JP4626115B2 - Exhaust gas purification catalyst and method for producing exhaust gas purification catalyst - Google Patents

Description

【００５１】
−実験Ｂ−
容量２５ｃｃのハニカムを水に浸して引き上げ、エアーブローによって水を落とし、ハニカムの吸水量を求めた。また、容量２５ｃｃのハニカムにβ型ゼオライトを１００ｇ／Ｌ担持させた後、同様の吸水処理を施して、当該ゼオライト担持ハニカムの吸水量を求めた。結果は表２に示す通りである。
【００５２】
【表２】

【００５３】
表２の結果からハニカムの吸水量が２．０ｇのときのβ型ゼオライトの吸水量は０．４ｇ（２．４ｇ−２．０ｇ＝０．４ｇ）である。すなわち、吸水量の比はゼオライト／ハニカム＝1/5 である。従って、β型ゼオライトへのＢａ、Ｓｒ及びＭｇを合わせた総担持量は触媒粉末Ｂの総担持量の０．４８％（２．４％×1/5＝０．４８％）である。
【００５４】
よって、内側触媒層１２におけるＢａ、Ｓｒ及びＭｇを合わせた総担持量は外側触媒層１３の同総担持量の１％未満となる。
【００５５】
＜評価テスト＞
上記触媒について、フレッシュ時、並びに大気雰囲気において８００℃で２４時間のエージングを施した後の各々におけるＨＣ浄化性能、すなわちＨＣ吸着率、ＨＣ酸化率（吸着したＨＣのうち酸化した割合）及びＨＣ浄化率（ＨＣ吸着率×ＨＣ酸化率）、並びにリーンＮＯｘ浄化率をリグテストで調べた。
【００５６】
ＨＣ浄化性能の評価モードは、(1)供試触媒をＮ_２気流中において触媒入口ガス温度を８０℃まで昇温し、(2)その温度に保持した状態で、ＨＣ（ベンゼン）が１５００ｐｐｍＣ、ＮＯが１００ｐｐｍ、Ｏ_２が１．０％となるように当該Ｎ_２ガスにＨＣ、ＮＯ及びＯ_２のガスを２分間導入し、(3)しかる後にＨＣガスの導入のみを止めて触媒入口ガス温度を８０℃から４００℃まで３０℃／分の速度で昇温させる、というものである。空間速度ＳＶは２５０００ｈ^−１とした。
【００５７】
ＨＣ吸着率は、上記(2)の２分間の触媒入口ＨＣ濃度と触媒出口ＨＣ濃度とに基づいて算出した。ＨＣ酸化率は、上記(2)の２分間で触媒に吸着されたＨＣ量と、上記(3)の昇温時の触媒出口ＨＣ濃度とに基づいて算出した。
【００５８】
また、上記触媒に対して空燃比リーンの模擬排気ガス（ガス組成Ａ）を６０秒間流し、次にガス組成を切り換えて空燃比リッチの模擬排気ガス（ガス組成Ｂ）を６０秒間流す、というサイクルを５回繰り返した後、ガス組成を空燃比リーン（ガス組成Ａ）に切り換え、この切り換え時点から６０秒間のＮＯｘ浄化率を測定し、これをリーンＮＯｘ浄化率とした。触媒温度及び模擬排気ガス温度は３５０℃、そのガス組成は表３に示す通りであり、空間速度ＳＶは２５０００ｈ^−１とした。
【００５９】
【表３】

【００６０】
結果は図３に示されている。ＨＣ吸着率のエージングによる低下は少ない。一方、ＨＣ酸化率はエージングによって低下しているが、それほど大きな低下ではない。リーンＮＯｘ浄化率はエージングによって少し低下している。ＨＣ吸着率の低下が少ないことから、内側触媒層のβ型ゼオライトはエージングによって殆ど破壊されていないこと、つまり、その比表面積が殆ど低下していないことがわかる。
【００６１】
中間触媒層１４に含浸されたＢｉは、Ｐｄ原子の最近接原子として存在し、ＰｄとＡｇとが反応してＰｄ-Ａｇ合金が生成してしまうこと、つまり、ＰｄのＨＣ浄化に関する低温活性が低下してしまうこと、あるいはＨＣ吸着性能の向上に有効なＡｇ量が少なくなってしまうことを防止する。
【００６２】
［参考形態］
本形態の排気ガス浄化用触媒８は、図４に示すように、担体１１の表面に内側触媒層１２と外側触媒層１３とが層状に形成されてなる。担体１１及び内側触媒層１２は実施形態のそれと同じである。外側触媒層１３は、Ｐｔ、Ｒｈ、Ｐｄ、Ｂａ、Ｓｒ及びＭｇをサポート材としてのアルミナ及びセリア材に担持させてなる触媒成分と、バインダとによって形成されている。すなわち、実施形態とは違って、中間触媒層がなく、Ｐｄが外側触媒層１３に含まれている。他の構成は実施形態と同じである。
【００６３】
次に上記排気ガス浄化用触媒８の製法を説明する。
【００６４】
活性アルミナ粉末、上記セリア材、酢酸バリウム、酢酸ストロンチウム、酢酸マグネシウム、ジニトロジアミン白金硝酸塩、硝酸ロジウム、硝酸パラジウム及び水を混合し、乾燥及び５００℃での焼成を行なうことにより、触媒粉末Ｃを形成する。
【００６５】
内側触媒コート層を実施形態と同様にして形成する。この内側触媒コート層に硝酸銀及び酢酸ビスマスの混合溶液を含浸させて乾燥及び５００℃での焼成を行なう。しかる後に上記触媒粉末Ｃを用い、実施形態と同様にして外側触媒コート層を形成する。
【００６６】
＜参考例＞
上述の製法により、上記内側触媒層１２及び外側触媒層１３の各成分担持量を次のようにした排気ガス浄化用触媒を調製した。
内側触媒層１２；β型ゼオライト＝１００ｇ／Ｌ
外側触媒層１３；Ｐｔ＝３．５ｇ／Ｌ，Ｒｈ＝０．３ｇ／Ｌ，Ｐｄ＝２．０ｇ／ Ｌ，Ｂａ＝３０ｇ／Ｌ，Ｓｒ＝１０ｇ／Ｌ，Ｍｇ＝１０ｇ／Ｌ ，アルミナ＝１５０ｇ／Ｌ，セリア材＝１５０ｇ／Ｌ
内側触媒層１２におけるＡｇの含浸担持量は１０ｇ／Ｌ、Ｂｉの含浸担持量は０．５ｇ／Ｌである。また、内側触媒層１２におけるＢａ、Ｓｒ及びＭｇを合わせた総担持量は外側触媒層１３の同総担持量の１％未満である。
【００６７】
＜比較例＞
上記参考例と同様の担体に同様の内側触媒コート層を形成して同様にＡｇ及びＢｉを含浸担持させた。次に、活性アルミナ粉末、上記セリア材、アルミナバインダ及び水混合してなるスラリーを調製して、これを内側触媒コート層の上にコーティングし、乾燥及び５００℃での焼成を行なって外側触媒コート層を形成した。次に、酢酸バリウム、酢酸ストロンチウム、酢酸マグネシウム、ジニトロジアミン白金硝酸塩、硝酸ロジウム及び硝酸パラジウムの混合水溶液を上記内側及び外側の両触媒コート層に含浸させ、乾燥及び５００℃での焼成を行なうことにより、比較例触媒を得た。各成分担持量は次の通りである。
内側触媒層１２；β型ゼオライト＝１００ｇ／Ｌ
外側触媒層１３；アルミナ＝１５０ｇ／Ｌ，セリア材＝１５０ｇ／Ｌ
