JP2004337731A - Sheet-like catalyst structure using carbon nanotube and its production method - Google Patents
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 62
- 239000002041 carbon nanotube Substances 0.000 title claims abstract description 55
- 229910021393 carbon nanotube Inorganic materials 0.000 title claims abstract description 55
- 239000003054 catalyst Substances 0.000 title claims abstract description 36
- 238000004519 manufacturing process Methods 0.000 title claims description 9
- 229910052751 metal Inorganic materials 0.000 claims abstract description 52
- 239000002184 metal Substances 0.000 claims abstract description 52
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims abstract description 16
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 claims abstract description 8
- 229910052697 platinum Inorganic materials 0.000 claims abstract description 8
- KJTLSVCANCCWHF-UHFFFAOYSA-N Ruthenium Chemical compound [Ru] KJTLSVCANCCWHF-UHFFFAOYSA-N 0.000 claims abstract description 4
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 claims abstract description 4
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- 229910052741 iridium Inorganic materials 0.000 claims abstract description 4
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- 229910052763 palladium Inorganic materials 0.000 claims abstract description 4
- 229910052703 rhodium Inorganic materials 0.000 claims abstract description 4
- 239000010948 rhodium Substances 0.000 claims abstract description 4
- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 claims abstract description 4
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- 230000002708 enhancing effect Effects 0.000 abstract 1
- 229910052731 fluorine Inorganic materials 0.000 abstract 1
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- 239000007789 gas Substances 0.000 description 13
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 12
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- WSFSSNUMVMOOMR-UHFFFAOYSA-N Formaldehyde Chemical compound O=C WSFSSNUMVMOOMR-UHFFFAOYSA-N 0.000 description 6
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- 125000002534 ethynyl group Chemical group [H]C#C* 0.000 description 6
- 229910052742 iron Inorganic materials 0.000 description 6
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 6
