JP3799945B2 - Room temperature purification catalyst and method of using the same - Google Patents

Description

【００８１】
なお、実施例３の触媒について、空間速度を下げて２４０００ｈ^-1の条件で評価したところＣＯ浄化率は１００％であった。
【００８２】
上記の実施例の構成触媒は、常温（室温）においてＣＯをＣＯ₂に浄化することができることを示している。
【００８３】
特に実施例１〜実施例４に示すように還元処理をおこなうことでセリウム酸化物などの酸化物に酸素欠損状態が形成されるために、室温で貴金属による浄化反応を高めることができる。
【００８４】
セリウム酸化物を酸素欠損状態に保持するには、ＣｅＯ₂・ＺｒＯ₂の複合酸化物、または固溶体として存在すること（実施例２〜実施例４）が好ましい。さらに実施例２に示すようにＣｅＯ₂の配合モル量が多い場合（実施例３と比べて）に、浄化効率がより高いことが分かる。
【００８５】
比較例１の触媒は実施例２と同じ組成であるが還元処理がなされていない。したがって、酸化物は酸素欠損状態を形成していないため常温では浄化作用を示さない。比較例２の触媒は本発明で特定した酸化物でないケイ素の酸化物であるため還元処理を行ってもＣＯの浄化率は低い。比較例３の触媒も実施例１の触媒組成と同じであるが還元処理が行われていないため常温でのＣＯの浄化率が低い。したがって、還元処理により酸素欠損状態が形成できる本発明で特定した酸化物が、常温浄化触媒として有効であることを示している。
【００８６】
（実施例５）
５％Ｈ₂を含むＮ₂ガス中で５００℃１時間還元処理した実施例２と同じ触媒試料を用いて、アセトアルデヒドの浄化性能を評価した。
【００８７】
触媒試料量０．１ｇ
評価ガスはアセトアルデヒド（Ｏ₂２０％／Ｎ₂バランス）５Ｌ
アセトアルデヒドの初期濃度：３６ppm、７２ppm、２７０ppm、
評価方法は触媒試料と評価ガスを入れた臭気分析用匂い袋（近江オドエアーサービス社製）を室温にて静置し、１時間後、２時間後、３時間後、２４時間後および９６時間後の袋内残留アセトアルデヒド濃度を定量し、触媒試料を入れないブランク袋中のアセトアルデヒド濃度との差から、除去されたアセトアルデヒドの量を計算した。
【００８８】
（比較例４）
還元処理をしない実施例２で作製した触媒を比較例４の触媒試料とし、実施例５と同様の評価をした。
【００８９】
（比較例５）
比較例５は、触媒として活性炭粉末を用いて、実施例５と同様の条件で評価した。
【００９０】
結果を図１（初期濃度３６ppm）図２（初期濃度７２ppm）図３（初期濃度２７０ppm）のグラフに示す。
【００９１】
比較例４の触媒試料（還元処理無し）のアセトアルデヒド除去量は、比較例５の活性炭を用いた場合に比べていずれの濃度でも浄化率が低い。本発明の実施例５の触媒のアセトアルデヒド除去量は、比較例５の活性炭に比べて高いことを示している。よって、実施例５の触媒は常温でアセトアルデヒドを浄化する性能を有することを示している。
【００９２】
（実施例６）
実施例５で用いた本実施例触媒試料を０．１ｇ使用して、ホルムアルデヒドの浄化性能を調べた。
【００９３】
評価ガスはホルムアルデヒド（Ｏ₂２０％／Ｎ₂バランス）５Ｌ
評価方法は、触媒試料と評価ガスを入れた臭気分析用匂い袋（近江オドエアーサービス製）を室温にて静置し、１時間後、３時間後、２４時間後の袋内残留ホルムアルデヒド濃度をホルムアルデヒド用検知管（ジーエルサイエンス社製）で測定し、袋内のホルムアルデヒド濃度の経時変化を求めた。
【００９４】
（比較例６）
比較例５で用いた活性炭を使用して実施例６と同様に評価した。結果を図４に示す。
【００９５】
図４に示したように実施例６の触媒のホルムアルデヒド浄化性能は、比較例６の活性炭に比べて高いことが分かる。よって、実施例６の触媒は、常温でホルムアルデヒドも浄化可能であることを示している。
【００９６】
（実施例７）
実施例５で用いた触媒を０．１ｇ使用してメチルメルカプタンの浄化性能を調べた。
【００９７】
評価ガスはメチルメルカプタン（Ｏ₂２０％／Ｎ₂バランス）５Ｌ
評価方法は試料と評価ガスを入れた臭気分析用匂い袋（近江オドエアーサービス製）を室温にて静置し、１時間後、３時間後、２４時間後の袋内残留メチルメルカプタン濃度をＦＰＤ式ガスクロマトグラフ（島津製：ＧＣ−１５Ａ）にて測定し、袋内のメチルメルカプタン濃度の経時変化を求めた。
【００９８】
（比較例７）
比較例５で用いた活性炭を用いたこと以外は実施例７と同様にして浄化性能を評価した。結果を図５に示す。
【００９９】
図５に示したように本実施例７の触媒は、メチルメルカプタンの浄化性能が比較例７の活性炭より高いことが分かる。よって、実施例７の触媒は、常温でメチルメルカプタンのような臭気物質も浄化可能であることを示している。
【０１００】
（実施例８）
実施例５で用いた触媒を０．１ｇ使用してトリメチルアミンの浄化性能を調べた。
【０１０１】
評価ガスはトリメチルアミン（Ｏ₂２０％／Ｎ₂バランス）５Ｌ
評価方法は触媒試料と評価ガスを入れた臭気分析用匂い袋（近江オドエアーサービス製）を室温にて静置し、１時間後、３時間後、２４時間後の袋内残留トリメチルアミン濃度をＦＴＤ式ガスクロマトグラフ（島津製：ＧＣ−１４Ａ）にて測定し、トリメチルアミン濃度の経時変化を求めた。
【０１０２】
（比較例８）
比較例５で用いた活性炭を浄化触媒の代わりに用いたこと以外は実施例８と同様にして評価した。結果を図６に示す。
【０１０３】
図６に示したように本実施例８の触媒はトリメチルアミンの浄化性能が比較例８の活性炭よりも高いことが分かる。よって、実施例８の触媒は、常温でトリメチルアミンのような臭気物質も浄化可能であることを示している。
【０１０４】
（実施例９）
酸化セリウム粉末にＰｔ塩（「白金Ｐソルト」田中貴金属（株）製）の所定濃度の水溶液を所定量含浸させ、蒸発乾固後５００℃にて大気中で２時間焼成してＰｔを担持した。このとき酸化セリウム粉末中のＰｔ担持量は酸化セリウム粉末１５０ｇに対して１ｇである。その後、５％の水素ガスを含む窒素ガス中で５００℃で１時間処理して実施例９の触媒とした。このときの触媒粉末中のＣｅとＯ比はＸ線回折および元素分析から１：１．９であった。
【０１０５】
（実施例１０）
ＣｅとＯ比が１：１．８となるように調製した以外は、実施例９と同様にして実施例１０の触媒粉末を調製した。
【０１０６】
（実施例１１）
ＣｅとＯ比が１：１．７となるように調製した以外は、実施例９と同様にして実施例１１の触媒粉末を調製した。
【０１０７】
（実施例１２）
ＣｅとＯ比が１：１．６５となるように調製した以外は、実施例９と同様にして実施例１２の触媒粉末を調製した。
【０１０８】
（実施例１３）
ＣｅとＯ比が１：１．６となるように調製した以外は、実施例９と同様にして実施例１３の触媒粉末を調製した。
【０１０９】
（実施例１４）
ＣｅとＯ比が１：１．５５となるように調製した以外は、実施例９と同様にして実施例１４の触媒粉末を調製した。
【０１１０】
（実施例１５）
ＣｅとＯ比が１：１．５となるように調製した以外は、実施例９と同様にして実施例１５の触媒粉末を調製した。
【０１１１】
（実施例１６）
Ｐｔの担持量が酸化物セリウム１５０ｇに対して０．１ｇとなるように調製し、かつＣｅとＯ比が１：１．８となるように調製したこと以外は、実施例９と同様にして実施例１６の触媒粉末を調製した。
【０１１２】
（実施例１７）
Ｐｔの担持量が酸化物セリウム１５０ｇに対して０．５ｇとなるように調製したこと以外は、実施例１６と同様にして実施例１７の触媒粉末を調製した。
【０１１３】
（実施例１８）
Ｐｔの担持量が酸化物セリウム１５０ｇに対して５ｇとなるように調製したこと以外は、実施例１６と同様にして実施例１８の触媒粉末を調製した。
【０１１４】
（実施例１９）
Ｐｔの担持量が酸化物セリウム１５０ｇに対して１５ｇとなるように調製したこと以外は、実施例１６と同様にして実施例１９の触媒粉末を調製した。
【０１１５】
（実施例２０）
Ｐｔの担持量が酸化セリウム１５０ｇに対して１７ｇとなるように調製したこと以外は、実施例１６と同様にして実施例２０の触媒粉末を調製した。
【０１１６】
（実施例２１）
Ｐｔの担持量が酸化セリウム１５０ｇに対して０．０１ｇとなるように調製したこと以外は、実施例１６と同様にして実施例２１の触媒粉末を調製した。
【０１１７】
（実施例２２）
Ｐｔの代わりにＰｄを酸化物セリウム１５０ｇに対して１ｇとなるように調製したこと以外は、実施例１６と同様にして実施例２２の触媒粉末を調製した。
【０１１８】
（実施例２３）
Ｐｔの代わりにＲｈを酸化物セリウム１５０ｇに対して１ｇとなるように調製したこと以外は、実施例１６と同様にして実施例２３の触媒粉末を調製した。
【０１１９】
（実施例２４）
Ｐｔの代わりにＡｕを酸化物セリウム１５０ｇに対して１ｇとなるように調製したこと以外は、実施例１６と同様にして実施例２４の触媒粉末を調製した。
【０１２０】
（実施例２５）
Ｐｔの代わりにＲｕを酸化物セリウム１５０ｇに対して１ｇとなるように調製したこと以外は、実施例１６と同様にして実施例２５の触媒粉末を調製した。
【０１２１】
（実施例２６）
Ｐｔを酸化物セリウム１５０ｇに対して１ｇ、Ｐｄを酸化セリウム１５０ｇに対して１ｇとなるように調製したこと以外は、実施例１６と同様にして実施例２６の触媒粉末を調製した。
【０１２２】
（比較例９）
ＣｅとＯとの比が１：２．０となるように酸化物を調製したこと、つまり還元処理を行わないこと以外は、実施例９と同様にして比較例９の触媒粉末を作製した。
【０１２３】
（比較例１０）
活性炭（（株）キャタラー製 ＢＦＧ−３）をＰｔ担持酸化セリウム粉末の代わりに用いて比較例１０の触媒粉末を調製した。
【０１２４】
（触媒の評価）
評価ガスとして臭気物質であるホルムアルデヒド：１００ｐｐｂ、酸素：２０％、窒素：バランスのガスを用い、上記の各試料０．５ｇと評価ガスを入れた５リットル臭気分析用におい袋（近江オートエアサービス製）を室温度下で循環ポンプを用い１０リットル／分の循環速度で評価ガスを循環させた。空間速度は６０００００ｈ^-1であった。なお、上記測定においては試料が、におい袋から飛散しないようにガスポンプ前にフイルタを置いた。循環２０分後の評価ガス中のホルムアルデヒドの浄化率を測定した。測定には酵素−化学発光法によるホルムアルデヒド分析装置を用いホルムアルデヒド濃度を分析し次式によりホルムアルデヒド浄化率を求めた。
【０１２５】
ホルムアルデヒド浄化率（％）＝｛（反応前のにおい袋中のホルムアルデヒド濃度−試料共存２０分後のホルムアルデヒド濃度）／反応前のにおい袋中のホルムアルデヒド濃度｝×１００
結果を表２に示す。
【０１２６】
【表２】

