JP4465799B2 - Exhaust gas purification device, exhaust gas purification method, and exhaust gas purification catalyst - Google Patents

Description

【０１２４】
【表２】

【０１２５】
フレッシュ時のＮＯｘ浄化率、ＳＯ_２処理後のＮＯｘ浄化率、並びにＳＯ_２処理後に再生処理を行なった後のＮＯｘ浄化率の測定結果（但し、触媒入口ガス温度はいずれも３５０℃である。）は図１４に示されている。同図によれば、フレッシュ時のＮＯｘ浄化率については各触媒間で大差はない。しかし、ＳＯ_２処理後のＮＯｘ浄化率は、ＮＯｘ吸収材がＢａ単独の例１，２よりも、Ｂａに他の元素（Ｋ、Ｓｒ、Ｍｇ及びＬａのうちの少なくとも一種）を併用した例３〜１１の方が高くなる傾向を示し、特にＫを含有するものではその傾向が顕著である。一方、再生処理後のＮＯｘ浄化率についても、Ｋを含有するものは例５を除いて高くなる傾向を示し、Ｋの他にＭｇやＬａを併用したものではその傾向が顕著である。
【０１２６】
触媒入口ガス温度を３５０℃にした場合のフレッシュ時及び熱処理（熱劣化処理）後のＮＯｘ浄化率は図１５に示されている。同図によれば、例３〜６の触媒（上記耐Ｓ被毒性（上記再生処理後のＮＯｘ浄化特性）についてはそれほど効果が認められなかったもの）の熱処理後のＮＯｘ浄化率が高くなる傾向を示し、特に例５においてその傾向が顕著である。この傾向は、図１６に示す触媒入口ガス温度を４５０℃にした場合のフレッシュ時及び熱処理（熱劣化処理）後のＮＯｘ浄化をみても同様である。このように、例３〜６は、耐Ｓ被毒性については顕著な効果が認められないものの、耐熱性については優れた効果を示しており、再生処理が比較的高温で行なわれることを考慮すれば、再生処理によってＮＯｘ吸収性能を維持するうえで有利になる、ということができる。
【０１２７】
また、図１６によれば、例５，８，９の各触媒は、Ｂａの他にＫを含有し、さらにＳｒ、Ｍｇ及びＬａのいずれか一を含有するものであるが、フレッシュ時の４５０℃でのＮＯｘ浄化率がかなり高くなっている。これは、高速走行のように排気ガス温度が高くなる場合でも、ＮＯｘの排出をそれほど増やすことなく、空燃比リーンで走行することができることを意味する。
【０１２８】
＜Ｂａ−Ｋ−Ｓｒ系ＮＯｘ吸収材について＞
上記混合溶液として、ジニトロジアミン白金硝酸塩、酢酸ロジウム、酢酸バリウム、酢酸カリウム及び酢酸ストロンチウムの各水溶液を、Ｐｔ担持量が３．０ｇ／Ｌ、Ｒｈ担持量が０．１ｇ／Ｌ、Ｂａ担持量が３０ｇ／Ｌ、Ｋ担持量が６ｇ／Ｌとなり、Ｓｒ担持量が０ｇ／Ｌ、５ｇ／Ｌ、１０ｇ／Ｌ、１５ｇ／Ｌ、２０ｇ／Ｌ及び３０ｇ／Ｌの各量となるように秤量し混合してなる各溶液を用いる他は例１と同じ条件・方法によって各触媒を調製した。
【０１２９】
本例の場合、各触媒には、Ｐｔは外側コート層のＰｔ−Ｒｈ／ＭＦＩ触媒粉によって０．５ｇ／Ｌ担持され、上記混合溶液によって３．０ｇ／Ｌ担持されているから、Ｐｔ総担持量は３．５ｇ／Ｌとなり、ＲｈについてもＰｔ−Ｒｈ／ＭＦＩ触媒粉によって０．００６ｇ／Ｌ担持され、上記混合溶液によって０．１ｇ／Ｌ担持されているから、Ｒｈ総担持量は０．１０６ｇ／Ｌとなる。
【０１３０】
また、比較のために、上記混合溶液として、ジニトロジアミン白金硝酸塩、酢酸ロジウム及び酢酸バリウムの各水溶液を、Ｐｔ担持量が３．０ｇ／Ｌ、Ｒｈ担持量が０．１ｇ／Ｌ、Ｂａ担持量が３０ｇ／Ｌとなるように秤量し混合してなるもの（Ｋ担持量零，Ｓｒ担持量零）を用いる他は例１と同じ条件・方法によって比較触媒を調製した。この比較触媒もＰｔ総担持量は３．５ｇ／Ｌとなり、Ｒｈ総担持量は０．１０６ｇ／Ｌとなる。
【０１３１】
上記Ｓｒ担持量が異なる各触媒及び比較触媒について、先に説明した評価テストによりフレッシュ時、ＳＯ_２ 処理後及び再生後の各ＮＯｘ浄化率を測定した。Ｓｒ担持量が異なる各触媒の結果を図１７に示す。同図によれば、Ｓｒを担持させると、Ｓｒ担持量が零の場合よりも再生後のＮＯｘ浄化率が高くなること、但し、Ｓｒ担持量が２０ｇ／Ｌ以上になると、かえって再生後のＮＯｘ浄化率が低くなること、Ｓｒ担持量としては、５ｇ／Ｌ以上２０ｇ／Ｌ未満が良いこと、あるいは１０ｇ／Ｌ以上２０ｇ／Ｌ未満が良いこと、１５ｇ／Ｌが最も良いこと、従って、１３ｇ／Ｌ〜１７ｇ／Ｌであれば、再生後のＮＯｘ浄化率を高い値に維持する上で有利になることがわかる。
【０１３２】
また、比較触媒ではフレッシュ時のＮＯｘ浄化率が７２％、ＳＯ_２ 処理後のＮＯｘ浄化率が４１％、再生後のＮＯｘ浄化率が６３％であった。従って、Ｂａの他にＫ及びＳｒを担持させた場合、Ｓｒ担持量２０ｇ／Ｌまではフレッシュ時、ＳＯ_２ 処理後及び再生後の各ＮＯｘ浄化率がいずれもＢａのみの比較触媒よりも高くなることがわかる。
【０１３３】
図１８は上記Ｓｒ担持量が異なる各触媒及び比較触媒について、先に説明した熱劣化処理を施した後のＮＯｘ浄化率を測定した結果を示す。同図の１点鎖線のラインは比較触媒のＮＯｘ浄化率を示す。但し、空間速度は２５０００ｈ^−１とした。同図によれば、Ｓｒ担持量が３０ｇ／Ｌ以上になると、触媒の耐熱性が比較触媒よりも低くなっているが、それよりも少ない担持量であれば、触媒の耐熱性が向上し、上述の再生に有利であることがわかる。
【０１３４】
＜Ｂａ−Ｋ−Ｍｇ系ＮＯｘ吸収材について＞
上記混合溶液として、ジニトロジアミン白金硝酸塩、酢酸ロジウム、酢酸バリウム、酢酸カリウム及び酢酸マグネシウムの各水溶液を、Ｐｔ担持量が３．０ｇ／Ｌ、Ｒｈ担持量が０．１ｇ／Ｌ、Ｂａ担持量が３０ｇ／Ｌ、Ｋ担持量が６ｇ／Ｌとなり、Ｍｇ担持量が０ｇ／Ｌ、５ｇ／Ｌ、１０ｇ／Ｌ、１５ｇ／Ｌ及び２０ｇ／Ｌの各量となるように秤量し混合してなる各溶液を用いる他は例１と同じ条件・方法によって各触媒を調製した。本例の場合もＰｔ総担持量は３．５ｇ／Ｌとなり、Ｒｈ総担持量は０．１０６ｇ／Ｌとなる。
【０１３５】
上記Ｍｇ担持量が異なる各触媒について、先に説明した評価テストによりフレッシュ時、ＳＯ_２ 処理後及び再生後の各ＮＯｘ浄化率を測定した。その結果を図１９に示す。同図によれば、Ｍｇを担持させると、Ｍｇ担持量が零の場合よりも再生後のＮＯｘ浄化率が高くなること、Ｍｇ担持量が１０ｇ／Ｌのときに再生後のＮＯｘ浄化率が最も高くなること、Ｍｇ担持量が３ｇ／Ｌ〜１７ｇ／Ｌ、あるいは５ｇ／Ｌ〜１５ｇ／Ｌであれば、再生後のＮＯｘ浄化率を高い値に維持する上で有利になることがわかる。
【０１３６】
また、比較触媒（Ｂａ−Ｋ−Ｓｒ系ＮＯｘ吸収材の項で説明した比較触媒）ではフレッシュ時のＮＯｘ浄化率が７２％、ＳＯ_２ 処理後のＮＯｘ浄化率が４１％、再生後のＮＯｘ浄化率が６３％であるから、Ｂａの他にＫ及びＭｇを担持させた場合、フレッシュ時、ＳＯ_２ 処理後及び再生後の各ＮＯｘ浄化率がいずれもＢａのみの比較触媒よりも高くなることがわかる。
【０１３７】
図２０は上記Ｍｇ担持量が異なる各触媒及び比較触媒について、先に説明した熱劣化処理を施した後のＮＯｘ浄化率を測定した結果を示す。同図の１点鎖線のラインは比較触媒のＮＯｘ浄化率を示す。但し、空間速度は２５０００ｈ^−１とした。同図によれば、Ｍｇ担持量が２０ｇ／Ｌまでは触媒の耐熱性が向上し、上述の再生に有利であることがわかる。
【０１３８】
＜Ｂａ−Ｋ−Ｓｒ−Ｍｇ系ＮＯｘ吸収材について＞
上記混合溶液として、ジニトロジアミン白金硝酸塩、酢酸ロジウム、酢酸バリウム、酢酸カリウム、酢酸ストロンチウム及び酢酸マグネシウムの各水溶液を、Ｐｔ担持量が３．０ｇ／Ｌ、Ｒｈ担持量が０．１ｇ／Ｌ、Ｂａ担持量が３０ｇ／Ｌ、Ｋ担持量が６ｇ／Ｌ、Ｍｇ担持量が５ｇ／Ｌであり、Ｓｒ担持量が異なる各溶液を用いる他は例１と同じ条件・方法によって各触媒を調製した。また、Ｍｇ担持量を１０ｇ／Ｌとして同様にＳｒ担持量が異なる各触媒を調製し、さらにＭｇ担持量を１５ｇ／Ｌとして同様にＳｒ担持量が異なる各触媒を調製した。これらの各触媒の場合もＰｔ総担持量は３．５ｇ／Ｌとなり、Ｒｈ総担持量は０．１０６ｇ／Ｌとなる。
【０１３９】
上記Ｍｇ担持量及びＳｒ担持量が異なる各触媒について、先に説明した評価テストによりフレッシュ時、ＳＯ_２ 処理後及び再生後の各ＮＯｘ浄化率を測定した。Ｍｇ担持量５ｇ／Ｌのときの結果を図２１に、Ｍｇ担持量１０ｇ／Ｌのときの結果を図２２に、Ｍｇ担持量１５ｇ／Ｌのときの結果を図２３に示す。
【０１４０】
図２１によれば、Ｍｇ担持量５ｇ／Ｌのときは、Ｓｒ担持量が１５ｇ／Ｌのときに回復後のＮＯｘ浄化率が最も高くなり、且つＳＯ_２ 被毒からのＮＯｘ浄化率の回復率も高い。図２２によれば、Ｍｇ担持量１０ｇ／Ｌのときは、Ｓｒ担持量１０ｇ／Ｌのときに回復後のＮＯｘ浄化率が最も高くなり、且つＳＯ_２ 被毒からのＮＯｘ浄化率の回復率も高い。また、Ｓｒ担持量が５ｇ／ＬのときもＳＯ_２ 被毒からのＮＯｘ浄化率の回復率が高い。図２３によれば、Ｍｇ担持量１５ｇ／Ｌのときは、Ｓｒ担持量が５ｇ／Ｌ〜１５ｇ／ＬのいずれでもＳＯ_２ 被毒からのＮＯｘ浄化率の回復率が高い。
【０１４１】
以上から、Ｂａ及びＫの他にＳｒとＭｇとを併用すると、Ｓｒ担持量が少ない場合でもＳＯ_２ 被毒からのＮＯｘ浄化率の回復率が高くなることがわかる。
【０１４２】
また、比較触媒（Ｂａ−Ｋ−Ｓｒ系ＮＯｘ吸収材の項で説明した比較触媒）ではフレッシュ時のＮＯｘ浄化率が７２％、ＳＯ_２ 処理後のＮＯｘ浄化率が４１％、再生後のＮＯｘ浄化率が６３％であるから、Ｂａの他にＫ、Ｓｒ及びＭｇを担持させた場合、フレッシュ時、ＳＯ_２ 処理後及び再生後の各ＮＯｘ浄化率がいずれもＢａのみの比較触媒よりも高くなることがわかる。
【０１４３】
図２４は上記Ｍｇ担持量及びＳｒ担持量が異なる各触媒及び比較触媒について、先に説明した熱劣化処理を施した後のＮＯｘ浄化率を測定した結果を示す。同図の１点鎖線のラインは比較触媒のＮＯｘ浄化率を示す。但し、空間速度は２５０００ｈ^−１とした。同図によれば、Ｂａ及びＫの他にＳｒとＭｇとを併用した場合も触媒の耐熱性が向上し、上述の再生に有利であることがわかる。但し、Ｓｒ担持量又はＭｇ担持量が過剰になると、耐熱性の向上には不利になるということができる。
【０１４４】
−その他−
上記実施形態では硫黄脱離手段を空燃比制御と分割噴射制御とによって構成したが、触媒を加熱するヒータを設け、硫黄過吸収状態が判定されたときに、空燃比をλ＝１近傍に変更するとともに、そのヒータを作動させて触媒を加熱するようにしてもよい。
【０１４５】
また、上記実施形態のように触媒を内側触媒層と外側触媒層との二層構造とする場合、内側触媒層には上記ＣｅＯ_２−ＺｒＯ_２複合酸化物に代えて微粉ＣｅＯ_２を用いるようにしてもよい。その場合、微粉ＣｅＯ_２の粒径は１００ｎｍ以下であることが好ましい。
【０１４６】
また、本発明は自動車エンジンの排気ガスに限らず、定置式の産業用エンジンに適用することができ、その場合も上記実施形態のように構成することにより、所期の効果を得ることができる。この場合、産業用エンジンとは、例えば排ガスの熱を熱交換してビル等の空調に利用するものである。このとき、熱交換器を触媒よりも上流側に配置するときには、上記実施形態のように触媒温度を上昇させる際、熱交換水量を少なくするなどして熱交換効率を低減させることで、昇温が阻害されることを防止することができる。
【図面の簡単な説明】
【図１】 本発明の構成を示す説明図。
【図２】 本発明の実施形態に係る排気浄化装置の概略構成図。
【図３】 空燃比の変化に対するＯ_２センサの出力特性を示す図。
【図４】 触媒の概略構成を示す断面図。
【図５】 エンジンの成層燃焼モード、λ＝１分割モード及びエンリチモードの各運転領域を設定したマップの一例を示す図。
【図６】 エンジンの各運転領域における燃料噴射時期を示すタイムチャート図。
【図７】 エンジン回転数及びアクセル開度に対応するエンジンの目標トルクを設定したマップ（ａ）と、エンジン回転数及び目標トルクに対応するスロットル弁の開度を設定したマップ（ｂ）とをそれぞれ例示する説明図。
【図８】 基本的な燃料噴射量及び燃料噴射時期の設定手順を示すフローチャート図。
【図９】 ＮＯｘ放出制御の処理手順を示すフローチャート図。
【図１０】 ＳＯｘ脱離制御の処理手順を示すフローチャート図。
【図１１】 吸気行程噴射及び圧縮行程噴射の実行手順を示すフローチャート図。
【図１２】 ＥＧＲ制御の処理手順を示すフローチャート図。
【図１３】 エンジン運転中にＮＯｘ放出制御やＳＯｘ脱離制御が行なわれるときの空燃比の変化を示すタイムチャート図。
【図１４】 触媒の各具体例について、そのフレッシュ時、Ｓ被毒後及び再生後のＮＯｘ浄化率を示すグラフ図。
【図１５】 触媒の各具体例について、触媒入口ガス温度を３５０℃としたときのフレッシュ時と熱劣化処理後のＮＯｘ浄化率を示すグラフ図。
【図１６】 触媒の各具体例について、触媒入口ガス温度を４５０℃としたときのフレッシュ時と熱劣化処理後のＮＯｘ浄化率を示すグラフ図。
【図１７】 Ｂａ−Ｋ−Ｓｒ系ＮＯｘ吸収材を有する触媒に関し、そのフレッシュ時、Ｓ被毒後及び再生後の各ＮＯｘ浄化率にＳｒ担持量が与える影響を示すグラフ図。
【図１８】 Ｂａ−Ｋ−Ｓｒ系ＮＯｘ吸収材を有する触媒に関し、その耐熱性にＳｒ担持量が与える影響を示すグラフ図。
【図１９】 Ｂａ−Ｋ−Ｍｇ系ＮＯｘ吸収材を有する触媒に関し、そのフレッシュ時、Ｓ被毒後及び再生後の各ＮＯｘ浄化率にＭｇ担持量が与える影響を示すグラフ図。
【図２０】 Ｂａ−Ｋ−Ｍｇ系ＮＯｘ吸収材を有する触媒に関し、その耐熱性にＭｇ担持量が与える影響を示すグラフ図。
【図２１】 Ｂａ−Ｋ−Ｓｒ−Ｍｇ系ＮＯｘ吸収材を有する触媒に関し、Ｍｇ担持量５ｇ／Ｌのときの、フレッシュ時、Ｓ被毒後及び再生後の各ＮＯｘ浄化率にＳｒ担持量が与える影響を示すグラフ図。
【図２２】 Ｂａ−Ｋ−Ｓｒ−Ｍｇ系ＮＯｘ吸収材を有する触媒に関し、Ｍｇ担持量１０ｇ／Ｌのときの、フレッシュ時、Ｓ被毒後及び再生後の各ＮＯｘ浄化率にＳｒ担持量が与える影響を示すグラフ図。
【図２３】 Ｂａ−Ｋ−Ｓｒ−Ｍｇ系ＮＯｘ吸収材を有する触媒に関し、Ｍｇ担持量１ｇ／Ｌのときの、フレッシュ時、Ｓ被毒後及び再生後の各ＮＯｘ浄化率にＳｒ担持量が与える影響を示すグラフ図。
【図２４】 Ｂａ−Ｋ−Ｓｒ−Ｍｇ系ＮＯｘ吸収材を有する触媒の耐熱性に、Ｍｇ担持量及びＳｒ担持量が与える影響を示すグラフ図。
【符号の説明】
Ａ エンジンの排気浄化装置
１ エンジン
２ 気筒
４ 燃焼室
７ インジェクタ（燃料噴射弁）
２４ Ｏ_２センサ（酸素濃度検出手段）
２５ 触媒（ＮＯｘ吸収材）