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- 239000004917 carbon fiber Substances 0.000 description 5
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 4
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- 239000012298 atmosphere Substances 0.000 description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
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- 229910017052 cobalt Inorganic materials 0.000 description 2
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- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 2
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- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 description 2
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- HNPSIPDUKPIQMN-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Al]O[Al]=O HNPSIPDUKPIQMN-UHFFFAOYSA-N 0.000 description 1
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Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は、カーボンナノチューブを用いたシート状触媒構造体およびその製造方法に関するものである。カーボンナノチューブは、カーボン原子が網目状に結合してできた穴径ナノ（１ナノは１０億分の１）メートルサイズの極微細な筒（チューブ）状の物質である。本発明による触媒構造体は、例えば環境浄化用触媒材料として使用され、特に、ダイレクトメタノール型燃料電池において、燃料が酸化されるのに伴って発生するホルムアルデヒド等の中間生成物を空気中の酸素により常温で燃焼させる反応に好適に使用される。
【０００２】
【従来の技術】
従来、環境浄化触媒においては、触媒活性金属を高分散状に担持する担体として、ゼオライトや活性炭、炭素繊維などがよく用いられて来た。例えば、触媒活性金属を担持させた活性炭に有機系バインダーを加え、得られた混合物をハニカム状に成型してなる、酸化触媒性を有する金属酸化物担持活性炭成型体が知られている（特許文献１参照）。
【０００３】
しかし、このような担体を用いる場合、触媒活性を高めるために金属をナノレベルのサイズに微小化し、この微粒子を上記担体に分散状に担持するには、ゾル−ゲル法などの複雑な工程を経る必要があり、製造コストが高く付くという問題があった。また、これらの担体は元もと繊維状ないしは粒状のものであるので、これをシート状、さらにはハニカム状または螺旋状に成形するには大きなコストがかかるという問題があった。
【０００４】
【特許文献１】
特開平９−１９２４８５号公報、特にその特許請求の範囲の欄。
【０００５】
【発明が解決しようとする課題】
本発明は、上記の点に鑑み、大きな表面積を持たせることにより活性を高めることができ、ハニカム状や螺旋状のような使用に適した形状に容易に成形することができるシート状触媒構造体を提供することを課題とする。
【０００６】
【課題を解決するための手段】
本発明者らは、上記課題を解決すべく研究を重ねた結果、シート上にブラシ毛状に設けたカーボンナノチューブに触媒活性金属を担持させてなるシート状触媒構造体が好適であることを見出した。
【０００７】
すなわち、本発明によるシート状触媒構造体は、シート上に実質上垂直に設けられたブラシ毛状のカーボンナノチューブ上に触媒活性金属が担持されてなるものである。
【０００８】
本明細書において、「シート」とは、厚さに基づいて規定される狭義のシートだけでなく、通常フィルムと呼ばれる薄手のものも含むこととする。
【０００９】
該シートは、ポリエステル、ポリエチレン、フッ素樹脂、アクリル樹脂などの合成樹脂からなることが好ましい。シートは、カーボンナノチューブを植え込むためのベース層と同層を支持する層を少なくとも含む多層シートであってもよい。シートは耐熱性シートであることが好ましい。好ましい耐熱性シートはポリエチレンテレフタレートシートである。シートは酸、アルカリなどに対する耐食性に優れたものであることが好ましい。シートは、無数の貫通孔が開けられた多孔性シートであってもよい。この多孔性シートを用いて得られる触媒構造体は、ガス拡散が容易であり、環境浄化用触媒材料として好ましい。シートの厚みは好ましくは０．０１〜１ｍｍ、より好ましくは０．０５〜０．５ｍｍである。
【００１０】
