JP3745407B2

JP3745407B2 - Exhaust gas purification catalyst, production method thereof, and exhaust gas purification method

Info

Publication number: JP3745407B2
Application number: JP09510795A
Authority: JP
Inventors: 泰良加藤; 尚美今田; 邦彦小西
Original assignee: Babcock Hitachi KK
Current assignee: Mitsubishi Power Ltd
Priority date: 1995-04-20
Filing date: 1995-04-20
Publication date: 2006-02-15
Anticipated expiration: 2021-02-15
Also published as: JPH08290062A

Description

【０００１】
【産業上の利用分野】
本発明は未反応アンモニアの分解活性を有する排ガス浄化硝触媒とその製造方法および該触媒を用いる排ガスの浄化方法に係り、特に触媒の酸化活性をコントロールすることにより、二酸化硫黄（ＳＯ₂）の三酸化硫黄（ＳＯ₃）への転化抑制、アンモニア使用量の増加の抑制、およびひ素などの揮発性酸化物蒸気による未反応アンモニア分解活性の低下防止とを図って高い脱硝性能と未反応アンモニアのリーク量の低減を長期間維持できるようにしたアンモニア（ＮＨ₃）を還元剤とする排ガス浄化触媒とその製造方法および排ガス浄化方法に関する。
【０００２】
【従来の技術】
発電所、各種工場、自動車などから排出される排煙中のＮＯｘは、光化学スモッグや酸性雨の原因物質であり、その効果的な除去方法として、アンモニア（ＮＨ₃）を還元剤とした選択的接触還元による排煙脱硝法が火力発電所を中心に幅広く用いられている。触媒には、バナジウム（Ｖ）、モリブデン（Ｍｏ）あるいはタングステン（Ｗ）を活性成分にした酸化チタン（ＴｉＯ₂）系触媒が使用されており、特に活性成分の一つとしてバナジウムを含むものは活性が高いだけでなく、排ガス中に含まれている不純物による劣化が小さいこと、より低温から使用できることなどから、現在の脱硝触媒の主流になっている（特開昭５０−１２６８１号公報など）。
【０００３】
近年の環境保全の観点から発電所用大容量ボイラなどの固定発生源にはＮＯｘ排出量に総量規制が適用され、設備から排出される排ガス中のＮＯｘ量を極めて低いレベルに抑えて運転することが必須になってきている。このためアンモニア還元方式の脱硝装置でも触媒の充填量を増やし、アンモニア注入量を増加して脱硝装置を高脱硝率で運転するなどの方法が検討されている。このような高度な脱硝に対する需要に伴って、脱硝反応に使用されなかった未反応アンモニアを低減するため分解触媒の設置、アンモニアの増加は免れない。このため、未反応アンモニア（以下リークＮＨ₃）もＮＯｘレベルと同程度まで低減することが必須となってきているが、上記した高脱硝率運転では未反応アンモニアの増加は免れない。このため未反応アンモニアを低減するための分解触媒の設置、アンモニアの均一注入・混合などが検討されている。本発明者らも貴金属を担持した多孔体と酸化チタン系組成物とからなるアンモニアの分解活性を有する脱硝触媒を発明し、それを用いて高脱硝率・低リークＮＨ₃を実現できる排ガスの浄化方法を出願している（特願平３−３１２３０８号、特願平４−１３８５１４号など）。
【０００４】
【発明が解決しようとする課題】
上記従来技術の触媒の内、本発明者らの特願平３−３１２３０８号および特願平４−１３８５１４号になる触媒は、高い未反応アンモニア分解活性を有しており、ガス焚ボイラなどの比較的きれいな排ガス浄化に際しては非常に高い脱硝率と低リークＮＨ₃濃度を実現することができる画期的な触媒であったが、次の（イ）〜（ハ）に示すような多くの改良点も残されていた。
【０００５】
（イ）触媒成分である貴金属の酸化活性が高く、同一脱硝率を得るためにはＮＨ₃／ＮＯ比を高くする必要があり、アンモニア消費量が増大する。
図４は未反応アンモニアの分解活性を有しない脱硝触媒（Ａ）と特願平４−１３８５１４号になる未反応アンモニア分解活性を有する従来触媒（Ｂ）のＮＨ₃／ＮＯ比を変化させた場合の脱硝率とリークＮＨ₃量を示したものであるが、ＮＨ₃／ＮＯ比を高めれば高脱硝率と低リークＮＨ₃量を満足できるものの、式（１）
２ＮＨ₃＋３／２Ｏ₂ → Ｎ₂＋３Ｈ₂Ｏ（１）
のＮＨ₃の消費反応が無視できず、同一脱硝率を得るためにはＮＨ₃分解活性を持たないものに比し、多量のＮＨ₃注入が必要であった。
【０００６】
（ロ）ＮＨ₃の酸化成分である貴金属の酸化活性が高く、排ガスがＳＯ₂を含有する場合には下記式（２）
ＳＯ₂＋１／２Ｏ₂ → ＳＯ₃ （２）
のＳＯ₂酸化反応が生じ、排ガス中のＳＯ₃濃度が高くなり、後流機器の酸性腐食が増大する場合があった。
【０００７】
（ハ）石炭排ガスなどの排ガス中にひ素、セレン、レニウムなどの揮発性酸化物が含まれる場合などの酸化反応によって揮発性酸化物が不揮発化して触媒に蓄積し、リークＮＨ₃の分解率が経時的に低下するという問題があった。
【０００８】
本発明の目的は、上記した従来触媒の問題点をなくし、油、石炭燃焼排ガスで使用する場合の必須の性質であるＳＯ₂酸化活性の低減の防止と、ひ素酸化物などの揮発性酸化物による劣化を防止した排ガス浄化触媒とその製造方法および排ガス浄化方法を提供することである。また本発明の目的は、排ガス中に添加する還元剤であるＮＨ₃消費量の増大を低減することができる脱硝触媒とその製造方法および排ガス浄化方法を提供することである。
【０００９】
また、本発明の目的は、排ガス中の二酸化硫黄（ＳＯ₂）の三酸化硫黄（ＳＯ₃）への転化抑制、アンモニア使用量の増加の抑制、およびひ素などの揮発性酸化物蒸気による未反応アンモニア分解活性の低下防止とを図って高い脱硝性能と未反応アンモニアのリーク量の低減を長期間維持できるようにしたアンモニア（ＮＨ₃）を還元剤とする排ガス浄化触媒とその製造方法および排ガス浄化方法を提供することである。
【００１０】
【課題を解決するための手段】
上記目的を達成するための本発明は、次の構成からなる。チタン酸化物およびモリブデン（Ｍｏ）、タングステン（Ｗ）、バナジウム（Ｖ）から選ばれた一種以上の元素の酸化物からなる組成物または銅（Ｃｕ）もしくは鉄（Ｆｅ）を担持したゼオライトからなる組成物を第１成分とし、イリジウム（Ｉｒ）、パラジウム（Ｐｄ）、ロジウム（Ｒｈ）、ルテニウム（Ｒｕ）から選ばれる少なくとも一つの金属と白金（Ｐｔ）とからなり、前記金属の白金（Ｐｔ）に対する重量比が０を超えて５以下の割合で含まれる予め多孔体に担持した第２成分とからなる窒素酸化物のアンモニア還元機能とアンモニアの酸化分解機能を有する二酸化硫黄及び揮発性酸化物を含有する排ガスの浄化触媒である。
【００１１】
本発明の触媒は第１成分としてＮＯｘのアンモニアによる還元反応に活性な触媒組成物、第２成分として白金（Ｐｔ）を主成分とし、これにイリジウム（Ｉｒ）、パラジウム（Ｐｄ）、ロジウム（Ｒｈ）またはルテニウム（Ｒｕ）から選ばれる一種以上の貴金属とを高シリカゼオライト、シリカ、アルミナから選ばれる一種以上の多孔物質に担持せしめたものを用い、両者を混ぜ合せて得られる。