２６ ＥＧＲ通路（排気還流手段）
２７ ＥＧＲ弁（排気還流手段）
４０ コントロールユニット（ＥＣＵ）
４０ａ 硫黄過吸収判定手段
４０ｂ 硫黄脱離手段[0001]
BACKGROUND OF THE INVENTION
  According to the present invention, an NOx absorbent that absorbs NOx (nitrogen oxide) in an oxygen-excess atmosphere is provided in an exhaust passage of an engine or the like so that NOx in the exhaust can be removed even when the air-fuel ratio is lean. The present invention relates to a gas purification device and an exhaust gas purification method, and particularly to a technical field of catalyst regeneration that restores the performance of the NOx absorbent when the performance of the NOx absorbent is lowered.
[0002]
[Prior art]
  A NOx absorbent that absorbs NOx in the exhaust gas when the air-fuel ratio of the air-fuel mixture is lean and the oxygen concentration in the exhaust gas is high and releases the NOx when the oxygen concentration decreases is provided in the exhaust passage of the engine. A device that reduces and purifies released NOx is generally known.
[0003]
  However, if the fuel or engine oil contains a small amount of sulfur component (S), when this sulfur component is burned and discharged, the NOx absorbent is more SOx (sulfur oxide) than NOx in the exhaust gas. ), And once absorbed, the SOx is hardly released even if the oxygen concentration in the exhaust gas decreases, so the amount of SOx absorbed increases over time, and the NOx absorption performance gradually decreases. To do.
[0004]
  Regarding this problem of S poisoning, Japanese Patent Application Laid-Open No. 6-142458 discloses that when Ba as an NOx absorbent is combined with at least one of alkali metals, Fe, Ni, Co, and Mg, the S resistance of Ba. It has been suggested to be advantageous for improving toxicity.
[0005]
  Japanese Patent Laid-Open No. 10-118494 also relates to a NOx purification catalyst that purifies NOx even in an oxygen-rich atmosphere. In addition to supporting Pt and Rh as catalyst metals on an alumina carrier, in addition to K having high NOx affinity, It is described that Ce, Sr, Mg, etc. are supported and high NOx purification performance is obtained even in the presence of SOx.
[0006]
  Japanese Patent Laid-Open No. 10-274031 discloses that in a direct injection engine, by injecting fuel during its expansion stroke, the exhaust gas temperature is raised to desorb SOx absorbed in the NOx absorbent. It is described.
[0007]
[Problems to be solved by the invention]
  The object of the present invention is to desorb the sulfur component and restore its performance when the NOx absorbent absorbs the sulfur component in the exhaust gas and the NOx absorption performance is reduced, and particularly the NOx absorbent. Is to make the sulfur component easy to desorb and regenerate when given sulfur desorbing means is applied.
[0008]
[Means for Solving the Problems]
  The invention of this application is shown in FIG.1'sA NOx absorbent 25 that is disposed in the exhaust passage 22 and that absorbs NOx and sulfur components in the exhaust gas in an oxygen-excess atmosphere with a high oxygen concentration in the exhaust gas, while releasing the absorbed NOx as the oxygen concentration decreases; ,
  Sulfur excess absorption determining means a for determining the excessive absorption state of the sulfur component into the NOx absorbent 25, and
  When the excessive sulfur absorption state is determined by the excessive sulfur absorption determination means a, the sulfur component is removed from the NOx absorbent 25 by increasing the temperature of the NOx absorbent 25 and decreasing the oxygen concentration. A sulfur desorption means b to be released,
The sulfur desorbing means b is a fuel injection control means for operating a fuel injection valve so as to divide and inject fuel into the engine combustion chamber at least twice from the beginning of the intake stroke to the end of the compression stroke. With
  As an element constituting the NOx absorbent 25, SrBa and at least one of Mg and LaK andEquipped withThe NOx absorbent 25 is supported on ceria-zirconia composite oxide or ceria and alumina.It is characterized by that.
[0009]
  With this configuration, when the sulfur desorption means b is activated after the sulfur component is excessively absorbed by the NOx absorbent 25, the NOx absorption performance is easily recovered to a level close to that before the sulfur component is absorbed. That is, the NOx absorbent 25 has a higher NOx absorption performance after recovery (recovery from S poisoning; the same applies hereinafter) as compared to the case where the NOx absorbent is constituted by Ba alone, or high heat. The decrease in NOx absorption performance when exposed to water is reduced, that is, the heat resistance is increased. This improvement in heat resistance favors the recovery of the NOx absorbent 25. The relationship between this heat resistance improvement and the recovery of the NOx absorbent 25 is as follows.
[0010]
  That is, the sulfur desorption means b not only lowers the oxygen concentration in the exhaust gas, but also desorbs sulfur components from the NOx absorbent 25 by increasing the temperature of the NOx absorbent 25. Therefore, if the heat resistance of the NOx absorbent is low, it is difficult to increase the temperature of the NOx absorbent 25 due to the desorption of sulfur components, and the original purpose cannot be achieved. On the other hand, if the heat resistance of the NOx absorbent 25 is increased as in the present invention, the NOx absorption performance can be recovered by effectively utilizing the sulfur desorption means b. That is, it is possible to avoid the deterioration of the NOx absorbent 25 due to heat during the sulfur desorption process.
[0011]
  Thus, according to the present invention, the reason why the NOx absorption performance after recovery is higher than that in the case where the NOx absorbent is constituted by Ba alone or the heat resistance is increased is not clear, but is considered as follows.
[0012]
  That is, other elements other than Ba (K, Sr, Mg, or La) are more susceptible to S poisoning than Ba, so that the Ba is less susceptible to S poisoning and NOx after S poisoning. First, it is conceivable that the decrease in absorption performance is small. This is the case when Ba has higher NOx absorption performance than the other elements.
