JP2004283770A - Catalyst-deposited carrier and manufacturing method therefor - Google Patents
Catalyst-deposited carrier and manufacturing method therefor Download PDFInfo
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- JP2004283770A JP2004283770A JP2003080883A JP2003080883A JP2004283770A JP 2004283770 A JP2004283770 A JP 2004283770A JP 2003080883 A JP2003080883 A JP 2003080883A JP 2003080883 A JP2003080883 A JP 2003080883A JP 2004283770 A JP2004283770 A JP 2004283770A
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Abstract
Description
【０００１】
【技術分野】
本発明は，微細な細孔径を有する多孔質基体の細孔内に，金属等の触媒微粒子を担持した触媒担持体及びその製造方法に関する。
【０００２】
【従来技術】
従来より，金属等の触媒微粒子を基材に担持した触媒担持体は，触媒等の用途に用いられている。
このような触媒担持体は，例えば多孔質の基材に触媒微粒子を担持させて製造することができる。基材に触媒微粒子を担持する方法としては，例えば液相担持法及び気相担持法等がある。
【０００３】
上記液相担持法においては，水及びアルコール等の液相溶媒に，触媒微粒子の前駆体を溶解し，蒸発乾固により基材に担持した後，必要に応じて還元処理等を行うことにより触媒微粒子を担持した触媒担持体を得る（特許文献１参照）。
上記気相担持法においては，触媒微粒子の前駆体を揮発させて基材に担持した後，必要に応じて還元処理等を行うことにより触媒微粒子を担持した触媒担持体を得る（特許文献２参照）。
【０００４】
一方，近年，反応物の吸着等といった触媒機能以外の機能を同時に付与させるため，上記基材として微細な細孔構造を有する多孔体を用いた触媒担持体の有用性が注目されている。
【０００５】
【特許文献１】
特開平１１−２４６９０１号公報
【特許文献２】
特開２００２−１０２６９４号公報
【０００６】
【解決しようとする課題】
しかしながら，上記液相担持法においては，高粘性，低拡散性，濡れ性，凝縮性，及び強固な溶媒和構造により，特に，上記のような微細な細孔構造を有する多孔体の細孔の内部まで，上記触媒微粒子の前駆体を導入することが困難であった。そのため，多孔体の表面にのみ触媒粒子の前駆体が担持され，最終的な触媒担持体は，触媒としての特性を充分に発揮できないという問題があった。
【０００７】
また，ＣＶＤ等の気相担持法においては，触媒微粒子の前駆体が，これを担持させる際の温度及び雰囲気条件において安定で，かつ揮発性のものに限定されてしまう。さらに，気相中の触媒微粒子の密度が低くなるため効率が悪い。
また，臨界温度以下では細孔内で凝集してしまうという問題があった。そのため，得られた触媒担持体は，触媒としての特性を充分に発揮することができなかった。
【０００８】
本発明は，かかる従来の問題点に鑑みてなされたもので，微細な細孔径を有する多孔質基体の細孔の内部まで充分に触媒微粒子を有し，触媒特性の優れた触媒担持体及びその製造方法に関する。
【０００９】
【課題の解決手段】
第１の発明は，平均細孔径が３．４ｎｍ以下でかつ標準偏差が０．２ｎｍ以下の細孔を有する多孔質基体と，上記細孔内に配置された触媒微粒子とよりなる触媒担持体であって，
該触媒担持体は，超臨界流体に上記触媒微粒子の前駆体を溶解させて，これを上記多孔質基体に接触させて，上記超臨界流体を上記細孔に進入させ，上記前駆体を上記細孔内に配置することによって得られることを特徴とする触媒担持体にある（請求項１）。
【００１０】
上記第１の発明において最も注目すべき点は，超臨界流体を用いて上記触媒微粒子の前駆体を上記多孔質基体の細孔内に配置させて得られた触媒担持体であって，平均細孔径が３．４ｎｍ以下でかつ標準偏差が０．２ｎｍ以下という微細な細孔を有する多孔質基体の細孔内に触媒微粒子が配置されていることである。
そのため，上記第１の発明の触媒担持体は，同じ平均細孔径の多孔質基体を有するもの同士を比較した場合に，例えば上記液相担持法及び気相担持法にて得られる触媒担持体よりも優れた触媒活性を示すことができる。
【００１１】
また，上記多孔質基体は，平均細孔径が３．４ｎｍ以下でかつ標準偏差が０．２ｎｍ以下という微細な平均細孔径を有している。そのため，表面積が充分に大きく，充分な量の触媒微粒子を担持することができる。
上記第１の発明の触媒担持体は，例えば後述する第２の発明の製造方法により製造することができる。
【００１２】
第２の発明は，平均細孔径が３．４ｎｍ以下でかつ標準偏差が０．２ｎｍ以下の細孔を有する多孔質基体の細孔内に触媒微粒子を担持した触媒担持体の製造方法において，
超臨界流体に触媒微粒子の前駆体を溶解させて，これを上記多孔質基体に接触させて，上記超臨界流体を細孔に進入させ，上記前駆体を上記細孔内に配置する流体進入工程を有することを特徴とする触媒担持体の製造方法にある（請求項５）。
【００１３】
上記第２の発明において，最も注目すべき点は超臨界流体に触媒微粒子の前駆体を溶解させて，これを平均細孔径３．４ｎｍ以下でかつ標準偏差が０．２ｎｍ以下という微細な細孔に進入させ，上記前駆体を上記細孔内に配置することにある。
上記前駆体は，上記多孔質基体の細孔内に導入され，多孔質基体に接すると，そのままの状態または触媒微粒子となって細孔内に担持される。
上記前駆体のまま担持された前駆体は，後述するごとく，必要に応じて焼成，光照射，酸化及び還元等の後処理を行うことにより触媒微粒子とすることができる。
【００１４】
上記超臨界流体とは，通常物質の臨界点以上の温度及び圧力下におかれた流体を示す。本発明における超臨界流体とは，少なくとも臨界点の温度以上である流体であり，圧力は上記の定義の範囲である必要はない。この状態の流体は，液体と同等の溶解能力と，気体に近い拡散性，粘性を有する物質である。そのため，上記触媒微粒子の前駆体を溶解した超臨界流体は，平均細孔径３．４ｎｍ以下という微細な細孔の内部に，容易且つ迅速に多量の上記前駆体を進入させることができる。
【００１５】
また，一般に，上記触媒微粒子は，その粒子径が小さくなると，比表面積，即ち１ｇ当たりの表面積が増大し，触媒反応等の種々の表面反応が活性になる。しかしその反面，粒径が小さすぎても，触媒としての特性を充分に発現できなくなることが知られている。
【００１６】
