JP3605323B2 - Exhaust gas treatment catalyst, method for producing the same, and exhaust gas treatment method - Google Patents

Description

【００５９】
（実施例３、比較例２）
ＴｉＣｌ_４水溶液に、後述する組成になる量のＶＣｌ_３及びＣｒ（ＮＯ_３）_３を加え、さらに水を加えて水溶液中のＴｉＣｌ_４濃度を０．２モル／リットルに調製した。これを１規定のアンモニア水で中和し、得られた沈澱を１２０℃で２０時間乾燥し、さらに温度３００〜５５０℃、２時間、大気圧中で熱処理して、ＴｉＯ_２担持複合酸化物系触媒を得た。得られた触媒の比表面積を測定し、各組成に対してまとめたものが表２である。
【００６０】
表２の組成は、ＶはＶ_２Ｏ_５を、ＣｒはＣｒ_２Ｏ_３を表し、ＴｉＯ_２との合計を１００とした場合の、Ｖ_２Ｏ_５及びＣｒ_２Ｏ_３の各重量％を示したものである。また、＊印があるものは、水にエタノールを添加し、エタノール濃度２容量％の水溶液から共沈させて作製した触媒である。さらにまた、試料番号Ｓ２、Ｓ３は硫酸チタンを原料として作製した触媒である。なお、試料番号Ｒ１は、比較例２として、従来のＮＨ_４ＶＯ_３を原料とする含浸法によるバナジア系触媒のデータを付記したものである。
【００６１】
脱硝率の評価は、得られた触媒をガラス管中に充填し、一定組成の反応ガス（ＮＯ：１００ｐｐｍ、ＮＨ_３：１００ｐｐｍ，ＳＯ_２：１０ｐｐｍ、ＣＯ_２：１０％、Ｈ_２Ｏ：２０％、Ｏ_２：１０％、Ｎ_２：残部）を空間速度５０００ｈ^−１で流し、１５０℃及び１３０℃で１００時間継続して行った。ＮＯ濃度はＮＯ_ｘ計を用いて計測し、１５０℃での脱硝率の結果を表２の１５０℃脱硝率に、また１３０℃での脱硝率の結果を１３０℃脱硝率に示した。
【００６２】
また、表２の活性体は、符合Ａが活性体としてＶ_４Ｃｒ_２Ｏ_１３を担持した触媒、符合ＤがＶＣｒＯ_４を担持した触媒、符合ＢがＶ_４Ｃｒ_２Ｏ_１３とＶ_２Ｏ_５の混合状態を担持した触媒、符合ＣがＶ_４Ｃｒ_２Ｏ_１３とＶＣｒＯ_４の混合状態を担持した触媒、符合ＥがＶＣｒＯ_４とＣｒ_２Ｏ_３の混合状態を担持した触媒であったことを示す。また、符合Ｆは従来のＶ_２Ｏ_５を含浸法で担持した触媒を示す。
【００６３】
表２に示すように、本発明によって得られた触媒の比表面積は、１１７〜３０５ｍ^２／ｇであり、比較材の５８ｍ^２／ｇよりも顕著に大きいことがわかった。これは、共沈法で作製することにより複合酸化物粒子がＴｉＯ_２担体粒子上に均一に高分散したためと考えられる。
【００６４】
また、表２の試料番号１１〜１３に示されるように、熱処理温度が高くなると比表面積は減少した。これは高温では触媒粒子が粒成長するためと考えられる。６００℃以上に加熱すると酸化物は組成により溶融する危険性があるので（例えばＶ_２Ｏ_５、Ｖ_４Ｃｒ_２Ｏ_１３組成等）、これ以上の高温での熱処理は好ましくない。
【００６５】
さらにまた、表２の試料番号１９〜２３に示されるように、Ｖ_２Ｏ_５及びＣｒ_２Ｏ_３の各重量％の合計の増減によって脱硝率は変化し、その合計が３重量％未満に減少すると脱硝率は著しく低下した（比較例２）。
【００６６】
したがって、実施例３より、ＴｉＯ_２にバナジウムとクロムの複合酸化物であるＶ_４Ｃｒ_２Ｏ_１３又はＶＣｒＯ_４を３〜３０重量％担持した触媒は、従来の触媒に比べて、比表面積が大きく、従来の触媒では性能が低かった１５０℃以下、特に１３０℃程度の低温でも高い脱硝率を持つことがわかった。よって、本発明により、低温領域でも使用できる脱硝触媒を提供することができる。
【００６７】
【表２】