【００１２】
具体的には、第１成分としてはあらかじめ公知の方法で調製したＴｉ−Ｖ、Ｔｉ−Ｍｏ、Ｔｉ−Ｗ、Ｔｉ−Ｖ−Ｗ、Ｔｉ−Ｍｏ−Ｖの組み合わせの酸化物、ＣｕまたはＦｅを担持したゼオライト（モルデナイトなど）などのＮＯｘのＮＨ₃による還元活性を有するものを用い、第２成分としてはゼオライト、多孔質シリカ、多孔質アルミナにあらかじめ上記金属元素をイオン交換、含浸などにより担持せしめた組成物を焼成したものを用いる。
【００１３】
第２成分中の貴金属とは、Ｐｔを主成分にし、これにＩｒ、Ｐｄ、Ｒｈ、Ｒｕから選ばれる一種以上の貴金属を添加し、該貴金属の添加量は貴金属／Ｐｔの重量比が０を超えて５以下の範囲で添加したものであり、該貴金属は塩化物、硝酸塩、有機塩の混合溶液の形で同時に、あるいは逐次担持することにより複合化して用いられる。
【００１４】
また、両成分を混合して触媒体とする方法には、
▲１▼予め調製した第１成分と、第２成分粉末をそのまま乾式でペレット状に成形する方法、
▲２▼両成分粉体を所定割合で水の存在下、必要に応じて有機／無機バインダ、無機繊維などを添加して混練して得たペーストをハニカム状に成形したり金属基板に塗布する方法
など従来の脱硝触媒に用いる一般的方法を用いることができる。さらに得られた成形体は必要に応じて乾燥・焼成される。
【００１５】
例えば、チタン化合物にＶ、Ｍｏ、Ｗのうち少なくとも一種以上の元素の化合物を水とともに添加混合し、乾燥、焼成したもの、またはＣｕまたはＦｅをイオン交換して担持したゼオライトを第１成分とし、予めゼオライト、シリカ、アルミナなどの多孔体にＰｔとその他の金属としてＩｒ、Ｐｄ、Ｒｈ、Ｒｕから選ばれる少なくとも一つの金属を担持後、焼成して第２成分とし、第１成分と第２成分を混合後、所定形状に成形し、乾燥、焼成して本発明の触媒とする。
【００１６】
前記調製方法を含め、公知のどのような方法で本発明の触媒を製造してもよく、
（Ａ）Ｉｒ、Ｐｄ、ＲｈまたはＲｕがＰｔと共に多孔性担体に担持されており、Ｐｔに対するＩｒ、Ｐｄ、ＲｈまたはＲｕの重量比が０を超えて５以下、望ましくは０を超えて２以下の範囲にあること、
（Ｂ）貴金属担持多孔体（第２成分）に対するＮＯのＮＨ₃の酸化活性を有する触媒成分（第１成分）の重量比が、８０％以上であり、全体の貴金属含有量は１００ｐｐｍ以下であることが望ましい。
【００１７】
図３（ａ）〜（ｃ）に本発明の触媒の使用形態を示す。ボイラ１からの排ガスの流路に反応器２、熱交換機３、電気集塵機４、煙突５をこの順に配置する。また反応器２の前流部にはＮＨ₃注入ライン６を設ける。そして反応器２内の全部に、もしくは従来の酸化チタン系触媒などの公知の脱硝触媒８と組み合せて一部に本発明の触媒７を用いて脱硝触媒層を形成させる。図３（ａ）は反応器２内の全部に本発明の触媒７を用いて脱硝触媒層を形成させた例であり、図３（ｂ）は反応器２内に公知の脱硝触媒８の後流側に本発明の触媒７を配置して脱硝触媒層を形成させた例であり、図３（ｃ）は反応器２内に二つの公知の脱硝触媒８の間に本発明の触媒７を配置して脱硝触媒層を形成させた例である。図３（ａ）〜（ｃ）のいずれの場合にも本発明の触媒７の特色であるＮＨ₃による窒素酸化物（ＮＯｘ）の還元とその際の未反応アンモニアを窒素と水に酸化分解してリークＮＨ₃を低減させる効果が得られることはもとより、従来触媒に比べＮＨ₃の消費量を少なくでき、ＳＯ₂のＳＯ₃への添加を低レベルで維持できるので、後流機器への悪影響を小さくできるのみならず、長時間高い触媒活性を維持することができる。
【００１８】
本発明の触媒７の特徴は前述したように第２成分中の貴金属の種類と第２成分と第１成分を混合した点に特色があり、その調製法も前述の要件を満たせばどのような調製法であっても採用できることは言うまでもない。しかし、次のような方法を用いればより優れた触媒を得ることができる。
【００１９】
本発明の触媒７の第１成分は、前記したような各種のものを使用することができるが、特に触媒成分としてＴｉ−Ｖ、Ｔｉ−Ｖ−Ｍｏ、Ｔｉ−Ｗ−Ｖなどの元素からなる酸化物触媒を用いた場合に好結果をもたらす。これらは、チタメタン酸などの含水酸化チタンのスラリにバナジウム、モリブデン、タングステンの酸素酸塩などの塩類を添加し、加熱ニーダを用いて水を蒸発させながらペースト状にし、乾燥後、４００℃から７００℃で焼成、必要に応じて粉砕することによって得られる。
【００２０】
本発明の触媒７の第２成分は、あらかじめゼオライト、シリカ、アルミナから選ばれる一種以上の多孔体のミクロポア内にイオン交換や混練により担持して調製される。第２成分に用いられる多孔体はモルデナイト、クリノプチロライト、エリオナイト、Ｙ型ゼオライトなどの水素置換体、ナトリウム置換体、カルシウム置換体などのゼオライト、表面積が１００ｍ2／ｇから５００ｍ2／ｇのシリカ、アルミナなどが使用できる。使用に際しての粒径は１から１０μｍ程度が良く、あらかじめ粉砕して用いることもできる。これらにＰｔおよびその他の貴金属（Ｉｒ、Ｐｄ、ＲｈあるいはＲｕ）から選ばれる少なくとも一以上の貴金属をその塩化物、硝酸塩、あるいはアンミン錯体の形で溶解した水溶液中に浸漬してイオン交換するか、水溶液と共に蒸発乾固し、前記貴金属を０．０１ｗｔ％〜０．１ｗｔ％担持後焼成して貴金属塩を金属に分解して用いる。Ｐｔに添加するその他の貴金属の添加比率はＰｔに対する重量比で０を超えて５以下、望ましくは２以下が適当である。
【００２１】
第１、第２成分の混合比率は第２成分中の貴金属担持量により最適値が異なるが、第２成分／第１成分比（以下第２成分／第１成分比）として２０／８０〜０．５／９９．５望ましくは１０／９０〜１／９９（重量比）の範囲が適当である。
【００２２】
第１、第２成分の両方の成分の粉末に、水と必要に応じて無機バインダ、成形助剤、無機繊維など周知の成形性向上剤を添加し、ニーダなどの混練機で混練してペースト状にする。
【００２３】
得られたペースト状触媒は無機繊維製網状基材、溶射などにより粗面化した金属基板などに塗布され板状触媒に成形されるか、押出成形機により柱状あるいはハニカム状に成形される。成形体は乾燥後硫酸塩が硫酸塩として残存する温度、通常４５０℃〜５５０℃で焼成して用いられる。
【００２４】
得られた本発明の触媒７は、図３のように反応器２の脱硝触媒層の全部もしくは従来の公知の脱硝触媒８と組み合わせて、その一部を構成する触媒７として充填され、排ガス中のＮＯｘ濃度が高い領域では脱硝触媒として、また、排ガス中のＮＯｘ濃度が低下した領域では未反応（余剰）アンモニアの分解触媒として作用する。使用条件としては、特に制限はないが、本発明の触媒７の特徴であるリークＮＨ₃の低減効果が大きいのは排ガス中のＮＯｘと還元剤であるＮＨ₃のモル比（ＮＨ₃／ＮＯｘ比）が０．８以上の場合であり、高脱硝率運転を行う脱硝装置として好適である。
【００２５】
本発明の触媒７の第２成分中のＰｔとこれに添加する貴金属の重量比率は特に重要であり、Ｐｔに対する他の貴金属の添加重量比が小さい場合には式（１）〜（３）の副反応の抑制が十分でなく、また大きすぎる場合には式（５）の反応が生じにくくなり、リークＮＨ₃の分解率の低下を招くようになる。前記重量比率は０を超えて５重量比以下で選定できるが、２重量比以下、または添加する貴金属によっては１重量比以下に選定した場合に好結果を得易い。