[0013]
  In addition, the other elements (K, Sr, Mg, or La) are more likely to recover from S poisoning than Ba, and therefore it is considered that the NOx absorption performance after recovery is higher. That is, sulfates in which SOx is combined with Ba are stable, but sulfates of the other elements described above are more unstable than Ba sulfates, and SOx is desorbed at high temperatures in a low oxygen concentration atmosphere. It is considered easy. Alternatively, Ba and the other elements (K, Sr, Mg, or La) can form a composite oxide, but when sulfur poisoning, Ba and the other elementselementIt is considered that these form complex sulfates and are not so stable that they are easily recovered by desorbing SOx.
[0014]
  Furthermore, even if the element constituting the NOx absorbent 25 is Ba alone, and the amount thereof is increased, the NOx absorption performance before S poisoning and the NOx absorption performance after recovery are not improved so much, but this is the amount of Ba amount. This is considered to be because the specific surface area does not increase even if the particle diameter increases beyond the range only by increasing the particle diameter. On the other hand, when Ba and other elements (at least one of K, Sr, Mg, and La) are combined, each exists separately due to the difference in properties of these elements, and the specific surface area or reaction site It is considered that the sintering due to heat hardly occurs. Furthermore, it is considered that sulfur is easily desorbed by the interaction between different elements constituting the NOx absorbent.
[0015]
  Further, as an element constituting the NOx absorbent 25, K is included as an essential element in addition to Ba. As a result, the NOx absorption performance before S poisoning is enhanced, the decrease in the NOx absorption performance when subjected to S poisoning is reduced, and the NOx absorption performance after recovery is also enhanced. The weight ratio of Ba and K is preferably, for example, Ba: K = 30: (1-30).
[0016]
  When Ba and other elements are supported on a honeycomb-shaped carrier, the amount of Ba supported per liter of the carrier is preferably about 10 to 50 g, more preferably 20 to 40 g. For the other elements, the amount supported is Ba. It is preferable that the amount is equal to or less than the loading amount.
[0017]
  The oxygen-excess exhaust gas having a high oxygen concentration is, for example, an exhaust gas (oxygen concentration of 4 to 20) when the engine is operated with a lean air-fuel ratio of A / F> 16 (particularly A / F = 18 to 50). %) Is equivalent to this.
[0018]
the aboveAs the elements constituting the NOx absorbent 25, the above Ba, K and Mg are adopted and these are used.Using the above ceria-zirconia composite oxide or ceria and alumina as a support materialWhen supported on a carrier having a honeycomb shape or the like, the amount of Ba supported per liter of carrier is 10 to 50 g, the amount of K supported is 1 g or more (the upper limit is 15 g, for example), and the amount of Mg supported is 3 to 3 g. 17 g is preferable. Moreover, it is more preferable that the amount of Mg supported is 5 to 15 g, more preferably 8 to 12 g. Thereby, heat resistance is obtained and recovery from S poisoning is also improved. The weight ratio of Ba, K, and Mg is preferably, for example, Ba: K: Mg = 30: (1-30) :( 1-30).
[0019]
  As the elements constituting the NOx absorbent 25, the above Ba, K and Sr are adopted and these are used.Using the above ceria-zirconia composite oxide or ceria and alumina as a support materialWhen supported on a carrier having a honeycomb shape or the like, it is preferable that the supported amount of Ba and the amount of supported K per 1 L of the carrier is 10 to 20 g in the same manner as the Ba—K—Mg system. The Sr loading is more preferably 13 to 17 g. Thereby, heat resistance is obtained and recovery from S poisoning is also improved. The weight ratio of Ba, K, and Sr is preferably, for example, Ba: K: Sr = 30: (1-30) :( 1-30).
[0020]
  As an element constituting the NOx absorbent 25, BaAnd KIn addition to Sr, it is preferable to contain Sr. This increases the heat resistance of the NOx absorbent 25, which is advantageous in avoiding thermal degradation during the sulfur desorption process.
[0021]
  As an element constituting the NOx absorbent 25, the Ba, KIn addition to Sr, it is preferable to contain at least one of Mg and La. Thereby, the heat resistance of the NOx absorbent 25 is increased, which is further advantageous in avoiding thermal degradation during the sulfur desorption process.
[0022]
  As an element constituting the NOx absorbent 25, BaAnd KIn addition to Mg, it is preferable to contain Mg. This increases the heat resistance of the NOx absorbent 25, which is advantageous in avoiding thermal degradation during the sulfur desorption process.
[0023]
  As an element constituting the NOx absorbent 25, the Ba, KIt is preferable that La is contained in addition to Mg. Thereby, the heat resistance of the NOx absorbent 25 is increased, which is further advantageous in avoiding thermal degradation during the sulfur desorption process.
[0024]
  The temperature rise of the NOx absorbent 25 by the sulfur desorption means b is the exhaust gas temperature.RiseRealized byIsFor example, if the exhaust gas temperature is set to 500 to 1100 ° C. (preferably 600 to 1100 ° C.), it is advantageous for desorption of sulfur from the NOx absorbent 25.. AlsoThe reduction of the oxygen concentration in the exhaust gas by the sulfur desorbing means b can be realized by controlling the air-fuel ratio of the engine, for example, so that λ (oxygen excess rate) is around 1 or 1 or less. As a result, the oxygen concentration in the exhaust gas becomes 0.5% or less, which is advantageous for desorption of the sulfur component from the NOx absorbent 25.
[0025]
  Also, the aboveSplit injectionByIncrease CO concentration in exhaust gasBecause I didThis is further advantageous for desorption of the sulfur component from the NOx absorbent 25.
[0026]
  That is, when the NOx absorbent 25 is Ba, SOx is adsorbed on the surface of the barium particles in the form of sulfate, and this barium sulfate proceeds with the following reaction by the supply of CO, so that barium carbonate and sulfur dioxide. Are considered to generate.
[0027]
      BaSO_Four+ CO → BaCO_Three+ SO₂↑ (Coefficient omitted)
  Further, when the CO concentration increases, a so-called water gas shift reaction proceeds between the CO and moisture in the exhaust gas, thereby generating hydrogen at the reaction site of the catalyst.
[0028]
      CO + H₂O → H₂+ CO₂
And, since the sulfur adsorbed on the NOx absorbent 25 is desorbed by this hydrogen in the form of hydrogen sulfide, it becomes advantageous for desorption of the sulfur component, and this water gas shift reaction proceeds even at a relatively low temperature. The temperature of the NOx absorbent 25too muchIt doesn't have to be high.
[0029]
  Further, as the sulfur excessive absorption determining means a for determining the excessive absorption state of the sulfur component to the NOx absorbent 25, for example, based on the travel distance of the vehicle and the total amount of fuel consumed during that time, In consideration of the temperature state of the NOx absorbent 25, the SOx absorption amount of the NOx absorbent 25 is estimated, and when the estimated amount exceeds a predetermined value, it is determined that the sulfur component is excessively absorbed. Things can be adopted.
[0030]
  Other inventions in this application are:Exhausted from the engineAn exhaust gas purification method for purifying exhaust gas containing NOx and sulfur components,
  When the exhaust gas is in an oxygen-excess state with a high oxygen concentration, SrBa and at least one of Mg and LaK andEquipped withAnd supported by ceria-zirconia composite oxide or ceria and alumina.By contacting the NOx absorbent, the NOx absorbent absorbs the NOx and sulfur components,
  When the sulfur component absorption state of the NOx absorbent becomes a predetermined excessive absorption state,Operate the fuel injection valve so that fuel is injected into the engine combustion chamber at least twice in the period from the beginning of the intake stroke to the end of the compression stroke.The sulfur component is desorbed from the NOx absorbent by increasing the temperature of the NOx absorbent and reducing the oxygen concentration in the exhaust gas.
[0031]
  That is, according to such a method, as apparent from the above description, when the NOx absorption performance of the NOx absorbent 25 is reduced by S poisoning, the sulfur component is desorbed from the NOx absorbent 25. It becomes easy to recover the NOx absorption performance to a high level, which is advantageous for NOx purification.
[0032]
  Still another invention of this application is:EngineA NOx absorbent that is disposed in the exhaust passage and absorbs NOx and sulfur components in the exhaust gas in an oxygen-excess atmosphere with a high oxygen concentration in the exhaust gas, while releasing the absorbed NOx as the oxygen concentration decreases. An exhaust gas purifying catalyst,
  Elements constituting the NOx absorbent are Ba, K, Mg,SrAnd La, and these are supported on ceria-zirconia composite oxide or ceria and alumina.It is characterized by that.
[0033]
  In other words, such an exhaust gas purifying catalyst can provide heat resistance and is advantageous in improving recovery from S poisoning. In this case, it is considered that a part of Ba, K, Mg, and Sr forms a Ba (x) -K (y) -Mg (z) -Sr (m) based composite oxide. Here, x, y, z, and m represent the ratio of the number of constituent atoms. When x + y + z + m = 1, x = 0.3 to 0.9, y = 0.01 to 0.5, z = 0.01. -0.5, m = 0.01-0.7.
[0034]
【The invention's effect】
  As described above, according to the invention relating to the exhaust gas purification apparatus of this application, the NOx absorbent material is, SrBa and at least one of Mg and LaK andEquipped withAnd supported by ceria-zirconia composite oxide or ceria and alumina.The means for determining the excessive absorption state of the sulfur component in the NOx absorbent material, and when the excessive absorption state of the sulfur component is determined, the temperature of the NOx absorbent material is increased and the oxygen concentration in the exhaust gas is decreased. And sulfur desorption means bThe sulfur desorption means b is a fuel injection control means for operating the fuel injection valve so as to divide and inject fuel into the combustion chamber of the engine at least twice during the period from the beginning of the intake stroke to the end of the compression stroke. WithBecauseThe NOx absorption performance of the NOx absorbent before S poisoning is increased, and the decrease in NOx absorption performance when subjected to S poisoning is reduced,This is advantageous for recovery from NO poisoning of the NOx absorbent, and the NOx purification performance can be improved.
[0035]
  According to the invention relating to the exhaust gas purification method of this application,SrBa and at least one of Mg and LaK andEquipped withAnd supported by ceria-zirconia composite oxide or ceria and alumina.By contacting the NOx absorbent with the NOx absorbent, the NOx absorbent absorbs the NOx and the sulfur component, and when the NOx absorbent has absorbed the sulfur component excessively,Actuating the fuel injection valve to inject fuel into the engine combustion chamber at least two times between the beginning of the intake stroke and the end of the compression stroke;While increasing the temperature of the NOx absorbent and reducing the oxygen concentration in the exhaust gas,The NOx absorption performance of the NOx absorbent before S poisoning is increased, and the decrease in NOx absorption performance when subjected to S poisoning is reduced,The NOx absorbent can be recovered from S poisoning and the NOx absorption performance can be maintained at a high level, which is advantageous for NOx purification.
[0036]
  Further, according to the invention relating to the exhaust gas purifying catalyst of this application, the elements constituting the NOx absorbent are Ba, K, Mg,SrAnd La, which are supported on ceria-zirconia composite oxide or ceria and aluminaHeat resistance,The NOx absorption performance of the NOx absorbent before S poisoning is increased, the decrease in NOx absorption performance when receiving S poisoning is reduced,This is also advantageous in improving the recovery from S poisoning.
[0037]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0038]
  (Entire engine configuration)
  FIG. 2 shows the overall configuration of an engine equipped with an exhaust gas purifying apparatus A according to an embodiment of the present invention. In the figure, reference numeral 1 denotes a multi-cylinder engine mounted on an automobile, for example, and a combustion chamber 4 is defined in the cylinder 2 by a piston 3 fitted into each cylinder 2. A spark plug 6 connected to the ignition circuit 5 is attached to a position on the cylinder axial center on the upper wall of the combustion chamber 4 so as to face the combustion chamber 4. An injector (fuel injection valve) 7 that directly injects fuel into the combustion chamber 4 is attached to the peripheral edge of the combustion chamber 4.
[0039]
  Although not shown, the injector 7 is connected to a fuel supply circuit having a high pressure fuel pump, a pressure regulator, and the like. This fuel supply circuit is for supplying the fuel from the fuel tank to the injector 7 while adjusting the fuel to an appropriate pressure, and includes a fuel pressure sensor 8 for detecting the fuel pressure. When the fuel is injected by the injector 7 in the latter half of the compression stroke of the cylinder 2, the fuel spray is trapped in a cavity (not shown) recessed in the top surface of the piston 3 and compared with the vicinity of the spark plug 6. A thick mixture layer is formed. On the other hand, when the fuel is injected by the injector 7 in the intake stroke of the cylinder 2, the fuel spray is diffused into the combustion chamber 4 and mixed with the intake air (air), so that a uniform mixture is formed in the combustion chamber 4. .