【００６８】
次に、更に改良された本発明の触媒について説明する。
【００６９】
（１）本発明の触媒は、排ガス中の有害物質を接触的に還元又は分解し無害化できる高比表面積の共沈及び原子価制御法による複合金属酸化物系触媒である。沈澱を作製する時の溶液中のチタン化合物（ＴｉＣｌ_{４ ）}の濃度は０．５〜０．０５モル／リットルの範囲とすることが望ましく、より好ましくは０．０５〜０．３モル／リットルの範囲とする。ＴｉＣｌ_４濃度をこの範囲にするためには水で希釈するが、メタノール、エタノール等の水溶性アルコールと水との混合物で希釈することもできる。沈澱を作製する時の溶液中のＴｉＣｌ_４濃度が０．５モル／リットルより大きいと、濃度が高すぎて沈澱が糊状になり攪拌しにくくなる等、取扱いにくくなるので、該チタン化合物の濃度の上限値は０．５モル／リットルとする。なお、該チタン化合物の濃度を０．３モル／リットル以下にすると、さらに沈殿物の攪拌性が向上して取扱いが容易になる。一方、該チタン化合物の濃度が０．０５モル／リットルよりも小さいと、溶液が薄くなりすぎて触媒を製造するのに多量の溶液が必要になり実用的でないので、該チタン化合物の濃度の下限値は０．０５モル／リットルとする。
【００７０】
（２）アルカリ性水溶液の濃度は０．５〜３モル／リットルの範囲とすることが望ましく、より好ましくは０．５〜２モル／リットルの範囲とする。中和に使用するアルカリ性水溶液としては、アンモニア水、苛性ソーダ水溶液等を用いることができるが、本発明の実施例ではアンモニア水を用いた。アルカリ性水溶液としてのアンモニア水の濃度が３モル／リットルよりも濃い場合は、滴下したアンモニア水のまわりに沈澱が固まって生成するため不均一となり、粗大化して沈澱の比表面積が小さくなるので、アンモニア水の濃度は３規定以下とすることが望ましい。さらにアンモニア水の濃度を２モル／リットルよりも小さくすると、沈殿物の均一性および微細化が促進されるので一層好ましい。一方、アルカリ性水溶液としてのアンモニア水の濃度が０．５モル／リットルよりも薄い場合は、多量のアンモニア水を中和のために加える必要があり、溶液の体積が増えすぎて実用的でないので、アンモニア水の濃度は０．５規定以上とすることが望ましい。なお、中和剤としてアンモニア水の代わりに尿素を用いても本発明の例外とするものでは無い。
【００７１】
（３）アナターゼ型の酸化チタン又は酸化チタンに酸化珪素、酸化スズから一種以上を添加した酸化チタン系複合酸化物を担体とする。添加した酸化珪素と酸化スズは酸化チタンに一部固溶し複合酸化物を形成するので、酸化チタン担体の酸点量を増加させるとともに、ＮＯの中間還元生成物であるＮ_２Ｏの吸着力を弱くするので、触媒の活性向上、Ｎ_２生成反応の選択性向上と劣化抑制による安定性向上に有効であるからである。酸化珪素と酸化スズの添加量は、特に制限するものではないが、０〜２０重量％の範囲とすることが好ましい。酸化珪素と酸化スズを２０重量％を超えて過剰に添加すると、酸化チタンの優れた担体効果が減じられるからである。複合酸化物を得るための珪素化合物、スズ化合物としては、珪酸エチル、メタ珪酸エチル、塩化スズ等を用いることができる。珪酸エチルは加水分解しにくいので、エタノールに溶かし酸を加え加水分解させてから原料水溶液に加えることがより好ましい実施態様である。メタ珪酸ソーダ水溶液はアルカリ性であるので、透明な塩酸酸性溶液にしてから原料水溶液に加えることがより好ましい実施態様である。
【００７２】
（４）担体に対し酸化バナジウム−酸化クロム系複合酸化物微粒子又はこの複合酸化物と酸化バナジウムとの混合酸化物微粒子を活性体として３〜３０重量％担持させる。活性体としてＶ_７Ｃｒ_３Ｏ_２２，Ｖ_４Ｃｒ_２Ｏ_１３，ＶＣｒＯ_４等のバナジウムとクロムの複合酸化物を用いる理由を次に述べる。
【００７３】
酸化バナジウムの脱硝機構としては、酸化バナジウムにＮＨ_３が吸着し、その上にＮＯが吸着し、反応中間体を形成した後、Ｎ_２とＨ_２Ｏに分解して脱離することが知られているが、この反応は２００℃以下では反応速度が遅くなる。一方、酸化クロムは低温でＮＯ吸着力があり、ＮＯがまず吸着しその上にＮＨ_３が吸着し、脱硝反応が進むことが考えられる。そこで両者の特徴を活かして複合酸化物とし、結晶のなかにＶとＣｒを均質に取り込むことにより、一つの結晶粒子上でＮＨ_３とＮＯが同時に吸着可能となり、低温でも脱硝性能が向上すると考えられる。ＴｉＯ_２担体に対し担持させる触媒の担持量を３重量％未満にすると、脱硝性能が低下するので、活性体の担持量の下限値は３重量％とする。一方、３０重量％より多くしても脱硝率はある値以上には増えなくなり（効果が飽和する）、逆に熱処理により粒成長し比表面積が小さくなる等の不具合が生ずるので、活性体の担持量の上限値は３０重量％とする。なお、より好ましい活性体の担持量の範囲は５〜１５重量％である。
【００７４】
（５）活性体として担持した酸化バナジウム−酸化クロム系複合酸化物中のＣｒ／（Ｃｒ＋Ｖ）モル濃度比は０．２〜０．４である。触媒の脱硝率の組成依存性を詳細に調べた結果、この組成範囲で活性が１３０℃〜１５０℃の低温でも最も高いことが判明した。これは、この組成領域であれば、次に示す複合酸化物が最も活性が高い活性相として存在するためである。
【００７５】
（６）触媒の主要な活性体はＶ_７Ｃｒ_３Ｏ_２２又はＶ_４Ｃｒ_２Ｏ_１３で表せられる複合酸化物である。なお、触媒活性体としては、Ｖ_７Ｃｒ_３Ｏ_２２，Ｖ_４Ｃｒ_２Ｏ_１３以外にこれら複合酸化物とＶ_２Ｏ_５，ＶＣｒＯ_４との共存状態を用いることもできる。従来のＶ_２Ｏ_５−Ｃｒ_２Ｏ_３系状態図ではＶ_４Ｃｒ_２Ｏ_１３とＶＣｒＯ_４の複合酸化物が存在することが知られている。本発明者らは、共沈法により均質な試料を合成し、Ｘ線回折と示差熱分析により状態図を検討し、存在する化合物はＶ_７Ｃｒ_３Ｏ_２２とＶＣｒＯ_４であるとの実験結果を得た。即ち、従来Ｖ_４Ｃｒ_２Ｏ_１３と言われていた化合物は正確にはＶ_７Ｃｒ_３Ｏ_２２組成の化合物であり、従来の文献では固相反応で試料を合成していたため均質な試料が得られず、両者の組成を誤認していた可能性がある。両者のＸ線回折図形はほぼ同じであるので、組成式は異なってもＶ_７Ｃｒ_３Ｏ_２２とＶ_４Ｃｒ_２Ｏ_１３は本来同じ複合酸化物であると考えられる。
【００７６】
（７）触媒の調製方法として共沈及び原子価制御法を採用する。均一な複合酸化物の微粒子を調製するためには、金属イオンが均一に固溶した水酸化物沈澱を合成する必要がある。このため原料としては、ＶＣｌ_３，Ｃｒ（ＮＯ_３）_３等のＶ（３価）とＣｒ（３価）の化合物を用いる必要がある。従来の５価のＶ化合物を用いるとＶとＣｒが固溶した均質な水酸化物を合成できない。共沈法で得た沈澱物は３価の金属化合物であり、活性が無いので、酸化雰囲気中で熱処理し、バナジウムの価数を３価から５価にかえること（原子価制御）が必要である。沈澱を作製するときの水溶液中のＶ，Ｃｒ遷移金属イオンの濃度は、ＴｉＯ_２に対し何％活性体を担持させるかという担持量で決まるものであり、特に制限するものではない。なお、酸化チタン担体を共沈法で作成した後、バナジウム化合物とクロム化合物の溶液を含浸させ、酸化雰囲気中で熱処理する方法を用いることも可能である。
【００７７】
（８）沈澱を洗浄し乾燥した後、酸化雰囲気中で３００〜５５０℃の温度で熱処理する。アンモニア水で中和し沈澱を作製すると多量のＮＨ_４Ｃｌが生成するため、これを洗浄により除去する必要がある。得られた沈澱はＶとＣｒの固溶した水酸化物であるので、これを加熱し酸化物粒子に変えるとともに、３００〜５５０℃の温度で酸化雰囲気中で熱処理し、Ｖの価数を３価から５価に変え、Ｖ_７Ｃｒ_３Ｏ_２２，ＶＣｒＯ_４の複合酸化物にする必要がある。３００℃よりも低温では、非晶質の酸化物が含まれ、目的とする結晶質の複合酸化物が得られない。５５０℃よりも高温では触媒中の酸化物粒子が粒成長し、比表面積が低くなり、低温での活性が落ちるからである。原子価制御するためのより好ましい熱処理温度は３５０〜５００℃である。熱処理時間は得に制限する必要はないが、１〜２時間で十分である。
【００７８】
（９）ダイオキシン等のハロゲン化芳香族化合物を分解できる。種々の試験を行った結果、クロロフェノール、クロロトルエン等のハロゲン化芳香族化合物は、本発明の触媒により一部分塩酸と炭酸ガスにまで分解されるのが確認され、これら化合物に対しても分解能力があることが判明した。これは、共沈法による本発明の触媒が、比表面積が大きいため芳香族化合物に対しても酸化力が大きいためと考えられる。本発明の触媒で分解できる排ガス中の有害物質は、窒素酸化物とハロゲン化芳香族化合物であるが、本触媒の酸化作用により分解できる化合物であれば、これらに限定されるものではない。
【００７９】
（１０）１１０℃から２５０℃の温度で排ガスと接触させ、排ガス中の有害物質を分解する。排ガス温度が２５０℃よりも高いと、排ガス中の塩素化合物によりダイオキシン類が再合成される危険性があるので、排ガス温度の上限値は２５０℃とする。さらに安全側を見込み、排ガス温度を２００℃以下とすることが望ましい。これによりダイオキシン類の再合成のおそれがなくなる。一方、排ガス温度が１１０℃よりも低いと、触媒の活性が低くなりすぎて実用的でなくなるので、排ガス温度の下限値は１１０℃とする。さらに安全側を見込み、排ガス温度を１３０℃以上とすることが望ましい。これにより腐食性成分を含んだ水が凝縮し結露するおそれがなくなる。このように排ガス中の窒素酸化物とハロゲン化芳香族化合物とを同時に分解するためには、排ガス温度を１１０〜２５０℃の範囲とする必要があり、さらに１３０〜２００℃の範囲とすることが一層好ましい。
【００８０】
（１１）本発明の触媒の使用形態としては、顆粒状で用いる、成形してペレット状にして用いる、触媒粉末をバグフイルターに担持させて用いる、触媒粉末をハニカム状に押出し成形してハニカム形状触媒として用いる、ハニカムの上に触媒粉末を含むスラリーをかけて塗布（ウォッシュコート）して用いる等の使用形態が可能である。
【００８１】
（実施例４）
初めに、ＶＣｌ_３とＣｒ（ＮＯ_３）_３を０．１モル／リットル含む水溶液を調製し、アンモニア水を滴下して沈澱を作製し、適正なアンモニア水の濃度を把握する試験を行った。アンモニア水の濃度が３規定よりも大きいと、中和により沈澱が局所的に生成し、不均質に反応が起こるとともに、刺激臭のため局所排気設備が必要である。アンモニア水の濃度が０．５〜３規定であれば、中和により溶液の色が次第に変化し、均一に沈澱が生成するのが観察された。なお、アンモニア水の濃度が０．５規定よりも薄いと、多量のアンモニア水を加える必要があり、実用的でない。
【００８２】
本実施例４の触媒は、共沈及び原子価制御法により粗大化することなく均一に沈殿する生成物として得られた。
【００８３】
（実施例５）
ＶＣｌ_３とＣｒ（ＮＯ_３）_３を種々の組成比で０．１モル／リットル含む水溶液を調製し、１規定のアンモニア水で中和し沈澱を作製した。得られた沈澱は水酸化物であり、加熱により２００℃で水酸化物から酸化物に変わる。この酸化物は非晶質であり、さらに加熱すると約３００℃で発熱し結晶化して結晶質の複合酸化物に変わることが熱分析とＸ線回折により明らかになった。すなわち、結晶質の複合酸化物を得るためには、約３００℃以上に加熱する必要がある。５００℃で２時間大気中で熱処理した種々の組成の酸化物粒子の結晶構造をＸ線回折で調べた結果、Ｃｒ／（Ｃｒ＋Ｖ）比０．３でＶ_７Ｃｒ_３Ｏ_２２組成の化合物１相のみが、Ｃｒ／（Ｃｒ＋Ｖ）比０．３３即ちＶ_４Ｃｒ_２Ｏ_１３組成ではＶ_７Ｃｒ_３Ｏ_２２とＶＣｒＯ_４の２相共存状態が、Ｃｒ／（Ｃｒ＋Ｖ）比０．５でＶＣｒＯ_４組成の化合物が生成することが明らかになった。Ｃｒ／（Ｃｒ＋Ｖ）比が、０と０．３の間ではＶ_２Ｏ_５＋Ｖ_７Ｃｒ_３Ｏ_２２，０．３と０．５の間ではＶ_７Ｃｒ_３Ｏ_２２＋ＶＣｒＯ_４，０．５と１の間ではＶＣｒＯ_４＋Ｃｒ_２Ｏ_３の２相共存状態であった。３価のＶ化合物を原料としても、酸化雰囲気で熱処理することにより５価のＶの複合酸化物であるＶ_７Ｃｒ_３Ｏ_２２とＶＣｒＯ_４を提供できることが実証できた。本試験により、Ｖ_４Ｃｒ_２Ｏ_１３組成の化合物は、正確にはＶ_７Ｃｒ_３Ｏ_２２組成に存在することが明らかになったが、それらのＸ線回折図形は良く似ているので、実質的には両者は同じ化合物を示すと考えてよい。
【００８４】
（実施例６）
ＴｉＣｌ_４とその１／２０量の珪酸エチル、珪酸ソーダ、ＳｎＣｌ_４の添加剤の１種以上を含む塩酸酸性水溶液に酸化バナジウム−酸化クロム系（Ｖ−Ｃｒ系と略記）複合酸化物を調製するのに必要な組成のＶＣｌ_３とＣｒ（ＮＯ_３）_８を所定濃度担持するのに必要な量だけ加え、さらに水を加えて溶液中のＴｉＣｌ_４濃度を０．２モル／リットルに調製し、１規定のアンモニア水で中和し、得られた沈澱を洗浄後１２０℃で２０時間乾燥し、さらに３００〜５５０℃で２時間大気中で熱処理してＴｉＯ_２担持Ｖ−Ｃｒ系複合酸化物の触媒を得た。得られた触媒の比表面積は表３に示すように実施例の触媒（サンプル３１〜４６）は何れも１００〜３１０ｍ^２／ｇの範囲内であり、従来のＮＨ_４ＶＯ_３を原料とする含浸法によるバナジア系触媒（比較例サンプルＲ１）よりも大きいことが判明した。これは、共沈法で作製することにより複合酸化物粒子がＴｉＯ_２担体粒子上に均一に高分散したためと考えられる。熱処理温度が高くなると比表面積は減少するが、これは高温で触媒粒子が粒成長するためと考えられる。６００℃以上に加熱すると酸化物は組成により溶融する危険性があるので（例：Ｖ_２Ｏ_５，Ｖ_７Ｃｒ_３Ｏ_２２組成）、これ以上の高温での熱処理は好ましくない。
【００８５】
なお、表３中の記号＊は、原料水溶液にエタノールを添加してエタノール濃度２容量％の水溶液から共沈させて調製した触媒である。また、サンプルＳ１，Ｓ２は硫酸チタンを原料としてそれぞれ調製した触媒である。
【００８６】
（実施例７）
４塩化チタンを０．１モル／リットル含有する水溶液に濃度１モル／リットルのアンモニア水を滴下して中和し、酸化チタン又は酸化チタン系複合酸化物の沈澱物を形成させ、この沈澱物を洗浄、乾燥した後、活性体を１３重量％担持させるのに必要なＶＣｌ_３とＣｒ（ＮＯ_３）_３を含有する溶液を添加して含浸させ、４００℃の温度で酸化雰囲気中で熱処理することにより、該当する複合酸化物を担体に担持させた触媒を調製した。この実施例７の触媒を表３中に記号Ｋ１で示した。
【００８７】
（実施例８）
脱硝率の評価は、得られた顆粒状の触媒をガラス管中に充填し、一定組成の反応ガス（ＮＯ：１００ｐｐｍ、ＮＨ_３：１００ｐｐｍ、ＳＯ_２：１０ｐｐｍ、ＣＯ_２：１０％、Ｈ_２Ｏ：２０％、Ｏ_２：１０％、Ｎ_２：残部）を空間速度５０００ｈ^−１で流し、１５０℃及び１３０℃で２００時間継続して行った。その結果を表３に示す。ＮＯ濃度はＮＯｘ計を用いて計測した。活性体として主としてＶ_７Ｃｒ_３Ｏ_２２を担持した触媒は、１３０℃程度の低温でも活性が８０％以上と非常に高いことがわかった。ＴｉＯ_２にＶ_７Ｃｒ_３Ｏ_２２を主成分とする複合酸化物を３〜３０重量％担持した触媒は、比表面積が大きく、従来の触媒では性能が低かった１３０℃〜１５０℃の低い温度領域でも高い脱硝率を備えていることが確認された。
【００８８】
このように本実施例８の触媒は、低温度領域であっても安定して優れた脱硝性能を有する。
【００８９】
【表３】

