JP3782993B2 - Manufacturing method of hollow nanofiber - Google Patents

Description

コバルトの担体としては、コバルト金属微粒子を高分散担持できることが必要であり、かつ、上述の通りコバルト金属微粒子に電子を与えられることが必要である。この条件を満たす担体であれば特に限定されないが、無機酸化物、ゼオライト、シリコン、グラファイト、カーボンナノチューブ等が好しく使用される。特に、担体の電子吸引性が高い場合、触媒金属から担体へ電子が移動し、触媒金属上の電子密度が低くなる。その結果、コバルト上の電子の結合エネルギーがより高くなる。逆に、担体の電子供与性が高い場合、担体から触媒金属へ電子が移動し、触媒金属上の電子密度が高くなる。その結果、コバルト上の電子の結合エネルギーが低くなる。これらのことから、適度な電子吸引／供与性を有する担体が好ましく、特に、ゼオライトを用いた場合は、シリカアルミナ比が小さく極性が高いゼオライトより、ＵＳＹ型やチタノシリケートなど、極性が低いゼオライトが好んで用いられる。
【００４０】
本発明において、中空状ナノファイバーを製造するために触媒と炭素含有化合物とを接触させるときの温度は、５００〜１２００℃であり、好ましくは６００℃〜１０００℃の範囲にするのがよい。温度が５００℃よりも低いと、ナノファイバーの収率が悪くなり、また温度が１２００℃よりも高いと、使用する反応器の材質に制約があると共に、ナノファイバー同士の接合が始まり、ナノファイバーの形状のコントロールが困難になる。特に細いナノファイバー（単層カーボンナノチューブや２層〜５層カーボンナノチューブ等の細いカーボンナノチューブ）は、比較的高い温度で接触させることにより得ることができる。炭素源にもよるが、７５０℃以上で接触させることが好ましい。
【００４１】
触媒と炭素含有化合物との接触のさせ方は、特に限定されない。例えば、管状炉に設置された石英製、アルミナ製等の耐熱性の反応管内に、上述した触媒を置き、加熱下に炭素含有化合物ガスを流すことにより達成することができる。触媒と炭素含有化合物の接触方法は、上記のような方法のほかに、触媒を噴霧する方法、触媒を攪拌しながら接触させる方法であってもよい。接触させている時間（反応時間）は、目的とするナノファイバーや炭化水素のガス流量、炭化水素の濃度によって最適値は変わるが、数分から数時間が一般的である。反応時間は短いほうが細いナノファイバーが得られるが、収量は少なくなる。また、反応時間が長くなると収量は増加するが、ナノファイバーは太くなる傾向がある。
【００４２】
本発明において、炭素含有化合物は特に限定されないが、好ましくは炭化水素又は一酸化炭素を使うとよい。
【００４３】
炭化水素は芳香族であっても、非芳香族であってもよい。芳香族の炭化水素では、例えばベンゼン、トルエン、キシレン、クメン、エチルベンゼン、ジエチルベンゼン、トリメチルベンゼン、ナフタレン、フェナントレン、アントラセン又はこれらの混合物などを使用することができる。また、非芳香族の炭化水素では、例えばメタン、エタン、プロパン、ブタン、ペンタン、ヘキサン、ヘプタン、エチレン、プロピレンもしくはアセチレン、又はこれらの混合物等を使用することができる。炭化水素には、また酸素を含むもの、例えばメタノール若しくはエタノール、プロパノール、ブタノールのごときアルコール類、アセトンのごときケトン類、及びホルムアルデヒドもしくはアセトアルデヒドのごときアルデヒド類、トリオキサン、ジオキサン、ジメチルエーテル、ジエチルエーテルのごときカルボン酸類、酢酸エチルなどのエステル類又はこれらの混合物であってもよい。これらの中でも、特に非芳香族の炭化水素は、質の良い中空状ナノファイバーを得ることができるため、最も好ましい炭素源である。
【００４４】
上記金属触媒を担持する担体には、無機酸化物、シリコン、グラファイト、カーボンナノチューブ等が好んで用いられる。特に、ゼオライトが好ましい。ゼオライトは、コバルト金属微粒子を高分散担持することができ、かつ、上述の通りコバルト金属微粒子に電子を与えられるからである。
【００４５】
本発明においてゼオライトとは、分子サイズの細孔径を有した結晶性無機酸化物からなるものである。ここに分子サイズとは、世の中に存在する分子のサイズの範囲であり、一般的には、０．２ｎｍから２ｎｍ程度の範囲を意味する。さらに具体的には、結晶性シリケート、結晶性アルミノシリケート、結晶性メタロシリケート、結晶性メタロアルミノシリケート、結晶性アルミノフォスフェート、あるいは結晶性メタロアルミノフォスフェート等で構成された結晶性マイクロポーラス物質のことである。
【００４６】
結晶性シリケート、結晶性アルミノシリケート、結晶性メタロシリケート、結晶性メタロアルミノシリケート、結晶性アルミノフォスフェート、結晶性メタロアルミノフォスフェートとしては、特に種類は制限されないが、例えば、アトラス オブ ゼオライト ストラクチュア タイプス（マイヤー、オルソン、バエロチャー、ゼオライツ、１７（１／２）、１９９６）（Atlas of Zeolite Structure types(W. M. Meier, D. H. Olson, Ch. Baerlocher, Zeolites, 17(1/2),1996)）に掲載されている構造をもつ結晶性無機多孔性物質が挙げられる。また、本発明に使用されるゼオライトは、本文献に掲載されているものに限定されるものではなく、近年次々と合成されている新規な構造を有するゼオライトも含まれる。好ましい構造は、入手が容易なＦＡＵ型、ＭＦＩ型、ＭＯＲ型、ＢＥＡ型であるが、これに限定されない。
【００４７】
また、前記ゼオライトとして、構造骨格内にケイ素以外のヘテロ元素を、ケイ素／ヘテロ原子モル比で２５以上となるように含むアルミノシリケートゼオライト、メタロシリケートゼオライト、またはメタロアルミノシリケートが好ましく使用することができる。ヘテロ原子がアルミニウムであるゼオライトはアルミノシリケートであり、ケイ素／アルミニウムモル比が２５以上ということは、ハイシリカゼオライトに属する。このようなシリカアルミナ比をとることができれば、その結晶構造は特に限定されないが、例えば、ＭＦＩ型、ＭＯＲ型、ＦＡＵ型、ＣＩＴ−５型が好んで用いられる。特に、高耐熱性ＦＡＵ型ゼオライトであるＵＳＹ型ゼオライトは好ましい。
【００４８】
また、アルミニウムやシリコン以外のヘテロ元素を含むゼオライトは、メタロシリケートと言われる。ヘテロ元素の種類は特に限定されないが、例えば、ホウ素、ガリウム、鉄、コバルト、チタン、ゲルマニウム、ジルコニウム、バナジウム、クロム、マンガン、亜鉛が好んで用いられる。メタロシリケートゼオライトは、種類は特に限定されないが、耐熱性が高いほうが好ましい。反応温度以上の温度に対して耐熱性を有することが好ましく、特に８００℃以上の耐熱性を有するものが好ましい。
【００４９】
ゼオライトが８００℃の耐熱性を有するとは、窒素または乾燥空気の雰囲気中で８００℃で３０分間焼成した時、その焼成前後において室温で粉末Ｘ線回折（ＸＲＤ）を行った時、そのゼオライトのピーク位置、ピーク高さ比が共に同様のピークを有していることを意味する。好ましくは、８００℃で加熱後、粉末Ｘ線回折を行った時、焼成前のゼオライトと同様のピークを有するだけでなく、実質的構造変化がないものがよい。メタロシリケートの結晶構造は特に限定されないが、ＭＦＩ型はメタロシリケート構造が安定で好んで用いられる。
【００５０】
金属触媒微粒子をゼオライト担体表面に析出させる方法として、コバルトシリケート、鉄シリケートなどのメタロシリケートを合成し、これを高温で焼成し、骨格中のコバルト、鉄をゼオライト表面に析出させ、微粒子化する方法を用いることもできる。本方法を用いることで、数十ｎｍ以上の大きさを持つ金属粒子の生成を抑制できるため、６層以上の多層カーボンナノチューブや、外径が５０ｎｍ以上のナノファイバーの生成を抑制することができる。本方法として、コバルトシリケート、鉄シリケートなど、１種類のヘテロ原子を骨格内に有するゼオライトだけでなく、鉄、コバルト、チタンなど、２種類以上のヘテロ原子を骨格内に有するゼオライトも好ましく使用することができる。
【００５１】
本発明において、担体としては、構造骨格内にシリコン以外のヘテロ元素を、ケイ素／ヘテロ原子モル比で２５以上となるように含むものが好ましい。ヘテロ原子がアルミニウムや３価の元素である場合は、ケイ素／ヘテロ原子比が２５より小さいと、骨格中の電荷バランスを補償するイオン交換点が多くなり、耐熱性が低くなる。その結果、中空状ナノファイバーの合成温度が低くなり、生成する中空状ナノファイバーのグラファイト化度が低くなる。
【００５２】
ケイ素／ヘテロ原子比が高い（１００以上）ゼオライトは、それだけ耐熱性が高くなり、中空状ナノファイバーの合成温度を上げることができるため好ましい。また、ケイ素／ヘテロ原子比が低い（２５以上１００以下）ゼオライトでは、骨格中のヘテロ原子がゼオライト外表面金属に及ぼす影響が大きく、中空状ナノファイバー合成において、触媒反応を制御しやすい点で好ましい。また、ヘテロ元素が４価の元素である場合、ケイ素／ヘテロ原子比が２５より小さいメタロシリケートの合成は極めて困難であり、かつ、安定性が低いため、ケイ素／ヘテロ原子比は２５以上が好ましい。ヘテロ原子は骨格にあることが好ましいが、焼成中などに骨格外へ抜け出ていても構わない。たとえ抜け出ていても、金属との相互作用の点では十分に効果を奏するものと考えられる。
【００５３】
ゼオライト骨格中のＳｉ／ヘテロ原子の原子比は、２９Ｓｉ ＭＡＳ ＮＭＲで測定することができる。また、骨格から抜け出たヘテロ原子も含めて測定する場合には、エネルギー分散型Ｘ線分光分析法（ＥＤＸ）により測定することができる。
【００５４】
上述のコバルトの電子状態を作り出すために、担体であるゼオライトの種類が重要である。チタンのような遷移金属を構造骨格に持ったゼオライトは、特にこのような状態を作り出しやすくすることができる。その理由は、遷移金属はｄ軌道に電子を有しており、その電子がゼオライト上の金属種に電子を与えているものと推定することができる。
【００５５】
実質的にアルミニウムなどの３価の成分を含まないゼオライトを後処理により製造する方法としては、予めアルミニウムなどを含んだ結晶性アルミノシリケートを製造し、キールの方法（ジャーナル・オブ・フィジカル・ケミストリー、71巻、4155頁、（1967年））又はスキールらの方法（第６回国際ゼオライト学会予稿集、87ページ（1984年））で、脱アルミニウムしてハイシリカゼオライトにして、耐熱性を向上させる方法もある。しかし、通常は、このままでは、焼成中にゼオライトは構造変化を起こす。それは、アルミニウムが抜けたところが構造欠陥となるためである。この構造欠陥が焼成中に構造変化を起こす原因となる。
【００５６】
本発明において、金属触媒の担体に使用するゼオライトには、構造骨格内にアルミニウムを含むアルミノシリケート、アルミニウムやケイ素以外のヘテロ元素を含むメタロシリケート、およびアルミニウムとヘテロ原子の両方を含むメタロアルミノシリケートを使用することができる。本発明者らが鋭意検討した結果によれば、触媒となる金属と担体との親和性が、高品質のカーボンナノチューブを作る上で、またカーボンナノチューブの層数や太さを制御する上で重要な因子になっていることを知見した。特に、チタノシリケート、コバルトシリケート、およびボロシリケートから選ばれる少なくとも一つを担体に用いることで、細い中空状ナノファイバーを製造しやすくなることを見出した。
【００５７】
上記のようなゼオライトの結晶の大きさは特に制限はない。一般には数１０ｎｍから数１０μｍである。結晶が小さい方が外表面積が大きいので、カーボンナノチューブの収量を多くすることができるため好ましい。しかし、余り小さくても凝集がはげしく、実質的な外表面積が減少するので、大きさとしては、０．１〜１０μｍの結晶であることが好ましい。
【００５８】
本発明では原料として炭素含有化合物が使用され、その詳細は前述した通りである。しかし、炭素含有化合物以外に希釈ガスを好ましく使用することができる。希釈ガスとしては、特に限定されないが、酸素ガス以外のものが好ましく使用される。酸素は爆発の可能性があるので通常使用しないが、爆発範囲外であればかまわない。窒素、アルゴン、水素、ヘリウム等が好ましく使用される。
【００５９】
これらのガスは、炭素含有化合物ガスの濃度のコントロールや、キャリヤガスとして作用する。このうち水素は、特に触媒金属の活性化に効果があるので好ましい。アルゴンの如き分子量が大きいガスは、アニーリング効果が大きいので好ましい。キャリアガス中の炭素含有化合物の蒸気の濃度が高くなると、収量は向上するが、太いカーボンナノチューブができる傾向がある。また、キャリアガス中の炭素含有化合物の蒸気の濃度が低くなると、細いカーボンナノチューブができるが、収量が低くなる傾向がある。
【００６０】
生成された炭素を主成分とする中空状ナノファイバーは、中空状であれば特に制限はない。ナノファイバーが中空状であることは、透過型電子顕微鏡で確認することができる。本発明から得られる中空状ナノファイバーは、外径が５０ｎｍ以下で、内径が０．３ｎｍ以上１５ｎｍ以下の極細の中空状ナノファイバーにすることができる。特に、中空状ナノファイバーの壁を欠陥の少ないグラファイト層で形成することができる。このように欠陥の少ないグラファイト層からなることは、高分解能透過型電子顕微鏡によって確認することができる。
【００６１】
上記のような極細の中空状ナノファイバーは、一般的にカーボンナノチューブと定義される。多層カーボンナノチューブ、単層カーボンナノチューブは、ともに炭素を主成分とする中空状ナノファイバーに含まれる。
【００６２】
また、本発明の製造法によれば、中空状ナノファイバーが下記（１）〜（３）の要件の全てを満たす中空状ナノファイバーを得ることができる。
【００６３】
（１）高分解能透過型電子顕微鏡で２層カーボンナノチューブが観察されること。
（２）共鳴ラマン散乱測定により、１５０〜３５０ｃｍ^-1の領域にピークが観察されること。
（３）共鳴ラマン散乱測定により、１５６０〜１６００ｃｍ^-1の範囲内で最大のピーク強度をＧ、１３１０〜１３５０ｃｍ^-1の範囲内で最大のピーク強度をＤとしたとき、Ｇ／Ｄの比が１．０以上であること。
【００６４】
ここでいう高分解能透過型電子顕微鏡による２層カーボンナノチューブの観察手法は、特に限定されるものではないが、例えば、中空状ナノファイバーを含有する試料をエタノールなど揮発性の高い溶媒に添加し、中空状ナノファイバーを溶媒中に分散させた後、中空状ナノファイバーを含む溶媒数滴をマイクログリッド上に滴下し、溶媒を揮発させた後に、高分解能透過型電子顕微鏡で観察する手法が好ましく用いられる。
【００６５】
２層カーボンナノチューブを観察するためには、倍率を５０万倍以上、好ましくは１００万倍以上に上げる手法が用いられる。観察されるカーボンナノチューブの壁を構成するグラフェンシートが２本で観察されるものが２層カーボンナノチューブである。また、単層カーボンナノチューブの壁が部分的に２層になっていたり、多層カーボンナノチューブの壁が部分的に２層になっているものは２層カーボンナノチューブとは言わない。カーボンナノチューブの壁を構成するグラフェンシートが２本で観察される領域が、少なくとも３０ｎｍ以上連続していなければ、２層カーボンナノチューブとは言わない。グラフェンシートが２本で観察される領域が長ければ長いほど、均質な２層カーボンナノチューブと言えるため好ましい。
【００６６】
また、共鳴ラマン散乱測定により、１５０〜３５０ｃｍ^-1の領域にピークが観察されるとは、ＲＢＭ（Ｒａｄｉａｌ Ｂｒｅａｔｈｉｎｇ Ｍｏｄｅ）が観察されることを言う。ＲＢＭとは、細いカーボンナノチューブの伸縮振動に起因するピークであり、直径０．７〜１．６ｎｍのカーボンナノチューブが存在することを示唆している。
【００６７】
また、共鳴ラマン散乱測定により、１５６０〜１６００ｃｍ^-1の範囲内で最大のピーク強度をＧ、１３１０〜１３５０ｃｍ^-1の範囲内で最大のピーク強度をＤとしたとき、Ｇ／Ｄ比が１．０以上であることとは、生成する中空状ナノファイバーのグラファイト化度が高いことを意味している。共鳴ラマン散乱測定では、１５６０〜１６００ｃｍ^-1付近の構造がG-bandであり、その他に不純物のアモルファスやカーボンナノチューブの欠陥に起因するものとして、１３１０〜１３５０ｃｍ^-1付近のD-bandと呼ばれるピークが観測される。ラマン強度はグラファイトの1000倍程度に達し、共鳴効果が支配的である。
【００６８】
カーボンナノチューブは、キラリティー、直径により、それぞれ異なった電子構造を取る。その中で、励起光がカーボンナノチューブのEgと一致する場合に共鳴が起こり、ラマンスペクトルが発現する。そのため、励起光波長を変えていくと、次々とスペクトルは変化する。カーボンナノチューブのG-bandは共鳴効果により強調されるため、試料の純度によって強度が大きく変化する。一方、１３３０ｃｍ^-1付近のブロードなD-bandは不純物による寄与が大きく、これは共鳴効果により強い強調を受けないため、G-bandとD-bandの強度比を取ることにより、ナノチューブ試料の純度を見積ることが可能となる。本発明にある製造方法を用いることで、純度の高い中空状ナノファイバーを製造することができ、その結果、Ｇ／Ｄ比は１．０以上となる。
【００６９】
本発明によれば、主成分が１層〜５層カーボンナノチューブからなる中空状ナノファイバーが得られやすく、かつバンドル状（束状）で得られることが多い。１層〜５層カーボンナノチューブを選択的に合成する場合、ゼオライト担体にはＵＳＹ型ゼオライトやチタノシリケートを好ましく使用することができる。
【００７０】
また、本発明によれば、主成分が２層から５層カーボンナノチューブである中空状ナノファイバーが得やすく、特に２層カーボンナノチューブをバンドル状（束状）で得ることができる。２層から５層カーボンナノチューブを選択的に合成する場合は、ゼオライト担体にはチタノシリケート、コバルトシリケートを好ましく使用することができる。
【００７１】
本発明の製造法によれば、触媒調製法のコントロールによりカーボンナノチューブのコントロールが容易である。そのうちの一つの２層カーボンナノチューブは、平均内径が約２ｎｍよりも大きくできるのが特徴である。一般に内径が大きい２層カーボンナノチューブは比較的ゆがみが多く、太さが均一にならない場合が多いが、本発明の製造法で生成された２層〜５層カーボンナノチューブによれば、太さが均一であり、しかも触媒金属粒子を多く含まないという特徴を有している。
【００７２】
