JP3793283B2

JP3793283B2 - Exhaust gas purification catalyst and exhaust gas purification apparatus using the same

Info

Publication number: JP3793283B2
Application number: JP15978996A
Authority: JP
Inventors: 泰良加藤; 尚美今田
Original assignee: Babcock Hitachi KK
Current assignee: Mitsubishi Power Ltd
Priority date: 1996-06-20
Filing date: 1996-06-20
Publication date: 2006-07-05
Anticipated expiration: 2016-06-20
Also published as: JPH105591A

Description

【０００１】
【発明の属する技術分野】
本発明は、排ガス浄化用触媒に係り、特に排ガス中の窒素酸化物（ＮＯｘ）と一酸化炭素（ＣＯ）とを同時に除去することが可能なアンモニア（ＮＨ₃）還元脱硝触媒、および未反応なままリークするＮＨ₃（リークＮＨ₃）の分解活性と脱硝反応活性とを合わせ持つ高活性な多元機能脱硝触媒とその製造法および該触媒を排ガス流路に配置した排ガス浄化装置に関する。
【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）、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に主流になっている。
【０００３】
近年、環境の保全に関する気運が高まり、排ガス中のＮＯｘ、硫黄酸化物（ＳＯｘ）だけでなく、ＣＯや接触還元脱硝法の還元剤に用いる未反応ＮＨ₃の排出をも抑えることが望まれてきている。本発明者らはこうした社会的ニーズに対応すべく、白金（Ｐｔ），イリジウム（Ｉｒ）等の金属を多孔体に担持したものと脱硝活性を有する酸化チタン系触媒成分とを混合して前者を触媒内に不均質に存在させることによる触媒（多元機能脱硝触媒）を発明している（特願平３−３１２３０８号、特願平７−９５１０７号等）。これらの触媒は、アンモニアを還元剤とする脱硝活性に優れるだけでなく、ＮＯｘと同時にＣＯも除去できる他、未反応ＮＨ₃を水と窒素に酸化分解して脱硝装置からの未反応ＮＨ₃リーク量を大幅に低減できるものであり、多元機能触媒と呼べるものであった。
【０００４】
【発明が解決しようとする課題】
しかしながら、従来上記技術になる多元機能触媒を使用した装置では、還元剤として注入するＮＨ₃の消費量が増大する傾向があり、その防止という点では充分対策されているとはいえなかった。また、同一の注入ＮＨ₃対処理ガス中ＮＯｘ比（以下ＮＨ₃／ＮＯ比）では脱硝率が低く、改善すべき余地があった。
【０００５】
この点を具体的に示したものが図６と図７である。図６は上記従来技術になる触媒の脱硝率とＣＯ酸化率との関係を示したものであり、図７は脱硝率とリークＮＨ₃分解活性との関係を示したものである。
【０００６】
従来技術のなかでＣＯ酸化活性またはリークＮＨ₃分解活性を有する触媒（多元機能脱硝触媒）では、それらの活性を持たない他の従来触媒（単機能脱硝触媒）に比べ脱硝率が低く、同一脱硝率を得るためには図７に示したようにＮＨ₃／ＮＯ比を増大する必要がある。このように、従来技術ではＣＯ酸化活性またはＮＨ₃の分解活性を脱硝触媒に合わせ持たせようとすると高い脱硝率が得られなかったり、同一脱硝率を得るためにＮＨ₃の消費量が増大したりする。この傾向は、より高いＣＯ酸化率やＮＨ₃分解率を得ようとすると顕著になり、上記従来の多元機能脱硝触媒の欠点となっていた。
【０００７】
本発明の課題は、上記した従来型の多元機能脱硝触媒の有する排ガス中の脱硝率の低下やＮＨ₃の消費量の増大を防止できる排ガス処理技術を提供し、脱硝活性はもとよりＣＯ酸化活性およびリークＮＨ₃分解活性の高い触媒を得ることにある。
【０００８】
【課題を解決するための手段】
本発明の上記課題は次の構成により達成できる。
すなわち、ＣＯの酸化活性およびＮＨ₃の酸化分解活性を有する成分を含む成形体表面に、ＣＯとＮＨ₃の酸化活性を有しない１ｍ ² 当たり０を超えて１００ｇ／ｍ ² 以下の量の脱硝活性成分からなる被覆層が存在する排ガス浄化用触媒、またはＮＯｘの分解活性を有する成分とＣＯの酸化活性およびＮＨ₃の酸化分解活性を有する成分を含む成形体の表面に、ＣＯとＮＨ₃の酸化活性を有しない１ｍ ² 当たり０を超えて１００ｇ／ｍ ² 以下の量の脱硝活性成分からなる被覆層を有する排ガス浄化用触媒である。
【０００９】
また、上記本発明の排ガス浄化用触媒を触媒層の一部または全部に充填し、排ガス中に還元剤を添加後排ガス中のＮＯｘの還元除去と同時にＣＯの酸化除去を行う排ガス浄化方法および排ガス浄化装置も本発明の範囲内である。
【００１０】
また、上記本発明の排ガス浄化用触媒の層をＮＨ₃還元法脱硝触媒の後流部に設置し、上流触媒層から流出する未反応ＮＨ₃を酸化分解して除去する排ガス浄化方法および排ガス浄化装置も本発明の範囲内である。
【００１１】
上記本発明をより具体的に説明すると次のような構成の触媒などを用いる。
（ａ）酸化チタン（ＴｉＯ₂）、酸化チタンとモリブデン（Ｍｏ）酸化物、酸化チタンとタングステン（Ｗ）酸化物またはこれらの酸化物とバナジウム（Ｖ）酸化物を主成分とする脱硝活性を有する触媒成分を第１成分、
（ｂ）白金（Ｐｔ）、イリジウム（Ｉｒ）、パラジウム（Ｐｄ）あるいはロジウム（Ｒｈ）を担持したシリカ、アルミナ、ゼオライトなどの多孔体粉末を第２成分
とする触媒成形体の表面にＶ含有量の高い触媒成分などの脱硝触媒層を形成させるものである。
【００１２】
すなわち、例えば図１に示すようにＴｉ、Ｍｏ、ＷまたはＶの酸化物を主成分とする第１成分にＰｔ、Ｉｒ、ＰｄまたはＲｈを担持したシリカ等の上記第２成分の混合物を金属基板やセラミック製網状物、織布等の基板に塗布してなる触媒成形体層２の表面にＴｉＯ₂、ＴｉＯ₂とＭｏ酸化物、ＴｉＯ₂とＷ酸化物またはこれらの酸化物とＶ酸化物を主成分とする触媒成分を被覆してなる被覆層１を新たに形成したことを特徴とするものである。
【００１３】
ここで触媒成形体層２は通常の方法により成形されたハニカム状または板状の成形体であり、
（１）脱硝活性を有する触媒成分と上記した各種貴金属を単独または複数担持したシリカ、アルミナ、ゼオライト等からなる組成物成形体、または
（２）Ｐｔ−ゼオライト、Ｐｔ−Ｉｒ−シリカなどの貴金属担持無機多孔体の成形体等である。
【００１４】
前記触媒成形体層２の表面の被覆層１はＴｉ、Ｍｏ、ＷあるいはＶとからなる触媒成分であり、基材となるハニカムまたは板状体が成形された後、粉末状または水を分散媒とするスラリの形でＴｉ、Ｍｏ、ＷあるいはＶとからなる触媒成分を付着させて被覆層１は形成され、被覆層１の触媒成分の付着量は小さく、５〜１００ｇ／ｍ²であり、被覆層１の厚みは０．１ｍｍ以下と薄い。
【００１５】
表面被覆層１の組成はその内部の触媒成形体層２の脱硝活性成分のそれと同一であってもよいが、触媒成形体層２の脱硝活性成分よりＶ成分の含有量を高くした方が一般に表面被覆による触媒特性改善効果が大きい。
【００１６】
