JP3551472B2 - Exhaust gas purification catalyst - Google Patents

Description

【００２１】
式 （Ｉ）の触媒担体においては、イオン半径の大きな元素に対しイオン半径の小さな元素は１０〜４０％含まれることが好ましい。より比表面積の大きなものが得られるからである。
【００２２】
式 （Ｉ）の触媒担体にＰｔ等の貴金属を担持させることにより本発明の有効な窒素酸化物吸収分解型、高温耐熱性排ガス浄化用触媒が得られる。貴金属を担持させる方法は特に限定されず、従来用いられている方法、例えば含浸法、等を用いることができる。こうして形成された触媒は、燃焼ガスをリーン、ストイキを交互に制御することによりＮＯ_ｘを吸収分解する。式 （Ｉ）の触媒担体である無定形粉末中のＢａもしくはＫはリーン排ガス中でＮＯ_ｘを吸収する性能に優れ、Ａｌ_２Ｏ_３にＢａもしくはＫをコーティングしたものと同等の性能を示す。しかも１１００℃以下であれば、高温に曝されてもＢａもしくはＫは安定な化合物を形成しないので、ＮＯ_ｘ吸収能は低下しない。
【００２３】
以下、本発明を実施例により説明するが、本発明はこれらに制限されるものではない。
実施例１
金属バリウム４．３ｇ（０．０３１モル）を５０ｍｌの２−プロパノールの溶解した溶液を、８０℃においてアルミニウムトリイソプロポキシド７６．７ｇ（０．３７６ モル）を２５０ｍｌ の２−プロパノールに溶解した溶液と混合した（Ａｌ／Ｂａ＝１２）。この混合溶液を８０℃において５時間還流攪拌し、その後この溶液にイオン交換水１２．８ｍｌと２−プロパノール５５ｍｌの混合溶液を８０℃に保ちながら滴下した。滴下開始後８０℃に保ちながら５時間攪拌し、次いで減圧乾燥し、白色粉末を得た。この粉末を大気中、８００ ℃において５時間の焼成を行うことにより、比表面積２２６ｍ^２／ｇ を有する微細粉末を得た。またＸ線回折の結果、非晶質構造であることが確認された。
【００２４】
実施例２
金属バリウムの代わりに、バリウムジイソプロポキシド（Ｂａ（Ｏ−ｉ−Ｃ_３Ｈ_７）_２） を８．０ｇ（０．０３ モル） 用いることを除き、実施例１と同様にして粉末を得た（Ａｌ／Ｂａ１２）。この粉末を大気中、８００ ℃において５時間の焼成を行うことにより、比表面積２３０ｍ^２／ｇ を有する微細粉末を得た。またＸ線回折の結果、非晶質構造であることが確認された。
【００２５】
実施例３
バリウムジイソプロポキシド６．４ｇ（０．０２５モル） 、硝酸ランタン１．０ｇ（０．００２３ モル） 及び酢酸カリウム０．３ｇ（０．００３５ モル） を５０ｍｌの２−プロパノールに溶解した溶液を、８０℃においてアルミニウムトリイソプロポキシド７６．７ｇ（０．３７６ モル） を２５０ｍｌ の２−プロパノールに溶解した溶液に混合し、その後の処理は実施例１と同様にして粉末を得た（Ａｌ／（Ｂａ＋Ｌａ＋Ｋ）＝１２）。この粉末を大気中、８００ ℃において５時間の焼成を行うことにより、比表面積２３５ｍ^２／ｇ を有する微細粉末を得た。またＸ線回折の結果、非晶質構造であることが確認された。
【００２６】
実施例４
バリウムジイソプロポキシド４．８ｇ（０．０１９モル） 及び硝酸カルシウム２．０ｇ（０．０１２モル） を５０ｍｌの２−プロパノールに溶解した溶液を、８０℃においてアルミニウムトリイソプロポキシド７６．７ｇ（０．３７６ モル） を２５０ｍｌ の２−プロパノールに溶解した溶液に混合し、その後の処理は実施例１と同様にして粉末を得た（Ａｌ／（Ｂａ＋Ｃａ）＝１２）。この粉末を大気中、８００ ℃において５時間の焼成を行うことにより、比表面積２１８ｍ^２／ｇ を有する微細粉末を得た。またＸ線回折の結果、非晶質構造であることが確認された。
【００２７】
実施例５
金属バリウム４．３ｇ（０．０３１モル）を５０ｍｌの２−プロパノールの溶解した溶液を、８０℃においてアルミニウムトリイソプロポキシド７６．７ｇ（０．３７６ モル）を２５０ｍｌ の２−プロパノールに溶解した溶液と混合した（Ａｌ／Ｂａ＝１２）。この混合溶液を８０℃において２時間還流攪拌し、その後２，４−ペンタジオン１２．２ｇ を添加し、さらに３時間還流攪拌を行った。次いでこの溶液を８０℃に保ちながらイオン交換水４２．７ｍｌと２−プロパノール１８２ｍｌ の混合溶液を８０℃に保ちながら滴下した。滴下開始後８０℃に保ちながら５時間攪拌し、次いで減圧乾燥し、白色粉末を得た。この粉末を大気中、８００ ℃において５時間の焼成を行うことにより、比表面積２３６ｍ^２／ｇ を有する微細粉末を得た。またＸ線回折の結果、非晶質構造であることが確認された。
【００２８】
実施例６
バリウムジイソプロポキシド６．４ｇ（０．０２５モル） 、硝酸ランタン１．０ｇ（０．００２３ モル） 及び酢酸カリウム０．３ｇ（０．００３５ モル） を５０ｍｌの２−プロパノールに溶解した溶液を、８０℃においてアルミニウムトリイソプロポキシド７６．７ｇ（０．３７６ モル） を２５０ｍｌ の２−プロパノールに溶解した溶液に混合し（実施例３と同様）、その後の処理は実施例５と同様にして粉末を得た。この粉末を大気中、８００ ℃において５時間の焼成を行うことにより、比表面積２４１ｍ^２／ｇ を有する微細粉末を得た。またＸ線回折の結果、非晶質構造であることが確認された。
【００２９】
実施例７
バリウムジイソプロポキシド１１．２ｇ（０．０４４ モル） を５０ｍｌの２−プロパノールに溶解した溶液を、８０℃においてアルミニウムトリイソプロポキシド５３．４ｇ（０．２６２ モル） を２５０ｍｌ の２−プロパノールに溶解した溶液と混合した（Ａｌ／Ｂａ＝６）。この混合溶液を８０℃において２時間還流攪拌した後、２，４−ペンタジオン９．２ｇを添加し、さらに３時間還流攪拌を行った。次いでこの溶液を８０℃に保ちながらイオン交換水３１．４ｍｌと２−プロパノール１３４ｍｌ の混合溶液を滴下した。滴下開始後８０℃に保ちながら５時間攪拌し、次いで減圧乾燥し、白色粉末を得た。この粉末を大気中、８００ ℃において５時間の焼成を行うことにより、比表面積１５３ｍ^２／ｇ を有する微細粉末を得た。またＸ線回折の結果、非晶質構造であることが確認された。