[0040]
  The combustion chamber 4 communicates with an intake passage 10 via an intake port (not shown) that is opened and closed by an intake valve 9. The intake passage 10 supplies the intake air filtered by the air cleaner 11 to the combustion chamber 4 of the engine 1, and includes a hot wire type air flow sensor 12 that detects the intake air amount in order from the upstream side to the downstream side. An electric throttle valve 13 for restricting the intake passage 10 and a surge tank 14 are provided. The electric throttle valve 13 is not mechanically connected to an accelerator pedal (not shown), and is driven by a motor 15 to open and close. Further, a throttle opening sensor 16 for detecting the opening of the throttle valve 13 and an intake pressure sensor 17 for detecting the intake pressure in the surge tank 14 are provided.
[0041]
  The intake passage 10 on the downstream side of the surge tank 14 is an independent passage branched for each cylinder 2, and the downstream end portion of each independent passage further branches into two and communicates with the intake port. A swirl control valve 18 is provided on one of the branch paths. The swirl control valve 18 is driven by an actuator 19 to open and close. When the swirl control valve 18 is closed, intake air is supplied to the combustion chamber 4 only from the other branch path, and strong intake air is supplied to the combustion chamber 4. While the swirl is generated, the intake swirl is weakened as the swirl control valve 18 opens. Further, a swirl control valve opening sensor 20 that detects the opening of the swirl control valve 18 is provided.
[0042]
  In FIG. 2, reference numeral 22 denotes an exhaust passage for discharging combustion gas from the combustion chamber 4. The upstream end of the exhaust passage 22 branches for each cylinder 2 and communicates with the combustion chamber 4 via an exhaust valve 23 by an exhaust port (not shown). Has been. The exhaust passage 22 detects oxygen concentration in the exhaust gas in order from the upstream side to the downstream side.₂A sensor 24 and a catalyst 25 for purifying exhaust gas are provided. O above₂As shown in FIG. 3, the output (electromotive force) of the sensor 24 becomes the reference value E1 when the oxygen concentration in the exhaust gas is a concentration (about 0.5%) substantially corresponding to the theoretical air-fuel ratio. However, when it is darker (rich side), it increases rapidly, while when it is thinner (lean side), it decreases rapidly. In other words, O₂The sensor 24 is a so-called lambda O whose output reverses stepwise from the theoretical air-fuel ratio.₂It consists of sensors.
[0043]
  The catalyst 25 is of the NOx absorption reduction type that absorbs NOx in an oxygen-excess atmosphere with a high oxygen concentration in the exhaust gas, and releases and reduces and purifies NOx absorbed by the decrease in oxygen concentration. As shown in FIG. 4, this lean NOx catalyst 25 has a cordierite-made honeycomb structure carrier 25a, and has an inner catalyst layer 25b on the wall surface of each through hole formed in the carrier 25a, and an outer layer on the inner catalyst layer 25b. A catalyst layer 25c is formed.
[0044]
  Furthermore, O₂An upstream end of the EGR passage 26 is connected to the exhaust passage 22 upstream of the sensor 24, and the downstream end thereof is connected to the intake passage 10 between the throttle valve 13 and the surge tank 14. A part of is returned to the intake system. An electric EGR valve 27 for adjusting the opening degree of the EGR passage 26 is disposed near the downstream end of the EGR passage 26 so as to adjust an exhaust gas recirculation amount (hereinafter referred to as an EGR amount) through the EGR passage 26. ing. The EGR passage 26 and the EGR valve 27 constitute exhaust recirculation means. Further, a lift sensor 28 for detecting the lift amount of the EGR valve 27 is provided.
[0045]
  The ignition circuit 5 of the spark plug 6, the injector 7, the drive motor 15 of the electric throttle valve 13, the actuator 19 of the swirl control valve 18, the electric EGR valve 27 and the like are controlled by a control unit 40 (hereinafter referred to as ECU). It has become so. On the other hand, the ECU 40 includes an air flow sensor 12, a throttle opening sensor 16, an intake pressure sensor 17, a swirl control valve opening sensor 20, an O₂The output signals of the sensor 24 and the lift sensor 28 of the EGR valve 27 are inputted, and in addition, a water temperature sensor 30 for detecting the coolant temperature (engine water temperature) of the engine 1, an intake air temperature sensor 31 for detecting the intake air temperature, Output signals of an atmospheric pressure sensor 32 that detects atmospheric pressure, a rotation speed sensor 33 that detects engine rotation speed, and an accelerator opening sensor 34 that detects the opening of the accelerator pedal (accelerator operation amount) are input.
[0046]
  (Outline of engine control)
  The engine 1 according to this embodiment is operated in different combustion states by switching the fuel injection mode (fuel injection timing, air-fuel ratio, etc.) by the injector 7 according to the operating state. That is, when the engine 1 is warm, for example, as shown in FIG. 5, a predetermined region on the low load and low rotation side is a stratified combustion region, and as shown in FIG. And a combustion mode in which combustion is performed in a stratified state where the air-fuel mixture is unevenly distributed in the vicinity of the spark plug 6. In this stratified combustion mode, the opening degree of the throttle valve 13 is increased in order to reduce the pump loss of the engine 1, whereby the average air-fuel ratio of the combustion chamber 4 is in a significantly lean state (for example, A / F). = About 30).
[0047]
  On the other hand, the other operation region is a uniform combustion region, and in the low load side λ = 1 division region, the fuel is divided into two times by the injector 7 in the intake stroke and the compression stroke, respectively. The fuel injection amount and the throttle opening are controlled so that the air-fuel ratio of the air-fuel mixture in the combustion chamber 4 becomes substantially the stoichiometric air-fuel ratio (A / F = 14.7) (hereinafter referred to as λ = 1 division). Mode). Further, in the high load or high rotation rich region in the uniform combustion region, the fuel is injected collectively by the injector 7 in the first half of the intake stroke, and the air-fuel ratio is richer than the stoichiometric air-fuel ratio (for example, A / F = 13-14) (hereinafter referred to as an enrichment mode).
[0048]
  In the region indicated by hatching in the control map of FIG. 5, the EGR valve 27 is opened so that a part of the exhaust gas is recirculated to the intake passage 10 through the EGR passage 26. Although not shown in the drawings, the entire operation region of the engine 1 is a uniform combustion region in order to improve combustion stability when the engine is cold.
[0049]
  More specifically, the ECU 40 includes, as various control parameters related to the engine output, for example, the fuel injection amount and injection timing by the injector 7, the intake air amount adjusted by the throttle valve 13, and the intake swirl adjusted by the swirl control valve 18. The strength, the EGR amount adjusted by the EGR valve 27, and the like are determined according to the operating state of the engine 1.
[0050]
  That is, first, the target torque trq of the engine 1 is calculated based on the accelerator opening degree accel and the engine speed ne. This target torque trq is obtained in advance by a bench test or the like so as to obtain a correspondence relationship between the accelerator opening degree accel and the engine speed ne so that the required output performance can be obtained, and this correspondence relationship is stored in the memory of the ECU 40 as a map. Thus, values corresponding to the actual accelerator opening degree accel and the engine speed ne are read from this map. The correspondence relationship between the accelerator opening degree accel and the engine speed ne and the target torque trq is, for example, as shown in FIG. 7A. The target torque trq increases as the accelerator opening degree accel increases. And the higher the engine speed ne, the larger.
[0051]
  Subsequently, the operation mode is set based on the target torque trq and the engine speed ne obtained as described above. That is, for example, when the engine is warm, as shown in FIG. 5, when the target torque trq is lower than a predetermined low load side threshold value trq * and the engine speed ne is low, the stratified combustion mode is set. In this operating state, the uniform combustion mode is set, and in this case, λ = 1 split mode or enrichment mode is selected according to the target torque trq and the engine speed ne.
[0052]
  Subsequently, the target air-fuel ratio afw is set for each operation mode. That is, in the stratified combustion mode and the enrich mode, the target air-fuel ratio afw is obtained from a map prepared in advance according to the target torque trq and the engine speed ne, and in the λ = 1 split mode, the target air-fuel ratio afw is theoretically calculated. Let the air-fuel ratio. A target charging efficiency ce is calculated based on the target air-fuel ratio afw, the engine speed ne, and the target torque trq, and is created in advance according to the target charging efficiency ce and the engine speed ne. The throttle opening tvo is obtained from the map (see FIG. 7B). The correspondence relationship between the engine speed and the throttle opening varies depending on the presence or absence of EGR, and the throttle opening tvo is made larger than when there is no EGR.
[0053]
  An actual charging efficiency ce of the engine 1 is calculated based on an output signal from the air flow sensor 12, and a basic fuel injection amount qbase is calculated based on the actual charging efficiency ce and the target air-fuel ratio afw. The
[0054]
      qbase = KGKF x ce / afw (where KGKF is a conversion factor)
At the same time, the fuel split ratio between the intake stroke injection and the compression stroke injection is set for each operation mode. In the stratified combustion mode, the intake stroke injection ratio becomes 0%, while in the enrich mode, the intake stroke injection ratio becomes 100%. In the λ = 1 split mode, the split ratio is set according to the target air-fuel ratio afw and the engine speed ne.
[0055]
  Further, the fuel injection timing is set for each of the above operation modes, and although not shown, in the stratified combustion mode, the injection timing Inj_TT for compression stroke injection is obtained from a map prepared in advance according to the target torque trq and the engine speed ne. On the other hand, in the uniform combustion mode, the injection timing Inj_TL for intake stroke injection is obtained from a table set in advance according to the engine speed ne. In the case of split injection, the data in the stratified combustion mode is diverted as the injection timing Inj_TT for compression stroke injection, and intake stroke injection is performed from a map prepared in advance according to the target air-fuel ratio afw and the engine speed ne. Injection timing Inj_TL is obtained.
[0056]
  In addition, the ignition timing of the engine 1 is also set for each operation mode. In the stratified combustion mode, the basic ignition timing is obtained mainly on the basis of the target torque trq and the engine speed ne, while the λ = 1 split mode and the enrichment mode. In the mode, the basic ignition timing is obtained based on the charging efficiency ce and the engine speed ne, and the basic ignition timing is corrected based on the engine water temperature or the like. Further, the swirl control valve 18 is also controlled for each operation mode. In the stratified combustion mode, the opening of the swirl control valve 18 is increased as the target torque trq is increased and the engine speed ne is increased. On the other hand, in the λ = 1 split mode and the enrich mode, the opening degree of the swirl control valve 18 is decreased as the target torque trq is increased and the engine speed ne is increased. Although described in detail later, the EGR amount is also controlled for each operation mode according to the operating state of the engine 1.
[0057]
  (Composition of catalyst and its regeneration)
  In this embodiment, as described above, the engine 1 is placed in the stratified combustion state in the low load region to greatly improve fuel efficiency, and NOx in the exhaust gas even when the air-fuel ratio is extremely lean as in the stratified combustion state. So as to reduce the amount of NOx absorbed in the catalyst 25 to a certain extent in order to stably exhibit the purification performance of the catalyst 25. NOx is released to reduce and purify. Further, if a small amount of SOx contained in the exhaust gas is gradually absorbed by the NOx absorbent and the amount of SOx absorbed in the catalyst 25 gradually increases with time, and the NOx purification performance is hindered, the SOx Is forcibly desorbed from the catalyst 25.
[0058]
  The inner catalyst layer 25b of the lean NOx catalyst 25 is formed by supporting a catalyst metal and a NOx absorbent on a porous support material. Pt is adopted as the catalyst metal, at least one of K, Sr, Mg and La and Ba are adopted as the NOx absorbent, and alumina and ceria-zirconia composite oxide are adopted as the support material. Yes.
[0059]
  The outer catalyst layer 25c is also formed by supporting a catalyst metal and a NOx absorbent on a porous support material, and has Pt and Rh as the catalyst metal, and K, It has at least one of Sr, Mg and La and Ba, and zeolite is adopted as the support material.
[0060]
  Note that zeolite may be used as the support material for the inner catalyst layer 25b, and in that case, alumina or ceria may be used as the support material for the outer catalyst layer 25c. Further, as the catalyst 25, although not shown, a support layer is formed of alumina or ceria on the wall surface of the carrier, and this support material is a one-layer coat type in which a catalyst metal and a NOx absorbent are supported. Also good.