上記第２の発明においては，平均細孔径が３．４ｎｍ以下でかつ標準偏差が０．２ｎｍ以下の細孔を有する多孔質基体を用いている。
そのため，上記細孔内において，例えば金属粒子等の触媒微粒子が互いに結合して粒成長をするシンタリングが起こったとしても，その粒径は３．４ｎｍ以上にはならない。それ故，上記触媒微粒子は，最適な粒子径を形成することができる。また，上記触媒微粒子は均一な大きさで担持され，その粒子径は標準偏差の少ないものとなる。
したがって，上記触媒担持体は，触媒特性に優れたものとなる。
【００１７】
このように，上記第２の発明によれば，微細な細孔径を有する多孔質基体の細孔の内部まで充分に触媒微粒子を有し，触媒特性の優れた触媒担持体の製造方法を提供することができる。
【００１８】
【発明の実施の形態】
上記第２の発明における上記流体進入工程においては，上記前駆体を上記細孔内に配置する。上記前駆体は，上記多孔質基体の細孔内に導入され，多孔質基体に接すると，上記のように，上記前駆体のままの状態または触媒微粒子となって細孔内に担持される。前駆体のままで上記多孔質基体の細孔内に担持された場合には，次のような処理を行う。
【００１９】
即ち，上記流体進入工程後に，上記多孔質基体の細孔内に上記前駆体が残存する場合には，上記流体進入工程後に，上記前駆体を上記細孔内に配置した上記多孔質基体に，焼成，光照射，酸化及び還元等から選ばれる１種以上の後処理を施すことができる（請求項７）。
この場合には，上記多孔質基体に残存する上記前駆体を上記触媒微粒子にすることができる。
【００２０】
次に，上記第１の発明（請求項１）及び第２の発明（請求項５）において，上記超臨界流体としては，例えばメタン，エタン，プロパン，ブタン，エチレン，プロピレン等の炭化水素，メタノール，エタノール，プロパノール，ｉｓｏ−プロパノール，ブタノール，ｉｓｏ−ブタノール，ｓｅｃ−ブタノール，ｔｅｒｔ−ブタノール等のアルコール，アセトン，メチルエチルケトン等のケトン類，二酸化炭素，水，アンモニア，塩素，クロロホルム，フレオン類等を用いることができる。
【００２１】
また，上記触媒微粒子の前駆体の上記超臨界流体への溶解度を調整するために，メタノール，エタノール，プロパノール等のアルコール，アセトン，エチルメチルケトン等のケトン類，ベンゼン，トルエン，キシレン等の芳香族炭化水素等をエントレーナーとして用いることができる。
【００２２】
また，上記触媒微粒子の前駆体としては，金属又は／及び半金属のアルコキシド，金属又は／及び半金属のアセチルアセトナート，金属又は／及び半金属の有機酸塩，金属又は／及び半金属の硝酸塩，金属又は／及び半金属のオキシ塩化物，金属又は／及び半金属の塩化物等の単独，又は２種以上よりなる混合物を用いることができる。
【００２３】
次に，上記多孔質基材としては，例えば活性炭等の多孔質炭素，多孔質アルミや多孔質タンタル等の多孔質金属，多孔質シリカ，多孔質アルミナ，多孔質アルミナシリカ，多孔質酸化ルテニウム，多孔質酸化バナジウム，多孔質酸化インジウム，多孔質酸化錫，多孔質酸化ニッケル等の金属又は／及び半金属の酸化物からなる多孔体，或いはポリオレフィン，ポリウレタン等の高分子発泡体等を用いることができる。また，多孔質シリカとしては，後述するメソ多孔体の１種であるメソポーラスシリカが好ましい。メソポーラスシリカは微細で均一な細孔直径を有するため，上記触媒微粒子を充分に結合することができる。
【００２４】
また，上記多孔質基材としては，メソ多孔体が好ましい。
上記メソ多孔体は微細な細孔を有し，このような細孔内においては，細孔壁からのファンデルワールス力が重なって３次元的に作用することによって強いポテンシャル場が形成される。そして，このポテンシャル場によって触媒反応は更に向上する。そのため，この場合には，上記触媒担持体は，より一層触媒反応に優れたものとなる。
さらに上記多孔質基材は，その細孔が１ｎｍ以上の間隔で配列した規則的な構造を有することが好ましい。この場合には，上記多孔質基材は，上記触媒微粒子を充分且つ規則的に結合することができる。
【００２５】
上記メソ多孔体としては，トンネル状の細孔構造（２次元ヘキサゴナル構造）を有するＦＳＭ（或いはＦＳＭ−１６），ＭＣＭ−４１及びＳＢＡ−１５，３次元チャネル構造（キュービックＩａ−３ｄ構造）を有するＭＣＭ−４８，３次元構造で且つキュービックＰｍ−３ｎ構造のＳＢＡ−１，ＳＢＡ−１６及びＫＩＴ−１，並びにラメラ構造のＭＣＭ−５０等がある。
【００２６】
これらのうち，例えばＦＳＭは，図６〜図８に示すごとく，以下のようにして作製することができる。
層状シリケート２３及び親水基と疎水基とを有する界面活性剤４５を混合し，イオン交換を行い層状シリケート２３のシートを折り曲げさせることにより，界面活性剤４５のミセル４が複数の細孔２５を形成し，細孔２５内にミセル４を有する多孔質基体２を得る。この多孔質基体２から界面活性剤４５を除去することにより，図８に示すごとく，最終的な多孔質基体２を得ることができる。この場合には，上記界面活性剤４５が有する有機鎖等の疎水基の分子量（分子長）を変えることにより，上記多孔質基体２の細孔径を制御することができる。
【００２７】
また，上記多孔質基体は，多数の細孔を有する基材であり，その平均細孔径は，３．４ｎｍ以下である。
上記平均細孔径が３．４ｎｍを越える場合には，超臨界流体を用いて触媒担持体を作製する利点が失われ，上記触媒担持体の触媒活性は，例えば従来の液相担持法によって得られる触媒担持体と同程度のものとなる。
上記多孔質基体の細孔径は，窒素吸着データから細孔分布計算を行うことにより測定することができる。
【００２８】
また，上記多孔質基体の細孔径は，２．１ｎｍを越えることが好ましい。
上記多孔質基体の細孔径が２．１ｎｍ以下の場合には，上記触媒担持体の触媒活性が充分に得られないおそれがある。
【００２９】
次に，上記細孔の細孔径の標準偏差は，０．２ｎｍ以下である。
上記細孔の細孔径の標準偏差が０．２ｎｍを越える場合には，細孔内に担持される触媒微粒子の粒径のバラツキが大きくなり，触媒活性の劣る触媒微粒子が細孔内に作製されるおそれがある。
上記細孔径の標準偏差は，細孔径と同様に，窒素吸着データから細孔分布計算を行うことにより測定することができる。
【００３０】
また，上記触媒微粒子の平均粒径は，２．９ｎｍ未満であることが好ましい（請求項２及び請求項７）
上記触媒微粒子の平均粒径が２．９ｎｍ以上の場合には，上記触媒担持体の触媒としての特性が低下するおそれがある。
また，上記触媒微粒子の平均粒径は，１．７ｎｍを越えることが好ましい。
上記触媒微粒子の平均粒径が１．７ｎｍ以下の場合には，上記触媒担持体の触媒としての特性が低下するおそれがある。
上記触媒微粒子の平均粒径は，透過型電子顕微鏡（ＴＥＭ）写真より算出することができる。
【００３１】
また，上記触媒微粒子の粒径の標準偏差は，０．２ｎｍ以下であることが好ましい（請求項３及び請求項８）。
上記粒径の標準偏差が０．２ｎｍを越える場合には，細孔内に担持される触媒微粒子に，触媒活性の劣る触媒微粒子が多く含まれるおそれがある。