該触媒活性金属は、好ましくは、白金、金、ルテニウム、ロジウム、イリジウムおよびパラジウムからなる群より選ばれる。
【００１１】
カーボンナノチューブの構造は単層すなわち単一のチューブであってもよいし、多層すなわち同心状の複数の異径チューブであってもよい。
【００１２】
シート上のカーボンナノチューブの直径は好ましくは１〜１００ｎｍ、より好ましくは２〜５０ｎｍ、高さは好ましくは１〜２００μｍである。
【００１３】
カーボンナノチューブ上に担持される触媒活性成分の粒子はカーボンナノチューブの直径より小さい粒径を有することが好ましい。
【００１４】
本発明によるシート状触媒構造体は、反応装置に充填される際に好適である形状、例えば、ハニカム状または螺旋状に容易に成形される。
【００１５】
本発明によるシート状触媒構造体を製造するには、基板上に点在状に形成した金属微粒子を核として成長させたブラシ毛状のカーボンナノチューブをシートに実質上垂直に転写し、次いで該カーボンナノチューブ上に触媒活性金属を担持させる方法、または、基板上に点在状に形成した金属微粒子を核として成長させたブラシ毛状のカーボンナノチューブ上に触媒活性金属を担持させ、次いで該カーボンナノチューブをシートに実質上垂直に転写する方法が好ましい。
【００１６】
ブラシ毛状カーボンナノチューブは、公知の方法で作製できる。例えば、シリコン基板またはガラス基板の少なくとも片面上に、ニッケル、コバルト、鉄などの金属またはその化合物を含む溶液をスプレーや刷毛で塗布し、または金属を電子ビーム蒸着した後、この塗膜または蒸着膜を加熱して形成した点在状の金属微粒子に、あるいは、クラスター銃で打ち付けて形成した金属微粒子に、アセチレン（Ｃ２Ｈ２）ガスを用いて一般的な化学蒸着法（ＣＶＤ法）を施すことにより、
触媒として働く金属微粒子を核として直径１２〜３８ｎｍのカーボンナノチューブが多層構造で基板上に実質上垂直に起毛される。
【００１７】
シート上または基板上のカーボンナノチューブ上に触媒活性金属を担持させるには、金属塩を含む溶液でカーボンナノチューブを含浸する湿式法、または、化学蒸着法、真空蒸着法または陰極スパッタリング法のように乾式法が採用できる。 転写の際のシートの温度をシートを構成する合成樹脂の軟化温度以上で溶融温度以下にすることが好ましい。転写の後は、シートをその軟化温度以下に冷却することが好ましい。
【００１８】
本発明による触媒構造体は、例えば環境浄化用触媒材料として使用され、特に、ダイレクトメタノール型燃料電池において、燃料が酸化されるのに伴って発生するホルムアルデヒド等の中間生成物を空気中の酸素により常温で燃焼させる酸化反応に好適に使用される。
【００１９】
【発明の実施の形態】
以下に、本発明の実施の形態について説明する。
【００２０】
まず、基板上に金属微粒子を形成し、金属微粒子を核として高温雰囲気で原料ガスからカーボンナノチューブを成長させる。基板は金属微粒子を支持するものであればよく、金属微粒子が濡れにくいものが好ましく、シリコン基板やガラス基板であってよい。金属微粒子はニッケル、コバルト、鉄などの粒子であってよい。これらの金属またはその錯体等の化合物の溶液をスプレーや刷毛で基板に塗布し、乾燥させ、必要であれば加熱し、皮膜を形成する。皮膜の厚みは、厚過ぎると加熱による金属粒子化が困難になるので、好ましくは１〜１００ｎｍである。皮膜は電子ビーム蒸着法によって形成してもよい。次いでこの皮膜を好ましくは減圧下または非酸化雰囲気中で好ましくは６５０〜８００℃に加熱すると、直径１〜５０ｎｍ程度の金属微粒子が形成される。金属微粒子はクラスター銃を用いて形成することもできる。
【００２１】
カーボンナノチューブの原料ガスとしては、アセチレン、メタン、エチレン等の脂肪族炭化水素が使用でき、とりわけアセチレンガスが好ましい。アセチレンの場合、多層構造で太さ１２〜３８ｎｍのカーボンナノチューブが金属微粒子を核として基板上にブラシ毛状に形成される。カーボンナノチューブの形成温度は、好ましくは６５０〜８００℃である。
【００２２】
成長させたブラシ毛状カーボンナノチューブをシートに転写する。転写の際、シートの温度をシートの軟化温度以上で溶融温度以下にすることにより、カーボンナノチューブをシートに実質上垂直方向に配向させることが容易になる。また、転写後は、シートの温度を軟化温度以下に冷却することにより、カーボンナノチューブをシートに固定できる。シートに植え付けたカーボンナノチューブから基板を剥がす際の温度を５０〜０℃、好ましくは３５〜０℃とするのがよい。
【００２３】
こうしてシートに転写したブラシ毛状カーボンナノチューブ上に触媒活性金属を担持させるには、金属塩を含む溶液でカーボンナノチューブを含浸する湿式法、または、化学蒸着法、真空蒸着法または陰極スパッタリング法のように乾式法が採用できる。湿式法では金属塩は、好ましくは、白金、金、ルテニウム、ロジウム、イリジウム、パラジウムなどの金属のハロゲン物、金属酸ハロゲン物、金属の無機酸塩、金属の有機酸塩、金属錯塩等である。金属塩を含む溶液は、水溶液でも有機溶媒溶液でもよい。有機溶媒はアルコール、エーテル、ケトン、ハロゲン化炭化水素等、金属塩を溶かすものであればよい。金属塩の濃度は、金属の担持量に従って決められる。金属塩を含む溶液でカーボンナノチューブを含浸するには、カーボンナノチューブに該溶液を滴下または散布するか、カーボンナノチューブを該溶液に浸漬し、その後カーボンナノチューブを乾燥する方法が好ましい。