本発明の製造法では、比較的内径が大きく５〜１５ｎｍである２層〜５層カーボンナノチューブを選択的に得ることが出来る。カーボンナノチューブの中空部分には、金属を始めとした様々な物質を取り込めるが、内径が大きい２層〜５層カーボンナノチューブは、その内容積の大きさから、将来的に取り込める物質の種類が増えるだけでなく、分子ふるい効果を付与できる可能性を有している。
【００７３】
さらに、反応条件、触媒前処理条件を選べば、今まで得られたことがない、内径が１ｎｍ以下の２層〜５層カーボンナノチューブも得ることができる。これは１ｎｍ以下のゼオライト特有の微細孔に金属触媒が入れ子状に担持されているためであり、ゼオライトを担体に使うことにより始めて得られるものである。ゼオライトの細孔入口径に近い０．４〜１．０ｎｍ、特に０．６〜０．９ｎｍの内径を有する２層〜５層のカーボンナノチューブを得ることができる。単層カーボンナノチューブ中にフラーレンを導入した後、加熱して得られるナノチューブは２層であるが、その２層部分は極めて短いものしか得られていない（約１０ｎｍ：Chemical Physics Letters, 337(2001) 48-54 ）。このように２層部分の短いカーボンナノチューブは、本発明においては、２層カーボンナノチューブとはいわない。
【００７４】
本発明で合成される２層カーボンナノチューブには、内径が１ｎｍ以下であると共に、長さが１５ｎｍ以上のものを得ることができる。その長さは２０ｎｍ以上にすることができ、特に好ましくは３０ｎｍ以上にすることができる。本発明の製造法では、更に今までに見られたことのない内径が１ｎｍ以下の細い２層カーボンナノチューブのバンドルを得ることができる。
【００７５】
本発明によれば、２層カーボンナノチューブを選択的に合成することもできる。なお、純度１００％の２層カーボンナノチューブを得ることは困難であり、それを同定することも困難であるため、ここで言う２層カーボンナノチューブとは２０万倍以上の倍率で透過型電子顕微鏡で見たときに２層カーボンナノチューブがその電子顕微鏡の視野の中に２５％以上あれば２層カーボンナノチューブと言って差し支えない。担体には、チタノシリケートゼオライト、コバルトシリケートゼオライト、ボロシリケートゼオライトから選ばれる少なくとも一つを用い、コバルト原料には、コバルトの酢酸塩、硝酸塩、および錯体から選ばれる少なくとも一つを用い、７００℃以上の反応条件で炭化水素ガスと接触させることで、特に良好に２層カーボンナノチューブを選択合成することができる。
【００７６】
以下、実施例により本発明を具体的に説明するが、下記の実施例は例示のために示すものであって、いかなる意味においても、本発明を限定的に解釈するものとして使用してはならない。
【００７７】
【実施例】
（実施例１）
（Ｃｏ＋Ｆｅ）／シリカライト
〔シリカライトの合成〕
１８．９ｇのピペラジンヘキサハイドレート（アルドリッチ）と、５．２ｇのテトラプロピルアンモニウムブロマイド（アルドリッチ）に蒸留水１６４ｇを添加して攪拌した。加熱しながら溶けるまで攪拌した。それに、さらに１１．７ｇのヒュームドシリカ（アルドリッチ）を添加し、８０℃に加熱して透明な水溶液を得た。これをポリ４フッ化エチレン・ラインのオートクレーブに入れ、１５０℃で５日間加熱した。その後冷却して、濾過、水洗、乾燥を行った後、５５０℃で空気中で焼成した。
【００７８】
得られた粉末のＸ線回折（ＸＲＤ）を測定したところ、ＭＦＩ型の構造を有するシリカライト−１であることがわかった。
【００７９】
〔シリカライトへの金属塩の担持〕
酢酸第一鉄（アルドリッチ社製）０．０８ｇと酢酸コバルト４水和物（ナカライテスク）社製）０．１１ｇとをメタノール（ナカライテスク社製）７ｍｌに加え、超音波洗浄機で１０分間懸濁した。この懸濁液に上記シリカライト−１の粉末１．０ｇを加え、超音波洗浄機で１０分間処理し、６０℃の恒温下でメタノールを除去することにより、シリカライト−１の結晶表面に金属塩が担持した触媒を得た。
【００８０】
〔触媒の光電子分光測定〕
上述のシリカライト−１に金属塩を担持した触媒をアルゴンガス中で８００℃で３０分焼成した後、アルゴンガス中で室温まで冷却した後、一旦空気中に取り出し、Ｘ線光電子分光法装置で触媒を測定した（１０ｋＶ，１８ｍＡ）。測定されたコバルト２Ｐ3/2 の電子の結合エネルギーが７８０．３ｅＶであった。Ｆｅ２Ｐ２／３電子の結合エネルギーは、７１０．６ｅＶであった。また、担体表面のコバルトの原子比は０．７％、鉄の原子比は０．３％であった。
【００８１】
〔ナノファイバーの合成（８００℃）〕
内径３０ｍｍの石英管の中央部の石英プレート上に、金属塩を担持したシリカライト−１を０．０３４ｇ取り、アルゴンを３０ｍｌ／分で供給した。石英管を電気炉中に設置して中心温度を８００℃に加熱した。超高純度アセチレンガス（高圧ガス工業製）を１ｍｌ／分で３０分間供給した後、アセチレンガスの供給をやめ、温度を室温まで冷却した。
【００８２】
石英プレート上に堆積した反応物の一部の形状を透過型電子顕微鏡で測定したところ、外径が２０ｎｍ以下で内径が５ｎｍ程度の細い中空状ナノファイバーであった。また、高分解能透過型電子顕微鏡で中空状ナノファイバーを観察したところ、ナノファイバーの壁はきれいなグラファイト層で構成されており、層数は１〜２０層、特に２〜５層の２層を主成分とする細いカーボンナノチューブが見られた。また、直径が２０ｎｍ以上のナノファイバーは多く観察された。
【００８３】
以上の結果を表１に示した。
（実施例２）
（Ｃｏ＋Ｆｅ）／ＴＳ−１
〔結晶性チタノシリケートの合成〕
シリカゾル（ＤｕＰｏｎｔ社製、ＬｕｄｏｘＨＳ−４０）６ｇと、テトラプロピルアンモニウムヒドロキシド２２％水溶液（東京化成製）をビーカーにとり、約１時間激しく攪拌した。ここへ、テトライソプロポキシチタン０．３４ｇ（ナカライ製）を加え、１５分間攪拌した。ここへ蒸留水１２．４ｇを加え、これをテフロン（登録商標）ラインのオートクレーブへ移し、７５℃で３時間静置した。次いで、１７５℃で４８時間加熱した。その後冷却して、濾過、水洗、乾燥を行った後、５５０℃で空気中で焼成した。この粉末のＸ線回折（ＸＲＤ）を測定したところ、ＭＦＩ型の構造を有するＴＳ−１であることがわかった。
【００８４】
〔耐熱性ゼオライトへの金属塩の担持〕
酢酸第一鉄（アルドリッチ社製）０．０４ｇと酢酸コバルト４水和物（ナカライテスク）社製）０．１１ｇとをメタノール（ナカライテスク社製）７ｍｌに加え、超音波洗浄機で１０分間懸濁した。この懸濁液に上記ＴＳ−１の粉末１．０ｇを加え、超音波洗浄機で１０分間処理し、６０℃の恒温下でメタノールを除去することにより、ＴＳ−１の結晶表面に金属塩を担持した触媒を得た。
【００８５】
〔触媒の光電子分光測定〕
上述のＴＳ−１に金属塩を担持した触媒をアルゴンガス中で９００℃で３０分焼成した後、アルゴンガス中で室温まで冷却した後、一旦空気中に取り出し、Ｘ線光電子分光法装置で触媒を測定した。測定されたコバルト２Ｐ3/2 の電子の結合エネルギーが７７９．８ｅＶであった。Ｆｅ２Ｐ２／３電子の結合エネルギーは、７１０．６ｅＶであった。また、担体表面のコバルトの原子比は０．６％、鉄の原子比は０．１％であった。
【００８６】
透過型電子顕微鏡観察の結果、図１に示すように、ゼオライト表面に直径約３ｎｍの金属微粒子が形成していることが観察された。
【００８７】
〔２層ナノチューブの合成（９００℃）〕
内径１００ｍｍの石英管の中央部の石英プレート上に、金属塩を担持したＴＳ−１を０．０９ｇ取り、アルゴンを２５０ｍｌ／分で供給した。石英管を電気炉中に設置して、中心温度を９００℃に加熱した（昇温時間約３０分）。９００℃に到達した後、超高純度アセチレンガス（高圧ガス工業製）を１０ｍｌ／分で３０分間供給した後、アセチレンガスの供給をやめ、温度を室温まで冷却した。
【００８８】
石英プレート上に堆積した反応物の一部の形状を透過型電子顕微鏡で測定したところ、外径が１５ｎｍ以下、内径約３ｎｍの２層ナノチューブで構成されたバンドルや、一部が３層以上になった２層カーボンナノチューブが生成していた。これ以外の主生成物は外径１５ｎｍ以下で、かつ層数が２〜５層の２層を主成分とするカーボンナノチューブでが多く見られた。また、直径が２０ｎｍ以上のナノファイバーは若干量観察された。
【００８９】
以上の結果を表１に示した。
（実施例３）
（Ｃｏ＋Ｍｎ）／ＴＳ−１
〔結晶性チタノシリケートへの金属塩の担持〕
硝酸マンガン（片山化学製）０．００８ｇと酢酸コバルト４水和物（ナカライテスク）社製）０．１１ｇとをメタノール（ナカライテスク社製）７ｍｌに加え、超音波洗浄機で１０分間懸濁した。この懸濁液に実施例２のＴＳ−１の粉末１．０ｇを加え、超音波洗浄機で１０分間処理し、６０℃の恒温下でメタノールを除去することにより、ＴＳ−１の結晶表面に金属塩を担持した触媒を得た。
【００９０】
〔触媒の光電子分光測定〕
上述のＴＳ−１に金属塩を担持した触媒をアルゴンガス中で９００℃で３０分焼成した後、アルゴンガス中で室温まで冷却した後、一旦空気中に取り出し、Ｘ線光電子分光法装置で触媒を測定した。測定されたコバルト２Ｐ3/2 の電子の結合エネルギーが７８０．０ｅＶであった。また、担体表面のコバルトの原子比は０．６％、鉄の原子比は０．０３％であった。
【００９１】
〔ナノファイバーの合成（８００℃）〕
内径３０ｍｍの石英管の中央部の石英プレート上に、金属塩を担持したＴＳ−１を０．０３２ｇ取り、アルゴンを３０ｍｌ／分で供給した。石英管を電気炉中に設置して中心温度を８００℃に加熱した。超高純度アセチレンガス（高圧ガス工業製）を１ｍｌ／分で３０分間供給した後、アセチレンガスの供給をやめ、温度を室温まで冷却した。
【００９２】
石英プレート上に堆積した反応物の一部の形状を透過型電子顕微鏡で測定したところ、外径が１０ｎｍ以下で内径が３ｎｍ程度の２〜５層カーボンナノチューブが大量に観察された。また、直径が２０ｎｍ以上のナノファイバーはほとんど観察されなかった。
【００９３】
以上の結果を表１に示した。
（実施例４）
（Ｃｏ＋Ｆｅ）／シリカライト（低耐熱性）
〔低耐熱性シリカライトの合成〕
２０ｇのテトラプロピルアンモニウムハイドロオキサイド（TPAOH）の２０〜２５％水溶液（東京化成社製２０〜２５％水溶液）に、０．２８ｇの水酸化ナトリウム（片山化学社製試薬１級）を添加して攪拌した。それに、さらに５ｇのヒュームドシリカ（アルドリッチ)を添加し、８０℃に加熱することにより透明な水溶液を得た。これをポリ４フッ化エチレン・ラインのオートクレーブに入れ、１２５℃で８時間加熱したところ、シリカライトの微粒子（平均粒径約８０nm）が得られた。
【００９４】
得られた粉末のＸ線回折（ＸＲＤ）を測定したところ、ＭＦＩ型の構造を有するシリカライト−１であることがわかった。この粉末を、（株）島津製作所製の熱分析装置ＤＴＧ−５０で窒素50 ml/分の気流中で、５℃／分の昇温速度で８００℃まで加熱したところ、７００℃から８００℃の間にＤＴＡ曲線に発熱ピークが現れた。
【００９５】
〔ゼオライトへの金属塩の担持〕
酢酸第一鉄（アルドリッチ社製）０．０８ｇと酢酸コバルト４水和物（ナカライテスク）社製）０．１１ｇとをメタノール（ナカライテスク社製）７ｍｌに加え、超音波洗浄機で１０分間懸濁した。この懸濁液に上記シリカライト−１の粉末１．０ｇを加え、超音波洗浄機で１０分間処理し、６０℃の恒温下でメタノールを除去することにより、シリカライト−１の結晶表面に金属塩が担持した触媒を得た。
【００９６】
〔触媒の光電子分光測定〕
上述のシリカライト−１に金属塩を担持した触媒をアルゴンガス中で８００℃で３０分焼成した後、アルゴンガス中で室温まで冷却した後、一旦空気中に取り出し、Ｘ線光電子分光法装置で触媒を測定した（１０ｋＶ，１８ｍＡ）。測定されたコバルト２Ｐ3/2 の電子の結合エネルギーが７８０．２ｅＶであった。Ｆｅ２Ｐ２／３電子の結合エネルギーは、７１０．９ｅＶであった。また、担体表面のコバルトの原子比は０．７％、鉄の原子比は０．３％であった。
【００９７】
〔ナノファイバーの合成（８００℃）〕
内径３０ｍｍの石英管の中央部の石英プレート上に、金属塩を担持したシリカライト−１を０．０３１ｇ取り、アルゴンを３０ｍｌ／分で供給した。石英管を電気炉中に設置して中心温度を８００℃に加熱した。超高純度アセチレンガス（高圧ガス工業製）を１ｍｌ／分で３０分間供給した後、アセチレンガスの供給をやめ、温度を室温まで冷却した。
【００９８】
石英プレート上に堆積した反応物の一部の形状を透過型電子顕微鏡で測定したところ、外径が２０ｎｍ以下で内径が５ｎｍ程度の細い中空状ナノファイバーであった。また、高分解能透過型電子顕微鏡で中空状ナノファイバーを観察したところ、ナノファイバーの壁は比較的きれいなグラファイト層で構成されており、層数は１〜２０層、特に２〜５層のカーボンナノチューブが多く見られた。また、直径が２０ｎｍ以上のナノファイバーは多く観察された。
【００９９】
以上の結果を表１に示した。
（実施例５）
（Ｃｏ＋Ｆｅ）／ＵＳＹ（シリカアルミナ比４０）
〔ＵＳＹ型ゼオライトへの金属塩の担持〕
ＵＳＹ型ゼオライト（ＰＱコーポレーション製、シリカアルミナ比４０）５ｇを０．１規定ＮａＯＨ水溶液３００ｍｌに加え、室温で３時間攪拌した。これをろ過、水洗した。次に、酢酸第一鉄（アルドリッチ社製）０．０８ｇと酢酸コバルト４水和物（ナカライテスク）社製）０．１１ｇとをエタノール（ナカライテスク社製）７ｍｌに加え、超音波洗浄機で１０分間懸濁した。この懸濁液に先述のＮａＯＨ処理したＵＳＹ型ゼオライトを１．０ｇ加え、超音波洗浄機で１０分間処理し、６０℃の恒温下でエタノールを除去して、ＵＳＹ型ゼオライト粉末に金属塩が担持された触媒を得た。
【０１００】
〔触媒の光電子分光測定〕
上述のＵＳＹ型ゼオライトに金属塩を担持した触媒をアルゴンガス中で９００℃で３０分焼成した後、アルゴンガス中で室温まで冷却した後、一旦空気中に取り出し、Ｘ線光電子分光法装置で触媒を測定した。測定されたコバルト２Ｐ3/2 の電子エネルギーが７７９．５ｅＶであった。また、担体表面のコバルトの原子比は０．２％、鉄の原子比は０．２％であった。
【０１０１】
〔ナノファイバーの合成（８００℃）〕
内径３０ｍｍの石英管の中央部の石英プレート上に、上記で得た金属塩を担持したＵＳＹ型ゼオライト粉末を０．０２９ｇ取り、アルゴンを３０ｍｌ／分で供給した。石英管を電気炉中に設置して中心温度を８００℃に加熱した。超高純度アセチレンガス（高圧ガス工業製）を１ｍｌ／分で３０分間供給した後、アセチレンガスの供給をやめ、温度を室温まで冷却した。
【０１０２】
石英プレート上に堆積した反応物反応物の形状を透過型電子顕微鏡で測定したところ、外径が２０ｎｍ以下で内径が５ｎｍ程度の細い中空状ナノファイバーであった。また、高分解能透過型電子顕微鏡で中空状ナノファイバーを観察したところ、ナノファイバーの壁は比較的きれいなグラファイト層で構成されており、層数は１〜２０層のカーボンナノチューブであり、特に１〜５層のカーボンナノチューブが多く観察された。また、直径が２０ｎｍ以上のナノファイバーも大量に観察された。
【０１０３】
以上の結果を表１に示した。
（実施例６）
（Ｃｏ＋Ｆｅ）／ＴＳ−１
〔ＴＳ−１型ゼオライトへの金属塩の担持〕
酢酸第一鉄（アルドリッチ社製）０．００８ｇと酢酸コバルト４水和物（ナカライテスク）社製）０．１１ｇとをエタノール（ナカライテスク社製）７ｍｌに加え、超音波洗浄機で１０分間懸濁した。この懸濁液に、ＴＳ−１ゼオライト（エヌイーケムキャット製、ケイ素／チタン比５０）を１．０ｇ加え、超音波洗浄機で１０分間処理し、６０℃の恒温下でエタノールを除去して、ＴＳ−１型ゼオライト粉末に金属塩が担持された触媒を得た。
【０１０４】
〔触媒の光電子分光測定〕
上述のＴＳ−１型ゼオライトに金属塩を担持した触媒をアルゴンガス中で９００℃で３０分焼成した後、アルゴンガス中で室温まで冷却した後、一旦空気中に取り出し、Ｘ線光電子分光法装置で触媒を測定した。測定されたコバルト２Ｐ3/2 の電子エネルギーが７７９．９ｅＶであった。また、担体表面のコバルトの原子比は０．８％、鉄の原子比は０．０６％であった。また、コバルトとチタンの原子比は０．８７であった。
【０１０５】
〔ナノファイバーの合成（８００℃）〕
内径３０ｍｍの石英管の中央部の石英プレート上に、上記で得た金属塩を担持したＴＳ−１型ゼオライト粉末を０．０２９ｇ取り、アルゴンを３０ｍｌ／分で供給した。石英管を電気炉中に設置して中心温度を８００℃に加熱した。超高純度アセチレンガス（高圧ガス工業製）を１ｍｌ／分で３０分間供給した後、アセチレンガスの供給をやめ、温度を室温まで冷却した。
【０１０６】
石英プレート上に堆積した反応物反応物の形状を透過型電子顕微鏡で測定したところ、外径が１５ｎｍ以下で内径が５ｎｍ程度の細い中空状ナノファイバーであった。高分解能透過型電子顕微鏡で観察したところ、ナノファイバーの壁は比較的きれいなグラファイト層で構成されており、ほとんどの層数は２〜５層のカーボンナノチューブであり、直径２０ｎｍ以上のナノファイバーはほとんど観察されなかった。
【０１０７】
以上の結果を表１に示した。
（実施例７）
（Ｃｏ＋Ｆｅ）／ＴＳ−１
〔ＴＳ−１型ゼオライトへの金属塩の担持〕
酢酸第一鉄（アルドリッチ社製）０．０６４ｇと酢酸コバルト４水和物（ナカライテスク）社製）０．０８８ｇとをエタノール（ナカライテスク社製）７ｍｌに加え、超音波洗浄機で１０分間懸濁した。この懸濁液に、ＴＳ−１ゼオライト（エヌイーケムキャット製、ケイ素／チタン比５０）を１．０ｇ加え、超音波洗浄機で１０分間処理し、６０℃の恒温下でエタノールを除去して、ＴＳ−１型ゼオライト粉末に金属塩が担持された触媒を得た。
【０１０８】
〔触媒の光電子分光測定〕
上述のＴＳ−１型ゼオライトに金属塩を担持した触媒をアルゴンガス中で９００℃で３０分焼成した後、アルゴンガス中で室温まで冷却した後、一旦空気中に取り出し、Ｘ線光電子分光法装置で触媒を測定した。測定されたコバルト２Ｐ3/2 の電子エネルギーが７７９．５ｅＶであった。また、担体表面のコバルトの原子比は０．６％、鉄の原子比は０．０５％であった。
【０１０９】
〔ナノファイバーの合成（８００℃）〕
内径３０ｍｍの石英管の中央部の石英プレート上に、上記で得た金属塩を担持したＴＳ−１型ゼオライト粉末を０．０２９ｇ取り、アルゴンを３０ｍｌ／分で供給した。石英管を電気炉中に設置して中心温度を８００℃に加熱した。超高純度アセチレンガス（高圧ガス工業製）を１ｍｌ／分で３０分間供給した後、アセチレンガスの供給をやめ、温度を室温まで冷却した。
【０１１０】