【００３０】
実施例８
バリウムジイソプロポキシド３．７ｇ（０．０１４５ モル） を５０ｍｌの２−プロパノールに溶解した溶液を、８０℃においてアルミニウムトリイソプロポキシド７１．１ｇ（０．３４９ モル） を２５０ｍｌ の２−プロパノールに溶解した溶液と混合した（Ａｌ／Ｂａ＝２４）。この混合溶液を８０℃において２時間還流攪拌した後、２，４−ペンタジオン１０．９ｇ を添加し、さらに３時間還流攪拌を行った。次いでこの溶液を８０℃に保ちながらイオン交換水３８．７ｍｌと２−プロパノール１６５ｍｌ の混合溶液を滴下した。滴下開始後８０℃に保ちながら５時間攪拌し、次いで減圧乾燥し、白色粉末を得た。この粉末を大気中、８００ ℃において５時間の焼成を行うことにより、比表面積２２８ｍ^２／ｇ を有する微細粉末を得た。またＸ線回折の結果、非晶質構造であることが確認された。
【００３１】
上記実施例１〜８において得られた焼成後の粉末を２５０ｍｌ のジニトロジアミンＰｔ硝酸塩水溶液（Ｐｔ量：０．００３ｍｏｌ） 中に含浸し、室温において１時間攪拌機で攪拌した。このスラリーを遠心分離機により粉末と上澄液に分離し、上澄液を廃棄した。得られた粉末を１２０ ℃において１２時間乾燥し、さらに２５０ ℃において１時間熱処理を行った。元素分析により、Ｐｔは担体粉末に対し、１．０２重量％担持されていた。
【００３２】
こうして得られたＰｔを担持した粉末を以下の方法によりハニカム担体にコーティングした。
前記粉末１００ｇにアルミナゾル３ｇ 、硝酸アルミニウム４０％水溶液５０ｇ 及び水１０８ｇを加えてスラリーを調製した。このスラリーにコージェライト製ハニカム担体（外容積１リットル）を浸漬し、過剰のスラリーを吹き払う方法によって前記スラリーをハニカム担体にコートし、１２０ ℃において３時間乾燥後、５００ ℃において１時間電気炉で焼成し、触媒試料を得た。
【００３３】
このようにして製造したハニカム触媒について、新品触媒の浄化性能及びモデルガス（リーン）８００ ℃×２４時間の耐久後の浄化性能を以下の条件において評価した。
【００３４】
（１） モデルガス組成
▲１▼ リーン
ＣＯ：０．０８％、Ｃ_３Ｈ_８：８００ｐｐｍ、ＣＯ_２ ：１２．０％、Ｏ_２： ４．５％、
Ｈ_２Ｏ ：３％、ＮＯ：１０００ｐｐｍ 、ＳＯ_２ ：５０ｐｐｍ 、Ｎ_２：残部
▲２▼ ストイキ
ＣＯ：１．０５％、Ｃ_３Ｈ_８：１０００ｐｐｍ 、ＣＯ_２ ：１０．０％、Ｏ_２：変動
Ｈ_２Ｏ ：１０％、ＮＯ：２０００ｐｐｍ 、ＳＯ_２ ：５０ｐｐｍ 、Ｎ_２：残部
（２） 空間速度：２０００００ ｈ^−１
【００３５】
（３） 浄化率測定方法
ハニカムをセットしたステンレス管を管状炉内で加熱し、ハニカム内を３００ ℃に保持した状態においてモデルガスをこのハニカム内に流す。そしてハニカム通過後のガスを分析する。リーン１分−ストイキ１分を２回繰り返した４分間のガス成分の平均量と４分間に流したモデルガス量から、浄化された量を算出する。こうして、３００ ℃でのＣＯ、ＨＣ、ＮＯ_ｘ の平均浄化率を測定した。結果を以下の表２に示す。また、耐久後のＢａＳＯ_４ 生成量をＸ線回折ピーク強度により評価した。この結果も表２に示す。
【００３６】
比較例１
比表面積１５０ｍ^２／ｇ のγアルミナに上記と同様にしてＰｔを担持させた。この粉末を２５ｗｔ％Ｂａとなるように調製した酢酸バリウム水溶液内に含浸し、１時間攪拌した後、遠心分離機により粉末を分離した。この粉末を１２０ ℃において１２時間乾燥した後、５００／℃において１時間の熱処理を行った。この粉末を上記と同様にしてハニカムにコートし、触媒試料を得た後、同様にして評価を行った。
【００３７】
比較例２
金属バリウム２１．８ｇ（０．１５９ モル） を８０ｍｌの２−プロパノールに溶解した溶液を、８０℃においてアルミニウムトリイソプロポキシド６５．０ｇ（０．３１９ モル） を２５０ｍｌ の２−プロパノールに溶解した溶液と混合した（Ａｌ／Ｂａ＝２）。この混合溶液を８０℃において２時間還流攪拌した後、２，４−ペンタンジオン１４．３ｇ を添加し、さらに３時間還流攪拌を行った。この溶液にイオン交換水４５．９ｍｌと２−プロパノール１９５ｍｌ の混合溶液を８０℃に保ちながら滴下した。滴下開始後８０℃に保ちながら５時間攪拌し、次いで減圧乾燥し、白色粉末を得た。この粉末を大気中、８００ ℃において５時間の焼成を行うことにより微細粉末を得た。この粉末の比表面積は３４ｍ^２／ｇであった。またＸ線回折の結果、ＢａＯ・Ａｌ_２ Ｏ_３ が生成していることが明らかとなった。
【００３８】
比較例３
実施例７においてバリウムイソプロポキシドを３．０ｇ（０．０１１８ モル） 、アルミニウムイソプロポキシドを６２．３ｇ（０．３０５ モル） 、２，４−ペンタンジオンを９．５ｇ、イオン交換水を３３．９ｍｌ、そして２−プロパノールを１４５ｍｌ 用いることを除き、他は同様にして粉末を得た（Ａｌ／Ｂａ＝２６）。この粉末を大気中、８００ ℃において５時間の焼成を行うことにより微細粉末を得た。この粉末の比表面積は２１５ｍ^２／ｇ であった。またＸ線回折の結果、非晶質であった。
【００３９】
上記比較例２及び３において得られた焼成後の粉末について、上記実施例と同様にしてＰｔを担持させ、ハニカムにコートし、触媒試料を得た後、同様にして評価した。比較例１〜３において得られた結果を表２に示す。
【００４０】
【表２】