【０１２７】
表２に示すように実施例９〜１５の各触媒はホルムアルデヒド浄化率が、同量の貴金属を担持し、還元処理をしない比較例９より浄化率が高いこと、比較例１０の活性炭よりも高いことを示し常温でのホルムアルデヒドの浄化に有効であることを示している。特に実施例１３の触媒は浄化率が８８％という高い浄化率を示し、酸素欠損度合いが高い場合に貴金属量が多い場合よりも浄化率が高い。したがって、酸化物の酸素欠損状態が大きい程、触媒の浄化性能を高めるのにより有効であることを示唆している。
【０１２８】
実施例１６〜実施例２１では最適Ｐｔ担持量があることを示し、セリウム酸化物に担持されて使用するＰｔの量は、セリウム酸化物１５０ｇに対して０．０１ｇから２０ｇ、より好ましくは０．５ｇから５ｇ含まれることで有害物質を室温で浄化することができる。実施例２２〜実施例２６ではＰｔ以外の他の担持貴金属も有効であることを示している。
（実施例２７）
酸化鉄２００ｇに白金が２ｇの割合になるように酸化鉄粉末にジニトロジアンミン白金水溶液を加え、攪拌、加熱して溶液を蒸発乾固させることにより、白金塩を担持した酸化鉄粉末を得た。この粉末を大気中５００℃で３時間焼成することにより白金担持酸化鉄触媒を得た。この触媒は常温での一酸化炭素の酸化活性の測定前に、ＣＯを１％含む窒素気流中において３００℃で１５分還元処理を行うことによって触媒中に酸素欠損を導入する活性処理をおこなった。
（実施例２８）
酸化鉄粉末の代わりに酸化マンガン粉末を用いること以外は実施例２７と同様に調製した白金担持酸化マンガン触媒を作製した。尚実施例２８は参考例とする。
（比較例１１）
酸化鉄粉末の代わりにシリカを用いること以外は実施例２７と同様にして白金担持シリカ触媒を調製した。
（比較例１２）
酸化鉄粉末の代わりにジルコニアを用いること以外は実施例２７と同様にして白金担持ジルコニア触媒を調製した。
（比較例１３）
酸化鉄粉末の代わりにアルミナを用いること以外は実施例２７と同様にして白金担持アルミナ触媒を調製した。
【０１２９】
上記で調製した各触媒（実施例２７〜２８、比較例１１〜１３）の浄化性能の評価は、２０ｇの触媒をガス流量５Ｌ／min、ＣＯ濃度２５０ppm、酸素濃度２０％の条件で行った。結果を表３に示す。
【０１３０】
【表３】

【０１３１】
実施例２７の酸化鉄触媒、実施例２８の酸化マンガン触媒の酸素欠損率とＣＯ転化率との関係のグラフを図７および図８に示す。実施例２７では触媒２０ｇ、ガス流量５Ｌ／minの条件で、実施例２８では触媒量５ｇ、ガス流量１０Ｌ/minの条件で触媒活性を測定した。なお、評価ガス組成のＣＯ₂２５０ppm、Ｏ₂２０％の条件は共通とした。両者共に酸素欠損率が１０％前後にＣＯ転化率のピークが認められるが、酸素欠損が存在すればＣＯは浄化できることを示している。図７より酸化鉄触媒の場合、酸素欠損率が２〜１１％の範囲が好ましく、図８より酸化マンガン触媒の場合、酸素欠損率が５〜１８％の範囲が好ましいことが分かる。ここで、酸化鉄の酸素欠損率、酸化マンガンの酸素欠損率とはＦｅ₂Ｏ₃、ＭｎＯ₂に含まれる酸素量に対する欠損した酸素量の比率を示す。
【０１３２】
表３に示すように本発明の酸化物を含む触媒は、常温でＣＯを浄化する性能を有することを示している。
【０１３３】
（実施例２９）
酸化セリウムに硝酸ジルコニウム水溶液をモル比でＣｅ／Ｚｒ＝１０／１となるように混合したスラリーを調製した。このスラリーを１３０℃３時間乾燥後、大気中５００℃で３時間焼成した。このようにして得られたＣｅＯ₂・ＺｒＯ₂粉末１５０ｇにＰｔを２ｇの割合で担持した。この粉末を１〜２ｍｍ径のペレット状に成形した。その後５％の水素を含む窒素ガス中で５００℃１時間還元処理したものを実施例２９の触媒試料とした。
【０１３４】
この触媒試料１ｇをエチレンガスに対する浄化性能を評価した。
【０１３５】
評価ガスは、エチレン（初期濃度２００ｐｐｍ）を含む酸素２０％窒素バランスを５リットル。
【０１３６】
評価方法は、試料と評価ガスを入れた臭気分析用におい袋（近江オートエアサービス製）を１０℃の恒温槽に静置し１時間、２時間、３時間、２４時間後のエチレン濃度をＦＩＤ式ガスクロマトグラフ（島津製作所製：ＨＣＭ−１Ｂ）にて測定しエチレン濃度の経時変化を求めた。結果を図９に示す。
【０１３７】
比較例として本発明の触媒を使用しない場合（比較例１４）、本実施例２９の触媒の代わりに活性炭粉末（キャタラー製ＢＦＧ−３）を実施例２９と同じ割合の量用いた場合（比較例１５）も同様に評価した。
【０１３８】
図９に示すように本実施例２９は比較例１５の活性炭に比べてエチレンの除去能が高いことが分かる。
（実施例３０）
流通途上で黄化や花蕾が開花するなどして品質低下が生じ易いブロッコリーを生鮮食料品として選び、花蕾の黄化度合いから鮮度保持について検討した。なお、黄化度合いは目視による官能評価で、黄化度＝０は黄化変化無し、黄化度＝１は黄化変化少し、黄化度＝２は黄化変化かなり、黄化度＝３すべて黄化の基準に基づき行った。
【０１３９】
市販されているブロッコリー一房（品種：唐嶺）を１リットルの臭気分析用サンプリングバック（ジーエルサイエンス（株）製 素材：フッ素樹脂、フィルムの厚さ５０μｍ）に入れ、さらに実施例２９で用いた触媒をブロッコリー１ｋｇあたり１ｇ同封・密閉し、予め用意した空気ボンベよりサンプリングバック中の触媒が飛散しないように注意して１リットル導入した。
【０１４０】
次にこのサンプリングバックを１０℃の恒温槽の中に入れ、定期的にこのサンプリング中のブロッコリーの黄化度合いを経時的に評価した。
【０１４１】
比較例として本発明の触媒を使用しない場合（比較例１６）、本実施例３０の触媒の代わりに活性炭粉末（キャタラー製ＢＦＧ−３）を実施例３０と同じ割合の量用いた場合（比較例１７）も同様に評価した。
【０１４２】
結果を表４に示す。
【０１４３】
【表４】

【０１４４】
表４に示すように、実施例３０では比較例１６、１７に比べて花蕾の黄化度の進行が遅く、ブロッコリーの鮮度保持に効果を有することが分かる。
（実施例３１）
リンゴを生鮮食品として選び、本発明の触媒による鮮度保持効果を果皮の変色、果実の硬度、食味指数から評価した。
【０１４５】
市販されているリンゴ２個（品種：ふじ）を１リットルの臭気分析用サンプリングバック（アルミニウム製、フイルム厚さ１３０μｍ、ジーエルサイエンス（株）製）に入れ、さらに実施例３０の触媒をリンゴ１ｋｇあたり０．５ｇ同封した。
【０１４６】
次にこのサンプリングバックを１５℃の恒温槽の中にいれ定期的にこのサンプリング中のリンゴの果皮の変色、果実の硬度、食味指数から評価した。
【０１４７】
比較例として実施例３１の触媒を使用しない場合（比較例１８）、本実施例３１の触媒の代わりに活性炭粉末（キャタラー製ＢＦＧ−３）を実施例３１と同じ割合の量用いた場合（比較例１９）も同様に評価した。
【０１４８】
果実の硬度；１：硬い、２：やや軟化、３：軟化
食味指数；常に不良：０、不良：０．５、やや不良：１、良好：１．５、非常に良好：２、の５段階評価
【０１４９】
【表５】