被覆層は、具体的にはハニカムあるいは板状の湿式成形体がまだ湿った状態の時点で、上記した例えばＶ成分の量を多く含有する触媒成分の粉末やそのスラリと接することにより付着させるか、乾燥状態もしくはいったん焼成したものに触媒スラリを塗布または転着することにより形成することができる。
【００１７】
ここで重要なことは、触媒成形体層２と表面に形成する被覆層１が分離されている方が良く、その点、触媒成形体層２が乾燥される前の湿った状態で、被覆する触媒成分のスラリをローラ等で塗布転着する方法が好結果を与える。
【００１８】
表面に触媒の被覆層１を形成された触媒成形体層２は必要に応じて成形、乾燥、焼成工程等公知の触媒製造工程を経て、排ガス浄化に供される。
【００１９】
図２は従来の単機能触媒について反応時におけるＮＯｘ、ＣＯおよびＮＨ₃濃度の表面から内部への分布（反応速度に基づく理論的計算図）を示したものである。
【００２０】
図２において、ＮＯｘとＮＨ₃は脱硝活性成分の作用により窒素（Ｎ₂）と水（Ｈ₂Ｏ）に変換されるため、触媒表面から触媒内部に向かってその濃度は急激に減少する。これとは別に第２成分である貴金属成分の触媒作用により、ＣＯおよびＮＨ₃は酸化分解され、触媒表面から触媒内部に向かってその濃度が順次減少していく。このように２つの触媒作用を利用して触媒内部に各成分が拡散する過程で図２のような分布を持つようにすることにより、同一触媒で脱硝−ＣＯ酸化、脱硝−ＮＨ₃分解、あるいは脱硝−ＣＯ酸化−ＮＨ₃分解を可能にしているのが従来型の多元機能触媒である。
【００２１】
ここでＮＨ₃に注目すると、ＮＨ₃は脱硝反応と酸化分解反応との両者に使われるため、次に示す脱硝反応の反応ＮＨ₃／反応ＮＨ₃量論比＝１以上に消費され、触媒内部でのＮＨ₃濃度がＮＯ濃度を下回るようになる。このように従来型の多元機能触媒では、触媒内部で一部分ＮＨ₃の不足状態のゾーンが形成され、ＮＯが一定濃度以下にならない。この現象が脱硝率の低下、あるいは一定の脱硝率を得るためのＮＨ₃注入量の増大を引き起こしている原因となっている。
【００２２】
図３は図２と同様にＮＯ、ＮＨ₃およびＣＯについて、本発明になる触媒の表面と内部での分布を示したものである。本発明になる触媒では、脱硝活性のみを有する触媒層が表面層に薄く形成されており、その層内部で脱硝反応がまず進行し、大半のＮＯとＮＨ₃は脱硝反応に利用される。そして残存したＮＨ₃とＮＯが触媒内部に拡散し、脱硝活性と酸化活性とを有する触媒層に達する。触媒内部の層（内層）内にはＮＨ₃はＮＯに対して大過剰に存在するので、内層でＮＨ₃の酸化分解に加え、脱硝反応も高速で進行させることができる。
【００２３】
脱硝反応の大半は直ちに完結し、余剰となるＮＨ₃のみが内層の貴金属担持成分で酸化分解されることになり、脱硝率の低下を招くことがない。一方ＣＯの酸化分解に関しては触媒成形体の表面層は拡散抵抗として作用するが、その厚みが薄いのでＣＯの酸化分解性能にほとんど影響することがない。
【００２４】
このように、触媒成形体表面に脱硝活性のみを有する触媒成分層を形成することにより脱硝反応の低下をほとんど招くことなく、ＣＯもしくは余剰ＮＨ₃の分解を行うことが可能になる。
【００２５】
さらに、上記した原理から明らかなように、表面の被覆層を活性成分であるＶ化合物の増量などによって脱硝活性に優れるようにすれば、表面層の厚みは極めて薄くでき、ＣＯ酸化活性や余剰ＮＨ₃の分解活性はほとんど低下することがないようにできる。
【００２６】
また、内層における脱硝反応はほとんど生じないので次のような実用上優れた特徴を持った触媒を得ることが可能になる。
（１）内層の第１成分に相当する脱硝触媒成分の活性が低くても全体として高い脱硝活性が得られるため安価な触媒成分が使用できる。
（２）内層の貴金属成分濃度を増大する方法等によりＣＯあるいは余剰ＮＨ₃の分解活性を高くしても脱硝性能への影響がほとんどないため、高い脱硝−ＣＯ酸化−余剰ＮＨ₃分解活性共に優れた触媒を実現できる。
【００２７】
【発明の実施の形態】
以下、具体例を用いて本発明を詳細に説明する。
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）３．７５ｋｇおよびメタバナジン酸アンモン１．４６ｋｇを加え、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の粒径が６０％以上になるように粉砕し、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＝４．５／５／９０．５（原子比）である。
【００２８】
また、塩化白金酸（Ｈ₂［ＰｔＣｌ₆］・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（富田製薬製マイコンＦ）５００ｇを加えて砂浴上で蒸発乾固して貴金属塩を担持した。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、第２成分にした。このときのＩｒ−Ｐｔ重量比は１である。
【００２９】
これとは別に、繊維径９μｍのＥガラス性繊維１，４００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％、ポリビニルアルコール１％のスラリを含浸させ、１５０℃で乾燥して剛性を持たせ触媒基材を得た。
【００３０】
第１成分１９．６ｋｇと第２成分４００ｇ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枚の間に前記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、基材の編目間及び表面に触媒を圧着して厚さ約１ｍｍの板状の触媒成形体を得た。
【００３１】
一方、酸化チタン粉末２０ｋｇにモリブデン酸アンモニウム（（ＮＨ₄）₆・Ｍｏ₇Ｏ₂₄・４Ｈ₂Ｏ）２．５ｋｇ、メタバナジン酸アンモニウム２．３３ｋｇ、しゅう酸３．０ｋｇおよび水を加えてニーダで混練してペースト状にしたものを３φの柱状に造粒後、流動層乾燥器で乾燥し、さらに５００℃で２時間焼成し、続いてハンマーミルで粉砕して粒径１μｍ以下のものが５０％以上存在する脱硝触媒粉末を得た（Ｖ含有量：３．５６ｗｔ％）。得られた粉末１００ｇに水を加えてスラリにし、本スラリをゴムローラに薄くつけ、これを前記触媒成形体の表面に転がすことにより、上記板状の触媒成形体表面に触媒成分が１ｍ²当たり３５ｇになるように塗布し、その後１５０℃で乾燥後、５００℃で２時間焼成して触媒を得た。
【００３２】
本実施例の触媒成形体表面の脱硝触媒被覆層の厚みは０．１ｍｍ以下であり、密度から計算した被覆層の厚みは０．０３５ｍｍに相当する。
【００３３】
比較例１
実施例１における触媒成形体表面に脱硝触媒スラリを塗布しない触媒を調製した。
実施例１および比較例１の触媒について、表１の条件で脱硝活性とＣＯ酸化活性を測定し、結果を図４に示した。
【００３４】
本発明になる実施例１の触媒は高いＣＯ除去率であるにもかかわらず、脱硝率も高い結果が得られている。これに対し、比較例１の触媒はＣＯ除去率が高い点は実施例１と同様であるが、図４に示したＣＯ酸化成分の脱硝率への悪影響が顕著に現れ、極めて低い脱硝率しか得られていない。
【００３５】
また、図５には実施例１と比較例１の触媒について表２の条件でＮＨ₃注入量を変えることによりＮＨ₃／ＮＯ比を変化させて脱硝率と未反応ＮＨ₃の分解率を測定し、その結果を示す。
【００３６】
なお、リークＮＨ₃分解率（未反応ＮＨ₃分解率）は次の関係式で求めた。