【００２４】
基板上に成長させたブラシ毛状のカーボンナノチューブ上に触媒活性金属を担持させ、次いで該カーボンナノチューブをシートに実質上垂直に転写する方法も、上記方法の工程順序を変えることにより実施できる。
【００２５】
つぎに、本発明を実施例に基づいて具体的に説明する。
【００２６】
実施例１
（第一工程）
５０ｍｍ×５０ｍｍ、厚さ０．５ｍｍのシリコン基板上に電子ビーム蒸着法により厚さ５ｎｍの鉄皮膜を生成させた。
【００２７】
（第二工程）
鉄皮膜を有する基板を内径５０ｍｍの石英製反応管に入れた。ヘリウムガスを流量２００ｍｌ／ｍｉｎ反応管内に流し、温度を約７３０℃に上げた。この加熱により鉄皮膜は粒子化した。次いでヘリウムガス流通と共に、カーボンナノチューブの原料ガスとしてアセチレンガスを流量３０ｍｌ／ｍｉｎ、温度約７３０℃、時間１０分、反応管内に流した。その後、アセチレンガスの導入を止め、反応管を常温まで冷却した。
【００２８】
この操作により、鉄微粒子を核として直径２０ｎｍ、高さ５０μｍの多層構造のブラシ毛状カーボンナノチューブが成長した。
【００２９】
（第三工程）
ホットプレート上に厚さ５００μｍのポリエステル製シートを置き、このシートの上に、基板状のブラシ毛状カーボンナノチューブを先端がシートを向くように配し、先端から１ｋｇ／ｃｍ２でシートに押し付けながらシートを１００℃まで昇温した。この状態を１０分間保った後、シートを常温まで冷却すると共に押し付け圧をリリースした。次いで、基板をカーボンナノチューブから外して転写を完了し、カーボンナノチューブをブラシ毛状に植え付けたシートを得た。
【００３０】
（第四工程）
シートに植え付けたカーボンナノチューブを上向きにし、カーボンナノチューブに塩化白金酸のエタノール溶液（５０ｍｇ／ｍｌ）をピペットを用いて均等に７μｌ／ｃｍ２滴下した。次いで、カーボンナノチューブを備えたシートを アルゴン雰囲気中で２５０℃で２時間熱処理した。こうして、シート上に実質上垂直に設けられたブラシ毛状のカーボンナノチューブ上に白金が担持されてなるシート状触媒構造体を得た。
【００３１】
この触媒構造体を走査型電子顕微鏡で観察したところ、直径２０ｎｍ、高さ５０μｍのカーボンナノチューブ上に直径２〜５μｍの白金微粒子が均一分散状に担持されていることが認められた。
【００３２】
比較例１
シートに植え付けたカーボンナノチューブの代わりに、カーボン繊維シート（カーボン繊維の直径：５μｍ）を用いた以外、実施例１の第四工程と同じ操作を行い、カーボン繊維シート上に白金が担持されてなるシート状触媒構造体を得た。
【００３３】
この触媒構造体を走査型電子顕微鏡で観察したところ、直径５μｍのカーボン繊維上に直径２〜５μｍの白金微粒子が担持されていることが認められた。
【００３４】
触媒活性試験
実施例１および比較例１で得られたシート状触媒構造体をそれぞれ、反応管に充填し、反応管に常温で５０００ｐｐｍ水素／空気の混合ガスを流し、サーモグラフ分析を行った。この分析により、実施例１のシート状触媒構造体を用いた場合、反応管内で水素の燃焼が起きており、比較例１のシート状触媒構造体を用いた場合、このような燃焼が起きていないことが確認された。
【００３５】
【発明の効果】
本発明による触媒構造体では、カーボンナノチューブの表面および筒内面に触媒活性金属が担持されているので、従来の触媒担体に比べ触媒表面積が極めて大きく、したがって触媒活性が高い。また、カーボンナノチューブはシートに対し実質上垂直であるので、反応すべきガスの流通性がよく、同ガスがカーボンナノチューブ上の触媒活性金属とよく接触して、この点でも触媒活性が高い。
【００３６】
また、シート状触媒構造体をハニカム状や螺旋状のような使用に適した形状に容易に成形することができ、これらを低コストで大量生産するのに好適である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a sheet-like catalyst structure using carbon nanotubes and a method for producing the same. A carbon nanotube is an extremely fine tube-shaped substance having a hole diameter of nanometers (one nano is one billionth) meters formed by bonding carbon atoms in a network. The catalyst structure according to the present invention is used, for example, as a catalyst material for environmental purification. In particular, in a direct methanol fuel cell, an intermediate product such as formaldehyde generated as fuel is oxidized by oxygen in the air. It is preferably used for a reaction burning at room temperature.