【００４１】
この結果より、本発明の触媒担体を用いて製造した触媒は初期浄化能が高く、かつ耐久後の浄化能も高く高温耐熱性に優れている。また、耐久後の硫酸塩の生成量が低く、優れた分解再生性を有している。
【００４２】
実施例９
２，４−ペンタンジオン１２．２ｇ の代わりにアセト酢酸エチル５．３ｇを用いることを除き、実施例５と同様にして焼成粉末を得た。
【００４３】
実施例１０
アセト酢酸エチルの添加量を１５．９ｇ とすることを除き、実施例９と同様にして焼成粉末を得た。
【００４４】
実施例１１
アセト酢酸エチルの添加量を３１．８ｇ とすることを除き、実施例９と同様にして焼成粉末を得た。
【００４５】
実施例１２
アセト酢酸エチルの代わりにトリエタノールアミンを６．１ｇ用いることを除き、実施例９と同様にして焼成粉末を得た。
【００４６】
実施例１３
トリエタノールアミンの添加量を１８．２ｇ とすることを除き、実施例１２と同様にして焼成粉末を得た。
【００４７】
実施例１４
トリエタノールアミンの添加量を３６．４ｇ とすることを除き、実施例１２と同様にして焼成粉末を得た。
【００４８】
上記実施例９〜１４において得られた焼成粉末の比表面積を測定し、その結果を以下の表３に示す。これらの粉末は、Ｘ線回折の結果、いずれも結晶性のピークはみられず、非晶質構造であることが確認された。
【００４９】
【表３】

【００５０】
実施例１５
金属バリウム１２．９ｇ（０．０９４ モル）を７０ｍｌの２−プロパノールに溶解した溶液を、８０℃においてアルミニウムトリイソプロポキシド７６．７ｇ（０．３７６ モル）を２５０ｍｌ の２−プロパノールに溶解した溶液と混合した（Ａｌ／Ｂａ＝４）。この混合溶液を８０℃において２時間還流攪拌し、その後２，４−ペンタジオン７６．７ｇ を添加し、さらに３時間還流攪拌を行った。次いでこの溶液を８０℃に保ちながらイオン交換水４２．７ｍｌと２−プロパノール２０２ｍｌ の混合溶液を８０℃に保ちながら滴下した。滴下開始後８０℃に保ちながら５時間攪拌し、次いで減圧乾燥し、白色粉末を得た。この粉末を大気中、８００ ℃において５時間の焼成を行うことにより、比表面積７２ｍ^２／ｇを有する微細粉末を得た。またＸ線回折の結果、非晶質構造であることが確認された。
【００５１】
実施例１６（水の添加量の効果）
実施例２において、水の添加量を変え、得られた粉末の比表面積及び同様にして調製した触媒の耐久後の結晶化時の生成相を調べ、その結果を以下の表４に示す。
【００５２】
【表４】

水の添加量は、原料中のアルキル基に対し、０．３ 〜０．８ 倍が好ましい。
【００５３】
実施例１７（Ｂａ量の効果）
実施例２において、Ｂａの添加量を変え，同様にして触媒化し、リーン４分−ストイキ１分の繰り返しにより３００ ℃でのＮＯ_ｘ の平均浄化率を測定した。この結果を図１に示す。この図から明らかなように、ＮＯ_ｘ の吸収容量が多く要求される条件においてはＢａ量の多い領域において特に優位性が認められる。
【００５４】
実施例１８
トリイソプロポキシアルミニウム２０４ｇ（１モル） 、ジイソプロポキシバリウム１７．０ｇ（０．０６７ モル） 、エトキシナトリウム１．１３ｇ（０．０１７ モル） を２−プロパノール中で８０℃において５時間攪拌した（Ｂａ＋Ｎａ／Ａｌ＝１２）。イオン交換水５７．６ｍｌ含む２００ｍｌ の２−プロパノール溶液を１ｍｌ／ｍｉｎで滴下し、加水分解を行った。次いで５時間加熱し、減圧乾燥した。こうして得られた粉末を１０００℃において５時間焼成を行った。この焼成粉末は２６０ｍ^２／ｇ の比表面積を有しており、実施例１〜４で得られた粉末よりも高かった。
【００５５】
実施例１９
トリイソプロポキシアルミニウム２０４ｇ（１モル） 、硝酸ルビジウム１０．３ｇ（０．０７モル） 、ジイソプロポキシストロンチウム６．１７ｇ（０．０３モル） を２−プロパノール中で８０℃において５時間攪拌した（Ｒｂ＋Ｓｒ／Ａｌ＝１０）。イオン交換水５７．６ｍｌ含む２００ｍｌ の２−プロパノール溶液を１ｍｌ／ｍｉｎで滴下し、加水分解を行った。次いで５時間加熱し、減圧乾燥した。こうして得られた粉末を１０００℃において５時間焼成を行った。この焼成粉末は２３０ｍ^２／ｇ の比表面積を有していた。
【００５６】
上記実施例１８及び１９において得られた粉末を担体として触媒化し、排気ガスの浄化率を測定した。すなわち、これらの粉末に硝酸アルミニウム及び水を加えてスラリーを調製した。このスラリーにコージェライト製ハニカム担体を浸漬し、余分についたスラリーを吹き払う方法によってスラリーをコートし、１２０ ℃において３時間乾燥後、５００ ℃で１時間電気炉内で焼成した。次いでジニトロアミンＰｔの硝酸塩溶液に３０分含浸し、粉末１００ｇあたり１ｇのＰｔを担持させ、１２０ ℃において３時間乾燥後、２５０ ℃で１時間電気炉内で熱処理した。さらに、硝酸Ｒｈ水溶液に３０分含浸し、粉末１００ｇあたり１ｇのＲｈを担持させ、１２０ ℃において３時間乾燥後、２５０ ℃で１時間電気炉内で熱処理し、モノリックハニカム触媒を得た。
【００５７】
こうして製造したハニカム触媒について新品触媒の浄化性能を以下の条件において上記のようにして測定した。
（１） 評価ガス組成（Ａ／Ｆ（空燃比）＝１８）
ＣＯ：０．１ ％、Ｃ_３Ｈ_８：６００ｐｐｍ、Ｈ_２：０．０５％、ＣＯ_２ ：１１．５％、
Ｏ_２： ３．５％、Ｈ_２Ｏ ：１０％、ＮＯ：２５００ｐｐｍ 、Ｎ_２：残部
（２） 空間速度：２０００００ｈ ^−１
この結果を表５に示す。
【００５８】
【表５】