内側触媒層１２のＡｇの含浸担持量は１０ｇ／Ｌ、Ｂｉの含浸担持量は０．５ｇ／Ｌである。また、内側触媒層１２及び外側触媒層１３を合わせた各貴金属及び各ＮＯｘ吸着材の担持量は、Ｐｔ＝３．５ｇ／Ｌ、Ｒｈ＝０．３ｇ／Ｌ、Ｐｄ＝２．０ｇ／Ｌ、Ｂａ＝３０ｇ／Ｌ、Ｓｒ＝１０ｇ／Ｌ、Ｍｇ＝１０ｇ／Ｌである。
【００６８】
＜比較テスト＞
上記参考例及び比較例の両触媒について、実施形態の場合と同じ方法でエージング後のＨＣ浄化性能及びリーンＮＯｘ浄化性能を調べた。結果は図５に示されている。同図によれば、リーンＮＯｘ浄化率には殆ど差がないものの、ＨＣ吸着率は参考例の方が格段に高くなっている。これは、参考例の場合、エージング後でも内側触媒層１２のゼオライトの構造破壊ないしは比表面積の低下が少なかったためと考えられる。
【００６９】
また、ＨＣ酸化率に関しても参考例の方が格段に高い。これは、比較例の場合はＰｔ等の貴金属類がゼオライトにも含浸担持されているが、それがゼオライトの破壊によってシンタリングを生じていると考えられる。つまり、参考例の場合は貴金属類が外側触媒層１３のアルミナ及びセリア材に担持されていて、ゼオライトの構造破壊による活性低下の問題がないためと考えられる。
【００７０】
＜ＮＯｘ吸着材担持量がゼオライトの比表面積に与える影響＞
図６はβ型ゼオライト１００ｇにＭｇ、Ｃａ、Ｓｒ及びＢａの各々を０．２mol担持したサンプルと０．０５mol担持したサンプルとについて、エージング後のＢＥＴ比表面積を測定して比較したものである。
【００７１】
同図から、Ｍｇ、Ｃａ、Ｓｒ、Ｂａ（ＮＯｘ吸着材）のゼオライトへの担持量が多い場合はエージングによってゼオライトの構造破壊が進み、その比表面積が低下すること、従って、本発明のようにゼオライトへのＮＯｘ吸蔵材の担持量を可及的に少なくすることがＨＣ浄化性能に有効であることがわかる。
【００７２】
＜リーンバーンエンジン制御について＞
上記実施形態に係る排気ガス浄化用触媒は、Ｂａ等のＮＯｘ吸着材を含有し、空燃比リーンのときに排気ガス中のＮＯｘを吸着する。従って、そのＮＯｘ吸着量が多くなると、空燃比をリッチにして（排気ガスの酸素濃度を下げて）これを放出させて還元浄化する必要がある。また、ＮＯｘ吸着材は、排気ガス中に含まれる硫黄を硫黄酸化物の形で吸着して塩を形成することによりＮＯｘ吸着材としての機能を喪失する、いわゆる硫黄被毒という問題がある。従って、その場合は触媒を高温化することによって再生を図る必要がある。以下、ＮＯｘ放出及び硫黄被毒からの再生のための燃料噴射制御について説明する。
【００７３】
図７に示すように、スタート後のステップＳ１において、エンジンの吸入空気量、エンジン回転数、アクセル開度、触媒温度等の各種データを入力する。続いて、ステップＳ２において、各種データからエンジンの運転状態に応じた適切な目標空燃比を設定し、基本燃料噴射量Ｑpbを設定する。
【００７４】
続くステップＳ３において当該触媒のＮＯｘ吸着量ＮＯeを推定し、続くステップＳ４において当該触媒のＳＯｘ（硫黄酸化物）吸着量ＳＯeを推定する。空燃比リーンのときは、予め実験によって各エンジン運転状態（エンジン回転数及びエンジン負荷）におけるＮＯｘ吸着量及びＳＯｘ吸着量を求めて作成したマップを参照し、そのときのエンジン運転状態からＮＯｘ吸着量及びＳＯｘ吸着量を求め、これを積算していくことでＮＯｘ吸着量ＮＯe及びＳＯｘ吸着量ＳＯeを推定するようにしている。空燃比リッチ（空気過剰率λ≦１）のときは、λが小さいほど、また、リッチ時間が長いほど大きな減算定数でＮＯｘ吸着量ＮＯe及びＳＯｘ吸着量ＳＯeを減じていくようにしている。
【００７５】
続くステップＳ５においてＮＯｘ吸着量ＮＯeが予め定めた閾値ＮＯo（ＮＯｘ放出制御をすべきほどに多くなった（ＮＯｘ吸着能が低下する）と考えられるＮＯｘ吸着量）よりも大きくなったか否かを判定する。ＮＯe＞ＮＯoのときはステップＳ６に進んでカウンタＴＮの前回値が零か否かを判定する。このカウンタＴＮは燃料噴射量の増量制御を行なっている時間に相当するものである。
【００７６】
カウンタＴＮの前回値が零のときはステップＳ７に進んでカウンタ閾値ＴＮoをセットした後、ステップＳ８に進んでカウンタＴＮをインクリメントし、ＴＮの前回値が零でないときはステップＳ６からＳ８に直接進んでカウンタＴＮのインクリメントを行なう。閾値ＴＮoは、現在の触媒温度に基づき、ＮＯｘを放出しやすい温度域（例えば２００〜４００℃）では小さな値に、他の温度域では大きな値にセットする。閾値ＴＮoは実時間で０．５〜５秒程度となる範囲でセットすればよい。
【００７７】
続くステップＳ９においてカウンタＴＮが閾値ＴＮoよりも大きいか否かを判定する。カウンタＴＮが閾値ＴＮo以下であれば、ステップＳ１０に進んで燃料噴射量Ｑpbとしてリッチ用燃料噴射量Ｑpλを与え、これを燃料噴射量Ｑpとして所定のクランク時期になったときに燃料噴射を実行する（ステップＳ１１，Ｓ１２）。ステップＳ９においてカウンタＴＮ＞閾値ＴＮoであれば、ステップＳ１３に進んでカウンタＴＮ及びＮＯｘ吸着量の推定値ＮＯeをリセットし、基本燃料噴射量Ｑpbで燃料噴射を実行する。
【００７８】
一方、ステップＳ５においてＮＯｘ吸着量の推定値ＮＯeが閾値ＮＯ以下であるときはステップＳ１４に進んでカウンタＴＮのカウント中か否かを判定する。カウント中であればステップＳ８に進んでＮＯｘ放出制御を続行する。カウント中でなければステップＳ１５に進んでＳＯｘ吸着量の推定値ＳＯeが予め定めた閾値ＳＯo（ＳＯｘ放出制御をすべきほどに硫黄被毒したと考えられるＳＯｘ吸着量）よりも大きくなったか否かを判定する。ＳＯeがＳＯo以下であるときは、ステップＳ１１に進んで基本燃料噴射量Ｑpbで燃料噴射を実行する（ステップＳ１１，Ｓ１２）。
【００７９】
ＳＯｘ吸着量の推定値ＳＯeがＳＯoよりも大きいときはステップＳ１６に進んでカウンタＴＳの前回値が零か否かを判定する。このカウンタＴＳは燃料噴射量の増量制御を行なっている時間に相当するものである。ＴＳの前回値が零のときはステップＳ１７に進んでカウンタ閾値ＴＳoをセットした後、ステップＳ１８に進んでカウンタＴＳをインクリメントし、ＴＳの前回値が零でないときはステップＳ１６からＳ１８に直接進んでカウンタＴＳのインクリメントを行なう。閾値ＴＳoは現在の触媒温度に基づきそれが所定値（例えば４００℃）以上であれば、該触媒温度が高いほど小さな値にセットする。閾値ＴＳoは実時間で１〜１０分程度となる範囲でセットすればよい。
【００８０】