【００３２】
また，上記触媒微粒子は，Ｐｔ，Ｐｄ，Ｒｈ，Ｉｒ，Ｒｕ，Ａｕ等の貴金属元素，及びＹ，Ｌａ，Ｃｅ，Ｐｒ，Ｎｄ，Ｅｕ，Ｇｄ，Ｔｂ，Ｄｙ，Ｓｉ，Ｈｏ，Ｅｒ，Ｔｍ，Ｙｂ，Ｌｕ，Ｃａ，Ｍｇ，Ａｌ，Ｋ，Ｔｉ，Ｃｒ，Ｍｎ，Ｆｅ，Ｃｏ，Ｎｉ，Ｃｕ，Ｇａ，Ｒｂ，Ｓｒ，Ｚｒ，Ｎｂ，Ｍｏ，Ｉｎ，Ｓｎ，Ｃｓ，Ｂａ，Ｔａ，Ｗ等の卑金属元素から選ばれる一種以上の金属又は／及びその酸化物からなる粒子であることが好ましい（請求項４及び請求項９）。
【００３３】
この場合には，上記金属又は／及びその酸化物が有する触媒作用を生かすことができる。即ち，このような金属又は／及びその酸化物を担持した上記触媒担持体は，上記金属又は／及びその酸化物が有する優れた触媒作用を発揮することができる。上記金属又は／及びその酸化物が有する触媒作用としては，例えば酸化触媒作用，還元触媒作用，光触媒作用，添加触媒作用，合成触媒作用，分解触媒作用，縮合触媒作用，重合触媒作用，縮重合触媒作用，及び液化触媒作用等がある。
【００３４】
【実施例】
（実施例１）
次に，本発明の実施例につき，図１〜図５を用いて説明する。
図１及び図２に示すごとく，本例の触媒担持体１は，平均細孔径が３．４ｎｍ以下の細孔２５を有する多孔質基体２と，上記細孔２５内に配置された触媒微粒子３とよりなる。
【００３５】
本例の触媒担持体１の製造に当たっては，超臨界流体に触媒微粒子３の前駆体を溶解させて，これを多孔質基体２に接触させて，上記超臨界流体を細孔２５に進入させ，上記前駆体を上記細孔２５内に配置する流体進入工程を行う。
【００３６】
以下，本例の触媒担持体１の製造方法につき，図１〜図３を用いて，詳細に説明する。
まず，上記触媒微粒子３の前駆体としての白金アセチルアセトナート，及びエントレーナ（助溶剤）としてのアセトンを準備した。また，上記多孔質基体２として，平均細孔径１．６ｎｍ，細孔径の標準偏差０．０６ｎｍのシリカ多孔体（ＦＳＭ）を準備した。
【００３７】
多孔質基体２への触媒微粒子３の担持は，図３に示すごとく，多孔質基体２を配置して加熱するためのオートクレーブ７と超臨界流体供給部８とからなる担持装置を用いて行われる。
オートクレーブ７は内部を加熱する加熱機能を有すると共に，オートクレーブ７内の圧力を下げるための排気弁７１が配設されている。オートクレーブ７の内部の容量は１０００ｍＬである。
【００３８】
上記超臨界流体供給部８には，同図に示すごとく，超臨界流体の媒体としてのＣＯ２を貯蔵するボンベ８１，該ボンベ８１から送られるＣＯ２を冷却するための冷却ユニット８３，ボンベ８１からオートクレーブ内へＣＯ２を圧送するための加圧ポンプ８５，さらにオートクレーブ７内に送られるＣＯ２の圧力を調整するための圧力調整弁８７が設置されている。
【００３９】
ボンベ８１と送液ポンプ８５，及び送液ポンプ８５とオートクレーブ７とは，それぞれ配管９２，９３によって接続されている。また，冷却ユニット８３と加圧ポンプ８５との間，及び圧力調整弁８７とオートクレーブ７との間には，それぞれ弁部８４，８６が設けられている。
圧力調節弁８７と弁部８６との間には，配管９３を外部から加熱するためのプレヒータ部８９が設けられている。
【００４０】
次に，オートクレーブ７内の下部に，上記前駆体５ｇとエントレーナ４０ｍＬとの混合物７８を入れ，また上記多孔質基体８ｇを入れた試料バスケット７５をオートクレーブ７内の上部に設置し，１５０℃にて２時間加熱した。
このとき，弁部８４，８６を解放してボンベからＣＯ２をオートクレーブ内に導入した。そのときの圧力は，３０ＭＰａであった。またこのとき，オートクレーブ７内に導入されたＣＯ２は，超臨界状態となり，オートクレーブ７内の下部に配置された上記触媒微粒子の前駆体を分散させて溶解すると共に，オートクレーブ７の上部に配置された試料バスケット７５内の多孔質基体に，上記触媒微粒子を担持させて触媒担持体を得た。
【００４１】
続いて，多孔質基体に残存する触媒微粒子の前駆体を完全に触媒微粒子するため，管状炉を用いて還元処理を行った。還元処理は，Ｈ２及びＮ２をそれぞれ流速１００ｍｌ／ｍｉｎ及び９００ｍｌ／ｍｉｎで流通させる共に，４００℃で１時間保持することにより行った。
ここで得られた触媒担持体を試料Ｅ１とする。
【００４２】
図１及び図２に示すごとく，試料Ｅ１としての触媒担持体１は，多孔質基体２の細孔２５の内部に，充分かつ均一に触媒微粒子３が導入されていた。
【００４３】
続いて，上記試料Ｅ１について，担持された触媒微粒子の平均粒径を測定した。平均粒径は，透過型電子顕微鏡（ＴＥＭ）写真より触媒微粒子の粒径をランダムに測定し，その平均値をもって平均粒径とした。また，触媒微粒子の標準偏差も同様にして測定した。
その結果を表１に示す。
【００４４】
次に，試料Ｅ１の触媒としての特性を調べるために，以下のようにしてＣＯの浄化率から活性化エネルギーを算出した。
触媒担持体（試料Ｅ１）５ｍｇを石英管に入れ，この石英管に，石英管内を通過する１時間当たりの処理気体量を石英管内の触媒担持体の容量で除した値としての空間速度が７００００ｈ−１という条件で，ＣＯを１％，Ｏ２を０．５％含むＮ２を３５００ｍＬ／ｍｉｎで導入した。続いて，石英管の内部を５００℃まで１２Ｋ／ｍｉｎで昇温し，このときのＣＯの浄化率を測定し，活性化エネルギーを算出した。ＣＯの浄化率は，導入前後のＣＯ濃度から算出した。また，活性化エネルギーは，浄化率の温度依存性データのアレニウスプロットから算出した。
その結果を表１に示す。
【００４５】
また，本例では，平均細孔径が２．１ｎｍ（標準偏差０．０４ｎｍ）及び２．４ｎｍ（標準偏差０．０５ｎｍ）のＦＳＭを上記多孔質基材として用い，他は上記試料Ｅ１と同様にして触媒担持体を作製し，これらをそれぞれ試料Ｅ２及び試料Ｅ３とした。また，試料Ｅ２及び試料Ｅ３についても上記試料Ｅ１と同様に，触媒微粒子の平均粒径及び標準偏差，並びに活性化エネルギーを測定した。
その結果を表１に示す。
【００４６】
さらに，本例においては，本発明に係る触媒担持体の優れた特性を明らかにするため，比較用として，液相担持法により触媒担持体を作製した。
具体的には，まず，上記試料Ｅ１〜Ｅ３とそれぞれ同様の平均細孔径及び標準偏差を有する，３種類のＦＳＭを上記多孔質基材として準備した。
【００４７】
１０００ｍｌのオートクレーブに，白金アセチルアセトナート５ｇとアセトン１０００ｍｌをいれ，さらに多孔質基材８ｇを入れ，１５０℃にて２時間加熱した。
【００４８】
次に，上記試料Ｅ１と同様にして，還元処理を行い，細孔径の異なる３種類の触媒担持体を作製した。これらをそれぞれ試料Ｃ１〜試料Ｃ３とした。
なお，上記試料Ｅ１と試料Ｃ１，試料Ｅ２と試料Ｃ２，及び試料Ｅ３と試料Ｃ３とは，それぞれ互いに同じ平均細孔径のＦＳＭよりなっている。
【００４９】
続いて，上記試料Ｃ１〜試料Ｃ３についても，上記試料Ｅ１〜Ｅ３と同様に，触媒微粒子の平均粒径及び標準偏差，並びに活性化エネルギーを測定した。
その結果を表１に示す。