【００３７】
実施例１および比較例１の触媒ともＮＨ₃分解率が高いことは同じであるが、同一ＮＨ₃／ＮＯ比における脱硝率を比較すると、比較例１の触媒に比べて実施例１の触媒は非常に高く、量論線に近い脱硝率が得られ、ＮＨ₃のロスが極めて少ないことが分かる。
【００３８】
一方、比較例１は同一ＮＨ₃／ＮＯ比における脱硝率が低いだけでなく、ＮＨ₃／ＮＯ比をいくら高くしても高脱硝率が得られなかった。
【００３９】
このように本発明になる触媒は、ＮＨ₃分解成分あるいはＣＯ酸化成分による脱硝性能の悪化を大幅に軽減し、多元機能触媒でありながら脱硝単機能触媒と同等の高い脱硝活性を得ることができる極めて優れた特徴を有するものである。
【００４０】
【表１】

【００４１】
【表２】

【００４２】
実施例２〜６
実施例１における第２成分の製法における塩化白金酸を０．６６４ｇに代えると共に塩化イリジウムを用いないで第２成分を調製した。これを用いて他は実施例１と同様に板状の触媒成形体を得、この表面へ実施例１と同一の脱硝触媒スラリを１ｍ²当たり、５、１０、３０、５０、１００ｇになるようにそれぞれ転着し、他は実施例１と同様にして触媒を得た。
【００４３】
本触媒の被覆層の厚みはいずれも０．１ｍｍ以下であり、密度から計算した被覆層の厚みはそれぞれ約０．００５、０．０１、０．０３、０．０５、０．１ｍｍに相当する。
【００４４】
実施例７
実施例１の触媒において、第１成分のパラタングステン酸アンモニウムを等モルのモリブデン酸アンモニウム（（ＮＨ₄）₆・Ｍｏ₇Ｏ₂₄・４Ｈ₂Ｏ）に代え、逆に実施例１の板状の触媒成形体表面に転着する脱硝触媒成分の調製におけるモリブデン酸アンモニウムを等モルのパラタングステン酸アンモニウムに変更して触媒を調製した。
【００４５】
実施例８
実施例１の第１成分と第２成分の混合比を０／１００、すなわち第２成分のみを用いて、板状の触媒成形体を調製し、この表面に脱硝触媒成分スラリを実施例１と同様に転着して触媒を得た。
【００４６】
比較例２
実施例２の触媒調製における板状触媒成形体への脱硝触媒スラリの転着を行わないことを除いて実施例２と同様の方法で本比較例の触媒を得た。
【００４７】
比較例３
実施例７の調製法における触媒スラリの転着を行わないことを除いて実施例７と同様の方法で本比較例の触媒を得た。
【００４８】
比較例４
実施例１において第２成分を用いないことを除いて実施例１と同様にして触媒を調製した。
【００４９】
比較例５
実施例８の調製法において脱硝触媒成分の表面転着を行わないことを除いて実施例８と同様にして触媒を調製した。
実施例１〜８および比較例１〜５の各触媒について表１の条件で３５０℃における脱硝率とＣＯの酸化率を測定し、また表２の条件で注入ＮＨ₃／ＮＯ比が１．２ｍｏｌ／ｍｏｌにおける脱硝率とリークＮＨ₃分解率を測定した。
【００５０】
得られた結果を表３にまとめて示した。
【表３】