【００２６】
本発明では、第２成分／第１成分比も重要で前述した範囲のうち、貴金属担持量の大きいゼオライト、シリカ、アルミナなどを用いて第２成分／第１成分比が小さくなるように選定し、かつ触媒全体の貴金属担持量が１から１０００ｐｐｍ望ましくは１０から１００ｐｐｍの範囲にすることが好結果を与える。これは第２成分の形成するミクロポアが第１成分の形成するマクロポア内にまばらに存在してＮＨ₃が選択的に第１成分に吸着し、脱硝反応に用いられ易くするためである。また貴金属量を少なくすることは触媒単価を低くできるという経済的効果以外に、脱硝反応とアンモニアの酸化反応をＮＯの存在の有無によって分離され易くする効果もある。
【００２７】
また、第２成分／第１成分比は、触媒層全体を本発明の触媒７で構成する場合には小さく選定し、従来触媒と組み合わせて一部に本発明の触媒７を使用する時には大きくすると同時に貴金属含有量も多くすると好結果を得易い。
【００２８】
排ガスがひ素（Ａｓ）、セレン（Ｓｅ）および／またはレニウム（Ｒｅ）の揮発性酸化物を含有していても本発明の触媒活性は低下しない。
【００２９】
【作用】
従来の未反応アンモニアの分解活性を有する脱硝触媒は、貴金属を担持した多孔性担体とＴｉ−Ｗ−Ｖ系などに代表されるＮＯｘのＮＨ₃による還元化性を有する触媒成分とで構成されることを特徴としている（特願平３−３１２３０８号および特願平４−１３８５１４号など）。これらの従来の触媒は、Ｔｉ−Ｗ−Ｖ系などの成分上で生じる下記式（４）の脱硝反応で余った／もしくは使用されなかった未反応アンモニアを、貴金属表面で式（５）の反応により一部ＮＯに酸化し、その後残留する未反応アンモニアで再び式（４）の反応により窒素にまで還元することにより高い脱硝率と高い未反応アンモニア分解活性とを発現するようにした画期的なものであった。
ＮＨ₃＋ＮＯ＋１／４Ｏ₂ → Ｎ₂＋３／２Ｈ₂Ｏ（４）
ＮＨ₃＋３／２Ｏ₂ → ＮＯ＋３／２Ｈ₂Ｏ（５）
【００３０】
ところが、これらの触媒では、Ｐｔ、Ｐｄ、Ｒｈなどの貴金属を単独で多孔性担体に担持せしめた成分を用いていたため高い未反応アンモニア分解率を得ようとすると触媒の酸化活性が高くなることに起因する問題を生じていた。すなわち、式（１）のＮＨ₃消費反応が大きく、高脱硝率を得るためには多くのＮＨ₃の添加が必要となること、式（２）による反応で排ガス中のＳＯ₂をＳＯ₃に酸化し、排ガス流路の後流側に配置した機器へ悪影響を与えること、式（３）に例示される揮発性酸化物が不揮発性酸化物に転化する反応で触媒表面に不揮発性酸化物が蓄積することにより石炭排ガス中で劣化が生じ易いことなどである。
２ＮＨ₃＋３／２Ｏ₂ → Ｎ₂＋３Ｈ₂Ｏ（１）
ＳＯ₂＋１／２Ｏ₂ → ＳＯ₃ （２）
Ａｓ₂Ｏ₃＋Ｏ₂ → Ａｓ₂Ｏ₅ （３）
【００３１】
本発明の触媒７では、式（５）の反応に特に優れるＰｔをベースに、これにＩｒ、Ｐｄ、ＲｈあるいはＲｕを添加されている点に特徴がある。このような組成にすることにより、式（５）の反応活性は前記本発明者らの従来触媒と同等で、しかも式（１）〜（３）の副反応を大きく抑制することができる。その結果、未反応アンモニアを効率よく除去できるにもかかわらず、アンモニア消費量の増大やＳＯ₂のＳＯ₃への転化をほとんど招くことがない上、揮発性酸化物の不揮発化による触媒の劣化も生じにくい。
【００３２】
これにより従来の触媒が使用できなかった石油、石炭燃焼排ガスなどのＳＯ₂含有排ガスの脱硝装置の未反応アンモニアの分解が可能になるほか、ＮＨ₃使用量の増大を招かない高脱硝率・低リークＮＨ₃の脱硝装置を実現することが可能になる。
【００３３】
【実施例】
本発明の一実施例を説明する。本発明は以下の実施例に限定されるものではない。
以下、具体的実施例を用いて本発明を詳細に説明する。
【００３４】
実施例１
メタチタン酸スラリ（ＴｉＯ₂含有量：３０ｗｔ％、ＳＯ₄含有量：８ｗｔ％）６７ｋｇにパラタングステン酸アンモニウム（（ＮＨ₄）₁₀Ｈ₁₀・Ｗ₁₂Ｏ₄₆・６Ｈ₂Ｏ）を２．４１ｋｇおよびメタバナジン酸アンモン０．６３ｋｇとを加えて加熱ニーダを用いて水を蒸発させながら混練し水分約３６％のペーストを得た。これを３φの柱状に押し出し造粒後、流動層乾燥機で乾燥し、次に大気中５５０℃で２時間焼成した。得られた顆粒をハンマーミルで１μｍ以下の粒径が６０％以上になるように粉砕して第１成分である脱硝触媒粉末を得た。このときの組成はＶ／Ｗ／Ｔｉ＝２／５／９２（原子比）である。
【００３５】
一方、塩化白金酸（Ｈ₂［ＰｔＣ₁₆］・６Ｈ₂Ｏ）０．３３２ｇと塩化イリジウム（ＩｒＣｌ₄）０．２１７ｇとを水１リットルに溶解したものに、高表面積微粒シリカ（富田製薬（株）：マイコンＦ）５００ｇを加え、砂浴上で蒸発乾固してＰｔを担持した。これを１８０℃で２時間乾燥後、５００℃で２時間焼成し、０．０２５ｗｔ％Ｐｔ−０．０２５ｗｔ％Ｉｒ−シリカを調製して第２成分にした。このときのＩｒ／Ｐｔ重量比は１である。
【００３６】
これとは別に繊維径９μｍのＥガラス製繊維１４００本の捻糸を１０本／インチの粗さで平織りした網状物にチタニア４０％、シリカゾル２０％、ポリビニールアルコール１％のスラリーを含浸し、１５０℃で乾燥して剛性を持たせ触媒基材を得た。
【００３７】
第１成分１９．８ｋｇと第２成分２００ｇとに、シリカ・アルミナ系無機繊維５．３ｋｇ、水１７ｋｇを加えてニーダで混練し、触媒ペーストを得た。上記基材２枚の間に調製したペースト状触媒混合物を置き、加圧ローラを通過させることにより基材の編目間および表面に触媒を圧着して厚さ約１ｍｍの板状触媒を得た。得られた触媒は、１８０℃で２時間乾燥後、大気中５５０℃で２時間焼成した。本触媒中の第１成分と第２成分の第２成分／第１成分比（重量比）は１／９９で有り、貴金属含有量は触媒基材・無機繊維を除いて５ｐｐｍに相当する。
【００３８】
実施例２〜４
実施例１の塩化イリジウムを硝酸パラジウム（Ｐｄ（ＮＯ₃）₂）０．２７１ｇ（実施例２）、硝酸ロジウム（Ｒｈ（ＮＯ₃）₃・２Ｈ₂Ｏ）０．３９３ｇ（実施例３）および塩化ルテニウム（ＲｕＣＬ₄・５Ｈ₂Ｏ）０．２３７ｇ（実施例４）に代え、他は実施例１と同様にして触媒を調製した。
【００３９】
調製した触媒の貴金属含有量は５ｐｐｍであり、Ｐｄ／Ｐｔ、Ｒｈ／ＰｔおよびＲｕ／Ｐｔ重量比はともに１である。
【００４０】
比較例１〜５
実施例１の貴金属に代え塩化白金酸、塩化イリジウム、塩化パラジウム、塩化ロジウムおよび塩化ルテニウムの単独塩類とし、添加量をそれぞれ０．６６５ｇ、０．４３４ｇ、０．５４２ｇ、０．７８６ｇ、０．４７４ｇとして実施例１と同様に触媒を調製した。
【００４１】
実施例１〜４および比較例１〜５の触媒を幅２０ｍｍ×長さ１００ｍｍに切断し、３ｍｍ間隔で反応器２（図３）に３枚充填し、表１に示した条件で脱硝率と反応器２出口で検出される未反応アンモニアの濃度を測定し、未反応アンモニアの分解率を算出した。これと同時に、反応器２内の触媒層の前後でのＳＯ₂の濃度を測定してＳＯ₂の減少率からＳＯ₂の酸化率を算出した。
【００４２】
【表１】