【００５９】
さらに、この触媒をストイキ（Ａ／Ｆ＝１４．５）の排気ガス中、９００ ℃において１０時間の耐久処理を行った後に、Ａ／Ｆ＝１８の浄化率を測定した。この結果を以下の表６に示す。
【００６０】
【表６】

【００６１】
【発明の効果】
本発明の触媒担体は、Ａｌ／Ｍｅ＝４〜２４の比とすることにより層状アルミネート構造の前駆体の非晶質構造となり、比表面積が大きく、また構造の自由度により活性種の低下がなく、そのため十分な触媒機能を与える。この層状アルミネート構造の前駆体は他のアルミナ等の前駆体に比べて結晶化する温度が高いため十分な高温耐熱性を維持することができる。また、本発明の触媒担体の製造時において、加水分解速度を制御することにより、ＮＯ_ｘ 吸蔵元素が高分散状態で含まれる担体が得られ、硫黄被毒時における硫酸塩の粒成長が起こりにくく、分解再生性が良好である。さらに、ＮＯ_ｘ 吸蔵元素として、特定のイオン半径の差を有する２種以上の元素を用いることにより、より比表面積の高い担体が得られる。この担体にＰｔ等を担持させることにより、高温耐熱性に優れたＮＯ_ｘ 吸収分解型触媒が得られる。
【図面の簡単な説明】
【図１】本発明の触媒担体におけるＢａ量と、この担体より製造した触媒のＮＯ_ｘ 浄化能との関係を示すグラフである。[0001]
[Industrial applications]
The present invention relates to an exhaust gas purifying catalyst , and more particularly, to a nitrogen oxide absorption-decomposition type catalyst excellent in high-temperature heat resistance.
[0002]
[Prior art]
Air pollution was taken up as an environmental problem, and particularly with the spread of automobiles, its exhaust gas became a problem, and various regulations were applied. For this reason, various systems such as an engine improvement, a reactor system, and a catalyst system were applied at an early stage, but at present, a catalyst system capable of performing exhaust gas treatment most efficiently is predominant.
[0003]
Automotive catalysts are mounted directly on the engine exhaust manifold or under the floor of the vehicle. Currently used catalytic converters are called “Molinos type”, which have a large number of through holes (cells) formed in the flow direction of exhaust gas, and a wash coat layer is provided on the inner surface of each cell. Have been. This washcoat layer is a substantial part of the catalyst for purifying the exhaust gas.
[0004]
As the catalyst, noble metals such as platinum (Pt), rhodium (Rh), and palladium (Pd) are known, and these are fine particles on a porous and large surface area carrier such as alumina (Al ₂ O ₃ ). As dispersed. The exhaust gas diffuses into the fine pores of the alumina, and a catalytic reaction occurs on the catalyst surface. Since such a catalytic reaction is performed on the surface of the noble metal particles, the noble metal particles are preferably as small as possible.
[0005]
However, in the conventional catalyst, the noble metal particles aggregate in a high temperature range of 600 ° C. or more, and the catalyst surface area decreases. At a high temperature of 1000 ° C. or higher, γ-Al ₂ O ₃ currently used as a carrier undergoes a structural transition to α-Al ₂ O ₃ , the surface area decreases, and micropores disappear. Therefore, in order to prevent this α-formation, a catalyst to which a rare earth element has been added has been developed. However, even with such a catalyst, the durability is limited to about 800 ° C., and at a temperature higher than 800 ° C. No results were obtained.
[0006]
In order to solve the above problem, a carrier having a magnetoplumbite type layered aluminate structure having high crystallinity has been developed (Japanese Patent Application Laid-Open No. 2-78438). This carrier contains an alkaline earth metal oxide and an aluminum oxide, and there is no reaction between the alkaline earth metal and the aluminum oxide at a high temperature, and the specific surface area and the activity are not reduced. However, because of the structure of the layered aluminate, the activity itself of the active species is reduced, the specific surface area itself is reduced, and a sufficient catalytic function cannot be obtained.
[0007]
[Problems to be solved by the invention]
The present invention solves the above-mentioned drawbacks of the conventional catalyst carrier and provides a catalyst having sufficient high-temperature heat resistance.
[0008]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to solve the above-mentioned problems of the catalyst support, and as a result, when an amorphous structure was formed by a precursor of a layered aluminate structure, the specific surface area was large. Further, the present inventors have found that a sufficient catalytic function can be obtained because the active species are not reduced due to the degree of freedom of the structure, and the present invention has been completed.
[0009]
The present invention relates to the following formula (I)
_{Me x Al y O 2 (I} )
(In the above formula, Me is at least one element selected from the group consisting of alkali metals, alkaline earth metals, and rare earth elements, y / x = 4 to 24, and z is determined by Me, x, and y. Value)
Is a precursor of a layered aluminate structure represented by, and a noble metal is supported on a catalyst carrier made of an amorphous composition that has been heat-treated at a temperature that does not crystallize, and the combustion gas is alternately controlled in a lean-stoichiometric manner. This provides an exhaust gas purifying catalyst used for reducing NO _x in sulfur-containing exhaust gas by storing it in Me in the catalyst carrier.
[0010]
In the present invention, Me in the above formula (I) may be composed of two or more kinds of elements, each of which has a hexacoordinate ionic radius of 0.95 ° or more, and a difference in ionic radius between the elements. The present invention provides an exhaust gas purifying catalyst characterized in that the difference between the element having the largest ion radius and the other element having a smaller ion radius is 0.3 ° or more.
[0011]
[Action]
Using the exhaust gas purifying catalyst of the present invention, the combustion gas lean - by controlling the stoichiometric alternately, NO _x in the exhaust gas is occluded reduced. The NO _x storage element (Me) in the amorphous powder has an excellent NO _x storage capacity, and exhibits the same performance as when the NO _x storage element is supported on Al ₂ O ₃ . In addition, in the amorphous catalyst carrier of the above formula (I) , the NO _x occluding element does not form a stable compound with Al ₂ O _{3 of the} carrier at a temperature at which crystallization does not occur, so that the NO _x occluding ability does not decrease.
[0012]
Further, in the amorphous catalyst carrier of the formula (I) , since the NO _x occluding element is mixed in a highly dispersed state in the carrier, grain growth of sulfate hardly occurs at the time of sulfur poisoning. It has decomposition and regeneration properties.
[0013]
In the amorphous catalyst carrier of the formula (I) , when the ionic radius of the NO _x occluding element is large, the NO _x occluding element suppresses the phase change of Al ₂ O ₃ of the carrier. Is obtained. Furthermore, the presence of two or more types of NO _x occluding elements having a difference in ionic radius equal to or greater than a certain value suppresses crystallization of the layered aluminate, and the difference in ionic radius causes distortion in the layered structure. As a result, a powder having a high specific surface area can be obtained.
[0014]
[Description of capture of means for solving the problem]
The catalyst support of the formula (I) is produced by a so-called sol-gel method. That is, a solution is prepared by using an aluminum alkoxide and a metal or a metal oxide in the ratio of the above formula, and this solution is stirred under reflux to effect hydrolysis and polycondensation of the alkoxide. Then, metal oxide particles are generated and the solution becomes a sol. As the reaction proceeds further, the whole becomes a solidified gel. By heating this gel, an amorphous composition represented by the above formula is obtained.
[0015]
The content ratio (Al / Me ) of aluminum and Me of the formula (I) is 4 to 24, preferably 9 to 15, and more preferably 10 to 13 in molar ratio. If this ratio is larger than 24, the amount of NOx storage elements is too small, and the initial purification ability is 40% or less, and the effect is low. On the other hand, when this ratio is less than 4, a large amount of sulfate is formed at the time of sulfur poisoning, and the deterioration of the durability purifying ability becomes large.
[0016]
The hydrolysis in the sol-gel method proceeds rapidly. There is no problem if the above ratio is in the range of 9 to 15, but if it exceeds this range, the dispersibility of the NO _x occluding element becomes poor, and as a result, grain growth of the sulfate tends to occur during sulfur poisoning. Therefore, by controlling the hydrolysis rate, the dispersibility of the NO _x occluding element is enhanced, the grain growth of the sulfate during sulfur poisoning is suppressed, and the deterioration of the durability purifying ability is prevented.
[0017]
The hydrolysis rate is controlled by adjusting the amount of water and adding a reaction inhibitor. As the reaction inhibitor, β-diketone (for example, 2,4-pentadiene), β-keto acid ester (for example, ethyl acetoacetate), alkanolamine (for example, triethanolamine) and the like can be used. Such control of hydrolysis makes it possible to use aluminum and Me in the above ratio range of 4 to 24.
[0018]
Thus temperature not crystallized powder obtained by the sol-gel method, for example, by heat treatment at 800 to 1100 ° C., the resulting catalyst carrier gas of formula (I) which is a precursor of the layer-like aluminate structure.
[0019]
The alkali metal, alkaline earth metal and rare earth element contained in the carrier are not particularly limited, and various types can be used.
In the present invention, the element is composed of two or more elements, each of which has a hexacoordinate ionic radius of 0.95 ° or more, and a difference in ionic radius between the elements, the maximum ionic radius It is preferable that the distance between the element and the other element is 0.3 ° or more. Examples of such elements and their ionic radii are shown in Table 1 below.
[0020]
[Table 1]