【００９０】
（実施例９）
実施例８と同じ方法で代表的な触媒の脱硝率を１３０〜２５０℃で測定した。反応時間は各２００時間である。その結果を表４に示す。得られた触媒（サンプル３２，３４，４０，４２）は、この温度範囲で比較例サンプルＲ１よりも脱硝率が高いことが確認された。
【００９１】
【表４】

【００９２】
（実施例１０）
ハロゲン化芳香族化合物の一例としてオルソクロロフェノールを用い、触媒によるその分解率を試験した。空気をキャリアーガスとしてオルソクロロフェノールを顆粒状の触媒を入れたマイクロリアクターに空間速度５０００ｈ^−１で流通させ、出てきたガスをガスクロマトグラフで分析した。
【００９３】
その結果、表５に示すように、本実施例１０の触媒（サンプル３２，３４，４０，４２）は何れも１５０℃における分解率の初期性能が８０％以上であり、従来の含浸法による触媒（サンプルＲ１）よりも低温でも分解活性が高いことが判明した。共沈法により高比表面積の触媒が得られたので、触媒の酸化力が向上し、ハロゲン化芳香族化合物の分解性能が向上したと考えられる。
【００９４】
【表５】

【００９５】
（実施例１１）
ゴミ焼却炉において１５０℃の除塵装置を通過した後の排ガスの一部を分岐させ、ハニカム状にした本発明の触媒を充填した排ガス処理装置に流通させ、装置の入り口と出口における酸化窒素とダイオキシン類の濃度を測定した。装置入り口のＮＯ濃度は１１０ｐｐｍ、ダイオキシン類の濃度は１．２ｎｇ−ＴＥＱ／Ｎｍ^３であり、空間速度は９０００ｈ^−１であった。ＮＯの還元剤として添加したＮＨ_３量は排ガス中のＮＯ量と当量である。その結果を表６に示す。本発明の触媒（サンプル３４，４０）を用いることにより１５０℃の低温度領域でも脱硝率が従来の触媒（サンプルＲ１）よりも高く８０％以上となることが判明した。
【００９６】
本実施例１１の触媒を用いた場合は、ダイオキシン類の濃度が１５０℃の低温であっても０．１ｎｇ−ＴＥＱ／Ｎｍ^３以下を達成しており、本発明の触媒により排ガス温度が従来の排ガス処理よりも低い２００℃以下でも酸化窒素とハロゲン化芳香族化合物の同時分解ができることが明らかになった。なお、ＴＥＱは、２，３，６，７−テトラクロロジベンゾダイオキシンを基準物質として換算した毒性当量値を示す。
【００９７】
【表６】