【０１５０】
【表６】

【０１５１】
【表７】

【０１５２】
表５〜表７に示したように比較例１８、１９では硬度や食味指数の低下が顕著であるのに対し、本実施例３１ではリンゴ購入直後の状態に近い状態を保持しており、リンゴの鮮度保持に効果があることが分かる。
【０１５３】
したがって、本実施例３１の常温浄化触媒は常温でのエチレンの除去能力を有することを示している。
【０１５４】
（実施例３２）
粒度０．５〜２mmに整粒した活性炭７５ｇの吸水量に相当する量の脱イオン水に、硝酸セリウム・６水和物（ＣｅＯ₂換算で７５ｇ相当）とＰｔ（ＮＯ₂）₂（ＮＨ₃）₂（Ｐｔ換算で０．５ｇ相当）を溶解した後、この水溶液を活性炭７５ｇに吸水させた。得られた触媒前駆体の活性炭を大気中で、１１０℃で６時間乾燥した。次いで５％の水素を含む窒素ガス雰囲気下で５℃／min以下の昇温速度で５００℃まで昇温した後、そのまま１時間保持した。その後、室温まで冷却し、本実施例の触媒を得た。
【０１５５】
（実施例３３）
粒度０．５〜２mmに整粒した活性炭７５ｇの吸水量に相当する量の脱イオン水に、硝酸セリウム・６水和物（ＣｅＯ₂換算で７５ｇ相当）を溶解した後、この水溶液を活性炭７５ｇに吸水させた。得られた前駆体の活性炭を大気中で１１０℃６時間乾燥した後、５％の水素を含む窒素ガス雰囲気下で５℃／min以下の昇温速度で５００℃まで昇温した後、そのまま１時間保持した。次にＰｔ（ＮＯ₂）₂（ＮＨ₃）₂（Ｐｔ換算で０．５ｇ相当）を含む水溶液を用いて前記活性炭にＰｔを担持し、５％の水素を含む窒素ガス雰囲気下で５℃／min以下の昇温速度で５００℃まで昇温した後、そのまま１時間保持した。その後、室温まで冷却してPt/CeO₂/活性炭触媒を得た。
【０１５６】
（実施例３４）
硝酸セリウム・６水和物 （ＣｅＯ₂換算で６０ｇ相当）と粉末状の活性炭７５ｇとを脱イオン水５００ｇ中に加え、良く攪拌した後、中和当量の１．２倍モル量のアンモニア水溶液を加えて触媒前駆体の活性炭を得た。この前駆体の活性炭を窒素雰囲気下、５℃／min以下の昇温速度で５００℃まで昇温しそのまま３時間加熱した。得られた生成物にＰｔ（ＮＯ₂）₂（ＮＨ₃）₂（Ｐｔ換算で０．５ｇ相当）を含む水溶液を用いて前記生成活性炭にＰｔを担持し、５％の水素を含む窒素ガス雰囲気下で５℃／min以下の昇温速度で５００℃まで昇温した後、そのまま１時間保持した。室温まで冷却した後に得られたＰｔ担持活性炭をセリアゾル（ＣｅＯ₂量として１５ｇ）、脱イオン水６８ｇと混合、混練した後、粒度０．５〜２mmに造粒した。得られたペレットを大気中で１１０℃で６時間乾燥し、さらに５％水素を含む窒素ガス雰囲気下で５００℃で１時間加熱したあと室温まで冷却して触媒を調製した。
【０１５７】
（実施例３５）
硝酸セリウム・６水和物（ＣｅＯ₂換算で６０ｇ相当）、オキシ硝酸ジルコニウム・２水和物（ＺｒＯ₂換算で９ｇ相当）および粉末状の活性炭７５ｇとを脱イオン水５００ｇ中に加え、良く攪拌した後、中和当量の１．２倍モル量のアンモニア水溶液を加えて触媒前駆体活性炭を得ること以外は、実施例３４と同様にして触媒を調製した。
【０１５８】
（実施例３６）
硝酸セリウム・６水和物 （ＣｅＯ₂換算で６０ｇ相当）と粉末状の活性炭７５ｇ、さらにＰｔ（ＮＯ₂）₂（ＮＨ₃）₂（Ｐｔ換算で０．５ｇ相当）を脱イオン水５００ｇ中に加え、良く攪拌した後、中和当量の１．２倍モル当量のアンモニア水溶液を加えて触媒前駆体を得た。この触媒前駆体を５％水素を含む窒素ガス雰囲気下で、５℃／min以下の昇温速度で５００℃まで昇温しそのまま３時間加熱した。得られた粉末とセリアゾル（ＣｅＯ₂量として１５ｇ）脱イオン水６８ｇ、と混合、混練した後、粒度０．５〜２mmに造粒した。得られたペレットを大気中で１１０℃で６時間乾燥、さらに５％水素を含む窒素ガス雰囲気下で５００℃で１時間加熱し、室温まで冷却して触媒を調製した。
【０１５９】
（実施例３７）
粉末状の活性炭とＰｔ(O.5g）を担持して大気中、５００℃で１時間加熱したＰｔ（０．５ｇ）／ＣｅＯ₂（６０ｇ）、バインダとしてセリアゾル（ＣｅＯ₂として１５ｇ）および脱イオン水（６８ｇ）とを混合、混練した後、大気中で１１０℃で６時間乾燥した。次いで５％水素を含む窒素ガス雰囲気下で、５００℃で１時間加熱し、室温まで冷却して触媒を調製した。
【０１６０】
（比較例２０）
ＰｔおよびＣｅＯ₂のいずれも添加していない活性炭を触媒とした。
【０１６１】
（比較例２１）
活性炭７５ｇの吸水量に相当する脱イオン水中にＰｔ（ＮＯ₂）₂（ＮＨ₃）₂（Ｐｔ換算で０．２５ｇ相当）を溶解したこと以外は実施例３２と同様に調製したＰｔ／活性炭触媒を調製した。
【０１６２】
（比較例２２）
粉末状の活性炭を用いて比較例２１と同様にしてＰｔ０．５ｇを活性炭７５ｇに担持して調製したＰｔ（０．５ｇ）／活性炭（７５ｇ）とＣｅＯ₂粉末（６０ｇ）、セリアゾル（ＣｅＯ₂として１５ｇ）および脱イオン水（６８ｇ）とを混合、混練後、粒度０．５〜２mmに造粒した。さらに５％水素を含む窒素ガス雰囲気下で、５００℃、１時間加熱して室温まで冷却して触媒を得た。なお、この比較例ではＰｔの大部分が活性炭に担持されている。
（評価）
上記で調製した各触媒のアセトアルデヒドの浄化率を図１０に、ＣＯの浄化率を図１１に示した。
【０１６３】
臭気物質除去試験（臭気物質の代表例としてアセトアルデヒドを使用）
１パス試験
触媒量：２ｇ
使用ガス：アセトアルデヒド（２０ppm）＋酸素（２０％）残り窒素ガス
流量：５リットル／ｍｉｎ、反応温度：室温
評価法：ガス流通開始から１時間後のアセトアルデヒドの除去率をアセトアルデヒドの浄化率として評価した。
【０１６４】
ＣＯ浄化試験
１パス試験
触媒量：２ｇ
使用ガス：ＣＯ（２５０ppm）＋酸素（２０％）残り窒素ガス、流量：１０リットル／ｍｉｎ
反応温度：室温
評価法：ガス流通開始から１時間後のＣＯの除去率をＣＯ浄化率として評価した。
【０１６５】
活性炭のみを用いた比較例２０では浄化率が３０％程度と低く、活性炭にＰｔを担持した比較例２１でもその浄化率は５０％以下である。またＰｔ担持活性炭とＣｅＯ₂とをブレンドした比較例２２の活性は比較例２１とほぼ同等である。
【０１６６】
これに対して還元処理したＰｔ担持ＣｅＯ₂と活性炭とをブレンドした実施例３７では約８０％の浄化性能を示し、ＰｔがＣｅＯ₂上に担持されている必要性が示唆される。その他の実施例でもＰｔがＣｅＯ₂上に担持されているため、比較例に対して高い浄化性能を示すと考えられる。活性炭にＰｔとＣｅＯ₂を担持する方法としては実施例３２および実施例３３に示したように、ＣｅＯ₂、次いでＰｔと逐次担持しても良いし、両者を同時に担持してもよい。これは実施例３４と実施例３６においても同様である。
【０１６７】
さらに実施例３５と実施例３４の比較から、活性炭以外の担体成分として、ＣｅＯ₂とＺｒＯ₂を含有する場合はＣｅＯ₂のみの場合に比べて浄化性能が高いことが分かる。
【０１６８】
【発明の効果】
本発明の常温浄化触媒は、還元処理によって少なくとも一部に酸素欠損状態を持つ酸化物が貴金属を担持しているので、酸化物と貴金属との両者の作用により常温で環境負荷物質を除去浄化することができる。特に空気中の存在する少量の有害物質も浄化することが可能である。特にセリウム酸化物および貴金属を含む場合は空気中のホルムアルデヒドを室温度下で効率よく除去することができる。よってこの常温浄化触媒により、住環境における人体への負荷を低減でき住環境の向上に貢献することができるものである。
【０１６９】
また、本発明の常温浄化触媒では、常温の温度域でエチレンが分解除去できるので、青果物の生理作用を抑制し経時的に追熟老化の進行を押さえ青果物の鮮度を簡便に保持できる。
【０１７０】
さらに、この常温浄化触媒は酸化反応であるのでエチレン分解に伴い酸素を消費して二酸化炭素を生成するので、青果物の鮮度保持に望ましいガス構成である低酸素濃度、高二酸化炭素濃度、低エチレン濃度の雰囲気を形成することができる。
【０１７１】
活性炭に酸素欠損状態のセリウム酸化物と貴金属を担持した触媒では、活性炭の吸着能力を活用しているので、有害物質が単位時間当たりに貴金属およびセリウム酸化物に接触する量を低減でき、触媒活性部が吸着物による被毒が抑制でき、浄化性能を長期間保持することができる。
【図面の簡単な説明】
【図１】実施例５、比較例４および５のアセトアルデヒド濃度３６ppmでの各試料の１、２、３時間後、２４時間後および９６時間後の浄化率を比較したグラフである。
【図２】実施例５、比較例４および５のアセトアルデヒド濃度７２ppmでの各試料の１、２、３時間後、２４時間後および９６時間後の浄化率を比較したグラフである。
【図３】実施例５、比較例４および５のアセトアルデヒド濃度２７０ppmでの各試料の１、２、３時間後、２４時間後および９６時間後の浄化率を比較したグラフである。
【図４】本実施例６の触媒と活性炭とのホルムアルデヒドの除去率を比較したグラフである。
【図５】本実施例７の触媒と活性炭とのメチルメルカプタンの除去率を比較したグラフである。
【図６】本実施例８の触媒と活性炭とのトリメチルアミンの除去率を比較したグラフである。
【図７】実施例２７の酸化鉄の酸素欠損度合いとＣＯ転化率の関係を示すグラフである。
【図８】実施例２８の酸化マンガンの酸素欠損度合いとＣＯ転化率の関係を示すグラフである。
【図９】実施例２９の常温浄化触媒、常温浄化触媒を使用しない場合、および活性炭を用いエチレン濃度の経時変化を調べたグラフである。
【図１０】本実施例３２〜３７および比較例２０〜２２のアセトアルデヒドの浄化率を示す棒グラフである。
【図１１】本実施例３２〜３７および比較例２０〜２２の一酸化炭素の浄化率を示す棒グラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to environmentally hazardous substances such as carbon monoxide (CO) and odorous substances, nitrogen oxides (NOx), hydrocarbons (HC), formaldehyde often generated in houses, and ethylene that causes a decrease in the freshness of food. The present invention relates to a room temperature purification catalyst that can easily purify and remove gases and the like at room temperature (room temperature).
[0002]
[Prior art]
Conventionally, adsorbents such as activated carbon and zeolite are used to remove odorous substances and harmful gases, but these adsorbents require means for treating the adsorbed components.
[0003]
In addition, the purification of carbon monoxide gas, which is a harmful gas, requires the ability to purify and remove in a short time in a lower temperature range. However, the conventional catalyst still lacks the purification capability at room temperature, and further improvement in purification performance is required.
[0004]
The effects of formaldehyde on the human body are mainly stimulating effects on the eyes, nose and throat, and specifically include symptoms such as discomfort, tearing, sneezing, coughing, nausea and dyspnea. Smoking, use of heating appliances, household items, furniture and building materials are considered as sources in the residential space. Formaldehyde is also used as a raw material for plywood / particle board adhesives, which are often used as urea-formaldehyde adhesives, and as a preservative for wallpaper adhesives. In contrast, in the Ministry of Health and Welfare, the standard value of formaldehyde concentration in the room is 0.1 mg / Nm.^Three(= 80 ppb) or less.
[0005]
In recent years, formaldehyde has been recognized as one of the causative substances of sick house syndrome, and materials manufacturers and housing manufacturers have aged the interior of the house before using it with materials that do not generate formaldehyde or handing it over to the client after the construction. Efforts are being made to reduce the concentration, but the above treatment does not necessarily meet the standards set by the Ministry of Health and Welfare.
[0006]
On the other hand, adsorbents such as activated carbon and zeolite are used to remove volatile formaldehyde. However, these adsorbents have a long life, require periodic replacement, and require economic expenses. Also, a means for newly treating the component adsorbed on the adsorbent is required.
[0007]
A filter for an air purifier incorporating activated carbon is generally known as a means for removing indoor odorous substances at room temperature. Air purifier filters using a photocatalyst are also commercially available.
[0008]
In addition, a method for removing using ozone, a method using a photocatalyst, an apparatus and a filter thereof are put on the market. However, in order to make the effect appear for ozone, a concentration exceeding the regulation value of the ozone concentration is required, and a catalyst for treating ozone is required. As for the photocatalyst, an artificial light source serving as an excitation source for the photocatalyst is required. When the photocatalyst is constantly irradiated with the light source, an electricity bill for operating the light source is also required, which is expensive.
[0009]
JP-A-6-219721 discloses CeO in which noble metal particles are uniformly mixed.₂It is comprised from the metal oxide particle containing, and CeO is added to the metal oxide.₂, ZrO₂TiO₂And SnO₂Catalysts containing one or more of these are disclosed. This catalyst is a catalyst that forms anionic vacancies on the surface of a metal oxide containing precious metal particles as a catalyst for purifying carbon monoxide into carbon dioxide gas, and has high reactivity without hydrogen reduction treatment. Is shown. However, the purification performance is evaluated under a temperature condition of 150 ° C. or higher, and no mention is made of the purification activity in the room temperature region.
[0010]
On the other hand, a specific catalyst has been proposed as a method for oxidizing and decomposing odorous substances and harmful gases in the atmosphere. For example, Japanese Patent Application Laid-Open No. 10-296087 discloses that a catalyst containing zirconia or ceria essential and supporting one or more of Ag, Pd, Pt, Mn, and Rh can be used as an oxidation decomposition catalyst for trimethylamine. However, even in this case, the disclosed catalyst has only been evaluated for purifying performance under the temperature condition of 200 ° C. in the examples. Moreover, there is no description about oxygen deficiency about the oxide used for said catalyst. Therefore, it is unlikely that the above catalyst retains sufficient trimethylamine decomposition ability in the room temperature range.
[0011]
International Patent Application WO-91 / 01175 discloses a catalyst selected from iron oxide, ceria, zirconia, copper oxide, rare earth elements, manganese oxide, vanadium oxide, and chromium oxide as a catalyst for oxidizing an oxidizing substance in a low temperature range. There is a disclosure that a catalyst having a noble metal supported on a reducing metal oxide oxidizes an oxidizing substance having a molecular weight of 50 or less at a temperature up to 30 ° C. If attention is paid to the reduction temperature as a production condition of the catalyst, there is a description that the reduction treatment is performed at room temperature. However, it is impossible to introduce oxygen vacancies having the functions of the present invention into the metal oxide at room temperature.
[0012]
Japanese Patent Laid-Open No. 7-51567 discloses a catalyst in which activated carbon is suspended in an aqueous solution in which molybdenum or cerium and platinum are dissolved, and the molybdenum or cerium and platinum are supported on the activated carbon using heat or a reducing agent. is there. However, this catalyst does not mention any kind of treatment after loading.
[0013]
In general, an air purifier filter using activated carbon exhibits a deodorizing ability by physically adsorbing an odor substance on the activated carbon. However, there is an upper limit for the adsorption amount of activated carbon, and deodorization performance exceeding the saturated adsorption amount is not exhibited. Therefore, the life of the filter is short, and regeneration processing is indispensable for long-term use. When regeneration is not performed, replacement of the filter is essential.
[0014]
Moreover, in the filter using a photocatalyst, the light irradiation for operating a photocatalyst is indispensable for purification | cleaning of a harmful substance, and a light source, such as a mercury lamp, is required for this. For this reason, an air cleaner or the like using a photocatalyst filter has a problem that the equipment cost and running cost are very high.
[0015]
Moreover, it is thought that the freshness of fruits and vegetables falls by the ethylene gas contained in the air promoting the physiological action of fruits and vegetables and progressing ripening aging. Therefore, methods for decomposing ethylene with ozone or hydrogen peroxide or adsorbing and removing ethylene have been proposed for maintaining the freshness of fresh food.
[0016]
However, among the above methods, the adsorption type has a short duration of effect. Therefore, when ozonolysis used to compensate for the disadvantages of adsorption type and photocatalyst are used together, there are problems such as a large equipment for removal means and cost, equipment space is required, and there are practical problems .
[0017]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and includes harmful gases and harmful organic substances contained in the air at normal temperature (a region including normal room temperature that does not require special heating and cooling and lower temperature). It is an object to propose a room temperature purification catalyst that can decompose and purify substances such as formaldehyde and ethylene and has little deterioration with time.
[0018]
[Means for Solving the Problems]
The room temperature purification catalyst of the present invention comprises a noble metal supported on an oxide into which oxygen deficiency has been introduced by a reduction treatment. It has the function of purifying environmentally hazardous substances in the air at room temperature by supporting noble metals on oxides with oxygen deficiency. Examples of the environmental additive include odorous substances, hydrocarbons such as carbon monoxide and ethylene, and nitrogen compounds.
[0019]
  The oxide constituting the room temperature purification catalyst of the present invention,At least one selected from oxides of zirconium, iron and ceriumCan be used.
[0020]
The oxide that constitutes the room temperature purification catalyst of the present invention preferably contains cerium oxide, and at least part of the cerium oxide is present in an oxygen-deficient state by reduction treatment. The oxygen deficiency is preferably in a state of 1.5 ≦ n <2 in CeOn. Further, CeOn preferably has an oxygen deficiency state of 1.5 ≦ n ≦ 1.8. The catalyst containing cerium oxide is suitable for purifying at least one of environmentally hazardous substances such as formaldehyde, trimethylamine, methyl mercaptan, and acetaldehyde in the air at room temperature.
[0021]
The oxide constituting the room temperature purification catalyst of the present invention preferably contains cerium oxide and zirconium oxide, and at least part of the cerium oxide is present in an oxygen deficient state mainly by reduction treatment. Further, these cerium oxide and zirconium oxide preferably form a solid solution or composite oxide.
[0022]
These oxides composed of cerium oxide and zirconium oxide have a specific surface area of 50 m after reduction at 500 ° C. for 1 hour.²/ G or more is preferable. Under different conditions, these cerium oxide and zirconium oxide oxides have a specific surface area of 15 m after reduction at 800 ° C. for 1 hour.²/ G or more is preferable.
[0023]
The temperature of the reduction treatment is 100 ° C to 800 ° C, more preferably 200 ° C to 600 ° C.
[0024]
The room temperature purification catalyst of the present invention may be used by being supported on at least one carrier selected from titanium oxide, alumina, silica, zeolite, cordierite, sepiolite, and activated carbon.
[0025]
The purification reaction for the odorous substance of the room temperature purification catalyst of the present invention is a purification reaction temperature of 25 ° C. and a space velocity of 600000 h.^-1Under these conditions, the purification rate after 20 minutes from the start of the purification reaction is 50% or more. Further, the purification reaction for carbon monoxide of the room temperature purification catalyst of the present invention is a purification reaction temperature of 25 ° C. and a space velocity of 120,000 h.^-1Under these conditions, the purification rate 30 minutes after the start of the chemical reaction is 40% or more.
[0026]
The method of using the room temperature purification catalyst of the present invention is based on the above-mentioned room temperature purification catalyst obtained from carbon monoxide, nitrogen oxides, ethylene, aldehydes, amines, mercaptans, fatty acids, odorous substances, and aromatic hydrocarbons. These environmentally hazardous substances are purified at normal temperature by contacting with air containing at least one kind.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
The room temperature purification catalyst of the present invention is a catalyst in which a noble metal is supported on an oxide into which oxygen deficiency has been introduced by reduction treatment. With this room temperature purification catalyst, harmful substances in the air can be purified at room temperature.
[0028]
In the oxide that is in an oxygen deficient state by this reduction treatment, part of the oxygen forming the oxide is released from the oxide by the reduction treatment, and the oxide is activated in an oxygen deficient state. Since the noble metal is supported on the activated oxide, durability can be maintained in a normal temperature range, and purification of harmful substances can be performed. The term “normal temperature” as used herein refers to a temperature range in which the introduced oxygen deficient state described later is not lost by the normal temperature purification catalyst of the present invention. That is, it is a temperature range of 50 ° C. or less, more preferably 10 to 40 ° C.
[0029]
  As an oxide,At least one selected from oxides of zirconium, iron and ceriumCan be used.
[0030]
As the noble metal component supported on the oxide, at least one of Pt, Pd, Rh, Ir, Au, and Ru is used.
[0031]
The oxygen deficient state introduced by the reduction treatment refers to a state where the molar amount of oxygen bonded as an oxide is less than a predetermined value. For example, in the case of cerium oxide, this corresponds to the fact that oxygen atoms are less than 2 mole times the amount of cerium atoms. That is, the reduction treatment as described below causes the oxide to undergo a reducing action, and a part of oxygen is desorbed to form an oxide in a state where oxygen is lost. The formation of this oxygen deficient state enhances the activation of the oxide itself, weakens the adsorption state of the harmful substance to the noble metal, and uses the oxygen activated through the oxygen deficient part to Since the oxidation reaction proceeds, it is considered that the harmful substances can be purified in the normal temperature range.
[0032]
In the reduction treatment referred to here, it is preferable to treat the above-mentioned oxide mixed with a noble metal in a reducing gas stream for about 1 hour in a temperature range of 100 ° C. to 800 ° C. That is, when the oxide comes into contact with the reducing gas at a high temperature, part of the oxide oxygen is combined with the reducing gas and removed. As a result, a part of the oxide becomes an oxygen deficient state, and an oxygen deficient oxide is formed. Examples of the reducing gas used in the reduction treatment include reducing gases such as hydrogen and carbon monoxide, hydrocarbons such as methane, and formaldehydes. The concentration of these reducing gases is 0.1% to 100% by volume, more preferably 1% to 100% by volume. Furthermore, the transition metal oxides and rare earth oxides described above can be brought into an oxygen deficient state by reduction treatment with a reducing agent such as hydrazine and aluminum borohydride. The shape of the sample used for the reduction process is not particularly limited.
[0033]