[0021]
In the catalyst support of the formula (I) , it is preferable that an element having a small ionic radius is contained in an amount of 10 to 40% of an element having a large ionic radius. This is because a material having a larger specific surface area can be obtained.
[0022]
By supporting a noble metal such as Pt on the catalyst carrier of the formula (I) , an effective nitrogen oxide absorption / decomposition type, high temperature heat resistant exhaust gas purifying catalyst of the present invention can be obtained. The method for supporting the noble metal is not particularly limited, and a conventionally used method, for example, an impregnation method or the like can be used. The catalyst thus formed is absorbed decomposes NO _x by controlling the combustion gas lean, stoichiometric alternately. Ba or K amorphous powder is a catalyst carrier of the formula (I) is excellent in ability to absorb NO _x in lean exhaust gas, shows the Al ₂ to O ₃ obtained by coating the Ba or K equivalent performance. In addition, when the temperature is 1100 ° C. or less, Ba or K does not form a stable compound even when exposed to a high temperature, so that the NO _x absorption ability does not decrease.
[0023]
Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto.
Example 1
A solution prepared by dissolving 4.3 g (0.031 mol) of metal barium in 50 ml of 2-propanol and a solution prepared by dissolving 76.7 g (0.376 mol) of aluminum triisopropoxide in 250 ml of 2-propanol at 80 ° C. (Al / Ba = 12). The mixed solution was refluxed and stirred at 80 ° C. for 5 hours, and then a mixed solution of 12.8 ml of ion-exchanged water and 55 ml of 2-propanol was added dropwise to the solution while maintaining the temperature at 80 ° C. After the dropwise addition, the mixture was stirred for 5 hours while maintaining the temperature at 80 ° C., and then dried under reduced pressure to obtain a white powder. This powder was fired in the air at 800 ° C. for 5 hours to obtain a fine powder having a specific surface area of 226 m ² / g. As a result of X-ray diffraction, it was confirmed that the film had an amorphous structure.
[0024]
Example 2
A powder was obtained in the same manner as in Example 1 except that 8.0 g (0.03 mol) of barium diisopropoxide (Ba (OiC ₃ H ₇ ) ₂ ) was used instead of metal barium. (Al / Ba12). This powder was fired at 800 ° C. in the air for 5 hours to obtain a fine powder having a specific surface area of 230 m ² / g. As a result of X-ray diffraction, it was confirmed that the film had an amorphous structure.
[0025]
Example 3
A solution prepared by dissolving 6.4 g (0.025 mol) of barium diisopropoxide, 1.0 g (0.0023 mol) of lanthanum nitrate and 0.3 g (0.0035 mol) of potassium acetate in 50 ml of 2-propanol was used. At 80 ° C., 76.7 g (0.376 mol) of aluminum triisopropoxide were mixed with a solution of 250 ml of 2-propanol, and the subsequent treatment was carried out in the same manner as in Example 1 to obtain a powder (Al / ( Ba + La + K) = 12). This powder was fired at 800 ° C. in the air for 5 hours to obtain a fine powder having a specific surface area of 235 m ² / g. As a result of X-ray diffraction, it was confirmed that the film had an amorphous structure.
[0026]
Example 4
A solution prepared by dissolving 4.8 g (0.019 mol) of barium diisopropoxide and 2.0 g (0.012 mol) of calcium nitrate in 50 ml of 2-propanol was used at 80 ° C. for 76.7 g of aluminum triisopropoxide (80 g). (0.376 mol) in a solution of 250 ml of 2-propanol, and the subsequent treatment was carried out in the same manner as in Example 1 to obtain a powder (Al / (Ba + Ca) = 12). This powder was fired at 800 ° C. in the air for 5 hours to obtain a fine powder having a specific surface area of 218 m ² / g. As a result of X-ray diffraction, it was confirmed that the film had an amorphous structure.
[0027]
Example 5
A solution prepared by dissolving 4.3 g (0.031 mol) of metal barium in 50 ml of 2-propanol and a solution prepared by dissolving 76.7 g (0.376 mol) of aluminum triisopropoxide in 250 ml of 2-propanol at 80 ° C. (Al / Ba = 12). The mixed solution was refluxed and stirred at 80 ° C. for 2 hours, and thereafter, 12.2 g of 2,4-pentadione was added, and the mixture was further refluxed and stirred for 3 hours. Then, a mixed solution of 42.7 ml of ion-exchanged water and 182 ml of 2-propanol was added dropwise while maintaining the solution at 80 ° C. After the dropwise addition, the mixture was stirred for 5 hours while maintaining the temperature at 80 ° C., and then dried under reduced pressure to obtain a white powder. This powder was fired at 800 ° C. in the air for 5 hours to obtain a fine powder having a specific surface area of 236 m ² / g. As a result of X-ray diffraction, it was confirmed that the film had an amorphous structure.
[0028]
Example 6
A solution prepared by dissolving 6.4 g (0.025 mol) of barium diisopropoxide, 1.0 g (0.0023 mol) of lanthanum nitrate and 0.3 g (0.0035 mol) of potassium acetate in 50 ml of 2-propanol was used. At 80 ° C., 76.7 g (0.376 mol) of aluminum triisopropoxide were mixed with a solution of 250 ml of 2-propanol (same as in Example 3). Got. This powder was fired at 800 ° C. in the air for 5 hours to obtain a fine powder having a specific surface area of 241 m ² / g. As a result of X-ray diffraction, it was confirmed that the film had an amorphous structure.
[0029]
Example 7
A solution obtained by dissolving 11.2 g (0.044 mol) of barium diisopropoxide in 50 ml of 2-propanol was converted into 53.4 g (0.262 mol) of aluminum triisopropoxide in 250 ml of 2-propanol at 80 ° C. It was mixed with the dissolved solution (Al / Ba = 6). After refluxing and stirring this mixed solution at 80 ° C. for 2 hours, 9.2 g of 2,4-pentadione was added, and the solution was further refluxed and stirred for 3 hours. Then, a mixed solution of 31.4 ml of ion-exchanged water and 134 ml of 2-propanol was added dropwise while maintaining the solution at 80 ° C. After the dropwise addition, the mixture was stirred for 5 hours while maintaining the temperature at 80 ° C., and then dried under reduced pressure to obtain a white powder. This powder was fired in air at 800 ° C. for 5 hours to obtain a fine powder having a specific surface area of 153 m ² / g. As a result of X-ray diffraction, it was confirmed that the film had an amorphous structure.