【００５０】
【表１】
表１から知られるごとく，試料Ｅ１〜試料Ｅ３は，それぞれ同じ平均細孔径の試料Ｃ１〜Ｃ３と比較すると，活性化エネルギーが低く，触媒としての特性が優れていた。特に，平均細孔径が２．４ｎｍ（標準偏差は０．０５ｎｍ）の多孔質基体を用いて得られた試料Ｅ３においては，多孔質基体に担持された触媒微粒子の平均粒径が２．３ｎｍ（標準偏差は０．０８ｎｍ）となっており，この試料Ｅ３は活性化エネルギーが２３．６ｋＪ／ｍｏｌという特に優れた触媒特性を示した。
【００５２】
一方，試料Ｃ１〜試料Ｃ３においては，図４及び図５に示すごとく，上記多孔質基体２の細孔２５の内部には，ほとんど触媒微粒子３が担持されておらず，触媒微粒子３は，多孔質基体２の側面に担持されていた。そして，触媒微粒子３としての白金粒子は，多孔質基体２の側面で互い結合して粒成長を起こしていた。
その結果，試料Ｃ１〜Ｃ３は，表２により知られるごとく，触媒微粒子の粒径及び標準偏差が非常に大きなものとなり，試料Ｅ１〜Ｅ３と同じ細孔径のもの同士でそれぞれ比較すると，試料Ｅ１〜Ｅ３よりも活性化エネルギーが高く，触媒として劣っていた。
【００５３】
（実施例２）
本例では，さらに細孔径の異なる多孔質基体を用いて上記触媒担持体を作製した例を示す。
まず，平均細孔径が３．５ｎｍ（標準偏差０．０６ｎｍ）及び４．６ｎｍ（標準偏差０．１０ｎｍ）のＦＳＭを上記多孔質基材として準備した。
次に，これらの多孔質基材を用いて，他は実施例１の試料Ｅ１〜試料Ｅ３と同様に超臨界流体を用いて触媒担持体を作製し，これらを試料Ｅａ４及び試料Ｅａ５とした。続いて，これらの試料Ｅａ４及び試料Ｅａ５について，実施例１の試料Ｅ１〜Ｅ３と同様に，触媒微粒子の平均粒径及び標準偏差，並びに活性化エネルギーを測定した。
その結果を表２に示す。
【００５４】
さらに，上記試料Ｅａ４及び試料Ｅａ５に用いたものと同様の多孔質基体を用いて，上記液相担持法により触媒担持体を作製し，これらをそれぞれ試料Ｃ４及び試料Ｃ５とした。続いて，これらの試料Ｃ４及び試料Ｃ５についても，実施例１と同様に，触媒微粒子の平均粒径及び標準偏差，並びに活性化エネルギーを測定した。液相担持法による触媒担持体の作製方法は，実施例１の上記試料Ｃ１〜Ｃ３と同様である。
なお，表２には，比較のため，実施例１の試料Ｅ１〜Ｅ３及び試料Ｃ１〜Ｃ３の結果を併せて示した。
【００５５】
【表２】
表２より知られるごとく，３．５ｎｍ以上の細孔径を有する多孔質基板を用いて得られた試料Ｅａ４及び試料Ｅａ５を，同じ細孔径を有する試料Ｃ４及び試料Ｃ５とそれぞれ比較すると，試料Ｅａ４と試料Ｃ４，及び試料Ｅａ５と試料Ｃ５とは，それぞれ互いに同程度の活性化エネルギーを示した。
また，試料Ｅ１〜Ｅ３，試料Ｅａ４及び試料Ｅａ５の結果から，本例の触媒担持体は，上記多孔質基体の平均細孔径が２．１ｎｍを越え，かつ３．５ｎｍ未満（３．４ｎｍ以下）のとき，また上記触媒微粒子の平均粒子径が１．７ｎｍを越え，かつ２．９ｎｍ未満のときに，活性化エネルギーが低く，優れた触媒活性を示すことがわかる。
【００５７】
これに対し，試料Ｅ１〜試料Ｅ３においては，同じ細孔径の多孔質基体を有する試料Ｃ１〜試料Ｃ３とそれぞれ比較しても，試料Ｅ１〜試料Ｅ３の方が触媒としての活性が優れていた。
【図面の簡単な説明】
【図１】実施例１にかかる，触媒担持体を斜め上方から見た様子を示す説明図。
【図２】図１のＡ−Ａ線断面矢視図。
【図３】実施例１にかかる，超臨界流体を用いて触媒微粒子を多孔質基体に担持させるための担持装置の概略図。
【図４】実施例１にかかる，多孔質基体の側面に触媒微粒子が担持された試料Ｃ１〜試料Ｃ３としての触媒担持体を示す説明図。
【図５】図４のＢ−Ｂ線断面矢視図。
【図６】層状シリケート及び界面活性剤のミセルを示す説明図。
【図７】界面活性剤のミセルにより，細孔が形成された多孔質基体を示す説明図。
【図８】多孔質基体を斜め上方から見た様子を示す説明図。
【符号の説明】
１．．．触媒担持体，
２．．．多孔質基体，
２５．．．細孔，
３．．．触媒微粒子，[0001]
【Technical field】
The present invention relates to a catalyst carrier in which fine particles of a catalyst such as a metal are supported in pores of a porous substrate having a fine pore diameter, and a method for producing the same.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a catalyst carrier in which a catalyst fine particle such as a metal is carried on a substrate has been used for applications such as a catalyst.
Such a catalyst carrier can be produced, for example, by supporting catalyst fine particles on a porous substrate. As a method for supporting the catalyst fine particles on the base material, for example, there are a liquid phase supporting method and a gas phase supporting method.
[0003]
In the above-mentioned liquid phase supporting method, the catalyst fine particles are dissolved in a liquid phase solvent such as water and alcohol, and the catalyst is carried out by evaporating to dryness and then carrying out a reduction treatment or the like as necessary. A catalyst carrier carrying fine particles is obtained (see Patent Document 1).
In the vapor-phase supporting method, after a catalyst fine particle precursor is volatilized and supported on a base material, a reduction treatment or the like is performed as necessary to obtain a catalyst supporting body supporting the catalyst fine particles (see Patent Document 2). ).
