JP3786522B2 - Exhaust gas purification catalyst - Google Patents
Exhaust gas purification catalyst Download PDFInfo
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- JP3786522B2 JP3786522B2 JP20050098A JP20050098A JP3786522B2 JP 3786522 B2 JP3786522 B2 JP 3786522B2 JP 20050098 A JP20050098 A JP 20050098A JP 20050098 A JP20050098 A JP 20050098A JP 3786522 B2 JP3786522 B2 JP 3786522B2
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
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Description
【0001】
【発明の属する技術分野】
本発明は、内燃機関、殊にディーゼルエンジンからの排ガス中に含まれる窒素酸化物(NOx)を低減させ、排ガスを浄化するための触媒に関する。
【0002】
【従来の技術】
自動車等の内燃機関での燃料の燃焼に伴って発生するNOxを含む排ガスを処理して、そのNOx含量を低減させるための触媒として種々のものが提案されている。その例として銅−ゼオライト触媒、すなわちNa型のZSM−5ゼオライトのNaイオンをCuイオンで交換した、銅イオン交換ゼオライト触媒、あるいは白金−アルミナ触媒等がある。これらのものは、典型的にはコージェライトなどのセラミックスから作られた多数の透通孔を有するモノリスハニカム担体、あるいはステンレス鋼の様な金属の平坦な箔とコルゲート箔を組合せて(すなわち積重して)作成されるモノリスハニカム担体等の表面にバインダーを用いてコーティングされ、排ガス管中に配置され、排ガス接触処理のために使用される。銅−ゼオライト触媒では、ゼオライト細孔内に銅イオンが存在することにより約300〜500℃の温度範囲でNOx低減活性が発現するが、銅−ゼオライト触媒は排ガス中の水熱共存条件下で活性が使用時間の経過によって低下(劣化)するという欠点がある。この原因はゼオライトの細孔中へ排ガスから水分やSO2が入り込み、そこに存在する銅(イオン状態)に対し悪作用を及ぼすためと考えられる。従って銅−ゼオライト触媒は満足すべき実用性を有しない。また公知のPt−アルミナ触媒については、NOx低減活性温度範囲が狭く、一般的には約160〜300℃の温度で有意なNOx低減効果を示すが、この範囲外ではNOx低減の実用的効果が認め難い。
【0003】
従って、排ガス浄化用触媒の使用寿命を延長し、NOx低減活性温度範囲を拡張し、かつNOx低減効果を改善する必要性がある。
【0004】
【発明が解決しようとする課題】
本発明者は、上記の公知技術の欠点に鑑み、排ガス浄化用触媒のNOx低減作用が排ガスの低温域から高温域までの広い温度範囲にわたって、高い効率で発揮され、そのNOx低減作用が長期間維持される触媒の構成を見出すべく鋭意研究検討を実施し、その結果として本発明を完成するに至った。
【0005】
【課題を解決するための手段】
従って本発明の一態様によれば、ゼオライト及び/または金属フェライトからなるマトリックス上または中に銅酸化物粒子を分散させてなる排ガス浄化触媒が提供される。本発明のこの態様の排ガス浄化触媒は、一般に該マトリックス材の粉末と銅酸化物をバインダーと共に均質混合物となし、バインダーで固結した状態にあり、銅酸化物粒子が触媒活性種としてマトリックス中または上に分散されている。
【0006】
本発明の排ガス浄化触媒におけるゼオライト及び/または金属フェライトからなるマトリックスと銅酸化物の組成割合は、前者(マトリックス)が50〜99.9重量%、好ましくは65〜99.5重量%、さらに好ましくは70〜99重量%、そして後者が0.1〜50重量%、好ましくは0.5〜35重量%、さらに好ましくは1〜30重量%である。触媒のマトリックスをなすゼオライト及び金属フェライトはそれぞれ単独で、あるいは任意の混合比率の混合物で使用することができるが、金属フェライトは触媒活性種の銅酸化物(殊に亜酸化銅)の触媒活性を向上させその劣化を遅らせ、触媒寿命を延長する傾向があることが認められた。
【0007】