石英プレート上に堆積した反応物反応物の形状を透過型電子顕微鏡で測定したところ、外径が１５ｎｍ以下で内径が５ｎｍ程度の細い中空状ナノファイバーであった。高分解能透過型電子顕微鏡で観察したところ、ナノファイバーの壁は比較的きれいなグラファイト層で構成されており、ほとんどの層数は２〜５層のカーボンナノチューブであった。直径２０ｎｍ以上のナノファイバーは多く観察された。
【０１１１】
以上の結果を表１に示した。
（比較例１）
（Ｃｏ＋Ｆｅ）／ＵＳＹ（シリカアルミナ比３９０）
〔ＵＳＹ型ゼオライトへの金属塩の担持〕
酢酸第一鉄（アルドリッチ社製）０．０６４ｇと酢酸コバルト４水和物（ナカライテスク社製）０．０８８ｇとをエタノール（ナカライテスク社製）７ｍｌに加え、超音波洗浄機で１０分間懸濁した。この懸濁液に、ＵＳＹ型ゼオライト（東ソー製HSZ-390HUA、シリカ／アルミナ比３９０）を１．０ｇ加え、超音波洗 浄機で１０分間処理し、６０℃の恒温下でエタノールを除去して、ＵＳＹ型ゼオライト粉末に金属塩が担持された触媒を得た。
【０１１２】
〔触媒の光電子分光測定〕
上述のＵＳＹ型ゼオライトに金属塩を担持した触媒をアルゴンガス中で９００℃で３０分焼成した後、アルゴンガス中で室温まで冷却した後、一旦空気中に取り出し、Ｘ線光電子分光法装置で触媒を測定した。測定されたコバルト２Ｐ3/2 の電子エネルギーが７８１．１ｅＶであった。また、担体表面のコバルトの原子比は１．４％、鉄の原子比は０．５％であった。
【０１１３】
〔ナノファイバーの合成（８００℃）〕
内径３０ｍｍの石英管の中央部の石英プレート上に、上記で得た金属塩を担持したＵＳＹ型ゼオライト粉末を０．０２９ｇ取り、アルゴンを３０ｍｌ／分で供給した。石英管を電気炉中に設置して中心温度を８００℃に加熱した。超高純度アセチレンガス（高圧ガス工業製）を１ｍｌ／分で３０分間供給した後、アセチレンガスの供給をやめ、温度を室温まで冷却した。
【０１１４】
石英プレート上に堆積した反応物反応物の形状を透過型電子顕微鏡で測定したところ、外径が２０ｎｍ以下で内径が１〜３ｎｍ程度の細い中空状ナノファイバーであった。高分解能透過型電子顕微鏡で観察したところ、ナノファイバーの壁は比較的きれいなグラファイト層で構成されており、ほとんどの層数は１〜２０層のカーボンナノチューブであった。特に単層や１〜５層のカーボンナノチューブが多く観察された。また、直径２０ｎｍ以上のナノファイバーは若干観察された。単層カーボンナノチューブの比率が高かったが、収率がよくなかった。
【０１１９】
（比較例２）
（Ｃｏ＋Ｆｅ）／ＵＳＹ（シリカアルミナ比３９０）
〔ＵＳＹ型ゼオライトへの金属塩の担持〕
酢酸第一鉄（アルドリッチ社製）０．０６４ｇと酢酸コバルト４水和物（ナカライテスク社製）０．０８８ｇとをエタノール（ナカライテスク社製）７ｍｌに加え、超音波洗浄機で１０分間懸濁した。この懸濁液に、ＵＳＹ型ゼオライト（東ソー製HSZ-390HUA、シリカ／アルミナ比３９０）を１．０ｇ加え、超音波洗浄機で１０分間処理し、６０℃の恒温下でエタノールを除去して、ＵＳＹ型ゼオライト粉末に金属塩が担持された触媒を得た。
【０１２０】
〔触媒の光電子分光測定〕
上述のＵＳＹ型ゼオライトに金属塩を担持した触媒をアルゴンガス中で９００℃で３０分焼成した後、アルゴンガス中で室温まで冷却した後、一旦空気中に取り出し、Ｘ線光電子分光法装置で触媒を測定した。測定されたコバルト２Ｐ3/2 の電子エネルギーが７８１．１ｅＶであった。また、担体表面のコバルトの原子比は１．４％、鉄の原子比は０．５％であった。
【０１２１】
〔単層カーボンナノチューブの選択合成〕
内径３０ｍｍの石英管の中央部の石英プレート上に、上記で得た金属塩を担持したＵＳＹ型ゼオライト粉末を０．０２９ｇ取り、アルゴンを３０ｍｌ／分で供給した。石英管を電気炉中に設置して中心温度を８００℃に加熱した。エタノール（試薬特級、東京化成製）をマイクロフィーダーで２．１ｍｇ／分で３０分間供給した後、エタノールの供給をやめ、温度を室温まで冷却した。
【０１２２】
反応管中の石英プレート上に堆積した生成物の形状を日本電子データム（株）走査電子顕微鏡ＪＳＭ−６３０１ＮＦで測定したところ、極めて細いナノファイバー状物質が多く見られた。更に、高分解能透過型電子顕微鏡で観察したところ、生成物のほとんどが、直径２ｎｍ以下の単層カーボンナノチューブであった。直径２０ｎｍ以上のナノファイバーは全く観察されなかった。しかし、収率がよくなかった。
【０１２７】
（実施例８）
（Ｃｏ＋Ｆｅ）／ＴＳ−１
〔ＴＳ−１型ゼオライトへの金属塩の担持〕
鉄アセチルアセトナート錯体（日本化学産業製）０．０２１ｇとコバルトアセチルアセトナート錯体（日本化学産業製）０．２ｇとをアセトン（ナカライテスク社製）７ｍｌに加え、超音波洗浄機で１０分間懸濁した。この懸濁液に、ＴＳ−１ゼオライト（エヌイーケムキャット製、ケイ素／チタン比５０）を２．０ｇ加え、超音波洗浄機で１０分間処理し、６０℃の恒温下でエタノールを除去して、ＴＳ−１型ゼオライト粉末に金属塩が担持された触媒を得た。
【０１２８】
〔触媒の光電子分光測定〕
上述のＴＳ−１型ゼオライトに金属塩を担持した触媒をアルゴンガス中で９００℃で３０分焼成した後、アルゴンガス中で室温まで冷却し、しかる後、一旦空気中に取り出してＸ線光電子分光法装置で触媒を測定した。測定されたコバルト２Ｐ3/2 の電子エネルギーは７８０．０ｅＶであった。また、担体表面のコバルトの原子比は１．４％、鉄の原子比は０．１４％であった。
【０１２９】
〔ナノファイバーの合成（８００℃）〕
内径３０ｍｍの縦型石英管の中央部の石英ウール上に、上記で得た金属錯体を担持したＴＳ−１型ゼオライト粉末を１．０ｇ取り、アルゴンを６０ｍｌ／分で供給した。石英管を電気炉中に設置して中心温度を８００℃に加熱した。超高純度アセチレンガス（高圧ガス工業製）を０．５ｍｌ／分で３００分間供給した後、アセチレンガスの供給をやめ、温度を室温まで冷却した。
【０１３０】
石英プレート上に堆積した反応物反応物の形状を透過型電子顕微鏡で測定したところ、外径が１５ｎｍ以下で内径が５ｎｍ程度の細い中空状ナノファイバーであった。高分解能透過型電子顕微鏡で観察したところ、ナノファイバーの壁は比較的きれいなグラファイト層で構成されており、全ての層数は２〜５層のカーボンナノチューブで、特に２層が主成分であった。直径２０ｎｍ以上のナノファイバーは全く観察されなかった。
【０１３１】
以上の結果を表１に示した。
（実施例９）
（Ｃｏ＋Ｆｅ）／ボロシリケート
〔ボロシリケート型ゼオライトへの金属塩の担持〕
酢酸第一鉄（アルドリッチ社製）０．０６４ｇと酢酸コバルト４水和物（ナカライテスク社製）０．０８８ｇとをエタノール（ナカライテスク社製）７ｍｌに加え、超音波洗浄機で１０分間懸濁した。この懸濁液に、ボロシリケートゼオライト（エヌイーケムキャット製、ケイ素／ホウ素比５０）を１．０ｇ加え、超音波洗浄機で１０分間処理し、６０℃の恒温下でエタノールを除去して、ボロシリケート型ゼオライト粉末に金属塩が担持された触媒を得た。
【０１３２】
〔触媒の光電子分光測定〕
上述のボロシリケートゼオライトに金属塩を担持した触媒をアルゴンガス中で９００℃で３０分焼成した後、アルゴンガス中で室温まで冷却した後、一旦空気中に取り出し、Ｘ線光電子分光法装置で触媒を測定した。測定されたコバルト２Ｐ3/2 の電子エネルギーが７８０．１ｅＶであった。また、担体表面のコバルトの原子比は１．４％、鉄の原子比は０．０７％であった。
【０１３３】
〔ナノファイバーの合成（８００℃）〕
内径３０ｍｍの縦型石英管の中央部の石英ウール上に、上記で得た金属錯体を担持したＴＳ−１型ゼオライト粉末を１．０ｇ取り、アルゴンを６０ｍｌ／分で供給した。石英管を電気炉中に設置して中心温度を８００℃に加熱した。エタノールをマイクロフィーダーでガスとして０．５ｍｌ／分で３００分間供給した後、エタノールの供給をやめ、温度を室温まで冷却した。
【０１３４】
石英プレート上に堆積した反応物反応物の形状を透過型電子顕微鏡で測定したところ、外径が５ｎｍ以下の細い中空状ナノファイバーであった。高分解能透過型電子顕微鏡で観察したところ、ナノファイバーの壁は比較的きれいなグラファイト層で構成されており、全ての層数は１〜５層のカーボンナノチューブであった。直径２０ｎｍ以上のナノファイバーは全く観察されなかった。
【０１３５】
以上の結果を表１に示した。
（実施例１０）
〔耐熱性ゼオライトへの金属塩の担持（高流速）〕
酢酸第一鉄（アルドリッチ社製）０．１０ｇと酢酸コバルト４水和物（ナカライテスク社製）０．０６ｇとをメタノール（ナカライテスク社製）７ｍｌに加え、超音波洗浄機で１０分間懸濁した。この懸濁液に上記ＴＳ−１の粉末１．０ｇを加え、超音波洗浄機で１０分間処理し、６０℃の恒温下でメタノールを除去 することにより、ＴＳ−１の結晶表面に金属塩を担持した触媒を得た。
【０１３６】
〔２層カーボンナノチューブの合成（８００℃）〕
内径３０ｍｍの縦型石英管の中央部に石英ウールを詰め、その上に上記で得た金属塩を担持したＴＳ−１を１．０ｇ取り、アルゴンを６００ｍｌ／分で供給した。石英管を電気炉中に設置して、中心温度を８００℃に加熱した（昇温時間約３０分）。８００℃に到達した後、超高純度アセチレンガス（高圧ガス工業製）を５ｍｌ／分で３０分間供給した後、アセチレンガスの供給をやめ、温度を室温まで冷却した。
【０１３７】
石英ウール上に堆積した反応物の一部の形状を高分解能透過型電子顕微鏡で測定したところ、内径約４ｎｍの２層カーボンナノチューブが多く生成していた。そのラマンスペクトルの結果、Ｇ／Ｄ比は２．７５、１５０〜３５０ｃｍ^-1内に多数のピークが観察された。
【０１３８】
以上の結果を表１に示した。
（比較例３）
（Ｃｏ＋Ｆｅ）／ＵＳＹ（シリカアルミナ比３９０）
〔Ｙ型ゼオライトへの金属塩の担持〕
酢酸第一鉄（アルドリッチ社製）０．０８ｇと酢酸コバルト４水和物（ナカライテスク社製）０．１１ｇとをエタノール（ナカライテスク社製）７ｍｌに加え、超音波洗浄機で１０分間懸濁した。この懸濁液に比較例１と同じＵＳＹ型ゼオライト粉末（東ソー製）を１．０ｇ加え、超音波洗浄機で１０分間処理し、６０℃の恒温下でエタノールを除去して、ＵＳＹ型ゼオライト粉末に金属塩が担持された触媒を得た。
【０１３９】
〔触媒の光電子分光測定〕
上述のＵＳＹ型ゼオライトに金属塩を担持した触媒をアルゴンガス中で９００℃で３０分焼成した後、アルゴンガス中で室温まで冷却した後、一旦空気中に取り出し、Ｘ線光電子分光法装置で触媒を測定した。測定されたコバルト２Ｐ3/2 の電子エネルギーが７８１．３ｅＶであった。Ｆｅ２Ｐ２／３電子の結合エネルギーは、７１０．９ｅＶであった。
【０１４０】
〔ナノファイバーの合成（６００℃）〕
内径３０ｍｍの石英管の中央部の石英プレート上に、上記で得た金属塩を担持したＵＳＹ型ゼオライト粉末を０．０２９ｇ取り、窒素を３０ｍｌ／分で供給した。石英管を電気炉中に設置して中心温度を６００℃に加熱した。超高純度アセチレンガス（高圧ガス工業製）を６ｍｌ／分で３０分間供給した後、アセチレンガスの供給をやめ、温度を室温まで冷却した。
【０１４１】
石英プレート上に堆積した反応物反応物の形状を日本電子データム（株）製の走査電子顕微鏡ＪＳＭ−６３０１ＮＦで測定したところ、中空状ナノファイバーの生成量は極めて少なかったが、外径が２０ｎｍ以下で内径が５ｎｍ程度の細い中空状ナノファイバーが少量観察された。高分解能透過型電子顕微鏡で観察したところ、ナノファイバーの壁は比較的きれいなグラファイト層で構成されており、ほとんどの層数は１〜２０層のカーボンナノチューブであり、特に２〜５層のカーボンナノチューブはほとんど観察されず、全体的に太めであった。また、直径２０ｎｍ以上のナノファイバーは多く観察された。
【０１４２】
以上の結果を表１に示した。
（比較例４）
（Ｃｏ＋Ｆｅ）／Ｎａ−Ｙ型
〔Ｎａ−Ｙ型ゼオライトへの金属塩の担持〕
酢酸第一鉄（アルドリッチ社製）０．０８ｇと酢酸コバルト４水和物（ナカライテスク社製）０．１１ｇとをエタノール（ナカライテスク社製）７ｍｌに加え、超音波洗浄機で１０分間懸濁した。この懸濁液にＮａ−Ｙ型ゼオライト（東ソー製シリカアルミナ比５．１）の粉末を１．０ｇずつ加え、超音波洗浄機で１０分間処理し、１２０℃の恒温下でエタノールを除去し、触媒とした。
【０１４３】
〔触媒の光電子分光測定〕
上述のＮａ−Ｙ型ゼオライトに金属塩を担持した触媒をアルゴンガス中で８００℃で３０分焼成した後、アルゴンガス中で室温まで冷却した後、一旦空気中に取り出し、Ｘ線光電子分光法装置で触媒を測定した。測定されたコバルト２Ｐ3/2 の電子の結合エネルギーが７７９．２ｅＶであった。Ｆｅ２Ｐ２／３電子の結合エネルギーは、７０９．９ｅＶであった。また、担体表面のコバルトの原子比は２．９％、鉄の原子比は０．６％であった。
【０１４４】
〔ナノファイバーの合成（８００℃）〕
内径３０ｍｍの石英管の中央部の石英プレート上に、上記触媒を０．０３ｇ取り、アルゴンを３０ｍｌ／分で供給した。各石英管を電気炉中に設置して中心温度を８００℃に加熱した。超高純度アセチレンガス（高圧ガス工業製）を６ｍｌ／分で３０分間供給した後、アセチレンガスの供給をやめ、温度を室温まで冷却した。
【０１４５】
反応管中の石英プレート上に堆積した反応物の形状を高分解能透過型電子顕微鏡で観察したところ、外径２０ｎｍ以上の大量の中空状ナノファイバーと外径２０ｎｍ以下、層数５〜２０層のカーボンナノチューブが少量観察された。得られたカーボンナノチューブのグラファイト層は欠陥が少なく、２〜５層のカーボンナノチューブはほとんど観察されず、全体的に太めであった。
【０１４６】
以上の結果を表１に示した。
【０１４７】
【表１】

【０１４８】
【発明の効果】
本発明の製造法によると、Ｘ線光電子分光法で測定したコバルト２Ｐ3/2 の電子の結合エネルギーが７７９．３ｅＶ以上で、７８１．０ｅＶ以下であるコバルト微粒子を担体に担持させた触媒、Ｘ線光電子分光法で１０ｋＶ、１８ｍＡで測定した担体表面のコバルト原子比が０．１から１．５％であるコバルト微粒子を担体に担持した触媒、Ｘ線光電子分光法で１０ｋＶ、１８ｍＡで測定した担体表面のコバルトとチタンの原子比が０．３以上かつ２．０以下であるコバルト微粒子をチタンを含有する担体に担持した触媒、或いは担体表面のコバルトと第２金属成分との重量比（（コバルトの重量）／（第２金属成分の重量））が２．５以上であるコバルト微粒子を担体に担持した触媒を用い、その触媒と炭素含有化合物とを温度５００〜１２００℃で接触させることにより、触媒となるコバルト微粒子の電子状態を制御することでグラファイト層の欠陥が少なく、かつ太さと層数を制御した太さの細い良質な中空状ナノファイバーを効率良く得ることができる。
【０１４９】
また、グラファイト層の欠陥が少ないカーボンナノチューブを直接生成するため、後処理でグラファイト化するための費用がかかる高温の熱処理を不要にすることが可能になり、また太さを外径３０ｎｍ以下、内径０．３ｎｍ以上１５ｎｍ以下の細いカーボンナノチューブと定義される領域の良質の中空状ナノファイバーを製造することができる。
【図面の簡単な説明】
【図１】チタノシリケート上に担持されたコバルト、鉄金属微粒子の透過型電子顕微鏡写真の模式図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing hollow nanofibers, and more particularly, to a method for producing hollow nanofibers in a region defined as carbon nanotubes, in which the number and diameter of layers can be controlled and the number of defects in a graphite layer is small. .
[0002]
[Prior art]
The carbon nanotube has a shape in which one surface of graphite is wound into a cylindrical shape. A single-walled carbon nanotube is a single-walled carbon nanotube, and a multi-walled carbon nanotube is a single-walled carbon nanotube. Among multi-walled carbon nanotubes, those with two layers are called double-walled carbon nanotubes. These carbon nanotubes are highly expected as composite materials because they have high mechanical strength and high conductivity, as adsorbent materials because they have nano-sized spaces, and as electron sources for field emission due to their extremely thin tips. Has been. In any application, the thinner nanotube is advantageous, and the smaller the defects in the graphite layer, the better the characteristics.
[0003]
As a method for producing such a carbon nanotube, a method using an arc discharge method and a chemical vapor deposition method (sometimes called a chemical vapor deposition method, hereinafter referred to as a CVD method) is known.
[0004]