【００５１】
表３から本発明の実施例になる触媒は、脱硝活性およびＣＯ酸化活性、リークＮＨ₃の分解率がいずれも高いことが解る。一方、表面に脱硝活性のみを有する触媒成分の転着を行わなかった比較例１〜３の触媒では脱硝率が極めて低かった。
【００５２】
このことから、本発明の触媒における表面への脱硝触媒成分の転着がＣＯ酸化活性やＮＨ₃の分解活性を高く維持したまま脱硝率を高くするのに極めて大きな効果があることは明らかである。
【００５３】
また、ＮＨ₃やＣＯの酸化成分である第２成分を含まない比較例４ではＣＯ酸化活性、ＮＨ₃分解活性が共に低く、第２成分のみの比較例５ではＣＯ酸化活性とＮＨ₃分解活性は高い値を示したもののＮＨ₃酸化によるＮＯｘ生成のため脱硝率はマイナスを示した。
【００５４】
これらの結果は、脱硝−ＣＯ酸化−リークＮＨ₃分解に共に高い性能を得るために、図１に示す触媒の構成が極めて有効であることを示しているものである。
【００５５】
【発明の効果】
本発明によれば、脱硝率、ＣＯ酸化率、未反応ＮＨ₃の分解率共に高い触媒が容易に得られる。これにより、各種発生源から放出されるＮＯｘの他ＣＯをも除去できるシステムが実現できるだけでなく、脱硝反応で使用されなかった未反応ＮＨ₃の大気への放出を大幅に低減できる。
また、上記用途に用いる従来触媒に比べ、同一脱硝率を得るためのＮＨ₃注入量を少なくでき経済的にも有利になる。
【図面の簡単な説明】
【図１】本発明の触媒の概要を示す図である。
【図２】本発明の要点を説明するための従来触媒および本発明の触媒における触媒内部の反応成分の分布を示す図である。
【図３】本発明の要点を説明するための従来触媒および本発明の触媒における触媒内部の反応成分の分布を示す図である。
【図４】本発明の効果を示す図である。
【図５】本発明の効果を示す図である。
【図６】従来触媒の問題点を明らかにするための図である。
【図７】従来触媒の問題点を明らかにするための図である。
【符号の説明】
１脱硝活性のみを有する被覆層
２脱硝活性、ＣＯ酸化活性、ＮＨ₃の酸化分解活性を有する触媒成形体層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification catalyst, and in particular, an ammonia (NH ₃ ) reduction denitration catalyst capable of simultaneously removing nitrogen oxide (NOx) and carbon monoxide (CO) in exhaust gas, and an unreacted catalyst. The present invention relates to a highly active multi-functional denitration catalyst having both decomposition activity and denitration reaction activity of NH ₃ (leak NH ₃ ) that leaks as it is, a manufacturing method thereof, and an exhaust gas purification device in which the catalyst is arranged in an exhaust gas flow path.
[0002]
[Prior art]
NOx in flue gas emitted from power plants, various factories, automobiles, etc. is a causative substance of photochemical smog and acid rain. As an effective removal method, NOx is emitted by selective catalytic reduction using NH ₃ as a reducing agent. Smoke denitration is widely used mainly in thermal power plants. As the catalyst, a titanium oxide (TiO ₂ ) -based catalyst containing vanadium (V), molybdenum (Mo), and tungsten (W) as active components is used, and those containing vanadium as one of the active components are particularly active. In addition to being high, the deterioration due to impurities contained in the exhaust gas is small, and it can be used from a lower temperature.
[0003]
In recent years, there has been an increase in the mood for environmental conservation, and it has been desired to suppress not only NOx and sulfur oxide (SOx) in exhaust gas but also emission of unreacted NH ₃ used as a reducing agent in CO and catalytic reduction denitration. ing. In order to respond to such social needs, the present inventors mixed a porous body with a metal such as platinum (Pt) and iridium (Ir) and a titanium oxide catalyst component having denitration activity to A catalyst (multi-functional denitration catalyst) by inhomogeneously existing in the catalyst has been invented (Japanese Patent Application No. 3-31308, Japanese Patent Application No. 7-95107, etc.). These catalysts not only have excellent denitration activity using ammonia as a reducing agent, but also can remove CO simultaneously with NOx, and oxidatively decompose unreacted NH ₃ into water and nitrogen to cause unreacted NH ₃ leakage from the denitration device. The amount can be greatly reduced, and it can be called a multi-functional catalyst.
[0004]
[Problems to be solved by the invention]
However, in the conventional apparatus using the multi-functional catalyst as described above, the consumption of NH ₃ to be injected as a reducing agent tends to increase, and it cannot be said that sufficient measures have been taken in terms of prevention thereof. In addition, the NOx ratio in the same injected NH ₃ to the processing gas (hereinafter referred to as NH ₃ / NO ratio) has a low denitration rate, and there is room for improvement.
[0005]
FIG. 6 and FIG. 7 specifically show this point. FIG. 6 shows the relationship between the NOx removal rate and the CO oxidation rate of the catalyst according to the prior art, and FIG. 7 shows the relationship between the NOx removal rate and the leakage NH ₃ decomposition activity.
[0006]
Among conventional technologies, catalysts that have CO oxidation activity or leak NH ₃ decomposition activity (multifunctional denitration catalysts) have a lower denitration rate than other conventional catalysts (single function denitration catalysts) that do not have these activities, and the same denitration In order to obtain the rate, it is necessary to increase the NH ₃ / NO ratio as shown in FIG. As described above, in the prior art, if the CO oxidation activity or NH ₃ decomposition activity is combined with the denitration catalyst, a high denitration rate cannot be obtained, or the consumption of NH ₃ increases to obtain the same denitration rate. Or This tendency becomes conspicuous when trying to obtain a higher CO oxidation rate and NH ₃ decomposition rate, which has been a drawback of the conventional multi-functional denitration catalyst.
[0007]
An object of the present invention is to provide an exhaust gas treatment technology capable of preventing a decrease in the denitration rate in an exhaust gas and an increase in NH ₃ consumption in the exhaust gas possessed by the above-described conventional multi-functional denitration catalyst. The object is to obtain a catalyst with high leak NH ₃ decomposition activity.
[0008]
[Means for Solving the Problems]
The said subject of this invention can be achieved by the following structure.
That is, denitration activity in an amount of more than 0 and less than 100 g / m ² per m ² not having CO and NH ₃ oxidation activity on the surface of the molded article containing a component having CO oxidation activity and NH ₃ oxidation decomposition activity CO and NH ₃ oxidation on the surface of a molded article containing an exhaust gas purification catalyst having a coating layer composed of components, or a component having NOx decomposition activity and CO oxidation activity and NH ₃ oxidation decomposition activity activity is a catalyst for exhaust gas purification having the coating layer exceeds the no 1 m ² per 0 consisting denitration active components of 100 g / m ² or less of the amount of.
[0009]