本発明で使用しうるゼオライトの例としては、ZSM−5、モルデナイト、フェリエライト、Y型、SAPO等及びその他があるが、ZSM−5が好適である。本発明で使用しうる金属フェライトは、一般式MO・Fe2O3で表わされる組成の鉄酸化物類であり、Mは2価の金属イオン(例:マンガン、鉄、コバルト、ニッケル、銅、亜鉛等の2価イオン)である。使用しうる金属フェライトの例はCoFe2O4、CuFe2O4、ZnFe2O4等である。本発明における銅酸化物とは、CuO(酸化銅)、Cu2O(亜酸化銅)等を包含するものである。マトリックス及び銅酸化物を固結するためのバインダーの好適な例としては、アルミナゾル、シリカゾルがあり、硝酸アルミニウム、タルク等を使用することもでき、また炭水化物(デンプン等)類及びポリビニルアルコール等の有機系バインダーも公知である。
【0008】
本発明の触媒を調製するには、マトリックス材料の粉末及び銅酸化物粉末を前記の割合で混合し、さらに水及びバインダーを混入して、均質になるまで撹拌しスラリーを形成する。一般的にはコージェライト等の耐火性セラミック製のハニカム担体の表面に上記スラリーをコーティングし、乾燥し、焼成処理することにより、ハニカム担体の表面上に固結した状態の触媒とすることができる。この場合の組成の一例を挙げると:
酸化銅(CuO) 10重量部
マトリックス材料(単独または混合物) 40重量部
バインダー(シリカゾル) 10重量部
水 50重量部
コーティング後の乾燥は約90〜110℃程度の温度で数時間例えば1〜5時間行ない、次の焼成処理工程は約400〜800℃好ましくは約500〜600℃前後の温度で約2〜10時間、例えば6時間実施する。
【0009】
あるいは別法として上記スラリーの粘度を、水の少量使用によって、押出加工可能な粘度まで上げ、ペレット、あるいはハニカム等の成形品となし、これを乾燥、焼成することにより固結した触媒を得ることができる。上記のスラリーの組成例における水の代りに、またはそれに加えて、揮発性または蒸発性の有機溶媒、例えばアルコールを用いることもできる。
【0010】
本発明の上記の態様による銅酸化物−ゼオライト触媒を排ガス処理に使用する場合、ゼオライトは排ガスが例えばほぼ250℃位までの低温であるときに炭化水素を吸蔵する傾向を示し、排ガスが高温になるとその吸蔵炭化水素が脱離される。また排ガスが低温であるとき、NOxは銅酸化物に吸着されその際に例えばNOが一層反応性の高いNO2にまで酸化され、排ガスが高温となったときにはそのNO2が放出され、ゼオライトから脱離される炭化水素がそのNO2のための還元剤として直ちに有効に作用できる状態が発生するものと考えられる。従って高温の際に炭化水素を放出するゼオライト粒子に隣接している銅酸化物粒子の近傍においてその放出炭化水素(還元剤)とNOxとの反応が容易に進行する微小環境が形成しているものと推量される。そのため銅酸化物粒子の数に対応する多数の微小反応活性環境(活性点)が触媒体内に存在しNOx低減効果及び効率を高めるものと考えられる。さらには銅酸化物は銅イオン(従来の銅−ゼオライト触媒における銅の存在形態)よりも硫黄化合物からの化学的攻撃を受け難いものと思われ、このことは本発明の触媒の高耐久性(長寿命)に反映している。
【0011】
本発明の上記態様による銅酸化物−金属フェライト触媒において触媒活性が高い理由としては、排ガス流中で金属フェライト中のFeが高温度になるに従って2価から3価に酸化され、それに隣接している酸化銅が連動的にかつ相対的に還元される傾向となり、それにより触媒活性が発現され、増進されると考えられ、温度が低くなると逆の傾向が生じ、酸化銅が安定化されて例えばS化合物等により攻撃され難くなり触媒寿命が延長されるのではないかと推量される。
【0012】
さらに本発明の研究開発中に上記銅酸化物−ゼオライト(及び/または金属フェライト)触媒に対して白金、ロジウム、イリジウム及び銀から選択される少なくとも1種の貴金属粒子を添加すると排ガス低温時のNOx低減効果が顕著に改善され、それにより有効な触媒活性温度範囲が大幅に拡張されることを見出した。
【0013】
従って本発明の別の一態様によれば、ゼオライト及び/または金属フェライトからなるマトリックス上または中に白金(Pt)、ロジウム(Rh)、イリジウム(Ir)及び銀(Ag)から選択される少なくとも1種の貴金属粒子、及び銅酸化物粒子を分散させてなる排ガス浄化触媒が提供される。この態様による触媒の組成割合は、例えば、マトリックス材料が50〜99.8重量%、好ましくは65〜99.4重量%、さらに好ましくは70〜99重量%;銅酸化物が0.1〜49.9重量%、好ましくは0.5〜40重量%、さらに好ましくは1〜30重量%;そして上記貴金属が0.01〜20重量%、好ましくは0.05〜15重量%、さらに好ましくは0.1〜15重量%;である。この態様による銅酸化物−貴金属−マトリックス触媒の調製は、前記の銅酸化物−ゼオライト触媒と同様な技法で行なうことができる。