[0030]
Example 8
A solution prepared by dissolving 3.7 g (0.0145 mol) of barium diisopropoxide in 50 ml of 2-propanol was converted into 71.1 g (0.349 mol) of aluminum triisopropoxide in 250 ml of 2-propanol at 80 ° C. It was mixed with the dissolved solution (Al / Ba = 24). After refluxing and stirring this mixed solution at 80 ° C. for 2 hours, 10.9 g of 2,4-pentadione was added, and the mixture was further refluxed and stirred for 3 hours. Next, a mixed solution of 38.7 ml of ion-exchanged water and 165 ml of 2-propanol was added dropwise while keeping the solution at 80 ° C. After the dropwise addition, the mixture was stirred for 5 hours while maintaining the temperature at 80 ° C., and then dried under reduced pressure to obtain a white powder. This powder was fired at 800 ° C. in the air for 5 hours to obtain a fine powder having a specific surface area of 228 m ² / g. As a result of X-ray diffraction, it was confirmed that the film had an amorphous structure.
[0031]
The fired powder obtained in Examples 1 to 8 was impregnated with 250 ml of an aqueous solution of dinitrodiamine Pt nitrate (Pt amount: 0.003 mol), and stirred at room temperature for 1 hour with a stirrer. This slurry was separated into a powder and a supernatant by a centrifuge, and the supernatant was discarded. The obtained powder was dried at 120 ° C. for 12 hours and heat-treated at 250 ° C. for 1 hour. According to elemental analysis, Pt was supported by 1.02% by weight based on the carrier powder.
[0032]
The thus-obtained Pt-supported powder was coated on a honeycomb carrier by the following method.
A slurry was prepared by adding 3 g of alumina sol, 50 g of a 40% aqueous solution of aluminum nitrate and 108 g of water to 100 g of the powder. A honeycomb carrier made of cordierite (1 liter outer volume) is immersed in the slurry, the slurry is coated on the honeycomb carrier by a method of blowing off excess slurry, dried at 120 ° C. for 3 hours, and then heated at 500 ° C. for 1 hour. And a catalyst sample was obtained.
[0033]
With respect to the honeycomb catalyst thus manufactured, the purification performance of a new catalyst and the purification performance after endurance at 800 ° C. for 24 hours of a model gas (lean) were evaluated under the following conditions.
[0034]
(1) Model gas composition ▲ 1 ▼ lean _{CO: 0.08%, C 3 H} 8: 800ppm, CO 2: 12.0%, O 2: 4.5%,
_{H 2 O: 3%, NO} : 1000ppm, SO 2: 50ppm, N 2: balance ▲ 2 ▼ stoichiometric _{CO: 1.05%, C 3 H} 8: 1000ppm, CO 2: 10.0%, O 2: variation H ₂ O: 10%, NO: 2000 ppm, SO ₂ : 50 ppm, N ₂ : balance (2) Space velocity: 200000 h ⁻¹
[0035]
(3) Purification rate measuring method A stainless steel tube in which a honeycomb is set is heated in a tubular furnace, and a model gas is flowed into the honeycomb while the inside of the honeycomb is maintained at 300 ° C. Then, the gas after passing through the honeycomb is analyzed. The purified amount is calculated from the average amount of gas components for 4 minutes in which 1 minute of lean-one minute of stoichiometry is repeated twice and the amount of model gas flowing for 4 minutes. Thus, CO at 300 ° C., HC, and measuring the average purification rate of NO _x. The results are shown in Table 2 below. Further, the amount of BaSO ₄ produced after the durability test was evaluated by the X-ray diffraction peak intensity. The results are also shown in Table 2.
[0036]
Comparative Example 1
Pt was carried on γ-alumina having a specific surface area of 150 m ² / g in the same manner as described above. This powder was impregnated in a barium acetate aqueous solution prepared to have a concentration of 25 wt% Ba, stirred for 1 hour, and then separated by a centrifuge. This powder was dried at 120 ° C. for 12 hours, and then heat-treated at 500 / ° C. for 1 hour. This powder was coated on a honeycomb in the same manner as described above, and a catalyst sample was obtained.
[0037]
Comparative Example 2
A solution prepared by dissolving 21.8 g (0.159 mol) of metal barium in 80 ml of 2-propanol and a solution prepared by dissolving 65.0 g (0.319 mol) of aluminum triisopropoxide in 250 ml of 2-propanol at 80 ° C. (Al / Ba = 2). After refluxing and stirring this mixed solution at 80 ° C. for 2 hours, 14.3 g of 2,4-pentanedione was added, and the mixture was further refluxed and stirred for 3 hours. To this solution, a mixed solution of 45.9 ml of ion-exchanged water and 195 ml of 2-propanol was added dropwise while maintaining the temperature at 80 ° C. After the dropwise addition, the mixture was stirred for 5 hours while maintaining the temperature at 80 ° C., and then dried under reduced pressure to obtain a white powder. This powder was fired at 800 ° C. in the air for 5 hours to obtain a fine powder. The specific surface area of this powder was 34 m ² / g. As a result of X-ray diffraction, it was found that BaO.Al ₂ O ₃ was generated.
[0038]
Comparative Example 3
In Example 7, 3.0 g (0.0118 mol) of barium isopropoxide, 62.3 g (0.305 mol) of aluminum isopropoxide, 9.5 g of 2,4-pentanedione, and 33 of ion-exchanged water were used. 2.9 ml and 145 ml of 2-propanol were used, except that powder was obtained in the same way (Al / Ba = 26). This powder was fired at 800 ° C. in the air for 5 hours to obtain a fine powder. The specific surface area of this powder was 215 m ² / g. As a result of X-ray diffraction, it was amorphous.
[0039]
The fired powders obtained in Comparative Examples 2 and 3 were loaded with Pt in the same manner as in the above Examples, coated on honeycombs, and catalyst samples were obtained. Table 2 shows the results obtained in Comparative Examples 1 to 3.
[0040]
[Table 2]