【００９８】
【発明の効果】
本発明の触媒は、バナジウムとクロムとの複合酸化物を活性体として用いることにより、従来の触媒よりも低温での脱硝性能が顕著に高く、さらに劣化が小さい。
【００９９】
さらに、本発明の触媒の製造方法によれば、共沈法を用いることにより、従来の含浸法に比べて、触媒の比表面積を著しく大きくすることができ、低温での脱硝性能を顕著に高くすることができる。
【０１００】
本発明により、窒素酸化物とハロゲン化芳香族化合物等の有害物質を含む排ガスに対して従来の触媒よりも低温で分解処理活性が高い高比表面積の排ガス処理触媒を提供することができ、環境浄化に寄与することができ、産業上の利用価値が高い。特にゴミ焼却炉等の排ガス処理においては、排ガスを１５０℃程度の低い温度域で除塵装置を通過させた後、２００℃以上に再加熱することなく、そのままの低温で有害物質を分解できるので、排ガス処理装置の小型化や低コスト化ができ、環境浄化に有効である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas treatment catalyst capable of efficiently purifying nitrogen oxides and harmful halogenated aromatic compounds in exhaust gas at a lower temperature than conventional catalysts, a production method thereof, and an exhaust gas treatment method.
[0002]
[Prior art]
Nitrogen oxides (NOx) in exhaust gas from boilers, waste incinerators, and the like are one of the environmental pollutants. As a method for detoxifying NOx for environmental purification, for example, a titanium oxide (TiO 2) disclosed in Japanese Patent No. 2633316 is disclosed.₂) To vanadium pentoxide (V₂O₅) And tungsten trioxide (WO₃) Supported on ammonia (NH₃) Is used as a reducing agent to reduce NOx. However, this conventional method has a problem that when the exhaust gas temperature is lower than about 200 ° C., the denitration rate is greatly reduced. Also, TiO₂Dichromic trioxide (Cr₂O₃) Is also used, but this catalyst has a high denitration performance even at a low temperature, but has a problem of great deterioration.
[0003]
[Problems to be solved by the invention]
Recently, dioxin generation has become a new problem in garbage incinerators and industrial waste incinerators. Dioxin is composed of a highly toxic aromatic chlorine compound that is harmful to the human body, is produced as a secondary product when incinerating garbage, and is a major social problem as an environmental pollutant.
[0004]
In order to remove dioxin, it is necessary to lower the exhaust gas temperature to a low temperature of 200 ° C. or lower at which the vapor pressure decreases. Therefore, in the conventional technology, the exhaust gas is cooled, dioxin is removed at a low temperature of about 150 ° C., and then TiO 2 is removed.₂-V₂O₅In order to denitrate with a system catalyst, there is a problem that the exhaust gas temperature must be heated to 200 ° C. or more again.
[0005]
The present invention has been made in order to solve the above-mentioned problems, and the object thereof is to optimize the composition of the carrier in consideration of the above technical level and to improve the stability by narrowing down the composition of the active substance. It is still another object of the present invention to provide a novel, high activity, high performance, high specific surface area exhaust gas treatment catalyst and a method for producing the same.
[0006]
An object of the present invention is to clarify the decomposition performance of halogenated aromatic compounds such as dioxin and to provide an exhaust gas treatment catalyst capable of simultaneously detoxifying harmful substances of nitric oxide and halogenated aromatic compounds.
[0007]
[Means for Solving the Problems]
The reason that the conventional catalyst has a low denitration rate at low temperature is that the specific surface area is 50 to 90 m²It is conceivable that only a catalyst as small as / g can be obtained.
[0008]
The present inventors have intensively studied to develop an excellent denitration catalyst having a high denitration activity even at a low temperature and a small deterioration, and a method for producing the same. As a result, the present inventors_ThreeIt has been found that such a problem can be solved by using a composite oxide of V and Cr, which is a composite of vanadium (V) having a high adsorption capacity and chromium (Cr) having a high NO adsorption capacity, as a catalytic activator. . Furthermore, as a method for producing a denitration catalyst, a coprecipitation method capable of obtaining a catalyst having a high specific surface area is used instead of the conventionally used impregnation method.And valence control method to change vanadium valence from trivalent to pentavalentHas solved such a problem. Based on such findings, the present inventors have completed the present invention.
[0009]
The exhaust gas treatment catalyst according to the present invention uses titanium dioxide as a carrier, a trivalent vanadium salt as a raw material, a coprecipitation method, and a valence control method of heat-treating the coprecipitate to a temperature of 300 to 550 ° C. in an oxidizing atmosphere. V generated_FourCr_TwoO₁₃, V₇Cr_ThreeO_{twenty two}And VCrO_FourOr a mixture of two or more composite oxides selected from the group consisting of, or an oxide fine particle comprising a mixture of at least one of the composite oxides and vanadium oxide or chromium oxide as an activator. 3 to 30% by mass of the active substance is supported on the carrier, and the specific surface area is 100 m^Two/ G or more.
Further, the exhaust gas treatment catalyst according to the present invention uses a titanium dioxide-based composite oxide obtained by adding at least one of silicon oxide and tin oxide to titanium dioxide as a carrier, and uses a trivalent vanadium salt as a raw material in a coprecipitation method and a coprecipitation method. Generated by using a valence control method of heat-treating to a temperature of 300 to 550 ° C. in an oxidizing atmosphere. _Four Cr _Two O ₁₃ , V ₇ Cr _Three O _{twenty two} And VCrO _Four A single oxide of a complex selected from the group consisting of or a mixture of two or more complex oxides, or an oxide fine particle comprising a mixture of at least one of the complex oxides and vanadium oxide or chromium oxide as an activator. 3 to 30% by mass of the active substance is supported on the carrier, and the specific surface area is 100 m ^Two / G or more.
[0010]
The method for producing an exhaust gas treatment catalyst according to the present invention comprises adding a solution containing trivalent vanadium ions and chromium ions to a titanium aqueous solution containing titanium tetrachloride or titanium sulfate, and further adding water or water and a water-soluble alcohol. In addition, after adjusting the concentration of titanium ions in the aqueous solution to be 0.5 to 0.05 mol / liter, the aqueous solution is neutralized by dropwise addition of aqueous ammonia having a concentration of 0.5 to 3 N. Forming a co-precipitate of titanium dioxide and trivalent vanadium and chromium hydroxide, washing and drying the co-precipitate, followed by heat treatment at a temperature of 300 to 550 ° C. in an oxidizing atmosphere. The valence of vanadium in the coprecipitate is changed from trivalent to pentavalent, and titanium dioxide is used as a carrier;_FourCr_TwoO₁₃, V₇Cr_ThreeO_{twenty two}And VCrO_FourOr a mixture of two or more composite oxides selected from the group consisting of, or an oxide fine particle comprising a mixture of at least one of the composite oxides and vanadium oxide or chromium oxide as an activator. 3 to 30% by mass is supported on the carrier, and the specific surface area is 100 m.^Two/ G or more.
In addition, the method for producing an exhaust gas treatment catalyst according to the present invention includes the steps of: adding a solution containing trivalent vanadium ions and chromium ions to a titanium aqueous solution containing titanium tetrachloride or titanium sulfate; Is further added to the titanium aqueous solution, and water or water and a water-soluble alcohol are further added to adjust the concentration of titanium ions in the aqueous solution to 0.5 to 0.05 mol / L. By neutralizing the aqueous solution by dropwise addition of 0.5 to 3 N aqueous ammonia, titanium dioxide composite oxide in which at least one of silicon oxide and tin oxide is added to titanium dioxide, trivalent vanadium and A coprecipitate with chromium hydroxide is formed, which is washed, dried and then heated in an oxidizing atmosphere at a temperature of 300-550 ° C. The valence of vanadium in the joint precipitate by physical change from trivalent to pentavalent, titanium dioxide-based composite oxide in which at least one of which is the addition of silicon oxide and tin oxide in the titanium dioxide as a carrier, V _Four Cr _Two O ₁₃ , V ₇ Cr _Three O _{twenty two} And VCrO _Four Or a mixture of two or more composite oxides selected from the group consisting of, or an oxide fine particle comprising a mixture of at least one of the composite oxides and vanadium oxide or chromium oxide as an activator. 3 to 30% by mass is supported on the carrier, and the specific surface area is 100 m. ^Two / G or more.
[0011]
The catalyst thus obtained uses titanium dioxide as a carrier, and V is a composite oxide of vanadium and chromium.₄Cr₂O_ThirteenOr VCrO₄Or a mixture thereof, or an oxide fine particle comprising a mixture of the above-mentioned composite oxide and vanadium oxide or chromium oxide, as an active substance, 3 to 30% by weight of the active substance on the carrier, and a specific surface area of 100 m²/ G or more. Further, ethanol can be used as the water-soluble alcohol.
[0012]
In view of the above technical level, the present inventors can obtain a novel high specific surface area catalyst by a novel coprecipitation and valence control method using a trivalent vanadium compound as a raw material. TiO₂-V₂O₅It has been clarified that a catalyst having higher denitration activity can be obtained at a lower temperature than the base catalyst.
[0013]
Incidentally, it is expected that the performance of the catalyst of this composition system can be further improved by optimizing the composition of the catalytically active substance and the carrier. Further, since the catalyst of this composition system is expected to have a high oxidizing ability for aromatic compounds, it may function as a catalyst for decomposing halogenated aromatic compounds such as dioxin. The present invention has been made based on such findings.
[0014]
aboveTitanium dioxide carrierAdded at least one of silicon oxide and tin oxide to titanium dioxideTitanium dioxide typeIt can be a composite oxide. like thisTitanium dioxide typeThe composite oxide is prepared by adding at least one of a silicon compound and a tin compound together with a solution containing trivalent vanadium ions and chromium ions to a predetermined titanium aqueous solution, adjusting the concentration thereof, and co-precipitating the hydroxide. The precipitate is washed, dried, and produced by changing the valence of vanadium in the precipitate from trivalent to pentavalent using a valence control method under a predetermined heat treatment condition. In addition, the addition amount of silicon oxide and tin oxide is not particularly limited, but is preferably 0 to 20% by mass. Excess addition of more than 20% by mass of thesetitanium dioxideThis is because the excellent carrier effect is reduced.
[0015]
Such a catalyst can selectively reduce and decompose nitrogen oxides in the presence of ammonia and, as harmful substances in exhaust gas, halogenated aromatic compounds such as dioxins, polychlorinated biphenyls, and chlorophenol. Can be decomposed and made harmless.
[0016]
The titanium oxide contained in the carrier has an anatase structure. The active substance has a loading amount of 3 to 30% by weight and a specific surface area of 100 m.²/ G or more.
[0017]
The active form is V₇Cr₃O₂₂Or V₄Cr₂O_ThirteenA composite oxide or a mixture of the composite oxide and vanadium oxide;₄Mixture, and also VCrO₄Complex oxide or VCrO₄And a mixture of chromium oxide.
[0018]
Further, by providing a composition in which the Cr mole concentration / (Cr mole concentration + V mole concentration) ratio in the vanadium oxide-chromium oxide composite oxide supported as an activator is 0.2 to 0.4, the main activity is obtained. Body is V₇Cr₃O₂₂Or V₄Cr₂O_ThirteenIt is preferably a composite oxide.
[0019]
In the method for producing an exhaust gas treatment catalyst according to the present invention, 3 to 30% by weight of an activator is supported in an aqueous solution containing a titanium compound such as titanium tetrachloride and titanium sulfate, and at least one member selected from the group consisting of a silicon compound and a tin compound. A solution containing trivalent vanadium ions and chromium ions necessary for the addition of water, and water or water and a water-soluble alcohol are further added, so that the concentration of the titanium compound in the solution is 0.5 to 0.05 mol / L. Then, an alkaline aqueous solution having a concentration of 3 to 0.5 mol / liter is added dropwise to the solution to neutralize the solution, thereby precipitating the precipitate of titanium oxide, vanadium and chromium hydroxide. The precipitate is washed and dried, and then heat-treated in an oxidizing atmosphere at a temperature range of 300 to 550 ° C. to change the valence of vanadium from trivalent to pentavalent. A composite oxide equivalent to be characterized by preparing a catalyst supported on a carrier.
[0021]
An exhaust gas treatment method according to the present invention is an exhaust gas treatment method for purifying exhaust gas, in which the exhaust gas is brought into contact with the catalyst in a temperature range of 110 ° C to 250 ° C to treat harmful substances in the exhaust gas. It is characterized by.
[0023]