すなわち、上記のような組成割合のマトリックス材料の粉末、銅酸化物粉末及び上記の貴金属源(金属の粉末;あるいは塩化白金酸のような貴金属化合物)を混合し、さらに水及びバインダー(例:シリカゾルまたはアルミナゾル)を混入して均質になるまで撹拌しスラリーを形成する。耐火性セラミック製または耐熱性金属箔製等のハニカム担体の表面に上記スラリーをコーティングし、乾燥し、焼成処理をすることにより、ハニカム担体の表面上に固結した状態の触媒を得ることができ、このものは排気ガス管中に装着して使用できる。貴金属源として貴金属自体の粉末ではなく塩化金属酸のような貴金属化合物を用いる場合には、焼成処理段階においては公知の条件下、例えば少量の水素(1%程度)を含む窒素ガス雰囲気中で約500〜900℃の温度で数時間(例えば約3.5〜10時間)の処理時間で実施して焼成を完結するのが好ましい。銅酸化物−貴金属(Pt、Rh、Ir、Agの少なくとも1種)−マトリックス触媒において使用される各成分の概略の組成(重量部基準)範囲の例を挙げると下記の通りである。
【0014】
マトリックス材料(単独または混合物) 約90〜99重量部
銅酸化物 約0.1〜20重量部
貴金属 約0.01〜20重量部
この態様の触媒も、前記と同様に可塑性スラリーの押出加工によってペレットあるいは好ましくはハニカムの成型品となし、これを乾燥、焼成することにより使用に供することができる。スラリー形成にアルコールような有機溶媒を採用しうることも同様である。
【0015】
(実施例)
本発明の触媒を以下の実施例及び比較例によりさらに詳しく説明するが、本発明はこれらの実施例に限定されるものではない。
【0016】
比較例(対照Cuイオン交換ゼオライト触媒の調製)
ナトリウム(Na+)型ZSM−5ゼオライトを用い、公知方法により、硝酸銅[Cu(NO3)2]溶液を用いCu++イオンで交換処理することにより、2重量%のCuを含むCuイオン交換ゼオライトZSM−5を得た。この粉末を乾燥(105℃、5時間)及び焼成(500℃、3時間)の処理を行ないCuイオンをゼオライトに固定した。この生成物(乾燥物;50重量部)、シリカゾルバインダー(10重量部)及び水(50重量部)を良く混合して均質スラリーとした。コージェライト製円筒状ハニカム(直径30mm;容積21cc;セル数400cpi)を上記のスラリーに浸漬し、引き上げ、余剰付着スラリーを空気ジェットで吹き払い、乾燥し(105℃×5時間)、空気雰囲気中500℃で5時間焼成し触媒ユニットを得た。以下これを「Cu−ZSM−5」と表示する。
【0017】
実施例1(CuO−ゼオライト触媒の調製)
プロトン型ZSM−5ゼオライト粉末(47重量部)、酸化銅(CuO)粉(1.2重量部)、シリカゾルバインダー(11.8重量部)及び水(50重量部)を混合して均質スラリーとなし、これに比較例で使用のものと同じハニカム担体を浸漬し、引き上げたハニカム担体の表面の余剰付着スラリーを空気ジェットで吹き払い、105℃で5時間乾燥し、次いで空気雰囲気中500℃で5時間焼成した。この触媒ユニットを(CuO−ZSM−5)と表示する。
【0018】
実施例2(Cu2O−ゼオライト触媒の調製)
実施例1の操作において酸化銅の代りに同量の亜酸化銅(Cu2O)粉末を用いて実施例1の操作を繰り返した。この触媒ユニットを「Cu2O−ZSM−5」と表示する。
【0019】
実施例3(CuO−ロジウム−ゼオライト触媒の調製)
実施例1の操作のスラリー形成工程において金属ロジウム粉末(0.7重量部)を添加して均質スラリーとし、それ以外は実施例1の操作に準拠して触媒ユニットを調製した。これを「CuO−Rh−ZSM−5」と表示する。
【0020】
実施例4(Cu2O−イリジウム−ゼオライト触媒の調製)
実施例2の操作のスラリー形成工程において金属イリジウム粉末(0.7重量部)を添加して均質スラリーとし、それ以外は実施例2の操作に準拠して触媒ユニットを調製した。これを「Cu2O−Ir−ZSM−5」と表示する。
【0021】
実施例5(Cu2O−銀−ゼオライト触媒の調製)
実施例3の金属イリジウム粉末の代りに同量の金属銀粉末を用いて、実施例3の操作に準拠して触媒ユニットを得た。これを「Cu2O−Ag−ZSM−5」と表示する。
【0022】
NOx低減試験
上記の比較例及び実施例のそれぞれの触媒ユニットを固定床流通式反応装置に装着しディーゼルエンジン排ガスを模擬した下記組成のガス混合物を空間速度(SV)=50,000hr-1で、触媒入口温度を種々に変えて、触媒ユニットから流出するガス組成を分析することによりNOx低減率を測定した。種々の触媒入口温度でのNOx低減率(%)のデータは下記の通りであった。