[0041]
From these results, the catalyst produced by using the catalyst carrier of the present invention has high initial purification ability, high purification ability after durability, and excellent high-temperature heat resistance. In addition, the amount of sulfate produced after durability is low, and it has excellent decomposition and regeneration properties.
[0042]
Example 9
A fired powder was obtained in the same manner as in Example 5, except that 5.3 g of ethyl acetoacetate was used instead of 12.2 g of 2,4-pentanedione.
[0043]
Example 10
A baked powder was obtained in the same manner as in Example 9, except that the amount of ethyl acetoacetate added was 15.9 g.
[0044]
Example 11
A baked powder was obtained in the same manner as in Example 9, except that the amount of ethyl acetoacetate added was 31.8 g.
[0045]
Example 12
A baked powder was obtained in the same manner as in Example 9, except that 6.1 g of triethanolamine was used instead of ethyl acetoacetate.
[0046]
Example 13
A baked powder was obtained in the same manner as in Example 12, except that the addition amount of triethanolamine was changed to 18.2 g.
[0047]
Example 14
A baked powder was obtained in the same manner as in Example 12, except that the addition amount of triethanolamine was 36.4 g.
[0048]
The specific surface areas of the calcined powders obtained in Examples 9 to 14 were measured, and the results are shown in Table 3 below. As a result of X-ray diffraction, none of these powders showed any crystalline peak, and it was confirmed that these powders had an amorphous structure.
[0049]
[Table 3]