The former arc discharge method is to produce carbon nanotubes by carrying out high voltage and high current arc discharge using a carbon rod as an electrode in a vacuum or in an inert gas atmosphere. It can be obtained together with graphite, carbon nanoparticles, etc. In the latter CVD method, carbon nanotubes are produced by reacting a raw material gas at several hundred degrees Celsius in the presence of fine metal particles such as iron and nickel. As the raw material gas at this time, benzene, toluene, orthomethyl diallyl ketone, acetylene, ethylene, methane, or the like is used.
[0005]
The carbon nanotubes produced by the arc discharge method can obtain nanotubes with few defects in the graphite layer, but have the disadvantage that there are many impurities such as amorphous carbon. In addition, the carbon nanotube produced by the CVD method has an advantage that the carbon nanotube can be produced at a low cost with few impurities. However, since the produced carbon nanotube has many defects in the graphite layer, the post treatment is performed at 2900 ° C. Unless the heat treatment is performed to the extent, there is a disadvantage that a graphite layer with few defects is not formed.
[0006]
As a method for solving such a problem, Shinohara et al. Can produce multi-walled carbon nanotubes of about 10 layers with few defects by using a catalyst in which cobalt and vanadium are supported on a powdery Y-type zeolite. (Non-Patent Document 1).
[0007]
Also, JB Nagy et al. Used two or more layers of multi-layer carbon with few defects by using a powdery Y-type zeolite or a catalyst in which cobalt and iron, cobalt and vanadium, or cobalt and molybdenum are supported on alumina. It has been reported that nanotubes can be produced (Non-patent Document 2).
[0008]
Thus, according to the production method using a catalyst in which a metal is supported on zeolite, multi-walled carbon nanotubes with few defects in the graphite layer can be produced at low cost. However, there has been no example of controlling the physical properties of the metal catalyst that governs the catalytic reaction, and as a result, the number and the diameter of the carbon nanotubes to be produced have not been controlled. In particular, a method for synthesizing single-walled carbon nanotubes and double-walled carbon nanotubes with high selectivity and yield has not been found. This is because the Y-type zeolite is highly hydrophilic and has many ion exchange points, so that the metal salt aqueous solution is easily adsorbed in the zeolite pores when the catalyst metal is supported, and the metal has priority over the ion exchange points in the zeolite pores. It is thought that it was introduced. As a result, it is estimated that the amount of metal supported on the outer surface of the zeolite used for the synthesis of carbon nanotubes was small.
[0009]
[Non-Patent Document 1]
Chemical Physics Letters 303 (1999), 117-124
[Non-Patent Document 2]
Chemical Physics Letters 317 (2000), 7-76
[0010]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for producing hollow nanofibers in which the number of layers and diameter can be controlled and carbon nanotubes with few defects in a graphite layer can be obtained in a production method using a metal catalyst. is there.
[0011]
[Means for Solving the Problems]
The method for producing hollow nanofibers according to the present invention that achieves the above object comprises the steps of: Cobalt fine particles having an electron binding energy of cobalt 2P3 / 2 measured by X-ray photoelectron spectroscopy of 779.3 eV or more and 781.0 eV or less. As the second metal component other than cobalt At least one selected from vanadium, molybdenum, manganese, iron, nickel, palladium Using a catalyst in which a group 3-12 metal is supported on a support and contacting with a carbon-containing material at 500 to 1200 ° C., to produce hollow nanofibers mainly composed of 1 to 5 carbon nanotubes It is characterized by.
[0015]
Thus, when producing hollow nanofibers, the electronic state of the cobalt fine particles used as a catalyst, the cobalt atomic ratio on the support surface, the atomic ratio of cobalt and titanium on the support surface, or the cobalt and second metal component on the support surface By controlling the weight ratio, hollow nanofibers with few defects in the graphite layer, little generation of impurities such as amorphous carbon, and controlled thickness and number of layers can be obtained.
[0016]
In addition, when the support is made of zeolite, the electronic state of the supported metal catalyst changes, so that the physical properties of the produced hollow nanofiber can be controlled.
[0017]
Further, since carbon nanotubes with few defects in the graphite layer are directly generated, a heat treatment (temperature of 2900 ° C. or higher), which is expensive for graphitization in post-treatment, is unnecessary. In addition, it is possible to produce high-quality hollow nanofibers in a region defined as carbon nanotubes having a thin outer diameter of 50 nm or less and an inner diameter of 0.3 nm to 15 nm.
[0018]
When aluminosilicate is used as a carrier for a metal catalyst, especially in the case of USY type, a single-walled carbon nanotube bundle, a single-walled carbon nanotube with a part of two or more layers, or a single-walled carbon nanotube with a very thin inner diameter Can be obtained. When metallosilicate zeolite is used as a carrier for a metal catalyst, particularly in the case of titanosilicate zeolite, a bundle of two-walled carbon nanotubes, a double-walled carbon nanotube with a part of three or more layers, However, a very thin double-walled carbon nanotube can be obtained.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
In the method for producing hollow nanofibers of the present invention, cobalt fine particles whose electron binding energy of cobalt 2P3 / 2 measured by X-ray photoelectron spectroscopy is 779.3 eV or more and 781.0 eV or less are supported on a carrier. A catalyst is used. This catalyst is used in the form of a catalyst composition supported on a support, and it is essential to contain cobalt (Co) as a metal type. Cobalt is effective for synthesizing thin hollow nanofibers, and cobalt in a state where electrons are given from a carrier is particularly preferable.
[0020]
X-ray photoelectron spectroscopy is effective as a method for determining whether cobalt is provided with electrons from the carrier. The X-ray photoelectron spectroscopy referred to here is one type of electron spectroscopy. Electron spectroscopy refers to a substance by applying an electromagnetic wave such as light or X-rays, charged particles such as electrons or ions, or excited electrons to the substance, and measuring the momentum distribution or energy distribution of the electron generated at that time. It is a method of measuring the physical state of Among photoelectron spectroscopy using light as incident rays, X-ray photoelectron spectroscopy (XPS, ESCA) by X-ray irradiation is particularly effective for this application.
[0021]
The method for measuring the electronic state of cobalt is shown below.
Cobalt is supported on the carrier, calcined at 900 ° C. for 30 minutes in argon gas, cooled to room temperature in argon gas, and then exposed to the atmosphere, and X-ray photoelectron spectroscopy is measured. In this method, since the catalyst is exposed to the air after cooling, the catalyst metal that is fine particles is oxidized, which is different from the catalyst state during the actual reaction, but the transfer of electrons from the support to the metal should be evaluated. Can do.
[0022]
The sample is placed in an ultra-high vacuum, the sample surface is irradiated with condensed soft X-rays (150 to 1000 μm), and photoelectrons emitted from the vicinity of the surface (˜several nm) are detected by an analyzer. The type of element present on the surface is identified from the binding energy value of the bound electrons, and the valence and bonding state are measured from the peak energy shift. It is presumed that electrons are attracted from cobalt to the carrier as the electron binding energy is larger, and conversely, electrons are donated from the carrier to cobalt as the electron binding energy is smaller. By controlling the binding energy of electrons around cobalt, the physical properties of the generated nanofiber can be controlled.