貴金属を添加した触媒についての種々の触媒温度でのNOx低減率(%)のデータは下記の通りであった。
【0023】
炭化水素(HC)低減率
上記のNOx低減率の測定と並行して、触媒ユニットCu−ZSM−5(比較例)、CuO−ZSM−5(実施例1)及びCu2O−ZSM−5(実施例2)についてHC低減率(%)を測定した。
【0024】
触媒の耐久性の試験
前記組成の模擬ガスを用いて劣化促進(水、SO2共存下)連続耐久試験を実施し試験の前後でのNOx低減率の比較をした。前記のNOx低減率試験と同一の装置を用い500℃の一定触媒入口温度で模擬ガスを50,000hr-1の空間速度で連続50時間供給した。この試験期間の初期及び終期におけるNOx低減率は下記の通りであった。
【0025】
実施例6(Cu2O−金属フェライト触媒の調製)
CoFe2O4フェライト粉末(47重量部)、亜酸化銅(Cu2O)粉末(1.2重量部)、シリカゾルバインダー(11重量部)及び水(50重量部)を混合撹拌して均質スラリーとした。コージェライト製円筒状ハニカム(直径30mm;容積21cc;セル数400cpi)を上記スラリーに浸漬し、引き上げ、余剰付着スラリーを空気ジェットで吹き払い、乾燥し(105℃×5時間)、空気雰囲気中500℃で5時間焼成し触媒ユニットを得た。以下これを「Cu2O−Coフェライト」と表示する。
【0026】
実施例7
CoFe2O4フェライト粉末の代りに同量のCuFe2O4フェライト粉末を用いて実施例6の操作を繰り返した。以下この触媒ユニットを「Cu2O−Cuフェライト」と表示する。
【0027】
実施例8(Cu2O−ゼオライト−金属フェライト触媒の調製)
47重量部のCoFe2O4フェライト粉末の代りに、実施例1で使用のプロント型ZSM−5ゼオライト粉末(23.5重量部)及びZnFe2O4フェライト粉末(23.5重量部)を用いて実施例6の操作を繰り返した。以下この触媒を「Cu2O−ZSM−5−Znフェライト」と表示する。
【0028】
実施例9(Cu2O−イリジウム−金属フェライト触媒の調製)
実施例7のスラリー形成工程において金属イリジウム粉末(0.7重量部)を添加して、実施例7の操作を繰り返した。以下この触媒を「Cu2O−Ir−Cuフェライト」と表示する。
【0029】
実施例10(Cu2O−ロジウム−ゼオライト−金属フェライト触媒の調製)
実施例8のスラリー形成工程において金属ロジウム粉末(0.7重量部)を添加して、実施例8の操作を繰り返した。以下この触媒を「Cu2O−Rh−ZSM−5−Znフェライト」と表示する。
【0030】
NOx低減試験
実施例6(Cu2O−Coフェライト)、実施例7(Cu2O−Cuフェライト)、実施例8(Cu2O−ZSM−5−Znフェライト)、実施例9(Cu2O−Ir−Cuフェライト)及び実施例10(Cu2O−Rh−ZSM−5−Znフェライト)の各触媒を前記NOx低減試験に付し、下記のNOx低減率(%)のデータを得た。
NOx低減率(%)
【0031】
炭化水素(HC)低減率
これらのNOx低減率と平行して測定した炭化水素(HC)低減性能は、すべての触媒について、前記の実施例1及び2の触媒と同様に良好であった。
【0032】
耐久性
実施例6〜10の触媒を前記耐久性試験に付し、所定の試験期間の初期及び終期におけるNOx低減率の差(△%)を求めた。
【0033】
【発明の効果】
以上から明らかなように本発明の銅酸化物粒子を分散させたゼオライト及び/または金属フェライトからなる触媒及び銅酸化物粒子及び貴金属粒子を分散させたゼオライト及び/または金属フェライトからなる触媒は、排ガスの浄化効率(活性)及び有効活性温度範囲において顕著な改善効果を奏しさらには耐使用期間においても大幅な改善を示した。
【図面の簡単な説明】
【図1】比較例、実施例1〜2の触媒の種々の触媒入口温度におけるNOx低減率を示すグラフ。
【図2】比較例、実施例1〜2の触媒の炭化水素低減率の比較を示すグラフ。
【図3】比較例、実施例1、実施例3の触媒のNOx低減率の比較を示すグラフ。
【図4】比較例、実施例2、実施例4の触媒のNOx低減率の比較を示すグラフ。
【図5】比較例、実施例2、実施例5の触媒のNOx低減率の比較を示すグラフ。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a catalyst for purifying exhaust gas by reducing nitrogen oxides (NOx) contained in exhaust gas from an internal combustion engine, particularly a diesel engine.