【００４３】
なお、ここで未反応アンモニアの分解率は次式で求められるものである。
未反応ＮＨ₃分解率（％）＝(［ＮＨ₃］in−［ＮＨ₃］denox−［ＮＨ₃］out)
÷(［ＮＨ₃］in−［ＮＨ₃］denox）×１００
［ＮＨ₃］in ：反応器入口ＮＨ₃濃度
［ＮＨ₃］out ：反応器出口ＮＨ₃濃度（リークＮＨ₃濃度）
［ＮＨ₃］denox ：脱硝反応に使用されたＮＨ₃の濃度
得られた結果を表２にまとめて示す。
【００４４】
【表２】

【００４５】
表２から明らかなように、比較例１の触媒は高い未反応アンモニア分解率を有するもののＳＯ₂酸化率は著しく高く、後流機器への悪影響が懸念される上、脱硝率も低くＳＯ₂含有排ガス触媒としては不適当である。また、比較例２〜５の触媒は、ＳＯ₂酸化率は低いが未反応アンモニアの分解率は非常に低く、リークＮＨ₃の低減を目的とする用途には不適当であることは自明である。
【００４６】
一方、本発明になる実施例１〜５の触媒は未反応アンモニアの分解率が高いにもかかわらず、高い脱硝率を得ることができる上、ＳＯ₂酸化率は比較例１の触媒の１／４〜１／１０以下と低い値である。
【００４７】
このように、本発明の上記実施例の触媒は、Ｐｔと他の貴金属を組み合わせることにより、高脱硝率、高未反応アンモニア分解率を維持しつつ、ＳＯ₂酸化率を抑制した点に特徴がある。
【００４８】
また、実施例１の触媒と未反応アンモニア分解率の高かった比較例１の触媒について、表１の条件下でＮＨ₃濃度を変化させた場合の脱硝率と反応器２の触媒層出口で検出されるアンモニア濃度（リークＮＨ₃濃度）を測定し、図１に示した。実施例１および比較例１の触媒ともに未反応アンモニアのリーク濃度が低い点は同様であるが、脱硝率の挙動は大きく異なっている。すなわち、比較例１の触媒では高脱硝率を得るためにはＮＨ₃／ＮＯ比を１を大きく超えてＮＨ₃を添加する必要があるのに対し、実施例１の触媒では脱硝反応の量論量である１近辺のＮＨ₃注入量で高脱硝率が達成でき、脱硝装置の運転経費を大きく低減できることが可能である。
【００４９】
実施例５〜８
実施例１〜４の全貴金属量は５ｐｐｍとそれぞれ同じ含有量とし、Ｉｒ、Ｐｄ、Ｒｈ、ＲｕのＰｔに対する重量比を０．１、０．５、１、２、５とそれぞれ変化させて触媒を調製した。
【００５０】
得られた触媒について、表１の条件でＳＯ₂酸化率、脱硝率、未反応アンモニアの分解率を測定して得られた触媒について、表１の条件でＳＯ₂酸化率、脱硝率、未反応アンモニアの分解率を測定した結果を図２に示す。Ｐｔに対する他の貴金属の添加量が０の点の比較例１の触媒と比較すると、実施例５〜８の触媒は、いずれの貴金属を添加した場合にもＳＯ₂酸化率の顕著な抑制効果がみられると同時に脱硝率の向上が認められる。しかしながら、貴金属の添加量が増大するにしたがって、未反応アンモニアの分解率の低下が認められ、Ｉｒ、Ｐｄ、Ｒｈ、ＲｕのＰｔに対する重量比は５以下望ましくは２以下がよいことが解る。
【００５１】
実施例９
実施例１の触媒の第２成分中の貴金属担持量を０．０１ｗｔ％に変更すると同時に、第２成分と第１成分の混合比を０．５／９９．５に変更し全貴金属量０．５ｐｐｍの触媒を調製した。
【００５２】
実施例１０〜１２
比較例２〜４の触媒における第２成分の貴金属に代え、Ｐｄ／Ｐｔ、Ｒｈ／Ｐｔ、Ｒｕ／Ｐｔを重量比を２とし、第２成分／第１成分比をそれぞれ２／９８、２０／８０、１０／９０に変更して触媒を調製した。この場合の貴金属含有量は各々１０ｐｐｍ、１００ｐｐｍ、５０ｐｐｍである。
【００５３】
比較例６〜９
実施例９〜１０触媒における第２成分の貴金属をすべてＰｔに置き換えてＰｔ担持量が０．５、１０、１００、５０ｐｐｍの触媒を調製した。
【００５４】
得られた実施例９〜１２および比較例６〜９の触媒について、実施例１の場合と同様に表１の条件で脱硝率、未反応アンモニア分解率、ＳＯ₂酸化率を測定し表３にまとめた。
【００５５】
【表３】

【００５６】
表３からわかるように、本発明になる触媒はＰｔと他貴金属の組み合わせにより、貴金属担持量の少ないものから多いものまで、高脱硝率、高未反応分解率および低ＳＯ₂酸化率を保つことができることが分かる。
【００５７】
実施例１３〜１６
石炭排ガスなどに含まれる酸化ひ素などの揮発性酸化物を用いて本発明の触媒の劣化を加速させる試験をするため、実施例１〜４の触媒と比較例１の触媒を用い、表１の組成のガス中に亜酸化ひ素（Ａｓ₂Ｏ₃）水溶液を添加・蒸発させ、Ａｓ₂Ｏ₃濃度が５０ｐｐｍになるように調整した。この条件で５時間保持して触媒にひ素酸化物を吸着させ、触媒性能の変化を調べた。
表４に上記加速劣化試験前後の触媒の未反応アンモニア分解率の変化をまとめた。
【００５８】
【表４】