続くステップＳ１９においてカウンタＴＳが閾値ＴＳoよりも大きいか否かを判定する。カウンタＴＳが閾値ＴＳoよりも大きいときは、ステップＳ１０に進んで燃料噴射量Ｑpbとしてリッチ用燃料噴射量Ｑpλを与え、これを燃料噴射量Ｑpとして所定のクランク時期になったときに燃料噴射を実行する（ステップＳ１１，Ｓ１２）。ステップＳ１９においてカウンタＴＳ＞閾値ＴＳoであれば、ステップＳ２０に進んでカウンタＴＳ、ＳＯｘ吸着量の推定値ＳＯe及びＮＯｘ吸着量の推定値ＮＯeをリセットし、基本燃料噴射量Ｑpbで燃料噴射を実行する（ステップＳ１１，Ｓ１２）。
【００８１】
以上のように、ＮＯｘ吸着材のＮＯｘ吸着量が多くなると、エンジンが空燃比リーンの運転状態にあっても、燃料噴射量が増量されて空燃比のリッチ化が図られ、それによって排気ガスの酸素濃度が低下するため、ＮＯｘ吸着材からＮＯｘが放出される。この放出されたＮＯｘは外側触媒層１３の貴金属触媒によって還元浄化される。
【００８２】
また、ＮＯｘ吸着材の硫黄被毒の度合が高くなると、同じく燃料噴射量が増量されて空燃比のリッチ化が図られ、それによって排気ガス温度が上昇するとともに、触媒での酸化反応が活発になって、触媒温度が上昇するため、ＮＯｘ吸着材からＳＯｘが脱離する。よって、ＮＯｘ吸着材のＮＯｘ吸着能を再生させることができる。
【００８３】
なお、硫黄被毒時には空燃比をリッチにするとともに、点火時期のリタードによりさらに排気ガス温度の上昇を図るようにしてもよく、また、二次エアを触媒上流部位に供給して触媒における酸化反応を促進して、触媒の更なる昇温を図るようにしてもよい。
【図面の簡単な説明】
【図１】 本発明に係るエンジンの排気ガス浄化装置を示す図。
【図２】 本発明の実施形態に係る排気ガス浄化用触媒の層構造を示す断面図。
【図３】 同実施形態の実施例のフレッシュ時及びエージング後各々におけるＨＣ吸着率、ＨＣ酸化率、トータルのＨＣ浄化率、並びにＮＯｘ浄化率を示すグラフ図。
【図４】 本発明の参考形態に係る排気ガス浄化用触媒の層構造を示す断面図。
【図５】 同参考形態の参考例及び比較例のエージング後のＨＣ吸着率、ＨＣ酸化率、トータルのＨＣ浄化率、並びにＮＯｘ浄化率を示すグラフ図。
【図６】 β型ゼオライトへのＭｇ、Ｃａ、Ｓｒ及びＢａの担持量と、エージング後の該ゼオライトのＢＥＴ比表面積との関係を示すグラフ図。
【図７】 本発明に係るエンジンの燃料噴射制御を示すフロー図。
【図８】 各種のアルカリ金属又はアルカリ土類金属を担持させたβ型ゼオライトと、それら金属を担持していないβ型ゼオライトのエージング後の比表面積を示すグラフ図。
【符号の説明】
１ エンジン
２ 気筒
３ 燃料噴射弁
４ 燃焼室
５ 点火プラグ
６ 吸気通路
７ 排気通路
８ 排気ガス浄化用触媒
１１ 担体
１２ 内側触媒層
１３ 外側触媒層
１４ 中間触媒層[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to an exhaust gas purification catalyst and a method for producing the same.
[0002]
[Prior art]
  As an exhaust gas purifying catalyst for engines such as automobiles, a three-way catalyst that simultaneously performs oxidation of HC (hydrocarbon) and CO (carbon monoxide) and reduction of NOx (nitrogen oxide) is known. This is generally made of noble metals such as Pd, Pt, and Rh as active metals, alumina as a support material that stabilizes the active metals and expands the contact area with the gas to improve purification performance, and oxygen storage materials It is often constituted by ceria (co-catalyst) as (OSC). However, this three-way catalyst has poor purification performance when the exhaust gas temperature is low, and the NOx purification performance is greatly deteriorated when the engine air-fuel ratio becomes lean.
[0003]
  On the other hand, Japanese Patent Laid-Open No. 2001-113173 adsorbs HC and NOx discharged in the cold region immediately after starting the engine, and after the catalytic metal becomes active, the HC and NOx are removed. It is described that it is released and purified. The catalyst is formed by laminating a hydrocarbon adsorbent layer containing zeolite on the support surface and a catalyst metal layer containing noble metal and NOx adsorbent so that the former is on the inside. As the NOx adsorbent, an alkali metal or an alkaline earth metal is used, and the content ratio of the NOx adsorbent in the catalyst metal layer and the hydrocarbon adsorbent layer is 60/40 to 99/1 by weight.