[0002]
[Prior art]
Various catalysts have been proposed as a catalyst for treating exhaust gas containing NOx generated by combustion of fuel in an internal combustion engine such as an automobile and reducing the NOx content. Examples include a copper-zeolite catalyst, that is, a copper ion-exchanged zeolite catalyst obtained by exchanging Na ions of Na-type ZSM-5 zeolite with Cu ions, or a platinum-alumina catalyst. These are typically monolith honeycomb carriers with a large number of through holes made from ceramics such as cordierite, or a combination of flat and corrugated foils of metal such as stainless steel (ie stacking). The surface of a monolith honeycomb carrier or the like to be produced is coated with a binder, placed in an exhaust gas pipe, and used for exhaust gas contact treatment. The copper-zeolite catalyst exhibits NOx reduction activity in the temperature range of about 300 to 500 ° C. due to the presence of copper ions in the zeolite pores, but the copper-zeolite catalyst is active under hydrothermal coexistence conditions in the exhaust gas. However, there exists a fault that it falls (deteriorates) with progress of use time. This is thought to be because moisture and SO 2 enter the pores of the zeolite from the exhaust gas and have an adverse effect on the copper (ionic state) present there. Accordingly, copper-zeolite catalysts do not have satisfactory utility. In addition, the known Pt-alumina catalyst has a narrow NOx reduction activation temperature range, and generally shows a significant NOx reduction effect at a temperature of about 160 to 300 ° C., but outside this range, there is a practical effect of NOx reduction. It's hard to recognize.
[0003]
Therefore, there is a need to extend the service life of the exhaust gas purifying catalyst, extend the NOx reduction activation temperature range, and improve the NOx reduction effect.
[0004]
[Problems to be solved by the invention]
In view of the above-mentioned drawbacks of the known technology, the present inventor has demonstrated that the NOx reduction action of the exhaust gas purifying catalyst is exhibited with high efficiency over a wide temperature range from the low temperature range to the high temperature range of the exhaust gas, and the NOx reduction action is long-term In order to find out the composition of the catalyst to be maintained, intensive research and examination were conducted, and as a result, the present invention was completed.
[0005]
[Means for Solving the Problems]
Therefore, according to one aspect of the present invention, there is provided an exhaust gas purification catalyst in which copper oxide particles are dispersed on or in a matrix made of zeolite and / or metal ferrite. The exhaust gas purifying catalyst of this aspect of the present invention generally comprises a powder of the matrix material and copper oxide in a homogeneous mixture together with a binder, and is solidified with the binder, and the copper oxide particles are used as catalytically active species in the matrix or Distributed over.
[0006]
The composition ratio of the matrix composed of zeolite and / or metal ferrite and the copper oxide in the exhaust gas purification catalyst of the present invention is 50 to 99.9% by weight, preferably 65 to 99.5% by weight, more preferably 50% to 99.5% by weight. Is 70 to 99% by weight, and the latter is 0.1 to 50% by weight, preferably 0.5 to 35% by weight, more preferably 1 to 30% by weight. Zeolite and metal ferrite that form the catalyst matrix can be used alone or in a mixture of any mixing ratio. However, metal ferrite has the catalytic activity of catalytically active copper oxide (especially cuprous oxide). It has been observed that there is a tendency to improve and delay its degradation and prolong catalyst life.
[0007]
Examples of zeolites that can be used in the present invention include ZSM-5, mordenite, ferrierite, Y-type, SAPO, and others, with ZSM-5 being preferred. The metal ferrite that can be used in the present invention is an iron oxide having a composition represented by the general formula MO · Fe 2 O 3 , and M is a divalent metal ion (eg, manganese, iron, cobalt, nickel, copper, Divalent ions such as zinc). Examples of metal ferrite that can be used are CoFe 2 O 4 , CuFe 2 O 4 , ZnFe 2 O 4 and the like. The copper oxide in the present invention includes CuO (copper oxide), Cu 2 O (cuprous oxide) and the like. Preferable examples of the binder for consolidating the matrix and the copper oxide include alumina sol and silica sol. Aluminum nitrate, talc and the like can also be used, and carbohydrates (such as starch) and organic materials such as polyvinyl alcohol are used. System binders are also known.
[0008]
In order to prepare the catalyst of the present invention, the matrix material powder and the copper oxide powder are mixed in the above proportions, and water and a binder are further mixed and stirred until homogeneous to form a slurry. In general, the above-mentioned slurry is coated on the surface of a honeycomb carrier made of a refractory ceramic such as cordierite, dried and fired to obtain a catalyst solidified on the surface of the honeycomb carrier. . An example of the composition in this case is:
Copper oxide (CuO) 10 parts by weight Matrix material (single or mixture) 40 parts by weight Binder (silica sol) 10 parts by weight Water 50 parts by weight Drying after coating is at a temperature of about 90-110 ° C. for several hours, for example 1-5 hours The next baking step is carried out at a temperature of about 400-800 ° C., preferably about 500-600 ° C. for about 2-10 hours, for example 6 hours.