Among the room temperature purification catalysts of the present invention, there are those containing cerium oxide, zirconium oxide and noble metals as oxides. In this catalyst, at least part of the cerium oxide is present in an oxygen deficient state due to the reduction treatment, and thus shows activity in the normal temperature range. Carbon monoxide, nitrogen oxides, bad odors in air Organic substances such as amines, mercaptans, aldehydes, fatty acids, odorous substances, and aromatic hydrocarbons having odor can be purified by oxidative decomposition at room temperature.
[0034]
The purification reaction of odorous substances by this catalyst preferably has a purification rate of 50% or more at 25 ° C. 20 minutes after the start of the purification reaction. In this case, the initial concentration of the odorous substance is, for example, 100 ppb in the case of formaldehyde, and the space velocity is 600000 h.^-1It is.
[0035]
The carbon monoxide purification reaction is performed at 25 ° C. and a space velocity of 120,000 h.^-1Under these conditions, the purification rate after 30 minutes from the start of the purification reaction is preferably 40% or more. In this case, the initial concentration of carbon monoxide is 220 ppm.
[0036]
The air referred to in the present invention includes exhaust gas discharged from the atmosphere and an internal combustion engine, etc., and indicates the atmosphere in a residential space, the atmosphere in a vehicle interior, etc., and refers to the so-called general atmosphere of living space.
[0037]
When the oxygen-deficient oxide of the room temperature purification catalyst of the present invention is a mixture of cerium oxide and zirconium oxide, it is preferable that both exist in the form of a solid solution or a complex oxide. Since the cerium oxide and the zirconium oxide form a solid solution or a composite oxide, the oxygen deficiency state of the oxide can be easily formed, and the oxygen deficiency state formed by the reduction treatment can be stably maintained. It becomes possible to maintain the catalytic activity in the normal temperature range for a long time. Therefore, this room temperature purification catalyst can more effectively purify harmful substances in the air over a long period of time in the normal temperature range.
[0038]
The room temperature purification catalyst of the present invention includes a noble metal, oxygen-deficient cerium oxide and zirconium oxide, and a rare earth oxide such as yttrium, lanthanum, neodymium, and praseodymium as a third component, iron oxide, manganese oxide, cobalt oxide, 1 type chosen from transition metal oxides, such as chromium, nickel, and copper, may be included. By blending these third components, the oxygen deficiency state of cerium oxide and zirconium oxide is stably maintained, and the purification performance is maintained.
[0039]
When both cerium oxide and zirconium oxide are used, the molar ratio of Ce and Zr is 100: 1 to 1: 100, preferably 20: 1 to 1:10, more preferably 5: 1 to 1: 1. . By setting it as this range, said oxygen deficient state can be maintained stably. A larger amount of cerium oxide is preferable because an oxygen-deficient state is easily formed.
[0040]
The amount of the noble metal is 0.01 to 20% by weight, more preferably 0.6 to 3.0% by weight, based on the oxide of cerium and zirconium. If the amount of noble metal is less than 0.01% by weight, the activity of the catalyst cannot be obtained. Further, even if the amount exceeds 20% by weight, the purification efficiency is not improved for the addition, and a large amount of expensive noble metal is used, which is not preferable.
[0041]
The solid solution or composite oxide of cerium and zirconium is preferably formed by a coprecipitation method, but any method other than the coprecipitation method can be used as long as it is a method that can be synthesized at the above-described mixing ratio. The precipitate produced by the coprecipitation method can be converted into an oxide by firing or the like.
[0042]
The noble metal is supported on cerium oxide and zirconium oxide by impregnation method, evaporation to dryness method, supercritical fluid method or the like. Further, when formed by the coprecipitation method with the composite oxide, a noble metal may be coexisted and supported. After the noble metal is loaded, so-called reduction treatment can be performed using a reducing gas as described above to form an oxygen-deficient state of the oxide and impart catalytic activity.
[0043]
The noble metal supported on the room temperature purification catalyst preferably has a particle size of 5 nm or less, more preferably 1 nm or less, in order to maintain the activity of the catalyst.
[0044]
The catalyst component can be used by being supported on at least one carrier selected from titanium oxide, alumina, silica, zeolite, sepiolite, and activated carbon, which are generally known as catalyst carriers. The catalyst component can be used by being supported on the carrier selected above, shaped as a pellet, and held on a honeycomb-like substrate.
[0045]
The mechanism of this room temperature purification catalyst is not clear, but the cerium oxide and zirconium oxide are at least partially oxygen deficient by the reduction treatment, and the oxygen activated by the oxide is more reactive on the noble metal. And the oxidation reaction by noble metals is promoted, and the presence of oxygen deficiency weakens the adsorption state of odors and harmful substances to noble metals. Allow the purification reaction to proceed. It is estimated that the cerium oxide and zirconium oxide purify the purified oxide by promoting desorption from the catalytic active point. For this reason, it is presumed that the adsorption poisoning of the noble metal to the catalytic active point is suppressed, the catalytic activity in the normal temperature range is maintained, and the purification performance is improved.
[0046]
The reduction treatment is the same as in the case of the above oxide, and it is preferable to treat the compounded and molded catalyst in a reducing gas stream at a temperature of 100 ° C. to 800 ° C. If the treatment temperature is less than 100 ° C., the reduction does not proceed and a desired oxygen deficient state cannot be formed. On the other hand, when the treatment temperature exceeds 800 ° C., the specific surface area of the oxide is reduced, and the catalytic activity is lowered.
[0047]
Examples of the reducing gas include hydrocarbons such as hydrogen, carbon monoxide, and methane, and reducing gases such as formaldehyde. These reducing gas concentrations are preferably 0.1% by volume to 100% by volume. However, the reduction gas can be reduced by other chemicals and is not particularly limited.
[0048]
For example, a cerium oxide and a zirconium oxide that have undergone a reduction treatment at 500 ° C. have a total specific surface area of 50 m.²/ G or more is preferable. Furthermore, in the case of the condition of 800 ° C., the total of the specific surface areas of both is 15 m.²/ G or more is preferable.
[0049]
The room temperature purification catalyst of the present invention containing cerium oxide and a noble metal, wherein the cerium oxide is present in an oxygen deficient state at least partly by reduction treatment, the noble metal and the cerium oxide partly oxygen deficient state, In particular, it has an excellent effect on the purification of harmful substances at room temperature.
[0050]
The room temperature purification catalyst containing cerium oxide and noble metal has an oxygen composition ratio of 1.5 ≦ n <2, more preferably 1.5 ≦ n ≦ 1.8 in the cerium oxide CeOn in the reduction treatment. When present in a deficient state, it exhibits an excellent effect particularly in purifying formaldehyde in the air. It is difficult to produce a state where the n value is less than 1.5 under normal reduction and elemental analysis conditions. In order to form oxygen vacancies, it is necessary that the n value is less than 2. When oxygen vacancies of 1.8 or less are formed, more activity as a catalyst can be obtained. Note that the oxygen deficiency state of the oxide can be measured by, for example, X-ray diffraction.
[0051]
The oxygen deficiency in the surface layer of the cerium oxide particles is preferably 1.5 ≦ n ≦ 1.8 in order to enhance the activity of the catalyst. Here, the surface layer refers to a layer of about 100 nm from the surface.
[0052]
The amount of the noble metal supported on the cerium oxide is 0.1 to 20 g, more preferably 0.5 to 5 g with respect to 150 g of the cerium oxide so that harmful substances are purified in the room temperature range. Can do. If it is less than 0.1 g, the activity of the catalyst cannot be obtained, which is not preferable. Further, even if the precious metal is used in excess of 20 g, the purification efficiency is not improved for the addition, and a large amount of expensive precious metal is used, which is not preferable.
[0053]
As the noble metal component, at least one of Pt, Pd, Rh, Au, and Ru is used. The noble metal is supported on the cerium oxide by an impregnation method, evaporation to dryness method, supercritical fluid method or the like. After the noble metal is supported, catalytic activity can be obtained by reducing the cerium oxide with hydrogen or the like as in the above catalyst.
[0054]
The reduction treatment is the same as in the case of the above oxide, and it is preferable to treat the compounded and molded catalyst in a reducing gas stream at a temperature of 100 ° C. to 800 ° C. Examples of the reducing gas include hydrocarbons such as hydrogen, carbon monoxide, and methane, and reducing gases such as formaldehyde. These reducing gas concentrations are preferably 0.1% by volume to 100% by volume. However, reduction with other chemicals than the above reducing gas is also possible and is not particularly limited.
[0055]
This catalyst can also be used by being supported on at least one carrier selected from clay minerals typified by alumina, silica, zeolite, titanium oxide, cordierite, activated carbon, and sepiolite, in the same manner as the catalyst described above. Further, the catalyst component may be coated on the substrate in a powder state, or may be supported on the carrier selected above and formed as a pellet. Furthermore, it can be used by being held on a honeycomb-like substrate or the like.
[0056]
By configuring the cerium oxide and the noble metal as catalyst components, it is possible to purify volatile organic compounds called VOC and odorous substances including formaldehyde in the room temperature range.
[0057]
This room temperature purification catalyst of the present invention can effectively remove ethylene which is generated from fruits and vegetables such as vegetables and fruits and is said to reduce the freshness of fresh food products.
[0058]
In the case of a catalyst used for purification of ethylene, the catalyst composition may contain one or more selected from yttrium oxide, lanthanum oxide, iron oxide, manganese oxide, and copper oxide as the third component. When placing fresh food products in an environment for maintaining freshness (for example, cases, container boxes, etc.), the air introduced into the environment and after contact with fresh food products is passed through the catalyst. Thus, freshness can be maintained.
[0059]
In this case, the catalyst may be applied in the form of powder, monolith, filter, or the inner wall of the container. Moreover, you may pack said catalyst with an air-permeable material. By using this ethylene purification catalyst, ethylene can be decomposed even at room temperature or lower, so that the physiological action of fruits and vegetables can be suppressed and ripening aging can be suppressed over time, so that freshness can be easily maintained. Furthermore, since this room temperature purification catalyst is an oxidation reaction, it generates carbon dioxide and consumes oxygen as the ethylene is decomposed. Therefore, the low oxygen concentration, high carbon dioxide concentration, and low ethylene concentration, which are desirable gas compositions for maintaining the freshness of fruits and vegetables. An atmosphere can be formed.
[0060]
Although the mechanism of the purification catalyst of the present invention is not necessarily clear, the presence of oxygen-deficient cerium oxide or the like activates the noble metal, weakens the adsorption state of the substance to be purified on the noble metal, and activates via oxygen deficiency. It is presumed that the oxygenated oxygen reacts with the ethylene to be purified and is desorbed and purified as an oxide. For this reason, it is presumed that the adsorption poisoning to the noble metal is suppressed, the catalytic activity in the room temperature region is maintained, and the purification performance is improved.
[0061]
The room temperature purification catalyst of the present invention can be used at room temperature. However, it can be used in a temperature range as long as the catalyst does not lose the oxygen deficient state. That is, even if it is used not only at room temperature but also in a temperature range of about 50 ° C. to 100 ° C., the effect can be sufficiently exhibited. However, when the room temperature purification catalyst of the present invention is exposed to 200 ° C. or higher for a long time, oxygen deficiency disappears and high activity is lost. For this reason, the operating temperature is 200 ° C. or lower, more preferably 100 ° C. or lower.
[0062]
The room temperature purification catalyst of the present invention may contain activated carbon. It is preferable that at least a part of the oxide contains cerium oxide in an oxygen deficient state. By adopting this configuration, in addition to the adsorption ability of activated carbon, the purification performance can be maintained for a long time together with the purification reaction at room temperature due to the interaction between the oxide and the noble metal.
[0063]
The reduction treatment temperature of the room temperature purification catalyst is preferably in the range of 200 ° C. to 600 ° C. in order to prevent the activated carbon from burning out. The catalyst that has been subjected to the reduction treatment under these conditions retains the activated carbon and the cerium oxide is in an oxygen deficient state, so that high removal performance can be imparted to environmentally hazardous substances such as formaldehyde, acetaldehyde, and carbon monoxide. .
[0064]
The normal temperature purification catalyst of the present invention is less deteriorated in purification capacity than the conventionally known activated carbon. For example, the CO purification rate by a one-pass test under the flow of CO (250 ppm) + oxygen (20%) + nitrogen (balance) is 20% for activated carbon after 1 hour from the start of the reaction, whereas the present invention 70% of this catalyst can be maintained.
[0065]
The purification of acetaldehyde will be described as an example. Acetaldehyde is adsorbed on activated carbon and then Pt / CeO present in the vicinity.₂The acetaldehyde can be purified by catalytic reaction before the activated carbon reaches saturation adsorption. As a result, a decrease in adsorption removal performance can be suppressed.
[0066]
Further, the substance to be purified is adsorbed on the activated carbon, for example, Pt / CeO having catalytic action.₂It is possible to reduce the amount of the reactant that comes into contact per unit time, suppress poisoning by the adsorbate, and maintain the catalyst purification performance.
[0067]
This catalyst is preferably used by being supported on a carrier or formed into a pellet or honeycomb.
[0068]
【Example】
Hereinafter, the present invention will be described specifically by way of examples.
[0069]
(Example 1)
2 g of Pt was supported on 150 g of cerium oxide powder, and this powder was formed into pellets having a diameter of 1 to 2 mm. Then 5% H₂N including₂A normal temperature purification catalyst was prepared by reduction treatment at 500 ° C. for 1 hour in a gas.
[0070]
(Example 2)
Prepare a mixed aqueous solution in which cerium (III) nitrate and zirconium nitrate were dissolved in a molar ratio of Ce / Zr = 5/1, and ammonia water was added dropwise while stirring the aqueous solution to neutralize the aqueous solution. I let you. Subsequently, an aqueous solution containing a hydrogen peroxide solution having a molar number of ½ of the cerium ion contained in the aqueous solution and 10% of alkylbenzenesulfonic acid by weight of the resulting oxide was added dropwise and mixed and stirred.
[0071]
The obtained slurry was dried and the coexisting ammonium nitrate was removed by evaporation and decomposition to remove the oxide solid solution powder CeO.₂・ ZrO₂Got.
[0072]
This oxide solid solution powder CeO₂・ ZrO₂150 g of Pt was supported at a rate of 2 g. This Pt-supported oxide solid solution powder was formed into pellets having a diameter of 1 to 2 mm. Thereafter, under the same conditions as in Example 1, reduction treatment was performed in a reducing atmosphere with hydrogen to prepare a room temperature purification catalyst.
[0073]
(Example 3)
A room temperature purification catalyst was prepared in the same manner as in Example 2 except that the molar ratio of Ce / Zr was set to 1/1 in Example 2.
[0074]
(Example 4)
Aluminum nitrate, zirconium nitrate, and cerium nitrate were mixed and dissolved in a molar ratio of 2.4: 0.25: 0.25, a 6 liter aqueous solution (A solution), ammonia water, and ammonium carbonate in a molar ratio of 8.3. A solution (liquid B) prepared by mixing and dissolving at 0.08 was prepared, and both liquids A and B were mixed and stirred. The oxide precursor precipitated from the mixed solution was washed, dried, and fired at 650 ° C. for 1 hour. A composite oxide in which alumina, ceria and zirconia were uniformly dispersed was obtained. Thereafter, reduction treatment was performed under the same conditions as in Example 2 to prepare a room temperature purification catalyst.
[0075]
(Comparative Example 1)
The catalyst of Comparative Example 1 is a catalyst prepared without performing reduction treatment in the catalyst preparation step of Example 2.
[0076]
(Comparative Example 2)
2 g of Pt was supported on 150 g of silicon oxide powder, and this powder was formed into pellets having a diameter of 1 to 2 mm. Thereafter, the catalyst was formed by reduction treatment in a reducing atmosphere with hydrogen under the same conditions as in Example 1.
[0077]
(Comparative Example 3)
Pt / CeO by coprecipitation using cerium nitrate, chloroplatinic acid and solid NaOH₂A powder was prepared. The supported amount of Pt is 2g / 150gCeO₂It is. The produced precipitate was filtered, washed, and calcined at 500 ° C. This catalyst was not reduced.
[0078]
(Evaluation of catalyst)
Each catalyst produced above was evaluated for CO purification performance under the following conditions.
[0079]
The measurement of the CO purification rate is CO: 220 ppm, O₂: 20%, N₂: Flow rate is 5L / min and space velocity is 120,000h.^-1The test was performed at room temperature. The CO purification rate was determined by measuring the residual CO concentration after 30 minutes from the start of the reaction. The results are shown in Table 1.
[0080]
[Table 1]