[0023]
By using a catalyst containing cobalt having an electron binding energy of cobalt 2P3 / 2 measured by the above method of 779.3 eV or more and 781.0 eV or less, thin hollow nanofibers, particularly carbon nanotubes (single-wall or 2 to 5 layers of carbon nanotubes) are easy to manufacture. More preferably, in the case of cobalt having an electron binding energy of 779.5 eV or more and 780.5 eV or less, 2 to 5 layers of carbon nanotubes are easily obtained. If the binding energy of electrons of cobalt 2P3 / 2 is less than 779.3 eV or more than 781.0 eV, the yield of hollow nanofibers containing carbon nanotubes and the physical properties of the product are significantly reduced.
[0024]
The metal catalyst used in the present invention has a cobalt atomic ratio of 0.1 to 1.5% on the surface of the carrier when the amount of cobalt supported on the carrier is measured by X-ray photoelectron spectroscopy at 10 kV and 18 mA. It may be.
[0025]
Regarding the measurement of the atomic ratio of cobalt on the surface of the support, the sample preparation method and the measurement method are the same as the above-described electronic state measurement method. Using the area of the peak obtained as a result of the measurement, the elements near the sample surface can be quantified. At this time, the information obtained from the vicinity of the sample surface differs depending on the output of the X-ray, and the higher the output, the more the information inside the sample cannot be ignored. Therefore, in the present invention, the X-ray output is defined as 10 kV and 18 mA. When a sample is measured under these measurement conditions, a hollow nanofiber with particularly good quality can be obtained when the cobalt atomic ratio on the support surface is 0.1 to 1.5%.
[0026]
If the atomic ratio of cobalt is less than 0.1%, the amount of catalytic metal is too small, and the amount of hollow nanofibers produced is small. When the atomic ratio of cobalt exceeds 1.5%, the aggregation of cobalt particles proceeds as described later. Moreover, since there is too much cobalt, the contribution of the electron from the support | carrier with respect to each cobalt atom reduces, and it becomes difficult to control the physical property of the hollow nanofiber to produce | generate. As a result, carbon nanotubes and hollow nanofibers having a large diameter are preferentially produced, and production of thin carbon nanotubes typified by 2 to 5 layers is suppressed.
[0027]
Further, as the metal catalyst used in the present invention, cobalt fine particles having an atomic ratio of cobalt to titanium on the support surface measured by X-ray photoelectron spectroscopy at 10 kV and 18 mA of 0.3 to 2.0 and titanium are used. You may use the catalyst carry | supported by the support | carrier to contain. The following two requirements are important when using this catalyst.
[0028]
(1) The carrier contains titanium.
(2) The atomic ratio of cobalt to titanium on the surface of the carrier measured by X-ray photoelectron spectroscopy at 10 kV and 18 mA is 0.3 or more and 2.0 or less.
[0029]
Examples of the carrier containing titanium include metallic titanium, titanium oxide, titanate, a mixture of titanium oxide and other oxides, a composite oxide containing titanium, and a zeolite containing titanium in the skeleton. In order that the atomic ratio of cobalt and titanium on the surface of the carrier measured by X-ray photoelectron spectroscopy at 10 kV and 18 mA is 0.3 or more and 2.0 or less, it is preferable that the titanium concentration in the carrier is too high. Absent. From this point, a mixture of titanium oxide and another oxide, a composite oxide containing titanium, and a zeolite containing titanium in the skeleton are preferably used. Here, since cobalt is used as a catalyst for producing hollow nanofibers, if the atomic ratio is too low, the yield of hollow nanofibers is not preferable. Titanium serves as a co-catalyst for cobalt. If the atomic ratio of titanium is too high, the catalytic action of titanium becomes too strong, which is not preferable. From the above, the atomic ratio of cobalt to titanium is preferably 0.3 or more and 2.0 or less, and particularly preferably 0.5 or more and 1.5 or less.
[0030]
In addition, as the metal catalyst used in the present invention, the weight ratio of the support surface to the second metal component other than cobalt and cobalt ((weight of cobalt) / (weight of second component metal)) is 2.5 or more. Alternatively, cobalt fine particles having an atomic ratio ((cobalt atom number) / (secondary component metal atom number)) of 5 to 15 may be supported on a carrier. This is because, when cobalt functions as a synthesis catalyst for hollow nanofibers, the physical properties of the hollow nanofibers can be easily controlled. When the abundance ratio of the second metal component increases, the second metal component becomes hollow nanofibers. This is because, as a result, it becomes difficult to control the physical properties of the hollow nanofiber.
[0031]
The second metal component other than cobalt means a Group 3-12 metal having the largest abundance ratio other than the carrier and cobalt as a result of elemental analysis of the carrier surface by ESCA or the like. The second metal component is considered to function as a co-catalyst for the cobalt catalyst or to form an alloy with cobalt to control the particle size and electronic state of the metal catalyst. This second metal component as, Group 3-12 metals home Vanadium, molybdenum, manganese, iron, nickel, palladium At least one kind of Is used.
[0032]
As the ratio of (cobalt) / (second component metal) is higher, the catalytic reaction due to cobalt becomes dominant, and high-performance hollow nanofibers can be synthesized. Therefore, the larger the ratio of (cobalt) / (second component metal) is, the better the weight ratio is 2.5 or more, preferably 3.0 or more, more preferably 5.0 or more. In the case of 5.0 or more, the effect is particularly high, and the generation of nanofibers having a diameter of 20 nm or more is extremely suppressed. Further, when the atomic ratio is 5 to 15, particularly in the case of 6 to 12, the effect is particularly high, and the generation of nanofibers having a diameter of 20 nm or more is extremely suppressed. This is particularly remarkable when metallosilicate is used as a carrier. The weight ratio of the carrier surface can be measured by using X-ray photoelectron spectroscopy in which the X-ray output is defined as 10 kV and 18 mA.
[0033]
Further, as the metal species on the surface of the carrier, metal species other than cobalt and the second metal component may be present, and in particular, three or more metal species are used for the purpose of controlling the physical properties of the produced hollow nanofibers. It may be.
[0034]
In the above-described catalyst metal used in the present invention, it is preferable that 80% or more of the metal fine particles supported on the carrier have a size of 0.5 to 10 nm. Since it is considered that the particle size of the metal fine particles affects the diameter of the hollow nanofibers to be produced, metal fine particles having a small particle size are required when aiming to produce thin hollow nanofibers. Therefore, it is preferable that 80% or more of the number of metal fine particles present on the carrier has a size of 0.5 to 10 nm. By using the metal catalyst loading method described above, the diameter of such metal fine particles can be achieved.
[0035]
The method for supporting a metal containing cobalt on the support is not particularly limited. For example, a carrier is impregnated in a non-aqueous solution (for example, ethanol solution) or an aqueous solution in which a metal salt such as cobalt is dissolved, thoroughly dispersed and mixed, and then dried, in nitrogen, hydrogen, an inert gas, or a mixed gas thereof The metal can be supported on the carrier by heating at a high temperature (300 to 900 ° C.) (impregnation method).
[0036]
In particular, when the support is a porous material, the adsorption is performed by reducing the amount of the metal salt solution containing cobalt as much as possible, allowing the aqueous solution to be adsorbed in the pores of the support, and removing the excess aqueous solution by filtration and drying. The adsorption method is most preferred. The reason is that when the metal is supported on the pores of the porous material by the equilibrium adsorption method, the diameter of the relatively supported metal becomes uniform and the diameter of the generated hollow nanofiber becomes uniform. In addition, since the metal is present near the pore entrance of the carrier and hardly aggregates even at high temperatures, the equilibrium adsorption method is an effective metal loading method particularly when a carrier having heat resistance is used.
[0037]
Alternatively, an aqueous solution of a metal salt containing cobalt is impregnated with a carrier, the metal salt is supported by an impregnation method or an equilibrium adsorption method, and then dried, and then heated at a high temperature (300 to 900 in nitrogen, hydrogen, an inert gas, or a mixed gas thereof. The metal can also be supported on the crystal surface of the carrier by heating at a temperature of ° C. Of course, the metal can be supported on the carrier by supporting the metal salt, calcining it in air to form a metal oxide, and then reducing it using hydrogen.
[0038]
Although the cobalt raw material used here is not specifically limited, from the ease of preparation of the metal salt solution used by the above-mentioned method and price, inorganic acid salts, such as cobalt nitrate, cobalt acetate, and cobalt sulfate, ethylenediaminetetraacetic acid cobalt complex, the following Cobalt acetylacetonate complex analogues represented by Chemical Formula 1 (In Chemical Formula 1, R is methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, t-butyl group) And at least one selected from phenyl groups), halides such as cobalt chloride, cobalt bromide and cobalt fluoride, and organic acid salts such as cobalt oxalate and cobalt stearate are preferably used. .
[0039]
[Chemical 1]

The cobalt carrier needs to be able to carry highly dispersed cobalt metal fine particles, and as described above, it is necessary to be able to give electrons to the cobalt metal fine particles. Although it will not specifically limit if it is the support | carrier which satisfy | fills this condition, An inorganic oxide, a zeolite, a silicon | silicone, a graphite, a carbon nanotube etc. are used preferably. In particular, when the electron withdrawing property of the carrier is high, electrons move from the catalyst metal to the carrier, and the electron density on the catalyst metal is lowered. As a result, the binding energy of electrons on cobalt is higher. On the other hand, when the electron donating property of the carrier is high, electrons move from the carrier to the catalyst metal, and the electron density on the catalyst metal becomes high. As a result, the binding energy of electrons on cobalt is lowered. Therefore, a carrier having an appropriate electron withdrawing / donating property is preferable. Particularly, when a zeolite is used, a zeolite having a low polarity such as a USY type or a titanosilicate than a zeolite having a small silica alumina ratio and a high polarity. Is preferred.
[0040]
In the present invention, the temperature at which the catalyst and the carbon-containing compound are brought into contact with each other in order to produce hollow nanofibers is 500 to 1200 ° C, preferably 600 ° C to 1000 ° C. When the temperature is lower than 500 ° C., the yield of nanofibers is deteriorated, and when the temperature is higher than 1200 ° C., there are restrictions on the material of the reactor to be used, and the joining of the nanofibers starts. It becomes difficult to control the shape. In particular, thin nanofibers (thin carbon nanotubes such as single-walled carbon nanotubes and 2- to 5-walled carbon nanotubes) can be obtained by contacting them at a relatively high temperature. Although it depends on the carbon source, the contact is preferably performed at 750 ° C. or higher.
[0041]
There is no particular limitation on the method of contacting the catalyst and the carbon-containing compound. For example, this can be achieved by placing the above-described catalyst in a heat-resistant reaction tube made of quartz, alumina, or the like installed in a tubular furnace and flowing a carbon-containing compound gas under heating. The contact method of the catalyst and the carbon-containing compound may be a method of spraying the catalyst or a method of bringing the catalyst into contact with stirring in addition to the above method. The optimum contact time (reaction time) varies depending on the target nanofiber, hydrocarbon gas flow rate, and hydrocarbon concentration, but is generally from several minutes to several hours. The shorter the reaction time, the finer nanofibers can be obtained, but the yield decreases. In addition, the yield increases as the reaction time increases, but the nanofibers tend to be thick.
[0042]
In the present invention, the carbon-containing compound is not particularly limited, but preferably hydrocarbon or carbon monoxide is used.
[0043]
The hydrocarbon may be aromatic or non-aromatic. As the aromatic hydrocarbon, for example, benzene, toluene, xylene, cumene, ethylbenzene, diethylbenzene, trimethylbenzene, naphthalene, phenanthrene, anthracene, or a mixture thereof can be used. As non-aromatic hydrocarbons, for example, methane, ethane, propane, butane, pentane, hexane, heptane, ethylene, propylene or acetylene, or a mixture thereof can be used. Hydrocarbons also contain oxygen, for example alcohols such as methanol or ethanol, propanol, butanol, ketones such as acetone, and aldehydes such as formaldehyde or acetaldehyde, carboxylic acids such as trioxane, dioxane, dimethyl ether, diethyl ether. It may be an acid, an ester such as ethyl acetate, or a mixture thereof. Among these, non-aromatic hydrocarbons are the most preferable carbon sources because they can obtain high-quality hollow nanofibers.
[0044]
As the carrier for supporting the metal catalyst, inorganic oxides, silicon, graphite, carbon nanotubes and the like are preferably used. In particular, zeolite is preferable. This is because zeolite can carry cobalt metal fine particles in a highly dispersed manner and can give electrons to the cobalt metal fine particles as described above.
[0045]
In the present invention, the zeolite is composed of a crystalline inorganic oxide having a pore size of molecular size. Here, the molecular size is a size range of molecules existing in the world, and generally means a range of about 0.2 nm to 2 nm. More specifically, a crystalline microporous material composed of crystalline silicate, crystalline aluminosilicate, crystalline metallosilicate, crystalline metalloaluminosilicate, crystalline aluminophosphate, crystalline metalloaluminophosphate, or the like. That is.
[0046]
Crystalline silicate, crystalline aluminosilicate, crystalline metallosilicate, crystalline metalloaluminosilicate, crystalline aluminophosphate, crystalline metalloaluminophosphate are not particularly limited, but for example, Atlas of Zeolite Structure Types ( Meyer, Olson, Baerochar, Zeolites, 17 (1/2), 1996) (Atlas of Zeolite Structure types (WM Meier, DH Olson, Ch. Baerlocher, Zeolites, 17 (1/2), 1996)) A crystalline inorganic porous material having a structure of Further, the zeolite used in the present invention is not limited to those described in this document, and includes zeolites having novel structures synthesized one after another in recent years. Preferred structures are FAU type, MFI type, MOR type, and BEA type, which are easily available, but are not limited thereto.
[0047]
Moreover, as the zeolite, an aluminosilicate zeolite, a metallosilicate zeolite, or a metalloaluminosilicate containing a heteroelement other than silicon in the structure skeleton so as to have a silicon / heteroatom molar ratio of 25 or more can be preferably used. . A zeolite whose hetero atom is aluminum is an aluminosilicate, and a silicon / aluminum molar ratio of 25 or more belongs to high silica zeolite. The crystal structure is not particularly limited as long as such a silica-alumina ratio can be obtained. For example, MFI type, MOR type, FAU type, and CIT-5 type are preferably used. In particular, USY type zeolite which is a high heat resistant FAU type zeolite is preferable.
[0048]
A zeolite containing a hetero element other than aluminum or silicon is called a metallosilicate. The type of the hetero element is not particularly limited, but, for example, boron, gallium, iron, cobalt, titanium, germanium, zirconium, vanadium, chromium, manganese, and zinc are preferably used. The type of metallosilicate zeolite is not particularly limited, but higher heat resistance is preferred. It is preferable to have heat resistance with respect to a temperature equal to or higher than the reaction temperature.
[0049]
Zeolite has a heat resistance of 800 ° C. means that when it is calcined at 800 ° C. for 30 minutes in an atmosphere of nitrogen or dry air, when the powder X-ray diffraction (XRD) is performed at room temperature before and after the calcining, It means that both the peak position and the peak height ratio have the same peak. Preferably, when the powder is subjected to powder X-ray diffraction after heating at 800 ° C., it not only has the same peak as that of the zeolite before calcination but also has no substantial structural change. The crystal structure of the metallosilicate is not particularly limited, but the MFI type is preferably used because the metallosilicate structure is stable.
[0050]
As a method of depositing metal catalyst fine particles on the surface of the zeolite carrier, a method of synthesizing metallosilicates such as cobalt silicate and iron silicate, firing this at a high temperature, and precipitating cobalt and iron in the framework on the zeolite surface to form fine particles Can also be used. By using this method, generation of metal particles having a size of several tens of nanometers or more can be suppressed, so that generation of multi-walled carbon nanotubes having six or more layers or nanofibers having an outer diameter of 50 nm or more can be suppressed. . As this method, not only zeolite having one kind of heteroatom in the skeleton such as cobalt silicate and iron silicate but also zeolite having two or more kinds of heteroatoms in the skeleton such as iron, cobalt and titanium should be preferably used. Can do.
[0051]
In the present invention, the carrier preferably contains a heteroelement other than silicon in the structural skeleton so that the silicon / heteroatom molar ratio is 25 or more. When the heteroatom is aluminum or a trivalent element, if the silicon / heteroatom ratio is less than 25, the number of ion exchange points for compensating the charge balance in the skeleton increases, and the heat resistance decreases. As a result, the synthesis temperature of the hollow nanofibers is lowered, and the degree of graphitization of the produced hollow nanofibers is lowered.
[0052]
Zeolite having a high silicon / heteroatom ratio (100 or more) is preferable because it has higher heat resistance and can increase the synthesis temperature of hollow nanofibers. In addition, zeolite having a low silicon / heteroatom ratio (25 to 100) has a large influence on the outer surface metal of the heteroatom in the skeleton, which is preferable in terms of easy control of the catalytic reaction in the synthesis of hollow nanofibers. . Further, when the hetero element is a tetravalent element, it is extremely difficult to synthesize a metallosilicate having a silicon / hetero atom ratio of less than 25, and since the stability is low, the silicon / hetero atom ratio is preferably 25 or more. . The heteroatom is preferably in the skeleton, but may escape from the skeleton during firing or the like. Even if it is missing, it is considered that it is sufficiently effective in terms of interaction with the metal.