[0009]
Alternatively, the viscosity of the slurry is increased to a viscosity that allows extrusion processing by using a small amount of water, and formed into a molded product such as a pellet or honeycomb, and dried and fired to obtain a solidified catalyst. Can do. In place of or in addition to water in the slurry composition example above, volatile or evaporative organic solvents such as alcohols may also be used.
[0010]
When the copper oxide-zeolite catalyst according to the above aspect of the present invention is used for exhaust gas treatment, the zeolite tends to occlude hydrocarbons when the exhaust gas is at a low temperature of, for example, about 250 ° C., and the exhaust gas is heated to a high temperature. Then, the occluded hydrocarbon is desorbed. Further, when the exhaust gas is at a low temperature, NOx is adsorbed by the copper oxide, and at that time, for example, NO is oxidized to a more reactive NO 2 , and when the exhaust gas becomes a high temperature, the NO 2 is released and is emitted from the zeolite. It is considered that a state in which the hydrocarbon to be desorbed can immediately act effectively as a reducing agent for the NO 2 occurs. Therefore, a microenvironment is formed in which the reaction between the released hydrocarbon (reducing agent) and NOx easily proceeds in the vicinity of the copper oxide particles adjacent to the zeolite particles that release hydrocarbons at high temperatures. It is guessed. For this reason, it is considered that a large number of minute reaction active environments (active points) corresponding to the number of copper oxide particles are present in the catalyst body to enhance the NOx reduction effect and efficiency. Furthermore, copper oxide seems to be less susceptible to chemical attack from sulfur compounds than copper ions (the form of copper present in conventional copper-zeolite catalysts), which indicates the high durability ( Long life).
[0011]
The reason why the copper oxide-metal ferrite catalyst according to the above aspect of the present invention has high catalytic activity is that, in the exhaust gas stream, Fe in the metal ferrite is oxidized from divalent to trivalent as the temperature rises, and adjacent thereto. It is considered that the copper oxide that is being linked and is relatively reduced, and thereby, the catalytic activity is expressed and promoted, and the reverse tendency occurs when the temperature is lowered, and the copper oxide is stabilized, for example It is presumed that the catalyst life will be prolonged due to the difficulty of being attacked by the S compound.
[0012]
Further, when at least one kind of noble metal particles selected from platinum, rhodium, iridium and silver is added to the copper oxide-zeolite (and / or metal ferrite) catalyst during the research and development of the present invention, NOx at low temperature of exhaust gas is added. It has been found that the reduction effect is significantly improved, thereby greatly extending the effective catalytic activity temperature range.
[0013]
Therefore, according to another aspect of the present invention, at least one selected from platinum (Pt), rhodium (Rh), iridium (Ir) and silver (Ag) on or in a matrix comprising zeolite and / or metal ferrite. There is provided an exhaust gas purifying catalyst in which seed noble metal particles and copper oxide particles are dispersed. The composition ratio of the catalyst according to this embodiment is, for example, 50 to 99.8% by weight of the matrix material, preferably 65 to 99.4% by weight, more preferably 70 to 99% by weight; 9.9 wt%, preferably 0.5-40 wt%, more preferably 1-30 wt%; and 0.01-20 wt%, preferably 0.05-15 wt%, more preferably 0 noble metals. 1 to 15% by weight; The copper oxide-noble metal-matrix catalyst according to this embodiment can be prepared by the same technique as the copper oxide-zeolite catalyst described above. That is, the matrix material powder, the copper oxide powder and the noble metal source (metal powder; or a noble metal compound such as chloroplatinic acid) having the above composition ratio are mixed, and further water and a binder (eg, silica sol). Alternatively, alumina sol) is mixed and stirred until homogeneous to form a slurry. By coating the slurry on the surface of a honeycomb carrier made of refractory ceramic or heat-resistant metal foil, drying, and firing treatment, a catalyst in a solidified state on the surface of the honeycomb carrier can be obtained. This can be used in an exhaust gas pipe. When a noble metal compound such as a metal chloride chloride is used as the noble metal source instead of the powder of the noble metal itself, the firing treatment stage is performed under known conditions, for example, in a nitrogen gas atmosphere containing a small amount of hydrogen (about 1%). It is preferable to complete the firing by carrying out the treatment at a temperature of 500 to 900 ° C. for a treatment time of several hours (for example, about 3.5 to 10 hours). Copper oxide-noble metal (at least one of Pt, Rh, Ir, Ag) -Examples of approximate composition (parts by weight) range of each component used in the matrix catalyst are as follows.