The coprecipitation and valence control method used in the method for producing an exhaust gas treatment catalyst according to the present invention uses vanadium trichloride (VCl 3), which is a trivalent vanadium compound which has not been focused on as a raw material.₃) As a raw material, a solid solution of vanadium hydroxide (trivalent) and chromium hydroxide₂The particles can be supported, and then heat-treated in an oxidizing atmosphere to convert the hydroxide to an oxide and change the valence of vanadium from trivalent to pentavalent (valence control), thereby forming a composite containing pentavalent vanadium. This corresponds to a technique for synthesizing a catalyst supporting an oxide.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
The denitration catalyst of the present invention is TiO₂Is a denitration catalyst carrying 3 to 30% by weight of a composite oxide described later as an activator as a carrier and having a specific surface area of 100 m²/ G or more.
[0025]
The carrier used in the present invention is TiO₂And preferably TiO having an anatase type structure₂It is. TiO₂There are three kinds of crystal types, namely, a red stone (rutile) type, an anatase (anatase) type, and a plate titanium (brookite) type. The rutile type is a high-temperature stable type, and the anatase type is a low-temperature stable type.
[0026]
The activator used in the present invention is a composite oxide of vanadium and chromium, V₄Cr₂O_ThirteenOr VCrO₄It is. Note that the active substance is V₄Cr₂O_ThirteenAnd VCrO₄Can also be used. Further, the activator is in a coexistence state of the composite oxide and vanadium oxide or chromium oxide, for example, V₄Cr₂O_ThirteenAnd V₂O₅, VCrO₄And Cr₂O₃For example, an oxide in a two-phase mixed state can be used.
[0027]
Vanadia (V₂O₅The denitration mechanism of system₃Is adsorbed and NO is adsorbed thereon to form a reaction intermediate.₂And H₂It is known to decompose and desorb to O. However, this reaction has a disadvantage that the reaction rate is slow at 200 ° C. or lower. On the other hand, chromia (Cr₂O₃System) has NO adsorbing power even at low temperatures, and after NO is first adsorbed, NH₃Adsorption promotes the denitration reaction. Therefore, in order to improve the denitration rate at a low temperature and to produce an excellent denitration catalyst with little deterioration, the conventional V₂O₅System and Cr₂O₃It is difficult only with a system catalyst.
[0028]
Therefore, taking advantage of both features, V is a composite oxide of vanadium and chromium.₄Cr₂O_ThirteenOr VCrO₄Is synthesized, V and Cr are homogeneously incorporated in the crystal, and NH is formed on one crystal particle.₃And NO can be simultaneously adsorbed, and the denitration performance at low temperatures is improved.
[0029]
The range of the loading amount of the above-mentioned activator is 3 to 30% by weight, and the more preferable range of the loading amount is 5 to 15% by weight. If the amount of the activated body is less than 3% by weight, the denitration performance of the catalyst is significantly reduced. Therefore, the lower limit of the amount of the activated body is set to 3% by weight. On the other hand, even if the loading amount of the active substance is more than 30% by weight, the denitration rate is improved only to a certain value, and conversely, a problem such as grain growth due to heat treatment and a decrease in specific surface area occurs. The upper limit of the amount of body carried is 30% by weight.
[0030]
The denitration catalyst of the present invention has a specific surface area of 100 m.²/ G or more. A conventional denitration catalyst has a specific surface area of 50 to 90 m.²/ G, so that the denitration rate at low temperatures is low.
[0031]
Next, a method for producing the denitration catalyst of the present invention will be described.
[0032]
To an aqueous solution containing titanium tetrachloride or titanium sulfate, a solution containing trivalent vanadium ions and chromium ions in an amount necessary to support 3 to 30% by weight of the active substance is added. A water-soluble alcohol was added to adjust the concentration of titanium ions in the aqueous solution to 0.05 to 0.5 mol / L. Next, a coprecipitate of titanium oxide and hydroxides of vanadium and chromium is formed by neutralizing the aqueous solution by dropwise addition of 0.5 to 3 N aqueous ammonia. After the precipitate is washed and dried, it is heat-treated at a temperature of 300 to 550 ° C. in an oxidizing atmosphere. As a result, 3 to 30% by weight of a composite oxide described later was supported as an activator using titanium dioxide as a carrier, and the specific surface area was 100 m.²/ G or more.
[0033]
In the method for producing a denitration catalyst of the present invention, first, titanium tetrachloride (TiCl₄) Is added to a solution containing trivalent vanadium ions and chromium ions in an amount necessary to support 3 to 30% by weight of the active substance.
[0034]
In order to prepare uniform composite oxide fine particles, it is necessary to synthesize a hydroxide precipitate in which metal ions are uniformly dissolved. Therefore, as a raw material, vanadium trichloride (VCl 3) which is a compound of trivalent vanadium and chromium is used.₃) And chromium nitrate (Cr (NO₃)₃) Must be used.
[0035]
Conventionally, pentavalent vanadium ammonium metavanadate (NH₄VO₃) Is used as a raw material. However, as long as this is used as a raw material, there is only a method of impregnation. When a catalyst is prepared by the impregnation method, V₂O₅And Cr₂O₃Particles are unevenly supported, and a uniform composite oxide cannot be obtained. Further, when pentavalent vanadium is used, a hydroxide in which vanadium and chromium are dissolved in a solid solution cannot be synthesized.
[0036]
On the other hand, according to the present invention, VCl which is trivalent vanadium is used.₃Is used as a raw material, and vanadium hydroxide, which is trivalent vanadium, is converted into TiO 2 by a coprecipitation method described later.₂It can be carried on particles. Thereafter, this is heat-treated in an oxidizing atmosphere to change the valence of vanadium from trivalent to pentavalent, whereby a catalyst containing pentavalent vanadium can be synthesized.
[0037]
This method is called a coprecipitation and valence control method, and a composite oxide catalyst having a high specific surface area can be obtained by this method.
[0038]
The concentration of V, Cr transition metal ions in the aqueous solution at the time of preparing the precipitate was TiO 2₂% Of the active substance is determined based on the amount of the active substance. Furthermore, the above TiCl₄Instead of titanium sulfate (Ti (SO₄)₂) Can also be used.
[0039]
Next, water is added to the aqueous solution containing titanium, vanadium, and chromium so that the concentration of titanium ions in the aqueous solution is 0.05 to 0.5 mol / L, more preferably 0.05 to 0.3 mol / L. Make up to liters.
[0040]
If the concentration of titanium ions in the aqueous solution is more than 0.5 mol / liter, the concentration is too high, and when the precipitate is formed, the solution becomes paste-like and becomes difficult to stir. . On the other hand, when the concentration is less than 0.05 mol / liter, since the aqueous solution is thin, a large amount of the aqueous solution is required to prepare a catalyst, which is not practical and not preferable.
[0041]
Also, TiCl₄The concentration is adjusted to the above range by diluting with water, but may also be diluted with a mixture of water and a water-soluble alcohol such as methanol or ethanol. In particular, when a mixture of ethanol and water is used, the specific surface area tends to be larger than when diluted with water alone.
[0042]
Subsequently, 0.5 to 3 normal ammonia water, preferably 0.5 to 2 normal ammonia water is dropped into the aqueous solution to neutralize the aqueous solution, whereby titanium oxide and hydroxides of vanadium and chromium are neutralized. To form a coprecipitate.
[0043]
If the concentration of the aqueous ammonia is 0.5 to 3N, the color of the aqueous solution gradually changes due to the neutralization, and a uniform precipitate is formed. When the concentration of the aqueous ammonia is higher than 3N, the aqueous solution solidifies around the dropped aqueous ammonia to form a precipitate. This is not preferable because it becomes non-uniform, coarsens and the specific surface area of the precipitate becomes small. Further, since a pungent odor is also generated, a local exhaust system is required. On the other hand, when the concentration of the aqueous ammonia is less than 0.5 normal, the precipitate is uniformly formed, but it is necessary to add a large amount of aqueous ammonia for neutralization, and the volume of the aqueous solution becomes too large to be practical. Not preferred.
[0044]
Finally, the precipitate is washed and dried, and then heat-treated at a temperature of 300 to 550 ° C. in an oxidizing atmosphere to support 3 to 30% by weight of a titanium oxide as a carrier and a complex oxide described later as an activator. The specific surface area is 100m²/ G or more can be obtained.
[0045]
When a precipitate is produced by neutralization with aqueous ammonia, a large amount of NH₄Since Cl is generated, it needs to be removed by washing.
[0046]
The obtained precipitate is a hydroxide in which V and Cr are dissolved in a solid solution, and changes from hydroxide to oxide at about 200 ° C. by heating in an oxidizing atmosphere. This oxide is amorphous, and when further heated, generates heat at about 300 ° C., crystallizes, and changes to a crystalline composite oxide. That is, the valence of V is changed from trivalent to pentavalent, and V₄Cr₂O_ThirteenOr VCrO₄In order to obtain such a composite oxide, it is necessary to heat to about 300 ° C. or higher. If the temperature is lower than 300 ° C., an amorphous oxide is contained, and the desired crystalline composite oxide cannot be obtained, which is not preferable. On the other hand, when the temperature is higher than 550 ° C., the oxide particles in the catalyst are grown, and the specific surface area is decreased, and the activity at a low temperature is lowered. A more preferred heat treatment temperature is 350 to 500 ° C. The heat treatment time does not need to be particularly limited, and 1 to 2 hours is sufficient.
[0047]
The composite oxide finally obtained depends on the composition ratio of V and Cr added first. When the composition ratio of V and Cr is about 2: 1, V₄Cr₂O_ThirteenIs generated, and in the case of about one-to-one, VCrO₄Is generated. Further, in the case of other composition ratios of V and Cr, oxides in a two-phase mixed state containing the above-mentioned composite oxide, for example, V₄Cr₂O_ThirteenAnd VCrO₄, V₄Cr₂O_ThirteenAnd V₂O₅, VCrO₄And Cr₂O₃Etc. are generated.
[0048]
Note that the denitration catalyst of the present invention has a₃By using as a reducing agent, nitrogen oxides can be rendered harmless with high performance, but hydrocarbons and the like can also be used as a reducing agent.
[0049]
Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples.
[0050]
【Example】
(Example 1)
VCl₃And Cr (NO₃)₃Was prepared at various composition ratios and neutralized with 1N aqueous ammonia to produce a precipitate.
[0051]
The resulting precipitate was a hydroxide, which changed from hydroxide to oxide at 200 ° C. upon heating. The thermal analysis and X-ray diffraction revealed that this oxide was amorphous, and when heated further, it generated heat at about 300 ° C. and crystallized to change into a crystalline composite oxide.
[0052]
Furthermore, heat treatment was performed at 400 ° C. for 1 hour under atmospheric pressure, and the crystal structure of oxide particles having various compositions was examined by X-ray diffraction. As a result, V / Cr ratio was about 2/1 and V₄Cr₂O_ThirteenIs generated, and the VCrO₄Was generated, and that oxides in a two-phase mixed state were generated with compositions having other V / Cr ratios. Even when a trivalent V compound is used as a raw material, a heat treatment in an oxidizing atmosphere is performed to obtain a pentavalent V compound oxide V₄CrO_ThirteenAnd VCrO₄Can be provided.
[0053]
(Example 2, Comparative Example 1)
TiCl₄The aqueous solution is adjusted to a predetermined concentration described below, neutralized with 1N aqueous ammonia,₂A precipitate formed. The obtained precipitate was heat-treated at 300 ° C. for 1 hour,₂The specific surface area of the fine particles was measured. Table 1 shows the results of the specific surface area for each concentration.
[0054]
TiCl₄When the concentration of the aqueous solution was in the range of 0.05 to 0.3 mol / liter, a catalyst having a high specific surface area was obtained, and the handleability of the aqueous solution was good. When the concentration was too high, the liquid became like paste when a precipitate was formed, and handling was difficult (Comparative Example 1).
[0055]
Also, TiCl₄Instead of using titanium sulfate as the raw material, other conditions₂Fine particles were produced. The result is sample number S1 in Table 1. Even when titanium sulfate is used, TiCl₄The same specific surface area was obtained. The crystal structure was found to be anatase by an X-ray diffraction.
[0056]
Furthermore, TiCl₄When preparing the aqueous solution, 5% by volume of ethanol was added at the same time as the water, and the other conditions were the same as described above.₂Fine particles were produced. The results are shown in Table 1 as sample numbers A1 and A2.
[0057]
By preparing by adding ethanol, TiO₂It was recognized that the specific surface area of the fine particles tended to increase.
[0058]
[Table 1]