[0004]
  In JP-A-11-13462, as a catalyst having a hydrocarbon adsorbent and a NOx adsorbent, a hydrocarbon adsorbent layer containing zeolite is formed on the surface of the carrier, and a catalyst metal layer is formed thereon. Alternatively, two layers are formed, and these layers are impregnated with a barium acetate solution and fired. Japanese Patent Application Laid-Open No. 9-79026 describes that a catalyst formed by coating a NOx adsorbent, an HC adsorbent, and a three-way catalyst on the same carrier is disposed in the middle of an exhaust pipe of an engine.
[0005]
[Problems to be solved by the invention]
  As described above, when the zeolite as the HC adsorbent and the alkali metal or the alkaline earth metal as the NOx adsorbent are used in combination, according to the study of the present inventors, the NOx adsorbing ability does not change much when exposed to high temperatures. However, it was found that the HC adsorption ability was significantly reduced. When the cause was studied, it was found that alkali metals and alkaline earth metals promote the structural destruction of zeolite when exposed to high temperatures.
[0006]
  FIG. 8 shows the results of examining the specific surface area after thermal aging of β-type zeolite not supporting NOx adsorbent and β-type zeolite supporting various alkali metals or alkaline earth metals as NOx adsorbent. Show. Thermal aging is to hold the specimen at a temperature of 800 ° C. for 24 hours. According to the figure, the specific surface area of the β-type zeolite carrying the NOx adsorbent is considerably lower than that of the β-type zeolite not carrying the NOx adsorbent.
[0007]
  An object of the present invention is to solve the problem of structural destruction of zeolite due to alkali metal or alkaline earth metal in an exhaust gas purifying catalyst using such zeolite and alkali metal or alkaline earth metal in combination. It is to improve.
[0008]
[Means for Solving the Problems]
  The present invention employs a technique for separating zeolite and alkali metal or alkaline earth metal on the same carrier in order to deal with such problems.
[0009]
  That is, the invention according to claim 1 is provided with a first layer containing zeolite and a second layer containing at least one metal selected from alkali metals and alkaline earth metals on the support surface,
The first layer is disposed on the inner side of the second layer,
  The metal content in the first layer is less than 1% of the metal content in the second layer.The
An intermediate layer is provided between the first layer and the second layer to prevent the metal from moving from the second layer to the first layer.This is an exhaust gas purifying catalyst.
[0010]
  Therefore, when the catalyst is exposed to a high temperature, it is avoided that the zeolite of the first layer is destroyed by the alkali metal or the alkaline earth metal, and the decrease in the specific surface area of the zeolite is prevented. Metals or alkaline earth metals can be effectively used to purify exhaust gas in each layer.
[0011]
Moreover, since the zeolite of the first layer is covered with the second layer, direct exposure to high-temperature exhaust gas is avoided, which is advantageous for preventing thermal degradation.
[0012]
Further, the zeolite of the first layer is protected from the alkali metal or alkaline earth metal of the second layer by the intermediate layer, and the structural destruction of the zeolite or the reduction of the specific surface area due to the alkali metal or alkaline earth metal is prevented.
[0013]
  As the zeolite, β-type zeolite is preferable, but other zeolites such as MFI may be adopted.
[0014]
  Claim 2The invention according toClaim 1In the exhaust gas purification catalyst described in
  The intermediate layer contains an oxide having the property of a solid acid.
[0015]
  Therefore, even if the alkali metal or alkaline earth metal in the second layer moves toward the first layer, it is captured by the acidic oxide or amphoteric oxide in the intermediate layer. A reduction in surface area is prevented. Examples of the oxide having the property of a solid acid include titania, zirconia, alumina, zeolite, silica, and ceria.
[0016]
  Claim 3The invention according to the present invention provides an exhaust gas purifying catalyst comprising, on a support surface, a first layer containing zeolite and a second layer containing at least one metal selected from alkali metals and alkaline earth metals. A manufacturing method of
  Coating the zeolite with the support to form the first layer;
  Step B carrying the metal on the support material;
  Coating the carrier with the metal-carrying support material to form the second layer, and
  The step A is performed before the step C.
[0017]
  Accordingly, since the alkali metal or alkaline earth metal is applied to the coating of Step C while being supported on the support material, it can be mixed into the previously formed first layer and adversely affect the zeolite. Less.
[0018]
  Claim 4The invention according toClaim 3In the method for producing an exhaust gas purifying catalyst described in
  In step B, firing is performed after the metal is supported on the support material,
  In the step C, the fired metal-supporting support material and a basic binder are mixed to form a slurry, and the second layer is formed by coating the slurry.
[0019]
  Therefore, since the alkali metal or alkaline earth metal is firmly supported on the support material by the firing in Step B, even if the slurry is formed in Step C, the amount eluted into the slurry is reduced. In addition, since the basic binder is used to form the second layer, the slurry becomes basic, and the amount of alkali metal or alkaline earth metal, which is a solid base, eluted further into the slurry. Therefore, when the second layer is formed, the alkali metal or alkaline earth metal is less likely to be mixed into the first layer and cause destruction of the zeolite.
[0020]
  Claim 5The invention according toClaim 4In the method for producing an exhaust gas purifying catalyst described in
  The basic binder is a zirconia binder.
[0021]
  Zirconia is a basic oxide, and since the slurry becomes basic, elution of alkali metal or alkaline earth metal into the slurry is reduced.
[0022]
  Claim 6The invention according toClaim 3In the method for producing an exhaust gas purifying catalyst described in
  A step D for forming an intermediate layer is provided between the step A and the step C.
[0023]
  Accordingly, the intermediate layer prevents the alkali metal or alkaline earth metal from moving toward the first layer, and the zeolite is protected from the alkali metal or alkaline earth metal.
[0024]
  Claim 7The invention according toClaim 6In the method for producing an exhaust gas purifying catalyst described in
  Step D is characterized in that the intermediate layer is formed of an oxide having the property of a solid acid.
[0025]
  Therefore, even if the alkali metal or alkaline earth metal moves toward the first layer, it is caught by the acidic oxide or amphoteric oxide in the intermediate layer, and the zeolite in the first layer is protected from the alkali metal or alkaline earth metal. The
[0026]
【The invention's effect】
  As described above, according to the first aspect of the invention, the first layer containing zeolite and the second layer containing at least one kind of metal selected from alkali metals and alkaline earth metals on the support surface. The content of the metal in the first layer is less than 1% of the content of the metal in the second layer, so that destruction of the zeolite by the alkali metal or alkaline earth metal is avoided, and the heat resistance of the catalyst Improves.Also,Since the first layer is disposed on the inner side of the second layer, direct exposure of the zeolite in the first layer to the high-temperature exhaust gas is avoided, which is advantageous for preventing thermal degradation.further,Since an intermediate layer is provided between the first layer and the second layer to prevent the movement of the metal from the second layer to the first layer, the zeolite is protected from alkali metal or alkaline earth metal, This is further advantageous for improving the heat resistance of the catalyst.