[0014]
Matrix material (single or mixture) About 90 to 99 parts by weight Copper oxide About 0.1 to 20 parts by weight Precious metal About 0.01 to 20 parts by weight The catalyst of this embodiment can be formed by extrusion of a plastic slurry in the same manner as described above. Alternatively, it is preferably formed as a honeycomb molded product, which can be used by drying and firing. Similarly, an organic solvent such as alcohol can be used for forming the slurry.
[0015]
(Example)
The catalyst of the present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited to these examples.
[0016]
Comparative Example ( Preparation of Control Cu Ion Exchange Zeolite Catalyst)
By using a sodium (Na + ) type ZSM-5 zeolite and exchanging with Cu ++ ions using a copper nitrate [Cu (NO 3 ) 2 ] solution by a known method, Cu ions containing 2% by weight of Cu Exchanged zeolite ZSM-5 was obtained. This powder was dried (105 ° C., 5 hours) and calcined (500 ° C., 3 hours) to fix Cu ions to the zeolite. This product (dried product; 50 parts by weight), silica sol binder (10 parts by weight) and water (50 parts by weight) were mixed well to obtain a homogeneous slurry. A cordierite cylindrical honeycomb (diameter 30 mm; volume 21 cc; number of
[0017]
Example 1 (Preparation of CuO-zeolite catalyst)
Proton type ZSM-5 zeolite powder (47 parts by weight), copper oxide (CuO) powder (1.2 parts by weight), silica sol binder (11.8 parts by weight) and water (50 parts by weight) were mixed to form a homogeneous slurry. None, the same honeycomb carrier used in the comparative example was immersed in this, and the surplus adhered slurry on the surface of the pulled up honeycomb carrier was blown off with an air jet, dried at 105 ° C. for 5 hours, and then in an air atmosphere at 500 ° C. Baked for 5 hours. This catalyst unit is denoted as (CuO-ZSM-5).
[0018]
Example 2 (Preparation of Cu 2 O-zeolite catalyst)
The operation of Example 1 was repeated using the same amount of cuprous oxide (Cu 2 O) powder instead of copper oxide in the operation of Example 1. This catalyst unit is denoted as “Cu 2 O—ZSM-5”.
[0019]
Example 3 (Preparation of CuO-rhodium-zeolite catalyst)
In the slurry forming step of the operation of Example 1, metal rhodium powder (0.7 parts by weight) was added to obtain a homogeneous slurry, and a catalyst unit was prepared in accordance with the operation of Example 1 except that. This is indicated as “CuO-Rh-ZSM-5”.
[0020]
Example 4 (Preparation of Cu 2 O-iridium-zeolite catalyst)
In the slurry forming step of the operation of Example 2, metal iridium powder (0.7 parts by weight) was added to obtain a homogeneous slurry, and a catalyst unit was prepared according to the operation of Example 2 except that. This is indicated as “Cu 2 O—Ir-ZSM-5”.
[0021]
Example 5 (Preparation of Cu 2 O-silver-zeolite catalyst)
A catalyst unit was obtained in accordance with the operation of Example 3 using the same amount of metallic silver powder instead of the metallic iridium powder of Example 3. This is indicated as “Cu 2 O—Ag—ZSM-5”.
[0022]
NOx reduction test A gas mixture having the following composition simulating exhaust gas from a diesel engine by mounting the catalyst units of the above comparative examples and examples in a fixed bed flow type reactor, space velocity (SV) = 50,000 hr The NOx reduction rate was measured by analyzing the gas composition flowing out from the catalyst unit with various catalyst inlet temperatures at -1 . The data of NOx reduction rate (%) at various catalyst inlet temperatures were as follows.
The data of the NOx reduction rate (%) at various catalyst temperatures for the catalyst to which the noble metal was added were as follows.
[0023]
In parallel with the measurement of hydrocarbons (HC) reduction rate <br/> NOx reduction rate of the catalytic unit Cu-ZSM-5 (Comparative Example), CuO-ZSM-5 (Example 1) and Cu 2 O- The HC reduction rate (%) was measured for ZSM-5 (Example 2).
[0024]
Degradation promoted with simulated gas durability test <br/> the composition of the catalyst was a comparison of NOx reduction rate before and after the implementation tested (water, SO 2 presence) continuous durability test. Using the same apparatus as the NOx reduction rate test described above, a simulated gas was supplied continuously at a space velocity of 50,000 hr −1 at a constant catalyst inlet temperature of 500 ° C. for 50 hours. The NOx reduction rate at the beginning and end of the test period was as follows.
[0025]
Example 6 (Preparation of Cu 2 O-metal ferrite catalyst)
CoFe 2 O 4 ferrite powder (47 parts by weight), cuprous oxide (Cu 2 O) powder (1.2 parts by weight), silica sol binder (11 parts by weight) and water (50 parts by weight) are mixed and stirred to form a homogeneous slurry. It was. A cordierite cylindrical honeycomb (diameter 30 mm; volume 21 cc; number of
[0026]
Example 7
The procedure of Example 6 was repeated using the same amount of CuFe 2 O 4 ferrite powder instead of CoFe 2 O 4 ferrite powder. Hereinafter, this catalyst unit is referred to as “Cu 2 O—Cu ferrite”.