Further, an exhaust gas purification method and exhaust gas in which the catalyst for exhaust gas purification of the present invention is filled in a part or all of the catalyst layer, and after the addition of the reducing agent in the exhaust gas, the NOx in the exhaust gas is reduced and removed simultaneously with oxidation of CO. A purification device is also within the scope of the present invention.
[0010]
Further, the exhaust gas purification catalyst layer of the present invention is installed in the downstream portion of the NH ₃ reduction denitration catalyst, and the unreacted NH ₃ flowing out from the upstream catalyst layer is oxidized and removed to remove the exhaust gas purification method and exhaust gas purification. Devices are also within the scope of the present invention.
[0011]
More specifically, the present invention uses a catalyst having the following structure.
(A) Denitration activity mainly composed of titanium oxide (TiO ₂ ), titanium oxide and molybdenum (Mo) oxide, titanium oxide and tungsten (W) oxide, or these oxides and vanadium (V) oxide The catalyst component is the first component,
(B) V content on the surface of the catalyst molded body containing a porous powder of silica, alumina, zeolite or the like carrying platinum (Pt), iridium (Ir), palladium (Pd) or rhodium (Rh) as a second component. A denitration catalyst layer such as a high catalyst component is formed.
[0012]
That is, for example, as shown in FIG. 1, a mixture of the second component such as silica supporting Pt, Ir, Pd or Rh as a first component mainly composed of an oxide of Ti, Mo, W or V is used as a metal substrate. TiO ₂ , TiO ₂ and Mo oxide, TiO ₂ and W oxide, or these oxide and V oxide on the surface of the catalyst molded body layer 2 applied to a substrate such as a ceramic network or woven fabric. The coating layer 1 formed by coating a catalyst component as a main component is newly formed.
[0013]
Here, the catalyst molded body layer 2 is a honeycomb-shaped or plate-shaped molded body formed by a normal method,
(1) A molded composition composed of silica, alumina, zeolite or the like on which a catalyst component having denitration activity and the above-mentioned various noble metals are supported alone, or (2) Noble metal support such as Pt-zeolite or Pt-Ir-silica. An inorganic porous body molded body or the like.
[0014]
The coating layer 1 on the surface of the catalyst molded body layer 2 is a catalyst component made of Ti, Mo, W, or V. After the honeycomb or plate-like body serving as the base material is molded, powder or water is used as a dispersion medium. The coating layer 1 is formed by adhering a catalyst component composed of Ti, Mo, W or V in the form of a slurry, and the coating amount of the catalyst component of the coating layer 1 is small, being 5 to 100 g / m ² . The thickness of the coating layer 1 is as thin as 0.1 mm or less.
[0015]
The composition of the surface coating layer 1 may be the same as that of the denitration active component of the catalyst molded body layer 2 inside, but generally the content of the V component is higher than the denitration active component of the catalyst molded body layer 2. The effect of improving catalyst properties by surface coating is great.
[0016]
Specifically, when the honeycomb or plate-like wet molded body is still wet, the coating layer is attached by contacting the catalyst component powder containing a large amount of the above-described V component, for example, or its slurry. It can be formed by applying or transferring a catalyst slurry to a dry state or once fired.
[0017]
What is important here is that the catalyst molded body layer 2 and the coating layer 1 formed on the surface should be separated, and the catalyst molded body layer 2 is coated in a wet state before being dried. A method of applying and transferring the slurry of the catalyst component with a roller or the like gives a good result.
[0018]
The catalyst molded body layer 2 having the catalyst coating layer 1 formed on the surface is subjected to exhaust gas purification through known catalyst manufacturing processes such as molding, drying, and firing processes as necessary.
[0019]
FIG. 2 shows the distribution of NOx, CO and NH ₃ concentrations from the surface to the inside (theoretical calculation diagram based on the reaction rate) during the reaction of the conventional monofunctional catalyst.
[0020]
In FIG. 2, since NOx and NH ₃ are converted into nitrogen (N ₂ ) and water (H ₂ O) by the action of the denitration active component, their concentrations rapidly decrease from the catalyst surface toward the inside of the catalyst. Apart from this, CO and NH ₃ are oxidatively decomposed by the catalytic action of the precious metal component, which is the second component, and the concentration thereof gradually decreases from the catalyst surface toward the inside of the catalyst. In this way, by using the two catalytic actions to have the distribution as shown in FIG. 2 in the process of diffusion of each component inside the catalyst, denitration-CO oxidation, denitration-NH ₃ decomposition, or It is the conventional multi-functional catalyst that enables denitration-CO oxidation-NH ₃ decomposition.
[0021]
Here, paying attention to NH ₃ , since NH ₃ is used for both the denitration reaction and the oxidative decomposition reaction, the following denitration reaction reaction NH ₃ / reaction NH ₃ stoichiometric ratio = 1 or more is consumed, and the catalyst inside The NH ₃ concentration at this point becomes lower than the NO concentration. Thus, in the conventional multi-functional catalyst, a zone in which NH ₃ is partially deficient is formed inside the catalyst, and NO does not fall below a certain concentration. This phenomenon causes a decrease in the denitration rate or an increase in the amount of NH ₃ injection for obtaining a constant denitration rate.
[0022]