[0059]
(Example 3, Comparative Example 2)
TiCl₄In an aqueous solution, VCl is added in an amount to give a composition described below.₃And Cr (NO₃)₃Is added, and water is further added to the solution so that TiCl in the aqueous solution is added.₄The concentration was adjusted to 0.2 mol / l. This was neutralized with 1N aqueous ammonia, and the obtained precipitate was dried at 120 ° C. for 20 hours, and further heat-treated at a temperature of 300 to 550 ° C. for 2 hours under atmospheric pressure to obtain TiO 2.₂A supported composite oxide catalyst was obtained. Table 2 shows the specific surface areas of the obtained catalysts, which are summarized for each composition.
[0060]
In the composition of Table 2, V is V₂O₅And Cr is Cr₂O₃Represents TiO₂V when the sum of₂O₅And Cr₂O₃Are shown by weight%. Those marked with * are catalysts prepared by adding ethanol to water and coprecipitating from an aqueous solution having an ethanol concentration of 2% by volume. Furthermore, sample numbers S2 and S3 are catalysts prepared using titanium sulfate as a raw material. In addition, the sample number R1 is a comparative example 2,₄VO₃The data of the vanadia-based catalyst by the impregnation method using as a raw material are added.
[0061]
To evaluate the denitration rate, the obtained catalyst was filled in a glass tube, and a reaction gas having a constant composition (NO: 100 ppm, NH₃: 100 ppm, SO₂: 10 ppm, CO₂: 10%, H₂O: 20%, O₂: 10%, N₂: The rest) at a space velocity of 5000h^-1At 150 ° C. and 130 ° C. for 100 hours. NO concentration is NO_xThe results of the denitration at 150 ° C. are shown in Table 2 at 150 ° C. denitration rate, and the results of the denitration rate at 130 ° C. are shown at 130 ° C. denitration rate.
[0062]
In addition, in the active forms in Table 2, the symbol A indicates V₄Cr₂O_Thirteen, The symbol D is VCrO₄, A catalyst supporting B₄Cr₂O_ThirteenAnd V₂O₅A catalyst supporting a mixed state of₄Cr₂O_ThirteenAnd VCrO₄A catalyst supporting a mixed state of₄And Cr₂O₃This indicates that the catalyst supported the mixed state of. The symbol F is the same as the conventional V₂O₅Is shown by the impregnation method.
[0063]
As shown in Table 2, the specific surface area of the catalyst obtained by the present invention was 117 to 305 m²/ G, 58 m of the comparative material²/ G was found to be significantly larger. This is because the composite oxide particles are made of TiO₂This is probably because the particles were uniformly and highly dispersed on the carrier particles.
[0064]
Further, as shown in Sample Nos. 11 to 13 in Table 2, the specific surface area decreased as the heat treatment temperature increased. This is thought to be because catalyst particles grow at high temperatures. If the oxide is heated to 600 ° C. or more, the oxide may be melted depending on the composition (for example, V₂O₅, V₄Cr₂O_ThirteenComposition, etc.), heat treatment at a higher temperature than this is not preferred.
[0065]
Furthermore, as shown in Sample Nos. 19 to 23 in Table 2, V₂O₅And Cr₂O₃The denitration rate was changed by the increase / decrease of the total of each weight%, and the denitration rate was significantly reduced when the total was reduced to less than 3% by weight (Comparative Example 2).
[0066]
Therefore, from Example 3, TiO₂V, a composite oxide of vanadium and chromium₄Cr₂O_ThirteenOr VCrO₄The catalyst carrying 3 to 30% by weight of has a large specific surface area as compared with the conventional catalyst, and has a high denitration rate even at a low temperature of about 150 ° C. or lower, particularly about 130 ° C., which was low in performance of the conventional catalyst. Was. Therefore, according to the present invention, a denitration catalyst that can be used even in a low temperature range can be provided.
[0067]
[Table 2]