[0004]
On the other hand, in recent years, the usefulness of a catalyst carrier using a porous body having a fine pore structure as the base material has attracted attention in order to simultaneously impart functions other than the catalyst function such as adsorption of a reactant.
[0005]
[Patent Document 1]
JP-A-11-246901 [Patent Document 2]
JP-A-2002-102694
[Problem to be solved]
However, in the above-mentioned liquid phase supporting method, the high viscosity, low diffusivity, wettability, condensability, and strong solvation structure cause the pores of the porous body having the fine pore structure as described above to be particularly difficult. It was difficult to introduce the precursor of the catalyst particles into the inside. Therefore, there is a problem that the precursor of the catalyst particles is supported only on the surface of the porous body, and the final catalyst carrier cannot sufficiently exhibit the characteristics as a catalyst.
[0007]
Further, in a gas phase supporting method such as CVD, the precursor of the catalyst fine particles is limited to a volatile and stable one at a temperature and an atmosphere condition at the time of supporting the catalyst fine particles. Furthermore, the efficiency is poor because the density of the catalyst particles in the gas phase is low.
In addition, there is a problem that when the temperature is lower than the critical temperature, the particles aggregate in the pores. Therefore, the obtained catalyst carrier could not sufficiently exhibit the characteristics as a catalyst.
[0008]
The present invention has been made in view of such a conventional problem, and has a catalyst carrier having excellent catalyst characteristics, having sufficient catalyst fine particles to the inside of the pores of a porous substrate having a fine pore diameter, and a catalyst carrier having the same. It relates to a manufacturing method.
[0009]
[Means for solving the problem]
The first invention is a catalyst carrier comprising a porous substrate having pores having an average pore diameter of 3.4 nm or less and a standard deviation of 0.2 nm or less, and catalyst fine particles arranged in the pores. So,
The catalyst carrier dissolves a precursor of the catalyst fine particles in a supercritical fluid, and brings the precursor into contact with the porous substrate to allow the supercritical fluid to enter the pores, and to convert the precursor into the fine particles. The catalyst carrier is obtained by disposing the catalyst carrier in a hole (claim 1).
[0010]
The most remarkable point in the first invention is a catalyst carrier obtained by arranging the precursor of the catalyst fine particles in the pores of the porous substrate using a supercritical fluid. That is, the catalyst fine particles are arranged in pores of a porous substrate having fine pores having a pore diameter of 3.4 nm or less and a standard deviation of 0.2 nm or less.