【００５９】
この表４から明らかなように本発明になる触媒は、石炭排ガスなどに含まれる亜酸化ひ素の蒸気による劣化に対しても耐久性を示し、ダーティ排ガス脱硝用触媒に最適なものである。
【００６０】
実施例１７
実施例１の第１成分を８％のＣｕをイオン交換したモルデナイトに代えて、その他は実施例１と同様にして触媒を調製した。この触媒を用いて実施例１の場合と同様に表１の条件で脱硝率、未反応アンモニアの分解率、ＳＯ₂酸化率を測定したところ、それぞれ９８％、９７％、１．９％と、実施例１と同等の性能が得られた。
【００６１】
【発明の効果】
従来のＮＨ₃分解活性を有する脱硝触媒の欠点であるＮＨ₃消費量の増大を低減できるとともに、ＳＯ₂酸化活性が非常に低くでき、脱硝触媒後流側の被処理ガス流路に配置される機器の酸性腐食などの悪影響を小さくできる。
【００６２】
さらに本発明になる触媒は、酸化ひ素を始めとする揮発性酸化物蒸気を触媒毒として含有する石炭燃焼排ガス、産業廃棄物燃焼炉排ガス、ゴミ焼却炉排ガス処理に用いても未反応アンモニアの分解活性が長期間低下せず、これらの排ガスを処理する脱硝反応器からリークするアンモニアを低減するために使用できる。
【図面の簡単な説明】
【図１】本発明の一実施例になる脱硝触媒がアンモニアの使用量の低減に効果があることを示す図である。
【図２】本発明の一実施例の触媒組成がＳＯ₂の酸化率の抑制に好適であることを示す図である。
【図３】本発明の触媒を被処理ガス流路に配置する実施態様を示す図である。
【図４】従来の本発明者らの発明した脱硝触媒の解決すべき課題を示すための説明図である。
【符号の説明】
１…ボイラ、２…反応器、３…熱交換器、４…電気集塵機、５…煙突、
６…アンモニア注入ライン、７…本発明の触媒、８…公知脱硝触媒[0001]
[Industrial application fields]
The present invention relates to an exhaust gas purification nitrate catalyst having an activity of decomposing unreacted ammonia, a method for producing the same, and a purification method for exhaust gas using the catalyst. In particular, by controlling the oxidation activity of the catalyst, sulfur dioxide (SO ₂ ) Sulfur trioxide (SO _Three Longer reduction of unreacted ammonia and leakage of unreacted ammonia by suppressing the conversion to), suppressing the increase in the amount of ammonia used, and preventing the degradation of unreacted ammonia decomposition activity by volatile oxide vapors such as arsenic Ammonia (NH that can be maintained for a period of time _Three The present invention relates to an exhaust gas purification catalyst using a reducing agent as a reducing agent, a production method thereof, and an exhaust gas purification method.
[0002]
[Prior art]
NOx in flue gas discharged from power plants, various factories, automobiles, etc. is a causative substance of photochemical smog and acid rain. As an effective removal method, ammonia (NH _Three ) Is widely used mainly in thermal power plants. For the catalyst, titanium oxide (TiO2) containing vanadium (V), molybdenum (Mo) or tungsten (W) as an active component is used. ₂ ) Based catalysts are used, especially those containing vanadium as one of the active components are not only high in activity, but also less deteriorated due to impurities contained in the exhaust gas, and can be used from a lower temperature. The current mainstream of denitration catalyst is disclosed in JP-A-50-12681.
[0003]
From the viewpoint of environmental conservation in recent years, the total amount restriction is applied to NOx emissions for fixed sources such as large-capacity boilers for power plants, and it is possible to operate with the NOx content in the exhaust gas discharged from the facility kept at a very low level. It has become essential. For this reason, a method of increasing the catalyst filling amount in the ammonia reduction type denitration apparatus and increasing the ammonia injection amount to operate the denitration apparatus at a high denitration rate has been studied. With the demand for such advanced denitration, it is inevitable to install a decomposition catalyst and increase ammonia in order to reduce unreacted ammonia that was not used in the denitration reaction. For this reason, unreacted ammonia (hereinafter referred to as leak NH) _Three ) Also has become essential to reduce to the same level as the NOx level, but the increase in unreacted ammonia is inevitable in the above-described high denitration rate operation. For this reason, installation of a decomposition catalyst for reducing unreacted ammonia, uniform injection / mixing of ammonia, and the like have been studied. The present inventors also invented a denitration catalyst having a decomposition activity of ammonia comprising a porous body supporting a noble metal and a titanium oxide-based composition, and using it, a high denitration rate and a low leak NH _Three Have been filed (Japanese Patent Application No. 3-31308, Japanese Patent Application No. 4-138514, etc.).
[0004]
[Problems to be solved by the invention]
Among the above prior art catalysts, the catalysts of the present inventors' Japanese Patent Application No. 3-312308 and Japanese Patent Application No. 4-138514 have high unreacted ammonia decomposition activity, such as gas fired boilers. Very high denitration rate and low leak NH for clean exhaust gas purification _Three Although it was an epoch-making catalyst capable of realizing the concentration, many improvements as shown in the following (a) to (c) were also left.
[0005]
(B) The oxidation activity of the precious metal that is a catalyst component is high, and in order to obtain the same denitration rate, NH _Three It is necessary to increase the / NO ratio, and ammonia consumption increases.
FIG. 4 shows a denitration catalyst (A) having no decomposition activity of unreacted ammonia and NH of a conventional catalyst (B) having an unreacted ammonia decomposition activity as disclosed in Japanese Patent Application No. 4-138514 _Three NOx removal rate and leak NH when the / NO ratio is changed _Three The amount is shown as NH _Three High NOx removal rate and low leakage NH by increasing / NO ratio _Three Although the amount can be satisfied, the formula (1)
2NH _Three + 3 / 2O ₂ → N ₂ + 3H ₂ O (1)
NH _Three In order to obtain the same denitration rate, NH cannot be ignored. _Three Compared to those that do not have decomposition activity, a large amount of NH _Three An injection was required.
[0006]
(B) NH _Three Oxidizing component of noble metal has high oxidation activity and exhaust gas is SO ₂ In the case of containing the following formula (2)
SO ₂ + 1 / 2O ₂ → SO _Three (2)
SO ₂ Oxidation reaction occurs, SO in exhaust gas _Three In some cases, the concentration increased and acid corrosion of the downstream equipment increased.
[0007]
(C) Volatile oxides become non-volatile by an oxidation reaction such as when volatile oxides such as arsenic, selenium, and rhenium are contained in exhaust gas such as coal exhaust gas, and accumulate in the catalyst. _Three There was a problem that the decomposition rate of the ash decreased with time.
[0008]
The object of the present invention is to eliminate the problems of the conventional catalysts described above, and to provide SO, which is an essential property when used in oil and coal combustion exhaust gas. ₂ An object of the present invention is to provide an exhaust gas purification catalyst that prevents reduction in oxidation activity and prevents deterioration due to volatile oxides such as arsenic oxide, a method for producing the same, and an exhaust gas purification method. Another object of the present invention is NH, which is a reducing agent added to exhaust gas. _Three An object of the present invention is to provide a denitration catalyst that can reduce an increase in consumption, a method for producing the catalyst, and a method for purifying exhaust gas.
[0009]
Another object of the present invention is to provide sulfur dioxide (SO ₂ ) Sulfur trioxide (SO _Three Longer reduction of unreacted ammonia and leakage of unreacted ammonia by suppressing the conversion to), suppressing the increase in the amount of ammonia used, and preventing the degradation of unreacted ammonia decomposition activity by volatile oxide vapors such as arsenic Ammonia (NH that can be maintained for a period of time _Three ) As a reducing agent, a manufacturing method thereof, and an exhaust gas purification method.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the present invention has the following configuration. A composition comprising an oxide of one or more elements selected from titanium oxide and molybdenum (Mo), tungsten (W), vanadium (V), or a composition comprising a zeolite carrying copper (Cu) or iron (Fe) The first component is made of at least one metal selected from iridium (Ir), palladium (Pd), rhodium (Rh), and ruthenium (Ru) and platinum (Pt). It has an ammonia reduction function of nitrogen oxide and an oxidative decomposition function of ammonia comprising a second component previously supported on a porous body, the weight ratio of which exceeds 0 and is 5 or less. Contains sulfur dioxide and volatile oxides Exhaust gas of It is a purification catalyst.
[0011]
The catalyst of the present invention is a catalyst composition that is active in the reduction reaction of NOx with ammonia as the first component, and platinum (Pt) as the main component as the second component, and iridium (Ir), palladium (Pd), rhodium (Rh) ) Or one or more noble metals selected from ruthenium (Ru) and high silica zeolite, silica, alumina More than one kind selected from It is obtained by mixing the two using a porous material.
[0012]
Specifically, as the first component, Ti-V, Ti-Mo, Ti-W, Ti-V-W, Ti-Mo-V combination oxides prepared in advance by a known method, Cu or Fe are used. NH of NOx such as supported zeolite (such as mordenite) _Three As the second component, a material obtained by firing a composition in which the above metal element is supported in advance by ion exchange, impregnation, or the like on zeolite, porous silica, or porous alumina is used as the second component.
[0013]
The precious metal in the second component is mainly composed of Pt, and one or more precious metals selected from Ir, Pd, Rh, and Ru are added to the precious metal. The amount of the precious metal added is such that the weight ratio of precious metal / Pt is 0. The noble metal is added in the range of 5 or less, and the noble metal is used in the form of a mixed solution of chloride, nitrate, and organic salt simultaneously or sequentially by being combined and used.
[0014]
In addition, in the method of mixing both components into a catalyst body,
(1) A method in which a first component prepared in advance and a second component powder are directly formed into pellets by a dry process,
(2) A paste obtained by kneading both component powders in the presence of water at a predetermined ratio and adding an organic / inorganic binder or inorganic fiber as necessary is formed into a honeycomb or applied to a metal substrate. Method
The general method used for the conventional denitration catalyst can be used. Furthermore, the obtained molded body is dried and fired as necessary.
[0015]
For example, at least one elemental compound of V, Mo, and W is added to a titanium compound and mixed with water, dried and calcined, or zeolite supported by ion exchange of Cu or Fe as the first component, First, Pt and at least one metal selected from Ir, Pd, Rh, Ru as a porous material such as zeolite, silica, alumina, etc. are supported, and then fired as the second component. The first component and the second component Are mixed, then formed into a predetermined shape, dried and fired to obtain the catalyst of the present invention.
[0016]
The catalyst of the present invention may be produced by any known method including the preparation method,
(A) Ir, Pd, Rh or Ru is supported on a porous support together with Pt, and the weight ratio of Ir, Pd, Rh or Ru to Pt is more than 0 and less than 5, preferably more than 0 and less than 2 In the range of
(B) NH of NO with respect to the noble metal-supported porous body (second component) _Three It is desirable that the weight ratio of the catalyst component (first component) having the above oxidation activity is 80% or more and the total noble metal content is 100 ppm or less.
[0017]
3 (a) to 3 (c) show usage forms of the catalyst of the present invention. A reactor 2, a heat exchanger 3, an electrostatic precipitator 4, and a chimney 5 are arranged in this order in the exhaust gas flow path from the boiler 1. In addition, NH in the upstream part of the reactor 2 _Three An injection line 6 is provided. Then, a denitration catalyst layer is formed using the catalyst 7 of the present invention in part in the reactor 2 or in combination with a known denitration catalyst 8 such as a conventional titanium oxide catalyst. FIG. 3A shows an example in which a denitration catalyst layer is formed in the entire reactor 2 using the catalyst 7 of the present invention, and FIG. FIG. 3C shows an example in which the catalyst 7 of the present invention is arranged on the flow side to form a denitration catalyst layer. FIG. 3C shows the catalyst 7 of the present invention between two known denitration catalysts 8 in the reactor 2. This is an example in which a denitration catalyst layer is formed by arranging. 3 (a) to 3 (c), NH which is a feature of the catalyst 7 of the present invention _Three Of nitrogen oxides (NOx) by oxygen and oxidative decomposition of unreacted ammonia into nitrogen and water to leak NH _Three In addition to the effect of reducing the NO, the NH _Three Can reduce the consumption of SO ₂ SO _Three Can be maintained at a low level, not only the adverse effect on the downstream equipment can be reduced, but also high catalytic activity can be maintained for a long time.