[0061]
  The regeneration of the catalyst 25 by the desorption of NOx and SOx is performed when it is determined that the sulfur component is excessively absorbed in the NOx absorbent. While controlling the air-fuel ratio of the combustion chamber 4 to substantially the stoichiometric air-fuel ratio, the fuel injection by the injector 7 is divided into two, thereby raising the temperature of the exhaust gas and raising the temperature of the NOx absorbent. This is done by greatly increasing the CO concentration in the exhaust gas. At that time, the CO concentration and the HC concentration in the exhaust gas are periodically changed by changing the air-fuel ratio so as to alternately switch between the rich side and the lean side.
[0062]
  -Fuel injection control for catalyst regeneration-
  Next, a specific processing procedure of the fuel injection control including the control procedure for regenerating the catalyst 25 will be described with reference to flowcharts shown in FIGS.
[0063]
  First, as shown in FIG. 8, in step SA1 after the start, the air flow sensor 12, O₂While receiving various sensor signals such as the sensor 24, the water temperature sensor 30, the rotation speed sensor 33, the accelerator opening degree sensor 34, etc., various data are input from the memory of the ECU 40. Subsequently, in step SA2, the basic fuel injection amount qbase is calculated and set based on the charging efficiency ce, the target air-fuel ratio afw and the like as described above.
[0064]
  Subsequently, in steps SA3 to SA9, the injection pulse widths τL and τT of the intake stroke injection and the compression stroke injection and the injection timings Inj_TL and Inj_TT are obtained for each operation mode. That is, in step SA3, it is determined whether or not λ = 1 split mode. If YES, the process proceeds to step SA4, and the basic fuel injection amount qbase is divided into an intake stroke and a compression stroke according to the split ratio. The corresponding injection pulse widths τ are set as the intake stroke injection pulse width τL = τL1 and the compression stroke injection pulse width τT = τT2, respectively, based on the flow rate characteristics of the injector 7. Subsequently, in step SA5, the injection timings of the intake stroke injection and the compression stroke injection are set (Inj_TL = Inj_TL1, Inj_TT = Inj_TT1).
[0065]
  If it is determined in step SA3 that NO is not the λ = 1 split mode, the process proceeds to step SA6 to determine whether or not it is the stratified combustion mode. If YES, the process proceeds to step SA7 and the intake stroke injection pulse width τL. And the compression stroke injection pulse width τT is set to a value τT1 corresponding to the basic fuel injection amount qbase. Subsequently, in step SA8, the injection timing of the compression stroke injection is set (Inj_TT = Inj_TT2). On the other hand, if it is determined in step SA6 that NO is not the stratified combustion mode, the process proceeds to step SA9 to determine whether or not to perform fuel cut control. If YES, the process returns. If NO, the process proceeds to step SA10. The intake stroke injection pulse width τL is set to a value τL1 corresponding to the basic fuel injection amount qbase, the compression stroke injection pulse width τT = 0, and in step SA11, the injection timing of the intake stroke injection is set (Inj_TL = Inj_TL3). ).
[0066]
  Subsequent to steps SA5, SA8, and SA11 in FIG. 8, in step SB1 shown in FIG. 9, the NOx absorption amount in the catalyst 25 is estimated. This estimation is performed, for example, based on the distance traveled since the last NOx release control (NOx release control) and the total amount of fuel consumed during that time, and in the subsequent step SB2 based on the estimation result. Then, it is determined whether or not the NOx absorption amount is equal to or greater than a predetermined value set in advance, that is, whether or not the NOx absorption is excessive. If this judgment is YES, it will progress to Step SB3 and will turn on flag F1 which shows that it is a period which performs NOx discharge control (F1 = 1). In step SB2, when the engine 1 is accelerating, the determination may be YES regardless of the amount of NOx absorbed, and NOx release control described later may be performed.
[0067]
  Subsequently, in step SB4, the first timer value T1 having an initial value 0 is incremented, and in the subsequent step SB5, it is determined whether or not the first timer value T1 is equal to or greater than a preset threshold value T10. If this determination is YES, it is determined that the period for performing NOx release control has ended, the process proceeds to steps SB11 and SB12, the flag F1 is cleared (F1 = 0), and the first timer is reset (T1 = 0). ). On the other hand, if the determination in step SB5 is NO, the process proceeds to step SB6. In each of steps SB6 to SB9, O₂A feedback control calculation based on a signal from the sensor 24 is performed.
[0068]
  That is, in step SB6, O₂The output E from the sensor 24 is compared with a reference value E1 corresponding to the theoretical air fuel ratio. If the output E is greater than the reference value E1, the process proceeds to step SB7 where the feedback correction values τCL and τCT are subtracted from the previous values by the constants α and β, respectively, to obtain the current value. On the other hand, if the output E is NO equal to or less than the reference value E1, the process proceeds to step SB8, and constants α and β are added to the previous values of the feedback correction values τCL and τCT to obtain the current value.
[0069]
  Subsequently, at step SB9, the injection pulse widths τL4, τT4 obtained according to the actual charging efficiency ce so that the air-fuel ratio of the combustion chamber 4 becomes the stoichiometric air-fuel ratio, and the feedback correction value τCL obtained at steps SB7, SB8. , ΤCT, the intake stroke and the compression stroke injection pulse widths τL, τT at the time of NOx release control are calculated, and the injection timings are set again.
[0070]
      τL = τL4 + τCL, Inj_TL = Inj_TL4
      τT = τT4 + τCT, Inj_TT = Inj_TT4
  In other words, O₂While the output E from the sensor 24 is larger than the reference value E1, the air-fuel ratio is richer than the stoichiometric air-fuel ratio. Therefore, the fuel injection amount in the intake and compression strokes is gradually increased by a fixed amount α and β every control cycle. Decrease and change the air-fuel ratio to the lean side. On the other hand, if the output E becomes smaller than the reference value E1, the air-fuel ratio becomes lean this time, so the fuel injection amount is gradually increased to change the air-fuel ratio to the rich side. In steps SB7 to SB9, both the intake stroke and the compression stroke injection amount are feedback-corrected, but only the intake stroke injection amount may be feedback-corrected. This is because even if the fuel injection amount in the intake stroke is changed, there is little adverse effect on the combustion state and the exhaust gas.
[0071]
  If NO is determined in step SB2, the process proceeds to step SB10 to determine the state of the flag F1. If the flag is ON (F1 = 1), it is determined that it is a period for performing NOx release control. On the other hand, if the flag is off (F1 = 0), it is determined that it is not a period for performing NOx release control, and the process proceeds to steps SB11 and SB12.
[0072]
  Subsequent to steps SB9 and SB12 in FIG. 9, in step SC1 shown in FIG. 10, the degree of S poisoning of the catalyst 25, that is, the SOx absorption amount is estimated. Similar to the estimation of the NOx absorption amount in the above step SB1, this estimation is also based on the distance traveled since the last control for urging SOx desorption (SOx desorption control) and the total amount of fuel consumed during that time. , Taking into account the temperature state of the catalyst in the meantime. Based on the estimation result, in the subsequent step SC2, it is determined whether or not the SOx absorption amount is equal to or greater than a predetermined value set in advance, that is, whether or not the SOx absorption is excessive. Here, since the sulfur component in the exhaust gas is small, the travel distance until the SOx absorption excessive state is reached is usually much longer than the travel distance until the NOx absorption excessive state is reached.
[0073]
  If the determination in step SC2 is YES, the process proceeds to step SC3, and a flag F2 indicating that it is a period for performing SOx desorption control is turned on (F2 = 1). In step SC4, the exhaust temperature thg, that is, the temperature state of the catalyst 25 is estimated. This estimation is mainly based on the actual charging efficiency ce and engine speed ne at the time of estimation, and taking into account the operation time in the stratified combustion mode and the time of split injection within a predetermined time before the estimation. However, the exhaust temperature thg tends to increase as the charging efficiency and the engine speed increase, and also to increase due to split injection. On the other hand, in the stratified combustion mode, the exhaust gas temperature thg becomes considerably low. Therefore, the longer the operation time in the stratified combustion mode, the lower the temperature state of the catalyst 25.
[0074]
  Subsequently, in step SC5, it is determined whether the exhaust temperature thg is equal to or higher than a set temperature thg0 (for example, 450 ° C.). If this determination is NO, the process proceeds to step SD1 in FIG. Then, the SOx desorption control is executed. The reason why the SOx desorption control is performed only when the exhaust gas temperature is high to some extent is that the SOx desorption property is not improved unless the temperature state of the catalyst 25 is higher than a certain level.
[0075]
  In step SC6, the second timer value T2 having an initial value of 0 is incremented. In step SC7, it is determined whether or not the second timer value T2 has become equal to or greater than a preset threshold value T20. While this determination is NO, the process proceeds to steps SC8 to SC11.₂A feedback control calculation based on a signal from the sensor 24 is performed. The specific procedure of this feedback control calculation is the same as steps SB6 to SB9 in FIG. If the time corresponding to the threshold value T20 elapses and SOx is sufficiently desorbed from the catalyst 25, the determination in step SC7 is YES and the process proceeds to step SC12, where the flag F2 is cleared ( F2 = 0), the process proceeds to step SD1 in FIG.
[0076]
  On the other hand, if it is determined NO in step SC2, the process proceeds to step SC13 to determine the state of flag F2, and if it is on (F2 = 1), it is determined that it is a period for performing SOx desorption control. While the process proceeds to SC4, if it is off (F2 = 0), it is determined that it is not the period for performing the SOx desorption control, the process proceeds to steps SC14 and SC15, the flag F2 is cleared (F2 = 0), and the second timer is reset. (T2 = 0), the process proceeds to step SD1 in FIG.
[0077]
  Subsequent to steps SC5, SC12, and SC15, in step SD1 in FIG. 11, it is first determined whether or not the intake stroke injection pulse width τL is zero. If YES (τL = 0), the process proceeds to step SD4. On the other hand, if NO (τL ≠ 0), the routine proceeds to step SD2, where it is determined whether or not the intake stroke injection timing Inj_TL has come. And it waits until it becomes an injection timing, and if it becomes an injection timing (it is YES at step SD2), it will progress to step SD3 and will perform intake stroke injection by the injector 7. FIG. Subsequently, in each of steps SD4 to SD6, the compression stroke injection is executed in the same manner as described above, and then the process returns.
[0078]
  Therefore, steps SC1 and SC2 in the flow shown in FIG. 10 constitute the sulfur excess absorption determining means 40a for determining that the SOx absorption amount in the catalyst 25 is a SOx absorption excessive state that is greater than a predetermined value. Steps SC8 to SC11 constitute a sulfur desorption means 40b for desorbing SOx from the NOx absorbent of the catalyst 25 when the SOx absorption excessive state is determined by the sulfur excessive absorption determination means 40a.
[0079]
  That is, when the exhaust gas temperature thg is equal to or higher than the set temperature thg0, the sulfur desorbing means 40b controls the air-fuel ratio to be close to the stoichiometric air-fuel ratio to reduce the oxygen concentration in the exhaust gas and is richer than the stoichiometric air-fuel ratio. While the fuel is periodically changed so as to alternately change between the intake side and the lean side, the fuel is injected into the injector 25 by being divided into two parts each in the intake stroke and the compression stroke of the cylinder by the injector 7 so that the catalyst 25 is in a high temperature state. The CO concentration in the exhaust gas is greatly increased, and the CO concentration is also increased by correcting the fuel injection amount to be increased.
[0080]
  (EGR control)
  Next, the processing procedure of the EGR control will be described in detail with reference to the flowchart shown in FIG. 12. In step SE1 after the start, various sensor signals such as the air flow sensor 12 and the rotation speed sensor 33 are accepted, and the ECU 40 Input various data from memory. In the subsequent step SE2, a target EGR rate is calculated based on the actual charging efficiency ce and the engine speed ne, and an EGR amount that achieves this target EGR rate is set as a basic EGR amount EGRb. The target EGR rate has a correspondence relationship with the charging efficiency ce and the engine speed ne obtained in advance by a bench test or the like, and this correspondence relationship is stored in the memory of the ECU 40 as a map.
[0081]
  Subsequently, in step SE3, based on the value of the first flag F1, it is determined whether or not it is a period for performing NOx release control. If this determination is YES, the process proceeds to step SE5. If the determination is NO, the process proceeds to step SE4. Next, based on the value of the second flag F2, it is determined whether it is a period for performing the SOx desorption control. If this determination is YES, the process proceeds to step SE5, and the correction value EGRc for increasing / decreasing the EGR amount is set to a predetermined value γ (γ <0), while if the determination is NO, the process proceeds to step SE6 and the correction value is corrected. The value of EGRc is set to zero (EGRc = 0). Then, following step SE5 or step SE6, in step SE7, the basic EGR amount EGRb and the correction value EGRc are added to calculate the final EGR amount EGRt, and in step SE8, the control signal is sent to the EGR valve 27. Is output to drive to an opening corresponding to the final EGR amount EGRt, and then return.