[0027]
Example 8 ( Preparation of Cu 2 O-Zeolite-Metal Ferrite Catalyst)
Instead of 47 parts by weight of CoFe 2 O 4 ferrite powder, the Pronto type ZSM-5 zeolite powder (23.5 parts by weight) and ZnFe 2 O 4 ferrite powder (23.5 parts by weight) used in Example 1 were used. Then, the operation of Example 6 was repeated. Hereinafter, this catalyst is denoted as “Cu 2 O—ZSM-5-Zn ferrite”.
[0028]
Example 9 ( Preparation of Cu 2 O-iridium-metal ferrite catalyst)
In the slurry forming step of Example 7, metal iridium powder (0.7 parts by weight) was added, and the operation of Example 7 was repeated. Hereinafter, this catalyst is referred to as “Cu 2 O—Ir—Cu ferrite”.
[0029]
Example 10 ( Preparation of Cu 2 O-rhodium-zeolite-metal ferrite catalyst)
In the slurry forming step of Example 8, metal rhodium powder (0.7 parts by weight) was added, and the operation of Example 8 was repeated. Hereinafter, this catalyst is referred to as “Cu 2 O—Rh—ZSM-5-Zn ferrite”.
[0030]
NOx reduction Test <br/> Example 6 (Cu 2 O-Co ferrite), Example 7 (Cu 2 O-Cu ferrite), Example 8 (Cu 2 O-ZSM- 5-Zn ferrite), Example 9 Each catalyst of (Cu 2 O—Ir—Cu ferrite) and Example 10 (Cu 2 O—Rh—ZSM-5-Zn ferrite) was subjected to the NOx reduction test, and the following NOx reduction rate (%) data Got.
NOx reduction rate (%)
[0031]
Hydrocarbon (HC) reduction rate The hydrocarbon (HC) reduction performance measured in parallel with these NOx reduction rates is as good as the catalysts of Examples 1 and 2 above for all the catalysts. there were.
[0032]
Durability The catalysts of Examples 6 to 10 were subjected to the durability test, and the difference (Δ%) in the NOx reduction rate between the initial stage and the end of the predetermined test period was obtained.
[0033]
【The invention's effect】
As is apparent from the above, the catalyst comprising the zeolite and / or metal ferrite in which the copper oxide particles are dispersed and the catalyst comprising the zeolite and / or metal ferrite in which the copper oxide particles and noble metal particles are dispersed are exhaust gas. In the purification efficiency (activity) and the effective activation temperature range, there was a significant improvement effect, and also a significant improvement was observed in the service life.
[Brief description of the drawings]
FIG. 1 is a graph showing NOx reduction rates at various catalyst inlet temperatures of the catalysts of Comparative Examples and Examples 1-2.
FIG. 2 is a graph showing a comparison of hydrocarbon reduction rates of the catalysts of Comparative Examples and Examples 1-2.
FIG. 3 is a graph showing a comparison of NOx reduction rates of the catalysts of Comparative Example, Example 1, and Example 3.
FIG. 4 is a graph showing a comparison of NOx reduction rates of the catalysts of Comparative Example, Example 2 and Example 4.
FIG. 5 is a graph showing a comparison of NOx reduction rates of the catalysts of Comparative Example, Example 2, and Example 5.
Claims (3)
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GB0013609D0 (en) * | 2000-06-06 | 2000-07-26 | Johnson Matthey Plc | Emission control |
US7399729B2 (en) | 2003-12-22 | 2008-07-15 | General Electric Company | Catalyst system for the reduction of NOx |
WO2012090922A1 (en) | 2010-12-27 | 2012-07-05 | 三菱樹脂株式会社 | Catalyst for nitrogen oxide removal |
JP5991662B2 (en) * | 2011-07-21 | 2016-09-14 | 国立大学法人大阪大学 | Nitrogen oxide purification catalyst and method for producing the same |
JP2013173112A (en) * | 2012-02-27 | 2013-09-05 | Tohoku Univ | Exhaust gas cleaning catalyst |
KR101879695B1 (en) * | 2016-12-02 | 2018-07-18 | 희성촉매 주식회사 | Zeolite structures with specific Cu2+ (α)/ Cu2+ (β) ratio in NO DRIFTS spectrum, a method for preparing zeolite structures, and a catalyst composition comprising the zeolite structures |
CN108892196B (en) * | 2018-07-09 | 2020-12-29 | 沈阳理工大学 | Preparation method of water purification material |
EP3919165A1 (en) * | 2020-06-03 | 2021-12-08 | Johnson Matthey Public Limited Company | Method for forming a catalyst article |
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