[0018]
The characteristics of the catalyst 7 of the present invention are characterized in that the kind of the noble metal in the second component and the second component and the first component are mixed as described above, and the preparation method also satisfies any of the above requirements. It goes without saying that even a preparation method can be adopted. However, a superior catalyst can be obtained by using the following method.
[0019]
As the first component of the catalyst 7 of the present invention, various types as described above can be used, and in particular, the catalyst component is composed of elements such as Ti-V, Ti-V-Mo, Ti-W-V and the like. Good results are obtained when oxide catalysts are used. These are prepared by adding a salt such as vanadium, molybdenum, or tungsten oxyacid salt to a slurry of hydrous titanium oxide such as titamethanoic acid, evaporating water using a heating kneader, drying, and after drying, 400 ° C. to 700 ° C. It can be obtained by baking at 0 ° C. and grinding if necessary.
[0020]
The second component of the catalyst 7 of the present invention is zeolite, silica, alumina in advance. More than one kind selected from It is prepared by being supported in the micropores of the porous body by ion exchange or kneading. Porous materials used for the second component are mordenite, clinoptilolite, erionite, zeolites such as Y-type zeolite, sodium-substituted, calcium-substituted, etc., silica having a surface area of 100 m2 / g to 500 m2 / g Alumina or the like can be used. The particle size at the time of use is preferably about 1 to 10 μm, and can be pulverized in advance. These are immersed in an aqueous solution in which at least one or more precious metals selected from Pt and other precious metals (Ir, Pd, Rh, or Ru) are dissolved in the form of chlorides, nitrates, or ammine complexes, and are subjected to ion exchange. Evaporated to dryness with an aqueous solution, supported by 0.01 wt% to 0.1 wt% of the noble metal, and then fired to decompose the noble metal salt into a metal. The addition ratio of the other noble metal added to Pt is more than 0 and 5 or less, preferably 2 or less in weight ratio to Pt.
[0021]
The mixing ratio of the first and second components varies depending on the amount of noble metal supported in the second component, but the second component / first component ratio (hereinafter referred to as second component / first component ratio) is 20 / 80-0. 5 / 99.5 Desirably, the range of 10/90 to 1/99 (weight ratio) is appropriate.
[0022]
To the powders of both the first and second components, water and a known moldability improver such as an inorganic binder, a molding aid, and inorganic fibers are added as necessary, and the paste is kneaded with a kneader such as a kneader Shape.
[0023]
The obtained paste-like catalyst is applied to an inorganic fiber network substrate, a metal substrate roughened by thermal spraying or the like and formed into a plate-like catalyst, or formed into a columnar shape or a honeycomb shape by an extruder. The molded body is used after being dried and fired at a temperature at which sulfate remains as a sulfate, usually 450 ° C. to 550 ° C.
[0024]
The obtained catalyst 7 of the present invention is packed as a catalyst 7 constituting a part of the denitration catalyst layer of the reactor 2 or a conventional known denitration catalyst 8 as shown in FIG. In the region where the NOx concentration is high, it functions as a denitration catalyst, and in the region where the NOx concentration in the exhaust gas decreases, it functions as a decomposition catalyst for unreacted (surplus) ammonia. Use conditions are not particularly limited, but leak NH which is a feature of the catalyst 7 of the present invention. _Three NOx in exhaust gas and NH that is a reducing agent _Three Molar ratio (NH _Three / NOx ratio) is 0.8 or more, and is suitable as a denitration apparatus that performs high denitration rate operation.
[0025]
The weight ratio of Pt in the second component of the catalyst 7 of the present invention and the precious metal added thereto is particularly important. When the weight ratio of the other precious metal to Pt is small, the formulas (1) to (3) When the side reaction is not sufficiently suppressed and is too large, the reaction of the formula (5) becomes difficult to occur and leak NH _Three This leads to a decrease in the decomposition rate. The weight ratio can be selected from more than 0 to 5 weight ratio or less, but good results can be easily obtained when it is selected to be 2 weight ratio or less, or depending on the noble metal to be added, 1 weight ratio or less.
[0026]
In the present invention, the ratio of the second component / first component is also important. Among the ranges described above, the ratio of the second component / first component is selected to be small by using zeolite, silica, alumina, etc. with a large amount of noble metal supported. In addition, it is preferable that the amount of noble metal supported by the entire catalyst is in the range of 1 to 1000 ppm, preferably 10 to 100 ppm. This is because the micropores formed by the second component are sparsely present in the macropores formed by the first component, and NH _Three Is selectively adsorbed on the first component and is easily used in the denitration reaction. Further, reducing the amount of noble metal has an effect of facilitating separation of the denitration reaction and the oxidation reaction of ammonia depending on the presence or absence of NO, in addition to the economic effect of reducing the unit cost of the catalyst.
[0027]
Further, the second component / first component ratio should be selected to be small when the entire catalyst layer is composed of the catalyst 7 of the present invention, and should be increased when a part of the catalyst 7 of the present invention is used in combination with the conventional catalyst. At the same time, if the noble metal content is increased, good results are easily obtained.
[0028]
Even if the exhaust gas contains a volatile oxide of arsenic (As), selenium (Se) and / or rhenium (Re), the catalytic activity of the present invention does not decrease.
[0029]
[Action]
A conventional denitration catalyst having an activity of decomposing unreacted ammonia is a porous carrier supporting a noble metal and a NOx NH represented by a Ti-W-V system or the like. _Three And a catalytic component having reducibility by the method (Japanese Patent Application No. 3-31308 and Japanese Patent Application No. 4-138514). In these conventional catalysts, unreacted ammonia that has remained or was not used in the denitration reaction of the following formula (4) generated on components such as Ti-W-V system is reacted with the reaction of formula (5) on the surface of the noble metal. Is epoch-making by partially oxidizing to NO, and then reducing the remaining unreacted ammonia to nitrogen again by the reaction of formula (4) to express a high denitration rate and a high unreacted ammonia decomposition activity It was something.
NH _Three + NO + 1 / 4O ₂ → N ₂ + 3 / 2H ₂ O (4)
NH _Three + 3 / 2O ₂ → NO + 3 / 2H ₂ O (5)
[0030]
However, in these catalysts, since a component in which a noble metal such as Pt, Pd, Rh, etc. is supported alone on a porous carrier is used, an attempt to obtain a high unreacted ammonia decomposition rate increases the oxidation activity of the catalyst. Caused problems. That is, NH in formula (1) _Three The consumption reaction is large, and in order to obtain a high denitration rate, many NH _Three In the exhaust gas due to the reaction of formula (2) ₂ SO _Three Which is oxidized on the downstream side of the exhaust gas flow path, and the volatile oxide exemplified in Formula (3) is converted into a non-volatile oxide, which causes a non-volatile oxide on the catalyst surface. It is easy to deteriorate in coal exhaust gas by accumulating.
2NH _Three + 3 / 2O ₂ → N ₂ + 3H ₂ O (1)
SO ₂ + 1 / 2O ₂ → SO _Three (2)
As ₂ O _Three + O ₂ → As ₂ O _Five (3)
[0031]
The catalyst 7 of the present invention is characterized in that Ir, Pd, Rh, or Ru is added to Pt, which is particularly excellent in the reaction of the formula (5). By setting it as such a composition, the reaction activity of Formula (5) is equivalent to the said conventional catalyst of the present inventors, and the side reaction of Formula (1)-(3) can be suppressed greatly. As a result, despite the fact that unreacted ammonia can be efficiently removed, an increase in ammonia consumption and SO ₂ SO _Three The catalyst is hardly deteriorated due to the non-volatility of the volatile oxide.
[0032]
As a result, SO, such as petroleum and coal combustion exhaust gas, for which conventional catalysts could not be used. ₂ In addition to decomposing unreacted ammonia in the denitration equipment for contained exhaust gas, NH _Three High denitration rate and low leakage NH without increasing usage _Three It is possible to realize a denitration apparatus.
[0033]
【Example】
An embodiment of the present invention will be described. The present invention is not limited to the following examples.
Hereinafter, the present invention will be described in detail using specific examples.
[0034]
Example 1
Metatitanate slurry (TiO ₂ Content: 30wt%, SO _Four Content: 8 wt%) 67 kg and ammonium paratungstate ((NH _Four ) _Ten H _Ten ・ W ₁₂ O ₄₆ ・ 6H ₂ 2.4) kg of O) and 0.63 kg of ammonium metavanadate were added and kneaded while evaporating water using a heating kneader to obtain a paste having a water content of about 36%. This was extruded into a 3φ columnar shape, granulated, dried in a fluidized bed dryer, and then calcined in the atmosphere at 550 ° C. for 2 hours. The obtained granule was pulverized with a hammer mill so that the particle size of 1 μm or less was 60% or more to obtain a denitration catalyst powder as the first component. The composition at this time is V / W / Ti = 2/5/92 (atomic ratio).
[0035]
On the other hand, chloroplatinic acid (H ₂ [PtC ₁₆ ] 6H ₂ O) 0.332 g and iridium chloride (IrCl _Four ) 0.217 g was dissolved in 1 liter of water, 500 g of high surface area fine silica (Tonda Pharmaceutical Co., Ltd .: Microcomputer F) was added and evaporated to dryness on a sand bath to carry Pt. This was dried at 180 ° C. for 2 hours and then calcined at 500 ° C. for 2 hours to prepare 0.025 wt% Pt-0.025 wt% Ir-silica as a second component. At this time, the Ir / Pt weight ratio is 1.
[0036]
Separately, a mesh of 1400 E-glass fibers with a fiber diameter of 9 μm and plain weave with a roughness of 10 / inch is impregnated with a slurry of 40% titania, 20% silica sol, 1% polyvinyl alcohol, The catalyst base material was obtained by drying at 150 ° C. to give rigidity.
[0037]
To 19.8 kg of the first component and 200 g of the second component, 5.3 kg of silica / alumina inorganic fiber and 17 kg of water were added and kneaded with a kneader to obtain a catalyst paste. The prepared catalyst mixture was placed between the two substrates, and the catalyst was pressure-bonded between the stitches and the surface of the substrate by passing through a pressure roller to obtain a plate catalyst having a thickness of about 1 mm. The obtained catalyst was dried at 180 ° C. for 2 hours and then calcined in the atmosphere at 550 ° C. for 2 hours. The second component / first component ratio (weight ratio) of the first component and the second component in the catalyst is 1/99, and the noble metal content corresponds to 5 ppm excluding the catalyst substrate and inorganic fibers.
[0038]
Examples 2-4
The iridium chloride of Example 1 was converted to palladium nitrate (Pd (NO _Three ) ₂ ) 0.271 g (Example 2), rhodium nitrate (Rh (NO _Three ) _Three ・ 2H ₂ O) 0.393 g (Example 3) and ruthenium chloride (RuCL) _Four ・ 5H ₂ O) A catalyst was prepared in the same manner as in Example 1 except that 0.237 g (Example 4) was used.
[0039]
The prepared catalyst has a noble metal content of 5 ppm, and the Pd / Pt, Rh / Pt and Ru / Pt weight ratios are all 1.
[0040]
Comparative Examples 1-5
Instead of the noble metal of Example 1, chloroplatinic acid, iridium chloride, palladium chloride, rhodium chloride and ruthenium chloride are used alone, and the addition amounts are 0.665 g, 0.434 g, 0.542 g, 0.786 g and 0.474 g, respectively. As in Example 1, a catalyst was prepared.
[0041]
The catalysts of Examples 1 to 4 and Comparative Examples 1 to 5 were cut into a width of 20 mm and a length of 100 mm, and three reactors 2 (FIG. 3) were packed at intervals of 3 mm. The concentration of unreacted ammonia detected at the outlet of the reactor 2 was measured, and the decomposition rate of unreacted ammonia was calculated. At the same time, SO before and after the catalyst layer in the reactor 2 ₂ Measure the concentration of SO ₂ From the rate of decrease in SO ₂ The oxidation rate of was calculated.
[0042]
[Table 1]