[0002]
[Prior art]
BACKGROUND ART Conventionally, in an environmental purification catalyst, zeolite, activated carbon, carbon fiber, and the like have been often used as a carrier for supporting a catalytically active metal in a highly dispersed state. For example, a metal oxide-supported activated carbon molded body having oxidation catalytic properties, which is obtained by adding an organic binder to activated carbon supporting a catalytically active metal and molding the resulting mixture into a honeycomb shape (Patent Document 1) 1).
[0003]
However, when such a carrier is used, in order to enhance the catalytic activity, the metal is miniaturized to a nanometer size, and a complex process such as a sol-gel method is required to disperse the fine particles on the carrier. However, there is a problem that the manufacturing cost is high. In addition, since these carriers are originally fibrous or granular, there is a problem that it is costly to form them into a sheet, or a honeycomb or spiral shape.
[0004]
[Patent Document 1]
JP-A-9-192485, especially the claims section.
[0005]
[Problems to be solved by the invention]
In view of the above, the present invention provides a sheet-shaped catalyst structure that can be easily formed into a shape suitable for use, such as a honeycomb shape or a spiral shape, by increasing the activity by giving a large surface area. The task is to provide
[0006]
[Means for Solving the Problems]
The present inventors have conducted studies to solve the above-mentioned problems, and as a result, have found that a sheet-like catalyst structure in which a catalytically active metal is supported on carbon nanotubes provided in a brush-like shape on a sheet is suitable. Was.
[0007]
That is, the sheet-like catalyst structure according to the present invention is obtained by supporting a catalytically active metal on brush-like carbon nanotubes provided substantially vertically on a sheet.
[0008]
In the present specification, the term “sheet” includes not only a sheet in a narrow sense defined based on a thickness but also a thin sheet usually called a film.
[0009]
The sheet is preferably made of a synthetic resin such as polyester, polyethylene, fluororesin, and acrylic resin. The sheet may be a multilayer sheet including at least a layer supporting the same layer as a base layer for implanting carbon nanotubes. The sheet is preferably a heat-resistant sheet. A preferred heat-resistant sheet is a polyethylene terephthalate sheet. The sheet preferably has excellent corrosion resistance to acids, alkalis, and the like. The sheet may be a porous sheet having countless through holes. The catalyst structure obtained by using this porous sheet can easily diffuse gas and is preferable as a catalyst material for environmental purification. The thickness of the sheet is preferably 0.01 to 1 mm, more preferably 0.05 to 0.5 mm.
[0010]
The catalytically active metal is preferably selected from the group consisting of platinum, gold, ruthenium, rhodium, iridium and palladium.
[0011]
The structure of the carbon nanotube may be a single-walled or single tube, or may be a multi-walled or concentric plurality of different-diameter tubes.
[0012]
The diameter of the carbon nanotubes on the sheet is preferably 1 to 100 nm, more preferably 2 to 50 nm, and the height is preferably 1 to 200 μm.
[0013]
It is preferable that the particles of the catalytically active component supported on the carbon nanotube have a particle size smaller than the diameter of the carbon nanotube.
[0014]
The sheet-shaped catalyst structure according to the present invention is easily formed into a shape suitable for filling in a reactor, for example, a honeycomb shape or a spiral shape.
[0015]
To manufacture the sheet-like catalyst structure according to the present invention, brush bristle-like carbon nanotubes grown with metal fine particles formed in a dotted pattern on a substrate as nuclei are transferred substantially vertically to a sheet, and then the carbon A method of supporting a catalytically active metal on a nanotube, or a method of supporting a catalytically active metal on a brush-like carbon nanotube grown with metal fine particles formed in a dotted manner on a substrate as a nucleus. A method of transferring substantially vertically to a sheet is preferred.
[0016]
The brush-like carbon nanotubes can be produced by a known method. For example, on at least one side of a silicon substrate or a glass substrate, a solution containing a metal such as nickel, cobalt, iron or a compound thereof is applied by spraying or brushing, or after electron beam evaporation of the metal, the coating film or the deposited film is formed. Is subjected to a general chemical vapor deposition (CVD) method using acetylene (C 2 H 2 ) gas on scattered metal fine particles formed by heating the metal particles or on metal fine particles formed by hitting with a cluster gun. By
Carbon nanotubes having a diameter of 12 to 38 nm are raised substantially vertically on the substrate in a multilayer structure with metal fine particles acting as a catalyst as nuclei.