[0050]
Example 15
A solution prepared by dissolving 12.9 g (0.094 mol) of metal barium in 70 ml of 2-propanol and a solution prepared by dissolving 76.7 g (0.376 mol) of aluminum triisopropoxide in 250 ml of 2-propanol at 80 ° C. (Al / Ba = 4). This mixed solution was stirred under reflux at 80 ° C. for 2 hours, and then 76.7 g of 2,4-pentadione was added, and further stirred under reflux for 3 hours. Then, a mixed solution of 42.7 ml of ion-exchanged water and 202 ml of 2-propanol was added dropwise while maintaining the solution at 80 ° C. After the dropwise addition, the mixture was stirred for 5 hours while maintaining the temperature at 80 ° C., and then dried under reduced pressure to obtain a white powder. This powder was fired at 800 ° C. in the air for 5 hours to obtain a fine powder having a specific surface area of 72 m ² / g. As a result of X-ray diffraction, it was confirmed that the film had an amorphous structure.
[0051]
Example 16 (Effect of water addition amount)
In Example 2, the amount of water was changed, and the specific surface area of the obtained powder and the generated phase during crystallization after the durability of the catalyst prepared in the same manner were examined. The results are shown in Table 4 below.
[0052]
[Table 4]

The amount of water added is preferably 0.3 to 0.8 times the alkyl group in the raw material.
[0053]
Example 17 (Effect of Ba amount)
In Example 2, varying the amount of Ba, Similarly catalyzed lean 4 minutes - were measured average purification rate of the NO _x at 300 ° C. By repeating the stoichiometric 1 minute. The result is shown in FIG. As it is apparent from this figure, in particular advantage is observed in the rich region Ba amount in conditions absorption capacity of the NO _x is a number required.
[0054]
Example 18
204 g (1 mol) of aluminum triisopropoxy, 17.0 g (0.067 mol) of diisopropoxybarium and 1.13 g (0.017 mol) of sodium ethoxy were stirred at 80 ° C. for 5 hours in 2-propanol (Ba + Na). / Al = 12). 200 ml of 2-propanol solution containing 57.6 ml of ion-exchanged water was added dropwise at 1 ml / min to effect hydrolysis. Then, the mixture was heated for 5 hours and dried under reduced pressure. The powder thus obtained was calcined at 1000 ° C. for 5 hours. This calcined powder had a specific surface area of 260 m ² / g, which was higher than the powders obtained in Examples 1 to 4.
[0055]
Example 19
204 g (1 mol) of aluminum triisopropoxy, 10.3 g (0.07 mol) of rubidium nitrate and 6.17 g (0.03 mol) of diisopropoxystrontium were stirred in 2-propanol at 80 ° C. for 5 hours (Rb + Sr). / Al = 10). 200 ml of 2-propanol solution containing 57.6 ml of ion-exchanged water was added dropwise at 1 ml / min to effect hydrolysis. Then, the mixture was heated for 5 hours and dried under reduced pressure. The powder thus obtained was calcined at 1000 ° C. for 5 hours. This calcined powder had a specific surface area of 230 m ² / g.
[0056]
The powders obtained in Examples 18 and 19 were catalyzed as a carrier, and the purification rate of exhaust gas was measured. That is, a slurry was prepared by adding aluminum nitrate and water to these powders. A honeycomb carrier made of cordierite was immersed in the slurry, the slurry was coated by a method of blowing off excess slurry, dried at 120 ° C. for 3 hours, and then fired at 500 ° C. for 1 hour in an electric furnace. Then, it was impregnated with a nitrate solution of dinitroamine Pt for 30 minutes, loaded with 1 g of Pt per 100 g of powder, dried at 120 ° C. for 3 hours, and then heat-treated in an electric furnace at 250 ° C. for 1 hour. Further, the resultant was impregnated with an aqueous Rh nitrate solution for 30 minutes to carry 1 g of Rh per 100 g of the powder, dried at 120 ° C. for 3 hours, and then heat-treated in an electric furnace at 250 ° C. for 1 hour to obtain a monolithic honeycomb catalyst.
[0057]
The purification performance of the new catalyst was measured for the honeycomb catalyst thus manufactured under the following conditions as described above.
(1) Evaluation gas composition (A / F (air-fuel ratio) = 18)
_{CO: 0.1%, C 3 H} 8: 600ppm, H 2: 0.05%, CO 2: 11.5%,
O ₂ : 3.5%, H ₂ O: 10%, NO: 2500 ppm, N ₂ : balance (2) Space velocity: 200000h ⁻¹
Table 5 shows the results.
[0058]
[Table 5]

[0059]
Further, after subjecting this catalyst to endurance treatment at 900 ° C. for 10 hours in stoichiometric (A / F = 14.5) exhaust gas, the purification rate of A / F = 18 was measured. The results are shown in Table 6 below.
[0060]
[Table 6]

[0061]
【The invention's effect】
The catalyst carrier of the present invention has an amorphous structure of a precursor having a layered aluminate structure by setting the ratio of Al / Me = 4 to 24, has a large specific surface area, and a reduction in active species due to the degree of freedom of the structure. And thus provide sufficient catalytic function. Since the precursor having a layered aluminate structure has a higher crystallization temperature than other precursors such as alumina, it is possible to maintain sufficient high-temperature heat resistance. Further, during the production of the catalyst carrier of the present invention, by controlling the hydrolysis rate, a carrier containing the NO _x storage element in a highly dispersed state is obtained, and the grain growth of sulfate during sulfur poisoning is less likely to occur. Good decomposition and reproducibility. Furthermore, a carrier having a higher specific surface area can be obtained by using two or more elements having a specific difference in ionic radius as the NO _x storage element. By supporting the Pt or the like on the carrier, the absorption of NO _x decomposition catalyst having excellent high-temperature heat resistance.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the amount of Ba in a catalyst carrier of the present invention and the NO _x purification ability of a catalyst produced from the carrier.

Claims (2)

The following formula (I)
_{Me x Al y O 2 (I} )
(In the above formula, Me is at least one element selected from the group consisting of alkali metals, alkaline earth metals, and rare earth elements, y / x = 4 to 24, and z is determined by Me, x, and y. Value)
Is a precursor of a layered aluminate structure represented by, and a noble metal is supported on a catalyst carrier made of an amorphous composition that has been heat-treated at a temperature that does not crystallize, and the combustion gas is alternately controlled in a lean-stoichiometric manner. By doing so, an exhaust gas purifying catalyst used to reduce NO _x in sulfur-containing exhaust gas by storing it in Me in the catalyst carrier. Me is composed of two or more types of elements, each of which has a hexacoordinate ionic radius of 0.95 ° or more, and a difference in ionic radius between the elements is an element having the largest ionic radius and an 2. The exhaust gas purifying catalyst according to claim 1, wherein the angle is 0.3 [deg.] Or more with another element having a small radius.

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