[0068]
Next, a further improved catalyst of the present invention will be described.
[0069]
(1) The catalyst of the present invention is a composite metal oxide-based catalyst by a coprecipitation and valence control method with a high specific surface area capable of catalytically reducing or decomposing harmful substances in exhaust gas to make them harmless. The titanium compound (TiCl) in the solution when preparing the precipitate_{4 )}Is preferably in the range of 0.5 to 0.05 mol / l, more preferably in the range of 0.05 to 0.3 mol / l. TiCl₄The concentration is adjusted to this range by diluting with water, but it can also be diluted with a mixture of water and a water-soluble alcohol such as methanol or ethanol. TiCl in solution when making a precipitate₄If the concentration is more than 0.5 mol / l, the concentration is too high and the precipitate becomes paste-like, and it becomes difficult to stir, and the handling becomes difficult. Therefore, the upper limit of the concentration of the titanium compound is 0.5 mol / l. I do. When the concentration of the titanium compound is 0.3 mol / liter or less, the sedimentability of the precipitate is further improved and handling becomes easy. On the other hand, if the concentration of the titanium compound is less than 0.05 mol / liter, the solution becomes too thin and a large amount of solution is required to produce a catalyst, which is not practical. The value is 0.05 mol / liter.
[0070]
(2) The concentration of the alkaline aqueous solution is desirably in the range of 0.5 to 3 mol / l, more preferably in the range of 0.5 to 2 mol / l. As the alkaline aqueous solution used for neutralization, ammonia water, caustic soda aqueous solution and the like can be used. In the embodiment of the present invention, ammonia water was used. When the concentration of the aqueous ammonia as an alkaline aqueous solution is higher than 3 mol / liter, the precipitate is solidified around the dropped aqueous ammonia and becomes non-uniform, and becomes coarse, and the specific surface area of the precipitate becomes small. It is desirable that the concentration of water be 3N or less. Further, when the concentration of the aqueous ammonia is smaller than 2 mol / liter, uniformity and fineness of the precipitate are promoted, which is more preferable. On the other hand, when the concentration of aqueous ammonia as an alkaline aqueous solution is less than 0.5 mol / liter, it is necessary to add a large amount of aqueous ammonia for neutralization, and the volume of the solution becomes too large to be practical. It is desirable that the concentration of the aqueous ammonia be 0.5 normal or more. The use of urea instead of ammonia water as a neutralizing agent is not an exception of the present invention.
[0071]
(3) An anatase type titanium oxide or a titanium oxide-based composite oxide obtained by adding one or more of silicon oxide and tin oxide to titanium oxide is used as a carrier. Since the added silicon oxide and tin oxide partially dissolve in titanium oxide to form a composite oxide, the amount of acid sites on the titanium oxide carrier is increased and N, which is an intermediate reduction product of NO, is increased.₂Since the adsorption power of O is weakened, the activity of the catalyst is improved,₂This is because it is effective for improving the selectivity of the production reaction and improving the stability by suppressing deterioration. The addition amounts of silicon oxide and tin oxide are not particularly limited, but are preferably in the range of 0 to 20% by weight. This is because when silicon oxide and tin oxide are added in excess of 20% by weight, the excellent carrier effect of titanium oxide is reduced. As the silicon compound and the tin compound for obtaining the composite oxide, ethyl silicate, ethyl metasilicate, tin chloride and the like can be used. Since ethyl silicate is not easily hydrolyzed, it is a more preferred embodiment to dissolve it in ethanol, add an acid, hydrolyze the mixture, and then add it to the raw material aqueous solution. Since the aqueous sodium metasilicate solution is alkaline, it is a more preferable embodiment to add a transparent hydrochloric acid solution to the raw material aqueous solution.
[0072]
(4) The carrier is loaded with 3 to 30% by weight of an active substance of vanadium oxide-chromium oxide composite oxide fine particles or mixed oxide fine particles of this composite oxide and vanadium oxide. V as active₇Cr₃O₂₂, V₄Cr₂O_Thirteen, VCrO₄The reason for using a composite oxide of vanadium and chromium, such as described above, will be described below.
[0073]
The vanadium oxide denitration mechanism includes vanadium oxide with NH₃Is adsorbed, NO is adsorbed thereon to form a reaction intermediate, and then N₂And H₂It is known that it decomposes and desorbs to O, but the reaction rate of this reaction becomes slow at 200 ° C. or lower. On the other hand, chromium oxide has NO adsorbing power at low temperature, NO is adsorbed first, and NH₃Is adsorbed, and the denitration reaction may proceed. Therefore, by taking advantage of both features to form a composite oxide, V and Cr are homogeneously incorporated into the crystal, so that NH on one crystal particle is obtained.₃And NO can be adsorbed simultaneously, and it is considered that the denitration performance is improved even at a low temperature. TiO₂If the amount of the catalyst supported on the carrier is less than 3% by weight, the denitration performance is reduced. Therefore, the lower limit of the amount of the activated body is set to 3% by weight. On the other hand, even if it is more than 30% by weight, the denitration rate does not increase to a certain value or more (the effect is saturated), and on the contrary, the heat treatment causes problems such as grain growth and a decrease in the specific surface area. The upper limit of the amount is 30% by weight. A more preferable range of the amount of the active substance to be carried is 5 to 15% by weight.
[0074]
(5) The molar concentration ratio of Cr / (Cr + V) in the vanadium oxide-chromium oxide composite oxide supported as an activator is 0.2 to 0.4. As a result of a detailed examination of the composition dependency of the denitration rate of the catalyst, it was found that the activity was the highest even at a low temperature of 130 ° C to 150 ° C in this composition range. This is because, in this composition region, the following composite oxide exists as the active phase having the highest activity.
[0075]
(6) The main active form of the catalyst is V₇Cr₃O₂₂Or V₄Cr₂O_ThirteenIs a composite oxide represented by In addition, as a catalyst active body, V₇Cr₃O₂₂, V₄Cr₂O_ThirteenOther than these composite oxides and V₂O₅, VCrO₄Can also be used. Conventional V₂O₅−Cr₂O₃V in the system state diagram₄Cr₂O_ThirteenAnd VCrO₄Is known to exist. The present inventors synthesized a homogeneous sample by the coprecipitation method, examined the phase diagram by X-ray diffraction and differential thermal analysis, and found that the compound present was V₇Cr₃O₂₂And VCrO₄Was obtained. That is, the conventional V₄Cr₂O_ThirteenThe compound that was said to be exactly V₇Cr₃O₂₂It is a compound having a composition. In the conventional literature, since a sample was synthesized by a solid-phase reaction, a homogeneous sample could not be obtained, and there was a possibility that both compositions were misidentified. Since both X-ray diffraction patterns are almost the same, V₇Cr₃O₂₂And V₄Cr₂O_ThirteenAre originally considered to be the same composite oxide.
[0076]
(7) Co-precipitation and valence control methods are employed as catalyst preparation methods. In order to prepare uniform composite oxide fine particles, it is necessary to synthesize a hydroxide precipitate in which metal ions are uniformly dissolved. Therefore, the raw material is VCl₃, Cr (NO₃)₃It is necessary to use a compound of V (trivalent) and Cr (trivalent). When a conventional pentavalent V compound is used, a homogeneous hydroxide in which V and Cr are dissolved cannot be synthesized. The precipitate obtained by the coprecipitation method is a trivalent metal compound and has no activity. Therefore, it is necessary to heat-treat in an oxidizing atmosphere to change the valence of vanadium from trivalent to pentavalent (valence control). is there. The concentration of the V, Cr transition metal ion in the aqueous solution when preparing the precipitate is TiO 2₂% Of the active substance is determined based on the amount of the active substance, and is not particularly limited. It is also possible to use a method in which a titanium oxide carrier is prepared by a coprecipitation method, then impregnated with a solution of a vanadium compound and a chromium compound, and heat-treated in an oxidizing atmosphere.
[0077]
(8) After the precipitate is washed and dried, heat treatment is performed at a temperature of 300 to 550 ° C. in an oxidizing atmosphere. When neutralized with aqueous ammonia to form a precipitate, a large amount of NH₄Since Cl is generated, it needs to be removed by washing. Since the obtained precipitate is a hydroxide in which V and Cr are dissolved in a solid solution, the precipitate is heated to be converted into oxide particles, and is heat-treated in an oxidizing atmosphere at a temperature of 300 to 550 ° C. to reduce the valence of V to 3 Change from valence to pentavalent, V₇Cr₃O₂₂, VCrO₄Need to be a composite oxide of At a temperature lower than 300 ° C., an amorphous oxide is contained, and a target crystalline composite oxide cannot be obtained. If the temperature is higher than 550 ° C., the oxide particles in the catalyst grow grains, the specific surface area decreases, and the activity at low temperatures decreases. A more preferred heat treatment temperature for controlling valence is 350 to 500 ° C. The heat treatment time does not need to be particularly limited, but 1-2 hours is sufficient.
[0078]
(9) A halogenated aromatic compound such as dioxin can be decomposed. As a result of various tests, it was confirmed that halogenated aromatic compounds such as chlorophenol and chlorotoluene were partially decomposed into hydrochloric acid and carbon dioxide gas by the catalyst of the present invention, and the decomposition ability was also confirmed for these compounds. It turned out that there is. This is presumably because the catalyst of the present invention obtained by the coprecipitation method has a large specific surface area and thus has a large oxidizing power even for aromatic compounds. The harmful substances in the exhaust gas that can be decomposed by the catalyst of the present invention are nitrogen oxides and halogenated aromatic compounds, but are not limited to these as long as they can be decomposed by the oxidizing action of the present catalyst.
[0079]
(10) Contact with exhaust gas at a temperature of 110 ° C. to 250 ° C. to decompose harmful substances in the exhaust gas. If the exhaust gas temperature is higher than 250 ° C., there is a risk that dioxins may be resynthesized by chlorine compounds in the exhaust gas. Therefore, the upper limit of the exhaust gas temperature is set to 250 ° C. Further, considering the safe side, it is desirable that the exhaust gas temperature be 200 ° C. or lower. This eliminates the risk of resynthesis of dioxins. On the other hand, if the exhaust gas temperature is lower than 110 ° C., the activity of the catalyst becomes too low to be practical, so the lower limit of the exhaust gas temperature is 110 ° C. Further, considering the safe side, it is desirable that the exhaust gas temperature be 130 ° C. or higher. This eliminates the risk that water containing corrosive components will condense and condense. In order to simultaneously decompose the nitrogen oxide and the halogenated aromatic compound in the exhaust gas, the exhaust gas temperature must be in the range of 110 to 250 ° C, and more preferably in the range of 130 to 200 ° C. More preferred.
[0080]
(11) The catalyst of the present invention may be used in the form of granules, formed into pellets, used by supporting the catalyst powder on a bag filter, or formed by extruding the catalyst powder into a honeycomb to form a honeycomb. Use forms such as use as a catalyst, application of a slurry containing catalyst powder on a honeycomb, and application (wash coating) are possible.
[0081]
(Example 4)
First, VCl₃And Cr (NO₃)₃An aqueous solution containing 0.1 mol / l was prepared, ammonia water was added dropwise to form a precipitate, and a test was conducted to ascertain an appropriate concentration of aqueous ammonia. If the concentration of the aqueous ammonia is higher than 3N, a precipitate is locally formed due to the neutralization, the reaction occurs heterogeneously, and a local exhaust facility is required due to a pungent odor. When the concentration of the aqueous ammonia was 0.5 to 3N, it was observed that the color of the solution gradually changed due to the neutralization, and a uniform precipitate was formed. If the concentration of ammonia water is lower than 0.5N, a large amount of ammonia water must be added, which is not practical.
[0082]
The catalyst of Example 4 was obtained as a product which was uniformly precipitated without coarsening by a coprecipitation and valence control method.
[0083]
(Example 5)
VCl₃And Cr (NO₃)₃Was prepared at various composition ratios and neutralized with 1N aqueous ammonia to produce a precipitate. The precipitate obtained is a hydroxide, which changes from hydroxide to oxide at 200 ° C. upon heating. The thermal analysis and X-ray diffraction revealed that this oxide was amorphous, and when heated further, it generated heat at about 300 ° C. and crystallized to change into a crystalline composite oxide. That is, in order to obtain a crystalline composite oxide, it is necessary to heat to about 300 ° C. or more. As a result of examining the crystal structures of oxide particles having various compositions heat-treated at 500 ° C. for 2 hours in the air by X-ray diffraction, it was found that V was obtained at a Cr / (Cr + V) ratio of 0.3.₇Cr₃O₂₂Only the compound 1 phase of the composition has a Cr / (Cr + V) ratio of 0.33 or V₄Cr₂O_ThirteenV in composition₇Cr₃O₂₂And VCrO₄The two-phase coexistence state of VCrO with a Cr / (Cr + V) ratio of 0.5₄It was found that a compound having the composition was formed. When the Cr / (Cr + V) ratio is between 0 and 0.3, V₂O₅+ V₇Cr₃O₂₂, Between 0.3 and 0.5₇Cr₃O₂₂+ VCrO₄, Between 0.5 and 1, VCrO₄+ Cr₂O₃Was in a two-phase coexistence state. Even when a trivalent V compound is used as a raw material, a heat treatment in an oxidizing atmosphere is performed to obtain a pentavalent V compound oxide V₇Cr₃O₂₂And VCrO₄Can be provided. According to this test, V₄Cr₂O_ThirteenThe compound of composition is exactly V₇Cr₃O₂₂Although they were found to be present in the composition, their X-ray diffraction patterns are very similar, so that it may be considered that they both show substantially the same compound.
[0084]
(Example 6)
TiCl₄And ethyl silicate, sodium silicate, SnCl in 1/20 amount thereof₄VCl having a composition necessary for preparing a vanadium oxide-chromium oxide (abbreviated as V-Cr) composite oxide in an aqueous hydrochloric acid solution containing at least one of the following additives:₃And Cr (NO₃)₈Is added in an amount necessary to support a predetermined concentration, and water is further added to the TiCl in the solution.₄The concentration was adjusted to 0.2 mol / L, neutralized with 1N aqueous ammonia, and the obtained precipitate was washed, dried at 120 ° C. for 20 hours, and further heat-treated at 300 to 550 ° C. for 2 hours in the air. TiO₂A supported V-Cr-based composite oxide catalyst was obtained. As shown in Table 3, the specific surface area of the obtained catalyst was 100 to 310 m for all of the catalysts of the examples (samples 31 to 46).²/ G and conventional NH 3₄VO₃It was found to be larger than a vanadia-based catalyst prepared by using an impregnation method (Comparative Sample R1). This is because the composite oxide particles are made of TiO₂This is probably because the particles were uniformly and highly dispersed on the carrier particles. Although the specific surface area decreases as the heat treatment temperature increases, it is considered that catalyst particles grow at high temperatures. If the oxide is heated to 600 ° C. or more, there is a risk that the oxide may melt depending on the composition (eg, V₂O₅, V₇Cr₃O₂₂Composition), heat treatment at a higher temperature than this is not preferred.
[0085]
The symbol * in Table 3 is a catalyst prepared by adding ethanol to a raw material aqueous solution and co-precipitating from an aqueous solution having an ethanol concentration of 2% by volume. Samples S1 and S2 are catalysts prepared using titanium sulfate as a raw material.
[0086]
(Example 7)
Aqueous ammonia having a concentration of 1 mol / l is dropped into an aqueous solution containing 0.1 mol / l of titanium tetrachloride to neutralize the solution, thereby forming a precipitate of titanium oxide or a titanium oxide-based composite oxide. After washing and drying, VCl necessary to carry 13% by weight of the active substance was used.₃And Cr (NO₃)₃Was added and impregnated, and heat-treated at a temperature of 400 ° C. in an oxidizing atmosphere to prepare a catalyst having the corresponding composite oxide supported on a carrier. The catalyst of Example 7 is shown in Table 3 by the symbol K1.
[0087]
(Example 8)
The denitration rate was evaluated by filling the obtained granular catalyst in a glass tube and reacting a reaction gas having a constant composition (NO: 100 ppm, NH₃: 100 ppm, SO₂: 10 ppm, CO₂: 10%, H₂O: 20%, O₂: 10%, N₂: The rest) at a space velocity of 5000h^-1At 150 ° C. and 130 ° C. for 200 hours. Table 3 shows the results. The NO concentration was measured using a NOx meter. Mainly V₇Cr₃O₂₂It was found that the activity of the catalyst loaded with was extremely high at 80% or more even at a low temperature of about 130 ° C. TiO₂To V₇Cr₃O₂₂The catalyst supporting 3 to 30% by weight of a composite oxide containing as a main component has a large specific surface area and has a high denitration rate even in a low temperature range of 130 ° C. to 150 ° C., which was low in performance of the conventional catalyst. Was confirmed.
[0088]
As described above, the catalyst of Example 8 has stable and excellent denitration performance even in a low temperature range.
[0089]
[Table 3]