FIG. 3 shows the distribution on the surface and inside of the catalyst according to the present invention for NO, NH ₃ and CO as in FIG. In the catalyst according to the present invention, the catalyst layer having only the denitration activity is formed thinly on the surface layer, the denitration reaction first proceeds inside the layer, and most of NO and NH ₃ are utilized for the denitration reaction. Then, the remaining NH ₃ and NO diffuse into the catalyst and reach a catalyst layer having denitration activity and oxidation activity. Since NH ₃ exists in a large excess with respect to NO in the inner layer (inner layer) of the catalyst, denitration reaction can proceed at a high speed in addition to oxidative decomposition of NH _{3 in} the inner layer.
[0023]
Most of the denitration reaction is completed immediately, and only the excess NH ₃ is oxidatively decomposed by the noble metal-supported component in the inner layer, so that the denitration rate is not lowered. On the other hand, regarding the oxidative decomposition of CO, the surface layer of the catalyst molded body acts as a diffusion resistance, but since the thickness thereof is thin, the oxidative decomposition performance of CO is hardly affected.
[0024]
Thus, by forming the catalyst component layer having only the denitration activity on the surface of the catalyst molded body, it is possible to decompose CO or excess NH ₃ with almost no decrease in the denitration reaction.
[0025]
Further, as apparent from the above principle, if the surface coating layer is made to have excellent denitration activity by increasing the amount of the active compound V, etc., the thickness of the surface layer can be extremely reduced, and the CO oxidation activity and excess NH can be reduced. The degradation activity of ₃ can be made to hardly decrease.
[0026]
Further, since almost no denitration reaction occurs in the inner layer, it is possible to obtain a catalyst having the following practically excellent characteristics.
(1) Even if the activity of the denitration catalyst component corresponding to the first component of the inner layer is low, a high denitration activity is obtained as a whole, so that an inexpensive catalyst component can be used.
(2) Even if the decomposition activity of CO or surplus NH ₃ is increased by increasing the concentration of noble metal components in the inner layer, etc., there is almost no influence on the denitration performance, so both high denitration-CO oxidation-surplus NH ₃ decomposition activity is excellent. Catalyst can be realized.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail using specific examples.
Example 1
Metatitanic acid slurry (TiO ₂ content: 30wt%, SO ₄ content: 8 wt%) of ammonium paratungstate to _{_{67kg ((NH 4) 10 H}} 10 · W 12 O 46 · 6H 2 O) 3.75kg and metavanadate 1.46 kg of Ammon was 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 3φ columnar shapes, granulated, dried in a fluidized bed dryer, and then baked at 550 ° C. for 2 hours in the atmosphere. The obtained granule was pulverized with a hammer mill so that the particle size of 1 μm was 60% or more to obtain a denitration catalyst powder as the first component. The composition at this time is V / W / Ti = 4.5 / 5 / 90.5 (atomic ratio).
[0028]
In addition, 0.332 g of chloroplatinic acid (H ₂ [PtCl ₆ ] · 6H ₂ O) and 0.217 g of iridium chloride (IrCl ₄ ) dissolved in 1 liter of water are mixed with a high surface area fine silica (Tomita Pharmaceutical microcomputer). F) 500 g was added and evaporated to dryness on a sand bath to carry a noble metal salt. 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. The Ir—Pt weight ratio at this time is 1.
[0029]
Separately, a mesh of 1,400 twisted 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, and 1% polyvinyl alcohol. And dried at 150 ° C. to give rigidity to obtain a catalyst substrate.
[0030]
To 19.6 kg of the first component and 400 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. Placing the prepared paste-like catalyst mixture between the two substrates and passing it through a pressure roller, the catalyst is pressure-bonded between the stitches and the surface of the substrate to form a plate-shaped catalyst having a thickness of about 1 mm. Got the body.
[0031]
On the other hand, 20 kg of titanium oxide powder, 2.5 kg of ammonium molybdate ((NH ₄ ) ₆ · Mo ₇ O ₂₄ · 4H ₂ O), 2.33 kg of ammonium metavanadate, 3.0 kg of oxalic acid and water were added and kneaded with a kneader. The pasty product is granulated into a 3φ columnar shape, dried in a fluidized bed dryer, further baked at 500 ° C. for 2 hours, and then pulverized with a hammer mill to have a particle size of 1 μm or less. The present denitration catalyst powder was obtained (V content: 3.56 wt%). Water is added to 100 g of the obtained powder to make a slurry, and this slurry is thinly attached to a rubber roller, and this is rolled onto the surface of the catalyst molded body, whereby 35 g of catalyst component per 1 m ² is formed on the surface of the plate-shaped catalyst molded body. the coating is in, then dried at 0.99 ° C., to obtain a catalyst was calcined for 2 hours at 500 ° C..
[0032]
The thickness of the denitration catalyst coating layer on the surface of the catalyst molded body of this example is 0.1 mm or less, and the thickness of the coating layer calculated from the density corresponds to 0.035 mm.
[0033]
Comparative Example 1
A catalyst in which the denitration catalyst slurry was not applied to the surface of the catalyst molded body in Example 1 was prepared.
The catalyst of Example 1 and Comparative Example 1 were measured for denitration activity and CO oxidation activity under the conditions shown in Table 1, and the results are shown in FIG.
[0034]
Although the catalyst of Example 1 according to the present invention has a high CO removal rate, a high denitration rate is obtained. In contrast, the catalyst of Comparative Example 1 is similar to Example 1 in that the CO removal rate is high, but the adverse effect of the CO oxidation component shown in FIG. Not obtained.
[0035]
FIG. 5 also shows the NOx removal rate and the unreacted NH ₃ decomposition rate by changing the NH ₃ / NO ratio by changing the NH ₃ injection amount for the catalysts of Example 1 and Comparative Example 1 under the conditions shown in Table 2. And show the results.
[0036]
The leak NH ₃ decomposition rate (unreacted NH ₃ decomposition rate) was determined by the following relational expression.