Therefore, the catalyst carrier of the first aspect of the present invention is, for example, a catalyst carrier obtained by the above-described liquid-phase supporting method and gas-phase supporting method when compared with those having a porous substrate having the same average pore diameter. Can also show excellent catalytic activity.
[0011]
Further, the porous substrate has a fine average pore diameter of not more than 3.4 nm and a standard deviation of not more than 0.2 nm. Therefore, the surface area is sufficiently large, and a sufficient amount of catalyst fine particles can be supported.
The catalyst carrier of the first invention can be manufactured, for example, by a manufacturing method of a second invention described later.
[0012]
According to a second aspect of the present invention, there is provided a method for producing a catalyst carrier in which catalyst fine particles are supported in pores of a porous substrate having pores having an average pore diameter of 3.4 nm or less and a standard deviation of 0.2 nm or less,
A fluid entry step of dissolving a precursor of catalyst fine particles in a supercritical fluid, bringing the precursor into contact with the porous substrate, allowing the supercritical fluid to enter the pores, and disposing the precursor in the pores A method for producing a catalyst carrier, characterized by having the following (claim 5).
[0013]
In the above second invention, the most remarkable point is that a precursor of catalyst fine particles is dissolved in a supercritical fluid, and the precursor is finely divided into fine pores having an average pore diameter of 3.4 nm or less and a standard deviation of 0.2 nm or less. , And disposing the precursor in the pores.
The precursor is introduced into the pores of the porous substrate, and when it comes into contact with the porous substrate, it is supported as it is or as fine catalyst particles in the pores.
The precursor supported as described above can be converted into catalyst fine particles by performing post-treatments such as baking, light irradiation, oxidation and reduction, if necessary, as described later.
[0014]
The supercritical fluid is a fluid which is usually placed under a temperature and a pressure higher than a critical point of a substance. The supercritical fluid in the present invention is a fluid having at least a temperature at a critical point, and the pressure does not need to be in the range defined above. The fluid in this state is a substance having the same dissolving power as a liquid, and diffusivity and viscosity similar to a gas. Therefore, the supercritical fluid in which the precursor of the catalyst fine particles is dissolved can easily and quickly enter a large amount of the precursor into the fine pores having an average pore diameter of 3.4 nm or less.
[0015]
In general, when the particle size of the catalyst fine particles is reduced, the specific surface area, that is, the surface area per 1 g, increases, and various surface reactions such as a catalytic reaction become active. However, on the other hand, it is known that if the particle size is too small, the characteristics as a catalyst cannot be sufficiently exhibited.
[0016]
In the second invention, a porous substrate having pores having an average pore diameter of 3.4 nm or less and a standard deviation of 0.2 nm or less is used.
For this reason, even if sintering occurs in which fine particles of catalyst such as metal particles are bonded to each other and grow in the pores, the particle size does not exceed 3.4 nm. Therefore, the catalyst fine particles can form an optimum particle size. In addition, the catalyst fine particles are supported in a uniform size, and the particle diameter has a small standard deviation.
Therefore, the above-mentioned catalyst carrier has excellent catalytic properties.
[0017]
As described above, according to the second aspect of the present invention, there is provided a method for producing a catalyst carrier having excellent catalytic properties, having sufficient fine catalyst particles up to the inside of the pores of a porous substrate having a fine pore diameter. be able to.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
In the fluid entering step in the second invention, the precursor is disposed in the pore. The precursor is introduced into the pores of the porous substrate, and when it comes into contact with the porous substrate, as described above, the precursor remains as it is or as catalyst fine particles, and is supported in the pores. When the precursor is supported as it is in the pores of the porous substrate, the following treatment is performed.
[0019]
That is, if the precursor remains in the pores of the porous substrate after the fluid entry step, the precursor is placed in the pores after the fluid entry step. One or more post-treatments selected from calcination, light irradiation, oxidation, reduction and the like can be applied (claim 7).
In this case, the precursor remaining on the porous substrate can be used as the catalyst fine particles.
[0020]
Next, in the first invention (Claim 1) and the second invention (Claim 5), the supercritical fluid includes, for example, hydrocarbons such as methane, ethane, propane, butane, ethylene, and propylene; , Ethanol, propanol, iso-propanol, butanol, alcohols such as iso-butanol, sec-butanol, tert-butanol, ketones such as acetone and methyl ethyl ketone, carbon dioxide, water, ammonia, chlorine, chloroform, freons, etc. be able to.
[0021]
Further, in order to adjust the solubility of the precursor of the catalyst fine particles in the supercritical fluid, alcohols such as methanol, ethanol and propanol, ketones such as acetone and ethyl methyl ketone, and aromatics such as benzene, toluene and xylene are used. Hydrocarbons and the like can be used as the entrainer.
[0022]
Examples of the precursor of the catalyst fine particles include metal or metalloid alkoxide, metal metalloid metalloid acetylacetonate, metal acid salt metalloid organic acid salt, metal metalloid salt metalloid nitrate. , Metal or / and metalloid oxychloride, metal or / and / or metalloid chloride, or a mixture of two or more thereof.
[0023]
Next, examples of the porous substrate include porous carbon such as activated carbon, porous metal such as porous aluminum and porous tantalum, porous silica, porous alumina, porous alumina silica, porous ruthenium oxide, and the like. It is possible to use a porous body made of a metal or metalloid oxide such as porous vanadium oxide, porous indium oxide, porous tin oxide, and porous nickel oxide, or a polymer foam such as polyolefin or polyurethane. it can. Further, as the porous silica, mesoporous silica, which is one type of a mesoporous body described later, is preferable. Since mesoporous silica has a fine and uniform pore diameter, the catalyst fine particles can be sufficiently bonded.
[0024]
Further, as the porous substrate, a mesoporous body is preferable.
The mesoporous body has fine pores, and in such pores, a strong potential field is formed by the action of the van der Waals force from the pore walls overlapping and acting three-dimensionally. And the catalytic reaction is further improved by this potential field. Therefore, in this case, the catalyst carrier becomes more excellent in the catalytic reaction.
Further, the porous substrate preferably has a regular structure in which the pores are arranged at intervals of 1 nm or more. In this case, the porous substrate can sufficiently and regularly bind the catalyst fine particles.