[0027]
  Claim 2According to the invention according toClaim 1In the exhaust gas purifying catalyst described in 1), since the intermediate layer contains an oxide having the property of a solid acid, the alkali metal or alkaline earth metal of the second layer moves toward the first layer. However, it remains in the intermediate layer, which is more advantageous for protecting the zeolite by the intermediate layer.
[0028]
  Claim 3According to the invention according to the present invention, in order to form the first layer containing zeolite, step A for coating the support on the support, and at least one metal selected from alkali metal and alkaline earth metal as the support material And the step C of coating the metal-supporting support material on the first layer of the carrier to form the second layer, so that the first layer is formed when the second layer is formed. The amount of alkali metal or alkaline earth metal mixed in the layer is reduced.
[0029]
  Claim 4According to the invention according toClaim 3In the method for producing an exhaust gas purifying catalyst described in the above, in step B, the metal is supported on the support material and then fired. In step C, the fired metal-supported support material and the basic material are basic. Since the slurry is formed by mixing with a binder and the second layer is formed by coating the slurry, the amount of alkali metal or alkaline earth metal eluted into the slurry is reduced, and the alkali metal or alkaline earth metal is reduced. Preventing mixing into the first layer is further advantageous.
[0030]
  Claim 5According to the invention according toClaim 4In the method for producing an exhaust gas purifying catalyst described in 1), the basic binder is a zirconia binder, which is advantageous for preventing elution of alkali metal or alkaline earth metal into a slurry.
[0031]
  Claim 6According to the invention according toClaim 3In the method for producing an exhaust gas purifying catalyst described in 1), since the step D for forming an intermediate layer is provided between the step A and the step C, the zeolite is protected from alkali metal or alkaline earth metal. This is advantageous.
[0032]
  Claim 7According to the invention according toClaim 6In the method for producing an exhaust gas purifying catalyst described in 1), in the above step D, the intermediate layer is formed by an oxide having the property of a solid acid, so that the zeolite is protected from alkali metal or alkaline earth metal. It becomes even more advantageous.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0034]
  In FIG. 1, 1 is a spark ignition engine of an automobile, 2 is its cylinder, 3 is a fuel injection valve for directly injecting fuel into the combustion chamber 4, 5 is an ignition plug, 6 is an intake passage, 7 is an exhaust passage. It is. An exhaust gas purification catalyst 8 is disposed in the exhaust passage 7.
[0035]
  [Practical formstate]
  <Configuration of exhaust gas purification catalyst>
  As shown in FIG. 2, the exhaust gas purification catalyst 8 includes an inner catalyst layer 12, an outer catalyst layer 13, and an intermediate catalyst layer 14 disposed between the catalyst layers 12 and 13 on the surface of the carrier 11. Is formed in layers.
[0036]
  The carrier 11 is a cordierite honeycomb carrier. The inner catalyst layer 12 contains zeolite and a binder, and further contains Ag and Bi. The outer catalyst layer 13 is formed of a catalyst component in which Pt, Rh, Ba, Sr, and Mg are supported on alumina and a ceria material as support materials, and a binder. The intermediate catalyst layer 14 contains a catalyst component in which Pd is supported on alumina and a ceria material as a support material, and a binder, and further contains Ag and Bi.
[0037]
  The zeolite functions as an HC adsorbent, and β-type zeolite having a Keiban ratio of 300 is used. The component in which Pt and Rh are supported on alumina and ceria serves as a three-way catalyst. Ba, Sr, and Mg adsorb NOx in the exhaust gas when the oxygen concentration of the exhaust gas is high (eg, 4% or more, A / F> 16 at the air-fuel ratio), and the oxygen concentration of the exhaust gas decreases ( When it becomes 2% or less, for example, it functions as a NOx adsorbent that releases adsorbed NOx. Activated alumina powder (γ-alumina) is employed as the alumina. The ceria material is an oxide containing a ceria component. In this example, the Ce · Pr double oxide (Ce_0.9Pr_0.1O₂) Is adopted. This ceria material acts as an oxygen storage material (OSC). An alumina binder is used as a binder for the inner catalyst layer 12 and the intermediate catalyst layer 14, and a basic binder (zirconia) is used as a binder for the outer catalyst layer 13.
[0038]
  Therefore, it can be said that the exhaust gas purification catalyst 8 is a lean NOx adsorption catalyst having an HC trap function.
[0039]
  <Method for producing exhaust gas purifying catalyst 8>
  Next, a method for producing the exhaust gas purification catalyst 8 will be described.
[0040]
  -Formation of catalyst powder-
  Activated alumina powder, the above-mentioned ceria material, palladium nitrate and water are mixed, dried and fired at 500 ° C. to form catalyst powder A.
[0041]
  Activated alumina powder, the above ceria material, barium acetate, strontium acetate, magnesium acetate, dinitrodiamine platinum nitrate, rhodium nitrate and water are mixed, dried and calcined at 500 ° C. to form catalyst powder B (step) B).
[0042]
  -Formation of inner catalyst coat layer-
  Zeolite and alumina binder (hydrated alumina) are mixed, water is added thereto, and mixed and stirred with a disperser to obtain a slurry. By immersing the honeycomb carrier 11 in this slurry and pulling it up and removing excess slurry by air blow, a predetermined amount of slurry is coated on the carrier. Thereafter, drying and baking at 500 ° C. are performed to form an inner catalyst coat layer (step A).
[0043]
  -Formation of intermediate catalyst coat layer-
  Using the catalyst powder A instead of the zeolite, an intermediate catalyst coat layer is formed by the same method as the formation of the inner catalyst coat layer (step D).
[0044]
  -Impregnation of Ag and Bi-
  The inner catalyst coat layer and the intermediate catalyst coat layer are impregnated with a mixed solution of silver nitrate and bismuth acetate, dried and fired at 500 ° C.
[0045]
  -Formation of outer catalyst coat layer-
  The catalyst powder B is used in place of the zeolite, the zirconia binder is used in place of the alumina binder, and the outer catalyst coat layer is formed by the same method as the formation of the inner catalyst coat layer (Step C).
[0046]
  <Example>
  By the above-described manufacturing method, an exhaust gas purifying catalyst was prepared in which the amount of each component supported on the inner catalyst layer 12, the outer catalyst layer 13, and the intermediate catalyst layer 14 was as follows.