[0043]
Here, the decomposition rate of unreacted ammonia is obtained by the following equation.
Unreacted NH _Three Decomposition rate (%) = ([NH _Three ] In- [NH _Three ] Denox- [NH _Three ] Out)
÷ ([NH _Three ] In- [NH _Three ] Denox) × 100
[NH _Three ] In: Reactor inlet NH _Three concentration
[NH _Three ] Out: Reactor outlet NH _Three Concentration (Leak NH _Three concentration)
[NH _Three ] Denox: NH used for denitration reaction _Three Concentration of
The obtained results are summarized in Table 2.
[0044]
[Table 2]

[0045]
As is apparent from Table 2, the catalyst of Comparative Example 1 has a high unreacted ammonia decomposition rate, but has an SO decomposition rate. ₂ Oxidation rate is remarkably high, and there is concern about adverse effects on downstream equipment. ₂ It is unsuitable as a contained exhaust gas catalyst. The catalysts of Comparative Examples 2 to 5 are SO ₂ Although the oxidation rate is low, the decomposition rate of unreacted ammonia is very low and leak NH _Three It is obvious that it is unsuitable for the use aiming at the reduction of the above.
[0046]
On the other hand, the catalysts of Examples 1 to 5 according to the present invention can obtain a high NOx removal rate despite the high decomposition rate of unreacted ammonia, and SO ₂ The oxidation rate is as low as 1/4 to 1/10 or less that of the catalyst of Comparative Example 1.
[0047]
As described above, the catalyst of the above-described embodiment of the present invention combines SO and other noble metals to maintain a high denitration rate and a high unreacted ammonia decomposition rate, while maintaining SO ₂ It is characterized in that the oxidation rate is suppressed.
[0048]
Further, with respect to the catalyst of Example 1 and the catalyst of Comparative Example 1 having a high unreacted ammonia decomposition rate, NH 3 under the conditions shown in Table 1 were used. _Three Denitration rate when the concentration is changed and ammonia concentration detected at the catalyst layer outlet of the reactor 2 (leak NH _Three Concentration) was measured and shown in FIG. The catalyst of Example 1 and Comparative Example 1 is similar in that the leak concentration of unreacted ammonia is low, but the behavior of the denitration rate is greatly different. That is, in order to obtain a high denitration rate in the catalyst of Comparative Example 1, NH _Three / NO ratio greatly exceeds 1 and NH _Three In contrast to the catalyst of Example 1, NH in the vicinity of 1 which is the stoichiometric amount of the denitration reaction is required. _Three A high denitration rate can be achieved with the injection amount, and the operating cost of the denitration apparatus can be greatly reduced.
[0049]
Examples 5-8
In Examples 1 to 4, the total precious metal content is 5 ppm, and the weight ratio of Ir, Pd, Rh, and Ru to Pt is changed to 0.1, 0.5, 1, 2, and 5, respectively. Was prepared.
[0050]
About the obtained catalyst, it was SO under the conditions shown in Table 1. ₂ The catalyst obtained by measuring the oxidation rate, the denitration rate, and the decomposition rate of unreacted ammonia was subjected to SO under the conditions shown in Table 1. ₂ The results of measuring the oxidation rate, the denitration rate, and the decomposition rate of unreacted ammonia are shown in FIG. Compared with the catalyst of Comparative Example 1 in which the amount of other noble metal added to Pt is 0, the catalysts of Examples 5 to 8 are SO. ₂ A remarkable suppression effect of the oxidation rate is seen and at the same time an improvement in the denitration rate is observed. However, as the amount of noble metal added increases, the decomposition rate of unreacted ammonia decreases, and the weight ratio of Ir, Pd, Rh, Ru to Pt is 5 or less, preferably 2 or less.
[0051]
Example 9
At the same time that the amount of noble metal supported in the second component of the catalyst of Example 1 was changed to 0.01 wt%, the mixing ratio of the second component and the first component was changed to 0.5 / 99.5, and the total noble metal amount was changed to 0. A 5 ppm catalyst was prepared.
[0052]
Examples 10-12
In place of the precious metal of the second component in the catalysts of Comparative Examples 2 to 4, the weight ratio of Pd / Pt, Rh / Pt, Ru / Pt is 2, and the ratio of the second component / first component is 2/98, 20 / The catalyst was prepared by changing to 80, 10/90. In this case, the noble metal contents are 10 ppm, 100 ppm and 50 ppm, respectively.
[0053]
Comparative Examples 6-9
Examples 9 to 10 Catalysts having Pt loadings of 0.5, 10, 100, and 50 ppm were prepared by replacing all precious metals of the second component in the catalysts with Pt.
[0054]
For the obtained catalysts of Examples 9 to 12 and Comparative Examples 6 to 9, the NOx removal rate, the unreacted ammonia decomposition rate, the SO ₂ The oxidation rates were measured and summarized in Table 3.
[0055]
[Table 3]