[0081]
For the catalyst of Example 3, the space velocity was reduced to 24000 h.^-1When evaluated under the conditions, the CO purification rate was 100%.
[0082]
The constituent catalysts of the above-described examples are obtained by converting CO into CO at room temperature (room temperature).₂Shows that it can be purified.
[0083]
In particular, since the oxygen deficiency state is formed in the oxide such as cerium oxide by performing the reduction treatment as shown in Examples 1 to 4, the purification reaction by the noble metal can be enhanced at room temperature.
[0084]
To maintain cerium oxide in an oxygen deficient state, CeO₂・ ZrO₂It is preferable that it exists as a composite oxide or a solid solution (Examples 2 to 4). Further, as shown in Example 2, CeO₂It can be seen that the purification efficiency is higher when the blending molar amount of is large (compared with Example 3).
[0085]
The catalyst of Comparative Example 1 has the same composition as Example 2, but has not been subjected to reduction treatment. Therefore, since the oxide does not form an oxygen deficient state, it does not have a purification action at room temperature. Since the catalyst of Comparative Example 2 is an oxide of silicon that is not an oxide specified in the present invention, the CO purification rate is low even when reduction treatment is performed. The catalyst of Comparative Example 3 has the same catalyst composition as that of Example 1, but has a low CO purification rate at room temperature because no reduction treatment is performed. Therefore, the oxide specified in the present invention that can form an oxygen deficient state by reduction treatment is effective as a room temperature purification catalyst.
[0086]
(Example 5)
5% H₂N including₂The purification performance of acetaldehyde was evaluated using the same catalyst sample as that of Example 2 reduced in gas at 500 ° C. for 1 hour.
[0087]
Catalyst sample amount 0.1g
Evaluation gas is acetaldehyde (O₂20% / N₂Balance) 5L
Initial concentration of acetaldehyde: 36 ppm, 72 ppm, 270 ppm,
The evaluation method is that an odor analysis odor bag (Omi Odo Air Service Co., Ltd.) containing a catalyst sample and an evaluation gas is allowed to stand at room temperature, 1 hour, 2 hours, 3 hours, 24 hours and 96 hours. The residual acetaldehyde concentration in the bag afterwards was quantified, and the amount of acetaldehyde removed was calculated from the difference from the acetaldehyde concentration in the blank bag without the catalyst sample.
[0088]
(Comparative Example 4)
The catalyst produced in Example 2 that was not subjected to the reduction treatment was used as the catalyst sample of Comparative Example 4, and the same evaluation as in Example 5 was performed.
[0089]
(Comparative Example 5)
Comparative Example 5 was evaluated under the same conditions as in Example 5 using activated carbon powder as the catalyst.
[0090]
The results are shown in the graphs of FIG. 1 (initial concentration 36 ppm), FIG. 2 (initial concentration 72 ppm), and FIG. 3 (initial concentration 270 ppm).
[0091]
The amount of acetaldehyde removed from the catalyst sample of Comparative Example 4 (without reduction treatment) is low in purification rate at any concentration compared to the case of using the activated carbon of Comparative Example 5. The acetaldehyde removal amount of the catalyst of Example 5 of the present invention is higher than that of the activated carbon of Comparative Example 5. Therefore, it is shown that the catalyst of Example 5 has the ability to purify acetaldehyde at room temperature.
[0092]
(Example 6)
Using 0.1 g of the catalyst sample of this example used in Example 5, the purification performance of formaldehyde was examined.
[0093]
Evaluation gas is formaldehyde (O₂20% / N₂Balance) 5L
The evaluation method is that the odor analysis odor bag (Omi Odo Air Service) containing the catalyst sample and evaluation gas is allowed to stand at room temperature, and the residual formaldehyde concentration in the bag after 1 hour, 3 hours, and 24 hours. Measured with a detector tube for formaldehyde (manufactured by GL Sciences Inc.), the change with time of the formaldehyde concentration in the bag was determined.
[0094]
(Comparative Example 6)
Evaluation was performed in the same manner as in Example 6 using the activated carbon used in Comparative Example 5. The results are shown in FIG.
[0095]
As shown in FIG. 4, it can be seen that the formaldehyde purification performance of the catalyst of Example 6 is higher than that of the activated carbon of Comparative Example 6. Therefore, the catalyst of Example 6 shows that formaldehyde can also be purified at room temperature.
[0096]
(Example 7)
Purifying performance of methyl mercaptan was examined using 0.1 g of the catalyst used in Example 5.
[0097]
Evaluation gas is methyl mercaptan (O₂20% / N₂Balance) 5L
The odor analysis odor bag (Omi Odo Air Service) containing the sample and evaluation gas was allowed to stand at room temperature, and the residual methyl mercaptan concentration in the bag after 1 hour, 3 hours, and 24 hours was measured using FPD. Measured with a gas chromatograph (manufactured by Shimadzu: GC-15A), the change with time in the methyl mercaptan concentration in the bag was determined.
[0098]
(Comparative Example 7)
The purification performance was evaluated in the same manner as in Example 7 except that the activated carbon used in Comparative Example 5 was used. The results are shown in FIG.
[0099]
As shown in FIG. 5, it can be seen that the catalyst of this Example 7 has higher methyl mercaptan purification performance than the activated carbon of Comparative Example 7. Therefore, the catalyst of Example 7 shows that odorous substances such as methyl mercaptan can be purified at room temperature.
[0100]
(Example 8)
Trimethylamine purification performance was examined using 0.1 g of the catalyst used in Example 5.
[0101]
Evaluation gas is trimethylamine (O₂20% / N₂Balance) 5L
The odor analysis odor bag (Omi Odo Air Service) containing the catalyst sample and evaluation gas was allowed to stand at room temperature, and the residual trimethylamine concentration in the bag after 1 hour, 3 hours, and 24 hours was calculated as FTD. Measured with a gas chromatograph (manufactured by Shimadzu: GC-14A), the change with time in the trimethylamine concentration was determined.
[0102]
(Comparative Example 8)
Evaluation was performed in the same manner as in Example 8 except that the activated carbon used in Comparative Example 5 was used instead of the purification catalyst. The results are shown in FIG.
[0103]
As shown in FIG. 6, it can be seen that the catalyst of Example 8 has a higher trimethylamine purification performance than the activated carbon of Comparative Example 8. Therefore, the catalyst of Example 8 shows that odorous substances such as trimethylamine can be purified at room temperature.
[0104]
Example 9
A cerium oxide powder was impregnated with a predetermined amount of an aqueous solution of a Pt salt (“Platinum P Salt” manufactured by Tanaka Kikinzoku Co., Ltd.), evaporated to dryness, and calcined in the atmosphere at 500 ° C. for 2 hours to carry Pt. . At this time, the amount of Pt supported in the cerium oxide powder is 1 g with respect to 150 g of the cerium oxide powder. Then, the catalyst of Example 9 was obtained by treating at 500 ° C. for 1 hour in nitrogen gas containing 5% hydrogen gas. The Ce and O ratio in the catalyst powder at this time was 1: 1.9 from X-ray diffraction and elemental analysis.
[0105]
(Example 10)
A catalyst powder of Example 10 was prepared in the same manner as Example 9 except that the Ce and O ratio was adjusted to 1: 1.8.
[0106]
(Example 11)
A catalyst powder of Example 11 was prepared in the same manner as Example 9 except that the Ce and O ratio was adjusted to 1: 1.7.
[0107]
Example 12
A catalyst powder of Example 12 was prepared in the same manner as in Example 9, except that the Ce and O ratio was adjusted to 1: 1.65.
[0108]
(Example 13)
A catalyst powder of Example 13 was prepared in the same manner as in Example 9, except that the Ce and O ratio was adjusted to 1: 1.6.
[0109]
(Example 14)
A catalyst powder of Example 14 was prepared in the same manner as in Example 9, except that the Ce and O ratio was adjusted to 1: 1.55.
[0110]
(Example 15)
A catalyst powder of Example 15 was prepared in the same manner as Example 9 except that the Ce and O ratio was adjusted to 1: 1.5.
[0111]
(Example 16)
Except that the amount of Pt supported was adjusted to 0.1 g with respect to 150 g of cerium oxide and the ratio of Ce and O was adjusted to 1: 1.8, the same as in Example 9. A catalyst powder of Example 16 was prepared.
[0112]
(Example 17)
A catalyst powder of Example 17 was prepared in the same manner as Example 16 except that the amount of Pt supported was 0.5 g with respect to 150 g of cerium oxide.
[0113]
(Example 18)
A catalyst powder of Example 18 was prepared in the same manner as in Example 16 except that the amount of Pt supported was 5 g with respect to 150 g of cerium oxide.
[0114]
(Example 19)
A catalyst powder of Example 19 was prepared in the same manner as in Example 16, except that the amount of Pt supported was 15 g with respect to 150 g of cerium oxide.
[0115]
(Example 20)
A catalyst powder of Example 20 was prepared in the same manner as in Example 16, except that the amount of Pt supported was 17 g with respect to 150 g of cerium oxide.
[0116]
(Example 21)
A catalyst powder of Example 21 was prepared in the same manner as in Example 16, except that the amount of Pt supported was 0.01 g with respect to 150 g of cerium oxide.
[0117]
(Example 22)
A catalyst powder of Example 22 was prepared in the same manner as in Example 16 except that Pd was prepared to be 1 g with respect to 150 g of cerium oxide instead of Pt.
[0118]
(Example 23)
A catalyst powder of Example 23 was prepared in the same manner as in Example 16, except that Rh was adjusted to 1 g with respect to 150 g of cerium oxide instead of Pt.
[0119]
(Example 24)
A catalyst powder of Example 24 was prepared in the same manner as Example 16 except that Au was adjusted to 1 g with respect to 150 g of cerium oxide instead of Pt.
[0120]
(Example 25)
A catalyst powder of Example 25 was prepared in the same manner as in Example 16, except that Ru was adjusted to 1 g with respect to 150 g of cerium oxide instead of Pt.
[0121]
(Example 26)
A catalyst powder of Example 26 was prepared in the same manner as in Example 16 except that Pt was adjusted to 1 g with respect to 150 g of cerium oxide and Pd was adjusted to 1 g with respect to 150 g of cerium oxide.
[0122]
(Comparative Example 9)
A catalyst powder of Comparative Example 9 was produced in the same manner as in Example 9 except that the oxide was prepared so that the ratio of Ce to O was 1: 2.0, that is, no reduction treatment was performed.
[0123]
(Comparative Example 10)
A catalyst powder of Comparative Example 10 was prepared using activated carbon (BFG-3 manufactured by Cataler Co., Ltd.) instead of Pt-supported cerium oxide powder.
[0124]
(Evaluation of catalyst)
Odor bag for analysis of odor using formaldehyde: 100 ppb, oxygen: 20%, nitrogen: balance gas as evaluation gas, and 0.5 g of each sample and evaluation gas (Omi Auto Air Service) The evaluation gas was circulated at a circulation rate of 10 liters / minute using a circulation pump at room temperature. Space velocity is 600,000h^-1Met. In the above measurement, a filter was placed in front of the gas pump so that the sample did not scatter from the odor bag. The purification rate of formaldehyde in the evaluation gas after 20 minutes of circulation was measured. The formaldehyde concentration was analyzed using a formaldehyde analyzer by an enzyme-chemiluminescence method, and the formaldehyde purification rate was determined by the following formula.
[0125]
Formaldehyde purification rate (%) = {(formaldehyde concentration in odor bag before reaction−formaldehyde concentration after 20 minutes of sample coexistence) / formaldehyde concentration in odor bag before reaction} × 100
The results are shown in Table 2.
[0126]
[Table 2]