[0082]
  That is, as described above, at least one of NOx release control or SOx desorption control is performed, and the fuel injection amount by the injector 7 is feedback controlled to maintain the air-fuel ratio of the combustion chamber 4 near the stoichiometric air-fuel ratio. The opening degree of the EGR valve 27 is corrected so that the EGR amount is slightly reduced.
[0083]
  -Effect-
  Next, the function and effect of the embodiment will be described.
[0084]
  For example, as shown in FIG. 13, the engine 1 is operated in the acceleration operation state with the fuel injection amount increased and operated in the λ = 1 split mode or the enrich mode. At this time, NOx absorbed in the catalyst 25 is released. Reduced and purified. Further, when the steady operation state continues, the NOx absorption excessive state of the catalyst 25 is determined based on the travel distance since the last release of NOx and the fuel consumption during that time (flag F1 = 1). NOx release control as shown in the flow of 9 is performed.
[0085]
  On the other hand, for example, when the travel distance of the automobile reaches several thousand km, there is a possibility that the NOx absorption performance may be lowered due to the gradual accumulation of SOx in the catalyst 25 during the operation of the engine 1. In that case, as shown in the flow of FIG. 10, when the excessive absorption state of SOx is determined by the sulfur excessive absorption determination means during the operation of the engine 1 and the flag F2 is turned on (see FIG. 13), the catalyst is If 25 is in a high temperature state (for example, 450 ° C. or higher), SOx release control is performed.
[0086]
  This NOx release and SOx release are both performed by fuel split injection and feedback control in the vicinity of the stoichiometric air-fuel ratio of the air-fuel ratio. As the oxygen concentration in the exhaust gas decreases, the CO concentration in the exhaust gas and The desorption of NOx and SOx from the catalyst 25 is promoted by the HC concentration greatly increasing and periodically changing, and further, the exhaust gas temperature rises.
[0087]
  That is, the fuel is divided into two parts and injected by the injector 7 so that a part of the fuel injected in the intake stroke of each cylinder 2 is uniformly diffused into the combustion chamber 4 to form a lean air-fuel mixture. On the other hand, the remaining fuel injected in the compression stroke forms a rich mixture in the vicinity of the spark plug 6. Then, although the initial combustion rate immediately after ignition is high in this rich mixture portion, since oxygen is insufficient, CO is likely to be generated by local incomplete combustion. On the other hand, the combustion in the portion of the lean air-fuel mixture becomes slow, and part of the fuel is discharged before it burns, so that the exhaust temperature rises due to afterburning and CO is more likely to be generated. Become. Furthermore, if the number of times the injector 7 is opened due to the division of fuel injection increases, the proportion of coarse fuel droplets injected at the initial stage of opening the valve increases, and this also facilitates the generation of CO.
[0088]
  Further, the fuel injection amount by the injector 7 is increased, and the air-fuel ratio of the combustion chamber 4 is controlled to be approximately the stoichiometric air-fuel ratio, so that the concentration of reducing agent components such as CO and HC in the exhaust gas increases. The fuel injection amount is O₂By performing feedback correction based on the signal from the sensor 24, the air-fuel ratio periodically fluctuates so as to alternately change between the rich side and the lean side. Therefore, the concentrations of CO, HC, etc. in the exhaust gas are cyclic. Fluctuates. As a result, the action of CO, HC, etc. on the NOx and SOx adsorbed on the catalyst 25 is strengthened, and the release of NOx and SOx from the catalyst 25 is promoted.
[0089]
  As a result, the time required for sufficiently desorbing SOx from the catalyst 25, that is, the time required to control the air-fuel ratio to a substantially stoichiometric air-fuel ratio only for that purpose is shortened. 25 can be sufficiently regenerated to ensure stable NOx removal performance.
[0090]
  About NOx release
  Specifically, in the catalyst 25, NOx is adsorbed in the form of nitrate on the surface of the NOx absorbent (Ba particles or the like), and the nitrate radicals of this nitrate are replaced by the supply of CO, so that carbonate and nitrogen dioxide. Are considered to generate. For example, the case of Ba particles is as follows.
[0091]
      Ba (NO₃)₂+ CO → BaCO₃+ NO₂↑ (Coefficient omitted)
Then, nitrogen dioxide reacts with HC, CO and the like on the catalyst metal to be reduced and purified.
[0092]
      NO₂ + HC + CO → N₂+ H₂O + CO₂     (Coefficient omitted)
  That is, since NOx is released from the catalyst 25 and reduced and purified, the catalyst 25 again becomes able to sufficiently absorb NOx in the exhaust gas (regeneration of the catalyst).
[0093]
  Here, in the catalyst 25, since CO and HC in the exhaust gas are adsorbed and held by the zeolite in the outer catalyst layer 25c, the NOx released as described above can be reliably reduced and purified. Even if the amount of NOx released from 25 decreases, CO and HC are not discharged into the atmosphere. Therefore, most of the NOx absorbed by the catalyst 25 is released, that is, the catalyst 25 can be sufficiently regenerated.
[0094]
  In addition, since Pt and Rh are supported on the outer catalyst layer 25c, even in a relatively low temperature state (for example, 200 to 250 ° C.), NO₂Can be effectively reduced and decomposed. This is particularly advantageous when the engine 1 is operated in a stratified combustion state as in this embodiment. This is because in such stratified combustion, the air-fuel ratio becomes extremely lean and the exhaust temperature becomes considerably low.
[0095]
  Release of SOx
  Next, recovery from S poisoning of the catalyst 25, that is, regeneration, will be described. In the catalyst 25, SOx is adsorbed on the surface of the NOx absorbent (Ba particles, etc.) in the form of sulfate in the same manner as NOx. It is considered that the sulfate group of this sulfate is replaced by the supply of CO to produce carbonate and sulfur dioxide. For example, in the case of Ba particles, it is as follows.
[0096]
      BaSO₄+ CO → BaCO₃+ SO₂↑ (Coefficient omitted)
  Further, when the CO concentration increases, the CO and the moisture H in the exhaust gas.₂A so-called water gas shift reaction proceeds with O, whereby hydrogen is generated at the reaction site of the catalyst.
[0097]
      CO + H₂O → H₂+ CO₂
Since SOx is desorbed in the form of hydrogen sulfide by the action of hydrogen, the desorption of the sulfur component from the catalyst 25 is also promoted by this. Since the water gas shift reaction proceeds even at a relatively low temperature, the SOx desorption can be promoted even if the temperature of the catalyst 25 is not so high.
[0098]
  Further, zeolite is supported on the outer catalyst layer 25c of the catalyst 25, and the HC in the exhaust gas is partially oxidized by the zeolite and converted to HCO or CO. Therefore, the zeolite is adsorbed on the NOx absorbent surface of the inner catalyst layer 25b. The concentration of CO acting on the SOx being added further increases.
[0099]
  In addition, if other elements (K, Sr, Mg, or La) other than Ba are more susceptible to S poisoning than Ba, therefore, Ba is less susceptible to S poisoning, and S poisoning. The subsequent decrease in NOx absorption performance is reduced. If the other elements (K, Sr, Mg or La) are more easily recovered from S poisoning than Ba, the NOx absorption performance after recovery is enhanced. Furthermore, when the presence of the other elements (K, Sr, Mg, or La) leads to an increase in the specific surface area or reaction site of the NOx absorbent, the NOx absorbent performance of the NOx absorbent is enhanced. In addition, when such other elements act as an obstacle to sintering due to the heat of Ba, thermal degradation due to the sulfur desorption treatment of the NOx absorbent is avoided.
[0100]
  (Concrete example)
  -Example 1-
  Formation of Pt-Rh / MFI catalyst powder
  An aqueous solution of dinitrodiamine platinum and an aqueous solution of rhodium nitrate have a Pt carrying amount (the carrying amount is a dry weight per 1 L of carrier when it is carried on a honeycomb carrier described later. The same applies hereinafter). And weighed and mixed so that the Rh loading was 0.006 g / L, and this was mixed with MFI-type zeolite (SiO 2₂/ Al₂O₃ = 80), the catalyst powder was formed by performing spray-drying by a spray-drying method, and further drying and baking. The total amount of Pt and Rh in the catalyst powder is about 2.5 wt%. Drying was performed at a temperature of 150 ° C. for 1 hour, and firing was performed at a temperature of 540 ° C. for 2 hours. The drying conditions and firing conditions are the same for “drying” and “firing” in the following description.
[0101]
  Preparation of mixed solution (for impregnation)
  A mixed solution was prepared by weighing and mixing an aqueous solution of dinitrodiamine platinum nitrate and an aqueous solution of barium acetate so that the Pt loading was 6.0 g / L and the Ba loading was 30 g / L.
[0102]
  Formation of inner coat layer
  γ-alumina and CeO₂-ZrO₂The composite oxide and the alumina binder are weighed and mixed so that the γ-alumina support amount is 150 g / L, the composite oxide support amount is 150 g / L, and the binder support amount is 30 g / L. A slurry was prepared by adding ion exchange water thereto. A cordierite honeycomb carrier (capacity 25 mL, weight 420 g / L per carrier L) was dipped in this slurry, pulled up, and excess slurry was blown away, and the slurry was wash coated on the carrier. Next, this was dried and baked to form an inner coat layer.
[0103]
  Formation of outer coat layer
  The Pt-Rh / MFI catalyst powder and alumina binder are weighed and mixed so that the catalyst powder loading is 20 g / L and the binder loading is 4 g / L, and ion exchange water is added thereto. Thus, a slurry was prepared, and the slurry was wash-coated on the carrier on which the inner coat layer was formed, and dried and fired to form an outer coat layer.
[0104]
  Impregnation process
  The mixed solution was impregnated into the inner and outer coat layers of the carrier, and dried and fired.
[0105]
  Therefore, in the case of the catalyst, Pt is supported at 0.5 g / L by the Pt-Rh / MFI catalyst powder of the outer coat layer and is supported at 6.0 g / L by the mixed solution. Therefore, the total supported amount of Pt is 6 .5 g / L.
[0106]
  The resulting catalyst has an impurity content of less than 1%. This also applies to the other examples of catalysts described below.
[0107]
  -Example 2-
  As the above mixed solution, a solution obtained by weighing and mixing an aqueous solution of dinitrodiamine platinum nitrate and an aqueous solution of barium acetate so that the supported amount of Pt is 6.0 g / L and the supported amount of Ba is 50 g / L is used. Other than that, a catalyst was prepared by the same conditions and method as in Example 1. Also in this example, Pt is supported at 0.5 g / L by the Pt-Rh / MFI catalyst powder of the outer coat layer and is supported at 6.0 g / L by the mixed solution, so that the total supported amount of Pt is 6. 5 g / L.
[0108]
  -Example 3-
  As the above mixed solution, aqueous solutions of dinitrodiamine platinum nitrate, barium acetate, strontium acetate and lanthanum acetate, Pt loading amount 6.0 g / L, Ba loading amount 30 g / L, Sr loading amount 10 g / L, La A catalyst was prepared by the same conditions and method as in Example 1 except that a supported amount was 10 g / L and mixed. Also in this example, Pt is supported at 0.5 g / L by the Pt-Rh / MFI catalyst powder of the outer coat layer and is supported at 6.0 g / L by the mixed solution, so that the total supported amount of Pt is 6. 5 g / L.
[0109]
  -Example 4-
  As the above mixed solution, aqueous solutions of dinitrodiamine platinum nitrate, barium acetate, magnesium acetate and lanthanum acetate, Pt loading amount 6.0 g / L, Ba loading amount 30 g / L, Mg loading amount 10 g / L, La A catalyst was prepared by the same conditions and method as in Example 1 except that a supported amount was 10 g / L and mixed. Also in this example, Pt is supported at 0.5 g / L by the Pt-Rh / MFI catalyst powder of the outer coat layer and is supported at 6.0 g / L by the mixed solution, so that the total supported amount of Pt is 6. 5 g / L.
[0110]
  -Example 5-
  As the above mixed solution, aqueous solutions of dinitrodiamine platinum nitrate, barium acetate, potassium acetate, and strontium acetate were used. The supported amount of Pt was 6.0 g / L, the supported amount of Ba was 30 g / L, the supported amount of K was 10 g / L, Sr. A catalyst was prepared by the same conditions and method as in Example 1 except that a supported amount was 10 g / L and mixed. Also in this example, Pt is supported at 0.5 g / L by the Pt-Rh / MFI catalyst powder of the outer coat layer and is supported at 6.0 g / L by the mixed solution, so that the total supported amount of Pt is 6. 5 g / L.