[0037]
Although the catalyst of Example 1 and Comparative Example 1 have the same NH ₃ decomposition rate, the NOx removal rate at the same NH ₃ / NO ratio is the same as that of the catalyst of Example 1 compared to the catalyst of Comparative Example 1. It can be seen that the denitration rate is very high and close to the stoichiometric line, and the loss of NH ₃ is extremely small.
[0038]
On the other hand, Comparative Example 1 not only had a low denitration rate at the same NH ₃ / NO ratio, but could not obtain a high denitration rate no matter how high the NH ₃ / NO ratio was.
[0039]
As described above, the catalyst according to the present invention greatly reduces the deterioration of the denitration performance due to the NH ₃ decomposition component or the CO oxidation component, and can obtain a high denitration activity equivalent to that of the denitration monofunctional catalyst while being a multi-functional catalyst. It has extremely excellent characteristics.
[0040]
[Table 1]

[0041]
[Table 2]

[0042]
Examples 2-6
The second component was prepared by replacing chloroplatinic acid in the production method of the second component in Example 1 with 0.664 g and without using iridium chloride. Using this, a plate-shaped catalyst molded body was obtained in the same manner as in Example 1, and the same denitration catalyst slurry as in Example 1 was applied to this surface at 5, 10, 30, 50, 100 g per m ^2. The catalyst was obtained in the same manner as in Example 1 except for the above.
[0043]
The thickness of the coating layer of this catalyst is 0.1 mm or less, and the thickness of the coating layer calculated from the density corresponds to about 0.005, 0.01, 0.03, 0.05, and 0.1 mm, respectively. .
[0044]
Example 7
In the catalyst of Example 1, the ammonium paratungstate as the first component was replaced with an equimolar ammonium molybdate ((NH ₄ ) ₆ .Mo ₇ O ₂₄ .4H ₂ O). A catalyst was prepared by changing the ammonium molybdate in the preparation of the denitration catalyst component transferred to the surface of the catalyst molded body to equimolar ammonium paratungstate.
[0045]
Example 8
A mixing ratio of the first component and the second component of Example 1 was 0/100, that is, a plate-shaped catalyst molded body was prepared using only the second component, and a denitration catalyst component slurry was applied to this surface as in Example 1. Transfer was carried out in the same manner to obtain a catalyst.
[0046]
Comparative Example 2
A catalyst of this comparative example was obtained in the same manner as in Example 2 except that the denitration catalyst slurry was not transferred to the plate-shaped catalyst molded body in the catalyst preparation of Example 2.
[0047]
Comparative Example 3
A catalyst of this comparative example was obtained in the same manner as in Example 7 except that the catalyst slurry was not transferred in the preparation method of Example 7.
[0048]
Comparative Example 4
A catalyst was prepared in the same manner as in Example 1 except that the second component was not used in Example 1.
[0049]
Comparative Example 5
A catalyst was prepared in the same manner as in Example 8 except that surface transfer of the denitration catalyst component was not performed in the preparation method of Example 8.
For each of the catalysts of Examples 1 to 8 and Comparative Examples 1 to 5, the NOx removal rate and CO oxidation rate at 350 ° C. were measured under the conditions shown in Table 1, and the injected NH ₃ / NO ratio was 1.2 mol under the conditions shown in Table 2. The denitration rate and leak NH ₃ decomposition rate at / mol were measured.
[0050]
The results obtained are summarized in Table 3.
[Table 3]