[0127]
As shown in Table 2, each catalyst of Examples 9 to 15 has a formaldehyde purification rate higher than that of Comparative Example 9 that carries the same amount of noble metal and does not undergo reduction treatment, and is higher than the activated carbon of Comparative Example 10. This indicates that it is effective for purifying formaldehyde at room temperature. In particular, the catalyst of Example 13 exhibits a high purification rate of 88%, and the purification rate is higher when the degree of oxygen deficiency is higher than when the amount of noble metal is large. Therefore, it is suggested that the larger the oxygen deficiency state of the oxide, the more effective it is to improve the purification performance of the catalyst.
[0128]
  Examples 16 to 21 show that there is an optimum amount of Pt supported, and the amount of Pt used by being supported on cerium oxide is 0.01 to 20 g, more preferably 0.8 g, based on 150 g of cerium oxide. By containing 5 to 5 g, harmful substances can be purified at room temperature. Examples 22 to 26 show that other supported noble metals other than Pt are also effective.
(Example 27)
  An aqueous solution of dinitrodiammine platinum was added to the iron oxide powder so that the amount of platinum was 2 g in 200 g of iron oxide, and the solution was evaporated and dried by stirring and heating to obtain an iron oxide powder carrying a platinum salt. This powder was calcined in the atmosphere at 500 ° C. for 3 hours to obtain a platinum-supported iron oxide catalyst. Before measuring the oxidation activity of carbon monoxide at room temperature, the catalyst was subjected to an activation treatment for introducing oxygen deficiency into the catalyst by performing a reduction treatment at 300 ° C. for 15 minutes in a nitrogen stream containing 1% CO. .
(Example 28)
  A platinum-supported manganese oxide catalyst prepared in the same manner as in Example 27 was prepared except that manganese oxide powder was used instead of iron oxide powder.Example 28 is a reference example.
(Comparative Example 11)
  A platinum-supported silica catalyst was prepared in the same manner as in Example 27 except that silica was used in place of the iron oxide powder.
(Comparative Example 12)
  A platinum-supported zirconia catalyst was prepared in the same manner as in Example 27 except that zirconia was used in place of the iron oxide powder.
(Comparative Example 13)
  A platinum-supported alumina catalyst was prepared in the same manner as in Example 27 except that alumina was used in place of the iron oxide powder.
[0129]
The purification performance of each of the catalysts prepared above (Examples 27 to 28, Comparative Examples 11 to 13) was evaluated under the conditions of a gas flow rate of 5 g / min, a CO concentration of 250 ppm, and an oxygen concentration of 20%. The results are shown in Table 3.
[0130]
[Table 3]