[0090]
(Example 9)
The denitration ratio of a representative catalyst was measured at 130 to 250 ° C. in the same manner as in Example 8. The reaction time is 200 hours each. Table 4 shows the results. It was confirmed that the obtained catalysts (samples 32, 34, 40, and 42) had a higher denitration rate than the comparative sample R1 in this temperature range.
[0091]
[Table 4]

[0092]
(Example 10)
Orthochlorophenol was used as an example of a halogenated aromatic compound, and its catalytic decomposition rate was tested. Space velocity of 5000 h in a microreactor containing orthochlorophenol and granular catalyst using air as carrier gas^-1And the gas that came out was analyzed by gas chromatography.
[0093]
As a result, as shown in Table 5, all of the catalysts (samples 32, 34, 40, and 42) of Example 10 had an initial performance of the decomposition rate at 150 ° C. of 80% or more. It was found that the decomposition activity was higher even at a lower temperature than (Sample R1). It is considered that since the catalyst having a high specific surface area was obtained by the coprecipitation method, the oxidizing power of the catalyst was improved, and the decomposition performance of the halogenated aromatic compound was improved.
[0094]
[Table 5]

[0095]
(Example 11)
A part of the exhaust gas after passing through a dust remover at 150 ° C. in a garbage incinerator is branched and passed to an exhaust gas treatment device filled with a catalyst of the present invention in a honeycomb shape, and nitric oxide and dioxin at an entrance and an exit of the device. Were measured. The NO concentration at the entrance of the device is 110 ppm, and the concentration of dioxins is 1.2 ng-TEQ / Nm.³And the space velocity is 9000h^-1Met. NH added as a reducing agent for NO₃The amount is equivalent to the amount of NO in the exhaust gas. Table 6 shows the results. It has been found that the use of the catalyst of the present invention (samples 34 and 40) has a denitration ratio higher than that of the conventional catalyst (sample R1) and is 80% or more even in a low temperature range of 150 ° C.
[0096]
When the catalyst of Example 11 was used, even when the concentration of dioxins was as low as 150 ° C., 0.1 ng-TEQ / Nm³The following results have been achieved, and it has been clarified that the catalyst of the present invention can simultaneously decompose nitrogen oxide and a halogenated aromatic compound even at an exhaust gas temperature of 200 ° C. or lower, which is lower than conventional exhaust gas treatment. In addition, TEQ shows the toxic equivalent value converted using 2,3,6,7-tetrachlorodibenzodioxin as a reference substance.
[0097]
[Table 6]

[0098]
【The invention's effect】
Since the catalyst of the present invention uses a composite oxide of vanadium and chromium as an activator, the denitration performance at a lower temperature is remarkably higher than that of a conventional catalyst, and the deterioration is further reduced.
[0099]
Furthermore, according to the method for producing a catalyst of the present invention, by using the coprecipitation method, the specific surface area of the catalyst can be significantly increased as compared with the conventional impregnation method, and the denitration performance at a low temperature is significantly increased. can do.
[0100]
Advantageous Effects of Invention According to the present invention, it is possible to provide an exhaust gas treatment catalyst having a high specific surface area that has higher decomposition treatment activity at a lower temperature than conventional catalysts for exhaust gas containing harmful substances such as nitrogen oxides and halogenated aromatic compounds, and It can contribute to purification and has high industrial utility value. Especially in the exhaust gas treatment of garbage incinerators, etc., after passing the exhaust gas through a dust removing device in a low temperature range of about 150 ℃, it is possible to decompose harmful substances at low temperature without reheating to 200 ℃ or more, The exhaust gas treatment device can be reduced in size and cost, and is effective for environmental purification.

Claims (8)

V ₄ Cr ₂ O produced by a coprecipitation method using titanium dioxide as a carrier, a trivalent vanadium salt as a raw material, and a valence control method in which the coprecipitate is heat-treated at a temperature of 300 to 550 ° C. in an oxidizing atmosphere. ₁₃ , a complex oxide alone or a mixture of two or more complex oxides selected from the group consisting of V ₇ Cr ₃ O ₂₂ and VCrO ₄ , or at least one of the complex oxides and vanadium oxide or chromium oxide An exhaust gas treating catalyst, characterized in that the carrier has 3 to 30% by mass of the active substance as an active substance, and the specific surface area is 100 m ² / g or more. A co-precipitation method and a co-precipitate are prepared by using a titanium dioxide-based composite oxide obtained by adding at least one of silicon oxide and tin oxide to titanium dioxide as a carrier and using a trivalent vanadium salt as a raw material at a temperature of 300 to 550 ° C. in an oxidizing atmosphere. Generated using the valence control method of heat treatment _Four Cr _Two O ₁₃ , V ₇ Cr _Three O _{twenty two} And VCrO _Four Or a mixture of two or more composite oxides selected from the group consisting of, or an oxide fine particle comprising a mixture of at least one of the composite oxides and vanadium oxide or chromium oxide as an activator. 3 to 30% by mass of the active substance is supported on the carrier, and the specific surface area is 100 m ^Two / G or more. By forming the composition in which the Cr mole concentration / (Cr mole concentration + V mole concentration) ratio in the vanadium oxide-chromium oxide composite oxide supported as the active body is 0.2 to 0.4, the main active body is formed. Is a V ₇ Cr ₃ O ₂₂ or V ₄ Cr ₂ O ₁₃ composite oxide, the exhaust gas treatment catalyst according to claim 1 or 2. The exhaust gas treatment catalyst according to any one of claims 1 to 3, wherein nitrogen oxides are selectively reduced and decomposed in the presence of ammonia. The exhaust gas treating catalyst according to any one of claims 1 to 4, wherein halogenated aromatic compounds such as dioxins, polychlorinated biphenyls, and chlorophenol are decomposed and made harmless as harmful substances in the exhaust gas. A solution containing trivalent vanadium ions and chromium ions is added to a titanium aqueous solution containing titanium tetrachloride or titanium sulfate, and water or water and a water-soluble alcohol are further added to reduce the concentration of titanium ions in the aqueous solution to 0.1. After adjusting the concentration to 5 to 0.05 mol / L, the aqueous solution is neutralized by dropwise addition of 0.5 to 3 N aqueous ammonia, thereby neutralizing titanium dioxide and trivalent vanadium and chromium. A co-precipitate with the hydroxide is formed, and the co-precipitate is washed, dried, and heat-treated in an oxidizing atmosphere at a temperature of 300 to 550 ° C. to reduce the valence of vanadium in the co-precipitate to three. changed to pentavalent from the valence, the titanium dioxide as a _{carrier, V 4 Cr 2 O 13,} V 7 Cr 3 O 22 , and composite oxides selected from the group consisting of VCRO ₄ alone or two or more composite oxides Mixture, or said composite oxide is supported 3-30 wt% to the carrier as an active substance oxide fine particles consisting of a mixture of at least one vanadium oxide or chromium oxide of the specific surface area of 100 m ² / g of A method for producing an exhaust gas treatment catalyst, comprising obtaining the above catalyst. A solution containing trivalent vanadium ions and chromium ions is added to a titanium aqueous solution containing titanium tetrachloride or titanium sulfate, and at least one of a silicon compound and a tin compound is further added to the titanium aqueous solution. Alternatively, after adding water and a water-soluble alcohol to adjust the concentration of titanium ions in the aqueous solution to 0.5 to 0.05 mol / liter, ammonia water having a concentration of 0.5 to 3 N is dropped into the aqueous solution. And neutralizing to form a co-precipitate of titanium dioxide-based composite oxide obtained by adding at least one of silicon oxide and tin oxide to titanium dioxide and trivalent vanadium and chromium hydroxide, After washing and drying the coprecipitate, the coprecipitate is subjected to a heat treatment at a temperature of 300 to 550 ° C. in an oxidizing atmosphere to thereby form vanadium in the coprecipitate. Changing the valence pentavalent trivalent, titanium dioxide-based composite oxide in which at least one of which is the addition of silicon oxide and tin oxide in the titanium dioxide as a carrier, V _Four Cr _Two O ₁₃ , V ₇ Cr _Three O _{twenty two} And VCrO _Four An oxide fine particle consisting of a complex oxide alone or a mixture of two or more complex oxides selected from the group consisting of, or a mixture of at least one of the complex oxides and vanadium oxide or chromium oxide is used as an activator. 3 to 30% by weight of the carrier, and the specific surface area is 100 m ^Two A method for producing an exhaust gas treatment catalyst, characterized in that a catalyst having a concentration of at least / g is obtained. An exhaust gas treatment method for purifying exhaust gas, comprising contacting the exhaust gas with the catalyst according to any one of claims 1 to 5 in a temperature range from 130 ° C to 200 ° C to treat harmful substances in the exhaust gas. Exhaust gas treatment method characterized.