[0053]
The atomic ratio of Si / heteroatom in the zeolite framework can be measured by 29Si MAS NMR. Moreover, when measuring also including the hetero atom which escaped from frame | skeleton, it can measure by energy dispersive X-ray-spectroscopy (EDX).
[0054]
In order to create the electronic state of cobalt as described above, the type of zeolite that is the carrier is important. Zeolite having a transition metal such as titanium in the structural skeleton can particularly easily make such a state. The reason for this can be presumed that the transition metal has an electron in the d orbital, and that the electron gives an electron to the metal species on the zeolite.
[0055]
As a method for producing a zeolite substantially free of trivalent components such as aluminum by post-treatment, crystalline aluminosilicate containing aluminum or the like is produced in advance, and the method of Kiel (Journal of Physical Chemistry, 71, 4155, (1967)) or the method of Skeel et al. (6th International Zeolite Society Preliminary Proceedings, page 87 (1984)) to improve the heat resistance by dealuminating to high silica zeolite. There is also a method. Usually, however, the zeolite undergoes a structural change during calcination as it is. This is because the location where aluminum is removed becomes a structural defect. This structural defect causes a structural change during firing.
[0056]
In the present invention, the zeolite used for the support of the metal catalyst includes an aluminosilicate containing aluminum in the structure skeleton, a metallosilicate containing a heteroelement other than aluminum or silicon, and a metalloaluminosilicate containing both aluminum and a heteroatom. Can be used. According to the results of intensive studies by the present inventors, the affinity between the catalyst metal and the support is important for producing high-quality carbon nanotubes and for controlling the number and thickness of the carbon nanotubes. It was found that this is a significant factor. In particular, it has been found that by using at least one selected from titanosilicate, cobalt silicate, and borosilicate as a carrier, it becomes easy to produce thin hollow nanofibers.
[0057]
The size of the zeolite crystals as described above is not particularly limited. Generally, it is several tens of nm to several tens of μm. Smaller crystals are preferable because the outer surface area is larger and the yield of carbon nanotubes can be increased. However, even if it is too small, agglomeration is rapid and the substantial outer surface area is reduced, so that the size is preferably a crystal of 0.1 to 10 μm.
[0058]
In the present invention, a carbon-containing compound is used as a raw material, and details thereof are as described above. However, a diluent gas can be preferably used in addition to the carbon-containing compound. The diluent gas is not particularly limited, but a gas other than oxygen gas is preferably used. Oxygen is not normally used because it may explode, but it can be outside the explosive range. Nitrogen, argon, hydrogen, helium and the like are preferably used.
[0059]
These gases act as a control of the concentration of the carbon-containing compound gas and as a carrier gas. Of these, hydrogen is preferable because it is particularly effective for activating the catalytic metal. A gas having a high molecular weight such as argon is preferable because of its great annealing effect. When the concentration of the vapor of the carbon-containing compound in the carrier gas is increased, the yield is improved, but thick carbon nanotubes tend to be formed. Further, when the concentration of the vapor of the carbon-containing compound in the carrier gas is lowered, fine carbon nanotubes are formed, but the yield tends to be lowered.
[0060]
If the hollow nanofiber which has produced | generated carbon as a main component is hollow, there will be no restriction | limiting in particular. It can be confirmed with a transmission electron microscope that the nanofiber is hollow. The hollow nanofibers obtained from the present invention can be made into ultrafine hollow nanofibers having an outer diameter of 50 nm or less and an inner diameter of 0.3 nm to 15 nm. In particular, the walls of hollow nanofibers can be formed with a graphite layer with few defects. Such a graphite layer having few defects can be confirmed by a high-resolution transmission electron microscope.
[0061]
The ultrafine hollow nanofiber as described above is generally defined as a carbon nanotube. Both multi-walled carbon nanotubes and single-walled carbon nanotubes are included in hollow nanofibers mainly composed of carbon.
[0062]
Moreover, according to the manufacturing method of this invention, the hollow nanofiber which satisfy | fills all the requirements of following (1)-(3) can be obtained.
[0063]
(1) A double-walled carbon nanotube is observed with a high-resolution transmission electron microscope.
(2) 150 to 350 cm by resonance Raman scattering measurement ^-1 A peak is observed in the region of.
(3) 1560-1600 cm by resonance Raman scattering measurement ^-1 The maximum peak intensity within the range of G, 1310 to 1350 cm ^-1 When the maximum peak intensity within the range is D, the G / D ratio is 1.0 or more.
[0064]
Although the observation method of the double-walled carbon nanotube by the high-resolution transmission electron microscope here is not particularly limited, for example, a sample containing hollow nanofibers is added to a highly volatile solvent such as ethanol, The method of observing with a high-resolution transmission electron microscope after the hollow nanofibers are dispersed in the solvent, after dropping several drops of the solvent containing the hollow nanofibers on the microgrid and volatilizing the solvent is preferably used. It is done.
[0065]
In order to observe the double-walled carbon nanotube, a method of increasing the magnification to 500,000 times or more, preferably 1,000,000 times or more is used. A double-walled carbon nanotube is observed by two graphene sheets constituting the wall of the observed carbon nanotube. In addition, a single-walled carbon nanotube having a partially double-walled wall or a multilayered carbon nanotube having a partially double-walled wall is not called a double-walled carbon nanotube. If the area where two graphene sheets constituting the wall of the carbon nanotube are observed is not continuous for at least 30 nm, it is not called a double-walled carbon nanotube. The longer the area where two graphene sheets are observed, the more preferable it is because it can be said to be a homogeneous double-walled carbon nanotube.
[0066]
Also, by resonance Raman scattering measurement, 150-350 cm ^-1 That the peak is observed in the region of R means that RBM (Radial Breathing Mode) is observed. RBM is a peak due to stretching vibration of thin carbon nanotubes, and suggests that carbon nanotubes having a diameter of 0.7 to 1.6 nm exist.
[0067]
Also, by resonance Raman scattering measurement, 1560-1600 cm ^-1 The maximum peak intensity within the range of G, 1310 to 1350 cm ^-1 When the maximum peak intensity in the range is D, the G / D ratio being 1.0 or more means that the resulting hollow nanofibers have a high degree of graphitization. For resonance Raman scattering measurement, 1560-1600 cm ^-1 The nearby structure is a G-band, and it is also caused by impurities amorphous and carbon nanotube defects. ^-1 A nearby peak called D-band is observed. The Raman intensity reaches about 1000 times that of graphite, and the resonance effect is dominant.
[0068]
Carbon nanotubes have different electronic structures depending on their chirality and diameter. Among them, resonance occurs when the excitation light coincides with Eg of the carbon nanotube, and a Raman spectrum appears. Therefore, the spectrum changes one after another as the excitation light wavelength is changed. Since the G-band of the carbon nanotube is emphasized by the resonance effect, the strength varies greatly depending on the purity of the sample. Meanwhile, 1330cm ^-1 The nearby broad D-band is greatly contributed by impurities, which does not receive strong emphasis due to the resonance effect, so it is possible to estimate the purity of the nanotube sample by taking the intensity ratio of G-band and D-band. It becomes. By using the production method according to the present invention, high-purity hollow nanofibers can be produced, and as a result, the G / D ratio is 1.0 or more.
[0069]
According to the present invention, it is easy to obtain hollow nanofibers whose main component is composed of 1 to 5 carbon nanotubes, and it is often obtained in a bundle shape (bundle shape). When selectively synthesizing one- to five-walled carbon nanotubes, USY-type zeolite or titanosilicate can be preferably used for the zeolite carrier.
[0070]
Moreover, according to the present invention, hollow nanofibers whose main component is a two-layer to five-wall carbon nanotube can be easily obtained, and in particular, the double-walled carbon nanotube can be obtained in a bundle shape (bundle shape). In the case of selectively synthesizing two- to five-walled carbon nanotubes, titanosilicate and cobalt silicate can be preferably used for the zeolite carrier.
[0071]
According to the production method of the present invention, it is easy to control the carbon nanotubes by controlling the catalyst preparation method. One of the two-walled carbon nanotubes is characterized in that the average inner diameter can be larger than about 2 nm. In general, a double-walled carbon nanotube with a large inner diameter is relatively distorted and often does not have a uniform thickness. However, according to the two- to five-walled carbon nanotube produced by the production method of the present invention, the thickness is uniform. Moreover, it has a feature that it does not contain many catalytic metal particles.
[0072]
In the production method of the present invention, it is possible to selectively obtain 2- to 5-walled carbon nanotubes having a relatively large inner diameter of 5 to 15 nm. The hollow part of carbon nanotubes can take in various materials including metals, but 2- to 5-walled carbon nanotubes with large inner diameters only increase the types of materials that can be taken in the future due to the size of the inner volume. In addition, there is a possibility that a molecular sieving effect can be imparted.
[0073]
Furthermore, if reaction conditions and catalyst pretreatment conditions are selected, 2- to 5-walled carbon nanotubes having an inner diameter of 1 nm or less, which has never been obtained, can be obtained. This is because the metal catalyst is nested and supported in fine pores peculiar to zeolite of 1 nm or less, and is obtained only by using zeolite as a support. It is possible to obtain 2- to 5-walled carbon nanotubes having an inner diameter of 0.4 to 1.0 nm, particularly 0.6 to 0.9 nm, which is close to the pore inlet diameter of zeolite. Nanotubes obtained by introducing fullerene into single-walled carbon nanotubes and then heating them are two-walled nanotubes, but the two-layer portions are only very short (about 10 nm: Chemical Physics Letters, 337 (2001). 48-54). Thus, the short carbon nanotube of a two-layer part is not called a double-walled carbon nanotube in this invention.
[0074]
The double-walled carbon nanotubes synthesized in the present invention can be obtained with an inner diameter of 1 nm or less and a length of 15 nm or more. The length can be 20 nm or more, and particularly preferably 30 nm or more. In the production method of the present invention, a bundle of thin double-walled carbon nanotubes having an inner diameter of 1 nm or less, which has never been seen before, can be obtained.
[0075]
According to the present invention, it is possible to selectively synthesize double-walled carbon nanotubes. In addition, since it is difficult to obtain a double-walled carbon nanotube having a purity of 100% and it is difficult to identify it, the double-walled carbon nanotube referred to here is a magnification of 200,000 times or more with a transmission electron microscope. If the double-walled carbon nanotube is 25% or more in the field of view of the electron microscope when viewed, it can be said to be a double-walled carbon nanotube. The carrier is at least one selected from titanosilicate zeolite, cobalt silicate zeolite, and borosilicate zeolite, and the cobalt raw material is at least one selected from cobalt acetate, nitrate, and complex at 700 ° C. By contacting with a hydrocarbon gas under the above reaction conditions, a double-walled carbon nanotube can be selectively synthesized particularly well.
[0076]
EXAMPLES Hereinafter, the present invention will be specifically described by way of examples. However, the following examples are given for illustrative purposes and should not be used in any way as a limited interpretation of the present invention. .
[0077]
【Example】
Example 1
(Co + Fe) / Silicalite
[Synthesis of silicalite]
To 18.9 g piperazine hexahydrate (Aldrich) and 5.2 g tetrapropylammonium bromide (Aldrich), 164 g of distilled water was added and stirred. Stir while dissolving until heated. A further 11.7 g of fumed silica (Aldrich) was added thereto and heated to 80 ° C. to obtain a transparent aqueous solution. This was placed in a polytetrafluoroethylene line autoclave and heated at 150 ° C. for 5 days. Thereafter, the mixture was cooled, filtered, washed with water, and dried, followed by firing at 550 ° C. in the air.
[0078]
When X-ray diffraction (XRD) of the obtained powder was measured, it was found to be silicalite-1 having an MFI type structure.
[0079]
[Support of metal salt on silicalite]
Add 0.08 g of ferrous acetate (Aldrich) and 0.11 g of cobalt acetate tetrahydrate (Nacalai Tesque) to 7 ml of methanol (Nacalai Tesque) and suspend for 10 minutes with an ultrasonic cleaner. It became cloudy. To this suspension, 1.0 g of the silicalite-1 powder was added, treated with an ultrasonic cleaner for 10 minutes, and methanol was removed at a constant temperature of 60 ° C. A salt-supported catalyst was obtained.
[0080]
[Photoelectron spectroscopy measurement of catalyst]
The above-mentioned catalyst having a metal salt supported on silicalite-1 was calcined in argon gas at 800 ° C. for 30 minutes, cooled to room temperature in argon gas, and then taken out into the air, and then X-ray photoelectron spectrometer. The catalyst was measured (10 kV, 18 mA). The measured electron binding energy of cobalt 2P3 / 2 was 780.3 eV. The binding energy of Fe2P2 / 3 electrons was 710.6 eV. Further, the atomic ratio of cobalt on the support surface was 0.7%, and the atomic ratio of iron was 0.3%.
[0081]
[Synthesis of nanofiber (800 ℃)]
0.034 g of silicalite-1 carrying a metal salt was taken on a quartz plate at the center of a quartz tube having an inner diameter of 30 mm, and argon was supplied at 30 ml / min. The quartz tube was placed in an electric furnace and the center temperature was heated to 800 ° C. After supplying ultrapure acetylene gas (manufactured by High Pressure Gas Industry) at 1 ml / min for 30 minutes, the supply of acetylene gas was stopped and the temperature was cooled to room temperature.
[0082]
When the shape of a part of the reactant deposited on the quartz plate was measured with a transmission electron microscope, it was a thin hollow nanofiber having an outer diameter of 20 nm or less and an inner diameter of about 5 nm. In addition, when the hollow nanofibers were observed with a high-resolution transmission electron microscope, the walls of the nanofibers were composed of clean graphite layers, and the number of layers was 1 to 20 layers, particularly 2 to 5 layers. A thin carbon nanotube as a component was observed. Many nanofibers having a diameter of 20 nm or more were observed.
[0083]
The above results are shown in Table 1.
(Example 2)
(Co + Fe) / TS-1
(Synthesis of crystalline titanosilicate)
6 g of silica sol (manufactured by DuPont, Ludox HS-40) and tetrapropylammonium hydroxide 22% aqueous solution (manufactured by Tokyo Chemical Industry) were placed in a beaker and stirred vigorously for about 1 hour. To this, 0.34 g of tetraisopropoxy titanium (manufactured by Nacalai) was added and stirred for 15 minutes. Distilled water 12.4g was added here, this was moved to the autoclave of a Teflon (trademark) line, and it left still at 75 degreeC for 3 hours. Subsequently, it heated at 175 degreeC for 48 hours. Thereafter, the mixture was cooled, filtered, washed with water, and dried, followed by firing at 550 ° C. in the air. When X-ray diffraction (XRD) of this powder was measured, it was found to be TS-1 having an MFI type structure.
[0084]
[Support of metal salt on heat-resistant zeolite]
Add ferrous acetate (Aldrich) 0.04g and cobalt acetate tetrahydrate (Nacalai Tesque) 0.11g to methanol (Nacalai Tesque) 7ml and suspend for 10 minutes with an ultrasonic cleaner. It became cloudy. To this suspension, 1.0 g of the above TS-1 powder was added, treated with an ultrasonic cleaner for 10 minutes, and methanol was removed at a constant temperature of 60 ° C., whereby a metal salt was formed on the crystal surface of TS-1. A supported catalyst was obtained.
[0085]
[Photoelectron spectroscopy measurement of catalyst]
The catalyst having a metal salt supported on TS-1 is calcined in argon gas at 900 ° C. for 30 minutes, cooled to room temperature in argon gas, taken out into the air, and then catalyst is obtained using an X-ray photoelectron spectrometer. Was measured. The measured electron binding energy of cobalt 2P3 / 2 was 779.8 eV. The binding energy of Fe2P2 / 3 electrons was 710.6 eV. Further, the atomic ratio of cobalt on the support surface was 0.6%, and the atomic ratio of iron was 0.1%.
[0086]
As a result of transmission electron microscope observation, as shown in FIG. 1, it was observed that metal fine particles having a diameter of about 3 nm were formed on the zeolite surface.
[0087]
[Synthesis of double-walled nanotube (900 ℃)]
On a quartz plate at the center of a quartz tube having an inner diameter of 100 mm, 0.09 g of TS-1 carrying a metal salt was taken, and argon was supplied at 250 ml / min. The quartz tube was placed in an electric furnace, and the center temperature was heated to 900 ° C. (temperature raising time: about 30 minutes). After reaching 900 ° C., ultra high purity acetylene gas (manufactured by High Pressure Gas Industry) was supplied at 10 ml / min for 30 minutes, and then the supply of acetylene gas was stopped and the temperature was cooled to room temperature.