[0056]
As can be seen from Table 3, the catalyst according to the present invention has a high denitration rate, a high unreacted decomposition rate, and a low SO, depending on the combination of Pt and other noble metals, from those with a small amount of noble metal supported. ₂ It can be seen that the oxidation rate can be maintained.
[0057]
Examples 13-16
In order to perform a test for accelerating the deterioration of the catalyst of the present invention using a volatile oxide such as arsenic oxide contained in coal exhaust gas, the catalysts of Examples 1 to 4 and the catalyst of Comparative Example 1 were used. Arsenic suboxide (As ₂ O _Three ) Add and evaporate the aqueous solution, As ₂ O _Three The concentration was adjusted to 50 ppm. Under these conditions, the arsenic oxide was adsorbed on the catalyst by maintaining for 5 hours, and the change in the catalyst performance was examined.
Table 4 summarizes changes in the unreacted ammonia decomposition rate of the catalyst before and after the accelerated deterioration test.
[0058]
[Table 4]

[0059]
As is apparent from Table 4, the catalyst according to the present invention exhibits durability against deterioration due to the vapor of arsenic oxide contained in coal exhaust gas and the like, and is optimal for a dirty exhaust gas denitration catalyst.
[0060]
Example 17
A catalyst was prepared in the same manner as in Example 1 except that the first component of Example 1 was replaced with mordenite obtained by ion exchange of 8% Cu. Using this catalyst, the denitration rate, the decomposition rate of unreacted ammonia, the SO ₂ When the oxidation rate was measured, 98%, 97%, and 1.9% were obtained, respectively, and the same performance as in Example 1 was obtained.
[0061]
【The invention's effect】
Conventional NH _Three NH, which is a disadvantage of denitration catalyst with cracking activity _Three Increase in consumption can be reduced and SO ₂ Oxidation activity can be very low, and adverse effects such as acidic corrosion of equipment disposed in the gas flow path to be treated on the downstream side of the denitration catalyst can be reduced.
[0062]
Furthermore, the catalyst according to the present invention decomposes unreacted ammonia even if it is used for the treatment of coal combustion exhaust gas, industrial waste combustion furnace exhaust gas, and waste incinerator exhaust gas containing volatile oxide vapor such as arsenic oxide as catalyst poison. The activity does not decrease for a long period of time and can be used to reduce ammonia leaking from the denitration reactor for treating these exhaust gases.
[Brief description of the drawings]
FIG. 1 is a diagram showing that a denitration catalyst according to an embodiment of the present invention is effective in reducing the amount of ammonia used.
FIG. 2 shows that the catalyst composition of one embodiment of the present invention is SO. ₂ It is a figure which shows that it is suitable for suppression of the oxidation rate of this.
FIG. 3 is a view showing an embodiment in which the catalyst of the present invention is disposed in a gas flow path to be treated.
FIG. 4 is an explanatory diagram for illustrating a problem to be solved by a conventional denitration catalyst invented by the present inventors.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Boiler, 2 ... Reactor, 3 ... Heat exchanger, 4 ... Electric dust collector, 5 ... Chimney,
6 ... Ammonia injection line, 7 ... Catalyst of the present invention, 8 ... Known denitration catalyst

Claims

A composition comprising a titanium oxide and an oxide of one or more elements selected from molybdenum, tungsten and vanadium or a composition comprising a zeolite supporting copper or iron is used as the first component, from iridium, palladium, rhodium and ruthenium. Nitrogen oxidation characterized by comprising at least one selected metal and platinum, and comprising a second component previously supported on the porous body, the weight ratio of the metal to platinum being greater than 0 and not greater than 5 A catalyst for purification of exhaust gas containing sulfur dioxide and volatile oxides, which has an ammonia reduction function of substances and an oxidative decomposition function of ammonia.

2. The ammonia reduction of nitrogen oxide according to claim 1, wherein the weight ratio of at least one metal selected from iridium, palladium, rhodium, and ruthenium in the second component to platinum is more than 0 and 2 or less. A purification catalyst for exhaust gas containing sulfur dioxide and volatile oxide having a function and an oxidative decomposition function of ammonia.

3. The ratio of the second component / first component (weight ratio) is 20/80 to 0.5 / 95.5, and the content of the noble metal in the catalyst is 100 ppm or less. A catalyst for purifying exhaust gas containing sulfur dioxide and volatile oxide, which has an ammonia reduction function and an oxidative decomposition function of ammonia.

At least one elemental compound of vanadium, molybdenum, or tungsten is added to and mixed with water in a titanium compound, dried and calcined, or a zeolite loaded with copper or iron ion-exchanged as a first component. At least one metal selected from iridium, palladium, rhodium, and ruthenium as platinum and other metals is supported on one or more porous bodies selected from silica, alumina, and fired to form a second component. It contains sulfur dioxide and volatile oxides, which have a nitrogen oxide reduction function and ammonia oxidative decomposition function, which are formed by mixing the two components, then shaping them into a predetermined shape, drying and firing to form a catalyst. method for producing a purifying catalyst of the exhaust gas.

Each component is mixed at a weight ratio of the second component / first component ratio of 20/80 to 0.5 / 95.5, and the precious metal is mixed so that the content of the precious metal in the catalyst is 100 ppm or less. The method for producing a purification catalyst for exhaust gas containing sulfur dioxide and a volatile oxide having a nitrogen oxide reduction function and an ammonia oxidative decomposition function according to claim 4.

The exhaust gas purification catalyst according to any one of claims 1 to 3 is contacted with exhaust gas in the presence of ammonia to reduce and remove nitrogen oxides in the exhaust gas, and to oxidatively decompose unreacted ammonia. A method for purifying exhaust gas containing sulfur dioxide and volatile oxide .

Exhaust gas containing nitrogen oxides and sulfur dioxide according to claim 6, wherein the mixing of ammonia with the exhaust gas so that the molar ratio of ammonia to nitrogen oxides in the exhaust gas is 0.8 or more A method for purifying exhaust gas containing volatile oxides .

It said volatile oxides Gahiso, selenium and method for purifying exhaust gas containing the claims 6 or 7 sulfur dioxide and volatile oxides, wherein the at least one element of rhenium.

A combination of the exhaust gas purification catalyst according to any one of claims 1 to 3 with a denitration catalyst to reduce and remove nitrogen oxides in the exhaust gas, and oxidatively decompose unreacted ammonia and sulfur dioxide, A method for purifying exhaust gas containing volatile oxides .