[0025]
The mesoporous material has FSM (or FSM-16), MCM-41 and SBA-15 having a tunnel-like pore structure (two-dimensional hexagonal structure), three-dimensional channel structure (cubic Ia-3d structure). Examples include MCM-48, SBA-1, SBA-16 and KIT-1 having a three-dimensional structure and a cubic Pm-3n structure, and MCM-50 having a lamella structure.
[0026]
Among them, for example, the FSM can be manufactured as follows, as shown in FIGS.
The layered
[0027]
The porous substrate is a substrate having a large number of pores, and the average pore diameter is 3.4 nm or less.
When the average pore diameter exceeds 3.4 nm, the advantage of preparing a catalyst carrier using a supercritical fluid is lost, and the catalyst activity of the catalyst carrier can be obtained by, for example, a conventional liquid phase supporting method. It is about the same as the catalyst carrier.
The pore diameter of the porous substrate can be measured by calculating the pore distribution from the nitrogen adsorption data.
[0028]
Further, the pore diameter of the porous substrate preferably exceeds 2.1 nm.
When the pore diameter of the porous substrate is 2.1 nm or less, there is a possibility that the catalytic activity of the catalyst carrier may not be sufficiently obtained.
[0029]
Next, the standard deviation of the pore diameter of the above pores is 0.2 nm or less.
When the standard deviation of the pore diameter of the above pores exceeds 0.2 nm, the dispersion of the particle diameter of the catalyst fine particles carried in the pores becomes large, and the catalyst fine particles having poor catalytic activity are produced in the pores. May be present.
The standard deviation of the pore diameter can be measured by calculating the pore distribution from the nitrogen adsorption data in the same manner as the pore diameter.
[0030]
The average particle diameter of the catalyst fine particles is preferably less than 2.9 nm (
When the average particle diameter of the catalyst fine particles is 2.9 nm or more, the catalyst characteristics of the catalyst carrier may be deteriorated.
The average particle size of the catalyst fine particles preferably exceeds 1.7 nm.
If the average particle size of the catalyst fine particles is 1.7 nm or less, the catalyst characteristics of the catalyst carrier may be deteriorated.
The average particle diameter of the catalyst fine particles can be calculated from a transmission electron microscope (TEM) photograph.
[0031]
The standard deviation of the particle diameter of the catalyst fine particles is preferably 0.2 nm or less (
If the standard deviation of the particle diameter exceeds 0.2 nm, the catalyst fine particles supported in the pores may contain many catalyst fine particles having poor catalytic activity.
[0032]
The catalyst fine particles include noble metal elements such as Pt, Pd, Rh, Ir, Ru, and Au, and Y, La, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Si, Ho, Er, Tm, Yb, Lu, Ca, Mg, Al, K, Ti, Cr, Mn, Fe, Co, Ni, Cu, Ga, Rb, Sr, Zr, Nb, Mo, In, Sn, Cs, Ba, Ta, W, etc. It is preferable that the particles are made of one or more metals selected from the base metal elements described above and / or oxides thereof (
[0033]
In this case, the catalytic action of the metal and / or oxide thereof can be utilized. That is, the above-mentioned catalyst carrier supporting such a metal or / and its oxide can exert an excellent catalytic action of the above-mentioned metal or / and its oxide. Examples of the catalytic action of the metal and / or its oxide include oxidation catalyst action, reduction catalyst action, photocatalysis, addition catalyst action, synthesis catalyst action, decomposition catalyst action, condensation catalyst action, polymerization catalyst action, condensation polymerization catalyst. Action, and liquefaction catalytic action.
[0034]
【Example】
(Example 1)
Next, an embodiment of the present invention will be described with reference to FIGS.
As shown in FIGS. 1 and 2, the
[0035]
In the production of the
[0036]
Hereinafter, a method for manufacturing the
First, platinum acetylacetonate as a precursor of the catalyst
[0037]
As shown in FIG. 3, the loading of the catalyst
The
[0038]
As shown in the figure, the supercritical
[0039]
The
A
[0040]
Next, a
At this time, the
[0041]
Subsequently, a reduction treatment was performed using a tubular furnace in order to completely convert the precursor of the catalyst fine particles remaining on the porous substrate into fine catalyst particles. The reduction treatment was carried out by flowing H 2 and N 2 at flow rates of 100 ml / min and 900 ml / min, respectively, and maintaining the mixture at 400 ° C. for 1 hour.
The catalyst carrier obtained here is designated as sample E1.
[0042]
As shown in FIGS. 1 and 2, in the
[0043]
Subsequently, for the sample E1, the average particle size of the supported catalyst fine particles was measured. The average particle size was determined by randomly measuring the particle size of the catalyst fine particles from a transmission electron microscope (TEM) photograph, and the average value was used as the average particle size. The standard deviation of the catalyst fine particles was measured in the same manner.
Table 1 shows the results.
[0044]
Next, in order to examine the characteristics of the sample E1 as a catalyst, the activation energy was calculated from the CO purification rate as follows.
A catalyst support (sample E1) (5 mg) was placed in a quartz tube, and the space velocity as a value obtained by dividing the processing gas volume per hour passing through the quartz tube by the capacity of the catalyst support in the quartz tube was 70000 h. Under the condition of −1, N 2 containing 1% of CO and 0.5% of O 2 was introduced at 3500 mL / min. Subsequently, the inside of the quartz tube was heated to 500 ° C. at a rate of 12 K / min, the CO purification rate at this time was measured, and the activation energy was calculated. The CO purification rate was calculated from the CO concentration before and after the introduction. The activation energy was calculated from the Arrhenius plot of the temperature dependence data of the purification rate.
Table 1 shows the results.
[0045]
In this example, FSM having an average pore diameter of 2.1 nm (standard deviation 0.04 nm) and 2.4 nm (standard deviation 0.05 nm) was used as the porous substrate, and the other conditions were the same as those of the sample E1. Thus, a catalyst carrier was prepared, and these were designated as Sample E2 and Sample E3, respectively. The average particle diameter and standard deviation of the catalyst fine particles and the activation energy of the sample E2 and the sample E3 were measured in the same manner as the sample E1.
Table 1 shows the results.
[0046]
Further, in this example, in order to clarify the excellent characteristics of the catalyst carrier according to the present invention, a catalyst carrier was produced by a liquid phase carrier method for comparison.