[0017]
In order to support the catalytically active metal on the carbon nanotubes on the sheet or substrate, a wet method in which the carbon nanotubes are impregnated with a solution containing a metal salt, or a dry method such as a chemical vapor deposition method, a vacuum vapor deposition method or a cathode sputtering method is used. Law can be adopted. It is preferable that the temperature of the sheet during transfer be equal to or higher than the softening temperature of the synthetic resin constituting the sheet and equal to or lower than the melting temperature. After transfer, the sheet is preferably cooled below its softening temperature.
[0018]
The catalyst structure according to the present invention is used, for example, as a catalyst material for environmental purification. In particular, in a direct methanol fuel cell, an intermediate product such as formaldehyde generated as fuel is oxidized by oxygen in the air. It is suitably used for an oxidation reaction burning at room temperature.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0020]
First, metal fine particles are formed on a substrate, and carbon nanotubes are grown from a source gas in a high-temperature atmosphere using the metal fine particles as nuclei. The substrate only needs to support the metal fine particles, and is preferably one in which the metal fine particles are hardly wetted, and may be a silicon substrate or a glass substrate. The metal fine particles may be particles of nickel, cobalt, iron, or the like. A solution of a compound such as a metal or a complex thereof is applied to a substrate by spraying or brushing, dried, and, if necessary, heated to form a film. The thickness of the coating is preferably 1 to 100 nm, because if it is too thick, it becomes difficult to form metal particles by heating. The film may be formed by an electron beam evaporation method. Next, when this film is heated to preferably 650 to 800 ° C., preferably under reduced pressure or in a non-oxidizing atmosphere, metal fine particles having a diameter of about 1 to 50 nm are formed. The metal fine particles can also be formed using a cluster gun.
[0021]
As a raw material gas for carbon nanotubes, aliphatic hydrocarbons such as acetylene, methane, and ethylene can be used, and acetylene gas is particularly preferable. In the case of acetylene, carbon nanotubes having a multilayer structure and a thickness of 12 to 38 nm are formed on a substrate in the form of brush hairs with metal fine particles as nuclei. The formation temperature of the carbon nanotube is preferably 650 to 800 ° C.
[0022]
The grown brush-like carbon nanotubes are transferred to a sheet. By making the temperature of the sheet equal to or higher than the softening temperature of the sheet and equal to or lower than the melting temperature at the time of transfer, the carbon nanotubes can be easily oriented substantially vertically to the sheet. After the transfer, the carbon nanotubes can be fixed to the sheet by cooling the sheet to a temperature lower than the softening temperature. The temperature at which the substrate is peeled off from the carbon nanotubes planted on the sheet is preferably 50 to 0 ° C, more preferably 35 to 0 ° C.
[0023]
In order to support the catalytically active metal on the brush-like carbon nanotubes thus transferred to the sheet, a wet method of impregnating the carbon nanotubes with a solution containing a metal salt, or a chemical vapor deposition method, a vacuum vapor deposition method or a cathode sputtering method The dry method can be adopted. In the wet method, the metal salt is preferably a metal halide such as platinum, gold, ruthenium, rhodium, iridium, palladium, a metal acid halide, a metal inorganic acid salt, a metal organic acid salt, a metal complex salt, or the like. . The solution containing the metal salt may be an aqueous solution or an organic solvent solution. The organic solvent may be any solvent that dissolves a metal salt such as alcohol, ether, ketone, and halogenated hydrocarbon. The concentration of the metal salt is determined according to the amount of metal carried. In order to impregnate the carbon nanotubes with a solution containing a metal salt, a method of dropping or spraying the solution on the carbon nanotubes or dipping the carbon nanotubes in the solution and then drying the carbon nanotubes is preferable.
[0024]
A method of supporting a catalytically active metal on brush-like carbon nanotubes grown on a substrate and then transferring the carbon nanotubes to a sheet substantially vertically can also be carried out by changing the process order of the above method.