[0131]
The graph of the relationship between the oxygen deficiency rate and the CO conversion rate of the iron oxide catalyst of Example 27 and the manganese oxide catalyst of Example 28 is shown in FIGS. In Example 27, the catalyst activity was measured under the conditions of 20 g of catalyst and a gas flow rate of 5 L / min, and in Example 28, the catalyst activity was measured under the conditions of a catalyst amount of 5 g and a gas flow rate of 10 L / min. In addition, CO of evaluation gas composition₂250ppm, O₂The 20% condition was common. In both cases, a peak of the CO conversion rate is observed at an oxygen deficiency rate of around 10%, indicating that CO can be purified if oxygen deficiency exists. 7 that the oxygen deficiency rate is preferably in the range of 2 to 11% in the case of the iron oxide catalyst, and the oxygen deficiency rate is preferably in the range of 5 to 18% in the case of the manganese oxide catalyst. Here, the oxygen deficiency rate of iron oxide and the oxygen deficiency rate of manganese oxide are Fe₂O_Three, MnO₂The ratio of the missing oxygen amount to the oxygen amount contained in is shown.
[0132]
As shown in Table 3, the catalyst containing the oxide of the present invention has the ability to purify CO at room temperature.
[0133]
(Example 29)
A slurry was prepared by mixing cerium oxide with an aqueous zirconium nitrate solution so that the molar ratio was Ce / Zr = 10/1. The slurry was dried at 130 ° C. for 3 hours and then calcined at 500 ° C. in the air for 3 hours. CeO obtained in this way₂・ ZrO₂Pt was supported at a rate of 2 g on 150 g of the powder. This powder was formed into pellets having a diameter of 1 to 2 mm. The catalyst sample of Example 29 was then subjected to reduction treatment at 500 ° C. for 1 hour in nitrogen gas containing 5% hydrogen.
[0134]
The purification performance for 1 g of this catalyst sample against ethylene gas was evaluated.
[0135]
The evaluation gas is 5 liters of oxygen 20% nitrogen balance containing ethylene (initial concentration 200 ppm).
[0136]
In the evaluation method, an odor analysis smell bag (Omi Auto Air Service Co., Ltd.) containing a sample and an evaluation gas is allowed to stand in a thermostatic bath at 10 ° C., and the ethylene concentration after 1, 2, 3 and 24 hours is expressed by FID. Measurement with a gas chromatograph (manufactured by Shimadzu Corporation: HCM-1B) was carried out to determine the change over time in the ethylene concentration. The results are shown in FIG.
[0137]
When the catalyst of the present invention is not used as a comparative example (Comparative Example 14), when activated carbon powder (BFG-3 manufactured by Cataler) is used in the same proportion as Example 29 instead of the catalyst of Example 29 (Comparative Example) 15) was similarly evaluated.
[0138]
As shown in FIG. 9, it can be seen that Example 29 has a higher ethylene removal capability than the activated carbon of Comparative Example 15.
(Example 30)
Broccoli, which is prone to quality degradation due to yellowing and flowering in the middle of distribution, was selected as a fresh food product, and the maintenance of freshness was examined from the degree of yellowing of flowering. The degree of yellowing is a visual sensory evaluation. Yellowing degree = 0 indicates no yellowing change, yellowing degree = 1 indicates little yellowing change, yellowing degree = 2 indicates significant yellowing change, and yellowing degree = 3. All were performed based on the standard of yellowing.
[0139]
A commercially available broccoli bunch (variety: Karatsu) was placed in a 1 liter sampling bag for odor analysis (manufactured by GL Sciences Inc., material: fluororesin, film thickness 50 μm), and further used in Example 29. 1 g of the catalyst per 1 kg of broccoli was enclosed and sealed, and 1 liter was introduced from a previously prepared air bomb so that the catalyst during sampling back was not scattered.
[0140]
Next, this sampling bag was put into a 10 degreeC thermostat, and the yellowing degree of the broccoli during this sampling was evaluated periodically over time.
[0141]
When the catalyst of the present invention is not used as a comparative example (Comparative Example 16), when activated carbon powder (BFG-3 manufactured by Cataler) is used in the same proportion as in Example 30 instead of the catalyst of Example 30 (Comparative Example) 17) was similarly evaluated.
[0142]
The results are shown in Table 4.
[0143]
[Table 4]

[0144]
As shown in Table 4, it can be seen that in Example 30, the progress of the yellowing degree of the florets is slower than in Comparative Examples 16 and 17, and it has an effect on maintaining the freshness of broccoli.
(Example 31)
Apple was selected as a fresh food, and the freshness retention effect by the catalyst of the present invention was evaluated from the discoloration of the skin, the hardness of the fruit, and the taste index.
[0145]
Two commercially available apples (variety: Fuji) were placed in a 1 liter sampling bag for odor analysis (aluminum, film thickness 130 μm, manufactured by GL Sciences Inc.), and the catalyst of Example 30 was added per kg of apple. 0.5 g was enclosed.
[0146]
Next, the sampling bag was placed in a thermostatic bath at 15 ° C., and periodically evaluated from the discoloration of apple skin, the hardness of the fruit, and the taste index during the sampling.
[0147]
When the catalyst of Example 31 is not used as a comparative example (Comparative Example 18), when activated carbon powder (BFG-3 manufactured by Cataler) is used in the same proportion as Example 31 instead of the catalyst of Example 31 (Comparison) Example 19) was similarly evaluated.
[0148]
Fruit hardness; 1: Hard 2: Slightly softened 3: Softened
Taste index; 5-level evaluation of always bad: 0, bad: 0.5, slightly bad: 1, good: 1.5, very good: 2.
[0149]
[Table 5]

[0150]
[Table 6]

[0151]
[Table 7]