Inner catalyst layer 12; β-type zeolite = 100 g / L
Outer catalyst layer 13; Pt = 3.5 g / L, Rh = 0.3 g / L, Ba = 30 g / L, Sr = 10 g / L, Mg = 10 g / L, alumina = 100 g / L, ceria material = 100 g / L
Intermediate catalyst layer 14; Pd = 2.0 g / L, alumina = 30 g / L, ceria material = 10 g / L
  The impregnation loading amount of Ag is 10 g / L, and the impregnation loading amount of Bi is 0.5 g / L.
[0047]
  The total supported amount of Ba, Sr and Mg in the inner catalyst layer 12 is less than 1% of the same total supported amount of the outer catalyst layer 13. This point was confirmed by the following experiments A and B.
[0048]
  In addition, the impurity in each catalyst layer is 1% or less. This also applies to other examples and comparative examples described later.
[0049]
  -Experiment A-
  10 g of the catalyst powder B, 3.8 g of zirconia binder, and 50 g of water were weighed and mixed, and the elution amounts of Ba, Sr and Mg from the catalyst powder B were quantitatively analyzed. The results are as shown in Table 1. According to the table, the total dissolution amount of Ba, Sr, and Mg is very small, 2.4% of the total supported amount of the catalyst powder B. In the catalyst powder B, Ba, Sr and Mg are carbonated by firing, but since the zirconia binder is basic and the mixed solution becomes basic, carbonates such as Ba are difficult to elute. . On the other hand, in the case of an alumina binder, the solution when mixed with the catalyst powder B and water by the acetic acid component contained therein is acidic, and carbonates such as Ba are easily eluted.
[0050]
[Table 1]

[0051]
  -Experiment B-
  A honeycomb having a capacity of 25 cc was dipped in water and pulled up, and water was dropped by air blow to determine the water absorption amount of the honeycomb. Further, after a β-type zeolite was supported at 100 g / L on a honeycomb having a capacity of 25 cc, the same water absorption treatment was performed, and the water absorption amount of the zeolite supported honeycomb was determined. The results are as shown in Table 2.
[0052]
[Table 2]

[0053]
  From the results in Table 2, the water absorption of β-type zeolite when the water absorption of the honeycomb is 2.0 g is 0.4 g (2.4 g−2.0 g = 0.4 g). That is, the ratio of water absorption is zeolite / honeycomb = 1/5. Accordingly, the total supported amount of Ba, Sr, and Mg on the β-type zeolite is 0.48% (2.4% × 1/5 = 0.48%) of the total supported amount of the catalyst powder B.
[0054]
  Accordingly, the total supported amount of Ba, Sr, and Mg in the inner catalyst layer 12 is less than 1% of the total supported amount of the outer catalyst layer 13.
[0055]
  <Evaluation test>
  About the said catalyst, HC purification performance, ie, HC adsorption rate, HC oxidation rate (percentage of adsorbed HC) and HC purification in fresh and after aging for 24 hours at 800 ° C. in the air atmosphere The rate (HC adsorption rate × HC oxidation rate) and the lean NOx purification rate were examined by rig testing.
[0056]
  The evaluation mode of HC purification performance is as follows.₂In the air stream, the catalyst inlet gas temperature was raised to 80 ° C. (2) With this temperature maintained, HC (benzene) was 1500 ppmC, NO was 100 ppm, O₂So that N becomes 1.0%₂HC, NO and O in gas₂(3) After that, only the introduction of HC gas is stopped, and the catalyst inlet gas temperature is raised from 80 ° C. to 400 ° C. at a rate of 30 ° C./min. Space velocity SV is 25000h^-1It was.
[0057]
  The HC adsorption rate was calculated based on the catalyst inlet HC concentration and the catalyst outlet HC concentration for 2 minutes in (2) above. The HC oxidation rate was calculated based on the amount of HC adsorbed on the catalyst in 2 minutes in (2) above and the concentration at the catalyst outlet HC at the time of temperature increase in (3) above.
[0058]
  Further, a cycle in which a simulated exhaust gas (gas composition A) of lean air-fuel ratio is flowed to the catalyst for 60 seconds, and then the simulated exhaust gas (gas composition B) rich in air-fuel ratio is flowed for 60 seconds by switching the gas composition. Was repeated five times, the gas composition was switched to the air-fuel ratio lean (gas composition A), the NOx purification rate for 60 seconds was measured from this switching point, and this was defined as the lean NOx purification rate. The catalyst temperature and simulated exhaust gas temperature are 350 ° C., the gas composition is as shown in Table 3, and the space velocity SV is 25000 h.^-1It was.
[0059]
[Table 3]

[0060]
  The result is shown in FIG. The decrease in HC adsorption rate due to aging is small. On the other hand, the HC oxidation rate is reduced by aging, but not so much. The lean NOx purification rate is slightly reduced by aging. Since the decrease in the HC adsorption rate is small, it can be seen that the β-type zeolite in the inner catalyst layer is hardly destroyed by aging, that is, its specific surface area is hardly decreased.
[0061]
  Bi impregnated in the intermediate catalyst layer 14 exists as the closest atom of the Pd atom, and Pd and Ag react to form a Pd—Ag alloy, that is, low temperature activity related to HC purification of Pd. It prevents the decrease or the amount of Ag effective for improving the HC adsorption performance from decreasing.
[0062]
  [Reference form]
  As shown in FIG. 4, the exhaust gas purifying catalyst 8 of this embodiment has an inner catalyst layer 12 and an outer catalyst layer 13 formed on the surface of a carrier 11 in layers. The support 11 and the inner catalyst layer 12 are implemented.StateIt is the same. The outer catalyst layer 13 is formed of a catalyst component in which Pt, Rh, Pd, Ba, Sr, and Mg are supported on alumina and a ceria material as a support material, and a binder. That is, the implementation formState andIn contrast, there is no intermediate catalyst layer, and Pd is contained in the outer catalyst layer 13. Other configurations are implementationsState andThe same.
[0063]
  Next, a method for producing the exhaust gas purification catalyst 8 will be described.
[0064]
  Activated alumina powder, the above ceria material, barium acetate, strontium acetate, magnesium acetate, dinitrodiamine platinum nitrate, rhodium nitrate, palladium nitrate and water are mixed, dried and calcined at 500 ° C. to form catalyst powder C To do.
[0065]
  Implementation of inner catalyst coat layerState andIt is formed in the same manner. The inner catalyst coat layer is impregnated with a mixed solution of silver nitrate and bismuth acetate and dried and fired at 500 ° C. After that, using the catalyst powder C,State andSimilarly, an outer catalyst coat layer is formed.