[0088]
When the shape of a part of the reaction product deposited on the quartz plate was measured with a transmission electron microscope, a bundle composed of a double-walled nanotube having an outer diameter of 15 nm or less and an inner diameter of about 3 nm, or a part of which was composed of three or more layers. The resulting double-walled carbon nanotube was produced. The main products other than this were mostly carbon nanotubes having an outer diameter of 15 nm or less and having 2 to 5 layers as a main component. A small amount of nanofibers having a diameter of 20 nm or more was observed.
[0089]
The above results are shown in Table 1.
Example 3
(Co + Mn) / TS-1
[Support of metal salt on crystalline titanosilicate]
Manganese nitrate (manufactured by Katayama Chemical) 0.008 g and cobalt acetate tetrahydrate (manufactured by Nacalai Tesque) 0.11 g were added to 7 ml of methanol (manufactured by Nacalai Tesque) and suspended in an ultrasonic cleaner for 10 minutes. . To this suspension, 1.0 g of the TS-1 powder of Example 2 was added, treated with an ultrasonic cleaner for 10 minutes, and methanol was removed at a constant temperature of 60 ° C. A catalyst carrying a metal salt was obtained.
[0090]
[Photoelectron spectroscopy measurement of catalyst]
The catalyst having a metal salt supported on TS-1 is calcined in argon gas at 900 ° C. for 30 minutes, cooled to room temperature in argon gas, taken out into the air, and then catalyst is obtained using an X-ray photoelectron spectrometer. Was measured. The measured electron binding energy of cobalt 2P3 / 2 was 780.0 eV. Further, the atomic ratio of cobalt on the support surface was 0.6%, and the atomic ratio of iron was 0.03%.
[0091]
[Synthesis of nanofiber (800 ℃)]
On a quartz plate at the center of a quartz tube having an inner diameter of 30 mm, 0.032 g of TS-1 carrying a metal salt was taken, and argon was supplied at 30 ml / min. The quartz tube was placed in an electric furnace and the center temperature was heated to 800 ° C. After supplying ultrapure acetylene gas (manufactured by High Pressure Gas Industry) at 1 ml / min for 30 minutes, the supply of acetylene gas was stopped and the temperature was cooled to room temperature.
[0092]
When the shape of a part of the reaction product deposited on the quartz plate was measured with a transmission electron microscope, a large amount of 2 to 5 carbon nanotubes having an outer diameter of 10 nm or less and an inner diameter of about 3 nm were observed. Moreover, the nanofiber whose diameter is 20 nm or more was hardly observed.
[0093]
The above results are shown in Table 1.
(Example 4)
(Co + Fe) / Silicalite (low heat resistance)
[Synthesis of low heat-resistant silicalite]
To 20 g of a 20 to 25% aqueous solution of tetrapropylammonium hydroxide (TPAOH) (20 to 25% aqueous solution manufactured by Tokyo Chemical Industry Co., Ltd.), 0.28 g of sodium hydroxide (reagent grade 1 manufactured by Katayama Chemical Co., Ltd.) is added and stirred. did. A further 5 g of fumed silica (Aldrich) was added thereto and heated to 80 ° C. to obtain a transparent aqueous solution. When this was put into an autoclave of a polytetrafluoroethylene line and heated at 125 ° C. for 8 hours, silicalite fine particles (average particle diameter of about 80 nm) were obtained.
[0094]
When X-ray diffraction (XRD) of the obtained powder was measured, it was found to be silicalite-1 having an MFI type structure. When this powder was heated to 800 ° C. at a rate of temperature increase of 5 ° C./min in a stream of nitrogen 50 ml / min with a thermal analyzer DTG-50 manufactured by Shimadzu Corporation, the temperature was 700 ° C. to 800 ° C. In the meantime, an exothermic peak appeared in the DTA curve.
[0095]
[Support of metal salt on zeolite]
Add 0.08 g of ferrous acetate (Aldrich) and 0.11 g of cobalt acetate tetrahydrate (Nacalai Tesque) to 7 ml of methanol (Nacalai Tesque) and suspend for 10 minutes with an ultrasonic cleaner. It became cloudy. To this suspension, 1.0 g of the silicalite-1 powder was added, treated with an ultrasonic cleaner for 10 minutes, and methanol was removed at a constant temperature of 60 ° C. A salt-supported catalyst was obtained.
[0096]
[Photoelectron spectroscopy measurement of catalyst]
The above-mentioned catalyst having a metal salt supported on silicalite-1 was calcined in argon gas at 800 ° C. for 30 minutes, cooled to room temperature in argon gas, and then taken out into the air, and then X-ray photoelectron spectrometer. The catalyst was measured (10 kV, 18 mA). The measured electron binding energy of cobalt 2P3 / 2 was 780.2 eV. The binding energy of Fe2P2 / 3 electrons was 710.9 eV. Further, the atomic ratio of cobalt on the support surface was 0.7%, and the atomic ratio of iron was 0.3%.
[0097]
[Synthesis of nanofiber (800 ℃)]
0.031 g of silicalite-1 carrying a metal salt was taken on a quartz plate at the center of a quartz tube having an inner diameter of 30 mm, and argon was supplied at 30 ml / min. The quartz tube was placed in an electric furnace and the center temperature was heated to 800 ° C. After supplying ultrapure acetylene gas (manufactured by High Pressure Gas Industry) at 1 ml / min for 30 minutes, the supply of acetylene gas was stopped and the temperature was cooled to room temperature.
[0098]
When the shape of a part of the reactant deposited on the quartz plate was measured with a transmission electron microscope, it was a thin hollow nanofiber having an outer diameter of 20 nm or less and an inner diameter of about 5 nm. Further, when hollow nanofibers were observed with a high-resolution transmission electron microscope, the walls of the nanofibers were composed of relatively clean graphite layers, and the number of layers was 1 to 20, particularly 2 to 5 carbon nanotubes. Many were seen. Many nanofibers having a diameter of 20 nm or more were observed.
[0099]
The above results are shown in Table 1.
(Example 5)
(Co + Fe) / USY (silica alumina ratio 40)
[Support of metal salt on USY-type zeolite]
5 g of USY-type zeolite (manufactured by PQ Corporation, silica alumina ratio 40) was added to 300 ml of 0.1N NaOH aqueous solution and stirred at room temperature for 3 hours. This was filtered and washed with water. Next, 0.08 g of ferrous acetate (manufactured by Aldrich) and 0.11 g of cobalt acetate tetrahydrate (manufactured by Nacalai Tesque) are added to 7 ml of ethanol (manufactured by Nacalai Tesque), and an ultrasonic cleaner is used. Suspended for 10 minutes. To this suspension, 1.0 g of the above-mentioned NaOH-treated USY zeolite was added, treated with an ultrasonic cleaner for 10 minutes, ethanol was removed at a constant temperature of 60 ° C., and the metal salt was supported on the USY-type zeolite powder. The catalyst obtained was obtained.
[0100]
[Photoelectron spectroscopy measurement of catalyst]
The above-mentioned catalyst in which a metal salt is supported on USY-type zeolite is calcined in argon gas at 900 ° C. for 30 minutes, then cooled to room temperature in argon gas, once taken out into the air, and then the catalyst is obtained using an X-ray photoelectron spectrometer. Was measured. The measured electron energy of cobalt 2P3 / 2 was 779.5 eV. Further, the atomic ratio of cobalt on the support surface was 0.2%, and the atomic ratio of iron was 0.2%.
[0101]
[Synthesis of nanofiber (800 ℃)]
On a quartz plate at the center of a quartz tube having an inner diameter of 30 mm, 0.029 g of the USY-type zeolite powder carrying the metal salt obtained above was taken, and argon was supplied at 30 ml / min. The quartz tube was placed in an electric furnace and the center temperature was heated to 800 ° C. After supplying ultrapure acetylene gas (manufactured by High Pressure Gas Industry) at 1 ml / min for 30 minutes, the supply of acetylene gas was stopped and the temperature was cooled to room temperature.
[0102]
When the shape of the reactant reactant deposited on the quartz plate was measured with a transmission electron microscope, it was a thin hollow nanofiber having an outer diameter of 20 nm or less and an inner diameter of about 5 nm. Moreover, when hollow nanofibers were observed with a high-resolution transmission electron microscope, the walls of the nanofibers were composed of a relatively clean graphite layer, and the number of layers was 1 to 20 carbon nanotubes. Many 5-walled carbon nanotubes were observed. A large amount of nanofibers having a diameter of 20 nm or more was also observed.
[0103]
The above results are shown in Table 1.
(Example 6)
(Co + Fe) / TS-1
[Support of metal salt on TS-1 type zeolite]
Add ferrous acetate (Aldrich) 0.008g and cobalt acetate tetrahydrate (Nacalai Tesque) 0.11g to ethanol (Nacalai Tesque) 7ml and suspend for 10 minutes with an ultrasonic cleaner. It became cloudy. To this suspension, 1.0 g of TS-1 zeolite (manufactured by NE Chemcat, silicon / titanium ratio 50) was added, treated with an ultrasonic cleaner for 10 minutes, ethanol was removed at a constant temperature of 60 ° C., and TS A catalyst having a metal salt supported on -1 type zeolite powder was obtained.
[0104]
[Photoelectron spectroscopy measurement of catalyst]
The catalyst having a metal salt supported on the TS-1 type zeolite described above was calcined in argon gas at 900 ° C. for 30 minutes, cooled to room temperature in argon gas, and then taken out into the air to obtain an X-ray photoelectron spectrometer. The catalyst was measured at The measured electron energy of cobalt 2P3 / 2 was 779.9 eV. The atomic ratio of cobalt on the support surface was 0.8%, and the atomic ratio of iron was 0.06%. The atomic ratio of cobalt to titanium was 0.87.
[0105]
[Synthesis of nanofiber (800 ℃)]
On a quartz plate at the center of a quartz tube having an inner diameter of 30 mm, 0.029 g of TS-1 type zeolite powder carrying the metal salt obtained above was taken, and argon was supplied at 30 ml / min. The quartz tube was placed in an electric furnace and the center temperature was heated to 800 ° C. After supplying ultrapure acetylene gas (manufactured by High Pressure Gas Industry) at 1 ml / min for 30 minutes, the supply of acetylene gas was stopped and the temperature was cooled to room temperature.
[0106]
When the shape of the reactant reactant deposited on the quartz plate was measured with a transmission electron microscope, it was a thin hollow nanofiber having an outer diameter of 15 nm or less and an inner diameter of about 5 nm. When observed with a high-resolution transmission electron microscope, the walls of the nanofibers are composed of relatively clean graphite layers, most of which are 2 to 5 carbon nanotubes, and most of the nanofibers having a diameter of 20 nm or more. Not observed.
[0107]
The above results are shown in Table 1.
(Example 7)
(Co + Fe) / TS-1
[Support of metal salt on TS-1 type zeolite]
Add ferrous acetate (Aldrich) 0.064g and cobalt acetate tetrahydrate (Nacalai Tesque) 0.088g to ethanol (Nacalai Tesque) 7ml and suspend for 10 minutes with an ultrasonic cleaner. It became cloudy. To this suspension, 1.0 g of TS-1 zeolite (manufactured by NE Chemcat, silicon / titanium ratio 50) was added, treated with an ultrasonic cleaner for 10 minutes, ethanol was removed at a constant temperature of 60 ° C., and TS A catalyst having a metal salt supported on -1 type zeolite powder was obtained.
[0108]
[Photoelectron spectroscopy measurement of catalyst]
The catalyst having a metal salt supported on the TS-1 type zeolite described above was calcined in argon gas at 900 ° C. for 30 minutes, cooled to room temperature in argon gas, and then taken out into the air to obtain an X-ray photoelectron spectrometer. The catalyst was measured at The measured electron energy of cobalt 2P3 / 2 was 779.5 eV. Further, the atomic ratio of cobalt on the support surface was 0.6%, and the atomic ratio of iron was 0.05%.
[0109]
[Synthesis of nanofiber (800 ℃)]
On a quartz plate at the center of a quartz tube having an inner diameter of 30 mm, 0.029 g of TS-1 type zeolite powder carrying the metal salt obtained above was taken, and argon was supplied at 30 ml / min. The quartz tube was placed in an electric furnace and the center temperature was heated to 800 ° C. After supplying ultrapure acetylene gas (manufactured by High Pressure Gas Industry) at 1 ml / min for 30 minutes, the supply of acetylene gas was stopped and the temperature was cooled to room temperature.
[0110]
When the shape of the reactant reactant deposited on the quartz plate was measured with a transmission electron microscope, it was a thin hollow nanofiber having an outer diameter of 15 nm or less and an inner diameter of about 5 nm. When observed with a high-resolution transmission electron microscope, the walls of the nanofibers were composed of a relatively clean graphite layer, and most of the layers were 2 to 5 carbon nanotubes. Many nanofibers having a diameter of 20 nm or more were observed.
[0111]
The above results are shown in Table 1.
( Comparative Example 1 )
(Co + Fe) / USY (silica alumina ratio 390)
[Support of metal salt on USY-type zeolite]
Ferrous acetate (Aldrich) 0.064 g and cobalt acetate tetrahydrate (Nacalai Tesque) 0.088 g are added to 7 ml of ethanol (Nacalai Tesque) and suspended in an ultrasonic cleaner for 10 minutes. did. To this suspension, 1.0 g of USY-type zeolite (Tosoh HSZ-390HUA, silica / alumina ratio 390) was added, treated with an ultrasonic cleaner for 10 minutes, and ethanol was removed at a constant temperature of 60 ° C. Thus, a catalyst having a metal salt supported on a USY-type zeolite powder was obtained.
[0112]
[Photoelectron spectroscopy measurement of catalyst]
The above-mentioned catalyst in which a metal salt is supported on USY-type zeolite is calcined in argon gas at 900 ° C. for 30 minutes, then cooled to room temperature in argon gas, once taken out into the air, and then the catalyst is obtained using an X-ray photoelectron spectrometer. Was measured. The measured electron energy of cobalt 2P3 / 2 was 781.1 eV. The atomic ratio of cobalt on the support surface was 1.4%, and the atomic ratio of iron was 0.5%.
[0113]
[Synthesis of nanofiber (800 ℃)]
On a quartz plate at the center of a quartz tube having an inner diameter of 30 mm, 0.029 g of the USY-type zeolite powder carrying the metal salt obtained above was taken, and argon was supplied at 30 ml / min. The quartz tube was placed in an electric furnace and the center temperature was heated to 800 ° C. After supplying ultrapure acetylene gas (manufactured by High Pressure Gas Industry) at 1 ml / min for 30 minutes, the supply of acetylene gas was stopped and the temperature was cooled to room temperature.
[0114]
When the shape of the reactant reactant deposited on the quartz plate was measured with a transmission electron microscope, it was a thin hollow nanofiber having an outer diameter of 20 nm or less and an inner diameter of about 1 to 3 nm. When observed with a high-resolution transmission electron microscope, the walls of the nanofibers were composed of a relatively clean graphite layer, and most of them were 1 to 20 carbon nanotubes. In particular, many single-walled and 1 to 5 carbon nanotubes were observed. Some nanofibers with a diameter of 20 nm or more were observed. . single The ratio of single-walled carbon nanotubes was high But the yield was not good .
[0119]
( Comparative Example 2 )
(Co + Fe) / USY (silica alumina ratio 390)
[Support of metal salt on USY-type zeolite]
Ferrous acetate (Aldrich) 0.064 g and cobalt acetate tetrahydrate (Nacalai Tesque) 0.088 g are added to 7 ml of ethanol (Nacalai Tesque) and suspended in an ultrasonic cleaner for 10 minutes. did. To this suspension, 1.0 g of USY zeolite (Tosoh HSZ-390HUA, silica / alumina ratio 390) was added, treated with an ultrasonic cleaner for 10 minutes, and ethanol was removed at a constant temperature of 60 ° C. A catalyst having a metal salt supported on USY zeolite powder was obtained.
[0120]
[Photoelectron spectroscopy measurement of catalyst]
The above-mentioned catalyst in which a metal salt is supported on USY-type zeolite is calcined in argon gas at 900 ° C. for 30 minutes, then cooled to room temperature in argon gas, once taken out into the air, and then the catalyst is obtained using an X-ray photoelectron spectrometer. Was measured. The measured electron energy of cobalt 2P3 / 2 was 781.1 eV. The atomic ratio of cobalt on the support surface was 1.4%, and the atomic ratio of iron was 0.5%.
[0121]
[Selective synthesis of single-walled carbon nanotubes]
On a quartz plate at the center of a quartz tube having an inner diameter of 30 mm, 0.029 g of the USY-type zeolite powder carrying the metal salt obtained above was taken, and argon was supplied at 30 ml / min. The quartz tube was placed in an electric furnace and the center temperature was heated to 800 ° C. Ethanol (special reagent grade, manufactured by Tokyo Chemical Industry Co., Ltd.) was supplied at 2.1 mg / min for 30 minutes with a microfeeder, and then ethanol supply was stopped and the temperature was cooled to room temperature.
