed in an evaluation apparatus, and a stoichiometric atmosphere gas and a lean atmosphere gas shown in Table 3 are alternately flowed for 2 minutes each at a gas flow rate of 30 L / min. The NO x purification rate at 500 ° C. was measured. Further, the amount of Cs in each catalyst after the heat treatment was measured, and the residual ratio relative to the amount of Cs before the heat treatment was measured. The volume of each catalyst is 35 cc. The results are shown in Table 4.
[0026]
[Table 3]
[Table 4]
From Table 4, each Example shows a higher NO x purification rate in the low temperature range to the high temperature range than Comparative Example 3, and is excellent in NO x purification performance. This is clearly the effect of coexisting Zr or Si with Cs. In addition, as in Comparative Examples 1 and 2, it can be seen that the above-mentioned effect cannot be obtained when the amount of Zr or Si supported falls outside the predetermined range.
[0028]
That is, in Comparative Example 3, since Zr and Si are not included, the residual ratio of Cs after the heat treatment is low. In Comparative Example 1, since the Zr content is small, the residual ratio of Cs after the heat treatment is low. Therefore, in Comparative Example 1 and Comparative Example 3, the NO x purification rate is lower than in the example. Then, in Comparative Example 2, although Cs residual ratio of after heat treatment for the content of Zr is high high, it became excessive Zr is the NO x purification rate to reduce the absorption of NO x capacity of Cs is lower as compared with Examples ing.
[0029]
On the other hand, since each embodiment contains an appropriate range of Zr or Si, the residual ratio of Cs after heat treatment is as high as 76% or more, and Cs transpiration is suppressed. Therefore, the NO x storage capacity of Cs is maintained high even after the heat treatment, and thereby a high NO x purification rate is obtained.
[0030]
【The invention's effect】
That is, according to the exhaust gas purifying catalyst and the exhaust gas purifying method of the present invention, transpiration of alkali metal at high temperatures is prevented, so a high NO x purification rate can be obtained from a low temperature range to a high temperature range, and excellent high temperature durability. ing.
Claims (4)
多孔質酸化物と、
該多孔質酸化物に担持されたジルコニウム又はケイ素と、触媒貴金属及びアルカリ金属とからなり、
ジルコニウムはアルカリ金属に対するモル比で０．０５〜２含まれ、ケイ素はアルカリ金属に対するモル比で０．００３〜１含まれることを特徴とする排ガス浄化用触媒。The nitrogen concentration in the exhaust gas is absorbed in an oxygen-excess atmosphere in which the oxygen concentration in the exhaust gas exceeds the stoichiometric ratio necessary for oxidizing the reducing component in the exhaust gas, and the oxygen concentration in the exhaust gas is A catalyst for exhaust gas purification that reduces and purifies the nitrogen oxides absorbed in a chemical equivalence point that is less than the stoichiometric ratio or in a reducing atmosphere with the reducing component,
A porous oxide ;
Consisting of zirconium or silicon supported on the porous oxide , a catalytic noble metal and an alkali metal,
Zirconium is contained in an amount of 0.05 to 2 in terms of a molar ratio to an alkali metal, and silicon is contained in an amount of 0.003 to 1 in terms of a molar ratio to an alkali metal.
多孔質酸化物と、該多孔質酸化物に担持されたジルコニウム又はケイ素と、触媒貴金属及びアルカリ金属とからなり、ジルコニウムはアルカリ金属に対するモル比で０．０５〜２含まれ、ケイ素はアルカリ金属に対するモル比で０．００３〜１含まれる排ガス浄化用触媒に排ガスを接触させ、該排ガス中の窒素酸化物を還元浄化させることを特徴とする排ガス浄化方法。The nitrogen concentration in the exhaust gas is absorbed in an oxygen-excess atmosphere in which the oxygen concentration in the exhaust gas exceeds the stoichiometric ratio necessary for oxidizing the reducing component in the exhaust gas, and the oxygen concentration in the exhaust gas is An exhaust gas purification method for reducing and purifying the nitrogen oxides absorbed in a chemical equivalence point that is less than a stoichiometric ratio or in a reducing atmosphere with the reducing component,
It consists of a porous oxide, zirconium or silicon supported on the porous oxide , a catalyst noble metal and an alkali metal, and zirconium is contained in a molar ratio of 0.05 to 2 with respect to the alkali metal, and silicon with respect to the alkali metal. An exhaust gas purification method comprising contacting exhaust gas with an exhaust gas purification catalyst contained in a molar ratio of 0.003 to 1, and reducing and purifying nitrogen oxides in the exhaust gas.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP24434195A JP3839860B2 (en) | 1995-09-22 | 1995-09-22 | Exhaust gas purification catalyst and exhaust gas purification method |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP24434195A JP3839860B2 (en) | 1995-09-22 | 1995-09-22 | Exhaust gas purification catalyst and exhaust gas purification method |
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| Publication Number | Publication Date |
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| JPH0985092A JPH0985092A (en) | 1997-03-31 |
| JP3839860B2 true JP3839860B2 (en) | 2006-11-01 |
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| JP24434195A Expired - Lifetime JP3839860B2 (en) | 1995-09-22 | 1995-09-22 | Exhaust gas purification catalyst and exhaust gas purification method |
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| JP2001232195A (en) | 1999-12-17 | 2001-08-28 | Ngk Insulators Ltd | Catalyst body |
| JP4645786B2 (en) | 2001-06-08 | 2011-03-09 | 三菱自動車工業株式会社 | Exhaust gas purification catalyst |
| EP2826558A4 (en) * | 2012-03-12 | 2016-01-06 | Otsuka Chem Holdings Co Ltd | Exhaust gas purification catalyst, exhaust gas purification device and filter, and production method for said catalyst |
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