[0111]
  -Example 6
  As the above mixed solution, an aqueous solution of dinitrodiamine platinum nitrate, barium acetate, strontium acetate and magnesium acetate, Pt loading amount 6.0 g / L, Ba loading amount 30 g / L, Sr loading amount 10 g / L, Mg A catalyst was prepared by the same conditions and method as in Example 1 except that a supported amount was 10 g / L and mixed. Also in this example, Pt is supported at 0.5 g / L by the Pt-Rh / MFI catalyst powder of the outer coat layer and is supported at 6.0 g / L by the mixed solution, so that the total supported amount of Pt is 6. 5 g / L.
[0112]
  -Example 7-
  As the above mixed solution, each aqueous solution of dinitrodiamine platinum nitrate, barium acetate, and potassium acetate was weighed so that the Pt loading was 6.0 g / L, the Ba loading was 30 g / L, and the K loading was 10 g / L. A catalyst was prepared by the same conditions and method as in Example 1 except that a mixture was used. Also in this example, Pt is supported at 0.5 g / L by the Pt-Rh / MFI catalyst powder of the outer coat layer and is supported at 6.0 g / L by the mixed solution, so that the total supported amount of Pt is 6. 5 g / L.
[0113]
  -Example 8-
  As the above mixed solution, aqueous solutions of dinitrodiamine platinum nitrate, barium acetate, potassium acetate, and magnesium acetate, Pt loading amount 6.0 g / L, Ba loading amount 30 g / L, K loading amount 10 g / L, Mg A catalyst was prepared by the same conditions and method as in Example 1 except that a supported amount was 10 g / L and mixed. Also in this example, Pt is supported at 0.5 g / L by the Pt-Rh / MFI catalyst powder of the outer coat layer and is supported at 6.0 g / L by the mixed solution, so the total supported amount of Pt is 6. 5 g / L.
[0114]
  -Example 9-
  As the above mixed solution, aqueous solutions of dinitrodiamine platinum nitrate, barium acetate, potassium acetate and lanthanum acetate, Pt loading amount 6.0 g / L, Ba loading amount 30 g / L, K loading amount 10 g / L, La A catalyst was prepared by the same conditions and method as in Example 1 except that a supported amount was 10 g / L and mixed. Also in this example, Pt is supported at 0.5 g / L by the Pt-Rh / MFI catalyst powder of the outer coat layer and is supported at 6.0 g / L by the mixed solution, so that the total supported amount of Pt is 6. 5 g / L.
[0115]
  -Example 10-
  As the above mixed solution, each aqueous solution of dinitrodiamine platinum nitrate, barium acetate, potassium acetate, strontium acetate, magnesium acetate and lanthanum acetate has a Pt carrying amount of 6.0 g / L, a Ba carrying amount of 30 g / L, and a K carrying amount. The same conditions and method as in Example 1 except that a mixture of 10 g / L, Sr loading of 10 g / L, Mg loading of 10 g / L, and La loading of 10 g / L is used. The catalyst was prepared by Also in this example, Pt is supported at 0.5 g / L by the Pt-Rh / MFI catalyst powder of the outer coat layer and is supported at 6.0 g / L by the mixed solution, so that the total supported amount of Pt is 6. 5 g / L.
[0116]
  -Example 11-
  As the above mixed solution, aqueous solutions of dinitrodiamine platinum nitrate, rhodium acetate, barium acetate, potassium acetate, strontium acetate and magnesium acetate were used, the Pt loading was 6.5 g / L, the Rh loading was 0.1 g / L, Ba The same conditions as in Example 1 except that the amount supported is 30 g / L, the amount of K is 6 g / L, the amount of Sr is 10 g / L, and the amount of Mg is 10 g / L. A catalyst was prepared by the method.
[0117]
  In this example, Pt is supported on the catalyst by 0.5 g / L of Pt-Rh / MFI catalyst powder of the outer coat layer and 6.5 g / L of the mixed solution. The amount is 3.5 g / L, and Rh is also supported by 0.006 g / L by the Pt-Rh / MFI catalyst powder and 0.1 g / L by the above mixed solution. 106 g / L.
[0118]
  -Evaluation test of each catalyst-
  Measuring method of NOx purification rate
  The measuring method of the NOx purification rate is as follows. That is, each catalyst is attached to a fixed bed flow-type reaction evaluation apparatus, and simulated exhaust gas of lean air-fuel ratio shown in Table 1 with a gas composition A is passed through the catalyst until the NOx purification rate is stabilized. Next, the simulated exhaust gas is switched to the air-fuel ratio rich gas gas composition B shown in Table 1 and allowed to flow for 3 minutes to desorb the NOx previously absorbed by the NOx absorbent. Thereafter, the simulated exhaust gas is switched to the gas composition A, and the NOx purification rate (lean NOx purification rate) for 130 seconds is measured from this switching point.
[0119]
  The measurement temperature of the NOx purification rate (catalyst inlet gas temperature) is 350 ° C. or 450 ° C. The space velocity SV is 55000h at any temperature except for Example 11.^-1It is. In Example 11, the space velocity is 25000h.^-1It was. In addition, the NOx purification rate can be measured with a fresh catalyst that has not been subjected to deterioration treatment, or with a SO₂After processing (S poisoning deterioration processing), SO₂This was performed after the regeneration treatment after the treatment and after the heat deterioration treatment. SO₂The conditions for the treatment, the regeneration treatment and the heat deterioration treatment are as follows.
[0120]
  SO₂processing
  SO₂In the treatment, a simulated exhaust gas having a gas composition C shown in Table 1 is allowed to flow for 60 minutes with respect to the catalyst attached to the fixed bed flow reaction evaluation apparatus. The catalyst inlet gas temperature is 350 ° C., and the space velocity is 55000h.^-1It is.
[0121]
  Playback processing
  In the regeneration process, the three types of simulated exhaust gases shown in Table 2 are appropriately switched over and flow for 10 minutes with respect to the catalyst attached to the fixed bed flow reaction evaluation apparatus. In this case, the gas composition is (1) A / F = 14.7 → (2) A / F = 13.8 → (3) A / F = 14.7 → (4) A / F = 15.6 (→ (1) A / F = 14.7), and the period was set to 1 second. The catalyst inlet gas temperature is 600 ° C., and the space velocity is 120,000 h.^-1It is.
[0122]
  Thermal degradation treatment
  In the thermal deterioration treatment, the state in which the catalyst is heated to 900 ° C. in an air atmosphere is maintained for 24 hours.
[0123]
[Table 1]

[0124]
[Table 2]

[0125]
  NOx purification rate when fresh, SO₂NOx purification rate after treatment and SO₂FIG. 14 shows the measurement results of the NOx purification rate after the regeneration treatment after the treatment (however, the catalyst inlet gas temperature is 350 ° C.). According to the figure, there is no significant difference between the catalysts in the NOx purification rate during fresh. But SO₂The NOx purification rate after treatment is higher in Examples 3 to 11 in which other elements (at least one of K, Sr, Mg and La) are used in combination with Ba than in Examples 1 and 2 where the NOx absorbent is Ba alone. Tends to be high, particularly in the case of containing K. On the other hand, as for the NOx purification rate after the regeneration treatment, those containing K show a tendency to be high except for Example 5, and the tendency is remarkable in the case of using Mg or La in addition to K.
[0126]
  FIG. 15 shows the NOx purification rate during freshness and after heat treatment (thermal deterioration treatment) when the catalyst inlet gas temperature is 350 ° C. According to the figure, the NOx purification rate after heat treatment of the catalysts of Examples 3 to 6 (the effect of which the above-mentioned S poisoning resistance (the NOx purification characteristics after the regeneration treatment was not so effective)) tends to increase. In particular, the tendency is remarkable in Example 5. This tendency is the same when NOx purification at the time of freshness and after heat treatment (thermal deterioration treatment) when the catalyst inlet gas temperature shown in FIG. As described above, Examples 3 to 6 show an excellent effect on the heat resistance, although a remarkable effect is not recognized on the S poison resistance, and it is considered that the regeneration process is performed at a relatively high temperature. Thus, it can be said that the regeneration process is advantageous in maintaining the NOx absorption performance.
[0127]
  Further, according to FIG. 16, each catalyst of Examples 5, 8, and 9 contains K in addition to Ba and further contains any one of Sr, Mg, and La. The NOx purification rate at ℃ is considerably high. This means that even when the exhaust gas temperature becomes high as in high-speed traveling, the vehicle can travel at a lean air-fuel ratio without significantly increasing NOx emissions.
[0128]
  <About Ba-K-Sr-based NOx absorbent>
  As the above mixed solution, aqueous solutions of dinitrodiamine platinum nitrate, rhodium acetate, barium acetate, potassium acetate and strontium acetate have a Pt carrying amount of 3.0 g / L, a Rh carrying amount of 0.1 g / L, and a Ba carrying amount. Weigh and mix to 30 g / L, K loading 6 g / L, Sr loading 0 g / L, 5 g / L, 10 g / L, 15 g / L, 20 g / L and 30 g / L. Each catalyst was prepared by the same conditions and method as in Example 1 except that each solution thus prepared was used.
[0129]
  In the case of this example, Pt is supported on each catalyst by 0.5 g / L by the Pt-Rh / MFI catalyst powder of the outer coat layer and by 3.0 g / L by the above mixed solution. The amount is 3.5 g / L, and Rh is also supported by 0.006 g / L by the Pt-Rh / MFI catalyst powder and 0.1 g / L by the above mixed solution. 106 g / L.
[0130]
  For comparison, as the above mixed solution, aqueous solutions of dinitrodiamine platinum nitrate, rhodium acetate and barium acetate were used. The supported amount of Pt was 3.0 g / L, the supported amount of Rh was 0.1 g / L, and the supported amount of Ba. A comparative catalyst was prepared by the same conditions and method as in Example 1 except that a mixture obtained by weighing and mixing so as to be 30 g / L (zero K loading, zero Sr loading). This comparative catalyst also has a total Pt loading of 3.5 g / L and a total Rh loading of 0.106 g / L.
[0131]
  For each of the catalysts and comparative catalysts having different Sr loadings, the freshness and SO₂Each NOx purification rate after treatment and after regeneration was measured. FIG. 17 shows the results of the catalysts with different Sr loadings. According to the figure, when Sr is carried, the NOx purification rate after regeneration becomes higher than when the Sr carrying amount is zero. However, when the Sr carrying amount is 20 g / L or more, the NOx after regeneration is rather The purification rate is low, the Sr loading is preferably 5 g / L or more and less than 20 g / L, or 10 g / L or more and less than 20 g / L, 15 g / L is the best, and therefore 13 g / L. It can be seen that L to 17 g / L is advantageous in maintaining the NOx purification rate after regeneration at a high value.
[0132]
  Further, the comparative catalyst has a NOx purification rate of 72% when fresh and SO₂The NOx purification rate after treatment was 41%, and the NOx purification rate after regeneration was 63%. Therefore, when K and Sr are supported in addition to Ba, the amount of Sr supported up to 20 g / L is up to 20 g / L when fresh.₂It can be seen that each NOx purification rate after treatment and regeneration is higher than that of the comparative catalyst of Ba alone.
[0133]
  FIG. 18 shows the results of measuring the NOx purification rate after performing the above-described thermal deterioration treatment for each catalyst and comparative catalyst having different Sr loadings. The one-dot chain line in the figure shows the NOx purification rate of the comparative catalyst. However, space velocity is 25000h^-1It was. According to the figure, when the amount of supported Sr is 30 g / L or more, the heat resistance of the catalyst is lower than that of the comparative catalyst, but if the amount is smaller than that, the heat resistance of the catalyst is improved. It turns out that it is advantageous to the reproduction | regeneration mentioned above.
[0134]
  <About Ba-K-Mg-based NOx absorbent>
  As the above mixed solution, aqueous solutions of dinitrodiamine platinum nitrate, rhodium acetate, barium acetate, potassium acetate, and magnesium acetate, Pt loading amount is 3.0 g / L, Rh loading amount is 0.1 g / L, Ba loading amount is 30 g / L, K loading is 6 g / L, Mg loading is 0 g / L, 5 g / L, 10 g / L, 15 g / L, and 20 g / L. Each catalyst was prepared by the same conditions and method as in Example 1 except that the solution was used. Also in this example, the total supported amount of Pt is 3.5 g / L, and the total supported amount of Rh is 0.106 g / L.