[0122]
When the shape of the product deposited on the quartz plate in the reaction tube was measured with a scanning electron microscope JSM-6301NF, JEOL Datum Co., Ltd., many very thin nanofibrous substances were observed. Furthermore, when observed with a high-resolution transmission electron microscope, most of the products were single-walled carbon nanotubes having a diameter of 2 nm or less. Nanofibers having a diameter of 20 nm or more were not observed at all. However, the yield was not good .
[0127]
(Example 8 )
(Co + Fe) / TS-1
[Support of metal salt on TS-1 type zeolite]
Add 0.021 g of iron acetylacetonate complex (manufactured by Nippon Kagaku Sangyo) and 0.2 g of cobalt acetylacetonate complex (manufactured by Nippon Kagaku Sangyo) to 7 ml of acetone (manufactured by Nacalai Tesque) and suspend for 10 minutes with an ultrasonic cleaner. It became cloudy. To this suspension, 2.0 g of TS-1 zeolite (manufactured by NE Chemcat, silicon / titanium ratio 50) was added, treated with an ultrasonic cleaner for 10 minutes, ethanol was removed at a constant temperature of 60 ° C., and TS A catalyst having a metal salt supported on -1 type zeolite powder was obtained.
[0128]
[Photoelectron spectroscopy measurement of catalyst]
The catalyst having a metal salt supported on the above TS-1 type zeolite is calcined in argon gas at 900 ° C. for 30 minutes, then cooled to room temperature in argon gas, and then taken out into the air and X-ray photoelectron spectroscopy. The catalyst was measured with a process apparatus. The measured electron energy of cobalt 2P3 / 2 was 780.0 eV. The atomic ratio of cobalt on the support surface was 1.4%, and the atomic ratio of iron was 0.14%.
[0129]
[Synthesis of nanofiber (800 ℃)]
On the quartz wool at the center of a vertical quartz tube having an inner diameter of 30 mm, 1.0 g of TS-1 type zeolite powder carrying the metal complex obtained above was taken, and argon was supplied at 60 ml / min. The quartz tube was placed in an electric furnace and the center temperature was heated to 800 ° C. After supplying ultrahigh purity acetylene gas (manufactured by High Pressure Gas Industry) at 0.5 ml / min for 300 minutes, the supply of acetylene gas was stopped and the temperature was cooled to room temperature.
[0130]
When the shape of the reactant reactant deposited on the quartz plate was measured with a transmission electron microscope, it was a thin hollow nanofiber having an outer diameter of 15 nm or less and an inner diameter of about 5 nm. When observed with a high-resolution transmission electron microscope, the walls of the nanofibers were composed of relatively clean graphite layers, all of which were composed of 2 to 5 carbon nanotubes, with 2 layers being the main components. . Nanofibers having a diameter of 20 nm or more were not observed at all.
[0131]
The above results are shown in Table 1.
(Example 9 )
(Co + Fe) / borosilicate
[Support of metal salt on borosilicate type zeolite]
Ferrous acetate (Aldrich) 0.064 g and cobalt acetate tetrahydrate (Nacalai Tesque) 0.088 g are added to 7 ml of ethanol (Nacalai Tesque) and suspended in an ultrasonic cleaner for 10 minutes. did. To this suspension, 1.0 g of borosilicate zeolite (manufactured by NE Chemcat, silicon / boron ratio 50) was added, treated with an ultrasonic cleaner for 10 minutes, ethanol was removed at a constant temperature of 60 ° C., and borosilicate was obtained. A catalyst in which a metal salt was supported on the zeolite powder was obtained.
[0132]
[Photoelectron spectroscopy measurement of catalyst]
The above-mentioned catalyst having a metal salt supported on borosilicate zeolite is calcined in argon gas at 900 ° C. for 30 minutes, cooled to room temperature in argon gas, and then taken out into the air, and then the catalyst is obtained using an X-ray photoelectron spectrometer. Was measured. The measured electron energy of cobalt 2P3 / 2 was 780.1 eV. Further, the atomic ratio of cobalt on the support surface was 1.4%, and the atomic ratio of iron was 0.07%.
[0133]
[Synthesis of nanofiber (800 ℃)]
On the quartz wool at the center of a vertical quartz tube with an inner diameter of 30 mm, 1.0 g of the TS-1 type zeolite powder carrying the metal complex obtained above was taken, and argon was supplied at 60 ml / min. The quartz tube was placed in an electric furnace and the center temperature was heated to 800 ° C. After supplying ethanol as a gas with a microfeeder at 0.5 ml / min for 300 minutes, the supply of ethanol was stopped and the temperature was cooled to room temperature.
[0134]
When the shape of the reactant reactant deposited on the quartz plate was measured with a transmission electron microscope, it was a thin hollow nanofiber having an outer diameter of 5 nm or less. When observed with a high-resolution transmission electron microscope, the walls of the nanofibers were composed of relatively clean graphite layers, and the number of all layers was 1 to 5 carbon nanotubes. Nanofibers having a diameter of 20 nm or more were not observed at all.
[0135]
The above results are shown in Table 1.
( Example 10 )
[Support of metal salt on heat-resistant zeolite (high flow rate)]
0.10 g of ferrous acetate (Aldrich) and 0.06 g of cobalt acetate tetrahydrate (Nacalai Tesque) are added to 7 ml of methanol (Nacalai Tesque) and suspended in an ultrasonic cleaner for 10 minutes. did. To this suspension, 1.0 g of the TS-1 powder was added, treated with an ultrasonic cleaner for 10 minutes, and methanol was removed at a constant temperature of 60 ° C., whereby a metal salt was formed on the crystal surface of TS-1. A supported catalyst was obtained.
[0136]
[Synthesis of double-walled carbon nanotubes (800 ° C)]
Quartz wool was filled in the center of a vertical quartz tube having an inner diameter of 30 mm, 1.0 g of TS-1 carrying the metal salt obtained above was taken on it, and argon was supplied at 600 ml / min. The quartz tube was installed in an electric furnace, and the center temperature was heated to 800 ° C. (temperature raising time: about 30 minutes). After reaching 800 ° C., ultra high purity acetylene gas (manufactured by High Pressure Gas Industry) was supplied at 5 ml / min for 30 minutes, and then the supply of acetylene gas was stopped and the temperature was cooled to room temperature.
[0137]
When the shape of a part of the reaction product deposited on the quartz wool was measured with a high-resolution transmission electron microscope, many double-walled carbon nanotubes having an inner diameter of about 4 nm were generated. As a result of the Raman spectrum, the G / D ratio is 2.75, 150 to 350 cm. ^-1 A number of peaks were observed within.
[0138]
The above results are shown in Table 1.
(Comparative example 3 )
(Co + Fe) / USY (silica alumina ratio 390)
[Support of metal salt on Y-type zeolite]
Ferrous acetate (manufactured by Aldrich) 0.08 g and cobalt acetate tetrahydrate (manufactured by Nacalai Tesque) 0.11 g are added to 7 ml of ethanol (manufactured by Nacalai Tesque) and suspended in an ultrasonic cleaner for 10 minutes. did. Into this suspension Comparative Example 1 1.0 g of the same USY-type zeolite powder (manufactured by Tosoh Corp.), treated with an ultrasonic cleaner for 10 minutes, removed ethanol at a constant temperature of 60 ° C., and a catalyst in which a metal salt is supported on the USY-type zeolite powder Got.
[0139]
[Photoelectron spectroscopy measurement of catalyst]
The above-mentioned catalyst in which a metal salt is supported on USY-type zeolite is calcined in argon gas at 900 ° C. for 30 minutes, then cooled to room temperature in argon gas, once taken out into the air, and then the catalyst is obtained using an X-ray photoelectron spectrometer. Was measured. The measured electron energy of cobalt 2P3 / 2 was 781.3 eV. The binding energy of Fe2P2 / 3 electrons was 710.9 eV.
[0140]
[Synthesis of nanofiber (600 ℃)]
On a quartz plate at the center of a quartz tube having an inner diameter of 30 mm, 0.029 g of the USY-type zeolite powder carrying the metal salt obtained above was taken, and nitrogen was supplied at 30 ml / min. A quartz tube was placed in an electric furnace and the center temperature was heated to 600 ° C. After supplying ultrapure acetylene gas (manufactured by High Pressure Gas Industry) at 6 ml / min for 30 minutes, the supply of acetylene gas was stopped and the temperature was cooled to room temperature.
[0141]
When the shape of the reactant reaction product deposited on the quartz plate was measured with a scanning electron microscope JSM-6301NF manufactured by JEOL Datum Co., Ltd., the amount of hollow nanofibers produced was very small, but the outer diameter was 20 nm or less. A small amount of thin hollow nanofibers having an inner diameter of about 5 nm was observed. When observed with a high-resolution transmission electron microscope, the walls of the nanofibers are composed of relatively clean graphite layers, most of which are 1-20 carbon nanotubes, especially 2-5 carbon nanotubes. Was hardly observed and was generally thick. Many nanofibers having a diameter of 20 nm or more were observed.
[0142]
The above results are shown in Table 1.
(Comparative example 4 )
(Co + Fe) / Na-Y type
[Support of metal salt on Na-Y zeolite]
Ferrous acetate (manufactured by Aldrich) 0.08 g and cobalt acetate tetrahydrate (manufactured by Nacalai Tesque) 0.11 g are added to 7 ml of ethanol (manufactured by Nacalai Tesque) and suspended in an ultrasonic cleaner for 10 minutes. did. To this suspension, 1.0 g of Na-Y type zeolite (Tosoh silica-alumina ratio 5.1) powder was added at a time, treated with an ultrasonic cleaner for 10 minutes, and ethanol was removed at a constant temperature of 120 ° C. A catalyst was obtained.
[0143]
[Photoelectron spectroscopy measurement of catalyst]
The above-mentioned catalyst having a metal salt supported on Na-Y zeolite is calcined in argon gas at 800 ° C. for 30 minutes, cooled to room temperature in argon gas, once taken out into the air, and an X-ray photoelectron spectrometer. The catalyst was measured at The measured electron binding energy of cobalt 2P3 / 2 was 779.2 eV. The binding energy of Fe2P2 / 3 electrons was 709.9 eV. Further, the atomic ratio of cobalt on the support surface was 2.9%, and the atomic ratio of iron was 0.6%.
[0144]
[Synthesis of nanofiber (800 ℃)]
0.03 g of the catalyst was taken on a quartz plate at the center of a quartz tube having an inner diameter of 30 mm, and argon was supplied at 30 ml / min. Each quartz tube was placed in an electric furnace and the center temperature was heated to 800 ° C. After supplying ultrapure acetylene gas (manufactured by High Pressure Gas Industry) at 6 ml / min for 30 minutes, the supply of acetylene gas was stopped and the temperature was cooled to room temperature.
[0145]
When the shape of the reactant deposited on the quartz plate in the reaction tube was observed with a high-resolution transmission electron microscope, a large amount of hollow nanofibers having an outer diameter of 20 nm or more, an outer diameter of 20 nm or less, and 5 to 20 layers. A small amount of carbon nanotubes was observed. The obtained carbon nanotube graphite layer had few defects, and 2 to 5 layers of carbon nanotubes were hardly observed, and were generally thick.
[0146]
The above results are shown in Table 1.
[0147]
[Table 1]

[0148]
【The invention's effect】
According to the production method of the present invention, a catalyst in which cobalt fine particles having an electron binding energy of cobalt 2P3 / 2 measured by X-ray photoelectron spectroscopy of 779.3 eV or more and 781.0 eV or less supported on a carrier, A catalyst having cobalt fine particles with a cobalt atomic ratio of 0.1 to 1.5% measured on a carrier surface measured by photoelectron spectroscopy at 10 kV and 18 mA, a carrier surface measured by X-ray photoelectron spectroscopy at 10 kV and 18 mA. A catalyst in which cobalt fine particles having an atomic ratio of cobalt to titanium of 0.3 to 2.0 are supported on a support containing titanium, or a weight ratio of cobalt to the second metal component on the support surface ((cobalt (Weight) / (weight of second metal component)) is 2.5 or more, and a catalyst in which cobalt fine particles are supported on a carrier is used. By contacting at 00 ° C., it is possible to efficiently obtain high-quality hollow nanofibers with small thickness and controlled thickness and the number of layers by controlling the electronic state of cobalt fine particles as a catalyst and controlling the electronic state of cobalt fine particles. be able to.
[0149]
In addition, since carbon nanotubes with fewer defects in the graphite layer are directly generated, it is possible to eliminate the need for high-temperature heat treatment, which is expensive to graphitize in the post-treatment, and the thickness is 30 nm or less and the inner diameter is 30 nm or less. A high-quality hollow nanofiber in a region defined as a thin carbon nanotube of 0.3 nm or more and 15 nm or less can be produced.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a transmission electron micrograph of cobalt and iron metal fine particles supported on titanosilicate.

Claims (17)

Cobalt fine particles having an electron binding energy of cobalt 2P3 / 2 measured by X-ray photoelectron spectroscopy of 779.3 eV or more and 781.0 eV or less and second metal components other than cobalt include vanadium, molybdenum, manganese, iron, Using a catalyst in which at least one kind of group 3-12 metal selected from nickel and palladium is supported on a carrier and contacting with a carbon-containing material at 500-1200 ° C., the main component is 1-5 carbon nanotubes A method for producing a hollow nanofiber comprising producing a hollow nanofiber.   The method for producing hollow nanofibers according to claim 1, wherein the cobalt atomic ratio of the carrier surface measured by X-ray photoelectron spectroscopy at 10 kV and 18 mA is 0.1 to 1.5%.   The atomic ratio of titanium on the surface of the carrier in the carrier containing cobalt and titanium on the surface of the carrier measured at 10 kV and 18 mA by X-ray photoelectron spectroscopy is 0.3 or more and 2.0 or less. 3. A method for producing a hollow nanofiber according to 1 or 2.   The weight ratio ((weight of cobalt) / (weight of second metal component)) of cobalt and the second metal component on the surface of the support is 2.5 or more. Process for producing hollow nanofibers.   The hollow nanofiber according to claim 4, wherein the atomic ratio of cobalt to the second metal component on the surface of the carrier ((number of cobalt atoms) / (number of atoms of the second metal component)) is 5 to 15. Law. The method for producing hollow nanofibers according to any one of claims 1 to 5 , wherein 80% or more of the metal fine particles supported on the carrier have a size of 0.5 to 10 nm. Wherein the metal fine particles, at least after one was supported on a carrier as a raw material, according to any one of claims 1 to 6 in which the fine particles by heat treatment selected from metal acetates, metal nitrates, and metal complexes Manufacturing method of hollow nanofiber. The method for producing hollow nanofibers according to any one of claims 1 to 7 , wherein the carrier is zeolite. The method for producing hollow nanofibers according to claim 8 , wherein the zeolite is at least one selected from USY-type zeolite, MFI-type zeolite, and MFI-type metallosilicate. The hollow according to any one of claims 1, 2, 4 to 9 , wherein the carrier is zeolite, and the zeolite contains at least one selected from titanosilicate, cobalt silicate, and borosilicate. Of nanofiber.   The method for producing hollow nanofiber according to claim 3, wherein the carrier is zeolite, and the zeolite contains titanosilicate. The method for producing hollow nanofiber according to any one of claims 1 to 11 , wherein the carbon-containing compound is a hydrocarbon or carbon monoxide. The hollow nanofiber production method according to any one of claims 1 to 12 , wherein the hollow nanofiber after generation has an outer diameter of 50 nm or less and an inner diameter of 0.3 nm or more and 15 nm or less. The method for producing hollow nanofibers according to claim 13 , wherein the hollow nanofibers are carbon nanotubes. The method for producing a hollow nanofiber according to any one of claims 1 to 14 , wherein the hollow nanofiber after generation satisfies all the following requirements (1) to (3).
(1) A double-walled carbon nanotube is observed with a high-resolution transmission electron microscope.
(2) A peak is observed in the region of 150 to 350 cm ⁻¹ by resonance Raman scattering measurement.
(3) By resonance Raman scattering measurement, the maximum peak intensity in the range of 1560~1600cm ^-1 G, when the maximum peak intensity is D within the 1310～1350Cm ^-1, the ratio of G / D 1.0 or more. The method for producing a hollow nanofiber according to any one of claims 1 to 14 , wherein a main component of the hollow nanofiber is a 2- to 5-walled carbon nanotube. The method for producing a hollow nanofiber according to claim 16 , wherein a main component of the hollow nanofiber is a double-walled carbon nanotube.

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