[0066]
  <Reference example>
  By the above-described manufacturing method, an exhaust gas purification catalyst was prepared in which the respective component loadings of the inner catalyst layer 12 and the outer catalyst layer 13 were as follows.
Inner catalyst layer 12; β-type zeolite = 100 g / L
Outer catalyst layer 13; Pt = 3.5 g / L, Rh = 0.3 g / L, Pd = 2.0 g / L, Ba = 30 g / L, Sr = 10 g / L, Mg = 10 g / L, alumina = 150 g / L, ceria material = 150 g / L
  The inner catalyst layer 12 has an Ag impregnation load of 10 g / L and Bi has an impregnation load of 0.5 g / L. The total supported amount of Ba, Sr and Mg in the inner catalyst layer 12 is less than 1% of the same total supported amount of the outer catalyst layer 13.
[0067]
  <Comparative example>
  the aboveReference exampleThe same inner catalyst coat layer was formed on the same carrier and Ag and Bi were impregnated and supported in the same manner. Next, a slurry formed by mixing activated alumina powder, the above ceria material, alumina binder and water is prepared, and this is coated on the inner catalyst coating layer, dried and baked at 500 ° C. to form the outer catalyst coating. A layer was formed. Next, by impregnating both the inner and outer catalyst coat layers with a mixed aqueous solution of barium acetate, strontium acetate, magnesium acetate, dinitrodiamine platinum nitrate, rhodium nitrate and palladium nitrate, drying and firing at 500 ° C. A comparative catalyst was obtained. The amount of each component supported is as follows.
Inner catalyst layer 12; β-type zeolite = 100 g / L
Outer catalyst layer 13; alumina = 150 g / L, ceria material = 150 g / L
  The inner catalyst layer 12 has an Ag impregnation load of 10 g / L and Bi has an impregnation load of 0.5 g / L. The amount of each precious metal and NOx adsorbent supported by the inner catalyst layer 12 and the outer catalyst layer 13 is Pt = 3.5 g / L, Rh = 0.3 g / L, Pd = 2.0 g / L, Ba = 30 g / L, Sr = 10 g / L, Mg = 10 g / L.
[0068]
  <Comparison test>
  the aboveReference exampleAnd the comparative example for both catalystsStateThe HC purification performance and lean NOx purification performance after aging were investigated by the same method as in the case. The result is shown in FIG. According to the figure, although there is almost no difference in the lean NOx purification rate, the HC adsorption rate isReference exampleIs much higher. this is,Reference exampleIn this case, it is considered that the structure destruction of the zeolite in the inner catalyst layer 12 or the decrease in the specific surface area was small even after aging.
[0069]
  Also, regarding HC oxidation rateReference exampleIs much higher. In the case of the comparative example, noble metals such as Pt are impregnated and supported on the zeolite, which is considered to cause sintering due to the destruction of the zeolite. That meansReference exampleIn this case, it is considered that noble metals are supported on the alumina and ceria material of the outer catalyst layer 13 and there is no problem of a decrease in activity due to structural destruction of the zeolite.
[0070]
  <Effect of NOx adsorbent loading on specific surface area of zeolite>
  FIG. 6 shows a comparison between a sample in which 0.2 mol of Mg, Ca, Sr and Ba are supported on 100 g of β-type zeolite and a sample in which 0.05 mol is supported, by measuring the BET specific surface area after aging.
[0071]
  From the figure, when the amount of Mg, Ca, Sr, Ba (NOx adsorbent) supported on the zeolite is large, the structural destruction of the zeolite progresses due to aging, and the specific surface area decreases. It can be seen that reducing the amount of NOx occlusion material supported on zeolite as much as possible is effective for the HC purification performance.
[0072]
  <About lean burn engine control>
  The exhaust gas purification catalyst according to the above embodiment contains a NOx adsorbent such as Ba and adsorbs NOx in the exhaust gas when the air-fuel ratio is lean. Therefore, when the NOx adsorption amount increases, it is necessary to reduce and purify the air-fuel ratio by making it rich (lowering the oxygen concentration of the exhaust gas). Further, the NOx adsorbent has a problem of so-called sulfur poisoning, in which sulfur contained in the exhaust gas is adsorbed in the form of sulfur oxide to form a salt, thereby losing the function as the NOx adsorbent. Therefore, in this case, it is necessary to regenerate the catalyst by increasing the temperature. Hereinafter, fuel injection control for regeneration from NOx release and sulfur poisoning will be described.
[0073]
  As shown in FIG. 7, in step S1 after the start, various data such as the intake air amount of the engine, the engine speed, the accelerator opening, and the catalyst temperature are input. Subsequently, in step S2, an appropriate target air-fuel ratio corresponding to the operating state of the engine is set from various data, and a basic fuel injection amount Qpb is set.
[0074]
  In the subsequent step S3, the NOx adsorption amount NOe of the catalyst is estimated, and in the subsequent step S4, the SOx (sulfur oxide) adsorption amount SOe of the catalyst is estimated. When the air-fuel ratio is lean, a map prepared by previously obtaining the NOx adsorption amount and SOx adsorption amount in each engine operating state (engine speed and engine load) by experiment is referred to, and the NOx adsorption amount is determined from the engine operating state at that time. Then, the NOx adsorption amount NOe and the SOx adsorption amount SOe are estimated by obtaining and integrating the SOx adsorption amount. When the air-fuel ratio is rich (the excess air ratio λ ≦ 1), the NOx adsorption amount NOe and the SOx adsorption amount SOe are decreased with a larger subtraction constant as λ is smaller and the rich time is longer.
[0075]
  In the following step S5, it is determined whether or not the NOx adsorption amount NOe is larger than a predetermined threshold NOo (NOx adsorption amount that is considered to have increased to the extent that NOx release control should be performed (NOx adsorption capacity decreases)). To do. When NOe> NOo, the routine proceeds to step S6, where it is determined whether or not the previous value of the counter TN is zero. This counter TN corresponds to the time during which the fuel injection amount increase control is performed.
[0076]
  When the previous value of the counter TN is zero, the process proceeds to step S7 to set the counter threshold value TNO, and then proceeds to step S8 to increment the counter TN. When the previous value of TN is not zero, the process proceeds directly from step S6 to S8. Then, the counter TN is incremented. The threshold value TNO is set to a small value in a temperature range (for example, 200 to 400 ° C.) at which NOx is likely to be released, and to a large value in other temperature ranges based on the current catalyst temperature. The threshold value TN0 may be set in a range of about 0.5 to 5 seconds in real time.