Specifically, first, three types of FSMs having the same average pore diameter and standard deviation as those of the samples E1 to E3 were prepared as the porous base material.
[0047]
5 g of platinum acetylacetonate and 1000 ml of acetone were put into a 1000 ml autoclave, and 8 g of a porous substrate was further put therein, and heated at 150 ° C. for 2 hours.
[0048]
Next, a reduction treatment was performed in the same manner as in the sample E1, to prepare three types of catalyst carriers having different pore diameters. These were designated as Sample C1 to Sample C3, respectively.
The sample E1 and the sample C1, the sample E2 and the sample C2, and the sample E3 and the sample C3 are made of FSMs having the same average pore diameter.
[0049]
Subsequently, for the samples C1 to C3, the average particle diameter and the standard deviation of the catalyst fine particles and the activation energy were measured in the same manner as the samples E1 to E3.
Table 1 shows the results.
[0050]
[Table 1]
As can be seen from Table 1, Samples E1 to E3 had lower activation energy and better catalyst properties as compared with Samples C1 to C3 having the same average pore diameter. In particular, in sample E3 obtained using a porous substrate having an average pore diameter of 2.4 nm (standard deviation is 0.05 nm), the average particle diameter of the catalyst fine particles supported on the porous substrate was 2.3 nm ( The standard deviation was 0.08 nm), and this sample E3 showed particularly excellent catalytic properties with an activation energy of 23.6 kJ / mol.
[0052]
On the other hand, in the samples C1 to C3, as shown in FIGS. 4 and 5, the catalyst
As a result, as can be seen from Table 2, the samples C1 to C3 have very large catalyst fine particle diameters and standard deviations. The activation energy was higher than that of E3, and the catalyst was inferior.
[0053]
(Example 2)
In this example, an example is shown in which the above-mentioned catalyst carrier is manufactured using a porous substrate having a different pore diameter.
First, FSM having an average pore diameter of 3.5 nm (standard deviation 0.06 nm) and 4.6 nm (standard deviation 0.10 nm) was prepared as the porous substrate.
Next, using these porous substrates, a catalyst carrier was prepared using a supercritical fluid in the same manner as in Samples E1 to E3 of Example 1 and used as Samples Ea4 and Ea5. Subsequently, for these samples Ea4 and Ea5, similarly to the samples E1 to E3 of Example 1, the average particle diameter and the standard deviation of the catalyst fine particles, and the activation energy were measured.
Table 2 shows the results.
[0054]
Further, using the same porous substrate as that used for Samples Ea4 and Ea5, catalyst carriers were produced by the liquid phase supporting method, and these were designated as Samples C4 and C5, respectively. Subsequently, for these samples C4 and C5, the average particle diameter and standard deviation of the catalyst fine particles and the activation energy were measured in the same manner as in Example 1. The method for producing the catalyst carrier by the liquid phase carrier method is the same as that for the samples C1 to C3 in Example 1.
Table 2 also shows the results of samples E1 to E3 and samples C1 to C3 of Example 1 for comparison.
[0055]
[Table 2]
As is known from Table 2, when the samples Ea4 and Ea5 obtained using the porous substrate having a pore diameter of 3.5 nm or more are compared with the samples C4 and C5 having the same pore diameter, respectively, Sample C4, Sample Ea5, and Sample C5 each showed the same level of activation energy.
Further, from the results of Samples E1 to E3, Sample Ea4 and Sample Ea5, in the catalyst carrier of this example, the average pore diameter of the porous substrate exceeded 2.1 nm and was less than 3.5 nm (3.4 nm or less). In addition, when the average particle diameter of the catalyst fine particles exceeds 1.7 nm and is less than 2.9 nm, the activation energy is low and the catalyst exhibits excellent catalytic activity.
[0057]
On the other hand, in Samples E1 to E3, even when compared to Samples C1 to C3 having the same porous diameter of the porous substrate, Samples E1 to E3 had better activity as a catalyst.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing a state in which a catalyst carrier according to a first embodiment is viewed obliquely from above.
FIG. 2 is a sectional view taken along line AA of FIG.
FIG. 3 is a schematic view of a supporting device for supporting catalyst fine particles on a porous substrate using a supercritical fluid according to the first embodiment.
FIG. 4 is an explanatory view showing catalyst carriers as samples C1 to C3 in which catalyst fine particles are carried on the side surface of a porous substrate according to Example 1.
FIG. 5 is a sectional view taken along line BB of FIG. 4;
FIG. 6 is an explanatory view showing micelles of a layered silicate and a surfactant.
FIG. 7 is an explanatory view showing a porous substrate in which pores are formed by micelles of a surfactant.
FIG. 8 is an explanatory view showing a state where a porous substrate is viewed obliquely from above.
[Explanation of symbols]
1. . . Catalyst carrier,
2. . . Porous substrate,
25. . . pore,
3. . . Catalyst particles,
Claims (9)
該触媒担持体は，超臨界流体に上記触媒微粒子の前駆体を溶解させて，これを上記多孔質基体に接触させて，上記超臨界流体を上記細孔に進入させ，上記前駆体を上記細孔内に配置することによって得られることを特徴とする触媒担持体。A catalyst carrier comprising a porous substrate having pores having an average pore diameter of 3.4 nm or less and a standard deviation of 0.2 nm or less, and catalyst fine particles arranged in the pores,
The catalyst carrier dissolves the precursor of the catalyst fine particles in a supercritical fluid, and brings the precursor into contact with the porous substrate to allow the supercritical fluid to enter the fine pores, and convert the precursor into the fine pores. A catalyst carrier obtained by disposing in a hole.
超臨界流体に触媒微粒子の前駆体を溶解させて，これを上記多孔質基体に接触させて，上記超臨界流体を細孔に進入させ，上記前駆体を上記細孔内に配置する流体進入工程を有することを特徴とする触媒担持体の製造方法。In a method for producing a catalyst carrier in which catalyst fine particles are supported in pores of a porous substrate having pores having an average pore diameter of 3.4 nm or less and a standard deviation of 0.2 nm or less,
A fluid entry step of dissolving a precursor of catalyst fine particles in a supercritical fluid, bringing the precursor into contact with the porous substrate, allowing the supercritical fluid to enter the pores, and disposing the precursor in the pores; A method for producing a catalyst carrier, comprising:
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