[0051]
It can be seen from Table 3 that the catalyst according to the example of the present invention has high denitration activity, CO oxidation activity, and decomposition rate of leaked NH ₃ . On the other hand, in the catalysts of Comparative Examples 1 to 3 in which the catalyst component having only the denitration activity on the surface was not transferred, the denitration rate was extremely low.
[0052]
From this, it is clear that transfer of the denitration catalyst component to the surface of the catalyst of the present invention has a very large effect in increasing the denitration rate while maintaining high CO oxidation activity and NH ₃ decomposition activity. .
[0053]
In Comparative Example 4 which does not include the second component which is an oxidation component of NH ₃ or CO, both CO oxidation activity and NH ₃ decomposition activity are low, and in Comparative Example 5 having only the second component, CO oxidation activity and NH ₃ decomposition activity are low. Was high, but the NOx removal rate due to NH ₃ oxidation was negative.
[0054]
These results show that the structure of the catalyst shown in FIG. 1 is extremely effective in order to obtain high performance for both denitration-CO oxidation-leak NH ₃ decomposition.
[0055]
【The invention's effect】
According to the present invention, a catalyst having high denitration rate, CO oxidation rate, and decomposition rate of unreacted NH ₃ can be easily obtained. This not only realizes a system capable of removing CO in addition to NOx released from various generation sources, but also significantly reduces the release of unreacted NH ₃ that has not been used in the denitration reaction to the atmosphere.
Further, compared with the conventional catalyst used for the above-mentioned application, the NH ₃ injection amount for obtaining the same denitration rate can be reduced, which is economically advantageous.
[Brief description of the drawings]
FIG. 1 is a view showing an outline of a catalyst of the present invention.
FIG. 2 is a diagram showing the distribution of reaction components in the catalyst in the conventional catalyst and the catalyst of the present invention for explaining the essential points of the present invention.
FIG. 3 is a diagram showing the distribution of reaction components in the catalyst in the conventional catalyst and the catalyst of the present invention for explaining the essential points of the present invention.
FIG. 4 is a diagram showing the effect of the present invention.
FIG. 5 is a diagram showing the effect of the present invention.
FIG. 6 is a diagram for clarifying problems of a conventional catalyst.
FIG. 7 is a diagram for clarifying problems of a conventional catalyst.
[Explanation of symbols]
1 Coating layer having only denitration activity 2 Catalyst molded body layer having denitration activity, CO oxidation activity, and NH ₃ oxidative decomposition activity

Claims

Denitration activity in an amount of more than 0 and less than 100 g / m ² per m ² having no oxidation activity of carbon monoxide and ammonia on the surface of the molded body containing a component having oxidation activity of carbon monoxide and oxidative decomposition activity of ammonia An exhaust gas purifying catalyst comprising a coating layer made of components.

2. The exhaust gas purifying catalyst according to claim 1, wherein the molded body of a component having carbon monoxide oxidation activity or ammonia oxidative decomposition activity is a molded body of a porous body supporting a noble metal.

The exhaust gas according to claim 1 or 2, wherein the coating layer made of a denitration active component having no oxidation activity of carbon monoxide and ammonia contains one or more oxides of titanium, tungsten, molybdenum, and vanadium. Purification catalyst.

Molding of a molded body, wherein the coating layer formed on the surface of the exhaust gas purifying catalyst according to any one of claims 1 to 3 comprises a wet-formed component having carbon monoxide oxidation activity and ammonia oxidative decomposition activity. A method for producing an exhaust gas purifying catalyst, characterized in that the exhaust gas purifying catalyst is formed by covering a wet surface immediately after that with a slurry of the coating layer component.

The method for producing an exhaust gas purifying catalyst according to claim 4, wherein the coating layer component slurry adhered to the roller is transferred onto the surface of the molded body to coat the coating layer component slurry on the surface of the molded body.

A catalyst for purifying exhaust gas according to any one of claims 1 to 3 is filled in part or all of the catalyst layer, a reducing agent is added to the exhaust gas, and then reduction and / or oxidation of nitrogen oxides in the exhaust gas is performed. An exhaust gas purification method comprising removing carbon by oxidation.

An exhaust gas purification apparatus, wherein a catalyst layer containing the exhaust gas purification catalyst according to any one of claims 1 to 3 is installed in a downstream portion of an ammonia reduction denitration catalyst layer.

The surface of the molded article containing a component having nitrogen oxide decomposition activity, carbon monoxide oxidation activity, and ammonia oxidative decomposition activity exceeds 0 per 1 m ² having no carbon monoxide and ammonia oxidation activity. A catalyst for exhaust gas purification comprising a coating layer comprising a denitration active component in an amount of 100 g / m ² or less .

A molded body comprising a component having nitrogen oxide decomposition activity and a component having carbon monoxide oxidation activity and ammonia oxidation decomposition activity is formed of one or more oxides of titanium, tungsten, molybdenum, and vanadium and a noble metal-supported porous material. The exhaust gas-purifying catalyst according to claim 8 , comprising a body.

The exhaust gas according to claim 8 or 9 , wherein the coating layer made of a denitration active component having no oxidation activity of carbon monoxide and ammonia contains one or more oxides of titanium, tungsten, molybdenum, and vanadium. Purification catalyst.

The coating layer formed on the surface of the exhaust gas purifying catalyst according to any one of claims 8 to 10, wherein the component having a wet activity of decomposing nitrogen oxides, the oxidation activity of carbon monoxide, and the oxidative decomposition of ammonia A method for producing an exhaust gas purifying catalyst, characterized in that it is formed by covering a wet surface immediately after molding of a molded body containing an active component with a slurry of the coating layer component.

12. The method for producing an exhaust gas purifying catalyst according to claim 11, wherein the coating layer component slurry adhered to the roller is transferred onto the surface of the molded body to coat the coating layer component slurry on the surface of the molded body.

The exhaust gas-purifying catalyst according to any one of claims 8 to 10 is filled in a part or all of the catalyst layer, and after adding a reducing agent to the exhaust gas, the reduction and removal of nitrogen oxides in the exhaust gas are simultaneously performed. exhaust gas purification how, characterized in that an oxidation removal.

A catalyst for purifying exhaust gas according to any one of claims 8 to 10 is filled in a part or all of a catalyst layer, and nitrogen oxides contained therein are reduced and removed after injecting a reducing agent into the exhaust gas. Exhaust gas purification method.

Exhaust gas purifying device, characterized in that installed in the flow portion after the ammonia reduction method denitration catalyst layer a catalyst layer catalyst has an accommodating exhaust gas purification according to any one of claims 8 to 10.