[0135]
  For each of the catalysts having different Mg loadings, the SO₂Each NOx purification rate after treatment and after regeneration was measured. The result is shown in FIG. According to the figure, when Mg is loaded, the NOx purification rate after regeneration becomes higher than when the Mg loading amount is zero, and the NOx purification rate after regeneration is the highest when the Mg loading amount is 10 g / L. It can be seen that an increase in the Mg loading is 3 g / L to 17 g / L, or 5 g / L to 15 g / L, which is advantageous in maintaining the NOx purification rate after regeneration at a high value.
[0136]
  Further, the comparative catalyst (the comparative catalyst described in the section of Ba—K—Sr-based NOx absorbent) has a NOx purification rate of 72% when fresh, SO₂Since the NOx purification rate after treatment is 41% and the NOx purification rate after regeneration is 63%, when K and Mg are supported in addition to Ba, SO₂It can be seen that each NOx purification rate after treatment and regeneration is higher than that of the comparative catalyst of Ba alone.
[0137]
  FIG. 20 shows the results of measuring the NOx purification rate after performing the above-described thermal deterioration treatment for each catalyst and comparative catalyst having different Mg loadings. The one-dot chain line in the figure shows the NOx purification rate of the comparative catalyst. However, space velocity is 25000h^-1It was. According to the figure, it can be seen that the heat resistance of the catalyst is improved up to 20 g / L of Mg, which is advantageous for the regeneration described above.
[0138]
  <About Ba-K-Sr-Mg-based NOx absorbent>
  As the above mixed solution, aqueous solutions of dinitrodiamine platinum nitrate, rhodium acetate, barium acetate, potassium acetate, strontium acetate, and magnesium acetate, Pt loading amount is 3.0 g / L, Rh loading amount is 0.1 g / L, Ba Each catalyst was prepared by the same conditions and method as in Example 1 except that each of the supported amounts was 30 g / L, the K supported amount was 6 g / L, the Mg supported amount was 5 g / L, and the Sr supported amount was different. In addition, each catalyst having a different amount of Sr supported was prepared with an Mg supported amount of 10 g / L, and each catalyst having a different Sr supported amount similarly prepared with an Mg supported amount of 15 g / L. In the case of each of these catalysts, the total supported amount of Pt is 3.5 g / L, and the total supported amount of Rh is 0.106 g / L.
[0139]
  For each of the catalysts having different Mg loadings and Sr loadings, the evaluation test described above, when fresh, SO₂Each NOx purification rate after treatment and after regeneration was measured. FIG. 21 shows the results when the Mg loading is 5 g / L, FIG. 22 shows the results when the Mg loading is 10 g / L, and FIG. 23 shows the results when the Mg loading is 15 g / L.
[0140]
  According to FIG. 21, when the Mg loading is 5 g / L, the NOx purification rate after recovery is the highest when the Sr loading is 15 g / L, and the SO₂The recovery rate of NOx purification rate from poisoning is also high. According to FIG. 22, when the Mg loading is 10 g / L, the NOx purification rate after recovery becomes the highest when the Sr loading is 10 g / L, and the SO₂The recovery rate of NOx purification rate from poisoning is also high. Also, when the Sr loading is 5 g / L, SO₂The recovery rate of NOx purification rate from poisoning is high. According to FIG. 23, when the Mg loading is 15 g / L, the Sr loading is 5 g / L to 15 g / L, and the SO loading is 5 g / L.₂The recovery rate of NOx purification rate from poisoning is high.
[0141]
  From the above, when Sr and Mg are used in combination with Ba and K, SO is supported even when the amount of supported Sr is small.₂It turns out that the recovery rate of the NOx purification rate from poisoning becomes high.
[0142]
  Further, the comparative catalyst (the comparative catalyst described in the section of Ba—K—Sr-based NOx absorbent) has a NOx purification rate of 72% when fresh, SO₂Since the NOx purification rate after the treatment is 41% and the NOx purification rate after the regeneration is 63%, when K, Sr and Mg are supported in addition to Ba,₂It can be seen that each NOx purification rate after treatment and regeneration is higher than that of the comparative catalyst of Ba alone.
[0143]
  FIG. 24 shows the results of measuring the NOx purification rate after the thermal deterioration treatment described above was performed for the catalysts and comparative catalysts having different Mg loadings and Sr loadings. The one-dot chain line in the figure shows the NOx purification rate of the comparative catalyst. However, space velocity is 25000h^-1It was. According to the figure, it can be seen that the heat resistance of the catalyst is improved when Sr and Mg are used in addition to Ba and K, which is advantageous for the regeneration described above. However, it can be said that an excessive amount of Sr or Mg is disadvantageous for improving heat resistance.
[0144]
  -Others-
  In the above embodiment, the sulfur desorbing means is configured by air-fuel ratio control and split injection control. However, a heater for heating the catalyst is provided, and the air-fuel ratio is changed to near λ = 1 when a sulfur excessive absorption state is determined. In addition, the catalyst may be heated by operating the heater.
[0145]
  Further, when the catalyst has a two-layer structure of the inner catalyst layer and the outer catalyst layer as in the above embodiment, the CeO is not included in the inner catalyst layer.₂-ZrO₂Fine powder CeO instead of complex oxide₂May be used. In that case, fine powder CeO₂The particle size of is preferably 100 nm or less.
[0146]
  Further, the present invention is not limited to the exhaust gas of an automobile engine, but can be applied to a stationary industrial engine. In this case, the desired effect can be obtained by configuring as in the above embodiment. . In this case, the industrial engine is used for air conditioning of buildings or the like by exchanging heat of exhaust gas, for example. At this time, when the heat exchanger is disposed upstream of the catalyst, when the catalyst temperature is increased as in the above embodiment, the heat exchange efficiency is reduced by reducing the amount of heat exchange water, etc. Can be prevented.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a configuration of the present invention.
FIG. 2 is a schematic configuration diagram of an exhaust purification device according to an embodiment of the present invention.
[Fig. 3] O in response to changes in air-fuel ratio₂The figure which shows the output characteristic of a sensor.
FIG. 4 is a cross-sectional view showing a schematic configuration of a catalyst.
FIG. 5 is a diagram showing an example of a map in which operating regions of an engine stratified combustion mode, λ = 1 split mode, and enriched mode are set.
FIG. 6 is a time chart showing fuel injection timing in each operation region of the engine.
FIG. 7 is a map (a) in which target engine torque corresponding to engine speed and accelerator opening is set, and a map (b) in which throttle valve opening corresponding to engine speed and target torque is set. Explanatory drawing which illustrates each.
FIG. 8 is a flowchart showing a procedure for setting a basic fuel injection amount and fuel injection timing.
FIG. 9 is a flowchart showing a processing procedure for NOx release control.
FIG. 10 is a flowchart showing a processing procedure for SOx desorption control.
FIG. 11 is a flowchart showing an execution procedure of intake stroke injection and compression stroke injection.
FIG. 12 is a flowchart showing a processing procedure of EGR control.
FIG. 13 is a time chart showing changes in the air-fuel ratio when NOx release control and SOx desorption control are performed during engine operation.
FIG. 14 is a graph showing NOx purification rates after fresh, after S poisoning, and after regeneration for each specific example of the catalyst.
FIG. 15 is a graph showing the NOx purification rate at fresh time and after heat deterioration treatment when the catalyst inlet gas temperature is 350 ° C. for each specific example of the catalyst.
FIG. 16 is a graph showing the NOx purification rate at fresh time and after heat deterioration treatment when the catalyst inlet gas temperature is 450 ° C. for each specific example of the catalyst.
FIG. 17 is a graph showing the influence of the amount of Sr supported on the NOx purification rate after fresh, S poisoning and after regeneration for a catalyst having a Ba—K—Sr-based NOx absorbent.
FIG. 18 is a graph showing the influence of the amount of Sr supported on the heat resistance of a catalyst having a Ba—K—Sr-based NOx absorbent.
FIG. 19 is a graph showing the influence of Mg loading on the NOx purification rate after fresh, S poisoning and after regeneration for a catalyst having a Ba—K—Mg-based NOx absorbent.
FIG. 20 is a graph showing the influence of the amount of Mg supported on the heat resistance of a catalyst having a Ba—K—Mg-based NOx absorbent.
FIG. 21 relates to a catalyst having a Ba—K—Sr—Mg-based NOx absorbent, and the amount of Sr supported on each NOx purification rate after fresh, after S poisoning, and after regeneration when the amount of Mg supported is 5 g / L. The graph which shows the influence which gives.
FIG. 22 relates to a catalyst having a Ba—K—Sr—Mg-based NOx absorbent, and the amount of Sr supported on each NOx purification rate after fresh, after S poisoning, and after regeneration when the amount of Mg supported is 10 g / L. The graph which shows the influence which gives.
FIG. 23 relates to a catalyst having a Ba—K—Sr—Mg-based NOx absorbent, and the amount of Sr supported on each NOx purification rate during fresh, S poisoning and after regeneration when the Mg supported amount is 1 g / L. The graph which shows the influence which gives.
FIG. 24 is a graph showing the influence of the Mg loading and Sr loading on the heat resistance of a catalyst having a Ba—K—Sr—Mg-based NOx absorbent.
[Explanation of symbols]
  A Engine exhaust purification system
  1 engine
  2-cylinder
  4 Combustion chamber
  7 Injector (fuel injection valve)
  24 O₂Sensor (oxygen concentration detection means)
  25 Catalyst (NOx absorbent)
  26 EGR passage (exhaust gas recirculation means)
  27 EGR valve (exhaust gas recirculation means)
  40 Control unit (ECU)
  40a Sulfur excess absorption judging means
  40b Sulfur desorption means

Claims (5)

An NOx absorbent that is disposed in the exhaust passage of the engine and absorbs NOx and sulfur components in the exhaust gas in an oxygen-excess atmosphere with a high oxygen concentration in the exhaust gas, while releasing the absorbed NOx by a decrease in the oxygen concentration; ,
Sulfur excess absorption determining means for determining an excessive absorption state of the sulfur component in the NOx absorbent,
Sulfur that desorbs sulfur components from the NOx absorbent by increasing the temperature of the NOx absorbent and lowering the oxygen concentration when the sulfur overabsorption state is determined by the sulfur excess absorption determining means. An exhaust gas purifying device comprising a desorption means,
The sulfur desorption means comprises a fuel injection control means for operating a fuel injection valve so as to divide and inject fuel into the engine combustion chamber at least twice during the period from the start of the intake stroke to the end of the compression stroke. Prepared
As an element constituting the NOx absorbent, at least one of Sr , Mg, and La and Ba and K are included , and the NOx absorbent is supported on ceria-zirconia composite oxide or ceria and alumina. exhaust gas purifying device being. In the exhaust gas purification device according to claim 1,
The elements constituting the NOx absorbent include Ba, K, and Mg, which are supported on a support using the ceria-zirconia composite oxide or ceria and alumina as a support material, and the amount of Mg per liter of the support Is an exhaust gas purification device of 3 to 17 g. In the exhaust gas purification device according to claim 1,
The elements constituting the NOx absorbent include Ba, K, and Sr, which are supported on the support using the ceria-zirconia composite oxide or ceria and alumina as a support material, and the amount of Sr per liter of the support Is an exhaust gas purifying apparatus. An exhaust gas purification method for purifying exhaust gas containing NOx and sulfur components discharged from an engine ,
When the exhaust gas is in an oxygen-excess state with a high oxygen concentration, it comprises at least one of Sr , Mg and La, Ba and K , and is supported on ceria-zirconia composite oxide or ceria and alumina. The NOx absorbent is made to absorb the NOx and sulfur components by contacting the NOx absorbent,
When the sulfur component absorption state of the NOx absorbent becomes a predetermined excessive absorption state, the fuel is injected into the combustion chamber of the engine at least twice from the beginning of the intake stroke to the end of the compression stroke. An exhaust gas purification method for operating the fuel injection valve to increase the temperature of the NOx absorbent and desorbing the sulfur component from the NOx absorbent by reducing the oxygen concentration in the exhaust gas. A NOx absorbent that is disposed in the exhaust passage of the engine and absorbs NOx and sulfur components in the exhaust gas in an oxygen-excess atmosphere with a high oxygen concentration in the exhaust gas, while releasing the absorbed NOx as the oxygen concentration decreases. An exhaust gas purifying catalyst provided,
The element constituting the NOx absorbent contains Ba, K, Mg 2 , Sr and La, and these are supported on ceria-zirconia composite oxide or ceria and alumina, for exhaust gas purification catalyst.

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