[0077]
  In a succeeding step S9, it is determined whether or not the counter TN is larger than the threshold value TNo. If the counter TN is equal to or smaller than the threshold value TNo, the process proceeds to step S10, where the rich fuel injection amount Qpλ is given as the fuel injection amount Qpb, and fuel injection is executed when this is the predetermined crank timing. (Steps S11 and S12). If counter TN> threshold value TNO in step S9, the process proceeds to step S13 to reset the counter TN and the NOx adsorption amount estimated value NOe, and execute fuel injection with the basic fuel injection amount Qpb.
[0078]
  On the other hand, when the estimated value NOe of the NOx adsorption amount is equal to or less than the threshold value NO in step S5, the process proceeds to step S14 to determine whether or not the counter TN is counting. If it is counting, it will progress to step S8 and will continue NOx discharge | release control. If not counting, the process proceeds to step S15, and whether or not the estimated value SOe of the SOx adsorption amount has become larger than a predetermined threshold value SOo (the SOx adsorption amount that is considered to have been poisoned with sulfur enough to perform SOx release control). Determine. When SOe is equal to or less than SOo, the routine proceeds to step S11, where fuel injection is executed with the basic fuel injection amount Qpb (steps S11, S12).
[0079]
  When the estimated value SOe of the SOx adsorption amount is larger than SOo, the process proceeds to step S16 to determine whether or not the previous value of the counter TS is zero. This counter TS corresponds to the time during which the fuel injection amount increase control is performed. When the previous value of TS is zero, the process proceeds to step S17 to set the counter threshold value TSo and then proceeds to step S18 to increment the counter TS. When the previous value of TS is not zero, the process proceeds directly from step S16 to S18. The counter TS is incremented. The threshold value TSo is set to a smaller value as the catalyst temperature is higher if it is equal to or higher than a predetermined value (for example, 400 ° C.) based on the current catalyst temperature. The threshold value TSo may be set within a range of about 1 to 10 minutes in real time.
[0080]
  In a succeeding step S19, it is determined whether or not the counter TS is larger than the threshold value TSo. When the counter TS is larger than the threshold value TSo, the routine proceeds to step S10, where the rich fuel injection amount Qpλ is given as the fuel injection amount Qpb, and the fuel injection is executed when this is the predetermined crank timing as the fuel injection amount Qp. (Steps S11 and S12). If counter TS> threshold value TSo in step S19, the process proceeds to step S20 to reset the counter TS, the SOx adsorption amount estimated value SOe, and the NOx adsorption amount estimated value NOe, and execute fuel injection at the basic fuel injection amount Qpb. (Steps S11 and S12).
[0081]
  As described above, when the NOx adsorption amount of the NOx adsorbent increases, the fuel injection amount is increased and the air-fuel ratio is enriched even when the engine is in an air-fuel ratio lean operation state. Since the oxygen concentration decreases, NOx is released from the NOx adsorbent. The released NOx is reduced and purified by the noble metal catalyst of the outer catalyst layer 13.
[0082]
  In addition, when the degree of sulfur poisoning of the NOx adsorbent increases, the fuel injection amount is also increased and the air-fuel ratio is enriched. As a result, the exhaust gas temperature rises and the oxidation reaction at the catalyst becomes active. Thus, since the catalyst temperature rises, SOx is desorbed from the NOx adsorbent. Therefore, the NOx adsorption capacity of the NOx adsorbent can be regenerated.
[0083]
  When sulfur is poisoned, the air-fuel ratio may be made rich, and the exhaust gas temperature may be further increased by retarding the ignition timing. Also, secondary air is supplied to the upstream portion of the catalyst to oxidize the catalyst. May be promoted to further increase the temperature of the catalyst.
[Brief description of the drawings]
FIG. 1 is a diagram showing an exhaust gas purification device for an engine according to the present invention.
FIG. 2 is an embodiment of the present invention.StateSectional drawing which shows the layer structure of the catalyst for exhaust gas purification which concerns.
[Fig. 3] Same embodimentStateThe graph which shows HC adsorption | suction rate, HC oxidation rate, total HC purification rate, and NOx purification rate at the time of fresh and after aging of an Example.
FIG. 4 of the present inventionReference formSectional drawing which shows the layer structure of the exhaust gas purification catalyst which concerns on.
[Figure 5] SameReference formofreferenceThe graph which shows HC adsorption | suction rate after aging of an example and a comparative example, HC oxidation rate, total HC purification rate, and NOx purification rate.
FIG. 6 is a graph showing the relationship between the amount of Mg, Ca, Sr and Ba supported on β-type zeolite and the BET specific surface area of the zeolite after aging.
FIG. 7 is a flowchart showing fuel injection control of the engine according to the present invention.
FIG. 8 is a graph showing the specific surface area after aging of β-type zeolite supporting various alkali metals or alkaline earth metals and β-type zeolite not supporting these metals.
[Explanation of symbols]
    1 engine
    2-cylinder
    3 Fuel injection valve
    4 Combustion chamber
    5 Spark plug
    6 Air intake passage
    7 Exhaust passage
    8 Exhaust gas purification catalyst
  11 Carrier
  12 Inner catalyst layer
  13 Outer catalyst layer
  14 Intermediate catalyst layer

Claims (7)

The support surface includes a first layer containing zeolite and a second layer containing at least one metal selected from alkali metals and alkaline earth metals,
The first layer is disposed on the inner side of the second layer,
The content of the metal in the first layer Ri der less than 1% of the content of the metal in the second layer,
An exhaust gas purifying catalyst, characterized in that an intermediate layer that prevents movement of the metal from the second layer to the first layer is provided between the first layer and the second layer . In the exhaust gas purifying catalyst according to claim 1 ,
The exhaust gas purifying catalyst, wherein the intermediate layer contains an oxide having the property of a solid acid. A method for producing an exhaust gas purifying catalyst, comprising: a first layer containing zeolite on a support surface; and a second layer containing at least one metal selected from alkali metals and alkaline earth metals. And
Coating the zeolite with the support to form the first layer;
Step B carrying the metal on the support material;
Coating the carrier with the metal-carrying support material to form the second layer, and
A method for producing an exhaust gas purifying catalyst, characterized in that the step A is performed before the step C. In the manufacturing method of the exhaust gas purifying catalyst according to claim 3 ,
In step B, firing is performed after the metal is supported on the support material,
In the step C, the fired metal-supporting support material and a basic binder are mixed to form a slurry, and the second layer is formed by coating the slurry. Method. In the manufacturing method of the exhaust gas purifying catalyst according to claim 4 ,
The method for producing an exhaust gas purifying catalyst, wherein the basic binder is a zirconia binder. In the manufacturing method of the exhaust gas purifying catalyst according to claim 3 ,
A method for producing an exhaust gas purifying catalyst, comprising the step D of forming an intermediate layer between the step A and the step C. In the manufacturing method of the exhaust gas purifying catalyst according to claim 6 ,
In step D, the intermediate layer is formed of an oxide having a solid acid property.

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