[0152]
As shown in Tables 5 to 7, in Comparative Examples 18 and 19, the decrease in hardness and taste index is significant, whereas in Example 31, the state close to the state immediately after the purchase of the apple is maintained. It can be seen that there is an effect in maintaining the freshness of the rice.
[0153]
Therefore, it is shown that the room temperature purification catalyst of Example 31 has the ability to remove ethylene at room temperature.
[0154]
(Example 32)
To deionized water in an amount equivalent to the water absorption of 75 g of activated carbon adjusted to a particle size of 0.5 to 2 mm, cerium nitrate hexahydrate (CeO₂75g equivalent) and Pt (NO₂)₂(NH_Three)₂After dissolving (corresponding to 0.5 g in terms of Pt), this aqueous solution was absorbed into 75 g of activated carbon. The obtained activated carbon of the catalyst precursor was dried in air at 110 ° C. for 6 hours. Next, the temperature was raised to 500 ° C. at a rate of temperature rise of 5 ° C./min or less in a nitrogen gas atmosphere containing 5% hydrogen, and then kept for 1 hour. Then, it cooled to room temperature and obtained the catalyst of a present Example.
[0155]
(Example 33)
To deionized water in an amount equivalent to the water absorption of 75 g of activated carbon adjusted to a particle size of 0.5 to 2 mm, cerium nitrate hexahydrate (CeO₂The equivalent aqueous solution was dissolved in 75 g of activated carbon. The precursor activated carbon thus obtained was dried at 110 ° C. for 6 hours in the air, then heated to 500 ° C. at a temperature increase rate of 5 ° C./min or less in a nitrogen gas atmosphere containing 5% hydrogen, and then 1 Held for hours. Next, Pt (NO₂)₂(NH_Three)₂Pt was supported on the activated carbon using an aqueous solution containing (corresponding to 0.5 g in terms of Pt), and the temperature was raised to 500 ° C. at a rate of temperature increase of 5 ° C./min or less in a nitrogen gas atmosphere containing 5% hydrogen. Thereafter, it was kept for 1 hour. After cooling to room temperature, Pt / CeO₂/ Activated carbon catalyst was obtained.
[0156]
(Example 34)
Cerium nitrate hexahydrate (CeO₂60 g in terms of conversion) and 75 g of powdered activated carbon were added to 500 g of deionized water and stirred well, and then an aqueous ammonia solution having a molar amount of 1.2 times the neutralization equivalent was added to obtain activated carbon as a catalyst precursor. . The precursor activated carbon was heated to 500 ° C. at a temperature rising rate of 5 ° C./min or less in a nitrogen atmosphere and heated as it was for 3 hours. The product obtained was added to Pt (NO₂)₂(NH_Three)₂Pt is supported on the generated activated carbon using an aqueous solution containing (equivalent to 0.5 g in terms of Pt), and the temperature is raised to 500 ° C. at a rate of temperature increase of 5 ° C./min or less in a nitrogen gas atmosphere containing 5% hydrogen. And then kept for 1 hour. The Pt-supported activated carbon obtained after cooling to room temperature was converted to ceria sol (CeO₂15 g) as an amount, mixed with 68 g of deionized water, kneaded, and granulated to a particle size of 0.5 to 2 mm. The obtained pellets were dried in air at 110 ° C. for 6 hours, further heated at 500 ° C. for 1 hour in a nitrogen gas atmosphere containing 5% hydrogen, and then cooled to room temperature to prepare a catalyst.
[0157]
(Example 35)
Cerium nitrate hexahydrate (CeO₂Equivalent to 60 g), zirconium oxynitrate dihydrate (ZrO₂9 g in terms of conversion) and 75 g of powdered activated carbon are added to 500 g of deionized water, and after stirring well, a catalyst precursor activated carbon is obtained by adding an aqueous ammonia solution having a molar amount of 1.2 times the neutralization equivalent. Prepared a catalyst in the same manner as in Example 34.
[0158]
(Example 36)
Cerium nitrate hexahydrate (CeO₂Equivalent to 60 g), 75 g of powdered activated carbon, and Pt (NO₂)₂(NH_Three)₂(Equivalent to 0.5 g in terms of Pt) was added to 500 g of deionized water and stirred well, and then an aqueous ammonia solution having a molar equivalent of 1.2 times the neutralization equivalent was added to obtain a catalyst precursor. The catalyst precursor was heated to 500 ° C. at a rate of temperature increase of 5 ° C./min or less in a nitrogen gas atmosphere containing 5% hydrogen and heated as it was for 3 hours. The obtained powder and ceria sol (CeO₂After mixing and kneading with 15 g) 68 g of deionized water, it was granulated to a particle size of 0.5 to 2 mm. The obtained pellets were dried in air at 110 ° C. for 6 hours, further heated at 500 ° C. for 1 hour in a nitrogen gas atmosphere containing 5% hydrogen, and cooled to room temperature to prepare a catalyst.
[0159]
(Example 37)
Pt (0.5 g) / CeO supported on powdered activated carbon and Pt (O.5 g) and heated in air at 500 ° C. for 1 hour₂(60 g), ceria sol (CeO as binder)₂And 15 g) and deionized water (68 g) were mixed and kneaded, and then dried in air at 110 ° C. for 6 hours. Subsequently, it heated at 500 degreeC under nitrogen gas atmosphere containing 5% hydrogen for 1 hour, and cooled to room temperature, and the catalyst was prepared.
[0160]
(Comparative Example 20)
Pt and CeO₂Activated carbon to which none of these was added was used as a catalyst.
[0161]
(Comparative Example 21)
Pt (NO in deionized water equivalent to the amount of water absorbed by 75 g of activated carbon)₂)₂(NH_Three)₂A Pt / activated carbon catalyst prepared in the same manner as in Example 32 was prepared except that (equivalent to 0.25 g in terms of Pt) was dissolved.
[0162]
(Comparative Example 22)
Pt (0.5 g) / activated carbon (75 g) and CeO prepared by supporting 0.5 g of Pt on 75 g of activated carbon in the same manner as in Comparative Example 21 using powdered activated carbon₂Powder (60 g), ceria sol (CeO₂15 g) and deionized water (68 g) were mixed and kneaded, and granulated to a particle size of 0.5 to 2 mm. Furthermore, in a nitrogen gas atmosphere containing 5% hydrogen, the catalyst was obtained by heating to 500 ° C. for 1 hour and cooling to room temperature. In this comparative example, most of Pt is supported on activated carbon.
(Evaluation)
The acetaldehyde purification rate of each catalyst prepared above is shown in FIG. 10, and the CO purification rate is shown in FIG.
[0163]
Odorous substance removal test (Acetaldehyde is used as a representative example of odorous substances)
1 pass test
Catalyst amount: 2g
Gas used: Acetaldehyde (20ppm) + Oxygen (20%) Remaining nitrogen gas
Flow rate: 5 liters / min, reaction temperature: room temperature
Evaluation method: The removal rate of acetaldehyde 1 hour after the start of gas flow was evaluated as the purification rate of acetaldehyde.
[0164]
CO purification test
1 pass test
Catalyst amount: 2g
Gas used: CO (250 ppm) + oxygen (20%) remaining nitrogen gas, flow rate: 10 liters / min
Reaction temperature: room temperature
Evaluation method: The CO removal rate 1 hour after the start of gas flow was evaluated as the CO purification rate.
[0165]
In Comparative Example 20 using only activated carbon, the purification rate is as low as about 30%, and even in Comparative Example 21 in which Pt is supported on activated carbon, the purification rate is 50% or less. Pt-supported activated carbon and CeO₂The activity of Comparative Example 22 blended with was almost the same as that of Comparative Example 21.
[0166]
On the other hand, reduced Pt-supported CeO₂In Example 37 blended with activated carbon, the purification performance was about 80%, and Pt was CeO.₂The need to be supported on top is suggested. In other examples, Pt is CeO.₂Since it is carried on the surface, it is considered that high purification performance is exhibited with respect to the comparative example. Activated carbon with Pt and CeO₂As a method of loading the CeO, as shown in Example 32 and Example 33, CeO₂Subsequently, Pt may be sequentially supported, or both may be simultaneously supported. The same applies to the embodiment 34 and the embodiment 36.
[0167]
Further, from a comparison between Example 35 and Example 34, as a carrier component other than activated carbon, CeO₂And ZrO₂In the case of containing CeO₂It can be seen that the purification performance is higher than that of the case of only the case.
[0168]
【The invention's effect】
The room temperature purification catalyst of the present invention removes and purifies environmentally hazardous substances at room temperature by the action of both the oxide and the noble metal because the oxide having an oxygen deficient state at least partially carries the noble metal by reduction treatment. be able to. In particular, a small amount of harmful substances present in the air can be purified. Particularly when cerium oxide and noble metal are contained, formaldehyde in the air can be efficiently removed at room temperature. Therefore, this room temperature purification catalyst can reduce the load on the human body in the living environment and can contribute to the improvement of the living environment.
[0169]
Moreover, in the normal temperature purification catalyst of the present invention, ethylene can be decomposed and removed in the normal temperature range, so that the physiological action of the fruits and vegetables can be suppressed, the progress of ripening aging can be suppressed over time, and the freshness of the fruits and vegetables can be easily maintained.
[0170]
Furthermore, because this room temperature purification catalyst is an oxidation reaction, it consumes oxygen along with ethylene decomposition to produce carbon dioxide, which is a desirable gas composition for maintaining the freshness of fruits and vegetables. Low oxygen concentration, high carbon dioxide concentration, low ethylene concentration The atmosphere can be formed.
[0171]
Catalysts that carry cerium oxide and noble metals in an oxygen deficient state on activated carbon utilize the adsorption capacity of activated carbon, so the amount of harmful substances that come into contact with noble metals and cerium oxide per unit time can be reduced, resulting in catalytic activity. The portion can suppress poisoning due to the adsorbate, and can maintain the purification performance for a long time.
[Brief description of the drawings]
FIG. 1 is a graph comparing the purification rates of Examples 5, Comparative Examples 4 and 5 at acetaldehyde concentration of 36 ppm after 1, 2, 3 hours, 24 hours and 96 hours.
FIG. 2 is a graph comparing the purification rates of Examples 5, Comparative Examples 4 and 5 with acetaldehyde concentration of 72 ppm after 1, 2, 3 hours, 24 hours and 96 hours.
FIG. 3 is a graph comparing the purification rates of Examples 5, Comparative Examples 4 and 5 with acetaldehyde concentration of 270 ppm after 1, 2, 3 hours, 24 hours and 96 hours.
FIG. 4 is a graph comparing formaldehyde removal rates of the catalyst of Example 6 and activated carbon.
FIG. 5 is a graph comparing methyl mercaptan removal rates of the catalyst of Example 7 and activated carbon.
FIG. 6 is a graph comparing trimethylamine removal rates of the catalyst of Example 8 and activated carbon.
7 is a graph showing the relationship between the degree of oxygen deficiency of iron oxide and the CO conversion rate in Example 27. FIG.
8 is a graph showing the relationship between the degree of oxygen deficiency of manganese oxide and the CO conversion rate in Example 28. FIG.
FIG. 9 is a graph obtained by examining the change over time in ethylene concentration when the normal temperature purification catalyst of Example 29, the normal temperature purification catalyst were not used, and when activated carbon was used.
FIG. 10 is a bar graph showing the purification rate of acetaldehyde in Examples 32-37 and Comparative Examples 20-22.
FIG. 11 is a bar graph showing the purification rate of carbon monoxide of Examples 32-37 and Comparative Examples 20-22.

Claims (27)

A room temperature purification catalyst comprising a noble metal supported on an oxide into which oxygen deficiency has been introduced by a reduction treatment , wherein the oxide is at least one selected from oxides of zirconium, iron and cerium Room temperature purification catalyst. The cerium oxide and the zirconium oxide are included as the oxide, and the cerium oxide and the zirconium oxide are mainly present in a state where at least a part of the cerium oxide is in an oxygen deficient state by reduction treatment. Room temperature purification catalyst. The normal temperature purification catalyst according to claim 2 , which has a function of purifying environmental load substances in the air at normal temperature. 4. The room temperature purification catalyst according to claim 3 , wherein the environmental load substance is an odor substance. 4. The room temperature purification catalyst according to claim 3 , wherein the environmental load substance is carbon monoxide. 4. The room temperature purification catalyst according to claim 3 , wherein the environmental load substance is nitrogen oxide. 4. The room temperature purification catalyst according to claim 3 , wherein the environmental load substance is ethylene. The room temperature purification catalyst according to any one of claims 2 to 7 , wherein the cerium oxide and the zirconium oxide form a solid solution or a composite oxide. The room temperature purification catalyst according to any one of claims 2 to 7 , which is supported on at least one carrier selected from titanium oxide, alumina, silica, zeolite, cordierite, sepiolite, and activated carbon. The room temperature purification catalyst according to claim 1, comprising cerium oxide as the oxide. 11. The room temperature purification catalyst according to claim 10 , wherein the cerium oxide is present in a state in which at least a part thereof is oxygen deficient by reduction treatment and has a function of purifying odorous substances and / or carbon monoxide in air at room temperature. 12. The room temperature purification catalyst according to claim 11 , wherein the cerium oxide is in a state of oxygen deficiency of 1.5 ≦ n <2 in CeOn after the reduction treatment. The room temperature purification catalyst according to claim 12 , wherein the cerium oxide is in a state of oxygen deficiency of 1.5 ≦ n ≦ 1.8 in CeOn after the reduction treatment. The room temperature purification catalyst according to claim 12 , which purifies at least one environmental load substance such as formaldehyde, trimethylamine, methyl mercaptan, and acetaldehyde in the air at room temperature. The room temperature purification catalyst according to any one of claims 10 to 14 , wherein at least one selected from silica, alumina, zeolite, titanium oxide, cordierite, sepiolite, and activated carbon is used as the carrier. 5. The room temperature purification catalyst according to claim 4 , wherein the purification reaction of the odorous substance is a purification reaction temperature of 25 ° C. and a purification rate after 20 minutes has elapsed after the start of the purification reaction under the condition of a space velocity of 600,000 h ^−1. . Purification reaction of the carbon monoxide, at a purification reaction temperature of 25 ° C., according to claim 5, wherein the purification rate of the conversion reaction starting 30 minutes after the conditions of a space velocity 120000H ^-1 is 40% or more Room temperature purification catalyst. 3. The room temperature purification catalyst according to claim 2 , wherein the oxide composed of cerium oxide and zirconium oxide has a specific surface area of 50 m ² / g or more after reduction treatment at 500 ° C. for 1 hour. 19. The room temperature purification catalyst according to claim 18 , wherein the oxide composed of cerium oxide and zirconium oxide has a specific surface area of 15 m ² / g or more after reduction treatment at 800 ° C. for 1 hour. The normal temperature purification catalyst according to claim 1, wherein the noble metal has a particle size of 5 nm or less. The room temperature purification catalyst according to claim 20 , wherein the noble metal has a particle size of 1 nm or less. The room temperature purification catalyst according to claim 1, wherein the reduction treatment has a treatment temperature of 100C to 800C. The room temperature purification catalyst according to claim 22 , wherein the reduction treatment has a treatment temperature of 200C to 600C. The room temperature purification catalyst according to claim 12 , wherein an amount of oxygen deficiency in a surface layer of the cerium oxide particles is 1.5 ≦ n ≦ 1.8. Furthermore, the normal temperature purification catalyst of Claim 1 which contains activated carbon and contains the cerium oxide in which at least one part exists in the state of oxygen deficiency as said oxide. 26. The room temperature purification catalyst according to claim 25 , wherein at least part of the noble metal is supported on the cerium oxide. The room temperature purification catalyst according to any one of claims 1 to 2 , comprising at least one of carbon monoxide, nitrogen oxides, ethylene, aldehydes, amines, mercaptans, fatty acids, odorous substances, and aromatic hydrocarbons. A method of using a room temperature purification catalyst, wherein the environmental load substance is purified at room temperature by contacting with the air it contains.

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