[0025]
Next, the present invention will be specifically described based on examples.
[0026]
Example 1
(First step)
An iron film having a thickness of 5 nm was formed on a silicon substrate having a size of 50 mm × 50 mm and a thickness of 0.5 mm by an electron beam evaporation method.
[0027]
(Second step)
The substrate having the iron coating was placed in a quartz reaction tube having an inner diameter of 50 mm. Helium gas was flowed into the reaction tube at a flow rate of 200 ml / min, and the temperature was raised to about 730 ° C. This heating turned the iron coating into particles. Then, along with the helium gas flow, an acetylene gas as a raw material gas for the carbon nanotubes was flowed into the reaction tube at a flow rate of 30 ml / min, at a temperature of about 730 ° C. for 10 minutes. Thereafter, the introduction of the acetylene gas was stopped, and the reaction tube was cooled to room temperature.
[0028]
By this operation, a brush-like carbon nanotube having a multilayer structure with a diameter of 20 nm and a height of 50 μm was grown with iron fine particles as nuclei.
[0029]
(Third step)
A polyester sheet having a thickness of 500 μm is placed on a hot plate, and brush-like carbon nanotubes in the form of a substrate are arranged on the sheet so that the tip is directed to the sheet, and pressed against the sheet at 1 kg / cm 2 from the tip. The sheet was heated to 100 ° C. After maintaining this state for 10 minutes, the sheet was cooled to room temperature and the pressing pressure was released. Next, the substrate was removed from the carbon nanotubes to complete the transfer, and a sheet in which the carbon nanotubes were planted in a brush bristle shape was obtained.
[0030]
(Fourth step)
With the carbon nanotubes implanted on the sheet facing upward, an ethanol solution of chloroplatinic acid (50 mg / ml) was evenly dropped on the carbon nanotubes at 7 μl / cm 2 using a pipette. Next, the sheet provided with the carbon nanotubes was heat-treated at 250 ° C. for 2 hours in an argon atmosphere. Thus, a sheet-like catalyst structure in which platinum was supported on brush bristle-like carbon nanotubes provided substantially vertically on the sheet was obtained.
[0031]
Observation of the catalyst structure with a scanning electron microscope revealed that platinum fine particles having a diameter of 2 to 5 μm were uniformly dispersed on carbon nanotubes having a diameter of 20 nm and a height of 50 μm.
[0032]
Comparative Example 1
The same operation as in the fourth step of Example 1 was carried out except that a carbon fiber sheet (diameter of carbon fiber: 5 μm) was used instead of the carbon nanotubes planted on the sheet, and platinum was supported on the carbon fiber sheet. A sheet-like catalyst structure was obtained.
[0033]
Observation of this catalyst structure with a scanning electron microscope revealed that platinum fine particles having a diameter of 2 to 5 μm were supported on carbon fibers having a diameter of 5 μm.
[0034]
Catalyst activity test Each of the sheet-shaped catalyst structures obtained in Example 1 and Comparative example 1 was filled in a reaction tube, and a mixed gas of 5000 ppm hydrogen / air was flowed into the reaction tube at room temperature, and thermographic analysis was performed. According to this analysis, when the sheet-shaped catalyst structure of Example 1 was used, hydrogen combustion occurred in the reaction tube, and when the sheet-shaped catalyst structure of Comparative Example 1 was used, such combustion occurred. Not confirmed.
[0035]
【The invention's effect】
In the catalyst structure according to the present invention, since the catalytically active metal is supported on the surface of the carbon nanotube and the inner surface of the cylinder, the catalytic surface area is extremely large as compared with the conventional catalyst carrier, and therefore the catalytic activity is high. Further, since the carbon nanotubes are substantially perpendicular to the sheet, the gas to be reacted has good flowability, and the gas comes into good contact with the catalytically active metal on the carbon nanotubes, and the catalytic activity is also high in this respect.
[0036]
In addition, the sheet-shaped catalyst structure can be easily formed into a shape suitable for use such as a honeycomb shape or a spiral shape, which is suitable for mass production at low cost.
Claims (8)
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